Protease-activated receptors in health and disease.

Proteases are signaling molecules that specifically control cellular functions by cleaving protease-activated receptors (PARs). The four known PARs are members of the large family of G protein-coupled receptors. These transmembrane receptors control most physiological and pathological processes and are the target of a large proportion of therapeutic drugs. Signaling proteases include enzymes from the circulation; from immune, inflammatory epithelial, and cancer cells; as well as from commensal and pathogenic bacteria. Advances in our understanding of the structure and function of PARs provide insights into how diverse proteases activate these receptors to regulate physiological and pathological processes in most tissues and organ systems. The realization that proteases and PARs are key mediators of disease, coupled with advances in understanding the atomic level structure of PARs and their mechanisms of signaling in subcellular microdomains, has spurred the development of antagonists, some of which have advanced to the clinic. Herein we review the discovery, structure, and function of this receptor system, highlight the contribution of PARs to homeostatic control, and discuss the potential of PAR antagonists for the treatment of major diseases.

Therapeutic antagonism of the neurokinin 1 receptor in endosomes provides sustained pain relief.

The hypothesis that sustained G protein-coupled receptor (GPCR) signaling from endosomes mediates pain is based on studies with endocytosis inhibitors and lipid-conjugated or nanoparticle-encapsulated antagonists targeted to endosomes. GPCR antagonists that reverse sustained endosomal signaling and nociception are needed. However, the criteria for rational design of such compounds are ill-defined. Moreover, the role of natural GPCR variants, which exhibit aberrant signaling and endosomal trafficking, in maintaining pain is unknown. Herein, substance P (SP) was found to evoke clathrin-mediated assembly of endosomal signaling complexes comprising neurokinin 1 receptor (NK1R), Gαq/i, and ßarrestin-2. Whereas the FDA-approved NK1R antagonist aprepitant induced a transient disruption of endosomal signals, analogs of netupitant designed to penetrate membranes and persist in acidic endosomes through altered lipophilicity and pKa caused sustained inhibition of endosomal signals. When injected intrathecally to target spinal NK1R+ve neurons in knockin mice expressing human NK1R, aprepitant transiently inhibited nociceptive responses to intraplantar injection of capsaicin. Conversely, netupitant analogs had more potent, efficacious, and sustained antinociceptive effects. Mice expressing C-terminally truncated human NK1R, corresponding to a natural variant with aberrant signaling and trafficking, displayed attenuated SP-evoked excitation of spinal neurons and blunted nociceptive responses to SP. Thus, sustained antagonism of the NK1R in endosomes correlates with long-lasting antinociception, and domains within the C-terminus of the NK1R are necessary for the full pronociceptive actions of SP. The results support the hypothesis that endosomal signaling of GPCRs mediates nociception and provides insight into strategies for antagonizing GPCRs in intracellular locations for the treatment of diverse diseases.

Mice expressing fluorescent PAR2 reveal that endocytosis mediates colonic inflammation and pain.

G protein-coupled receptors (GPCRs) regulate many pathophysiological processes and are major therapeutic targets. The impact of disease on the subcellular distribution and function of GPCRs is poorly understood. We investigated trafficking and signaling of protease-activated receptor 2 (PAR2) in colitis. To localize PAR2 and assess redistribution during disease, we generated knockin mice expressing PAR2 fused to monomeric ultrastable green fluorescent protein (muGFP). PAR2-muGFP signaled and trafficked normally. PAR2 messenger RNA was detected at similar levels in Par2-mugfp and wild-type mice. Immunostaining with a GFP antibody and RNAScope in situ hybridization using F2rl1 (PAR2) and Gfp probes revealed that PAR2-muGFP was expressed in epithelial cells of the small and large intestine and in subsets of enteric and dorsal root ganglia neurons. In healthy mice, PAR2-muGFP was prominently localized to the basolateral membrane of colonocytes. In mice with colitis, PAR2-muGFP was depleted from the plasma membrane of colonocytes and redistributed to early endosomes, consistent with generation of proinflammatory proteases that activate PAR2 PAR2 agonists stimulated endocytosis of PAR2 and recruitment of Gαq, Gαi, and ß-arrestin to early endosomes of T84 colon carcinoma cells. PAR2 agonists increased paracellular permeability of colonic epithelial cells, induced colonic inflammation and hyperalgesia in mice, and stimulated proinflammatory cytokine release from segments of human colon. Knockdown of dynamin-2 (Dnm2), the major colonocyte isoform, and Dnm inhibition attenuated PAR2 endocytosis, signaling complex assembly and colonic inflammation and hyperalgesia. Thus, PAR2 endocytosis sustains protease-evoked inflammation and nociception and PAR2 in endosomes is a potential therapeutic target for colitis.

N-terminomics profiling of naïve and inflamed murine colon reveals proteolytic signatures of legumain.

Legumain is a cysteine protease broadly associated with inflammation. It has been reported to cleave and activate protease-activated receptor 2 to provoke pain associated with oral cancer. Outside of gastric and colon cancer, little has been reported on the roles of legumain within the gastrointestinal tract. Using a legumain-selective activity-based probe, LE28, we report that legumain is activated within colonocytes and macrophages of the murine colon, and that it is upregulated in models of acute experimental colitis. We demonstrated that loss of legumain activity in colonocytes, either through pharmacological inhibition or gene deletion, had no impact on epithelial permeability in vitro. Moreover, legumain inhibition or deletion had no obvious impacts on symptoms or histological features associated with dextran sulfate sodium-induced colitis, suggesting its proteolytic activity is dispensable for colitis initiation. To gain insight into potential functions of legumain within the colon, we performed field asymmetric waveform ion mobility spectrometry-facilitated quantitative proteomics and N-terminomics analyses on naïve and inflamed colon tissue from wild-type and legumain-deficient mice. We identified 16 altered cleavage sites with an asparaginyl endopeptidase signature that may be direct substrates of legumain and a further 16 cleavage sites that may be indirectly mediated by legumain. We also analyzed changes in protein abundance and proteolytic events broadly associated with colitis in the gut, which permitted comparison to recent analyses on mucosal biopsies from patients with inflammatory bowel disease. Collectively, these results shed light on potential functions of legumain and highlight its potential roles in the transition from inflammation to colorectal cancer.

Females have lower salivary flow than males, before and after radiation therapy for head/neck cancer.

OBJECTIVE: To compare salivary flow rates between females and males, before and after radiation therapy (RT) for head and neck cancer (HNC). METHODS: Prospective observational multicenter cohort study (OraRad). Stimulated whole salivary flow was measured before RT and at 6 and 18 months after RT. RESULTS: Mean (95% confidence interval) salivary flow in g/min before RT was 0.81 (0.71, 0.90) in females (n = 107) and 1.20 (1.15, 1.25) in males (n = 391) (p < 0.001); at 6 months was 0.34 (0.24, 0.44) in females and 0.50 (0.44, 0.55) in males (p = 0.01); at 18 months was 0.49 (0.38, 0.59) in females and 0.70 (0.64, 0.75) in males (p < 0.001). Median nadir salivary flow after RT was 0.22 in females and 0.35 in males (p < 0.001). A lower nadir salivary flow in females, but not males, was associated with an increased risk for tooth failure (p = 0.02). CONCLUSIONS: Females with HNC have lower stimulated whole salivary flow than males, before and after RT. Low salivary flow after RT may be a risk factor for tooth failure among females. The lower pre-RT salivary flow rates in females, combined with prior literature in other populations, indicates that, in general, females have lower stimulated salivary flow than males.

Oral health-related quality of life after radiation therapy for head and neck cancer: the OraRad study.

PURPOSE: Head and neck cancer (HNC) treatment results in morbidity impacting quality of life (QOL) in survivorship. This analysis evaluated changes in oral health-related QOL (OH-QOL) up to 2 years after curative intent radiation therapy (RT) for HNC patients and factors associated with these changes. METHODS: 572 HNC patients participated in a multicenter, prospective observational study (OraRad). Data collected included sociodemographic, tumor, and treatment variables. Ten single-item questions and 2 composite scales of swallowing problems and senses problems (taste and smell) from a standard QOL instrument were assessed before RT and at 6-month intervals after RT. RESULTS: The most persistently impacted OH-QOL variables at 24 months included: dry mouth; sticky saliva, and senses problems. These measures were most elevated at the 6-month visit. Aspects of swallowing were most impacted by oropharyngeal tumor site, chemotherapy, and non-Hispanic ethnicity. Problems with senses and dry mouth were worse with older age. Dry mouth and sticky saliva increased more among men and those with oropharyngeal cancer, nodal involvement, and use of chemotherapy. Problems with mouth opening were increased by chemotherapy and were more common among non-White and Hispanic individuals. A 1000 cGy increase in RT dose was associated with a clinically meaningful change in difficulty swallowing solid food, dry mouth, sticky saliva, sense of taste, and senses problems. CONCLUSIONS: Demographic, tumor, and treatment variables impacted OH-QOL for HNC patients up to 2 years after RT. Dry mouth is the most intense and sustained toxicity of RT that negatively impacts OH-QOL of HNC survivors. GOV IDENTIFIER: NCT02057510; first posted February 7, 2014.

Endosomal signaling of delta opioid receptors is an endogenous mechanism and therapeutic target for relief from inflammatory pain.

Whether G protein-coupled receptors signal from endosomes to control important pathophysiological processes and are therapeutic targets is uncertain. We report that opioids from the inflamed colon activate δ-opioid receptors (DOPr) in endosomes of nociceptors. Biopsy samples of inflamed colonic mucosa from patients and mice with colitis released opioids that activated DOPr on nociceptors to cause a sustained decrease in excitability. DOPr agonists inhibited mechanically sensitive colonic nociceptors. DOPr endocytosis and endosomal signaling by protein kinase C (PKC) and extracellular signal-regulated kinase (ERK) pathways mediated the sustained inhibitory actions of endogenous opioids and DOPr agonists. DOPr agonists stimulated the recruitment of Gαi/o and ß-arrestin1/2 to endosomes. Analysis of compartmentalized signaling revealed a requirement of DOPr endocytosis for activation of PKC at the plasma membrane and in the cytosol and ERK in the nucleus. We explored a nanoparticle delivery strategy to evaluate whether endosomal DOPr might be a therapeutic target for pain. The DOPr agonist DADLE was coupled to a liposome shell for targeting DOPr-positive nociceptors and incorporated into a mesoporous silica core for release in the acidic and reducing endosomal environment. Nanoparticles activated DOPr at the plasma membrane, were preferentially endocytosed by DOPr-expressing cells, and were delivered to DOPr-positive early endosomes. Nanoparticles caused a long-lasting activation of DOPr in endosomes, which provided sustained inhibition of nociceptor excitability and relief from inflammatory pain. Conversely, nanoparticles containing a DOPr antagonist abolished the sustained inhibitory effects of DADLE. Thus, DOPr in endosomes is an endogenous mechanism and a therapeutic target for relief from chronic inflammatory pain.

Agonist that activates the µ-opioid receptor in acidified microenvironments inhibits colitis pain without side effects.

OBJECTIVE: The effectiveness of µ-opioid receptor (MOPr) agonists for treatment of visceral pain is compromised by constipation, respiratory depression, sedation and addiction. We investigated whether a fentanyl analogue, (±)-N-(3-fluoro-1-phenethylpiperidine-4-yl)-N-phenyl propionamide (NFEPP), which preferentially activates MOPr in acidified diseased tissues, would inhibit pain in a preclinical model of inflammatory bowel disease (IBD) without side effects in healthy tissues. DESIGN: Antinociceptive actions of NFEPP and fentanyl were compared in control mice and mice with dextran sodium sulfate colitis by measuring visceromotor responses to colorectal distension. Patch clamp and extracellular recordings were used to assess nociceptor activation. Defecation, respiration and locomotion were assessed. Colonic migrating motor complexes were assessed by spatiotemporal mapping of isolated tissue. NFEPP-induced MOPr signalling and trafficking were studied in human embryonic kidney 293 cells. RESULTS: NFEPP inhibited visceromotor responses to colorectal distension in mice with colitis but not in control mice, consistent with acidification of the inflamed colon. Fentanyl inhibited responses in both groups. NFEPP inhibited the excitability of dorsal root ganglion neurons and suppressed mechanical sensitivity of colonic afferent fibres in acidified but not physiological conditions. Whereas fentanyl decreased defecation and caused respiratory depression and hyperactivity in mice with colitis, NFEPP was devoid of these effects. NFEPP did not affect colonic migrating motor complexes at physiological pH. NFEPP preferentially activated MOPr in acidified extracellular conditions to inhibit cAMP formation, recruit ß-arrestins and evoke MOPr endocytosis. CONCLUSION: In a preclinical IBD model, NFEPP preferentially activates MOPr in acidified microenvironments of inflamed tissues to induce antinociception without causing respiratory depression, constipation and hyperactivity.

Legumain Induces Oral Cancer Pain by Biased Agonism of Protease-Activated Receptor-2.

Oral squamous cell carcinoma (OSCC) is one of the most painful cancers, which interferes with orofacial function including talking and eating. We report that legumain (Lgmn) cleaves protease-activated receptor-2 (PAR2) in the acidic OSCC microenvironment to cause pain. Lgmn is a cysteine protease of late endosomes and lysosomes that can be secreted; it exhibits maximal activity in acidic environments. The role of Lgmn in PAR2-dependent cancer pain is unknown. We studied Lgmn activation in human oral cancers and oral cancer mouse models. Lgmn was activated in OSCC patient tumors, compared with matched normal oral tissue. After intraplantar, facial or lingual injection, Lgmn evoked nociception in wild-type (WT) female mice but not in female mice lacking PAR2 in NaV1.8-positive neurons (Par2Nav1.8), nor in female mice treated with a Lgmn inhibitor, LI-1. Inoculation of an OSCC cell line caused mechanical and thermal hyperalgesia that was reversed by LI-1. Par2Nav1.8 and Lgmn deletion attenuated mechanical allodynia in female mice with carcinogen-induced OSCC. Lgmn caused PAR2-dependent hyperexcitability of trigeminal neurons from WT female mice. Par2 deletion, LI-1, and inhibitors of adenylyl cyclase or protein kinase A (PKA) prevented the effects of Lgmn. Under acidified conditions, Lgmn cleaved within the extracellular N terminus of PAR2 at Asn30↓Arg31, proximal to the canonical trypsin activation site. Lgmn activated PAR2 by biased mechanisms in HEK293 cells to induce Ca2+ mobilization, cAMP formation, and PKA/protein kinase D (PKD) activation, but not ß-arrestin recruitment or PAR2 endocytosis. Thus, in the acidified OSCC microenvironment, Lgmn activates PAR2 by biased mechanisms that evoke cancer pain.SIGNIFICANCE STATEMENT Oral squamous cell carcinoma (OSCC) is one of the most painful cancers. We report that legumain (Lgmn), which exhibits maximal activity in acidic environments, cleaves protease-activated receptor-2 (PAR2) on neurons to produce OSCC pain. Active Lgmn was elevated in OSCC patient tumors, compared with matched normal oral tissue. Lgmn evokes pain-like behavior through PAR2 Exposure of pain-sensing neurons to Lgmn decreased the current required to generate an action potential through PAR2 Inhibitors of adenylyl cyclase and protein kinase A (PKA) prevented the effects of Lgmn. Lgmn activated PAR2 to induce calcium mobilization, cAMP formation, and activation of protein kinase D (PKD) and PKA, but not ß-arrestin recruitment or PAR2 endocytosis. Thus, Lgmn is a biased agonist of PAR2 that evokes cancer pain.

Exposed bone in patients with head and neck cancer treated with radiation therapy: An analysis of the Observational Study of Dental Outcomes in Head and Neck Cancer Patients (OraRad).

BACKGROUND: Patients with head and neck cancer (HNC) treated with radiation therapy (RT) are at risk for jaw osteoradionecrosis (ORN), which is largely characterized by the presence of exposed necrotic bone. This report describes the incidence and clinical course of and risk factors for exposed intraoral bone in the multicenter Observational Study of Dental Outcomes in Head and Neck Cancer Patients (OraRad) cohort. METHODS: Participants were evaluated before RT and at 6, 12, 18, and 24 months after RT. Exposed bone was characterized by location, sequestrum formation, and other associated features. The radiation dose to the affected area was determined, and the history of treatment for exposed bone was recorded. RESULTS: The study enrolled 572 participants; 35 (6.1%) were diagnosed with incident exposed bone at 6 (47% of reports), 12 (24%), 18 (20%), and 24 months (8%), with 60% being sequestrum and with 7 cases (20%) persisting for >6 months. The average maximum RT dose to the affected area of exposed bone was 5456 cGy (SD, 1768 cGy); the most frequent associated primary RT sites were the oropharynx (42.9%) and oral cavity (31.4%), and 76% of episodes occurred in the mandible. The diagnosis of ORN was confirmed in 18 participants for an incidence rate of 3.1% (18 of 572). Risk factors included pre-RT extractions (P = .008), a higher RT dose (P = .039), and tobacco use (P = .048). CONCLUSIONS: The 2-year incidence of exposed bone in the OraRad cohort was 6.1%; the incidence of confirmed ORN was 3.1%. Exposed bone after RT for HNC is relatively uncommon and, in most cases, is a short-term complication, not a recurring or persistent one.

Oral cancer patients experience mechanical and chemical sensitivity at the site of the cancer.

INTRODUCTION: Oral cancer patients suffer severe chronic and mechanically-induced pain at the site of the cancer. Our clinical experience is that oral cancer patients report new sensitivity to spicy foods. We hypothesized that in cancer patients, mechanical and chemical sensitivity would be greater when measured at the cancer site compared to a contralateral matched normal site. METHODS: We determined mechanical pain thresholds (MPT) on the right and left sides of the tongue of 11 healthy subjects, and at the cancer and contralateral matched normal site in 11 oral cancer patients in response to von Frey filaments in the range of 0.008 to 300 g (normally not reported as painful). We evaluated chemical sensitivity in 13 healthy subjects and seven cancer patients, who rated spiciness/pain on a visual analog scale in response to exposure to six paper strips impregnated with capsaicin (0-10 mM). RESULTS: Mechanical detection thresholds (MDT) were recorded for healthy subjects, but not MPTs. By contrast, MPTs were measured at the site of the cancer in oral cancer patients (7/11 patients). No MPTs were measured at the cancer patients' contralateral matched normal sites. Measured MPTs were correlated with patients' responses to the University of California Oral Cancer Pain Questionnaire. Capsaicin sensitivity at the site of the cancer was evident in cancer patients by a leftward shift of the cancer site capsaicin dose-response curve compared to that of the patient's contralateral matched normal site. We detected no difference in capsaicin sensitivity on the right and left sides of tongues of healthy subjects. CONCLUSIONS: Mechanical and chemical sensitivity testing was well tolerated by the majority of oral cancer patients. Sensitivity is greater at the site of the cancer than at a contralateral matched normal site.

Targeting G protein-coupled receptors for the treatment of chronic pain in the digestive system.

Chronic pain is a hallmark of functional disorders, inflammatory diseases and cancer of the digestive system. The mechanisms that initiate and sustain chronic pain are incompletely understood, and available therapies are inadequate. This review highlights recent advances in the structure and function of pronociceptive and antinociceptive G protein-coupled receptors (GPCRs) that provide insights into the mechanisms and treatment of chronic pain. This knowledge, derived from studies of somatic pain, can guide research into visceral pain. Mediators from injured tissues transiently activate GPCRs at the plasma membrane of neurons, leading to sensitisation of ion channels and acute hyperexcitability and nociception. Sustained agonist release evokes GPCR redistribution to endosomes, where persistent signalling regulates activity of channels and genes that control chronic hyperexcitability and nociception. Endosomally targeted GPCR antagonists provide superior pain relief in preclinical models. Biased agonists stabilise GPCR conformations that favour signalling of beneficial actions at the expense of detrimental side effects. Biased agonists of µ-opioid receptors (MOPrs) can provide analgesia without addiction, respiratory depression and constipation. Opioids that preferentially bind to MOPrs in the acidic microenvironment of diseased tissues produce analgesia without side effects. Allosteric modulators of GPCRs fine-tune actions of endogenous ligands, offering the prospect of refined pain control. GPCR dimers might function as distinct therapeutic targets for nociception. The discovery that GPCRs that control itch also mediate irritant sensation in the colon has revealed new targets. A deeper understanding of GPCR structure and function in different microenvironments offers the potential of developing superior treatments for GI pain.

Protease-activated receptor-2 in endosomes signals persistent pain of irritable bowel syndrome.

Once activated at the surface of cells, G protein-coupled receptors (GPCRs) redistribute to endosomes, where they can continue to signal. Whether GPCRs in endosomes generate signals that contribute to human disease is unknown. We evaluated endosomal signaling of protease-activated receptor-2 (PAR2), which has been proposed to mediate pain in patients with irritable bowel syndrome (IBS). Trypsin, elastase, and cathepsin S, which are activated in the colonic mucosa of patients with IBS and in experimental animals with colitis, caused persistent PAR2-dependent hyperexcitability of nociceptors, sensitization of colonic afferent neurons to mechanical stimuli, and somatic mechanical allodynia. Inhibitors of clathrin- and dynamin-dependent endocytosis and of mitogen-activated protein kinase kinase-1 prevented trypsin-induced hyperexcitability, sensitization, and allodynia. However, they did not affect elastase- or cathepsin S-induced hyperexcitability, sensitization, or allodynia. Trypsin stimulated endocytosis of PAR2, which signaled from endosomes to activate extracellular signal-regulated kinase. Elastase and cathepsin S did not stimulate endocytosis of PAR2, which signaled from the plasma membrane to activate adenylyl cyclase. Biopsies of colonic mucosa from IBS patients released proteases that induced persistent PAR2-dependent hyperexcitability of nociceptors, and PAR2 association with ß-arrestins, which mediate endocytosis. Conjugation to cholestanol promoted delivery and retention of antagonists in endosomes containing PAR2 A cholestanol-conjugated PAR2 antagonist prevented persistent trypsin- and IBS protease-induced hyperexcitability of nociceptors. The results reveal that PAR2 signaling from endosomes underlies the persistent hyperexcitability of nociceptors that mediates chronic pain of IBS. Endosomally targeted PAR2 antagonists are potential therapies for IBS pain. GPCRs in endosomes transmit signals that contribute to human diseases.

Protein kinase D and Gßγ mediate sustained nociceptive signaling by biased agonists of protease-activated receptor-2.

Proteases sustain hyperexcitability and pain by cleaving protease-activated receptor-2 (PAR2) on nociceptors through distinct mechanisms. Whereas trypsin induces PAR2 coupling to Gαq, Gαs, and ß-arrestins, cathepsin-S (CS) and neutrophil elastase (NE) cleave PAR2 at distinct sites and activate it by biased mechanisms that induce coupling to Gαs, but not to Gαq or ß-arrestins. Because proteases activate PAR2 by irreversible cleavage, and activated PAR2 is degraded in lysosomes, sustained extracellular protease-mediated signaling requires mobilization of intact PAR2 from the Golgi apparatus or de novo synthesis of new receptors by incompletely understood mechanisms. We found here that trypsin, CS, and NE stimulate PAR2-dependent activation of protein kinase D (PKD) in the Golgi of HEK293 cells, in which PKD regulates protein trafficking. The proteases stimulated translocation of the PKD activator Gßγ to the Golgi, coinciding with PAR2 mobilization from the Golgi. Proteases also induced translocation of a photoconverted PAR2-Kaede fusion protein from the Golgi to the plasma membrane of KNRK cells. After incubation of HEK293 cells and dorsal root ganglia neurons with CS, NE, or trypsin, PAR2 responsiveness initially declined, consistent with PAR2 cleavage and desensitization, and then gradually recovered. Inhibitors of PKD, Gßγ, and protein translation inhibited recovery of PAR2 responsiveness. PKD and Gßγ inhibitors also attenuated protease-evoked mechanical allodynia in mice. We conclude that proteases that activate PAR2 by canonical and biased mechanisms stimulate PKD in the Golgi; PAR2 mobilization and de novo synthesis repopulate the cell surface with intact receptors and sustain nociceptive signaling by extracellular proteases.

G-Protein-Coupled Receptors Are Dynamic Regulators of Digestion and Targets for Digestive Diseases.

G-protein-coupled receptors (GPCRs) are the largest family of transmembrane signaling proteins. In the gastrointestinal tract, GPCRs expressed by epithelial cells sense contents of the lumen, and GPCRs expressed by epithelial cells, myocytes, neurons, and immune cells participate in communication among cells. GPCRs control digestion, mediate digestive diseases, and coordinate repair and growth. GPCRs are the target of more than one third of therapeutic drugs, including many drugs used to treat digestive diseases. Recent advances in structural, chemical, and cell biology research have shown that GPCRs are not static binary switches that operate from the plasma membrane to control a defined set of intracellular signals. Rather, GPCRs are dynamic signaling proteins that adopt distinct conformations and subcellular distributions when associated with different ligands and intracellular effectors. An understanding of the dynamic nature of GPCRs has provided insights into the mechanism of activation and signaling of GPCRs and has shown opportunities for drug discovery. We review the allosteric modulation, biased agonism, oligomerization, and compartmentalized signaling of GPCRs that control digestion and digestive diseases. We highlight the implications of these concepts for the development of selective and effective drugs to treat diseases of the gastrointestinal tract.

A Pre-Existing Myogenic Temporomandibular Disorder Increases Trigeminal Calcitonin Gene-Related Peptide and Enhances Nitroglycerin-Induced Hypersensitivity in Mice.

Migraine is commonly reported among patients with temporomandibular disorders (TMDs), especially myogenic TMD. The pathophysiologic mechanisms related to the comorbidity of the two conditions remain elusive. In the present study, we combined masseter muscle tendon ligation (MMTL)-produced myogenic TMD with systemic injection of nitroglycerin (NTG)-induced migraine-like hypersensitivity in mice. Facial mechanical allodynia, functional allodynia, and light-aversive behavior were evaluated. Sumatriptan, an FDA-approved medication for migraine, was used to validate migraine-like hypersensitivity. Additionally, we examined the protein level of calcitonin gene-related peptide (CGRP) in the spinal trigeminal nucleus caudalis using immunohistochemistry. We observed that mice with MMTL pretreatment have a prolonged NTG-induced migraine-like hypersensitivity, and MMTL also enabled a non-sensitizing dose of NTG to trigger migraine-like hypersensitivity. Systemic injection of sumatriptan inhibited the MMTL-enhanced migraine-like hypersensitivity. MMTL pretreatment significantly upregulated the protein level of CGRP in the spinal trigeminal nucleus caudalis after NTG injection. Our results indicate that a pre-existing myogenic TMD can upregulate NTG-induced trigeminal CGRP and enhance migraine-like hypersensitivity.

TRPV1 expression level in isolectin B4-positive neurons contributes to mouse strain difference in cutaneous thermal nociceptive sensitivity.

Differential thermal nociception across inbred mouse strains has genetic determinants. Thermal nociception is largely attributed to the heat/capsaicin receptor transient receptor potential vanilloid 1 (TRPV1); however, the contribution of this channel to the genetics of thermal nociception has not been revealed. In this study we compared TRPV1 expression levels and electrophysiological properties in primary sensory neurons and thermal nociceptive behaviors between two (C57BL/6 and BALB/c) inbred mouse strains. Using immunofluorescence and patch-clamp physiology methods, we demonstrated that TRPV1 expression was significantly higher in isolectin B4 (IB4)-positive trigeminal sensory neurons of C57BL/6 relative to BALB/c; the expression in IB4-negative neurons was similar between the strains. Furthermore, using electrophysiological cell classification (current signature method), we showed differences between the two strains in capsaicin sensitivity in IB4-positive neuronal cell types 2 and 13, which were previously reported as skin nociceptors. Otherwise electrophysiological membrane properties of the classified cell types were similar in the two mouse strains. In publicly available nocifensive behavior data and our own behavior data from the using the two mouse strains, C57BL/6 exhibited higher sensitivity to heat stimulation than BALB/c, independent of sex and anatomical location of thermal testing (the tail, hind paw, and whisker pad). The TRPV1-selective antagonist JNJ-17203212 inhibited thermal nociception in both strains; however, removing IB4-positive trigeminal sensory neurons with IB4-conjugated saporin inhibited thermal nociception on the whisker pad in C57BL/6 but not in BALB/c. These results suggest that TRPV1 expression levels in IB4-positive type 2 and 13 neurons contributed to differential thermal nociception in skin of C57BL/6 compared with BALB/c.

The Neurobiology of Cancer Pain.

Oral cancers are often severely painful and clinically difficult to manage. Few researchers have investigated the neurobiologic factors responsible for cancer pain; however, the study of oral cancer pain might inform us about the fundamental biology of cancer. The purpose of the present report was to summarize the clinical challenges inherent in oral cancer pain management, oral cancer pain mechanisms and mediators, and the convergence of the investigation of carcinogenesis and pain.

Disease and treatment characteristics do not predict symptom occurrence profiles in oncology outpatients receiving chemotherapy.

BACKGROUND: A large amount of interindividual variability exists in the occurrence of symptoms in patients receiving chemotherapy (CTX). The purposes of the current study, which was performed in a sample of 582 oncology outpatients who were receiving CTX, were to identify subgroups of patients based on their distinct experiences with 25 commonly occurring symptoms and to identify demographic and clinical characteristics associated with subgroup membership. In addition, differences in quality of life outcomes were evaluated. METHODS: Oncology outpatients with breast, gastrointestinal, gynecological, or lung cancer completed the Memorial Symptom Assessment Scale before their next cycle of CTX. Latent class analysis was used to identify subgroups of patients with distinct symptom experiences. RESULTS: Three distinct subgroups of patients were identified (ie, 36.1% in Low class; 50.0% in Moderate class, and 13.9% in All High class). Patients in the All High class were significantly younger and more likely to be female and nonwhite, and had lower levels of social support, lower socioeconomic status, poorer functional status, and a higher level of comorbidity. CONCLUSIONS: Findings from the current study support the clinical observation that some oncology patients experience a differentially higher symptom burden during CTX. These high-risk patients experience significant decrements in quality of life.

Variations in potassium channel genes are associated with breast pain in women prior to breast cancer surgery.

Preoperative breast pain in women with breast cancer may result from a number of causes. Previous work from our team found that breast pain occurred in 28.2% of women (n = 398) who were about to undergo breast cancer surgery. The occurrence of preoperative breast pain was associated with a number of demographic and clinical characteristics, as well as variation in two cytokine genes. Given that ion channels regulate excitability of sensory neurons, we hypothesized that variations in potassium channel genes would be associated with preoperative breast pain in these patients. Therefore, in this study, we evaluated for associations between single-nucleotide polymorphisms and inferred haplotypes among 10 potassium channel genes and the occurrence of preoperative breast pain in patients scheduled to undergo breast cancer surgery. Multivariable logistic regression analyses were used to identify those genetic variations that were associated with the occurrence of preoperative breast pain while controlling for age and genomic estimates of and self-reported race/ethnicity. Variations in four potassium channel genes: (1) potassium voltage-gated channel, delayed rectifier, subfamily S, member 1 (KCNS1); (2) potassium inwardly rectifying channel, subfamily J, member 3 (KCNJ3); (3) KCNJ6; and (4) potassium channel, subfamily K, member 9 (KCNK9) were associated with the occurrence of breast pain. Findings from this study warrant replication in an independent sample of women who report breast pain following one or more breast biopsies.