Long-term changes in metabolic brain network drive memory impairments in rats following neonatal hypoxia-ischemia

Lactate administration causes long-term neuroprotective effects following neonatal hypoxia-ischemia

Neonatal hypoxia-ischemia (HI) is one of the main causes of mortality and long-term disabilities in newborns, and the only clinical approach to treat this condition is therapeutic hypothermia, which shows some limitations. Thus, putative neuroprotective agents have been tested in animal models of HI. Lactate is a preferential metabolic substrate of the neonatal brain and has already been shown to produce beneficial neuroprotective outcomes in neonatal animals exposed to HI. Here, we administered lactate as a treatment in neonatal rats previously exposed to HI and evaluated the impact of this treatment in adulthood. Seven-day-old (P7) male and female Wistar rats underwent permanent common right carotid occlusion combined with an exposition to a hypoxic atmosphere (8% oxygen) for 60 min. Animals were assigned to one of four experimental groups: HI, HI+LAC, SHAM, SHAM+LAC. Lactate was administered intraperitoneally 30 min and 2 h after hypoxia in HI+LAC and SHAM+LAC groups, whereas HI and SHAM groups received vehicle. Animals were tested in the behavioral tasks of negative geotaxis and righting reflex (P8), cylinder test (P24), and the modified neurological severity score was calculated (P25). Open field (OF), and novel object recognition (NOR) were evaluated in adulthood. Animals were killed at P60, and the brains were harvested and processed to evaluate the volume of brain injury. Our results showed that lactate administration reduced the volume of brain lesion and improved sensorimotor and cognitive behaviors in neonatal, juvenile, and adult life in HI animals from both sexes. Thus, lactate administration might be considered as a potential neuroprotective strategy for the treatment of neonatal HI, which is a prevalent disorder affecting newborns.

Unraveling the Triad: Hypoxia, Oxidative Stress and Inflammation in Neurodegenerative Disorders

The mammalian brain's complete dependence on oxygen for ATP production makes it highly susceptible to hypoxia, at high altitudes or in clinical scenarios including anemia or pulmonary disease. Hypoxia plays a crucial role in the development of various brain disorders, such as Alzheimer's, Parkinson's, and other age-related neurodegenerative diseases. On the other hand, a decrease in environmental oxygen levels, such as prolonged stays at high elevations, may have beneficial impacts on the process of ageing and the likelihood of death. Additionally, the utilization of controlled hypoxia exposure could potentially serve as a therapeutic approach for age-related brain diseases. Recent findings indicate that the involvement of HIF-1α and the NLRP3 inflammasome is of significant importance in the development of Alzheimer's disease. HIF-1α serves as a pivotal controller of various cellular reactions to oxygen deprivation, exerting influence on a multitude of physiological mechanisms such as energy metabolism and inflammatory responses. The NLRP3 plays a crucial role in the innate immune system by coordinating the initiation of inflammatory reactions through the assembly of the inflammasome complex. This review examines the information pertaining to the contrasting effects of hypoxia on the brain, highlighting both its positive and deleterious effects and molecular pathways that are involved in mediating these different effects. This study explores potential strategies for therapeutic intervention that focus on restoring cellular balance and reducing neuroinflammation, which are critical aspects in addressing this severe neurodegenerative condition and addresses crucial inquiries that warrant further future investigations.

Effect of Early Inhibition of Toll-Like Receptor 4 on Hippocampal Plasticity in a Neonatal Rat Model of Hypoxic-Ischemic Brain Damage

Hippocampal plasticity is closely related to physiological brain functions such as learning and memory. However, the effect of toll-like receptor 4 (TLR4) activation on hippocampal plasticity after neonatal hypoxic-ischaemic brain damage (HIBD) remains unclear. In our study, seven-day-old rat pups were randomly categorised into three groups: control, hypoxic-ischemia (HI), and HI + TAK-242 (TAK-242). The pups were ligated in the left common carotid artery and then subjected to hypoxia to establish the neonatal HIBD model.The expression of the TLR4 in the left hippocampus of the HI group was increased compared to the control group, while TAK-242 reduced the expression level at 3 days after HIBD. Additionally, TAK-242 reversed the increased Zea-Longa score, increased the left/right hippocampal weight ratio, and increased the number of Nissl-positive neurons in the hippocampal CA1 region compared to HI group at 3 days after HIBD. Pre-injection of TAK-242 alleviated the decrease in PSD95, Aggrecan and NR1, BDNF, CREB, and pCREB expression in the hippocampus at 24 h after HIBD. It also alleviated the decrease in PSD95, BDNF, and NR2A/NR1 expression in the hippocampus at 7 days after HIBD. Furthermore, Pre-injection of TAK-242 alleviated the decrease in NR2A/NR1 expression at 21 days after HIBD. Finally,TAK-242 increased the percentage of third-grade dendritic mushroom spines processes in the basal and apical segments of neurons in the hippocampal CA1 region at 21 days after HIBD.Therefore, we conclude that preinhibition of TLR4 prior to neonatal HIBD improved the plasticity of the hippocampus.

Lactate Protects Microglia and Neurons from Oxygen-Glucose Deprivation/Reoxygenation

Lactate has received attention as a potential therapeutic intervention for brain diseases, particularly those including energy deficit, exacerbated inflammation, and disrupted redox status, such as cerebral ischemia. However, lactate roles in metabolic or signaling pathways in neural cells remain elusive in the hypoxic and ischemic contexts. Here, we tested the effects of lactate on the survival of a microglial (BV-2) and a neuronal (SH-SY5Y) cell lines during oxygen and glucose deprivation (OGD) or OGD followed by reoxygenation (OGD/R). Lactate signaling was studied by using 3,5-DHBA, an exogenous agonist of lactate receptor GPR81. Inhibition of lactate dehydrogenase (LDH) or monocarboxylate transporters (MCT), using oxamate or 4-CIN, respectively, was performed to evaluate the impact of lactate metabolization and transport on cell viability. The OGD lasted 6 h and the reoxygenation lasted 24 h following OGD (OGD/R). Cell viability, extracellular lactate concentrations, microglial intracellular pH and TNF-ɑ release, and neurite elongation were evaluated. Lactate or 3,5-DHBA treatment during OGD increased microglial survival during reoxygenation. Inhibition of lactate metabolism and transport impaired microglial and neuronal viability. OGD led to intracellular acidification in BV-2 cells, and reoxygenation increased the release of TNF-ɑ, which was reverted by lactate and 3,5-DHBA treatment. Our results suggest that lactate plays a dual role in OGD, acting as a metabolic and a signaling molecule in BV-2 and SH-SY5Y cells. Lactate metabolism and transport are vital for cell survival during OGD. Moreover, lactate treatment and GPR81 activation during OGD promote long-term adaptations that potentially protect cells against secondary cell death during reoxygenation.

Resveratrol Reduces Neuroinflammation and Hippocampal Microglia Activation and Protects Against Impairment of Memory and Anxiety-Like Behavior in Experimental Cerebral Palsy

Cerebral palsy (CP) is a neurodevelopmental disorder characterized by motor and postural impairments. However, early brain injury can promote deleterious effects on the hippocampus, impairing memory. This study aims to investigate the effects of resveratrol treatment on memory, anxiety-like behavior, and neuroinflammation markers in rats with CP. Male Wistar rats were subjected to perinatal anoxia (P0-P1) and sensory-motor restriction (P2-P28). They were treated with resveratrol (10 mg/kg, 0.1 ml/100 g) or saline from P3-P21, being divided into four experimental groups: CS (n = 15), CR (n = 15), CPS (n = 15), and CPR (n = 15). They were evaluated in the tests of novel object recognition (NORT), T-Maze, Light-Dark Box (LDB), and Elevated Plus Maze (EPM). Compared to the CS group, the CPS group has demonstrated a reduced discrimination index on the NORT (p < 0.0001) and alternation on the T-Maze (p < 0.01). In addition, the CPS group showed an increase in permanence time on the dark side in LDB (p < 0.0001) and on the close arms of the EPM (p < 0.001). The CPR group demonstrated an increase in the object discrimination index (p < 0.001), on the alternation (p < 0.001), on the permanence time on the light side (p < 0.0001), and on the open arms (p < 0.001). The CPR group showed a reduction in gene expression of IL-6 (p = 0.0175) and TNF-α (p = 0.0007) and an increase in Creb-1 levels (p = 0.0020). The CPS group showed an increase in the activated microglia and a reduction in cell proliferation in the hippocampus, while CPR animals showed a reduction of activated microglia and an increase in cell proliferation. These results demonstrate promising effects of resveratrol in cerebral palsy behavior impairment through reduced neuroinflammation in the hippocampus.

Identification of hypoxia- and immune-related biomarkers in patients with ischemic stroke

Background

The immune microenvironment and hypoxia play crucial roles in the pathophysiology of ischemic stroke (IS). Hence, in this study, we aimed to identify hypoxia- and immune-related biomarkers in IS.

Methods

The IS microarray dataset GSE16561 was examined to determine differentially expressed genes (DEGs) utilizing bioinformatics-based analysis. The intersection of hypoxia-related genes and DEGs was conducted to identify differentially expressed hypoxia-related genes (DEHRGs). Then, using weighted correlation network analysis (WGCNA), all of the genes in GSE16561 dataset were examined to create a co-expression network, and module-clinical trait correlations were examined for the purpose of examining the genes linked to immune cells. The immune-related DEHRGs were submitted to gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses. A protein-protein interaction (PPI) network was constructed by Cytoscape plugin MCODE, in order to extract hub genes. The miRNet was used to predict hub gene-related transcription factors (TFs) and miRNAs. Finally, a diagnostic model was developed by least absolute shrinkage and selection operator (LASSO) logistic regression.

Results

Between the control and IS samples, 4171 DEGs were found. Thereafter, the intersection of hypoxia-related genes and DEGs was conducted to obtain 45 DEHRGs. Ten significantly differentially infiltrated immune cells were found-namely, CD56dim natural killer cells, activated CD8 T cells, activated dendritic cells, activated B cells, central memory CD8 T cells, effector memory CD8 T cells, natural killer cells, gamma delta T cells, plasmacytoid dendritic cells, and neutrophils-between IS and control samples. Subsequently, we identified 27 immune-related DEHRGs through the intersection of DEHRGs and genes in important modules of WGCNA. The immune-related DEHRGs were primarily enriched in response to hypoxia, cellular polysaccharide metabolic process, response to decreased oxygen levels, polysaccharide metabolic process, lipid and atherosclerosis, and HIF-1 signaling pathway H. Using MCODE, FOS, DDIT3, DUSP1, and NFIL3 were found to be hub genes. In the validation cohort and training set, the AUC values of the diagnostic model were 0.9188034 and 0.9395085, respectively.

Conclusion

In brief, we identified and validated four hub genes-FOS, DDIT3, DUSP1, and NFIL3-which might be involved in the pathological development of IS, potentially providing novel perspectives for the diagnosis and treatment of IS.

HIF-1α promotes astrocytic production of macrophage migration inhibitory factor following spinal cord injury

BACKGROUND

Macrophage migration inhibitory factor (MIF) is an important mediator of neuropathology in various central nervous system (CNS) diseases. However, little is known about its inducers for production from the nerve cells, as well as the underlying regulatory mechanism. Injury-induced HIF-1α has been shown to exacerbate neuroinflammation by activating multiple downstream target molecules. It is postulated that HIF-1α is involved in the regulation of MIF following spinal cord injury (SCI).

METHODS

SCI model of Sprague-Dawley rats was established by cord contusion at T8-T10. The dynamic changes of HIF-1α and MIF protein levels at lesion site of rat spinal cord were determined by Western blot. The specific cell types of HIF-1α and MIF expression were examined by immunostaining. Primary astrocytes were isolated from the spinal cord, cultured and stimulated with various agonist or inhibitor of HIF-1α for analysis of HIF-1α-mediated expression of MIF. Luciferase report assay was used to determine the relationship between HIF-1α and MIF. The Basso, Beattie, and Bresnahan (BBB) locomotor scale was used to assess the locomotor function following SCI.

RESULTS

The protein levels of HIF-1α and MIF at lesion site were significantly elevated by SCI. Immunofluorescence demonstrated that both HIF-1α and MIF were abundantly expressed in the astrocytes of the spinal cord. By using various agonists or inhibitors of HIF-1α, it was shown that HIF-1α sufficiently induced astrocytic production of MIF. Mechanistically, HIF-1α promoted MIF expression through interaction with MIF promoter. Inhibition of HIF-1α activity using specific inhibitor markedly reduced the protein levels of MIF at lesion site following SCI, which in turn favored for the functional recovery.

CONCLUSION

SCI-induced activation of HIF-1α is able to promote MIF production from astrocytes. Our results have provided new clues for SCI-induced production of DAMPs, which may be helpful for clinical treatment of neuroinflammation.

Early Neuroprotective Effects of Bovine Lactoferrin Associated with Hypothermia after Neonatal Brain Hypoxia-Ischemia in Rats

Neonatal hypoxic-ischemic (HI) encephalopathy (HIE) in term newborns is a leading cause of mortality and chronic disability. Hypothermia (HT) is the only clinically available therapeutic intervention; however, its neuroprotective effects are limited. Lactoferrin (LF) is the major whey protein in milk presenting iron-binding, anti-inflammatory and anti-apoptotic properties and has been shown to protect very immature brains against HI damage. We hypothesized that combining early oral administration of LF with whole body hypothermia could enhance neuroprotection in a HIE rat model. Pregnant Wistar rats were fed an LF-supplemented diet (1 mg/kg) or a control diet from (P6). At P7, the male and female pups had the right common carotid artery occluded followed by hypoxia (8% O2 for 60') (HI). Immediately after hypoxia, hypothermia (target temperature of 32.5-33.5 °C) was performed (5 h duration) using Criticool®. The animals were divided according to diet, injury and thermal condition. At P8 (24 h after HI), the brain neurochemical profile was assessed using magnetic resonance spectroscopy (1H-MRS) and a hyperintense T2W signal was used to measure the brain lesions. The mRNA levels of the genes related to glutamatergic excitotoxicity, energy metabolism and inflammation were assessed in the right hippocampus. The cell markers and apoptosis expression were assessed using immunofluorescence in the right hippocampus. HI decreased the energy metabolites and increased lactate. The neuronal-astrocytic coupling impairments observed in the HI groups were reversed mainly by HT. LF had an important effect on astrocyte function, decreasing the levels of the genes related to glutamatergic excitotoxicity and restoring the mRNA levels of the genes related to metabolic support. When combined, LF and HT presented a synergistic effect and prevented lactate accumulation, decreased inflammation and reduced brain damage, pointing out the benefits of combining these therapies. Overall, we showed that through distinct mechanisms lactoferrin can enhance neuroprotection induced by HT following neonatal brain hypoxia-ischemia.

Gestational hypoxia in late pregnancy differentially programs subcortical brain maturation in male and female rat offspring

BACKGROUND

Hypoxia is associated with pregnancy complications, such as preeclampsia, placental abruption, and gestational sleep apnea. Hypoxic insults during gestation can impact the brain maturation of cortical and subcortical pathways, such as the nigrostriatal pathway. However, the long-term effects of in utero hypoxic stress exposure on brain maturation in offspring are unclear, especially exposure during late gestation. The purpose of this study was to determine the impact of gestational hypoxia in late pregnancy on developmental programming of subcortical brain maturation by focusing on the nigrostriatal pathway.

METHODS

Timed pregnant Long-Evans rats were exposed to chronic intermittent hypoxia or room air normoxia from gestational day (GD) 15-19 (term 22-23 days). Male and female offspring were assessed during two critical periods: puberty from postnatal day (PND) 40-45 or young adulthood (PND 60-65). Brain maturation was quantified by examining (1) the structural development of the nigrostriatal pathway via analysis of locomotor behaviors and the substantia nigra dopaminergic neuronal cell bodies and (2) the refinement of the nigrostriatal pathway by quantifying ultrasonic vocalizations (USVs).

RESULTS

The major findings of this study are gestational hypoxia has age- and sex-dependent effects on subcortical brain maturation in offspring by adversely impacting the refinement of the nigrostriatal pathway in the absence of any effects on the structural development of the pathway. During puberty, female offspring were impacted more than male offspring, as evidenced by decreased USV call frequency, chirp USV call duration, and simple call frequency. In contrast, male offspring were impacted more than female offspring during young adulthood, as evidenced by increased latency to first USV, decreased simple USV call intensity, and increased harmonic USV call bandwidth. No effects of gestational hypoxia on the structural development of the nigrostriatal pathway were observed.

CONCLUSIONS

These novel findings demonstrate hypoxic insults during pregnancy mediate developmental programming of the cortical and subcortical pathways, in which male offspring exhibit long-term adverse effects compared to female offspring. Impairment of cortical and subcortical pathways maturation, such as the nigrostriatal pathway, may increase risk for neuropsychiatric disorders (e.g., mood disorders, cognitive dysfunction, brain connectivity dysfunction).

Plinia trunciflora Extract Administration Prevents HI-Induced Oxidative Stress, Inflammatory Response, Behavioral Impairments, and Tissue Damage in Rats

The disruption of redox homeostasis and neuroinflammation are key mechanisms in the pathogenesis of brain hypoxia–ischemia (HI); medicinal plants have been studied as a therapeutic strategy, generally associated with the prevention of oxidative stress and inflammatory response. This study evaluates the neuroprotective role of the Plinia trunciflora fruit extract (PTE) in neonatal rats submitted to experimental HI. The HI insult provoked a marked increase in the lipoperoxidation levels and glutathione peroxidase (GPx) activity, accompanied by a decrease in the brain concentration of glutathione (GSH). Interestingly, PTE was able to prevent most of the HI-induced pro-oxidant effects. It was also observed that HI increased the levels of interleukin-1β in the hippocampus, and that PTE-treatment prevented this effect. Furthermore, PTE was able to prevent neuronal loss and astrocyte reactivity induced by HI, as demonstrated by NeuN and GFAP staining, respectively. PTE also attenuated the anxiety-like behavior and prevented the spatial memory impairment caused by HI. Finally, PTE prevented neural tissue loss in the brain hemisphere, the hippocampus, cerebral cortex, and the striatum ipsilateral to the HI. Taken together our results provide good evidence that the PTE extract has the potential to be investigated as an adjunctive therapy in the treatment of brain insult caused by neonatal hypoxia–ischemia.

Hypoxia-Inducible Factor (HIF) in Ischemic Stroke and Neurodegenerative Disease

Hypoxia is one of the most common pathological conditions, which can be induced by multiple events, including ischemic injury, trauma, inflammation, tumors, etc. The body's adaptation to hypoxia is a highly important phenomenon in both health and disease. Most cellular responses to hypoxia are associated with a family of transcription factors called hypoxia-inducible factors (HIFs), which induce the expression of a wide range of genes that help cells adapt to a hypoxic environment. Basic mechanisms of adaptation to hypoxia, and particularly HIF functions, have being extensively studied over recent decades, leading to the 2019 Nobel Prize in Physiology or Medicine. Based on their pivotal physiological importance, HIFs are attracting increasing attention as a new potential target for treating a large number of hypoxia-associated diseases. Most of the experimental work related to HIFs has focused on roles in the liver and kidney. However, increasing evidence clearly demonstrates that HIF-based responses represent an universal adaptation mechanism in all tissue types, including the central nervous system (CNS). In the CNS, HIFs are critically involved in the regulation of neurogenesis, nerve cell differentiation, and neuronal apoptosis. In this mini-review, we provide an overview of the complex role of HIF-1 in the adaptation of neurons and glia cells to hypoxia, with a focus on its potential involvement into various neuronal pathologies and on its possible role as a novel therapeutic target.

Pregnancy swimming prevents early brain mitochondrial dysfunction and causes sex-related long-term neuroprotection following neonatal hypoxia-ischemia in rats

Neonatal hypoxia-ischemia (HI) is a major cause of cognitive impairments in infants. Antenatal strategies improving the intrauterine environment can have high impact decreasing pregnancy-derived intercurrences. Physical exercise alters the mother-fetus unity and has been shown to prevent the energetic challenge imposed by HI. This study aimed to reveal neuroprotective mechanisms afforded by pregnancy swimming on early metabolic failure and late cognitive damage, considering animals' sex as a variable. Pregnant Wistar rats were submitted to daily swimming exercise (20' in a tank filled with 32 °C water) during pregnancy. Neonatal HI was performed in male and female pups at postnatal day 7. Electron chain transport, mitochondrial mass and function and ROS formation were assessed in the right brain hemisphere 24 h after HI. From PND45, reference and working spatial memory were tested in the Morris water maze. MicroPET-FDG images were acquired 24 h after injury (PND8) and at PND60, following behavioral analysis. HI induced early energetic failure, decreased enzymatic activity in electron transport chain, increased production of ROS in cortex and hippocampus as well as caused brain glucose metabolism dysfunction and late cognitive impairments. Maternal swimming was able to prevent mitochondrial dysfunction and to improve spatial memory. The intergenerational effects of swimming were sex-specific, since male rats were benefited most. In conclusion, maternal swimming was able to affect the mitochondrial response to HI in the offspring's brains, preserving its function and preventing cognitive damage in a sex-dependent manner, adding relevant information on maternal exercise neuroprotection and highlighting the importance of mitochondria as a therapeutic target for HI neuropathology.

Pre- and early postnatal enriched environmental experiences prevent neonatal hypoxia-ischemia late neurodegeneration via metabolic and neuroplastic mechanisms

Prenatal and early postnatal periods are important for brain development and neural function. Neonatal insults such as hypoxia-ischemia (HI) causes prolonged neural and metabolic dysregulation, affecting central nervous system maturation. There is evidence that brain hypometabolism could increase the risk of adult-onset neurodegenerative diseases. However, the impact of non-pharmacologic strategies to attenuate HI-induced brain glucose dysfunction is still underexplored. This study investigated the long-term effects of early environmental enrichment in metabolic, cell, and functional responses after neonatal HI. Thereby, male Wistar rats were divided according to surgical procedure, sham, and HI (performed at postnatal day 3), and the allocation to standard (SC) or enriched condition (EC) during gestation and lactation periods. In-vivo cerebral metabolism was assessed by means of [¹⁸ F]-FDG micro-positron emission tomography, and cognitive, biochemical, and histological analyses were performed in adulthood. Our findings reveal that HI causes a reduction in glucose metabolism and glucose transporter levels as well as hyposynchronicity in metabolic brain networks. However, EC during prenatal or early postnatal period attenuated these metabolic disturbances. A positive correlation was observed between [¹⁸ F]-FDG values and volume ratios in adulthood, indicating that preserved tissue by EC is metabolically active. EC promotes better cognitive scores, as well as down-regulation of amyloid precursor protein in the parietal cortex and hippocampus of HI animals. Furthermore, growth-associated protein 43 was up-regulated in the cortex of EC animals. Altogether, results presented support that EC during gestation and lactation period can reduce HI-induced impairments that may contribute to functional decline and progressive late neurodegeneration.

The Function of the NMDA Receptor in Hypoxic-Ischemic Encephalopathy

Hypoxic-ischemic encephalopathy (HIE) is one of the main forms of neonatal brain injury which could lead to neonatal disability or even cause neonatal death. Therefore, HIE strongly affects the health of newborns and brings heavy burden to the family and society. It has been well studied that N-methyl-D-aspartate (NMDA) receptors are involved in the excitotoxicity induced by hypoxia ischemia in adult brain. Recently, it has been shown that the NMDA receptor also plays important roles in HIE. In the present review, we made a summary of the molecular mechanism of NMDA receptor in the pathological process of HIE, focusing on the distinct role of GluN2A- and GluN2B-containing NMDA receptor subtypes and aiming to provide some insights into the clinical treatment and drug development of HIE.