Inhibition of natural killer cells protects the liver against acute injury in the absence of glycine N-methyltransferase.

Gomez-Santos L, Luka Z, Wagner C, Fernandez-Alvarez S, Lu SC, Mato JM, Martinez-Chantar ML, Beraza N
Hepatology. 2012 56 (2): 747-59

PMID: 22392635 · PMCID: PMC3378767 · DOI:10.1002/hep.25694

UNLABELLED - Glycine N-methyltransferase (GNMT) catabolizes S-adenosylmethionine (SAMe), the main methyl donor of the body. Patients with cirrhosis show attenuated GNMT expression, which is absent in hepatocellular carcinoma (HCC) samples. GNMT(-/-) mice develop spontaneous steatosis that progresses to steatohepatitis, cirrhosis, and HCC. The liver is highly enriched with innate immune cells and plays a key role in the body's host defense and in the regulation of inflammation. Chronic inflammation is the major hallmark of nonalcoholic steatohepatitis (NASH) progression. The aim of our study was to uncover the molecular mechanisms leading to liver chronic inflammation in the absence of GNMT, focusing on the implication of natural killer (NK) / natural killer T (NKT) cells. We found increased expression of T helper (Th)1- over Th2-related cytokines, tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL)-R2/DR5, and several ligands of NK cells in GNMT(-/-) livers. Interestingly, NK cells from GNMT(-/-) mice were spontaneously activated, expressed more TRAIL, and had strong cytotoxic activity, suggesting their contribution to the proinflammatory environment in the liver. Accordingly, NK cells mediated hypersensitivity to concanavalin A (ConA)-mediated hepatitis in GNMT(-/-) mice. Moreover, GNMT(-/-) mice were hypersensitive to endotoxin-mediated liver injury. NK cell depletion and adoptive transfer of TRAIL(-/-) liver-NK cells protected the liver against lipopolysaccharide (LPS) liver damage.

CONCLUSION - Our data allow us to conclude that TRAIL-producing NK cells actively contribute to promote a proinflammatory environment at early stages of fatty liver disease, suggesting that this cell compartment may contribute to the progression of NASH.

Copyright © 2012 American Association for the Study of Liver Diseases.

MeSH Terms (17)

Acute Disease Adoptive Transfer Animals Apoptosis Chemical and Drug Induced Liver Injury Concanavalin A Disease Models, Animal Fatty Liver Glycine N-Methyltransferase Killer Cells, Natural Lipopolysaccharides Lymphocyte Depletion Male Mice Mice, Knockout Mitogens TNF-Related Apoptosis-Inducing Ligand

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