Small molecules modulate chromatin accessibility to promote NEUROG2-mediated fibroblast-to-neuron reprogramming [RNA-seq]

Pro-neural transcription factors and small molecules can induce the transdifferentiation of fibroblasts into functional neurons; however, a molecular mechanism detailing the immediate-early events that catalyze this conversion has not been well defined. We previously demonstrated that NEUROG2, forskolin (F), and dorsomorphin (D) can induce functional neurons with high-efficiency. Here, we used this model to define the genetic and epigenetic events that initiate an acquisition of neuronal identity. We demonstrate that NEUROG2 is a pioneer factor, FD enhances both genome-wide NEUROG2 chromatin occupancy and H3K27 acetylation, and synergistic transcription by these factors is essential to successful reprogramming. CREB1, activated by FD, promotes neuron survival and acts with NEUROG2 to upregulate SOX4, which co-activates NEUROD1 and NEUROD4. In addition to this hierarchical function, SOX4 targets SWI/SNF subunits and SOX4 knockdown results in extensive loss of open chromatin and abolishes reprogramming. Applying these insights, adult human glioblastoma and skin fibroblast reprogramming was improved using SOX4, SMARCA4, and chromatin modifying chemicals. Overall design: Total RNA (36 datasets: Time course analysis of changes in gene expression using MRC-5 fibroblasts, MRC-5 fibroblasts transduced with NEUROG2-encoding lentivirus, and MRC-5 fibroblasts transduced with NEUROG2-encoding lentivirus exposed to forskolin and dorsomorphin)