Characterization, differentiation and therapeutic application of NG2+ progenitor cells.
Ju, Pei Jun.
Date of Issue2013
School of Biological Sciences
The widespread NG2-expressing cells in the central nervous system (CNS) are considered as heterogeneous populations with plastic lineage potential. They rapidly proliferate and differentiate in response to CNS injuries, thereby possessing a therapeutic potential. In order to elucidate the lineage potential of NG2+ cells, twenty-four NG2+ clones were generated and induced for neuronal-glial lineage differentiation. In vitro differentiation analysis revealed that all the clones could differentiate into oligodendrocytes, and seven of them were bipotent of differentiating into both oligodendrocytes and astrocytes. One clone exhibited a multipotent capacity of differentiating into not only neuronal-glial lineages, but also chondrocytes. These distinct subtypes of NG2+ cells were further found to exhibit phenotypic heterogeneity based on the examination of a spectrum of neural progenitor markers (NG2, PDGFαR, Nestin, and A2B5). These results collectively suggest that the NG2+ cells contain heterogeneous progenitors with distinct differentiation capacities. Based on the clonal analysis of NG2+ cells, we verified that NG2+ cells could be induced to acquire neuronal phenotypes by inhibiting epidermal growth factor receptor (EGFR) signaling pathway under the gliogenic conditions. We further confirmed this phenomenon with an independent glial cell line, Central Glial 4 (CG4) cells, and found that the EGFR downstream Ras-ERK axis played a key role during neuronal differentiation of NG2+ cells. To explore the therapeutic significance of neurogenesis from NG2+ cells by EGFR inhibition, we set up the experimental contusive spinal cord injury (SCI) model. We found that antagonizing EGFR functions with a specific EGFR inhibitor (PD168393) caused significant numbers of NG2+ cells (either in situ or through ex-vivo transplantation) to acquire neuronal phenotypes in mouse SCI, which presumably led to accumulation of newly-generated neurons and contributed to the improved neural behavioral performance of these animals. Additionally, by attenuating EGFR signaling in the injured niche, improved histological recovery, reduced astrogliosis and microglia/macrophages post SCI were also observed, probably due to the synergetic benefit from EGFR inhibition after injury. Taken together, the whole study suggests that NG2+ cells, well-known as glial progenitors, are heterogeneous populations with distinct lineage potentials at clonal level. Intriguingly, they could be manipulated for repairing neuronal loss post SCI by EGFR inhibition. These findings support the possibility of evoking endogenous neuronal replacement from NG2+ cells and suggest that EGFR inhibition may be beneficial for treating CNS trauma.