Elevated expression of the molecular clock suppressors Period 1 and Period 2 promote myotube atrophy in vitro with implications to the loss of limb muscle mass following androgen deprivation

Low testosterone levels in men (hypogonadism) are associated with loss of limb muscle mass. We previously showed molecular clock function is disrupted in limb muscle by androgen deprivation. That clock disruption coincided with higher protein levels of the molecular clock suppressor, Period 2 (Per2). The primary purpose of this study was to assess whether Per2 regulates muscle size. Transducing fully differentiated C2C12 myotubes with adenovirus overexpressing Per2 was sufficient to lower myotube diameter. Moreover, deletion of Per2 in male mice partially maintained mass of the tibialis anterior (TA) muscle following castration-induced androgen deprivation. The partial maintenance of mass was specific to the TA even though molecular clock disruption is evident in other limb muscles. Thus, the secondary purpose of this study was to assess whether Per1 also regulates muscle size. Overexpression of the other primary molecular clock suppressor, Per1, in C2C12 myotubes was also sufficient to decrease myotube diameter. The lower myotube diameter in response to Per1 or Per2 overexpression was due in part to an autocrine-mediated inflammatory signals as conditioned media from Per1 or Per2 overexpressing myotubes contained elevated cytokines/chemokines, and the Per conditioned media was sufficient to lower C2C12 myotube diameter. The mRNA contents of inflammatory genes altered following Per1 or Per2 overexpression in vitro were altered in limb muscle in vivo following castration. These data define a novel muscle mass/size regulatory function of the primary molecular clock suppressors with direct implications for their role in regulating limb muscle mass loss in response to low androgen levels