Transcriptome profiling of the newborn mouse brain after hypoxia–reoxygenation: hyperoxic reoxygenation induces inflammatory and energy failure responsive genes

Abstract

Background: Supplemental oxygen used during resuscitation can be detrimental to the newborn brain. The aim was to determine how different oxygen therapies affect gene transcription in a hypoxia-reoxygenation model. Methods: C57BL/6 mice (n = 56), postnatal day 7, were randomized either to 120 min of hypoxia 8% O 2 followed by 30 min of reoxygenation with 21, 40, 60, or 100% O 2 , or to normoxia followed by 30 min of 21 or 100% O 2 . Affymetrix 750k expression array was applied with RT-PCR used for validation. Histopathology and immunohistochemistry 3 d after hypoxiareoxygenation compared groups reoxygenated with 21 or 100% O 2 with normoxic controls (n = 22). results: In total, ~81% of the gene expression changes were altered in response to reoxygenation with 60 or 100% O 2 and constituted many inflammatory-responsive genes (i.e., C5ar2, Stat3, and Ccl12). Oxidative phosphorylation was downregulated after 60 or 100% O 2 . Iba1 + cells were significantly increased in the striatum and hippocampal CA1 after both 21 and 100% O 2 . conclusion: In the present model, hypoxia-reoxygenation induces microglial accumulation in subregions of the brain. The transcriptional changes dominating after applying hyperoxic reoxygenation regimes include upregulating genes related to inflammatory responses and suppressing the oxidative phosphorylation pathway.

Increased expression of inflammatory genes in the neonatal mouse brain after hyperoxic reoxygenation

“…Perez-Polo and coworkers found a stronger inflammatory response after hyperoxic reoxygenation following HI in rats (24,25). We also found increased protein concentration of CCL12, a proinflammatory chemokine, after hyperoxic reoxygenation, consistent with our recent reports of increased Ccl12 expression in the eye and brain of neonatal mice after hyperoxic reoxygenation (17,26). Mojsilovic-Petrovic et al (27) found increased expression of Ccl12 in astrocyte cultures from P7 mice after hypoxia alone.…”

“…In our transcriptome profiling study, we have recently shown that hyperoxic reoxygenation induced increased expression of inflammatory genes in the neonatal mice brain (17). Previously, we have reported a dose dependent increase in markers of …”

“…The striatum is one of the first regions to show damage on magnetic resonance imaging after mild to moderate asphyxia (19). In our transcriptome profiling study, there were many differentially expressed genes after reoxygenation with 60% O 2 (17). 100% O 2 is less clinically relevant after the International Liaison Committee on Resuscitation guidelines changed in 2010 (7); thus we decided on 60% O 2 as hyperoxia.…”

“…100% O 2 is less clinically relevant after the International Liaison Committee on Resuscitation guidelines changed in 2010 (7); thus we decided on 60% O 2 as hyperoxia. Forty-four target genes were selected ( Table 1) based on our transcriptome profiling studies (14,17), a pilot study and literature search. The objective of the present study was to compare the gene expression changes in the hippocampus and striatum of P7 mice after hypoxia followed by reoxygenation with 60% O 2 or air (21% O 2 ), and to make a temporal profile of the genes up to 3 d after the intervention.…”

“…Moderate and late preterm neonates have a higher risk of neonatal mortality and morbidity and also a higher risk of later sequelae than term neonates, and there has been a call for research into this large group of neonates (16). In a recent study from our group, we presented the transcriptome profile in the forebrain of P7 mice 2.5 h after hypoxia and reoxygenation (17). Hyperoxic reoxygenation gave increased expression of inflammatory genes and decreased expression of genes of the oxidative phosphorylation pathway.…”