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The Role of NG2+ Cells in Regeneration Failure After Spinal Cord Injury

Filous, Angela R, Ph.D.
http://rave.ohiolink.edu/etdc/view?acc_num=case1396605992

Abstract Details

2014, Doctor of Philosophy, Case Western Reserve University, Neurosciences.
Macrophage infiltration into the lesion core after spinal cord injury causes injured dystrophic axons to dieback from the lesion center. Although it was once thought these fibers would retract until they reached a collateral, previous work from our laboratory showed that injured sensory axons actually stabilize just caudal to the lesion on a population of cells that express high amounts of neural-glial 2 (NG2). NG2 is a member of the chondroitin sulfate proteoglycan family, a family of molecules known to exhibit inhibitory effects on neurons. Therefore, the finding that cells expressing this molecule can stabilize dystrophic endings of neurons after injury was surprising. Here we utilized a dorsal column crush injury to investigate the interactions that occur between this progenitor cell population and the injured neurons. We found that injured fibers persist in an area of high NG2 expression for weeks after injury. Using an NG2+ cell population cultured from adult spinal cords in co-cultures with adult dorsal root ganglion neurons, we observed that these neurons are not inhibited by the NG2+ cell surface, but actually prefer to grow upon the surface of these cells over other growth-permissive substrates. Over time, the cultured neurons no longer extend processes off the NG2+ cell surface, an adhesion that can be overcome at acute timepoints by degrading the NG2 glycosaminoglycan side chains with an enzyme known as chondroitinase ABC. However, by five days in co-culture, chondroitinase is no longer effective at releasing neurites from the NG2+ cell surface, suggesting these connections become more permanent. Studies using various concentrations of proteoglycans and growth-permissive extracellular matrix molecules laminin or fibronectin further illustrate the role of proteoglycans in mediating the entrapment phenomenon. By two days in vitro, neurons cultured on a monolayer of NG2+ cells begin to express synaptic vesicle proteins in puncta along their neurites. Electron microscopy and FM studies were used to further investigate the interaction of these two cell types in culture and suggest that these two cells form synaptic-like connections in a dish. Similiarly, at 21 days after injury, labeled dystrophic fibers begin to express synaptic markers when associated with NG2+ cells in vivo. Double-conditioning of the sciatic nerve after the dorsal column crush allowed fibers to regenerate beyond the rostral end of the glial scar, as has been shown previously. The fibers that reach beyond the rostral end of the lesion appear to express less synaptic protein than those that remain associated with the NG2+ cell population at the caudal end of the lesion. Consistent with the idea that NG2 plays a role in stabilizing dystrophic fibers, we observed that injured axons in NG2 KO mice dieback further than those of wild-type mice at 14 days after injury. These data suggest a novel cause of regeneration failure, entrapment, which adds to the complexity of achieving successful regeneration after SCI. In a separate study within this work, we demonstrate the therapeutic potential of combining cell transplantation strategies, specifically with immature astrocytes, with chondroitinase. Immature, but not mature astrocytes, were able to cross the inhibitory rim of an in vitro model of the glial scar through an MMP-2 dependent mechanism, as demonstrated using selective enzyme inhibitors. Alone, neither immature astrocyte transplantation nor chondroitinase ABC treatment was capable of promoting regeneration. However, when combined with chondroitinase ABC injections, immature astrocytes were able to form bridges to allow for axon regeneration across microlesions of the cingulum. These studies demonstrate the importance of combinatorial strategies to promote regeneration. Together with the NG2 data, this work addresses the complexity of achieving functional regeneration after CNS injury, providing helpful insight for future therapeutic strategies.
Jerry Silver, Ph.D. (Advisor)
Lynn Landmesser, Ph.D. (Committee Chair)
Robert Miller, Ph.D. (Committee Member)
Paul Tesar, Ph.D. (Committee Member)
181 p.
Neurosciences
NG2; chondroitin sulfate proteoglycans; spinal cord injury, axonal dieback; regeneration; glial scar; spinal cord; entrapment; neuroscience; oligodendrocyte precursor cells

Recommended Citations

Citations

  • Filous, A. R. (2014). The Role of NG2+ Cells in Regeneration Failure After Spinal Cord Injury [Doctoral dissertation, Case Western Reserve University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=case1396605992

    APA Style (7th edition)

  • Filous, Angela. The Role of NG2+ Cells in Regeneration Failure After Spinal Cord Injury. 2014. Case Western Reserve University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=case1396605992.

    MLA Style (8th edition)

  • Filous, Angela. "The Role of NG2+ Cells in Regeneration Failure After Spinal Cord Injury." Doctoral dissertation, Case Western Reserve University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=case1396605992

    Chicago Manual of Style (17th edition)

case1396605992
637
© 2014, all rights reserved.
This open access ETD is published by Case Western Reserve University School of Graduate Studies and OhioLINK.