Deletion of Crmp4 attenuates CSPG-induced inhibition of axonal growth and induces nociceptive recovery after spinal cord injury.

Abstract

The capacity for regeneration in the injured adult mammalian central nervous system (CNS) is largely limited by potent inhibitory barriers. Chondroitin sulfate proteoglycans (CSPGs) are major inhibitors of axonal regeneration/sprouting and accumulate at lesion sites after CNS trauma. Despite extensive research during the two decades since their discovery, the molecular mechanisms remain elusive, including intracellular phosphorylation events. Collapsin response mediator protein 4 (CRMP4) is known to directly regulate cytoskeletal dynamics and neurite extension, while phosphorylated CRMP4 loses its binding affinity for cytoskeletal proteins. We have previously found that spinal cord injury (SCI) induces CRMP4 upregulation and phosphorylation and that CRMP4 knockout (Crmp4-/-) mice show behavioral recovery of locomotor function after SCI. However, the role of CRMP4 in the recovery of other forms of physiological function such as sensation remains largely unknown. We here have demonstrated CRMP4 involvement in CSPG-induced inhibitory signaling and nociceptive recovery in Crmp4-/- mice after SCI. We cultured dorsal root ganglion (DRG) neurons on CSPG-coated dishes; Crmp4 deletion overrode CSPG-induced inhibition of axon growth in vitro. CRMP4 levels were increased in DRGs in vivo after SCI. Crmp4-/- mice exhibited axonal growth of sensory neurons and recovery of nociceptive function after spinal transection. These results support Crmp4 deletion as a therapeutic target in the treatment of SCI.