Caspase-1-processed interleukins in hyperoxia-induced cell death in the developing brain

Mechanistic advances of hyperoxia-induced immature brain injury

The impact of hyperoxia-induced brain injury in preterm infants is being increasingly investigated. However, the parameters and protocols used to study this condition in animal models lack consistency. Research is further hampered by the fact that hyperoxia exerts both direct and indirect effects on oligodendrocytes and neurons, with the precise underlying mechanisms remaining unclear. In this article, we aim to provide a comprehensive overview of the conditions used to induce hyperoxia in animal models of immature brain injury. We discuss what is known regarding the mechanisms underlying hyperoxia-induced immature brain injury, focusing on the effects on oligodendrocytes and neurons, and briefly describe therapies that may counteract the effects of hyperoxia. We also identify further studies required to fully elucidate the effects of hyperoxia on the immature brain as well as discuss the leading therapeutic options.

A review of the effects of early postnatal hyperoxia exposure on the immature brain

Preterm birth is a public health priority worldwide, with approximately 15 million premature babies born each year. Oxygen supplementation is one of the most common interventions for preterm infants. However, prolonged oxygen inhalation at supraphysiological concentrations can lead to the development of bronchopulmonary dysplasia (BPD). In addition to lifelong pulmonary sequelae, clinical evidence suggests that BPD is associated with adverse neurodevelopmental outcomes, such as motor impairment, cognitive impairment, and behavioral deficits, severely affecting the quality of life of preterm infants. However, the mechanisms underlying the combination of neurodevelopmental impairment with BPD remain unclear. Therefore, in recent years, attention has also been focused on the effects of hyperoxia on brain development in preterm infants. In this review, we outline the pathophysiological mechanisms of brain injury caused by developmental hyperoxia exposure in current animal models and briefly describe the pharmacological therapies that may be applicable to the associated brain injury. Overall, more studies are needed to assess the effects of hyperoxia on the immature brain, particularly combined analyses of the lungs and brain in the same experimental setting, to elucidate the potential causes of combined neurodevelopmental impairment in BPD.

GSDMD gene knockout alleviates hyperoxia-induced hippocampal brain injury in neonatal mice

BACKGROUND

Neonatal hyperoxia exposure is associated with brain injury and poor neurodevelopment outcomes in preterm infants. Our previous studies in neonatal rodent models have shown that hyperoxia stimulates the brain's inflammasome pathway, leading to the activation of gasdermin D (GSDMD), a key executor of pyroptotic inflammatory cell death. Moreover, we found pharmacological inhibition of caspase-1, which blocks GSDMD activation, attenuates hyperoxia-induced brain injury in neonatal mice. We hypothesized that GSDMD plays a pathogenic role in hyperoxia-induced neonatal brain injury and that GSDMD gene knockout (KO) will alleviate hyperoxia-induced brain injury.

METHODS

Newborn GSDMD knockout mice and their wildtype (WT) littermates were randomized within 24 h after birth to be exposed to room air or hyperoxia (85% O2) from postnatal days 1 to 14. Hippocampal brain inflammatory injury was assessed in brain sections by immunohistology for allograft inflammatory factor 1 (AIF1) and CD68, markers of microglial activation. Cell proliferation was evaluated by Ki-67 staining, and cell death was determined by TUNEL assay. RNA sequencing of the hippocampus was performed to identify the transcriptional effects of hyperoxia and GSDMD-KO, and qRT-PCR was performed to confirm some of the significantly regulated genes.

RESULTS

Hyperoxia-exposed WT mice had increased microglia consistent with activation, which was associated with decreased cell proliferation and increased cell death in the hippocampal area. Conversely, hyperoxia-exposed GSDMD-KO mice exhibited considerable resistance to hyperoxia as O2 exposure did not increase AIF1 + , CD68 + , or TUNEL + cell numbers or decrease cell proliferation. Hyperoxia exposure differentially regulated 258 genes in WT and only 16 in GSDMD-KO mice compared to room air-exposed WT and GSDMD-KO, respectively. Gene set enrichment analysis showed that in the WT brain, hyperoxia differentially regulated genes associated with neuronal and vascular development and differentiation, axonogenesis, glial cell differentiation, hypoxia-induced factor 1 pathway, and neuronal growth factor pathways. These changes were prevented by GSDMD-KO.

CONCLUSIONS

GSDMD-KO alleviates hyperoxia-induced inflammatory injury, cell survival and death, and alterations of transcriptional gene expression of pathways involved in neuronal growth, development, and differentiation in the hippocampus of neonatal mice. This suggests that GSDMD plays a pathogenic role in preterm brain injury, and targeting GSDMD may be beneficial in preventing and treating brain injury and poor neurodevelopmental outcomes in preterm infants.

Prevention of Chronic Morbidities in Extremely Premature Newborns with LISA-nCPAP Respiratory Therapy and Adjuvant Perinatal Strategies

Less invasive surfactant administration techniques, together with nasal continuous airway pressure (LISA-nCPAP) ventilation, an emerging noninvasive ventilation (NIV) technique in neonatology, are gaining more significance, even in extremely premature newborns (ELBW), under 27 weeks of gestational age. In this review, studies on LISA-nCPAP are compiled with an emphasis on short- and long-term morbidities associated with prematurity. Several perinatal preventative and therapeutic investigations are also discussed in order to start integrated therapies as numerous organ-saving techniques in addition to lung-protective ventilations. Two thirds of immature newborns can start their lives on NIV, and one third of them never need mechanical ventilation. With adjuvant intervention, these ratios are expected to be increased, resulting in better outcomes. Optimized cardiopulmonary transition, especially physiologic cord clamping, could have an additively beneficial effect on patient outcomes gained from NIV. Organ development and angiogenesis are strictly linked not only in the immature lung and retina, but also possibly in the kidney, and optimized interventions using angiogenic growth factors could lead to better morbidity-free survival. Corticosteroids, caffeine, insulin, thyroid hormones, antioxidants, N-acetylcysteine, and, moreover, the immunomodulatory components of mother's milk are also discussed as adjuvant treatments, since immature newborns deserve more complex neonatal interventions.

Protective Effect of Dexmedetomidine against Hyperoxia-Damaged Cerebellar Neurodevelopment in the Juvenile Rat

Impaired cerebellar development of premature infants and the associated impairment of cerebellar functions in cognitive development could be crucial factors for neurodevelopmental disorders. Anesthetic- and hyperoxia-induced neurotoxicity of the immature brain can lead to learning and behavioral disorders. Dexmedetomidine (DEX), which is associated with neuroprotective properties, is increasingly being studied for off-label use in the NICU. For this purpose, six-day-old Wistar rats (P6) were exposed to hyperoxia (80% O₂) or normoxia (21% O₂) for 24 h after DEX (5 µg/kg, i.p.) or vehicle (0.9% NaCl) application. An initial detection in the immature rat cerebellum was performed after the termination of hyperoxia at P7 and then after recovery in room air at P9, P11, and P14. Hyperoxia reduced the proportion of Calb1+-Purkinje cells and affected the dendrite length at P7 and/or P9/P11. Proliferating Pax6+-granule progenitors remained reduced after hyperoxia and until P14. The expression of neurotrophins and neuronal transcription factors/markers of proliferation, migration, and survival were also reduced by oxidative stress in different manners. DEX demonstrated protective effects on hyperoxia-injured Purkinje cells, and DEX without hyperoxia modulated neuronal transcription in the short term without any effects at the cellular level. DEX protects hyperoxia-damaged Purkinje cells and appears to differentially affect cerebellar granular cell neurogenesis following oxidative stress.

Pseudorabies Virus Infection Activates the TLR-NF-κB Axis and AIM2 Inflammasome To Enhance Inflammatory Responses in Mice

Pseudorabies virus (PRV) infection activates inflammatory responses to release robust proinflammatory cytokines, which are critical for controlling viral infection and clearance of PRV. However, the innate sensors and inflammasomes involved in the production and secretion of proinflammatory cytokines during PRV infection remain poorly studied. In this study, we report that the transcription and expression levels of some proinflammatory cytokines, including interleukin 1β (IL-1β), IL-6, and tumor necrosis factor alpha (TNF-α), are upregulated in primary peritoneal macrophages and in mice during PRV infection. Mechanistically, Toll-like receptor 2 (TLR2), TLR3, TLR4, and TLR5 were induced by the PRV infection to enhance the transcription levels of pro-IL-1β, pro-IL-18, and gasdermin D (GSDMD). Additionally, we found that PRV infection and transfection of its genomic DNA triggered AIM2 inflammasome activation, apoptosis-related speckle-like protein (ASC) oligomerization, and caspase-1 activation to enhance the secretion of IL-1β and IL-18, which was mainly dependent on GSDMD, but not GSDME, in vitro and in vivo. Taken together, our findings reveal that the activation of the TLR2-TLR3-TRL4-TLR5-NF-κB axis and AIM2 inflammasome, as well as GSDMD, is required for proinflammatory cytokine release, which resists the PRV replication and plays a critical role in host defense against PRV infection. Our findings provide novel clues to prevent and control PRV infection. IMPORTANCE PRV can infect several mammals, including pigs, other livestock, rodents, and wild animals, causing huge economic losses. As an emerging and reemerging infectious disease, the emergence of PRV virulent isolates and increasing human PRV infection cases indicate that PRV is still a high risk to public health. It has been reported that PRV infection leads to robust release of proinflammatory cytokines through activating inflammatory responses. However, the innate sensor that activates IL-1β expression and the inflammasome involved in the maturation and secretion of proinflammatory cytokines during PRV infection remain poorly studied. In this study, our findings reveal that, in mice, activation of the TLR2-TLR3-TRL4-TLR5-NF-κB axis and AIM2 inflammasome, as well as GSDMD, is required for proinflammatory cytokine release during PRV infection, and it resists PRV replication and plays a critical role in host defense against PRV infection. Our findings provide novel clues to prevent and control PRV infection.

IL-18BP Alleviates Anxiety-Like Behavior Induced by Traumatic Stress via Inhibition of the IL-18R-NLRP3 Signaling Pathway in a Mouse Model of Hemorrhagic Shock and Resuscitation

Psychological distress and posttraumatic stress, including anxiety, severely influence life quality. Previously, we reported that interleukin-18 (IL-18) was involved in pyroptosis-induced emotional changes in a rodent model of hemorrhagic shock and resuscitation (HSR). Here, we aimed to continue our investigation on the role of IL-18 binding protein (IL-18BP), which exhibits excellent anti-inflammatory effects as an IL-18 negative regulator. Mice were administered with an intraperitoneal injection of IL-18BP after HSR exposure and anxiety-like behavior was examined using the open-field test and elevated plus maze test. Moreover, the following variables post-HSR were measured: (1) the activation of astrocytes; (2) pyroptosis-associated factors including cleaved caspase-1, GSDMD, IL-18; (3) the roles of IL-18 receptor (IL-18R)-NOD-like receptor pyrin domain-containing-3 (NLRP3) signal with the application of the NLRP3 specific agonist or astrocyte-specific NLRP3 knockout mice. IL-18BP administration remarkably alleviated HSR-induced anxiety-like behavior, astrocytic activation, and increases in pyroptosis-associated factors, while NLRP3 agonist nigericin partially reversed IL-18BP-induced neuroprotective effects. Astrocyte-specific NLRP3 knockout mice exhibited relatively less anxiety-like behavior. Similarly, IL-18BP exhibited an anti-pyroptosis effect in astrocytes in an in vitro model of low oxygen-glucose deprivation. These findings offer unique perspectives on HSR-induced posttraumatic stress and indicate that inhibition of IL-18R-NLRP3 signal via IL-18BP can attenuate astrocytic activation and pyroptosis, broadening the therapeutic landscape for patients with psychological distress and posttraumatic stress.

Role of sirtuin1 in impairments of emotion-related behaviors in mice with chronic mild unpredictable stress during adolescence

Long-term exposure to physical and/or psychosocial stress during early life and/or adolescence increases the risk of psychiatric disorders such as major depressive disorder and anxiety disorders. However, the molecular mechanisms underlying early stress-induced brain dysfunction are poorly understood. In the present study, mice at 4 weeks old were subjected to chronic mild unpredictable stress (CMUS) for 4 weeks, and subsequently to assays of emotion-related behaviors. Thereafter, they were sacrificed and their brains were collected for real-time quantitative polymerase chain reaction (RT-qPCR). Mice with CMUS during adolescence showed despair behavior, anxiety-like behavior, social behavior deficits, and anhedonia in forced-swim, marble-burying, social interaction, and sucrose preference tests, respectively. Additionally, RT-qPCR revealed that the expression levels of sirtuin1 (SIRT1), a NAD⁺-dependent deacetylase that mediates stress responses, were down-regulated in the prefrontal cortex and hippocampus of mice with CMUS compared with control mice. Next, to investigate the pathophysiological role of decreased Sirt1 expression levels in stress-induced behavioral deficits, we assessed the effects of resveratrol, a pharmacological activator of SIRT1, in mice exposed to CMUS. Chronic treatment with resveratrol prevented -induced social behavior deficits and depression-like behaviors. These results suggest that CMUS during adolescence decreases Sirt1 expression in the brain, leading to deficits in emotional behavior. Accordingly, SIRT1 activators, such as resveratrol, may be preventive agents against abnormalities in emotional behavior following stress during an immature period.

Oxygen toxicity: cellular mechanisms in normobaric hyperoxia

In clinical settings, oxygen therapy is administered to preterm neonates and to adults with acute and chronic conditions such as COVID-19, pulmonary fibrosis, sepsis, cardiac arrest, carbon monoxide poisoning, and acute heart failure. In non-clinical settings, divers and astronauts may also receive supplemental oxygen. In addition, under current standard cell culture practices, cells are maintained in atmospheric oxygen, which is several times higher than what most cells experience in vivo. In all the above scenarios, the elevated oxygen levels (hyperoxia) can lead to increased production of reactive oxygen species from mitochondria, NADPH oxidases, and other sources. This can cause cell dysfunction or death. Acute hyperoxia injury impairs various cellular functions, manifesting ultimately as physiological deficits. Chronic hyperoxia, particularly in the neonate, can disrupt development, leading to permanent deficiencies. In this review, we discuss the cellular activities and pathways affected by hyperoxia, as well as strategies that have been developed to ameliorate injury.

NLRP1 Inflammasomes: A Potential Target for the Treatment of Several Types of Brain Injury

NOD-like receptor (NLR) family pyrin domain-containing 1 (NLRP1) is a member of the NLR family. The NLRP1 inflammasome consists of the NLRP1 protein, the adaptor protein apoptosis-associated speck-like protein containing a CARD domain, and the effector molecule pro-caspase-1. When stimulated, the inflammasome initiates the cleavage of pro-caspase-1 and converts it into its active form, caspase-1; then, caspase-1 facilitates the cleavage of the proinflammatory cytokines interleukin-1β and interleukin-18 into their active and secreted forms. In addition, caspase-1 also mediates the cleavage of gasdermin D, which leads to pyroptosis, an inflammatory form of cell death. Pathological events that damage the brain and result in neuropathological conditions can generally be described as brain injury. Neuroinflammation, especially that driven by NLRP1, plays a considerable role in the pathophysiology of brain injury, such as early brain injury (EBI) of subarachnoid hemorrhage, ischemic brain injury during stroke, and traumatic brain injury (TBI). In this article, a thorough overview of NLRP1 is presented, including its structure, mechanism of activation, and role in neuroinflammation. We also present recent studies on NLRP1 as a target for the treatment of EBI, ischemic brain injury, TBI, and other types of brain injury, thus highlighting the perspective of NLRP1 as an effective mediator of catastrophic brain injury.

Perinatal Hyperoxia and Developmental Consequences on the Lung-Brain Axis

Approximately 11.1% of all newborns worldwide are born preterm. Improved neonatal intensive care significantly increased survival rates over the last decades but failed to reduce the risk for the development of chronic lung disease (i.e., bronchopulmonary dysplasia (BPD)) and impaired neurodevelopment (i.e., encephalopathy of prematurity (EoP)), two major long-term sequelae of prematurity. Premature infants are exposed to relative hyperoxia, when compared to physiological in-utero conditions and, if needed to additional therapeutic oxygen supplementation. Both are associated with an increased risk for impaired organ development. Since the detrimental effects of hyperoxia on the immature retina are known for many years, lung and brain have come into focus in the last decade. Hyperoxia-induced excessive production of reactive oxygen species leading to oxidative stress and inflammation contribute to pulmonary growth restriction and abnormal neurodevelopment, including myelination deficits. Despite a large body of studies, which unraveled important pathophysiological mechanisms for both organs at risk, the majority focused exclusively either on lung or on brain injury. However, considering that preterm infants suffering from BPD are at higher risk for poor neurodevelopmental outcome, an interaction between both organs seems plausible. This review summarizes recent findings regarding mechanisms of hyperoxia-induced neonatal lung and brain injury. We will discuss common pathophysiological pathways, which potentially link both injured organ systems. Furthermore, promises and needs of currently suggested therapies, including pharmacological and regenerative cell-based treatments for BPD and EoP, will be emphasized. Limited therapeutic approaches highlight the urgent need for a better understanding of the mechanisms underlying detrimental effects of hyperoxia on the lung-brain axis in order to pave the way for the development of novel multimodal therapies, ideally targeting both severe preterm birth-associated complications.

Intrauterine growth restriction followed by oxygen support uniquely interferes with genetic regulators of myelination

Intrauterine growth restriction (IUGR) and oxygen exposure in isolation and combination adversely affect the developing brain, putting infants at risk for neurodevelopmental disability including cerebral palsy. Rodent models of IUGR and postnatal hyperoxia have demonstrated oligodendroglial injury with subsequent white matter injury (WMI) and motor dysfunction. Here we investigate transcriptomic dysregulation in IUGR with and without hyperoxia exposure to account for the abnormal brain structure and function previously documented. We performed RNA sequencing and analysis using a mouse model of IUGR and found that IUGR, hyperoxia, and the combination of IUGR with hyperoxia (IUGR/hyperoxia) produced distinct changes in gene expression. IUGR in isolation demonstrated the fewest differentially expressed genes compared to control. In contrast, we detected several gene alterations in IUGR/hyperoxia; genes involved in myelination were strikingly downregulated. We also identified changes to specific regulators including TCF7L2, BDNF, SOX2, and DGCR8, through Ingenuity Pathway Analysis, that may contribute to impaired myelination in IUGR/hyperoxia. Our findings show that IUGR with hyperoxia induces unique transcriptional changes in the developing brain. These indicate mechanisms for increased risk for WMI in IUGR infants exposed to oxygen and suggest potential therapeutic targets to improve motor outcomes.Significance StatementThis study demonstrates that perinatal exposures of IUGR and/or postnatal hyperoxia result in distinct transcriptomic changes in the developing brain. In particular, we found that genes involved in normal developmental myelination, myelin maintenance, and remyelination were most dysregulated when IUGR was combined with hyperoxia. Understanding how multiple risk factors lead to WMI is the first step in developing future therapeutic interventions. Additionally, because oxygen exposure is often unavoidable after birth, an understanding of gene perturbations in this setting will increase our awareness of the need for tight control of oxygen use to minimize future motor disability.

Mesenchymal Stromal Cell-Derived Extracellular Vesicles Reduce Neuroinflammation, Promote Neural Cell Proliferation and Improve Oligodendrocyte Maturation in Neonatal Hypoxic-Ischemic Brain Injury

Background: Neonatal encephalopathy caused by hypoxia-ischemia (HI) is a major cause of childhood mortality and disability. Stem cell-based regenerative therapies seem promising to prevent long-term neurological deficits. Our previous work in neonatal HI revealed an unexpected interaction between mesenchymal stem/stromal cells (MSCs) and the brains' microenvironment leading to an altered therapeutic efficiency. MSCs are supposed to mediate most of their therapeutic effects in a paracrine mode via extracellular vesicles (EVs), which might be an alternative to cell therapy. In the present study, we investigated the impact of MSC-EVs on neonatal HI-induced brain injury.

Methods: Nine-day-old C57BL/6 mice were exposed to HI through ligation of the right common carotid artery followed by 1 h hypoxia (10% oxygen). MSC-EVs were injected intraperitoneally 1, 3, and 5 days after HI. One week after HI, brain injury was evaluated by regional neuropathological scoring, atrophy measurements and immunohistochemistry to assess effects on neuronal, oligodendrocyte and vessel densities, proliferation, oligodendrocyte maturation, myelination, astro-, and microglia activation. Immunohistochemistry analyses were complemented by mRNA expression analyses for a broad set of M1/M2- and A1/A2-associated molecules and neural growth factors.

Results: While total neuropathological scores and tissue atrophy were not changed, MSC-EVs significantly protected from HI-induced striatal tissue loss and decreased micro- and astroglia activation. MSC-EVs lead to a significant downregulation of the pro-inflammatory cytokine TNFa, accompanied by a significant upregulation of the M2 marker YM-1 and the anti-inflammatory cytokine TGFb. MSC-EVs significantly decreased astrocytic expression of the A1 marker C3, concomitant with an increased expression of neural growth factors (i.e., BDNF, VEGF, and EGF). These alterations were associated with an increased neuronal and vessel density, coinciding with a significant increase of proliferating cells in the neurogenic sub-ventricular zone juxtaposed to the striatum. MSC-EV-mediated neuroprotection went along with a significant improvement of oligodendrocyte maturation and myelination.

Conclusion: The present study demonstrates that MSC-EVs mediate anti-inflammatory effects, promote regenerative responses and improve key developmental processes in the injured neonatal brain. The present results suggest different cellular target mechanisms of MSC-EVs, preventing secondary HI-induced brain injury. MSC-EV treatment may be a promising alternative to risk-associated cell therapies in neonatal brain injury.

IL-18 binding protein (IL-18BP) as a novel radiation countermeasure after radiation exposure in mice

Recent studies suggested that radiation exposure causes local and systemic inflammatory responses and induces cell and tissue damage. We have reported that IL-18 plays an important role in radiation-induced injury. Here, we demonstrate that IL-18 binding protein (IL-18BP), a natural antagonist of IL-18, was significantly increased (1.7-63 fold) in mouse serum on day 1 after 0.5-10 Gy TBI. However, this high level of IL-18BP was not sufficient to neutralize the active IL-18 in irradiated mice, resulting in a radiation dose-dependent free IL-18 increase in these mice's serum which led to pathological alterations to the irradiated cells and tissues and finally caused animal death. Administration of recombinant human (rh) IL-18BP (1.5 mg/kg) with single (24, 48 or 72 h post-TBI) or double doses (48 h and 5 days post-TBI) subcutaneous (SC) injection increased 30-day survival of CD2F1 mice after 9 Gy TBI 12.5-25% compared with the vehicle control treated group, respectively. Furthermore, the mitigative effects of rhIL-18BP included balancing the ratio of IL-18/IL-18BP and decreasing the free IL-18 levels in irradiated mouse serum and significantly increasing blood cell counts, BM hematopoietic cellularity and stem and progenitor cell clonogenicity in mouse BM. Furthermore, IL-18BP treatment inhibited the IL-18 downstream target interferon (IFN)-γ expression in mouse BM, decreased reactive oxygen species (ROS) level in the irradiated mouse heart tissues, attenuated the stress responsive factor GDF-15 (growth differentiation factor-15) and increased the intestine protector citrulline level in total body irradiated mouse serum, implicating that IL-18BP may protect multiple organs from radiation-induced inflammation and oxidative stress. Our data suggest that IL-18 plays a key role in radiation-induced cell and tissue damage and dysfunction; and for the first time demonstrated that IL-18BP counters IL-18 activation and therefore may mitigate/treat radiation-induced multiple organ injuries and increase animal survival with a wider therapeutic window from 24 h and beyond after lethal doses of radiation exposure.

Nup133 and ERα mediate the differential effects of hyperoxia-induced damage in male and female OPCs

Background

Hyperoxia is a well-known cause of cerebral white matter injury in preterm infants with male sex being an independent and critical risk factor for poor neurodevelopmental outcome. Sex is therefore being widely considered as one of the major decisive factors for prognosis and treatment of these infants. But unfortunately, we still lack a clear view of the molecular mechanisms that lead to such a profound difference. Hence, using mouse-derived primary oligodendrocyte progenitor cells (OPCs), we investigated the molecular factors and underlying mechanisms behind the differential response of male and female cells towards oxidative stress.

Results

We demonstrate that oxidative stress severely affects cellular functions related to energy metabolism, stress response, and maturation in the male-derived OPCs, whereas the female cells remain largely unaffected. CNPase protein level was found to decline following hyperoxia in male but not in female cells. This impairment of maturation was accompanied by the downregulation of nucleoporin and nuclear lamina proteins in the male cells. We identify Nup133 as a novel target protein affected by hyperoxia, whose inverse regulation may mediate this differential response in the male and female cells. Nup133 protein level declined following hyperoxia in male but not in female cells. We show that nuclear respiratory factor 1 (Nrf1) is a direct downstream target of Nup133 and that Nrf1 mRNA declines following hyperoxia in male but not in female cells. The female cells may be rendered resistant due to synergistic protection via the estrogen receptor alpha (ERα) which was upregulated following hyperoxia in female but not in male cells. Both Nup133 and ERα regulate mitochondrial function and oxidative stress response by transcriptional regulation of Nrf1.

Conclusions

These findings from a basic cell culture model establish prominent sex-based differences and suggest a novel mechanism involved in the differential response of OPCs towards oxidative stress. It conveys a strong message supporting the need to study how complex cellular processes are regulated differently in male and female brains during development and for a better understanding of how the brain copes up with different forms of stress after preterm birth.

NLRP3 inflammasome-dependent pyroptosis and apoptosis in hippocampus neurons mediates depressive-like behavior in diabetic mice

A relatively large number of diabetic patients risk complications of clinical depression that lead to poorer quality of life, however the precise mechanisms for diabetes-associated depression are not fully understood. Links between hyperglycemia-induced oxidative stress and NACHT, LRR, and PYD domains-containing protein 3 (NLRP3) inflammasome activation have been reported in the pathogenesis of diabetes. The present study aimed to elucidate the contribution of NLRP3-mediated apoptotic/pyroptotic neuronal cell death to diabetes-associated depression. We found that depressive-like behavior in streptozotocin (STZ)-induced diabetic mice was associated with hippocampal NLRP3 inflammasome activation. Hyperglycemia increased reactive oxygen species (ROS) production, thus leading to NLRP3 inflammasome activation in hippocampal neurons. It was found that STZ treatment induced apoptotic and pyroptotic cell death in the hippocampus as evidenced by increases of cleaved caspase 3 positive hippocampal neurons, TUNEL-positive cells, protein levels of p53, Bax, Puma, and the cleaved GSDMD N-terminal fragment, all of which were decreased in NLRP3 deficient mice. Using murine hippocampal neuronal cell line HT22, we found that high glucose induced apoptotic and pyroptotic cell death in a NLRP3 inflammasome-dependent manner in vitro. In addition, NLRP3 deficiency alleviated depressive-like behavior in STZ-induced diabetic mice. Our results suggest that hyperglycemia results in apoptosis and pyroptosis of hippocampal neuron cells in a NLRP3-dependent manner, which was associated with the depressive phenotypes evoked by STZ-induced diabetes. The study identifies a novel function of NLRP3 activation in high glucose-induced neuronal cell death, which sheds further light on the pathogenesis and new therapeutic targets of diabetes-associated depression.

Current Evidence on Cell Death in Preterm Brain Injury in Human and Preclinical Models

Despite tremendous advances in neonatal intensive care over the past 20 years, prematurity carries a high burden of neurological morbidity lasting lifelong. The term encephalopathy of prematurity (EoP) coined by Volpe in 2009 encompasses all aspects of the now known effects of prematurity on the immature brain, including altered and disturbed development as well as specific lesional hallmarks. Understanding the way cells are damaged is crucial to design brain protective strategies, and in this purpose, preclinical models largely contribute to improve the comprehension of the cell death mechanisms. While neuronal cell death has been deeply investigated and characterized in (hypoxic–ischemic) encephalopathy of the newborn at term, little is known about the types of cell death occurring in preterm brain injury. Three main different morphological cell death types are observed in the immature brain, specifically in models of hypoxic–ischemic encephalopathy, namely, necrotic, apoptotic, and autophagic cell death. Features of all three types may be present in the same dying neuron. In preterm brain injury, description of cell death types is sparse, and cell loss primarily concerns immature oligodendrocytes and, infrequently, neurons. In the present review, we first shortly discuss the different main severe preterm brain injury conditions that have been reported to involve cell death, including periventricular leucomalacia (PVL), diffuse white matter injury (dWMI), and intraventricular hemorrhages, as well as potentially harmful iatrogenic conditions linked to premature birth (anesthesia and caffeine therapy). Then, we present an overview of current evidence concerning cell death in both clinical human tissue data and preclinical models by focusing on studies investigating the presence of cell death allowing discriminating between the types of cell death involved. We conclude that, to improve brain protective strategies, not only apoptosis but also other cell death (such as regulated necrotic and autophagic) pathways now need to be investigated together in order to consider all cell death mechanisms involved in the pathogenesis of preterm brain damage.

Chronic intrahippocampal interleukin-1β overexpression in adolescence impairs hippocampal neurogenesis but not neurogenesis-associated cognition

Both neuroinflammation and adult hippocampal neurogenesis (AHN) are implicated in many neurodegenerative disorders as well as in neuropsychiatric disorders, which often become symptomatic during adolescence. A better knowledge of the impact that chronic neuroinflammation has on the hippocampus during the adolescent period could lead to the discovery of new therapeutics for some of these disorders. The hippocampus is particularly vulnerable to altered concentrations of the pro-inflammatory cytokine interleukin-1β (IL-1β), with elevated levels implicated in the aetiology of neurodegenerative disorders such as Alzheimer's and Parkinson's, and stress-related disorders such as depression. The effect of acutely and chronically elevated concentrations of hippocampal IL-1β have been shown to reduce AHN in adult rodents. However, the effect of exposure to chronic overexpression of hippocampal IL-1β during adolescence, a time of increased vulnerability, hasn't been fully interrogated. Thus, in this study we utilized a lentiviral approach to induce chronic overexpression of IL-1β in the dorsal hippocampus of adolescent male Sprague Dawley rats for 5 weeks, during which time its impact on cognition and hippocampal neurogenesis were examined. A reduction in hippocampal neurogenesis was observed along with a reduced level of neurite branching on hippocampal neurons. However, there was no effect of IL-1β overexpression on performance in pattern separation, novel object recognition or spontaneous alternation in the Y maze. Our study has highlighted that chronic IL-1β overexpression in the hippocampus during the adolescent period exerts a negative impact on neurogenesis independent of cognitive performance, and suggests a degree of resilience of the adolescent hippocampus to inflammatory insult.

Role of microglial activation and neuroinflammation in neurotoxicity of acrylamide in vivo and in vitro

Acrylamide, a soft electrophile, is widely used in the industry and laboratories, and also contaminates certain foods. Neurotoxicity and neurodegenerative effects of acrylamide have been reported in humans and experimental animals, although the underlying mechanism remains obscure. Activation of microglia and neuroinflammation has been demonstrated in various neurodegenerative diseases as well as other pathologies of the brain. The present study aimed to investigate the role of microglial activation and neuroinflammation in acrylamide neurotoxicity. Male 10-week-old Wistar rats were exposed to acrylamide by gavage at 0, 0.2, 2, or 20 mg/kg BW, once per day for 5 weeks. The results showed that 5-week exposure to acrylamide induced inflammatory responses in the cerebral cortex, evident by upregulated mRNA and protein expression of pro-inflammatory cytokines IL-1β, IL-6, and IL-18. Acrylamide also induced activation of microglia, indicated by increased expression of microglial markers, CD11b and CD40, and increased CD11b/c-positive microglial area and microglial process length. In vitro studies using BV-2 microglial cells confirmed microglial inflammatory response, as evident by time- (0-36 h; 50 μM) and dose- (0-500 μM; 24 h) dependent increase in mRNA expression of IL-1β and IL-18, as well as the inflammatory marker iNOS. Furthermore, acrylamide-induced upregulation of pro-inflammatory cytokines was mediated through the NLRP3 inflammasome pathway, as evident by increased expression of NLRP3, caspase 1, and ASC in the rat cerebral cortex, and by the inhibitory effects of NLRP3 inflammasome inhibitor on the acrylamide-induced upregulation of NLRP3, caspase 1, IL-1β, and IL-18 in BV-2 microglia.

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

Perinatal brain injury is a leading cause of death and disability in young children. Recent advances in obstetrics, reproductive medicine and neonatal intensive care have resulted in significantly higher survival rates of preterm or sick born neonates, at the price of increased prevalence of neurological, behavioural and psychiatric problems in later life. Therefore, the current focus of experimental research shifts from immediate injury processes to the consequences for brain function in later life. The aetiology of perinatal brain injury is multi-factorial involving maternal and also labour-associated factors, including not only placental insufficiency and hypoxia-ischaemia but also exposure to high oxygen concentrations, maternal infection yielding excess inflammation, genetic factors and stress as important players, all of them associated with adverse long-term neurological outcome. Several animal models addressing these noxious stimuli have been established in the past to unravel the underlying molecular and cellular mechanisms of altered brain development. In spite of substantial efforts to investigate short-term consequences, preclinical evaluation of the long-term sequelae for the development of cognitive and neuropsychiatric disorders have rarely been addressed. This review will summarise and discuss not only current evidence but also requirements for experimental research providing a causal link between insults to the developing brain and long-lasting neurodevelopmental disorders.

Time Dependent Pathway Activation of Signalling Cascades in Rat Organs after Short-Term Hyperoxia

Administration of oxygen is one of the most common interventions in medicine. Previous research showed that differential regulated proteins could be linked to hyperoxia-associated signaling cascades in different tissues. However, it still remains unclear which signaling pathways are activated by hyperoxia. The present study analyses hyperoxia-induced protein alterations in lung, brain, and kidney tissue using a proteomic and bioinformatic approach. Pooled data of 36 Wistar rats exposed to hyperoxia were used. To identify possible hyperoxia biomarkers, and to evaluate the relationship between protein alterations in hyperoxia affected organs and blood, proteomics data from brain, lung, and kidney were analyzed. Functional network analyses (IPA^®, PathwaysStudio^®, and GENEmania^®) in combination with hierarchical cluster analysis (Perseus^®) was used to identify relevant pathways and key proteins. Data of 54 2D-gels with more than 2500 significantly regulated spots per gel were collected. Thirty-eight differentially expressed proteins were identified and consecutively analyzed by bioinformatic methods. Most differences between hyperoxia and normoxia (21 proteins up-regulated, 17 proteins down-regulated) were found immediately after hyperoxia (15 protein spots), followed by day 3 (13 spots), and day 7 (10 spots). A highly significant association with inflammation and the inflammatory response was found. Cell proliferation, oxidative stress, apoptosis and cell death as well as cellular functions were revealed to be affected. Three hours of hyperoxia resulted in significant alterations of protein expression in different organs (brain, lung, kidney) up to seven days after exposure. Further studies are required to interpret the relevance of protein alterations in signaling cascades during/after hyperoxia.

Ketamine exacerbates cortical neuroapoptosis under hyperoxic conditions by upregulating expression of the N-methyl-D-aspartate receptor subunit NR1 in the developing rat brain

BACKGROUND

Ketamine and hyperoxia are widely used in obstetric and pediatric settings. Either ketamine or hyperoxia has been reported to cause neuroapoptosis in the developing brain, and ketamine-induced neuronal apoptosis may involve a compensatory upregulation of the N-methyl-D-aspartate (NMDA) receptor NR1 subunit. This study investigated the impact of ketamine administration under hyperoxic conditions on cortical neuroapoptosis and NR1 subunit expression in the infant rat brain.

METHODS

Male, 7-day-old rats were randomly allocated to four groups: control, ketamine, hyperoxia, and ketamine + hyperoxia (n = 18 per group). Rats in the control and ketamine groups received subcutaneous injections of either vehicle (saline) or ketamine (50 mg/kg) in room air (21% oxygen). The hyperoxia and ketamine + hyperoxia groups were exposed to 60% oxygen for 2 h after receiving saline or ketamine. Physiological parameters and arterial oxygen saturation were observed. Neuronal apoptosis and the expressions of NR1 mRNA and protein in the frontal cortex were also examined by transferase dUTP nick end labeling (TUNEL) assays, qPCR and Western blot, respectively.

RESULTS

Ketamine alone had no effect on paO₂ (P > 0.05)_, but pups exposed to hyperoxia or hyperoxia + ketamine had significantly greater paO₂ values compared to control animals (P < 0.01). Animals exposed to ketamine and ketamine + hyperoxia showed higher apoptotic scores, mRNA and protein expression levels of NR1 than control animals (P < 0.01), and ketamine + hyperoxia caused a significantly greater increase than ketamine alone (P < 0.01).

CONCLUSIONS

These data suggest that ketamine administration under hyperoxic conditions exacerbates cortical neuroapoptosis in the developing brain, which may be closely associated with an enhancement in NMDA receptor NR1 subunit expression.

Early-life stress lastingly alters the neuroinflammatory response to amyloid pathology in an Alzheimer's disease mouse model

Exposure to stress during the sensitive period of early-life increases the risk to develop cognitive impairments and psychopathology later in life. In addition, early-life stress (ES) exposure, next to genetic causes, has been proposed to modulate the development and progression of Alzheimer's disease (AD), however evidence for this hypothesis is currently lacking. We here tested whether ES modulates progression of AD-related neuropathology and assessed the possible contribution of neuroinflammatory factors in this. We subjected wild-type (WT) and transgenic APP/PS1 mice, as a model for amyloid neuropathology, to chronic ES from postnatal day (P)2 to P9. We next studied how ES exposure affected; 1) amyloid β (Aβ) pathology at an early (4month old) and at a more advanced pathological (10month old) stage, 2) neuroinflammatory mediators immediately after ES exposure as well as in adult WT mice, and 3) the neuroinflammatory response in relation to Aβ neuropathology. ES exposure resulted in a reduction of cell-associated amyloid in 4month old APP/PS1 mice, but in an exacerbation of Aβ plaque load at 10months of age, demonstrating that ES affects Aβ load in the hippocampus in an age-dependent manner. Interestingly, ES modulated various neuroinflammatory mediators in the hippocampus of WT mice as well as in response to Aβ neuropathology. In WT mice, immediately following ES exposure (P9), Iba1-immunopositive microglia exhibited reduced complexity and hippocampal interleukin (IL)-1β expression was increased. In contrast, microglial Iba1 and CD68 were increased and hippocampal IL-6 expression was decreased at 4months, while these changes resolved by 10months of age. Finally, Aβ neuropathology triggered a neuroinflammatory response in APP/PS1 mice that was altered after ES exposure. APP/PS1 mice exhibited increased CD68 expression at 4months, which was further enhanced by ES, whereas the microglial response to Aβ neuropathology, as measured by Iba1 and CD11b, was less prominent after ES at 10months of age. Finally, the hippocampus appears to be more vulnerable for these ES-induced effects, since ES did not affect Aβ neuropathology and neuroinflammation in the entorhinal cortex of adult ES exposed mice. Overall, our results demonstrate that ES exposure has both immediate and lasting effects on the neuroinflammatory response. In the context of AD, such alterations in neuroinflammation might contribute to aggravated neuropathology in ES exposed mice, hence altering disease progression. This indicates that, at least in a genetic context, ES could aggravate AD pathology.

Neuronal survival in the brain: neuron type-specific mechanisms

Neurogenic regions of mammalian brain produce many more neurons that will eventually survive and reach a mature stage. Developmental cell death affects both embryonically produced immature neurons and those immature neurons that are generated in regions of adult neurogenesis. Removal of substantial numbers of neurons that are not yet completely integrated into the local circuits helps to ensure that maturation and homeostatic function of neuronal networks in the brain proceed correctly. External signals from brain microenvironment together with intrinsic signaling pathways determine whether a particular neuron will die. To accommodate this signaling, immature neurons in the brain express a number of transmembrane factors as well as intracellular signaling molecules that will regulate the cell survival/death decision, and many of these factors cease being expressed upon neuronal maturation. Furthermore, pro-survival factors and intracellular responses depend on the type of neuron and region of the brain. Thus, in addition to some common neuronal pro-survival signaling, different types of neurons possess a variety of 'neuron type-specific' pro-survival constituents that might help them to adapt for survival in a certain brain region. This review focuses on how immature neurons survive during normal and impaired brain development, both in the embryonic/neonatal brain and in brain regions associated with adult neurogenesis, and emphasizes neuron type-specific mechanisms that help to survive for various types of immature neurons. Importantly, we mainly focus on in vivo data to describe neuronal survival specifically in the brain, without extrapolating data obtained in the PNS or spinal cord, and thus emphasize the influence of the complex brain environment on neuronal survival during development.

Intratracheal transplantation of mesenchymal stem cells simultaneously attenuates both lung and brain injuries in hyperoxic newborn rats

BACKGROUND

Bronchopulmonary dysplasia is an independent risk factor for adverse neurodevelopmental outcomes in premature infants. We investigated whether attenuation of hyperoxic lung injury with intratracheal transplantation of human umbilical cord blood-derived mesenchymal stem cells (MSCs) could simultaneously mitigate brain damage in neonatal rats.

METHODS

Newborn Sprague-Dawley rats were exposed to hyperoxia or normoxia conditions for 14 d. MSCs (5 × 10(5) cells) were transplanted intratracheally at postnatal day (P) 5. At P14, lungs and brains were harvested for histological and biochemical analyses.

RESULTS

Hyperoxic lung injuries, such as impaired alveolarization evident from increased mean linear intercept (MLI) and elevated inflammatory cytokine levels were significantly alleviated with MSC transplantation. Hyperoxia decreased brain weight, increased brain cell death, and induced hypomyelination. MSC transplantation significantly ameliorated hyperoxia-induced increased terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL)-positive cells in the dentate gyrus and reduced myelin basic protein. In correlation analyses, brain weight and myelin basic protein (MBP) were significantly inversely correlated with lung MLI and inflammatory cytokines, while TUNEL-positive brain cell number showed a significant positive correlation with lung MLI.

CONCLUSION

Despite no significant improvement in short-term neurofunctional outcome, intratracheal transplantation of MSCs simultaneously attenuated hyperoxic lung and brain injuries in neonatal rats, with the extent of such attenuation being closely linked in the two tissues.

A ‘Best Practices’ Approach to Neuropathologic Assessment in Developmental Neurotoxicity Testing—for Today

A key trait of developmental neurotoxicants is their ability to cause structural lesions in the immature nervous system. Thus, neuropathologic assessment is an essential element of developmental neurotoxicity (DNT) studies that are designed to evaluate chemically-induced risk to neural substrates in young humans. The guidelines for conventional DNT assays have been established by regulatory agencies to provide a flexible scaffold for conducting such studies; recent experience has launched new efforts to update these recommendations. The present document was produced by an ad hoc subcommittee of the Society of Toxicologic Pathology (STP) tasked with examining conventional methods used in DNT neuropathology in order to define the ‘best practices’ for dealing with the diverse requirements of both national (EPA) and international (OECD) regulatory bodies. Recommendations (including citations for relevant neurobiological and technical references) address all aspects of the DNT neuropathology examination: study design; tissue fixation, collection, processing, and staining; qualitative and quantitative evaluation; statistical analysis; proper control materials; study documentation; and personnel training. If followed, these proposals will allow pathologists to meet the need for a sound risk assessment (balanced to address both regulatory issues and scientific considerations) in this field today while providing direction for the research needed to further refine DNT neuropathology ‘best practices’ in the future.

Effects of PMA (PHORBOL-12-MYRISTATE-13-ACETATE) on the Developing Rodent Brain

Perinatal infections have a negative impact on brain development. However, the underlying mechanisms leading to neurological impairment are not completely understood and reliable models of inflammation are urgently needed. Using phorbol-myristate-acetate as an activator of inflammation, we investigated the effect on the developing rodent brain. Neonatal rats and mice deficient in IL-18 or IRAK-4 were exposed to PMA. Brains were assessed for regulation of pro- and anti-inflammatory cytokines and cell death 24 hrs, 7 and 14 days after treatment. PMA induced an inflammatory response and caused widespread neurodegeneration in the brains of 3- and 7-day-old rats. In contrast, 14-day-old rats were resistant to the neurotoxic effect of PMA. Histological evaluation at the age of 14 and 21 days revealed a destruction of the cortical microstructure with decreased numerical density of neuronal cells. Mice deficient in IL-18 or IRAK-4 were protected against PMA induced brain injury. PMA treatment during a vulnerable period can alter brain development. IL-18 and IRAK-4 appear to be important for the development of PMA induced injury.

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

BACKGROUND

Hyperoxic reoxygenation following hypoxia increases the expression of inflammatory genes in the neonatal mouse brain. We have therefore compared the temporal profile of 44 a priori selected genes after hypoxia and hyperoxic or normoxic reoxygenation.

METHODS

Postnatal day 7 mice were subjected to 2 h of hypoxia (8% O2) and 30 min reoxygenation with 60% or 21% O2. After 0 to 72 h observation, mRNA and protein were examined in the hippocampus and striatum.

RESULTS

There were significantly higher gene expression changes in six genes after hyperoxic compared to normoxic reoxygenation. Three genes had a generally higher expression throughout the observation period: the inflammatory genes Hmox1 (mean difference: 0.52, 95% confidence interval (CI): 0.15-1.01) and Tgfb1 (mean difference: 0.099, CI: 0.003-0.194), and the transcription factor Nfkb1 (mean difference: 0.049, CI: 0.011-0.087). The inflammatory genes Cxcl10 and Il1b, and the DNA repair gene Neil3, had a higher gene expression change after hyperoxic reoxygenation at one time point only. Nineteen genes involved in inflammation, transcription regulation, apoptosis, angiogenesis, and glucose transport had significantly different gene expression changes with time in all intervention animals.

CONCLUSION

We confirm that hyperoxic reoxygenation induces a stronger inflammatory gene response than reoxygenation with air.

Neuroprotective effect of dexmedetomidine on hyperoxia-induced toxicity in the neonatal rat brain

Dexmedetomidine is a highly selective agonist of α2-receptors with sedative, anxiolytic, analgesic, and anesthetic properties. Neuroprotective effects of dexmedetomidine have been reported in various brain injury models. In the present study, we investigated the effects of dexmedetomidine on neurodegeneration, oxidative stress markers, and inflammation following the induction of hyperoxia in neonatal rats. Six-day-old Wistar rats received different concentrations of dexmedetomidine (1, 5, or 10 µg/kg bodyweight) and were exposed to 80% oxygen for 24 h. Sex-matched littermates kept in room air and injected with normal saline or dexmedetomidine served as controls. Dexmedetomidine pretreatment significantly reduced hyperoxia-induced neurodegeneration in different brain regions of the neonatal rat. In addition, dexmedetomidine restored the reduced/oxidized glutathione ratio and attenuated the levels of malondialdehyde, a marker of lipid peroxidation, after exposure to high oxygen concentration. Moreover, administration of dexmedetomidine induced downregulation of IL-1β on mRNA and protein level in the developing rat brain. Dexmedetomidine provides protections against toxic oxygen induced neonatal brain injury which is likely associated with oxidative stress signaling and inflammatory cytokines. Our results suggest that dexmedetomidine may have a therapeutic potential since oxygen administration to neonates is sometimes inevitable.

Postnatal hyperoxia exposure differentially affects hepatocytes and liver haemopoietic cells in newborn rats

Premature newborns are frequently exposed to hyperoxic conditions and experimental data indicate modulation of liver metabolism by hyperoxia in the first postnatal period. Conversely, nothing is known about possible modulation of growth factors and signaling molecules involved in other hyperoxic responses and no data are available about the effects of hyperoxia in postnatal liver haematopoiesis. The aim of the study was to analyse the effects of hyperoxia in the liver tissue (hepatocytes and haemopoietic cells) and to investigate possible changes in the expression of Vascular Endothelial Growth Factor (VEGF), Matrix Metalloproteinase 9 (MMP-9), Hypoxia-Inducible Factor-1α (HIF-1α), endothelial Nitric Oxide Synthase (eNOS), and Nuclear Factor-kB (NF-kB). Experimental design of the study involved exposure of newborn rats to room air (controls), 60% O₂ (moderate hyperoxia), or 95% O₂ (severe hyperoxia) for the first two postnatal weeks. Immunohistochemical and Western blot analyses were performed. Severe hyperoxia increased hepatocyte apoptosis and MMP-9 expression and decreased VEGF expression. Reduced content in reticular fibers was found in moderate and severe hyperoxia. Some other changes were specifically produced in hepatocytes by moderate hyperoxia, i.e., upregulation of HIF-1α and downregulation of eNOS and NF-kB. Postnatal severe hyperoxia exposure increased liver haemopoiesis and upregulated the expression of VEGF (both moderate and severe hyperoxia) and eNOS (severe hyperoxia) in haemopoietic cells. In conclusion, our study showed different effects of hyperoxia on hepatocytes and haemopoietic cells and differential involvement of the above factors. The involvement of VEGF and eNOS in the liver haemopoietic response to hyperoxia may be hypothesized.

Zonisamide attenuates hyperoxia-induced apoptosis in the developing rat brain

Oxygen therapy used in the treatment of perinatal hypoxia induces neurodegeneration in babies with immature antioxidant mechanisms. Zonisamide is a new antiepileptic drug used in childhood intractable seizures. Many studies demonstrated its neuroprotective effects. There is no study evaluating its effect on hyperoxic brain injury. The aim of this study was to investigate the neuroprotective effect of zonisamide on hyperoxia-induced neonatal brain injury. A total of 21 Wistar rat pups were used. The animals were divided into three groups: control group, hyperoxia group, and zonisamide-treated group. The zonisamide-treated group received an intraperitoneal injection of zonisamide. Zonisamide significantly preserved the number of neurons in CA1 and dentate gyrus parts of hippocampus, prefrontal, and parietal cortex. Zonisamide treatment also decreased the number of apoptotic neurons in all examined parts of hippocampus, prefrontal, and parietal cortex. We suggest that zonisamide treatment may be used as a neuroprotective agent in hyperoxic brain injury.

Minocycline protects the immature white matter against hyperoxia

Poor neurological outcome in preterm infants is associated with periventricular white matter damage and hypomyelination, often caused by perinatal inflammation, hypoxia-ischemia, and hyperoxia. Minocycline has been demonstrated in animal models to protect the immature brain against inflammation and hypoxia-ischemia by microglial inhibition. Here we studied the effect of minocycline on white matter damage caused by hyperoxia. To mimic the 3- to 4-fold increase of oxygen tension caused by preterm birth, we have used the hyperoxia model in neonatal rats providing 24h exposure to 4-fold increased oxygen concentration (80% instead of 21% O2) from P6 to P7. We analyzed whether minocycline prevents activation of microglia and damage of oligodendroglial precursor cell development, and whether acute treatment of hyperoxia-exposed rats with minocycline improves long term white matter integrity. Minocycline administration during exposure to hyperoxia resulted in decreased apoptotic cell death and in improved proliferation and maturation of oligodendroglial precursor cells (OPC). Minocycline blocked changes in microglial morphology and IL-1β release induced by hyperoxia. In primary microglial cell cultures, minocycline inhibited cytokine release while in mono-cultures of OPCs, it improved survival and proliferation. Long term impairment of white matter diffusivity in MRI/DTI in P30 and P60 animals after neonatal hyperoxia was attenuated by minocycline. Minocycline protects white matter development against oxygen toxicity through direct protection of oligodendroglia and by microglial inhibition. This study moreover demonstrates long term benefits of minocycline on white matter integrity.

Effects of postnatal hyperoxia exposure on the rat dentate gyrus and subventricular zone

Premature newborns may be exposed to hyperoxia in the first postnatal period, but clinical and experimental works have raised the question of oxygen toxicity for the developing brain. However, specific analysis of hyperoxia exposure on neurogenesis is still lacking. Thus, the aim of the present study was to evaluate possible changes in the morphometric parameters of the main neurogenic sites in newborn rats exposed to 60 or 95 % oxygen for the first 14 postnatal days. The optical disector, a morphometric method based upon unbiased sampling principles of stereology, was applied to analyse cell densities, total volumes, and total cell numbers of the dentate gyrus (DG) and subventricular zone (SVZ). Apoptosis and proliferation were also studied by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling method and anti-ki67 immunohistochemistry, respectively. Severe hyperoxia increased the percentage of apoptotic cells in the DG. Moderate and severe hyperoxia induced a proliferative response both in the DG and SVZ, but the two neurogenic sites showed different changes in their morphometric parameters. The DG of both the hyperoxic groups showed lower volume and total cell number than that of the normoxic one. Conversely, the SVZ of newborn rats exposed to 95 % hyperoxia showed statistically significant higher volume and total cell number than SVZ of rats raised in normoxia. Our findings indicate that hyperoxia exposure in the first postnatal period affects both the neurogenic areas, although in different ways, i.e. reduction of DG and expansion of SVZ.

CEACAM1 expression in oligodendrocytes of the developing rat brain shows a spatiotemporal relation to myelination and is altered in a model of encephalopathy of prematurity

CEACAM1 is the founder molecule of the family of 'carcinoembryonic antigen-related cell adhesion molecules' and part of the immunoglobulin superfamily. Due to its role as a coreceptor to many other receptors (e.g. Toll-like receptor 2, Toll-like receptor 4, T-cell receptor, B-cell receptor, epidermal growth factor receptor and vascular endothelial growth factor receptor) and its different isoforms, CEACAM1 is a multifunctional protein with an impact on proliferation and differentiation of multiple cell types. Although different modes of action in other tissues are described, the role of CEACAM1 in the developing brain remains elusive. Here we report for the first time that CEACAM1 is expressed ontogenetically in oligodendrocytes of the developing rat brain, and that CEACAM1 expression has a spatiotemporal relation to myelination. In addition, CEACAM1 expression is altered in a model of hyperoxia- and inflammation-induced encephalopathy of prematurity, a myelination disorder of children born preterm. Furthermore, primary oligodendrocytes stimulated with CEACAM1 show increased myelination. Therefore, we postulate that CEACAM1 is, at least in part, involved in hyperoxia- and inflammation-induced disruption of myelination, but may also play a role in intact myelination as it is ontogenetically expressed in myelinating oligodendrocytes.

Oxygen toxicity is reduced by acetylcholinesterase inhibition in the developing rat brain

The cholinergic anti-inflammatory pathway is a neural mechanism that suppresses the innate inflammatory response and controls inflammation employing acetylcholine as the key endogenous mediator. In this study, we investigated the effects of the cholinergic agonists, physostigmine and donepezil, on neurodegeneration, inflammation and oxidative stress during oxygen toxicity in the developing rat brain. The aim of this study was to investigate the level of neurodegeneration, expression of proinflammatory cytokines, glutathione and lipid peroxidation after hyperoxia and treatment with the acetylcholinesterase (AChE) inhibitors, physostigmine and donepezil in the brain of neonatal rats. Six-day-old Wistar rats were exposed to 80% oxygen for 12-24 h and received 100 μg/kg physostigmine or 200 μg/kg donepezil intraperitoneally. Sex-matched littermates kept in room air and injected with normal saline, physostigmine or donepezil served as controls. Treatment with both inhibitors significantly reduced hyperoxia-triggered activity of AChE, neural cell death and the upregulation of the proinflammatory cytokines IL-1β and TNF-α in the immature rat brain on the mRNA and protein level. In parallel, hyperoxia-induced oxidative stress was reduced by concomitant physostigmine and donepezil administration, as shown by an increased reduced/oxidized glutathione ratio and attenuated malondialdehyde levels, as a sign of lipid peroxidation. Our results suggest that a single treatment with AChE inhibitors at the beginning of hyperoxia attenuated the detrimental effects of oxygen toxicity in the developing brain and may pave the way for AChE inhibitors, which are currently used for the treatment of Alzheimer's disease, as potential candidates for adjunctive neuroprotective therapies to the immature brain.

Oligodendroglial alterations and the role of microglia in white matter injury: relevance to schizophrenia

Schizophrenia is a chronic and debilitating mental illness characterized by a broad range of abnormal behaviors, including delusions and hallucinations, impaired cognitive function, as well as mood disturbances and social withdrawal. Due to the heterogeneous nature of the disease, the causes of schizophrenia are very complex; its etiology is believed to involve multiple brain regions and the connections between them, and includes alterations in both gray and white matter regions. The onset of symptoms varies with age and severity, and there is some debate over a degenerative or developmental etiology. Longitudinal magnetic resonance imaging studies have detected progressive gray matter loss in the first years of disease, suggesting neurodegeneration; but there is also increasing recognition of a temporal association between clinical complications at birth and disease onset that supports a neurodevelopmental origin. Presently, neuronal abnormalities in schizophrenia are better understood than alterations in myelin-producing cells of the brain, the oligodendrocytes, which are the predominant constituents of white matter structures. Proper white matter development and its structural integrity critically impacts brain connectivity, which affects sensorimotor coordination and cognitive ability. Evidence of defective white matter growth and compromised white matter integrity has been found in individuals at high risk of psychosis, and decreased numbers of mature oligodendrocytes are detected in schizophrenia patients. Inflammatory markers, including proinflammatory cytokines and chemokines, are also associated with psychosis. A relationship between risk of psychosis, white matter defects and prenatal inflammation is being established. Animal models of perinatal brain injury are successful in producing white matter damage in the brain, typified by hypomyelination and/or dysmyelination, impaired motor coordination and prepulse inhibition of the acoustic startle reflex, recapitulating structural and functional characteristics observed in schizophrenia. In addition, elevated expression of inflammation-related genes in brain tissue and increased production of cytokines by blood cells from patients with schizophrenia indicate immunological dysfunction and abnormal inflammatory responses, which are also important underlying features in experimental models. Microglia, resident immune defenders of the central nervous system, play important roles in the development and protection of neural cells, but can contribute to injury under pathological conditions. This article discusses oligodendroglial changes in schizophrenia and focuses on microglial activity in the context of the disease, in neonatal brain injury and in various experimental models of white matter damage. These include disorders associated with premature birth, and animal models of perinatal bacterial and viral infection, oxygen deprivation (hypoxia) and excess (hyperoxia), and elevated systemic proinflammatory cytokine levels. We briefly review the effects of treatment with antipsychotic and anti-inflammatory agents in models of perinatal brain injury, and comment on the therapeutic potential of these strategies. By understanding the neurobiological basis of oligodendroglial abnormalities in schizophrenia, it is hoped that patients will benefit from the availability of targeted and more efficacious treatment options.

Erythropoietin as a neuroprotectant for neonatal brain injury: animal models

Prematurity and perinatal hypoxia-ischemia are common problems that result in significant neurodevelopmental morbidity and high mortality worldwide. The Vannucci model of unilateral brain injury was developed to model perinatal brain injury due to hypoxia-ischemia. Because the rodent brain is altricial, i.e., it develops postnatally, investigators can model either preterm or term brain injury by varying the age at which injury is induced. This model has allowed investigators to better understand developmental changes that occur in susceptibility of the brain to injury, evolution of brain injury over time, and response to potential neuroprotective treatments. The Vannucci model combines unilateral common carotid artery ligation with a hypoxic insult. This produces injury of the cerebral cortex, basal ganglia, hippocampus, and periventricular white matter ipsilateral to the ligated artery. Varying degrees of injury can be obtained by varying the depth and duration of the hypoxic insult. This chapter details one approach to the Vannucci model and also reviews the neuroprotective effects of erythropoietin (Epo), a neuroprotective treatment that has been extensively investigated using this model and others.

Interaction of inflammation and hyperoxia in a rat model of neonatal white matter damage

Intrauterine infection and inflammation are major reasons for preterm birth. The switch from placenta-mediated to lung-mediated oxygen supply during birth is associated with a sudden rise of tissue oxygen tension that amounts to relative hyperoxia in preterm infants. Both infection/inflammation and hyperoxia have been shown to be involved in brain injury of preterm infants. Hypothesizing that they might be additive or synergistic, we investigated the influence of a systemic lipopolysaccharide (LPS) application on hyperoxia-induced white matter damage (WMD) in newborn rats. Three-day-old Wistar rat pups received 0.25 mg/kg LPS i.p. and were subjected to 80% oxygen on P6 for 24 h. The extent of WMD was assessed by immunohistochemistry, western blots, and diffusion tensor (DT) magnetic resonance imaging (MRI). In addition, the effects of LPS and hyperoxia were studied in an in vitro co-culture system of primary rat oligodendrocytes and microglia cells. Both noxious stimuli, hyperoxia, and LPS caused hypomyelination as revealed by western blot, immunohistochemistry, and altered WM microstructure on DT-MRI. Even so, cellular changes resulting in hypomyelination seem to be different. While hyperoxia induces cell death, LPS induces oligodendrocyte maturity arrest without cell death as revealed by TUNEL-staining and immunohistological maturation analysis. In the two-hit scenario cell death is reduced compared with hyperoxia treated animals, nevertheless white matter alterations persist. Concordantly with these in vivo findings we demonstrate that LPS pre-incubation reduced premyelinating-oligodendrocyte susceptibility towards hyperoxia in vitro. This protective effect might be caused by upregulation of interleukin-10 and superoxide dismutase expression after LPS stimulation. Reduced expression of transcription factors controlling oligodendrocyte development and maturation further indicates oligodendrocyte maturity arrest. The knowledge about mechanisms that triggered hypomyelination contributes to a better understanding of WMD in premature born infants.

Identification and characterization of IL-1 receptor-associated kinase-4 (IRAK-4) in half-smooth tongue sole Cynoglossus semilaevis

As a crucial component in TLR/IL-1R signaling pathways, IRAK-4 plays a central role in innate and adaptive immunity. In the present study, the cDNA of IRAK-4 was cloned for the first time from half-smooth tongue sole (Cynoglossus semilaevis). The full-length cDNA of csIRAK-4 was 2149 bp and contained a 168 bp 5' UTR, a 580 bp 3' UTR and a 1401 bp CDS. The predicted protein sequence of csIRAK-4 had two typical domains, a death domain (DD) at the N terminus and a serine/threonine/tyrosine protein kinase domain (STYKc) at the C terminus. RT-PCR showed that csIRAK-4 mRNA was detected in all tested tissues, especially in immune-related organs, gonads and brain. After injected with inactivated Vibrio anguillarum, the expressions of csIRAK-4 were up-regulated significantly (P<0.05) in spleen and head kidney. During development, csIRAK-4 was expressed at all selected stages and low-level expression was detected at metamorphosis. Taken together, the present study indicated that csIRAK-4 played a crucial role in immune responses and might be involved in the process of development.

Overexpression of extracellular superoxide dismutase has a protective role against hyperoxia-induced brain injury in neonatal mice

There is increasing evidence that hyperoxia, particularly at the time of birth, may result in neurological injury, in particular to the susceptible vasculature of these tissues. This study was aimed at determining whether overexpression of extracellular superoxide dismutase (EC-SOD) is protective against brain injury induced by hyperoxia. Transgenic (TG) mice (with an extra copy of the human extracellular superoxide dismutase gene) and wild-type (WT) neonate mice were exposed to hyperoxia (95% of F(i) o(2) ) for 7 days after birth versus the control group in room air. Brain positron emission tomography (PET) scanning with fludeoxyglucose (FDG) isotope uptake was performed after exposure. To assess apoptosis induced by hyperoxia exposure, caspase 3 ELISA and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining were performed. Quantitative western blot for the following inflammatory markers was performed: glial fibrillary acidic protein, ionized calcium-binding adaptor molecule 1, macrophage-inhibiting factor, and phospho-AMP-activated protein kinase. PET scanning with FDG isotope uptake showed significantly higher uptake in the WT hyperoxia neonate brain group (0.14 ± 0.03) than in both the TG group (0.09 ± 0.01) and the control group (0.08 ± 0.02) (P< 0.05). Histopathological investigation showed more apoptosis and dead neurons in hippocampus and cerebellum brain sections of WT neonate mice after exposure to hyperoxia than in TG mice; this finding was also confirmed by TUNEL staining. The caspase 3 assay confirmed the finding of more apoptosis in WT hyperoxia neonates (0.814 ± 0.112) than in the TG hyperoxic group (0.579 ± 0.144) (P < 0.05); this finding was also confirmed by TUNEL staining. Quantitative western blotting for the inflammatory and metabolic markers showed significantly higher expression in the WT group than in the TG and control groups. Thus, overexpression of EC-SOD in the neonate brain offers significant protection against hyperoxia-induced brain damage.

Maternal prenatal omega-3 fatty acid supplementation attenuates hyperoxia-induced apoptosis in the developing rat brain

Supraphysiologic amounts of oxygen negatively influences brain maturation and development. The aim of the present study was to evaluate whether maternal ω-3 long-chain polyunsaturated fatty acid (ω-3 FA) supplementation during pregnancy protects the developing brain against hyperoxic injury. Thirty-six rat pups from six different dams were divided into six groups according to the diet modifications and hyperoxia exposure. The groups were: a control group (standard diet+room air), a hyperoxia group (standard diet+80% O₂ exposure), a hyperoxia+high-dose ω-3 FA-supplemented group, a hyperoxia+low-dose ω-3 FA-supplemented group, a room air+low-dose ω-3 FA-supplemented+group, and a room air+high dose ω-3 FA-supplemented group. The ω-3 FA's were supplemented as a mixture of docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) from the second day of pregnancy until birth. Rat pups in the hyperoxic groups were exposed to 80% oxygen from birth until postnatal day 5 (P5). At P5, all animals were sacrificed. Neuronal cell death and apoptosis were evaluated by cell count, TUNEL, and active Caspase-3 immunohistochemistry. Histopathological examination showed that maternally ω-3 FA deficient diet and postnatal hyperoxia exposure were associated with significantly lower neuronal counts and significantly higher apoptotic cell death in the selected brain regions. Ω-3 FA treatment significantly diminished apoptosis, in the selected brain regions, in a dose dependent manner. Our results suggest that the maternal ω-3 FA supply may protect the developing brain against hyperoxic injury.

Prevention of neonatal oxygen-induced brain damage by reduction of intrinsic apoptosis

Within the last decade, it became clear that oxygen contributes to the pathogenesis of neonatal brain damage, leading to neurocognitive impairment of prematurely born infants in later life. Recently, we have identified a critical role for receptor-mediated neuronal apoptosis in the immature rodent brain. However, the contribution of the intrinsic apoptotic pathway accompanied by activation of caspase-2 under hyperoxic conditions in the neonatal brain still remains elusive. Inhibition of caspases appears a promising strategy for neuroprotection. In order to assess the influence of specific caspases on the developing brain, we applied a recently developed pentapeptide-based group II caspase inhibitor (5-(2,6-difluoro-phenoxy)-3(R,S)-(2(S)-(2(S)-(3-methoxycarbonyl-2(S)-(3-methyl-2(S)-((quinoline-2-carbonyl)-amino)-butyrylamino)propionylamino)3-methylbutyrylamino)propionylamino)-4-oxo-pentanoic acid methyl ester; TRP601). Here, we report that elevated oxygen (hyperoxia) triggers a marked increase in active caspase-2 expression, resulting in an initiation of the intrinsic apoptotic pathway with upregulation of key proteins, namely, cytochrome c, apoptosis protease-activating factor-1, and the caspase-independent protein apoptosis-inducing factor, whereas BH3-interacting domain death agonist and the anti-apoptotic protein B-cell lymphoma-2 are downregulated. These results coincide with an upregulation of caspase-3 activity and marked neurodegeneration. However, single treatment with TRP601 at the beginning of hyperoxia reversed the detrimental effects in this model. Hyperoxia-mediated neurodegeneration is supported by intrinsic apoptosis, suggesting that the development of highly selective caspase inhibitors will represent a potential useful therapeutic strategy in prematurely born infants.

Cellular changes underlying hyperoxia-induced delay of white matter development

Impaired neurological development in premature infants frequently arises from periventricular white matter injury (PWMI), a condition associated with myelination abnormalities. Recently, exposure to hyperoxia was reported to disrupt myelin formation in neonatal rats. To identify the causes of hyperoxia-induced PWMI, we characterized cellular changes in the white matter (WM) using neonatal wild-type 2-3-cyclic nucleotide 3-phosphodiesterase-enhanced green fluorescent protein (EGFP) and glial fibrillary acidic protein (GFAP)-EGFP transgenic mice exposed to 48 h of 80% oxygen from postnatal day 6 (P6) to P8. Myelin basic protein expression and CC1(+) oligodendroglia decreased after hyperoxia at P8, but returned to control levels during recovery between P12 and P15. At P8, hyperoxia caused apoptosis of NG2(+)O4(-) progenitor cells and reduced NG2(+) cell proliferation. This was followed by restoration of the NG2(+) cell population and increased oligodendrogenesis in the WM after recovery. Despite apparent cellular recovery, diffusion tensor imaging revealed WM deficiencies at P30 and P60. Hyperoxia did not affect survival or proliferation of astrocytes in vivo, but modified GFAP and glutamate-aspartate transporter expression. The rate of [(3)H]-d-aspartic acid uptake in WM tissue was also decreased at P8 and P12. Furthermore, cultured astrocytes exposed to hyperoxia showed a reduced capacity to protect oligodendrocyte progenitor cells against the toxic effects of exogenous glutamate. This effect was prevented by 2,3-dioxo-6-nitro-1,2,3,4-tetrahydrobenzo[f]quinoxaline-7-sulfonamide treatment. Our analysis reveals a role for altered glutamate homeostasis in hyperoxia-induced WM damage. Understanding the cellular dynamics and underlying mechanisms involved in hyperoxia-induced PWMI will allow for future targeted therapeutic intervention.

Neuronal death and oxidative stress in the developing brain

The developing brain is particularly vulnerable to reactive oxygen and reactive nitrogen species-mediated damage because of its high concentrations of unsaturated fatty acids, high rate of oxygen consumption, low concentrations of antioxidants, high content of metals catalyzing free radical formation, and large proportion of sensitive immature cells. In this review, we outline the dynamic changes of energy resources, metabolic requirements, and endogenous free radical scavenging systems during physiologic brain development. We further discuss the involvement of oxidative stress in the pathogenesis of neuronal death after exposure of the infant brain to hyperoxia, hypoxia/ischemia, sedative drugs, ethanol, and mechanical trauma. Several approaches have been developed to combat oxidative stress, but neuroprotective treatment strategies are limited in the clinical setting.