CCP1, a tubulin deglutamylase, increases survival of rodent spinal cord neurons following glutamate-induced excitotoxicity
Microtubules (MTs) are cytoskeletal elements that provide structural support, establish morphology, and act as roadways for intracellular transport in cells. Neurons extend and must maintain long axons and dendrites to transmit information through the nervous system. Therefore, in neurons, the ability to independently regulate cytoskeletal stability and MT-based transport in different cellular compartments is essential. Post-translational modification of MTs is one mechanism by which neurons can regulate the cytoskeleton. The carboxypeptidase CCP1 negatively regulates post-translational glutamylation of MTs. We previously demonstrated that the CCP1 homolog in C. elegans is important for maintenance of cilia. In mammals, loss of CCP1, and the resulting hyperglutamylation of MTs, causes neurodegeneration. It has long been known that CCP1 expression is activated by neuronal injury; however, whether CCP1 plays a neuroprotective role after injury is unknown. Furthermore, it not yet clear whether CCP1 acts on ciliary MTs in spinal cord neurons. Using an in vitro model of excitotoxic neuronal injury coupled with shRNA-mediated knockdown of CCP1, we demonstrate that CCP1 protects neurons from excitotoxic death. Unexpectedly, excitotoxic injury reduced CCP1 expression in our system, and knockdown of CCP1 did not result in loss or shortening of cilia in cultured spinal cord neurons. Our results suggest that CCP1 acts on axonal and dendritic MTs to promote cytoskeletal rearrangements that support neuroregeneration and that enzymes responsible for glutamylation of MTs might be therapeutically targeted to prevent excitotoxic death after spinal cord injuries.