Inflammatory Responses are Sex Specific in Chronic Hypoxic–Ischemic Encephalopathy

Abstract

Neonatal hypoxic–ischemic encephalopathy (HIE) is increasingly recognized as a sexually dimorphic disease. Male infants are not only more vulnerable to ischemic insult; they also suffer more long-term cognitive deficits compared with females with comparable brain damage. The innate immune response plays a fundamental role in mediating acute neonatal HIE injury. However, the mechanism underlying the sex difference in chronic HIE is still elusive. The present study investigated the sex difference in HIE outcomes and inflammatory response in the chronic stage (30 days after HIE). Postnatal day 10 (P10) male and female C57BL/6 pups were subjected to 60-min Rice–Vanucci model (RVM) to induce HIE. Brain atrophy and behavioral deficits were analyzed to measure stroke outcomes at 30 days of HIE. Flow cytometry (FC) was performed to examine central (microglial activation) and peripheral immune responses. Serum levels of cytokines and sex hormones were determined by enzyme-linked immunosorbent assay (ELISA). Neurogenesis was quantified by 5-Bromo-2′-deoxyuridine (BrdU) incorporation with neurons. Results showed males had worse HIE outcomes than females at the endpoint. Female microglia exhibited a more robust anti-inflammatory response that was corresponding to an enhanced expression of CX3C chemokine receptor 1 (CX3CR1) than males. More infiltration of peripheral lymphocytes was seen in male vs. female HIE brains. Cytokine levels of tumor necrosis factor (TNF)-α and interleukin (IL)-10 were more upregulated in males and females respectively than their counterparts. Neurogenesis was more highly induced in females vs. males. No significant difference in circulating hormonal level was found between males and females after HIE. We conclude that a sex dichotomy in pro- and anti-inflammatory response underlies the sex-specific chronic HIE outcomes, and an enhanced neurogenesis in females also contribute to the sex difference.

Adverse neuropsychiatric development following perinatal brain injury: from a preclinical perspective

“…Major target mechanisms of sex hormones are supposed to be regulation of neurotransmitter dysfunction and synaptic plasticity 144,145 . Nevertheless, preclinical reports demonstrating no sex differences in hormone levels but differences in outcome regarding early and late inflammatory responses and histological outcomes after neonatal HI 137,146 imply that additional intrinsic mechanisms may play a role in divergent susceptibility to the development of neurological deficits. This was demonstrated in in vitro cultures of isolated cells or brain slices revealing differences in cell death pathways and differentiation of specific hippocampal neuron subpopulations independent of the presence of hormones 147,148 .…”

“…In addition to perinatal immune challenges, neonatal HI induces long-lasting immune responses, which differ between genders. For instance, in adolescent male mice circulating levels of tumour necrosis factor (TNF)alpha were increased and males revealed more lymphocyte infiltration in injured brain hemispheres accompanied by reduced neurogenesis 137 . Regarding HI-induced atrophy and neurobehavioural deficits, gender differences were observed after neonatal HI in P9 mice with reduced brain atrophy in females while deficits in OF behaviour were increased, likely representing injury not detectable by volume measurements alone 138 .…”

Potential microglia‐based interventions for stroke

“…Moreover, a large body of evidence has indicated that the stroke‐induced activation of inflammation is sexually dimorphic. After cerebral ischemia, microglia in female mice exhibit a more robust anti‐inflammatory response than those in males, and male mice exhibit an increase in CD11b immunoreactivity after MCAO . Clinically, patients with ischemic stroke present sex‐related differences in 3‐month outcomes and mortality, and sex‐related differences in prehospital data, molecular markers, and clinical variables have been documented .…”

“…After cerebral ischemia, microglia in female mice exhibit a more robust anti-inflammatory response than those in males, and male mice exhibit an increase in CD11b immunoreactivity after MCAO. [41][42][43] Clinically, patients with ischemic stroke present sex-related differences in 3-month outcomes and mortality, and sex-related differences in prehospital data, molecular markers, and clinical variables have been documented. 44 Further research has demonstrated a marked deregulation of microglial activation in ovariectomized and/or ERα knockout mice and increased vulnerability to ischemic injury, indicating that microglial heterogeneity poststroke is sex hormone-dependent.…”

Grape Seed Proanthocyanidin Extract Adjusts NeuN/GFAP in a Murine Model of Neonatal Hypoxic-ischemic Brain Injury

“…All procedures were approved by the Ethics Committee of Guangdong Pharmaceutical University and the guidelines of the Council on Animal Care were strictly followed. We established the HIE model by using the modified Rice-Vannucci method, which is widely accepted [13]. Briefly, 7-day-old pups were anesthetized with isoflurane and the common carotid artery (CCA) on the left side was ligated.…”