[Frontiers in Bioscience S3, 541-554, January 1, 2011]

Protective mechanisms by cystatin C in neurodegenerative diseases

Sebastien Gauthier1, Gurjinder Kaur1, Weiqian Mi1, Belen Tizon1, Efrat Levy1,2

1Nathan S. Kline Institute, Orangeburg, NY, 10962, U.S.A. 2Departments of Psychiatry and Pharmacology, New York University School of Medicine, New York, NY, 10016, U.S.A.


1. Abstract
2. Introduction
3. Mechanisms of neuroprotection by cystatin C
3.1. Neuroprotection by inhibition of cysteine proteases
3.2. Neuroprotection by induction of neurogenesis
3.3. Neuroprotection by induction of autophagy
3.4. Neuroprotection by inhibition of oligomerization and amyloid fibril formation
4. Perspective
5. Acknowledgements
6. References


Neurodegeneration occurs in acute pathological conditions such as stroke, ischemia, and head trauma and in chronic disorders such as Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. While the cause of neuronal death is different and not always known in these varied conditions, hindrance of cell death would be beneficial in the prevention of, slowing of, or halting disease progression. Enhanced cystatin C (CysC) expression in these conditions caused a debate as to whether CysC up-regulation facilitates neurodegeneration or it is an endogenous neuroprotective attempt to prevent the progression of the pathology. However, recent in vitro and in vivo data have demonstrated that CysC plays protective roles via pathways that are dependent on inhibition of cysteine proteases, such as cathepsin B, or by induction of autophagy, induction of proliferation, and inhibition of amyloid-beta aggregation. Here we review the data demonstrating the protective roles of CysC under conditions of neuronal challenge and the protective pathways induced under various conditions. These data suggest that CysC is a therapeutic candidate that can potentially prevent brain damage and neurodegeneration.


CysC (1), also known as gamma trace (2), belongs to the cystatin type 2 super family (3). It is a 120 amino acids protein preceded by a 26 amino acids amino-terminal secretory signal and contains two intramolecular disulfide bridges (4, 5). It is ubiquitously expressed by all mammalian tissues and is secreted into all body fluids (1, 6). CysC is a marker of kidney dysfunction (7) and has a broad spectrum of biological roles in numerous cellular systems, ranging from anti-viral and anti-bacterial properties (1), bone resorption (8), tumor metastasis (9), modulation of inflammatory responses (1, 10), and cell proliferation and growth (11, 12). Similar to a variety of activities that have been associated with other protease inhibitors in the brain (13-15), CysC has been implicated in the response of the nervous system to neuronal degeneration. While the involvement of CysC in pathological conditions of the central nervous system has been demonstrated, its role has been a matter of debate (reviewed in (16, 17)). Changes in the levels of CysC in the cerebral spinal fluid were documented in a number of neurodegenerative diseases and it was suggested to be of diagnostic importance (18-23). Enhanced CysC expression occurs in specific neuronal cell populations in the brains of human patients with Alzheimer's disease (AD) (24, 25) and in animal models of neurodegenerative conditions caused by facial nerve axotomy (26), noxious input to the sensory spinal cord (27), perforant path transections (28), hypophysectomy (29), transient forebrain ischemia (30, 31), photothrombotic stroke (32), and induction of epilepsy (33-35). Enhanced CysC gene expression and higher CysC protein levels were also shown in dopaminergic-depleted rat striatum following a 6-Hydroxydopamine (6-OHDA)-induced lesion in nigrostriatal neurons, astrocytes, and microglia cells (36). Administration of human CysC into the rat substantia nigra pars compacta partially rescued nigral dopaminergic neurons following a 6-OHDA-induced lesion. An in vitro study showed that loss of dopaminergic-neurons in fetal mesencephalic cultures due to exposure to 6-OHDA is partially reversed by treatment with human CysC (36). Augmented CysC expression was also observed in vitro in cultured rat brain neurons in response to oxidative stress (37). PC12 cell lines that stably expressed rat CysC showed resistance to high oxygen atmosphere and to glutamate- and 13-L-hydroperoxylinoleic acid (LOOH)-induced cell death (38). A similar up-regulation of CysC was shown in human cerebral microvascular smooth muscle cells and in aortic smooth muscle cells after 48 hours of hypoxia or hypoxia followed by reoxygenation (39).

Several hypotheses can be envisioned to explain the involvement of CysC in the brain: it can be involved in regulation of apoptosis, cell proliferation, mitogenic activity of the cell, promotion of survival, or prevention of cell death. The main focus of this review is to unfold the mechanisms of protection induced in different pathological processes based on observations from cell cultures and animal models of neurological disorders.


3.1. Neuroprotection by inhibition of cysteine proteases

CysC is considered an important endogenous inhibitor of cysteine protease activity because of its potent in vitro inhibition of cathepsins (Cat) B, H, K, L, and S (reviewed in (6, 40)). Cathepsins are proteinases required for housekeeping function during protein turnover that differ in structure, substrate-specificity, and biochemical characteristics (reviewed in (41)). CysC itself is a target of proteolysis (42, 43) and is inactivated by proteolytic degradation by Cat D and elastase (44, 45). Imbalance between endogenous inhibitors and cysteine proteinases has been associated with different diseases such as AD (46), rheumatoid arthritis (47), renal failure (48), multiple sclerosis (49, 50), muscular dystrophy (51), inflammatory periodontal disease (52), inflammatory lung disease (53), inflammation and trauma (54), and various types of cancer (55-58). Enhanced expression of several cathepsins in the brain has been documented in response to injuries, similar to those inducing CysC expression upregulation, such as in transient ischemia (59), and inhibitors of Cat B and Cat L have been found to reduce neuronal damage in the hippocampus after ischemia (60, 61).

There are data placing both cathepsins and CysC in intracellular as well as extracellular locations and establishing the respective subcellular distribution of these proteases and their endogenous inhibitors is fundamental to the understanding of the regulation of lysosomal proteolysis and its disruption in neurodegenerative diseases. The primary structure of CysC is indicative of a secreted protein and accordingly, it was demonstrated that most of the CysC synthesized by mouse neuroblastoma N2a cells (62), human embryonic kidney HEK293 cells (62), or human retinal pigment epithelial cells (63), is targeted extracellularly via the secretory pathway. However, CysC was also found in endocytic cellular compartments and it was shown that it inhibits cathepsin activities within the lysosomal system (64). Moreover, it was demonstrated that CysC added to cell-culture media is internalized (65, 66). Although Cat B and Cat D are typically localized in lysosomes, they are also found at other cellular sites (67) such as trans-Golgi vesicles (68), transport vesicles (69), secretory vesicles (70), clathrin-coated vesicles (71), and endosomes (72). Cathepsins may be released through exocytosis, and activated microglia secrete several proteases including Cat B (73) that can trigger neuronal apoptosis (74). It was suggested that, in degenerating neurons, cathepsins could be released into the cytoplasm and neuropil after disruption of lysosomes (75-78). Release of Cat B to the extracellular fluid can cause proteolytic tissue damage leading to organ failure, and matrix destruction associated with inflammation, tumor invasion, and metastasis (reviewed in (79-80)). Localization of cathepsins in senile plaques in the brain of AD patients led to the suggestion that degenerating neurons or their processes are a major source of extracellular Cat D and various other lysosomal hydrolases and hydrolase activities within amyloid deposits (81, 82).

Pharmacological inhibition of cathepsins has been shown to reduce neuronal damage after brain ischemia, thus it was suggested that CysC, an endogenous inhibitor of cathepsins, is an endogenous neuroprotectant. In vivo studies demonstrated increased Cat B activity in the brain of CysC knockout mice, confirming the inhibitory function of CysC (84). Larger brain infarcts were found in CysC knockout mice after focal ischemia induced by 40 minutes occlusion of the origin of the middle cerebral artery as compared to wild type mice (85). However, brain damage in the CA3 region of the hippocampus, the dentate gyrus, and cortex of CysC knockout mice was diminished after global ischemia induced by 12 minutes occlusion of both common carotid arteries (85). The different responses after focal and global ischemia in CysC knockout mice suggest that the protective role imparted by CysC is differential and restricted to certain brain regions or certain brain insults.

In vivo neuroprotection by CysC, modulated by inhibition of cysteine proteases was recently demonstrated in a mouse model of an inherited neurodegenerative disorder, progressive myoclonic epilepsy (86). Cystatin B (CysB) is an inhibitor of cysteine proteases, including Cat B, H, L, and S (3, 4), a member of the cystatin family 1 of cysteine protease inhibitors. It is mainly localized in lysosomes (86) and is diffusely distributed in the cytoplasm (86, 87). Loss-of-function mutations in the CysB gene lead to a rare autosomal disorder, Unverricht-Lundborg disease (EPM1) (87-89), the most common form of progressive myoclonus epilepsies (90). EPM1 has an onset of symptoms at 6-15 years of age and progression with age leads to myoclonic and tonic-clonic seizures (91, 92), neurological decline, and severe ataxia (91, 93). A CysB knockout (CysBKO) mouse model develops myoclonic seizures and ataxia, similar to symptoms seen in the human disease (94). Degeneration of cerebellar granule cells (94), hippocampal neurons, and cells within the entorhinal cortex was observed in the developing brains of CysBKO mice (95). These mice also show gliosis and increased expression of apoptotic and glial activation genes (95, 96). The progressive cerebellar atrophy caused by CysB deficiency implicates a required role for CysB expression in the development of the cerebellum and in normal neuronal survival. Increased mRNA, protein, and enzymatic activity levels of the two lysosomal enzymes Cat B and Cat D were demonstrated in the brains of CysBKO mice (86). Data suggest that increased proteolysis by lysosomal cathepsins is responsible for the phenotypic characteristics of EPM1 (87, 97, 98) and deletion of Cat B in CysBKO mice resulted in a reduction in the amount of cerebellar granule cell apoptosis depending on mouse age (87).

An endogenous upregulation of CysC mRNA and protein was observed in the brains of EPM1-mimicking CysBKO mice (86). The increase in CysC expression in CysBKO mice might represent a compensatory intrinsic neuroprotective mechanism to rescue neurons by inhibiting the apoptosis-promoting actions of cathepsins. However, the level of CysC expression in these mice may not be sufficient to counteract the progression of the disease. In order to test the hypothesis that CysC overexpression can rescue the loss-of-function of CysB, CysBKO mice were crossbred with CysC overexpressing transgenic mice. It was demonstrated that clinical symptoms and neuropathologies, including deficient motor coordination, cerebellar atrophy, neuronal loss in the cerebellum and cerebral cortex, and gliosis caused by CysB deficiency, are rescued by CysC overexpression (86). CysC overexpression in CysBKO mice decreased Cat B and Cat D activities in the brain (86). These data show that CysC partially prevents neurodegeneration in CysBKO mice through inhibition of cathepsins activity. These findings demonstrate that CysC could be a therapeutic candidate with a potential of preventing EPM1.

3.2. Neuroprotection by induction of neurogenesis

It has been shown that independent of its effects on Cat activity, CysC regulates cell proliferation (11, 12). In rats undergoing acute hippocampal injury or status epilepticus-induced epileptogenesis, the expression of CysC mRNA and protein are increased in the hippocampus and in the dentate gyrus (33-35). The time of increased CysC expression parallels the time of prominent neurogenesis (99, 100). In vitro experiments showed that rat CysC evokes the proliferation of glomerular rat mesangial cells in an autocrine manner (12). It was shown that fibroblast growth factor 2 (FGF-2)-responsive neural stem cell proliferation requires a glycosylated form of rat CysC (101). In vivo grafting of adult rat hippocampus-derived neural progenitor cells coexpressing a secreted form of FGF-2 and the glycosylated form of rat CysC to adult rat hippocampus showed a 4-fold increased proliferation of endogenous progenitor cells in the proximal areas to the grafts within the granular layer of the dentate gyrus, compared to cells not expressing both FGF-2 and this form of CysC (101). Moreover, the basal level of neurogenesis in the subgranular layer of dentate gyrus was decreased in CysC knockout mice, supporting a role for CysC in neurogenesis (101, 102). Finding further revealed CysC as a critical factor for differentiating embryonic stem cells into neural stem cells, when recombinant mouse CysC was added to embryonic stem cell cultures in the presence of FGF2 and EGF (103). The proliferation and migration of newborn granule cells in the dentate gyrus are impaired in CysC knockout mice (102).

CysC is also involved in astrocytic differentiation during mouse brain development. In vitro studies showed that CysC upregulates glial fibrillary acidic protein (GFAP) promoter activity in an immature astrocyte cell line (104). This regulating role of CysC in glial development has been further confirmed: addition of human CysC into the culture medium of primary brain cells increased the number of GFAP-positive and nestin-positive cells, as well as the number of neurospheres formed from embryonic brain (105). Furthermore, CysC gene expression started earlier than that of GFAP in astrocyte progenitor cells in the ventricular zone of mouse forebrain (104). Thus, stimulation of cell proliferation and promotion of the mitogenic activity of cells may be another avenue for CysC mediated neuroprotection.

3.3. Neuroprotection by induction of autophagy

In vitro studies have demonstrated a concentration dependent protective effect of exogenously applied human CysC on neuronal cell lines and primary cortical neurons against the toxicity induced by nutrition-deprivation, oxidative stress, the microtubule-depolymerizing agent colchicine, or staurosporine, a potent wide spectrum inhibitor of protein kinases (106). Moreover, endogenous CysC overexpression in primary cortical neurons isolated from brains of CysC transgenic mice also protected the cells from spontaneous death induced by culturing and from B27-supplement-deprivation (106). Consistent with a protective role for CysC, cells isolated from CysC knockout mice were more sensitive to in vitro toxicity compared to cells isolated from brains of wild type mice (106).

In neuronal cultures exposed to cytotoxic challenges, the neuroprotective action of CysC does not require Cat B inhibition but involves induction of fully functional autophagy (106). Autophagy usually occurs in normal cells to maintain cellular turnover, clearance, and regeneration of new cellular components to restore balance in the system and promote neuronal health, and is greatly increased in cells under pathological conditions that cause cell dysfunction such as trophic stress or nutritional deprivation, hypoxia, ischemia, endotoxin shock, and metabolic inhibition (reviewed in (107-109)). The autophagic pathway consists of sequestration and turnover of organelles and cytoplasm in autophagic vacuoles that following maturation fuse with lysosomes, leading to degradation of their content. Autophagy activation reduces the size of cells and thereby decreases their metabolic burden, while generating new substrates for energy and cellular remodeling. Excessive or imbalanced induction of autophagic recycling on the other hand can actively contribute to neuronal atrophy, neurite degeneration, and cell death. Autophagy induction may protect cells from apoptosis by eliminating damaged mitochondria and other organelles that have the potential to trigger apoptosis (reviewed in (110-111)). However, sustained over-activity or dysfunction of the autophagic pathway in pathologic states mediates a caspase-independent form of cell death that shares certain features with apoptosis (112-115). Multiple methods were used to demonstrate that CysC induces autophagy under nutrition-deprivation conditions above the levels of autophagy observed in stressed cells not treated with CysC. It was demonstrated (a) that the neuroprotective effects of CysC are prevented by inhibiting autophagy with beclin 1 siRNA or 3-methyladenine; (b) that CysC causes microtubule-associated protein Light Chain 3 (LC3-I) conversion to membrane bound LC3-II; (c) that CysC increases the number of autophagic vacuoles in the cytoplasm of cells with otherwise normal ultrastructural morphology; (d) that it reduces mTOR activity (p70S6 kinase dephosphorylation); (e) and that the rate of long-lived proteins breakdown following metabolic labeling is increased by CysC treatment under nutrition deprivation conditions. These assays demonstrated that the observed increase in the number of autophagosomes after exposure to CysC reflects induction of a fully functional autophagy via the mTOR pathway that includes competent proteolytic clearance of autophagy substrates by lysosomes (106). Thus, enhanced lysosomal turnover can protect against neurodegeneration and CysC serves to modulate the efficiency of the autophagic pathway. Maintaining a balanced level of autophagy, promoting clearance and regeneration of new cellular components, is thought to be necessary for the maintenance and restoration of neuronal health (116). It remains to be demonstrated that CysC induces autophagy in vivo as a protective mechanism in brain injury and in neurodegenerative disorders.

3.4. Neuroprotection by inhibition of oligomerization and amyloid fibril formation

A variant form of CysC composes the amyloid deposited in the cerebral vasculature of patients with hereditary cerebral hemorrhage with amyloidosis, Icelandic type (HCHWA-I). HCHWA-I (117, 118), also called hereditary CysC amyloid angiopathy (HCCAA) (119), is an autosomal dominant form of cerebral amyloid angiopathy (CAA). Amyloid deposition in cerebral and spinal arteries and arterioles leads to recurrent hemorrhagic strokes causing serious brain damage and eventually fatal stroke (118). The amyloid deposited is composed mainly of a Leu68Gln variant of CysC (120-124). A heterozygous point mutation, identical to that found in the CysC gene of these patients, was also identified in a Croatian man with CAA and intracerebral hemorrhage (125). Thus, sporadic CAA in some patients may be associated with mutations in the CysC gene. The molecular pathogenesis of variant CysC has been studied intensively (reviewed in (126)). While the variant form of CysC is amyloidogenic, data show that the soluble form of wild type CysC has anti-amyloidogenic properties (127-129).

AD is a progressive neurodegenerative disorder characterized by profound behavioral disorder, loss of memory and reasoning, and personality changes. Neuropathologic hallmarks of AD are loss of neurons with accelerated atrophy of specific brain areas, decreased synapse number in surviving neurons, formation of amyloid deposits in the brain composed mainly of amyloid-beta, a processing product of a larger amyloid beta protein precursor (APP), and presence of neurofibrillary tangles. Extensive research suggests that amyloid-beta has an important role in the pathogenesis of neuronal dysfunction in AD (for reviews see (130-132)), although the pathologically relevant amyloid-beta conformation remains unclear (133). While it was demonstrated that fibrillar amyloid-beta plays a central role in neurotoxicity in AD brains (for review see (134)), both in vitro and in vivo reports describe a potent neurotoxic activity for soluble, nonfibrillar, oligomeric assemblies of amyloid-beta (for reviews see (135, 136)).

Investigations of the roles of CysC in AD have revealed its participation in many of the pathologies that characterize the disease. The involvement of CysC in AD was originally suggested by its colocalization with amyloid-beta in amyloid-laden vascular walls, and in senile plaque cores of amyloid in brains of patients with AD, Down's syndrome, hereditary cerebral hemorrhage with amyloidosis, Dutch type (HCHWA-D), and cerebral infarction (25, 137-140). CysC also colocalizes with amyloid-beta amyloid deposits in the brain of non-demented aged individuals (25), aged rhesus and squirrel monkeys (141), and transgenic mice overexpressing human APP (25, 142).

More recently, genetic data were presented demonstrating linkage of the CysC gene (CST3), localized on chromosome 20 (143, 144), with B/B homozygosity associated with an increased risk of developing late-onset AD (145, 146). While some studies were unable to replicate these findings (147-149), the linkage was supported by others (150-152). For update on the linkage of the CST3 polymorphism with AD see the Alzgene Internet site of the Alzheimer Research Forum (153). The polymorphism in CST3 results in an amino acid exchange, which alters the hydrophobicity profile of the signal sequence (146), resulting in a less efficient cleavage of the signal peptide and thus a reduced secretion of CysC (154, 155), and decreased CysC in cerebrospinal fluid (18). Mutations in the presenilin 2 gene linked to familial AD (PS2 M239I and T122R) alter CysC trafficking in mouse primary neurons causing reduced CysC secretion (156). Reduced levels of CysC may represent the molecular factor responsible for the increased risk of AD and/or increased susceptibility to insult.

Immunohistochemical analyses have shown intensely CysC immunoreactive neurons and activated glia in the cerebral cortex of some aged human cases and of all AD patients (24, 157). Higher neuronal immunostaining of CysC in AD brains is primarily limited to pyramidal neurons in cortical layers III and V (24, 25). The regional distribution of CysC neuronal immunostaining duplicated the pattern of neuronal susceptibility in AD brains: the strongest staining was found in the entorhinal cortex, in the hippocampus, and in the temporal cortex; fewer pyramidal neurons were stained in the frontal, parietal, and occipital lobes (24). Pyramidal neurons in layers III and V in the cortex of AD patients have also displayed a quantitative increase in aspartic protease Cat D immunoreactivity (158). Immunostaining of CysC within neurons showed a punctate distribution, which colocalized with the endosomal/lysosomal protease Cat B (24). Upregulation of cathepsin synthesis in AD neurons and accumulation of hydrolase-laden lysosomes indicate an early activation of the endosomal/lysosomal system in vulnerable neuronal populations, possibly reflecting early regenerative or repair processes (159). Using an end-specific antibody to the carboxyl-terminus of amyloid-beta42, intracellular immunoreactivity was observed in the same neuronal subpopulation (25). These data suggest that amyloid-beta42 accumulates in a specific population of pyramidal neurons in the brain, the same cell type in which CysC is highly expressed.

The significance of the colocalization of CysC with amyloid-beta in the brain was revealed when it was shown that CysC has an anti-amyloidogenic property. It was demonstrated that CysC binds to the amyloid-beta region within full-length APP and that this association does not affect amyloid-beta generation both in vitro (127) and in vivo in transgenic mice expressing the human CysC gene (160). The association of CysC with APP was confirmed using a method for the in vivo mapping of protein interactions in intact mouse tissue (161). CysC does not bind only to amyloid-beta sequences within APP, but also to the peptide itself (127). Analysis of the association demonstrated that CysC interacts with both amyloid-beta40 and amyloid-beta42 in a concentration dependent manner at physiological pH and temperature. A specific, saturable, and high affinity binding between CysC and amyloid-beta was observed (127).

The binding between amyloid-beta and CysC was also observed in the human central nervous system. While CysC binding to soluble amyloid-beta was observed in tissues from AD patients and controls, an SDS-resistant CysC/amyloid-beta complex was detected exclusively in brains of neuropathologically normal controls (162). The association of CysC with amyloid-beta in brains of control individuals and in cerebrospinal fluid reveals an interaction of these two polypeptides in their soluble form. Most importantly, in vitro studies have demonstrated that CysC association with amyloid-beta inhibits amyloid-beta oligomerization and fibril formation (127, 163, 164). The same role of CysC was demonstrated in vivo in amyloid-beta depositing APP transgenic mice overexpressing human CysC. Several lines of transgenic mice, expressing human CysC either under control sequences of the human CysC gene (128), or specifically in cerebral neurons (129), were crossbred with mice overexpressing human APP. CysC bound to the soluble, non-pathological form of amyloid-beta in the brains and plasma of these mice and inhibited the aggregation and deposition of amyloid-beta plaques in the brain (128, 129). However, deletion of CysC in knockout mice resulted in an increase in Cat B activity and an enhanced amyloid-beta degradation (84). Unlike a complete deletion of CysC, reduced or enhanced levels of CysC expression affect the aggregation of amyloid-beta, not amyloid-beta levels (128, 129).

In addition to its anti-amyloidogenic property, CysC directly protects neuronal cells from amyloid-beta toxicity. The extracellular addition of human CysC together with preformed either oligomeric or fibrillar amyloid-beta to cultured primary hippocampal neurons and to a neuronal cell line increased cell survival (164). It was shown that CysC does not dissolve preformed amyloid-beta fibrils or oligomers (127, 163). The data obtained show that subtle modifications in CysC expression levels in the central nervous system, or possibly in the periphery, affect amyloid deposition and protect from the toxicity of aggregated amyloid-beta.

Multiple studies have shown changes in CysC serum concentrations associated with a variety of conditions, such as chronic kidney disease, urinary infection, cancer, hypertension, cardiovascular disease, rheumatoid arthritis, glucocorticoid treatment, thyroid function, and aging (reviewed in (7)). As described above, in the brain, enhanced CysC expression has been observed in response to different types of injury to the central nervous system, such as ischemia or induction of epilepsy as well as in specific neuronal population in AD compared to normal brains. Altered CysC trafficking and a reduction in its secretion are caused by two PS2 mutations (PS2 M239I and T122R), linked to familial AD. A decreased CysC secretion is associated with a polymorphism found in the CysC gene, revealing a mechanism for the increased-risk of late-onset sporadic AD conferred by this polymorphism and suggesting that a reduced CysC brain concentration is associated with the disease.

Recent studies have shown that proteins associated with neurodegenerative disorders are selectively incorporated into intraluminal vesicles of multivesicular bodies and released within exosomes. Exosomes are 40-100 nm bioactive vesicles of endocytic origin that are secreted by diverse cell types and are found in vivo in body fluids such as blood, cerebrospinal fluid, urine, and amniotic fluid. Exosomes can mediate communication between cells, facilitating processes such as antigen presentation and in trans signaling to neighboring cells, in tumor metastasis, and in transmitting infectious agents (for reviews see (165-167)). However, little is known about the biogenesis and function of exosomes in the brain. It has been suggested that exosomes in the brain are involved in cell-cell signaling and glial-neuronal communication, regulation of neurotransmitter receptor levels at the synapse by targeting certain subunits for degradation, and control the production and turnover of myelin membranes proteins (for reviews see (166, 167)). It was also proposed that exosomes have roles in removal of unwanted proteins, and the transfer of pathogens between cells, such as HIV-1. Recent studies have demonstrated that proteins associated with neurodegenerative disorders (AD and prion diseases such as Creutzfeldt-Jakob disease of humans or bovine spongiform encephalopathy of cattle) can be selectively incorporated into intraluminal vesicles of multivesicular bodies and subsequently released into the extracellular environment, enriched within exosomes (168). More recently it was shown that proteins and peptides associated with APP metabolism are released in association with exosomes. These include full-length APP, APP carboxyl-terminal fragments, amyloid-beta, and proteins involved in APP processing such as BACE, PS1, PS2, and ADAM10 (169-171). The identification of amyloid-beta in association with exosomes and of other exosomal proteins, such as alix and flotillin, in plaques deposited in AD brains (169) suggest a role for exosomal release of amyloid-beta in extracellular amyloid deposition in the brain (168-171). However, it is conceivable that exosomes are protective against amyloid aggregation by relieving the cells from toxic accumulation of peptides such as amyloid-beta or by releasing amyloid-beta together with anti-amyloidogenic proteins into the extracellular space.

Given the neuroprotective roles of CysC in neurodegenerative disorders and mainly in AD, determining whether CysC is localized in exosomes, is specifically imperative. The studies have shown that while CysC is constitutively targeted extracellularly via to the classical secretory pathway as a soluble protein, it is also secreted by mouse primary neurons in association with exosomes (172). The presence of CysC in exosomes was demonstrated by immunoelectron microscopy and by immunoproteomic analysis using SELDI TOF MS (172). Moreover, the over-expression of the two familial AD-associated PS2 mutations (PS2 M239I and T122R) that alter CysC trafficking in mouse primary neurons, reducing secretion of its glycosylated form (156), resulted in reduced levels of CysC and of APP metabolites within exosomes (172). The presence of both amyloid-beta and CysC in exosomes suggests an additional location for the anti-amyloidogenic function of CysC. A better understanding of the mechanisms involved in exosomal processing and release and the function of CysC within exosomes will have important implications for the development of therapies against AD and other neurodegenerative diseases.

We hypothesize that endogenous CysC is a carrier of soluble amyloid-beta in body fluids such as cerebral spinal fluid and blood, as well as in the neuropil. It has an ongoing role in inhibition of amyloid-beta oligomerization and amyloidogenesis and protection against neurotoxic insults during an individual's lifetime. Endogenous levels of CysC seem not to be sufficient to prevent amyloid deposition in diseased brain, especially under conditions of reduced CysC concentration. Thus, manipulation of CysC concentration or a CysC peptidomimetic compound that will have enhanced anti-amyloid-beta and neuroprotective properties will be useful for slowing, halting, or reversing AD progression.

Wild type CysC colocalization with amyloid, other than amyloid-beta, was observed in a variety of disorders, such as hereditary gelsolin amyloidosis (familial amyloidosis, Finnish type) (173, 174) and familial cerebral amyloid angiopathy, British type, (175). It remains to be determined whether, similar to beta-amyloidoses, CysC binds other amyloid proteins and prevents their aggregation.


In vitro and in vivo data have demonstrated that CysC, an endogenous secreted protein, plays important roles in neuroprotection against various toxic stimuli. The protective effects of CysC are conferred by several mechanisms that may be activated individually or together under specific conditions. The mechanisms include inhibition of cysteine proteases, induction of cell division, induction of autophagy, and anti-amyloidogenesis. Thus, CysC is an attractive candidate for the development of a novel therapeutic strategy for the prevention, attenuation, and/or treatment of brain injury, Alzheimer's disease and other neurodegenerative disorders.


Sebastien Gauthier and Gurjinder Kaur contributed equally to writing the review. Supported by grants from the National Institute of Neurological Disorders and Stroke (NS42029), the National Institute on Aging (AG017617), and the Alzheimer's Association (IIRG-07-59699).


1. L. A. Bobek and M. J. Levine: Cystatins-inhibitors of cysteine proteinases. Crit Rev Oral Biol M, 3, 307-332 (1992)

2. G. M. Hochwald, A. J. Pepe and G. J. Thorbecke: Trace proteins in biological fluids. IV. Physicochemical properties and sites of formation of gamma trace and beta trace proteins. Proc Soc Exp Med, 124, 961-966 (1967)

3. A. J. Barrett: The cystatins: a diverse superfamily of cysteine peptidase inhibitors. Biomed Biochim Acta, 45(11-12), 1363-1374 (1986)

4. V. Turk and W. Bode: The cystatins: protein inhibitors of cysteine proteinases. FEBS Lett, 285(2), 213-219 (1991)

5. B. Turk, V. Turk and D. Turk: Structural and functional aspects of papain-like cysteine proteinases and their protein inhibitors. Biol Chem, 378(3-4), 141-150 (1997)

6. V. Turk, V. Stoka and D. Turk: Cystatins: biochemical and structural properties, and medical relevance. Front Biosci, 13, 5406-5420 (2008)

7. G. Filler, A. Bokenkamp, W. Hofmann, T. Le Bricon, C. Martinez-Bru and A. Grubb: Cystatin C as a marker of GFR--history, indications, and future research. Clin Biochem, 38(1), 1-8 (2005)

8. U. H. Lerner and A. Grubb: Human cystatin C, a cysteine proteinase inhibitor, inhibits bone resorption in vitro stimulated by parathyroid hormone and parathyroid hormone-related peptide of malignancy. J Bone Miner Res, 7, 433-440 (1992)

9. C. G. Huh, K. Hakansson, C. M. Nathanson, U. P. Thorgeirsson, N. Jonsson, A. Grubb, M. Abrahamson and S. Karlsson: Decreased metastatic spread in mice homozygous for a null allele of the cystatin C protease inhibitor gene. Mol Pathol, 52(6), 332-340 (1999)

10. A. H. Warfel, D. Zucker-Franklin, B. Frangione and J. Ghiso: Constitutive secretion of cystatin C (gamma-trace) by monocytes and macrophages and its downregulation after stimulation. J Exp Med, 166, 1912-1917 (1987)

11. Q. Sun: Growth stimulation of 3T3 fibroblasts by cystatin. Exp Cell Res, 180, 150-160 (1989)

12. C. Tavera, J. Leung-Tack, D. Prevot, M. C. Gensac, J. Martinez, P. Fulcrand and A. Colle: Cystatin C secretion by rat glomerular mesangial cells: autocrine loop for in vitro growth-promoting activity. Biochem Biophys Res Commun, 182, 1082-1088 (1992)

13. T. Akopyan: Protein inhibitors of proteinases from brain. Neurochem Res, 16, 513-517 (1991)

14. M. C. Hoffmann, C. Nitsch, A. L. Scotti, E. Reinhard and D. Monard: The prolonged presence of glia-derived nexin, an endogenous protease inhibitor, in the hippocampus after ischemia-induced delayed neuronal death. Neuroscience, 49, 397-408 (1992)

15. K. S. Lee, S. Frank, P. Vanderklish, A. Arai and G. Lynch: Inhibition of proteolysis protects hippocampal neurons from ischemia. Proc Natl Acad Sci U S A, 88, 7233-7237 (1991)

16. A. Nagai, M. Terashima, A. M. Sheikh, Y. Notsu, K. Shimode, S. Yamaguchi, S. Kobayashi, S. U. Kim and J. Masuda: Involvement of cystatin C in pathophysiology of CNS diseases. Front Biosci, 13, 3470-3479 (2008)

17. E. Zerovnik: The emerging role of cystatins in Alzheimer's disease. Bioessays, 31(6), 597-599 (2009)

18. W. Maetzler, B. Schmid, M. Synofzik, C. Schulte, K. Riester, H. Huber, K. Brockmann, T. Gasser, D. Berg and A. Melms: The CST3 BB Genotype and Low Cystatin C Cerebrospinal Fluid Levels are Associated with Dementia in Lewy Body Disease. J Alzheimers Dis, 19(3), 937-942 (2009)

19. Y. Yang, S. Liu, Z. Qin, Y. Cui, Y. Qin and S. Bai: Alteration of cystatin C levels in cerebrospinal fluid of patients with Guillain-Barre Syndrome by a proteomical approach. Mol Biol Rep, 36(4), 677-682 (2009)

20. J. Mares, P. Kanovsky, R. Herzig, D. Stejskal, J. Vavrouskova, P. Hlustik, H. Vranova, S. Burval, J. Zapletalova, V. Pidrman, R. Obereigneru, A. Suchy, J. Vesely, J. Podivinsky and K. Urbanek: New laboratory markers in diagnosis of alzheimer dementia. Neurol Res, 31(10), 1056-1059 (2009)

21. F. Mori, K. Tanji, Y. Miki and K. Wakabayashi: Decreased cystatin C immunoreactivity in spinal motor neurons and astrocytes in amyotrophic lateral sclerosis. J Neuropath Exp Neur, 68(11), 1200-1206 (2009)

22. S. Tsuji-Akimoto, I. Yabe, M. Niino, S. Kikuchi and H. Sasaki: Cystatin C in cerebrospinal fluid as a biomarker of ALS. Neurosci Lett, 452(1), 52-55 (2009)

23. G. M. Pasinetti, L. H. Ungar, D. J. Lange, S. Yemul, H. Deng, X. Yuan, R. H. Brown, M. E. Cudkowicz, K. Newhall, E. Peskind, S. Marcus and L. Ho: Identification of potential CSF biomarkers in ALS. Neurology, 66(8), 1218-1222 (2006)

24. A. Deng, M. C. Irizarry, R. M. Nitsch, J. H. Growdon and G. W. Rebeck: Elevation of cystatin C in susceptible neurons in alzheimer's disease. Am J Pathol, 159(3), 1061-1068 (2001)

25. E. Levy, M. Sastre, A. Kumar, G. Gallo, P. Piccardo, B. Ghetti and F. Tagliavini: Codeposition of cystatin C with amyloid-beta protein in the brain of Alzheimer's disease patients. J Neuropath Exp Neurol, 60, 94-104 (2001)

26. T. Miyake, Y. Gahara, M. Nakayama, H. Yamada, K. Uwabe and T. Kitamura: Up-regulation of cystatin C by microglia in the rat facial nucleus following axotomy. Brain Res Mol Brain Res, 37(1-2), 273-282 (1996)

27. H. T. Yang, S. Wilkening and M. J. Iadarola: Spinal cord genes enriched in rat dorsal horn and induced by noxious stimulation identified by subtraction cloning and differential hybridization. Neuroscience, 103(2), 493-502 (2001)

28. G. X. Ying, C. Huang, Z. H. Jiang, X. Liu, N. H. Jing and C. F. Zhou: Up-regulation of cystatin C expression in the murine hippocampus following perforant path transections. Neuroscience, 112(2), 289-298 (2002)

29. K. Katakai, M. Shinoda, K. Kabeya, M. Watanabe, Y. Ohe, M. Mori and K. Ishikawa: Changes in distribution of cystatin C, apolipoprotein E and ferritin in rat hypothalamus after hypophysectomy. J Neuroendocrinol, 9(4), 247-253 (1997)

30. D. E. Palm, N. W. Knuckey, M. J. Primiano, A. G. Spangenberger and C. E. Johanson: Cystatin C, a protease inhibitor, in degenerating rat hippocampal neurons following transient forebrain ischemia. Brain Res, 691, 1-8 (1995)

31. H. Ishimaru, K. Ishikawa, Y. Ohe, A. Takahashi and Y. Maruyama: Cystatin C and apolipoprotein E immunoreactivities in CA1 neurons in ischemic gerbil hippocampus. Brain Res, 709(2), 155-162 (1996)

32. T. J. Pirttila and A. Pitkanen: Cystatin C expression is increased in the hippocampus following photothrombotic stroke in rat. Neurosci Lett, 395(2), 108-113 (2006)

33. K. Lukasiuk, T. J. Pirttila and A. Pitkanen: Upregulation of cystatin C expression in the rat hippocampus during epileptogenesis in the amygdala stimulation model of temporal lobe epilepsy. Epilepsia, 43 Suppl 5, 137-145 (2002)

34. H. Hendriksen, N. A. Datson, W. E. Ghijsen, E. A. van Vliet, F. H. da Silva, J. A. Gorter and E. Vreugdenhil: Altered hippocampal gene expression prior to the onset of spontaneous seizures in the rat post-status epilepticus model. Eur J Neurosci, 14(9), 1475-1484 (2001)

35. E. Aronica, E. A. van Vliet, E. Hendriksen, D. Troost, F. H. Lopes da Silva and J. A. Gorter: Cystatin C, a cysteine protease inhibitor, is persistently up-regulated in neurons and glia in a rat model for mesial temporal lobe epilepsy. Eur J Neurosci, 14(9), 1485-1491 (2001)

36. L. Xu, J. Sheng, Z. Tang, X. Wu, Y. Yu, H. Guo, Y. Shen, C. Zhou, L. Paraoan and J. Zhou: Cystatin C prevents degeneration of rat nigral dopaminergic neurons: in vitro and in vivo studies. Neurobiol Dis, 18(1), 152-165 (2005)

37. C. Nishio, K. Yoshida, K. Nishiyama, H. Hatanaka and M. Yamada: Involvement of cystatin C in oxidative stress-induced apoptosis of cultured rat CNS neurons. Brain Res, 873(2), 252-262 (2000)

38. K. Nishiyama, A. Konishi, C. Nishio, K. Araki-Yoshida, H. Hatanaka, M. Kojima, Y. Ohmiya, M. Yamada and H. Koshimizu: Expression of cystatin C prevents oxidative stress-induced death in PC12 cells. Brain Res Bull, 67(1-2), 94-99 (2005)

39. Z. Wang, D. Wu and H. V. Vinters: Hypoxia and reoxygenation of brain microvascular smooth muscle cells in vitro: cellular responses and expression of cerebral amyloid angiopathy-associated proteins. Apmis, 110(5), 423-434 (2002)

40. H. G. Bernstein, H. Kirschke, B. Wiederanders, K. H. Pollak, A. Zipress and A. Rinne: The possible place of cathepsins and cystatins in the puzzle of Alzheimer disease: a review. Mol Chem Neuropathol, 27, 225-247 (1996)

41. B. Turk, D. Turk and V. Turk: Lysosomal cysteine proteases: more than scavengers. Biochim Biophys Acta, 1477(1-2), 98-111 (2000)

42. A. Rudensky, P. Preston-Hurlburt, S. C. Hong, A. Barlow and C. A. Janeway, Jr.: Sequence analysis of peptides bound to MHC class II molecules. Nature, 353(6345), 622-627 (1991)

43. B. J. Rider, E. Fraga, Q. Yu and B. Singh: Immune responses to self peptides naturally presented by murine class II major histocompatibility complex molecules. Mol Immunol, 33(7-8), 625-633 (1996)

44. M. Abrahamson, D. J. Buttle, R. W. Mason, H. Hansson, A. O. Grubb, H. Lilja and K. Ohlsson: Regulation of cystatin C activity by serine proteinases. Biomedica Biochimica Acta, 50, 587-593 (1991)

45. B. Lenarcic, M. Krasovec, A. Ritonja, I. Olafsson and V. Turk: Inactivation of human cystatin C and kininogen by human cathepsin D. FEBS Letters, 280, 211-215 (1991)

46. Y. Nakamura, M. Takeda, H. Suzuki, H. Hattori, K. Tada, S. Hariguchi, S. Hashimoto and T. Nishimura: Abnormal distribution of cathepsins in the brain of patients with Alzheimer's disease. Neurosci Lett, 130, 195-198 (1991)

47. A. Trabandt, R. E. Gay, H. G. Fassbender and S. Gay: Cathepsin B in synovial cells at the site of joint destruction in rheumatoid arthritis. Arthritis Rheum, 34(11), 1444-1451 (1991)

48. A. Kabanda, E. Goffin, A. Bernard, R. Lauwerys and C. van Ypersele de Strihou: Factors influencing serum levels and peritoneal clearances of low molecular weight proteins in continuous ambulatory peritoneal dialysis. Kidney Int, 48(6), 1946-1952 (1995)

49. C. T. Bever, Jr. and D. W. Garver: Increased cathepsin B activity in multiple sclerosis brain. J Neurol Sci, 131(1), 71-73 (1995)

50. A. Nagai, M. Terashima, T. Harada, K. Shimode, H. Takeuchi, Y. Murakawa, M. Nagasaki, A. Nakano and S. Kobayashi: Cathepsin B and H activities and cystatin C concentrations in cerebrospinal fluid from patients with leptomeningeal metastasis. Clin Chim Acta, 329(1-2), 53-60 (2003)

51. I. Sohar, A. Laszlo, K. Gaal and F. Mechler: Cysteine and metalloproteinase activities in serum of Duchenne muscular dystrophic genotypes. Biol Chem Hoppe Seyler, 369 Suppl, 277-279 (1988)

52. T. T. Lah, J. Babnik, E. Schiffmann, V. Turk and U. Skaleric: Cysteine proteinases and inhibitors in inflammation: their role in periodontal disease. J Periodontol 64, 485-491 (1993)

53. D. J. Buttle, M. Abrahamson, D. Burnett, J. S. Mort, A. J. Barrett, P. M. Dando and S. L. Hill: Human sputum cathepsin B degrades proteoglycan, is inhibited by alpha 2-macroglobulin and is modulated by neutrophil elastase cleavage of cathepsin B precursor and cystatin C. Biochem J, 276, 325-331 (1991)

54. I. Assfalg-Machleidt, M. Jochum, D. Nast-Kolb, M. Siebeck, A. Billing, T. Joka, G. Rothe, G. Valet, R. Zauner, H. P. Scheuber and et al.: Cathepsin B-indicator for the release of lysosomal cysteine proteinases in severe trauma and inflammation. Biol Chem Hoppe Seyler, 371 Suppl, 211-222 (1990)

55. C. C. Calkins and B. F. Sloane: Mammalian cysteine protease inhibitors: biochemical properties and possible roles in tumor progression. Biol Chem Hoppe Seyler, 376(2), 71-80 (1995)

56. C. Thomssen, M. Schmitt, L. Goretzki, P. Oppelt, L. Pache, P. Dettmar, F. Janicke and H. Graeff: Prognostic value of the cysteine proteases cathepsins B and cathepsin L in human breast cancer. Clin Cancer Res, 1(7), 741-746 (1995)

57. M. J. Duffy: Proteases as prognostic markers in cancer. Clin Cancer Res, 2(4), 613-618 (1996)

58. J. Kos, B. Werle, T. Lah and N. Brunner: Cysteine proteinases and their inhibitors in extracellular fluids: markers for diagnosis and prognosis in cancer. Int J Biol Markers, 15(1), 84-89 (2000)

59. T. Nitatori, N. Sato, S. Waguri, Y. Karasawa, H. Araki, K. Shibanai, E. Kominami and Y. Uchiyama: Delayed neuronal death in the CA1 pyramidal cell layer of the gerbil hippocampus following transient ischemia is apoptosis. J Neurosci, 15(2), 1001-1011 (1995)

60. T. Yamashima, Y. Kohda, K. Tsuchiya, T. Ueno, J. Yamashita, T. Yoshioka and E. Kominami: Inhibition of ischaemic hippocampal neuronal death in primates with cathepsin B inhibitor CA-074: a novel strategy for neuroprotection based on 'calpain-cathepsin hypothesis'. Eur J Neurosci, 10(5), 1723-1733 (1998)

61. K. Tsuchiya, Y. Kohda, M. Yoshida, L. Zhao, T. Ueno, J. Yamashita, T. Yoshioka, E. Kominami and T. Yamashima: Postictal blockade of ischemic hippocampal neuronal death in primates using selective cathepsin inhibitors. Exp Neurol, 155(2), 187-194 (1999)

62. L. Wei, Y. Berman, E. M. Castano, M. Cadene, R. C. Beavis, L. Devi and E. Levy: Instability of the amyloidogenic cystatin C variant of hereditary cerebral hemorrhage with amyloidosis, Icelandic type. J Biol Chem, 273, 11806-11814 (1998)

63. L. Paraoan, M. R. White, D. G. Spiller, I. Grierson and B. E. Maden: Precursor cystatin C in cultured retinal pigment epithelium cells: evidence for processing through the secretory pathway. Mol Membr Biol, 18(3), 229-236 (2001)

64. P. Pierre and I. Mellman: Developmental regulation of invariant chain proteolysis controls MHC class II trafficking in mouse dendritic cells. Cell, 93(7), 1135-1145 (1998)

65. U. Ekstrom, H. Wallin, J. Lorenzo, B. Holmqvist, M. Abrahamson and F. X. Aviles: Internalization of cystatin C in human cell lines. Febs J, 275(18), 4571-4582 (2008)

66. R. Kolodziejczyk, K. Michalska, A. Hernandez-Santoyo, M. Wahlbom, A. Grubb and M. Jaskolski: Crystal structure of human cystatin C stabilized against amyloid formation. Febs J, 277(7), 1726-1737 (2010)

67. E. A. Runquist and R. J. Havel: Acid hydrolases in early and late endosome fractions from rat liver. J Biol Chem, 266, 22557-22563 (1991)

68. G. Lammers and J. C. Jamieson: The role of a cathepsin D-like activity in the release of Gal beta 1- 4GlcNAc alpha 2-6-sialyltransferase from rat liver Golgi membranes during the acute-phase response. Biochem J, 256, 623-631 (1988)

69. T. J. Krieger and V. Y. Hook: Purification and characterization of a cathepsin D protease from bovine chromaffin granules. Biochemistry, 31, 4223-4231 (1992)

70. H. Matsuba, T. Watanabe, M. Watanabe, Y. Ishii, S. Waguri, E. Kominami and Y. Uchiyama: Immunocytochemical localization of prorenin, renin, and cathepsins B, H, and L in juxtaglomerular cells of rat kidney. J Histochem Cytochem, 37(11), 1689-1697 (1989)

71. N. Marks, M. J. Berg, L. M. Chi, J. Choi, R. Durrie, J. Swistok, R. C. Makofske, W. Danho and V. S. Sapirstein: Hydrolysis of amyloid precursor protein-derived peptides by cysteine proteinases and extracts of rat brain clathrin-coated vesicles. Peptides, 15, 175-182 (1994)

72. K. P. Williams and J. A. Smith: Isolation of a membrane-associated cathepsin D-like enzyme from the model antigen presenting cell, A20, and its ability to generate antigenic fragments from a protein antigen in a cell-free system. Arch Biochem Biophys, 305, 298-306 (1993)

73. M. R. Buck, D. G. Karustis, N. A. Day, K. V. Honn and B. F. Sloane: Degradation of extracellular-matrix proteins by human cathepsin B from normal and tumour tissues. Biochem J, 282 ( Pt 1), 273-278 (1992)

74. P. J. Kingham and J. M. Pocock: Microglial secreted cathepsin B induces neuronal apoptosis. J Neurochem, 76(5), 1475-1484 (2001)

75. B. Boland and V. Campbell: Amyloid-beta -mediated activation of the apoptotic cascade in cultured cortical neurones: a role for cathepsin-L. Neurobiol Aging, 25(1), 83-91 (2004)

76. N. Bidere, H. K. Lorenzo, S. Carmona, M. Laforge, F. Harper, C. Dumont and A. Senik: Cathepsin D triggers Bax activation, resulting in selective apoptosis-inducing factor (AIF) relocation in T lymphocytes entering the early commitment phase to apoptosis. J Biol Chem, 278(33), 31401-31411 (2003)

77. K. Kagedal, M. Zhao, I. Svensson and U. T. Brunk: Sphingosine-induced apoptosis is dependent on lysosomal proteases. Biochem J, 359(Pt 2), 335-343 (2001)

78. K. Roberg and K. Ollinger: Oxidative stress causes relocation of the lysosomal enzyme cathepsin D with ensuing apoptosis in neonatal rat cardiomyocytes. Am J Pathol, 152(5), 1151-1156 (1998)

79. M. Jochum, C. Gippner-Steppert, W. Machleidt and H. Fritz: The role of phagocyte proteinases and proteinase inhibitors in multiple organ failure. Am J Respir Crit Care Med, 150(6 Pt 2), S123-30 (1994)

80. T. Nomura and N. Katunuma: Involvement of cathepsins in the invasion, metastasis and proliferation of cancer cells. J Med Invest, 52(1-2), 1-9 (2005)

81. A. M. Cataldo and R. A. Nixon: Enzymatically active lysosomal proteases are associated with amyloid deposits in Alzheimer brain. Proc Natl Acad Sci U S A, 87, 3861-3865 (1990)

82. A. M. Cataldo, C. Y. Thayer, E. D. Bird, T. R. Wheelock and R. A. Nixon: Lysosomal proteinase antigens are prominently localized within senile plaques of Alzheimer's disease: evidence for a neuronal origin. Brain Res, 513, 181-192 (1990)

83. A. M. Cataldo, D. J. Hamilton and R. A. Nixon: Lysosomal abnormalities in degenerating neurons link neuronal compromise to senile plaque development in Alzheimer disease. Brain Res, 640, 68-80 (1994)

84. B. Sun, Y. Zhou, B. Halabisky, I. Lo, S. H. Cho, S. Mueller-Steiner, N. Devidze, X. Wang, A. Grubb and L. Gan: Cystatin C-cathepsin B axis regulates amyloid beta levels and associated neuronal deficits in an animal model of Alzheimer's disease. Neuron, 60(2), 247-257 (2008)

85. T. Olsson, J. Nygren, K. Hakansson, C. Lundblad, A. Grubb, M. L. Smith and T. Wieloch: Gene deletion of cystatin C aggravates brain damage following focal ischemia but mitigates the neuronal injury after global ischemia in the mouse. Neuroscience, 128(1), 65-71 (2004)

86. G. Kaur, P. Mohan, M. Pawlik, S. Derosa, J. Fajiculay, S. Che, A. Grubbs, S. Ginsberg, R. Nixon and E. Levy: Cystatin C rescues degenerating neurons in a cystatin B-knockout mouse model of progressive myoclonus epilepsy. Am J Pathol, in press (2010)

87. M. K. Houseweart, L. A. Pennacchio, A. Vilaythong, C. Peters, J. L. Noebels and R. M. Myers: Cathepsin B but not cathepsins L or S contributes to the pathogenesis of Unverricht-Lundborg progressive myoclonus epilepsy (EPM1). J Neurobiol, 56(4), 315-327 (2003)

88. M. D. Lalioti, H. S. Scott, C. Buresi, C. Rossier, A. Bottani, M. A. Morris, A. Malafosse and S. E. Antonarakis: Dodecamer repeat expansion in cystatin B gene in progressive myoclonus epilepsy. Nature, 386(6627), 847-851 (1997)

89. L. A. Pennacchio, A. E. Lehesjoki, N. E. Stone, V. L. Willour, K. Virtaneva, J. Miao, E. D'Amato, L. Ramirez, M. Faham, M. Koskiniemi, J. A. Warrington, R. Norio, A. de la Chapelle, D. R. Cox and R. M. Myers: Mutations in the gene encoding cystatin B in progressive myoclonus epilepsy (EPM1). Science, 271(5256), 1731-1734 (1996)

90. R. G. Lafreniere, D. L. Rochefort, N. Chretien, J. M. Rommens, J. I. Cochius, R. Kalviainen, U. Nousiainen, G. Patry, K. Farrell, B. Soderfeldt, A. Federico, B. R. Hale, O. H. Cossio, T. Sorensen, M. A. Pouliot, T. Kmiec, P. Uldall, J. Janszky, M. R. Pranzatelli, F. Andermann, E. Andermann and G. A. Rouleau: Unstable insertion in the 5' flanking region of the cystatin B gene is the most common mutation in progressive myoclonus epilepsy type 1, EPM1. Nat Genet, 15(3), 298-302 (1997)

91. M. Koskiniemi, M. Donner, H. Majuri, M. Haltia and R. Norio: Progressive myoclonus epilepsy. A clinical and histopathological study. Acta Neurologica Scandinavica, 50(3), 307-332 (1974)

92. R. Norio and M. Koskiniemi: Progressive myoclonus epilepsy: genetic and nosological aspects with special reference to 107 Finnish patients. Clin Genet, 15(5), 382-398 (1979)

93. R. Eldridge, M. Iivanainen, R. Stern, T. Koerber and B. J. Wilder: "Baltic" myoclonus epilepsy: hereditary disorder of childhood made worse by phenytoin. Lancet, 2(8354), 838-842 (1983)

94. L. A. Pennacchio, D. M. Bouley, K. M. Higgins, M. P. Scott, J. L. Noebels and R. M. Myers: Progressive ataxia, myoclonic epilepsy and cerebellar apoptosis in cystatin B-deficient mice. Nat Genet, 20(3), 251-258 (1998)

95. P. Shannon, L. A. Pennacchio, M. K. Houseweart, B. A. Minassian and R. M. Myers: Neuropathological changes in a mouse model of progressive myoclonus epilepsy: cystatin B deficiency and Unverricht-Lundborg disease. J Neuropathol Exp Neurol, 61(12), 1085-1091 (2002)

96. A. E. Lehesjoki: Molecular background of progressive myoclonus epilepsy. Embo J, 22(14), 3473-3478 (2003)

97. R. Rinne, P. Saukko, M. Jarvinen and A. E. Lehesjoki: Reduced cystatin B activity correlates with enhanced cathepsin activity in progressive myoclonus epilepsy. Ann Med, 34(5), 380-385 (2002)

98. K. Lieuallen, L. A. Pennacchio, M. Park, R. M. Myers and G. G. Lennon: Cystatin B-deficient mice have increased expression of apoptosis and glial activation genes. Hum Mol Genet, 10(18), 1867-1871 (2001)

99. J. M. Parent, T. W. Yu, R. T. Leibowitz, D. H. Geschwind, R. S. Sloviter and D. H. Lowenstein: Dentate granule cell neurogenesis is increased by seizures and contributes to aberrant network reorganization in the adult rat hippocampus. J Neurosci, 17(10), 3727-3738 (1997)

100. J. Nairismagi, O. H. Grohn, M. I. Kettunen, J. Nissinen, R. A. Kauppinen and A. Pitkanen: Progression of brain damage after status epilepticus and its association with epileptogenesis: a quantitative MRI study in a rat model of temporal lobe epilepsy. Epilepsia, 45(9), 1024-1034 (2004)

101. P. Taupin, J. Ray, W. H. Fischer, S. T. Suhr, K. Hakansson, A. Grubb and F. H. Gage: FGF-2-Responsive neural stem cell proliferation requires CCg, a novel Autocrine/Paracrine cofactor. Neuron, 28(2), 385-397 (2000)

102. T. J. Pirttila, K. Lukasiuk, K. Hakansson, A. Grubb, M. Abrahamson and A. Pitkanen: Cystatin C modulates neurodegeneration and neurogenesis following status epilepticus in mouse. Neurobiol Dis, 20(2), 241-253 (2005)

103. T. Kato, T. Heike, K. Okawa, M. Haruyama, K. Shiraishi, M. Yoshimoto, M. Nagato, M. Shibata, T. Kumada, Y. Yamanaka, H. Hattori and T. Nakahata: A neurosphere-derived factor, cystatin C, supports differentiation of ES cells into neural stem cells. Proc Natl Acad Sci U S A, 103(15), 6019-6024 (2006)

104. T. Kumada, A. Hasegawa, Y. Iwasaki, H. Baba and K. Ikenaka: Isolation of cystatin C via functional cloning of astrocyte differentiation factors. Dev Neurosci, 26(1), 68-76 (2004)

105. A. Hasegawa, M. Naruse, S. Hitoshi, Y. Iwasaki, H. Takebayashi and K. Ikenaka: Regulation of glial development by cystatin C. J Neurochem, 100(1), 12-22 (2007)

106. B. Tizon, S. Sahoo, H. Yu, S. Gauthier, A. R. Kumar, P. Mohan, M. Figliola, M. Pawlik, A. Grubb, Y. Uchiyama, S. Bandyopadhyay, A. M. Cuervo, R. A. Nixon and E. Levy: Induction of autophagy by cystatin C: a mechanism that protects murine primary cortical neurons and neuronal cell lines. PLoS One, 5(3), e9819 (2010)

107. H. Glaumann, J. L. Ericsson and L. Marzella: Mechanisms of intralysosomal degradation with special reference to autophagocytosis and heterophagocytosis of cell organelles. Int Rev Cytol, 73, 149-182 (1981)

108. S. A. Tooze and G. Schiavo: Liaisons dangereuses: autophagy, neuronal survival and neurodegeneration. Curr Opin Neurobiol, 18(5), 504-515 (2008)

109. C. He and D. J. Klionsky: Regulation mechanisms and signaling pathways of autophagy. Annu Rev Genet, 43, 67-93 (2009)

110. K. E. Larsen and D. Sulzer: Autophagy in neurons: a review. Histol Histopathol, 17(3), 897-908 (2002)

111. A. M. Tolkovsky, L. Xue, G. C. Fletcher and V. Borutaite: Mitochondrial disappearance from cells: a clue to the role of autophagy in programmed cell death and disease? Biochimie, 84(2-3), 233-240 (2002)

112. W. Bursch: The autophagosomal-lysosomal compartment in programmed cell death. Cell Death Differ, 8(6), 569-581 (2001)

113. E. H. Baehrecke: Autophagic programmed cell death in Drosophila. Cell Death Differ, 10(9), 940-945 (2003)

114. T. Borsello, K. Croquelois, J. P. Hornung and P. G. Clarke: N-methyl-d-aspartate-triggered neuronal death in organotypic hippocampal cultures is endocytic, autophagic and mediated by the c-Jun N-terminal kinase pathway. Eur J Neurosci, 18(3), 473-485 (2003)

115. C. A. Guimaraes, M. Benchimol, G. P. Amarante-Mendes and R. Linden: Alternative programs of cell death in developing retinal tissue. J Biol Chem, 278(43), 41938-41946 (2003)

116. S. J. Cherra and C. T. Chu: Autophagy in neuroprotection and neurodegeneration: A question of balance. Future Neurol, 3(3), 309-323 (2008)

117. A. Arnason: Apoplexie und ihre Vererbung. Acta Psychiatr Neurol Scand (Suppl), VII, 1-180 (1935)

118. G. Gudmundsson, J. Hallgrimsson, T. A. Jonasson and O. Bjarnason: Hereditary cerebral haemorrhage with amyloidosis. Brain, 95, 387-404 (1972)

119. I. Olafsson, L. Thorsteinsson and O. Jensson: The molecular pathology of hereditary cystatin C amyloid angiopathy causing brain hemorrhage. Brain Pathol, 6, 121-126 (1996)

120. D. H. Cohen, H. Feiner, O. Jensson and B. Frangione: Amyloid fibril in hereditary cerebral hemorrhage with amyloidosis (HCHWA) is related to the gastroentero-pancreatic neuroendocrine protein, gamma trace. J Exp Med, 158, 623-628 (1983)

121. J. Ghiso, B. Pons-Estel and B. Frangione: Hereditary cerebral amyloid angiopathy: the amyloid fibrils contain a protein which is a variant of cystatin C, an inhibitor of lysosomal cysteine proteases. Biochem Biophys Res Commun, 136, 548-554 (1986)

122. A. Palsdottir, M. Abrahamson, L. Thorsteinsson, A. Arnason, I. Olafsson, A. O. Grubb and O. Jensson: Mutation in cystatin C gene causes hereditary brain haemorrhage. Lancet, 2, 603-604 (1988)

123. E. Levy, C. Lopez-Otin, J. Ghiso, D. Geltner and B. Frangione: Stroke in Icelandic patients with hereditary amyloid angiopathy is related to a mutation in the cystatin C gene, an inhibitor of cysteine proteases. J Exp Med, 169, 1771-1778 (1989)

124. M. Abrahamson, I. Olafsson, A. Palsdottir, M. Ulvsback, A. Lundwall, O. Jensson and A. O. Grubb: Structure and expression of the human cystatin C gene. Biochem J, 268, 287-294 (1990)

125. C. Graffagnino, M. H. Herbstreith, D. E. Schmechel, E. Levy, A. D. Roses and M. J. Alberts: Cystatin C mutation in an elderly man with sporadic amyloid angiopathy and intracerebral hemorrhage. Stroke, 26, 2190-2193 (1995)

126. E. Levy, M. Jaskolski and A. Grubb: The role of cystatin C in cerebral amyloid angiopathy and stroke: cell biology and animal models. Brain Pathol, 16(1), 60-70 (2006)

127. M. Sastre, M. Calero, M. Pawlik, P. M. Mathews, A. Kumar, V. Danilov, S. D. Schmidt, R. A. Nixon, B. Frangione and E. Levy: Binding of cystatin C to Alzheimer's amyloid beta inhibits amyloid fibril formation. Neurobiol Aging, 25, 1033-1043 (2004)

128. W. Mi, M. Pawlik, M. Sastre, S. S. Jung, D. S. Radvinsky, A. M. Klein, J. Sommer, S. D. Schmidt, R. A. Nixon, P. M. Mathews and E. Levy: Cystatin C inhibits amyloid-beta deposition in Alzheimer's disease mouse models. Nat Genet, 39(12), 1440-1442 (2007)

129. S. A. Kaeser, M. C. Herzig, J. Coomaraswamy, E. Kilger, M. L. Selenica, D. T. Winkler, M. Staufenbiel, E. Levy, A. Grubb and M. Jucker: Cystatin C modulates cerebral beta-amyloidosis. Nat Genet, 39(12), 1437-1439 (2007)

130. J. Hardy and D. Allsop: Amyloid deposition as the central event in the aetiology of Alzheimer's disease. Trends Pharmacol Sci, 12(10), 383-388 (1991)

131. J. Hardy and D. J. Selkoe: The amyloid hypothesis of Alzheimer's disease: progress and problems on the road to therapeutics. Science, 297(5580), 353-356 (2002)

132. D. J. Selkoe: The molecular pathology of Alzheimer's disease. Neuron, 6, 487-498 (1991)

133. W. B. Stine, Jr., K. N. Dahlgren, G. A. Krafft and M. J. LaDu: In vitro characterization of conditions for amyloid-beta peptide oligomerization and fibrillogenesis. J Biol Chem, 278(13), 11612-11622 (2003)

134. D. A. Butterfield and D. Boyd-Kimball: Amyloid beta-peptide(1-42) contributes to the oxidative stress and neurodegeneration found in Alzheimer disease brain. Brain Pathol, 14(4), 426-432 (2004)

135. W. L. Klein, G. A. Krafft and C. E. Finch: Targeting small amyloid-beta oligomers: the solution to an Alzheimer's disease conundrum? Trends Neurosci, 24(4), 219-224 (2001)

136. D. M. Walsh and D. J. Selkoe: Deciphering the molecular basis of memory failure in Alzheimer's disease. Neuron, 44(1), 181-193 (2004)

137. J. Haan, M. L. C. Maat-Schieman, S. G. van Duinen, O. Jensson, L. Thorsteinsson and R. A. C. Roos: Co-localization of beta/A4 and cystatin C in cortical blood vessels in Dutch, but not in Icelandic hereditary cerebral hemorrhage with amyloidosis. Acta Neurol Scand, 89, 367-371 (1994)

138. Y. Itoh, M. Yamada, M. Hayakawa, E. Otomo and T. Miyatake: Cerebral amyloid angiopathy: a significant cause of cerebellar as well as lobar cerebral hemorrhage in the elderly. J Neurol Sci, 116, 135-141 (1993)

139. K. Maruyama, S. Ikeda, T. Ishihara, D. Allsop and N. Yanagisawa: Immunohistochemical characterization of cerebrovascular amyloid in 46 autopsied cases using antibodies to beta protein and cystatin C. Stroke, 21, 397-403 (1990)

140. H. V. Vinters, G. S. Nishimura, D. L. Secor and W. M. Pardridge: Immunoreactive A4 and gamma-trace peptide colocalization in amyloidotic arteriolar lesions in brains of patients with Alzheimer's disease. Am J Pathol, 137, 233-240 (1990)

141. L. Wei, L. C. Walker and E. Levy: Cystatin C: Icelandic-like mutation in an animal model of cerebrovascular beta amyloidosis. Stroke, 27, 2080-2085 (1996)

142. T. Steinhoff, E. Moritz, M. A. Wollmer, M. H. Mohajeri, S. Kins and R. M. Nitsch: Increased cystatin C in astrocytes of transgenic mice expressing the K670N-M671L mutation of the amyloid precursor protein and deposition in brain amyloid plaques. Neurobiol Dis, 8(4), 647-654 (2001)

143. E. Saitoh, L. M. Sabatini, R. L. Eddy, T. B. Shows, E. A. Azen, S. Isemura and K. Sanada: The human cystatin C gene (CST3) is a member of the cystatin gene family which is localized on chromosome 20. Biochem Biophys Res Commun, 162, 1324-1331 (1989)

144. M. Abrahamson, M. Q. Islam, J. Szpirer, C. Szpirer and G. Levan: The human cystatin C gene (CST3), mutated in hereditary cystatin C amyloid angiopathy, is located on chromosome 20. Hum Genet, 82, 223-226 (1989)

145. F. C. Crawford, M. J. Freeman, J. A. Schinka, L. I. Abdullah, M. Gold, R. Hartman, K. Krivian, M. D. Morris, D. Richards, R. Duara, R. Anand and M. J. Mullan: A polymorphism in the cystatin C gene is a novel risk factor for late-onset Alzheimer's disease. Neurology, 55(6), 763-768 (2000)

146. U. Finckh, H. von Der Kammer, J. Velden, T. Michel, B. Andresen, A. Deng, J. Zhang, T. Muller-Thomsen, K. Zuchowski, G. Menzer, U. Mann, A. Papassotiropoulos, R. Heun, J. Zurdel, F. Holst, L. Benussi, G. Stoppe, J. Reiss, A. R. Miserez, H. B. Staehelin, G. W. Rebeck, B. T. Hyman, G. Binetti, C. Hock, J. H. Growdon and R. M. Nitsch: Genetic association of a cystatin C gene polymorphism with late-onset Alzheimer disease. Arch Neurol, 57(11), 1579-1583 (2000)

147. H. Maruyama, Y. Izumi, M. Oda, T. Torii, H. Morino, H. Toji, K. Sasaki, H. Terasawa, S. Nakamura and H. Kawakami: Lack of an association between cystatin C gene polymorphisms in Japanese patients with Alzheimer's disease. Neurology, 57(2), 337-339 (2001)

148. G. Roks, M. Cruts, A. J. Slooter, B. Dermaut, A. Hofman, C. Van Broeckhoven and C. M. Van Duijn: The cystatin C polymorphism is not associated with early onset Alzheimer's disease. Neurology, 57(2), 366-367 (2001)

149. R. C. Dodel, Y. Du, C. Depboylu, A. Kurz, B. Eastwood, M. Farlow, W. H. Oertel, U. Muller and M. Riemenschneider: A polymorphism in the cystatin C promoter region is not associated with an increased risk of AD. Neurology, 58(4), 664 (2002)

150. K. Beyer, J. I. Lao, M. Gomez, N. Riutort, P. Latorre, J. L. Mate and A. Ariza: Alzheimer's disease and the cystatin C gene polymorphism: an association study. Neurosci Lett, 315(1-2), 17-20 (2001)

151. J. M. Olson, K. A. Goddard and D. M. Dudek: A second locus for very-late-onset Alzheimer disease: a genome scan reveals linkage to 20p and epistasis between 20p and the amyloid precursor protein region. Am J Hum Genet, 71(1), 154-161 (2002)

152. K. A. Goddard, J. M. Olson, H. Payami, M. Van Der Voet, H. Kuivaniemi and G. Tromp: Evidence of linkage and association on chromosome 20 for late-onset Alzheimer disease. Neurogenetics, 5(2), 121-128 (2004)

153. Gene overview of all published AD-association studies for CST3: http://www.alzforum.org/res/com/gen/alzgene/geneoverview.php?geneid=66.

154. L. Benussi, R. Ghidoni, T. Steinhoff, A. Alberici, A. Villa, F. Mazzoli, F. Nicosia, L. Barbiero, L. Broglio, E. Feudatari, S. Signorini, U. Finckh, R. M. Nitsch and G. Binetti: Alzheimer disease-associated cystatin C variant undergoes impaired secretion. Neurobiol Dis, 13(1), 15-21 (2003)

155. L. Paraoan, A. Ratnayaka, D. G. Spiller, P. Hiscott, M. R. White and I. Grierson: Unexpected intracellular localization of the AMD-associated cystatin C variant. Traffic, 5(11), 884-895 (2004)

156. R. Ghidoni, L. Benussi, A. Paterlini, C. Missale, A. Usardi, R. Rossi, L. Barbiero, P. Spano and G. Binetti: Presenilin 2 mutations alter cystatin C trafficking in mouse primary neurons. Neurobiol Aging, 28(3), 371-376 (2007)

157. O. Yasuhara, K. Hanai, I. Ohkubo, M. Sasaki, P. L. McGeer and H. Kimura: Expression of cystatin C in rat, monkey and human brains. Brain Res, 628, 85-92 (1993)

158. A. M. Cataldo, J. L. Barnett, S. A. Berman, J. Li, S. Quarless, S. Bursztajn, C. Lippa and R. A. Nixon: Gene expression and cellular content of cathepsin D in Alzheimer's disease brain: evidence for early up-regulation of the endosomal-lysosomal system. Neuron, 14, 671-680 (1995)

159. A. M. Cataldo, D. J. Hamilton, J. L. Barnett, P. A. Paskevich and R. A. Nixon: Properties of the endosomal-lysosomal system in the human central nervous system: disturbances mark most neurons in populations at risk to degenerate in Alzheimer's disease. J Neurosci, 16, 186-199 (1996)

160. M. Pawlik, M. Sastre, M. Calero, P. M. Mathews, S. D. Schmidt, R. A. Nixon and E. Levy: Overexpression of human cystatin C in transgenic mice does not affect levels of endogenous brain amyloid beta peptide. J Mol Neurosci, 22(1-2), 13-18 (2004)

161. Y. Bai, K. Markham, F. Chen, R. Weerasekera, J. Watts, P. Horne, Y. Wakutani, R. Bagshaw, P. M. Mathews, P. E. Fraser, D. Westaway, P. St George-Hyslop and G. Schmitt-Ulms: The in vivo brain interactome of the amyloid precursor protein. Mol Cell Proteomics, 7(1), 15-34 (2008)

162. W. Mi, S. S. Jung, H. Yu, S. D. Schmidt, R. A. Nixon, P. M. Mathews, F. Tagliavini and E. Levy: Complexes of amyloid-beta and cystatin C in the human central nervous system. J Alzheimers Dis, 18(2), 273-280 (2009)

163. M. L. Selenica, X. Wang, L. Ostergaard-Pedersen, A. Westlind-Danielsson and A. Grubb: Cystatin C reduces the in vitro formation of soluble amyloid-beta 1-42 oligomers and protofibrils. Scand J Clin Lab Invest, 67(2), 179-190 (2007)

164. B. Tizon, E. M. Ribe, W. Mi, C. M. Troy and E. Levy: Cystatin C protects neuronal cells from amyloid beta-induced toxicity. J Alzheimers Dis, 19(3), 665-894 (2010)

165. R. J. Simpson, S. S. Jensen and J. W. Lim: Proteomic profiling of exosomes: current perspectives. Proteomics, 8(19), 4083-4099 (2008)

166. A. Lakkaraju and E. Rodriguez-Boulan: Itinerant exosomes: emerging roles in cell and tissue polarity. Trends Cell Biol, 18(5), 199-209 (2008)

167. N. R. Smalheiser: Exosomal transfer of proteins and RNAs at synapses in the nervous system. Biol Direct, 2, 35 (2007)

168. L. J. Vella, R. A. Sharples, R. M. Nisbet, R. Cappai and A. F. Hill: The role of exosomes in the processing of proteins associated with neurodegenerative diseases. Eur Biophys J, 37(3), 323-332 (2008)

169. L. Rajendran, M. Honsho, T. R. Zahn, P. Keller, K. D. Geiger, P. Verkade and K. Simons: Alzheimer's disease beta-amyloid peptides are released in association with exosomes. Proc Natl Acad Sci U S A, 103(30), 11172-11177 (2006)

170. R. A. Sharples, L. J. Vella, R. M. Nisbet, R. Naylor, K. Perez, K. J. Barnham, C. L. Masters and A. F. Hill: Inhibition of gamma-secretase causes increased secretion of amyloid precursor protein C-terminal fragments in association with exosomes. Faseb J, 22(5), 1469-1478 (2008)

171. V. Vingtdeux, M. Hamdane, A. Loyens, P. Gele, H. Drobeck, S. Begard, M. C. Galas, A. Delacourte, J. C. Beauvillain, L. Buee and N. Sergeant: Alkalizing drugs induce accumulation of amyloid precursor protein by-products in luminal vesicles of multivesicular bodies. J Biol Chem, 282(25), 18197-18205 (2007)

172. R. Ghidoni, A. Paterlini, V. Albertini, M. Glionna, E. Monti, L. Schiaffonati, L. Benussi, E. Levy and G. Binetti: Cystatin C is released in association with exosomes: A new tool of neuronal communication which is unbalanced in Alzheimer's disease. Neurobiol Aging, in press (2009)

173. S. Kiuru, O. Salonen and M. Haltia: Gelsolin-related spinal and cerebral amyloid angiopathy. Ann Neurol, 45, 305-311 (1999)

174. S. Kiuru-Enari, H. Somer, A. M. Seppalainen, I. L. Notkola and M. Haltia: Neuromuscular pathology in hereditary gelsolin amyloidosis. J Neuropathol Exp Neurol, 61(6), 565-571 (2002)

175. J. Ghiso, G. T. Plant, T. Revesz, T. Wisniewski and B. Frangione: Familial cerebral amyloid angiopathy (British type) with nonneuritic amyloid plaque formation may be due to a novel amyloid protein. J Neurol Sci, 129, 74-75 (1995)

Abbreviations: Alzheimer's disease (AD); amyloid beta protein precursor (APP); cathepsin (Cat); cerebral amyloid angiopathy (CAA); cystatin B (CysB); cystatin C (CysC); glial fibrillary acidic protein (GFAP); hereditary cerebral hemorrhage with amyloidosis (HCHWA); presenilin 2 (PS2); Unverricht-Lundborg disease (EPM1)

Key Words: Cystatin C (CysC), Cathepsin; Proliferation, Autophagy, Amyloid, Neurodegeneration, Alzheimer's disease, Review

Send correspondence to: Efrat Levy, Departments of Psychiatry and Pharmacology, New York University School of Medicine, and Nathan S. Kline Institute, Orangeburg, New York, 10962, Tel: 845-398-5540, Fax: 845-398-5422, E-mail:elevy@nki.rfmh.org