Our work centers on understanding how the extracellular matrix molecule
tenascin-C regulates neuronal growth. We have found that the region of
tenascin-C containing only alternately spliced
fibronectin type-III repeat D, called fnD, when used by itself, dramatically increases neurite outgrowth in culture. We used overlapping synthetic
peptides to localize the neurite outgrowth-promoting site within fnD to a 15 amino acid sequence, called D5. An antibody against D5 blocked promotion of neurite outgrowth by fnD as well as
tenascin-C, indicating that this
peptide sequence is functional in the context of the native molecule. Further testing of shorter synthetic
peptides restricted the neurite outgrowth-promoting site to eight
amino acids,
VFDNFVLK. Of these, "FD" and "FV" are conserved in
tenascin-C sequences derived from all the species available in the GenBank. To investigate the hypothesis that FD and FV are critical for the interaction with neurons, we tested a recombinant fnD
protein and synthetic
peptides with alterations in FD and/or FV. These molecules did not facilitate process extension, suggesting that the conserved
amino acids are required for formation of the active site in fnD. We next investigated whether
VFDNFVLK could be used as a
reagent to overcome the neurite outgrowth inhibitory properties of
chondroitin sulfate proteoglycans, the major inhibitory molecules in the
glial scar. The
peptide significantly enhanced outgrowth on
proteoglycans and was more effective than
laminin-1, L1-Fc, or intact
tenascin-C, thus demonstrating the potential applicability of
tenascin-C regions as therapeutic
reagents.