A calcium-induced signaling cascade leading to osteogenic differentiation of human bone marrow-derived mesenchymal stromal cells

The response of osteoprogenitors to calcium (Ca ²⁺) is of primary interest for both normal bone homeostasis and the clinical field of bone regeneration. The latter makes use of calcium phosphate-based bone void fillers to heal bone defects, but it is currently not known how Ca ²⁺ released from these ceramic materials influences cells in situ. Here, we have created an invitro environment with high extracellular Ca ²⁺ concentration and investigated the response of human bone marrow-derived mesenchymal stromal cells (hMSCs) to it. Ca ²⁺ enhanced proliferation and morphological changes in hMSCs. Moreover, the expression of osteogenic genes is highly increased. A 3-fold up-regulation of BMP-2 is observed after only 6h and pharmaceutical interference with a number of proteins involved in Ca ²⁺ sensing showed that not the calcium sensing receptor, but rather type L voltage-gated calcium channels are involved in mediating the signaling pathway between extracellular Ca ²⁺ and BMP-2 expression. MEK1/2 activity is essential for the effect of Ca ²⁺ and using microarray analysis, we have identified c-Fos as an early Ca ²⁺ response gene. We have demonstrated that hMSC osteogenesis can be induced via extracellular Ca ²⁺, a simple and economic way of priming hMSCs for bone tissue engineering applications.