AN ANALYSIS OF ASTROCYTIC CELL-LINES WITH DIFFERENT ABILITIES TO PROMOTE AXON GROWTH

The adult mammalian central nervous system (CNS) lacks the capacity to support axonal regeneration. There is increasing evidence to suggest that astrocytes, the major glial population in the CNS, may possess bo th axon-growth promoting and axon-growth inhibitory properties and the latter may contribute to the poor regenerative capacity of the CNS. I n order to examine the molecular differences between axon-growth permi ssive and axon-growth inhibitory astrocytes, a panel of astrocyte cell lines exhibiting a range of axon-growth promoting properties was gene rated and analysed. No clear correlation was found between the axon-gr owth promoting properties of these astrocyte cell lines with: (i) the expression of known neurite-outgrowth promoting molecules such as lami nin, fibronectin and N-cadherin; (ii) the expression of known inhibito ry molecules such tenascin and chondroitin sulphate proteoglycan; (iii ) plasminogen activator and plasminogen activator inhibitor activity; and (iv) growth cone collapsing activity. EM studies on aggregates for med from astrocyte cell lines, however, revealed the presence of an ab undance of extracellular matrix material associated with the more inhi bitory astrocyte cell lines. When matrix deposited by astrocyte cell l ines was assessed for axon-growth promoting activity, matrix from perm issive lines was found to be a good substrate, whereas matrix from the inhibitory astrocyte lines was a poor substrate for neuritic growth. Our findings, taken together, suggest that the functional differences between the permissive and the inhibitory astrocyte cell lines reside largely with the ECM.