Acute kidney injury (AKI) afflicts substantial numbers of hospitalized patients, particularly those who are critically ill. Because protection from AKI in females is observed both clinically and in animal models, a better elucidation of the underlying biology of this protection may be essential to providing novel, effective intervention to both females and males with AKI. In support of a sex-based susceptibility to AKI, we have shown that female mice undergoing cisplatin-induced AKI (CP) have preserved renal function compared to males, which have significantly worse AKI. Clarity in the mechanisms that underpin resistance of females to renal injury has the potential to illuminate unique pathological mechanisms and represents a critical gap in our knowledge. Mitochondrial dysfunction is noted consistently as a contributor to the outcomes of AKI, and estrogen alters mitochondrial bioenergetics, perhaps via estrogen receptors that may be present in mitochondria. The primacy of mitochondrial function in sex-defined susceptibility will be confirmed in this proposal by examining a novel mouse model, developed at our institution, of mitochondrial-nuclear exchange (MNX) (Aim 1). These mice have an exchange between two strains of mice such that the MNX mice have nuclear characteristics of one strain of mice and the mitochondrial characteristics of another strain of mice. Our preliminary data demonstrate that the parental strains of the MNX mice have different sex-based profiles in susceptibility to AKI allowing for the investigation of the influence of these organelles in an injury model. A second modulation of mitochondrial function will be examined with thermoneutrality, the ambient temperature at which no additional mitochondrial shunting to heat generation is required to maintain core body temperature. Standard vivarium temperatures are typically at ~22-23C (TS), while thermoneutral temperatures for rodents is ~30C (TT). Thermoneutrality alters sex-differences in other organ systems, but has not been studied in AKI and will be examined in these studies (Aim 2). Examination of changes in mitochondrial function with administration of estrogen or testosterone to modulate susceptibility to AKI have not investigated long-term hormone administration. Long-term administration of hormones, particularly cross-sex administration reflecting the status of transgender individuals, has been minimally studied, and not at all in the kidney (Aim 3). The integrated overall hypothesis is that mitochondrial bioenergetics and dynamics alters susceptibility to AKI in a sex-specific manner. In establishing how sex differences are modulated in these different paradigms, these studies will provide the baseline understanding needed to better define “female AKI” and determine nuanced differences that may be exploited in interventions.