Local and systemic responses in matrix metalloproteinase 8-deficient mice during Porphyromonas gingivalis-induced periodontitis

Abstract

Periodontitis is a bacterium-induced chronic inflammation that destroys tissues that attach teeth to jaw bone. Pathologically excessive matrix metalloproteinase 8 (MMP-8) is among the key players in periodontal destruction by initiating type I collagen degradation. We studied MMP-8 in Porphyromonas gingivalis-induced periodontitis by using MMP-8-deficient (MMP8(-/-)) and wild-type (WT) mice. Alveolar bone loss, inflammatory mediator expression, serum immunoglobulin, and lipoprotein responses were investigated to clarify the role of MMP-8 in periodontitis and systemic inflammatory responses. P. gingivalis infection induced accelerated site-specific alveolar bone loss in both MMP8(-/-) and WT mice relative to uninfected mice. The most extensive bone degradation took place in the P. gingivalis-infected MMP8(-/-) group. Surprisingly, MMP-8 significantly attenuated (P < 0.05) P. gingivalis-induced site-specific alveolar bone loss. Increased alveolar bone loss in P. gingivalis-infected MMP8(-/-) and WT mice was associated with increase in gingival neutrophil elastase production. Serum lipoprotein analysis demonstrated changes in the distribution of high-density lipoprotein (HDL) and very-low-density lipoprotein (VLDL) particles; unlike the WT mice, the MMP8(-/-) mice underwent a shift toward a smaller HDL/VLDL particle sizes. P. gingivalis infection increased the HDL/VLDL particle size in the MMP8(-/-) mice, which is an indicator of lipoprotein responses during systemic inflammation. Serum total lipopolysaccharide activity and the immunoglobulin G-class antibody level in response to P. gingivalis were significantly elevated in both infected mice groups. Thus, MMP-8 appears to act in a protective manner inhibiting the development of bacterium-induced periodontal tissue destruction, possibly through the processing anti-inflammatory cytokines and chemokines. Bacterium-induced periodontitis, especially in MMP8(-/-) mice, is associated with systemic inflammatory and lipoprotein changes that are likely involved in early atherosclerosis.

FIG. 1.

Alveolar bone loss assessment from the cemento-enamel junction (CEJ) to the alveolar ridge. (A) Schematic diagram showing measurement of the CEJ-A distance on an H&E-stained section of healthy WT mouse periodontium. The dotted line indicates the top of the alveolar crest, and the CEJ-A distance is the vertical distance from the CEJ to the alveolar crest (single-headed arrow). A, alveolar bone crest; CEJ, cemento-enamel junction; D, dentin; E, enamel; SE, epithelium. Scale bar, 500 μm. (B) Schematic diagram showing measurement of the CEJ-AC distance on an H&E-stained section of P. gingivalis-infected MMP8^−/− mouse periodontium. The dotted line shows the top of the alveolar crest, and the CEJ-A distance is the vertical distance from the CEJ to the alveolar crest (double-headed arrow). A, alveolar bone crest; CEJ, cemento-enamel junction; D, dentin; E, enamel; SE, epithelium. Scale bar, 500 μm. (C) Diagram showing measurements of the distance between the cemento-enamel junction and the alveolar bone crest. The red lines show the means of four separate measurements.

FIG. 2.

Expression of NE in P. gingivalis-infected mouse gingival tissue. Mouse gingival tissues were immunohistochemically stained with polyclonal anti-NE antibody as described in Materials and Methods. (A) WT + P. gingivalis group. The insert with the red square shows the area in the figure. A, alveolar bone; D, dentin; E, enamel. (B) MMP8^−/− + P. gingivalis group. (C) WT control group. (D) MMP8^−/− control group. Scale bars, 100 μm.

FIG. 3.

Expression of MMP-9 in P. gingivalis-infected mouse gingival tissue. Mouse gingival tissues were immunohistochemically stained with polyclonal anti-MMP-9 antibody as described in Materials and Methods. (A) WT + P. gingivalis group; (B) MMP8^−/− + P. gingivalis group; (C) WT control group; (D) MMP8^−/− control group. D, dentin; E, enamel; SE, sulcular epithelium. Scale bars, 200 μm.

FIG. 4.

Infection markers in serum. Mouse serum total-LPS activity (A) and IgG-class antibody levels to P. gingivalis (B) were analyzed as described in Materials and Methods from WT mice without (n = 10) or with (n = 8) P. gingivalis infection and from MMP8^−/− mice with (n = 12) or without (n = 10) P. gingivalis infection. Statistical comparisons were carried out between the infected mice and their corresponding controls (*, P < 0.05).

FIG. 5.

Serum lipid analysis. Mouse serum cholesterol (A), triglyceride (B), and apoA-I (C) concentrations were analyzed from WT mice without (n = 10) or with (n = 8) P. gingivalis infection and from MMP8^−/− mice with (n = 12) or without (n = 10) P. gingivalis infection. The statistical comparisons were carried out between the infected animals and their corresponding controls (*, P < 0.05).

FIG. 6.

Lipoprotein profiles in serum. Sera from WT mice without (n = 10) or with (n = 8) P. gingivalis infection and MMP8^−/− mice with (n = 12) or without (n = 10) P. gingivalis infection were pooled within the groups and applied to a Superose 6HR gel filtration column in PBS at a flow rate of 0.5 ml/min. We collected 0.5-ml fractions, from which we determined cholesterol (A), triglyceride (B), and apoA-I (C) concentrations.