Epimuscular fat in the human rotator cuff is a novel beige depot

Chronic rotator cuff (RC) tears are acommon and debilitating injury, characterized by dramatic expansion of adipose tissue, muscle atrophy, and limited functional recovery. The role of adipose expansion in RC pathology is unknown; however, given the identified paracrine/endocrine regulation by other adipose depots, it likely affects tissue function outside its boundaries. Therefore,wecharacterized the epimuscular (EM) fat depot of the human rotator cuff, defined its response to RC tears, and evaluated its influence on myogenesis in vitro. EM fat biopsies exhibited morphological and functional features of human beige fat compared with patient-matched s.c. biopsies, which appeared whiter. The transcriptional profile of EM fat and isolated EM adipose-derived stem cells (ASCs) shifted as a function of the tear state; EM fat from intact cuffs had significantly elevated expression of the genes associated with uncoupled respiration, and theEMfat from torn cuffs had increased expression of beige-selective genes. EM ASC cocultures with human- and mouse-derived myogenic cells exhibited increased levels of myogenesis compared with s.c. cultures. Increased fusion and decreased proliferation of myogenic cells, rather than changes to the ASCs, were found to underlie this effect. Taken together, these data suggest that EM fat in the human rotator cuff is a novel beige adipose depot influenced by cuff state with therapeutic potential for promoting myogenesis in neighboring musculature.