P2X4 purinoreceptors are sensing strain deprivation of marginal gingival fibroblasts

Alveolar bone resorption and loss of dentition are the major consequences of periodontitis and periodontal surgery, in humans. Based on clinical observations in humans and animal experiments we have recently proposed that the signal for alveolar bone resorption starts by disruption of dento-gingival collagen bundles of fibers, by surgery or by metallo-proteinases(MMP's) specifically in the marginal gingiva, producing an abrupt fall in cell physiological strain. Objective: was to identify the sensor and signaling molecules of strain deprivation in marginal gingival fibroblasts. Methods: Mucoperiosteum surgery was performed next to molars in 3 month old wistar rats disrupting the dento-gingival fibers. The tissue was removed after 20 minutes and processed for RNA or histology. Similar surgery in the apical region not disrupting the marginal gingival fibers was served as control. Results: Using molecular techniques like differential gene display (Affymetrix) and real time RT-PCR and immunostaining we have demonstrated that marginal gingival fibroblasts up-regulated significantly the ATP purinoreceptor P2X4 specifically, in the rat periodontal surgery model. The immunostained fibroblasts showed alignment with long axis of the collagen bundles. Apyrase which degrades ATP and G- or R- coomasie brilliant blue antagonists of purinoreceptors reduced significantly the alveolar bone resorption while suramin had no effect. Conclusion: We have shown here for the first time that fibroblasts in the marginal gingiva are sensing the mechanical strain deprivation, by disrupting dento-gingival fibers in marginal gingiva, up-regulating the P2X4 receptor which is activated by extracellular ATP released during surgery. The signal is then propagated by ATP and intercellular calcium toward the alveolar bone surface; it was shown before that ATP activates also other purinoreceptors on the osteoblasts and osteoclasts resulting in bone resorption.