Choi Inho, Lee Kisoo, Kim Myungjoo, Lee Moonyong, Park Kyoungsook
Department of Life Science, College of Liberal Arts and Science, Yonsei University, Wonju, Republic of Korea.
J Cell Biochem. 2005 Dec 15;96(6):1231-43. doi: 10.1002/jcb.20616.
Skeletal muscle undergoes a significant reduction in tension upon unloading. To explore intracellular signalling mechanisms underlying this phenomenon, we investigated twitch tension, the ratio of actin/myosin filaments, and activities of key signalling molecules in rat soleus muscle during a 3-week hindlimb suspension and 2-week reloading. Twitch tension and myofilament ratio (actin/myosin) gradually decreased during unloading but progressively recovered to initial levels during reloading. To study the involvement of stress-responsive signalling proteins during these changes, the activities of protein kinase C alpha (PKCalpha) and three mitogen-activated protein kinases (MAPKs)--c-Jun NH2-terminal kinase (JNK), extracellular signal-regulated protein kinase (ERK), and p38 MAPK--were examined using immunoblotting and immune complex kinase assays. PKCalpha phosphorylation correlated positively with the tension (Pearson's r = 0.97, P < 0.001) and the myofilament ratio (r = 0.83, P < 0.01) over the entire unloading and reloading period. Treatment of the soleus muscle with a PKC activator resulted in a similar paralleled increment in both PKCalpha phosphorylation and the alpha-sarcomeric actin expression. The three MAPKs differed in the pattern of activation in that JNK activity peaked only for the first hours of reloading, whereas ERK and p38 MAPK activities remained elevated during reloading. These results suggest that PKCalpha may play a pivotal role in converting loading stress to intracellular changes in contractile proteins that determine muscle tension. Differential activation of MAPKs may also help alleviate muscle damage, modulate energy transport and/or regulate the expression of contractile proteins upon altered loading.
卸载时骨骼肌张力会显著降低。为了探究这一现象背后的细胞内信号传导机制，我们研究了大鼠比目鱼肌在3周后肢悬吊和2周重新加载过程中的单收缩张力、肌动蛋白/肌球蛋白丝比例以及关键信号分子的活性。卸载过程中单收缩张力和肌丝比例（肌动蛋白/肌球蛋白）逐渐降低，但在重新加载过程中逐渐恢复到初始水平。为了研究应激反应信号蛋白在这些变化中的作用，我们使用免疫印迹和免疫复合物激酶测定法检测了蛋白激酶Cα（PKCα）和三种丝裂原活化蛋白激酶（MAPK）——c-Jun氨基末端激酶（JNK）、细胞外信号调节蛋白激酶（ERK）和p38 MAPK的活性。在整个卸载和重新加载期间，PKCα磷酸化与张力呈正相关（Pearson相关系数r = 0.97，P < 0.001），与肌丝比例也呈正相关（r = 0.83，P < 0.01）。用PKC激活剂处理比目鱼肌会导致PKCα磷酸化和α-肌节肌动蛋白表达出现类似的平行增加。三种MAPK的激活模式不同，JNK活性仅在重新加载的最初几个小时达到峰值，而ERK和p38 MAPK活性在重新加载期间持续升高。这些结果表明，PKCα可能在将加载应力转化为决定肌肉张力的收缩蛋白的细胞内变化中起关键作用。MAPK的差异激活也可能有助于减轻肌肉损伤、调节能量转运和/或在加载改变时调节收缩蛋白的表达。
