Signal‐Regulated Protein Kinases/Protein Kinase B‐p53‐BH3–Interacting Domain Death Agonist Pathway Regulates Gingipain‐Induced Apoptosis in Osteoblasts

Background: Gingipains are cysteine proteases produced by Porphyromonas gingivalis, the predominant pathogen in chronic periodontitis. The present study aimed to examine the role of gingipains in promoting apoptosis in osteoblasts.Methods: Human calvarial osteoblasts and osteoblast MC3T3-E1 cells were treated with 8.348 U/L gingipains. Flow cytometry analysis and terminal deoxynucleotidyl transferase (TdT)-mediated deoxy-UTP nick end labeling (TUNEL) staining were used to detect cell apoptosis. Protein expression was examined by Western blotting and gene expression was detected by real-time PCR. Small interfering RNA transfection was used to knockdown Bid expression.Results: Treatment with 8.348 U/L gingipains from 4 h to 72 h increased apoptosis, accompanied by elevated cleaved-caspase-3 levels. Notably, gingipain-induced apoptosis was associated with increase of BH3-interacting domain death agonist (Bid) and its truncated form, tBid, as well as p53. Transfection with Bid siRNA resulted in suppression of...