Spatial and temporal mapping of the age-related changes in human lens crystallins

Using the techniques of high performance liquid chromatography (HPLC), gel electrophoresis in the presence of sodium dodecyl sulfate (SDS), and immunoblotting, we have analyzed the age-related changes in soluble crystallins of the human lens. A 3 mm core along the optical axis of each lens was frozen-sectioned and the sections were biochemically analyzed for distribution and quantity of the various soluble protein species. Both cortical and nuclear samples show a monotonic decrease in the concentration of the 19 000 and 21 000 MW proteins with age. We find that these proteins behave anomalously on SDS-polyacrylamide gels, running near the top of the gel when the samples are not boiled before loading; this permitted us to observe the gradual, age-related loss of these bands from the gels of both nuclear and cortical samples. The high molecular weight, or TSK-3000 void volume, fraction (greater than 350,000) of the cortex contained alpha crystallin at all ages. However, in the nucleus, while this fraction is primarily composed of alpha crystallin early in life (i.e. before 15 years of age), there is a gradual incorporation of other crystallins into the void volume. This change in the composition of the high-molecular-weight, soluble protein fraction is reflected in: a change in the subunit mobility on SDS-polyacrylamide gels; reactivity of the fraction to crystallin antibodies, i.e. in the young nucleus there is reactivity to anti-alpha crystallin only, with a gradual increase in reactivity to anti-beta and anti-gamma crystallins. The void volume fraction of the nucleus persists as a major component of the soluble protein pool until 42-44 years of age, at which time the proportion of the total soluble protein represented by this void volume fraction decreases precipitously. These changes in the soluble protein profile are discussed in terms of their potential influence on the functioning of the lens.