TLR9 is up-regulated in human and murine NASH: pivotal role in inflammatory recruitment and cell survival.

UNLABELLED

Background and aims TLR9 deletion protects against steatohepatitis due to choline-amino acid depletion and high-fat diet. We measured in human non-alcoholic steatohepatitis (NASH) livers, and tested whether TLR9 mediates inflammatory recruitment in three murine models of non-alcoholic fatty liver disease (NAFLD). Methods We assayed TLR mRNA in liver biopsies from bariatric surgery patients. Wild-type (), appetite-dysregulated mutant , and C57BL6/J mice and bone marrow (BM) chimeras were fed 0.2% cholesterol, high-fat, high sucrose (atherogenic[Ath]) diet or chow, and NAFLD activity score (NAS)/NASH pathology, macrophage/neutrophil infiltration, cytokines/chemokines, and cell death markers measured in livers. Results Hepatic and mRNA were increased in human NASH but not simple steatosis, and in Ath-fed mice with metabolic syndrome-related NASH. Ath-fed mice showed simple steatosis and less Th1 cytokines than mice were obese and diabetic, but necroinflammatory changes were less severe than mice. TLR9-expressing myeloid cells were critical for Th1 cytokine production in BM chimeras. BM macrophages from mice showed M2 polarization, were resistant to M1 activation by necrotic hepatocytes/other pro-inflammatory triggers, and provoked less neutrophil chemotaxis than Livers from Ath-fed mice appeared to exhibit more markers of necroptosis [receptor interacting protein kinase (RIP)-1, RIP-3, and mixed lineage kinase domain-like protein (MLKL)] than , and ∼25% showed portal foci of mononuclear cells unrelated to NASH pathology.

CONCLUSION

Our novel clinical data and studies in overnutrition models, including those with diabetes and metabolic syndrome, clarify TLR9 as a pro-inflammatory trigger in NASH. This response is mediated via M1-macrophages and neutrophil chemotaxis.