SREBP-regulated adipocyte lipogenesis is dependent on substrate availability and redox modulation of mTORC1

Kaili sour soup in alleviation of hepatic steatosis in rats via lycopene route: an experimental study

BACKGROUND

Nonalcoholic fatty liver disease (NAFLD) is one of the most prevalent chronic liver diseases, with a range of manifestations, such as hepatic steatosis. Our previous study showed that Kaili Sour Soup (KSS) significantly attenuated hepatic steatosis in rats. This study explored the main components of KSS and the mechanisms by which it exerts its protective effects against NAFLD.

METHODS

Twenty-four 6-week-old male Sprague-Dowley (SD) rats were randomly assigned to three treatments: feeding a normal standard diet, a high-fat diet, or a high-fat diet plus gavage KSS. The effects of KSS treatment on hepatic lipid accumulation were assessed using biochemical, histological, and molecular experiments. The amounts of KSS ingredients were measured using biochemical assays. Network pharmacology analyses were performed to identify the hub genes of KSS targets and enriched pathways. CCK-8 assay was used to determine the effect of free fatty acids (FFA), lycopene, and estrogen on HepG2 viability. Quantitative Real-Time polymerase chain reaction (qRT-PCR) and Western blot assays were performed to determine the effect of KSS or lycopene on estrogen signaling and expression of lipid metabolism-related molecules. Statistical analyses were performed using GraphPad Prism and SPSS.

RESULTS

KSS alleviated fat deposition in rat liver tissue and affected the expression of hepatic lipid synthesis, catabolism, and oxidative molecules. Lycopene was identified as the ingredient with the highest amount in KSS. Network pharmacology analyses showed that the hub genes were enriched in the estrogen signaling pathway. Cellular experiments showed that lycopene increased the expression of Estrogen Receptor α (ERα), Carnitine palmitoyltransferase 1 A (CPT1A), Peroxisome proliferator-activated receptor α (PPARα) (all p < 0.01), and Hormone sensitive lipase (HSL) (p < 0.05), and reduced the expression of lipid metabolism-related factors 1c(SREBP-1c) (p < 0.01), Acetyl-CoA carboxylase 1 (ACC) and Lipoprotein lipase (LPL) (all p < 0.05).

CONCLUSIONS

KSS ameliorated abnormal lipid metabolism in patients with NAFLD. Lycopene was the major component of KSS, and it affected estrogen signaling and the expression of lipid metabolism molecules. In short, both KSS and LYC could change lipid metabolism by lowering lipid accumulation and raising lipolysis.

Understanding the Link Between Sterol Regulatory Element Binding Protein (SREBPs) and Metabolic Dysfunction Associated Steatotic Liver Disease (MASLD)

PURPOSE OF THE REVIEW

This review aims to summarize the current scientific understanding on the complex interplay between sterol regulatory element-binding proteins (SREBPs) and metabolic dysfunction associated steatotic liver disease (MASLD) by critically examining a few significant molecular pathways. Additionally, the review explores the potential of both natural and synthetic SREBP inhibitors as promising therapeutic candidates for MASLD.

RECENT FINDINGS

SREBPs are central regulators of lipid homeostasis, with SREBP-1c primarily controlling fatty acid synthesis and SREBP-2 regulating cholesterol metabolism. Dysregulation of SREBP activity, often triggered by excessive caloric intake, insulin resistance, or endoplasmic reticulum (ER) stress, contributes to the development of metabolic syndrome and MASLD. SREBP-1c overexpression leads to increased de novo lipogenesis (DNL), hepatic lipid accumulation, and insulin resistance, while SREBP-2 modulates cholesterol metabolism via miRNA-33 and ABCA1 regulation leading to the pathogenesis of MASLD. The PI3K-Akt-mTORC1 pathway plays a critical role in SREBP activation, linking nutrient availability to lipid synthesis. Synthetic SREBP inhibitors, such as fatostatin and 25-hydroxycholesterol, and natural compounds, including kaempferol and resveratrol, show promise in modulating SREBP activity in vivo.

CONCLUSION

While targeting SREBP pathways presents a promising avenue for mitigating MASLD, further scientific investigation is imperative to identify and validate potential molecular targets. Although current studies on synthetic and natural SREBP inhibitors demonstrate encouraging results, rigorous pre-clinical and clinical research is warranted to translate these findings into effective MASLD treatments.

Histone chaperone HIRA facilitates transcription elongation to regulate insulin sensitivity and obesity-associated adipose expansion

Adipose tissue is essential for maintaining glucose and lipid homeostasis in mammals. The histone chaperone HIRA has been reported to play a lineage- and stage-selective role during development. However, its role in adipose tissue development and function as well as its working mechanism remain unknown. Here we show that tissue-specific knockout of histone chaperone HIRA in mice impairs insulin sensitivity and alleviates adipose tissue expansion during high-fat diet-induced obesity, but only moderately affects embryonic development of adipose tissue. Mechanistically, HIRA is selectively required for expression of genes critical for insulin response and lipogenesis, rather than adipogenesis, in adipose tissue. By acute depletion of HIRA protein and by mapping HIRA genomic localization in adipocytes, we demonstrate that HIRA binds to promoters and enhancers of insulin response and lipogenesis genes and regulates their expression by facilitating transcription elongation. Our findings not only identify HIRA as an epigenomic regulator of insulin sensitivity, lipogenesis, and obesity-associated adipose expansion, but also reveal a novel mechanism by which HIRA regulates transcription.

The Influence of Physical Exercise, Ketogenic Diet, and Time-Restricted Eating on De Novo Lipogenesis: A Narrative Review

De novo lipogenesis (DNL) is a metabolic pathway that converts carbohydrates into fatty acids, primarily occurring in the liver and, to a lesser extent, in adipose tissue. While hepatic DNL is highly responsive to dietary carbohydrate intake and regulated by insulin via transcription factors like SREBP-1c, adipose DNL is more modest and less sensitive to dietary overfeeding. Dysregulated DNL contributes to metabolic disorders, including metabolic dysfunction-associated steatotic liver disease (MASLD). Lifestyle interventions, such as physical exercise, ketogenic diets, and time-restricted eating (TRE) offer promising strategies to regulate DNL and improve metabolic health. Physical exercise enhances glucose uptake in muscles, reduces insulin levels, and promotes lipid oxidation, thereby suppressing hepatic DNL. Endurance and resistance training also improve mitochondrial function, further mitigating hepatic triglyceride accumulation. Ketogenic diets shift energy metabolism toward fatty acid oxidation and ketogenesis, lower insulin, and directly downregulate lipogenic enzyme activity in the liver. TRE aligns feeding with circadian rhythms by optimizing AMP-activated protein kinase (AMPK) activation during fasting periods, which suppresses DNL and enhances lipid metabolism. The combined effects of these interventions demonstrate significant potential for improving lipid profiles, reducing hepatic triglycerides, and preventing lipotoxicity. By addressing the distinct roles of the liver and adipose DNL, these strategies target systemic and localized lipid metabolism dysregulation. Although further research is needed to fully understand their long-term impact, these findings highlight the transformative potential of integrating these approaches into clinical practice to manage metabolic disorders and their associated complications.

Lipid Dynamics in Pancreatic β-Cells: Linking Physiology to Diabetes Onset

Significance: Glucose-induced lipid metabolism is essential for preserving functional β-cells, and its disruption is linked to type 2 diabetes (T2D) development. Lipids are an integral part of the cells playing an indispensable role as structural components, energy storage molecules, and signals. Recent Advances: Glucose presence significantly impacts lipid metabolism in β-cells, where fatty acids are primarily synthesized de novo and/or are transported from the bloodstream. This process is regulated by the glycerolipid/free fatty acid cycle, which includes lipogenic and lipolytic reactions producing metabolic coupling factors crucial for insulin secretion. Disrupted lipid metabolism involving oxidative stress and inflammation is a hallmark of T2D. Critical Issues: Lipid metabolism in β-cells is complex involving multiple simultaneous processes. Exact compartmentalization and quantification of lipid metabolism and its intermediates, especially in response to glucose or chronic hyperglycemia, are essential. Current research often uses non-physiological conditions, which may not accurately reflect in vivo situations. Future Directions: Identifying and quantifying individual steps and their signaling, including redox, within the complex fatty acid and lipid metabolic pathways as well as the metabolites formed during acute versus chronic glucose stimulation, will uncover the detailed mechanisms of glucose-stimulated insulin secretion. This knowledge is crucial for understanding T2D pathogenesis and identifying pharmacological targets to prevent this disease. Antioxid. Redox Signal. 41, 865-889.

The Influence of the FFAR4 Agonist TUG-891 on Liver Steatosis in ApoE-Knockout Mice

BACKGROUND

Nonalcoholic fatty liver disease (NAFLD) constitutes an independent risk factor for the development of coronary heart disease. Low-grade inflammation has been shown to play an important role in the development of atherosclerosis and NAFLD. Free fatty acid receptor 4 (FFAR4/GPR120), which is involved in damping inflammatory reactions, may represent a promising target for the treatment of inflammatory diseases. Our objective was to evaluate the effect of TUG-891, the synthetic agonist of FFAR4/GPR120, on fatty liver in vivo.

METHODS

The effect of TUG-891 on fatty liver was investigated in apoE-/- mice fed a high-fat diet (HFD), using microscopic, biochemical, molecular, and proteomic methods.

RESULTS

Treatment with TUG-891 inhibited the progression of liver steatosis in apoE-/- mice, as evidenced by histological analysis, and reduced the accumulation of TG in the liver. This action was associated with a decrease in plasma AST levels. TUG-891 decreased the expression of liver genes and proteins involved in de novo lipogenesis (Srebp-1c, Fasn and Scd1) and decreased the expression of genes related to oxidation and uptake (Acox1, Ehhadh, Cd36, Fabp1). Furthermore, TUG-891 modified the levels of selected factors related to glucose metabolism (decreased Glut2, Pdk4 and Pklr, and increased G6pdx).

CONCLUSION

Pharmacological stimulation of FFAR4 may represent a promising lead in the search for drugs that inhibit NAFLD.

Lactococcus lactis KF140 Ameliorates Nonalcoholic Fatty Liver Disease Induced by Nε-Carboxymethyl-Lysine and High-Fat Diet

SCOPE

Long-term consumption of excessive dietary advanced glycation end-products such as Nε-carboxymethyl-lysine (CML), which are produced by the Maillard reaction during food thermal processing, leads to nonalcoholic fatty liver disease (NAFLD) along with high fat consumption. The study previously finds that administration of Lactococcus lactis KF140 (LL-KF140) detoxifies CML by decreasing CML absorption both in a rat model and clinical trial.

METHODS AND RESULTS

The present study evaluates the ameliorative effect of LL-KF140 on NAFLD and fatty liver-related biomarkers in a mouse model induced by CML and high fat. LL-KF140 is orally administered to mice at a concentration of 1 × 107 or 1 × 108 colony-forming unit (CFU) per mouse for 8 weeks. LL-KF140 administration ameliorates the NAFLD-related symptoms by reducing body weight and fat mass gain along with levels of serum aspartate transaminase, alanine transferase, and lipids as well as glucose intolerance and insulin resistance in CML-treated mice. In addition, histological analysis including staining and western blotting shows that LL-KF140 suppresses the lipogenesis pathway and CML absorption, thereby suppressing CML-induced NAFLD.

CONCLUSION

These findings suggest that LL-KF140 attenuates dietary CML-induced NAFLD by suppressing the de novo lipogenesis pathway, and it may be used as a probiotic strain.

Anti-obesity effects of a standardized ethanol extract of Eisenia bicyclis by regulating the AMPK signaling pathway in 3T3-L1 cells and HFD-induced mice

Obesity requires treatment to mitigate the potential development of further metabolic disorders, including diabetes, hyperlipidemia, tumor growth, and non-alcoholic fatty liver disease. We investigated the anti-obesity effect of a 30% ethanol extract of Eisenia bicyclis (Kjellman) Setchell (EEB) on 3T3-L1 preadipocytes and high-fat diet (HFD)-induced obese C57BL/6 mice. Adipogenesis transcription factors including peroxisome proliferator-activated receptor (PPAR)γ, CCAAT/enhancer-binding protein-alpha (C/EBPα), and sterol regulatory element-binding protein-1 (SREBP-1) were ameliorated through the AMP-activated protein kinase (AMPK) pathway by EEB treatment in differentiated 3T3-L1 cells. EEB attenuated mitotic clonal expansion by upregulating cyclin-dependent kinase inhibitors (CDKIs) while downregulating cyclins and CDKs. In HFD-fed mice, EEB significantly decreased the total body weight, fat tissue weight, and fat in the tissue. The protein expression of PPARγ, C/EBPα, and SREBP-1 was increased in the subcutaneous fat and liver tissues, while EEB decreased the expression levels of these transcription factors. EEB also inhibited lipogenesis by downregulating acetyl-CoA carboxylase (ACC) and fatty acid synthase (FAS) expression in the subcutaneous fat and liver tissues. Moreover, the phosphorylation of AMPK and ACC was downregulated in the HFD-induced mouse group, whereas the administration of EEB improved AMPK and ACC phosphorylation; thus, EEB treatment may be related to the AMPK pathway. Histological analysis showed that EEB reduced the adipocyte size and fat accumulation in subcutaneous fat and liver tissues, respectively. EEB promotes thermogenesis in brown adipose tissue and improves insulin and leptin levels and blood lipid profiles. Our results suggest that EEB could be used as a potential agent to prevent obesity.

A review of the role of transcription factors in regulating adipogenesis and lipogenesis in beef cattle

In the past few decades, genomic selection and other refined strategies have been used to increase the growth rate and lean meat production of beef cattle. Nevertheless, the fast growth rates of cattle breeds are often accompanied by a reduction in intramuscular fat (IMF) deposition, impairing meat quality. Transcription factors play vital roles in regulating adipogenesis and lipogenesis in beef cattle. Meanwhile, understanding the role of transcription factors in regulating adipogenesis and lipogenesis in beef cattle has gained significant attention to increase IMF deposition and meat quality. Therefore, the aim of this paper was to provide a comprehensive summary and valuable insight into the complex role of transcription factors in adipogenesis and lipogenesis in beef cattle. This review summarizes the contemporary studies in transcription factors in adipogenesis and lipogenesis, genome-wide analysis of transcription factors, epigenetic regulation of transcription factors, nutritional regulation of transcription factors, metabolic signalling pathways, functional genomics methods, transcriptomic profiling of adipose tissues, transcription factors and meat quality and comparative genomics with other livestock species. In conclusion, transcription factors play a crucial role in promoting adipocyte development and fatty acid biosynthesis in beef cattle. They control adipose tissue formation and metabolism, thereby improving meat quality and maintaining metabolic balance. Understanding the processes by which these transcription factors regulate adipose tissue deposition and lipid metabolism will simplify the development of marbling or IMF composition in beef cattle.

Endoplasmic reticulum stress: bridging inflammation and obesity-associated adipose tissue

Obesity presents a significant global health challenge, increasing the susceptibility to chronic conditions such as diabetes, cardiovascular disease, and hypertension. Within the context of obesity, lipid metabolism, adipose tissue formation, and inflammation are intricately linked to endoplasmic reticulum stress (ERS). ERS modulates metabolism, insulin signaling, inflammation, as well as cell proliferation and death through the unfolded protein response (UPR) pathway. Serving as a crucial nexus, ERS bridges the functionality of adipose tissue and the inflammatory response. In this review, we comprehensively elucidate the mechanisms by which ERS impacts adipose tissue function and inflammation in obesity, aiming to offer insights into targeting ERS for ameliorating metabolic dysregulation in obesity-associated chronic diseases such as hyperlipidemia, hypertension, fatty liver, and type 2 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.

Quantitative Determination of De Novo Fatty Acid Synthesis in Brown Adipose Tissue Using Deuterium Oxide

Fatty acid synthesis is a complex and highly energy demanding metabolic pathway with important functional roles in the control of whole-body metabolic homeostasis and other physiological and pathological processes. Contrary to other key metabolic pathways, such as glucose disposal, fatty acid synthesis is not routinely functionally assessed, leading to incomplete interpretations of metabolic status. In addition, there is a lack of publicly available detailed protocols suitable for newcomers in the field. Here, we describe an inexpensive quantitative method utilizing deuterium oxide and gas chromatography mass spectrometry (GCMS) for the analysis of total fatty acid de novo synthesis in brown adipose tissue in vivo. This method measures the synthesis of the products of fatty acid synthase independently of a carbon source, and it is potentially useful for virtually any tissue, in any mouse model, and under any external perturbation. Details on the sample preparation for GCMS and downstream calculations are provided. We focus on the analysis of brown fat due to its high levels of de novo fatty acid synthesis and critical roles in maintaining metabolic homeostasis.

Principal component analysis of adipose tissue gene expression of lipogenic and adipogenic factors in obesity

OBJECTIVE

A better understanding of mechanisms regulating lipogenesis and adipogenesis is needed to overcome the obesity pandemic. We aimed to study the relationship of the transcript levels of peroxisome proliferator activator receptor γ (PPARγ), CCAAT/enhancer-binding protein alpha (C/EBP-α), liver X receptor (LXR), sterol regulatory element-binding protein-1c (SREBP-1c), fatty acid synthase (FAS), and acetyl-CoA carboxylase (ACC) in subcutaneous adipose tissue (SAT) and visceral adipose tissue (VAT) from obese and normal-weight women with a variety of anthropometric indices, metabolic and biochemical parameters, and insulin resistance.

METHODS

Real-time PCR was done to evaluate the transcript levels of the above-mentioned genes in VAT and SAT from all participants.

RESULTS

Using principal component analysis (PCA) results, two significant principal components were identified for adipogenic and lipogenic genes in SAT (SPC1 and SPC2) and VAT (VPC1 and VPC2). SPC1 was characterized by relatively high transcript levels of SREBP1c, PPARγ, FAS, and ACC. However, the second pattern (SPC2) was associated with C/EBPα and LXR α mRNA expression. VPC1 was characterized by transcript levels of SREBP1c, FAS, and ACC. However, the VPC2 was characterized by transcript levels of C/EBPα, LXR α, and PPARγ. Pearson's correlation analysis showed that unlike SPC2, which disclosed an inverse correlation with body mass index, waist and hip circumference, waist to height ratio, visceral adiposity index, HOMA-IR, conicity index, lipid accumulation product, and weight-adjusted waist index, the VPC1 was positively correlated with above-mentioned obesity indices.

CONCLUSION

This study provided valuable data on multiple patterns for adipogenic and lipogenic genes in adipose tissues in association with a variety of anthropometric indices in obese subjects predicting adipose tissue dysfunction and lipid accumulation.

Inhibitory Effects of Loganin on Adipogenesis In Vitro and In Vivo

Obesity is characterized by the excessive accumulation of mature adipocytes that store surplus energy in the form of lipids. In this study, we investigated the inhibitory effects of loganin on adipogenesis in mouse preadipocyte 3T3-L1 cells and primary cultured adipose-derived stem cells (ADSCs) in vitro and in mice with ovariectomy (OVX)- and high-fat diet (HFD)-induced obesity in vivo. For an in vitro study, loganin was co-incubated during adipogenesis in both 3T3-L1 cells and ADSCs, lipid droplets were evaluated by oil red O staining, and adipogenesis-related factors were assessed by qRT-PCR. For in vivo studies, mouse models of OVX- and HFD-induced obesity were orally administered with loganin, body weight was measured, and hepatic steatosis and development of excessive fat were evaluated by histological analysis. Loganin treatment reduced adipocyte differentiation by accumulating lipid droplets through the downregulation of adipogenesis-related factors, including peroxisome proliferator-activated receptor γ (Pparg), CCAAT/enhancer-binding protein α (Cebpa), perilipin 2 (Plin2), fatty acid synthase (Fasn), and sterol regulatory element binding transcription protein 1 (Srebp1). Loganin administration prevented weight gain in mouse models of obesity induced by OVX and HFD. Further, loganin inhibited metabolic abnormalities, such as hepatic steatosis and adipocyte enlargement, and increased the serum levels of leptin and insulin in both OVX- and HFD-induced obesity models. These results suggest that loganin is a potential candidate for preventing and treating obesity.

Standardized Ethanol Extract of Cassia mimosoides var. nomame Makino Ameliorates Obesity via Regulation of Adipogenesis and Lipogenesis in 3T3-L1 Cells and High-Fat Diet-Induced Obese Mice

Obesity is a major cause of conditions such as type 2 diabetes and non-alcoholic fatty liver disease, posing a threat to public health worldwide. Here, we analyzed the anti-obesity effects of a standardized ethanol extract of Cassia mimosoides var. nomame Makino (EECM) in vitro and in vivo. Treatment of 3T3-L1 adipocytes with EECM suppressed adipogenesis and lipogenesis via the AMP-activated protein kinase pathway by downregulating the expression levels of CCAAT/enhancer-binding protein-alpha, peroxisome proliferator-activated receptor (PPAR)-γ, sterol regulatory element-binding protein-1, and fatty acid synthase and upregulating the acetyl-CoA carboxylase. EECM inhibited mitotic clonal expansion during early adipocyte differentiation. Oral administration of EECM for 10 weeks significantly alleviated body weight gain and body fat accumulation in high-fat diet (HFD)-fed mice. EECM mitigated adipogenesis and lipid accumulation in white adipose and liver tissues of HFD-induced obese mice. It regulated the levels of adipogenic hormones including insulin, leptin, and adipokine in the blood plasma. In brown adipose tissue, EECM induced the expression of thermogenic factors such as uncoupling protein-1, PPAR-α, PPARγ co-activator-1α, sirtuin 1, and cytochrome c oxidase IV. EECM restored the gut microbiome composition at the phylum level and alleviated dysbiosis. Therefore, EECM may be used as a promising therapeutic agent for the prevention of obesity.

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.

Functional Complementation of Anti-Adipogenic Phytonutrients for Obesity Prevention and Management

Obesity is an established risk factor for metabolic disease. This study explores the functional complementation of anti-adipogenic phytonutrients for obesity prevention and management. Nine phytonutrients were selected based on their ability to affect the expression of one or more selected adipogenic biomarker proteins. The phytonutrients include berberine, luteolin, resveratrol, fisetin, quercetin, fucoidan, epigallocatechin gallate, hesperidin, and curcumin. The selected adipogenic biomarker proteins include PPARɣ, SREBP1c, FASN, PLIN1, FABP4, and β-catenin. Individually, phytonutrients had variable effects on the expression level of selected adipogenic biomarker proteins. Collectively, the functional complementation of nine phytonutrients suppressed de novo fatty acid biosynthesis via the negative regulation of PPARɣ, FASN, PLIN1, and FABP4 expression; activated glycolysis via the positive regulation of SREBP1c expression; and preserved cell–cell adhesion via the inhibition of β-catenin degradation. In primary human subcutaneous preadipocytes, the composition of nine phytonutrients had more potent and longer lasting anti-adipogenic effects compared to individual phytonutrients. In a diet-induced obesity murine model, the composition of nine phytonutrients improved glucose tolerance and reduced weight gain, liver steatosis, visceral adiposity, circulating triglycerides, low-density lipoprotein cholesterol, and inflammatory cytokines and chemokines. The functional complementation of anti-adipogenic phytonutrients provides an effective approach toward engineering novel therapeutics for the prevention and management of obesity and metabolic syndrome.

A Botanical Mixture Consisting of Inula japonica and Potentilla chinensis Relieves Obesity via the AMPK Signaling Pathway in 3T3-L1 Adipocytes and HFD-Fed Obese Mice

Excessive lipid accumulation in white adipose tissue (WAT) is the major cause of obesity. Herein, we investigated the anti-obesity effect and molecular mechanism of a botanical mixture of 30% EtOH extract from the leaves of Inula japonica and Potentilla chinensis (EEIP) in 3T3-L1 preadipocytes and high-fat diet (HFD)-fed obese mice. In vitro, EEIP prevented lipid accumulation by downregulating the expression of lipogenesis-related transcription factors such as CCAAT/enhancer binding protein (C/EBP)α, peroxisome proliferator-activated receptor (PPAR)γ, and sterol regulatory element binding protein (SREBP)-1 via AMP-activated protein kinase (AMPK) activation and G0/G1 cell cycle arrest by regulating the Akt-mTOR pathways without inducing cytotoxicity. In vivo, EEIP significantly reduced body weight gain and body fat mass in the group administered concurrently with HFD (pre-) or administered during the maintenance of HFD (post-) including subcutaneous, gonadal, renal, and mesenteric fats, and improved blood lipid profiles and metabolic hormones. EEIP pre-administration also alleviated WAT hypertrophy and liver lipid accumulation by reducing C/EBPα, PPARγ, and SREBP-1 expression via AMPK activation. In the brown adipose tissue, EEIP pre-administration upregulated the expression of thermogenic factors. Furthermore, EEIP improved the HFD-induced altered gut microbiota in mice. Taken together, our data indicated that EEIP improves HFD-induced obesity through adipogenesis inhibition in the WAT and liver and is a promising dietary natural material for improving obesity.

Coral Hydrate, a Novel Antioxidant, Improves Alcohol Intoxication in Mice

Alcohol-drinking culture may cause individuals to periodically experience unpleasant hangovers. In addition, ethanol catabolism stimulates the production of free radicals that may cause liver injury and further lead to the development of chronic alcoholic fatty liver disease. Although a number of studies have suggested that hydrogenated water may be consumed to act as free radical scavenger, its instability limits its application. In this study, we used coral hydrate (i.e., hydrogenated coral materials) as a more stable hydrogen source and evaluated its effects in a murine model of alcohol intoxication. In solution, coral hydrate exhibited much more stable redox potential than did hydrogenated water. Furthermore, administration of coral hydrate by oral gavage significantly prolonged the time to fall asleep and decreased the total sleep time in mice that received intraperitoneal injection of ethanol. The mice receiving coral hydrate also had lower plasma ethanol and acetaldehyde levels than controls. In line with this observation, hepatic expression of alcohol dehydrogenase, acetaldehyde dehydrogenase, catalase and glutathione peroxidase were all significantly increased by the treatment. Meanwhile, alcohol-induced upregulation of pro-inflammatory factors was attenuated by the administration of coral hydrate. Taken together, our data suggest that coral hydrate might be an effective novel treatment for alcohol intoxication.

A compound directed against S6K1 hampers fat mass expansion and mitigates diet-induced hepatosteatosis

The ribosomal protein S6 kinase 1 (S6K1) is a relevant effector downstream of the mammalian target of rapamycin complex 1 (mTORC1), best known for its role in the control of lipid homeostasis. Consistent with this, mice lacking the S6k1 gene have a defect in their ability to induce the commitment of fat precursor cells to the adipogenic lineage, which contributes to a significant reduction of fat mass. Here, we assess the therapeutic blockage of S6K1 in diet-induced obese mice challenged with LY2584702 tosylate, a specific oral S6K1 inhibitor initially developed for the treatment of solid tumors. We show that diminished S6K1 activity hampers fat mass expansion and ameliorates dyslipidemia and hepatic steatosis, while modifying transcriptome-wide gene expression programs relevant for adipose and liver function. Accordingly, decreased mTORC1 signaling in fat (but increased in the liver) segregated with defective epithelial-mesenchymal transition and the impaired expression of Cd36 (coding for a fatty acid translocase) and Lgals1 (Galectin 1) in both tissues. All these factors combined align with reduced adipocyte size and improved lipidomic signatures in the liver, while hepatic steatosis and hypertriglyceridemia were improved in treatments lasting either 3 months or 6 weeks.

Anti-Obesity and Anti-Hyperglycemic Effects of Meretrix lusoria Protamex Hydrolysate in ob/ob Mice

Meretrix lusoria (M. lusoria) is an economically important shellfish which is widely distributed in South Eastern Asia that contains bioactive peptides, proteins, and enzymes. In the present study, the extracted meat content of M. lusoria was enzymatic hydrolyzed using four different commercial proteases (neutrase, protamex, alcalase, and flavourzyme). Among the enzymatic hydrolysates, M. lusoria protamex hydrolysate (MLPH) fraction with MW ≤ 1 kDa exhibited the highest free radical scavenging ability. The MLPH fraction was further purified and an amino acid sequence (KDLEL, 617.35 Da) was identified by LC-MS/MS analysis. The purpose of this study was to investigate the anti-obesity and anti-hyperglycemic effects of MLPH containing antioxidant peptides using ob/ob mice. Treatment with MLPH for 6 weeks reduced body and organ weight and ameliorated the effects of hepatic steatosis and epididymal fat, including a constructive effect on hepatic and serum marker parameters. Moreover, hepatic antioxidant enzyme activities were upregulated and impaired glucose tolerance was improved in obese control mice. In addition, MLPH treatment markedly suppressed mRNA expression related to lipogenesis and hyperglycemia through activation of AMPK phosphorylation. These findings suggest that MLPH has anti-obesity and anti-hyperglycemic potential and could be effectively applied as a functional food ingredient or pharmaceutical.

miR-302b promotes bovine preadipocyte differentiation and inhibits proliferation by targeting CDK2

MicroRNAs have been recently reported to act as key regulators of adipogenesis, a multifactorial complex process. One miRNA, miR-302b, is an important regulator of cell proliferation and differentiation and controls cancer development, but we speculate that miR-302b may also regulate bovine adipogenesis. Herein we have evaluated the role of this miRNA in bovine adipocyte differentiation using quantitative Real-Time Polymerase Chain Reaction (qRT-PCR), Oil Red O staining, a dual-luciferase reporter. CDK2 was identified as the target gene of miR-302b, and miR-302b agomir promoted mRNA and protein expression levels of adipocyte-specific genes. In addition, a CCK-8 kit was used to show that miR-302b agomir, but not the negative control, inhibits preadipocyte proliferation. In conclusion, miR-302b promotes bovine preadipocyte differentiation and inhibits proliferation by targeting CDK2.

Neohesperidin Dihydrochalcone and Neohesperidin Dihydrochalcone-O-Glycoside Attenuate Subcutaneous Fat and Lipid Accumulation by Regulating PI3K/AKT/mTOR Pathway In Vivo and In Vitro

Neohesperidin dihydrochalcone (NHDC), a semi-natural compound from bitter orange, is an intense sweetener. The anti-obesity effects of NHDC and its glycosidic compound, NHDC-O-glycoside (GNHDC), were investigated. C57BLKS/J db/db mice were supplemented with NHDC or GNHDC (100 mg/kg b.w.) for 4 weeks. Body weight gain, subcutaneous tissues, and total adipose tissues (sum of perirenal, visceral, epididymal, and subcutaneous adipose tissue) were decreased in the NHDC and GNHDC groups. Fatty acid uptake, lipogenesis, and adipogenesis-related genes were decreased, whereas β-oxidation and fat browning-related genes were up-regulated in the sweetener groups. Furthermore, both sweeteners suppressed the level of triacylglycerol accumulation, lipogenesis, adipogenesis, and proinflammatory cytokines in the 3T3-L1 cells. The PI3K/AKT/mTOR pathway was also down-regulated, and AMP-acttvated protein kinase (AMPK) was phosphorylated in the treatment groups. These results suggest that NHDC and GNHDC inhibited subcutaneous fat and lipid accumulation by regulating the PI3K/AKT/mTOR pathway and AMPK-related lipogenesis and fat browning.

Exosomal miR-122 promotes adipogenesis and aggravates obesity through the VDR/SREBF1 axis

OBJECTIVE

This study examined the effects of miR-122-enriched exosomes on the expression of vitamin D3 receptor (VDR) and sterol regulatory element-binding transcription factor 1 (SREBF1) and their roles during adipogenesis.

METHODS

The roles of miR-122, SREBF1, and VDR were investigated during adipogenesis. The relationships between VDR and miR-122 or SREBF1 were assessed by dual-luciferase reporter and chromatin immunoprecipitation assays. The potential role of miR-122/VDR/SREBF1 was evaluated in high-fat diet-induced obese male mice.

RESULTS

High levels of miR-122 were found only in adipose tissue-derived exosomes (Exo-AT) and Exo-AT-treated cells. Overexpression of miR-122 promoted adipogenesis, and inhibition of miR-122 prevented adipogenesis by regulating VDR, SREBF1, peroxisome proliferator-activated receptor gamma, lipoprotein lipase, and adiponectin. Knockdown of Srebf1 or overexpression of VDR could inhibit adipogenesis. However, exosomal miR-122 could reverse their inhibitory effects. The dual-luciferase reporter assay and chromatin immunoprecipitation assays confirmed that VDR was a direct target of miR-122. It could bind to the BS1 region of the SREBF1 promoter and inhibit SREBF1 expression. Moreover, miR-122 inhibition could alleviate obesity in high-fat diet-induced obese male mice, possibly through upregulating the VDR/SREBF1 axis.

CONCLUSION

MiR-122-enriched Exo-AT promoted adipogenesis by regulating the VDR/SREBF1 axis.

Adipose-Specific PPARα Knockout Mice Have Increased Lipogenesis by PASK-SREBP1 Signaling and a Polarity Shift to Inflammatory Macrophages in White Adipose Tissue

The nuclear receptor PPARα is associated with reducing adiposity, especially in the liver, where it transactivates genes for β-oxidation. Contrarily, the function of PPARα in extrahepatic tissues is less known. Therefore, we established the first adipose-specific PPARα knockout (PparaFatKO) mice to determine the signaling position of PPARα in adipose tissue expansion that occurs during the development of obesity. To assess the function of PPARα in adiposity, female and male mice were placed on a high-fat diet (HFD) or normal chow for 30 weeks. Only the male PparaFatKO animals had significantly more adiposity in the inguinal white adipose tissue (iWAT) and brown adipose tissue (BAT) with HFD, compared to control littermates. No changes in adiposity were observed in female mice compared to control littermates. In the males, the loss of PPARα signaling in adipocytes caused significantly higher cholesterol esters, activation of the transcription factor sterol regulatory element-binding protein-1 (SREBP-1), and a shift in macrophage polarity from M2 to M1 macrophages. We found that the loss of adipocyte PPARα caused significantly higher expression of the Per-Arnt-Sim kinase (PASK), a kinase that activates SREBP-1. The hyperactivity of the PASK-SREBP-1 axis significantly increased the lipogenesis proteins fatty acid synthase (FAS) and stearoyl-Coenzyme A desaturase 1 (SCD1) and raised the expression of genes for cholesterol metabolism (Scarb1, Abcg1, and Abca1). The loss of adipocyte PPARα increased Nos2 in the males, an M1 macrophage marker indicating that the population of macrophages had changed to proinflammatory. Our results demonstrate the first adipose-specific actions for PPARα in protecting against lipogenesis, inflammation, and cholesterol ester accumulation that leads to adipocyte tissue expansion in obesity.

Network pharmacology approach to evaluate the therapeutic effects of mulberry leaf components for obesity

Obesity is a chronic condition that has become a serious public health challenge globally due to the association with a high incidence of complications. Mulberry leaf is one of the most commonly used medicinal and herbal medicines that has been reported to ameliorate obesity and hyperlipidemia. However, the mechanism remains unclear. In the present study, a network pharmacology approach was used to explore the potential mechanism underlying the effects of mulberry leaf extract on obesity. First, the potential targets of mulberry leaf and obesity were predicted using SwissTargetPrediction, Online Mendelian Inheritance in Man, GeneCards and Comparative Toxicogenomics Database databases, which were then used to construct the protein-protein interaction networks. Gene ontology (GO) enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyzes were performed using R version 3.6.3. Finally, results of this network analysis were verified by using the mulberry leaf extract to treat high-fat diet-induced obese mice. In total, 24 target genes associated with obesity that could potentially be affected by mulberry leaf treatment were predicted by network pharmacology, using which top seven related pathways were determined by KEGG enrichment analysis. Triglyceride (TG) and total cholesterol (TC) levels in mice serum were detected using TG and TC assay kits. Hepatic fat accumulation was detected by H&E staining whereas liver lipid droplets were detected by Oil red O staining in mice tissues. The expression of IL-1β, NF-κB inhibitor α, inducible nitric oxide synthase, AMP-activated protein kinase (AMPK), sterol regulatory element-binding proteins and fatty acid synthase in the visceral white adipose tissues of mice was analyzed by western blotting. The expression of TNF-α, peroxisome proliferator activated receptor (PPAR)D, PPARG, fatty acid amide hydrolase (FAAH) and hydroxysteroid 11-β dehydrogenase 1 (HSD11B1) in the visceral white adipose tissues of mice was detected by reverse transcription-quantitative PCR. Mulberry leaf extract was found to reduce fat accumulation and hepatic lipid droplet formation. Mulberry leaf also alleviated inflammation and lipogenesis whilst promoting lipid catabolism and fatty acid oxidation by promoting the AMPK signaling pathway. The possible anti-obesity effects of mulberry leaf on the mice may be due to the downregulation of TNF-α, PPARD and PPARG and the upregulation of FAAH and HSD11B1. These results were consistent with the GO enrichment analysis and suggested that mulberry leaf may regulate lipid metabolism and catabolism, fatty acid metabolism and biosynthesis and the inflammatory response to reduce obesity.

Control of Adipocyte Thermogenesis and Lipogenesis through β3-Adrenergic and Thyroid Hormone Signal Integration

Here, we show that β adrenergic signaling coordinately upregulates de novo lipogenesis (DNL) and thermogenesis in subcutaneous white adipose tissue (sWAT), and both effects are blocked in mice lacking the cAMP-generating G protein-coupled receptor Gs (Adipo-GsαKO) in adipocytes. However, UCP1 expression but not DNL activation requires rapamycin-sensitive mTORC1. Furthermore, β3-adrenergic agonist CL316243 readily upregulates thermogenic but not lipogenic genes in cultured adipocytes, indicating that additional regulators must operate on DNL in sWAT in vivo. We identify one such factor as thyroid hormone T3, which is elevated locally by adrenergic signaling. T3 administration to wild-type mice enhances both thermogenesis and DNL in sWAT. Mechanistically, T3 action on UCP1 expression in sWAT depends upon cAMP and is blocked in Adipo-GsαKO mice even as elevated DNL persists. Thus, T3 enhances sWAT thermogenesis by amplifying cAMP signaling, while its control of adipocyte DNL can be mediated independently of both cAMP and rapamycin-sensitive mTORC1.

SIRT1 promotes lipid metabolism and mitochondrial biogenesis in adipocytes and coordinates adipogenesis by targeting key enzymatic pathways

The NAD+-dependent deacetylase SIRT1 controls key metabolic functions by deacetylating target proteins and strategies that promote SIRT1 function such as SIRT1 overexpression or NAD+ boosters alleviate metabolic complications. We previously reported that SIRT1-depletion in 3T3-L1 preadipocytes led to C-Myc activation, adipocyte hyperplasia, and dysregulated adipocyte metabolism. Here, we characterized SIRT1-depleted adipocytes by quantitative mass spectrometry-based proteomics, gene-expression and biochemical analyses, and mitochondrial studies. We found that SIRT1 promoted mitochondrial biogenesis and respiration in adipocytes and expression of molecules like leptin, adiponectin, matrix metalloproteinases, lipocalin 2, and thyroid responsive protein was SIRT1-dependent. Independent validation of the proteomics dataset uncovered SIRT1-dependence of SREBF1c and PPARα signaling in adipocytes. SIRT1 promoted nicotinamide mononucleotide acetyltransferase 2 (NMNAT2) expression during 3T3-L1 differentiation and constitutively repressed NMNAT1 and 3 levels. Supplementing preadipocytes with the NAD+ booster nicotinamide mononucleotide (NMN) during differentiation increased expression levels of leptin, SIRT1, and PGC-1α and its transcriptional targets, and reduced levels of pro-fibrotic collagens (Col6A1 and Col6A3) in a SIRT1-dependent manner. Investigating the metabolic impact of the functional interaction of SIRT1 with SREBF1c and PPARα and insights into how NAD+ metabolism modulates adipocyte function could potentially lead to new avenues in developing therapeutics for obesity complications.

Epigenetics in NAFLD/NASH: Targets and therapy

Recently non-alcoholic fatty liver disease (NAFLD) has grabbed considerable scientific attention, owing to its rapid increase in prevalence worldwide and growing burden on end-stage liver diseases. Metabolic syndrome including obesity, diabetes, and hypertension poses a grave risk to NAFLD etiology and progression. With no drugs available, the mainstay of NAFLD management remains lifestyle changes with exercise and dietary modifications. Nonselective drugs such as metformin, thiazolidinediones (TZDs), ursodeoxycholic acid (UDCA), silymarin, etc., are also being used to target the interrelated pathways for treating NAFLD. Considering the enormous disease burden and the unmet need for drugs, fresh insights into pathogenesis and drug discovery are required. The emergence of the field of epigenetics offers a convincing explanation for the basis of lifestyle, environmental, and other risk factors to influence NAFLD pathogenesis. Therefore, understanding these epigenetic modifications to target the primary cause of the disease might prove a rational strategy to prevent the disease and develop novel therapeutic interventions. Apart from describing the role of epigenetics in the pathogenesis of NAFLD as in other reviews, this review additionally provides an elaborate discussion on exploiting the high plasticity of epigenetic modifications in response to environmental cues, for developing novel therapeutics for NAFLD. Besides, this extensive review provides evidence for epigenetic mechanisms utilized by several potential drugs for NAFLD.

Natural Extracts to Augment Energy Expenditure as a Complementary Approach to Tackle Obesity and Associated Metabolic Alterations

Obesity is the epidemic of the 21st century. In developing countries, the prevalence of obesity continues to rise, and obesity is occurring at younger ages. Obesity and associated metabolic stress disrupt the whole-body physiology. Adipocytes are critical components of the systemic metabolic control, functioning as an endocrine organ. The enlarged adipocytes during obesity recruit macrophages promoting chronic inflammation and insulin resistance. Together with the genetic susceptibility (single nucleotide polymorphisms, SNP) and metabolic alterations at the molecular level, it has been highlighted that key modifiable risk factors, such as those related to lifestyle, contribute to the development of obesity. In this scenario, urgent therapeutic options are needed, including not only pharmacotherapy but also nutrients, bioactive compounds, and natural extracts to reverse the metabolic alterations associated with obesity. Herein, we first summarize the main targetable processes to tackle obesity, including activation of thermogenesis in brown adipose tissue (BAT) and in white adipose tissue (WAT-browning), and the promotion of energy expenditure and/or fatty acid oxidation (FAO) in muscles. Then, we perform a screening of 20 natural extracts (EFSA approved) to determine their potential in the activation of FAO and/or thermogenesis, as well as the increase in respiratory capacity. By means of innovative technologies, such as the study of their effects on cell bioenergetics (Seahorse bioanalyzer), we end up with the selection of four extracts with potential application to ameliorate the deleterious effects of obesity and the chronic associated inflammation.

Lipid Inhibitory Effect of (-)-loliolide Isolated from Sargassum horneri in 3T3-L1 Adipocytes: Inhibitory Mechanism of Adipose-Specific Proteins

Sargassum horneri (S. horneri) is a well-known brown seaweed widely distributed worldwide. Several biological activities of S. horneri have been reported. However, its effects on lipid metabolism and the underlying mechanisms remain elusive. In the present study, we examined the inhibitory effect of the active compound "(-)-loliolide ((6S,7aR)-6-hydroxy-4,4,7a-trimethyl-5,6,7,7a-tetrahydro-1-benzofuran-2(4H)-one (HTT))" from S. horneri extract on lipid accumulation in differentiated adipocytes. MTT assays demonstrated that (-)-loliolide is not toxic to 3T3-L1 adipocytes in a range of concentrations. (-)-loliolide significantly reduced intracellular lipid accumulation in the differentiated phase of 3T3-L1 adipocytes as shown by Oil Red O staining. Western blot analysis revealed that (-)-loliolide increased the expression of lipolytic protein phospho-hormone-sensitive lipase (p-HSL) and thermogenic protein peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1). Additionally, (-)-loliolide decreased expression of adipogenic and lipogenic proteins, including sterol regulatory element-binding protein-1 (SREBP-1), peroxisome proliferator-activated receptor-γ (PPAR-γ), CCAAT/enhancer-binding protein-α (C/EBP-α), and fatty acid-binding protein 4 (FABP4) in 3T3-L1 adipocytes. These results indicate that (-)-loliolide from S. horneri could suppress lipid accumulation via regulation of antiadipogenic and prolipolytic mechanisms in 3T3-L1 cells. Considering the multifunctional effect of (-)-loliolide, it can be useful as a lipid-lowering agent in the management of patients who suffer from obesity.

MiR-33a inhibits the adipogenic differentiation of ovine adipose-derived stromal vascular fraction cells by targeting SIRT6

Adipose tissue is important for the regulation of energy balance through its metabolic, cellular, and endocrine functions. Furthermore, the excessive storage of subcutaneous fat can seriously affect the health and carcass traits of domestic animals. Stromal vascular fraction (SVF) cell adipogenic differentiation increases the number of differentiated adipocytes and plays a role in lipid deposition. The adipogenic differentiation of SVF cells is regulated by various factors, including microRNAs and cytokines. Sirt6 and miR-33a are known to be involved in metabolism and adipogenesis, respectively; however, their effects on the adipogenic differentiation of ovine SVF cells were previously unknown. Thus, the aim of this study was to investigate this. The results showed that SIRT6 is a binding target for miR-33a. Moreover, overexpression or inhibition of miR-33a was found to change the expression of SIRT6 messenger RNA and protein. Furthermore, modulating SIRT6 altered the expression of adipogenic marker genes. In addition, miR-33a and SIRT6 were found to play opposing roles in adipogenesis. Specifically, we demonstrated that miR-33a is involved in the negative regulation of ovine SVF cell adipogenic differentiation by inhibiting the expression of SIRT6. These findings reveal a key role for miR-33a and SIRT6 in adipogenesis, which will enrich our understanding of the regulatory factors associated with SVF cell adipogenic differentiation and provide a basis for further study on this process.

Abeliophyllum distichum Ameliorates High-Fat Diet-Induced Obesity in C57BL/6J Mice by Upregulating the AMPK Pathway

The use of natural compounds as anti-obesity agents has been gaining attention over the past few years. Abeliophyllum distichum Nakai is endemic to Korea. In the present study, an A. distichum leaf extract (AE) was analyzed for its anti-obesity effects in mice fed a high-fat diet. Seven-week-old male C57BL/6J mice were divided into five groups, namely, normal diet (ND), high-fat diet (HD), HD + Garcinia (GE300), HD + AE low dose (AE100), and HD + AE high dose (AE300). After 8 weeks of the experimental period, treatment with AE reduced body weight and ameliorated high-fat diet-induced changes in serum lipid levels. Histological analysis revealed that treatment with AE decreased lipid accumulation in the liver and brown adipose tissue. Also, AE reduced the adipocyte size in epididymal fat. The reduction in adipose tissue mass in the AE-treated groups was clearly visible in micro-computed tomography images. The expression levels of lipogenic genes, such as PPARγ, C/EBPα, ACC, and FAS, were significantly reduced in the AE300 group. The levels of p-AMPK and p-ACC were increased in the AE300 group compared to the HD group, indicating that the anti-obesity effect of AE was mediated through the AMPK pathway.

Wnt/β-catenin signaling regulates adipose tissue lipogenesis and adipocyte-specific loss is rigorously defended by neighboring stromal-vascular cells

OBJECTIVE

Canonical Wnt/β-catenin signaling is a well-studied endogenous regulator of mesenchymal cell fate determination, promoting osteoblastogenesis and inhibiting adipogenesis. However, emerging genetic evidence in humans links a number of Wnt pathway members to body fat distribution, obesity, and metabolic dysfunction, suggesting that this pathway also functions in adipocytes. Recent studies in mice have uncovered compelling evidence that the Wnt signaling pathway plays important roles in adipocyte metabolism, particularly under obesogenic conditions. However, complexities in Wnt signaling and differences in experimental models and approaches have thus far limited our understanding of its specific roles in this context.

METHODS

To investigate roles of the canonical Wnt pathway in the regulation of adipocyte metabolism, we generated adipocyte-specific β-catenin (β-cat) knockout mouse and cultured cell models. We used RNA sequencing, ChIP sequencing, and molecular approaches to assess expression of Wnt targets and lipogenic genes. We then used functional assays to evaluate effects of β-catenin deficiency on adipocyte metabolism, including lipid and carbohydrate handling. In mice maintained on normal chow and high-fat diets, we assessed the cellular and functional consequences of adipocyte-specific β-catenin deletion on adipose tissues and systemic metabolism.

RESULTS

We report that in adipocytes, the canonical Wnt/β-catenin pathway regulates de novo lipogenesis (DNL) and fatty acid monounsaturation. Further, β-catenin mediates effects of Wnt signaling on lipid metabolism in part by transcriptional regulation of Mlxipl and Srebf1. Intriguingly, adipocyte-specific loss of β-catenin is sensed and defended by CD45^-/CD31^- stromal cells to maintain tissue-wide Wnt signaling homeostasis in chow-fed mice. With long-term high-fat diet, this compensatory mechanism is overridden, revealing that β-catenin deletion promotes resistance to diet-induced obesity and adipocyte hypertrophy and subsequent protection from metabolic dysfunction.

CONCLUSIONS

Taken together, our studies demonstrate that Wnt signaling in adipocytes is required for lipogenic gene expression, de novo lipogenesis, and lipid desaturation. In addition, adipose tissues rigorously defend Wnt signaling homeostasis under standard nutritional conditions, such that stromal-vascular cells sense and compensate for adipocyte-specific loss. These findings underscore the critical importance of this pathway in adipocyte lipid metabolism and adipose tissue function.

Wntless regulates lipogenic gene expression in adipocytes and protects against diet-induced metabolic dysfunction

OBJECTIVE

Obesity is a key risk factor for many secondary chronic illnesses, including type 2 diabetes and cardiovascular disease. Canonical Wnt/β-catenin signaling is established as an important endogenous inhibitor of adipogenesis. This pathway is operative in mature adipocytes; however, its roles in this context remain unclear due to complexities of Wnt signaling and differences in experimental models. In this study, we used novel cultured cell and mouse models to investigate functional roles of Wnts secreted from adipocytes.

METHODS

We generated adipocyte-specific Wntless (Wls) knockout mice and cultured cell models to investigate molecular and metabolic consequences of disrupting Wnt secretion from mature adipocytes. To characterize Wls-deficient cultured adipocytes, we evaluated the expression of Wnt target and lipogenic genes and the downstream functional effects on carbohydrate and lipid metabolism. We also investigated the impact of adipocyte-specific Wls deletion on adipose tissues and global glucose metabolism in mice fed normal chow or high-fat diets.

RESULTS

Many aspects of the Wnt signaling apparatus are expressed and operative in mature adipocytes, including the Wnt chaperone Wntless. Deletion of Wntless in cultured adipocytes results in the inhibition of de novo lipogenesis and lipid monounsaturation, likely through repression of Srebf1 (SREBP1c) and Mlxipl (ChREBP) and impaired cleavage of immature SREBP1c into its active form. Adipocyte-specific Wls knockout mice (Wls-/-) have lipogenic gene expression in adipose tissues and isolated adipocytes similar to that of controls when fed a normal chow diet. However, closer investigation reveals that a subset of Wnts and downstream signaling targets are upregulated within stromal-vascular cells of Wls-/- mice, suggesting that adipose tissues defend loss of Wnt secretion from adipocytes. Interestingly, this compensation is lost with long-term high-fat diet challenges. Thus, after six months of a high-fat diet, Wls-/- mice are characterized by decreased adipocyte lipogenic gene expression, reduced visceral adiposity, and improved glucose homeostasis.

CONCLUSIONS

Taken together, these studies demonstrate that adipocyte-derived Wnts regulate de novo lipogenesis and lipid desaturation and coordinate the expression of lipogenic genes in adipose tissues. In addition, we report that Wnt signaling within adipose tissues is defended, such that a loss of Wnt secretion from adipocytes is sensed and compensated for by neighboring stromal-vascular cells. With chronic overnutrition, this compensatory mechanism is lost, revealing that Wls-/- mice are resistant to diet-induced obesity, adipocyte hypertrophy, and metabolic dysfunction.

Viburnum opulus L. Juice Phenolics Inhibit Mouse 3T3-L1 Cells Adipogenesis and Pancreatic Lipase Activity

Viburnum opulus L. fruit is a rich source of phenolic compounds that may be involved in the prevention of metabolic diseases. The purpose of this study was to determine the effects of Viburnum opulus fresh juice (FJ) and juice purified by solid-phase extraction (PJ) on the adipogenesis process with murine 3T3-L1 preadipocyte cell line and pancreatic lipase activity in triolein emulsion, as well as their phenolic profiles by UPLC/Q-TOF-MS. Decrease of lipids and triacylglycerol accumulation in differentiated 3T3-L1 cells were in concordance with downregulation of the expression of peroxisome proliferator-activated receptor-gamma (PPARγ), CCAAT/enhancer-binding protein alpha (C/EBPβ/α), and sterol regulatory element-binding protein 1c (SREBP-1c). Furthermore, regulation of PPARγ-mediated β-lactamase expression by V. opulus components in reporter gene assay, as well as their binding affinity to ligand-binding domain of PPARγ, were tested. In addition, the levels of enzymes involved in lipid metabolism, like fatty acid synthase (FAS) or acetyl-CoA carboxylase (ACC), were decreased, along with inflammatory cytokines, like tumor necrosis factorα (TNFα), interleukin-6 (Il-6) and leptin. Moreover, FJ and PJ were able to inhibit pancreatic lipase, which potentially could reduce the fat absorption from the intestinal lumen and the storage of body fat in the adipose tissues. Thirty-two phenolic compounds with chlorogenic acid as the dominant compound were identified in PJ which revealed significant biological activity. These data contribute to elucidate V. opulus juice phenolic compounds’ molecular mechanism in adipogenesis regulation in 3T3-L1 cells and dietary fat lipolysis.

Chitosan oligosaccharide ameliorated obesity by reducing endoplasmic reticulum stress in diet-induced obese rats

OBJECTIVE

This study aimed to determine whether chitosan oligosaccharide (COST) improves overweight by reducing endoplasmic reticulum (ER) stress in the liver and liver cancer cells.

METHODS

An obesity model was established by feeding Sprague-Dawley rats (ORs) a high-fat diet (HFD) and treating them with COST for 8 weeks. A model of lipid accumulation in hepatocellular carcinoma cells was established by treating HepG2 cells with free fatty acids and COST for 24 h.

RESULTS

COST treatment of ORs reduced weight gain, inhibited adipose tissue hypertrophy and hyperplasia, and reduced the fat-to-weight ratio. COST improved dyslipidaemia, reduced liver weight and organ index, inhibited hepatic lipid accumulation, and prevented liver steatosis, and the high COST dose increased TC and TG excretion in the stool. Treatment of lipid accumulation in HepG2 cells with COST reduced lipid accumulation and TG levels. COST modulated the expression of genes related to fat metabolism and ER stress response pathway-related factors in liver tissue and HepG2 cells.

CONCLUSIONS

COST can inhibit weight gain and improve dyslipidaemia and lipid metabolism in ORs. The COST-mediated regulation of hepatic and HepG2 cell lipid metabolism might be related to inhibition of fat synthesis, acceleration of lipid oxidative catabolism and reduction in ER stress.

A combination of borage seed oil and quercetin reduces fat accumulation and improves insulin sensitivity in obese rats

The metabolic properties of omega-6 fatty acid consumption are being increasingly accepted. We had previously observed that supplementation with a borage seed oil (BSO), as a source of linoleic (18:2n-6; LA) and gamma-linolenic (18:3n-6; GLA) acids, reduces body weight and visceral adiposity and improves insulin sensitivity in a diet-induced obesity model of Wistar rats. Here, it was investigated whether the anti-obesogenic properties of BSO could be maintained in a pre-obese model of rats, and if these effects are enhanced by a combination with low doses of quercetin, together with its potential role in the regulation of the adipocyte biology. The combination of BSO and quercetin during 8 weeks was able to ameliorate glucose intolerance and insulin resistance, and to improve liver steatosis. Although no effects were observed on body weight, animals supplemented with this combination exhibited a lower proportion of visceral adiposity. In addition, in vitro differentiation of epididymal adipose-precursor cells of the BSO-treated animals exhibited a down-regulation of Fasn, Glut4, Pparg and Srebp1 genes, in comparison with the control group. Finally, in vitro evaluation of the components of BSO demonstrated that the anti-adipogenic activity of quercetin was significantly potentiated by the combination with both LA and GLA through the down-regulation of different adipogenesis-key genes in 3T3-L1 cells. All these data suggest that omega-6 fatty acids LA and GLA, and their natural sources such as BSO, could be combined with quercetin to potentiate their effects in the prevention of the excess of adiposity and the insulin resistance.

Comparative Transcriptomic Analysis of Subcutaneous Adipose Tissue from Local Pig Breeds

When compared to modern lean-type breeds, Portuguese local Alentejano (AL) and Bísaro (BI) pig breeds present a high potential for subcutaneous and intramuscular fat (IMF) deposition which contributes for better meat quality. The aim of this work was to explore the genome function to better understand the underlying physiological mechanisms associated with body fat accretion. Dorsal subcutaneous fat samples were collected at slaughter from adult animals (n = 4 for each breed) with ~150 kg body weight. Total RNA was obtained and sequenced for transcriptome analysis using DESeq2. A total of 458 differentially expressed (DE) genes (q-value < 0.05) were identified, with 263 overexpressed in AL and 195 in BI. Key genes involved in de novo fatty acid biosynthesis, elongation and desaturation were upregulated in AL such as ACLY, FASN, ME1, ELOVL6 and SCD. A functional enrichment analysis of the DE genes was performed using Ingenuity Pathway Analysis. Cholesterol synthesis is suggested to be higher in AL via SREBF2, SCAP and PPARG, while lipolytic activity may be more active in BI through GH and AMPK signalling. Increased signalling of CD40 together with the predicted activation of INSIG1 and INSIG2 in BI suggests that this breed is more sensitive to insulin whereas the AL is less sensitive like the Iberian breed.