The role of Ca2+ in acid-sensing ion channel 1a-mediated chondrocyte pyroptosis in rat adjuvant arthritis

Degrasyn alleviates osteoarthritis by blocking macrophagic pyroptosis via suppressing NLRP3/GSDMD signaling pathway and protecting chondrocytes

Synovitis and cartilage destruction are crucial characteristics of osteoarthritis (OA). Inflammatory cytokines, such as IL-1β, are secreted by synovial macrophages, leading to cartilage destruction. Pyroptosis is a lytic form of programmed cell death, which could be triggered by the NLRP3 inflammasome of macrophages. Pyroptosis promotes the secretion of IL-1β and is supposed as a potential biomarker for OA. However, the function of Pyroptosis and NLRP3 inflammasome and its regulatory mechanism for activation is unclear in OA. In this study, we found that Degrasyn could alleviate the GSDMD-mediated pyroptosis of macrophages and the release of IL-1β, caspase-1, and LDH. Furthermore, it selectively impedes the form of ASC oligomer and speckle to effectively suppress the NLRP3 inflammasome during its assembly phase. Notably, Degrasyn exhibited potential chondroprotective effects in a co-culture system. Additionally, these results also indicate that Degrasyn mitigates synovitis and cartilage damage in a murine model of destabilization of the medial meniscus (DMM)-induced OA. In summary, Degrasyn emerges as a promising pharmaceutical agent for synovitis, paving the way for innovative therapeutic approaches to OA. Our findings underscore the potential of Degrasyn as a viable candidate for OA therapeutics, demonstrating its ability to regulate pyroptosis and NLRP3 inflammasome activation.

Reperfusion Injury in Patients With Acute Myocardial Infarction: JACC Scientific Statement

Despite impressive improvements in the care of patients with ST-segment elevation myocardial infarction, mortality remains high. Reperfusion is necessary for myocardial salvage, but the abrupt return of flow sets off a cascade of injurious processes that can lead to further necrosis. This has been termed myocardial ischemia-reperfusion injury and is the subject of this review. The pathologic and molecular bases for myocardial ischemia-reperfusion injury are increasingly understood and include injury from reactive oxygen species, inflammation, calcium overload, endothelial dysfunction, and impaired microvascular flow. A variety of pharmacologic strategies have been developed that have worked well in preclinical models and some have shown promise in the clinical setting. In addition, there are newer mechanical approaches including mechanical unloading of the heart prior to reperfusion that are in current clinical trials.

The bone nonunion microenvironment: A place where osteogenesis struggles with osteoclastic capacity

Bone nonunion is a common and serious orthopedic disorder, the occurrence of which is associated with a disruption of the dynamic balance between osteoblasts and osteoclasts during bone repair. However, the critical molecular mechanisms affecting this homeostasis are not well understood, and it is essential to investigate the specific components of this mechanism and to restore the balance between osteoblasts and osteoclasts to promote bone repair. First, we defined this complex local environmental factor as the "bone nonunion microenvironment" and identified the importance of the "struggle" between osteoblasts and osteoclasts, which is the most essential element in determining the process of repair. On this basis, we also explored the cellular factors that influence osteogenesis and the molecular signals that influence the balance between osteoclast and osteoblasts, which are important for restoring homeostasis. Further, we explored other factors involved in osteogenesis, such as the biomechanical environment, the nutritional environment, the acid-base environment, and the temperature environment, which are important players in osteogenesis. In conclusion, we found that the balance between osteoblasts and osteoclasts is the essence of bone healing, which is based on the "bone nonunion microenvironment". Therefore, investigating the role of the bone nonunion microenvironment in the system of osteoblast-osteoclast "struggle" provides an important basis for further understanding of the mechanism of nonunion and the development of new therapeutic approaches.

Smart Hydrogels for Tissue Regeneration

The rapid growth in the portion of the aging population has led to a consequent increase in demand for biomedical hydrogels, together with an assortment of challenges that need to be overcome in this field. Smart hydrogels can autonomously sense and respond to the physiological/pathological changes of the tissue microenvironment and continuously adapt the response according to the dynamic spatiotemporal shifts in conditions. This along with other favorable properties, make smart hydrogels excellent materials for employing toward improving the precision of treatment for age-related diseases. The key factor during the smart hydrogel design is on accurately identifying the characteristics of natural tissues and faithfully replicating the composition, structure, and biological functions of these tissues at the molecular level. Such hydrogels can accurately sense distinct physiological and external factors such as temperature and biologically active molecules, so they may in turn actively and promptly adjust their response, by regulating their own biological effects, thereby promoting damaged tissue repair. This review summarizes the design strategies employed in the creation of smart hydrogels, their response mechanisms, as well as their applications in field of tissue engineering; and concludes by briefly discussing the relevant challenges and future prospects.

Endoplasmic reticulum aminopeptidase 2 regulates CD4+ T cells pyroptosis in rheumatoid arthritis

OBJECTIVE

Rheumatoid arthritis (RA) is a chronic, progressive autoimmune disease with a complex pathogenesis that has not yet been fully elucidated, and T-cell pyroptosis is an important pathogenetic factor in RA. This study aimed to investigate the role of endoplasmic reticulum aminopeptidase 2 (ERAP2) in the pyroptosis of CD4+ T cells in RA and the specific molecular mechanism.

METHODS

Peripheral venous blood was collected from human subjects, and CD4+ T cells were isolated and activated to measure the level of pyroptosis and ERAP2 expression. Pyroptosis levels were assessed using immunofluorescence, flow cytometry, qRT-PCR, and Western blotting. Changes in pyroptosis levels were observed upon knockdown or overexpression of ERAP2. To detect activated Caspase-1 in tissues, chimeric mice were engrafted with human synovial tissue and reconstituted with human CD4+ T cells. CD4 + T cells were treated with GLI1 antagonists and SMO receptor agonists to detect changes in pyroptosis levels.

RESULTS

CD4+ T cell levels undergoing pyroptosis were found to be elevated in the blood and synovium of RA patients. The gene and protein expression of ERAP2 were significantly higher in CD4+ T cells from RA patients. Deletion of ERAP2 suppressed pyroptosis of these cells, attenuated the activation of Caspase-1 in tissue T cells, and reduced tissue inflammatory responses. Reciprocally, overexpression of ERAP2 triggered inflammasome assembly, activated Caspase-1, and induced pyroptosis in CD4+ T cells. Mechanistically, ERAP2 inhibits the Hedgehog signaling pathway and upregulates the expression of nucleotide-binding oligomerization segment-like receptor family 3(NLRP3), cleaved Caspase-1, and Gasdermin D to promote pyroptosis in CD4+ T cells.

CONCLUSIONS

Taken together, our results identify a novel mechanism by which ERAP2 regulates RA development and document the effect of the ERAP2/Hedgehog signaling axis on pyroptosis of CD4+ T cells from RA patients.

The NLRP3 Inflammasome as a Pathogenic Player Showing Therapeutic Potential in Rheumatoid Arthritis and Its Comorbidities: A Narrative Review

Rheumatoid arthritis (RA) is an autoimmune inflammatory disease characterized by chronic synovitis and the progressive destruction of cartilage and bone. RA is commonly accompanied by extra-articular comorbidities. The pathogenesis of RA and its comorbidities is complex and not completely elucidated. The assembly of the NOD-, LRR- and pyrin domain-containing protein 3 (NLRP3) inflammasome activates caspase-1, which induces the maturation of interleukin (IL)-1β and IL-18 and leads to the cleavage of gasdermin D with promoting pyroptosis. Accumulative evidence indicates the pathogenic role of NLRP3 inflammasome signaling in RA and its comorbidities, including atherosclerotic cardiovascular disease, osteoporosis, and interstitial lung diseases. Although the available therapeutic agents are effective for RA treatment, their high cost and increased infection rate are causes for concern. Recent evidence revealed the components of the NLRP3 inflammasome as potential therapeutic targets in RA and its comorbidities. In this review, we searched the MEDLINE database using the PubMed interface and reviewed English-language literature on the NLRP3 inflammasome in RA and its comorbidities from 2000 to 2023. The current evidence reveals that the NLRP3 inflammasome contributes to the pathogenesis of RA and its comorbidities. Consequently, the components of the NLRP3 inflammasome signaling pathway represent promising therapeutic targets, and ongoing research might lead to the development of new, effective treatments for RA and its comorbidities.

A novel drug combination of Tofacitinib and Iguratimod alleviates rheumatoid arthritis and secondary osteoporosis

BACKGROUND

The inadequate response of some patients with rheumatoid arthritis (RA) to current therapies is an issue that needs to be addressed. Patients with refractory RA (RRA) are often accompanied by high Tumor necrosis factor (TNF) expression. We evaluated the synergistic therapeutic effects of the combination of Iguratimod (IGU) and Tofacitinib (TOF) on RRA and secondary osteoporosis.

METHODS

Pathological changes in the ankle joints of collagen-induced arthritis (CIA) + TNF model rats were assessed using hematoxylin and eosin (HE) staining. Immunohistochemistry (IHC) and immunofluorescence (IF) were used to evaluate pyroptosis-related protein levels in the synovial tissues. Moreover, the knee joint was investigated by performing HE staining, IHC, and micro-computed tomography. Furthermore, in vitro, western blotting and enzyme-linked immunosorbent assay (ELISA) were performed to detect the effects of TOF and IGU on TNF-α-induced pyroptosis in fibroblast-like synoviocytes of RA.

RESULTS

After treatment with TOF and/or IGU, the arthritis scores, inflammatory cell infiltration in synovial tissues, and levels of interleukin (IL)-18, IL-1β, and IL-6 in the plasma were remarkably increased in the CIA + TNF model and dramatically decreased in the combination group. The expression of pyroptosis-related proteins was significantly lower in the combination group than in the CIA + TNF group, and a consistent trend was observed in vitro. Bone destruction was significantly alleviated, and the bone turnover rate was remarkably increased in the combination group compared to that in the CIA + TNF model.

CONCLUSION

TOF + IGU alleviated the severity of RRA in the CIA + TNF rat model, relieving joint inflammation, reducing bone erosion, and suppressing pyroptosis. The combined application of TOF and IGU may have a superimposed therapeutic effect on RRA and secondary osteoporotic bone remodeling.

New Potentiality of Bioactive Substances: Regulating the NLRP3 Inflammasome in Autoimmune Diseases

The NOD-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome is an essential component of the human innate immune system, and is closely associated with adaptive immunity. In most cases, the activation of the NLRP3 inflammasome requires priming and activating, which are influenced by various ion flux signals and regulated by various enzymes. Aberrant functions of intracellular NLRP3 inflammasomes promote the occurrence and development of autoimmune diseases, with the majority of studies currently focused on rheumatoid arthritis, systemic lupus erythematosus and systemic sclerosis. In recent years, a number of bioactive substances have shown new potentiality for regulating the NLRP3 inflammasome in autoimmune diseases. This review provides a concise overview of the composition, functions, and regulation of the NLRP3 inflammasome. Additionally, we focus on the newly discovered bioactive substances for regulating the NLRP3 inflammasome in autoimmune diseases in the past three years.

Mechanistic and therapeutic insights into the function of NLRP3 inflammasome in sterile arthritis

The NLRP3 inflammasome, which belongs to the pyrin domain containing 3 family of NOD-like receptors, has a significant impact on both the innate and adaptive immune responses. Regulating host immune function and protecting against microbial invasion and cell damage, the NLRP3 inflammasome plays a crucial role. By triggering caspase-1, it facilitates the development of the inflammatory cytokines IL-1β and IL-18, and triggers cell pyroptosis, resulting in cell lysis and demise. Common sterile arthritis includes osteoarthritis (OA), rheumatoid arthritis (RA) and gouty arthritis (GA), all of which manifest as bone destruction and synovial inflammation in a complex inflammatory state, placing a significant medical burden on the families of patients and government agencies. In the past few years, there has been a growing interest in investigating the impact of cell pyroptosis on arthritis development, particularly the widespread occurrence of pyroptosis mediated by the NLRP3 inflammasome. The NLRP3 inflammasome's biological properties are briefly described in this review, along with the presentation of the fundamental processes of pyroptosis resulting from its activation. Furthermore, we provide a summary of the advancements made in studying the NLRP3 inflammasome in various forms of arthritis and enumerate the intervention approaches that target the NLRP3-mediated pyroptosis, either directly or indirectly. These discoveries lay the groundwork for future investigations on medications for arthritis, offering fresh approaches for the clinical identification and treatment of this condition.

Targeting regulated chondrocyte death in osteoarthritis therapy

In vivo articular cartilage degeneration is an essential hallmark of osteoarthritis (OA), involving chondrocyte senescence, extracellular matrix degradation, chondrocyte death, cartilage loss, and bone erosion. Among them, chondrocyte death is one of the major factors leading to cartilage degeneration. Many studies have reported that various cell death modes, including apoptosis, ferroptosis, and autophagy, play a key role in OA chondrocyte death. Currently, there is insufficient understanding of OA pathogenesis, and there remains a lack of treatment methods to prevent OA and inhibit its progression. Studies suggest that OA prevention and treatment are mainly directed to arrest premature or excessive chondrocyte death. In this review, we a) discuss the forms of death of chondrocytes and the associations between them, b) summarize the critical factors in chondrocyte death, c) discuss the vital role of chondrocyte death in OA, d) and, explore new approaches for targeting the regulation of chondrocyte death in OA treatment.

Understanding the role of NLRP3-mediated pyroptosis in allergic rhinitis: A review

Allergic rhinitis (AR) is a chronic, inflammatory disease of the nasal mucosa, caused by the immunoglobulin E-mediated immune response. The annual incidence rate of AR is on the rise, exerting a significant impact on individuals' physical and mental wellbeing. The treatment effect in some patients is still not ideal, as the pathogenesis of AR is complex and diverse. Recent studies have shown that NLRP3 inflammasome-mediated pyroptosis is widely involved in the occurrence and development of AR through various pathways. This article reviews the mechanism of pyroptosis and its research progress in the field of AR, and puts forward possible therapeutic targets to offer innovative approaches for its management.

Targeting macrophagic PIM-1 alleviates osteoarthritis by inhibiting NLRP3 inflammasome activation via suppressing mitochondrial ROS/Cl- efflux signaling pathway

BACKGROUND

Osteoarthritis (OA), in which macrophage-driven synovitis is considered closely related to cartilage destruction and could occur at any stage, is an inflammatory arthritis. However, there are no effective targets to cure the progression of OA. The NOD-, LRR-,and pyrin domain-containing protein 3 (NLRP3) inflammasome in synovial macrophages participates in the pathological inflammatory process and treatment strategies targeting it are considered to be an effective approach for OA. PIM-1 kinase, as a downstream effector of many cytokine signaling pathways, plays a pro-inflammatory role in inflammatory disease.

METHODS

In this study, we evaluated the expression of the PIM-1 and the infiltration of synovial macrophages in the human OA synovium. The effects and mechanism of PIM-1 were investigated in mice and human macrophages stimulated by lipopolysaccharide (LPS) and different agonists such as nigericin, ATP, Monosodium urate (MSU), and Aluminum salt (Alum). The protective effects on chondrocytes were assessed by a modified co-culture system induced by macrophage condition medium (CM). The therapeutic effect in vivo was confirmed by the medial meniscus (DMM)-induced OA in mice.

RESULTS

The expression of PIM-1 was increased in the human OA synovium which was accompanied by the infiltration of synovial macrophages. In vitro experiments, suppression of PIM-1 by SMI-4a, a specific inhibitor, rapidly inhibited the NLRP3 inflammasome activation in mice and human macrophages and gasdermin-D (GSDME)-mediated pyroptosis. Furthermore, PIM-1 inhibition specifically blocked the apoptosis-associated speck-like protein containing a CARD (ASC) oligomerization in the assembly stage. Mechanistically, PIM-1 inhibition alleviated the mitochondrial reactive oxygen species (ROS)/chloride intracellular channel proteins (CLICs)-dependent Cl- efflux signaling pathway, which eventually resulted in the blockade of the ASC oligomerization and NLRP3 inflammasome activation. Furthermore, PIM-1 suppression showed chondroprotective effects in the modified co-culture system. Finally, SMI-4a significantly suppressed the expression of PIM-1 in the synovium and reduced the synovitis scores and the Osteoarthritis Research Society International (OARSI) score in the DMM-induced OA model.

CONCLUSIONS

Therefore, PIM-1 represented a new class of promising targets as a treatment of OA to target these mechanisms in macrophages and widened the road to therapeutic strategies for OA.

Inhibitors of NLRP3 Inflammasome in Ischemic Heart Disease: Focus on Functional and Redox Aspects

Myocardial ischemia-reperfusion injury (MIRI) is caused by several mechanisms, including the production of reactive oxygen species (ROS), altered cellular osmolarity, and inflammatory response. Calcium overload, altered oxygen levels, and mitochondrial ROS are also involved in these MIRI processes, resulting in the irreversible opening of the mitochondrial permeability transition pore (mPTP). These mechanisms and processes are associated with NLRP3 inflammasome priming and activation, which can also induce cell death by pyroptosis through the up-regulation of the caspase-1 pathway and IL-18 release. In addition, endothelial dysfunction, both in the presence and absence of MIRI, is also accompanied by altered oxygen levels, decreased nitric oxide production, and ROS overproduction, resulting in the expression of adhesion molecules and leukocyte infiltration in which the NLRP3 inflammasome plays a central role, thus contributing, through endothelial dysfunction, to the alteration of coronary flow, typical of ischemic heart disease. Given the intricate interrelationship between ROS and NLRP3, ROS inhibitors can reduce NLRP3 inflammasome activation, while NLRP3 inhibitors can reduce oxidative stress and inflammation. NLRP3 inhibitors have been intensively studied as anti-inflammatory agents in basic cardiovascular sciences. In this review, we analyze the interrelation between ROS and NLRP3 in ischemic heart disease and the effects of some NLRP3 inhibitors as possible therapeutic agents in this disease condition. All compounds considered in this review need larger studies to confirm their appropriate use in clinical scenarios as anti-ischemic drugs.

Bioactive Molecules against Rheumatoid Arthritis by Suppressing Pyroptosis

Rheumatoid arthritis is an inflammatory disease, and pyroptosis is a form of death associated with an inflammatory response. Pyroptosis, which occurs in synovial and osteoblastic cells, can exacerbate the development of rheumatoid arthritis. The inhibition of pyroptosis of these cells can, therefore, clearly be used as a therapeutic strategy against rheumatoid arthritis. Here, we have summarized the current status of progress in the treatment of rheumatoid arthritis by targeting cellular pyroptosis. We have identified seven compounds, including a cyclic RNA, a microRNA, a peptide, and a cytokine (protein), that may influence the progression of rheumatoid arthritis by regulating the initiation of pyroptosis. All of these compounds have been shown to have anti-rheumatoid effects in vitro and/or in vivo and have the potential to be developed as anti-rheumatoid agents. These findings may help to accelerate the development of anti-rheumatoid arthritis drugs.

Acid-sensing ion channel 1a exacerbates renal ischemia-reperfusion injury through the NF-κB/NLRP3 inflammasome pathway

Ischemia-reperfusion injury (IRI) is the main cause of acute kidney injury (AKI), and there is no effective therapy. Microenvironmental acidification is generally observed in ischemic tissues. Acid-sensing ion channel 1a (ASIC1a) can be activated by a decrease in extracellular pH which mediates neuronal IRI. Our previous study demonstrated that, ASIC1a inhibition alleviates renal IRI. However, the underlying mechanisms have not been fully elucidated. In this study, we determined that renal tubule-specific deletion of ASIC1a in mice (ASIC1afl/fl/CDH16cre) attenuated renal IRI, and reduced the expression of NLRP3, ASC, cleaved-caspase-1, GSDMD-N, and IL-1β. Consistent with these in vivo results, inhibition of ASIC1a by the specific inhibitor PcTx-1 protected HK-2 cells from hypoxia/reoxygenation (H/R) injury, and suppressed H/R-induced NLRP3 inflammasome activation. Mechanistically, the activation of ASIC1a by either IRI or H/R induced the phosphorylation of NF-κB p65, which translocates to the nucleus and promotes the transcription of NLRP3 and pro-IL-1β. Blocking NF-κB by treatment with BAY 11-7082 validated the roles of H/R and acidosis in NLRP3 inflammasome activation. This further confirmed that ASIC1a promotes NLRP3 inflammasome activation, which requires the NF-κB pathway. In conclusion, our study suggests that ASIC1a contributes to renal IRI by affecting the NF-κB/NLRP3 inflammasome pathway. Therefore, ASIC1a may be a potential therapeutic target for AKI. KEY MESSAGES: Knockout of ASIC1a attenuated renal ischemia-reperfusion injury. ASIC1a promoted the NF-κB pathway and NLRP3 inflammasome activation. Inhibition of the NF-κB mitigated the NLRP3 inflammasome activation induced by ASIC1a.

Regulation of pain neurotransmitters and chondrocytes metabolism mediated by voltage-gated ion channels: A narrative review

Osteoarthritis (OA) is one of the leading causes of chronic pain and dysfunction. It is essential to comprehend the nature of pain and cartilage degeneration and its influencing factors on OA treatment. Voltage-gated ion channels (VGICs) are essential in chondrocytes and extracellular matrix (ECM) metabolism and regulate the pain neurotransmitters between the cartilage and the central nervous system. This narrative review focused primarily on the effects of VGICs regulating pain neurotransmitters and chondrocytes metabolism, and most studies have focused on voltage-sensitive calcium channels (VSCCs), voltage-gated sodium channels (VGSCs), acid-sensing ion channels (ASICs), voltage-gated potassium channels (VGKCs), voltage-gated chloride channels (VGCCs). Various ion channels coordinate to maintain the intracellular environment's homeostasis and jointly regulate metabolic and pain under normal circumstances. In the OA model, the ion channel transport of chondrocytes is abnormal, and calcium influx is increased, which leads to increased neuronal excitability. The changes in ion channels are strongly associated with the OA disease process and individual OA risk factors. Future studies should explore how VGICs affect the metabolism of chondrocytes and their surrounding tissues, which will help clinicians and pharmacists to develop more effective targeted drugs to alleviate the progression of OA disease.

Can pyroptosis be a new target in rheumatoid arthritis treatment?

Rheumatoid arthritis (RA) is a chronic systemic autoimmune disease of undefined etiology, with persistent synovial inflammation and destruction of articular cartilage and bone. Current clinical drugs for RA mainly include non-steroidal anti-inflammatory drugs (NSAIDs), glucocorticoids, disease modifying anti-rheumatic drugs (DMARDs) and so on, which can relieve patients' joint symptoms. If we want to have a complete cure for RA, there are still some limitations of these drugs. Therefore, we need to explore new mechanisms of RA to prevent and treat RA radically. Pyroptosis is a newly discovered programmed cell death (PCD) in recent years, which is characterized by the appearance of holes in cell membranes, cell swelling and rupture, and the release of intracellular pro-inflammatory factors into the extracellular space, resulting in a strong inflammatory response. The nature of pyroptosis is pro-inflammatory, and whether it is participating in the development of RA has attracted a wide interest among scholars. This review describes the discovery and mechanism of pyroptosis, the main therapeutic strategies for RA, and the role of pyroptosis in the mechanism of RA development. From the perspective of pyroptosis, the study of new mechanisms of RA may provide a potential target for the treatment of RA and the development of new drugs in the clinics.

In Vitro Anti-Inflammatory and Antioxidant Activities of pH-Responsive Resveratrol-Urocanic Acid Nano-Assemblies

Inflammatory environments provide vital biochemical stimuli (i.e., oxidative stress, pH, and enzymes) for triggered drug delivery in a controlled manner. Inflammation alters the local pH within the affected tissues. As a result, pH-sensitive nanomaterials can be used to effectively target drugs to the site of inflammation. Herein, we designed pH-sensitive nanoparticles in which resveratrol (an anti-inflammatory and antioxidant compound (RES)) and urocanic acid (UA) were complexed with a pH-sensitive moiety using an emulsion method. These RES-UA NPs were characterized by transmission electron microscopy, dynamic light scattering, zeta potential, and FT-IR spectroscopy. The anti-inflammatory and antioxidant activities of the RES-UA NPs were assessed in RAW 264.7 macrophages. The NPs were circular in shape and ranged in size from 106 to 180 nm. The RES-UA NPs suppressed the mRNA expression of the pro-inflammatory molecules inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), interleukin-1β (IL-1β), and tumor necrosis factor-α (TNF-α) in lipopolysaccharide (LPS)-stimulated RAW 264.7 macrophages in a concentration-dependent manner. Incubation of LPS-stimulated macrophages with RES-UA NPs reduced the generation of reactive oxygen species (ROS) in a concentration-dependent manner. These results suggest that pH-responsive RES-UA NPs can be used to decrease ROS generation and inflammation.

Pyroptosis in bone loss

Pyroptosis could be responsible for the bone loss from bone metabolic diseases, leading to the negative impact on people's health and life. It has been shown that osteoclasts, osteoblasts, macrophages, chondrocytes, periodontal and gingival cells may be involved in bone loss linked with pyroptosis. So far, the involved mechanisms have not been fully elucidated. In this review, we introduced the related cells involved in the pyroptosis associated with bone loss and summarized the role of these cells in the bone metabolism during the process of pyroptosis. We also discuss the clinical potential of targeting mechanisms in the osteoclasts, osteoblasts, macrophages, chondrocytes, periodontal and gingival cells touched upon pyroptosis to treat bone loss from bone metabolic diseases as well as the challenges of avoiding potential side effects and producing efficient treatment methods.

Modulators of ASIC1a and its potential as a therapeutic target for age-related diseases

Age-related diseases have become more common with the advancing age of the worldwide population. Such diseases involve multiple organs, with tissue degeneration and cellular apoptosis. To date, there is a general lack of effective drugs for treatment of most age-related diseases and there is therefore an urgent need to identify novel drug targets for improved treatment. Acid-sensing ion channel 1a (ASIC1a) is a degenerin/epithelial sodium channel family member, which is activated in an acidic environment to regulate pathophysiological processes such as acidosis, inflammation, hypoxia, and ischemia. A large body of evidence suggests that ASIC1a plays an important role in the development of age-related diseases (e.g., stroke, rheumatoid arthritis, Huntington's disease, and Parkinson's disease.). Herein we present: 1) a review of ASIC1a channel properties, distribution, and physiological function; 2) a summary of the pharmacological properties of ASIC1a; 3) and a consideration of ASIC1a as a potential therapeutic target for treatment of age-related disease.

Attenuation of experimental osteoarthritis with human adipose-derived mesenchymal stem cell therapy: inhibition of the pyroptosis in chondrocytes

AIM

To explore the role and mechanism of human adipose-derived mesenchymal stem cells (hAD-MSCs) in the treatment of osteoarthritis (OA).

METHODS

OA hulth model of Sprague Dawley (SD) rats and 20 ng/ml TNF-α treated chondrocytes were used as models of OA in vivo and in vitro, respectively. hAD-MSCs were administrated in the articular cavity by injection in vivo and co-cultured with chondrocytes using transwell in vitro. Haematoxylin and eosin staining and Safranin-O/Fast green staining were performed to detect tissue destruction and histopathology. Scanning electron microscopy and transmission electron microscopy were used to observe the ultrastructure of chondrocytes. The pyroptosis signaling pathway-related proteins were detected by immunohistochemistry, immunofluorescence, qRT-PCR and Western blot. And small interference technology was used to study the mechanism in depth.

RESULTS

hAD-MSCs could delay the development of rat OA, improve the pathological changes of joints, inhibit the expression of NLRP3, Caspase1, GSDMD and TNFR1. In vitro, the expression of pyroptosis signal proteins in chondrocytes was significantly elevated when stimulated with TNF-α, the level of inflammatory factors such as IL-1β, IL-18 was increased, and the cell morphology was significantly destroyed. While co-cultured with hAD-MSCs, these syndromes were reversed. Knockout of TNFR1 also returned the upregulation of pyroptosis signals which caused by TNF-α.

CONCLUSION

These results demonstrated that hAD-MSCs could inhibit pyroptosis signaling pathway of chondrocytes induced by TNF-α, which have raised our understanding of the role of hAD-MSCs as promising therapy for the management of OA.

Exploring the active ingredients and potential mechanisms of action of sinomenium acutum in the treatment of rheumatoid arthritis based on systems biology and network pharmacology

Objective: To investigate and predict the targets and signaling pathways of sinomenium acutum (SA) in the treatment of rheumatoid arthritis (RA) through systems biology and network pharmacology, and to elucidate its possible mechanisms of action. Methods: We screened the active ingredients and corresponding target proteins of SA in Traditional Chinese Medicine Systems Pharmacology Database and Analysis Platform (TCMSP), Traditional Chinese Medicines Integrated Database (TCMID) and Bioinformatics Analysis Tool for Molecular mechANism of Traditional Chinese Medicine (BATMAN); and obtained the targets of rheumatoid arthritis diseases in a database of gene-disease associations (DisGeNET), Online Mendelian Inheritance in Man (OMIM) database. The two targets were mapped by Venn diagram and the intersection was taken. The intersecting targets were used to construct protein-protein interaction (PPI) network maps in the String database, and Metascape was used for Gene Ontology (GO) functional annotation and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment. Finally, the molecular docking technique was applied to validate and further clarify the core target of SA for the treatment of rheumatoid arthritis. Results: A total of six active ingredients and 217 potential targets were obtained after screening; 2,752 rheumatoid arthritis-related targets and 66 targets common to RA and SA. GO function and KEGG pathway enrichment analysis yielded 751 GO function entries (652 GO biological processes, 59 GO molecular functions and 40 GO cellular components) and 77 KEGG signaling pathways. It mainly involves pathways related to neural activity ligand-receptor interaction pathways, cancer pathways, calcium signaling channels, Th17 cell differentiation and others, which are mainly classified into four categories, including regulation of immunity, anti-inflammation, regulation of cell growth and apoptosis, and signaling. The molecular docking results showed that the binding energy of PTGS2, CASP3, JUN and PPARG to the key components beta-sitosterol, 16-epi-Isositsirikine, Sinomenine and Stepholidine were ≤ -6.5 kcal/mol, suggesting the existence of molecular binding sites. Conclusion: SA acts on key targets such as PTGS2, CASP3, JUN, and PPARG to modulate signaling pathways such as neural activity ligand-receptor interaction, cancer, calcium ion, NF-κB, and Th17 cell differentiation to regulate immunity, anti-inflammation, modulation of cell cycle, bone metabolism, and signaling for the treatment of RA. It was also confirmed that the treatment of RA with SA has multi-component, multi-target, multi-pathway and multi-mechanism characteristics.

The regulatory role and therapeutic application of pyroptosis in musculoskeletal diseases

Pyroptosis is a controlled form of inflammatory cell death characterized by inflammasome activation, pore formation, and cell lysis. According to different caspases, pyroptosis can be divided into canonical, non-canonical, and other pathways. The role of pyroptosis in disease development has been paid more attention in recent years. The trigger factors of pyroptosis are often related to oxidative stress and proinflammatory substances, which coincide with the pathological mechanism of some diseases. Pyroptosis directly leads to cell lysis and death, and the release of cytosolic components and proinflammatory cytokines affects cell activity and amplifies the inflammatory response. All the above are involved in a series of basic pathological processes, such as matrix degradation, fibrosis, and angiogenesis. Since these pathological changes are also common in musculoskeletal diseases (MSDs), emerging studies have focused on the correlations between pyroptosis and MSDs in recent years. In this review, we first summarized the molecular mechanism of pyroptosis and extensively discussed the differences and crosstalk between pyroptosis, apoptosis, and necrosis. Next, we elaborated on the role of pyroptosis in some MSDs, including osteoarthritis, rheumatoid arthritis, osteoporosis, gout arthritis, ankylosing spondylitis, intervertebral disc degeneration, and several muscle disorders. The regulation of pyroptosis could offer potential therapeutic targets in MSDs treatment. Herein, the existing drugs and therapeutic strategies that directly or indirectly target pyroptosis pathway components have been discussed in order to shed light on the novel treatment for MSDs.

Arbutin-modified microspheres prevent osteoarthritis progression by mobilizing local anti-inflammatory and antioxidant responses

Osteoarthritis (OA) is a common degenerative joint disease worldwide and currently there is no effective strategy to stop its progression. It is known that oxidative stress and inflammation can promote the development of OA, and therapeutic strategies against these conditions may alleviate OA. Arbutin (ARB), a major ingredient of the Chinese medicinal herb cowberry leaf, exerts good antioxidant and anti-inflammatory activities yet has not been studied in OA. Here we developed ARB-loaded gelatine methacryloyl-Liposome (GM-Lipo@ARB) microspheres which showed long-term release of ARB and excellent cartilage-targeting effects. The ARB-loaded microspheres effectively reduced the inflammatory response in interleukin (IL)-1β-treated arthritic chondrocytes. Moreover, the synthesized GM-Lipo@ARB microspheres regulated cartilage extracellular matrix (ECM) homeostasis through anti-inflammation effect via inhibiting NF-κB signaling and anti-oxidative stress effect via activating Nrf2 pathway. Intra-articular use of GM-Lipo@ARB can effectively reduce inflammation and oxidative stress in the articular cartilage and thus, attenuating OA progression in a mouse model. The study proposed a novel ARB-laden functional microsphere, GM-Lipo@ARB, and demonstrated that this compound may be used as an alternative therapeutics for treating OA.

Pyroptosis in inflammatory bone diseases: Molecular insights and targeting strategies

Inflammatory bone diseases include osteoarthritis (OA) and rheumatoid arthritis (RA), which can cause severe bone damage in a chronic inflammation state, putting tremendous pressure on the patients' families and government agencies regarding medical costs. In addition, the complexity of osteoimmunology makes research on these diseases difficult. Hence, it is urgent to determine the potential mechanisms and find effective drugs to target inflammatory bone diseases to reduce the negative effects of these diseases. Recently, pyroptosis, a gasdermin-induced necrotic cell death featuring secretion of pro-inflammatory cytokines and lysis, has become widely known. Based on the effect of pyroptosis on immunity, this process has gradually emerged as a vital component in the etiopathogenesis of inflammatory bone diseases. Herein, we review the characteristics and mechanisms of pyroptosis and then focus on its clinical significance in inflammatory bone diseases. In addition, we summarize the current research progress of drugs targeting pyroptosis to enhance the therapeutic efficacy of inflammatory bone diseases and provide new insights for future directions.

The role of Nod-like receptor protein 3 inflammasome activated by ion channels in multiple diseases

The inflammasome is a multimeric protein complex located in the cytoplasm that is activated by many factors and subsequently promotes the release of proinflammatory factors such as interleukin (IL)-1β and IL-18, resulting in a series of inflammatory responses that ultimately lead to the occurrence of various diseases. The Nod-like receptor protein 3 (NLRP3) inflammasome is the most characteristic type and the most widely studied among many inflammasomes. Activation of the NLRP3 inflammasome is closely related to the occurrence of many diseases, such as Alzheimer's disease. At present, a large number of studies have focused on the mechanisms underlying the activation of the NLRP3 inflammasome. Plenty of articles have reported the activation of the NLRP3 inflammasome by various ions, such as K+ and Na+ reflux and Ca2+ influx. However, few articles have reviewed the effects of various ion channels on the activation of the NLRP3 inflammasome and the relationship between the diseases caused by these proteins. This article mainly summarizes the relationship between intracellular and extracellular ion activities and ion channels and the activation of the NLRP3 inflammasome. We also provide a general summary of the diseases of each system caused by NLRP3 activation. We hope that more research will provide options for the treatment of diseases driven by the NLRP3 inflammasome.

Research Progress on the Role of Pyroptosis in Myocardial Ischemia-Reperfusion Injury

Myocardial ischemia-reperfusion injury (MIRI) results in the aggravation of myocardial injury caused by rapid recanalization of the ischemic myocardium. In the past few years, there is a growing interest in investigating the complex pathophysiological mechanism of MIRI for the identification of effective targets and drugs to alleviate MIRI. Currently, pyroptosis, a type of inflammatory programmed death, has received greater attention. It is involved in the MIRI development in combination with other mechanisms of MIRI, such as oxidative stress, calcium overload, necroptosis, and apoptosis, thereby forming an intertwined association between different pathways that affect MIRI by regulating common pathway molecules. This review describes the pyroptosis mechanism in MIRI and its relationship with other mechanisms, and also highlights non-coding RNAs and non-cardiomyocytes as regulators of cardiomyocyte pyroptosis by mediating associated pathways or proteins to participate in the initiation and development of MIRI. The research progress on novel small molecule drugs, clinical drugs, traditional Chinese medicine, etc. for regulating pyroptosis can play a crucial role in effective MIRI alleviation. When compared to research on other mature mechanisms, the research studies on pyroptosis in MIRI are inadequate. Although many related protective drugs have been identified, these drugs generally lack clinical applications. It is necessary to further explore and verify these drugs to expand their applications in clinical setting. Early inhibition of MIRI by targeted regulation of pyroptosis is a key concern that needs to be addressed in future studies.

Calcium-Permeable Channels Cooperation for Rheumatoid Arthritis: Therapeutic Opportunities

Rheumatoid arthritis is a common autoimmune disease that results from the deposition of antibodies–autoantigens in the joints, leading to long-lasting inflammation. The main features of RA include cartilage damage, synovial invasion and flare-ups of intra-articular inflammation, and these pathological processes significantly reduce patients’ quality of life. To date, there is still no drug target that can act in rheumatoid arthritis. Therefore, the search for novel drug targets has become urgent. Due to their unique physicochemical properties, calcium ions play an important role in all cellular activities and the body has evolved a rigorous calcium signaling system. Calcium-permeable channels, as the main operators of calcium signaling, are widely distributed in cell membranes, endoplasmic reticulum membranes and mitochondrial membranes, and mediate the efflux and entry of Ca2+. Over the last century, more and more calcium-permeable channels have been identified in human cells, and the role of this large family of calcium-permeable channels in rheumatoid arthritis has gradually become clear. In this review, we briefly introduce the major calcium-permeable channels involved in the pathogenesis of RA (e.g., acid-sensitive ion channel (ASIC), transient receptor potential (TRP) channel and P2X receptor) and explain the specific roles and mechanisms of these calcium-permeable channels in the pathogenesis of RA, providing more comprehensive ideas and targets for the treatment of RA.

Current understanding of osteoarthritis pathogenesis and relevant new approaches

Osteoarthritis (OA) is the most common degenerative joint disease that causes painful swelling and permanent damage to the joints in the body. The molecular mechanisms of OA are currently unknown. OA is a heterogeneous disease that affects the entire joint, and multiple tissues are altered during OA development. To better understand the pathological mechanisms of OA, new approaches, methods, and techniques need to be used to understand OA pathogenesis. In this review, we first focus on the epigenetic regulation of OA, with a particular focus on DNA methylation, histone modification, and microRNA regulation, followed by a summary of several key mediators in OA-associated pain. We then introduce several innovative techniques that have been and will continue to be used in the fields of OA and OA-associated pain, such as CRISPR, scRNA sequencing, and lineage tracing. Next, we discuss the timely updates concerning cell death regulation in OA pathology, including pyroptosis, ferroptosis, and autophagy, as well as their individual roles in OA and potential molecular targets in treating OA. Finally, our review highlights new directions on the role of the synovial lymphatic system in OA. An improved understanding of OA pathogenesis will aid in the development of more specific and effective therapeutic interventions for OA.

CASP6 predicts poor prognosis in glioma and correlates with tumor immune microenvironment

Background

Glioma is an aggressive tumor of the central nervous system. Caspase-6 (CASP6) plays a crucial role in cell pyroptosis and is a central protein involved in many cellular signaling pathways. However, the association between CASP6 and prognosis of glioma patients remains unclear.

Methods

Four bioinformatic databases were analyzed to identify differentially expressed genes (DEGs) between glioma and healthy tissues. Eighty-one protein-coding pyroptosis-related genes (PRGs) were obtained from the GeneCards database. The pyroptosis-related DEGs (PRDEGs) were extracted from each dataset, and CASP6 was found to be aberrantly expressed in glioma. We then investigated the biological functions of CASP6 and the relationship between CASP6 expression and the tumor microenvironment and immunocyte infiltration. The half maximal inhibitory concentration of temozolomide and the response to immune checkpoint blockade in the high- and low-CASP6 expression groups were estimated using relevant bioinformatic algorithms. Quantitative real-time reverse transcription PCR and western blotting were carried out to confirm the different expression levels of CASP6 between human astrocytes and glioma cell lines (U251 and T98G). We determined the role of CASP6 in the tumorigenesis of glioma by knocking down CASP6 in U251 and T98G cell lines.

Results

We found that CASP6 was overexpressed in glioma samples and in glioma cell lines. CASP6 expression in patients with glioma correlated negatively with overall survival. In addition, CASP6 expression correlated positively with the degree of glioma progression. Functional analysis indicated that CASP6 was primarily involved in the immune response and antigen processing and presentation. Patients with high CASP6 levels responded more favorably to temozolomide, while patients with low expression of CASP6 had a better response to immunotherapy. Finally, in vitro experiments showed that CASP6 knockdown inhibited glioma proliferation.

Conclusions

The pyroptosis-related gene CASP6 might represent a sensitive prognostic marker for patients with glioma and might predict their response of immunotherapy and temozolomide therapy. Our results might lead to more precise immunotherapeutic strategies for patients with glioma.

Nesfatin-1 exerts protective effects on acidosis-stimulated chondrocytes and rats with adjuvant-induced arthritis by inhibiting ASIC1a expression

Nesfatin-1, a newly identified energy-regulating peptide, has been reported to possess antioxidant, anti-inflammatory, and antiapoptotic properties; however, to date, its effect on rheumatoid arthritis (RA) has not been previously explored in detail. We previously showed that activation of acid-sensing ion channel 1a (ASIC1a) by acidosis plays an important role in RA pathogenesis. Therefore, in this study, we evaluated the effects of nesfatin-1 on acidosis-stimulated chondrocyte injury in vitro and in vivo and examined the involvement of ASIC1a and the mechanism underlying the effects of nesfatin-1 on RA. Acid-stimulated articular chondrocytes were used to examine one of the several possible mechanisms underlying RA pathogenesis in vitro. The mRNA expression profile of acid-induced chondrocytes treated or not treated with nesfatin-1 was investigated by RNA sequencing. The effects of nesfatin-1 on oxidative stress, inflammation, and apoptosis in acid-induced chondrocytes were measured. The mechanistic effect of nesfatin-1 on ASIC1a expression and intracellular Ca²⁺ in acid-stimulated chondrocytes was studied. Rats with adjuvant-induced arthritis (AA) were used for in vivo analysis of RA pathophysiology. Cartilage degradation and ASIC1a expression in chondrocytes were detected in rats with AA after intraarticular nesfatin-1 injection. The in vitro experiments showed that nesfatin-1 decreased acidosis-induced cytotoxicity and elevation of intracellular Ca²⁺ levels in chondrocytes. Moreover, it attenuated acid-induced oxidative stress, inflammation, and apoptosis in chondrocytes. Nesfatin-1 decreased ASIC1a protein levels in acid-stimulated chondrocytes via the mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) and nuclear factor kappa-B (NF-κB) signaling pathways. In vivo analysis showed that nesfatin-1 ameliorated cartilage degradation and decreased ASIC1a expression in the chondrocytes of rats with AA. Collectively, nesfatin-1 suppressed acidosis-induced oxidative stress, inflammation, and apoptosis in acid-stimulated chondrocytes and alleviated arthritis symptoms in rats with AA, and its mechanism may be related to its ability to decrease ASIC1a protein levels via the MAPK/ERK and NF-κB pathways.

The Role of ASIC1a in Inflammatory Immune Diseases: A Potential Therapeutic Target

It is acknowledged that chronic inflammation is associated with a rise in extracellular proton concentrations. The acid-sensing ion channel 1a (ASIC1a) belongs to the extracellular H⁺-activated cation channel family. Recently, many studies have been conducted on ASIC1a and inflammatory immune diseases. Here, in this review, we will focus on the role of ASIC1a in several inflammatory immune diseases so as to provide new perspectives for clinical treatment.

Pyroptosis and Its Role in Autoimmune Disease: A Potential Therapeutic Target

Autoimmune diseases are a group of heterogeneous diseases with diverse clinical manifestations that can be divided into systemic and organ-specific. The common etiology of autoimmune diseases is the destruction of immune tolerance and the production of autoantibodies, which attack specific tissues and/or organs in the body. The pathogenesis of autoimmune diseases is complicated, and genetic, environmental, infectious, and even psychological factors work together to cause aberrant innate and adaptive immune responses. Although the exact mechanisms are unclear, recently, excessive exacerbation of pyroptosis, as a bond between innate and adaptive immunity, has been proven to play a crucial role in the development of autoimmune disease. Pyroptosis is characterized by pore formation on cell membranes, as well as cell rupture and the excretion of intracellular contents and pro-inflammatory cytokines, such as IL-1β and IL-18. This overactive inflammatory programmed cell death disrupts immune system homeostasis and promotes autoimmunity. This review examines the molecular structure of classical inflammasomes, including NLRP3, AIM2, and P2X7-NLRP3, as the switches of pyroptosis, and their molecular regulation mechanisms. The sophisticated pyroptosis pathways, including the canonical caspase-1-mediated pathway, the noncanonical caspase-4/5/11-mediated pathway, the emerging caspase-3-mediated pathway, and the caspase-independent pathway, are also described. We highlight the recent advances in pyroptosis in autoimmune diseases, such as systemic lupus erythematosus, rheumatoid arthritis, inflammatory bowel disease, Sjögren's syndrome and dermatomyositis, and attempt to identify its potential advantages as a therapeutic target or prognostic marker in these diseases.

Focus on the Role of the NLRP3 Inflammasome in Multiple Sclerosis: Pathogenesis, Diagnosis, and Therapeutics

Neuroinflammation is initiated with an aberrant innate immune response in the central nervous system (CNS) and is involved in many neurological diseases. Inflammasomes are intracellular multiprotein complexes that can be used as platforms to induce the maturation and secretion of proinflammatory cytokines and pyroptosis, thus playing a pivotal role in neuroinflammation. Among the inflammasomes, the nucleotide-binding oligomerization domain-, leucine-rich repeat- and pyrin domain-containing 3 (NLRP3) inflammasome is well-characterized and contributes to many neurological diseases, such as multiple sclerosis (MS), Alzheimer's disease (AD), and ischemic stroke. MS is a chronic autoimmune disease of the CNS, and its hallmarks include chronic inflammation, demyelination, and neurodegeneration. Studies have demonstrated a relationship between MS and the NLRP3 inflammasome. To date, the pathogenesis of MS is not fully understood, and clinical studies on novel therapies are still underway. Here, we review the activation mechanism of the NLRP3 inflammasome, its role in MS, and therapies targeting related molecules, which may be beneficial in MS.

AcidoCEST-UTE MRI Reveals an Acidic Microenvironment in Knee Osteoarthritis

A relationship between an acidic pH in the joints, osteoarthritis (OA), and pain has been previously demonstrated. Acidosis Chemical Exchange Saturation Transfer (acidoCEST) indirectly measures the extracellular pH through the assessment of the exchange of protons between amide groups on iodinated contrast agents and bulk water. It is possible to estimate the extracellular pH in the osteoarthritic joint using acidoCEST MRI. However, conventional MR sequences cannot image deep layers of cartilage, meniscus, ligaments, and other musculoskeletal tissues that present with short echo time and fast signal decay. Ultrashort echo time (UTE) MRI, on the other hand, has been used successfully to image those joint tissues. Here, our goal is to compare the pH measured in the knee joints of volunteers without OA and patients with severe OA using acidoCEST-UTE MRI. Patients without knee OA and patients with severe OA were examined using acidoCEST-UTE MRI and the mean pH of cartilage, meniscus, and fluid was calculated. Additionally, the relationship between the pH measurements and the Knee Injury and Osteoarthritis Outcome Score (KOOS) was investigated. AcidoCEST-UTE MRI can detect significant differences in the pH of knee cartilage, meniscus, and fluid between joints without and with OA, with OA showing lower pH values. In addition, symptoms and knee-joint function become worse at lower pH measurements.

Sa12b Improves Biological Activity of Human Degenerative Nucleus Pulposus Mesenchymal Stem Cells in a Severe Acid Environment by Inhibiting Acid-Sensitive Ion Channels

Sa12b is a wasp peptide that can inhibit acid-sensitive ion channels (ASICs). The biological effects of nucleus pulposus mesenchymal stem cells (NP-MSCs) have not been investigated. Therefore, this study investigated the effect of Sa12b on the biological activity of NP-MSCs through ASICs in the acidic environment of intervertebral disc degeneration (IVDD). In this study, NP-MSCs were isolated from the nucleus pulposus (NP) in patients who underwent lumbar disc herniation surgery, identified by flow cytometry and tertiary differentiation, and cultured in vitro in an acidic environment model of IVDD with a pH of 6.2. Proliferation, and apoptosis were observed after different Sa12b concentrations were added to P2 generation NP-MSCs. The Ca²⁺ influx was detected using flow cytometry and laser confocal scanning microscopy, and qPCR was used to detect the relative expression of stem cell–associated genes (Oct4, Nanog, Jag1, and Notch1), the relative expression of extracellular matrix (ECM)–associated genes (collagen II, aggrecan, and SOX-9), and the relative expression of genes encoding ASICs (ASIC1, ASIC2, ASIC3, and ASIC4). Western blotting was used to detect the protein expression of collagen II and aggrecan in different treatment groups. Cells isolated and cultured from normal NP were spindle-shaped and adherent, and they exhibited expansion in vitro. Flow cytometry results showed that the cells exhibited high expression of CD73 (98.1%), CD90 (97.5%), and CD105 (98.3%) and low expression of HLA-DR (0.93%), CD34 (2.63%), and CD45 (0.33%). The cells differentiated into osteoblasts, adipocytes, and chondrocytes. According to the International Society for Cellular Therapy criteria, the isolated and cultured cells were NP-MSCs. With an increase in Sa12b concentration, the cell proliferation rate of NP-MSCs increased, and the apoptosis rate decreased significantly, reaching the optimal level when the concentration of Sa12b was 8 μg/μl. When the Sa12b concentration was 8 μg/μl and contained the ASIC non-specific inhibitor amiloride, the Ca²⁺ influx was the lowest, followed by that when the Sa12b concentration was 8 μg/μl. The Ca²⁺ influx was the highest in the untreated control group. qPCR results showed that as the concentration of Sa12b increased, the relative expression of Oct4, Nanog, Jag1, Notch1, collagen II, aggrecan, and SOX-9 increased, while that of ASIC1, ASIC2, ASIC3, and ASIC4 decreased. The difference was statistically significant (p < 0.05). In conclusion, Sa12b can improve the biological activity of NP-MSCs in severely acidic environments of the intervertebral disc by reducing Ca²⁺ influx via AISC inhibition and, probably, the Notch signaling pathway. This study provides a new approach for the biological treatment of IVDD. Inhibition of AISCs by Sa12b may delay IVDD and improve low back pain.

Apoptosis, Autophagy, NETosis, Necroptosis, and Pyroptosis Mediated Programmed Cell Death as Targets for Innovative Therapy in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory joint disease that can lead to clinical manifestations of systemic diseases. Its leading features include chronic synovial inflammation and degeneration of the bones and joints. In the past decades, multiple susceptibilities for rheumatoid arthritis have been identified along with the development of a remarkable variety of drugs for its treatment; which include analgesics, glucocorticoids, nonsteroidal anti-inflammatory medications (NSAIDs), disease-modifying anti-rheumatic drugs (DMARDs), and biologic response modifiers (bDMARDs). Despite the existence of many clinical treatment options, the prognosis of some patients remains poor due to complex mechanism of the disease. Programmed cell death (PCD) has been extensively studied and ascertained to be one of the essential pathological mechanisms of RA. Its dysregulation in various associated cell types contributes to the development of RA. In this review, we summarize the role of apoptosis, cell death-associated neutrophil extracellular trap formation, necroptosis, pyroptosis, and autophagy in the pathophysiology of RA to provide a theoretical reference and insightful direction to the discovery and development of novel therapeutic targets for RA.

Tanshinone IIA alleviates NLRP3 inflammasome-mediated pyroptosis in Mycobacterium tuberculosis-(H37Ra-) infected macrophages by inhibiting endoplasmic reticulum stress

ETHNOPHARMACOLOGICAL RELEVANCE

Tanshinone IIA (Tan), extracted from Salvia miltiorrhiza Bunge, is a perennial herbal plant widely used as a folk remedy in Asian countries. Several studies have proved that Tanshinone IIA possesses many biological activities, such as anti-inflammatory, free-radical scavenging abilities, antioxidant properties, liver protection, and anti-cancer properties.

AIM OF THE STUDY

The objective of the present study was to examine the anti-inflammatory effects of Tan.

MATERIALS AND METHODS

The in vitro infection model of Mycobacterium tuberculosis-infected macrophages with the H37Ra strain was established. Murine macrophage Raw 264.7 and human monocyte THP-1 were used for the experiments. Cell viability was determined by the MTT assay. Western blot and lactate dehydrogenase (LDH) activity assays were used to detect the effects of Tan on cell pyroptosis and the level of NLRP3 inflammasome activation. Western blot, Co-immunoprecipitation and Immunofluorescence assays were used to observe the effect of Tan on the expression level of TXNIP. Immunofluorescence assays were applied to explore the effect of Tan on mtROS. Western blot and agarose gel electrophoresis were adopted to observe the effect of Tan on endoplasmic reticulum stress. The siRNA technique was applied to knockdown the expression levels of PERK/peIF2α, IRE1α and ATF6, and Western blot assay was employed to explore the NLRP3 inflammasome activation and possible molecular regulation mechanism of Tan.

RESULTS

This study demonstrated that Tan decreased Mtb-induced cell pyroptosis by measuring GSDMD-N and LDH release provoked by NLRP3 inflammasome activation. Additionally, Tan inhibited endoplasmic reticulum stress (ERS), mitochondrial damage, and TXNIP protein expression, all of which acted as upstream signals of NLRP3 inflammasome activation in Mtb-infected macrophages. Significantly, NLRP3 inflammasome activation was suppressed by knocking down ERS pathway proteins, which further clarified that Tan partly targeted ERS to exert anti-inflammatory and immunoregulatory actions.

CONCLUSION

This research confirms Tan's anti-inflammatory and immunoregulatory mechanisms in Mtb-infected macrophages by downregulating NLRP3 inflammasome activation-mediated pyroptosis provoked by ERS. Tan may function as an adjuvant drug to treat TB by adjusting host immune responses.

MCC950, the NLRP3 Inhibitor, Protects against Cartilage Degradation in a Mouse Model of Osteoarthritis

Osteoarthritis (OA), characterized by chronic systemic low-level inflammation and cartilage degeneration, is a type of arthritis closely associated with aging. Inflammation and aging play a pivotal role in the occurrence and progression of OA. NLRP3 inflammasome is involved in many inflammatory and aging diseases, and NLRP3 inhibitor MCC950 has anti-inflammatory and antisenescence effects on some diseases such as Alzheimer's disease. In the present study, we found that NLRP3 protein was upregulated in human and mouse OA cartilage. Moreover, NLRP3 and Caspase1 expression induced by IL-1β in chondrocytes was blocked by MCC950. In addition, MCC950 inhibited the expression of inflammatory mediators, matrix-degrading enzymes, senescence marker protein P16 (INK4A), and β-galactosidase, as well as excessive production of ROS. Meanwhile, MCC950 promoted autophagy-related protein expression and autophagy flux under the inflammatory condition. However, autophagy inhibitor 3-MA reversed anti-inflammatory and anticatabolic effects of MCC950. In in vivo experiments, intra-articular administration of MCC950 further showed its protective effect on cartilage degeneration. Bioinformatic analysis and in vitro experimental results revealed that MCC950 might play a protective role in cartilage by regulating Nrf2/HO-1/NQO1, PI3k/Akt/mTOR, P38/MAPK, and JNK/MAPK pathways. In conclusion, our work demonstrated that NLRP3 inhibitor MCC950 might serve as a promising strategy for OA treatment.

Cucurbitacin B inhibits non-small cell lung cancer in vivo and in vitro by triggering TLR4/NLRP3/GSDMD-dependent pyroptosis

Pyroptosis, a type of programmed cell death (PCD), is characterized by cell swelling with bubbles, and the release of inflammatory cell cytokines. Cucurbitacin B (CuB), extracted from muskmelon pedicel, is a natural bioactive product that could effectively exert anti-tumor activities in lung cancer. However, the exact molecular mechanisms and the direct targets of CuB in non-small cell lung cancer (NSCLC) remain to be discovered. Here, we firstly found that CuB exerted an anti-tumor effect via pyroptosis in NSCLC cells and NSCLC mice models. Next, based on the molecular docking and cellular thermal shift assay (CETSA), we identified that CuB directly bound to Toll-like receptor 4 (TLR4) to activate the NLRP3 inflammasome, which further caused the separation of N- and C-terminals of Gasdermin D (GSDMD) to execute pyroptosis. Moreover, CuB enhanced the mitochondrial reactive oxygen species (ROS), mitochondrial membrane protein Tom20 accumulation, and cytosolic calcium (Ca2+) release, leading to pyroptosis in NSCLC cells. Silencing of TLR4 inhibited CuB-induced pyroptosis and decreased the level of ROS and Ca2+ in A549 cells. In vivo study showed that CuB treatment suppressed lung tumor growth in mice via pyroptosis without dose-dependent manner, and CuB at 0.75 mg/kg had a better anti-tumor effect compared to the Gefitinib group. Taken together, our findings revealed the mechanisms and targets of CuB triggering pyroptosis in NSCLC, thus supporting the notion of developing CuB as a promising therapeutic agent for NSCLC.

Estrogen protects against acidosis-mediated articular chondrocyte injury by promoting ASIC1a protein degradation

Epidemiological data suggest that the incidence of rheumatoid arthritis (RA) increases in postmenopausal women, which may be related to estrogen deficiency. Tissue acidosis is a common symptom of RA. Acid-sensitive ion channel 1a (ASIC1a), a member of the extracellular H⁺-activated cation channel family, could be activated by changes in extracellular pH and plays a crucial role in the pathogenesis of RA. As the only cellular component in cartilage tissue, chondrocytes play an extremely important role in maintaining cartilage tissue homeostasis. The aim of this study was to investigate whether estrogen could protect acid-stimulated chondrocytes by regulating the expression of ASIC1a and explore the possible mechanism. The results showed that estrogen could protect against acid-induced chondrocyte injury by reducing ASIC1a protein expression. Moreover, lysosome inhibitor chloroquine (CQ) and autophagy inhibitor 3-methyladeniine (3-MA) could reverse the reduction of ASIC1a protein caused by estrogen, indicating that autophagy-lysosome pathway contributes to estrogen-induced degradation of ASIC1a protein. Furthermore, the down-regulation of ASIC1a expression by estrogen was attenuated by MPP, a specific inhibitor of estrogen-related receptor-alpha (Esrra), indicating that Esrra is involved in the process of estrogen regulating the expression of ASIC1a. Additionally, adenosine 5'-monophosphate (AMP)-activated protein kinase/unc-51-like kinase 1 (AMPK-ULK1) signaling pathway was activated by estrogen treatment, which was abrogated by Esrra-silencing, and AMPK-specific inhibitor Compound C pretreatment could reduce estrogen-induced downregulation of ASIC1a protein. Taken together, these results indicate that estrogen could promote autophagy-lysosome pathway-dependent ASIC1a protein degradation and protect against acidosis-induced cytotoxicity, the mechanisms of which might relate to Esrra-AMPK-ULK1 signaling pathway.

Autophagic Degradation of Gasdermin D Protects against Nucleus Pulposus Cell Pyroptosis and Retards Intervertebral Disc Degeneration In Vivo

Intervertebral disc degeneration (IDD) is the primary culprit of low back pain and renders heavy social burden worldwide. Pyroptosis is a newly discovered form of programmed cell death, which is also involved in nucleus pulposus (NP) cells during IDD progression. Moderate autophagy activity is critical for NP cell survival, but its relationship with pyroptosis remains unknown. This study is aimed at investigating the relationship between autophagy and pyroptotic cell death. The pyroptosis executor N-terminal domain of gasdermin D (GSDMD-N) and inflammation-related proteins were measured in lipopolysaccharide- (LPS-) treated human NP cells. Inhibition of autophagy by siRNA transfection and chemical drugs aggravated human NP cell pyroptosis. Importantly, we found that the autophagy-lysosome pathway and not the proteasome pathway mediated the degradation of GSDMD-N as lysosome dysfunction promoted the accumulation of cytoplasmic GSDMD-N. Besides, P62/SQSTM1 colocalized with GSDMD-N and mediated its degradation. The administration of the caspase-1 inhibitor VX-765 could reduce cell pyroptosis as confirmed in a rat disc IDD model in vivo, whereas ATG5 knockdown significantly accelerated the progression of IDD. In conclusion, our study indicated that autophagy protects against LPS-induced human NP cell pyroptosis via a P62/SQSTM1-mediated degradation mechanism and the inhibition of pyroptosis retards IDD progression in vivo. These findings deepen the understanding of IDD pathogenesis and hold implications in unraveling therapeutic targets for IDD treatment.

Hsa_circ_0044235 regulates the pyroptosis of rheumatoid arthritis via MiR-135b-5p-SIRT1 axis

Studies have found that cell pyroptosis is involved in the occurrence and development of rheumatoid arthritis (RA). Hsa_circ_0044235 has been found to be significantly low-expressed in RA patients. The purpose of this research was to reveal the regulatory mechanism of hsa_circ_0044235 in the pyroptosis pathway of RA. Serum expressions of hsa_circ_0044235 and SIRT were detected by RT-qPCR, and the relationship of the two genes was analyzed by Pearson. Next, a collagen-induced arthritis (CIA) mouse model was constructed to examine the effect of hsa_circ_0044235 on knee joint injury. The number of apoptotic cells and the level of inflammatory cytokines in synovial tissue were detected by TUNEL and ELISA. Fibroblast-like synoviocytes (FLSs) were extracted as in vitro study subject. Functional assays including flow cytometry and immunofluorescence staining, molecular experiments including RT-qPCR, Western blot and dual luciferase assay, and bioinformatics analysis were performed to analyze the mechanism of hsa_circ_0044235 in pyroptosis in FLSs. Hsa_circ_0044235 and SIRT1 expressions were suppressed in RA patients and the two were positively correlated. Overexpressed hsa_circ_0044235 attenuated joint inflammation, cell apoptosis, and joint damage, reduced foot pad thickness, clinical case scores, inhibited the NLRP3-mediated pyroptosis pathway but promoted SIRT1 expression in CIA mice. Overexpressed hsa_circ_0044235 inhibited caspase-1 content and the NLRP3-mediated pyroptosis pathway. Moreover, hsa_circ_0044235 promoted SIRT1 expression by sponging miR-135b-5p in FLSs. Additionally, the effect of overexpressed hsa_circ_0044235 on FLSs was reversed by miR-135b-5p mimic and siSIRT1, while the effect of siSIRT1 was reversed by miR-135b-5p inhibitor. Hsa_circ_0044235 regulated NLRP3-mediated pyroptosis through miR-135b-5p-SIRT1 axis to regulate the development of RA.

Blockade of TRPM7 Alleviates Chondrocyte Apoptosis and Articular Cartilage Damage in the Adjuvant Arthritis Rat Model Through Regulation of the Indian Hedgehog Signaling Pathway

Articular cartilage damage with subsequent impairment of joint function is a common feature of articular diseases, in particular, rheumatoid arthritis and osteoarthritis. While articular cartilage injury mediated by chondrocyte apoptosis is a known major pathological feature of arthritis, the specific mechanisms remain unclear at present. Transient receptor potential melastatin-like seven channel (TRPM7) is reported to play an important regulatory role in apoptosis. This study focused on the effects of TRPM7 on arthritic chondrocyte injury and its underlying mechanisms of action. Sodium nitroprusside (SNP)-induced rat primary chondrocyte apoptosis and rat adjuvant arthritis (AA) were used as in vitro and in vivo models, respectively. Blockage of TRPM7 with 2-APB or specific siRNA resulted in increased chondrocyte viability and reduced toxicity of SNP. Moreover, treatment with 2-APB enhanced the Bcl-2/Bax ratio and reduced cleaved PARP and IL-6, MMP-13 and ADAMTS-5 expression in SNP-treated chondrocytes. Activation of Indian Hedgehog with purmorphamine reversed the protective effects of 2-APB on SNP-induced chondrocyte apoptosis. Blockage of TRPM7 with 2-APB relieved the clinical signs of AA in the rat model and reduced the arthritis score and paw swelling. Similar to findings in SNP-treated chondrocytes, 2-APB treatment increased the Bcl-2/Bax ratio and suppressed cleaved PARP, IL-6, MMP-13, ADAMTS-5, TRPM7, and Indian hedgehog expression in articular cartilage of AA rats. Our collective findings suggest that blockade of TRPM7 could effectively reduce chondrocyte apoptosis and articular cartilage damage in rats with adjuvant arthritis through regulation of the Indian Hedgehog signaling pathway.

ASIC1 and ASIC3 mediate cellular senescence of human nucleus pulposus mesenchymal stem cells during intervertebral disc degeneration

Stem cell approaches have become an attractive therapeutic option for intervertebral disc degeneration (IVDD). Nucleus pulposus mesenchymal stem cells (NP-MSCs) participate in the regeneration and homeostasis of the intervertebral disc (IVD), but the molecular mechanisms governing these processes remain to be elucidated. Acid-sensing ion channels (ASICs) which act as key receptors for extracellular protons in central and peripheral neurons, have been implicated in IVDD where degeneration is associated with reduced microenvironmental pH. Here we show that ASIC1 and ASIC3, but not ASIC2 and ASIC4 are upregulated in human IVDs according to the degree of clinical degeneration. Subjecting IVD-derived NP-MSCs to pH 6.6 culture conditions to mimic pathological IVD changes resulted in decreased cell proliferation that was associated with cell cycle arrest and induction of senescence. Key molecular changes observed were increased expression of p53, p21, p27, p16 and Rb1. Instructively, premature senescence in NP-MSCs could be largely alleviated using ASIC inhibitors, suggesting both ASIC1 and ASIC3 act decisively upstream to activate senescence programming pathways including p53-p21/p27 and p16-Rb1 signaling. These results highlight the potential of ASIC inhibitors as a therapeutic approach for IVDD and broadly define an in vitro system that can be used to evaluate other IVDD therapies.

Acidosis induces synovial fibroblasts to release vascular endothelial growth factor via acid-sensitive ion channel 1a

Acid-sensitive ion channel 1a (ASIC1a) is a member of the extracellular H+ activated cation channel family. Studies have shown that tissue acidification contributes to the formation of microvessels in rheumatoid arthritis (RA) synovial tissue, but its underlying mechanisms remain unclear. The purpose of this study was to investigate the role of tissue acidification in microvascular formation of arthritic synovial tissue and the effect of ASIC1a on vascular endothelial growth factor (VEGF) release from arthritic synovial tissue. Our results indicate that ASIC1a expression, VEGF expression, and microvessel density (MVD) are elevated in RA synovial tissue and adjuvant arthritis (AA) rat synovial tissue. When AA rats were treated with ASIC1a-specific blocker psalmotoxin-1 (PcTx-1), the expression of ASIC1a, VEGF expression, and MVD were all reduced. Acidification of RA synovial fibroblasts (RASF) can promote the release of VEGF. PcTx-1 and ASIC1a-short hairpin RNA can inhibit acid-induced release of VEGF. In addition, the ASIC1a overexpression vector can promote acid-induced VEGF release. This indicates that extracellular acidification induces the release of VEGF by RASF via ASIC1a. These findings suggest that blocking ASIC1a mediates the release of VEGF from synoviocytes may provide a potential therapeutic strategy for RA therapy.

Ginsenoside Rb1 ameliorates cardiotoxicity triggered by aconitine via inhibiting calcium overload and pyroptosis

BACKGROUND

Aconitine-induced cardiotoxicity limits the clinical treatment of cardiotonic, cancers and immune-related diseases. Ginsenoside Rb1 (Rb1) is an active ingredient of traditional Chinese medicine with cardioprotective effect.

PURPOSE

This study aims to study the mechanism of aconitine cardiotoxicity and the detoxification mechanism of Rb1.

STUDY DESIGN

METHODS: The regulatory effect of Rb1 on aconitine was evaluated in vitro and in vivo by myocardial enzyme indicators, pathological analysis, CardioECR detection, calcium transient analysis, western blotting and immunohistochemistry.

RESULTS

Rb1 (10, 20, 40 mg/kg) alleviated apoptotic myocardial damage caused by aconitine in rats. Furthermore, Rb1 (25, 50, 100 μM) restored the contractile function and field potential of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) by regulating calcium channels and reduced myocardial cell damage by inhibiting the calcium transients of adult rat ventricular myocytes (ARVMs). Rb1 significantly reduced calcium levels in hiPSC-CMs, directly indicating that aconitine-induced calcium overload was alleviated by Rb1. Further, aconitine caused calcium overload by changing the expression of calcium pathway proteins, while Rb1 effectively restored calcium homeostasis. In addition, Rb1 also had a cardioprotective role by inhibiting cell pyroptosis. These results suggested that the maintenance of calcium homeostasis helped to suppress the inflammatory response related to pyroptosis of the heart.

CONCLUSION

Aconitine-induced cardiotoxicity can be alleviated by Rb1 via restoring calcium homeostasis and inhibiting apoptosis and pyroptosis.

Acid-Sensing Ion Channel-1a in Articular Chondrocytes and Synovial Fibroblasts: A Novel Therapeutic Target for Rheumatoid Arthritis

Acid-sensing ion channel 1a (ASIC1a) is a member of the extracellular H⁺-activated cation channel family. Emerging evidence has suggested that ASIC1a plays a crucial role in the pathogenesis of rheumatoid arthritis (RA). Specifically, ASIC1a could promote inflammation, synovial hyperplasia, articular cartilage, and bone destruction; these lead to the progression of RA, a chronic autoimmune disease characterized by chronic synovial inflammation and extra-articular lesions. In this review, we provided a brief overview of the molecular properties of ASIC1a, including the basic biological characteristics, tissue and cell distribution, channel blocker, and factors influencing the expression and function, and focused on the potential therapeutic targets of ASIC1a in RA and possible mechanisms of blocking ASIC1a to improve RA symptoms, such as regulation of apoptosis, autophagy, pyroptosis, and necroptosis of articular cartilage, and synovial inflammation and invasion of fibroblast-like cells in synovial tissue.

The NLRP3 inflammasome: Multiple activation pathways and its role in primary cells during ventricular remodeling

Inflammasomes are a group of multiprotein signaling complexes located in the cytoplasm. Several inflammasomes have been identified, including NLRP1, NLRP2, NLRP3, AIM2, and NLRC4. Among them, NLRP3 was investigated in most detail, and it was reported that it can be activated by many different stimuli. Increased NLRP3 protein expression and inflammasome assembly lead to caspase-1 mediated maturation and release of IL-1β, which triggers inflammation and pyroptosis. The activation of the NLRP3 inflammasome has been widely reported in studies of tumors and neurological diseases, but relatively few studies on the cardiovascular system. Ventricular remodeling (VR) is an important factor contributing to heart failure (HF) after myocardial infarction (MI). Consequently, delaying VR is of great significance for improving heart function. Studies have shown that the NLRP3 inflammasome plays an essential role in the process of VR. Here, we reviewed the latest studies on the activation pathway of the NLRP3 inflammasome, focusing on the effects of the NLRP3 inflammasome in primary cells during VR, and finally discuss future research directions in this field.