High dose insulin promotes the proliferation of vascular smooth muscle cells via AP-1/SM-α pathway

Proliferation of vascular smooth muscle cells (VSMCs) participates in multiple cardiovascular disorders, while the mechanism remains unclear. This study aims to investigate the effects of insulin on VSMC. Insulin was used to stimulate rat VSMCs, and the effects on cell cycle and proliferation were subsequently analyzed using flow cytometry. Furthermore, AP-1 and SM-alpha overexpression vectors were constructed and transfected into VSMCs. AP-1 and SM-alpha were inhibited by SR11302 and SM-alpha siRNA, respectively. The mRNA and protein expression levels were subsequently detected using the reverse-transcription quantitative polymerase chain reaction and western blotting, respectively. AP-1 and SM-alpha gene promoter binding sites were determined using luciferase and chromatin immunoprecipitation assays. As a result, we found that high dose of insulin promoted proliferation of VSMCs and increased the percentage of cells in the S phase by downregulating AP-1. AP-1 was identified to bind to the SM-alpha gene promoter at locus 2-177 to upregulate SM-alpha gene expression. Inhibition of AP-1 led to the decrease of SM-alpha expression. Overexpression of SM-alpha directly suppressed proliferation of VSMCs, while knocking it down promoted the process. Therefore, this study revealed that insulin downregulated the expression of the SM-alpha gene by inhibiting AP-1, which in turn facilitated proliferation of VSMCs.

Automated summary

The study revealed that high doses of insulin promoted VSMCs proliferation by downregulating AP-1, leading to an increase in cells in the S phase. AP-1 was found to bind to the SM-alpha gene promoter to upregulate SM-alpha gene expression. Overexpression of SM-alpha suppressed VSMCs proliferation, while knockdown of SM-alpha promoted it.