Sensory axon guidance with semaphorin 6A and nerve growth factor in a biomimetic choice point model

The direct effect of guidance cues on developing and regenerating axons in vivo is not fully understood, as the process involves a multiplicity of attractive and repulsive signals, presented both as soluble and membrane-bound ligands. A better understanding of axon guidance is critical to functional recovery following injury to the nervous system through improved outgrowth and mapping of damaged nerves. Due to their implications as inhibitors to central nervous system regeneration, we investigated the repulsive properties of semaphorin 6A and ephrin-B3 on E15 rat dorsal root ganglion explants, as well as possible interactions with soluble gradients of chemoattractive nerve growth factor (NGF). We employed a 3D biomimetic in vitro choice point model, which enabled the simple and rapid preparation of patterned gel growth matrices with quantifiable presentation of guidance cues in a specifiable manner that resembles the in vivo presentation of soluble and/or immobilized ligands. Neurites demonstrated an inhibitory response to immobilized Sema6A by lumbosacral dorsal root ganglion explants, while no such repulsion was observed for immobilized ephrin-B3 by explants at any spinal level. Interestingly, Sema6A inhibition could be partially attenuated in a concentration-dependent manner through the simultaneous presentation of soluble NGF gradients. The in vitro model described herein represents a versatile and valuable investigative tool in the quest for understanding developmental processes and improving regeneration following nervous system injury.