Figure 4.

P. gingivalis induces alveolar bone resorption through gingipain proteases. Secreted proteases, so-called gingipains (GPs), from the microbe Porphyromonas gingivalis (P. gingivalis) interact with the receptor activator of nuclear factor kappa-B ligand (RANK-L), osteoprotegerin (OPG), and receptor activator of nuclear factor kappa-B (RANK) system of osteocytes and osteoclasts. In the presence of GPs, OPG is degraded, which favors RANK-L binding to RANK. Consequently, osteoclasts differentiate out of pre-osteoclasts through upregulation of Cathepsin K, matrix metalloproteinase 9 (MMP-9), and alkaline phosphatase type 5 (AP). Subsequently, osteoclasts can bind to the alveolar bone via αVβ3 integrins (green, dimeric sticks), which regulate actin cytoskeletal tension (yellow lines). Altogether, these processes favor alveolar bone resorption within resorption pits. Details are given in the main text.