Qu X, Seale J P, Donnelly R
Department of Pharmacology, University of Sydney, Sydney, Australia.
J Endocrinol. 1999 Aug;162(2):207-14. doi: 10.1677/joe.0.1620207.
The mechanisms of insulin resistance in the obese Zucker rat have not been clearly established but increased diacylglycerol-protein kinase C (DAG-PKC) signalling has been associated with decreased glucose utilisation in states of insulin resistance and non-insulin-dependent diabetes mellitus. The purpose of this study was to characterise tissue- and isoform-selective differences in DAG-PKC signalling in insulin-sensitive tissues from obese Zucker rats, and to assess the effects of feeding on DAG-PKC pathways. Groups of male obese (fa/fa, n=24) and lean (fa/-, n=24) Zucker rats were studied after baseline measurements of fasting serum glucose, triglycerides, insulin and oral glucose tolerance tests. Liver, epididymal fat and soleus muscle samples were obtained from fed and overnight-fasted rats for measurements of DAG, PKC activity and individual PKC isoforms in cytosol and membrane fractions. Obese rats were heavier (488+/-7 vs 315+/-9 g) with fasting hyperglycaemia (10.5+/-0.8 vs 7.7+/-0.1 mM) and hyperinsulinaemia (7167+/-363 vs 251+/-62 pM) relative to lean controls. In fasted rats, PKC activity in the membrane fraction of liver was significantly higher in the obese group (174+/-16 vs 108+/-12 pmol/min/mg protein, P<0.05) but there were no differences in muscle and fat. The fed state was associated with increased DAG levels and threefold higher PKC activity in muscle tissue of obese rats, and increased expression of the major muscle isoforms, PKC-theta and PKC-epsilon: e.g. PKC activity in the membrane fraction of muscle from obese animals was 283+/-42 (fed) vs 107+/-20 pmol/min/mg protein (fasting) compared with 197+/-27 (fed) and 154+/-21 pmol/min/mg protein (fasting) in lean rats. In conclusion, hepatic PKC activity is higher in obese rats under basal fasting conditions and feeding-induced activation of DAG-PKC signalling occurs selectively in muscle of obese (fa/fa) rats due to increased DAG-mediated activation and/or synthesis of PKC-theta and PKC-epsilon. These changes in PKC are likely to exacerbate the hyperglycaemia and hypertriglyceridaemia associated with obesity-induced diabetes.
肥胖Zucker大鼠胰岛素抵抗的机制尚未完全明确，但二酰甘油-蛋白激酶C（DAG-PKC）信号增强与胰岛素抵抗和非胰岛素依赖型糖尿病状态下葡萄糖利用减少有关。本研究的目的是明确肥胖Zucker大鼠胰岛素敏感组织中DAG-PKC信号在组织和亚型上的选择性差异，并评估进食对DAG-PKC信号通路的影响。在对空腹血清葡萄糖、甘油三酯、胰岛素进行基线测量及口服葡萄糖耐量试验后，研究雄性肥胖（fa/fa，n = 24）和瘦型（fa/ -，n = 24）Zucker大鼠组。从进食和禁食过夜的大鼠获取肝脏、附睾脂肪和比目鱼肌样本，用于测量细胞溶质和膜组分中的DAG、PKC活性及各PKC亚型。相对于瘦型对照，肥胖大鼠体重更重（488±7 vs 315±9 g），伴有空腹高血糖（10.5±0.8 vs 7.7±0.1 mM）和高胰岛素血症（7167±363 vs 251±62 pM）。在禁食大鼠中，肥胖组肝脏膜组分中的PKC活性显著更高（174±16 vs 108±12 pmol/min/mg蛋白，P<0.05），但肌肉和脂肪中无差异。进食状态与肥胖大鼠肌肉组织中DAG水平升高及PKC活性高三倍相关，且主要肌肉亚型PKC-θ和PKC-ε的表达增加：例如，肥胖动物肌肉膜组分中的PKC活性在进食时为283±42（pmol/min/mg蛋白），禁食时为107±20，而瘦型大鼠在进食时为197±27，禁食时为154±21 pmol/min/mg蛋白。总之，在基础禁食条件下肥胖大鼠肝脏PKC活性更高，进食诱导的DAG-PKC信号激活在肥胖（fa/fa）大鼠肌肉中选择性发生，这是由于DAG介导的PKC-θ和PKC-ε激活和/或合成增加。PKC的这些变化可能会加重与肥胖诱导的糖尿病相关的高血糖和高甘油三酯血症。
