Detection of apoptotic gene expression in human osteoblast-like cells by cDNA microarrays

Global gene expression during the induction of ion pair-mediated apoptosis was evaluated by an apoptosis microarray system. Human bone marrow stromal cells were cultured in the presence of 10^–6M dexamethasone to promote osteogenesis. After 28 days, these cells expressed elevated alkaline phosphatase activity and maintained Cbfa1 expression even when challenged with an apoptogen. Apoptosis was initiated by treating cells with 3mM Ca²⁺ and 5mM Pi for 4h. ³²P-Labeled mRNA was hybridized to a human apoptosis microarray containing 205 cDNA fragments. We found that apoptosis influenced the expression of 15 genes mainly involved in cell cycle and cell signaling. These genes included IGFBPs and ERK1, known to play a role in cell survival; GST and GST mu, required for maintenance of thiol redox; TNFR1, a gene product that initiates cell death; and finally, BAD, a gene that encodes a proapoptotic protein. Real-time PCR analysis showed that the expression of ERK1, TNFR1, and GST was modulated by 1.89-, 2.66-, and 1.6 fold after 4h and by 1-, 1.91-, and 1.5 fold, respectively, after 8h treatment with the ion pair. In addition, we also measured the expression of Bcl-2 and Bax by quantitative RT-PCR. We noted that these two genes were increased 3.07 and 2.99 fold, respectively, after 8h treatment with the apoptogen. Results of this study suggest that the ion pair influenced ERK1 and TNFR1 signaling pathways and affected thiol metabolism, whereas Bcl-2 and Bax were expressed at late stages of the death process.