We previously reported a new cell transplantation method in which mesenchymal stem cells (MSCs) were cultured as cell sheets. The cultured MSC sheets showed high alkaline phosphatase (ALP) activities and osteocalcin (OC) contents. In the present study, we transplanted such sheets by injection to assess whether the injectable MSC sheets could form bone tissue at subcutaneous sites. At 4 weeks after the subcutaneous injection, the injected areas showed hard mass formation. Each mass consisted of newly formed bone, as evaluated by radiographic, histological and gene expression analyses as well as three-dimensional computed tomography (3D-CT). Histological analyses revealed extracellular bone matrix together with osteocytes and active osteoblasts. Real-time PCR analyses showed high ALP and OC mRNA expressions. We also injected the cell sheets into dead bone to determine whether the lost osteogenic potential could be rescued, and histological analyses revealed that the injected cell sheets supplied osteogenic potential to the dead bone. The present study clearly indicates that osteogenic MSC sheets can be transplanted via injection through a needle and that bone formation results in the injected areas. Owing to its usage of a needle for fabrication of in vivo bone tissue, this injection method can be applied as a minimally invasive approach for hard tissue reconstruction.
Abstract.Although mesenchymal stem cells (MSCs) are considered to be the cells of origin for most sarcomas, the role of MSCs as a source of tumor stroma is not fully understood in this tumor type. The current study investigated whether MSCs affect the tumor growth and metastatic ability in rat osteosarcoma model. Results from subcutaneous co-implantation of rat osteosarcoma COS1NR cells, established in our laboratory, with rat MSCs isolated from femur bone marrow showed that the incidence of tumor formation and tumor growth rate was higher until 5 weeks compared to COS1NR cell inoculation alone. However, no difference was observed in tumor growth afterwards and in the number of metastatic nodules at 9 weeks (0.75 vs. 1.2). Intravenous MSC injection at weeks 3 and 5 after subcutaneous inoculation of COS1NR cells significantly increased the number of lung nodules in the group with MSC injection compared to the group without MSC injection (17.33 vs. 2.0), while no difference was observed in subcutaneous tumor growth between those groups. Pathway analysis from gene expression profile identified that genes involved in focal adhesion, cytokine-cytokine receptor and extracellular matrix-receptor pathways such as CAMs (ICAM and VCAM)-integrins were highly expressed in MSCs, possibly participating in the tumor progression of osteosarcoma. These results suggest that MSCs could provide a source of microenvironments for osteosarcoma cells, and might enhance the ability of settlement and colonization which lead to early onset of growth and metastasis, possibly through their activated pathways interaction. IntroductionHistoric landmark of tumor microenvironment research was proposed as the 'seed and soil' hypothesis by Stephen Paget 120 years ago (1), and the importance of the microenvironment and stroma in the evolution and progression of solid tumors has drawn renewed interest in recent years. A complex structure of mixed cell types and tissues with endothelial cells, immune cells, stromal cells and extracellular matrix is essential for the growth and progression of solid tumors (2). Although all of these components in the tumor are integral in carcinogenesis and metastasis, the stroma is considered to be a 'co-conspirator' in the evolution and progression of the disease (3). Among the stromal elements, the progenitor cells of the stroma, the mesenchymal stem cells (MSCs), have been receiving focused attention lately.Mesenchymal stem cells (MSCs) are mainly derived from bone marrow, non-hematopoietic precursor cells possessing differentiation potential to skeletal mesodermal lineages such as osteoblasts, chondrocytes and adipocytes as well as some extra-mesodermal cell types including neural, pancreatic and hepatocytic phenotypes with strong proliferative capacity (4-6), and are of increasing interest as the future therapeutic tool in regenerative medicine (7,8). MSCs also display immune suppressive properties which could be the potentially exploited for therapeutic treatment of auto-immune diseases and the reduction of gra...
The periosteum is a thin membrane that surrounds the outer surface of bones and participates in fracture healing. However, the molecular signals that trigger/initiate the periosteal reaction are not well established. We fractured the rat femoral bone at the diaphysis and fixed it with an intramedullary inserted wire, and the expression of regenerating gene (Reg) I, which encodes a tissue regeneration/growth factor, was analyzed. Neither bone/marrow nor muscle showed Reg I gene expression before or after the fracture. By contrast, the periosteum showed an elevated expression after the fracture, thereby confirming the localization of Reg I expression exclusively in the periosteum around the fractured areas. Expression of the Reg family increased after the fracture, followed by a decrease to basal levels by six weeks, when the fracture had almost healed. In vitro cultures of periosteal cells showed no Reg I expression, but the addition of IL-6 significantly induced Reg I gene expression. The addition of IL-6 also increased the cell number and reduced pro-apoptotic gene expression of Bim. The increased cell proliferation and reduction in Bim gene expression were abolished by transfection with Reg I siRNA, indicating that these IL-6-dependent effects require the Reg I gene expression. These results indicate the involvement of the IL-6/Reg pathway in the osteogenic response of the periosteum, which leads to fracture repair.
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