d -Alanine Affects the Circadian Clock to Regulate Glucose Metabolism in the Kidney.

Key Points: d-Alanine affects the circadian clock to regulate gluconeogenesis in the kidney. d-Alanine itself has a clear intrinsic circadian rhythm, which is regulated by urinary excretion, and acts on the circadian rhythm. d-Alanine is a signal activator for circadian rhythm and gluconeogenesis through circadian transcriptional network.

Background: The aberrant glucose circadian rhythm is associated with the pathogenesis of diabetes. Similar to glucose metabolism in the kidney and liver, d-alanine, a rare enantiomer of alanine, shows circadian alteration, although the effect of d-alanine on glucose metabolism has not been explored. Here, we show that d-alanine acts on the circadian clock and affects glucose metabolism in the kidney.

Methods: The blood and urinary levels of d-alanine in mice were measured using two-dimensional high-performance liquid chromatography system. Metabolic effects of d-alanine were analyzed in mice and in primary culture of kidney proximal tubular cells from mice. Behavioral and gene expression analyses of circadian rhythm were performed using mice bred under constant darkness.

Results: d-Alanine levels in blood exhibited a clear intrinsic circadian rhythm. Since this rhythm was regulated by the kidney through urinary excretion, we examined the effect of d-alanine on the kidney. In the kidney, d-alanine induced the expressions of genes involved in gluconeogenesis and circadian rhythm. Treatment of d-alanine mediated glucose production in mice. glucose production assay demonstrated that the treatment of d-alanine induced glucose production in primary culture of kidney proximal tubular cells, where d-amino acids are known to be reabsorbed, but not in that of liver cells. Gluconeogenetic effect of d-alanine has an intraday variation, and this effect was in part mediated through circadian transcriptional network. Under constant darkness, treatment of d-alanine normalized the circadian cycle of behavior and kidney gene expressions.

Conclusions: d-Alanine induces gluconeogenesis in the kidney and adjusts the period of the circadian clock. Normalization of circadian cycle by d-alanine may provide the therapeutic options for life style–related diseases and shift workers.