Impaired function of hdac6 slows down axonal growth and interferes with axon initial segment development

Abstract

The development of morphological neuronal polarity starts by the formation and elongation of an axon. At the same timeó the axon initial segment (AIS) is generated and creates a diffusion barrier which differentiate axon and somatodendriticó compartment. Different structural and functional proteins that contribute to the generation of neuronal action potential areóconcentrated at the axon initial segment. While axonal elongation is controlled by signalling pathways that regulateócytoskeleton through microtubule associated proteins and tubulin modifications, the microtubule cytoskeleton under theóAIS is mostly unknown. Thus, understanding which proteins modify tubulin, where in the neuron and at whichódevelopmental stage is crucial to understanding how morphological and functional neuronal polarity is achieved. In thisóstudy performed in mice and using a well established model of murine cultured hippocampal neurons, we report that theótubulin deacetylase HDAC6 is localized at the distal region of the axon, and its inhibition with TSA or tubacin slows downóaxonal growth. Suppression of HDAC6 expression with HDAC6 shRNAs or expression of a non-active mutant of HDAC6 alsoóreduces axonal length. Furthermore, HDAC6 inhibition or suppression avoids the concentration of ankyrinG and sodiumóchannels at the axon initial segment (AIS). Moreover, treatment of mouse cultured hippocampal neurons with detergents toóeliminate the soluble pool of microtubules identified a pool of detergent resistant acetylated microtubules at the AIS, notópresent at the rest of the axon. Inhibition or suppression of HDAC6 increases acetylation all along the axon and disrupts theóspecificity of AIS cytoskeleton, modifying the axonal distal gradient localization of KIF5C to a somatodendritic and axonalólocalization. In conclusion, our results reveal a new role of HDAC6 tubulin deacetylase as a regulator of microtubuleócharacteristics in the axon distal region where axonal elongation takes place, and allowing the development of acetylatedómicrotubules microdomains where HDAC6 is not concentrated, such as the axon initial segment. © 2010 Tapia et al.