Laskin Grant R, Steiner Jennifer L, Ayers-Creech Wayne A, Rossetti Michael L, Dunlap Kirsten R, Vied Cynthia, Lee Choogon, Greene Nicholas P, Fix Dennis K, Laitano Orlando, Parvatiyar Kislay, Gordon Bradley S
Department of Health, Nutrition, and Food Sciences, Florida State University, Tallahassee, FL 32306, USA.
Institute of Sports Sciences and Medicine, Florida State University, Tallahassee, FL 32306, USA.
Function (Oxf). 2025 Aug 1;6(4). doi: 10.1093/function/zqaf030.
Low testosterone in males (hypogonadism) is associated with limb muscle mass loss, yet the underlying mechanisms of muscle mass loss remain largely unknown. We previously showed androgen deprivation disrupted limb muscle molecular clock function, and the disruption coincided with elevated levels of the primary molecular clock suppressor, Period 2 (Per2). The purposes herein were to determine if PER2 overexpression leads to muscle atrophy and if preventing PER2 accumulation blunts limb muscle mass loss in response to androgen deprivation. Here, we identify Per2 as a negative regulator of muscle size. Overexpression of Per2 in differentiated C2C12 myotubes reduced myotube diameter, while deletion of Per2 in male mice partially preserved tibialis anterior (TA) mass following castration. The muscle-sparing effect of Per2 deletion in vivo was specific to the TA despite evidence of molecular clock disruption and mass loss in other muscles. Subsequently, we show overexpression of the other primary clock suppressor, Period 1 (Per1) also reduced myotube diameter in differentiated C2C12 myotubes. Mechanistically, both Per1 and Per2 overexpression in vitro induced muscle atrophy in part by an autocrine-mediated mechanism likely involving inflammation as their overexpression induced an inflammatory gene expression signature and increased cytokine/chemokine secretion. Moreover, incubation of C2C12 myotubes in the media conditioned from Per1 or Per2 overexpressing myotubes reduced myotube diameter. Several inflammatory genes identified in vitro were also altered in the limb muscles in response to androgen deprivation. These findings identify a previously unrecognized role for Per1/2 in regulating skeletal muscle mass with implications for muscle loss during hypogonadism.
男性低睾酮水平（性腺功能减退）与肢体肌肉量减少有关，但肌肉量减少的潜在机制仍 largely 未知。我们之前表明雄激素剥夺会破坏肢体肌肉分子时钟功能，且这种破坏与主要分子时钟抑制因子 Period 2（Per2）水平升高同时发生。本文的目的是确定 PER2 过表达是否会导致肌肉萎缩，以及阻止 PER2 积累是否会减轻因雄激素剥夺引起的肢体肌肉量减少。在此，我们确定 Per2 是肌肉大小的负调节因子。在分化的 C2C12 肌管中过表达 Per2 会减小肌管直径，而在雄性小鼠中敲除 Per2 可在去势后部分保留胫骨前肌（TA）的质量。尽管有证据表明其他肌肉存在分子时钟破坏和质量损失，但 Per2 敲除在体内对肌肉的保留作用在 TA 中是特异性的。随后，我们表明另一个主要时钟抑制因子 Period 1（Per1）的过表达在分化的 C2C12 肌管中也会减小肌管直径。从机制上讲，Per1 和 Per2 在体外的过表达部分通过自分泌介导的机制诱导肌肉萎缩，这可能涉及炎症，因为它们的过表达会诱导炎症基因表达特征并增加细胞因子/趋化因子分泌。此外，将 C2C12 肌管在由过表达 Per1 或 Per2 的肌管条件培养基中培养会减小肌管直径。体外鉴定出的几种炎症基因在因雄激素剥夺的肢体肌肉中也发生了改变。这些发现确定了 Per1/2 在调节骨骼肌质量方面以前未被认识的作用，这对性腺功能减退期间的肌肉损失具有影响。
