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

BACKGROUND: The aberrant glucose circadian rhythm is associated with the pathogenesis of diabetes. Similar to glucose metabolism in 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 analysed in mice and in primary culture of kidney proximal tubular cells from mice. Behavioural 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 kidney. In kidney, d-alanine induced expressions of genes involved in gluconeogenesis and circadian rhythm. Treatment of d-alanine mediated glucose production in mice. Ex vivo glucose production assay demonstrated that 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 behaviour 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.