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Background Mitochondrial dysfunction is a newly established risk factor for the development of renal fibrosis. Cell survival and injury repair is facilitated by mitochondrial biogenesis. Nuclear respiratory factor 1 (NRF-1) is a transcriptional regulation factor that plays a central role in the regulation of mitochondrial biogenesis. However, the transcription factor of this process in renal fibrosis is unknown. Thus, we hereby discussed the correlations of NRF-1 and renal interstitial fibrosis. Materials and methods In vitro fibrosis model was established by treatment with transforming growth factor-β1 (TGF-β1) in NRK-49F (Normal Rat kidney fibroblast). We investigated the ROS production, mitochondrial biogenesis and fibrogenic marker (e.q. fibronectin) during the progression of renal fibrosis by kit and Western blotting assay. Here, we used that two distinct mechanisms regulate NRF-1 activation and degradation of NRF-1. NRF-1 was transfect by pcDNA-NRF-1 overexpression gene to evaluate the NRF-1 activity of the therapeutic effect in renal fibrosis. In addition, NRF-1 was silenced by shRNA-NRF-1 to evaluate the significance of NRF-1. ELISA was used to evaluate the secreted fibronectin. Immunofluorescence staining was used to assay the in situ expression of proteins (e.g. fibronectin, NRF-1). Results Under renal fibrosis conditions, TGF-β1 (5 ng/ml) increased ROS. Simultaneously, TGF-β1-induced extracellular fibronectin by ELISA assay. In addition, TGF-β1 decreased expression of mitochondrial biogenesis. This is the first time to demonstrate that expression of NRF-1 is significantly decreased in renal fibrosis. However, NRK49F was a transfection with pcDNA-NRF-1 (2 μg/ml) expression vector dramatically reverse TGF-β1-induced cellular fibrosis concomitantly with the suppression of fibronectin (both intracellular and extracellular fibronectin). More importantly, transfection with shRNA-NRF-1 (2 μg/ml) significantly increased the expression of fibronectin of both intercellular and extracellular origins in NRK-49F cells. Discussion These finding suggest that NRF-1 plays a pivotal role on renal cellular fibrosis. Moreover, NRF-1 might act as a novel renal fibrosis antagonist by down-regulating fibrosis signaling in renal fibroblast cells.

Peroxisome proliferator-activated receptor coactivator-1 alpha (PGC-1α) is a transcriptional coactivator that regulates energy metabolism and mitochondrial biogenesis. Recently, mitochondrial dysfunction has been indicated as an established risk factor for the development of renal fibrosis. However, whether PGC-1α is involved in the pathogenesis of renal fibrosis is unknown. In this study, we treated NRK-49F (normal rat kidney fibroblast) cells with transforming growth factor-beta 1 (TGF-β1) for 24 h to establish an in vitro fibrosis model. TGF-β1 induced the upregulation of type I collagen, fibronectin, TGF-β receptor I (TGFβ-RI), TGFβ-RII, Smad4, and pSmad2/3, as well as PGC-1α. NRK-49F cells transfected with pcDNA-PGC-1α showed significantly increased expression of fibronectin and type I collagen, as revealed by western blot assay. Interestingly, transfection with PGC-1α-siRNA caused a stark reversal of TGF-β1-induced cellular fibrosis, with concomitant suppression of fibronectin and type I collagen, as revealed by western blot and immunofluorescence assays. Moreover, SB431542 (TGFβ-RI), LY294002 (PI3K/Akt), and SB203580 (p38 MAPK), inhibitors of TGF-β-associated pathways, markedly suppressed TGF-β1-induced PGC-1α upregulation. These results implicate a role of PGC-1α in renal interstitial fibrosis mediated via the TGFβ-RI, PI3K/Akt, and p38 MAPK pathways. Our findings that PGC-1α-siRNA downregulates fibronectin and type I collagen suggest that it can be used as a novel molecular treatment for renal fibrosis.

Fibrosis is the important pathway for end-stage renal failure. Glucose has been demonstrated to be the most important fibrogenesis-inducing agent according to previous studies. Despite diosgenin has been demonstrated to be anti-inflammatory, the possible role in fibrosis regulation of diosgenin remain to be investigated. In this study, renal proximal tubular epithelial cells (designated as HK-2) were treated with high concentration of glucose (HG, 27.5mM) to determine whether diosgenin (0.1, 1 and 10 μM) has the effects to regulate renal cellular fibrosis. We found that 10 μM of diosgenin exert optimal inhibitory effects on high glucose-induced fibronectin expression in HK-2 cells. In addition, diosgenin markedly inhibited HG-induced increase in α-smooth muscle actin (α-SMA) and HG-induced decrease in E-cadherin. In addition, diosgenin antagonizes high glucose-induced epithelial-to-mesenchymal transition (EMT) signals partly by enhancing the catabolism of Snail in renal cells. Collectively, these data suggest that diosgenin has the potential to inhibit high glucose-induced renal tubular fibrosis possibly through EMT pathway.

Thymic stromal lymphopoietin (TSLP) has previously been linked to allergic inflammatory diseases, and tissue fibrosis and organ dysfunction may also arise from such inflammation. It remains unclear, however, whether TSLP plays any role in the occurrence of renal fibrosis, so this study investigated that possibility. An in vitro fibrosis model was established by treating normal rat kidney fibroblast (NRK-49F) cells with transforming growth factor-β1 (TGF-β1), after which the levels of various fibrogenic markers (e.g., fibronectin) and downstream fibrogenic signal proteins (e.g., smad 7) were investigated. Also, TSLP shRNA was used to silence the effects of TSLP, while an ELISA was conducted to evaluate the fibronectin secretions. The level of fibronectin in the NRK-49F cells was dose- and time-dependently increased by the administration of exogenous TSLP (P