Caffeine prevents oxalate-induced epithelial-mesenchymal transition of renal tubular cells by its anti-oxidative property through activation of Nrf2 signaling and suppression of Snail1 transcription factor.

Caffeine is an active ingredient found in coffee and energy beverages. Its hepatoprotective effects against liver fibrosis are well-documented. Nonetheless, its renoprotective effects against renal fibrogenesis and epithelial-mesenchymal transition (EMT) processes remain unclear and under-investigated. In this study, the protective effects of caffeine against oxalate-induced EMT in renal tubular cells were evaluated by various assays to measure expression levels of epithelial and mesenchymal markers, cell migrating activity, level of oxidized proteins, and expression of Nrf2 and Snail1. Oxalate at sublethal dose significantly suppressed cell proliferation but increased cell elongation, spindle index and migration. Oxalate also decreased expression of epithelial markers (zonula occludens-1 (ZO-1) and E-cadherin) but increased expression of mesenchymal markers (fibronectin, vimentin and α-smooth muscle actin (α-SMA)). All of these EMT-inducing effects of oxalate could be prevented by pretreatment with caffeine. While oxalate increased oxidized proteins and Snail1 levels, it decreased Nrf2 expression. Caffeine could preserve all these molecules to their basal (control) levels. Finally, silencing of Nrf2 expression by small interfering RNA (siRNA) could abolish such protective effects of caffeine on oxalate-induced EMT. Our data indicate that the renoprotective effects of caffeine against oxalate-induced EMT is mediated, at least in part, by its anti-oxidative property through activation of Nrf2 signaling and suppression of Snail1 transcription factor.

Kanlaya R ，Subkod C ，Nanthawuttiphan S ，Thongboonkerd V ... -  《-》

Protective roles of trigonelline against oxalate-induced epithelial-to-mesenchymal transition in renal tubular epithelial cells: An in vitro study.

Fibrogenesis is a common feature for all types of chronic kidney disease (CKD). Epithelial-to-mesenchymal transition (EMT) of renal tubular epithelial cells is one of the main processes involving renal fibrosis and its inhibition is considered as a preventive/therapeutic strategy for CKD. Trigonelline (TRIG), a plant alkaloid commonly found in herbs, coffee bean, soy bean and other edible food plants, has several beneficial effects on human health and has been proposed to reduce renal fibrosis but with unclear mechanisms. This study thus addressed cellular mechanism underlying the anti-fibrogenic effects of TRIG in renal tubular epithelial cells grown in vitro. EMT was successfully induced by oxalate treatment as indicated by morphological changes into spindle-shape cells, increased expression of mesenchymal proteins (fibronectin, vimentin and α-smooth muscle actin (α-SMA)), decreased expression of epithelial proteins (E-cadherin and zonula occludens-1 (ZO-1)) and increased activity of a profibrotic factor (matrix metalloproteinase-9 (MMP-9)). Interestingly, these oxalate-induced EMT features could be attenuated by TRIG pretreatment. Moreover, TRIG also prevented oxalate-induced cell migration, reactive oxygen species (ROS) overproduction, and down-regulation of Nrf-2 signaling molecule. These data indicated that TRIG could attenuate the effects of oxalate-induced EMT and thus may serve as the anti-fibrotic compound for prevention and/or treatment of CKD.

Peerapen P ，Thongboonkerd V 《-》

Epigallocatechin-3-gallate prevents TGF-β1-induced epithelial-mesenchymal transition and fibrotic changes of renal cells via GSK-3β/β-catenin/Snail1 and Nrf2 pathways.

Several lines of evidence have demonstrated anti-fibrotic property of epigallocatechin-3-gallate (EGCG) in many tissues/organs but with unclear mechanisms. This study thus aimed to define cellular mechanisms underlying such protective effect of EGCG. HK-2 renal cells were treated with 5 ng/ml TGF-β1 for 24 h with/without pretreatment by 5 μM EGCG for 1 h. The cells were then evaluated by morphological examination, immunofluorescence study, semi-quantitative RT-PCR, Western blotting, and atomic force microscopy (AFM). The results showed that TGF-β1-treated cells underwent epithelial mesenchymal transition (EMT) as evidenced by morphological change into fibroblast-like and increases in spindle index, mesenchymal markers (Snail1 and vimentin), extracellular matrix (fibronectin), cell stiffness (by AFM measurement) and actin stress fibers, whereas the epithelial markers (E-cadherin and ZO-1) were decreased. All of these features were abolished by EGCG pretreatment. Functional studies revealed that the anti-fibrotic property of EGCG was, at least in part, due to de-activation/stabilization of GSK-3β/β-catenin/Snail1 (EMT-triggering) signaling pathway that was activated by TGF-β1 as shown by maintaining phosphorylated GSK-3β, β-catenin and Snail1 to their basal levels. Additionally, Nrf2 knockdown by small interfering RNA could abolish the EGCG effect on β-catenin expression. These data indicate that EGCG attenuates TGF-β1-induced EMT in renal tubular cells through GSK-3β/β-catenin/Snail1 and Nrf2 pathways.

Kanlaya R ，Peerapen P ，Nilnumkhum A ，Plumworasawat S ，Sueksakit K ，Thongboonkerd V ... -  《-》

Protective effect of epigallocatechin-3-gallate (EGCG) via Nrf2 pathway against oxalate-induced epithelial mesenchymal transition (EMT) of renal tubular cells.

Kanlaya R ，Khamchun S ，Kapincharanon C ，Thongboonkerd V ... -  《Scientific Reports》

The protective effect of caffeine against oxalate-induced epithelial-mesenchymal transition in renal tubular cells via mitochondrial preservation.

Kanlaya R ，Subkod C ，Nanthawuttiphan S ，Thongboonkerd V ... -  《-》