Galanin Receptor 2 Is Involved in Galanin-Induced Analgesic Effect by Activating PKC and CaMKII in the Nucleus Accumbens of Inflammatory Pain Rats

Zinc promotes cell proliferation via regulating metal-regulatory transcription factor 1 expression and transcriptional activity in pulmonary arterial hypertension

Metal responsive transcription factor 1 (MTF-1) is a zinc-dependent transcription factor involved in the development of pulmonary arterial hypertension (PAH), which is a life-threatening disease characterized by elevated pulmonary artery pressure and pulmonary vascular remodeling. However, little is known about the role and regulatory signaling of MTF-1 in PAH. This study aimed to investigate the effect and mechanism of MTF-1 on the proliferation of pulmonary arterial smooth muscle cells (PASMCs). Several techniques including intracellular-free zinc detected by fluorescent indicator-fluozinc-3-AM, western blot, luciferase reporter, and cell proliferation assay were conducted to perform a comprehensive analysis of MTF-1 in proliferation of PASMCs in PAH. Increased cytosolic zinc was shown in monocrotaline (MCT)-PASMCs and ZnSO₄-treated PASMCs, which led to overexpression and overactivation of MTF-1, followed by the up-regulation of placental growth factor (PlGF). Elevated MTF-1 and PlGF were observed in western blot, and high transcriptional activity of MTF-1 was confirmed by luciferase reporter in ZnSO4-treated cells. Further investigation of cell proliferation revealed a favorable impact of zinc ions on PASMCs proliferation, with the deletion of Mtf-1/Plgf attenuating ZnSO4-induced proliferation. Flow cytometry analysis showed that blockade of PKC signaling inhibited the cell cycle of MCT-PASMCs and ZnSO4-treated PASMCs. The Zinc/PKC/MTF-1/PlGF pathway is involved in the up-regulatory effect on the PASMCs proliferation in the process of PAH. This study provided novel insight into zinc homeostasis in the pathogenesis of PAHs, and the regulation of MTF-1 might be a potential target for therapeutic intervention in PAH.

Electroacupuncture Reduces Ocular Surface Neuralgia in Dry-Eyed Guinea Pigs by Inhibiting the Trigeminal Ganglion and Spinal Trigeminal Nucleus Caudalis P2X3R-PKC Signaling Pathway

PURPOSE

To observe the effects of electroacupuncture on ocular surface neuralgia and the P2X₃R-PKC signaling pathway in guinea pigs with dry eye.

METHODS

A dry eye guinea pig model was established by subcutaneous injection of scopolamine hydrobromide. Guinea pigs were monitored for body weight, palpebral fissure height, number of blinks, corneal fluorescein staining score, phenol red thread test, and corneal mechanical perception threshold. Histopathological changes and mRNA expression of P2X₃R and protein kinase C in the trigeminal ganglion and spinal trigeminal nucleus caudalis were observed. We performed a second part of the experiment, which involved the P2X₃R-specific antagonist A317491 and the P2X₃R agonist ATP in dry-eyed guinea pigs to further validate the involvement of the P2X₃R-protein kinase C signaling pathway in the regulation of ocular surface neuralgia in dry eye. The number of blinks and corneal mechanical perception threshold were monitored before and 5 min after subconjunctival injection and the protein expression of P2X₃R and protein kinase C was detected in the trigeminal ganglion and spinal trigeminal nucleus caudalis of guinea pigs.

RESULTS

Dry-eyed guinea pigs showed pain-related manifestations and the expression of P2X₃R and protein kinase C in the trigeminal ganglion and spinal trigeminal nucleus caudalis was upregulated. Electroacupuncture reduced pain-related manifestations and inhibited the expression of P2X₃R and protein kinase C in the trigeminal ganglion and spinal trigeminal nucleus caudalis. Subconjunctival injection of A317491 attenuated corneal mechanoreceptive nociceptive sensitization in dry-eyed guinea pigs, while ATP blocked the analgesic effect of electroacupuncture.

CONCLUSIONS

Electroacupuncture reduced ocular surface sensory neuralgia in dry-eyed guinea pigs, and the mechanism of action may be associated with the inhibition of the P2X₃R-protein kinase C signaling pathway in the trigeminal ganglion and spinal trigeminal nucleus caudalis by electroacupuncture.

A New Gal in Town: A Systematic Review of the Role of Galanin and Its Receptors in Experimental Pain

Galanin is a neuropeptide expressed in a small percentage of sensory neurons of the dorsal root ganglia and the superficial lamina of the dorsal horn of the spinal cord. In this work, we systematically reviewed the literature regarding the role of galanin and its receptors in nociception at the spinal and supraspinal levels, as well as in chronic pain conditions. The literature search was performed in PubMed, Web of Science, Scopus, ScienceDirect, OVID, TRIP, and EMBASE using "Galanin" AND "pain" as keywords. Of the 1379 papers that were retrieved in the initial search, we included a total of 141 papers in this review. Using the ARRIVE guidelines, we verified that 89.1% of the works were of good or moderate quality. Galanin shows a differential role in pain, depending on the pain state, site of action, and concentration. Under normal settings, galanin can modulate nociceptive processing through both a pro- and anti-nociceptive action, in a dose-dependent manner. This peptide also plays a key role in chronic pain conditions and its antinociceptive action at both a spinal and supraspinal level is enhanced, reducing animals' hypersensitivity to both mechanical and thermal stimulation. Our results highlight galanin and its receptors as potential therapeutic targets in pain conditions.