TM6SF2 rs58542926 influences hepatic fibrosis progression in patients with non-alcoholic fatty liver disease

Associations of TM6SF2 167K allele with liver enzymes and lipid profile in children: the PANIC Study

BACKGROUND

The 167K allele in the TM6SF2 gene has been suggested to protect against cardiovascular disease at the cost of developing nonalcoholic fatty liver disease in adults.

METHODS

We performed a cross-sectional study in a population sample of 462 Caucasian children aged 6-9 y, genotyped the polymorphism using HumanCoreExome BeadChip, and assessed several cardiometabolic risk factors.

RESULTS

The 51 (11%) carriers of the 167K allele had higher plasma alanine aminotransferase (ALT) (20.8 vs. 18.4 U/l, P = 0.011) but lower plasma triglycerides (0.54 vs. 0.61 mmol/l, P = 0.024), total cholesterol (4.08 vs. 4.30 mmol/l, P = 0.016), and low-density lipoprotein (LDL) cholesterol (2.22 vs. 2.38 mmol/l, P = 0.012) than the 411 noncarriers. In factor analysis, the first factor was heavily loaded by plasma ALT (factor loading 0.63), triglycerides (-0.82), LDL cholesterol (-0.71), and waist circumference (0.61) in the carriers but not in the noncarriers.

CONCLUSIONS

The carriers of the 167K allele have higher plasma ALT but lower plasma triglycerides and total and LDL cholesterol than the noncarriers already in childhood.

Hepatic Transmembrane 6 Superfamily Member 2 Regulates Cholesterol Metabolism in Mice

BACKGROUND & AIMS

The rs58542926 C>T variant of the transmembrane 6 superfamily member 2 gene (TM6SF2), encoding an E167K amino acid substitution, has been correlated with reduced total cholesterol (TC) and cardiovascular disease. However, little is known about the role of TM6SF2 in metabolism. We investigated the long-term effects of altered TM6SF2 levels in cholesterol metabolism.

METHODS

C57BL/6 mice (controls), mice that expressed TM6SF2 specifically in the liver, and mice with CRISPR/Cas9-mediated knockout of Tm6sf2 were fed chow or high-fat diets. Blood samples were collected from all mice and plasma levels of TC, low-density lipoprotein cholesterol (LDL-c), high-density lipoprotein cholesterol, and triglycerides were measured. Liver tissues were collected and analyzed by histology, real-time polymerase chain reaction, and immunoblot assays. Adenovirus vectors were used to express transgenes in cultured Hep3B hepatocytes.

RESULTS

Liver-specific expression of TM6SF2 increased plasma levels of TC and LDL-c, compared with controls, and altered liver expression of genes that regulate cholesterol metabolism. Tm6sf2-knockout mice had decreased plasma levels of TC and LDL-c, compared with controls, and consistent changes in expression of genes that regulate cholesterol metabolism. Expression of TM6SF2 promoted cholesterol biosynthesis in hepatocytes.

CONCLUSIONS

TM6SF2 regulates cholesterol metabolism in mice and might be a therapeutic target for cardiovascular disease.

Noninvasive fatty liver markers predict liver disease mortality in the U.S. population

Nonalcoholic fatty liver disease (NAFLD) contributes to premature death along with obesity, diabetes, and cardiovascular disease (CVD). We examined whether hepatic steatosis (HS) on ultrasound and liver enzyme activities were associated with increased liver disease mortality in the U.S. National Health and Nutrition Examination Survey (NHANES), 1988-1994, with up to 23 years of linked-mortality data. Survey-linked National Death Index records were analyzed among 14,527 adult participants who were negative for viral hepatitis B and C and iron overload. HS on ultrasound was categorized as normal, mild, moderate, or severe. Alanine aminotransferase (ALT), aspartate aminotransferase (AST), and gamma-glutamyltransferase (GGT) elevation was defined as the highest sex-specific decile. Cumulative mortality was 36.2% from all causes, including 16.3% from CVD, 10.8% from cancer, 5.4% from diabetes, and 1.1% from liver disease. Severe HS was associated with increased liver disease mortality in both age-adjusted (hazard ratio [HR]: 3.92; 95% confidence interval [CI]: 1.49-10.27; P for trend: 0.011) and multivariate-adjusted analyses (HR, 2.68; 95% CI: 1.02-7.03; P for trend: 0.072). HS was not independently associated with mortality from all causes, CVD, cancer, or diabetes. Higher liver disease mortality was found with elevated ALT (HR, 4.08; 95% CI: 1.99-8.33), AST (HR, 4.33; 95% CI: 2.18-8.59), and GGT (HR, 7.91; 95% CI: 3.06-20.46). GGT elevation was associated with increased overall mortality (HR, 1.45; 95% CI: 1.21-1.74). Liver enzymes were otherwise unrelated to overall or cause-specific mortality.

CONCLUSIONS

In the U.S. population, severe hepatic steatosis on ultrasound and liver enzyme elevation were associated with increased liver disease mortality, but were not independently associated with mortality from all causes (except for GGT), CVD, cancer, or diabetes.

TM6SF2 Glu167Lys polymorphism is associated with low levels of LDL-cholesterol and increased liver injury in obese children

BACKGROUND

The Glu167Lys (E167K) transmembrane 6 superfamily member 2 (TM6SF2) variant has been associated with liver steatosis, high alanine transaminase (ALT) levels and reduced plasma levels of liver-derived triglyceride-rich lipoproteins.

OBJECTIVES

The objectives of this study were to investigate in a group of obese children the association among the 167K allele of TM6SF2 gene and ALT, cholesterol and triglycerides levels, and hepatic steatosis, and to evaluate the potential interaction between this variant and the I148M patatin like phospholipase 3 gene (PNPLA3) polymorphism on liver enzymes.

METHODS

We genotyped 1010 obese children for TM6SF2 E167K and PNPLA3 I148M polymorphisms. Anthropometrical and biochemical data were collected. Ultrasound imaging of the liver was performed.

RESULTS

The 167K allele showed an association with steatosis (P < 0.0001), higher ALT levels (P < 0.001) and lower total cholesterol (P < 0.00001), low-density lipoprotein cholesterol (P < 0.0001), triglycerides (P = 0.02) and non-high-density lipoprotein cholesterol levels (P < 0.000001). The subjects homozygous for the PNPLA3 148M allele carrying the rare variant of TM6SF2 showed an odds ratio of 12.2 (confidence interval 3.8-39.6, P = 0.000001) to present hypertransaminasaemia compared with the remaining patients.

CONCLUSION

Although the TMS6SF2 E167K variant predisposes the obese children to non-alcoholic fatty liver disease, there is an association between this variant and lower levels of cardiovascular risk factors. Overall, the data suggest differential effects of TMS6SF2 E167K variant on liver and heart health.

Management of NAFLD: a stage-based approach

NAFLD is the most prevalent form of liver disease in the USA, affecting an estimated 30% of the population. The condition is associated with increased mortality related to cardiovascular disease, malignancy and liver disease. Identification of patients who might be at increased risk of adverse outcomes is critical as it is not feasible to screen all patients with suspected NAFLD. Patients with NASH, the progressive subtype of NAFLD, should be targeted for treatment, especially if they have concomitant fibrosis because such patients are more likely than those without fibrosis to have adverse outcomes. Treatment goals in patients with NAFLD vary depending on the disease stage owing to differential risk of progression and the particularities of an individual's comorbid disease. Lifestyle intervention is important for all patients irrespective of disease stage, but other therapies should be targeted to those most likely to benefit. In this Review, we highlight risk factors for disease progression and offer a stage-based treatment approach for patients with NAFLD.

Inactivation of Tm6sf2, a Gene Defective in Fatty Liver Disease, Impairs Lipidation but Not Secretion of Very Low Density Lipoproteins

A missense mutation (E167K) in TM6SF2 (transmembrane 6 superfamily member 2), a polytopic protein of unknown function, is associated with the full spectrum of fatty liver disease. To investigate the role of TM6SF2 in hepatic triglyceride (TG) metabolism, we inactivated the gene in mice. Chronic inactivation of Tm6sf2 in mice is associated with hepatic steatosis, hypocholesterolemia, and transaminitis, thus recapitulating the phenotype observed in humans. No dietary challenge was required to elicit the phenotype. Immunocytochemical and cell fractionation studies revealed that TM6SF2 was present in the endoplasmic reticulum and Golgi complex, whereas the excess neutral lipids in the Tm6sf2(-/-) mice were located in lipid droplets. Plasma VLDL-TG levels were reduced in the KO animals due to a 3-fold decrease in VLDL-TG secretion rate without any associated reduction in hepatic apoB secretion. Both VLDL particle size and plasma cholesterol levels were significantly reduced in KO mice. Despite levels of TM6SF2 protein being 10-fold higher in the small intestine than in the liver, dietary lipid absorption was only modestly reduced in the KO mice. Our data, taken together, reveal that TM6SF2 is required to mobilize neutral lipids for VLDL assembly but is not required for secretion of apoB-containing lipoproteins. Despite TM6SF2 being located in the endoplasmic reticulum and Golgi complex, the lipids that accumulate in its absence reside in lipid droplets.

Bidirectional Relationships and Disconnects between NAFLD and Features of the Metabolic Syndrome

Non-alcoholic fatty liver disease (NAFLD) represents a wide spectrum of liver disease from simple steatosis, to steatohepatitis, (both with and without liver fibrosis), cirrhosis and end-stage liver failure. NAFLD also increases the risk of hepatocellular carcinoma (HCC) and both HCC and end stage liver disease may markedly increase risk of liver-related mortality. NAFLD is increasing in prevalence and is presently the second most frequent indication for liver transplantation. As NAFLD is frequently associated with insulin resistance, central obesity, dyslipidaemia, hypertension and hyperglycaemia, NAFLD is often considered the hepatic manifestation of the metabolic syndrome. There is growing evidence that this relationship between NAFLD and metabolic syndrome is bidirectional, in that NAFLD can predispose to metabolic syndrome features, which can in turn exacerbate NAFLD or increase the risk of its development in those without a pre-existing diagnosis. Although the relationship between NAFLD and metabolic syndrome is frequently bidirectional, recently there has been much interest in genotype/phenotype relationships where there is a disconnect between the liver disease and metabolic syndrome features. Such potential examples of genotypes that are associated with a dissociation between liver disease and metabolic syndrome are patatin-like phospholipase domain-containing protein-3 (PNPLA3) (I148M) and transmembrane 6 superfamily member 2 protein (TM6SF2) (E167K) genotypes. This review will explore the bidirectional relationship between metabolic syndrome and NAFLD, and will also discuss recent insights from studies of PNPLA3 and TM6SF2 genotypes that may give insight into how and why metabolic syndrome features and liver disease are linked in NAFLD.

Cirrhosis and Advanced Fibrosis in Hispanics in Texas: The Dominant Contribution of Central Obesity

Liver cirrhosis is a leading cause of death in Hispanics and Hispanics who live in South Texas have the highest incidence of liver cancer in the United States. We aimed at determining the prevalence and associated risk factors of cirrhosis in this population. Clinical and demographic variables were extracted for 2466 participants in the community-based Cameron County Hispanic Cohort in South Texas. Aspartate transaminase to Platelet Ratio Index (APRI) was used to predict cirrhosis in Cameron County Hispanic Cohort. The prevalence of cirrhosis using APRI≥2 was 0.94%, which is nearly 4-fold higher than the national prevalence. Using APRI≥1, the overall prevalence of cirrhosis/advanced fibrosis was 3.54%. In both analyses, highest prevalence was observed in males, specifically in the 25-34 age group. Risk factors independently associated with APRI≥2 and APRI≥1 included hepatitis C, diabetes and central obesity with a remarkable population attributable fraction of 52.5% and 65.3% from central obesity, respectively. Excess alcohol consumption was also independently associated with APRI≥2. The presence of patatin-like phospholipase domain-containing-3 gene variants was independently associated with APRI≥1 in participants >50 years old. Males with both central obesity and excess alcohol consumption presented with cirrhosis/advanced fibrosis at a young age. Alarmingly high prevalence of cirrhosis and advanced fibrosis was identified in Hispanics in South Texas, affecting young males in particular. Central obesity was identified as the major risk factor. Public health efforts are urgently needed to increase awareness and diagnosis of advanced liver fibrosis in Hispanics.

The common PNPLA3 variant p.I148M is associated with liver fat contents as quantified by controlled attenuation parameter (CAP)

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) is becoming the most prevalent liver disorder. The PNPLA3 (adiponutrin) variant p.I148M has been identified as common genetic modifier of NAFLD. Our aim was to assess the relationships between genetic risk and non-invasively measured liver fat content.

METHODS

Hepatic steatosis was quantified by transient elastography, using the controlled attenuation parameter (CAP) in 174 patients with chronic liver diseases (50% women, age 18-77 years). In addition, a cohort of 174 gender-matched healthy controls (50% women, age 32-77 years) was recruited. The PNPLA3 mutation as well as the novel NAFLD-predisposing genetic variant (TM6SF2 p.E167K) were genotyped with allele-specific probes.

RESULTS

The PNPLA3 genotype correlated significantly (P = 0.001) with hepatic CAP measurements. The p.148M risk allele increased the odds of developing liver steatosis (OR = 2.39, P = 0.023). In multivariate models, BMI and PNPLA3 mutation were both independently associated with CAP values (P < 0.001 and P = 0.007, respectively). Carriers of the TM6SF2 risk allele presented with increased aminotransferase activities (ALT: P = 0.007, AST: P = 0.004), but the presence of this variant did not affect CAP values.

CONCLUSIONS

The PNPLA3 p.I148M variant represents the most important prosteatotic genetic risk factor. NAFLD carriers of this variant should be followed up carefully, with elastography and CAP being ideally suited for this purpose.

A "systems medicine" approach to the study of non-alcoholic fatty liver disease

The prevalence of fatty liver (steatosis) in the general population is rapidly increasing worldwide. The progress of knowledge in the physiopathology of fatty liver is based on the systems biology approach to studying the complex interactions among different physiological systems. Similarly, translational and clinical research should address the complex interplay between these systems impacting on fatty liver. The clinical needs drive the applications of systems medicine to re-define clinical phenotypes, assessing the multiple nature of disease susceptibility and progression (e.g. the definition of risk, prognosis, diagnosis criteria, and new endpoints of clinical trials). Based on this premise and in light of recent findings, the complex mechanisms involved in the pathology of fatty liver and their impact on the short- and long-term clinical outcomes of cardiovascular, metabolic liver diseases associated with steatosis are presented in this review using a new "systems medicine" approach. A new data set is proposed for studying the impairments of different physiological systems that have an impact on fatty liver in different subsets of subjects and patients.

MERTK rs4374383 polymorphism affects the severity of fibrosis in non-alcoholic fatty liver disease

BACKGROUND & AIM

Homozygosity for a common non-coding rs4374383 G>A polymorphism in MERTK (myeloid-epithelial-reproductive tyrosine kinase) has been associated with the protection against fibrosis progression in chronic hepatitis C. The main study objective was to assess whether MERTK AA genotype influences liver fibrosis, and secondarily MERTK expression in patients with non-alcoholic fatty liver disease (NAFLD). We also investigated whether MERTK is expressed in human hepatic stellate cells (HSC) and in murine models of fibrogenesis.

METHODS

We considered 533 consecutive patients who underwent liver biopsy for suspected non-alcoholic steatohepatitis (NASH) without severe obesity from two Italian cohorts. As controls, we evaluated 158 patients with normal liver enzymes and without metabolic disturbances. MERTK rs4374383 genotype was assessed by 5'-nuclease assays. MERTK expression was analysed in mouse models of fibrosis, and the effect of the MERTK ligand GAS6 were investigated in human HSC.

RESULTS

Clinically significant fibrosis (stage F2-F4) was observed in 19% of patients with MERTK AA compared to 30% in those with MERTK GG/GA (OR 0.43, CI 0.21-0.88, p=0.02; adjusted for centre, and genetic, clinical-metabolic and histological variables). The protective rs4374383 AA genotype was associated with lower MERTK hepatic expression. MERTK was overexpressed in the liver of NAFLD patients with F2-F4 fibrosis and in in vivo models of fibrogenesis. Furthermore, exposure of cultured human HSC to the MERTK ligand GAS6, increased cell migration and induced procollagen expression. These effects were counteracted by inhibition of MERTK activity, which also resulted in apoptotic death of HSC.

CONCLUSIONS

The rs4374383 AA genotype, associated with lower intrahepatic expression of MERTK, is protective against F2-F4 fibrosis in patients with NAFLD. The mechanism may involve modulation of HSC activation.

Hepatocellular carcinoma and non-alcoholic steatohepatitis: The state of play

Hepatocellular carcinoma (HCC) is now the fifth cancer of greatest frequency and the second leading cause of cancer related deaths worldwide. Chief amongst the risks of HCC are hepatitis B and C infection, aflatoxin B1 ingestion, alcoholism and obesity. The latter can promote non-alcoholic fatty liver disease (NAFLD), that can lead to the inflammatory form non-alcoholic steatohepatitis (NASH), and can in turn promote HCC. The mechanisms by which NASH promotes HCC are only beginning to be characterized. Here in this review, we give a summary of the recent findings that describe and associate NAFLD and NASH with the subsequent HCC progression. We will focus our discussion on clinical and genomic associations that describe new risks for NAFLD and NASH promoted HCC. In addition, we will consider novel murine models that clarify some of the mechanisms that drive NASH HCC formation.

Association of PNPLA3 rs738409 and TM6SF2 rs58542926 with health services utilization in a population-based study

Background

Hepatic steatosis confers an increased risk of metabolic and cardiovascular disease and higher health services use. Associations of the single nucleotide polymorphisms (SNP) PNPLA3 rs738409 and TM6SF2 rs58542926 with hepatic steatosis have recently been established. This study investigates the association between rs738409 and rs58542926 with health services utilization in a general population.

Methods

Data of 3759 participants from Study of Health in Pomerania (SHIP), a population-based study in Germany, were obtained. The annual number of outpatient visits, hospitalization and length of hospital stay was regressed on rs738409 and rs58542926 and adjusted for socio-economic factors, lifestyle habits, clinical factors, and health status.

Results

Minor allele homozygous subjects of rs738409 had an increased odds of hospitalization as compared to major allele homozygous subjects (odds ratio [OR] 1.51; 95 % confidence interval [CI], 1.02 to 2.15). Heterozygous subjects did not differ from major allele homozygous subjects with respect to their odds of hospitalization. The three genotype groups of rs738409 were similar with respect to the number of outpatient visits and inpatient days. Minor allele homozygous and heterozygous subjects of rs58542926 had higher outpatient utilization (+53.04 % and +67.56 %, p < 0.05, respectively) and inpatient days than major allele homozygous subjects.

Conclusions

After adjustment for several confounding factors, PNPLA3 rs738409 and TM6SF2 rs58542926 were associated with the number of outpatient visits, hospitalization, and inpatient days. Further studies are warranted to replicate our findings and to evaluate whether genetic data can be used to identify subjects with excess health services utilization.

TM6SF2 rs58542926 is not associated with steatosis and fibrosis in large cohort of patients with genotype 1 chronic hepatitis C

BACKGROUND & AIMS

We tested the putative association of the rs58542926 variant of TM6SF2, a recently described genetic determinant of nonalcoholic fatty liver disease, with steatosis and fibrosis in genotype 1(G1) chronic hepatitis C(CHC) patients.

METHODS

A total of 694 consecutively biopsied Caucasian G1 CHC patients were genotyped for TM6SF2 rs58542926, IL28B rs12979860 and PNPLA3 rs738409. Steatosis was classified as absent (<5%), mild-moderate(5-29%) and severe(≥30%), Fibrosis was considered severe if=F3-F4.

RESULTS

Carriers of TM6SF2 rs58542926 (6.3% of patients) exhibited lower serum levels of cholesterol (P = 0.04) and triglycerides (P = 0.01), but a similar distribution of steatosis severity (P = 0.63), compared to noncarriers. Prevalence and severity of steatosis were reduced in IL28B C allele carriers (P = 0.005) and elevated in PNPLA3 G allele carriers (P < 0.001). After adjustment for age, gender, body mass index and homoeostasis model assessment score, steatosis severity was independently associated with IL28B rs12979860 (odds ratio [OR] 0.69, 95% confidence interval [CI] 0.55-0.86, P = 0.001) and PNPLA3 rs738409 (OR 1.84, 95% CI 1.46-2.83, P < 0.001), but not TM6SF2 rs58542926 (OR 1.48, 95% CI 0.82-2.69, P = 0.19). Variants of TM6SF2 (30.9% vs. 25%, P = 0.40), IL28B and PNPLA3 were not directly associated with fibrosis severity, although variants of IL28B and PNPLA3 promoted steatosis (OR 1.36, 95% CI 1.06-1.75, P = 0.01) that in turn is associated with severe fibrosis.

CONCLUSIONS

In G1 CHC patients, TM6SF2 rs58542926 does not affect the histological severity of liver damage. However, IL28B rs12979860 and PNPLA3 rs738409 modify steatosis.

PNPLA3 rs738409 and TM6SF2 rs58542926 variants increase the risk of hepatocellular carcinoma in alcoholic cirrhosis

BACKGROUND

PNPLA3 rs738409 polymorphism is associated with fatty liver disease, alcoholic or non-alcoholic (NAFLD) and hepatocellular carcinoma (HCC). TM6SF2 rs58542926 is clearly associated with NAFLD, but it is not clearly associated with HCC. The relationship between TM6SF2 rs58542926 and HCC and the potential synergistic effect of TM6SF2 and PNPLA3 variants in modifying the risk of HCC are not known.

AIM

This study assessed the interaction between PNPLA3 rs738409 and TM6SF2 rs58542926 variants in the conditioning of HCC development.

METHODS

A total of 511 cirrhotic patients (44% alcohol-related, 56% viral, 57.5% liver transplanted) were retrospectively investigated for HCC occurrence. PNPLA3 rs734809 and TM6SF2 rs58542926 were genotyped using restriction fragment length polymorphism and real-time allelic discrimination polymerase chain reaction methods.

RESULTS

Patients with HCC were more likely to be PNPLA3 rs734809 G/G homozygotes (41/150 vs. 60/361, p=0.009) or TM6SF2 rs58542926 C/T-T/T (27/150 vs. 41/361, p=0.044). The presence of either PNPLA3 G/G or TM6SF2*/T identified high-risk genotypes for HCC, which were strongly associated with HCC (64/150 vs. 93/361, p=0.0002). This association was evident in alcohol-related (p=0.0007) but not in viral cirrhosis.

CONCLUSION

TM6SF2 C/T or T/T in conjunction with PNPLA3 G/G variants may be potential genetic risk factors for developing HCC in alcohol-related cirrhosis.

How Useful Are Monogenic Rodent Models for the Study of Human Non-Alcoholic Fatty Liver Disease?

Improving understanding of the genetic basis of human non-alcoholic fatty liver disease (NAFLD) has the potential to facilitate risk stratification of affected patients, permit personalized treatment, and inform development of new therapeutic strategies. Animal models have been widely used to interrogate the pathophysiology of, and genetic predisposition to, NAFLD. Nevertheless, considerable interspecies differences in intermediary metabolism potentially limit the extent to which results can be extrapolated to humans. For example, human genome-wide association studies have identified polymorphisms in PNPLA3 and TM6SF2 as the two most prevalent determinants of susceptibility to NAFLD and its inflammatory component (NASH), but animal models of these mutations have had only variable success in recapitulating this link. In this review, we critically appraise selected murine monogenic models of NAFLD, NASH, and hepatocellular carcinoma (HCC) with a focus on how closely they mirror human disease.

Role of TM6SF2 rs58542926 in the pathogenesis of nonalcoholic pediatric fatty liver disease: A multiethnic study

We assessed the association between the single-nucleotide polymorphism (SNP) rs58542926 in the transmembrane 6 superfamily member 2 (TM6SF2) gene and fatty liver disease in obese youth. We genotyped the TM6SF2 rs58542926 SNP in a multiethnic cohort of 957 obese children and adolescents (42% Caucasians, 28% African Americans, 30% Hispanics). All underwent an oral glucose tolerance test, a liver panel, and a lipid profile. Of them, 454 children underwent a magnetic resonance imaging study to assess hepatic fat content and 11 underwent liver biopsy to assess the degree of disease severity. The minor allele of the rs58542926 SNP was associated with high hepatic fat content in Caucasians and African Americans (all P < 0.05), with high alanine aminotransferase levels in Hispanics (P < 0.05) and a more favorable lipoprotein profile (lower low-density lipoprotein, small dense low-density lipoprotein, and very small low-density lipoprotein) in Caucasians and Hispanics (all P < 0.05). The liver biopsy showed a higher prevalence of fibrosis (P = 0.04) and a higher nonalcoholic fatty liver disease activity score (P = 0.05) in subjects carrying the minor allele than in those homozygous for the common allele. Moreover, we observed a joint effect among the TM6SF2 rs58542926, the PNPLA3 rs738409, and the GCKR rs1260326 SNPs in determining intrahepatic fat accumulation (P < 0.05).

CONCLUSION

The rs58542926 SNP in the TM6SF2 gene is associated with pediatric nonalcoholic fatty liver disease but may confer protection against cardiovascular risk.

TM6SF2 E167K Variant, a Novel Genetic Susceptibility Variant, Contributing to Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is one of the most common causes of liver dysfunction worldwide, and its prevalence is highly associated with genetic susceptibility. The transmembrane 6 superfamily member 2 (TM6SF2) E167K variant represents a general genetic determinant of hepatic triglyceride content and lobular inflammation, and its presence appears to be directly involved in the pathogenesis and development of NAFLD. Although this variant appears to be a novel powerful modifier in the development of NAFLD, whether it is associated with an increased risk of NAFLD-related liver fibrosis and hepatocellular carcinoma (HCC) remains to be determined. The aim of this review is to describe the functions of the TM6SF2 E167K variant and its association with NAFLD, with particular emphasis on the underlying mechanisms of its role in the development and progression of NAFLD. Additionally, the links between the TM6SF2 E167K variant and NAFLD-related liver fibrosis and HCC will be discussed.

Nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is a disorder characterized by excess accumulation of fat in hepatocytes (nonalcoholic fatty liver (NAFL)); in up to 40% of individuals, there are additional findings of portal and lobular inflammation and hepatocyte injury (which characterize nonalcoholic steatohepatitis (NASH)). A subset of patients will develop progressive fibrosis, which can progress to cirrhosis. Hepatocellular carcinoma and cardiovascular complications are life-threatening co-morbidities of both NAFL and NASH. NAFLD is closely associated with insulin resistance; obesity and metabolic syndrome are common underlying factors. As a consequence, the prevalence of NAFLD is estimated to be 10-40% in adults worldwide, and it is the most common liver disease in children and adolescents in developed countries. Mechanistic insights into fat accumulation, subsequent hepatocyte injury, the role of the immune system and fibrosis as well as the role of the gut microbiota are unfolding. Furthermore, genetic and epigenetic factors might explain the considerable interindividual variation in disease phenotype, severity and progression. To date, no effective medical interventions exist that completely reverse the disease other than lifestyle changes, dietary alterations and, possibly, bariatric surgery. However, several strategies that target pathophysiological processes such as an oversupply of fatty acids to the liver, cell injury and inflammation are currently under investigation. Diagnosis of NAFLD can be established by imaging, but detection of the lesions of NASH still depend on the gold-standard but invasive liver biopsy. Several non-invasive strategies are being evaluated to replace or complement biopsies, especially for follow-up monitoring.

An overview of the genetics, mechanisms and management of NAFLD and ALD

Alcoholic liver disease (ALD) and, increasingly, non-alcoholic fatty liver disease (NAFLD) are common causes of advanced liver disease in many developed countries including the UK. Both diseases share parallel natural histories, progressing from steatosis, to steatohepatitis and fibrosis/cirrhosis; and are characterised by substantial interindividual variation in disease outcome. This article will provide an overview of disease mechanisms, genetic modifiers and management, focusing principally on NAFLD, while drawing parallels between the two conditions where appropriate.

The dual and opposite role of the TM6SF2-rs58542926 variant in protecting against cardiovascular disease and conferring risk for nonalcoholic fatty liver: A meta-analysis

The aim of this work was to estimate the strength of the effect of the TM6SF2 E167K (rs58542926 C/T) variant on blood lipid traits and nonalcoholic fatty liver disease (NAFLD) across different populations. We performed a systematic review by a meta-analysis; literature searches identified 10 studies. The rs58542926 exerts a significant role in modulating lipid traits, including total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), triglycerides (TG), and NAFLD. However, this influence on lipids and NAFLD is opposite between genotypes in the dominant model of inheritance. Pooled estimates of random effects in 101,326 individuals showed that carriers of the minor T allele (EK+KK individuals), compared with subjects homozygous for the ancestral C allele (EE genotype), are protected from cardiovascular disease (CVD), showing lower levels of TC, LDL-C, and TG; the differences in mean ± standard error (mg/dL) are -8.38 ± 1.56, -3.7 ± 0.9, and -9.4 ± 2.1, respectively. The rs58542926 variant was not associated with high-density lipoprotein cholesterol in a large sample (n = 91,937). In contrast, carriers of the T allele showed a moderate effect on the risk of NAFLD (odds ratio: 2.13; 95% confidence interval: 1.36-3.30; P = 0.0009; n = 3273) and approximately ∼2.2% higher lipid fat content when compared with homozygous EE (n = 3,413).

CONCLUSIONS

The rs58542926 appears to be an important modifier of blood lipid traits in different populations. As a challenge for personalized medicine, the C-allele, which has an overall frequency as high as 93%, is associated with higher blood lipids, whereas the T allele confers risk for NAFLD; in turn, CVD and NAFLD are strongly related outcomes. Although the variant confers protection against CVD at the expense of an increased risk of NAFLD, it does not explain the link between these two complex diseases.

Pathophysiology and Mechanisms of Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) encompasses a spectrum of liver disorders characterized by abnormal hepatic fat accumulation, inflammation, and hepatocyte dysfunction. Importantly, it is also closely linked to obesity and the metabolic syndrome. NAFLD predisposes susceptible individuals to cirrhosis, hepatocellular carcinoma, and cardiovascular disease. Although the precise signals remain poorly understood, NAFLD pathogenesis likely involves actions of the different hepatic cell types and multiple extrahepatic signals. The complexity of this disease has been a major impediment to the development of appropriate metrics of its progression and effective therapies. Recent clinical data place increasing importance on identifying fibrosis, as it is a strong indicator of hepatic disease-related mortality. Preclinical modeling of the fibrotic process remains challenging, particularly in the contexts of obesity and the metabolic syndrome. Future studies are needed to define the molecular pathways determining the natural progression of NAFLD, including key determinants of fibrosis and disease-related outcomes. This review covers the evolving concepts of NAFLD from both human and animal studies. We discuss recent clinical and diagnostic methods assessing NAFLD diagnosis, progression, and outcomes; compare the features of genetic and dietary animal models of NAFLD; and highlight pharmacological approaches for disease treatment.

Caring for children with NAFLD and navigating their care into adulthood

NAFLD is the most common chronic liver disease in children and adults, with its prevalence closely associated with obesity and other features of the metabolic syndrome. As young adults with NAFLD transition from the paediatric care environment to adult services, establishing a coordinated model of transition to ensure ongoing and appropriate care is critical. Enabling a smooth transfer begins with an understanding of the key differences between paediatric and adult NAFLD as well as the psychosocial factors that affect older adolescents. This Review summarizes the literature on paediatric NAFLD from the past two decades with a focus on the differences in epidemiology, pathology, pathophysiology and treatment that are relevant to clinicians who transition paediatric patients to adult care. An integrated model, which employs a team of adult and paediatric providers who can address the psychosocial, cognitive and logistical challenges of transition, provides the best opportunity for a seamless and coordinated transfer to adult care.

Genetic background in nonalcoholic fatty liver disease: A comprehensive review

In the Western world, nonalcoholic fatty liver disease (NAFLD) is considered as one of the most significant liver diseases of the twenty-first century. Its development is certainly driven by environmental factors, but it is also regulated by genetic background. The role of heritability has been widely demonstrated by several epidemiological, familial, and twin studies and case series, and likely reflects the wide inter-individual and inter-ethnic genetic variability in systemic metabolism and wound healing response processes. Consistent with this idea, genome-wide association studies have clearly identified Patatin-like phosholipase domain-containing 3 gene variant I148M as a major player in the development and progression of NAFLD. More recently, the transmembrane 6 superfamily member 2 E167K variant emerged as a relevant contributor in both NAFLD pathogenesis and cardiovascular outcomes. Furthermore, numerous case-control studies have been performed to elucidate the potential role of candidate genes in the pathogenesis and progression of fatty liver, although findings are sometimes contradictory. Accordingly, we performed a comprehensive literature search and review on the role of genetics in NAFLD. We emphasize the strengths and weaknesses of the available literature and outline the putative role of each genetic variant in influencing susceptibility and/or progression of the disease.

A genome-wide association study confirms PNPLA3 and identifies TM6SF2 and MBOAT7 as risk loci for alcohol-related cirrhosis

Alcohol misuse is the leading cause of cirrhosis and the second most common indication for liver transplantation in the Western world. We performed a genome-wide association study for alcohol-related cirrhosis in individuals of European descent (712 cases and 1,426 controls) with subsequent validation in two independent European cohorts (1,148 cases and 922 controls). We identified variants in the MBOAT7 (P = 1.03 × 10(-9)) and TM6SF2 (P = 7.89 × 10(-10)) genes as new risk loci and confirmed rs738409 in PNPLA3 as an important risk locus for alcohol-related cirrhosis (P = 1.54 × 10(-48)) at a genome-wide level of significance. These three loci have a role in lipid processing, suggesting that lipid turnover is important in the pathogenesis of alcohol-related cirrhosis.

Nonalcoholic fatty liver disease - current status and future directions

Nonalcoholic fatty liver disease (NAFLD) has emerged as the most common chronic liver disease worldwide with a reported prevalence ranging 6-33%, depending on the studied populations. It encompasses a spectrum of liver manifestations ranging from simple steatosis (also known as nonalcoholic fatty liver, NAFL) to nonalcoholic steatohepatitis (NASH), fibrosis and cirrhosis, which may ultimately progress to hepatocellular carcinoma. NAFLD is strongly associated with the components of metabolic syndrome, mainly obesity and type 2 diabetes mellitus. NAFLD patients are at increased risk of liver-related as well as cardiovascular mortality. Current paradigm suggests a benign course for NAFL whereas NASH is considered to be the progressive phenotype. Although previously under-recognized accumulating evidence suggests that NAFL may also progress, suggesting a higher number of patients at risk than previously appreciated. Liver biopsy remains the gold standard for definitive diagnosis, but the majority of patients can be diagnosed accurately by noninvasive methods. Approved therapies for NAFLD are still lacking and lifestyle modifications aiming at weight loss remain the mainstay of NAFLD treatment. Intensive research could identify insulin resistance, lipotoxicity and dysbiosis of the gut microbiota as major pathophysiological mechanisms, leading to the development of promising targeted therapies which are currently investigated in clinical trials. In this review we summarized the current knowledge of NAFLD epidemiology, natural history, diagnosis, pathogenesis and treatment and considered future directions.

Practical approach to non-alcoholic fatty liver disease in patients with diabetes

The prevalence of Type 2 diabetes is expected to increase in parallel with obesity rates and the ageing population. Recent studies show that Type 2 diabetes is associated with a twofold increase in the risk of non-alcoholic fatty liver disease, a leading cause of chronic liver disease. Individuals with non-alcoholic steatohepatitis, a more advanced stage of non-alcoholic fatty liver disease, are specifically at risk of developing fibrosis/cirrhosis (end-stage liver disease) and hepatocellular carcinoma; therefore, identifying individuals (with Type 2 diabetes) who are likely to develop hepatic complications is paramount. In the present clinical review, we discuss the potential impact of non-alcoholic fatty liver disease diagnosis on Type 2 diabetes, and the putative risk factors for developing non-alcoholic steatohepatitis and non-alcoholic steatohepatitis fibrosis. We highlight the limitations of currently used tools in non-alcoholic fatty liver disease diagnosis and staging, and provide an insight into future developments in the field. We present an example of a non-alcoholic fatty liver disease screening protocol and discuss the therapeutic options currently available to our patients.

TM6SF2 E167K variant is associated with severe steatosis in chronic hepatitis C, regardless of PNPLA3 polymorphism

BACKGROUND & AIMS

A common non-synonymous polymorphism, E167K, in transmembrane six superfamily member 2 (TM6SF2) gene has been recently associated with an increased hepatic triglyceride content, dyslipidemia and liver fibrosis in NAFLD patients. We investigated possible associations between the TM6SF2 variants and liver lesions in chronic hepatitis C.

PATIENTS AND METHODS

148 consecutive patients with biopsy proven anti-HCV/HCV-RNA-positive chronic hepatitis, naive for antiviral therapy, were genotyped for TM6SF2 E167K and PNPLA3 I148M variants.

RESULTS

The score of liver steatosis was higher in the 18 patients with TM6SF2 E167K variant (mean 1.9 ± 1.3) than in the 130 homozygotes for TM6SF2 167E allele (1.1 ± 1.1, P = 0.02), and the prevalence of a steatosis score ≥ 3 was 33.3% vs. 12.3% respectively (P = 0.02). No difference in necroinflammatory or fibrosis scores was found between the two groups. A general linear model identified as independent predictors of steatosis TM6SF2 E167K and PNPLA3 M148M variants and waist circumference (P = 0.0376, P = 0.0069 and P = 0.0273 respectively).

CONCLUSIONS

This is the first demonstration that TM6SF2 E167K variant is an independent predictor of liver steatosis in chronic hepatitis C.

Genetic Factors in the Pathogenesis of Nonalcoholic Fatty Liver and Steatohepatitis

Liver fat accumulation generally related to systemic insulin resistance characterizes nonalcoholic fatty liver disease (NAFLD), which in the presence of nonalcoholic steatohepatitis (NASH) can progress towards cirrhosis and hepatocellular carcinoma. Due to the epidemic of obesity, NAFLD is now the most frequent liver disease in Western countries. Epidemiological, familial, and twin studies provide evidence for a strong genetic component of NAFLD susceptibility. Recently, genome-wide association studies led to the identification of the major inherited determinants of hepatic fat accumulation: patatin-like phospholipase domain-containing 3 (PNPLA3) I148M gene and transmembrane 6 superfamily member 2 (TM6SF2) E167K gene variants, involved in lipid droplets remodelling and very low-density lipoproteins secretion, are the major determinants of interindividual differences in liver steatosis, and susceptibility to progressive NASH. In this review, we aimed to provide an overview of recent insights into the genetics of hepatic fat accumulation and steatohepatitis.

Transmembrane 6 superfamily member 2 gene E167K variant impacts on steatosis and liver damage in chronic hepatitis C patients

Steatosis and inherited host factors influence liver damage progression in chronic hepatitis C (CHC). The transmembrane 6 superfamily member 2 (TM6SF2) gene E167K variant increases liver fat and risk of progressive steatohepatitis by interfering with lipoprotein secretion. Our aim was to determine whether the E167K variant affects histological severity of steatosis, necroinflammation, and fibrosis in a cross-sectional cohort of 815 Italian therapy-naïve CHC patients. The association with clinically significant fibrosis was replicated in 645 Swiss/German patients. The TM6SF2 E167K variant was genotyped by TaqMan assays, steatosis graded according to the nonalcoholic fatty liver disease activity score, and necroinflammation and fibrosis graded and staged according to Ishak in Italian, and to Metavir in Swiss/German patients. The E167K variant was detected in 69 (9%) Italian patients and was associated with more severe steatosis, independently of confounders (P = 0.038). The association between E167K and steatosis severity was present in patients not infected by genotype 3 (G3) HCV (P = 0.031), but not in those infected by G3 HCV (P = 0.58). Furthermore, the E167K variant was associated with more severe necroinflammation (Ishak grade; adjusted P = 0.037) and nearly associated with more severe fibrosis (Ishak stage; adjusted P = 0.058). At multivariate logistic regression analysis, the E167K variant was independently associated with histologically probable or definite cirrhosis (Ishak stage S6; odds ratio [OR]: 2.19; 95% confidence interval [CI]: 1.18-3.93; P = 0.010). After further conditioning for steatosis and necroinflammation, the E167K variant remained associated with cirrhosis (OR, 3.15; 95% CI: 1.60-5.99; P < 0.001). In Swiss/German patients, the E167K variant was independently associated with clinically significant fibrosis Metavir stage F2-F4 (OR, 1.81; 95% CI: 1.12-3.02; P = 0.016).

CONCLUSION

TM6SF2 E167K variant impacts on steatosis severity and is associated with liver damage and fibrosis in patients with CHC.

Strategies, models and biomarkers in experimental non-alcoholic fatty liver disease research

Non-alcoholic fatty liver disease encompasses a spectrum of liver diseases, including simple steatosis, steatohepatitis, liver fibrosis and cirrhosis and hepatocellular carcinoma. Non-alcoholic fatty liver disease is currently the most dominant chronic liver disease in Western countries due to the fact that hepatic steatosis is associated with insulin resistance, type 2 diabetes mellitus, obesity, metabolic syndrome and drug-induced injury. A variety of chemicals, mainly drugs, and diets is known to cause hepatic steatosis in humans and rodents. Experimental non-alcoholic fatty liver disease models rely on the application of a diet or the administration of drugs to laboratory animals or the exposure of hepatic cell lines to these drugs. More recently, genetically modified rodents or zebrafish have been introduced as non-alcoholic fatty liver disease models. Considerable interest now lies in the discovery and development of novel non-invasive biomarkers of non-alcoholic fatty liver disease, with specific focus on hepatic steatosis. Experimental diagnostic biomarkers of non-alcoholic fatty liver disease, such as (epi)genetic parameters and '-omics'-based read-outs are still in their infancy, but show great promise. In this paper, the array of tools and models for the study of liver steatosis is discussed. Furthermore, the current state-of-art regarding experimental biomarkers such as epigenetic, genetic, transcriptomic, proteomic and metabonomic biomarkers will be reviewed.

Nonalcoholic fatty liver disease and type 2 diabetes: common pathophysiologic mechanisms

Nonalcoholic fatty liver disease (NAFLD) is an independent risk factor for advanced liver disease, type 2 diabetes (T2DM), and cardiovascular diseases. The prevalence of NAFLD in the general population is around 30 %, but it is up to three times higher in those with T2DM. Among people with obesity and T2DM, the NAFLD epidemic also is worsening. Therefore, it is important to identify early metabolic alterations and to prevent these diseases and their progression. In this review, we analyze the pathophysiologic mechanisms leading to NAFLD, particularly, those common to T2DM, such as liver and muscle insulin resistance. However, it is mainly adipose tissue insulin resistance that results in increased hepatic de novo lipogenesis, inflammation, and lipotoxicity. Although genetics predispose to NAFLD, an unhealthy lifestyle, including high-fat/high-sugar diets and low physical activity, increases the risk. In addition, alterations in gut microbiota and environmental chemical agents, acting as endocrine disruptors, may play a role.

Nonalcoholic fatty liver disease: new treatments

PURPOSE OF REVIEW

Nonalcoholic fatty liver disease is the most common cause of liver dysfunction in the western world because of its close association with obesity, insulin resistance and dyslipidaemia. Nonalcoholic steatohepatitis (NASH) is a particular health concern due to the increased morbidity and mortality associated with progressive disease. At present, without specific targeted pharmacological therapies, the mainstay of therapy remains weight loss through dietary modification and lifestyle change; thus, the purpose of this review is to summarize the recent evidence for current and emerging therapies in NASH.

RECENT FINDINGS

Some existing medications, including pioglitazones and angiotensin receptor antagonists, may be repurposed to help treat this condition. Vitamin E may improve histology in NASH, but safety issues limit its use. Recently, a number of novel agents specifically targeting nonalcoholic fatty liver disease pathogenesis have entered clinical trials, including the farnesoid X receptor agonist obeticholic acid, which has shown significant histological improvements in steatohepatitis and fibrosis.

SUMMARY

Diet/lifestyle modification remains the mainstay of treatment. For patients with NASH and advanced fibrosis, current liver-directed pharmacotherapy with vitamin E and pioglitazone offer some benefits; obeticholic acid appears promising and is currently being tested. Comorbidities must be diagnosed and treated; cardiovascular disease remains a primary cause of death in these patients.

Evidence of NAFLD progression from steatosis to fibrosing-steatohepatitis using paired biopsies: implications for prognosis and clinical management

BACKGROUND AND AIMS

There remains uncertainty about the natural history of non-alcoholic fatty liver disease (NAFLD). The spectrum of NAFLD includes non-alcoholic fatty liver (NAFL; steatosis without hepatocellular injury) and steatohepatitis (NASH; steatosis with hepatocyte ballooning degeneration±fibrosis). Our aim was to assess the histological severity of NAFLD in a cohort with serial biopsy data, and determine factors predicting progression.

METHODS

Patients with two liver biopsies more than a year apart were identified. Clinical and laboratory data were collected from the time of liver biopsy.

RESULTS

108 patients had serial biopsies (median interval 6.6years, range 1.3-22.6). 81 (75%) patients had NASH and 27 had NAFL. Overall, 45 (42%) patients had fibrosis progression, 43 (40%) had no change in fibrosis, while 20 (18%) had fibrosis regression. Importantly, no significant difference in the proportion exhibiting fibrosis progression was found between those with NAFL or NASH at index biopsy (37% vs. 43%, p=0.65). Progression to NASH was seen in 44% of patients with baseline NAFL. Of 10 patients with NAFL who had fibrosis progression, 3 progressed by 1 stage, 5 by 2 stages and 2 by 3 stages; all had NASH on follow-up biopsy. Of concern, 6 of 27 (22%) patients with baseline NAFL, reached stage 3 fibrosis at follow-up biopsy. Among the patients with NAFL, 80% of those having fibrosis progression were diabetic at the follow-up liver biopsy compared with 25% of non-progressors (p=0.005).

CONCLUSIONS

Contrary to current dogma, this study suggests that steatosis can progress to NASH and clinically significant fibrosis.

Paradoxical dissociation between hepatic fat content and de novo lipogenesis due to PNPLA3 sequence variant

CONTEXT

Nonalcoholic fatty liver disease (NAFLD) is an emerging epidemic disease characterized by increased hepatic fat, due to an imbalance between synthesis and removal of hepatic lipids. In particular, increased hepatic de novo lipogenesis (DNL) is a key feature associated with NAFLD. The genetic variations I148M in PNPLA3 and E167K in TM6SF2 confer susceptibility to NAFLD.

OBJECTIVE

Here we aimed to investigate the contribution of DNL to liver fat accumulation in the PNPLA3 I148M or TM6SF2 E167K genetic determinants of NAFLD.

PATIENTS AND METHODS

The PNPLA3 I148M and TM6SF2 E167K were genotyped in two well-characterized cohorts of Europeans. In the first cohort (Helsinki cohort; n = 88), we directly quantified hepatic DNL using deuterated water. In the second cohort (Milan cohort; n = 63), we quantified the hepatic expression of SREBP1c that we have found previously associated with increased fat content. Liver fat was measured by magnetic resonance proton spectroscopy in the Helsinki cohort, and by histological assessment of liver biopsies in the Milan cohort.

RESULTS

PNPLA3 148M was associated with lower DNL and expression of the lipogenic transcription factor SREBP1c despite substantial increased hepatic fat content.

CONCLUSIONS

Our data show a paradoxical dissociation between hepatic DNL and hepatic fat content due to the PNPLA3 148M allele indicating that increased DNL is not a key feature in all individuals with hepatic steatosis, and reinforces the contribution of decreased mobilization of hepatic triglycerides for hepatic lipid accumulation in subject with the PNPLA3 148M allele.

Genetics of liver disease: From pathophysiology to clinical practice

Paralleling the first 30 years of the Journal of Hepatology we have witnessed huge advances in our understanding of liver disease and physiology. Genetic advances have played no small part in that. Initial studies in the 1970s and 1980s identified the strong major histocompatibility complex associations in autoimmune liver diseases. During the 1990 s, developments in genomic technologies drove the identification of genes responsible for Mendelian liver diseases. Over the last decade, genome-wide association studies have allowed for the dissection of the genetic susceptibility to complex liver disorders, in which also environmental co-factors play important roles. Findings have allowed the identification and elaboration of pathophysiological processes, have indicated the need for reclassification of liver diseases and have already pointed to new disease treatments. In the immediate future genetics will allow further stratification of liver diseases and contribute to personalized medicine. Challenges exist with regard to clinical implementation of rapidly developing technologies and interpretation of the wealth of accumulating genetic data. The historical perspective of genetics in liver diseases illustrates the opportunities for future research and clinical care of our patients.

Recent advances in understanding/management of non-alcoholic steatohepatitis

Non-alcoholic steatohepatitis (NASH) can lead to advanced fibrosis, hepatocellular carcinoma, and end-stage liver disease requiring liver transplantation. A myriad of pathways and genetic influence contribute to NASH pathogenesis and liver disease progression. Diagnosing patients with NASH and advanced fibrosis is critical prior to treatment and prognostication. There has been ongoing interest in developing non-invasive biomarkers and tools for identifying NASH and advanced fibrosis. To date, there has been no approved therapy for NASH. Recently, the FLINT (Farnesoid X Receptor [FXR] Ligand Obeticholic Acid in NASH Treatment) trial provided promising results of the efficacy of obeticholic acid, a farnesoid X receptor agonist, in improving histological features of NASH and fibrosis. Long-term studies are needed to assess the safety of obeticholic acid and its effects on liver- and cardiovascular-related outcomes.

Circulating triacylglycerol signatures and insulin sensitivity in NAFLD associated with the E167K variant in TM6SF2

BACKGROUND & AIMS

The Glu167Lys (E167K) variant in the transmembrane 6 superfamily member 2 protein (TM6SF2) was recently shown to influence liver fat (LFAT) content. We aimed at studying how this variant influences circulating triacylglycerol (TAG) signatures and whether it influences hepatic or adipose tissue insulin sensitivity.

METHODS

We genotyped 300 Finnish subjects for the E167K (rs58542926) variant in TM6SF2 and for the I148M (rs738409) variant in the patatin-like phospholipase domain-containing protein 3 (PNPLA3) in whom LFAT was measured using 1H-MRS and circulating lipids by UPLC-MS. We compared the plasma lipidome between E167K carriers (TM6SF2EK/KK) and non-carriers (TM6SF2EE), and between three groups of NAFLD: (i) carriers of the E167K but not of the I148M variant in PNPLA3 ('TM6SF2 NAFLD'), (ii) carriers of the I148M but not of the E167K variant ('PNPLA3 NAFLD'), and (iii) non-carriers of either risk allele ('Non-risk NAFLD'). Hepatic and adipose tissue insulin sensitivities were measured using the euglycemic hyperinsulinemic clamp technique combined with infusion of [3-3H]glucose in 111 subjects.

RESULTS

The LFAT content was 34% higher in the TM6SF2EK/KK (13.07±1.57%) than in the TM6SF2EE group (9.77±0.58%, p=0.013). The effect of insulin on glucose production and lipolysis were significantly higher in the TM6SF2EK/KK than in the TM6SF2EE group. Comparison of the three NAFLD groups with similar LFATs showed that both the 'TM6SF2 NAFLD' and 'PNPLA3 NAFLD' had significantly lower triglyceride levels and were characterized by lower levels of most common TAGs compared to the 'Non-risk NAFLD' group.

CONCLUSIONS

We conclude that the E167K variant in TM6SF2 is associated with a distinct subtype of NAFLD, characterized by preserved insulin sensitivity with regard to lipolysis, hepatic glucose production and lack of hypertriglyceridemia despite a clearly increased LFAT content.