Sexual dimorphisms in renal mitochondrial bioenergetics
Authors: Spires Denisha R. , Schibalski Ryan S. , Sultanova Regina F. , Domondon Mark , Lysikova Daria , Stadler Krisztian , Ilatovskaya Daria 
Published: May 2022

Background

Studies have shown that men have higher incidences of end‐stage renal disease than women at every point across the lifespan. Animal models for various renal diseases have similar occurrence with males being affected more frequently. Recent efforts have been heavily focused on delineating the mechanisms behind these sex‐based differences from various angles, with the mitochondria being highlighted as a target for sex difference‐related renal pathologies. The goal of this study is to investigate the sexual dimorphisms of renal mitochondria and their dependency on renal hemodynamics before disease onset.

Methods

Mitochondria were isolated from PBS‐flushed kidneys of Sprague Dawley male (SDM) and female (SDF) rats at 11 weeks of age using differential centrifugation. Renal cortex (SDMC vs SDFC) and medulla (SDMMvs SDFM) were separated for individual measurements. Mitochondrial membrane potential and hydrogen peroxide production were measured in spectrofluorimetry using the fluorescent dyes TMRM and Amplex Red, respectively. A portion of mitochondria were submitted to a histology core for electron microscopy. Additionally, mitochondrial oxygen consumption rate (OCR) was also assessed using Seahorse assay. Lipid peroxide radical formation was detected using electron paramagnetic resonance (EPR) with in vivo spin trapping. As a measure of renal function, GFR was assessed using FITC‐Inulin in conscious animals.

Results

Electron microscopy revealed similar yield of mainly round‐shaped isolated mitochondria with retained cristae and membrane structures in all groups. SDFM showed a higher membrane potential than SDMM (238.1±12.4 vs 162.0±8.8 au, p<0.001; respectively). Both SDFC and SDFM had higher hydrogen peroxide production in comparison to their male counterparts (cortex: 99443.7±3061.7 vs 69943.4±1708.6 au/protein, p<0.001; respectively. medulla: 113366.7±5430.7 vs 60613±2297.1 au/protein, p<0.001; respectively). Overall female mitochondria exhibited decreases in their basal, ATP‐linked, leaked OCRs as well as spare capacity compared to males (spare capacity: cortex: 5.9±0.6 vs 14.3±1.3, p<0.001; respectively. medulla: 4.9±0.6 vs 11.6±0.7 pmol/min/protein, p<0.001; respectively). EPR showed similar lipid peroxide radical levels in both sexes and sections of kidney. In the next part of the study, we explored if renal mitochondrial bioenergetics correlated with the GFR of the animal. Our data show the following GFR values for male and female rats as normalized to two kidney weights (2KW) and 2KW/ total body weight (2KW/TBW), respectively: 1.4±0.2 vs 0.8±0.1 mL/min/2KW, p=0.1416 and 0.5±0.1 vs 0.2±0.02 mL/min/2KW/TBW, p=0.0143. We did not observe any correlation between mitochondrial membrane potential and ROS production (measured in the isolated renal cortical mitochondria) with GFR in male or female rats (n= 5 in each group).

Conclusions

Overall, we show here that female renal mitochondria exhibit lower oxygen consumption, higher ROS emission, and membrane potential vs males; however, lipid peroxidation is similar. Currently, we do not see a correlation between mitochondrial bioenergetics and GFR. More studies designed with higher statistical power are required to further elucidate the relationship between renal blood flow and mitochondrial bioenergetics.