title: Role of CD44+ stem cells in mural cell formation in the human choroid: evidence of vascular instability due to limited pericyte ensheathment.
abstract: OBJECTIVE
  To examine mural cell differentiation and pericyte ensheathment during human choroidal vascular formation and into adulthood.
  
  
  METHODS
  Triple- and double-labeled immunohistochemistry (alpha-smooth muscle actin [αSMA], desmin, NG2, calponin, caldesmon, CD44, CD34, and CD39) were applied to human fetal (8-32 weeks' gestation) and adult choroidal and retinal wholemounts and histologic cross-sections. Transmission electron microscopy (TEM) was also undertaken.
  
  
  RESULTS
  Early in development CD44+ stem cells also stained with αSMA and CD39, suggesting a common precursor. At 12 weeks' gestation, αSMA+ mural precursor cells, confirmed by TEM, were found scattered and isolated over the primordial vascular tree. During development, αSMA+ cells formed a continuous sheath around large arterioles; in veins there were gaps in αSMA expression. The choriocapillaris had an extensive vascular bed but limited coverage by αSMA+ and NG2+ mural cells. Calponin was expressed only on large vessels, and no caldesmon was detected. Pericyte ensheathment of adult capillaries was 11% for choroid versus 94% for retina. Remarkably, choroidal pericytes had no visible intermediate filaments (IFs) on TEM, though IFs were present in retinal pericytes. Neither retinal nor choroidal pericytes stained with desmin.
  
  
  CONCLUSIONS
  CD44+ stem cells are involved in the formation of mural cells in the human choroidal vasculature. A marked reduction in pericyte ensheathment of human choroidal vessels suggests a permanently open "plasticity window" and a predisposition to vascular instability and poor autoregulatory ability.
authors.affiliation: Department of Anatomy, Bosch Institute, University of Sydney, Sydney, Australia. talloi@anatomy.usyd.edu.au
authors.forename: Tailoi
authors.initials: T
authors.lastname: Chan-Ling
authors.forename: Mark E
authors.initials: ME
authors.lastname: Koina
authors.forename: Janet R
authors.initials: JR
authors.lastname: McColm
authors.forename: Jane E
authors.initials: JE
authors.lastname: Dahlstrom
authors.forename: Elaine
authors.initials: E
authors.lastname: Bean
authors.forename: Sam
authors.initials: S
authors.lastname: Adamson
authors.forename: Steven
authors.initials: S
authors.lastname: Yun
authors.forename: Louise
authors.initials: L
authors.lastname: Baxter
mesh_terms: D000199:Actins / Q000378:metabolism; D000328:Adult; D000941:Antigens / Q000378:metabolism; D015703:Antigens, CD / Q000378:metabolism; D001081:Apyrase / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000378:metabolism; D002148:Calmodulin-Binding Proteins / Q000378:metabolism; D002454:Cell Differentiation; D019070:Cell Lineage; D002829:Choroid / Q000098:blood supply*; D004730:Endothelium, Vascular / Q000196:embryology* / Q000378:metabolism; D005865:Gestational Age; D006412:Hematopoietic Stem Cells / Q000502:physiology*; D006801:Humans; D018960:Hyaluronan Receptors / Q000378:metabolism*; D008840:Microfilament Proteins / Q000378:metabolism; D018613:Microscopy, Confocal; D009131:Muscle, Smooth, Vascular / Q000196:embryology* / Q000378:metabolism / Q000648:ultrastructure; D032389:Myocytes, Smooth Muscle / Q000166:cytology / Q000378:metabolism; D018919:Neovascularization, Physiologic / Q000502:physiology*; D020286:Pericytes / Q000166:cytology*; D011509:Proteoglycans / Q000378:metabolism; D012171:Retinal Vessels / Q000648:ultrastructure; D055815:Young Adult; D000096985:Calponins; D000099216:Chondroitin Sulfate Proteoglycan 4
chemical_list: D000199:Actins; D000941:Antigens; D015703:Antigens, CD; D001081:Apyrase; D002135:Calcium-Binding Proteins; D002148:Calmodulin-Binding Proteins; D018960:Hyaluronan Receptors; D008840:Microfilament Proteins; D011509:Proteoglycans; D000096985:Calponins; D000099216:Chondroitin Sulfate Proteoglycan 4; C541116:ACTA2 protein, human; C497483:CD44 protein, human; C067869:CD39 antigen