Hypoxic-ischemic White Matter Injury Research Articles

FGF21 Alleviates Hypoxic-Ischemic White Matter Injury in Neonatal Mice by Mediating Inflammation and Oxidative Stress Through PPAR-γ Signaling Pathway.

White matter injury (WMI), the most common type of brain damage in infants born preterm, is characterized by failure in oligodendrocyte progenitor cell maturation and myelination, thereby contributing to long-term neurological impairments. Regrettably, effective therapies for promoting remyelination and improving function are currently lacking for this growing population affected by WMI. Recombinant human fibroblast growth factor (rhFGF) 21 modulated microglial activation and then ameliorated brain damage and improved neurological deficits in several central nervous system diseases. However, the effects of rhFGF21 treatment on WMI in preterm infants remain uncertain. In this study, we established an in vivo mouse model of cerebral hypoxia-ischemia (HI)-induced brain WMI and an in vitro model using oxygen-glucose deprivation (OGD)-treated HMC3 cells to investigate the neuroprotective effects of rhFGF21 against WMI and elucidated the potential mechanism. Our findings demonstrated that administration of rhFGF21 significantly ameliorated the retardation of oligodendrocyte differentiation, promoted myelination, and mitigated axonal deficits, synaptic loss, and GFAP scarring, thereby improving lifelong cognitive and neurobehavioral dysfunction associated with WMI. Moreover, rhFGF21 modulated microglial polarization, promoted a shift from the M1 to the M2 microglial phenotype, and suppressed microglial activation, thus ameliorating inflammatory response and oxidative stress. Additionally, rhFGF21 treatment significantly inhibited the HMGB1/NF-κB pathway linked to inflammation, and activated the NRF2 pathway associated with oxidative stress through the upregulation of PPAR-γ. Importantly, the beneficial effects of rhFGF21 on HI-induced WMI and microglial activation were dramatically inhibited by PPAR-γ antagonist and its siRNA. Our findings provide compelling evidence that rhFGF21 treatment mitigated the inflammatory response and oxidative stress through the modulation of microglial polarization via the PPAR-γ-mediated HMGB1/NF-κB pathway and the NRF2 pathway, respectively, contributes to neuroprotection and the amelioration of WMI in neonatal mice. Thus, rhFGF21 represents a promising therapeutic agent for the treatment of neonatal WMI.

The Neuroprotective Mechanisms of PPAR-γ: Inhibition of Microglia-Mediated Neuroinflammation and Oxidative Stress in a Neonatal Mouse Model of Hypoxic-Ischemic White Matter Injury.

Neuroinflammation and oxidative stress, mediated by microglial activation, hinder the development of oligodendrocytes (OLs) and delay myelination in preterm infants, leading to white matter injury (WMI) and long-term neurodevelopmental sequelae. Peroxisome proliferator-activated receptor gamma (PPAR-γ) has been reported to inhibit inflammation and oxidative stress via modulating microglial polarization in various central nervous system diseases. However, the relationship between PPAR-γ and microglial polarization in neonatal WMI is not well understood. Therefore, this study aimed to elucidate the role and mechanisms of PPAR-γ in preterm infants affected by WMI. In this study, an invivo hypoxia-ischemia (HI) induced brain WMI neonatal mouse model was established. The mice were administered intraperitoneally with either RSGI or GW9662 to activate or inhibit PPAR-γ, respectively. Additionally, an invitro oxygen-glucose deprivation (OGD) cell model was established and pretreated with pcDNA 3.1-PPAR-γ or si-PPAR-γ to overexpress or silence PPAR-γ, respectively. The neuroprotective effects of PPAR-γ were investigated invivo. Firstly, open field test, novel object recognization test, and beam-walking test were employed to assess the effects of PPAR-γ on neurobehavioral recovery. Furthermore, assessment of OLs loss and OL-maturation disorder, the number of myelinated axons, myelin thickness, synaptic deficit, activation of microglia and astrocyte, and blood-brain barrier (BBB) were used to evaluate the effects of PPAR-γ on pathological repair. The mechanisms of PPAR-γ were explored both invivo and invitro. Assessment of microglia polarization, inflammatory mediators, reactive oxygen species (ROS), MDA, and antioxidant enzymes was used to evaluate the anti-inflammatory and antioxidative effects of PPAR-γ activation. An assessment of HMGB1/NF-κB and NRF2/KEAP1 signaling pathway was conducted to clarify the mechanisms by which PPAR-γ influences HI-induced WMI in neonatal mice. Activation of PPAR-γ using RSGI significantly mitigated BBB disruption, promoted M2 polarization of microglia, inhibited activation of microglia and astrocytes, promoted OLs development, and enhanced myelination in HI-induced WMI. Conversely, inhibition of PPAR-γ using GW9662 further exacerbated the pathologic hallmark of WMI. Neurobehavioral tests revealed that neurological deficits were ameliorated by RSGI, while further aggravated by GW91662. In addition, activation of PPAR-γ significantly alleviated neuroinflammation and oxidative stress by suppressing HMGB1/NF-κB signaling pathway and activating NRF2 signaling pathway both invivo and invitro. Conversely, inhibition of PPAR-γ further exacerbated HI or OGD-induced neuroinflammation, oxidative stress via modulation of the same signaling pathway. Our findings suggest that PPAR-γ regulates microglial activation/polarization as well as subsequent neuroinflammation/oxidative stress via the HMGB1/NF-κB and NRF2/KEAP1 signaling pathway, thereby contributing to neuroprotection and amelioration of HI-induced WMI in neonatal mice.

Neonatal Brain MRI: Periventricular Germinal Matrix Mimicking Hypoxic-ischemic White Matter Injuries.

As pregnancy progresses, the germinal matrix volume decreases. Residual periventricular germinal matrix may be mistaken for hypoxic-ischemic white matter injury. This study aims to determine the prevalence and imaging characteristics of these findings. This retrospective study analyzed brain MRIs of newborns from 2012-2023, performed within the first week of life. MRIs were done for suspected hypoxic-ischemic injuries, post-natal neurological symptoms, and evaluation of prenatally diagnosed structural anomalies. Image analysis targeted the remnants of the frontal periventricular germinal matrix, assessing its imaging characteristics, including diffusion, T1, and T2 signal characteristics, and laterality. Frontal migrating cell bands were also assessed. Seventy newborns were included (mean gestational age at delivery was 38.3 ± 2.1 weeks, mean scan age 5.1 ± 1.9 days). Frontal periventricular gray matter was detected in 39 newborns (90% bilateral) on T2-weighted images, negatively correlated with gestational age (r = -0.31, p = 0.013); none showed decreased ADC or shortened T1 signal compared with the basal ganglia. Frontal periventricular bands were found in 37 newborns (97.3% bilateral), strongly correlating with periventricular gray matter (r = 0.71, p < 0.001). No correlation was found between clinical hypoxic-ischemic injuries and these features. The presence of frontal periventricular gray matter observed in early neonatal MRIs, without decreased ADC values or shortened T1 signal, is developmental, reflecting a late maturation phase. Careful interpretation of MRI characteristics, including diffusion, T1, and T2 signal intensities, is necessary before attributing these findings to hypoxic-ischemic white matter injury.

Effect of Hypoxia-Ischemia on the Expression of Iron-Related Proteins in Neonatal Rat Brains.

Hypoxic-ischemic white matter injury (WMI) pathogenesis in preterm infants is not well established, and iron-related proteins in the brain may play an important role in imbalanced iron metabolism. We aimed to investigate the iron-related protein changes in neonatal rats after hypoxia-ischemia (HI), clarify the role of iron-related proteins in hypoxic-ischemic WMI, and potentially provide a new target for the clinical treatment of hypoxic-ischemic WMI in preterm infants. We adopted a WMI animal model of bilateral common carotid artery electrocoagulation combined with hypoxia in neonatal 3-day-old Sprague-Dawley rats. We observed basic myelin protein (MBP) and iron-related protein expression in the brain (ferritin, transferrin receptor [TfR], and membrane iron transporter 1 [FPN1]) via Western blot and double immunofluorescence staining. The expression of MBP in the WMI group was significantly downregulated on postoperative days (PODs) 14, 28, and 56. Ferritin levels were significantly increased on PODs 3, 7, 14, and 28 and were most significant on POD 28, returning to the sham group level on POD 56. FPN1 levels were significantly increased on PODs 7, 28, and 56 and were still higher than those in the sham group on POD 56. TfR expression was significantly upregulated on PODs 1, 7, and 28 and returned to the sham group level on POD 56. Immunofluorescence staining showed that ferritin, TfR, and FPN1 were expressed in neurons, blood vessels, and oligodendrocytes in the cortex and corpus callosum on POD 28. Compared with the sham group, the immune-positive markers of three proteins in the WMI group were significantly increased. The expression of iron-related proteins in the brain (ferritin, FPN1, and TfR) showed spatiotemporal dynamic changes and may play an important role in hypoxic-ischemic WMI.

Dynamic Changes in Brain Iron Metabolism in Neonatal Rats after Hypoxia-Ischemia

ObjectivesThe pathogenesis of hypoxic-ischemic white matter injury (WMI) in premature infants is still unclear, and the imbalance of cerebral iron metabolism may play an important role. Our study set out to investigate the changes in iron distribution, iron content and malondialdehyde (MDA) in disparate brain regions (parietal cortex, corpus callosum, hippocampus) within 84 days after hypoxia-ischemia (HI) in neonatal rats and to clarify the role of iron metabolism in WMI. Materials and MethodsWe adopted a rat model of hypoxic-ischemic WMI. Alterations in iron metabolism were detected by iron staining and iron assay kits, and the degree of brain injury was determined by MDA assays. ResultsOur results showed that different degrees of brain iron deposition occurred within 28 days after HI, and iron staining was the most obvious 3 days after HI. The iron content increased remarkably at 1–7 d after HI in the mixed tissues, especially at 3 d after HI. While the iron content in the parietal cortex and corpus callosum elevated obviously 14 days after HI. And the change trend of MDA was almost consistent with that of the iron content. ConclusionsOur findings revealed that brain iron metabolism changed dynamically in 3-day-old neonatal rats suffering from HI, which may cause lipid peroxidation damage to brain tissues. This process may be one of the pathogeneses of hypoxic-ischemic WMI.

Histamine H2 receptor negatively regulates oligodendrocyte differentiation in neonatal hypoxic-ischemic white matter injury.

Neonatal hypoxic-ischemic encephalopathy (HIE) with the pathological characteristic of white matter injury often leads to lifelong cognitive and neurobehavioral dysfunction, but relevant therapies to promote remyelination are still unavailable. We found that histamine H2 receptor (H2R) negatively regulated the oligodendrocyte differentiation rate without affecting the oligodendrocytes at the oligodendrocyte precursor cell stage or mature stage following oxygen-glucose deprivation in vitro. Notably, selective deletion of the H2R gene (Hrh2) in differentiating oligodendrocytes (Hrh2fl/fl;CNPase-Cre) improved their differentiation, remyelination, and functional recovery following neonatal hypoxia-ischemia in mice. The regulation of oligodendrocyte differentiation by H2R is mediated by binding with Axin2, which leads to up-regulation of the Wnt/β-catenin signaling pathway. Furthermore, H2R antagonists also promoted oligodendrocyte differentiation and remyelination and the recovery of cognition and motor functions following neonatal hypoxia-ischemia. Thus, histamine H2R in oligodendrocytes could serve as a novel and effective therapeutic target for the retard of oligodendrocyte differentiation and remyelination following neonatal hypoxia-ischemia. The H2R antagonists may have potential therapeutic value for neonatal HIE.

Alterations in the Structural and Functional Connectivity of the Visuomotor Network of Children With Periventricular Leukomalacia

Children born preterm with periventricular leukomalacia (PVL) demonstrate increased difficulties with tasks requiring visuomotor integration. The visuomotor integration network encompasses brain regions within frontal, parietal, and occipital cortices. Because of their proximity to the lateral ventricle the underlying white matter pathways are at a high risk of damage following PVL-related hypoxic-ischemic white matter injury. This study provides an exploratory analysis of the structural and functional connections within the visuomotor integration network, along with an a priori evaluation of the superior longitudinal fasciculus, inferior fronto-occipital fasciculus, and frontal aslant tract. For each pathway, tracts within both hemispheres revealed decreased volume and number of reconstructed fibers and an increase in quantitative anisotropy and generalized fractional anisotropy. The connectivity results also indicate that there may be changes to both the structural integrity and functional integration of neural networks involved with visuomotor integration functions in children with PVL.

Enhanced autophagy contributes to excitotoxic lesions in a rat model of preterm brain injury

Cystic periventricular leukomalacia is commonly diagnosed in premature infants, resulting from severe hypoxic-ischemic white matter injury, and also involving some grey matter damage. Very few is known concerning the cell death pathways involved in these types of premature cerebral lesions. Excitotoxicity is a predominant mechanism of hypoxic-ischemic injury in the developing brain. Concomitantly, it has been recently shown that autophagy could be enhanced in excitotoxic conditions switching this physiological intracellular degradation system to a deleterious process. We here investigated the role of autophagy in a validated rodent model of preterm excitotoxic brain damage mimicking in some aspects cystic periventricular leukomalacia. An excitotoxic lesion affecting periventricular white and grey matter was induced by injecting ibotenate, a glutamate analogue, in the subcortical white matter (subcingulum area) of five-day old rat pups. Ibotenate enhanced autophagy in rat brain dying neurons at 24 h as shown by increased presence of autophagosomes (increased LC3-II and LC3-positive dots) and enhanced autophagic degradation (SQSTM1 reduction and increased number and size of lysosomes (LAMP1- and CATHEPSIN B-positive vesicles)). Co-injection of the pharmacological autophagy inhibitor 3-methyladenine prevented not only autophagy induction but also CASPASE-3 activation and calpain-dependent cleavage of SPECTRIN 24 h after the insult, thus providing a strong reduction of the long term brain injury (16 days after ibotenate injection) including lateral ventricle dilatation, decreases in cerebral tissue volume and in subcortical white matter thickness. The autophagy-dependent neuroprotective effect of 3-methyladenine was confirmed in primary cortical neuronal cultures using not only pharmacological but also genetic autophagy inhibition of the ibotenate-induced autophagy. Strategies inhibiting autophagy could then represent a promising neuroprotective approach in the context of severe preterm brain injuries.

Axon–glia synapses are highly vulnerable to white matter injury in the developing brain

The biology of cerebral white matter injury has been woefully understudied, in part because of the difficulty of reliably modeling this type of injury in rodents. Periventricular leukomalacia (PVL) is the predominant form of brain injury and the most common cause of cerebral palsy in premature infants. PVL is characterized by predominant white matter injury. No specific therapy for PVL is presently available, because the pathogenesis is not well understood. Here we report that two types of mouse PVL models have been created by hypoxia-ischemia with or without systemic coadministration of lipopolysaccharide (LPS). LPS coadministration exacerbated hypoxic-ischemic white matter injury and led to enhanced microglial activation and astrogliosis. Drug trials with the antiinflammatory agent minocycline, the antiexcitotoxic agent NBQX, and the antioxidant agent edaravone showed various degrees of protection in the two models, indicating that excitotoxic, oxidative, and inflammatory forms of injury are involved in the pathogenesis of injury to immature white matter. We then applied immunoelectron microscopy to reveal fine structural changes in the injured white matter and found that synapses between axons and oligodendroglial precursor cells (OPCs) are quickly and profoundly damaged. Hypoxia-ischemia caused a drastic decrease in the number of postsynaptic densities associated with the glutamatergic axon-OPC synapses defined by the expression of vesicular glutamate transporters, vGluT1 and vGluT2, on axon terminals that formed contacts with OPCs in the periventricular white matter, resulted in selective shrinkage of the postsynaptic OPCs contacted by vGluT2 labeled synapses, and led to excitotoxicity mediated by GluR2-lacking, Ca(2+) -permeable AMPA receptors. Overall, the present study provides novel mechanistic insights into the pathogenesis of PVL and reveals that axon-glia synapses are highly vulnerable to white matter injury in the developing brain. More broadly, the study of white matter development and injury has general implications for a variety of neurological diseases, including PVL, stroke, spinal cord injury, and multiple sclerosis.

Mutation in the AP4M1 Gene Provides a Model for Neuroaxonal Injury in Cerebral Palsy

Cerebral palsy due to perinatal injury to cerebral white matter is usually not caused by genetic mutations, but by ischemia and/or inflammation. Here, we describe an autosomal-recessive type of tetraplegic cerebral palsy with mental retardation, reduction of cerebral white matter, and atrophy of the cerebellum in an inbred sibship. The phenotype was recorded and evolution followed for over 20 years. Brain lesions were studied by diffusion tensor MR tractography. Homozygosity mapping with SNPs was performed for identification of the chromosomal locus for the disease. In the 14 Mb candidate region on chromosome 7q22, RNA expression profiling was used for selecting among the 203 genes in the area. In postmortem brain tissue available from one patient, histology and immunohistochemistry were performed. Disease course and imaging were mostly reminiscent of hypoxic-ischemic tetraplegic cerebral palsy, with neuroaxonal degeneration and white matter loss. In all five patients, a donor splice site pathogenic mutation in intron 14 of the AP4M1 gene (c.1137+1G-->T), was identified. AP4M1, encoding for the mu subunit of the adaptor protein complex-4, is involved in intracellular trafficking of glutamate receptors. Aberrant GluRdelta2 glutamate receptor localization and dendritic spine morphology were observed in the postmortem brain specimen. This disease entity, which we refer to as congenital spastic tetraplegia (CST), is therefore a genetic model for congenital cerebral palsy with evidence for neuroaxonal damage and glutamate receptor abnormality, mimicking perinatally acquired hypoxic-ischemic white matter injury.

Rolipram, a Phosphodiesterase Type IV Inhibitor, Exacerbates Periventricular White Matter Lesions in Rat Pups

Periventricular white matter injury is the leading cause of cerebral palsy in premature infants for which no effective treatments are available. Our previous studies have demonstrated that pharmacological activation of the cAMP response element-binding protein (CREB) signaling pathway, before hypoxic-ischemia protected against neuronal injury in neonatal rats. We examined whether rolipram, a phosphodiesterase type IV inhibitor, treatment after hypoxic-ischemia is protective against white matter injury in neonatal rats. Rats were exposed to hypoxia-ischemia (HI) on P7 and then treated with daily injections of various doses of rolipram (P7-P11). Immunohistochemical staining for myelin basic protein, ED1, glial fibrillary acidic protein, CREB and O1 were examined on P11. We found that the periventricular white matter and deep cortical lesions were exacerbated by rolipram administration after HI injury. The lesions in the rolipram-treated group also showed increased astrogliosis and increased CREB phosphorylation in the activated microglia and astrocytes. Furthermore, the rolipram-posttreated HI group had markedly depleted preoligodendrocytes in the ipsilateral hemisphere, which may be related to decreased preoligodendrocytes proliferation after rolipram treatment per se. These data suggest that rolipram treatment after hypoxic-ischemia is not protective; in contrast, rolipram may exacerbate hypoxic-ischemic white matter injury in neonatal rat brains.

Differentiation between peritrigonal terminal zones and hypoxic-ischemic white matter injury on magnetic resonance imaging

The differentiation between terminal zones and pathological signal intensity changes on MRI of children and young adults is of diagnostic importance. We assessed the diagnostic value of several morphological features on MRI to differentiate between terminal zones and hypoxic–ischemic white matter injury. We selected all brain MRI examinations performed in subjects up to 20 years of age showing increased signal intensity on T2-weighted images in the peritrigonal areas. Seventy-five individuals were assigned to a patient group (n=28) if there was evidence of hypoxia–ischemia during the perinatal period or a control group (n=47).

Differentiation between peritrigonal terminal zones and hypoxic-ischemic white matter injury on MRI

The differentiation between terminal zones and pathological signal intensity changes on MRI of children and young adults is of diagnostic importance. We assessed the diagnostic value of several morphological features on MRI to differentiate between terminal zones and hypoxic-ischemic white matter injury. We selected all brain MRI examinations performed in subjects up to 20 years of age showing increased signal intensity on T2-weighted images in the peritrigonal areas. 75 individuals were assigned to a patient group ( n = 28) if there was evidence of hypoxia-ischemia during the perinatal period or a control group ( n = 47). Aspect, location, extent, shape, and borders of signal intensity changes in the peritrigonal areas were studied. Signal intensity of the peritrigonal areas was related to signal intensity of surrounding white matter. Presence of Virchow Robin spaces, hypoxic-ischemic abnormalities, and local atrophy were also recorded. Chi-squared tests assessed whether presence or absence of morphological characteristics differed between patients and controls. Logistic regression analysis studied which characteristics were best to discriminate between the two groups. Very high signal intensity of the peritrigonal areas on FLAIR (Odds Ratio 25) and presence of local atrophy (Odds Ratio 14.3) were best predictors to discriminate between the two groups.

MR Imaging and Prognosis of Hypoxic-Ischemic Leukoencephalopathy

To correlate prognosis of hypoxic-ischemic white-matter injury with magnetic resonance imaging (MRI). In a retrospective review at an urban medical center, three adult and three pediatric patients with predominant white-matter involvement caused by hypoxic- ischemic injury were evaluated over a 15-month period. Five patients with MRI-defined hypoxic-ischemic leukoencephalopathy had a favorable outcome, and one with associated diffusion-weighted abnormality of deep gray structures died. The prognosis of hypoxic-ischemic leukoencephalopathy is more favorable than previously reported, and diffusion-weighted imaging abnormality of deep gray structures was associated with a poor outcome.