Cigarette smoke induces mitochondrial DNA damage and activates cGAS-STING pathway: application to a biomarker for atherosclerosis

Abstract

Cigarette smoking is a major risk factor for atherosclerosis. We previously reported that DNA damage was accumulated in atherosclerotic plaque, and was increased in human mononuclear cells by smoking. As vascular endothelial cells are known to modulate inflammation, we investigated the mechanism by which smoking activates innate immunity in endothelial cells focusing on DNA damage. Further, we sought to characterize the plasma level of cell-free DNA (cfDNA), a result of mitochondrial and/or genomic DNA damage, as a biomarker for atherosclerosis. Cigarette smoke extract (CSE) increased DNA damage in the nucleus and mitochondria in human endothelial cells. Mitochondrial damage induced minority mitochondrial outer membrane permeabilization, which was insufficient for cell death but instead led to nuclear DNA damage. DNA fragments, derived from the nucleus and mitochondria, were accumulated in the cytosol, and caused a persistent increase in IL-6 mRNA expression via the cGAS-STING pathway. cfDNA, quantified with quantitative PCR in culture medium was increased by CSE. Consistent with in vitro results, plasma mitochondrial cfDNA (mt-cfDNA) and nuclear cfDNA (n-cfDNA) were increased in young healthy smokers compared to age-matched non-smokers. Additionally, both mt-cfDNA and n-cfDNA were significantly increased in patients with atherosclerosis compared to the normal controls. Our multivariate analysis revealed that only mt-cfDNA predicted the risk of atherosclerosis. In conclusion, accumulated cytosolic DNA caused by cigarette smoke and the resultant activation of the cGAS-STING pathway may be a mechanism of atherosclerosis development. The plasma level of mt-cfDNA, possibly as a result of DNA damage, may be a useful biomarker for atherosclerosis.

Exploring mitochondrial DNA copy number in circulating cell‐free DNA and extracellular vesicles across cardiovascular health status: A prospective case–control pilot study

“…Wiersma et al 69 showed increased levels of ccf-mtDNAcn in paroxysmal atrial fibrillation (N = 100) but reduced levels in persistent atrial fibrillation (N = 116) and longstandingpersistent atrial fibrillation (N = 20) compared to controls (N = 84). Ueda et al 70 measured higher levels of both ccf-mtDNAcn and ccf-nDNAcn in patients with atherosclerotic plaques (N = 62) than controls (N = 21). Only Ye et al 39 selectively investigated the plasma exosomesderived mtDNA (by droplet digital PCR), showing that both the plasma exosome particle numbers and the exosomal mtDNAcn were elevated in chronic heart failure patients (N = 20) compared to controls (N = 20).…”

The cGAS-STING pathway in cardiovascular diseases: from basic research to clinical perspectives

“…Smoking is an important underlying trigger for CVD development, and cardiovascular vigilance will need to be a permanent concern in the coming decades. Ueda et al [ 75 ] found increased levels of free DNA in the serum of AS patients in a smoking population, and overexpression of free DNA was also detected in AS plaques, which activated the cGAS-STING pathway and became a AS marker. Clinical and experimental data suggest that cigarette smoking and secondhand smoke are equally detrimental in CVDs such as coronary artery disease, hypertension, and cardiac systolic and diastolic abnormalities.…”

Circulating cell-free DNA and its association with cardiovascular disease: what we know and future perspectives

“…More specifically, decreased cfDNA levels have been associated with a higher ratio of 18 : 2 linoleic acid to total fatty acids considered antiatherogenic [33]. Very little is published on the relationship of smoking and cfDNA; however, cfDNA may be increased in young healthy smokers compared to age-matched nonsmokers [34]. Furthermore cfDNA, including cell-free mitochondrial DNA (cf-mtDNA), has been reported higher in patients with atherosclerotic plaques compared to patients without atherosclerotic plaques [34].…”