Expression and Functions of Heat Shock Proteins in the Normal and Pathological Mammalian Eye

Heat shock proteins (Hsps) are expressed in mammalian embryonic, adult and aging lens, cornea and retina. These proteins, particularly those belonging to the family of small Hsps, such as alpha A-crystallin (HspB4) and alpha B-crystallin (HspB5), play important roles in the differentiation of lens cells and are essential for the maintenance and protection of the supraorganization of proteins in differentiated corneal and lens fiber cells. Hsps are molecular chaperones characterized by their protective activity against different types of stress. They also have anti-apoptotic and anti-oxidant functions that help lens and corneal cells to better cope with the oxidative conditions that result from light induced injuries. They are also effective to protect the retina against the high rate of oxidative metabolism observed in this tissue. The goal of this review is to highlight recent works describing the expression and function(s) of the different Hsps as an attempt to better understand their roles in the normal and pathological eye. Particular emphasis is given to the alpha-crystallin polypeptides which, in addition to their protective functions, are key structural polypeptides that are essential for the refractive and light focusing properties of the lens, a property demonstrated by the caractogenic potential of their mutations.