Lack of an association between cystatin C gene polymorphisms in Japanese patients with Alzheimer's disease

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.

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.

Candidate gene analysis for Alzheimer's disease in adults with Down syndrome

Individuals with Down syndrome (DS) overexpress many genes on chromosome 21 due to trisomy and have high risk of dementia due to the Alzheimer's disease (AD) neuropathology. However, there is a wide range of phenotypic differences (e.g., age at onset of AD, amyloid β levels) among adults with DS, suggesting the importance of factors that modify risk within this particularly vulnerable population, including genotypic variability. Previous genetic studies in the general population have identified multiple genes that are associated with AD. This study examined the contribution of polymorphisms in these genes to the risk of AD in adults with DS ranging from 30 to 78 years of age at study entry (N = 320). We used multiple logistic regressions to estimate the likelihood of AD using single-nucleotide polymorphisms (SNPs) in candidate genes, adjusting for age, sex, race/ethnicity, level of intellectual disability and APOE genotype. This study identified multiple SNPs in APP and CST3 that were associated with AD at a gene-wise level empirical p-value of 0.05, with odds ratios in the range of 1.5-2. SNPs in MARK4 were marginally associated with AD. CST3 and MARK4 may contribute to our understanding of potential mechanisms where CST3 may contribute to the amyloid pathway by inhibiting plaque formation, and MARK4 may contribute to the regulation of the transition between stable and dynamic microtubules.

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.

Evidence of Alternative Cystatin C Signal Sequence Cleavage Which Is Influenced by the A25T Polymorphism

Cystatin C (Cys C) is a small, potent, cysteine protease inhibitor. An Ala25Thr (A25T) polymorphism in Cys C has been associated with both macular degeneration and late-onset Alzheimer's disease. Previously, studies have suggested that this polymorphism may compromise the secretion of Cys C. Interestingly, we found that untagged A25T, A25T tagged C-terminally with FLAG, or A25T FLAG followed by green fluorescent protein (GFP), were all secreted as efficiently from immortalized human cells as their wild-type (WT) counterparts (e.g., 112%, 100%, and 88% of WT levels from HEK-293T cells, respectively). Supporting these observations, WT and A25T Cys C variants also showed similar intracellular steady state levels. Furthermore, A25T Cys C did not activate the unfolded protein response and followed the same canonical endoplasmic reticulum (ER)-Golgi trafficking pathway as WT Cys C. WT Cys C has been shown to undergo signal sequence cleavage between residues Gly26 and Ser27. While the A25T polymorphism did not affect Cys C secretion, we hypothesized that it may alter where the Cys C signal sequence is preferentially cleaved. Under normal conditions, WT and A25T Cys C have the same signal sequence cleavage site after Gly26 (referred to as 'site 2' cleavage). However, in particular circumstances when the residues around site 2 are modified (such as by the presence of an N-terminal FLAG tag immediately after Gly26, or by a Gly26Lys (G26K) mutation), A25T has a significantly higher likelihood than WT Cys C of alternative signal sequence cleavage after Ala20 ('site 1') or even earlier in the Cys C sequence. Overall, our results indicate that the A25T polymorphism does not cause a significant reduction in Cys C secretion, but instead predisposes the protein to be cleaved at an alternative signal sequence cleavage site if site 2 is hindered. Additional N-terminal amino acids resulting from alternative signal sequence cleavage may, in turn, affect the protease inhibition function of Cys C.

Positive Association of the Cathepsin D Ala224Val Gene Polymorphism With the Risk of Alzheimer's Disease

BACKGROUND

Alzheimer's disease (AD) is the most common cause of senile dementia. In Ecuador, the number of deaths caused by AD increases each year. Epidemiologically, the Ecuadorian population is composed of a mixture of several genetic backgrounds along with environmental factors, that make it unique and ideal for population studies. The main objective of this study was to determine the prevalence of Cystatin C (CST3), Cathepsin D (CTSD) and Manganese superoxide dismutase (MnSOD) amino acid-altering polymorphisms and their influence on the development of AD in the Ecuadorian population.

METHODS

This is a case-control study consisting of 56 patients with AD, from the Department of Neurology at Carlos Andrade Marín Hospital. The control group (n = 55) comprised healthy elderly adults. The inclusion period was from January to August of 2012. Peripheral blood was collected from both groups for DNA extraction, polymerase chain reaction and capillary sequencing.

RESULTS

There was a positive association between a CTSD polymorphism (Ala224Val) and the development of AD (odds ratio = 8.1, 95% confidence interval: 0.9-85.7; P < 0.025). However, the 3 other polymorphisms investigated did not show significant associations with AD.

CONCLUSIONS

Variations in CTSD and MnSOD showed no association with the development of AD, whereas the presence of the Ala224Val polymorphism in CTSD had a positive association with the development of AD.

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.

Genetics of late-onset Alzheimer's disease: update from the alzgene database and analysis of shared pathways

The genetics of late-onset Alzheimer's disease (LOAD) has taken impressive steps forwards in the last few years. To date, more than six-hundred genes have been linked to the disorder. However, only a minority of them are supported by a sufficient level of evidence. This review focused on such genes and analyzed shared biological pathways. Genetic markers were selected from a web-based collection (Alzgene). For each SNP in the database, it was possible to perform a meta-analysis. The quality of studies was assessed using criteria such as size of research samples, heterogeneity across studies, and protection from publication bias. This produced a list of 15 top-rated genes: APOE, CLU, PICALM, EXOC3L2, BIN1, CR1, SORL1, TNK1, IL8, LDLR, CST3, CHRNB2, SORCS1, TNF, and CCR2. A systematic analysis of gene ontology terms associated with each marker showed that most genes were implicated in cholesterol metabolism, intracellular transport of beta-amyloid precursor, and autophagy of damaged organelles. Moreover, the impact of these genes on complement cascade and cytokine production highlights the role of inflammatory response in AD pathogenesis. Gene-gene and gene-environment interactions are prominent issues in AD genetics, but they are not specifically featured in the Alzgene database.

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.

New laboratory markers in diagnosis of alzheimer dementia

OBJECTIVES

The aim of our work was to assess the role of tau protein, beta amyloid and cystatin C in diagnosis of Alzheimer dementia (AD) and other neurodegenerative diseases (NDs).

METHODS

The levels of tau protein, beta amyloid and cystatin C were assessed in a set of 79 patients with ND (38 men and 41 women; aged 22-90 years; mean, 61.6 +/- 15.6 years) and in a control group of 79 subjects with a healthy central nervous system (38 men and 41 women; aged 20-91 years; mean, 61.5 +/- 15.1 years).

RESULTS

When compared with the subjects in the control group, a statistically significant decrease in tau protein levels was found in patients with ND, an increase in tau protein levels in patients with AD and an increase in cystatin C cerebrospinal fluid/serum index in the ND + AD group.

DISCUSSION

Our work only confirmed the previously reported results in part. Although tau protein seems to be a quite reliable marker of AD, the role of beta amyloid in AD diagnosis remains at the least questionable. In the case of cystatin C, our results would seem to confirm the views of certain authors that cystatin C will probably not become a new 'revolutionary' marker contributing to differential diagnostics.

The assessment of beta amyloid, tau protein and cystatin C in the cerebrospinal fluid: laboratory markers of neurodegenerative diseases

To assess the role of tau protein, beta-amyloid(1-42) and cystatin C in the diagnostics of Alzheimer dementia (AD) and other neurodegenerative diseases (ND) by comparing to the control groups (CG). The levels of tau protein, beta-amyloid(1-42) and cystatin C were assessed in the set of 69 patients (AD + ND, 33 males, 36 females, aged 22-90, mean 60.5 + 16.1 years), and in a control group of 69 subjects without the affection of the central nervous system (CGAD + CGND, 33 males, 36 females, aged 20-91, mean 60.5 + 16.0 years). Statistically significant increased tau protein levels (P = 0.0001) and index tau/beta-amyloid(1-42) levels (P = 0.0002) were shown in the group of AD patients, compared to the group of ND patients. One-way ANOVA analysis with Bonferonni post hoc test did not show any significant differences of the cystatin C values between any of the compared groups. ROC analysis showed at least one tie between the positive actual state group (AD) and the negative actual state group (ND) by CSF cystatin C and at least one tie between the positive actual state group and the negative actual state group by CSF tau protein. Our study confirmed previously reported results only in part. While tau protein seems to be quite a reliable marker of AD, the role of beta-amyloid(1-42) and cystatin C in AD diagnosis remains at least questionable.

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.

Genotype and plasma concentration of cystatin C in patients with late-onset Alzheimer disease

BACKGROUND

A polymorphism locating at position 73 of cystatin C (CST3) exon 1 was suggested to be associated with Alzheimer disease (AD), but with contradictory results. The relationship between the CST3 genotype and the cystatin C plasma level in AD remains unknown.

OBJECTIVE

We aim to determine the association between CST3 polymorphism and the plasma levels of cystatin C in AD and nondemented control individuals.

METHOD

The polymorphisms of the CST3 genotype were determined using PCR followed by restriction fragment length polymorphism analysis, and the plasma cystatin C concentrations were quantified by sandwich ELISA in 175 AD and 461 control subjects.

RESULTS

Although the CST3A allele frequencies were similar between the two groups, the CST3A/A homozygote was significantly associated with late-onset AD. As expected, the established AD genetic risk factor APOE epsilon4 allele was overrepresented in the AD cohort. The plasma cystatin C levels were lower in the AD patients than in the control group. Furthermore, plasma cystatin C levels were associated positively with age and negatively with CST3A allele in the control group.

CONCLUSION

The homozygous CST3A/A genotype confers a risk for AD in Taiwan Chinese. Such an association may be due to the reduced level of cystatin C in the peripheral circulation.

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

There are an increasing number of genetic and neuropathological observations to suggest that cystatin C, an extracellular protein produced by all nucleated cells, might play a role in the pathophysiology of sporadic Alzheimer's disease (AD). Recent observations indicate that small and large soluble oligomers of the beta-amyloid protein (Abeta) impair synaptic plasticity and induce neurotoxicity in AD. The objective of the present study was to investigate the influence of cystatin C on the production of such oligomers in vitro. Co-incubation of cystatin C with monomeric Abeta1-42 significantly attenuated the in vitro formation of Abeta oligomers and protofibrils, as determined using electron microscopy (EM), dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE), immunoblotting, thioflavin T (ThT) spectrofluorimetry and gel chromatography. However, cystatin C did not dissolve preformed Abeta oligomers. Direct binding of cystatin C to Abeta was demonstrated with the formation of an initial 1:1 molar high-affinity complex. These observations suggest that cystatin C might be a regulating element in the transformation of monomeric Abeta to larger and perhaps more toxic molecular species in vivo.

The role of cystatin C in cerebral amyloid angiopathy and stroke: cell biology and animal models

A variant of the cysteine protease inhibitor, cystatin C, forms amyloid deposited in the cerebral vasculature of patients with hereditary cerebral hemorrhage with amyloidosis, Icelandic type (HCHWA-I), leading to cerebral hemorrhages early in life. However, cystatin C is also implicated in neuronal degenerative diseases in which it does not form the amyloid protein, such as Alzheimer disease (AD). Accumulating data suggest involvement of cystatin C in the pathogenic processes leading to amyloid deposition in cerebral vasculature and most significantly to cerebral hemorrhage in patients with cerebral amyloid angiopathy (CAA). This review focuses on cell culture and animal models used to study the role of cystatin C in these processes.

High frequency of open-angle glaucoma in Japanese patients with Alzheimer's disease

The clinical and genetic relationships between Alzheimer's disease (AD) and glaucoma remain obscure. The aim of this study was to determine the prevalence of open-angle glaucoma (OAG) in patients with AD and whether the apolipoprotein E (APOE) 4 allele is associated with AD, with or without OAG, in Japanese. The groups consisted of 172 patients with the diagnostic criteria of AD and 176 age-matched controls. Ophthalmic examinations were conducted, and genomic analysis was performed by PCR and digestion of products with an enzyme. OAG was found in 41 (23.8%) of the AD patients, which was a significantly (p = 0.0002) higher prevalence than that in the controls (9.9%). Furthermore, there was no significant difference between intraocular pressures (IOPs) in AD patients with OAG and without OAG. The percentage of AD patients who carried an APOE epsilon4 allele (29.5%) was significantly (p = 0.0007) higher than that of the controls (9.1%). However, the percentage of AD patients with OAG who carried an APOE epsilon4 allele (35.7%) was not significantly different than that of AD patients without OAG (27.7%, p = 0.42). In summary, the prevalence of OAG is high in Japanese patients with AD, suggesting that common factors other than APOE may contribute to the two diseases.

Genetic analysis of the cystatin C gene in familial and sporadic ALS patients

Bunina bodies, small eosinophilic intraneuronal inclusions, stain positive for cystatin C and are the only specific pathological hallmark of amyotrophic lateral sclerosis (ALS). We screened the cystatin C gene (CST3) for mutations in 57 sporadic ALS patients and 12 familial ALS cases that did not possess a SOD1 mutation. We detected the known polymorphism in exon 1, a G/A transition at +73, in both familial and sporadic ALS patients. However, the allelic and genotypic frequencies of the +73 G/A polymorphism did not differ between ALS patients and control samples. No other mutation was detected in the ALS patients. The results reported here indicate that there may not be a direct genetic link between cystatin C and ALS, and it may be that deficits occur in proteins that interact with cystatin C.

Genotype (cystatin C) and EEG phenotype in Alzheimer disease and mild cognitive impairment: A multicentric study

Previous findings demonstrated that haplotype B of CST3, the gene coding for cystatin C, is a recessive risk factor for late-onset Alzheimer's disease (AD; Finckh, U., von der Kammer, H., Velden, J., Michel, T., Andresen, B., Deng, A., Zhang, J., Muller-Thomsen, T., Zuchowski, K., Menzer, G., Mann, U., Papassotiropoulos, A., Heun, R., Zurdel, J., Holst, F., Benussi, L., Stoppe, G., Reiss, J., Miserez, A.R., Staehelin, H.B., Rebeck, G.W., Hyman, B.T., Binetti, G., Hock, C., Growdon, J.H., Nitsch, R.M., 2000. Genetic association of the cystatin C gene with late-onset Alzheimer disease. Arch. Neurol. 57, 1579-1583). In the present multicentric electroencephalographic (EEG) study, we analyzed the effects of CST3 haplotypes on resting cortical rhythmicity in subjects with AD and mild cognitive impairment (MCI) with the hypothesis that sources of resting EEG rhythms are more impaired in carriers of the CST3 B haplotype than non-carriers. We enrolled a population of 84 MCI subjects (42% with the B haplotype) and 65 AD patients (40% with the B haplotype). Resting eyes-closed EEG data were recorded in all subjects. EEG rhythms of interest were delta (2-4 Hz), theta (4-8 Hz), alpha 1 (8-10.5 Hz), alpha 2 (10.5-13 Hz), beta 1 (13-20 Hz), and beta 2 (20-30 Hz). EEG cortical sources were estimated by low-resolution brain electromagnetic tomography (LORETA). Results showed that the amplitude of alpha 1 (parietal, occipital, temporal areas) and alpha 2 (occipital area) was statistically lower in CST3 B carriers than non-carriers (P < 0.01). Whereas there was a trend towards statistical significance that amplitude of occipital delta sources was stronger in CST3 B carriers than in non-carriers. This was true for both MCI and AD subjects. The present findings represent the first demonstration of relationships between the AD genetic risk factor CST3 B and global neurophysiological phenotype (i.e., cortical delta and alpha rhythmicity) in MCI and AD subjects, prompting future genotype-EEG phenotype studies for the early prediction of AD conversion in individual MCI subjects.

Cystatin C and apoe polymorphisms in Italian Alzheimer's disease

Recent studies have reported a genetic association between the 73 G/A polymorphism within exon 1 of the cystatin C gene and Alzheimer's disease (AD) with conflicting results. To further investigate the proposed association and to clarify the role of CST3 as risk factor for AD, we analyzed the genotype and allele frequency distribution of CST3 G73A and apolipoprotein (ApoE) gene polymorphisms in 243 Italian patients with AD and 186 controls. Patients with AD were consecutively collected among the outpatients from the Neurology Department at the University of Florence. All 429 subjects were genotyped for CST3 and ApoE polymorphisms. After stratification according to age, the GG frequency resulted slightly higher in younger (<65 years) cases, but far from statistically significant. There was also no evidence of a statistical interaction between CST3 and ApoE polymorphisms. In conclusion, our data suggest that the CST3 genetic variant is not a susceptibility factor in AD, nor mitigate the effect of the ApoE varepsilon4 allele in the risk of developing AD.

Binding of cystatin C to Alzheimer’s amyloid β inhibits in vitro amyloid fibril formation

The colocalization of cystatin C, an inhibitor of cysteine proteases, with amyloid beta (Abeta) in parenchymal and vascular amyloid deposits in brains of Alzheimer's disease (AD) patients may reflect cystatin C involvement in amyloidogenesis. We therefore sought to determine the association of cystatin C with Abeta. Immunofluorescence analysis of transfected cultured cells demonstrated colocalization of cystatin C and beta amyloid precursor protein (betaAPP) intracellularly and on the cell surface. Western blot analysis of immunoprecipitated cell lysate or medium proteins revealed binding of cystatin C to full-length betaAPP and to secreted betaAPP (sbetaAPP). Deletion mutants of betaAPP localized the cystatin C binding site within betaAPP to the Abeta region. Cystatin C association with betaAPP resulted in increased sbetaAPP but did not affect levels of secreted Abeta. Analysis of the association of cystatin C and Abeta demonstrated a specific, saturable and high affinity binding between cystatin C and both Abeta(1-42) and Abeta(1-40). Notably, cystatin C association with Abeta results in a concentration-dependent inhibition of Abeta fibril formation.

Overexpression of human cystatin C in transgenic mice does not affect levels of endogenous brain amyloid Beta Peptide

Cystatin C, an inhibitor of cysteine proteases, colocalizes with amyloid beta (Abeta) in parenchymal and vascular amyloid deposits in brains of Alzheimer's disease (AD) patients, suggesting that cystatin C has a role in AD. Cystatin C also colocalizes with beta amyloid precursor protein (betaAPP) in transfected cultured cells. In vitro analysis of the association between the two proteins revealed that binding of cystatin C to full-length betaAPP does not affect the level of Abeta secretion. Here we studied the effect of in vivo overexpression of cystatin C on the levels of endogenous brain Abeta. We have generated lines of transgenic mice expressing either wild-type human cystatin C or the Leu68Gln variant that forms amyloid deposits in the cerebral vessels of Icelandic patients with hereditary cerebral hemorrhage, under control sequences of the human cystatin C gene. Western blot analysis of brain homogenates was used to select lines of mice expressing various levels of the transgene. Analysis of Abeta40 and Abeta42 concentrations in the brain showed no difference between transgenic mice and their nontransgenic littermates. Thus, in vivo overexpression of human cystatin C does not affect Abeta levels in mice that do not deposit Abeta.

Molecular Genetics of Late-Onset Alzheimer's Disease

Late-onset Alzheimer's disease (AD) is a complex and multifactorial disease with the possible involvement of several genes. Apolipoprotein E (APOE), especially the APOE*4 allele, has been established as a strong susceptibility marker that accounts for nearly 30% of the risk in late-onset AD. However, as the APOE*4 allele is neither necessary nor sufficient for the development of AD, it emphasizes the involvement of other genetic and/or environmental factors which, alone or in conjunction with APOE*4, can modify the risk of AD. Recently, genome-wide linkage or linkage disequilibrium studies on late-onset AD have provided informative data for the existence of multiple putative genes for AD on several chromosomes, with the strongest evidence on chromosomes 12, 10, 9 and 6. This paper attempts to review the current progress on the identification of additional genetic loci for late-onset AD.

Evidence of linkage and association on chromosome 20 for late-onset Alzheimer disease

Recently, we reported evidence of linkage on chromosome 20 for Alzheimer disease (AD) using a novel statistical approach to incorporate covariates (e.g., age, ApoE genotype) into the analysis. These results suggest that very elderly subjects (>85 years), and individuals who carry an epsilon2 allele at the ApoE locus are more likely to be linked to this candidate region. The region on chromosome 20 includes a strong candidate gene, cystatin C (CST3), which has previously been associated with AD in case-control studies. We investigated these findings further by genotyping additional markers to narrow the candidate region, and to identify evidence of linkage disequilibrium as additional support for a susceptibility locus on chromosome 20. We selected 43 elderly sibships (89 subjects) from the NIMH AD Genetics Initiative based on current age older than 84 years, and identified 129 unrelated control subjects who were older than 84 years from the Oregon Brain Aging Study to conduct linkage and association studies in this region. Fourteen additional markers were evaluated, including 4 markers located within or near CST3. We narrowed the candidate region on chromosome 20 to an 11.8-cM region between markers D20S174 and D20S471, which includes the CST3 candidate gene. In addition, we observed evidence of association for markers located near the CST3 candidate gene, with P values between 0.002 and 0.08 for two-locus haplotypes. These results support the presence of a susceptibility locus for AD in the vicinity of CST3 for very elderly subjects with AD.

Causative and susceptibility genes for Alzheimer's disease: a review

Alzheimer's disease (AD) is the most common type of dementia in the elderly population. Three genes have been identified as responsible for the rare early-onset familial form of the disease: the amyloid precursor protein (APP) gene, the presenilin 1 (PSEN1) gene and the presenilin 2 (PSEN2) gene. Mutations in these genes, however, account for less than 5% of the total number of AD cases. The remaining 95% of AD patients are mostly sporadic late-onset cases, with a complex aetiology due to interactions between environmental conditions and genetic features of the individual. In this paper, we review the most important genes supposed to be involved in the pathogenesis of AD, known as susceptibility genes, in an attempt to provide a comprehensive picture of what is known about the genetic mechanisms underlying the onset and progression of AD. Hypotheses about the role of each gene in the pathogenic pathway are discussed, taking into account the functions and molecular features, if known, of the coded protein. A major susceptibility gene, the apolipoprotein E (APOE) gene, found to be associated with sporadic late-onset AD cases and the only one, whose role in AD has been confirmed in numerous studies, will be included in a specific chapter. As the results reported by association studies are conflicting, we conclude that a better understanding of the complex aetiology that underlies AD may be achieved likely through a multidisciplinary approach that combines clinical and neurophysiological characterization of AD subtypes and in vivo functional brain imaging studies with molecular investigations of genetic components.

Alzheimer disease-associated cystatin C variant undergoes impaired secretion

CST3 is the coding gene for cystatin C (CysC). CST3 B/B homozygosity is associated with an increased risk of developing Alzheimer disease. We performed CysC analysis on human primary skin fibroblasts obtained from donors carrying A/A, A/B, and B/B CST3. Pulse-chase experiments demonstrated that the release of the B variant of CysC has a different temporal pattern compared to that of the A one. Fibroblasts B/B homozygous displayed a reduced secretion of CysC due to a less efficient cleavage of the signal peptide, as suggested by high-resolution Western blot analysis and by in vitro assay. In the brain, the reduced level of CysC may represent the molecular factor responsible for the increased risk of Alzheimer disease.

A second locus for very-late-onset Alzheimer disease: a genome scan reveals linkage to 20p and epistasis between 20p and the amyloid precursor protein region

We used a covariate-based linkage method to reanalyze genome scan data from affected sibships collected by the Alzheimer Disease (AD) Genetics Initiative of the National Institute of Mental Health. As reported in an earlier article, the amyloid-beta precursor protein (APP) region is strongly linked to affected sib pairs of the oldest current age (i.e., age either at last exam or at death) who lack E4 alleles at the apolipoprotein E (ApoE) locus. We now report that a region on 20p shows the same pattern. A model that includes current age and the number of E2 alleles as covariates gives a LOD score of 4.1. The signal on 20p is near the location of the gene coding for cystatin-C, previously shown to be associated with late-onset AD and to codeposit with APP in the brains of patients with AD. Two-locus analysis provides evidence of strong epistasis between 20p and the APP region, limited to the oldest age group and to those lacking ApoE4 alleles. We speculate that high-risk polymorphisms in both regions produce a biological interaction between these two proteins that increases susceptibility to a very-late-onset form of AD.

Pharmacogenomics for the treatment of dementia

Alzheimer's disease (AD) is a genetically complex disorder associated with multiple genetic defects either mutational or of susceptibility. Current AD genetics does not explain in full the etiopathogenesis of AD, suggesting that environmental factors and/or epigenetic phenomena may also contribute to AD pathology and phenotypic expression of dementia. The genomics of AD is still in its infancy, but is helping us to understand novel aspects of the disease including genetic epidemiology, multifactorial risk factors, pathogenic mechanisms associated with genetic networks and genetically-regulated metabolic cascades. AD genomics is also fostering new strategies in pharmacogenomic research and prevention. Functional genomics, proteomics, pharmacogenomics, high-throughput methods, combinatorial chemistry and modern bioinformatics will greatly contribute to accelerating drug development for AD and other complex disorders. The multifactorial genetic dysfunction in AD includes mutational loci (APP, PS1, PS2) and diverse susceptibility loci (APOE, A2M, AACT, LRP1, IL1A, TNF, ACE, BACE, BCHE, CST3, MTHFR, GSK3B, NOS3) distributed across the human genome, probably converging in common pathogenic mechanisms that lead to premature neuronal death. Genomic associations integrate polygenic matrix models to elucidate the genomic organization of AD in comparison to the control population. Using APOE-related monogenic models it has been demonstrated that the therapeutic response to drugs (e.g., cholinesterase inhibitors, non-cholinergic compounds) in AD is genotype-specific. A multifactorial therapy combining three different drugs yielded positive results during 6-12 months in approximately 60% of the patients. With this therapeutic strategy, APOE-4/4 carriers were the worst responders and patients with the APOE-3/4 genotype were the best responders. Other polymorphic variants (PS1, PS2) also influence the therapeutic response to different drugs in AD patients, suggesting that the final pharmacological outcome is the result of multiple genomic interactions, including AD-related genes and genes associated with drug metabolism, disposition, and elimination. The pharmacogenomics of AD may contribute in the future to optimise drug development and therapeutics, increasing efficacy and safety, and reducing side-effects and unnecessary costs.