Tamoxifen ameliorates obstructive nephropathy through Src and the PI3K/Akt/mTOR pathway

Background information Tubulointerstitial fibrosis is the end-point of chronic kidney diseases. Tamoxifen, a selective oestrogen receptor (ER) modulator, attenuates renal fibrosis, by regulating the transforming growth factor (TGF)-beta/Smad signalling. Src and phosphoinositide 3-kinase (PI3K)/Akt pathways play critical roles in the pathogenesis of renal fibrosis. However, the activation of the non-canonical TGF-beta signalling in renal fibrosis after treatment with tamoxifen remains unclear. Renal fibrosis was induced by unilateral ureteral obstruction (UUO) in rats. Tamoxifen was orally administered after UUO. Additionally, HK-2 cells were treated with tamoxifen in the presence or absence of TGF-beta 1. The selective ER down-regulator ICI and ER-alpha silencing were used to confirm the involvement of ER-alpha on the effect of tamoxifen on TGF-beta 1-stimulated fibrosis in HK-2 cells. Results Tamoxifen treatment ameliorated UUO-induced renal fibrosis as shown by decreased expression of alpha-smooth muscle actin (SMA), fibronectin and connective tissue growth factor (CTGF). The phosphorylation of Src, PI3K, Akt, mammalian target of rapamycin (mTOR) and p70S6K significantly decreased in UUO kidneys from tamoxifen-treated animals. Tamoxifen dose-dependently suppressed the TGF-beta 1-induced expression of alpha-SMA and CTGF, and phosphorylation of Src, PI3K, Akt, mTOR and p70S6K in HK-2 cells. These anti-fibrotic effects were reversed by treatment with ICI and silencing of ER-alpha. Moreover, inhibition of the PI3K/Akt and mTOR/p70S6K pathways was observed in HK-2 cells co-treated with PP1 (a Src kinase inhibitor) and tamoxifen. Conclusions The anti-fibrotic effects of tamoxifen are associated with the suppression of Src kinase function via ER-alpha, followed by inhibition of the PI3K/Akt and mTOR/p70S6K signalling pathways. Significance Our findings suggest that tamoxifen is a novel therapeutic option for the prevention and treatment of renal fibrosis.