INTERCELLULAR COMMUNICATION IN THE EYE LENS

Lens, an avascular organ, relies heavily on a network of transporting systems to deliver nutrients and otheressential components to bulky lens fibers and excrete wastes. Differentiated nuclear fiber cells never turn overand oxidative stress is a major cause of age related cataracts. Connexin (Cx)-forming gap junction channelsplay an essential role for the metabolic homeostasis of the lens. Besides gap junctions, connexins formhemichannels, permitting transport of molecules between the cell and its extracellular environment. Connexinsare truncated in nuclear fibers and this cleavage is increased with aging and oxidative stress. However, little isknown regarding the functional importance and regulation of hemichannels formed by full-length and truncatedconnexins in lens fibers. Our preliminary studies indicate that hemichannels in cortical lens fibers are activatedby mechanical loading, mediate uptake of glucose and glutathione, and exhibit self-protective roles againistoxidative damages. As such, we hypothesize that (1) The hemichannels formed by Cx50/Cx46 are activatedby mechanical stimulation in cortical lens fibers and mediate uptake of nutrients/antioxidants, which aredelivered to inner cortical and nuclear fibers via gap junctions to maintain cell homeostasis and viability; (2)Functional hemichannels formed by both full length and truncated Cx50/Cx46 exhibit self-protection againstoxidative damages. The goal is to understand distinctive, new roles of connexin hemichannels in lens fibercells under normal physiological and pathological (e.g. oxidative stress) conditions. In this proposal, first, wewill determine if connexin hemichannels activated by mechanical loading serve as a major transport pathwayfacilitating the uptake of nutrients and antioxidants into cortical lens fibers, and the role of integrins in regulatinghemichannels. Second, we will test if nutrients/antioxidants uptaken by hemichannels in cortical fibers aredelivered through gap junctions to inner cortical and nuclear fibers to meet metabolic needs of cellhomeostasis and protect inner fiber cells. Third, we will determine if hemichannels formed by both full-lengthand truncated Cx50/Cx46 offer a self-protective mechanism against oxidative insult. One of the majorinnovative aspects is that this proposal aims to uncover a novel role that connexin hemichannels formed byfull-length and truncated connexins play in facilitating metabolic function of lens fibers and protecting fiber cellsagainst oxidative damages. We will use established lens primary cultures and retroviral expression in lens insitu, a newly developed dominant negative ex vivo approach, and knockout mouse models. It is ourexpectation that elucidation of mechanistic roles of connexin channels in lens fibers will provide a betterunderstanding of the general homeostatic process of lens under normal and pathological conditions. Theoutcomes of our research will be significant because the discoveries should make novel and beneficialcontributions to new therapeutic strategies and identify drug targets for the treatment of lens disorders such asage-related cataracts.