Ca 2+ -deposition in cell matrix correlates significantly with osteocalcin-expression in osteogenic differentiated ATSC: Even in a coculture system with HUVEC

Background: Tissue engineering offers the means for replacing or repairing diseased organs within the patient's body. The current problem in its clinical use is sufficient and fast revascularization of the transplanted tissues. The idea of bone-reconstruction deals with three-dimensional bone equivalents that are composed of endothelial cells (ECs) and adipose tissue derived stromal cells (ATSCs) showing osteogenic differentiation. Materials and Methods: ATSC were isolated, cultivated until third passage and osteogenically differentiated by 1.25-dihydroxycholecalciferol. Coculture systems with human umbilical vein endothelial cells (HUVEC) were performed. Osteogenic differentiation was analyzed in FACS-analyses (n = 7), by the measurement of Ca 2+ -deposition in the cell matrix (marker for osteogenic differentiation) and the expression of alkaline phosphatase (AP). Results: Ca 2+ -deposition in the cell matrix and osteocalcin-expression correlated significantly (P = 0.030) during osteogenic differentiation (n = 7). The osteogenic cell differentiated ATSC in the coculture system (n = 6) even showed a clear increase of Ca 2+ -deposition. The time of starting the coculture did not influence the differentiation. Measurement of the Ca 2+ -deposition correlates significantly to the osteogenic differentiation and osteocalcin-expression. Conclusion: ATSC are a promising source for bone tissue engineering. They can be differentiated into osteoblasts in a coculture system with HUVEC without the loss of any differentiation capacity. For bone tissue-equivalent fabrication, this is an encouraging procedure that is feasible and provides fast revascularization of the bone-equivalents.