P.gingivalis Invade Osteoblast via Integrins α5β1 and Modulate Osteoblast Cytoskeleton/Apoptosis

Objectives: Our previous studies have shown that Porphyromonas gingivalis can invade osteoblasts and inhibit their differentiation and mineralization in vitro. In this study, we want to identify the receptors for the invasive process, and how internalization of P. gingivalis affects osteoblast cytoskeleton, signaling pathways and apoptosis.

Methods: Primary mouse calvarial osteoblasts were inoculated with PG 33277 at a Multiplicity of Infection (MOI) of 150 every other day for 4 weeks in most assays. The potential binding between P. gingivalis fimbriae and osteoblast cognate receptor integrins α5β1 and reassembly of osteoblast actin filament were examined by cofocal imaging. Modulations of osteoblast MAPK signaling pathways and apoptosis were evaluated by Western blot.

Results: Confocal imaging demonstrated colocalization of P. gingivalis fimbriae and osteoblast integrins α5β1, suggesting the potential binding between these molecules. Actin filament was condensed at osteoblast periphery upon invasion, which was more pronounced at later stage. ERK1/2 and JNK pathways were activated, with no change of p38 pathway in the invaded osteoblasts. P. gingivalis invasion initially suppressed osteoblast apoptosis and later promoted osteoblast apoptosis.  

Conclusions: P. gingivalis fimbriae bind osteoblast integrins α5β1 to enter osteoblast, cause reconfiguration of actin network, activation of MAPK pathways, and biphasic apoptotic pattern, potentially to facilitate intracellular persistence and intercellular dissemination of P. gingivalis in osteoblast cultures.