Inflammatory processes are primary contributors to the development and progression of alcoholic steatohepatitis (ASH), with severe alcoholic hepatitis characterised by non-resolving inflammation. ...Inflammation in the progression of ASH is a complex response to microbial dysbiosis, loss of barrier integrity in the intestine, hepatocellular stress and death, as well as inter-organ crosstalk. Herein, we review the roles of multiple cell types that are involved in inflammation in ASH, including resident macrophages and infiltrating monocytes, as well as other cell types in the innate and adaptive immune system. In response to chronic, heavy alcohol exposure, hepatocytes themselves also contribute to the inflammatory process; hepatocytes express a large number of chemokines and inflammatory mediators and can also release damage-associated molecular patterns during injury and death. These cellular responses are mediated and accompanied by changes in the expression of pro- and anti-inflammatory cytokines and chemokines, as well as by signals which orchestrate the recruitment of immune cells and activation of the inflammatory process. Additional mechanisms for cell-cell and inter-organ communication in ASH are also reviewed, including the roles of extracellular vesicles and microRNAs, as well as inter-organ crosstalk. We highlight the concept that inflammation also plays an important role in promoting liver repair and controlling bacterial infection. Understanding the complex regulatory processes that are disrupted during the progression of ASH will likely lead to better targeted strategies for therapeutic interventions.
Nonalcoholic steatohepatitis (NASH) is associated with caspase activation. However, a role for pro-inflammatory caspases or inflammasomes has not been explored in diet-induced liver injury. Our aims ...were to examine the role of caspase-1 in high fat-induced NASH. C57BL/6 wild-type and caspase 1-knockout (Casp1(-/-)) mice were placed on a 12-week high fat diet. Wild-type mice on the high fat diet increased hepatic expression of pro-caspase-1 and IL-1β. Both wild-type and Casp1(-/-) mice on the high fat diet gained more weight than mice on a control diet. Hepatic steatosis and TG levels were increased in wild-type mice on high fat diet, but were attenuated in the absence of caspase-1. Plasma cholesterol and free fatty acids were elevated in wild-type, but not Casp1(-/-) mice, on high fat diet. ALT levels were elevated in both wild-type and Casp1(-/-) mice on high fat diet compared to control. Hepatic mRNA expression for genes associated with lipogenesis was lower in Casp1(-/-) mice on high fat diet compared to wild-type mice on high fat diet, while genes associated with fatty acid oxidation were not affected by diet or genotype. Hepatic Tnfα and Mcp-1 mRNA expression was increased in wild-type mice on high fat diet, but not in Casp1(-/-) mice on high fat diet. αSMA positive cells, Sirius red staining, and Col1α1 mRNA were increased in wild-type mice on high fat diet compared to control. Deficiency of caspase-1 prevented those increases. In summary, the absence of caspase-1 ameliorates the injurious effects of high fat diet-induced obesity on the liver. Specifically, mice deficient in caspase-1 are protected from high fat-induced hepatic steatosis, inflammation and early fibrogenesis. These data point to the inflammasome as an important therapeutic target for NASH.
Alcoholic liver disease (ALD) and nonalcoholic fatty liver disease (NAFLD) are the two major types of chronic liver disease worldwide. Inflammatory processes play key roles in the pathogeneses of ...fatty liver diseases, and continuous inflammation promotes the progression of alcoholic steatohepatitis (ASH) and nonalcoholic steatohepatitis (NASH). Although both ALD and NAFLD are closely related to inflammation, their respective developmental mechanisms differ to some extent. Here, we review the roles of multiple immunological mechanisms and therapeutic targets related to the inflammation associated with fatty liver diseases and the differences in the progression of ASH and NASH. Multiple cell types in the liver, including macrophages, neutrophils, other immune cell types and hepatocytes, are involved in fatty liver disease inflammation. In addition, microRNAs (miRNAs), extracellular vesicles (EVs), and complement also contribute to the inflammatory process, as does intertissue crosstalk between the liver and the intestine, adipose tissue, and the nervous system. We point out that inflammation also plays important roles in promoting liver repair and controlling bacterial infections. Understanding the complex regulatory process of disrupted homeostasis during the development of fatty liver diseases may lead to the development of improved targeted therapeutic intervention strategies.
Hepatocyte cell death via apoptosis and necrosis are major hallmarks of ethanol‐induced liver injury. However, inhibition of apoptosis is not sufficient to prevent ethanol‐induced hepatocyte injury ...or inflammation. Because receptor‐interacting protein kinase (RIP) 3–mediated necroptosis, a nonapoptotic cell death pathway, is implicated in a variety of pathological conditions, we tested the hypothesis that ethanol‐induced liver injury is RIP3‐dependent and RIP1‐independent. Increased expression of RIP3 was detected in livers of mice after chronic ethanol feeding, as well as in liver biopsies from patients with alcoholic liver disease. Chronic ethanol feeding failed to induce RIP3 in the livers of cytochrome P450 2E1 (CYP2E1)‐deficient mice, indicating CYP2E1‐mediated ethanol metabolism is critical for RIP3 expression in response to ethanol feeding. Mice lacking RIP3 were protected from ethanol‐induced steatosis, hepatocyte injury, and expression of proinflammatory cytokines. In contrast, RIP1 expression in mouse liver remained unchanged following ethanol feeding, and inhibition of RIP1 kinase by necrostatin‐1 did not attenuate ethanol‐induced hepatocyte injury. Ethanol‐induced apoptosis, assessed by terminal deoxynucleotidyl transferase–mediated deoxyuridine triphosphate nick‐end labeling–positive nuclei and accumulation of cytokeratin‐18 fragments in the liver, was independent of RIP3. Conclusion: CYP2E1‐dependent RIP3 expression induces hepatocyte necroptosis during ethanol feeding. Ethanol‐induced hepatocyte injury is RIP3‐dependent, but independent of RIP1 kinase activity; intervention of this pathway could be targeted as a potential therapeutic strategy. (HEPATOLOGY 2013)
Alcohol-associated liver disease (ALD), which ranges from mild disease to alcohol-associated hepatitis and cirrhosis, is the most prevalent type of chronic liver disease and a leading cause of ...morbidity and mortality worldwide. Accumulating evidence reveals that programmed cell death (PCD) plays a crucial role in progression of ALD involving crosstalk between hepatocytes and immune cells. Multiple pathways of PCD, including apoptosis, necroptosis, autophagy, pyroptosis and ferroptosis, are reported in ALD. Interestingly, PCD pathways are intimately linked and interdependent, making it difficult to therapeutically target a single pathway. This review clarifies the multiple types of PCD occurring in liver and focuses on crosstalk between hepatocytes and innate immune cells in ALD.
Background and Aim
Impaired gut‐liver axis is a potential factor contributing to alcoholic liver disease. Ethanol depletes intestinal integrity and causes gut dysbiosis. Butyrate, a fermentation ...byproduct of gut microbiota, is altered negatively following chronic ethanol exposure. This study aimed to determine whether prophylactic tributyrin could protect the intestinal barrier and liver in mice during combined chronic‐binge ethanol exposure.
Methods
C57BL/6J mice exposed to 5% v/v ethanol‐containing diet for 10 days received a single ethanol gavage (5 g/kg) 9 h before euthanasia. Control mice were isocalorically pair‐fed maltose dextrin for ethanol. Diets were supplemented (5 mM) with tributyrin or glycerol. Intestine and liver disease activity was assessed histologically. Protein and mRNA expression of tight junction (TJ) proteins, toll‐like receptors, and tumor necrosis factor‐alpha were assessed. Caco‐2 monolayers with or without ethanol exposure and/or sodium butyrate were used to test butyrate's direct effects on intestinal integrity.
Results
Chronic‐binge ethanol feeding impaired intestinal TJ protein co‐localization staining; however, tributyrin co‐treatment mitigated these effects. Ethanol depleted TJ and transepithelial electrical resistance in Caco‐2 monolayers, but butyrate co‐treatment reduced these effects. Hepatic toll‐like receptor mRNA expression and tumor necrosis factor‐alpha protein expression was induced by ethanol; however, the response was significantly dampened in mice co‐treated with tributyrin. Tributyrin altered localization of both neutrophils and single hepatocyte death: Leukocytes and apoptotic hepatocytes localized predominantly around the portal tract in ethanol‐only treated mice, whereas localization predominated around the central vein in ethanol‐tributyrin mice.
Conclusions
Prophylactic tributyrin supplementation mitigated effects of combined chronic‐binge ethanol exposure on disruption of intestinal TJ localization and intestinal permeability and liver injury.
Macroautophagy/autophagy is critical in maintaining cellular functions and homeostasis. Dynamic regulation of autophagy is associated with development of nonalcoholic fatty liver disease (NAFLD) and ...nonalcoholic steatohepatitis (NASH); however, the mechanisms involved in the regulation of autophagy in NAFLD/NASH are not well understood. Here we discuss our recent work identifying MLKL as an important nexus between autophagy and necroptosis in models of NAFLD/NASH. Mlkl, but not Ripk3, deficiency protects mice from Western diet-induced liver injury. Mlkl deficiency also prevents the accumulation of SQSTM1/p62 and LC3-II in liver in response to Western diet feeding or challenge with the protease inhibitor leupeptin. Western diet increases expression, phosphorylation and oligomerization of MLKL. In hepatocytes, palmitic acid (PA) induces the expression and translocation of MLKL to autophagosomes prior to the plasma membrane. Importantly, Mlkl, but not Ripk3, deficiency prevents the inhibition of autophagy by PA or chloroquine in hepatocytes. In contrast, overexpression of Mlkl blocks autophagic flux. Importantly, inhibition of autophagy by leupeptin or chloroquine triggers MLKL translocation to the plasma membrane, suggesting that MLKL is intimately involved in the regulation of autophagy under multiple conditions. These data indicate that MLKL contributes to Western diet-induced liver injury through inhibition of autophagy and induction of necroptosis.
Background and Aims
Acute liver damage causes hepatocyte stress and death, but in chronic liver disease impaired hepatocyte regeneration and immune cell infiltration prevents recovery. While the ...roles of both impaired liver regeneration and immune infiltration have been studied extensively in chronic liver diseases, the differential contribution of these factors is difficult to assess.
Approach and Results
We combined single‐cell RNA‐sequencing (RNA‐seq) data from healthy livers and peripheral immune cells to measure cell proportions in chronic liver diseases. Using bulk RNA‐seq data from patients with early alcohol‐associated hepatitis, severe AH (sAH), HCV, HCV with cirrhosis, and NAFLD, we performed gene deconvolution to predict the contribution of different cell types in each disease. Patients with sAH had the greatest change in cell composition, with increases in both periportal hepatocytes and cholangiocyte populations. Interestingly, while central vein hepatocytes were decreased, central vein endothelial cells were expanded. Endothelial cells are thought to regulate liver regeneration through WNT signaling. WNT2, important in central vein hepatocyte development, was down in sAH, while multiple other WNTs and WNT receptors were up‐regulated. Immunohistochemistry revealed up‐regulation of FZD6, a noncanonical WNT receptor, in hepatocytes in sAH. Immune cell populations also differed in disease. In sAH, a specific group of inflammatory macrophages was increased and distinct from the macrophage population in patients with HCV. Network and correlation analyses revealed that changes in the cell types in the liver were highly correlated with clinical liver function tests.
Conclusions
These results identify distinct changes in the liver cell populations in chronic liver disease and illustrate the power of using single‐cell RNA‐seq data from a limited number of samples in understanding multiple different diseases.
Necroptosis, a programmed cell death mechanism distinct from apoptosis, has garnered attention for its role in various pathological conditions. While initially recognized for its involvement in cell ...death, recent research has revealed that key necroptotic mediators, including receptor-interacting protein kinases (RIPKs) and mixed lineage kinase domain-like protein (MLKL), possess additional functions that go beyond inducing cell demise. These functions encompass influencing critical aspects of metabolic regulation, such as energy metabolism, glucose homeostasis, and lipid metabolism. Dysregulated necroptosis has been implicated in metabolic diseases, including obesity, diabetes, metabolic dysfunction-associated steatotic liver disease (MASLD) and alcohol-associated liver disease (ALD), contributing to chronic inflammation and tissue damage. This review provides insight into the multifaceted role of necroptosis, encompassing both cell death and these extra-necroptotic functions, in the context of metabolic diseases. Understanding this intricate interplay is crucial for developing targeted therapeutic strategies in diseases that currently lack effective treatments.
This review discusses the different roles of necroptosis, including both cell death and extra-necroptotic functions, in the context of metabolic diseases.
Long non-coding RNAs (lncRNAs) are a large and diverse class of RNA molecules that are transcribed but not translated into proteins, with a length of more than 200 nucleotides. LncRNAs are involved ...in gene expression and regulation. The abnormal expression of lncRNAs is associated with disease pathogenesis. Small heterodimer partner (SHP, NR0B2) is a unique orphan nuclear receptor that plays a pivotal role in many biological processes by acting as a transcriptional repressor. In this review, we present the critical roles of SHP and summarize recent findings demonstrating the regulation between lncRNAs and SHP in liver disease.
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