RESUMO
The present study investigated whether exercise induces the expression of PGC-1α splice variants in human skeletal muscle and the possible influence of metabolic perturbation on this response. The subjects exercised one leg for 45 min with restricted blood flow (R-leg), followed by 45 min of exercise using the other leg at the same absolute workload but with normal blood flow (NR-leg). This ischemic model (R-leg) has been shown previously to induce a greater metabolic perturbation and enhance the expression of PGC-1α beyond that observed in the NR-leg. Cultured human myotubes were used to test suggested exercise-induced regulatory stimuli of PGC-1α. We showed, for the first time, that transcripts from both the canonical promoter (PGC-1α-a) and the proposed upstream-located promoter (PGC-1α-b) are present in human skeletal muscle. Both transcripts were upregulated after exercise in the R-leg, but the fold change increase of PGC-1α-b was much greater than that of PGC-1α-a. No differences were observed between the two conditions regarding the marker for calcineurin activation, MCIP1, or p38 phosphorylation. AMPK phosphorylation increased to a greater extent in the R-leg, and AICAR stimulation of cultured human myotubes induced the expression of PGC-1α-a and PGC-1α-b. AICAR combined with norepinephrine yielded an additive effect on the PGC-1α-b expression only. Our results indicate clearly that exercise can activate an upstream promoter in humans and support AMPK as a major regulator of transcripts from the canonical PGC-1α promoter and the involvement of ß-adrenergic stimulation in combination with AMPK in the regulation of PGC-1α-b.
Assuntos
Processamento Alternativo , Proteínas de Transporte/genética , Exercício Físico/fisiologia , Proteínas de Choque Térmico/genética , Músculo Esquelético/metabolismo , Fatores de Transcrição/genética , Adenilato Quinase/metabolismo , Adenilato Quinase/fisiologia , Adulto , Processamento Alternativo/efeitos dos fármacos , Processamento Alternativo/genética , Processamento Alternativo/fisiologia , Aminoimidazol Carboxamida/análogos & derivados , Aminoimidazol Carboxamida/farmacologia , Biópsia , Proteínas de Transporte/metabolismo , Células Cultivadas , Proteínas de Choque Térmico/metabolismo , Humanos , Masculino , Músculo Esquelético/irrigação sanguínea , Músculo Esquelético/efeitos dos fármacos , Músculo Esquelético/patologia , Coativador 1-alfa do Receptor gama Ativado por Proliferador de Peroxissomo , Cultura Primária de Células , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Proteínas de Ligação a RNA , Ribonucleotídeos/farmacologia , Fatores de Transcrição/metabolismo , Regulação para Cima/fisiologia , Adulto JovemRESUMO
A high potential for lipid oxidation is a sign of metabolic fitness and is important not only for exercise performance but also for health promotion. Despite considerable progress during recent years, our understanding of how lipid oxidation is controlled remains unclear. The rate of lipid oxidation reaches a peak at 50-60% of V(O2 max) after which the contribution of lipids decreases both in relative and absolute terms. In the high-intensity domain (>60% V(O2 max)), there is a pronounced decrease in energy state, which will stimulate the glycolytic rate in excess of the substrate requirements of mitochondrial oxidative processes. Accumulation of glycolytic products will impair lipid oxidation through an interaction with the carnitine-mediated transfer of FA into mitochondria. Another potential site of control is Acyl-CoA synthetase (ACS), which is the initial step in FA catabolism. The activity of ACS may be under control of CoASH and energy state. There is evidence that additional control points exist beyond mitochondrial influx of fatty acids. The electron transport chain (ETC) with associated feed-back control by redox state is one suggested candidate. In this review it is suggested that the control of FA oxidation during heavy exercise is distributed between ACS, CPT1, and ETC.