Satellite glial cells in sensory ganglia express functional transient receptor potential ankyrin 1 that is sensitized in neuropathic and inflammatory pain

Abstract

Transient receptor potential ankyrin 1 (TRPA1) is well documented as an important molecule in pain hypersensitivity following inflammation and nerve injury and in many other cellular biological processes. Here, we show that TRPA1 is expressed not only by sensory neurons of the dorsal root ganglia (DRG) but also in their adjacent satellite glial cells (SGCs), as well as nonmyelinating Schwann cells. TRPA1 immunoreactivity is also detected in various cutaneous structures of sensory neuronal terminals, including small and large caliber cutaneous sensory fibers and endings. The SGC-expressed TRPA1 is functional. Like DRG neurons, dissociated SGCs exhibit a robust response to the TRPA1-selective agonist allyl isothiocyanate (AITC) by an increase of intracellular Ca2+ concentration ([Ca2+]i). These responses are abolished by the TRPA1 antagonist HC030031 and are absent in SGCs and neurons from global TRPA1 null mice. SGCs and neurons harvested from DRG proximal to painful tissue inflammation induced by plantar injection of complete Freund’s adjuvant show greater AITC-evoked elevation of [Ca2+]i and slower recovery compared to sham controls. Similar TRPA1 sensitization occurs in both SGCs and neurons during neuropathic pain induced by spared nerve injury. Together, these results show that functional TRPA1 is expressed by sensory ganglia SGCs, and TRPA1 function in SGCs is enhanced after both peripheral inflammation and nerve injury, and suggest that TRPA1 in SGCs may contribute to inflammatory and neuropathic pain.

Piezo2 mechanosensitive ion channel is located to sensory neurons and non-neuronal cells in rat peripheral sensory pathway: implications in pain

“…Next, we performed IHC using various established glial cell markers for the satellite glial cells (SGCs) and Schwann cells (SCs), including glutamine synthetase (GS), glial fibrillary acidic protein (GFAP), S100, and myelin basic protein (MBP) [58]. This was performed in order to rule out Piezo2 expression in the perineuronal glial cells, which produce ring-like immunopositivity that resembles NKA1 α staining patterns.…”

“…After exposure to 0.1% trypsin inhibitor and centrifugation, the pellet was gently triturated and dissociated cells cultured in Neural basal media A (ThermoFisher) plus 0.5 μM glutamine at 37°C in humidified 95% air and 5% CO 2 . Neuron-free SGC culture was established by a differential attachment protocol for SGC isolation, as we described previously [58].…”

“…Intensity correlation analysis (ICA) was performed to determine colocalization of Piezo2 with neuronal plasma membrane (PM) marker sodium/potassium ATPase 1 alpha (NKA1a) and SGC marker glial fibrillary acidic protein (GFAP), as previously described using an ImageJ 1.46r software plugin colocalization analysis module (http://imagej.nih.gov/ij) [35, 58, 80]. In brief, fluorescence intensity was quantified in matched region of interests (the green and red colors varied in close synchrony) for each pair of images.…”

Upregulation of TRPM3 in nociceptors innervating inflamed tissue

“…These results seem at odds with our current findings, which did not reveal a statistically significant increase in TRPA1 mRNA in neurons innervating the inflamed paw. It should be noted, however, that in these earlier studies, bulk mRNA from entire ganglia was analyzed, which inevitably includes not only neurons that innervate injured tissue, but also neurons from the same DRG that innervate healthy tissue, as well as non-neuronal cells present in DRG such as satellite glia ( Shin et al, 2020 ). In contrast, our approach using quantitative in situ hybridization and retrograde labeling allowed us to specifically measure mRNA levels in the cell bodies of the sensory neurons that innervate the inflamed or control hind paw.…”

Investigational drugs in early phase clinical trials targeting thermotransient receptor potential (thermoTRP) channels

“…Gain-of-function mutations in the human gene cause a familial episodic pain syndrome, in which debilitating upper-body pain can be triggered by stressors [76]. In rodents, neuropathic injury increases neuronal expression of TRPA1 [77]. Furthermore, genetic deletion or pharmacological inhibition of TRPA1 reduces pain behaviors in inflammatory, visceral, and neuropathic pain states [78].…”