Neurokinin-1 Receptor Activation Research Articles

Association of Neurokinin-1 Receptor Signaling Pathways with Cancer.

Numerous biochemical reactions leading to altered cell proliferation cause tumorigenesis and cancer treatment resistance. The mechanisms implicated include genetic and epigenetic changes, modified intracellular signaling, and failure of control mechanisms caused by intrinsic and extrinsic factors alone or combined. No unique biochemical events are responsible; entangled molecular reactions conduct the resident cells in a tissue to display uncontrolled growth and abnormal migration. Copious experimental research supports the etiological responsibility of NK-1R (neurokinin-1 receptor) activation, alone or cooperating with other mechanisms, in cancer appearance in different tissues. Consequently, a profound study of this receptor system in the context of malignant processes is essential to design new treatments targeting NK-1R-deviated activity. This study reviews and discusses recent literature that analyzes the main signaling pathways influenced by the activation of neurokinin 1 full and truncated receptor variants. Also, the involvement of NK-1R in cancer development is discussed. NK-1R can signal through numerous pathways and cross-talk with other receptor systems. The participation of override or malfunctioning NK-1R in malignant processes needs a more precise definition in different types of cancers to apply satisfactory and effective treatments. A long way has already been traveled: the current disposal of selective and effective NK-1R antagonists and the capacity to develop new drugs with biased agonistic properties based on the receptor's structural states with functional significance opens immediate research action and clinical application.

Regional characterisation of TRPV1 and TRPA1 signalling in the mouse colon mucosa

Capsaicin and allyl isothiocyanate (AITC) activate transient receptor potential (TRP) vanilloid-1 (TRPV1) and TRP ankyrin-1 (TRPA1), respectively. TRPV1 and TRPA1 expression have been identified in the gastrointestinal (GI) tract. GI mucosal functions remain largely undefined for TRPV1 and TRPA1 with side-dependence and regional differences in signalling unclear. Here we investigated TRPV1- and TRPA1-induced vectorial ion transport as changes in short-circuit current (ΔIsc), in defined segments of mouse colon mucosa (ascending, transverse and descending) under voltage-clamp conditions in Ussing chambers. Drugs were applied basolaterally (bl) or apically (ap). Capsaicin responses were biphasic, with primary secretory and secondary anti-secretory phases, observed with bl application only, which predominated in descending colon. AITC responses were monophasic and secretory, with ΔIsc dependent on colonic region (ascending vs. descending) and sidedness (bl vs. ap). Aprepitant (neurokinin-1 (NK1) antagonist, bl) and tetrodotoxin (Na+ channel blocker, bl) significantly inhibited capsaicin primary responses in descending colon, while GW627368 (EP4 receptor antagonist, bl) and piroxicam (cyclooxygenase inhibitor, bl) inhibited AITC responses in ascending and descending colonic mucosae. Antagonism of the calcitonin gene-related peptide (CGRP) receptor had no effect on mucosal TRPV1 signalling, while tetrodotoxin and antagonists of the 5-hydroxytryptamine-3 and 4 receptors, CGRP receptor, and EP1/2/3 receptors had no effect on mucosal TRPA1 signalling. Our data demonstrates the regional-specificity and side-dependence of colonic TRPV1 and TRPA1 signalling, with involvement of submucosal neurons and mediation by epithelial NK1 receptor activation for TRPV1, and endogenous prostaglandins and EP4 receptor activation for TRPA1 mucosal responses.

Quantitative spatial analysis reveals that the local axons of lamina I projection neurons and interneurons exhibit distributions that predict distinct roles in spinal sensory processing.

Our knowledge about the detailed wiring of neuronal circuits in the spinal dorsal horn (DH), where initial sensory processing takes place, is still very sparse. While a substantial amount of data is available on the somatodendritic morphology of DH neurons, the laminar and segmental distribution patterns and consequential function of individual axons are much less characterized. In the present study, we fully reconstructed the axonal and dendritic processes of 10 projection neurons (PNs) and 15 interneurons (INs) in lamina I of the rat, to reveal quantitative differences in their distribution. We also performed whole-cell patch-clamp recordings to test the predicted function of certain axon collaterals. In line with our earlier qualitative description, we found that lamina I INs in the lateral aspect of the superficial DH send axon collaterals toward the medial part and occupy mostly laminae I-III, providing anatomical basis for a lateromedial flow of information within the DH. Local axon collaterals of PNs were more extensively distributed including dorsal commissural axon collaterals that might refer to those reported earlier linking the lateral aspect of the left and right DHs. PN collaterals dominated the dorsolateral funiculus and laminae IV-VI, suggesting propriospinal and ventral connections. Indeed, patch-clamp recordings confirmed the existence of a dorsoventral excitatory drive upon activation of neurokinin-1 receptors that, although being expressed in various lamina I neurons, are specifically enriched in PNs. In summary, lamina I PNs and INs have almost identical dendritic input fields, while their segmental axon collateral distribution patterns are distinct. INs, whose somata reside in lamina I, establish local connections, may show asymmetry, and contribute to bridging the medial and lateral halves of the DH. PNs, on the other hand, preferably relay their integrated dendritic input to deeper laminae of the spinal gray matter where it might be linked to other ascending pathways or the premotor network, resulting in a putative direct contribution to the nociceptive withdrawal reflex.

The effect of substance P and its common in vivo-formed metabolites on MRGPRX2 and human mast cell activation.

The tachykinin neuropeptide substance P (SP) is the canonical agonist peptide for the neurokinin 1 receptor (NK1R). More recently, it has also been shown to activate the Mas‐related G protein‐coupled receptor X2 (MRGPRX2) receptor on mast cells (MCs), triggering degranulation and release of inflammatory mediators. SP undergoes rapid C‐terminal truncation in vivo by a number of proteases to generate the metabolites SP(1–9)‐COOH and in particular SP(1–7)‐COOH. While the C terminus of SP is critical for NK1R activation, studies have shown that the peptide polycationic N terminus is key for MRGPRX2 and mast cell activation. The study thus aimed to determine if the C‐terminally truncated metabolites of SP, SP(1–9)‐COOH, and SP(1–7)‐COOH retained stimulatory activity at MRGPRX2. SP, SP(1–9)‐COOH, and SP(1–7)‐COOH were synthesized and tested on HEK293 cells expressing NK1R or MRGPRX2, and LAD2 human mast cells, to determine the activity of SP and its metabolites in Ca2+ mobilization, degranulation, and cytokine assays. As expected from prior studies, both C‐terminally truncated SP metabolites had essentially no activity at NK1R, even at very high concentrations. In contrast, the in vivo metabolite of SP, SP(1–9)‐COOH retained ability to activate MRGPRX2 across all parameters tested, albeit with reduced potency compared to intact SP. SP(1–7)‐COOH did not produce any significant MRGRPX2 activation. Our results suggest that the SP metabolite, SP(1–9)‐COOH, may play a regulatory role through the activation of MRGPRX2. However, given the relatively low potency of both SP and SP(1–9)‐COOH at MRGPRX2, additional work is needed to better understand the biological importance of this expanded SP/MRGPRX2 pathway.

The Therapeutic Potential of Aprepitant in Glioblastoma Cancer Cells through Redox Modification.

Although there is no doubt regarding the involvement of oxidative stress in the development of glioblastoma, many questions remained unanswered about signaling cascades that regulate the redox status. Given the importance of the substance P (SP)/neurokinin 1 receptor (NK1R) system in different cancers, it was of particular interest to evaluate whether the stimulation of this cascade in glioblastoma-derived U87 cells is associated with the induction of oxidative stress. Our results showed that SP-mediated activation of NK1R not only increased the intracellular levels of malondialdehyde (MDA) and reactive oxygen species (ROS) but also reduced the concentration of thiol in U87 cells. We also found that upon SP addition, there was a significant reduction in the cells' total antioxidant capacity (TAC), revealing that the SP/NK1R axis may be involved in the regulation of oxidative stress in glioblastoma cells. The significant role of SP/NK1R in triggering oxidative stress in glioblastoma has become more evident when we found that the abrogation of the axis using aprepitant reduced cell survival, probably through exerting antioxidant effects. The results showed that both MDA and ROS concentrations were significantly reduced in the presence of aprepitant, and the number of antioxidant components of the redox system increased. Overall, these findings suggest that aprepitant might exert its anticancer effect on U87 cells through shifting the balance of oxidant and antioxidant components of the redox system.

Substance P modulates BMSCs migration for tissue repair through NK-1R/CXCR4/p-Akt signal activation.

The migration of bone marrow-derived mesenchymal stem cells (BMSCs) to the wound site played an important role in tissue repair. Substance P (SP) has been studied and reported to be involved in tissue repair by promoting the growth of endothelial cells and the migration of BMSCs. However, the complicated process and the molecular mechanisms were not fully understood. Thus, we aimed to investigate the effect of SP-induced BMSCs migration on tissue repair and its possible mechanism. Western blot and q-PCR assay revealed that SP could induce the BMSCs migration through overexpression of CXCR4 and upregulation of Akt phosphorylation. And the upregulation was related to the activation of neurokinin-1 receptor (NK-1R). Besides, we found that the increased phosphorylation Akt caused by SP could be canceled by the inhibition of CXCR4 both in vitro and in vivo. Furthermore, a skin-injury animal model was established and used to observe the tissue repair process. Results showed that SP could accelerate wound closure, gain more granulation tissue accumulation, and more collagen deposition through the promotion of angiogenesis and induction of the BMSCs migration to the wound site. And these effects could be impaired by inhibition of CXCR4 and p-Akt. Our results suggested that SP promoted tissue repair through BMSCs migration via upregulation of CXCR4 and p-Akt. The expression of CXCR4 and p-Akt were regulated by NK-1R activation. These findings add more evidence in understanding the mechanisms of SP-induced BMSCs migration and highlight the potential for clinical implementation of SP in tissue repair.

Substance P and Neurokinin 1 Receptor in Chronic Inflammation and Cancer of the Head and Neck: A Review of the Literature.

Head and neck cancer is a growing worldwide public health problem, accounting for approximately 1,500,000 new cases and 500,000 deaths annually. Substance P (SP) is a peptide of the tachykinin family, which has roles related to a large number of physiological mechanisms in humans. The implications of SP in carcinogenesis have recently been reported through the stimulation of the neurokinin 1 receptor (NK1R), or directly, through the effects derived from the constitutive activation of NK1R. Consequently, SP/NK1R seems to play relevant roles in cancer, upregulating cell proliferation, cell migration and chronic inflammation, among other oncogenic actions. Furthermore, there is growing evidence pointing to a central role for SP in tumour progression, singularly so in laryngeal and oral squamous cell carcinomas. The current narrative review of the literature focuses on the relationship between the SP/NK1R system and chronic inflammation and cancer in the head-and-neck region. We described a role for SP/NK1R in the transition from chronic inflammation of the head and neck mucosa, to preneoplastic and neoplastic transformation and progression.

Aprepitant Promotes Caspase-Dependent Apoptotic Cell Death and G2/M Arrest through PI3K/Akt/NF-κB Axis in Cancer Stem-Like Esophageal Squamous Cell Carcinoma Spheres.

The antagonists of the neurokinin-1 receptor (NK1R) are known for their anti-inflammatory, anxiolytic, antiemetic, and anticancer activities. Aprepitant, a nonpeptide NK1R antagonist, is used in nausea and vomiting, the most common side effects of cancer chemotherapy in patients. It has been established that NK1R activation by substance P (SP), which links cancer promotion and progression to a neurokinin-mediated environment, became one mechanism that corresponds to the mitogenesis of tumor cells. Therefore, this study is aimed at explaining and evaluating the anticancer impacts of aprepitant on esophageal squamous cancer cell (ESCC) spheres by using in vitro experiments, such as resazurin, ROS, annexin-V binding, RT-PCR, and Western blot analysis. As a result, we showed that aprepitant had strong antiproliferative and cytotoxic effects on ESCC cell spheres. Also, aprepitant caused significant G2-M cell cycle arrest depending on concentration increase. Further, exposure of cells to this agent resulted in caspase -8/-9-dependent apoptotic pathway activation by modifying the expression of genes involved in apoptosis. Besides, treatment of the cells by aprepitant abrogates of the PI3K/Akt pathway, as shown by reducing the level of Akt, induces apoptotic cell death. In summary, pharmacological inhibition of NK1R with aprepitant seems to have a significant chance of treating ESCC as a single agent or in conjunction with other chemotherapeutic drugs.

Pathogenic role of the SP/ NK1R system in GBM cells through inhibiting the thioredoxin system.

Objective(s):Glioblastoma multiforme (GBM), a highly aggressive Grade IV brain tumor, is a significant public health issue due to its poor prognosis and incurability. Neuropeptide substance P (SP) plays a critical role in GBM tumor growth and development via activation of neurokinin-1receptor (NK1R). Moreover, SP is a pro-oxidant factor contributing to oxidative stress in various cell types. However, the link between SP and oxidative stress in cancer cells is not fully investigated. Here, we aimed to identify the effects of SP and NK1R antagonist, aprepitant, on the redox status of GBM cells.Materials and Methods:Resazurin assay was employed to determine the effect of aprepitant on viability of U87 glioblastoma cells. 2’,7’-dichlorodihydrofluorescein diacetate (H2DCFDA) assay was employed to measure the levels of intracellular reactive oxygen species (ROS). A quantitative real-time polymerase chain reaction was applied to measure the expression of proteins of the thioredoxin system. Commercial kits (ZellBio GmbH) were also used to measure the enzymatic activity of these proteins.Results:We found that SP increased ROS level in U87 GBM cells, and aprepitant significantly reduced this effect. Furthermore, we found that SP could also affect the thioredoxin system, a central antioxidant enzyme defense system. SP reduced both expression and enzymatic activity of the thioredoxin system’s proteins, Trx and thioredoxin reductase (TrxR) and these effects were significantly reduced by aprepitant. Conclusion:Our results indicated that SP activation of NK1R represented a link between oxidative stress and GBM and highlighted the need for further validations in future studies.

Neurokinin-1 receptor signaling induces a pro-inflammatory transcriptomic profile in CD16+ monocytes

Neurokinin-1 receptor (NK1R) signaling can be immunomodulatory and it can lead to preferential transmigration of CD14+CD16+ monocytes across the blood brain barrier, potentially promoting the development of inflammatory neurological diseases, such as neuroHIV. To evaluate how NK1R signaling alters monocyte biology, RNA sequencing was used to define NK1R-mediated transcriptional changes in different monocyte subsets. The data show that NK1R activation induces a greater number of changes in CD14+CD16+ monocytes (152 differentially expressed genes), than in CD14+CD16− monocytes (36 genes), including increases in the expression of NF-κB and components of the NLRP3 inflammasome pathway. These results suggest that NK1R may alter the inflammatory state of CD14+CD16+ monocytes, influencing the development of neuroinflammation.

Contribution of Histamine to Nociceptive Behaviors Induced by Intrathecally Administered Cholecystokinin-8.

The involvement of spinal release of histamine in the nociceptive behaviors induced by cholecystokinin-8 (CCK-8) was investigated in mice. Intrathecal (i.t.) injection of CCK-8 elicited the nociceptive behaviors consisting of biting and licking. The nociceptive behaviors induced by i.t. treatment with CCK-8 showed two bell-shaped patterns. The histamine H3 receptor antagonist significantly promoted the nociceptive behaviors induced by CCK-8 at doses of 1–100 fmol and 100 pmol. The nociceptive behaviors elicited by CCK-8 was inhibited by i.t. administration of the CCK-B receptor antagonist in a dose-dependent manner, but not by the CCK-A receptor antagonist. The nociceptive behaviors induced by CCK-8 were markedly suppressed by i.t. pretreatment with antiserum against histamine and were abolished in histidine decarboxylase-deleted gene mice. In histamine H1 receptor-deleted gene mice, the nociceptive behaviors induced at both 10 amol and 10 pmol of CCK-8 were not affected. The tachykinin neurokinin-1 (NK1) receptor antagonists inhibited CCK-8 (10 pmol)-induced nociceptive behaviors in a dose-dependent manner. CCK-8 (10 amol)-induced nociceptive behaviors was not antagonized by co-administration with the tachykinin NK1 receptor antagonists. The nociceptive behaviors elicited by CCK-8 were inhibited by i.t. administration of the antagonist for the N-methyl-D-aspartate (NMDA) receptor in a dose-dependent manner. Our results suggest that the nociceptive behaviors induced by i.t. administration of CCK-8 (10 pmol) are mediated through the spinal release of histamine and are elicited via activation of the tachykinin NK1 and NMDA receptors, whereas the nociceptive behaviors induced by i.t. administration of CCK-8 (10 amol) are mediated through the spinal release of histamine and elicited via NMDA receptor activation.

The Neurokinin-1 Receptor is Expressed with Gastrin-Releasing Peptide Receptor in Spinal Interneurons and Modulates Itch.

The neurokinin-1 receptor (NK1R; encoded by Tacr1) is expressed in spinal dorsal horn neurons and has been suggested to mediate itch in rodents. However, previous studies relied heavily on neurotoxic ablation of NK1R spinal neurons, which limited further dissection of their function in spinal itch circuitry. To address this limitation, we leveraged a newly developed Tacr1CreER mouse line to characterize the role of NK1R spinal neurons in itch. We show that pharmacological activation of spinal NK1R and chemogenetic activation of Tacr1CreER spinal neurons increases itch behavior in male and female mice, whereas pharmacological inhibition of spinal NK1R suppresses itch behavior. We use fluorescence in situ hybridization (FISH) to characterize the endogenous expression of Tacr1 throughout the superficial and deeper dorsal horn (DDH), as well as the lateral spinal nucleus (LSN), of mouse and human spinal cord. Retrograde labeling studies in mice from the parabrachial nucleus (PBN) show that less than 20% of superficial Tacr1CreER dorsal horn neurons are spinal projection neurons, and thus the majority of Tacr1CreER are local interneurons. We then use a combination of in situ hybridization and ex vivo two-photon Ca2+ imaging of the mouse spinal cord to establish that NK1R and the gastrin-releasing peptide receptor (GRPR) are coexpressed within a subpopulation of excitatory superficial dorsal horn (SDH) neurons. These findings are the first to suggest a role for NK1R interneurons in itch and extend our understanding of the complexities of spinal itch circuitry.SIGNIFICANCE STATEMENT The spinal cord is a critical hub for processing somatosensory input, yet which spinal neurons process itch input and how itch signals are encoded within the spinal cord is not fully understood. We demonstrate neurokinin-1 receptor (NK1R) spinal neurons mediate itch behavior in mice and that the majority of NK1R spinal neurons are local interneurons. These NK1R neurons comprise a subset of gastrin-releasing peptide receptor (GRPR) interneurons and are thus positioned at the center of spinal itch transmission. We show NK1R mRNA expression in human spinal cord, underscoring the translational relevance of our findings in mice. This work is the first to suggest a role for NK1R interneurons in itch and extends our understanding of the complexities of spinal itch circuitry.

Aprepitant for Cough in Lung Cancer. A Randomized Placebo-controlled Trial and Mechanistic Insights.

Rationale: Effective cough treatments are a significant unmet need in patients with lung cancer. Aprepitant is a licensed treatment for nausea and vomiting, which blocks substance P activation of NK-1 (neurokinin 1) receptors, a mechanism also implicated in cough.Objectives: To assess aprepitant in patients with lung cancer with cough and evaluate mechanisms in vagal nerve tissue.Methods: Randomized double-blind crossover trial of patients with lung cancer and bothersome cough. They received 3 days of aprepitant or matched placebo; after a 3-day washout, patients crossed to the alternative treatment. The primary endpoint was awake cough frequency measured at screening and Day 3 of each treatment; secondary endpoints included patient-reported outcomes. In vitro, the depolarization of isolated guinea pig and human vagus nerve sections in grease-gap recording chambers, indicative of sensory nerve activation, was measured to evaluate the mechanism.Measurements and Main Results: Twenty patients with lung cancer enrolled, with a mean age 66 years (±7.7); 60% were female and 80% had non-small cell cancer, 50% had advanced stage, and 55% had World Health Organization performance status 1. Cough frequency improved with aprepitant, reducing by 22.2% (95% confidence interval [CI], 2.8-37.7%) over placebo while awake (P = 0.03), 30.3% (95% CI, 12.7-44.3) over 24 hours (P = 0.002), and 59.8% (95% CI, 15.1-86.0) during sleep (P = 0.081). Patient-reported outcomes all significantly improved. Substance P depolarized both guinea pig and human vagus nerve. Aprepitant significantly inhibited substance P-induced depolarization by 78% in guinea pig (P = 0.0145) and 94% in human vagus (P = 0.0145).Conclusions: Substance P activation of NK-1 receptors appears to be an important mechanism driving cough in lung cancer, and NK-1 antagonists show promise as antitussive therapies.

Neurokinin 1 receptor activation in the rat spinal cord maintains latent sensitization, a model of inflammatory and neuropathic chronic pain

Latent sensitization is a model of chronic pain in which a persistent state of pain hypersensitivity is suppressed by opioid receptors, as evidenced by the ability of opioid antagonists to induce a period of mechanical allodynia. Our objective was to determine if substance P and its neurokinin 1 receptor (NK1R) mediate the maintenance of latent sensitization. Latent sensitization was induced by injecting rats in the hindpaw with complete Freund's adjuvant (CFA), or by tibial spared nerve injury (SNI). When responses to von Frey filaments returned to baseline (day 28), the rats were injected intrathecally with saline or the NK1R antagonist RP67580, followed 15 min later by intrathecal naltrexone. In both pain models, the saline-injected rats developed allodynia for 2 h after naltrexone, but not the RP67580-injected rats. Saline or RP67580 were injected daily for two more days. Five days later (day 35), naltrexone was injected intrathecally. Again, the saline-injected rats, but not the RP67580-injected rats, developed allodynia in response to naltrexone. To determine if there is sustained activation of NK1Rs during latent sensitization, NK1R internalization was measured in lamina I neurons in rats injected in the paw with saline or CFA, and then injected intrathecally with saline or naltrexone on day 28. The rats injected with CFA had a small amount of NK1R internalization that was significantly higher than in the saline-injected rats. Naltrexone increased NK1R internalization in the CFA-injected rats but nor in the saline-injected rats. Therefore, sustained activation of NK1Rs maintains pain hypersensitivity during latent sensitization.

Substance P enhances the local activation of NK1R-expressing c-kit+ cardiac progenitor cells in right atrium of ischemia/reperfusion-injured heart

BackgroundLocalization of neurokinin 1 receptor (NK1R), the endogenous receptor for neuropeptide substance P (SP), has already been described for the right atrium (RA) of the heart. However, the biological role of SP/NK1R signal pathways in the RA remains unclear.Sprague-Dawley rats were randomly divided into 4 groups (n = 22 each); subjected to sham, ischemia/reperfusion-injury (I/R), I/R with 5 nmole/kg SP injection (SP + I/R), and SP + I/R with 1 mg/kg RP67580 injection (RP, a selective non-peptide tachykinin NK1R antagonist) (RP/SP + I/R). The left anterior descending coronary artery was occluded for 40 min followed by 1 day reperfusion with SP or SP + RP or without either. After 1 day, both atria and ventricles as well as the heart apexes were collected.ResultsSP promoted the expression of c-Kit, GATA4, Oct4, Nanog, and Sox2 in only the RA of the SP + I/R rats via NK1R activation. In agreement with these observations, NK1R-expressing c-Kit+ Nkx2.5+GATA4+ cardiac progenitor cells (CPCs) in the ex vivo RA explant outgrowth assay markedly migrated out from RA1 day SP + I/R approximately 2-fold increase more than RA1 day I/R. Treatment of SP promoted proliferation, migration, cardiosphere formation, and potential to differentiate into cardiomyocytes. Using RP inhibitor, NK1R antagonist not only inhibited cell proliferation and migration but also reduced the formation of cardiosphere and differentiation of c-Kit+ CPCs.ConclusionSP/NK1R might play a role as a key mediator involved in the cellular response to c-Kit+ CPC expansion in RA of the heart within 24 h after I/R.

New insight into the role of substance P/neurokinin-1 receptor system in breast cancer progression and its crosstalk with microRNAs.

The neuropeptide substance P (SP) triggers a variety of tumor-promoting signaling pathways through the activation of neurokinin-1receptor (NK1R), a class of neurokinin G protein-coupled receptors superfamily. Recent researches in our and other laboratories have shown the overexpression of both SP and NK1R in breast cancer (BC) patients. SP/NK1R signaling is strongly implicated in the pathogenesis of BC through affecting cell proliferation, migration, metastasis, angiogenesis, and resistance. Therefore, SP/NK1R signaling responses must be rigorously regulated; otherwise, they would contribute to a more aggressive BC phenotype. Recently, microRNAs (miRNAs) as a specific class of epigenetic regulators have been shown to regulate NK1R and thus, controlling SP/NK1R signaling responses in BC. This review summarizes the current knowledge of the role of SP/NK1R signaling and its therapeutic potentials in BC. We also provide an overview regarding the effects of miRNA-mediated NK1R regulatory mechanisms in controlling BC tumorigenesis to gain a clearer view and thus better management of cancer.

Neurokinin-1 receptor activation is sufficient to restore the hypercapnic ventilatory response in the Substance P-deficient naked mole-rat.

Naked mole-rats (NMRs) live in large colonies within densely populated underground burrows. Their collective respiration generates significant metabolic carbon dioxide (CO2) that diffuses slowly out of the burrow network, creating a hypercapnic environment. Currently, the physiological mechanisms that underlie the ability of NMRs to tolerate environmental hypercapnia are largely unknown. To address this, we used whole-body plethysmography and respirometry to elucidate the hypercapnic ventilatory and metabolic responses of awake, freely behaving NMRs to 0%-10% CO2. We found that NMRs have a blunted hypercapnic ventilatory response (HCVR): ventilation increased only in 10% CO2. Conversely, metabolism was unaffected by hypercapnia. NMRs are insensitive to cutaneous acid-based pain caused by modified substance P (SP)-mediated peripheral neurotransmission, and SP is also an important neuromodulator of ventilation. Therefore, we re-evaluated physiological responses to hypercapnia in NMRs after an intraperitoneal injection of exogenous substance P (2 mg/kg) or a long-lived isoform of substance P {[pGlu5-MePhe8-MeGly9]SP(5-11), DiMe-C7; 40-400 μg/kg}. We found that both drugs restored hypercapnia sensitivity and unmasked an HCVR in animals breathing 2%-10% CO2. Taken together, our findings indicate that NMRs are remarkably tolerant of hypercapnic environments and have a blunted HCVR; however, the signaling network architecture required for a "normal" HCVR is retained but endogenously inactive. This muting of chemosensitivity likely suits the ecophysiology of this species, which presumably experiences hypercapnia regularly in their underground niche.

Heterosynaptic facilitation of mechanical nociceptive input is dependent on the frequency of conditioning stimulation.

High-frequency burstlike electrical conditioning stimulation (HFS) applied to human skin induces an increase in mechanical pinprick sensitivity of the surrounding unconditioned skin (a phenomenon known as secondary hyperalgesia). The present study assessed the effect of frequency of conditioning stimulation on the development of this increased pinprick sensitivity in humans. In a first experiment, we compared the increase in pinprick sensitivity induced by HFS, using monophasic non-charge-compensated pulses and biphasic charge-compensated pulses. High-frequency stimulation, traditionally delivered with non-charge-compensated square-wave pulses, may induce a cumulative depolarization of primary afferents and/or changes in pH at the electrode-tissue interface due to the accumulation of a net residue charge after each pulse. Both could contribute to the development of the increased pinprick sensitivity in a frequency-dependent fashion. We found no significant difference in the increase in pinprick sensitivity between HFS delivered with charge-compensated and non-charge-compensated pulses, indicating that the possible contribution of charge accumulation when non-charge-compensated pulses are used is negligible. In a second experiment, we assessed the effect of different frequencies of conditioning stimulation (5, 20, 42, and 100 Hz) using charge-compensated pulses on the development of increased pinprick sensitivity. The maximal increase in pinprick sensitivity was observed at intermediate frequencies of stimulation (20 and 42 Hz). It is hypothesized that the stronger increase in pinprick sensitivity at intermediate frequencies may be related to the stronger release of substance P and/or neurokinin-1 receptor activation expressed at lamina I neurons after C-fiber stimulation.NEW & NOTEWORTHY Burstlike electrical conditioning stimulation applied to human skin induces an increase in pinprick sensitivity in the surrounding unconditioned skin (a phenomenon referred to as secondary hyperalgesia). Here we show that the development of the increase in pinprick sensitivity is dependent on the frequency of the burstlike electrical conditioning stimulation.

Neurokinin-1 Receptor Deficiency Improves Survival in Murine Polymicrobial Sepsis Through Multiple Mechanisms in Aged Mice.

Substance P (SP) is a neuropeptide that contributes to a proinflammatory state by binding to the neurokinin 1 receptor (NK-1R). Limiting this interaction has been shown to attenuate the acute inflammation. Our hypothesis was that NK-1R activation would contribute to the morbidity and mortality of sepsis in a model using mice genetically deficient in the NK-1R. To investigate the role of the SP/NK-1R axis in a murine model of sepsis, cecal ligation and puncture (CLP) in NK-1R deficient and wild type (WT) aged mice was performed. Acute inflammation was assessed by measuring circulating cytokines and clinical parameters. Deletion of the NK-1R results in improved survival following CLP (NK-1R knockout mice survival = 100% vs. WT = 14%). A reduction in the inflammatory cytokines interleukin (IL) 6, macrophage inflammatory peptide 2, and IL-1 receptor antagonist, improved hemodynamic parameters, and increased neutrophilia were present in the NK-1R-deficient mice after CLP compared with WT mice. These data confirm the hypothesis that eliminating the SP/NK-1R interaction in a highly lethal murine model of sepsis leads to decreased morbidity and mortality through multiple mechanisms.

Sensory nerve-derived neuropeptides accelerate the development and fibrogenesis of endometriosis.

Do sensory nerves play any role in the development of endometriosis? Sensory nerves participate in all major steps (epithelial-mesenchymal transition (EMT), fibroblast-to-myofibroblast transdifferentiation (FMT) and smooth muscle metaplasia (SMM)) in the development and fibrogenesis of endometriotic lesions. Endometriotic lesions are known to be hyperinnervated due to neurogenesis resulting from neutrophins secreted by endometriotic lesions and possibly platelets. These neutrophins seem to preferentially favour production of sensory neurons at the expense of sympathetic neurons. Three independent, yet complementary, prospective, randomized mouse experimentations were conducted. A total of 143 female Balb/C mice and 24 female immunodeficient nude Balb/C mice were used. The mice were sacrificed 2 or 4 weeks after the induction of endometriosis. In Experiment 1, 21 mice were randomly divided into three groups of equal size for sympathetic denervation, sensory denervation and controls. Denervation was carried out chemically. In Experiment 2, 24 nude mice were randomly divided into three equal-sized groups: the BEFORE and AFTER groups that respectively received surgical denervation 3 days before or after the induction of endometriosis by subcutaneous grafting of human endometriotic tissues, and the Control group that received a sham surgery without denervation 3 days before induction. For Experiments 1 and 2, all mice were sacrificed two weeks after induction of endometriosis. In Experiment 3, substance P (SP) and aprepitant, a potent and selective neurokinin 1 receptor (NK1R) antagonist, were used to activate and inhibit the NK1R signalling pathway, respectively. A total of 32 mice were randomly divided into four groups of equal sizes: control (CTL), SP, Before-Induction and After-Induction. One day before the induction of endometriosis, mice in CTL, SP and Before-Induction groups were infused with sterile saline, SP and aprepitant, respectively, via Alzet osmotic pumps. Two weeks after the induction, the After-induction group was infused with aprepitant in similar fashion. All mice were sacrificed four weeks after the induction of endometriosis. In all three experiments, the bodyweight and hotplate latency were evaluated before induction and sacrifice. In addition, all lesions were excised, weighed and processed for quantification and immunohistochemistry analysis of markers for EMT, FMT and SMM, and the extent of fibrosis was evaluated by Masson trichrome staining. In Experiment 1, chemical denervation of sympathetic and sensory nerves reduced the lesion weight by 43.2% (±23.1%) and 68.7% (±20.3%), respectively, as compared with controls. In particular, sensory denervation led to significantly greater reduction in lesion weight than sympathetic denervation. Sensory denervation also resulted in significantly improved hyperalgesia as compared with controls. In contrast, sympathetic denervation yielded only transient improvement in hyperalgesia. Both sympathetic and sensory denervation resulted in lower immunoreactivity against markers of proliferation and fibrosis, especially sensory denervation.In Experiment 2, surgical denervation before or after induction of endometriosis also decelerated the development of endometriosis, as manifested by significantly reduced lesion weight and extent of lesional fibrosis, along with improved hyperalgesia.In Experiment 3, NK1R activation by SP infusion accelerated lesional development, as evidenced by significantly increased lesional weight, more thorough progression of EMT, FMT, SMM, exaggerated lesional fibrosis and deteriorated hyperalgesia. In contrast, NK1R antagonism decelerated lesional development and improved hyperalgesia. N/A. This study is limited by the use of histologic and immunohistochemistry analyses only and the lack of molecular data. Since sensory nerves are known to be important in wound healing and fibrogenesis, our findings also give more credence to the notion that endometriotic lesions are wounds undergoing repeated tissue injury and repair. As such, sensory nerves or the NK1R signalling pathway in particular may be potential targets for intervention. This research was supported by Grants 81471434 (SWG), 81530040 (SWG), 81771553 (SWG), 81671436 (XSL) and 81871144 (XSL) from the National Natural Science Foundation of China and an Excellence in Centres of Clinical Medicine grant (2017ZZ01016) from the Science and Technology Commission of Shanghai Municipality. None of the authors have anything to disclose.