Poricoic acid ZA, a novel RAS inhibitor, attenuates tubulo-interstitial fibrosis and podocyte injury by inhibiting TGF-β/Smad signaling pathway

Background: The pathogenesis of tubulo-interstitial fibrosis and glomerulosclerosisis was characterized by cellular hypertrophy, extracellular matrix accumulation and podocyte detachment. Poricoic acid ZA (PZA) is a tetracyclic triterpenoid compound extracted from the surface layer of Poria cocos (LPC), which have been used extensively for diuretic and renoprotective effects. Methods: The anti-fibrotic effect of PZA is investigated in HK-2 cells and podocytes induced by TGF-beta 1 and angiotensin II (ANGII). qRT-PCR, siRNA, immunofluorescence staining, co-immunoprecipitation and Western blot analyses are used to evaluate the expression of RAS signaling, TGF-beta/Smad pathway, epithelial-to-mesenchymal transition (EMT) and podocyte markers. Results: PZA restores the mRNA and protein expression of EMT in HK-2 cells. Specific TGF-beta 1-siRNA efficiently blocks ANGII-induced protein expression of TGF-beta 1 and further inhibits activated Smad signaling. PZA significantly attenuates up-regulation of angiotensinogen, renin, ACE and AT1. Further, PZA reverses up-regulation of TGF beta RII and suppresses Smad proteins. Simultaneously, PZA inhibits the protein interaction of TGF-beta receptor and Smads and PZA also inhibits activated RAS and TGF-beta/Smad signaling cascade and up-regulates protein expression of podocyte markers and mitigates podocyte injury. Conclusions: This study demonstrated the beneficial role of PZA in renal fibrosis and podocyte injury. Our study highlighted that PZA inhibits RAS and further suppresses TGF-beta/Smad pathway through inhibiting Smad2/3 phosphorylation via blocking Smad2/3-TGF beta RI protein interaction. PZA is implicated in activation of RAS/TGF beta/ Smad axis in HK-2 cells and podocytes. PZA could be considered as a novel RAS inhibitor for treating CKD.