Loss of transparency of the lens, or cataract, is the leading cause of blindness in the world. Two related forms of cataract, subcapsular cataract and secondary cataract, involve the increased proliferation and transformation of lens epithelial cells (LECs) into plaques of large """"""""spindle shaped"""""""" myofibroblasts which express the contractile filament, alpha-smooth muscle actin (alpha-SMA). The long-term goal of this project is to determine the extracellular signals, which alter the genetic makeup and phenotype of lens epithelial cells during subcapsular cataract formation. Specifically, the hypothesis that Matrix Metalloproteinases (MMPs), play a functional role in the transition of lens epithelial cells into mesenchymal or myofibroblast cells (EMT), a hallmark feature of subcapsular cataracts and secondary cataract will be investigated. Preliminary findings from this laboratory show that accompanying the EMT in the TGF-beta-induced cataract model in rats is the induction in expression of gelatinase A (MMP-2). This may reflect a downstream involvement of MMPs, secondary to the initial cause. However, it is equally probable that MMPs play a more active role in initiating the events leading up to cataract formation. For example, MMPs have been shown to directly influence the EMT of many cell types and to activate latent TGF-beta. The proposed studies will distinguish between these two alternate hypotheses. Using the TGF-beta induced model in rats, the timing and level of induction of MMP-2 and additional candidate MMPs, including MMP-3 and MMP-9 will be examined with immunohistochemistry, zymography and western blot analysis. Expression of these MMPs will be correlated with the appearance of myofibroblasts expressing alpha-SMA. Synthetic inhibitors of MMPs will be used in the culture model to determine if one or more of the MMPs are required for mediating the TGF-beta induced cataractous changes. If MMPs directly participate in cataractogenesis, the ability to block MMP expression and activity may be of high impact to lens and cataract research since it would provide the basis for investigation of a novel therapy for the prevention of cataracts. Finally, the TGF-beta model in rats will be adapted to the mouse lens in order to use MMP knockout mice for determining the individual role(s) of candidate MMPs in subcapsular cataract formation.
