Perinatal Asphyxia and Brain Development: Mitochondrial Damage Without Anatomical or Cellular Losses

Consequences of Early Maternal Deprivation on Neuroinflammation and Mitochondrial Dynamics in the Central Nervous System of Male and Female Rats

Early life stress (ELS) is associated with an increased risk for neuropsychiatric disorders, and both neuroinflammation and mitochondrial dysfunction seem to be central to mental health. Herein, using an animal model of ELS, a single episode of maternal deprivation (MD, 24 h on pnd 9) extensively documented to elicit behavioural anomalies in male and female Wistar rats, we investigated its consequences in terms of neuroinflammation and mitochondrial dynamics in the prefrontal cortex (PFC) and the hippocampal formation (HCF). MD differentially affected the brain content of cytokines: MD induced a transient increase in pro-inflammatory cytokines (IL-1β and IL-6) in the PFC, as well as in the levels of the anti-inflammatory cytokine IL-10 in the HCF. MD also induced a significant decrease mitochondria citrate synthase activity, but MD did not exert significant changes in mitochondria Complex IV activity, revealing a generalized decrease in mitochondrial density without any change in mitochondrial respiration. In the present study, we demonstrate that MD induces neuroinflammatory processes in specific brain regions. Additional research is needed to better understand the temporal pattern of such changes, their impact on the developing brain, and their participation in the already well-known behavioural consequences of MD.

Spontaneous running wheel exercise during pregnancy prevents later neonatal-anoxia-induced somatic and neurodevelopmental alterations

Introduction

About 15-20 % of babies that suffer perinatal asphyxia die and around 25 % of the survivors exhibit permanent neural outcomes. Minimization of this global health problem has been warranted. This study investigated if the offspring of pregnant female rats allowed to spontaneously exercise on running wheels along a 11-day pregnancy period were protected for somatic and neurodevelopmental disturbs that usually follow neonatal anoxia.

Methods

spontaneous exercise was applied to female rats which were housed in cages allowing free access to running wheels along a 11-day pregnancy period. Their offspring were submitted to anoxia 24-36 h after birth. Somatic and sensory-motor development of the pups were recorded until postnatal day 21 (P21). Myelin basic protein (MBP)-stained areas of sensory and motor cortices were measured at P21. Neuronal nuclei (NeuN)-immunopositive cells and synapsin-I levels in hippocampal formation were estimated at P21 and P75.

Results

gestational exercise and / or neonatal anoxia increased the weight and the size of the pups. In addition, gestational exercise accelerated somatic and sensory-motor development of the pups and protected them against neonatal-anoxia-induced delay in development. Further, neonatal anoxia reduced MBP stained area in the secondary motor cortex and decreased hippocampal neuronal estimates and synapsin-I levels at P21; gestational exercise prevented these effects. Therefore, spontaneous exercise along pregnancy is a valuable strategy to prevent neonatal-anoxia-induced disturbs in the offspring.

Conclusion

spontaneous gestational running wheel exercise protects against neonatal anoxia-induced disturbs in the offspring, including (1) physical and neurobehavioral developmental impairments, and (2) hippocampal and cortical changes. Thus, spontaneous exercise during pregnancy may represent a valuable strategy to prevent disturbs which usually follow neonatal anoxia.

HSPB1 overexpression improves hypoxic-ischemic brain damage by attenuating ferroptosis in rats through promoting G6PD expression

Heat-shock protein B (HSPB1) has a neuroprotective effect on brain injury and is a negative regulator of ferroptosis. Therefore, we infer that HSPB1 plays a protective role in hypoxic-ischemic (HI) brain damage by inhibiting ferroptosis. A neonatal rat model of hypoxic-ischemic (HI) brain damage was established. HSPB1 overexpression plasmid and the negative control were injected into the lateral ventricle of rats 48 h before HI brain damage surgery. HSPB1 and glucose-6-phosphate dehydrogenase (G6PD) levels, infarction rate, iron accumulation, apoptosis, and ferroptosis-related markers were estimated with the assistance of qRT-PCR, 2,3,5-triphenyl tetrazolium chloride (TTC) staining, Prussian blue staining, iron assay kit, TUNEL staining, and Western blot. In vitro, after transfection, HSPB1 and G6PD levels, oxygen-glucose deprivation (OGD)-mediated hippocampal neuron cell viability, apoptosis, iron content, and ferroptosis-related markers were assessed using qRT-PCR, MTT, flow cytometry, iron assay kit, and Western blot. HSPB1 and G6PD were overexpressed in the hippocampus tissues of HI rats. High expression of HSPB1 in HI rats lessened infarction rate and ferritin level, hindered iron accumulation and apoptosis, and promoted GPX4, SLC7A11, and TFR1 levels. In OGD-mediated hippocampal neuron cells, HSPB1 upregulation intensified the viability and repressed apoptosis and ferroptosis, whereas G6PD silencing reversed the effects of HSPB1 upregulation. We documented that HSPB1 overexpression unleashes neuroprotective effects via modulating G6PD expression, which offers a novel target for the prevention and treatment of HI brain damage.NEW & NOTEWORTHY HSPB1 and G6PD were overexpressed in the hippocampus tissues of HI rats. High expression of HSPB1 in HI rats mitigated infarction rate and iron accumulation. HSPB1 overexpression reduced ferritin level, attenuated apoptosis, yet augmented GPX4, SLC7A11, and TFR1 levels in the hippocampus tissues of HI rats. G6PD deletion impaired the protective role of HSPB1 overexpression against HI brain damage-induced ferroptosis.

Cognitive Impairments and blood-brain Barrier Damage in a Mouse Model of Chronic Cerebral Hypoperfusion

Chronic cerebral hypoperfusion (CCH) is commonly involved in various brain diseases. Tight junction proteins (TJs) are key components constituting the anatomical substrate of the blood-brain barrier (BBB). Changes in cognitive function and BBB after CCH and their relationship need further exploration. To investigate the effect of CCH on cognition and BBB, we developed a bilateral common carotid artery stenosis (BCAS) model in Tie2-GFP mice. Mice manifested cognitive impairments accompanied with increased microglia after the BCAS operation. BCAS mice also exhibited increased BBB permeability at all time points set from D1 to D42. Furthermore, BCAS mice showed reduced expression of TJs 42 d after the operation. In addition, correct entrances of mice in radial arm maze test had a moderate negative correlation with EB extravasation. Our data suggested that BCAS could lead to cognitive deficits, microglia increase and BBB dysfunction characterized by increased BBB permeability and reduced TJs expression level. BBB permeability may be involved in the cognitive impairments induced by CCH.

Revealing the Impact of Mitochondrial Fitness During Early Neural Development Using Human Brain Organoids

Mitochondrial homeostasis -including function, morphology, and inter-organelle communication- provides guidance to the intrinsic developmental programs of corticogenesis, while also being responsive to environmental and intercellular signals. Two- and three-dimensional platforms have become useful tools to interrogate the capacity of cells to generate neuronal and glia progeny in a background of metabolic dysregulation, but the mechanistic underpinnings underlying the role of mitochondria during human neurogenesis remain unexplored. Here we provide a concise overview of cortical development and the use of pluripotent stem cell models that have contributed to our understanding of mitochondrial and metabolic regulation of early human brain development. We finally discuss the effects of mitochondrial fitness dysregulation seen under stress conditions such as metabolic dysregulation, absence of developmental apoptosis, and hypoxia; and the avenues of research that can be explored with the use of brain organoids.

The Effects of In Utero Fetal Hypoxia and Creatine Treatment on Mitochondrial Function in the Late Gestation Fetal Sheep Brain

Near-term acute hypoxia in utero can result in significant fetal brain injury, with some brain regions more vulnerable than others. As mitochondrial dysfunction is an underlying feature of the injury cascade following hypoxia, this study is aimed at characterizing mitochondrial function at a region-specific level in the near-term fetal brain after a period of acute hypoxia. We hypothesized that regional differences in mitochondrial function would be evident, and that prophylactic creatine treatment would mitigate mitochondrial dysfunction following hypoxia; thereby reducing fetal brain injury. Pregnant Border-Leicester/Merino ewes with singleton fetuses were surgically instrumented at 118 days of gestation (dGa; term is ~145 dGA). A continuous infusion of either creatine (n = 15; 6 mg/kg/h) or isovolumetric saline (n = 16; 1.5 ml/kg/h) was administered to the fetuses from 121 dGa. After 10 days of infusion, a subset of fetuses (8 saline-, 7 creatine-treated) were subjected to 10 minutes of umbilical cord occlusion (UCO) to induce a mild global fetal hypoxia. At 72 hours after UCO, the fetal brain was collected for high-resolution mitochondrial respirometry and molecular and histological analyses. The results show that the transient UCO-induced acute hypoxia impaired mitochondrial function in the hippocampus and the periventricular white matter and increased the incidence of cell death in the hippocampus. Creatine treatment did not rectify the changes in mitochondrial respiration associated with hypoxia, but there was a negative relationship between cell death and creatine content following treatment. Irrespective of UCO, creatine increased the proportion of cytochrome c bound to the inner mitochondrial membrane, upregulated the mRNA expression of the antiapoptotic gene Bcl2, and of PCG1-α, a driver of mitogenesis, in the hippocampus. We conclude that creatine treatment prior to brief, acute hypoxia does not fundamentally modify mitochondrial respiratory function, but may improve mitochondrial structural integrity and potentially increase mitogenesis and activity of antiapoptotic pathways.

Prenatal Hypoxia Induces Premature Aging Accompanied by Impaired Function of the Glutamatergic System in Rat Hippocampus

Prenatal hypoxia is among leading causes of progressive brain pathologies in postnatal life. This study aimed to analyze the characteristics of the hippocampal glutamatergic system and behavior of rats in early (2 weeks), adult (3 months) and advanced (18 months) postnatal ontogenesis after exposure to prenatal severe hypoxia (PSH, 180 Torr, 5% O2, 3 h) during the critical period in the formation of the hippocampus (days 14-16 of gestation). We have shown an age-dependent progressive decrease in the hippocampal glutamate levels, a decrease of the neuronal cell number in the CA1 hippocampal region, as well as impairment of spatial long-term memory in the Morris water navigation task. The gradual decrease of glutamate was accompanied by decreased expression of the genes that mediate glutamate metabolism and recycling in the hippocampus. That deficiency apparently correlated with an increase of the metabotropic glutamate receptor type 1 (mGluR1) and synaptophysin expression. Generation of the lipid peroxidation products in the hippocampus of adult rats subjected to prenatal severe hypoxia (PSH rats) was not increased compared to the control animals when tested in a model of glutamate excitotoxicity induced by severe hypoxia. This demonstrates that excessive glutamate sensitivity in PSH rats does not compensate for glutamate deficiency. Our results show a significant contribution of the glutamate system dysfunction to age-associated decrease of this mediator, cognitive decline, and early neuronal loss in PSH rats.

Sleep Deprivation Induces Cognitive Impairment by Increasing Blood-Brain Barrier Permeability via CD44

Sleep deprivation occurs frequently in older adults, which can result in delirium and cognitive impairment. CD44 is a key molecular in blood-brain barrier (BBB) regulation. However, whether CD44 participates in the role of sleep deprivation in cognitive impairment remains unclear. In this study, the effect of sleep deprivation on cognitive ability, tissue inflammation, BBB permeability, and astrocyte activity were evaluated in vivo. The differentially expressed genes (DEGs) were identified by RNA sequencing. A CD44 overexpression in the BBB model was performed in vitro to assess the effect and mechanisms of CD44. Sleep deprivation impaired the learning and memory ability and increased the levels of inflammatory cytokines, along with increased BBB permeability and activated astrocytes in hippocampus tissue. RNA sequencing of the hippocampus tissue revealed that 329 genes were upregulated in sleep deprivation-induced mice compared to control mice, and 147 genes were downregulated. GO and pathways showed that DEGs were mainly involved in BBB permeability and astrocyte activation, including nervous system development, neuron development, and brain development, and neuroactive ligand-receptor interaction. Moreover, the PCR analysis revealed that CD44 was dramatically increased in mice with sleep deprivation induction. The overexpression of CD44 in astrocytes promoted BBB permeability in vitro and induced the expression of the downstream gene NANOG. Our results indicate that sleep deprivation upregulated CD44 expression in hippocampus tissue, and increased BBB permeability, resulting in cognitive impairment.

Excess cerebral oxygen delivery follows return of spontaneous circulation in near-term asphyxiated lambs

Hypoxic-ischaemia renders the neonatal brain susceptible to early secondary injury from oxidative stress and impaired autoregulation. We aimed to describe cerebral oxygen kinetics and haemodynamics immediately following return of spontaneous circulation (ROSC) and evaluate non-invasive parameters to facilitate bedside monitoring. Near-term sheep fetuses [139 ± 2 (SD) days gestation, n = 16] were instrumented to measure carotid artery (CA) flow, pressure, right brachial arterial and jugular venous saturation (SaO2 and SvO2, respectively). Cerebral oxygenation (crSO2) was measured using near-infrared spectroscopy (NIRS). Following induction of severe asphyxia, lambs received cardiopulmonary resuscitation using 100% oxygen until ROSC, with oxygen subsequently weaned according to saturation nomograms as per current guidelines. We found that oxygen consumption did not rise following ROSC, but oxygen delivery was markedly elevated until 15 min after ROSC. CrSO2 and heart rate each correlated with oxygen delivery. SaO2 remained > 90% and was less useful for identifying trends in oxygen delivery. CrSO2 correlated inversely with cerebral fractional oxygen extraction. In conclusion, ROSC from perinatal asphyxia is characterised by excess oxygen delivery that is driven by rapid increases in cerebrovascular pressure, flow, and oxygen saturation, and may be monitored non-invasively. Further work to describe and limit injury mediated by oxygen toxicity following ROSC is warranted.

Hypoxic-Ischemic Encephalopathy and Mitochondrial Dysfunction: Facts, Unknowns, and Challenges

Significance: Hypoxic-ischemic events due to intrapartum complications represent the second cause of neonatal mortality and initiate an acute brain disorder known as hypoxic-ischemic encephalopathy (HIE). In HIE, the brain undergoes primary and secondary energy failure phases separated by a latent phase in which partial neuronal recovery is observed. A hypoxic-ischemic event leads to oxygen restriction causing ATP depletion, neuronal oxidative stress, and cell death. Mitochondrial dysfunction and enhanced oxidant formation in brain cells are characteristic phenomena associated with energy failure. Recent Advances: Mitochondrial sources of oxidants in neurons include complex I of the mitochondrial respiratory chain, as a key contributor to O₂^•- production via succinate by a reverse electron transport mechanism. The reaction of O₂^•- with nitric oxide (^•NO) yields peroxynitrite, a mitochondrial and cellular toxin. Quantitation of the redox state of cytochrome c oxidase, through broadband near-infrared spectroscopy, represents a promising monitoring approach to evaluate mitochondrial dysfunction in vivo in humans, in conjunction with the determination of cerebral oxygenation and their correlation with the severity of brain injury. Critical Issues: The energetic failure being a key phenomenon in HIE connected with the severity of the encephalopathy, measurement of mitochondrial dysfunction in vivo provides an approach to assess evolution, prognosis, and adequate therapies. Restoration of mitochondrial redox homeostasis constitutes a key therapeutic goal. Future Directions: While hypothermia is the only currently accepted therapy in clinical management to preserve mitochondrial function, other mitochondria-targeted and/or redox-based treatments are likely to synergize to ensure further efficacy.

A single muscle contusion promotes an immediate alteration in mitochondrial bioenergetics response in skeletal muscle fibres with different metabolism

Skeletal muscle is the most abundant tissue in the human body and mechanical injuries are common; these are frequently of mechanical origins, such as contusion. However, the immediate mitochondrial response to injury and energetic substrate utilisation is still unclear. We evaluated the acute response in mitochondrial function after a single muscle contusion, either in fast twitch fibres (glycolytic metabolism), fast and slow twitch (oxidative and glycolytic metabolism), or slow twitch fibres (oxidative metabolism). Rats were assigned to two groups: control and Lesion (muscle contusion). We collected the gastrocnemius and soleus muscles. The fibres were analysed for mitochondrial respiration, lactate dehydrogenase (LDH), citrate synthase (CS) activity, Ca²⁺ uptake, and H₂O₂ production. We found that muscle injury was able to increase ATP synthesis-dependent and OXPHOS oxygen flux in the oxidative fibres when stimulated by complex I + II substrates. On the other hand, the muscle injury increased hydrogen peroxide (H₂O₂) production when compared to control fibres, and reduced citrate synthase activity; however, it did not change Ca²⁺ uptake. Surprisingly, injury in mixed fibres increased the OXPHOS and ATP synthesis oxygen consumption, and H₂O₂ production, but it reduced Ca²⁺ uptake. The injury in glycolytic fibres did not affect oxygen flux coupled to ATP synthesis, citrate synthase, and lactate dehydrogenase activity, but did reduce Ca²⁺ uptake. Finally, we demonstrated distinct mitochondrial responses between the different muscle fibres, indicating that the mitochondrial dynamics is related to flexibilities in metabolism, and that reactive oxygen species directly affect physiology and normal function.