Dynamic regulation of mitochondrial network and oxidative functions during 3T3-L1 fat cell differentiation
Pierre-Henri Ducluzeau & Mélanie Priou & Mireille Weitheimer & Melissa Flamment & Lucie Duluc & Fransceco Iacobazi & Raffaela Soleti & Gilles Simard & Annie Durand & Jennifer Rieusset & Ramaroson Andriantsitohaina & YvesMalthièry
Received: 22 June 2010 / Accepted: 7 January 2011 # University of Navarra 2011
Abstract Mitochondria have been shown to be impaired in insulin resistance-related diseases but have not been extensively studied during the first steps of adipose cell development. This study was designed to determine the sequence of changes of the mitochondrial network and function during the first daysof adipogenesis. 3T3L1 preadipocytes were differentiated into adipocytes without using glitazone compounds. At days 0, 3, 6, 9, and 12, mitochondrial network imaging, mitochondrial oxygen consumption, membrane potential, and oxidative phosphorylation efficiency were assessed in permeabilized cells. Gene and protein expressions related to fatty acid metabolism and mitochondrial network were alsodetermined. Compared to preadipocytes (day 0), new adipocytes (days 6 and 9) displayed profound changes of their mitochondrial network that underwent fragmentation and redistribution around lipid droplets. Drp1 and mitofusin 2 displayed a progressive increase in their gene expression and protein content during the first 9 days of differentiation. In parallel with
P.-H. Ducluzeau (*) : M. Priou :M. Weitheimer : M. Flamment : L. Duluc : F. Iacobazi : R. Soleti : G. Simard : R. Andriantsitohaina : Y. Malthièry INSERM U694, Univerité d’Angers, CHU Angers, 4 rue Larrey, Angers 49033, France e-mail: firstname.lastname@example.org A. Durand : J. Rieusset INSERM 870, INRA 1235, Université Lyon 1, Hospices Civils de Lyon, Lyon, France
the mitochondrial network redistribution, mitochondria switchedto uncoupled respiration with a tendency towards decreased membrane potential, with no variation of mtTFA and NRF1 gene expression. The expression of PGC1α and NRF2 genes and genes involved in lipid oxidation (UCP2, CD36, and CPT1) was increased. Reactive oxygen species (ROS) production displayed a nadir at day 6 with a concomitant increase in antioxidant enzyme gene expression. This 3T3-L1-basedin vitro model of adipogenesis showed that mitochondria adapted to the increased number of lipid droplets by network redistribution and uncoupling respiration. The timing and regulation of lipid oxidation-associated ROS production appeared to play an important role in these changes. Keywords Adipogenesis . Mitochondrial network . Lipid metabolism . Oxidative phosphorylation
Introduction Obesityis characterized by an increase of adipose tissue as a result of a positive imbalance between food intake and energy expenditure. Recent studies have indicated that adipocyte function is more complex than expected since these cells have multiple functions and are integrated in a homeostatic network to optimize energy resources . A better understanding of the mechanisms involved in adipocytedifferentiation is required to unravel mechanisms underlying obesity and its
P.-H. Ducluzeau et al.
symptomatic cohort of associated pathologies such as dyslipidemia, dysglycemia, steatosis, and possibly hypertension [5, 9]. On one hand, biochemical studies identified many genes that undergo transcription during the first days of differentiation. Among them, membrane fatty acid carrier CD36,allowing lipid entry into the cell, carnitine palmitoyltransferase-1 (CPT1), and UCP2, allowing lipid mitochondrial oxidation, are proteins involved in the adipocyte differentiation program which plays an important role in adipocyte physiology [22, 34]. On the other hand, several genes coding for transcription factors involved in mitochondrial development, such as the mitochondrial transcription...