AbstractIn our previous studies, programmed cell death (PCD) was induced in human periodontal ligament (PDL) cells, through activation of caspase‐3 and upregulation of CASP5 gene (encoding caspase‐5 protein), in response to mechanical stretch loading. The aim of this study is to explore the relationship between the inflammatory caspase, caspase‐5, and the apoptotic executioner protein, caspase‐3, in human PDL cells. Here, we found that cyclic stretching upregulated the activity and the protein expression level of caspase‐3 and ‐5 and the addition of the caspase‐3 inhibitor or caspase‐5 inhibitor significantly inhibited the stretch‐induced PCD. Meanwhile, the inhibition of caspase‐5 inhibited the activation of caspase‐3 and vice versa. The result of coimmunoprecipitation also demonstrated that the expression of caspase‐3 was immunoprecipitated with caspase‐5. Thus, our study revealed that the in vitro application of cyclic stretching induced PCD by activation of caspase‐3 and ‐5 in human PDL cells, and these two caspases could interact with each other after mechanical stretch loading. The study may facilitate further studies on the mechanism of stretch‐induced PCD and help us understand the force‐related periodontal homeostasis and remodeling better.