PARENT SESSION
MECHANISMS OF HORMONE ACTION

Tuesday, August 3, 2004
10:30 AM–12:30 PM
Buchanan Courtyard

(351) GENE EXPRESSION PROFILING OF 17-ESTRADIOL AND GENISTEIN EFFECTS ON MOUSE THYMUS.

Selvaraj, Vimal¹, Bunick, David¹, Johnson, Rodney², Liu, Lei^{2, 3}, Cooke, Paul¹, ¹ Department of Veterinary Biosciences, University of Illinois at Urbana-Champaign, Urbana, IL² Department of Animal Sciences, University of Illinois at Urbana-Champaign, Urbana, IL³ Bioinformatics Center, University of Illinois at Urbana-Champaign, Urbana, IL

ABSTRACT- Estrogen regulates thymic development and immune function. Despite the critical role of estrogenic actions in inducing thymic involution and modulating immune responses, the mechanism of this effect is not understood. Similarly, action of the estrogenic soy isoflavone genistein inducing thymic atrophy is also unclear. To provide an insight into mechanisms of estrogenic effects in the thymus, we analyzed thymic gene expression changes induced by 17-estradiol (E2) and genistein. Ovariectomized 30 day old C57BL/6 mice were given either daily injections of E2 (125ng/day) or fed a phytoestrogen-free diet with genistein (1500 ppm) for 0 (control), 2, 3 and 6 days (n=6/time point/group). RNA was extracted from thymuses, processed and hybridized on oligonucleotide arrays representing 22, 680 genes. E2 regulated a greater number of genes than genistein. More genes were up-regulated by E2 (318 genes) compared to genistein (161 genes) while genistein down-regulated more genes. Though a significant number of E2-regulated genes were also affected by genistein (36%), genistein regulated several genes not regulated by E2 and genistein did not affect all E2-regulated genes. Hierarchical clustering revealed distinct early, late and biphasic patterns and functional characterization indicated groups of genes involved in transcription, apoptosis, cell cycle and genes of importance in thymic development and function affected by E2 and genistein. Factors like GILZ, CD84, CCR5, IL-2 and IL-2R involved in thymocyte signaling and critical for thymocyte selection and maturation were modulated. There was up-regulation of caspases 7 and 9, indicative of passive cell death due to lack of crucial pro-survival signals and up-regulation of p27kip1 potentially impeding cell cycle progression in E2-treated thymus. IL-2 expression, necessary for activation-induced cell death (AICD) during negative selection of thymocytes, was down-regulated with E2 and genistein treatment. This can compromise central tolerance facilitating release of potential autoimmune T cells. Unknown genes regulated by E2 and genistein of potential importance in this system were identified. The findings in this study provide new mechanistic insights towards explaining estrogen action on T cell development and function. Supported by NIH grant ES011590

KEY WORDS: phytoestrogen, T cell, thymus, immune system