P620Alterations in cardiac levels and activities of toll-like receptor 9 and circulating levels of it's putative ligand, mitochondrial DNA, in human heart failure. (15th July 2014) - Holmen, Y D
Abstract: Background: Experimental studies have shown a central role for Toll-like receptor 9 (TLR9) in the pathogenesis of heart failure (HF). There is also evidence that mitochondrial DNA (mtDNA) not confined within the mitochondrion may act as a TLR9 ligand. However, it is unknown whether these findings also have a human correlate. Methods: Plasma from patients with ischemic or non-ischemic HF (n=86), as well as plasma from age and gender matched controls were analyzed for mtDNA by qPCR. Tissue from the left ventricular apical region was collected upon implantation of a Left Ventricular Assist Device (LVAD) in patients with end-stage HF. Upon heart transplantation of these patients, apical cardiac tissue was harvested from the explanted hearts. RNA and protein were isolated from these samples for subsequent analyses of TLR9 mRNA and protein expression. The antibody used for TLR9 immunoblot analyses was targeted against non-activated (non-cleaved) TLR9 and could therefore be used as an indirect marker for activated TLR9 receptors. Results: We found increased circulating levels of mtDNA in patients with symptomatic HF compared with controls (p=0.003). Higher level of mtDNA was found in plasma from symptomatic HF patients (NYHA III and IV, p=0.01) compared with asymptomatic patients (NYHA I and II, p=0.06). In cardiac tissue from patients treated with LVAD there was a reduction of TLR9 mRNA expression upon treatment with LVAD (Fig 1, p= 0.002). Reduced endogenous TLR9 activation was confirmed in the same samples as a higher level of non-cleaved receptor was shown after LVAD treatment. Conclusion: Human HF is associated with increased cardiac TLR9. Furthermore, the TLR9 ligand, mtDNA, is increased within the circulation of HF patients. These data suggest a pathophysiological role for TLR9 in human HF.