Many extracellular and intracellular stimuli, such as oxidants, high glucose levels, osmotic shock, UV radiation, cytokines, and growth factors, have been reported to activate the intracelluiar MAP kinase signaling pathway. Coincidentally, it has been suggested that some of these stimuli are the risk factors for human senile and diabetic cataracts. It seems likely, therefore, that a perturbed activation of the MAP kinase pathway, occurring under different stimuli during disease states or aging, is one of the early key events for causing pathological responses in the lens. Transgenic mice overexpressing a constitutively active MAP kinase in the lens develop macrophthalmia with osmotic cataracts that are similar to human diabetic cataracts. Alternative approaches, including the generation of lens-specific MAP kinase gene knockout mice and lens organ cultures treated with pharmacological inhibitors, will also be used to elucidate the role of the MAP kinase in the lens. In addition, several biochemical methods, such as two-dimensional protein gels with identification of proteins by matrix-assisted laser desorption/ionization mass spectrometry, will be used to identify the downstream targets of the MAP kinase pathway, which are responsible for cell swelling and vacuole formation in these transgenic lenses. Transgenic mice with an overexpression of the glucose transporter gene in their lenses will be generated to test the hypothesis that a significant increase in the glucose transporter level in the lens, which is found in the kinase transgenic mice, causes an alteration of the lens glucose metabolism or protein glycation, eventually inducing osmotic cataracts. The long-term goal of this proposal is to understand how the intracellular MAP kinase signaling pathways regulate the normal physiological condition of the lens. Moreover, because the phenotypic changes occurring in these transgenic mice are similar to human diabetic cataracts, studies of this mouse model may provide insights into the molecular basis for these pathological processes in human diseases.
