68. synovial fluid hyaluronan fluctuation in post-traumatic osteoarthritis: dependence on the dynamic balance between biosynthesis, loss, and fluid flux
Name: Aimee Rose Raleigh
Grad Year: 2018
Introduction: Injury to knee joint tissues (cartilage, subchondral bone, ligament, or meniscus) increases the likelihood of post-traumatic osteoarthritis (PTOA). PTOA may be due, in part, to a decrease in concentration of synovial fluid (SF) lubricants, including hyaluronan (HA). HA is a large, non-sulfated, anionic glycosaminoglycan, normally present at high concentrations in the SF and produced primarily by HA synthases (HAS) in fibroblast-like synoviocytes (FLS). However, the biophysical mechanisms affecting HA concentration are complex, involving cell, tissue, and organ scale-biology, modulating synthesis, degradation, and (in/ef)flux. The hypothesis of the present study is that the altered cSFHA in PTOA reflects changes in expression of specific HA synthases combined with SF volume changes and HA degradation/loss. Methods: 37 adult NZW rabbits were subjected to unilateral ACLT to induce PTOA. Knee joints were harvested at 1, 4, 7, 14, 28, and 42 days post-injury (n=6/group). Synovial lining (SL) and SF were harvested from ACLT and contralateral non-operated control (CTRL) joints. FLS from 4 additional healthy adult rabbits were isolated and cultured in basal media (DMEM + 0.5% FBS) + 0.1 or 1.0 ng/mL TGF-β1 and IL-1β. SL and cultured FLS were analyzed for expression of HAS1, HAS2, and HAS3 by qPCR with RPS18 and GAPDH as reference genes. HA, in SF and in conditioned media, was assessed using an ELISA-like assay. Data were analyzed using 1- or 2-way repeated measures ANOVA. A compartmental mass balance model was used to account for the rate of change of SF HA due to HA synthesis, HA loss, and net fluid influx. The loss rate, due to efflux and/or HA degradation, was the only unknown and was fit from the model and data. Results: In vitro cytokine stimulation of FLS led to stimulated HAS2 expression and HA secretion in a dose-dependent manner (r2=0.45, to 3.5-4.2X basal). In vivo, ACLT led to both acute and chronic changes. HAS2 expression was induced in ACLT SL (1.5-3.1X) as compared to CTRL. VSF was greater (to 1.9-4.4X) in ACLT knees, but cSFHA was lower (0.36-0.67X). Modeling to fit cSFHA indicated that the ACLT-induced increase in HA synthesis due to proliferation and expression per cell was countered both by net fluid influx, causing increased VSF, and increased rate of HA loss. Conclusions: Because SF lubricant function depends on concentration, a predictive model for changes during joint injury and arthritis could be used to inform the development of patient-specific therapies.
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