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: 6.75). 11/1999; 19(20):8778-88.
Source: PubMed

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, Jul 19, 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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    • "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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    Handbook of Clinical Neurology 01/2012; 109:503-22. DOI:10.1016/B978-0-444-52137-8.00031-0
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    • "Although it is not clear which exact glycosaminoglycans of CSPGs core proteins are recognized by the CS-56 antibody, it has been widely used as a marker for the injury-induced overexpression of CSPGs that are subject to ChABC digestion (Davies et al., 2006; Kim et al., 2006). The procedure for CS-56 immunolabeling has been previously described (Fidler et al., 1999). Briefly, all sections were circled with a hydrophobic resin and incubated for 1 h in a humidity chamber in PBS containing 0.4% Triton X-100 with 1:30 goat serum to block nonspecific binding. "
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