Prenatal alcohol exposure (PAE) remains a leading cause of permanent neurodevelopmental disability. Diagnosis is often initiated by a distinctive craniofacial appearance that originates, in part, from the apoptotic deletion of craniofacial progenitors, a stem cell lineage called the Neural Crest. In the prior award period, our transcriptome analysis revealed that gene clusters mediating Ribosome Biogenesis (RBG; 70 genes, all repressed) and Oxidative Phosphorylation (OxP; 60 genes, all repressed) exhibited the greatest differential expression 6hr following transient alcohol exposure (52mM, 90min). These gene clusters also had the greatest altered expression in genetic lineages of neural crest having differential vulnerability to alcohol, and haploinsufficiency in RBG sensitized neural crest to alcohol-induced apoptosis and facial deficits. Here, we test the hypothesis that disruption of RBG is mechanistic in alcohol's facial dysmorphology.
Aim 1 shows that alcohol reduces RBG and causes a nucleolar stress which then activates MDM2/p53-mediated apoptosis in neural crest.
Aim 2 shows this loss of RBG is due to alcohol's inactivation of mTORC1 and p70/S6K activity, which are the major transcription-level stimulators of RBG.
Aim 3 shows that alcohol inactivates mTORC1 because it depresses mitochondrial OxP and ATP generation and thus activates AMPK, which is a direct repressor of mTORC1. We will also test a role for canonical Wnt/?-catenin signaling, which indirectly stimulates RBG via TSC2 and is repressed by alcohol as we showed in the previous award period. Because RBG consumes ~80% of total ATP generation in rapidly dividing cells like neural crest, cells have coopted RBG to monitor their internal stress and have linked it to the p53-checkpoint pathway. In humans, impaired RBG is now understood to underlie a family of genetic syndromes featuring facial anomalies with similarities to those of FASD; these ribosomopathies cause the p53-mediated deletion of neural crest progenitors and are rescued by TORC1 activation. Studies in this proposal test the novel hypothesis that the facial deficits in FASD represent a ribosomopathy and establish the mechanism by which alcohol initiates the pro-apoptotic nucleolar stress in neural crest progenitors.
Fetal alcohol spectrum disorders (FASD) are a leading cause of neurodevelopmental disability. Affected individuals may display a characteristic facial dysmorphology, and studies herein investigate the mechanism by which alcohol causes the apoptotic deletion of neural crest progenitors, a unique neuroprogenitor stem cell population that forms these facial structures. Findings address our knowledge gap in understanding that mechanism, and will inform why the early embryo and fetus is so vulnerable to the damaging effects of prenatal alcohol exposure.
