Compositional differences between infant and adult human corneal basement membranes

Abstract

Purpose: Adult human corneal epithelial basement membrane (EBM) and Descemet's membrane (DM) components exhibit heterogeneous distribution. The purpose of the study was to identify changes of these components during postnatal corneal development.

Methods: Thirty healthy adult corneas and 10 corneas from 12-day- to 3-year-old children were studied by immunofluorescence with antibodies against BM components.

Results: Type IV collagen composition of infant corneal central EBM over Bowman's layer changed from alpha1-alpha2 to alpha3-alpha4 chains after 3 years of life; in the adult, alpha1-alpha2 chains were retained only in the limbal BM. Laminin alpha2 and beta2 chains were present in the adult limbal BM where epithelial stem cells are located. By 3 years of age, beta2 chain appeared in the limbal BM. In all corneas, limbal BM contained laminin gamma3 chain. In the infant DM, type IV collagen alpha1-alpha6 chains, perlecan, nidogen-1, nidogen-2, and netrin-4 were found on both faces, but they remained only on the endothelial face of the adult DM. The stromal face of the infant but not the adult DM was positive for tenascin-C, fibrillin-1, SPARC, and laminin-332. Type VIII collagen shifted from the endothelial face of infant DM to its stromal face in the adult. Matrilin-4 largely disappeared after the age of 3 years.

Conclusions: The distribution of laminin gamma3 chain, nidogen-2, netrin-4, matrilin-2, and matrilin-4 is described in the cornea for the first time. The observed differences between adult and infant corneal BMs may relate to changes in their mechanical strength, corneal cell adhesion and differentiation in the process of postnatal corneal maturation.

Figure 1

New BM components in infant and adult human corneas. Antibodies against laminin γ3 chain (LM γ3; pAb 6296 is shown) showed weak staining of infant and adult central corneal EBM (left). Limbal BM staining was more prominent (middle); some capillary BMs were also positive. Bowman's layer is located to the left; its end is marked by an arrow. Matrilin-2 (right) was present in both infant and adult central EBM. e, epithelium; s, stroma.

Figure 2

BM components and Bowman's layer. Infant corneas displayed distinct staining for perlecan, total fibronectin, and collagen VII (COL VII) in Bowman's layer (arrows). Such staining was absent in adult corneas. e, epithelium; s, stroma.

Figure 3

Collagen type IV chains in infant and adult human corneas. Infant corneas contained the α1(IV) and α2(IV) (not shown) chains in the central part, contrary to their absence in adult corneas. However, the infant central EBM displayed very weak staining for the α3(IV) (not shown) and α4(IV) chains that were abundant in the adult central corneas. e, epithelium; s, stroma.

Figure 4

Specific laminin chains and keratin 3 in infant and adult peripheral cornea. Infant corneas, unlike adult corneas, did not stain for laminin chains α2 (LM α2) and β2 (not shown) in the limbal EBM. The peripheral basal epithelium did not stain for keratin 3 in infant corneas, in contrast to adult corneas. Arrows: LM α2-positive limbal vessels. e, epithelium; s, stroma.

Figure 5

Different distribution of BM components in infant and adult DM. Type IV collagen α1 chain (COL α1(IV)), nidogen-2, the α4 chain of laminin 411 (LM α4; pAb 1101+), and netrin-4 were found on both faces of the DM (arrows) of infant corneas (“railroad” pattern). In adult corneas, these and other (see Table 3) BM components were found only on one DM face.

Figure 6

Collagen types VIII and XII in infant and adult DM. Infant and adult DM (arrows) displayed inverse patterns of type VIII collagen (COL VIII). Only infant DM contained the long form of type XII collagen (COL XII long; mAb I1C8) on its endothelial face. s, stroma.

Figure 7

Differential expression of specific BM components in infant and adult DM. Infant DM (arrows) contained laminin-332 (LM-332), tenascin-C (TEN-C, alternatively spliced repeat A1 is shown), fibrillin-1 (FIB-1), and matrilin-4, in contrast to adult DM. s, stroma.