α-Tubulin Acetyltransferase Is a Novel Target Mediating Neurite Growth Inhibitory Effects of Chondroitin Sulfate Proteoglycans and Myelin-Associated Glycoprotein

Damage to the CNS results in neuronal and axonal degeneration, and subsequent neurological dysfunction. Endogenous repair in the CNS is impeded by inhibitory chemical and physical barriers, such as chondroitin sulfate proteoglycans (CSPGs) and myelin-associated glycoprotein (MAG), which prevent axon regeneration. Previously, it has been demonstrated that the inhibition of axonal histone deacetylase-6 (HDAC6) can promote microtubule alpha-tubulin acetylation and restore the growth of CSPGs- and MAG-inhibited axons. Since the acetylation of alpha-tubulin is regulated by two opposing enzymes, HDAC6 (deacetylation) and alpha-tubulin acetyltransferase-1 (alpha-TAT1; acetylation), we have investigated the regulation of these enzymes downstream of a growth inhibitory signal. Our findings show that exposure of primary mouse cortical neurons to soluble CSPGs andMAG substrates cause an acute and RhoA-kinase-dependent reduction in alpha-tubulin acetylation and alpha-TAT1 protein levels, without changes to either HDAC6 levels or HDAC6 activity. The CSPGs-and MAG-induced reduction in alpha-TAT1 occurs primarily in the distal and middle regions of neurites and reconstitution of alpha-TAT1, either by Rho-associated kinase (ROCK) inhibition or lentiviral-mediated alpha-TAT1 overexpression, can restore neurite growth. Lastly, we demonstrate that CSPGs and MAG signaling decreases alpha-TAT1 levels posttranscriptionally via a ROCK-dependent increase in alpha-TAT1 protein turnover. Together, these findings define alpha-TAT1 as a novel potential therapeutic target for ameliorating CNS injury characterized by growth inhibitory substrates that are prohibitive to axonal regeneration.