Endothelial-Myofibroblast Transition Contributes to the Early Development of Diabetic Renal Interstitial Fibrosis in Streptozotocin-Induced Diabetic Mice

Diabetic nephropathy is the leading cause of chronic renal failure. Myofibroblasts play a major role in the synthesis and secretion of extracellular matrix in diabetic renal fibrosis. increasing evidence suggests that endothelial cells may undergo endothelial-myofibroblast transition under physiological and pathophysiological circumstances. Therefore, this study investigates whether endothelial-myofibroblast transition occurs and contributes to the development of diabetic renal interstitial fibrosis. Diabetes was induced by administration of streptozotocin to Tie2-Cre;LoxP-EGFP mice, an endothelial lineage-traceable mouse line generated by crossbreeding B6.Cg-Tg(Tek-cre) 12F1v/J mice with B6.Cg-Tg(ACTB-Bgeo)GFP)21Lbe/J mice. The endothelial-myofibroblast transition was also studied in MMECs (a mouse pancreatic microvascular endothelial cell line) and primary cultures of CD31(+)/EYFP(-) (enhanced yellow fluorescent protein) endothelial cells isolated from adult normal a-smooth muscle actin promoter-driven-EYFP (alpha-SMA/EYFP) mouse kidneys. Confocal microscopy demonstrated that 10.4 +/- 4.2 and 23.5 +/- 7.4% of renal interstitial myofibroblasts (alpha-SMA(+)) in 1- and 6-month streptozotocin-induced diabetic kidneys were of endothelial origin (EGFP(+)/alpha-SMA(+) cells), compared with just 0.2 +/- 0.1% of myofibroblasts in vehicle-treated Tie2-Cre;LoxP-EGFP mice (P < 0.01). Confocal microscopy and real-time PCR showed that transforming growth factor (TGF)-beta 1 induced de novo expression of alpha-SMA and loss of expression of VF-cadherin and CD31 in MMECs and primary cultures of renal endothelial cells in a time- and dose-dependent fashion. These findings demonstrate that the endothelial-myofibroblast transition occurs and contributes to the early development and progression of diabetic renal interstitial fibrosis and suggest that the endothelial-myofibroblast transition may be a therapeutic target. (Am J pathol 2009, 175:1380-1388; DOI: 10.2353/ajpath.2009.090096)