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A high-fat diet and regulatory T cells influence susceptibility to endotoxin-induced liver injury
Xiong Ma 1 4, Jing Hua 1 4, Abdiaziz R. Mohamood 2, Abdel Rahmin A. Hamad 2, Rajani Ravi 3, Zhiping Li 1 4 *
1Department of Gastroenterology, Renji Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai Institute of Digestive Disease, Shanghai, China
2Department of Pathology, Johns Hopkins University, Baltimore, MD
3Department of Oncology, Johns Hopkins University, Baltimore, MD
4Department of Medicine, Johns Hopkins University, Baltimore, MD
email: Zhiping Li (
*Correspondence to Zhiping Li, Johns Hopkins University, 912 Ross Building, 720 Rutland Avenue, Baltimore, MD 21205
Potential conflict of interest: Nothing to report.
fax: 410-955-9677.
Funded by:
American Gastroenterological Association Fellowship/Faculty Transition Award
American Gastroenterological Association Roche Research Scholar Award in Liver Diseases
Shanghai Leading Academic Discipline Project; Grant Number: Y0205
National Natural Science Foundation of China; Grant Number: 30571730
Hopkins Digestive Disease Basic Research Development Center; Grant Number: R24DK064388-04
Abstract
In nonalcoholic fatty liver disease, the pathogenesis of progression from simple steatosis to steatohepatitis has not been fully clarified. Many factors, including oxidative stress and hepatic immune regulation, contribute to the inflammation in steatosis. Because regulatory T cells (Tregs) are important components of immune regulation, we have now investigated their role in the pathogenesis of nonalcoholic steatohepatitis. Wild-type C57BL/6 mice were fed a high-fat (HF) diet to induce steatosis, and the hepatic lymphocyte population was analyzed by flow cytometry. HF-induced steatosis was associated with the depletion of hepatic Tregs and led to up-regulation of the inflammatory tumor necrosis factor- signaling pathway. When challenged by exogenous lipopolysaccharide, the HF-fed mice developed liver inflammation. In contrast, the adoptive transfer of Tregs decreased inflammation in HF-fed mice. In comparison with effector T cells, Tregs had a lower expression of Bcl-2 and, therefore, increased susceptibility to oxidative stress-induced apoptosis. The treatment of mice with the antioxidant Mn(III)tetrakis(4-benzoic acid)porphyrin chloride reduced Treg apoptosis, increased the number of hepatic Tregs, and decreased hepatic inflammation in HF-fed mice. Conclusion: Our results indicate that increased oxidative stress in a fatty liver causes the apoptosis of Tregs, reduces the number of hepatic Tregs, and leads to a lowered suppression of inflammatory responses. This scenario is likely one of the pathogenetic mechanisms that facilitate the transformation of simple steatosis into steatohepatitis when a fatty liver is exposed to second or third hits. (HEPATOLOGY 2007.)
