Effects of α/β-androstenediol immune regulating hormones on bone remodeling and apoptosis in osteoblasts

A large body of evidence suggests that the immune system directly impacts bone physiology. We tested whether immune regulating hormones (IRH), 17β-androstenediol (β-AED), 7β,17β-androstenetriol (β-AET) or the 17α-androstenediol (α-AED), and 7α,17β-androstenetriol (α-AET) metabolites could directly influence bone remodeling in vitro using human fetal osteoblasts (FOB-9). The impact on bone remodeling was examined by comparing the ratio of RANKL/OPG gene expression in response to AED and AET compounds. The α-AED was found to significantly increase in the ratio of RANKL/OPG gene expression and altering the morphology of RANKL stained FOB-9 cells. Cell viability was assessed using a Live/Dead assay. Again α-AED was unique in its ability to reduce the proportion of viable cells, and to induce mild apoptosis of FOB-9 cells. Treatment of FOB-9 cells with WY14643, an activator of PPAR-α and -γ, also significantly elevated the percentage of dead cells. This increase was abolished by co-treatment with GW9962, a specific inhibitor of PPAR-γ. Analysis of PPAR-γ mRNA by Quantitative RT-PCR and its activation by DNA binding demonstrated that α-AED increased PPAR-γ activation by 19%, while β-AED conferred a 37% decrease in PPAR-γ activation. In conclusion, α-AED opposed β-AED by elevating a bone resorption scenario in osteoblast cells. The increase in RANKL/OPG is modulated by an activation of PPAR-γ that in turn caused mild apoptosis of FOB-9 cells.