Central and peripheral neurite outgrowth differs in preference for heparin-binding versus integrin-binding sequences

Neurons of the CNS and PNS differ in their response to fibronectin (FN) and proteolytic fragments of FN. The 33 KDa C-terminal cell and heparin-binding fragment of FN, in particular, is a strong promoter of CNS neurite outgrowth. To define further the neurite-promoting activity of the 33 RDa fragment, and to investigate further the differences between PNS and CNS responses to FN and the 33 KDa fragment, we contrasted neurite outgrowth by CNS and PNS neurons on three synthetic peptides representing sequences from this fragment of FN: two heparin-binding peptides, FN-C/H I and FN-C/H II (McCarthy et al., 1990), and an integrin-binding peptide, CS1 (Humphries et al., 1987). Spinal cord (SC) neurons, from the CNS, differed from dorsal root ganglion (DRG) neurons, from the PNS, with respect to substratum preference for heparin-binding versus integrin-binding peptides. SC neurite outgrowth was greatest on the heparin-binding peptide FN-C/H II, while DRG neurite outgrowth was greatest on the a4β1 integrin-binding peptide CS1. To test whether the difference in substratum preference was due to differences in the molecular mechanism by which SC and DRG neurons interact with the 33 RDa fragment of FN, anti-β1 integrin antibodies and/or soluble heparin were added to the cultures as potential inhibitors of integrin-mediated or proteoglycan-mediated interactions with FN. SC neurite outgrowth was much more sensitive to the effect of heparin than anti-β1 integrin, indicating SC neurite outgrowth may involve predominantly a heparin-sensitive mechanism. In contrast, DRG neurite outgrowth was more sensitive to anti-β1 integrin, but also affected by heparin, indicating DRG neurite outgrowth involves predominantly a β1 integrin-mediated mechanism with some contribution by a heparin-sensitive mechanism.