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 alpha 1, alpha 2, alpha 5, and alpha 6 chains; collagens type VII, XV, XVI, XVII, and XVIII; laminin alpha 3, beta 1, beta 2, beta 3, gamma 1, and gamma 2 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 alpha 3 and alpha 4 chains, collagen type V, and laminin alpha 4 chain. Limbal basement membrane components, which were not detected in amniotic membrane, included laminin alpha 1, alpha 2, alpha 5, and gamma 3 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.