Strong and persistent microbial and inflammatory stimuli overcome the genetic predisposition to higher matrix metalloproteinase‐1 (MMP‐1) expression: a mechanistic explanation for the lack of association of MMP1‐1607 single‐nucleotide polymorphism genotypes with MMP‐1 expression in chronic periodontitis lesions

Aims: Our objective was to evaluate the association between the MMP1-1607 single-nucleotide polymorphism (SNP), periodontopathogens and inflammatory cytokines with matrix metalloproteinase-1 (MMP-1) mRNA levels in vitro and in vivo. Materials and Methods: This study investigated the influence of genetic (MMP1-1607 SNP), microbial (Porphyromonas gingivalis, Treponema denticola, Tannerella forsythia, Actinobacillus actinomycetemcomitans) and inflammatory [tumour necrosis factor-α (TNF-α) and interleukin-1β (IL-1β)] factors on the determination of MMP-1 mRNA levels in periodontal tissues of non-smoker chronic periodontitis (CP, N=178) and control (C, N=190) groups. The effects of single and repeated lipopolysaccharide (LPS) and inflammatory cytokine stimulation of macrophages with distinct MMP1-1607 SNP genotypes were also investigated. Results: In healthy tissues, the MMP1-1607 2G allele was associated with higher MMP-1 levels while in CP MMP-1 levels were associated with the presence and load of periodontopathogens, and also with TNF-α and IL-1β expression irrespective of the MMP1-1607 genotype. In vitro data demonstrate that in 2G macrophages low- and intermediate-dose LPS and TNF-α+IL-1β stimulation was associated with increased MMP-1 expression, while strong and repeated stimulation resulted in higher MMP-1 levels irrespective of the MMP1-1607 genotype. Conclusion: Our data demonstrate a limited role for MMP1-1607 SNP in periodontitis, where the extensive chronic antigenic challenge exposure overcomes the genetic control and plays a major role in the determination of MMP-1 expression.