Human cortical neurons rapidly generated by direct ES cell programming integrate into stroke-injured rat cortex

Stroke is a major cause of long-term disability in adult humans, the neuronal loss leading to motor, sensory, and cognitive impairments. Replacement of dead neurons by intracerebral transplantation of stem cell-derived neurons for reconstruction of injured neuronal networks has potential to become a novel therapeutic strategy to promote functional recovery after stroke. Here we describe a rapid and efficient protocol for the generation of cortical neurons via direct programming of human embryonic stem (hES) cells. Our results show that 7 days overexpression of the transcription factor neurogenin 2 (NGN2) in vitro was enough to generate hES-induced cells with cortical phenotype, as revealed by immunocytochemistry and RT-qPCR, and electrophysiological properties of neurons in an intermediate stage of maturity. At 3 months after translantation into the stroke-injured rat cortex, the hES-induced neurons (hES-iNs) showed immunocytochemical markers of mature layer-specific cortical neurons and sent widespread axonal projections to several areas in both hemispheres of the host brain. Their axons became myelinated and formed synaptic contacts with host neurons, as shown by immunoelectron microscopy. Our findings demonstrate for the first time that direct transcription factor programming of hES cells can efficiently and rapidly produce cortical neurons with capacity to integrate into the stroke-injured brain.