All-trans retinoic acid regulating angiopoietins-1 and alleviating extracellular matrix accumulation in interstitial fibrosis rats

All-trans retinoic acid (ATRA) is one of essentially active metabolite of vitamin A, and plays an important role in diverse physiological processes, such as cellular growth and function. Renal interstitial fibrosis (RIF) is a common pathological characteristic of chronic renal disease causing end-stage renal disease currently lacking effective treatment. Low level of Angiopoietins-1 (Angpt-1) is associated with extracellular matrix accumulation and fibrosis diseases. This study was performed to assess the association of ATRA with Angpt-1 in RIF disease. Rats were divided into three groups: group of sham (SHO group), group of unilateral ureteral obstruction group (UUO group), UUO mice administrated daily at the dose of ATRA (ATRA group). Masson-staining was used to detect the histologic lesion. Immunohistochemistry and Western-blot were applied to determine the targeted proteins. RIF score was significantly increased in UUO rats when compared with that of SHO group, and the fibrosis score was notably reduced in ATRA group. Transforming growth factor-β1 (TGF-β1), collagen IV (Col-IV) and fibronectin (FN) expressions in UUO group were significantly up-regulated, whereas Angpt-1 expression was significantly down-regulated compared with the SHO group. ATRA treatment reduced TGF-β1, Col-IV and FN expressions and improved Angpt-1 expression compared with the UUO group. The protein expression of Angpt-1 in kidney tissue of UUO group was negatively correlated with RIF index and protein expressions of Col-IV, FN and TGF-β1. In conclusion, low expression of Angpt-1 was associated with the RIF disease and ATRA treatment can increase the Angpt-1 and alleviate the RIF lesion in UUO rats.

Identification of CD2, CCL5 and CCR5 as potential therapeutic target genes for renal interstitial fibrosis

Background

We aimed to explore potential gene biomarkers of renal interstitial fibrosis (RIF) due to a lack of effective and non-invasive methods for diagnosis.

Methods

Three data sets (GSE22459, GSE76882 and GSE57731) including 350 samples were acquired from Gene Expression Omnibus (GEO) database. We used bioconductor limma package to perform background adjustment. Cluster analysis was conducted by 'edgeR' package to identify the differentially expressed genes (DEGs). We generated heat maps with using heatmap package in R software. Function annotation of genes was performed by Gene Ontology (GO) enrichment analysis. STRING (Search Tool for the Retrieval of Interacting Genes) database was employed to construct the protein-protein interaction (PPI) network and the results were visualized by Cytoscape 3.6.1. At last, we applied Graphpad Prism 7.0. to explore the correlation between three hub genes and pathological degrees of RIF.

Results

By applying the "edgeR" package in R, we detected 116 DEGs with three data sets. These genes were enriched in 19 GO biological process categories. Three main hub genes (CD2, CCL5 and CCR5) were identified after construction of PPI network. In Pearson correlation coefficient, CD2, CCL5 and CCR5 was found to hold higher expression patterns in RIF samples based on independent data set GSE57731. Besides, their gene expression levels were found significantly positive correlation with the degree of RIF (CD2: P<0.05, r=0.29; CCL5: P<0.05, r=0.31; CCR5: P<0.05, r=0.38).

Conclusions

CD2, CCL5 and CCR5 might serve as potential early biomarkers of RIF. The mechanism between these genes and RIF remains to be further studied.

PAK4 enhances TGF-β1-induced epithelial-mesenchymal transition through activating β-catenin signaling pathway in renal tubular epithelial cells

Epithelial-mesenchymal transition (EMT) of renal tubular epithelial cells contributes to development and progression of renal interstitial fibrosis in CKD. p21-activated kinase 4 (PAK4) is a member of serine/threonine protein kinases but the role of PAK4 in renal fibrosis remains unknown. In this study, we investigated the effects of PAK4 on transforming growth factor-β1 (TGF-β1)-treated human renal tubular epithelial cells (HK-2 cells) and aimed to elucidate probable mechanisms for its fibrogenic effects. Our results revealed that PAK4 was highly expressed in TGF-β1-treated HK-2 cells. Overexpressing PAK4 could further decrease TGF-β1-induced E-cadherin expression and increase TGF-β1-induced fibronectin and vimentin expression in HK-2 cells. In addition, overexpressing PAK4 could promote the translocation of β-catenin from cell membranes into the nucleus in TGF-β1-treated HK-2 cells. These results indicate that PAK4 could enhance TGF-β1-induced EMT in renal tubular epithelial cells. Our findings indicate that PAK4 may promote renal interstitial fibrosis by activating β-catenin signaling pathway. Thus, we suggest that PAK4 might be a potential therapeutic target for ameliorating renal interstitial fibrosis.

ILEI is an important intermediate participating in the formation of TGF-β1-induced renal tubular EMT

Renal interstitial fibrosis is the most common process by which chronic kidney diseases progress to end-stage renal failure. Epithelial-to-mesenchymal transitions (EMTs) play a crucial role in the progression of renal interstitial fibrosis. A newly identified cytokine, interleukin-like EMT inducer (ILEI), has been linked to EMT in some diseases. However, the effects of ILEI on renal tubular EMT have not yet been well established. Here, we characterize the expression of ILEI in tubular EMT and describe the role and mechanism of ILEI in transforming growth factor beta 1 (TGF-β1)-induced renal tubular EMT. The results indicate that ILEI is involved in renal tubular EMT induced by TGF-β1, as overexpression of ILEI not only induces EMT of HK-2 cells independently but also profoundly enhances EMT in response to TGF-β1. Supporting this finding, ILEI small interfering RNA was found to block the EMT of HK-2 cells induced by TGF-β1. This work additionally suggests ILEI mediates TGF-β1-dependent EMT via the extracellular regulated protein kinases (ERKs) and protein kinase B (Akt) signalling pathways. In conclusion, ILEI appears to play a crucial role in mediating TGF-β1-induced EMT through the Akt and ERK pathways, which may provide a therapeutic target for the treatment of fibrotic kidney diseases.

SIGNIFICANCE OF THE STUDY

There is no study reporting the effect of ILEI in renal EMTs. In this research, we examined the role and mechanism of ILEI in EMT using tubular epithelial cell; we found that ILEI participated in renal tubular EMT, and overexpression of ILEI can not only induce EMT of HK-2 cells independently but also enhance EMT in response to TGF-β1. Meanwhile, we found ILEI small interfering RNA blocked the EMT induced by TGF-β1, and ILEI participates in the EMT caused by TGF-β1 via ERK and Akt signalling pathways. We hoped to provide new ideas in further study on the prevention and treatment of fibrotic kidney diseases.