Abstract Background Neonatal hypoxia–ischemia (HI) is the leading cause of childhood mortality and neurodevelopmental disability. Despite therapeutic hypothermia as the only clinically established treatment to date, outcomes remain poor for a significant proportion of affected infants. Mechanistic understanding has been brain-oriented in the past, however the gut and immune system are increasingly recognized as active modulators of brain injury, recovery and neurodevelopment. Main Body Gut microbiota regulate microglial maturation, myelination and blood–brain barrier integrity. Neonatal HI induces gut dysbiosis and barrier failure, associated with neuroinflammation. First, faecal microbiota transplantation experiments in animal models suggest a causal relationship. Clinical data corroborate microbial perturbations in HIE infants, though antibiotic exposure and the NICU environment represent potential confounders. At the level of the immune system, dysregulated peripheral innate and adaptive immune responses are well documented in HI-affected neonates, with some alterations persisting into school age. The microbiota dimension of these immune responses remains largely unexplored, despite well-characterized microbiota–immune interactions in models of adult stroke. Therapeutic candidates include probiotics, human milk oligosaccharides and butyrate, each with preliminary preclinical support but no completed clinical trials in HIE. Conclusion Reframing neonatal HI as a systemic gut–brain–immune disease opens up new possibilities for adjunctive therapy and biomarker discovery. Progress requires longitudinal multi-omic clinical cohorts, sex-stratified and disease-phase-resolved preclinical analyses and rigorous evaluation of microbiome-targeted interventions.

Preterm infants are at high risk of developing long-term brain injury such as encephalopathy of prematurity (EoP). Hyperoxia is a major contributor to EoP, affecting white and grey matter, with immature oligodendrocytes and hippocampal neurons being particularly vulnerable. While no causal therapy is available, mesenchymal stromal cells (MSCs) show therapeutic potential and are considered a promising candidate, although their effector mechanisms remain incompletely understood. Primary oligodendrocytes were isolated from mixed glial cultures of P0–P2 rats and hippocampal neurons from E16 rat embryos. On day 3 (oligodendrocytes) and day 5 (neurons) after isolation, cells were exposed to hyperoxia for 8 h and subsequently co-cultured indirectly with naive or hypoxic-preconditioned human MSCs (hMSCs) for 48 h under standard culture conditions. Degeneration, proliferation, differentiation and mitochondrial respiration were assessed in both cell types. Both naive and hypoxic-preconditioned hMSCs attenuated hyperoxia-induced degeneration, reduced proliferation and mitochondrial respiration failure. Although oligodendrocyte differentiation, assessed by myelin basic protein (MBP) expression, was modulated neither by hyperoxia nor by hMSC treatment, the dendritic structure in hippocampal neurons was impaired by hyperoxia and improved by hMSC treatment. Notably, hypoxic-preconditioned hMSCs showed a stronger therapeutic effect than naive hMSCs on hyperoxia-damaged hippocampal neurons. These findings indicate that indirect hMSC co-culture mitigates hyperoxia-induced impairment of immature oligodendrocytes and hippocampal neurons and that hypoxic preconditioning may modulate this effect in a cell type-specific manner.

Despite improved neonatal intensive care, the risk of premature-born infants developing bronchopulmonary dysplasia (BPD) and encephalopathy of prematurity (EoP) remains high. With hyperoxia being a major underlying factor, both preterm-birth-related complications are suggested to be closely interrelated. However, experimental models are lacking for the assessment of the potentially close interplay between both organs. To establish a model, suitable for the assessment of both affected organs, Wistar rats were exposed to 80% oxygen from postnatal day 2 (P2) for seven days. Brain and lung tissues were analysed via histomorphometry, immunohistochemistry, real-time PCR, and western blot at term P11. In the brain, hyperoxia induced significant hypomyelination accompanied by a reduction in oligodendrocytes and CD68 expression on microglia cells. These changes correlate with arrested alveolarisation and an increased number of macrophages in the lung. Interestingly, in contrast to the reduced formation of pulmonary microvessels, an increased vascular density was detected in the brain. Seven days of hyperoxia induces typical characteristics of BPD and EoP in neonatal rats, thereby linking impaired alveolarisation with disturbed myelination in the brain and providing an experimental model for understanding pathophysiological mechanisms and identifying organ-spanning novel therapeutic interventions targeting both diseases.

Preterm infants often require oxygen supplementation, resulting in high risk for bronchopulmonary dysplasia (BPD) and neurodevelopmental deficits. Despite a growing number of studies, there is still little knowledge about brain injury in BPD models. Therefore, we exposed neonatal C57BL/6 mice to 85% oxygen from birth to postnatal day (P) 14. At P28, two weeks after recovery under normoxic conditions, right hemisphere was used for the analysis of mRNA and the left hemisphere for protein expression of neuronal cells, neuroinflammatory and vascularisation markers, analysed by real-time PCR and Western blot, respectively. Hyperoxia led to an altered expression of markers associated with neuronal and oligodendrocyte maturation and neuroinflammation such as Dcx, Nestin, Il-1β, Il-6, NG2, and YM1/2. These changes were accompanied by an increased expression of genes involved in angiogenesis and vascular remodelling, e.g., Vegf-a, Nrp-1, and Icam-1. Together, 14 days of hyperoxia triggered a phenotypic response, resembling signs of encephalopathy of prematurity (EoP).

Premature born infants are at high risk to develop white matter injury (WMI). Hyperoxia and perinatal inflammation are main risk factors for preterm birth and associated brain injury. To date the majority of experimental studies have focused on isolated insults. However, clinically, WMI injury is a multifactorial disorder caused by a variety of triggers. To establish a clinically relevant rodent model of WMI, we combined prenatal inflammation with postnatal hyperoxia to investigate individual, and additive or synergistic effects on inflammatory processes, myelination and grey matter development. At embryonic day 20, pregnant Wistar rat dams received either a single intraperitoneal injection of 100 µg/ kg lipopolysaccharide (LPS) or sodium chloride. Offspring were either exposed to hyperoxia (80

Neonatal encephalopathy caused by hypoxia-ischemia (HI) leads to a strong neutrophil infiltration. The long-held assumption that neutrophils act exclusively as tissue-damaging cells, is challenged by increasing evidence of a profound neutrophil heterogeneity. Here, we uncovered a pronounced phenotypical and functional diversification of neutrophils in neonatal mice depending on the disease stage. Neutrophil infiltration was biphasic, peaking 1 and 7 days after HI. Early brain-infiltrating neutrophils displayed a hyperactivated phenotype, whereas neutrophils at day 7 exhibited an angiogenic phenotype with high Siglec-F expression. Acute neutrophil depletion protected against neural cell death, associated with decreased hyperactivity in adolescent animals. Delayed neutrophil depletion impaired vascular and oligodendrocyte regeneration, resulting in exacerbated alterations of anxiety-related behavior and myelination deficits. These findings suggest a divergent function of neutrophils, with early neutrophils aggravating tissue damage and late neutrophils contributing to neurological recovery. The disease stage-dependent neutrophil diversification offers new possibilities to identify disease-stage-specific therapeutic targets.

In the naturally hypoxic in utero fetal environment of preterm infants, oxygen and oxygen-sensitive signaling pathways play an important role in brain development, with hypoxia-inducible factor-1α (HIF1α) being an important regulator. Early exposure to nonphysiological high oxygen concentrations by birth in room can induce HIF1α degradation and may affect neuronal and glial development. This involves the dysregulation of astroglial maturation and function, which in turn might contribute to oxygen-induced brain injury. In this study, we investigated the effects of early high oxygen exposure on astroglial maturation and, specifically, on astroglial stromal cell-derived factor 1 (SDF1) expression in vivo and in vitro. In our neonatal mouse model of hyperoxia preterm birth brain injury in vivo, high oxygen exposure affected astroglial development and cortical SDF1 expression. These results were further supported by reduced Sdf1 expression, impaired proliferation, decreased total cell number, and altered expression of astroglial markers in astrocytes in primary cultures grown under high oxygen conditions. Moreover, to mimic the naturally hypoxic in utero fetal environment, astroglial Sdf1 expression was increased after low oxygen exposure in vitro, which appears to be regulated by HIF1α activity. Additionally, the knockdown of Hif1α revealed HIF1α-dependent Sdf1 expression in vitro. Our results indicate HIF1α and oxygen-dependent chemokine expression in primary astrocytes and highlight the importance of oxygen conditions for brain development.

Die neuronale Entwicklung kann durch Veränderung der physiologischen Sauerstoffkonzentration beeinträchtigt werden. Speziell unreif geborene Kinder zeigen häufig eine Störung der Gehirnentwicklung durch eine erhöhte Sauerstoffexposition. Dabei spielen sauerstoffsensitive Signalwege eine entscheidende Rolle. Eine wichtige Funktion hat hierbei der Hypoxie-induzierte Faktor 1α (HIF1α). Bei niedrigen Sauerstoffkonzentrationen kommt es zu einer Aktivierung von HIF1α, höhere Sauerstoffkonzentrationen führen zu einer Degradation von HIF1α.