Bone Abstracts

Disorders of glucose metabolism are associated with adverse skeletal effects. Hyperglycemia impairs the function of osteoblast-like cells but the mechanisms underlying glucose toxicity are poorly understood. In this study we determined the effect of elevated extracellular glucose levels on the proliferation and osteogenic differentiation of mesenchymal stromal cells (MSC).

Bone marrow cells were isolated from rat long bones, plastic-adherent MSCs were enriched in vitro and differentiated in osteogenic conditions for up to 14 days. Culture medium (containing 5.5 mM glucose) was supplemented with different doses of glucose at various stages of differentiation for 24 h (acute exposure) or continuously through the culture period (chronic elevation). Mannitol was used as iso-osmolar control. Cultures were evaluated for cell viability, glucose utilization, bone formation, and the expression of osteoblast marker genes (Runx2, alkaline phosphatase, and osteocalcin).

High extracellular glucose significantly and dose-dependently impaired the proliferation of MSCs (P<0.001). Chronic exposure to high glucose resulted in reduced number of osteoblasts, as evaluated by alkaline phosphatase activity and osteocalcin secretion (P<0.01). Extracellular glucose also had an effect on the expression of osteoblast marker genes and glucose utilization during osteogenic differentiation. Treatment of MSCs with an equal concentration of mannitol partially mimicked the effects seen with glucose, but the changes in proliferation and differentiation were observed at higher concentrations than with glucose. This suggests that MSCs are sensitive to osmotic stress during differentiation and it may partially mediate the inhibitory effects of high glucose.

We conclude that MSCs are sensitive to increasing extracellular glucose levels, causing reduced growth and altered differentiation. The findings further suggest that the effects of high glucose may be partially mediated through osmotic response pathways. Modulation of the growth and osteogenic differentiation of MSCs is a potential component of the bone loss associated with hyperglycemia.