The association between the expression of PAR2 and TMEM16A and neuropathic pain

Abstract

Chronic constriction injury (CCI) of the sciatic nerve may induce dorsal root ganglion (DRG) neuronal hyperexcitability and behaviorally expressed hyperalgesia. CCI is a model of neuropathic pain. To investigate the association between the expression of protease activated receptor 2 (PAR2), TMEM16A and neuropathic pain, the expression of PAR2 and TMEM16A proteins in the DRG neurons of rats following CCI of the sciatic nerve was investigated. Following the creation of the CCI model, the thermal withdrawal latency (TWL) was examined by a hot plate test. An immunofluorescence assay and western blot assay were performed to determine the expression of PAR2 and TMEM16A proteins in the ipsilateral L4–6 DRG neurons. The concentration of inositol 1,4,5-triphosphate (IP3) in the L4–6 DRG was determined by ELISA. In the CCI-D7 (7 days after CCI) and CCI-D14 (14 days after CCI) treatment groups, the TWL of rats was significantly shorter than that in the sham operated group (P<0.01; n=12). The expression of PAR2 and TMEM16A proteins in the CCI-D7 and CCI-D14 groups were significantly upregulated compared with the sham operated group (P<0.05; n=12). Additionally, it was revealed that PAR2 and TMEM16A were co-expressed in DRG neurons. It was also observed that IP3 significantly increased in the CCI-D7 and CCI-D14 groups compared with the sham operation group (P<0.05; n=6) as PAR2 and TMEM16A also increased. These findings suggest that the upregulation of PAR2 and TMEM16A in DRG neurons, the co-expression of the two proteins and increasing IP3 are critical to the development of neuropathic pain.

Chloride – The Underrated Ion in Nociceptors

“…mRNA of all three anoctamins is expressed in mouse and human trigeminal and dorsal root ganglia (Boudes et al, 2009;Flegel et al, 2015). Ano1 is found primarily in small-diameter nociceptors and upregulated in formalin and neuropathic pain models and associated with increased excitability of sensory neurons (Yang et al, 2008;Liu et al, 2010;Cho et al, 2012;Jin et al, 2013;García et al, 2014;Deba and Bessac, 2015;Pineda-Farias et al, 2015;Takayama et al, 2015;Zhang et al, 2018;Chen et al, 2019). Depletion of Ano1 increases the response latency of mice to noxious heat stimuli and this stresses the importance of Ano1 as a physiological heat sensor (Cho et al, 2012).…”

“…Activation of Gq-PCR could thus activate Ano1 via Ca 2+ -release from the endoplasmic reticulum by IP 3 , but would counteract Ano1 activation due to PIP 2 depletion (Le et al, 2019). This is of particular interest in chronic pain states, because PIP 2 /Ca 2+signaling is altered under these conditions demonstrated by elevated IP 3 -levels in chronic constriction injury of the sciatic nerve (Zhang et al, 2018).…”

“…Similarly, compensating the CCC changes by viral delivery of KCC2 into DRG and spinal neurons reverses the depolarizing shift of the reversal potential for GABA-mediated currents and abolishes hypersensitivity induced by nerve injury (Li et al, 2016). Although these studies indicate great potential for targeting Cl − homeostasis in pain conditions, they have to be considered carefully since Cl − homeostasis mechanisms and nociceptor function may not be fully identical in rodents and humans (Funk et al, 2008;Rocha-Gonzalez et al, 2008;Zhang et al, 2018).…”

Nociceptor Signalling through ion Channel Regulation via GPCRs

“…On the other hand, the cyclic undecapeptide urotensin-II activates the urotensin-II receptor (UTR), which couples to Gαq/11 [252,253]. This leads to a reduction in IA in a dose-dependent fashion in trigeminal ganglion neurons, mediated via the activation of PKC [254]. The concomitant recruitment of ERK signaling cascade culminates in an enhanced excitability of TG neurons [254].…”

“…This leads to a reduction in IA in a dose-dependent fashion in trigeminal ganglion neurons, mediated via the activation of PKC [254]. The concomitant recruitment of ERK signaling cascade culminates in an enhanced excitability of TG neurons [254]. In rat TG neurons, the KV1.4, KV3.4, KV4.2 and KV4.3 channels are co-expressed with P2Y2 receptors [255], which in turn couple to different G proteins [256].…”