THU639 17α-Estradiol Signals Primarily Through Nongenomic Mechanisms: Implications For Its Beneficial Longevity Effects

Disclosure: P.S. Cooke: None. V.K. Sirohi: None. H.D. Zomer: None. J.B. Graceli: None. A. Mesa: None. T. Medrano: None. Recent work indicates that exogenous 17α-estradiol (17α-E2), a stereoisomer of 17β-E2, increases longevity 20% in male mice, despite previous literature that 17α-E2 is a weak estrogen with low affinity for nuclear (n)ESR1. This study aimed to obtain mechanistic insights into uterine 17α-E2 actions in vivo. We hypothesized that 17α-E2 signals preferentially through membrane (m)ESR1 to affect target tissues and promote longevity. To test this, we treated pre-pubertal (postnatal day 20) female CD-1 mice with 3 daily ip injections of vehicle or 10 mg/kg of 17α-E2 or 17β-E2. 17α-E2 treatment did not significantly increase uterine weight - a marker of nuclear (n)ESR1 signaling (20.3 ± 2.1 vs. vehicle 15.7 ± 2.0, p>0.05, n=4), while 17β-E2 strongly increased it to 41.4 + 1.1 mg; p<0.05). Accordingly, histological analysis revealed reduced cell proliferation in 17α-E2- vs. 17β-E2-treated uteri. Both 17α-E2 and 17β-E2 produced robust and similar epithelial p-ERK and p-AKT expression, the active phosphorylated forms of these protein kinases. Western blotting and immunofluorescence showed that 17α-E2 and 17β-E2 stimulated a strong and comparable stimulation of EZH2, a critical mediator of estrogen’s epigenetic effects linked to mESR1 signaling, as well as increases in NRF2 and CBP signaling. Progesterone pre-treatment blocks both the 17α-E2- and 17β-E2-mediated increases in p-ERK. In conclusion, despite limited actions through nESR1, 17α-E2 robustly signals through mESR1 to activate uterine protein kinase cascades and epigenetic effects. Thus, 17α-E2 acts preferentially through mESR1, which may explain its powerful longevity effects despite limited effects on classical markers of estrogen action such as uterine weight. Presentation: Thursday, June 15, 2023