Role of p38 Mitogen-Activated Protein Kinase Pathway inPorphyromonas gingivalisLipopolysaccharide–Induced VCAM-1 Expression in Human Aortic Endothelial Cells

Effects of nicotine and lipopolysaccharide stimulation on adhesion molecules in human gingival endothelial cells

Smoking is a risk factor for periodontitis, and the immune response of periodontal tissues in patients with periodontitis may be strongly affected by smoking. The purpose of this study was to elucidate the bioactivity and signal transduction of human gingival endothelial cells (HGECs) due to nicotinic stimulation using a cultured medium supplemented with lipopolysaccharide (LPS) as a model of periodontitis. HGECs were cultured in medium supplemented with LPS, nicotine, nicotine + LPS, and medium supplemented without nicotine or LPS (control). Cell proliferation was assessed using Alamar blue. Cytotoxicity was assessed by lactate dehydrogenase leakage. The expression of adhesion molecule-1 (ICAM-1, VCAM-1) was assessed by reverse transcription quantitative polymerase chain reaction (RT-qPCR) and enzyme-linked immunosorbent assay. The expression of nicotinic acetylcholine receptor (nAChR) subunits (α3, α5, α7, β2 and β4) was evaluated by RT-PCR. The involvement of p38 mitogen-activated protein kinase (p38MAPK) and protein kinase C (PKC) cell signaling pathways in ICAM-1 and VCAM-1 expression was investigated by RT-qPCR with specific inhibitors. HGECs stimulated with LPS, nicotine and nicotine + LPS showed inhibition of cell proliferation, increase of cell death, and increase of gene and protein expression of ICAM-1. Moreover, HGECs showed the presence of α5 and α7 nAChR subunits. The expression of ICAM-1 in HGECs stimulated with LPS, nicotine, and nicotine + LPS was significantly suppressed by p38MAPK inhibitor, but not by a PKC inhibitor. The nAChR subunits of HGECs are α5 and α7, and that HGECs stimulated with nicotine and LPS express ICAM-1 via p38MAPK pathway.

Treponema denticola Induces Neuronal Apoptosis by Promoting Amyloid-β Accumulation in Mice

Background: Neuronal apoptosis is a major contributor to Alzheimer's disease (AD). Periodontitis is a significant risk factor for AD. The periodontal pathogens Porphyromonas gingivalis and Treponema denticola have been shown to initiate the hallmark pathologies and behavioral symptoms of AD. Studies have found that T. denticola infection induced Tau hyperphosphorylation and amyloid β accumulation in the hippocampi of mice. Aβ accumulation is closely associated with neuronal apoptosis. However, the roles of T. denticola in neuronal apoptosis remain unclear and its roles in AD pathology need further study. Objective: This study aimed to investigate whether oral infection with T. denticola induced alveolar bone loss and neuronal apoptosis in mice. Methods: C57BL/6 mice were orally administered with T. denticola, Micro-CT was employed to assess the alveolar bone resorption. Western blotting, quantitative PCR, and TUNEL staining were utilized to detect the apoptosis-associated changes in mouse hippocampi. N2a were co-cultured with T. denticola to verify in vivo results. Results: Mice infected with T. denticola exhibited more alveolar bone loss compared with the control mice. T. denticola oral infection induced neuronal apoptosis in hippocampi of mice. Consistent results of the apoptosis-associated protein expression were observed in N2a cells treated with T. denticola and Aβ_1-42 in vitro. However, the Aβ inhibitor reversed these results, suggesting that Aβ_1-42 mediates T. denticola infection-induced neuronal apoptosis. Conclusions: This study found that oral infected T. denticola caused alveolar bone loss, and induced neuronal apoptosis by promoting Aβ accumulation in mice, providing evidence for the link between periodontitis and AD.

Virulence factors released from Porphyromonas gingivalis induce electrophysiological dysfunction in human pluripotent stem cell-derived cardiomyocytes

Background/purpose

Periodontal disease development correlates with the occurrence of systemic diseases. The present study investigated the association between periodontal disease and the development of cardiac arrhythmia.

Materials and methods

Human embryonic stem cell-derived cardiomyocytes (hESC-CMs) were treated with Porphyromonas gingivalis (Pg). Cardiotoxicity and electrophysiological properties of hESC-CMs were measured using the cell counting kit-8 assay and a multi-electrode array, respectively. Reverse-transcription-quantitative polymerase chain reaction (RT-qPCR) revealed the mRNA expression of S100 calcium binding protein A1 (S100A1), calsequestrin 2 (CASQ2), troponin I3 (TNNI3), myosin light chain 2 (MYL2), integrin subunit beta 1 (ITGB1), and cadherin 2 (CDH2) in hESC-CMs.

Results

Treatment with Pg broth significantly decreased the beat period, field potential duration, spike amplitude, and conduction velocity without affecting the viability of hESC-CMs. In addition, the mRNA expression of CASQ2, TNNI3, and MYL2, which are all associated with calcium handling, were downregulated by Pg broth treatment.

Conclusion

These findings indicate that Pg may induce cardiac arrhythmia mediated by virulence factors.

Do Periodontal Pathogens or Associated Virulence Factors Have a Deleterious Effect on the Blood-Brain Barrier, Contributing to Alzheimer's Disease?

The central nervous system (CNS) is protected by a highly selective barrier, the blood-brain barrier (BBB), that regulates the exchange and homeostasis of bloodborne molecules, excluding xenobiotics. This barrier forms the first line of defense by prohibiting pathogens from crossing to the CNS. Aging and chronic exposure of the BBB to pathogens renders it permeable, and this may give rise to pathology in the CNS such as Alzheimer's disease (AD). Researchers have linked pathogens associated with periodontitis to neuroinflammation and AD-like pathology in vivo and in vitro. Although the presence of periodontitis-associated bacteria has been linked to AD in several clinical studies as DNA and virulence factors were confirmed in brain samples of human AD subjects, the mechanism by which the bacteria traverse to the brain and potentially influences neuropathology is unknown. In this review, we present current knowledge about the association between periodontitis and AD, the mechanism whereby periodontal pathogens might provoke neuroinflammation and how periodontal pathogens could affect the BBB. We suggest future studies, with emphasis on the use of human in vitro models of cells associated with the BBB to unravel the pathway of entry for these bacteria to the CNS and to reveal the molecular and cellular pathways involved in initiating the AD-like pathology. In conclusion, evidence demonstrate that bacteria associated with periodontitis and their virulence factors are capable of inflecting damage to the BBB and have a role in giving rise to pathology similar to that found in AD.

Outer membrane vesicles of Porphyromonas gingivalis: Novel communication tool and strategy

Extracellular vesicles (EVs) have been recognized as a universal method of cellular communications and are reportedly produced in bacteria, archaea, and eukaryotes. Bacterial EVs are often called “Outer Membrane Vesicles” (OMVs) as they were the result of a controlled blebbing of the outer membrane of gram-negative bacteria such as Porphyromonas gingivalis (P. gingivalis). Bacterial EVs are natural messengers, implicated in intra- and inter-species cell-to-cell communication among microorganism populations present in microbiota. Bacteria can incorporate their pathogens into OMVs; the content of OMVs differs, depending on the type of bacteria. The production of distinct types of OMVs can be mediated by different factors and routes. A recent study highlighted OMVs ability to carry crucial molecules implicated in immune modulation, and, nowadays, they are considered as a way to communicate and transfer messages from the bacteria to the host and vice versa. This review article focuses on the current understanding of OMVs produced from major oral bacteria, P. gingivalis: generation, characteristics, and contents as well as the involvement in signal transduction of host cells and systemic diseases. Our recent study regarding the action of P. gingivalis OMVs in the living body is also summarized.

Porphyromonas gingivalis and Its Systemic Impact: Current Status

The relationship between periodontitis and systemic diseases, notably including atherosclerosis and diabetes, has been studied for several years. Porphyromonas gingivalis, a prominent component of oral microorganism communities, is the main pathogen that causes periodontitis. As a result of the extensive analysis of this organism, the evidence of its connection to systemic diseases has become more apparent over the last decade. A significant amount of research has explored the role of Porphyromonas gingivalis in atherosclerosis, Alzheimer's disease, rheumatoid arthritis, diabetes, and adverse pregnancy outcomes, while relatively few studies have examined its contribution to respiratory diseases, nonalcoholic fatty liver disease, and depression. Here, we provide an overview of the current state of knowledge about Porphyromonas gingivalis and its systemic impact in an aim to inform readers of the existing epidemiological evidence and the most recent preclinical studies. Additionally, the possible mechanisms by which Porphyromonas gingivalis is involved in the onset or exacerbation of diseases, together with its effects on systemic health, are covered. Although a few results remain controversial, it is now evident that Porphyromonas gingivalis should be regarded as a modifiable factor for several diseases.

Lipoteichoic acid of Enterococcus faecalis interferes with Porphyromonas gingivalis lipopolysaccharide signaling via IRAK-M upregulation in human periodontal ligament cells

Periodontitis is a chronic inflammatory disease of the gum caused by infection with multispecies oral bacteria. Since the periodontopathic bacteria, Porphyromonas gingivalis together with Enterococcus faecalis are frequently detected in patients with a severe form of periodontitis, interactions between their virulence factors might play an important role in progression of the disease. P. gingivalis and E. faecalis possess lipopolysaccharide (Pg.LPS) and lipoteichoic acid (Ef.LTA), respectively, as the major virulence factors inducing inflammatory responses. However, the combinatorial effect of these virulence factors on chemokine expression was poorly understood. Here, we examined the interaction between Ef.LTA and Pg.LPS on IL-8 induction in human periodontal ligament (PDL) cells. Pg.LPS, but not Ef.LTA, induced IL-8 expression at both mRNA and protein levels, which was suppressed in the presence of Ef.LTA. Although Ef.LTA and Pg.LPS could stimulate Toll-like receptor 2 (TLR2), Ef.LTA did not interfere with Pg.LPS induced-TLR2 activation. However, Ef.LTA decreased Pg.LPS-induced phosphorylation of ERK, JNK, and p38 kinase. Furthermore, Ef.LTA suppressed Pg.LPS-induced IL-8 promoter activity as well as AP-1, NF-IL6 and NF-κB transcription factors, which are indispensable for IL-8 expression. Interestingly, Ef.LTA enhanced only IL-1 receptor-associated kinase-M (IRAK-M) expression among the tested negative regulators of TLR intracellular signaling cascades in the presence of Pg.LPS. In addition, silencing IRAK-M restored the decreased IL-8 expression by Ef.LTA in the presence of Pg.LPS. Collectively, these results suggest that Ef.LTA inhibits Pg.LPS-induced IL-8 expression in human PDL cells via inducing the expression of a negative regulator of TLR signaling cascades, IRAK-M.

Crystal Structure of Human EOLA1 Implies Its Possibility of RNA Binding

Human endothelial-overexpressed lipopolysaccharide-associated factor 1 (EOLA1) has been suggested to regulate inflammatory responses in endothelial cells by controlling expression of proteins, interleukin-6 and vascular cell adhesion molecule-1, and by preventing apoptosis. To elucidate the structural basis of the EOLA1 function, we determined its crystal structure at 1.71 Å resolution and found that EOLA1 is structurally similar to an activating signal cointegrator-1 homology (ASCH) domain with a characteristic β-barrel fold surrounded by α-helices. Despite its low sequence identity with other ASCH domains, EOLA1 retains a conserved 'GxKxxExR' motif in its cavity structure. The cavity harbors aromatic and polar residues, which are speculated to accommodate nucleotide molecules as do YT521-B homology (YTH) proteins. Additionally, EOLA1 exhibits a positively charged cleft, similar to those observed in YTH proteins and the ASCH protein from Zymomonas mobilis that exerts ribonuclease activity. This implies that the positively charged cleft in EOLA1 could stabilize the binding of RNA molecules. Taken together, we suggest that EOLA1 controls protein expression through RNA binding to play protective roles against endothelial cell injuries resulting from lipopolysaccharide (LPS)-induced inflammation responses.

IMM-H004, a coumarin derivative, attenuated brain ischemia/reperfusion injuries and subsequent inflammation in spontaneously hypertensive rats through inhibition of VCAM-1

We studied the effect of IMM-H004 in treating brain I/R injury in spontaneously hypertensive rats and showed that IMM-H004 could efficiently ameliorate neurological defects and infarct volume in a time and dose dependent manner.

Inhibiting adhesion events by Panax notoginseng saponins and Ginsenoside Rb1 protecting arteries via activation of Nrf2 and suppression of p38 - VCAM-1 signal pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Asian countries, such as China, Japan, and Korea, have witnessed a history of more than 1000 years of Panax notoginseng (Burk.) F.H. Chen's application as a famous traditional medicine for cardiovascular diseases (Zhou et al., 2004). The use of Panax notoginseng (Sanqi) was first recorded in "Bencao Gangmu", which was written by Li Shizhen, a Chinese pharmacologist of the MING dynasty, in 1578. It is included in "The Plant List" as one species of genus Panax (family Araliaceae). Panax notoginseng saponins (PNS) are the major active ingredients extracted from Panax notoginseng.

AIM OF THE STUDY

This study investigated whether PNS and the active constituent Ginsenoside Rb1 inhibits adhesion events by regulating the NF-E2-related factor 2 (Nrf2) - p38 - vascular cell adhesion molecule (VCAM)-1 pathway.

MATERIALS AND METHODS

The AS model rats were treated once daily with PNS (100mg/kg, i.p.) or Rb1 (40mg/kg, i.p.), and pathological changes in the aortas were observed by electron microscopy and Sudan IV staining. The serum levels of NO, superoxide dismutase (SOD) and TNF-α were measured. Upon treatment with H₂O₂ to induce oxidative stress_, cell viability and LDH levels were measured after cells were cultured with PNS or Rb1. oxidized low density lipoprotein (oxLDL)-induced VCAM-1 and p38 protein expression and THP1 cell adhesion to ECs were assessed after treatment with PNS or Rb1. Nuclear translocation of Nrf2 and expression of its target protein heme oxygenase (HO)-1 were observed in the respective presence of PNS or Rb1.

RESULTS

Upon treatment with PNS or Rb1, pathological changes observed in the aortas of AS model rats were alleviated, and an increase in serum levels of NO and SOD and a decrease in TNF-α levels were observed. In vitro treatment with PNS or Rb1 protected endothelial cells (ECs) from H₂O₂-mediated cytotoxicity, suppressed oxLDL-induced p38 and VCAM-1 protein expression and inhibited THP1 cell adhesion to ECs. Finally, PNS and Rb1 treatment functionally activated Nrf2 in ECs.

CONCLUSIONS

Nrf2, an EC protective system, suppresses monocyte adhesion events via the inhibition of the ROS - TNF-α - p38 - VCAM-1 pathway following treatment with PNS, with Rb1 specifically playing an important role among PNS active components.

Effects of Porphyromonas gingivalis lipopolysaccharide on the expression of key genes involved in cholesterol metabolism in macrophages

INTRODUCTION

Cardiovascular diseases are positively correlated with periodontal disease. However, the molecular mechanisms linking atherosclerosis and periodontal infection are not clear. This study aimed to determine whether Porphyromonas gingivalis lipopolysaccharide (Pg-LPS) altered the expression of genes regulating cholesterol metabolism in macrophages in the presence of low-density lipoprotein (LDL).

MATERIAL AND METHODS

THP-1-derived macrophages were exposed to different concentrations (0.1, 1, 10 µg/ml) of LPS in the presence of 50 µg/ml native LDL. Macrophages were also incubated with 1 µg/ml LPS for varying times (0, 24, 48, or 72 h) in the presence of native LDL. Foam cell formation was determined by oil red O staining and cholesterol content quantification. CD36, lectin-like oxidized LDL receptor-1 (LOX-1), ATP-binding cassette G1 (ABCG1), and acetyl CoA acyltransferase 1 (ACAT1) expression levels were measured by western blot and qRT-PCR.

RESULTS

Foam cell formation was induced in a time- and concentration-dependent manner as assessed by both morphological and biochemical criteria. Pg-LPS caused downregulation of CD36 and ABCG1 but upregulation of ACAT1, while LOX-1 expression was not affected (p = 0.137).

CONCLUSIONS

Pg-LPS appears to be an important link in the development of atherosclerosis by mechanisms targeting cholesterol homeostasis, namely, excess cholesterol ester formation via ACAT1 and reduced cellular cholesterol efflux via ABCG1.

Sex-based differential regulation of bacterial-induced bone resorption

BACKGROUND AND OBJECTIVE

Periodontal disease pathogenesis is comprised of the complex inflammatory immune response to oral bacterial dysbiosis. Like other inflammatory diseases, there is sexual dimorphism evident in periodontal diseases. During periodontitis, inflammatory chemokines direct neutrophils to migrate to the site of infection to neutralize the pathogen. Interestingly, these same chemokines are also involved in regulating pathogen-induced osteoclast formation. Previous reports show differences in bone turnover and lymphocyte recruitment between sexes. We hypothesize that chemokine expression is differentially regulated by sex and thus results in differential osteoclast formation.

MATERIAL AND METHODS

Male and female mice were utilized to isolate neutrophils based on expression of Ly6G-specific, as well as defined osteoclast progenitors. Cells were stimulated with lipopolysaccharide (LPS; 100 ng/mL) then analyzed for neutrophil infiltration and gene expression. Defined osteoclast progenitors were primed: macrophage-colony stimulating factor (25 ng/mL), receptor activator of NF-κB ligand (50 ng/mL), then stimulated with LPS. Osteoclasts were enumerated via TRAP stain and mRNA isolated for gene expression analysis via quantitative polymerase chain reaction.

RESULTS

In response to LPS, male neutrophils in vitro respond with increased chemokine expression and significantly more osteoclast formed in response to LPS compared to females.

CONCLUSIONS

Findings support observations in humans regarding a sexual dimorphism in oral bacterial infections of alveolar bone loss. Males have a strong inflammatory response to bacterial infection, resulting in increased inflammatory microenvironment, reduced pathogenic bacteria clearance and increased osteoclast-driven bone loss in response to differential expression of key chemokines.

EOLA1 Inhibits Lipopolysaccharide-Induced Vascular Cell Adhesion Molecule-1 Expression by Association with MT2A in ECV304 Cells

Our research group firstly discovered endothelial-overexpressed lipopolysaccharide-associated factor 1 (EOLA1, GenBank number AY074889) as a lipopolysaccharide (LPS) responsive gene in ECV304 cells. The previous studies have further demonstrated the association of EOLA1 with metallothionein 2A (MT2A), while the role of EOLA1 during LPS-induced inflammatory response in ECV304 cells is unknown. In this report, we determined the subcellular localization of EOLA1 and the regulatory capacity of EOLA1 on vascular cell adhesion molecule-1 (VCAM-1) in response to LPS in ECV304 cells. Our results show that EOLA1 is broadly diffuse in the cells, and EOLA1 expression is dramatically induced by LPS. EOLA1 knockdown results in significant enhancement of LPS-induced VCAM-1 production. Consistent with this, overexpression of EOLA1 leads to the reduction of LPS-induced VCAM-1 production. Furthermore, MT2A knockdown reduces LPS-induced VCAM-1 production. Collectively, our results demonstrate a negative regulatory role of EOLA1 on LPS-induced VCAM-1 expression involving its association with MT2A in ECV304 cells.

Irradiated U937 cells trigger inflammatory bystander responses in human umbilical vein endothelial cells through the p38 pathway

Radiation-induced bystander effects are a well-known phenomenon that are observed when treating cancer and other diseases after radiotherapy, and even after occupational exposure to radiation. However, little is known about the crosstalk between irradiated macrophages and endothelial cells that line the circulatory system, which may play a role in the development of atherosclerosis. In the current study, we found that the expression of inducible nitric oxide synthase (iNOS) and the intracellular level of nitric oxide (NO) in gamma-irradiated U937 macrophage cells were significantly increased. When human umbilical vein endothelial cells (HUVECs) were co-cultured with gamma-irradiated U937 cells, additional micronuclei (MN) and apoptosis were induced so that the plating efficiency of the bystander HUVECs decreased and P38 was overexpressed in the bystander HUVECs cells. In addition, the contents of vascular cell adhesion molecule 1 (VCAM-1) and the activities of matrix metalloproteinase-9 (MMP-9) in the culture medium of bystander HUVECs were increased. Furthermore, during cell co-culture the adhesive ability of irradiated U937 cells to the bystander HUVECs increased. When U937 cells were treated with 500 μM S-methylisothiourea sulfate (SMT) (iNOS inhibitor) before irradiation, and HUVECs were treated with 10 μM SB203580 (p38 inhibitor) before cell co-culture or treated with 20 μM c-PTIO (NO scavenger) in the co-culture medium, the bystander micronuclei and the amounts of VCAM-1 and MMP-9 in the medium of bystander HUVECs were diminished, and the ability of irradiated U937 cells adhering to HUVECs was also reduced, while the plating efficiency of bystander HUVECs partially recovered. These results demonstrated that irradiated U937 cells appear to release nitric oxide and thereby further trigger apoptosis and inflammatory responses in the bystander HUVECs through a p38-dependent pathway.

Hemoglobin receptor protein from Porphyromonas gingivalis induces interleukin-8 production in human gingival epithelial cells through stimulation of the mitogen-activated protein kinase and NF-κB signal transduction pathways

Periodontitis is an inflammatory disease of polymicrobial origin affecting the tissues supporting the tooth. The oral anaerobic bacterium Porphyromonas gingivalis, which is implicated as an important pathogen for chronic periodontitis, triggers a series of host inflammatory responses that promote the destruction of periodontal tissues. Among the virulence factors of P. gingivalis, hemoglobin receptor protein (HbR) is a major protein found in culture supernatants. In this study, we investigated the roles of HbR in the production of inflammatory mediators. We found that HbR induced interleukin-8 (IL-8) production in the human gingival epithelial cell line Ca9-22. p38 mitogen-activated protein kinase (MAPK) and extracellular signal-related kinase 1/2 (Erk1/2) were activated in HbR-stimulated Ca9-22 cells. Inhibitors of p38 MAPK (SB203580) and Erk1/2 (PD98059) blocked HbR-induced IL-8 production. Additionally, HbR stimulated the translocation of NF-κB-p65 to the nucleus, consistent with enhancement of IL-8 expression by activation of the NF-κB pathway. In addition, small interfering RNA (siRNA) targeting activating transcription factor 2 (ATF-2) or cyclic AMP-response element-binding protein (CREB) inhibited HbR-induced IL-8 production. Moreover, pretreatment with SB203580 and PD98059 reduced HbR-induced phosphorylation of CREB and ATF-2, respectively. Combined pretreatment with an inhibitor of NF-κB (BAY11-7082) and SB203580 was more efficient in inhibiting the ability of HbR to induce IL-8 production than pretreatment with either BAY11-7082 or SB203580 alone. Thus, in Ca9-22 cells, the direct activation of p38 MAPK and Erk1/2 by HbR caused the activation of the transcription factors ATF-2, CREB, and NF-κB, thus resulting in the induction of IL-8 production.