Regionalized growth patterns of young chicken corneas

Extracellular matrix (ECM) accumulation, synthesis, and degradation were compared in central and peripheral corneal regions of 3-week-old chicks to identify regional differences within the cornea.

For collagen accumulation experiments, corneas were isolated at the scleral junction, the epithelium was removed, and the central corneal region was isolated from the peripheral region with a 3 mm trephine. After corneal stromas were digested with proteinase K, aliquots were used to estimate total collagen from hydroxyproline and cell number from DNA measurements. For biosynthesis experiments, corneas were placed in organ culture containing either in 3H-thymidine, 3H-proline, or 35SO4. After radiolabeling, the epithelium was removed, central and peripheral regions were isolated, and each corneal sample was analyzed for incorporated radioactivity. Gelatinolytic species present in each corneal region were compared qualitatively by gelatin zymography.

Measurement of hydroxyproline content indicated that the central corneal stroma contained significantly more collagen per DNA than the peripheral corneal region (+40%, P = 0.013) and incorporated significantly higher levels of 3H-thymidine/ng DNA (+92%, P < 0.001), 3H-proline/ng DNA (+980%, P = 0.004), and 35SO4/ng DNA (+650%, P = 0.01) than the peripheral corneal region. Results of gelatin zymography indicated that the central cornea contained the proenzyme form of gelatinase A, whereas the peripheral cornea contained both the proenzyme form and the active form of gelatinase A.

Fibroblasts located in the central cornea have a significantly higher rate of proliferation and ECM production than those of the peripheral cornea, whereas the presence of active gelatinase only in the peripheral cornea suggests higher gelatinolytic activity and ECM turnover in the periphery.