Peripherally Increased Artemin is a Key Regulator of TRPA1/V1 Expression in Primary Afferent Neurons

Abstract

BackgroundArtemin, a member of the glial cell line-derived neurotrophic factor family, is known to have a variety of neuronal functions, and has been the subject of attention because it has interesting effects, including bi-directional results in modulation in neuropathic and inflammatory pain. It has been shown that the overexpression of artemin is associated with an increase in the expression of TRP family channels in primary afferents and subsequent hyperalgesia, and an increase in neuronal activity. The purpose of this study was to examine the peripheral synthesis of artemin in inflammatory and neuropathic pain models, and to demonstrate the effects of long-term or repeated application of artemin in vivo on pain behaviors and on the expression of TRP family channels. Further, the regulatory mechanisms of artemin on TRPV1/A1 were examined using cultured DRG neurons.ResultsWe have demonstrated that artemin is locally elevated in skin over long periods of time, that artemin signals significantly increase in deep layers of the epidermis, and also that it is distributed over a broad area of the dermis. In contrast, NGF showed transient increases after peripheral inflammation. It was confirmed that the co-localization of TRPV1/A1 and GFRα3 was higher than that between TRPV1/A1 and TrkA. In the peripheral sciatic nerve trunk, the synthesis of artemin was found by RT-PCR and in situ hybridization to increase at a site distal to a nerve injury. We demonstrated that in vivo repeated artemin injections into the periphery changed the gene expression of TRPV1/A1 in DRG neurons without affecting GFRα3 expression. Repeated artemin injections also induced mechanical and heat hyperalgesia. Using primary cultured DRG neurons, we found that artemin application significantly increased TRPV1/A1 expression and Ca2+ influx. Artemin-induced p38 MAPK pathway regulated the TRPV1 channel expression, however TRPA1 upregulation by artemin is not mediated through p38 MAPK.ConclusionsThese data indicate the important roles of peripherally-derived artemin on the regulation of TRPV1/A1 in DRG neurons in pathological conditions such as inflammatory and neuropathic pain.

Inflammatory and neuropathic cold allodynia are selectively mediated by the neurotrophic factor receptor GFRα3

“…Similarly, GFLs potentiate capsaicin responses in dissociated DRG neurons recorded by Ca 2+ imaging, showing sensitization of TRPV1 + cells (45). However, specific changes in TRPV1 channel activity have not been reported, and the preponderance of data suggests that artemin-induced heat hyperalgesia is caused by increased TRPV1 expression (27,28,46,47). Moreover, unlike the established TRPM8 dependence of arteminand NGF-evoked cold allodynia (8) or the necessity of TRPV1 for NGF-induced heat hyperalgesia (36), the molecule determinants of GFL-evoked alterations in nociception in vivo are unknown (48).…”

“…contr, Contralateral; ipsi, ipsilateral; ns, not significant; oxal, oxaliplatin. ***P < 0.001. hyperalgesia as well as altered expression of molecules involved in sensory transduction (27,28). However, these studies involved either genetically induced artemin overexpression in the periphery (27) or multiple plantar injections of exogenous artemin (28), making it unclear if artemin-GFRα3 signaling influences afferent expression phenotypes under physiological conditions.…”

“…***P < 0.001. hyperalgesia as well as altered expression of molecules involved in sensory transduction (27,28). However, these studies involved either genetically induced artemin overexpression in the periphery (27) or multiple plantar injections of exogenous artemin (28), making it unclear if artemin-GFRα3 signaling influences afferent expression phenotypes under physiological conditions. Thus, to determine if the lack of a cold allodynic phenotype in Gfrα3 −/− mice is a result of alterations in sensory afferent development caused by the absence of GFRα3, we used quantitative PCR to determine expression of array markers involved in cold thermosensation (29).…”

“…However, in addition to direct sensitization of nociceptors, NGF also acts indirectly through activation of various peripheral cell types and the subsequent release of a host of inflammatory mediators, which in turn, sensitize sensory afferents (12,(39)(40)(41). Several inflammatory conditions stimulate artemin release from a number of peripheral cell types, including keratinocytes, fibroblasts, and immune cells (28,42,43), and we hypothesized that NGF-induced cold allodynia was mediated by NGF indirectly promoting artemin release. To test this hypothesis, we again used artemin-neutralizing antibodies and found that NGF-evoked cold allodynia observed in control mice (Fig.…”

Mechanism of TRPA1 and TRPV4 Participating in Mechanical Hyperalgesia of Rat Experimental Knee Osteoarthritis

“…Some study reports showed that expression changes of TRP channel protein super-family members in dorsal root ganglion can also affect peripheral pain perception, 21 which will be the focus of our further research. Meanwhile, the time points we selected for determining pain thresholds and measuring TRPA1 and TRPV4 expression levels of each group were one week before modeling, and two, four, six, and eight weeks after modeling, respectively, since two weeks are required for successful modeling and eighth week after modeling was the last time TRPA1 and TRPV4 inhibitors were applied.…”