Background and Aims Nonalcoholic fatty liver disease encompasses a spectrum of diseases ranging from simple steatosis to nonalcoholic steatohepatitis (NASH), cirrhosis, and liver cancer. At present, how simple steatosis progresses to NASH remains obscure and effective pharmacological therapies are lacking. Hepatic expression of C‐X‐C motif chemokine ligand 1 (CXCL1), a key chemokine for neutrophil infiltration (a hallmark of NASH), is highly elevated in NASH patients but not in fatty livers in obese individuals or in high‐fat diet (HFD)‐fed mice. The aim of this study was to test whether overexpression of CXCL1 itself in the liver can induce NASH in HFD‐fed mice and to test the therapeutic potential of IL‐22 in this new NASH model. Approach and Results Overexpression of Cxcl1 in the liver alone promotes steatosis‐to‐NASH progression in HFD‐fed mice by inducing neutrophil infiltration, oxidative stress, and stress kinase (such as apoptosis signal‐regulating kinase 1 and p38 mitogen‐activated protein kinase) activation. Myeloid cell‐specific deletion of the neutrophil cytosolic factor 1 (Ncf1)/p47phox gene, which encodes a component of the NADPH oxidase 2 complex that mediates neutrophil oxidative burst, markedly reduced CXCL1‐induced NASH and stress kinase activation in HFD‐fed mice. Treatment with interleukin (IL)‐22, a cytokine with multiple targets, ameliorated CXCL1/HFD‐induced NASH or methionine‐choline deficient diet‐induced NASH in mice. Mechanistically, IL‐22 blocked hepatic oxidative stress and its associated stress kinases via the induction of metallothionein, one of the most potent antioxidant proteins. Moreover, although it does not target immune cells, IL‐22 treatment attenuated the inflammatory functions of hepatocyte‐derived, mitochondrial DNA‐enriched extracellular vesicles, thereby suppressing liver inflammation in NASH. Conclusions Hepatic overexpression of CXCL1 is sufficient to drive steatosis‐to‐NASH progression in HFD‐fed mice through neutrophil‐derived reactive oxygen species and activation of stress kinases, which can be reversed by IL‐22 treatment via the induction of metallothionein.

Adipose tissue represents a large volume of biologically active tissue that exerts substantial systemic effects in health and disease. Alcohol consumption can profoundly disturb the normal functions of adipose tissue by inducing adipocyte death and altering secretion of adipokines, pro-inflammatory mediators and free fatty acids from adipose tissue, which have important direct and indirect effects on the pathogenesis of alcoholic liver disease (ALD). Cessation of alcohol intake quickly reverses inflammatory changes in adipose tissue, and pharmacological treatment that normalizes adipose tissue function improves experimental ALD. Obesity exacerbates liver injury induced by chronic or binge alcohol consumption, and obesity and alcohol can synergize to increase risk of ALD and progression. Physicians who care for individuals with ALD should be aware of the effects of adipose tissue dysfunction on liver function, and consider strategies to manage obesity and insulin resistance. This Review examines the effect of alcohol on adiposity and adipose tissue and the relationship between alcohol, adipose tissue and the liver.

Nonalcoholic fatty liver disease (NAFLD) represents a spectrum of diseases ranging from simple steatosis to more severe forms of liver injury including nonalcoholic steatohepatitis (NASH), fibrosis, and hepatocellular carcinoma (HCC). In humans, only 20%-40% of patients with fatty liver progress to NASH, and mice fed a high-fat diet (HFD) develop fatty liver but are resistant to NASH development. To understand how simple steatosis progresses to NASH, we examined hepatic expression of anti-inflammatory microRNA-223 (miR-223) and found that this miRNA was highly elevated in hepatocytes in HFD-fed mice and in human NASH samples. Genetic deletion of miR-223 induced a full spectrum of NAFLD in long-term HFD-fed mice including steatosis, inflammation, fibrosis, and HCC. Furthermore, microarray analyses revealed that, compared to wild-type mice, HFD-fed miR-223 knockout (miR-223KO) mice had greater hepatic expression of many inflammatory genes and cancer-related genes, including (C-X-C motif) chemokine 10 (Cxcl10) and transcriptional coactivator with PDZ-binding motif (Taz), two well-known factors that promote NASH development. In vitro experiments demonstrated that Cxcl10 and Taz are two downstream targets of miR-223 and that overexpression of miR-223 reduced their expression in cultured hepatocytes. Hepatic levels of miR-223, CXCL10, and TAZ mRNA were elevated in human NASH samples, which positively correlated with hepatic levels of several miR-223 targeted genes as well as several proinflammatory, cancer-related, and fibrogenic genes. Conclusion: HFD-fed miR-223KO mice develop a full spectrum of NAFLD, representing a clinically relevant mouse NAFLD model; miR-223 plays a key role in controlling steatosis-to-NASH progression by inhibiting hepatic Cxcl10 and Taz expression and may be a therapeutic target for the treatment of NASH. (Hepatology 2019;70:1150-1167).