Experimental Pediatric Arterial Ischemic Stroke Model Reveals Sex-specific Estrogen Signaling

Abstract

Background and Purpose Pediatric stroke, birth-18 years, is a significant cause of long-term disability in the United States, however there is currently little experimental data on the pathophysiology of childhood stroke due to lack of animal models. We developed a novel mouse model of experimental childhood-onset arterial ischemic stroke (AIS) in order to characterize the sex-specific response of the adolescent brain to cerebral ischemia and assess the neuroprotective effect of estrogen at this developmental stage. Methods Postnatal day 20–25 (P20-25) mice were subjected to 90 minutes experimental stroke via the intraluminal filament middle cerebral artery occlusion (MCAO) model and ischemic damage assessed 22 hr after reperfusion. Real-time quantitative RT-PCR (qPCR) was performed 22 hr after MCAO to determine the effects of ischemia and estrogen treatment on the pro-apoptotic gene Bax. Results Ischemic injury did not differ between male and female juvenile (P20-25) mice following MCAO. However, estrogen reduced ischemic injury in female mice, while having no effect in juvenile males. No differences in estrogen receptor expression was observed between P20 males and females. In contrast, estrogen minimized the ischemia-induced increase in the pro-apoptotic gene Bax in female mice, while having no effect on Bax induction in the male brain. Conclusions Focal ischemia has fundamentally different effects in the juvenile brain compared to the adult, as evidenced by the lack of gender difference in ischemic injury in the murine P20-25 MCAO model and the sexually dimorphic response to estrogen neuroprotection.

Androgens and stroke: Good, bad or indifferent?

“…Studies using neonatal animal models indicate that male neonates exhibit greater long-term deficits following injury than age matched females, including increased brain volume loss, enhanced dysmyelination and increased behavioral deficits following hypoxia and hypoxic-ischemic brain injury (Mayoral et al , 2009; Hill, Alexander, et al , 2011; Hill, Threlkeld, et al , 2011; Lan et al , 2011). Similar to the epidemiological data described above for 4–15 year old pre-pubertal children, a mouse model of pediatric stroke demonstrated equivalent injury in male and female pediatric mice following MCAO (Herson et al , 2013). These observations are consistent with a role for androgens in sensitizing the male brain to ischemic injury as neonates/infants, which is lost as androgen levels decline during early childhood.…”

The selective oestrogen receptor modulator, bazedoxifene, mimics the neuroprotective effect of 17β‐oestradiol in diabetic ischaemic stroke by modulating oestrogen receptor expression and the MAPK/ERK1/2 signalling pathway

“…In the same stroke model, decreased ERα expression has also been shown in the cortical peri‐infarct area of intact female rats, with no changes in ERβ or GPER expression . By contrast, ischaemia‐reperfusion has been reported to increase the expression of ERα and ERβ in male and female juvenile mice,, as well as in ovariectomised rats. Regarding GPER, increased distribution and expression in the peri‐infarct region of male but not in female mice has been reported .…”

Sex Steroids Do Not Modulate TRPM2-Mediated Injury in Females following Middle Cerebral Artery Occlusion

“…There is increasing evidence that genetic sex (XX vs XY) shapes cell death mechanisms and contributes to oxidative stress pathways being the dominant cell death pathway in males and caspase-dependent pathways being dominant in females ( Lang and McCullough, 2008 ; Liu et al, 2009 ; Yuan et al, 2009 ). Indeed, we have observed sex differences in estrogen neuroprotection in prepubertal juvenile mice subjected to MCAO, suggesting that sex differences in ischemic injury may already be established at this stage of development ( Herson et al, 2013 ). Therefore, it is likely that ischemic outcome and cell death mechanisms are influenced by the complex interaction of innate sex and hormonal influences.…”