Elevation of cystatin C in susceptible neurons in Alzheimer's disease

Proteolytic and Antiproteolytic Activity in the Skin: Gluing the Pieces Together

Epidermal differentiation is ultimately aimed at the formation of a functional barrier capable of protecting the organism from the environment while preventing loss of biologically vital elements. Epidermal differentiation entails a delicately regulated process of cell-cell junction formation and dissolution to enable upward cell migration and desquamation. Over the past two decades, the deciphering of the genetic basis of a number of inherited conditions has delineated the pivotal role played in this process by a series of proteases and protease inhibitors, including serpins, cathepsins, and cystatins, suggesting novel avenues for therapeutic intervention in both rare and common disorders of cornification.

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.

Cystatins: unravelling the biological implications for neuroprotection

Cystatins, a family of proteins known for their inhibitory role against cysteine proteases, have garnered significant attention in the field of neurodegeneration. Numerous genetic, experimental, and clinical studies concerning cystatin C suggest it plays an important role in the course of neurodegenerative diseases. Its beneficial effects are associated with cysteine protease inhibition, impact on β-amyloid aggregation, as well as regulation of cell proliferation, autophagy, and apoptosis. Cystatin isolated from chicken egg white, called ovocystatin, has been widely used in medical and pharmaceutical research due to its structural and biological similarities to human cystatin C. This article focuses on the potential use of cystatins, with special emphasis on easily obtained ovocystatin, in the treatment of neurodegenerative diseases, such as dementia. The current evidence on cystatin use has shed light on its mechanisms of action and therapeutic implications for neuroprotection and maintenance of cognitive functions.

Aggregation Limiting Cell-Penetrating Peptides Derived from Protein Signal Sequences

Alzheimer's disease (AD) is the most common neurodegenerative disease (ND) and the leading cause of dementia. It is characterized by non-linear, genetic-driven pathophysiological dynamics with high heterogeneity in the biological alterations and the causes of the disease. One of the hallmarks of the AD is the progression of plaques of aggregated amyloid-β (Aβ) or neurofibrillary tangles of Tau. Currently there is no efficient treatment for the AD. Nevertheless, several breakthroughs in revealing the mechanisms behind progression of the AD have led to the discovery of possible therapeutic targets. Some of these include the reduction in inflammation in the brain, and, although highly debated, limiting of the aggregation of the Aβ. In this work we show that similarly to the Neural cell adhesion molecule 1 (NCAM1) signal sequence, other Aβ interacting protein sequences, especially derived from Transthyretin, can be used successfully to reduce or target the amyloid aggregation/aggregates in vitro. The modified signal peptides with cell-penetrating properties reduce the Aβ aggregation and are predicted to have anti-inflammatory properties. Furthermore, we show that by expressing the Aβ-EGFP fusion protein, we can efficiently assess the potential for reduction in aggregation, and the CPP properties of peptides in mammalian cells.

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.

Dense core vesicle markers in CSF and cortical tissues of patients with Alzheimer's disease

Background

New fluid biomarkers for Alzheimer's disease (AD) that reveal synaptic and neural network dysfunctions are needed for clinical practice and therapeutic trial design. Dense core vesicle (DCV) cargos are promising cerebrospinal fluid (CSF) indicators of synaptic failure in AD patients. However, their value as biomarkers has not yet been determined.

Methods

Immunoassays were performed to analyze the secretory proteins prohormone convertases PC1/3 and PC2, carboxypeptidase E (CPE), secretogranins SgIII and SgII, and Cystatin C in the cerebral cortex (n = 45, provided by Bellvitge University Hospital) and CSF samples (n = 66, provided by The Sant Pau Initiative on Neurodegeneration cohort) from AD patients (n = 56) and age-matched controls (n = 55).

Results

In AD tissues, most DCV proteins were aberrantly accumulated in dystrophic neurites and activated astrocytes, whereas PC1/3, PC2 and CPE were also specifically accumulated in hippocampal granulovacuolar degeneration bodies. AD individuals displayed an overall decline of secretory proteins in the CSF. Interestingly, in AD patients, the CSF levels of prohormone convertases strongly correlated inversely with those of neurodegeneration markers and directly with cognitive impairment status.

Conclusions

These results demonstrate marked alterations of neuronal-specific prohormone convertases in CSF and cortical tissues of AD patients. The neuronal DCV cargos are biomarker candidates for synaptic dysfunction and neurodegeneration in AD.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40035-021-00263-0.

Kidney Function Is Not Related to Brain Amyloid Burden on PET Imaging in The 90+ Study Cohort

Cognitive decline is common in chronic kidney disease (CKD). While the evidence of vascular cognitive impairment in this population is robust, the role of Alzheimer's pathology is unknown. We evaluated serum cystatin C-estimated glomerular filtration rate (eGFR), brain amyloid-β positron emission tomography (PET) imaging, and cognitive function in 166 participants from The 90+ Study. Mean age was 93 years (range 90-107) and 101 (61%) were women; 107 participants had normal cognitive status while 59 participants had cognitive impairment no dementia (CIND) or dementia. Mean ± standard deviation cystatin C was 1.59 ± 0.54 mg/L with eGFR 40.7 ± 18.7 ml/min/1.73m2. Higher amyloid-β burden was associated with dementia, but not with age, diabetes, hypertension, or cardiovascular disease. We found no association between brain amyloid-β burden and cystatin C eGFR. We previously reported that kidney function was associated with cognition and cerebral microbleeds in the same cohort of oldest-old adults (90+ years old). Collectively, these findings suggest that microvascular rather than Alzheimer's pathology drives CKD-associated cognitive dysfunction in this population.

Multiomic Analyses of Dopaminergic Neurons Isolated from Human Substantia Nigra in Parkinson's Disease: A Descriptive and Exploratory Study

Dopaminergic neurons (DA) of the substantia nigra pars compacta (SNpc) selectively and progressively degenerate in Parkinson’s disease (PD). Until now, molecular analyses of DA in PD have been limited to genomic or transcriptomic approaches, whereas, to the best of our knowledge, no proteomic or combined multiomic study examining the protein profile of these neurons is currently available. In this exploratory study, we used laser capture microdissection to extract regions from DA in 10 human SNpc obtained at autopsy in PD patients and control subjects. Extracted RNA and proteins were identified by RNA sequencing and nanoliquid chromatography–mass spectrometry, respectively, and the differential expression between PD and control group was assessed. Qualitative analyses confirmed that the microdissection protocol preserves the integrity of our samples and offers access to specific molecular pathways. This multiomic analysis highlighted differential expression of 52 genes and 33 proteins, including molecules of interest already known to be dysregulated in PD, such as LRP2, PNMT, CXCR4, MAOA and CBLN1 genes, or the Aldehyde dehydrogenase 1 protein. On the other hand, despite the same samples were used for both analyses, correlation between RNA and protein expression was low, as exemplified by the CST3 gene encoding for the cystatin C protein. This is the first exploratory study analyzing both gene and protein expression of laser-dissected neuronal parts from SNpc in PD. Data are available via ProteomeXchange with identifier PXD024748 and via GEO with identifier GSE 169755.

Aggregation of Cystatin C Changes Its Inhibitory Functions on Protease Activities and Amyloid β Fibril Formation

Cystatin C (CST3) is an endogenous cysteine protease inhibitor, which is implicated in cerebral amyloid angiopathy (CAA). In CAA, CST3 is found to be aggregated. The purpose of this study is to investigate whether this aggregation could alter the activity of the protein relevant to the molecular pathology of CAA. A system of CST3 protein aggregation was established, and the aggregated protein was characterized. The results showed that CST3 aggregated both at 80 °C without agitation, and at 37 °C with agitation in a time-dependent manner. However, the levels of aggregation were high and appeared earlier at 80 °C. Dot-blot immunoassay for oligomers revealed that CST3 could make oligomeric aggregates at the 37 °C condition. Electron microscopy showed that CST3 could make short fibrillary aggregates at 37 °C. Cathepsin B activity assay demonstrated that aggregated CST3 inhibited the enzyme activity less efficiently at pH 5.5. At 7.4 pH, it lost the inhibitory properties almost completely. In addition, aggregated CST3 did not inhibit Aβ_1-40 fibril formation, rather, it slightly increased it. CST3 immunocytochemistry showed that the protein was positive both in monomeric and aggregated CST3-treated neuronal culture. However, His6 immunocytochemistry revealed that the internalization of exogenous recombinant CST3 by an astrocytoma cell culture was higher when the protein was aggregated compared to its monomeric form. Finally, MTT cell viability assay showed that the aggregated form of CST3 was more toxic than the monomeric form. Thus, our results suggest that aggregation may result in a loss-of-function phenotype of CST3, which is toxic and responsible for cellular degeneration.

NEBULA is a fast negative binomial mixed model for differential or co-expression analysis of large-scale multi-subject single-cell data

The increasing availability of single-cell data revolutionizes the understanding of biological mechanisms at cellular resolution. For differential expression analysis in multi-subject single-cell data, negative binomial mixed models account for both subject-level and cell-level overdispersions, but are computationally demanding. Here, we propose an efficient NEgative Binomial mixed model Using a Large-sample Approximation (NEBULA). The speed gain is achieved by analytically solving high-dimensional integrals instead of using the Laplace approximation. We demonstrate that NEBULA is orders of magnitude faster than existing tools and controls false-positive errors in marker gene identification and co-expression analysis. Using NEBULA in Alzheimer's disease cohort data sets, we found that the cell-level expression of APOE correlated with that of other genetic risk factors (including CLU, CST3, TREM2, C1q, and ITM2B) in a cell-type-specific pattern and an isoform-dependent manner in microglia. NEBULA opens up a new avenue for the broad application of mixed models to large-scale multi-subject single-cell data.

DMPC Phospholipid Bilayer as a Potential Interface for Human Cystatin C Oligomerization: Analysis of Protein-Liposome Interactions Using NMR Spectroscopy

Studies revolving around mechanisms responsible for the development of amyloid-based diseases lay the foundations for the recognition of molecular targets of future to-be-developed treatments. However, the vast number of peptides and proteins known to be responsible for fibril formation, combined with their complexity and complexity of their interactions with various cellular components, renders this task extremely difficult and time-consuming. One of these proteins, human cystatin C (hCC), is a well-known and studied cysteine-protease inhibitor. While being a monomer in physiological conditions, under the necessary stimulus—usually a mutation, it tends to form fibrils, which later participate in the disease development. This process can potentially be regulated (in several ways) by many cellular components and it is being hypothesized that the cell membrane might play a key role in the oligomerization pathway. Studies involving cell membranes pose several difficulties; therefore, an alternative in the form of membrane mimetics is a very attractive solution. Here, we would like to present the first study on hCC oligomerization under the influence of phospholipid liposomes, acting as a membrane mimetic. The protein–mimetic interactions are studied utilizing circular dichroism, nuclear magnetic resonance, and size exclusion chromatography.

Association between cystatin C gene polymorphism and the prevalence of white matter lesion in elderly healthy subjects

Cystatin C (CST3) is a cysteine protease inhibitor abundant in the central nervous system, and demonstrated to have roles in several pathophysiological processes including vascular remodeling and inflammation. Previously, we showed a relation of CST3 gene polymorphisms with deep and subcortical white matter hyperintensity (DSWMH) in a small case-control study. In this study, we aimed to investigate the relation in a larger cross-sectional study. Participants of a brain health examination program were recruited (n = 1795) in the study, who underwent routine blood tests and cognitive function tests. Cerebral white matter changes were analyzed by MRI. Additionally, 7 single nucleotide polymorphisms (SNPs) (−82G/C, −78T/G, −5G/A, +4A/C, +87C/T, +148G/A and +213G/A) in the promoter and coding regions of CST3 gene were examined. Among them, carriers of the minor allele haplotype −82C/+4C/+148A were significantly associated with decreased CST3 concentration in the plasma. Unadjusted analysis did not show significant relation between carriers of the minor allele haplotype and periventricular hyperintensity (PVH), but DSWMH was marginally (p < 0.054) increased in this group. After adjusting the effects of other variables like age and kidney function, logistic regression analysis revealed that carriers of the minor allele haplotype were at a significantly increased risk of developing both PVH and DSWMH. Thus, our results suggest that carriers of the minor allele haplotype −82C/+4C/+148A of CST3 gene could be at an increased risk to develop cerebral white matter disturbance.

Correlations between blood lipid, serum cystatin C, and homocysteine levels in patients with Parkinson's disease

AIM

The aim was too study the correlations between blood lipid, serum cystatin C (Cys C) and homocysteine (Hcy) levels in patients with Parkinson's disease (PD).

METHODS

A total of 322 PD patients and 214 healthy subjects were selected as case and control groups, respectively. The risk factors were explored by logistic regression analysis. The case group was subtyped according to main motor symptoms and age of onset. The correlations of significantly different indices with age, duration of disease, and equivalent dose of levodopa were studied by Spearman's correlation analysis. Receiver operating characteristic curves were plotted to analyze diagnostic values.

RESULTS

Compared to the control group, the PD group had lower serum total cholesterol, triglyceride, and apolipoprotein B (Apo B) levels and higher high-density lipoprotein cholesterol (HDL-C), Hcy, and Cys C levels (P < 0.05). Decreased Apo B level and increased HDL-C and Hcy levels were independent risk factors (P < 0.05). The Cys C level of early-onset patients was lower than of late-onset patients (P < 0.05). Hcy (r = 0.198, P < 0.05) and Cys C (r = 0.281, P < 0.05) levels were positively correlated with age. Triglyceride level was negatively correlated with age (r = -0.202, P < 0.05) and disease duration (r = -0.198, P < 0.05). Unified Parkinson's Disease Rating Scale III score was positively correlated with disease duration (r = 0.435, P < 0.05) and equivalent dose of levodopa (r = 0.423, P < 0.05). The areas under the curve for Apo B, HDL-C, and Hcy levels were 0.341, 0.588, and 0.643, respectively (P < 0.05). The combination of Apo B, HDL-C, and Hcy levels showed high diagnostic value, with a sensitivity of 76.4% and specificity of 69.5%.

CONCLUSIONS

Low serum levels of total cholesterol, triglyceride, and Apo B, and high levels of HDL-C, Hcy, and Cys C may be correlated with PD onset and progression. Decreased Apo B level and elevated HDL-C and Hcy levels are independent risk factors. Early-onset and late-onset PD may have different progression mechanisms.

Amyloid cross-seeding raises new dimensions to understanding of amyloidogenesis mechanism

Hallmarks of most of the amyloid pathologies are surprisingly found to be heterocomponent entities such as inclusions and plaques which contain diverse essential proteins and metabolites. Experimental studies have already revealed the occurrence of coaggregation and cross-seeding during amyloid formation of several proteins and peptides, yielding multicomponent assemblies of amyloid nature. Further, research reports on the co-occurrence of more than one type of amyloid-linked pathologies in the same individual suggest the possible cross-talk among the disease related amyloidogenic protein species during their amyloid growth. In this review paper, we have tried to gain more insight into the process of coaggregation and cross-seeding during amyloid aggregation of proteins, particularly focusing on their relevance to the pathogenesis of the protein misfolding diseases. Revelation of amyloid cross-seeding and coaggregation seems to open new dimensions in our mechanistic understanding of amyloidogenesis and such knowledge may possibly inspire better designing of anti-amyloid therapeutics.

Pathogenic Tau Protein Species: Promising Therapeutic Targets for Ocular Neurodegenerative Diseases

Tau is a microtubule-associated protein, which is highly expressed in the central nervous system as well as ocular neurons and stabilizes microtubule structure. It is a phospho-protein being moderately phosphorylated under physiological conditions but its abnormal hyperphosphorylation or some post-phosphorylation modifications would result in a pathogenic condition, microtubule dissociation, and aggregation. The aggregates can induce neuroinflammation and trigger some pathogenic cascades, leading to neurodegeneration. Taking these together, targeting pathogenic tau employing tau immunotherapy may be a promising therapeutic strategy in fighting with cerebral and ocular neurodegenerative disorders.

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.

Correlations of serum cystatin C level and gene polymorphism with vascular cognitive impairment after acute cerebral infarction

BACKGROUND

The aim of this study was to explore the possible correlations of serum cystatin C level and cystatin C gene (CST3) polymorphism with vascular cognitive impairment in patients who had acute cerebral infarction.

METHODS

A total of 152 patients with acute cerebral infarction were recruited in this case-control study. Patients were divided into vascular cognitive impairment (VCI) group (n = 71) and cognitive impairment no dementia (CIND) group (n = 81). The serum concentrations of cystatin C were measured with immunoturbidimetric assay while the gene polymorphisms of CST3 were determined by technique polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP).

RESULTS

In the VCI group, serum cystatin C level was significantly higher than that in the control group. The frequency of the B allele was found to be higher in the VCI group as compared with that of the CIND group (18.5% vs 7.7%, p = 0.006). In logistic regression analysis, significant associations of VCI with high serum cystatin C level (OR 3.837 (1.176-12.520), p = 0.026) and CST3 B allele (OR 2.038 (1.048-3.963), p = 0.036) were also found.

CONCLUSIONS

A high cystatin C level and CST3 B allele confer risks for VCI after acute cerebral infarction. It is probable that measurement of the serum cystatin C level and detection of CST3 gene polymorphism would aid in the early diagnosis of VCI, but further studies are warranted.

An Improved Assay for Quantitation of Cerebrospinal Fluid Cystatin C Using Liquid Chromatography Tandem Mass Spectrometry

Cystatin C (CST3) is expressed ubiquitously and implicated in several neurological diseases. It can be posttranscriptionally modified. CST3 is usually quantified in a biological sample using antibody-based methods. Posttranscriptional modification can hamper antibody-based detection systems by altering antibody-binding epitope(s). To circumvent this problem, enzymatic digestion and liquid chromatography tandem mass spectrometry (LC-MS/MS) technique can be employed to identify and measure peptides of a target protein in a complex biological mixture. This chapter describes an LC-MS/MS-based method for accurate measurement of CST3 in cerebrospinal fluid (CSF). Here, CSF was directly subjected to trypsin digestion and digested peptides were extracted using a solid-phase extraction column. Extracted peptide samples were directly used for LC-MS/MS-based identification and quantification of CST3 peptides. Comparing the concentration in a set of samples measured by LC-MS/MS with that of immunoassay shows that it was significantly higher when measured by LC-MS/MS method, suggesting it a better quantification method. This approach is particularly well suited when posttranscriptional modification of CST3 is suspected and sample volume of CSF is small.

Cystatin C Is an Important Biomarker for Cardiovascular Autonomic Dysfunction in Chinese Type 2 Diabetic Patients

BACKGROUND

Cardiovascular autonomic dysfunction is closely related to increased mortality in patients with diabetes. Previous studies have proved that cystatin C (CysC) is an important predictor of both peripheral neuropathy and cardiovascular events. However, whether CysC is also associated with cardiovascular autonomic dysfunction remains unclear. Therefore, the aim of this study was to investigate the relationship between CysC and cardiovascular autonomic dysfunction in type 2 diabetic patients without renal dysfunction.

METHODS

A total of 161 type 2 diabetic patients with normal serum creatinine (less than 133 μmol/l) and estimated glomerular filtration rate (eGFR) higher than 60 ml/min per 1.73 m² were recruited in our study. Cardiovascular autonomic dysfunction was determined by heart rate variability (HRV) measured by a 24-hour Holter monitor. Serum CysC was tested by particle-enhanced turbidimetric immunoassay, and subjects were divided into three groups based on the tertiles of CysC. Pearson correlation analysis was used to evaluate the association between different indexes, and the association of CysC with HRV indexes was assessed by multivariate linear regression analysis.

RESULTS

The HRV parameters were lower in the group with the highest CysC concentration than in the groups with lower levels of CysC (P < 0.05). Pearson correlation analysis showed a negative relationship between CysC and the HRV parameters, including SDNN (r = -0.31, P < 0.001), SDANN (r = -0.25, P = 0.002), and logLF (r = -0.18, P = 0.023). Furthermore, multivariate linear regression analysis revealed that CysC was independently correlated with SDNN (β = -24.11, P = 0.015) and SDANN (β = -19.88, P = 0.047) after adjusting for the confounding factors of gender, age, blood pressure, body mass index, eGFR, and hemoglobin A1c.

CONCLUSIONS

Serum CysC levels are associated with cardiovascular autonomic dysfunction; furthermore, CysC may be a reliable and convenient biomarker for detecting cardiovascular autonomic dysfunction.

Cystatin C promotes tau protein phosphorylation and causes microtubule instability by inhibiting intracellular turnover of GSK3β in neurons

In Alzheimer's disease (AD) tau protein hyperphosphorylation causes neurofibrillary tangle formation, microtubule instability and neurodegeneration. Determining the mechanism of tau hyperphosphorylation will provide a better understanding of AD pathology. Cystatin C (CysC) is a risk factor for late-onset AD and its level is upregulated in the brains of AD patients. The role of CysC is AD pathogenesis is not known. In this study, we found that CysC level is upregulated in 3xTg-AD mouse brain. We demonstrate that CysC does not affect cellular Aβ production. However, when overexpressed in neuron (NGF-differentiated PC12 cells), CysC inhibits turnover of GSK3β, promotes GSK3β-catalyzed tau phosphorylation at Ser^396/404 and causes microtubule instability. Our data provide a novel insight into the role of CysC in AD pathogenesis.

Proteomic studies in the discovery of cerebrospinal fluid biomarkers for amyotrophic lateral sclerosis

INTRODUCTION

Amyotrophic lateral sclerosis (ALS) is a progressive degenerative motor neuron disease, which usually leads to death within a few years. The diagnosis is mainly based on clinical symptoms and there is a need for ALS-specific biomarkers to make an early and precise diagnosis, for development of disease-modifying drugs and to gain new insights into pathophysiology. Areas covered: In the present review, we summarize studies using mass spectrometric (MS) approaches to identify protein alterations in the cerebrospinal fluid (CSF) of ALS patients. In total, we identified 11 studies fulfilling our criteria by searching in the PubMed database using the keywords 'ALS' and 'CSF' combined with 'proteome', 'proteomic', 'mass spectrometry' or 'protein biomarker'. Ten proteins were differently regulated in ALS CSF compared to controls in at least 2 studies. We will discuss the relevance of the identified proteins regarding the frequency of identification, extent of alteration and brain-specificity. Expert commentary: Most of the identified CSF biomarker candidates are irreproducible or mainly blood-derived. We assign the missing success of CSF proteomic studies in biomarker discovery to a lack of sensitivity, unsuitable normalization, low quality assurance and variations originating from sample preparation. These issues must be improved in future proteomic studies in CSF.

Early markers of kidney dysfunction and cognitive impairment among older adults

BACKGROUND

Age-related decline in kidney function can be an important risk factor for cognitive impairment in older adults. In this study, we examined several kidney function measures for the association with cognitive function in older adults in hope to identify early and sensitive markers that can be used for the detection or screening for cognitive impairment.

METHODS

A total of 1982 older participants (aged ≥60years) in the 1999-2002 National Health and Nutrition Examination Survey was analyzed for the association between kidney function and cognitive impairment using multivariate logistic regression and general linear models. Cognitive functioning was assessed during the household interview using a version of the Digit Symbol Substitution Test of the Wechsler Adult Intelligence Scale III. In our study, participants with a score of <31, the 25th percentiles of the distribution, or who were unable to complete the sample exercise due to cognitive limitations were classified as having cognitive impairment.

RESULTS

Of 1982 older adults, 503 were having cognitive impairment (weighted prevalence, 15.38%). Among the kidney function measures that we examined, the levels of serum cystatin C and urinary albumin were found being significantly associated with cognitive impairment after adjusting for age, sex, race/ethnicity, poverty status, education, physical activity, BMI, cigarette smoking, and alcohol consumption. Cognitive functioning scores were significantly decreasing with increasing levels of kidney dysfunction markers.

CONCLUSION

Serum cystatin C and urinary albumin that are early markers of chronic kidney disease might serve as early and effective markers for cognitive decline in older adults. Mechanisms underlying the observed association need to be further characterized.

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.

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.

Biomarkers of Renal Function in Type 2 Diabetic Patients with Cognitive Impairment

Kidney disease is associated with cognitive impairment in studies of nondiabetic adults. We examined the cross-sectional relation between three measures of renal function and cognitive impairment (CI) in type 2 diabetic patients. A total of 357 patients with type 2 diabetes were prospectively enrolled. There were 108 patients with CI and 249 patients without CI (control). We calculated the urinary albumin/creatinine ratio (UACR) from morning spot urine and the estimated glomerular filtration rate (eGFR) in serum samples. Serum Cystatin C (Cys C) was measured with an automated particle-enhanced turbidimetric immunoassay. UACR and Cystatin C levels were significantly higher in patients with CI than those without CI (P<0.001), and the eGFR was lower in patients with CI than those without (P=0.003). A logistic regression analysis indicates that kidney impairment biomarkers levels were significantly associated with an increased risk of CI after adjustment for age and gender. The OR of each kidney biomarker (eGFR, UACR, Cystatin C) for CI status was 1.78 (0.89-3.27), 2.36 (1.29-4.42), and 2.77 (1.36-5.97), respectively. Among three kidney biomarkers (eGFR, UACR, Cystatin C), only elevated serum Cystatin C was associated with increased risk of CI in type 2 diabetic patients, with an OR of 1.42 (1.25-4.24) after additional adjustment for duration of diabetes, hypertension, hyperlipidemia, hemoglobin A1c (HbA1c), high-sensitivity C-reactive protein (Hs-CRP), intima-media thickness (IMT), ankle brachial index (ABI), and brachial-ankle pulse wave velocity (ba-PWV). Furthermore, combination of conventional risk factors and Cystatin C levels exhibited a fair diagnostic value for CI, with an area under the curve (AUC) of 0.91. Among three kidney impairment biomarkers (eGFR, UACR, Cystatin C), only elevated serum Cystatin C was associated with increased risk of CI in type 2 diabetic patients, independent of conventional risk factors. Furthermore, Cystatin C may be a better marker for CI than eGFR and UACR, and exhibited diagnostic value.

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.

Association between serum cystatin C and diabetic peripheral neuropathy: a cross-sectional study of a Chinese type 2 diabetic population

OBJECTIVE

Serum cystatin C (CysC) is a sensitive marker of kidney function and recent studies have shown that CysC plays a critical role in degenerative diseases in both the central and the peripheral nervous systems. The aim of this study was to explore the relationship between serum CysC and diabetic peripheral neuropathy (DPN) in patients with type 2 diabetes.

METHODS

In total, 937 type 2 diabetic patients were enrolled in this cross-sectional study. Serum CysC concentration was measured by immunoturbidimetry. DPN was evaluated by neurological symptoms, neurological signs, neurothesiometer, and electromyogram.

RESULTS

Serum CysC levels were significantly higher in DPN patients (1.3 (1.1-1.5) mg/l) compared with patients with signs of DPN (1.1 (0.9-1.3) mg/l, P<0.001) and non-DPN patients (1.0 (0.9-1.3) mg/l, P<0.001). Multiple regression analysis revealed that DPN was associated with age, diabetes duration, HbA1c, and serum CysC. Spearman's correlation analysis showed that serum CysC was closely related with age, sex, diabetes duration, hypertension, glomerular infiltration rate, and serum creatinine (Cr) level. The patients were divided into quartiles according to the serum CysC levels. Compared with quartile 1 (referent), the risk of DPN was significantly higher in quartile 2 (odds ratio (OR), 1.753; 95% CI, 1.055-2.912; P<0.05), quartile 3 (OR, 2.463; 95% CI, 1.445-4.917; P<0.01), and quartile 4 (OR, 5.867; 95% CI, 2.075-16.589; P<0.01). Receiver-operating characteristic analysis revealed that the optimal cutoff point of serum CysC to indicate DPN was 1.25 mg/l in male patients and 1.05 mg/l in female patients. High serum CysC level indicated a onefold higher risk of DPN.

CONCLUSIONS

High serum CysC level is closely associated with DPN and may be a potential biomarker for DPN in type 2 diabetic patients.

Higher levels of cystatin C are associated with worse cognitive function in older adults with chronic kidney disease: the chronic renal insufficiency cohort cognitive study

OBJECTIVES

To determine the association between cognition and levels of cystatin C in persons with chronic kidney disease (CKD).

DESIGN

Prospective observational study.

SETTING

Chronic Renal Insufficiency Cohort Cognitive Study.

PARTICIPANTS

Individuals with a baseline cognitive assessment completed at the same visit as serum cystatin C measurement (N = 821; mean age 64.9, 50.6% male, 48.6% white).

MEASUREMENTS

Levels of serum cystatin C were categorized into tertiles; cognitive function was assessed using six neuropsychological tests. Scores on these tests were compared across tertiles of cystatin C using linear regression and logistic regression to examine the association between cystatin C level and cognitive performance (1 standard deviation difference from the mean).

RESULTS

After multivariable adjustment for age, race, education, and medical comorbidities in linear models, higher levels of cystatin C were associated with worse cognition on the modified Mini-Mental State Examination, Buschke Delayed Recall, Trail-Making Test Part (Trails) A and Part B, and Boston Naming (P < .05 for all). This association remained statistically significant for Buschke Delayed Recall (P = .01) and Trails A (P = .03) after additional adjustment for estimated glomerular filtration rate (eGFR). The highest tertile of cystatin C was associated with greater likelihood of poor performance on Trails A (odds ratio (OR) = 2.17, 95% confidence interval (CI) = 1.16-4.06), Trails B (OR = 1.89, 95% CI = 1.09-3.27), and Boston Naming (OR = 1.85, 95% CI = 1.07-3.19) than the lowest tertile after multivariate adjustment in logistic models.

CONCLUSION

In individuals with CKD, higher serum cystatin C levels were associated with worse cognition and greater likelihood of poor cognitive performance on attention, executive function, and naming. Cystatin C is a marker of cognitive impairment and may be associated with cognition independent of eGFR.

The effects of cystatin C and alkaline phosphatase changes on cognitive function 12-months after bariatric surgery

BACKGROUND

The mechanisms for improved cognitive function post-bariatric surgery are not well understood. Markers of kidney and liver function (i.e., cystatin C and alkaline phosphatase (ALP)) are elevated in obese individuals and associated with poor neurocognitive outcomes in other samples. Bariatric surgery can improve cystatin C and ALP levels, but no study has examined whether such changes correspond to post-operative cognitive benefits.

METHODS

78 bariatric surgery patients completed a computerized cognitive test battery prior to and 12-months after surgery. All participants underwent an eight-hour fasting blood draw to quantify cystatin C and ALP concentrations.

RESULTS

Cognitive function improved after surgery. Cystatin C levels decreased at the 12-month follow-up; however, no changes were found in ALP concentrations. At baseline, higher cystatin C levels predicted worse attention/executive function, but no such effects emerged for ALP. Regression analyses controlling for possible medical and demographic confounds and baseline factors revealed that decreased ALP levels following surgery predicted better attention/executive function and memory abilities. Post-surgery changes in cystatin C did not correspond to cognitive improvements.

CONCLUSIONS

Decreased ALP levels predicted better cognition following bariatric surgery, suggesting improved liver function as a possible mechanism of post-operative cognitive benefits. Future studies with neuroimaging and longer follow-up periods are needed to determine whether bariatric surgery can decrease risk for adverse brain changes and dementia in severely obese persons via improved metabolic function.

Cystatin C has a dual role in post-traumatic brain injury recovery

Cathepsin B is one of the major lysosomal cysteine proteases involved in neuronal protein catabolism. This cathepsin is released after traumatic injury and increases neuronal death; however, release of cystatin C, a cathepsin inhibitor, appears to be a self-protective brain response. Here we describe the effect of cystatin C intracerebroventricular administration in rats prior to inducing a traumatic brain injury. We observed that cystatin C injection caused a dual response in post-traumatic brain injury recovery: higher doses (350 fmoles) increased bleeding and mortality, whereas lower doses (3.5 to 35 fmoles) decreased bleeding, neuronal damage and mortality. We also analyzed the expression of cathepsin B and cystatin C in the brains of control rats and of rats after a traumatic brain injury. Cathepsin B was detected in the brain stem, cerebellum, hippocampus and cerebral cortex of control rats. Cystatin C was localized to the choroid plexus, brain stem and cerebellum of control rats. Twenty-four hours after traumatic brain injury, we observed changes in both the expression and localization of both proteins in the cerebral cortex, hippocampus and brain stem. An early increase and intralysosomal expression of cystatin C after brain injury was associated with reduced neuronal damage.

Autophagic/lysosomal dysfunction in Alzheimer's disease

Autophagy serves as the sole catabolic mechanism for degrading organelles and protein aggregates. Increasing evidence implicates autophagic dysfunction in Alzheimer's disease (AD) and other neurodegenerative diseases associated with protein misprocessing and accumulation. Under physiologic conditions, the autophagic/lysosomal system efficiently recycles organelles and substrate proteins. However, reduced autophagy function leads to the accumulation of proteins and autophagic and lysosomal vesicles. These vesicles contain toxic lysosomal hydrolases as well as the proper cellular machinery to generate amyloid-beta, the major component of AD plaques. Here, we provide an overview of current research focused on the relevance of autophagic/lysosomal dysfunction in AD pathogenesis as well as potential therapeutic targets aimed at restoring autophagic/lysosomal pathway function.

Homology modeling, molecular docking and MD simulation studies to investigate role of cysteine protease from Xanthomonas campestris in degradation of Aβ peptide

Cysteine protease is known to degrade amyloid beta peptide which is a causative agent of Alzheimer's disease. This cleavage mechanism has not been studied in detail at the atomic level. Hence, a three-dimensional structure of cysteine protease from Xanthomonas campestris was constructed by homology modeling using Geno3D, SWISS-MODEL, and MODELLER 9v7. All the predicted models were analyzed by PROCHECK and PROSA. Three-dimensional model of cysteine protease built by MODELLER 9v7 shows similarity with human cathepsin B crystal structure. This model was then used further for docking and simulation studies. The molecular docking study revealed that Cys17, His87, and Gln88 residues of cysteine protease form an active site pocket similar to human cathepsin B. Then the docked complex was refined by molecular dynamic simulation to confirm its stable behavior over the entire simulation period. The molecular docking and MD simulation studies showed that the sulfhydryl hydrogen atom of Cys17 of cysteine protease interacts with carboxylic oxygen of Lys16 of Aβ peptide indicating the cleavage site. Thus, the cysteine protease model from X. campestris having similarity with human cathepsin B crystal structure may be used as an alternate approach to cleave Aβ peptide a causative agent of Alzheimer's disease.

Cathepsin B degrades amyloid-β in mice expressing wild-type human amyloid precursor protein

Accumulation of amyloid-β (Aβ), believed to be a key trigger of Alzheimer disease (AD), could result from impaired clearance mechanisms. Previously, we showed that the cysteine protease cathepsin B (CatB) degrades Aβ, most likely by C-terminal truncation, in mice expressing human amyloid precursor protein with familial AD-linked mutations (hAPP(FAD)). In addition, the Aβ-degrading activity of CatB is inhibited by its endogenous inhibitor, cystatin C (CysC). Reducing CysC expression markedly lowers Aβ levels by enhancing CatB-mediated Aβ degradation in hAPP(FAD) mice. However, because a vast majority of AD patients do not carry familial mutations, we investigated how the CysC-CatB axis affects Aβ levels in mice expressing wild-type hAPP (hAPP(WT)). Enhancing CatB activity by CysC deletion significantly lowered total Aβ and Aβ42 levels in hAPP(WT) mice, whereas CatB deletion increased Aβ levels. To determine whether neuron-derived CatB degrades Aβ in vivo, we generated transgenic mice overexpressing CatB under the control of a neuron-specific enolase promoter. Enhancing neuronal CatB activity in hAPP(WT) mice significantly lowered Aβ42 levels. The processing of hAPP(WT) was unaffected by increasing or ablating CatB activity. Thus, the CysC-CatB axis affects degradation of Aβ42 derived from hAPP lacking familial mutations. These findings support the notion that enhancing CatB activity could lower Aβ, especially Aβ42, in AD patients with or without familial mutations.

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.

Involvement of dopaminergic neuronal cystatin C in neuronal injury-induced microglial activation and neurotoxicity

Factors released from injured dopaminergic (DA) neurons may trigger microglial activation and set in motion a vicious cycle of neuronal injury and inflammation that fuels progressive DA neurodegeneration in Parkinson's disease. In this study, using proteomic and immunoblotting analysis, we detected elevated levels of cystatin C in conditioned media (CM) from 1-methyl-4-phenylpyridinium and dieldrin-injured rat DA neuronal cells. Immunodepletion of cystatin C significantly reduced the ability of DA neuronal CM to induce activation of rat microglial cells as determined by up-regulation of inducible nitric oxide synthase, production of free radicals and release of proinflammatory cytokines as well as activated microglia-mediated DA neurotoxicity. Treatment of the cystatin C-containing CM with enzymes that remove O- and sialic acid-, but not N-linked carbohydrate moieties markedly reduced the ability of the DA neuronal CM to activate microglia. Taken together, these results suggest that DA neuronal cystatin C plays a role in the neuronal injury-induced microglial activation and neurotoxicity. These findings from the rat DA neuron-microglia in vitro model may help guide continued investigation to define the precise role of cystatin C in the complex interplay among neurons and glia in the pathogenesis of Parkinson's disease.

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.

Biomarkers of renal function and cognitive impairment in patients with diabetes

OBJECTIVE

Kidney disease is associated with cognitive impairment in studies of nondiabetic adults. We examined the cross-sectional relation between three measures of renal function and performance on four measures of cognitive function in the Action to Control Cardiovascular Risk in Diabetes Memory in Diabetes (ACCORD-MIND) study.

RESEARCH DESIGN AND METHODS

The relationships among estimated glomerular filtration rate (eGFR) <60 mL/min/1.73 m(2) (n = 2,968), albumin/creatinine ratio (ACR) ≥30 μg/mg (n = 2,957), and cystatin C level >1.0 mg/L (n = 532) with tertile of performance on the Mini-Mental State Examination, Rey Auditory Verbal Learning Test (RAVLT), Digit Symbol Substitution Test (DSST), and Stroop Test of executive function were measured.

RESULTS

In adjusted logistic regression models, ACR ≥30 μg/mg was associated with performance in the lowest tertile, compared with the highest two tertiles, on the RAVLT (odds ratio 1.30, 95% CI 1.09-1.56, P = 0.006), equivalent to 3.6 years of aging, and on the DSST (1.47, 1.20-1.80, P = 0.001), equivalent to 3.7 years of aging. Cystatin C >1.0 mg/L was borderline associated with the lowest tertile on the DSST (1.81, 0.93-3.55, P = 0.08) and Stroop (1.78, 0.97-3.23, P = 0.06) in adjusted models. eGFR was not associated with any measure of cognitive performance.

CONCLUSIONS

In diabetic people with HbA(1c) >7.5% at high risk for cardiovascular disease, decreased cognitive function was associated with kidney disease as measured by ACR, a measure of microvascular endothelial pathology, and cystatin C, a marker of eGFR.

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.

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.

Chronic kidney disease and cognitive function in older adults: findings from the chronic renal insufficiency cohort cognitive study

OBJECTIVES

To investigate cognitive impairment in older, ethnically diverse individuals with a broad range of kidney function, to evaluate a spectrum of cognitive domains, and to determine whether the relationship between chronic kidney disease (CKD) and cognitive function is independent of demographic and clinical factors.

DESIGN

Cross-sectional.

SETTING

Chronic Renal Insufficiency Cohort Study.

PARTICIPANTS

Eight hundred twenty-five adults aged 55 and older with CKD.

MEASUREMENTS

Estimated glomerular filtration rate (eGFR, mL/min per 1.73 m(2)) was estimated using the four-variable Modification of Diet in Renal Disease equation. Cognitive scores on six cognitive tests were compared across eGFR strata using linear regression; multivariable logistic regression was used to examine level of CKD and clinically significant cognitive impairment (score < or =1 standard deviations from the mean).

RESULTS

Mean age of the participants was 64.9, 50.4% were male, and 44.5% were black. After multivariable adjustment, participants with lower eGFR had lower cognitive scores on most cognitive domains (P<.05). In addition, participants with advanced CKD (eGFR<30) were more likely to have clinically significant cognitive impairment on global cognition (adjusted odds ratio (AOR) 2.0, 95% CI=1.1-3.9), naming (AOR=1.9, 95% CI=1.0-3.3), attention (AOR=2.4, 95% CI=1.3-4.5), executive function (AOR=2.5, 95% CI=1.9-4.4), and delayed memory (AOR=1.5, 95% CI=0.9-2.6) but not on category fluency (AOR=1.1, 95% CI=0.6-2.0) than those with mild to moderate CKD (eGFR 45-59).

CONCLUSION

In older adults with CKD, lower level of kidney function was associated with lower cognitive function on most domains. These results suggest that older patients with advanced CKD should be screened for cognitive impairment.

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.

Decreased cystatin C immunoreactivity in spinal motor neurons and astrocytes in amyotrophic lateral sclerosis

Cystatin C (CC), a cysteine protease inhibitor involved in protein degradation, is a marker of Bunina bodies in lower motor neurons in amyotrophic lateral sclerosis (ALS). TAR-DNA binding protein-43 (TDP-43)-immunoreactive inclusions are also histological hallmarks of ALS but whether CC is found in motor neurons with or without TDP-43-positive inclusions in ALS is not known. To determine whether inclusion body formation affects cytoplasmic CC immunoreactivity, we examined spinal cords from 9 ALS patients and 12 control subjects by immunohistochemistry. Most anterior horn cells (AHCs) showed moderate to intense immunoreactivity in controls, whereas CC immunoreactivity was markedly decreased in AHCs in ALS cases. The proportion of CC-immunolabeled AHCs was reduced regardless of whether they contained Bunina bodies. In contrast, the proportion of CC-immunolabeled AHCs was significantly reduced in those with TDP-43 inclusions. Cystatin C immunoreactivity of astrocytes in the spinal gray matter and white matter in ALS was significantly decreased compared with controls. These findings suggest that the formation of TDP-43 inclusions, but not of Bunina bodies, may be linked to the content of CC in spinal motor neurons and that perturbations in endogenous levels of CC in neuronal and glial cells may be part of the neurodegenerative processes in ALS.

Cystatin C-cathepsin B axis regulates amyloid beta levels and associated neuronal deficits in an animal model of Alzheimer's disease

Impaired degradation of amyloid beta (Abeta) peptides could lead to Abeta accumulation, an early trigger of Alzheimer's disease (AD). How Abeta-degrading enzymes are regulated remains largely unknown. Cystatin C (CysC, CST3) is an endogenous inhibitor of cysteine proteases, including cathepsin B (CatB), a recently discovered Abeta-degrading enzyme. A CST3 polymorphism is associated with an increased risk of late-onset sporadic AD. Here, we identified CysC as the key inhibitor of CatB-induced Abeta degradation in vivo. Genetic ablation of CST3 in hAPP-J20 mice significantly lowered soluble Abeta levels, the relative abundance of Abeta1-42, and plaque load. CysC removal also attenuated Abeta-associated cognitive deficits and behavioral abnormalities and restored synaptic plasticity in the hippocampus. Importantly, the beneficial effects of CysC reduction were abolished on a CatB null background, providing direct evidence that CysC regulates soluble Abeta and Abeta-associated neuronal deficits through inhibiting CatB-induced Abeta degradation.

Cystatins in Health and Diseases

The Cystatins constitute a large group of evolutionary related proteins with diverse biological activities. They have been recently realized as instrumental in myriad of pathophysiological conditions. They have been implicated in various pathological conditions. The degree of malignancy of various types of cancer cells has been found to be inversely associated with the expression of cystatins. Cystatins have been found to have various antimicrobial, antiviral and immunomodulatory properties. Keeping in view as their being prospective drug targets and anti-disease options this review explores the role of cytoplasmic and cell secreted cystatins in various human diseases.

Serum cystatin C and the risk of Alzheimer disease in elderly men

BACKGROUND

Multiple lines of research suggest that increased cystatin C activity in the brain protects against the development of Alzheimer disease (AD).

METHODS

Serum cystatin C levels were analyzed at two examinations of the Uppsala Longitudinal Study of Adult Men, a longitudinal, community-based study of elderly men (age 70 years, n = 1,153 and age 77 years, n = 761, a subset of the age 70 examination). Cox regressions were used to examine associations between serum cystatin C and incident AD. AD cases were identified by cognitive screening and comprehensive medical chart review in all subjects.

RESULTS

On follow-up (median 11.3 years), 82 subjects developed AD. At age 70 years, lower cystatin C was associated with higher risk of AD independently of age, APOE4 genotype, glomerular filtration rate, diabetes, hypertension, stroke, cholesterol, body mass index, smoking, education level, and plasma amyloid-beta protein 40 and 42 levels (hazard ratio [HR] for lowest [<1.12 micromol/L] vs highest [>1.30 micromol/L] tertile = 2.67, 95% CI 1.22-5.83, p < 0.02). The results were similar at age 77 years (43 participants developed AD during follow-up). Furthermore, a 0.1-mumol/L decrease of cystatin C between ages 70 and 77 years was associated with a 29% higher risk of incident AD (HR 1.29, 95% CI 1.03-1.63, p < 0.03).

CONCLUSIONS

Low levels of serum cystatin C precede clinically manifest Alzheimer disease (AD) in elderly men free of dementia at baseline and may be a marker of future risk of AD. These findings strengthen the evidence for a role for cystatin C in the development of clinical AD.