Avignon A, Yamada K, Zhou X, Spencer B, Cardona O, Saba-Siddique S, Galloway L, Standaert M L, Farese R V
J. A. Haley Veterans' Hospital, Tampa, Florida 33612, USA.
Diabetes. 1996 Oct;45(10):1396-404. doi: 10.2337/diab.45.10.1396.
We examined the possibility that protein kinase C (PKC) is chronically activated and may contribute to impaired glycogen synthesis and insulin resistance in soleus muscles of hyperinsulinemic type II diabetic Goto-Kakizaki (GK) rats. Relative to nondiabetic controls, PKC enzyme activity and levels of immunoreactive PKC-alpha, beta, epsilon, and delta were increased in membrane fractions and decreased cytosolic fractions of GK soleus muscles. In addition, PKC-theta levels were decreased in both membrane and cytosol fractios, whereas PKC-zeta levels were not changed in either fraction in GK soleus muscles. These increases in membrane PKC (alpha, beta, epsilon, and delta) could not be accounted for by alterations in PKC mRNA or total PKC levels but were associated with increases in membrane diacylglycerol (DAG) and therefore appeared to reflect translocative activation of PKC. In evaluation of potential causes for persistent PKC activation, membrane PKC levels were decreased in soleus muscles of hyperglycemic streptozotocin (STZ)-induced diabetic rats; thus, a role for simple hyperglycemia as a cause of PKC activation in GK rats was not evident in the STZ model. In support of the possibility that hyperinsulinemia contributed to PKC activation in GK soleus muscles, we found that DAG levels were increased, and PKC was translocated, in soleus muscles of both (1) normoglycemic hyperinsulinemic obese/aged rats and (2) mildly hyperglycemic hyperinsulinemic obese/Zucker rats. In keeping with the possibility that PKC activation may contribute to impaired glycogen synthase activation in GK muscles, phorbol esters inhibited, and a PKC inhibitor, RO 31-8220, increased insulin effects on glycogen synthesis in soleus muscles incubated in vitro. Our findings suggested that: (1) hyperinsulinemia, as observed in type II diabetic GK rats and certain genetic and nongenetic forms of obesity in rats, is associated with persistent translocation and activation of PKC in soleus muscles, and (2) this persistent PKC activation may contribute to impaired glycogen synthesis and insulin resistance.
我们研究了蛋白激酶C（PKC）长期激活并可能导致高胰岛素血症II型糖尿病Goto-Kakizaki（GK）大鼠比目鱼肌糖原合成受损和胰岛素抵抗的可能性。相对于非糖尿病对照组，GK比目鱼肌膜组分中的PKC酶活性以及免疫反应性PKC-α、β、ε和δ水平升高，而胞质组分中的水平降低。此外，GK比目鱼肌膜和胞质组分中的PKC-θ水平均降低，而PKC-ζ水平在这两个组分中均未改变。膜PKC（α、β、ε和δ）的这些升高不能用PKC mRNA或总PKC水平的改变来解释，但与膜二酰甘油（DAG）的增加有关，因此似乎反映了PKC的易位激活。在评估PKC持续激活的潜在原因时，高血糖链脲佐菌素（STZ）诱导的糖尿病大鼠比目鱼肌中的膜PKC水平降低；因此，在STZ模型中，单纯高血糖作为GK大鼠PKC激活原因的作用并不明显。为支持高胰岛素血症导致GK比目鱼肌中PKC激活的可能性，我们发现：（1）正常血糖高胰岛素血症肥胖/老年大鼠和（2）轻度高血糖高胰岛素血症肥胖/Zucker大鼠的比目鱼肌中DAG水平升高且PKC发生易位。与PKC激活可能导致GK肌肉中糖原合酶激活受损的可能性一致，佛波酯抑制体外培养的比目鱼肌中胰岛素对糖原合成的作用，而PKC抑制剂RO 31-8220则增强该作用。我们的研究结果表明：（1）如在II型糖尿病GK大鼠以及大鼠某些遗传和非遗传形式的肥胖中观察到的高胰岛素血症，与比目鱼肌中PKC的持续易位和激活有关；（2）这种持续的PKC激活可能导致糖原合成受损和胰岛素抵抗。
