Three distinct stages of lens opacification in transgenic mice expressing the HIV-1 protease

Scanning electron microscopy of the lenses from transgenic mice (TG(72)) co ntaining the HIV-1 protease linked to the lens alphaA-crystallin promoter s howed structural changes around postnatal day 16. Frank opacification of th e lens was observed at day 24. To relate the biochemical and biophysical ch anges that occur during the process of cataract development, high-resolutio n two-dimensional gel electrophoresis (2D), quantitative image analysis and ion measurements were carried out on lenses from postnatal day 10 and on d ays 15-24. The phase separation temperature (Tc), a measure of molecular in teractions between proteins, was also determined for normal and transgenic lenses. A comparison of the transgenic and normal lenses on day 10 revealed no significant differences in any of the measured parameters. However, sta rting around day 16 or the first stage of observed structural changes, the TG(72) crystallin profiles of the alphaA- alphaB-, beta A3-, beta A4-, beta B3 and one gamma -crystallin began to deviate from the normal. By postnata l day 20, a second stage was initiated with an influx of calcium and sodium ions that was accompanied by modifications of beta B1- and beta B2-crystal lin. In the third and final stage of the cataract process, a large increase in the proteolysis of crystallins was accompanied by the appearance of the frank cataract on day 24. The Tc initially increased in all of the mouse l enses until just prior to eyelid opening. After that time, the Tc decreased in all lenses. Although the Tc continued to decrease in the normal lenses with age, for the homozygous transgenic mice it exhibited a dramatic increa se that began on day 20. Thus, in the TG(72) transgenic mouse, cataract for mation occurs in a three-stage process. Tc and other biophysical parameters previously measured appeared to be insensitive to the modifications that o ccur during stage 1. However, during the second stage of cataract formation , there was a correspondence between abnormal Tc and the abnormal interacti ons between cellular constituents apparently resulting from lens hydration, the loss of ion homeostasis and continued proteolysis. The last stage of c ataract formation results in a total loss of lens transparency and leakage of lens proteins.