1. ¹Department of Ophthalmology, Wakayama Medical University, Wakayama, Japan
2. ²Laboratory of Cell Regulation and Carcinogenesis, National Cancer Institute, National Institutes of Health, Bethesda, MD, USA
3. ³Division of Molecular Immunology, Institute for Genetic Medicine, Hokkaido University, Kita-ku, Sapporo, Japan
4. ⁴Department of Ophthalmology, University of Cincinnati Medical Center, Cincinnati, OH, USA
5. ⁵Department of Genetics, Rutgers University, Piscataway, NJ, USA
6. ⁶Department of Cell Biology and Neuroscience, Rutgers University, Piscataway, NJ, USA

Correspondence: Professor S Saika, MD, PhD, Department of Ophthalmology, Wakayama Medical University, 811-1 Kimiidera, Wakayama, 641-0012, Japan. E-mail: shizuya@wakayama-med.ac.jp

Received 6 September 2006; Revised 20 October 2006; Accepted 23 October 2006; Published online 8 January 2007.

Abstract

We previously reported that osteopontin (OPN), a matrix structural glycophosphoprotein, is upregulated in the injured mouse lens prior to the epithelial–mesenchymal transition (EMT). Here, we investigated the role of this protein in EMT of the lens epithelium during wound healing. The crystalline lens was injured by needle puncture in OPN-null (KO, n=40) and wild-type (WT, n=40) mice. The animals were killed at day 1, 2, 5, and 10 postinjury. Immunohistochemistry was employed to detect -smooth muscle action (SMA), a marker of EMT, collagen type I, transforming growth factor 1 (TGF1), TGF2, and phospho-Smad2/3. Cell proliferation was assayed by examining uptake of bromodeoxyuridine (BrdU). The results showed that injury-induced EMT of mouse lens epithelium, as evaluated by histology, expression pattern of SMA and collagen I, was altered in the absence of OPN with reduced phospho-Smad2/3 signaling. Upregulation of TGF1 and TGF2 in the epithelium 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. An in vitro experiment shows OPN facilitates cell adhesion of lens epithelial cell line. OPN is required for activation of Smad2/3 signal in an injured lens epithelium and lens cell EMT.