Sexually dimorphic outcomes and inflammatory responses in hypoxic-ischemic encephalopathy
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Updated: Apr 14, 2026
Sex Differences in Mouse Hippocampal Astrocytes after In-Vitro Ischemia
Published on: October 25, 2016
Mehwish A Mirza1, Rodney Ritzel2, Yan Xu3
1Department of Neuroscience, University of Connecticut Health Center, 263 Farmington Avenue, Farmington, CT, 06030, USA. memirza@uchc.edu.
Insights
Neonatal hypoxic-ischemic encephalopathy (HIE) causes sex-specific brain injury. While initial injury is similar, males show worse outcomes due to greater microglial activation and inflammation.
Area of Science:
- Neuroscience
- Immunology
- Developmental Biology
Background:
- Neonatal hypoxic-ischemic encephalopathy (HIE) is a leading cause of pediatric motor and cognitive impairments.
- Male infants exhibit greater vulnerability and long-term deficits following ischemic insults compared to females, but the underlying mechanisms are unclear.
- Microglial activation and inflammation are key in HIE pathophysiology, with existing evidence suggesting basal sex differences in neonatal microglia.
Purpose of the Study:
- To investigate sex differences in brain injury and inflammation following HIE.
- To determine if microglial activation and inflammatory responses contribute to sexual dimorphism in HIE outcomes.
Main Methods:
- Male and female C57BL6 mice at postnatal day 10 were subjected to Rice-Vanucci modeling for 60 minutes to induce HIE.
- Stroke outcomes, including infarct volume, seizure scores, and behavioral deficits, were assessed at 1, 3, 7, and 30 days post-injury.
- Microglial activation and inflammatory cytokine levels were analyzed using flow cytometry and cytokine assays.
Main Results:
- No acute sex differences in infarct volume or seizure scores were observed at day 1 post-HIE.
- Female neonates showed significantly smaller infarcts, fewer seizures, reduced brain tissue loss, and fewer behavioral deficits at later time points (days 3-30) compared to males.
- Males exhibited heightened microglial activation and a more pronounced inflammatory response at day 3 post-HIE.
Conclusions:
- HIE induces equivalent primary brain injury in male and female neonates acutely, but leads to sexually dimorphic outcomes later.
- The innate immune response, specifically microglial activation and inflammation, plays a critical role in the development of sex differences in HIE outcomes.
- These findings highlight the importance of considering sex as a biological variable in HIE research and therapeutic strategies.
Background:
Neonatal hypoxic-ischemic encephalopathy (HIE) is an important cause of motor and cognitive impairment in children. Clinically, male infants are more vulnerable to ischemic insults and suffer more long-term deficits than females; however, the mechanisms underlying this sex difference remain elusive. Inflammatory processes initiated by microglial activation are fundamental in the pathophysiology of ischemia. Recent studies report a sexual dimorphism in microglia numbers and expression of activation markers in the neonatal brain under normal conditions. How these basal sex differences in microglia affect HIE remains largely unexplored. This study investigated sex differences in ischemic outcomes and inflammation triggered by HIE. We hypothesize that ischemia induces sex-specific brain injury in male and female neonates and that microglial activation and inflammatory responses play an important role in this sexual dimorphism.
Methods:
Male and female C57BL6 mice were subjected to 60-min Rice-Vanucci modeling (RVM) at post-natal day 10 (P10) to induce HIE. Stroke outcomes were measured 1, 3, 7, and 30 days after stroke. Microglial activation and inflammatory responses were evaluated by flow cytometry and cytokine analysis.
Results:
On day 1 of HIE, no difference in infarct volumes or seizure scores was seen between male and female neonates. However, female neonates exhibited significantly smaller infarct size and fewer seizures compared to males 3 days after HIE. Females also had less brain tissue loss and behavioral deficits compared to males at the chronic stage of HIE. Male animals demonstrated increased microglial activation and up-regulated inflammatory response compared to females at day 3.
Conclusions:
HIE leads to an equivalent primary brain injury in male and female neonates at the acute stage that develops into sexually dimorphic outcomes at later time points. An innate immune response secondary to the primary injury may contribute to sexual dimorphism in HIE.
