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Sexually dimorphic outcomes and inflammatory responses in hypoxic-ischemic encephalopathy.

Mirza MA, Ritzel R, Xu Y, McCullough LD, Liu F - J Neuroinflammation (2015)

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Department of Neuroscience, University of Connecticut Health Center, 263 Farmington Avenue, Farmington, CT, 06030, USA. memirza@uchc.edu.

ABSTRACT

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.

No MeSH data available.


Related in: MedlinePlus

Microglial activation after HIE. (A) Gating strategy used to isolate peripheral myeloid cells, microglia, and lymphocytes. (B, C) Analysis of gated microglia at 1 day (B) and 3 days (C) of HIE: the upper right quadrant indicates MHC II+ microglia. (D, E) Quantification of MHC II+ microglia percentage of total microglia at 1 day (D) and 3 days (E) of HIE. *P < .05 vs. HIE counterpart; **P < .05 vs. HIE males.
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Fig3: Microglial activation after HIE. (A) Gating strategy used to isolate peripheral myeloid cells, microglia, and lymphocytes. (B, C) Analysis of gated microglia at 1 day (B) and 3 days (C) of HIE: the upper right quadrant indicates MHC II+ microglia. (D, E) Quantification of MHC II+ microglia percentage of total microglia at 1 day (D) and 3 days (E) of HIE. *P < .05 vs. HIE counterpart; **P < .05 vs. HIE males.

Mentions: We next examined microglial activation after HIE with flow cytometry as microglial activation is a key element in initiating and perpetuating inflammatory responses to ischemia [30,31]. MHC II is a well-established marker of microglial activation [32,33]. We quantified the percentage of MHC II+ microglia to total microglia using flow cytometry. The gating strategy is shown in Figure 3A (CD45lowCD11b+ for microglia). As shown in Figure 3B, D, no difference in the percentage of MHC II+/total microglia (upper right quadrant in each flow plot) was seen between sham and stroke or between males and females at 1 day of HIE. However, both males and females had higher percentage than their corresponding shams at 3 days; in addition, the percentage was significantly higher in males vs. females in HIE groups (Figure 3E).Figure 3


Sexually dimorphic outcomes and inflammatory responses in hypoxic-ischemic encephalopathy.

Mirza MA, Ritzel R, Xu Y, McCullough LD, Liu F - J Neuroinflammation (2015)

Microglial activation after HIE. (A) Gating strategy used to isolate peripheral myeloid cells, microglia, and lymphocytes. (B, C) Analysis of gated microglia at 1 day (B) and 3 days (C) of HIE: the upper right quadrant indicates MHC II+ microglia. (D, E) Quantification of MHC II+ microglia percentage of total microglia at 1 day (D) and 3 days (E) of HIE. *P < .05 vs. HIE counterpart; **P < .05 vs. HIE males.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4359482&req=5

Fig3: Microglial activation after HIE. (A) Gating strategy used to isolate peripheral myeloid cells, microglia, and lymphocytes. (B, C) Analysis of gated microglia at 1 day (B) and 3 days (C) of HIE: the upper right quadrant indicates MHC II+ microglia. (D, E) Quantification of MHC II+ microglia percentage of total microglia at 1 day (D) and 3 days (E) of HIE. *P < .05 vs. HIE counterpart; **P < .05 vs. HIE males.
Mentions: We next examined microglial activation after HIE with flow cytometry as microglial activation is a key element in initiating and perpetuating inflammatory responses to ischemia [30,31]. MHC II is a well-established marker of microglial activation [32,33]. We quantified the percentage of MHC II+ microglia to total microglia using flow cytometry. The gating strategy is shown in Figure 3A (CD45lowCD11b+ for microglia). As shown in Figure 3B, D, no difference in the percentage of MHC II+/total microglia (upper right quadrant in each flow plot) was seen between sham and stroke or between males and females at 1 day of HIE. However, both males and females had higher percentage than their corresponding shams at 3 days; in addition, the percentage was significantly higher in males vs. females in HIE groups (Figure 3E).Figure 3

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Department of Neuroscience, University of Connecticut Health Center, 263 Farmington Avenue, Farmington, CT, 06030, USA. memirza@uchc.edu.

ABSTRACT

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.

No MeSH data available.


Related in: MedlinePlus