Morphological study of the cataractous lens of the senescence accelerated mouse

A murine model of accelerated aging, the senescence accelerated mouse (SAM), has been developed. There are three accelerated senescence-resistant (SAM-R) strains and eight senescence-prone (SAM-P) strains. The SAM-P strains have an earlier onset and more rapid advancement of senescence resulting from a significantly shorter lifespan compared with the SAM-R strains. Spontaneous cataracts have been found in some individuals of the SAM-P/9 strain. The SAM-P/1 strain, which was used in the present study, has such systemic senescent characteristics as senile amyloidosis and alopecia, but it was previously thought that cataract does not occur in this strain. However, we found cataractous changes in the lens of these animals at early stages of their life. The earliest change was the appearance of a ripple-mark body at about 3 months of age. The number of rippled rings increased with age. These changes later induced refractive distortion of retinal vessels. Whole-mount flat preparations of the epithelium showed that the number of cells was markedly decreased at the advanced stages of cataract. At the late stages of life the lens cortex became liquefied and developed into a mature cataract. Cataract formation in this strain may be related to reduced viability of the lens epithelium.