Hepatocyte mitochondrial DNA drives nonalcoholic steatohepatitis by activation of TLR9

Abstract

Nonalcoholic steatohepatitis (NASH) is the most common liver disease in industrialized countries. NASH is a progressive disease that can lead to cirrhosis, cancer, and death, and there are currently no approved therapies. The development of NASH in animal models requires intact TLR9, but how the TLR9 pathway is activated in NASH is not clear. Our objectives in this study were to identify NASH-associated ligands for TLR9, establish the cellular requirement for TLR9, and evaluate the role of obesity-induced changes in TLR9 pathway activation. We demonstrated that plasma from mice and patients with NASH contains high levels of mitochondrial DNA (mtDNA) and intact mitochondria and has the ability to activate TLR9. Most of the plasma mtDNA was contained in microparticles (MPs) of hepatocyte origin, and removal of these MPs from plasma resulted in a substantial decrease in TLR9 activation capacity. In mice, NASH development in response to a high-fat diet required TLR9 on lysozyme-expressing cells, and a clinically applicable TLR9 antagonist blocked the development of NASH when given prophylactically and therapeutically. These data demonstrate that activation of the TLR9 pathway provides a link between the key metabolic and inflammatory phenotypes in NASH.

Mitochondrial DNA–enriched microparticles promote acute-on-chronic alcoholic neutrophilia and hepatotoxicity

“…As illustrated in Figure 1, A and B, the serum levels of particles were higher in EAU + RD patients compared with those in controls and EAU -RD. A previous study reported the presence of plasma mtDNA within MPs in mice and patients with nonalcoholic steatohepatitis (18). We therefore purified exosomes and MPs from human sera and examined whether mtDNA is located either in the MPs or exosomes in these subjects.…”

“…Circulating mtDNA levels were elevated and contributed to the pathogenesis of NASH by activating macrophages (18). It is possible that the elevation of mtDNA-enriched MPs in our E10d + 1B model also promotes macrophage activation and likely hepatic inflammation.…”

“…Human sera were centrifuged at 3,000 g for 30 minutes to remove cell debris and then at 15,000 g for 30 minutes at 4°C to pellet MPs as previously described (18). The supernatant was added to the appropriate volume of ExoQuick Exosome precipitation solution (catalog EXOQ5A-1, System Biosciences).…”

“…Blockage of the CXCL1 receptor CXCR1/2 ameliorated alcoholic steatohepatitis in mice (14). In addition to chemokines, extracellular vesicles (EVs) are new players in cellto-cell communication and play an important role in promoting inflammation and neutrophil infiltration in a variety of diseases (15,16), including liver diseases (17)(18)(19)(20)(21)(22)(23)(24)(25). EVs are nanometer-sized, membrane-bound extracellular milieu vesicles derived from cells (17).…”

“…The functions of EVs are mediated by delivering their contents from one cell to another. For example, stressed hepatocytes can activate macrophages via the release of EVs that contain lipids, proteins, chemokines, and nucleic acids (e.g., mitochondrial DNA [mtDNA]) (17)(18)(19)(20)(21)(22)(23)(24)(25). However, whether EVs also contribute to the elevation of circulating and hepatic neutrophils induced by acute-on-chronic alcoholic liver injury in human and mice remains unknown.…”