NRSA for Samaneh DiMartino: Alterations of Branched Chain Amino Acid (BCAA) Catabolism in Acute Kidney Injury and Fibrosis

Abstract/Project Summary Acute kidney injury (AKI) is a major risk factor for fibrosis and chronic kidney disease (CKD), but no therapies currently exist to slow or reverse this process. AKI affects 10-15% of hospitalized patients and over 50% in the intensive care unit (ICU). Proximal tubule (PT) cells are highly susceptible to AKI and undergo significant metabolic changes, directly contributing to injury. PT cells use fatty acid oxidation (FAO) and branched chain amino acid (BCAA) catabolism to generate ATP, however during AKI, both pathways are downregulated. Therefore, activation of these metabolic pathways may attenuate kidney injury, as shown by promising studies of FAO activation in mice. We have recently shown that pharmacological activation of BCAA catabolism protected male mice from aristolochic acid (AAI) nephrotoxic AKI by improving mitochondrial bioenergetics and attenuating mechanistic target of rapamycin complex 1 (mTORC1) signaling. Therefore, this study aims to elucidate the effect of activation of BCAA catabolism in treating AKI and the transition to fibrosis. Recent studies have showed that women are protected from AKI compared to men, which may be due to sex hormones and/or X- inactivation in women, and this is also the case in female versus male mice. Most studies of AKI and fibrosis have utilized male mice, which is a limitation to further application of potential treatments. My preliminary data analyzing kidney cortex RNA-seq from male and female AKI patients versus healthy subjects showed that the BCAA pathway was downregulated in both sexes; however, the downregulated genes were different. Interestingly in these human data set, the FAO pathway was downregulated in AKI males versus healthy males but not in AKI females. Primary PT cells from littermate male and female mice showed transcriptional downregulation of BCAA enzymes in both sexes. Activation of BCAA catabolism improved mitochondrial respiration and attenuated the BCAA accumulation in male primary PT cells but not female cells. Furthermore, female mice injected with the same dose of AAI which causes kidney injury in males, showed no injury. Therefore, this study will also elucidate the different metabolic and non-metabolic pathway disturbances and their downstream effects e.g. on mTORC1 signaling in male and female AKI mice models. To fulfill this approach, we will undertake comparative snRNA-seq and phospho-proteomics in male AAI-induced AKI mice, AAI dose-matched female mice (no injury), and injury-matched female mice (higher AAI dose). The long- term goal of this proposal is to investigate defective sex-dependent metabolic and non-metabolic pathways in the PT during AKI which may have implications for targeted sex-specific therapeutic strategies for AKI and transition to fibrosis. Under the mentorship of Dr. Piret and Dr. Mallipattu, the training plan includes advanced laboratory techniques such as snRNA-seq, phospho-proteomics, alongside courses on Responsible Conduct of Research to ensure ethical standards. Moreover, Stony Brook University provides a dynamic and collaborative environment for this proposal, supported by a network of core facilities, expertise and advanced technologies.