Cystatin C reduces the in vitro formation of soluble Abeta1-42 oligomers and protofibrils

Copper interaction with cystatin C: effects on protein structure and oligomerization

Human cystatin C (hCC), a small secretory protein, has gained attention beyond its classical role as a cysteine protease inhibitor owing to its potential involvement in neurodegenerative disorders. This study investigates the interaction between copper(II) ions [Cu(II)] and hCC, specifically targeting histidine residues known to participate in metal binding. Through various analytical techniques, including mutagenesis, circular dichroism, fluorescence assays, gel filtration chromatography, and electron microscopy, we evaluated the impact of Cu(II) ions on the structure and oligomerization of hCC. The results show that Cu(II) does not influence the secondary and tertiary structure of the studied hCC variants but affects their stability. To explore the Cu(II)-binding site, nuclear magnetic resonance (NMR) and X-ray studies were conducted. NMR experiments revealed notable changes in signal intensities and linewidths within the region 86His-Asp-Gln-Pro-His90, suggesting its involvement in Cu(II) coordination. Both histidine residues from this fragment were found to serve as a primary anchor of Cu(II) in solution, depending on the structural context and the presence of other Cu(II)-binding agents. The presence of Cu(II) led to significant destabilization and altered thermal stability of the wild-type and H90A variant, confirming differentiation between His residues in Cu(II) binding. In conclusion, this study provides valuable insights into the interaction between Cu(II) and hCC, elucidating the impact of copper ions on protein stability and identifying potential Cu(II)-binding residues. Understanding these interactions enhances our knowledge of the role of copper in neurodegenerative disorders and may facilitate the development of therapeutic strategies targeting copper-mediated processes in protein aggregation and associated pathologies.

Human cystatin C induces the disaggregation process of selected amyloid beta peptides: a structural and kinetic view

Neurodegenerative diseases, such as Alzheimer's disease (AD) and various types of amyloidosis, are incurable; therefore, understanding the mechanisms of amyloid decomposition is crucial to develop an effective drug against them for future therapies. It has been reported that one out of three people over the age of 85 are suffering from dementia as a comorbidity to AD. Amyloid beta (Aβ), the hallmark of AD, transforms structurally from monomers into β-stranded aggregates (fibrils) via multiple oligomeric states. Astrocytes in the central nervous system secrete the human cystatin C protein (HCC) in response to various proteases and cytokines. The codeposition of Aβ and HCC in the brains of patients with AD led to the hypothesis that cystatin C is implicated in the disease process. In this study, we investigate the intermolecular interactions between different atomic structures of fibrils formed by Aβ peptides and HCC to understand the pathological aggregation of these polypeptides into neurotoxic oligomers and then amyloid plaques. To characterize the interactions between Aβ and HCC, we used a complementary approach based on the combination of small-angle neutron scattering analysis, atomic force microscopy and computational modelling, allowing the exploration of the structures of multicomponent protein complexes. We report here an optimized protocol to study that interaction. The results show a dependency of the sequence length of the Aβ peptide on the ability of the associated HCC to disaggregate it.

Effect of Ovocystatin on Amyloid β 1-42 Aggregation—In Vitro Studies

Amyloid β peptides (Aβ) aggregating in the brain have a potential neurotoxic effect and are believed to be a major cause of Alzheimer’s disease (AD) development. Thus, inhibiting amyloid polypeptide aggregation seems to be a promising approach to the therapy and prevention of this neurodegenerative disease. The research presented here is directed at the determination of the inhibitory activity of ovocystatin, the cysteine protease inhibitor isolated from egg white, on Aβ42 fibril genesis in vitro. Thioflavin-T (ThT) assays, which determine the degree of aggregation of amyloid peptides based on fluorescence measurement, circular dichroism spectroscopy (CD), and transmission electron microscopy (TEM) have been used to assess the inhibition of amyloid fibril formation by ovocystatin. Amyloid beta 42 oligomer toxicity was measured using the MTT test. The results have shown that ovocystatin possesses Aβ42 anti-aggregation activity and inhibits Aβ42 oligomer toxicity in PC12 cells. The results of this work may help in the development of potential substances able to prevent or delay the process of beta-amyloid aggregation—one of the main reasons for Alzheimer’s disease.

Protein Interactome of Amyloid-β as a Therapeutic Target

The amyloid concept of Alzheimer's disease (AD) assumes the β-amyloid peptide (Aβ) as the main pathogenic factor, which injures neural and other brain cells, causing their malfunction and death. Although Aβ has been documented to exert its cytotoxic effect in a solitary manner, there is much evidence to claim that its toxicity can be modulated by other proteins. The list of such Aβ co-factors or interactors includes tau, APOE, transthyretin, and others. These molecules interact with the peptide and affect the ability of Aβ to form oligomers or aggregates, modulating its toxicity. Thus, the list of potential substances able to reduce the harmful effects of the peptide should include ones that can prevent the pathogenic interactions by specifically binding Aβ and/or its partners. In the present review, we discuss the data on Aβ-based complexes in AD pathogenesis and on the compounds directly targeting Aβ or the destructors of its complexes with other polypeptides.

Amyloid Protein Cross-Seeding Provides a New Perspective on Multiple Diseases In Vivo

Amyloid protein cross-seeding is a peculiar phenomenon of cross-spreading among different diseases. Unlike traditional infectious ones, diseases caused by amyloid protein cross-seeding are spread by misfolded proteins instead of pathogens. As a consequence of the interactions among misfolded heterologous proteins or polypeptides, amyloid protein cross-seeding is considered to be the crucial cause of overlapping pathological transmission between various protein misfolding disorders (PMDs) in multiple tissues and cells. Here, we briefly review the phenomenon of cross-seeding among amyloid proteins. As an interesting example worth mentioning, the potential links between the novel coronavirus pneumonia (COVID-19) and some neurodegenerative diseases might be related to the amyloid protein cross-seeding, thus may cause an undesirable trend in the incidence of PMDs around the world. We then summarize the theoretical models as well as the experimental techniques for studying amyloid protein cross-seeding. Finally, we conclude with an outlook on the challenges and opportunities for basic research in this field. Cross-seeding of amyloid opens up a new perspective in our understanding of the process of amyloidogenesis, which is crucial for the development of new treatments for diseases. It is therefore valuable but still challenging to explore the cross-seeding system of amyloid protein as well as to reveal the structural basis and the intricate processes.

Ovocystatin Induced Changes in Expression of Alzheimer's Disease Relevant Proteins in APP/PS1 Transgenic Mice

Background: Ovocystatin is marked by structural and biological similarities to human cystatin C, which plays an important role in the course of neurodegenerative diseases. Recently, it has been shown that ovocystatin might prevent aging-related cognitive impairment in rats and reduce memory decline in an APP/PS1 mice model. Thus, this study aimed to assess the effect of ovocystatin on histopathological changes in APP/PS1 mice. Materials and methods: Ovocystatin was administered intraperitoneally for four weeks (40 μg/mouse) to 35-weeks-old transgenic (AD, n = 14) and wild type (NCAR, n = 15) mice (stock B6C3-Tg(APPswe, PSEN1dE9)85Dbo/Mmjax). A histopathological evaluation comprised antibodies directed against β-amyloid (1:400, SIG-39320-1000, Covance) and Tau (1:4000, AHB0042, Invitrogen). Three regions of the hippocampus— the dentate gyrus (DG) and the cornu ammonis (CA1 and CA3)—were analyzed by immunohistochemistry in each animal. All differences are expressed as percentage relative to the control group. Results: The main results showed that the percentage of immunoreactive area of β-amyloid, tau protein deposits in APP/PS1+ovCYS was decreased in DG, CA1, and CA3 regions compared with the APP/PS1 control, respectively (p < 0.05). Conclusions: Ovocystatin caused significant changes in the expression pattern of all investigated proteins in hippocampal tissues both in APP/PS1 and NCAR mice.

Changes in Serum Cystatin C Levels and the Associations With Cognitive Function in Alzheimer's Disease Patients

Background and Objective

Cystatin C is indicated to be involved in the pathogenesis of Alzheimer's disease (AD) and cognitive impairment. Our objective is to examine the serum Cystatin C levels, and to clarify the correlations between serum Cystatin C and cognitive performance in Chinese AD patients.

Methods

The serum Cystatin C concentrations in AD patients and age, sex, and body mass index (BMI) matched-healthy controls were measured. The cognitive functions of the AD patients were evaluated by using the Mini-mental State Examination (MMSE) and the Montreal Cognitive Assessment (MoCA). The severity of dementia was determined with clinical dementia rating (CDR).

Results

A total of 463 AD patients and 1,389 matched healthy subjects were included. AD patients had higher serum Cystatin C than healthy controls. Serum cystatin C levels were correlated with MoCA scores in AD patients. In an ordinal logistic regression model, AD patients with higher serum cystatin C levels had increased odds of severe cognitive dysfunction.

Conclusion

Our study suggested that AD patients had higher levels of serum cystatin C than age/sex/BMI-matched normal control subjects. Higher serum cystatin C may be associated with worse cognitive performance, but more studies are required to verify such association.

Human serum albumin fusion protein as therapeutics for targeting amyloid beta in Alzheimer's diseases

Alzheimer's disease (AD) is characterized by amyloid beta (Aβ) plaques and neurofibrillary tangles. AD drug development has been limited due to the presence of the blood-brain barrier (BBB), which prevents efficient uptake of therapeutics into the brain. To solve this problem, we used trans-activator of transcription (TAT)-transducing domain and added the human serum albumin (HSA) carrier to increase the half-life of the drug within the body. In addition, we included the protein of interest for lowering Aβ deposition and/or neurofibrillary tangles. We made HSA fusion protein (designated AL04) which contains Cystatin C (CysC) as core mechanism of action moiety in the construct containing tandem repeat TAT (dTAT). After purification of 80KDa AL04, we investigate the therapeutic potential of AL04 in vitro and AD mouse model Tg2576. We evaluated the permeability of AL04 through the BBB using a cell-basedhuman BBB model and show that dTAT plays a role in facilitating the delivery of 80 kDa protein. We found out that AL04 attenuates Aβ-induced neurotoxicity in PC12 cells. In Tg2576 mice brain, Aβ plaques were dramatically reduced in AL04 treated mice. These data suggest that BBB-crossing albumin fusion protein AL04 with CysC active moiety can be a disease modifying treatment for AD.

Extracellular protein components of amyloid plaques and their roles in Alzheimer's disease pathology

Alzheimer's disease (AD) is pathologically defined by the presence of fibrillar amyloid β (Aβ) peptide in extracellular senile plaques and tau filaments in intracellular neurofibrillary tangles. Extensive research has focused on understanding the assembly mechanisms and neurotoxic effects of Aβ during the last decades but still we only have a brief understanding of the disease associated biological processes. This review highlights the many other constituents that, beside Aβ, are accumulated in the plaques, with the focus on extracellular proteins. All living organisms rely on a delicate network of protein functionality. Deposition of significant amounts of certain proteins in insoluble inclusions will unquestionably lead to disturbances in the network, which may contribute to AD and copathology. This paper provide a comprehensive overview of extracellular proteins that have been shown to interact with Aβ and a discussion of their potential roles in AD pathology. Methods that can expand the knowledge about how the proteins are incorporated in plaques are described. Top-down methods to analyze post-mortem tissue and bottom-up approaches with the potential to provide molecular insights on the organization of plaque-like particles are compared. Finally, a network analysis of Aβ-interacting partners with enriched functional and structural key words is presented.

Neuroprotection mediated by cystatin C-loaded extracellular vesicles

Cystatin C (CysC) is implicated in neuroprotection and repair in the nervous system in response to diverse neurotoxic conditions. In addition to being secreted from cells in a soluble form, CysC is released by cells in association with extracellular vesicles (EVs), including exosomes. We demonstrate that EVs containing CysC protect cultured cells from starvation-induced death. Moreover, while EVs secreted by CysC-deficient cells were not protective, EVs secreted by CysC-deficient cells treated with exogenous human CysC significantly enhanced the survival of the cells. CysC also plays a role in modulating the secretion of EVs, enhancing secretion of EVs by primary cortical neurons and primary cortical smooth muscle cells. Confirming these in vitro findings, higher EV levels were observed in the brain extracellular space of transgenic mice expressing human CysC as compared to littermate controls. Regulation of cell-secreted EV levels and content in the brain is likely to be essential to maintaining normal brain function. We propose that enhanced EV release could rescue the deleterious effects of dysfunction of the endosomal-lysosomal system in neurodegenerative disorders. Moreover, a higher level of CysC-loaded EVs released from cells in the central nervous system has important protective functions, representing a potential therapeutic tool for disorders of the central nervous system.

The Functional Mammalian CRES (Cystatin-Related Epididymal Spermatogenic) Amyloid is Antiparallel β-Sheet Rich and Forms a Metastable Oligomer During Assembly

An amyloid matrix composed of several family 2 cystatins, including the reproductive cystatin CRES, is an integral structure in the mouse epididymal lumen and has proposed functions in sperm maturation and protection. Understanding how CRES amyloid assembles in vitro may provide clues on how the epididymal amyloid matrix forms in vivo. We therefore purified full-length CRES under nondenaturing conditions and followed its aggregation from monomer to amyloid under conditions that may approximate those in the epididymal lumen. CRES transitioned into a metastable oligomer that was resistant to aggregation and only over extended time formed higher-ordered amyloids. High protein concentrations facilitated oligomer assembly and also were required to maintain the metastable state since following dilution the oligomer was no longer detected. Similar to other amyloid precursors, the formation of CRES amyloids correlated with a loss of α-helix and a gain of β-sheet content. However, CRES is unique in that its amyloids are rich in antiparallel β-sheets instead of the more common parallel β-sheets. Taken together, our studies suggest that early metastable oligomers may serve as building blocks for functional amyloid assembly and further reveal that antiparallel β-sheet-rich amyloids can be functional forms.

Beneficial effect of ovocystatin on the cognitive decline in APP/PS1 transgenic mice

PURPOSE

Cystatin C plays an important role in the course of neurodegenerative diseases and has a beneficial effect through inhibiting cysteine proteases and amyloid-β aggregation. It also induces proliferation and autophagy. Cystatin isolated from chicken egg white, called ovocystatin, has been widely used in the medical and pharmaceutical research due to its structural and biological similarities to human cystatin C. The aim of this study was to assess the effect of administering ovocystatin on the development of dementia-specific cognitive deficits in APP/PS1 transgenic mice.

MATERIALS/METHODS

The study was conducted on transgenic B6C3-Tg(APPswe,PSEN1dE9)85Dbo/Mmjax mice. Ovocystatin was administered to four-month-old transgenic (AD) and wild type (NCAR) mice in drinking water for 24 weeks (at a dose of 40 and 4 μg/ mouse). The locomotor activity and cognitive functions were determined using an actimeter and the Morris water maze test, respectively.

RESULTS

The results of the study indicate that ovocystatin has a beneficial effect on the cognitive functions in APP/PS1 transgenic mice. The strongest effects of ovocystatin were found in the group of AD mice, where ovocystatin was administered in drinking water at a dose of 40 μg/mouse (p < 0.05). Mice from the AD group swam statistically significantly further in the target zone during the trial in the Morris water maze compared to the AD (vehiculum) group (p < 0.05).

CONCLUSIONS

The obtained results encourage further research into the protective effect, which may be used as an adjuvant in the treatment of deteriorating cognitive functions.

Cystatin C prevents neuronal loss and behavioral deficits via the endosomal pathway in a mouse model of down syndrome

Cystatin C (CysC) plays diverse protective roles under conditions of neuronal challenge. We investigated whether CysC protects from trisomy-induced pathologies in a mouse model of Down syndrome (DS), the most common cause of developmental cognitive and behavioral impairments in humans. We have previously shown that the segmental trisomy mouse model, Ts[Rb(12.1716)]2Cje (Ts2) has DS-like neuronal and behavioral deficiencies. The current study reveals that transgene-mediated low levels of human CysC overexpression has a preventive effect on numerous neuropathologies in the brains of Ts2 mice, including reducing early and late endosome enlargement in cortical neurons and decreasing loss of basal forebrain cholinergic neurons (BFCNs). Consistent with these cellular benefits, behavioral dysfunctions were also prevented, including deficits in nesting behavior and spatial memory. We determined that the CysC-induced neuroprotective mechanism involves activation of the phosphotidylinositol kinase (PI3K)/AKT pathway. Activating this pathway leads to enhanced clearance of accumulated endosomal substrates, protecting cells from DS-mediated dysfunctions in the endosomal system and, for BFCNs, from neurodegeneration. Our findings suggest that modulation of the PI3/AKT pathway offers novel therapeutic interventions for patients with DS.

A Parallel Reaction Monitoring Mass Spectrometric Method for Analysis of Potential CSF Biomarkers for Alzheimer's Disease

SCOPE

The aim of this study was to develop and evaluate a parallel reaction monitoring mass spectrometry (PRM-MS) assay consisting of a panel of potential protein biomarkers in cerebrospinal fluid (CSF).

EXPERIMENTAL DESIGN

Thirteen proteins were selected based on their association with neurodegenerative diseases and involvement in synaptic function, secretory vesicle function, or innate immune system. CSF samples were digested and two to three peptides per protein were quantified using stable isotope-labeled peptide standards.

RESULTS

Coefficients of variation were generally below 15%. Clinical evaluation was performed on a cohort of 10 patients with Alzheimer's disease (AD) and 15 healthy subjects. Investigated proteins of the granin family exhibited the largest difference between the patient groups. Secretogranin-2 (p<0.005) and neurosecretory protein VGF (p<0.001) concentrations were lowered in AD. For chromogranin A, two of three peptides had significantly lowered AD concentrations (p<0.01). The concentrations of the synaptic proteins neurexin-1 and neuronal pentraxin-1, as well as neurofascin were also significantly lowered in AD (p<0.05). The other investigated proteins, β2-microglobulin, cystatin C, amyloid precursor protein, lysozyme C, neurexin-2, neurexin-3, and neurocan core protein, were not significantly altered.

CONCLUSION AND CLINICAL RELEVANCE

PRM-MS of protein panels is a valuable tool to evaluate biomarker candidates for neurodegenerative disorders.

SNPs in Aβ clearance proteins: Lower CSF Aβ1-42 levels and earlier onset of dementia in PD

OBJECTIVE

To evaluate whether genetic variants in β-amyloid (Aβ) clearance proteins are associated with CSF levels of Aβ_1-42 on a biological level and the onset of dementia on a clinical level in Parkinson disease (PD).

METHODS

We analyzed genetic variants known to be involved in Aβ clearance in a PD group comprising 456 patients, 103 of them with dementia. Single nucleotide polymorphisms in the genes APOE, cystatin C (CST), and membrane metalloendopeptidase (MME) were evaluated in relation to demographic variables, clinical phenotypes, and CSF Aβ_1-42 levels using a cross-sectional approach.

RESULTS

Risk variants in the genes APOE and CST were associated with lower CSF Aβ_1-42 levels. Clinically, patients with 2 risk alleles in CST tended to show a shorter interval from age at onset of PD to age at onset of dementia.

CONCLUSIONS

This study suggests that genetic variants associated with Aβ clearance are involved in the pathogenesis of dementia in PD and possibly influence the onset of dementia.

A mechanistic model to predict effects of cathepsin B and cystatin C on β-amyloid aggregation and degradation

β-Amyloid (Aβ) aggregation is thought to initiate a cascade of neurodegenerative events in Alzheimer's disease (AD). Much effort is underway to develop strategies to reduce Aβ concentration or inhibit aggregation. Cathepsin B (CatB) proteolytically degrades Aβ into non-aggregating fragments but is potently inhibited by cystatin C (CysC). It has been suggested that decreasing CysC would facilitate Aβ clearance by relieving CatB inhibition. However, CysC binds Aβ and inhibits Aβ aggregation, suggesting that an intervention that increases CysC would prevent Aβ aggregation. Both approaches have been tested in animal models, yielding contradictory results, possibly because of the opposing influences of CysC on Aβ degradation versus aggregation. Here, we sought to develop a model that quantitatively predicts the effects of CysC and CatB on Aβ aggregation. Aβ aggregation kinetics in the absence of CatB or CysC was measured. The rate constant for Aβ degradation by CatB and the equilibrium constant for binding of CysC to Aβ were determined. We derived a mathematical model that combines material balances and kinetic rate equations. The model accurately predicted Aβ aggregation kinetics at various CatB and CysC concentrations. We derived approximate expressions for the half-times of degradation and aggregation and show that their ratio can be used to estimate, at any given Aβ, CatB, or CysC concentration, whether Aβ aggregation or degradation will result. Our results may be useful for designing experiments and interpreting results from investigations of manipulation of CysC concentration as an AD therapy.

Insights into the mechanism of cystatin C oligomer and amyloid formation and its interaction with β-amyloid

Cystatin C (CysC) is a versatile and ubiquitously-expressed member of the cysteine protease inhibitor family that is present at notably high concentrations in cerebrospinal fluid. Under mildly denaturing conditions, CysC forms inactive domain-swapped dimers. A destabilizing mutation, L68Q, increases the rate of domain-swapping and causes a fatal amyloid disease, hereditary cystatin C amyloid angiopathy. Wild-type (wt) CysC will also aggregate into amyloid fibrils under some conditions. Propagated domain-swapping has been proposed as the mechanism by which CysC fibrils grow. We present evidence that a CysC mutant, V57N, stabilized against domain-swapping, readily forms fibrils, contradicting the propagated domain-swapping hypothesis. Furthermore, in physiological buffer, wt CysC can form oligomers without undergoing domain-swapping. These non-swapped oligomers are identical in secondary structure to CysC monomers and completely retain protease inhibitory activity. However, unlike monomers or dimers, the oligomers bind fluorescent dyes that indicate they have characteristics of pre-amyloid aggregates. Although these oligomers appear to be a pre-amyloid assembly, they are slower than CysC monomers to form fibrils. Fibrillation of CysC therefore likely initiates from the monomer and does not require domain-swapping. The non-swapped oligomers likely represent a dead-end offshoot of the amyloid pathway and must dissociate to monomers prior to rearranging to amyloid fibrils. These prefibrillar CysC oligomers were potent inhibitors of aggregation of the Alzheimer's-related peptide, β-amyloid. This result illustrates an example where heterotypic interactions between pre-amyloid oligomers prevent the homotypic interactions that would lead to mature amyloid fibrils.

Cystatin C in aging and in Alzheimer's disease

Under normal conditions, the function of catalytically active proteases is regulated, in part, by their endogenous inhibitors, and any change in the synthesis and/or function of a protease or its endogenous inhibitors may result in inappropriate protease activity. Altered proteolysis as a result of an imbalance between active proteases and their endogenous inhibitors can occur during normal aging, and such changes have also been associated with multiple neuronal diseases, including Amyotrophic Lateral Sclerosis (ALS), rare heritable neurodegenerative disorders, ischemia, some forms of epilepsy, and Alzheimer's disease (AD). One of the most extensively studied endogenous inhibitor is the cysteine-protease inhibitor cystatin C (CysC). Changes in the expression and secretion of CysC in the brain have been described in various neurological disorders and in animal models of neurodegeneration, underscoring a role for CysC in these conditions. In the brain, multiple in vitro and in vivo findings have demonstrated that CysC plays protective roles via pathways that depend upon the inhibition of endosomal-lysosomal pathway cysteine proteases, such as cathepsin B (Cat B), via the induction of cellular autophagy, via the induction of cell proliferation, or via the inhibition of amyloid-β (Aβ) aggregation. We review the data demonstrating the protective roles of CysC under conditions of neuronal challenge and the protective pathways induced by CysC under various conditions. Beyond highlighting the essential role that balanced proteolytic activity plays in supporting normal brain aging, these findings suggest that CysC is a therapeutic candidate that can potentially prevent brain damage and neurodegeneration.

Identifying biomarkers of dementia prevalent among amnestic mild cognitively impaired ethnic female patients

Background

There is a need to investigate biomarkers that are indicative of the progression of dementia in ethnic patient populations. The disparity of information in these populations has been the focus of many clinical and academic centers, including ours, to contribute to a higher success rate in clinical trials. In this study, we have investigated plasma biomarkers in amnestic mild cognitively impaired (aMCI) female patient cohorts in the context of ethnicity and cognitive status.

Method

A panel of 12 biomarkers involved in the progression of brain pathology, inflammation, and cardiovascular disorders were investigated in female cohorts of African American, Hispanic, and White aMCI patients. Both biochemical and algorithmic analyses were applied to correlate biomarker levels measured during the early stages of the disease for each ethnicity.

Results

We report elevated plasma Aβ₄₀, Aβ₄₂, YKL-40, and cystatin C levels in the Hispanic cohort at early aMCI status. In addition, elevated plasma Aβ₄₀ levels were associated with the aMCI status in both White and African American patient cohorts by the decision tree algorithm. Eotaxin-1 levels, as determined by the decision tree algorithm and biochemically measured total tau levels, were associated with the aMCI status in the African American cohort.

Conclusions

Overall, our data displayed novel differences in the plasma biomarkers of the aMCI female cohorts where the plasma levels of several biomarkers distinguished between each ethnicity at an early aMCI stage. Identification of these plasma biomarkers encourages new areas of investigation among aMCI ethnic populations, including larger patient cohorts and longitudinal study designs.

Electronic supplementary material

The online version of this article (doi:10.1186/s13195-016-0211-0) contains supplementary material, which is available to authorized users.

Characteristics of C-terminal, β-amyloid peptide binding fragment of neuroprotective protease inhibitor, cystatin C

Cystatin C originally identified as a cysteine proteases inhibitor has a broad spectrum of biological roles ranging from inhibition of extracellular cysteine protease activities, bone resorption, and modulation of inflammatory responses to stimulation of fibroblasts proliferation. There is an increasing number of evidence to suggest that human cystatin C (hCC) might play a protective role in the pathophysiology of sporadic Alzheimer's disease. In vivo and in vitro results well documented the association of hCC with Aβ and the hCC-induced inhibition of Aβ fibril formation. In our earlier work, using a combination of selective proteolytic methods and MS spectroscopy, C-terminal fragment hCC(101-117) was identified as the Aβ-binding region. The fragment of Aβ peptide responsible for the complex formation with hCC was found in the middle, highly hydrophobic part, Aβ(17-24). Structures and affinities of both Aβ and hCC binding sites were characterized by the enzyme-linked immunosorbent assay-like assay, by surface plasmon resonance, and by nano-ESI-FTICR MS of the hCC-Aβ-binding peptide complexes. In the in vitro inhibition studies, the binding cystatin sequence, hCC(101-117), revealed the highest relative inhibitory effect toward Aβ-fibril formation. Herein, we present further studies on molecular details of the hCC-Aβ complex. With Ala substitution, affinity experiments, and enzyme-linked immunosorbent assay-like assays for the Aβ-binding fragment, hCC(101-117), and its variants, the importance of individual amino acid residues for the protein interaction was evaluated. The results were analyzed using hCC(101-117) nuclear magnetic resonance structural data with molecular dynamics calculations and molecular modeling of the complexes. The results point to conformational requirements and special importance of some amino acid residues for the protein interaction. The obtained results might be helpful for the design of low molecular compounds modulating the biological role of both proteins. Copyright © 2016 John Wiley & Sons, Ltd.

Cystatin C Shifts APP Processing from Amyloid-β Production towards Non-Amyloidgenic Pathway in Brain Endothelial Cells

Amyloid-β (Aβ), the major component of neuritic plaques in Alzheimer's disease (AD), is derived from sequential proteolytic cleavage of amyloid protein precursor (APP) by secretases. In this study, we found that cystatin C (CysC), a natural cysteine protease inhibitor, is able to reduce Aβ40 secretion in human brain microvascular endothelial cells (HBMEC). The CysC-induced Aβ40 reduction was caused by degradation of β-secretase BACE1 through the ubiquitin/proteasome pathway. In contrast, we found that CysC promoted secretion of soluble APPα indicating the activated non-amyloidogenic processing of APP in HBMEC. Further results revealed that α-secretase ADAM10, which was transcriptionally upregulated in response to CysC, was required for the CysC-induced sAPPα secretion. Knockdown of SIRT1 abolished CysC-triggered ADAM10 upregulation and sAPPα production. Taken together, our results demonstrated that exogenously applied CysC can direct amyloidogenic APP processing to non-amyloidgenic pathway in brain endothelial cells, mediated by proteasomal degradation of BACE1 and SIRT1-mediated ADAM10 upregulation. Our study unveils previously unrecognized protective role of CysC in APP processing.

Cystatin-related epididymal spermatogenic subgroup members are part of an amyloid matrix and associated with extracellular vesicles in the mouse epididymal lumen

STUDY QUESTION

Do the CRES (cystatin-related epididymal spermatogenic) subgroup members, including CRES2, CRES3 and cystatin E2, contribute to the formation of a nonpathological, functional amyloid matrix in the mouse epididymal lumen?

SUMMARY ANSWER

CRES2, CRES3 and cystatin E2 self-assemble with different aggregation properties into amyloids in vitro, are part of a common amyloid matrix in the mouse epididymal lumen and are present in extracellular vesicles.

WHAT IS KNOWN ALREADY

Although previously thought only to be pathological, accumulating evidence has established that amyloids, which are highly ordered protein aggregates, can also carry out functional roles in the absence of pathology. We previously demonstrated that nonpathological amyloids are present in the epididymis; specifically, that the reproductive cystatin CRES forms amyloid and is present in the mouse epididymal lumen in a film-like amyloid matrix that is intimately associated with spermatozoa. Because the related proteins CRES2, CRES3 and cystatin E2 are also expressed in the epididymis, the present studies were carried out to determine if these proteins are also amyloidogenic in vitro and in vivo and thus may coordinately function with CRES as an amyloid structure.

STUDY DESIGN, SAMPLES/MATERIALS, METHODS

The epididymides from CD1 and Cst8 (CRES)129SvEv/B6 gene knockout (KO) and wild-type mice and antibodies that specifically recognize each CRES subgroup member were used for immunohistochemical and biochemical analyzes of CRES subgroup proteins. Methods classically used to identify amyloid, including the conformation-dependent dyes thioflavin S (ThS) and thioflavin T (ThT), conformation-dependent antibodies, protein aggregation disease ligand (which binds any amyloid independent of sequence) and negative stain electron microscopy (EM) were carried out to examine the amyloidogenic properties of CRES subgroup members. Immunofluorescence analysis and confocal microscopy were used for colocalization studies.

MAIN RESULTS AND THE ROLE OF CHANCE

Immunoblot and immunofluorescence analyzes showed that CRES2, CRES3 and cystatin E2 were primarily found in the initial segment and intermediate zone of the epididymis and were profoundly downregulated in epididymides from CRES KO mice, suggesting integrated functions. Except for CRES3, which was only detected in a particulate form, proteins were present in the epididymal lumen in both soluble and particulate forms including in a film-like matrix and in extracellular vesicles. The use of amyloid-specific reagents determined that all CRES subgroup members were present as amyloids and colocalized to a common amyloid matrix present in the epididymal lumen. Negative stain EM, dot blot analysis and ThT plate assays showed that recombinant CRES2, CRES3 and cystatin E2 formed amyloid in vitro, albeit with different aggregation properties. Together, our studies demonstrate that a unique amyloid matrix composed of the CRES family of reproductive-specific cystatins and cystatin C is a normal component of the mouse epididymal lumen and may play a functional role in sperm maturation by coordinating interactions between the luminal fluid and spermatozoa.

LIMITATIONS, REASONS FOR CAUTION

The structures examined in our studies were isolated from luminal fluid obtained by puncture of the epididymis and therefore we cannot rule out some contamination by epithelial cells. Although our studies show CRES family members are associated with extracellular vesicles, we have yet to determine if proteins are present on the surface or are within the vesicles. We also have not established if narrow/apical cells are the source of the CRES family extracellular vesicles. CRES and CRES2 have been previously found in the human epididymis and associated with spermatozoa; however, we have yet to determine if the human CRES subgroup proteins are amyloidogenic and if an amyloid matrix is present in the human epididymal lumen.

WIDER IMPLICATIONS OF THE FINDINGS

Understanding the regulation and biological roles of amyloids, such as the CRES subgroup amyloid matrix that functions without causing pathology, could have broad implications for understanding pathological amyloids including those associated with neurodegenerative diseases and prionopathies.

LARGE SCALE DATA

None.

STUDY FUNDING AND COMPETING INTERESTS

This work was supported by NIH grants RO1HD033903 and RO1HD056182 to G.A.C. The authors declare there are no conflicts of interest.

Cross-interactions between the Alzheimer Disease Amyloid-β Peptide and Other Amyloid Proteins: A Further Aspect of the Amyloid Cascade Hypothesis

Many protein folding diseases are intimately associated with accumulation of amyloid aggregates. The amyloid materials formed by different proteins/peptides share many structural similarities, despite sometimes large amino acid sequence differences. Some amyloid diseases constitute risk factors for others, and the progression of one amyloid disease may affect the progression of another. These connections are arguably related to amyloid aggregates of one protein being able to directly nucleate amyloid formation of another, different protein: the amyloid cross-interaction. Here, we discuss such cross-interactions between the Alzheimer disease amyloid-β (Aβ) peptide and other amyloid proteins in the context of what is known from in vitro and in vivo experiments, and of what might be learned from clinical studies. The aim is to clarify potential molecular associations between different amyloid diseases. We argue that the amyloid cascade hypothesis in Alzheimer disease should be expanded to include cross-interactions between Aβ and other amyloid proteins.

Expression, purification, and characterization of human cystatin C monomers and oligomers

Human cystatin C (cysC) is a soluble basic protein belonging to the cysteine protease inhibitor family. CysC is a potent inhibitor of cathepsins--proteolytic enzymes that degrade intracellular and endocytosed proteins, remodel extracellular matrix, and trigger apoptosis. Inhibition is via tight reversible binding involving the N-terminus as well as two β-hairpin loops of cysC. As a significant component of cerebrospinal fluid, cysC has numerous other functions, including support of neural stem cell growth and differentiation. Several studies suggest that cysC may bind to the Alzheimer-related protein beta-amyloid (Aβ), and inhibit its aggregation and toxicity. Because of an increasing recognition of its important biological roles, there is considerable interest in methods to produce full-length recombinant human cysC. Several researchers have reported success, but with processes that require multiple purification steps. Here we report successful production of human cysC using an intein-based expression system and a simple one-column purification scheme. The recombinant protein so obtained was natively folded and active as an enzyme inhibitor. Unexpectedly, even mild concentration by ultrafiltration caused significant oligomerization. The oligomers are noncovalent and retain the native secondary structure and inhibitory activity of the monomer. The oligomers, but not the monomers, were highly effective at inhibiting aggregation of Aβ. These results demonstrate the critical importance of careful physicochemical characterization of recombinant cysC protein prior to evaluation of its biological functions.

Cystatin C is a disease-associated protein subject to multiple regulation

A protease inhibitor, cystatin C (Cst C), is a secreted cysteine protease inhibitor abundantly expressed in body fluids. Clinically, it is mostly used to measure glomerular filtration rate as a marker for kidney function due to its relatively small molecular weight and easy detection. However, recent findings suggest that Cst C is regulated at both transcriptional and post‐translational levels, and Cst C production from haematopoietic cell lineages contributes significantly to the systematic pools of Cst C. Furthermore, Cst C is directly linked to many pathologic processes through various mechanisms. Thus fluctuation of Cst C levels might have serious clinical implications rather than a mere reflection of kidney functions. Here, we summarize the pathophysiological roles of Cst C dependent and independent on its inhibition of proteases, outline its change of expression by various stimuli, and elucidate the regulatory mechanisms to control this disease‐related protease inhibitor. Finally, we discuss the clinical implications of these findings for translational gains.

Transthyretin-derived peptides as β-amyloid inhibitors

Self-association of β-amyloid (Aβ) into soluble oligomers and fibrillar aggregates is associated with Alzheimer's disease pathology, motivating the search for compounds that selectively bind to and inhibit Aβ oligomerization and/or neurotoxicity. Numerous small-molecule inhibitors of Aβ aggregation or toxicity have been reported in the literature. However, because of their greater size and complexity, peptides and peptidomimetics may afford improved specificity and affinity as Aβ aggregation modulators compared to small molecules. Two divergent strategies have been employed in the search for peptides that bind Aβ: (i) using recognition domains corresponding to sequences in Aβ itself (such as KLVFF) and (ii) screening random peptide-based libraries. In this study, we propose a third strategy, specifically, designing peptides that mimic binding domains of Aβ-binding proteins. Transthyretin, a plasma transport protein that is also relatively abundant in cerebrospinal fluid, has been shown to bind to Aβ, inhibit aggregation, and reduce its toxicity. Previously, we identified strand G of transthyretin as a specific Aβ binding domain. In this work we further explore and define the necessary features of this binding domain. We demonstrate that peptides derived from transthyretin bind Aβ and inhibit its toxicity. We also show that, although both transthyretin and transthyretin-derived peptides bind Aβ and inhibit toxicity, they differ significantly in their effect on Aβ aggregation.

Plasma β-amyloid 40 levels are positively associated with mortality risks in the elderly

BACKGROUND

We evaluated if plasma β-amyloid (Aβ) levels were associated with mortality risks in a subsample of the French Three-City (3C) prospective cohort study.

METHODS

Analyses were based on 1254 participants randomly selected from the initial 3C cohort stratified by center, sex, and age in the context of a nested case-cohort study to investigate biological variables. Associations between plasma Aβ and mortality were assessed with the Cox regression model with delayed entry including various potential confounding factors and testing possible mediators.

RESULTS

A relationship between high plasma Aβ1-40 concentrations and risk of mortality (hazards ratio, 1.15; 95% confidence interval, 1.01-1.31, P = .03) was unveiled independently of age, educational level, vascular risk factors, diet, physical activity, cognitive impairment, or frailty status. It was only modified when we included cystatin C levels.

CONCLUSIONS

Further investigations are needed to determine precisely the pathophysiological roles of plasma Aβ1-40 and cystatin C and before envisioning any future clinical applications.

Fertility defects in mice expressing the L68Q variant of human cystatin C: a role for amyloid in male infertility

Hereditary cystatin C amyloid angiopathy is an autosomal dominant disorder in which a variant form of cystatin C (L68Q) readily forms amyloid deposits in cerebral arteries in affected individuals resulting in early death. L68Q protein deposits in human cystatin C amyloid angiopathy patients have also been found in tissues outside of the brain including the testis, suggesting possible effects on fertility. Heterozygous transgenic mice (L68Q) that express the human L68Q variant of cystatin C under the control of the mouse cystatin C promoter were unable to generate offspring, suggesting the presence of L68Q cystatin C amyloid affected sperm function. In vitro studies showed that epididymal spermatozoa from L68Q mice were unable to fertilize oocytes and exhibited poor sperm motility. Furthermore, spermatozoa from L68Q mice exhibited reduced cell viability compared with wild type (WT) spermatozoa and often were detected in large agglutinated clumps. Examination of the epididymal fluid and spermatozoa from L68Q mice showed increased levels and distinct forms of cystatin C amyloid that were not present in WT mice. The addition of epididymal fluid from L68Q mice to WT spermatozoa resulted in a recapitulation of the L68Q phenotype in that WT spermatozoa showed reduced cell viability and motility compared with WT spermatozoa incubated in epididymal fluid from WT mice. L68Q epididymal fluid that was depleted of cystatin C amyloids, however, did not impair the motility of WT spermatozoa. Taken together these studies suggest that amyloids in the epididymal fluid can be cytotoxic to the maturing spermatozoa resulting in male infertility.

Alterations of CSF cystatin C levels and their correlations with CSF Αβ40 and Αβ42 levels in patients with Alzheimer's disease, dementia with lewy bodies and the atrophic form of general paresis

Immunohistochemical studies have revealed that cystatin C (CysC) co-localizes with amyloid-β (Αβ) in amyloid-laden vascular walls and in the senile plaque cores of amyloid. In vitro and in vivo animal studies suggest that CysC protects against neurodegeneration by inhibition of cysteine proteases, inhibition of Αβ aggregation, induction of autophagy and induction of cell division. CysC levels may be altered and may have a potential link with cerebrospinal fluid (CSF) Aβ levels in various types of dementia with characteristic amyloid deposits, such as Alzheimer's disease (AD), dementia with Lewy bodies (DLB) and the atrophic form of general paresis (AF-GP). We assessed the serum and CSF levels of CysC and the CSF levels of Aβ40 and Aβ42 in patients with AD (n = 51), DLB (n = 26) and AF-GP (n = 43) and normal controls (n = 30). Using these samples, we explored the correlation between CSF CysC and CSF Aβ levels. We found that in comparison to the normal control group, both CSF CysC and CSF Aβ42 levels were significantly lower in all three dementia groups (all p<0.001); serum CysC levels were the same in the AD and DLB groups, and were lower in the AF-GP group (p = 0.008). The CSF CysC levels were positively correlated with both the CSF Aβ40 and Aβ42 levels in the AD, AF-GP and normal control groups (r = 0.306∼0.657, all p<0.05). Lower CSF CysC levels might be a common feature in dementia with characteristic amyloid deposits. Our results provide evidence for the potential role of CysC involvement in Aβ metabolism and suggest that modulation of the CysC level in the brain might produce a disease-modifying effect in dementia with characteristic amyloid deposits.

Vitamin D-binding protein interacts with Aβ and suppresses Aβ-mediated pathology

The level of vitamin D-binding protein (DBP) is increased in the cerebrospinal fluid of patients with Alzheimer's disease (AD), suggesting a relationship with its pathogenesis. In this study, we investigated whether and how DBP is related to AD using several different approaches. A pull-down assay and a surface plasmon resonance binding assay indicated direct interactions between purified DBP and amyloid beta (Aβ), which was confirmed in the brain of AD patients and transgenic AD model mice by immunoprecipitation assay and immunohistochemical double-staining method. Moreover, atomic force microscopic examination revealed that DBP reduced Aβ aggregation in vitro. DBP also prevented Aβ-mediated death in cultured mouse hippocampal HT22 cell line. Finally, DBP decreased Aβ-induced synaptic loss in the hippocampus and rescued memory deficits in mice after injection of Aβ into the lateral ventricle. These results provide converging evidence that DBP attenuates the harmful effects of Aβ by a direct interaction, and suggest that DBP is a promising therapeutic agent for the treatment of AD.

Protein clearance mechanisms of alpha-synuclein and amyloid-Beta in lewy body disorders

Protein clearance is critical for the maintenance of the integrity of neuronal cells, and there is accumulating evidence that in most-if not all-neurodegenerative disorders, impaired protein clearance fundamentally contributes to functional and structural alterations eventually leading to clinical symptoms. Dysfunction of protein clearance leads to intra- and extraneuronal accumulation of misfolded proteins and aggregates. The pathological hallmark of Lewy body disorders (LBDs) is the abnormal accumulation of misfolded proteins such as alpha-synuclein (Asyn) and amyloid-beta (Abeta) in a specific subset of neurons, which in turn has been related to deficits in protein clearance. In this paper we will highlight common intraneuronal (including autophagy and unfolded protein stress response) and extraneuronal (including interaction of neurons with astrocytes and microglia, phagocytic clearance, autoimmunity, cerebrospinal fluid transport, and transport across the blood-brain barrier) protein clearance mechanisms, which may be altered across the spectrum of LBDs. A better understanding of the pathways underlying protein clearance-in particular of Asyn and Abeta-in LBDs may result in the identification of novel biomarkers for disease onset and progression and of new therapeutic targets.

Identification of a beta-amyloid-binding plasma protein, LRP1: implications for biomarker research and therapy in Alzheimer's disease

Evaluation of Sagare A, Deane R, Bell RD et al.: Clearance of amyloid-beta by circulating lipoprotein receptors. Nat. Med. (2007) (Epub ahead of print) [1] . Sagare and coworkers have identified a major amyloid-beta (Abeta)-binding protein in plasma low-density lipoprotein receptor-related protein-1 (LRP1). This protein may bind 70-90% of the Abeta that circulates in peripheral blood and seems to function as a peripheral sink for Alzheimer's disease (AD) causing brain Abeta. Using a mouse model of AD, the authors demonstrate that boosting the capacity of the sink by administering a recombinant form of soluble LRP1 (sLRP1) reduces brain amyloid plaque load and improves learning and memory. They extend these results by demonstrating that patients with AD have depressed plasma sLRP1 levels. Their data suggest that exogenously administered, recombinant sLRP1 may provide a novel approach to reduce or reverse the AD-related build up of Abeta in the brain. Furthermore, it would be interesting to explore the possibility that reduced sLRP1 levels in plasma may be a specific biochemical sign of incipient AD.

Human stefin B normal and patho-physiological role: molecular and cellular aspects of amyloid-type aggregation of certain EPM1 mutants

Epilepsies are characterized by abnormal electrophysiological activity of the brain. Among various types of inherited epilepsies different epilepsy syndromes, among them progressive myoclonus epilepsies with features of ataxia and neurodegeneration, are counted. The progressive myoclonus epilepsy of type 1 (EPM1), also known as Unverricht-Lundborg disease presents with features of cerebellar atrophy and increased oxidative stress. It has been found that EPM1 is caused by mutations in human cystatin B gene (human stefin B). We first describe the role of protein aggregation in other neurodegenerative conditions. Protein aggregates appear intraneurally but are also excreted, such as is the case with senile plaques of amyloid-β (Aβ) that accumulate in the brain parenchyma and vessel walls. A common characteristic of such diseases is the change of the protein conformation toward β secondary structure that accounts for the strong tendency of such proteins to aggregate and form amyloid fibrils. Second, we describe the patho-physiology of EPM1 and the normal and aberrant roles of stefin B in a mouse model of the disease. Furthermore, we discuss how the increased protein aggregation observed with some of the mutants of human stefin B may relate to the neurodegeneration that occurs in rare EPM1 patients. Our hypothesis (Ceru et al., 2005) states that some of the EPM1 mutants of human stefin B may undergo aggregation in neural cells, thus gaining additional toxic function (apart from loss of normal function). Our in vitro experiments thus far have confirmed that four mutants undergo increased aggregation relative to the wild-type protein. It has been shown that the R68X mutant forms amyloid-fibrils very rapidly, even at neutral pH and forms perinuclear inclusions, whereas the G4R mutant exhibits a prolonged lag phase, during which the toxic prefibrillar aggregates accumulate and are scattered more diffusely over the cytoplasm. Initial experiments on the G50E and Q71P missense EPM1 mutants are described.

In vitro assays measuring protection by proteins such as cystatin C of primary cortical neuronal and smooth muscle cells

Neuronal cell culture models have been used to demonstrate the protective effects of cystatin C against a variety of insults, including the toxicity induced by oligomeric and fibrillar amyloid β (Aβ). Here, we describe assays quantifying cystatin C protective effects against cytotoxicity induced by nutrient deprivation, oxidative stress, or cytotoxic forms of Aβ. Three methods for the evaluation of either cell death or cell survival are described: measurement of metabolic activity, cell death, and cell division. The cell culture models used are murine primary cortical neurons and murine primary cerebral smooth muscle cells. The effects of exogenously applied cystatin C are studied by comparing the viability of nonstressed control, stressed control, and cystatin C-treated stressed cells. The effect of endogenous level of cystatin C expression is studied by comparing stressed primary cells isolated from brains of cystatin C transgenic, cystatin C knockout, and wild-type mice.

Amyloid oligomers exacerbate tau pathology in a mouse model of tauopathy

BACKGROUND

We aimed to investigate the influence of oligomeric forms of β-amyloid (Aβ) and the influence of the duration of exposure on the development of tau phosphorylation.

METHODS

Aβ oligomers were injected intracranially either acutely into 5-month-old rTg4510 mice and tissue was collected 3 days later, or chronically into 3-month-old mice and tissue was collected 2 months later. Several forms of phosphorylated tau (p-tau), GSK3 (glycogen synthase kinase-3) and microglial and astrocyte activation were measured.

RESULTS

Acute injections of Aβ oligomers had no effect on p-tau epitopes but did result in elevation of phosphorylated/activated GSK3 (pGSK3). Chronic infusion of Aβ oligomers into the right hippocampus resulted in 3- to 4-fold elevations in several p-tau isoforms with no changes in total tau levels. A significant elevation in pGSK3 accompanied these changes. Microglial staining with CD68 paralleled the increase in tau phosphorylation, however, CD45 staining was unaffected by Aβ. Control experiments revealed that the infusion of Aβ from the minipumps was largely complete by 10 days after implantation. Thus, the elevation in p-tau 2 months after implantation implies that the changes are quite persistent.

CONCLUSION

Soluble Aβ(1-42) oligomers have long-lasting effects on tau phosphorylation in the rTg4510 model, possibly due to elevations in GSK3. These data suggest that even brief elevations in Aβ production, may have enduring impact on the risk for tauopathy.

Cystatin C in Alzheimer's disease

Changes in expression and secretion levels of cystatin C (CysC) in the brain in various neurological disorders and in animal models of neurodegeneration underscore a role for CysC in these conditions. A polymorphism in the CysC gene (CST3) is linked to increased risk for Alzheimer's disease (AD). AD pathology is characterized by deposition of oligomeric and fibrillar forms of amyloid β (Aβ) in the neuropil and cerebral vessel walls, neurofibrillary tangles composed mainly of hyperphosphorylated tau, and neurodegeneration. The implication of CysC in AD was initially suggested by its co-localization with Aβ in amyloid-laden vascular walls, and in senile plaque cores of amyloid in the brains of patients with AD, Down's syndrome, hereditary cerebral hemorrhage with amyloidosis, Dutch type (HCHWA-D), and cerebral infarction. CysC also co-localizes with Aβ amyloid deposits in the brains of non-demented aged individuals. Multiple lines of research show that CysC plays protective roles in AD. In vitro studies have shown that CysC binds Aβ and inhibits Aβ oligomerization and fibril formation. In vivo results from the brains and plasma of Aβ-depositing transgenic mice confirmed the association of CysC with the soluble, non-pathological form of Aβ and the inhibition of Aβ plaques formation. The association of CysC with Aβ was also found in brain and in cerebrospinal fluid (CSF) from AD patients and non-demented control individuals. Moreover, in vitro results showed that CysC protects neuronal cells from a variety of insults that may cause cell death, including cell death induced by oligomeric and fibrillar Aβ. These data suggest that the reduced levels of CysC manifested in AD contribute to increased neuronal vulnerability and impaired neuronal ability to prevent neurodegeneration. This review elaborates on the neuroprotective roles of CysC in AD and the clinical relevance of this protein as a therapeutic agent.

Multiplexed immunoassay panel identifies novel CSF biomarkers for Alzheimer's disease diagnosis and prognosis

BACKGROUND

Clinicopathological studies suggest that Alzheimer's disease (AD) pathology begins ∼10-15 years before the resulting cognitive impairment draws medical attention. Biomarkers that can detect AD pathology in its early stages and predict dementia onset would, therefore, be invaluable for patient care and efficient clinical trial design. We utilized a targeted proteomics approach to discover novel cerebrospinal fluid (CSF) biomarkers that can augment the diagnostic and prognostic accuracy of current leading CSF biomarkers (Aβ42, tau, p-tau181).

METHODS AND FINDINGS

Using a multiplexed Luminex platform, 190 analytes were measured in 333 CSF samples from cognitively normal (Clinical Dementia Rating [CDR] 0), very mildly demented (CDR 0.5), and mildly demented (CDR 1) individuals. Mean levels of 37 analytes (12 after Bonferroni correction) were found to differ between CDR 0 and CDR>0 groups. Receiver-operating characteristic curve analyses revealed that small combinations of a subset of these markers (cystatin C, VEGF, TRAIL-R3, PAI-1, PP, NT-proBNP, MMP-10, MIF, GRO-α, fibrinogen, FAS, eotaxin-3) enhanced the ability of the best-performing established CSF biomarker, the tau/Aβ42 ratio, to discriminate CDR>0 from CDR 0 individuals. Multiple machine learning algorithms likewise showed that the novel biomarker panels improved the diagnostic performance of the current leading biomarkers. Importantly, most of the markers that best discriminated CDR 0 from CDR>0 individuals in the more targeted ROC analyses were also identified as top predictors in the machine learning models, reconfirming their potential as biomarkers for early-stage AD. Cox proportional hazards models demonstrated that an optimal panel of markers for predicting risk of developing cognitive impairment (CDR 0 to CDR>0 conversion) consisted of calbindin, Aβ42, and age.

CONCLUSIONS/SIGNIFICANCE

Using a targeted proteomic screen, we identified novel candidate biomarkers that complement the best current CSF biomarkers for distinguishing very mildly/mildly demented from cognitively normal individuals. Additionally, we identified a novel biomarker (calbindin) with significant prognostic potential.

Proteomic research in psychiatry

Psychiatric disorders such as Alzheimer's disease, schizophrenia and mood disorders are severe and disabling conditions of largely unknown origin and poorly understood pathophysiology. An accurate diagnosis and treatment of these disorders is often complicated by their aetiological and clinical heterogeneity. In recent years proteomic technologies based on mass spectrometry have been increasingly used, especially in the search for diagnostic and prognostic biomarkers in neuropsychiatric disorders. Proteomics enable an automated high-throughput protein determination revealing expression levels, post-translational modifications and complex protein-interaction networks. In contrast to other methods such as molecular genetics, proteomics provide the opportunity to determine modifications at the protein level thereby possibly being more closely related to pathophysiological processes underlying the clinical phenomenology of specific psychiatric conditions. In this article we review the theoretical background of proteomics and its most commonly utilized techniques. Furthermore the current impact of proteomic research on diverse psychiatric diseases, such as Alzheimer's disease, schizophrenia, mood and anxiety disorders, drug abuse and autism, is discussed. Proteomic methods are expected to gain crucial significance in psychiatric research and neuropharmacology over the coming decade.

Identification and validation of novel cerebrospinal fluid biomarkers for staging early Alzheimer's disease

BACKGROUND

Ideally, disease modifying therapies for Alzheimer disease (AD) will be applied during the 'preclinical' stage (pathology present with cognition intact) before severe neuronal damage occurs, or upon recognizing very mild cognitive impairment. Developing and judiciously administering such therapies will require biomarker panels to identify early AD pathology, classify disease stage, monitor pathological progression, and predict cognitive decline. To discover such biomarkers, we measured AD-associated changes in the cerebrospinal fluid (CSF) proteome.

METHODS AND FINDINGS

CSF samples from individuals with mild AD (Clinical Dementia Rating [CDR] 1) (n = 24) and cognitively normal controls (CDR 0) (n = 24) were subjected to two-dimensional difference-in-gel electrophoresis. Within 119 differentially-abundant gel features, mass spectrometry (LC-MS/MS) identified 47 proteins. For validation, eleven proteins were re-evaluated by enzyme-linked immunosorbent assays (ELISA). Six of these assays (NrCAM, YKL-40, chromogranin A, carnosinase I, transthyretin, cystatin C) distinguished CDR 1 and CDR 0 groups and were subsequently applied (with tau, p-tau181 and Aβ42 ELISAs) to a larger independent cohort (n = 292) that included individuals with very mild dementia (CDR 0.5). Receiver-operating characteristic curve analyses using stepwise logistic regression yielded optimal biomarker combinations to distinguish CDR 0 from CDR>0 (tau, YKL-40, NrCAM) and CDR 1 from CDR<1 (tau, chromogranin A, carnosinase I) with areas under the curve of 0.90 (0.85-0.94 95% confidence interval [CI]) and 0.88 (0.81-0.94 CI), respectively.

CONCLUSIONS

Four novel CSF biomarkers for AD (NrCAM, YKL-40, chromogranin A, carnosinase I) can improve the diagnostic accuracy of Aβ42 and tau. Together, these six markers describe six clinicopathological stages from cognitive normalcy to mild dementia, including stages defined by increased risk of cognitive decline. Such a panel might improve clinical trial efficiency by guiding subject enrollment and monitoring disease progression. Further studies will be required to validate this panel and evaluate its potential for distinguishing AD from other dementing conditions.

Protective mechanisms by cystatin C in neurodegenerative diseases

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.

Cystatin C rescues degenerating neurons in a cystatin B-knockout mouse model of progressive myoclonus epilepsy

In vitro studies have shown that cystatin C (CysC) is neuroprotective. Here we demonstrate that CysC is neuroprotective in vivo, in a mouse model of the inherited neurodegenerative disorder, progressive myoclonic epilepsy type 1 (EPM1). Loss-of-function mutations in the cystatin B (CysB) gene, an intracellular cysteine protease inhibitor, lead to this human disease. A CysB-knockout (CysBKO) mouse model develops symptoms that mimic EPM1. CysB deficiency in these mice results in enhanced cathepsin B and D activities, indicating lysosomal dysfunction. We show that expression of CysC is enhanced in the brains of CysBKO mice. Crossbreeding of CysBKO mice with either CysC-overexpressing transgenic mice or CysC-knockout mice demonstrates that clinical symptoms and neuropathologies, including motor coordination disorder, cerebellar atrophy, neuronal loss in the cerebellum and cerebral cortex, and gliosis caused by CysB deficiency, are rescued by CysC overexpression and exacerbated by CysC deficiency. Thus, CysC effectively rescues the CysB loss-of-function mutations, facilitating the reversal of pathophysiological changes and suggesting a novel therapeutic intervention for patients with EPM1 and other neurodegenerative disorders.

Induction of autophagy by cystatin C: a mechanism that protects murine primary cortical neurons and neuronal cell lines

Cystatin C (CysC) expression in the brain is elevated in human patients with epilepsy, in animal models of neurodegenerative conditions, and in response to injury, but whether up-regulated CysC expression is a manifestation of neurodegeneration or a cellular repair response is not understood. This study demonstrates that human CysC is neuroprotective in cultures exposed to cytotoxic challenges, including nutritional-deprivation, colchicine, staurosporine, and oxidative stress. While CysC is a cysteine protease inhibitor, cathepsin B inhibition was not required for the neuroprotective action of CysC. Cells responded to CysC by inducing fully functional autophagy via the mTOR pathway, leading to enhanced proteolytic clearance of autophagy substrates by lysosomes. Neuroprotective effects of CysC were prevented by inhibiting autophagy with beclin 1 siRNA or 3-methyladenine. Our findings show that CysC plays a protective role under conditions of neuronal challenge by inducing autophagy via mTOR inhibition and are consistent with CysC being neuroprotective in neurodegenerative diseases. Thus, modulation of CysC expression has therapeutic implications for stroke, Alzheimer's disease, and other neurodegenerative disorders.

Cystatin C protects neuronal cells from amyloid-beta-induced toxicity

Multiple studies suggest that cystatin C (CysC) has a role in Alzheimer's disease (AD) and a decrease in CysC secretion is linked to the disease in patients with a polymorphism in the CysC gene. CysC binds amyloid-beta (Abeta) and inhibits formation of Abeta fibrils and oligomers both in vitro and in mouse models of amyloid deposition. Here we studied the effect of CysC on cultured primary hippocampal neurons and a neuronal cell line exposed to either oligomeric or fibrillar cytotoxic forms of Abeta. The extracellular addition of the secreted human CysC together with preformed either oligomeric or fibrillar Abeta increased cell survival. While CysC inhibits Abeta aggregation, it does not dissolve preformed Abeta fibrils or oligomers. Thus, CysC has multiple protective effects in AD, by preventing the formation of the toxic forms of Abeta and by direct protection of neuronal cells from Abeta toxicity. Therapeutic manipulation of CysC levels, resulting in slightly higher concentrations than physiological could protect neuronal cells from cell death in AD.

Complexes of amyloid-beta and cystatin C in the human central nervous system

A role for cystatin C (CysC) in the pathogenesis of Alzheimer's disease (AD) has been suggested by the genetic linkage of a CysC gene (CST3) polymorphism with late-onset AD, the co-localization of CysC with amyloid-beta (Abeta) in AD brains, and binding of CysC to soluble Abeta in vitro and in mouse models of AD. This study investigates the binding between Abeta and CysC in the human central nervous system. While CysC binding to soluble Abeta was observed in AD patients and controls, a SDS-resistant CysC/Abeta complex was detected exclusively in brains of neuropathologically normal controls, but not in AD cases. The association of CysC with Abeta in brain from control individuals and in cerebrospinal fluid reveals an interaction of these two polypeptides in their soluble form. The association between Abeta and CysC prevented Abeta accumulation and fibrillogenesis in experimental systems, arguing that CysC plays a protective role in the pathogenesis of AD in humans and explains why decreases in CysC concentration caused by the CST3 polymorphism or by specific presenilin 2 mutations can lead to the development of the disease. Thus, enhancing CysC expression or modulating CysC binding to Abeta have important disease-modifying effects, suggesting a novel therapeutic intervention for AD.

Chaperon-mediated single molecular approach toward modulating Abeta peptide aggregation

We report here a single molecular approach using chaperone-like molecular modulators for modulating the aggregation behavior of a vital analogue of beta-amyloid peptide (Abeta) by using scanning tunneling microscopy. The molecular structures of the beta-sheets for Abeta33-42 peptide are revealed, which are keen to the aggregation of Abeta42 relating to Alzheimer's disease. It was identified that the introduction of chaperone-like modulators could regulate the assembling behavior of the peptide at molecular level. Furthermore, the modulators could also significantly accelerate the aggregation of the peptide in aqueous solution as revealed by light scattering studies. These observations of the molecular modulator effect in peptide assemblies could provide a novel approach toward modulating Abeta peptide aggregations.

Binding epitopes and interaction structure of the neuroprotective protease inhibitor cystatin C with beta-amyloid revealed by proteolytic excision mass spectrometry and molecular docking simulation

Human cystatin C (HCC) is a protease inhibitor with a propensity to form beta-amyloid (Abeta)-like fibrils and to coassociate with amyloidogenic proteins. Recently, a specific interaction between HCC and Abeta has been found. Here, we report the identification of the Abeta and HCC binding epitopes in the Abeta-HCC complex, using a combination of selective proteolytic excision and high resolution mass spectrometry. Proteolytic excision of Abeta(1-40) on sepharose-immobilized HCC and MALDI-MS identified the epitope Abeta(17-28). On immobilized Abeta(1-40), affinity MS of HCC fragments identified a specific C-terminal epitope, HCC(101-117). Binding specificities of both epitopes were ascertained by ELISA and surface plasmon resonance and by direct electrospray MS of the HCC-Abeta epitope peptide complexes. A structure model of the HCC-Abeta complex by molecular docking simulation showed full agreement with the identified Abeta and HCC epitopes. Inhibition studies in vitro revealed Abeta-fibril inhibiting activity of the HCC(101-117)-epitope. The Abeta-HCC interacting epitopes provide lead structures of neuroprotective inhibitors for AD and HCC amyloidosis therapy.