RESUMO
OBJECTIVE: Increase in adipose cAMP-responsive element binding protein (CREB) activity promotes adipocyte dysfunction and systemic insulin resistance in obese mice. This is achieved by increasing the expression of activating transcription factor 3 (ATF3). In this study, we investigated whether impaired expression of the inducible cAMP early repressor (ICER), a transcriptional antagonist of CREB, is responsible for the increased CREB activity in adipocytes of obese mice and humans. RESEARCH DESIGN AND METHODS: Total RNA and nuclear proteins were prepared from visceral adipose tissue (VAT) of human nonobese or obese subjects and white adipose tissue (WAT) of C57Bl6-Rj mice that were fed with normal or high-fat diet for 16 weeks. The expression of genes was monitored by real-time PCR, Western blotting, and electromobility shift assays. RNA interference was used to silence the expression of Icer. RESULTS: The expression of Icer/ICER was reduced in VAT and WAT of obese humans and mice, respectively. Diminution of Icer/ICER was restricted to adipocytes and was accompanied by a rise of Atf3/ATF3 and diminution of Adipoq/ADIPOQ and Glut4/GLUT4. Silencing the expression of Icer in 3T3-L1 adipocytes mimicked the results observed in human and mice cells and hampered glucose uptake, thus confirming the requirement of Icer for appropriate adipocyte function. CONCLUSIONS: Impaired expression of ICER contributes to elevation in CREB target genes and, therefore, to the development of insulin resistance in obesity.
Assuntos
Modulador de Elemento de Resposta do AMP Cíclico/metabolismo , Proteína de Ligação ao Elemento de Resposta ao AMP Cíclico/metabolismo , Obesidade/metabolismo , Células 3T3-L1 , Fator 3 Ativador da Transcrição/genética , Fator 3 Ativador da Transcrição/metabolismo , Adiponectina/genética , Adiponectina/metabolismo , Tecido Adiposo Branco/metabolismo , Animais , Western Blotting , Modulador de Elemento de Resposta do AMP Cíclico/genética , Proteína de Ligação ao Elemento de Resposta ao AMP Cíclico/genética , Ensaio de Desvio de Mobilidade Eletroforética , Transportador de Glucose Tipo 4/genética , Transportador de Glucose Tipo 4/metabolismo , Humanos , Gordura Intra-Abdominal/metabolismo , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Obesidade/genética , Reação em Cadeia da Polimerase em Tempo RealRESUMO
OBJECTIVE: Recent observations indicate that the delivery of nitric oxide by endothelial nitric oxide synthase (eNOS) is not only critical for metabolic homeostasis, but could also be important for mitochondrial biogenesis, a key organelle for free fatty acid (FFA) oxidation and energy production. Because mice deficient for the gene of eNOS (eNOS(-/-)) have increased triglycerides and FFA levels, in addition to hypertension and insulin resistance, we hypothesized that these knockout mice may have decreased energy expenditure and defective beta-oxidation. RESEARCH DESIGN AND METHODS: Several markers of mitochondrial activity were assessed in C57BL/6J wild-type or eNOS(-/-) mice including the energy expenditure and oxygen consumption by indirect calorimetry, in vitro beta-oxidation in isolated mitochondria from skeletal muscle, and expression of genes involved in fatty acid oxidation. RESULTS: eNOS(-/-) mice had markedly lower energy expenditure (-10%, P < 0.05) and oxygen consumption (-15%, P < 0.05) than control mice. This was associated with a roughly 30% decrease of the mitochondria content (P < 0.05) and, most importantly, with mitochondrial dysfunction, as evidenced by a markedly lower beta-oxidation of subsarcolemmal mitochondria in skeletal muscle (-30%, P < 0.05). Finally, impaired mitochondrial beta-oxidation was associated with a significant increase of the intramyocellular lipid content (30%, P < 0.05) in gastrocnemius muscle. CONCLUSIONS: These data indicate that elevated FFA and triglyceride in eNOS(-/-) mice result in defective mitochondrial beta-oxidation in muscle cells.