Effects of oral administration of nonselective Trk inhibitor on bladder overactivity in rodent models of prostatic inflammation

BACKGROUND

Our research focused on the assessment of the impact of systemic inhibition of Trk receptors, which bind to nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF), on bladder hypersensitivity in two distinct rodent models of prostatic inflammation (PI).

METHODS

Male Sprague-Dawley rats were divided into three groups (n = 6 each): the control group (no PI, vehicle administration), the untreated group (PI, vehicle administration), and the treated group (PI, nonselective Trk inhibitor, GNF 5837, administration). PI in rats was induced by a intraprostatic injection of 5% formalin. Posttreatment, we carried out conscious cystometry and a range of histological and molecular analyses. Moreover, the study additionally evaluated the effects of a nonselective Trk inhibitor on bladder overactivity in a mouse model of PI, which was induced by prostate epithelium-specific conditional deletion of E-cadherin.

RESULTS

The rat model of PI showed upregulations of NGF and BDNF in both bladder and prostate tissues in association with bladder overactivity and inflammation in the ventral lobes of the prostate. GNF 5837 treatment effectively mitigated these PI-induced changes, along with reductions in TrkA, TrkB, TrkC, and TRPV1 mRNA expressions in L6-S1 dorsal root ganglia. Also, in the mouse PI model, GNF 5837 treatment similarly improved bladder overactivity.

CONCLUSIONS

The findings of our study suggest that Trk receptor inhibition, which reduced bladder hypersensitivity and inflammatory responses in the prostate, along with a decrease in overexpression of Trk and TRPV1 receptors in sensory pathways, could be an effective treatment strategy for male lower urinary tract symptoms associated with PI and bladder overactivity.

Transcriptome Analysis of Rheumatoid Arthritis Uncovers Genes Linked to Inflammation-Induced Pain

Autoimmune diseases such as rheumatoid arthritis (RA) can promote states of chronic Inflammation with accompanying tissue destruction and pain. RA can cause inflammatory synovitis in peripheral joints, particularly within the hands and feet, but can also sometimes trigger temporomandibular joint (TMJ) arthralgia. To better understand the effects of ongoing Inflammation-induced pain signaling, dorsal root ganglia (DRGs) were acquired from individuals with RA for transcriptomic study. We conducted RNA sequencing from the L5 DRGs because it contains the soma of the sensory neurons that innervate the affected joints in the foot. DRGs from 5 RA patients were compared with 9 non-arthritic controls. RNA-seq of L5 DRGs identified 128 differentially expressed genes (DEGs) that were dysregulated in the RA subjects as compared to the non-arthritic controls. The DRG resides outside the blood brain barrier and, as such, our initial transcriptome analysis detected signs of an autoimmune disorder including the upregulated expression of immunoglobulins and other immunologically related genes within the DRGs of the RA donors. Additionally, we saw the upregulation in genes implicated in neurogenesis that could promote pain hypersensitivity. overall, our DRG analysis suggests that there are upregulated inflammatory and pain signaling pathways that can contribute to chronic pain in RA.

Nerve growth factor receptor limits inflammation to promote remodeling and repair of osteoarthritic joints

Osteoarthritis (OA) is a painful, incurable disease affecting over 500 million people. Recent clinical trials of the nerve growth factor (NGF) inhibitors in OA patients have suggested adverse effects of NGF inhibition on joint structure. Here we report that nerve growth factor receptor (NGFR) is upregulated in skeletal cells during OA and plays an essential role in the remodeling and repair of osteoarthritic joints. Specifically, NGFR is expressed in osteochondral cells but not in skeletal progenitor cells and induced by TNFα to attenuate NF-κB activation, maintaining proper BMP-SMAD1 signaling and suppressing RANKL expression in mice. NGFR deficiency hyper-activates NF-κB in murine osteoarthritic joints, which impairs bone formation and enhances bone resorption as exemplified by a reduction in subchondral bone and osteophytes. In human OA cartilage, NGFR is also negatively associated with NF-κB activation. Together, this study suggests a role of NGFR in limiting inflammation for repair of diseased skeletal tissues.

Exploring Localized Provoked Vulvodynia: Insights from Animal Model Research

Provoked vulvodynia represents a challenging chronic pain condition, characterized by its multifactorial origins. The inherent complexities of human-based studies have necessitated the use of animal models to enrich our understanding of vulvodynia's pathophysiology. This review aims to provide an exhaustive examination of the various animal models employed in this research domain. A comprehensive search was conducted on PubMed, utilizing keywords such as "vulvodynia", "chronic vulvar pain", "vulvodynia induction", and "animal models of vulvodynia" to identify pertinent studies. The search yielded three primary animal models for vulvodynia: inflammation-induced, allergy-induced, and hormone-induced. Additionally, six agents capable of triggering the condition through diverse pathways were identified, including factors contributing to hyperinnervation, mast cell proliferation, involvement of other immune cells, inflammatory cytokines, and neurotransmitters. This review systematically outlines the various animal models developed to study the pathogenesis of provoked vulvodynia. Understanding these models is crucial for the exploration of preventative measures, the development of novel treatments, and the overall advancement of research within the field.

Synovial fibroblast gene expression is associated with sensory nerve growth and pain in rheumatoid arthritis

It has been presumed that rheumatoid arthritis (RA) joint pain is related to inflammation in the synovium; however, recent studies reveal that pain scores in patients do not correlate with synovial inflammation. We developed a machine-learning approach (graph-based gene expression module identification or GbGMI) to identify an 815-gene expression module associated with pain in synovial biopsy samples from patients with established RA who had limited synovial inflammation at arthroplasty. We then validated this finding in an independent cohort of synovial biopsy samples from patients who had early untreated RA with little inflammation. Single-cell RNA sequencing analyses indicated that most of these 815 genes were most robustly expressed by lining layer synovial fibroblasts. Receptor-ligand interaction analysis predicted cross-talk between human lining layer fibroblasts and human dorsal root ganglion neurons expressing calcitonin gene-related peptide (CGRP+). Both RA synovial fibroblast culture supernatant and netrin-4, which is abundantly expressed by lining fibroblasts and was within the GbGMI-identified pain-associated gene module, increased the branching of pain-sensitive murine CGRP+ dorsal root ganglion neurons in vitro. Imaging of solvent-cleared synovial tissue with little inflammation from humans with RA revealed CGRP+ pain-sensing neurons encasing blood vessels growing into synovial hypertrophic papilla. Together, these findings support a model whereby synovial lining fibroblasts express genes associated with pain that enhance the growth of pain-sensing neurons into regions of synovial hypertrophy in RA.

Integration of Whole-Genome Resequencing and Transcriptome Sequencing Reveals Candidate Genes in High Glossiness of Eggshell

Eggshell gloss is an important characteristic for the manifestation of eggshell appearance. However, no study has yet identified potential candidate genes for eggshell gloss between high-gloss (HG) and low-gloss (LG) chickens. The aim of this study was to perform a preliminary investigation into the formation mechanism of eggshell gloss and to identify potential genes. The eggshell gloss of 300-day-old Rhode Island Red hens was measured from three aspects. Uterine tissues of the selected HG and LG (n = 5) hens were collected for RNA-seq. Blood samples were also collected for whole-genome resequencing (WGRS). RNA-seq analysis showed that 150 differentially expressed genes (DEGs) were identified in the uterine tissues of HG and LG hens. These DEGs were mainly enriched in the calcium signaling pathway and the neuroactive ligand-receptor interaction pathway. Importantly, these two pathways were also significantly enriched in the WGRS analysis results. Further joint analysis of WGRS and RNA-seq data revealed that 5-hydroxytryptamine receptor 1F (HTR1F), zinc finger protein 536 (ZNF536), NEDD8 ubiquitin-like modifier (NEDD8), nerve growth factor (NGF) and calmodulin 1 (CALM1) are potential candidate genes for eggshell gloss. In summary, our research provides a reference for the study of eggshell gloss and lays a foundation for improving egg glossiness in layer breeding.

Nerve Growth Factor Shows Biphasic Expression during Adjuvant-Induced Neurogenic Inflammation

Chronic inflammatory diseases are considered the most significant cause of death worldwide. Current treatments for inflammatory diseases are limited due to the lack of understanding of the biological factors involved in early-stage disease progression. Nerve growth factor (NGF) is a neurotrophic factor directly associated with inflammatory and autoimmune diseases like osteoarthritis, multiple sclerosis, and rheumatoid arthritis. It has been shown that NGF levels are significantly upregulated at the site of inflammation and play a crucial role in developing a robust inflammatory response. However, little is known about NGF's temporal expression profile during the initial progressive phase of inflammation. This study aimed to determine the temporal expression patterns of NGF in rat skin (epidermis) during adjuvant-induced arthritis (AIA). Sprague Dawley rats were randomly divided into control and complete Freund's adjuvant (CFA)-treated groups. Levels of NGF were evaluated following unilateral AIA at different time points, and it was found that peripheral inflammation due to AIA significantly upregulated the expression of NGF mRNA and protein in a biphasic pattern. These results suggest that NGF signaling is crucial for initiating and maintaining peripheral neurogenic inflammation in rats during AIA.

Inflammation in osteoarthritis: Our view on its presence and involvement in disease development over the years

Inflammation, both locally in the joint and systemic, is nowadays considered among the mechanisms involved in osteoarthritis (OA). However, this concept has not always been generally accepted. In fact, for long OA has been described as a relatively simple degeneration of articular cartilage as the result of wear and tear only. In this narrative review, we present what our understanding of OA was at the time of the inaugural release of Osteoarthritis and Cartilage about 30 years ago and discuss a set of pivotal papers that changed our view on the role of inflammation in OA development. Furthermore, we briefly discuss the current view on the involvement of inflammation in OA. Next, we use the example of transforming growth factor-β signaling to show how inflammation might influence processes in the joint in a manner that is beyond the simple interaction of ligand and receptor leading to the release of inflammatory and catabolic mediators. Finally, we discuss our view on what should be done in the future to bring the field forward.

Nerve Growth Factor/Tyrosine Kinase A Receptor Pathway Enhances Analgesia in an Experimental Mouse Model of Bone Cancer Pain by Increasing Membrane Levels of δ-Opioid Receptors

BACKGROUND

The role of nerve growth factor (NGF)/tyrosine kinase A receptor (TrKA) signaling, which is activated in a variety of pain states, in regulating membrane-associated δ-opioid receptor (mDOR) expression is poorly understood. The hypothesis was that elevated NGF in bone cancer tumors could upregulate mDOR expression in spinal cord neurons and that mDOR agonism might alleviate bone cancer pain.

METHODS

Bone cancer pain (BCP) was induced by inoculating Lewis lung carcinoma cells into the femoral marrow cavity of adult C57BL/6J mice of both sexes. Nociceptive behaviors were evaluated by the von Frey and Hargreaves tests. Protein expression in the spinal dorsal horn of animals was measured by biochemical analyses, and excitatory synaptic transmission was recorded in miniature excitatory synaptic currents.

RESULTS

The authors found that mDOR expression was increased in BCP mice (BCP vs. sham, mean ± SD: 0.18 ± 0.01 g vs. mean ± SD: 0.13 ± 0.01 g, n = 4, P < 0.001) and that administration of the DOR agonist deltorphin 2 (Del2) increased nociceptive thresholds (Del2 vs. vehicle, median [25th, 75th percentiles]: 1.00 [0.60, 1.40] g vs. median [25th, 75th percentiles]: 0.40 [0.16, 0.45] g, n = 10, P = 0.001) and reduced miniature excitatory synaptic current frequency in lamina II outer neurons (Del2 vs. baseline, mean ± SD: 2.21 ± 0.81 Hz vs. mean ± SD: 2.43 ± 0.90 Hz, n = 12, P < 0.001). Additionally, NGF expression was increased in BCP mice (BCP vs. sham, mean ± SD: 0.36 ± 0.03 vs. mean ± SD: 0.16 ± 0.02, n = 4, P < 0.001), and elevated NGF was associated with enhanced mDOR expression via TrKA signaling.

CONCLUSIONS

Activation of mDOR produces analgesia that is dependent on the upregulation of the NGF/TrKA pathway by increasing mDOR levels under conditions of BCP in mice.

EDITOR’S PERSPECTIVE

Potential therapeutic strategies for osteoarthritis via CRISPR/Cas9 mediated gene editing

Osteoarthritis (OA) is an incapacitating and one of the most common physically degenerative conditions with an assorted etiology and a highly complicated molecular mechanism that to date lacks an efficient treatment. The capacity to design biological networks and accurately modify existing genomic sites holds an apt potential for applications across medical and biotechnological sciences. One of these highly specific genomes editing technologies is the CRISPR/Cas9 mechanism, referred to as the clustered regularly interspaced short palindromic repeats, which is a defense mechanism constituted by CRISPR associated protein 9 (Cas9) directed by small non-coding RNAs (sncRNA) that bind to target DNA through Watson-Crick base pairing rules where subsequent repair of the target DNA is initiated. Up-to-date research has established the effectiveness of the CRISPR/Cas9 mechanism in targeting the genetic and epigenetic alterations in OA by suppressing or deleting gene expressions and eventually distributing distinctive anti-arthritic properties in both in vitro and in vivo osteoarthritic models. This review aims to epitomize the role of this high-throughput and multiplexed gene editing method as an analogous therapeutic strategy that could greatly facilitate the clinical development of OA-related treatments since it's reportedly an easy, minimally invasive technique, and a comparatively less painful method for osteoarthritic patients.

A phenotypic screening platform for chronic pain therapeutics using all-optical electrophysiology

ABSTRACT

Chronic pain associated with osteoarthritis (OA) remains an intractable problem with few effective treatment options. New approaches are needed to model the disease biology and to drive discovery of therapeutics. We present an in vitro model of OA pain, where dorsal root ganglion (DRG) sensory neurons were sensitized by a defined mixture of disease-relevant inflammatory mediators, here called Sensitizing PAin Reagent Composition or SPARC. Osteoarthritis-SPARC components showed synergistic or additive effects when applied in combination and induced pain phenotypes in vivo. To measure the effect of OA-SPARC on neural firing in a scalable format, we used a custom system for high throughput all-optical electrophysiology. This system enabled light-based membrane voltage recordings from hundreds of neurons in parallel with single cell and single action potential resolution and a throughput of up to 500,000 neurons per day. A computational framework was developed to construct a multiparameter OA-SPARC neuronal phenotype and to quantitatively assess phenotype reversal by candidate pharmacology. We screened ∼3000 approved drugs and mechanistically focused compounds, yielding data from over 1.2 million individual neurons with detailed assessment of functional OA-SPARC phenotype rescue and orthogonal "off-target" effects. Analysis of confirmed hits revealed diverse potential analgesic mechanisms including ion channel modulators and other mechanisms including MEK inhibitors and tyrosine kinase modulators. Our results suggest that the Raf-MEK-ERK axis in DRG neurons may integrate the inputs from multiple upstream inflammatory mediators found in osteoarthritis patient joints, and MAPK pathway activation in DRG neurons may contribute to chronic pain in patients with osteoarthritis.

Neuropilin-1 is a co-receptor for NGF and TrkA-evoked pain

Nerve growth factor (NGF) monoclonal antibodies (mAb) are one of the few patient-validated non-opioid treatments for chronic pain, despite failing to gain FDA approval due to worsened joint damage in some osteoarthritis patients. Herein, we demonstrate that neuropilin-1 (NRP1) is a nociceptor-enriched co-receptor for NGF that is necessary for tropomyosin-related kinase A (TrkA) signaling of pain. NGF binds NRP1 with nanomolar affinity. NRP1 and G Alpha Interacting Protein C-terminus 1 (GIPC1), a NRP1/TrkA adaptor, are coexpressed with TrkA in human and mouse nociceptors. NRP1 small molecule inhibitors and blocking mAb prevent NGF-stimulated action potential firing and activation of Na+ and Ca2+ channels in human and mouse nociceptors and abrogate NGF-evoked and inflammatory nociception in mice. NRP1 knockdown blunts NGF-stimulated TrkA phosphorylation, kinase signaling and transcription, whereas NRP1 overexpression enhances NGF and TrkA signaling. As well as interacting with NGF, NRP1 forms a heteromeric complex with TrkA. NRP1 thereby chaperones TrkA from the biosynthetic pathway to the plasma membrane and then to signaling endosomes, which enhances NGF-induced TrkA dimerization, endocytosis and signaling. Knockdown of GIPC1, a PDZ-binding protein that scaffolds NRP1 and TrkA to myosin VI, abrogates NGF-evoked excitation of nociceptors and pain-like behavior in mice. We identify NRP1 as a previously unrecognized co-receptor necessary for NGF/TrkA pain signaling by direct NGF binding and by chaperoning TrkA to the plasma membrane and signaling endosomes via the adaptor protein GIPC1. Antagonism of NRP1 and GIPC1 in nociceptors offers a long-awaited alternative to systemic sequestration of NGF with mAbs for the treatment of pain.

From pain to tumor immunity: influence of peripheral sensory neurons in cancer

The nervous and immune systems are the primary sensory interfaces of the body, allowing it to recognize, process, and respond to various stimuli from both the external and internal environment. These systems work in concert through various mechanisms of neuro-immune crosstalk to detect threats, provide defense against pathogens, and maintain or restore homeostasis, but can also contribute to the development of diseases. Among peripheral sensory neurons (PSNs), nociceptive PSNs are of particular interest. They possess a remarkable capability to detect noxious stimuli in the periphery and transmit this information to the brain, resulting in the perception of pain and the activation of adaptive responses. Pain is an early symptom of cancer, often leading to its diagnosis, but it is also a major source of distress for patients as the disease progresses. In this review, we aim to provide an overview of the mechanisms within tumors that are likely to induce cancer pain, exploring a range of factors from etiological elements to cellular and molecular mediators. In addition to transmitting sensory information to the central nervous system, PSNs are also capable, when activated, to produce and release neuropeptides (e.g., CGRP and SP) from their peripheral terminals. These neuropeptides have been shown to modulate immunity in cases of inflammation, infection, and cancer. PSNs, often found within solid tumors, are likely to play a significant role in the tumor microenvironment, potentially influencing both tumor growth and anti-tumor immune responses. In this review, we discuss the current state of knowledge about the degree of sensory innervation in tumors. We also seek to understand whether and how PSNs may influence the tumor growth and associated anti-tumor immunity in different mouse models of cancer. Finally, we discuss the extent to which the tumor is able to influence the development and functions of the PSNs that innervate it.

Auricular Vagal Nerve Stimulation Inhibited Central Nerve Growth Factor/Tropomyosin Receptor Kinase A/Phospholipase C-Gamma Signaling Pathway in Functional Dyspepsia Model Rats With Gastric Hypersensitivity

OBJECTIVE

Functional dyspepsia (FD), which has a complicated pathophysiologic process, is a common functional gastrointestinal disease. Gastric hypersensitivity is the key pathophysiological factor in patients with FD with chronic visceral pain. Auricular vagal nerve stimulation (AVNS) has the therapeutic effect of reducing gastric hypersensitivity by regulating the activity of the vagus nerve. However, the potential molecular mechanism is still unclear. Therefore, we investigated the effects of AVNS on the brain-gut axis through the central nerve growth factor (NGF)/ tropomyosin receptor kinase A (TrkA)/phospholipase C-gamma (PLC-γ) signaling pathway in FD model rats with gastric hypersensitivity.

MATERIALS AND METHODS

We established the FD model rats with gastric hypersensitivity by means of colon administration of trinitrobenzenesulfonic acid on ten-day-old rat pups, whereas the control rats were given normal saline. AVNS, sham AVNS, K252a (an inhibitor of TrkA, intraperitoneally), and K252a + AVNS were performed on eight-week-old model rats for five consecutive days. The therapeutic effect of AVNS on gastric hypersensitivity was determined by the measurement of abdominal withdrawal reflex response to gastric distention. NGF in gastric fundus and NGF, TrkA, PLC-γ, and transient receptor potential vanilloid 1 (TRPV1) in the nucleus tractus solitaries (NTS) were detected separately by polymerase chain reaction, Western blot, and immunofluorescence tests.

RESULTS

It was found that a high level of NGF in gastric fundus and an upregulation of the NGF/TrkA/PLC-γ signaling pathway in NTS were manifested in model rats. Meanwhile, both AVNS treatment and the administration of K252a not only decreased NGF messenger ribonucleic acid (mRNA) and protein expressions in gastric fundus but also reduced the mRNA expressions of NGF, TrkA, PLC-γ, and TRPV1 and inhibited the protein levels and hyperactive phosphorylation of TrkA/PLC-γ in NTS. In addition, the expressions of NGF and TrkA proteins in NTS were decreased significantly after the immunofluorescence assay. The K252a + AVNS treatment exerted a more sensitive effect on regulating the molecular expressions of the signal pathway than did the K252a treatment.

CONCLUSION

AVNS can regulate the brain-gut axis effectively through the central NGF/TrkA/PLC-γ signaling pathway in the NTS, which suggests a potential molecular mechanism of AVNS in ameliorating visceral hypersensitivity in FD model rats.

N-Acetylcysteine Antagonizes NGF Activation of TrkA through Disulfide Bridge Interaction, an Effect Which May Contribute to Its Analgesic Activity

N-acetylcysteine (NAC), a mucolytic agent and an antidote to acetaminophen intoxication, has been studied in experimental conditions and trials exploring its analgesic activity based on its antioxidant and anti-inflammatory properties. The purpose of this study is to investigate additional mechanisms, namely, the inhibition of nerve growth factor (NGF) and the activation of the Tropomyosin receptor kinase A (TrkA) receptor, which is responsible for nociception. In silico studies were conducted to evaluate dithiothreitol and NAC's interaction with TrkA. We also measured the autophosphorylation of TrkA in SH-SY5Y cells via ELISA to assess NAC's in vitro activity against NGF-induced TrkA activation. The in silico and in vitro tests show that NAC interferes with NGF-induced TrkA activation. In particular, NAC breaks the disulfide-bound Cys 300-345 of TrkA, perturbing the NGF-TrkA interaction and producing a rearrangement of the binding site, inducing a consequent loss of their molecular recognition and spatial reorganization, which are necessary for the induction of the autophosphorylation process. The latter was inhibited by 40% using 20 mM NAC. These findings suggest that NAC could have a role as a TrkA antagonist, an action that may contribute to the activity and use of NAC in various pain states (acute, chronic, nociplastic) sustained by NGF hyperactivity and/or accompanied by spinal cord sensitization.

Nerve Growth Factor Receptor Limits Inflammation to Promote Remodeling and Repair of Osteoarthritic Joints

Osteoarthritis (OA) is a painful, incurable disease affecting over 500 million people. The need for relieving OA pain is paramount but inadequately addressed, partly due to limited understandings of how pain signaling regulates non-neural tissues. Here we report that nerve growth factor receptor (NGFR) is upregulated in skeletal cells during OA and plays an essential role in the remodeling and repair of osteoarthritic joints. Specifically, NGFR is expressed in osteochondral cells but not in skeletal progenitor cells and induced by TNFα to attenuate NF-κB activation, maintaining proper BMP-SMAD1 signaling and suppressing RANKL expression. NGFR deficiency hyper-activates NF-κB in murine osteoarthritic joints, which impairs bone formation and enhances bone resorption as exemplified by a reduction in subchondral bone and osteophytes. In human OA cartilage, NGFR is also negatively associated with NF-κB activation. Together, this study uncovers a role of NGFR in limiting inflammation for repair of diseased skeletal tissues.

Integrin α10β1-Selected Mesenchymal Stem Cells Reduce Pain and Cartilage Degradation and Increase Immunomodulation in an Equine Osteoarthritis Model

OBJECTIVE

Integrin α10β1-selected mesenchymal stem cells (integrin α10-MSCs) have previously shown potential in treating cartilage damage and osteoarthritis (OA) in vitro and in animal models in vivo. The aim of this study was to further investigate disease-modifying effects of integrin α10-MSCs.

DESIGN

OA was surgically induced in 17 horses. Eighteen days after surgery, horses received 2 × 107 integrin α10-MSCs intra-articularly or were left untreated. Lameness and response to carpal flexion was assessed weekly along with synovial fluid (SF) analysis. On day 52 after treatment, horses were euthanized, and carpi were evaluated by computed tomography (CT), MRI, histology, and for macroscopic pathology and integrin α10-MSCs were traced in the joint tissues.

RESULTS

Lameness and response to carpal flexion significantly improved over time following integrin α10-MSC treatment. Treated horses had milder macroscopic cartilage pathology and lower cartilage histology scores than the untreated group. Prostaglandin E2 and interleukin-10 increased in the SF after integrin α10-MSC injection. Integrin α10-MSCs were found in SF from treated horses up to day 17 after treatment, and in the articular cartilage and subchondral bone from 5 of 8 treated horses after euthanasia at 52 days after treatment. The integrin α10-MSC injection did not cause joint flare.

CONCLUSION

This study demonstrates that intra-articular (IA) injection of integrin α10-MSCs appears to be safe, alleviate pathological changes in the joint, and improve joint function in an equine post-traumatic osteoarthritis (PTOA) model. The results suggest that integrin α10-MSCs hold promise as a disease-modifying osteoarthritis drug (DMOAD).

Stellate ganglion block catheter for paroxysmal sympathetic hyperactivity: calming the 'neuro-storm'

BACKGROUND

Paroxysmal sympathetic hyperactivity (PSH) is an autonomic disorder affecting patients with severe acquired brain injury characterized by intermittent sympathetic discharges with limited therapeutic options. We hypothesized that the PSH pathophysiology could be interrupted via stellate ganglion blockade (SGB).

CASE PRESENTATION

A patient with PSH after midbrain hemorrhage followed by hydrocephalus obtained near-complete resolution of sympathetic events for 140 days after SGB.

CONCLUSION

SGB is a promising therapy for PSH, overcoming the limitations of systemic medications and may serve to recalibrate aberrant autonomic states.

Multimodal non-invasive non-pharmacological therapies for chronic pain: mechanisms and progress

BACKGROUND

Chronic pain conditions impose significant burdens worldwide. Pharmacological treatments like opioids have limitations. Non-invasive non-pharmacological therapies (NINPT) encompass diverse interventions including physical, psychological, complementary and alternative approaches, and other innovative techniques that provide analgesic options for chronic pain without medications.

MAIN BODY

This review elucidates the mechanisms of major NINPT modalities and synthesizes evidence for their clinical potential across chronic pain populations. NINPT leverages peripheral, spinal, and supraspinal mechanisms to restore normal pain processing and limit central sensitization. However, heterogeneity in treatment protocols and individual responses warrants optimization through precision medicine approaches.

CONCLUSION

Future adoption of NINPT requires addressing limitations in standardization and accessibility as well as synergistic combination with emerging therapies. Overall, this review highlights the promise of NINPT as a valuable complementary option ready for integration into contemporary pain medicine paradigms to improve patient care and outcomes.

Chitin Conduits with Different Inner Diameters at Both Ends Combined with Dual Growth Factor Hydrogels Promote Nerve Transposition Repair in Rats

Severe peripheral nerve injuries, such as deficits over long distances or proximal nerve trunk injuries, pose complex reconstruction challenges that often result in unfavorable outcomes. Innovative techniques, such as nerve transposition repair with conduit suturing, can be employed to successfully treat severe peripheral nerve damage. However, cylindrical nerve guides are typically unsuitable for nerve transposition repair. Furthermore, angiogenic and neurotrophic factors are necessary to stimulate the emergence of axonal lateral sprouts, proximal growth, and the rehabilitation of neuron structures and functions. In the current study, we used chitosan to make chitin conduits with different inner diameters at both ends, combined with gelatin methacrylate hydrogels that can continuously release dual growth factors, namely, the vascular endothelial growth factor (VEGF) and the nerve growth factor (NGF), and evaluated its impact on nerve transposition repair in rats. At 16 weeks after the operation, our findings showed that the conduit combined with the dual growth factor hydrogel significantly improved the restoration of both motor and conduction functions of the nerve. In addition, histological analysis showed significant recovery of nerve fibers, target muscles, and neurons. In conclusion, the combination of chitin conduits with different inner diameters and dual growth factor hydrogels can significantly improve the effect of nerve transposition repair, which has important potential clinical value.

Machine Learning Reveals Synovial Fibroblast Genes Associated with Pain Affect Sensory Nerve Growth in Rheumatoid Arthritis

It has been presumed that rheumatoid arthritis (RA) joint pain is related to inflammation in the synovium; however, recent studies reveal that pain scores in patients do not correlate with synovial inflammation. We identified a module of 815 genes associated with pain, using a novel machine learning approach, Graph-based Gene expression Module Identification (GbGMI), in samples from patients with longstanding RA, but limited synovial inflammation at arthroplasty, and validated this finding in an independent cohort of synovial biopsy samples from early, untreated RA patients. Single-cell RNA-seq analyses indicated these genes were most robustly expressed by lining layer fibroblasts and receptor-ligand interaction analysis predicted robust lining layer fibroblast crosstalk with pain sensitive CGRP+ dorsal root ganglion sensory neurons. Netrin-4, which is abundantly expressed by lining fibroblasts and associated with pain, significantly increased the branching of pain-sensitive CGRP+ neurons in vitro . We conclude GbGMI is a useful method for identifying a module of genes that associate with a clinical feature of interest. Using this approach, we find that Netrin-4 is produced by synovial fibroblasts in the absence of inflammation and can enhance the outgrowth of CGRP+ pain sensitive nerve fibers.

One Sentence Summary

Machine Learning reveals synovial fibroblast genes related to pain affect sensory nerve growth in Rheumatoid Arthritis addresses unmet clinical need.

The Sphingosine 1-Phosphate Axis: an Emerging Therapeutic Opportunity for Endometriosis

Endometriosis is a common condition in women of reproductive age, but its current interventions are unsatisfactory. Recent research discovered a dysregulation of the sphingosine 1-phosphate (S1P) signaling pathway in endometriosis and showed a positive outcome by targeting it. The S1P axis participates in a series of fundamental pathophysiological processes. This narrative review is trying to expound the reported and putative (due to limited reports in this area for now) interactions between the S1P axis and endometriosis in those pathophysiological processes, to provide some perspectives for future research. In short, S1P signaling pathway is highly activated in the endometriotic lesion. The S1P concentration has a surge in the endometriotic cyst fluid and the peritoneal fluid, with the downstream dysregulation of its receptors. The S1P axis plays an essential role in the migration and activation of the immune cells, fibrosis, angiogenesis, pain-related hyperalgesia, and innervation. S1P receptor (S1PR) modulators showed an impressive therapeutic effect by targeting the different S1P receptors in the endometriosis model, and many other conditions resemble endometriosis. And several of them already got approval for clinical application in many diseases, which means a drug repurposing direction and a rapid clinical translation for endometriosis treatments.

Understanding the initiation, delivery and processing of bone cancer pain from the peripheral to the central nervous system

Bone cancer pain is a complex condition characterized by persistent, sudden, spontaneous pain accompanied by hyperalgesia that typically arises from bone metastases or primary bone tumors, causing severe discomfort and significantly diminishing cancer patients' quality of life and confidence in their ability to overcome the disease. It is widely known that peripheral nerves are responsible for detecting harmful stimuli, which are then transmitted to the brain via the spinal cord, resulting in the perception of pain. In the case of bone cancer, tumors and stromal cells within the bone marrow release various chemical signals, including inflammatory factors, colony-stimulating factors, chemokines, and hydrogen ions. Consequently, the nociceptors located at the nerve endings within the bone marrow sense these chemical signals, generating electrical signals that are then transmitted to the brain through the spinal cord. Subsequently, the brain processes these electrical signals in a complex manner to create the sensation of bone cancer pain. Numerous studies have investigated the transmission of bone cancer pain from the periphery to the spinal cord. However, the processing of pain information induced by bone cancer within the brain remains unclear. With the continuous advancements in brain science and technology, the brain mechanism of bone cancer pain would become more clearly understood. Herein, we focus on summarizing the peripheral nerve perception of the spinal cord transmission of bone cancer pain and provide a brief overview of the ongoing research regarding the brain mechanisms involved in bone cancer pain.

Anti-NGF treatment worsens subchondral bone and cartilage measures while improving symptoms in floor-housed rabbits with osteoarthritis

Objective: Osteoarthritis (OA) is a common joint disorder often affecting the knee. It is characterized by alterations of various joint tissues including subchondral bone and by chronic pain. Anti-nerve growth factor (NGF) antibodies have demonstrated improvement in pain associated with OA in phase 3 clinical trials but have not been approved due to an increased risk of developing rapidly progressive OA. The aim of this study was to investigate effects of systemic anti-NGF-treatment on structure and symptoms in rabbits with surgically induced joint instability. Methods: This was elicited by anterior cruciate ligament transection and partial resection of the medial meniscus in right knee of 63 female rabbits, housed altogether in a 56 m² floor husbandry. Rabbits received either 0.1, 1 or 3 mg/kg anti-NGF antibody intra-venously at weeks 1, 5 and 14 after surgery or vehicle. During in-life phase, static incapacitance tests were performed and joint diameter was measured. Following necropsy, gross morphological scoring and micro-computed tomography analysis of subchondral bone and cartilage were performed. Results: After surgery, rabbits unloaded operated joints, which was improved with 0.3 and 3 mg/kg anti-NGF compared to vehicle injection during the first half of the study. The diameter of operated knee joints increased over contralateral measures. This increase was bigger in anti-NGF treated rabbits beginning 2 weeks after the first IV injection and became dose-dependent and more pronounced with time. In the 3 mg/kg anti-NGF group, the bone volume fraction and trabecular thickness increased in the medio-femoral region of operated joints compared to contralateral and to vehicle-treated animals, while cartilage volume and to a lesser extent thickness decreased. Enlarged bony areas were found in right medio-femoral cartilage surfaces of animals receiving 1 and 3 mg/kg anti-NGF. Alterations of all structural parameters were particularly distinct in a subgroup of three rabbits, which also exhibited more prominent symptomatic improvement. Conclusion: This study showed that anti-NGF administration exerted negative impact on structure in destabilized joints of rabbits, while pain-induced unloading of joints was improved. Our findings open up the possibility to better understand the effects of systemic anti-NGF, particularly on subchondral bone, and thus the occurrence of rapidly progressive OA in patients.

Confronting the loss of trophic support

Classic experiments with peripheral sympathetic neurons established an absolute dependence upon NGF for survival. A forgotten problem is how these neurons become resistant to deprivation of trophic factors. The question is whether and how neurons can survive in the absence of trophic support. However, the mechanism is not understood how neurons switch their phenotype to lose their dependence on trophic factors, such as NGF and BDNF. Here, we approach the problem by considering the requirements for trophic support of peripheral sympathetic neurons and hippocampal neurons from the central nervous system. We developed cellular assays to assess trophic factor dependency for sympathetic and hippocampal neurons and identified factors that rescue neurons in the absence of trophic support. They include enhanced expression of a subunit of the NGF receptor (Neurotrophin Receptor Homolog, NRH) in sympathetic neurons and an increase of the expression of the glucocorticoid receptor in hippocampal neurons. The results are significant since levels and activity of trophic factors are responsible for many neuropsychiatric conditions. Resistance of neurons to trophic factor deprivation may be relevant to the underlying basis of longevity, as well as an important element in preventing neurodegeneration.

Pain Biomarkers in Fibromyalgia Syndrome: Current Understanding and Future Directions

Fibromyalgia is a complex and heterogeneous clinical syndrome, mainly characterized by the presence of widespread pain, possibly associated with a variety of other symptoms. Fibromyalgia can have an extremely negative impact on the psychological, physical and social lives of people affected, sometimes causing patients to experience dramatically impaired quality of life. Nowadays, the diagnosis of fibromyalgia is still clinical, thus favoring diagnostic uncertainties and making its clear identification challenging to establish, especially in primary care centers. These difficulties lead patients to undergo innumerable clinical visits, investigations and specialist consultations, thus increasing their stress, frustration and even dissatisfaction. Unfortunately, research over the last 25 years regarding a specific biomarker for the diagnosis of fibromyalgia has been fruitless. The discovery of a reliable biomarker for fibromyalgia syndrome would be a critical step towards the early identification of this condition, not only reducing patient healthcare utilization and diagnostic test execution but also providing early intervention with guideline-based treatments. This narrative article reviews different metabolite alterations proposed as possible biomarkers for fibromyalgia, focusing on their associations with clinical evidence of pain, and highlights some new, promising areas of research in this context. Nevertheless, none of the analyzed metabolites emerge as sufficiently reliable to be validated as a diagnostic biomarker. Given the complexity of this syndrome, in the future, a panel of biomarkers, including subtype-specific biomarkers, could be considered as an interesting alternative research area.

A Three-Fold Integrated Perspective on Healthy Development: An Opinion Paper

Mental health and wellbeing are increasingly threatened in the current post-pandemic times, with stress, especially in students, reaching preoccupying levels. In addition, while many educational programs are unidimensional (i.e., lacking integration between physical, emotional and cognitive elements), there are ways to promote physical, social and mental health in children and adolescents. In this opinion paper, we will discuss the importance of an integrative approach for health development and examine relevant factors, such as awareness and emotional intelligence. We will highlight evidence ranging from behavioral to electrophysiological, structural and molecular, and report several recent studies supporting the effectiveness of a holistic approach in supporting wellbeing and creativity in children and adults, and detailing a specific paradigm named the Quadrato Motor Training (QMT). QMT is a specifically structured movement meditation, involving cognitive, motor and affective components. Finally, we will support a holistic view on education, integrating motion, emotion and cognition to develop a person-centered, or in this case student-centered, approach to wellbeing and health.

Piezo2 expressing nociceptors mediate mechanical sensitization in experimental osteoarthritis

Non-opioid targets are needed for addressing osteoarthritis pain, which is mechanical in nature and associated with daily activities such as walking and climbing stairs. Piezo2 has been implicated in the development of mechanical pain, but the mechanisms by which this occurs remain poorly understood, including the role of nociceptors. Here we show that nociceptor-specific Piezo2 conditional knock-out mice were protected from mechanical sensitization associated with inflammatory joint pain in female mice, joint pain associated with osteoarthritis in male mice, as well as both knee swelling and joint pain associated with repeated intra-articular injection of nerve growth factor in male mice. Single cell RNA sequencing of mouse lumbar dorsal root ganglia and in situ hybridization of mouse and human lumbar dorsal root ganglia revealed that a subset of nociceptors co-express Piezo2 and Ntrk1 (the gene that encodes the nerve growth factor receptor TrkA). These results suggest that nerve growth factor-mediated sensitization of joint nociceptors, which is critical for osteoarthritic pain, is also dependent on Piezo2, and targeting Piezo2 may represent a therapeutic option for osteoarthritis pain control.

Serum nerve growth factor in horses with osteoarthritis-associated lameness

BACKGROUND

Nerve growth factor (NGF) is a neurotrophin that is increased in osteoarthritic joints of horses. In humans, NGF has been associated with pain, and both synovial and serum NGF concentrations are increased in osteoarthritic patients. Studies in humans also have shown that serum NGF concentration can increase with stress. Serum NGF concentration should be evaluated in horses with osteoarthritis-associated lameness.

OBJECTIVES

Quantify and compare serum NGF concentration in horses with osteoarthritis-associated lameness and sound horses. Additionally, the impact of short-term stress on serum NGF concentration was investigated.

ANIMALS

Lame horses with radiographic evidence of osteoarthritis (n = 20), lame horses without radiographic changes in the affected joint (n = 20) and sound horses (n = 20). In addition, horses with acute fractures (n = 9) were sampled. To determine the effect of stress, serum from horses subjected to a stressful event (transportation, n = 5; stress confirmed by increased serum cortisol concentration) was analyzed.

METHODS

Cross-sectional clinical study (lame, sound, and fracture cohorts) and experimental longitudinal study (stress cohort). Serum NGF concentration was determined using a quantitative sandwich ELISA.

RESULTS

Serum NGF concentration was increased in lame horses with radiographic evidence of osteoarthritis (P < .0001; median, 238 pg/mL; interquartile range [IQR], 63-945 pg/mL) and in lame horses without radiographic evidence of osteoarthritis in the painful joint (P < .05; median, 31 pg/mL; IQR, 31-95 pg/mL) compared with sound horses (median, 31 pg/mL; IQR, 31-46 pg/mL). Serum NGF concentration did not increase with short-term stress and was low in horses with fracture-associated pain.

CONCLUSIONS AND CLINICAL IMPORTANCE

Serum NGF concentration was high in the cohort with advanced osteoarthritis and should be investigated as a marker for osteoarthritis-associated pain.

Human TrkAR649W mutation impairs nociception, sweating and cognitive abilities: a mouse model of HSAN IV

A functional nerve growth factor NGF-Tropomyosin Receptor kinase A (TrkA) system is an essential requisite for the generation and maintenance of long-lasting thermal and mechanical hyperalgesia in adult mammals. Indeed, mutations in the gene encoding for TrkA are responsible for a rare condition, named Hereditary Sensory and Autonomic Neuropathy type IV (HSAN IV), characterized by the loss of response to noxious stimuli, anhidrosis and cognitive impairment. However, to date, there is no available mouse model to properly understand how the NGF-TrkA system can lead to pathological phenotypes that are distinctive of HSAN IV. Here, we report the generation of a knock-in mouse line carrying the HSAN IV TrkAR649W mutation. First, by in vitro biochemical and biophysical analyses, we show that the pathological R649W mutation leads to kinase-inactive TrkA also affecting its membrane dynamics and trafficking. In agreement with the HSAN IV human phenotype, TrkAR649W/m mice display a lower response to thermal and chemical noxious stimuli, correlating with reduced skin innervation, in addition to decreased sweating in comparison to TrkAh/m controls. Moreover, the R649W mutation decreases anxiety-like behavior and compromises cognitive abilities, by impairing spatial-working and social memory. Our results further uncover unexplored roles of TrkA in thermoregulation and sociability. In addition to accurately recapitulating the clinical manifestations of HSAN IV patients, our findings contribute to clarifying the involvement of the NGF-TrkA system in pain sensation.

Role of TMEM100 in mechanically insensitive nociceptor un-silencing

Mechanically silent nociceptors are sensory afferents that are insensitive to noxious mechanical stimuli under normal conditions but become sensitized to such stimuli during inflammation. Using RNA-sequencing and quantitative RT-PCR we demonstrate that inflammation upregulates the expression of the transmembrane protein TMEM100 in silent nociceptors and electrophysiology revealed that over-expression of TMEM100 is required and sufficient to un-silence silent nociceptors in mice. Moreover, we show that mice lacking TMEM100 do not develop secondary mechanical hypersensitivity-i.e., pain hypersensitivity that spreads beyond the site of inflammation-during knee joint inflammation and that AAV-mediated overexpression of TMEM100 in articular afferents in the absence of inflammation is sufficient to induce mechanical hypersensitivity in remote skin regions without causing knee joint pain. Thus, our work identifies TMEM100 as a key regulator of silent nociceptor un-silencing and reveals a physiological role for this hitherto enigmatic afferent subclass in triggering spatially remote secondary mechanical hypersensitivity during inflammation.

ARMS/Kidins220 regulates nociception by controlling brain-derived neurotrophic factor secretion

ABSTRACT

Pain is an alarm mechanism to prevent body damage in response to noxious stimuli. The nerve growth factor (NGF)/TrkA axis plays an essential role as pain mediator, and several clinical trials using antibodies against NGF have yielded promising results, but side effects have precluded their clinical approval. A better understanding of the mechanism of NGF/TrkA-mediated nociception is needed. Here, we find that ARMS/Kidins220, a scaffold protein for Trk receptors, is a modulator of nociception. Male mice, with ARMS/Kidins220 reduction exclusively in TrkA-expressing cells, displayed hyperalgesia to heat, inflammatory, and capsaicin stimuli, but not to cold or mechanical stimuli. Simultaneous deletion of brain-derived neurotrophic factor (BDNF) reversed the effects of ARMS/Kidins220 knock down alone. Mechanistically, ARMS/Kidins220 levels are reduced in vitro and in vivo in response to capsaicin through calpains, and this reduction leads to enhanced regulated BDNF secretion from dorsal root ganglion. Altogether, these data indicate that ARMS/Kidins220 protein levels have a role as a pain modulator in the NGF/TrkA axis regulating BDNF secretion.

The NGF R100W Mutation, Associated with Hereditary Sensory Autonomic Neuropathy Type V, Specifically Affects the Binding Energetic Landscapes of NGF and of Its Precursor proNGF and p75NTR

Nerve Growth Factor (NGF), the prototype of the neurotrophin family, stimulates morphological differentiation and regulates neuronal gene expression by binding to TrkA and p75NTR receptors. It plays a critical role in maintaining the function and phenotype of peripheral sensory and sympathetic neurons and in mediating pain transmission and perception during adulthood. A point mutation in the NGFB gene (leading to the amino acid substitution R100W) is responsible for Hereditary Sensory and Autonomic Neuropathy type V (HSAN V), leading to a congenital pain insensitivity with no clear cognitive impairments, but with alterations in the NGF/proNGF balance. The available crystal structures of the p75NTR/NGF and 2p75NTR/proNGF complexes offer a starting point for Molecular Dynamics (MD) simulations in order to capture the impact of the R100W mutation on their binding energetic landscapes and to unveil the molecular determinants that trigger their different physiological and pathological outcomes. The present in silico studies highlight that the stability and the binding energetic fingerprints in the 2p75NTR/proNGF complex is not affected by R100W mutation, which on the contrary, deeply affects the energetic landscape, and thus the stability in the p75NTR/NGF complex. Overall, these findings present insights into the structural basis of the molecular mechanisms beyond the clinical manifestations of HSAN V patients.

Wogonin, a Bioactive Ingredient from Huangqi Guizhi Formula, Alleviates Discogenic Low Back Pain via Suppressing the Overexpressed NGF in Intervertebral Discs

Purpose

To investigate whether wogonin, a key bioactive ingredient of Huangqi Guizhi formula (HQGZ formula; a Traditional Chinese Medicine herbal formula) according to network pharmacology analysis, has analgesic effects on discogenic low back pain (LBP) via regulating the nerve growth factor (NGF) in intervertebral discs (IVDs).

Methods

The lumbar IVDs of rats were punctured to discogenic LBP, and the therapeutic effect of orally administrated HQGZ for discogenic LBP was investigated by measuring mechanical and cold allodynia and histological analysis. A network pharmacology analysis was conducted to search for bioactive ingredients from the HQGZ formula, and wogonin was suggested to be the most possible bioactive ingredient for LBP treatment. Subsequently, the analgesic effect of wogonin was investigated in the LBP model, and the gene expression of propain peptides in the bilateral dorsal root ganglia was analyzed using RT-PCR. Finally, immunohistochemical staining was performed for NGF expression of NGF in the IVDs to determine whether wogonin treatment would ameliorate NGF-induced LBP.

Results

Oral administration of HQGZ for two weeks significantly ameliorated puncture-induced IVD degeneration (IDD) and LBP. In addition, the network pharmacology analysis revealed that wogonin, quercetin, and kaempferol were the potential candidate components of HQGZ for LBP treatment. Furthermore, we proved that wogonin had significant analgesic effects in the LBP model. Finally, wogonin was demonstrated to suppress the upregulated NGF in the IVD and ameliorate NGF-induced LBP in rats.

Conclusions

The HQGZ formula has significant analgesic effects for LBP. In addition, the bioactive ingredient of wogonin was extracted from HQGZ and ameliorated LBP by suppressing the overexpressed NGF in degenerated IVDs. Therefore, wogonin has potential to be alternative treatment for LBP in clinical.

Molecular Mechanism Operating in Animal Models of Neurogenic Detrusor Overactivity: A Systematic Review Focusing on Bladder Dysfunction of Neurogenic Origin

Neurogenic detrusor overactivity (NDO) is a severe lower urinary tract disorder, characterized by urinary urgency, retention, and incontinence, as a result of a neurologic lesion that results in damage in neuronal pathways controlling micturition. The purpose of this review is to provide a comprehensive framework of the currently used animal models for the investigation of this disorder, focusing on the molecular mechanisms of NDO. An electronic search was performed with PubMed and Scopus for literature describing animal models of NDO used in the last 10 years. The search retrieved 648 articles, of which reviews and non-original articles were excluded. After careful selection, 51 studies were included for analysis. Spinal cord injury (SCI) was the most frequently used model to study NDO, followed by animal models of neurodegenerative disorders, meningomyelocele, and stroke. Rats were the most commonly used animal, particularly females. Most studies evaluated bladder function through urodynamic methods, with awake cystometry being particularly preferred. Several molecular mechanisms have been identified, including changes in inflammatory processes, regulation of cell survival, and neuronal receptors. In the NDO bladder, inflammatory markers, apoptosis-related factors, and ischemia- and fibrosis-related molecules were found to be upregulated. Purinergic, cholinergic, and adrenergic receptors were downregulated, as most neuronal markers. In neuronal tissue, neurotrophic factors, apoptosis-related factors, and ischemia-associated molecules are increased, as well as markers of microglial and astrocytes at lesion sites. Animal models of NDO have been crucial for understanding the pathophysiology of lower urinary tract (LUT) dysfunction. Despite the heterogeneity of animal models for NDO onset, most studies rely on traumatic SCI models rather than other NDO-driven pathologies, which may result in some issues when translating pre-clinical observations to clinical settings other than SCI.

Involvement of nerve growth factor (NGF) in chronic neuropathic pain - a systematic review

Pain is a complex experience, encompassing physiological and psychological components. Amongst the different types of pain, neuropathic pain, resulting from injuries to the peripheral or central nervous system, still constitutes a challenge for researchers and clinicians. Nerve growth factor (NGF) is currently regarded as a key contributor and may serve as a therapeutic target in many types of pain, likely including neuropathic pain. Here, we reviewed the role of NGF in neuropathic pain of peripheral and central origin, also addressing its potential use as a pharmacological target to better help patients dealing with this condition that severely impacts the everyday life. For this, we conducted a search in the databases PubMed and Scopus. Our search resulted in 1103 articles (458 in PubMed and 645 in Scopus). Only articles related to the involvement of NGF in pain or articles that approached its potential use as a target in treatment of pain symptoms were included. Duplicates were eliminated and 274 articles were excluded. After careful analysis, 23 articles were selected for review. Original articles studying the role of NGF in pathology as well as its modulation as a possible therapeutic target were included. We found that NGF is widely regarded as a key player in neuropathic pain and seen as a putative therapeutic target. However, evidence obtained from years of clinical trials highlights the toxic adverse effects of anti-NGF therapeutics, precluding its use in clinical context. Further studies are, thus, needed to improve treatment of chronic neuropathic pain.

Intramuscular injection of nerve growth factor as a model of temporomandibular disorder: nature, time-course, and sex differences characterising the pain experience

Background

Temporomandibular disorder (TMD) is a common condition that frequently transitions to chronic symptoms. Experimental pain models that mimic the symptoms of clinical TMD may be useful in understanding the mechanisms, and sex differences, present in this disorder. Here we aimed to comprehensively characterise the nature and time-course of pain, functional impairment and hyperalgesia induced by repeated intramuscular injection of nerve growth factor (NGF) into the masseter muscle, and to investigate sex differences in the NGF-induced pain experience.

Methods

94 healthy individuals participated in a longitudinal study with 30-day follow-up. NGF was injected into the right masseter muscle on Day 0 and Day 2. Participants attended laboratory sessions to assess pain (Numerical Rating Scale; NRS), functional limitation (mouth opening distance, Jaw Functional Limitation Scale; JFLS) and mechanical sensitization (pressure pain thresholds; PPTs) on Days 0, 2 and 5 and completed twice daily electronic pain dairies from Day 0 to day 30.

Results

Peak pain averaged 2.0/10 (95 % CI: 1.6-2.4) at rest and 4.3/10 (95 % CI: 3.9-4.8) on chewing. Pain-free mouth opening distance reduced from 5.0 cm (95 % CI: 4.8-5.1 cm) on Day 0 to 3.7 cm (95 % CI: 3.5-3.9 cm) on Day 5. The greatest reduction in PPTs was observed over the masseter muscle. Females experienced higher pain, greater functional impairment, and greater sensitivity to mechanical stimuli than males.

Conclusion

Intramuscular injection of NGF is a useful model with which to explore the mechanisms, and sex differences, present in clinical TMD.

Changes of local microenvironment and systemic immunity after acupuncture stimulation during inflammation: A literature review of animal studies

An increasing number of studies have demonstrated the underlying mechanisms by which acupuncture therapy mediates both local and systemic immunomodulation. However, the connection between alterations in the local microenvironment and the resulting change in systemic immunity remains unclear. In this review, we focus on cell-specific changes in local immune responses following acupuncture stimulation and their link to systemic immune modulation. We have gathered the most recent evidence for chemo- and mechano-reactive changes in endothelial cells, neutrophils, macrophages, and mast cells in response to acupuncture. Local signaling is then related to the activation of systemic neuro-immunity including the cholinergic, adrenal, and splenic nervous systems and pain-related neuromodulation. This review aims to serve as a reference for further research in this field.

Bipartite Activation of Sensory Neurons by a TRPA1 Agonist Allyl Isothiocyanate Is Reflected by Complex Ca2+ Influx and CGRP Release Patterns: Enhancement by NGF and Inhibition with VAMP and SNAP-25 Cleaving Botulinum Neurotoxins

The trafficking of transient receptor potential (TRP) channels to the plasma membrane and the release of calcitonin gene-related peptide (CGRP) from trigeminal ganglion neurons (TGNs) are implicated in some aspects of chronic migraines. These exocytotic processes are inhibited by cleavage of SNAREs with botulinum neurotoxins (BoNTs); moreover, type A toxin (/A) clinically reduces the frequency and severity of migraine attacks but not in all patients for unknown reasons. Herein, neonatal rat TGNs were stimulated with allyl isothiocyanate (AITC), a TRPA1 agonist, and dose relationships were established to link the resultant exocytosis of CGRP with Ca2+ influx. The CGRP release, quantified by ELISA, was best fit by a two-site model (EC50 of 6 and 93 µM) that correlates with elevations in intracellular Ca2+ [Ca2+]i revealed by time-lapse confocal microscopy of fluo-4-acetoxymethyl ester (Fluo-4 AM) loaded cells. These signals were all blocked by two TRPA1 antagonists, HC-030031 and A967079. At low [AITC], [Ca2+]i was limited because of desensitisation to the agonist but rose for concentrations > 0.1 mM due to a deduced non-desensitising second phase of Ca2+ influx. A recombinant BoNT chimera (/DA), which cleaves VAMP1/2/3, inhibited AITC-elicited CGRP release to a greater extent than SNAP-25-cleaving BoNT/A. /DA also proved more efficacious against CGRP efflux evoked by a TRPV1 agonist, capsaicin. Nerve growth factor (NGF), a pain-inducing sensitiser of TGNs, enhanced the CGRP exocytosis induced by low [AITC] only. Both toxins blocked NGF-induced neuropeptide secretion and its enhancement of the response to AITC. In conclusion, NGF sensitisation of sensory neurons involves TRPA1, elevated Ca2+ influx, and CGRP exocytosis, mediated by VAMP1/2/3 and SNAP-25 which can be attenuated by the BoNTs.

Mechanisms of primordial follicle activation and new pregnancy opportunity for premature ovarian failure patients

Primordial follicles are the starting point of follicular development and the basic functional unit of female reproduction. Primordial follicles are formed around birth, and most of the primordial follicles then enter a dormant state. Since primordial follicles are limited in number and can't be renewed, dormant primordial follicles cannot be reversed once they enter the growing state. Thus, the orderly occurrence of primordial follicles selective activation directly affects the rate of follicle consumption and thus determines the length of female reproductive lifespan. Studies have found that appropriately inhibiting the activation rate of primordial follicles can effectively slow down the rate of follicle consumption, maintain fertility and delay ovarian aging. Based on the known mechanisms of primordial follicle activation, primordial follicle in vitro activation (IVA) technique has been clinically developed. IVA can help patients with premature ovarian failure, middle-aged infertile women, or infertile women due to gynecological surgery treatment to solve infertility problems. The study of the mechanism of selective activation of primordial follicles can contribute to the development of more efficient and safe IVA techniques. In this paper, recent mechanisms of primordial follicle activation and its clinical application are reviewed.

Transient receptor potential (TRP) channels mRNA transcripts in the lumbar intervertebral discs: biomarkers for inflammation, pain, disability, and clinical outcome

Transient receptor potential (TRP) channels are widely expressed cation channels that play an essential role in mediating Ca2+ homeostasis and are considered potential regulators of inflammatory pain. This study investigates the expression of the TRP channel subtypes TRPV1, TRPV4, TRPC6, TRPM2, TRPM8 in lumbar intervertebral disc (IVD) biopsies from patients with chronic low back pain (LBP). We determined the expression of these TRP channel subtypes in the annulus fibrosus (AF) and the nucleus pulposus (NP) from 46 patients with LBP undergoing 1-2 level lumbar fusion surgery for degenerative disc disease. The mRNA transcripts were analyzed using quantitative real-time polymerase chain reaction (RT-qPCR), and the expression levels were compared against visual analog scale (VAS) and oswestry disability index (ODI) scores (0-100) for pain and disability. A significant positive correlation was demonstrated between VAS score and the mRNA expression of TRPV1, TRPC6, TRPM2, TRPM8 in the AF. We also found a significant positive correlation between ODI scores and expression of TRPV1 and TRPM8. Further, there is a significant positive correlation between TNF-α and TRPV1, TRPM2 and TRPM8 expression in the AF, and IL-6 to TRPV1 in the NP. Interestingly, when investigating treatment response via a 12-month postoperative follow-up ODI, we found a significant correlation between only TRPV1 expression at baseline and the follow-up ODI scores, which indicates this marker could predict the effectiveness of surgery. These results strongly suggest an association between pain, inflammatory mediators, and TRP channel expression in lumbar disc biopsies of patients with chronic LBP.

A reciprocal feedback between colon cancer cells and Schwann cells promotes the proliferation and metastasis of colon cancer

BACKGROUND

Research has indicated that the emergence of Schwann cells around premalignant lesions of colon cancer might be an early indicator promoting the onset of tumorigenesis. The present study explored the communication between colon cancer cells and Schwann cells.

METHODS

Immunofluorescence analyses were conducted to examine the differential distribution of Schwann cells within colon cancer tissues and normal colon tissues. CCK8 assay, colony formation assay, wound healing assay, and transwell assay were performed to investigate the interaction between colon cancer cells and Schwann cells. Exosomes derived from colon cancer cells were isolated to further explore the effect of colon cancer cells on Schwann cells. Gain- and loss-of function experiments, luciferase reporter assays, chromatin immunoprecipitation assays, and immunohistochemistry assays were performed to reveal the cross-talk between colon cancer cells and Schwann cells. Furthermore, colon cancer cells co-cultured with Schwann cells were transplanted into nude mice for evaluating their effect on tumor proliferation and metastasis in vivo.

RESULTS

The clinicopathological characteristics indicated that Schwann cells were enriched in colon cancer tissues and were associated with tumor metastasis and poor prognosis. The co-culture of Schwann cells with colon cancer cells promoted the proliferation and migration of colon cancer cells and Schwann cells, which was mediated by nerve growth factor (NGF) secreted from Schwann cells. Exosomal miR-21-5p released by colon cancer cells inhibited VHL expression in Schwann cells, which in turn stabilized the HIF-1α protein and increased the transcription of NGF. Meanwhile, the Schwann cells-derived NGF activated TrkA/ERK/ELK1/ZEB1 signaling pathway in colon cancer cells, which further enhanced the expression of exosomal miR-21-5p. Inhibition of either NGF or miR-21-5p significantly inhibited the proliferation and metastasis of transplanted colon cancer cells in nude mice. Coincidently, miR-21-5p was positively associated with the expression of NGF, p-ERK, p-ELK1, and ZEB1 in human colon cancer tissues.

CONCLUSIONS

Our results implicated a reciprocal communication between colon cancer cells and Schwan cells that promoted the proliferation and metastasis of colon cancer, and identified NGF and exosomal miR-21-5p as potential therapeutic targets for the treatment of colon cancer.

Increase in serum nerve growth factor but not intervertebral disc degeneration following whole-body vibration in rats

BACKGROUND

Low back pain is a leading cause of disability and is frequently associated with whole-body vibration exposure in industrial workers and military personnel. While the pathophysiological mechanisms by which whole-body vibration causes low back pain have been studied in vivo, there is little data to inform low back pain diagnosis. Using a rat model of repetitive whole-body vibration followed by recovery, our objective was to determine the effects of vibration frequency on hind paw withdrawal threshold, circulating nerve growth factor concentration, and intervertebral disc degeneration.

METHODS

Male Sprague-Dawley rats were vibrated for 30 min at an 8 Hz or 11 Hz frequency every other day for two weeks and then recovered (no vibration) for one week. Von Frey was used to determine hind paw mechanical sensitivity every two days. Serum nerve growth factor concentration was determined every four days. At the three-week endpoint, intervertebral discs were graded histologically for degeneration.

FINDINGS

The nerve growth factor concentration increased threefold in the 8 Hz group and twofold in the 11 Hz group. The nerve growth factor concentration did not return to baseline by the end of the one-week recovery period for the 8 Hz group. Nerve growth factor serum concentration did not coincide with intervertebral disc degeneration, as no differences in degeneration were observed among groups. Mechanical sensitivity generally decreased over time for all groups, suggesting a habituation (desensitization) effect.

INTERPRETATION

This study demonstrates the potential of nerve growth factor as a diagnostic biomarker for low back pain due to whole-body vibration.

Effects of pharmacological neurotrophin receptor inhibition on bladder function in female mice with cyclophosphamide-induced cystitis

Interstitial cystitis/bladder pain syndrome is a chronic inflammatory pelvic pain syndrome of unknown etiology characterized by a number of lower urinary tract symptoms, including increased urinary urgency and frequency, bladder discomfort, decreased bladder capacity, and pelvic pain. While its etiology remains unknown, a large body of evidence suggests a role for changes in neurotrophin signaling, particularly that of nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF). Here, we evaluated the effects of pharmacological inhibition of the NGF receptor TrkA, BDNF receptor TrkB, and pan-neurotrophin receptor p75NTR on bladder function in acute (4-hour) and chronic (8-day) mouse models of cyclophosphamide (CYP)-induced cystitis. TrkA inhibition via ARRY-954 significantly increased intermicturition interval and bladder capacity in control and acute and chronic CYP-treatment conditions. TrkB inhibition via ANA-12 significantly increased intermicturition interval and bladder capacity in acute, but not chronic, CYP-treatment conditions. Interestingly, intermicturition interval and bladder capacity significantly increased following p75NTR inhibition via LM11A-31 in the acute CYP-treatment condition, but decreased in the chronic condition, potentially due to compensatory changes in neurotrophin signaling or increased urothelial barrier dysfunction in the chronic condition. Our findings demonstrate that these receptors represent additional potent therapeutic targets in mice with cystitis and may be useful in the treatment of interstitial cystitis and other inflammatory disorders of the bladder.

Sensory Neuron-Specific Deletion of Tropomyosin Receptor Kinase A (TrkA) in Mice Abolishes Osteoarthritis (OA) Pain via NGF/TrkA Intervention of Peripheral Sensitization

Tropomyosin receptor kinase A (TrkA/NTRK1) is a high-affinity receptor for nerve growth factor (NGF), a potent pain mediator. NGF/TrkA signaling elevates synovial sensory neuronal distributions in the joints and causes osteoarthritis (OA) pain. We investigated the mechanisms of pain transmission as to whether peripheral sensory neurons are linked to the cellular plasticity in the dorsal root ganglia (DRG) and are critical for OA hyperalgesia. Sensory neuron-specific deletion of TrkA was achieved by tamoxifen injection in 4-week-old TrkA^fl/fl;Na_V1.8^CreERT2 (Ntrk1 ^fl/fl;Scn10a^CreERT2) mice. OA was induced by partial medial meniscectomy (PMM) in 12-week-old mice, and OA-pain-related behavior was analyzed for 12 weeks followed by comprehensive histopathological examinations. OA-associated joint pain was markedly improved without cartilage protection in sensory-neuron-specific conditional TrkA knock-out (cKO) mice. Alleviated hyperalgesia was associated with suppression of the NGF/TrkA pathway and reduced angiogenesis in fibroblast-like synovial cells. Elevated pain transmitters in the DRG of OA-induced mice were significantly diminished in sensory-neuron-specific TrkA cKO and global TrkA cKO mice. Spinal glial activity and brain-derived neurotropic factor (BDNF) were significantly increased in OA-induced mice but were substantially eliminated by sensory-neuron-specific deletion. Our results suggest that augmentation of NGF/TrkA signaling in the joint synovium and the peripheral sensory neurons facilitate pro-nociception and centralized pain sensitization.

The expression of nerve growth factor in healthy and inflamed equine chondrocytes analysed by capillary western immunoassay

Nerve Growth Factor (NGF) is a signalling molecule for pain and inflammation. NGF is increased in synovial fluid from osteoarthritic humans and animals, compared to healthy controls. Monoclonal antibody therapy directed against NGF has been approved to treat pain in osteoarthritic dogs but despite many years of trialling, therapy has not been approved for human use. One reason for this is that adverse reactions with rapidly progressing osteoarthritis has occurred in some individuals. More detailed knowledge of NGF expression in joints is needed. In this study, capillary-based Simple Western was used to analyse NGF in cultured equine chondrocytes. Chondrocytes were collected post mortem from three macroscopically healthy intercarpal joints and three intercarpal joints with mild osteoarthritic changes. The chondrocytes were expanded to passage one and seeded in chondrogenic medium to maintain the phenotype. On day four, cells were either stimulated with LPS or kept untreated in medium. All cells were harvested on day five. Wes analysis of lysates did not show mature NGF but two proforms, 40 and 45 kDa, were identified. Results were confirmed with western blot. The same proforms were expressed in chondrocytes from healthy and osteoarthritic joints. Acute inflammation induced by LPS stimulation did not change the forms of expressed NGF. Capillary Simple Western offers a sensitive and sample-sparing alternative to traditional western blot. However, confirmation of peaks is imperative in order to avoid misinterpretation of findings. In addition, in this case the method did not offer the possibility of quantification advertised by the manufacturers.

Etv4 regulates nociception by controlling peptidergic sensory neuron development and peripheral tissue innervation

The perception of noxious environmental stimuli by nociceptive sensory neurons is an essential mechanism for the prevention of tissue damage. Etv4 is a transcriptional factor expressed in most nociceptors in dorsal root ganglia (DRG) during the embryonic development. However, its physiological role remains unclear. Here, we show that Etv4 ablation results in defects in the development of the peripheral peptidergic projections in vivo, and in deficits in axonal elongation and growth cone morphology in cultured sensory neurons in response to NGF. From a mechanistic point of view, our findings reveal that NGF regulates Etv4-dependent gene expression of molecules involved in extracellular matrix (ECM) remodeling. Etv4-null mice were less sensitive to noxious heat stimuli and chemical pain, and this behavioral phenotype correlates with a significant reduction in the expression of the pain-transducing ion channel TRPV1 in mutant mice. Together, our data demonstrate that Etv4 is required for the correct innervation and function of peptidergic sensory neurons, regulating a transcriptional program that involves molecules associated with axonal growth and pain transduction.

Prdm12 modulates pain-related behavior by remodeling gene expression in mature nociceptors

ABSTRACT

Prdm12 is a conserved epigenetic transcriptional regulator that displays restricted expression in nociceptors of the developing peripheral nervous system. In mice, Prdm12 is required for the development of the entire nociceptive lineage. In humans, PRDM12 mutations cause congenital insensitivity to pain, likely because of the loss of nociceptors. Prdm12 expression is maintained in mature nociceptors suggesting a yet-to-be explored functional role in adults. Using Prdm12 inducible conditional knockout mouse models, we report that in adult nociceptors Prdm12 is no longer required for cell survival but continues to play a role in the transcriptional control of a network of genes, many of them encoding ion channels and receptors. We found that disruption of Prdm12 alters the excitability of dorsal root ganglion neurons in culture. Phenotypically, we observed that mice lacking Prdm12 exhibit normal responses to thermal and mechanical nociceptive stimuli but a reduced response to capsaicin and hypersensitivity to formalin-induced inflammatory pain. Together, our data indicate that Prdm12 regulates pain-related behavior in a complex way by modulating gene expression in adult nociceptors and controlling their excitability. The results encourage further studies to assess the potential of Prdm12 as a target for analgesic development.

Endothelial TrkA coordinates vascularization and innervation in thermogenic adipose tissue and can be targeted to control metabolism

OBJECTIVE

Brown adipogenesis and thermogenesis in brown and beige adipose tissue (AT) involve vascular remodeling and sympathetic neuronal guidance. Here, we investigated the molecular mechanism coordinating these processes.

METHODS

We used mouse models to identify the molecular target of a peptide CPATAERPC homing to the endothelium of brown and beige AT.

RESULTS

We demonstrate that CPATAERPC mimics nerve growth factor (NGF) and identify a low molecular weight isoform of NGF receptor, TrkA, as the CPATAERPC cell surface target. We show that the expression of truncated endothelial TrkA is selective for brown and subcutaneous AT. Analysis of mice with endothelium-specific TrkA knockout revealed the role of TrkA in neuro-vascular coordination supporting the thermogenic function of brown adipocytes. A hunter-killer peptide D-BAT, composed of CPATAERPC and a pro-apoptotic domain, induced cell death in the endothelium and adipocytes. This resulted in thermogenesis impairment, and predisposed mice to obesity and glucose intolerance. We also tested if this treatment can inhibit the tumor recruitment of lipids mobilized from adipocytes from adjacent AT. Indeed, in a mouse model of breast cancer D-BAT suppressed tumor-associated AT lipolysis, which resulted in reduced fatty acid utilization by cancer cells.

CONCLUSION

Our study demonstrates that TrkA signaling in the endothelium supports neuro-vascular coordination enabling beige adipogenesis.