Human skeletal muscle fibroblasts, but not myogenic cells, readily undergo adipogenic differentiation

Abstract

We characterised the adherent cell types isolated from human skeletal muscle by enzymatic digestion, and demonstrate that even at 72 hours post-isolation these cultures consist predominantly of myogenic cells (CD56+, Desmin+) and fibroblasts (TE-7+, Collagen VI+, PDGFRα+, Vimentin+, Fibronectin+). To evaluate the behaviour of the cell types obtained, we optimised a double immuno-magnetic cell sorting method for the separation of myogenic cells from fibroblasts. This procedure gave purities of >96% for myogenic (CD56+/desmin+) cells. The CD56- fraction obtained from the first sort was highly enriched in TE-7+ fibroblasts. Using quantitative analysis of immunofluorescent staining for lipid content, lineage markers and transcription factors, we tested if the purified cell populations could differentiate into adipocytes in response to treatment with either fatty acids or Adipocyte Inducing Medium. Both treatments caused the fibroblasts to differentiate into adipocytes, as evidenced by loss of intracellular TE-7, upregulation of the adipogenic transcription factors PPARγ and C/EBPα, and adoption of a lipid-laden adipocyte morphology. In contrast, myogenic cells did not undergo adipogenesis and showed differential regulation of PPARγ and C/EBPα in response to these adipogenic treatments. The data show that human skeletal muscle fibroblasts are at least bipotent progenitors, capable of remaining as extracellular matrix-producing cells or differentiating into adipocytes.