De novo lipogenesis in human fat and liver is linked to ChREBP-β and metabolic health

Metabolic remodeling of visceral and subcutaneous white adipose tissue during reacclimation of rats after cold

Deciphering lipid metabolism in white adipose tissue (WAT) depots during weight gain is important to understand the heterogeneity of WAT and its roles in obesity. Here, we examined the expression of key enzymes of lipid metabolism and changes in the morphology of representative visceral (epididymal) and subcutaneous (inguinal) WAT (eWAT and iWAT, respectively)-in adult male rats acclimated to cold (4 ± 1 °C) for 45 days and reacclimated to room temperature (RT, 22 ± 1 °C) for 1, 3, 7, 12, 21, or 45 days. The relative mass of both depots decreased to a similar extent after cold acclimation. However, fatty acid synthase (FAS), glucose-6-phosphate dehydrogenase (G6PDH), and medium-chain acyl-CoA dehydrogenase (ACADM) protein level increased only in eWAT, whereas adipose triglyceride lipase (ATGL) expression increased only in iWAT. During reacclimation, the relative mass of eWAT reached control values on day 12 and that of iWAT on day 45 of reacclimation. The faster recovery of eWAT mass is associated with higher expression of FAS, acetyl-CoA carboxylase (ACC), G6PDH, and ACADM during reacclimation and a delayed increase in ATGL. The absence of an increase in proliferating cell nuclear antigen suggests that the observed depot-specific mass increase is predominantly due to metabolic adjustments. In summary, this study shows a differential rate of visceral and subcutaneous adipose tissue weight regain during post-cold reacclimation of rats at RT. Faster recovery of the visceral WAT as compared to subcutaneous WAT during reacclimation at RT could be attributed to observed differences in the expression patterns of lipid metabolic enzymes.

Parenteral nutrition emulsion inhibits CYP3A4 in an iPSC derived liver organoids testing platform

OBJECTIVES

Parenteral nutrition (PN) is used for patients of varying ages with intestinal failure to supplement calories. Premature newborns with low birth weight are at a high risk for developing PN associated liver disease (PNALD) including steatosis, cholestasis, and gallbladder sludge/stones. To optimize nutrition regimens, models are required to predict PNALD.

METHODS

We have exploited induced pluripotent stem cell derived liver organoids to provide a testing platform for PNALD. Liver organoids mimic the developing liver and contain the different hepatic cell types. The organoids have an early postnatal maturity making them a suitable model for premature newborns. To mimic PN treatment we used medium supplemented with either clinoleic (80% olive oil/20% soybean oil) or intralipid (100% soybean oil) for 7 days.

RESULTS

Homogenous HNF4a staining was found in all organoids and PN treatments caused accumulation of lipids in hepatocytes. Organoids exhibited a dose dependent decrease in CYP3A4 activity and expression of hepatocyte functional genes. The lipid emulsions did not affect overall organoid viability and glucose levels had no contributory effect to the observed results.

CONCLUSIONS

Liver organoids could be utilized as a potential screening platform for the development of new, less hepatotoxic PN solutions. Both lipid treatments caused hepatic lipid accumulation, a significant decrease in CYP3A4 activity and a decrease in the RNA levels of both CYP3A4 and CYP1A2 in a dose dependent manner. The presence of high glucose had no additive effect, while Clinoleic at high dose, caused significant upregulation of interleukin 6 and TLR4 expression.

CDK6 inhibits de novo lipogenesis in white adipose tissues but not in the liver

Increased de novo lipogenesis (DNL) in white adipose tissue is associated with insulin sensitivity. Under both Normal-Chow-Diet and High-Fat-Diet, mice expressing a kinase inactive Cyclin-dependent kinase 6 (Cdk6) allele (K43M) display an increase in DNL in visceral white adipose tissues (VAT) as compared to wild type mice (WT), accompanied by markedly increased lipogenic transcriptional factor Carbohydrate-responsive element-binding proteins (CHREBP) and lipogenic enzymes in VAT but not in the liver. Treatment of WT mice under HFD with a CDK6 inhibitor recapitulates the phenotypes observed in K43M mice. Mechanistically, CDK6 phosphorylates AMP-activated protein kinase, leading to phosphorylation and inactivation of acetyl-CoA carboxylase, a key enzyme in DNL. CDK6 also phosphorylates CHREBP thus preventing its entry into the nucleus. Ablation of runt related transcription factor 1 in K43M mature adipocytes reverses most of the phenotypes observed in K43M mice. These results demonstrate a role of CDK6 in DNL and a strategy to alleviate metabolic syndromes.

CD73-dependent generation of extracellular adenosine by vascular endothelial cells modulates de novo lipogenesis in adipose tissue

Next to white and brown adipocytes present in white and brown adipose tissue (WAT, BAT), vascular endothelial cells, tissue-resident macrophages and other immune cells have important roles in maintaining adipose tissue homeostasis but also contribute to the etiology of obesity-associated chronic inflammatory metabolic diseases. In addition to hormonal signals such as insulin and norepinephrine, extracellular adenine nucleotides modulate lipid storage, fatty acid release and thermogenic responses in adipose tissues. The complex regulation of extracellular adenine nucleotides involves a network of ectoenzymes that convert ATP via ADP and AMP to adenosine. However, in WAT and BAT the processing of extracellular adenine nucleotides and its relevance for intercellular communications are still largely unknown. Based on our observations that in adipose tissues the adenosine-generating enzyme CD73 is mainly expressed by vascular endothelial cells, we studied glucose and lipid handling, energy expenditure and adaptive thermogenesis in mice lacking endothelial CD73 housed at different ambient temperatures. Under conditions of thermogenic activation, CD73 expressed by endothelial cells is dispensable for the expression of thermogenic genes as well as energy expenditure. Notably, thermoneutral housing leading to a state of low energy expenditure and lipid accumulation in adipose tissues resulted in enhanced glucose uptake into WAT of endothelial CD73-deficient mice. This effect was associated with elevated expression levels of de novo lipogenesis genes. Mechanistic studies provide evidence that extracellular adenosine is imported into adipocytes and converted to AMP by adenosine kinase. Subsequently, activation of the AMP kinase lowers the expression of de novo lipogenesis genes, most likely via inactivation of the transcription factor carbohydrate response element binding protein (ChREBP). In conclusion, this study demonstrates that endothelial-derived extracellular adenosine generated via the ectoenzyme CD73 is a paracrine factor shaping lipid metabolism in WAT.

Fatty acid synthesis suppresses dietary polyunsaturated fatty acid use

Dietary polyunsaturated fatty acids (PUFA) are increasingly recognized for their health benefits, whereas a high production of endogenous fatty acids - a process called de novo lipogenesis (DNL) - is closely linked to metabolic diseases. Determinants of PUFA incorporation into complex lipids are insufficiently understood and may influence the onset and progression of metabolic diseases. Here we show that fatty acid synthase (FASN), the key enzyme of DNL, critically determines the use of dietary PUFA in mice and humans. Moreover, the combination of FASN inhibition and PUFA-supplementation decreases liver triacylglycerols (TAG) in mice fed with high-fat diet. Mechanistically, FASN inhibition causes higher PUFA uptake via the lysophosphatidylcholine transporter MFSD2A, and a diacylglycerol O-acyltransferase 2 (DGAT2)-dependent incorporation of PUFA into TAG. Overall, the outcome of PUFA supplementation may depend on the degree of endogenous DNL and combining PUFA supplementation and FASN inhibition might be a promising approach to target metabolic disease.

Hepatic ChREBP orchestrates intrahepatic carbohydrate metabolism to limit hepatic glucose 6-phosphate and glycogen accumulation in a mouse model for acute Glycogen Storage Disease type Ib

OBJECTIVE

Carbohydrate Response Element Binding Protein (ChREBP) is a glucose 6-phosphate (G6P)-sensitive transcription factor that acts as a metabolic switch to maintain intracellular glucose and phosphate homeostasis. Hepatic ChREBP is well-known for its regulatory role in glycolysis, the pentose phosphate pathway, and de novo lipogenesis. The physiological role of ChREBP in hepatic glycogen metabolism and blood glucose regulation has not been assessed in detail, and ChREBP's contribution to carbohydrate flux adaptations in hepatic Glycogen Storage Disease type 1 (GSD I) requires further investigation.

METHODS

The current study aimed to investigate the role of ChREBP as a regulator of glycogen metabolism in response to hepatic G6P accumulation, using a model for acute hepatic GSD type Ib. The immediate biochemical and regulatory responses to hepatic G6P accumulation were evaluated upon G6P transporter inhibition by the chlorogenic acid S4048 in mice that were either treated with a short hairpin RNA (shRNA) directed against ChREBP (shChREBP) or a scrambled shRNA (shSCR). Complementary stable isotope experiments were performed to quantify hepatic carbohydrate fluxes in vivo.

RESULTS

ShChREBP treatment normalized the S4048-mediated induction of hepatic ChREBP target genes to levels observed in vehicle- and shSCR-treated controls. In parallel, hepatic shChREBP treatment in S4048-infused mice resulted in a more pronounced accumulation of hepatic glycogen and further reduction of blood glucose levels compared to shSCR treatment. Hepatic ChREBP knockdown modestly increased glucokinase (GCK) flux in S4048-treated mice while it enhanced UDP-glucose turnover as well as glycogen synthase and phosphorylase fluxes. Hepatic GCK mRNA and protein levels were induced by shChREBP treatment in both vehicle- and S4048-treated mice, while glycogen synthase 2 (GYS2) and glycogen phosphorylase (PYGL) mRNA and protein levels were reduced. Finally, knockdown of hepatic ChREBP expression reduced starch domain binding protein 1 (STBD1) mRNA and protein levels while it inhibited acid alpha-glucosidase (GAA) activity, suggesting reduced capacity for lysosomal glycogen breakdown.

CONCLUSIONS

Our data show that ChREBP activation controls hepatic glycogen and blood glucose levels in acute hepatic GSD Ib through concomitant regulation of glucose phosphorylation, glycogenesis, and glycogenolysis. ChREBP-mediated control of GCK enzyme levels aligns with corresponding adaptations in GCK flux. In contrast, ChREBP activation in response to acute hepatic GSD Ib exerts opposite effects on GYS2/PYGL enzyme levels and their corresponding fluxes, indicating that GYS2/PYGL expression levels are not limiting to their respective fluxes under these conditions.

Lipid Metabolism in Metabolic-Associated Steatotic Liver Disease (MASLD)

Metabolic-associated steatotic liver disease (MASLD) is a cluster of pathological conditions primarily developed due to the accumulation of ectopic fat in the hepatocytes. During the severe form of the disease, i.e., metabolic-associated steatohepatitis (MASH), accumulated lipids promote lipotoxicity, resulting in cellular inflammation, oxidative stress, and hepatocellular ballooning. If left untreated, the advanced form of the disease progresses to fibrosis of the tissue, resulting in irreversible hepatic cirrhosis or the development of hepatocellular carcinoma. Although numerous mechanisms have been identified as significant contributors to the development and advancement of MASLD, altered lipid metabolism continues to stand out as a major factor contributing to the disease. This paper briefly discusses the dysregulation in lipid metabolism during various stages of MASLD.

Replacement of dietary carbohydrate with protein increases fat mass and reduces hepatic triglyceride synthesis and content in female obese Zucker rats

Previous studies have demonstrated both energy restriction (ER) and higher protein (HP), lower carbohydrate (LC) diets downregulate hepatic de novo lipogenesis. Little is known about the independent and combined impact of ER and HP/LC diets on tissue-specific lipid kinetics in leptin receptor-deficient, obese rodents. This study investigated the effects of ER and dietary macronutrient content on body composition; hepatic, subcutaneous adipose tissue (SAT), and visceral AT (VAT) lipid metabolic flux (2 H2 O-labeling); and blood and liver measures of cardiometabolic health in six-week-old female obese Zucker rats (Leprfa+/fa+ ). Animals were randomized to a 10-week feeding intervention: ad libitum (AL)-HC/LP (76% carbohydrate/15% protein), AL-HP/LC (35% protein/56% carbohydrate), ER-HC/LP, or ER-HP/LC. ER groups consumed 60% of the feed consumed by AL. AL gained more fat mass than ER (P-energy = 0.012) and HP/LC gained more fat mass than HC/LP (P-diet = 0.025). Hepatic triglyceride (TG) concentrations (P-interaction = 0.0091) and absolute hepatic TG synthesis (P-interaction = 0.012) were lower in ER-HP/LC versus ER-HC/LP. ER had increased hepatic, SAT, and VAT de novo cholesterol fractional synthesis, absolute hepatic cholesterol synthesis, and serum cholesterol (P-energy≤0.0035). A HP/LC diet, independent of energy intake, led to greater gains in fat mass. A HP/LC diet, in the context of ER, led to reductions in absolute hepatic TG synthesis and TG content. However, ER worsened cholesterol metabolism. Increased adipose tissue TG retention with the HP/LC diet may reflect improved lipid storage capacity and be beneficial in this genetic model of obesity.

Sympathetic overdrive and unrestrained adipose lipolysis drive alcohol-induced hepatic steatosis in rodents

OBJECTIVE

Hepatic steatosis is a key initiating event in the pathogenesis of alcohol-associated liver disease (ALD), the most detrimental organ damage resulting from alcohol use disorder. However, the mechanisms by which alcohol induces steatosis remain incompletely understood. We have previously found that alcohol binging impairs brain insulin action, resulting in increased adipose tissue lipolysis by unrestraining sympathetic nervous system (SNS) outflow. Here, we examined whether an impaired brain-SNS-adipose tissue axis drives hepatic steatosis through unrestrained adipose tissue lipolysis and increased lipid flux to the liver.

METHODS

We examined the role of lipolysis, and the brain-SNS-adipose tissue axis and stress in alcohol induced hepatic triglyceride accumulation in a series of rodent models: pharmacological inhibition of the negative regulator of insulin signaling protein-tyrosine phosphatase 1β (PTP1b) in the rat brain, tyrosine hydroxylase (TH) knockout mice as a pharmacogenetic model of sympathectomy, adipocyte specific adipose triglyceride lipase (ATGL) knockout mice, wildtype (WT) mice treated with β3 adrenergic agonist or undergoing restraint stress.

RESULTS

Intracerebral administration of a PTP1b inhibitor, inhibition of adipose tissue lipolysis and reduction of sympathetic outflow ameliorated alcohol induced steatosis. Conversely, induction of adipose tissue lipolysis through β3 adrenergic agonism or by restraint stress worsened alcohol induced steatosis.

CONCLUSIONS

Brain insulin resistance through upregulation of PTP1b, increased sympathetic activity, and unrestrained adipose tissue lipolysis are key drivers of alcoholic steatosis. Targeting these drivers of steatosis may provide effective therapeutic strategies to ameliorate ALD.

Dietary triacetin, but not medium chain triacylglycerides, blunts weight gain in diet-induced rat model of obesity

Consumption of a Western diet (WD) is known to increase the risk of obesity. Short or medium chain fatty acids influence energy metabolism, and triacetin, a synthetic short chain triacylglyceride, has been shown to lower body fat under normal conditions. This study aimed to investigate if triacetin as part of a WD modifies rat weight and body fat. Male rats were fed a control diet or WD for 8 weeks. At week 8, rats in the WD group were maintained on a WD diet or switched to a WD diet containing 30% energy from medium-chain triacylglyceride (WD-MCT) or triacetin (WD-T) for another 8 weeks. At week 16, rats were euthanized and liver, adipose and blood were collected. Tissue fatty acids (FAs) were quantified by gas chromatography (GC) and hepatic FAs were measured by GC-combustion-isotope ratio mass spectrometry for δ13 C-palmitic acid (PAM)-a novel marker of de novo lipogenesis (DNL). Rats fed WD-T had a body weight not statistically different to the control group, and gained less body weight than rats fed WD alone. Furthermore, WD-T fed rats had a lower fat mass, and lower total liver and plasma FAs compared to the WD group. Rats fed WD-T did not differ from WD in blood ketone or glucose levels, however, had a significantly lower hepatic δ13 C-PAM value than WD fed rats; suggestive of lower DNL. In summary, we show that triacetin has the potential to blunt weight gain and adipose tissue accumulation in a rodent model of obesity, possibly due to a decrease in DNL.

Dietary Regulation of Hepatic Triacylglycerol Content-the Role of Eucaloric Carbohydrate Restriction with Fat or Protein Replacement

Accumulation of hepatic triacylglycerol (TG) is highly associated with impaired whole-body insulin-glucose homeostasis and dyslipidemia. The summarized findings from human intervention studies investigating the effect of reduced dietary carbohydrate and increased fat intake (and in studies also increased protein) while maintaining energy intake at eucaloric requirements reveal a beneficial effect of carbohydrate reduction on hepatic TG content in obese individuals with steatosis and indices of insulin resistance. Evidence suggests that the reduction of hepatic TG content after reduced intake of carbohydrates and increased fat/protein intake in humans, results from regulation of fatty acid (FA) metabolism within the liver, with an increase in hepatic FA oxidation and ketogenesis, together with a concomitant downregulation of FA synthesis from de novo lipogenesis. The adaptations in hepatic metabolism may result from reduced intrahepatic monosaccharide and insulin availability, reduced glycolysis and increased FA availability when carbohydrate intake is reduced.

Single-cell metabolic profiling reveals subgroups of primary human hepatocytes with heterogeneous responses to drug challenge

BACKGROUND

Xenobiotics are primarily metabolized by hepatocytes in the liver, and primary human hepatocytes are the gold standard model for the assessment of drug efficacy, safety, and toxicity in the early phases of drug development. Recent advances in single-cell genomics demonstrate liver zonation and ploidy as main drivers of cellular heterogeneity. However, little is known about the impact of hepatocyte specialization on liver function upon metabolic challenge, including hepatic metabolism, detoxification, and protein synthesis.

RESULTS

Here, we investigate the metabolic capacity of individual human hepatocytes in vitro. We assess how chronic accumulation of lipids enhances cellular heterogeneity and impairs the metabolisms of drugs. Using a phenotyping five-probe cocktail, we identify four functional subgroups of hepatocytes responding differently to drug challenge and fatty acid accumulation. These four subgroups display differential gene expression profiles upon cocktail treatment and xenobiotic metabolism-related specialization. Notably, intracellular fat accumulation leads to increased transcriptional variability and diminishes the drug-related metabolic capacity of hepatocytes.

CONCLUSIONS

Our results demonstrate that, upon a metabolic challenge such as exposure to drugs or intracellular fat accumulation, hepatocyte subgroups display different and heterogeneous transcriptional responses.

Steviol glycosides from Stevia rebaudiana Bertoni mitigate lipid metabolism abnormalities in diabetes by modulating selected gene expression - An in vivo study

In diabetes, in parallel to hyperglycaemia, elevated serum lipids are also diagnosed, representing a high-risk factor for coronary heart disease and cardiovascular complications. The objective of this study was to unravel the mechanisms that underlie the potential of steviol glycosides (stevioside or rebaudioside A) administered at two doses (500 or 2500 mg/kg body weight for 5 weeks) to regulate lipid metabolism. In this paper, the expression of selected genes responsible for glucose and lipid metabolism (Glut4, Pparγ, Cebpa, Fasn, Lpl and Egr1) in the peripheral tissues (adipose, liver and muscle tissue) was determined using quantitative real-time PCR method. It was found that the supplementation of steviol glycosides affected the expression of Glut4, Cebpa and Fasn genes, depending on the type of the glycoside and its dose, as well as the type of tissue, whish in part may explain the lipid-regulatory potential of steviol glycosides in hyperglycaemic conditions. Nevertheless, more in-depth studies, including human trials, are needed to confirm these effects, before steviol glycosides can be used in the therapy of type 2 diabetes.

mir-98-5p regulates gluconeogenesis and lipogenesis by targeting PPP1R15B in hepatocytes

Several reports suggest that circulatory miRNAs are deregulated in diverse diseases and used as markers for disease diagnosis and prognosis. Here we show that miR-98-5p, that is down-regulated in the circulation during diabetes, regulates hepatic gluconeogenesis and lipogenesis by targeting PPP1R15B. miR-98-5p overexpression significantly decreased the transcript and protein levels of PPP1R15B in hepatic HepG2 cells and increased p-eIF2α expression and these were prevented in the presence of its inhibitor. Two major hepatic hallmarks during diabetes i.e. hepatic lipid accumulation and glucose output were explored towards physiological relevance. As compared to scramble, overexpression of miR-98-5p decreased the transcript levels of both gluconeogenic and lipogenic genes together with a significant reduction in hepatic glucose production and fat accumulation in HepG2 cells. Using PASTAA to detect common transcription factors regulating these altered genes, CREB emerged as the most significantly enriched transcription factor. While miR-98-5p overexpression did not change the transcript levels of CREB, there was a significant change in its protein levels. While similar effects on gluconeogenic and lipogenic gene expression were detected using the PPP1R15B siRNA, the opposite was observed in the presence of miR-98-5p inhibitor alone. All these suggest that by targeting PPP1R15B, miR-98-5p regulates hepatic steatosis and glucose output; deregulation of which are characteristic hepatic features during diabetes. Therapeutic intervention of the miR-98/PPP1R15B axis might offer a potential strategy to target aberrant hepatic metabolism during diabetes.

Rottlerin suppresses lipid accumulation by inhibiting de novo lipogenesis and adipogenesis via LRP6/mTOR/SREBP1C in 3T3-L1 adipocytes

Rottlerin is isolated from Mallotus japonicus, a plant rich in polyphenols. Rottlerin is a selective PKCδ-inhibitor and is also known as an uncoupler of oxidative phosphorylation and anti-neoplastic agent. However, its anti-obesity effect is yet to be established. Therefore, this study tested whether rottlerin inhibits adipogenesis and de novo lipogenesis via the LRP6/mTOR/SREBP1C pathway in 3T3-L1 adipocytes. Rottlerin dramatically decreased lipid accumulation assessed by Oil Red O as evidence to support the cellular phenotype (p < 0.001). Pivotal messenger RNA and protein expressions associated with de novo lipogenesis (SREBP1C, ACC1, FAS, and SCD1) and adipogenesis (PPARγ and C/EBPα) were subsequentially verified by rottlerin in a dose-dependent manner (p < 0.05). Further investigation revealed that rottlerin reduced the AKT/mTOR pathway via diminished total protein of LRP6 (p < 0.05). Collectively, these findings establish a causal link between rottlerin, LRP6, and the altered nutrient-sensing mTOR pathway, in which rottlerin regulates de novo lipogenesis and adipogenesis in white adipocytes.

Adipocyte gene expression in obesity - insights gained and challenges ahead

White adipocytes possess extraordinary plasticity with an unparalleled capacity to expand in size with nutritional overload. Several lines of evidence indicate that limitations to this plasticity, as found in both lipodystrophy and obesity, drive several of the comorbidities of these disease, thereby underscoring the need to understand the mechanisms of healthy and unhealthy adipose expansion. Recent single-cell technologies and studies of isolated adipocytes have allowed researchers to gain insight into the molecular mechanisms of adipocyte plasticity. Here, we review current insight into the effect of nutritional overload on white adipocyte gene expression and function. We review the role of adipocyte size and heterogeneity and discuss the challenges and future directions.

Associations of fatty acids composition and estimated desaturase activities in erythrocyte phospholipids with biochemical and clinical indicators of cardiometabolic risk in non-diabetic Serbian women: the role of level of adiposity

Introduction

Fatty acids (FAs) composition and desaturase activities can be altered in different metabolic conditions, but the adiposity-independent associations with clinical and biochemical indicators of cardiometabolic risk are still unclear. This study aimed to analyze the associations of FAs composition and estimated desaturase activities with anthropometric, clinical, and biochemical cardiometabolic risk indicators in non-diabetic Serbian women, and to investigate if these associations were independent of the level of adiposity and other confounders.

Methods

In 76 non-diabetic, otherwise healthy Serbian women, aged 24-68 years, with or without metabolic syndrome or obesity (BMI=23.6±5.6 kg/m2), FA composition in erythrocyte phospholipids was measured by gas-liquid chromatography. Desaturase activities were estimated from product/precursor FAs ratios (D9D:16:1n-7/16:0; D6D:20:3n-6/18:2n-6; D5D:20:4n-6/20:3n-6). Correlations were made with anthropometric, biochemical (serum glucose, triacylglycerols, LDL-C, HDL-C, ALT, AST, and their ratios) and clinical (blood pressure) indicators of cardiometabolic risk. Linear regression models were performed to test the independence of these associations.

Results

Estimated desaturase activities and certain FAs were associated with anthropometric, clinical and biochemical indicators of cardiometabolic risk: D9D, D6D, 16:1n-7 and 20:3n-6 were directly associated, while D5D and 18:0 were inversely associated. However, the associations with clinical and biochemical indicators were not independent of the associations with the level of adiposity, since they were lost after controlling for anthropometric indices. After controlling for multiple confounders (age, postmenopausal status, education, smoking, physical activity, dietary macronutrient intakes, use of supplements, alcohol consumption), the level of adiposity was the most significant predictor of desaturase activities and aforementioned FAs levels, and mediated their association with biochemical/clinical indicators. Vice versa, desaturase activities predicted the level of adiposity, but not other components of cardiometabolic risk (if the level of adiposity was accounted). While the associations of anthropometric indices with 16:1n-7, 20:3n-6, 18:0 and D9D and D6D activities were linear, the associations with D5D activity were the inverse U-shaped. The only adiposity-independent association of FAs profiles with the indicators of cardiometabolic risk was a positive association of 20:5n-3 with ALT/AST ratio, which requires further exploration.

Discussion

Additional studies are needed to explore the mechanisms of the observed associations.

The effect of weight loss on whole-body and tissue-specific insulin sensitivity and hepatic lipid content and composition: SWEET substudy

OBJECTIVE

This study (1) investigated the effect of weight loss on whole-body and tissue-specific insulin sensitivity and on intrahepatic lipid (IHL) content and composition and (2) investigated the association between weight-loss-induced changes in insulin sensitivity and IHL content in individuals with overweight or obesity.

METHODS

In this secondary analysis of the European SWEET project, 50 adults (age 18-65 years) with overweight or obesity (BMI ≥ 25 kg/m² ) followed a low-energy diet (LED) for 2 months. At baseline and after the LED, body composition (dual-energy x-ray absorptiometry), IHL content and composition (proton magnetic resonance spectroscopy), whole-body insulin sensitivity (Matsuda index), muscle insulin sensitivity index (MISI), and hepatic insulin resistance index (HIRI) were determined (7-point oral glucose tolerance test).

RESULTS

The LED reduced body weight (p < 0.001). This was accompanied by increased Matsuda index and reduced HIRI (both p < 0.001) but no change in MISI (p = 0.260). Weight loss decreased IHL content (mean [SEM], 3.9% [0.7%] vs. 1.6% [0.5%], p < 0.001) and the hepatic saturated fatty acid fraction (41.0% [1.5%] vs. 36.6% [1.9%], p = 0.039). The reduced IHL content was associated with an improvement in HIRI (r = 0.402, p = 0.025).

CONCLUSIONS

Weight loss decreased IHL content and the hepatic saturated fatty acid fraction. The decrease in IHL content was associated with weight-loss-induced improvement in hepatic insulin sensitivity in individuals with overweight or obesity.

Characterization of lipid signatures in the plasma and insulin-sensitive tissues of the C57BL/6J mice fed on obesogenic diets

Diet-induced obesity mouse models are widely utilized to investigate the underlying mechanisms of dyslipidemia, glucose intolerance, insulin resistance, hepatic steatosis, and type 2 diabetes mellitus (T2DM), as well as for screening potential drug compounds. However, there is limited knowledge regarding specific signature lipids that accurately reflect dietary disorders. In this study, we aimed to identify key lipid signatures using LC/MS-based untargeted lipidomics in the plasma, liver, adipose tissue (AT), and skeletal muscle tissues (SKM) of male C57BL/6J mice that were fed chow, LFD, or obesogenic diets (HFD, HFHF, and HFCD) for a duration of 20 weeks. Furthermore, we conducted a comprehensive lipid analysis to assess similarities and differences with human lipid profiles. The mice fed obesogenic diets exhibited weight gain, glucose intolerance, elevated BMI, glucose and insulin levels, and a fatty liver, resembling characteristics of T2DM and obesity in humans. In total, we identified approximately 368 lipids in plasma, 433 in the liver, 493 in AT, and 624 in SKM. Glycerolipids displayed distinct patterns across the tissues, differing from human findings. However, changes in sphingolipids, phospholipids, and the expression of inflammatory and fibrotic genes showed similarities to reported human findings. Significantly modulated pathways in the obesogenic diet-fed groups included ceramide de novo synthesis, sphingolipid remodeling, and the carboxylesterase pathway, while lipoprotein-mediated pathways were minimally affected.

The Function of MondoA and ChREBP Nutrient-Sensing Factors in Metabolic Disease

Obesity is a major global public health concern associated with an increased risk of many health problems, including type 2 diabetes, heart disease, stroke, and some types of cancer. Obesity is also a critical factor in the development of insulin resistance and type 2 diabetes. Insulin resistance is associated with metabolic inflexibility, which interferes with the body's ability to switch from free fatty acids to carbohydrate substrates, as well as with the ectopic accumulation of triglycerides in non-adipose tissue, such as that of skeletal muscle, the liver, heart, and pancreas. Recent studies have demonstrated that MondoA (MLX-interacting protein or MLXIP) and the carbohydrate response element-binding protein (ChREBP, also known as MLXIPL and MondoB) play crucial roles in the regulation of nutrient metabolism and energy homeostasis in the body. This review summarizes recent advances in elucidating the function of MondoA and ChREBP in insulin resistance and related pathological conditions. This review provides an overview of the mechanisms by which MondoA and ChREBP transcription factors regulate glucose and lipid metabolism in metabolically active organs. Understanding the underlying mechanism of MondoA and ChREBP in insulin resistance and obesity can foster the development of new therapeutic strategies for treating metabolic diseases.

Physiological and pathological roles of lipogenesis

Lipids are essential metabolites, which function as energy sources, structural components and signalling mediators. Most cells are able to convert carbohydrates into fatty acids, which are often converted into neutral lipids for storage in the form of lipid droplets. Accumulating evidence suggests that lipogenesis plays a crucial role not only in metabolic tissues for systemic energy homoeostasis but also in immune and nervous systems for their proliferation, differentiation and even pathophysiological roles. Thus, excessive or insufficient lipogenesis is closely associated with aberrations in lipid homoeostasis, potentially leading to pathological consequences, such as dyslipidaemia, diabetes, fatty liver, autoimmune diseases, neurodegenerative diseases and cancers. For systemic energy homoeostasis, multiple enzymes involved in lipogenesis are tightly controlled by transcriptional and post-translational modifications. In this Review, we discuss recent findings regarding the regulatory mechanisms, physiological roles and pathological importance of lipogenesis in multiple tissues such as adipose tissue and the liver, as well as the immune and nervous systems. Furthermore, we briefly introduce the therapeutic implications of lipogenesis modulation.

Dysglycemia Shapes Visceral Adipose Tissue's Response to GIP, GLP-1 and Glucagon in Individuals with Obesity

Visceral adipose tissue (VAT) metabolic fingerprints differ according to body mass index (BMI) and glycemic status. Glucagon-like peptide 1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP) and glucagon are gut-associated hormones that play an important role in regulating energy and glucose homeostasis, although their metabolic actions in VAT are still poorly characterized. Our aim was to assess whether GLP-1, GIP and glucagon influence the VAT metabolite profile. To achieve this goal, VAT harvested during elective surgical procedures from individuals (N = 19) with different BMIs and glycemic statuses was stimulated with GLP-1, GIP or glucagon, and culture media was analyzed using proton nuclear magnetic resonance. In the VAT of individuals with obesity and prediabetes, GLP-1 shifted its metabolic profile by increasing alanine and lactate production while also decreasing isoleucine consumption, whereas GIP and glucagon decreased lactate and alanine production and increased pyruvate consumption. In summary, GLP-1, GIP and glucagon were shown to distinctively modulate the VAT metabolic profile depending on the subject's BMI and glycemic status. In VAT from patients with obesity and prediabetes, these hormones induced metabolic shifts toward gluconeogenesis suppression and oxidative phosphorylation enhancement, suggesting an overall improvement in AT mitochondrial function.

The role of ChREBP in carbohydrate sensing and NAFLD development

Excessive sugar consumption and defective glucose sensing by hepatocytes contribute to the development of metabolic diseases including type 2 diabetes mellitus (T2DM) and nonalcoholic fatty liver disease (NAFLD). Hepatic metabolism of carbohydrates into lipids is largely dependent on the carbohydrate-responsive element binding protein (ChREBP), a transcription factor that senses intracellular carbohydrates and activates many different target genes, through the activation of de novo lipogenesis (DNL). This process is crucial for the storage of energy as triglycerides in hepatocytes. Furthermore, ChREBP and its downstream targets represent promising targets for the development of therapies for the treatment of NAFLD and T2DM. Although lipogenic inhibitors (for example, inhibitors of fatty acid synthase, acetyl-CoA carboxylase or ATP citrate lyase) are currently under investigation, targeting lipogenesis remains a topic of discussion for NAFLD treatment. In this Review, we discuss mechanisms that regulate ChREBP activity in a tissue-specific manner and their respective roles in controlling DNL and beyond. We also provide in-depth discussion of the roles of ChREBP in the onset and progression of NAFLD and consider emerging targets for NAFLD therapeutics.

Fatty Acid Induced Hypermethylation in the Slc2a4 Gene in Visceral Adipose Tissue Is Associated to Insulin-Resistance and Obesity

De novo lipogenesis (DNL) in visceral adipose tissue (VAT) is associated with systemic insulin sensitivity. DNL in VAT is regulated through ChREBP activity and glucose uptake through Glut4 (encoded by Slc2a4). Slc2a4 expression, ChREBP activity, and DNL are decreased in obesity, the underlying cause however remains unidentified. We hypothesize that increased DNA methylation in an enhancer region of Slc2a4 decreases Slc2a4 expression in obesity and insulin resistance. We found that SLC2A4 expression in VAT of morbidly obese subjects with high HbA1c (>6.5%, n = 35) is decreased, whereas DNA methylation is concomitantly increased compared to morbidly obese subjects with low HbA1c (≤6.5%, n = 65). In diet-induced obese (DIO) mice, DNA methylation of Slc2a4 persistently increases with the onset of obesity and insulin resistance, while gene expression progressively decreases. The regulatory impact of DNA methylation in the investigated enhancer region on SLC2A4 gene expression was validated with a reporter gene assay. Additionally, treatment of 3T3 pre-adipocytes with palmitate/oleate during differentiation decreased DNA methylation and increased Slc2a4 expression. These findings highlight a potential regulation of Slc2a4 by DNA methylation in VAT, which is induced by fatty acids and may play a role in the progression of obesity and insulin resistance in humans.

Adipose tissue at single-cell resolution

Adipose tissue exhibits remarkable plasticity with capacity to change in size and cellular composition under physiological and pathophysiological conditions. The emergence of single-cell transcriptomics has rapidly transformed our understanding of the diverse array of cell types and cell states residing in adipose tissues and has provided insight into how transcriptional changes in individual cell types contribute to tissue plasticity. Here, we present a comprehensive overview of the cellular atlas of adipose tissues focusing on the biological insight gained from single-cell and single-nuclei transcriptomics of murine and human adipose tissues. We also offer our perspective on the exciting opportunities for mapping cellular transitions and crosstalk, which have been made possible by single-cell technologies.

Futile cycle of β-oxidation and de novo lipogenesis are associated with essential fatty acids depletion in lipoatrophy

Total absence of adipose tissue (lipoatrophy) is associated with the development of severe metabolic disorders including hepatomegaly and fatty liver. Here, we sought to investigate the impact of severe lipoatrophy induced by deletion of peroxisome proliferator-activated receptor gamma (PPARγ) exclusively in adipocytes on lipid metabolism in mice. Untargeted lipidomics of plasma, gastrocnemius and liver uncovered a systemic depletion of the essential linoleic (LA) and α-linolenic (ALA) fatty acids from several lipid classes (storage lipids, glycerophospholipids, free fatty acids) in lipoatrophic mice. Our data revealed that such essential fatty acid depletion was linked to increased: 1) capacity for liver mitochondrial fatty acid β-oxidation (FAO), 2) citrate synthase activity and coenzyme Q content in the liver, 3) whole-body oxygen consumption and reduced respiratory exchange rate in the dark period, and 4) de novo lipogenesis and carbon flux in the TCA cycle. The key role of de novo lipogenesis in hepatic steatosis was evidenced by an accumulation of stearic, oleic, sapienic and mead acids in liver. Our results thus indicate that the simultaneous activation of the antagonic processes FAO and de novo lipogenesis in liver may create a futile metabolic cycle leading to a preferential depletion of LA and ALA. Noteworthy, this previously unrecognized cycle may also explain the increased energy expenditure displayed by lipoatrophic mice, adding a new piece to the metabolic regulation puzzle in lipoatrophies.

TREM2 Regulates the Removal of Apoptotic Cells and Inflammatory Processes during the Progression of NAFLD

Nonalcoholic fatty liver disease (NAFLD) is the most common liver pathology worldwide. In mice and humans, NAFLD progression is characterized by the appearance of TREM2-expressing macrophages in the liver. However, their mechanistic contributions to disease progression have not been completely elucidated. Here, we show that TREM2⁺ macrophages prevent the generation of a pro-inflammatory response elicited by LPS-laden lipoproteins in vitro. Further, Trem2 expression regulates bone-marrow-derived macrophages (BMDMs) and Kupffer cell capacity to phagocyte apoptotic cells in vitro, which is dependent on CD14 activation. In line with this, loss of Trem2 resulted in an increased pro-inflammatory response, which ultimately aggravated liver fibrosis in murine models of NAFLD. Similarly, in a human NAFLD cohort, plasma levels of TREM2 were increased and hepatic TREM2 expression was correlated with higher levels of liver triglycerides and the acquisition of a fibrotic gene signature. Altogether, our results suggest that TREM2⁺ macrophages have a protective function during the progression of NAFLD, as they are involved in the processing of pro-inflammatory lipoproteins and phagocytosis of apoptotic cells and, thereby, are critical contributors for the re-establishment of liver homeostasis.

HGFAC is a ChREBP-regulated hepatokine that enhances glucose and lipid homeostasis

Carbohydrate response element-binding protein (ChREBP) is a carbohydrate-sensing transcription factor that regulates both adaptive and maladaptive genomic responses in coordination of systemic fuel homeostasis. Genetic variants in the ChREBP locus associate with diverse metabolic traits in humans, including circulating lipids. To identify novel ChREBP-regulated hepatokines that contribute to its systemic metabolic effects, we integrated ChREBP ChIP-Seq analysis in mouse liver with human genetic and genomic data for lipid traits and identified hepatocyte growth factor activator (HGFAC) as a promising ChREBP-regulated candidate in mice and humans. HGFAC is a protease that activates the pleiotropic hormone hepatocyte growth factor. We demonstrate that HGFAC-KO mice had phenotypes concordant with putative loss-of-function variants in human HGFAC. Moreover, in gain- and loss-of-function genetic mouse models, we demonstrate that HGFAC enhanced lipid and glucose homeostasis, which may be mediated in part through actions to activate hepatic PPARγ activity. Together, our studies show that ChREBP mediated an adaptive response to overnutrition via activation of HGFAC in the liver to preserve glucose and lipid homeostasis.

Cranberry Proanthocyanidins as a Therapeutic Strategy to Curb Metabolic Syndrome and Fatty Liver-Associated Disorders

While the prevalence of metabolic syndrome (MetS) is steadily increasing worldwide, no optimal pharmacotherapy is readily available to address its multifaceted risk factors and halt its complications. This growing challenge mandates the development of other future curative directions. The purpose of the present study is to investigate the efficacy of cranberry proanthocyanidins (PACs) in improving MetS pathological conditions and liver complications; C57BL/6J mice were fed either a standard chow or a high fat/high sucrose (HFHS) diet with and without PACs (200 mg/kg), delivered by daily gavage for 12 weeks. Our results show that PACs lowered HFHS-induced obesity, insulin resistance, and hyperlipidemia. In conjunction, PACs lessened circulatory markers of oxidative stress (OxS) and inflammation. Similarly, the anti-oxidative and anti-inflammatory capacities of PACs were noted in the liver in association with improved hepatic steatosis. Inhibition of lipogenesis and stimulation of beta-oxidation could account for PACs-mediated decline of fatty liver as evidenced not only by the expression of rate-limiting enzymes but also by the status of AMPKα (the key sensor of cellular energy) and the powerful transcription factors (PPARα, PGC1α, SREBP1c, ChREBP). Likewise, treatment with PACs resulted in the downregulation of critical enzymes of liver gluconeogenesis, a process contributing to increased rates of glucose production in type 2 diabetes. Our findings demonstrate that PACs prevented obesity and improved insulin resistance likely via suppression of OxS and inflammation while diminishing hyperlipidemia and fatty liver disease, as clear evidence for their strength of fighting the cluster of MetS abnormalities.

Association between de novo lipogenesis susceptibility genes and coronary artery disease

BACKGROUND AND AIMS

Coronary artery disease (CAD) is the principal cause of death in individuals with non-alcoholic fatty liver disease (NAFLD). The aim of this study was to use genetic epidemiology to study the association between de novo lipogenesis (DNL), one of the major pathways leading to NAFLD, and CAD risk.

METHODS AND RESULTS

DNL susceptibility genes were used as instruments and selected using three approaches: 1) genes that are associated with both high serum triglycerides and low sex hormone-binding globulin, both downstream consequences of DNL (unbiased approach), 2) genes that have a known role in DNL (biased approach), and 3) genes that have been associated with serum fatty acids, used as a proxy of DNL. Gene-CAD effect estimates were retrieved from the meta-analysis of CARDIoGRAM and the UK Biobank (∼76014 cases and ∼264785 controls). Effect estimates were clustered using a fixed-effects meta-analysis. Twenty-two DNL susceptibility genes were identified by the unbiased approach, nine genes by the biased approach and seven genes were associated with plasma fatty acids. Clustering of genes selected in the unbiased and biased approach showed a statistically significant association with CAD (OR:1.016, 95%CI:1.012; 1.020 and OR:1.013, 95%CI:1.007; 1.020, respectively), while clustering of fatty acid genes did not (OR:1.004, 95%CI:0.996-1.011). Subsequent exclusion of potential influential outliers did reveal a statistically significant association (OR:1.009, 95%CI:1.000; 1.018).

CONCLUSIONS

DNL susceptibility genes are associated with an increased risk of CAD. These findings suggest that DNL may be involved in the pathogenesis of CAD and favor further development of strategies that target NAFLD through DNL.

The regulation of adipocyte growth in white adipose tissue

Adipocytes can increase in volume up to a thousand-fold, storing excess calories as triacylglycerol in large lipid droplets. The dramatic morphological changes required of adipocytes demands extensive cytoskeletal remodeling, including lipid droplet and plasma membrane expansion. Cell growth-related signalling pathways are activated, stimulating the production of sufficient amino acids, functional lipids and nucleotides to meet the increasing cellular needs of lipid storage, metabolic activity and adipokine secretion. Continued expansion gives rise to enlarged (hypertrophic) adipocytes. This can result in a failure to maintain growth-related homeostasis and an inability to cope with excess nutrition or respond to stimuli efficiently, ultimately leading to metabolic dysfunction. We summarize recent studies which investigate the functional and cellular structure remodeling of hypertrophic adipocytes. How adipocytes adapt to an enlarged cell size and how this relates to cellular dysfunction are discussed. Understanding the healthy and pathological processes involved in adipocyte hypertrophy may shed light on new strategies for promoting healthy adipose tissue expansion.

Differential Gene Expression of Subcutaneous Adipose Tissue among Lean, Obese, and after RYGB (Different Timepoints): Systematic Review and Analysis

The main roles of adipose tissue include triglycerides storage and adipokine secretion, which regulate energy balance and inflammation status. In obesity, adipocyte dysfunction leads to proinflammatory cytokine production and insulin resistance. Bariatric surgery is the most effective treatment for obesity, the gold-standard technique being Roux-en-Y gastric bypass (RYGB). Since metabolic improvements after RYGB are clear, a better understanding of adipose tissue molecular modifications could be derived from this study. Thus, the aim of this systematic review was to find differentially expressed genes in subcutaneous adipose tissue of lean, obese and post-RYGB (distinct timepoints). To address this objective, publications from 2015-2022 reporting gene expression (candidate genes or transcriptomic approach) of subcutaneous adipose tissue from lean and obese individuals before and after RGYB were searched in PubMed, Elsevier, and Springer Link. Excluded publications were reviews, studies analyzing serum, other types of tissues, or bariatric procedures. A risk-of-bias summary was created for each paper using Robvis, to finally include 17 studies. Differentially expressed genes in post-RYGB vs. obese and lean vs. obese were obtained and the intersection among these groups was used for analysis and gene classification by metabolic pathway. Results showed that the lean state as well as the post-RYGB is similar in terms of increased expression of insulin-sensitizing molecules, inducing lipogenesis over lipolysis and downregulating leukocyte activation, cytokine production and other factors that promote inflammation. Thus, massive weight loss and metabolic improvements after RYGB are accompanied by gene expression modifications reverting the "adipocyte dysfunction" phenomenon observed in obesity conditions.

Aging Increases Susceptibility to Develop Cardiac Hypertrophy following High Sugar Consumption

Aging and poor diet are independent risk factors for heart disease, but the impact of high-sucrose (HS) consumption in the aging heart is understudied. Aging leads to impairments in mitochondrial function that result in muscle dysfunction (e.g., cardiac remodeling and sarcopenia). We tested whether HS diet (60%kcal sucrose) would accelerate muscle dysfunction in 24-month-old male CB6F1 mice. By week 1 on HS diet, mice developed significant cardiac hypertrophy compared to age-matched chow-fed controls. The increased weight of the heart persisted throughout the 4-week treatment, while body weight and strength declined more rapidly than controls. We then tested whether HS diet could worsen cardiac dysfunction in old mice and if the mitochondrial-targeted drug, elamipretide (ELAM), could prevent the diet-induced effect. Old and young mice were treated with either ELAM or saline as a control for 2 weeks, and provided with HS diet or chow on the last week. As demonstrated in the previous experiment, old mice had age-related cardiac hypertrophy that worsened after one week on HS and was prevented by ELAM treatment, while the HS diet had no detectable effect on hypertrophy in the young mice. As expected, mitochondrial respiration and reactive oxygen species (ROS) production were altered by age, but were not significantly affected by HS diet or ELAM. Our findings highlight the vulnerability of the aged heart to HS diet that can be prevented by systemic targeting of the mitochondria with ELAM.

Dual roles of B lymphocytes in mouse models of diet-induced nonalcoholic fatty liver disease

BACKGROUND AND AIMS

Growing evidence suggests an important role of B cells in the development of NAFLD. However, a detailed functional analysis of B cell subsets in NAFLD pathogenesis is lacking.

APPROACH AND RESULTS

In wild-type mice, 21 weeks of high fat diet (HFD) feeding resulted in NAFLD with massive macrovesicular steatosis, modest hepatic and adipose tissue inflammation, insulin resistance, and incipient fibrosis. Remarkably, B^null (JHT) mice were partially protected whereas B cell harboring but antibody-deficient IgMi mice were completely protected from the development of hepatic steatosis, inflammation, and fibrosis. The common feature of JHT and IgMi mice is that they do not secrete antibodies, whereas HFD feeding in wild-type mice led to increased levels of serum IgG2c. Whereas JHT mice have no B cells at all, regulatory B cells were found in the liver of both wild-type and IgMi mice. HFD reduced the number of regulatory B cells and IL-10 production in the liver of wild-type mice, whereas these increased in IgMi mice. Livers of patients with advanced liver fibrosis showed abundant deposition of IgG and stromal B cells and low numbers of IL-10 expressing cells, compatible with our experimental data.

CONCLUSIONS

B lymphocytes have both detrimental and protective effects in HFD-induced NAFLD. The lack of secreted pathogenic antibodies protects partially from NAFLD, whereas the presence of certain B cell subsets provides additional protection. IL-10-producing regulatory B cells may represent such a protective B cell subset.

Approaches to Measuring the Activity of Major Lipolytic and Lipogenic Enzymes In Vitro and Ex Vivo

Since the 1950s, one of the goals of adipose tissue research has been to determine lipolytic and lipogenic activity as the primary metabolic pathways affecting adipocyte health and size and thus representing potential therapeutic targets for the treatment of obesity and associated diseases. Nowadays, there is a relatively large number of methods to measure the activity of these pathways and involved enzymes, but their applicability to different biological samples is variable. Here, we review the characteristics of mean lipogenic and lipolytic enzymes, their inhibitors, and available methodologies for assessing their activity, and comment on the advantages and disadvantages of these methodologies and their applicability in vivo, ex vivo, and in vitro, i.e., in cells, organs and their respective extracts, with the emphasis on adipocytes and adipose tissue.

Changes in plasma free fatty acids in obese patients before and after bariatric surgery highlight alterations in lipid metabolism

Obesity is a complex disease that increases an individual’s risk of developing other diseases and health-related problems. A common feature is dyslipidemia characterized by increased levels of plasma lipids, which include non-esterified fatty acids (NEFAs). The role of NEFAs in obesity-related morbidity is interesting as NEFAs constitute a reservoir of metabolic energy, are principal components of cell membranes and are precursors for signalling molecules. Bariatric surgery promotes sustained weight loss in severely obese patients, reducing the incidence and severity of co-morbidities. In this study we measure changes in circulating NEFA species in plasma samples taken from 25 obese individuals before and 9 months after Roux-en-Y gastric bypass surgery. The mean weight of the cohort reduced by 29.2% from 149.0 ± 25.1 kg pre-surgery to 105.5 ± 19.8 kg post-surgery and the BMI by 28.2% from 51.8 ± 6.3 kg/m² pre-surgery to 37.2 ± 5.4 kg/m². Mean glycated haemoglobin (HbA1c) reduced from 6.5 ± 1.3 to 5.5 ± 0.5%, consistent with the intervention leading to improved glycaemic control, particularly in those who were dysglycemic prior to surgery. Total and LDL cholesterol concentrations were markedly reduced following surgery. Concentrations of seven NEFAs were found to decrease 9 months after surgery compared to pre-surgery levels: myristate, palmitoleate, palmitate, linoleate, oleate, stearate and arachidonate. Bariatric surgery led to increased lipogenesis and elongase activity and decreased stearoyl-CoA desaturase 1 activity. This study therefore highlights metabolic changes that take place following gastric bypass surgery in severely obese patients.

Population-based plasma lipidomics reveals developmental changes in metabolism and signatures of obesity risk: a mother-offspring cohort study

BACKGROUND

Lipids play a vital role in health and disease, but changes to their circulating levels and the link with obesity remain poorly characterized in expecting mothers and their offspring in early childhood.

METHODS

LC-MS/MS-based quantitation of 480 lipid species was performed on 2491 plasma samples collected at 4 time points in the mother-offspring Asian cohort GUSTO (Growing Up in Singapore Towards healthy Outcomes). These 4 time points constituted samples collected from mothers at 26-28 weeks of gestation (n=752) and 4-5 years postpartum (n=650), and their offspring at birth (n=751) and 6 years of age (n=338). Linear regression models were used to identify the pregnancy and developmental age-specific variations in the plasma lipidomic profiles, and their association with obesity risk. An independent birth cohort (n=1935), the Barwon Infant Study (BIS), comprising mother-offspring dyads of Caucasian origin was used for validation.

RESULTS

Levels of 36% of the profiled lipids were significantly higher (absolute fold change > 1.5 and P_adj < 0.05) in antenatal maternal circulation as compared to the postnatal phase, with phosphatidylethanolamine levels changing the most. Compared to antenatal maternal lipids, cord blood showed lower concentrations of most lipid species (79%) except lysophospholipids and acylcarnitines. Changes in lipid concentrations from birth to 6 years of age were much higher in magnitude (log₂FC=-2.10 to 6.25) than the changes observed between a 6-year-old child and an adult (postnatal mother) (log₂FC=-0.68 to 1.18). Associations of cord blood lipidomic profiles with birth weight displayed distinct trends compared to the lipidomic profiles associated with child BMI at 6 years. Comparison of the results between the child and adult BMI identified similarities in association with consistent trends (R²=0.75). However, large number of lipids were associated with BMI in adults (67%) compared to the children (29%). Pre-pregnancy BMI was specifically associated with decrease in the levels of phospholipids, sphingomyelin, and several triacylglycerol species in pregnancy.

CONCLUSIONS

In summary, our study provides a detailed landscape of the in utero lipid environment provided by the gestating mother to the growing fetus, and the magnitude of changes in plasma lipidomic profiles from birth to early childhood. We identified the effects of adiposity on the circulating lipid levels in pregnant and non-pregnant women as well as offspring at birth and at 6 years of age. Additionally, the pediatric vs maternal overlap of the circulating lipid phenotype of obesity risk provides intergenerational insights and early opportunities to track and intervene the onset of metabolic adversities.

CLINICAL TRIAL REGISTRATION

This birth cohort is a prospective observational study, which was registered on 1 July 2010 under the identifier NCT01174875 .

Impact of NAFLD and its pharmacotherapy on lipid profile and CVD

Atherosclerotic cardiovascular disease (ASCVD) remains the leading cause of death worldwide. Increasing evidence suggests that, in addition to traditional metabolic risk factors such as obesity, hypercholesterolemia, hypertension, diabetes mellitus, and insulin resistance (IR), nonalcoholic fatty liver disease (NAFLD) is an emerging driver of ASCVD via multiple mechanisms, mainly by disrupting lipid metabolism. The lack of pharmaceutical treatment has spurred substantial investment in the research and development of NAFLD drugs. However, many reagents with promising therapeutic potential for NAFLD also have considerable impacts on the circulating lipid profile. In this review, we first summarize the mechanisms linking lipid dysregulation in NAFLD to the progression of ASCVD. Importantly, we highlight the potential risks of/benefits to ASCVD conferred by NAFLD pharmaceutical treatments and discuss potential strategies and next-generation drugs for treating NAFLD without the unwanted side effects.

Neurosecretory Protein GL Promotes Normotopic Fat Accumulation in Male ICR Mice

Neurosecretory protein GL (NPGL) is a small secretory protein identified in the hypothalamus of birds and mammals. We recently reported that NPGL exerts obesogenic effects in obesity-prone C57BL6/J mice. However, whether NPGL elicits adiposity in different mouse strains is poorly understood. In this study, we generated transgenic mice overexpressing Npgl using the ICR strain (Npgl Tg mice) to elucidate the obesogenic effects of NPGL in different strains. Npgl Tg mice showed increased white adipose tissue (WAT) mass. Although the mass of brown adipose tissue (BAT) was slightly altered in Npgl Tg mice, hypertrophy of lipid droplets was also observed in BAT. In contrast, fat accumulation was not induced in the liver, with the upregulation of mRNAs related to hepatic lipolysis. These results support the hypothesis that NPGL causes obesity in several strains and species. This report highlights the pivotal role of NPGL in fat accumulation in adipose tissues and contributes to the elucidation of the biological mechanisms underlying obesity and metabolic diseases in heterogeneous populations.

Fatty acid synthase (Fasn) inhibits the expression levels of immune response genes via alteration of alternative splicing in islet cells

BACKGROUND

Increasing evidence has shown that fatty acid synthase (Fasn) is associated with diabetes mellitus (DM) and insulin resistance, however, it remains unclear how Fasn upregulation leads to dysregulation of energy homeostasis in islet cells. Consequently, uncovering the function of Fasn in islet cells. Consequently, uncovering the function of FASN in islet cells is immensely important for finding a treatment target.

AIM

In this study, we elucidated the biological function of Fasn on the target genes in a rat insulinoma INS-1 cell line.

METHODS

We created a Fasn overexpressing rat insulinoma cell line (Fasn-OE), and performed bulk RNA-sequencing (RNA-seq) experiments on Fasn-OE and INS-1 (control) cells. We first identified differentially expressed genes (DEGs) using Bioconductor package edgeR, and then discovered enriched gene ontology terms and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways using the KEGG Orthology Based Annotation System (KOBAS) 2.0 web server. Furthermore, we identified alternative splicing events (ASEs) and regulated alternative splicing events (RASEs) by applying the ABLas pipeline. The reverse transcription-quantitative polymerase chain reaction (RT-qPCR) was used for validation of selected differentially expressed genes (DEGs) and Fasn-regulated alternative splicing genes (RASGs).

RESULTS

In this study we found that Fasn overexpression led to significant changes of gene expression profiles, including downregulations of mRNA levels of immune related genes, including Bst2, Ddit3, Isg15, Mx2, Oas1a, Oasl, and RT1-S3 in INS-1 cell line. Furthermore, Fasn positively regulated the expression of transcription factors such as Fat1 and Ncl diabetes-related genes. Importantly, Fasn overexpression to result in alternative splicing events including in a metabolism-associated ATP binding protein mRNA Abcc5. In Gene Ontology analysis, the downregulated genes in Fasn-OE cells were mainly enriched in inflammatory response and innate immune response. In Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis, the downregulated genes were mainly enriched in TNF signaling pathway and cytokine-mediated signaling pathways.

CONCLUSIONS

Our findings showed that upregulation of Fasn may play a critical role in islet cell immunmetabolism via modifications of immune/inflammatory related genes on transcription and alternative splicing level, which provide novel insights into characterizing the function of Fasn in islet cell immunity and for the development of chemo/immune therapies.

Branched-Chain Fatty Acids Alter the Expression of Genes Responsible for Lipid Synthesis and Inflammation in Human Adipose Cells

Recently, we have demonstrated a decreased level of iso-branched-chain fatty acids (iso-BCFAs) in patients with excessive weight. However, it is still unclear whether BCFAs may influence lipid metabolism and inflammation in lipogenic tissues. To verify this, human visceral adipocytes were cultured with three different concentrations of selected iso-BCFA (14-methylpentadecanoic acid) and anteiso-BCFA (12-methyltetradecanoic acid), and then the expression of genes associated with lipid metabolism (FASN-fatty acid synthase; SREBP1-sterol regulatory element-binding protein 1; SCD1-stearoyl-CoA desaturase; ELOVL4-fatty acid elongase 4; ELOVL6-fatty acid elongase 6; FADS2-fatty acid desaturase 2; FADS1-fatty acid desaturase 1) and inflammation (COX-2-cyclooxygenase 2; ALOX-15-lipoxygenase 15; IL-6-interleukin 6) were determined. This study demonstrates for the first time that incubation with iso-BCFA decreases the expression of adipocyte genes that are associated with lipid metabolism (except FASN) and inflammation. These findings suggest that changes in the iso-BCFA profile in obese patients may contribute to adipose inflammation and dyslipidemia. Further studies should evaluate whether iso-BCFA supplementation in obese patients would be beneficial.

Hepatic Hedgehog Signaling Participates in the Crosstalk between Liver and Adipose Tissue in Mice by Regulating FGF21

The Hedgehog signaling pathway regulates many processes during embryogenesis and the homeostasis of adult organs. Recent data suggest that central metabolic processes and signaling cascades in the liver are controlled by the Hedgehog pathway and that changes in hepatic Hedgehog activity also affect peripheral tissues, such as the reproductive organs in females. Here, we show that hepatocyte-specific deletion of the Hedgehog pathway is associated with the dramatic expansion of adipose tissue in mice, the overall phenotype of which does not correspond to the classical outcome of insulin resistance-associated diabetes type 2 obesity. Rather, we show that alterations in the Hedgehog signaling pathway in the liver lead to a metabolic phenotype that is resembling metabolically healthy obesity. Mechanistically, we identified an indirect influence on the hepatic secretion of the fibroblast growth factor 21, which is regulated by a series of signaling cascades that are directly transcriptionally linked to the activity of the Hedgehog transcription factor GLI1. The results of this study impressively show that the metabolic balance of the entire organism is maintained via the activity of morphogenic signaling pathways, such as the Hedgehog cascade. Obviously, several pathways are orchestrated to facilitate liver metabolic status to peripheral organs, such as adipose tissue.

Genome-wide analysis of cis-regulatory changes underlying metabolic adaptation of cavefish

Cis-regulatory changes are key drivers of adaptative evolution. However, their contribution to the metabolic adaptation of organisms is not well understood. Here, we used a unique vertebrate model, Astyanax mexicanus-different morphotypes of which survive in nutrient-rich surface and nutrient-deprived cave waters-to uncover gene regulatory networks underlying metabolic adaptation. We performed genome-wide epigenetic profiling in the liver tissues of Astyanax and found that many of the identified cis-regulatory elements (CREs) have genetically diverged and have differential chromatin features between surface and cave morphotypes, while retaining remarkably similar regulatory signatures between independently derived cave populations. One such CRE in the hpdb gene harbors a genomic deletion in cavefish that abolishes IRF2 repressor binding and derepresses enhancer activity in reporter assays. Selection of this mutation in multiple independent cave populations supports its importance in cave adaptation, and provides novel molecular insights into the evolutionary trade-off between loss of pigmentation and adaptation to food-deprived caves.

Quality More Than Quantity: The Use of Carbohydrates in High-Fat Diets to Tackle Obesity in Growing Rats

Childhood obesity prevention is important to avoid obesity and its comorbidities into adulthood. Although the energy density of food has been considered a main obesogenic factor, a focus on food quality rather that the quantity of the different macronutrients is needed. Therefore, this study investigates the effects of changing the quality of carbohydrates from rapidly to slowly digestible carbohydrates on metabolic abnormalities and its impact on obesity in growing rats fed a high-fat diet (HFD). Growing rats were fed on HFD containing carbohydrates with different digestion rates: a HFD containing rapid-digesting carbohydrates (OBE group) or slow-digesting carbohydrates (ISR group), for 4 weeks and the effect on the metabolism and signaling pathways were analyzed in different tissues. Animals from OBE group presented an overweight/obese phenotype with a higher body weight gain and greater accumulation of fat in adipose tissue and liver. This state was associated with an increase of HOMA index, serum diacylglycerols and triacylglycerides, insulin, leptin, and pro-inflammatory cytokines. In contrast, the change of carbohydrate profile in the diet to one based on slow digestible prevented the obesity-related adverse effects. In adipose tissue, GLUT4 was increased and UCPs and PPARγ were decreased in ISR group respect to OBE group. In liver, GLUT2, FAS, and SRBP1 were lower in ISR group than OBE group. In muscle, an increase of glycogen, GLUT4, AMPK, and Akt were observed in comparison to OBE group. In conclusion, this study demonstrates that the replacement of rapidly digestible carbohydrates for slowly digestible carbohydrates within a high-fat diet promoted a protective effect against the development of obesity and its associated comorbidities.

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.

The Role of Medicinal and Aromatic Plants against Obesity and Arthritis: A Review

Obesity is a significant health concern, as it causes a massive cascade of chronic inflammations and multiple morbidities. Rheumatoid arthritis and osteoarthritis are chronic inflammatory conditions and often manifest as comorbidities of obesity. Adipose tissues serve as a reservoir of energy as well as releasing several inflammatory cytokines (including IL-6, IFN-γ, and TNF-α) that stimulate low-grade chronic inflammatory conditions such as rheumatoid arthritis, osteoarthritis, diabetes, hypertension, cardiovascular disorders, fatty liver disease, oxidative stress, and chronic kidney diseases. Dietary intake, low physical activity, unhealthy lifestyle, smoking, alcohol consumption, and genetic and environmental factors can influence obesity and arthritis. Current arthritis management using modern medicines produces various adverse reactions. Medicinal plants have been a significant part of traditional medicine, and various plants and phytochemicals have shown effectiveness against arthritis and obesity; however, scientifically, this traditional plant-based treatment option needs validation through proper clinical trials and toxicity tests. In addition, essential oils obtained from aromatic plants are being widely used as for complementary therapy (e.g., aromatherapy, smelling, spicing, and consumption with food) against arthritis and obesity; scientific evidence is necessary to support their effectiveness. This review is an attempt to understand the pathophysiological connections between obesity and arthritis, and describes treatment options derived from medicinal, spice, and aromatic plants.

ChREBP-regulated lipogenesis is not required for the thermogenesis of brown adipose tissue

Objectives

Brown adipose tissue (BAT) plays a critical role in energy expenditure by uncoupling protein 1 (UCP1)-mediated thermogenesis and represents an important therapeutic target for metabolic diseases. Carbohydrate response element-binding protein (ChREBP) is a key transcription factor regulating de novo lipogenesis, and its activity is associated with UCP1 expression and thermogenesis in BAT. However, the exact physiological role of endogenous ChREBP in BAT thermogenesis remains unclear.

Methods

We used the Cre/LoxP system to generate ChREBP BAT-specific knockout mice, and examined their BAT thermogenesis under acute cold exposure and long-term cold acclimation. Gene expression was analyzed at the mRNA and protein levels, and lipogenesis was examined by ³H-H₂O incorporation assay.

Results

The mice lacking ChREBP specifically in BAT displayed a significant decrease in the expression levels of lipogenic genes and the activity of de novo lipogenesis in BAT after cold exposure, with UCP1 expression decreased under thermoneutral conditions or after acute cold exposure but not chronic cold acclimation. Unexpectedly, BAT-specific ChREBP deletion did not significantly affect body temperature as well as local temperature or morphology of BAT after acute cold exposure or chronic cold acclimation. Of note, ChREBP deletion mildly aggravated glucose intolerance induced by a high-fat diet.

Conclusions

Our work indicates that ChREBP regulates de novo lipogenesis in BAT and glucose tolerance, but is not required for non-shivering thermogenesis by BAT under acute or long-term cold exposure.

ChREBPβ is dispensable for the control of glucose homeostasis and energy balance

Impaired glucose metabolism is observed in obesity and type 2 diabetes. Glucose controls gene expression through the transcription factor ChREBP in liver and adipose tissues. Mlxipl encodes 2 isoforms: ChREBPα, the full-length form (translocation into the nucleus is under the control of glucose), and ChREBPβ, a constitutively nuclear shorter form. ChREBPβ gene expression in white adipose tissue is strongly associated with insulin sensitivity. Here, we investigated the consequences of ChREBPβ deficiency on insulin action and energy balance. ChREBPβ-deficient male and female C57BL6/J and FVB/N mice were produced using CRISPR/Cas9-mediated gene editing. Unlike global ChREBP deficiency, lack of ChREBPβ showed modest effects on gene expression in adipose tissues and the liver, with variations chiefly observed in brown adipose tissue. In mice fed chow and 2 types of high-fat diets, lack of ChREBPβ had moderate effects on body composition and insulin sensitivity. At thermoneutrality, ChREBPβ deficiency did not prevent the whitening of brown adipose tissue previously reported in total ChREBP-KO mice. These findings revealed that ChREBPβ is dispensable for metabolic adaptations to nutritional and thermic challenges.

Lipogenesis inhibitors: therapeutic opportunities and challenges

Fatty acids are essential for survival, acting as bioenergetic substrates, structural components and signalling molecules. Given their vital role, cells have evolved mechanisms to generate fatty acids from alternative carbon sources, through a process known as de novo lipogenesis (DNL). Despite the importance of DNL, aberrant upregulation is associated with a wide variety of pathologies. Inhibiting core enzymes of DNL, including citrate/isocitrate carrier (CIC), ATP-citrate lyase (ACLY), acetyl-CoA carboxylase (ACC) and fatty acid synthase (FAS), represents an attractive therapeutic strategy. Despite challenges related to efficacy, selectivity and safety, several new classes of synthetic DNL inhibitors have entered clinical-stage development and may become the foundation for a new class of therapeutics.

De novo lipogenesis (DNL) is vital for the maintenance of whole-body and cellular homeostasis, but aberrant upregulation of the pathway is associated with a broad range of conditions, including cardiovascular disease, metabolic disorders and cancers. Here, Steinberg and colleagues provide an overview of the physiological and pathological roles of the core DNL enzymes and assess strategies and agents currently in development to therapeutically target them.