Extracellular Vesicles Released From Articular Chondrocytes Play a Major Role in Cell–Cell Communication

The purpose of this investigation was to determine the role of extracellular vesicles (EVs), released from articular chondrocytes in a physiological or pathological state, in cell–cell communication with other articular chondrocytes or chondrocyte precursor cells. The conditioned medium from interleukin-1β (IL-1β)-treated human articular chondrocytes stimulated catabolic events and inhibited type II collagen expression in articular chondrocytes to a much greater degree than medium from IL-1β-treated chondrocytes after complete removal of EVs. The vehicle-treated and IL-1β-treated human articular chondrocytes released EVs of similar size; however, the number of EVs released by IL-1β-treated chondrocytes was markedly higher than the number of EVs released from the vehicle-treated cells. Furthermore, our findings demonstrate that similar to medium from IL-1β-treated chondrocytes containing EVs, EVs isolated from medium of IL-1β-treated chondrocytes stimulated catabolic events in articular chondrocytes, whereas EVs isolated from the medium of vehicle-treated chondrocytes inhibited catabolic events and increased messenger RNA levels of aggrecan and type II collagen in IL-1β-treated chondrocytes. Furthermore, the medium containing EVs from vehicle-treated articular chondrocytes or EVs isolated from this medium stimulated chondrogenesis of C3H10T1/2 cells, whereas medium containing EVs from IL-1β-treated chondrocytes or EVs isolated from this medium inhibited chondrogenesis. Our findings suggest that EVs released by articular chondrocytes play a key role in the communication between joint cells and ultimately in joint homeostasis, maintenance, pathology, and repair.