SIRT1 Limits Adipocyte Hyperplasia through c-Myc Inhibition

Houari Abdesselem,Aisha Madani,Ahmad Hani,Muna Al-Noubi,Neha Goswami,Hisham Ben Hamidane,Anja M Billing,Jennifer Pasquier,Michael S Bonkowski,Najeeb Halabi,Rajaa Dalloul,Mohamed Z Sheriff,Nasrin Mesaeli,Mohamed Elrayess,David A Sinclair,Johannes Graumann,Nayef A Mazloum

doi:10.1074/jbc.m115.675645

Abstract

The expansion of fat mass in the obese state is due to increased adipocyte hypertrophy and hyperplasia. The molecular mechanism that drives adipocyte hyperplasia remains unknown. The NAD+-dependent protein deacetylase sirtuin 1 (SIRT1), a key regulator of mammalian metabolism, maintains proper metabolic functions in many tissues, counteracting obesity. Here we report that differentiated adipocytes are hyperplastic when SIRT1 is knocked down stably in mouse 3T3-L1 preadipocytes. This phenotype is associated with dysregulated adipocyte metabolism and enhanced inflammation. We also demonstrate that SIRT1 is a key regulator of proliferation in preadipocytes. Quantitative proteomics reveal that the c-Myc pathway is altered to drive enhanced proliferation in SIRT1-silenced 3T3-L1 cells. Moreover, c-Myc is hyperacetylated, levels of p27 are reduced, and cyclin-dependent kinase 2 (CDK2) is activated upon SIRT1 reduction. Remarkably, differentiating SIRT1-silenced preadipocytes exhibit enhanced mitotic clonal expansion accompanied by reduced levels of p27 as well as elevated levels of CCAAT/enhancer-binding protein β (C/EBPβ) and c-Myc, which is also hyperacetylated. c-Myc activation and enhanced proliferation phenotype are also found to be SIRT1-dependent in proliferating mouse embryonic fibroblasts and differentiating human SW872 preadipocytes. Reducing both SIRT1 and c-Myc expression in 3T3-L1 cells simultaneously does not induce the adipocyte hyperplasia phenotype, confirming that SIRT1 controls adipocyte hyperplasia through c-Myc regulation. A better understanding of the molecular mechanisms of adipocyte hyperplasia will open new avenues toward understanding obesity.

Highlights

The expansion of fat mass in the obese state is due to increased adipocyte hypertrophy and hyperplasia
Differentiating sirtuin 1 (SIRT1)-silenced preadipocytes exhibit enhanced mitotic clonal expansion accompanied by reduced levels of p27 as well as elevated levels of CCAAT/enhancer-binding protein ␤ (C/EBP␤) and c-Myc, which is hyperacetylated. c-Myc activation and enhanced proliferation phenotype are found to be SIRT1dependent in proliferating mouse embryonic fibroblasts and differentiating human SW872 preadipocytes
Using Western blot analysis, we demonstrated that the infection of 3T3-L1 preadipocytes with the lentiviral construct containing shRNA-targeting SIRT1 (shSirt1) results in undetectable levels of the SIRT1 protein compared with control cells (Fig. 1A)

Summary

Introduction

The expansion of fat mass in the obese state is due to increased adipocyte hypertrophy and hyperplasia. Using Western blot analysis, we demonstrated that the infection of 3T3-L1 preadipocytes with the lentiviral construct containing shSirt1 results in undetectable levels of the SIRT1 protein compared with control cells (uninfected and shScramble-expressing 3T3-L1 cells) (Fig. 1A).

Results

Conclusion