Autologous stem-cell-based tissue engineering holds great potential for treating trauma and pathologies in a patient specific manner. Adult stem cells can be derived from various source tissues such as bone marrow, epidermal tissue, and adipose tissue. Initially, bone-marrow-derived mesenchymal stem cells (MSC) received the most attention for musculoskeletal tissue engineering applications given their direct lineage capability. More recently however, adipose-derived stem cells (ASC) have received increasing interest for tissue engineering applications due to their relative ease of harvest, abundance, and multi-lineage differentiation potential. To better implement the use of stem and progenitor cells for cell-based therapy and tissue repair, understanding of how these cells are committed to, or differentiate into, a specific cell lineage is needed.

Previous studies have shown the ability of hMSC and hASC to differentiate into bone, fibrous tissue, cartilage, and smooth muscle cells in response to appropriate chemical and/or mechanical stimuli. In this dissertation, the effect of allograft extracellular matrix, soluble inductive factors, and a specific mechanical stimulus (10% uniaxial cyclic tensile strain) on hASC/hMSC osteo- and chondrogenic differentiation and gene expression were examined. In the first study, hASC were seeded into a decellularized human meniscal allograft to determine the effects of inherent soluble cues provided by the extracellular matrix (ECM) on hASC viability, proliferation, differentiation and histology of the hASC-seeded meniscus. In the second study, hASC osteogenic differentiation and response to combined chemical and mechanical stimuli were investigated. Gene expression profiles of proliferating or osteogenically induced hASC in 3D collagen I culture in the presence and absence of 10% uniaxial cyclic tensile strain were examined using microarray analysis. In the final study, hMSC isolated from aged, postmenopausal osteoporotic donors were cultured in three-dimensional (3D) collagen constructs and analyzed for changes in mRNA expression in response to 10% uniaxial cyclic tensile strain in an attempt to identify potential mechanisms underlying the use of appropriate mechanical loading for prevention and treatment of osteoporosis.

The results of the first study show promising initial results of the use of hASC combined with a decellularized meniscal allograft for improved approaches for meniscal allograft transplants. The following studies of hASC and hMSC in response to tensile strain expanded findings from the first study to determine the effects of combined chemical and mechanical stimuli for regeneration of other musculoskeletal tissues in addition to fibrocartilage, with particular emphasis on bone formation. Application of cyclic tensile strain at different magnitudes is a stimulus for fibrous tissue, fibrocartilage and bone formation during normal secondary fracture healing or distraction osteogenesis. Specifically, our lab has previously shown that 10% cyclic tensile enhances osteogenesis of both hASC and hMSC in vitro. However, the molecular mechanisms underlying this potential are not yet known. The research performed in this thesis identified angiogenesis as a potential mechanism in response of hMSC and hASC to 10% cyclic tensile strain. Potential key genes identified to play important roles in hASC and hMSC in response to 10% tensile strain included PDLIM4, an actin binding protein. PDLIM4 knockdown was also shown to increase hMSC osteogenesis via enhanced expression of bone marker genes and alkaline phosphatase activity.