Aims: The activation of Ras signaling and vascular endothelial growth factor (VEGF) expression in mesangial cells is a pathogenic consequence of diabetic nephropathy. We examined the role of simvastatin in modulating Ras signaling and the expression of VEGF in mesangial cells stressed with high doses of glucose in vitro and in vivo.
Methods: For the in vitro studies, we cultured mesangial cells, with or without simvastatin or manumycin A pretreatment, in 35 mM glucose and assayed VEGF activity. For the in vivo studies, we administered simvastatin or manumycin A to streptozocin-induced diabetic rats for 28 days and dissected renal tissues for an immunohistological assessment of Ras and VEGF expression in glomerular cells.
Results: We showed that high glucose significantly increased VEGF gene expression and Ras activation. The pretreatment with 10 microM simvastatin and inhibition of Ras activity by manumycin A significantly reversed high glucose promotion of VEGF mRNA expression. Pretreatment with simvastatin and manumycin A clearly affected the activation of Ras promoted by high glucose. Tube-like formations were abundant in high glucose-treated mesangial cells co-cultured with HUVEC. However, the simvastatin and manumycin A treatment group's down-regulated tube formation was comparable to the mesangial cells treated only with high glucose. Exogenous simvastatin and manumycin A treatment alleviated urinary albumin secretion and attenuated Ras activation and VEGF protein expression in the kidneys of diabetic rats.
Conclusions: Ras protein activation is a key mediator of VEGF-induced diabetic nephropathy. By inhibiting Ras activation, simvastatin modulates the high glucose-induced VEGF-mediated signaling pathway in vitro and in vivo.