Figure 3

RANKL prevents activation of caspase-9 and increases Mcl-1 in osteoclasts but does not prevent inhibition of protein prenylation. Cultures of mature osteoclasts from rabbit bones were treated with 100 μM ALN ± 100 ng/mL RANKL for 48 hours and stained using an Apofluor Green Caspase-9 Activity Assay kit and Hoechst 33342. (a) A representative non-apoptotic and apoptotic osteoclast. (b) Quantification of caspase-9-positive osteoclasts after treatment with alendronate ± RANKL for 48 hours. *P ≤ 0.05 compared with ALN alone or ^#P ≤ 0.05 compared with control (CTL) (analysis of variance). Values are the mean ± standard error of the mean (n = 3 replicates) (100 to 150 cells counted per well). The data shown are representative of three independent experiments. (c) Purified rabbit osteoclasts were treated for 48 hours with 100 μM ALN ± 100 ng/mL RANKL or with RANKL alone. Cell lysates were then analysed by Western blotting for the unprenylated form of Rap1A and for β-actin. (d) Purified rabbit osteoclasts were treated for 48 hours with 100 μM ALN ± 100 ng/mL RANKL or with 100 ng/mL RANKL alone. Cell lysates were then analysed by Western blotting for Mcl-1 and Bcl-2. The level of Mcl-2 or Bcl-2 was quantified by densitometric analysis and expressed as a ratio of the level in control cells. Data shown are representative of three independent experiments. ALN, 4-amino-1-hydroxy-butylidene-1,1-bisphosphonate (alendronate); RANKL, receptor activator of nuclear factor-kappa-B ligand.