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GRAMD1C regulates autophagy initiation and mitochondrial bioenergetics

ABSTRACT: During autophagy, cytosolic cargo is sequestered into double-membrane vesicles called autophagosomes. The origin and identity of the membranes that form the autophagosome remain to be fully characterized. Here, we investigated the role of cholesterol in starvation-induced autophagy and identify a role for the ER-localized cholesterol transport protein GRAMD1C in the regulation of autophagy and mitochondrial function. We demonstrate that cholesterol depletion leads to a rapid induction of autophagy and a corresponding increased abundance of curved autophagy membranes. We further show that GRAMD1C is a negative regulator of starvation-induced autophagy. Similar to its yeast orthologue, GRAMD1C is recruited to mitochondria through its GRAM domain. Additionally, we find that GRAMD1C depletion leads to increased mitochondrial cholesterol accumulation and mitochondrial oxidative phosphorylation. Finally, we demonstrate that expression of GRAM family genes is linked to clear cell renal carcinoma survival, highlighting the pathophysiological relevance of cholesterol transport proteins.

INSTRUMENT(S): Q Exactive HF

ORGANISM(S): Homo Sapiens (human)

SUBMITTER: Tuula Nyman

LAB HEAD: Tuula Nyman

PROVIDER: PXD033125 | Pride | 2022-10-19

REPOSITORIES: Pride

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: GRAMD1C regulates autophagy initiation and mitochondrial bioenergetics through ER-Mitochondria cholesterol transport

Project description:During autophagy, cytosolic cargo is sequestered into double-membrane vesicles called autophagosomes. The origin and identity of the membranes that form the autophagosome remain to be fully characterized. Here, we investigated the role of cholesterol in starvation-induced autophagy and identify a role for the ER-localized cholesterol transport protein GRAMD1C in the regulation of autophagy and mitochondrial function. We demonstrate that cholesterol depletion leads to a rapid induction of autophagy, possibly caused by a corresponding increased abundance of curved autophagy membranes. We further show that GRAMD1C is a negative regulator of starvation-induced autophagy. Similar to its yeast orthologue, GRAMD1C is recruited to mitochondria through its GRAM domain. Additionally, we find that GRAMD1C depletion leads to increased mitochondrial cholesterol accumulation and mitochondrial oxidative phosphorylation. Finally, we demonstrate that expression of GRAM family genes is linked to clear cell renal carcinoma survival, highlighting the pathophysiological relevance of cholesterol transport proteins.

2022-10-19 | PXD027502 | Pride

Cholesterol depletion increases expression of autophagy-related genes in mink lung Mv1Lu cells

Project description:Purpose: Employ next generation sequencing (NGS) to study the transcriptomic response to prolonged reduction in the cholesterol level, with emphasis on autophagy-related genes. Methods: Mv1Lu cells were subjected (or not; control) to cholesterol depletion (16 h, with lovastatin and mevalonate in the presence of lipoprotein deficient serum (LPDS), resulting in 30% reduction in the level of free cholesterol). mRNA profiles were generated by deep sequencing, in triplicates, using Illumina NextSeq500. See methods and protocols for details regarding downstream bioinformatic analysis. Results: Using an optimized data analysis workflow sequencing data from lung samples and identified that cholesterol depletion resulted in 2844 and 2822 genes with significantly increased or reduced expression, respectively. The set of differentially expressed genes was significantly enriched with functional annotations relating to cholesterol metabolic regulation and autophagy. These results were correlated with the upregulation of autophagy in biochemical studies. Conclusions: Mild reduction in the cholesterol level leads to a highly significant increase in the expression of multiple autophagy-related genes. The autophagy genes whose expression was modified by cholesterol depletion were scattered onto multiple steps of the autophagy process, and suggested a mainly positive regulation of autophagy by statin treatment.

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mRNA expression data from keratinocytes with disorganized lipid raft structures (by cholesterol depletion by methyl-beta-cyclodextrin)

Project description:Lipid rafts are cholesterol-rich cell signaling platforms and their physiological role can be explored by cholesterol depletion. To dress a global picture of transcriptional changes ongoing after lipid raft disruption, we performed whole-genome expression profiling in epidermal keratinocytes, a cell type which synthesizes its cholesterol in situ. We used microarrays to identify transcriptional changes in gene expression of cholesterol-depleted keratinocytes. Cholesterol depletion by methyl-beta-cyclodextrin disrupts the organization of lipid rafts, which are cholesterol- and sphingolipid-rich membrane microdomains. Transcript levels were measured in autocrine confluent cultures of normal human epidermal keratinocytes were either left untreated (Ctrl), cholesterol-depleted for 1h with 7.5mM methyl-beta-cyclodextrin (MBCD), or mock cholesterol-depleted for 1h with 7.5mM cholesterol-charged methyl-beta-cyclodextrin complexes (MBCD/chol) (Mock cholesterol depletion is a suppementary negative control as this treatment does not extract cholesterol from cell membranes). Samples are analysed either immediately after the treatment (R0h) or after recovery times of 1h (R1h) respectively 8h (R8h). in total 9 samples are analysed and no replicates are performed.

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Deletions in the ATAD3 gene cluster cause cerebellar developmental defects with mitochondrial DNA abnormalities owing to local cholesterol insufficiency

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2017-06-23 | GSE86550 | GEO

Epigenetic and transcriptional regulation of starvation-induced atrophy and autophagy programs by Foxk1 and Sin3A

Project description:Autophagy is the primary catabolic process triggered in response to starvation. Although autophagic regulation within the cytosolic compartment is well established, it is becoming clear that nuclear events also regulate the induction or repression of autophagy. Nevertheless, a thorough understanding of the mechanisms by which sequence-specific transcription factors modulate expression of genes required for autophagy is lacking. Here, we identify Foxk proteins (Foxk1 and Foxk2) as transcriptional repressors of autophagy in muscle cells and fibroblasts. Interestingly, Foxk1/2 serve to counter-balance another forkhead transcription factor, Foxo3, which induces an overlapping set of autophagic and atrophic targets in muscle. Foxk1/2 specifically recruits Sin3A-HDAC complexes to restrict acetylation of histone H4 and expression of critical autophagy genes. Remarkably, mTOR promotes the transcriptional activity of Foxk1 by facilitating nuclear entry to specifically limit basal levels of autophagy in nutrient-rich conditions. Our study highlights an ancient, conserved mechanism whereby nutritional status is interpreted by mTOR to restrict autophagy by repressing essential autophagy genes via Foxk-Sin3-mediated transcriptional control. Examination of (1) chromatin binding of Foxk1 and Sin3A in non-starved myoblasts and (2) gene expression profiling upon either starvation or siRNA-mediated depletion of Foxk1 relative to a non-starved control.

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The class 3 PI3K coordinates autophagy and mitochondrial lipid catabolism by controlling nuclear receptor PPARα

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