Resumen de Peptide 19 of Porphyromonas gingivalis Heat Shock Protein Is a Potent Inducer of Low-Density Lipoprotein Oxidation
Ji Young Joo, Gil Sun Cha, Jin Chung, Ju Youn Lee, Sung Jo Kim, Jeomil Choi
Background: Although periodontal pathogens show a strong association with development of atherosclerosis, little is known about how a microorganism contributes to disease onset and progression. Oxidation of low-density lipoprotein (LDL) is a major risk factor of atherogenesis. The principal objective of this study is to evaluate the ability of peptide 19 (Pep19) of Porphyromonas gingivalis (Pg) heat shock protein (HSP) as a potent inducer of LDL oxidation, and a secondary objective is to compare this ability with that of Pep19 from different bacteria.
Methods: HSP60, Pep14, and Pep19 from Pg and THP-1 monocytes were cultured, and the extent of LDL oxidation induced by each peptide was evaluated by an assay for thiobarbituric acid-reactive substances (TBARS). Pep19 and HSP60 from Chlamydia pneumoniae and Mycobacterium tuberculosis were also cultured with THP-1 monocytes and evaluated by the TBARS assay. After incubation of macrophages with LDL and peptides from Pg, Oil Red O staining was performed for examination of foam cells, macrophages that took up the oxidized LDL.
Results: Monocyte-mediated native-LDL oxidation under the influence of Pep19 or HSP60 from Pg was significantly stronger than oxidation induced by the counterpart Pep19 or HSP60 from C. pneumoniae or M. tuberculosis. Pep19 from Pg HSP60 showed a stronger ability to induce LDL oxidation than did Pep14 from Pg HSP60.
Conclusion: These results suggest Pep19 from Pg HSP60 has a distinct ability to induce native-LDL oxidation as a plausible mechanism by which this peptide may drive epitope spreading to the neoantigen, i.e., oxidized LDL, in the pathogenesis of atherosclerosis.
Atherosclerosis, which is the narrowing of blood vessels caused by deposition of inflammatory plaques in the vessel wall, is the leading cause of death in industrialized countries.1 A key risk factor of atherosclerosis is elevation of a particular type of plasma cholesterol known as low-density lipoprotein (LDL).2 Oxidation of LDL appears to be a risk factor of atherogenesis3 because this oxidation promotes cell injury, proliferation of smooth muscle cells, foam cell formation, cellular secretion of inflammatory mediators, and other events that modulate atheroma biology.4 Some reports have described an association between atherosclerosis and various pathogens,5-7 which is strengthened by the fact that antibiotic treatment of infected rabbits inhibits atheromatous changes.6 Antichlamydial antibiotics reduce cardiovascular problems in patients with a cardiovascular disease.5 Aggregatibacter actinomycetemcomitans and Porphyromonas gingivalis (Pg) accelerate progression of atherosclerosis in apolipoprotein E-deficient spontaneously hyperlipidemic mice.7 Although these data revealed a strong association between the pathogen and atherosclerosis, little is known about how the microorganism contributes to disease onset and progression.
Heat shock protein (HSP) 60 is thought to play a significant role in the link between microbial infections and autoimmunity because of its highly conserved amino acid sequence and strong immunogenicity.8 Peptides from HSP have been shown to promote production of anti-inflammatory cytokines, indicating that HSPs have an immunoregulatory potential in patients with chronic inflammatory diseases.9 There is a growing body of evidence that HSP60 from infectious organisms triggers or suppresses autoimmune responses, depending on its antigenic properties and regulatory T cells.10 HSP60 of Pg, a major periodontal pathogen, may be a trigger molecule linking infectious periodontitis and autoimmune atherosclerosis. The latter pathology can be triggered and aggravated by a pathogen-driven antigenic peptide from Pg HSP60.11 Among HSP60 peptides from Pg, peptide 19 (Pep19) represents the epitope that has been predominantly and most consistently recognized in serum samples of patients with periodontitis-associated autoimmune diseases. It also was found to be an immunodominant T-cell epitope and cross-reactive B-cell epitope in the periodontitis-atherosclerosis axis and may serve as an autoimmune target.12 Indeed, Pep19 was reported to perform a proatherogenic function in infection-triggered atherosclerosis via distinct mechanisms related to polarization of peptide-specific T cells.13 Epitope spreading was initially defined as the diversification of epitope specificity from the initial dominant epitope-specific immune response to subdominant epitopes.14 Inter- or intramolecular epitope spreading is one mechanism by which antigens of infectious organisms can propagate immunogenicity to various human autoantigens to trigger adaptive autoimmune responses. Chronic or persistent infections may trigger, sustain, or exacerbate an autoimmune disease through epitope spreading via antigen presentation of epitopes released within an injured tissue.15 Therefore, identifying the target antigenic peptide responsible for epitope spreading may facilitate development of a vaccine strategy for suppression of autoimmune disease over antigen-specific therapy.
Notably, the mechanism underlying the Pep19-driven epitope spreading to human neoantigens in patients with a periodontitis-associated autoimmune disease and ongoing periodontal disease was recently demonstrated.16 It would be interesting to verify the ability of Pep19 from Pg HSP60 to promote monocyte-mediated native-LDL oxidation as a plausible mechanism by which this peptide may induce epitope spreading to the neoantigen, i.e., oxidized LDL, during atherogenesis.
The principal objective of this study was to evaluate the ability of Pep19 from Pg HSP as a potent inducer of LDL oxidation, and a secondary objective was to compare this ability with that of Pep19 from different bacterial HSPs.
