The Cardiovascular Benefit of Menopause Hormone Treatment is Age-Dependent in Ldlr-/- Mice

Background: The risk of Atherosclerotic cardiovascular disease (ASCVD) increases in women after menopause, coinciding with declining estrogen levels. However, menopausal hormone therapy (MHT) has not consistently reduced ASCVD events in post-menopausal women, despite improvements in lipid profiles. The mechanisms underlying the diminished cardiovascular protective effects of estrogens during MHT remain poorly understood. Methods: Atherosclerosis was established in 11-month-old female Ldlr-/- mice through Western diet feeding. To investigate the effects of menopause and 17{beta}-estradiol (E2) treatment on atherosclerotic burden during lipid normalization, mice were switched to a chow diet and subjected to ovariectomy (OVX) with and without E2 treatment. To determine the contribution of inflammation to ASCVD risk during MHT, a cohort of mice received Ifn{gamma}-/- bone marrow transplant (Ifn{gamma}-/-BM) before hormone treatment. To assess the influence of age on ASCVD risk during MHT, parallel studies were conducted in young mice, beginning at 12 weeks of age. Outcomes included lipid profiles, HDL function, circulating cytokines, atherosclerotic burden, liver lipid metabolic pathways and transcriptomic profiles, and hepatic estrogen receptor signaling. Results: OVX increased atherosclerotic burden compared with sham-operation. E2 treatment following OVX failed to reduce established atherosclerosis in older mice but reduced atherosclerosis in young mice during diet-induced lipid normalization. In older mice, E2 treatment increased circulating IFNγ, 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 the ability of E2 treatment to reduce atherosclerosis in older mice. In contrast, E2 treatment following OVX in young mice limited inflammation and improved HDL function. E2 treatment increased liver fatty acid metabolic signaling in both older and young mice but increased liver 4-hydroxynonenal (4-HNE) levels only in older mice. This age-dependent response was associated with remodeling of hepatic estrogen receptor (ER) expression, characterized by reduced ERα and increased in G protein-coupled ER expression with aging. Liver transcriptomic analyses identified inflammatory and interferon-associated signatures following OVX+E2 treatment in older mice. qPCR analyses across older and young mice suggested age-associated differences in inflammatory transcripts in response to E2. Conclusions: These findings suggest that aging alters the hepatic response to E2 treatment following ovariectomy, promoting oxidative stress and inflammatory signaling that contribute to persistent systemic inflammation and compromise the ability of E2 to reduce atherosclerosis.