Cell Mol Gastroenterol Hepatol. 2021 Sep 07. pii: S2352-345X(21)00186-7. [Epub ahead of print]
BACKGROUND & AIMS: Hepatic immune microenvironment plays a pivotal role in the development of non-alcoholic steatohepatitis (NASH). However, the role of natural killer cells (NK cells), accounting for 10-20% of liver lymphocytes, in NASH is still unclear. In this study, we aim to investigate the functional significance of NK cells in NASH evolution.
METHODS: NASH was induced in mice fed methionine- and choline-deficient diet (MCD), choline-deficient high fat diet (CD-HFD) or high fat diet (HFD) with streptozotocin injection (STAMTM model). NK cell deficient mice (Nfil3-/-) and neutralization antibody (PK136) were used in this study.
RESULTS: Activated liver NK cells were identified with increased expression of NKG2D, CD107a, IFN-γ but decreased inhibitory NKG2A. With NK cell deficiency Nfil3-/- mice, the absence of NK cells ameliorated both MCD- and CDHF- induced NASH development with significantly decreased hepatic triglycerides, peroxides, serum ALT and AST compared to Nfil3+/+ mice. Further molecular analysis unveiled suppressed pro-inflammatory cytokines and associated signaling. Mechanistically, NK cells isolated from NASH liver secreted higher levels of pro-inflammatory cytokines (IFN-γ, IL-1β, IL-12, CCL4, CCL5 and GM-CSF), which could activate hepatic JAK-STAT1/3 and NF-κB signaling and induce hepatocytes damage evidenced by elevated ROS and apoptosis rate. Moreover, neutralization antibody PK136-dependent NK cells depletion can significantly alleviate MCD induced steatohepatitis with suppressed cytokine levels and JAK-STAT1/3 activity.
CONCLUSION: NK cells in NASH liver are activated with a more pro-inflammatory cytokine milieu, and promote NASH development via cytokine-JAK-STAT1/3 axis. Modulation of NK cells provides a potential therapeutic strategy for NASH.
Keywords: JAK/STAT; cytokine; natural killer cell; nonalcoholic steatohepatitis