title: Lack of MK2 inhibits myofibroblast formation and exacerbates pulmonary fibrosis.
abstract: Fibroblasts play a major role in tissue repair and remodeling. Their differentiation into myofibroblasts, marked by increased expression of smooth muscle-specific alpha-actin (alpha-SMA), is believed to be important in wound healing and fibrosis. We have recently described a role for MK2 in this phenotypic differentiation in culture. In this article, we demonstrate that MK2 also regulates myofibroblasts in vivo. Disruption of MK2 in mice prevented myofibroblast formation in a model of pulmonary fibrosis. However, MK2 disruption and consequent lack of myofibroblast formation exacerbated fibrosis rather than ameliorated it as previously postulated. When mice lacking MK2 (MK2-/-) were exposed to bleomycin, more collagen accumulated and more fibroblasts populated fibrotic regions in their lungs than in similarly treated wild-type mice. While there were many vimentin-positive cells in the bleomycin-treated MK2-/- mouse lungs, few alpha-SMA-positive cells were observed in these lungs compared with wild-type mouse lungs. siRNA against MK2 reduced alpha-SMA expression in wild-type mouse embryonic fibroblasts (MEF), consistent with its suppression in MK2-/- MEF. On the other hand expressing constitutively active MK2 in MK2-/- MEF significantly increased alpha-SMA expression. MK2-/-MEF proliferated at a faster rate and produced more collagen; however, they migrated at a slower rate than wild-type MEF. Overexpressing phosphomimicking HSP27, a target of MK2, did not reverse the effect of MK2 disruption on fibroblast migration. MK2 disruption did not affect Smad2 activation by transforming growth factor-beta. Thus, MK2 appears to mediate myofibroblast differentiation, and inhibiting that differentiation might contribute to fibrosis rather than protect against it.
authors.affiliation: Pulmonary and Critical Care Division, Department of Medicine/Tupper Research Institute, Tufts-New England Medical Center, and Tufts University School of Medicine, Boston, Massachusetts 02111, USA.
authors.forename: Tiegang
authors.initials: T
authors.lastname: Liu
authors.forename: Rod R
authors.initials: RR
authors.lastname: Warburton
authors.forename: Oscar E
authors.initials: OE
authors.lastname: Guevara
authors.forename: Nicholas S
authors.initials: NS
authors.lastname: Hill
authors.forename: Barry L
authors.initials: BL
authors.lastname: Fanburg
authors.forename: Matthias
authors.initials: M
authors.lastname: Gaestel
authors.forename: Usamah S
authors.initials: US
authors.lastname: Kayyali
mesh_terms: D000818:Animals; D002454:Cell Differentiation / Q000235:genetics*; D005347:Fibroblasts / Q000166:cytology / Q000201:enzymology* / Q000473:pathology; D020022:Genetic Predisposition to Disease; D047908:Intracellular Signaling Peptides and Proteins / Q000172:deficiency / Q000235:genetics*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D032446:Myoblasts / Q000166:cytology / Q000201:enzymology* / Q000473:pathology; D017346:Protein Serine-Threonine Kinases / Q000172:deficiency / Q000235:genetics*; D011658:Pulmonary Fibrosis / Q000201:enzymology / Q000235:genetics* / Q000473:pathology; D000099190:MAP-Kinase-Activated Kinase 2
chemical_list: D047908:Intracellular Signaling Peptides and Proteins; D017346:Protein Serine-Threonine Kinases; D000099190:MAP-Kinase-Activated Kinase 2