From fat to cartilage [electronic resource] : harnessing stem cells to catalyze cartilege regeneration

Cartilage loss is a leading cause of disability among adults and represents a huge socioeconomic burden. Articular cartilage has limited self-repair potential and damage is often irreversible. Tissue engineering holds great promise for cartilage repair using a combination of cells, biomaterials and/or biological factors. However, one of the key barriers is the lack of abundant cell sources that can effectively regenerate articular cartilage. Conventional tissue engineering strategies for cartilage repair often utilize adult chondrocytes, which is limited by donor site morbidity, the need for multiple surgeries, and tendency to de-differentiate during in vitro expansion. Unlike adult chondrocytes, neonatal chondrocytes (NChons) are highly proliferative, immune-privileged, and can readily produce abundant extracellular matrix with retained articular cartilage phenotype. However, donor availability for NChons is scarce, which greatly hinders their broad application. The goal of this thesis is to examine the potential of ADSCs to catalyze cartilage tissue formation by NChons in 3D hydrogels. Specifically, we explored the feasibility of substituting the majority of NChons with ADSCs, an abundant autologous cell source that can be obtained in a minimally invasive manner. Using three different co-culture models, we demonstrated that the effects of co-culture on cartilage tissue formation were highly dependent on intercellular distance and cell distribution in 3D. Unexpectedly, increasing ADSC ratio in mixed co-culture led to increased synergy between NChons and ADSCs, and robust cartilage formation could be achieved using as few as 2% NChons in the mixed cell population. Cell tracking indicated that the newly formed cartilage was contributed by NChons alone, whereas ADSCs catalyzed such cartilage formation via paracrine signaling. We then demonstrated that catalyzed cartilage formation was retained under hypoxia, supporting the feasibility of translating such therapy for repairing cartilage tissue in situ. Furthermore, we examined the effects of transient priming of ADSCs with transforming growth factor (TGF)-[beta] on their ability to catalyze cartilage formation by NChons. Our results showed that ADSCs with short-term TGF-[beta] priming led to optimal catalyzed cartilage formation. Finally, we validated the efficacy of utilizing a mixed population of ADSCs with a small number of NChons for cartilage regeneration in vivo with robust hyaline cartilage formation over 12 weeks. In summary, the findings of this thesis raise the potential of utilizing stem cells to catalyze tissue formation by NChons, which may accelerate the broad translation of NChons for cartilage repair by alleviating donor scarcity limitation. Furthermore, the concept of harnessing paracrine signaling between two or more cell types in 3D scaffolds to catalyze tissue formation may be broadly applicable to regenerating other tissue types.

Keywords: Mechanical Engineering.
Advisor: Levenston Marc Elliot primary advisor. Thesis advisor
Yang Fan (Bioengineering researcher and teacher) primary advisor. Thesis advisor
Smith R. Lane (Robert Lane) advisor. Thesis advisor