Expression and function of receptors for insulin-like growth factor-I and insulin in human coronary artery smooth muscle cells

Aims/hypothesis: Hyperinsulinaemia and insulin resistance, as well as low IGF-I, have been implicated in the pathogenesis of cardiovascular disease. Little is known about direct effects of IGF-I and insulin on human coronary artery smooth muscle cells (HCASMCs). Our aim was to characterise the expression and function of IGF-I receptor (IGF-IR) and insulin receptor (IR) in HCASMCs. Materials and methods: Cultured HCASMCs were used. mRNA expression was measured by quantitative real-time RT-PCR analysis. Receptor proteins, phosphorylation of beta-subunits and the presence of hybrid IR/IGF-IR were analysed by immunoprecipitation and western blotting. DNA synthesis and glucose metabolism were assessed using [H-3] thymidine incorporation and D-[U-C-14] glucose accumulation respectively. Results: The mRNA expression of IGF-IR was approximately eight-fold higher than that of IR in HCASMCs. The presence of IGF-IR and IR could be demonstrated by immunoprecipitation and western blot analysis. Phosphorylation of the IGF-IR beta-subunit was obtained by IGF-I at 10(-10) - 10(-8) mol/l and insulin at 10(-8) mol/l. Insulin and IGF-I at 10(-10) - 10(-9) mol/l phosphorylated the IR beta-subunit. When immunoprecipitated with monoclonal anti-IR alpha-subunit or IGF-IR alpha-subunit antibodies, we found bands in slightly different positions, suggesting the presence of hybrid IR/IGF-IR. IGF-I at 10(-9) - 10(-8) mol/l significantly stimulated [H-3] thymidine incorporation and at a concentration of 10(-9) - 10(-7) mol/l also D-[U-C-14] glucose accumulation in HCASMCs. Insulin at 10- 9 - 10- 7 mol/ l had no effect on DNA synthesis, but increased glucose accumulation at 10(-7) mol/l. Conclusions/ interpretation: Our study provides experimental evidence that IGF-IR and possibly hybrid IR/IGF-IR play a role in HCASMCs.