Mitochondrial transcription factor A and respiratory complex IV increase in response to exercise training in humans

Protein levels of mitochondrial transcription factor A (Tfam) and nuclear- and mitochondrial-encoded subunits of respiratory chain complex IV (COX I a nd COX IV) as well as citrate synthase activity were analysed in muscle bio psy samples of vastus lateralis in six healthy male subjects before and aft er 4 weeks of one-legged cycle training. One leg was trained with restricte d blood flow. The other leg was trained with the same power profile but wit h non-restricted blood flow. Tfam, COX I and COX IV levels all increased wi th training, with no differences observed between the legs. The training-in duced increase in citrate synthase activity was greater in the leg trained with restricted blood flow. These findings indicate that changed expression of Tfam protein could be one mechanism of exercise-induced mitochondrial b iogenesis. The increases of COX I and COX IV indicate a concurrent increase of nuclear- and mitochondrial-encoded subunits of respiratory enzyme compl ex IV at the protein level in skeletal muscle in response to increased musc le activity. In this study, it was not possible to demonstrate that the gre ater energy disturbance induced by reduced blood flow further stimulates th e expression of mitochondrial proteins, even though it did cause a greater enhancement of citrate synthase activity in concordance with earlier studie s.