Dual blockade of Angiotensin II and prorenin receptors ameliorates podocytic apoptosis in IgA nephropathy through inhibition of the notch signaling pathway

Abstract

BACKGROUND: Glomerulo-podocytic communication plays an important role in podocytic injury in IgA nephropathy (IgAN). We examined the roles of podocytic angiotensin II receptor subtype 1 (ATR1) and prorenin receptor (PRR) in podocytic apoptosis in IgAN. METHODS: Conditioned medium was prepared from growth arrested mesangial cells incubated with polymeric IgA from patients (IgA-medium, n=28) or controls (Ctl-medium, n=25). An immortalized human podocyte cell line was used to study the regulation of ATR1, PRR, TNF-α and TGF-β by IgA-medium. Expression of p53 and cleaved caspase 3 was used as functional readout of podocytic apoptosis. RESULTS: Podocytic expression of ATR1 and PRR were up-regulated by IgA-HMC medium dose and time dependently (p<0.01). There was increased expression of ATR1 and release of TGF-β, but not PRR, by podocyte cultured with TNF-α (p<0.05). The IgA-medium, TNF-α or TGF-β induced podocytic apoptosis. We further examined the anti-apoptotic effects of mono- or combined blockade of ATR1, PRR, TNF-α and TGF-β; with losartan, PRR siRNA transfection and anti-TNF-α and anti-TGF-β antibodies. Mono-blockade of ATR1, PRR or TNF-α partially reduced podocytic apoptosis. Dual blockade of ATR1 and PRR, or mono-blockade with anti-TGF-β, effectively rescued podocyte from IgA-medium induced apoptosis. Interestingly, IgA-medium or TGF-β up-regulated the expression of Jag1, notch1 and Hes1 by podocyte. The related podocytic apoptosis was abolished by the γ-secretase blocker, suggesting the important role of notch signaling pathway in this apoptotic process. Blockade of PRR or ATR1 decreased the IgA-medium induced TGF-β release and notch1 expression by podocyte, and these TGF-β release and notch1 expression were further reduced through dual blockade of ATR1 and PRR. CONCLUSIONS: Our data suggest that the TGF-β and notch signaling pathway are the key players in podocytic apoptosis induced by glomerulo-podocytic communication in IgAN. Targeting the notch signaling pathway, AT1R and prorenin receptor could be a potential therapeutic option to reduce the podocytic injury in IgAN.