Dietary Protein Quality Influences Liver Circadian Rhythms in a GCN2‐dependent Manner

Abstract

Circadian disruption correlates with a wide range of metabolic and neurological disorders. General control non‐derepressible 2 (GCN2) activation, the primary sensory mechanism of amino acid insufficiency, also plays an integral role in maintaining the circadian clock in peripheral tissues such as the liver. The objective of this work is to examine the regulation of the circadian clock via GCN2‐mediated sensing of dietary protein quality. We hypothesized that low protein quality feeding will alter the circadian clock in a GCN2 dependent manner. To test this, wild type (WT) and whole body GCN2 knockout (GCN2KO) mice were housed in total darkness within an environmentally‐controlled indirect calorimetry cabinet and provided a diet either devoid of leucine (LeuD) or amino acid replete (Control) for 8‐days and then killed at 2 circadian time (CT) points 12‐hours apart (CT3, CT15). Following the treatment period, LeuD‐fed GCN2KO mice displayed a 40% reduction in the circadian oscillation of their energy expenditure (p<.001) relative to Controls whereas no such difference was present in their WT counterparts. Measurements of the 12‐hour expression pattern of various circadian oscillatory genes within the liver revealed that GCN2 is necessary for circadian oscillation of Bmal2 mRNA expression independent of diet (p<0.01). Furthermore, LeuD feeding alters the expression pattern of the clock‐controlled genes (CCGs) Ciart, Klf10and Noctby over 5‐, 10‐, and 2‐fold respectively (p<0.05) in a GCN2 dependent manner. Together, these findings demonstrate that dietary protein quality plays a role in the maintenance of circadian rhythms within the liver. Furthermore, GCN2 is required to maintain whole body metabolic rhythms when challenged with a diet of poor protein quality. In observing the alterations in the circadian expression pattern of these CCGs with feeding a low protein quality diet, our findings expand our understanding of the role of dietary amino acid intake and the maintenance of circadian metabolic rhythms within the liver.