Angiogenic potential of human mesenchymal stromal cell and circulating mononuclear cell cocultures is reflected in the expression profiles of proangiogenic factors leading to endothelial cell and pericyte differentiation.

Endothelial progenitors found among the peripheral blood (PB) mononuclear cells (MNCs) are interesting cells for their angiogenic properties. Mesenchymal stromal cells (MSCs) in turn can produce proangiogenic factors as well as differentiate into mural pericytes, making MSCs and MNCs an attractive coculture setup for regenerative medicine. In this study, human bone marrow-derived MSCs and PB-derived MNCs were cocultured in basal or osteoblastic medium without exogenously supplied growth factors to demonstrate endothelial cell, pericyte and osteoblastic differentiation. The expression levels of various proangiogenic factors, as well as endothelial cell, pericyte and osteoblast markers in cocultures were determined by quantitative polymerase chain reaction. Immunocytochemistry for vascular endothelial growth factor receptor-1 and α-smooth muscle actin as well as staining for alkaline phosphatase were performed after 10 and 14 days. Messenger ribonucleic acid expression of endothelial cell markers was highly upregulated in both basal and osteoblastic conditions after 5 days of coculture, indicating an endothelial cell differentiation, which was supported by immunocytochemistry for vascular endothelial growth factor receptor-1. Stromal derived factor-1 and vascular endothelial growth factor were highly expressed in MSC-MNC coculture in basal medium but not in osteoblastic medium. On the contrary, the expression levels of bone morphogenetic protein-2 and angiopoietin-1 were significantly higher in osteoblastic medium. Pericyte markers were highly expressed in both cocultures after 5 days. In conclusion, it was demonstrated endothelial cell and pericyte differentiation in MSC-MNC cocultures both in basal and osteoblastic medium indicating a potential for neovascularization for tissue engineering applications

Regulation of Osteoblast Differentiation - A Novel Function for FGF-8.

Several members of the fibroblast growth factor (FGF) family have an important role in the development of skeletal tissues. FGF-8 is widely expressed in the developing skeleton, but its function there has remained unknown. We asked in this study whether FGF-8 could have a role in the differentiation of mesenchymal stem cells to an osteoblastic lineage. Addition of FGF-8 to mouse bone marrow cultures effectively increased initial cell proliferation as well as subsequent osteoblast-specific alkaline phosphatase production, bone nodule formation, and calcium accumulation if it was added to the cultures at an early stage of osteoblastic differentiation. Exogenous FGF-8 also stimulated the proliferation of MG63 osteosarcoma cells, which was blocked by a neutralizing antibody to FGF-8b. In addition, the heparin-binding growth factor fraction of Shionogi 115 (S115) mouse breast cancer cells, which express and secrete FGF-8 at a very high level, had an effect in bone marrow cultures similar to that of exogenous FGF-8. Interestingly, experimental nude mouse tumors of S115 cells present ectopic bone and cartilage formation as demonstrated by typical histology and expression of markers specific for cartilage (type II and IX collagen) and bone (osteocalcin). These results demonstrate that FGF-8 effectively predetermines bone marrow cells to differentiate to osteoblasts and increases bone formation in vitro. It is possible that FGF-8 also stimulates bone formation in vivo. The results suggest that FGF-8, which is expressed by a great proportion of malignant breast and prostate tumors, may, among other factors, also be involved in the formation of osteosclerotic bone metastases

Microdamage detection and repair in bone: Fracture mechanics, histology, cell biology

Bone is an elementary component in the human skeleton. It protects vital organs, regulates calcium levels and allows mobility. As a result of daily activities, bones are cyclically strained causing microdamage. This damage, in the form of numerous microcracks, can cause bones to fracture and therefore poses a threat to mechanical integrity. Bone is able to repair the microcracks through a process called remodelling which is tightly regulated by bone forming and resorbing cells. However, the manner by which microcracks are detected, and repair initiated, has not been elucidated until now. Here we show that microcrack accumulation causes damage to the network of cellular processes, resulting in the release of RANKL which stimulates the differentiation of cells specialising in repair