Protection by vascular prostaglandin E2 signaling in hypoxic-ischemic encephalopathy

Transcriptional regulation of NRF1 on metabotropic glutamate receptors in a neonatal hypoxic‑ischemic encephalopathy rat model

BACKGROUND

Neonatal hypoxic-ischemic encephalopathy (HIE) is a kind of brain injury that causes severe neurological disorders in newborns. Metabotropic glutamate receptors (mGluRs) and ionotropic glutamate receptors (iGluRs) are significantly associated with HIE and are involved in ischemia-induced excitotoxicity. This study aimed to investigate the upstream mechanisms of mGluRs and the transcriptional regulation by nuclear respiratory factor 1 (NRF1).

METHODS

The rat model of neonatal HIE was created using unilateral carotid artery ligation and in vitro oxygen-glucose deprivation paradigm. We used western blot, immunofluorescence, Nissl staining, and Morris water maze to investigate the impact of NRF1 on brain damage and learning memory deficit by HIE. We performed ChIP and luciferase activities to identify the transcriptional regulation of NRF1 on mGluRs.

RESULTS

The neuronal NRF1 and some glutamatergic genes expression synchronously declined in infarcted tissues. The NRF1 overexpression effectively restored the expression of some glutamatergic genes and improved cognitive performance. NRF1 regulated some members of mGluRs and iGluRs in hypoxic-ischemic neurons. Finally, NRF1 is bound to the promoter regions of Grm1, Grm2, and Grm8 to activate their transcription.

CONCLUSIONS

NRF1 is involved in the pathology of the neonatal HIE rat model, suggesting a novel therapeutic approach to neonatal HIE.

IMPACT

NRF1 and some glutamatergic genes were synchronously downregulated in the infarcted brain of the neonatal HIE rat model. NRF1 overexpression could rescue cognitive impairment caused by the neonatal HIE rat model. NRF1 regulated the expressions of Grm1, Grm2, and Grm8, which activated their transcription by binding to the promoter regions.

Chorioamnionitis, Inflammation and Neonatal Apnea: Effects on Preterm Neonatal Brainstem and on Peripheral Airways: Chorioamnionitis and Neonatal Respiratory Functions

Background: The present manuscript aims to be a narrative review evaluating the association between inflammation in chorioamnionitis and damage on respiratory centers, peripheral airways, and lungs, explaining the pathways responsible for apnea in preterm babies born by delivery after chorioamnionitis. Methods: A combination of keywords and MESH words was used, including: "inflammation", "chorioamnionitis", "brainstem", "cytokines storm", "preterm birth", "neonatal apnea", and "apnea physiopathology". All identified papers were screened for title and abstracts by the two authors to verify whether they met the proper criteria to write the topic. Results: Chorioamnionitis is usually associated with Fetal Inflammatory Response Syndrome (FIRS), resulting in injury of brain and lungs. Literature data have shown that infections causing chorioamnionitis are mostly associated with inflammation and consequent hypoxia-mediated brain injury. Moreover, inflammation and infection induce apneic episodes in neonates, as well as in animal samples. Chorioamnionitis-induced inflammation favors the systemic secretion of pro-inflammatory cytokines that are involved in abnormal development of the respiratory centers in the brainstem and in alterations of peripheral airways and lungs. Conclusions: Preterm birth shows a suboptimal development of the brainstem and abnormalities and altered development of peripheral airways and lungs. These alterations are responsible for reduced respiratory control and apnea. To date, mostly animal studies have been published. Therefore, more clinical studies on the role of chorioamninitis-induced inflammation on prematurity and neonatal apnea are necessary.

[Molecular mechanisms of hypoxia and adaptation to it. Part II]

Reprogramming of the mitochondrial electron transport chain (ETC) is the most important physiological mechanism that provides short- and long-term adaptation to hypoxia. The possibilities of additional pharmacological regulation of ETC activity are of considerable practical interest in correcting hypoxia-associated disorders. This review considers the main groups of antihypoxic compounds that exhibit their effect at the interface of ETC and the cycle of tricarboxylic acids, including succinate-containing and succinate-forming antihypoxants. The role of succinate during adaptation to hypoxia, the biological activity of the succinate, and its potentially adverse effects are currently not fully understood and require further clarification.

Pathophysiology of Cerebral Hyperperfusion in Term Neonates With Hypoxic-Ischemic Encephalopathy: A Systematic Review for Future Research

Worldwide neonatal hypoxic-ischemic encephalopathy (HIE) is a common cause of mortality and neurologic disability, despite the implementation of therapeutic hypothermia treatment. Advances toward new neuroprotective interventions have been limited by incomplete knowledge about secondary injurious processes such as cerebral hyperperfusion commonly observed during the first 1-5 days after asphyxia. Cerebral hyperperfusion is correlated with adverse neurodevelopmental outcome and it is a process that remains poorly understood. In order to provide an overview of the existing knowledge on the pathophysiology and highlight the gaps in current understanding of cerebral hyperperfusion in term animals and neonates with HIE, we performed a systematic research. We included papers scoping for study design, population, number of participants, study technique and relevant findings. Methodological quality was assessed using the checklist for cohort studies from The Joanna Briggs Institute. Out of 2,690 results, 34 studies were included in the final review-all prospective cohort studies. There were 14 studies of high, 17 moderate and 3 of low methodological quality. Data from the literature were analyzed in two main subjects: (1) Hemodynamic Changes subdivided into macro- and microscopic hemodynamic changes, and (2) Endogenous Pathways which was subdivided into N-methyl-D-aspartate/Mitogen activated protein kinase (NDMA/MAPK), Nitric Oxide (NO), prostanoids and other endogenous studies. Cerebral hyperperfusion in term neonates with HIE was found to be present 10-30 min after the hypoxic-ischemic event and was still present around day 10 and up to 1 month after birth. Cerebral hyperperfusion was also characterized by angiogenesis and cerebral vasodilation. Additionally, cerebral vasodilation was mediated by endogenous pathways such as MAPK through urokinase Plasminogen Activator (uPA), by neuronal NO synthase following NMDA and by prostanoid synthesis. Future research should elucidate the precise role of NMDA, MAPK and prostanoids in cerebral hyperperfusion. Moreover, research should focus on possible interventions and the effect of hypothermia on hyperperfusion. These findings should be taken into account simultaneously with brain imagining techniques, becoming a valuable asset in assessing the impact in neurodevelopmental outcome.

Time dependent dual effect of anti-inflammatory treatments on sarin-induced brain inflammation: Suggested role of prostaglandins

A common consequence of exposure to organophosphate nerve agents is the centrally mediated seizure activity that appears even after conventional treatment with atropine and oximes. We have previously demonstrated a major inflammatory response with subsequent brain damage which was correlated with the duration of the sarin-induced seizures (Chapman et al., 2006). In the present work seizures were induced by the nerve agent sarin (1.2 LD50) insufficiently treated 1 min later by atropine and trimedoxime bromide (TA), with additional midazolam treatment either 5 or 30 min after continuous seizure activity. The efficacy of both steroidal and nonsteroidal anti-inflammatory drugs (NSAIDs), as well as other drugs that were reported as beneficial in neuroprotection, were evaluated for their contribution as adjunct treatment against sarin induced seizures and the ensuing inflammatory brain damage. Results show that both steroids and NSAIDs were harmful when administered during convulsions, and steroids were at best ineffective if administered at their termination. However, if administered at termination of convulsions, the NSAID ibuprofen, the selective COX 2 inhibitor nimesulide and the PLA2 inhibitor quinacrine were partially effective in reducing brain inflammatory markers. Administration of exogenous analogs of prostaglandins (PGE2) immediately following sarin-induced convulsions was found to have a beneficial effect in reducing brain inflammatory markers measured at 24 h and one week post sarin exposure. These findings support the hypothesis that elevated levels of PGE2 have a beneficial role immediately following sarin induced seizures, and that early inhibition of PGE2 production by both steroids and NSAID is contraindicative.

Discovery of 2-Piperidinyl Phenyl Benzamides and Trisubstituted Pyrimidines as Positive Allosteric Modulators of the Prostaglandin Receptor EP2

Prostaglandin E2 (PGE2) via its Gαs-coupled EP2 receptor protects cerebral cortical neurons from excitotoxic and anoxic injury, though EP2 receptor activation can also cause secondary neurotoxicity in chronic inflammation. We performed a high-throughput screen of a library of 292 000 small molecules and identified several compounds that have a 2-piperidinyl phenyl benzamide or trisubstituted pyrimidine core as positive modulators for human EP2 receptor. The most active compounds increased the potency of PGE2 on EP2 receptor 4-5-fold at 20 μM without altering efficacy, indicative of an allosteric mechanism. These compounds did not augment the activity of the other Gαs-coupled PGE2 receptor subtype EP4 and showed neuroprotection against N-methyl-d-aspartate (NMDA)-induced excitotoxicity. These newly developed compounds represent second-generation allosteric potentiators for EP2 receptor and shed light on a promising neuroprotective strategy. They should prove valuable as molecular tools to achieve a better understanding of the dichotomous action of brain EP2 receptor activation.

Protective Effects of L-902,688, a Prostanoid EP4 Receptor Agonist, against Acute Blood-Brain Barrier Damage in Experimental Ischemic Stroke

Ischemic stroke occurs when a clot forms in the brain vasculature that starves downstream tissue of oxygen and nutrients resulting in cell death. The tissue immediately downstream of the blockage, the core, dies within minutes, but the surrounding tissue, the penumbra is potentially salvageable. Prostaglandin E₂ binds to four different G-protein coupled membrane receptors EP1–EP4 mediating different and sometimes opposing responses. Pharmacological activation of the EP4 receptor has already been established as neuroprotective in stroke, but the mechanism(s) of protection are not well-characterized. In this study, we hypothesized that EP4 receptor activation reduces ischemic brain injury by reducing matrix metalloproteinase (MMP)-3/-9 production and blood-brain barrier (BBB) damage. Rats underwent transient ischemic stroke for 90 min. Animals received an intravenous injection of either the vehicle or L-902,688, a highly specific EP4 agonist, at the onset of reperfusion. Brain tissue was harvested at 24 h. We established a dose-response curve and used the optimal dose that resulted in the greatest infarct reduction to analyze BBB integrity compared to vehicle-treated rats. The presence of IgG, a blood protein, in the brain parenchyma is a marker of BBB damage, and L-902,688 (1 mg/kg; i.v.) dramatically reduced IgG extravasation (P < 0.05). Consistent with these data, we assessed zona occludens-1 and occludin, tight junction proteins integral to the maintenance of the BBB, and found reduced degradation with L-902,688 administration. With immunoblotting, qRT-PCR, and/or a fluorescence resonance energy transfer (FRET)-based activity assay, we next measured MMP-3/-9 since they are key effectors of BBB breakdown in stroke. In the cerebral cortex, not only was MMP-3 activity significantly decreased (P < 0.05), but L-902,688 treatment also reduced MMP-9 mRNA, protein, and enzymatic activity (P < 0.001). In addition, post-ischemic administration of the EP4 agonist significantly reduced pro-inflammatory cytokines IL-1β (P < 0.05) and IL-6 (P < 0.01) in the ischemic cerebral cortex. Most importantly, one injection of L-902,688 (1 mg/kg; i.v) at the onset of reperfusion significantly reduces neurological deficits up to 3 weeks later (P < 0.05). Our data show for the first time that pharmacological activation of EP4 with L-902,688 is neuroprotective in ischemic stroke by reducing MMP-3/-9 and BBB damage.

The Consequences of Preterm Birth and Chorioamnionitis on Brainstem Respiratory Centers: Implications for Neurochemical Development and Altered Functions by Inflammation and Prostaglandins

Preterm birth is a major cause for neonatal morbidity and mortality, and is frequently associated with adverse neurological outcomes. The transition from intrauterine to extrauterine life at birth is particularly challenging for preterm infants. The main physiological driver for extrauterine transition is the establishment of spontaneous breathing. However, preterm infants have difficulty clearing lung liquid, have insufficient surfactant levels, and underdeveloped lungs. Further, preterm infants have an underdeveloped brainstem, resulting in reduced respiratory drive. These factors facilitate the increased requirement for respiratory support. A principal cause of preterm birth is intrauterine infection/inflammation (chorioamnionitis), and infants with chorioamnionitis have an increased risk and severity of neurological damage, but also demonstrate impaired autoresuscitation capacity and prevalent apnoeic episodes. The brainstem contains vital respiratory centers which provide the neural drive for breathing, but the impact of preterm birth and/or chorioamnionitis on this brain region is not well understood. The aim of this review is to provide an overview of the role and function of the brainstem respiratory centers, and to highlight the proposed mechanisms of how preterm birth and chorioamnionitis may affect central respiratory functions.

Prostaglandin E2 EP4 Receptor Activation Attenuates Neuroinflammation and Early Brain Injury Induced by Subarachnoid Hemorrhage in Rats

Activation of E prostanoid 4 receptor (EP4) shows neuroprotective effects in multiple central nervous system (CNS) lesions, but the roles of EP4 receptor in subarachnoid hemorrhage (SAH) are not explored. This study was designed to research the effects of EP4 modulation on early brain injury (EBI) after experimental SAH in rats. We found that the administration of EP4 selective agonist AE1-329 significantly improved neurological dysfunction, blood brain barrier (BBB) damage and brain edema at 24 h after SAH. Furthermore, AE1-329 obviously reduced the number of activated microglia and the mRNA and protein levels of pro-inflammatory cytokines, and increased Ser1177 phosphorylated endothelial nitric oxide synthase (Ser1177 p-eNOS). Moreover, AE1-329 significantly reduced the number of TUNEL-positive cells and active caspase-3 in cortex after SAH. The EP4 selective antagonist AE3-208 was also administrated and the opposite effects were achieved. Our results indicate that activation of EP4 protects brain from EBI through downregulating neuroinflammation reaction after SAH.

The potential neuroprotective role of a histone deacetylase inhibitor, sodium butyrate, after neonatal hypoxia-ischemia

Background

Histone deacetylase inhibitor (HDACi), sodium butyrate (SB), has been shown to be neuroprotective in adult brain injury models. Potential explanation for the inhibitor action involves among others reduced inflammation. We therefore anticipated that SB will provide a suitable option for brain injury in immature animals. The aim of our study was to test the hypothesis that one of the mechanisms of protection afforded by SB after neonatal hypoxia-ischemia is associated with anti-inflammatory action. We examined the effect of SB on the production of inflammatory factors including analysis of the microglial and astrocytic cell response. We also examined the effect of SB on molecular mediators that are crucial for inducing cerebral damage after ischemia (transcription factors, HSP70, as well as pro- and anti-apoptotic proteins).

Methods

Seven-day-old rat pups were subjected to unilateral carotid artery ligation followed by 60 min of hypoxia (7.6% O₂). SB (300 mg/kg) was administered in a 5-day regime with the first injection given immediately after hypoxic exposure. The damage of the ipsilateral hemisphere was evaluated by hematoxylin-eosin staining (HE) 6 days after the insult. Samples were collected at 24 and 48 h and 6 days. Effects of SB on hypoxia-ischemia (HI)-induced inflammation (cytokines and chemokine) were assessed by Luminex assay and immunohistochemistry. Expression of molecular mediators (NFκB, p53, HSP70, COX-2, pro- and anti-apoptotic factors Bax, Bcl-2, caspase-3) were assayed by Western blot analysis.

Results

SB treatment-reduced brain damage, as assessed by HE staining, suppressed the production of inflammatory markers—IL-1β, chemokine CXCL10, and blocked ischemia-elicited upregulation of COX-2 in the damaged ipsilateral hemisphere. Furthermore, administration of SB promoted the conversion of microglia phenotype from inflammatory M1 to anti-inflammatory M2. None of the investigated molecular mediators that are known to be affected by HDACis in adults were modified after SB administration.

Conclusions

Administration of SB is neuroprotective in neonatal hypoxia-ischemia injury. This neuroprotective activity prevented the delayed rise in chemokine CXCL10, IL-1β, and COX-2 in the ipsilateral hemisphere. SB appears to exert a beneficial effect via suppression of HI-induced cerebral inflammation.

Anti-Inflammatory and Neuroprotective Effects of PGE2 EP4 Signaling in Models of Parkinson's Disease

Inflammation is a ubiquitous factor accompanying normal aging and neurodegeneration, and recent studies indicate a major contribution of inducible cyclooxygenase (COX-2) and its downstream prostaglandin signaling pathways in modulating neuroinflammatory responses and neuronal function. We have previously shown that the prostaglandin PGE₂ receptor EP4 suppresses innate immune responses in models of systemic inflammation. Here we investigated the role of the EP4 receptor in models of Parkinson's disease (PD). Systemic co-administration of the EP4 agonist ONO-AE1-329 with the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) prevented loss of dopaminergic (DA) neurons in the substantia nigra pars compacta (SNpc) without significant changes in glial activation, suggesting a potent neuroprotective effect of EP4 signaling in this acute model of DA neuronal loss. Cell-specific conditional ablation of EP4 in Cd11bCre;EP4^lox/lox mice exacerbated MPTP-associated glial activation and T-cell infiltration in SNpc, consistent with anti-inflammatory functions of microglial EP4 signaling. In vitro, in primary microglia stimulated with oligomeric α-synuclein, EP4 receptor activation suppressed generation of pro-inflammatory and oxidative stress factors. Taken together, these findings suggest a dual neuroprotective and anti-inflammatory mechanism of action by the EP4 receptor in models of PD.

Monitoring of cerebral blood flow during hypoxia-ischemia and resuscitation in the neonatal rat using laser speckle imaging

Neonatal hypoxic-ischemic encephalopathy (HIE) is associated with alterations in cerebral blood flow (CBF) as a result of perinatal asphyxia. The extent to whichCBFchanges contribute to injury, and whether treatments that ameliorate these changes might be neuroprotective, is still unknown. Higher throughput techniques to monitorCBFchanges in rodent models ofHIEcan help elucidate the underlying pathophysiology. We developed a laser speckle imaging (LSI) technique to continuously monitorCBFin six postnatal-day 10 (P10) rats simultaneously before, during, and after unilateral hypoxia-ischemia (HI, ligation of the left carotid artery followed by hypoxia in 8% oxygen). After ligation,CBFto the ligated side fell by 30% compared to the unligated side (P < 0.0001). Hypoxia induced a bilateral 55% reduction inCBF, which was partially restored by resuscitation. Compared to resuscitation in air, resuscitation in 100% oxygen increasedCBFto the ligated side by 45% (P = 0.033). Individual variability inCBFresponse to hypoxia between animals accounted for up to 24% of the variability in hemispheric area loss to the ligated side. In both P10 and P7 models of unilateralHI, resuscitation in 100% oxygen did not affect hemispheric area loss, or hippocampalCA1 pyramidal neuron counts, after 1-week survival. ContinuousCBFmonitoring usingLSIin multiple rodents simultaneously can screen potential treatment modalities that affectCBF, and provide insight into the pathophysiology ofHI.

Brain barrier properties and cerebral blood flow in neonatal mice exposed to cerebral hypoxia-ischemia

Insults to the developing brain often result in irreparable damage resulting in long-term deficits in motor and cognitive functions. The only treatment today for hypoxic-ischemic encephalopathy (HIE) in newborns is hypothermia, which has limited clinical benefit. We have studied changes to the blood-brain barriers (BBB) as well as regional cerebral blood flow (rCBF) in a neonatal model of HIE to further understand the underlying pathologic mechanisms. Nine-day old mice pups, brain roughly equivalent to the near-term human fetus, were subjected to hypoxia-ischemia. Hypoxia-ischemia increased BBB permeability to small and large molecules within hours after the insult, which normalized in the following days. The opening of the BBB was associated with changes to BBB protein expression whereas gene transcript levels were increased showing direct molecular damage to the BBB but also suggesting compensatory mechanisms. Brain pathology was closely related to reductions in rCBF during the hypoxia as well as the areas with compromised BBB showing that these are intimately linked. The transient opening of the BBB after the insult is likely to contribute to the pathology but at the same time provides an opportunity for therapeutics to better reach the infarcted areas in the brain.

The role of inflammation in perinatal brain injury

Inflammation is increasingly recognized as being a critical contributor to both normal development and injury outcome in the immature brain. The focus of this Review is to highlight important differences in innate and adaptive immunity in immature versus adult brain, which support the notion that the consequences of inflammation will be entirely different depending on context and stage of CNS development. Perinatal brain injury can result from neonatal encephalopathy and perinatal arterial ischaemic stroke, usually at term, but also in preterm infants. Inflammation occurs before, during and after brain injury at term, and modulates vulnerability to and development of brain injury. Preterm birth, on the other hand, is often a result of exposure to inflammation at a very early developmental phase, which affects the brain not only during fetal life, but also over a protracted period of postnatal life in a neonatal intensive care setting, influencing critical phases of myelination and cortical plasticity. Neuroinflammation during the perinatal period can increase the risk of neurological and neuropsychiatric disease throughout childhood and adulthood, and is, therefore, of concern to the broader group of physicians who care for these individuals.