Differential gene expression in male and female rat lenses undergoing cataract induction by transforming growth...

Epidemiologic studies in humans as well as immunohistologic studies in animals have demonstrated significant sex differences in the propensity to develop cataract. Several studies suggest that estrogen may play a protective role against cataractogenesis. Indeed, male and ovariectomized female rat lenses have a greater susceptibility to cataract induced by transforming growth factor-beta (TGF-beta) than do normal female lenses. However, in spite of the current evidence that estrogen may play a pivotal role in cataractogenesis, the molecular mechanisms behind this phenomenon are largely undetermined. Our study utilized the differential display procedure to examine gene up- and down-regulation in male, normal female and ovariectomized female rat lenses exposed to TGF-beta. Male and normal female rat lenses were cultured with or without 0.15 ng ml(-1)TGF-beta. Lenses were then harvested, and total RNA was isolated for analysis by reverse-transcriptase differential display. Differentially expressed mRNAs were subcloned, sequenced and identified through GenBank database searches. The original experiment was repeated with the addition of ovariectomized female TGF-beta(+/-) conditions, and all differential patterns of gene expression were verified using Northern blot and RT-PCR analysis. Screening of approximately 12% of the mRNA population led to the identification of 27 differentially expressed cDNAs. Notably, strong gender differences were found in expression levels of gammaB-crystallin. In addition, proteasome Z subunit was up-regulated in TGF-beta-treated male and ovariectomized female lenses, but was down-regulated in TGF-beta-treated normal female lenses. This pattern of expression is consistent with the increased susceptibility of male and ovariectomized lenses to TGF-beta-induced cataract. We conclude that differential display is a useful and expedient method for analysing changes in gene expression in the lens. Structural and functional studies of the genes identified in this study may further elucidate mechanisms underlying the TGF-beta-induced cataract formation and differential rates of cataractogenesis in males vs females. In particular, our data suggest that the role of proteasome Z subunit in TGF-beta-induced anterior subcapsular cataract warrants further investigation.