Regulation of bone marrow mesenchymal stem cells, cell-cell, and cell-matrix interactions

Bone marrow mesenchymal stem cells (MSCs) represent one of the most important adult stem cell types for regenerative medicine. These cells provide a reliable cell source for tissue engineering and cell-based therapies. Although MSCs have been isolated from many tissues in addition to bone marrow, their regulation in highly specialized physiological microenvironments is still largely unclear. This thesis addressed this issue from three important aspects using well-defined in vitro models and attempted to utilize the information obtained from these model systems for tissue engineering applications.; First, this thesis addressed the regulation of MSCs by the neighboring cells in their physiological microenvironment using a well-defined MSC-osteoblast coculture system, as osteoblasts coexist with MSCs in bone in close proximity. Osteoblasts have been found to regulate bone marrow hematopoietic stem cells, but their role in MSC regulation is unclear. This thesis discovered that osteoblasts regulate MSCs through WNT and cadherin pathways and the regulation mechanism depends on cell-cell contact modes (direct vs. indirect).; The second aspect of MSC regulation addressed in this thesis is the interaction between MSCs and extracellular matrix in a 2D environment. This was realized by a model system, in which a vitamin-C functionalized polymer was used to create a highly specific matrix for MSCs. The results showed that the vitamin-C functionalized polymer matrix regulates MSCs attachment, spreading, proliferation, and differentiation. More importantly, this functionalized polymer was capable of preserving the differentiation capacity of the MSCs, a phenomenon related to cellular aging.; The third part of this thesis focuses on the regulation of MSCs in 3D environments, created by an engineered porous silk scaffold with highly connected pore structures. Silk as the strongest naturally occurring polymer material has gained increasing interest in biomedical applications, as reviewed extensively in this thesis. The 3D porous silk scaffold provides a suitable environment for MSCs to differentiate into chondrocytes in serum free medium supplemented by dexamethasone and transforming growth factor-beta. It was also found that MSC (i.e. stem cell) based cartilage tissue engineering has fundamental differences from chondrocyte (i.e. primary cell) based cartilage tissue engineering.; In summary, this thesis addressed three essential aspects of the regulation of MSCs and the findings have important implications in MSC biology and MSC-based cellular therapy.