Porphyromonas gingivalis LPS stimulates autophagy using a TLR mediated pathway.

Abstract

Resum: Porphyromonas gingivalis often subverts host cell autophagic processes for its own survival. Our previous studies document the association of the cargo sorting protein, melanoregulin (MREG), with its binding partner, the autophagic protein, microtubule-associated protein 1 light chain 3 (LC3) in macrophages incubated with P. gingivalis (strain 33277). Differences in the lipid A moiety of lipopolysaccharide (LPS) affect the virulence of P. gingivalis; penta-acylated LPS1690 is a weak Toll-like receptor 4 agonist compared with Escherichia coli LPS, whereas tetra-acylated LPS1435/1449 acts as an LPS1690 antagonist. To determine how P. gingivalis LPS1690 affects autop- hagy we assessed LC3-dependent and MREG- dependent processes in green fluorescent protein (GFP)-LC3-expressing Saos-2 cells. LPS1690 stimu- lated the formation of very large LC3-positive vac- uoles and MREG puncta. This LPS1690-mediated LC3 lipidation decreased in the presence of LPS1435/1449. When Saos-2 cells were incubated with P. gingivalis the bacteria internalized but did not traffic to GFP-LC3-positive structures. Never- theless, increases in LC3 lipidation and MREG puncta were observed. Collectively, these results suggest that P. gingivalis internalization is not necessary for LC3 lipidation. Primary human gin- gival epithelial cells isolated from patients with periodontitis showed both LC3II and MREG puncta whereas cells from disease-free individu- als exhibited little co-localization of these two pro- teins. These results suggest that the prevalence of a particular LPS moiety may modulate the degradative capacity of host cells, so influencing bacterial survival.