Microglia and Stem-Cell Mediated Neuroprotection after Neonatal Hypoxia-Ischemia

M2 microglia-derived exosomes reduce neuronal ferroptosis via FUNDC1-mediated mitophagy by activating AMPK/ULK1 signaling

Neuronal ferroptosis plays a vital role in the progression of neonatal hypoxic-ischemic brain damage (HIBD). M2-type microglia-derived exosomes (M2-exos) have been shown to protect neurons from ischemia-reperfusion (I/R) brain injury, but their impact on I/R-induced neuronal ferroptosis and the underlying mechanisms remain poorly understood. In this study, we used an in vitro oxygen-glucose deprivation/reoxygenation (OGD/R) model in HT-22 neuronal cells to investigate how M2-exos modulate ferroptosis. We found that M2-exos were internalized by HT-22 cells and significantly attenuated OGD/R-induced ferroptosis. Mechanistically, M2-exos enhanced mitophagy, which was mediated by the upregulation of FUN14 domain-containing protein 1 (FUNDC1), thereby inhibiting ferroptosis. Further analysis revealed that M2-exos activated FUNDC1-dependent mitophagy through the AMP-activated protein kinase (AMPK)/UNC-51-like kinase 1 (ULK1) signaling pathway. Taken together, these findings suggest that M2-exos ameliorate I/R-induced neuronal ferroptosis by enhancing FUNDC1-mediated mitophagy through the activation of AMPK/ULK1 signaling pathway.

Neuroprotection for neonatal hypoxic-ischemic encephalopathy: A review of novel therapies evaluated in clinical studies

Therapeutic hypothermia is an effective therapy for moderate-to-severe hypoxic-ischemic encephalopathy (HIE) in infants born at term or near-term in high-resource settings. Yet there remains a substantial proportion of infants who do not benefit or who will have significant disability despite therapeutic hypothermia. Novel investigational therapies that may confer additional neuroprotection by targeting known pathogenic mechanisms of hypoxic-ischemic brain injury are under development. This review focuses on putative neuroprotective agents that have shown promise in animal models of HIE, and that have been translated to clinical studies in neonates with HIE. We include agents that have been studied both with and without concurrent therapeutic hypothermia. Our review therefore addresses not just neonatal HIE in high-resource countries where therapeutic hypothermia is the standard of care, but also neonatal HIE in low- and middle-income countries where therapeutic hypothermia has been shown to be ineffective, and where the greatest burden of HIE-related morbidity and mortality exists.

Proteomic analysis of hippocampus reveals metabolic reprogramming in a piglet model of mild hypoxic ischemic encephalopathy

Neonatal hypoxic-ischemic encephalopathy (HIE) remains a leading cause of long-term neurologic morbidity. Fifty percent of HIE cases are mild and do not have clearly defined therapeutic interventions. Emergent evidence now demonstrates that up to 25% of children with mild HIE suffer motor and developmental delay by 18 months and 35% have cognitive impairments by age 5 years. Interestingly, the hippocampus, which is responsible for learning and memory, does not show overt injury but does demonstrate volume changes on imaging that correlate with cognitive and behavioral outcomes. Although there is extensive data regarding pathophysiological changes following moderate and severe HIE, there is a paucity of understanding regarding the extent, duration, and compensatory adaptations in the mild neonatal HIE brain. We performed hippocampal proteomic analysis using a swine model of mild neonatal hypoxia-asphyxia. Hippocampi were collected at 24 or 72 hours after injury, and proteomics was performed by liquid chromatography tandem mass spectrometry (LC-MS/MS). Pathway analysis demonstrated that several metabolic pathways are temporally regulated after mild HIE. Specifically, amino acid, carbohydrate, and one-carbon metabolism increased at 24 hours while fat metabolism and oxidative phosphorylation decreased at 24 hours. Downregulation of oxidative phosphorylation was more pronounced at 72 hours. Our data demonstrate that metabolic reprogramming occurs after mild HIE, and these changes persist up to 72 hours after injury. These results provide new evidence that mild HIE disrupts brain metabolism, emphasizing the need for a better understanding of the underlying pathophysiology of mild HIE and development of targeted therapeutic interventions for this population.

Novel peptidomimetic compounds attenuate hypoxic-ischemic brain injury in neonatal rats

Hypoxic-ischemic (HI) brain injury is a common neurological problem in neonates. The postsynaptic density protein-95 (PSD-95) is an excitatory synaptic scaffolding protein that regulates synaptic function, and represents a potential therapeutic target to attenuate HI brain injury. Syn3 and d-Syn3 are novel high affinity cyclic peptides that bind the PDZ3 domain of PSD-95. We investigated the neuroprotective efficacy of Syn3 and d-Syn3 after exposure to HI in neonatal rodents. Postnatal (P) day-7 rats were treated with Syn3 and d-Syn3 at zero, 24, and 48-h after carotid artery ligation and 90-min of 8 % oxygen. Hemispheric volume atrophy and Iba-1 positive microglia were quantified by cresyl violet and immunohistochemical staining. Treatment with Syn3 and d-Syn3 reduced tissue volume loss by 47.0 % and 41.0 % in the male plus female, and by 42.1 % and 65.0 % in the male groups, respectively. Syn3 reduced tissue loss by 52.3 % in females. D-Syn3 reduced Iba-1 positive microglia/DAPI ratios in the pooled group, males, and females. Syn3 effects were observed in the pooled group and females. Changes in Iba-1 positive microglia/DAPI cellular ratios correlated directly with reduced hemispheric volume loss, suggesting that Syn3 and d-Syn3 provide neuroprotection in part by their effects on Iba-1 positive microglia. The pathogenic cis phosphorylated Thr231 in Tau (cis P-tau) is a marker of neuronal injury. Cis P-tau was induced in cortical cells of the placebo-treated pooled group, males and females after HI, and reduced by treatment with d-Syn3. Therefore, treatment with these peptidomimetic agents exert neuroprotective effects after exposure of neonatal subjects to HI related brain injury.

Hypoxic-Ischemic Encephalopathy: Pathogenesis and Promising Therapies

Hypoxic-ischemic encephalopathy (HIE) is a brain lesion caused by inadequate blood supply and oxygen deprivation, often occurring in neonates. It has emerged as a grave complication of neonatal asphyxia, leading to chronic neurological damage. Nevertheless, the precise pathophysiological mechanisms underlying HIE are not entirely understood. This paper aims to comprehensively elucidate the contributions of hypoxia-ischemia, reperfusion injury, inflammation, oxidative stress, mitochondrial dysfunction, excitotoxicity, ferroptosis, endoplasmic reticulum stress, and apoptosis to the onset and progression of HIE. Currently, hypothermia therapy stands as the sole standard treatment for neonatal HIE, albeit providing only partial neuroprotection. Drug therapy and stem cell therapy have been explored in the treatment of HIE, exhibiting certain neuroprotective effects. Employing drug therapy or stem cell therapy as adjunctive treatments to hypothermia therapy holds great significance. This article presents a systematic review of the pathogenesis and treatment strategies of HIE, with the goal of enhancing the effect of treatment and improving the quality of life for HIE patients.

METTL3 inhibits microglial pyroptosis in neonatal hypoxia-ischemia encephalopathy by regulating GPR39 expression in an m6A-HuR-dependent manner

BACKGROUND

Neonatal hypoxia-ischemia encephalopathy (HIE) is a significant reason for neonatal mortality and prolonged disability. We have previously revealed that GPR39 activation attenuates neuroinflammation in a neonatal HIE rat model. This study aimed to investigate whether GPR39 affected microglial pyroptosis post-HIE.

METHODS

A neonatal rat model of HIE and a microglia cell model of oxygen-glucose deprivation (OGD) were established. Neuronal loss and cerebral infarction were assessed by using TTC, H&E staining, and Nissl staining. Pyroptosis was evaluated with western blot, LDH assay kit, ELISA, and flow cytometry. Total m6A level and GPR39 m6A modification were determined using m6A dot blot and MeRIP. The interaction between METTL3/HuR/GSK3β and GPR39 was analyzed by performing molecular interaction experiments. GPR39 mRNA stability was examined with actinomycin D.

RESULTS

The level of GPR39 was increased in neonatal HIE rats and OGD-treated microglia. Brain injury and neuronal loss were significantly increased in the HIE model when GPR39 was knocked down. GPR39 knockdown aggravated NLRP3 inflammasome-mediated microglial pyroptosis. METTL3 upregulated GPR39 expression in an m6A-dependent manner. METTL3 enhanced the interaction of HuR and GPR39. In OGD-exposed microglia, METTL3 elevated GPR39 expression and mRNA stability, which declined after HuR depletion. METTL3 knockdown promoted microglial pyroptosis, which was reversed by GPR39 agonist. Furthermore, microglial pyroptosis was inhibited by GPR39 upregulation, but the outcome was reverted by GSK3β activator SNP.

CONCLUSION

METTL3 inhibits microglial pyroptosis in neonatal HIE via regulating m6A-HuR dependent stabilization of GPR39, which contributes to therapeutics development for neonatal HIE.

The role of microglia in neuronal and cognitive function during high altitude acclimatization

Due to their interactions with the neurovasculature, microglia are implicated in maladaptive responses to hypobaric hypoxia at high altitude (HA). To explore these interactions at HA, pharmacological depletion of microglia with the colony-stimulating factor-1 receptor inhibitor, PLX5622, was employed in male C57BL/6J mice maintained at HA or sea level (SL) for 3-weeks, followed by assessment of ex-vivo hippocampal long-term potentiation (LTP), fear memory recall and microglial dynamics/physiology. Our findings revealed that microglia depletion decreased LTP and reduced glucose levels by 25% at SL but did not affect fear memory recall. At HA, the absence of microglia did not significantly alter HA associated deficits in fear memory or HA mediated decreases in peripheral glucose levels. In regard to microglial dynamics in the cortex, HA enhanced microglial surveillance activity, ablation of microglia resulted in increased chemotactic responses and decreased microglia tip proliferation during ball formation. In contrast, vessel ablation increased cortical microglia tip path tortuosity. In the hippocampus, changes in microglial dynamics were only observed in response to vessel ablation following HA. As the hippocampus is critical for learning and memory, poor hippocampal microglial context-dependent adaptation may be responsible for some of the enduring neurological deficits associated with HA.

Role of Natural Compounds Modulating Heme Catabolic Pathway in Gut, Liver, Cardiovascular, and Brain Diseases

The crucial physiological process of heme breakdown yields biliverdin (BV) and bilirubin (BR) as byproducts. BV, BR, and the enzymes involved in their production (the "yellow players-YP") are increasingly documented as endogenous modulators of human health. Mildly elevated serum bilirubin concentration has been correlated with a reduced risk of multiple chronic pro-oxidant and pro-inflammatory diseases, especially in the elderly. BR and BV per se have been demonstrated to protect against neurodegenerative diseases, in which heme oxygenase (HMOX), the main enzyme in the production of pigments, is almost always altered. HMOX upregulation has been interpreted as a tentative defense against the ongoing pathologic mechanisms. With the demonstration that multiple cells possess YP, their propensity to be modulated, and their broad spectrum of activity on multiple signaling pathways, the YP have assumed the role of an adjustable system that can promote health in adults. Based on that, there is an ongoing effort to induce their activity as a therapeutic option, and natural compounds are an attractive alternative to the goal, possibly requiring only minimal changes in the life style. We review the most recent evidence of the potential of natural compounds in targeting the YP in the context of the most common pathologic condition of adult and elderly life.

Microglia dynamic response and phenotype heterogeneity in neural regeneration following hypoxic-ischemic brain injury

Hypoxic-ischemic brain injury poses a significant threat to the neural niche within the central nervous system. In response to this pathological process, microglia, as innate immune cells in the central nervous system, undergo rapid morphological, molecular and functional changes. Here, we comprehensively review these dynamic changes in microglial response to hypoxic-ischemic brain injury under pathological conditions, including stroke, chronic intermittent hypoxia and neonatal hypoxic-ischemic brain injury. We focus on the regulation of signaling pathways under hypoxic-ischemic brain injury and further describe the process of microenvironment remodeling and neural tissue regeneration mediated by microglia after hypoxic-ischemic injury.

The RNA m6A modification might participate in microglial activation during hypoxic-ischemic brain damage in neonatal mice

BACKGROUND

The RNA m6A modification has been implicated in multiple neurological diseases as well as macrophage activation. However, whether it regulates microglial activation during hypoxic-ischemic brain damage (HIBD) in neonates remains unknown. Here, we aim to examine whether the m6A modification is involved in modulating microglial activation during HIBD. We employed an oxygen and glucose deprivation microglial model for in vitro studies and a neonatal mouse model of HIBD. The brain tissue was subjected to RNA-seq to screen for significant changes in the mRNA m6A regulator. Thereafter, we performed validation and bioinformatics analysis of the major m6A regulators.

RESULTS

RNA-seq analysis revealed that, among 141 m6A regulators, 31 exhibited significant differential expression (FC (abs) ≥ 2) in HIBD mice. We then subjected the major m6A regulators Mettl3, Mettl14, Fto, Alkbh5, Ythdf1, and Ythdf2 to further validation, and the results showed that all were significantly downregulated in vitro and in vivo. GO analysis reveals that regulators are mainly involved in the regulation of cellular and metabolic processes. The KEGG results indicate the involvement of the signal transduction pathway.

CONCLUSIONS

Our findings demonstrate that m6A modification of mRNA plays a crucial role in the regulation of microglial activation in HIBD, with m6A-associated regulators acting as key modulators of microglial activation.

Hypothermia Does Not Boost the Neuroprotection Promoted by Umbilical Cord Blood Cells in a Neonatal Hypoxia-Ischemia Rat Model

Neonatal hypoxic-ischemic encephalopathy (HIE) is one of the leading causes of death and long-term disability in the perinatal period. Currently, therapeutic hypothermia is the standard of care for this condition with modest efficacy and strict enrollment criteria. Therapy with umbilical cord blood cells (UCBC) has come forward as a strong candidate for the treatment of neonatal HIE, but no preclinical studies have yet compared the action of UCBC combined with hypothermia (HT) with the action of each therapy by itself. Thus, to evaluate the potential of each therapeutic approach, a hypoxic-ischemic brain lesion was induced in postnatal day ten rat pups; two hours later, HT was applied for 4 h; and 24, 48, and 72 h post-injury, UCBC were administered intravenously. The neonatal hypoxic-ischemic injury led to a brain lesion involving about 48% of the left hemisphere that was not improved by HT (36%) or UCBC alone (28%), but only with the combined therapies (25%; p = 0.0294). Moreover, a decrease in glial reactivity and improved functional outcomes were observed in both groups treated with UCBC. Overall, these results support UCBC as a successful therapeutic approach for HIE, even when treatment with therapeutic hypothermia is not possible.

Ambient Temperature Is Correlated With the Severity of Neonatal Hypoxic-Ischemic Brain Injury via Microglial Accumulation in Mice

BACKGROUND

The pathophysiology of neonatal hypoxic-ischemic encephalopathy (HIE) has been studied in several rodent models to develop novel treatments. Although it is well known that high ambient temperature results in severe HIE, the effect of subtle changes in ambient temperature during a hypoxic-ischemic (HI) insult has not been studied. Therefore, in order to clarify the difference of pathophysiological change among the HIE models due to the influence of small changes in chamber temperature, three-step gradual change of 0.5°C each were prepared in ambient temperature during hypoxic exposure.

METHODS

Blood flow in the left common carotid artery (CCA) of neonatal mice was interrupted using bipolar electronic forceps under general and local anesthesia. The mice were subsequently subjected to 10% hypoxic exposure for 50 min at 36.0, 36.5, or 37.0°C. A control group was also included in the study. The size of the striatum and hippocampus and the volume reduction rate of the hemisphere in the section containing them on the ischemic side were evaluated using microtubule associated protein 2 (MAP2) immunostaining. The accumulation of Iba1-positive cells was investigated to assess inflammation. Additionally, rotarod and open-field tests were performed 2 weeks after HI insult to assess its effect on physiological conditions.

RESULTS

MAP2 staining revealed that the higher the temperature during hypoxia, the more severe the volume reduction rate in the hemisphere, striatum, and hippocampus. The number of Iba1-positive cells in the ipsilateral lesion gradually increased with increasing temperature, and there was a significant difference in motor function in the 36.5 and 37.0°C groups compared with the sham group. In the open-field tests, there was a significant decrease in performance in the 37.0°C groups compared with the 36.0°C and sham groups.

CONCLUSIONS

Even a small gradual change of 0.5°C produced a significant difference in pathological and behavioral changes and contributed to the accumulation of Iba1-positive cells. The arrangement of ambient temperature is useful for creating a rodent model with the appropriate severity of the targeted neuropsychological symptoms to establish a novel therapy for HIE.