title: Lens Biology and Biochemistry.
abstract: The primary function of the lens resides in its transparency and ability to focus light on the retina. These require both that the lens cells contain high concentrations of densely packed lens crystallins to maintain a refractive index constant over distances approximating the wavelength of the light to be transmitted, and a specific arrangement of anterior epithelial cells and arcuate fiber cells lacking organelles in the nucleus to avoid blocking transmission of light. Because cells in the lens nucleus have shed their organelles, lens crystallins have to last for the lifetime of the organism, and are specifically adapted to this function. The lens crystallins comprise two major families: the βγ-crystallins are among the most stable proteins known and the α-crystallins, which have a chaperone-like function. Other proteins and metabolic activities of the lens are primarily organized to protect the crystallins from damage over time and to maintain homeostasis of the lens cells. Membrane protein channels maintain osmotic and ionic balance across the lens, while the lens cytoskeleton provides for the specific shape of the lens cells, especially the fiber cells of the nucleus. Perhaps most importantly, a large part of the metabolic activity in the lens is directed toward maintaining a reduced state, which shelters the lens crystallins and other cellular components from damage from UV light and oxidative stress. Finally, the energy requirements of the lens are met largely by glycolysis and the pentose phosphate pathway, perhaps in response to the avascular nature of the lens. Together, all these systems cooperate to maintain lens transparency over time.
authors: Ophthalmic Genetics and Visual Function Branch, National Eye Institute, National Institutes of Health, Bethesda, Maryland, USA.
authors: J Fielding
authors: JF
authors: Hejtmancik
authors: The Wilmer Eye Institute, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
authors: S Amer
authors: SA
authors: Riazuddin
authors: Department of Genetics and Ophthalmology, Albert Einstein College of Medicine, Bronx, New York, USA; Department of Ophthalmology and Visual Sciences, Albert Einstein College of Medicine, Bronx, New York, USA.
authors: Rebecca
authors: R
authors: McGreal
authors: Department of Genetics and Ophthalmology, Albert Einstein College of Medicine, Bronx, New York, USA; Department of Ophthalmology and Visual Sciences, Albert Einstein College of Medicine, Bronx, New York, USA.
authors: Wei
authors: W
authors: Liu
authors: Department of Genetics and Ophthalmology, Albert Einstein College of Medicine, Bronx, New York, USA; Department of Ophthalmology and Visual Sciences, Albert Einstein College of Medicine, Bronx, New York, USA.
authors: Ales
authors: A
authors: Cvekl
authors: Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, St. Louis, Missouri, USA. Electronic address: Shiels@vision.wustl.edu.
authors: Alan
authors: A
authors: Shiels
mesh_terms: D003459:Crystallins / Q000378:metabolism; D003598:Cytoskeletal Proteins / Q000378:metabolism; D017629:Gap Junctions / Q000378:metabolism; D006801:Humans; D007908:Lens, Crystalline / Q000378:metabolism / Q000502:physiology*; D008565:Membrane Proteins / Q000378:metabolism; D008954:Models, Biological
chemical_list: D003459:Crystallins; D003598:Cytoskeletal Proteins; D008565:Membrane Proteins
keywords: Crystallins; Lens; Membrane proteins; Transparency