Housing temperature affects the circadian rhythm of hepatic metabolism and clock genes.

Environmental temperature remarkably impacts on metabolic homeostasis, raising a serious concern about the optimum housing temperature for translational studies. Recent studies suggested that mice should be housed slightly below their thermoneutral temperature (26°C). On the other hand, the external temperature, also known as a zeitgeber, can reset the circadian rhythm. However, whether housing temperature affects the circadian oscillators of the liver remains unknown. Therefore, we have compared the effect of two housing temperatures, namely 21°C (conventional; TC) and 26°C (thermoneutral; TN), on the circadian rhythms in mice. We found that the rhythmicity of food intake showed an advanced phase at TC, while the activity was more robust at TN, with a prolonged period onset. The serum levels of norepinephrine were remarkably induced at TC, but failed to oscillate rhythmically at both temperatures. Likewise, circulating glucose levels were increased but were non-rhythmic under TC. Both total cholesterol and triglycerides levels were induced at TN, but showed an advanced phase under TC. Additionally, the expression of hepatic metabolic genes and clock genes remained rhythmic at both temperatures, with the exception of G6Pase, Fasn, Cpt1a and Cry2, at TN. Nevertheless, the liver histology examination did not show any significant changes in response to housing temperature. Although the non-consistent trends of phase changes in each temperature, our results suggest a non-reductant role of temperature in mouse internal rhythmicity resetting. Thus, the temperature-controlled internal circadian synchronization within organs should be taken into consideration when optimizing housing temperature for mice.