The overall goal of this project is to understand the role of water channels and gap junctions in the fluid balance of the ocular lens. The lens must remain transparent, refractive and flexible in order to focus an image on the retina and provide for accommodation. These requirements impose severe restrictions on the physiology of the lens, notably a lack of blood vessels. This in turn requires that the lens itself somehow generate an internal circulation to supply it metabolic needs. How this circulation is generated and regulated is the subject of our research. Three proteins are probably major players in regulating this intrinsic circulation. These are MIP, a water channel, and the gap junction proteins, Cx46 and Cx50. Defects in each of these cause cataracts in mice and humans. MIP and both fiber cell connexins are regulated by Ca2+ and pH. Low Ca2+, increases the water permeability induced by MIP. Cx50 hemichannels, but not cx46 hemichannels close at low external pH, probably because of two histidines in the third transmembrane segment. Replacing either or both of these with the corresponding amino acids in cx46 relieves the pH sensitivity and produces two interesting mutants. One forms only full gap junctions and one has hemichannel properties that resemble those of a naturally occurring, cataract inducing mutant.
Specific aims of this project are: 1. To understand the mechanisms of pH and calcium regulation of MIP-induced water permeability and its role in the lens circulation. 2. To understand the mechanisms of pH, calcium and voltage regulation of connexins 46 and 50. 3. To formulate hypotheses for regulation of the intrinsic circulation of the lens. 4. To determine if mutants defective in regulation alter lens physiology in transgenic mice. Results will expand our understanding of the physiology of the normal lens and aid in the design of strategies for prevention and treatment of cataracts.
| Fields, James B; Németh-Cahalan, Karin L; Freites, J Alfredo et al. (2017) Calmodulin Gates Aquaporin 0 Permeability through a Positively Charged Cytoplasmic Loop. J Biol Chem 292:185-195 |
| Reichow, Steve L; Clemens, Daniel M; Freites, J Alfredo et al. (2013) Allosteric mechanism of water-channel gating by Ca2+-calmodulin. Nat Struct Mol Biol 20:1085-92 |
| Clemens, Daniel M; Németh-Cahalan, Karin L; Trinh, Lien et al. (2013) In vivo analysis of aquaporin 0 function in zebrafish: permeability regulation is required for lens transparency. Invest Ophthalmol Vis Sci 54:5136-43 |
| Hall, James E (2012) Through a glass darkly. EMBO Mol Med 4:1-2 |
