Sakamoto Kei, Aschenbach William G, Hirshman Michael F, Goodyear Laurie J
Research Division, Joslin Diabetes Center and Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts 02215, USA.
Am J Physiol Endocrinol Metab. 2003 Nov;285(5):E1081-8. doi: 10.1152/ajpendo.00228.2003. Epub 2003 Jul 1.
Akt/protein kinase B is a serine/threonine kinase that has emerged as a critical signaling component for mediating numerous cellular responses. Contractile activity has recently been demonstrated to stimulate Akt signaling in skeletal muscle. Whether physiological exercise in vivo activates Akt is controversial, and the initiating factors that result in the stimulation of Akt during contractile activity are unknown. In the current study, we demonstrate that treadmill running exercise of rats using two different protocols (intermediate high or high-intensity exhaustive exercise) significantly increases Akt activity and phosphorylation in skeletal muscle composed of various fiber types. To determine if Akt activation during contractile activity is triggered by mechanical forces applied to the skeletal muscle, isolated skeletal muscles were incubated and passively stretched. Passive stretch for 10 min significantly increased Akt activity (2-fold) in the fast-twitch extensor digitorum longus (EDL) muscle. However, stretch had no effect on Akt in the slow-twitch soleus muscle, although there was a robust phosphorylation of the stress-activated protein kinase p38. Similar to contraction, stretch-induced Akt activation in the EDL was fully inhibited in the presence of the phosphatidylinositol 3-kinase inhibitor wortmannin, whereas glycogen synthase kinase-3 (GSK3) phosphorylation was only partially inhibited. Stretch did not cause dephosphorylation of glycogen synthase on GSK3-targeted sites in the absence or presence of wortmannin. We conclude that physiological exercise in vivo activates Akt in multiple skeletal muscle fiber types and that mechanical tension may be a part of the mechanism by which contraction activates Akt in fast-twitch muscles.
Akt/蛋白激酶B是一种丝氨酸/苏氨酸激酶，已成为介导多种细胞反应的关键信号成分。最近有研究表明，收缩活动可刺激骨骼肌中的Akt信号传导。体内的生理性运动是否会激活Akt仍存在争议，且在收缩活动期间导致Akt被刺激的起始因素尚不清楚。在本研究中，我们证明，使用两种不同方案（中等高强度或高强度力竭运动）对大鼠进行跑步机跑步运动，可显著增加由各种纤维类型组成的骨骼肌中的Akt活性和磷酸化水平。为了确定收缩活动期间Akt的激活是否由施加于骨骼肌的机械力触发，对分离的骨骼肌进行孵育并被动拉伸。对快肌趾长伸肌（EDL）进行10分钟的被动拉伸可显著增加Akt活性（2倍）。然而，拉伸对慢肌比目鱼肌中的Akt没有影响，尽管应激激活蛋白激酶p38发生了强烈的磷酸化。与收缩类似，在磷脂酰肌醇3激酶抑制剂渥曼青霉素存在的情况下，EDL中拉伸诱导的Akt激活被完全抑制，而糖原合酶激酶-3（GSK3）的磷酸化仅被部分抑制。在不存在或存在渥曼青霉素的情况下，拉伸均未导致GSK3靶向位点上糖原合酶的去磷酸化。我们得出结论，体内的生理性运动可激活多种骨骼肌纤维类型中的Akt，并且机械张力可能是收缩在快肌中激活Akt的机制的一部分。
