Oxidative injury in the cerebral cortex and subplate neurons in periventricular leukomalacia

Maternal DHA intake in mice increased DHA metabolites in the pup brain and ameliorated MeHg-induced behavioral disorder

Although pregnant women's fish consumption is beneficial for the brain development of the fetus due to the DHA in fish, seafood also contains methylmercury (MeHg), which adversely affects fetal brain development. Epidemiological studies suggest that high DHA levels in pregnant women's sera may protect the fetal brain from MeHg-induced neurotoxicity, but the underlying mechanism is unknown. Our earlier study revealed that DHA and its metabolite 19,20-dihydroxydocosapentaenoic acid (19,20-DHDP) produced by cytochrome P450s (P450s) and soluble epoxide hydrolase (sEH) can suppress MeHg-induced cytotoxicity in mouse primary neuronal cells. In the present study, DHA supplementation to pregnant mice suppressed MeHg-induced impairments of pups' body weight, grip strength, motor function, and short-term memory. DHA supplementation also suppressed MeHg-induced oxidative stress and the decrease in the number of subplate neurons in the cerebral cortex of the pups. DHA supplementation to dams significantly increased the DHA metabolites 19,20-epoxydocosapentaenoic acid (19,20-EDP) and 19,20-DHDP as well as DHA itself in the fetal and infant brains, although the expression levels of P450s and sEH were low in the fetal brain and liver. DHA metabolites were detected in the mouse breast milk and in human umbilical cord blood, indicating the active transfer of DHA metabolites from dams to pups. These results demonstrate that DHA supplementation increased DHA and its metabolites in the mouse pup brain and alleviated the effects of MeHg on fetal brain development. Pregnant women's intake of fish containing high levels of DHA (or DHA supplementation) may help prevent MeHg-induced neurotoxicity in the fetus.

A Novel Murine Multi-Hit Model of Perinatal Acute Diffuse White Matter Injury Recapitulates Major Features of Human Disease

The selection of an appropriate animal model is key to the production of results with optimal relevance to human disease. Particularly in the case of perinatal brain injury, a dearth of affected human neonatal tissue available for research purposes increases the reliance on animal models for insight into disease mechanisms. Improvements in obstetric and neonatal care in the past 20 years have caused the pathologic hallmarks of perinatal white matter injury (WMI) to evolve away from cystic necrotic lesions and toward diffuse regions of reactive gliosis and persistent myelin disruption. Therefore, updated animal models are needed that recapitulate the key features of contemporary disease. Here, we report a murine model of acute diffuse perinatal WMI induced through a two-hit inflammatory–hypoxic injury paradigm. Consistent with diffuse human perinatal white matter injury (dWMI), our model did not show the formation of cystic lesions. Corresponding to cellular outcomes of dWMI, our injury protocol produced reactive microgliosis and astrogliosis, disrupted oligodendrocyte maturation, and disrupted myelination.. Functionally, we observed sensorimotor and cognitive deficits in affected mice. In conclusion, we report a novel murine model of dWMI that induces a pattern of brain injury mirroring multiple key aspects of the contemporary human clinical disease scenario.

Revisiting the Neuropathology of Sudden Infant Death Syndrome (SIDS)

Background: Sudden infant death syndrome (SIDS) is one of the leading causes of infant mortality in the United States (US). The extent to which SIDS manifests with an underlying neuropathological mechanism is highly controversial. SIDS correlates with markers of poor prenatal and postnatal care, generally rooted in the lack of access and quality of healthcare endemic to select racial and ethnic groups, and thus can be viewed in the context of health disparities. However, some evidence suggests that at least a subset of SIDS cases may result from a neuropathological mechanism. To explain these issues, a triple-risk hypothesis has been proposed, whereby an underlying biological abnormality in an infant facing an extrinsic risk during a critical developmental period SIDS is hypothesized to occur. Each SIDS decedent is thus thought to have a unique combination of these risk factors leading to their death. This article reviews the neuropathological literature of SIDS and uses machine learning tools to identify distinct subtypes of SIDS decedents based on epidemiological data.

Methods: We analyzed US Period Linked Birth/Infant Mortality Files from 1990 to 2017 (excluding 1992–1994). Using t-SNE, an unsupervised machine learning dimensionality reduction algorithm, we identified clusters of SIDS decedents. Following identification of these groups, we identified changes in the rates of SIDS at the state level and across three countries.

Results: Through t-SNE and distance based statistical analysis, we identified three groups of SIDS decedents, each with a unique peak age of death. Within the US, SIDS is geographically heterogeneous. Following this, we found low birth weight and normal birth weight SIDS rates have not been equally impacted by implementation of clinical guidelines. We show that across countries with different levels of cultural heterogeneity, reduction in SIDS rates has also been distinct between decedents with low vs. normal birth weight.

Conclusions: Different epidemiological and extrinsic risk factors exist based on the three unique SIDS groups we identified with t-SNE and distance based statistical measurements. Clinical guidelines have not equally impacted the groups, and normal birth weight infants comprise more of the cases of SIDS even though low birth weight infants have a higher SIDS rate.

Transient Hypoxemia Chronically Disrupts Maturation of Preterm Fetal Ovine Subplate Neuron Arborization and Activity

Preterm infants are at risk for a broad spectrum of neurobehavioral disabilities associated with diffuse disturbances in cortical growth and development. During brain development, subplate neurons (SPNs) are a largely transient population that serves a critical role to establish functional cortical circuits. By dynamically integrating into developing cortical circuits, they assist in consolidation of intracortical and extracortical circuits. Although SPNs reside in close proximity to cerebral white matter, which is particularly vulnerable to oxidative stress, the susceptibility of SPNs remains controversial. We determined SPN responses to two common insults to the preterm brain: hypoxia-ischemia and hypoxia. We used a preterm fetal sheep model using both sexes that reproduces the spectrum of human cerebral injury and abnormal cortical growth. Unlike oligodendrocyte progenitors, SPNs displayed pronounced resistance to early or delayed cell death from hypoxia or hypoxia-ischemia. We thus explored an alternative hypothesis that these insults alter the maturational trajectory of SPNs. We used DiOlistic labeling to visualize the dendrites of SPNs selectively labeled for complexin-3. SPNs displayed reduced basal dendritic arbor complexity that was accompanied by chronic disturbances in SPN excitability and synaptic activity. SPN dysmaturation was significantly associated with the level of fetal hypoxemia and metabolic stress. Hence, despite the resistance of SPNs to insults that trigger white matter injury, transient hypoxemia disrupted SPN arborization and functional maturation during a critical window in cortical development. Strategies directed at limiting the duration or severity of hypoxemia during brain development may mitigate disturbances in cerebral growth and maturation related to SPN dysmaturation.SIGNIFICANCE STATEMENT The human preterm brain commonly sustains blood flow and oxygenation disturbances that impair cerebral cortex growth and cause life-long cognitive and learning disabilities. We investigated the fate of subplate neurons (SPNs), which are a master regulator of brain development that plays critical roles in establishing cortical connections to other brain regions. We used a preterm fetal sheep model that reproduces key features of brain injury in human preterm survivors. We analyzed the responses of fetal SPNs to transient disturbances in fetal oxygenation. We discovered that SPNs are surprisingly resistant to cell death from low oxygen states but acquire chronic structural and functional changes that suggest new strategies to prevent learning problems in children and adults that survive preterm birth.

Neonatal Intermittent Hypoxia, Reactive Oxygen Species, and Oxygen-Induced Retinopathy

Most of the major morbidities in the preterm newborn are caused by or are associated with oxygen-induced injuries and are aptly called "oxygen radical diseases in neonatology or ORDIN". These include bronchopulmonary dysplasia, retinopathy of prematurity, periventricular leukomalacia, intraventricular hemorrhage, necrotizing enterocolitis and others. Relative hyperoxia immediately after birth, immature antioxidant systems, biomolecular events favoring oxidative stress such as iron availability and the role of hydrogen peroxide as a key molecular mediator of these events are reviewed. Potential therapeutic strategies such as caffeine, antioxidants, non-steroidal anti-inflammatory drugs, and others targeted to these critical sites may help prevent oxidative radical diseases in the newborn resulting in improved neonatal outcomes.

Pathogenesis, neuroimaging and management in children with cerebral palsy born preterm

With advances in obstetric and perinatal management, the incidence of intraventricular hemorrhage in premature infants has declined, while periventricular leukomalacia remains a significant concern. It is now known that brain injury in children born preterm also involves neuronal-axonal disease in supratentorial and infratentorial structures. The developing brain is especially vulnerable to white matter (WM) injury from 23 to 34 weeks gestation when blood vessels serving the periventricular WM are immature. Oligodendrocyte progenitors, which are beginning to form myelin during this time, are susceptible to attack from oxygen free radicals, glutamate, and inflammatory cytokines. Advances in imaging techniques such as diffusion tensor imaging provide a more complete picture of the location and extent of injury. Effective management of children born preterm with cerebral palsy is predicated on an understanding of sequential links from etiological antecedents to brain neuropathology as revealed with neuroimaging techniques to clinical phenotypes, toward focused interventions with measurable outcomes.

12/15-lipoxygenase expression is increased in oligodendrocytes and microglia of periventricular leukomalacia

Oxidative stress involving premyelinating oligodendrocytes (OLs) is a major factor in the pathogenesis of preterm white matter injury. In animal and cell culture studies, activation of the lipid-oxidizing enzyme 12/15-lipoxygenase (12/15-LOX) plays a central role as an inflammatory mediator in the pathology of oxidative stress and OL cell death, as well as ischemia and neuronal death. The role of 12/15-LOX, however, is unclear in the developing human brain. The mechanism of 12/15-LOX involves the production of reactive oxygen species through the metabolism of arachidonic acid, as well as direct detrimental effects on organelle membranes. Here we tested the hypothesis that the density of 12/15-LOX-expressing cells is increased in periventricular leukomalacia (PVL). Using immunocytochemistry (ICC) in human paraffin-embedded tissue, 12/15-LOX expression was seen in macrophages of the focally necrotic lesions in the periventricular white matter, as well as in glial cells throughout the surrounding white matter with reactive gliosis. Interestingly, no significant 12/15-LOX expression was detected in neurons in the cerebral cortex overlying the damaged white matter. Using a scoring system from 0 to 3, we assessed the density of 12/15-LOX-expressing cells in diffusely gliotic white matter from 20 to 43 postconceptional (PC) weeks in 19 PVL cases (median = 36 PC weeks) and 10 control (non-PVL) cases (median = 34 PC weeks). The density of 12/15-LOX-positive cells was significantly increased in the diffuse component of PVL (score = 1.17 ± 0.15) compared to controls (score = 0.48 ± 0.21; p = 0.014). Using double-label ICC, 12/15-LOX was observed in PVL in OLs of the O4 and O1 premyelinating stages, as well as in mature OLs as determined with the mature OL marker adenomatous polyposis coli (APC). In addition, 12/15-LOX expression was present in a population of CD68-positive activated microglia. There was no 12/15-LOX expression in reactive astrocytes. Finally we observed terminal deoxynucleotide transferase dUTP nick end-labeling-positive cells within the white matter of PVL that expressed 12/15-LOX and/or within close proximity of 12/15-LOX-positive cells. Our data support a role for 12/15-LOX activation as an inflammatory mediator of injury in PVL, with a contribution of 12/15-LOX to PVL-induced damage to or cell death of OLs, including those at the O1 and O4 stages.

Brainstem deficiency of the 14-3-3 regulator of serotonin synthesis: a proteomics analysis in the sudden infant death syndrome

Impaired brainstem responses to homeostatic challenges during sleep may result in the sudden infant death syndrome (SIDS). Previously we reported a deficiency of serotonin (5-HT) and its key biosynthetic enzyme, tryptophan hydroxylase (TPH2), in SIDS infants in the medullary 5-HT system that modulates homeostatic responses during sleep. Yet, the underlying basis of the TPH2 and 5-HT deficiency is unknown. In this study, we tested the hypothesis that proteomics would uncover previously unrecognized abnormal levels of proteins related to TPH2 and 5-HT regulation in SIDS cases compared with controls, which could provide novel insight into the basis of their deficiency. We first performed a discovery proteomic analysis of the gigantocellularis of the medullary 5-HT system in the same data set with deficiencies of TPH2 and 5-HT levels. Analysis in 6 SIDS cases and 4 controls revealed a 42-75% reduction in abundance in 5 of the 6 isoforms identified of the 14-3-3 signal transduction family, which is known to influence TPH2 activity (p < 0.07). These findings were corroborated in an additional SIDS and control sample using an orthogonal MS(E)-based quantitative proteomic strategy. To confirm these proteomics results in a larger data set (38 SIDS, 11 controls), we applied Western blot analysis in the gigantocellularis and found that 4/7 14-3-3 isoforms identified were significantly reduced in SIDS cases (p ≤ 0.02), with a 43% reduction in all 14-3-3 isoforms combined (p < 0.001). Abnormalities in 5-HT and TPH2 levels and 5-HT(1A) receptor binding were associated with the 14-3-3 deficits in the same SIDS cases. These data suggest a potential molecular defect in SIDS related to TPH2 regulation, as 14-3-3 is critical in this process.

Developmental regulation of the neuroinflammatory responses to LPS and/or hypoxia-ischemia between preterm and term neonates: An experimental study

Background

Preterm and term newborns are at high risk of brain damage as well as subsequent cerebral palsy and learning disabilities. Indeed, hypoxia-ischemia (HI), pathogen exposures, and associated intracerebral increase of pro-inflammatory cytokines have all been linked to perinatal brain damage. However, the developmental effects of potential variations of pro- and anti-inflammatory cytokine ratios remain unknown.

Methods

Using rat models of perinatal brain damage induced by exposures to lipopolysaccharide (LPS) and/or HI at distinct levels of maturity, we compared cytokine expression at stages of cerebral development equivalent to either preterm (postnatal day 1, P1) or term (P12) newborns.

Results

At P1, expression of anti-inflammatory cytokine within the brain was either not modulated (IL-6, IL-10) or down-regulated (IL-1ra, TGF-β1) by HI, LPS or LPS+HI. In contrast, there was at P12 an up-regulation of all anti-inflammatory cytokines studied in HI or LPS+HI condition, but not after LPS exposure. Interestingly, IL-1β was the main pro-inflammatory cytokine up-regulated moderately at P1, and strongly at P12, with a weak co-expression of TNF-α observed mainly at P12. These age-dependant inflammatory reactions were also accompanied, under HI and LPS+HI conditions, at P12 only, by combined: (i) expression of chemokines CINC-1 and MCP-1, (ii) blood-brain barrier (BBB) leakage, and (iii) intracerebral recruitment of systemic immune cells such as neutrophils. In contrast, sole LPS induced IL-1β responses mainly within white matter at P1 and mainly within gray matter at P12, that were only associated with early MCP-1 (but no CINC-1) induction at both ages, without any recruitment of neutrophils and CD68+ cells.

Conclusion

HI and LPS+HI induce pro-inflammatory oriented immune responses in both preterm and term like brains, with a maximal inflammatory response triggered by the combination of LPS+HI. The profile of these neuroinflammatory responses presented striking variations according to age: no or down-regulated anti-inflammatory responses associated with mainly IL-1β release in preterm-like brains (P1), in sharp contrast to term-like brains (P12) presenting stronger anti-and pro-inflammatory responses, including both IL-1β and TNF-α releases, and BBB leakage. These developmental-dependant variations of neuroinflammatory response could contribute to the differential pattern of brain lesions observed across gestational ages in humans. This also highlights the necessity to take into consideration the maturation stage, of both brain and immune systems, in order to develop new anti-inflammatory neuroprotective strategies.

The cerebral cortex overlying periventricular leukomalacia: analysis of pyramidal neurons

The role of the cerebral cortex in the cognitive deficits in preterm survivors is poorly understood. Periventricular leukomalacia (PVL), the key feature of encephalopathy of prematurity, is characterized by periventricular necrotic foci and diffuse gliosis in the surrounding cerebral white matter. Here, we tested the hypothesis that reductions in the density of layer I neurons and/or pyramidal neurons in layers III and/or V are associated with PVL, indicating cortical pathology potentially associated with cognitive deficits in long-term survivors. In controls (23 gestational weeks to 18 postnatal months) (n = 15), a lack of significant differences in pyramidal density among incipient Brodmann areas suggested that cytoarchitectonic differences across functional areas are not fully mature in the fetal and infant periods. There was a marked reduction (38%) in the density of layer V neurons in all areas sampled in the PVL cases (n = 17) compared to controls (n = 12) adjusted for postconceptional age at or greater than 30 weeks, when the six-layer cortex is visually distinct (P < 0.024). This may reflect a dying-back loss of somata complicating transection of layer V axons projecting through the necrosis in the underlying white matter. This study underscores the potential role of secondary cortical injury in the encephalopathy of prematurity.

Nitrosative stress and inducible nitric oxide synthase expression in periventricular leukomalacia

Periventricular leukomalacia (PVL) is a lesion of the immature cerebral white matter in the perinatal period and associated predominantly with prematurity and cerebral ischemia/reperfusion as well as inflammation due to maternofetal infection. It consists of focal necrosis in the periventricular region and diffuse gliosis with microglial activation and premyelinating oligodendrocyte (pre-OL) injury in the surrounding white matter. We previously showed nitrotyrosine in pre-OLs in PVL, suggesting involvement of nitrosative stress in this disorder. Here we hypothesize that inducible nitric oxide synthase (iNOS) expression is increased in PVL relative to controls. Using immunocytochemistry in human archival tissue, the density of iNOS-expressing cells was determined in the cerebral white matter of 15 PVL cases [29-51 postconceptional (PC) weeks] and 16 control cases (20-144 PC weeks). Using a standardization score of 0-3, the density of iNOS-positive cells was significantly increased in the diffuse component of PVL (score of 1.8 +/- 0.3) cases compared to controls (score of 0.7 +/- 0.3) (P = 0.01). Intense iNOS expression occurred in reactive astrocytes in acute through chronic stages and in activated microglia primarily in the acute stage, suggesting an early role for microglial iNOS in PVL's pathogenesis. This study supports an important role for iNOS-induced nitrosative stress in the reactive/inflammatory component of PVL.

Sensory and motor deficits in children with cerebral palsy born preterm correlate with diffusion tensor imaging abnormalities in thalamocortical pathways

AIM

Cerebral palsy (CP) is frequently linked to white matter injury in children born preterm. Diffusion tensor imaging (DTI) is a powerful technique providing precise identification of white matter microstructure. We investigated the relationship between DTI-observed thalamocortical (posterior thalamic radiation) injury, motor (corticospinal tract) injury, and sensorimotor function.

METHOD

Twenty-eight children born preterm (16 males, 12 females; mean age 5y 10mo, SD 2y 6mo, range 16mo-13y; mean gestational age at birth 28wks, SD 2.7wks, range 23-34wks) were included in this case-control study. Twenty-one children had spastic diplegia, four had spastic quadriplegia, two had hemiplegia, and one had ataxic/hypotonic CP; 15 of the participants walked independently. Normative comparison data were obtained from 35 healthy age-matched children born at term (19 males, 16 females; mean age 5y 9mo, SD 4y 4mo, range 15mo-15y). Two-dimensional DTI color maps were created to evaluate 26 central white matter tracts, which were graded by a neuroradiologist masked to clinical status. Quantitative measures of touch, proprioception, strength (dynamometer), and spasticity (modified Ashworth scale) were obtained from a subset of participants.

RESULTS

All 28 participants with CP had periventricular white-matter injury on magnetic resonance imaging. Using DTI color maps, there was more severe injury in the posterior thalamic radiation pathways than in the descending corticospinal tracts. Posterior thalamic radiation injury correlated with reduced contralateral touch threshold, proprioception, and motor severity, whereas corticospinal tract injury did not correlate with motor or sensory outcome measures.

INTERPRETATION

These findings extend previous research demonstrating that CP in preterm children reflects disruption of thalamocortical connections as well as descending corticospinal pathways.