In periodontitis, levels of inflammatory cytokine IL-1 are high and correlate with disease severity, while levels of anti-inflammatory IL-4 are low or undetectable and decreasing levels of IL-4 correlate with increasing severity. IL-1 contributes to loss of attachment and alveolar bone destruction by increasing expression of matrix metalloproteinases. MMP-3 has broad substrate specificity and can activate other pro-MMP. It is found in increased levels in diseased sites, and levels are correlated with severity and progression. Previous studies identified the SIRE site (stromelysin IL-1 responsive element) as a repressor element involved in suppressing the IL-1 induction of MMP-3. Others also identified this site as a common 5T/6T polymorphism, with the 6T site being a more effective repressor element. Genotype at this site has been linked to tissue levels of MMP-3 and to susceptibility or severity of a number of diseases. In cardiovascular disease (a condition associated with periodontitis), homozygosity for the higher-expressing 5T allele is associated with myocardial infarction and aneurysm, while the lower-expressing 6T allele is associated with atherosclerosis. It is therefore clear that regulation of this gene must be tightly controlled to maintain correct tissue homeostasis, and that understanding these control mechanisms is important for a variety of pathologies. We recently found that proteins binding to the SIRE site include NF-kappaB p50 and p65 and ZBP-89. We also recently showed that IL-1 induction of MMP-3 is suppressed by IL-4 in human gingival fibroblasts isolated from patients with periodontitis.
The Specific Aims of this application are to: 1) study the roles of transcription factors interacting with the polymorphic SIRE site in the MMP-3 promoter, and 2) determine the mechanism of suppression of MMP-3 expression by IL-4. In doing so, we hope to gain information about complex gene regulatory mechanisms involved in MMP-3 regulation, but also continue to contribute to the research environment at PCOM and to the training of its students in research in general, and molecular biology in particular.
