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The lipid handling capacity of subcutaneous fat is programmed by mTORC2 during development

ABSTRACT: Obesity causes type 2 diabetes, cardiovascular diseases, NAFLD, and cancer, but all fat is not equal as subcutaneous white adipose tissue (SWAT) is more metabolically favorable than visceral fat. Here, we investigate mTORC2 function in SWAT growth by deleting its essential subunit Rictor in SWAT precursor cells and examining its effect on adipocyte differentiation and tissue development. We found that Rictor/mTORC2 is not required for SWAT preadipocyte differentiation per se; however, SWAT preadipocytes differentiating without Rictor cannot fully induce the lipid storage transcriptional program. In vivo, this results in smaller adipocytes, reduced SWAT size, lipid re-distribution to visceral and brown fat, and gender-distinct effects on systemic metabolic fitness. Mechanistically, mTORC2 promotes PPARg activity towards specific lipid metabolism genes independently of ChREBP, but in coordination, to set the lipid handling capacity of SWAT. Further exploring this pathway may uncover new strategies to stimulate lipid storage in more metabolically favorable SWAT.

ORGANISM(S): Mus musculus

PROVIDER: GSE146470 | GEO | 2020/10/06

REPOSITORIES: GEO

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Project description:Nearly 50% of cutaneous melanomas carry activating mutations on the BRAF oncogene, and the combination of BRAF- and MEK-inhibitors (BRAF/MEKi) is frequently used for their clinical management. One major drawback of BRAF/MEKi targeted therapy is the rapid development of therapeutic resistance, which can occur via multiple mechanisms, including the metabolic rewiring of cancer cells that often involves the upregulation of mitochondrial bionergetics and NAD+ biosynthetic pathways. mTORC2 is a signaling complex that requires the presence of its essential RICTOR subunit to play its regulatory functions in cell growth and metabolism. mTORC2 is believed to play mostly pro-oncogenic roles in several tumor types, including melanoma. However, bioinformatics analysis of TCGA melanoma patients’ database revealed that low RICTOR levels in tumors correlate with an overall worse clinical outcome. GSEA analysis of low-RICTOR tumors evidenced also a gene expression signature suggestive of activation of mitochondrial energy producing pathways. On these bases, we have hypothesized that inhibition of mTORC2 activity may render BRAFV600E melanoma cells resistant to BRAFi/MEKi. We show here that RICTOR/mTORC2-deficient cells are intrinsically tolerant to BRAFi/MEKi, and anticipate the onset of resistance to BRAFi after sustained drug exposure both in vitro and in vivo, indicating that mTORC2 activity normally opposes the acquisition of targeted therapy resistance in BRAFV600E melanomas. Mechanistically, RICTOR-deficient cells show an enhanced mitochondrial respiratory potential and increased expression of nicotinamide phosphoribosyltransferase (NAMPT) protein, the rate-limiting enzyme of NAD+ salvage pathway, and pharmacological inhibition of these processes in RICTOR-deficient cells is sufficient to restore sensitivity to BRAFi. Thus, our work identifies a novel role for mTORC2 in favoring the responses of BRAF-mutated melanoma cells to targeted therapy, and suggest that the evaluation of the intratumor level of RICTOR may help to predict the responses of melanoma patients to these treatments.

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The lipid handling capacity of subcutaneous fat is programmed by mTORC2 during development

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