High-dose insulin inhibits gap junction intercellular communication in vascular smooth muscle cells

Gap junction intercellular communication (GJIC) is important in mediating intercellular substance and signal transmission. Connexin (Cx)43 is a major component involved in GJIC in vascular tissue and its abnormal expression is closely associated with various vascular diseases. Insulin resistance is the central component of metabolic syndrome, and high doses of insulin can affect vascular function through multiple pathways, resulting in cardiovascular disease. However, the effects of insulin on GJIC function and connexin (Cx)43 expression in vascular smooth muscle cells (VSMCs) remain unclear. Following treatment of VSMCs with different doses of insulin, a fluorescence recovery after photobleaching (FRAP) assay was performed to evaluate GJIC function in treated VSMCs. The results showed that high-dose insulin suppressed GJIC function. Western blot assays further demonstrated that high-dose insulin induced the phosphorylation of Cx43 at s368 and downregulated the expression of Cx43. H2O2 release assays demonstrated that high-dose insulin treatment significantly elevated the cellular H2O2 level. In addition, compared with cells treated with high-dose insulin, pretreatment with catalase significantly restored the cellular GJIC function, decreased the phosphorylation level of Cx43 at s368, and enhanced Cx43 expression. In conclusion, these data indicate that high-dose insulin inhibits cellular GJIC function through the oxidative stress-activated signaling pathway. This phenomenon may also constitute a potential mechanism underlying the pathogenesis of insulin resistance and its complications.