Insulin like growth factor-1 receptors mediate infragenicular vascular smooth muscle cell proliferation in response to glucose and insulin not by insulin receptors

PURPOSE: Vascular smooth muscle cell (VSMC) proliferation is an early event in the pathogenesis of atherosclerosis. Insulin and glucose are known to stimulate the growth of VSMC, Cell membrane receptors play an important role in the proliferation of VSMC in response to growth factors. Insulin and insulin-like growth factor-1 (IGF-1) have demonstrated a cross reactivity for receptor binding and function. By using monoclonal antibodies directed against insulin (IRA) and IGF-1 (IGF-IRA) receptors, we attempt to further delineate the mechanism for the proliferation of VSMC in response to insulin and glucose. METHODS: Human infragenicular VSMC isolated from diabetic patients undergoing below-knee amputations were used. Cells from passages 3 to 6 were grown in serum-free media with a glucose concentrations of 0.1% or 0.2%, both with and without insulin (100 ng/mL). The baseline cell density was 4,635 +/- 329 cells/mL, IRA or IGF-1RA was added to the media, with the control group receiving neither antibody. Cells were grown in 5% CO2 at 37 degrees C for 6 days. Analysis of variance was used for statistical analysis, with P <0.05 considered significant. In addition, DNA synthesis was measured using thymidine incorporation assays in the same groups of cells receiving IRA, IGF-IRA, and no antibody. RESULTS: IGF-1RA prevented the proliferation of VSMC in response to insulin and glucose, while IRA had no effect on cell growth. There was no significant growth when IGF-1RA was added to the media, while the control group and the group receiving IRA demonstrated significant growth compared with the baseline concentration of 4,635 +/- 329 cells/mL at all concentrations of insulin and glucose. [H-3]thymidine incorporation assays confirmed the cell count results. CONCLUSIONS: These results suggest that the mitogenic effects of insulin and glucose on infragenicular VSMC are due to stimulation of the IGF-I receptor. VSMC antiproliferative strategies employing receptor blockade should be directed against the IGF-1 receptor, not the insulin receptor. Am J Surg. 1999;178:156-161. (C) 1999 by Excerpta Medica, Inc.