SORL1 is genetically associated with neuropathologically characterized late-onset Alzheimer's disease

Polygenic effects on the risk of Alzheimer's disease in the Japanese population

BACKGROUND

Polygenic effects have been proposed to account for some disease phenotypes; these effects are calculated as a polygenic risk score (PRS). This score is correlated with Alzheimer's disease (AD)-related phenotypes, such as biomarker abnormalities and brain atrophy, and is associated with conversion from mild cognitive impairment (MCI) to AD. However, the AD PRS has been examined mainly in Europeans, and owing to differences in genetic structure and lifestyle, it is unclear whether the same relationships between the PRS and AD-related phenotypes exist in non-European populations. In this study, we calculated and evaluated the AD PRS in Japanese individuals using genome-wide association study (GWAS) statistics from Europeans.

METHODS

In this study, we calculated the AD PRS in 504 Japanese participants (145 cognitively unimpaired (CU) participants, 220 participants with late mild cognitive impairment (MCI), and 139 patients with mild AD dementia) enrolled in the Japanese Alzheimer's Disease Neuroimaging Initiative (J-ADNI) project. In order to evaluate the clinical value of this score, we (1) determined the polygenic effects on AD in the J-ADNI and validated it using two independent cohorts (a Japanese neuropathology (NP) cohort (n = 565) and the North American ADNI (NA-ADNI) cohort (n = 617)), (2) examined the AD-related phenotypes associated with the PRS, and (3) tested whether the PRS helps predict the conversion of MCI to AD.

RESULTS

The PRS using 131 SNPs had an effect independent of APOE. The PRS differentiated between CU participants and AD patients with an area under the curve (AUC) of 0.755 when combined with the APOE variants. Similar AUC was obtained when PRS calculated by the NP and NA-ADNI cohorts was applied. In MCI patients, the PRS was associated with cerebrospinal fluid phosphorylated-tau levels (β estimate = 0.235, p value = 0.026). MCI with a high PRS showed a significantly increased conversion to AD in APOE ε4 noncarriers with a hazard rate of 2.22. In addition, we also developed a PRS model adjusted for LD and observed similar results.

CONCLUSIONS

We showed that the AD PRS is useful in the Japanese population, whose genetic structure is different from that of the European population. These findings suggest that the polygenicity of AD is partially common across ethnic differences.

Brain Transcriptome Analysis of a Protein-Truncating Mutation in Sortilin-Related Receptor 1 Associated With Early-Onset Familial Alzheimer's Disease Indicates Early Effects on Mitochondrial and Ribosome Function

BACKGROUND

The early cellular stresses leading to Alzheimer's disease (AD) remain poorly understood because we cannot access living, asymptomatic human AD brains for detailed molecular analyses. Sortilin-related receptor 1 (SORL1) encodes a multi-domain receptor protein genetically associated with both rare, early-onset familial AD (EOfAD) and common, sporadic, late-onset AD (LOAD). SORL1 protein has been shown to act in the trafficking of the amyloid β A4 precursor protein (AβPP) that is proteolysed to form one of the pathological hallmarks of AD, amyloid-β (Aβ) peptide. However, other functions of SORL1 in AD are less well understood.

OBJECTIVE

To investigate the effects of heterozygosity for an EOfAD-like mutation in SORL1 on the brain transcriptome of young-adult mutation carriers using zebrafish as a model organism.

METHODS

We performed targeted mutagenesis to generate an EOfAD-like mutation in the zebrafish orthologue of SORL1 and performed RNA-sequencing on mRNA isolated from the young adult brains of siblings in a family of fish either wild type (non-mutant) or heterozygous for the EOfAD-like mutation.

RESULTS

We identified subtle differences in gene expression indicating changes in mitochondrial and ribosomal function in the mutant fish. These changes appear to be independent of changes in mitochondrial content or the expression of AβPP-related proteins in zebrafish.

CONCLUSION

These findings provided evidence supporting that EOfAD mutations in SORL1 affect mitochondrial and ribosomal function and provide the basis for future investigation elucidating the nature of these effects.

Novel Rare SORL1 Variants in Early-Onset Dementia

BACKGROUND

Rare variants of SORL1 have been associated with an increased risk of early-onset or late-onset Alzheimer's disease (AD). However, a lot remains to be clarified about their significance in the pathogenesis of the disease.

OBJECTIVE

To evaluate the role of SORL1 variants among Finnish patients with early-onset AD (EOAD).

METHODS

The rare SORL1variants were screened in a cohort of 115 Finnish EOAD patients (mean age at onset 58.3 years, range 46-65 years) by using the whole-exome sequencing.

RESULTS

We found one novel nonsense variant (p.Gln290*) and eight missense variants in SORL1. This is the first study reporting the SORL1 variants p.Lys80Arg, p.Ala789Val and p.Arg866Gln in EOAD patients. Furthermore, two of these three missense variants were overrepresented in EOAD patients compared to gnomAD non-neuro Finnish samples.

CONCLUSION

This study strengthens the earlier findings, that the rare variants in SORL1 are associated with EOAD.

Single Nucleotide Polymorphisms in Alzheimer's Disease Risk Genes Are Associated with Intrinsic Connectivity in Middle Age

BACKGROUND

It is critical to identify individuals at risk for Alzheimer's disease (AD) earlier in the disease time course, such as middle age and preferably well prior to the onset of clinical symptoms, when intervention efforts may be more successful. Genome-wide association and candidate gene studies have identified single nucleotide polymorphisms (SNPs) in APOE, CLU, CR1, PICALM, and SORL1 that confer increased risk of AD.

OBJECTIVE

In the current study, we investigated the associations between SNPs in these genes and resting-state functional connectivity within the default mode network (DMN), frontoparietal network (FPN), and executive control network (ECN) in healthy, non-demented middle-aged adults (age 40 -60; N = 123; 74 females).

METHODS

Resting state networks of interest were identified through independent components analysis using a template-matching procedure and individual spatial maps and time courses were extracted using dual regression.

RESULTS

Within the posterior DMN, functional connectivity was associated with CR1 rs1408077 and CLU rs9331888 polymorphisms (p's < 0.05). FPN connectivity was associated with CR1 rs1408077, CLU rs1136000, SORL1 rs641120, and SORL1 rs689021 (p's < 0.05). Functional connectivity within the ECN was associated with the CLU rs11136000 (p < 0.05). There were no APOE- or PICALM-related differences in any of the networks investigated (p's > 0.05).

CONCLUSION

This is the first demonstration of the relationship between intrinsic network connectivity and AD risk alleles in CLU, CR1, and SORL1 in healthy, middle-aged adults. These SNPs should be considered in future investigations aimed at identifying potential preclinical biomarkers for AD.

Sorting Out the Role of the Sortilin-Related Receptor 1 in Alzheimer's Disease

Sortilin-related receptor 1 (SORL1) encodes a large, multi-domain containing, membrane-bound receptor involved in endosomal sorting of proteins between the trans-Golgi network, endosomes and the plasma membrane. It is genetically associated with Alzheimer's disease (AD), the most common form of dementia. SORL1 is a unique gene in AD, as it appears to show strong associations with the common, late-onset, sporadic form of AD and the rare, early-onset familial form of AD. Here, we review the genetics of SORL1 in AD and discuss potential roles it could play in AD pathogenesis.

Genetic Study of Alzheimer's Disease in Saudi Population

BACKGROUND

Alzheimer's disease (AD) is a chronic neurological disorder associated with mental decline and dementia. Several studies focused on investigating the molecular basis of the disease that led to the identification of several causative genes and risk associated alleles. Replication of these studies and findings from different populations is very important.

OBJECTIVE

Molecular assessment of a cohort of 117 familial and sporadic AD cases from Saudi Arabia.

METHODS

Comprehensive screening for point mutations was carried out by direct sequencing of coding regions in the three known AD causative genes: PSEN1, PSEN2, APP, as well as the AD associated gene SORL1. All patients were also genotyped for APOE alleles. In silico 3D protein structure analysis was performed for two novel SORL1 variants.

RESULTS

We identified a total of eight potential pathogenic missense variants in all studied genes. Five of these variants were not previously reported including four in SORL1 (p.Val297Met, p.Arg1084Cys, p.Asp1100Asn, and p.Pro1213Ser) and one in APP (p.Glu380Lys). The frequency of APOE-ɛ4 allele was 21.37% of total investigated cases. In silico 3D protein structure analysis of two SORL1 novel missense variants (p.Pro1213Ser and p.Arg1084Cys) suggested that these variants may affect the folding of the proteins and disturb their structure.

CONCLUSIONS

Our comprehensive analysis of the open reading frame of the known genes have identified potential pathogenic rare variants in 18/117 cases. We found that point mutations in AD main genes (PSEN1, PSEN2, and APP) were underrepresented in our cohort of patients. Our results confirm involvement of SORL1 in familial and sporadic AD cases.

CHIP modulates APP-induced autophagy-dependent pathological symptoms in Drosophila

Dysregulation of autophagy is associated with the neurodegenerative processes in Alzheimer's disease (AD), yet it remains controversial whether autophagy is a cause or consequence of AD. We have previously expressed the full-length human APP in Drosophila and established a fly AD model that exhibits multiple AD-like symptoms. Here we report that depletion of CHIP effectively palliated APP-induced pathological symptoms, including morphological, behavioral, and cognitive defects. Mechanistically, CHIP is required for APP-induced autophagy dysfunction, which promotes Aβ production via increased expression of BACE and Psn. Our findings suggest that aberrant autophagy is not only a consequence of abnormal APP activity, but also contributes to dysregulated APP metabolism and subsequent AD pathogenesis.

Lack of human-like extracellular sortilin neuropathology in transgenic Alzheimer's disease model mice and macaques

BACKGROUND

Alzheimer's disease (AD) is a devastating neurodegenerative disorder bearing multiple pathological hallmarks suggestive of complex cellular/molecular interplay during pathogenesis. Transgenic mice and nonhuman primates are used as disease models for mechanistic and translational research into AD; the extent to which these animal models recapitulate AD-type neuropathology is an issue of importance. Putative C-terminal fragments from sortilin, a member of the vacuolar protein sorting 10 protein (Vps10p) family, have recently been shown to deposit in the neuritic β-amyloid (Aβ) plaques in the human brain.

METHODS

We set out to explore if extracellular sortilin neuropathology exists in AD-related transgenic mice and nonhuman primates. Brains from different transgenic strains and ages developed overt cerebral Aβ deposition, including the β-amyloid precursor protein and presenilin 1 double-transgenic (APP/PS1) mice at ~ 14 months of age, the five familial Alzheimer's disease mutations transgenic (5×FAD) mice at ~ 8 months, the triple-transgenic Alzheimer's disease (3×Tg-AD) mice at ~ 22 months, and aged monkeys (Macaca mulatta and Macaca fascicularis) were examined. Brain samples from young transgenic mice, middle-aged/aged monkeys, and AD humans were used as negative and positive pathological controls.

RESULTS

The C-terminal sortilin antibody, which labeled senile plaques in the AD human cerebral sections, did not display extracellular immunolabeling in the transgenic mouse or aged monkey brain sections with Aβ deposition. In Western blot analysis, sortilin fragments ~ 15 kDa were not detectable in transgenic mouse cortical lysates, but they occurred in control AD lysates.

CONCLUSIONS

In reference to their human brain counterparts, neuritic plaques seen in transgenic AD model mouse brains represent an incomplete form of this AD pathological hallmark. The species difference in neuritic plaque constituents also indicates more complex secondary proteopathies in the human brain relative to rodents and nonhuman primates during aging and in AD.

Genetics of Alzheimer's disease: From pathogenesis to clinical usage

Alzheimer's disease (AD) is the most common type of dementia and has caused a major global health concern. Understanding the etiology of AD can be beneficial for the diagnosis and intervention of this disease. Genetics plays a vital role in the pathogenesis of AD. Research methods in genetics such as the linkage analysis, study of candidate genes, genome-wide association study (GWAS), and next-generation sequencing (NGS) technology help us map the genetic information in AD, which can not only provide a new insight into the pathogenesis of AD but also be beneficial for early targeted intervention of AD. This review summarizes the pathogenesis as well as the diagnostic and therapeutic value of genetics in AD.

Interaction between PPAR γ and SORL1 gene with Late-Onset Alzheimer's disease in Chinese Han Population

AIMS

To investigate the impact of sortilin-related receptor 1 gene 1 (SORL1) and peroxisome proliferator activated receptor gamma (PPAR G) gene single nucleotide polymorphisms (SNPs), gene- gene and gene- environment interactions and haplotype on late-onset Alzheimer's disease (LOAD) risk.

METHODS

Hardy-Weinberg equilibrium (HWE), haplotype analysis and pairwise linkage disequilibrium (LD) analysis were investigated by using SNPStats (available online at http://bioinfo.iconcologia.net/SNPstats). Logistic regression was performed to investigate association between SNPs and LOAD. Generalized multifactor dimensionality reduction (GMDR) was used to investigate the interaction among gene- gene and gene- environment interaction.

RESULTS

Logistic regression analysis showed that LOAD risk was significantly higher in carriers of the A allele of rs1784933 polymorphism than those with GG (GA+ AA versus GG), adjusted OR (95%CI) = 1.63(1.27-1.98), and higher in carriers of G allele of the rs1805192 polymorphism than those with CC (CG+ GG versus CC), adjusted OR (95%CI) = 1.70 (1.25-2.27). GMDR analysis suggested a significant two-locus model (p = 0.0010) involving rs1784933 and rs1805192, and a significant two-locus model (p = 0.0100) involving rs1784933 and alcohol drinking. Haplotype containing the rs1784933- A and rs689021- C alleles were associated with a statistically increased LOAD risk (OR = 1.86, 95%CI = 1.37- 2.52, p < 0.001).

CONCLUSIONS

We conclude that rs1784933 and rs1805192 minor alleles, gene- gene interaction between rs1784933 and rs1805192, gene- environment interaction between rs1784933 and alcohol drinking, and haplotype containing the rs1784933- A and rs689021- C alleles are all associated with increased LOAD risk.

Sortilin Fragments Deposit at Senile Plaques in Human Cerebrum

Genetic variations in the vacuolar protein sorting 10 protein (Vps10p) family have been linked to Alzheimer’s disease (AD). Here we demonstrate deposition of fragments from the Vps10p member sortilin at senile plaques (SPs) in aged and AD human cerebrum. Sortilin changes were characterized in postmortem brains with antibodies against the extracellular and intracellular C-terminal domains. The two antibodies exhibited identical labeling in normal human cerebrum, occurring in the somata and dendrites of cortical and hippocampal neurons. The C-terminal antibody also marked extracellular lesions in some aged and all AD cases, appearing as isolated fibrils, mini-plaques, dense-packing or circular mature-looking plaques. Sortilin and β-amyloid (Aβ) deposition were correlated overtly in a region/lamina- and case-dependent manner as analyzed in the temporal lobe structures, with co-localized immunofluorescence seen at individual SPs. However, sortilin deposition rarely occurred around the pia, at vascular wall or in areas with typical diffuse Aβ deposition, with the labeling not enhanced by section pretreatment with heating or formic acid. Levels of a major sortilin fragment ~15 kDa, predicted to derive from the C-terminal region, were dramatically elevated in AD relative to control cortical lysates. Thus, sortilin fragments are a prominent constituent of the extracellularly deposited protein products at SPs in human cerebrum.

Impact of SORL1 genetic variations on MRI markers in non-demented elders

The sorting protein-related receptor 1 (SORL1 or LR11) gene has been verified to play an important role in the pathologic process of β-amyloid (Aβ) formation and trafficking in Alzheimer's Disease (AD) by plenty of cytological and molecular biological studies. But there were few studies investigated the association of SORL1 gene and neurodegeneration features from a rather macroscopic perspective. In the present study, we explored the effect of SORL1 genotypes on AD-related brain atrophy. We recruited 812 individuals with both baseline and two-year follow-up information from the Alzheimer's Disease Neuroimaging Initiative (ADNI) database and applied multiple linear regression models to examine the association between eight single nucleotide polymorphisms (SNPs) and neuroimaging phenotypes. Finally, four SNPs (rs11219350, rs2298813, rs3781836, rs3824968) showed trend of association with the volume of hippocampus and parahippocampal gyrus but failed to survive the false discovery rate (FDR) correction. Only rs1784933 and rs753780 showed significant association with right parahippocampal gyrus. According to our findings, SORL1 variations influence the atrophy of specific AD-related brain structures, which suggested the potential role of SORL1 in the neurodegeneration of cognitive related regions.

Meta-analysis of the Association between Alzheimer Disease and Variants in GAB2, PICALM, and SORL1

The genetic variants play a crucial role in the pathogenesis of Alzheimer's disease (AD), while the relationships of specific single nucleotide polymorphisms (SNPs) with AD are still controversial. We performed the meta-analysis to obtain a more precise estimation of whether growth factor receptor-bound protein-associated binding protein 2 (GAB2), phosphatidylinositol binding clathrin assembly protein (PICALM), and sortilin-related receptor (SORL1) variants are associated with AD. Databases including PubMed, Embase, and Cochrane Library were searched to find relevant studies. Cochran's Q-statistic and I ² were used to assess the heterogeneity among the included studies. Odds ratios (OR) and 95 % confidence intervals (95 % CIs) were conducted to evaluate the association between the SNP and the susceptibility to AD. Publication bias was estimated by funnel plots. All of the statistical analyses were implemented using R Version 3.2.1 software. A total of 35 case-control studies involving 15 SNPs were included. There was no significant association between SNPs of GAB2 rs2373115 (G > T) and PICALM rs541458 (C > T) and AD. The allele T of rs3851179 in PICALM was associated with a 13 % increase in the risk of AD. Seven SNPs on SORL1 were significantly associated with AD. Four SNPs, including rs1010159*T, rs641120*A, rs668387*T, and rs689021*A, were associated with a decreased risk of AD, while the other three SNPs, including rs12285364*T, rs2070045*G, and rs2282649*T, were all associated with an increased risk of AD. The results of the present study suggested that multiple gene variants were associated with AD. The SNP of rs3851179 (PICALM), rs12285364 (SORL1), rs2070045 (SORL1), and rs2282649 (SORL1) was associated with an increased risk of AD, whereas SORL1 rs1010159, rs641120, rs668387, and rs689021 were associated with a decreased risk of AD.

Early Life Epidemiology of Alzheimer's Disease--A Critical Review

BACKGROUND

As adult brain structure is primarily established in early life, genetic and environmental exposures in infancy and childhood influence the risk for Alzheimer disease (AD). In this systematic review, we identified several early life risk factors and discussed the evidence and underlying mechanism for each.

SUMMARY

Early risk factors for AD may alter brain anatomy, causing vulnerability to AD-related dementia later in life. In the perinatal period, both genes and learning disabilities have been associated with the development of distinct AD phenotypes. During early childhood, education and intellect, as well as body growth, may predispose to AD through alterations in cognitive and brain reserve, though the specific mediators of neural injury are disputed. Childhood socioeconomic status (SES) may predispose to AD by influencing adult SES and cognition. Association of these risk factors with underlying AD pathology (rather than just clinical diagnosis) has not been sufficiently examined.

KEY MESSAGES

Factors that impede or alter brain growth during early life could render certain brain regions or networks selectively vulnerable to the onset, accumulation or spread of AD-related pathology during later life. Careful life-course epidemiology could provide clues as to why the brain systematically degenerates during AD.

Cerebral small vessel disease and Alzheimer's disease

Cerebral small vessel disease (CSVD) is a group of pathological processes with multifarious etiology and pathogenesis that are involved into the small arteries, arterioles, venules, and capillaries of the brain. CSVD mainly contains lacunar infarct or lacunar stroke, leukoaraiosis, Binswanger's disease, and cerebral microbleeds. CSVD is an important cerebral microvascular pathogenesis as it is the cause of 20% of strokes worldwide and the most common cause of cognitive impairment and dementia, including vascular dementia and Alzheimer's disease (AD). It has been well identified that CSVD contributes to the occurrence of AD. It seems that the treatment and prevention for cerebrovascular diseases with statins have such a role in the same function for AD. So far, there is no strong evidence-based medicine to support the idea, although increasing basic studies supported the fact that the treatment and prevention for cerebrovascular diseases will benefit AD. Furthermore, there is still lack of evidence in clinical application involved in specific drugs to benefit both AD and CSVD.

Elucidating molecular phenotypes caused by the SORL1 Alzheimer's disease genetic risk factor using human induced pluripotent stem cells

Predisposition to sporadic Alzheimer's disease (SAD) involves interactions between a person's unique combination of genetic variants and the environment. The molecular effect of these variants may be subtle and difficult to analyze with standard in vitro or in vivo models. Here we used hIPSCs to examine genetic variation in the SORL1 gene and possible contributions to SAD-related phenotypes in human neurons. We found that human neurons carrying SORL1 variants associated with an increased SAD risk show a reduced response to treatment with BDNF, at the level of both SORL1 expression and APP processing. shRNA knockdown of SORL1 demonstrates that the differences in BDNF-induced APP processing between genotypes are dependent on SORL1 expression. We propose that the variation in SORL1 expression induction by BDNF is modulated by common genetic variants and can explain how genetic variation in this one locus can contribute to an individual's risk of developing SAD.

Genome-Wide Analyses of Working-Memory Ability: A Review

Working memory, a theoretical construct from the field of cognitive psychology, is crucial to everyday life. It refers to the ability to temporarily store and manipulate task-relevant information. The identification of genes for working memory might shed light on the molecular mechanisms of this important cognitive ability and-given the genetic overlap between, for example, schizophrenia risk and working-memory ability-might also reveal important candidate genes for psychiatric illness. A number of genome-wide searches for genes that influence working memory have been conducted in recent years. Interestingly, the results of those searches converge on the mediating role of neuronal excitability in working-memory performance, such that the role of each gene highlighted by genome-wide methods plays a part in ion channel formation and/or dopaminergic signaling in the brain, with either direct or indirect influence on dopamine levels in the prefrontal cortex. This result dovetails with animal models of working memory that highlight the role of dynamic network connectivity, as mediated by dopaminergic signaling, in the dorsolateral prefrontal cortex. Future work, which aims to characterize functional variants influencing working-memory ability, might choose to focus on those genes highlighted in the present review and also those networks in which the genes fall. Confirming gene associations and highlighting functional characterization of those associations might have implications for the understanding of normal variation in working-memory ability and also for the development of drugs for mental illness.

The role of the retromer complex in aging-related neurodegeneration: a molecular and genomic review

The retromer coat complex is a vital component of the intracellular trafficking mechanism sorting cargo from the endosomes to the trans-Golgi network or to the cell surface. In recent years, genes encoding components of the retromer coat complex and members of the vacuolar protein sorting 10 (Vps10) family of receptors, which play pleiotropic functions in protein trafficking and intracellular/intercellular signaling in neuronal and non-neuronal cells and are primary cargos of the retromer complex, have been implicated as genetic risk factors for sporadic and autosomal dominant forms of several neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease and frontotemporal lobar degeneration. In addition to their functions in protein trafficking, the members of the Vps10 receptor family (sortilin, SorL1, SorCS1, SorCS2, and SorCS3) modulate neurotrophic signaling pathways. Both sortilin and SorCS2 act as cell surface receptors to mediate acute responses to proneurotrophins. In addition, sortilin can modulate the intracellular response to brain-derived neurotrophic factor (BDNF) by direct control of BDNF levels and regulating anterograde trafficking of Trk receptors to the synapse. This review article summarizes the emerging data from this rapidly growing field of intracellular trafficking signaling in the pathogenesis of neurodegeneration.

Eph receptors: new players in Alzheimer's disease pathogenesis

Alzheimer's disease (AD) is devastating and leads to permanent losses of memory and other cognitive functions. Although recent genetic evidences strongly argue for a causative role of Aβ in AD onset and progression (Jonsson et al., 2012), its role in AD etiology remains a matter of debate. However, even if not the sole culprit or pathological trigger, genetic and anatomical evidences in conjunction with numerous pharmacological studies, suggest that Aβ peptides, at least contribute to the disease. How Aβ contributes to memory loss remains largely unknown. Soluble Aβ species referred to as Aβ oligomers have been shown to be neurotoxic and induce network failure and cognitive deficits in animal models of the disease. In recent years, several proteins were described as potential Aβ oligomers receptors, amongst which are the receptor tyrosine kinases of Eph family. These receptors together with their natural ligands referred to as ephrins have been involved in a plethora of physiological and pathological processes, including embryonic neurogenesis, learning and memory, diabetes, cancers and anxiety. Here we review recent discoveries on Eph receptors-mediated protection against Aβ oligomers neurotoxicity as well as their potential as therapeutic targets in AD pathogenesis.

The Role of SORL1 in Alzheimer's Disease

Genetic variation in SORL1 gene, also known as LR11, has been identified to associate with Alzheimer's disease (AD) through replicated genetic studies. As a type I transmembrane protein, SORL1 is composed of several distinct domains and belongs to both the low-density lipoprotein receptor (LDLR) family and the vacuolar protein sorting 10 (VPS10) domain receptor family. The level of SORL1 was found to be decreased in the AD brain which positively correlated with β-amyloid (Aβ) accumulation. Emerging data suggests that SORL1 contributes to AD through various pathways, including emerging as a central regulator of the trafficking and processing of amyloid precursor protein (APP), involvement in Aβ destruction, and interaction with ApoE and tau protein. Primarily, SORL1 interacts with distinct sets of cytosolic adaptors for anterograde and retrograde movement of APP between the trans-Golgi network (TGN) and early endosomes, thereby restricting the delivery of the precursor to endocytic compartments that favor amyloidogenic breakdown. In this article, we review recent epidemiological and genetical findings of SORL1 that related with AD and speculate the possible roles of SORL1 in the progression of this disease. Finally, given the potential contributions of SORL1 to AD pathogenesis, targeting SORL1 might present novel opportunities for AD therapy.

The SORL1 polymorphism rs985421 may confer the risk for amnestic mild cognitive impairment and Alzheimer's disease in the Han Chinese population

Although the pathogenetic mechanisms driving Alzheimer's disease (AD) are unclear, genetic variations may play an important role. Previous studies have identified that single nucleotide polymorphisms (SNPs) in the sortilin-related receptor, L (DLR class) A repeats containing (SORL1) gene are associated with AD or amnestic mild cognitive impairment (aMCI) patients. However, the association of SORL1 variants with AD or aMCI susceptibility in the Han Chinese population has not been adequately reported. Thus, we conducted a case-control study in 106 sporadic AD patients, 67 aMCI patients, and 179 healthy control Han Chinese subjects to determine whether SORL1 genetic variations alter the risk for AD or aMCI. Using the LDR-PCR method to genotype five polymorphisms in SORL1, we found significant associations (for AD: OR=1.968, 95% CI=1.273-3.042; for aMCI: OR=2.210, 95% CI=1.353-3.610) between the 'A' allele of the SORL1 SNP rs985421 and AD and aMCI, which may represent an ApoE ɛ4-independent risk factor for SAD. These findings suggest that the SORL1 SNP rs985421 may alter the risk for sporadic AD and aMCI in the Han Chinese population.