HNF4A P2 isoform alleviates kidney fibrosis by inhibiting dedifferentiation of proximal tubular cells through JAG1/NOTCH signaling

Tubulointerstitial fibrosis is a critical and irreversible process of chronic kidney disease. Dedifferentiated proximal tubular cells (PTCs) after injury are important for tubulointerstitial fibrosis. Hepatocyte nuclear factor 4 alpha (HNF4A) is the main regulatory factor for PTC differentiation. However, its role in PTC dedifferentiation and kidney fibrosis remains unclear. To investigate the role of HNF4A in kidney fibrosis, bioinformatics analysis and in vivo models were used to evaluate its expression in kidney tissues. The mechanisms through which the HNF4A P2 isoform inhibits kidney fibrosis were examined by using both in vivo and in vitro models. In this study, we revealed that the sustained downregulation of HNF4A expression was a key characteristic of abnormally repaired PTCs after injury and was associated with cell dedifferentiation. It was confirmed that the HNF4A P2 isoform, rather than the P1 isoform, inhibited TGF-β1-induced PTC dedifferentiation. The activation of fibroblasts, which was induced by dedifferentiated PTCs through paracrine signalling, was also inhibited. In vivo experiments confirmed that HNF4A P2 was more effective than HNF4A P1 was in alleviating kidney fibrosis. Mechanistically, on one hand, HNF4A P2 antagonized the TGF-β1-induced dedifferentiation of PTCs by inhibiting the JAG1/NOTCH pathway. On the other hand, the distinct structure of HNF4A P2 from that of P1 made it unaffected by TGF-β1-activated SRC, allowing HNF4A P2 to perform transcriptional regulatory functions. These findings suggest that targeting the HNF4A P2 isoform could serve as a novel therapeutic strategy to alleviate kidney fibrosis.