title: Connective tissue cells expressing fibro/adipogenic progenitor markers increase under chronic damage: relevance in fibroblast-myofibroblast differentiation and skeletal muscle fibrosis.
abstract: Fibrosis occurs in skeletal muscle under various pathophysiological conditions such as Duchenne muscular dystrophy (DMD), a devastating disease characterized by fiber degeneration that results in progressive loss of muscle mass, weakness and increased extracellular matrix (ECM) accumulation. Fibrosis is also observed after skeletal muscle denervation and repeated cycles of damage followed by regeneration. The ECM is synthesized largely by fibroblasts in the muscle connective tissue under normal conditions. Myofibroblasts, cells that express α-smooth muscle actin (α-SMA), play a role in many tissues affected by fibrosis. In skeletal muscle, fibro/adipogenic progenitors (FAPs) that express cell-surface platelet-derived growth factor receptor-α (PDGFR-α) and the transcription factor Tcf4 seem to be responsible for connective tissue synthesis and are good candidates for the origin of myofibroblasts. We show that cells positive for Tcf4 and PDGFR-α are expressed in skeletal muscle under normal conditions and are increased in various skeletal muscles of mdx mice, a murine model for DMD, wild type muscle after sciatic denervation and muscle subjected to chronic damage. These cells co-label with the myofibroblast marker α-SMA in dystrophic muscle but not in normal tissue. The Tcf4-positive cells lie near macrophages mainly concentrated in dystrophic necrotic-regenerating foci. The close proximity of Tcf4-positive cells to inflammatory cells and their previously described role in muscle regeneration might reflect an active interaction between these cell types and growth factors, possibly resulting in a muscular regenerative or fibrotic condition.
authors.affiliation: Center for Aging and Regeneration, CARE Chile UC and Department of Cell and Molecular Biology, Faculty of Biological Sciences, Pontificia Universidad Católica de Chile, Libertador Bernardo O´Higgins 340, 8331150, Santiago, Chile.
authors.forename: Osvaldo
authors.initials: O
authors.lastname: Contreras
authors.affiliation: Center for Aging and Regeneration, CARE Chile UC and Department of Cell and Molecular Biology, Faculty of Biological Sciences, Pontificia Universidad Católica de Chile, Libertador Bernardo O´Higgins 340, 8331150, Santiago, Chile.
authors.forename: Daniela L
authors.initials: DL
authors.lastname: Rebolledo
authors.affiliation: Center for Aging and Regeneration, CARE Chile UC and Department of Cell and Molecular Biology, Faculty of Biological Sciences, Pontificia Universidad Católica de Chile, Libertador Bernardo O´Higgins 340, 8331150, Santiago, Chile.
authors.forename: Juan Esteban
authors.initials: JE
authors.lastname: Oyarzún
authors.affiliation: Center for Aging and Regeneration, CARE Chile UC and Department of Cell and Molecular Biology, Faculty of Biological Sciences, Pontificia Universidad Católica de Chile, Libertador Bernardo O´Higgins 340, 8331150, Santiago, Chile.
authors.forename: Hugo C
authors.initials: HC
authors.lastname: Olguín
authors.affiliation: Center for Aging and Regeneration, CARE Chile UC and Department of Cell and Molecular Biology, Faculty of Biological Sciences, Pontificia Universidad Católica de Chile, Libertador Bernardo O´Higgins 340, 8331150, Santiago, Chile. ebrandan@bio.puc.cl.
authors.forename: Enrique
authors.initials: E
authors.lastname: Brandan
mesh_terms: D050156:Adipogenesis; D000818:Animals; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors / Q000378:metabolism; D015415:Biomarkers / Q000378:metabolism*; D002452:Cell Count; D002454:Cell Differentiation; D002908:Chronic Disease; D003238:Connective Tissue / Q000473:pathology*; D003714:Denervation; D005355:Fibrosis; D008264:Macrophages / Q000378:metabolism / Q000473:pathology; D008810:Mice, Inbred C57BL; D018482:Muscle, Skeletal / Q000294:innervation / Q000378:metabolism* / Q000473:pathology*; D009137:Muscular Dystrophy, Animal / Q000473:pathology; D058628:Myofibroblasts / Q000473:pathology*; D009336:Necrosis; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D017479:Receptors, Platelet-Derived Growth Factor / Q000378:metabolism; D000073940:Transcription Factor 4; D053773:Transforming Growth Factor beta1 / Q000235:genetics / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics / Q000378:metabolism
chemical_list: D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D015415:Biomarkers; D012333:RNA, Messenger; C090743:Tcf4 protein, mouse; D000073940:Transcription Factor 4; D053773:Transforming Growth Factor beta1; D014409:Tumor Necrosis Factor-alpha; D017479:Receptors, Platelet-Derived Growth Factor
keywords: Fibroblasts; Fibrosis; Muscular dystrophy; PDGFR-α; Tcf4