Jeffrey B. Hodgin, Ph.D., M.D.

Dissertation research performed under the guidence of Dr. Nobuyo N. Maeda

ABSTRACT
    Clinical and epidemiological evidence supports a protective role for estrogens in prevention of coronary heart disease (CHD). The natural estrogen 17b-estradiol (E2) inhibits atherosclerosis in a variety of animal models, but the mechanism is unclear. I have employed a genetic and pharmacologic treatment study design to dissect the molecular mechanisms of 17b-estradiol-mediated inhibition of atherosclerosis. Using knockout mice on an atherosclerotic genetic background (apolipoprotein E-deficient), I have studied the atheroprotective effects of chronic exogenous E2 treatment in mice that also lack functional candidate genes for the atheroprotective effects of E2. I ovariectomized one month old female mice that lack apolipoprotein E alone (ee) or lack both apoliprotein E and the candidate gene of interest, and treated them with E2 or control for three months. The long-term, atheroprotective effects of estrogen are generally thought to be mediated through estrogen receptors (ER), of which two are known (ERa and ERb). E2 treatment of ee females dramatically reduced lesion size and histological complexity compared to control. In contrast, E2 treatment caused minimal reduction in lesion size of ERa and apolipoprotein E-deficient females (aa;ee), demonstrating that ERa is a major mediator of the atheroprotective effect of 17b-estradiol. Nevertheless, the existence of some ERa-independent atheroprotective effects of E2 remained. E2 treatment of females that lacked ERb and apolipoprotein E (bb;ee) resulted in full inhibition of plaque formation. The atheroprotective effects of E2 have been attributed to an increase in nitric oxide synthesis. Chronic E2 treatment of endothelial nitric oxide synthase (eNOS)-deficient or inducible NOS (iNOS)-deficient females on an apolipoprotein E-deficient background (nnee and iiee respectively) resulted in full inhibition of atherosclerotic lesion progression. Thus, a major role for either eNOS or iNOS in the E2-mediated inhibition of atherogenesis is ruled-out. Finally I use microarray gene chip technology on mRNA from aorta to identify novel, ERα-dependent candidate genes in the mechanism of E2-mediated atheroprotection. The research presented here should lead to further elucidation of the protective mechanisms of E2 against atherosclerosis and aid in the design of pharmacologic agents to target the atheroprotective effects of E2.