The Effect of Proteoglycans on Neurite Outgrowth and Functional Recovery in an Animnal Model with Spinal Cored Injury

Spinal cord injury (SCI) often causes permanent disability or loss of movement (paralysis) and sensation below the site of the injury. The reasons of axon regeneration failure including difficiency ability of axon regeneration and the inhibitory environment around the glial scar that countered by injuried axon. Chondroitin sulfate proteoglycans (CSPGs) were up-regulated in the glial scar after injury and inhibit neurite regeneration by the chondroitin sulfate glycosaminoglycan chains (CS-GAG chains). Removal of CS-GAG chains by enzymatic digestion or genetic manipulation after SCI could enhance axon growth and functional recovery, suggesting that CS-GAG chain is the key molecule contributing to the inhibitory effect of CSPG on neurite outgrowth. However, the treatment may not improve functional recovery, implicating that the underlying regulatory mechanism of CSPG on neuronal plasticity maybe more complicated. Our recent studies found that the inhibition effect of CS-GAG chains on neurite outgrowth of PC12 cells and DRG neurons was mediated by annexin VI, which is present on the surface of neurons. Observations in PC12 cells and primary cultured dorsal root ganglion (DRG) neurons showed that siRNA-induced knockdown of annexin VI expression or a treatment with a monoclonal antibody against annexin VI improved neurite outgrowth of the cells cultured with CS-GAG. It suggests that annexin VI serves as a receptor to mediate the CS-GAG–induced inhibition of neurite outgrowth in damaged neurons. Perlecan, one of the heparin sulfate proteoglycan is a main component in the basal laminae. Previous studies showed that recombinant perlecan domain V promote the axon outgrowth of dorsal root ganglion (DRG) neurons on a laminin substrate. Both of perlecan domain I and domain V bind with acetylcholineesterase (AchE), which can promote neurite outgrowth in a non-enzymatic activity mechanism. In addition, whether perlecan participates in synaptogenesis is also interesting. Based on the previous studies, we will further investigate (1) The active domain and signaling pathway of annexin VI, which mediates CS-GAG inhibitory effect on neurite outgrowth. (2) The interaction of perlecan domain V and AchE in promoting neurite outgrowth and synaptogenesis will be investigated. In addition, the findingsfrom cell based studies will be extended from in vitro to in vivo. The novel therapeutic approaches based on the two CSPG and HSPG mechanisms in our findindings will be designed and investigated in a SCI rat mode. The effects of the treatments by investigating the descending and ascending neurite regeneration and functional behavior test will be also studies. This project will help to develop novel drugs and biomaterials for the treatment of SCI.