Low nitric oxide bioavailability upregulates renal heparin binding EGF-like growth factor expression

Decreased nitric oxide bioavailability has an important role in the initiation and progression of diabetic nephropathy, but the underlying mechanisms remain unclear. Here, we found that heparin-binding epidermal growth factor-like growth factor (HB-EGF) expression levels increased in the kidneys of both endothelial nitric oxide synthase (eNOS)-knockout and eNOS-knockout diabetic (Leprdb/db) mice as early as at 8 weeks of age. Further increases in expression were only seen in eNOS-knockout diabetic mice and paralleled the progression of glomerulopathy. HB-EGF expression increased in endothelium, podocytes, and tubular epithelial cells. In cultured glomerular endothelial cells, the nitric oxide synthase inhibitors NG-nitro-l-arginine methyl ester (l-NAME) or l-N5-(1-iminoethyl) ornithine increased HB-EGF protein expression. Administration of l-NAME dramatically increased renal HB-EGF expression and urinary HB-EGF excretion in diabetic mice. On the other hand, replenishing nitric oxide with sodium nitrate in eNOS-knockout diabetic mice reduced urinary HB-EGF excretion and inhibited the progression of diabetic nephropathy. Furthermore, specific deletion of HB-EGF expression in the endothelium attenuated renal injury in diabetic eNOS-knockout mice. Thus, our results suggest that decreased nitric oxide bioavailability leads to increased HB-EGF expression, which may be an important mediator of the resulting progressive diabetic nephropathy in eNOS-knockout diabetic mice.