title: Human skeletal muscle fibroblasts stimulate in vitro myogenesis and in vivo muscle regeneration.
abstract: Accumulation of skeletal muscle extracellular matrix is an unfavourable characteristic of many muscle diseases, muscle injury and sarcopenia. The extent of cross-talk between fibroblasts, as the source of matrix protein, and satellite cells in humans is unknown. We studied this in human muscle biopsies and cell-culture studies. We observed a strong stimulation of myogenesis by human fibroblasts in cell culture. In biopsies collected 30 days after a muscle injury protocol, fibroblast number increased to four times control levels, where fibroblasts were found to be preferentially located immediately surrounding regenerating muscle fibres. These novel findings indicate an important role for fibroblasts in supporting the regeneration of muscle fibres, potentially through direct stimulation of satellite cell differentiation and fusion, and contribute to understanding of cell-cell cross-talk during physiological and pathological muscle remodelling.
  
  
  
  Accumulation of skeletal muscle extracellular matrix is an unfavourable characteristic of many muscle diseases, muscle injury and sarcopenia. In addition to the indispensable role satellite cells play in muscle regeneration, there is emerging evidence in rodents for a regulatory influence on fibroblast activity. However, the influence of fibroblasts on satellite cells and muscle regeneration in humans is unknown. The purpose of this study was to investigate this in vitro and during in vivo regeneration in humans. Following a muscle injury protocol in young healthy men (n = 7), the number of fibroblasts (TCF7L2+), satellite cells (Pax7+), differentiating myogenic cells (myogenin+) and regenerating fibres (neonatal/embryonic myosin+) was determined from biopsy cross-sections. Fibroblasts and myogenic precursor cells (MPCs) were also isolated from human skeletal muscle (n = 4) and co-cultured using different cell ratios, with the two cell populations either in direct contact with each other or separated by a permeable membrane. MPC proliferation, differentiation and fusion were assessed from cells stained for BrdU, desmin and myogenin. On biopsy cross-sections, fibroblast number was seen to increase, along with myogenic cell number, by d7 and increase further by d30, where fibroblasts were observed to be preferentially located immediately surrounding regenerating muscle fibres. In vitro, the presence of fibroblasts in direct contact with MPCs was found to moderately stimulate MPC proliferation and strongly stimulate both MPC differentiation and MPC fusion. It thus appears, in humans, that fibroblasts exert a strong positive regulatory influence on MPC activity, in line with observations during in vivo skeletal muscle regeneration.
authors.affiliation: Institute of Sports Medicine, Department of Orthopaedic Surgery M, Bispebjerg Hospital, and Center for Healthy Aging, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark.|Center for Healthy Aging, Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark.
authors.forename: Abigail L
authors.identifier: 0000-0002-2017-4580
authors.initials: AL
authors.lastname: Mackey
authors.affiliation: Institut Cochin, INSERM U1016, CNRS UMR8104, Université Paris Descartes, Paris, France.
authors.forename: Mélanie
authors.initials: M
authors.lastname: Magnan
authors.affiliation: Institut Cochin, INSERM U1016, CNRS UMR8104, Université Paris Descartes, Paris, France.|Institut NeuroMyoGène, INSERM U1217, UMR CNRS 5310, Université Claude Bernard Lyon 1, Villeurbanne, France.
authors.forename: Bénédicte
authors.identifier: 0000-0002-1262-502X
authors.initials: B
authors.lastname: Chazaud
authors.affiliation: Institute of Sports Medicine, Department of Orthopaedic Surgery M, Bispebjerg Hospital, and Center for Healthy Aging, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark.
authors.forename: Michael
authors.initials: M
authors.lastname: Kjaer
mesh_terms: D000328:Adult; D015703:Antigens, CD / Q000502:physiology; D015214:Antigens, Differentiation, Myelomonocytic / Q000502:physiology; D002478:Cells, Cultured; D018920:Coculture Techniques; D004558:Electric Stimulation; D005347:Fibroblasts / Q000502:physiology*; D061307:Human Umbilical Vein Endothelial Cells / Q000502:physiology; D006801:Humans; D017493:Leukocyte Common Antigens / Q000502:physiology; D008264:Macrophages / Q000502:physiology; D008297:Male; D009119:Muscle Contraction; D024510:Muscle Development / Q000502:physiology*; D018482:Muscle, Skeletal / Q000293:injuries* / Q000502:physiology*; D032446:Myoblasts / Q000502:physiology*; D012038:Regeneration / Q000502:physiology*; D058118:Transcription Factor 7-Like 2 Protein / Q000502:physiology; D000097382:CD68 Molecule
chemical_list: D015703:Antigens, CD; D015214:Antigens, Differentiation, Myelomonocytic; D017493:Leukocyte Common Antigens; D058118:Transcription Factor 7-Like 2 Protein; C067980:CD68 antigen, human; D000097382:CD68 Molecule; C544894:TCF7L2 protein, human; C516769:PTPRC protein, human
keywords: co-culture; myogenesis; satellite cells; skeletal muscle derived fibroblasts; skeletal muscle regeneration