The Secreted Products ofPorphyromonas gingivalisAlter Human Gingival Fibroblast Morphology by Selective Damage to Integrin-Substrate Interactions

Porphyromonas gingivalis is implicated in periodontal diseases characterised by connective tissue destruction. This study examines the damaging effects of products of P. gingivalis strain W83 on human gingival fibroblast (HGF) integrins and cytoskeletal components. Within 18 h of exposure of subconfluent monolayers of HGF to the culture supernatant of P. gingivalis, diluted from 1/2 to 1/32 (protein concentrations 5.15 to 0.32 mg/ml), morphological changes leading to significant detachment from the surface of the culture vessel (P<0.05) were observed. Loss of attachment was concentration-dependent, not accompanied by cell death and due primarily to heat-labile component(s) of the supernatant. These changes were preceded by rapid loss of α5 and β1 integrin subunit expression and fibronectin which all occurred within 60 min and became more marked on incubation for 18 h. Pretreatment of the culture supernatant with the protease inhibitors leupeptin (50 μM) or Nα-p-tosyl-L-lysine chloromethyl ketone (TLCK, 2 mM) abolished hydrolysis of Nα-benzoyl-L-arginine p-nitroanilide (L-BApNA) but failed to prevent cell detachment or the loss of β1 integrin expression, implicating heat-labile factor(s) other than arginine- or lysine-specific proteinases. Reduction in αv and β3 integrin subunit expression was seen 18 h after exposure to culture supernatant (≥0.16 mg protein/ml) and loss of F-actin stress fibres at ≥1.28 mg protein/ml. However, the actin-binding protein vinculin remained unaffected under these conditions. These differential effects of P. gingivalis on the membrane-associated integrins and cytoskeletal components of human gingival fibroblasts may contribute to the pathogenic mechanisms involved in the loss of connective tissue which characterises destructive periodontitis.