Developmental dynamics and maturation of transplanted human embryonic stem cell-derived neural precursors in the adult rodent CNS

Abstract

Human embryonic stem cells (HESC) are an unlimited source of cells for stem cell therapies. We investigated the dynamics of integration of HESC-derived neural precursors (NPs) into host neural circuitry. Methods: NP cultures were derived from the NIH-approved HESC line BG01 with noggin in B27/N2-supplemented medium. These NPs were grafted into the forebrain and ventral brain stem of immunodeficient rats (NIH-RNU). Brain tissues were prepared at 6, 15 and 26 weeks post-grafting. Results: The HESC-NPs showed a site-dependent fate, i.e. a greater mitotic activity and ongoing neuroepithelial structure formation in the brain stem and a lower mitotic activity and eventual resolution and dedifferentiation of early neuroepithelial structures in the forebrain. The later almost disappeared at 15 weeks post-grafting. By 15 weeks, a large percentage (57.8–80.8%) had differentiated into early (TUJ-1[+]) neurons that extended axons along pre-established CNS pathways (cortico-striatal, internal capsule, external capsule) and formed dense synaptic fields, especially in the graft area in the form of local innervation and in the host subventricular zone (SVZ). An especially strong affinity for SVZ and the pia mater was noted. Some migration was seen along white matter tracts; in the case of ventral brain stem injections, migration of nestin/NCAM (+) precursors could be followed several segments down the cervical cord. The extensive ability of HESC-NPs to differentiate into neurons, migrate and possibly establish synaptic contacts with other graft and host cells demonstrates their potential to repair neural circuits damaged by either trauma or neurodegeneration. The successful outcomes of human NP xenografts in rats demonstrate the value of human-to-rodent experimental approaches in the preclinical evaluation of human ES cells. In addition, HESNPs may prove to be valuable instruments for studying novel inductive signals that influence not only graft differentiation and integration, but also host repair mechanisms, including neurogenesis and synaptic plasticity after trauma.