The lens epithelium: Focus on the expression and function of the alpha-crystallin chaperones

Lens epithelial cells are the parental cells responsible for growth and development of the transparent ocular lens. Many elegant investigations into their biology have focused on the factors that initiate and regulate lens epithelial cell differentiation. Because they serve key transport and cell maintenance functions throughout life, and are the primary source of metabolic activity in the lens, mechanisms to maintain lens epithelial cell integrity and survival are critical for lens transparency. The molecular chaperones alpha-crystallins are abundant proteins synthesized in the differentiated lens fiber cell cytoplasm. However, their expression in lens epithelial cells has only been appreciated very recently. Besides their important roles in the refractive and fight focusing properties of the lens, alpha-crystallins have been implicated in a number of non-refractive pathways including those involving stress response, apoptosis and cell survival. The most convincing evidence for their importance in the lens epithelium has been shown by studies on the properties of lens epithelial cells from alpha A and alpha B-crystallin gene knockout mice. Novel combination of genetics, cell and molecular biology should lead to a greater understanding of how lens epithelial cells proliferate, differentiate and survive. Cell facts Lens epithelial cells are responsible for the growth and development of the entire ocular lens Lens development is controlled by cell cycle regulators, signaling molecules and growth factors such as FGF Lens epithelial cells express members of the small heat shock protein family of molecular chaperones, alpha A-crystallin and alpha B-crystallin, the first crystallins to be expressed during lens development alpha-Crystallins likely protect lens epithelial cells from environmental stress throughout life, and thus may delay the onset of age-related cataract Lens epithelial cell proliferation is deregulated in posterior capsule opacification leading to secondary cataract, a complication in up to 50% of cataract surgeries (c) 2007 Elsevier Ltd. All rights reserved.