Hemokinin-1 Gene Expression Is Upregulated in Trigeminal Ganglia in an Inflammatory Orofacial Pain Model: Potential Role in Peripheral Sensitization

Abstract

A large percentage of primary sensory neurons in the trigeminal ganglia (TG) contain neuropeptides such as tachykinins or calcitonin gene-related peptide. Neuropeptides released from the central terminals of primary afferents sensitize the secondary nociceptive neurons in the trigeminal nucleus caudalis (TNC), but also activate glial cells contributing to neuroinflammation and consequent sensitization in chronic orofacial pain and migraine. In the present study, we investigated the newest member of the tachykinin family, hemokinin-1 (HK-1) encoded by the Tac4 gene in the trigeminal system. HK-1 had been shown to participate in inflammation and hyperalgesia in various models, but its role has not been investigated in orofacial pain or headache. In the complete Freund’s adjuvant (CFA)-induced inflammatory orofacial pain model, we showed that Tac4 expression increased in the TG in response to inflammation. Duration-dependent Tac4 upregulation was associated with the extent of the facial allodynia. Tac4 was detected in both TG neurons and satellite glial cells (SGC) by the ultrasensitive RNAscope in situ hybridization. We also compared gene expression changes of selected neuronal and glial sensitization and neuroinflammation markers between wild-type and Tac4-deficient (Tac4-/-) mice. Expression of the SGC/astrocyte marker in the TG and TNC was significantly lower in intact and saline/CFA-treated Tac4-/- mice. The procedural stress-related increase of the SGC/astrocyte marker was also strongly attenuated in Tac4-/- mice. Analysis of TG samples with a mouse neuroinflammation panel of 770 genes revealed that regulation of microglia and cytotoxic cell-related genes were significantly different in saline-treated Tac4-/- mice compared to their wild-types. It is concluded that HK-1 may participate in neuron-glia interactions both under physiological and inflammatory conditions and mediate pain in the trigeminal system.

Novel Pituitary Actions of TAC4 Gene Products in Teleost

“…These findings, as a whole, indicated that (i) the F residue in the "FXGLM" motif played a crucial role in the bioactivity of tachykinins in the fish model, and (ii) the Phe to Val mutation form in the "VXGLM" motif represented the molecular determinant in HK1 leading to weak agonistic actions on SLα regulation, presumably by interfering the interaction with target receptors. Our findings were also in agreement with the previous studies in mammalian cell models, e.g., COS-7 cells with NK3 receptor [9,12], confirming that the C-terminal "FXGLM" motif was essential for the bioactivity and receptor binding [32,50].…”

Hemokinin-1 as a Mediator of Arthritis-Related Pain via Direct Activation of Primary Sensory Neurons

“…Tissue samples were thawed out on ice and homogenized in TRI reagent. After homegenization, total RNA was extracted using Direct-zol RNA MicroPrep (Zymo Research) according to the manufacturer’s instructions ( Aczél et al, 2020 ). The quantity of the extracted RNA was examined using Nanodrop ND-1000 Spectrophotometer V3.5 (Nano-Drop Technologies, Inc.).…”

“…SensiFAST™ Probe Lo-ROX Kit (Meridiane Bioscience, Memphis, United States) was used according to the manual in the QuantStudio five Real-Time PCR System (Thermo Fisher Scientific). Transcripts of the reference gene glucuronidase beta ( Gusb , Kecskés et al, 2020 ) and the target gene Tac4 were evaluated using FAM-conjugated specific probes (Mm01197698_m1, and Mm00474083_m1 respectively, Thermo Fisher Scientific). The gene expression was calculated using ΔΔCt method ( Pfaffl, 2001 ).…”

Trigeminal neuralgia and genetics: A systematic review

“…Genes coding for proteins in the tachykinin family have recently been examined in two separate studies. 57 , 58 Neurokinin 3 receptor and hemokinin-1 receptor, coded by Tacr3 and Tac4 respectively, are suggested to contribute to development of trigeminal neuropathic pain. Downregulation of Tacr3 worked protective against pain, while upregulation of Tac4 was seen after CFA-injection in mice.…”

“…The authors suggest that the downregulation plays a protective role in treating allodynia, by suppressing the hyperexcitability in neurons. Another study 58 observed upregulation of Tac4 gene, encoding Hemokinin-1 (HK-1), concluding that HK-1 participates in pain transmission in the trigeminal system by interacting between sensory neurons and satellite glial cells.…”