Functional polymorphisms of the FPR1 gene and aggressive periodontitis in Japanese

Evaluation of the Genetic Association and Methylation of Immune Response Pathway Genes with the Risk of Chronic Periodontitis in the Uighur Population

Aim: The aim of this study was to explore the possible associations between single nucleotide polymorphisms (SNPs) and DNA methylation levels of seven genes in the inflammatory response pathway with susceptibility to chronic periodontitis (CP) among the Uighur population of the Xinjiang Autonomous Region of China. Methods: A total of 444 eligible subjects (279 CP patients and 165 healthy controls) were enrolled in the study. Genomic DNA was obtained from gingival tissue for genotyping eight SNPs and performing methylation measurements of seven genes. Results: SNP rs2070745 in the formyl peptide receptor 1 (FPR1) gene achieved statistical significance in a standard allelic association analysis for CP (p = 0.02). The frequency of the rs2070745 minor allele G was higher in the cases than in controls (0.367 vs. 0.291). Additionally, rs2070745 was significantly associated with CP under the dominant genetic model (p = 0.03). Using logistic regression analysis, rs2070745 was found to be consistently associated with CP under the additive dominant model, and this association remained significant after covariates were taken into account [odds ratio (OR) = 1.49 (1.09-2.05), p = 0.014; OR = 1.58 (1.04-2.40), p = 0.031, respectively]. No significant gene-gene interactions were identified. Although we did not find a polymorphism in interleukin 6 (IL6) associated with CP in our study, the methylation level of a CpG island region located within the promoter region of IL6 was significantly less in CP patients compared with controls (p < 0.05). Conclusions: The genetic polymorphism rs2070745 in FPR1 and the methylation level of the promoter region of IL6 might be associated with CP in the Uighur population of China.

Formyl peptide receptors in the mucosal immune system

Formyl peptide receptors (FPRs) belong to the G protein-coupled receptor (GPCR) family and are well known as chemotactic receptors and pattern recognition receptors (PRRs) that recognize bacterial and mitochondria-derived formylated peptides. FPRs are also known to detect a wide range of ligands, including host-derived peptides and lipids. FPRs are highly expressed not only in phagocytes such as neutrophils, monocytes, and macrophages but also in nonhematopoietic cells such as epithelial cells and endothelial cells. Mucosal surfaces, including the gastrointestinal tract, the respiratory tract, the oral cavity, the eye, and the reproductive tract, separate the external environment from the host system. In mucosal surfaces, the interaction between the microbiota and host cells needs to be strictly regulated to maintain homeostasis. By sharing the same FPRs, immune cells and epithelial cells may coordinate pathophysiological responses to various stimuli, including microbial molecules derived from the normal flora. Accumulating evidence shows that FPRs play important roles in maintaining mucosal homeostasis. In this review, we summarize the roles of FPRs at mucosal surfaces.

The repertoire of family A-peptide GPCRs in archaic hominins

Given the importance of G-protein coupled receptors in the regulation of many physiological functions, deciphering the relationships between genotype and phenotype in past and present hominin GPCRs is of main interest to understand the evolutionary process that contributed to the present-day variability in human traits and health. Here, we carefully examined the publicly available genomic and protein sequence databases of the archaic hominins (Neanderthal and Denisova) to draw up the catalog of coding variations in GPCRs for peptide ligands, in comparison with living humans. We then searched in the literature the functional changes, phenotypes and risk of disease possibly associated with the detected variants. Our survey suggests that Neanderthal and Denisovan hominins were likely prone to lower risk of obesity, to enhanced platelet aggregation in response to thrombin, to better response to infection, to less anxiety and aggressiveness and to favorable sociability. While some archaic variants were likely advantageous in the past, they might be responsible for maladaptive disorders today in the context of modern life and/or specific regional distribution. For example, an archaic haplotype in the neuromedin receptor 2 is susceptible to confer risk of diabetic nephropathy in type 1 diabetes in present-day Europeans. Paying attention to the pharmacological properties of some of the archaic variants described in this study may be helpful to understand the variability of therapeutic efficacy between individuals or ethnic groups.

RNA sequencing for ligature induced periodontitis in mice revealed important role of S100A8 and S100A9 for periodontal destruction

Periodontitis is an inflammatory disease caused by pathogenic oral microorganisms that induce the destruction of periodontal tissue. We sought to identify the relevant differentially expressed genes (DEGs) and clarify the mechanism underlying the rapid alveolar bone loss by using ligature-induced periodontitis in mice. A silk ligature was tied around the maxillary left second molar in 9-week-old C57BL/6 J male mice. In-vivo micro-CT analysis revealed that ligation induced severe bone loss. RNA-sequencing analysis, to examine host responses at 3 days post-ligation, detected 12,853 genes with fragments per kilobase of exon per million mapped reads ≥ 1, and 78 DEGs. Gene ontology term enrichment analysis revealed the expression profiles related to neutrophil chemotaxis and inflammatory responses were significantly enriched in the ligated gingiva. The expression levels of innate immune response-related genes, including S100a8 and S100a9, were significantly higher in the ligated side. S100A8 was strongly detected by immunohistochemistry at the attached epithelium in ligated sites. Inhibition of S100A8 and S100A9 expression revealed that they regulated IL1B and CTSK expression in Ca9-22 cells. Thus, innate immune response-related molecules might be associated with the burst-destruction of periodontal tissue in ligature-induced periodontitis. Especially, S100A8 and S100A9 may play an important role in alveolar bone resorption.

Periodontal tissue destruction in aggressive periodontitis: Determination of gene or environmental factors

Aim

This study observed the role of defective neutrophil function in aggressive periodontitis through FPR1 gene polymorphism and the level of Il-8 compared with the role of dental plaque presence towards periodontal tissue damage (Clinical Attachment Loss/CAL) in patients in Indonesia.

Methods

Case-control study was used to detect differences in polymorphism expression of FPR1 gene, the level of Il-8, dental plaque, and Clinical Attachment Loss/CAL from 32 Aggressive Periodontitis (AP) and 29 Non-Aggressive Periodontitis (NAP) samples, selected with consecutive sampling method. Polymorphism was identified using polymerase chain reaction (PCR) technique, and the level of IL-8 in the gingival crevicular fluid was identified using the enzyme-linked immunosorbent assay (ELISA) test. The Clinical Attachment Loss was analysed by using William periodontal probe, and the oral environment analysis was performed by using the OHI-S plaque index. Statistical analysis was used to determine the significance of the polymorphism difference of FPR gene, Il-8, Plaque and CAL amongst all subjects and also the control and correlations among these factors.

Results

The results showed that in the Aggressive Periodontitis (AP), the presence of the polymorphism of c576 T > C > G of FPR1 gene caused as much as 5.04 times higher occurrence of aggressive periodontitis (p = 0.006; OR = 5.040 (1.51–16.74)). The low level of Il-8 (below 0.064 pg/μl), showed as much as 34.5 times higher occurrence of aggressive periodontitis (OR = 34.5 (6.76–176.08)). The oral hygiene of the AP samples were better significantly (p = 0.002), and on the Clinical Attachment Loss (CAL) sample was even more (p = 0.02). The polymorphism of c301 G > C of FPR1 gene correlated with the CAL (r = 0.37; p = 0.039). The polymorphism of c576 T > C > G correlated significantly with the Il-8 (r = 0.5; p = 0.0287). The polymorphism of c348 T > C correlated significantly with the dental plaque (r = 0.355; p = 0.049), whereas the dental plaque correlation with CAL was not significant.

Conclusion

The research conclusion showed that in aggressive periodontitis, genetic and environmental factors were correlated with the cause of periodontal tissue injury, and the role of genetic factors was more prominent on the injury.

Formyl-Peptide Receptors in Infection, Inflammation, and Cancer

Formyl-peptide receptors (FPRs) recognize bacterial and mitochondrial formylated peptides as well as endogenous non-formylated peptides and even lipids. FPRs are expressed on various host cell types but most strongly on neutrophils and macrophages. After the discovery of FPRs on leukocytes, it was assumed that these receptors predominantly govern a proinflammatory response resulting in chemotaxis, degranulation, and oxidative burst during infection. However, it is clear that the activation of FPRs has more complex consequences and can also promote the resolution of inflammation. Recent studies have highlighted associations between FPR function and inflammatory conditions, including inflammatory disorders, cancer, and infection. In this review we discuss these recent findings.

V101L of human formyl peptide receptor 1 (FPR1) increases receptor affinity and augments the antagonism mediated by cyclosporins

Genetic variation plays a major role in drug response variability. CsA (cyclosporin A), a widely used immunosuppressive agent, is a specific antagonist for FPR1 (formyl peptide receptor 1), which is an important G-protein-coupled chemoattractant receptor in the innate immune system. In order to study the variable responses of cyclosporins to different FPR1 mutants, we investigated the distribution of human FPR1 haplotypes among 209 healthy Han Chinese subjects. The haplotype pattern in Han Chinese were characterized on the basis of five SNPs (single nucleotide polymorphisms), including rs5030878 (p.T11I), rs2070745 (p.V101L), rs5030880 (p.R190W), rs1042229 (p.N192K) and rs867228 (p.A346E). Receptor binding affinity of cyclosporins to FPR1 haplotypes was assessed using N-formyl-Nle-Leu-Phe-Nle-Tyr-Lys–FITC in CHO-G_α16 cells stably transfected with cDNAs encoding the top 12 FPR1 haplotypes in the Han Chinese. Variants of FPR1 carrying a single amino acid substitution of leucine for valine at position 101 (p.Leu¹⁰¹) displayed significantly higher pK_i values for CsA and CsH (cyclosporin H), indicative of an improved receptor affinity. The polymorphism of FPR1 p.Leu¹⁰¹ also enhanced the inhibitory effects of cyclosporins on fMLF (N-formyl-methionyl-leucyl-phenylalanine)-induced activities, including calcium mobilization, cell chemotaxis and MAPK (mitogen-activated protein kinase) phosphorylation. These results point to a possible complication for clinical use of CsA in patients carrying the p.Leu¹⁰¹ allele of FPR1.

Neutrophils in periodontal inflammation

Neutrophils (also called polymorphonuclear leukocytes) are the most abundant leukocytes whose primary purpose as anti-microbial professional phagocytes is to kill extracellular pathogens. Neutrophils and macrophages are phagocytic cell types that along with other cells effectively link the innate and adaptive arms of the immune response, and help promote inflammatory resolution and tissue healing. Found extensively within the gingival crevice and epithelium, neutrophils are considered the key protective cell type in the periodontal tissues. Histopathology of periodontal lesions indicates that neutrophils form a 'wall' between the junctional epithelium and the pathogen-rich dental plaque which functions as a robust anti-microbial secretory structure and as a unified phagocytic apparatus. However, neutrophil protection is not without cost and is always considered a two-edged sword in that overactivity of neutrophils can cause tissue damage and prolong the extent and severity of inflammatory periodontal diseases. This review will cover the innate and inflammatory functions of neutrophils, and describe the importance and utility of neutrophils to the host response and the integrity of the periodontium in health and disease.

Oestrogen receptors are involved in the osteogenic differentiation of periodontal ligament stem cells

The existence of PDLSCs [PDL (periodontal ligament) stem cells] in PDL has been identified and such cells may function in periodontal reconstruction, including bone formation. Oestrogens/ERs (oestrogen receptors; ERα and ERβ) exert important effects in bone formation, however, the relationship between ERs and PDLSCs has not been established. In the present study, PDLSCs were isolated and assays for detecting stem-cell biomarkers and multipotential differentiation potential confirmed the validity of human PDLSCs. The results of RT–PCR (reverse transcription–PCR) and Western blotting showed that ERα and ERβ were expressed at higher levels in PDLSCs as compared with PDLCs (PDL cells), and 17β-oestradiol obviously induced the osteogenic differentiation of PDLSCs in vitro. Furthermore, a pan-ER inhibitor or lentivirus-mediated siRNA (small interfering RNA) targeting ERα or ERβ blocked the oestrogen-induced osteogenic differentiation of PDLSCs. The results indicate that both ERα and ERβ were involved in the process of osteogenic differentiation of PDLSCs.

Therapeutic anti-inflammatory potential of formyl-peptide receptor agonists

The need for novel anti-inflammatory drugs justifies the search for innovative targets that could satisfy this goal. For quite some time now, we have proposed the study of endogenous anti-inflammation as a distinctive approach to the discovery of new drugs. This approach requires development of new compounds that activate specific receptor targets to downregulate the cellular and tissue pathways operative in the host during inflammation. Here we dwell on a family of G-protein coupled receptors (GPCR) termed FPRs, acronym for formyl-peptide receptors. With three and seven members in man and mouse, respectively, these receptors harness many biological functions, spanning odour perception and hair growth, to the control of multiple facets (pain; cell migration; oxidative burst; xenobiotic engulfment) of the inflammatory reaction. We focus on FPR biology with particular attention to molecules able to produce pharmacological effects by interacting with these GPCRs, describing endogenous agonists of FPRs and, more relevantly, the current development of synthetic agonists. Besides being potential leads for the development of the anti-inflammatory therapeutics of the future, these compounds could also help clarify the properties and roles that each FPR might play in the complex network of pathways that is inflammation. We conclude that FPR2 agonists could be valid warhorses for defining a novel philosophy for anti-inflammatory drug discovery programmes: mimicking - with new compounds - the way our body disposes of inflammation could be a viable approach to regulate aberrant inflammatory responses as in the case of several chronic rheumatic and cardiovascular pathologies.

Formylpeptide receptor single nucleotide polymorphism 348T>C and its relationship to polymorphonuclear leukocyte chemotaxis in aggressive periodontitis

BACKGROUND

Aggressive periodontitis (AgP) is associated with impaired polymorphonuclear leukocyte (PMN) chemotaxis toward bacterial N-formylpeptides. Formylpeptide receptors (FPRs) play a major role in guiding PMNs to infection sites. Previous work revealed a significant association between FPR1 single nucleotide polymorphism (SNP) 348T>C and AgP in African Americans. We tested the hypothesis that 348T impairs PMN chemotaxis by decreasing FPR mRNA expression, thereby increasing susceptibility to AgP.

METHODS

Blood samples were obtained from African American subjects (37 AgP cases and 38 controls). Chemotaxis to N-formyl-methionine-leucine-phenylalanine by freshly isolated PMNs was assayed in a modified Boyden chamber. RNA was isolated from PMNs, and FPR1 gene expression was quantified by real-time polymerase chain reaction (PCR). To detect FPR1 5' SNPs, genomic DNA was isolated, and four fragments spanning the FPR1 5' region were PCR-amplified and sequenced. Haplotype associations between SNP 348T>C and 5' SNPs were analyzed.

RESULTS

The homozygous 348T genotype was only found in AgP cases (P = 0.017; odds ratio, 18.9). Subjects with this genotype exhibited a significantly lower PMN chemotactic response relative to controls and to subjects with the 348C/C or 348T/C genotype (P <0.05). There were no significant differences in PMN FPR1 expression among subjects with the 348C/C, 348T/C, and 348T/T genotypes. Eleven FPR1 5' SNPs were detected, but none of the predicted haplotypes reflected associations with AgP or with 348T.

CONCLUSIONS

Although the 348T/T genotype is relatively rare, it is associated with significantly impaired PMN chemotaxis and an increased risk for developing AgP in African Americans. These associations do not seem to be related to significant reductions in FPR1 transcripts in subjects expressing 348T.

Neutrophil formylpeptide receptor single nucleotide polymorphism 348T>C in aggressive periodontitis

BACKGROUND

Neutrophil formylpeptide receptors (FPRs) play an important role in bacterial recognition and chemotaxis. Defective FPR1 expression and impaired polymorphonuclear leukocyte chemotaxis toward bacterial formylpeptides are associated with aggressive periodontitis (AgP). The objective of this study was to determine whether single nucleotide polymorphisms (SNPs) in FPR1 are associated with AgP.

METHODS

Genomic DNA was isolated from blood samples obtained from African Americans (30 subjects with AgP and 33 healthy controls) and Turks (75 subjects with AgP and 63 healthy controls). A highly polymorphic fragment of the FPR1 gene was amplified by polymerase chain reaction and sequenced for analysis of SNPs.

RESULTS

Five previously identified SNPs were detected in African Americans, whereas six were detected in Turkish subjects. The frequency of synonymous SNP c.348T>C was significantly higher in African Americans with AgP than in controls (P = 0.029). The 348T allele was significantly associated with AgP (P = 0.010). Seven of the subjects with AgP, but none of the controls, were homozygous for 348T. FPR1 haplotypes 348T.568A, 348T.576T, and 348T.568A.576T were significantly increased in African Americans with AgP (P <0.02). The Turkish population did not exhibit significant differences in FPR1 SNP frequencies between subjects with AgP and controls.

CONCLUSIONS

FPR1 SNP c.348T>C is associated with AgP in African Americans. Individuals who are homozygous for 348T may have an increased risk for developing this disorder.

International Union of Basic and Clinical Pharmacology. LXXIII. Nomenclature for the formyl peptide receptor (FPR) family

Formyl peptide receptors (FPRs) are a small group of seven-transmembrane domain, G protein-coupled receptors that are expressed mainly by mammalian phagocytic leukocytes and are known to be important in host defense and inflammation. The three human FPRs (FPR1, FPR2/ALX, and FPR3) share significant sequence homology and are encoded by clustered genes. Collectively, these receptors bind an extraordinarily numerous and structurally diverse group of agonistic ligands, including N-formyl and nonformyl peptides of different composition, that chemoattract and activate phagocytes. N-formyl peptides, which are encoded in nature only by bacterial and mitochondrial genes and result from obligatory initiation of bacterial and mitochondrial protein synthesis with N-formylmethionine, is the only ligand class common to all three human receptors. Surprisingly, the endogenous anti-inflammatory peptide annexin 1 and its N-terminal fragments also bind human FPR1 and FPR2/ALX, and the anti-inflammatory eicosanoid lipoxin A4 is an agonist at FPR2/ALX. In comparison, fewer agonists have been identified for FPR3, the third member in this receptor family. Structural and functional studies of the FPRs have produced important information for understanding the general pharmacological principles governing all leukocyte chemoattractant receptors. This article aims to provide an overview of the discovery and pharmacological characterization of FPRs, to introduce an International Union of Basic and Clinical Pharmacology (IUPHAR)-recommended nomenclature, and to discuss unmet challenges, including the mechanisms used by these receptors to bind diverse ligands and mediate different biological functions.

Human formyl peptide receptor 1 (FPR1) c.32C>T SNP is associated with decreased soluble E-selectin levels

Aims: The human formyl peptide receptor (FPR) is a G protein-coupled chemoattractant receptor that is thought to mediate inflammatory responses. The FPR1 gene is highly polymorphic. In a recent study, the FPR1 c.32C>T SNP, resulting in the amino-acid substitution I11T, was reported to be significantly associated with C-reactive protein levels. Therefore, this study sought to determine if the impact of such a genetic variation extends to other clinical parameters associated with inflammation, including cytokines, adhesion molecules and inflammatory markers. Materials & methods: This study was carried out on a subsample of 325 adults selected from the STANISLAS cohort study. The FPR1 c.32C>T SNP was genotyped using PCR amplification followed by restriction enzyme digestion. Anthropometric measurements and biochemical profiles were assessed for each individual. Results: The allele frequencies of FPR1 c.32C>T were 0.74 for the 32C allele and 0.26 for the 32T allele. Genotype frequencies were 0.55 for C/C, 0.38 for C/T and 0.07 for T/T. After adjusting for age, sex, BMI, alcohol and cigarette consumption, oral contraceptive, antibiotics and anti-inflammatory drug use, statistical analysis (under a recessive model of inheritance) demonstrated that serum E-selectin levels were 68% lower in individuals homozygous for T/T than in those with C/T or C/C genotypes (p = 0.001). However, no significant correlations were found for C-reactive protein or the other 18 tested clinical parameters that were analyzed in this study. Conclusion: The FPR1 c.32C>T SNP may be associated with E-selectin levels in the French population. Although of importance, these findings need confirmation in larger studies.