Loss of tumor protein 53 protects against alcohol-induced facial malformations in mice and zebrafish

Efcab7 deletion sensitizes mice to the teratogenic effects of gastrulation-stage alcohol exposure

Alcohol exposure during the gastrulation stage of development can disrupt Sonic hedgehog (Shh) signaling and cause eye, craniofacial, and brain defects. One of the genes that regulates Shh signaling is Efcab7, which encodes a protein that facilitates the actions of Smoothened (Smo), a critical component of the Shh pathway. Previous work from our lab has demonstrated that Efcab7 is differentially expressed between two sub-strains of C57BL/6 mice that differ in their sensitivity to gastrulation-stage alcohol exposure. The more alcohol-sensitive C57BL/6 J mice express lower levels of Efcab7 during gastrulation than do the less alcohol-sensitive C57BL/6NHsd mice. The current study examined whether partial or full Efcab7 deletions render mice more sensitive to gastrulation-stage alcohol exposure and affect the sensitivity to other modulators of Shh signaling that cause craniofacial malformations. Efcab7+/- dams were mated with Efcab7+/- sires to produce Efcab7+/+, Efcab7+/-, and Efcab7-/- fetuses. On gestational day 7 (GD 7), they received either alcohol (two doses of 2.9 g/kg, i.p., given 4 hours apart), the Smo antagonist vismodegib (40 mg/kg, or vehicle, p.o.), the Smo agonist SAG (20 mg/kg) or the appropriate vehicles. GD 17 fetuses were collected and examined for ocular and craniofacial dysmorphology. As compared to Efcab7+/+ fetuses, Efcab7-/- fetuses exposed to alcohol or vismodegib treatment had more severe ocular and craniofacial malformations. In contrast, Efcab7-/- fetuses had less severe malformations induced by SAG. These results confirm that Efcab7 can modify responses to Shh agonists and antagonists and further identify Efcab7 as a gene important for the sensitivity to gastrulation-stage alcohol exposure.

The convergence of mTOR signaling and ethanol teratogenesis

Ethanol is one of the most common teratogens and causes of human developmental disabilities. Fetal alcohol spectrum disorders (FASD), which describes the wide range of deficits due to prenatal ethanol exposure, are estimated to affect between 1.1 % and 5.0 % of births in the United States. Ethanol dysregulates numerous cellular mechanisms such as programmed cell death (apoptosis), protein synthesis, autophagy, and various aspects of cell signaling, all of which contribute to FASD. The mechanistic target of rapamycin (mTOR) regulates these cellular mechanisms via sensing of nutrients like amino acids and glucose, DNA damage, and growth factor signaling. Despite an extensive literature on ethanol teratogenesis and mTOR signaling, there has been less attention paid to their interaction. Here, we discuss the impact of ethanol teratogenesis on mTORC1's ability to coordinate growth factor and amino acid sensing with protein synthesis, autophagy, and apoptosis. Notably, the effect of ethanol exposure on mTOR signaling depends on the timing and dose of ethanol as well as the system studied. Overall, the overlap between the functions of mTORC1 and the phenotypes observed in FASD suggest a mechanistic interaction. However, more work is required to fully understand the impact of ethanol teratogenesis on mTOR signaling.

Alcohol induces p53-mediated apoptosis in neural crest by stimulating an AMPK-mediated suppression of TORC1, S6K, and ribosomal biogenesis

Prenatal alcohol exposure is a leading cause of permanent neurodevelopmental disability and can feature distinctive craniofacial deficits that partly originate from the apoptotic deletion of craniofacial progenitors, a stem cell lineage called the neural crest (NC). We recently demonstrated that alcohol causes nucleolar stress in NC through its suppression of ribosome biogenesis (RBG) and this suppression is causative in their p53/MDM2-mediated apoptosis. Here, we show that this nucleolar stress originates from alcohol's activation of AMPK, which suppresses TORC1 and the p70/S6K-mediated stimulation of RBG. Alcohol-exposed cells of the pluripotent, primary cranial NC line O9-1 were evaluated with respect to their S6K, TORC1, and AMPK activity. The functional impact of these signals with respect to RBG, p53, and apoptosis were assessed using gain-of-function constructs and small molecule mediators. Alcohol rapidly (<2 hr) increased pAMPK, pTSC2, and pRaptor, and reduced both total and pS6K in NC cells. These changes persisted for at least 12 hr to 18 hr following alcohol exposure. Attenuation of these signals via gain- or loss-of-function approaches that targeted AMPK, S6K, or TORC1 prevented alcohol's suppression of rRNA synthesis and the induction of p53-stimulated apoptosis. We conclude that alcohol induces ribosome dysbiogenesis and activates their p53/MDM2-mediated apoptosis via its activation of pAMPK, which in turn activates TSC2 and Raptor to suppress the TORC1/S6K-mediated promotion of ribosome biogenesis. This represents a novel mechanism underlying alcohol's neurotoxicity and is consistent with findings that TORC1/S6K networks are critical for cranial NC survival.

Alcohol induces p53-mediated apoptosis in neural crest by stimulating an AMPK-mediated suppression of TORC1, S6K, and ribosomal biogenesis

Prenatal alcohol exposure is a leading cause of permanent neurodevelopmental disability and can feature distinctive craniofacial deficits that partly originate from the apoptotic deletion of craniofacial progenitors, a stem cell lineage called the neural crest (NC). We recently demonstrated that alcohol causes nucleolar stress in NC through its suppression of ribosome biogenesis (RBG) and this suppression is causative in their p53/MDM2-mediated apoptosis. Here, we show that this nucleolar stress originates from alcohol's activation of AMPK, which suppresses TORC1 and the p70/S6K-mediated stimulation of RBG. Alcohol-exposed cells of the pluripotent, primary cranial NC line O9-1 were evaluated with respect to their S6K, TORC1, and AMPK activity. The functional impact of these signals with respect to RBG, p53, and apoptosis were assessed using gain-of-function constructs and small molecule mediators. Alcohol rapidly (<2hr) increased pAMPK, pTSC2, and pRaptor, and reduced both total and pS6K in NC cells. These changes persisted for at least 12hr to 18hr following alcohol exposure. Attenuation of these signals via gain- or loss-of-function approaches that targeted AMPK, S6K, or TORC1 prevented alcohol's suppression of rRNA synthesis and the induction of p53-stimulated apoptosis. We conclude that alcohol induces ribosome dysbiogenesis and activates their p53/MDM2-mediated apoptosis via its activation of pAMPK, which in turn activates TSC2 and Raptor to suppress the TORC1/S6K-mediated promotion of ribosome biogenesis. This represents a novel mechanism underlying alcohol's neurotoxicity and is consistent with findings that TORC1/S6K networks are critical for cranial NC survival.

foxe1 mutant zebrafish show indications of a hypothyroid phenotype and increased sensitivity to ethanol for craniofacial malformations

BACKGROUND

FOXE1 mutations in humans are associated with cleft palate and hypothyroidism. We previously developed a foxe1 mutant zebrafish demonstrating mineralization defects in larvae. In the present study, we investigate the thyroid status and skeletal phenotype of adult foxe1 mutants.

RESULTS

Mutant fish have increased expression of tshβ in the pituitary, and of hepatic dio1 and dio2. In plasma, we found higher Mg levels. Together these findings are indicative of hypothyroidism. We further observed mineralization defects in scales due to enhanced osteoclast activity as measured by increased expression levels of tracp, ctsk, and rankl. Gene-environment interactions in the etiology of FOXE1-related craniofacial abnormalities remain elusive, which prompts the need for models to investigate genotype-phenotype associations. We here investigated whether ethanol exposure increases the risk of developing craniofacial malformations in foxe1 mutant larvae that we compared to wild types. We found in ethanol-exposed mutants an increased incidence of developmental malformations and marked changes in gene expression patterns of cartilage markers (sox9a), apoptotic markers (casp3b), retinoic acid metabolism (cyp26c1), and tissue hypoxia markers (hifaa, hifab).

CONCLUSION

Taken together, this study shows that the foxe1 mutant zebrafish recapitulates phenotypes associated with FOXE1 mutations in human patients and a clear foxe1-ethanol interaction.

Alcohol exposure suppresses ribosome biogenesis and causes nucleolar stress in cranial neural crest cells

Prenatal alcohol exposure (PAE) causes cognitive impairment and a distinctive craniofacial dysmorphology, due in part to apoptotic losses of the pluripotent cranial neural crest cells (CNCs) that form facial bones and cartilage. We previously reported that PAE rapidly represses expression of >70 ribosomal proteins (padj = 10-E47). Ribosome dysbiogenesis causes nucleolar stress and activates p53-MDM2-mediated apoptosis. Using primary avian CNCs and the murine CNC line O9-1, we tested whether nucleolar stress and p53-MDM2 signaling mediates this apoptosis. We further tested whether haploinsufficiency in genes that govern ribosome biogenesis, using a blocking morpholino approach, synergizes with alcohol to worsen craniofacial outcomes in a zebrafish model. In both avian and murine CNCs, pharmacologically relevant alcohol exposure (20mM, 2hr) causes the dissolution of nucleolar structures and the loss of rRNA synthesis; this nucleolar stress persisted for 18-24hr. This was followed by reduced proliferation, stabilization of nuclear p53, and apoptosis that was prevented by overexpression of MDM2 or dominant-negative p53. In zebrafish embryos, low-dose alcohol or morpholinos directed against ribosomal proteins Rpl5a, Rpl11, and Rps3a, the Tcof homolog Nolc1, or mdm2 separately caused modest craniofacial malformations, whereas these blocking morpholinos synergized with low-dose alcohol to reduce and even eliminate facial elements. Similar results were obtained using a small molecule inhibitor of RNA Polymerase 1, CX5461, whereas p53-blocking morpholinos normalized craniofacial outcomes under high-dose alcohol. Transcriptome analysis affirmed that alcohol suppressed the expression of >150 genes essential for ribosome biogenesis. We conclude that alcohol causes the apoptosis of CNCs, at least in part, by suppressing ribosome biogenesis and invoking a nucleolar stress that initiates their p53-MDM2 mediated apoptosis. We further note that the facial deficits that typify PAE and some ribosomopathies share features including reduced philtrum, upper lip, and epicanthal distance, suggesting the facial deficits of PAE represent, in part, a ribosomopathy.

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.

Combined exposure to alcohol and cannabis during development: Mechanisms and outcomes

Exposure to substances of abuse during pregnancy can have long-lasting effects on offspring. Alcohol is one of the most widely used substances of abuse that leads to the most severe consequences. Recent studies in the United States, Canada, and the United Kingdom showed that between 1% and 7% of all children exhibit signs and symptoms of fetal alcohol spectrum disorder (FASD). Despite preventive campaigns, the rate of children with FASD has not decreased during recent decades. Alcohol consumption often accompanies exposure to such drugs as tobacco, cocaine, opioids, and cannabis. These interactions can be synergistic and exacerbate the deleterious consequences of developmental alcohol exposure. The present review focuses on interactions between alcohol and cannabis exposure and the potential consequences of these interactions.

Loss of Nicotinamide nucleotide transhydrogenase sensitizes embryos to ethanol-induced neural crest and neural apoptosis via generation of reactive oxygen species

Fetal alcohol spectrum disorders (FASD) are a continuum of birth defects caused by prenatal alcohol exposure. FASD are the most common environmentally induced birth defect and are highly variable. The genetics of an individual influence the severity of their FASD phenotype. However, the genes that sensitize an individual to ethanol-induced birth defects are largely unknown. The ethanol-sensitive mouse substrain, C57/B6J, carries several known mutations including one in Nicotinamide nucleotide transhydrogenase (Nnt). Nnt is a mitochondrial transhydrogenase thought to have an important role in detoxifying reactive oxygen species (ROS) and ROS has been implicated in ethanol teratogenesis. To directly test the role of Nnt in ethanol teratogenesis, we generated zebrafish nnt mutants via CRISPR/Cas9. Zebrafish embryos were dosed with varying concentrations of ethanol across different timepoints and assessed for craniofacial malformations. We utilized a ROS assay to determine if this could be a contributing factor of these malformations. We found that exposed and unexposed mutants had higher levels of ROS compared to their wildtype counterparts. When treated with ethanol, nnt mutants experienced elevated apoptosis in the brain and neural crest, a defect that was rescued by administration of the antioxidant, N-acetyl cysteine (NAC). NAC treatment also rescued most craniofacial malformations. Altogether this research demonstrates that ethanol-induced oxidative stress leads to craniofacial and neural defects due to apoptosis in nnt mutants. This research further supports the growing body of evidence implicating oxidative stress in ethanol teratogenesis. These findings suggest that antioxidants can be used as a potential therapeutic in the treatment of FASD.

High-throughput detection of craniofacial defects in fluorescent zebrafish

Losses and malformations of cranial neural crest cell (cNCC) derivatives are a hallmark of several common brain and face malformations. Nevertheless, the etiology of these cNCC defects remains unknown for many cases, suggesting a complex basis involving interactions between genetic and/or environmental factors. However, the sheer number of possible factors (thousands of genes and hundreds of thousands of toxicants) has hindered identification of specific interactions. Here, we develop a high-throughput analysis that will enable faster identification of multifactorial interactions in the genesis of craniofacial defects. Zebrafish embryos expressing a fluorescent marker of cNCCs (fli1:EGFP) were exposed to a pathway inhibitor standard or environmental toxicant, and resulting changes in fluorescence were measured in high-throughput using a fluorescent microplate reader to approximate cNCC losses. Embryos exposed to the environmental Hedgehog pathway inhibitor piperonyl butoxide (PBO), a Hedgehog pathway inhibitor standard, or alcohol (ethanol) exhibited reduced fli1:EGFP fluorescence at one day post fertilization, which corresponded with craniofacial defects at five days post fertilization. Combining PBO and alcohol in a co-exposure paradigm synergistically reduced fluorescence, demonstrating a multifactorial interaction. Using pathway reporter transgenics, we show that the plate reader assay is sensitive at detecting alterations in Hedgehog signaling, a critical regulator of craniofacial development. We go on to demonstrate that this technique readily detects defects in other important cell types, namely neurons. Together, these findings demonstrate this novel in vivo platform can predict developmental abnormalities and multifactorial interactions in high-throughput.

Short-term transcriptomic changes in the mouse neural tube induced by an acute alcohol exposure

Alcohol exposure during the formation and closure of the neural tube, or neurulation (embryonic day [E] 8-10 in mice; ∼4th week of human pregnancy), perturbs development of midline brain structures and significantly disrupts gene expression in the rostroventral neural tube (RVNT). Previously, alcohol exposure during neurulation was found to alter gene pathways related to cell proliferation, p53 signaling, ribosome biogenesis, immune signaling, organogenesis, and cell migration 6 or 24 h after administration. Our current study expands upon this work by investigating short-term gene expression changes in the RVNT following a single binge-like alcohol exposure during neurulation. Female C57BL/6J mice were administered a single dose of 2.9 g/kg alcohol or vehicle on E9.0 to target mid-neurulation. The RVNTs of stage-matched embryos were collected 2 or 4 h after exposure and processed for RNA-seq. Functional profiling was performed with g:Profiler, as well as with the CiliaCarta and DisGeNet databases. Two hours following E9.0 alcohol exposure, 650 genes in the RVNT were differentially expressed. Functional enrichment analysis revealed that pathways related to cellular metabolism, gene expression, cell cycle, organogenesis, and Hedgehog signaling were down-regulated, and pathways related to cellular stress response, p53 signaling, and hypoxia were up-regulated by alcohol. Four hours after alcohol exposure, 225 genes were differentially expressed. Biological processes related to metabolism, RNA binding, ribosome biogenesis, and methylation were down-regulated, while protein localization and binding, autophagy, and intracellular signaling pathways were up-regulated. Two hours after alcohol exposure, the differentially expressed genes were associated with disease terms related to eye and craniofacial development and anoxia. These data provide further information regarding the biological functions targeted by alcohol exposure during neurulation in regions of the neural tube that give rise to alcohol-sensitive midline brain structures. Disruption of these gene pathways contributes to the craniofacial and brain malformations associated with prenatal alcohol exposure.

The pro-apoptotic Bax gene modifies susceptibility to craniofacial dysmorphology following gastrulation-stage alcohol exposure

BACKGROUND

During early development, alcohol exposure causes apoptotic cell death in discrete regions of the embryo which are associated with distinctive patterns of later-life abnormalities. In gastrulation, which occurs during the third week of human pregnancy, alcohol targets the ectoderm, the precursor of the eyes, face, and brain. This midline tissue loss leads to the craniofacial dysmorphologies, such as microphthalmia and a smooth philtrum, which define fetal alcohol syndrome (FAS). An important regulator of alcohol-induced cell death is the pro-apoptotic protein Bax. The current study determines if mice lacking the Bax gene are less susceptible to the pathogenic effects of gastrulation-stage alcohol exposure.

METHODS

Male and female Bax^+/- mice mated to produce embryos with full (^-/- ) or partial (^+/- ) Bax deletions, or Bax^+/+ wild-type controls. On Gestational Day 7 (GD 7), embryos received two alcohol (2.9 g/kg, 4 hr apart), or control exposures. A subset of embryos was collected 12 hr later and examined for the presence of apoptotic cell death, while others were examined on GD 17 for the presence of FAS-like facial features.

RESULTS

Full Bax deletion reduced embryonic apoptotic cell death and the incidence of fetal eye and face malformations, indicating that Bax normally facilitates the development of alcohol-induced defects. An RNA-seq analysis of GD 7 Bax^+/+ and Bax^-/- embryos revealed 63 differentially expressed genes, some of which may interact with the Bax deletion to further protect against apoptosis.

CONCLUSIONS

Overall, these experiments identify that Bax is a primary teratogenic mechanism of gastrulation-stage alcohol exposure.

Embryonic Nicotine Exposure Disrupts Adult Social Behavior and Craniofacial Development in Zebrafish

Cigarette smoking remains the leading cause of preventable death and morbidity worldwide. Smoking during pregnancy is associated with numerous adverse birth outcomes, including craniofacial and behavioral abnormalities. Although tobacco smoke contains more than 4000 toxic substances, nicotine is addictive and is likely the most teratogenic substance in cigarette smoke. However, much remains to be determined about the effects of embryonic nicotine exposure on behavior and craniofacial development. Therefore, this study evaluated adult social behavior in zebrafish, craniofacial defects, and nicotine metabolism in embryos after embryonic nicotine exposure. Zebrafish embryos were exposed to different doses of nicotine beginning at 6 h post fertilization. To evaluate craniofacial defects, the embryos were collected at 4 days post fertilization and stained with Alizarin Red and Alcian Blue. For behavioral testing, embryos were reared to adulthood. To evaluate nicotine metabolism, cotinine levels were analyzed at various time points. Our findings demonstrate that embryonic exposure to nicotine modifies social behavior in adulthood, causes craniofacial defects with reduced size of craniofacial cartilages, and that zebrafish metabolize nicotine to cotinine, as in humans. Together, our data suggest that zebrafish are useful as a model for studying nicotine-related diseases.