Moderate Hypothermia Has the Potential to Reveal the Dominant/Submissive Relationship in a Co-Culture System Consisting of Osteoblasts and Endothelial Cells

Microvessels in bone are indispensable for maintaining bone homeostasis based on a dynamic remodeling system. In cell-based tissue engineering, vascularization into the regenerative bone is a key strategy to avoid hypoxia and necrosis around re-implanted tissues. Previous studies have shown that direct contact between osteoblasts and endothelial cells stimulates differentiation of both cell types. However, no studies have revealed the dominant/submissive relationship. In the present study, we examined the effect of hypothermia on monoculture and co-culture to assess which cells tightly coordinated osteogenesis and angiogenesis in the co-culture system. As for osteoblasts, exposure to hypothermia suppressed cellular proliferation, migration, and differentiation. Evaluation of the behavior of endothelial cells showed that hypothermia should not affect basic functions such as proliferation and migration. Under co-culture conditions, both osteogenic differentiation and the formation of vessel-like angiogenic structures were suppressed by hypothermia, but the spatial organization of alkaline phosphatase-positive cell clusters, which tend to localize around microvascular lumens, was not altered. These data suggest that hypothermia attenuates heterotypic intercellular crosstalk which robustly depends on osteoblasts to inhibit both osteogenesis and angiogenesis in the co-culture system. Taken together, this approach will provide new insights into the relationship between osteoblasts and endothelial cells in tissue engineering.