Porphyromonas gingivalis lipopolysaccharide increases lipid accumulation by affecting CD36 and ATP-binding cassette transporter A1 in macrophages

Abstract

Porphyromonas gingivalis lipopolysaccharide (P. gingivalis LPS) promotes macrophage-derived foam cell formation, however, the mechanisms are not well established. In macrophages, lipid uptake is mediated by scavenger receptors including SR-A and CD36, while the cholesterol efflux is mediated by ATP-binding cassette transporter G1 (ABCG1), ABCA1 and SR-BI. We further investigated the mechanisms underlying the dysregulation by P. gingivalis LPS of these regulators resulting in the promotion of lipid accumulation in THP-1-derived macrophages. Our results showed that P. gingivalis LPS exacerbated lipid accumulation in oxidized low-density lipoprotein (oxLDL)-treated macrophages. However, cholesterol efflux was inhibited by P. gingivalis LPS in THP-1-derived macrophages. In oxLDL-untreated macrophages, P. gingivalis LPS treatment caused an increase in CD36 mRNA and protein levels, and a decrease in ABCA1 mRNA and protein levels, while having no effect on SR-A, SR-BI or ABCG1 expression. Upregulation of CD36 by P. gingivalis LPS resulted from activation of c-Jun/AP-1, and this was confirmed by the inhibition of increased CD36 expression after AP-1 inhibition using SP600125. However, the decreased protein stability of ABCA1 by P. gingivalis LPS was a result of increased calpain activity. Moreover, small hairpin RNA (shRNA) targeting heme oxygenase-1 (HO-1) augmented the P. gingivalis LPS-induced atherogenic effects on the expression of c-Jun/AP-1, CD36, ABCA1 and calpain activity. Accordingly, P. gingivalis LPS-regulated promotion of lipid accumulation in foam cells was also exacerbated by HO-1 shRNA. These results indicate that P. gingivalis LPS confers a exacerbation effect on the formation of foam cells by a novel HO-1-dependent mediation of cholesterol efflux and lipid accumulation in macrophages.