Stem Cell-Based Strategies to Study, Prevent, and Treat Cartilage Injury and Osteoarthritis

Articular cartilage is a smooth connective tissue that covers the ends of bones and protects joints from wear. Cartilage has a poor healing capacity, and the lack of treatment options motivates the development of tissue engineering strategies. The widespread cartilage degeneration associated with osteoarthritis (OA) is dramatically accelerated by joint injury, but the defined initiating event presents a therapeutic window for preventive treatments. In vitro model systems allow investigation of OA risk factors and screening of potential therapeutics. This dissertation develops stem-cell based strategies to 1) treat cartilage injury and OA using tissue-engineered cartilage, 2) prevent the development of OA by delivering stem cells to the joint after injury, and 3) study cartilage by establishing systems to model genetic and environmental contributors to OA.

Adipose-derived stem cells (ASCs) and bone marrow-derived mesenchymal stem cells (MSCs) are promising human adult cell sources for cartilage tissue engineering, but require distinct chondrogenic conditions. As compared to ASCs, MSCs demonstrated enhanced chondrogenesis in both alginate beads and cartilage-derived matrix scaffolds.

We hypothesized that MSC therapy would prevent post-traumatic arthritis (PTA) by altering the balance of inflammation and regeneration. Highly purified MSCs (CD45-TER119-PDGFRα+Sca-1+) rapidly expanded under hypoxic conditions. Unexpectedly, MSCs from control C57BL/6 (B6) mice proliferated and differentiated more than MSCs from MRL/MpJ (MRL) "superhealer" mice. We injected B6 or MRL MSCs into mouse knees immediately after fracture, and MSCs of either strain were sufficient to prevent PTA.

Genetically reprogramming adult cells into induced pluripotent stem cells (iPSCs) generates large numbers of patient-matched cells with chondrogenic potential for therapy and cartilage modeling. We produced murine iPSC-derived cartilage constructs with a multi-phase approach involving micromass culture with bone morphogenetic protein-4, flow cytometry cell sorting of chondrocyte-like cells, monolayer expansion, and pellet culture with transforming growth factor-beta 3. Successful differentiation was confirmed by increased chondrogenic gene expression, robust synthesis of glycosaminoglycans and type II collagen, and the repair of an in vitro cartilage defect.

The diverse applications pursued in this research illustrate the power of stem cells to deepen the understanding of cartilage and guide the development of therapies to prevent and treat cartilage injury and OA.