Unraveling Molecular Pathways Altered in MeCP2-Related Syndromes, in the Search for New Potential Avenues for Therapy

iPSC-derived healthy human astrocytes selectively load miRNAs targeting neuronal genes into extracellular vesicles

Astrocytes are in constant communication with neurons during the establishment and maturation of functional networks in the developing brain. Astrocytes release extracellular vesicles (EVs) containing microRNA (miRNA) cargo that regulates transcript stability in recipient cells. Astrocyte released factors are thought to be involved in neurodevelopmental disorders. Healthy astrocytes partially rescue Rett Syndrome (RTT) neuron function. EVs isolated from stem cell progeny also correct aspects of RTT. EVs cross the blood-brain barrier (BBB) and their cargo is found in peripheral blood which may allow non-invasive detection of EV cargo as biomarkers produced by healthy astrocytes. Here we characterize miRNA cargo and sequence motifs in healthy human astrocyte derived EVs (ADEVs). First, human induced Pluripotent Stem Cells (iPSC) were differentiated into Neural Progenitor Cells (NPCs) and subsequently into astrocytes using a rapid differentiation protocol. iPSC derived astrocytes expressed specific markers, displayed intracellular calcium transients and secreted ADEVs. miRNAs were identified by RNA-Seq on astrocytes and ADEVs and target gene pathway analysis detected brain and immune related terms. The miRNA profile was consistent with astrocyte identity, and included approximately 80 miRNAs found in astrocytes that were relatively depleted in ADEVs suggestive of passive loading. About 120 miRNAs were relatively enriched in ADEVs and motif analysis discovered binding sites for RNA binding proteins FUS, SRSF7 and CELF5. miR-483-5p was the most significantly enriched in ADEVs. This miRNA regulates MECP2 expression in neurons and has been found differentially expressed in blood samples from RTT patients. Our results identify potential miRNA biomarkers selectively sorted into ADEVs and implicate RNA binding protein sequence dependent mechanisms for miRNA cargo loading.

Epigenetic genes and epilepsy - emerging mechanisms and clinical applications

An increasing number of epilepsies are being attributed to variants in genes with epigenetic functions. The products of these genes include factors that regulate the structure and function of chromatin and the placing, reading and removal of epigenetic marks, as well as other epigenetic processes. In this Review, we provide an overview of the various epigenetic processes, structuring our discussion around five function-based categories: DNA methylation, histone modifications, histone-DNA crosstalk, non-coding RNAs and chromatin remodelling. We provide background information on each category, describing the general mechanism by which each process leads to altered gene expression. We also highlight key clinical and mechanistic aspects, providing examples of genes that strongly associate with epilepsy within each class. We consider the practical applications of these findings, including tissue-based and biofluid-based diagnostics and precision medicine-based treatments. We conclude that variants in epigenetic genes are increasingly found to be causally involved in the epilepsies, with implications for disease mechanisms, treatments and diagnostics.