Effect of adrenal-specific BMAL1 knockout on clock gene expression in the liver

Abstract

Brain and muscle ARNT-Like 1 (BMAL1) is a circadian clock transcription factor that regulates physiological functions. Circadian rhythms are 24-hour oscillations that are regulated by a molecular clock that exists in nearly every tissue in the body. The core proteins that coordinate this clock are BMAL1, CLOCK, CRY, and PER. Male adrenal-specific Bmal1 (ASCre/+::Bmal1) KO mice displayed blunted serum corticosterone rhythms, altered blood pressure rhythm, and altered timing of eating, but there is a lack of knowledge in females. This study investigates the role of adrenal BMAL1 in hepatic clock RNA expression. Mice were placed in metabolic cages to measure 12-h urinary aldosterone after a standard diet and 7 days low-salt diet, as well as daily body weight, 12-h food and water intake, and renal sodium and potassium balance. Using adrenal-specific Bmal1 knockout (ASCre/+::Bmal1) mice and littermate controls of both sexes, livers were collected at 06:00 and 18:00. KO mice exhibited abnormal eating behaviors, pointing to possible liver function implications. Adrenal glands and livers were collected at 6am and 6pm to measure the expression of aldosterone synthesis genes and clock genes. Hepatic RNA was isolated and core clock transcripts were quantified by qPCR.  In the liver, we observed significant sex differences in Bmal1, Clock, Cry1, Cry2, and Per1 expression, along with time-of-day and genotype effects notably in Clock. These findings support robust sex differences in hepatic circadian gene expression but do not support adrenal BMAL1 as a primary driver of liver clock transcriptional rhythms. Future work will seek to understand protein expression and lipid metabolism to determine sex-specific mechanisms of behavior and hepatic clock function.