Kinase-specific responsiveness to incremental contractile activity in skeletal muscle with low and high mitochondrial content

Abstract

Ljubicic V, Hood DA. Kinase-specific responsiveness to incremental contractile activity in skeletal muscle with low and high mitochondrial content. Am J Physiol Endocrinol Metab 295: E195-E204, 2008. First published May 20, 2008 doi:10.1152/ajpendo.90276.2008.-Muscle contractions activate protein kinases, leading to signal transduction. We hypothesized that kinase activation would be influenced by mitochondrial content, as well as by contractile activity-induced increases in muscle O 2 consumption (V O2). Kinase phosphorylation in high-oxidative red and low-oxidative white tibialis anterior (TA) muscle (RTA and WTA, respectively) with 2.5-fold differences in mitochondrial content were compared. Stimulation of the TA muscle elicited large increases in V O2 (3-to 6-fold and 4-to 60-fold above resting levels in WTA and RTA, respectively). At rest, AMP-activated protein kinase (AMPK), p38, p42, and p44 activation were nearly twofold greater in WTA than in RTA, suggesting an inverse relationship between mitochondrial content and kinase activation in resting muscle. During contractions, similar degrees of phosphorylation in RTA and WTA were evident as a function of V O2 for p38 and p42. During increases in V O2 up to sixfold above rest, greater responses were observed in RTA than in WTA for AMPK and p44, whereas Akt activation was greater in WTA. In RTA, elevations in V O2 elicited increases in AMPK and p44 activation, whereas Akt, p38, and p42 were less sensitive to increments in V O2. Reactive oxygen species (ROS) production was greater in mitochondria from white muscle, but when it was calculated in the context of the whole muscle, ROS production was twofold greater in red than in white myofibers. Thus mitochondrial content influences ROS production and is inversely related to kinase activation in resting muscle. During contractions, kinases are differentially sensitive to contraction-induced increments in V O2, suggesting that muscle mitochondrial content is important, but it is not the sole determinant of kinase activation during exercise of different intensities. muscle oxygen consumption; kinase activation; muscle plasticity; signal transduction; mitochondrial biogenesis WITHIN SECONDS OF THE ONSET of contractile activity in skeletal muscle, a number of rapid events occur that form part of the initial signaling process leading to downstream protein and lipid synthesis. These changes include Ca 2ϩ flux, ATP turnover, and stimulation of O 2 consumption (V O 2 ) within the contracting muscle cells. Accumulating evidence supports the link between chronic alterations in these conditions and distinctive programs of gene expression that establish phenotypic diversity among skeletal myofibers, such as hypertrophy or mitochondrial biogenesis. For example, raising cytosolic Ca 2ϩ

Contractile activity-induced mitochondrial biogenesis and mTORC1

“…For example, following endurance exercise, the phosphorylation of Akt is immediately increased, but subsequently becomes markedly reduced by 5 h into the recovery phase (43). We also noted this time-dependent phenomenon in other studies (23), and in the current investigation with respect to AMPK phosphorylation 2 h post-contractile activity. In addition, kinase activation is also typically reduced in response to contractile activity if mitochondrial content is elevated (24) within the muscle.…”

Control of Reactive Oxygen Species Production in Contracting Skeletal Muscle

“…The inability to activate NFjB in response to an acute contraction protocol is associated with severe attenuation of normal changes in expression of cytoprotective genes (36,47,62,76). We have shown that the increases in HSP content and antioxidant enzyme activities stimulated by isometric contractions in muscles of adult rodents were abolished in muscles of old rodents (76).…”

Sirtuin 1-mediated Effects of Exercise and Resveratrol on Mitochondrial Biogenesis

“…Immunoblotting-Protein extractions from frozen quadriceps sections were performed as described previously (32). Protein extracts of C2C12 myotubes or muscle homogenates were separated via electrophoresis through SDS-polyacrylamide gels and were then transferred to nitrocellulose membranes (Amersham Biosciences).…”

“…Myotubes-To document the effectiveness of RSV in differentiated muscle cells, we examined the phosphorylation of AMPK and p38 as early indicators of the onset of downstream metabolic effects, as is seen with acute contractile activity (32). Following short term RSV treatment (1 h), AMPK phosphorylation increased by 1.7-fold (p Ͻ 0.05), although p38 phosphorylation was not significantly increased ( Fig.…”