Research ArticleGasdermin D plays a key role as a pyroptosis executor of non-alcoholic steatohepatitis in humans and mice
Graphical abstract
Introduction
Non-alcoholic fatty liver disease (NAFLD) represents a multi-step biological disorder in the liver, increasing the risk of cirrhosis and tumorigenesis.[1], [2] The key aspects of steatohepatitis have been precisely mimicked by extensive basic and translation research. This has enabled the reductionist assessment of genes and dietary factors involved in the pathogenesis of NAFLD.[3], [4] Toxic lipid accumulation in the liver acts as the primary insult which initiates and propagates damage, leading to hepatocyte injury and resultant inflammation.[5], [6] It is important to note that inflammation in the liver is believed to be the compelling feature that transforms simple steatosis to steatohepatitis, perpetuating hepatocellular injury and subsequent cell death, and promoting liver fibrosis.[7], [8], [9] However, the molecular basis behind the inflammatory response leading to steatohepatitis is still largely unknown.
Inflammatory caspases, including caspase-1, murine caspase-11, and human caspase-4/5, play important roles as mediators of inflammation.[10], [11], [12] Accumulating evidence has suggested that excessive activation of inflammatory caspases is implicated in the pathogenesis of hepatitis C viral infection, alcoholic liver disease and non-alcoholic steatohepatitis (NASH).13 Pyroptosis is the dominant response following the activation of inflammatory caspases, leading to pore formation in the plasma membrane, cell swelling, and massive release of the pro-inflammatory cellular contents.[12], [14], [15] Gasdermin D (GSDMD), a generic substrate for inflammatory caspases, has been shown to play a specific role in inflammatory caspase-mediated pyroptosis and also acts as a downstream effector of multiple inflammasomes.[16], [17] GSDMD exerts its pyroptosis executor function by releasing the cleaved gasdermin-N domain (GSDMD-N) that bears intrinsic pyroptosis-inducing activity and controls interleukin (IL)-1β release.[11], [18] As demonstrated by the crucial role of pyroptosis in immunity and disease, excessive uncontrolled pyroptosis may be detrimental to the host.[11], [12] Yet, despite these important functions, the potential effects of GSDMD and the mechanism of its action in steatohepatitis are still unknown. Moreover, no evidence is currently available on whether GSDMD-driven pyroptosis may represent a new avenue of therapeutic intervention for steatohepatitis. In this study, we investigated the significance of GSDMD in human and experimentally-induced NAFLD, particularly in steatohepatitis, and elucidated the pivotal role of GSDMD in steatohepatitis pathogenesis, by mediating lipogenesis and the amplification cascade of the nuclear factor-kappa B (NF-ĸB) signaling pathway. More importantly, we explored the clinical impact of GSDMD-N in patients with NASH, and demonstrated that GSDMD-N is positively correlated with the NAFLD activity score (NAS) and fibrosis, providing new insight into the potential treatment of NASH in humans.
Section snippets
Human samples
Human liver tissue samples of NAFLD/NASH were selected from bariatric surgery patients with no history of liver disease of other etiology from the Xijing Hospital, the Fourth Military Medical University. Histological assessments were determined by two pathologists in a double-blind manner.[19], [20] Samples from control individuals with normal liver histology were collected under percutaneous liver biopsy, from patients with no evidence of diabetes or hypertension. Patients with NAFLD were
Characteristics of the patient population
The main clinicopathological parameters of the patients evaluated in this study are described (Table S1). The histological characteristics of the patients are shown (Table S2). There were no statistically differences in age or gender between the three histological groups. Serum alkaline phosphatase (ALP), gamma glutamyl transpeptidase, and high-density lipoprotein cholesterol (HDL-C) levels did not differ statistically among the groups; whereas, serum alanine aminotransferase (ALT), aspartate
Discussion
The most important finding from this study is that GSDMD-induced pyroptosis was involved in human and murine steatohepatitis. Gsdmd−/− mice fed an MCD diet showed significantly reduced steatohepatitis compared with WT control mice fed with the same diet. Consistently, a noticeable improvement in liver inflammation, as well as a reduction in serum ALT levels and hepatic TG content, was observed in MCD-fed Gsdmd−/− mice. In addition, liver fibrosis was strongly attenuated in Gsdmd−/− mice after
Financial support
This work was supported by grants from National Natural Science Foundation of China (Nos. 81421003, 81730016, 81322037, 81572302, 81772650) and Independent Funds of the Key Laboratory (CBSKL2015Z12).
Conflict of interest
The authors have no conflicts to disclose.
Please refer to the accompanying ICMJE disclosure forms for further details.
Authors’ contributions
JL and KCW designed the experiments, supervised the study and revised the paper; FS commented on the study and provided the material support. BX, MZJ, YC and WJW completed the main experiments, wrote the first draft of the paper, prepared the figures and analyzed the data; DC and XWL helped with the main experiments; ZZ and DZ helped with the preparation of human samples; DMF and YZN helped with the experimental design and paper writing; All authors have reviewed the final version of the
Acknowledgements
We thank Professor Jun Yu, Xiang Zhang (Digestive Disease and The Department of Medicine and Therapeutics, The Chinese University of Hong Kong, Hong Kong) for recommendations for animal models and experimental design. We thank Professor Gang Ji and Professor Jianyong Zheng (Xijing Hospital, The Fourth Military Medical University, Xi’an, China) for the material support. We thank members of the State Key Laboratory of Cancer Biology & Institute of Digestive Diseases for helpful discussions and
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These authors contributed equally to this work.