Understanding why the bone marrow gives rise to both CNS and PNS glia : implications for remyelination therapy

Abstract

Human bone marrow is a rich reservoir from which stem cells can be harvested and used for cell-based regenerative therapies. A subpopulation of human bone marrow stromal cells (hBMSCs) is thought to be derived from the neural crest (NC). NC cells are a transient multipotent cell population arising from the neural ectoderm that migrate to the periphery after undergoing epithelial to mesenchymal transition (EMT) and can directly give rise to Schwann cells (SCs), a myelin-forming cell of the peripheral nervous system (PNS). Oligodendrocytes are myelin-forming cells within the central nervous system (CNS) and are derived from oligodendrocyte precursor cells (OPCs) arising from the ventral pMN zone of the neural tube. In prior studies we generated functional Schwann cells from hBMSCs via a neurosphere intermediary generated in low-adherent conditions with EGF/bFGF supplementation. Using these same neurospheres, we more recently generated OPC-like cells from rat BMSCs. Understanding how these two types of glia, with different embryonic origins, could be derived from the same adult progenitor cell source, is a basic developmental question and also of great relevance to cellular therapy in regenerative medicine.

In this study, we characterized hBMSCs and hBMSC-derived neurospheres against reference atlases of human embryonic and adult bone marrow to understand neural progenitor identity as well as developmental origin. We then proceeded to apply a ventralization protocol to putative NC progenitors within hBMSCs consisting of dual Smad inhibition, sonic hedgehog (SHH) signaling enhancement, and glial induction phases to effect a PNS to CNS progenitor transition. As a proof-of-concept, we used single-cell RNA sequencing (scRNA-seq) to characterize the transcriptional landscape of cell populations at single-cell resolution during this ventralization process, to analyze both cellular identity as well as differentiation trajectories. The findings of this study were 1) the confirmation of NC derivatives residing within human embryonic and adult long bone marrow, 2) enrichment of NC progenitors within bone marrow via neurosphere culture conditions that demonstrated multipotency and stereotypic migration upon transplantation into the chick neural tube, and 3) OPC-like cell generated from NC progenitors harvested from the embryonic rat DRG and human bone marrow, with demonstrable change from a PNS to CNS phenotype.

A unique advantage of our approach in generating both CNS and PNS myelinating glia from BMSCs is safely in the avoidance of genetic manipulation. Therefore, adult human bone marrow may be used as a safe and accessible source to generate Schwann cells and oligodendrocyte. Derived myelinating glia can be autologously transplanted into patients suffering from traumatic and demyelinating diseases, as well as utilized for disease modelling.