title: The transcription factor scleraxis is a critical regulator of cardiac fibroblast phenotype.
abstract: BACKGROUND
  Resident fibroblasts synthesize the cardiac extracellular matrix, and can undergo phenotype conversion to myofibroblasts to augment matrix production, impairing function and contributing to organ failure. A significant gap in our understanding of the transcriptional regulation of these processes exists. Given the key role of this phenotype conversion in fibrotic disease, the identification of such novel transcriptional regulators may yield new targets for therapies for fibrosis.
  
  
  RESULTS
  Using explanted primary cardiac fibroblasts in gain- and loss-of-function studies, we found that scleraxis critically controls cardiac fibroblast/myofibroblast phenotype by direct transcriptional regulation of myriad genes that effectively define these cells, including extracellular matrix components and α-smooth muscle actin. Scleraxis furthermore potentiated the TGFβ/Smad3 signaling pathway, a key regulator of myofibroblast conversion, by facilitating transcription complex formation. While scleraxis promoted fibroblast to myofibroblast conversion, loss of scleraxis attenuated myofibroblast function and gene expression. These results were confirmed in scleraxis knockout mice, which were cardiac matrix-deficient and lost ~50% of their complement of cardiac fibroblasts, with evidence of impaired epithelial-to-mesenchymal transition (EMT). Scleraxis directly transactivated several EMT marker genes, and was sufficient to induce mesenchymal/fibroblast phenotype conversion of A549 epithelial cells. Conversely, loss of scleraxis attenuated TGFβ-induced EMT marker expression.
  
  
  CONCLUSIONS
  Our results demonstrate that scleraxis is a novel and potent regulator of cellular progression along the continuum culminating in the cardiac myofibroblast phenotype. Scleraxis was both sufficient to drive conversion, and required for full conversion to occur. Scleraxis fulfills this role by direct transcriptional regulation of key target genes, and by facilitating TGFβ/Smad signaling. Given the key role of fibroblast to myofibroblast conversion in fibrotic diseases in the heart and other tissue types, scleraxis may be an important target for therapeutic development.
authors.affiliation: Institute of Cardiovascular Sciences, Boniface Hospital Albrechtsen Research Centre and Department of Physiology and Pathophysiology, University of Manitoba, R4008 St. Boniface Hospital Albrechtsen Research Centre, 351 Tache Avenue, Winnipeg, MB, R2H 2A6, Canada.
authors.forename: Rushita A
authors.initials: RA
authors.lastname: Bagchi
authors.affiliation: Institute of Cardiovascular Sciences, Boniface Hospital Albrechtsen Research Centre and Department of Physiology and Pathophysiology, University of Manitoba, R4008 St. Boniface Hospital Albrechtsen Research Centre, 351 Tache Avenue, Winnipeg, MB, R2H 2A6, Canada.
authors.forename: Patricia
authors.initials: P
authors.lastname: Roche
authors.affiliation: Institute of Cardiovascular Sciences, Boniface Hospital Albrechtsen Research Centre and Department of Physiology and Pathophysiology, University of Manitoba, R4008 St. Boniface Hospital Albrechtsen Research Centre, 351 Tache Avenue, Winnipeg, MB, R2H 2A6, Canada.
authors.forename: Nina
authors.initials: N
authors.lastname: Aroutiounova
authors.affiliation: Institute of Cardiovascular Sciences, Boniface Hospital Albrechtsen Research Centre and Department of Physiology and Pathophysiology, University of Manitoba, R4008 St. Boniface Hospital Albrechtsen Research Centre, 351 Tache Avenue, Winnipeg, MB, R2H 2A6, Canada.
authors.forename: Leon
authors.initials: L
authors.lastname: Espira
authors.affiliation: Institute of Cardiovascular Sciences, Boniface Hospital Albrechtsen Research Centre and Department of Physiology and Pathophysiology, University of Manitoba, R4008 St. Boniface Hospital Albrechtsen Research Centre, 351 Tache Avenue, Winnipeg, MB, R2H 2A6, Canada.
authors.forename: Bernard
authors.initials: B
authors.lastname: Abrenica
authors.affiliation: Shriners Hospital for Children, Research Division and Department of Cell and Developmental Biology, Oregon Health and Science University, Portland, OR, 97239, USA.
authors.forename: Ronen
authors.initials: R
authors.lastname: Schweitzer
authors.affiliation: Institute of Cardiovascular Sciences, Boniface Hospital Albrechtsen Research Centre and Department of Physiology and Pathophysiology, University of Manitoba, R4008 St. Boniface Hospital Albrechtsen Research Centre, 351 Tache Avenue, Winnipeg, MB, R2H 2A6, Canada. mczubryt@sbrc.ca.
authors.forename: Michael P
authors.initials: MP
authors.lastname: Czubryt
mesh_terms: D000199:Actins / Q000235:genetics; D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics / Q000378:metabolism*; D002454:Cell Differentiation; D002460:Cell Line; D002478:Cells, Cultured; D005347:Fibroblasts / Q000166:cytology* / Q000378:metabolism; D017353:Gene Deletion; D005786:Gene Expression Regulation; D006801:Humans; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009206:Myocardium / Q000166:cytology* / Q000378:metabolism; D058628:Myofibroblasts / Q000166:cytology* / Q000378:metabolism; D041681:NIH 3T3 Cells; D010641:Phenotype; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction; D051900:Smad3 Protein / Q000378:metabolism; D015533:Transcriptional Activation
chemical_list: D000199:Actins; D051792:Basic Helix-Loop-Helix Proteins; D051900:Smad3 Protein; C503815:Scx protein, mouse; C544013:alpha-smooth muscle actin, mouse
keywords: EMT; Extracellular matrix; Fibroblast; Gene expression; Myofibroblast; Phenoconversion; Transcription