LPS-Induced Endotoxemia Evokes Epigenetic Alterations in Mitochondrial DNA That Impacts Inflammatory Response

Abstract

Mitochondrial DNA (mtDNA) plays a vital role as a damage-associated molecular pattern in sepsis being able to shape the immune response. Since pathogen recognition receptors of innate immune cells are activated by demethylated DNA only, we set out to investigate the amount of DNA methyltransferase 1 (DNMT1) in mitochondria and the extent of mtDNA methylation in a human endotoxin model. Peripheral blood mononuclear cells of 20 healthy individuals were isolated from whole blood and stimulated with lipopolysaccharide (LPS) for 48 h. Subsequently, DNMT1 protein abundance was assessed in whole cells and a mitochondrial fraction. At the same time, methylation levels of mtDNA were quantified, and cytokine expression in the supernatant was measured. Despite increased cellular expression of DNMT1 after LPS stimulation, the degree of mtDNA methylation slightly decreased. Strikingly the mitochondrial protein abundance of DNMT1 was reduced by 50% in line with the lower degree of mtDNA methylation. Although only modest alterations were seen in the degree of mtDNA methylation, these strongly correlated with IL-6 and IL-10 expression. Our data may hint at a protein import problem for DNMT1 into the mitochondria under LPS stimulation and suggest a role of demethylated mtDNA in the regulation of the inflammatory immune response.

Mitochondrial DNA Methylation and Human Diseases

“…Global 5-mC and 5-hmC mtDNA content Global hypomethylation of mtDNA in fructose-fed rats as well as higher mtDNA content and transcription of several mtDNA genes [116] It has been reported that mtDNA methylation is modulated by exposure to particulate matter (PM 1 and PM 2.5 ), air benzene, traffic-derived elemental carbon [56,108,113], particle-containing welding fumes [120], endocrine disruptors [109], maternal smoking [112,118,129], chrome [117], arsenic [59] and iron [121], as well as to the pharmacological agent valproic acid [51], to the demethylating agents 5-azacytidine and vitamin C [70,122] and to HIV infection and cocaine [125]. Variations in mtDNA methylation patterns have also been associated with various endogenous metabolites, including thyroid hormones [119], homocysteine [114,126], betaine [110], glucose [79,80], L-carnitine [124], lipopolysaccharides [127] and mitochondrial-derived peptides [123]. Moreover, nutrients from the diet, including lipids and fructose, were also able to modulate mtDNA methylation levels in animal models [111,115,116].…”

“…However, several other studies that have carefully followed the necessary precautions for the study of mtDNA methylation, or that used techniques for which bisulfite treatment was not necessary, successfully identified the presence of methylation in the mitochondrial genome [ 61 , 73 , 84 , 110 , 127 , 137 ]. For example, Patil and co-workers performed a whole-genome bisulfite sequencing after linearization of mtDNA, finding a higher degree and frequency of methylation, particularly in the L-strand when compared to the H-strand in various human cell cultures [ 61 ].…”

Succinate mediates inflammation-induced adrenocortical dysfunction

“…In specific, we demonstrate that IL-1β reduces SDHB expression through DNMT1-dependent DNA methylation of the SDHB promoter. Several studies have shown that inflammation promotes DNA methylation and thereby regulates gene expression [62–66]. Particularly IL-1β was demonstrated to increase DNA methylation in different genes in a cell type-specific manner [63,67].…”

Hypomethylation of AHRR (cg05575921) Is Related to Smoking Status in the Mexican Mestizo Population

“…It should be noted that the studies shown in Figure 5 employed bisulfite conversion to determine the methylation level, and in the present study, we used a technique without this conversion because it was previously reported that incomplete bisulfite conversion can introduce artifacts [53]; however, despite the different techniques used to assess the level of methylation, hypomethylation was found to exist only in subjects with cigarette consumption.…”