Proteinase-activated receptor 2 (PAR2) deficiency protects against cartilage degradation in experimental osteoarthritis (OA). The wider impact of this pathway upon OA-associated pathologies such as ...osteophyte formation and pain is unknown. Herein, we investigated early temporal bone and cartilage changes in experimental OA in order to further elucidate the role of PAR2 in OA pathogenesis.
OA was induced in wild-type (WT) and PAR2-deficient (PAR2
) mice by destabilisation of the medial meniscus (DMM). Inflammation, cartilage degradation and bone changes were monitored using histology and microCT. In gene rescue experiments, PAR2
mice were intra-articularly injected with human PAR2 (hPAR2)-expressing adenovirus. Dynamic weight bearing was used as a surrogate of OA-related pain.
Osteophytes formed within 7 days post-DMM in WT mice but osteosclerosis was only evident from 14 days post induction. Importantly, PAR2 was expressed in the proliferative/hypertrophic chondrocytes present within osteophytes. In PAR2
mice, osteophytes developed significantly less frequently but, when present, were smaller and of greater density; no osteosclerosis was observed in these mice up to day 28. The pattern of weight bearing was altered in PAR2
mice, suggesting reduced pain perception. The expression of hPAR2 in PAR2
mice recapitulated osteophyte formation and cartilage damage similar to that observed in WT mice. However, osteosclerosis was absent, consistent with lack of hPAR2 expression in subchondral bone.
This study clearly demonstrates PAR2 plays a critical role, via chondrocytes, in osteophyte development and subchondral bone changes, which occur prior to PAR2-mediated cartilage damage. The latter likely occurs independently of OA-related bone changes.
Trypsin-like proteases (TLPs) belong to a family of serine enzymes with primary substrate specificities for the basic residues, lysine and arginine, in the P1 position. Whilst initially perceived as ...soluble enzymes that are extracellularly secreted, a number of novel TLPs that are anchored in the cell membrane have since been discovered. Muco-obstructive lung diseases (MucOLDs) are characterised by the accumulation of hyper-concentrated mucus in the small airways, leading to persistent inflammation, infection and dysregulated protease activity. Although neutrophilic serine proteases, particularly neutrophil elastase, have been implicated in the propagation of inflammation and local tissue destruction, it is likely that the serine TLPs also contribute to various disease-relevant processes given the roles that a number of these enzymes play in the activation of both the epithelial sodium channel (ENaC) and protease-activated receptor 2 (PAR2). More recently, significant attention has focused on the activation of viruses such as SARS-CoV-2 by host TLPs. The purpose of this review was to highlight key TLPs linked to the activation of ENaC and PAR2 and their association with airway dehydration and inflammatory signalling pathways, respectively. The role of TLPs in viral infectivity will also be discussed in the context of the inhibition of TLP activities and the potential of these proteases as therapeutic targets.
3-Hydroxy-3-methylglutaryl-CoA reductase inhibitors (statins) exert favorable effects on lipoprotein metabolism, but may also possess anti-inflammatory properties. Therefore, we explored the ...activities of simvastatin, a lipophilic statin, in a Th1-driven model of murine inflammatory arthritis. We report in this study that simvastatin markedly inhibited not only developing but also clinically evident collagen-induced arthritis in doses that were unable to significantly alter cholesterol concentrations in vivo. Ex vivo analysis demonstrated significant suppression of collagen-specific Th1 humoral and cellular immune responses. Moreover, simvastatin reduced anti-CD3/anti-CD28 proliferation and IFN-gamma release from mononuclear cells derived from peripheral blood and synovial fluid. Proinflammatory cytokine production in vitro by T cell contact-activated macrophages was suppressed by simvastatin, suggesting that such observations have direct clinical relevance. These data clearly illustrate the therapeutic potential of statin-sensitive pathways in inflammatory arthritis.
Protease-activated receptor-2 (PAR2) is one member of a small family of transmembrane, G-protein-coupled receptors. These receptors are activated
cleavage of their N terminus by serine proteases ...(e.g., tryptase), unveiling an N terminus tethered ligand which binds to the second extracellular loop of the receptor. Increasing evidence has emerged identifying key pathophysiological roles for PAR2 in both rheumatoid arthritis (RA) and osteoarthritis (OA). Importantly, this includes both pro-inflammatory and destructive roles. For example, in murine models of RA, the associated synovitis, cartilage degradation, and subsequent bone erosion are all significantly reduced in the absence of PAR2. Similarly, in experimental models of OA, PAR2 disruption confers protection against cartilage degradation, subchondral bone osteosclerosis, and osteophyte formation. This review focuses on the role of PAR2 in rheumatic disease and its potential as an important therapeutic target for treating pain and joint degradation.
Abstract
Osteoarthritis (OA) is the most prevalent of the musculoskeletal conditions and represents a significant public health burden. While degeneration of articular cartilage is a key feature, it ...is now increasingly recognized as a complex condition affecting the whole joint, with synovial inflammation present in a significant proportion of patients. As a secretory tissue, the OA synovium is a rich source of both soluble inflammatory mediators and extracellular vesicles, including exosomes, which have been implicated in cell–cell communication. Exosome cargo has been found to include proteins, lipids and various RNA subtypes such as mRNA and miRNA, potentially capable of regulating gene expression in target cells and tissues. Profiling of exosome cargo and understanding effects on cartilage could elucidate novel regulatory mechanisms within the joint, providing insight for targeted treatment. The aim of this article is to review current literature on exosome biology, highlighting the relevance and application for OA pathogenesis.
Exacerbations are frequently occurring events in the progression of COPD and are characterised by a sudden reduction in lung function associated with increased airway inflammation and sputum ...production. Triggers such as bacterial infection can lead to hospitalisation and increased mortality.
The aim of this study was to investigate differences in the response of COPD and healthy airway cells to bacterial stimulus by measuring levels of host inflammatory mediators.
Two clinically relevant strains of bacteria (Streptococcus pneumoniae and Haemophilus influenzae) were heat‐inactivated and co‐cultured at an established non‐toxic multiplicity of infection (MOI) 25:1 for 24 hours with primary human airway epithelial cells obtained from a healthy and COPD donor, grown at air‐liquid interface. Cell‐conditioned media was removed and analysed using the Bio‐Plex Pro™ Human Inflammation Panel 1, 37‐Plex assay (Bio‐Rad)
Cytokines and other pro‐inflammatory proteins, as previously established, were generally stimulated in response to heat‐inactivated pathogens. However, on assessment of the Bioplex panel as a whole, H. influenzae showed increased potential to induce the production of cytokines/proteins to a greater level than S. pneumoniae. The greatest overall increases were seen with the healthy cells (28/37 analytes), indicating that they are potentially more capable of mounting an acute inflammatory response than COPD cells.
Support or Funding Information
BREATH (Border and REgions Airways Training Hub) is funded by the EU's INTERREG Va programme managed by the Special EU Programmes Body (SEUPB).
This is from the Experimental Biology 2019 Meeting. There is no full text article associated with this published in The FASEB Journal.
Haemophilus influenzae is the most common cause of bacterial infection in the lungs of chronic obstructive pulmonary disease (COPD) patients and contributes to episodes of acute exacerbation which ...are associated with increased hospitalization and mortality. Due to the ability of H. influenzae to adhere to host epithelial cells, initial colonization of the lower airways can progress to a persistent infection and biofilm formation. This is characterized by changes in bacterial behaviour such as reduced cellular metabolism and the production of an obstructive extracellular matrix (ECM). Herein we discuss the multiple mechanisms by which H. influenzae contributes to the pathogenesis of COPD. In particular, mechanisms that facilitate bacterial adherence to host airway epithelial cells, biofilm formation, and microbial persistence through immune system evasion and antibiotic tolerance will be discussed.
Proteinase-activated receptor-2 (PAR(2)) has been implicated in inflammatory articular pathology. Using the collagen-induced arthritis model (CIA) the authors have explored the capacity of PAR(2) to ...regulate adaptive immune pathways that could promote autoimmune mediated articular damage.
Using PAR(2) gene deletion and other approaches to inhibit or prevent PAR(2) activation, the development and progression of CIA were assessed via clinical and histological scores together with ex vivo immune analyses.
The progression of CIA, assessed by arthritic score and histological assessment of joint damage, was significantly (p<0.0001) abrogated in PAR(2) deficient mice or in wild-type mice administered either a PAR(2) antagonist (ENMD-1068) or a PAR(2) neutralising antibody (SAM11). Lymph node derived cell suspensions from PAR(2) deficient mice were found to produce significantly less interleukin (IL)-17 and IFNγ in ex vivo recall collagen stimulation assays compared with wild-type littermates. In addition, substantial inhibition of TNFα, IL-6, IL-1β and IL-12 along with GM-CSF and MIP-1α was observed. However, spleen and lymph node histology did not differ between groups nor was any difference detected in draining lymph node cell subsets. Anticollagen antibody titres were significantly lower in PAR(2) deficient mice.
These data support an important role for PAR(2) in the pathogenesis of CIA and suggest an immunomodulatory role for this receptor in an adaptive model of inflammatory arthritis. PAR(2) antagonism may offer future potential for the management of inflammatory arthritides in which a proteinase rich environment prevails.
The cAMP-metabolising enzyme, phosphodiesterase 4 (PDE4), has been implicated in a number of immune responses, including tumour necrosis factor α (TNFα) production. To date, few data have directly ...addressed whether synovial cytokine and chemokine production is modified by PDE4.
Using specific PDE4 inhibitors, roflumilast plus two novel inhibitors, INH 0061 and INH 0062, the authors studied the effect of PDE4 inhibition on proinflammatory cytokine and chemokine release from primary rheumatoid arthritis (RA) synovial digest suspensions and in a macrophage T cell co-culture assay system.
All PDE4 inhibitors dose-dependently reduced the release of TNFα from primary synovial membrane cultures (n=5), half maximal inhibitory concentration (IC(50)) 300-30 nM, p<0.05. Similarly, a significant suppression in the release the proinflammatory chemokines, monocyte chemoattractant protein-1 (MCP-1), macrophage inflammatory protein (MIP)-1α, MIP-1β (IC(50) 300-30 nM) and regulated upon activation normal T-cell expressed and secreted (RANTES) (IC(50) 3 nM) was also observed, p<0.05. While interleukin 1β was also reduced, it did not achieve an IC(50). These observations were further confirmed in a macrophage T cell co-culture system, demonstrating the importance of PDE4 pathways in regulating cytokine/chemokine release in a cellular interaction implicated in inflammatory synovitis. Subsequent studies using the human monocytic cell line U937 also demonstrated cytokine regulation with PDE4 knockdown utilising a small interfering RNA approach.
These data provide direct evidence of PDE4-dependent pathways in human RA synovial inflammatory cytokine and chemokine release and may provide a novel approach in treating chronic autoimmune conditions such as RA.
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