Changes in the structure of crystallins, the major lens protein, are thought to account for the loss of lens transparency that occurs with aging. Aged and cataractous human lenses show increased crystallin proteolysis and aggregation as compared to young, non-cataractous lenses. However, the molecular mechanisms for age-related protein aggregation are not fully understood. We hypothesize that protein aggregation in the aging lens (>40 years old) is initiated by the actions of novel proteases, which recognize a specific sequence in crystallins and are responsible for cleavage of crystallin and generation of crystallin fragments with anti-chaperone activity and toxic properties. The crystallin fragments with anti-chaperone activity interact with 1A- and 1B-crystallins at chaperone sites, contributing to the loss of the 1-crystallin chaperone activity known to occur in aged, less transparent lenses and cataractous lenses. Additionally the interactions between crystallin fragments and intact, modified or truncated crystallins lead to age-related protein aggregation and insolubilization of 1-crystallin in the nuclear region of the lens, resulting in loss of transparency and cataract formation. In support of our hypothesis that crystallin-derived anti-chaperone peptides have a key role in the age-related loss of lens transparency, we have demonstrated that in vivo-generated human lens crystallin fragments generate H2O2, display anti-chaperone activity and induce lens protein aggregation and precipitation. Studies will be performed in both human lenses and in the guinea pig model of age-related cataractogenesis. We propose to undertake studies to identify the origin of crystallin fragments and to characterize the proteolytic mechanisms responsible for the cleavage of crystallins and the generation of anti-chaperone peptides. Using state-of-the-art mass spectrometric tools and analytical techniques, we will expand our understanding of the molecular mechanisms involved in crystallin-derived-peptide mediated protein aggregation and cataractogenesis. The proposed studies will accomplish the following Specific Aims: 1) Investigate the low-molecular weight crystallin fragments present in young, adult, aged and cataractous human lenses and in lenses of normal and hyperbaric oxygen (HBO)-treated guinea pigs. 2) Characterize the crystallin-derived anti-chaperone peptides and determine their ability to induce 1- crystallin aggregation in vitro and ex vivo. 3) Investigate whether sequence-specific proteases or non-enzymatic cleavages are responsible for the generation of crystallin-derived anti-chaperone peptides and isolate and characterize the novel protease involved.
Understanding why the lens so commonly develops a cataract may lead to the development of methods for preventing this common cause of vision loss. During aging, for some unknown reason, the lens begins to accumulate peptides (breakdown products) derived from crystallin (peptides), the major protein in the lens. Over time, these peptides become toxic in the lens as they accumulate, leading to loss of lens transparency and cataract.
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