Tipping the balance — the move of aging females towards higher ERβ:ERα ratio and away from estrogen mediated vascular protection

Objective: The menopausal transition, marked by the cessation of endogenous estrogen production, is a hallmark of vascular aging in women, as the vascular function radically declines in the years hereafter (Parker et al. 2010). Primarily based on animal and in-vitro studies (Novella et al. 2012; Novensà et al. 2011; Park et al. 2017) it has been hypothesized that this is linked to menopause-dependent changes in the balance between the two dominant estrogen receptors, ERα and ERβ; as previous studies suggest that ERα favors NO-bioavailability whereas ERβ mediates increases in oxidative stress. However, it remains unresolved how aging actually influences changes in the balance between ERα and ERβ in skeletal muscle of females and how changes are related to downstream protein targets such as eNOS and NADPH oxidases. Study design: We measured skeletal muscle protein expression of estrogen receptors, androgen receptors, eNOS, SOD2, GPX1, gp91phox/-NOX2 and NOX4 in 82 females ranging from 20-70 yrs. of age. For age comparisons, data from the muscle biopsies were grouped by 5-year intervals. Statistical analyses were conducted by on one-way ANOVA and Pearson’s product moment correlations Results: The ERβ:ERα ratio was significantly higher in the 65+ yrs. compared to all other groups (p<0.01) and correlation analysis revealed that the ERβ/ERα ratio increased with aging (p=0.02, R 2 =0.07). The 65+ yrs. group presented a lower eNOS expression (p<0.05) than the 20-54 yrs. groups and correlation analysis showed a decrease in eNOS expression with aging (p=0.0002 R 2 =0.16). Gp91phox/-NOX2 expression correlated with ERβ and the expression of gp91phox/NOX2 (p=<0.0001 R 2 =0.4) was lower in the three middle groups, 45-59 yrs., compared with both the younger and older groups (p<0.05). ERα correlated with the antioxidants SOD2 and GPX1 (p=0.0001 R 2 =0.18 and p=<0.0001 R 2 =0.21, respectively). Conclusions: This study is the first to show that skeletal muscle expression of ERβ:ERα increases with age and that the expression of eNOS in skeletal muscle declines as a function of age in females. Our data also provides indirect support for that aging is associated with a shift from a more prominent ERα coupled antioxidant effect, through - SOD2/GPX1 related mechanisms, towards a more pro-oxidant environment through an ERβ mediated upregulation of Gp91phox/-NOX2. This shift, combined with the observation of an age induced decline in eNOS expression, could be mechanisms underlying reduced NO bioavailability in aging females. Further analyses are ongoing to throw light in these mechanisms and additional studies are warranted to fully elucidate the mechanistic pathways involved. Funding The study was funded by The Danish Ministry of Culture Fund for Research in Sports, The Independent Research Fund Denmark, Eva and Henry Frænkel Memorial Fund, and the Toyota Foundation. The study is part of The Copenhagen Women Study for which fi- nancial support was provided by the University of Copenhagen Excellence Programme for Interdisciplinary Research. The study was also supported by The Danish Ministry of Culture: Sports Research. Financial support is greatly appreciated from the Aarhus University Research Foundation (AUFF); the Hartmann Foundation; the A.P. Møller Foundation; the Toyota-Fonden, Denmark; and the Augustinus Foundation and Team Denmark. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.