#2372 Investigating the effects of low-level and transient DNA damage on kidney health in a novel mouse model of aging

Abstract Background and Aims Increasing life expectancy worldwide underscores the importance of addressing the effects of aging on organ and cell function. Aging is characterized by a gradual decline in organ function that varies among individuals and is influenced by lifestyle choices and various external factors that induce DNA stress. This mismatch between kidney aging and an individual's lifespan contributes to the increase in end-stage renal disease. Among the kidney's constituent cells, the proximal tubules are frequently damaged by external factors such as ischemia and drugs. Our research has focused on DNA damage and its repair mechanisms (DDR) caused by these injuries, and we have previously shown that extensive DNA damage beyond the capacity of DDR or abnormalities in DDR cause cellular senescence in proximal tubules, resulting in incomplete renal repair after injury (Kishi et al. Sci Transl Med 2019, J Clin Invest 2019). In this study, we extend these studies and test whether acquired and mild DNA stress induces renal senescence using a novel mouse model of aging, the Inducible Changes to the Epigenome (ICE) mouse (Hayano et al. Cell. 2023). Method ICE mice were generated by mating I-PpoI STOP/+ mice with CreERT2/+ mice. I-PpoI, an endonuclease, cleaves DNA only upon administration of tamoxifen and the resulting DNA damage is subsequently repaired by the DDR. To induce transient DNA damage, 4- to 6-month-old mice were fed a tamoxifen-containing diet for 3 weeks and then housed until they reached 14 months of age. A comprehensive renal analysis was then performed, which included renal tissue evaluation, single-nucleus RNA sequencing, q-PCR, and Western blot analysis for phenotypic analysis of mouse kidneys. Results No significant histological changes were observed in the kidney tissues between the ICE mice and the control group, and the levels of interstitial fibrosis were comparable. To ensure unbiased evaluation, we performed single-nucleus RNA-seq. In ICE mice, there was an increased presence of proximal tubules with incomplete repair expressing KIM-1 and VCAM-1. In addition, ICE mice showed increased gene expression of DNA repair-related enzymes (Mgmt) in proximal tubules and evidence of cellular senescence. No differences in mitochondrial number or biosynthetic capacity were observed. Conclusion The consequences of short-term and transient DNA damage were found to have lasting effects on the kidney. In particular, significant changes were observed in the proximal tubules, where DNA instability and accelerated cellular senescence were evident, suggesting an impaired repair phenotype within the proximal tubules. This may be related to increased susceptibility to various external stimuli. For further detailed analysis, studies using proximal tubule-specific ICE mice are currently performed.