Key renal metabolic differences in healthy male and female Sprague Dawley rats

Abstract

IntroductionUnderstanding and identifying differences in biological processes between males and females are critical for developing the sex‐based treatments for diseases. Mitochondrial dysfunction has been implemented in various kidney diseases yet baseline mitochondrial function and related sex differences within the kidney are not well established. Our previous data obtained in isolated renal mitochondria showed higher oxygen consumption and overall antioxidant capacity, and attenuated mitochondrial permeability transition in males. There is a pressing need for a more complete understanding of normal kidney function; to close this gap in knowledge, we hypothesized that divergent metabolic processes may influence the differences in mitochondrial bioenergetics and antioxidant capacity that we have previously identified.MethodsTissues were isolated from the kidneys collected from male and female Sprague Dawley (SD) rats at 11 weeks of age (Charles River labs, USA). The kidneys were perfused via the abdominal aorta with PBS/heparin solution to remove excess blood. Immediately following kidney collection, the cortex and medulla were isolated and snap frozen for metabolomic analysis. Metabolic profiles of renal cortices and medullae were generated using UHPLC‐HRMS, and metabolites were identified by retention time exact mass using MAVEN and MetaboAnalyst software. Ingenuity Pathway Analysis (IPA) was used to visualize and identify pathways of interests.Results. A total of 174 mitochondria‐focused metabolites were measured; to be considered significant, cutoffs of a 1.2 fold change (FC) with a corresponding p‐value of 0.05 were used. In the renal cortex and medulla, respectively, 22 and 38 metabolites were identified as increased or decreased in males compared to the females. Initial analysis demonstrated clear stratification of metabolite groups between male and female samples, as well as cortical and medullary tissues. Females exhibited upregulated metabolites implicated in protein and nucleic acid synthesis pathways such as UDP‐glucuronic acid (cortex/medulla, FC=1.796/1.615, p=0.013/<0.001), UDP‐D‐glucose (cortex/medulla, FC=1.415/1.594, p=<0.001/<0.001), guanosine(cortex/medulla, FC=1.290, p=0.018), and thymidine (cortex, FC=1.227, p=<0.001). Males, on the other hand, showed an upregulation of metabolites involved in the Kynurenine pathway (such as xanthurenic acid (cortex, FC=2.023, p=0.02), which is involved in NAD+ synthesis. Most interestingly, male kidneys also exhibited a major upregulation 5’‐methylthioadenosine (MTA) compared to females in both the cortex and the medulla (cortex/medulla, FC=41.88/62.88, p=0.002/0.004). MTA is involved in the polyamine metabolism and spermine/spermidine signaling, known to have antioxidant properties and attenuate diabetic kidney disease and AKI.ConclusionsWe report differences in metabolites in the cortex and medulla of young healthy male and female rats, primarily, related to their ability to utilize glucose and metabolize protein, and regulate spermine/spermidine pathway, which could explain differences in antioxidant capacity. The observed sex‐related dissimilarities indicate that male and female kidneys at least partially rely on different metabolic pathways, which opens up opportunities to develop new renal disease treatments targeting males and females separately.