Inhibition of phosphodiesterase-4 in the spinal dorsal horn ameliorates neuropathic pain via cAMP-cytokine-Cx43 signaling in mice

Genome-wide association study on chronic postsurgical pain after abdominal surgeries in the UK Biobank

INTRODUCTION

Chronic pain is one of the most common and severe complications after surgery, affecting quality of life and overall wellbeing of patients. Several risk factors have been identified but the mechanisms of chronic postsurgical pain development remain unclear. This study aimed to identify single-nucleotide polymorphisms associated with developing chronic postsurgical pain after abdominal surgery, one of the most common types of surgery.

METHODS

A genome-wide association study was performed on 27,603 patients from the UK Biobank who underwent abdominal surgery. The robustness of identified loci was validated by split-half validation analysis. Functionally related top loci were selected for expression validation in clinical samples of adhesions from patients with and without pain.

RESULTS

One locus (rs185545327) reached genome-wide significance for association with chronic postsurgical pain development, and 10 loci surpassed the suggestively significant threshold (p < 1 × 10-6). In the robustness analysis, eight loci had at least nominal significance. The loci passing the suggestively significant threshold were mapped to 15 genes, of which two loci contained pain-related genes (SRPK2, PDE4D). Although marginally approaching statistical significance in the expression validation of clinical samples, the detection rate and expression level of PDE4D were modestly higher in patients with pain compared with those in the control group.

DISCUSSION

This study provides preliminary evidence for genetic risk factors implicated in chronic postsurgical pain following abdominal surgery, particularly the PDE4D gene, which has been associated with pain in previous studies. The findings add to evidence suggesting potential for the future development of a clinically applicable tool for personalised risk prediction, aiding clinicians in stratifying patients and enhancing clinical decision-making through individualised risk assessments.

Cytokines reprogram airway sensory neurons in asthma

Nociceptor neurons play a crucial role in maintaining the body's homeostasis by detecting and responding to potential environmental dangers. However, this function can be detrimental during allergic reactions, as vagal nociceptors contribute to immune cell infiltration, bronchial hypersensitivity, and mucus imbalance in addition to causing pain and coughing. Despite this, the specific mechanisms by which nociceptors acquire pro-inflammatory characteristics during allergic reactions are not yet fully understood. In this study, we investigate the changes in the molecular profile of airway nociceptor neurons during allergic airway inflammation and identify the signals driving such reprogramming. Using retrograde tracing and lineage reporting, we identify a specific class of inflammatory vagal nociceptor neurons that exclusively innervate the airways. In the ovalbumin mouse model of allergic airway inflammation, these neurons undergo significant reprogramming characterized by the upregulation of the neuropeptide Y (NPY) receptor Npy1r. A screening of cytokines and neurotrophins reveals that interleukin 1β (IL-1β), IL-13, and brain-derived neurotrophic factor (BDNF) drive part of this reprogramming. IL-13 triggers Npy1r overexpression in nociceptors via the JAK/STAT6 pathway. In parallel, NPY is released into the bronchoalveolar fluid of asthmatic mice, which limits the excitability of nociceptor neurons. Single-cell RNA sequencing of lung immune cells reveals that a cell-specific knockout of NPY1R in nociceptor neurons in asthmatic mice altered T cell infiltration. Opposite findings are observed in asthmatic mice in which nociceptor neurons are chemically ablated. In summary, allergic airway inflammation reprograms airway nociceptor neurons to acquire a pro-inflammatory phenotype, while a compensatory mechanism involving NPY1R limits the activity of nociceptor neurons.

CaV3.2 T-type calcium channels contribute to CGRP- induced allodynia in a rodent model of experimental migraine

BACKGROUND

Migraine is a painful neurological syndrome characterized by attacks of throbbing headache, of moderate to severe intensity, which is associated with photo- and phono- sensitivity as well as nausea and vomiting. It affects about 15% of the world's population being 2-3 times more prevalent in females. The calcitonin gene-related peptide (CGRP) is a key mediator in the pathophysiology of migraine, and a significant advance in the field has been the development of anti-CGRP therapies. The trigeminal ganglion (TG) is thought to be an important site of action for these drugs. Moreover, experimental migraine can be induced by CGRP injection in the TG. The signaling pathway induced by CGRP in the TG is not fully understood, but studies suggest that voltage-gated calcium channels contribute to CGRP effects relevant to migraine.

OBJECTIVE

We hypothesised that CGRP injection in the TG enhances CaV3.2 T-type calcium channel currents to contribute to the development of periorbital mechanical allodynia.

RESULTS

A Co-Immunoprecipitation assay in tsA-201 cells revealed that CaV3.2 channels form a complex with RAMP-1, a component of the CGRP receptor. Constitutive CGRPR activity was able to inhibit CaV3.2 channels and induce a depolarizing shift in both activation and inactivation curves. Incubation of TG neurons with CGRP increased T-type current density by ~ 3.6 fold, an effect that was not observed in TG neurons from CaV3.2 knockout mice. Incubation of TG neurons with Z944, a pan T-type channel blocker, resulted in an approximately 80% inhibition of T-type currents. In vivo, this treatment abolished the development of periorbital mechanical allodynia induced by CGRP in male and female mice. Likewise, CaV3.2 knockout mice did not develop periorbital mechanical allodynia after intraganglionic CGRP injection. Finally, we demonstrated that the CGRP effect depends on the activation of its canonical GPCR, followed by protein kinase A activation.

CONCLUSION

The present study suggests that CGRP modulates CaV3.2 in the TG, an effect possibly mediated by the canonical CGRP receptor and PKA activation. The increase in T-type currents in the TG may represent a contributing factor for the initiation and maintenance of the headache pain during migraine.

Genomic variations associated with risk and protection against vincristine-induced peripheral neuropathy in pediatric cancer patients

Vincristine-induced peripheral neuropathy is a common and highly debilitating toxicity from vincristine treatment that affects quality of life and often requires dose reduction, potentially affecting survival. Although previous studies demonstrated genetic factors are associated with vincristine neuropathy risk, the clinical relevance of most identified variants is limited by small sample sizes and unclear clinical phenotypes. A genome-wide association study was conducted in 1100 cases and controls matched by vincristine dose and genetic ancestry, uncovering a statistically significant (p < 5.0 × 10-8) variant in MCM3AP gene that substantially increases the risk of neuropathy and 12 variants protective against neuropathy within/near SPDYA, METTL8, PDE4D, FBN2, ZFAND3, NFIB, PAPPA, LRRTM3, NRG3, VTI1A, ARHGAP5, and ACTN1. A follow-up pathway analysis reveals the involvement of four key pathways, including nerve structure and development, myelination, neuronal transmission, and cytoskeleton/microfibril function pathways. These findings present potential actionable genomic markers of vincristine neuropathy and offer opportunities for tailored interventions to improve vincristine safety in children with cancer. This study is registered with ClinicalTrials.gov under the title National Active Surveillance Network and Pharmacogenomics of Adverse Drug Reactions in Children (ID NCT00414115, registered on December 21, 2006).

TLR-4: a promising target for chemotherapy-induced peripheral neuropathy

Chemotherapy-induced peripheral neuropathy (CIPN) affects a significant majority of cancer patients, with up to 80% experiencing this severe and dose-limiting side effect while undergoing anti-cancer treatment. CIPN can be induced by a variety of drugs commonly employed in the management of both solid tumors and hematologic cancers. The inadequacies in comprehending the pharmacological interventions associated with CIPN and the subsequent signaling pathways have significantly contributed to the disappointing outcomes of several drugs in clinical trials. Recent investigations in pain research have demonstrated a growing inclination toward addressing neuro-inflammation as a strategy for managing chronic pain conditions. Notably, toll-like receptor-4 (TLR-4) has emerged as a key player in immune system activation and is undergoing extensive research. In this review, we emphasize the potential role of TLR-4 in neuropathic pain, highlighting its promise as a target for CIPN treatment. Furthermore, we explore and analyse the intricate interplay between TLR-4, diverse immune cells, downstream pathways, and receptors within the context of CIPN. A comprehensive exploration of these interactions provides valuable insights into the central role of TLR-4 in CIPN development, paving the way for potential ground-breaking therapeutic approaches to alleviate this debilitating condition.

Upregulation of Phosphodiesterase 7A Contributes to Concurrent Pain and Depression via Inhibition of cAMP-PKA-CREB-BDNF Signaling and Neuroinflammation in the Hippocampus of Mice

BACKGROUND

Phosphodiesterases (PDEs) are enzymes that catalyze the hydrolysis of cyclic adenosine monophosphate AMP (cAMP) and/or cyclic guanosine monophosphate (cGMP). PDE inhibitors can mitigate chronic pain and depression when these disorders occur individually; however, there is limited understanding of their role in concurrent chronic pain and depression. We aimed to evaluate the mechanisms of action of PDE using 2 mouse models of concurrent chronic pain and depression.

METHODS

C57BL/6J mice were subjected to partial sciatic nerve ligation (PSNL) to induce chronic neuropathic pain or injected with complete Freund's adjuvant (CFA) to induce inflammatory pain, and both animals showed depression-like behavior. First, we determined the change in PDE expression in both animal models. Next, we determined the effect of PDE7 inhibitor BRL50481 or hippocampal PDE7A knockdown on PSNL- or CFA-induced chronic pain and depression-like behavior. We also investigated the role of cAMP-protein kinase A (PKA)-cAMP response element binding protein (CREB)-brain-derived neurotrophic factor (BDNF) signaling and neuroinflammation in the effect of PDE7A inhibition on PSNL- or CFA-induced chronic pain and depression-like behavior.

RESULTS

This induction of chronic pain and depression in the 2 animal models upregulated hippocampal PDE7A. Oral administration of PDE7 inhibitor, BRL50481, or hippocampal PDE7A knockdown significantly reduced mechanical hypersensitivity and depression-like behavior. Hippocampal PDE7 inhibition reversed PSNL- or CFA-induced downregulation of cAMP and BDNF and the phosphorylation of PKA, CREB, and p65. cAMP agonist forskolin reversed these changes and caused milder behavioral symptoms of pain and depression. BRL50481 reversed neuroinflammation in the hippocampus in PSNL mice.

CONCLUSIONS

Hippocampal PDE7A mediated concurrent chronic pain and depression in both mouse models by inhibiting cAMP-PKA-CREB-BDNF signaling. Inhibiting PDE7A or activating cAMP-PKA-CREB-BDNF signaling are potential strategies to treat concurrent chronic pain and depression.

Neuropathic pain, antidepressant drugs, and inflammation: a narrative review

BACKGROUND

Neuropathic pain (NP) is a chronic and disabling condition, caused by a lesion or disease of the somatosensory nervous system, characterized by a systemic inflammatory state. Signs and associated symptoms are rarely recognized, and response to usual analgesic drugs is poor. Antidepressant drugs are first-line agents for the treatment of NP. This narrative review aims to summarize the role of antidepressant drugs in treating NP and their mechanism of action, focusing on the effects on inflammatory cytokines.

MAIN TEXT

Peripheral nerve injury leads to a local inflammatory response and to the disruption of the blood-medullary barrier, allowing the influx of peripheral immune cells into the central nervous system. Antidepressants have antinociceptive effects because they recruit long-term neuronal plasticity. Amitriptyline modulates the inflammatory response due to the reduction of the mRNA of pro-inflammatory cytokines acting as an adenosine agonist and leading to the activation of the A3AR receptor. Through toll-like receptors, local inflammation determines the release of pro-inflammatory cytokines such as tumor necrosis factor-alpha (TNF-α) that drives and stimulates the hyperflammation in NP. Nortriptyline has an important antiallodynic effect in NP as it determines the recruitment of norepinephrine in the dorsal root ganglia. By modulating the β2-adrenoreceptors expressed by non-neuronal satellite cells, it inhibits the local production of TNF-α and determines a reduction of NP symptoms. Following the administration of antidepressants, there is a reduction in the production of TNF-α in the brain which in turn transforms the function of the α2-adrenergic receptor from an inhibitor to an activator of the release of norepinephrine. This is important to prevent the development of chronic pain.

CONCLUSION

Inflammatory cytokines are the main players in a bidirectional communication between the central and peripheral nervous system and the immune system in NP. Antidepressants have an important role in NP. Further research should explore the interaction between neuroinflammation in NP, the effects of antidepressants and the clinical relevance of this interaction.

Cytokines reprogram airway sensory neurons in asthma

Nociceptor neurons play a crucial role in maintaining the body's homeostasis by detecting and responding to potential dangers in the environment. However, this function can be detrimental during allergic reactions, since vagal nociceptors can contribute to immune cell infiltration, bronchial hypersensitivity, and mucus imbalance, in addition to causing pain and coughing. Despite this, the specific mechanisms by which nociceptors acquire pro-inflammatory characteristics during allergic reactions are not yet fully understood. In this study, we aimed to investigate the molecular profile of airway nociceptor neurons during allergic airway inflammation and identify the signals driving such reprogramming. Using retrograde tracing and lineage reporting, we identified a unique class of inflammatory vagal nociceptor neurons that exclusively innervate the airways. In the ovalbumin mouse model of airway inflammation, these neurons undergo significant reprogramming characterized by the upregulation of the NPY receptor Npy1r. A screening of cytokines and neurotrophins revealed that IL-1β, IL-13 and BDNF drive part of this reprogramming. IL-13 triggered Npy1r overexpression in nociceptors via the JAK/STAT6 pathway. In parallel, sympathetic neurons and macrophages release NPY in the bronchoalveolar fluid of asthmatic mice, which limits the excitability of nociceptor neurons. Single-cell RNA sequencing of lung immune cells has revealed that a cell-specific knockout of Npy1r in nociceptor neurons in asthmatic mice leads to an increase in airway inflammation mediated by T cells. Opposite findings were observed in asthmatic mice in which nociceptor neurons were chemically ablated. In summary, allergic airway inflammation reprograms airway nociceptor neurons to acquire a pro-inflammatory phenotype, while a compensatory mechanism involving NPY1R limits nociceptor neurons' activity.

Targeting connexins: possible game changer in managing neuropathic pain?

Neuropathic pain is a chronic debilitating condition caused by nerve injury or a variety of diseases. At the core of neuropathic pain lies the aberrant neuronal excitability in the peripheral and/or central nervous system (PNS and CNS). Enhanced connexin expression and abnormal activation of connexin-assembled gap junctional channels are prominent in neuropathic pain along with reactive gliosis, contributing to neuronal hypersensitivity and hyperexcitability. In this review, we delve into the current understanding of how connexin expression and function contribute to the pathogenesis and pathophysiology of neuropathic pain and argue for connexins as potential therapeutic targets for neuropathic pain management.

Chronic pain exacerbates memory impairment and pathology of Aβ and tau by upregulating IL-1β and p-65 signaling in a mouse model of Alzheimer's disease

BACKGROUND

Chronic pain is linked to cognitive impairment; however, the underlying mechanisms remain unclear. In the present study, we examined these mechanisms in a well-established mouse model of Alzheimer's disease (AD).

METHODS

Neuropathic pain was modeled in 5-month-old transgenic APPswe/PS1dE9 (APP/PS1) mice by partial ligation of the sciatic nerve on the left side, and chronic inflammatory pain was modeled in another group of APP/PS1 mice by injecting them with complete Freund's adjuvant on the plantar surface of the left hind paw. Six weeks after molding, the animals were tested to assess pain threshold (von Frey filament), learning, memory (novel object recognition, Morris water maze, Y-maze, and passive avoidance), and depression-like symptoms (sucrose preference, tail suspension, and forced swimming). After behavioral testing, mice were sacrificed and the levels of p65, amyloid-β (residues 1-42) and phospho-tau in the hippocampus and cerebral cortex were assayed using western blotting, while interleukin (IL)-1β levels were measured by enzyme-linked immunosorbent assay.

RESULTS

Animals subjected to either type of chronic pain showed lower pain thresholds, more severe deficits in learning and memory, and stronger depression-like symptoms than the corresponding control animals. Either type of chronic pain was associated with upregulation of p65, amyloid-β (1-42), and IL-1β in the hippocampus and cerebral cortex, as well as higher levels of phosphorylated tau.

CONCLUSIONS

Chronic pain may exacerbate cognitive deficits and depression-like symptoms in APP/PS1 mice by worsening pathology related to amyloid-β and tau and by upregulating signaling involving IL-1β and p65.

Rolipram-loaded PgP nanoparticle reduces secondary injury and enhances motor function recovery in a rat moderate contusion SCI model

Spinal cord injury (SCI) results in immediate axonal damage and cell death, as well as a prolonged secondary injury consist of a cascade of pathophysiological processes. One important aspect of secondary injury is activation of phosphodiesterase 4 (PDE4) that leads to reduce cAMP levels in the injured spinal cord. We have developed an amphiphilic copolymer, poly (lactide-co-glycolide)-graft-polyethylenimine (PgP) that can deliver Rolipram, the PDE4 inhibitor. The objective of this work was to investigate the effect of rolipram loaded PgP (Rm-PgP) on secondary injury and motor functional recovery in a rat moderate contusion SCI model. We observed that Rm-PgP can increase cAMP level at the lesion site, and reduce secondary injury such as the inflammatory response by macrophages/microglia, astrogliosis by activated astrocytes and apoptosis as well as improve neuronal survival at 4 weeks post-injury (WPI). We also observed that Rm-PgP can improve motor functional recovery after SCI over 4 WPI.

EphA1 aggravates neuropathic pain by activating CXCR4/RhoA/ROCK2 pathway in mice

Neuropathic pain is a refractory disease with limited treatment options due to its complex mechanisms. Whereas erythropoietin-producing hepatocyte A1 (EphA1) mediates the production of inflammatory factors that are important in the progression of neurological diseases, its role and molecular mechanisms in neuropathic pain remain unclear. In the present study, we established a mouse model of chronic constriction injury (CCI). EphA1 expression was observed to be progressively upregulated at the mRNA and protein levels with the progression of the disease. Subsequently, knockdown of EphA1 expression levels using adenovirus short hairpin RNA (AAV-shEphA1) revealed an increase in mechanical stimulation withdrawal threshold (PWT) and withdrawal latency (PWL) when EphA1 expression was decreased, accompanied by improved dorsal root ganglion injury, increased leukocytosis, decreased microglia, and decreased levels of pro-inflammatory factors. For the underlying mechanism, it was found that EphA1 regulates the activity of the RhoA/ROCK2 pathway by modulating the level of CXCR4. Inhibition of CXCR4 and RhoA/ROCK2 could effectively alleviate the promoting effect of EphA1 upregulation on neuropathic pain. In conclusion, our study suggests that depletion of EphA1 ameliorates neuropathic pain by modulating the CXCR4/RhoA/ROCK2 signaling pathway, and targeting EphA1 may be a potential clinical treatment for neuropathic pain.

Connexins and Pannexins: Important Players in Neurodevelopment, Neurological Diseases, and Potential Therapeutics

Cell-to-cell communication is essential for proper embryonic development and its dysfunction may lead to disease. Recent research has drawn attention to a new group of molecules called connexins (Cxs) and pannexins (Panxs). Cxs have been described for more than forty years as pivotal regulators of embryogenesis; however, the exact mechanism by which they provide this regulation has not been clearly elucidated. Consequently, Cxs and Panxs have been linked to congenital neurodegenerative diseases such as Charcot-Marie-Tooth disease and, more recently, chronic hemichannel opening has been associated with adult neurodegenerative diseases (e.g., Alzheimer's disease). Cell-to-cell communication via gap junctions formed by hexameric assemblies of Cxs, known as connexons, is believed to be a crucial component in developmental regulation. As for Panxs, despite being topologically similar to Cxs, they predominantly seem to form channels connecting the cytoplasm to the extracellular space and, despite recent research into Panx1 (Pannexin 1) expression in different regions of the brain during the embryonic phase, it has been studied to a lesser degree. When it comes to the nervous system, Cxs and Panxs play an important role in early stages of neuronal development with a wide span of action ranging from cellular migration during early stages to neuronal differentiation and system circuitry formation. In this review, we describe the most recent available evidence regarding the molecular and structural aspects of Cx and Panx channels, their role in neurodevelopment, congenital and adult neurological diseases, and finally propose how pharmacological modulation of these channels could modify the pathogenesis of some diseases.