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SIRT1 controls lipolysis in adipocytes via FOXO1-mediated expression of ATGL.

ABSTRACT: Recent studies have established SIRT1 as an important regulator of lipid metabolism, although the mechanism of its action at the molecular level has not been revealed. Here, we show that knockdown of SIRT1 with the help of small hairpin RNA decreases basal and isoproterenol-stimulated lipolysis in cultured adipocytes. This effect is attributed, at least in part, to the suppression of the rate-limiting lipolytic enzyme, adipose triglyceride lipase (ATGL), at the level of transcription. Mechanistically, SIRT1 controls acetylation status and functional activity of FoxO1 that directly binds to the ATGL promoter and regulates ATGL gene transcription. We have also found that depletion of SIRT1 decreases AMP-dependent protein kinase (AMPK) activity in adipocytes. To determine the input of AMPK in regulation of lipolysis, we have established a stable adipose cell line that expresses a dominant-negative ?1 catalytic subunit of AMPK under the control of the inducible TET-OFF lentiviral expression vector. Reduction of AMPK activity does not have a significant effect on the rates of lipolysis in this cell model. We conclude, therefore, that SIRT1 controls ATGL transcription primarily by deacetylating FoxO1.

SUBMITTER: Chakrabarti P

PROVIDER: S-EPMC3151689 | biostudies-literature | 2011 Sep

REPOSITORIES: biostudies-literature

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SIRT1 controls lipolysis in adipocytes via FOXO1-mediated expression of ATGL.

Chakrabarti Partha P English Taylor T Karki Shakun S Qiang Li L Tao Rong R Kim Juyoun J Luo Zhijun Z Luo Zhijun Z Farmer Stephen R SR Kandror Konstantin V KV

Journal of lipid research 20110708 9

Recent studies have established SIRT1 as an important regulator of lipid metabolism, although the mechanism of its action at the molecular level has not been revealed. Here, we show that knockdown of SIRT1 with the help of small hairpin RNA decreases basal and isoproterenol-stimulated lipolysis in cultured adipocytes. This effect is attributed, at least in part, to the suppression of the rate-limiting lipolytic enzyme, adipose triglyceride lipase (ATGL), at the level of transcription. Mechanisti ...[more]

PMID: 21743036

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Project description:Nicotinamide adenine dinucleotide (NAD+) -dependent protein deacetylase SIRT1 plays an important role in the regulation of metabolism. Although the administration of nicotinamide mononucleotide (NMN), a key NAD+ intermediate, has been shown to ameliorate metabolic disorders, such as insulin resistance and glucose intolerance, the direct effect of NMN on the regulation of lipid metabolism in adipocytes remains unclear. We here investigated the effect of NMN on lipid storage in 3T3-L1 differentiated adipocytes. Oil-red O staining showed that NMN treatment reduced lipid accumulation in these cells. NMN was found to enhance lipolysis in adipocytes since the concentration of glycerol in the media was increased by NMN treatment. Western blotting and real-time RT-PCR analysis revealed that adipose triglyceride lipase (ATGL) expression at both protein and mRNA level was increased with NMN treatment in 3T3-L1 adipocytes. Whereas NMN increased SIRT1 expression and AMPK activation, an AMPK inhibitor compound C restored the NMN-dependent upregulation of ATGL expression in these cells, suggesting that NMN upregulates ATGL expression through the SIRT1-AMPK axis. NMN administration significantly decreased subcutaneous fat mass in mice on a high-fat diet. We also found that adipocyte size in subcutaneous fat was decreased with NMN treatment. Consistent with the alteration of fat mass and adipocyte size, the ATGL expression in subcutaneous fat was slightly, albeit significantly, increased with NMN treatment. These results indicate that NMN suppresses subcutaneous fat mass in diet-induced obese mice, potentially in part via the upregulation of ATGL. Unexpectedly, the reduction in fat mass as well as ATGL upregulation with NMN treatment were not observed in epididymal fat, implying that the effects of NMN are site-specific in adipose tissue. Thus, these findings provide important insights into the mechanism of NMN/NAD+ in the regulation of metabolism. Highlights • NMN induces lipolysis by increasing ATGL expression in 3T3-L1 adipocytes.• NMN enhances ATGL expression through SIRT1/AMPK axis in 3T3-L1 adipocytes.• NMN ameliorates diet-induced obesity in mice by suppressing adipocyte hypertrophy.

Project description:Background/Aims: Diabetic non-healing skin ulcers represent a serious challenge in clinical practice, in which the hyperglycemia-induced disturbance of angiogenesis, and endothelial dysfunction play a crucial role. Resveratrol (RES), a silent information regulator 1 (SIRT1) agonist, can improve endothelial function and has strong pro-angiogenic properties, and has thus become a research focus for the treatment of diabetic non-healing skin ulcers; however, the underlying mechanism by which RES regulates these processes remains unclear. Therefore, the present study was intended to determine if RES exerts its observed protective role in diabetic wound healing by alleviating hyperglycemia-induced endothelial dysfunction and the disturbance of angiogenesis. Methods: We investigated the effects of RES on cell migration, cell proliferation, apoptosis, tube formation, and the underlying molecular mechanisms in 33 mM high glucose-stimulated human umbilical vein endothelial cells (HUVECs) by semi-quantitative RT-PCR, western blot analysis, terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) staining, and immunofluorescence in vitro. We further explored the role of RES on endothelial dysfunction and wound healing disturbance in db/db mice by TUNEL staining, immunofluorescence, and photography in vivo. Results: We observed an obvious inhibition of hyperglycemia-triggered endothelial dysfunction and a disturbance of angiogenesis, followed by the promotion of diabetic wound healing via RES, along with restoration of the activity of the hyperglycemia-impaired SIRT1 signaling pathway. Pretreatment with EX-527, a SIRT1 inhibitor, abolished the RES-mediated endothelial protection and pro-angiogenesis action, and then delayed diabetic wound healing. Furthermore, examination of the overexpression of forkhead box O1 (FOXO1), a transcription factor substrate of SIRT1, in HUVECs and db/db mice revealed that RES activated SIRT1 to restore hyperglycemia-triggered endothelial dysfunction and disturbance of angiogenesis, followed by the promotion of diabetic wound healing in a c-Myc-dependent manner. Pretreatment with 10058-F4, a c-Myc inhibitor, repressed RES-mediated endothelial protection, angiogenesis, and diabetic wound healing. Conclusion: Our findings indicate that the positive role of RES in diabetic wound healing via its SIRT1-dependent endothelial protection and pro-angiogenic effects involves the inhibition of FOXO1 and the de-repression of c-Myc expression.

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SIRT1 controls lipolysis in adipocytes via FOXO1-mediated expression of ATGL.

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SIRT1 controls lipolysis in adipocytes via FOXO1-mediated expression of ATGL.

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