The role of Cx43 and stem cell derived exosomes for the regeneration of cartilage lesioned due to osteoarthritic processes

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Damaged joint cartilage which occurs in the course of ostoarthritis is one of the main causes for lameness in horses. Etiology and pathogenesis of ostoarthritis are still not clarified and up to now reliable therapeutic options for the treatment of osteoarthritis, which also includes the subchondral bone, are not available. However, the therapeutic use of mesenchymal stem cells (MSC) becomes increasingly important in human and veterinary medicine as according to currently available information MSCs do not necessarily need to differentiate in situ into chondrocytes to replace OA induced cartilage defects. Moreover, it is generally assumed that therapeutic effects of MSC are based on exosomes which are released into the extracellular space by MSC. Exosomes can be harvested from MSC cell culture supernatants by ultrafiltration as has been shown in previous studies. They can be characterized by the expression of surface markers such as CD9, CD63 and CD83. It is well known that micro RNAs as exosome cargo may modulate the equilibrium between cell proliferation and cell differentiation within the stem cell niche in vivo. Additionally, according to the present knowledge, connexin 43 of exosomes and chondrocytes play an instrumental role in the maintenance of tissue homeostasis within the microenvironment of healthy joint cartilage. Hence, the aim of the anticipated project is to investigate the protective effects of exosomes, which are harvested from the supernatant of equine cultivated adipose tissue derived MSC in an in vitro osteoarthritis model using lesioned equine chondrocytes. The main focus of this investigation will be to substantiate the working hypothesis, namely that different expression patterns of Cx43 and various cultivation conditions of MSC including their exosomes will induce different therapeutic effects in the OA model. Furthermore, we will examine whether upregulation of Cx43 induced in the course of OA might be counteracted by the exosome cargo. The therapeutic potency of exosomes shall be analyzed by the characterization of included therapeutic substances such as miRNA, proteins, cytokines and growth factors. Elaborated data of this project have the potency to establish basic principles for a useful stem cell-based but cell-free OA-therapy in veterinary and human medicine.