TRPV1 Gene Knockout Impairs Postischemic Recovery in Isolated Perfused Heart in Mice

Morphine timing-dependent modulation of TRPV1 phosphorylation correlates with differential morphine effects on myocardial ischemia/reperfusion injury

Opioids are used for pain relief in patients suffering from acute myocardial ischemia or infarction. Clinical and laboratory studies demonstrate that morphine treated patients or the experimental animal model suffering acute myocardial ischemia and reperfusion, may worsen myocardial viability. As transient receptor potential vanilloid 1 (TRPV1) plays important roles in pain sensation and cardio-protection, we query whether opioids may exacerbate myocardial viability via interaction with TRPV1 activity in the pain relief. We found the co-expressions of TRPV1 and opioid μ, δ and κ receptors in adult rat cardiomyocytes. Intravenous injection of morphine (0.3 mg/kg) at 20 min after induction of myocardial ischemia, in the rat model of acute myocardial ischemia and reperfusion, induced significant reduction of phosphorylated TRPV1 (p-TRPV1) in the ventricular myocardium and increase in serum cardiac troponin I (cTnI), compared with the ischemia/reperfusion controls (all P < 0.05). The effects of morphine were completely reversed by selective opioid μ, δ and κ receptor antagonists. While significant upregulation of p-TRPV1 (P < 0.05) and improvement of ±dP/dt max (all P < 0.05) were detected in the animals giving the same dose of morphine before induction of myocardial ischemia. The changes in p-TRPV1 correlate with the alterations of cTnI (r = -0.5840, P = 0.0283) and ±dP/dt max (r = 0.8084, P = 0.0005 and r = -0.8133, P = 0.0004, respectively). The findings of this study may indicate that potentiation and attenuation of TRPV1 sensitivity correlate with the improvement of the cardiac performance and the aggravation of myocardial viability, respectively, by giving morphine before and during myocardial ischemia and reperfusion.

Cellular metabolism of substance P produces neurokinin-1 receptor peptide agonists with diminished cyclic AMP signaling

Substance P (SP) is released from sensory nerves in the arteries and heart. It activates neurokinin-1 receptors (NK1Rs) causing vasodilation, immune modulation, and adverse cardiac remodeling. The hypothesis was tested: SP and SP metabolites activate different second messenger signaling pathways. Macrophages, endothelial cells, and fibroblasts metabolized SP to N- and C-terminal metabolites to varying extents. SP 5-11 was the most abundant metabolite followed by SP 1-4, SP 7-11, SP 6-11, SP 3-11, and SP 8-11. In NK1R-expressing human embryonic kidney 293 (HEK293) cells, SP and some C-terminal SP metabolites stimulate the NK1R, promoting the dissociation of several Gα proteins, including Gαs and Gαq from their βγ subunits. SP increases intracellular calcium concentrations ([Ca]i) and cyclic 3',5'-adenosine monophosphate (cAMP) accumulation with similar -log EC50 values of 8.5 ± 0.3 and 7.8 ± 0.1 M, respectively. N-terminal metabolism of SP by up to five amino acids and C-terminal deamidation of SP produce peptides that retain activity to increase [Ca]i but not to increase cAMP. C-terminal metabolism results in the loss of both activities. Thus, [Ca]i and cAMP signaling are differentially affected by SP metabolism. To assess the role of N-terminal metabolism, SP and SP 6-11 were compared with cAMP-mediated activities in NK1R-expressing 3T3 fibroblasts. SP inhibits nuclear factor κB (NF-κB) activity, cell proliferation, and wound healing and stimulates collagen production. SP 6-11 had little or no activity. Cyclooxygenase-2 (COX-2) expression is increased by SP but not by SP 6-11. Thus, metabolism may select the cellular response to SP by inhibiting or redirecting the second messenger signaling pathway activated by the NK1R.NEW & NOTEWORTHY Endothelial cells, macrophages, and fibroblasts metabolize substance P (SP) to N- and C-terminal metabolites with SP 5-11 as the most abundant metabolite. SP activates neurokinin-1 receptors to increase intracellular calcium and cyclic AMP. In contrast, SP metabolites of N-terminal metabolism and C-terminal deamidation retain the ability to increase calcium but lose the ability to increase cyclic AMP. These new insights indicate that the metabolism of SP directs cellular functions by regulating specific signaling pathways.

Lysophosphatidic acid contributes to myocardial ischemia/reperfusion injury by activating TRPV1 in spinal cord

Lysophosphatidic acid (LPA) is a bioactive phospholipid that plays a crucial role in cardiovascular diseases. Here, we question whether LPA contributes to myocardial ischemia/reperfusion (I/R) injury by acting on transient receptor potential vanilloid 1 (TRPV1) in spinal cord. By ligating the left coronary artery to establish an in vivo I/R mouse model, we observed a 1.57-fold increase in LPA level in the cerebrospinal fluid (CSF). The I/R-elevated CSF LPA levels were reduced by HA130, an LPA synthesis inhibitor, compared to vehicle treatment (4.74 ± 0.34 vs. 6.46 ± 0.94 μg/mL, p = 0.0014). Myocardial infarct size was reduced by HA130 treatment compared to the vehicle group (26 ± 8% vs. 46 ± 8%, p = 0.0001). To block the interaction of LPA with TRPV1 at the K710 site, we generated a K710N knock-in mouse model. The TRPV1K710N mice were resistant to LPA-induced myocardial injury, showing a smaller infarct size relative to TRPV1WT mice (28 ± 4% vs. 60 ± 7%, p < 0.0001). Additionally, a sequence-specific TRPV1 peptide targeting the K710 region produced similar protective effects against LPA-induced myocardial injury. Blocking the K710 region through K710N mutation or TRPV1 peptide resulted in reduced neuropeptides release and decreased activity of cardiac sensory neurons, leading to a decrease in cardiac norepinephrine concentration and the restoration of intramyocardial pro-survival signaling, namely protein kinase B/extracellular regulated kinase/glycogen synthase kinase-3β pathway. These findings suggest that the elevation of CSF LPA is strongly associated with myocardial I/R injury. Moreover, inhibiting the interaction of LPA with TRPV1 by blocking the K710 region uncovers a novel strategy for preventing myocardial ischemic injury.

Epidural administration of large dose of opioid μ receptor agonist may impair cardiac functions and myocardial viability via desensitizing transient receptor potential vanilloid 1

The incidence of postoperative myocardial injury remains high as the underlying pathogenesis is still unknown. The dorsal root ganglion (DRG) neurons express transient receptor potential vanilloid 1 (TRPV1) and its downstream effector, calcitonin gene-related peptide (CGRP) participating in transmitting pain signals and cardiac protection. Opioids remain a mainstay therapeutic option for moderate-to-severe pain relief clinically, as a critical component of multimodal postoperative analgesia via intravenous and epidural delivery. Evidence indicates the interaction of opioids and TRPV1 activities in DRG neurons. Here, we verify the potential impairment of myocardial viability by epidural usage of opioids in postoperative analgesia. We found that large dose of epidural morphine (50 μg) significantly worsened the cardiac performance (+dP/dtmax reduction by 11% and -dP/dtmax elevation by 24%, all P < 0.001), the myocardial infarct size (morphine vs Control, 0.54 ± 0.09 IS/AAR vs. 0.23 ± 0.06 IS/AAR, P < 0.001) and reduced CGRP in the myocardium (morphine vs. Control, 9.34 ± 2.24 pg/mg vs. 21.23 ± 4.32 pg/mg, P < 0.001), while induced definite suppression of nociception in the postoperative animals. It was demonstrated that activation of μ-opioid receptor (μ-OPR) induced desensitization of TRPV1 by attenuating phosphorylation of the channel in the dorsal root ganglion neurons, via inhibiting the accumulation of cAMP. CGRP may attenuated the buildup of ROS and the reduction of mitochondrial membrane potential in cardiomyocytes induced by hypoxia/reoxygenation. The findings of this study indicate that epidurally giving large dose of μ-OPR agonist may aggravate myocardial injury by inhibiting the activity of TRPV1/CGRP pathway.

Transient receptor potential vanilloid type 1: cardioprotective effects in diabetic models

Cardiovascular disease, especially heart failure (HF) is the leading cause of death in patients with diabetes. Individuals with diabetes are prone to a special type of cardiomyopathy called diabetic cardiomyopathy (DCM), which cannot be explained by heart diseases such as hypertension or coronary artery disease, and can contribute to HF. Unfortunately, the current treatment strategy for diabetes-related cardiovascular complications is mainly to control blood glucose levels; nonetheless, the improvement of cardiac structure and function is not ideal. The transient receptor potential cation channel subfamily V member 1 (TRPV1), a nonselective cation channel, has been shown to be universally expressed in the cardiovascular system. Increasing evidence has shown that the activation of TRPV1 channel has a potential protective influence on the cardiovascular system. Numerous studies show that activating TRPV1 channels can improve the occurrence and progression of diabetes-related complications, including cardiomyopathy; however, the specific mechanisms and effects are unclear. In this review, we summarize that TRPV1 channel activation plays a protective role in the heart of diabetic models from oxidation/nitrification stress, mitochondrial function, endothelial function, inflammation, and cardiac energy metabolism to inhibit the occurrence and progression of DCM. Therefore, TRPV1 may become a latent target for the prevention and treatment of diabetes-induced cardiovascular complications.

New Drug Targets and Preclinical Modelling Recommendations for Treating Acute Myocardial Infarction

Acute myocardial infarction (AMI) is the leading cause of morbidity and mortality worldwide and the primary underlying risk factor for heart failure. Despite decades of research and clinical trials, there are no drugs currently available to prevent organ damage from acute ischaemic injuries of the heart. In order to address the increasing global burden of heart failure, drug, gene, and cell-based regeneration technologies are advancing into clinical testing. In this review we highlight the burden of disease associated with AMI and the therapeutic landscape based on market analyses. New studies revealing the role of acid-sensitive cardiac ion channels and other proton-gated ion channels in cardiac ischaemia are providing renewed interest in pre- and post-conditioning agents with novel mechanisms of action that may also have implications for gene- and cell-based therapeutics. Furthermore, we present guidelines that couple new cell technologies and data resources with traditional animal modelling pipelines to help de-risk drug candidates aimed at treating AMI. We propose that improved preclinical pipelines and increased investment in drug target identification for AMI is critical to stem the increasing global health burden of heart failure.

A human TRPV1 genetic variant within the channel gating domain regulates pain sensitivity in rodents

Pain signals are relayed to the brain via a nociceptive system, and in rare cases, this nociceptive system contains genetic variants that can limit the pain response. Here, we questioned whether a human transient receptor potential vanilloid 1 (TRPV1) missense variant causes a resistance to noxious stimuli and, further, whether we could target this region with a cell-permeable peptide as a pain therapeutic. Initially using a computational approach, we identified a human K710N TRPV1 missense variant in an otherwise highly conserved region of mammalian TRPV1. After generating a TRPV1K710N-knockin mouse using CRISPR/Cas9, we discovered that the K710N variant reduced capsaicin-induced calcium influx in dorsal root ganglion neurons. The TRPV1K710N rodents also had less acute behavioral responses to noxious chemical stimuli and less hypersensitivity to nerve injury, while their response to noxious heat remained intact. Furthermore, blocking this K710 region in WT rodents using a cell-penetrating peptide limited acute behavioral responses to noxious stimuli and returned pain hypersensitivity induced by nerve injury to baseline levels. These findings identify K710 TRPV1 as a discrete site that is crucial for the control of nociception and provide insights into how to leverage rare genetic variants in humans to uncover fresh strategies for developing pain therapeutics.

How do phytocannabinoids affect cardiovascular health? An update on the most common cardiovascular diseases

Cardiovascular disease (CVD) causes millions of deaths worldwide each year. Despite the great progress in therapies available for patients with CVD, some limitations, including drug complications, still exist. Hence, the endocannabinoid system (ECS) was proposed as a new avenue for CVDs treatment. The ECS components are widely distributed through the body, including the heart and blood vessels, thus the action of its endogenous and exogenous ligands, in particular, phytocannabinoids play a key role in various pathological states. The cardiovascular action of cannabinoids is complex as they affect vasculature and myocardium directly via specific receptors and exert indirect effects through the central and peripheral nervous system. The growing interest in phytocannabinoid studies, however, has extended the knowledge about their molecular targets as well as therapeutical properties; nonetheless, some areas of their actions are not yet fully recognized. Researchers have reported various cannabinoids, especially cannabidiol, as a promising approach to CVDs; hence, the purpose of this review is to summarize and update the cardiovascular actions of the most potent phytocannabinoids and the potential therapeutic role of ECS in CVDs, including ischemic reperfusion injury, arrhythmia, heart failure as well as hypertension.

Progress on role of ion channels of cardiac fibroblasts in fibrosis

Cardiac fibrosis is defined as excessive deposition of extracellular matrix (ECM) in pathological conditions. Cardiac fibroblasts (CFs) activated by injury or inflammation differentiate into myofibroblasts (MFs) with secretory and contractile functions. In the fibrotic heart, MFs produce ECM which is composed mainly of collagen and is initially involved in maintaining tissue integrity. However, persistent fibrosis disrupts the coordination of excitatory contractile coupling, leading to systolic and diastolic dysfunction, and ultimately heart failure. Numerous studies have demonstrated that both voltage- and non-voltage-gated ion channels alter intracellular ion levels and cellular activity, contributing to myofibroblast proliferation, contraction, and secretory function. However, an effective treatment strategy for myocardial fibrosis has not been established. Therefore, this review describes the progress made in research related to transient receptor potential (TRP) channels, Piezo1, Ca²⁺ release-activated Ca²⁺ (CRAC) channels, voltage-gated Ca²⁺ channels (VGCCs), sodium channels, and potassium channels in myocardial fibroblasts with the aim of providing new ideas for treating myocardial fibrosis.

Dietary Capsaicin: A Spicy Way to Improve Cardio-Metabolic Health?

Today's sedentary lifestyle with too much food and too little exercise has made metabolic syndrome a pandemic. Metabolic syndrome is a major risk factor for type-2 diabetes and cardiovascular disease. New knowledge of medical and nutraceutical intervention in the early stages of metabolic syndrome is central to prevent these deadly complications. People who eat chili pepper on a regular basis seem to stay healthier and live longer than those who do not. Animal experiments suggest a therapeutic potential for dietary capsaicin, the active principle in hot chili pepper, to reduce the risk of developing metabolic syndrome. This is an attractive theory since capsaicin has been a culinary staple for thousands of years, and is generally deemed safe when consumed in hedonically acceptable doses. The broad expression of the capsaicin receptor TRPV1 in metabolically active tissues lends experimental support to this theory. This review critically evaluates the available experimental and clinical evidence for and against dietary capsaicin being an effective dietary means to improve cardio-metabolic health. It comes to the conclusion that although a chili pepper-rich diet is associated with a reduced risk of dying due to cardiovascular disease, dietary capsaicin has no clear effect on blood glucose or lipid profiles. Therefore, the reduced mortality risk may reflect the beneficial action of digested capsaicin on gut microbiota.

Spinal cord astrocytes regulate myocardial ischemia-reperfusion injury

Astrocytes play a key role in the response to injury and noxious stimuli, but its role in myocardial ischemia-reperfusion (I/R) injury remains largely unknown. Here we determined whether manipulation of spinal astrocyte activity affected myocardial I/R injury and the underlying mechanisms. By ligating the left coronary artery to establish an in vivo I/R rat model, we observed a 1.7-fold rise in glial fibrillary acidic protein (GFAP) protein level in spinal cord following myocardial I/R injury. Inhibition of spinal astrocytes by intrathecal injection of fluoro-citrate, an astrocyte inhibitor, decreased GFAP immunostaining and reduced infarct size by 29% relative to the I/R group. Using a Designer Receptor Exclusively Activated by Designer Drugs (DREADD) chemogenetic approach, we bi-directionally manipulated astrocyte activity employing GFAP promoter-driven Gq- or Gi-coupled signaling. The Gq-DREADD-mediated activation of spinal astrocytes caused transient receptor potential vanilloid 1 (TRPV1) activation and neuropeptide release leading to a 1.3-fold increase in infarct size, 1.2-fold rise in serum norepinephrine level and higher arrhythmia score relative to I/R group. In contrast, Gi-DREADD-mediated inhibition of spinal astrocytes suppressed TRPV1-mediated nociceptive signaling, resulting in 35% reduction of infarct size and 51% reduction of arrhythmia score from I/R group, as well as lowering serum norepinephrine level from 3158 ± 108 to 2047 ± 95 pg/mL. Further, intrathecal administration of TRPV1 or neuropeptide antagonists reduced infarct size and serum norepinephrine level. These findings demonstrate a functional role of spinal astrocytes in myocardial I/R injury and provide a novel potential therapeutic approach targeting spinal cord astrocytes for the prevention of cardiac injury.

Electroacupuncture Treats Myocardial Infarction by Influencing the Regulation of Substance P in the Neurovascular to Modulate PGI2/TXA2 Metabolic Homeostasis via PI3K/AKT Pathway: A Bioinformatics-Based Multiomics and Experimental Study

Acute myocardial infarction (AMI) is the most severe form of coronary heart disease caused by ischemia and hypoxia. The study is aimed at investigating the role of neuropeptides and the mechanism of electroacupuncture (EA) in acute myocardial infarction (AMI) treatment. Compared with the normal population, a significant increase in substance P (SP) was observed in the serum of patients with AMI. PGI2 expression was increased in the SP-treated AMI mouse model, and TXA2 expression was decreased. And PI3K pathway-related genes, including Pik3ca, Akt, and Mtor, were upregulated in myocardial tissue of SP-treated AMI patients. Human cardiomyocyte cell lines (HCM) treated with SP increased mRNA and protein expression of PI3K pathway-related genes (Pik3ca, Pik3cb, Akt, and Mtor). Compared to MI control and EA-treated MI rat models, Myd88, MTOR, Akt1, Sp, and Irak1 were differentially expressed, consistent with in vivo and in vitro studies. EA treatment significantly enriched PI3K/AKT signaling pathway genes within MI-associated differentially expressed genes (DEGs) according to Kyoto Encyclopedia of Genes and Genomes (KEGG). Furthermore, it was confirmed by molecular docking analysis that PIK3CA, AKT1, and mTOR form stable dockings with neuropeptide SP. PI3K/AKT pathway activity may be affected directly or indirectly by EA via SP, which corrects the PGI2/TXA2 metabolic imbalance in AMI. MI treatment is now better understood as a result of this finding.

Transient receptor potential vanilloid subtype 1: A potential therapeutic target for fibrotic diseases

The transient receptor potential vanilloid subtype 1 (TRPV1), belonging to the TRPV channel family, is a non-selective, calcium-dependent, cation channel implicated in several pathophysiological processes. Collagen, an extracellular matrix component, can accumulate under pathological conditions and may lead to the destruction of tissue structure, organ dysfunction, and organ failure. Increasing evidence indicates that TRPV1 plays a role in the development and occurrence of fibrotic diseases, including myocardial, renal, pancreatic, and corneal fibrosis. However, the mechanism by which TRPV1 regulates fibrosis remains unclear. This review highlights the comprehensive role played by TRPV1 in regulating pro-fibrotic processes, the potential of TRPV1 as a therapeutic target in fibrotic diseases, as well as the different signaling pathways associated with TRPV1 and fibrosis.

A TRPV1 common missense variant affected the prognosis of ischemic cardiomyopathy

The purpose was to identify the Transient receptor potential (TRP) superfamily gene variants associate with the prognosis of ischemic cardiomyopathy (ICM). A whole-exome sequencing study involving 252 ICM and 252 healthy controls participants enrolled from March 2003 to November 2017. Optimal sequence kernel association test and Cox regression dominant was conducted to identify the cause genes of TRP with ICM and association of common SNPs with prognosis of ICM. Rs224534 was verified in the replication population. Besides, the expression of TRPV1 was detectable in human failed heart ventricular tissues. The TRPs was not associated with the risk of ICM (P > .05). Rs224534 was significantly associated with the prognosis of ICM (Hazard ratio, 2.27, 95%CI: 1.31-3.94; P = 3.7 × 10-3), in the replication cohort, (hazard ratio 1.47, 95%CI: 1.04-2.07; P = 2.9 × 10-2), and in combined cohort hazard ratio 1.62 (95%CI: 1.21-2.18; P = 1.1 × 10-3). The common SNP of TRPV1 (rs224534) is associated with the prognosis of ICM, and homozygote rs224534-AA showed an unfavorable prognosis of ICM in the dominant model tested. Genotyping the variant may benefit to further progress judgment of ICM.

Does Transient Receptor Potential Vanilloid Type 1 Alleviate or Aggravate Pathological Myocardial Hypertrophy?

Transient receptor potential vanilloid type 1 (TRPV1) is a non-selective cation channel, which is involved in the endogenous stress adaptation mechanism for protection of the heart as well as the occurrence and development of some heart diseases. Although the effect of activation of the TRPV1 channel on different types of non-neural cells in the heart remains unclear, most data show that stimulation of sensory nerves expressing TRPV1 or stimulation/overexpression of the TRPV1 channel has a beneficial role in heart disease. Some studies have proven that TRPV1 has an important relationship with pathological myocardial hypertrophy, but the specific mechanism and effect are not clear. In order to help researchers better understand the relationship between TRPV1 and pathological myocardial hypertrophy, this paper aims to summarize the effect of TRPV1 and the related mechanism in the occurrence and development of pathological myocardial hypertrophy from the following three points of view: 1) role of TRPV1 in alleviation of pathological myocardial hypertrophy; 2) role of TRPV1 in aggravation of pathological myocardial hypertrophy; and 3) the point of view of our team of researchers. It is expected that new therapies can provide potential targets for pathological myocardial hypertrophy.

Channelling the Force to Reprogram the Matrix: Mechanosensitive Ion Channels in Cardiac Fibroblasts

Cardiac fibroblasts (CF) play a pivotal role in preserving myocardial function and integrity of the heart tissue after injury, but also contribute to future susceptibility to heart failure. CF sense changes to the cardiac environment through chemical and mechanical cues that trigger changes in cellular function. In recent years, mechanosensitive ion channels have been implicated as key modulators of a range of CF functions that are important to fibrotic cardiac remodelling, including cell proliferation, myofibroblast differentiation, extracellular matrix turnover and paracrine signalling. To date, seven mechanosensitive ion channels are known to be functional in CF: the cation non-selective channels TRPC6, TRPM7, TRPV1, TRPV4 and Piezo1, and the potassium-selective channels TREK-1 and KATP. This review will outline current knowledge of these mechanosensitive ion channels in CF, discuss evidence of the mechanosensitivity of each channel, and detail the role that each channel plays in cardiac remodelling. By better understanding the role of mechanosensitive ion channels in CF, it is hoped that therapies may be developed for reducing pathological cardiac remodelling.

Extraction, purification, bioactivity and pharmacological effects of capsaicin: a review

Capsaicin (trans-8-methyl-N-vanillyl-6-nonenamide), a well-known vanilloid, which is the main spicy component in chili peppers, showing several biological activities and the potential applications range from food flavorings to therapeutics. Traditional extraction of capsaicin by organic solvents was time-consuming, some new methods such as aqueous two-phase method and ionic liquid extraction method have been developed. During past few decades, an ample variety of biological effects of capsaicin have been evaluated. Capsaicin can be used in biofilms and antifouling coatings due to its antimicrobial activity, allowing it has a promising application in food packaging, food preservation, marine environment and dental therapy. Capsaicin also play a crucial role in metabolic disorders, including weight loss, pressure lowing and insulin reduction effects. In addition, capsaicin was identified effective on preventing human cancers, such as lung cancer, stomach cancer, colon cancer and breast cancer by inducing apoptosis and inhibiting cell proliferation of tumor cells. Previous research also suggest the positive effects of capsaicin on pain relief and cognitive impairment. Capsaicin, the agonist of transient receptor potential vanilloid type 1 (TRPV1), could selectively activate TRPV1, inducing Ca²⁺ influx and related signaling pathways. Recently, gut microbiota was also involved in some diseases therapeutics, but its influence on the effects of capsaicin still need to be deeply studied. In this review, different extraction and purification methods of capsaicin, its biological activities and pharmacological effects were systematically summarized, as well as the possible mechanisms were also deeply discussed. This article will give an updated and better understanding of capsaicin-related biological effects and provide theoretical basis for its further research and applications in human health and manufacture development.

Beyond Neuronal Heat Sensing: Diversity of TRPV1 Heat-Capsaicin Receptor-Channel Functions

Transient receptor potential vanilloid 1 (TRPV1) is a calcium-permeable ion channel best known for its ability to be gated by the pungent constituent of red chili pepper, capsaicin, and related chemicals from the group of vanilloids as well as by noxious heat. As such, it is mostly expressed in sensory neurons to act as a detector of painful stimuli produced by pungent chemicals and high temperatures. Its activation is also sensitized by the numerous endogenous inflammatory mediators and second messengers, making it an important determinant of nociceptive signaling. Except for such signaling, though, neuronal TRPV1 activation may influence various organ functions by promoting the release of bioactive neuropeptides from sensory fiber innervation organs. However, TRPV1 is also found outside the sensory nervous system in which its activation and function is not that straightforward. Thus, TRPV1 expression is detected in skeletal muscle; in some types of smooth muscle; in epithelial and immune cells; and in adipocytes, where it can be activated by the combination of dietary vanilloids, endovanilloids, and pro-inflammatory factors while the intracellular calcium signaling that this initiates can regulate processes as diverse as muscle constriction, cell differentiation, and carcinogenesis. The purpose of the present review is to provide a clear-cut distinction between neurogenic TRPV1 effects in various tissues consequent to its activation in sensory nerve endings and non-neurogenic TRPV1 effects due to its expression in cell types other than sensory neurons.

Thermosensation involving thermo-TRPs

The transient receptor potential (TRP) channels constitute a superfamily of large ion channels that are activated by a wide range of chemical, mechanical and thermal stimuli. TRP channels with temperature sensitivity are called thermo-TRPs. They are involved in diverse physiological functions through their detection of external environmental temperature and internal body temperature. Each thermo-TRP has its own characteristic temperature threshold for activation. As a group, they cover temperatures ranging from cold to nociceptive high temperatures. Recently, many studies have identified the functions of thermo-TRPs residing in deep organs where they are exposed to body temperature. Importantly, temperature thresholds of thermo-TRPs can be regulated by physiological factors enabling their function at relatively constant body temperature. Moreover, several thermo-TRPs are reportedly engaged in body temperature regulation. This review will summarize the current understanding of thermo-TRPs, including their roles in thermosensation and functional regulation of physiological responses at body temperature and the regulation of body temperature.

TRPV1 expressed throughout the arterial circulation regulates vasoconstriction and blood pressure

KEY POINTS

The functional roles of the capsaicin receptor, TRPV1, outside of sensory nerves are unclear. We mapped TRPV1 in the mouse circulation, revealing extensive expression in the smooth muscle of resistance arterioles supplying skeletal muscle, heart and adipose tissue.  Activation of TRPV1 in vascular myocytes constricted arteries, reduced coronary flow in isolated hearts and increased systemic blood pressure. These functional effects were retained after sensory nerve ablation, indicating specific signalling by arterial TRPV1.  TRPV1 mediated the vasoconstrictive and blood pressure responses to the endogenous inflammatory lipid lysophosphatidic acid.  These results show that TRPV1 in arteriolar myocytes modulates regional blood flow and systemic blood pressure, and suggest that TRPV1 may be a target of vasoactive inflammatory mediators.

ABSTRACT

The capsaicin receptor, TRPV1, is a key ion channel involved in inflammatory pain signalling. Although mainly studied in sensory nerves, there are reports of TRPV1 expression in isolated segments of the vasculature, but whether the channel localizes to vascular endothelium or smooth muscle is controversial and the distribution and functional roles of TRPV1 in arteries remain unknown. We mapped functional TRPV1 expression throughout the mouse arterial circulation. Analysis of reporter mouse lines TRPV1^PLAP-nlacZ and TRPV1-Cre:tdTomato combined with Ca²⁺ imaging revealed specific localization of TRPV1 to smooth muscle of terminal arterioles in the heart, adipose tissue and skeletal muscle. Capsaicin evoked inward currents (current density ∼10% of sensory neurons) and raised intracellular Ca²⁺ levels in arterial smooth muscle cells, constricted arterioles ex vivo and in vivo and increased systemic blood pressure in mice and rats. Further, capsaicin markedly and dose-dependently reduced coronary flow. Pharmacological and/or genetic disruption of TRPV1 abolished all these effects of capsaicin as well as vasoconstriction triggered by lysophosphatidic acid, a bioactive lipid generated by platelets and atherogenic plaques. Notably, ablation of sensory nerves did not affect the responses to capsaicin revealing a vascular smooth muscle-restricted signalling mechanism. Moreover, unlike in sensory nerves, TRPV1 function in arteries was resistant to activity-induced desensitization. Thus, TRPV1 activation in vascular myocytes enables a persistent depolarizing current, leading to constriction of coronary, skeletal muscle and adipose arterioles and a sustained increase in systemic blood pressure.

MiR-98-5p promotes ischemia/reperfusion-induced microvascular dysfunction by targeting NGF and is a potential biomarker for microvascular reperfusion

OBJECTIVE

This study examined the correlation between serum miR-98-5p levels and indices of microvascular reperfusion in patients undergoing primary percutaneous coronary intervention (pPCI) after ST-segment elevation myocardial infarction (STEMI). Additionally, we evaluated the mechanisms by which miR-98-5p promoted ischemia/reperfusion (I/R)-induced injury in both cultured cell lines and an animal model.

METHODS

Circulating miR-98-5p levels were measured and compared from 171 STEMI patients undergoing pPCI, who were divided into two groups: no-reflow and reflow. The levels of miR-98-5p, nerve growth factor (NGF), and transient receptor potential vanilloid 1 (TRPV1) were analyzed in cultured human coronary endothelial cells (HCECs) exposed to hypoxia/reoxygenation (H/R). The effects of antagomir-98-5p on myocardial I/R-induced microvascular dysfunction in vivo were evaluated. Target gene expression and activity were assessed.

RESULTS

Higher miR-98-5p levels were associated with compromised indices of microvascular reperfusion. In vitro experiments on HCECs showed that exposure to H/R significantly increased miR-98-5p levels. We identified NGF as a novel target of miR-98-5p. Further, antagomir-98-5p relieved microvascular dysfunction and enhanced the expression of NGF and TRPV1 in the rat myocardial I/R model.

CONCLUSIONS

MiR-98-5p promotes microvascular dysfunction by targeting the NGF-TRPV1 axis. Serum miR-98-5p serves as a potential biomarker for microvascular reperfusion.

The potential role of TRPV1 in pulmonary hypertension: Angel or demon?

Pulmonary hypertension (PH) is a pathological state defined by increased pulmonary artery pressure, the pathogenesis of which is related to genetic mutations, intracellular calcium ([Ca²⁺]_i), inflammation and proliferation. Transient receptor potential vanilloid subfamily member 1 (TRPV1) is a nonselective cation channel expressed in neural and nonneural cells, including pulmonary vessels and nerves. As a calcium channel, TRPV1 can make vessels contracted, and promote smooth muscle cells proliferation through calcium-dependent transcription factors. Activation of TRPV1 in sensory nerves can release neuropeptides, including calcitonin gene-related peptide (CGRP), substance P (SP), and somatostatin (SST), which can regulate inflammation via transcription factor NF-kB. Considering the increased level of [Ca²⁺]_i and inflammation in the pathogenesis of PH, our review summarizes the role of TRPV1 in PH with regard to [Ca²⁺]_i, neuropeptides, and inflammation. In view of the limited research illustrating the relationship between TRPV1 and PH directly, our review also considers the role of TRPV1 in other types of vascular inflammation. Through this review, we hope to raise awareness about the function of TRPV1 in PH.

Capsaicin-Sensitive Sensory Nerves and the TRPV1 Ion Channel in Cardiac Physiology and Pathologies

Cardiovascular diseases, including coronary artery disease, ischemic heart diseases such as acute myocardial infarction and postischemic heart failure, heart failure of other etiologies, and cardiac arrhythmias, belong to the leading causes of death. Activation of capsaicin-sensitive sensory nerves by the transient receptor potential vanilloid 1 (TRPV1) capsaicin receptor and other receptors, as well as neuropeptide mediators released from them upon stimulation, play important physiological regulatory roles. Capsaicin-sensitive sensory nerves also contribute to the development and progression of some cardiac diseases, as well as to mechanisms of endogenous stress adaptation leading to cardioprotection. In this review, we summarize the role of capsaicin-sensitive afferents and the TRPV1 ion channel in physiological and pathophysiological functions of the heart based mainly on experimental results and show their diagnostic or therapeutic potentials. Although the actions of several other channels or receptors expressed on cardiac sensory afferents and the effects of TRPV1 channel activation on different non-neural cell types in the heart are not precisely known, most data suggest that stimulation of the TRPV1-expressing sensory nerves or stimulation/overexpression of TRPV1 channels have beneficial effects in cardiac diseases.

Effect and Molecular Mechanisms of Collateral Vessel Growth Mediated by Activation of Transient Receptor Potential Vanilloid Type 1

Information on the function of transient receptor potential vanilloid 1 (TRPV1) in arteriogenesis is limited. We aimed to verify whether TRPV1 is involved in collateral vessel growth in rat hind limbs and elucidate the possible subcellular action mechanisms. Adult Sprague Dawley rats were chosen to establish the hind limb ischemic model and treatment with capsaicin. Angiographies were performed, and tissue was isolated for immunohistochemistry. In vitro, rat aortic endothelial cells (RAECs) were treated with capsaicin and antagonist capsazepine. The RAEC proliferation was determined, and the protein and mRNA levels of Ca2+-dependent transcription factors were assessed. In vivo, the collateral vessels exhibited positive outward remodeling characterized by enhanced inflammatory cell/macrophage accumulation in the adventitia and activated cell proliferation in all layers of the vascular wall and elevated endothelial NO synthetase expression in the rats with hind limb ligation. In RAECs, TRPV1 activation-induced Ca2+-dependent transcriptional factors, nuclear factor of activated T cells 1, calsenilin and myocyte enhancer factor 2C increase, and augmented RAEC proliferation could be a subcellular mechanism for TRPV1 in endothelial cells and ultimately contribute to collateral vessel growth. TRPV1, a novel candidate, positively regulates arteriogenesis, meriting further studies to unravel the potential therapeutic target leading to improved collateral vessel growth for treating ischemic diseases.

CCL17 in Inflammation and Pain

It has been reported that a GM-CSF→CCL17 pathway, originally identified in vitro in macrophage lineage populations, is implicated in the control of inflammatory pain, as well as arthritic pain and disease. We explore, in this study and in various inflammation models, the cellular CCL17 expression and its GM-CSF dependence as well as the function of CCL17 in inflammation and pain. This study used models allowing the convenient cell isolation from Ccl17^E/+ reporter mice; it also exploited both CCL17-dependent and unique CCL17-driven inflammatory pain and arthritis models, the latter permitting a radiation chimera approach to help identify the CCL17 responding cell type(s) and the mediators downstream of CCL17 in the control of inflammation and pain. We present evidence that 1) in the particular inflammation models studied, CCL17 expression is predominantly in macrophage lineage populations and is GM-CSF dependent, 2) for its action in arthritic pain and disease development, CCL17 acts on CCR4⁺ non-bone marrow-derived cells, and 3) for inflammatory pain development in which a GM-CSF→CCL17 pathway appears critical, nerve growth factor, CGRP, and substance P all appear to be required.

Endothelial TRPV1 as an Emerging Molecular Target to Promote Therapeutic Angiogenesis

Therapeutic angiogenesis represents an emerging strategy to treat ischemic diseases by stimulating blood vessel growth to rescue local blood perfusion. Therefore, injured microvasculature may be repaired by stimulating resident endothelial cells or circulating endothelial colony forming cells (ECFCs) or by autologous cell-based therapy. Endothelial Ca²⁺ signals represent a crucial player in angiogenesis and vasculogenesis; indeed, several angiogenic stimuli induce neovessel formation through an increase in intracellular Ca²⁺ concentration. Several members of the Transient Receptor Potential (TRP) channel superfamily are expressed and mediate Ca²⁺-dependent functions in vascular endothelial cells and in ECFCs, the only known truly endothelial precursor. TRP Vanilloid 1 (TRPV1), a polymodal cation channel, is emerging as an important player in endothelial cell migration, proliferation, and tubulogenesis, through the integration of several chemical stimuli. Herein, we first summarize TRPV1 structure and gating mechanisms. Next, we illustrate the physiological roles of TRPV1 in vascular endothelium, focusing our attention on how endothelial TRPV1 promotes angiogenesis. In particular, we describe a recent strategy to stimulate TRPV1-mediated pro-angiogenic activity in ECFCs, in the presence of a photosensitive conjugated polymer. Taken together, these observations suggest that TRPV1 represents a useful target in the treatment of ischemic diseases.

Cardiac innervation in acute myocardial ischaemia/reperfusion injury and cardioprotection

Acute myocardial infarction (AMI) and the heart failure (HF) that often complicates this condition, are among the leading causes of death and disability worldwide. To reduce myocardial infarct (MI) size and prevent heart failure, novel therapies are required to protect the heart against the detrimental effects of acute ischaemia/reperfusion injury (IRI). In this regard, targeting cardiac innervation may provide a novel therapeutic strategy for cardioprotection. A number of cardiac neural pathways mediate the beneficial effects of cardioprotective strategies such as ischaemic preconditioning and remote ischaemic conditioning, and nerve stimulation may therefore provide a novel therapeutic strategy for cardioprotection. In this article, we provide an overview of cardiac innervation and its impact on acute myocardial IRI, the role of extrinsic and intrinsic cardiac neural pathways in cardioprotection, and highlight peripheral and central nerve stimulation as a cardioprotective strategy with therapeutic potential for reducing MI size and preventing HF following AMI. This article is part of a Cardiovascular Research Spotlight Issue entitled 'Cardioprotection Beyond the Cardiomyocyte', and emerged as part of the discussions of the European Union (EU)-CARDIOPROTECTION Cooperation in Science and Technology (COST) Action, CA16225.

Myocardial ischaemia reperfusion injury and cardioprotection in the presence of sensory neuropathy: Therapeutic options

During the last decades, mortality from acute myocardial infarction has been dramatically reduced. However, the incidence of post‐infarction heart failure is still increasing. Cardioprotection by ischaemic conditioning had been discovered more than three decades ago. Its clinical translation, however, is still an unmet need. This is mainly due to the disrupted cardioprotective signalling pathways in the presence of different cardiovascular risk factors, co‐morbidities and the medication being taken. Sensory neuropathy is one of the co‐morbidities that has been shown to interfere with cardioprotection. In the present review, we summarize the diverse aetiology of sensory neuropathies and the mechanisms by which these neuropathies may interfere with ischaemic heart disease and cardioprotective signalling. Finally, we suggest future therapeutic options targeting both ischaemic heart and sensory neuropathy simultaneously.

LINKED ARTICLES

This article is part of a themed issue on Risk factors, comorbidities, and comedications in cardioprotection. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v177.23/issuetoc

The timing of propofol administration affects the effectiveness of remote ischemic preconditioning induced cardioprotection in rats

The cardioprotection of remote ischemic preconditioning (RIPC) is abolished under propofol maintained anesthesia. Transient receptor potential vanilloid 1 (TRPV1) channel is present in the heart, and its activation could induce cardioprotection. Therefore, we tested whether the anesthetic propofol administration phase interfered with the RIPC-induced cardioprotection, and RIPC-induced cardioprotection via the cardiac TRPV1 channel. Male Sprague-Dawley rats were subjected to myocardial 30 minutes of ischemia followed by 2 hours of reperfusion. RIPC consisted of three cycles of 5-minute ischemia/reperfusion applied to a hindlimb. Propofol infusion at 12 mg/kg/h was commenced either at 10 minutes before the start of RIPC in the P-pre + RIPC group, or immediately after myocardial ischemia at the onset of reperfusion (P-post + RIPC) while performing RIPC. These two propofol infusion regimes were applied to another two grou bs without RIPC (P-pre and P-post groups). Infarct size (IS) was assessed by triphenyltetrazolium staining. Heart TRPV1 expression was detected by Western blot and immunofluorescence. RIPC significantly reduced myocardial IS compared with the control group (36.7 ± 3% versus 57.2 ± 4%; P < .01). When propofol was started before RIPC, the IS sparing effect of RIPC was completely abolished. However, propofol infusion starting immediately after myocardial ischemia did not affect RIPC-induced cardioprotection. TRPV1 expression significant increase after RIPC, then propofol inhibited the TRPV1 activation of RIPC if given before RIPC but not after. Our results suggest that the timing of propofol administration is critical to preserve the cardioprotection of RIPC. Propofol might cancel RIPC-induced cardioprotection via the cardiac TRPV1 receptor.

Transient receptor potential channels in cardiac health and disease

Transient receptor potential (TRP) channels are nonselective cationic channels that are generally Ca²⁺ permeable and have a heterogeneous expression in the heart. In the myocardium, TRP channels participate in several physiological functions, such as modulation of action potential waveform, pacemaking, conduction, inotropy, lusitropy, Ca²⁺ and Mg²⁺ handling, store-operated Ca²⁺ entry, embryonic development, mitochondrial function and adaptive remodelling. Moreover, TRP channels are also involved in various pathological mechanisms, such as arrhythmias, ischaemia-reperfusion injuries, Ca²⁺-handling defects, fibrosis, maladaptive remodelling, inherited cardiopathies and cell death. In this Review, we present the current knowledge of the roles of TRP channels in different cardiac regions (sinus node, atria, ventricles and Purkinje fibres) and cells types (cardiomyocytes and fibroblasts) and discuss their contribution to pathophysiological mechanisms, which will help to identify the best candidates for new therapeutic targets among the cardiac TRP family.

Inhibition of DRG-TRPV1 upregulation in myocardial ischemia contributes to exogenous cardioprotection

Myocardium ischemia-reperfusion injury (IRI) is the major cause of postoperative cardiac dysfunction. While intrathecal morphine preconditioning (ITMP) can reduce IRI in animals, the molecular processes underlying IRI and ITMP remain elusive. Transient receptor potential vanilloid type 1 (TRPV1) is highly expressed in cardiac sensory neurons and has a crucial role in detecting myocardial ischemia. This study aimed to determine the role of up-regulated dorsal root ganglion (DRG)-TRPV1 in IRI and whether its inhibition contributes to ITMP-induced cardioprotection. Animal model of IRI was established by left coronary artery occlusion (30 min) and reperfusion (2 h) in rats. Intrathecal intubation was prepared for morphine preconditioning, TRPV1-shRNA or selective TRPV1 antagonist administration. After IRI, both protein and phosphorylation levels of TRPV1 were significantly increased, and the immunofluorescence intensity of TRPV1 was increased and colocalized with μ-opioid receptors in DRG. Intrathecal pre-administration of either TRPV1-shRNA or TRPV1 antagonist significantly reduced myocardial injury and the upregulation of TRPV1 in DRG induced by IRI. Simultaneously, ITMP significantly suppressed TRPV1 protein expression and phosphorylation in DRG, as well as the heart infarct size and arrhythmia score caused by IRI. The suppression of TRPV1 elevation and activation by ITMP were reversed by intrathecal injection of the selective μ receptor antagonist. Furthermore, IRI elevated DRG cAMP, while intrathecal administration of the selective cAMP-PKA inhibitor reduced myocardial injury. Finally, we showed that activation of opioid receptor by morphine inhibited PKA activator-induced TRPV1 channel activity at the cellular level. These findings suggest that the elevation and activation of TRPV1 in DRG during myocardial ischemia-reperfusion might be responsible for cardiac injury. ITMP exerts cardioprotection by inhibiting DRG-TRPV1 activity via modulation cAMP. Therefore, inhibition of TRPV1 upregulation in DRG might be used as a novel therapeutic mechanism for myocardium ischemia-reperfusion injury.

N-octanoyl dopamine is superior to dopamine in protecting graft contractile function when administered to the heart transplant recipients from brain-dead donors

The major source of heart transplantation comes from brain-dead (BD) donors. However, brain death and myocardial ischemia/reperfusion injury during transplantation may lead to cardiac dysfunction and hemodynamic instability. A previous work demonstrated that pre-treatment of BD donors with dopamine improved the graft survival of heart allograft in recipient after transplantation. However, low-dose dopamine treatment might result in tachycardia and hypertension. Our previous experimental study showed that pre-treatment of BD donor rats with the dopamine derivate N-octanoyl dopamine (NOD), devoid of any hemodynamic effects, improved graft function after transplantation. Herein, we hypothesized that NOD confers superior myocardial protection than dopamine, in terms of graft function. Male Lewis donor rats were either subjected to sham-operation or brain death via a subdurally placed balloon followed by 5.5 h monitoring. Then, the hearts were explanted and heterotopically transplanted into Lewis recipient rats. Shortly before the onset of reperfusion, continuous intravenous infusion of either NOD (14.7 μg/kg/min, BD + NOD group, n = 9), dopamine (10 μg/kg/min, BD + Dopamine group, n = 8) or physiological saline vehicle (sham, n = 9 and BD group, n = 9) were administered to the recipient rats. In vivo left-ventricular (LV) graft function was evaluated after 1.5 h reperfusion. Additionally, immunohistochemical detection of 4-hydroxy-2-nonenal (HNE, an indicator of oxidative stress) and nitrotyrosine (a nitro-oxidative stress marker), was performed. After heart transplantation, systolic and diastolic functions were significantly decreased in the BD group compared to sham. Treatment with NOD but not dopamine, resulted in better LV graft systolic functional recovery (LV systolic pressure BD + NOD 90 ± 8 vs BD + Dopamine 66 ± 5 vs BD 65 ± 4 mmHg; maximum rate of rise of LV pressure dP/dt_max BD + NOD 2686 ± 225 vs BD + Dopamine 2243 ± 70 vs BD 1999 ± 147 mmHg/s, at an intraventricular volume of 140 μl, p < 0.05) and myocardial work compared to BD group. The re-beating time (time to restoration of heartbeat) was significantly shorter in BD + NOD group than that of BD hearts (32 ± 4 s vs. 48 ± 6 s, p < 0.05), Dopamine treatment had no impact on all of these parameters. Furthermore, NOD as well as dopamine decreased HNE and nitrotyrosine immunoreactivity to the same level. NOD is superior to dopamine in terms of protecting LV graft contractile function when administered to the heart transplant recipients from BD donors.

Protease-activated receptor 2 protects against myocardial ischemia-reperfusion injury through the lipoxygenase pathway and TRPV1 channels

This study tests the hypothesis that the lipoxygenase (LOX) pathway mediates protease-activated receptor (PAR) 2-induced activation of the transient receptor potential vanilloid receptor 1 (TRPV1) to protect the heart from ischemia/reperfusion (I/R) injury. SLIGRL, a PAR2 activating peptide, was administered prior to reperfusion following left anterior descending coronary artery ligation in wild type (WT) and TRPV1 knockout (TRPV1^-/-) mice. In a Langendorffly perfused heart I/R model, hemodynamic parameters, including left ventricular end-diastolic pressure, left ventricular developed pressure, coronary blood flow and left ventricular peak +dP/dt were evaluated after I/R. SLIGRL reduced the cardiac infarct size in WT and TRPV1^-/- mice with a greater effect in the former strain (P<0.05). SLIGRL increased plasma levels of calcitonin gene-related peptide (CGRP) and substance P in WT (both P<0.05) but not in TRPV1^-/- mice. Pretreatment with CGRP8-37 (a CGRP receptor antagonist) or RP67580 (a neurokinin-1 receptor antagonist) alone had no effect on SLIGRL-induced cardiac protection in either strain. However, combined administration of CGRP8-37 and RP67580 abolished SLIGRL-induced cardiac protection in WT but not in TRPV1^-/- mice. Nordihydroguaiaretic acid (a general LOX inhibitor) and baicalein (a 12-LOX inhibitor), but not indomethacin (a cyclooxygenase inhibitor) and hexanamide (a selective cytochrome P450 epoxygenase inhibitor), abolished the protective effects of SLIGRL in WT (all P<0.05) but not in TRPV1^-/- hearts. These data suggested that PAR2, possibly via 12-LOX, activates TRPV1 and leads to CGRP and substance P release to prevent I/R injury in the heart, indicating that the 12-LOX-TRPV1 pathway conveys cardiac protection to alleviate myocardial infarction.

Ca2+ Signaling in Cardiac Fibroblasts and Fibrosis-Associated Heart Diseases

Cardiac fibrosis is the excessive deposition of extracellular matrix proteins by cardiac fibroblasts and myofibroblasts, and is a hallmark feature of most heart diseases, including arrhythmia, hypertrophy, and heart failure. This maladaptive process occurs in response to a variety of stimuli, including myocardial injury, inflammation, and mechanical overload. There are multiple signaling pathways and various cell types that influence the fibrogenesis cascade. Fibroblasts and myofibroblasts are central effectors. Although it is clear that Ca2+ signaling plays a vital role in this pathological process, what contributes to Ca2+ signaling in fibroblasts and myofibroblasts is still not wholly understood, chiefly because of the large and diverse number of receptors, transporters, and ion channels that influence intracellular Ca2+ signaling. Intracellular Ca2+ signals are generated by Ca2+ release from intracellular Ca2+ stores and by Ca2+ entry through a multitude of Ca2+-permeable ion channels in the plasma membrane. Over the past decade, the transient receptor potential (TRP) channels have emerged as one of the most important families of ion channels mediating Ca2+ signaling in cardiac fibroblasts. TRP channels are a superfamily of non-voltage-gated, Ca2+-permeable non-selective cation channels. Their ability to respond to various stimulating cues makes TRP channels effective sensors of the many different pathophysiological events that stimulate cardiac fibrogenesis. This review focuses on the mechanisms of Ca2+ signaling in fibroblast differentiation and fibrosis-associated heart diseases and will highlight recent advances in the understanding of the roles that TRP and other Ca2+-permeable channels play in cardiac fibrosis.

Protective Effects of TRPV1 Activation Against Cardiac Ischemia/ Reperfusion Injury is Blunted by Diet-Induced Obesity

BACKGROUND

Activation of Transient Receptor Potential Vanilloid Subtype 1 (TRPV1) channels protects the heart from Ischemia/Reperfusion (I/R) injury through releasing Calcitonin Gene-Related Peptide (CGRP) and Substance P (SP). The current study aimed to study the cardioprotective effects of TRPV1 in obesity.

METHODS

TRPV1 gene knockout (TRPV1-/-) and Wild-Type (WT) mice were Fed a High-Fat Diet (HFD) or a control diet or for 20 weeks, and then the hearts were collected for I/R injury ex vivo. The hearts were mounted on a Langendorff apparatus and subjected to ischemia (30 min) and reperfusion (40 min) after incubated with capsaicin (10 nmol/L), CGRP (0.1 μmol/L) and SP (0.1 μmol/L). Then, Coronary Flow (CF), left ventricular peak positive dP/dt (+dP/dt), Left Ventricular Developed Pressure (LVDP) and Left Ventricular End-Diastolic Pressure (LVEDP) were measured.

RESULTS

HFD intake remarkably reduced CF, +dP/dt and LVDP and elevated LVEDP in both strains (P<0.05). Treatment with capsaicin decreased infarct size, increased CF, +dP/dt and LVDP, and decreased LVEDP in WT mice on control diet (P<0.05), but did not do so in other three groups. Treatment with CGRP and SP decreased infarct size in both strains fed with control diet (P<0.05). In contrast, not all the parameters of cardiac postischemic recovery in HFD-fed WT and TRPV1-/- mice were improved by CGRP and SP.

CONCLUSION

These results suggest that HFD intake impairs cardiac postischemic recovery. HFDinduced impairment of recovery is alleviated by CGRP in both strains and by SP only in TRPV1-/- mice, indicating that the effects of CGRP and SP are differentially regulated during HFD intake.

The Role of Transient Receptor Potential Vanilloid 1 in Common Diseases of the Digestive Tract and the Cardiovascular and Respiratory System

Transient receptor potential vanilloid subtype 1 (TRPV1), a member of the transient receptor potential vanilloid (TRPV) channel family, is a nonselective cation channel that is widely expressed in sensory nerve fibers and nonneuronal cells, including certain vascular endothelial cells and smooth muscle cells. The activation of TRPV1 may be involved in the regulation of various physiological functions, such as the release of inflammatory mediators in the body, gastrointestinal motility function, and temperature regulation. In recent years, a large number of studies have revealed that TRPV1 plays an important role in the physiological and pathological conditions of the digestive system, cardiovascular system, and respiratory system, but there is no systematic report on TRPV1. The objective of this review is to explain the function and effects of TRPV1 on specific diseases, such as irritable bowel syndrome, hypertension, and asthma, and to further investigate the intrinsic relationship between the expression and function of TRPV1 in those diseases to find new therapeutic targets for the cure of related diseases.

Protective Role of α-Calcitonin Gene-Related Peptide in Cardiovascular Diseases

α-Calcitonin gene-related peptide (α-CGRP) is a regulatory neuropeptide of 37 amino acids. It is widely distributed in the central and peripheral nervous system, predominantly in cell bodies of the dorsal root ganglion (DRG). It is the most potent vasodilator known to date and has inotropic and chronotropic effects. Using pharmacological and genetic approaches, our laboratory and other research groups established the protective role of α-CGRP in various cardiovascular diseases such as heart failure, experimental hypertension, myocardial infarction, and myocardial ischemia/reperfusion injury (I/R injury). α-CGRP acts as a depressor to attenuate the rise in blood pressure in three different models of experimental hypertension: (1) DOC-salt, (2) subtotal nephrectomy-salt, and (3) L-NAME-induced hypertension during pregnancy. Subcutaneous administration of α-CGRP lowers the blood pressure in hypertensive and normotensive humans and rodents. Recent studies also demonstrated that an α-CGRP analog, acylated α-CGRP, with extended half-life (~7 h) reduces blood pressure in Ang-II-induced hypertensive mouse, and protects against abdominal aortic constriction (AAC)-induced heart failure. Together, these studies suggest that α-CGRP, native or a modified form, may be a potential therapeutic agent to treat patients suffering from cardiac diseases.

Nonclinical safety evaluation of erenumab, a CGRP receptor inhibitor for the prevention of migraine

Calcitonin gene-related peptide (CGRP) and its receptor have been implicated as a key mediator in the pathophysiology of migraine. Thus, erenumab, a monoclonal antibody antagonist of the CGRP receptor, administered as a once monthly dose of 70 or 140 mg has been approved for the preventive treatment of migraine in adults. Due to the species specificity of erenumab, the cynomolgus monkey was used in the pharmacology, pharmacokinetics, and toxicology studies to support the clinical program. There were no effects of erenumab on platelets in vitro (by binding, activation or phagocytosis assays). Specific staining of human tissues with erenumab did not indicated any off-target binding. There were no erenumab-related findings in a cardiovascular safety pharmacology study in cynomolgus monkeys or in vitro in human isolated coronary arteries. Repeat-dose toxicology studies conducted in cynomolgus monkeys at dose levels up to 225 mg/kg (1 month) or up to 150 mg/kg (up to 6 months) with twice weekly subcutaneous (SC) doses showed no evidence of erenumab-mediated adverse toxicity. There were no effects on pregnancy, embryo-fetal or postnatal growth and development in an enhanced pre-postnatal development study in the cynomolgus monkey. There was evidence of placental transfer of erenumab based on measurable serum concentrations in the infants up to 3 months post birth. The maternal and developmental no-observed-effect level (NOEL) was the highest dose tested (50 mg/kg SC Q2W). These nonclinical data in total indicate no safety signal of concern to date and provide adequate margins of exposure between the observed safe doses in animals and clinical dose levels.

A generally conserved response to hypoxia in iPSC-derived cardiomyocytes from humans and chimpanzees

Despite anatomical similarities, there are differences in susceptibility to cardiovascular disease (CVD) between primates; humans are prone to myocardial ischemia, while chimpanzees are prone to myocardial fibrosis. Induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) allow for direct inter-species comparisons of the gene regulatory response to CVD-relevant perturbations such as oxygen deprivation, a consequence of ischemia. To gain insight into the evolution of disease susceptibility, we characterized gene expression levels in iPSC-CMs in humans and chimpanzees, before and after hypoxia and re-oxygenation. The transcriptional response to hypoxia is generally conserved across species, yet we were able to identify hundreds of species-specific regulatory responses including in genes previously associated with CVD. The 1,920 genes that respond to hypoxia in both species are enriched for loss-of-function intolerant genes; but are depleted for expression quantitative trait loci and cardiovascular-related genes. Our results indicate that response to hypoxic stress is highly conserved in humans and chimpanzees.

Hydromorphine postconditioning protects isolated rat heart against ischemia-reperfusion injury via activating P13K/Akt/eNOS signaling

INTRODUCTION

Myocardial ischemia/reperfusion injury (myocardial I/R injury) has a high disability rate and mortality. Novel treatments for myocardial I/R injury are necessary.

AIM

In order to explore the protective effect of hydromorphine on myocardial I/R injury, we illuminate the underlying mechanism of the protective effect.

RESULTS

Hydromorphine significantly reduced myocardial infarct size (IFN/AAR), CKMB (Creatine Kinase MB) and TN-T (Troponin T) release, and improved cardiac function compared with I/R group. However, these advantageous effects were partly suppressed in the presence of hydromorphine. Myocardial I/R injury significantly decreased the phosphorylation of Akt and eNOS, and down-regulated total nitric oxide and nitrotyrosine content, while these inhibitory effects were partly abolished by hydromorphine. Conversely, the activated effects of hydromorphine on the phosphorylation of Akt and eNOS, and NO release were totally reversed by LY294002, which, used individually, show the same influence on reperfusion injury.

CONCLUSIONS

These findings suggest that hydromorphine postconditioning may protect isolated rat heart against reperfusion injury via activating P13K/Akt/eNOS signaling.

TRP Channels: Current Perspectives in the Adverse Cardiac Remodeling

Calcium is an important second messenger required not only for the excitation-contraction coupling of the heart but also critical for the activation of cell signaling pathways involved in the adverse cardiac remodeling and consequently for the heart failure. Sustained neurohumoral activation, pressure-overload, or myocardial injury can cause pathologic hypertrophic growth of the heart followed by interstitial fibrosis. The consequent heart’s structural and molecular adaptation might elevate the risk of developing heart failure and malignant arrhythmia. Compelling evidences have demonstrated that Ca²⁺ entry through TRP channels might play pivotal roles in cardiac function and pathology. TRP proteins are classified into six subfamilies: TRPC (canonical), TRPV (vanilloid), TRPM (melastatin), TRPA (ankyrin), TRPML (mucolipin), and TRPP (polycystin), which are activated by numerous physical and/or chemical stimuli. TRP channels participate to the handling of the intracellular Ca²⁺ concentration in cardiac myocytes and are mediators of different cardiovascular alterations. This review provides an overview of the current knowledge of TRP proteins implication in the pathologic process of some frequent cardiac diseases associated with the adverse cardiac remodeling such as cardiac hypertrophy, fibrosis, and conduction alteration.

Transient Receptor Potential Vanilloid 1 Modulates Central Inflammation in Multiple Sclerosis

Introduction: Disease course of multiple sclerosis (MS) is negatively influenced by proinflammatory molecules released by activated T and B lymphocytes and local immune cells. The endovanilloid system plays different physiological functions, and preclinical data suggest that transient receptor potential vanilloid type 1 (TRPV1) could modulate neuroinflammation in this disorder.

Methods: The effect of TRPV1 activation on the release of two main proinflammatory cytokines, tumor necrosis factor (TNF) and interleukin (IL)-6, was explored in activated microglial cells. Furthermore, in a group of 132 MS patients, the association between the cerebrospinal fluid (CSF) levels of TNF and IL-6 and a single nucleotide polymorphisms (SNP) influencing TRPV1 protein expression and function (rs222747) was assessed.

Results: In in vitro experiments, TRPV1 stimulation by capsaicin significantly reduced TNF and IL-6 release by activated microglial cells. Moreover, the anti-inflammatory effect of TRPV1 activation was confirmed by another TRPV1 agonist, the resiniferatoxin (RTX), whose effects were significantly inhibited by the TRPV1 antagonist, 5-iodoresiniferatoxin (5-IRTX). Vice versa, BV2 pre-treatment with 5-IRTX increased the inflammatory response induced by LPS. Moreover, in MS patients, a significant association emerged between TRPV1 SNP rs222747 and CSF TNF levels. In particular, the presence of a G allele, known to result in increased TRPV1 protein expression and function, was associated to lower CSF levels of TNF.

Conclusions: Our results indicate that TRPV1 influences central inflammation in MS by regulating cytokine release by activated microglial cells. The modulation of the endovanilloid system may represent a useful approach to contrast neuroinflammation in MS.

Physiological and Pathological Role of TRPV1, TRPV2 and TRPV4 Channels in Heart

Transient receptor potential vanilloid channel 2 (TRPV2) is required for normal cardiac contractility. The stimulation of TRPV1 in isolated cardiomyocytes can aggravate the effect of hypoxia/ reoxygenation (H/R) on H9C2 cells. The knockout of the TRPV1 gene promotes increased tolerance of the isolated perfused heart to the impact of ischemia/reperfusion (I/R). However, activation of TRPV1 increases the resistance of the heart to I/R due to calcitonin gene-related peptide (CGRP) release from afferent nerve endings. It has been established that TRPV1 and TRPV2 are involved in the pathogenesis of myocardial infarction and, in all likelihood, ensure the cardiac tolerance to the ischemia/reperfusion. It has also been documented that the activation of TRPV4 negatively affects the stability of cardiomyocytes to the H/R. The blockade of TRPV4 can be considered as a new approach to the prevention of I/R injury of the heart. Studies also indicate that TRPV1 is involved in the pathogenesis of cardiac hypertrophy and that TRPV2 channels participate in the pathogenesis of dilated cardiomyopathy. Excessive expression of TRPV2 leads to chronic Ca2+- overload of cardiomyocytes, which may contribute to the development of cardiomyopathy.

Focal selective chemo-ablation of spinal cardiac afferent nerve by resiniferatoxin protects the heart from pressure overload-induced hypertrophy

Resiniferatoxin (RTX), a selective transient receptor potential vanilloid 1 (TRPV1) receptor agonist, can eliminate TRPV1+ primary sensory afferents and blunt cardiac sympathetic afferent reflex for a relatively long period. The present study determined the effects of intrathecal RTX administration on transverse aortic constriction (TAC)-induced cardiac dysfunction and cardiac remodeling in rats. Five days before TAC, RTX (2 μg/10 μl) was injected intrathecally into the T2/T3 interspace of rats. Cardiac sympathetic nerve activities (CSNAs) and cardiac structure and function were determined eight weeks after TAC. Intrathecal RTX administration abolished TRPV1 expression in the dorsal horn and reduced over-activated CSNA in the TAC rat model. Hemodynamic analysis revealed that RTX reduced left ventricular end-diastolic pressure, indicating the improvement of cardiac compliance. Histologic analysis, real-time reverse transcription-polymerase chain reaction, and Western blots showed that RTX prevented TAC-induced cardiac hypertrophy, cardiac fibrosis, and cardiac apoptosis and reduced the expression of apoptotic proteins and myocardial mRNAs. In conclusion, these results demonstrate that focal chemo-ablation of TRPV1+ afferents in the spinal cord protects the heart from pressure overload-induced cardiac remodeling and cardiac dysfunction, which suggest a novel promising therapeutic method for cardiac hypertrophy and diastolic dysfunction.

The Dipeptidyl Peptidase 4 Substrate CXCL12 Has Opposing Cardiac Effects in Young Mice and Aged Diabetic Mice Mediated by Ca2+ Flux and Phosphoinositide 3-Kinase γ

Blood glucose-lowering therapies can positively or negatively affect heart function in type 2 diabetes, or they can have neutral effects. Dipeptidyl peptidase 4 (DPP-4) inhibitors lower blood glucose by preventing the proteolytic inactivation of glucagon-like peptide 1 (GLP-1). However, GLP-1 is not the only peptide substrate of DPP-4. Here, we investigated the GLP-1-independent cardiac effects of DPP-4 substrates. Pointing to GLP-1 receptor (GLP-1R)-independent actions, DPP-4 inhibition prevented systolic dysfunction equally in pressure-overloaded wild-type and GLP-1R knockout mice. Likewise, DPP-4 inhibition or the DPP-4 substrates substance P or C-X-C motif chemokine ligand 12 (CXCL12) improved contractile recovery after no-flow ischemia in the hearts of otherwise healthy young adult mice. Either DPP-4 inhibition or CXCL12 increased phosphorylation of the Ca²⁺ regulatory protein phospholamban (PLN), and CXCL12 directly enhanced cardiomyocyte Ca²⁺ flux. In contrast, hearts of aged obese diabetic mice (which may better mimic the comorbid patient population) had diminished levels of PLN phosphorylation. In this setting, CXCL12 paradoxically impaired cardiac contractility in a phosphoinositide 3-kinase γ-dependent manner. These findings indicate that the cardiac effects of DPP-4 inhibition primarily occur through GLP-1R-independent processes and that ostensibly beneficial DPP-4 substrates can paradoxically worsen heart function in the presence of comorbid diabetes.