Comparing astrocytic cell lines that are inhibitory or permissive for axon growth: The major axon-inhibitory proteoglycan is NG2

Department of Physiology and Medical Research Council, Cambridge Centre for Brain Repair, University of Cambridge, Cambridge CB2 3EG, United Kingdom.
The Journal of Neuroscience : The Official Journal of the Society for Neuroscience (Impact Factor: 6.34). 11/1999; 19(20):8778-88.
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ABSTRACT Astrocytes, oligodendrocytes, and oligodendrocyte/type 2 astrocyte progenitors (O2A cells) can all produce molecules that inhibit axon regeneration. We have shown previously that inhibition of axon growth by astrocytes involves proteoglycans. To identify inhibitory mechanisms, we created astrocyte cell lines that are permissive or nonpermissive and showed that nonpermissive cells produce inhibitory chondroitin sulfate proteoglycans (CS-PGs). We have now tested these cell lines for the production and inhibitory function of known large CS-PGs. The most inhibitory line, Neu7, produces three CS-PGs in much greater amounts than the other cell lines: NG2, versican, and the CS-56 antigen. The contribution of NG2 to inhibition by the cells was tested using a function-blocking antibody. This allowed increased growth of dorsal root ganglion (DRG) axons over Neu7 cells and matrix and greatly increased the proportion of cortical axons able to cross from permissive A7 cells onto inhibitory Neu7 cells; CS-56 antibody had a similar effect. Inhibitory fractions of conditioned medium contained NG2 coupled to CS glycosaminoglycan chains, whereas noninhibitory fractions contained NG2 without CS chains. Enzyme preparations that facilitated axon growth in Neu7 cultures were shown to either degrade the NG2 core protein or remove CS chains. Versican is present as patches on Neu7 monolayers, but DRG axons do not avoid these patches. Therefore, NG2 appears to be the major axon-inhibitory factor made by Neu7 astrocytes. In the CNS, NG2 is expressed by O2A cells, which react rapidly after injury to produce a dense NG2-rich network, and by some reactive astrocytes. Our results suggest that NG2 may be a major obstacle to axon regeneration.

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Available from: Andreas Faissner, Sep 25, 2015
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    • "In rat brain, TAM exhibits an antagonist action on oestrogen receptor ␤ (ER␤) (Zhao et al., 2005). Glial scar is a barrier for reconnecting axons in the central nervous system (Hatten et al., 1991; Fidler et al., 1999). In the spinal cord, TAM reduces the inhibitor molecules of axonal regeneration, such as Nogo-A, glycoprotein associated to myelin (MAG) and oligodendrocytes myelin glycoprotein (OMgp) (Tian et al., 2009) therefore favouring axonal regeneration. "
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    ABSTRACT: A penetrating brain injury produces a glial scar formed by astrocytes, oligodendrocytes, microglia and NG2 cells. Glial scar is a barrier preventing the extent of damage but it has deleterious effects in the regeneration of the axons. Estradiol and tamoxifen reduce gliosis and have neuroprotective effects in the hippocampus and the spinal cord. We evaluated the proliferation of glia and the electrocorticogram in the sensorial cortex in a brain injury model. At seven days post-injury, estradiol, tamoxifen and estradiol plus tamoxifen reduced the number of resident and proliferative NG2 and reactive astrocyte vimentin+ cells. Estradiol and tamoxifen effects on NG2 cells could be produced by the classical estrogen receptors found in these cells. The glial scar was also reduced by tamoxifen. At thirty days post-injury, the amount of resident and proliferative astrocytes increased significantly, except in the estradiol plus tamoxifen group, whilst the oligodendrocytes proliferation in the glial scar was reduced in treated animals. Tamoxifen promotes the survival of FOX-3+ neurons in the injured area and a recovery in the amplitude of electrocorticogram waves. At thirty days, estradiol did not favour the suvival of neurons but produced a greater number of reactive astrocytes. In contrast, the number of oligodendrocytes was reduced. Tamoxifen could favour brain repair promoting neuron survival and adjusting glial cell number. It seems to recover adequate neural communication.
    Brain research bulletin 07/2013; 98. DOI:10.1016/j.brainresbull.2013.07.007 · 2.72 Impact Factor
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    • "Apart from this correlation, the recognition that CSPGs are blockers of axon regeneration in scar tissue came from two types of experiment. In the first, astrocytes that were inhibitory or permissive to axon regeneration were compared, and the inhibitory activity was found to reside in secreted molecules of the extracellular matrix which could be identified in various ways as CSPGs (Snow et al., 1990; Fidler et al., 1999). In the second, the ability of the enzyme chondroitinase to remove the inhibitory glycan chains from CSPGs has been used to show that digestion of CSPGs renders the CNS scar less inhibitory (Crespo et al., 2007). "
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    ABSTRACT: Axon regeneration and the sprouting processes that underlie plasticity are blocked by inhibitory factors in the central nervous system (CNS) environment, several of which are upregulated after injury. The major inhibitory molecules are those associated with myelin and those associated with the glial scar. In myelin, NogoA, MAG, and OMgp are present on normal oligodendrocytes and on myelin debris. They act partly via the Nogo receptor, partly via an unidentified amino-Nogo receptor. In the glial scar, chondroitin sulphate proteoglycans, semaphorins, and the formation of a collagen-based membrane are all inhibitory. Methods to counteract these forms of inhibition have been identified, and these treatments promote axon regeneration in the damaged spinal cord, and in some cases recovery of function through enhanced plasticity.
    Handbook of Clinical Neurology 10/2012; 109:503-22. DOI:10.1016/B978-0-444-52137-8.00031-0
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    • "The differential expression and contribution of individual members of the CSPG family have also been studied. NG2, the most important component, is a major inhibitory proteoglycan for sensory axons [49]. NG2 is expressed by oligodendrocyte progenitor cells, which react rapidly following CNS injury, and by some reactive astrocytes. "
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    ABSTRACT: Injured primary sensory axons fail to regenerate into the spinal cord, leading to chronic pain and permanent sensory loss. Re-entry is prevented at the dorsal root entry zone (DREZ), the CNS-PNS interface. Why axons stop or turn around at the DREZ has generally been attributed to growth-repellent molecules associated with astrocytes and oligodendrocytes/myelin. The available evidence challenges the contention that these inhibitory molecules are the critical determinant of regeneration failure. Recent imaging studies that directly monitored axons arriving at the DREZ in living animals raise the intriguing possibility that axons stop primarily because they are stabilized by forming presynaptic terminals on non-neuronal cells that are neither astrocytes nor oligodendrocytes. These observations revitalized the idea raised many years ago but virtually forgotten, that axons stop by forming synapses at the DREZ.
    09/2012; 21(3):83-93. DOI:10.5607/en.2012.21.3.83
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