Aggressive periodontitis (AgP) is a rapidly progressive periodontal disease that is associated with impaired polymorphonuclear leukocyte (PMN) chemotaxis toward bacterial N-formyl peptides. Formylpeptide receptors (FPRs) on the PMN surface guide PMNs to infection sites. Several single nucleotide polymorphisms (SNPs) have been characterized in FPR1. We hypothesized that FPR1 SNPs can impair PMN chemotaxis by decreasing FPR expression, thereby increasing the risk of developing AgP.
We assessed the relationship between FPR1 SNPs, PMN chemotaxis, FPR1 expression and susceptibility to AgP in African-Americans (37 cases and 38 controls). A polymorphic portion of the FPR1 coding region was amplified by polymerase chain reaction (PCR) and sequenced to detect SNPs. PMNs were isolated and chemotaxis to N-formyl-Met-Leu-Phe was assayed in a modified Boyden chamber. Relative FPR1 expression in PMNs was quantified by real time PCR. FPR1 5 ‘SNPs were detected by PCR and sequencing. Haplotype associations between 348T>C and 5’ SNPs were analyzed. Secondary mRNA structures associated with 348T and 348C were predicted using the mfold web server.
Five FPR1 coding region SNPs were identified. Synonymous SNP 348T>C was significantly associated with AgP. The homozygous 348T genotype was only found among AgP cases (P=0.017, odds ratio=18.9). These individuals exhibited a significantly lower PMN chemotactic response relative to subjects with the 348C/C and 348T/C genotypes (P<0.05). There were no significant differences in PMN FPR1 expression between subjects with the 348C/C, 348C/T and 348 T/T genotypes. Eleven FPR1 5’ SNPs were detected, including 4 not previously characterized. None of the predicted haplotypes reflected associations of 5’SNPs with AgP or 348T. The predicted mRNA structures of haplotypes containing 348T exhibited higher free energy (lower stability) and a different secondary structure than haplotypes containing 348C.
In African Americans, the 348T/T genotype is associated with significantly impaired PMN chemotaxis and an increased risk of developing AgP. These associations do not appear to be related to significant reductions in FPR1 transcription. However, our studies suggest that 348T could potentially alter FPR expression by decreasing mRNA stability.