Tetrahydrobiopterin levels regulate endothelial cell proliferation

Vascular abnormalities, including altered angiogenesis, are major factors c ontributing to the morbidity and mortality of diabetes. We hypothesized tha t impaired angiogenesis in diabetes results from decreased tetrahydrobiopte rin (BH4)-dependent synthesis of nitric oxide (NO) by endothelial cells (EC ). To test this hypothesis, we utilized EC from spontaneously diabetic BB ( BBd) and nondiabetes-prone BB (BBn) rats to investigate the link between BH 4 and EC proliferation. There were significant decreases in the proliferati on rate and expression of proliferating cell nuclear antigen in BBd versus BBn EC, with no evidence of apoptosis in either group. Sepiapterin (a precu rsor of BH4 via the salvage pathway) increased BH4 synthesis and enhanced p roliferation of BBd EC. The stimulating effect of sepiapterin on EC prolife ration was attenuated by N-G-monomethyl-L-arginine, a NO synthase inhibitor . Reducing BH4 concentrations in BBn EC caused a decrease in proliferation, which was attenuated by a long-acting NO donor. Our results suggest that B H4 levels regulate proliferation of normal EC and that a BH4 deficiency imp airs NO-dependent proliferation of BBd EC.