A genetic variation of cathepsin D is a major risk factor for Alzheimer's disease

Correlative cryo-soft X-ray tomography and cryo-structured illumination microscopy reveal changes to lysosomes in amyloid-β-treated neurons

Protein misfolding is common to neurodegenerative diseases (NDs) including Alzheimer's disease (AD), which is partly characterized by the self-assembly and accumulation of amyloid-beta in the brain. Lysosomes are a critical component of the proteostasis network required to degrade and recycle material from outside and within the cell and impaired proteostatic mechanisms have been implicated in NDs. We have previously established that toxic amyloid-beta oligomers are endocytosed, accumulate in lysosomes, and disrupt the endo-lysosomal system in neurons. Here, we use pioneering correlative cryo-structured illumination microscopy and cryo-soft X-ray tomography imaging techniques to reconstruct 3D cellular architecture in the native state revealing reduced X-ray density in lysosomes and increased carbon dense vesicles in oligomer treated neurons compared with untreated cells. This work provides unprecedented visual information on the changes to neuronal lysosomes inflicted by amyloid beta oligomers using advanced methods in structural cell biology.

Transcriptomic evaluation of tau and TDP-43 synergism shows tauopathy predominance and reveals potential modulating targets

Alzheimer's disease (AD), the most common aging-associated neurodegenerative dementia disorder, is defined by the presence of amyloid beta (Aβ) and tau aggregates in the brain. However, more than half of patients also exhibit aggregates of the protein TDP-43 as a secondary pathology. The presence of TDP-43 pathology in AD is associated with increased tau neuropathology and worsened clinical outcomes in AD patients. Using C. elegans models of mixed pathology in AD, we have previously shown that TDP-43 specifically synergizes with tau but not Aβ, resulting in enhanced neuronal dysfunction, selective neurodegeneration, and increased accumulation of pathological tau. However, cellular responses to co-morbid tau and TDP-43 preceding neurodegeneration have not been characterized. In this study, we evaluate transcriptomic changes at time-points preceding frank neuronal loss using a C. elegans model of tau and TDP-43 co-expression (tau-TDP-43 Tg). We find significant differential expression and exon usage in genes enriched in multiple pathways including lipid metabolism and lysosomal degradation. We note that early changes in tau-TDP-43 Tg resemble changes with tau alone, but a unique expression signature emerges during aging. We test loss-of-function mutations in a subset of tau and TDP-43 responsive genes, identifying new modifiers of neurotoxicity. Characterizing early cellular responses to tau and TDP-43 co-pathology is critical for understanding protective and pathogenic responses to mixed proteinopathies, and an important step in developing therapeutic strategies protecting against pathological tau and TDP-43 in AD.

From Lysosomal Storage Disorders to Parkinson's Disease - Challenges and Opportunities

Lysosomes are specialized organelles with an acidic pH that act as recycling hubs for intracellular and extracellular components. They harbour numerous different hydrolytic enzymes to degrade substrates like proteins, peptides, and glycolipids. Reduced catalytic activity of lysosomal enzymes can cause the accumulation of these substrates and loss of lysosomal integrity, resulting in lysosomal dysfunction and lysosomal storage disorders (LSDs). Post-mitotic cells, such as neurons, seem to be highly sensitive to damages induced by lysosomal dysfunction, thus LSDs often manifest with neurological symptoms. Interestingly, some LSDs and Parkinson's disease (PD) share common cellular pathomechanisms, suggesting convergence of aetiology of the two disease types. This is further underlined by genetic associations of several lysosomal genes involved in LSDs with PD. The increasing number of lysosome-associated genetic risk factors for PD makes it necessary to understand functions and interactions of lysosomal proteins/enzymes both in health and disease, thereby holding the potential to identify new therapeutic targets. In this review, we highlight genetic and mechanistic interactions between the complex lysosomal network, LSDs and PD, and elaborate on methodical challenges in lysosomal research.

Autophagy in health and disease: From molecular mechanisms to therapeutic target

Macroautophagy/autophagy is an evolutionally conserved catabolic process in which cytosolic contents, such as aggregated proteins, dysfunctional organelle, or invading pathogens, are sequestered by the double‐membrane structure termed autophagosome and delivered to lysosome for degradation. Over the past two decades, autophagy has been extensively studied, from the molecular mechanisms, biological functions, implications in various human diseases, to development of autophagy‐related therapeutics. This review will focus on the latest development of autophagy research, covering molecular mechanisms in control of autophagosome biogenesis and autophagosome–lysosome fusion, and the upstream regulatory pathways including the AMPK and MTORC1 pathways. We will also provide a systematic discussion on the implication of autophagy in various human diseases, including cancer, neurodegenerative disorders (Alzheimer disease, Parkinson disease, Huntington's disease, and Amyotrophic lateral sclerosis), metabolic diseases (obesity and diabetes), viral infection especially SARS‐Cov‐2 and COVID‐19, cardiovascular diseases (cardiac ischemia/reperfusion and cardiomyopathy), and aging. Finally, we will also summarize the development of pharmacological agents that have therapeutic potential for clinical applications via targeting the autophagy pathway. It is believed that decades of hard work on autophagy research is eventually to bring real and tangible benefits for improvement of human health and control of human diseases.

Impairment of the autophagy-lysosomal pathway in Alzheimer's diseases: Pathogenic mechanisms and therapeutic potential

Alzheimer's disease (AD), the most common neurodegenerative disorder, is characterized by memory loss and cognitive dysfunction. The accumulation of misfolded protein aggregates including amyloid beta (Aβ) peptides and microtubule associated protein tau (MAPT/tau) in neuronal cells are hallmarks of AD. So far, the exact underlying mechanisms for the aetiologies of AD have not been fully understood and the effective treatment for AD is limited. Autophagy is an evolutionarily conserved cellular catabolic process by which damaged cellular organelles and protein aggregates are degraded via lysosomes. Recently, there is accumulating evidence linking the impairment of the autophagy–lysosomal pathway with AD pathogenesis. Interestingly, the enhancement of autophagy to remove protein aggregates has been proposed as a promising therapeutic strategy for AD. Here, we first summarize the recent genetic, pathological and experimental studies regarding the impairment of the autophagy–lysosomal pathway in AD. We then describe the interplay between the autophagy–lysosomal pathway and two pathological proteins, Aβ and MAPT/tau, in AD. Finally, we discuss potential therapeutic strategies and small molecules that target the autophagy–lysosomal pathway for AD treatment both in animal models and in clinical trials. Overall, this article highlights the pivotal functions of the autophagy–lysosomal pathway in AD pathogenesis and potential druggable targets in the autophagy–lysosomal pathway for AD treatment.

Lysosomal gene Hexb displays haploinsufficiency in a knock-in mouse model of Alzheimer’s disease

Lysosomal network abnormalities are an increasingly recognised feature of Alzheimer’s disease (AD), which appear early and are progressive in nature. Sandhoff disease and Tay-Sachs disease (neurological lysosomal storage diseases caused by mutations in genes that code for critical subunits of β-hexosaminidase) result in accumulation of amyloid-β (Aβ) and related proteolytic fragments in the brain. However, experiments that determine whether mutations in genes that code for β-hexosaminidase are risk factors for AD are currently lacking. To determine the relationship between β-hexosaminidase and AD, we investigated whether a heterozygous deletion of Hexb, the gene that encodes the beta subunit of β-hexosaminidase, modifies the behavioural phenotype and appearance of disease lesions in App^{NL-G-F/NL-G-F}(App^KI/KI) mice. App^KI/KI and Hexb^+/- mice were crossed and evaluated in a behavioural test battery. Neuropathological hallmarks of AD and ganglioside levels in the brain were also examined. Heterozygosity of Hexb in App^KI/KI mice reduced learning flexibility during the Reversal Phase of the Morris water maze. Contrary to expectation, heterozygosity of Hexb caused a small but significant decrease in amyloid beta deposition and an increase in the microglial marker IBA1 that was region- and age-specific. Hexb heterozygosity caused detectable changes in the brain and in the behaviour of an AD model mouse, consistent with previous reports that described a biochemical relationship between HEXB and AD. This study reveals that the lysosomal enzyme gene Hexb is not haplosufficient in the mouse AD brain.

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The App NL-G-F Alzheimer mouse has lysosomal defects and stores ganglioside lipids.

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Heterozygous lysosomal Hexb did not drive amyloidosis in the App NL-G-F mouse.

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Heterozygous Hexb on an Alzheimer’s background reduced learning flexibility.

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Heterozygous Hexb on a wild-type mouse background produced hypoactivity.

Pharmacological modulation of autophagy for Alzheimer’s disease therapy: Opportunities and obstacles

Alzheimer's disease (AD) is a prevalent and deleterious neurodegenerative disorder characterized by an irreversible and progressive impairment of cognitive abilities as well as the formation of amyloid β (Aβ) plaques and neurofibrillary tangles (NFTs) in the brain. By far, the precise mechanisms of AD are not fully understood and no interventions are available to effectively slow down progression of the disease. Autophagy is a conserved degradation pathway that is crucial to maintain cellular homeostasis by targeting damaged organelles, pathogens, and disease-prone protein aggregates to lysosome for degradation. Emerging evidence suggests dysfunctional autophagy clearance pathway as a potential cellular mechanism underlying the pathogenesis of AD in affected neurons. Here we summarize the current evidence for autophagy dysfunction in the pathophysiology of AD and discuss the role of autophagy in the regulation of AD-related protein degradation and neuroinflammation in neurons and glial cells. Finally, we review the autophagy modulators reported in the treatment of AD models and discuss the obstacles and opportunities for potential clinical application of the novel autophagy activators for AD therapy.

Anthocyanin-rich blueberry extracts and anthocyanin metabolite protocatechuic acid promote autophagy-lysosomal pathway and alleviate neurons damage in in vivo and in vitro models of Alzheimer's disease

OBJECTIVES

As the global aging phenomenon intensifies, the incidence of Alzheimer's disease (AD) is gradually increasing. Diet appears to be an effective way to prevent and delay the progression of AD. Previous studies have found that cognitive impairment and neuronal damage were effectively alleviated by blueberry extract (BBE) in AD mice, but its mechanism is still unclear. The aims of this study were to detect the main anthocyanins of BBE; then to verify the protective effects of anthocyanin-rich BBE on hippocampal neurons and the promotion of autophagy; and finally to investigate the main protective effects and mechanisms of protocatechuic acid (PCA), a major metabolite of BBE, for promoting autophagy and thus playing a neuroprotective role.

METHODS

APP/PS1 mice were given 150 mg/kg BBE daily for 16 wk. Morphology of neurons was observed and autophagy-related proteins were detected.

RESULTS

Neuron damage in morphology was reduced and the expression of autophagy-related proteins in APP/PS1 mice were promoted after BBE treatment. In vitro, Aβ_25-35-induced cytotoxicity, including decreased neuron viability and increased levels of lactate dehydrogenase and reactive oxygen species, was effectively reversed by PCA. Furthermore, by adding autophagy inducers rapamycin and autophagy inhibitors Bafilomycin A1, it was verified that degradation of autophagosomes was upregulated and autophagy was promoted by PCA.

CONCLUSION

This study elucidated the mechanism of BBE for reducing neuronal damage by promoting neuronal autophagy and proved PCA may be the main bioactive metabolite of BBE for neuroprotective effects, providing a basis for dietary intervention in AD.

Tau Protein Interaction Partners and Their Roles in Alzheimer's Disease and Other Tauopathies

Tau protein plays a critical role in the assembly, stabilization, and modulation of microtubules, which are important for the normal function of neurons and the brain. In diseased conditions, several pathological modifications of tau protein manifest. These changes lead to tau protein aggregation and the formation of paired helical filaments (PHF) and neurofibrillary tangles (NFT), which are common hallmarks of Alzheimer's disease and other tauopathies. The accumulation of PHFs and NFTs results in impairment of physiological functions, apoptosis, and neuronal loss, which is reflected as cognitive impairment, and in the late stages of the disease, leads to death. The causes of this pathological transformation of tau protein haven't been fully understood yet. In both physiological and pathological conditions, tau interacts with several proteins which maintain their proper function or can participate in their pathological modifications. Interaction partners of tau protein and associated molecular pathways can either initiate and drive the tau pathology or can act neuroprotective, by reducing pathological tau proteins or inflammation. In this review, we focus on the tau as a multifunctional protein and its known interacting partners active in regulations of different processes and the roles of these proteins in Alzheimer's disease and tauopathies.

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.

Protein Homeostasis Networks and the Use of Yeast to Guide Interventions in Alzheimer's Disease

Alzheimer's Disease (AD) is a progressive multifactorial age-related neurodegenerative disorder that causes the majority of deaths due to dementia in the elderly. Although various risk factors have been found to be associated with AD progression, the cause of the disease is still unresolved. The loss of proteostasis is one of the major causes of AD: it is evident by aggregation of misfolded proteins, lipid homeostasis disruption, accumulation of autophagic vesicles, and oxidative damage during the disease progression. Different models have been developed to study AD, one of which is a yeast model. Yeasts are simple unicellular eukaryotic cells that have provided great insights into human cell biology. Various yeast models, including unmodified and genetically modified yeasts, have been established for studying AD and have provided significant amount of information on AD pathology and potential interventions. The conservation of various human biological processes, including signal transduction, energy metabolism, protein homeostasis, stress responses, oxidative phosphorylation, vesicle trafficking, apoptosis, endocytosis, and ageing, renders yeast a fascinating, powerful model for AD. In addition, the easy manipulation of the yeast genome and availability of methods to evaluate yeast cells rapidly in high throughput technological platforms strengthen the rationale of using yeast as a model. This review focuses on the description of the proteostasis network in yeast and its comparison with the human proteostasis network. It further elaborates on the AD-associated proteostasis failure and applications of the yeast proteostasis network to understand AD pathology and its potential to guide interventions against AD.

Autophagy Dysfunction in Alzheimer's Disease: Mechanistic Insights and New Therapeutic Opportunities

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by progressive memory loss due to aberrant accumulation of misfolded proteins inside and outside neurons and glial cells, leading to a loss of cellular protein homeostasis. Today, no therapy is available to block or slow down AD progression, and the mechanisms of the disease are not fully understood. Autophagy is an intracellular degradation pathway crucial to maintaining cellular homeostasis by clearing damaged organelles, pathogens, and unwanted protein aggregates. In recent years, autophagy dysfunction has gained considerable attention in AD and other neurodegenerative diseases because it has been linked to the accumulation of misfolded proteins that ultimately causes neuronal death in many of these disorders. Interestingly, autophagy-activating compounds have also shown some promising results in both clinical trials and preclinical studies. This review aims at summarizing the current knowledge on autophagy dysfunction in the context of AD pathophysiology, providing recent mechanistic insights on AD-mediated autophagic flux disruption and highlighting potential and novel therapeutic opportunities that target this system for AD therapy.

The Protective Effect of Vanadium on Cognitive Impairment and the Neuropathology of Alzheimer's Disease in APPSwe/PS1dE9 Mice

Alzheimer's disease (AD) is a widely distributed neurodegenerative disease characterized clinically by cognitive deficits and pathologically by formation of amyloid-β (Aβ) plaque and neurofibrillary tangles (NFTs) in the brain. Vanadium is a biological trace element that has a function to mimic insulin for diabetes. Bis(ethylmaltolato) oxidovanadium (IV) (BEOV) has been reported to have a hypoglycemic property, but its effect on AD remains unclear. In this study, BEOV was supplemented at doses of 0.2 and 1.0 mmol/L to the AD model mice APPSwe/PS1dE9 for 3 months. The results showed that BEOV substantially ameliorated glucose metabolic disorder as well as synaptic and behavioral deficits of the AD mice. Further investigation revealed that BEOV significantly reduced Aβ generation by increasing the expression of peroxisome proliferator-activated receptor gamma and insulin-degrading enzyme and by decreasing β-secretase 1 in the hippocampus and cortex of AD mice. BEOV also reduced tau hyperphosphorylation by inhibiting protein tyrosine phosphatase-1B and regulating the pathway of insulin receptor/insulin receptor substrate-1/protein kinase B/glycogen synthase kinase 3 beta. Furthermore, BEOV could enhance autophagolysosomal fusion and restore autophagic flux to increase the clearance of Aβ deposits and phosphorylated tau in the brains of AD mice. Collectively, the present study provides solid data for revealing the function and mechanism of BEOV on AD pathology.

Dipeptidyl-Peptidase Activity of Meprin β Links N-truncation of Aβ with Glutaminyl Cyclase-Catalyzed pGlu-Aβ Formation

The formation of amyloid-β (Aβ) peptides is causally involved in the development of Alzheimer's disease (AD). A significant proportion of deposited Aβ is N-terminally truncated and modified at the N-terminus by a pGlu-residue (pGlu-Aβ). These forms show enhanced neurotoxicity compared to full-length Aβ. Although the truncation may occur by aminopeptidases after formation of Aβ, recently discovered processing pathways of amyloid-β protein precursor (AβPP) by proteases such as meprin β may also be involved. Here, we assessed a role of meprin β in forming Aβ3-40/42, which is the precursor of pGlu-Aβ3-40/42 generated by glutaminyl cyclase (QC). Similar to QC, meprin β mRNA is significantly upregulated in postmortem brain from AD patients. A histochemical analysis supports the presence of meprin β in neurons and astrocytes in the vicinity of pGlu-Aβ containing deposits. Cleavage of AβPP-derived peptides by meprin β in vitro results in peptides Aβ1-x, Aβ2-x, and Aβ3-x. The formation of N-truncated Aβ by meprin β was also corroborated in cell culture. A subset of the generated peptides was converted into pGlu-Aβ3-40 by an addition of glutaminyl cyclase, supporting the preceding formation of Aβ3-40. Further analysis of the meprin β cleavage revealed a yet unknown dipeptidyl-peptidase-like activity specific for the N-terminus of Aβ1-x. Thus, our data suggest that meprin β contributes to the formation of N-truncated Aβ by endopeptidase and exopeptidase activity to generate the substrate for QC-catalyzed pGlu-Aβ formation.

Spontaneous Isomerization of Long-Lived Proteins Provides a Molecular Mechanism for the Lysosomal Failure Observed in Alzheimer's Disease

Proteinaceous aggregation is a well-known observable in Alzheimer's disease (AD), but failure and storage of lysosomal bodies within neurons is equally ubiquitous and actually precedes bulk accumulation of extracellular amyloid plaque. In fact, AD shares many similarities with certain lysosomal storage disorders though establishing a biochemical connection has proven difficult. Herein, we demonstrate that isomerization and epimerization, which are spontaneous chemical modifications that occur in long-lived proteins, prevent digestion by the proteases in the lysosome (namely, the cathepsins). For example, isomerization of aspartic acid into l-isoAsp prevents digestion of the N-terminal portion of Aβ by cathepsin L, one of the most aggressive lysosomal proteases. Similar results were obtained after examination of various target peptides with a full series of cathepsins, including endo-, amino-, and carboxy-peptidases. In all cases peptide fragments too long for transporter recognition or release from the lysosome persisted after treatment, providing a mechanism for eventual lysosomal storage and bridging the gap between AD and lysosomal storage disorders. Additional experiments with microglial cells confirmed that isomerization disrupts proteolysis in active lysosomes. These results are easily rationalized in terms of protease active sites, which are engineered to precisely orient the peptide backbone and cannot accommodate the backbone shift caused by isoaspartic acid or side chain dislocation resulting from epimerization. Although Aβ is known to be isomerized and epimerized in plaques present in AD brains, we further establish that the rates of modification for aspartic acid in positions 1 and 7 are fast and could accrue prior to plaque formation. Spontaneous chemistry can therefore provide modified substrates capable of inducing gradual lysosomal failure, which may play an important role in the cascade of events leading to the disrupted proteostasis, amyloid formation, and tauopathies associated with AD.

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.

Apolipoprotein E4 Elicits Lysosomal Cathepsin D Release, Decreased Thioredoxin-1 Levels, and Apoptosis

The major genetic risk factor for Alzheimer’s disease (AD), apolipoprotein E4 (ApoE4), has been suggested to have detrimental effects on neurons, including direct toxicity via apoptosis. Thioredoxin-1 (Trx1) is an endogenous antioxidant protein important for redox regulation and participates in the regulation of apoptosis through the inhibition of apoptosis signal-regulating kinase-1 (Ask-1). In this study, we have investigated the effects of ApoE on Trx1 in the brain. Our results showed that the protein levels of Trx1 were reduced in the hippocampus of ApoE4 targeted replacement (TR) mice compared to ApoE3 TR mice. The reduction was also seen in vitro after treatment of both human primary cortical neurons and neuroblastoma cells with human recombinant ApoE4 (rApoE4). Furthermore, ApoE4 caused a disruption of lysosomal integrity and a shift in the localization of Cathepsin D, an enzyme known to degrade Trx1. ApoE4 treatment induced in addition apoptosis through translocation of Death-domain associated protein-6 (Daxx) from the nucleus to the cytosol, suggesting an activation of the Ask-1 pathway. This toxicity was prevented by overexpression of Trx1 and other endogenous Ask-1 inhibitors. Our data suggests that down-regulation of Trx1 is involved in the toxicity caused by ApoE4. An activated ASK-1 pathway might indeed make cells more vulnerable to other insults such as amyloid-β, which could partially explain the mechanism behind the strongest genetic risk factor for AD.

Selenium-enriched yeast inhibited β-amyloid production and modulated autophagy in a triple transgenic mouse model of Alzheimer's disease

Se-yeast reduced the burden of Aβ accumulation by both decreased the generation and inhibited the initiation of autophagy pathway, enhanced autophagic clearance of Aβ in the brains of AD mice.

Haplodeficiency of Cathepsin D does not affect cerebral amyloidosis and autophagy in APP/PS1 transgenic mice

Autophagy and lysosomal function are important for protein homeostasis and their dysfunction have been associated with Alzheimer's disease (AD). Increased immunoreactivities of an important lysosomal protease, cathepsin D (Cat D), are evident in amyloid plaques and neurons in patients with AD. This study tests the hypothesis that deleting one allele of the cathepsin D gene (Ctsd) impacts cerebral β-amyloidosis in amyloid-β precursor protein (APP)sw/PS1dE9 (APP/PS1) double transgenic mice. Despite a significant 38% decrease in Cat D level in APP/PS1/Ctsd+/- compared with APP/PS1/Ctsd+/+ mice, no changes in steady state levels and deposition of Aβ were found in the brain. There were also no differences in APP processing, the levels of two other Aβ-degrading proteases, the levels of autophagy related protein, such as LAMP2, P62, LC3-I, LC3-II, and Beclin-1, or the markers of neuroinflammation, observed between the APP/PS1/Ctsd+/+ and APP/PS1/Ctsd+/- mice. Our findings demonstrate that in wild-type mice, Cat D protein levels are either in excess or redundant with other factors in the brain, and at least one allele of Ctsd is dispensable for cerebral β-amyloidosis and autophagy in APP/PS1 transgenic mice.

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.

Cellular Signature of SIL1 Depletion: Disease Pathogenesis due to Alterations in Protein Composition Beyond the ER Machinery

SIL1 acts as nucleotide exchange factor for the endoplasmic reticulum chaperone BiP. Mutations of SIL1 cause Marinesco-Sjögren syndrome (MSS), a neurodegenerative disorder. Moreover, a particular function of SIL1 for etiopathology of amyotrophic lateral sclerosis (ALS) was highlighted, thus declaring the functional SIL1-BiP complex as a modifier for neurodegenerative disorders. Thereby, depletion of SIL1 was associated with an earlier manifestation and in strengthened disease progression in ALS. Owing to the absence of appropriate in vitro models, the precise cellular pathophysiological mechanisms leading to neurodegeneration in MSS and triggering the same in further disorders like ALS are still elusive. We found that SIL1 depletion in human embryonic kidney 293 (HEK293) cells led to structural changes of the endoplasmic reticulum (ER) including the nuclear envelope and mitochondrial degeneration that closely mimic pathological alterations in MSS and ALS. Functional studies revealed disturbed protein transport, cytotoxicity with reduced proliferation and viability, accompanied by activation of cellular defense mechanisms including the unfolded protein response, ER-associated degradation pathway, proteolysis, and expression of apoptotic and survival factors. Our data moreover indicated that proteins involved in cytoskeletal organization, vesicular transport, mitochondrial function, and neurological processes contribute to SIL1 pathophysiology. Altered protein expression upon SIL1 depletion in vitro could be confirmed in Sil1-deficient motoneurones for paradigmatic proteins belonging to different functional classes. Our results demonstrate that SIL1-depleted HEK293 cells are an appropriate model to identify proteins modulated by SIL1 expression level and contributing to neurodegeneration in MSS and further disorders like ALS. Thereby, our combined results point out that proteins beyond such involved ER-related protein processing are affected by SIL1 depletion.

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.

Mass spectrometry (LC-MS/MS) identified proteomic biosignatures of breast cancer in proximal fluid

We have begun an early phase of biomarker discovery in three clinically important types of breast cancer using a panel of human cell lines: HER2 positive, hormone receptor positive and HER2 negative, and triple negative (HER2-, ER-, PR-). We identified and characterized the most abundant secreted, sloughed, or leaked proteins released into serum free media from these breast cancer cell lines using a combination of protein fractionation methods before LC-MS/MS mass spectrometry analysis. A total of 249 proteins were detected in the proximal fluid of 7 breast cancer cell lines. The expression of a selected group of high abundance and/or breast cancer-specific potential biomarkers including thromobospondin 1, galectin-3 binding protein, cathepsin D, vimentin, zinc-α2-glycoprotein, CD44, and EGFR from the breast cancer cell lines and in their culture media were further validated by Western blot analysis. Interestingly, mass spectrometry identified a cathepsin D protein single-nucleotide polymorphism (SNP) by alanine to valine replacement from the MCF-7 breast cancer cell line. Comparison of each cell line media proteome displayed unique and consistent biosignatures regardless of the individual group classifications, demonstrating the potential for stratification of breast cancer. On the basis of the cell line media proteome, predictive Tree software was able to categorize each cell line as HER2 positive, HER2 negative, and hormone receptor positive and triple negative based on only two proteins, muscle fructose 1,6-bisphosphate aldolase and keratin 19. In addition, the predictive Tree software clearly identified MCF-7 cell line overexpresing the HER2 receptor with the SNP cathepsin D biomarker.

Lysosomal dysfunction promotes cleavage and neurotoxicity of tau in vivo

Expansion of the lysosomal system, including cathepsin D upregulation, is an early and prominent finding in Alzheimer's disease brain. Cell culture studies, however, have provided differing perspectives on the lysosomal connection to Alzheimer's disease, including both protective and detrimental influences. We sought to clarify and molecularly define the connection in vivo in a genetically tractable model organism. Cathepsin D is upregulated with age in a Drosophila model of Alzheimer's disease and related tauopathies. Genetic analysis reveals that cathepsin D plays a neuroprotective role because genetic ablation of cathepsin D markedly potentiates tau-induced neurotoxicity. Further, generation of a C-terminally truncated form of tau found in Alzheimer's disease patients is significantly increased in the absence of cathepsin D. We show that truncated tau has markedly increased neurotoxicity, while solubility of truncated tau is decreased. Importantly, the toxicity of truncated tau is not affected by removal of cathepsin D, providing genetic evidence that modulation of neurotoxicity by cathepsin D is mediated through C-terminal cleavage of tau. We demonstrate that removing cathepsin D in adult postmitotic neurons leads to aberrant lysosomal expansion and caspase activation in vivo, suggesting a mechanism for C-terminal truncation of tau. We also demonstrate that both cathepsin D knockout mice and cathepsin D–deficient sheep show abnormal C-terminal truncation of tau and accompanying caspase activation. Thus, caspase cleavage of tau may be a molecular mechanism through which lysosomal dysfunction and neurodegeneration are causally linked in Alzheimer's disease.

Neurodegenerative disorders, like Alzheimer's disease, are a devastating group of conditions that exact a heavy toll on patients and their families. These disorders also represent a significant and growing public health challenge as our population ages because no effective treatments are available. Research over the past two decades has strongly suggested that a fundamental problem in affected nerve cells relates to accumulation of cellular “garbage,” or proteins and other material that is too old to function properly. Thus, understanding how the neuron handles these outdated molecules is of great significance. Here we find that upregulation of one such cellular degrading pathway, the lysosome, can have significant deleterious effects to the neuron. We specifically show that expanding the lysosomal compartment can markedly increase production of a very toxic form of tau, a protein strongly implicated in neuronal dysfunction and death in Alzheimer's disease and related disorders. Our findings have important implications for the development of neurodegenerative disease therapies that seek to manipulate the lysosome and the proteins within the lysosome.

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.

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.

Proteomic identification of proteins in the human brain: Towards a more comprehensive understanding of neurodegenerative disease

Proteomics has revealed itself as a powerful tool in the identification and determination of proteins and their biological significance. More recently, several groups have taken advantage of the high-throughput nature of proteomics in order to gain a more in-depth understanding of the human brain. In turn, this information has provided researchers with invaluable insight into the potential pathways and mechanisms involved in the pathogenesis of several neurodegenerative disorders, e.g., Alzheimer and Parkinson disease. Furthermore, these findings likely will improve methods to diagnose disease and monitor disease progression as well as generate novel targets for therapeutic intervention. Despite these advances, comprehensive understanding of the human brain proteome remains challenging, and requires development of improved sample enrichment, better instrumentation, and innovative analytic techniques. In this review, we will focus on the most recent progress related to identification of proteins in the human brain under normal as well as pathological conditions, mainly Alzheimer and Parkinson disease, their potential application in biomarker discovery, and discuss current advances in protein identification aimed at providing a more comprehensive understanding of the brain.

Neuronal gene expression in non-demented individuals with intermediate Alzheimer's Disease neuropathology

While the clinical and neuropathological characterization of Alzheimer's Disease (AD) is well defined, our understanding of the progression of pathologic mechanisms in AD remains unclear. Post-mortem brains from individuals who did not fulfill clinical criteria for AD may still demonstrate measurable levels of AD pathologies to suggest that they may have presented with clinical symptoms had they lived longer or are able to stave off disease progression. Comparison between such individuals and those clinically diagnosed and pathologically confirmed to have AD will be key in delineating AD pathogenesis and neuroprotection. In this study, we expression profiled laser capture microdissected non-tangle bearing neurons in 6 post-mortem brain regions that are differentially affected in the AD brain from 10 non-demented individuals demonstrating intermediate AD neuropathologies (NDAD; Braak stage of II through IV and CERAD rating of moderate to frequent) and evaluated this data against that from individuals who have been diagnosed with late onset AD as well as healthy elderly controls. We identified common statistically significant expression changes in both NDAD and AD brains that may establish a degenerative link between the two cohorts, in addition to NDAD specific transcriptomic changes. These findings pinpoint novel targets for developing earlier diagnostics and preventative therapies for AD prior to diagnosis of probable AD. We also provide this high-quality, low post-mortem interval (PMI), cell-specific, and region-specific NDAD/AD reference data set to the community as a public resource.

Effect of multiple genetic polymorphisms on antigen presentation and susceptibility to Mycobacterium tuberculosis infection

Several molecules related to antigen presentation, including gamma interferon (IFN-gamma) and the major histocompatibility complex (MHC), are encoded by polymorphic genes. Some polymorphisms were found to affect susceptibility to tuberculosis (TB) when they were considered singly in epidemiological studies, but how multiple polymorphisms interact to determine susceptibility to TB in an individual remains an open question. We hypothesized that polymorphisms in some genes may counteract or intensify the effects of polymorphisms in other genes. For example, an increase in IFN-gamma expression may counteract the weak binding that a particular MHC variant displays for a peptide from Mycobacterium tuberculosis to establish the same T-cell response as another, more strongly binding MHC variant. To test this hypothesis, we developed a mathematical model of antigen presentation based on experimental data for the known effects of genetic polymorphisms and simulated time courses when multiple polymorphisms were present. We found that polymorphisms in different genes could affect antigen presentation to the same extent and therefore compensate for each other. Furthermore, we defined the conditions under which such relationships could exist. For example, increased IFN-gamma expression compensated for decreased peptide-MHC affinity in the model only above a certain threshold of expression. Below this threshold, changes in IFN-gamma expression were ineffectual compared to changes in peptide-MHC affinity. The finding that polymorphisms exhibit such relationships could explain discrepancies in the epidemiological literature, where some polymorphisms have been inconsistently associated with susceptibility to TB. Furthermore, the model allows polymorphisms to be ranked by effect, providing a new tool for designing association studies.

Cluster analysis of risk factor genetic polymorphisms in Alzheimer's disease

Multiple genetic variants may contribute to the risk of developing Alzheimer's disease. We have analyzed polymorphisms in 9 genes to determine whether particular combinations would contribute to this risk. The genes were APOE, LDLr, CST3, CTSD, TNF, BACE1, MAPT, STH, eNOS, and TFCP2. Three risk groups for the disease were identified. Risk group I was younger, was heterozygous for the CST3 (GA), CTSD2936 (AG), TNF -308 (AG) genetic variants. Risk group II was older, was homozygous for the -427 APOE promoter polymorphism (TT), and heterozygous for the MAPT deletion and for the STH variant (QR). Group III had both the youngest and oldest subjects, were heterozygous for the -863 (AC) and -1031 (CT) TNF promoter polymorphisms. All three groups carried the APOE 4 allele and were heterozygous for both BACE1 polymorphisms. The control groups were carriers of the APOE 3 allele and were homozygous for the BACE1 genetic variants.

Proteomics Identification of Proteins in Human Cortex Using Multidimensional Separations and MALDI Tandem Mass Spectrometer

It is essential to characterize the proteome of various regions of human brain because most, if not all, neurodegenerative diseases are region-specific. Here we report an in-depth proteomics identification of proteins extracted from the frontal cortex, a region playing a critical role in cognitive function. The integrated proteomics analytical flow consisted of biochemical fractionation, strong cation exchange chromatography, reverse phase liquid chromatography, and MALDI-TOF/TOF mass spectrometric analysis. In total, 812 proteins were confidently identified with two or more peptides. These proteins demonstrated diverse isoelectric points and molecular weights and are involved in several molecular functions, including protein binding, catalytic activity, transport, structure, and signal transduction. A number of proteins known to be associated with neurodegenerative diseases were also identified. Detailed characterization of these proteins will supply the necessary information to appropriately interpret proteins associated with aging and/or age-related neurodegenerative diseases. Finally 140 proteins found in the cortical proteome were present in the proteome of cerebrospinal fluid, providing tissue-specific candidates for biomarker discovery in body fluid.

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.

Membership in genetic groups predicts Alzheimer disease

The multiple polymorphisms contributing to Alzheimer disease (AD) have been difficult to identify. Three essentially sufficient risk sets were found using a fuzzy latent classification statistical model; that is, grade-of-membership analysis, and genotypes for APOE, APOCI, LDLr, cystatin C, and cathepsin D (180 cases, 120 controls). These were: (a) CST3:GA and CTSD:CT; (b) APOE44 and LDLr8:GG and LDLr13:TT; and (c) APOE34 and LDLr13:TC. Consonance with one of the groups and high aggregate membership carried >800-fold elevated risk for AD. The absence of these combinations defined low risk. APOE3/- with heterozygous promoter and receptor genotypes predicted long life without dementia.

Investigating cognitive genetics and its implications for the treatment of cognitive deficit

Cognitive impairment in the elderly, caused by either normal ageing process or dementia, is an increasing problem in developed countries that has enormous social and economic considerations. Research investigating the genetic basis of cognition is a new and rapidly developing field that may aid in the development of new treatments for age-related cognitive deficit. Over the past 6 years, a number of quantitative trait loci (QTLs) have been associated with cognitive functioning in humans including loci within the genes catechol-o-methyltransferase, brain-derived neurotrophic factor, muscle segment homeobox 1, serotonin transporter 2A (HTR2A), cholinergic muscarinic receptor 2, cathepsin D, metabotrophic glutamate receptor and most recently the class II human leukocyte antigens. Unfortunately, inconsistency within the literature, which is a hallmark of almost all association studies investigating complex diseases and traits, is casting doubt as to which genes are truly associated with cognition and which are a result of Type 2 error. This review will highlight implicated intelligence QTLs, examine the probable reasons for the current discrepancies between reports and discuss the potential advantages that may be procured from the study of cognitive genetics.

Influence and interactions of cathepsin D, HLA-DRB1 and APOE on cognitive abilities in an older non-demented population

Cathepsin D (CTSD), human leukocyte antigen DRB1 (HLA-DRB1) and apolipoprotein E (APOE) have all been associated with cognitive ability in both demented and non-demented individuals. CTSD is a pleiotrophic protein whose functions include the processing of proteins prior to presentation by HLA. Several studies have also reported that a functional exon 2 polymorphism in the CTSD gene interacts with APOEepsilon4 resulting in an increased risk of developing Alzheimer's disease (AD). We have previously reported that the CTSD exon 2 polymorphism regulates fluid intelligence. In this study, we extend this finding to other cognitive domains and investigate interactions with APOE and HLA-DRB1. Using a cohort of 766 non-demented volunteers, we found that the CTSD exon 2 T allele was associated with a decrease in several cognitive domains that comprise processing speed [random letters (RLs) test, P = 0.012; alphabet-coding task (ACT), P = 0.001], spatial recall (SR) (P = 0.016) and an additional test of fluid intelligence (P = 0.010). We also observed that the HLA-DR1 was associated with enhanced cumulative recall ability (P = 0.006), and conversely HLA-DR5 was associated with diminished delayed verbal recall and SR abilities (P = 0.014 and P = 0.003, respectively). When analysed independently, APOEepsilon4 did not influence any cognitive domains. In contrast, CTSD T/APOEepsilon4-positive volunteers scored lower on tests of fluid intelligence (P = 0.015), processing speed (ACT, P = 0.001; RL, P = 0.013) and immediate recall (P = 0.029). Scores were lower for all these tests than when CTSD and APOE were analysed independently. This supports previous findings in AD that have also reported an epistatic interaction. In addition, we found that CTSD T/HLA-DR2-positive volunteers had reduced processing speed (ACT, P = 0.040; RL, P = 0.014) and had significantly lower cumulative and SR abilities (P = 0.003 and P = 0.001, respectively). Biological interaction between these two proteins has previously been shown where HLA-DR2 binds more readily to the myelin basic protein (MBP) compared with other DR antigens, preventing MBP cleavage by CTSD.

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.

Association between cathepsin D polymorphism and Alzheimer's disease in a Chinese Han population

Cathepsin D (CTSD) is an intracellular aspartyl protease, which is active in the endosomal/lysosomal system. CTSD may play a role in Alzheimer's disease (AD) through cleaving the amyloid precursor protein into beta-amyloid peptide and degrading tau protein into fragments. A functional polymorphism in exon 2 of the cathepsin D gene (C-->T, Ala224Val) has recently been reported to increase the risk for AD in some of the Caucasian populations, with a significant overrepresentation of the T allele, but these reports have not been universally duplicated. We performed an association study between CTSD polymorphism and AD in 156 sporadic AD patients and 183 controls of Chinese Han ethnicity. Our data revealed that the distribution of CTSD genotypes and alleles was similar in patients and controls. No direct association was found between CTSD polymorphism and AD risk. There might be a weak synergistic interaction between CTSD T and APOEepsilon4 allele in increasing the risk for developing AD.

Putative association of polymorphism in the mannose 6-phosphate receptor gene with major depression and Alzheimer's disease

The endosomal lysosomal system might play a role in Alzheimer's disease, but its impact in major depression is unknown. The expression of the cation-dependent mannose 6-phosphate receptor (CD-MPR) is increased in Alzheimer's disease and the CD-MPR gene is located next to a region on chromosome 12 possibly linked to Alzheimer's disease. We investigated a C/T polymorphism in the CD-MPR gene in 188 Alzheimer's disease patients, in a control sample of 193 patients with major depression, as hospitalized controls, and in 259 healthy controls. We examined the interaction of the CD-MPR polymorphism with the putative risk factor for Alzheimer's disease, the cathepsin D T-allele. No significant association of the CD-MPR C-allele with Alzheimer's disease was observed. However, exploratory data analysis revealed an increased frequency of the CD-MPR C-allele in patients with major depression; thus, the C-allele may be a risk factor for depression. Gene location and function of the CD-MPR suggest an involvement in Alzheimer's disease; however, we could not find an association of the CD-MPR polymorphism with Alzheimer's disease. Since exploratory data suggest an involvement of the endosomal lysosomal system in major depression, further studies are warranted to investigate the biological role of the CD-MPR in major depression.

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 exon 2 polymorphism associated with general intelligence in a healthy older population

General intelligence is a heritable trait that is a risk factor for both the onset of dementia and the rate of cognitive decline in community-dwelling older persons. Previous studies screening for quantitative trait loci (QTLs) that influence general intelligence in healthy individuals have identified four loci, two of which are located within the genes insulin-like growth factor 2 receptor (IGF2R) and the Msx1 homeobox. Here, we report the finding of another QTL associated with general intelligence that is located within exon 2 of the cathepsin D (CTSD) gene. A group of 767 healthy adults with a follow-up period of over 15 years have been analyzed for cross-sectional and longitudinal trends in cognitive change using the Heim intelligence test score (AH4-1). We observed a significant association (P = 0.01) between a functional C > T (Ala > Val) transition within exon 2 of the CTSD gene that increases the secretion of pro-CTSD from the cell, and the AH4-1 score at initial testing on entry to the longitudinal study. Interestingly, CTSD is transported by IGF2R from the trans Golgi network to the lysosome.