Perinatal Nutritional Reprogramming of the Epigenome Promotes Subsequent Development of Nonalcoholic Steatohepatitis

Envisioning how to advance the MASH field

Since 1980, the cumulative effort of scientists and health-care stakeholders has advanced the prerequisites to address metabolic dysfunction-associated steatotic liver disease (MASLD), a prevalent chronic non-communicable liver disease. This effort has led to, among others, the approval of the first drug specific for metabolic dysfunction-associated steatohepatitis (MASH; formerly known as nonalcoholic steatohepatitis). Despite substantial progress, MASLD is still a leading cause of advanced chronic liver disease, including primary liver cancer. This Perspective contextualizes the nomenclature change from nonalcoholic fatty liver disease to MASLD and proposes important considerations to accelerate further progress in the field, optimize patient-centric multidisciplinary care pathways, advance pharmacological, behavioural and diagnostic research, and address health disparities. Key regulatory and other steps necessary to optimize the approval and access to upcoming additional pharmacological therapeutic agents for MASH are also outlined. We conclude by calling for increased education and awareness, enhanced health system preparedness, and concerted action by policy-makers to further the public health and policy agenda to achieve at least parity with other non-communicable diseases and to aid in growing the community of practice to reduce the human and economic burden and end the public health threat of MASLD and MASH by 2030.

Glycogen synthase kinase 3 activity enhances liver inflammation in MASH

Background & Aims

Metabolic dysfunction-associated steatohepatitis (MASH) is characterized by excessive circulating toxic lipids, hepatic steatosis, and liver inflammation. Monocyte adhesion to liver sinusoidal endothelial cells (LSECs) and transendothelial migration (TEM) are crucial in the inflammatory process. Under lipotoxic stress, LSECs develop a proinflammatory phenotype known as endotheliopathy. However, mediators of endotheliopathy remain unclear.

Methods

Primary mouse LSECs isolated from C57BL/6J mice fed chow or MASH-inducing diets rich in fat, fructose, and cholesterol (FFC) were subjected to multi-omics profiling. Mice with established MASH resulting from a choline-deficient high-fat diet (CDHFD) or FFC diet were also treated with two structurally distinct GSK3 inhibitors (LY2090314 and elraglusib [9-ING-41]).

Results

Integrated pathway analysis of the mouse LSEC proteome and transcriptome indicated that leukocyte TEM and focal adhesion were the major pathways altered in MASH. Kinome profiling of the LSEC phosphoproteome identified glycogen synthase kinase (GSK)-3β as the major kinase hub in MASH. GSK3β-activating phosphorylation was increased in primary human LSECs treated with the toxic lipid palmitate and in human MASH. Palmitate upregulated the expression of C-X-C motif chemokine ligand 2, intracellular adhesion molecule 1, and phosphorylated focal adhesion kinase, via a GSK3-dependent mechanism. Congruently, the adhesive and transendothelial migratory capacities of primary human neutrophils and THP-1 monocytes through the LSEC monolayer under lipotoxic stress were reduced by GSK3 inhibition. Treatment with the GSK3 inhibitors LY2090314 and elraglusib ameliorated liver inflammation, injury, and fibrosis in FFC- and CDHFD-fed mice, respectively. Immunophenotyping using cytometry by mass cytometry by time of flight of intrahepatic leukocytes from CDHFD-fed mice treated with elraglusib showed reduced infiltration of proinflammatory monocyte-derived macrophages and monocyte-derived dendritic cells.

Conclusion

GSK3 inhibition attenuates lipotoxicity-induced LSEC endotheliopathy and could serve as a potential therapeutic strategy for treating human MASH.

Impact and Implications

LSECs under lipotoxic stress in MASH develop a proinflammatory phenotype known as endotheliopathy, with obscure mediators and functional outcomes. The current study identified GSK3 as the major driver of LSEC endotheliopathy, examined its pathogenic role in myeloid cell-associated liver inflammation, and defined the therapeutic efficacy of pharmacological GSK3 inhibitors in murine MASH. This study provides preclinical data for the future investigation of GSK3 pharmacological inhibitors in human MASH. The results of this study are important to hepatologists, vascular biologists, and investigators studying the mechanisms of inflammatory liver disease and MASH, as well as those interested in drug development.

Maternal Obesogenic Diet Attenuates Microbiome-Dependent Offspring Weaning Reaction with Worsening of Steatotic Liver Disease

The mechanisms by which maternal obesity increases the susceptibility to steatotic liver disease in offspring are incompletely understood. Models using different maternal obesogenic diets (MODEs) display phenotypic variability, likely reflecting the influence of timing and diet composition. This study compared three maternal obesogenic diets using standardized exposure times to identify differences in offspring disease progression. This study found that the severity of hepatic inflammation and fibrosis in the offspring depends on the composition of the maternal obesogenic diet. Offspring cecal microbiome composition was shifted in all MODE groups relative to control. Decreased α-diversity in some MODE offspring with shifts in abundance of multiple genera were suggestive of delayed maturation of the microbiome. The weaning reaction typically characterized by a spike in intestinal expression of Tnfa and Ifng was attenuated in MODE offspring in an early microbiome-dependent manner using cross-fostering. Cross-fostering also switched the severity of disease progression in offspring dependent on the diet of the fostering dam. These results identify maternal diet composition and timing of exposure as modifiers in mediating transmissible changes in the microbiome. These changes in the early microbiome alter a critical window during weaning that drives susceptibility to progressive liver disease in the offspring.

Gestational and Developmental Contributors of Pediatric MASLD

Pediatric metabolic dysfunction-associated steatotic liver disease (MASLD) is common and can be seen as early as in utero. A growing body of literature suggests that gestational and early life exposures modify the risk of MASLD development in children. These include maternal risk factors, such as poor cardiometabolic health (e.g., obesity, gestational diabetes, rapid weight gain during pregnancy, and MASLD), as well as periconceptional dietary exposures, degree of physical activity, intestinal microbiome, and smoking. Paternal factors, such as diet and obesity, also appear to play a role. Beyond gestation, early life dietary exposures, as well as the rate of infant weight gain, may further modify the risk of future MASLD development. The mechanisms linking parental health and environmental exposures to pediatric MASLD are complex and not entirely understood. In conclusion, investigating gestational and developmental contributors to MASLD is critical and may identify future interventional targets for disease prevention.

Mitochondrial dysfunction and epigenetics underlying the link between early-life nutrition and non-alcoholic fatty liver disease

Early-life malnutrition plays a critical role in foetal development and predisposes to metabolic diseases later in life, according to the concept of 'developmental programming'. Different types of early nutritional imbalance, including undernutrition, overnutrition and micronutrient deficiency, have been related to long-term metabolic disorders. Accumulating evidence has demonstrated that disturbances in nutrition during the period of preconception, pregnancy and primary infancy can affect mitochondrial function and epigenetic mechanisms. Moreover, even though multiple mechanisms underlying non-alcoholic fatty liver disease (NAFLD) have been described, in the past years, special attention has been given to mitochondrial dysfunction and epigenetic alterations. Mitochondria play a key role in cellular metabolic functions. Dysfunctional mitochondria contribute to oxidative stress, insulin resistance and inflammation. Epigenetic mechanisms have been related to alterations in genes involved in lipid metabolism, fibrogenesis, inflammation and tumorigenesis. In accordance, studies have reported that mitochondrial dysfunction and epigenetics linked to early-life nutrition can be important contributing factors in the pathogenesis of NAFLD. In this review, we summarise the current understanding of the interplay between mitochondrial dysfunction, epigenetics and nutrition during early life, which is relevant to developmental programming of NAFLD.

Maternal Weight Management to Prevent the Developmental Programming of MAFLD in Offspring of Obese Mothers

The global surge of obesity amongst women of reproductive age has raised concerns surrounding the health consequences for their offspring as there is a formidable link between an obesogenic maternal environment and the developmental programming of metabolic dysfunction in the offspring. Specifically, the offspring of mothers with obesity have a three-fold higher risk of developing metabolic-associated fatty liver disease (MAFLD) compared to the offspring of healthy-weight mothers. Given the burgeoning burden of obesity and its comorbidities, it is essential to focus research efforts on methods to alleviate the intergenerational onset of obesity and MAFLD. This review summarizes the current research surrounding the developmental programming of MAFLD in the offspring of mothers with obesity and examines the potential for weight interventions to prevent such metabolic dysfunction in the offspring. It focuses on the benefits of pre-pregnancy interventional strategies, including dietary and exercise intervention, to ameliorate adverse liver health outcomes in the offspring. The utility and translation of these interventions for humans may be difficult for prospective mothers with obesity, thus the use of pre-pregnancy therapeutic weight loss aids, such as glucagon-like peptide-1 receptor agonists, is also discussed.

Adverse Maternal Environments Perturb Hepatic DNA Methylome and Transcriptome Prior to the Adult-Onset Non-Alcoholic Fatty Liver Disease in Mouse Offspring

Exposure to adverse early-life environments (AME) increases the incidence of developing adult-onset non-alcoholic fatty liver disease (NAFLD). DNA methylation has been postulated to link AME and late-onset diseases. This study aimed to investigate whether and to what extent the hepatic DNA methylome was perturbed prior to the development of NAFLD in offspring exposed to AME in mice. AME constituted maternal Western diet and late-gestational stress. Male offspring livers at birth (d0) and weaning (d21) were used for evaluating the DNA methylome and transcriptome using the reduced representation of bisulfite sequencing and RNA-seq, respectively. We found AME caused 5879 differentially methylated regions (DMRs) and zero differentially expressed genes (DEGs) at d0 and 2970 and 123, respectively, at d21. The majority of the DMRs were distal to gene transcription start sites and did not correlate with DEGs. The DEGs at d21 were significantly enriched in GO biological processes characteristic of liver metabolic functions. In conclusion, AME drove changes in the hepatic DNA methylome, which preceded perturbations in the hepatic metabolic transcriptome, which preceded the onset of NAFLD. We speculate that subtle impacts on dynamic enhancers lead to long-range regulatory changes that manifest over time as gene network alternations and increase the incidence of NAFLD later in life.

Prenatal Choline Supplement in a Maternal Obesity Model Modulates Offspring Hepatic Lipidomes

Maternal obesity during pregnancy adversely impacts offspring health, predisposing them to chronic metabolic diseases characterized by insulin resistance, dysregulated macronutrient metabolism, and lipid overload, such as metabolic-associated fatty liver disease (MAFLD). Choline is a semi-essential nutrient involved in lipid and one-carbon metabolism that is compromised during MAFLD progression. Here, we investigated under high-fat (HF) obesogenic feeding how maternal choline supplementation (CS) influenced the hepatic lipidome of mouse offspring. Our results demonstrate that maternal HF+CS increased relative abundance of a subclass of phospholipids called plasmalogens in the offspring liver at both embryonic day 17.5 and after 6 weeks of postnatal HF feeding. Consistent with the role of plasmalogens as sacrificial antioxidants, HF+CS embryos were presumably protected with lower oxidative stress. After postnatal HF feeding, the maternal HF+CS male offspring also had higher relative abundance of both sphingomyelin d42:2 and its side chain, nervonic acid (FA 24:1). Nervonic acid is exclusively metabolized in the peroxisome and is tied to plasmalogen synthesis. Altogether, this study demonstrates that under the influence of obesogenic diet, maternal CS modulates the fetal and postnatal hepatic lipidome of male offspring, favoring plasmalogen synthesis, an antioxidative response that may protect the mouse liver from damages due to HF feeding.

Maternal Exercise Protects Male Offspring From Maternal Diet-Programmed Nonalcoholic Fatty Liver Disease Progression

Maternal obesity programs the risk for development of nonalcoholic fatty liver disease (NAFLD) in offspring. Maternal exercise is a potential intervention to prevent developmentally programmed phenotypes. We hypothesized that maternal exercise would protect from progression of NAFLD in offspring previously exposed to a maternal obesogenic diet. Female mice were fed chow (CON) or high fat, fructose, cholesterol (HFFC) and bred with lean males. A subset had an exercise wheel introduced 4 weeks after starting the diet to allow for voluntary exercise. The offspring were weaned to the HFFC diet for 7 weeks to induce NAFLD. Serum, adipose, and liver tissue were collected for metabolic, histologic, and gene expression analyses. Cecal contents were collected for 16S sequencing. Global metabolomics was performed on liver. Female mice fed the HFFC diet had increased body weight prior to adding an exercise wheel. Female mice fed the HFFC diet had an increase in exercise distance relative to CON during the preconception period. Exercise distance was similar between groups during pregnancy and lactation. CON-active and HFFC-active offspring exhibited decreased inflammation compared with offspring from sedentary dams. Fibrosis increased in offspring from HFFC-sedentary dams compared with CON-sedentary. Offspring from exercised HFFC dams exhibited less fibrosis than offspring from sedentary HFFC dams. While maternal diet significantly affected the microbiome of offspring, the effect of maternal exercise was minimal. Metabolomics analysis revealed shifts in multiple metabolites including several involved in bile acid, 1-carbon, histidine, and acylcarnitine metabolism. This study provides preclinical evidence that maternal exercise is a potential approach to prevent developmentally programmed liver disease progression in offspring.

Liver sinusoidal endothelial cell expressed vascular cell adhesion molecule 1 promotes liver fibrosis

Background

During liver injury, liver sinusoidal endothelial cells (LSECs) dysfunction and capillarization promote liver fibrosis. We have previously reported that the LSEC vascular cell adhesion molecule 1 (VCAM1) plays a key role in liver inflammation in nonalcoholic steatohepatitis (NASH) and we now aim to uncover its role in LSEC capillarization and liver fibrosis.

Methods

Wild-type C57BL/6J mice were fed either chow or high fat, fructose and cholesterol diet to induce NASH and treated with either anti-VCAM1 neutralizing antibody or control isotype antibody. Inducible endothelial cell-specific Vcam1 deleted mice (Vcam1^Δend ) and control mice (Vcam1^fl/fl ) were fed choline-deficient high-fat diet (CD-HFD) to induce NASH or injected with carbon tetrachloride to induce liver fibrosis. LSECs isolated from Vcam1^fl/fl or Vcam1^Δend and hepatic stellate cells (HSCs) isolated from wild-type mice were cocultured in a 3-D system or a μ-Slide 2 well co-culture system.

Results

Immunostaining for Lyve1 (marker of differentiated LSECs) was reduced in Vcam1^fl/fl mice and restored in Vcam1^Δend mice in both NASH and liver fibrosis models. Co-immunostaining showed increased α-smooth muscle actin in the livers of Vcam1^fl/fl mice in areas lacking Lyve1. Furthermore, scanning electron microscopy showed reduced LSEC fenestrae in the Vcam1^fl/fl mice but not Vcam1^Δend mice in both injury models, suggesting that VCAM1 promotes LSEC capillarization during liver injury. HSCs profibrogenic markers were reduced when cocultured with LSECs from CD-HFD fed Vcam1^Δend mice compared to Vcam1^fl/fl mice. Furthermore, recombinant VCAM1 activated the Yes-associated protein 1 pathway and induced a fibrogenic phenotype in HSCs in vitro, supporting the profibrogenic role of LSEC VCAM1.

Conclusion

VCAM1 is not just a scaffold for leukocyte adhesion during liver injury, but also a modulator of LSEC capillarization and liver fibrosis.

Maternal obesogenic diet regulates offspring bile acid homeostasis and hepatic lipid metabolism via the gut microbiome in mice

Mice exposed in gestation to maternal high-fat/high-sucrose (HF/HS) diet develop altered bile acid (BA) homeostasis. We hypothesized that these reflect an altered microbiome and asked if microbiota transplanted from HF/HS offspring change hepatic BA and lipid metabolism to determine the directionality of effect. Female mice were fed HF/HS or chow (CON) for 6 wk and bred with lean males. 16S sequencing was performed to compare taxa in offspring. Cecal microbiome transplantation (CMT) was performed from HF/HS or CON offspring into antibiotic-treated mice fed chow or high fructose. BA, lipid metabolic, and gene expression analyses were performed in recipient mice. Gut microbiomes from HF/HS offspring segregated from CON offspring, with increased Firmicutes to Bacteriodetes ratios and Verrucomicrobial abundance. After CMT was performed, HF/HS-recipient mice had larger BA pools, increased intrahepatic muricholic acid, and decreased deoxycholic acid species. HF/HS-recipient mice exhibited downregulated hepatic Mrp2, increased hepatic Oatp1b2, and decreased ileal Asbt mRNA expression. HF/HS-recipient mice exhibited decreased cecal butyrate and increased hepatic expression of Il6. HF/HS-recipient mice had larger livers and increased intrahepatic triglyceride versus CON-recipient mice after fructose feeding, with increased hepatic mRNA expression of lipogenic genes including Srebf1, Fabp1, Mogat1, and Mogat2. CMT from HF/HS offspring increased BA pool and shifted the composition of the intrahepatic BA pool. CMT from HF/HS donor offspring increased fructose-induced liver triglyceride accumulation. These findings support a causal role for vertical transfer of an altered microbiome in hepatic BA and lipid metabolism in HF/HS offspring.NEW & NOTEWORTHY We utilized a mouse model of maternal obesogenic diet exposure to evaluate the effect on offspring microbiome and bile acid homeostasis. We identified shifts in the offspring microbiome associated with changes in cecal bile acid levels. Transfer of the microbiome from maternal obesogenic diet-exposed offspring to microbiome-depleted mice altered bile acid homeostasis and increased fructose-induced hepatic steatosis.

The Origins of NAFLD: The Potential Implication of Intrauterine Life and Early Postnatal Period

Fetal life and the first few months after birth represent a plastic age, defined as a “window of opportunity”, as the organism is particularly susceptible to environmental pressures and has to adapt to environmental conditions. Several perturbations in pregnancy, such as excessive weight gain, obesity, gestational diabetes mellitus and an inadequate or high-fat diet, have been associated with long-term metabolic consequences in offspring, even without affecting birth weight. Moreover, great interest has also been focused on the relationship between the gut microbiome of early infants and health status in later life. Consistently, in various epidemiological studies, a condition of dysbiosis has been associated with an increased inflammatory response and metabolic alterations in the host, with important consequences on the intestinal and systemic health of the unborn child. This review aims to summarize the current knowledge on the origins of NAFLD, with particular attention to the potential implications of intrauterine life and the early postnatal period. Due to the well-known association between gut microbiota and the risk of NAFLD, a specific focus will be devoted to factors affecting early microbiota formation/composition.

Aberrant DNA Methylation Mediates the Transgenerational Risk of Metabolic and Chronic Disease Due to Maternal Obesity and Overnutrition

Maternal obesity is a rapidly evolving universal epidemic leading to acute and long-term medical and obstetric health issues, including increased maternal risks of gestational diabetes, hypertension and pre-eclampsia, and the future risks for offspring's predisposition to metabolic diseases. Epigenetic modification, in particular DNA methylation, represents a mechanism whereby environmental effects impact on the phenotypic expression of human disease. Maternal obesity or overnutrition contributes to the alterations in DNA methylation during early life which, through fetal programming, can predispose the offspring to many metabolic and chronic diseases, such as non-alcoholic fatty liver disease, obesity, diabetes, and chronic kidney disease. This review aims to summarize findings from human and animal studies, which support the role of maternal obesity in fetal programing and the potential benefit of altering DNA methylation to limit maternal obesity related disease in the offspring.

Hepatic Steatosis in Infancy: The Beginning of Pediatric Nonalcoholic Fatty Liver Disease?

Nonalcoholic fatty liver disease is clinically silent and the age of its onset is unknown. Fatty liver can occur as early as in utero in the context of an unfavorable maternal metabolic environment. Our objective was to determine the prevalence of hepatic steatosis in a cohort of previously healthy infants less than 3 months of age.

Methods

Retrospective study of all abdominal computed tomography (CT) scans performed from 2009 to 2019 for the investigation of trauma. Two independent reviewers applied published criteria to determine the presence of hepatic steatosis. Descriptive statistics were used. The groups with and without steatosis were compared using Wilcoxon-Mann Whitney or Fisher exact test.

Results

Of 119 CT scans available in infants younger than 3 months of age, 65 were performed in previously healthy infants for the investigation of trauma. The included population was predominantly male, non-Hispanic, with a median age of 60 days (interquartile range, 34-73 d). Depending on the criteria used, 23% or 26% of infants had evidence of fatty liver. The prevalence of maternal obesity and/or diabetes was 11% (of the 65 pregnancies) but there was no significant difference in maternal risk factors between infants with and without evidence of steatosis.

Conclusions

Findings suggest CT evidence of hepatic steatosis in up to a quarter of otherwise healthy infants ≤3 months of age. This may represent early manifestation of pediatric nonalcoholic fatty liver disease. The natural history and pathophysiology of this condition need to be studied to determine optimal detection, prevention and early intervention strategies.

Perspectives on youth-onset nonalcoholic fatty liver disease

BACKGROUND

The prevalence and incidence of youth-onset nonalcoholic fatty liver disease (NAFLD) far exceeds other paediatric chronic liver diseases and represents a considerable public health issue globally.

METHODS

Here, we performed a narrative review of current knowledge regarding the epidemiology of paediatric NAFLD, selected concepts in pathogenesis, comorbidities, diagnosis, and management, and issues related to the transition to adulthood.

RESULTS

Paediatric NAFLD has become increasingly more prevalent, especially in certain subgroups, such as children with obesity and certain races/ethnicities. The pathophysiology of paediatric NAFLD is complex and multifactorial, driven by an interaction of environmental and genetic factors. Once developed, NAFLD in childhood is associated with type 2 diabetes, hypertension, increased cardiovascular disease risk, and end-stage liver disease. This predicts an increased burden of morbidity and mortality in adolescents and young adults. Early screening and diagnosis are therefore crucial, and the development of noninvasive biomarkers remains an active area of investigation. Currently, treatment strategies are focused on lifestyle changes, but there is also research interest in pharmacological and surgical options. In the transition from paediatric to adult care, there are several potential challenges/barriers to treatment and research is needed to understand how best to support patients during this time.

CONCLUSIONS

Our understanding of the epidemiology and pathophysiology of paediatric NAFLD has increased considerably over recent decades, but several critical knowledge gaps remain and must be addressed in order to better mitigate the short-term and long-term risks of youth-onset NAFLD.

Developmental Programming of NAFLD by Parental Obesity

The surge of obesity across generations has become an increasingly relevant issue, with consequences for associated comorbidities in offspring. Data from longitudinal birth cohort studies support an association between maternal obesity and offspring nonalcoholic fatty liver disease (NAFLD), suggesting that perinatal obesity or obesogenic diet exposure reprograms offspring liver and increases NAFLD susceptibility. In preclinical models, offspring exposed to maternal obesogenic diet have increased hepatic steatosis after diet-induced obesity; however, the implications for later NAFLD development and progression are still unclear. Although some models show increased NAFLD incidence and progression in offspring, development of nonalcoholic steatohepatitis with fibrosis may be model dependent. Multigenerational programming of NAFLD phenotypes occurs after maternal obesogenic diet exposure; however, the mechanisms for such programming remain poorly understood. Likewise, emerging data on the role of paternal obesity in offspring NAFLD development reveal incomplete mechanisms. This review will explore the impact of parental obesity and obesogenic diet exposure on offspring NAFLD and areas for further investigation, including the impact of parental diet on disease progression, and consider potential interventions in preclinical models.

From genome sequencing to the discovery of potential biomarkers in liver disease

Chronic liver disease progresses through several stages, fatty liver, steatohepatitis, cirrhosis, and eventually, it leads to hepatocellular carcinoma (HCC) over a long period of time. Since a large proportion of patients with HCC are accompanied by cirrhosis, it is considered to be an important factor in the diagnosis of liver cancer. This is because cirrhosis leads to an irreversible harmful effect, but the early stages of chronic liver disease could be reversed to a healthy state. Therefore, the discovery of biomarkers that could identify the early stages of chronic liver disease is important to prevent serious liver damage. Biomarker discovery at liver cancer and cirrhosis has enhanced the development of sequencing technology. Next generation sequencing (NGS) is one of the representative technical innovations in the biological field in the recent decades and it is the most important thing to design for research on what type of sequencing methods are suitable and how to handle the analysis steps for data integration. In this review, we comprehensively summarized NGS techniques for identifying genome, transcriptome, DNA methylome and 3D/4D chromatin structure, and introduced framework of processing data set and integrating multi-omics data for uncovering biomarkers.

Fructose-mediated effects on gene expression and epigenetic mechanisms associated with NAFLD pathogenesis

Nonalcoholic fatty liver disease (NAFLD) is a chronic, frequently progressive condition that develops in response to excessive hepatocyte fat accumulation (i.e., steatosis) in the absence of significant alcohol consumption. Liver steatosis develops as a result of imbalanced lipid metabolism, driven largely by increased rates of de novo lipogenesis and hepatic fatty acid uptake and reduced fatty acid oxidation and/or disposal to the circulation. Fructose is a naturally occurring simple sugar, which is most commonly consumed in modern diets in the form of sucrose, a disaccharide comprised of one molecule of fructose covalently bonded with one molecule of glucose. A number of observational and experimental studies have demonstrated detrimental effects of dietary fructose consumption not only on diverse metabolic outcomes such as insulin resistance and obesity, but also on hepatic steatosis and NAFLD-related fibrosis. Despite the compelling evidence that excessive fructose consumption is associated with the presence of NAFLD and may even promote the development and progression of NAFLD to more clinically severe phenotypes, the molecular mechanisms by which fructose elicits effects on dysregulated liver metabolism remain unclear. Emerging data suggest that dietary fructose may directly alter the expression of genes involved in lipid metabolism, including those that increase hepatic fat accumulation or reduce hepatic fat removal. The aim of this review is to summarize the current research supporting a role for dietary fructose intake in the modulation of transcriptomic and epigenetic mechanisms underlying the pathogenesis of NAFLD.

Liver Diseases in the Perinatal Period: Interactions Between Mother and Infant

Liver diseases affecting the mother and infant dyad may present in the perinatal period from 20 weeks of gestation to 28 days of life. This review will focus on the current approach to neonatal acute liver failure and the progress made in the diagnosis and management of gestational alloimmune liver disease. It will highlight mother-to-child transmission of viral hepatitis, both management and public health implications. Emerging concepts implicating maternal obesity and nutrition in the development of a rapidly progressive nonalcoholic steatohepatitis phenotype in the offspring will be discussed. Finally, the presentation and management of acute fatty liver of pregnancy and intrahepatic cholestasis of pregnancy, and their impact on the fetus, will be reviewed.

Primary Alcohol-Activated Human and Mouse Hepatic Stellate Cells Share Similarities in Gene-Expression Profiles

Alcoholic liver disease (ALD) is a leading cause of cirrhosis in the United States, which is characterized by extensive deposition of extracellular matrix proteins and formation of a fibrous scar. Hepatic stellate cells (HSCs) are the major source of collagen type 1 producing myofibroblasts in ALD fibrosis. However, the mechanism of alcohol-induced activation of human and mouse HSCs is not fully understood. We compared the gene-expression profiles of primary cultured human HSCs (hHSCs) isolated from patients with ALD (n = 3) or without underlying liver disease (n = 4) using RNA-sequencing analysis. Furthermore, the gene-expression profile of ALD hHSCs was compared with that of alcohol-activated mHSCs (isolated from intragastric alcohol-fed mice) or CCl₄-activated mouse HSCs (mHSCs). Comparative transcriptome analysis revealed that ALD hHSCs, in addition to alcohol-activated and CCl₄-activated mHSCs, share the expression of common HSC activation (Col1a1 [collagen type I alpha 1 chain], Acta1 [actin alpha 1, skeletal muscle], PAI1 [plasminogen activator inhibitor-1], TIMP1 [tissue inhibitor of metalloproteinase 1], and LOXL2 [lysyl oxidase homolog 2]), indicating that a common mechanism underlies the activation of human and mouse HSCs. Furthermore, alcohol-activated mHSCs most closely recapitulate the gene-expression profile of ALD hHSCs. We identified the genes that are similarly and uniquely up-regulated in primary cultured alcohol-activated hHSCs and freshly isolated mHSCs, which include CSF1R (macrophage colony-stimulating factor 1 receptor), PLEK (pleckstrin), LAPTM5 (lysosmal-associated transmembrane protein 5), CD74 (class I transactivator, the invariant chain), CD53, MMP9 (matrix metallopeptidase 9), CD14, CTSS (cathepsin S), TYROBP (TYRO protein tyrosine kinase-binding protein), and ITGB2 (integrin beta-2), and other genes (compared with CCl₄-activated mHSCs). Conclusion: We identified genes in alcohol-activated mHSCs from intragastric alcohol-fed mice that are largely consistent with the gene-expression profile of primary cultured hHSCs from patients with ALD. These genes are unique to alcohol-induced HSC activation in two species, and therefore may become targets or readout for antifibrotic therapy in experimental models of ALD.

Hepatocyte apoptosis is tumor promoting in murine nonalcoholic steatohepatitis

Nonalcoholic fatty liver disease is the most common chronic liver disease and may progress to nonalcoholic steatohepatitis (NASH) and hepatocellular carcinoma (HCC). The molecular determinants of this pathogenic progression, however, remain largely undefined. Since liver tumorigenesis is driven by apoptosis, we examined the effect of overt hepatocyte apoptosis in a mouse model of NASH using mice lacking myeloid cell leukemia 1 (Mcl1), a pro-survival member of the BCL-2 protein family. Hepatocyte-specific Mcl1 knockout (Mcl1^∆hep) mice and control littermates were fed chow or FFC (high saturated fat, fructose, and cholesterol) diet, which induces NASH, for 4 and 10 months. Thereafter, liver injury, inflammation, fibrosis, and tumor development were evaluated biochemically and histologically. Mcl1^∆hep mice fed with the FFC diet for 4 months displayed a marked increase in liver injury, hepatocyte apoptosis, hepatocyte proliferation, macrophage-associated liver inflammation, and pericellular fibrosis in contrast to chow-fed Mcl1^∆hep and FFC diet-fed Mcl1-expressing littermates. After 10 months of feeding, 78% of FFC diet-fed Mcl1^∆hep mice developed liver tumors compared to 38% of chow-fed mice of the same genotype. Tumors in FFC diet-fed Mcl1^∆hep mice were characterized by cytologic atypia, altered liver architecture, immunopositivity for glutamine synthetase, and histologically qualified as HCC. In conclusion, this study provides evidence that excessive hepatocyte apoptosis exacerbates the NASH phenotype with enhancement of tumorigenesis in mice.

Maternal Diet Alters Trained Immunity in the Pathogenesis of Pediatric NAFLD

Pediatric nonalcoholic fatty liver disease (NAFLD) affects 1 in 10 children in the US, increases risk of cirrhosis and transplantation in early adulthood, and shortens lifespan, even after transplantation. Exposure to maternal obesity and/or a diet high in fat, sugar and cholesterol is strongly associated with development of NAFLD in offspring. However, mechanisms by which "priming" of the immune system in early life increases susceptibility to NAFLD are poorly understood. Recent studies have focused on the role "non-reparative" macrophages play in accelerating inflammatory signals promoting fibrogenesis. In this Commentary, we review evidence that the pioneering gut bacteria colonizing the infant intestinal tract remodel the naïve immune system in the offspring. Epigenetic changes in hematopoietic stem and progenitor cells, induced by exposure to an obesogenic diet in utero, may skew lineage commitment of myeloid cells during gestation. Further, microbial dysbiosis in neonatal life contributes to training innate immune cell responsiveness in the gut, bone marrow, and liver, leading to developmental programming of pediatric NAFLD. Comprehensive understanding of how different gut bacteria and their byproducts shape development of the early innate immune system and microbiome will uncover early interventions to prevent NAFLD pathophysiology.

Transgenerational impact of maternal obesogenic diet on offspring bile acid homeostasis and nonalcoholic fatty liver disease

Studies show maternal obesity is a risk factor for metabolic syndrome and nonalcoholic fatty liver disease (NAFLD) in offspring. Here we evaluated potential mechanisms underlying these phenotypes. Female C57Bl6 mice were fed chow or an obesogenic high-fat/high-sucrose (HF/HS) diet with subsequent mating of F1 and F2 female offspring to lean males to develop F2 and F3 generations, respectively. Offspring were fed chow or fibrogenic (high transfat, cholesterol, fructose) diets, and histopathological, metabolic changes, and bile acid (BA) homeostasis was evaluated. Chow-fed F1 offspring from maternal HF/HS lineages (HF/HS) developed periportal fibrosis and inflammation with aging, without differences in hepatic steatosis but increased BA pool size and shifts in BA composition. F1, but not F2 or F3, offspring from HF/HS showed increased steatosis on a fibrogenic diet, yet inflammation and fibrosis were paradoxically decreased in F1 offspring, a trend continued in F2 and F3 offspring. HF/HS feeding leads to increased periportal fibrosis and inflammation in chow-fed offspring without increased hepatic steatosis. By contrast, fibrogenic diet-fed F1 offspring from HF/HS dams exhibited worse hepatic steatosis but decreased inflammation and fibrosis. These findings highlight complex adaptations in NAFLD phenotypes with maternal diet.