Human articular chondrocytes. Plasticity and differentiation potentials

Sammanfattning: Articular cartilage has no or very low ability for self-repair and untreated lesions may lead tothe development of Osteoarthritis (OA). One method, which has been proved to result in longterm repair of isolated lesions, is autologous chondrocyte transplantation (ACT). In this methodculture expanded chondrocytes isolated from full-thickness biopsies taken from the supromedialedge, a non-weight bearing area of the femoral condyle, are transplanted back to the patientunder a cover of periosteum. To be able to improve the method and widen the treatmentindication to patients with fully developed OA, the general aim of this thesis was to increasethe knowledge of the cellular and molecular mechanisms underlying the repair tissue generatedby culture expanded chondrocytes.Our initial hypothesis to be tested was whether chondrocytes have stem cell properties. Thisquestion was addressed by using the established differentiation protocols for mesenchymalstem cells (MSCs) on culture expanded dedifferentiated human articular chondrocytes isolatedfrom non OA patients. The chondrocytes were found to exhibit a level of phenotypic plasticitythat is comparable with that of MSCs. By utilizing a cartilage selective agarose culture system,the plasticity of the cartilage progenitor cells was further shown to originate from clonal true chondrocytes and not from the heterogenous population of cells generated from acartilage biopsy that could harbor contaminating bone marrow stromal cells.By supplementing monolayer cultured chondrocytes with human serum instead of foetal calfserum a higher proliferative rate was achieved without losing the ability for cartilageredifferentiation in a 3D environment under serum free culture conditions. With microarraytechnology, the dynamic process of chondrocyte redifferentiation was shown to involve genesknown to be expressed in early embryonic chondrogenesis.Chondrocytes from OA patients were shown to have a proliferation potential in monolayercultures and an ability to redifferentiate in a pellet model at the same level as chondrocytesfrom non-OA patients. The cells could also be loaded into a hyaluronic acid based scaffold inwhich they did bind and produce cartilage proteoglycans and collagen. However, even if theOA cells produced cartilage specific matrix proteins, the cells did not produce the sameamount of total collagen as cells from patients without OA. The OA cells also continued theirproliferation within the redifferentiation model, indicating a potentially disturbed control intheir cell cycle.These findings demonstrate that treatment with ACT utilizes chondroprogenitor cells whichhave the potential to recapitulate embryonic genes during redifferentiation. This knowledgeis important for ongoing research in identifying strategies for regenerative therapies of othertissues and organs.