Temporal Extracellular Vesicle Protein Changes following Intraarticular Treatment with Integrin α10β1-selected Mesenchymal Stem Cells in Equine Osteoarthritis

Abstract: Equine osteoarthritis is a heterogeneous, degenerative disease of the musculoskeletal system with multifactorial causation, characterised by a joint metabolic imbalance. Extracellular vesicles are nanoparticles involved in intracellular communication. Mesenchymal stem cell (MSC) therapy is a form of regenerative medicine that utilises their properties to repair damaged tissues. Despite its wide use in veterinary practice, the exact mechanism of action of MSCs is not fully understood. The aim of this study was to determine the synovial fluid extracellular vesicle protein cargo following integrin aplha 10 beta 1-selected mesenchymal stem cell treatment in an experimental model of equine osteoarthritis with longitudinal sampling. Adipose tissue derived, integrin aplha 10 beta 1-MSCs were injected into the osteoarthritis afflicted joint after 18 days post surgery. Sixty-nine synovial fluid samples were collected via aseptic arthrocentesis at day 0, 18, 21, 28, 35, and 70. Synovial fluid was hyaluronidase treated and extracellular vesicles isolated using differential ultracentrifugation. Extracellular vesicles were characterised using the Exoview human tetraspanin chip. Extracellular vesicle concentration, surface marker identification, fluorescent microscopy and tetraspanin colocalization analysis was undertaken, in conjunction with nanoparticle tracking analysis. For proteomics, extracellular vesicle pellets were suspended in urea lysis buffer. Samples were reduced, alkylated and digested on SP3 beads with trypsin/LysC. A data independent acquisition mode was utilised for nano liquid chromatography tandem mass spectrometry analysis on a Triple TOF 6600 mass spectrometer. A total of 442 proteins were identified across all samples, with 48 proteins differentially expressed (FDR≤ 0.05) between control and osteoarthritis treated with MSCs. The most significant pathways following functional enrichment analysis of the differentially abundant protein dataset were serine endopeptidase activity (p=0.023), complement activation (classical pathway) (p=0.023), and collagen containing extracellular matrix (p=0.034). To date this is the first study to quantify the global extracellular vesicle proteome in synovial fluid following MSC treatment of osteoarthritis. Changes in the proteome of the synovial fluid-derived EVs following MSC injection suggest EVs may play a role in mediating the effect of cell therapy through altered joint homeostasis and an improved phenotype.