Retromer Function Research Articles

Noncanonical roles of ATG5 and membrane atg8ylation in retromer assembly and function.

ATG5 is one of the core autophagy proteins with additional functions such as noncanonical membrane atg8ylation, which among a growing number of biological outputs includes control of tuberculosis in animal models. Here we show that ATG5 associates with retromer's core components VPS26, VPS29 and VPS35 and modulates retromer function. Knockout of ATG5 blocked trafficking of a key glucose transporter sorted by the retromer, GLUT1, to the plasma membrane. Knockouts of other genes essential for membrane atg8ylation, of which ATG5 is a component, affected GLUT1 sorting, indicating that membrane atg8ylation as a process affects retromer function and endosomal sorting. The contribution of membrane atg8ylation to retromer function in GLUT1 sorting was independent of canonical autophagy. These findings expand the scope of membrane atg8ylation to specific sorting processes in the cell dependent on the retromer and its known interactors.

Chemical genomic analysis reveals the interplay between iron chelation, zinc homeostasis, and retromer function in the bioactivity of an ethanol adduct of the feijoa fruit-derived ellagitannin vescalagin.

Nature has been a rich source of pharmaceutical compounds, producing 80% of our currently prescribed drugs. The feijoa plant, Acca sellowiana, is classified in the family Myrtaceae, native to South America, and currently grown worldwide to produce feijoa fruit. Feijoa is a rich source of bioactive compounds with anticancer, anti-inflammatory, antibacterial, and antifungal activities; however, the mechanism of action of these compounds is largely not known. Here, we used chemical genetic analyses in the model organism Saccharomyces cerevisiae to investigate the mechanism of action of a feijoa-derived ethanol adduct of vescalagin (EtOH-vescalagin). Genome-wide barcode sequencing analysis revealed yeast strains lacking genes in iron metabolism, zinc metabolism, retromer function, or mitochondrial function were hypersensitive to 0.3 µM EtOH-vescalagin. This treatment increased expression of iron uptake proteins at the plasma membrane, which was a compensatory response to reduced intracellular iron. Likewise, EtOH-vescalagin increased expression of the Cot1 protein in the vacuolar membrane that transports zinc into the vacuole to prevent cytoplasmic accumulation of zinc. Each individual subunit in the retromer complex was required for the iron homeostatic mechanism of EtOH-vescalagin, while only the cargo recognition component in the retromer complex was required for the zinc homeostatic mechanism. Overexpression of either retromer subunits or high-affinity iron transporters suppressed EtOH-vescalagin bioactivity in a zinc-replete condition, while overexpression of only retromer subunits increased EtOH-vescalagin bioactivity in a zinc-deficient condition. Together, these results indicate that EtOH-vescalagin bioactivity begins with extracellular iron chelation and proceeds with intracellular transport of zinc via the retromer complex. More broadly, this is the first report of a bioactive compound to further characterize the poorly understood interaction between zinc metabolism and retromer function.

OXR1 maintains the retromer to delay brain aging under dietary restriction

Dietary restriction (DR) delays aging, but the mechanism remains unclear. We identified polymorphisms in mtd, the fly homolog of OXR1, which influenced lifespan and mtd expression in response to DR. Knockdown in adulthood inhibited DR-mediated lifespan extension in female flies. We found that mtd/OXR1 expression declines with age and it interacts with the retromer, which regulates trafficking of proteins and lipids. Loss of mtd/OXR1 destabilized the retromer, causing improper protein trafficking and endolysosomal defects. Overexpression of retromer genes or pharmacological restabilization with R55 rescued lifespan and neurodegeneration in mtd-deficient flies and endolysosomal defects in fibroblasts from patients with lethal loss-of-function of OXR1 variants. Multi-omic analyses in flies and humans showed that decreased Mtd/OXR1 is associated with aging and neurological diseases. mtd/OXR1 overexpression rescued age-related visual decline and tauopathy in a fly model. Hence, OXR1 plays a conserved role in preserving retromer function and is critical for neuronal health and longevity.

Elucidating the role of the AD risk gene SORL1 in hiPSC‐derived microglial cells

AbstractBackgroundhiPSC models, from which all cell types of the CNS can be generated, have provided key insights into cell‐type specific processes implicated by AD genetics. Endo‐lysosomal network (ELN) trafficking is a biological pathway implicated in AD and the endosomal receptor SORL1 is strongly associated with AD risk, however studies of SORL1 function in glial cells are lacking. Because ELN trafficking is highly related to neuroimmune function, we modeled SORL1 deficiency in hiPSC‐derived microglia and tested whether pharmacologic or genetic rescue with components of retromer improve cellular phenotypes.MethodWe used an established isogenic series of hiPSC lines that harbor deficiencies in SORL1 (SORL1 KO or SORL1 +/‐) or missense variants in SORL1 (SORL1Var) associated with AD. We differentiated microglial‐like cells (hiPSC‐MGLs) and used cellular assays that examined the function of the ELN. In hiPSC‐MGLs we measured phagocytosis, lysosome function, and pro‐inflammatory cytokine release. For rescue experiments, we treated cells with TPT‐260, a pharmacologic chaperone that stabilizes retromer, and lentiviral vectors expressing retromer subunits.ResultIn SORL1 deficient and SORL1 variant hiPSC‐MGLs, we document ELN phenotypes that converge on the lysosome, including lysosomal swelling and impaired degradation. Interestingly, we also document decreased lysosomal exocytosis, a calcium‐regulated process by which immune cells release lysosomal enzymes and undegraded substrates to the extracellular space to aid in cellular homeostasis, immune‐related signaling and tissue remodeling. In SORL1 deficient cells, lysosomal impairments were observed with abnormal neuroimmune function including differential expression and secretion of cytokines, in response to pro‐inflammatory stimuli Our preliminary data suggests that enhancement of retromer function, either genetically or pharmacologically, can improve these phenotypes.ConclusionUsing an hiPSC‐based model, we show that we can uncover dynamic phenotypes that are linked to AD risk genes. Mutations in SORL1 are now frequently discovered in early‐onset AD patients and the SORL1 locus has a strong genome‐wide signal for late‐onset AD. Together, this suggests that therapeutic strategies targeting the SORL1‐retromer pathway are greatly needed. In this study, we elucidate a role for the SORL1‐retromer pathway in neuroimmune function and provide validation that enhancing this pathway can improve cell‐type specific AD phenotypes in a human model.

Autophagy captures the retromer-TBC1D5 complex to inhibit receptor recycling

ABSTRACT Retromer prevents the destruction of numerous receptors by recycling them from endosomes to the trans-Golgi network or plasma membrane. This enables retromer to fine-tune the activity of many signaling pathways in parallel. However, the mechanism(s) by which retromer function adapts to environmental fluctuations such as nutrient withdrawal and how this affects the fate of its cargoes remains incompletely understood. Here, we reveal that macroautophagy/autophagy inhibition by MTORC1 controls the abundance of retromer+ endosomes under nutrient-replete conditions. Autophagy activation by chemical inhibition of MTOR or nutrient withdrawal does not affect retromer assembly or its interaction with the RAB7 GAP protein TBC1D5, but rather targets these endosomes for bulk destruction following their capture by phagophores. This process appears to be distinct from amphisome formation. TBC1D5 and its ability to bind to retromer, but not its C-terminal LC3-interacting region (LIR) or nutrient-regulated dephosphorylation, is critical for retromer to be captured by autophagosomes following MTOR inhibition. Consequently, endosomal recycling of its cargoes to the plasma membrane and trans-Golgi network is impaired, leading to their lysosomal turnover. These findings demonstrate a mechanistic link connecting nutrient abundance to receptor homeostasis. Abbreviations: AMPK, 5’-AMP-activated protein kinase; APP, amyloid beta precursor protein; ATG, autophagy related; BafA, bafilomycin A1; CQ, chloroquine; DMEM, Dulbecco’s minimum essential medium; DPBS, Dulbecco’s phosphate-buffered saline; EBSS, Earle’s balanced salt solution; FBS, fetal bovine serum; GAP, GTPase-activating protein; MAP1LC3/LC3, microtubule associated protein 1 light chain 3; LIR, LC3-interacting region; LANDO, LC3-associated endocytosis; LP, leupeptin and pepstatin; MTOR, mechanistic target of rapamycin kinase; MTORC1, MTOR complex 1; nutrient stress, withdrawal of amino acids and serum; PDZ, DLG4/PSD95, DLG1, and TJP1/zo-1; RPS6, ribosomal protein S6; RPS6KB1/S6K1, ribosomal protein S6 kinase B1; SLC2A1/GLUT1, solute carrier family 2 member 1; SORL1, sortillin related receptor 1; SORT1, sortillin 1; SNX, sorting nexin; TBC1D5, TBC1 domain family member 5; ULK1, unc-51 like autophagy activating kinase 1; WASH, WASH complex subunit.

Diversity of retromer-mediated vesicular trafficking pathways in plants.

The plant endomembrane system is organized and regulated by large gene families that encode proteins responsible for the spatiotemporal delivery and retrieval of cargo throughout the cell and to and from the plasma membrane. Many of these regulatory molecules form functional complexes like the SNAREs, exocyst, and retromer, which are required for the delivery, recycling, and degradation pathways of cellular components. The functions of these complexes are well conserved in eukaryotes, but the extreme expansion of the protein subunit families in plants suggests that plant cells require more regulatory specialization when compared with other eukaryotes. The retromer is associated with retrograde sorting and trafficking of protein cargo back towards the TGN and vacuole in plants, while in animals, there is new evidence that the VPS26C ortholog is associated with recycling or 'retrieving' proteins back to the PM from the endosomes. The human VPS26C was shown to rescue vps26c mutant phenotypes in Arabidopsis thaliana, suggesting that the retriever function could be conserved in plants. This switch from retromer to retriever function may be associated with core complexes that include the VPS26C subunit in plants, similar to what has been suggested in other eukaryotic systems. We review what is known about retromer function in light of recent findings on functional diversity and specialization of the retromer complex in plants.

Retromer Chaperones: Potential Therapeutics for Treatment of Skin Disease?

Retromer Chaperones: Potential Therapeutics for Treatment of Skin Disease?

Multi-omic approach characterises the neuroprotective role of retromer in regulating lysosomal health

Retromer controls cellular homeostasis through regulating integral membrane protein sorting and transport and by controlling maturation of the endo-lysosomal network. Retromer dysfunction, which is linked to neurodegenerative disorders including Parkinson’s and Alzheimer’s diseases, manifests in complex cellular phenotypes, though the precise nature of this dysfunction, and its relation to neurodegeneration, remain unclear. Here, we perform an integrated multi-omics approach to provide precise insight into the impact of Retromer dysfunction on endo-lysosomal health and homeostasis within a human neuroglioma cell model. We quantify widespread changes to the lysosomal proteome, indicative of broad lysosomal dysfunction and inefficient autophagic lysosome reformation, coupled with a reconfigured cell surface proteome and secretome reflective of increased lysosomal exocytosis. Through this global proteomic approach and parallel transcriptomic analysis, we provide a holistic view of Retromer function in regulating lysosomal homeostasis and emphasise its role in neuroprotection.

Retromer Proteins Reduced in Down Syndrome and the Dp16 Model: Impact of APP Dose and Preclinical Studies of a γ-Secretase Modulator.

The retromer complex plays an essential role in intracellular endosomal sorting. Deficits in the retromer complex are linked to enhanced Aβ production. The levels of the components of the retromer complex are reported to be downregulated in Alzheimer disease (AD). Down syndrome (DS) shares neuropathological features with AD. Recent evidence points to dysregulation of the retromer complex in DS. The mechanisms underlying retromer deficits in DS and AD are poorly understood. We measured the levels of retromer components in the frontal cortex of cases of DS-AD (AD in DS) as well as DS; the frontal cortex of a person partially trisomic (PT-DS) for human chromosome 21 (HSA21), whose genome had only the normal 2 copies of the APP gene, was also examined. We also analyzed these proteins in the Dp16 mouse model of DS. To further explore the molecular mechanism for changes in the retromer complex, we treated Dp16 mice with a γ-secretase modulator (GSM; 776890), a treatment that reduces the levels of Aβ42 and Aβ40. We found VPS26A, VPS26B, and VPS29, but not VPS35, were significantly reduced in both DS and DS-AD, but not in PT-DS. Downregulation of VPS26A, VPS26B, and VPS29 was recapitulated in the brains of old Dp16 mice (at 16 months of age) and required increased App gene dose. Significantly, GSM treatment completely prevented reductions of the retromer complex. Our studies point to increased APP gene dose as a compromising retromer function in DS and suggest a causal role for Aβ42 and Aβ40. ANN NEUROL 2023;94:245-258.

Dimerization of the Alzheimer’s disease pathogenic receptor SORLA regulates its association with retromer

SORL1, the gene encoding the large multidomain SORLA protein, has emerged as only the fourth gene that when mutated can by itself cause Alzheimer's disease (AD), and as a gene reliably linked to both the early- and late-onset forms of the disease. SORLA is known to interact with the endosomal trafficking regulatory complex called retromer in regulating the recycling of endosomal cargo, including the amyloid precursor protein (APP) and the glutamate receptor GluA1. Nevertheless, SORLA's precise structural-functional relationship in endosomal recycling tubules remains unknown. Here, we address these outstanding questions by relying on crystallographic and artificial-intelligence evidence to generate a structural model for how SORLA folds and fits into retromer-positive endosomal tubules, where it is found to dimerize via both SORLA's fibronectin-type-III (3Fn)- and VPS10p-domains. Moreover, we identify a SORLA fragment comprising the 3Fn-, transmembrane, and cytoplasmic domains that has the capacity to form a dimer, and to enhance retromer-dependent recycling of APP by decreasing its amyloidogenic processing. Collectively, these observations generate a model for how SORLA dimer (and possibly polymer) formation can function in stabilizing and enhancing retromer function at endosome tubules. These findings can inform investigation of the many AD-associated SORL1 variants for evidence of pathogenicity and can guide discovery of novel drugs for the disease.

Exploring therapeutic strategies for infantile neuronal axonal dystrophy (INAD/PARK14).

Infantile neuroaxonal dystrophy (INAD) is caused by recessive variants in PLA2G6 and is a lethal pediatric neurodegenerative disorder. Loss of the Drosophila homolog of PLA2G6, leads to ceramide accumulation, lysosome expansion, and mitochondrial defects. Here, we report that retromer function, ceramide metabolism, the endolysosomal pathway, and mitochondrial morphology are affected in INAD patient-derived neurons. We show that in INAD mouse models, the same features are affected in Purkinje cells, arguing that the neuropathological mechanisms are evolutionary conserved and that these features can be used as biomarkers. We tested 20 drugs that target these pathways and found that Ambroxol, Desipramine, Azoramide, and Genistein alleviate neurodegenerative phenotypes in INAD flies and INAD patient-derived neural progenitor cells. We also develop an AAV-based gene therapy approach that delays neurodegeneration and prolongs lifespan in an INAD mouse model.

SORL1 regulates the generation of APOE selectively in human neurons

AbstractBackgroundSORL1 is a neuronal sorting receptor that has been strongly implicated in the pathogenesis of Alzheimer’s disease (AD). While SORL1 has structural similarities to low‐density lipoprotein (LDL) receptors, it is unclear if it plays a role in regulating lipoprotein levels in the brain. We aimed to utilize human induced pluripotent stem cells (iPSCs) to understand the intersection of SORL1 and APOE biology and interrogate the potential role of SORL1 as an LDL receptor.MethodWe differentiated iPSC lines derived from the ROS and MAP cohorts that span the cognitive and neuropathological spectrum of aging to neuron and astrocyte fates and performed unbiased proteomic profiling, Western blotting, and ELISA to quantify protein levels of SORL1 and APOE. We next used CRISPR/Cas9 to generate SORL1 null iPSC lines and differentiated to neuron, astrocyte, and microglial fates. In neurons and astrocytes, AD‐relevant phenotypes such as APOE, Abeta, and phospho‐tau were assessed. Rescue experiments were performed in SORL1 KO neurons using pharmacological perturbations and shRNA to elucidate the pathways downstream of loss of SORL1 that lead to altered Abeta, tau and APOE.ResultWe observed a strong correlation between SORL1 and APOE protein expression in neurons derived from ROSMAP cohort individuals that was not apparent in astrocytes. Next, we validated previously reported findings that loss of SORL1 in neurons results in an elevation in Abeta levels. We expanded upon these findings to show that SORL1 null neurons display elevated phospho‐tau levels and a significant reduction of extracellular and intracellular APOE. While enhancing retromer and autophagy function rescued the elevation of phosphorylated tau in SORL1 null neurons, these treatments did not rescue reduced APOE levels. Rather, loss of SORL1 resulted in a reduction in APOE RNA expression, suggesting that loss of SORL1 leads to a downregulation of APOE at the transcriptional level. Integration of profiling data from ROSMAP iNs and SORL1 knock out iNs implicate the transcription factors NFkB and REV‐ERB as potentially mediating the effect of loss of SORL1 on APOE RNA levels.ConclusionSORL1 has a neuron‐specific function in regulating APOE levels that is separable from its role in regulating Abeta and phospho‐tau levels.

Pharmacologic Stabilization of Retromer Rescues Endosomal Pathology Induced by Defects in the Alzheimer’s gene SORL1

AbstractBackgroundDefects in the Sortilin‐related receptor 1 gene, SORL1, are highly pathogenic Alzheimer’s disease (AD), on par with other causal AD genes. SORL1 is a key regulator of endosomal trafficking in neurons, and loss of SORL1 function disrupts trafficking pathways that are vital for neuronal health. SORL1 has been found to interact with retromer, a trafficking complex that is a ‘master conductor’ of endosomal outflow. Here we rely on retromer pharmacological chaperones that stabilize retromer in vitro, and thus enhance retromer function in cells to test the hypothesis that they will correct AD‐associated neuronal pathologies.MethodWe used an isogenic series of human induced pluripotent cell lines either deficient in SORL1 expression (SORL1 KO or SORL1+/−) or harboring a one copy of a missense variant linked to increased risk for AD (SORL1Var). We treated neurons derived from these hiPSCs with the established retromer chaperone, TPT‐260, and tested whether they corrected indicators of AD’s defining endosomal, amyloid, and tau pathologies.ResultWe observed that TPT‐260 treatment was able to correct all of these pathological indicators, however the degree of rescue of some of the phenotypes was dependent one whether the neurons harbor at least one functional copy of SORL1 or whether they are fully deficient.ConclusionMore than just validating that SORL1‐retromer acts a trafficking functional unit in neurons, our work sheds new light on how SORL1‐retromer is linked to AD’s cardinal pathologies and illuminates how this pathway can be therapeutically harnessed.

Epidermal stratification requires retromer-mediated desmoglein-1 recycling.

Sorting transmembrane cargo is essential for tissue development and homeostasis. However, mechanisms of intracellular trafficking in stratified epidermis are poorly understood. Here, we identify an interaction between the retromer endosomal trafficking component, VPS35, and the desmosomal cadherin, desmoglein-1 (Dsg1). Dsg1 is specifically expressed in stratified epidermis and, when properly localized on the plasma membrane of basal keratinocytes, promotes stratification. We show that the retromer drives Dsg1 recycling from the endo-lysosomal system to the plasma membrane to support human keratinocyte stratification. The retromer-enhancing chaperone, R55, promotes the membrane localization of Dsg1 and a trafficking-deficient mutant associated with a severe inflammatory skin disorder, enhancing its ability to promote stratification. In the absence of Dsg1, retromer association with and expression of the glucose transporter GLUT1 increases, exposing a potential link between Dsg1 deficiency and epidermal metabolism. Our work provides evidence for retromer function in epidermal regeneration, identifying it as a potential therapeutic target.

WASH activation controls endosomal recycling and EGFR and Hippo signaling during tumor-suppressive cell competition

Cell competition is a conserved homeostatic mechanism whereby epithelial cells eliminate neighbors with lower fitness. Cell communication at the interface of wild-type “winner” cells and polarity-deficient (scrib−/−) “losers” is established through Sas-mediated Ptp10D activation in polarity-deficient cells. This tumor-suppressive cell competition restrains EGFR and Hippo signaling and enables Eiger-JNK mediated apoptosis in scrib−/− clones. Here, we show that the activation state of the endosomal actin regulator WASH is a central node linking EGFR and Hippo signaling activation. The tyrosine kinase Btk29A and its substrate WASH are required downstream of Ptp10D for “loser” cell elimination. Constitutively active, phosphomimetic WASH is sufficient to induce both EGFR and Yki activation leading to overgrowth. On the mechanistic level we show that Ptp10D is recycled by the WASH/retromer complex, while EGFR is recycled by the WASH/retriever complex. Constitutive WASH activation selectively interferes with retromer function leading to Ptp10D mistargeting while promoting EGFR recycling and signaling activation. Phospho-WASH also activates aberrant Arp2/3 actin polymerization, leading to cytoskeletal imbalance, Yki activation and reduced apoptosis. Selective manipulation of WASH phosphorylation on sorting endosomes may restrict epithelial tumorous growth.

Retromer dysfunction in amyotrophic lateral sclerosis

Retromer is a heteropentameric complex that plays a specialized role in endosomal protein sorting and trafficking. Here, we report a reduction in the retromer proteins-vacuolar protein sorting 35 (VPS35), VPS26A, and VPS29-in patients with amyotrophic lateral sclerosis (ALS) and in the ALS model provided by transgenic (Tg) mice expressing the mutant superoxide dismutase-1 G93A. These changes are accompanied by a reduction of levels of the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor subunit GluA1, a proxy of retromer function, in spinal cords from Tg SOD1G93A mice. Correction of the retromer deficit by a viral vector expressing VPS35 exacerbates the paralytic phenotype in Tg SOD1G93A mice. Conversely, lowering Vps35 levels in Tg SOD1G93A mice ameliorates the disease phenotype. In light of these findings, we propose that mild alterations in retromer inversely modulate neurodegeneration propensity in ALS.

Endosomal Recycling Defects and Neurodevelopmental Disorders.

The quality and quantity of membrane proteins are precisely and dynamically maintained through an endosomal recycling process. This endosomal recycling is executed by two protein complexes: retromer and recently identified retriever. Defects in the function of retromer or retriever cause dysregulation of many membrane proteins and result in several human disorders, including neurodegenerative disorders such as Alzheimer’s disease and Parkinson’s disease. Recently, neurodevelopmental disorders caused by pathogenic variants in genes associated with retriever were identified. This review focuses on the two recycling complexes and discuss their biological and developmental roles and the consequences of defects in endosomal recycling, especially in the nervous system. We also discuss future perspectives of a possible relationship of the dysfunction of retromer and retriever with neurodevelopmental disorders.

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.

Dysfunction of the retromer complex system contributes to amyloid and tau pathology in a stem cell model of Down syndrome.

IntroductionRetromer complex proteins are decreased in Down syndrome (DS) brains and correlate inversely with brain amyloidosis. However, whether retromer dysfunction contributes to the amyloid beta (Aβ) and tau neuropathology of DS remains unknown.MethodsHuman trisomic induced Pluripotent Stem Cells (iPSCs) and isogenic controls were differentiated into forebrain neurons, and changes in retromer proteins, tau phosphorylated epitopes, and Aβ levels were assessed in euploid and trisomic neurons using western blot and enzyme‐linked immunosorbent assay (ELISA). Genetic overexpression and pharmacological retromer stabilization were used to determine the functional role of the retromer complex system in modulating amyloid and tau pathology.ResultsTrisomic neurons developed age‐dependent retromer core protein deficiency associated with accumulation of Aβ peptides and phosphorylated tau isoforms. Enhancing retromer function through overexpression or pharmacological retromer stabilization reduced amyloid and tau pathology in trisomic neurons. However, the effect was greater using a pharmacological approach, suggesting that targeting the complex stability may be more effective in addressing this neuropathology in DS.DiscussionOur results demonstrate that the retromer complex is directly involved in the development of the neuropathologic phenotype in DS, and that pharmacological stabilization of the complex should be considered as a novel therapeutic tool in people with DS.

Age-Related Neuroprotection by Dietary Restriction Requires OXR1-Mediated Retromer Function

Dietary restriction (DR) is the most robust method to delay aging and the onset of neurogenerative disorders across multiple species, though the mechanisms behind this phenomenon remain unknown. To elucidate how DR mediates lifespan extension, we analyzed natural genetic variants that associate with increased longevity under DR conditions in the Drosophila Genetic Reference Panel. We found that neuronal expression of the fly homolog of human Oxidation Resistance 1 (OXR1) is necessary for DR-mediated lifespan extension. Neuronal knockdown of OXR1 also accelerated visual decline but not physical decline, arguing for a specific role of OXR1 in neuronal signaling. Further, we find that overexpression of the TLDc domain from human OXR1 is sufficient for lifespan extension in a diet-dependent manner. Studies from the Accelerating Medicines Partnership - Alzheimer's Disease network show that patients with reduced OXR1 protein levels are more prone to Alzheimer's disease diagnosis, and we find that overexpression of human OXR1 is protective in animal and cell Alzheimer's models. In seeking the mechanism by which OXR1 protects against age-related neuronal decline, we discovered that it provides a necessary function in regulating the neuronal retromer complex, which is essential for the recycling of transmembrane receptors and for maintenance of autophagy. We further discovered that OXR1 deficiency can be rescued by genetic or pharmacological enhancement of retromer function, and that this enhancement extends lifespan and healthspan. Understanding how OXR1 operates could help uncover novel mechanisms to slow neurodegeneration including Alzheimer's disease.