TAFA4 Reverses Mechanical Allodynia through Activation of GABAergic Transmission and Microglial Process Retraction

Publication date: 13 March 2018
Source:Cell Reports, Volume 22, Issue 11
Author(s): Charline Kambrun, Olivier Roca-Lapirot, Chiara Salio, Marc Landry, Aziz Moqrich, Yves Le Feuvre
C-low-threshold mechanoreceptors (C-LTMRs) are sensory neurons that, beyond conveying pleasant touch, modulate nociceptive transmission within the spinal cord. However, pain alleviation by C-LTMRs remains poorly understood. Here, we show that the C-LTMR-derived TAFA4 chemokine induces a reinforcement of inhibitory synaptic transmission within spinal networks, which consequently depresses local excitatory synapses and impairs synaptic transmission from high-threshold C-fibers. In animals with inflammation induced by Freund's complete adjuvant, TAFA4 decreases the noxious stimulus-induced neuronal responses recorded in vivo and alleviates mechanical pain. Both effects are blocked by antagonists of GABAergic transmission. Furthermore, TAFA4 promotes microglial retraction in inflammation and increases the number of inhibitory synapses on lamina IIi somata. Altogether, these results demonstrate GABAergic interneurons to be the first integration relay for C-LTMRs and highlight a tight interplay between sensory neurons, microglial cells, and spinal interneurons, which fine-tunes inhibitory activity and nociceptive transmission in pathological conditions.

Graphical abstract

Teaser

TAFA4 is a recently discovered chemokine secreted by C-low-threshold mechanoreceptors (C-LTMRs). Kambrun et al. describe the interplay between C-LTMRs, spinal GABAergic neurons, and microglial cells that is responsible for the mechanical pain alleviation induced by TAFA4 by inflammation.


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