Abstract
The lymphatic system has been proposed to play a crucial role in preventing the development and progression of osteoarthritis (OA). As OA develops and progresses, inflammatory cytokines and degradation by-products of joint tissues build up in the synovial fluid (SF) providing a feedback system to exacerbate disease. The lymphatic system plays a critical role in resolving inflammation and maintaining overall joint homeostasis; however, there is some evidence that the lymphatics can become dysfunctional during OA. We hypothesized that the functional mechanics of lymphatic vessels (LVs) draining the joint could be directly compromised due to factors within SF derived from osteoarthritis patients (OASF). Here, we utilized OASF and SF derived from healthy (non-OA) individuals (healthy SF (HSF)) to investigate potential effects of SF entering the draining lymph on migration of lymphatic endothelial cells (LECs) in vitro, and lymphatic contractile activity of rat femoral LVs (RFLVs) ex vivo. Dilutions of both OASF and HSF containing serum resulted in a similar LEC migratory response to the physiologically endothelial basal medium-treated LECs (endothelial basal medium containing serum) in vitro. Ex vivo, OASF and HSF treatments were administered within the lumen of isolated LVs under controlled pressures. OASF treatment transiently enhanced the RFLVs tonic contractions while phasic contractions were significantly reduced after 1 h of treatment and complete ceased after overnight treatment. HSF treatment on the other hand displayed a gradual decrease in lymphatic contractile activity (both tonic and phasic contractions). 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.