The HDAC6 Inhibitor Trichostatin A Acetylates Microtubules and Protects Axons From Excitotoxin-Induced Degeneration in a Compartmented Culture Model

Abstract

Axon degeneration has been implicated as a pathological process in several neurodegenerative diseases and acquired forms of neural injury. We have previously shown that stabilizing microtubules can protect axons against excitotoxin-induced fragmentation, however, the alterations of microtubules following excitotoxicity that results in axon degeneration are currently unknown. Hence, this study investigated whether excitotoxicity affects the post-translational modifications of microtubules and microtubule-associated proteins, and whether reversing these changes has the potential to rescue axons from degeneration. To investigate microtubule alterations, primary mouse cortical neurons at 10 days in vitro were treated with 10 or 25 μM kainic acid to induce excitotoxicity and axon degeneration. Post-translational modifications of microtubules and associated proteins were examined at 6 h following kainic acid exposure, relative to axon degeneration. While there were no changes to tyrosinated tubulin or MAP1B, acetylated tubulin was significantly (p < 0.05) decreased by 40% at 6 h post-treatment. To determine whether increasing microtubule acetylation prior to kainic acid exposure could prevent axon fragmentation, we investigated the effect of reducing microtubule deacetylation with the HDAC6 inhibitor, trichostatin A. We found that trichostatin A prevented kainic acid-induced microtubule deacetylation and significantly (p < 0.05) protected axons from fragmentation. These data suggest that microtubule acetylation is a potential target for axonal protection where excitotoxicity may play a role in neuronal degeneration.

HDAC6 Modulates Signaling Pathways Relevant to Synaptic Biology and Neuronal Differentiation in Human Stem Cell-Derived Neurons

“…In an another study using mouse cortical neuron cultures, it was shown that axonal degeneration from kainic acid was accompanied by significant decrease in α-tubulin acetylation [25]. Treatment with an HDAC inhibitor resulted in higher levels of α-tubulin acetylation, as expected, but it also protected the neurons from kainic acid-induced axonal degeneration [25].…”

“…In mouse cortical neuron cultures, it was shown that inhibiting HDAC6 through genetic and pharmacological methods led to increased survival and neuronal regeneration in the setting of oxidative stress [24]. In an another study using mouse cortical neuron cultures, it was shown that axonal degeneration from kainic acid was accompanied by significant decrease in α-tubulin acetylation [25]. Treatment with an HDAC inhibitor resulted in higher levels of α-tubulin acetylation, as expected, but it also protected the neurons from kainic acid-induced axonal degeneration [25].…”

The microtubule regulator ringer functions downstream from the RNA repair/splicing pathway to promote axon regeneration

“…Early studies found that HDAC6 was neuroprotective after a CNS injury and associated these findings with HDAC6's role in transcriptional regulation (Rivieccio et al 2009). However, more recent studies found that HDAC6 is neuroprotective in a manner that was associated with its deacetylation of microtubules (Li et al 2011;Hanson et al 2018;Prior et al 2018). Other studies have shown that HDAC6 is essential for healthy axonal transport and influences MAP-microtubule interactions (Iwata et al 2005;Dompierre et al 2007;Ding et al 2008;Chen et al 2010;Simoes-Pires et al 2013).…”

“…HDAC6 inhibition has been shown to be neuroprotective (Rivieccio et al 2009;Li et al 2011;Cho and Cavalli 2014;Hanson et al 2018;Prior et al 2018). More specifically, HDAC6 has been implicated in injury-mediated microtubule deacetylation, and through its inhibition dorsal root ganglia (DRG) neurons enhance their neurite outgrowth in vitro (Rivieccio et al 2009;Li et al 2011;Cho and Cavalli 2014;Hanson et al 2018;Prior et al 2018). We first assessed the regeneration-incompetent C3da neurons and found that HDAC6KO strongly enhanced their axon regeneration, increasing the regeneration percentage to 54% and the regeneration index to 0.34 (Fig.…”

Microtubule Dysfunction: A Common Feature of Neurodegenerative Diseases

“…Moreover, Hanson and colleagues have recently demonstrated that TSA prevents the decrease in tubulin acetylation precluding axon fragmentation and axonal loss in mouse cortical neurons exposed to kainic acid, an excitotoxic agent commonly used to induce epilepsy in rodents [ 300 ].…”