Osteoprotegrin (OPG) as a therapeutic target to combat age associated muscle loss.

背景护骨素(OPG)是一种更常见的与骨吸收调节有关的循环因子。OPG作为RANK分子的配体(RANKL)的诱饵受体。RANKL和OPG的比例必须保持平衡以维持骨转换(Grimaud等人，2003 Kong等人，1999；Lacey等人，1998)；当RANKL水平升高时，OPG被释放，确保当RANK/RANKL结合时不会持续发生骨吸收。在退行性疾病的小鼠模型中，OPG也从肌肉中释放出来。然而，导致这些变化的具体途径尚未确定(沈等人，2017年；杜弗雷恩等人，2016a；杜弗雷恩等人，2016b；杜弗雷纳等人，2015年)。骨保护素对衰老的影响50岁后，肌肉质量每年下降1-2%，50岁至75岁之间总下降约25%(Delmonico等人，2009；Marcell，2003；LaPier，1997；Waters等人，2008)。对骨质疏松症的最新定义包括三个关键参数：低水平的肌肉力量、肌肉质量/数量和身体表现。肌肉质量和数量是可能的石棺减少症的主要指标(Cruz-Jentoft等人，2018年)。早期诊断和治疗石棺减少症对于减轻因不治疗而加重的个人、社会和经济负担至关重要(Cruz-Jentoft等人，2018年)。

BackgroundOsteoprotegerin (OPG) is a circulating factor more commonly associated with the regulation of bone resorption. OPG acts as a decoy receptor to the ligand of the RANK molecule (RANKL). The proportion of RANKL to OPG must remain balanced to maintain bone turnover (Grimaud et al., 2003 Kong et al., 1999; Lacey et al., 1998); OPG is released when RANKL levels are elevated, ensuring bone resorption does not continually occur when RANK/RANKL are bound. OPG is also released from muscle in murine models of degenerative diseases. However, the specific pathway that causes these changes has not been identified (Shen et al., 2017; Dufresne et al., 2016a; Dufresne et al., 2016b; Dufresne et al., 2015). The Impact of Osteoprotegerin in AgeingAfter the age of 50 years old, muscle mass declines by 1-2% per year, with a total decline of ~25% between the ages of 50 and 75 years (Delmonico et al., 2009; Marcell, 2003; LaPier, 1997; Waters et al., 2008). The most recent definition of sarcopenia includes three key parameters; low levels of muscle strength, muscle quality/quantity and physical performance. Muscle quality and quantity are the primary indicators of probable sarcopenia (Cruz-Jentoft et al., 2018). Early diagnosis and treatment of sarcopenia is essential to mitigate the high personal, social and economic burdens that it becomes associated with when left untreated (Cruz-Jentoft et al., 2018).