title: Megakaryoblastic leukemia-1 is required for the development of bleomycin-induced pulmonary fibrosis.
abstract: BACKGROUND
  Fibrosing disorders of the lung, such as idiopathic pulmonary fibrosis, are characterized by progressive extracellular matrix accumulation that is driven by myofibroblasts. The transcription factor megakaryoblastic leukemia-1 (MKL1) mediates myofibroblast differentiation in response to several profibrotic stimuli, but the role it plays in mediating pulmonary fibrosis has not been fully elucidated. In this study, we utilized mice that had a germline deletion of MKL1 (MKL1 (-,-)) to determine the role that MKL1 plays in the development of bleomycin-induced pulmonary fibrosis.
  
  
  METHODS
  Bleomycin or normal saline were intratracheally delivered to 9 to 12 week old female MKL1 (+,+) and MKL1 (-,-) mice. Mice were assessed for weight loss and survival to 28 days. Inflammatory responses were assessed through bronchoalveolar lavage at days 3 and 7 post-treatment. The development of pulmonary fibrosis was characterized using hydroxyproline assay and histological staining. MKL1 (+,+) and MKL1 (-,-) mouse lung fibroblasts were isolated to compare morphologic, gene expression and functional differences.
  
  
  RESULTS
  MKL1 (-,-) mice demonstrated increased survival, attenuated weight loss, and decreased collagen accumulation compared to wild-type animals 28-days after intratracheal instillation of bleomycin. Histological analysis demonstrated decreased trichrome, smooth muscle α-actin, and fibronectin staining in MKL1(-,-) mice compared to MKL1 (+,+) controls. Differential cell counts from bronchoalveolar lavage demonstrated that there was attenuated neutrophilia 3 days after bleomycin administration, but no difference at day 7. Isolated mouse lung fibroblasts from MKL1 (-,-) mice had decreased contractility and deposited less fibronectin matrix compared to wild-type controls, suggesting a defect in key remodeling functions.
  
  
  CONCLUSIONS
  Altogether, these data demonstrate that MKL1 plays a significant role in mediating the fibrotic response to bleomycin injury. Loss of MKL1 attenuated early neutrophil influx, as well as myofibroblast-mediated remodeling. Targeting MKL1 activity may therefore be a useful strategy in treating pulmonary fibrosis.
authors.affiliation: Department of Medicine, University of Wisconsin-Madison, Madison, WI, USA. kbernau@medicine.wisc.edu.
authors.forename: Ksenija
authors.initials: K
authors.lastname: Bernau
authors.affiliation: Department of Medicine, University of Wisconsin-Madison, Madison, WI, USA. caitlyn.ngam@gmail.com.
authors.forename: Caitlyn
authors.initials: C
authors.lastname: Ngam
authors.affiliation: Department of Medicine, University of Wisconsin-Madison, Madison, WI, USA. eetorr@medicine.wisc.edu.
authors.forename: Elizabeth E
authors.initials: EE
authors.lastname: Torr
authors.affiliation: Department of Medicine, University of Wisconsin-Madison, Madison, WI, USA. acton.benjamin@gmail.com.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Acton
authors.affiliation: Department of Medicine, University of Chicago, Chicago, IL, USA. jakach@gmail.com.
authors.forename: Jacob
authors.initials: J
authors.lastname: Kach
authors.affiliation: Department of Medicine, University of Chicago, Chicago, IL, USA. ndulin@medicine.bsd.uchicago.edu.
authors.forename: Nickolai O
authors.initials: NO
authors.lastname: Dulin
authors.affiliation: Department of Medicine, University of Wisconsin-Madison, Madison, WI, USA. nsandbo@medicine.wisc.edu.
authors.forename: Nathan
authors.initials: N
authors.lastname: Sandbo
mesh_terms: D000818:Animals; D001761:Bleomycin; D001992:Bronchoalveolar Lavage Fluid / Q000737:chemistry; D048430:Cell Shape; D002478:Cells, Cultured; D003094:Collagen / Q000378:metabolism; D005260:Female; D005347:Fibroblasts / Q000378:metabolism* / Q000473:pathology; D005353:Fibronectins / Q000378:metabolism; D005838:Genotype; D018095:Germ-Line Mutation; D018836:Inflammation Mediators / Q000378:metabolism; D008168:Lung / Q000378:metabolism* / Q000473:pathology; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D020556:Neutrophil Infiltration; D010641:Phenotype; D011658:Pulmonary Fibrosis / Q000139:chemically induced* / Q000235:genetics / Q000378:metabolism* / Q000473:pathology / Q000517:prevention & control; D015398:Signal Transduction; D013997:Time Factors; D015534:Trans-Activators / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*
chemical_list: D005353:Fibronectins; D018836:Inflammation Mediators; C511173:Mrtfa protein, mouse; D015534:Trans-Activators; D001761:Bleomycin; D003094:Collagen