Mitochondrial dysfunction induces triglyceride accumulation in 3T3-L1 cells: role of fatty acid -oxidation and glucose

Mitochondrial cytopathy has been associated with modifications of lipid metabolism in various situations, such as the acquisition of an abnormal adipocyte phenotype observed in multiple symmetrical lipomatosis or triglyceride (TG) accumulation in muscles associated with the myoclonic epilepsy with ragged red fibers syndrome. However, the molecular signaling leading to fat metabolism dysregulation in cells with impaired mitochondrial activity is still poorly understood. Here, we found that preadipocytes incubated with inhibitors of mitochondrial respiration such as antimycin A (AA) accumulate TG vesicles but do not acquire specific markers of adipocytes. Although the uptake of TG precursors is not stimulated in 3T3-L1 cells with impaired mitochondrial activity, we found a strong stimulation of glucose uptake in AA-treated cells mediated by calcium and phosphatidylinositol 3-kinase/Akt1/glycogen synthase kinase 3 , a pathway known to trigger the translocation of glucose transporter 4 to the plasma membrane in response to insulin. TG accumulation in AA-treated cells is mediated by a reduced peroxisome proliferator-activated receptor activity that downregulates muscle carnitine palmitoyl transferase-1 expression and fatty acid -oxidation, and by a direct conversion of glucose into TGs accompanied by the activation of carbohydrate-responsive element binding protein, a lipogenic transcription factor. Taken together, these results could explain how mitochondrial impairment leads to the multivesicular phenotype found in some mitochondria-originating diseases associated with a dysfunction in fat metabolism. —Vankoningsloo, S., M. Piens, C. Lecocq, A. Gilson, A. De Pauw, P. Renard, C. Demazy, A. Houbion, M. Raes, and T. Arnould. Mitochondrial dysfunction induces triglyceride accumulation in 3T3-L1 cells: role of fatty acid -oxidation and glucose. J. Lipid Res. 2005. 46: 1133–1149. Supplementary key words muscle carnitine palmitoyl transferase-1 • phosphatidylinositol 3-kinase/Akt1/glycogen synthase kinase 3 • AMPdependent kinase • carbohydrate-responsive element binding protein • peroxisome proliferator-activated receptor The role of mitochondria in lipid homeostasis has been strongly emphasized in recent studies focusing on mitochondrial respiratory deficiency. Indeed, chronic mitochondrial dysfunction can lead to diseases characterized by lipid metabolism disorders and pathological triglyceride (TG) accumulation in several cell types (1–3). Genetic mitochondrial pathologies usually result from point mutations or deletions in mitochondrial DNA that finally impair oxidative phosphorylation capacity (4). Interestingly, some mitochondrial disorders affect lipid-metabolizing tissues such as muscular and adipose tissues. For example, the myoclonic epilepsy with ragged red fibers (MERRF) syndrome, commonly caused by a point mutation in the mitochondrial tRNA Lys -encoding gene (A8344G), is associated with myopathy, TG accumulation in muscles (5), and, in some cases, multiple symmetrical lipomatosis (MSL) (2, 6). MSL is a pathology characterized by the formation of lipomas containing abnormal white adipocytes smaller than normal adipocytes showing a multivesicular phenotype (1, 2, 7). Moreover, biochemical analyses have shown that cytochrome c oxidase activity is impaired in muscles from patients with MSL (8), supporting the fact that the disease is linked to mitochondrial dysfunction (6, 9). The role of mitochondria in the lipid metabolism of white adipose tissue was also strengthened in the pathogenesis of Abbreviations: AA, antimycin A; ACC, acetyl-coenzyme A carboxylase; AICAR, 5-aminoimidazole-4-carboxamide-1d -ribofuranoside; AMPK, AMP-dependent kinase; BAPTA-AM, 1,2-bis(2-aminophenoxy)ethaneN , N , N , N -tetraacetic acid; C/EBP , CCAAT/enhancer-binding protein ; ChREBP, carbohydrate-responsive element binding protein; 2-DG, 2-deoxyd -[ 3 H]glucose; EGCG, ( )-epigallocatechin gallate; FABP4, fatty acid binding protein 4; FCCP, carbonyl cyanide ( p -trifluoromethoxy)phenylhydrazone; FCS, fetal calf serum; GLUT, glucose transporter; GSK3 , glycogen synthase kinase 3 ; HB, hypotonic buffer; IRS-1, insulin receptor substrate-1; L-PK, liver pyruvate kinase; M-CPT-1, muscle carnitine palmitoyl transferase-1; MERRF, myoclonic epilepsy with ragged red fibers; MSL, multiple symmetrical lipomatosis; NAC, N -acetyll -cysteine; PI 3-kinase, phosphatidylinositol 3-kinase; PPAR , peroxisome proliferator-activated receptor ; ROS, reactive oxygen species; RXR , retinoid X receptor ; TBP, TATA box binding protein; TG, triglyceride; UCP-2, uncoupling protein-2. 1 To whom correspondence should be addressed. e-mail: [email protected] Manuscript received 19 November 2004 and in revised form 25 January 2005 and in re-revised form 15 February 2005. Published, JLR Papers in Press, March 1, 2005. DOI 10.1194/jlr.M400464-JLR200 by gest, on S etem er 7, 2016 w w w .j.org D ow nladed fom