Association of circulating MtDNA with CVD in hemodialysis patients: involvement of MtDNA-induced cardiac microvascular inflammation

Abstract

Background Previous studies have shown a role of mitochondrial DNA (MtDNA) in innate immunity. However, the specific role of MtDNA in chronic kidney disease (CKD)-related cardiovascular disease (CVD) remains elusive. This study was designed to investigate the potential relationship between circulating MtDNA and CVD in maintenance hemodialysis (MHD) patients, and to examine the damaging effect of exogenous MtDNA on cardiac microvascular endothelial cells (CMECs) in the uremic milieu. Methods Forty-two MHD patients and 36 health controls were enrolled in this study. Plasma cell-free MtDNA was detected by TaqMan-based qPCR assay. The CVD risk markers including high-sensitive C-reactive protein (Hs-CRP), monocyte chemoattractant protein-1 (MCP-1), fibrinogen, and erythrocyte sedimentation rate (ESR) were measured by using standard assays. The ten-year cardiovascular risk was assessed using the framingham risk score (FRS). Dialysis systems in MHD patients were used to evaluate the effect of different dialysis modes on the clearance of circulating MtDNA. In vitro study, human cardiac microvascular endothelial cells (HCMECs) were incubated with normal or uremic serum with or without exogenous MtDNA stimulation. Intracellular toll-like receptor 9 (TLR9), adhesion molecule 1 (ICAM-1), MCP-1 and tumor necrosis factor-α (TNF-α) mRNA levels and cytosolic MtDNA contents were detected by qPCR. Results Plasma MtDNA was significantly elevated in patients with MHD relative to healthy controls. The MHD patients were subsequently classified into two groups based on the median value of MtDNA. In stratified analyses, the levels of Hs-CRP and MCP-l, and FRS in the high plasma MtDNA group were higher than those in the low plasma MtDNA group. In vitro study, exogenous MtDNA aggravated uremic serum-induced upregulation of ICAM-1 and TNF-α in HCMECs. Also, the addition of MtDNA to the medium resulted in increased cytosolic MtDNA amounts and TLR9 mRNA levels in uremic serum-treated cells. Single routine hemodialysis and hemodiafiltration could partially reduce plasma MtDNA in MHD patients. These two methods seem similar in terms of MtDNA clearance. Conclusions We concluded that MtDNA released into the circulation under the uremic toxin environment may has a detrimental effect on cardiovascular system through aggravating microvascular inflammation, and that reducing circulating MtDNA might be a future therapeutic strategy for the prevention of MHD-related CVD.