Increased FAT/CD36 Cycling and Lipid Accumulation in Myotubes Derived from Obese Type 2 Diabetic Patients Celine Aguer 1,2¤a , Marc Foretz 3,4,5 , Louise Lantier 3,4,5 , Sophie Hebrard 3,4,5 , Benoit Viollet 3,4,5 , Jacques Mercier 1,2,6 , Magali Kitzmann 1,2 * ¤b 1 INSERM, U1046 Physiologie et Me ´decine Expe ´rimentale du Cœur et des Muscles, Montpellier, France, 2 Universite ´ Montpellier 1, Universite ´ Montpellier 2, Montpellier, France, 3 Inserm, U1016, Institut Cochin, Paris, France, 4 CNRS, UMR8104, Paris, France, 5 Universite ´ Paris Descartes, Paris, France, 6 CHRU Montpellier, Montpellier, France Abstract Background: Permanent fatty acid translocase (FAT/)CD36 relocation has previously been shown to be related to abnormal lipid accumulation in the skeletal muscle of type 2 diabetic patients, however mechanisms responsible for the regulation of FAT/CD36 expression and localization are not well characterized in human skeletal muscle. Methodology/Principal Findings: Primary muscle cells derived from obese type 2 diabetic patients (OBT2D) and from healthy subjects (Control) were used to examine the regulation of FAT/CD36. We showed that compared to Control myotubes, FAT/CD36 was continuously cycling between intracellular compartments and the cell surface in OBT2D myotubes, independently of lipid raft association, leading to increased cell surface FAT/CD36 localization and lipid accumulation. Moreover, we showed that FAT/CD36 cycling and lipid accumulation were specific to myotubes and were not observed in reserve cells. However, in Control myotubes, the induction of FAT/CD36 membrane translocation by the activation of (AMP)-activated protein kinase (AMPK) pathway did not increase lipid accumulation. This result can be explained by the fact that pharmacological activation of AMPK leads to increased mitochondrial beta-oxidation in Control cells. Conclusion/Significance: Lipid accumulation in myotubes derived from obese type 2 diabetic patients arises from abnormal FAT/CD36 cycling while lipid accumulation in Control cells results from an equilibrium between lipid uptake and oxidation. As such, inhibiting FAT/CD36 cycling in the skeletal muscle of obese type 2 diabetic patients should be sufficient to diminish lipid accumulation. Citation: Aguer C, Foretz M, Lantier L, Hebrard S, Viollet B, et al. (2011) Increased FAT/CD36 Cycling and Lipid Accumulation in Myotubes Derived from Obese Type 2 Diabetic Patients. PLoS ONE 6(12): e28981. doi:10.1371/journal.pone.0028981 Editor: Jean-Marc A. Lobaccaro, Clermont Universite ´, France Received July 29, 2011; Accepted November 18, 2011; Published December 16, 2011 Copyright: ß 2011 Aguer et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This work was supported by grants from Association Franc ¸aise contre les Myopathies (AFM, MNM2 2005, nu11330), Institut National de Sante ´ et de la Recherche Me ´dicale (INSERM, ERI25), Languedoc Roussillon Region, University of Montpellier 1 (EA4202) and CHU of Montpellier. The authors are grateful to the Centre de Recherche National Scientifique (CNRS) for its support to M. Kitzmann and to AFM and EMO International for their fellowships to C. Aguer. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: magali.kitzmann@igh.cnrs.fr ¤a Current address: Mitochondrial Bioenergetics Laboratory, Faculty of Medicine, Department of Biochemistry, Microbiology and Immunology, University of Ottawa, Ottawa, Ontario, Canada ¤b Current address: IGH, UPR1142, Montpellier, France Introduction Intramyocellular lipid accumulation in skeletal muscle is abnormally high in type 2 diabetes and contributes to the etiology of the pathology [1]. Long chain fatty acid (such as palmitate) uptake is achieved by a concert of co-existing mechanisms. These lipids can passively diffuse, but certain membrane proteins can also accelerate the transport. Membrane fatty acid transporters can modulate the balance between fatty acid uptake and subsequent storage and/or oxidation in muscle tissue. The principal muscle fatty acid transporter FAT/CD36 (fatty acid translocase) is involved in regulating the uptake of long-chain fatty acids into skeletal muscle [2,3]. Abnormal increased fatty acid transport [4] and membrane FAT/CD36 relocation [4,5] independent of mitochondrial dysfunction result in an excessive accumulation of intramyocellular lipid in skeletal muscle tissue of type 2 diabetic patients. To date, little is known about FAT/CD36 regulation in human skeletal muscle. In this tissue, the mechanisms known to induce FAT/CD36 translocation from intracellular storage compartments towards plasma membrane are insulin, (AMP)- activated protein kinase (AMPK) signaling pathways and muscle contraction [6,7]. Mature muscles possess a population of satellite cells located on their surface. In vitro satellite cells differentiation is characterized by withdrawal of myoblasts from the cell cycle, induction of muscle- specific gene expression, and cell fusion into multinucleated myotubes. After differentiation in vitro, satellite cells are composed of two populations of cells: mature myotubes and quiescent undifferentiated myoblasts (reserve cells) [8]. In adipocytes, FAT/ CD36 expression appeared to be closely linked to preadipocyte PLoS ONE | www.plosone.org 1 December 2011 | Volume 6 | Issue 12 | e28981