Incident HIV-Associated Wasting/Low Weight Is Associated with Nearly Doubled Mortality Risk in the Modern ART Era.

HIV-associated wasting (HIVAW) is an underappreciated AIDS-defining illness, despite highly effective antiretroviral therapy (ART). We (a) assessed the association between incident HIVAW/low weight and all-cause mortality and (b) described virologic outcomes after people with HIV (PWH) experienced HIVAW/low weight while on ART. In the Observational Pharmaco-Epidemiology Research & Analysis (OPERA®) cohort, PWH without prior HIVAW/low weight who were active in care in 2016-2020 were followed through the first of the following censoring events: death, loss to follow-up, or study end (October 31, 2021). HIVAW/low weight was a diagnosis of wasting or low body mass index (BMI)/underweight or a BMI measurement <20 kg/m2. Hazard ratios (HRs) and 95% confidence intervals (CIs) for the association between time-dependent HIVAW/low weight and mortality were estimated with extended Cox regression models. Over a median follow-up of 45 months (interquartile range: 27, 65), there were 4,755 (8%) cases of HIVAW/low weight and 1,354 (2%) deaths among 62,314 PWH. PWH who experienced HIVAW/low weight had a significantly higher risk of death than those who did not (HR: 1.96; 95% CI: 1.68, 2.27) after adjusting for age, race, ethnicity, and changes in viral load (VL) and Veterans Aging Cohort Study Mortality Index scores over follow-up. Among 4,572 PWH on ART at HIVAW/low weight, 68% were suppressed (VL of <200 copies/mL); subsequent virologic failure was uncommon (7%). Among viremic PWH, 70% and 60% achieved suppression and undetectability (VL of <50 copies/mL), respectively, over follow-up. HIVAW remains a challenge for some PWH. Particular attention needs to be paid to HIVAW/low weight and virologic control to restore health and potentially reduce the risk of death.

Inhibition of METTL3 Results in a Cell-Intrinsic Interferon Response That Enhances Antitumor Immunity.

Therapies that enhance antitumor immunity have altered the natural history of many cancers. Consequently, leveraging nonoverlapping mechanisms to increase immunogenicity of cancer cells remains a priority. Using a novel enzymatic inhibitor of the RNA methyl-transferase METTL3, we demonstrate a global decrease in N6-methyladenosine (m6A) results in double-stranded RNA (dsRNA) formation and a profound cell-intrinsic interferon response. Through unbiased CRISPR screens, we establish dsRNA-sensing and interferon signaling are primary mediators that potentiate T-cell killing of cancer cells following METTL3 inhibition. We show in a range of immunocompetent mouse models that although METTL3 inhibition is equally efficacious to anti-PD-1 therapy, the combination has far greater preclinical activity. Using SPLINTR barcoding, we demonstrate that anti-PD-1 therapy and METTL3 inhibition target distinct malignant clones, and the combination of these therapies overcomes clones insensitive to the single agents. These data provide the mole-cular and preclinical rationale for employing METTL3 inhibitors to promote antitumor immunity in the clinic. SIGNIFICANCE: This work demonstrates that METTL3 inhibition stimulates a cell-intrinsic interferon response through dsRNA formation. This immunomodulatory mechanism is distinct from current immunotherapeutic agents and provides the molecular rationale for combination with anti-PD-1 immune-checkpoint blockade to augment antitumor immunity. This article is featured in Selected Articles from This Issue, p. 2109.

Definition, Burden, and Predictors of HIV-Associated Wasting and Low Weight in the OPERA Cohort.

We aimed to describe the prevalence, incidence, and predictors of HIV-associated wasting (HIVAW)/low weight among people with HIV (PWH) in the United States. We conducted an observational, clinical cohort analysis, utilizing prospectively collected electronic health record data obtained from the Observational Pharmaco-Epidemiology Research & Analysis (OPERA®) cohort. HIVAW/low weight included a wasting or low body-mass index (BMI)/underweight diagnosis (ICD codes and title search) or BMI <20 kg/m2. Prevalence was estimated among adult PWH in care from 2012 to 2015 and 2016 to 2020. Incidence from January 1, 2016, to October 31, 2021, was estimated using univariate Poisson regression among eligible PWH without prior HIVAW/low weight. Demographic and clinical predictors of incident HIVAW/low weight were included in multivariable logistic regression models, stratified by antiretroviral therapy (ART) experience. The period prevalence of HIVAW/low weight was 12% in both 2012-2015 and 2016-2020. Among 67,119 PWH without any prior HIVAW/low weight, 7% experienced incident HIVAW/low weight a median 64 months from HIV diagnosis. In multivariable regression models, similar predictor patterns were observed among ART-naïve and ART-experienced PWH without any prior HIVAW/low weight: lower odds of HIVAW/low weight with older age, female sex, Black race, and Hispanic ethnicity and higher odds with Medicaid. Notably, there was a dose-response relationship between increasing Veterans Aging Cohort Study Mortality Index scores and incident HIVAW/low weight in both groups. Wasting/low weight remains a challenge for PWH and may be underappreciated by providers. Advanced HIV and comorbidities significantly predict incident HIVAW/low weight. Increasing awareness of HIVAW, especially among frailer PWH, could improve the care of affected PWH.

The economic burden of HIV-associated wasting in the era of modern antiretroviral therapy.

BACKGROUND: HIV-associated wasting (HIVAW) is associated with increased morbidity and mortality in people living with HIV (PWH). Evaluating health care resource utilization and cost predictors of HIVAW is important in understanding the overall economic burden of the disease. OBJECTIVE: To evaluate the economic burden and cost predictors associated with HIVAW. METHODS: This analysis of the IBM MarketScan Commercial, Medicare Supplemental, and Medicaid databases included members with a claim for HIV (using International Classification of Diseases, Ninth Revision and Tenth Revision, Clinical Modification codes) between July 2012 and September 2018, with the HIV index date defined as the first HIV diagnosis claim in the dataset. PWH were excluded if they were aged less than 18 years, had any malignancy claim, or had less than 6 months of enrollment data pre-HIV or post-HIV index date. Members were defined as having HIVAW using an algorithm of claims for weight loss-related diagnoses, appetite stimulant or nontestosterone anabolic agents, or enteral/parenteral nutrition at any time post-HIV index. Taking antiretroviral therapy (ART) was defined as having at least 1 pharmacy claim of any ART 12 months post-HIV index. Total all-cause costs were calculated as the sum of payments for hospitalizations, emergency department visits, outpatient visits, and pharmacy use. A multivariate generalized linear model with log-link and γ distribution was used to estimate the impact of HIVAW predictors of total all-cause costs. RESULTS: Among 42,587 members with HIV included in the study (64.6% male; mean age: 44 years; 67.5% insured with Medicaid; and 63.9% taking ART), the overall prevalence of HIVAW was 18.3% during the study period. HIVAW prevalence was 17.9% for those taking ART and 19.1% for those not taking ART. Prevalence by payer type was 7.5% for Commercial ± Medicare Supplemental and 23.5% for Medicaid. Members with HIVAW had more comorbidities and opportunistic infections compared with members without HIVAW. Members with HIVAW were also more than twice as likely to be hospitalized (71.1% vs 32.1%) and had 5 times the number of hospitalizations (1.0 vs 0.2) and twice the number of emergency department visits (3.0 vs 1.3) per year post-index compared with members without HIVAW (P < 0.01). HIVAW was associated with 1.3-times-higher mean annualized total all-cause costs per member (95% CI = 1.26-1.36). CONCLUSIONS: HIVAW remains prevalent despite advances in ART and is associated with additional health care resource utilization and costs. Further research is needed to better understand the relationship between HIVAW and comorbidity burden and ART utilization and payer types. DISCLOSURES: This study was sponsored by EMD Serono, Inc., Rockland, MA, USA (CrossRef Funder ID: 10.13039/100004755). Dr Siddiqui has received consulting and speaking fees from AbbVie, BioFire, Cumberland, EMD Serono, Inc., Rockland, MA, USA, and Merck. Dr Samuel, Ms Hayward, Ms Wirka, Dr Phillips, and Dr Harbour are employees of EMD Serono, Inc., Rockland, MA, USA. Drs Deering and Harshaw are employees of EPI-Q, Inc., which received payment from EMD Serono, Inc., Rockland, MA, USA, for the development and execution of this study.

HIV-associated wasting prevalence in the era of modern antiretroviral therapy.

OBJECTIVE: To understand the prevalence of HIV-associated wasting (HIVAW) in the United States. DESIGN: Medical and pharmacy claims study using IBM MarketScan Commercial, Medicare Supplemental and Medicaid Databases. METHODS: Study period: July 2012-September 2018 (first HIV diagnosis claim = HIV index date). People with HIV (PWH) were excluded if they were aged less than 18 years, had any malignancy claim or had less than 6 months of enrollment data pre or post-HIV index date. HIVAW was defined by proxy using claims for weight loss-related diagnoses, appetite stimulant/nontestosterone anabolic agents or enteral/parenteral nutrition. Prevalence was reported cumulatively, by insurance type and antiretroviral therapy (ART) pharmacy claims (defined as ≥1 pharmacy claim of any ART within 12 months post-HIV index date). Statistical analysis assessed factors potentially associated with HIVAW. RESULTS: The study population comprised 42 587 PWH (64.6% male, mean age 44 years, 67.5% on Medicaid, 63.9% on ART). Cumulative HIVAW prevalence (2012-2018) was 18.3% (n = 7804) for all PWH (17.9% on ART, 19.1% not on ART). HIVAW prevalence by payer was 7.5% for Commercial and Medicare Supplemental and 23.5% for Medicaid. The strongest associations with the likelihood of meeting the definition of HIVAW were for individuals with Medicaid and hospitalization(s) post-HIV index date; race and ART status were not associated. CONCLUSIONS: Findings suggest HIVAW remains prevalent in PWH. ART use was not found to be associated with HIVAW. HIVAW was highest among those with Medicaid coverage or any hospitalization(s). Further research is needed to better understand additional factors associated with and contributing to HIVAW.

Quantitative density gradient analysis by mass spectrometry (qDGMS) and complexome profiling analysis (ComPrAn) R package for the study of macromolecular complexes.

Many cellular processes involve the participation of large macromolecular assemblies. Understanding their function requires methods allowing to study their dynamic and mechanistic properties. Here we present a method for quantitative analysis of native protein or ribonucleoprotein complexes by mass spectrometry following their separation by density - qDGMS. Mass spectrometric quantitation is enabled through stable isotope labelling with amino acids in cell culture (SILAC). We provide a complete guide, from experimental design to preparation of publication-ready figures, using a purposely-developed R package - ComPrAn. As specific examples, we present the use of sucrose density gradients to inspect the assembly and dynamics of the human mitochondrial ribosome (mitoribosome), its interacting proteins, the small subunit of the cytoplasmic ribosome, cytoplasmic aminoacyl-tRNA synthetase complex and the mitochondrial PDH complex. ComPrAn provides tools for analysis of peptide-level data as well as normalization and clustering tools for protein-level data, dedicated visualization functions and graphical user interface. Although, it has been developed for the analysis of qDGMS samples, it can also be used for other proteomics experiments that involve 2-state labelled samples separated into fractions. We show that qDGMS and ComPrAn can be used to study macromolecular complexes in their native state, accounting for the dynamics inherent to biological systems and benefiting from its proteome-wide quantitative and qualitative capability.

Duplexing complexome profiling with SILAC to study human respiratory chain assembly defects.

Complexome Profiling (CP) combines size separation, by electrophoresis or other means, of native multimeric complexes with protein identification by mass spectrometry (MS). Peptide MS analysis of the multiple fractions in which the sample is separated, results in the creation of protein abundance profiles in function of molecular size, providing a visual output of the assembly status of a group of proteins of interest. Stable isotope labeling by amino acids in cell culture (SILAC) is an established quantitative proteomics technique that allows duplexing in the MS analysis as well as the comparison of relative protein abundances between the samples, which are processed and analyzed together. Combining SILAC and CP permitted the direct comparison of migration and abundance of the proteins present in the mitochondrial respiratory chain complexes in two different samples. This analysis, however, introduced a level of complexity in data processing for which bioinformatic tools had to be developed in order to generate the normalized protein abundance profiles. The advantages and challenges of using of this type of analysis for the characterization of two cell lines carrying pathological variants in MT-CO3 and MT-CYB is reviewed. An additional unpublished example of SILAC-CP of a cell line with an in-frame 18-bp deletion in MT-CYB is presented. In these cells, in contrast to other MT-CYB deficient models, a small proportion of complex III2 is formed and it is found associated with fully assembled complex I. This analysis also revealed a profuse accumulation of assembly intermediates containing complex III subunits UQCR10 and CYC1, as well as a profound early-stage complex IV assembly defect.

Stable mitochondrial CICIII2 supercomplex interactions in reptiles versus homeothermic vertebrates.

The association of complex I (CI), complex III (CIII) and complex IV (CIV) of the mitochondrial electron transport chain into stable high molecular weight supercomplexes (SCs) has been observed in several prokaryotes and eukaryotes, but among vertebrates it has only been examined in mammals. The biological role of these SCs is unclear but suggestions so far include enhanced electron transfer between complexes, decreased production of the reactive oxygen species (ROS) O2- and H2O2, or enhanced structural stability. Here, we provide the first overview on the stability, composition and activity of mitochondrial SCs in representative species of several vertebrate classes to determine patterns of SC variation across endotherms and ectotherms. We found that the stability of the CICIII2 SC and the inclusion of CIV within the SC varied considerably. Specifically, when solubilized by the detergent DDM, mitochondrial CICIII2 SCs were unstable in endotherms (birds and mammals) and highly stable in reptiles. Using mass-spectrometric complexomics, we confirmed that the CICIII2 is the major SC in the turtle, and that 90% of CI is found in this highly stable SC. Interestingly, the presence of stable SCs did not prevent mitochondrial H2O2 production and was not associated with elevated respiration rates of mitochondria isolated from the examined species. Together, these data show that SC stability varies among vertebrates and is greatest in poikilothermic reptiles and weakest in endotherms. This pattern suggests an adaptive role of SCs to varying body temperature, but not necessarily a direct effect on electron transfer or in the prevention of ROS production.

Respiratory supercomplexes act as a platform for complex III-mediated maturation of human mitochondrial complexes I and IV.

Mitochondrial respiratory chain (MRC) enzymes associate in supercomplexes (SCs) that are structurally interdependent. This may explain why defects in a single component often produce combined enzyme deficiencies in patients. A case in point is the alleged destabilization of complex I in the absence of complex III. To clarify the structural and functional relationships between complexes, we have used comprehensive proteomic, functional, and biogenetical approaches to analyze a MT-CYB-deficient human cell line. We show that the absence of complex III blocks complex I biogenesis by preventing the incorporation of the NADH module rather than decreasing its stability. In addition, complex IV subunits appeared sequestered within complex III subassemblies, leading to defective complex IV assembly as well. Therefore, we propose that complex III is central for MRC maturation and SC formation. Our results challenge the notion that SC biogenesis requires the pre-formation of fully assembled individual complexes. In contrast, they support a cooperative-assembly model in which the main role of complex III in SCs is to provide a structural and functional platform for the completion of overall MRC biogenesis.

METTL15 introduces N4-methylcytidine into human mitochondrial 12S rRNA and is required for mitoribosome biogenesis.

Post-transcriptional RNA modifications, the epitranscriptome, play important roles in modulating the functions of RNA species. Modifications of rRNA are key for ribosome production and function. Identification and characterization of enzymes involved in epitranscriptome shaping is instrumental for the elucidation of the functional roles of specific RNA modifications. Ten modified sites have been thus far identified in the mammalian mitochondrial rRNA. Enzymes responsible for two of these modifications have not been characterized. Here, we identify METTL15, show that it is the main N4-methylcytidine (m4C) methyltransferase in human cells and demonstrate that it is responsible for the methylation of position C839 in mitochondrial 12S rRNA. We show that the lack of METTL15 results in a reduction of the mitochondrial de novo protein synthesis and decreased steady-state levels of protein components of the oxidative phosphorylation system. Without functional METTL15, the assembly of the mitochondrial ribosome is decreased, with the late assembly components being unable to be incorporated efficiently into the small subunit. We speculate that m4C839 is involved in the stabilization of 12S rRNA folding, therefore facilitating the assembly of the mitochondrial small ribosomal subunits. Taken together our data show that METTL15 is a novel protein necessary for efficient translation in human mitochondria.

The yeast mitochondrial pyruvate carrier is a hetero-dimer in its functional state.

The mitochondrial pyruvate carrier (MPC) is critical for cellular homeostasis, as it is required in central metabolism for transporting pyruvate from the cytosol into the mitochondrial matrix. MPC has been implicated in many diseases and is being investigated as a drug target. A few years ago, small membrane proteins, called MPC1 and MPC2 in mammals and Mpc1, Mpc2 and Mpc3 in yeast, were proposed to form large protein complexes responsible for this function. However, the MPC complexes have never been isolated and their composition, oligomeric state and functional properties have not been defined. Here, we identify the functional unit of MPC from Saccharomyces cerevisiae In contrast to earlier hypotheses, we demonstrate that MPC is a hetero-dimer, not a multimeric complex. When not engaged in hetero-dimers, the yeast Mpc proteins can also form homo-dimers that are, however, inactive. We show that the earlier described substrate transport properties and inhibitor profiles are embodied by the hetero-dimer. This work provides a foundation for elucidating the structure of the functional complex and the mechanism of substrate transport and inhibition.

The F1 -ATPase from Trypanosoma brucei is elaborated by three copies of an additional p18-subunit.

The F-ATPases (also called the F1 Fo -ATPases or ATP synthases) are multi-subunit membrane-bound molecular machines that produce ATP in bacteria and in eukaryotic mitochondria and chloroplasts. The structures and enzymic mechanisms of their F1 -catalytic domains are highly conserved in all species investigated hitherto. However, there is evidence that the F-ATPases from the group of protozoa known as Euglenozoa have novel features. Therefore, we have isolated pure and active F1 -ATPase from the euglenozoan parasite, Trypanosoma brucei, and characterized it. All of the usual eukaryotic subunits (α, ß, γ, δ, and ε) were present in the enzyme, and, in addition, two unique features were detected. First, each of the three α-subunits in the F1 -domain has been cleaved by proteolysis in vivo at two sites eight residues apart, producing two assembled fragments. Second, the T. brucei F1 -ATPase has an additional subunit, called p18, present in three copies per complex. Suppression of expression of p18 affected in vitro growth of both the insect and infectious mammalian forms of T. brucei. It also reduced the levels of monomeric and multimeric F-ATPase complexes and diminished the in vivo hydrolytic activity of the enzyme significantly. These observations imply that p18 plays a role in the assembly of the F1 domain. These unique features of the F1 -ATPase extend the list of special characteristics of the F-ATPase from T. brucei, and also, demonstrate that the architecture of the F1 -ATPase complex is not strictly conserved in eukaryotes.

TTC19 Plays a Husbandry Role on UQCRFS1 Turnover in the Biogenesis of Mitochondrial Respiratory Complex III.

Loss-of-function mutations in TTC19 (tetra-tricopeptide repeat domain 19) have been associated with severe neurological phenotypes and mitochondrial respiratory chain complex III deficiency. We previously demonstrated the mitochondrial localization of TTC19 and its link with complex III biogenesis. Here we provide detailed insight into the mechanistic role of TTC19, by investigating a Ttc19?/? mouse model that shows progressive neurological and metabolic decline, decreased complex III activity, and increased production of reactive oxygen species. By using both the Ttc19?/? mouse model and a range of human cell lines, we demonstrate that TTC19 binds to the fully assembled complex III dimer, i.e., after the incorporation of the iron-sulfur Rieske protein (UQCRFS1). The in situ maturation of UQCRFS1 produces N-terminal polypeptides, which remain bound to holocomplex III. We show that, in normal conditions, these UQCRFS1 fragments are rapidly removed, but when TTC19 is absent they accumulate within complex III, causing its structural and functional impairment.

MR-1S Interacts with PET100 and PET117 in Module-Based Assembly of Human Cytochrome c Oxidase.

The biogenesis of human cytochrome c oxidase (COX) is an intricate process in which three mitochondrial DNA (mtDNA)-encoded core subunits are assembled in a coordinated way with at least 11 nucleus-encoded subunits. Many chaperones shared between yeast and humans are involved in COX assembly. Here, we have used a MT-CO3 mutant cybrid cell line to define the composition of assembly intermediates and identify new human COX assembly factors. Quantitative mass spectrometry analysis led us to modify the assembly model from a sequential pathway to a module-based process. Each module contains one of the three core subunits, together with different ancillary components, including HIGD1A. By the same analysis, we identified the short isoform of the myofibrillogenesis regulator 1 (MR-1S) as a new COX assembly factor, which works with the highly conserved PET100 and PET117 chaperones to assist COX biogenesis in higher eukaryotes.

Subunit NDUFV3 is present in two distinct isoforms in mammalian complex I.

Complex I (NADH:ubiquinone oxidoreductase) is the first enzyme of the electron transport chain in mammalian mitochondria. Extensive proteomic and structural analyses of complex I from Bos taurus heart mitochondria have shown it comprises 45 subunits encoded on both the nuclear and mitochondrial genomes; 44 of them are different and one is present in two copies. The bovine heart enzyme has provided a model for studying the composition of complex I in other mammalian species, including humans, but the possibility of additional subunits or isoforms in other species or tissues has not been explored. Here, we describe characterization of the complexes I purified from five rat tissues and from a rat hepatoma cell line. We identify a~50kDa isoform of subunit NDUFV3, for which the canonical isoform is only ~10kDa in size. We combine LC-MS and MALDI-TOF mass spectrometry data from two different purification methods (chromatography and immuno-purification) with information from blue native PAGE analyses to show the long isoform is present in the mature complex, but at substoichiometric levels. It is also present in complex I in cultured human cells. We describe evidence that the long isoform is more abundant in both the mitochondria and purified complexes from brain (relative to in heart, liver, kidney and skeletal muscle) and more abundant still in complex I in cultured cells. We propose that the long 50kDa isoform competes with its canonical 10kDa counterpart for a common binding site on the flavoprotein domain of complex I.

Fasting, but Not Aging, Dramatically Alters the Redox Status of Cysteine Residues on Proteins in Drosophila melanogaster.

Altering the redox state of cysteine residues on protein surfaces is an important response to environmental challenges. Although aging and fasting alter many redox processes, the role of cysteine residues is uncertain. To address this, we used a redox proteomic technique, oxidative isotope-coded affinity tags (OxICAT), to assess cysteine-residue redox changes in Drosophila melanogaster during aging and fasting. This approach enabled us to simultaneously identify and quantify the redox state of several hundred cysteine residues in vivo. Cysteine residues within young flies had a bimodal distribution with peaks at ∼10% and ∼85% reversibly oxidized. Surprisingly, these cysteine residues did not become more oxidized with age. In contrast, 24 hr of fasting dramatically oxidized cysteine residues that were reduced under fed conditions while also reducing cysteine residues that were initially oxidized. We conclude that fasting, but not aging, dramatically alters cysteine-residue redox status in D. melanogaster.

The purification and characterization of ATP synthase complexes from the mitochondria of four fungal species.

The ATP synthases have been isolated by affinity chromatography from the mitochondria of the fungal species Yarrowia lipolytica, Pichia pastoris, Pichia angusta and Saccharomyces cerevisiae. The subunit compositions of the purified enzyme complexes depended on the detergent used to solubilize and purify the complex, and the presence or absence of exogenous phospholipids. All four enzymes purified in the presence of n-dodecyl-ß-D-maltoside had a complete complement of core subunits involved directly in the synthesis of ATP, but they were deficient to different extents in their supernumerary membrane subunits. In contrast, the enzymes from P. angusta and S. cerevisiae purified in the presence of n-decyl-ß-maltose neopentyl glycol and the phospholipids 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine, 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine, cardiolipin (diphosphatidylglycerol) and 1-palmitoyl-2-oleoyl-sn-glycero-3-[phospho-rac-(1-glycerol)] had a complete complement of core subunits and also contained all of the known supernumerary membrane subunits, e, f, g, j, k and ATP8 (or Aap1), plus an additional new membrane component named subunit l, related in sequence to subunit k. The catalytic domain of the enzyme from P. angusta was more resistant to thermal denaturation than the enzyme from S. cerevisiae, but less stable than the catalytic domain of the bovine enzyme, but the stator and the integrity of the transmembrane proton pathway were most stable in the enzyme from P. angusta. The P. angusta enzyme provides a suitable source of enzyme for studying the structure of the membrane domain and properties associated with that sector of the enzyme complex.

VARP is recruited on to endosomes by direct interaction with retromer, where together they function in export to the cell surface.

VARP is a Rab32/38 effector that also binds to the endosomal/lysosomal R-SNARE VAMP7. VARP binding regulates VAMP7 participation in SNARE complex formation and can therefore influence VAMP7-mediated membrane fusion events. Mutant versions of VARP that cannot bind Rab32:GTP, designed on the basis of the VARP ankyrin repeat/Rab32:GTP complex structure described here, unexpectedly retain endosomal localization, showing that VARP recruitment is not dependent on Rab32 binding. We show that recruitment of VARP to the endosomal membrane is mediated by its direct interaction with VPS29, a subunit of the retromer complex, which is involved in trafficking from endosomes to the TGN and the cell surface. Transport of GLUT1 from endosomes to the cell surface requires VARP, VPS29, and VAMP7 and depends on the direct interaction between VPS29 and VARP. Finally, we propose that endocytic cycling of VAMP7 depends on its interaction with VARP and, consequently, also on retromer.

Mutation in VPS35 associated with Parkinson's disease impairs WASH complex association and inhibits autophagy.

Endosomal protein sorting controls the localization of many physiologically important proteins and is linked to several neurodegenerative diseases. VPS35 is a component of the retromer complex, which mediates endosome-to-Golgi retrieval of membrane proteins such as the cation-independent mannose 6-phosphate receptor. Furthermore, retromer is also required for the endosomal recruitment of the actin nucleation promoting WASH complex. The VPS35 D620N mutation causes a rare form of autosomal-dominant Parkinson's disease (PD). Here we show that this mutant associates poorly with the WASH complex and impairs WASH recruitment to endosomes. Autophagy is impaired in cells expressing PD-mutant VPS35 or lacking WASH. The autophagy defects can be explained, at least in part, by abnormal trafficking of the autophagy protein ATG9A. Thus, the PD-causing D620N mutation in VPS35 restricts WASH complex recruitment to endosomes, and reveals a novel role for the WASH complex in autophagosome formation.