Background and aims: TLR9 deletion protects against steatohepatitis due to choline–amino acid depletion and high-fat diet. We measured TLR9 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 (Wt), appetite-dysregulated Alms1 mutant (foz/foz), Tlr9−/−, and Tlr9−/−.foz/foz 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 TLR9 and TLR4 mRNA were increased in human NASH but not simple steatosis, and in Ath-fed foz/foz mice with metabolic syndrome-related NASH. Ath-fed Tlr9−/− mice showed simple steatosis and less Th1 cytokines than Wt. Tlr9−/−.foz/foz mice were obese and diabetic, but necroinflammatory changes were less severe than Tlr9+/+.foz/foz mice. TLR9-expressing myeloid cells were critical for Th1 cytokine production in BM chimeras. BM macrophages from Tlr9−/− mice showed M2 polarization, were resistant to M1 activation by necrotic hepatocytes/other pro-inflammatory triggers, and provoked less neutrophil chemotaxis than Wt. Livers from Ath-fed Tlr9−/− 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 Wt, 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.
TLR9 is up-regulated in human and murine NASH: pivotal role in inflammatory recruitment and cell survival
Auvro R. Mridha, Fahrettin Haczeyni, Matthew M. Yeh, W. Geoffrey Haigh, George N. Ioannou, Vanessa Barn, Hussam Ajamieh, Leon Adams, Jeffrey M. Hamdorf, Narci C. Teoh, Geoffrey C. Farrell; TLR9 is up-regulated in human and murine NASH: pivotal role in inflammatory recruitment and cell survival. Clin Sci (Lond) 15 August 2017; 131 (16): 2145–2159. doi: https://doi.org/10.1042/CS20160838
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