Effect of nighttime light exposure on glucose metabolism in protein-restricted mice.

Disruption of biological rhythms due exposure to artificial light at night (ALAN) has been emerged as new risk factor for metabolic diseases. However, it remains largely unexplored the effects induced by exposure to ALAN on energy metabolism with concomitant misalignment in the circadian system caused by nutritional imbalance. Objective: Here we evaluate whether low-protein diet could enhance the effects induced by exposure to ALAN on the energy metabolism and consequently predispose to metabolic disorders. Male C57BL6/J mice were weaned on a normal protein (NP) or a low-protein (LP) diet and housed on 12h light/dark (L/D) cycle. After 6 weeks, mice maintained on their respective diets were subdivided into normal light/dark cycle or exposed to ALAN for 8 weeks. We observed that exposure to ALAN concomitant to LP diet disrupts the behavioral rhythms, without shifting the timing of food intake. Furthermore, exposure to ALAN lead to increased body and fat pad weights, higher levels of fast and fed glycemia and glucose intolerance independent of the diet consumed. Importantly the insulin resistance developed in mice exposed to ALAN was diet-dependent. At the molecular level, exposure to ALAN concurrent with LP diet increased the expression of Phosphoenolpyruvate carboxykinase 1 in both periods analyzed and inverted the pattern of Fibroblast growth factor 21 (Fgf21) expression in the liver. Our data suggest that dietary protein restriction modulates the effects induced by nighttime light exposure on glucose metabolism, which could be partially related with the dysregulation on hepatic Fgf21 expression.