Hypoxic regulation of mesenchymal stem cell migration: the role of RhoA and HIF-1α.

A variety of pathologies such as skeletal fracture, neoplasia and inflammation compromise tissue perfusion and thereby decrease tissue oxygen tension. We and others have demonstrated that hypoxia is a potent stimulant for MSC (mesenchymal stem cell) recruitment and differentiation, yet to date little research has focused on the effects of oxygen tension on MSC migration. In the present study, we examined the effects of hypoxia and the potential role of the GTPase RhoA and HIF-1α (hypoxia-inducible factor 1α) on MSC migration.

Hypoxia decreases sclerostin expression and increases Wnt signaling in osteoblasts.

Mutations in sclerostin function or expression cause sclerosing bone dysplasias, involving decreased antagonism of Wnt/Lrp5 signaling. Conversely, deletion of the VHL tumor suppressor in osteoblasts, which stabilize HIF-alpha isoforms and thereby enables HIF-alpha/beta-driven gene transcription, increases bone mineral content and cross-sectional area compared to wild-type controls. We examined the influence of cellular hypoxia (1% oxygen) upon sclerostin expression and canonical Wnt signaling.

The effect of oxygen tension on the long-term osteogenic differentiation and MMP/TIMP expression of human mesenchymal stem cells.

The use of mesenchymal stem cells in tissue engineering to augment the repair of a variety of tissues including bone is a rapidly growing and exciting field. Although oxygen tension is a powerful stimulus for cells both in vitro and in vivo, the oxygen environment in which such cells would undergo differentiation is commonly overlooked. We examined the effect of long-term (21-days) low oxygen tension (1, 2 and 5%) on the osteogenic differentiation and matrix metalloproteinase (MMP)/tissue inhibitor of MMP (TIMP) expression of human mesenchymal stem cells (MSCs).

Hypoxic osteocytes recruit human MSCs through an OPN/CD44-mediated pathway.

Little is known about the role or identity of signaling molecules released by osteocytes to recruit MSCs to areas of matrix damage. Vascular disruption at fracture sites results in hypoxia which is known to up-regulate genes involved in cell migration including osteopontin (OPN). We examined the effect of conditioned media from hypoxic osteocytes on MSC migration.