Lipoprotein Lipase Up-regulation in Hepatic Stellate Cells Exacerbates Liver Fibrosis in Nonalcoholic Steatohepatitis in Mice

Perilipin 5 deletion protects against nonalcoholic fatty liver disease and hepatocellular carcinoma by modulating lipid metabolism and inflammatory responses

The molecular mechanisms underlying the transition from nonalcoholic fatty liver disease (NAFLD) to hepatocellular carcinoma (HCC) are incompletely understood. During the development of NAFLD, Perilipin 5 (PLIN5) can regulate lipid metabolism by suppressing lipolysis and preventing lipotoxicity. Other reports suggest that the lack of PLIN5 decreases hepatic injury, indicating a protective role in NAFLD pathology. To better understand the role of PLIN5 in liver disease, we established mouse models of NAFLD and NAFLD-induced HCC, in which wild-type and Plin5 null mice were exposed to a single dose of acetone or 7,12-dimethylbenz[a]anthracene (DMBA) in acetone, followed by a 30-week high-fat diet supplemented with glucose/fructose. In the NAFLD model, RNA-seq revealed significant changes in genes related to lipid metabolism and immune response. At the intermediate level, pathways such as AMP-activated protein kinase (AMPK), signal transducer and activator of transcription 3 (STAT3), c-Jun N-terminal kinase (JNK), and protein kinase B (AKT) were blunted in Plin5-deficient mice (Plin5-/-) compared to wild-type mice (WT). In the NAFLD-HCC model, only WT mice developed liver tumors, while Plin5-/- mice were resistant to tumorigenesis. Furthermore, only 32 differentially expressed genes associated with NALFD progession were identified in Plin5 null mice. The markers of mitochondrial function and immune response, such as the peroxisome proliferator-activated receptor-γ, coactivator 1-α (PGC-1α) and phosphorylated STAT3, were decreased. Lipidomic analysis revealed differential levels of some sphingomyelins between WT and Plin5-/- mice. Interestingly, these changes were not detected in the HCC model, indicating a possible shift in the metabolism of sphingomelins during carcinogenesis.

Found in translation-Fibrosis in metabolic dysfunction-associated steatohepatitis (MASH)

Metabolic dysfunction-associated steatohepatitis (MASH) is a severe form of liver disease that poses a global health threat because of its potential to progress to advanced fibrosis, leading to cirrhosis and liver cancer. Recent advances in single-cell methodologies, refined disease models, and genetic and epigenetic insights have provided a nuanced understanding of MASH fibrogenesis, with substantial cellular heterogeneity in MASH livers providing potentially targetable cell-cell interactions and behavior. Unlike fibrogenesis, mechanisms underlying fibrosis regression in MASH are still inadequately understood, although antifibrotic targets have been recently identified. A refined antifibrotic treatment framework could lead to noninvasive assessment and targeted therapies that preserve hepatocellular function and restore the liver's architectural integrity.

Metabolic dysfunctions following chronic oral corticosterone are modified by adolescence and sex in mice

Adolescence is a period of development in which shifts in responses to glucocorticoids is well-documented. Obesity and metabolic syndrome are substantial health issues whose rates continue to rise in both adult and adolescent populations. Though many interacting factors contribute to these dysfunctions, how these shifts in glucocorticoid responses may be related remain unknown. Using a model of oral corticosterone (CORT) exposure in male and female mice, we demonstrate differential responses during adolescence (30-58 days of age) or adulthood (70-98 day of age) in endpoints relevant to metabolic function. Our data indicate that CORT resulted in significant weight gain in adult- and adolescent-exposed females and adult-exposed males, but not adolescent-exposed males. Despite this difference, all animals treated with high levels of CORT showed significant increases in white adipose tissue, indicating a dissociation between weight gain and adiposity in adolescent-treated males. Similarly, all experimental groups showed significant increases in plasma insulin, leptin, and triglyceride levels, further suggesting potential disconnects between overt weight gain, and underlying metabolic dysregulation. Finally, we found age- and dose-dependent changes in the expression of hepatic genes important in glucocorticoid receptor and lipid regulation, which showed different patterns in males and females. Thus, altered transcriptional pathways in the liver might be contributing differentially to the similar metabolic phenotype observed among these experimental groups. We also show that despite little CORT-induced changes in the hypothalamic levels of orexin-A and NPY, we found that food and fluid intake were elevated in adolescent-treated males and females. These data indicate chronic exposure to elevated glucocorticoid levels results in metabolic dysfunction in both males and females, which can be further modulated by developmental stage.

Cold Exposure Regulates Hepatic Glycogen and Lipid Metabolism in Newborn Goats

Cold exposure influences liver metabolism, thereby affecting energy homeostasis. However, the gene regulatory network of the liver after cold exposure remains poorly understood. In this study, we found that 24 h cold exposure (COLD, 6 °C) increased plasma glucose (GLU) levels, while reducing plasma non-esterified fatty acid (NEFA) and triglyceride (TG) levels compared to the room temperature (RT, 25 °C) group. Cold exposure increased hepatic glycogen content and decreased hepatic lipid content in the livers of newborn goats. We conducted RNA-seq analysis on the livers of newborn goats in both the RT and cold exposure groups. A total of 1600 genes were identified as differentially expressed genes (DEGs), of which 555 genes were up-regulated and 1045 genes were down-regulated in the cold exposure group compared with the RT group. Cold exposure increased the expression of genes involved in glycolysis, glycogen synthesis, and fatty acid degradation pathways. These results can provide a reference for hepatic lipid and glycogen metabolism in newborn goats after cold exposure.

Identification of metabolic biomarkers associated with nonalcoholic fatty liver disease

BACKGROUND

Nonalcoholic fatty liver disease (NAFLD) is the most common liver disease. Metabolism-related genes significantly influence the onset and progression of the disease. Hence, it is necessary to screen metabolism-related biomarkers for the diagnosis and treatment of NAFLD patients.

METHODS

GSE48452, GSE63067, and GSE89632 datasets including nonalcoholic steatohepatitis (NASH) and healthy controls (HC) analyzed in this study were retrieved from the Gene Expression Omnibus (GEO) database. First, differentially expressed genes (DEGs) between NASH and HC samples were obtained. Next, metabolism-related DEGs (MR-DEGs) were identified by overlapping DEGs and metabolism-related genes (MRG). Further, a protein-protein interaction (PPI) network was developed to show the interaction among MR-DEGs. Subsequently, the "Least absolute shrinkage and selection operator regression" and "Random Forest" algorithms were used to screen metabolism-related genes (MRGs) in patients with NAFLD. Next, immune cell infiltration and gene set enrichment analyses (GSEA) were performed on these metabolism-related genes. Finally, the expression of metabolism-related gene was determined at the transcription level.

RESULTS

First, 129 DEGs related to NAFLD development were identified among patients with nonalcoholic steatohepatitis (NASH) and healthy control. Next, 18 MR-DEGs were identified using the Venn diagram. Subsequently, four genes, including AMDHD1, FMO1, LPL, and P4HA1, were identified using machine learning algorithms. Moreover, a regulatory network consisting of four genes, 25 microRNAs (miRNAs), and 41 transcription factors (TFs) was constructed. Finally, a significant increase in FMO1 and LPL expression levels and a decrease in AMDHD1 and P4HA1 expression levels were observed in patients in the NASH group compared to the HC group.

CONCLUSION

Metabolism-related genes associated with NAFLD were identified, containing AMDHD1, FMO1, LPL, and P4HA1, which provide insights into diagnosing and treating patients with NAFLD.

Chronic-binge ethanol feeding aggravates systemic dyslipidemia in Ldlr-/- mice, thereby accelerating hepatic fibrosis

Objective

Chronic ethanol consumption is known to cause alcohol-associated liver disease, which poses a global health concern as almost a quarter of heavy drinkers develop severe liver damage. Alcohol-induced liver disease ranges from a mild, reversible steatotic liver to alcoholic steatohepatitis and irreversible liver fibrosis and cirrhosis, ultimately requiring liver transplantation. While ethanol consumption is associated with dysregulated lipid metabolism and altered cholesterol homeostasis, the impact of dyslipidemia and pre-existing hypercholesterolemia on the development of alcohol-associated liver disease remains to be elucidated.

Design

To address the influence of systemic dyslipidemia on ethanol-induced liver disease, chronic-binge ethanol feeding was applied to female C57BL/6J (wild type) mice and mice deficient for the low-density lipoprotein receptor (Ldlr-/-), which display a human-like lipoprotein profile with elevated cholesterol and triglyceride levels in circulation. Respective control groups were pair-fed an isocaloric diet.

Results

Chronic-binge ethanol feeding did not alter systemic lipid levels in wild type mice. While increased systemic cholesterol levels in Ldlr-/- mice were not affected by ethanol feeding, chronic-binge ethanol diet aggravated elevated plasma triglyceride levels in Ldlr-/- mice. Despite higher circulatory triglyceride levels in Ldlr-/- mice, hepatic lipid levels and the development of hepatic steatosis were not different from wild type mice after ethanol diet, while hepatic expression of genes related to lipid metabolism (Lpl) and transport (Cd36) showed minor changes. Immunohistochemical assessment indicated a lower induction of infiltrating neutrophils in the livers of ethanol-fed Ldlr-/- mice compared to wild type mice. In line, hepatic mRNA levels of the pro-inflammatory genes Ly6g, Cd11b, Ccr2, Cxcl1 and F4/80 were reduced, indicating less inflammation in the livers of Ldlr-/- mice which was associated with reduced Tlr9 induction. While systemic ALT and hepatic MDA levels were not different, Ldlr-deficient mice showed accelerated liver fibrosis development after chronic-binge ethanol diet than wild type mice, as indicated by increased levels of Sirius Red staining and higher expression of pro-fibrotic genes Tgfb, Col1a1 and Col3a1. Ldlr-/- and wild type mice had similar plasma ethanol levels and did not show differences in the hepatic mRNA levels of Adh1 and Cyp2e1, important for ethanol metabolism.

Conclusion

Our results highlight that chronic-binge ethanol feeding enhances systemic dyslipidemia in Ldlr-/- mice which might accelerate the development of hepatic fibrosis, independent of hepatic lipid levels.

Mechanisms of liver fibrosis in metabolic syndrome

The understanding of the mechanisms of liver fibrosis has been dominated by models in which chronic hepatocellular injury is the initiating step as is seen with viral infections. The increased prevalence of the metabolic syndrome, and the increases in liver fibrosis due to metabolic syndrome driven non-alcoholic steatohepatitis (NASH), has made it a priority to understand how this type of liver fibrosis is similar to, and different from, pure hepatocellular injury driven liver fibrosis. Both types of liver fibrosis have the transformation of the hepatic stellate cell (HSC) into a myofibroblast as a key step. In metabolic syndrome, there is little evidence that metabolite changes such as high levels of glucose and free fatty acids are directly inducing HSC transdifferentiation, however, metabolite changes may lead to reductions in immunomodulatory and hepatoprotective molecules such as lipoxins, resolvins and Interleukin (IL)-22. Cells of the innate immune system are known to be important intermediaries between hepatocellular damage and HSC transdifferentiation, primarily by producing cytokines such as transforming growth factor-β (TGF-β) and platelet derived growth factor (PDGF). Resident and infiltrating macrophages are the dominant innate immune cells, but others (dendritic cells, neutrophils, natural killer T cells and mucosal-associated invariant T cells) also have important roles in inducing and resolving liver fibrosis. CD8+ and CD4+ T cells of the adaptive immune system have been identified to have greater profibrotic roles than previously realised by inducing hepatocyte death (auto-aggressive CD8+T) cells and cytokines producing (TH17 producing CD4+T) cells. Finally, the cellular networks present in NASH fibrosis are being identified and suggest that once fibrosis has developed cell-to-cell communication is dominated by myofibroblasts autocrine signalling followed by communication with cholangiocytes and endothelial cells, with myofibroblast-hepatocyte, and myofibroblast-macrophage signalling having minor roles. Such information is essential to the development of antifibrotic strategies for different stages of fibrosis.

Ameliorating effect of probiotic on nonalcoholic fatty liver disease and lipolytic gene expression in rabbits

Nonalcoholic fatty liver disease (NAFLD) is a condition that affects about 24% of people worldwide. Increased liver fat, inflammation, and, in the most severe cases, cell death are all characteristics of NAFLD. However, NAFLD pathogenesis and therapy are still not clear enough. Thus, this study aimed to determine the effect of a high-cholesterol diet (HCD) inducing NAFLD on lipolytic gene expression, liver function, lipid profile, and antioxidant enzymes in rabbits and the modulatory effects of probiotic Lactobacillus acidophilus (L. acidophilus) on it. A total of 45 male New Zealand white rabbits, eight weeks old, were randomly divided into three groups of three replicates (5 rabbits/replicate). Rabbits in group I were given a basal diet; rabbits in group II were given a high-cholesterol diet that caused NAFLD; and rabbits in group III were given a high-cholesterol diet as well as probiotics in water for 8 weeks. The results showed that a high-cholesterol diet caused hepatic vacuolation and upregulated the genes for lipoprotein lipase (LPL), hepatic lipase (HL), and cholesteryl ester transfer protein (CETP). Downregulated low-density lipoprotein receptor (LDLr) gene, increased liver enzymes [alanine transaminase (ALT), aspartate transaminase (AST), alkaline phosphatase (ALP), lactate dehydrogenase (LDH)], cholesterol, triglycerides (TG), low-density lipoprotein (LDL), glucose, and total bilirubin. On the other hand, it decreased high-density lipoprotein (HDL), total protein, albumin, and liver antioxidants [glutathione peroxidase (GPx), catalase (CAT), reduced glutathione (GSH), and superoxide dismutase (SOD)]. Supplementing with probiotics helped to return all parameters to normal levels. In conclusion, probiotic supplementation, especially L. acidophilus, protected against NAFLD, and restored lipolytic gene expression, liver functions, and antioxidants to normal levels.

High producer variant of lipoprotein lipase may protect from hepatocellular carcinoma in alcohol-associated cirrhosis

Background & Aims

Progression of alcohol-associated liver disease (ALD) is driven by genetic predisposition. The rs13702 variant in the lipoprotein lipase (LPL) gene is linked to non-alcoholic fatty liver disease. We aimed at clarifying its role in ALD.

Methods

Patients with alcohol-associated cirrhosis, with (n = 385) and without hepatocellular carcinoma (HCC) (n = 656), with HCC attributable to viral hepatitis C (n = 280), controls with alcohol abuse without liver damage (n = 366), and healthy controls (n = 277) were genotyped regarding the LPL rs13702 polymorphism. Furthermore, the UK Biobank cohort was analysed. LPL expression was investigated in human liver specimens and in liver cell lines.

Results

Frequency of the LPL rs13702 CC genotype was lower in ALD with HCC in comparison to ALD without HCC both in the initial (3.9% vs. 9.3%) and the validation cohort (4.7% vs. 9.5%; p <0.05 each) and compared with patients with viral HCC (11.4%), alcohol misuse without cirrhosis (8.7%), or healthy controls (9.0%). This protective effect (odds ratio [OR] = 0.5) was confirmed in multivariate analysis including age (OR = 1.1/year), male sex (OR = 3.0), diabetes (OR = 1.8), and carriage of the PNPLA3 I148M risk variant (OR = 2.0). In the UK Biobank cohort, the LPL rs13702 C allele was replicated as a risk factor for HCC. Liver expression of LPL mRNA was dependent on LPL rs13702 genotype and significantly higher in patients with ALD cirrhosis compared with controls and alcohol-associated HCC. Although hepatocyte cell lines showed negligible LPL protein expression, hepatic stellate cells and liver sinusoidal endothelial cells expressed LPL.

Conclusions

LPL is upregulated in the liver of patients with alcohol-associated cirrhosis. The LPL rs13702 high producer variant confers protection against HCC in ALD, which might help to stratify people for HCC risk.

Impact and implications

Hepatocellular carcinoma is a severe complication of liver cirrhosis influenced by genetic predisposition. We found that a genetic variant in the gene encoding lipoprotein lipase reduces the risk for hepatocellular carcinoma in alcohol-associated cirrhosis. This genetic variation may directly affect the liver, because, unlike in healthy adult liver, lipoprotein lipase is produced from liver cells in alcohol-associated cirrhosis.

Cyanotoxin exposure and hepatocellular carcinoma

Cyanobacteria are ubiquitous in aquatic and terrestrial environments worldwide and include a number of species producing tumor-promoting hepatotoxins. Human exposure to cyanobacteria and cyanotoxins primarily occurs though ingestion of contaminated drinking water and food sources. In a Northeast U.S. population, we recently reported an independent association of oral cyanobacteria with risk of hepatocellular carcinoma (HCC). In a cross-sectional study of 55 HCC patients in Hawaii, U.S.A., serum microcystin/nodularin (MC/NOD), cylindrospermopsin (CYN), and anabaenopeptin (AB) were measured by ELISA. In a subset of 16 patients, cyanotoxin levels were compared by tumor expression of over 700 genes analyzed via the Nanostring nCounter Fibrosis panel. MC/NOD, CYN, and AB were detected in all HCC patients. MC/NOD and CYN levels significantly varied by etiology with the highest levels in cases attributed to metabolic risk factors, specifically, hyperlipidemia, type 2 diabetes, and non-alcoholic fatty liver disease/non-alcoholic steatohepatitis. Cyanotoxin levels were significantly positively correlated with tumor expression of genes functioning in PPAR signaling and lipid metabolism. Our study provides novel albeit limited evidence that cyanotoxins may a role in the pathogenesis of HCC through the dysregulation of lipid metabolism and progression of hepatic steatosis.

HDLBP Promotes Hepatocellular Carcinoma Proliferation and Sorafenib Resistance by Suppressing Trim71-dependent RAF1 Degradation

BACKGROUND & AIMS

The contribution of abnormal metabolic targets to hepatocellular carcinoma (HCC) progression and the associated regulatory mechanisms are attractive research areas. High-density lipoprotein binding protein (HDLBP) is an important transporter that protects cells from excessive cholesterol accumulation, but few studies have identified a role for HDLBP in HCC progression.

METHODS

HDLBP expression was determined in HCC tissues and published datasets. The biological roles of HDLBP in vitro and in vivo were examined by performing a series of functional experiments.

RESULTS

An integrated analysis confirmed that HDLBP expression was significantly elevated in HCC compared with noncancerous liver tissues. The knockdown or overexpression of HDLBP substantially inhibited or enhanced, respectively, HCC proliferation and sorafenib resistance. Subsequently, a mass spectrometry screen identified RAF1 as a potential downstream target of HDLBP. Mechanistically, when RAF1 was stabilized by HDLBP, MEKK1 continuously induced RAF1^Ser259-dependent MAPK signaling. Meanwhile, HDLBP interacted with RAF1 by competing with the TRIM71 E3 ligase and inhibited RAF1 degradation through the ubiquitin-proteasome pathway.

CONCLUSIONS

Our study reveals that HDLBP is an important mediator that stabilizes the RAF1 protein and maintains its activity, leading to HCC progression and sorafenib resistance. Thus, HDLBP might represent a potential biomarker and future therapeutic target for HCC.

Canary Seed (Phalaris canariensis L.) Peptides Prevent Obesity and Glucose Intolerance in Mice Fed a Western Diet

Previous research showed that canary seed (Phalaris canariensis L.) peptides (CSP) possess robust in vitro antiobesity properties via inhibition of pancreatic lipase (PL). Nevertheless, no studies have yet explored their antiobesity properties in vivo. Consequently, we investigated the effects of CSP in C57BL/6J mice under a Western diet (WD). Mice were assigned into groups and fed a normal diet (ND) or a WD accompanied by an oral dose of CSP (250 or 500 mg/kg/day), orlistat (40 mg/kg/day), or distilled water. The results showed that consuming CSP can provide metabolic benefits, including preventing weight gain by up to 20%, increasing glucose tolerance, and reducing insulin, leptin, and LDL/VLDL levels in plasma. Conversely, total ghrelin was unaffected by CSP-500, but decreased by CSP-250, and amplified by orlistat. Surprisingly, CSP-250 was more effective in preventing weight gain and promoting satiety than CSP-500. Parallel to this, protein absorption in CSP-500 was decreased, supported by a rise in fecal crude protein (+3.5%). Similarly, fecal fat was increased by orlistat (38%) and was unaffected by CSP-250 (3.0%) and CSP (3.0%), comparatively to WD (2.5%). Despite this, both CSP treatments were equally effective in decreasing hepatic steatosis and avoiding hyperlipidemia. Furthermore, the enzymatic analysis showed that CSP-PL complexes dissociated faster (15 min) than orlistat-PL complexes (41 min). Lastly, CSP did not affect expression of hepatic lipid oxidation genes ACO and PPAR-α, but reduced the expression of the hydrolase gene LPL, and lipogenesis related genes FAS and ACC. Taken together, these results suggest that CSP antiobesity mechanism relies on lipid metabolism retardation to increase fat transit time and subsequently suppress hunger.

Comprehensive analyses of the microRNA-messenger RNA-transcription factor regulatory network in mouse and human renal fibrosis

Objective: The aim of this study was to construct a microRNA (miRNA)-messenger RNA (mRNA)-transcription factor (TF) regulatory network and explore underlying molecular mechanisms, effective biomarkers, and drugs in renal fibrosis (RF). Methods: A total of six datasets were downloaded from Gene Expression Omnibus. "Limma" and "DESeq2" packages in R software and GEO2R were applied to identify the differentially expressed miRNAs and mRNAs (DEmiRNAs and DEmRNAs, respectively). The determination and verification of DEmiRNAs and DEmRNAs were performed through the integrated analysis of datasets from five mouse 7 days of unilateral ureteral obstruction datasets and one human chronic kidney disease dataset and the Human Protein Atlas (http://www.proteinatlas.org). Target mRNAs of DEmiRNAs and TFs were predicted by prediction databases and the iRegulon plugin in Cytoscape, respectively. A protein-protein interaction network was constructed using STRING, Cytoscape v3.9.1, and CytoNCA. Functional enrichment analysis was performed by DIANA-miRPath v3.0 and R package "clusterProfiler." A miRNA-mRNA-TF network was established using Cytoscape. Receiver operating characteristic (ROC) curve analysis was used to examine the diagnostic value of the key hub genes. Finally, the Comparative Toxicogenomics Database and Drug-Gene Interaction database were applied to identify potential drugs. Results: Here, 4 DEmiRNAs and 11 hub genes were determined and confirmed in five mouse datasets, of which Bckdha and Vegfa were further verified in one human dataset and HPA, respectively. Moreover, Bckdha and Vegfa were also predicted by miR-125a-3p and miR-199a-5p, respectively, in humans as in mice. The sequences of miR-125a-3p and miR-199a-5p in mice were identical to those in humans. A total of 6 TFs were predicted to regulate Bckdha and Vegfa across mice and humans; then, a miRNA-mRNA-TF regulatory network was built. Subsequently, ROC curve analysis showed that the area under the curve value of Vegfa was 0.825 (p = 0.002). Finally, enalapril was identified to target Vegfa for RF therapy. Conclusion: Pax2, Pax5, Sp1, Sp2, Sp3, and Sp4 together with Bckdha-dependent miR-125a-3p/Vegfa-dependent miR-199a-5p formed a co-regulatory network enabling Bckdha/Vegfa to be tightly controlled in the underlying pathogenesis of RF across mice and humans. Vegfa could act as a potential novel diagnostic marker and might be targeted by enalapril for RF therapy.

The lipid transporter HDLBP promotes hepatocellular carcinoma metastasis through BRAF-dependent epithelial-mesenchymal transition

Tumor metastasis is a major cause of cancer mortality. However, little is known regarding the regulation of abnormal cholesterol metabolism in hepatocellular carcinoma (HCC) metastasis. Here, we show that the expression of high-density lipoprotein binding protein (HDLBP), a lipid transporter, is clinically correlated with tumor metastasis in HCC patients. Moreover, HDLBP was required for cholesterol-induced HCC metastasis. We revealed that knockdown and overexpression of HDLBP significantly inhibited and enhanced, respectively, the metastasis, invasion and epithelial-mesenchymal transition (EMT) of HCC cells in vitro and in vivo. Mechanistically, coimmunoprecipitation and mass spectrometry screening uncovered BRAF as a protein target of HDLBP. HDLBP was found to promote EMT signaling in a BRAF-dependent manner. Furthermore, HDLBP interacts with BRAF and inhibits its ubiquitinated degradation by abrogating BRAF-ITCH interactions. Notably, further studies suggest that dabrafenib exhibited a greater metastasis-suppressive effect in HDLBP knockout HCC than isolated treatment. Overall, our findings imply that cholesterol-induced HDLBP contributes to the metastasis and invasion of HCC through BRAF-dependent EMT signaling and that HDLBP may be applied as a biomarker and therapeutic target for HCC.

Liver-specific overexpression of lipoprotein lipase improves glucose metabolism in high-fat diet-fed mice

The liver is the main organ that regulates lipid and glucose metabolism. Ectopic lipid accumulation in the liver impairs insulin sensitivity and glucose metabolism. Lipoprotein lipase (LPL), mainly expressed in the adipose tissue and muscle, is a key enzyme that regulates lipid metabolism via the hydrolysis of triglyceride in chylomicrons and very-low-density lipoproteins. Here, we aimed to investigate whether the suppression level of hepatic lipid accumulation via overexpression of LPL in mouse liver leads to improved metabolism. To overexpress LPL in the liver, we generated an LPL-expressing adenovirus (Ad) vector using an improved Ad vector that exhibited considerably lower hepatotoxicity (Ad-LPL). C57BL/6 mice were treated with Ad vectors and simultaneously fed a high-fat diet (HFD). Lipid droplet formation in the liver decreased in Ad-LPL-treated mice relative to that in control Ad vector-treated mice. Glucose tolerance and insulin resistance were remarkably improved in Ad-LPL-treated mice compared to those in control Ad vector-treated mice. The expression levels of fatty acid oxidation-related genes, such as peroxisome proliferator-activated receptor α, carnitine palmitoyltransferase 1, and acyl-CoA oxidase 1, were 1.7–2.0-fold higher in Ad-LPL-treated mouse livers than that in control Ad-vector-treated mouse livers. Furthermore, hepatic LPL overexpression partly maintained mitochondrial content in HFD-fed mice. These results indicate that LPL overexpression in the livers of HFD-fed mice attenuates the accumulation of lipid droplets in the liver and improves glucose metabolism. These findings may enable the development of new drugs to treat metabolic syndromes such as type 2 diabetes mellitus and non-alcoholic fatty liver disease.

Identification and action mechanism of lipid regulating components from Rhei Radix et rhizoma

ETHNOPHARMACOLOGICAL RELEVANCE

Rhei Radix et Rhizoma is widely used in Traditional Chinese Medicine to attack stagnation, clear damp heat, relieve fire, cool blood, remove blood stasis and detoxify recorded in Chinese Pharmacopoeia. Modern pharmacological research has showed the extract of Rhei Radix et Rhizoma has the effect of lowering blood lipids, but the main active components and their mechanisms are still not clear.

AIM OF THE STUDY

To reveal the lipid regulating components from Rhei Radix et Rhizoma and preliminarily explore their related action mechanisms.

MATERIALS AND METHODS

A rat model of dyslipidemia was established by administration of a high-fat emulsion via gavage, and the intervention effect of different polar fractions of Rhei Radix et Rhizoma on rat blood lipids as well as their related action mechanisms were preliminarily investigated. The effective components were inferred based on the above tests and identified by high performance liquid chromatography in comparison with reference substances, their UV absorption and high resolution mass spectra characteristics.

RESULTS

The extract with dichloromethane fraction (DF) containing rhubarb free anthraquinones (aloe-emodin, rhein, emodin, chrysophanol and physcion) significantly regulated the disordered blood lipids, lowered TC and LDLC, reversed TG and increased HDLC level in dyslipidemic rats and also showed lipid-lowering effect on lipid abnormalities in HepG2 cells. DF could alter the signaling pathways such as PPARα and AMPK implicated in lipid metabolism, and it down-regulated the mRNA expression of liver APOA2, SCD-1, HMGCR, SREBP-2 and PCSK9, but up-regulated the expressions of liver APOE, LPL and intestinal ABCG8. Besides, it could change the composition of Firmicutes, Bacteroidetes and Proteobacteria in dyslipidemic rat feces samples.

CONCLUSIONS

Rhubarb free anthraquinones have a significant regulating effect on the levels of serum TC, LDLC and HDLC, and probably possess a bidirectional regulatory effect on TG level in dyslipidemic rats. These effects may be achieved by regulating the expressions of the liver PPARα and SREBP target genes, PCSK9 and the intestinal ABCG8 genes, which are involved in blood cholesterol transport, liver lipid metabolism and intestinal cholesterol excretion. Rhubarb free anthraquinones may also affect energy metabolism by changing the composition of gut microflora related to lipid metabolism in dyslipidemic rats.

Very-low-density lipoprotein receptor-enhanced lipid metabolism in pancreatic stellate cells promotes pancreatic fibrosis

Lipoprotein disorder is a common feature of chronic pancreatitis (CP); however, the relationship between lipoprotein disorder and pancreatic fibrotic environment is unclear. Here, we investigated the occurrence and mechanism of pancreatic stellate cell (PSC) activation by lipoprotein metabolites and the subsequent regulation of type 2 immune responses, as well as the driving force of fibrotic aggressiveness in CP. Single-cell RNA sequencing revealed the heterogeneity of PSCs and identified very-low-density lipoprotein receptor (VLDLR)⁺ PSCs that were characterized by a higher lipid metabolism. VLDLR promoted intracellular lipid accumulation, followed by interleukin-33 (IL-33) expression and release in PSCs. PSC-derived IL-33 strongly induced pancreatic group 2 innate lymphoid cells (ILC2s) to trigger a type 2 immune response accompanied by the activation of PSCs, eventually leading to fibrosis during pancreatitis. Our findings indicate that VLDLR-enhanced lipoprotein metabolism in PSCs promotes pancreatic fibrosis and highlight a dominant role of IL-33 in this pro-fibrotic cascade.

Betaine Promotes Fat Accumulation and Reduces Injury in Landes Goose Hepatocytes by Regulating Multiple Lipid Metabolism Pathways

Betaine is a well-established supplement used in livestock feeding. In our previous study, betaine was shown to result in the redistribution of body fat, a healthier steatosis phenotype, and an increased liver weight and triglyceride storage of the Landes goose liver, which is used for foie-gras production. However, these effects are not found in other species and strains, and the underlying mechanism is unclear. Here, we studied the underpinning molecular mechanisms by developing an in vitro fatty liver cell model using primary Landes goose hepatocytes and a high-glucose culture medium. Oil red-O staining, a mitochondrial membrane potential assay, and a qRT-PCR were used to quantify lipid droplet characteristics, mitochondrial β-oxidation, and fatty acid metabolism-related gene expression, respectively. Our in vitro model successfully simulated steatosis caused by overfeeding. Betaine supplementation resulted in small, well-distributed lipid droplets, consistent with previous experiments in vivo. In addition, mitochondrial membrane potential was restored, and gene expression of fatty acid synthesis genes (e.g., sterol regulatory-element binding protein, diacylglycerol acyltransferase 1 and 2) was lower after betaine supplementation. By contrast, the expression of lipid hydrolysis transfer genes (mitochondrial transfer protein and lipoprotein lipase) was higher. Overall, the results provide a scientific basis and theoretical support for the use of betaine in animal production.

Effects of Keemun and Dianhong Black Tea in Alleviating Excess Lipid Accumulation in the Liver of Obese Mice: A Comparative Study

Schematic diagram of the effects of two black teas in alleviating excess hepatic lipid accumulation.

Semi-automated approach for generation of biological networks on drug-induced cholestasis, steatosis, hepatitis, and cirrhosis

Drug-induced liver injury (DILI) is one of the leading reasons for discontinuation of a new drug development project. Diverse machine learning or deep learning models have been developed to predict DILI. However, these models have not provided an adequate understanding of the mechanisms leading to DILI. The development of safer drugs requires novel computational approaches that enable the prompt understanding of the mechanism of DILI. In this study, the mechanisms leading to the development of cholestasis, steatosis, hepatitis, and cirrhosis were explored using a semi-automated approach for data gathering and associations. Diverse data from ToxCast, Comparative Toxicogenomic Database (CTD), Reactome, and Open TG-GATEs on reference molecules leading to the development of the respective diseases were extracted. The data were used to create biological networks of the four diseases. As expected, the four networks had several common pathways, and a joint DILI network was assembled. Such biological networks could be used in drug discovery to identify possible molecules of concern as they provide a better understanding of the disease-specific key events. The events can be target-tested to provide indications for potential DILI effects.

The S100 calcium binding protein A11 promotes liver fibrogenesis by targeting TGF-β signaling

Liver fibrosis is a key transformation stage and also a reversible pathological process in various types of chronic liver diseases. However, the pathogenesis of liver fibrosis still remains elusive. Here, we report that the calcium binding protein A11 (S100A11) is consistently upregulated in the integrated data from GSE liver fibrosis and tree shrew liver proteomics. S100A11 is also experimentally activated in liver fibrosis in mouse, rat, tree shrew, and human with liver fibrosis. While overexpression of S100A11 in vivo and in vitro exacerbates liver fibrosis, the inhibition of S100A11 improves liver fibrosis. Mechanistically, S100A11 activates hepatic stellate cells (HSCs) and the fibrogenesis process via the regulation of the deacetylation of Smad3 in the TGF-β signaling pathway. S100A11 physically interacts with SIRT6, a deacetylase of Smad2/3, which may competitively inhibit the interaction between SIRT6 and Smad2/3. The subsequent release and activation of Smad2/3 promote the activation of HSCs and fibrogenesis. Additionally, a significant elevation of S100A11 in serum is observed in clinical patients. Our study uncovers S100A11 as a novel profibrogenic factor in liver fibrosis, which may represent both a potential biomarker and a promising therapy target for treating liver fibrosis and fibrosis-related liver diseases.

Integrated analysis of potential gene crosstalk between non-alcoholic fatty liver disease and diabetic nephropathy

BACKGROUND

Growing evidence indicates that non-alcoholic fatty liver disease (NAFLD) is related to the occurrence and development of diabetic nephropathy (DN). This bioinformatics study aimed to explore optimal crosstalk genes and related pathways between NAFLD and DN.

METHODS

Gene expression profiles were downloaded from Gene Expression Omnibus. CIBERSORT algorithm was employed to analyze the similarity of infiltrating immunocytes between the two diseases. Protein-protein interaction (PPI) co-expression network and functional enrichment analysis were conducted based on the identification of common differentially expressed genes (DEGs). Least absolute shrinkage and selection operator (LASSO) regression and Boruta algorithm were implemented to initially screen crosstalk genes. Machine learning models, including support vector machine, random forest model, and generalized linear model, were utilized to further identify the optimal crosstalk genes between DN and NAFLD. An integrated network containing crosstalk genes, transcription factors, and associated pathways was developed.

RESULTS

Four gene expression datasets, including GSE66676 and GSE48452 for NAFLD and GSE30122 and GSE1009 for DN, were involved in this study. There were 80 common DEGs between the two diseases in total. The PPI network built with the 80 common genes included 77 nodes and 83 edges. Ten optimal crosstalk genes were selected by LASSO regression and Boruta algorithm, including CD36, WIPI1, CBX7, FCN1, SLC35D2, CP, ZDHHC3, PTPN3, LPL, and SPP1. Among these genes, LPL and SPP1 were the most significant according to NAFLD-transcription factor network. Five hundred twenty-nine nodes and 1,113 edges comprised the PPI network of activated pathway-gene. In addition, 14 common pathways of these two diseases were recognized using Gene Ontology (GO) analysis; among them, regulation of the lipid metabolic process is closely related to both two diseases.

CONCLUSIONS

This study offers hints that NAFLD and DN have a common pathogenesis, and LPL and SPP1 are the most relevant crosstalk genes. Based on the common pathways and optimal crosstalk genes, our proposal carried out further research to disclose the etiology and pathology between the two diseases.

Hepatic Branch Vagotomy Modulates the Gut-Liver-Brain Axis in Murine Cirrhosis

BACKGROUND

Cirrhosis and hepatic encephalopathy (HE) are linked with an altered gut-liver-brain axis, however, the relative contribution of hepatic vagal innervation is unclear. We aimed to determine the impact of hepatic vagotomy on the gut microbiome, brain, and liver in murine cirrhosis.

METHODS

10-15-week-old male C57BL/6 mice with and without hepatic vagotomy underwent carbon tetrachloride (CCl4) gavage for 8 weeks. Frontal cortex [inflammation, glial/microglial activation, BDNF (brain-derived neurotrophic factor)], liver [histology including inflammation and steatosis, fatty acid synthesis (sterol-responsive binding protein-1) SREBP-1, insulin-induced gene-2 (Insig2) and BDNF], and colonic mucosal microbiota (16srRNA microbial sequencing) were evaluated on sacrifice. Conventional mice with and without cirrhosis were compared to vagotomized counterparts.

RESULTS

Conventional control vs. cirrhosis: Cirrhosis resulted in dysbiosis, hepatic/neuro-inflammation with glial/microglial activation, and low brain BDNF vs. controls. Conventional control vs. vagotomy controls: Vagotomized control mice had a lower colonic dysbiosis than conventional mice but the rest of the hepatic/brain parameters were similar. Conventional cirrhosis vs. vagotomized cirrhosis: After vagotomy + cirrhosis, we found lower dysbiosis but continuing neuroinflammation in the absence of glial/microglial activation vs. conventional cirrhosis. Vagotomy + Cirrhosis groups showed higher hepatic steatosis due to higher SREBP1 and low Insig2 protein and altered activation of key genes involved in hepatic lipid metabolism and inflammation. BDNF levels in the brain were higher but low in the liver in vagotomy + cirrhosis, likely a protective mechanism.

CONCLUSIONS

Hepatic vagal innervation affects the gut microbial composition, hepatic inflammation and steatosis, and cortical inflammation and BDNF expression and could be a critical modulator of the gut-liver-brain axis with consequences for HE development.

Angiopoietin-like protein 4 deficiency augments liver fibrosis in liver diseases such as nonalcoholic steatohepatitis in mice through enhanced free cholesterol accumulation in hepatic stellate cells

AIM

We recently reported that lipoprotein lipase (LPL)-mediated free cholesterol (FC) accumulation in hepatic stellate cells (HSCs) augmented liver fibrosis in non-alcoholic steatohepatitis (NASH). The aim of the present study was to explore the role of angiopoietin-like protein 4 (Angptl4), an LPL inhibitor, in the pathogenesis of liver fibrosis in NASH.

METHODS

Angptl4-deficient or wild-type mice were used to investigate the role of Angptl4 in the pathogenesis of NASH induced by feeding a methionine- and choline-deficient diet. We also examined the effect of Angptl4 on FC accumulation in HSCs, and the subsequent activation of HSCs, using Angptl4-deficient HSCs.

RESULTS

In the NASH model, Angptl4-deficient mice had significantly aggravated liver fibrosis and activated HSCs without enhancement of hepatocellular injury, liver inflammation, or liver angiogenesis. FC levels were significantly higher in HSCs from Angptl4-deficient mice than in those from wild-type mice. Treatment with Angptl4 reversed low-density lipoprotein-induced FC accumulation in HSCs through the inhibition of LPL. The Angptl4 deficiency-induced FC accumulation in HSCs suppressed HSC expression of the transforming growth factor-β (TGF-ß) pseudoreceptor, bone morphogenetic protein, and activin membrane-bound inhibitor, and sensitized HSCs to TGF-β-induced activation in vivo and in vitro.

CONCLUSIONS

Angptl4 plays an important role in the pathogenesis of FC accumulation in HSCs. In addition, regulation of FC levels in HSCs by Angptl4 plays a critical role in the pathogenesis of liver fibrosis in NASH. Thus, Angptl4 could represent a novel therapeutic option for NASH.

High-fat diet accelerate hepatic fatty acids synthesis in offspring male rats induced by perinatal exposure to nonylphenol

BACKGROUND

Low dose of NP exposure can alter adipose tissue formation, and the intake of high-fat diet (HFD) can also lead to the fatty liver disease. We investigated the combined effect of NP and HFD on the first offspring of rats, and whether this effect can be passed to the next generation and the possible mechanisms involved.

METHODS

Pregnant rats had access to be treated with 5 μg/kg/day NP and normal diet. The first generation rats were given normal diet and HFD on postnatal day 21, respectively. Then the second generation rats started to only receive normal diet without NP or HFD. Body weight, organ coefficient of liver tissues, lipid profile, biochemical indexes and the expression of genes involved in lipid metabolism, as well as liver histopathology were investigated in male offspring of rats.

RESULTS

NP and HFD interaction had significant effect on the birth weight, body weight and liver tissue organ coefficient of first generation male rats. And HFD aggravated abnormal lipid metabolism, even abnormal liver function and liver histopathological damage of first generation male rats produced by the NP. And this effect can be passed on to the second generation rats. HFD also accelerated the mRNA level of fatty acid synthesis genes such as Lpl, Fas, Srebp-1 and Ppar-γ of first generation rats induced by perinatal exposure to NP, even passed on to the second generation of male rats. NP and HFD resulted in synergistical decrease of the protein expression level of ERα in liver tissue in F2 male rats.

CONCLUSION

HFD and NP synergistically accelerated synthesis of fatty acids in liver of male offspring rats through reducing the expression of ERα, which induced abnormal lipid metabolism, abnormal liver function and hepatic steatosis. Moreover, all of these damage passed on to the next generation rats.

Extra virgin olive oil improved body weight and insulin sensitivity in high fat diet-induced obese LDLr-/-.Leiden mice without attenuation of steatohepatitis

Dietary fatty acids play a role in the pathogenesis of obesity-associated non-alcoholic fatty liver disease (NAFLD), which is associated with insulin resistance (IR). Fatty acid composition is critical for IR and subsequent NAFLD development. Extra-virgin olive oil (EVOO) is the main source of monounsaturated fatty acids (MUFA) in Mediterranean diets. This study examined whether EVOO-containing high fat diets may prevent diet-induced NAFLD using Ldlr−/−. Leiden mice. In female Ldlr−/−.Leiden mice, the effects of the following high fat diets (HFDs) were examined: a lard-based HFD (HFD-L); an EVOO-based HFD (HFD-EVOO); a phenolic compounds-rich EVOO HFD (HFD-OL). We studied changes in body weight (BW), lipid profile, transaminases, glucose homeostasis, liver pathology and transcriptome. Both EVOO diets reduced body weight (BW) and improved insulin sensitivity. The EVOOs did not improve transaminase values and increased LDL-cholesterol and liver collagen content. EVOOs and HFD-L groups had comparable liver steatosis. The profibrotic effects were substantiated by an up-regulation of gene transcripts related to glutathione metabolism, chemokine signaling and NF-kappa-B activation and down-regulation of genes relevant for fatty acid metabolism. Collectivelly, EVOO intake improved weight gain and insulin sensitivity but not liver inflammation and fibrosis, which was supported by changes in hepatic genes expression.

Nonalcoholic Fatty Liver Disease: Focus on New Biomarkers and Lifestyle Interventions

Nonalcoholic fatty liver disease (NAFLD) is considered a hepatic manifestation of metabolic syndrome, characterized from pathological changes in lipid and carbohydrate metabolism. Its main characteristics are excessive lipid accumulation and oxidative stress, which create a lipotoxic environment in hepatocytes leading to liver injury. Recently, many studies have focused on the identification of the genetic and epigenetic modifications that also contribute to NAFLD pathogenesis and their prognostic implications. The present review is aimed to discuss on cellular and metabolic alterations associated with NAFLD, which can be helpful to identify new noninvasive biomarkers. The identification of accumulated lipids in the cell membranes, as well as circulating cytokeratins and exosomes, provides new insights in understanding of NAFLD. This review also suggests that lifestyle modifications remain the main prevention and/or treatment for NAFLD.

How does hepatic lipid accumulation lead to lipotoxicity in non-alcoholic fatty liver disease?

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD), characterized as excess lipid accumulation in the liver which is not due to alcohol use, has emerged as one of the major health problems around the world. The dysregulated lipid metabolism creates a lipotoxic environment which promotes the development of NAFLD, especially the progression from simple steatosis (NAFL) to non-alcoholic steatohepatitis (NASH).

PURPOSEAND AIM

This review focuses on the mechanisms of lipid accumulation in the liver, with an emphasis on the metabolic fate of free fatty acids (FFAs) in NAFLD and presents an update on the relevant cellular processes/mechanisms that are involved in lipotoxicity. The changes in the levels of various lipid species that result from the imbalance between lipolysis/lipid uptake/lipogenesis and lipid oxidation/secretion can cause organellar dysfunction, e.g. ER stress, mitochondrial dysfunction, lysosomal dysfunction, JNK activation, secretion of extracellular vesicles (EVs) and aggravate (or be exacerbated by) hypoxia which ultimately lead to cell death. The aim of this review is to provide an overview of how abnormal lipid metabolism leads to lipotoxicity and the cellular mechanisms of lipotoxicity in the context of NAFLD.

Assessment of common and differentially expressed proteins between diabetes mellitus and fatty liver disease: a network analysis

AIM

This study aimed to introduce the main biomarkers related to NFLD and diabetes II to determine common pathogenic and metabolite factors linking NFLD to diabetes II.

BACKGROUND

Nonalcoholic fatty liver disease (NFLD) is chronic hepatic failure with a broad range of hepatic disorders. NFLD and diabetes type 2 coexist regularly to drive adverse outcomes such as hepatocellular carcinoma and vascular complications.

METHODS

The proteins related to NFDL and diabetes mellitus were extracted from String database. Proteins related to each disease were included in protein-protein interaction networks in Cytoscape software. Obtained networks were analyzed using Cytoscape network analyzer. The central nodes were determined as top hubs based on degree value. The top hubs related to NFLD and diabetes mellites were compared.

RESULTS

In total, 200 proteins related to NFDL and diabetes mellitus were found separately in String database and connected through undirected edges in individual networks. Central nodes based on degree value were determined for each disease. Ten percent of top nodes were selected based on degree value as the 20 top hubs for each disease. Target common hub proteins between NFDL and diabetes mellitus comprised INS, AKT1, ALB, PPARG, IL6, GPDPH, LEP, TNF, ADIPOQ, IGF1, TP53, MAPK3, and SIRT1.

CONCLUSION

According to the results, 13 common and 14 discriminatory central dysregulated proteins were determined for NAFLD and diabetes mellitus.

Microbe-set enrichment analysis facilitates functional interpretation of microbiome profiling data

The commensal microbiome is known to influence a variety of host phenotypes. Microbiome profiling followed by differential abundance analysis has been established as an effective approach to study the mechanisms of host-microbiome interactions. However, it is challenging to interpret the collective functions of the resultant microbe-sets due to the lack of well-organized functional characterization of commensal microbiome. We developed microbe-set enrichment analysis (MSEA) to enable the functional interpretation of microbe-sets by examining the statistical significance of their overlaps with annotated groups of microbes that share common attributes such as biological function or phylogenetic similarity. We then constructed microbe-set libraries by query PubMed to find microbe-mammalian gene associations and disease associations by parsing the Disbiome database. To demonstrate the utility of our novel MSEA methodology, we carried out three case studies using publicly available curated knowledge resource and microbiome profiling datasets focusing on human diseases. We found MSEA not only yields consistent findings with the original studies, but also recovers insights about disease mechanisms that are supported by the literature. Overall, MSEA is a useful knowledge-based computational approach to interpret the functions of microbes, which can be integrated with microbiome profiling pipelines to help reveal the underlying mechanism of host-microbiome interactions.

Regulation of peroxisome proliferator-activated receptor-gamma activity affects the hepatic stellate cell activation and the progression of NASH via TGF-β1/Smad signaling pathway

Development of liver fibrosis is associated with activation of quiescent hepatic stellate cells (HSCs) into myofibroblasts (activated HSCs), which produce excessive extracellular matrix. Peroxisome proliferator-activated receptor-gamma (PPAR-γ) exerts protective effects on hepatic inflammation and fibrosis. The current study was to explore the function of PPAR-γ on HSC activation and progression of nonalcoholic steatohepatitis (NASH). Our study found that HSCs were gradually activated during the progression of methionine-choline-deficient (MCD) diet-induced NASH, accompanied by decreased PPAR-γ expression and activated TGF-β1/Smad signaling pathway in the liver. PPAR-γ agonist was found to inhibit primary HSCs and NIH/3T3 fibroblast activation and reverted their phenotypical morphology induced by TGF-β1 in vitro. In addition to this, PPAR-γ agonist decreased expression of TGF-β1 and phosphorylation of Smad2/3 while increased expression of Smad7. In vivo, rosiglitazone, a PPAR-γ agonist, inhibited HSC activation and alleviated liver fibrosis and inflammation similarly via inhibiting the activation of TGF-β1/Smad signaling pathway. In parallel, rosiglitazone alleviated hepatic lipid accumulation and peroxidation, beneficial to reverse of NASH. From these findings, it can be concluded that the gradual activation of HSCs is crucial to the progression of NASH and modulating PPAR-γ expression can affect HSC activation via TGF-β1/Smad signaling pathway and thereby influence hepatic fibrogenesis.

Macrophage-derived thrombospondin 1 promotes obesity-associated non-alcoholic fatty liver disease

Background & Aims

Thrombospondin 1 (TSP1) is a multifunctional matricellular protein. We previously showed that TSP1 has an important role in obesity-associated metabolic complications, including inflammation, insulin resistance, cardiovascular, and renal disease. However, its contribution to obesity-associated non-alcoholic fatty liver disease/non-alcoholic steatohepatitis (NAFLD or NASH) remains largely unknown; thus, we aimed to determine its role.

Methods

High-fat diet or AMLN (amylin liver NASH) diet-induced obese and insulin-resistant NAFLD/NASH mouse models were utilised, in addition to tissue-specific Tsp1-knockout mice, to determine the contribution of different cellular sources of obesity-induced TSP1 to NAFLD/NASH development.

Results

Liver TSP1 levels were increased in experimental obese and insulin-resistant NAFLD/NASH mouse models as well as in obese patients with NASH. Moreover, TSP1 deletion in adipocytes did not protect mice from diet-induced NAFLD/NASH. However, myeloid/macrophage-specific TSP1 deletion protected mice against obesity-associated liver injury, accompanied by reduced liver inflammation and fibrosis. Importantly, this protection was independent of the levels of obesity and hepatic steatosis. Mechanistically, through an autocrine effect, macrophage-derived TSP1 suppressed Smpdl3b expression in liver, which amplified liver proinflammatory signalling (Toll-like receptor 4 signal pathway) and promoted NAFLD progression.

Conclusions

Macrophage-derived TSP1 is a significant contributor to obesity-associated NAFLD/NASH development and progression and could serve as a therapeutic target for this disease.

Lay summary

Obesity-associated non-alcoholic fatty liver disease is a most common chronic liver disease in the Western world and can progress to liver cirrhosis and cancer. No treatment is currently available for this disease. The present study reveals an important factor (macrophage-derived TSP1) that drives macrophage activation and non-alcoholic fatty liver disease development and progression and that could serve as a therapeutic target for non-alcoholic fatty liver disease/steatohepatitis.

Mechanisms of Fibrosis Development in Nonalcoholic Steatohepatitis

Nonalcoholic fatty liver disease is the most prevalent liver disease worldwide, affecting 20%-25% of the adult population. In 25% of patients, nonalcoholic fatty liver disease progresses to nonalcoholic steatohepatitis (NASH), which increases the risk for the development of cirrhosis, liver failure, and hepatocellular carcinoma. In patients with NASH, liver fibrosis is the main determinant of mortality. Here, we review how interactions between different liver cells culminate in fibrosis development in NASH, focusing on triggers and consequences of hepatocyte-macrophage-hepatic stellate cell (HSC) crosstalk. We discuss pathways through which stressed and dead hepatocytes instigate the profibrogenic crosstalk with HSC and macrophages, including the reactivation of developmental pathways such as TAZ, Notch, and hedgehog; how clearance of dead cells in NASH via efferocytosis may affect inflammation and fibrogenesis; and insights into HSC and macrophage heterogeneity revealed by single-cell RNA sequencing. Finally, we summarize options to therapeutically interrupt this profibrogenic hepatocyte-macrophage-HSC network in NASH.

Cellular Interactions in the Human Fatty Liver

Non-alcoholic steatohepatitis morbidity and mortality is on the rise due to the obesity pandemic. Its pathophysiology is not well understood and implies complex interactions between local hepatic cells populations, adipocytes, immune effectors that lead to hepatic lipid excess, lipotoxicity, cellular stress and inflammation, as well as programmed cell death. A better understanding of these pathogenic interactions would allow better identification of therapeutic targets in a disease that has no known pharmacological therapy until now.