title: Alternative splicing of endothelial fibronectin is induced by disturbed hemodynamics and protects against hemorrhage of the vessel wall.
abstract: OBJECTIVE
  Abnormally low-flow conditions, sensed by the arterial endothelium, promote aneurysm rupture. Fibronectin (FN) is among the most abundant extracellular matrix proteins and is strongly upregulated in human aneurysms, suggesting a possible role in disease progression. Altered FN splicing can result in the inclusion of EIIIA and EIIIB exons, generally not expressed in adult tissues. We sought to explore the regulation of FN and its splicing and their possible roles in the vascular response to disturbed flow.
  
  
  RESULTS
  We induced low and reversing flow in mice by partial carotid ligation and assayed FN splicing in an endothelium-enriched intimal preparation. Inclusion of EIIIA and EIIIB was increased as early as 48 hours, with negligible increases in total FN expression. To test the function of EIIIA and EIIIB inclusion, we induced disturbed flow in EIIIAB(-/-) mice unable to include these exons and found that they developed focal lesions with hemorrhage and hypertrophy of the vessel wall. Acute deletion of floxed FN caused similar defects in response to disturbed flow, consistent with a requirement for the upregulation of the spliced isoforms, rather than a developmental defect. Recruited macrophages promote FN splicing because their depletion by clodronate liposomes blocked the increase in endothelial EIIIA and EIIIB inclusion in the carotid model.
  
  
  CONCLUSIONS
  These results uncover a protective mechanism in the inflamed intima that develops under disturbed flow, by showing that splicing of FN mRNA in the endothelium, induced by macrophages, inhibits hemorrhage of the vessel wall.
authors.affiliation: From the Howard Hughes Medical Institute, David H. Koch Institute for Integrative Cancer Research, Massachusetts Institute of Technology, Cambridge, MA.
authors.forename: Patrick A
authors.initials: PA
authors.lastname: Murphy
authors.affiliation: From the Howard Hughes Medical Institute, David H. Koch Institute for Integrative Cancer Research, Massachusetts Institute of Technology, Cambridge, MA. rohynes@mit.edu.
authors.forename: Richard O
authors.initials: RO
authors.lastname: Hynes
mesh_terms: D063194:Adventitia / Q000378:metabolism; D017398:Alternative Splicing; D000818:Animals; D016893:Carotid Stenosis / Q000235:genetics / Q000473:pathology*; D004195:Disease Models, Animal; D018450:Disease Progression; D004730:Endothelium, Vascular / Q000378:metabolism* / Q000473:pathology; D005091:Exons; D005109:Extracellular Matrix / Q000473:pathology; D005353:Fibronectins / Q000096:biosynthesis / Q000172:deficiency / Q000235:genetics*; D017353:Gene Deletion; D018056:Hemorheology; D006470:Hemorrhage / Q000209:etiology / Q000503:physiopathology / Q000517:prevention & control*; D006984:Hypertrophy; D008026:Ligation; D008264:Macrophages / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D017539:Tunica Intima / Q000293:injuries* / Q000378:metabolism / Q000473:pathology; D017540:Tunica Media / Q000378:metabolism
chemical_list: D005353:Fibronectins; C572454:extra domain A fibronectin, mouse
keywords: alternative splicing; fibronectins; hemorrhage; macrophages