Comparative Analysis of the Basement Membrane Composition of the Human Limbus Epithelium and Amniotic Membrane Epithelium

Purpose: Human amniotic membrane has been widely used as substrate for ex vivo expansion and transplantation of limbal epithelial cells. To further clarify its suitability as a surrogate niche for limbal stem cells and progenitor cells, we analyzed the composition of the amniotic epithelial basement membrane, with special focus on the expression of limbus-specific matrix components. Methods: Cryosections of corneoscleral specimens obtained from 10 human donor eyes and of 6 amniotic membrane specimens obtained at cesarean section were stained by indirect immunofluorescence using a broad panel of antibodies against basement membrane components. Results: Both amniotic and limbal epithelial basement membranes showed positive immunoreactivity for collagen type IV α1, α2, α5, and α6 chains; collagens type VII, XV, XVI, XVII, and XVIII; laminin α3, β1, β2, β3, γ1, and γ2 chains; laminin-111 and laminin-332; nidogen-1 and nidogen-2; fibronectin; fibulin-2; fibrillin-2; perlecan; and agrin. Both types of basement membrane were negative for collagen type IV α3 and α4 chains, collagen type V, and laminin α4 chain. Limbal basement membrane components, which were not detected in amniotic membrane, included laminin α1, α2, α5, and γ3 chains; BM40/SPARC; tenascin-C; matrilin-2; endostatin; and collagen type XVIII. Conclusions: Despite extensive similarities in basement membrane composition between amniotic and corneolimbal epithelia, the lack of limbus-specific environmental factors argues against the potential of denuded amniotic membrane as a surrogate niche for limbal stem cells but supports its suitability as a substrate to promote the formation of a well-differentiated stratified corneal epithelial equivalent for tissue engineering strategies.