Abstract TP316: Treatment With Tamoxifen, a Selective Estrogen Receptor Modulator, Has a Cell Type-Specific Effect on Mitochondrial Stress From Oxygen Glucose Deprivation in Astrocytes and Microglia

Introduction: Tamoxifen (TAM), a selective estrogen receptor modulator, is a first-line treatment to prevent recurrence of hormone receptor positive breast cancer. Stroke risk is increased in women with low estrogen and doubles in women after the age of 55 (average age of menopause). Critically, women taking TAM as breast cancer therapy had increased risk of ischemic stroke (82%). We hypothesize treatment with TAM will increase stroke severity, which is associated with increased blood brain barrier (BBB) damage and worsened neuroinflammation. We investigated effects of TAM on mitochondrial stress and cellular function in astrocytes and microglia, key cells of the BBB and neuroimmune response, respectively.

Methods: Cultured female human astrocytes and HMC3 microglia were treated with TAM (1uM), 17ß-estradiol (10nM, E2), or vehicle (DMSO) for 24 hours. Cells were separated into two groups: normoxic (21% O ₂ , 25mM glucose) or oxygen and glucose deprivation (OGD) conditions 6 hours before analysis. Mitochondrial function was assessed using a Seahorse XFe96 Analyzer. Microglial expression of mitochondrial proteins (Complex I & III and DRP1) was analyzed with western blot, and function was assessed with flow cytometry after in vitro phagocytosis of pHrodo red zymosan.

Results: TAM reduced maximal (p =0.0174) and basal respiration (p =0.0149) under OGD conditions in microglia compared with DMSO or E2 treatment. However, in astrocytes, maximal and basal respiration were increased in OGD (p =0.0003, p =0.0002). There was no significant difference in expression of mitochondrial proteins or phagocytic function in HMC3 microglia under either normoxic or OGD conditions after TAM treatment.

Conclusions: TAM treatment resulted in a cell type-specific alteration in mitochondrial stress response. Since mitochondrial stress is a hallmark of stroke pathophysiology, and microglia and astrocytes are among the earliest cells to respond to ischemia, treatment with tamoxifen might alter the cellular environment, by its divergent actions on these two cell types, leading to worsened stroke outcomes. These data support the need for in vivo investigation to elucidate the mechanism by which TAM is altering cellular response. Support: RFAG042189 to FS, 1F30NS131053 to MEZ