Dysregulation of platelet serotonin, 14-3-3, and GPIX in sudden infant death syndrome

Sudden infant death syndrome (SIDS) is the leading cause of post-neonatal infant mortality, but the underlying cause(s) are unclear. A subset of SIDS infants has abnormalities in the neurotransmitter, serotonin (5-hydroxytryptamine [5-HT]) and the adaptor molecule, 14-3-3 pathways in regions of the brain involved in gasping, response to hypoxia, and arousal. To evaluate our hypothesis that SIDS is, at least in part, a multi-organ dysregulation of 5-HT, we examined whether blood platelets, which have 5-HT and 14-3-3 signaling pathways similar to brain neurons, are abnormal in SIDS. We also studied platelet surface glycoprotein IX (GPIX), a cell adhesion receptor which is physically linked to 14-3-3. In infants dying of SIDS compared to infants dying of known causes, we found significantly higher intra-platelet 5-HT and 14-3-3 and lower platelet surface GPIX. Serum and plasma 5-HT were also elevated in SIDS compared to controls. The presence in SIDS of both platelet and brainstem 5-HT and 14-3-3 abnormalities suggests a global dysregulation of these pathways and the potential for platelets to be used as a model system to study 5-HT and 14-3-3 interactions in SIDS. Platelet and serum biomarkers may aid in the forensic determination of SIDS and have the potential to be predictive of SIDS risk in living infants.

Multimodal MRI reveals brainstem connections that sustain wakefulness in human consciousness

Consciousness is composed of arousal (i.e., wakefulness) and awareness. Substantial progress has been made in mapping the cortical networks that underlie awareness in the human brain, but knowledge about the subcortical networks that sustain arousal in humans is incomplete. Here, we aimed to map the connectivity of a proposed subcortical arousal network that sustains wakefulness in the human brain, analogous to the cortical default mode network (DMN) that has been shown to contribute to awareness. We integrated data from ex vivo diffusion magnetic resonance imaging (MRI) of three human brains, obtained at autopsy from neurologically normal individuals, with immunohistochemical staining of subcortical brain sections. We identified nodes of the proposed default ascending arousal network (dAAN) in the brainstem, hypothalamus, thalamus, and basal forebrain. Deterministic and probabilistic tractography analyses of the ex vivo diffusion MRI data revealed projection, association, and commissural pathways linking dAAN nodes with one another and with DMN nodes. Complementary analyses of in vivo 7-tesla resting-state functional MRI data from the Human Connectome Project identified the dopaminergic ventral tegmental area in the midbrain as a widely connected hub node at the nexus of the subcortical arousal and cortical awareness networks. Our network-based autopsy methods and connectivity data provide a putative neuroanatomic architecture for the integration of arousal and awareness in human consciousness.

Multiomic Analysis of Neuroinflammation and Occult Infection in Sudden Infant Death Syndrome

Importance

Antemortem infection is a risk factor for sudden infant death syndrome (SIDS)-the leading postneonatal cause of infant mortality in the developed world. Manifestations of infection and inflammation are not always apparent in clinical settings or by standard autopsy; thus, enhanced resolution approaches are needed.

Objective

To ascertain whether a subset of SIDS cases is associated with neuroinflammation and occult infection.

Design, Setting, and Participants

In this case-control study, postmortem fluids from SIDS cases and controls collected between July 2011 and November 2018 were screened for elevated inflammatory markers, specifically cerebrospinal fluid (CSF) neopterin and CSF and serum cytokines. CSF, liver, and brain tissue from SIDS cases with elevated CSF neopterin were subjected to metagenomic next-generation sequencing (mNGS) to probe for infectious pathogens. Brainstem tissue from a subset of these cases was analyzed by single-nucleus RNA sequencing (snRNAseq) to measure cell type-specific gene expression associated with neuroinflammation and infection. All tissue and fluid analyses were performed from April 2019 to January 2023 in a pathology research laboratory. Included was autopsy material from infants dying of SIDS and age-matched controls dying of known causes.

Exposures

There were no interventions or exposures.

Main Outcomes and Measures

CSF neopterin levels were measured by high-performance liquid chromatography. Cytokines were measured by multiplex fluorometric assay. mNGS was performed on liver, CSF, brain, and brainstem tissue. snRNAseq was performed on brainstem tissue.

Results

A cohort of 71 SIDS cases (mean [SD] age, 55.2 [11.4] postconceptional weeks; 42 male [59.2%]) and 20 controls (mean [SD] age, 63.2 [16.9] postconceptional weeks; 11 male [55.0%]) had CSF and/or serum available. CSF neopterin was screened in 64 SIDS cases and 15 controls, with no exclusions. Tissues from 6 SIDS cases were further analyzed. For CSF neopterin measures, SIDS samples were from infants with mean (SD) age of 54.5 (11.3) postconceptional weeks (38 male [59.4%]) and control samples were from infants with mean (SD) age of 61.5 (17.4) postconceptional weeks (7 male [46.7%]). A total of 6 SIDS cases (9.3%) with high CSF neopterin were identified, suggestive of neuroinflammation. mNGS detected human parechovirus 3 (HPeV3) in tissue and CSF from 1 of these 6 cases. snRNAseq of HPeV3-positive brainstem tissue (medulla) revealed dramatic enrichment of transcripts for genes with predominately inflammatory functions compared with 3 age-matched SIDS cases with normal CSF neopterin levels.

Conclusions and Relevance

Next-generation molecular tools in autopsy tissue provide novel insight into pathogens that go unrecognized by normal autopsy methodology, including in infants dying suddenly and unexpectedly.

Altered 5-HT2A/C receptor binding in the medulla oblongata in the sudden infant death syndrome (SIDS): Part II. Age-associated alterations in serotonin receptor binding profiles within medullary nuclei supporting cardiorespiratory homeostasis

The failure of chemoreflexes, arousal, and/or autoresuscitation to asphyxia may underlie some sudden infant death syndrome (SIDS) cases. In Part I, we showed that some SIDS infants had altered 5-hydroxytryptamine (5-HT)2A/C receptor binding in medullary nuclei supporting chemoreflexes, arousal, and autoresuscitation. Here, using the same dataset, we tested the hypotheses that the prevalence of low 5-HT1A and/or 5-HT2A/C receptor binding (defined as levels below the 95% confidence interval of controls-a new approach), and the percentages of nuclei affected are greater in SIDS versus controls, and that the distribution of low binding varied with age of death. The prevalence and percentage of nuclei with low 5-HT1A and 5-HT2A/C binding in SIDS were twice that of controls. The percentage of nuclei with low 5-HT2A/C binding was greater in older SIDS infants. In >80% of older SIDS infants, low 5-HT2A/C binding characterized the hypoglossal nucleus, vagal dorsal nucleus, nucleus of solitary tract, and nuclei of the olivocerebellar subnetwork (important for blood pressure regulation). Together, our findings from SIDS infants and from animal models of serotonergic dysfunction suggest that some SIDS cases represent a serotonopathy. We present new hypotheses, yet to be tested, about how defects within serotonergic subnetworks may lead to SIDS.

Sustaining wakefulness: Brainstem connectivity in human consciousness

Consciousness is comprised of arousal (i.e., wakefulness) and awareness. Substantial progress has been made in mapping the cortical networks that modulate awareness in the human brain, but knowledge about the subcortical networks that sustain arousal is lacking. We integrated data from ex vivo diffusion MRI, immunohistochemistry, and in vivo 7 Tesla functional MRI to map the connectivity of a subcortical arousal network that we postulate sustains wakefulness in the resting, conscious human brain, analogous to the cortical default mode network (DMN) that is believed to sustain self-awareness. We identified nodes of the proposed default ascending arousal network (dAAN) in the brainstem, hypothalamus, thalamus, and basal forebrain by correlating ex vivo diffusion MRI with immunohistochemistry in three human brain specimens from neurologically normal individuals scanned at 600-750 μm resolution. We performed deterministic and probabilistic tractography analyses of the diffusion MRI data to map dAAN intra-network connections and dAAN-DMN internetwork connections. Using a newly developed network-based autopsy of the human brain that integrates ex vivo MRI and histopathology, we identified projection, association, and commissural pathways linking dAAN nodes with one another and with cortical DMN nodes, providing a structural architecture for the integration of arousal and awareness in human consciousness. We release the ex vivo diffusion MRI data, corresponding immunohistochemistry data, network-based autopsy methods, and a new brainstem dAAN atlas to support efforts to map the connectivity of human consciousness.

Altered 5-HT2A/C receptor binding in the medulla oblongata in the sudden infant death syndrome (SIDS): Part I. Tissue-based evidence for serotonin receptor signaling abnormalities in cardiorespiratory- and arousal-related circuits

The sudden infant death syndrome (SIDS), the leading cause of postneonatal infant mortality in the United States, is typically associated with a sleep period. Previously, we showed evidence of serotonergic abnormalities in the medulla (e.g. altered serotonin (5-HT)1A receptor binding), in SIDS cases. In rodents, 5-HT2A/C receptor signaling contributes to arousal and autoresuscitation, protecting brain oxygen status during sleep. Nonetheless, the role of 5-HT2A/C receptors in the pathophysiology of SIDS is unclear. We hypothesize that in SIDS, 5-HT2A/C receptor binding is altered in medullary nuclei that are key for arousal and autoresuscitation. Here, we report altered 5-HT2A/C binding in several key medullary nuclei in SIDS cases (n = 58) compared to controls (n = 12). In some nuclei the reduced 5-HT2A/C and 5-HT1A binding overlapped, suggesting abnormal 5-HT receptor interactions. The data presented here (Part 1) suggest that a subset of SIDS is due in part to abnormal 5-HT2A/C and 5-HT1A signaling across multiple medullary nuclei vital for arousal and autoresuscitation. In Part II to follow, we highlight 8 medullary subnetworks with altered 5-HT receptor binding in SIDS. We propose the existence of an integrative brainstem network that fails to facilitate arousal and/or autoresuscitation in SIDS cases.

Copy Number Variation and Structural Genomic Findings in 116 Cases of Sudden Unexplained Death between 1 and 28 Months of Age

In sudden unexplained death in pediatrics (SUDP) the cause of death is unknown despite an autopsy and investigation. The role of copy number variations (CNVs) in SUDP has not been well-studied. Chromosomal microarray (CMA) data are generated for 116 SUDP cases with age at death between 1 and 28 months. CNVs are classified using the American College of Medical Genetics and Genomics guidelines and CNVs in our cohort are compared to an autism spectrum disorder (ASD) cohort, and to a control cohort. Pathogenic CNVs are identified in 5 of 116 cases (4.3%). Variants of uncertain significance (VUS) favoring pathogenic CNVs are identified in 9 cases (7.8%). Several CNVs are associated with neurodevelopmental phenotypes including seizures, ASD, developmental delay, and schizophrenia. The structural variant 47,XXY is identified in two cases (2/69 boys, 2.9%) not previously diagnosed with Klinefelter syndrome. Pathogenicity scores for deletions are significantly elevated in the SUDP cohort versus controls (p = 0.007) and are not significantly different from the ASD cohort. The finding of pathogenic or VUS favoring pathogenic CNVs, or structural variants, in 12.1% of cases, combined with the observation of higher pathogenicity scores for deletions in SUDP versus controls, suggests that CMA should be included in the genetic evaluation of SUDP.

Genetic Determinants of Sudden Unexpected Death in Pediatrics

PURPOSE

This study aimed to evaluate genetic contributions to sudden unexpected death in pediatrics (SUDP).

METHODS

We phenotyped and performed exome sequencing for 352 SUDP cases. We analyzed variants in 294 "SUDP genes" with mechanisms plausibly related to sudden death. In a subset of 73 cases with parental data (trios), we performed exome-wide analyses and conducted cohort-wide burden analyses.

RESULTS

In total, we identified likely contributory variants in 37 of 352 probands (11%). Analysis of SUDP genes identified pathogenic/likely pathogenic variants in 12 of 352 cases (SCN1A, DEPDC5 [2], GABRG2, SCN5A [2], TTN [2], MYBPC3, PLN, TNNI3, and PDHA1) and variants of unknown significance-favor-pathogenic in 17 of 352 cases. Exome-wide analyses of the 73 cases with family data additionally identified 4 de novo pathogenic/likely pathogenic variants (SCN1A [2], ANKRD1, and BRPF1) and 4 de novo variants of unknown significance-favor-pathogenic. Comparing cases with controls, we demonstrated an excess burden of rare damaging SUDP gene variants (odds ratio, 2.94; 95% confidence interval, 2.37-4.21) and of exome-wide de novo variants in the subset of 73 with trio data (odds ratio, 3.13; 95% confidence interval, 1.91-5.16).

CONCLUSION

We provide strong evidence for a role of genetic factors in SUDP, involving both candidate genes and novel genes for SUDP and expanding phenotypes of disease genes not previously associated with sudden death.

Medullary Serotonergic Binding Deficits and Hippocampal Abnormalities in Sudden Infant Death Syndrome: One or Two Entities?

Sudden infant death syndrome (SIDS) is understood as a syndrome that presents with the common phenotype of sudden death but involves heterogenous biological causes. Many pathological findings have been consistently reported in SIDS, notably in areas of the brain known to play a role in autonomic control and arousal. Our laboratory has reported abnormalities in SIDS cases in medullary serotonin (5-HT) receptor 1A and within the dentate gyrus of the hippocampus. Unknown, however, is whether the medullary and hippocampal abnormalities coexist in the same SIDS cases, supporting a biological relationship of one abnormality with the other. In this study, we begin with an analysis of medullary 5-HT1A binding, as determined by receptor ligand autoradiography, in a combined cohort of published and unpublished SIDS (n = 86) and control (n = 22) cases. We report 5-HT1A binding abnormalities consistent with previously reported data, including lower age-adjusted mean binding in SIDS and age vs. diagnosis interactions. Utilizing this combined cohort of cases, we identified 41 SIDS cases with overlapping medullary 5-HT1A binding data and hippocampal assessment and statistically addressed the relationship between abnormalities at each site. Within this SIDS analytic cohort, we defined abnormal (low) medullary 5-HT1A binding as within the lowest quartile of binding adjusted for age and we examined three specific hippocampal findings previously identified as significantly more prevalent in SIDS compared to controls (granular cell bilamination, clusters of immature cells in the subgranular layer, and single ectopic cells in the molecular layer of the dentate gyrus). Our data did not find a strong statistical relationship between low medullary 5-HT1A binding and the presence of any of the hippocampal abnormalities examined. It did, however, identify a subset of SIDS (~25%) with both low medullary 5-HT1A binding and hippocampal abnormalities. The subset of SIDS cases with both low medullary 5-HT1A binding and single ectopic cells in the molecular layer was associated with prenatal smoking (p = 0.02), suggesting a role for the exposure in development of the two abnormalities. Overall, our data present novel information on the relationship between neuropathogical abnormalities in SIDS and support the heterogenous nature and overall complexity of SIDS pathogenesis.

Association of Prenatal Exposure to Maternal Drinking and Smoking With the Risk of Stillbirth

IMPORTANCE

Prenatal smoking is a known modifiable risk factor for stillbirth; however, the contribution of prenatal drinking or the combination of smoking and drinking is uncertain.

OBJECTIVE

To examine whether prenatal exposure to alcohol and tobacco cigarettes is associated with the risk of stillbirth.

DESIGN, SETTING, AND PARTICIPANTS

The Safe Passage Study was a longitudinal, prospective cohort study with data collection conducted between August 1, 2007, and January 31, 2015. Pregnant women from Cape Town, South Africa, and the Northern Plains region of the US were recruited and followed up throughout pregnancy. Data analysis was performed from November 1, 2018, to November 20, 2020.

EXPOSURE

Maternal consumption of alcohol and tobacco cigarettes in the prenatal period.

MAIN OUTCOMES AND MEASURES

The main outcomes were stillbirth, defined as fetal death at 20 or more weeks' gestation, and late stillbirth, defined as fetal death at 28 or more weeks' gestation. Self-reported alcohol and tobacco cigarette consumption was captured at the recruitment interview and up to 3 scheduled visits during pregnancy. Participants were followed up during pregnancy to obtain delivery outcome.

RESULTS

Of 11663 pregnancies (mean [SD] gestational age at enrollment, 18.6 [6.6] weeks) in 8506 women for whom the pregnancy outcome was known by 20 weeks' gestation or later and who did not terminate their pregnancies, there were 145 stillbirths (12.4 per 1000 pregnancies) and 82 late stillbirths (7.1 per 1000 pregnancies). A total of 59% of pregnancies were in women from South Africa, 59% were in multiracial women, 23% were in White women, 17% were in American Indian women, and 0.9% were in women of other races. A total of 8% were older than 35 years. In 51% of pregnancies, women reported no alcohol or tobacco cigarette exposure (risk of stillbirth, 4 per 1000 pregnancies). After the first trimester, 18% drank and smoked (risk of stillbirth, 15 per 1000 births), 9% drank only (risk of stillbirth, 10 per 1000 pregnancies), and 22% smoked only (risk of stillbirth, 8 per 1000 pregnancies). Compared with the reference group (pregnancies not prenatally exposed or without any exposure after the first trimester), the adjusted relative risk of late stillbirth was 2.78 (98.3% CI, 1.12-6.67) for pregnancies prenatally exposed to drinking and smoking, 2.22 (98.3% CI, 0.78-6.18) for pregnancies prenatally exposed to drinking only after the first trimester, and 1.60 (98.3% CI, 0.64-3.98) for pregnancies prenatally exposed to smoking only after the first trimester. The adjusted relative risk for all stillbirths was 1.75 (98.3% CI, 0.96-3.18) for dual exposure, 1.26 (98.3% CI, 0.58-2.74) for drinking only, and 1.27 (98.3% CI, 0.69-2.35) for smoking only compared with the reference group.

CONCLUSIONS AND RELEVANCE

These results suggest that combined drinking and smoking after the first trimester of pregnancy, compared with no exposure or quitting before the end of the first trimester, may be associated with a significantly increased risk of late stillbirth.

Airway basal stem cells generate distinct subpopulations of PNECs

Pulmonary neuroendocrine cells (PNECs) have crucial roles in airway physiology and immunity by producing bioactive amines and neuropeptides (NPs). A variety of human diseases exhibit PNEC hyperplasia. Given accumulated evidence that PNECs represent a heterogenous population of cells, we investigate how PNECs differ, whether the heterogeneity is similarly present in mouse and human cells, and whether specific disease involves discrete PNECs. Herein, we identify three distinct types of PNECs in human and mouse airways based on single and double positivity for TUBB3 and the established NP markers. We show that the three PNEC types exhibit significant differences in NP expression, homeostatic turnover, and response to injury and disease. We provide evidence that these differences parallel their distinct cell of origin from basal stem cells (BSCs) or other airway epithelial progenitors.

Nicotinic Receptors in the Brainstem Ascending Arousal System in SIDS With Analysis of Pre-natal Exposures to Maternal Smoking and Alcohol in High-Risk Populations of the Safe Passage Study

Pre-natal exposures to nicotine and alcohol are known risk factors for sudden infant death syndrome (SIDS), the leading cause of post-neonatal infant mortality. Here, we present data on nicotinic receptor binding, as determined by 125I-epibatidine receptor autoradiography, in the brainstems of infants dying of SIDS and of other known causes of death collected from the Safe Passage Study, a prospective, multicenter study with clinical sites in Cape Town, South Africa and 5 United States sites, including 2 American Indian Reservations. We examined 15 pons and medulla regions related to cardiovascular control and arousal in infants dying of SIDS (n = 12) and infants dying from known causes (n = 20, 10 pre-discharge from time of birth, 10 post-discharge). Overall, there was a developmental decrease in 125I-epibatidine binding with increasing postconceptional age in 5 medullary sites [raphe obscurus, gigantocellularis, paragigantocellularis, centralis, and dorsal accessory olive (p = 0.0002-0.03)], three of which are nuclei containing serotonin cells. Comparing SIDS with post-discharge known cause of death (post-KCOD) controls, we found significant decreased binding in SIDS in the nucleus pontis oralis (p = 0.02), a critical component of the cholinergic ascending arousal system of the rostral pons (post-KCOD, 12.1 ± 0.9 fmol/mg and SIDS, 9.1 ± 0.78 fmol/mg). In addition, we found an effect of maternal smoking in SIDS (n = 11) combined with post-KCOD controls (n = 8) on the raphe obscurus (p = 0.01), gigantocellularis (p = 0.02), and the paragigantocellularis (p = 0.002), three medullary sites found in this study to have decreased binding with age and found in previous studies to have abnormal indices of serotonin neurotransmission in SIDS infants. At these sites, 125I-epibatidine binding increased with increasing cigarettes per week. We found no effect of maternal drinking on 125I-epibatidine binding at any site measured. Taken together, these data support changes in nicotinic receptor binding related to development, cause of death, and exposure to maternal cigarette smoking. These data present new evidence in a prospective study supporting the roles of developmental factors, as well as adverse exposure on nicotinic receptors, in serotonergic nuclei of the rostral medulla-a finding that highlights the interwoven and complex relationship between acetylcholine (via nicotinic receptors) and serotonergic neurotransmission in the medulla.

The Serotonin Brainstem Hypothesis for the Sudden Infant Death Syndrome

The sudden infant death syndrome (SIDS) is the leading cause of postneonatal infant mortality in the United States today, with an overall rate of 0.39/1000 live births. It is defined as the sudden and unexpected death of an infant <12 months of age that remains unexplained after a complete autopsy, death scene investigation, and review of the clinical history. The serotonin brainstem hypothesis has been a leading hypothesis for SIDS over the last 2 decades. Our laboratory has studied this hypothesis over time with a variety of tissue techniques, including tissue receptor autoradiography, high performance liquid chromatography, Western blot analysis, immunocytochemistry, and proteomics. The purpose of this article is to review the progress in our laboratory toward supporting this hypothesis. We conclude that an important subset of SIDS infants has serotonergic abnormalities resulting from a "core lesion" in the medullary reticular formation comprised of nuclei that contain serotonin neurons. This lesion could lead to a failure of protective brainstem responses to homeostatic challenges during sleep in a critical developmental period which cause sleep-related sudden death.

Prenatal intermittent hypoxia sensitizes the laryngeal chemoreflex, blocks serotoninergic shortening of the reflex, and reduces 5-HT3 receptor binding in the NTS in anesthetized rat pups

We tested the hypothesis that exposure to intermittent hypoxia (IH) during pregnancy would prolong the laryngeal chemoreflex (LCR) and diminish the capacity of serotonin (5-hydroxytryptamine; 5-HT) to terminate the LCR. Prenatal exposure to IH was associated with significant prolongation of the LCR in younger, anesthetized, postnatal day (P) rat pups age P8 to P16 compared to control, room air (RA)-exposed rat pups of the same age. Serotonin microinjected into the NTS shortened the LCR in rat pups exposed to RA during gestation, but 5-HT failed to shorten the LCR in rat pups exposed to prenatal IH. Given these observations, we tested the hypothesis that prenatal hypoxia would decrease binding to 5-HT3 receptors in the nucleus of the solitary tract (NTS) where 5-HT acts to shorten the LCR. Serotonin 3 receptor binding was reduced in younger rat pups exposed to IH compared to control, RA-exposed rat pups in the age range P8 to P12. Serotonin 3 receptor binding was similar in older animals (P18-P24) regardless of gas exposure during gestation. The failure of the 5-HT injected into the NTS to shorten the LCR was correlated with a developmental decrease in 5-HT3 receptor binding in the NTS associated with exposure to prenatal IH. In summary, prenatal IH sensitized reflex apnea and blunted processes that terminate reflex apneas in neonatal rat pups, processes that are essential to prevent death following apneas such as those seen in babies who died of SIDS.

Concurrent prenatal drinking and smoking increases risk for SIDS: Safe Passage Study report

BACKGROUND

Sudden infant death syndrome (SIDS) is the leading cause of postneonatal mortality. Although the rate has plateaued, any unexpected death of an infant is a family tragedy thus finding causes and contributors to risk remains a major public health concern. The primary objective of this investigation was to determine patterns of drinking and smoking during pregnancy that increase risk of SIDS.

METHODS

The Safe Passage Study was a prospective, multi-center, observational study with 10,088 women, 11,892 pregnancies, and 12,029 fetuses, followed to 1-year post delivery. Subjects were from two sites in Cape Town, South Africa and five United States sites, including two American Indian Reservations. Group-based trajectory modeling was utilized to categorize patterns of drinking and smoking exposure during pregnancy.

FINDINGS

One-year outcome was ascertained in 94·2% infants, with 28 SIDS (2·43/1000) and 38 known causes of death (3·30/1000). The increase in relative risk for SIDS, adjusted for key demographic and clinical characteristics, was 11·79 (98·3% CI: 2·59-53·7, p < 0·001) in infants whose mothers reported both prenatal drinking and smoking beyond the first trimester, 3.95 (98·3% CI: 0·44-35·83, p = 0·14), for drinking only beyond the first trimester and 4·86 (95% CI: 0·97-24·27, p = 0·02) for smoking only beyond the first trimester as compared to those unexposed or reported quitting early in pregnancy.

INTERPRETATION

Infants prenatally exposed to both alcohol and cigarettes continuing beyond the first trimester have a substantially higher risk for SIDS compared to those unexposed, exposed to alcohol or cigarettes alone, or when mother reported quitting early in pregnancy. Given that prenatal drinking and smoking are modifiable risk factors, these results address a major global public health problem.

FUNDING

National Institute on Alcohol Abuse and Alcoholism, Eunice Kennedy Shriver National Institute of Child Health and Human Development, and the National Institute on Deafness and Other Communication Disorders.

SCN1A variants associated with sudden infant death syndrome

We identified SCN1A variants in 2 infants who died of sudden infant death syndrome (SIDS) with hippocampal abnormalities from an exome sequencing study of 10 cases of SIDS but no history of seizures. One harbored SCN1A G682V, and the other had 2 SCN1A variants in cis: L1296M and E1308D, a variant previously associated with epilepsy. Functional evaluation in a heterologous expression system demonstrated partial loss of function for both G682V and the compound variant L1296M/E1308D. Our cases represent a novel association between SCN1A and SIDS, extending the SCN1A spectrum from epilepsy to SIDS. Our findings provide insights into SIDS and support genetic evaluation focused on epilepsy genes in SIDS.

The Lateral Temporal Lobe in Early Human Life

Abnormalities of lateral temporal lobe development are associated with a spectrum of genetic and environmental pathologic processes, but more normative data are needed for a better understanding of gyrification in this brain region. Here, we begin to establish guidelines for the analysis of the lateral temporal lobe in humans in early life. We present quantitative methods for measuring gyrification at autopsy using photographs of the gross brain and simple computer-based quantitative tools in a cohort of 28 brains ranging in age from 27 to 70 postconceptional weeks (end of infancy). We provide normative ranges for different indices of gyrification and identify a constellation of qualitative features that should also be considered in these analyses. The ratio of the temporal area to the whole brain area increased dramatically in the second half of gestation, but then decelerated after birth before increasing linearly around 50 postconceptional weeks. Tertiary gyrification continued beyond birth in a linear process through infancy with considerable variation in patterns. Analysis of 2 brains with gyral disorders of the lateral temporal lobe demonstrated proof-of-principle that the proposed methods are of diagnostic value. These guidelines are proposed for assessments of temporal lobe pathology in pediatric brains in early life.

Long-Term Neuropathological Changes Associated with Cerebral Palsy in a Nonhuman Primate Model of Hypoxic-Ischemic Encephalopathy

BACKGROUND

Cerebral palsy (CP) is the most common motor disability in childhood, with a worldwide prevalence of 1.5-4/1,000 live births. Hypoxic-ischemic encephalopathy (HIE) contributes to the burden of CP, but the long-term neuropathological findings of this association remain limited.

METHODOLOGY

Thirty-four term Macaca nemestrina macaques were included in this long-term neuropathological study: 9 control animals delivered by cesarean section and 25 animals with perinatal asphyxia delivered by cesarean section after 15-18 min of umbilical cord occlusion (UCO). UCO animals were randomized to saline (n = 11), therapeutic hypothermia (TH; n = 6), or TH + erythropoietin (Epo; n = 8). Epo was given on days 1, 2, 3, and 7. Animals had serial developmental assessments and underwent magnetic resonance imaging with diffusion tensor imaging at 9 months of age followed by necropsy. Histology and immunohistochemical (IHC) staining of brain and brainstem sections were performed.

RESULTS

All UCO animals demonstrated and met the standard diagnostic criteria for human neonates with moderate-to-severe HIE. Four animals developed moderate-to-severe CP (3 UCO and 1 UCO + TH), 9 had mild CP (2 UCO, 3 UCO + TH, 3 UCO + TH + Epo, and 1 control), and 2 UCO animals died. None of the animals treated with TH + Epo died, had moderate-to-severe CP, or demonstrated signs of long-term neuropathological toxicity. Compared to animals grouped together as having no CP (no-CP; controls and mild CP only), animals with CP (moderate and severe) demonstrated decreased fractional anisotropy of multiple white-matter tracts including the corpus callosum and internal capsule, when using Tract-Based Spatial Statistics (TBSS). Animals with CP had decreased staining for cortical neurons and increased brainstem glial scarring compared to animals without CP. The cerebellar cell density of the internal granular layer and white matter was decreased in CP animals compared to that in control animals without CP.

CONCLUSIONS/SIGNIFICANCE

In this nonhuman primate HIE model, animals treated with TH + Epo had less brain pathology noted on TBSS and IHC staining, which supports the long-term safety of TH + Epo in the setting of HIE. Animals that developed CP showed white-matter changes noted on TBSS, subtle histopathological changes in both the white and gray matter, and brainstem injury that correlated with CP severity. This HIE model may lend itself to further study of the relationship between brainstem injury and CP.

Hippocampal Formation Maldevelopment and Sudden Unexpected Death across the Pediatric Age Spectrum

Sudden infant death syndrome (SIDS) and sudden unexplained death in childhood (SUDC) are defined as sudden death in a child remaining unexplained despite autopsy and death scene investigation. They are distinguished from each other by age criteria, i.e. with SIDS under 1 year and SUDC over 1 year. Our separate studies of SIDS and SUDC provide evidence of shared hippocampal abnormalities, specifically focal dentate bilamination, a lesion classically associated with temporal lobe epilepsy, across the 2 groups. In this study, we characterized the clinicopathologic features in a retrospective case series of 32 children with sudden death and hippocampal formation (HF) maldevelopment. The greatest frequency of deaths was between 3 weeks and 3 years (81%, 26/32). Dentate anomalies were found across the pediatric age spectrum, supporting a common vulnerability that defies the 1-year age cutoff between SIDS and SUDC. Twelve cases (38%) had seizures, including 7 only with febrile seizures. Subicular anomalies were found in cases over 1 year of age and were associated with increased risk of febrile seizures. Sudden death associated with HF maldevelopment reflects a complex interaction of intrinsic and extrinsic factors that lead to death at different pediatric ages, and may be analogous to sudden unexplained death in epilepsy.

Serotonin Receptors in the Medulla Oblongata of the Human Fetus and Infant: The Analytic Approach of the International Safe Passage Study

The Safe Passage Study is an international, prospective study of approximately 12 000 pregnancies to determine the effects of prenatal alcohol exposure (PAE) upon stillbirth and the sudden infant death syndrome (SIDS). A key objective of the study is to elucidate adverse effects of PAE upon binding to serotonin (5-HT) 1A receptors in brainstem homeostatic networks postulated to be abnormal in unexplained stillbirth and/or SIDS. We undertook a feasibility assessment of 5-HT_1A receptor binding using autoradiography in the medulla oblongata (6 nuclei in 27 cases). 5-HT_1A binding was compared to a reference dataset from the San Diego medical examiner’s system. There was no adverse effect of postmortem interval ≤100 h. The distribution and quantitated values of 5-HT_1A binding in Safe Passage Study cases were essentially identical to those in the reference dataset, and virtually identical between stillbirths and live born fetal cases in grossly non-macerated tissues. The pattern of binding was present at mid-gestation with dramatic changes in binding levels in the medullary 5-HT nuclei over the second half of gestation; there was a plateau at lower levels in the neonatal period and into infancy. This study demonstrates feasibility of 5-HT_1A binding analysis in the medulla in the Safe Passage Study.

A Century of Germinal Matrix Intraventricular Hemorrhage in Autopsied Premature Infants: A Historical Account

The care of premature infants in the 20th century is remarkable for technical advances that have dramatically improved survival, but little is known about temporal changes in the neuropathology of the premature infant over this time frame. We hypothesize that the autopsy rate of germinal matrix hemorrhage changed in the 20th century relative to combined influences of clinical interventions that were both harmful and helpful. We examined germinal matrix hemorrhage with intraventricular hemorrhage (GMH-IVH) in 345 premature infants (gestational age 25-36 weeks) autopsied at Boston Children's Hospital from 1914 to 2015. There was a median of 19 cases/decade (range 7-68). Over the course of the study median gestational age decreased from 33 to 27 gestational weeks (P<0.001), and median postnatal survival increased from 2 to 26 days (P=0.02). The incidence of GMH-IVH increased from 4.7% before 1960 to 50.0% from 1975 to 1980, and then decreased to 12.5% after 2005 (P<0.001). The incidence of GMH-IVH increased >3-fold around the time of the introduction of positive pressure ventilation into premature intensive care in the mid-1960s. The increased incidence of GMH-IVH in the 1970s-1980s likely reflects respiratory and hemodynamic imbalances complicating mechanical ventilation. We speculate that the subsequent decreased incidence of GMH-IVH likely reflects stabilization of respiratory function with improvements in ventilators and in ventilator management beginning in the 1970s and the use of surfactant and antenatal steroids in the 1980s.

Dentate gyrus abnormalities in sudden unexplained death in infants: morphological marker of underlying brain vulnerability

Sudden unexplained death in infants, including the sudden infant death syndrome, is likely due to heterogeneous causes that involve different intrinsic vulnerabilities and/or environmental factors. Neuropathologic research focuses upon the role of brain regions, particularly the brainstem, that regulate or modulate autonomic and respiratory control during sleep or transitions to waking. The hippocampus is a key component of the forebrain-limbic network that modulates autonomic/respiratory control via brainstem connections, but its role in sudden infant death has received little attention. We tested the hypothesis that a well-established marker of hippocampal pathology in temporal lobe epilepsy-focal granule cell bilamination in the dentate, a variant of granule cell dispersion-is associated with sudden unexplained death in infants. In a blinded study of hippocampal morphology in 153 infants with sudden and unexpected death autopsied in the San Diego County medical examiner's office, deaths were classified as unexplained or explained based upon autopsy and scene investigation. Focal granule cell bilamination was present in 41.2% (47/114) of the unexplained group compared to 7.7% (3/39) of the explained (control) group (p < 0.001). It was associated with a cluster of other dentate developmental abnormalities that reflect defective neuronal proliferation, migration, and/or survival. Dentate lesions in a large subset of infants with sudden unexplained death may represent a developmental vulnerability that leads to autonomic/respiratory instability or autonomic seizures, and sleep-related death when the infants are challenged with homeostatic stressors. Importantly, these lesions can be recognized in microscopic sections prepared in current forensic practice. Future research is needed to determine the relationship between hippocampal and previously reported brainstem pathology in sudden infant death.

Neuropathologic studies of the encephalopathy of prematurity in the late preterm infant

It has been widely suggested that brain damage in survivors of late preterm deliveries is similar to that in early preterm infants, only less severe. This report addresses this concept through reanalysis of published neuropathologic data obtained according to late preterm in comparison with early preterm ages. Findings suggest that the spectrum of brain injury in the late preterm infant, as determined in an autopsy population, is similar to that found in early preterm infants, with potential differential susceptibility for different neuronal, glial, and vascular indices. Further research is needed to more clearly define developmental cellular susceptibilities in preterm populations.

Development of brainstem 5-HT1A receptor-binding sites in serotonin-deficient mice

The sudden infant death syndrome is associated with a reduction in brainstem serotonin 5-hydroxytryptamine (5-HT) and 5-HT(1A) receptor binding, yet it is unknown if and how these findings are linked. In this study, we used quantitative tissue autoradiography to determine if post-natal development of brainstem 5-HT(1A) receptors is altered in two mouse models where the development of 5-HT neurons is defective, the Lmx1b(f/f/p) , and the Pet-1⁻/⁻ mouse. 5-HT(1A) receptor agonist-binding sites were examined in both 5-HT-source nuclei (autoreceptors) and in sites that receive 5-HT innervation (heteroreceptors). In control mice between post-natal day (P) 3 and 10, 5-HT(1A) receptor binding increased in several brainstem sites; by P25, there were region-specific increases and decreases, refining the overall binding pattern. In the Lmx1b(f/f/p) and Pet-1⁻/⁻ mice, 5-HT(1A)-autoreceptor binding was significantly lower than in control mice at P3, and remained low at P10 and P25. In contrast, 5-HT(1A) heteroreceptor levels were comparable between control and 5-HT-deficient mice. These data define the post-natal development of 5-HT(1A)-receptor binding in the mouse brainstem. Furthermore, the data suggest that 5-HT(1A)-heteroreceptor deficits detected in sudden infant death syndrome are not a direct consequence of a 5-HT neuron dysfunction nor reduced brain 5-HT levels. To elucidate the developmental relationship between serotonin (5-HT) levels and 5-HT(1A) receptors in the brainstem, we examined 5-HT(1A) binding in two 5-HT-deficient mouse models. In nuclei containing 5-HT neurons, 5-HT(1A) binding was decreased (autoreceptors), while binding was maintained in projection sites (heteroreceptors). Thus, brainstem 5-HT(1A)-heteroreceptor-binding sites do not appear developmentally sensitive to reduced brain 5-HT levels.

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.

Radial coherence of diffusion tractography in the cerebral white matter of the human fetus: neuroanatomic insights

High angular resolution diffusion imaging (HARDI) demonstrates transient radial coherence of telencephalic white matter in the human fetus. Our objective was to define the neuroanatomic basis of this radial coherence through correlative HARDI- and postmortem tissue analyses. Applying immunomarkers to radial glial fibers (RGFs), axons, and blood vessels in 18 cases (19 gestational weeks to 3 postnatal years), we compared their developmental profiles to HARDI tractography in brains of comparable ages (n = 11). At midgestation, radial coherence corresponded with the presence of RGFs. At 30-31 weeks, the transition from HARDI-defined radial coherence to corticocortical coherence began simultaneously with the transformation of RGFs to astrocytes. By term, both radial coherence and RGFs had disappeared. White matter axons were radial, tangential, and oblique over the second half of gestation, whereas penetrating blood vessels were consistently radial. Thus, radial coherence in the fetal white matter likely reflects a composite of RGFs, penetrating blood vessels, and radial axons of which its transient expression most closely matches that of RGFs. This study provides baseline information for interpreting radial coherence in tractography studies of the preterm brain in the assessment of the encephalopathy of prematurity.

Neuron deficit in the white matter and subplate in periventricular leukomalacia

OBJECTIVE

The cellular basis of cognitive abnormalities in preterm infants with periventricular leukomalacia (PVL) is uncertain. One important possibility is that damage to white matter and subplate neurons that are critical to the formation of the cerebral cortex occurs in conjunction with oligodendrocyte and axonal injury in PVL. We tested the hypothesis that the overall density of neurons in the white matter and subplate region is significantly lower in PVL cases compared to non-PVL controls.

METHODS

We used a computer-based method for the determination of the density of microtubule-associated protein 2-immunolabeled neurons in the ventricular/subventricular region, periventricular white matter, central white matter, and subplate region in PVL cases and controls.

RESULTS

There were 5 subtypes of subcortical neurons: granular, unipolar, bipolar, inverted pyramidal, and multipolar. The neuronal density of the granular neurons in each of the 4 regions was 54 to 80% lower (p≤0.01) in the PVL cases (n=15) compared to controls adjusted for age and postmortem interval (n=10). The overall densities of unipolar, bipolar, multipolar, and inverted pyramidal neurons did not differ significantly between the PVL cases and controls. No granular neurons expressed markers of neuronal and glial immaturity (Tuj1, doublecortin, or NG2).

INTERPRETATION

These data suggest that quantitative deficits in susceptible granular neurons occur in the white matter distant from periventricular foci, including the subplate region, in PVL, and may contribute to abnormal cortical formation and cognitive dysfunction in preterm survivors.

The serotonergic anatomy of the developing human medulla oblongata: implications for pediatric disorders of homeostasis

The caudal serotonergic (5-HT) system is a critical component of a medullary "homeostatic network" that regulates protective responses to metabolic stressors such as hypoxia, hypercapnia, and hyperthermia. We define anatomically the caudal 5-HT system in the human medulla as 5-HT neuronal cell bodies located in the raphé (raphé obscurus, raphé magnus, and raphé pallidus), extra-raphé (gigantocellularis, paragigantocellularis lateralis, intermediate reticular zone, lateral reticular nucleus, and nucleus subtrigeminalis), and ventral surface (arcuate nucleus). These 5-HT neurons are adjacent to all of the respiratory- and autonomic-related nuclei in the medulla where they are positioned to modulate directly the responses of these effector nuclei. In the following review, we highlight the topography and development of the caudal 5-HT system in the human fetus and infant, and its inter-relationships with nicotinic, GABAergic, and cytokine receptors. We also summarize pediatric disorders in early life which we term "developmental serotonopathies" of the caudal (as well as rostral) 5-HT domain and which are associated with homeostatic imbalances. The delineation of the development and organization of the human caudal 5-HT system provides the critical foundation for the neuropathologic elucidation of its disorders directly in the human brain.

Potential neuronal repair in cerebral white matter injury in the human neonate

Periventricular leukomalacia (PVL) in the premature infant represents the major substrate underlying cognitive deficits and cerebral palsy and is characterized as focal periventricular necrosis and diffuse gliosis in the immature cerebral white matter. We have recently shown a significant decrease in the density of neurons in PVL relative to controls throughout the white matter, including the subventricular, periventricular, and subcortical regions. These neurons are likely to be remnants of the subplate and/or GABAergic neurons in late migration to the cerebral cortex, both of which are important for proper cortical circuitry in development and throughout adulthood. Here, we tested the hypothesis that intrinsic repair occurs in PVL to attempt to compensate for the deficits in white matter neurons. By using doublecortin (DCX) immunopositivity as a marker of postmitotic migrating neurons, we found significantly increased densities (p < 0.05) of DCX-immunopositive cells in PVL cases (n = 9) compared with controls (n = 7) in the subventricular zone (their presumed site of origin), necrotic foci, and subcortical white matter in the perinatal time-window, i.e. 35-42 postconceptional weeks. These data provide the first evidence suggestive of an attempt at neuronal repair or regeneration in human neonatal white matter injury.

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.

Thalamic damage in periventricular leukomalacia: novel pathologic observations relevant to cognitive deficits in survivors of prematurity

Despite major advances in the long-term survival of premature infants, cognitive deficits occur in 30-50% of very preterm (<32 gestational weeks) survivors. Impaired working memory and attention despite average global intelligence are central to the academic difficulties of the survivors. Periventricular leukomalacia (PVL), characterized by periventricular necrosis and diffuse gliosis in the cerebral white matter, is the major brain pathology in preterm infants. We tested the novel hypothesis that pathology in thalamic nuclei critical for working memory and attention, i.e. mediodorsal nucleus and reticular nucleus, respectively, occurs in PVL. In 22 PVL cases (gestational age 32.5 +/- 4.8 wk) and 16 non-PVL controls (36.7 +/- 5.2 wk) who died within infancy, the incidence of thalamic pathology was significantly higher in PVL cases (59%; 13/22) compared with controls (19%; 3/16) (p = 0.01), with substantial involvement of the mediodorsal, and reticular nuclei in PVL. The prevention of thalamic damage may be required for the eradication of defects in survivors with PVL.

Diffuse axonal injury in periventricular leukomalacia as determined by apoptotic marker fractin

Periventricular leukomalacia (PVL), the major substrate of neurologic deficits in premature infants, is associated with reduced white matter volume. Using immunomarkers of axonal pathology [beta-amyloid precursor protein (beta-APP) and apoptotic marker fractin], we tested the hypothesis that widespread (diffuse) axonal injury occurs in the gliotic white matter beyond the foci of necrosis in PVL, thus contributing to the white matter volume reduction. In a cohort of 17 control cases and 13 PVL cases with lesions of different chronological ages, diffuse axonal damage in PVL was detected by fractin in white matter sites surrounding and distant from acute and organizing foci of necrosis. Using beta-APP, axonal spheroids were detected within necrotic foci in the acute and organizing (subacute) stages, a finding consistent with others. Interestingly, GAP-43 expression was also detected in spheroids in the necrotic foci, suggesting attempts at axonal regeneration. Thirty-one percent of the PVL cases had thalamic damage and 15% neuronal injury in the cerebral cortex overlying PVL. We conclude that diffuse axonal injury, as determined by apoptotic marker fractin, occurs in PVL and that its cause likely includes primary ischemia and trophic degeneration secondary to corticothalamic neuronal damage.

Myelin abnormalities without oligodendrocyte loss in periventricular leukomalacia

The cellular basis of myelin deficits detected by neuroimaging in long-term survivors of periventricular leukomalacia (PVL) is poorly understood. We tested the hypothesis that oligodendrocyte lineage (OL) cell density is reduced in PVL, thereby contributing to subsequent myelin deficits. Using computer-based methods, we determined OL cell density in sections from 18 PVL and 18 age-adjusted control cases, immunostained with the OL-lineage marker Olig2. Myelination was assessed with myelin basic protein (MBP) immunostaining. We found no significant difference between PVL and control cases in Olig2 cell density in the periventricular or intragyral white matter. We did find, however, a significant increase in Olig2 cell density at the necrotic foci, compared with distant areas. Although no significant difference was found in the degree of MBP immunostaining, we observed qualitative abnormalities of MBP immunostaining in both the diffuse and necrotic components of PVL. Abnormal MBP immunostaining in PVL despite preserved Olig2 cell density may be secondary to arrested OL maturation, damage to OL processes, and/or impaired axonal-OL signaling. OL migration toward the "core" of injury may occur to replenish OL cell number. This study provides new insight into the cellular basis of the myelin deficits observed in survivors of PVL.

TLR8: an innate immune receptor in brain, neurons and axons

Toll-like receptors (TLRs) play essential roles in generating innate immune responses, and are evolutionarily conserved across species. In mammals, TLRs specifically recognize the conserved microbial structural motifs referred to as pathogen-associated molecular patterns (PAMPs). Ligand recognition by TLRs activates signaling cascades that culminate in proinflammatory cytokine production and eventual elimination of invading pathogens. Although TLRs in mammals are expressed predominantly in the immune system, certain TLRs with poorly characterized function are also found in neurons. We recently profiled TLR8 expression during mouse brain development and established its localization in neurons and axons. We uncovered a novel role for TLR8 as a suppressor of neurite outgrowth as well as an inducer of neuronal apoptosis, and found that TLR8 functions in neurons through an NF-kappaB-independent mechanism. These findings add a new layer of complexity for TLR signaling, and expand the realm of mammalian TLR function to the CNS beyond the originally discovered immune context. Herein, we complement our earlier report with additional data, discuss their biological and mechanistic implications in central nervous system (CNS) developmental and pathological processes, and thus further our perspective on TLR signaling and potential physiological roles in mammals.

Is the late preterm infant more vulnerable to gray matter injury than the term infant?

This article addresses the issue of whether the late preterm infant is more susceptible to gray matter injury induced by hypoxia-ischemia than the term infant. Although different gray matter regions display varying patterns of neuronal injury in the face of hypoxia-ischemia during advancing gestational development, little is known about the specific patterns of injury faced by the late preterm infant. This changing pattern of neuronal vulnerability with age likely reflects developmental changes of susceptibility and protective factors essential for responding to energy deprivation at the molecular, cellular, biochemical, and vascular levels. Future research involving closer examination of the late preterm period is essential to provide a greater understanding of the neuronal vulnerability in the face of hypoxic-ischemic injury.

Development of microglia in the cerebral white matter of the human fetus and infant

Although microglial activation may be an initial beneficial response to a variety of insults, prolonged activation can release toxic substances and lead to cell death. Microglial activation secondary to hypoxia-ischemia and/or infection in immature cerebral white matter is important in the pathogenesis of periventricular leukomalacia (PVL), the major pathological substrate of cerebral palsy in the premature infant. We hypothesize that a transient overexpression in activated microglial density occurs normally in the cerebral white matter of the human fetus during the peak window of vulnerability for PVL. Such an increase could render this region susceptible to insults that cause prolonged microglial activation, as conceptualized in PVL. To examine the developmental profile of microglia in the human fetus and infant brain, immunocytochemistry with microglial specific markers were used in 23 control (non-PVL) cases ranging from 20 to 183 postconceptional (PC) weeks. Tomato lectin, used to identify microglial morphology, revealed that the cerebral white matter of the human fetus and infant is densely populated with intermediate and amoeboid microglia; the latter is indicative of an activated state. Quantitative analysis with CD68 showed increased density of activated microglia in the cerebral white matter of the fetus (<37 PC weeks) relative to the neonate/infant (> or =37 PC weeks) and to the overlying cortex of either age group (P = 0.01). The primary finding of a transient, developmental-dependent overabundance of CD68-activated microglia in the cerebral white matter of the fetus suggests a potential "priming" of this area for diverse brain insults characterized by activation of microglia, particularly PVL. J.

Lipid Peroxidation During Human Cerebral Myelination

The critical period of human cerebral myelination is characterized by rapid production of cellular membranes. We hypothesize that this period is subject to the "physiological" generation of free radicals resulting in lipid peroxidation (LPO). In this study, oxidative markers were examined in developing human parietal white matter using 4-hydroxy-2-nonenal (HNE) protein adducts as an indicator of LPO. Immunocytochemistry showed an increase in HNE-positive glia from 40 gestational weeks to 1.5 postnatal years encompassing the peak period of myelin sheath synthesis at this site. Western blots showed a distinct pattern of HNE-modified proteins at fetal/term ages 26 to 42 gestational weeks and a second, different pattern at 45 gestational weeks to 2.5 postnatal years. Proteins modified by HNE in the latter period, corresponding to active myelination, were identified using mass spectrometry. The most prominent category of HNE modification included cytoskeletal proteins such as tubulins and neurofilaments. Other categories included cell type-specific proteins for mature oligodendrocytes and astrocytes and proteins involved in cell cycle and energy metabolism. We conclude that human brain development involves basal levels of oxidative stress and resulting LPO and that these processes target different proteins in an age-specific manner, thereby likely playing distinct roles during different periods of brain maturation.

Oxidative and nitrative injury in periventricular leukomalacia: a review

Periventricular leukomalacia (PVL) is the major substrate of cerebral palsy in survivors of prematurity. Its pathogenesis is complex and likely involves ischemia/reperfusion in the critically ill premature infant, with impaired regulation of cerebral blood flow, as well as inflammatory mechanisms associated with maternal and/or fetal infection. During the peak period of vulnerability for PVL, developing oligodendrocytes (OLs) predominate in the white matter. We hypothesize that free radical injury to the developing OLs underlies, in part, the pathogenesis of PVL and the hypomyelination seen in long-term survivors. In human PVL, free radical injury is supported by evidence of oxidative and nitrative stress with markers to lipid peroxidation and nitrotyrosine, respectively. Evidence in normal human cerebral white matter suggests an underlying vulnerability of the premature infant to free radical injury resulting from a developmental mismatch of antioxidant enzymes (AOE) and subsequent imbalance in oxidant metabolism. In vitro studies using rodent OLs suggest that maturational susceptibility to reactive oxygen species is dependent, not only on levels of individual AOE, but also on specific interactions between these enzymes. Rodent in vitro data further suggest 2 mechanisms of nitric oxide damage: one involving the direct effect of nitric oxide on OL mitochondrial integrity and function, and the other involving an activation of microglia and subsequent release of reactive nitrogen species. The latter mechanism, while important in rodent studies, remains to be determined in the pathogenesis of human PVL. These observations together expand our knowledge of the role that free radical injury plays in the pathogenesis of PVL, and may contribute to the eventual development of therapeutic strategies to alleviate the burden of oxidative and nitrative injury in the premature infant at risk for PVL.

Axonal development in the cerebral white matter of the human fetus and infant

After completion of neuronal migration to form the cerebral cortex, axons undergo rapid elongation to their intra- and subcortical targets, from midgestation through infancy. We define axonal development in the human parietal white matter in this critical period. Immunocytochemistry and Western blot analysis were performed on 46 normative cases from 20-183 postconceptional (PC) weeks. Anti-SMI 312, a pan-marker of neurofilaments, stained axons as early as 23 weeks. Anti-SMI 32, a marker for nonphosphorylated neurofilament high molecular weight (NFH), primarily stained neuronal cell bodies (cortical, subcortical, and Cajal-Retzius). Anti-SMI 31, which stains phosphorylated NFH, was used as a marker of axonal maturity, and showed relatively low levels of staining (approximately one-fourth of adult levels) from 24-34 PC weeks. GAP-43, a marker of axonal growth and elongation, showed high levels of expression in the white matter from 21-64 PC weeks and lower, adult-like levels beyond 17 postnatal months. The onset of myelination, as seen by myelin basic protein expression, was approximately 54 weeks, with progression to "adult-like" staining by 72-92 PC weeks. This study provides major insight into axonal maturation during a critical period of growth, over an age range not previously examined and one coinciding with the peak period of periventricular leukomalacia (PVL), the major disorder underlying cerebral palsy in premature infants. These data suggest that immature axons are susceptible to damage in PVL and that the timing of axonal maturation must be considered toward establishing its pathology relative to the oligodendrocyte/myelin/axonal unit.

Developmental lag in superoxide dismutases relative to other antioxidant enzymes in premyelinated human telencephalic white matter

Periventricular leukomalacia (PVL) involves free radical injury to developing oligodendrocytes (OLs), resulting from ischemia/reperfusion, particularly between 24 and 32 gestational weeks. Using immunocytochemistry and Western blots, we tested the hypothesis that this vulnerability to free radical toxicity results, in part, from developmental lack of superoxide dismutases (SOD)-1 and -2, catalase, and glutathione peroxidase (GPx) in the telencephalic white matter of the human fetus. During the period of greatest PVL risk and through term (> or = 37 weeks), expression of both SODs (for conversion of O2- to H2O2) significantly lagged behind that of catalase and GPx (for breakdown of H2O2), which, in contrast, superseded adult levels by 30 gestational weeks. Our data indicate that a developmental "mismatch" in the sequential antioxidant enzyme cascade likely contributes to the vulnerability to free radical toxicity of the immature cerebral white matter, which is "unprepared" for the transition from a hypoxic intrauterine to an oxygen-rich postnatal environment. All enzymes, localized to astrocytes and OLs, had higher-than-adult expression at 2 to 5 postnatal months (peak of myelin sheath synthesis), suggesting an adaptive mechanism to protect against lipid peroxidation during myelin sheath (lipid) synthesis. The previously unrecognized dissociation between the expression of the SODs and that of catalase and GPx in the fetal period has potential implications for future antioxidant therapy in PVL.

Interferon-gamma expression in periventricular leukomalacia in the human brain

Periventricular leukomalacia (PVL), the major lesion underlying cerebral palsy in survivors of prematurity, is characterized by focal periventricular necrosis and diffuse gliosis of immature cerebral white matter. Causal roles have been ascribed to hypoxiaischemia and maternal-fetal infection, leading to cytokine responses, inflammation, and oligodendrocyte cell death. Because interferon-gamma (IFN-gamma) is directly toxic to immature oligodendrocytes, we tested the hypothesis that it is expressed in PVL (N = 13) compared to age-adjusted controls (N = 31) using immunocytochemistry. In PVL, IFN-gamma immunopositive macrophages were clustered in necrotic foci, and IFN-gamma immunopositive reactive astrocytes were present throughout the surrounding white matter (WM). The difference in the number of IFN-gamma immunopositive glial cells/high power field (IFN-gamma score, Grades 0-3) between PVL cases (age-adjusted mean 2.59+/-0.25) and controls (age-adjusted mean 1.39+/-0.16) was significant (p<0.001). In the gliotic WM, the IFN-gamma score correlated with markers for lipid peroxidation, but not nitrative stress. A subset of premyelinating (04+) oligodendrocytes expressed IFN-gamma receptors in PVL and control cases, indicating that these cells are vulnerable to IFN-gamma toxicity via receptor-mediated interactions. In PVL, IFN-gamma produced by macrophages and reactive astrocytes may play a role in cytokine-induced toxicity to premyelinating oligodendrocytes as part of a cytokine response stimulated by ischemia and/or infection.

Nitrosative and oxidative injury to premyelinating oligodendrocytes in periventricular leukomalacia

Periventricular leukomalacia (PVL), the major substrate of cerebral palsy in survivors of prematurity, is defined as focal periventricular necrosis and diffuse gliosis in immature cerebral white matter. We propose that nitrosative and/or oxidative stress to premyelinating oligodendrocytes complicating cerebral ischemia in the sick premature infant is a key mechanism of injury interfering with maturation of these cells to myelin-producing oligodendrocytes and subsequent myelination. Using immunocytochemical markers in autopsy brain tissue from 17 PVL cases and 28 non-PVL controls, we found in the PVL cases: 1) selective regionalization of white matter injury, including preferential involvement of the deep compared to intragyral white matter; 2) prominent activation of microglia diffusely throughout the white matter; 3) protein nitration and lipid peroxidation in premyelinating oligodendrocytes in the diffuse component; 4) preferential death of premyelinating oligodendrocytes diffusely; and 5) virtual sparing of the overlying cerebral cortex, as demonstrated by markers of activated astrocytes and microglia. These data establish that PVL is primarily a white matter disease that involves injury to premyelinating oligodendrocytes, potentially through activation of microglia and release of reactive oxygen and nitrogen species. Agents that prevent nitrosative and oxidative stress may play a key role in ameliorating PVL in premature infants in the intensive care nursery.

Apoptosis in RAW 264.7 cells exposed to 4-hydroxy-2-nonenal: dependence on cytochrome C release but not p53 accumulation

The toxic reactive aldehyde lipid peroxidation byproduct 4-hydroxy-2-nonenal (HNE) is thought to be a major contributor to oxidant stress-mediated cell injury. HNE induced apoptosis in RAW 264.7 murine macrophage cells in a dose-dependent manner within 6-8 h after exposure. Expression of the antiapoptotic protein Bcl-2 in stably transfected RAW 264.7 cells prevented HNE-induced internucleosomal DNA fragmentation and apoptosis, and these cells resume growth after a temporary (24-48 h) growth delay. While parental RAW 264.7 cells released mitochondrial cytochrome c within 3 h after HNE exposure, expression of Bcl-2 prevented cytochrome c release. In control cells, p53 protein levels peaked at 6-9 h after HNE exposure and then declined, while in Bcl-2 expressing cells, p53 levels were maximal at 6-9 h and remained elevated up to 96 h. Expression of SV40 large T-antigen, which forms a stable complex with p53 protein, via stable transfection-blocked transactivation of the p53-regulated gene p21(WAF1/CIP1), but did not affect induction of apoptosis by HNE, suggesting that p53 function is not important in HNE-induced apoptosis. These results suggest that cytochrome c release, but not p53 accumulation, plays an essential role in HNE-induced apoptosis in RAW 264.7 cells.

Selective protection by stably transfected human ALDH3A1 (but not human ALDH1A1) against toxicity of aliphatic aldehydes in V79 cells

Toxic medium chain length alkanals, alkenals, and 4-hydroxyalkenals that are generated during lipid peroxidation are potential substrates for aldehyde dehydrogenase (ALDH) isoforms. We have developed transgenic cell lines to examine the potential for either human ALDH1A1 or ALDH3A1 to protect against damage mediated by these toxic aldehydes. Using crude cytosols from stably transfected cell lines, these aldehydes were confirmed to be excellent substrates for ALDH3A1, but were poorly oxidized by ALDH1A1. Expression of ALDH3A1 by stable transfection in V79 cells conferred a high level of protection against growth inhibition by the medium-chain length aldehyde substrates with highest substrate activity, including hexanal, trans-2-hexenal, trans-2-octenal, trans-2-nonenal, and 4-hydroxy-2-nonenal (HNE). This was reflected in a parallel ability of ALDH3A1 to prevent depletion of glutathione by these aldehydes. Expression of hALDH3 completely blocked the potent induction of apoptosis by HNE in both V79 cells and in a RAW 264.7 murine macrophage cell line, consistent with the observed total prevention of HNE-protein adduct formation. Structure-activity studies indicated that the rank order of potency for the contributions of HNE functional groups to toxicity was aldehyde >/=C2=C3 double bond>>C4-hydroxyl group. Oxidation of the aldehyde moiety of HNE to a carboxyl by ALDH3A1 expressed in stably transfected cell lines drastically reduced its potency for growth inhibition and apoptosis induction. In contrast, ALDH1A1 expression provided only moderate protection against trans-2-nonenal (t2NE), and none against the other six-nine carbon aldehydes. Neither ALDH1A1 nor ALDH3A1 conferred any protection against acrolein, acetaldehyde, or chloroacetaldehyde. A small degree of protection against malondialdehyde was afforded by ALDH1A1, but not ALDH3A1. Paradoxically, cells expressing ALDH3A1 were 1.5-fold more sensitive to benzaldehyde toxicity than control V79 cells. These studies demonstrate that expression of class 3 ALDH, but not class 1 ALDH, can be an important determinant of cellular resistance to toxicity mediated by aldehydes of intermediate chain length that are produced during lipid peroxidation.

Structure-activity relationships for growth inhibition and induction of apoptosis by 4-hydroxy-2-nonenal in raw 264.7 cells

4-Hydroxy-2-nonenal (HNE) is a highly reactive lipid aldehyde byproduct of the peroxidation of cellular membranes. The structure of HNE features three functional groups, a C1 aldehyde, a C2==C3 double bond, and a C4- hydroxyl group, each of which may contribute to the toxicity of the compound. In addition, the length of the aliphatic chain may influence toxic potency by altering lipophilicity. Using analogous compounds that lacked one or more of the structural moieties, the role of each of these structural motifs in the cytotoxicity of HNE was examined in a mouse alveolar macrophage cell line (RAW 264.7) by a cell survival and growth assay. The importance of these functional groups in the potency of HNE for induction of apoptosis was also examined. The rank order of effects on toxicity was C1---aldehyde >/= C2==C3 double bond >> C4---hydroxyl, with parallel results in both the survival/growth inhibition and apoptosis induction assays. The chain length also influenced toxicity in a series of alpha,beta-unsaturated alkenyl aldehydes, with increasing chain length yielding increasing toxicity. To confirm the importance of the aldehyde moiety, and to examine the role of metabolic detoxification in cellular defenses against HNE toxicity, a RAW 264.7 cell line overexpressing human aldehyde dehydrogenase-3 (hALDH3) was generated. This cell line exhibited nearly complete protection against HNE-protein adduct formation as well as HNE-induced apoptosis. These results illustrate the comparative significance of key structural features of HNE in relation to its potent toxicity and induction of apoptosis.

Chemoprotective functions of glutathione S-transferases in cell lines induced to express specific isozymes by stable transfection

The authors have shown that expression of mGSTM1-1 or hGSTP1-1 in MCF-7 cells protects against DNA alkylation by 4-nitroquinoline-1-oxide (NQO) in an isozyme-specific manner and is commensurate with relative specific activity. Expression of GSTs also conferred protection against both DNA strand breaks and sister-chromatid exchange induced by NQO. Interestingly, GST expression did not protect against NQO cytotoxicity in transfected MCF-7 cell lines, although resistance to NQO cytotoxicity was observed in a T47D pi transfectant line, expressing much higher specific activity of the transfected hGSTP1-1. However, high level expression of hGSTP1-1 or mGSTM1-1 in V79 transfectants did not confer resistance to cytotoxicity, indicating that expression of GST alone is not sufficient. The authors have also shown protection against AFB1 in cell lines expressing transfected rat CYP2B1 (V79MZr2B1) and transfected mGST-Yc (mGSTA3-3). Protection was observed against both alkylation of DNA (3-fold) by [3H]AFB1 and against AFB1 cytotoxicity (7-fold). Similarly, V79MZr1A1 cells that express CYP1A1 and either transfected human or murine GSTP1-1 (< 5000 mIU/mg, CDNB) exhibited > 70% decrease in covalent labeling of total nucleic acids by [3H]BPDE. However, no protection against the cytotoxicity of BPDE was conferred by expression of hGSTP1-1. Overall, these results indicate that in some (NQO or BPDE), but not all (AFB1) cases, protection by GST expression against DNA damage is more effective than protection against cytotoxicity. In addition, there is evidence to indicate that additional factor(s) other than high GST isozyme expression level and good substrate efficacy affect the degree of protection against cytotoxicity of reactive electrophiles. This includes the differential protection against NQO cytotoxicity in T47D pi, but not V79 Xh pi-33 cells and also the recent studies which showed that expression of the MRP GS-X conjugate efflux transporter confers synergistic protection against NQO cytotoxicity when co-expressed with transfected human GSTP1-1 in MCF-7 cells. Thus, protective efficacy conferred by GST expression can vary with different cellular targets and/or experimental end-points, as well as with variations in relative specific activity or in different cellular phenotypic contexts.