Oral bacteria modulate scavenger receptor expression in macrophage

Studies support a connection between periodontitis and atherosclerosis. The cell most associated with early atherosclerotic lesions is the macrophage which has a central role in formation of foam cell “fatty streaks” - the first visible changes in arteries leading to atheroma formation.  This is a result of dysfunctional lipid handling involving a group of structurally heterogeneous but functionally similar receptors, the Scavenger Receptors (SR) which facilitate endocytosis and efflux of altered serum lipid particles as part of arterial wall homeostasis. SR also endocytose bacteria as a component of innate immunity. The combination of these two functions suggests a role for these receptors in periodontal disease induction or exacerbation of atherosclerosis. Objectives: To determine if macrophage binding by oral bacteria results in differential SR expression. Methods: Macrophage-differentiated THP-1 cells (10⁶/mL) were combined with each bacterial species at an MOI of 100 for one hour. mRNA was extracted and used to produce cDNA using random primers. The level of SR message was determined by quantitative RT-PCR using specific primer sets for each receptor (SuperArray). Results are expressed as fold increase compared to untreated controls.

Results:

	SR mRNA fold-increase compared to untreated controls (±SD)
	SRA-1	SRB-1	MSR-1	SR-PSOX	CD91
C.rectus	4.8±0.3	8.4±0.5	2.9±0.8	6.3±0.2	5.5±0.3
E.coli	0.7±0.1	2.0±0.5	1.1±0.3	0.5±0.1	3.2±0.2
P.gingivalis	0.3±0.1	3.5±0.6	0.7±0.2	1.3±0.4	2.5±0.3
S.gordonii	3.6±0.4	0.1±0.1	0.6±0.2	1.4±0.4	1.6±0.6

Conclusion: These results support the notion that oral bacteria can induce differential expression of SR mRNA. They also suggest that not all oral bacteria induce this gene expression equally. Interestingly, C.rectus, the only bacteria tested with an S-layer was the most active. Supported by NIH/NIDCR DE00017.