Figure 3. Caspase-3 activity increased via the caspase-8 signaling cascade. (A) Force-dependent caspase-3 induction. Relative absorbance of caspase-3 is shown following the application of a compressive force of 2.04 x 10–4 or 4.08 x 10–4 N/cm2 for 24 hrs. Values represent the mean ± SD of the relative absorbance of 3 experimental samples (exp.) per control sample (cont.). Caspase-3 activity in the cells increased markedly under continuous compressive forces of 2.04 x 10–4 and 4.08 x 10–4 N/cm2. Caspase-3 activity increased with greater compressive force. Significantly different from controls at each weight: ** p < 0.01 (Bonferroni/Dunn method) (n = 3). (B) Effects of caspase-8 and -9 inhibitors on caspase-3 activity. Relative absorbance of caspase-3 activity is shown following the application of a compressive force of 4.08 x 10–4 N/cm2 for 24 hrs. To examine the signal pathway of the compressive-force-induced caspase-3 activation, we treated the cells with an inhibitor specific for caspase-8 (LETD-CHO) or caspase-9 (LEHD-CHO) before applying the compressive force, and then measured caspase-3 activity in the cells. The caspase-8 inhibitor significantly reduced the compressive-force-induced caspase-3 activation, while the caspase-9 inhibitor did not. Values represent the mean ± SD of the relative absorbance of 3 experimental samples (exp.) per control sample (cont.). ** p < 0.01 (Student’s t test). White columns, non-compressive force; black columns, the application of a compressive force of 4.08 x 10–4 N/cm2 (n = 3).