Interplay between ChREBP and SREBP-1c coordinates postprandial glycolysis and lipogenesis in livers of mice

Aging and aging-related diseases: from molecular mechanisms to interventions and treatments

Aging is a gradual and irreversible pathophysiological process. It presents with declines in tissue and cell functions and significant increases in the risks of various aging-related diseases, including neurodegenerative diseases, cardiovascular diseases, metabolic diseases, musculoskeletal diseases, and immune system diseases. Although the development of modern medicine has promoted human health and greatly extended life expectancy, with the aging of society, a variety of chronic diseases have gradually become the most important causes of disability and death in elderly individuals. Current research on aging focuses on elucidating how various endogenous and exogenous stresses (such as genomic instability, telomere dysfunction, epigenetic alterations, loss of proteostasis, compromise of autophagy, mitochondrial dysfunction, cellular senescence, stem cell exhaustion, altered intercellular communication, deregulated nutrient sensing) participate in the regulation of aging. Furthermore, thorough research on the pathogenesis of aging to identify interventions that promote health and longevity (such as caloric restriction, microbiota transplantation, and nutritional intervention) and clinical treatment methods for aging-related diseases (depletion of senescent cells, stem cell therapy, antioxidative and anti-inflammatory treatments, and hormone replacement therapy) could decrease the incidence and development of aging-related diseases and in turn promote healthy aging and longevity.

Higher carbohydrate intake in relation to non-alcoholic fatty liver disease in patients with type 2 diabetes

Background

Non-alcoholic fatty liver disease (NAFLD) is an overlooked complication of type 2 diabetes (T2D). Current recommendations for the management of NAFLD are mainly focused on weight reduction, overlooking the role of macronutrient composition. Although dietary carbohydrates play a major role in intrahepatic fat synthesis, their association with the progression of liver steatosis has not been fully investigated in patients with T2D.

Aim

To investigate the association between higher carbohydrate intake and the presence of liver steatosis in patients with T2D.

Methods

This cross-sectional study included men and women aged 18-60 years diagnosed with T2D. Anthropometric measurements, hepatic steatosis assessment using the controlled attenuation parameter (CAP), blood samples, and dietary data were analyzed. Participants were divided into two groups: NAFLD and NAFLD-free. A two-sample t-test was used to evaluate the differences between the two groups. Stepwise multiple linear regression models adjusted for potential confounders were used to determine the association between CAP values and higher carbohydrate intake.

Results

In total, 358 participants were included. NAFLD was present in 79.3% of the participants. Body mass index, waist circumference, ALT, HbA1c, and triglycerides showed direct, while HDL-Cholesterol revealed inverse associations with CAP values. No significant relationship was found between carbohydrate intake and steatosis in the total study sample; however, multiple linear regression analysis revealed a significant relationship between carbohydrate intake and CAP values in patients aged ≤50 years.

Conclusion

In patients with T2D, higher carbohydrate intake was associated with liver steatosis in those aged 50 years and below. Further studies are required to confirm the causality between carbohydrate intake and liver steatosis.

The conserved Mediator subunit cyclin C (CCNC) is required for brown adipocyte development and lipid accumulation

OBJECTIVE

Cyclin C (CCNC) is the most conserved subunit of the Mediator complex, which is an important transcription cofactor. Recently, we have found that CCNC facilitates brown adipogenesis in vitro by activating C/EBPα-dependent transcription. However, the role of CCNC in brown adipose tissue (BAT) in vivo remains unclear.

METHODS

We generated conditional knock-out mice by crossing Ccncflox/flox mice with Myf5Cre, Ucp1Cre or AdipoqCre transgenic mice to investigate the role of CCNC in BAT development and function. We applied glucose and insulin tolerance test, cold exposure and indirect calorimetry to capture the physiological phenotypes and used immunostaining, immunoblotting, qRT-PCR, RNA-seq and cell culture to elucidate the underlying mechanisms.

RESULTS

Here, we show that deletion of CCNC in Myf5+ progenitor cells caused BAT paucity, despite the fact that there was significant neonatal lethality. Mechanistically different from in vitro, CCNC deficiency impaired the proliferation of embryonic brown fat progenitor cells without affecting brown adipogenesis or cell death. Interestingly, CCNC deficiency robustly reduced age-dependent lipid accumulation in differentiated brown adipocytes in all three mouse models. Mechanistically, CCNC in brown adipocytes is required for lipogenic gene expression through the activation of the C/EBPα/GLUT4/ChREBP axis. Consistent with the importance of de novo lipogenesis under carbohydrate-rich diets, high-fat diet (HFD) feeding abolished CCNC deficiency -caused defects of lipid accumulation in BAT. Although insulin sensitivity and response to acute cold exposure were not affected, CCNC deficiency in Ucp1+ cells enhanced the browning of white adipose tissue (beiging) upon prolonged cold exposure.

CONCLUSIONS

Together, these data indicate an important role of CCNC-Mediator in the regulation of BAT development and lipid accumulation in brown adipocytes.

Exercise and Metformin Intervention Prevents Lipotoxicity-Induced Hepatocyte Apoptosis by Alleviating Oxidative and ER Stress and Activating the AMPK/Nrf2/HO-1 Signaling Pathway in db/db Mice

Objective

Nonalcoholic fatty liver disease (NAFLD) and type 2 diabetes (T2DM) commonly coexist and act synergistically to drive adverse clinical outcomes. This study is aimed at investigating the effects of exercise intervention and oral hypoglycaemic drug of metformin (MET) alone or combined on hepatic lipid accumulation. To investigate if oxidative stress and endoplasmic reticulum stress (ERS) are involved in lipotoxicity-induced hepatocyte apoptosis in diabetic mice and whether exercise and/or MET alleviated oxidative stress or ERS-apoptosis by AMPK-Nrf2-HO-1 signaling pathway.

Methods

Forty db/db mice with diabetes (random blood glucose ≥ 250 mg/dL) were randomly allocated into four groups: control (CON), exercise training alone (EX), metformin treatment alone (MET), and exercise combined with metformin (EM) groups. Hematoxylin-eosin and oil red O staining were carried out to observe hepatic lipid accumulation. Immunohistochemical and TUNEL methods were used to detect the protein expression of the binding immunoglobulin protein (BiP) and superoxide dismutase-1 (SOD1) and the apoptosis level of hepatocytes. ERS-related gene expression and the AMPK-Nrf2-HO-1 signaling pathway were tested by western blotting.

Results

Our data showed that db/db mice exhibited increased liver lipid accumulation, which induced oxidative and ER stress of the PERK-eIF2α-ATF4 pathway, and hepatocyte apoptosis. MET combined with exercise training significantly alleviated hepatic lipid accumulation by suppressing BiP expression, the central regulator of ER homeostasis, and its downstream PERK-eIF2α-ATF4 pathway, as well as upregulated the AMPK-Nrf2-HO-1 signaling pathway. Moreover, the combination of exercise and MET displayed protective effects on hepatocyte apoptosis by downregulating Bax expression and TUNEL-positive staining, restoring the balance of cleaved-caspase-3 and caspase-3, and improving the antioxidant defense system to prevent oxidative damage in db/db mice.

Conclusion

Compared to MET or exercise intervention alone, the combined exercise and metformin exhibited significant effect on ameliorating hepatic steatosis, inhibiting oxidative and ER stress-induced hepatocyte apoptosis via improving the capacity of the antioxidant defense system and suppression of the PERK-eIF2α-ATF4 pathway. Furthermore, upregulation of AMPK-Nrf2-HO-1 signaling pathway might be a key crosstalk between MET and exercise, which may have additive effects on alleviating hepatic lipid accumulation.

Peroxisome Proliferator-Activated Receptor α Has a Protective Effect on Fatty Liver Caused by Excessive Sucrose Intake

Sterol regulatory element binding protein (SREBP)-1c is a transcription factor that regulates lipid synthesis from glucose in the liver. It is activated by sucrose, which activates the fatty acid synthesis pathway. On the other hand, peroxisome proliferator-activated receptor (PPAR) α regulates the transcription of several genes encoding enzymes involved in fatty acid β-oxidation in the liver. To evaluate the beneficial effects of PPARα on fatty liver caused by excessive sucrose intake, we investigated the molecular mechanisms related to the development of fatty liver in PPARα-deficient mice that were fed a high-sucrose diet (Suc). The SREBP-1c target gene expression was increased by sucrose intake, leading to the development of fatty liver. Furthermore, PPARα−/− mice developed severe fatty liver. Male and female PPARα−/− mice fed Suc showed 3.7- and 3.1-fold higher liver fat content than Suc-fed male and female wild-type mice, respectively. Thus, PPARα may work to prevent the development of fatty liver caused by excessive sucrose intake. Liver TG accumulation differed between male and female PPARα−/− mice. A possible explanation is that male mice show the increased expression of Pparγ, which usually contributes to triglyceride synthesis in the liver, to compensate for Pparα deficiency. In contrast, female wild-type mice inherently have low Pparα levels. Thus, Pparα deficiency has less pronounced effects in female mice. A diet that activates PPARα may be effective for preventing the development of fatty liver due to excessive sucrose intake.

AMPK-ChREBP axis mediates de novo milk fatty acid synthesis promoted by glucose in the mammary gland of lactating goats

To investigate the role of glucose in regulating milk fatty acid synthesis, 6 lactating Guanzhong dairy goats were infused with 0, 60, or 100 g/d glucose via the external pubic artery in a 3 × 3 repeated Latin square experiment. A concomitant in vitro experiment was conducted to investigate possible mechanisms whereby glucose regulates milk fatty acid synthesis. RNA sequencing was used for cellular transcriptome analysis. Drugs, MK-2206, rapamycin, and dorsomorphin were used to block cellular mammalian AMP-activated protein kinase (AMPK), AKT serine/threonine kinase 1, and mechanistic target of rapamycin kinase signaling pathways, respectively. Carbohydrate response element binding protein (ChREBP) was knockdown and overexpressed to investigate its role in regulating milk fatty acid synthesis in mammary epithelial cells. Glucose infusion linearly elevated the concentration of C8:0 (P = 0.039) and C10:0 (P = 0.041) in milk fat while it linearly decreased (P = 0.049) that of C16:0. This result was in agreement with the upregulation of genes related to de novo synthesis of fatty acids and lipid droplet formation, including adipose differentiation-related protein, butyrophilin subfamily 1 member A1, fatty acid synthase (FASN) and ChREBP. Their expression increased (P < 0.05) linearly in the lactating goat mammary gland. In vitro, glucose linearly stimulated the expression of genes related to de novo synthesis of fatty acids and cellular triacylglycerol in cultured mammary epithelial cells. RNA sequencing and inhibition studies revealed that glucose induced transcriptomic changes increasing lipogenic pathways, with AMPK responding to glucose by controlling ChREBP and FASN. Knockdown and overexpression of ChREBP highlighted its essential role in lipogenesis. The knockdown and overexpression of ChREBP protein also revealed an essential role in regulating the de novo synthesis of fatty acids. Collectively, our data highlight that glucose supplementation promotes de novo fatty acid synthesis via the AMPK-ChREBP axis, hence increasing milk fat yield in the goat mammary gland. Results from the current study provide possible strategies to manipulate the fatty acid composition as well as improve ruminant milk quality.

Exercise performed during pregnancy positively modulates liver metabolism and promotes mitochondrial biogenesis of female offspring in a rat model of diet-induced gestational diabetes

Gestational diabetes mellitus (GDM) is associated with a high-risk for metabolic complications in offspring. However, exercise is recognized as a non-pharmacological strategy against metabolic disorders and is recommended in GDM treatment. This study aimed to investigate whether gestational exercise (GE) could modulate maternal high-fat high-sucrose (HFHS) diet-related hepatic metabolic and mitochondrial outcomes in female offspring of mothers with HFHS-induced GDM. Female Sprague-Dawley rats were fed with control or HFHS diet and kept sedentary or submitted to GE. Their female offspring were fed with control diet and kept sedentary. Hepatic lipid accumulation, lipid metabolism regulators, mitochondrial biogenesis and dynamics markers, and microRNAs associated to the regulation of these markers were evaluated. Female offspring of GDM mothers showed increased body weight at early age, whereas GE prevented this effect of maternal HFHS-feeding and reduced hepatic lipid accumulation. GE stimulated hepatic mRNA transcription and protein expression of mitochondrial biogenesis markers (peroxisome proliferator-activated receptor-gamma co-activator-1alpha and mitochondrial transcription factor A) and mRNA transcription of mitochondrial dynamics markers (mitofusin-1, mitofusin-2, and dynamin-related protein-1) that were altered by maternal GDM, while mitochondrial dynamics markers protein expression was not affected by maternal diet/GE except for optic atrophy-1. MicroRNAs associated with these processes (miR-122, miR-34a, miR-130b, miR-494), and the expression of auto/mitophagy- and apoptosis-related proteins were not substantially influenced by altered intrauterine environment. Our findings suggest that GE is an important regulator of the intrauterine environment positively affecting liver metabolism and promoting liver mitochondrial biogenesis in female offspring despite eventual effects of maternal HFHS-feeding and related GDM.

Effects of Amino Acids Supplementation on Lipid and Glucose Metabolism in HepG2 Cells

Non-alcoholic fatty liver disease and type 2 diabetes are representing symptoms of metabolic syndrome, which is often accompanied with hepatic fat accumulation and insulin resistance. Since liver is the major site of glucose and lipid metabolism, this study aimed to understand the effects of SCAAs and BCAAs supplementations on glucose and lipid metabolism in HepG2 cells. These cells were pretreated with SAMe, betaine, taurine, and BCAA for 24 h, followed by treatments of a high concentration of glucose (50 mM) or palmitic acid (PA, 0.5 mM) for 48 h to simulate high-glucose and high-fat environments. Pretreatment of BCAA and SCAAs inhibited the fat accumulation. At the transcriptional level, glucose and PA treatment led to significant increase of mRNA gluconeogenic enzyme. The mRNA expression level of GLUT2 was decreased by 20% in the SAMe-treated group and inhibited glucose synthesis by reducing the level of gluconeogenic enzyme. After SAMe or BCAA pretreatment, the mRNA expression of lipogenic enzymes was decreased. The PPAR-γ expression was increased after BCAA pretreatment, but SAMe not only downregulated the expression of PPAR-γ, but also inhibited the expression of ChREBP approximately 20% and SREBP-1c decreased by about 15%. Taken together, the effect of SAMe on glucose and lipid metabolism is significant especially on inhibiting hepatic lipogenesis and gluconeogenesis under the metabolic syndrome environment.

The Activity of Prebiotics and Probiotics in Hepatogastrointestinal Disorders and Diseases Associated with Metabolic Syndrome

The components of metabolic syndrome (MetS) and hepatogastrointestinal diseases are widespread worldwide, since many factors associated with lifestyle and diet influence their development and correlation. Due to these growing health problems, it is necessary to search for effective alternatives for prevention or adjuvants in treating them. The positive impact of regulated microbiota on health is known; however, states of dysbiosis are closely related to the development of the conditions mentioned above. Therefore, the role of prebiotics, probiotics, or symbiotic complexes has been extensively evaluated; the results are favorable, showing that they play a crucial role in the regulation of the immune system, the metabolism of carbohydrates and lipids, and the biotransformation of bile acids, as well as the modulation of their central receptors FXR and TGR-5, which also have essential immunomodulatory and metabolic activities. It has also been observed that they can benefit the host by displacing pathogenic species, improving the dysbiosis state in MetS. Current studies have reported that paraprobiotics (dead or inactive probiotics) or postbiotics (metabolites generated by active probiotics) also benefit hepatogastrointestinal health.

KHK, PNPLA3 and PPAR as Novel Targets for the Anti-Steatotic Action of Bempedoic Acid

Bempedoic acid (BemA) is an ATP-citrate lyase (ACLY) inhibitor used to treat hypercholesterolemia. We studied the anti-steatotic effect of BemA, and the mechanisms involved, in a model of fatty liver in female rats obtained through the administration of a high-fat diet supplemented with liquid fructose (HFHFr) for three months. In the third month, a group of rats was treated with BemA (30 mg/kg/day) by gavage. Plasma analytes, liver histology, adiposity, and the expression of key genes controlling fatty acid metabolism were determined, and PPAR agonism was explored by using luciferase reporter assays. Our results showed that, compared to HFHFr, BemA-treated rats exhibited lower body weight, higher liver/body weight, and reduced hepatic steatosis. In addition to ACLY inhibition, we found three novel mechanisms that could account for the anti-steatotic effect: (1) reduction of liver ketohexokinase, leading to lower fructose intake and reduced de novo lipogenesis; (2) increased expression of patatin-like phospholipase domain-containing protein 3, a protein related to the export of liver triglycerides to blood; and (3) PPARα agonist activity, leading to increased hepatic fatty acid β-oxidation. In conclusion, BemA may represent a novel approach to treat hepatic steatosis, and therefore to avoid progression to advanced stages of non-alcoholic fatty liver disease.

The Role of Insulin Resistance in Fueling NAFLD Pathogenesis: From Molecular Mechanisms to Clinical Implications

Non-alcoholic fatty liver disease (NAFLD) represents a predominant hepatopathy that is rapidly becoming the most common cause of hepatocellular carcinoma worldwide. The close association with metabolic syndrome’s extrahepatic components has suggested the nature of the systemic metabolic-related disorder based on the interplay between genetic, nutritional, and environmental factors, creating a complex network of yet-unclarified pathogenetic mechanisms in which the role of insulin resistance (IR) could be crucial. This review detailed the clinical and pathogenetic evidence involved in the NAFLD–IR relationship, presenting both the classic and more innovative models. In particular, we focused on the reciprocal effects of IR, oxidative stress, and systemic inflammation on insulin-sensitivity disruption in critical regions such as the hepatic and the adipose tissue, while considering the impact of genetics/epigenetics on the regulation of IR mechanisms as well as nutrients on specific insulin-related gene expression (nutrigenetics and nutrigenomics). In addition, we discussed the emerging capability of the gut microbiota to interfere with physiological signaling of the hormonal pathways responsible for maintaining metabolic homeostasis and by inducing an abnormal activation of the immune system. The translation of these novel findings into clinical practice could promote the expansion of accurate diagnostic/prognostic stratification tools and tailored pharmacological approaches.

Chronic intake of nutritive sweeteners and saccharin increases levels of glycolytic and lipogenic enzymes in rat liver

There are doubts about the impact of non-nutritive sweeteners consumption on lipogenic and glycolytic metabolism. Therefore, the objective was to determine the effects of chronic consumption of sweeteners on the activity levels of the enzymes glucokinase (GK), phosphofructokinase-1 (PFK-1), pyruvate kinase (PKL), acetyl coenzyme A carboxylase (ACC), and fatty acid synthase (FAS) in livers' extracts. Groups of male and female Wistar rats drank solutions of sweeteners for 480 days: Sucrose 10%, glucose 14%, fructose 7%, acesulfame K 0.05%, aspartame:acesulfame mixture 1.55%, sucralose 0.017%, saccharin 0.033%, and a control group. The enzymatic activity in livers' extracts was determined. Likewise, the levels of glucose, triglycerides, insulin, glucagon, and leptin were determined. In both genders, there were significant differences in the levels of enzymatic activity, hormonal, and biochemical parameters due to sweeteners consumption. The highest glycolytic and lipogenic enzyme activity levels were observed in the groups that ingested nutritive sweeteners and saccharin.

Bifidobacterium animalis ssp. lactis MG741 Reduces Body Weight and Ameliorates Nonalcoholic Fatty Liver Disease via Improving the Gut Permeability and Amelioration of Inflammatory Cytokines

Diet-induced obesity is one of the major causes of the development of metabolic disorders such as insulin resistance and nonalcoholic fatty liver disease (NAFLD). Recently, specific probiotic strains have been found to improve the symptoms of NAFLD. We examined the effects of Bifidobacterium animalis ssp. lactis MG741 (MG741) on NAFLD and weight gain, using a mouse model of high-fat-diet (HFD)-induced obesity. HFD-fed mice were supplemented daily with MG741. After 12 weeks, MG741-administered mice exhibited reduced fat deposition, and serum metabolic alterations, including fasting hyperinsulinemia, were modulated. In addition, MG741 regulated Acetyl-CoA carboxylase (ACC), fatty acid synthase (FAS), sterol regulatory element-binding protein 1 (SREBP-1), and carbohydrate-responsive element-binding protein (ChREBP) expression and lipid accumulation in the liver, thereby reducing the hepatic steatosis score. To determine whether the effects of MG741 were related to improvements in gut health, MG741 improved the HFD-induced deterioration in gut permeability by reducing toxic substances and inflammatory cytokine expression, and upregulating tight junctions. These results collectively demonstrate that the oral administration of MG741 could prevent NAFLD and obesity, thereby improving metabolic health.

HM-Chromanone Ameliorates Hyperglycemia and Dyslipidemia in Type 2 Diabetic Mice

The effects of (E)-5-hydroxy-7-methoxy-3-(2-hydroxybenzyl)-4-chromanone (HMC) on hyperglycemia and dyslipidemia were investigated in diabetic mice. Mice were separated into three groups: db/db, rosiglitazone and HMC. Blood glucose or glycosylated hemoglobin values in HMC-treated mice were significantly lower compared to db/db mice. Total cholesterol, LDL-cholesterol, and triglyceride values were lower, and HDL-C levels were higher, in the HMC group compared to the diabetic and rosiglitazone groups. HMC markedly increased IRS-1Tyr612, AktSer473 and PI3K levels and plasma membrane GLUT4 levels in skeletal muscle, suggesting improved insulin resistance. HMC also significantly stimulated AMPKThr172 and PPARα in the liver, and ameliorated dyslipidemia by inhibiting SREBP-1c and FAS. Consequently, HMC reduced hyperglycemia by improving the expression of insulin-resistance-related genes and improved dyslipidemia by regulating fatty acid synthase and oxidation-related genes in db/db mice. Therefore, HMC could ameliorate hyperglycemia and dyslipidemia in type 2 diabetic mice.

D-Mannose Regulates Hepatocyte Lipid Metabolism via PI3K/Akt/mTOR Signaling Pathway and Ameliorates Hepatic Steatosis in Alcoholic Liver Disease

This study investigated the protective properties and mechanisms of D-mannose against hepatic steatosis in experimental alcoholic liver disease (ALD). Drinking-water supplementation of D-mannose significantly attenuated hepatic steatosis in a standard mouse ALD model established by chronic-binge ethanol feeding, especially hepatocyte lipid deposition. This function of D-mannose on lipid accumulation in hepatocytes was also confirmed using ethanol-treated primary mouse hepatocytes (PMHs) with a D-mannose supplement. Meanwhile, D-mannose regulated lipid metabolism by rescuing ethanol-mediated reduction of fatty acid oxidation genes (PPARα, ACOX1, CPT1) and elevation of lipogenic genes (SREBP1c, ACC1, FASN). PI3K/Akt/mTOR signaling pathway was involved in this effect of D-mannose on lipid metabolism since PI3K/Akt/mTOR pathway inhibitors or agonists could abolish this effect in PMHs. Overall, our findings suggest that D-mannose exhibits its anti-steatosis effect in ALD by regulating hepatocyte lipid metabolism via PI3K/Akt/mTOR signaling pathway.

Impact of Dietary Palmitic Acid on Lipid Metabolism

Palmitic acid (PA) is ubiquitously present in dietary fat guaranteeing an average intake of about 20 g/d. The relative high requirement and relative content in the human body, which accounts for 20–30% of total fatty acids (FAs), is justified by its relevant nutritional role. In particular physiological conditions, such as in the fetal stage or in the developing brain, the respectively inefficient placental and brain blood–barrier transfer of PA strongly induces its endogenous biosynthesis from glucose via de novo lipogenesis (DNL) to secure a tight homeostatic control of PA tissue concentration required to exert its multiple physiological activities. However, pathophysiological conditions (insulin resistance) are characterized by a sustained DNL in the liver and aimed at preventing the excess accumulation of glucose, which result in increased tissue content of PA and disrupted homeostatic control of its tissue concentration. This leads to an overaccumulation of tissue PA, which results in dyslipidemia, increased ectopic fat accumulation, and inflammatory tone via toll-like receptor 4. Any change in dietary saturated FAs (SFAs) usually reflects a complementary change in polyunsaturated FA (PUFA) intake. Since PUFA particularly n-3 highly PUFA, suppress lipogenic gene expression, their reduction in intake rather than excess of dietary SFA may promote endogenous PA production via DNL. Thereby, the increase in tissue PA and its deleterious consequences from dysregulated DNL can be mistakenly attributed to dietary intake of PA.

An RNAi therapeutic targeting hepatic DGAT2 in a genetically obese mouse model of nonalcoholic steatohepatitis

Nonalcoholic steatohepatitis (NASH) is a severe liver disorder characterized by triglyceride accumulation, severe inflammation, and fibrosis. With the recent increase in prevalence, NASH is now the leading cause of liver transplant, with no approved therapeutics available. Although the exact molecular mechanism of NASH progression is not well understood, a widely held hypothesis is that fat accumulation is the primary driver of the disease. Therefore, diacylglycerol O-acyltransferase 2 (DGAT2), a key enzyme in triglyceride synthesis, has been explored as a NASH target. RNAi-based therapeutics is revolutionizing the treatment of liver diseases, with recent chemical advances supporting long-term gene silencing with single subcutaneous administration. Here, we identified a hyper-functional, fully chemically stabilized GalNAc-conjugated small interfering RNA (siRNA) targeting DGAT2 (Dgat2-1473) that, upon injection, elicits up to 3 months of DGAT2 silencing (>80%-90%, p < 0.0001) in wild-type and NSG-PiZ "humanized" mice. Using an obesity-driven mouse model of NASH (ob/ob-GAN), Dgat2-1473 administration prevents and reverses triglyceride accumulation (>85%, p < 0.0001) without increased accumulation of diglycerides, resulting in significant improvement of the fatty liver phenotype. However, surprisingly, the reduction in liver fat did not translate into a similar impact on inflammation and fibrosis. Thus, while Dgat2-1473 is a practical, long-lasting silencing agent for potential therapeutic attenuation of liver steatosis, combinatorial targeting of a second pathway may be necessary for therapeutic efficacy against NASH.

TM6SF2: A Novel Genetic Player in Nonalcoholic Fatty Liver and Cardiovascular Disease

Transmembrane 6 superfamily member 2 (TM6SF2) is located on chromosome 19 (19p12) and encodes for a protein of undetermined function. Genetic studies have reported the association between a nonsynonymous variant in TM6SF2 (E167K, rs58542926) with hepatic triglyceride content and its impact on the cardiovascular system. Clinical and epidemiological studies have confirmed the role of TM6SF2 in the development of nonalcoholic fatty liver disease (NAFLD). Recently, TM6SF2 was also shown to play an important role in promoting hepatic fibrosis and hepatocellular cancer in mouse models. This review aims to capture the physiological role of TM6SF2 in the regulation of lipid metabolism and its involvement in cardiometabolic diseases.

Update on dyslipidemia in hypothyroidism: the mechanism of dyslipidemia in hypothyroidism

Hypothyroidism is often associated with elevated serum levels of total cholesterol, LDL-C and triglycerides. Thyroid hormone (TH) affects the production, clearance and transformation of cholesterol, but current research shows that thyroid-stimulating hormone (TSH) also participates in lipid metabolism independently of TH. Therefore, the mechanism of hypothyroidism-related dyslipidemia is associated with the decrease of TH and the increase of TSH levels. Some newly identified regulatory factors, such as proprotein convertase subtilisin/kexin type 9, angiogenin-like proteins and fibroblast growth factors are the underlying causes of dyslipidemia in hypothyroidism. HDL serum concentration changes were not consistent, and its function was reportedly impaired. The current review focuses on the updated understanding of the mechanism of hypothyroidism-related dyslipidemia.

Increased mitochondrial fission drives the reprogramming of fatty acid metabolism in hepatocellular carcinoma cells through suppression of Sirtuin 1

Background

Mitochondria are dynamic organelles that constantly change their morphology through fission and fusion processes. Recently, abnormally increased mitochondrial fission has been observed in several types of cancer. However, the functional roles of increased mitochondrial fission in lipid metabolism reprogramming in cancer cells remain unclear. This study aimed to explore the role of increased mitochondrial fission in lipid metabolism in hepatocellular carcinoma (HCC) cells.

Methods

Lipid metabolism was determined by evaluating the changes in the expressions of core lipid metabolic enzymes and intracellular lipid content. The rate of fatty acid oxidation was evaluated by [³H]‐labelled oleic acid. The mitochondrial morphology in HCC cells was evaluated by fluorescent staining. The expression of protein was determined by real‐time PCR, iimmunohistochemistry and Western blotting.

Results

Activation of mitochondrial fission significantly promoted de novo fatty acid synthesis in HCC cells through upregulating the expression of lipogenic genes fatty acid synthase (FASN), acetyl‐CoA carboxylase1 (ACC1), and elongation of very long chain fatty acid protein 6 (ELOVL6), while suppressed fatty acid oxidation by downregulating carnitine palmitoyl transferase 1A (CPT1A) and acyl‐CoA oxidase 1 (ACOX1). Consistently, suppressed mitochondrial fission exhibited the opposite effects. Moreover, in vitro and in vivo studies revealed that mitochondrial fission‐induced lipid metabolism reprogramming significantly promoted the proliferation and metastasis of HCC cells. Mechanistically, mitochondrial fission increased the acetylation level of sterol regulatory element‐binding protein 1 (SREBP1) and peroxisome proliferator‐activated receptor coactivator 1 alpha (PGC‐1α) by suppressing nicotinamide adenine dinucleotide (NAD+)/Sirtuin 1 (SIRT1) signaling. The elevated SREBP1 then upregulated the expression of FASN, ACC1 and ELOVL6 in HCC cells, while PGC‐1α/PPARα suppressed the expression of CPT1A and ACOX1.

Conclusions

Increased mitochondrial fission plays a crucial role in the reprogramming of lipid metabolism in HCC cells, which provides strong evidence for the use of this process as a drug target in the treatment of this malignancy.

Non-Alcoholic Fatty Liver Disease in HIV/HBV Patients - a Metabolic Imbalance Aggravated by Antiretroviral Therapy and Perpetuated by the Hepatokine/Adipokine Axis Breakdown

Non-alcoholic fatty liver disease (NAFLD) is strongly associated with the metabolic syndrome and is one of the most prevalent comorbidities in HIV and HBV infected patients. HIV plays an early and direct role in the development of metabolic syndrome by disrupting the mechanism of adipogenesis and synthesis of adipokines. Adipokines, molecules that regulate the lipid metabolism, also contribute to the progression of NAFLD either directly or via hepatic organokines (hepatokines). Most hepatokines play a direct role in lipid homeostasis and liver inflammation but their role in the evolution of NAFLD is not well defined. The role of HBV in the pathogenesis of NAFLD is controversial. HBV has been previously associated with a decreased level of triglycerides and with a protective role against the development of steatosis and metabolic syndrome. At the same time HBV displays a high fibrogenetic and oncogenetic potential. In the HIV/HBV co-infection, the metabolic changes are initiated by mitochondrial dysfunction as well as by the fatty overload of the liver, two interconnected mechanisms. The evolution of NAFLD is further perpetuated by the inflammatory response to these viral agents and by the variable toxicity of the antiretroviral therapy. The current article discusses the pathogenic changes and the contribution of the hepatokine/adipokine axis in the development of NAFLD as well as the implications of HIV and HBV infection in the breakdown of the hepatokine/adipokine axis and NAFLD progression.

Follistatin Alleviates Hepatic Steatosis in NAFLD via the mTOR Dependent Pathway

PURPOSE

In this study, we aimed to investigate the effect of follistatin (FST) on hepatic steatosis in NAFLD and the underlying mechanism, which has rarely been reported before.

METHODS

Liver samples from NAFLD patients and normal liver samples (from liver donors) were collected to investigate hepatic FST expression in humans. Additionally, human liver cells (LO2) were treated with free fatty acid (FFA) to induce lipid accumulation. Furthermore, lentivirus with FST overexpression or knockdown vectors were used to generate stable cell lines, which were subsequently treated with FFA or FFA and rapamycin. In the animal experiments, male C57BL/6J mice were fed with a high-fat diet (HFD) to induce NAFLD, after which the adeno-associated virus (AAV) gene vectors for FST overexpression were administered. In both cell culture and mice, we evaluated morphological changes and the protein expression of sterol regulatory element-binding protein1 (SREBP1), acetyl-CoA carboxylase1 (ACC1), carbohydrate-responsive element-binding protein (ChREBP), fatty acid synthase (FASN), and Akt/mTOR signaling. The body weight and serum parameters of the mice were also measured.

RESULTS

Hepatic FST expression level was higher in NAFLD patients compared to normal samples. In LO2 cells, FST overexpression alleviated lipid accumulation and lipogenesis, whereas FST knockdown aggravated hepatic steatosis. FST could regulate Akt/mTOR signaling, and the mTOR inhibitor rapamycin abolished the effect of FST knockdown on hepatic de novo lipogenesis (DNL). Furthermore, FST expression was increased in HFD mice compared to the corresponding controls. FST overexpression in mice reduced body weight gain, hyperlipidemia, hepatic DNL, and suppressed Akt/mTOR signaling.

CONCLUSION

Hepatic FST expression increases in NAFLD and plays a protective role in hepatic steatosis. FST overexpression gene therapy alleviates hepatic steatosis via the mTOR pathway.Therefore, gene therapy for FST is a promising treatment in NAFLD.

Molecular aspects of fructose metabolism and metabolic disease

Excessive sugar consumption is increasingly considered as a contributor to the emerging epidemics of obesity and the associated cardiometabolic disease. Sugar is added to the diet in the form of sucrose or high-fructose corn syrup, both of which comprise nearly equal amounts of glucose and fructose. The unique aspects of fructose metabolism and properties of fructose-derived metabolites allow for fructose to serve as a physiological signal of normal dietary sugar consumption. However, when fructose is consumed in excess, these unique properties may contribute to the pathogenesis of cardiometabolic disease. Here, we review the biochemistry, genetics, and physiology of fructose metabolism and consider mechanisms by which excessive fructose consumption may contribute to metabolic disease. Lastly, we consider new therapeutic options for the treatment of metabolic disease based upon this knowledge.

(+)-Dehydrovomifoliol Alleviates Oleic Acid-Induced Lipid Accumulation in HepG2 Cells via the PPARα-FGF21 Pathway

An overload of hepatic fatty acids, such as oleic acid is a key trigger of non-alcoholic fatty liver disease (NAFLD). Here, we investigated whether Artemisia frigida, a valuable traditional medicine used to treat various diseases, could mitigate OA-induced lipid accumulation in HepG2 cells. Then, to identify the active substances in A. frigida, a phytochemistry investigation was conducted using a bioassay-guided isolation method. Consequently, one terpene (1) and one flavone (2) were identified. Compound 1 ((+)-dehydrovomifoliol) exhibited potent effects against lipid accumulation in OA-induced HepG2 cells, without causing cyto-toxicity. Notably, treatment with (+)-dehydrovomifoliol decreased the expression levels of three genes related to lipogenesis (SREBP1, ACC, and FASN) and increased those of three genes related to fatty acid oxidation (PPARα, ACOX1, and FGF21). In addition, similar results were observed for SREBP1, PPARα, and FGF21 protein levels. The effects of (+)-dehydrovomifoliol were partially reversed by treatment with the PPARα antagonist GW6471, indicating the important role of the PPARα-FGF21 axis in the effects of (+)-dehydrovomifoliol. Based on its effects on hepatic lipogenesis and fatty acid oxidation signaling via the PPARα-FGF21 axis, (+)-dehydrovomifoliol isolated from A. frigida could be a useful early lead compound for developing new drugs for NAFLD prevention.

Mechanism and Therapeutic Opportunities of Histone Modifications in Chronic Liver Disease

Chronic liver disease (CLD) represents a global health problem, accounting for the heavy burden of disability and increased health care utilization. Epigenome alterations play an important role in the occurrence and progression of CLD. Histone modifications, which include acetylation, methylation, and phosphorylation, represent an essential part of epigenetic modifications that affect the transcriptional activity of genes. Different from genetic mutations, histone modifications are plastic and reversible. They can be modulated pharmacologically without changing the DNA sequence. Thus, there might be chances to establish interventional solutions by targeting histone modifications to reverse CLD. Here we summarized the roles of histone modifications in the context of alcoholic liver disease (ALD), metabolic associated fatty liver disease (MAFLD), viral hepatitis, autoimmune liver disease, drug-induced liver injury (DILI), and liver fibrosis or cirrhosis. The potential targets of histone modifications for translation into therapeutics were also investigated. In prospect, high efficacy and low toxicity drugs that are selectively targeting histone modifications are required to completely reverse CLD and prevent the development of liver cirrhosis and malignancy.

Thyroid hormone signaling promotes hepatic lipogenesis through the transcription factor ChREBP

Thyroid hormone (TH) action is essential for hepatic lipid synthesis and oxidation. Analysis of hepatocyte-specific thyroid receptor β1 (TRβ1) knockout mice confirmed a role for TH in stimulating de novo lipogenesis and fatty acid oxidation through its nuclear receptor. Specifically, TRβ1 and its principal corepressor NCoR1 in hepatocytes repressed de novo lipogenesis, whereas the TH-mediated induction of lipogenic genes depended on the transcription factor ChREBP. Mice with a hepatocyte-specific deficiency in ChREBP lost TH-mediated stimulation of the lipogenic program, which, in turn, impaired the regulation of fatty acid oxidation. TH regulated ChREBP activation and recruitment to DNA, revealing a mechanism by which TH regulates specific signaling pathways. Regulation of the lipogenic pathway by TH through ChREBP was conserved in hepatocytes derived from human induced pluripotent stem cells. These results demonstrate that TH signaling in the liver acts simultaneously to enhance both lipogenesis and fatty acid oxidation.

Fasting-Induced Upregulation of MKP-1 Modulates the Hepatic Response to Feeding

The liver plays a key role in whole-body, glucose and lipid homeostasis. Nutritional signals in response to fasting and refeeding regulate hepatic lipid synthesis. It is established that activation of mitogen-activated protein kinase (MAPK) phosphatase-1 (MKP-1) in response to overnutrition regulates MAPK-dependent pathways that control lipid metabolism in the liver. However, the regulatory mechanisms and the impact of the actions of MKP-1 in hepatic response to fasting remains unclear. We investigated the effect of fasting on the expression of MKP-1 and the impact on hepatic response to feeding. In this study, we demonstrate that fasting stress induced upregulation of hepatic MKP-1 protein levels with a corresponding downregulation of p38 MAPK and JNK phosphorylation in mouse livers. We found that MKP-1-deficient livers are resistant to fasting-induced hepatic steatosis. Hepatic MKP-1 deficiency impaired fasting-induced changes in the levels of key transcription factors involved in the regulation of fatty acid and cholesterol metabolism including Srebf2 and Srebf1c. Mechanistically, MKP-1 negatively regulates Srebf2 expression by attenuating p38 MAPK pathway, suggesting its contribution to the metabolic effects of MKP-1 deficiency in the fasting liver. These findings support the hypothesis that upregulation of MKP-1 is a physiological relevant response and might be beneficial in hepatic lipid utilization during fasting in the liver. Collectively, these data unravel some of the complexity and tissue specific interaction of MKP-1 action in response to changes in nutritional cues, including fasting and excess nutrients

Integrative lipidomic and transcriptomic study unravels the therapeutic effects of saikosaponins A and D on non-alcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) has become one of the most prominent causes of chronic liver diseases and malignancies. However, few therapy has been approved. Radix Bupleuri (RB) is the most frequently used herbal medicine for the treatment of liver diseases. In the current study, we aim to systemically evaluate the therapeutic effects of saikosaponin A (SSa) and saikosaponin D (SSd), the major bioactive monomers in RB, against NAFLD and to investigate the underlying mechanisms. Our results demonstrated that both SSa and SSd improved diet-induced NAFLD. Integrative lipidomic and transcriptomic analysis revealed that SSa and SSd modulated glycerolipid metabolism by regulating related genes, like Lipe and Lipg. SSd profoundly suppressed the fatty acid biosynthesis by downregulating Fasn and Acaca expression and promoted fatty acid degradation by inducing Acox1 and Cpt1a expression. Bioinformatic analysis further predicted the implication of master transcription factors, including peroxisome proliferator-activated receptor alpha (PPARα), in the protective effects of SSa and SSd. These results were further confirmed in vitro in mouse primary hepatocytes. In summary, our study uncoded the complicated mechanisms underlying the promising anti-steatosis activities of saikosaponins (SSs), and provided critical evidence inspiring the discovery of innovative therapies based on SSa and SSd for the treatment of NAFLD and related complications.

LH Induces De Novo Cholesterol Biosynthesis via SREBP Activation in Granulosa Cells During Ovulation in Female Mice

In the liver, the sterol response element binding protein (SREBP) and the SREBP cleavage-activated protein (SCAP) complex upregulate cholesterol biosynthesis by gene induction of de novo cholesterol synthetic enzymes (Hmgcr, Cyp51, and Dhcr7). Insulin induced gene 1 (INSIG1) negatively regulates cholesterol biosynthesis by the inhibition of de novo cholesterol biosynthetic gene expression. In the ovary, cholesterol is de novo synthesized; however, the roles of SREBP and its regulators (SCAP and INSIG1) are not well understood. In this study, when immature mice were treated with gonadotropins (eCG followed by hCG), eCG induced and hCG maintained the expression of SREBP-1a, -2, and SCAP granulosa cells, whereas INSIG1 expression was dramatically downregulated after hCG injection. Downregulation of INSIG1 led to generate the SREBPs active form and translocate the SREBPs active form to nuclei. Inhibition of generation of the SREBPs active form by fatostatin or Scap siRNA in both in vivo and in vitro significantly decreased the expressions of de novo cholesterol biosynthetic enzymes, cholesterol accumulation, and progesterone (P4) production compared with the control group. Fatostatin treatment inhibited the ovulation and increased the formation of abnormal corpus luteum which trapped the matured oocyte in the corpus luteum; however, the phenomenon was abolished by P4 administration. The results showed that decreasing INSIG1 level after hCG stimulation activated SREBP-induced de novo cholesterol biosynthesis in granulosa cells of preovulatory follicles, which is essential for P4 production and the rupture of matured oocyte during ovulation process.

SREBP-1c and lipogenesis in the liver: an update1

Sterol Regulatory Element Binding Protein-1c is a transcription factor that controls the synthesis of lipids from glucose in the liver, a process which is of utmost importance for the storage of energy. Discovered in the early nineties by B. Spiegelman and by M. Brown and J. Goldstein, it has generated more than 5000 studies in order to elucidate its mechanism of activation and its role in physiology and pathology. Synthetized as a precursor found in the membranes of the endoplasmic reticulum, it has to be exported to the Golgi and cleaved by a mechanism called regulated intramembrane proteolysis. We reviewed in 2002 its main characteristics, its activation process and its role in the regulation of hepatic glycolytic and lipogenic genes. We particularly emphasized that Sterol Regulatory Element Binding Protein-1c is the mediator of insulin effects on these genes. In the present review, we would like to update these informations and focus on the response to insulin and to another actor in Sterol Regulatory Element Binding Protein-1c activation, the endoplasmic reticulum stress.

Ameliorative Effect of Myricetin on Nonalcoholic Fatty Liver Disease in ob/ob Mice

Obesity, insulin resistance, and oxidative stress are important risk factors for nonalcoholic fatty liver disease (NAFLD). This study aimed at determining the beneficial effects of myricetin against NAFLD in ob/ob mice. C57BL/6-Lep^ob/ob mice (n = 21) were fed an AIN-93G diet (ob/ob control group) or diet containing 0.04% (low myricetin; LMTN group) or 0.08% (high myricetin; HMTN group) myricetin, and lean heterozygous littermates (lean control group, n = 7) were fed AIN-93G diet for 10 weeks. HMTN consumption significantly lowered serum glucose levels and homeostasis model assessment for insulin resistance values in ob/ob mice. In addition to reducing serum triglyceride (TG) and cholesterol levels, HMTN significantly decreased total hepatic lipid and TG levels partly through downregulation of carbohydrate response element-binding protein and sterol regulatory element-binding protein 1c expression. The reduction in the levels of hepatic thiobarbituric acid reactive substances by HMTN likely resulted from the elevation of nuclear factor erythroid-2-related factor 2 expression. Tumor necrosis factor-α and monocyte chemoattractant protein 1 expressions were reduced by LMTN and HMTN, and HMTN also decreased interleukin-6 expression. These results suggest that myricetin has beneficial effects against NAFLD by regulating the expression of transcription factors of hepatic lipid metabolism, the antioxidant system, and pro-inflammatory cytokines.

A Systems Approach Dissociates Fructose-Induced Liver Triglyceride from Hypertriglyceridemia and Hyperinsulinemia in Male Mice

The metabolic syndrome (MetS), defined as the co-occurrence of disorders including obesity, dyslipidemia, insulin resistance, and hepatic steatosis, has become increasingly prevalent in the world over recent decades. Dietary and other environmental factors interacting with genetic predisposition are likely contributors to this epidemic. Among the involved dietary factors, excessive fructose consumption may be a key contributor. When fructose is consumed in large amounts, it can quickly produce many of the features of MetS both in humans and mice. The mechanisms by which fructose contributes to metabolic disease and its potential interactions with genetic factors in these processes remain uncertain. Here, we generated a small F2 genetic cohort of male mice derived from crossing fructose-sensitive and -resistant mouse strains to investigate the interrelationships between fructose-induced metabolic phenotypes and to identify hepatic transcriptional pathways that associate with these phenotypes. Our analysis indicates that the hepatic transcriptional pathways associated with fructose-induced hypertriglyceridemia and hyperinsulinemia are distinct from those that associate with fructose-mediated changes in body weight and liver triglyceride. These results suggest that multiple independent mechanisms and pathways may contribute to different aspects of fructose-induced metabolic disease.

Supplementation With Lycium barbarum Polysaccharides Reduce Obesity in High-Fat Diet-Fed Mice by Modulation of Gut Microbiota

Lycium barbarum polysaccharides (LBPs) have been proved to prevent obesity and modulate gut microbiota. However, the underlying mechanisms of LBPs’ regulating lipid metabolism remain entirely unclear. Therefore, the purpose of this study was to determine whether LBPs are able to modulate the gut microbiota to prevent obesity. The results showed that oral administration of LBPs alleviated dyslipidemia by decreasing the serum levels of total triglycerides, total cholesterol, and low-density lipoprotein-cholesterol and elevating the high-density lipoprotein cholesterol in obese mice. Furthermore, LBP treatment decreased the number and size of adipocytes in epididymal adipose tissues and downregulated the expression of adipogenesis-related genes, including acetyl-CoA carboxylase 1, fatty acid synthase, stearoyl-CoA desaturase 1, sterol regulatory element-binding protein-1c, peroxisome proliferator-activated receptor γ, and CCAAT/enhancer-binding protein α. 16S rRNA gene sequencing analysis showed that LBPs increased the diversity of bacteria, reduced the Firmicutes/Bacteroidetes ratio, and improved the gut dysbiosis induced by a high-fat diet; for example, LBPs increased the production of short-chain fatty acid-producing bacteria Lacticigenium, Lachnospiraceae_NK4A136_group, and Butyricicoccus. LBPs treatment also increased the content of fecal short-chain fatty acids, including butyric acid. These findings illustrate that LBPs might be developed as a potential prebiotic to improve lipid metabolism and intestinal diseases.

Cannabinoid receptor-1 signaling in hepatocytes and stellate cells does not contribute to NAFLD

The endocannabinoid system regulates appetite and energy expenditure and inhibitors of the cannabinoid receptor-1 (CB-1) induce weight loss with improvement in components of the metabolic syndrome. While CB-1 blockage in brain is responsible for weight loss, many of the metabolic benefits associated with CB-1 blockade have been attributed to inhibition of CB-1 signaling in the periphery. As a result, there has been interest in developing a peripherally restricted CB-1 inhibitor for the treatment of nonalcoholic fatty liver disease (NAFLD) that would lack the unwanted centrally mediated side effects. Here, we produced mice that lacked CB-1 receptors in hepatocytes or stellate cells to determine if CB-1 signaling contributes to the development of NAFLD or liver fibrosis. Deletion of CB-1 receptors in hepatocytes did not alter the development of NAFLD in mice fed a high sucrose high fat diet or high fat diet (HFD). Similarly, deletion of CB-1 deletion specifically in stellate cells also did not prevent the development of NAFLD in mice fed the HFD nor did it protect mice for carbon tetrachloride (CCl4)-induced fibrosis. Combined, these studies do not support a direct role for hepatocyte or stellate cell CB-1 signaling in the development of NAFLD or liver fibrosis.

Baicalein Enhances the Effect of Acarbose on the Improvement of Nonalcoholic Fatty Liver Disease Associated with Prediabetes via the Inhibition of De Novo Lipogenesis

Prediabetes is a prevalent metabolic disorder with multiple complications, including nonalcoholic fatty liver disease (NAFLD). In this study, we investigated the combinatorial effect of baicalein, a dietary flavonoid abundant in multiple edible plants, and acarbose on prediabetes-associated NAFLD. Baicalein and its metabolites inhibited de novo lipogenesis (DNL), thereby decreasing lipid accumulation and hepatokine secretion in oleic acid-induced hepatocytes. Carbohydrate restriction, which mimicked the effect of acarbose, led to comparable results. The combinatorial effect of baicalein and acarbose was further verified in prediabetic mice with NAFLD. Through the 16-week intervention, baicalein and acarbose inhibited DNL and improved glucose tolerance, oxidative stress, liver histology, and hepatokine secretion, thereby ameliorating insulin resistance and NAFLD. Our study demonstrated that baicalein enhanced the effect of acarbose on improving NAFLD and explored the underlying multitarget mechanism, laying a theoretical foundation for the development of flavonoid dietary supplements for the simultaneous improvement of NAFLD and prediabetes.

Regulation of cholesterol biosynthesis and lipid metabolism: A microRNA management perspective

Cellular disruption of lipid and cholesterol metabolism results in pathological processes linked to metabolic and cardiovascular diseases. Classically, at the transcription stages, the Cholesterol levels are controlled by two cellular pathways. First, the SREBP transcription factor family controls Cholesterol biosynthesis via transcriptional regulation of critical rate-limiting cholesterogenic and lipogenic proteins. Secondly, The LXR/RXR transcription factor family controls cholesterol shuttling via transcriptional regulation of cholesterol transport proteins. In addition, the posttranscriptional control of gene expression of various enzymes and proteins of cholesterol biosynthesis pathways is mediated by small non-coding microRNAs. Regulatory noncoding miRNAs are critical regulators of biological processes, including developmental and metabolic functions. miRNAs function to fine-tune lipid and cholesterol metabolism pathways by controlling the mRNA levels and translation of critical molecules in each pathway. This review discusses the regulatory roles of miRNAs in cholesterol and lipid metabolism via direct and indirect effects on their target genes, including SREBP, LXR, HDL, LDL, and ABCA transporters. We also discuss the therapeutic implications of miRNA functions and their purported role in the potentiation of small molecule therapies.

Amelioration of Hepatic Steatosis in Mice through Bacteroides uniformis CBA7346-Mediated Regulation of High-Fat Diet-Induced Insulin Resistance and Lipogenesis

Dietary habits and gut microbiota play an essential role in non-alcoholic fatty liver disease (NAFLD) and related factors such as insulin resistance and de novo lipogenesis. In this study, we investigated the protective effects of Bacteroides uniformis CBA7346, isolated from the gut of healthy Koreans, on mice with high-fat diet (HFD)-induced NAFLD. Administration of B. uniformis CBA7346 reduced body and liver weight gain, serum alanine aminotransferase and aspartate aminotransferase levels, liver steatosis, and liver triglyceride levels in mice on an HFD; the strain also decreased homeostatic model assessment for insulin resistance values, as well as serum cholesterol, triglyceride, lipopolysaccharide, leptin, and adiponectin levels in mice on an HFD. Moreover, B. uniformis CBA7346 controlled fatty liver disease by attenuating steatosis and inflammation and regulating de novo lipogenesis-related proteins in mice on an HFD. Taken together, these findings suggest that B. uniformis CBA7346 ameliorates HFD-induced NAFLD by reducing insulin resistance and regulating de novo lipogenesis in obese mice.

Diet-Induced Models of Non-Alcoholic Fatty Liver Disease: Food for Thought on Sugar, Fat, and Cholesterol

Non-alcoholic fatty liver disease (NAFLD) affects approximately 1 in 4 people worldwide and is a major burden to health care systems. A major concern in NAFLD research is lack of confidence in pre-clinical animal models, raising questions regarding translation to humans. Recently, there has been renewed interest in creating dietary models of NAFLD with higher similarity to human diets in hopes to better recapitulate disease pathology. This review summarizes recent research comparing individual roles of major dietary components to NAFLD and addresses common misconceptions surrounding frequently used diet-based NAFLD models. We discuss the effects of glucose, fructose, and sucrose on the liver, and how solid vs. liquid sugar differ in promoting disease. We consider studies on dosages of fat and cholesterol needed to promote NAFLD versus NASH, and discuss important considerations when choosing control diets, mouse strains, and diet duration. Lastly, we provide our recommendations on amount and type of sugar, fat, and cholesterol to include when modelling diet-induced NAFLD/NASH in mice.

Sugar-Sweetened Beverage Consumption May Modify Associations Between Genetic Variants in the CHREBP (Carbohydrate Responsive Element Binding Protein) Locus and HDL-C (High-Density Lipoprotein Cholesterol) and Triglyceride Concentrations

Supplemental Digital Content is available in the text.

Background:

ChREBP (carbohydrate responsive element binding protein) is a transcription factor that responds to sugar consumption. Sugar-sweetened beverage (SSB) consumption and genetic variants in the CHREBP locus have separately been linked to HDL-C (high-density lipoprotein cholesterol) and triglyceride concentrations. We hypothesized that SSB consumption would modify the association between genetic variants in the CHREBP locus and dyslipidemia.

Methods:

Data from 11 cohorts from the Cohorts for Heart and Aging Research in Genomic Epidemiology consortium (N=63 599) and the UK Biobank (N=59 220) were used to quantify associations of SSB consumption, genetic variants, and their interaction on HDL-C and triglyceride concentrations using linear regression models. A total of 1606 single nucleotide polymorphisms within or near CHREBP were considered. SSB consumption was estimated from validated questionnaires, and participants were grouped by their estimated intake.

Results:

In a meta-analysis, rs71556729 was significantly associated with higher HDL-C concentrations only among the highest SSB consumers (β, 2.12 [95% CI, 1.16–3.07] mg/dL per allele; P<0.0001), but not significantly among the lowest SSB consumers (P=0.81; P_Diff <0.0001). Similar results were observed for 2 additional variants (rs35709627 and rs71556736). For triglyceride, rs55673514 was positively associated with triglyceride concentrations only among the highest SSB consumers (β, 0.06 [95% CI, 0.02–0.09] ln-mg/dL per allele, P=0.001) but not the lowest SSB consumers (P=0.84; P_Diff=0.0005).

Conclusions:

Our results identified genetic variants in the CHREBP locus that may protect against SSB-associated reductions in HDL-C and other variants that may exacerbate SSB-associated increases in triglyceride concentrations.

Registration:

URL: https://www.clinicaltrials.gov; Unique identifier: NCT00005133, NCT00005121, NCT00005487, and NCT00000479.

DHT causes liver steatosis via transcriptional regulation of SCAP in normal weight female mice

Hyperandrogenemia (HA) is a hallmark of polycystic ovary syndrome (PCOS) and is an integral element of non-alcoholic fatty liver disease (NALFD) in females. Administering low-dose dihydrotestosterone (DHT) induced a normal weight PCOS-like female mouse model displaying NAFLD. The molecular mechanism of HA-induced NAFLD has not been fully determined. We hypothesized that DHT would regulate hepatic lipid metabolism via increased SREBP1 expression leading to NAFLD. We extracted liver from control and low-dose DHT female mice; and performed histological and biochemical lipid profiles, Western blot, immunoprecipitation, chromatin immunoprecipitation, and real-time quantitative PCR analyses. DHT lowered the 65 kD form of cytosolic SREBP1 in the liver compared to controls. However, DHT did not alter the levels of SREBP2 in the liver. DHT mice displayed increased SCAP protein expression and SCAP-SREBP1 binding compared to controls. DHT mice exhibited increased AR binding to intron-8 of SCAP leading to increased SCAP mRNA compared to controls. FAS mRNA and protein expression was increased in the liver of DHT mice compared to controls. p-ACC levels were unaltered in the liver. Other lipid metabolism pathways were examined in the liver, but no changes were observed. Our findings support evidence that DHT increased de novo lipogenic proteins resulting in increased hepatic lipid content via regulation of SREBP1 in the liver. We show that in the presence of DHT, the SCAP-SREBP1 interaction was elevated leading to increased nuclear SREBP1 resulting in increased de novo lipogenesis. We propose that the mechanism of action may be increased AR binding to an ARE in SCAP intron-8.

Measurement of lipogenic flux by deuterium resolved mass spectrometry

De novo lipogenesis (DNL) is disrupted in a wide range of human disease. Thus, quantification of DNL may provide insight into mechanisms and guide interventions if it can be performed rapidly and noninvasively. DNL flux is commonly measured by ²H incorporation into fatty acids following deuterated water (²H₂O) administration. However, the sensitivity of this approach is limited by the natural abundance of ¹³C, which masks detection of ²H by mass spectrometry. Here we report that high-resolution Orbitrap gas-chromatography mass-spectrometry resolves ²H and ¹³C fatty acid mass isotopomers, allowing DNL to be quantified using lower ²H₂O doses and shorter experimental periods than previously possible. Serial measurements over 24-hrs in mice detects the nocturnal activation of DNL and matches a ³H-water method in mice with genetic activation of DNL. Most importantly, DNL is detected in overnight-fasted humans in less than an hour and is responsive to feeding during a 4-h study. Thus, ²H specific MS provides the ability to study DNL in settings that are currently impractical.

Hyperlipidemic hypersensitivity to lethal microbial inflammation and its reversal by selective targeting of nuclear transport shuttles

Hyperlipidemia, the hallmark of Metabolic Syndrome that afflicts millions of people worldwide, exacerbates life-threatening infections. We present a new evidence for the mechanism of hyperlipidemic hypersensitivity to microbial inflammation caused by pathogen-derived inducer, LPS. We demonstrate that hyperlipidemic animals succumbed to a non-lethal dose of LPS whereas normolipidemic controls survived. Strikingly, survival of hyperlipidemic animals was restored when the nuclear import of stress-responsive transcription factors (SRTFs), Sterol Regulatory Element-Binding Proteins (SREBPs), and Carbohydrate-Responsive Element-Binding Proteins (ChREBPs) was impeded by targeting the nuclear transport checkpoint with cell-penetrating, biselective nuclear transport modifier (NTM) peptide. Furthermore, the burst of proinflammatory cytokines and chemokines, microvascular endothelial injury in the liver, lungs, heart, and kidneys, and trafficking of inflammatory cells were also suppressed. To dissect the role of nuclear transport signaling pathways we designed and developed importin-selective NTM peptides. Selective targeting of the importin α5, ferrying SRTFs and ChREBPs, protected 70-100% hyperlipidemic animals. Targeting importin β1, that transports SREBPs, was only effective after 3-week treatment that lowered blood triglycerides, cholesterol, glucose, and averted fatty liver. Thus, the mechanism of hyperlipidemic hypersensitivity to lethal microbial inflammation depends on metabolic and proinflammatory transcription factors mobilization, which can be counteracted by targeting the nuclear transport checkpoint.

The Mediator complex kinase module is necessary for fructose regulation of liver glycogen levels through induction of glucose-6-phosphatase catalytic subunit (G6pc)

OBJECTIVE

Liver glycogen levels are dynamic and highly regulated by nutrient availability as the levels decrease during fasting and are restored during the feeding cycle. However, feeding in the presence of fructose in water suppresses glycogen accumulation in the liver by upregulating the expression of the glucose-6-phosphatase catalytic subunit (G6pc) gene, although the exact mechanism is unknown. We generated liver-specific knockout MED13 mice that lacked the transcriptional Mediator complex kinase module to examine its effect on the transcriptional activation of inducible target gene expression, such as the ChREBP- and FOXO1-dependent control of the G6pc gene promoter.

METHODS

The relative changes in liver expression of lipogenic and gluconeogenic genes as well as glycogen levels were examined in response to feeding standard low-fat laboratory chow supplemented with water or water containing sucrose or fructose in control (Med13fl/fl) and liver-specific MED13 knockout (MED13-LKO) mice.

RESULTS

Although MED13 deficiency had no significant effect on constitutive gene expression, all the dietary inducible gene transcripts were significantly reduced despite the unchanged insulin sensitivity in the MED13-LKO mice compared to that in the control mice. G6pc gene transcription displayed the most significant difference between the Med13 fl/fl and MED13-LKO mice, particularly when fed fructose. Following fasting that depleted liver glycogen, feeding induced the restoration of glycogen levels except in the presence of fructose. MED13 deficiency rescued the glycogen accumulation defect in the presence of fructose. This resulted from the suppression of G6pc expression and thus G6PC enzymatic activity. Among two transcriptional factors that regulate G6pc gene expression, FOXO1 binding to the G6pc promoter was not affected, whereas ChREBP binding was dramatically reduced in MED13-LKO hepatocytes. In addition, there was a marked suppression of FOXO1 and ChREBP-β transcriptional activities in MED13-LKO hepatocytes.

CONCLUSIONS

Taken together, our data suggest that the kinase module of the Mediator complex is necessary for the transcriptional activation of metabolic genes such as G6pc and has an important role in regulating glycogen levels in the liver through altering transcription factor binding and activity at the G6pc promoter.

Fructose and metabolic diseases: too much to be good

ABSTRACT

Excessive consumption of fructose, the sweetest of all naturally occurring carbohydrates, has been linked to worldwide epidemics of metabolic diseases in humans, and it is considered an independent risk factor for cardiovascular diseases. We provide an overview about the features of fructose metabolism, as well as potential mechanisms by which excessive fructose intake is associated with the pathogenesis of metabolic diseases both in humans and rodents. To accomplish this aim, we focus on illuminating the cellular and molecular mechanisms of fructose metabolism as well as its signaling effects on metabolic and cardiovascular homeostasis in health and disease, highlighting the role of carbohydrate-responsive element-binding protein in regulating fructose metabolism.

The interaction between the gut microbiota and dietary carbohydrates in nonalcoholic fatty liver disease

Imbalance between fat production and consumption causes various metabolic disorders. Nonalcoholic fatty liver disease (NAFLD), one such pathology, is characterized by abnormally increased fat synthesis and subsequent fat accumulation in hepatocytes1,2. While often comorbid with obesity and insulin resistance, this disease can also be found in lean individuals, suggesting specific metabolic dysfunction2. NAFLD has become one of the most prevalent liver diseases in adults worldwide, but its incidence in both children and adolescents has also markedly increased in developed nations3,4. Progression of this disease into nonalcoholic steatohepatitis (NASH), cirrhosis, liver failure, and hepatocellular carcinoma in combination with its widespread incidence thus makes NAFLD and its related pathologies a significant public health concern. Here, we review our understanding of the roles of dietary carbohydrates (glucose, fructose, and fibers) and the gut microbiota, which provides essential carbon sources for hepatic fat synthesis during the development of NAFLD.

From Food to Genes: Transcriptional Regulation of Metabolism by Lipids and Carbohydrates

Lipids and carbohydrates regulate gene expression by means of molecules that sense these macronutrients and act as transcription factors. The peroxisome proliferator-activated receptor (PPAR), activated by some fatty acids or their derivatives, and the carbohydrate response element binding protein (ChREBP), activated by glucose-derived metabolites, play a key role in metabolic homeostasis, especially in glucose and lipid metabolism. Furthermore, the action of both factors in obesity, diabetes and fatty liver, as well as the pharmacological development in the treatment of these pathologies are indeed of high relevance. In this review we present an overview of the discovery, mechanism of activation and metabolic functions of these nutrient-dependent transcription factors in different tissues contexts, from the nutritional genomics perspective. The possibility of targeting these factors in pharmacological approaches is also discussed. Lipid and carbohydrate-dependent transcription factors are key players in the complex metabolic homeostasis, but these factors also drive an adaptive response to non-physiological situations, such as overeating. Possibly the decisive role of ChREBP and PPAR in metabolic regulation points to them as ideal therapeutic targets, but their pleiotropic functions in different tissues makes it difficult to "hit the mark".

The functional activity of the miR-1914-5p in lipid metabolism of the hepatocarcinoma cell line HepG2: a potential molecular tool for controlling hepatic cellular migration

Hepatocellular carcinoma is one of the most common types of cancer in the world with high mortality rate and new therapies that control of fatty acid metabolism may limit the proliferation of cancer cells. In the last two decades, the non-coding RNAs have been considered as promising molecular tools to treat diseases, because they are able to modulate gene expression and the metabolic routes; however, deep investigation of their mechanistic behavior in pathologies must be performed. Thus, our aim was to evaluate the modulatory effect of the miR-1914-5p in controlling lipid metabolism in HepG2, a widely used human hepatocarcinoma cell line. The molecular and cellular analyses demonstrated that the functional inhibition of the investigated microRNA completely changed the cellular metabolism and behavior, compared to control groups. The in vitro inhibition of the miR-1914-5p increased the energy expenditure pointed in different analyses, decreasing cell doubling time and migration rate verified in wound healing and in the classical transwell chambers invasion assays, which makes the miR-1914-5p a candidate for further translational and preclinical studies to validate its function in controlling metastasis in liver cancer or even treat those diseases.