Disrupted Macrophage Metabolic Reprogramming in Aged Soleus Muscle During Early Recovery following Disuse Atrophy

Aged skeletal muscle is characterized by impaired muscle recovery following disuse and coincides with an impaired muscle pro-inflammatory macrophage response. Macrophage inflammatory status (polarization) is regulated by its metabolic state, but to date, little is understood of macrophage metabolism and its relation to macrophage polarization in the context of muscle recovery and aging. Therefore, the purpose of this study was to thoroughly characterize macrophage metabolism and polarization in aged muscle during early recovery from disuse atrophy using single cell RNA sequencing and functional assays. Young (4-5 mo) and old (20-22 mo) male C57BL/6 mice underwent 14 days of hindlimb unloading followed by 4 days of ambulatory recovery. CD45+ cells were isolated from solei muscles and analyzed using 10x Genomics single cell RNA sequencing. We found that aged M1 macrophage clusters were characterized with an impaired inflammatory and glycolytic transcriptome and this impairment was accompanied by a suppression of HIF-1a and its immediate downstream target GLUT1. Overall design: Examination of CD45+ cells from young and old mouse muscle across varying conditions of ambulation, disuse, and recovery.