title: Rare, nonsynonymous variant in the smooth muscle-specific isoform of myosin heavy chain, MYH11, R247C, alters force generation in the aorta and phenotype of smooth muscle cells.
abstract: BACKGROUND
  Mutations in myosin heavy chain (MYH11) cause autosomal dominant inheritance of thoracic aortic aneurysms and dissections. At the same time, rare, nonsynonymous variants in MYH11 that are predicted to disrupt protein function but do not cause inherited aortic disease are common in the general population and the vascular disease risk associated with these variants is unknown.
  
  
  OBJECTIVE
  To determine the consequences of the recurrent MYH11 rare variant, R247C, through functional studies in vitro and analysis of a knock-in mouse model with this specific variant, including assessment of aortic contraction, response to vascular injury, and phenotype of primary aortic smooth muscle cells (SMCs).
  
  
  RESULTS
  The steady state ATPase activity (actin-activated) and the rates of phosphate and ADP release were lower for the R247C mutant myosin than for the wild-type, as was the rate of actin filament sliding in an in vitro motility assay. Myh11(R247C/R247C) mice exhibited normal growth, reproduction, and aortic histology but decreased aortic contraction. In response to vascular injury, Myh11(R247C/R247C) mice showed significantly increased neointimal formation due to increased SMC proliferation when compared with the wild-type mice. Primary aortic SMCs explanted from the Myh11(R247C/R247C) mice were dedifferentiated compared with wild-type SMCs based on increased proliferation and reduced expression of SMC contractile proteins. The mutant SMCs also displayed altered focal adhesions and decreased Rho activation, associated with decreased nuclear localization of myocardin-related transcription factor-A. Exposure of the Myh11(R247C/R247C) SMCs to a Rho activator rescued the dedifferentiated phenotype of the SMCs.
  
  
  CONCLUSIONS
  These results indicate that a rare variant in MYH11, R247C, alters myosin contractile function and SMC phenotype, leading to increased proliferation in vitro and in response to vascular injury.
authors.affiliation: Department of Internal Medicine, The University of Texas Medical School at Houston, Houston, TX 77030, USA.
authors.forename: Shao-Qing
authors.initials: SQ
authors.lastname: Kuang
authors.forename: Callie S
authors.initials: CS
authors.lastname: Kwartler
authors.forename: Katerina L
authors.initials: KL
authors.lastname: Byanova
authors.forename: John
authors.initials: J
authors.lastname: Pham
authors.forename: Limin
authors.initials: L
authors.lastname: Gong
authors.forename: Siddharth K
authors.initials: SK
authors.lastname: Prakash
authors.forename: Jian
authors.initials: J
authors.lastname: Huang
authors.forename: Kristine E
authors.initials: KE
authors.lastname: Kamm
authors.forename: James T
authors.initials: JT
authors.lastname: Stull
authors.forename: H Lee
authors.initials: HL
authors.lastname: Sweeney
authors.forename: Dianna M
authors.initials: DM
authors.lastname: Milewicz
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001011:Aorta / Q000378:metabolism; D001665:Binding Sites; D002339:Carotid Arteries / Q000378:metabolism / Q000473:pathology; D020212:Carotid Artery Injuries / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D002454:Cell Differentiation; D049109:Cell Proliferation; D002478:Cells, Cultured; D004195:Disease Models, Animal; D022001:Focal Adhesions / Q000378:metabolism / Q000473:pathology; D055879:Gene Knock-In Techniques; D005838:Genotype; D007700:Kinetics; D051379:Mice; D057507:Mice, 129 Strain; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009131:Muscle, Smooth, Vascular / Q000378:metabolism*; D009154:Mutation; D032389:Myocytes, Smooth Muscle / Q000378:metabolism*; D018995:Myosin Heavy Chains / Q000235:genetics / Q000378:metabolism*; D010641:Phenotype; D015534:Trans-Activators / Q000378:metabolism; D014162:Transfection; D014661:Vasoconstriction / Q000235:genetics; D020741:rho GTP-Binding Proteins / Q000378:metabolism
chemical_list: C509903:MYH11 protein, human; C511173:Mrtfa protein, mouse; D015534:Trans-Activators; C573943:myosin 11, mouse; D000255:Adenosine Triphosphate; D018995:Myosin Heavy Chains; D020741:rho GTP-Binding Proteins