Fig. 2

Skeletal muscle FAPs are quiescent cells with multipotency to differentiate towards all the mesenchymal lineages, depending on the degree of activation and tissue damage. Tissue injury and its associated biochemical cues and cell-secreted factors activate muscle FAPs. Activated FAPs act as immunomodulatory stromal cells and signaling hubs before their commitment to more specialized cells. Usually, muscle injury induces the differentiation of them into activated fibroblasts and adipocytes. Severe damage and chronic pathologies tip their differentiation also into chondrogenic and osteogenic lineages. The figure also shows different molecules and factors as well as ligands that regulate their differentiation potential and fate. Notably, many of these molecules hold several steps of FAP life. As quiescent FAPs find their way into activation and cell differentiation, they lose the expression of quiescence markers and their FAP identity but gain cell differentiation markers