Polyploid tubular cells initiate a TGF-β1 controlled loop that sustains polyploidization and fibrosis after acute kidney injury

Polyploidization of tubular cells (TC) is triggered by acute kidney injury (AKI) to allow survival in the early phase after AKI, but inthe long run promotesfibrosis and AKI-chronic kidney disease (CKD) transition. The molecular mechanism governing the linkbetween polyploid TC and kidneyfibrosis remains to be clarified. In this study, we demonstrate that immediately after AKI,expression of cell cycle markers mostly identifies a population of DNA-damaged polyploid TC. Using transgenic mouse modelsand single-cell RNA sequencing we show that, unlike diploid TC, polyploid TC accumulate DNA damage and survive, eventuallyresting in the G1 phase of the cell cycle. In vivo and in vitro single-cell RNA sequencing along with sorting of polyploid TC showsthat these cells acquire a profibrotic phenotype culminating in transforming growth factor (TGF)-b1 expression and that TGF-b1directly promotes polyploidization. This demonstrates that TC polyploidization is a self-sustained mechanism. Interactome analy-sis by single-cell RNA sequencing revealed that TGF-b1 signaling fosters a reciprocal activation loop among polyploid TC, macro-phages, andfibroblasts to sustain kidneyfibrosis and promote CKD progression. Collectively, this study contributes to theongoing revision of the paradigm of kidney tubule response to AKI, supporting the existence of a tubulointerstitial cross talkmediated by TGF-b1 signaling produced by polyploid TC following DNA damage.