Abstract: Objectives In this study, inhibitory effects of apelin on transforming growth factor-β (TGF-β)-induced epithelial-mesenchymal transition (EMT) in human proximal renal tubular epithelial cells were examined and related mechanism was elucidated. Methods Human proximal renal tubular epithelial cells were cultured in vitro. Cells were incubated with TGF-β1 (2 μg/L) and/or different concentrations of apelin-13 for 48 hours. Six groups were established (n=5 in each group): Control group, TGF-β group, TGF-β+Apelin (10-8, 10-7 and 10-6mol/L) group, apelin (10-6mol/L) group. Immunofluorescence was performed to visualize the distribution of epithelial marker E-cadherin and mesenchymal marker α-smooth muscle actin (α-SMA). Western blot analysis was performed to determine the level of E-cadherin, α-SMA, and expression of key Smads signaling molecules p-Smad2/3, Smad2/3 and Smad-7. RT-PCR analysis was performed to evaluate the mRNA level of fibronectin and CollagenⅠ, and expression of endogenous apelin and APJ. Results Compared with control group, cells in TGF-β group was long spindle shape, together with decreased expression of E-cadherin and increased expression of α-SMA. Morever, transcripts of fibronectin and collagen I mRNAs were also increased in TGF-β group. However, these effects were obviously inhibited in TGFβ+Apelin group in a concentration-dependent manner. Compared with TGF-β group, the level of p-Smad2/3 was decreased (P<0.05), while the level of Smad7 was increased (P<0.05) in TGF-β+Apelin group . In TGF-β group, expression of APJ was upregulated (P<0.05). Remarkably, this effect was also inhibited in TGFβ+Apelin group in a concentration-dependent manner. Conclusions This study provides the first evidence that apelin is able to protect against tubular EMT through antagonism of TGF-β/Smads pathway. The endogenous apelinergic system may promote some compensatory response in tubular EMT process.

Key words: Epithelial-mesenchymal transition, Apelin, Transforming growth factor-β, Signaling pathway