Human ES cell-derived neurons recapitulate endogenous fiber projections upon transplantation into the adult rodent brain

The potential of neural grafts to replace adult brain tissue in a structurally and functionally relevant way is an essential prerequisite for reconstructive approaches. While numerous studies have focused on the controlled derivation of neuronal subtypes from human ES cells, the ability of these in vitro generated neurons to innervate the host CNS has remained largely unexplored.

To evaluate the potential of human ES cell-derived neurons to differentiate and grow projections in the adult brain, micrografts were stereotactically targeted at the primary motor cortex or the hippocampus of rodents. Most donor neurons acquired an inhibitory (GAD+) phenotype, excitatory (vGlut2+) neurons were, in both locations present to a lesser extent. Six months after transplantation, no markers indicative of immature cells or ongoing proliferation were detectable. Donor neurons with complex morphologies were detected up until at least one year after transplantation without any evidence of tumor formation.

Remarkably, engrafted human neurons frequently showed projection patterns comparable to neighboring endogenous cells. Donor cells transplanted into the dentate gyrus preferentially projected via the mossy fiber pathway to the ipsi-lateral CA3 region, where xenogeneic synapses were identified. In addition, donor axons entered the fimbria, crossed to the contra-lateral hemisphere and established contact with the contra-lateral hippocampus.

Human neurons engrafted in the motorcortex projected into the corpus callosum from where they re-entered the cortex on the contra-lateral side, thereby mimicking the projection pattern of commissural neurons. Subsets of human axons also entered the capsula interna as well as the basal ganglia.

The ability of human ES cell-derived neurons to establish a region specific long-range axonal projection profile in the adult brain suggests that these cells are responsive to endogenous guidance cues and may thus be particularly suitable for circuit reconstruction.

Supported by the DFG and the Hertie Foundation.