The Role Of α-crystallin As A Molecular Chaperone And Its Post-translational Modifications In Cataractogenesis

The role of a - crystallin as a molecular chaperone and its post-translational modifications in cataractogenesis (A Dissertation Submitted for the Degree of Ph. D) Postgraduate Student: Yan Hong Dissertation Supervisor: Professor Hui Yannian (Department of Ophthalmology, Xijing Hospital. The Fourth Military Medical University, Xi?an 710032, P. R.China) Abstract Purposes: Cataract, the major cause of blindness ~vorldwide. may be caused partly b~ post-translational modifications (PTM) of lens proteins that leads to the loss of lens transparency c~-Crvstallin is a major structural protein ~vithin the lens and contributes approximately 40% of total lens structural protein mass. It has been known for mans ~ears that its main function is to serve as a structural and refractive elements in the lens. In 1992. Honvitz suggested that i-crvstallin could act in a molecular chaperone-like manner. Many studied have showed that u~-crvstal1in can protect enzvnies and other crvstallins against both chemicall~? and thermally-induced inactivation and aggregation. which may pla~?an important role in maintaining transparent of the lens for so long. The glvcation. carbanwlation. corticosteroid and UV irradiation, acting as a part of PTM. are major risk factors for cataract formation. E~抜denee from epidemiological and animal studies has accumulated to support the idea that aspirin and ibuprofen as nonsteroidal anti-inflammatory drugs protect against cataract. However, the exact mechanism is still unkno~vn. Here ~ve concentrated on evaluating the role of r~-crvstallin as a molecular 6 chaperone and its PTM in cataractogenesis of age-related cataract. experimental selenite cataract and ageing. We also investigated the protection of aspirin-like drugs against PTM-induced inactivation of enzymes and decrease of molecular chaperone function. The results ~vill provide evidence for potential application of aspirin-like drugs. Methods: i-Crvstallin was from the soluble of the cortex and nucleus. 26 human clear and 1(11 age-related cataractous lenses (45-64 and 65-85 ~ears, nuclei only: Grade 11 or IV Pine Scale); 80 rat clear and 78 selenite cataract lenses; 10 old. 30 young. 20 newborn rabbit lenses and 8 bovine lenses ~vere separated by chromatograph~?on Sephacrvl 5- 300HR as described b~ Derham and Harding. respectively. The fractions corresponding to ri-high. ~-low. ~3 -high. 13 -lo~v and v -cry stallin were pooled separatel~? The protective effects of both (LH -and 憕L-cr~stallin on glv cation and thermally-induced inactivation and aggregation of catalase. thermally-induced aggregation of catalase and Ii L-crystallilI ~vere measured specti-ophotometrica11~. The assays complemented each other. Chaperone- like protection was represented as the percentage of protection by ~-crvstallin of the scattering produced by the target protein control at 360 nm in aggregation assa~s. or ~vas expressed relative to the original solution activit-v in inactivation of enzymes. The effects of g1~cation and UV irradiation on molecular chaperone function of several ~-crvstal1in were observed. We also investigated the protection of aspirin and ibuprofen. as nonsteroidal anti-inflammatory drugs. against glv cation-induced inactivation of...