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.
Source: PubMed


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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    • "ospheres and P2 rat brain revealed that the 0 . 7 M frac - tion mainly contained Phosphacan / RPTPb / f and to less extent Brevican . In contrast , Neurocan was not present in our PG enriched fractions ( Supp . Info . Fig . S2A , B ) . NG2 repre - sents a known CSPG expressed by OPCs and occurs in a gly - cosylated and non - glycosylated isoform ( Fidler et al . , 1999 ; Morgenstern et al . , 2003 ) . Thus , we additionally analysed its expression in our PG fractions . Non - glycosylated NG2 was detectable as a distinct band in the 0 . 3 M fraction . In con - trast , a smear in the high molecular mass range was indicative of glycosylated NG2 in the 0 . 7 M fraction . Yet , the NG2 - level in this frac"
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    • "Among them, chondroitin sulfate proteoglycans (CSPGs), which inhibit axonal growth in vitro (Snow et al., 1990; Dou and Levine, 1994; Friedlander et al., 1994), are upregulated by astrocytes and oligodendrocyte precursor cells after injury and are speculated to be a major inhibitory factor in glial scar tissue (McKeon et al., 1995, 1999; Fitch and Silver, 1997; Haas et al., 1999; Asher et al., 2000, 2002; Jones et al., 2002, 2003a; Tang et al., 2003). NG2, a major CSPG that inhibits axonal growth in vitro and in vivo, increases at the lesion site after CNS injury in mammals (Dou and Levine, 1994; Levine, 1994; Fidler et al., 1999; Chen et al., 2002; Ughrin et al., 2003; Tan et al., 2006). The scar also contains ECM molecules with permissive roles for axonal regeneration, such as laminin (reviewed by Condic and Lemons, 2002). "
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