Session 9

A novel pathway of stress resistance in the brain has recently been described that is mediated by the transcriptional repressor REST/NRSF. We have provided evidence that this pathway is involved in lifespan regulation and the pathogenesis of neurodegenerative disorders (Lu et al., 2014; Meyer et al., 2019; Zullo et al. 2019). REST also plays an essential role in early brain development by regulating neural specification and neuronal differentiation. As such, we asked whether the REST corepressor pathway might play a role in the pathogenesis of neuropsychiatric disorders that may arise from altered brain development. Examination of recent GWAS studies showed that genetic variants associated with bipolar disorder are significantly enriched for REST target genes. Immunofluorescence microscopy showed that nuclear REST levels in neurons of the prefrontal cortex were significantly reduced in patients with bipolar disorder relative to normal controls. Furthermore, studies of gene expression showed that REST target genes, such as ASCL1 and synapsin 1, were upregulated in the prefrontal cortex of patients with bipolar disorder, consistent with loss-of-function of the REST transcriptional repressor. Reduced REST expression and function were recapitulated in vitro in iPS cell-derived neurons from patients with bipolar disorder, suggesting that loss of REST may be an early event in bipolar disorder. To explore the consequences of loss of REST in the adult brain, we established conditional REST-deficient mice. Neural excitation was globally increased in the cerebral cortex of REST-deficient mice, as determined by PET/CT scanning and electroencephalography. Moreover, loss of REST elevated the sensitivity of cortical neurons to excitatory stimuli. These results suggest that loss-of-function in the REST corepressor pathway can destabilize neural networks predisposing to neural hyperexcitation. Transcriptional dysregulation might therefore lead to loss of neural network homeostasis in the brain, a potential mechanism for mood instability in bipolar disorder.
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We will share our exciting findings that resulted from the 2016 NIH-New Innovator Award entitled: "A New Paradigm in Nanomedicine: can structural interiors of nanoparticles regulate cellular delivery?
The scientific community is witnessing the enormous societal impact of research in lipid-based mRNA cellular delivery with the deployment of the COVID-19 vaccine. These lipid nanoparticle (LNP) materials could be useful in many more therapies, but the technology is not always successful because the delivery of RNA to certain cells fails. Some cell types do not undergo endocytosis or, most often, LNPs and RNA remain trapped in endosomal compartments. The development of ionizable lipids was an important discovery for LNPs. Ionizable lipids in combination with other lipids in the LNPs have been recently referred to as "structural lipids". This is because as endosomal membrane-proteins pump protons onto the endosomal lumen, these lipids become charged and flip the internal structure of the LNPs to a honey-comb arrangement. This structure has been elusively observed to lead to more efficient RNA release into the cytosol before the onset of the endosome-lysosome degradation pathway. Indeed, LNP internal structure controls RNA delivery efficiency. We have discovered that LNP nanostructure regulates endosomal escape via a process of protein-free fusion between LNPs and endosomal membranes. 

We have developed a methodology to stabilize LNPs with nanostructures that go beyond the traditional layered lamellar and the hexagonal structure with ionizable lipids. Specifically, we have developed the first bicontinuous cubic LNP (see Figure above) for the delivery of RNA to living cells. Depending on the LNP nanostructure, membrane elasticity and curvature properties can be engineered such that LNP-endosome fusion and formation of fusion pores is energetically favorable without the need of ionizable lipids. 

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SIGNIFICANCE: Use of menthol cigarettes in the United States is strongly associated with race. Driven by decades of targeted marketing, approximately 85% of Black smokers use menthol cigarettes; conversely, over 70% of white smokers prefer non-menthol styles. This study uses regional sales data to examine longitudinal changes in menthol and non-menthol cigarette sales and associations with regional racial composition.
METHODS: Using Nielsen sales data from 30 US market areas, we computed the percent change in per capita menthol and non-menthol cigarette sales between 2016-2018. Demographic characteristics of counties comprising each region were compiled from the US Census Bureau. Correlation analyses assessed the relationship between consumption changes and regional racial composition, including the dissimilarity index to measure the spatial distribution of Black-white residential segregation.
RESULTS: On average, menthol cigarettes held a third of the market share across regions (range: 22-49%); market share was highly correlated with the percent of Black residents (r=0.69). Between 2016-2018, the rate of decline in per capita pack sales was slower for menthol (-8%) versus non-menthol (-11%) cigarettes. No demographic factors were associated with the decline in menthol sales, but the dissimilarity index was negatively correlated with non-menthol sales (r=-0.44, p=0.02). That is, the greater a region's Black-white residential segregation, the faster the decline in non-menthol sales.
CONCLUSION: Given that over 80% of non-menthol smokers are white, it is plausible that this group is driving changes in non-menthol consumption. This study suggests that beyond racial composition, greater residential segregation between Black and white residents is related to declines in non-menthol cigarette sales. Future research should examine individual and structural factors at the local level (e.g., retail marketing, unequal policy impact, treatment access) to identify possible mechanisms of this relationship.

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How does a cell construct its microtubule cytoskeleton? According to Feynman's principle "what I cannot create, I do not understand", my lab pursues this question by building the chromosome segregation machinery from scratch. I will first tell you how the microtubule framework is generated in a cell. Upon deciphering the function of the most important microtubule accessory proteins, I will present how we use those building blocks to reconstitute a spindle substructure in vitro and determine its building plan. Finally, I will outline how we combine spindle substructures like pieces of a puzzle to assemble and thereby understand a functioning spindle that segregates chromosomes. By studying how the MT cytoskeleton is built, I hope to help explain how hundreds of proteins can self-assemble on the nm scale into a complex molecular machine 1000-fold larger than its constituents, a challenge for the biochemistry of the 21st century.

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