Signaling defects in iPSC-derived fragile X premutation neurons.

Fragile X-associated tremor/ataxia syndrome (FXTAS) is a leading monogenic neurodegenerative disorder affecting premutation carriers of the fragile X (FMR1) gene. To investigate the underlying cellular neuropathology, we produced induced pluripotent stem cell-derived neurons from isogenic subclones of primary fibroblasts of a female premutation carrier, with each subclone bearing exclusively either the normal or the expanded (premutation) form of the FMR1 gene as the active allele. We show that neurons harboring the stably-active, expanded allele (EX-Xa) have reduced postsynaptic density protein 95 protein expression, reduced synaptic puncta density and reduced neurite length. Importantly, such neurons are also functionally abnormal, with calcium transients of higher amplitude and increased frequency than for neurons harboring the normal-active allele. Moreover, a sustained calcium elevation was found in the EX-Xa neurons after glutamate application. By excluding the individual genetic background variation, we have demonstrated neuronal phenotypes directly linked to the FMR1 premutation. Our approach represents a unique isogenic, X-chromosomal epigenetic model to aid the development of targeted therapeutics for FXTAS, and more broadly as a model for the study of common neurodevelopmental (e.g. autism) and neurodegenerative (e.g. Parkinsonism, dementias) disorders.

Role of miRNAs in neuronal differentiation from human embryonic stem cell-derived neural stem cells.

microRNAs (miRNAs) are important modulators in regulating gene expression at the post-transcriptional level and are therefore emerging as strong mediators in neural fate determination. Here, by use of the model of human embryonic stem cell (hESC)-derived neurogenesis, miRNAs involved in the differentiation from neural stem cells (hNSC) to neurons were profiled and identified. hNSC were differentiated into the neural lineage, out of which the neuronal subset was enriched through cell sorting based on select combinatorial biomarkers: CD15-/CD29(Low)/CD24(High). This relatively pure and viable subpopulation expressed the neuronal marker ß III-tubulin. The miRNA array demonstrated that a number of miRNAs were simultaneously induced or suppressed in neurons, as compared to hNSC. Real-time PCR further validated the decrease in levels of miR214, but increase in brain-specific miR7 and miR9 in the derived neurons. For functional studies, hNSC were stably transduced with lentiviral vectors carrying specific constructs to downregulate miR214 or to upregulate miR7. Manipulation of either miR214 or miR7 did not affect the expression of ß III-tubulin or neurofilament, however miR7 overexpression gave rise to enhanced synapsin expression in the derived neurons. This indicated that miR7 might play an important role in neurite outgrowth and synapse formation. In conclusion, our data demonstrate that miRNAs function as important modulators in neural lineage determination. These studies shed light on strategies to optimize in vitro differentiation efficiencies to mature neurons for use in drug discovery studies and potential future clinical applications.