title: Decreased neurotrophin TrkB receptor expression reduces lesion size in the apolipoprotein E-null mutant mouse.
abstract: BACKGROUND
  Accumulation of macrophages and smooth muscle cells in the vascular wall is critical for the development of atherosclerotic lesions. Although much is known about the factors that regulate macrophage recruitment to the vascular wall, the ability of growth factors to regulate smooth muscle cell recruitment in lesion development in vivo is unclear. Our previous studies demonstrated that neurotrophins and their receptors, the Trk receptor tyrosine kinases, are potent chemotactic factors for smooth muscle cells, and the expression of brain-derived neurotrophic factor (BDNF) and its cognate receptor, TrkB, is upregulated in human atherosclerotic lesions.
  
  
  RESULTS
  TrkB(+/-) mice on a 129/B6 background were backcrossed to apolipoprotein E (ApoE)-null (ApoE(-/-)) mice on the C57Bl/6 background for 6 to 8 generations. Immunohistochemical analysis demonstrated BDNF immunoreactivity in areas of macrophage and smooth muscle cell infiltration, whereas TrkB immunoreactivity was predominant in areas of neointimal smooth muscle cells. Moreover, haplodeficient expression of TrkB in ApoE(-/-) mice was associated with a 30% to 40% reduction in lesion size compared with ApoE(-/-) mice with normal expression of TrkB and a 45% decrease in smooth muscle cell accumulation in the lesions. Finally, reconstitution with bone marrow from ApoE(-/-) mice with normal TrkB expression did not restore lesion development in TrKB(+/-)/ApoE(-/-) mice.
  
  
  CONCLUSIONS
  These results suggest that TrkB expression on smooth muscle cells contributes to lesion development in the cholesterol-fed ApoE-null mutant mouse. These data demonstrate, for the first time, a role for the neurotrophin TrkB receptor in atherosclerotic lesion development.
authors.affiliation: Department of Pathology, Weill Medical College of Cornell University, New York, NY 10021, USA. rtkraeme@med.cornell.edu
authors.forename: Rosemary
authors.initials: R
authors.lastname: Kraemer
authors.forename: Peter James
authors.initials: PJ
authors.lastname: Baker
authors.forename: K Craig
authors.initials: KC
authors.lastname: Kent
authors.forename: Yuanfen
authors.initials: Y
authors.lastname: Ye
authors.forename: Jun Ji
authors.initials: JJ
authors.lastname: Han
authors.forename: Rafael
authors.initials: R
authors.lastname: Tejada
authors.forename: Michael
authors.initials: M
authors.lastname: Silane
authors.forename: Rita
authors.initials: R
authors.lastname: Upmacis
authors.forename: Ruba
authors.initials: R
authors.lastname: Deeb
authors.forename: Yaoxin
authors.initials: Y
authors.lastname: Chen
authors.forename: Daniel M
authors.initials: DM
authors.lastname: Levine
authors.forename: Barbara
authors.initials: B
authors.lastname: Hempstead
mesh_terms: D000818:Animals; D001057:Apolipoproteins E / Q000172:deficiency; D001161:Arteriosclerosis / Q000209:etiology* / Q000473:pathology; D019208:Brain-Derived Neurotrophic Factor / Q000032:analysis; D002633:Chemotaxis; D002784:Cholesterol / Q000008:administration & dosage; D005786:Gene Expression Regulation / Q000502:physiology; D008264:Macrophages / Q000737:chemistry / Q000502:physiology; D051379:Mice; D018345:Mice, Knockout; D032389:Myocytes, Smooth Muscle / Q000737:chemistry / Q000502:physiology; D020813:Receptor, trkB / Q000235:genetics* / Q000502:physiology*
chemical_list: D001057:Apolipoproteins E; D019208:Brain-Derived Neurotrophic Factor; D002784:Cholesterol; D020813:Receptor, trkB