Nephron-Specific Deletion of Circadian Clock Gene Bmal1 Alters the Plasma and Renal Metabolome and Impairs Drug Disposition

Abstract

The circadian clock controls a wide variety of metabolic and homeostatic processes in a number of tissues, including the kidney. However, the role of the renal circadian clocks remains largely unknown. To address this question, we performed a combined functional, transcriptomic, and metabolomic analysis in mice with inducible conditional knockout (cKO) of BMAL1, which is critically involved in the circadian clock system, in renal tubular cells (Bmal1/Pax8-rtTA/LC1 mice). Induction of cKO in adult mice did not produce obvious abnormalities in renal sodium, potassium, or water handling. Deep sequencing of the renal transcriptome revealed significant changes in the expression of genes related to metabolic pathways and organic anion transport in cKO mice compared with control littermates. Furthermore, kidneys from cKO mice exhibited a significant decrease in the NAD-to-NADH ratio, which reflects the oxidative phosphorylation-to-glycolysis ratio and/or the status of mitochondrial function. Metabolome profiling showed significant changes in plasma levels of amino acids, biogenic amines, acylcarnitines, and lipids. In-depth analysis of two selected pathways revealed a significant increase in plasma urea level correlating with increased renal Arginase II activity, hyperargininemia, and increased kidney arginine content as well as a significant increase in plasma creatinine concentration and a reduced capacity of the kidney to secrete anionic drugs (furosemide) paralleled by an approximate 80% decrease in the expression level of organic anion transporter 3 (SLC22a8). Collectively, these results indicate that the renal circadian clocks control a variety of metabolic/homeostatic processes at the intrarenal and systemic levels and are involved in drug disposition.

Circadian regulation of renal function

“…The proximal tubule may also play a significant role in chronopharmacology by way of its ability to control renal tubular handling of drugs through various organic acid and base transporters, which display a circadian pattern of expression that is regulated by clock genes [28]. In the nephron-specific Bmal1 KO mouse, organic anion transporter 3 (OAT3) expression is severely reduced and impairs the natriuretic response to furosemide [28].…”

“…In the nephron-specific Bmal1 KO mouse, organic anion transporter 3 (OAT3) expression is severely reduced and impairs the natriuretic response to furosemide [28]. …”

“…The Bmal1 knockout mouse lacks a circadian blood pressure rhythm, but is considered hypotensive since blood pressure is similar to genetic controls during the inactive phase, but fails to increase during the active phase [43,83,84]. Mice with a loss of Bmal1 in the renal tubules maintain a normal circadian rhythm, although with a slight but significantly lower systolic BP [28]. A mouse model where the renin promoter drive Bmal1 gene deletion displays a significantly lower systolic and diastolic BP compared to controls [43].…”

“…Recently, the circadian clock in the renal tubules was shown to play a role in drug and metabolite breakdown. They observed altered metabolism when the Bmal1 gene was deleted specifically throughout the length of the nephron of mice [28]. In addition, they found that the organic anion transporter 3 (OAT3), a transporter important for the secretion of creatinine among other substances [87], had reduced mRNA and protein levels, leading to a reduction in the amount of the loop diuretic furosemide excreted in the urine [28].…”

“…They observed altered metabolism when the Bmal1 gene was deleted specifically throughout the length of the nephron of mice [28]. In addition, they found that the organic anion transporter 3 (OAT3), a transporter important for the secretion of creatinine among other substances [87], had reduced mRNA and protein levels, leading to a reduction in the amount of the loop diuretic furosemide excreted in the urine [28]. This study provides the only evidence to our knowledge that the renal molecular clock can regulate the excretion of drugs and control metabolism, but has important implications for chronotheraputic research.…”