Male Kidney‐specific Bmal1 Knockout Mice Show a Similar, Exaggerated Active‐Inactive Period Difference in Ammonia Excretion to Controls after Potassium Deprivation
Authors: Johnston Jermaine G. , Crislip G. Ryan , Douma Lauren G. , Masten Sarah H. , Cheng Kit‐Yan , Lynch I. Jeanette , Barral Dominique , Glasford Krystal , Esser Karen A. , Gumz Michelle L. , Wingo Charles S. 
Published: June 2021

The influence of the circadian clock is manifested in the time‐of‐day variation in commonly recognized renal function parameters such as blood pressure and sodium excretion. Acid‐base balance is another important component of renal function, however the effect of the circadian clock on the diurnal variation of acid excretion, specifically the excretion of ammonia (NH3), has not yet been determined. We used a kidney‐specific Bmal1 knockout mouse model (KS‐Bmal1KO) created by crossing a distal nephron‐specific Ksp‐cadherin cre mouse with mice containing two loxP sites flanking exon 8 of the Bmal1 gene. Based on differences our lab has seen in the expression of genes related to acid‐base homeostasis between KS‐Bmal1KO mice and their littermate Cre‐ controls (CNTL), we hypothesized that there would be genotype differences in urinary NH3 excretion. Male control and KS‐Bmal1KO mice were placed in metabolic cages and had their urine collected in 12‐hour intervals, spanning the active (6pm‐6am) or inactive (6am‐6pm) periods. After three days on a normal potassium (K+) diet, the mice were switched to a nominally potassium‐free (0 K+) diet for five days with free access to water. Urine samples from the last two time points of the normal K+ and 0 K+ diets were analyzed for NH3. Under a normal K+ diet, CNTL mice displayed a significant time‐of‐day difference in urinary NH3 excretion, with values greater during the active period compared to the inactive period (66 ± 10 vs. 19 ± 5 μmol/12hr NH3, n=5, P<.05). KS‐Bmal1KO exhibited a similar pattern on normal K+, excreting more NH3 during the active period (78 ± 3 vs. 16 ± 3 μmol/12hr NH3, n=5, P<.05). After five days on the 0 K+ diet, the active‐inactive (A‐I) difference of NH3 excretion was exacerbated in CNTL mice, resulting in a significantly greater difference compared to normal K+diet (137 ± 15 vs. 47 ± 10 μmol/12hr NH3 P<0.05). KS‐Bma11KO mice also displayed an increased A‐I difference compared to their normal K+ diet values (142 ± 33 vs. 62 ± 5 μmol/12hr NH3, P<0.05). There were no differences however, in the A‐I difference between genotypes. Despite not observing any major effects of Bmal1 deletion in the distal nephron of the kidney on NH3 excretion under the conditions tested, these results suggest that the time‐of‐day differences in NH3 excretion observed in male mice are augmented in response to dietary K+ deprivation.Support or Funding InformationThis research was supported in part by the research project grant on Per1 and the Kidney Clock in Hypertension (NIH grant DK109570‐02), and the T32 training grant on Pre‐ and Postdoctoral Training in Nephrology and Hypertension (T32 DK104721).This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.