Begum N, Song Y, Rienzie J, Ragolia L
The Diabetes Research Laboratory, Winthrop University Hospital, Mineola, ny 11501, USA. 11574, USA.
Am J Physiol. 1998 Jul;275(1):C42-9. doi: 10.1152/ajpcell.1998.275.1.C42.
Hyperinsulinemia (HI) and insulin resistance (IR) are frequently associated with hypertension and atherosclerosis. However, the exact roles of HI and IR in the development of hypertension are unclear. Mitogen-activated protein kinases (MAPK) are well-characterized intracellular mediators of cell proliferation. In this study, we examined the contribution of MAPK pathway in insulin-stimulated mitogenesis using primary vascular smooth muscle cells (VSMCs) isolated from aortas of normotensive Wistar-Kyoto rats (WKY) and spontaneous hypertensive rats (SHR). VSMCs were grown to confluence in culture, serum starved, and examined for DNA synthesis (using [3H]thymidine (TDR), immunoprecipitated MAPK activity, and MAPK phosphatase (MKP-1) induction). Basal rate of TDR incorporation into DNA was twofold higher in SHR compared with WKY (P < 0.005). Insulin caused a dose-dependent increase in TDR incorporation (150% over basal levels with 100 nM in 12 h). Stimulation was sustained for 24 h with a decline toward basal in 36 h. Pretreatment with insulin-like growth factor I (IGF-I) receptor antibody did not abolish mitogenesis mediated by 10-100 nM insulin, suggesting that insulin effect is mediated via its own receptors. Insulin had a small mitogenic effect in WKY (33% over basal). Insulin-stimulated mitogenesis was accompanied by a dose-dependent increase in MAPK activity in SHR, with a peak activation (>2-fold over basal) between 5 and 10 min with 100 nM insulin. Insulin had very small effects on MAPK activity in WKY. In contrast, serum-stimulated MAPK activation was comparable in WKY and SHR. Pretreatment with MEK inhibitor, PD-98059, completely blocked insulin's effect on MAPK activation and mitogenesis. Inhibition of phosphatidylinositol 3-kinase with wortmannin also prevented insulin's effects on MAPK activation and mitogenesis. In WKY, insulin and IGF-I treatment resulted in a rapid induction of MKP-1, the dual-specificity MAPK phosphatase. In contrast, VSMCs from SHR were resistant to insulin with respect to MPK-1 expression. We conclude that insulin is mitogenic in SHR, and the effect appears to be mediated by sustained MAPK activation due to impaired insulin-mediated MKP-1 mRNA expression, which may act as an inhibitory feedback loop in attenuating MAPK signaling.
高胰岛素血症（HI）和胰岛素抵抗（IR）常与高血压和动脉粥样硬化相关。然而，HI和IR在高血压发生发展中的确切作用尚不清楚。丝裂原活化蛋白激酶（MAPK）是细胞增殖中特征明确的细胞内介质。在本研究中，我们使用从正常血压的Wistar-Kyoto大鼠（WKY）和自发性高血压大鼠（SHR）主动脉分离的原代血管平滑肌细胞（VSMC），研究了MAPK途径在胰岛素刺激的有丝分裂中的作用。VSMC在培养中生长至汇合，血清饥饿，然后检测DNA合成（使用[3H]胸苷（TDR））、免疫沉淀的MAPK活性和MAPK磷酸酶（MKP-1）诱导情况。与WKY相比，SHR中TDR掺入DNA的基础速率高两倍（P<0.005）。胰岛素导致TDR掺入呈剂量依赖性增加（12小时内100 nM时比基础水平高150%）。刺激持续24小时，36小时时降至基础水平。用胰岛素样生长因子I（IGF-I）受体抗体预处理并未消除10 - 100 nM胰岛素介导的有丝分裂，这表明胰岛素效应是通过其自身受体介导的。胰岛素在WKY中有较小的促有丝分裂作用（比基础水平高33%）。胰岛素刺激的有丝分裂伴随着SHR中MAPK活性的剂量依赖性增加，100 nM胰岛素作用下5至10分钟时激活峰值（比基础水平高>2倍）。胰岛素对WKY中的MAPK活性影响非常小。相比之下，血清刺激的MAPK激活在WKY和SHR中相当。用MEK抑制剂PD - 98059预处理完全阻断了胰岛素对MAPK激活和有丝分裂的作用。用渥曼青霉素抑制磷脂酰肌醇3 -激酶也阻止了胰岛素对MAPK激活和有丝分裂的作用。在WKY中，胰岛素和IGF - I处理导致双特异性MAPK磷酸酶MKP - 1的快速诱导。相比之下，SHR的VSMC在MPK - 1表达方面对胰岛素有抗性。我们得出结论，胰岛素在SHR中具有促有丝分裂作用，并且该效应似乎是由于胰岛素介导的MKP - 1 mRNA表达受损导致MAPK持续激活所介导的，MKP - 1可能作为一种抑制性反馈环来减弱MAPK信号传导。
