ABSTRACT
In mammals, males and females exhibit anatomical, hormonal, and metabolic differences. A major example of such sex dimorphism in mouse involves hepatic drug metabolism, which is also a noticeable target of circadian timekeeping. However, whether the circadian clock itself contributes to sex-biased metabolism has remained unknown, although several daily output parameters differ between sexes in a number of species, including humans. Here we show that dimorphic liver metabolism is altered when the circadian regulators Cryptochromes, Cry1 and Cry2, are inactivated. Indeed, double mutant Cry1(-/-) Cry2(-/-) male mice that lack a functional circadian clock express a number of sex-specific liver products, including several cytochrome P450 enzymes, at levels close to those measured in females. In addition, body growth of Cry-deficient mice is impaired, also in a sex-biased manner, and this phenotype goes along with an altered pattern of circulating growth hormone (GH) in mutant males, specifically. It is noteworthy that hormonal injections able to mimic male GH pulses reversed the feminized gene expression profile in the liver of Cry1(-/-) Cry2(-/-) males. Altogether, our observations suggest that the 24-h clock paces the dimorphic ultradian pulsatility of GH that is responsible for sex-dependent liver activity. We thus conclude that circadian timing, sex dimorphism, and liver metabolism are finely interconnected.
