#2592 Tubular cell polyploidy is involved in kidney compensatory hypertrophy

Abstract Background and Aims Chronic kidney disease (CKD) affects more than 10% of the population and it is associated with high risk of death for cardiovascular causes or progression towards end stage kidney disease (ESKD) requiring dialysis or kidney transplantation. CKD is characterized by progressive loss of nephrons, with consequent structural degeneration and fibrosis. Nephron number is established during prenatal kidney development and cannot increase. Consequently, following a reduction in kidney mass or in condition of altered metabolic demands, the remaining nephrons undergo compensatory hypertrophy. Compensatory hypertrophy results in increased functional output and has been observed in the absence of direct tissue injury after nephrectomy. Recently, we have identified a previously unknown mechanism of cellular adaptation: polyploidization of tubular epithelial cells (TC), and demonstrated that this is the essential mediator of kidney hypertrophy after acute kidney injury (AKI). Here, we hypothesize that TC polyploidy is involved in compensatory hypertrophy following nephrectomy. Method Polyploid TC are characterized by an increased DNA content in the absence of cell division. To discriminate polyploid cells from actively proliferating cells, we employed a series of in vitro and in vivo transgenic models based on the Fluorescence Ubiquitin Cell Cycle Indicator (FUCCI2aR) technology. Nephrectomy was performed by removing the left kidney and mice were sacrificed at different days after uni- Nephrectomy (Nfx). Cytofluorimetric techniques were employed to characterize a subpopulation of polyploid TC and histology investigation was employed analyze fibrosis development. These results were further corroborated by single cell RNA-sequencing (scRNA-seq) analyses in vitro and in vivo. Results Employing mice that express the FUCCI2aR reported under the Pax8 promoter (which marks all TC), we found that TC polyploidy increases immediately after uni-Nfx. This was accompanied by an increased kidney to body mass ratio with a maximum peaks 3 days afterwards. Importantly, after uni-Nfx, YAP1 expression and nuclei localization (i.e., implying pathway activation) was exponentially increased, suggesting that the same mechanism that drives TC polyploidy after AKI controls TC polyploidization response after uni-Nfx. However, unlike in AKI, polyploidy after nephrectomy was not accompanied by structural alterations as shown by PAS and Masson's trichrome staining. Conversely, after uni-Nfx YAP1 knock-out mice, that are unable to undergo rapid polyploidization, displayed an impaired kidney function in the long term, characterized by extensive tubular dilations. Conclusion Polyploidization of TC mediates compensatory hypertrophy following nephrectomy via YAP1 activation