Cardiovascular Benefits of Menopause Hormone Treatment is Age-Dependent

Background: Hormone therapy (HT) has not consistently reduced atherosclerotic cardiovascular disease (ASCVD) events in post-menopausal women, yet the underlying mechanisms remain poorly understood. Methods: Female Ldlr-/- mice with established atherosclerosis were subjected to surgical menopause and treated with 17{beta}-estradiol (E2) following lipid normalization. Studies were performed in aging and young mice. To determine whether inflammation mediates the age-dependent response to HT, a cohort of aging mice underwent transplantation with Ifn{gamma}-/-bone marrow (BM) before hormone treatments. Metabolic parameters, HDL function, systemic inflammation, atherosclerotic burden, liver metabolic and oxidative stress signaling, and hepatic estrogen receptor signaling were evaluated. Results: In aging mice, menopause E2 treatment failed to reduce established atherosclerosis as shown in sham operated mice during lipid normalization. Instead, E2 treatment increased circulating IFN{gamma} and IL-6, impaired HDL antioxidant and cholesterol efflux functions, and promoted inflammatory and vulnerable plaque phenotypes. Suppression of inflammation through Ifn{gamma}-/-BM transplantation restored HDL function and significantly reduced atherosclerosis in E2-treated aging mice. In contrast to aging mice, young mice exhibited reduced systemic and plaque inflammation, improved HDL functions, and regression of atherosclerosis following E2 treatment. Liver RNA sequencing and qPCR validation identified activation of inflammatory, oxidative stress, and lipid metabolic pathways in aging E2-treated mice, which were largely attenuated following Ifn{gamma}-/- bone marrow transplantation as well as in young mice. Compared to young mice, aging mice presented hepatic estrogen receptor remodeling characterized by reduced estrogen receptor (ER) expression and increased G-protein coupled estrogen receptor (GPER) expression. Constitutive GPER activation was accompanied by induction of NOX1-dependent oxidative stress, which was further exacerbated by E2 treatment, leading to persistent inflammation. Conclusions: The cardiovascular effects of estrogen therapy are fundamentally age dependent. Aging shifts estrogen signaling toward hepatic oxidative stress and inflammation through increased GPER. While E2 treatment preserves both metabolic and cardiovascular protection in young mice, aging exacerbates GPER-NOX1-mediated oxidative stress, resulting in impaired HDL function and persistent residual ASCVD risk. These findings identify inflammation-driven, non-lipid mechanisms as potential therapeutic targets to improve cardiovascular outcomes during hormone therapy in postmenopausal women.