Connexin-forming gap junction intercellular communication (GJIC) is essential for the metabolic homeostasis of the lens. In addition to gap junctions, connexins forms hemichannels, permitting exchange of molecules across the cell. However, little is known regarding the function and regulation of hemichannels in the lens. In addition, lens connexin is subjected to posttranslational modifications;phosphorylation in differentiating lens fibers and proteolytic truncation in mature lens fibers. Our long-range goal i to understand the molecular mechanism(s) and functional significance of connexin molecules in lens homeostasis and transparency. The objective is to elucidate the distinctive, mechanistic roles of gap junctions and hemichannels, and role of posttranslational modifications of connexin (Cx) 50 under normal and oxidative stress conditions. The central hypotheses are: (1) GJIC and hemichannels play distinctive roles in the lens;(2) Increased GJIC and/or hemichannel function due to Cx50 phosphorylation by PKA in differentiating fibers and adaptive-regulation of gap junctions/hemichannels due to Cx50 truncation in mature fibers enhance lens resistance to oxidative damages.
Three specific aims will be pursued: 1) Determine the distinctive roles of gap junctions and hemichannels in the differentiating lens fibers. 2) Determine the functional importance of PKA phosphorylation of Cx50 in the lens. 3) Determine the mechanistic role of developmentally associated truncation of Cx50 in mature lens fibers. One of the innovative aspects is that this proposal aims to dissect distinctive roles of gap junctions and hemichannels, and posttranslational modifications in differentiating and mature lens fibers. Moreover, we will use our newly developed ex vivo approach to dissect the roles of Cx50 and its truncation in cortex and center core of the lens. It is our expectation that elucidation of the molecular mechanism(s) involved in the regulation of lens connexins and the channels formed by them will provide a better understanding of the general homeostatic process of lens under normal and pathological conditions. The outcomes of our research will be significant because the newly discovered knowledge should make novel and beneficial contributions to new strategies for the treatment of lens disorders, e.g. age-related cataracts, and pave way for drug discovery and development.

Public Health Relevance

Cataracts are one of the most common eye diseases and also one of the leading causes for blindness worldwide. Connexins play important roles in lens homeostasis and mutations in connexin genes lead to human congenital cataracts. The proposed research activity will help in understanding the molecular mechanism underlying the function of connexins under physiological and pathological conditions, and should make novel contributions to new ideas and strategies for drug discovery and development in treatment of cataracts.

National Institute of Health (NIH)
National Eye Institute (NEI)
Research Project (R01)
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Araj, Houmam H
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University of Texas Health Science Center
Schools of Medicine
San Antonio
United States
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