Nordt T K, Schneider D J, Sobel B E
Cardiovascular Division, Washington University School of Medicine, St Louis, Mo. 63110.
Circulation. 1994 Jan;89(1):321-30. doi: 10.1161/01.cir.89.1.321.
Both vascular disease and elevated concentrations in plasma of plasminogen activator inhibitor type-1 (PAI-1) are prominent in patients with non-insulin-dependent diabetes mellitus (NIDDM). We and others have hypothesized that the increased PAI-1 may contribute to acceleration of atherosclerosis in this condition and in other states characterized by insulin resistance as well. Surprisingly, however, elevations of PAI-1 decrease when type II diabetic patients are treated with exogenous insulin, as do circulating concentrations of the precursor of insulin, proinsulin, in plasma. Accordingly, the increased PAI-1 in patients with NIDDM may reflect effects of precursors of insulin rather than or in addition to those of insulin itself. To assess this possibility directly, this study was performed to identify potential direct effects of proinsulin and proinsulin split products on synthesis of PAI-1 in liver cells, thought to be the major source of circulating PAI-1 in vivo.
Hep G2 cells (highly differentiated human hepatoma cells) were exposed to human proinsulin, des(31,32)proinsulin and des(64,65)proinsulin (split products of proinsulin), or C-peptide. Accumulation of PAI-1 in conditioned media increased in a time- and concentration-dependent fashion in response to the two des-intermediates [3.3-fold with des(31,32)proinsulin and 4.5-fold with des(64,65)proinsulin]. C-peptide elicited no increase. Stimulation was transduced at least in part by the insulin receptor as shown by inhibition of stimulation by insulin receptor antibodies, mediated at the level of PAI-1 gene expression as shown by the 2.2- to 2.9-fold increases in steady-state concentrations of PAI-1 mRNA, and indicative of newly synthesized protein as shown by results in metabolic labeling experiments.
Our results are consistent with the hypothesis that precursors of insulin (proinsulin and proinsulin split products), known to be present in relatively high concentrations in plasma in patients with NIDDM and conditions characterized by insulin resistance, may directly stimulate PAI-1 synthesis, thereby attenuating fibrinolysis and accelerating atherogenesis.
血管疾病以及纤溶酶原激活物抑制剂1型（PAI-1）的血浆浓度升高在非胰岛素依赖型糖尿病（NIDDM）患者中都很突出。我们和其他人曾推测，PAI-1升高可能导致这种情况下以及其他以胰岛素抵抗为特征的状态下动脉粥样硬化的加速。然而，令人惊讶的是，当II型糖尿病患者接受外源性胰岛素治疗时，PAI-1水平会下降，血浆中胰岛素前体胰岛素原的循环浓度也是如此。因此，NIDDM患者中PAI-1升高可能反映了胰岛素前体的作用，而非胰岛素本身的作用，或者是除胰岛素本身作用之外还反映了胰岛素前体的作用。为了直接评估这种可能性，本研究旨在确定胰岛素原和胰岛素原裂解产物对肝细胞中PAI-1合成的潜在直接影响，肝细胞被认为是体内循环PAI-1的主要来源。
将Hep G2细胞（高度分化的人肝癌细胞）暴露于人类胰岛素原、去（31,32）胰岛素原和去（64,65）胰岛素原（胰岛素原的裂解产物）或C肽。响应于两种去中间产物，条件培养基中PAI-1的积累呈时间和浓度依赖性增加[去（31,32）胰岛素原增加3.3倍，去（64,65）胰岛素原增加4.5倍]。C肽未引起增加。如胰岛素受体抗体抑制刺激所示，至少部分刺激是通过胰岛素受体转导的；如PAI-1 mRNA稳态浓度增加2.2至2.9倍所示，是在PAI-1基因表达水平介导的；如代谢标记实验结果所示，表明是新合成的蛋白质。
我们的结果与以下假设一致，即胰岛素前体（胰岛素原和胰岛素原裂解产物）在NIDDM患者和以胰岛素抵抗为特征的状态下血浆中浓度相对较高，可能直接刺激PAI-1合成，从而减弱纤维蛋白溶解并加速动脉粥样硬化的发生。
