Differential effects of the clock protein BMAL1, diet, and sex on purinergic receptor expression in the distal nephron

Abstract

The circadian clock protein BMAL1 is a core component of the intrinsic molecular clock mechanism that governs circadian rhythms. We use a kidney-specific Bmal1 knockout mouse model (KS-BMAL1KO) with loss of BMAL1 expression in the distal segments of the kidney. When placed on a potassium-deficient, high salt diet (0K+HS), male KS-BMAL1KO mice do not show an elevation in blood pressure compared to their littermate controls (CNTL), suggesting a protective effect due to loss of BMAL1 in the distal nephron. A low K+ diet predisposes to salt-sensitive hypertension by a high salt diet, in part due to increased sodium retention. Our lab has previously shown that inappropriately high ENaC activity in mice on a high salt diet is due in part to impaired purinergic signaling. The purinergic signaling pathway regulates water and electrolytes in the kidney via purinergic receptors (P2) and our gene expression data show their oscillation in a circadian manner in the kidney. We hypothesized that BMAL1 in distal segments contributes to the regulation of P2 receptor expression. Kidneys from male and female KS-BMAL1KO and CNTL mice were harvested at zeitgeber time (ZT) 0 or ZT12 from mice on a normal or a 0K+HS diet for 10 days. RNA was isolated from the renal medulla and prepared for RNA sequencing (5-9 pooled samples for males, 4-8 for females). Expression levels of P2X and P2Y receptor transcripts were examined. Loss of BMAL1 in distal segments modified P2 receptor expression, as KS-BMAL1KO mice exhibited lower P2Y14 gene expression than CNTL after 0K+HS in both males (78 ± 0, n=7 vs. 49.5 ± 0.7 CPM, n=7, P<.05) and females (85.5 ± 3.5 n=4 vs. 46 ± 8.5 CPM, n=4, P<.05). 0K+HS diet increased P2X7 in CNTL mice compared to normal diet in both males (88.5 ± 9.2, n=5 vs. 189.50 ± 33.2 CPM 114.1, n=7, P<.05) and females (79.5 ± 3.5, n=5 vs. 130.50 ± 3.5 CPM, n=4, P<.05) with no difference in genotype (P=NS). Sex differences were also apparent, as P2Y2 also increased following 0K+HS, but only in male CNTL (327.5 ± 27.6, n=5 vs. 499 ± 24 CPM, n=7, P<.05) and KS-BMAL1KO mice (264 ± 41, n=6 vs. 510 ± 11.3 CPM n=7, P<.05), without a genotype difference. These results support our hypothesis that BMAL1 in distal segments of the nephron contributes to the regulation of selective P2 receptors in the renal medulla, potentially modulating P2 receptor expression through interactions with circadian clock-, dietary- and sex-dependent factors. Our work is supported by the NIH, NIDDK, ASN, and 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.