A new model of anterior subcapsular cataract: involvement of TGFbeta/Smad signaling.

PURPOSE To develop a new animal model of anterior subcapsular cataract formation by topical application of alkali to the eye and to examine the role of Transforming growth factorbeta/Smad3 (TGFbeta/Smad3) signaling in the formation of this cataract model. METHODS Under anesthesia, one eye of adult Wistar rats (n=142) was subjected to alkali burn by topical application of 1 N NaOH. The eye was then histologically examined at specific time intervals. Immunohistochemistry with a battery of antibodies was carried out to examine the epithelial-mesenchymal transition (EMT) in lens epithelium. Enzyme immunoassay was employed to determine the level of growth factors in aqueous humor and lens tissue. Smad3-null mice were also used to examine the role of Smad3 signaling in cataractogenesis in this model. RESULTS Two days post-burn of the ocular surface, lens epithelium underwent EMT as evidenced by the upregulation of Snail and alpha-smooth muscle actin and formed a multilayer of cells beneath the capsule. Smad signaling was found to be activated in EMT-type lens cells. The majority of myofibroblast-type lens cells expressed proliferative cell nuclear antigen (PCNA). The total amount of active TGFbeta2, total TGFbeta2, and Fibroblast growth factor 2 (FGF2) increased in the aqueous humor and lens. Loss of Smad3 attenuated, but did not completely abolish, EMT in the lens epithelium. CONCLUSIONS Topical alkali treatment of the ocular surface readily induces an EMT-type anterior subcapsular cataract. Smad3 signaling is involved, but not required, for achievement of EMT in the lens epithelium in this cataract model.