Sarcosine decreases in sarcopenia and enhances muscle regeneration and adipose thermogenesis by activating anti-inflammatory macrophages.

Age-related changes in circulating metabolites influence systemic physiology and may contribute to diseases such as sarcopenia. Although metabolic dysregulation is closely linked to sarcopenia, the roles of specific metabolites remain unclear. In this study, we performed comprehensive plasma metabolomic and lipidomic analyses across two cohorts comprising 1,013 individuals, uncovering the metabolic characteristics of sarcopenia, including a notable decline in plasma sarcosine levels in both aging patients and those with sarcopenia. Functional studies in mice showed that sarcosine helps maintain muscle mass homeostasis during aging, promotes adipose thermogenesis and enhances muscle regeneration. We demonstrate here that sarcosine activated the GCN2 signaling pathway to enhance anti-inflammatory macrophage polarization, promoting adipose thermogenesis and muscle regeneration. These effects may increase energy expenditure and restore metabolic balance to reduce chronic inflammation and improve insulin sensitivity, which are crucial for managing sarcopenia. This study underscores the potential of sarcosine supplementation as an adjunctive strategy via macrophage modulation for preventing sarcopenia in older adults.