Indirect regulation of PCSK9 gene in inflammatory response by Porphyromonas gingivalis infection

Abstract

Pro-protein convertase subtilisin/kexin type 9 (PCSK9), a secreted serine protease, regulates serum low-density lipoprotein (LDL) cholesterol levels by targeting the degradation of LDL receptor (LDLR) in the liver. Although previous reports describe elevated levels of PCSK9 in patients with periodontitis, the mechanisms that trigger this increase in serum PCSK9 levels and induce the related inflammatory response remain unclear. In an unc93b1-deficient mouse of Porphyromonas gingivalis infection, nucleic acid antigen recognition via Toll-like receptors was found to promote PCSK9 production, suggesting an indirect role for tumor necrosis factor-α as an inducer of PCSK9 in contrast to that reported in previous studies. Furthermore, PCSK9 production was independent of the TIR domain-containing adapter-inducing interferon-β-dependent signaling pathway. These results indicate that changes in LDLR expression precede an increase in the serum PCSK9 level in the context of an infectious disease such as periodontitis.

Keywords: Immunology.

Fig. 1

(A) Serum PCSK9 concentrations in wild-type (WT) and 3d mice after Porphyromonas gingivalis infection. N = 5 mice per group. Results are expressed as means ± SEM. **, P < 0.01. (B) Serum PCSK9 concentrations in WT mice after the administration of nucleic acid antigens (Poly (I:C), R848, and CpG-DNA). N = 5 mice per group. Results are expressed as means ± SEM. *, P < 0.05.

Fig. 2

Expression levels of genes encoding inflammatory mediators (relative to Gapdh) in the livers of wild-type mice: (A) Saa1, (B) Tnfα, (C) Ifnα, and (D) Ifnβ. N = 5 mice per group. Results are expressed as means ± SEM. *, P < 0.05; **, P < 0.01.

Fig. 3

Changes in serum lipid levels following the administration of P. gingivalis and nucleic acid antigens: (A) total cholesterol (TC), (B) low-density lipoprotein cholesterol (LDL-C), (C) high-density lipoprotein cholesterol (HDL-C), and (D) triglycerides (TG). N = 5 mice per group. Results are expressed as means ± SEM. *, P < 0.05; **, P < 0.01. Analysis of serum cholesterol levels.: Correlations between the serum lipids and serum PCSK9 level or hepatic TNF-α gene expression in wild-type mice. (E) LDL-C versus PCSK9, (F) HDL-C levels versus PCSK9, (G) TC versus PCSK9, (H) LDL-C versus Tnfα, (I) HDL-C versus Tnfα, and (J) TC versus Tnfα. The ratio of each LDL-C fraction level to the total: (K) large (φ28.6 nm), (L) medium (φ25.5 nm), (M) small (φ23.0 nm), or (N) very small (φ16.7–20.7 nm). N = 5 mice per group. Results are expressed as means ± SEM. *, P < 0.05; **, P < 0.01.

Fig. 4

Expression of PCSK9 and LDLR relative to GAPDH in HepG2 cells. The cells were directly stimulated with Porphyromonas gingivalis (A and B) or recombinant TNF-α at the indicated concentration (C and D). The cells were co-cultured with macrophage-like differentiated THP-1 cells and then stimulated with P. gingivalis (MOI: 100) (E and F). The cells are transfected with TNFRI specific siRNA and then co-cultured with THP-1 cells (G). N = 3 wells per group. Results are expressed as means ± SEM. *, P < 0.05; **, P < 0.01.