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Background: Histologic acute graft pyelonephritis (HAGPN) after kidney transplantation (KT) has been assessed less frequently than urinary tract infections (UTIs) or clinical acute graft pyelonephritis. Risk factors for HAGPN, its association with graft loss, and measures that might prevent it are not known. Methods:We performed a retrospective review of HAGPN cases identified from KT occurring between January 2008 and December 2017 at our institution. We compared the HAGPN cases to a randomly selected control group of KTs to identify risk factors using univariate and multivariate Cox regression models. The association between HAGPN and graft loss was also assessed, similarly. Results: HAGPN was identified in 46 of 1391 patients (cumulative incidence, 5% [95% CI, 3%-7%]) undergoing KT at a single center from January 2008 through December 2017 (median time to diagnosis, 241 days after KT; interquartile range, 122-755 days). Indications for biopsy were follow-up of treated rejection (n = 20 [43%]), KT protocol biopsy (n = 19 [41%]), and acute kidney injury (n = 7 [15%]). Histologic rejection, UTI, and asymptomatic bacteriuria (ASB) were present in 23 (50%), 9 (20%), and 16 (35%). Multivariate Cox proportional hazards models comparing KT recipients with or without HAGPN (n = 46 and n = 138, respectively) showed that HAGPN was associated with urologic complication by day 30, delayed graft function, previous UTI or ASB, and a history of rejection. In the univariate and multivariate analyses, HAGPN was associated with an increased risk of graft loss. Conclusion: HAGPN is an infrequent, unanticipated, and clinically significant complication of KT.

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DNA damaging agents are a constant threat to genomes in both the nucleus and the mitochondria. To combat this threat, a suite of DNA repair pathways cooperate to repair numerous types of DNA damage. If left unrepaired, these damages can result in the accumulation of mutations which can lead to deleterious consequences including cancer and neurodegenerative disorders. The base excision repair (BER) pathway is highly conserved from bacteria to humans and is primarily responsible for the removal and subsequent repair of toxic and mutagenic oxidative DNA lesions. Although the biochemical steps that occur in the BER pathway have been well defined, little is known about how the BER machinery is regulated. The budding yeast, Saccharomyces cerevisiae is a powerful model system to biochemically and genetically dissect BER. BER is initiated by DNA N-glycosylases, such as S. cerevisiae Ntg1. Previous work demonstrates that Ntg1 is post-translationally modified by SUMO in response to oxidative DNA damage suggesting that this modification could modulate the function of Ntg1. In this study, we mapped the specific sites of SUMO modification within Ntg1 and identified the enzymes responsible for sumoylating/desumoylating Ntg1. Using a non-sumoylatable version of Ntg1, ntg1ΔSUMO, we performed an initial assessment of the functional impact of Ntg1 SUMO modification in the cellular response to DNA damage. Finally, we demonstrate that, similar to Ntg1, the human homologue of Ntg1, NTHL1, can also be SUMO-modified in response to oxidative stress. Our results suggest that SUMO modification of BER proteins could be a conserved mechanism to coordinate cellular responses to DNA damage.