Upon its mucosal transmission, HIV type 1 (HIV-1) rapidly targets genital antigen-presenting Langerhans cells (LCs), which subsequently transfer infectious virus to CD4+ T cells. We previously described an inhibitory neuroimmune cross talk, whereby calcitonin gene-related peptide (CGRP), a neuropeptide secreted by peripheral pain-sensing nociceptor neurons innervating all mucosal epithelia and associating with LCs, strongly inhibits HIV-1 transfer. As nociceptors secret CGRP following the activation of their Ca2+ ion channel transient receptor potential vanilloid 1 (TRPV1), and as we reported that LCs secret low levels of CGRP, we investigated whether LCs express functional TRPV1. We found that human LCs expressed mRNA and protein of TRPV1, which was functional and induced Ca2+ influx following activation with TRPV1 agonists, including capsaicin (CP). The treatment of LCs with TRPV1 agonists also increased CGRP secretion, reaching its anti-HIV-1 inhibitory concentrations. Accordingly, CP pretreatment significantly inhibited LCs-mediated HIV-1 transfer to CD4+ T cells, which was abrogated by both TRPV1 and CGRP receptor antagonists. Like CGRP, CP-induced inhibition of HIV-1 transfer was mediated via increased CCL3 secretion and HIV-1 degradation. CP also inhibited direct CD4+ T cells HIV-1 infection, but in CGRP-independent manners. Finally, pretreatment of inner foreskin tissue explants with CP markedly increased CGRP and CCL3 secretion, and upon subsequent polarized exposure to HIV-1, inhibited an increase in LC-T cell conjugate formation and consequently T cell infection. Our results reveal that TRPV1 activation in human LCs and CD4+ T cells inhibits mucosal HIV-1 infection, via CGRP-dependent/independent mechanisms. Formulations containing TRPV1 agonists, already approved for pain relief, could hence be useful against HIV-1.

Calcitonin gene-related peptide (CGRP) is considered a major player in migraine pathophysiology. However, the location and mechanisms of CGRP actions in migraine are not clearly elucidated. One important question yet to be answered is: Does central CGRP signaling play a role in migraine? One candidate site is the cerebellum, which serves as a sensory and motor integration center and is activated in migraine patients. The cerebellum has the most CGRP binding sites in the central nervous system and a deep cerebellar nucleus, the medial nucleus (MN), expresses CGRP (MNCGRP). A previous study demonstrated that CGRP delivery into the cerebellum induced migraine-like behaviors. We hypothesized that stimulation of MNCGRP neurons might induce migraine-like behaviors. To test the hypothesis, we used an optogenetic strategy using CalcaCre/+ mice to drive Cre-dependent expression of channelrhodopsin-2 selectively in CGRP neurons in the cerebellar MN. A battery of behavioral tests was done to assess preclinical behaviors that are surrogates of migraine symptoms, including light aversion, cutaneous allodynia, and spontaneous pain when MNCGRP neurons were optically stimulated. Motor functions were also assessed. Optical stimulation of MNCGRP neurons decreased the time spent in the light, which was coupled to increased time spent resting in the dark, but not the light. These changes were only significant in female mice. Plantar tactile sensitivity was increased in the ipsilateral paws of both sexes, but contralateral paw data were less clear. There was no significant increase in anxiety-like behavior, spontaneous pain (squint), or changes in gait. These discoveries reveal that MNCGRP neurons may contribute to migraine-like sensory hypersensitivity to light and touch.

The activation of mast cells (MCs) and mediator release are closely related to the pathophysiology of irritable bowel syndrome (IBS). However, the exact underlying mechanisms are still not completely understood. The nuclear receptor subfamily 4a (Nr4a) is a family of orphan nuclear receptors implicated in regulating MC activation, degranulation, cytokine/chemokine synthesis and release. Acute and chronic stress trigger hypothalamic-pituitaryadrenal axis (HPA) activation to induce the release of corticotropin-releasing hormone (CRH), resulting in MC activation and induction of the Nr4a family. Our newest data showed that Nr4a members were specially over-expressed in colonic MCs of the chronic water-avoidance stress (WAS)-induced visceral hyperalgesia mice, suggesting that Nr4a members might be involved in the pathophysiology of visceral hypersensitivity. In this review, we highlight the present knowledge on roles of Nr4a members in the activation of MCs and the pathophysiology of IBS, and discuss signaling pathways that modulate the activation of Nr4a family members. We propose that a better understanding of Nr4a members and their modulators may facilitate the development of more selective and effective therapies to treat IBS patients.

Receptor activity-modulating proteins (RAMPs) are accessory molecules that form complexes with specific G protein-coupled receptors (GPCRs) and modulate their functions. It is established that RAMP interacts with the glucagon receptor family of GPCRs but the underlying mechanism is poorly understood. In this study, we used a bioluminescence resonance energy transfer (BRET) approach to comprehensively investigate such interactions. In conjunction with cAMP accumulation, Gα q activation and β-arrestin1/2 recruitment assays, we not only verified the GPCR-RAMP pairs previously reported, but also identified new patterns of GPCR-RAMP interaction. While RAMP1 was able to modify the three signaling events elicited by both glucagon receptor (GCGR) and glucagon-like peptide-1 receptor (GLP-1R), and RAMP2 mainly affected β-arrestin1/2 recruitment by GCGR, GLP-1R and glucagon-like peptide-2 receptor, RAMP3 showed a widespread negative impact on all the family members except for growth hormone-releasing hormone receptor covering the three pathways. Our results suggest that RAMP modulates both G protein dependent and independent signal transduction among the glucagon receptor family members in a receptor-specific manner. Mapping such interactions provides new insights into the role of RAMP in ligand recognition and receptor activation.

COVID-19 infection was mainly associated with respiratory symptoms, but lately, ischemic stroke (IS) has been reported in several cases. The incidence of IS in SARS-CoV-2 infection is increasing, and its mechanism is still not fully understood. Calcitonin gene-related peptide (CGRP) -the abundantly expressed protein in the peripheral and central nervous system- showed low expression in SARS-CoV-2 patients. This peptide is strongly implicated in regulating cerebral blood flow (CBF) and improving neurological deficits after cerebral arterial occlusion. We assume that a possible interplay between the low circulating levels of CGRP may affect CBF, thus worsening the symptoms of IS in SARS-CoV-2 patients.

Knee osteoarthritis (KOA) showed synovial fibrosis and hyperalgesia, although the correlation between the two is unclear. Besides, the specific changes of sensory innervation in animal models are still controversial, which makes it difficult to choose the modeling methods for KOA pain research.
Study the characteristics of sensory innervation within three commonly used KOA rat models and the correlation between synovial fibrosis and hyperalgesia.
KOA models were induced by destabilization of medial meniscus (DMM), anterior cruciate ligament transection (ACLT), and monoiodoacetate (MIA), respectively. Mechanical, cold and thermal withdrawal threshold (MWT, CWT and TWT) were measured. The harvested tissues were used for pathological sections, immunofluorescence and quantitative analysis.
KOA synovium showed more type I collagen deposition, increased expression of CD31, VEGF and TGF-β. These changes were most pronounced in surgical models, with DMM presenting the most prominent at Day 14 and ACLT at Day 28. Day 14, changes in mechanical hyperalgesia and cold hyperalgesia were most typical in DMM model and statistically different from MIA. There was a negative correlation between the percentage of type I collagen and MWT value (r = -0.88), as well as CWT value (r = -0.95). DMM synovium showed more axonal staining, upregulated CGRP, TRPV1, NGF and Netrin1 compared with MIA. Above changes were also observed at Day 28, but ACLT replaced DMM as the most typical. In DRG, only the levels of CGRP and NGF were different among KOA models at Day 14, and the highest in DMM, which was statistically different compared with MIA.
This study described the details of sensory innervation in different KOA model of rats, and the degree of synovial fibrosis was positively correlated with the pain sensitivity of KOA model rats. Additionally, surgical modeling especially ACLT method is more recommended for KOA pain research.

Bone is one of the preferential target organs of cancer metastasis. Bone metastasis is associated with various complications, of which bone pain is most common and debilitating. The cancer-associated bone pain (CABP) is induced as a consequence of increased neurogenesis, reprogramming and axonogenesis of sensory nerves (SNs) in harmony with sensitization and excitation of SNs in response to the tumor microenvironment created in bone. Importantly, CABP is associated with increased mortality, of which precise cellular and molecular mechanism remains poorly understood. Bone is densely innervated by autonomic nerves (ANs) (sympathetic and parasympathetic nerves) and SNs. Recent studies have shown that the nerves innervating the tumor microenvironment establish intimate communications with tumors, producing various stimuli for tumors to progress and disseminate. In this review, our current understanding of the role of SNs innervating bone in the pathophysiology of CABP will be overviewed. Then the hypothesis that SNs facilitate cancer progression in bone will be discussed in conjunction with our recent findings that SNs play an important role not only in the induction of CABP but also the progression of bone metastasis using a preclinical model of CABP. It is suggested that SNs are a critical component of the bone microenvironment that drives the vicious cycle between bone and cancer to progress bone metastasis. Suppression of the activity of bone-innervating SNs may have potential therapeutic effects on the progression of bone metastasis and induction of CABP.

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Posttraumatic headache (PTH) is a common debilitating condition arising from head injury and is highly prevalent among military service members and veterans with traumatic brain injury (TBI). Diagnosis and treatment for PTH is still evolving, and surprisingly little is known about the putative mechanisms that drive these headaches. This manuscript describes the design of a randomized clinical trial of two nonpharmacological (i.e., behavioral) interventions for posttraumatic headache. Design of this trial required careful consideration of PTH diagnosis and inclusion criteria, which was challenging due to the lack of standard clinical characteristics in PTH unique from other types of headaches. The treatments under study differed in clinical focus and dose (i.e., number of treatment sessions), but the trial was designed to balance the treatments as well as possible. Finally, while the primary endpoints for pain research can vary from assessments of pain intensity to objective and subjective functional measures, this trial of PTH interventions chose carefully to establish clinically relevant endpoints and to maximize the opportunity to detect significant differences between groups with two primary outcomes. All these issues are discussed in this manuscript.

Bone pain is a common complication of breast cancer (BC) bone metastasis and is a major cause of increased morbidity and mortality. Although the mechanism of BC-associated bone pain (BCABP) remains poorly understood, involvement of BC products in the pathophysiology of BCABP has been proposed. Aggressive cancers secrete damage-associated molecular patterns (DAMPs) that bind to specific DAMP receptors and modulate cancer microenvironment. A prototypic DAMP, high mobility group box 1 (HMGB1), which acts as a ligand for the receptor for advanced glycation end products (RAGE) and toll-like receptors (TLRs), is increased in its expression in BC patients with poor outcomes. Here we show that 4T1 mouse BC cells colonizing bone up-regulate the expression of molecular pain markers, phosphorylated ERK1/2 (pERK) and pCREB, in the dorsal root ganglia (DRGs) innervating bone and induced BCABP as evaluated by hind-paw mechanical hypersensitivity. Importantly, silencing HMGB1 in 4T1 BC cells by shRNA reduced pERK and pCREB and BCABP with decreased HMGB1 levels in bone. Further, administration of a neutralizing antibody to HMGB1 or an antagonist for RAGE, FPS-ZM1, ameliorated pERK, pCREB and BCABP, while a TLR4 antagonist, TAK242, showed no effects. Consistent with these in vivo results, co-cultures of F11 sensory neuron-like cells with 4T1 BC cells in microfluidic culture platforms increased neurite outgrowth of F11 cells, which was blocked by HMGB1 antibody. Our results show that HMGB1 secreted by BC cells induces BCABP via binding to RAGE of sensory neurons and suggest that the HMGB1/RAGE axis may be a potential novel therapeutic target for BCABP.