Title: Targeting osteoarthritic pain through Proteinase Activated Receptor 2 (PAR2)
Funder: Versus Arthritis

Abstract: According to the World Health Organisation (WHO) osteoarthritis (OA) is already one of the ten most disabling diseases in developed countries, with 9.6% of men and 18% of women over the age of 60 affected by the disease. With an increasingly ageing population, these statistics are expected to increase. The disability originates from the development of chronic pain and reduced joint mobility. Lacking any disease modifying drugs to treat either the cause, or the symptoms, patients are expected to endure the pain with non-steroidal analgesics until surgery is deemed necessary. The absence of effective pain management for patients with OA calls for new treatments to successfully target the chronic pain many patients with OA suffer. Proteinase activated receptor 2 (PAR2) is a G-protein coupled transmembrane receptor (GPCR) that has been shown to mediate pro-inflammatory and nociceptive pathways. In a diverse range of diseases, such as irritable bowel syndrome (IBS) and bone cancer, studies have shown that PAR2 has a crucial role in hypersensitivity. Notably, absence or inhibition of PAR2 induces a higher pain threshold (individuals feel less pain). Our previous OA studies have also indicated a role of PAR2 in enhancing pain. PAR2 knockout mice display substantially decreased levels of cartilage damage, synovitis and pain. Traditional preclinical models of OA, such as destabilisation of the medial meniscus (DMM) lack clearly defined pain behaviours and show variability between operators, which makes data comparison difficult. Recently we have developed a new model, which combines DMM with surgically defined cartilage damage. This dual injury DMM and cartilage scratch (DCS) model is less variable between operators and more importantly displays early changes in gait and weight-bearing, which are surrogate measurements of pain (McCulloch K, 2019). Thus, this provides us with the opportunity to test and measure important therapies targeting PAR2 in nociceptive pain. The overall aim of our proposed studies is to test the feasibility of targeting PAR2 for the treatment of OA pain, with the added benefit of targeting the cartilage and bone-associated pathology. To achieve this, initial studies (using both knockout mice and a promising new PAR2 antagonist from AstraZeneca) will comprehensively characterise pain in the DCS model using techniques (von Frey filaments and thermal sensitivity) complementing the dynamic weight bearing we have used in the past. We will also monitor gait with a state-of-the-art DigiGait and general activity and food consumption. This work will be complemented with in vitro experimentation to interrogate the action of the new PAR2 antagonist in cells derived from the dorsal root ganglion (DRG). The final aim is to explore PAR2-mediated pathways that regulate pain sensitization. In brief, RNA sequencing of the L4 DRG will be conducted on OA and sham operated mice (WT and PAR2-/-). Using already established bioinformatics pipelines we will specifically identify PAR2 controlled pathways that are involved in pain sensitization in OA, thereby opening new avenues of research and therapeutic tractability.


Research activity codes: 2.1 BIOLOGICAL AND ENDOGENOUS FACTORS
Health categories: MUSCULOSKELETAL