Role of microvesicles in gonarthrosis and their modulation by hyaluronic acid administered in viscosupplementation for the rational development of innovative medical devices

Gonarthrosis (GA) is the most common joint disease in the adult population worldwide. This pathology is the result of multiple mechanisms that lead to the degradation of the extracellular matrix (ECM) of the joint and determine a chronic inflammation of the knee. In addition to the multiple causes and risk factors, extracellular vesicles (EVs) are emerging as important players in GA and, more generally, in osteoarthritis (OA). EVs, such as exosomes and membranous EVs, are being extensively studied for their role in a vast number of processes, such as intercellular communication and cell-to-cell transfer of biologically active material due to their precipual capacity to transfer proteins, lipids, DNA, mRNA, miRNA to target cells, modifying their phenotype. As to OA, the latest scientific evidence indicates that EVs act in a bimodal pattern, i.e. either in a pro-inflammatory or anti-inflammatory fashion depending on the joint conditions and disease status. In the present thesis, we focused on the detrimental role of EVs in OA. As an example of this deleterious activity, it is known that the macrophages infiltrated in the synovial fluid release specific EVs containing proinflammatory cytokines such as IL-1β; these cytokines then stimulate the chondrocytes to release further EVs which are capable of increasing the levels of metalloproteinase-13 (MMP-13) and a disintegrin and metallopeptidase with thrombospondin motif 5 Type 1 (ADAMTS-5), the main enzymes responsible for cartilage degradation. Hyaluronic acid (HA) is a polysaccharide composed of disaccharide units containing N-acetylglucosamine and glucuronic acid produced by chondrocytes, synoviocytes and fibroblasts. Native HA is typically released inside the synovial space where it lubricates and cushions the joint. HA conditions have a very high impact on GA: indeed, in the course of GA and accordingly to its progression, a significant decrease in both HA concentration and mean molecular weight can be observed. These modifications influence the HA viscoelastic properties, resulting in the joints’ parallel deterioration. This is the reason why intra-articular infiltrative HA viscosupplementation has been established as safe and first choice treatment for Kellgren II-III GA. As it will be discussed in the next chapters, besides its rheological properties, which can be considered merely mechanical, HA is known to act on numerous pathologically relevant targets, i.e. directly triggering protective biochemical pathways and/or blunting harmful processes. Commercially available, injectable preparations for intra-articular viscosupplementation consist of linear or cross-linked HA, this latter reputed to have a longer-lasting activity due to its higher resistance to enzymatic degradation. In this thesis we studied the differential effects of EVs collected from non-stimulated or IL-1β-stimulated human monocytic cells (THP-1) on primary chondrocytes from GA patients (COA) and their modulation upon treatment with cross-linked and linear intercalated HA (CLHA) formulation.