PNPLA3 Expression Is Related to Liver Steatosis in Morbidly Obese Women with Non-Alcoholic Fatty Liver Disease

Effects of lifestyle interventions on epigenetic signatures of liver fat: Central randomized controlled trial

BACKGROUND AND AIMS

In the CENTRAL trial context, we found diverse liver fat dynamics in response to different dietary interventions. Epigenetic mechanisms may contribute to the intraindividual variation. Moreover, genetic factors are involved in developing nonalcoholic fatty-liver disease (NAFLD), a disease reflected by an increase in intrahepatic fat (IHF). In this exploratory analysis, we primarily aimed to examine the effect of lifestyle interventions on DNA-methylation of NAFLD related genes associated with IHF.

METHODS

For 120 participants from the CENTRAL trial, an 18-month regimen of either low-fat (LF) or Mediterranean-low carbohydrate (MED/LC) diets, with or without physical activity (PA+/PA-), was instructed. Magnetic resonance imaging was used to measure IHF%, which was analysed for association with CpG specific DNA-methylation levels of 41 selected candidate genes. Single-nucleotide polymorphisms known to be associated with NAFLD within the studied genes were genotyped by TaqMan assays.

RESULTS

At baseline, participants (92% men; body mass index = 30.2 kg/m² ) had mean IHF of 10.7% (59% NAFLD). Baseline-IHF% was inversely correlated with DNA-methylation at individual CpGs within AC074286.1, CRACR2A, A2MP1, FARP1 (P < .05 for all multivariate models). FARP1 rs9584805 showed association with IHF, with the prevalence of NAFLD and baseline methylation level of the CpG site (cg00071727) associated with IHF%. Following 18-month lifestyle intervention, differential DNA-methylation patterns were observed between diets at cg14335324 annotated to A2MP1 (P = .04, LF vs. MED/LC), and differential DNA-methylation between PA groups within AC074286.1, CRACR2A, and FARP1 CpGs (P < .05 for all, PA-vs. PA+).

CONCLUSIONS

This study suggests epigenetic markers for IHF and potential epigenetic remodeling after long-term lifestyle interventions.

PNPLA3 I148M is involved in the variability in anti-NAFLD response to exenatide

PURPOSE

GLP-1 receptor agonists, such as exenatide, have been proven to attenuate nonalcoholic fatty liver disease (NAFLD) in vivo and in vitro. However, the efficiency of exenatide had interindividual differences. PNPLA3 is a major susceptibility gene for NAFLD and its I148M polymorphism increases the risk of all disorders of the NAFLD spectrum. Whether this variant contributes to variability in exenatide response is still unclear.

METHODS

PNPLA3 148I knockin HepG2 cells were constructed using the Cas9/sgRNA system. Oil Red O staining combined with TG quantification was used to evaluate lipid accumulation. Western blotting and qRT-qPCR were conducted, respectively, to measure the protein and mRNA expression of lipid metabolic and endoplasmic reticulum (ER) stress-related inflammatory markers. PNPLA3 I148M was genotyped in type 2 diabetics using Sanger sequencing. The exenatide-induced changes in liver fat content and other clinical parameters were compared between PNPLA3 I148M genotypes.

RESULTS

Lipid deposition increased in both PNPLA3 148I/I and 148M/M HepG2 cells treated with palmitoleic acid, while cells with 148M/M had a higher TG content than those with 148I/I. Exendin-4 treatment was showed to be more significant in 148I/I cells than in 148M/M cells in terms of reducing the intrahepatic fat content, inhibiting SREBP-1c and ER stress-related inflammation, and activating AMPK-ACC lipid oxidation pathway. In patients with type 2 diabetes, 24-week treatment with exenatide improved liver fat content in patients carrying PNPLA3 148I/I better than in patients with 148M/M.

CONCLUSIONS

PNPLA3 I148M might modify the anti-NAFLD response to exenatide.

Abnormal metabolic processes involved in the pathogenesis of non-alcoholic fatty liver disease (Review)

Non-alcoholic fatty liver disease (NAFLD) is one of the most common chronic liver diseases and can lead to liver cirrhosis or liver cancer in severe cases. In recent years, the incidence of NAFLD has increased substantially. The trend has continued to increase and has become a key point of concern for health systems. NAFLD is often associated with metabolic abnormalities caused by increased visceral obesity, including insulin resistance, diabetes mellitus, hypertension, dyslipidemia, atherosclerosis and systemic microinflammation. Therefore, the pathophysiological mechanisms of NAFLD must be clarified to develop new drug treatment strategies. Recently, researchers have conducted numerous studies on the pathogenesis of NAFLD and have identified various important regulatory factors and potential molecular mechanisms, providing new targets and a theoretical basis for the treatment of NAFLD. However, the pathogenesis of NAFLD is extremely complex and involves the interrelationship and influence of multiple organs and systems. Therefore, the condition must be explored further. In the present review, the abnormal metabolic process, including glucose, lipid, amino acid, bile acid and iron metabolism are reviewed. It was concluded that NAFLD is associated with an imbalanced metabolic network that involves glucose, lipids, amino acids, bile acids and iron, and lipid metabolism is the core metabolic process. The current study aimed to provide evidence and hypotheses for research and clinical treatment of NAFLD.

Impaired Hepatic Vitamin A Metabolism in NAFLD Mice Leading to Vitamin A Accumulation in Hepatocytes

BACKGROUND & AIMS

Systemic retinol (vitamin A) homeostasis is controlled by the liver, involving close collaboration between hepatocytes and hepatic stellate cells (HSCs). Genetic variants in retinol metabolism (PNPLA3 and HSD17B13) are associated with non-alcoholic fatty liver disease (NAFLD) and disease progression. Still, little mechanistic details are known about hepatic vitamin A metabolism in NAFLD, which may affect carbohydrate and lipid metabolism, inflammation, oxidative stress and the development of fibrosis and cancer, e.g. all risk factors of NAFLD.

METHODS

Here, we analyzed vitamin A metabolism in 2 mouse models of NAFLD; mice fed a high-fat, high-cholesterol (HFC) diet and Leptinob mutant (ob/ob) mice.

RESULTS

Hepatic retinol and retinol binding protein 4 (RBP4) levels were significantly reduced in both mouse models of NAFLD. In contrast, hepatic retinyl palmitate levels (the vitamin A storage form) were significantly elevated in these mice. Transcriptome analysis revealed a hyperdynamic state of hepatic vitamin A metabolism, with enhanced retinol storage and metabolism (upregulated Lrat, Dgat1, Pnpla3, Raldh's and RAR/RXR-target genes) in fatty livers, in conjunction with induced hepatic inflammation (upregulated Cd68, Tnfα, Nos2, Il1β, Il-6) and fibrosis (upregulated Col1a1, Acta2, Tgfβ, Timp1). Autofluorescence analyses revealed prominent vitamin A accumulation in hepatocytes rather than HSC in HFC-fed mice. Palmitic acid exposure increased Lrat mRNA levels in primary rat hepatocytes and promoted retinyl palmitate accumulation when co-treated with retinol, which was not detected for similarly-treated primary rat HSCs.

CONCLUSION

NAFLD leads to cell type-specific rearrangements in retinol metabolism leading to vitamin A accumulation in hepatocytes. This may promote disease progression and/or affect therapeutic approaches targeting nuclear receptors.

Influence of LGALS3 and PNPLA3 genes in non-alcoholic steatohepatitis (NASH) in patients undergone bariatric surgery

AIM

This study evaluated the genesPNPLA3 and LGALS3 in patients who have undergone bariatric surgery.

METHODS

Individuals with NAFLD and NASH were evaluated, the DNA was extracted from total blood for genotyping of rs4644, rs4652 from LGALS3 and rs738409 from PNPLA3 genes, the total RNA was obtained from liver biopsy. For the detection of the molecular targets, real-time PCR through Taqman probes was used.

RESULTS

From a total of 46 collected patients, of those 21 (456%) were included as NASH and 25 (544%) as steatosis group. This groups showed significant difference to aspartate aminotransferase (AST), alanine aminotransferase (ALT) and Glutamyl transpeptidase (GGT) (p = 0.0108, p = 0.0090 and p = 0.0044). Regarding to gene expression in studied groups, hepatic steatosis vs NASH, we observed a higher expression of the LGALS3 gene in NASH (p = 0.0273). In addition, patients with C allele in homozygous for rs4644 and rs4652 of LGALS3 gene had higher expression, in NASH group (p = 0.0500 and p = 0.0242, respectively), furthermore for rs4644 both alleles in homozygous showed higher expression (AA/CC vs AC) (p = 0.0500), when analyzed PNPLA3 rs738409, NASH patients with G allele in homozygous had higher expression (p = 0.0494).

CONCLUSIONS

Therefore, an increased expression of the LGALS3 gene in patients with NASH may be important in the etiopathogenesis of the disease, as well as the presence of rs4652 and rs4644 SNPs in the regulation of transcriptional levels of the gene in patients with NAFLD and NASH.

Characterization of an antibacterial dodecapeptide from pig as a potential food preservative and its antibacterial mechanism

A membrane-active dodecapeptide was generated from porcine antimicrobial peptide with promising antimicrobial activity for application in the food industry as a potential bio-preservative to prevent microbial spoilage.

Deregulated Lysophosphatidic Acid Metabolism and Signaling in Liver Cancer

Liver cancer is one of the leading causes of death worldwide due to late diagnosis and scarcity of treatment options. The major risk factor for liver cancer is cirrhosis with the underlying causes of cirrhosis being viral infection (hepatitis B or C), metabolic deregulation (Non-alcoholic fatty liver disease (NAFLD) in the presence of obesity and diabetes), alcohol or cholestatic disorders. Lysophosphatidic acid (LPA) is a bioactive phospholipid with numerous effects, most of them compatible with the hallmarks of cancer (proliferation, migration, invasion, survival, evasion of apoptosis, deregulated metabolism, neoangiogenesis, etc.). Autotaxin (ATX) is the enzyme responsible for the bulk of extracellular LPA production, and together with LPA signaling is involved in chronic inflammatory diseases, fibrosis and cancer. This review discusses the most important findings and the mechanisms related to ATX/LPA/LPAR involvement on metabolic, viral and cholestatic liver disorders and their progression to liver cancer in the context of human patients and mouse models. It focuses on the role of ATX/LPA in NAFLD development and its progression to liver cancer as NAFLD has an increasing incidence which is associated with the increasing incidence of liver cancer. Bearing in mind that adipose tissue accounts for the largest amount of LPA production, many studies have implicated LPA in adipose tissue metabolism and inflammation, liver steatosis, insulin resistance, glucose intolerance and lipogenesis. At the same time, LPA and ATX play crucial roles in fibrotic diseases. Given that hepatocellular carcinoma (HCC) is usually developed on the background of liver fibrosis, therapies that both delay the progression of fibrosis and prevent its development to malignancy would be very promising. Therefore, ATX/LPA signaling appears as an attractive therapeutic target as evidenced by the fact that it is involved in both liver fibrosis progression and liver cancer development.

Association between PNPLA3 rs738409 polymorphism and nonalcoholic fatty liver disease (NAFLD) susceptibility and severity: A meta-analysis

OBJECTIVE

This meta-analysis is to investigate the relationship between the patatin-like phospholipase domain containing 3 (PNPLA3) rs738409 polymorphism and the susceptibility and severity of nonalcoholic fatty liver disease (NAFLD).

METHODS

Chinese Journal Full-text Database, Wanfang Database, VIP Database, and PubMed Database were subjected to case-control study retrieving, from January 2008 to December 2014. Following key words were used: fatty liver, PNPLA3, and rs738409 gene or variants or polymorphism or alleles. Meta-analysis was performed based on the retrieved articles.

RESULTS

In total 65 studies were first retrieved according to the key words, and finally 21 studies with 14,266 subjects were included. Meta-analysis showed that PNPLA3 rs738409 polymorphism exerted strong influence not only on fatty liver but also on the histological injury. PNPLA3 rs738409 [G] allele was a risk factor for NAFLD (GG vs CC, OR = 4.01, 95% CI 2.93-5.49; GC vs CC, OR = 1.88, 95% CI 1.58-2.24). PNPLA3 gene variant was significantly associated with the increased serum alanine aminotransferase (ALT) levels (GG vs CC, standardized mean difference  = 0.47, 95% CI 0.14-0.81). In addition, nonalcoholic steatohepatitis (NASH) was more frequently observed in G allele carriers (GG vs CC, OR = 3.24, 95% CI 2.79-3.76; GC vs CC, OR = 2.14, 95% CI 1.43-3.19).

CONCLUSION

PNPLA3 rs738409 polymorphism is not only a factor significantly associated with the susceptibility of NAFLD, but also related to the susceptibility of aggressive diseases.

Lipidomic characterisation discovery for coronary heart disease diagnosis based on high-throughput ultra-performance liquid chromatography and mass spectrometry

Although many diagnostic tools have been developed for coronary heart disease (CHD), its diagnosis is still challenging. Lipids play an important role in diseases and a lipidomics approach could offer a platform to clarify the pathogenesis and pathologic changes of this disease. To the best of our knowledge, no lipidomics studies on serum have been attempted to improve the diagnosis and identify the potential biomarkers of CHD. The aim of this study was to investigate the distinctive lipid changes in serum samples of CHD patients and to identify candidate biomarkers for the reliable diagnosis of CHD using this platform. In this study, the serum lipid profiles of CHD patients were measured via ultra-performance liquid chromatography-G2-Si-high definition mass spectrometry combined with multivariate data analysis. A MetaboAnalyst tool was used for the analysis of the receiver operating-characteristic, while the IPA software was applied for the pathway analysis. The obtained results inferred that 33 lipid molecular species involving 6 fatty acids, 21 glycerophospholipids and 6 sphingolipids have significant differences in the serum of CHD patients. Simultaneously, 4 upstream regulatory proteins related to lipid metabolism disorders of CHD were predicted. Ten lipids have high clinical diagnostic significance according to the receiver operating-characteristic curves. This research shows that the in-depth study of lipids in the serum contributes to the clinical diagnosis of CHD and interprets the occurrence and development of CHD.

Although many diagnostic tools have been developed for coronary heart disease (CHD), its diagnosis is still challenging.

Hepcidin in morbidly obese women with non-alcoholic fatty liver disease

Background

Non-alcoholic fatty liver disease (NAFLD) is the most common cause of chronic liver disease in Western countries. Both iron and lipid metabolism seem to be involved in its pathogenesis. We aimed to assess the relationship between levels of hepcidin, the master iron-regulatory protein, in plasma and the presence of NAFLD in morbidly obese (MO) patients, and to investigate the association between the hepatic expression of the main iron and lipid metabolism -related genes.

Materials and methods

Enzyme-linked immunosorbent assay was used to measure plasma hepcidin levels in 49 normal-weight control women, 23 MO women with normal liver (NL) histology and 46 MO women with NAFLD. The mRNA expression of hepcidin, the main iron metabolism-related genes, and the main lipid-metabolism genes was quantified by qRT-PCR in liver biopsies from members of the MO group undergoing bariatric surgery.

Results

Circulating hepcidin levels were significantly greater in MO than in normal-weight control women. However, there were no significant differences between MO women with NL and those with NAFLD. PCR analysis showed increased expression of hepcidin, FPN1, TfR1 and TfR2 in the liver of MO NAFLD women compared to those with NL. Moreover, a positive association of hepatic hepcidin mRNA expression and the iron metabolism-related genes was found with some key genes involved in the lipid metabolism.

Conclusion

These findings suggest that circulating hepcidin levels are associated with obesity but not with the presence of NAFLD. However, the hepatic expression of hepcidin and the iron metabolism-related genes seem to play a role in regulating lipid metabolism pathways in liver, which has implications for NAFLD pathogenesis.

NAFLD: Is There Anything New under the Sun?

Nonalcoholic fatty liver disease (NAFLD) is an "umbrella" definition that encompasses a spectrum of histological liver changes ranging from simple steatosis to nonalcoholic steatohepatitis (NASH) with/without fibrosis, "cryptogenic" cirrhosis, and hepatocellular carcinoma (HCC), occurring in a dysmetabolic milieu, though in the absence of excessive alcohol consumption and other competing etiologies of chronic liver disease [1].[...].

Network analyses identify liver-specific targets for treating liver diseases

We performed integrative network analyses to identify targets that can be used for effectively treating liver diseases with minimal side effects. We first generated co-expression networks (CNs) for 46 human tissues and liver cancer to explore the functional relationships between genes and examined the overlap between functional and physical interactions. Since increased de novo lipogenesis is a characteristic of nonalcoholic fatty liver disease (NAFLD) and hepatocellular carcinoma (HCC), we investigated the liver-specific genes co-expressed with fatty acid synthase (FASN). CN analyses predicted that inhibition of these liver-specific genes decreases FASN expression. Experiments in human cancer cell lines, mouse liver samples, and primary human hepatocytes validated our predictions by demonstrating functional relationships between these liver genes, and showing that their inhibition decreases cell growth and liver fat content. In conclusion, we identified liver-specific genes linked to NAFLD pathogenesis, such as pyruvate kinase liver and red blood cell (PKLR), or to HCC pathogenesis, such as PKLR, patatin-like phospholipase domain containing 3 (PNPLA3), and proprotein convertase subtilisin/kexin type 9 (PCSK9), all of which are potential targets for drug development.

Weight loss induced by bariatric surgery restores adipose tissue PNPLA3 expression

BACKGROUND & AIMS

Obesity and its related co-morbidities such as non-alcoholic fatty liver disease (NAFLD) are increasing dramatically worldwide. The genetic variation in Patatin-like phospholipase domain-containing protein 3 (PNPLA3), which is also called adiponutrin (ADPN), in residue 148 (I148M, rs738409) has been associated with NAFLD. However, the regulation and function of PNPLA3 in metabolic diseases remains unclear. Laparoscopic gastric banding (LAGB) of severely obese patients reduces body weight, liver and adipose tissue inflammation. In this study, we investigated whether weight loss induced by LAGB affected PNPLA3 expression in hepatic and adipose tissue.

METHODS

Liver and subcutaneous adipose tissue samples were collected from 28 severely obese patients before and 6 months after LAGB. PNPLA3 expression was assessed by quantitative real-time PCR. To understand whether inflammatory stimuli regulated PNPLA3 expression, we studied the effect of tumour necrosis factor alpha (TNFα) and lipopolysaccharide (LPS) on PNPLA3 expression in human adipocytes and hepatocytes.

RESULTS

PNPLA3 was strongly expressed in the liver and clearly detectable in subcutaneous adipose tissue of obese patients. Weight loss induced by LAGB of severely obese patients led to significantly increased adipose, but not hepatic, tissue expression of PNPLA3. Subcutaneous PNPLA3 expression negatively correlated with body-mass-index, fasting glucose and fasting insulin. TNFα potently suppressed PNPLA3 expression in adipocytes but not hepatocytes.

CONCLUSIONS

Weight loss induced by LAGB restored adipose tissue PNPLA3 expression which is suppressed by TNFα. Further studies will be required to determine the functional impact of PNPLA3 and its related genetic variation on adipose tissue inflammation and NAFLD.

Hepatic steatosis in HCV-infected persons in the direct-acting antiviral era

Hepatitis C virus (HCV) infects 130-170 million people worldwide. Recently, direct-acting antivirals have been shown to eradicate HCV infection in 90-95 % of non-cirrhotic patients depending on genotype, treatment experience, and regimen used. Similar rates are achieved among compensated cirrhotics, although longer treatment duration and/or ribavirin may be required. HCV uses host lipid metabolism for its lifecycle and can cause hepatic steatosis and insulin resistance. Hepatic steatosis, defined as excessive triglyceride deposition in hepatocytes, affects approximately half of HCV-infected individuals. Genetic factors and co-morbidities can drive further steatosis, which in turn can instigate fibrosis and progression to cirrhosis and hepatocellular carcinoma. Polymorphisms in genes that modulate lipid deposition in hepatocytes such as patatin-like phospholipase domain-containing protein 3 (PNPLA3) and transmembrane six superfamily member 2 (TM6SF2) predispose people to steatosis. Metabolic syndrome, obesity, and insulin resistance are increasing worldwide and further contribute to hepatic steatosis, and alcohol has long been recognized as a cause of lipid deposition in the liver. HIV and antiretroviral drugs, but not HBV, may further drive hepatic steatosis. While many of these factors limit response to interferon-based regimens for treating HCV, responses to direct-acting antivirals appear not to be impaired. The effect of HCV eradication on hepatic steatosis and progression to fibrosis, cirrhosis, and hepatocellular carcinoma warrants further study in the era of direct-acting antivirals.