Mechanosensitive ion channels in articular nociceptors drive mechanical allodynia in osteoarthritis

SIRT3 Activation a Promise in Drug Development? New Insights into SIRT3 Biology and Its Implications on the Drug Discovery Process

Sirtuins catalyze deacetylation of lysine residues with a NAD+-dependent mechanism. In mammals, the sirtuin family is composed of seven members, divided into four subclasses that differ in substrate specificity, subcellular localization, regulation, as well as interactions with other proteins, both within and outside the epigenetic field. Recently, much interest has been growing in SIRT3, which is mainly involved in regulating mitochondrial metabolism. Moreover, SIRT3 seems to be protective in diseases such as age-related, neurodegenerative, liver, kidney, heart, and metabolic ones, as well as in cancer. In most cases, activating SIRT3 could be a promising strategy to tackle these health problems. Here, we summarize the main biological functions, substrates, and interactors of SIRT3, as well as several molecules reported in the literature that are able to modulate SIRT3 activity. Among the activators, some derive from natural products, others from library screening, and others from the classical medicinal chemistry approach.

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.

Dental Pulp Stem Cell-Derived Exosomes Alleviate Mice Knee Osteoarthritis by Inhibiting TRPV4-Mediated Osteoclast Activation

Osteoarthritis (OA) is a degenerative disease that causes chronic pain and joint swelling and even disables millions of patients. However, current non-surgical treatment for OA can only relieve pain without obvious cartilage and subchondral bone repair. Mesenchymal stem cell (MSC)-secreted exosomes have promising therapeutic effects on knee OA, but the efficacy of MSC-exosome therapy is not well determined, and the mechanisms involved are still unclear. In this study, we isolated dental pulp stem cell (DPSC)-derived exosomes by ultracentrifugation and determined the therapeutic effects of a single intra-articular injection of DPSC-derived exosomes in a mice knee OA model. The results showed that the DPSC-derived exosomes effectively improved abnormal subchondral bone remodeling, inhibited the occurrence of bone sclerosis and osteophytes, and alleviated cartilage degradation and synovial inflammation in vivo. Moreover, transient receptor potential vanilloid 4 (TRPV4) was activated during the progression of OA. Enhanced TRPV4 activation facilitated osteoclast differentiation, and TRPV4 inhibition blocked this process in vitro. DPSC-derived exosomes repressed osteoclast activation in vivo by inhibiting TRPV4 activation. Our findings demonstrated that a topical, single injection of DPSC-derived exosomes is a potential strategy for knee OA treatment, and that the exosomes regulated osteoclast activation by TRPV4 inhibition, which may act as a promising target for clinical OA treatment.

Gsmtx4 Alleviated Osteoarthritis through Piezo1/Calcineurin/NFAT1 Signaling Axis under Excessive Mechanical Strain

Excessive mechanical strain is the prominent risk factor for osteoarthritis (OA), causing cartilage destruction and degeneration. However, the underlying molecular mechanism contributing to mechanical signaling transduction remains unclear in OA. Piezo type mechanosensitive ion channel component 1 (Piezo1) is a calcium-permeable mechanosensitive ion channel and provides mechanosensitivity to cells, but its role in OA development has not been determined. Herein, we found up-regulated expression of Piezo1 in OA cartilage, and that its activation contributes to chondrocyte apoptosis. The knockdown of Piezo1 could protect chondrocytes from apoptosis and maintain the catabolic and anabolic balance under mechanical strain. In vivo, Gsmtx4, a Piezo1 inhibitor, markedly ameliorated the progression of OA, inhibited the chondrocyte apoptosis, and accelerated the production of the cartilage matrix. Mechanistically, we observed the elevated activity of calcineurin (CaN) and the nuclear transfection of nuclear factor of activated T cells 1 (NFAT1) under mechanical strain in chondrocytes. Inhibitors of CaN or NFAT1 rescued the pathologic changes induced by mechanical strain in chondrocytes. Overall, our findings revealed that Piezo1 was the essential molecule response to mechanical signals and regulated apoptosis and cartilage matrix metabolism via the CaN/NFAT1 signaling axis in chondrocytes, and that Gsmtx4 could be an attractive therapeutic drug for OA treatment.

Peripheral sensory neurons and non-neuronal cells express functional Piezo1 channels

Here, we present evidence showing Piezo1 protein expression in the primary sensory neurons (PSNs) and non-neuronal cells of rat peripheral nervous system. Using a knockdown/knockout validated antibody, we detected Piezo1 immunoreactivity (IR) in ∼60% of PSNs of rat dorsal root ganglia (DRG) with higher IR density in the small- and medium-sized neurons. Piezo1-IR was clearly identified in DRG perineuronal glia, including satellite glial cells (SGCs) and Schwann cells; in sciatic nerve Schwann cells surrounding the axons and cutaneous afferent endings; and in skin epidermal Merkel cells and melanocytes. Neuronal and non-neuronal Piezo1 channels were functional since various cells (dissociated PSNs and SGCs from DRGs, isolated Schwann cells, and primary human melanocytes) exhibited a robust response to Piezo1 agonist Yoda1 by an increase of intracellular Ca2+ concentration ([Ca2+]i). These responses were abolished by non-specific Piezo1 antagonist GsMTx4. Immunoblots showed elevated Piezo1 protein in DRG proximal to peripheral nerve injury-induced painful neuropathy, while PSNs and SGCs from rats with neuropathic pain showed greater Yoda1-evoked elevation of [Ca2+]i and an increased frequency of cells responding to Yoda1, compared to controls. Sciatic nerve application of GsMTx4 alleviated mechanical hypersensitivity induced by Yoda1. Overall, our data show that Piezo1 is widely expressed by the neuronal and non-neuronal cells in the peripheral sensory pathways and that painful nerve injury appeared associated with activation of Piezo1 in PSNs and peripheral glial cells.

Injectable Decorin/Gellan Gum Hydrogel Encapsulating Adipose-Derived Stem Cells Enhances Anti-Inflammatory Effect in Cartilage Injury via Autophagy Signaling

Adipose-derived stem cells (ADSCs) are employed as a promising alternative in treating cartilage injury. Regulating the inflammatory "fingerprint" of ADSCs to improve their anti-inflammatory properties could enhance therapy efficiency. Herein, a novel injectable decorin/gellan gum hydrogel combined with ADSCs encapsulation for arthritis cartilage treatment is proposed. Decorin/gellan gum hydrogel was prepared according to the previous manufacturing protocol. The liquid-solid form transition of gellan gum hydrogel is perfectly suitable for intra-articular injection. Decorin-enriched matrix showing an immunomodulatory ability to enhance ADSCs anti-inflammatory phenotype under inflammation microenvironment by regulating autophagy signaling. This decorin/gellan gum/ADSCs hydrogel efficiently reverses interleukin-1β-induced cellular injury in chondrocytes. Through a mono-iodoacetate-induced arthritis mice model, the synergistic therapeutic effect of this ADSCs-loaded hydrogel, including inflammation attenuation and cartilage protection, is demonstrated. These results make the decorin/gellan gum hydrogel laden with ADSCs an ideal candidate for treating inflammatory joint disorders.

Analgesic dorsal root ganglion field stimulation blocks both afferent and efferent spontaneous activity in sensory neurons of rats with monosodium iodoacetate-induced osteoarthritis

OBJECTIVES

Chronic joint pain is common in patients with osteoarthritis (OA). Non-steroidal anti-inflammatory drugs and opioids are used to relieve OA pain, but they are often inadequately effective. Dorsal root ganglion field stimulation (GFS) is a clinically used neuromodulation approach, although it is not commonly employed for patients with OA pain. GFS showed analgesic effectiveness in our previous study using the monosodium iodoacetate (MIA) - induced OA rat pain model. This study was to evaluate the mechanism of GFS analgesia in this model.

METHODS

After osteoarthritis was induced by intra-articular injection of MIA, pain behavioral tests were performed. Effects of GFS on the spontaneous activity (SA) were tested with in vivo single-unit recordings from teased fiber saphenous nerve, sural nerve, and dorsal root.

RESULTS

Two weeks after intra-articular MIA injection, rats developed pain-like behaviors. In vivo single unit recordings from bundles teased from the saphenous nerve and third lumbar (L3) dorsal root of MIA-OA rats showed a higher incidence of SA than those from saline-injected control rats. GFS at the L3 level blocked L3 dorsal root SA. MIA-OA reduced the punctate mechanical force threshold for inducing AP firing in bundles teased from the L4 dorsal root, which reversed to normal with GFS. After MIA-OA, there was increased retrograde SA (dorsal root reflex), which can be blocked by GFS.

CONCLUSIONS

These results indicate that GFS produces analgesia in MIA-OA rats at least in part by producing blockade of afferent inputs, possibly also by blocking efferent activity from the dorsal horn.

Selective block of sensory neuronal T-type/Cav3.2 activity mitigates neuropathic pain behavior in a rat model of osteoarthritis pain

BACKGROUND

Peripheral and central nociceptive sensitization is a critical pathogenetic component in osteoarthritis (OA) chronic pain. T-type calcium channel 3.2 (CaV3.2) regulates neuronal excitability and plays important roles in pain processing. We previously identified that enhanced T-type/CaV3.2 activity in the primary sensory neurons (PSNs) of dorsal root ganglia (DRG) is associated with neuropathic pain behavior in a rat model of monosodium iodoacetate (MIA)-induced knee OA. PSN-specific T-type/CaV3.2 may therefore represent an important mediator in OA painful neuropathy. Here, we test the hypothesis that the T-type/CaV3.2 channels in PSNs can be rationally targeted for pain relief in MIA-OA.

METHODS

MIA model of knee OA was induced in male and female rats by a single injection of 2 mg MIA into intra-knee articular cavity. Two weeks after induction of knee MIA-OA pain, recombinant adeno-associated viruses (AAV)-encoding potent CaV3.2 inhibitory peptide aptamer 2 (CaV3.2iPA2) that have been characterized in our previous study were delivered into the ipsilateral lumbar 4/5 DRG. Effectiveness of DRG-CaV3.2iPA2 treatment on evoked (mechanical and thermal) and spontaneous (conditioned place preference) pain behavior, as well as weight-bearing asymmetry measured by Incapacitance tester, in the arthritic limbs of MIA rats were evaluated. AAV-mediated transgene expression in DRG was determined by immunohistochemistry.

RESULTS

AAV-mediated expression of CaV3.2iPA2 selective in the DRG-PSNs produced significant and comparable mitigations of evoked and spontaneous pain behavior, as well as normalization of weight-bearing asymmetry in both male and female MIA-OA rats. Analgesia of DRG-AAV-CaV3.2iPA1, another potent CaV3.2 inhibitory peptide, was also observed. Whole-cell current-clamp recordings showed that AAV-mediated CaV3.2iPA2 expression normalized hyperexcitability of the PSNs dissociated from the DRG of MIA animals, suggesting that CaV3.2iPA2 attenuated pain behavior by reversing MIA-induced neuronal hyperexcitability.

CONCLUSIONS

Together, our results add therapeutic support that T-type/CaV3.2 in primary sensory pathways contributes to MIA-OA pain pathogenesis and that CaV3.2iPAs are promising analgesic leads that, combined with AAV-targeted delivery in anatomically segmental sensory ganglia, have the potential for further development as a peripheral selective T-type/CaV3.2-targeting strategy in mitigating chronic MIA-OA pain behavior. Validation of the therapeutic potential of this strategy in other OA models may be valuable in future study.

Peedanil Gold, Herbo-Mineral Formulation, Moderates Cytokine Levels and Attenuates Pathophysiology in Monosodium Iodoacetate Induced Osteoarthritis in SD Rat Model

The inflammatory cartilaginous degeneration of the articular joints, mostly those of knee, hips and hands, is osteoarthritis (OA). The available treatment strategies for osteoarthritis are designed for pain relief, molecular targeting, cartilage regeneration and surgical intervention. However, meta-analysis of clinical trials has shown these strategies to be sub-optimal, thereby, eliciting a need for investigating alternative options. The herbo-mineral formulation, Peedanil Gold (PN-G) has been used against joint pains and inflammation. In the current study, anti-osteoarthritic effects of PN-G were investigated in rat model of OA, induced by intra-articular injection of monosodium-iodoacetate. PN-G treatment improved the clinical and Kellgren & Lawrence scores; and rescued the osteoarthritic rats from hyperalgesia and allodynia. Besides, PN-G treatment ameliorated joint inflammation and abrogated in vivo osteoarthritic pathology through effective cartilage regeneration, measured radiologically and histopathologically. PN-G also reduced the levels of interleukin-6 (IL-6) and interleukin-1 beta (IL-1β), in a dose dependent manner, in inflamed human macrophagic THP-1 cells, thereby, reaffirming its anti-inflammatory property at cytosafe concentrations. Ultra High performance liquid chromatography (UHPLC) revealed the presence of several analgesic and anti-inflammatory phytocompounds, like ellagic acid, guggulsterone E, guggulsterone Z, 5-(hydroxymethyl) furfural, corilagin, cinnamic acid, ferulic acid, gallic acid and protocatechuic acid in PN-G. In conclusion, this study has succinctly demonstrated that PN-G is capable of relieving the clinical symptoms of osteoarthritis, which is measurable through the established osteoarthritic serum biomarker, Cartilage Oligomeric Matrix Protein (COMP).

Mechanosensory and mechanotransductive processes mediated by ion channels in articular chondrocytes: Potential therapeutic targets for osteoarthritis

Articular cartilage consists of an extracellular matrix including many proteins as well as embedded chondrocytes. Articular cartilage formation and function are influenced by mechanical forces. Hind limb unloading or simulated microgravity causes articular cartilage loss, suggesting the importance of the healthy mechanical environment in articular cartilage homeostasis and implying a significant role of appropriate mechanical stimulation in articular cartilage degeneration. Mechanosensitive ion channels participate in regulating the metabolism of articular chondrocytes, including matrix protein production and extracellular matrix synthesis. Mechanical stimuli, including fluid shear stress, stretch, compression and cell swelling and decreased mechanical conditions (such as simulated microgravity) can alter the membrane potential and regulate the metabolism of articular chondrocytes via transmembrane ion channel-induced ionic fluxes. This process includes Ca2+ influx and the resulting mobilization of Ca2+ that is due to massive released Ca2+ from stores, intracellular cation efflux and extracellular cation influx. This review brings together published information on mechanosensitive ion channels, such as stretch-activated channels (SACs), voltage-gated Ca2+ channels (VGCCs), large conductance Ca2+-activated K+ channels (BKCa channels), Ca2+-activated K+ channels (SKCa channels), voltage-activated H+ channels (VAHCs), acid sensing ion channels (ASICs), transient receptor potential (TRP) family channels, and piezo1/2 channels. Data based on epithelial sodium channels (ENaCs), purinergic receptors and N-methyl-d-aspartate (NMDA) receptors are also included. These channels mediate mechanoelectrical physiological processes essential for converting physical force signals into biological signals. The primary channel-mediated effects and signaling pathways regulated by these mechanosensitive ion channels can influence the progression of osteoarthritis during the mechanosensory and mechanoadaptive process of articular chondrocytes.

Mechanosensitive ion channels contribute to mechanically evoked rapid leaflet movement in Mimosa pudica

Mechanoperception, the ability to perceive and respond to mechanical stimuli, is a common and fundamental property of all forms of life. Vascular plants such as Mimosa pudica use this function to protect themselves against herbivory. The mechanical stimulus caused by a landing insect triggers a rapid closing of the leaflets that drives the potential pest away. While this thigmonastic movement is caused by ion fluxes accompanied by a rapid change of volume in the pulvini, the mechanism responsible for the detection of the mechanical stimulus remains poorly understood. Here, we examined the role of mechanosensitive ion channels in the first step of this evolutionarily conserved defense mechanism: the mechanically evoked closing of the leaflet. Our results demonstrate that the key site of mechanosensation in the Mimosa leaflets is the pulvinule, which expresses a stretch-activated chloride-permeable mechanosensitive ion channel. Blocking these channels partially prevents the closure of the leaflets following mechanical stimulation. These results demonstrate a direct relation between the activity of mechanosensitive ion channels and a central defense mechanism of M. pudica.

Time-integrated propulsive and braking impulses do not depend on walking speed

BACKGROUND

Enhancing propulsion during walking is often a focus in physical therapy for those with impaired gait. However, there is no consensus in the literature for assessing braking and propulsion. Both are typically measured from the anterior-posterior ground reaction force (AP-GRF). While normalization of AP-GRF force by bodyweight is commonly done in the analysis, different methods for AP-GRF time axis normalization are used.

RESEARCH QUESTION

Does walking speed affect propulsion and/or braking, and how do different methods for calculating propulsion and braking impact the conclusion, in both healthy adults and those with lower limb impairment?

METHODS

We investigated three different analysis methods for assessing propulsion. 1. BW-TimeIntegration: Bodyweight (BW) normalized time integration of AP-GRF (units of BWs). 2. BW-%StanceIntegration: BW normalized AP-GRF is resampled to percent stance phase prior to integration (units of BW%Stance). 3. BW-Peak: BW normalized peak force (units of BW). We applied these methods to two data sets. One data set included AP-GRFs from trials of slow, self-selected, and fast walking speeds for 203 healthy controls (HCs); a second data set included subjects with lower limb orthopedic injuries.

RESULTS

Using the BW-TimeIntegration method, we found no effect of walking speed on propulsion for HCs. Time integration over the longer stance phase of slower walking balanced the lower magnitude AP-GRFs of slower walking, resulting in a time-integrated impulse that was the same regardless of walking speed. In contrast, the other two methods that are not time integration methods found that propulsion increased with walking speed. Similarly, in the gait pathology data set, differences in results were found depending on the analysis method used.

SIGNIFICANCE

For many gait studies concerning propulsion and/or braking, the impulse measure used should be related to the body's change of momentum, necessitating an analysis method with a time integration of the AP-GRF.

Piezo Channels: Awesome Mechanosensitive Structures in Cellular Mechanotransduction and Their Role in Bone

Piezo channels are mechanosensitive ion channels located in the cell membrane and function as key cellular mechanotransducers for converting mechanical stimuli into electrochemical signals. Emerged as key molecular detectors of mechanical forces, Piezo channels' functions in bone have attracted more and more attention. Here, we summarize the current knowledge of Piezo channels and review the research advances of Piezo channels' function in bone by highlighting Piezo1's role in bone cells, including osteocyte, bone marrow mesenchymal stem cell (BM-MSC), osteoblast, osteoclast, and chondrocyte. Moreover, the role of Piezo channels in bone diseases is summarized.

Peripheral and central nervous system alterations in a rat model of inflammatory arthritis

It is consistently reported that in inflammatory arthritis (IA), pain may continue despite well-controlled inflammation, most likely due to interactions between joint pathology and pain pathway alterations. Nervous system alterations have been described, but much remains to be understood about neuronal and central non-neuronal changes in IA. Using a rat model of IA induced by intra-articular complete Freund's adjuvant injection, this study includes a thorough characterization of joint pathology and objectives to identify peripheral innervation changes and alterations in the spinal dorsal horn (DH) that could alter DH excitatory balancing. Male and female rats displayed long-lasting pain-related behavior, but, in agreement with our previous studies, other pathological alterations emerged only at later times. Cartilage vascularization, thinning, and decreased proteoglycan content were not detectable in the ipsilateral cartilage until 4 weeks after complete Freund's adjuvant. Sympathetic and peptidergic nociceptive fibers invaded the ipsilateral cartilage alongside blood vessels, complex innervation changes were observed in the surrounding skin, and ipsilateral nerve growth factor protein expression was increased. In the DH, we examined innervation by peptidergic and nonpeptidergic nociceptors, inhibitory terminal density, the KCl cotransporter KCC2, microgliosis, and astrocytosis. Here, we detected the presence of microgliosis and, interestingly, an apparent loss of inhibitory terminals and decreased expression of KCC2. In conclusion, we found evidence of anatomical, inflammatory, and neuronal alterations in the peripheral and central nervous systems in a model of IA. Together, these suggest that there may be a shift in the balance between incoming and outgoing excitation, and modulatory inhibitory tone in the DH.

Neuronal interleukin-1 receptors mediate pain in chronic inflammatory diseases

Chronic pain is a major comorbidity of chronic inflammatory diseases. Here, we report that the cytokine IL-1β, which is abundantly produced during multiple sclerosis (MS), arthritis (RA), and osteoarthritis (OA) both in humans and in animal models, drives pain associated with these diseases. We found that the type 1 IL-1 receptor (IL-1R1) is highly expressed in the mouse and human by a subpopulation of TRPV1⁺ dorsal root ganglion neurons specialized in detecting painful stimuli, termed nociceptors. Strikingly, deletion of the Il1r1 gene specifically in TRPV1⁺ nociceptors prevented the development of mechanical allodynia without affecting clinical signs and disease progression in mice with experimental autoimmune encephalomyelitis and K/BxN serum transfer–induced RA. Conditional restoration of IL-1R1 expression in nociceptors of IL-1R1–knockout mice induced pain behavior but did not affect joint damage in monosodium iodoacetate–induced OA. Collectively, these data reveal that neuronal IL-1R1 signaling mediates pain, uncovering the potential benefit of anti–IL-1 therapies for pain management in patients with chronic inflammatory diseases.

Neuroscience and Neuroimmunology Solutions for Osteoarthritis Pain: Biological Drugs, Growth Factors, Peptides and Monoclonal Antibodies Targeting Peripheral Nerves

Neuroscience is a vast discipline that deals with the anatomy, biochemistry, molecular biology, physiology and pathophysiology of central and peripheral nerves. Advances made through basic, translational, and clinical research in the field of neuroscience have great potential for long-lasting and beneficial impacts on human and animal health. The emerging field of biological therapy is intersecting with the disciplines of neuroscience, orthopaedics and rheumatology, creating new horizons for interdisciplinary and applied research. Biological drugs, growth factors, therapeutic peptides and monoclonal antibodies are being developed and tested for the treatment of painful arthritic and rheumatic diseases. This concise communication focuses on the solutions provided by the fields of neuroscience and neuroimmunology for real-world clinical problems in the field of orthopaedics and rheumatology, focusing on synovial joint pain and the emerging biological treatments that specifically target pathways implicated in osteoarthritis pain in peripheral nerves.

Mitochondria: Potential Targets for Osteoarthritis

Osteoarthritis (OA) is a common and disabling joint disorder that is mainly characterized by cartilage degeneration and narrow joint spaces. The role of mitochondrial dysfunction in promoting the development of OA has gained much attention. Targeting endogenous molecules to improve mitochondrial function is a potential treatment for OA. Moreover, research on exogenous drugs to improve mitochondrial function in OA based on endogenous molecular targets has been accomplished. In addition, stem cells and exosomes have been deeply researched in the context of cartilage regeneration, and these factors both reverse mitochondrial dysfunctions. Thus, we hypothesize that biomedical approaches will be applied to the treatment of OA. Furthermore, we have summarized the global status of mitochondria and osteoarthritis research in the past two decades, which will contribute to the research field and the development of novel treatment strategies for OA.

Involvement of TACAN, a Mechanotransducing Ion Channel, in Inflammatory But Not Neuropathic Hyperalgesia in the Rat

TACAN (Tmem120A), a mechanotransducing ion channel highly expressed in a subset of nociceptors, has recently been shown to contribute to detection of noxious mechanical stimulation. In the present study we evaluated its role in sensitization to mechanical stimuli associated with preclinical models of inflammatory and chemotherapy-induced neuropathic pain (CIPN). Intrathecal administration of an oligodeoxynucleotide antisense (AS-ODN) to TACAN mRNA attenuated TACAN protein expression in rat dorsal root ganglia (DRG). While TACAN AS-ODN produced only a modest increase in mechanical nociceptive threshold, it markedly reduced mechanical hyperalgesia produced by intradermal administration of prostaglandin E₂, tumor necrosis factor alpha, and low molecular weight hyaluronan, and systemic administration of lipopolysaccharide, compatible with a prominent role of TACAN in mechanical hyperalgesia produced by inflammation. In contrast, TACAN AS-ODN had no effect on mechanical hyperalgesia associated with CIPN produced by oxaliplatin or paclitaxel. Our results provide evidence that TACAN plays a role in mechanical hyperalgesia induced by pronociceptive inflammatory mediators, but not CIPN, compatible with multiple mechanisms mediating mechanical nociception, and sensitization to mechanical stimuli in preclinical models of inflammatory versus CIPN. PERSPECTIVE: We evaluated the role of TACAN, a mechanotransducing ion channel in nociceptors, in preclinical models of inflammatory and CIPN. Attenuation of TACAN expression reduced hyperalgesia produced by inflammatory mediators but had not chemotherapeutic agents. Our findings support the presence of multiple mechanotransducers in nociceptors.

Dietary Supplementation with Palmitoyl-Glucosamine Co-Micronized with Curcumin Relieves Osteoarthritis Pain and Benefits Joint Mobility

Simple Summary

Canine osteoarthritis is a chronic degenerative joint disease and a major cause of elective euthanasia. The disorder increasingly limits joint motion, might cause lameness as well as pain, and impacts quality of life. An unmet need remains for safe and effective therapies for osteoarthritis. Palmitoyl-glucosamine and curcumin are used in animal nutrition. A co-micronized formulation, with the two substances being jointly processed to reduce their particle size and increase the extent to which they can be absorbed, is currently available on the European market. The present study investigated if this formulation could relieve joint pain and benefit mobility. Two well-established rat models of inflammation and osteoarthritis pain were used. Results from the first set of experiments showed that the dietary supplement relieved experimentally induced paw edema, infiltration of inflammatory cells, and decreased sensitivity to painful stimuli (thermal hyperalgesia). In the osteoarthritis model, the supplement proved to protect joint cartilage against degradation and successfully address neuropathic pain (i.e., pain from normally non-painful stimuli). Locomotor function recovered by 45% under supplement administration. The present findings suggest that the dietary supplement with palmitoyl-glucosamine co-micronized with curcumin might help manage osteoarthritis.

Abstract

Chronic mixed pain and orthopedic dysfunction are the most frequently associated consequences of canine osteoarthritis (OA). An unmet need remains for safe and effective therapies for OA. Palmitoyl-glucosamine (PGA) and curcumin are safe and naturally occurring compounds whose use is limited by poor bioavailability. Micronization is an established technique to increase bioavailability. The aim of this study was to investigate if the dietary supplementation with PGA co-micronized with curcumin (PGA-Cur, 2:1 ratio by mass) could limit pathologic process in two well-established rat models of inflammation and OA pain, i.e., subplantar carrageenan (CAR) and knee injection of sodium monoiodoacetate (MIA), respectively. In CAR-injected animals, a single dose of PGA-cur significantly reduced paw edema and hyperalgesia, as well as tissue damage and neutrophil infiltration. The repeated administration of PGA-Cur three times per week for 21 days, starting the third day after MIA injection resulted in a significant anti-allodynic effect. Protection against cartilage damage and recovery of locomotor function by 45% were also recorded. Finally, PGA-cur significantly counteracted MIA-induced increase in serum levels of TNF-α, IL-1β, NGF, as well as metalloproteases 1, 3, and 9. All the effects of PGA-Cur were superior compared to the compounds used singly. PGA-Cur emerged as a useful dietary intervention for OA.

Peripheral mechanisms of arthritic pain: A proposal to leverage large animals for in vitro studies

Pain arising from musculoskeletal disorders such as arthritis is one of the leading causes of disability. Whereas the past 20-years has seen an increase in targeted therapies for rheumatoid arthritis (RA), other arthritis conditions, especially osteoarthritis, remain poorly treated. Although modulation of central pain pathways occurs in chronic arthritis, multiple lines of evidence indicate that peripherally driven pain is important in arthritic pain. To understand the peripheral mechanisms of arthritic pain, various in vitro and in vivo models have been developed, largely in rodents. Although rodent models provide numerous advantages for studying arthritis pathogenesis and treatment, the anatomy and biomechanics of rodent joints differ considerably to those of humans. By contrast, the anatomy and biomechanics of joints in larger animals, such as dogs, show greater similarity to human joints and thus studying them can provide novel insight for arthritis research. The purpose of this article is firstly to review models of arthritis and behavioral outcomes commonly used in large animals. Secondly, we review the existing in vitro models and assays used to study arthritic pain, primarily in rodents, and discuss the potential for adopting these strategies, as well as likely limitations, in large animals. We believe that exploring peripheral mechanisms of arthritic pain in vitro in large animals has the potential to reduce the veterinary burden of arthritis in commonly afflicted species like dogs, as well as to improve translatability of pain research into the clinic.

Role of mechanosensitive ion channels in the sensation of pain

Our ability to sense mechanical cues from our environment depend on the capacity of molecular sensor capable of converting mechanical energy into biochemical or electrical signals. This process, termed mechanotransduction, relies on the activity of mechanosensitive ion channels (MSCs) that are expressed in most tissues, including cells of the inner and outer ear, sensory and sympathetic neurons, and vascular cells. However, the precise role these channels play in the physiology of the cells and organs, where they are expressed is not completely understood. In this review, we will explore some of the recent findings on the role of MSCs to our sense of mechanical pain.

Effects of Neurodynamic Mobilizations on Pain Hypersensitivity in Patients With Hand Osteoarthritis Compared to Robotic Assisted Mobilization: A Randomized Controlled Trial

OBJECTIVE

To evaluate the effectiveness of the neurodynamic mobilization techniques compared with passive robotic physiologic movement in patients with hand osteoarthritis (OA).

METHODS

We conducted a randomized controlled trial. A total of 72 patients (mean ± SD age 71 ± 11 years) with dominant symptomatic hand OA were randomized in 2 groups, and both received 12 treatment sessions over 4 weeks. The experimental group received neurodynamic mobilization of the median, radial, and ulnar nerves, and the control group received robotic-assisted passive movement treatment. Both groups also participated in a program of hand stability exercises. Outcome measures included pain intensity, pressure pain thresholds (PPTs), and strength measurements. Group-by-time effects were compared using mixed-model analyses of variance.

RESULTS

After the intervention, the experimental group had statistically significant, higher PPTs than the control group at the thumb carpometacarpal joint by 0.7 kg/cm² (95% confidence interval [95% CI] 0.6, 0.8), the median nerve by 0.7 kg/cm² (95% CI 0.6, 0.7), and the radial nerve by 0.5 kg/cm² (95% CI 0.3, 0.6); however, the difference was not statistically significant at 3 months postintervention. Although mean values in the experimental group were higher than in the control group at all PPT sites at both assessments, these differences were not statistically significant. The experimental group experienced a statistically significant reduction in pain immediately postintervention, but this was not present at the 3-month follow-up. There were no statistically significant differences in pinch or grip strength between groups.

CONCLUSION

We found that neurodynamic mobilizations decreased hypersensitivity in patients with hand OA immediately after the intervention; however, differences were no longer present at 3 months. The results suggest that these techniques may have some limited value in the short term but do not have lasting effects.

The neuropeptide GsMTx4 inhibits a mechanosensitive BK channel through the voltage-dependent modification specific to mechano-gating

The cardiac mechanosensitive BK (Slo1) channels are gated by Ca²⁺, voltage, and membrane stretch. The neuropeptide GsMTx4 is a selective inhibitor of mechanosensitive (MS) channels. It has been reported to suppress stretch-induced cardiac fibrillation in the heart, but the mechanism underlying the specificity and even the targeting channel(s) in the heart remain elusive. Here, we report that GsMTx4 inhibits a stretch-activated BK channel (SAKcaC) in the heart through a modulation specific to mechano-gating. We show that membrane stretching increases while GsMTx4 decreases the open probability (P _o) of SAKcaC. These effects were mostly abolished by the deletion of the STREX axis-regulated (STREX) exon located between RCK1 and RCK2 domains in BK channels. Single-channel kinetics analysis revealed that membrane stretch activates SAKcaC by prolonging the open-time duration (τ_O) and shortening the closed-time constant (τ_C). In contrast, GsMTx4 reversed the effects of membrane stretch, suggesting that GsMTx4 inhibits SAKcaC activity by interfering with mechano-gating of the channel. Moreover, GsMTx4 exerted stronger efficacy on SAKcaC under membrane-hyperpolarized/resting conditions. Molecular dynamics simulation study revealed that GsMTx4 appeared to have the ability to penetrate deeply within the bilayer, thus generating strong membrane deformation under the hyperpolarizing/resting conditions. Immunostaining results indicate that BK variants containing STREX are also expressed in mouse ventricular cardiomyocytes. Our results provide common mechanisms of peptide actions on MS channels and may give clues to therapeutic suppression of cardiac arrhythmias caused by excitatory currents through MS channels under hyper-mechanical stress in the heart.

SIRT3 Activation by Dihydromyricetin Suppresses Chondrocytes Degeneration via Maintaining Mitochondrial Homeostasis

Mitochondrial dysfunction is an important contributor to the development of osteoarthritis (OA). Sirtuin 3 (SIRT3) regulates diverse mitochondrial proteins to maintain mitochondrial homeostasis, and dihydromyricetin (DHM) is reported as a potential SIRT3 activator. This study aims to explore the relevance of SIRT3 and OA, as well as the therapeutic effects of DHM on mitochondrial homeostasis in TNF-α-treated chondrocytes. The relationship between SIRT3 and OA was confirmed by detecting SIRT3 level in vitro and in vivo. Mitochondrial dysfunction was evaluated in chondrocytes with or without SIRT3 knockdown. Furthermore, the effects of DHM on mitochondrial homeostasis were performed in TNF-α-treated rat chondrocytes in vitro. In this study, our results showed that the SIRT3 level was decreased in mouse OA cartilage, corresponding to the reduced SIRT3 level in TNF-α-treated chondrocytes in vitro. SIRT3 knockdown induced mitochondrial dysfunction in chondrocytes. Moreover, our study demonstrated that DHM might activate SIRT3 to protect rat chondrocytes from TNF-α-induced degeneration and protective effects of DHM on mitochondrial homeostasis in chondrocytes attributed to enhanced SIRT3. Collectively, SIRT3 deficiency is implicated in OA development and DHM exerts anti-degeneration effect by maintaining mitochondrial homeostasis via a SIRT3-dependent manner in chondrocytes.

Dynamic regulation of TREK1 gating by Polycystin 2 via a Filamin A-mediated cytoskeletal Mechanism

Mechanosensing is essential for several physiological functions including touch and pain sensations, osmoregulation, and controlling the myogenic tone of resistance arteries. Understanding how mechanosensitive ion channels (MSCs) are gated can provide important information regarding these processes. We have previously demonstrated that during pathological conditions such as polycystic kidney disease, polycystin 2 (TRPP2) inhibits the activity of potassium-selective MSCs through a filamin A-mediated cytoskeletal effect, and renders tubular epithelial cells susceptible to apoptosis. However, the nature of this cytoskeletal inhibition remains poorly understood. In this study we use a combination of electrophysiology, structured illumination microscopy, and fluorescence recovery after photobleaching (FRAP) to examine the dynamic nature of the TRPP2-mediated cytoskeletal inhibition of the potassium-selective MSC TREK1. Our data indicate that this inhibition of MSC activity occurs through an accelerated cytoskeletal inhibition, and ultimately decreases the open probability of the TREK1 channel. These results shed light on a novel mode of regulation of MSCs gating, which may be at play in several physiological functions.

Osteoarthritis pain: What are we learning from animal models?

All experimental models of osteoarthritis (OA)-like joint damage are accompanied by behaviors indicative of pain. In experimental knee OA, evoked pain responses to exogenously applied stimuli suggest that animals become sensitized to mechanical stimuli. Neurobiological techniques including electrophysiology and in vivo calcium imaging confirm that joint damage is associated with mechanical stimuli through peripheral sensitization. Several mediators present in the OA joint can cause peripheral sensitization, most notably the neurotrophin nerve growth factor (NGF). Furthermore, experimental OA is associated with neuroinflammation in the peripheral nervous system and central nervous system (CNS), including macrophage infiltration of the dorsal root ganglia and microglial activation in the spinal cord. Increasingly, researchers are employing models that are slowly progressive, and this approach has revealed that distinct pain mechanisms operate in a time-dependent manner, which may have important translational significance. While the study of pain in experimental OA is rapidly evolving, with the application of increasingly sophisticated techniques to assess pain and unravel the neurobiology of its genesis, important gaps and limitations in our current approaches exist, which our research community needs to address.