Reynet C, Kahn C R, Loeken M R
Research Division, Joslin Diabetes Center, Boston, Massachusetts 02215, USA.
Diabetologia. 1996 Feb;39(2):183-9. doi: 10.1007/BF00403961.
Glycogen phosphorylase regulates the breakdown of glycogen into glucose, but as previous studies have demonstrated, the control of glycogen metabolism becomes deregulated in diabetes mellitus. Messenger RNA levels encoding several different proteins are altered in skeletal muscle biopsies of patients with insulin-dependent and non-insulin-dependent diabetes. The possible alteration of expression of the gene encoding the skeletal muscle isoform of glycogen phosphorylase during diabetes has not previously been investigated. We examined the effect of streptozotocin-induced diabetes and insulin treatment on glycogen phosphorylase mRNA in rat skeletal muscle; glycogen phosphorylase mRNA levels were elevated in diabetic rat muscle tissue, but were partially suppressed in diabetic rat muscle following insulin treatment. To distinguish between the effects of insulin and counter-regulatory hormones on glycogen phosphorylase mRNA levels, we employed differentiating rat L6 myoblasts in culture. Insulin stimulated the accumulation of glycogen phosphorylase mRNA as determined by Northern blot analysis. Moreover, insulin and dibutyryl cAMP stimulated expression of a transiently transfected chloramphenicol acetyl transferase reporter gene under the control of the muscle glycogen phosphorylase promoter in differentiating myotubes in culture, suggesting that the effects of insulin and counter-regulatory hormones on glycogen phosphorylase mRNA are at the level of transcription. These results suggest that insulin and epinephrine may participate in the induction of the glycogen phosphorylase gene during myogenesis; moreover, activation of this gene in muscle tissue may be a contributing factor in impaired glycogen storage during uncontrolled diabetes.
糖原磷酸化酶调节糖原分解为葡萄糖，但正如先前研究所表明的，糖尿病患者的糖原代谢控制会失调。在胰岛素依赖型和非胰岛素依赖型糖尿病患者的骨骼肌活检中，编码几种不同蛋白质的信使核糖核酸水平会发生改变。此前尚未研究糖尿病期间编码糖原磷酸化酶骨骼肌同工型的基因表达是否可能发生改变。我们研究了链脲佐菌素诱导的糖尿病和胰岛素治疗对大鼠骨骼肌中糖原磷酸化酶信使核糖核酸的影响；糖尿病大鼠肌肉组织中糖原磷酸化酶信使核糖核酸水平升高，但胰岛素治疗后糖尿病大鼠肌肉中的该水平部分受到抑制。为了区分胰岛素和反调节激素对糖原磷酸化酶信使核糖核酸水平的影响，我们在培养中使用了分化的大鼠L6成肌细胞。通过Northern印迹分析确定，胰岛素刺激了糖原磷酸化酶信使核糖核酸的积累。此外，胰岛素和二丁酰环磷腺苷在培养的分化肌管中，刺激了在肌肉糖原磷酸化酶启动子控制下瞬时转染的氯霉素乙酰转移酶报告基因的表达，这表明胰岛素和反调节激素对糖原磷酸化酶信使核糖核酸的影响是在转录水平。这些结果表明，胰岛素和肾上腺素可能参与了成肌过程中糖原磷酸化酶基因的诱导；此外，该基因在肌肉组织中的激活可能是糖尿病失控期间糖原储存受损的一个促成因素。
