Integrated Regulation of Hepatic Lipid and Glucose Metabolism by Adipose Triacylglycerol Lipase and FoxO Proteins

SIRT1 and FOXO1 role on MASLD risk: effects of DHA-rich n-3 PUFA supplementation and exercise in aged obese female mice and in post-menopausal overweight/obese women

Sirtuins 1 (SIRT1) and Forkhead box protein O1 (FOXO1) expression have been associated with obesity and metabolic dysfunction-associated steatotic liver disease (MASLD). Exercise and/or docosahexaenoic acid (DHA) supplementation have shown beneficial effects on MASLD. The current study aims to assess the relationships between Sirt1, Foxo1 mRNA levels and several MASLD biomarkers, as well as the effects of DHA-rich n-3 PUFA supplementation and/or exercise in the steatotic liver of aged obese female mice, and in peripheral blood mononuclear cells (PBMCs) of postmenopausal women with overweight/obesity. In the liver of 18-month-old mice, Sirt1 levels positively correlated with the expression of genes related to fatty acid oxidation, and negatively correlated with lipogenic and proinflammatory genes. Exercise (long-term treadmill training), especially when combined with DHA, upregulated hepatic Sirt1 mRNA levels. Liver Foxo1 mRNA levels positively associated with hepatic triglycerides (TG) content and the expression of lipogenic and pro-inflammatory genes, while negatively correlated with the lipolytic gene Hsl. In PBMCs of postmenopausal women with overweight/obesity, FOXO1 mRNA expression negatively correlated with the hepatic steatosis index (HSI) and the Zhejiang University index (ZJU). After 16-weeks of DHA-rich PUFA supplementation and/or progressive resistance training (RT), most groups exhibited reduced MASLD biomarkers and risk indexes accompanying with body fat mass reduction, but no significant changes were found between the intervention groups. However, in PBMCs n-3 supplementation upregulated FOXO1 expression, and the RT groups exhibited higher SIRT1 expression. In summary, SIRT1 and FOXO1 could be involved in the beneficial mechanisms of exercise and n-3 PUFA supplementation related to MASLD manifestation.

Glutathione inhibits lung cancer development by reducing interleukin-6 expression and reversing the Warburg effect

Reduced glutathione (GSH) is widely used as an antioxidant in clinical practice, but whether GSH affects the development of early lung cancer remains unclear. Herein, we investigated the mechanism underlying the anticancer effect of GSH in patients with pulmonary nodules. Thirty patients with pulmonary nodules were treated with GSH intravenously for 10 days at a dose of 1.8 g/d, followed by oral administration of the drug at a dose of 0.4 g three times daily for 6 months. The results showed that GSH treatment promoted nodule absorption and reduced the IL-6 level in the peripheral blood of the patients. GSH reduced IL-6 expression in inflammatory BEAS-2B and lung cancer cells and inhibited the proliferation of lung cancer cell lines in vitro. In addition, GSH reduced IL-6 expression by decreasing ROS via down-regulating PI3K/AKT/FoxO pathways. Finally, GSH reversed the Warburg effect, restored mitochondrial function, and reduced the IL-6 expression via PI3K/AKT/FoxO pathways. The in vivo experiment confirmed that GSH inhibited lung cancer growth, improved mitochondrial function, and reduced the IL-6 expression by regulating key enzymes via the PI3K/AKT/FoxO pathway. In conclusion, we uncovered that GSH exerts an unprecedentedly potent anti-cancer effect to prevent the transformation of lung nodules to lung cancer by improving the mitochondrial function and suppressing inflammation via PI3K/AKT/FoxO pathway. This investigation innovatively positions GSH as a potentially safe and efficacious old drug with new uses, inhibiting inflammation and early lung cancer. The use of the drug offers a promising preventive strategy when administered during the early stages of lung cancer.

Epinephrine promotes breast cancer metastasis through a ubiquitin-specific peptidase 22-mediated lipolysis circuit

Chronic stress-induced epinephrine (EPI) accelerates breast cancer progression and metastasis, but the molecular mechanisms remain unclear. Herein, we found a strong positive correlation between circulating EPI levels and the tumoral expression of ubiquitin-specific peptidase 22 (USP22) in patients with breast cancer. USP22 facilitated EPI-induced breast cancer progression and metastasis by enhancing adipose triglyceride lipase (ATGL)-mediated lipolysis. Targeted USP22 deletion decreased ATGL expression and lipolysis, subsequently inhibiting EPI-mediated breast cancer lung metastasis. USP22 acts as a bona fide deubiquitinase for the Atgl gene transcription factor FOXO1, and EPI architects a lipolysis signaling pathway to stabilize USP22 through AKT-mediated phosphorylation. Notably, USP22 phosphorylation levels are positively associated with EPI and with downstream pathways involving both FOXO1 and ATGL in breast cancers. Pharmacological USP22 inhibition synergized with β-blockers in treating preclinical xenograft breast cancer models. This study reveals a molecular pathway behind EPI's tumor-promoting effects and provides a strong rationale for combining USP22 inhibition with β-blockers to treat aggressive breast cancer.

Hepatic glucagon action: beyond glucose mobilization

Glucagon's ability to promote hepatic glucose production has been known for over a century, with initial observations touting this hormone as a diabetogenic agent. However, glucagon receptor agonism [when balanced with an incretin, including glucagon-like peptide 1 (GLP-1) to dampen glucose excursions] is now being developed as a promising therapeutic target in the treatment of metabolic diseases, like metabolic dysfunction-associated steatotic disease/metabolic dysfunction-associated steatohepatitis (MASLD/MASH), and may also have benefit for obesity and chronic kidney disease. Conventionally regarded as the opposing tag-team partner of the anabolic mediator insulin, glucagon is gradually emerging as more than just a "catabolic hormone." Glucagon action on glucose homeostasis within the liver has been well characterized. However, growing evidence, in part thanks to new and sensitive "omics" technologies, has implicated glucagon as more than just a "glucose liberator." Elucidation of glucagon's capacity to increase fatty acid oxidation while attenuating endogenous lipid synthesis speaks to the dichotomous nature of the hormone. Furthermore, glucagon action is not limited to just glucose homeostasis and lipid metabolism, as traditionally reported. Glucagon plays key regulatory roles in hepatic amino acid and ketone body metabolism, as well as mitochondrial turnover and function, indicating broader glucagon signaling consequences for metabolic homeostasis mediated by the liver. Here we examine the broadening role of glucagon signaling within the hepatocyte and question the current dogma, to appreciate glucagon as more than just that "catabolic hormone."

Inhibitory Regulation of FOXO1 in PPARδ Expression Drives Mitochondrial Dysfunction and Insulin Resistance

Forkhead box O1 (FOXO1) regulates muscle growth, but the metabolic role of FOXO1 in skeletal muscle and its mechanisms remain unclear. To explore the metabolic role of FOXO1 in skeletal muscle, we generated skeletal muscle-specific Foxo1 inducible knockout (mFOXO1 iKO) mice and fed them a high-fat diet to induce obesity. We measured insulin sensitivity, fatty acid oxidation, mitochondrial function, and exercise capacity in obese mFOXO1 iKO mice and assessed the correlation between FOXO1 and mitochondria-related protein in the skeletal muscle of patients with diabetes. Obese mFOXO1 iKO mice exhibited improved mitochondrial respiratory capacity, which was followed by attenuated insulin resistance, enhanced fatty acid oxidation, and improved skeletal muscle exercise capacity. Transcriptional inhibition of FOXO1 in peroxisome proliferator-activated receptor δ (PPARδ) expression was confirmed in skeletal muscle, and deletion of PPARδ abolished the beneficial effects of FOXO1 deficiency. FOXO1 protein levels were higher in the skeletal muscle of patients with diabetes and negatively correlated with PPARδ and electron transport chain protein levels. These findings highlight FOXO1 as a new repressor in PPARδ gene expression in skeletal muscle and suggest that FOXO1 links insulin resistance and mitochondrial dysfunction in skeletal muscle via PPARδ.

ARTICLE HIGHLIGHTS

FOXO1 induced fatty acid oxidation in hepatic cells by targeting ALDH1L2

BACKGROUND AND AIM

Lipid metabolism disorder is the primary feature of numerous refractory chronic diseases. Fatty acid oxidation, an essential aerobic biological process, is closely related to the progression of NAFLD. The forkhead transcription factor FOXO1 has been reported to play an important role in lipid metabolism. However, the molecular mechanism through which FOXO1 regulates fatty acid oxidation remains unclear.

METHODS

Transcriptomic analysis was performed to examine the cellular expression profile to determine the functional role of FOXO1 in HepG2 cells with palmitic acid (PA)-induced lipid accumulation. FOXO1-binding motifs at the promoter region of aldehyde dehydrogenase 1 family member L2 (ALDH1L2) were predicted via bioinformatic analysis and confirmed via luciferase reporter assay. Overexpression of ALDH1L2 was induced to recover the impaired fatty acid oxidation in FOXO1-knockout cells.

RESULTS

Knockout of FOXO1 aggravated lipid deposition in hepatic cells. Transcriptomic profiling revealed that knockout of FOXO1 increased the expression of genes associated with fatty acid synthesis but decreased the expression of carnitine palmitoyltransferase1a (CPT1α) and adipose triglyceride lipase (ATGL), which contribute to fatty acid oxidation. Mechanistically, FOXO1 was identified as a transcription factor of ALDH1L2. Knockout of FOXO1 significantly decreased the protein expression of ALDH1L2 and CPT1α in vitro and in vivo. Furthermore, overexpression of ALDH1L2 restored fatty acid oxidation in FOXO1-knockout cells.

CONCLUSION

The findings of this study indicate that FOXO1 modulates fatty acid oxidation by targeting ALDH1L2.

Theabrownin as a Potential Prebiotic Compound Regulates Lipid Metabolism via the Gut Microbiota, Microbiota-Derived Metabolites, and Hepatic FoxO/PPAR Signaling Pathways

The dysregulation of lipid metabolism poses a significant health threat, necessitating immediate dietary intervention. Our previous research unveiled the prebiotic-like properties of theabrownin. This study aimed to further investigate the theabrownin-gut microbiota interactions and their downstream effects on lipid metabolism using integrated physiological, genomic, metabolomic, and transcriptomic approaches. The results demonstrated that theabrownin significantly ameliorated dyslipidemia, hepatic steatosis, and systemic inflammation induced by a high-fat/high-cholesterol diet (HFD). Moreover, theabrownin significantly improved HFD-induced gut microbiota dysbiosis and induced significant alterations in microbiota-derived metabolites. Additionally, the detailed interplay between theabrownin and gut microbiota was revealed. Analysis of hepatic transcriptome indicated that FoxO and PPAR signaling pathways played pivotal roles in response to theabrownin-gut microbiota interactions, primarily through upregulating hepatic Foxo1, Prkaa1, Pck1, Cdkn1a, Bcl6, Klf2, Ppara, and Pparg, while downregulating Ccnb1, Ccnb2, Fabp3, and Plin1. These findings underscored the critical role of gut-liver axis in theabrownin-mediated improvements in lipid metabolism disorders and supported the potential of theabrownin as an effective prebiotic compound for targeted regulation of metabolic diseases.

Strain-Specific Benefits of Bacillus Probiotics in Hybrid Grouper: Growth Enhancement, Metabolic Health, Immune Modulation, and Vibrio harveyi Resistance

In the realm of modern aquaculture, the utilization of probiotics has gained prominence, primarily due to their ability to enhance growth, boost immunity, and prevent diseases in aquatic species. This study primarily investigates the efficacy of Bacillus subtilis strains, both host-derived and from other sources, in influencing fish growth, immunity, lipid metabolism, and disease resistance. Employing a 42-day feeding trial, we divided hybrid grouper into four distinct groups: a control group on a basal diet and three experimental groups supplemented with 1 × 108 CFU/g of different Bacillus subtilis strains-BS, 6-3-1, and HAINUP40. Remarkably, the study demonstrated that the 6-3-1 and HAINUP40 groups exhibited significant enhancements across key growth parameters: final body weight (FBW), weight gain rate (WGR), feed intake (FI), feed efficiency ratio (FER), and feed conversion ratio (FCR). The investigation into lipid metabolism revealed that the 6-3-1 strain upregulated seven metabolism-related genes, HAINUP40 affected four metabolism-related genes, and the BS strain influenced two metabolism-related genes, indicating diverse metabolic impacts by different strains. Further, a notable reduction in liver enzymes AST and ALT was observed across all supplemented groups, implying improved liver health. Noteworthy was the BS strain's superior antioxidative capabilities, positively affecting all four measured parameters (CAT, GSH-Px, MDA). In the sphere of immune-related gene expression, the BS strain significantly decreased the expression of both inflammation and apoptosis-related genes, whereas the HAINUP40 strain demonstrated an upregulation in these genes. The challenge test results were particularly telling, showcasing improved survival rates against Vibrio harveyi infection in the BS and 6-3-1 groups, unlike the HAINUP40 group. These outcomes highlight the strain-specific nature of probiotics and their varying mechanisms of action within the host. In conclusion, this study reveals that probiotic strains, varying by source, demonstrate unique, strain-specific effects in promoting growth and modulating immunity in hybrid grouper. This research highlights the promise of tailored probiotic applications in improving aquaculture practices. Such advancements contribute to more sustainable and efficient fish farming methods.

Aerobic exercise-induced decrease of chemerin improved glucose and lipid metabolism and fatty liver of diabetes mice through key metabolism enzymes and proteins

Our previous studies have implicated an important role of adipokine chemerin in exercise-induced improvements of glycolipid metabolism and fatty liver in diabetes rat, but the underlying mechanisms remain unknown. This study first used an exogenous chemerin supplement to clarify the roles of decreased chemerin in exercised diabetes mice and possible mechanisms of glucose and lipid metabolism key enzymes and proteins [such as adipose triglyceride lipase (ATGL), lipoprotein lipase (LPL), phosphoenolpyruvate carboxykinase (PEPCK), and glucose transporter 4 (GLUT4)]. In addition, two kinds of adipose-specific chemerin knockout mice were generated to demonstrate the regulation of chemerin on glucose and lipid metabolism enzymes and proteins. We found that in diabetes mice, exercise-induced improvements of glucose and lipid metabolism and fatty liver, and exercise-induced increases of ATGL, LPL, and GLUT4 in liver, gastrocnemius and fat were reversed by exogenous chemerin. Furthermore, in chemerin knockdown mice, chemerin(-/-)∙adiponectin mice had lower body fat mass, improved blood glucose and lipid, and no fatty liver; while chemerin(-/-)∙fabp4 mice had hyperlipemia and unchanged body fat mass. Peroxisome proliferator-activated receptor γ (PPARγ), ATGL, LPL, GLUT4 and PEPCK in the liver and gastrocnemius had improve changes in chemerin(-/-)·adiponectin mice while deteriorated alterations in chemerin(-/-)·fabp4 mice, although PPARγ, ATGL, LPL, and GLUT4 increased in the fat of two kinds of chemerin(-/-) mice. CONCLUSIONS: Decreased chemerin exerts an important role in exercise-induced improvements of glucose and lipid metabolism and fatty liver in diabetes mice, which was likely to be through PPARγ mediating elevations of ATGL, LPL and GLUT4 in peripheral metabolic organs.

FoxK1 associated gene regulatory network in hepatic insulin action and its relationship to FoxO1 and insulin receptor mediated transcriptional regulation

OBJECTIVE

Insulin acts on the liver via changes in gene expression to maintain glucose and lipid homeostasis. This study aimed to the Forkhead box protein K1 (FOXK1) associated gene regulatory network as a transcriptional regulator of hepatic insulin action and to determine its role versus FoxO1 and possible actions of the insulin receptor at the DNA level.

METHODS

Genome-wide analysis of FoxK1 binding were studied by chromatin immunoprecipitation sequencing and compared to those for IR and FoxO1. These were validated by knockdown experiments and gene expression analysis.

RESULTS

Chromatin immunoprecipitation (ChIP) sequencing shows that FoxK1 binds to the proximal promoters and enhancers of over 4000 genes, and insulin enhances this interaction for about 75% of them. These include genes involved in cell cycle, senescence, steroid biosynthesis, autophagy, and metabolic regulation, including glucose metabolism and mitochondrial function and are enriched in a TGTTTAC consensus motif. Some of these genes are also bound by FoxO1. Comparing this FoxK1 ChIP-seq data to that of the insulin receptor (IR) reveals that FoxK1 may act as the transcription factor partner for some of the previously reported roles of IR in gene regulation, including for LARS1 and TIMM22, which are involved in rRNA processing and cell cycle.

CONCLUSION

These data demonstrate that FoxK1 is an important regulator of gene expression in response to insulin in liver and may act in concert with FoxO1 and IR in regulation of genes in metabolism and other important biological pathways.

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.

The endoribonuclease Arlr is required to maintain lipid homeostasis by downregulating lipolytic genes during aging

While disorders in lipid metabolism have been associated with aging and age-related diseases, how lipid metabolism is regulated during aging is poorly understood. Here, we characterize the Drosophila endoribonuclease CG2145, an ortholog of mammalian EndoU that we named Age-related lipid regulator (Arlr), as a regulator of lipid homeostasis during aging. In adult adipose tissues, Arlr is necessary for maintenance of lipid storage in lipid droplets (LDs) as flies age, a phenotype that can be rescued by either high-fat or high-glucose diet. Interestingly, RNA-seq of arlr mutant adipose tissues and RIP-seq suggest that Arlr affects lipid metabolism through the degradation of the mRNAs of lipolysis genes - a model further supported by the observation that knockdown of Lsd-1, regucalcin, yip2 or CG5162, which encode genes involved in lipolysis, rescue the LD defects of arlr mutants. In addition, we characterize DendoU as a functional paralog of Arlr and show that human ENDOU can rescue arlr mutants. Altogether, our study reveals a role of ENDOU-like endonucleases as negative regulator of lipolysis.

IGFBP-3 promotes cachexia-associated lipid loss by suppressing insulin-like growth factor/insulin signaling

BACKGROUND

Progressive lipid loss of adipose tissue is a major feature of cancer-associated cachexia. In addition to systemic immune/inflammatory effects in response to tumor progression, tumor-secreted cachectic ligands also play essential roles in tumor-induced lipid loss. However, the mechanisms of tumor-adipose tissue interaction in lipid homeostasis are not fully understood.

METHODS

The yki -gut tumors were induced in fruit flies. Lipid metabolic assays were performed to investigate the lipolysis level of different types of insulin-like growth factor binding protein-3 (IGFBP-3) treated cells. Immunoblotting was used to display phenotypes of tumor cells and adipocytes. Quantitative polymerase chain reaction (qPCR) analysis was carried out to examine the gene expression levels such as Acc1 , Acly , and Fasn et al .

RESULTS

In this study, it was revealed that tumor-derived IGFBP-3 was an important ligand directly causing lipid loss in matured adipocytes. IGFBP-3, which is highly expressed in cachectic tumor cells, antagonized insulin/IGF-like signaling (IIS) and impaired the balance between lipolysis and lipogenesis in 3T3-L1 adipocytes. Conditioned medium from cachectic tumor cells, such as Capan-1 and C26 cells, contained excessive IGFBP-3 that potently induced lipolysis in adipocytes. Notably, neutralization of IGFBP-3 by neutralizing antibody in the conditioned medium of cachectic tumor cells significantly alleviated the lipolytic effect and restored lipid storage in adipocytes. Furthermore, cachectic tumor cells were resistant to IGFBP-3 inhibition of IIS, ensuring their escape from IGFBP-3-associated growth suppression. Finally, cachectic tumor-derived ImpL2, the IGFBP-3 homolog, also impaired lipid homeostasis of host cells in an established cancer-cachexia model in Drosophila . Most importantly, IGFBP-3 was highly expressed in cancer tissues in pancreatic and colorectal cancer patients, especially higher in the sera of cachectic cancer patients than non-cachexia cancer patients.

CONCLUSION

Our study demonstrates that tumor-derived IGFBP-3 plays a critical role in cachexia-associated lipid loss and could be a biomarker for diagnosis of cachexia in cancer patients.

The effect of G0S2 on insulin sensitivity: A proteomic analysis in a G0S2-overexpressed high-fat diet mouse model

BACKGROUND

Previous research has shown a tight relationship between the G0/G1 switch gene 2 (G0S2) and metabolic diseases such as non-alcoholic fatty liver disease (NAFLD) and obesity and diabetes, and insulin resistance has been shown as the major risk factor for both NAFLD and T2DM. However, the mechanisms underlying the relationship between G0S2 and insulin resistance remain incompletely understood. Our study aimed to confirm the effect of G0S2 on insulin resistance, and determine whether the insulin resistance in mice fed a high-fat diet (HFD) results from G0S2 elevation.

METHODS

In this study, we extracted livers from mice that consumed HFD and received tail vein injections of AD-G0S2/Ad-LacZ, and performed a proteomics analysis.

RESULTS

Proteomic analysis revealed that there was a total of 125 differentially expressed proteins (DEPs) (56 increased and 69 decreased proteins) among the identified 3583 proteins. Functional enrichment analysis revealed that four insulin signaling pathway-associated proteins were significantly upregulated and five insulin signaling pathway -associated proteins were significantly downregulated.

CONCLUSION

These findings show that the DEPs, which were associated with insulin resistance, are generally consistent with enhanced insulin resistance in G0S2 overexpression mice. Collectively, this study demonstrates that G0S2 may be a potential target gene for the treatment of obesity, NAFLD, and diabetes.

The FoxO1-ATGL axis alters milk lipolysis homeostasis through PI3K/AKT signaling pathway in dairy goat mammary epithelial cells

Goat milk is enriched in fatty acids which are beneficial to human health. Previous research has revealed that 98% of milk fat is composed of triglycerides. However, the mechanisms regulating milk fat composition remain unclear. Forkhead box protein O1 (FoxO1) is a crucial regulatory factor involved in lipid metabolism across various cell types. Chromatin immunoprecipitation sequencing (ChIP)-seq data) and RNA sequencing (RNA-seq) data revealed that have indicated a close association between FoxO1 was closely related to lipid metabolism during lactation in dairy goats. The objective of this study was to investigate the mechanisms by which FoxO1 regulates lipid metabolism in goat mammary epithelial cells (GMECs). FoxO1 knockdown significantly downregulated the expression of adipose triglyceride lipase (ATGL) and suppressed the activity of the ATGL promoter. Consistently, the number of lipid droplets decreased significantly in FoxO1-overexpressing cells and increased in ATGL-knockdown cells. To further verify the effect of FoxO1 on ATGL promoter activity, cells were transfected with four promoter fragments of different lengths. We found that the core region of the ATGL promoter was located between -882 bp and -524 bp, encompassing two FoxO1 binding sites (FKH1 and FKH2). Mutations in the FoxO1 binding sites significantly downregulated ATGL promoter activity in GMECs. Luciferase reporter assays demonstrated that FoxO1 overexpression markedly enhanced ATGL promoter activity. Furthermore, site-directed mutation confirmed that FKH1 and FKH2 sites were simultaneously mutated significantly attenuated the stimulatory effect of FoxO1 on ATGL promoter activities simultaneous mutation of FKH1 and FKH2 sites significantly attenuated the stimulatory effect of FoxO1 on ATGL promoter activity. ChIP assays showed that FoxO1 directly binds to the FKH2 element located in the ATGL promoter in vivo. Finally, immunofluorescence staining revealed that insulin promotes the translocation of FoxO1 from the nucleus to the cytoplasm, thereby attenuating the FoxO1-induced activation of the ATGL promoter. Collectively, these findings uncover a novel pathway where by FoxO1 may regulate lipid metabolism in GMECs specifically by modulating the transcriptional activity of ATGL.

Selenoprotein F (SELENOF)-mediated AKT1-FOXO3a-PYGL axis contributes to selenium supranutrition-induced glycogenolysis and lipogenesis

Mounting evidence showed that excess selenium (10.0-15.0-fold of adequate Se) intake caused severe hepatic lipid deposition in the vertebrate. However, the underlying mechanism remains unclear. The study was performed to elucidate the mechanism of Se supranutrition mediated-changes of lipid deposition and metabolism. We found that dietary excessive Se addition increased hepatic TGs and glucose contents, up-regulated lipogenic enzyme activities and reduced hepatic glycogen contents. Transcriptomic and immunoblotting analysis showed that Se supranutrition significantly influenced serine/threonine kinase 1 (AKT1)-forkhead box O3a (FOXO3a)-PYGL signaling and protein levels of SELENOF. Knockdown of SELENOF and PYGL by RNA interference revealed that the AKT1-FOXO3a-PYGL axis was critical for Se supranutrition-induced lipid accumulation. Moreover, Se supranutrition-induced lipid accumulation was via the increased DNA binding capacity of FOXO3a to PYGL promoter, which increased glycogenolysis, and accordingly promoted lipogenesis and lipid accumulation. Our finding provides new insight into the mechanism of Se supranutrition-induced lipid accumulation and suggests that SELENOF may be a therapeutic target for Se supranutrition induced-lipid disorders in the vertebrates.

Integrated Analyses Identify Key Molecules and Reveal the Potential Mechanism of miR-182-5p/FOXO1 Axis in Alcoholic Liver Disease

Background: Alcoholic liver disease (ALD) is one of the most common chronic liver diseases worldwide. However, the potential molecular mechanism in ALD development remains unclear. The objective of this work was to identify key molecules and demonstrate the underlying regulatory mechanisms.

Methods: RNA-seq datasets were obtained from Gene Expression Omnibus (GEO), and key molecules in ALD development were identified with bioinformatics analysis. Alcoholic liver disease mouse and cell models were constructed using Lieber-DeCarli diets and alcohol medium, respectively. Quantitative real-time PCR and Western blotting were conducted to confirm the differential expression level. Dual-luciferase reporter assays were performed to explore the targeting regulatory relationship. Overexpression and knockdown experiments were applied to reveal the potential molecular mechanism in ALD development.

Results: Between ALD patients and healthy controls, a total of 416 genes and 21 microRNAs (miRNAs) with significantly differential expression were screened. A comprehensive miRNA-mRNA network was established; within this network, the miR-182-5p/FOXO1 axis was considered a significant pathway in ALD lipid metabolism. Mouse and cell experiments validated that miR-182-5p was substantially higher in ALD than in normal livers, whereas the expression of FOXO1 was dramatically decreased by alcohol consumption (P < 0.05). Next, dual-luciferase reporter assays demonstrated that miR-182-5p directly targets the binding site of the FOXO1 3′UTR and inhibits its mRNA and protein expression. In addition, miR-182-5p was found to promote hepatic lipid accumulation via targeting the FOXO1 signaling pathway, and inhibition of the miR-182-5p/FOXO1 axis improved hepatic triglyceride (TG) deposition in ALD by regulating downstream genes involved in lipid metabolism.

Conclusion: In summary, key molecules were identified in ALD development and a comprehensive miRNA–mRNA network was established. Meanwhile, our results suggested that miR-182-5p significantly increases lipid accumulation in ALD by targeting FOXO1, thereby providing novel scientific insights and potential therapeutic targets for ALD.

Insulin-Responsive Transcription Factors

The hormone insulin executes its function via binding and activating of the insulin receptor, a receptor tyrosine kinase that is mainly expressed in skeletal muscle, adipocytes, liver, pancreatic β-cells, and in some areas of the central nervous system. Stimulation of the insulin receptor activates intracellular signaling cascades involving the enzymes extracellular signal-regulated protein kinase-1/2 (ERK1/2), phosphatidylinositol 3-kinase, protein kinase B/Akt, and phospholipase Cγ as signal transducers. Insulin receptor stimulation is correlated with multiple physiological and biochemical functions, including glucose transport, glucose homeostasis, food intake, proliferation, glycolysis, and lipogenesis. This review article focuses on the activation of gene transcription as a result of insulin receptor stimulation. Signal transducers such as protein kinases or the GLUT4-induced influx of glucose connect insulin receptor stimulation with transcription. We discuss insulin-responsive transcription factors that respond to insulin receptor activation and generate a transcriptional network executing the metabolic functions of insulin. Importantly, insulin receptor stimulation induces transcription of genes encoding essential enzymes of glycolysis and lipogenesis and inhibits genes encoding essential enzymes of gluconeogenesis. Overall, the activation or inhibition of insulin-responsive transcription factors is an essential aspect of orchestrating a wide range of insulin-induced changes in the biochemistry and physiology of insulin-responsive tissues.

Organ-differential Roles of Akt/FoxOs Axis as a Key Metabolic Modulator during Aging

FoxOs and their post-translational modification by phosphorylation, acetylation, and methylation can affect epigenetic modifications and promote the expression of downstream target genes. Therefore, they ultimately affect cellular and biological functions during aging or occurrence of age-related diseases including cancer, diabetes, and kidney diseases. As known for its key role in aging, FoxOs play various biological roles in the aging process by regulating reactive oxygen species, lipid accumulation, and inflammation. FoxOs regulated by PI3K/Akt pathway modulate the expression of various target genes encoding MnSOD, catalases, PPARγ, and IL-1β during aging, which are associated with age-related diseases. This review highlights the age-dependent differential regulatory mechanism of Akt/FoxOs axis in metabolic and non-metabolic organs. We demonstrated that age-dependent suppression of Akt increases the activity of FoxOs (Akt/FoxOs axis upregulation) in metabolic organs such as liver and muscle. This Akt/FoxOs axis could be modulated and reversed by antiaging paradigm calorie restriction (CR). In contrast, hyperinsulinemia-mediated PI3K/Akt activation inhibited FoxOs activity (Akt/FoxOs axis downregulation) leading to decrease of antioxidant genes expression in non-metabolic organs such as kidneys and lungs during aging. These phenomena are reversed by CR. The results of studies on the process of aging and CR indicate that the Akt/FoxOs axis plays a critical role in regulating metabolic homeostasis, redox stress, and inflammation in various organs during aging process. The benefical actions of CR on the Akt/FoxOs axis in metabolic and non-metabolic organs provide further insights into the molecular mechanisms of organ-differential roles of Akt/FoxOs axis during aging.

Two Foxo1 homologues in the orange-spotted grouper Epinephelus coioides: sequences, expression, and possible involvement in the activation of cyp19a1a expression in the ovary

Foxo1, a member of Foxo transcription factor family, is involved in a number of physiological processes including metabolism, cell cycle progression, aging, and apoptosis. In the ovarian granulosa cell of mouse, Foxo1 is implicated to inhibit the expression of Cyp19a1, a gene encoding the aromatase that converts androgens into estrogens. Currently, the information about the expression and physiological relevance of Foxo1 homologues in the ovary of teleosts is scarce. In the present study, cDNAs encoding two forms of Foxo1, Foxo1a and Foxo1b, were isolated from the orange-spotted grouper. Phylogenetic analysis indicated that the orange-spotted groupers Foxo1a and Foxo1b were closely related to the counterparts of the ricefield eel. RT-PCR analysis showed that the orange-spotted groupers foxo1a and foxo1b were expressed in a wide range of tissues, with high levels detected in the brain regions, liver, and intestine. Quantitative real-time PCR analysis showed similar expression profiles for cyp19a1a, foxo1a, and foxo1b in the ovary during development from the primary growth to mature stages, with peak values detected at the vitellogenic stage. In situ hybridization detected mRNA of foxo1a, foxo1b, and cyp19a1a in granulosa cells surrounding vitellogenic oocytes. In vitro transfection showed that both Foxo1a and Foxo1b upregulated the orange-spotted grouper cyp19a1a promoter activities, possibly through the conserved Foxo binding site. Collectively, these results suggest that both Foxo1a and Foxo1b may be involved in the regulation of the ovarian functions in the orange-spotted grouper and the physiological roles of Foxo1 homologues in the ovary may be diversified in vertebrates.

Signal Transduction and Molecular Regulation in Fatty Liver Disease

Significance: Fatty liver disease is a major liver disorder in the modern societies. Comprehensive understanding of the pathophysiology and molecular mechanisms is essential for the prevention and treatment of the disease. Recent Advances: Remarkable progress has been made in the recent years in basic and translational research in the field of fatty liver disease. Multiple signaling pathways have been implicated in the development of fatty liver disease, including AMP-activated protein kinase, mechanistic target of rapamycin kinase, endoplasmic reticulum stress, oxidative stress, inflammation, transforming growth factor β, and yes1-associated transcriptional regulator/transcriptional coactivator with PDZ-binding motif (YAP/TAZ). In addition, critical molecular regulations at the transcriptional and epigenetic levels have been linked to the pathogenesis of fatty liver disease. Critical Issues: Some critical issues remain to be solved so that research findings can be translated into clinical applications. Robust and reliable biomarkers are needed for diagnosis of different stages of the fatty liver disease. Effective and safe molecular targets remain to be identified and validated. Prevention strategies require solid scientific evidence and population-wide feasibility. Future Directions: As more data are generated with time, integrative approaches are needed to comprehensively understand the disease pathophysiology and mechanisms at multiple levels from population, organismal system, organ/tissue, to cell. The interactions between genes and environmental factors require deeper investigation for the purposes of prevention and personalized treatment of fatty liver disease. Antioxid. Redox Signal. 35, 689-717.

Ins and Outs of the TCA Cycle: The Central Role of Anaplerosis

The reactions of the tricarboxylic acid (TCA) cycle allow the controlled combustion of fat and carbohydrate. In principle, TCA cycle intermediates are regenerated on every turn and can facilitate the oxidation of an infinite number of nutrient molecules. However, TCA cycle intermediates can be lost to cataplerotic pathways that provide precursors for biosynthesis, and they must be replaced by anaplerotic pathways that regenerate these intermediates. Together, anaplerosis and cataplerosis help regulate rates of biosynthesis by dictating precursor supply, and they play underappreciated roles in catabolism and cellular energy status. They facilitate recycling pathways and nitrogen trafficking necessary for catabolism, and they influence redox state and oxidative capacity by altering TCA cycle intermediate concentrations. These functions vary widely by tissue and play emerging roles in disease. This article reviews the roles of anaplerosis and cataplerosis in various tissues and discusses how they alter carbon transitions, and highlights their contribution to mechanisms of disease. Expected final online publication date for the Annual Review of Nutrition, Volume 41 is September 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Hepatic transcriptional profile reveals the role of diet and genetic backgrounds on metabolic traits in female progenitor strains of the Collaborative Cross

Mice have provided critical mechanistic understandings of clinical traits underlying metabolic syndrome (MetSyn) and susceptibility to MetSyn in mice is known to vary among inbred strains. We investigated the diet- and strain-dependent effects on metabolic traits in the eight Collaborative Cross (CC) founder strains (A/J, C57BL/6J, 129S1/SvImJ, NOD/ShiLtJ, NZO/HILtJ, CAST/EiJ, PWK/PhJ, and WSB/EiJ). Liver transcriptomics analysis showed that both atherogenic diet and host genetics have profound effects on the liver transcriptome, which may be related to differences in metabolic traits observed between strains. We found strain differences in circulating trimethylamine N-oxide (TMAO) concentration and liver triglyceride content, both of which are traits associated with metabolic diseases. Using a network approach, we identified a module of transcripts associated with TMAO and liver triglyceride content, which was enriched in functional pathways. Interrogation of the module related to metabolic traits identified NADPH oxidase 4 (Nox4), a gene for a key enzyme in the production of reactive oxygen species, which showed a strong association with plasma TMAO and liver triglyceride. Interestingly, Nox4 was identified as the highest expressed in the C57BL/6J and NZO/HILtJ strains and the lowest expressed in the CAST/EiJ strain. Based on these results, we suggest that there may be genetic variation in the contribution of Nox4 to the regulation of plasma TMAO and liver triglyceride content. In summary, we show that liver transcriptomic analysis identified diet- or strain-specific pathways for metabolic traits in the Collaborative Cross (CC) founder strains.

Dual regulation of TxNIP by ChREBP and FoxO1 in liver

TxNIP (Thioredoxin-interacting protein) is considered as a potential drug target for type 2 diabetes. Although TxNIP expression is correlated with hyperglycemia and glucotoxicity in pancreatic β cells, its regulation in liver cells has been less investigated. In the current study, we aim at providing a better understanding of Txnip regulation in hepatocytes in response to physiological stimuli and in the context of hyperglycemia in db/db mice. We focused on regulatory pathways governed by ChREBP (Carbohydrate Responsive Element Binding Protein) and FoxO1 (Forkhead box protein O1), transcription factors that play central roles in mediating the effects of glucose and fasting on gene expression, respectively. Studies using genetically modified mice reveal that hepatic TxNIP is up-regulated by both ChREBP and FoxO1 in liver cells and that its expression strongly correlates with fasting, suggesting a major role for this protein in the physiological adaptation to nutrient restriction.

Palmitate induces fat accumulation via repressing FoxO1-mediated ATGL-dependent lipolysis in HepG2 hepatocytes

Obesity is closely associated with non-alcoholic fatty liver disease (NAFLD), and elevated serum palmitate is the link between obesity and excessive hepatic lipid accumulation. Forkhead box O-1 (FoxO1) is one of the FoxO family members of transcription factors and can stimulate adipose triglyceride lipase (ATGL) and suppress its inhibitor G0/G1 switch gene 2 (G0S2) expression in the liver. However, previous researches have also shown conflicting results regarding the role of FoxO1 in hepatic lipid accumulation. We therefore examined the role of FoxO1 as a downstream suppressor to palmitate-stimulated hepatic steatosis. Palmitate significantly promoted lipid accumulation but inhibited lipid decomposition in human HepG2 hepatoma cells. Palmitate also significantly reduced FoxO1, ATGL and its activator comparative gene identification-58 (CGI-58) expression but increased peroxisome proliferator-activated receptorγ (PPARγ) and its target gene G0S2 expression. FoxO1 overexpression significantly increased palmitate-inhibited ATGL and CGI-58 expression but reduced palmitate-stimulated PPARγ and its target gene G0S2 expression. FoxO1 overexpression also inhibited lipid accumulation and promoted lipolysis in palmitate-treated hepatocytes. Overall, these results indicate that FoxO1-mediated ATGL-dependent lipolysis may be an effective molecular mechanism in protecting hepatocytes from palmitate-induced fat accumulation.

Explore the Effect and Target of Liraglutide on Islet Function in Type 2 Diabetic Rats by miRNA Omics Technology

PURPOSE

To analyze the effect and potential therapeutic targets of liraglutide in type 2 diabetes through miRNA expression profiling.

METHODS

Ten of 30 SPF Wistar rats, males at 4 weeks old, were randomly selected as the control group and given conventional feed, the other rats adopted high-sugar and high-fat diet combined with an intraperitoneal injection of streptozotocin to establish a T2DM model. One unsuccessful rat was excluded, and the remaining rats were randomized to the model and the liraglutide group. Liraglutide group was subcutaneously injected with liraglutide 0.11 mg/kg for 8 weeks. The biochemical indicators and staining HE were detected. The expression of miRNA in pancreatic tissue was detected by miRNA sequencing. The intersection of miRNA difference was used to predict the target gene, then functional enrichment was performed to identify its possible biological functions and signal transduction paths. Finally, qRT-PCR was used to verify the results.

RESULTS

Compared to the model group, the level of fasting blood glucose (FBG), glucagon and insulin resistance index (HOMA-IR) in the liraglutide group were significantly decreased, fasting insulin (FINS) and insulin sensitivity index (ISI) were increased. Nine differential miRNAs (miR-135a-5p, miR-144-5p, miR-21-3p, miR-215, miR-451-5p, miR-486, miR-122-5p, miR-181d-5p and miR-345-5p) were identified at the intersection through two miRNA sequencing. A total of 3359 related target gene predictions were obtained. GO and pathway analyses demonstrated that differentially expressed genes were closely related to cell proliferation, angiogenesis, and proteolysis. Significant signaling pathways included PI signaling system, autophagy, FoxO and HIF-1 signaling pathway.

CONCLUSION

Liraglutide could improve islet function by regulating nine miRNAs, and the related signaling pathways included PI signaling system, autophagy, FoxO and HIF-1 signaling pathway. Our study provided the basis and direction for further exploring the molecular mechanism of liraglutide on T2DM.

Remodeling of whole-body lipid metabolism and a diabetic-like phenotype caused by loss of CDK1 and hepatocyte division

Cell cycle progression and lipid metabolism are well-coordinated processes required for proper cell proliferation. In liver diseases that arise from dysregulated lipid metabolism, hepatocyte proliferation is diminished. To study the outcome of CDK1 loss and blocked hepatocyte proliferation on lipid metabolism and the consequent impact on whole-body physiology, we performed lipidomics, metabolomics, and RNA-seq analyses on a mouse model. We observed reduced triacylglycerides in liver of young mice, caused by oxidative stress that activated FOXO1 to promote the expression of Pnpla2/ATGL. Additionally, we discovered that hepatocytes displayed malfunctioning β-oxidation, reflected by increased acylcarnitines (ACs) and reduced β-hydroxybutyrate. This led to elevated plasma free fatty acids (FFAs), which were transported to the adipose tissue for storage and triggered greater insulin secretion. Upon aging, chronic hyperinsulinemia resulted in insulin resistance and hepatic steatosis through activation of LXR. Here, we demonstrate that loss of hepatocyte proliferation is not only an outcome but also possibly a causative factor for liver pathology.

FoxO1 signaling as a therapeutic target for type 2 diabetes and obesity

Glucose production and the consumption of high levels of carbohydrate increase the chance of insulin resistance, especially in cases of obesity. Therefore, maintaining a balanced glucose homeostasis might form a strategy to prevent or cure diabetes and obesity. The activation and inhibition of glucose production is complicated due to the presence of many interfering pathways. These pathways can be viewed at the downstream level because they activate certain transcription factors, which include the Forkhead-O1 (FoxO1). This has been identified as a significant agent in the pancreas, liver, and adipose tissue, which is significant in the regulation of lipids and glucose. The objective of this review is to discuss the intersecting portrayal of FoxO1 and its parallel cross-talk which highlights obesity-induced insulin susceptibility in the discovery of a targeted remedy. The review also analyses current progress and provides a blueprint on therapeutics, small molecules, and extracts/phytochemicals which are explored at the pre-clinical level.

Hepatic lipid droplets: A balancing act between energy storage and metabolic dysfunction in NAFLD

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) is defined by the abundance of lipid droplets (LDs) in hepatocytes. While historically considered simply depots for energy storage, LDs are increasingly recognized to impact a wide range of biological processes that influence cellular metabolism, signaling, and function. While progress has been made toward understanding the factors leading to LD accumulation (i.e. steatosis) and its progression to advanced stages of NAFLD and/or systemic metabolic dysfunction, much remains to be resolved.

SCOPE OF REVIEW

This review covers many facets of LD biology. We provide a brief overview of the major pathways of lipid accretion and degradation that contribute to steatosis and how they are altered in NAFLD. The major focus is on the relationship between LDs and cell function and the detailed mechanisms that couple or uncouple steatosis from the severity and progression of NAFLD and systemic comorbidities. The importance of specific lipids and proteins within or on LDs as key components that determine whether LD accumulation is linked to cellular and metabolic dysfunction is presented. We discuss emerging areas of LD biology and future research directions that are needed to advance our understanding of the role of LDs in NAFLD etiology.

MAJOR CONCLUSIONS

Impairments in LD breakdown appear to contribute to disease progression, but inefficient incorporation of fatty acids (FAs) into LD-containing triacylglycerol (TAG) and the consequential changes in FA partitioning also affect NAFLD etiology. Increased LD abundance in hepatocytes does not necessarily equate to cellular dysfunction. While LD accumulation is the prerequisite step for most NAFLD cases, the protein and lipid composition of LDs are critical factors in determining the progression from simple steatosis. Further defining the detailed molecular mechanisms linking LDs to metabolic dysfunction is important for designing effective therapeutic approaches targeting NAFLD and its comorbidities.

Therapeutic strategies targeting FOXO transcription factors

FOXO proteins are transcription factors that are involved in numerous physiological processes and in various pathological conditions, including cardiovascular disease, cancer, diabetes and chronic neurological diseases. For example, FOXO proteins are context-dependent tumour suppressors that are frequently inactivated in human cancers, and FOXO3 is the second most replicated gene associated with extreme human longevity. Therefore, pharmacological manipulation of FOXO proteins is a promising approach to developing therapeutics for cancer and for healthy ageing. In this Review, we overview the role of FOXO proteins in health and disease and discuss the pharmacological approaches to modulate FOXO function.

FoxO1 Knockdown Promotes Fatty Acid Synthesis via Modulating SREBP1 Activities in the Dairy Goat Mammary Epithelial Cells

FoxO1 is a crucial transcription factor involved in lipid metabolism in mouse liver through repressing a key regulator of lipogenesis, sterol regulatory element binding protein 1 (SREBP1). However, it remains elusive whether FoxO1 plays roles in the regulation of fatty acid metabolism during lactation in dairy goats. In this study, we aim to investigate the function of FoxO1 in goat mammary epithelial cells (GMECs). We found that the expression of FoxO1 is significantly upregulated during lactation compared with the dry period. FoxO1 knockdown enhanced the expression of genes related to de novo fatty acid synthesis (e.g., FASN, ELOVL6 and SCD1) and triacylglycerol (TAG) synthesis (e.g., DGAT2 and GPAM). Consistently, intracellular TAG was significantly increased in FoxO1 knockdown cells and reduced in FoxO1 overexpression cells. Immunofluorescence staining revealed that insulin suppresses FoxO1 transcription by promoting its nuclear export. Further, we found that FoxO1 inhibits insulin-induced SREBP1 promoter activities in GMECs. Moreover, FoxO1 suppresses SREBP1 transcription via the LXR response element (LXRE) and SREBP response element (SRE) located in the SREBP1 promoter. Our data reveal that FoxO1 plays critical roles in regulating the synthesis of the fatty acid and triacylglycerol (TAG) in GMECs.

Curcumin metabolites contribute to the effect of curcumin on ameliorating insulin sensitivity in high-glucose-induced insulin-resistant HepG2 cells

ETHNOPHARMACOLOGICAL EVIDENCE

Curcumin (CUR) is the active ingredient of Traditional Chinese Medicine turmeric (Curcuma longa L.), which has been used for treatment of diabetes in Ayurveda and China. CUR exerts potent anti-insulin-resistant effects in various cell lines. However, previous studies indicated CUR was metabolized extensively in vivo and massively degraded in a medium alkaline buffer solution. The real active component of the anti-insulin-resistant activity of CUR in vitro is not clear.

AIM OF THE STUDY

Our study identified the functional contribution of the metabolites of CUR and the related molecular mechanism in improving insulin sensitivity.

MATERIALS AND METHODS

HPLC and UPLC-QQQ-MS analyses were used to investigate the stability and metabolism of CUR in HepG2 cells. The effect of the metabolic products of CUR on insulin sensitivity was evaluated in high glucose (HG)-induced insulin-resistant HepG2 cells. A network pharmacology approach was used to examine the potential targets of the metabolites, and Western blotting was performed to verify changes in the targets.

RESULTS

CUR was unstable in the cell culture medium, but the prototypes, metabolites and degradation products of CUR coexisted in the HepG2 cell culture experiment. The insulin sensitivity assay demonstrated that CUR and its metabolites enhanced insulin sensitivity in HG-induced insulin-resistant HepG2 cells, but the total degradation products of CUR may not play the major role. Similar to CUR, hexahydrocurcumin (HHC) and octahydrocurcumin (OHC) improved insulin sensitivity by strengthening the PI3K-AKT-GSK3B signal and suppressing the phosphorylation of ERK/JNK in HG-induced insulin-resistant HepG2 cells.

CONCLUSIONS

Metabolites of CUR played a critical role in counteracting insulin resistance in HG-induced HepG2 cells. CUR exerted anti-insulin resistance effect in HepG2 cells in a multi-component, multi-target, and multi-pathway manner.

C. elegans ACAT regulates lipolysis and its related lifespan in fasting through modulation of the genes in lipolysis and insulin/IGF-1 signaling

Overly active acyl-coenzyme A: cholesterol acyltransferases (ACATs) are known to contribute to the development of atherosclerosis, cancer cell proliferation and de novo lipogenesis. However, the role of ACAT in systemic lipid metabolism and its consequence of aging is unknown. Using avasimibe, a clinically proven ACAT inhibitor, and mboa-1 mutant strain, a homologous to mammalian ACAT, herein, we found that Ava treatment and mboa-1 mutant exhibited a decreased fat accumulation during feeding and increased lipolysis with extended lifespan of C. elegans during fasting. Our study highlights the essential role of ACAT inhibitor and mboa-1 in fat mobilization and the survival of C. elegans in fasting through the modulation of the genes involved in lipolysis and insulin/IGF-1 signaling.

An in vitro model of hepatic steatosis using lipid loaded induced pluripotent stem cell derived hepatocyte like cells

Hepatic steatosis is a metabolic disease, characterized by selective and progressive accumulation of lipids in liver, leading to progressive non-alcoholic fatty liver disease (NAFLD), non-alcoholic steatohepatitis (NASH), and cirrhosis. The existing in vitro models of hepatic steatosis to elucidate the molecular mechanisms behind the onset of hepatic steatosis and to profile small molecule modulators uses lipid loaded primary hepatocytes, and cell lines like HepG2. The limitation of these models includes high variability between the different donor samples, reproducibility, and translatability to physiological context. An in vitro human hepatocyte derived model that mimics the pathophysiological changes seen in hepatic steatosis may provide an alternative tool for pre-clinical drug discovery research. We report the development of an in vitro experimental model of hepatic steatosis using human induced pluripotent stem cell (iPSC) derived hepatocytes like cells (HLC), loaded with lipids. Our data suggests that HLC carry some of the functional characteristics of primary hepatocytes and are amenable for development of an in vitro steatosis model using lipid loading method. The in vitro experimental model of hepatic steatosis was further characterized using biomarker analysis and validated using telmisartan. With some refinement and additional validation, our in vitro steatosis model system may be useful for profiling small molecule inhibitors and studying the mechanism of action of new drugs.

Ginsenoside Rg1 protects against d-galactose induced fatty liver disease in a mouse model via FOXO1 transcriptional factor

AIMS

Rg1 is the most active component of traditional Chinese medicine ginseng, having anti-aging and anti-oxidative stress features in multiple organs. Cellular senescence of hepatocytes is involved in the progression of a wide spectrum of chronic liver diseases. In this study, we investigated the potential benefits and mechanism of action of Rg1 on aging-driven chronic liver diseases.

MATERIALS AND METHODS

A total of 40 male C57BL/6 mice were randomly divided into four groups: control group; Rg1 group; Rg1+d-gal group; and d-gal group. Blood and liver tissue samples were collected for determination of liver function, biochemical and molecular markers, as well as histopathological investigation.

KEY FINDINGS

Rg1 played an anti-aging role in reversing d-galactose induced increase in senescence-associated SA-β-gal staining and p53, p21 protein in hepatocytes of mice and sustained mitochondria homeostasis. Meanwhile, Rg1 protected livers from d-galactose caused abnormal elevation of ALT and AST in serum, hepatic steatosis, reduction in hepatic glucose production, hydrogenic degeneration, inflammatory phenomena including senescence-associated secretory phenotype (SASP) IL-1β, IL-6, MCP-1 elevation and lymphocyte infiltration. Furthermore, Rg1 suppressed drastic elevation in FOXO1 phosphorylation resulting in maintaining FOXO1 protein level in the liver after d-galactose treatment, followed by FOXO1 targeted antioxidase SOD and CAT significant up-regulation concurrent with marked decrease in lipid peroxidation marker MDA.

SIGNIFICANCE

Rg1 exerts pharmaceutic effects of maintaining FOXO1 activity in liver, which enhances anti-oxidation potential of Rg1 to ameliorate SASP and to inhibit inflammation, also promotes metabolic homeostasis, and thus protects livers from senescence induced fatty liver disease. The study provides a potential therapeutic strategy for alleviating chronic liver pathology.

Emerging targets and potential therapeutic agents in non-alcoholic fatty liver disease treatment

Nonalcoholic Fatty Liver Disease (NAFLD) is the most common chronic liver disease in the world, which is characterized by liver fat accumulation unrelated to excessive drinking. Indeed, it attracts growing attention and becomes a global health problem. Due to the complexity of the NAFLD pathogenic mechanism, no related drugs were approved by Food and Drug Administration (FDA) till now. However, it is encouraging that a series of candidate drugs have entered the clinical trial stage with expectation to treat NAFLD. In this review, we summarized the main pathways and pathogenic mechanisms of NAFLD, as well as introduced the main potential therapeutic targets and the corresponding compounds involved in metabolism, inflammation and fibrosis. Furthermore, we also discuss the progress of these compounds, such as drug design and optimization, the choice of pharmacological properties and druglikeness, and the analysis of structure-activity relationship. This review offers a medium on future drug design and development, to be beneficial to relevant studies.

Fatty liver diseases, mechanisms, and potential therapeutic plant medicines

The liver is an important metabolic organ and controls lipid, glucose and energy metabolism. Dysruption of hepatic lipid metabolism is often associated with fatty liver diseases, including nonalcoholic fatty liver disease (NAFLD), alcoholic fatty liver diseases (AFLD) and hyperlipidemia. Recent studies have uncovered the contribution of hormones, transcription factors, and inflammatory cytokines to the pathogenesis of dyslipidemia and fatty liver diseases. Moreover, a significant amount of effort has been put to examine the mechanisms underlying the potential therapeutic effects of many natural plant products on fatty liver diseases and metabolic diseases. We review the current understanding of insulin, thyroid hormone and inflammatory cytokines in regulating hepatic lipid metabolism, focusing on several essential transcription regulators, such as Sirtuins (SIRTs), Forkhead box O (FoxO), Sterol-regulatory element-binding proteins (SREBPs). We also discuss a few representative natural products with promising thereapeutic effects on fatty liver disease and dyslipidemia.

FoxO3 regulates hepatic triglyceride metabolism via modulation of the expression of sterol regulatory-element binding protein 1c

Background

Excessive intrahepatic lipid accumulation is the major characteristic of nonalcoholic fatty liver disease (NAFLD). We sought to identify the mechanisms involved in hepatic triglyceride (TG) homeostasis. Forkhead box class O (FoxO) transcription factors have been shown to play an important role in hepatic metabolism. However, little is known about the effect of FoxO3 on hepatic TG metabolism.

Methods

Liver biopsy samples from patients with NALFD and liver tissues from high glucose and high sucrose (HFHS) fed mice, ob/ob mice and db/db mice were collected for protein and mRNA analysis. HepG2 cells were transfected with small interfering RNA to mediate FoxO3 knockdown, or adenovirus and plasmid to mediate FoxO3 overexpression. FoxO3-cDNA was delivered by adenovirus to the liver of C57BL/6 J male mice on a chow diet or on a high-fat diet, followed by determination of hepatic lipid metabolism. Sterol regulatory element-binding protein 1c (SREBP1c) luciferase reporter gene plasmid was co-transfected into HepG2 cells with FoxO3 overexpression plasmid.

Results

FoxO3 expression was increased in the livers of HFHS mice, ob/ob mice, db/db mice and patients with NAFLD. Knockdown of FoxO3 reduced whereas overexpression of FoxO3 increased cellular TG concentrations in HepG2 cells. FoxO3 gain-of-function caused hepatic TG deposition in C57BL/6 J mice on a chow diet and aggravated hepatic steatosis when fed a high-fat diet. Analysis of the transcripts established the increased expression of genes related to TG synthesis, including SREBP1c, SCD1, FAS, ACC1, GPAM and DGAT2 in mouse liver. Mechanistically, overexpression of FoxO3 stimulated the expression of SREBP1c, whereas knockdown of FoxO3 inhibited the expression of SREBP1c. Luciferase reporter assays showed that SREBP1c regulated the transcriptional activity of the SREBP1c promoter.

Conclusions

FoxO3 promotes the transcriptional activity of the SREBP1c promoter, thus leading to increased TG synthesis and hepatic TG accumulation.

Maternal di-(2-ethylhexyl) phthalate exposure alters hepatic insulin signal transduction and glucoregulatory events in rat F1 male offspring

Di-(2-ethylhexyl) phthalate (DEHP) is a commonly used plasticizer with endocrine disrupting properties. Its widespread use resulted in constant human exposure including fetal development and postnatal life. Epidemiological and experimental data have shown that DEHP has a negative influence on glucose homeostasis. However, the evidence regarding the effect of maternal DEHP exposure on hepatic glucose homeostasis is scarce. Hence, we investigated whether DEHP exposure during gestation and lactation disrupts glucose homeostasis in the rat F₁ male offspring at adulthood. Pregnant rats were divided into three groups and administered with DEHP (10 and 100 mg/kg/day) or olive oil from gestational day 9 to postnatal day 21 (lactation period) through oral gavage. DEHP-exposed offspring exhibited hyperglycemia, impaired glucose and insulin tolerances along with hyperinsulinemia at postnatal day 80. DEHP exposure significantly reduced the levels of insulin signaling molecules such as insulin receptors, IRS1, Akt and its phosphorylated forms. GSK3β and FoxO1 proteins increased in DEHP-exposed groups whereas its phosphorylated forms decreased. Treated groups showed decreased glycogen synthase activity and glycogen concentration. Glucose-6-phosphatase and phosphoenolpyruvate carboxykinase mRNA level and enzyme activity increased in DEHP-treated groups. The interaction between FoxO1-glucose-6-phosphatase and FoxO1-phosphoenolpyruvate carboxykinase was also increased. This study suggests that DEHP exposure impairs insulin signal transduction and alters glucoregulatory events leading to the development of type 2 diabetes in F₁ male offspring.

Forkhead box protein O1 (FoxO1) regulates hepatic serine protease inhibitor B1 (serpinB1) expression in a non-cell-autonomous fashion

FoxO proteins are major targets of insulin action, and FoxO1 mediates the effects of insulin on hepatic glucose metabolism. We reported previously that serpinB1 is a liver-secreted factor (hepatokine) that promotes adaptive β-cell proliferation in response to insulin resistance in the liver-specific insulin receptor knockout (LIRKO) mouse. Here we report that FoxO1 plays a critical role in promoting serpinB1 expression in hepatic insulin resistance in a non-cell-autonomous manner. Mice lacking both the insulin receptor and FoxO1 (LIRFKO) exhibit reduced β-cell mass compared with LIRKO mice because of attenuation of β-cell proliferation. Although hepatic expression of serpinB1 mRNA and protein levels was increased in LIRKO mice, both the mRNA and protein levels returned to control levels in LIRFKO mice. Furthermore, liver-specific expression of constitutively active FoxO1 in transgenic mice induced an increase in hepatic serpinB1 mRNA and protein levels in refed mice. Conversely, serpinB1 mRNA and protein levels were reduced in mice lacking FoxO proteins in the liver. ChIP studies demonstrated that FoxO1 binds to three distinct sites located ∼9 kb upstream of the serpinb1 gene in primary mouse hepatocytes and that this binding is enhanced in hepatocytes from LIRKO mice. However, adenoviral expression of WT or constitutively active FoxO1 and insulin treatment are sufficient to regulate other FoxO1 target genes (IGFBP-1 and PEPCK) but not serpinB1 expression in mouse primary hepatocytes. These results indicate that liver FoxO1 promotes serpinB1 expression in hepatic insulin resistance and that non-cell-autonomous factors contribute to FoxO1-dependent effects on serpinB1 expression in the liver.

Resolving the Paradox of Hepatic Insulin Resistance

Insulin resistance is associated with numerous metabolic disorders, such as obesity and type II diabetes, that currently plague our society. Although insulin normally promotes anabolic metabolism in the liver by increasing glucose consumption and lipid synthesis, insulin-resistant individuals fail to inhibit hepatic glucose production and paradoxically have increased liver lipid synthesis, leading to hyperglycemia and hypertriglyceridemia. Here, we detail the intrahepatic and extrahepatic pathways mediating insulin's control of glucose and lipid metabolism. We propose that the interplay between both of these pathways controls insulin signaling and that mis-regulation between the 2 results in the paradoxic effects seen in the insulin-resistant liver instead of the commonly proposed deficiencies in particular branches of only the direct hepatic pathway.

Myeloid-specific deletion of Zfp36 protects against insulin resistance and fatty liver in diet-induced obese mice

Obesity is associated with adipose tissue inflammation that contributes to insulin resistance. Zinc finger protein 36 (Zfp36) is an mRNA-binding protein that reduces inflammation by binding to cytokine transcripts and promoting their degradation. We hypothesized that myeloid-specific deficiency of Zfp36 would lead to increased adipose tissue inflammation and reduced insulin sensitivity in diet-induced obese mice. As expected, wild-type (Control) mice became obese and diabetic on a high-fat diet, and obese mice with myeloid-specific loss of Zfp36 [knockout (KO)] demonstrated increased adipose tissue and liver cytokine mRNA expression compared with Control mice. Unexpectedly, in glucose tolerance testing and hyperinsulinemic-euglycemic clamp studies, myeloid Zfp36 KO mice demonstrated improved insulin sensitivity compared with Control mice. Obese KO and Control mice had similar macrophage infiltration of the adipose depots and similar peripheral cytokine levels, but lean and obese KO mice demonstrated increased Kupffer cell (KC; the hepatic macrophage)-expressed Mac2 compared with lean Control mice. Insulin resistance in obese Control mice was associated with enhanced Zfp36 expression in KCs. Compared with Control mice, KO mice demonstrated increased hepatic mRNA expression of a multitude of classical (M1) inflammatory cytokines/chemokines, and this M1-inflammatory hepatic milieu was associated with enhanced nuclear localization of IKKβ and the p65 subunit of NF-κB. Our data confirm the important role of innate immune cells in regulating hepatic insulin sensitivity and lipid metabolism, challenge-prevailing models in which M1 inflammatory responses predict insulin resistance, and indicate that myeloid-expressed Zfp36 modulates the response to insulin in mice.

Inactivating hepatic follistatin alleviates hyperglycemia

Unsuppressed hepatic glucose production (HGP) contributes substantially to glucose intolerance and diabetes, which can be modeled by the genetic inactivation of hepatic insulin receptor substrate 1 (Irs1) and Irs2 (LDKO mice). We previously showed that glucose intolerance in LDKO mice is resolved by hepatic inactivation of the transcription factor FoxO1 (that is, LTKO mice)-even though the liver remains insensitive to insulin. Here, we report that insulin sensitivity in the white adipose tissue of LDKO mice is also impaired but is restored in LTKO mice in conjunction with normal suppression of HGP by insulin. To establish the mechanism by which white adipose tissue insulin signaling and HGP was regulated by hepatic FoxO1, we identified putative hepatokines-including excess follistatin (Fst)-that were dysregulated in LDKO mice but normalized in LTKO mice. Knockdown of hepatic Fst in the LDKO mouse liver restored glucose tolerance, white adipose tissue insulin signaling and the suppression of HGP by insulin; however, the expression of Fst in the liver of healthy LTKO mice had the opposite effect. Of potential clinical significance, knockdown of Fst also improved glucose tolerance in high-fat-fed obese mice, and the level of serum Fst was reduced in parallel with glycated hemoglobin in obese individuals with diabetes who underwent therapeutic gastric bypass surgery. We conclude that Fst is a pathological hepatokine that might be targeted for diabetes therapy during hepatic insulin resistance.

Mechanisms controlling the anti-neoplastic functions of FoxO proteins

The Forkhead box O (FoxO) proteins comprise a family of evolutionarily conserved transcription factors that predominantly function as tumor suppressors. These proteins assume diverse roles in the cellular anti-neoplastic response, including regulation of apoptosis and autophagy, cancer metabolism, cell-cycle arrest, oxidative stress and the DNA damage response. More recently, FoxO proteins have been implicated in cancer immunity and cancer stem-cell (CSC) homeostasis. Interestingly, in some sporadic sub-populations, FoxO protein function may also be manipulated by factors such as β-catenin whereby they instead can facilitate cancer progression via maintenance of CSC properties or promoting drug resistance or metastasis and invasion. This review highlights the essential biological functions of FoxOs and explores the areas that may be exploited in FoxO protein signaling pathways in the development of novel cancer therapeutic agents.

Mammalian target of rapamycin complex 1 and FoxO1 in the transcriptional control of lipolysis and de novo lipogenesis

PURPOSE OF REVIEW

Postprandial suppression of lipolysis in adipose tissue and stimulation of de novo lipogenesis (DNL) in the liver by insulin are essential for the metabolic homeostasis in the mammalian organism. The mechanism of coregulation of lipolysis and DNL is not clear.

RECENT FINDINGS

Insulin controls both lipolysis and DNL at the level of transcription via the same mammalian target of rapamycin complex 1 (mTORC1) and FoxO1-mediated signaling pathways.

SUMMARY

mTORC1 suppresses lipolysis in adipose tissue and activates DNL in the liver, whereas FoxO1 has the opposite effect. Individual inputs of either mTORC1 or FoxO1 in the regulation of lipid metabolism may be difficult to evaluate because of the cross talk between these pathways.