Morphological and Mechanical Characterization of Extracellular Vesicles and Parent Human Synoviocytes under Physiological and Inflammatory Conditions

The morphology of fibroblast-like synoviocytes (FLS) issued from the synovial fluid (SF) of patients suffering from osteoarthritis (OA), rheumatoid arthritis (RA), or from healthy subjects (H), as well as the ultrastructure and mechanical properties of the FLS-secreted extracellular vesicles (EV), were analyzed by confocal microscopy, transmission electron microscopy, atomic force microscopy, and tribological tests. EV released under healthy conditions were constituted of several lipid bilayers surrounding a viscous inner core. This gel-in vesicular structure ensured high mechanical resistance of single vesicles and good tribological properties of the lubricant. RA, and to a lesser extent OA, synovial vesicles had altered morphology, corresponding to a gel-out situation with vesicles surrounded by a viscous gel, poor mechanical resistance, and poor lubricating qualities. When subjected to inflammatory conditions, healthy cells developed phenotypes similar to that of RA samples, which reinforces the importance of inflammatory processes in the loss of lubricating properties of SF.

Automated summary

This study analyzed the morphology of fibroblast-like synoviocytes (FLS) and the ultrastructure and mechanical properties of FLS-secreted extracellular vesicles (EV) from the synovial fluid of patients with osteoarthritis (OA), rheumatoid arthritis (RA), and healthy subjects (H). It was found that under inflammatory conditions, healthy cells developed phenotypes similar to that of RA samples, indicating the importance of inflammatory processes in the loss of lubricating properties of the synovial fluid.