Preconditioning of mesenchymal stem cells with mechanobiological load and hypoxia for joint regeneration in moderate osteoarthritis

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The presence of osteoarthritic changes in a joint is a contraindication for current tissue engineering approaches, which are designed for regeneration of localized traumatic osteochondral lesions. Our long-term goal is the restoration of degenerative osteochondral lesions and beyond that, the treatment of chondral and osteochondral defects in an OA environment. To be successful we need to understand the constructive and destructive interactions between chondrogenesis, mechanical stress, oxygen tension and inflammation. We propose that mesenchymal stem cells can be preconditioned with mechanobiological load and/or hypoxia prior to implantation in order to achieve a stable chondrogenic phenotype. This preconditioning could allow regeneration of osteochondral defects even in an OA environment. Mechanical load in physiological range is an important factor for maintenance of the healthy status of joint cartilage. On the other hand, overloading is believed to increase the risk of osteoarthritis. Therefore we will apply hydrostatic pressure in different mechanobiological loading regimes to MSCs undergoing chondrogenesis in an in vitro 3D-aggregate culture system. We will identify loading conditions that show the strongest chondrogenic (increased anabolism and decreased catabolism) difference between loaded and unloaded conditions. We plan to achieve this under physiological conditions, but also in OA conditions, which will be mimicked by addition of IL-1ß to the culture medium.Hypoxic culture conditions have also been shown to have beneficial preconditioning for chondrogenic cells. We propose that hypoxia will promote differentiation and suppress markers of hypertrophy in both healthy and osteoarthritic culture conditions. We will apply hypoxia to MSCs undergoing in vitro chondrogenesis and analyse for anabolic and catabolic effects. We will focus on the suppression of hypertrophy in order to achieve a stable chondrogenic phenotype. We plan to identify key signaling pathways involved in the preconditioning process. In particular, we will analyse the PI3K/Akt-dependent pathway, because this cascade is involved in the modulation of chondrogenesis through mechanotransduction and also hypoxia. Finally we want to examine the effect of MSC-sponge constructs, preconditionend with mechanobiological load and/or hypoxia, to repair posttraumatic osteochondral defects in an animal model in a healthy and an early osteoarthritic condition.