Loss of Osteopontin Perturbs the Epithelial-Mesenchymal Transition in an Injured Mouse Lens Epithelium

Abstract

Purpose:: To investigate the role of osteopontin (OPN) in the wound healing process of the lens epithelium. We previously reported that OPN is up-regulated in the injured mouse lens prior to the epithelial-mesenchymal transition (EMT).

Methods:: The role of endogenous OPN in the injury-induced EMT of the lens epithelium was examined by using a lens injury model in OPN-null (KO, n = 40) and wild-type (WT, n = 40) mice. The crystalline lens was punctured and the animals were killed at day 1, 2, 5 and 10 post-injury. Immunohistochemistry was employed to detect a-smooth muscle action (aSMA), collagen type I, transforming growth factor b1 (TGFb1), TGFb2 and phospho-Smad2/3. Cell proliferation was assayed by examining uptake of bromodeoxyuridine (BrdU).

Results:: Injury-induced EMT of mouse lens epithelium, as evaluated by histology, expression pattern of aSMA and collagen I, was altered in the absence of OPN with reduced phospho-Smad2/3 signaling; up-regulation of TGFb1 and TGFb2 was also inhibited. Cell proliferation was more active in KO mice as compared with WT mice at day 1 and 2, but not at day 5 and 10.

Conclusions:: OPN is required for activation of Smad2/3 signal in an injured lens epithelium and lens cell EMT.

Keywords: extracellular matrix • cell adhesions/cell junctions • wound healing