Impact of the loss of tenascin X on tissue architecture and wound healing of the murine corneal stroma.

We investigated the role of tenascin X in the maintenance and healing of the corneal stroma using a tenascin X-null (Tnxb-/-, KO) mouse. While eye globe size and corneal diameter were unaffected, loss of tenascin X resulted in an age-dependent reduction in the ratio of the corneal height to axial length compared to wild-type (WT) mice. Deletion of Tnxb gene reduced mRNA expression of Col 1a1, 5a1, 6a1, 6a2 and 12a1 in the cornea. Immunohistochemistry also showed less staining intensity for collagen types III, V and VI in KO corneal stroma. Ultrastructural examination showed that the density of collagen fibrils was less and the diameter of each fibril was larger in KO stroma than in WT stroma. Second harmonic generation imaging identified what appeared to be altered 3D collagen lamellar organization consistent with the loss of collagen types that help control fibril packing and macroscopic organization. Tenascin X was upregulated in WT corneal epithelium and stroma during wound closure of full-thickness corneal incisions. Loss of Tnxb gene impaired stromal wound healing in association with suppression of expression of α-smooth muscle actin and F4/80, a macrophage marker. Although expression of TGFβ1 was unaffected in KO healing tissue, Smad3 activation was impaired. Tnxb gene deletion suppressed mRNA expression of Col 1a1, 5a1, 6a1, 6a2 and 6a3 in cultured ocular fibroblasts derived from eye shell of a newborn WT mouse. Taken together, tenascin X is indispensable to maintenance of cornea architecture and tissue repair of the corneal stroma in mice.