Higginson James, Wackerhage Henning, Woods Niall, Schjerling Peter, Ratkevicius Aivaras, Grunnet Niels, Quistorff Bjørn
Muscle Research Group, Department of Biological Sciences, University of Central Lancashire, Preston PR1 2HE, UK.
Pflugers Arch. 2002 Dec;445(3):437-43. doi: 10.1007/s00424-002-0939-1. Epub 2002 Oct 24.
Activation of either the calcineurin or the extracellular signal-regulated kinase (ERK1/2) pathway increases the percentage of slow fibres in vivo suggesting that both pathways can regulate fibre phenotypes in skeletal muscle. We investigated the effect of calcineurin blockade with cyclosporin A and mitogen-activated protein kinase kinase (MEK1/2) blockade with U0126 upon myosin heavy chain (MHC) isoform mRNA levels and activities of metabolic enzymes after 1 day, 3 days and 7 days of treatment in primary cultures of spontaneously twitching rat skeletal muscle. U0126 treatment significantly decreased MHC Ibeta mRNA levels and significantly increased MHC IIX, MHC IIB, embryonal MHC and perinatal MHC mRNA levels when compared to control. In addition, U0126 treatment significantly increased lactate dehydrogenase, creatine kinase, hexokinase, malate dehydrogenase and beta-hydroxyacyl-CoA dehydrogenase activities above control values while a significant reduction in the percentage of pyruvate dehydrogenase in the active form was also observed. Calcineurin blockade significantly decreased both MHC Ibeta and embryonal mRNA levels below control and significantly increased MHC IIX mRNA levels. Significant increases in the activities of both lactate dehydrogenase and creatine kinase above control values were also seen following cyclosporin A treatment. In conclusion, the results suggest that calcineurin upregulates slow-fibre genes and suppresses fast-fibre genes. Similarly, the ERK1/2 pathway upregulates slow-fibre MHC and suppresses fast-fibre MHC isoforms. However, the effect on enzyme activities is not fibre-type specific. The effect of U0126 on the percentage of pyruvate dehydrogenase in the active form suggests that the ERK1/2 pathway may also be involved in regulation of the phosphorylation state of this enzyme.
钙调神经磷酸酶或细胞外信号调节激酶（ERK1/2）通路的激活会增加体内慢肌纤维的比例，这表明两条通路均可调节骨骼肌的纤维表型。我们研究了用环孢素A阻断钙调神经磷酸酶以及用U0126阻断丝裂原活化蛋白激酶激酶（MEK1/2），对自发抽搐的大鼠骨骼肌原代培养物进行1天、3天和7天治疗后，肌球蛋白重链（MHC）亚型mRNA水平和代谢酶活性的影响。与对照组相比，U0126治疗显著降低了MHC Iβ mRNA水平，并显著增加了MHC IIX、MHC IIB、胚胎型MHC和围生期MHC mRNA水平。此外，U0126治疗使乳酸脱氢酶、肌酸激酶、己糖激酶、苹果酸脱氢酶和β-羟酰基辅酶A脱氢酶的活性显著高于对照值，同时还观察到活性形式的丙酮酸脱氢酶百分比显著降低。钙调神经磷酸酶阻断使MHC Iβ和胚胎型mRNA水平均显著低于对照，并显著增加了MHC IIX mRNA水平。环孢素A治疗后，乳酸脱氢酶和肌酸激酶的活性也显著高于对照值。总之，结果表明钙调神经磷酸酶上调慢肌纤维基因并抑制快肌纤维基因。同样，ERK1/2通路上调慢肌纤维MHC并抑制快肌纤维MHC亚型。然而，对酶活性的影响并非纤维类型特异性的。U0126对活性形式丙酮酸脱氢酶百分比的影响表明，ERK1/2通路可能也参与了该酶磷酸化状态的调节。
