Characterization of extracellular vesicles in plasma and synovial fluid of horses with naturally occurring post-traumatic osteoarthritis: An exploratory study to identify transcriptomic profiles.

Objective: The objective of this study was to characterize extracellular vesicles (EVs) in plasma and synovial fluid obtained from horses with and without naturally occurring post-traumatic osteoarthritis (PTOA). Animals (Samples): EVs were isolated from plasma and synovial fluid from horses with (n = 6) and without (n = 6) PTOA. Methods: Plasma and synovial fluid EVs were characterized with respect to quantity, size, and surface markers. Small RNA sequencing was performed and differentially expressed miRNAs underwent bioinformatic analysis to identify putative targets and to explore potential associations with specific biological processes. Results: Plasma and synovial fluid samples from horses with PTOA had a significantly higher proportion of exosomes and a lower proportion of microvesicles compared to horses without PTOA. Small RNA sequencing revealed several differentially expressed miRNAs including miR-144, miR-219-3p, and miR-199a-3p in plasma and miR-199a-3p, miR-214, and miR-9094 in synovial fluid EVs. Bioinformatics analysis of the differentially expressed miRNAs highlighted their potential role in fibrosis, differentiation of chondrocytes, apoptosis, and inflammation pathways in PTOA. Clinical Relevance: We have identified dynamic molecular changes in small non-coding signatures of plasma and synovial fluid EVs in horses with naturally occurring PTOA. These findings could serve to identify promising biomarkers in the pathogenesis of PTOA, to facilitate the development of targeted therapies, and to aid in establishing appropriate translational models of PTOA. A single pooled sample containing EVs from 6 horses for each group including plasma control (n=1), plasma PTOA (n=1), synovial fluid control (n=1), synovial fluid PTOA (n=1) **Submitter states that the intact R2 (raw data) mate file for the Synovial fluid control sample ('SynFld-Control_R2_001.fastq.gz') is unavailable and thus only R1 file is provided**