Abstract
Purpose: :
To undertake the first complete study of human choroidal vascular formation & determine the role played by stem cells.
Methods: :
Human foetal eyes aged 8-40 weeks gestation (WG) were examined. Choroidal & retinal wholemounts & histological sections were examined using antibodies for stem & precursor cell populations: Vimentin, CD14, CD34, CD39 & αSMA; the vasculature: CD39, CD34, CD31 & Factor VIII; & mural cells: αSMA, Desmin, NG2, Calponin & Caldesmon. Endothelial proliferation was examined by double-labelling with BrdU & CD34. TEM and H & E histology was also undertaken.
Results: :
Vimentin+ mesenchymal precursor cells were evident in the region of the incipient choroid at 9 WG, & down regulation of Vimentin was evident with maturation. CD14+ vascular precursor cells (VPCs) were evident in the choroidal stroma throughout foetal life. CD39+/CD34+ VPCs were evident within the choroidal stroma from 10 WG, interspersed amongst CD39+ solid vascular chords in the central one-third of the choroid surrounding the optic nerve head. SMA+ mural precursor cells (MPCs) were scattered & isolated over the primordial vascular tree at 12WG. Non vascular-associated αSMA+/CD34+/--/ NG2+/desmin- presumed MPCs were associated with immature choroidal blood vessels at 12, 18 & 20 WG. Calponin & caldesmon were expressed only on the large vessels.
Conclusions: :
We conclude that formation of the human choroid takes place via transformation from Vimentin+ mesenchymal precursor cells to CD14+/CD39+/αSMA+ precursor cells representing the monocytic vascular and mural cell lineages respectively. Vasculogenesis plays a greater role in formation of human choroid than previously reported but angiogenesis also contribute to vascular density in the formation of the human choroid. We have shown that CD44+ stem cells give rise to αSMA+ smooth muscle cells & CD39+ vascular endothelial cells in the human choroid.
Keywords: retinal development • choroid: neovascularization • age-related macular degeneration