Sex‐Dependent Interplay of the Circadian Clock Protein PER1 and Aldosterone on Renal Sodium Handling
Authors: Douma Lauren Grace , Crislip G. Ryan , Cheng Kit-Yan , Barral Dominique , Masten Sarah , Roig Emilio M. , Beguiristain Kevin , Bratanatawira Phillip , Lynch I. Jeanette , Cain Brian D. , Wingo Charles S. , Gumz Michelle L. 
Published: April 2020

IntroductionThe molecular circadian clock regulates thousands of genes in a tissue‐specific manner, contributing to 24‐hr circadian rhythms of physiological functions, including blood pressure (BP). Healthy individuals exhibit at least a 10% dip in their BP during rest. Loss of this dip is termed non‐dipping and is associated with higher incidence of adverse cardiovascular outcomes and kidney disease. We have shown that global KO of the circadian clock protein PER1 causes non‐dipping hypertension (HTN) in male, but not female mice, in a model of salt‐sensitive HTN (high salt diet plus DOCP, HSDOCP). The altered rhythms in BP are associated with reduced night/day sodium (Na) excretion, suggesting alterations in rhythms of renal function.HypothesisSince the female global PER1 KO mice do not develop non‐dipping HTN, we hypothesize that the female KO mice will maintain normal rhythms of Na excretion, unlike the male KO mice. Additionally, we hypothesize that sex differences in Na excretion will be associated with differences in the renin‐angiotensin‐aldosterone system (RAAS).MethodsMice were acclimated to metabolic cages followed by 12‐hr urine collections during 3 days each of normal Na diet (NS), high Na (HS) diet, and HSDOCP treatment. Urine Na content was measured by flame photometry. Aldosterone (Aldo) was measured by ELISA. Gene expression studies were performed using quantitative RT‐PCR. Genotype and treatment effects were measured by T‐test and 2‐way ANOVA with or without repeated measures. All studies had 6 mice per group.ResultsUnlike male global PER1 KO mice, female global PER1 KO mice maintain normal Na excretion rhythms on HSDOCP (P>0.05). At baseline, urinary Aldo is significantly increased in the male global PER1 KO mice compared to WT (8.5 vs. 4.2ng/24hr, P<0.05), but not in the female KO (10.1 vs. 8.6 ng/24hr, P>0.05). In response to HSDOCP, WT mice decrease renin expression by 50% (P<0.01), but male global PER1 KO mice fail to decrease renin (P>0.05). Female WT and global PER1 KO respond to HSDOCP by downregulating renin expression by 70% (P<0.001). Kidney‐specific KO of PER1 (KS‐PER1) was generated using KSP‐Cadherin Cre to study the role of PER1 in the Aldo‐sensitive distal nephron and collecting duct. Male KS‐PER1 KO mice have higher cumulative Na balance compared to control mice (3.7mEq vs. 2.7mEq, P<0.01), but maintain night/day Na excretion rhythms. Interestingly, KS‐PER1 KO male mice also have higher plasma Aldo compared to control mice at baseline and after HSDOCP treatment (NS: 21 vs. 12; HSDOCP: 4 vs. 2 pg/mL/gBW, P<0.01).ConclusionsGlobal and KS‐PER1 KO results in altered renal Na handling and changes in Aldo levels in male mice. These differences are not observed in the global female KO mice. These results indicate that PER1 in the distal nephron and collecting duct is important for maintaining electrolyte homeostasis and may affect renal Na handling through a sex‐specific mechanism dependent on the RAAS.Support or Funding InformationNIH/NIDDK R01DK109570 to MLG & AHA Fellowship 18POST34030210 to LGD