Alternative polyadenylation writer CSTF2 forms a positive loop with FGF2 to promote tubular epithelial-mesenchymal transition and renal fibrosis.

Effective therapies for renal fibrosis, the common endpoint for most kidney diseases, are lacking. We previously reported that alternative polyadenylation (APA) drives transition from acute kidney injury to chronic kidney disease, suggesting a potential role for APA in renal fibrogenesis. Here, we found that among canonical APA writers, CSTF2 expression was upregulated in tubular epithelial cells (TEC) of fibrotic kidneys. CSTF2 was also identified as a TGF-β-inducible pro-fibrotic gene. Further analysis revealed that CSTF2 promoted epithelial-mesenchymal transition (EMT) and extracellular matrix (ECM) overproduction in TEC by inducing 3'UTR shortening and upregulation of the expression of basic fibroblast growth factor 2 (FGF2). Additionally, 3'UTR shortening stabilised FGF2 mRNA through miRNA evasion. Interestingly, FGF2 enhanced CSTF2 expression, leading to the forming of a CSTF2-FGF2 positive loop in TEC. Furthermore, CSTF2 knockdown alleviated unilateral ureteral obstruction-induced renal fibrosis in vivo. Finally, we developed a CSTF2-targeted antisense oligonucleotide (ASO) and validated its effectiveness in vitro. These results indicate that the expression of the APA writer, CSTF2, is upregulated by TGF-β and CSTF2 facilitates TGF-β-induced FGF2 overexpression, forming a TGF-β-CSTF2-FGF2 pro-fibrotic axis in TEC. CSTF2 is a potentially promising target for renal fibrosis that does not directly disrupt TGF-β.