| Human bone marrow-derived mesenchymal stem cells (BMSCs) have been used extensively in skeletal tissue engineering and regeneration. However, maintaining the properties of BMSCs in culture for subsequent applications still remains a great challenge for researchers. To this end, an emerging research approach of constructing a culture environment mimicking the bone marrow stem cell niche for regulation of BMSCs has been developed. This dissertation work aims to investigate the regulatory effects of soluble factors in the bone marrow niche on BMSCs, and further apply the knowledge to the maintenance of BMSC properties for tissue regeneration applications. First, using soluble factors extracted from bone marrow for BMSC culture, we found that bone marrow extract can maintain properties of BMSCs. We also found that the treatment of bone marrow extract can support cell quiescence, delay cellular senescence, enhance cell proliferation, and inhibit the multilineage differentiation of BMSCs while directing the cell fate toward osteogenic and chondrogenic cell lineages. Second, by analyzing the composition of bone marrow extract, we identified that lipocalin-2 (LCN2) and prolactin (PRL) are responsible for the regulatory effects of bone marrow extract on BMSCs. Treating BMSCs with the combination of LCN2 and PRL can delay cellular senescence and direct the cells toward osteogenic and chondrogenic lineages. Third, we also identified that bone marrow extract contains endothelin-1 (ET1). We demonstrated that endothelial cells secrete ET1 to direct cell fates of BMSCs through the AKT signaling pathway. Lastly, we found that pretreatment with LCN2 and PRL in BMSC culture can enhance the in vivo bone forming capacity of these cells. Together, we demonstrated that understanding the in vivo regulation of BMSC activities in the bone marrow stem cell niche can aid in improving BMSC-based tissue regeneration. |
