C-peptide prevents NF-κB from recruiting p300 and binding to the inos promoter in diabetic nephropathy

C-peptide (CP) has demonstrated unique beneficial effects in diabetic nephropathy (DN), but whether and how CP regulates NF-kappa B and its coactivator, p300, to suppress inducible iNOS and antagonize DN are unknown. iNOS expression, NF-kappa B nuclear translocation, colocalization and binding of NF-kappa B to p300, binding of NF-kappa B to the inos promoter, and the bound NF-kappa B, p300, and histone 3 lysine 9 acetylation (H3K9ac) at binding sites were measured in high glucose-stimulated mesangial cells. We evaluated pathologic changes, iNOS expression, NF-kappa B, and p300 contents in diabetic rats. We found that CP inhibited iNOS expression and notably prevented colocalization and binding of NF-kappa B and p300. CP prevented NF-kappa B from binding to the inos promoter, especially at the distal site, and reduced bound NF-kappa B, p300, and H3K9ac. N-terminal plus middle fragment could mostly mimic the antagonizing effects of CP against the pathologic changes of DN and equally suppresses renal iNOS expression as CP. In conclusion, CP prevented NF-kappa B from recruiting p300 and binding to the inos promoter, and decreased H3K9ac at the binding sites to suppress iNOS expression and antagonize DN, with the effect region identified as N-terminal plus middle fragment.