Role of nitric oxide in high glucose-induced mitogenic response in renal fibroblasts

Nitric oxide (NO) has been suggested to be associated with tubulointerstitial fibrosis in diabetic nephropathy. Abnormal glucose handling in the tubulointerstitium may play an important role in the development of diabetic nephropathy. This study was designed to investigate the effect of NO generation and action in renal fibroblasts exposed to high glucose (HG). We found that HG (500 mg/dl) significantly decreased nitrite production compared with normal glucose (100 mg/dl) when the incubation period was for 12, 18, or 24 h. HG inhibited cGMP-dependent protein kinase (PKG) activation at 4, 8, and 12 h. Both NO donors and PKG activator treatment induced high levels of NO, inducible nitric oxide synthase, and PKG in HG-incubated cells. Interestingly, HG-induced Janus kinase 2-signal transducers and activators of transcription 1 (STAT1) activation but not STAT3 or STAT5 activation at 30 min were blocked by NO donors and PKG activator. Moreover, HG-enhanced Raf-1 and p42/p44 MAPK phosphorylation were markedly suppressed by NO donors or PKG activator. The ability of NO-PKG to inhibit HG-induced cell cycle progression was verified by the observation that NO donors and PKG activator inhibited cdk4 activation and increased p21(Waf1/Cip1) and p16(INK4a) (but not p27(Kip1)) expression in HG-treated renal fibroblasts. Collectively, these data suggest that HG significantly blunted NO signaling, and activation of the NO-PKG pathway may modulate HG-enhanced mitogenic response via specific pathways.