1Chinese PLA General Hospital, Medical School of Chinese PLA, 100853 Beijing, China.
2Center for Cardiovascular Research and Alternative Medicine, University of Wyoming College of Health Sciences, Laramie, WY 82071 USA.
Signal Transduct Target Ther. 2019 Dec 6;4:56. doi: 10.1038/s41392-019-0094-1. eCollection 2019.
DNA-dependent protein kinase catalytic subunit (DNA-PKcs) is a novel housekeeper of hepatic mitochondrial homeostasis outside the DNA repair process. In this study, DNA-PKcs was upregulated in the livers of mice that were exposed to alcohol; the expression of DNA-PKcs positively correlated with hepatic steatosis, fibrosis, apoptosis, and mitochondrial damage. Functional studies revealed that liver-specific DNA-PKcs knockout (DNA-PKcs ) mice were protected from chronic ethanol-induced liver injury and mitochondrial damage. Mechanistic investigations established that DNA-PKcs promoted p53 activation, which elevated dynamin-related protein 1 (Drp1)-related mitochondrial fission but repressed FUN14 domain containing 1 (FUNDC1)-required mitophagy. Excessive fission and defective mitophagy triggered mtDNA damage, mitochondrial respiratory inhibition, mROS overproduction, cardiolipin oxidation, redox imbalance, calcium overload, and hepatic mitochondrial apoptosis. In contrast, the deletion of DNA-PKcs rescued these phenotypic alterations, which alleviated the susceptibility of hepatocytes to alcohol-induced cytotoxicity. Additionally, we also showed that orphan nuclear receptor subfamily 4 group A member 1 (NR4A1) was the upstream signal for DNA-PKcs activation and that the genetic ablation of NR4A1 ameliorated the progression of alcohol-related liver disease (ARLD); these results were similar to those obtained in DNA-PKcs knockout mice. Collectively, our results identified the NR4A1/DNA-PKcs/p53 axis as a novel signaling pathway responsible for ARLD pathogenesis that acts by activating Drp1-related mitochondrial fission and restricting FUNDC1-required mitophagy. The findings have potential implications for new approaches for ARLD therapy.
DNA 依赖性蛋白激酶催化亚基（DNA-PKcs）是一种新型的管家蛋白，在 DNA 修复过程之外维持肝线粒体的稳态。在本研究中，酒精暴露的小鼠肝脏中 DNA-PKcs 上调；DNA-PKcs 的表达与肝脂肪变性、纤维化、细胞凋亡和线粒体损伤呈正相关。功能研究表明，肝特异性 DNA-PKcs 敲除（DNA-PKcs ）小鼠可预防慢性乙醇诱导的肝损伤和线粒体损伤。机制研究表明，DNA-PKcs 促进 p53 激活，进而增加与 dynamin-related protein 1（Drp1）相关的线粒体裂变，但抑制 FUN14 结构域包含蛋白 1（FUNDC1）所需的线粒体自噬。过度的裂变和有缺陷的线粒体自噬会引发 mtDNA 损伤、线粒体呼吸抑制、mROS 过度产生、心磷脂氧化、氧化还原失衡、钙超载和肝线粒体凋亡。相反，DNA-PKcs 的缺失可挽救这些表型改变，从而减轻肝细胞对酒精诱导的细胞毒性的敏感性。此外，我们还发现孤儿核受体亚家族 4 组 A 成员 1（NR4A1）是 DNA-PKcs 激活的上游信号，而 NR4A1 的遗传缺失可改善酒精相关肝病（ARLD）的进展；这些结果与 DNA-PKcs 敲除小鼠的结果相似。综上所述，我们的研究结果确定了 NR4A1/DNA-PKcs/p53 轴作为一种新的信号通路，负责 ARLD 的发病机制，其作用方式是激活与 Drp1 相关的线粒体裂变，并限制 FUNDC1 所需的线粒体自噬。这些发现为 ARLD 的治疗提供了新的方法。
