Changes in a variety of T cells in the liver and visceral adipose tissue play a key role in the pathogenesis of nonalcoholic steatohepatitis, according to the results of a murine study.
Mikhaïl A. Van Herck, of the University of Antwerp (Belgium), and associates fed 8-week old mice a high-fat, high-fructose diet for 20 weeks, and then switched the mice to standard mouse chow for 12 weeks. The high-fat, high-fructose diet induced the metabolic syndrome and nonalcoholic steatohepatitis (NASH), accompanied by shifts in T cells. Interleukin-17–producing (Th17 cells increased in the liver, visceral adipose tissue, and blood, while regulatory T cells decreased in visceral adipose tissue, and cytotoxic T (Tc) cells rose in visceral adipose tissue while dropping in the blood and spleen.
These are “important immune disruptions,” the researchers wrote in Cellular and Molecular Gastroenterology and Hepatology. “In particular, visceral adipose tissue Tc cells are critically involved in NASH pathogenesis, linking adipose tissue inflammation to liver disease.”
After the mice were switched from the high-fat, high-fructose diet to standard mouse chow, their body weight, body fat, and plasma cholesterol significantly decreased and their glucose tolerance and insulin sensitivity improved to resemble the metrics of mice fed standard mouse chow throughout the study. Mice who underwent diet reversal also had significantly decreased liver weight and levels of plasma ALT, compared with mice that remained on the high-fat, high-fructose diet. Diet reversal also improved liver histology (nonalcoholic fatty liver disease activity scores), compared with the high-fat, high-fructose diet, the researchers wrote. “Importantly, the NASH was not significantly different between diet-reversal mice and mice fed the control diet for 32 weeks.”
Genetic tests supported these findings. On multiplex RNA analysis, hepatic expression of Acta2, Col1a1, and Col1a3 reverted to normal with diet reversal, indicating a normalization of hepatic collagen. Hepatic expression of the metabolic genes Ppara, Pparg, and Fgf21 also returned to normal, while visceral adipose tissue showed a decrease in Lep and Fgf21 expression and resolution of adipocyte hypertrophy.
However, diet reversal did not reverse inflammatory changes in T-cell subsets. Administering anti-CD8a antibodies after diet reversal decreased Tc cells in all tissue types that were tested, signifying “a biochemical and histologic attenuation of the high-fat, high-fructose diet-induced NASH,” the investigators wrote. Treating the mice with antibodies targeting IL-17A did not attenuate NASH but did reduce hepatic inflammation.
The fact that “the most pronounced effect” on NASH resulted from correcting immune disruption in visceral adipose tissue underscored “the immense importance of adipose tissue inflammation in [NASH] pathogenesis,” the researchers wrote. The finding that diet reversal alone did not reverse inflammation in hepatic or visceral adipose tissue “challeng[es] our current understanding of the reversibility of NASH and other obesity-related conditions.” They called for studies of underlying mechanisms as part of “the search for a medical treatment for NASH.”
Funders included the University Research Fund, University of Antwerp, and Research Foundation Flanders. The researchers reported having no conflicts of interest except that one coinvestigator is the chief science officer at Biocellvia, which performed some histologic analyses.
SOURCE: Van Herck MA et al. Cell Molec Gastroenterol Hepatol. 2020 Apr 20. doi: 10.1016/j.jcmgh.2020.04.010.
