No evidence for genetic association or linkage of the cathepsin D (CTSD) exon 2 polymorphism and Alzheimer disease

Association study of cathepsin D gene polymorphism in Iranian patients with sporadic late-onset Alzheimer's disease

One of the most prevalent forms of dementia is Alzheimer's disease (AD). Complex inheritance and multifactorial patterns of late-onset AD (LOAD) along with its heterogeneity are due to the presence of different AD-predisposing genes with different influence on disease development among various populations. A key event in the pathogenesis of AD is the deposition of β-amyloid peptide, which is derived from the amyloid precursor protein by β- and γ-secretases. Cathepsin D (CTSD) is an acid protease with β- and γ-secretase-like features in vitro. An exonic C→T polymorphism at position 224 of the CTSD gene (rs: 17571) has been shown to be associated with the enzyme function of CTSD and with AD. Two studies in the German population reported a strong association of this polymorphism with an increased risk of developing AD, while other studies did not confirm this observation. We tested for this association in a case-control study in 100 Iranian sporadic LOAD patients based on diagnostic criteria of DSM-IV-TR and NINCDS-ADRDA and in 100 normal controls without any personal and family history of AD or other related dementias. Polymerase chain reaction-restriction fragment length polymorphism was set up to detect this polymorphism. Our study demonstrated that T-carrying genotype frequency in AD patients is significantly higher than in controls and there was a 2.5-fold increased risk for developing AD in the T-carrying genotype compared to C/C genotype (odds ratio = 2.5, p = 0.010). The odds ratio for subjects with the apolipoprotein E ε4 (APOE ε4) allele was 2.91 (p = 0.003) and carriers of the CTSD T and APOE ε4 alleles had a 6.25-fold increased risk of the disease (p = 0.0). Our results indicate that CTSD genotype is associated with the disease and a combination of the above risk factors significantly alters the risk for developing AD.

Human stefin B role in cell's response to misfolded proteins and autophagy

Alternative functions, apart from cathepsins inhibition, are being discovered for stefin B. Here, we investigate its role in vesicular trafficking and autophagy. Astrocytes isolated from stefin B knock-out (KO) mice exhibited an increased level of protein aggregates scattered throughout the cytoplasm. Addition of stefin B monomers or small oligomers to the cell medium reverted this phenotype, as imaged by confocal microscopy. To monitor the identity of proteins embedded within aggregates in wild type (wt) and KO cells, the insoluble cell lysate fractions were isolated and analyzed by mass spectrometry. Chaperones, tubulins, dyneins, and proteosomal components were detected in the insoluble fraction of wt cells but not in KO aggregates. In contrast, the insoluble fraction of KO cells exhibited increased levels of apolipoprotein E, fibronectin, clusterin, major prion protein, and serpins H1 and I2 and some proteins of lysosomal origin, such as cathepsin D and CD63, relative to wt astrocytes. Analysis of autophagy activity demonstrated that this pathway was less functional in KO astrocytes. In addition, synthetic dosage lethality (SDL) gene interactions analysis in Saccharomyces cerevisiae expressing human stefin B suggests a role in transport of vesicles and vacuoles These activities would contribute, directly or indirectly to completion of autophagy in wt astrocytes and would account for the accumulation of protein aggregates in KO cells, since autophagy is a key pathway for the clearance of intracellular protein aggregates.

Lack of association between cathepsin D C224T polymorphism and Alzheimer's disease risk: an update meta-analysis

BACKGROUND

Cathepsin D C224T polymorphism has been reported to associate with AD susceptibility. But the results were inconsistent. This study aimed to assess the relationship between C224T polymorphism and AD risk.

METHODS

The relevant studies were identified by searching PubMed, Embase, Web of Science, Google Scholar and Wan fang electronic databases updated on July 2013. The relationship between Cathepsin D C224T polymorphism and AD risk was evaluated by ORs and 95% CIs.

RESULTS

A total of 25 case-control studies including 5,602 cases and 11,049 controls were included in the meta-analysis. There was no association between C224T polymorphism and AD risk with all the studies were pooled in the meta-analysis (CT vs. CC: OR = 1.125, 95% CI = 0.974-1.299, P = 0.109; CT + TT vs. CC: OR = 1.136, 95% CI = 0.978-1.320, P = 0.094). Furthermore, when stratified by ethnicity, age of onset and APOEϵ4 status, significant association did not found in all subgroups.

CONCLUSION

The present meta-analysis suggested that the Cathepsin D C224T polymorphism was not associated with AD susceptibility.

The cathepsin D (224C/T) polymorphism confers an increased risk to develop Alzheimer's disease in men

The lysosomal protease cathepsin D is likely involved in beta-amyloidogenesis in Alzheimer's disease (AD). There is evidence for a single nucleotide polymorphism (rs17571) of the cathepsin D gene to be associated with increased AD risk. However, little is known about gender-specific differences. Therefore, we performed a genetic association study focusing on gender-specific differences in 434 participants (219 AD and 215 controls). Screening of the rs17571 shows a significantly higher proportion of T-allele carriers among male Alzheimer patients (28.5%) when compared with male controls (13.8%, p = .013, p(corr) = .039). The odds ratio was 2.48 (95% confidence interval: 1.14-5.58). There was no significant difference in the T-allele distribution in women. Including APOE4 status and age did not have an additional effect on the morbidity risk. Thus, our results support the idea that rs17571 confers an increased risk for AD in men but not in women. Further investigation should substantiate the role of gender for AD risk of rs17571.

Cathepsin D gene and the risk of Alzheimer's disease: a population-based study and meta-analysis

Cathepsin D (CTSD) is a gene involved in amyloid precursor protein processing and is considered a candidate for Alzheimer's disease (AD). The aim of the current study was to examine if variation in CTSD increases the risk of AD. We performed a candidate-gene analysis in a population-based cohort study (N=7983), and estimated the effect of CTSD on the risk of AD. Additionally, a large meta-analysis was performed incorporating our data and previously published data. The T-allele of CTSD rs17571 was associated with an increased risk of AD (p-value 0.007) in the Rotterdam Study. This association was predominantly found in APOE ε4 noncarriers. A meta-analysis of previously published data showed a significantly increased risk of AD in carriers of the T-allele of rs17571 (OR 1.22, 95% CI 1.03-1.44), irrespective of APOE ε4 carrier status. This study adds to the evidence that CTSD increases the risk of AD, although the effect size is moderate.

Non-apolipoprotein E and apolipoprotein E genetics of sporadic Alzheimer's disease

The genetic epidemiology of sporadic Alzheimer's disease (SAD) remains a very active area of research,making it one of the most prolifically published areas in medicine and biology. Numerous putative candidate genes have been proposed. However, with the exception of apolipoprotein E (APOE), the only confirmed genetic risk factor for SAD, all the other data appear to be not consistent. Nevertheless, the genetic risk for SAD attributable to the APOE gene in the general population is 20-0%, providing a strong evidence for the existence of additional genetic risk factors. The first part of the present article was dedicated to non-APOE genetics of SAD, reviewing chromosomes-by-chromosomes the available data concerning the major candidate genes. The second part of this article focused on some recently discovered aspects of the APOE polymorphism and their implications for SAD. An attempt to identify the future directions for non-APOE genetic research in SAD was also discussed.

The cathepsin D rs17571 polymorphism: effects on CSF tau concentrations in Alzheimer disease

The lysosomal protease cathepsin D (CtsD, EC 3.4.23.5; gene, CTSD) has been associated with Alzheimer disease (AD) due to its cerebral expression being increased early in the course of AD; additionally, a CTSD exon 2 polymorphism (rs17571; NT_009237.17:g.569834T>C) may confer risk to AD. Functionally, it may be implicated in amyloid precursor protein (APP) processing and tau protein degradation. The objective of this study was to determine whether the CTSD exon 2 polymorphism affects cerebrospinal fluid (CSF), concentrations of beta-amyloid (Abeta42) and tau in two independent samples from Germany (n=73) and Sweden (n=66). Patients carrying the CTSD rs17571-T allele had significantly decreased CSF levels of tau (Munich, p=0.003; Swedish, p=0.029; combined sample, p<0.001), whereas no significant effect was observed on Abeta42 concentrations. Likewise, no significant impact was observed on Mini Mental State Examination (MMSE) scores. The data of both independent samples suggest that the CTSD rs17571 polymorphism does not affect APP processing but shows significant effects on tau processing. The result may corroborate the implication of the lysosomal system in the pathogenesis of AD and is of particular importance if CSF tau is used as a diagnostic biomarker.

Interaction of CTSD and A2M polymorphisms in the risk for Alzheimer's disease

The proteins cathepsin D, encoded by CTSD gene, and alpha2-macroglobulin, encoded by A2M gene, are involved in the biochemical pathway leading to deposition of beta-amyloid. In these proteins two amino acid polymorphisms (CTSD-Ala/Val C-->T and A2M-Ile/Val A-->G) have been associated with an increased risk for Alzheimer's disease (AD), but conflicting results have been reported. We studied the association and the mutual interactions of the CTSD-C/T and A2M-A/G polymorphisms with sporadic AD in 100 patients with late-onset AD and 136 healthy elderly subjects as controls. The CTSD-T allele and the CTSD-C/T genotype are significantly more frequent in AD than in controls. The odds ratio (OR) for CTSD-T subjects is 1.93 [95% confidence interval (CI)=1.01-3.72], and 2.07 (95% CI=1.01-4.21) after adjustment for age, sex and APOE epsilon4+ status, while no significant association was found for the A2M-A/G polymorphism. The coexistence of the CTSD-T with the A2M-G allele synergistically increased the OR for AD to 2.69 (95% CI=1.13-6.34) [2.82 (95% CI=1.12-7.17) after adjustment], and to 3.29 (95% CI=1.33-8.16) if estimated for the allelic combination. Our data suggest that the CTSD-T allele of the CTSD-C/T polymorphism is associated with an increased relative risk for late-onset AD and, more interestingly, the combination of CTSD-T with the A2M-G allele seems to increase this risk.

The cathepsin D gene exon 2 (C224T) polymorphism and sporadic Alzheimer's disease in European populations

The cathepsin D gene (CTSD) exon 2 (C224T) polymorphism has been associated with an increased risk for sporadic Alzheimer's disease (AD), but with controversial findings. We studied CTSD exon 2 (C224T) and apolipoprotein E (APOE) genotype frequencies in 168 AD patients and 218 age-matched healthy controls from Southern Italy. No statistically significant differences were found in CTSD allele or genotype frequencies between AD patients and controls, and there were no interactions with sex or APOE genotype. Furthermore, comparing our results with the findings from other European populations, the CTSD*T allele frequency showed a statistically significant increasing trend from Northern to Southern regions of Europe in AD patients and controls (z=2.51, p<.01; z=4.02, p<.001, respectively), with a concomitant inverse trend for CTSD*C allele frequency. The regional differences in CTSD allele frequencies could be related to the different patterns of association between this polymorphism and AD in various European studies.

Lack of association of cathepsin D genetic polymorphism with Alzheimer's disease in Koreans

Cathepsin D (CatD) is a good candidate susceptibility marker for Alzheimer's disease (AD), since it was found to be involved in the processing of the amyloid precursor protein and the formation of the hyperphosphorylated tau. And recently, a CatD genetic polymorphism was found to be associated with the risk of Alzheimer's disease (AD) in a German population. However, the CatD T-AD association has not been replicated in a series of the successive independent studies in other races. Therefore, we determined CatD genotypes to examine the possible association of the CatD polymorphism with AD in Koreans. We failed to find significant association between the CatD T allele and AD. In addition, the CatD T--AD association was not significant regardless of the age at onset or the occurrence of the apolipoprotein epsilon4 allele. However, we cannot exclude the possible contribution of the CatD in the development of AD, since the power of the present study was not high enough because of low allelic frequency of the CatD T in Koreans and small sample size. In conclusion, the association between the CatD genetic polymorphism and AD was not found in Koreans, although it waits for further replication in an extended sample.

Contribution of apolipoprotein E and cathepsin D genotypes to the familial aggregation of Alzheimer's disease

OBJECTIVE

The familial aggregation of late-onset Alzheimer's disease (AD) might be caused by the clustering of genetic risk factors in families. This study investigates the influence of variants of candidate genes on the familial aggregation of AD.

METHODS

The occurrence of AD was examined in 1,420 first-degree relatives of 70 AD patients and 144 nondemented controls classified by the presence of AD and relevant candidate genes in index subjects.

RESULTS

Relatives of nondemented controls with an apolipoprotein E4 or a cathepsin D T allele had a higher cumulative lifetime incidence of AD than relatives of subjects without the respective alleles. This effect was not detected in relatives of AD patients. Variants of the interleukin-6, bleomycin hydrolase and alpha(2)-macroglobulin genes did not significantly influence the (age-adjusted) risk of AD in relatives.

CONCLUSIONS

Familial aggregation of late-onset AD is likely to be caused by several genetic risk factors. Variants of the apolipoprotein E and cathepsin D genes influenced the risk of AD in relatives of nondemented control subjects. The lack of an influence of these genotypes on the risk of AD in relatives of AD subjects may be the consequence of complementary reductions of other genetic risk factors such as various, yet unknown susceptibility genes in patients and, consequently, in their first-degree relatives.

Cathepsin D polymorphism in Italian elderly subjects with sporadic late-onset Alzheimer's disease

Alzheimer's disease (AD) is the most frequent cause of dementia in elderly people. Different pathological pathways have been involved in the development of late-onset AD. Among them, numerous genes have been proposed as pathogenetic factors acting independently or interactively. It has been suggested that the cathepsin D gene (CTSD) is associated with late-onset AD. We analyzed an exonic polymorphism of the CTSD gene [C-->T (Ala-->Val) transition at position 224] in 142 AD patients and 120 controls. Our data indicate no significant association between this polymorphism and the risk of AD. Likewise there was no association between CTSD polymorphism and the apolipoprotein E genotype in the risk of developing 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.

Cathepsin D polymorphism in Italian sporadic and familial Alzheimer's disease

A recent study has shown that a genetic variation in the Cathepsin D (catD) gene is a major risk factor for the development of Alzheimer's disease (AD). CatD is an intracellular aspartyl protease involved in neurodegeneration. A C-->T (Ala-->Val) transition at position 224 has been associated with altered intracellular maturation. Recently, a significant overrepresentation of the T allele of the catD gene in AD patients compared with controls was reported. However, this finding has not yet been confirmed. We analyzed the distribution of catD and apolipoprotein E polymorphisms in Italian patients with sporadic and familial AD (FAD). Our studies revealed that the distribution of catD polymorphism did not differ in AD and FAD patients and controls. Thus, our data do not support a role for the catD gene as a genetic risk factor in the development of AD.

Candidate gene association studies in sporadic Alzheimer's disease

The genetics of Alzheimer's disease (AD) is complex. Three genes (amyloid precursor protein, presenilin 1 and presenilin 2) have been described in the relatively rare, early-onset, autosomal dominant familial form of AD. In the common, non-familial (sporadic) late-onset AD, the major known genetic risk factor is the epsilon4 allele of the apolipoprotein E (APOE) gene. However, at least half of the people who develop AD do not carry this allele, and not all people who do carry this allele develop AD even if they live to an old age. Therefore, approximately 30 other candidate genes involving a protein in a critical pathway in the pathogenesis of disease (principally interaction with amyloid-beta, oxidative stress and inflammation/apoptosis) have been considered as risk factors for sporadic AD. Then these genes have been sequenced in search of genetic variability or polymorphisms, and each putative polymorphism has been reported to alter the risk of AD either directly or by an interaction with the APOE epsilon4 allele. However, positive-association studies with these candidate genes have not been consistently confirmed.

Cerebrospinal fluid levels of beta-amyloid(42) in patients with Alzheimer's disease are related to the exon 2 polymorphism of the cathepsin D gene

The intracellular aspartyl protease cathepsin D (catD) is involved in such Alzheimer's disease (AD)-related processes as the activation of the endosomal/lysosomal system and the cleavage of the amyloid precursor protein into amyloidogenic components, which may initiate neurodegeneration. A non-synonymous polymorphism (exon 2, C to T exchange leading to ala-->val substitution) of the gene encoding catD (CTSD) was previously associated with AD, in that the T allele increased the risk for AD. To investigate whether the T allele is associated with disease-related traits, we measured the concentration of the amyloid beta-peptide 1-42 (Abeta(42)) and 1-40 (Abeta(40)) in patients and control subjects. The T allele of the CTSD genotype was associated with a 50% decrease in Abeta(42) levels in the cerebrospinal fluid. Thus, we demonstrate a significant impact of the CTSD genotype on Abeta(42) levels in the cerebrospinal fluid of AD patients and underpin the importance of the validation of susceptibility genes by examining their potential pathophysiological relevance.

Alzheimer's disease-related overexpression of the cation-dependent mannose 6-phosphate receptor increases Abeta secretion: role for altered lysosomal hydrolase distribution in beta-amyloidogenesis

Prominent endosomal and lysosomal changes are an invariant feature of neurons in sporadic Alzheimer's disease (AD). These changes include increased levels of lysosomal hydrolases in early endosomes and increased expression of the cation-dependent mannose 6-phosphate receptor (CD-MPR), which is partially localized to early endosomes. To determine whether AD-associated redistribution of lysosomal hydrolases resulting from changes in CD-MPR expression affects amyloid precursor protein (APP) processing, we stably transfected APP-overexpressing murine L cells with human CD-MPR. As controls for these cells, we also expressed CD-MPR trafficking mutants that either localize to the plasma membrane (CD-MPRpm) or to early endosomes (CD-MPRendo). Expression of CD-MPR resulted in a partial redistribution of a representative lysosomal hydrolase, cathepsin D, to early endosomal compartments. Turnover of APP and secretion of sAPPalpha and sAPPbeta were not altered by overexpression of any of the CD-MPR constructs. However, secretion of both human Abeta40 and Abeta42 into the growth media nearly tripled in CD-MPR- and CD-MPRendo-expressing cells when compared with parental or CD-MPRpm-expressing cells. Comparable increases were confirmed for endogenous mouse Abeta40 in L cells expressing these CD-MPR constructs but not overexpressing human APP. These data suggest that redistribution of lysosomal hydrolases to early endocytic compartments mediated by increased expression of the CD-MPR may represent a potentially pathogenic mechanism for accelerating Abeta generation in sporadic AD, where the mechanism of amyloidogenesis is unknown.

Lack of association between cathepsin D genetic polymorphism and Alzheimer disease in a Spanish sample

Cathepsin D (catD) is an intracellular aspartyl protease that exhibits beta and gamma secretase-like activity to cleave amyloid precursor protein into beta amyloid peptide. The T-allele of a biallelic (alleles C and T) polymorphism in the exon 2 of the catD gene has been found to be associated with increased risk of Alzheimer disease (AD) in two independent German populations. Other groups have been unable to replicate this association in Caucasian American and Northern Ireland populations. Moreover, a small and no significant tendency for the T-allele to be protective for AD has been demonstrated in Caribbean Hispanics. A case control study utilizing a clinically well-defined group of 311 sporadic AD patients and 346 control subjects was performed to test this association in an ethnically homogeneous population from Spain. We did not observe any association between the T-allele of the catD gene and the disease. Furthermore, catD was not predictive of AD in an interactive fashion when considering apolipoprotein E, age, or gender.

Of replications and refutations: the status of Alzheimer's disease genetic research

Alzheimer's disease (AD) is a genetically complex and heterogeneous disorder. To date, mutations in three genes (APP, PSEN1, PSEN2) have been described to cause familial early-onset AD. In addition, a common polymorphism in the gene encoding apolipoprotein E (APOE) has been associated with the more common late-onset form of the disease. However, many studies have shown that genetic factors other than APOE play an important role in late-onset AD. Along these lines, a recent report predicted the existence of at least four additional late-onset AD genes, one of which was estimated to have a much greater contribution to age of onset variation than the APOE epsilon 4-allele. However, most of the nearly three dozen loci that have been proposed as putative AD genes to date have been followed by both replications and refutations, making consensus impossible. In this overview, we discuss the current status of genetic research in AD, including a brief summary of applicable analytic tools, and a summary of recent findings suggesting the existence of novel AD genes on chromosomes 10, 11, and 12.

Evidence against association of the FE65 gene (APBB1) intron 13 polymorphism in Alzheimer's patients

A genetic polymorphism in intron 13 of the FE65 gene (APBB1) was reported to be associated with Alzheimer's disease (AD). Our analyses of this polymorphism, both in a family-based or a case-control sample, fail to support the association between the FE65 intron 13 polymorphism and AD. We performed the sibship disequilibrium test (SDT, P=0.77) and the sib transmission/disequilibrium test (Sib-TDT, P=0.56) in a family-based study which included 526 subjects from 158 sibships. In addition, we compared the genotype and allele frequencies of this biallelic polymorphism in 311 AD patients to those of a control group consisting of 260 subjects and found no significant difference (chi(2), P=0.847 and P=0.586, respectively). Furthermore, our two-point linkage analysis in a family-based sample was in agreement with a genome wide scan for linkage to AD and showed no evidence for linkage to the short arm of chromosome 11 where the FE65 gene is located. We conclude that the association of the FE65 intron 13 polymorphism with AD, if any, is smaller than previously reported.