DNA methyltransferase 1 may be a therapy target for attenuating diabetic nephropathy and podocyte injury.

The contribution of DNA methylation to diabetic nephropathy, especially the effect on podocyte integrity, is not clarified. Here we found that albuminuria in a db/db mouse model was markedly attenuated after treatment with a DNA methylation inhibitor. This was accompanied by alleviation of glomerular hypertrophy, mesangial matrix expansion, and podocyte injury. The expression of DNA methyltransferase 1 (Dnmt1), nuclear factor Sp1, and nuclear factor kappa B (NFκB)-p65 markedly increased in podocytes in vivo and in vitro under the diabetic state. The increased expression of Dnmt1 was attenuated after treatment with 5-azacytidine or 5-aza-2'-deoxycytidine or Dnmt1 knockdown, accompanied by restored decreased podocyte slit diaphragm proteins resulting from hypermethylation and improved podocyte motility. Further studies found that increased Sp1 and NFκB-p65 interacted in the nucleus of podocytes incubated with high glucose, and Sp1 bound to the Dnmt1 promoter region. The involvement of the Sp1/NFκB-p65 complex in Dnmt1 regulation was confirmed by the observation that Sp1 knockdown using mithramycin A or siRNA decreased Dnmt1 protein levels. The luciferase reporter assay further indicated that Dnmt1 was a direct target of Sp1. Thus, inhibition of DNA methylation may be a new therapeutic avenue for treating diabetic nephropathy. Hence, the Sp1/NFκB p65-Dnmt1 pathway may be exploited as a therapeutic target for protecting against podocyte injury in diabetic nephropathy.

Spironolactone inhibits podocyte motility via decreasing integrin ß1 and increasing integrin ß3 in podocytes under high-glucose conditions.

Integrin ß1 and ß3 expression by podocytes is required to maintain glomerular structural integrity. Previous studies have shown that aldosterone (ALD) is involved in glomerular podocyte injury, and mineralocorticoid receptor (MR) blocker spironolactone effectively reduces proteinuria in patients with diabetic nephropathy. The present study was designed to observe the effects of spironolactone on ß1 and ß3 integrin expression and podocyte motility under in vitro diabetic conditions. Immortalized mouse podocytes were cultured in media containing normal glucose (NG) levels, high glucose (HG) or HG plus spironolacton. The expression of ß1 and ß3 integrin in podocytes was detected by reverse transcription quantitative polymerase chain reaction, immunofluorescence and western blot analyses. The effects of spironolacton on podocyte motility was further evaluated using a wound healing assay. HG stimulation markedly decreased mRNA and protein expression of integrin ß1, and significantly increased mRNA and protein expression of integrin ß3 in cultured podocytes. However, simultaneous treatment with spironolacton (10­7 mol/l) significantly attenuated HG-mediated increases in integrin ß3 and decreases in integrin ß1 expression. Furthermore, the migration of podocytes induced by HG was abrogated by concomitant treatment with spironolacton. In conclusion, the present study suggested that HG decreased the expression of integrin ß1 in cultured podocytes, accompanied with an increase of integrin ß3. Spironolactone inhibited cell motility and stabilized podoctyes treated with HG, probably through partly normalizing the expression of integrin ß1 and decreasing the expression of integrin ß3.