Induction of antiviral interferon-stimulated genes by neuronal STING promotes the resolution of pain in mice.

Inflammation and pain are intertwined responses to injury, infection, or chronic diseases. While acute inflammation is essential in determining pain resolution and opioid analgesia, maladaptive processes occurring during resolution can lead to the transition to chronic pain. Here we found that inflammation activates the cytosolic DNA-sensing protein stimulator of IFN genes (STING) in dorsal root ganglion nociceptors. Neuronal activation of STING promotes signaling through TANK-binding kinase 1 (TBK1) and triggers an IFN-ß response that mediates pain resolution. Notably, we found that mice expressing a nociceptor-specific gain-of-function mutation in STING exhibited an IFN gene signature that reduced nociceptor excitability and inflammatory hyperalgesia through a KChIP1-Kv4.3 regulation. Our findings reveal a role of IFN-regulated genes and KChIP1 downstream of STING in the resolution of inflammatory pain.

Biofilm exopolysaccharides alter sensory-neuron-mediated sickness during lung infection.

Infections of the lung cause observable sickness thought to be secondary to inflammation. Signs of sickness are crucial to alert others via behavioral-immune responses to limit contact with contagious individuals. Gram-negative bacteria produce exopolysaccharide (EPS) that provides microbial protection; however, the impact of EPS on sickness remains uncertain. Using genome-engineered Pseudomonas aeruginosa (P. aeruginosa) strains, we compared EPS-producers versus non-producers and a virulent Escherichia coli (E. coli) lung infection model in male and female mice. EPS-negative P. aeruginosa and virulent E. coli infection caused severe sickness, behavioral alterations, inflammation, and hypothermia mediated by TLR4 detection of the exposed lipopolysaccharide (LPS) in lung TRPV1+ sensory neurons. However, inflammation did not account for sickness. Stimulation of lung nociceptors induced acute stress responses in the paraventricular hypothalamic nuclei by activating corticotropin-releasing hormone neurons responsible for sickness behavior and hypothermia. Thus, EPS-producing biofilm pathogens evade initiating a lung-brain sensory neuronal response that results in sickness.

Non-Intoxicating Cannabinoids in Visceral Pain.

Cannabis and cannabis products are becoming increasingly popular options for symptom management of inflammatory bowel diseases, particularly abdominal pain. While anecdotal and patient reports suggest efficacy of these compounds for these conditions, clinical research has shown mixed results. To date, clinical research has focused primarily on delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD). THC is a ligand of classical cannabinoid receptors (CBRs). CBD is one of a large group of nonintoxicating cannabinoids (niCBs) that mediate their effects on both CBRs and through non-CBR mechanisms of action. Because they are not psychotropic, there is increasing interest and availability of niCBs. The numerous niCBs show potential to rectify abnormal intestinal motility as well as have anti-inflammatory and analgesic effects. The effects of niCBs are frequently not mediated by CBRs, but rather through actions on other targets, including transient receptor potential channels and voltage-gated ion channels. Additionally, evidence suggests that niCBs can be combined to increase their potency through what is termed the entourage effect. This review examines the pre-clinical data available surrounding these niCBs in treatment of abdominal pain with a focus on non-CBR mechanisms.

The neuronal tyrosine kinase receptor ligand ALKAL2 mediates persistent pain.

The anaplastic lymphoma kinase (ALK) is a receptor tyrosine kinase known for its oncogenic potential that is involved in the development of the peripheral and central nervous system. ALK receptor ligands ALKAL1 and ALKAL2 were recently found to promote neuronal differentiation and survival. Here, we show that inflammation or injury enhanced ALKAL2 expression in a subset of TRPV1+ sensory neurons. Notably, ALKAL2 was particularly enriched in both mouse and human peptidergic nociceptors, yet weakly expressed in nonpeptidergic, large-diameter myelinated neurons or in the brain. Using a coculture expression system, we found that nociceptors exposed to ALKAL2 exhibited heightened excitability and neurite outgrowth. Intraplantar CFA or intrathecal infusion of recombinant ALKAL2 led to ALK phosphorylation in the lumbar dorsal horn of the spinal cord. Finally, depletion of ALKAL2 in dorsal root ganglia or blocking ALK with clinically available compounds crizotinib or lorlatinib reversed thermal hyperalgesia and mechanical allodynia induced by inflammation or nerve injury, respectively. Overall, our work uncovers the ALKAL2/ALK signaling axis as a central regulator of nociceptor-induced sensitization. We propose that clinically approved ALK inhibitors used for non-small cell lung cancer and neuroblastomas could be repurposed to treat persistent pain conditions.

Monitoring TRPC7 Conformational Changes by BRET Following GPCR Activation.

Transient receptor potential canonical (TRPC) channels are membrane proteins involved in regulating Ca2+ homeostasis, and whose functions are modulated by G protein-coupled receptors (GPCR). In this study, we developed bioluminescent resonance energy transfer (BRET) biosensors to better study channel conformational changes following receptor activation. For this study, two intramolecular biosensors, GFP10-TRPC7-RLucII and RLucII-TRPC7-GFP10, were constructed and were assessed following the activation of various GPCRs. We first transiently expressed receptors and the biosensors in HEK293 cells, and BRET levels were measured following agonist stimulation of GPCRs. The activation of GPCRs that engage Gαq led to a Gαq-dependent BRET response of the functional TRPC7 biosensor. Focusing on the Angiotensin II type-1 receptor (AT1R), GFP10-TRPC7-RLucII was tested in rat neonatal cardiac fibroblasts, expressing endogenous AT1R and TRPC7. We detected similar BRET responses in these cells, thus validating the use of the biosensor in physiological conditions. Taken together, our results suggest that activation of Gαq-coupled receptors induce conformational changes in a novel and functional TRPC7 BRET biosensor.

Skin-resident dendritic cells mediate postoperative pain via CCR4 on sensory neurons.

Inflammatory pain, such as hypersensitivity resulting from surgical tissue injury, occurs as a result of interactions between the immune and nervous systems with the orchestrated recruitment and activation of tissue-resident and circulating immune cells to the site of injury. Our previous studies identified a central role for Ly6Clow myeloid cells in the pathogenesis of postoperative pain. We now show that the chemokines CCL17 and CCL22, with their cognate receptor CCR4, are key mediators of this response. Both chemokines are up-regulated early after tissue injury by skin-resident dendritic and Langerhans cells to act on peripheral sensory neurons that express CCR4. CCL22, and to a lesser extent CCL17, elicit acute mechanical and thermal hypersensitivity when administered subcutaneously; this response abrogated by pharmacological blockade or genetic silencing of CCR4. Electrophysiological assessment of dissociated sensory neurons from naïve and postoperative mice showed that CCL22 was able to directly activate neurons and enhance their excitability after injury. These responses were blocked using C 021 and small interfering RNA (siRNA)-targeting CCR4. Finally, our data show that acute postoperative pain is significantly reduced in mice lacking CCR4, wild-type animals treated with CCR4 antagonist/siRNA, as well as transgenic mice depleted of dendritic cells. Together, these results suggest an essential role for the peripheral CCL17/22:CCR4 axis in the genesis of inflammatory pain via direct communication between skin-resident dendritic cells and sensory neurons, opening therapeutic avenues for its control.

Spinal A3 adenosine receptor activation acutely restores morphine antinociception in opioid tolerant male rats.

Opioids are potent analgesics, but their pain-relieving effects diminish with repeated use. The reduction in analgesic potency is a hallmark of opioid analgesic tolerance, which hampers opioid pain therapy. In the central nervous system, opioid analgesia is critically modulated by adenosine, a purine nucleoside implicated in the beneficial and detrimental actions of opioid medications. Here, we focus on the A3 adenosine receptor (A3 AR) in opioid analgesic tolerance. Intrathecal administration of the A3 AR agonist MRS5698 with daily systemic morphine in male rats attenuated the reduction in morphine antinociception over 7 days. In rats with established morphine tolerance, intrathecal MRS5698 partially restored the antinociceptive effects of morphine. However, when MRS5698 was discontinued, these animals displayed a reduced antinociceptive response to morphine. Our results suggest that MRS5698 acutely and transiently potentiates morphine antinociception in tolerant rats. By contrast, in morphine-naïve rats MRS5698 treatment did not impact thermal nociceptive threshold or affect antinociceptive response to a single injection of morphine. Furthermore, we found that morphine-induced adenosine release in cerebrospinal fluid was blunted in tolerant animals, but total spinal A3 AR expression was not affected. Collectively, our findings indicate that spinal A3 AR activation acutely potentiates morphine antinociception in the opioid tolerant state.

Gut-innervating TRPV1+ Neurons Drive Chronic Visceral Pain via Microglial P2Y12 Receptor.

BACKGROUND & AIMS: Chronic abdominal pain is a common symptom of inflammatory bowel diseases (IBDs). Peripheral and central mechanisms contribute to the transition from acute to chronic pain during active disease and clinical remission. Lower mechanical threshold and hyperexcitability of visceral afferents induce gliosis in central pain circuits, leading to persistent visceral hypersensitivity (VHS). In the spinal cord, microglia, the immune sentinels of the central nervous system, undergo activation in multiple models of VHS. Here, we investigated the mechanisms of microglia activation to identify centrally acting analgesics for chronic IBD pain. METHODS: Using Designer Receptors Exclusively Activated by Designer Drugs (DREADD) expressed in transient receptor potential vanilloid member 1-expressing visceral neurons that sense colonic inflammation, we tested whether neuronal activity was indispensable to control microglia activation and VHS. We then investigated the neuron-microglia signaling system involved in visceral pain chronification. RESULTS: We found that chemogenetic inhibition of transient receptor potential vanilloid member 1+ visceral afferents prevents microglial activation in the spinal cord and subsequent VHS in colitis mice. In contrast, chemogenetic activation, in the absence of colitis, enhanced microglial activation associated with VHS. We identified a purinergic signaling mechanism mediated by neuronal adenosine triphosphate (ATP) and microglial P2Y12 receptor, triggering VHS in colitis. Inhibition of P2RY12 prevented microglial reactivity and chronic VHS post-colitis. CONCLUSIONS: Overall, these data provide novel insights into the central mechanisms of chronic visceral pain and suggest that targeting microglial P2RY12 signaling could be harnessed to relieve pain in patients with IBD who are in remission.

Nr4A1 modulates inflammation-associated intestinal fibrosis and dampens fibrogenic signaling in myofibroblasts.

Intestinal fibrosis is a common complication of the inflammatory bowel diseases (IBDs), contributing to tissue stiffening and luminal narrowing. Human nuclear receptor 4A 1 (NR4A1) was previously reported to regulate mesenchymal cell function and dampen fibrogenic signaling. NR4A1 gene variants are associated with IBD risk, and it has been shown to regulate intestinal inflammation. Here, we tested the hypothesis that NR4A1 acts as a negative regulator of intestinal fibrosis through regulating myofibroblast function. Using the SAMP1/YitFc mouse, we tested whether two pharmacological agents known to enhance NR4A1 signaling, cytosporone B (Csn-B) or 6-mercaptopurine (6-MP), could reduce fibrosis. We also used the dextran sulfate sodium (DSS) model of colitis and assessed the magnitude of colonic fibrosis in mouse nuclear receptor 4A 1 (Nr4a1-/-) and their wild-type littermates (Nr4a1+/+). Lastly, intestinal myofibroblasts isolated from Nr4a1-/- and Nr4a1+/+ mice or primary human intestinal myofibroblasts were stimulated with transforming growth factor-ß1 (TGF-ß1), in the presence or absence of Csn-B or 6-MP, and proliferation and ECM gene expression assessed. Csn-B or 6-MP treatment significantly reduced ileal thickness, collagen, and overall ECM content in SAMP1/YitFc mice. This was associated with a reduction in proliferative markers within the mesenchymal compartment. Nr4a1-/- mice exposed to DSS exhibited increased colonic thickening and ECM content. Nr4a1-/- myofibroblasts displayed enhanced TGF-ß1-induced proliferation. Furthermore, Csn-B or 6-MP treatment was antiproliferative in Nr4a1+/+ but not Nr4a1-/- cells. Lastly, activating NR4A1 in human myofibroblasts reduced TGF-ß1-induced collagen deposition and fibrosis-related gene expression. Our data suggest that NR4A1 can attenuate fibrotic processes in intestinal myofibroblasts and could provide a valuable clinical target to treat inflammation-associated intestinal fibrosis.NEW & NOTEWORTHY Fibrosis and increased muscle thickening contribute to stricture formation and intestinal obstruction, a complication that occurs in 30%-50% of patients with CD within 10 yr of disease onset. More than 50% of those who undergo surgery to remove the obstructed bowel will experience stricture recurrence. To date, there are no drug-based approaches approved to treat intestinal strictures. In the current submission, we identify NR4A1 as a novel target to treat inflammation-associated intestinal fibrosis.

TRPV1 Activation Promotes ß-arrestin2 Interaction with the Ribosomal Biogenesis Machinery in the Nucleolus:Implications for p53 Regulation and Neurite Outgrowth.

Transient receptor potential vanilloids (TRPV1) are non-selective cation channels that sense and transduce inflammatory pain signals. We previously reported that activation of TRPV1 induced the translocation of ß-arrestin2 (ARRB2) from the cytoplasm to the nucleus, raising questions about the functional role of ARRB2 in the nucleus. Here, we determined the ARRB2 nuclear signalosome by conducting a quantitative proteomic analysis of the nucleus-sequestered L395Q ARRB2 mutant, compared to the cytosolic wild-type ARRB2 (WT ARRB2), in a heterologous expression system. We identified clusters of proteins that localize to the nucleolus and are involved in ribosomal biogenesis. Accordingly, L395Q ARRB2 or WT ARRB2 after capsaicin treatment were found to co-localize and interact with the nucleolar marker nucleophosmin (NPM1), treacle protein (TCOF1) and RNA polymerase I (POL I). We further investigated the role of nuclear ARRB2 signaling in regulating neuroplasticity. Using neuroblastoma (neuro2a) cells and dorsal root ganglia (DRG) neurons, we found that L395Q ARRB2 mutant increased POL I activity, inhibited the tumor suppressorp53 (p53) level and caused a decrease in the outgrowth of neurites. Together, our results suggest that the activation of TRPV1 promotes the ARRB2-mediated regulation of ribosomal biogenesis in the nucleolus. The ARRB2-TCOF1-p53 checkpoint signaling pathway might be involved in regulating neurite outgrowth associated with pathological pain conditions.

PKCε stimulation of TRPV1 orchestrates carotid body responses to asthmakines.

KEY POINTS: We have previously shown that carotid body stimulation by lysophosphatidic acid elicits a reflex stimulation of vagal efferent activity sufficient to cause bronchoconstriction in asthmatic rats. Here, we show that pathophysiological concentrations of asthma-associated prototypical Th2 cytokines also stimulate the carotid bodies. Stimulation of the carotid bodies by these asthmakines involves a PKCε-transient receptor potential vanilloid 1 (TRPV1) signalling mechanism likely dependent on TRPV1 S502 and T704 phosphorylation sites. As the carotid bodies' oxygen sensitivity is independent of PKCε-TRPV1 signalling, systemic blockade of PKCε may provide a novel therapeutic target to reduce allergen-induced asthmatic bronchoconstriction. Consistent with the therapeutic potential of blocking the PKCε-TRPV1 pathway, systemic delivery of a PKCε-blocking peptide suppresses asthmatic respiratory distress in response to allergen and reduces airway hyperresponsiveness to bradykinin. ABSTRACT: The autonomic nervous system orchestrates organ-specific, systemic and behavioural responses to inflammation. Recently, we demonstrated a vital role for lysophosphatidic acid in stimulating the primary autonomic oxygen chemoreceptors, the carotid bodies, in parasympathetic-mediated asthmatic airway hyperresponsiveness. However, the cacophony of stimulatory factors and cellular mechanisms of carotid body activation are unknown. Therefore, we set out to determine the intracellular signalling involved in carotid body-mediated sensing of asthmatic blood-borne inflammatory mediators. We employed a range of in vitro and rat in situ preparations, site-directed mutagenesis, patch-clamp, nerve recordings and pharmacological inhibition to assess cellular signalling. We show that the carotid bodies are also sensitive to asthma-associated prototypical Th2 cytokines which elicit sensory nerve excitation. This provides additional asthmatic ligands contributing to the previously established reflex arc resulting in efferent vagal activity and asthmatic bronchoconstriction. This novel sensing role for the carotid body is mediated by a PKCε-dependent stimulation of transient receptor potential vanilloid 1 (TRPV1), likely via TRPV1 phosphorylation at sites T704 and S502. Importantly, carotid body oxygen sensing was unaffected by blocking either PKCε or TRPV1. Further, we demonstrate that systemic PKCε blockade reduces asthmatic respiratory distress in response to allergen and airway hyperresponsiveness. These discoveries support an inflammation-dependent, oxygen-independent function for the carotid body and suggest that targeting PKCε provides a novel therapeutic option to abate allergic airway disease without altering life-saving autonomic hypoxic reflexes.

TRPV1-Targeted Drugs in Development for Human Pain Conditions.

The transient receptor potential vanilloid-1 (TRPV1) is a non-specific cation channel known for its sensitivity to pungent vanilloid compound (i.e. capsaicin) and noxious stimuli, including heat, low pH or inflammatory mediators. TRPV1 is found in the somatosensory system, particularly primary afferent neurons that respond to damaging or potentially damaging stimuli (nociceptors). Stimulation of TRPV1 evokes a burning sensation, reflecting a central role of the channel in pain. Pharmacological and genetic studies have validated TRPV1 as a therapeutic target in several preclinical models of chronic pain, including cancer, neuropathic, postoperative and musculoskeletal pain. While antagonists of TRPV1 were found to be a valuable addition to the pain therapeutic toolbox, their clinical use has been limited by detrimental side effects, such as hyperthermia. In contrast, capsaicin induces a prolonged defunctionalisation of nociceptors and thus opened the door to the development of a new class of therapeutics with long-lasting pain-relieving effects. Here we review the list of TRPV1 agonists undergoing clinical trials for chronic pain management, and discuss new indications, formulations or combination therapies being explored for capsaicin. While the analgesic pharmacopeia for chronic pain patients is ancient and poorly effective, modern TRPV1-targeted drugs could rapidly become available as the next generation of analgesics for a broad spectrum of pain conditions.

The cool things to know about TRPM8!

Transient receptor potential melastatin 8 (TRPM8) channels play a central role in the detection of environmental cold temperatures in the somatosensory system. TRPM8 is found in a subset of unmyelinated (C-type) afferents located in the dorsal root (DRG) and trigeminal ganglion (TG). Cold hypersensitivity is a common symptom of neuropathic pain conditions caused by cancer therapy, spinal cord injury, viral infection, multiple sclerosis, diabetes, or withdrawal symptoms associated with chronic morphine treatment. Therefore, TRPM8 has received great attention as a therapeutic target. However, as the activity of TRPM8 is unique in sensing cool temperature as well as warming, it is critical to understand the signaling transduction pathways that control modality-specific activity of TRPM8 in healthy versus pathological settings. This review summarizes recent advances in our understanding of the mechanisms involved in the regulation of the TRPM8 activity.

Neural control of gut homeostasis.

The gut-brain axis is a coordinated communication system that not only maintains homeostasis, but significantly influences higher cognitive functions and emotions, as well as neurological and behavioral disorders. Among the large populations of sensory and motor neurons that innervate the gut, insights into the function of primary afferent nociceptors, whose cell bodies reside in the dorsal root ganglia and nodose ganglia, have revealed their multiple crosstalk with several cell types within the gut wall, including epithelial, vascular, and immune cells. These bidirectional communications have immunoregulatory functions, control host response to pathogens, and modulate sensations associated with gastrointestinal disorders, through activation of immune cells and glia in the peripheral and central nervous system, respectively. Here, we will review the cellular and neurochemical basis of these interactions at the periphery, in dorsal root ganglia, and in the spinal cord. We will discuss the research gaps that should be addressed to get a better understanding of the multifunctional role of sensory neurons in maintaining gut homeostasis and regulating visceral sensitivity.

Colitis-Induced Microbial Perturbation Promotes Postinflammatory Visceral Hypersensitivity.

BACKGROUND & AIMS: Despite achieving endoscopic remission, more than 20% of inflammatory bowel disease patients experience chronic abdominal pain. These patients have increased rectal transient receptor potential vanilloid-1 receptor (TRPV1) expression, a key transducer of inflammatory pain. Because inflammatory bowel disease patients in remission exhibit dysbiosis and microbial manipulation alters TRPV1 function, our goal was to examine whether microbial perturbation modulated transient receptor potential function in a mouse model. METHODS: Mice were given dextran sodium sulfate (DSS) to induce colitis and were allowed to recover. The microbiome was perturbed by using antibiotics as well as fecal microbial transplant (FMT). Visceral and somatic sensitivity were assessed by recording visceromotor responses to colorectal distention and using hot plate/automated Von Frey tests, respectively. Calcium imaging of isolated dorsal root ganglia neurons was used as an in vitro correlate of nociception. The microbiome composition was evaluated via 16S rRNA gene variable region V4 amplicon sequencing, whereas fecal short-chain fatty acids (SCFAs) were assessed by using targeted mass spectrometry. RESULTS: Postinflammatory DSS mice developed visceral and somatic hyperalgesia. Antibiotic administration during DSS recovery induced visceral, but not somatic, hyperalgesia independent of inflammation. FMT of postinflammatory DSS stool into antibiotic-treated mice increased visceral hypersensitivity, whereas FMT of control stool reversed antibiotics' sensitizing effects. Postinflammatory mice exhibited both increased SCFA-producing species and fecal acetate/butyrate content compared with controls. Capsaicin-evoked calcium responses were increased in naive dorsal root ganglion neurons incubated with both sodium butyrate/propionate alone and with colonic supernatants derived from postinflammatory mice. CONCLUSIONS: The microbiome plays a central role in postinflammatory visceral hypersensitivity. Microbial-derived SCFAs can sensitize nociceptive neurons and may contribute to the pathogenesis of postinflammatory visceral pain.

Chronic morphine regulates TRPM8 channels via MOR-PKCß signaling.

Postoperative shivering and cold hypersensitivity are major side effects of acute and chronic opioid treatments respectively. TRPM8 is a cold and menthol-sensitive channel found in a subset of dorsal root ganglion (DRG) nociceptors. Deletion or inhibition of the TRPM8 channel was found to prevent the cold hyperalgesia induced by chronic administration of morphine. Here, we examined the mechanisms by which morphine was able to promote cold hypersensitivity in DRG neurons and transfected HEK cells. Mice daily injected with morphine for 5 days developed cold hyperalgesia. Treatment with morphine did not alter the expressions of cold sensitive TREK-1, TRAAK and TRPM8 in DRGs. However, TRPM8-expressing DRG neurons isolated from morphine-treated mice exhibited hyperexcitability. Sustained morphine treatment in vitro sensitized TRPM8 responsiveness to cold or menthol and reduced activation-evoked desensitization of the channel. Blocking phospholipase C (PLC) as well as protein kinase C beta (PKCß), but not protein kinase A (PKA) or Rho-associated protein kinase (ROCK), restored channel desensitization. Identification of two PKC phosphorylation consensus sites, S1040 and S1041, in the TRPM8 and their site-directed mutation were able to prevent the MOR-induced reduction in TRPM8 desensitization. Our results show that activation of MOR by morphine 1) promotes hyperexcitability of TRPM8-expressing neurons and 2) induces a PKCß-mediated reduction of TRPM8 desensitization. This MOR-PKCß dependent modulation of TRPM8 may underlie the onset of cold hyperalgesia caused by repeated administration of morphine. Our findings point to TRPM8 channel and PKCß as important targets for opioid-induced cold hypersensitivity.

Mutations in calmodulin-binding domains of TRPV4/6 channels confer invasive properties to colon adenocarcinoma cells.

Transient receptor potential (TRP) channels form a family of polymodal cation channels gated by thermal, mechanical, or chemical stimuli, with many of them involved in the control of proliferation, apoptosis, or cell cycle. From an evolutionary point of view, TRP family is characterized by high conservation of duplicated genes originating from whole-genome duplication at the onset of vertebrates. The conservation of such "ohnolog" genes is theoretically linked to an increased probability of generating phenotypes deleterious for the organism upon gene mutation. We aimed to test experimentally the hypothesis that TRP mutations, in particular gain-of-function, could be involved in the generation of deleterious phenotypes involved in cancer, such as gain of invasiveness. Indeed, a number of TRP channels have been linked to cancer progression, and exhibit changes in expression levels in various types of cancers. However, TRP mutations in cancer have been poorly documented. We focused on 2 TRPV family members, TRPV4 and TRPV6, and studied the effect of putative gain-of-function mutations on invasiveness properties. TRPV channels have a C-terminal calmodulin-binding domain (CaMBD) that has important functions for regulating protein function, through different mechanisms depending on the channel (channel inactivation/potentiation, cytoskeleton regulation). We studied the effect of mutations mimicking constitutive phosphorylation in TRPV4 and TRPV6 CaMBDs: TRPV4 S823D, S824D and T813D, TRPV6 S691D, S692D and T702. We found that most of these mutants induced a strong gain of invasiveness of colon adenocarcinoma SW480 cells, both for TRPV4 and TRPV6. While increased invasion with TRPV6 S692D and T702D mutants was correlated to increased mutant channel activity, it was not the case for TRPV4 mutants, suggesting different mechanisms with the same global effect of gain in deleterious phenotype. This highlights the potential importance to search for TRP mutations involved in cancer.

Microbiota: a novel regulator of pain.

Among the various regulators of the nervous system, the gut microbiota has been recently described to have the potential to modulate neuronal cells activation. While bacteria-derived products can induce aversive responses and influence pain perception, recent work suggests that "abnormal" microbiota is associated with neurological diseases such as Alzheimer's, Parkinson's disease or autism spectrum disorder (ASD). Here we review how the gut microbiota modulates afferent sensory neurons function and pain, highlighting the role of the microbiota/gut/brain axis in the control of behaviors and neurological diseases. We outline the changes in gut microbiota, known as dysbiosis, and their influence on painful gastrointestinal disorders. Furthermore, both direct host/microbiota interaction that implicates activation of "pain-sensing" neurons by metabolites, or indirect communication via immune activation is discussed. Finally, treatment options targeting the gut microbiota, including pre- or probiotics, will be proposed. Further studies on microbiota/nervous system interaction should lead to the identification of novel microbial ligands and host receptor-targeted drugs, which could ultimately improve chronic pain management and well-being.