Sex-specific differences in kidney clock gene expression in mice in response to a low potassium, high salt diet
Authors: Costello Hannah , Cheng Kit-Yan , Johnstone Jermaine , Juffre Alexandria , Douma Lauren , Gumz Michelle , Crislip G. Ryan 
Published: May 2023

Clinical studies demonstrate that women have exacerbated salt-sensitive blood pressure (BP) responses compared to men. However, most studies examining the molecular mechanisms involved in salt-sensitive hypertension focus on males. Accumulating evidence suggests the molecular circadian clock is crucial for BP control and our lab has a particular interest in how kidney circadian clocks contribute to BP and salt-sensitivity in males and females. Core components of the circadian clock are the proteins BMAL1, CLOCK, CRY, and PER. BMAL1 and CLOCK are the positive arm and PER and CRY are the negative arm of this transcriptional/translational feedback loop. We have found sex-specific responses in BP/electrolyte handling in circadian gene knockout models, suggesting the clock mechanism may differ between males and females. Therefore, we hypothesize that kidney clock gene expression differs between males and females and that this is altered in response to the salt-sensitive environment created by a low potassium, high salt diet. To test this, we performed RNAseq analysis on kidney medulla from male and female mice on a C57BL/6 background on either a control diet or in response to a 0% potassium, high salt (0KHS; 4% NaCl) diet. Dissected kidney medulla RNA samples were collected at the onset of the rest phase and the active phase (6AM and 6PM; n=4-7). RNA sequencing was performed using pooled samples and analyses from raw counts were performed. Clock gene expression was assessed and initial comparisons were made using 3-way ANOVA to determine the effect of time, sex and diet with Sidak multiple comparisons post hoc analysis.As expected, we show significant time-of-day effects on all clock gene expression assessed in the kidney medulla, including Bmal1, Clock, Cry1, and Per1 (time effect p<0.0001). There were sex-specific differences as Bmal1, Clock, Cry1, and Per1 were higher both at 6AM and 6PM in females compared to males on a control diet (sex effect p<0.0001). Interestingly, these sex differences were lost in Clock and Per1 expression in animals on a 0KHS diet. This was caused by Clock significantly decreasing at 6AM in females ( p=0.0019) but increasing at 6AM in males ( p=0.0360). Furthermore, 0KHS diet caused Per1 expression to decrease at 6PM in females ( p=0.0026) with no change in males. Bmal1 expression decreased at both 6AM ( p<0.0001) and 6PM ( p=0.0076), with no change in Bmal1 expression in males in response to 0KHS. Unlike Bmal1, Cry1 expression increased at both 6AM ( p=0.0002) and 6PM ( p=0.0007) in males in response to 0KHS diet, with no change in females and expression remaining higher in females.Consistent with our hypothesis, clock gene expression in the kidney medulla differs between males and females with sex-specific alterations in clock gene expression in response to a 0KHS diet. Future work will focus on whether these sex-specific differences in the kidney clock contribute to regulation of BP and salt-sensitivity. NIDDK, ASN, AHA This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.