RESUMO
Conjugated linoleic acid (CLA) reduces body weight and adipose mass in a variety of species. The mechanisms by which CLA depletes adipose mass are unclear, but two independent microarray analyses indicate that in white adipose tissue (WAT), uncoupling protein 1 (UCP1) was among genes most changed by CLA. The objective of this study was to determine whether CLA induces ectopic expression of UCP1 in WAT, which may contribute to increased energy expenditure and weight loss. Six-week old, male ob/ob mice were fed either a control diet (CON) or a diet supplemented with 1.5% mixed isomer CLA (CLA) for 4 weeks. A third group of mice (LEPTIN) was fed the control diet and received daily injections of recombinant leptin as a positive control for adipose depletion in ob/ob mice. CLA did not alter several mRNA markers of lipid oxidation in epididymal white adipose tissue (eWAT) , but significantly increased carnitine palmitoyltransferase-1b (CPT1b) and PPAR gamma coactivator-1alpha (PGC1alpha) expression. Notably, CLA increased both mRNA and protein expression of uncoupling protein-1 (UCP1). beta3-adrenoceptor mRNA and phosphorylated-p38 mitogen activated protein kinase (MAPK) protein levels were not affected by CLA, but were upregulated by LEPTIN. These data suggest the increased CPT1b, PGC1alpha, and UCP1, in WAT of CLA-fed mice may contribute to the depletion of adipose, and CLA does not appear to increase UCP1 through beta3-adrenergic signaling. Future studies will focus on understanding how CLA increases mitochondrial oxidation and energy dissipation in white adipose tissue.
Assuntos
Tecido Adiposo Branco/metabolismo , Canais Iônicos/genética , Ácidos Linoleicos Conjugados/farmacologia , Proteínas Mitocondriais/genética , Tecido Adiposo Branco/efeitos dos fármacos , Animais , Peso Corporal , Carnitina O-Palmitoiltransferase/genética , Carnitina O-Palmitoiltransferase/metabolismo , Metabolismo Energético , Canais Iônicos/metabolismo , Leptina/metabolismo , Masculino , Camundongos , Camundongos Transgênicos , Proteínas Mitocondriais/metabolismo , Obesidade/genética , Obesidade/metabolismo , RNA Mensageiro/metabolismo , Proteína Desacopladora 1RESUMO
Conjugated linoleic acid (CLA) induces insulin resistance preceded by rapid depletion of the adipokines leptin and adiponectin, increased inflammation, and hepatic steatosis in mice. To determine the role of leptin in CLA-mediated insulin resistance and hepatic steatosis, recombinant leptin was coadministered with dietary CLA in ob/ob mice to control leptin levels and to, in effect, negate the leptin depletion effect of CLA. In a 2 x 2 factorial design, 6 week old male ob/ob mice were fed either a control diet or a diet supplemented with CLA and received daily intraperitoneal injections of either leptin or vehicle for 4 weeks. In the absence of leptin, CLA significantly depleted adiponectin and induced insulin resistance, but it did not increase hepatic triglyceride concentrations or adipose inflammation, marked by interleukin-6 and tumor necrosis factor-alpha mRNA expression. Insulin resistance, however, was accompanied by increased macrophage infiltration (F4/80 mRNA) in adipose tissue. In the presence of leptin, CLA depleted adiponectin but did not induce insulin resistance or macrophage infiltration. Despite this, CLA induced hepatic steatosis. In summary, CLA worsened insulin resistance without evidence of inflammation or hepatic steatosis in mice after 4 weeks. In the presence of leptin, CLA failed to worsen insulin resistance but induced hepatic steatosis in ob/ob mice.