GLYCATION MEDIATED CROSS-LINKING BETWEEN ALPHA-CRYSTALLIN AND MP26 ININTACT LENS MEMBRANES

With advancing age, progressive crosslinking occurs between lens cryst allin proteins and other lenticular components. This crosslinking may be involved in the development of senile cataracts. Experiments were c onducted to determine whether non-enzymatic glycation could be involve d in the crosslinking between lens alpha-crystallin and MP26, an abund ant lens fiber cell membrane intrinsic protein. In vitro crosslinking of alpha-crystallin and MP26 of bovine lens membranes was observed in presence of two degradation products of ascorbic acid (ASA), dehydroas corbic acid (DHA) and threose. Alkali-washed bovine lens membranes, is olated after glycation with DHA and threose, contained both alpha-crys tallin and MP26, as determined by immunoblot and double immunocytochem ical labeling studies. In contrast, membranes incubated without these glycating compounds contained only MP26. SDS-PAGE analysis of [I-125]a lpha-crystallin incubated with lens membranes in the presence of threo se showed a higher amount of radioactivity in high molecular weight ag gregates than in the aggregates produced when alpha-crystallin and thr eose were incubated without membranes. A slot-blot immunoassay of alka li-washed human lens membranes showed a higher amount of covalently bo und alpha-crystallin in aged, cataractous or diabetic lens membranes t han was present in lens membranes from young normal donors. Based on t he in vitro results, we hypothesize that non-enzymatic glycation is on e of the in vivo mechanisms in the crosslinking of alpha-crystallin to lens membrane proteins, such as MP26. This crosslinking may contribut e significantly to the development of age-related and diabetic catarac ts.