Sex differences in astrocyte and microglia responses immediately following middle cerebral artery occlusion in adult mice

- Astrocyte Ca2+ dynamics are different in male and female mice after ischemia.
- Sex differences in astrocyte AQP4 polarity and non-somatic S100β after ischemia.
- Constitutive microglia CD11b is high in female sham cortex when compared to males.
- After ischemia, microglia CD11b immunoreactivity is not changed in female mice.
- Low baseline CD11b immunoreactivity is increased after ischemia in male mice.

Epidemiological studies report that infarct size is decreased and stroke outcomes are improved in young females when compared to males. However, mechanistic insight is lacking. We posit that sex-specific differences in glial cell functions occurring immediately after ischemic stroke are a source of dichotomous outcomes. In this study we assessed astrocyte Ca2+ dynamics, aquaporin 4 (AQP4) polarity, S100β expression pattern, as well as, microglia morphology and phagocytic marker CD11b in male and female mice following 60 min of middle cerebral artery (MCA) occlusion. We reveal sex differences in the frequency of intracellular astrocyte Ca2+ elevations (F(1,86) = 8.19, P = 0.005) and microglia volume (F(1,40) = 12.47, P = 0.009) immediately following MCA occlusion in acute brain slices. Measured in fixed tissue, AQP4 polarity was disrupted (F(5,86) = 3.30, P = 0.009) and the area of non-S100β immunoreactivity increased in ipsilateral brain regions after 60 min of MCA occlusion (F(5,86) = 4.72, P = 0.007). However, astrocyte changes were robust in male mice when compared to females. Additional sex differences were discovered regarding microglia phagocytic receptor CD11b. In sham mice, constitutively high CD11b immunofluorescence was observed in females when compared to males (P = 0.03). When compared to sham, only male mice exhibited an increase in CD11b immunoreactivity after MCA occlusion (P = 0.006). We posit that a sex difference in the presence of constitutive CD11b has a role in determining male and female microglia phagocytic responses to ischemia. Taken together, these findings are critical to understanding potential sex differences in glial physiology as well as stroke pathobiology which are foundational for the development of future sex-specific stroke therapies.