Acute Estrogen Treatment Exacerbates Mitochondrial Membrane Potential Depolarization and Cerebrovascular Apoptosis to Oxidative Stress in Ovariectomized but not Ovary-Intact Mice

Stroke and traumatic brain injury increase reactive oxygen species (ROS) production leading to vascular apoptosis. Young females exhibit greater resilience to vascular injury compared to age-matched males. Yet the mechanisms underlying this protection remain undefined. We hypothesized that estrogen protects cerebral arteries from acute oxidative stress by preserving mitochondrial membrane potential (ΔΨm) and thus limiting apoptosis. Posterior cerebral arteries (PCA; ~80 µm diameter) from control (SHAM) and ovariectomized (OVX) female mice (3-6 months old) were isolated, cannulated, and pressurized to 90 cm H 2 O at 36°C. Smooth muscle cell (SMC) and endothelial cell (EC) death were quantified using Hoechst 33342 (1 µM; stains all nuclei) and propidium iodide (1 µM; stains dead nuclei) after 50 min exposure to H 2 O 2 (200 μM) in the presence and absence of supplemental estrogen (10 μM; 1-hour preincubation). SMC death was significantly higher in OVX vs. SHAM mice (16% vs. 7%; P < 0.05) while EC was unaffected (8% vs. 5%). Loss of ΔΨm is essential for initiating intrinsic apoptosis. Resting ΔΨm (JC-1, 5 μM) was unaltered by ovariectomy. We assessed changes in ΔΨm with TMRM (10 nM). Exposure to H 2 O 2 evoked greater depolarization of ΔΨm in pressurized PCAs from OVX compared to SHAM mice. Contrary to our hypothesis, estrogen treatment did not improve vascular resilience in OVX mice and unexpectedly increased depolarization of ΔΨm in addition to SMC and EC death. In contrast, acute estrogen treatment had no effect in vessels from SHAM mice. Treating PCAs with the protonophore FCCP (10 μM) led to greater depolarization of ΔΨm in OVX compared to SHAM vessels; estrogen treatment had no effect on responses to FCCP. We conclude that loss of ovarian hormones heightens susceptibility to ΔΨm depolarization and apoptosis, whereas estrogen treatment unexpectedly increases damage to oxidative stress in OVX mice. Although there is a protective effect of endogenous ovarian hormones, our findings highlight the potential for estrogen therapy to enhance vascular injury in postmenopausal women. SUPPORT: NIH R01NS134690 This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.