Gag-like proteins: Novel mediators of prenatal alcohol exposure in neural development

Sex and age effects on gray matter volume trajectories in young children with prenatal alcohol exposure

Prenatal alcohol exposure (PAE) occurs in ~11% of North American pregnancies and is the most common known cause of neurodevelopmental disabilities such as fetal alcohol spectrum disorder (FASD; ~2-5% prevalence). PAE has been consistently associated with smaller gray matter volumes in children, adolescents, and adults. A small number of longitudinal studies show altered gray matter development trajectories in late childhood/early adolescence, but patterns in early childhood and potential sex differences have not been characterized in young children. Using longitudinal T1-weighted MRI, the present study characterized gray matter volume development in young children with PAE (N = 42, 84 scans, ages 3-8 years) compared to unexposed children (N = 127, 450 scans, ages 2-8.5 years). Overall, we observed altered global and regional gray matter development trajectories in the PAE group, wherein they had attenuated age-related increases and more volume decreases relative to unexposed children. Moreover, we found more pronounced sex differences in children with PAE; females with PAE having the smallest gray matter volumes and the least age-related changes of all groups. This pattern of altered development may indicate reduced brain plasticity and/or accelerated maturation and may underlie the cognitive/behavioral difficulties often experienced by children with PAE. In conjunction with previous research on older children, adolescents, and adults with PAE, our results suggest that gray matter volume differences associated with PAE vary by age and may become more apparent in older children.

DNMT1 Y495C mutation interferes with maintenance methylation of imprinting control regions

Hereditary Sensory and Autonomic Neuropathy Type 1E (HSAN1E) is a rare autosomal dominant neurological disorder due to missense mutations in DNA methyltransferase 1 (DNMT1). To investigate the nature of the dominant effect, we compared methylomes of transgenic R1wtDnmt1 and R1Dnmt1Y495C mouse embryonic stem cells (mESCs) overexpressing WT and the mutant mouse proteins respectively, with the R1 (wild-type) cells. In case of R1Dnmt1Y495C, 15 out of the 20 imprinting control regions were hypomethylated with transcript level dysregulation of multiple imprinted genes in ESCs and neurons. Non-imprinted regions, minor satellites, major satellites, LINE1 and IAP repeats were unaffected. These data mirror the specific imprinting defects associated with transient removal of DNMT1 in mESCs, deletion of the maternal-effect DNMT1o variant in preimplantation mouse embryos, and in part, reprogramming to naïve human iPSCs. This is the first DNMT1 mutation demonstrated to specifically affect Imprinting Control Regions (ICRs), and reinforces the differences in maintenance methylation of ICRs over non-imprinted regions. Consistent with nervous system abnormalities in the HSAN1E disorder and involvement of imprinted genes in normal development and neurogenesis, R1Dnmt1Y495C cells showed dysregulated pluripotency and neuron marker genes, and yielded more slender, shorter, and extensively branched neurons. We speculate that R1Dnmt1Y495C cells produce predominantly dimers containing mutant proteins, leading to a gradual and specific loss of ICR methylation during early human development.

Alcohol Exposure Induces Nucleolar Stress and Apoptosis in Mouse Neural Stem Cells and Late-Term Fetal Brain

Prenatal alcohol exposure (PAE) is a leading cause of neurodevelopmental disability through its induction of neuronal growth dysfunction through incompletely understood mechanisms. Ribosome biogenesis regulates cell cycle progression through p53 and the nucleolar cell stress response. Whether those processes are targeted by alcohol is unknown. Pregnant C57BL/6J mice received 3 g alcohol/kg daily at E8.5-E17.5. Transcriptome sequencing was performed on the E17.5 fetal cortex. Additionally, primary neural stem cells (NSCs) were isolated from the E14.5 cerebral cortex and exposed to alcohol to evaluate nucleolar stress and p53/MDM2 signaling. Alcohol suppressed KEGG pathways involving ribosome biogenesis (rRNA synthesis/processing and ribosomal proteins) and genes that are mechanistic in ribosomopathies (Polr1d, Rpl11; Rpl35; Nhp2); this was accompanied by nucleolar dissolution and p53 stabilization. In primary NSCs, alcohol reduced rRNA synthesis, caused nucleolar loss, suppressed proliferation, stabilized nuclear p53, and caused apoptosis that was prevented by dominant-negative p53 and MDM2 overexpression. Alcohol's actions were dose-dependent and rapid, and rRNA synthesis was suppressed between 30 and 60 min following alcohol exposure. The alcohol-mediated deficits in ribosomal protein expression were correlated with fetal brain weight reductions. This is the first report describing that pharmacologically relevant alcohol levels suppress ribosome biogenesis, induce nucleolar stress in neuronal populations, and involve the ribosomal/MDM2/p53 pathway to cause growth arrest and apoptosis. This represents a novel mechanism of alcohol-mediated neuronal damage.

Microbiota and nutrition as risk and resiliency factors following prenatal alcohol exposure

Alcohol exposure in adulthood can result in inflammation, malnutrition, and altered gastroenteric microbiota, which may disrupt efficient nutrient extraction. Clinical and preclinical studies have documented convincingly that prenatal alcohol exposure (PAE) also results in persistent inflammation and nutrition deficiencies, though research on the impact of PAE on the enteric microbiota is in its infancy. Importantly, other neurodevelopmental disorders, including autism spectrum and attention deficit/hyperactivity disorders, have been linked to gut microbiota dysbiosis. The combined evidence from alcohol exposure in adulthood and from other neurodevelopmental disorders supports the hypothesis that gut microbiota dysbiosis is likely an etiological feature that contributes to negative developmental, including neurodevelopmental, consequences of PAE and results in fetal alcohol spectrum disorders. Here, we highlight published data that support a role for gut microbiota in healthy development and explore the implication of these studies for the role of altered microbiota in the lifelong health consequences of PAE.

Sex differences in the transcriptome of extracellular vesicles secreted by fetal neural stem cells and effects of chronic alcohol exposure

BACKGROUND

Prenatal alcohol (ethanol) exposure (PAE) results in brain growth restriction, in part, by reprogramming self-renewal and maturation of fetal neural stem cells (NSCs) during neurogenesis. We recently showed that ethanol resulted in enrichment of both proteins and pro-maturation microRNAs in sub-200-nm-sized extracellular vesicles (EVs) secreted by fetal NSCs. Moreover, EVs secreted by ethanol-exposed NSCs exhibited diminished efficacy in controlling NSC metabolism and maturation. Here we tested the hypothesis that ethanol may also influence the packaging of RNAs into EVs from cell-of-origin NSCs.

METHODS

Sex-specified fetal murine iso-cortical neuroepithelia from three separate pregnancies were maintained ex vivo, as neurosphere cultures to model the early neurogenic niche. EVs were isolated by ultracentrifugation from NSCs exposed to a dose range of ethanol. RNA from paired EV and cell-of-origin NSC samples was processed for ribosomal RNA-depleted RNA sequencing. Differential expression analysis and exploratory weighted gene co-expression network analysis (WGCNA) identified candidate genes and gene networks that were drivers of alterations to the transcriptome of EVs relative to cells.

RESULTS

The RNA content of EVs differed significantly from cell-of-origin NSCs. Biological sex contributed to unique transcriptome variance in EV samples, where > 75% of the most variant transcripts were also sex-variant in EVs but not in cell-of-origin NSCs. WGCNA analysis also identified sex-dependent enrichment of pathways, including dopamine receptor binding and ectoderm formation in female EVs and cell-substrate adhesion in male EVs, with the top significant DEGs from differential analysis of overall individual gene expressions, i.e., Arhgap15, enriched in female EVs, and Cenpa, enriched in male EVs, also serving as WCGNA hub genes of sex-biased EV WGCNA clusters. In addition to the baseline RNA content differences, ethanol exposure resulted in a significant dose-dependent change in transcript expression in both EVs and cell-of-origin NSCs that predominantly altered sex-invariant RNAs. Moreover, at the highest dose, ~ 73% of significantly altered RNAs were enriched in EVs, but depleted in NSCs.

CONCLUSIONS

The EV transcriptome is distinctly different from, and more sex-variant than, the transcriptome of cell-of-origin NSCs. Ethanol, a common teratogen, results in dose-dependent sorting of RNA transcripts from NSCs to EVs which may reprogram the EV-mediated endocrine environment during neurogenesis.

Dose-related shifts in proteome and function of extracellular vesicles secreted by fetal neural stem cells following chronic alcohol exposure

Accumulating evidence indicates that extracellular vesicles (EVs) mediate endocrine functions and also pathogenic effects of neurodevelopmental perturbagens like ethanol. We performed mass-spectrometry on EVs secreted by fetal murine cerebral cortical neural stem cells (NSCs), cultured ex-vivo as sex-specific neurosphere cultures, to identify overrepresented proteins and signaling pathways in EVs relative to parental NSCs in controls, and following exposure of parental NSCs to a dose range of ethanol. EV proteomes differ substantially from parental NSCs, and though EVs sequester proteins across sub-cellular compartments, they are enriched for distinct morphogenetic signals including the planar cell polarity pathway. Ethanol exposure favored selective protein sequestration in EVs and depletion in parental NSCs, and also resulted in dose-independent overrepresentation of cell-cycle and DNA replication pathways in EVs as well as dose-dependent overrepresentation of rRNA processing and mTor stress pathways. Transfer of untreated EVs to naïve cells resulted in decreased oxidative metabolism and S-phase, while EVs derived from ethanol-treated NSCs exhibited diminished effect. Collectively, these data show that NSCs secrete EVs with a distinct proteome that may have a general growth-inhibitory effect on recipient cells. Moreover, while ethanol results in selective transfer of proteins from NSCs to EVs, the efficacy of these exposure-derived EVs is diminished.