Molecular mechanisms of estrogen receptor regulation and signaling in human monocytes and macrophages

Sexual dimorphism in immune responses suggests that sex steroid hormones are involved in modulating immune mechanisms in vivo. Sepsis-related mortality rates increase after menopause, implicating 17beta-estradiol (estradiol) as an important factor in combating infection. Monocytes and macrophages are key effector cells of the innate immune system whose function is influenced by estradiol. However, little is known regarding the mechanisms by which estradiol affects immune function. Estradiol mediates its effects through binding to both isoforms of its receptor (ERalpha and ERbeta). Although estradiol has direct effects on monocyte and macrophage function, little is known about estrogen receptor (ER) isoform expression and the ability of estradiol to modulate expression of ER isoforms in these cells. This thesis demonstrates that ERalpha and ERbeta are differentially expressed in monocytes and macrophages and also identifies a splice variant of ERalpha, ERalpha46, that is up-regulated by estradiol in macrophages.;Macrophages recognize microbial pathogens through expression of toll-like receptors (TLRs) and respond by activation of the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-kappaB) signaling pathway, culminating in the production of proinflammatory cytokines, including tumor necrosis factor-alpha (TNF-alpha). As presented in this thesis, estradiol attenuates TNF-alpha production in response to TLR ligation through a reduction in NF-kappaB activation. A novel mechanism for NF-kappaB regulation by estradiol is proposed where expression of kappaB-Ras2, a negative regulator of NF-kappaB signaling, is upregulated by estradiol treatment.;Macrophage phenotype is influenced by the milieu of growth and differentiation factors present in the microenvironment. This thesis examines the influence of estradiol on macrophage differentiation in terms of expression of phenotypic markers and the secretion profile of cytokines in response to activation. Macrophages present in the human uterine endometrium are exposed to high levels of estradiol throughout the menstrual cycle; therefore, the repertoire of phenotypic markers and the profile of soluble factors produced by isolated endometrial macrophages in response to LPS were characterized. Whereas estradiol does not have a dramatic effect on macrophage phenotype, evidence presented in this thesis suggests that this hormone may skew macrophages towards an alternative, less inflammatory phenotype, similar to that of macrophages present within the uterine endometrium.