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.

中文翻译：

---

LPS 诱导的内毒素血症引起线粒体 DNA 的表观遗传改变，从而影响炎症反应


线粒体 DNA (mtDNA) 作为败血症中损伤相关的分子模式发挥着至关重要的作用，能够塑造免疫反应。由于先天免疫细胞的病原体识别受体仅由去甲基化 DNA 激活，因此我们着手研究线粒体中 DNA 甲基转移酶 1 (DNMT1) 的量以及人内毒素模型中 mtDNA 甲基化的程度。从全血中分离出 20 名健康个体的外周血单核细胞，并用脂多糖 (LPS) 刺激 48 小时。随后，评估了全细胞和线粒体部分中的 DNMT1 蛋白丰度。同时，对线粒体DNA的甲基化水平进行定量，并测量上清液中细胞因子的表达。尽管 LPS 刺激后 DNMT1 的细胞表达增加，但线粒体 DNA 甲基化程度略有下降。引人注目的是，DNMT1 的线粒体蛋白丰度降低了 50%，与 mtDNA 甲基化程度较低相一致。尽管 mtDNA 甲基化程度仅发生适度变化，但这些变化与 IL-6 和 IL-10 表达密切相关。我们的数据可能暗示在 LPS 刺激下 DNMT1 进入线粒体的蛋白质输入问题，并表明去甲基化 mtDNA 在调节炎症免疫反应中的作用。