Extracellular vesicles in synovial fluid from juvenile horses: No age-related changes in the quantitative profile.

Extracellular vesicle (EV) concentration, characteristics and function in equine synovial fluid (SF) during normal growth and development has not previously been studied. Isolation of EVs was performed in SF from three healthy foals and two adult horses by differential ultracentrifugation (10,000g and 200,000g); EVs were purified by sucrose density gradient floatation and analysed by high-resolution flow cytometry (FCM), buoyant density and western blotting. Additionally, repeated biomarker analysis of sulphated glycosaminoglycans (GAG), matrix metalloproteinase (MMP), C-terminal crosslinked telopeptide type II collagen (CTX-II), collagenase cleaved neopeptide type II collagen (C2C) was performed in SF from 10 foals and six adult horses. In contrast with the quantitative EV profile, the biomarker profile in SF from juvenile joints was substantially different from that in SF from adult animals. However, there were qualitative differences in the high-resolution FCM scatter plots. Future in-depth functional analyses may reveal differences between juvenile and mature EVs in SF.