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The p97-UBXD8 complex regulates ER-Mitochondria contact sites by altering membrane lipid saturation and composition

ABSTRACT: The intimate association between the endoplasmic reticulum (ER) and mitochondrial membranes at ER-mitochondria contact sites (ERMCS) serves as a platform for several critical cellular processes, particularly lipid synthesis. How contacts are remodeled and the subsequent biological consequences of altered contacts such as perturbed lipid metabolism remains poorly understood. Here we show that the p97 AAA-ATPase and its ER-tethered ubiquitin-X domain adaptor 8 (UBXD8) regulate the prevalence of ERMCS. The p97-UBXD8 complex localizes to contacts and its loss increases contacts in a manner that is dependent on p97 catalytic activity. Quantitative proteomics and lipidomics of ERMCS demonstrates alterations in proteins regulating lipid metabolism and a significant change in saturated or monounsaturated lipid species in UBXD8 knockout cells. We show that loss of p97-UBXD8 results in perturbed contacts due to an increase in membrane lipid saturation via SREBP1 and the lipid desaturase SCD1. These aberrant contacts can be rescued by supplementation with unsaturated fatty acids or overexpression of SCD1. Notably, we find that the SREBP1-SCD1 pathway is negatively impacted in the brains of mice with p97 mutations that cause neurodegeneration. Our results suggest that contacts are exquisitely sensitive to alterations to membrane lipid composition and saturation in a p97-UBXD8 dependent manner.

INSTRUMENT(S): Orbitrap Fusion Lumos

ORGANISM(S): Homo Sapiens (human)

SUBMITTER: Joao Paulo

LAB HEAD: Malavika Raman

PROVIDER: PXD039061 | Pride | 2023-01-25

REPOSITORIES: Pride

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Project description:Cis-9, trans-11-conjugated linoleic acid (c9, t11-CLA), a functional fatty acid, is one of the research hotspots in the fields of functional dairy products development because of its multiple beneficial effects in humans and animals. In milk, most c9, t11-CLA is de novo synthesized from trans-11-octadecenoic acid (TVA) and it is confirmed that genes such as stearoyl-coA desaturase 1 (SCD1) play a key role in the synthesis. However, few studies have been reported to deeply elucidate the SCD1-dependent molecular mechanism of cis9, trans11-CLA synthesis and its relationship with the pathways of energy metabolism and lipid metabolism. Therefore, in the present study, MAC-T cells were divided into three groups: CAY group (SCD1-inhibited MAC-T cell model with the addition of CAY, TVA), TVA group (only TVA), and Control group (without CAY, TVA). The relative mRNA expression of SCD1 was measured using real-time PCR, while TVA accumulation and c9, t11 -CLA synthesis were analyzed using gas chromatography (GC). The SCD1-related proteins were firstly screened in MAC-T cells by Tandem Mass Tag (TMT)-based quantitative proteomics analysis, then their functions were annotated by bioinformatic analysis, and finally their relationships with SCD1 were evaluated by parallel reaction monitoring (PRM) analysis and small RNA interference. The results showed that the deficiency of SCD1 led by CAY10566 blocked the synthesis of c9, t11-CLA in MAC-T cells. Sixty-one SCD1-associated proteins were screened and found to be mainly involved in the pathways of energy metabolism and lipid metabolism, such as glycolytic pathway, pentose phosphate pathway, fatty acid elongation pathway, and unsaturated fatty acid biosynthesis. Among these genes, 17 proteins were validated under the PRM analysis. PGAM1 (phosphoglycerate mutase 1), TPI1 (triosephosphate isomerase 1), LDHB (lactate dehydrogenase B), and ALDOA (aldolase, fructose-bisphosphate A) were verified to have a negative relationships with SCD1. This study furthered our understanding of the molecular mechanisms of c9, t11-CLA synthesis in the mammary glands of dairy cows.

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The p97-UBXD8 complex regulates ER-Mitochondria contact sites by altering membrane lipid saturation and composition

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