TOLL-LIKE RECEPTOR 9 REGULATION OF COAGULATION IN ACUTE CORONARY ARTERY DISEASE


Janos G. Filep, M.D., Maisonneuve-Rosemont Hospital, Montreal, Quebec, Canada

Bacteriemia has recently been reported to be associated with increased risk of acute coronary artery disease and stroke. Bacterial DNA containing unmethyled CpG dinucleotide motifs is potent inducer of immune responses predominantly through Toll-like receptor 9 (TLR9). Bacterial DNA has been detected in atherosclerotic plaques in human coronary arteries and can persist in tissues and contribute to ongoing inflammation even in the absence of bacteria. Endothelial cells of human atherosclerotic plaques express TLR9. Human coronary artery cells (HCAEC) constitutively express TLR9 intracellularly, but not on the cell surface. Bacterial DNA, but not eukaryotic DNA, evoked concentration-dependent increases in the expression of tissue factor (TF), a key initiator of coagulation. Bacterial DNA enhanced TF gene transcription through induction of NF-êB and increased TF activity on the surface of HCAEC. Furthermore, bacterial DNA attenuated transcription of tissue factor pathway inhibitor (TFPI), reduced intracellular TFPI level and TFPI activity of the cell surface. Pharmacological blockade with telomere-derived TLR9 inhibitory oligodeoxynucleotide or transient knockdown of TLR9 with siRNA markedly attenuated HCAEC response to bacterial DNA. Methylation of cytosines in CpG motifs in bacterial DNA resulted in complete loss of activity on HCAEC, lending additional support for involvement of TLR9. Our results provide a novel mechanism by which bacterial DNA may contribute to a hypercoagulable state in the coronary circulation. These results also identify TLR9 inhibitory oligonucleotides as potential therapeutic agents for the prevention of coagulation in acute coronary artery disease where bacterial DNA may abundantly be present.
(Supported by grant MOP-97742 from the Canadian Institutes of Health Research).