Hurrell D G, Pedersen O, Kahn C R
Department of Medicine, Brigham and Women's Hospital, Boston, Massachusetts.
Endocrinology. 1989 Nov;125(5):2454-62. doi: 10.1210/endo-125-5-2454.
Obesity is associated with insulin resistance and type II diabetes mellitus. In the present study, we have characterized hepatic insulin receptor function in two animal models of obesity: the Zucker fatty rat (ZFR), a model of genetic obesity with severe hyperinsulinemia, and the Sprague-Dawley rat with dietary obesity, a model of acquired obesity. Zucker fatty rats were also treated with streptozotocin (STZ) in an effort to examine the effects of relative insulin deficiency and hyperglycemia in the setting of obesity. Using wheat germ agglutinin-purified insulin receptor extracted from liver, no significant difference in insulin binding was identified in either model of obesity. beta-Subunit autophosphorylation was significantly decreased in both obese models relative to that in controls (72% in the obese ZFR and 49% in the overfed Sprague-Dawley model). Kinase activity, as measured by phosphorylation of the 1142-1153 synthetic peptide, was also decreased in both models of obesity by 22% and 64%, respectively. In the Zucker rat, STZ treatment led to an 80% increase in receptor concentration and a further 70% increase in beta-subunit autophosphorylation per receptor, whereas tyrosine kinase activity toward substrate was not altered. Since kinase activity is closely linked to autophosphorylation, we determined the fraction of autophosphorylated (activated) receptors vs. non-phosphorylated (inactive) receptors by using antiphosphotyrosine antibody to precipitate receptors bound with [125I]insulin. There was no significant difference in the percentage of activated insulin receptors in the dietary obese, ZFR, or STZ-treated Zucker rat vs. that in the controls. In all models, the percentage of activated receptors ranged from 32-46% of the total receptor pool. These data suggest that in genetic and acquired obesity, autophosphorylation of the beta-subunit is reduced and is a limiting factor in insulin receptor activation. A similar fraction of all receptors appears to undergo some level of autophosphorylation; however, full autophosphorylation and, thus, activation of the receptor do not occur, and this results in a decrease in kinase activity. This block in autophosphorylation may account for significant reductions in insulin receptor kinase function in obesity.
肥胖与胰岛素抵抗及II型糖尿病相关。在本研究中，我们已对两种肥胖动物模型的肝脏胰岛素受体功能进行了表征：Zucker肥胖大鼠（ZFR），一种伴有严重高胰岛素血症的遗传性肥胖模型，以及饮食性肥胖的Sprague-Dawley大鼠，一种获得性肥胖模型。还对Zucker肥胖大鼠用链脲佐菌素（STZ）进行处理，以研究在肥胖背景下相对胰岛素缺乏和高血糖的影响。使用从肝脏中提取的麦胚凝集素纯化的胰岛素受体，在两种肥胖模型中均未发现胰岛素结合有显著差异。相对于对照组，两种肥胖模型中的β亚基自身磷酸化均显著降低（肥胖的ZFR中为72%，过度喂养的Sprague-Dawley模型中为49%）。通过1142 - 1153合成肽的磷酸化来测定的激酶活性，在两种肥胖模型中也分别降低了22%和64%。在Zucker大鼠中，STZ处理导致受体浓度增加80%，并且每个受体的β亚基自身磷酸化进一步增加70%，而针对底物的酪氨酸激酶活性未改变。由于激酶活性与自身磷酸化密切相关，我们使用抗磷酸酪氨酸抗体沉淀与[125I]胰岛素结合的受体，从而确定自身磷酸化（活化）受体与未磷酸化（无活性）受体的比例。饮食性肥胖大鼠、ZFR或经STZ处理的Zucker大鼠中活化胰岛素受体的百分比与对照组相比无显著差异。在所有模型中，活化受体的百分比占总受体池的32 - 46%。这些数据表明，在遗传性和获得性肥胖中，β亚基的自身磷酸化减少，并且是胰岛素受体激活的限制因素。似乎所有受体中有相似比例的受体经历了一定程度的自身磷酸化；然而，受体并未发生完全自身磷酸化，因此也未被激活，这导致激酶活性降低。这种自身磷酸化的阻断可能是肥胖中胰岛素受体激酶功能显著降低的原因。
