Inserm, U674, Paris, France.
Diabetes Metab. 2010 Apr;36(2):120-8. doi: 10.1016/j.diabet.2009.09.004. Epub 2010 Feb 10.
The mechanisms underlying the age-related decrease in insulin-receptor (IR) binding in genetically obese Zucker rats are not well understood. For this reason, the present study analyzed the expression of IR mRNA and protein in selected tissues from 1- to 4-month-old obese (fa/fa) Zucker rats and lean (Fa/-) age-matched controls.
The following parameters were evaluated: (1) IR mRNA level, and proportion of isotypes A (exon 11-) and B (exon 11+) of IR mRNA in liver, brain and kidney; (2) level, molecular size and tyrosine phosphorylation of IR-beta subunit in liver subcellular fractions; and (3) stability of liver IR based on sensitivity in vivo of insulin-binding activity and IR-beta levels in response to tunicamycin, a glycosylation inhibitor.
At one month, IR mRNA level was increased in liver and brain, but decreased in kidneys and, at four months, both mRNA level and isotype B proportion were decreased in liver. From age two months, the following changes in liver IR protein expression were observed: (1) decreased IR-beta level in whole homogenates, but increased IR-beta levels in endosomal fractions; (2) increased IR-beta tyrosine phosphorylation; and (3) at four months, increased levels of both intact IR-beta (95 kDa) and IR-beta fragments (72 and 52 kDa) in lysosomal fractions, along with decreased stability in vivo of the IR.
These data show that obese Zucker rats display age-related alterations of IR gene expression at both pre- and post-translational stages and, in particular, increased endocytosis and degradation of IR protein.
胰岛素受体（IR）结合在遗传肥胖 Zucker 大鼠中随年龄下降的机制尚不清楚。因此，本研究分析了 1 至 4 月龄肥胖（fa/fa） Zucker 大鼠和同龄 lean（Fa/-）对照大鼠各组织中 IR mRNA 和蛋白的表达。
评估了以下参数：（1）肝、脑和肾中 IR mRNA 的水平和异构体 A（外显子 11-）和 B（外显子 11+）的比例；（2）肝亚细胞组分中 IR-β 亚基的水平、分子大小和酪氨酸磷酸化；（3）基于胰岛素结合活性和 IR-β 水平对 tunicamycin（一种糖基化抑制剂）的体内敏感性，检测肝 IR 的稳定性。
在 1 月龄时，IR mRNA 的水平在肝和脑中增加，但在肾脏中降低，而在 4 月龄时，肝中 IR mRNA 的水平和 B 型异构体的比例均降低。从 2 月龄开始，观察到肝 IR 蛋白表达的以下变化：（1）整个匀浆中 IR-β 水平降低，但内体部分的 IR-β 水平增加；（2）IR-β 酪氨酸磷酸化增加；（3）在 4 月龄时，溶酶体部分中完整的 IR-β（95 kDa）和 IR-β 片段（72 和 52 kDa）水平增加，同时体内 IR 的稳定性降低。
这些数据表明，肥胖 Zucker 大鼠在翻译前和翻译后阶段均表现出与年龄相关的 IR 基因表达改变，特别是 IR 蛋白的内吞和降解增加。
