Microtubule organization and sensory neuron dysfunction in neuropathic pain states in mice and humans
Final Report Abstract
Neuropathic pain is a major and debilitating condition that arises from lesion of the nervous system. In this work we investigated a relatively unexplored factor in the pathogenesis of neuropathic pain, the role of sensory neuron microtubules. In the first part of the project we explored the functional significance of a prominent microtubule posttranslation modification in neurons, tubulin acetylation. We focused on a recently identified microtubule modifying enzyme, Atat1, the major α-tubulin acetyltransferase in ciliated organisms. In mice, with a targeted deletion of Atat1 we observed a loss of detectable K40 α-tubulin acetylation across multiple tissues and in cellular structures such as cilia and axons where acetylation is normally enriched. Mice were however viable and developed normally apart from mild defects in sperm physiology and male fertility. We further used conditional transgenesis to examine the function of Atat1 in peripheral sensory neurons. We found that mice lacking Atat1 in sensory neurons displayed profound deficits in their ability to detect mechanical stimuli. We showed that all cutaneous afferent subtypes, including nociceptors have strongly reduced mechanosensitivity upon Atat1 deletion, and that consequently, mice are largely insensitive to mechanical touch and pain. We established that this broad loss of mechanosensitivity is dependent upon the acetyltransferase activity of Atat1, which when absent leads to a decrease in cellular elasticity. By mimicking α-tubulin acetylation genetically, we showed both cellular rigidity and mechanosensitivity can be restored in Atat1 deficient sensory neurons. Hence, our results indicate that by influencing cellular stiffness, α-tubulin acetylation sets the force required for touch. In further work, we investigated microtubule function in neuropathic pain states. Using clinically relevant mouse models of neuropathy we measured nociceptive behavior in Atat1 mutant mice and found that mechanical hypersensitivity is abolished in these mice. We explored potential mechanisms at the ultrastructural level but were unable to detect any changes in microtubule organization in Atat1 knockout mice. In summary, this work shows that microtubule acetylation plays a prominent role in sensory mechanotransduction and suggests that targeting of Atat1, the enzyme responsible for this modification, may lead to the development of a novel class of analgesics.
Publications
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(2013). alphaTAT1 is the major alpha-tubulin acetyltransferase in mice. Nature communications 4, 1962
Kalebic, N., Sorrentino, S., Perlas, E., Bolasco, G., Martinez, C., and Heppenstall, P.A.
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(2016). Acetylated tubulin is essential for touch sensation in mice. Elife. 5. pii: e20813
Morley SJ, Qi Y, Iovino L, Andolfi L, Guo D, Kalebic N, Castaldi L, Tischer C, Portulano C, Bolasco G, Shirlekar K, Fusco CM, Asaro A, Fermani F, Sundukova M, Matti U, Reymond L, De Ninno A, Businaro L, Johnsson K, Lazzarino M, Ries J, Schwab Y, Hu J, Heppenstall PA
