Small Molecules Enhance Reprogramming of Adult Human Dermal Fibroblasts to Dorsal Forebrain Precursor Cells

The development of human cell-based platforms for disease modeling, drug discovery, and regenerative therapy relies on robust and practical methods to derive high yields of relevant neuronal subtypes. Direct reprogramming strategies have sought to provide a means of deriving human neurons that mitigate the low conversion efficiencies, and protracted timing of human embryonic stem cell and induced pluripotent stem cell-derived neuron specification in vitro. However, few studies have demonstrated the direct conversion of adult human fibroblasts into multipotent neural precursors with the capacity to differentiate into cortical neurons with high efficiency. In this study, we demonstrate a reprogramming strategy using chemically modified mRNA encoding the proneural genes SOX2 and PAX6 coupled with small molecule supplementation to enhance the derivation of human-induced dorsal forebrain precursors directly from adult human dermal fibroblasts (aHDFs). Through transcriptional and phenotypic analysis of lineage-specific precursor and cortical neuron markers, we have demonstrated that this combined strategy significantly enhances the direct derivation of dorsal forebrain precursors from aHDFs, which, after timely exposure to defined differentiation media, gives rise to high yields of functional glutamatergic neurons. We propose that this combined strategy provides a highly tractable and efficient human cell-based platform for disease modeling and drug discovery.