Substrate-bound human recombinant L1 selectively promotes neuronal attachment and outgrowth in the presence of astrocytes and fibroblasts

Axonal pathfinding is a complex process that is mediated through cell–matrix and cell–cell interactions. A large number of studies have demonstrated that ECM and ECM-derived proteins and peptides are potent promoters of neurite outgrowth, however much less attention is given to the fact that these same ligands also elicit responses in a wide variety of non-neuronal cell types. We examined the use of a substrate-bound recombinant form of human L1, an integral membrane protein, as a ligand for bridging materials for repairing the CNS by studying its effectiveness in promoting specific responses of neuronal cells in the presence of astrocytes and fibroblasts. L1, a cell adhesion molecule expressed in the developing CNS and PNS, has strong neurite promoting activity, and contributes to axonal guidance and axonal fasciculation during development. In this study, substrates treated with L1–Fc were compared to subtrates treated with fibronectin and poly-lysine (PDL) with respect to their interaction with a variety of cell types, including three types of neurons (DRG neurons, cerebellar granule neurons, and hippocampal neurons), astrocytes, dermal fibroblasts, and meningeal cells. L1–Fc-treated substrates supported significantly higher levels of neurite outgrowth relative to fibronectin and PDL, while inhibiting the attachment of astrocytes, meningeal cells, and fibroblasts. We also show that neuronal cells attach to and extend neurites on 30 μm diameter L1–Fc-treated filaments as an example of a potentially useful bridging substrate. The high level of biological specificity displayed by surface-bound L1, along with the fact that it is a potent promoter of neurite outgrowth, is normally expressed on axons and regulates axonal fasciculation during normal development bodes well for its use on bridging materials for the repair of the CNS, and suggests that cell adhesion molecules, in general, may be useful for biomaterial modification. Moreover, small diameter filaments coated with L1–Fc may function in an analogous way to pioneering axons that guide the growth of axons to distal targets during development.