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

Pro-cathepsin D prevents aberrant protein aggregation dependent on endoplasmic reticulum protein CLN6

We previously expressed a chimeric protein in which the small heat-shock protein αB-crystallin (αBC) is fused at its N-terminus to the C-terminus of the first transmembrane segment of the endoplasmic reticulum (ER) protein mitsugumin 23 and confirmed its localization to the ER. Moreover, overexpression of this N-terminally modified αBC was shown to prevent the aggregation of the coexpressed R120G αBC variant, which is highly aggregation-prone and associated with the hereditary myopathy αB-crystallinopathy. To uncover a molecular mechanism by which the ER-anchored αBC negatively regulates the protein aggregation, we isolated proteins that bind to the ER-anchored αBC and identified the lysosomal protease cathepsin D (CTSD) as one such interacting protein. Proteolytically active CTSD is produced by multi-step processing of pro-cathepsin D (proCTSD), which is initially synthesized in the ER and delivered to lysosomes. When overexpressed, CTSD itself prevented the coexpressed R120G αBC variant from aggregating. This anti-aggregate activity was also elicited upon overexpression of the W383C CTSD variant, which is predominantly sequestered in the ER and consequently remains unprocessed, suggesting that proCTSD, rather than mature CTSD, serves to suppress the aggregation of the R120G αBC variant. Meanwhile, overexpression of the A58V CTSD variant, which is identical to wild-type CTSD except for the Ala58Val substitution within the pro-peptide, did not suppress the protein aggregation, indicating that the integrity of the pro-peptide is required for proCTSD to exert its anti-aggregate activity. Based on our previous finding that overexpression of the ER transmembrane protein CLN6 (ceroid-lipofuscinosis, neuronal 6), identified as an interacting protein of the ER-anchored αBC, prevents the R120G αBC variant from aggregating, the CLN6-proCTSD coupling was hypothesized to underpin the functionality of proCTSD within the ER. Indeed, CTSD, when overexpressed in CLN6-depleted cells, was unable to exert its anti-aggregate activity, supporting our view. Collectively, we show here that proCTSD prevents the protein aggregation through the functional association with CLN6 in the microenvironment surrounding the ER membrane, shedding light on a novel aspect of proCTSD and its potential involvement in CTSD-related disorders characterized by the accumulation of aberrant protein aggregates.

Prominent tauopathy and intracellular β-amyloid accumulation triggered by genetic deletion of cathepsin D: implications for Alzheimer disease pathogenesis

BACKGROUND

Cathepsin D (CatD) is a lysosomal protease that degrades both the amyloid-β protein (Aβ) and the microtubule-associated protein, tau, which accumulate pathognomonically in Alzheimer disease (AD), but few studies have examined the role of CatD in the development of Aβ pathology and tauopathy in vivo.

METHODS

CatD knockout (KO) mice were crossed to human amyloid precursor protein (hAPP) transgenic mice, and amyloid burden was quantified by ELISA and immunohistochemistry (IHC). Tauopathy in CatD-KO mice, as initially suggested by Gallyas silver staining, was further characterized by extensive IHC and biochemical analyses. Controls included human tau transgenic mice (JNPL3) and another mouse model of a disease (Krabbe A) characterized by pronounced lysosomal dysfunction. Additional experiments examined the effects of CatD inhibition on tau catabolism in vitro and in cultured neuroblastoma cells with inducible expression of human tau.

RESULTS

Deletion of CatD in hAPP transgenic mice triggers large increases in cerebral Aβ, manifesting as intense, exclusively intracellular aggregates; extracellular Aβ deposition, by contrast, is neither triggered by CatD deletion, nor affected in older, haploinsufficient mice. Unexpectedly, CatD-KO mice were found to develop prominent tauopathy by just ∼ 3 weeks of age, accumulating sarkosyl-insoluble, hyperphosphorylated tau exceeding the pathology present in aged JNPL3 mice. CatD-KO mice exhibit pronounced perinuclear Gallyas silver staining reminiscent of mature neurofibrillary tangles in human AD, together with widespread phospho-tau immunoreactivity. Striking increases in sarkosyl-insoluble phospho-tau (∼ 1250%) are present in CatD-KO mice but notably absent from Krabbe A mice collected at an identical antemortem interval. In vitro and in cultured cells, we show that tau catabolism is slowed by blockade of CatD proteolytic activity, including via competitive inhibition by Aβ42.

CONCLUSIONS

Our findings support a major role for CatD in the proteostasis of both Aβ and tau in vivo. To our knowledge, the CatD-KO mouse line is the only model to develop detectable Aβ accumulation and profound tauopathy in the absence of overexpression of hAPP or human tau with disease-associated mutations. Given that tauopathy emerges from disruption of CatD, which can itself be potently inhibited by Aβ42, our findings suggest that impaired CatD activity may represent a key mechanism linking amyloid accumulation and tauopathy in AD.

Prominent tauopathy and intracellular β-amyloid accumulation triggered by genetic deletion of cathepsin D: Implications for Alzheimer disease pathogenesis

Background

Cathepsin D (CatD) is a lysosomal protease that degrades both the amyloid-β protein (Aβ) and the microtubule-associated protein, tau, which accumulate pathognomonically in Alzheimer disease (AD), but few studies have examined the role of CatD in the development of Aβ pathology and tauopathy in vivo.

Methods

CatD knockout (KO) mice were crossed to human amyloid precursor protein (hAPP) transgenic mice, and amyloid burden was quantified by ELISA and immunohistochemistry (IHC). Tauopathy in CatD-KO mice, as initially suggested by Gallyas silver staining, was further characterized by extensive IHC and biochemical analyses. Controls included human tau transgenic mice (JNPL3) and another mouse model characterized by pronounced lysosomal dysfunction (Krabbe A). Additional experiments examined the effects of CatD inhibition on tau catabolism in vitro and in cultured neuroblastoma cells with inducible expression of human tau.

Results

Deletion of CatD in hAPP transgenic mice triggers large increases in cerebral Aβ, manifesting as intense, exclusively intracellular aggregates; extracellular Aβ deposition, by contrast, is neither triggered by CatD deletion, nor affected in older, haploinsufficient mice. Unexpectedly, CatDKO mice were found to develop prominent tauopathy by just ~ 3 weeks of age, accumulating sarkosyl-insoluble, hyperphosphorylated tau exceeding the pathology in aged JNPL3 mice. CatDKO mice exhibit pronounced perinuclear Gallyas silver staining reminiscent of mature neurofibrillary tangles in human AD, together with widespread phospho-tau immunoreactivity. Striking increases in sarkosyl-insoluble phospho-tau (~ 1250%) are present in CatD-KO mice, but notably absent from Krabbe A mice collected at an identical antemortem interval. In vitro and in cultured cells, we show that tau catabolism is slowed by blockade of CatD proteolytic activity, including via competitive inhibition by Aβ42.

Conclusions

Our findings support a major role for CatD in the proteostasis of both Aβ and tau in vivo. To our knowledge, CatD-KO mice are the only model to develop detectable Aβ acumulation and profound tauopathy in the absence of overexpression of hAPP or human tau with disease-associated mutations. Given that tauopathy emerges from disruption of CatD, which can itself be potently inhibited by Aβ42, our findings suggest that impaired CatD activity may represent a key mechanism linking amyloid accumulation and tauopathy in AD.

Converging links between adult-onset neurodegenerative Alzheimer's disease and early life neurodegenerative neuronal ceroid lipofuscinosis?

Evidence from genetics and from analyzing cellular and animal models have converged to suggest links between neurodegenerative disorders of early and late life. Here, we summarize emerging links between the most common late life neurodegenerative disease, Alzheimer's disease, and the most common early life neurodegenerative diseases, neuronal ceroid lipofuscinoses. Genetic studies reported an overlap of clinically diagnosed Alzheimer's disease and mutations in genes known to cause neuronal ceroid lipofuscinoses. Accumulating data strongly suggest dysfunction of intracellular trafficking mechanisms and the autophagy-endolysosome system in both types of neurodegenerative disorders. This suggests shared cytopathological processes underlying these different types of neurodegenerative diseases. A better understanding of the common mechanisms underlying the different diseases is important as this might lead to the identification of novel targets for therapeutic concepts, the transfer of therapeutic strategies from one disease to the other and therapeutic approaches tailored to patients with specific mutations. Here, we review dysfunctions of the endolysosomal autophagy pathway in Alzheimer's disease and neuronal ceroid lipofuscinoses and summarize emerging etiologic and genetic overlaps.

The role of lysosomal cathepsins in neurodegeneration: Mechanistic insights, diagnostic potential and therapeutic approaches

Lysosomes are ubiquitous organelles with a fundamental role in maintaining cellular homeostasis by mediating degradation and recycling processes. Cathepsins are the most abundant lysosomal hydrolyses and are responsible for the bulk degradation of various substrates. A correct autophagic function is essential for neuronal survival, as most neurons are post-mitotic and thus susceptible to accumulate cellular components. Increasing evidence suggests a crucial role of the lysosome in neurodegeneration as a key regulator of aggregation-prone and disease-associated proteins, such as α-synuclein, β-amyloid and huntingtin. Particularly, alterations in lysosomal cathepsins CTSD, CTSB and CTSL can contribute to the pathogenesis of neurodegenerative diseases as seen for neuronal ceroid lipofuscinosis, synucleinopathies (Parkinson's disease, Dementia with Lewy Body and Multiple System Atrophy) as well as Alzheimer's and Huntington's disease. In this review, we provide an overview of recent evidence implicating CTSD, CTSB and CTSL in neurodegeneration, with a special focus on the role of these enzymes in α-synuclein metabolism. In addition, we summarize the potential role of lysosomal cathepsins as clinical biomarkers in neurodegenerative diseases and discuss potential therapeutic approaches by targeting lysosomal function.

Cathepsin D Variants Associated With Neurodegenerative Diseases Show Dysregulated Functionality and Modified α-Synuclein Degradation Properties

Cathepsin D (CTSD) is a lysosomal protease important for the degradation of various substrates, including disease-associated proteins like α-synuclein (a-syn), amyloid precursor protein (APP) and tau, all of which tend to aggregate if not efficiently degraded. Hence, it is not surprising that genetic variants within the CTSD gene have been linked to neurodegenerative diseases, like Parkinson’s and Alzheimer’s disease (PD, AD), as well as the lysosomal storage disorder neuronal ceroid lipofuscinosis type-10 (NCL10). Although recent studies have shown the molecular dependence of substrate degradation via CTSD within autophagic pathways, only little is known about the precise role of lysosomal CTSD function in disease development. We here performed biochemical, cellular and structural analyses of eleven disease-causing CTSD point mutations found in genomic sequencing data of patients to understand their role in neurodegeneration. These CTSD variants were analyzed for cellular localization, maturation and enzymatic activity in overexpression analyses. Moreover, for PD-associated mutants, intracellular degradation of a-syn was monitored. In summary, our results suggest that NCL10-associated CTSD variants are significantly impaired in lysosomal maturation and enzymatic activity, whereas the AD- and PD-associated variants seemed rather unaffected, indicating normal maturation, and lysosomal presence. Interestingly, a PD-associated CTSD variant (A239V) exhibited increased enzymatic activity accompanied by enhanced a-syn degradation. By structural analyses of this mutant utilizing molecular dynamics simulation (MDS), we identified a structural change within a loop adjacent to the catalytic center leading to a higher flexibility and potentially accelerated substrate exchange rates. Our data sheds light onto the role of CTSD in disease development and helps to understand the structural regulation of enzymatic function, which could be utilized for targeted CTSD activation. Because of the degradative function of CTSD, this enzyme is especially interesting for therapeutic strategies tackling protein aggregates in neurodegenerative disorders.

Identification of Cathepsin D as a Plasma Biomarker for Alzheimer's Disease

Although Alzheimer’s disease (AD) is the most common neurodegenerative disease, there are still no drugs available to treat or prevent AD effectively. Here, we examined changes in levels of selected proteins implicated in the pathogenesis of AD using plasma samples of control subjects and patients with cognition impairment. To precisely categorize the disease, fifty-six participants were examined with clinical cognitive tests, amyloid positron emission tomography (PET) scan, and white matter hyperintensities scored by magnetic resonance imaging. Plasma cathepsin D levels of the subjects were examined by immunoblotting and enzyme-linked immunosorbent assay (ELISA). Correlation of plasma cathepsin D levels with AD-related factors and clinical characteristics were examined by statistical analysis. By analyzing quantitative immunoblot and ELISA, we found that the plasma level of cathepsin D, a major lysosomal protease, was decreased in the group with amyloid plaque deposition at the brain compared to the control group. The level of plasma cathepsin D was negatively correlated with clinical dementia rating scale sum of boxes (CDR-SB) scores. In addition, our integrated multivariable logistic regression model suggests the high performance of plasma cathepsin D level for discriminating AD from non-AD. These results suggest that the plasma cathepsin D level could be developed as a diagnostic biomarker candidate for AD.

The ZiBuPiYin recipe regulates proteomic alterations in brain mitochondria-associated ER membranes caused by chronic psychological stress exposure: Implications for cognitive decline in Zucker diabetic fatty rats

Chronic psychological stress (PS) cumulatively affects memory performance through the deleterious effects on hypothalamic-pituitary-adrenal axis regulation. Several functions damaged in cognitive impairment-related diseases are regulated by mitochondria-associated ER membranes (MAMs). To elucidate the role of ZiBuPiYin recipe (ZBPYR) in regulating the MAM proteome to improve PS-induced diabetes-associated cognitive decline (PSD), differentially expressed MAM proteins were identified among Zucker diabetic fatty rats, PSD rats, and PS combined with ZBPYR administration rats via iTRAQ with LC-MS/MS. Proteomic analysis revealed that the expressions of 85 and 33 proteins were altered by PS and ZBPYR treatment, respectively. Among these, 21 proteins were differentially expressed under both PS and ZBPYR treatments, whose functional categories included energy metabolism, lipid and protein metabolism, and synaptic dysfunction. Furthermore, calcium signaling and autophagy-related proteins may play roles in the pathogenesis of PSD and the mechanism of ZBPYR, respectively. Notably, KEGG pathway analysis suggested that ‘Alzheimer's disease’ and ‘oxidative phosphorylation’ pathways may be impaired in PSD pathogenesis, while ZBPYR could play a neuroprotective role through regulating the above pathways. Overall, exposure to chronic PS contributes to the evolution of diabetes-associated cognitive decline and ZBPYR might prevent and treat PSD by regulating the MAM proteome.

Cathepsin D regulates cerebral Aβ42/40 ratios via differential degradation of Aβ42 and Aβ40

BACKGROUND

Cathepsin D (CatD) is a lysosomal protease that degrades both the amyloid β-protein (Aβ) and the microtubule-associated protein, tau, and has been genetically linked to late-onset Alzheimer disease (AD). Here, we sought to examine the consequences of genetic deletion of CatD on Aβ proteostasis in vivo and to more completely characterize the degradation of Aβ42 and Aβ40 by CatD.

METHODS

We quantified Aβ degradation rates and levels of endogenous Aβ42 and Aβ40 in the brains of CatD-null (CatD-KO), heterozygous null (CatD-HET), and wild-type (WT) control mice. CatD-KO mice die by ~ 4 weeks of age, so tissues from younger mice, as well as embryonic neuronal cultures, were investigated. Enzymological assays and surface plasmon resonance were employed to quantify the kinetic parameters (K_M, k_cat) of CatD-mediated degradation of monomeric human Aβ42 vs. Aβ40, and the degradation of aggregated Aβ42 species was also characterized. Competitive inhibition assays were used to interrogate the relative inhibition of full-length human and mouse Aβ42 and Aβ40, as well as corresponding p3 fragments.

RESULTS

Genetic deletion of CatD resulted in 3- to 4-fold increases in insoluble, endogenous cerebral Aβ42 and Aβ40, exceeding the increases produced by deletion of an insulin-degrading enzyme, neprilysin or both, together with readily detectable intralysosomal deposits of endogenous Aβ42-all by 3 weeks of age. Quite significantly, CatD-KO mice exhibited ~ 30% increases in Aβ42/40 ratios, comparable to those induced by presenilin mutations. Mechanistically, the perturbed Aβ42/40 ratios were attributable to pronounced differences in the kinetics of degradation of Aβ42 vis-à-vis Aβ40. Specifically, Aβ42 shows a low-nanomolar affinity for CatD, along with an exceptionally slow turnover rate that, together, renders Aβ42 a highly potent competitive inhibitor of CatD. Notably, the marked differences in the processing of Aβ42 vs. Aβ40 also extend to p3 fragments ending at positions 42 vs. 40.

CONCLUSIONS

Our findings identify CatD as the principal intracellular Aβ-degrading protease identified to date, one that regulates Aβ42/40 ratios via differential degradation of Aβ42 vs. Aβ40. The finding that Aβ42 is a potent competitive inhibitor of CatD suggests a possible mechanistic link between elevations in Aβ42 and downstream pathological sequelae in AD.

Expression profiling of precuneus layer III cathepsin D-immunopositive pyramidal neurons in mild cognitive impairment and Alzheimer's disease: Evidence for neuronal signaling vulnerability

The precuneus (PreC; Brodmann area 7), a key hub within the default mode network (DMN) displays amyloid and tau-containing neurofibrillary tangle (NFT) pathology during the onset of Alzheimer's disease (AD). PreC layer III projection neurons contain lysosomal hydrolase cathepsin D (CatD), a marker of neurons vulnerable to NFT pathology. Here we applied single population laser capture microdissection coupled with custom-designed microarray profiling to determine the genetic signature of PreC CatD-positive-layer III neurons accrued from postmortem tissue obtained from the Rush Religious Orders Study (RROS) cases with a premortem clinical diagnosis of no cognitive impairment (NCI), mild cognitive impairment (MCI) and AD. Expression profiling revealed significant differential expression of key transcripts in MCI and AD compared to NCI that underlie signaling defects, including dysregulation of genes within the endosomal-lysosomal and autophagy pathways, cytoskeletal elements, AD-related genes, ionotropic and metabotropic glutamate receptors, cholinergic enzymes and receptors, markers of monoamine neurotransmission as well as steroid-related transcripts. Pervasive defects in both MCI and AD were found in select transcripts within these key gene ontology categories, underscoring the vulnerability of these corticocortical projection neurons during the onset and progression of dementia. Select PreC dysregulated genes detected via custom-designed microarray analysis were validated using qPCR. In summary, expression profiling of PreC CatD -positive layer III neurons revealed significant dysregulation of a mosaic of genes in MCI and AD that were not previously appreciated in terms of their indication of systems-wide signaling defects in a key hub of the DMN.

Progranulin Stimulates the In Vitro Maturation of Pro-Cathepsin D at Acidic pH

Single-copy loss-of-function mutations in the progranulin gene (PGRN) underlie the neurodegenerative disease frontotemporal lobar degeneration, while homozygous loss-of-function of PGRN results in the lysosomal storage disorder neuronal ceroid lipofuscinosis. Despite evidence that normal PGRN levels are critical for neuronal health, the function of this protein is not yet understood. Here, we show that PGRN stimulates the in vitro maturation of the lysosomal aspartyl protease cathepsin D (CTSD). CTSD is delivered to the endolysosomal system as an inactive precursor (proCTSD) and requires sequential cleavage steps via intermediate forms to achieve the mature state (matCTSD). In co-immunoprecipitation experiments, PGRN interacts predominantly with immature pro- and intermediate forms of CTSD. PGRN enhances in vitro conversion of proCTSD to matCTSD in a concentration-dependent manner. Differential scanning fluorimetry shows a destabilizing effect induced by PGRN on proCTSD folding (∆T_m = -1.7 °C at a 3:1 molar ratio). We propose a mechanism whereby PGRN binds to proCTSD, destabilizing the propeptide from the enzyme catalytic core and favoring conversion to mature forms of the enzyme. Further understanding of the role of PGRN in CTSD maturation will assist in the development of targeted therapies for neurodegenerative disease.

Autophagy and Alzheimer's Disease: From Molecular Mechanisms to Therapeutic Implications

Alzheimer’s disease (AD) is the most common cause of progressive dementia in the elderly. It is characterized by a progressive and irreversible loss of cognitive abilities and formation of senile plaques, composed mainly of amyloid β (Aβ), and neurofibrillary tangles (NFTs), composed of tau protein, in the hippocampus and cortex of afflicted humans. In brains of AD patients the metabolism of Aβ is dysregulated, which leads to the accumulation and aggregation of Aβ. Metabolism of Aβ and tau proteins is crucially influenced by autophagy. Autophagy is a lysosome-dependent, homeostatic process, in which organelles and proteins are degraded and recycled into energy. Thus, dysfunction of autophagy is suggested to lead to the accretion of noxious proteins in the AD brain. In the present review, we describe the process of autophagy and its importance in AD. Additionally, we discuss mechanisms and genes linking autophagy and AD, i.e., the mTOR pathway, neuroinflammation, endocannabinoid system, ATG7, BCL2, BECN1, CDK5, CLU, CTSD, FOXO1, GFAP, ITPR1, MAPT, PSEN1, SNCA, UBQLN1, and UCHL1. We also present pharmacological agents acting via modulation of autophagy that may show promise in AD therapy. This review updates our knowledge on autophagy mechanisms proposing novel therapeutic targets for the treatment of AD.

Loss of Cathepsin B and L Leads to Lysosomal Dysfunction, NPC-Like Cholesterol Sequestration and Accumulation of the Key Alzheimer's Proteins

Proper function of lysosomes is particularly important in neurons, as they cannot dilute accumulated toxic molecules and aggregates by cell division. Thus, impairment of lysosomal function plays an important role in neuronal degeneration and in the pathogenesis of numerous neurodegenerative diseases. In this work we analyzed how inhibition and/or loss of the major lysosomal proteases, the cysteine cathepsins B and L (CtsB/L), affects lysosomal function, cholesterol metabolism and degradation of the key Alzheimer's disease (AD) proteins. Here, we show that cysteine CtsB/L, and not the aspartyl cathepsin D (CtsD), represent a major lysosomal protease(s) that control lysosomal function, intracellular cholesterol trafficking and AD-like amyloidogenic features. Intriguingly, accumulation of free cholesterol in late endosomes/lysosomes upon CtsB/L inhibition resembled a phenotype characteristic for the rare neurodegenerative disorder Niemann-Pick type C (NPC). CtsB/L inhibition and not the inhibition of CtsD led to lysosomal impairment assessed by decreased degradation of EGF receptor, enhanced LysoTracker staining and accumulation of several lysosomal proteins LC3II, NPC1 and NPC2. By measuring the levels of NPC1 and ABCA1, the two major cholesterol efflux proteins, we showed that CtsB/L inhibition or genetic depletion caused accumulation of the NPC1 in lysosomes and downregulation of ABCA1 protein levels and its expression. Furthermore, we revealed that CtsB/L are involved in degradation of the key Alzheimer's proteins: amyloid-β peptides (Aβ) and C-terminal fragments of the amyloid precursor protein (APP) and in degradation of β-secretase (BACE1). Our results imply CtsB/L as major regulators of lysosomal function and demonstrate that CtsB/L may play an important role in intracellular cholesterol trafficking and in degradation of the key AD proteins. Our findings implicate that enhancing the activity or levels of CtsB/L could provide a promising and a common strategy for maintaining lysosomal function and for preventing and/or treating neurodegenerative diseases.

Proteomic Analysis of Protein Expression Throughout Disease Progression in a Mouse Model of Alzheimer's Disease

Alzheimer's disease (AD) is the most common cause of dementia. Mice in the transgenic AβPPswe/PS1dE9 mouse line express a chimeric mouse/human amyloid-β protein precursor (Mo/HuAβPP695swe) and mutant human presenilin 1 (PS1-dE9) associated with early-onset AD. Knowing the protein expression in these mice may offer better understanding of the pathological changes in AD. In this study, we used two-dimensional gel electrophoresis combined with mass spectrometry techniques to compare protein expression in AβPPswe/PS1dE9 mice with age-matched wild-type mice throughout the disease progression. We identified 15 proteins that were significantly different between the AβPPswe/PS1dE9 mice and age-matched controls and also changed with disease development. Among those, the expression levels of the following proteins in AβPPswe/PS1dE9 mice were at least 1.5 times higher than those in normal mice: DCC-interacting protein 13-beta, serum albumin, creatine kinase B-type, heat shock 70 kDa protein 1A, T-complex protein 1 subunit beta, adenylate kinase isoenzyme 1, pyruvate dehydrogenase E1 component subunit beta mitochondrial, and V-type proton ATPase catalytic subunit A. Levels of the following proteins in AβPPswe/PS1dE9 mice were at least 1.5 times lower than those in normal mice: dihydropyrimidinase-related protein 2, actin cytoplasmic 2, isoform 1 of V-type proton ATPase catalytic subunit, tubulin alpha-1C chain, F-actin-capping protein subunit alpha-2, ubiquitin carboxyl-terminal hydrolase isozyme L1, and actin cytoplasmic 1. These proteins are involved in regulating various cellular functions, including cytoskeletal structure, energy metabolism, synaptic components, and protein degradation. These findings indicate altered protein expression in the pathogenesis of AD and illuminate novel therapeutic avenues for treatment in AD.

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.

Proteomic analysis of Alzheimer's disease cerebrospinal fluid from neuropathologically diagnosed subjects

A crucial need exists for reliable Alzheimer's disease (AD) diagnostic and prognostic tests. Given its intimate communication with the brain, the cerebrospinal fluid (CSF) has been surveyed intensively for reliable AD biomarkers. The heterogeneity of AD pathology and the unavoidable difficulties associated with the clinical diagnosis and differentiation of this dementia from other pathologies have confounded biomarker studies in antemortem CSF samples. Using postmortem ventricular CSF (V-CSF) pools, two-dimensional difference gel electrophoresis (2D DIGE) analyses revealed a set of proteins that showed significant differences between neuropathologically-diagnosed AD and elderly non-demented controls (NDC), as well as subjects with non-AD dementias. The 2D DIGE system identified a set of 21 different protein biomarkers. This panel of proteins probably reflects fundamental pathological changes that are divergent from both normal aging and non-AD dementias.

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.

Cathepsin D--many functions of one aspartic protease

For years, it has been held that cathepsin D (CD) is involved in rather non-specific protein degradation in a strongly acidic milieu of lysosomes. Studies with CD knock-out mice revealed that CD is not necessary for embryonal development, but it is indispensable for postnatal tissue homeostasis. Mutation that abolishes CD enzymatic activity causes neuronal ceroid lipofuscinosis (NCL) characterized by severe neurodegeneration, developmental regression, visual loss and epilepsy in both animals and humans. In the last decade, however, an increasing number of studies demonstrated that enzymatic function of CD is not restricted solely to acidic milieu of lysosomes with important consequences in regulation of apoptosis. In addition to CD enzymatic activity, it has been shown that apoptosis is also regulated by catalytically inactive mutants of CD which suggests that CD interacts with other important molecules and influences cell signaling. Moreover, procathepsin D (pCD), secreted from cancer cells, acts as a mitogen on both cancer and stromal cells and stimulates their pro-invasive and pro-metastatic properties. Numerous studies found that pCD/CD level represents an independent prognostic factor in a variety of cancers and is therefore considered to be a potential target of anti-cancer therapy. Studies dealing with functions of cathepsin D are complicated by the fact that there are several simultaneous forms of CD in a cell-pCD, intermediate enzymatically active CD and mature heavy and light chain CD. It became evident that these forms may differently regulate the above-mentioned processes. In this article, we review the possible functions of CD and its various forms in cells and organisms during physiological and pathological conditions.

Cathepsin D SNP associated with increased risk of variant Creutzfeldt-Jakob disease

Background

Variant Creutzfeldt-Jakob disease (vCJD) originally resulted from the consumption of foodstuffs contaminated by bovine spongiform encephalopathy (BSE) material, with 163 confirmed cases in the UK to date. Many thousands are likely to have been exposed to dietary infection and so it is important (for surveillance, epidemic modelling, public health and understanding pathogenesis) to identify genetic factors that may affect individual susceptibility to infection. This study looked at a polymorphism in the cathepsin D gene (refSNP ID: rs17571) previously examined in Alzheimer's disease (AD).

Methods

Blood samples taken from 110 vCJD patients were tested for the C-T base change, and genotype data were compared with published frequencies for a control population using multiple logistic regression.

Results

There was a significant excess of the cathepsin D polymorphism TT genotype in the vCJD cohort compared to controls. The TT genotype was found to have a 9.75 fold increase in risk of vCJD compared to the CT genotype and a 10.92 fold increase compared to the CC genotype.

Conclusion

This mutation event has been observed to alter the protease activity of the cathepsin D protein and has been linked to an increase in amyloid beta plaque formation in AD. vCJD neuropathology is characterised by the presence of amyloid plaques, formed from the prion protein, and therefore alterations in the amyloid processing activity of cathepsin D may affect the neuropathogenesis of this disease.

Fine mapping of the MAPT locus using quantitative trait analysis identifies possible causal variants in Alzheimer's disease

In addition to senile plaques, neurofibrillary tangles are characteristic of Alzheimer's disease (AD) pathology, suggesting a clear involvement of the microtubule-associated protein tau (MAPT) in AD. Recent findings, suggesting that the H1c haplotype is associated with increased risk, now also implicate MAPT genetically. In this study, we aim to clarify this association by a fine mapping approach using both a traditional phenotypic association analysis and a quantitative trait (QT) analysis using cerebrospinal fluid (CSF) tau protein levels in the German population. Here, we report that both methodologies identify that the H1c haplotype may play important role in AD (AD risk, P=0.007, uncorrected; CSF tau levels, P=0.027, uncorrected). Further, the use of a sliding window approach in the QT analysis allowed for the narrowing down of the region where a probable causal variant may be located. The data suggest that this may lie at or within close proximity to the rs242557 single nucleotide polymorphism as association with CSF tau levels seems to be primarily driven by rs242557 in a gene dosage-dependent manner (trend model: P=0.002, uncorrected). These findings provide functional evidence to support the genetic association of MAPT with AD.

Cathepsin D, a Lysosomal Protease, Regulates ABCA1-mediated Lipid Efflux

To identify genes involved in the regulation of plasma high density lipoprotein (HDL) cholesterol (HDL-C) levels, patients with low HDL-C and age- and sex-matched controls (normal HDL-C) were extensively characterized. Comparative transcriptome analysis was carried out in cholesterol-loaded monocyte-derived macrophages from low HDL subjects segregated into groups with or without cholesterol efflux defects or ABCA1 mutations. Clusters of differentially regulated genes were evident in the low HDL groups as compared with controls. Of particular note, expression of cathepsin D (CTSD), a lysosomal proteinase, was reduced by approximately 50% in monocyte-derived macrophages of low HDL-C subjects, most significantly those with cholesterol efflux defects but without mutations in ABCA1 (p < 0.01). These results were verified by reverse transcription-PCR and replicated in a second cohort. We show here that blocking the activity or expression of CTSD, by pepstatin or CTSD small interfering RNA, respectively, reduced ABCA1 expression and protein abundance in both macrophages and CHO cells and apolipoprotein A-I-mediated lipid efflux by more than 70%. Conversely, expression of CTSD increased both ABCA1 mRNA expression and cellular ABCA1 protein. Consistent with its role in the proteolytic processing of prosaposin, inactivation of CTSD function resulted in the accumulation of glycosphingo-lipid and free cholesterol in late endosomes/lysosomes, a phenotype similar to NPC1 deficiency. Inhibition of CTSD also caused retention of ABCA1 in lysosomal compartments, reducing its trafficking to the plasma membrane. These studies demonstrate a novel and potentially important role for CTSD in intracellular cholesterol trafficking and ABCA1-mediated efflux. Therefore, decreased CTSD expression may contribute to low plasma HDL-C levels.