Sortilin-related Receptor Research Articles

Endo-Lysosomal Network Disorder Reprograms Energy Metabolism in SorL1-Null Rat Hippocampus.

Sortilin-related receptor 1 (SorL1) deficiency is a genetic predisposition to familial Alzheimer's disease (AD), but its pathology is poorly understood. In SorL1-null rats, a disorder of the global endosome-lysosome network (ELN) is found in hippocampal neurons. Deletion of amyloid precursor protein (APP) in SorL1-null rats could not completely rescue the neuronal abnormalities in the ELN of the hippocampus and the impairment of spatial memory in SorL1-null young rats. These in vivo observations indicated that APP is one of the cargoes of SorL1 in the regulation of the ELN, which affects hippocampal-dependent memory. When SorL1 is depleted, the endolysosome takes up more of the lysosome flux and damages lysosomal digestion, leading to pathological lysosomal storage and disturbance of cholesterol and iron homeostasis in the hippocampus. These disturbances disrupt the original homeostasis of the material-energy-subcellular structure and reprogram energy metabolism based on fatty acids in the SorL1-null hippocampus, instead of glucose. Although fatty acid oxidation increases ATP supply, it cannot reduce the levels of the harmful byproduct ROS during oxidative phosphorylation, as it does in glucose catabolism. Therefore, the SorL1-null rats exhibit hippocampal degeneration, and their spatial memory is impaired. Our research sheds light on the pathology of SorL1 deficiency in AD.

Genetic biomarkers of cognitive impairment and dementia of potential interest in CKD patients.

This review discusses genetic variants associated with cognitive dysfunction in chronic kidney disease (CKD) patients, emphasising the limited research in this area. Four studies have explored genetic markers of cognitive dysfunction in CKD, with findings suggesting shared genetic biomarkers between Alzheimer's Disease and CKD.Because of the limited specific research on genetic markers of cognitive dysfunction and dementia in CKD, we extracted data from the current literature studies on genetic markers in the general population that may be relevant to the CKD population. These markers include Apolipoprotein E (APOE), Complement Receptor 1 (CR1), Clusterin (CLU), Sortilin-related receptor 1 (SORL1), Catechol-O-methyltransferase (COMT), and Brain-derived neurotrophic factor (BDNF), all of which are known to be associated with cognitive dysfunction and dementia in other populations. These genes play various roles in lipid metabolism, inflammation, Aβ clearance, and neuronal function, making them potential candidates for studying cognitive decline in CKD patients.CKD-specific research is needed to understand the role of these genetic markers in CKD-related cognitive dysfunction. Investigating how these genes influence cognitive decline in CKD patients could provide valuable insights into early detection, targeted interventions, and personalised treatment strategies. Overall, genetic studies to enhance our understanding and management of cognitive dysfunction in CKD represent a clinical research priority in this population.

SORL1 is a receptor for tau that promotes tau seeding

Sortilin-related receptor 1 (SORL1) is an intracellular sorting receptor genetically implicated in Alzheimer's disease (AD) that impacts amyloid precursor protein trafficking. The objective of these studies was to test the hypothesis that SORL1 binds tau, modulates its cellular trafficking and impacts the aggregation of cytoplasmic tau induced by pathological forms of tau. Using surface plasmon resonance measurements, we observed high-affinity binding of tau to SORL1 and the vacuolar protein sorting 10 domain of SORL1. Interestingly, unlike LDL receptor-related protein 1, SORL1 binds tau at both pH 7.4 and pH 5.5, revealing its ability to bind tau at endosomal pH. Immunofluorescence studies confirmed that exogenously added tau colocalized with SORL1 in H4 neuroglioma cells, while overexpression of SORL1 in LDL receptor-related protein 1-deficient Chinese hamster ovary (CHO) cells resulted in a marked increase in the internalization of tau, indicating that SORL1 can bind and mediate the internalization of monomeric forms of tau. We further demonstrated that SORL1 mediates tau seeding when tau RD P301S FRET biosensor cells expressing SORL1 were incubated with high molecular weight forms of tau isolated from the brains of patients with AD. Seeding in H4 neuroglioma cells is significantly reduced when SORL1 is knocked down with siRNA. Finally, we demonstrate that the N1358S mutant of SORL1 significantly increases tau seeding when compared to WT SORL1, identifying for the first time a potential mechanism that connects this specific SORL1 mutation to Alzheimer's disease. Together, these studies identify SORL1 as a receptor that contributes to trafficking and seeding of pathogenic tau.

Mice and minipigs with compromised expression of the Alzheimer's disease gene SORL1 show cerebral metabolic disturbances on hyperpolarized [1-13C]pyruvate and sodium MRI.

The sortilin-related receptor 1 (SORL1) gene, encoding the cellular endosomal sorting-related receptor with A-type repeats (SORLA), is now established as a causal gene for Alzheimer's disease. As the latest addition to the list of causal genes, the pathophysiological effects and biomarker potential of SORL1 variants remain relatively undiscovered. Metabolic dysfunction is, however, well described in patients with Alzheimer's disease and is used as an imaging biomarker in clinical diagnosis settings. To understand the metabolic consequences of loss-of-function SORL1 mutations, we applied two metabolic MRI technologies, sodium (23Na) MRI and MRI with hyperpolarized [1-13C]pyruvate, in minipigs and mice with compromised expression of SORL1. At the age analysed here, both animal models display no conventional imaging evidence of neurodegeneration but show biochemical signs of elevated amyloid production, thus representing the early preclinical disease. With hyperpolarized MRI, the exchange from [1-13C]pyruvate to [1-13C]lactate and 13C-bicarbonate was decreased by 32 and 23%, respectively, in the cerebrum of SORL1-haploinsufficient minipigs. A robust 11% decrease in the sodium content was observed with 23Na-MRI in the same minipigs. Comparably, the brain sodium concentration gradually decreased from control to SORL1 haploinsufficient (-11%) to SORL1 knockout mice (-23%), suggesting a gene dose dependence in the metabolic dysfunction. The present study highlights that metabolic MRI technologies are sensitive to the functional, metabolic consequences of Alzheimer's disease and Alzheimer's disease-linked genotypes. Further, the study suggests a potential avenue of research into the mechanisms of metabolic alterations by SORL1 mutations and their potential role in neurodegeneration.

R953C Mutation in SORL1 Gene Causes Functional Abnormality of the Protein

AbstractBackgroundThe SORL1 (Sortilin Related Receptor 1) gene encodes for an endosomal sorting receptor, SORLA, and recent genetic studies have shown that it is the gene most frequently affected in patients with Alzheimer’s disease (AD). In the current study, we have identified a variant, R953C, (residing in the YWTD‐domain of SORLA) in a family where it segregates with early‐onset AD. We used cell biological assays to evaluate maturation and sorting defects of the mutant receptor.MethodTo investigate molecular consequences of R953C mutation, we transiently expressed SORLA‐WT and SORLA‐R953C in HEK293 and N2a cell lines. We analyzed the maturation and shedding of the receptor by Western blotting. Using flow cytometry, we determined the cell surface expression of the mutant compared to WT. Finally, the intracellular localization of the mutant was assessed by immunocytochemistry and confocal microscopy.ResultWe observed a significant decrease in the maturation and shedding of the mutant receptor, leading to an overall 80% reduction in soluble SORLA present in the culture media of cells transfected with R953C construct compared to WT. Our flow cytometry analysis demonstrated that in 80% of the cells expressing the mutant receptor, the SORLA protein is retrained intracellularly. In comparison, only 10‐15% of cells expressing the WT receptor showed intracellular retention. Within the cells, the R953C mutant receptor was primarily localized to the endoplasmic reticulum (ER) whereas the WT was mainly localized to the endosomes, suggesting the retention of the mutant in the ER and uncovering possible defects in entering the endosomal sorting pathway.ConclusionIn conclusion, we have elucidated some of the molecular mechanisms that appear to have a role in pathogenicity of R953C mutation.

Agomelatine improves memory and learning impairments in a rat model of LPS-induced neurotoxicity by modulating the ERK/SorLA/BDNF/TrkB pathway

The mutual interplay between neuroinflammation, synaptic plasticity, and autophagy has piqued researchers’ interest, particularly when it comes to linking their impact and relationship to cognitive deficits. Being able to reduce inflammation and apoptosis, melatonin has shown to have positive neuroprotective effects; that is why we thought to check the possible role of agomelatine (AGO) as a promising candidate that could have a positive impact on cognitive deficits. In the current study, AGO (40 mg/kg/day, p.o., 7 days) successfully ameliorated the cognitive and learning disabilities caused by lipopolysaccharide (LPS) in rats (250 μg/kg/day, i.p., 7 days). This positive impact was supported by improved histopathological findings and improved spatial memory as assessed using Morris water maze. AGO showed a strong ability to control BACE1 activity and to rein in the hippocampal amyloid beta (Aβ) deposition. Also, it improved neuronal survival, neuroplasticity, and neurogenesis by boosting BDNF levels and promoting its advantageous effects and by reinforcing the pTrkB expression. In addition, it upregulated the pre- and postsynaptic neuroplasticity biomarkers resembled in synapsin I, synaptophysin, and PSD-95. Furthermore, AGO showed a modulatory action on Sortilin-related receptor with A-type repeats (SorLA) pathway and adjusted autophagy. It is noteworthy that all of these actions were abolished by administering PD98059 a MEK/ERK pathway inhibitor (0.3 mg/kg/day, i.p., 7 days). In conclusion, AGO administration significantly improves memory and learning disabilities associated with LPS administration by modulating the ERK/SorLA/BDNF/TrkB signaling pathway parallel to its capacity to adjust the autophagic process.

Epitope mapping of nanobodies binding the Alzheimer's disease receptor SORLA.

Reduced levels of the Sortilin-related receptor with A-type repeats (SORLA) in different brain regions as well as in the cerebrospinal fluid have been associated with Alzheimer's disease. Methods and reagents to develop reliable detection assays to quantify SORLA and its specific isoforms are therefore much needed. Nanobodies (Nbs) are unique biomolecules derived from the blood of camelids that display advantageous physicochemical and antigen affinity properties, making them attractive tools with great relevance to both diagnostic and therapeutic applications. Here, we purified and characterized eight Nbs that were isolated from the blood of an alpaca immunized with the recombinant extracellular domain of SORLA. The selected Nbs showed high affinity to SORLA in the low nanomolar range as observed by surface plasmon resonance. For mapping of the Nbs' epitopes within the antigen, we transiently transfected HEK293 cells with a panel of SORLA deletion constructs, and developed a protocol of immunostaining by applying fluorescent dye conjugated Nbs. With this method, we showed that the selected Nbs specifically recognize a part of SORLA containing Fibronectin-type III domains, representing promising tools not only for disease clarifying research, but also for translational medicine as candidates for clinical diagnostic purposes.

SORL1 stabilizes ABCB1 to promote cisplatin resistance in ovarian cancer.

Ovarian cancer (OC) has the worst prognosis among gynecological malignancies. Cisplatin (CDDP) is one of the most commonly used treatments for OC, but recurrence and metastasis are common due to endogenous or acquired resistance. High expression of ATP-binding cassette (ABC) transporters is an important mechanism of resistance to OC chemotherapy, but targeting ABC transporters in OC therapy remains a challenge. The expression of sortilin-related receptor 1 (SORL1; SorLA) in the response of OC to CDDP was determined by analysis of TCGA and GEO public datasets. Immunohistochemistry and western blotting were utilized to evaluate the expression levels of SORL1 in OC tissues and cells that were sensitive or resistant to CDDP treatment. The in vitro effect of SORL1 on OC cisplatin resistance was proven by CCK-8 and cell apoptosis assays. The subcutaneous xenotransplantation model verified the in vivo significance of SORL1 in OC. Finally, the molecular mechanism by which SORL1 regulates OC cisplatin resistance was revealed by coimmunoprecipitation, gene set enrichment analysis and immunofluorescence analysis. This study demonstrated that SORL1 is closely related to CDDP resistance and predicts a poor prognosis in OC. In vivo xenograft experiments showed that SORL1 knockdown significantly enhanced the effect of CDDP on CDDP-resistant OC cells. Mechanistically, silencing of SORL1 inhibits the early endosomal antigen 1 (EEA1) pathway, which impedes the stability of ATP-binding cassette B subfamily member 1 (ABCB1), sensitizing CDDP-resistant OC cells to CDDP. The findings of this study suggest that targeting SORL1 may represent a promising therapeutic approach for overcoming CDDP resistance in OC.

Golgi fragmentation - One of the earliest organelle phenotypes in Alzheimer's disease neurons.

Alzheimer's disease (AD) is the most common cause of dementia, with no current cure. Consequently, alternative approaches focusing on early pathological events in specific neuronal populations, besides targeting the well-studied amyloid beta (Aβ) accumulations and Tau tangles, are needed. In this study, we have investigated disease phenotypes specific to glutamatergic forebrain neurons and mapped the timeline of their occurrence, by implementing familial and sporadic human induced pluripotent stem cell models as well as the 5xFAD mouse model. We recapitulated characteristic late AD phenotypes, such as increased Aβ secretion and Tau hyperphosphorylation, as well as previously well documented mitochondrial and synaptic deficits. Intriguingly, we identified Golgi fragmentation as one of the earliest AD phenotypes, indicating potential impairments in protein processing and post-translational modifications. Computational analysis of RNA sequencing data revealed differentially expressed genes involved in glycosylation and glycan patterns, whilst total glycan profiling revealed minor glycosylation differences. This indicates general robustness of glycosylation besides the observed fragmented morphology. Importantly, we identified that genetic variants in Sortilin-related receptor 1 (SORL1) associated with AD could aggravate the Golgi fragmentation and subsequent glycosylation changes. In summary, we identified Golgi fragmentation as one of the earliest disease phenotypes in AD neurons in various in vivo and in vitro complementary disease models, which can be exacerbated via additional risk variants in SORL1.

Alzheimer’s Disease risk gene SORL1 affects synaptic function in hiPSC‐derived cortical neurons

AbstractBackgroundThe cellular endo‐lysosomal network (ELN) is implicated in Alzheimer’s Disease pathology and Sortilin‐related receptor 1 (SORL1) is important for normal function of the neuronal ELN. Loss of SORL1 in human induced pluripotent stem cell (hiPSC) derived neurons replicates early AD cytopathology, such as enlarged early endosomes. Work in our laboratory has shown that SORL1 deficiency results in decreased cell‐surface expression of glutamate receptor subunit GLUR1 and neurotrophic receptor TRKB. RNAseq of SORL1 deficient neurons revealed alterations in synaptic‐associated gene ontology transcripts. Together, these data implicate a potential functional consequence for SORL1 deletion. Here we investigate the impact of SORL1 on hiPSC‐derived neuronal synaptic function.MethodNeuronal cultures were differentiated using dual SMAD inhibition of previously generated wild‐type and SORL1 deficient hiPSCs. Following differentiation, neuronal cultures were either purified using cell surface markers CD44, CD184, and CD271 or passaged as mixed cultures for immunocytochemical (ICC) or electrophysiological experiments, respectively. For ICC, neurons were then fixed with paraformaldehyde and stained with experiment‐appropriate antibodies before imaging on a confocal scanning microscope. Mixed cultures were plated onto Axion Biosystems multiple electrode array (MEA) culture plates for electrophysiological analysis. MEA cultures were recorded twice a week for up to ten weeks post‐plating. Recordings and analysis were performed using Axion Biosystems Maestro Pro system.ResultUsing ICC, we find alterations in alterations in synaptic protein and glutamate receptor co‐localization in SORL1 deficient neuronal cultures. When cultured on MEA plates, wild‐type and SORL1 deficient neuronal cultures are active and robust. Neuronal cultures develop glutamate signaling dependent patterns of activity, or network bursting. Neural firing rates are increased in SORL1 deficient neurons. Network bursting properties in SORL1 deficient are altered in comparison to wild‐type cultures, consistent with increased neural excitability.ConclusionLoss of SORL1 alters hiPSC‐derived neuronal activity and synapse‐dependent activity. Further investigation is warranted into the alterations in neuronal physiology and will help us understand the role AD‐related ELN disruption plays in synaptic pathologies.

Endophenotypic effects of the SORL1 variant rs2298813 on regional brain volume in patients with late-onset Alzheimer's disease.

Introduction: Two common variants of sortilin-related receptor 1 gene (SORL1), rs2298813 and rs1784933, have been associated with late-onset Alzheimer’s disease (AD) in the Han Chinese population in Taiwan. However, neuroimaging correlates of these two SORL1 variants remain unknown. We aimed to determine whether the two SORL1 polymorphisms were associated with any volumetric differences in brain regions in late-onset AD patients.Methods: We recruited 200 patients with late-onset AD from Taipei Veterans General Hospital. All patients received a structural magnetic resonance (MR) imaging brain scan and completed a battery of neurocognitive tests at enrollment. We followed up to assess changes in Mini-Mental State Examination (MMSE) scores in 155 patients (77.5%) at an interval of 2 years. Volumetric measures and cortical thickness of various brain regions were performed using FreeSurfer. Regression analysis controlled for apolipoprotein E status. Multiple comparisons were corrected for using the false discovery rate.Results: The homozygous major allele of rs2298813 was associated with larger volumes in the right putamen (p = 0.0442) and right pallidum (p = 0.0346). There was no link between the rs1784933 genotypes with any regional volume or thickness of the brain. In the rs2298813 homozygous major allele carriers, the right putaminal volume was associated with verbal fluency (p = 0.008), and both the right putaminal and pallidal volumes were predictive of clinical progression at follow-up (p = 0.020). In the minor allele carriers, neither of the nuclei was related to cognitive test performance or clinical progression.Conclusion: The major and minor alleles of rs2298813 had differential effects on the right lentiform nucleus volume and distinctively modulated the association between the regional volume and cognitive function in patients with AD.

Evaluation of the relationship between SORL1 gene polymorphism and Parkinson's disease in the Chinese population

ObjectiveThere is increasing evidence that lysosomal pathway dysfunction is closely linked to the pathogenesis of Parkinson's disease (PD). Considering the relationship between sortilin-related receptor 1 (SORL1) and lysosomal dysfunction, the abnormal aggregation of misfolded proteins in neurodegenerative disorders, especially in PD, and that glial cell-derived neurotrophic factor (GDNF) is the most effective neurotrophic factor affecting the activity of the dopamine system, and that SORL1 may induce PD by affecting GDNF, we investigated the correlation between three genetic variants (rs1010159, rs1629493, and rs2298813) of SORL1 gene polymorphisms and the risk of PD in the northern Chinese population in order to broaden the perspective for PD therapy. MethodsThree single-nucleotide polymorphisms (SNPs) of SORL1 genes (rs1010159, rs1629493, and rs2298813) were genotyped by polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP) on the DNA of 400 patients with PD and 400 healthy controls matched by age and gender. The chi-square test was used to analyze the statistical differences in genotypic and allelic polymorphism frequency between PD patients and healthy controls. Logistic regression analysis was used to calculate odds ratios (ORs) and 95% confidence intervals (CIs) to estimate potential correlations. ResultsThe frequencies of the T allele of rs1010159 and the A allele of rs2298813 in patients with PD were much higher than those in the controls (P = 0.003, P = 0.042, respectively). For rs1010159, subgroup analysis showed statistical changes in the frequency of the T allele in all subgroups (P = 0.021, P = 0.036, P = 0.001, P = 0.030, respectively); however, genotypic frequency distributions were statistically significant only between male patients with PD and matched healthy male controls (P = 0.001), and between early onset PD (EOPD) and late-onset PD (LOPD) and controls (P = 0.001, P = 0.001). For rs2298813, the explicit model showed that the GA + AA genotype had an increased risk of PD compared with the GG genotype (P = 0.020, OR = 1.518, 95% CI = 1.065–2.162), and the additive model showed that GA was also associated with a higher trend in PD compared with the GG genotype (P = 0.037, OR = 1.475, 95% CI = 1.024–2.125), and the allelic and genotypic frequencies of the LOPD were statistically different from those of the healthy group (P = 0.013, P = 0.044; respectively). No distinct correlation was found between rs1629493 and PD risk. The GAT haplotype, together with the AGT haplotype, was associated with PD susceptibility. ConclusionsThe rs1010159 and rs2298813 polymorphisms of the SORL1 gene rather than the rs1629493 polymorphism may be implicated in the susceptibility to PD in the northern Chinese population. Studies in different ethnicities and larger populations are indispensable for understanding the intrinsic correlation between the SORL1 gene and PD pathogenesis.

The Alzheimer\u2019s gene SORL1 is a regulator of endosomal traffic and recycling in human neurons

BackgroundLoss of the Sortilin-related receptor 1 (SORL1) gene seems to act as a causal event for Alzheimer’s disease (AD). Recent studies have established that loss of SORL1, as well as mutations in autosomal dominant AD genes APP and PSEN1/2, pathogenically converge by swelling early endosomes, AD’s cytopathological hallmark. Acting together with the retromer trafficking complex, SORL1 has been shown to regulate the recycling of the amyloid precursor protein (APP) out of the endosome, contributing to endosomal swelling and to APP misprocessing. We hypothesized that SORL1 plays a broader role in neuronal endosomal recycling and used human induced pluripotent stem cell-derived neurons (hiPSC-Ns) to test this hypothesis. We examined endosomal recycling of three transmembrane proteins linked to AD pathophysiology: APP, the BDNF receptor Tropomyosin-related kinase B (TRKB), and the glutamate receptor subunit AMPA1 (GLUA1).MethodsWe used isogenic hiPSCs engineered to have SORL1 depleted or to have enhanced SORL1 expression. We differentiated neurons from these cell lines and mapped the trafficking of APP, TRKB and GLUA1 within the endosomal network using confocal microscopy. We also performed cell surface recycling and lysosomal degradation assays to assess the functionality of the endosomal network in both SORL1-depleted and -overexpressing neurons. The functional impact of GLUA1 recycling was determined by measuring synaptic activity. Finally, we analyzed alterations in gene expression in SORL1-depleted neurons using RNA sequencing.ResultsWe find that as with APP, endosomal trafficking of GLUA1 and TRKB is impaired by loss of SORL1. We show that trafficking of all three cargoes to late endosomes and lysosomes is affected by manipulating SORL1 expression. We also show that depletion of SORL1 significantly impacts the endosomal recycling pathway for APP and GLUA1 at the level of the recycling endosome and trafficking to the cell surface. This has a functional effect on neuronal activity as shown by multi-electrode array (MEA). Conversely, increased SORL1 expression enhances endosomal recycling for APP and GLUA1. Our unbiased transcriptomic data further support SORL1’s role in endosomal recycling. We observe altered expression networks that regulate cell surface trafficking and neurotrophic signaling in SORL1-depleted neurons.ConclusionCollectively, and together with other recent observations, these findings suggest that one role for SORL1 is to contribute to endosomal degradation and recycling pathways in neurons, a conclusion that has both pathogenic and therapeutic implications for Alzheimer’s disease.

Cryo-EM structures reveal distinct apo conformations of sortilin-related receptor SORLA

Sorting-related receptor with A-type repeats (SORLA) is an important receptor for regulating normal cellular functions via protein sorting. Here, we determined the structures of the full-length SORLA and identified two distinct conformations of apo-SORLA using single-particle cryogenic electron microscopy. In contrast to homologous proteins, both monomer and dimer forms of SORLA existed in a neutral solution. Only three hydrogen bonds in the vicinity of the dimer interface implied the involvement in dimerization. The orientation of residue R490 was a key point for ligand binding. These results suggest a unique mechanism of SORLA dimerization for protein trafficking.

The neuronal retromer can regulate both neuronal and microglial phenotypes of Alzheimer's disease.

SUMMARYDisruption of retromer-dependent endosomal trafficking is considered pathogenic in late-onset Alzheimer’s disease (AD). Here, to investigate this disruption in the intact brain, we turn to a genetic mouse model where the retromer core protein VPS35 is depleted in hippocampal neurons, and then we replete VPS35 using an optimized viral vector protocol. The VPS35 depletion-repletion studies strengthen the causal link between the neuronal retromer and AD-associated neuronal phenotypes, including the acceleration of amyloid precursor protein cleavage and the loss of synaptic glutamate receptors. Moreover, the studies show that the neuronal retromer can regulate a distinct, dystrophic, microglia morphology, phenotypic of hippocampal microglia in AD. Finally, the neuronal and, in part, the microglia responses to VPS35 depletion were found to occur independent of tau. Showing that the neuronal retromer can regulate AD-associated pathologies in two of AD’s principal cell types strengthens the link, and clarifies the mechanism, between endosomal trafficking and late-onset sporadic AD.

SorLA Targeting - A Method to Overcome Therapy Resistance in Breast Cancer

In breast cancer, tyrosine kinase-type cell surface receptor HER2-targeted therapies do not achieve a sustained inhibition of oncogenic signaling. Therapy-resistant tumors compensate for HER2 inhibition through several mechanisms, including increased expression of other cell-surface receptors most notably HER3. HER3 remains currently undruggable despite extensive clinical efforts. Durable efficacy of HER2-based therapy regimens requires, therefore, effective inhibition of HER2 and HER3. Our recent work has unraveled a previously unappreciated role of HER2 and HER3 intracellular trafficking in promoting drug resistance in breast cancer. Sortilinrelated receptor (SorLA) is a sorting receptor mainly investigated with regard to neuronal and metabolic diseases. We discovered oncogenic properties of SorLA through supporting HER2 and HER3 expression and signaling, thus mediating cancer response to growth factors to promote HER2-therapy resistance. Here we briefly review the mechanisms of SorLA supported oncogenic signaling in breast cancer and discuss their translational and clinical potential.

Identification and Mechanism of the PD-1/PD-L1 Genomic Signature SORL1 as Protective Factor in Bladder Cancer.

Background: Immunotherapy has recently shown remarkable efficacy for advanced bladder cancer patients. Accordingly, identifying a biomarker associated with the programmed cell death protein 1 (PD-1)/its ligand (PD-L1) genomic signature to predict patient prognosis is necessary. Methods: In this study, we used mutation data and RNA-seq data of bladder cancer samples acquired from The Cancer Genome Atlas (TCGA) database to combine PD-1/PD-L1-associated mutational signatures with PD-1/PD-L1-associated differentially expressed genes (DEGs). Then, we performed a Kaplan-Meier analysis on the corresponding clinical data of the TCGA bladder urothelial carcinoma (BLCA) cohort to identify prognostic genes, and the results were validated using the GSE48075 cohort. The online platform UCSC Xena was used to analyze the relationship between the candidate genes and clinical parameters. We utilized the Human Protein Atlas (HPA) database to validate the protein expression levels. Then, correlation analysis, cell-type identification by estimating relative subsets of RNA transcripts (CIBERSORT) analysis, and gene set enrichment analysis (GSEA) were used to clarify the mechanism. Results: We identified one prognostic gene, sortilin related receptor 1 (SORL1), whose downregulation was associated with a comparatively advanced BLCA stage. While further exploring this finding, we found that SORL1 expression was negatively correlated with PD-1/PD-L1 expression and M2 macrophage levels. Furthermore, we found that the downregulation of SORL1 expression was significantly associated with a higher epithelial-mesenchymal transition (EMT) score. Conclusion: We described a novel PD-1/PD-L1-associated signature, SORL1, that predicts favorable outcomes in bladder cancer. SORL1 might reduce immune suppression and inhibit the M2 macrophage-induced EMT phenotype of tumor cells.

Characterization of an Alzheimer disease-associated deletion in SORL1.

Greater than 20 genetic loci have been consistently associated with Alzheimer disease (AD). Accumulating evidence has implicated the endolysosomal pathway in disease pathology. The sortilin-related receptor 1 (SORL1) gene has been associated with AD through multiple studies and has been suggested to function as a guide for amyloid precursor protein (APP) to the endocytic pathway. We identified a family with multiple AD affected individuals that have a single base pair deletion (g.4292delG) resulting in a frameshift alteration and premature termination of the protein (p.Cys143Cys*1). Although previous studies have implicated SORL1 in AD pathogenesis, it remains unclear how this deletion impacts SORL1 protein function in AD development. Patient-specific induced pluripotent stem cells (iPSC) lines were derived to examine the molecular consequences of this SORL1 deletion in neuronal and glial cells (astrocytes and microglia), which can otherwise only be collected from autopsy samples. Each iPSC line generated was validated for pluripotency through immunocytochemical staining and karyotypic stability. Patient iPSC lines and control lines were differentiated into cortical neurons and glia for functional characteristics, including amyloid beta production and uptake, vesicular trafficking, and neurite outgrowth. We have derived iPSC lines bearing the SORL1 deletion and have confirmed pluripotency by immunocytochemistry. These iPSC lines were differentiated into cortical neurons whose identity was confirmed by immunocytochemical staining for neuronal markers. The SORL1 variant bearing cortical neurons showed enlarged endosomes, as measured by RAB5 staining and fluorescent microscopy, compared to the neurons derived from control iPSCs. In addition, the SORL1 deletion bearing neurons showed an upregulation in the ratio of amyloid beta 42:amyloid beta 40 compared to control neurons as measured by ELISA. Finally, SORL1 deletion bearing neurons had reduced neurite outgrowth and branch point numbers compared to controls. In summary, our results support that the p.Cys143Ser*1 variant is pathogenic and alters the functionality of cells from the central nervous system. iPSC-derived neurons and glia cells bearing the deletion in SORL1 p.Cys143Ser*1 variant shows cellular deficits associated with AD pathology, particularly in endolysomal trafficking defects. Studies are continuing to determine if this effect is due to a gain or loss of function.

Sortilin-related receptor is a druggable therapeutic target in breast cancer.

In breast cancer, the currently approved anti‐receptor tyrosine‐protein kinase erbB‐2 (HER2) therapies do not fully meet the expected clinical goals due to therapy resistance. Identifying alternative HER2‐related therapeutic targets could offer a means to overcome these resistance mechanisms. We have previously demonstrated that an endosomal sorting protein, sortilin‐related receptor (SorLA), regulates the traffic and signaling of HER2 and HER3, thus promoting resistance to HER2‐targeted therapy in breast cancer. This study aims to assess the feasibility of targeting SorLA using a monoclonal antibody. Our results demonstrate that anti‐SorLA antibody (SorLA ab) alters the resistance of breast cancer cells to HER2 monoclonal antibody trastuzumab in vitro and in ovo. We found that SorLA ab and trastuzumab combination therapy also inhibits tumor cell proliferation and tumor cell density in a mouse xenograft model of HER2‐positive breast cancer. In addition, SorLA ab inhibits the proliferation of breast cancer patient‐derived explant three‐dimensional cultures. These results provide, for the first time, proof of principle that SorLA is a druggable target in breast cancer.

Identification of two pathogenic mutations in SORL1 in early-onset Alzheimer’s disease

The sortilin-related receptor 1 (SORL1) gene has been the subject of many studies focusing on frequent polymorphisms, which is associated with increased risk for Alzheimer’s Disease (AD). By whole-exome sequencing (WES), we identified two pathogenic missense mutations c.579C > G (p.F193L) and c.1397A > G (p.N466S) in SORL1. The two mutations were located in the same protein domain, and the two unrelated probands both had an onset of memory problems at less than 65 years of age, but their clinical manifestations and cranial imaging are different. The protein structure and function affected by these mutations were predicted using bioinformatics analysis, which suggested they were pathogenic. 3D protein structural analysis revealed that these amino acid substitutions might result in instability of protein structure and adverse intramolecular interactions. These findings suggest that both F193L and N466S should be thought as potential causative mutations in early-onset Alzheimer’s disease (EOAD) patients. Further functional studies are warranted to evaluate their roles in the pathogenesis of AD.