#2145 Sexual dimorphism in kidney regenerative capacity decline and in progressive tubular cell polyploidization during aging

Abstract Background and Aims Aging is characterized by a progressive kidney function decline, resulting in chronic kidney disease (CKD), which is steeper in men than in women. However, sex-related differences in mechanisms underpinning CKD development during aging still remain to be clarified. In most organs regenerative capacity declines overtime from a pool of resident stem cells leading to tissue aging. In the kidney, we have revealed that two adaptive responses co-exist to recover kidney function after injury. On one hand a population of renal progenitors (RPC), which is interspersed among parietal epithelial cells of Bowman's capsule and tubular cells (TC) of nephron segments, proliferate and generate new podocytes and TC to recover structural integrity during the regenerative processes occurring in glomerular and tubular diseases. On the other, TC enter the alternative cell cycles to become polyploid in order to increase their functional capacity and maintain the residual kidney function after injury. However, a continuous TC polyploidization comes with the long term trade-offs (fibrosis and senescence), driving CKD. Here, we aimed to investigate the role of sexual dimorphism in these two different adaptive responses during aging. Method To trace RPC (Pax2+cells) we used the inducible Pax2/Confetti or Pax2/mTmG mice (RPC are randomly labelled by one of the four fluorescent reporter genes or with GFP respectively). To study polyploid TC, we used the inducible Pax8/FUCCI2aR mice (polyploid TC are identified by expression of cell cycle fluorescent proteins in combination with DNA content analysis). Mice were analyzed at 2, 5, 12 and 20 months of age. scRNA sequencing was performed at 2 and 20 months of age. Results Pax2/Confetti mice revealed that the number of Pax2+RPC either of the Bowman's capsule or in tubules was higher in female than in male mice at all ages. Specifically, tracing analysis during aging showed that in females Pax2+RPC of the Bowman's capsule generated new podocytes, resulting in glomeruli with a better integrity of the slit-diaphragm compared with aged males. Moreover, tubular Pax2+RPC in females clonally expanded, generating a higher number of clones, which were longer than those in males. scRNAseq analysis on kidneys showed that females were endowed with a greater number of Pax2+RPC with a higher expression of Pax2 than males, suggesting that RPC in females kept a higher regenerative capacity than males during aging. Simultaneously, analysis of tubular polyploidy demonstrated that, whereas in females the polyploid fraction progressively increased, it was drastically reduced in males during aging. These results suggested that whereas in females the increase of polyploid TC provided a better maintenance of kidney function overtime, loss of polyploid response in males made them more susceptible to develop CKD. Indeed, aged male mice showed a higher percentage of polyploid TC undergoing further cycles of polyploidization, which were associated with fibrosis and senescence. In agreement with these findings, we observed a progressive kidney function decline along with an increase of glomerulosclerosis, interstitial fibrosis and blood pressure, which were significantly greater in males than in females. Conclusion Female mice showed a higher regenerative and polyploid response compared to male mice, aimed likely to cope kidney function decline during aging. These results reveal the intriguing role of a new kidney adaptive response, which may explain the higher susceptibility of males to develop a more premature CKD during aging.