Hypoxia induces osteogenic/angiogenic responses of bone marrow-derived mesenchymal stromal cells seeded on bone-derived scaffolds via ERK1/2 and p38 pathways.

Osteogenesis and angiogenesis are tightly coupled processes during bone development and formation. It is thus well known that the enhancement of vascularization is of great importance in bone tissue engineering. As a potential approach for repairing bone defects, bone tissue constructs should therefore replicate the essential components in vivo microenvironments to promote cell osteogenic differentiation while at same time induce angiogenic response. In light of standpoint above, a combination of human bone-derived scaffolds and BMSCs that subjected to hypoxia was used to mimic in vivo conditions. Also the underlying cellular/molecular regulation was fully investigated. The results showed that hypoxia (5-10% O2 ) greatly enhanced the proliferation of BMSCs seeded in scaffolds, although the hypoxia (5% O2 )-induced proliferative effect on BMSC cellular scaffolds was not apparent to those cultured in plates. However, such a kind of model was able to significantly induce the osteogenic/angiogenic responses of BMSCs as reflected by osteogenesis or angiogenesis-related highly expressed genes or proteins, such as alkaline phosphatase, osteocalcin, hypoxia-inducible factor-1α and vascular endothelial growth factor. Moreover, ERK1/2 and/or p38 pathways were demonstrated to play essential roles in hypoxia-induced osteogenic/angiogenic responses. Our results indicated that the combination of bone-derived scaffolds, a material that has a three dimensional network structure, and hypoxia, an environment that replicates in vivo BMSCs hypoxic living conditions, may be a potential approach for creating functional tissue-engineered bone.

Osteogenic differentiation of bone marrow-derived mesenchymal stromal cells on bone-derived scaffolds: effect of microvibration and role of ERK1/2 activation.

Although in vivo studies have shown that low-magnitude, high-frequency (LMHF) vibration (LM: < 1 ×g; HF: 20-90 Hz) exhibits anabolic effects on skeletal homeostasis, the underlying cellular/molecular regulation involved in bone adaptation to LMHF vibration is little known. In this report, we tested the effects of microvibration (magnitude: 0.3 ×g, frequency: 40 Hz, amplitude: ± 50 µm, 30 min/12 h) on proliferation and osteodifferentiation of bone marrow-derived mesenchymal stromal cells (BMSCs) seeded on human bone-derived scaffolds. The scaffolds were prepared by partial demineralisation and deproteinisation. BMSCs were allowed to attach to the scaffolds for 3 days. Morphological study showed that spindle-shaped BMSCs almost completely covered the surface of bone-derived scaffold and these cells expressed higher ALP activity than those cultured on plates. After microvibration treatment, BMSC proliferation was decreased on day 7 and 10; however, numbers of genes and proteins expressed during osteogenesis, including Cbfa1, ALP, collagen I and osteocalcin were greatly increased. ERK1/2 activation was involved in microvibration-induced BMSC osteogenesis. Taken together, this study suggests that bone-derived scaffolds have good biocompatibility and show osteoinductive properties. By increasing the osteogenic lineage commitment of BMSCs and enhancing osteogenic gene expressions, microvibration promotes BMSC differentiation and increase bone formation of BMSCs seeded on bone-derived scaffolds. Moreover, ERK1/2 pathway plays an important role in microvibration-induced osteogenesis in BMSC cellular scaffolds.