Effect of human synovial fluid from osteoarthritis patients and healthy individuals on lymphatic contractility

The lymphatic system has been proposed to play a crucial role in the development and progression of osteoarthritis (OA). The synovial fluid (SF) of arthritic joints contains mediators of the inflammatory response and products of the injury to articular tissues, while lymphatic system plays a critical role in resolving inflammation and overall joint homeostasis. Despite the importance of both the lymphatic system and SF in OA disease, their relationship is still poorly understood. Here, we utilized SF derived from osteoarthritis patients (OASF) and healthy individuals (HSF) to investigate potential effects of SF on migration of lymphatic endothelial cells (LECs) in vitro, and lymphatic contractility of femoral lymphatic vessels (LVs) ex vivo. Both OASF and HSF treatments led to an increased migratory response in vitro compared to LECs treatment with media without serum. Ex vivo, both OASF and HSF treatments to the lumen of isolated LVs led to significant differences in the tonic and phasic contractions and these observations were dependent on the SF treatment time. Specifically, OASF treatment transiently enhanced the RFLVs tonic contractions. Regarding the phasic contractions, OASF generated either an abrupt reduction after 1 hr of treatment or a complete cease of contractions after an overnight treatment, while HSF treatment displayed a gradual decrease in lymphatic contractility. The observed variations after SF treatments suggest that the pump function of lymphatic vessel draining the joint could be directly compromised in OA and thus might present a new therapeutic target.