Destabilization of the Medial Meniscus and Cartilage Scratch Murine Model of Accelerated Osteoarthritis

Osteoarthritis is the most prevalent musculoskeletal disease in people over 45, leading to an increasing economic and societal cost. Animal models are ...

University of the West of Scotland

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.

Immunomodulatory role of proteinase-activated receptor-2.

Proteinase-activated receptor-2 (PAR-2) was shown to influence immune regulation; however, its role in human macrophage subset development and function has not been addressed. Here, PAR-2 expression and activation was investigated on granulocyte macrophage (GM)-CSF(M1) and macrophage (M)-CSF(M2) macrophages. In both macrophages, the PAR-2-activating peptide, SLIGKV, increased PAR-2 expression and regulated TNF-α and IL-10 secretion in a manner similar to LPS. In addition, HLA-DR on M1 cells also increased. Monocytes matured to an M1 phenotype in the presence of SLIGKV had reduced cell area, and released less TNF-α after LPS challenge compared with vehicle (P < 0.05, n = 3). Cells matured to an M2 phenotype with SLIGKV also had a reduced cell area and made significantly more TNF-α after LPS exposure compared to vehicle (P < 0.05, n = 3) with reduced IL-10 secretion (P < 0.05, n = 3). Thus, PAR-2 activation on macrophage subsets regulates HLA-DR and PAR-2 surface expression, and drives cytokine production. In contrast, PAR-2 activation during M1 or M2 maturation induces altered cell morphology and skewing of phenotype, as evidenced by cytokine secretion. These data suggest a complex role for PAR-2 in macrophage biology and may have implications for macrophage-driven disease in which proteinase-rich environments can influence the immune process directly. 

Proteinase-activated receptor-2 modulates human macrophage differentiation and effector function.

Rheumatoid arthritis (RA) is associated with high cardiovascular mortality. Impaired endothelial cell (EC) function and elevated angiotensin II levels may be central to the link between vascular dysfunction and RA. Here we investigated the action of angiotensin type 1 receptor (AT1R) blockade on endothelium-dependent relaxation of the isolated saphenous artery in a rat model of monoarthritis.

Angiotensin II Type 1 receptor blockade protects endothelium-derived hyperpolarising factor-mediated relaxation in a rat model of monoarthritis.

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.

Proteinase-activated receptor 2 modulates OA-related pain, cartilage and bone pathology.

A role for endothelium-derived constricting factors (EDCF), and the angiotensin II type 1 receptor (AT1R) pathway, in the vascular impairment found in the rat Freund's complete adjuvant (FCA)-model of rheumatoid arthritis (RA) was examined. FCA arthritis was induced in rats±losartan. Vehicle-treated rats served as controls. Knee-joint swelling and red blood cell (RBC) aggregation were measured as indicators of inflammation and endothelium reactivity assessed by response to acetylcholine (ACh) on aortic rings. Results show that knee-joint swelling and RBC aggregation were elevated in the FCA+vehicle group and restored to control levels in the FCA+losartan-treated animals. ACh-induced relaxation of aortic rings taken from FCA+vehicle animals was significantly impaired compared to vehicle-controls and this vasoreactivity was restored to control levels in the FCA+losartan-treated group. Further examination of aorta from the FCA+vehicle animals revealed an EDCF that was reliant on cyclooxygenase-2 (but not cyclooxygenase-1), generation of superoxide anion generation (but not hydrogen peroxide) and activation of thromboxane-prostanoid receptor. Losartan administration in vivo or ex vivo (to aortic rings) prevented the generation of the EDCF. In summary, this is the first evidence of an EDCF in a model of RA and identifies this mechanism as potentially significant in the cardiovascular disorder associated with the disease.

Endothelium-derived contraction in a model of rheumatoid arthritis is mediated via angiotensin II type 1 receptors.

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.

Rheumatic Disease: Protease-Activated Receptor-2 in Synovial Joint Pathobiology.

Joint injury involving destabilisation of the joint and damage to the articular cartilage (e.g., sports-related injury) can result in accelerated post-traumatic osteoarthritis (PTOA). Destabilised medial meniscotibial ligament (DMM) surgery is one of the most commonly used murine models and whilst it recapitulates Osteoarthritis (OA) pathology, it does not necessarily result in multi-tissue injury, as occurs in PTOA. We hypothesised that simultaneous cartilage damage and joint destabilisation would accelerate the onset of OA pathology.

Accelerated post traumatic osteoarthritis in a dual injury murine model.

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.

Exosomes in intercellular communication and implications for osteoarthritis.

The aim of this study was to determine the presence of protease-activated receptor 2 (PAR2) and matriptase proteins and quantify PAR2 and matriptase mRNA expression in the articular cartilage and synovial membrane of cats with and without osteoarthritis (OA).

Protease activated receptor 2 and matriptase expression in the joints of cats with and without osteoarthritis.

Angiotensin II-type 1 receptor stimulation is recognised to promote inflammation, a state central to the development and maintenance of rheumatoid arthritis. Herein we examined the use of losartan, an angiotensin II-type 1 receptor antagonist, on vascular reactivity, knee joint diameter and behavioural assessment of pain in a Freund's complete adjuvant (FCA) mouse model of joint inflammation. Monoarthritis was induced via FCA in the presence or absence of losartan with naive mice serving as controls. Knee joint swelling, joint pain (assessed by dynamic weight bearing of limb use), knee joint artery reactivity (assessed ex vivo) and blood perfusion of the knee joint (assessed in vivo) were determined. FCA mediated a significant increase in knee joint diameter and reduced weight-bearing (a surrogate for pain sensation) of the affected limb. Notably, these phenomena were substantially reduced when mice were prophylactically treated with losartan. Assessment of arterial relaxation and blood perfusion with acetylcholine stimulation revealed that FCA resulted in significant vascular dysfunction, which was resolved to naïve levels with losartan treatment. Through the actions of losartan, these findings indicate that the angiotensin II-type 1 receptor is a likely therapeutic target of importance in the development of the physical changes, pain sensation and vascular dysfunction found in inflammatory arthritis.

Losartan protects endothelium-dependent relaxation in vivo in a murine model of rheumatoid arthritis.

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.

Trypsin-Like Proteases and Their Role in Muco-Obstructive Lung Diseases.

Chronic obstructive pulmonary disease (COPD) is a debilitating heterogeneous disease characterised by unregulated proteolytic destruction of lung tissue mediated via a protease-antiprotease imbalance. In COPD, the relationship between the neutrophil serine protease, neutrophil elastase, and its endogenous inhibitor, alpha-1-antitrypsin (AAT) is the best characterised. AAT belongs to a superfamily of serine protease inhibitors known as serpins. Advances in screening technologies have, however, resulted in many members of the serpin superfamily being identified as having differential expression across a multitude of chronic lung diseases compared to healthy individuals. Serpins exhibit a unique suicide-substrate mechanism of inhibition during which they undergo a dramatic conformational change to a more stable form. A limitation is that this also renders them susceptible to disease-causing mutations. Identification of the extent of their physiological/pathological role in the airways would allow further expansion of knowledge regarding the complexity of protease regulation in the lung and may provide wider opportunity for their use as therapeutics to aid the management of COPD and other chronic airways diseases.

John C. Lockhart

Institute of Biomedical and Environmental Health Research

University of the West of Scotland

Destabilization of the Medial Meniscus and Cartilage Scratch Murine Model of Accelerated Osteoarthritis

John C. Lockhart

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Institute of Biomedical and Environmental Health Research

University of the West of Scotland

Destabilization of the Medial Meniscus and Cartilage Scratch Murine Model of Accelerated Osteoarthritis

Institute of Biomedical and Environmental Health Research