Modelling Sex Differences in Circadian Regulation of Kidney Function of the Mouse

Kidney function is regulated by the circadian clock. Not only do glomerular filtration rate (GFR) and urinary excretion oscillate during the day, the expressions of several renal transporter proteins also exhibit circadian rhythms. Interestingly, the circadian regulation of these transporters may be sexually dimorphic. Thus, the goal of this study is to investigate the mechanisms by which kidney function of the mouse is modulated by sex and time of day. To accomplish this, we have developed the first computational models of epithelial water and solute transport along the mouse nephrons that represent the effects of sex and circadian clock on renal hemodynamics and transporter activity. We conduct simulations to study how the circadian control of renal transport genes affects overall kidney function, and how that process differs between male and female mice. Simulation results predict that tubular transport differs substantially among segments, with relative variations in water and Na+ reabsorption along the proximal tubules and thick ascending limb tracking that of GFR. In contrast, relative variations in distal segment transport are much larger, with Na+ reabsorption almost doubling during the active phase. Oscillations in Na+ transport drive K+ transport variations in the opposite direction. Model simulations of BMAL1 knockout mice predict a significant reduction in net Na+ reabsorption along the distal segments in both sexes, but more so in males than females. This can be attributed to the reduction of mean ENaC activity in males only, a sex-specific effect that may lead to a reduction in blood pressure in males.