Hepatic SIRT1 attenuates hepatic steatosis and controls energy balance in mice by inducing fibroblast growth factor 21

Discovery and characterization of a new class of NAD+-independent SIRT1 activators

The activity of sirtuin 1 (SIRT1, a member of the NAD+-dependent deacetylases family) decreases during aging as NAD+ levels naturally decline, thus increasing the risk of several age-associated diseases. Several sirtuin-activating compounds (STACs) have been developed to counteract the age-associated reduction in SIRT1 activity, and some of them are currently under development in clinical trials. STACs induce SIRT1 activation, either through allosteric activation of the enzyme in the presence of NAD+, or by increasing NAD+ levels by inhibiting its degradation or by supplying a key precursor in biosynthesis. In this study, we have identified (E)-2'-des-methyl sulindac analogues as a novel class of STACs that act also in the absence of NAD+, a peculiar behavior demonstrated through enzymatic and mass spectrometry experiments, both in vitro and in cell lines. The activation of the SIRT1 pathway was confirmed in vivo through gene expression and metabolomics analysis. Our data suggest that these compounds could serve as candidate leads for a novel therapeutic strategy aimed at addressing a key metabolic deficiency that may contribute to metabolic and age-associated diseases.

Regulation and targeting of SREBP-1 in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is an increasing burden on global public health and is associated with enhanced lipogenesis, fatty acid uptake, and lipid metabolic reprogramming. De novo lipogenesis is under the control of the transcription factor sterol regulatory element-binding protein 1 (SREBP-1) and essentially contributes to HCC progression. Here, we summarize the current knowledge on the regulation of SREBP-1 isoforms in HCC based on cellular, animal, and clinical data. Specifically, we (i) address the overarching mechanisms for regulating SREBP-1 transcription, proteolytic processing, nuclear stability, and transactivation and (ii) critically discuss their impact on HCC, taking into account (iii) insights from pharmacological approaches. Emphasis is placed on cross-talk with the phosphatidylinositol-3-kinase (PI3K)-protein kinase B (Akt)-mechanistic target of rapamycin (mTOR) axis, AMP-activated protein kinase (AMPK), protein kinase A (PKA), and other kinases that directly phosphorylate SREBP-1; transcription factors, such as liver X receptor (LXR), peroxisome proliferator-activated receptors (PPARs), proliferator-activated receptor γ co-activator 1 (PGC-1), signal transducers and activators of transcription (STATs), and Myc; epigenetic mechanisms; post-translational modifications of SREBP-1; and SREBP-1-regulatory metabolites such as oxysterols and polyunsaturated fatty acids. By carefully scrutinizing the role of SREBP-1 in HCC development, progression, metastasis, and therapy resistance, we shed light on the potential of SREBP-1-targeting strategies in HCC prevention and treatment.

SLC25A28 Overexpression Promotes Adipogenesis by Reducing ATGL

Adipose tissue dysfunction is seen among obese and type 2 diabetic individuals. Adipocyte proliferation and hypertrophy are the root causes of adipose tissue expansion. Solute carrier family 25 member 28 (SLC25A28) is an iron transporter in the inner mitochondrial membrane. This study is aimed at validating the involvement of SLC25A28 in adipose accumulation by tail vein injection of adenovirus (Ad)-SLC25A28 and Ad-green fluorescent protein viral particles into C57BL/6J mice. After 16 weeks, the body weight of the mice was measured. Subsequently, morphological analysis was performed to establish a high-fat diet (HFD)-induced model. SLC25A28 overexpression accelerated lipid accumulation in white and brown adipose tissue (BAT), enhanced body weight, reduced serum triglyceride (TG), and impaired serum glucose tolerance. The protein expression level of lipogenesis, lipolysis, and serum adipose secretion hormone was evaluated by western blotting. The results showed that adipose TG lipase (ATGL) protein expression was reduced significantly in white and BAT after overexpression SLC25A28 compared to the control group. Moreover, SLC25A28 overexpression inhibited the BAT formation by downregulating UCP-1 and the mitochondrial biosynthesis marker PGC-1α. Serum adiponectin protein expression was unregulated, which was consistent with the expression in inguinal white adipose tissue (iWAT). Remarkably, serum fibroblast growth factor (FGF21) protein expression was negatively related to the expansion of adipose tissue after administrated by Ad-SLC25A28. Data from the current study indicate that SLC25A28 overexpression promotes diet-induced obesity and accelerates lipid accumulation by regulating hormone secretion and inhibiting lipolysis in adipose tissue.

Fibroblast growth factor 21: An emerging pleiotropic regulator of lipid metabolism and the metabolic network

Fibroblast growth factor 21 (FGF21) was originally identified as an important metabolic regulator which plays a crucial physiological role in regulating a variety of metabolic parameters through the metabolic network. As a novel multifunctional endocrine growth factor, the role of FGF21 in the metabolic network warrants extensive exploration. This insight was obtained from the observation that the FGF21-dependent mechanism that regulates lipid metabolism, glycogen transformation, and biological effectiveness occurs through the coordinated participation of the liver, adipose tissue, central nervous system, and sympathetic nerves. This review focuses on the role of FGF21-uncoupling protein 1 (UCP1) signaling in lipid metabolism and how FGF21 alleviates non-alcoholic fatty liver disease (NAFLD). Additionally, this review reveals the mechanism by which FGF21 governs glucolipid metabolism. Recent research on the role of FGF21 in the metabolic network has mostly focused on the crucial pathway of glucolipid metabolism. FGF21 has been shown to have multiple regulatory roles in the metabolic network. Since an adequate understanding of the concrete regulatory pathways of FGF21 in the metabolic network has not been attained, this review sheds new light on the metabolic mechanisms of FGF21, explores how FGF21 engages different tissues and organs, and lays a theoretical foundation for future in-depth research on FGF21-targeted treatment of metabolic diseases.

Research progress on Sirtuins (SIRTs) family modulators

Sirtuins (SIRTs) represent a class of nicotinamide adenine dinucleotide (NAD+)-dependent protein deacetylases that exert a crucial role in cellular signal transduction and various biological processes. The mammalian sirtuins family encompasses SIRT1 to SIRT7, exhibiting therapeutic potential in counteracting cellular aging, modulating metabolism, responding to oxidative stress, inhibiting tumors, and improving cellular microenvironment. These enzymes are intricately linked to the occurrence and treatment of diverse pathological conditions, including cancer, autoimmune diseases, and cardiovascular disorders. Given the significance of histone modification in gene expression and chromatin structure, maintaining the equilibrium of the sirtuins family is imperative for disease prevention and health restoration. Mounting evidence suggests that modulators of SIRTs play a crucial role in treating various diseases and maintaining physiological balance. This review delves into the molecular structure and regulatory functions of the sirtuins family, reviews the classification and historical evolution of SIRTs modulators, offers a systematic overview of existing SIRTs modulation strategies, and elucidates the regulatory mechanisms of SIRTs modulators (agonists and inhibitors) and their clinical applications. The article concludes by summarizing the challenges encountered in SIRTs modulator research and offering insights into future research directions.

The contribution of genetics and epigenetics to MAFLD susceptibility

Metabolic dysfunction-associated fatty liver disease (MAFLD) is the most common liver disease worldwide. The risk of developing MAFLD varies among individuals, due to a combination of environmental inherited and acquired genetic factors. Genome-wide association and next-generation sequencing studies are leading to the discovery of the common and rare genetic determinants of MAFLD. Thanks to the great advances in genomic technologies and bioinformatics analysis, genetic and epigenetic factors involved in the disease can be used to develop genetic risk scores specific for liver-related complications, which can improve risk stratification. Genetic and epigenetic factors lead to the identification of specific sub-phenotypes of MAFLD, and predict the individual response to a pharmacological therapy. Moreover, the variant transcripts and protein themselves represent new therapeutic targets. This review will discuss the current status of research into genetic as well as epigenetic modifiers of MAFLD development and progression.

Role of liver FGF21-KLB signaling in ketogenic diet-induced amelioration of hepatic steatosis

BACKGROUND

The effectiveness of ketogenic diet (KD) in ameliorating fatty liver has been established, although its mechanism is under investigation. Fibroblast growth factor 21 (FGF21) positively regulates obesity-associated metabolic disorders and is elevated by KD. FGF21 conventionally initiates its intracellular signaling via receptor β-klotho (KLB). However, the mechanistic role of FGF21-KLB signaling for KD-ameliorated fatty liver remains unknown. This study aimed to delineate the critical role of FGF21 signaling in the ameliorative effects of KD on hepatic steatosis.

METHODS

Eight-week-old C57BL/6 J mice were fed a chow diet (CD), a high-fat diet (HFD), or a KD for 16 weeks. Adeno-associated virus-mediated liver-specific KLB knockdown mice and control mice were fed a KD for 16 weeks. Phenotypic assessments were conducted during and after the intervention. We investigated the mechanism underlying KD-alleviated hepatic steatosis using multi-omics and validated the expression of key genes.

RESULTS

KD improved hepatic steatosis by upregulating fatty acid oxidation and downregulating lipogenesis. Transcriptional analysis revealed that KD dramatically activated FGF21 pathway, including KLB and fibroblast growth factor receptor 1 (FGFR1). Impairing liver FGF21 signaling via KLB knockdown diminished the beneficial effects of KD on ameliorating fatty liver, insulin resistance, and regulating lipid metabolism.

CONCLUSION

KD demonstrates beneficial effects on diet-induced metabolic disorders, particularly on hepatic steatosis. Liver FGF21-KLB signaling plays a critical role in the KD-induced amelioration of hepatic steatosis.

Neonatal resveratrol administration promotes skeletal muscle growth and insulin sensitivity in intrauterine growth-retarded suckling piglets associated with activation of FGF21-AMPKα pathway

BACKGROUND

Skeletal muscle is a major insulin-sensitive tissue with a pivotal role in modulating glucose homeostasis. This study aimed to investigate the effect of resveratrol (RES) intervention during the suckling period on skeletal muscle growth and insulin sensitivity of neonates with intrauterine growth retardation (IUGR) in a pig model.

RESULTS

Twelve pairs of normal birth weight (NBW) and IUGR neonatal male piglets were selected. The NBW and IUGR piglets were fed basal formula milk diet or identical diet supplemented with 0.1% RES from 7 to 21 days of age. Myofiber growth and differentiation, inflammation and insulin sensitivity in skeletal muscle were assessed. Early RES intervention promoted myofiber growth and maturity in IUGR piglets by ameliorating the myogenesis process and increasing thyroid hormone level. Administering RES also reduced triglyceride concentration in skeletal muscle of IUGR piglets, along with decreased inflammatory response, increased plasma fibroblast growth factor 21 (FGF21) concentration and improved insulin signaling. Meanwhile, the improvement of insulin sensitivity by RES may be partly regulated by activation of the FGF21/AMP-activated protein kinase α/sirtuin 1/peroxisome proliferator activated receptor-γ coactivator-1α pathway.

CONCLUSION

Our results suggest that RES has beneficial effects in promoting myofiber growth and maturity and increasing skeletal muscle insulin sensitivity in IUGR piglets, which open a novel field of application of RES in IUGR infants for improving postnatal metabolic adaptation. © 2023 Society of Chemical Industry.

Inhibitory protein-protein interactions of the SIRT1 deacetylase are choreographed by post-translational modification

Regulation of SIRT1 activity is vital to energy homeostasis and plays important roles in many diseases. We previously showed that insulin triggers the epigenetic regulator DBC1 to prime SIRT1 for repression by the multifunctional trafficking protein PACS-2. Here, we show that liver DBC1/PACS-2 regulates the diurnal inhibition of SIRT1, which is critically important for insulin-dependent switch in fuel metabolism from fat to glucose oxidation. We present the x-ray structure of the DBC1 S1-like domain that binds SIRT1 and an NMR characterization of how the SIRT1 N-terminal region engages DBC1. This interaction is inhibited by acetylation of K112 of DBC1 and stimulated by the insulin-dependent phosphorylation of human SIRT1 at S162 and S172, catalyzed sequentially by CK2 and GSK3, resulting in the PACS-2-dependent inhibition of nuclear SIRT1 enzymatic activity and translocation of the deacetylase in the cytoplasm. Finally, we discuss how defects in the DBC1/PACS-2-controlled SIRT1 inhibitory pathway are associated with disease, including obesity and non-alcoholic fatty liver disease.

Lipodystrophy in methylmalonic acidemia associated with elevated FGF21 and abnormal methylmalonylation

A distinct adipose tissue distribution pattern was observed in patients with methylmalonyl-CoA mutase deficiency, an inborn error of branched-chain amino acid (BCAA) metabolism, characterized by centripetal obesity with proximal upper and lower extremity fat deposition and paucity of visceral fat, that resembles familial multiple lipomatosis syndrome. To explore brown and white fat physiology in methylmalonic acidemia (MMA), body composition, adipokines, and inflammatory markers were assessed in 46 patients with MMA and 99 matched controls. Fibroblast growth factor 21 levels were associated with acyl-CoA accretion, aberrant methylmalonylation in adipose tissue, and an attenuated inflammatory cytokine profile. In parallel, brown and white fat were examined in a liver-specific transgenic MMA mouse model (Mmut-/- TgINS-Alb-Mmut). The MMA mice exhibited abnormal nonshivering thermogenesis with whitened brown fat and had an ineffective transcriptional response to cold stress. Treatment of the MMA mice with bezafibrates led to clinical improvement with beiging of subcutaneous fat depots, which resembled the distribution seen in the patients. These studies defined what we believe to be a novel lipodystrophy phenotype in patients with defects in the terminal steps of BCAA oxidation and demonstrated that beiging of subcutaneous adipose tissue in MMA could readily be induced with small molecules.

Circadian Regulation of Endocrine Fibroblast Growth Factors on Systemic Energy Metabolism

The circadian clock is an endogenous biochemical timing system that coordinates the physiology and behavior of organisms to earth's ∼24-hour circadian day/night cycle. The central circadian clock synchronized by environmental cues hierarchically entrains peripheral clocks throughout the body. The circadian system modulates a wide variety of metabolic signaling pathways to maintain whole-body metabolic homeostasis in mammals under changing environmental conditions. Endocrine fibroblast growth factors (FGFs), namely FGF15/19, FGF21, and FGF23, play an important role in regulating systemic metabolism of bile acids, lipids, glucose, proteins, and minerals. Recent evidence indicates that endocrine FGFs function as nutrient sensors that mediate multifactorial interactions between peripheral clocks and energy homeostasis by regulating the expression of metabolic enzymes and hormones. Circadian disruption induced by environmental stressors or genetic ablation is associated with metabolic dysfunction and diurnal disturbances in FGF signaling pathways that contribute to the pathogenesis of metabolic diseases. Time-restricted feeding strengthens the circadian pattern of metabolic signals to improve metabolic health and prevent against metabolic diseases. Chronotherapy, the strategic timing of medication administration to maximize beneficial effects and minimize toxic effects, can provide novel insights into linking biologic rhythms to drug metabolism and toxicity within the therapeutical regimens of diseases. Here we review the circadian regulation of endocrine FGF signaling in whole-body metabolism and the potential effect of circadian dysfunction on the pathogenesis and development of metabolic diseases. We also discuss the potential of chrononutrition and chronotherapy for informing the development of timing interventions with endocrine FGFs to optimize whole-body metabolism in humans. SIGNIFICANCE STATEMENT: The circadian timing system governs physiological, metabolic, and behavioral functions in living organisms. The endocrine fibroblast growth factor (FGF) family (FGF15/19, FGF21, and FGF23) plays an important role in regulating energy and mineral metabolism. Endocrine FGFs function as nutrient sensors that mediate multifactorial interactions between circadian clocks and metabolic homeostasis. Chronic disruption of circadian rhythms increases the risk of metabolic diseases. Chronological interventions such as chrononutrition and chronotherapy provide insights into linking biological rhythms to disease prevention and treatment.

Involvement of the vagus nerve and hepatic gene expression in serum adiponectin concentrations in mice

Several humoral factors, such as adiponectin and urate, have been suggested to affect metabolic syndromes. Previously, we reported a reduction in blood adiponectin concentrations after a high-fructose diet partially via the vagus nerve in rats. Although a lithogenic diet (LD), i.e., supplementation of a normal control diet (CT) with 0.6% cholesterol and 0.2% sodium cholate, reduced blood adiponectin concentrations, the involvement of the vagus nerve in this mechanism remains unclear. To estimate the involvement of the vagus nerve in the regulation of blood adiponectin concentrations using an LD, male imprinting control region mice that had been vagotomized (HVx) or only laparotomized (Sham) were administered a CT or an LD for 10 weeks. Serum adiponectin concentrations in the Sham-LD, HVx-CT, and HVx-LD groups were reduced by half compared with the Sham-CT group. The hepatic mRNA levels of fibroblast growth factor 21 (Fgf21), which reportedly stimulates adiponectin secretion from white adipose tissue, were lower in the LD groups compared with the CT groups. HepG2 hepatoma cells showed that various bile acids reduced the mRNA expression of FGF21. Moreover, the LD increased serum urate concentrations and reduced hepatic expressions of the acyl-CoA oxidase 1 (Acox1) mRNA and glucokinase, suggesting insufficient regeneration of ATP from AMP. In conclusion, serum adiponectin concentration may be regulated via the vagus nerve in normal mice, whereas a reduction of hepatic Fgf21 mRNA by bile acids may also lower serum adiponectin levels. Moreover, the LD may promote hepatic AMP accumulation and subsequently increase the serum urate concentration in mice.

Trodusquemine (MSI-1436) Restores Metabolic Flexibility and Mitochondrial Dynamics in Insulin-Resistant Equine Hepatic Progenitor Cells (HPCs)

Equine metabolic syndrome (EMS) is a significant global health concern in veterinary medicine. There is increasing interest in utilizing molecular agents to modulate hepatocyte function for potential clinical applications. Recent studies have shown promising results in inhibiting protein tyrosine phosphatase (PTP1B) to maintain cell function in various models. In this study, we investigated the effects of the inhibitor Trodusquemine (MSI-1436) on equine hepatic progenitor cells (HPCs) under lipotoxic conditions. We examined proliferative activity, glucose uptake, and mitochondrial morphogenesis. Our study found that MSI-1436 promotes HPC entry into the cell cycle and protects them from palmitate-induced apoptosis by regulating mitochondrial dynamics and biogenesis. MSI-1436 also increases glucose uptake and protects HPCs from palmitate-induced stress by reorganizing the cells' morphological architecture. Furthermore, our findings suggest that MSI-1436 enhances 2-NBDG uptake by increasing the expression of SIRT1, which is associated with liver insulin sensitivity. It also promotes mitochondrial dynamics by modulating mitochondria quantity and morphotype as well as increasing the expression of PINK1, MFN1, and MFN2. Our study provides evidence that MSI-1436 has a positive impact on equine hepatic progenitor cells, indicating its potential therapeutic value in treating EMS and insulin dysregulation.

Linalool attenuates lipid accumulation and oxidative stress in metabolic dysfunction-associated steatotic liver disease via Sirt1/Akt/PPRA-α/AMPK and Nrf-2/HO-1 signaling pathways

INTRODUCTION

Linalool is a monoterpene that occurs naturally in various aromatic plants and is identified in our previous study as a potential candidate for protection against high-fat diet (HFD)-induced metabolic dysfunction-associated steatotic liver disease (MASLD). However, little is known about its direct effects on hepatic lipid metabolism and oxidative stress. Therefore, this study aims to investigate the therapeutic effect of linalool against MASLD and the underlying mechanism.

METHODS

To establish a rat model of MASLD, male Wistar rats were fed HFD for 16 weeks and orally administered linalool (100 mg/kg body weight) for 45 days starting from week 14.

RESULTS

Linalool significantly reduced HFD-induced liver lipid accumulation and restored altered adipokine levels. Mechanistically, linalool downregulated the mRNA expression of sterol regulatory element binding protein 1 and its lipogenesis target genes fatty acid synthase and acetyl-CoA carboxylase, and upregulated the mRNA expression of genes involved in fatty acid oxidation (peroxisome proliferator-activated receptor (PPAR)-alpha [PPAR-α], lipoprotein lipase and protein kinase B [Akt]) as well as the upstream mediators sirtuin 1 (Sirt1) and AMP-activated protein kinase (AMPK) in the liver of MASLD rats. In addition, linalool also curbed oxidative stress by increasing antioxidant enzymes and activating nuclear erythroid-2-related factor 2 (Nrf-2) and its downstream target genes involved in antioxidant properties.

CONCLUSION

Therefore, this study concludes that linalool attenuates lipid accumulation in the liver by inhibiting de novo lipogenesis, promoting fatty acid oxidation, and attenuating oxidative stress by regulating Sirt1/Akt/PPRA-α/AMPK and Nrf-2/ HO-1 signaling pathways.

Sirtuin 1 alleviates alcoholic liver disease by inhibiting HMGB1 acetylation and translocation

Background

Alcoholic liver disease (ALD) encompasses a spectrum of liver disorders resulting from prolonged alcohol consumption and is influenced by factors such as oxidative stress, inflammation, and apoptosis. High Mobility Group Box 1 (HMGB1) plays a pivotal role in ALD due to its involvement in inflammation and immune responses. Another key factor, Sirtuin 1 (SIRT1), an NAD+-dependent deacetylase, is known for its roles in cellular stress responses and metabolic regulation. Despite individual studies on HMGB1 and SIRT1 in ALD, their specific molecular interactions and combined effects on disease advancement remain incompletely understood.

Methods

Alcohol-induced liver injury (ALI) models were established using HepG2 cells and male C57BL/6 mice. HMGB1 and SIRT1 expressions were assessed at the mRNA and protein levels usingreverse transcription-quantitative polymerase chain reaction, western blot, and immunofluorescence staining. The physical interaction between HMGB1 and SIRT1 was investigated using co-immunoprecipitation and immunofluorescence co-expression analyses. Cellular viability was evaluated using the CCK-8 assay.

Results

In patients with clinical ALI, HMGB1 mRNA levels were elevated, while SIRT1 expression was reduced, indicating a negative correlation between the two. ALI models were successfully established in cells and mice, as evidenced by increased markers of cellular and liver damage. HMGB1 acetylation and translocation were observed in both ALI cells and mouse models. Treatment with the SIRT1 agonist, SRT1720, reversed the upregulation of HMGB1 acetylation, nuclear translocation, and release in the ethyl alcohol (EtOH) group. Furthermore, SIRT1 significantly attenuated ALI. Importantly, in vivo binding was confirmed between SIRT1 and HMGB1.

Conclusions

SIRT1 alleviates HMGB1 acetylation and translocation, thereby ameliorating ALI.

Treatment with recombinant Sirt1 rewires the cardiac lipidome and rescues diabetes-related metabolic cardiomyopathy

BACKGROUND

Metabolic cardiomyopathy (MCM), characterized by intramyocardial lipid accumulation, drives the progression to heart failure with preserved ejection fraction (HFpEF). Although evidence suggests that the mammalian silent information regulator 1 (Sirt1) orchestrates myocardial lipid metabolism, it is unknown whether its exogenous administration could avoid MCM onset. We investigated whether chronic treatment with recombinant Sirt1 (rSirt1) could halt MCM progression.

METHODS

db/db mice, an established model of MCM, were supplemented with intraperitoneal rSirt1 or vehicle for 4 weeks and compared with their db/ + heterozygous littermates. At the end of treatment, cardiac function was assessed by cardiac ultrasound and left ventricular samples were collected and processed for molecular analysis. Transcriptional changes were evaluated using a custom PCR array. Lipidomic analysis was performed by mass spectrometry. H9c2 cardiomyocytes exposed to hyperglycaemia and treated with rSirt1 were used as in vitro model of MCM to investigate the ability of rSirt1 to directly target cardiomyocytes and modulate malondialdehyde levels and caspase 3 activity. Myocardial samples from diabetic and nondiabetic patients were analysed to explore Sirt1 expression levels and signaling pathways.

RESULTS

rSirt1 treatment restored cardiac Sirt1 levels and preserved cardiac performance by improving left ventricular ejection fraction, fractional shortening and diastolic function (E/A ratio). In left ventricular samples from rSirt1-treated db/db mice, rSirt1 modulated the cardiac lipidome: medium and long-chain triacylglycerols, long-chain triacylglycerols, and triacylglycerols containing only saturated fatty acids were reduced, while those containing docosahexaenoic acid were increased. Mechanistically, several genes involved in lipid trafficking, metabolism and inflammation, such as Cd36, Acox3, Pparg, Ncoa3, and Ppara were downregulated by rSirt1 both in vitro and in vivo. In humans, reduced cardiac expression levels of Sirt1 were associated with higher intramyocardial triacylglycerols and PPARG-related genes.

CONCLUSIONS

In the db/db mouse model of MCM, chronic exogenous rSirt1 supplementation rescued cardiac function. This was associated with a modulation of the myocardial lipidome and a downregulation of genes involved in lipid metabolism, trafficking, inflammation, and PPARG signaling. These findings were confirmed in the human diabetic myocardium. Treatments that increase Sirt1 levels may represent a promising strategy to prevent myocardial lipid abnormalities and MCM development.

The pan-liver network theory: From traditional chinese medicine to western medicine

In traditional Chinese medicine (TCM), the liver is the "general organ" that is responsible for governing/maintaining the free flow of qi over the entire body and storing blood. According to the classic five elements theory, zang-xiang theory, yin-yang theory, meridians and collaterals theory, and the five-viscera correlation theory, the liver has essential relationships with many extrahepatic organs or tissues, such as the mother-child relationships between the liver and the heart, and the yin-yang and exterior-interior relationships between the liver and the gallbladder. The influences of the liver to the extrahepatic organs or tissues have been well-established when treating the extrahepatic diseases from the perspective of modulating the liver by using the ancient classic prescriptions of TCM and the acupuncture and moxibustion. In modern medicine, as the largest solid organ in the human body, the liver has the typical functions of filtration and storage of blood; metabolism of carbohydrates, fats, proteins, hormones, and foreign chemicals; formation of bile; storage of vitamins and iron; and formation of coagulation factors. The liver also has essential endocrine function, and acts as an immunological organ due to containing the resident immune cells. In the perspective of modern human anatomy, physiology, and pathophysiology, the liver has the organ interactions with the extrahepatic organs or tissues, for example, the gut, pancreas, adipose, skeletal muscle, heart, lung, kidney, brain, spleen, eyes, skin, bone, and sexual organs, through the circulation (including hemodynamics, redox signals, hepatokines, metabolites, and the translocation of microbiota or its products, such as endotoxins), the neural signals, or other forms of pathogenic factors, under normal or diseases status. The organ interactions centered on the liver not only influence the homeostasis of these indicated organs or tissues, but also contribute to the pathogenesis of cardiometabolic diseases (including obesity, type 2 diabetes mellitus, metabolic [dysfunction]-associated fatty liver diseases, and cardio-cerebrovascular diseases), pulmonary diseases, hyperuricemia and gout, chronic kidney disease, and male and female sexual dysfunction. Therefore, based on TCM and modern medicine, the liver has the bidirectional interaction with the extrahepatic organ or tissue, and this established bidirectional interaction system may further interact with another one or more extrahepatic organs/tissues, thus depicting a complex "pan-hepatic network" model. The pan-hepatic network acts as one of the essential mechanisms of homeostasis and the pathogenesis of diseases.

Targeting hepatic serine-arginine protein kinase 2 ameliorates alcohol-associated liver disease by alternative splicing control of lipogenesis

BACKGROUND AND AIMS

Lipid accumulation induced by alcohol consumption is not only an early pathophysiological response but also a prerequisite for the progression of alcohol-associated liver disease (ALD). Alternative splicing regulates gene expression and protein diversity; dysregulation of this process is implicated in human liver diseases. However, how the alternative splicing regulation of lipid metabolism contributes to the pathogenesis of ALD remains undefined.

APPROACH AND RESULTS

Serine-arginine-rich protein kinase 2 (SRPK2), a key kinase controlling alternative splicing, is activated in hepatocytes in response to alcohol, in mice with chronic-plus-binge alcohol feeding, and in patients with ALD. Such induction activates sterol regulatory element-binding protein 1 and promotes lipogenesis in ALD. Overexpression of FGF21 in transgenic mice abolishes alcohol-mediated induction of SRPK2 and its associated steatosis, lipotoxicity, and inflammation; these alcohol-induced pathologies are exacerbated in FGF21 knockout mice. Mechanistically, SRPK2 is required for alcohol-mediated impairment of serine-arginine splicing factor 10, which generates exon 7 inclusion in lipin 1 and triggers concurrent induction of lipogenic regulators-lipin 1β and sterol regulatory element-binding protein 1. FGF21 suppresses alcohol-induced SRPK2 accumulation through mammalian target of rapamycin complex 1 inhibition-dependent degradation of SRPK2. Silencing SRPK2 rescues alcohol-induced splicing dysregulation and liver injury in FGF21 knockout mice.

CONCLUSIONS

These studies reveal that (1) the regulation of alternative splicing by SRPK2 is implicated in lipogenesis in humans with ALD; (2) FGF21 is a key hepatokine that ameliorates ALD pathologies largely by inhibiting SRPK2; and (3) targeting SRPK2 signaling by FGF21 may offer potential therapeutic approaches to combat ALD.

SIRT1 activation promotes energy homeostasis and reprograms liver cancer metabolism

BACKGROUND

Cancer cells are characterized by uncontrolled cell proliferation and impaired bioenergetics. Sirtuins are a family of highly conserved enzymes that play a fundamental role in energy metabolism regulation. SIRT1, in particular, drives many physiological stress responses and metabolic pathways following nutrient deprivation. We previously showed that SIRT1 activation using SCIC2.1 was able to attenuate genotoxic response and senescence. Here, we report that in hepatocellular carcinoma (HCC) cells under glucose-deprived conditions, SCIC2.1 treatment induced overexpression of SIRT1, SIRT3, and SIRT6, modulating metabolic response.

METHODS

Flow cytometry was used to analyze the cell cycle. The MTT assay and xCELLigence system were used to measure cell viability and proliferation. In vitro enzymatic assays were carried out as directed by the manufacturer, and the absorbance was measured with an automated Infinite M1000 reader. Western blotting and immunoprecipitation were used to evaluate the expression of various proteins described in this study. The relative expression of genes was studied using real-time PCR. We employed a Seahorse XF24 Analyzer to determine the metabolic state of the cells. Oil Red O staining was used to measure lipid accumulation.

RESULTS

SCIC2.1 significantly promoted mitochondrial biogenesis via the AMPK-p53-PGC1α pathway and enhanced mitochondrial ATP production under glucose deprivation. SIRT1 inhibition by Ex-527 further supported our hypothesis that metabolic effects are dependent on SIRT1 activation. Interestingly, SCIC2.1 reprogrammed glucose metabolism and fatty acid oxidation for bioenergetic circuits by repressing de novo lipogenesis. In addition, SCIC2.1-mediated SIRT1 activation strongly modulated antioxidant response through SIRT3 activation, and p53-dependent stress response via indirect recruitment of SIRT6.

CONCLUSION

Our results show that SCIC2.1 is able to promote energy homeostasis, attenuating metabolic stress under glucose deprivation via activation of SIRT1. These findings shed light on the metabolic action of SIRT1 in the pathogenesis of HCC and may help determine future therapies for this and, possibly, other metabolic diseases.

Nicotinamide riboside and pterostilbene reduces markers of hepatic inflammation in NAFLD: A double-blind, placebo-controlled clinical trial

BACKGROUND AND AIMS

The prevalence of NAFLD is increasing globally and on a path to becoming the most frequent cause of chronic liver disease. Strategies for the prevention and treatment of NAFLD are urgently needed.

APPROACH AND RESULTS

A 6-month prospective, randomized, double-blind, placebo-controlled clinical trial was conducted to assess the efficacy of daily NRPT (commercially known as Basis, a combination of nicotinamide riboside and pterostilbene) supplementation in 111 adults with NAFLD. The study consisted of three arms: placebo, recommended daily dose of NRPT (NRPT 1×), and a double dose of NRPT (NRPT 2×). NRPT appeared safe and well tolerated. At the end of the study, no significant change was seen in the primary endpoint of hepatic fat fraction with respect to placebo. However, among prespecified secondary outcomes, a time-dependent decrease in the circulating levels of the liver enzymes alanine aminotransferase (ALT) and gamma-glutamyltransferase (GGT) was observed in the NRPT 1× group, and this decrease was significant with respect to placebo. Furthermore, a significant decrease in the circulating levels of the toxic lipid ceramide 14:0 was also observed in the NRPT 1× group versus placebo, and this decrease was associated with a decrease in ALT in individuals of this group. A dose-dependent effect was not observed with respect to ALT, GGT, or ceramide 14:0 in the NRPT 2× group.

CONCLUSIONS

This study demonstrates that NRPT at the recommended dose is safe and may hold promise in lowering markers of hepatic inflammation in patients with NAFLD.

Fibroblast growth factor 21 in metabolic syndrome

Metabolic syndrome is a complex metabolic disorder that often clinically manifests as obesity, insulin resistance/diabetes, hyperlipidemia, and hypertension. With the development of social and economic systems, the incidence of metabolic syndrome is increasing, bringing a heavy medical burden. However, there is still a lack of effective prevention and treatment strategies. Fibroblast growth factor 21 (FGF21) is a member of the human FGF superfamily and is a key protein involved in the maintenance of metabolic homeostasis, including reducing fat mass and lowering hyperglycemia, insulin resistance and dyslipidemia. Here, we review the current regulatory mechanisms of FGF21, summarize its role in obesity, diabetes, hyperlipidemia, and hypertension, and discuss the possibility of FGF21 as a potential target for the treatment of metabolic syndrome.

Resveratrol intervention attenuates chylomicron secretion via repressing intestinal FXR-induced expression of scavenger receptor SR-B1

Two common features of dietary polyphenols have hampered our mechanistic understanding of their beneficial effects for decades: targeting multiple organs and extremely low bioavailability. We show here that resveratrol intervention (REV-I) in high-fat diet (HFD)-challenged male mice inhibits chylomicron secretion, associated with reduced expression of jejunal but not hepatic scavenger receptor class B type 1 (SR-B1). Intestinal mucosa-specific SR-B1-/- mice on HFD-challenge exhibit improved lipid homeostasis but show virtually no further response to REV-I. SR-B1 expression in Caco-2 cells cannot be repressed by pure resveratrol compound while fecal-microbiota transplantation from mice on REV-I suppresses jejunal SR-B1 in recipient mice. REV-I reduces fecal levels of bile acids and activity of fecal bile-salt hydrolase. In Caco-2 cells, chenodeoxycholic acid treatment stimulates both FXR and SR-B1. We conclude that gut microbiome is the primary target of REV-I, and REV-I improves lipid homeostasis at least partially via attenuating FXR-stimulated gut SR-B1 elevation.

Independent, but not co-supplementation, with nitrate and resveratrol improves glucose tolerance and reduces markers of cellular stress in high-fat-fed male mice

Independent supplementation with nitrate (NIT) and resveratrol (RSV) enriches various aspects of mitochondrial biology in key metabolic tissues. Although RSV is known to activate Sirt1 and initiate mitochondrial biogenesis, the metabolic benefits elicited by dietary nitrate appear to be dependent on 5'-adenosine monophosphate-activated protein kinase (AMPK)-mediated signaling events, a process also linked to the activation of Sirt1. Although the benefits of individual supplementation with these compounds have been characterized, it is unknown if co-supplementation may produce superior metabolic adaptations. Thus, we aimed to determine if treatment with combined +NIT and +RSV (+RN) could additively alter metabolic adaptations in the presence of a high-fat diet (HFD). Both +RSV and +NIT improved glucose tolerance compared with HFD (P < 0.05); however, this response was attenuated following combined +RN supplementation. Within skeletal muscle, all supplements increased mitochondrial ADP sensitivity compared with HFD (P < 0.05), without altering mitochondrial content. Although +RSV and +NIT decreased hepatic lipid deposition compared with HFD (P < 0.05), this effect was abolished with +RN, which aligned with significant reductions in Sirt1 protein content (P < 0.05) after combined treatment, in the absence of changes to mitochondrial content or function. Within epididymal white adipose tissue (eWAT), all supplements reduced crown-like structure accumulation compared with HFD (P < 0.0001) and mitochondrial reactive oxygen species (ROS) emission (P < 0.05), alongside reduced adipocyte cross-sectional area (CSA) (P < 0.05), with the greatest effect observed after +RN treatment (P = 0.0001). Although the present data suggest additive changes in adipose tissue metabolism after +RN treatment, concomitant impairments in hepatic lipid homeostasis appear to prevent improvements in whole body glucose homeostasis observed with independent treatment, which may be Sirt1 dependent.

Cardiac Hepatopathy: New Perspectives on Old Problems through a Prism of Endogenous Metabolic Regulations by Hepatokines

Cardiac hepatopathy refers to acute or chronic liver damage caused by cardiac dysfunction in the absence of any other possible causative reasons of liver injury. There is a large number of evidence of the fact that cardiac hepatopathy is associated with poor clinical outcomes in patients with acute or actually decompensated heart failure (HF). However, the currently dominated pathophysiological background does not explain a role of metabolic regulative proteins secreted by hepatocytes in progression of HF, including adverse cardiac remodeling, kidney injury, skeletal muscle dysfunction, osteopenia, sarcopenia and cardiac cachexia. The aim of this narrative review was to accumulate knowledge of hepatokines (adropin; fetuin-A, selenoprotein P, fibroblast growth factor-21, and alpha-1-microglobulin) as adaptive regulators of metabolic homeostasis in patients with HF. It is suggested that hepatokines play a crucial, causative role in inter-organ interactions and mediate tissue protective effects counteracting oxidative stress, inflammation, mitochondrial dysfunction, apoptosis and necrosis. The discriminative potencies of hepatokines for HF and damage of target organs in patients with known HF is under on-going scientific discussion and requires more investigations in the future.

A Randomized Trial on Resveratrol Supplement Affecting Lipid Profile and Other Metabolic Markers in Subjects with Dyslipidemia

Resveratrol is a polyphenol with a well-established beneficial effect on dyslipidemia and hyperuricemia in preclinical experiments. Nonetheless, its efficacy and dose-response relationship in clinical trials remains unclear. This study examined whether resveratrol supplement improves the serum lipid profile and other metabolic markers in a dose-response manner in individuals with dyslipidemia. A total of 168 subjects were randomly assigned to placebo (n = 43) and resveratrol treatment groups of 100 mg/d (n = 41), 300 mg/d (n = 43), and 600 mg/d (n = 41). Anthropometric and biochemical parameters were analyzed at baseline and 4 and 8 weeks. Resveratrol supplementation for 8 weeks did not significantly change the lipid profile compared with the placebo. However, a significant decrease of serum uric acid was observed at 8 weeks in 300 mg/d (-23.60 ± 61.53 μmol/L, p < 0.05) and 600 mg/d resveratrol groups (-24.37 ± 64.24 μmol/L, p < 0.01) compared to placebo (8.19 ± 44.60 μmol/L). Furthermore, xanthine oxidase (XO) activity decreased significantly in the 600 mg/d resveratrol group (-0.09 ± 0.29 U/mL, p < 0.05) compared with placebo (0.03 ± 0.20 U/mL) after 8 weeks. The reduction of uric acid and XO activity exhibited a dose-response relationship (p for trend, <0.05). Furthermore, a marked correlation was found between the changes in uric acid and XO activity in the resveratrol groups (r = 0.254, p < 0.01). Resveratrol (10 μmol/L) treatment to HepG2 cells significantly reduced the uric acid levels and intracellular XO activity. Nevertheless, we failed to detect significant differences in glucose, insulin, or oxidative stress biomarkers between the resveratrol groups and placebo. In conclusion, resveratrol supplementation for 8 weeks had no significant effect on lipid profile but decreased uric acid in a dose-response manner, possibly due to XO inhibition in subjects with dyslipidemia. The trial was registered on ClinicalTrials.gov (NCT04886297).

Vanin 1 Gene Role in Modulation of iNOS/MCP-1/TGF-β1 Signaling Pathway in Obese Diabetic Patients

INTRODUCTION

Cysteamine, a powerful endogenous antioxidant, is produced mostly by the vanin-1 with pantetheinase activity. With regard to glycemic, inflammatory, and redox factors, the current study sought to evaluate the association between the expression of the vanin-1 gene, oxidative stress, and inflammatory and iNOS signaling pathway in obese diabetic patients.

METHODS

We enrolled 67 male subjects with an average age of 53.5 ± 5.0 years, divided into 4 groups according to the WHO guideline. We determined their plasma levels of glucose, insulin, IRI, HbA1c, TC, TG, HDL-C, TNF- α, MCP-1, TGF-β1, SOD, CAT, and TBARs, as well as expression of the iNOS and Vanin1 genes.

RESULTS

Overweight and obese class I and II diabetics had significantly higher levels of plasma glucose, insulin, HbA1c, TNF-α, MCP-1, TGF-β1, CAT, and TBAR as well as iNOS and vanin-1 gene expression compared to healthy control individuals. In addition, as compared to healthy control individuals, overweight obese class I and II diabetics' plasma HDL-C levels and blood SOD activity were significantly lower. In addition, ultrasound and computed tomography showed that the presence of a mild obscuring fatty liver with mild hepatic echogenicity appeared in overweight, class I and II obese diabetic patients.

CONCLUSION

These findings provide important information for understanding the correlation between Vanin 1 and glycemic, inflammatory, and redox factors in obese patients. Furthermore, US and CT analysis were performed to visualize the observed images of fatty liver due to obesity.

Ketogenic Diet Increases Serum and White Adipose Tissue SIRT1 Expression in Mice

Overnutrition and its sequelae have become a global concern due to the increasing incidence of obesity and insulin resistance. A ketogenic diet (KD) is widely used as a dietary treatment for metabolic disorders. Sirtuin1 (SIRT1), a metabolic sensor which regulates fat homeostasis, is modulated by dietary interventions. However, the influence of nutritional ketosis on SIRT1 is still debated. We examined the effect of KD on adipose tissue, liver, and serum levels of SIRT1 in mice. Adult C57BL/6J male mice were randomly assigned to two isocaloric dietary groups and fed with either high-fat KD or normal chow (NC) for 4 weeks. Serum SIRT1, beta-hydroxybutyrate (βHB), glucose, and triglyceride levels, as well as SIRT1 expression in visceral (VAT), subcutaneous (SAT), and brown (BAT) adipose tissues, and in the liver, were measured. KD-fed mice showed an increase in serum βHB in parallel with serum SIRT1 (r = 0.732, p = 0.0156), and increased SIRT1 protein expression in SAT and VAT. SIRT1 levels remained unchanged in BAT and in the liver, which developed steatosis. Normal glycemia and triglycerides were observed. Under a KD, serum and white fat phenotypes show higher SIRT1, suggesting that one of the molecular mechanisms underlying a KD's potential benefits on metabolic health involves a synergistic interaction with SIRT1.

SIRT6: therapeutic target for nonalcoholic fatty liver disease

Recently, Hou et al. shifted the research focus from the function of nuclear sirtuin (SIRT)6 to that of cytoplasmic SIRT6, which deacetylates and activates long-chain acyl-CoA synthase 5 (ACSL5). Their findings provide mechanistic insight into the role of cytoplasmic SIRT6 in fatty acid oxidation, acting as a therapeutic target for combating nonalcoholic fatty liver disease (NAFLD).

Reduction of Obesity and Insulin Resistance through Dual Targeting of VAT and BAT by a Novel Combination of Metabolic Cofactors

Obesity is an epidemic disease worldwide, characterized by excessive fat accumulation associated with several metabolic perturbations, such as metabolic syndrome, insulin resistance, hypertension, and dyslipidemia. To improve this situation, a specific combination of metabolic cofactors (MC) (betaine, N-acetylcysteine, L-carnitine, and nicotinamide riboside) was assessed as a promising treatment in a high-fat diet (HFD) mouse model. Obese animals were distributed into two groups, orally treated with the vehicle (obese + vehicle) or with the combination of metabolic cofactors (obese + MC) for 4 weeks. Body and adipose depots weights; insulin and glucose tolerance tests; indirect calorimetry; and thermography assays were performed at the end of the intervention. Histological analysis of epidydimal white adipose tissue (EWAT) and brown adipose tissue (BAT) was carried out, and the expression of key genes involved in both fat depots was characterized by qPCR. We demonstrated that MC supplementation conferred a moderate reduction of obesity and adiposity, an improvement in serum glucose and lipid metabolic parameters, an important improvement in lipid oxidation, and a decrease in adipocyte hypertrophy. Moreover, MC-treated animals presented increased adipose gene expression in EWAT related to lipolysis and fatty acid oxidation. Furthermore, MC supplementation reduced glucose intolerance and insulin resistance, with an increased expression of the glucose transporter Glut4; and decreased fat accumulation in BAT, raising non-shivering thermogenesis. This treatment based on a specific combination of metabolic cofactors mitigates important pathophysiological characteristics of obesity, representing a promising clinical approach to this metabolic disease.

Sirtuins: Key players in obesity-associated adipose tissue remodeling

Obesity, a complex disease involving an excessive amount of body fat and a major threat to public health all over the world, is the determining factor of the onset and development of metabolic disorders, including type 2 diabetes, cardiovascular diseases, and non-alcoholic fatty liver disease. Long-term overnutrition results in excessive expansion and dysfunction of adipose tissue, inflammatory responses and over-accumulation of extracellular matrix in adipose tissue, and ectopic lipid deposit in other organs, termed adipose tissue remodeling. The mammalian Sirtuins (SIRT1-7) are a family of conserved NAD⁺-dependent protein deacetylases. Mounting evidence has disclosed that Sirtuins and their prominent substrates participate in a variety of physiological and pathological processes, including cell cycle regulation, mitochondrial biogenesis and function, glucose and lipid metabolism, insulin action, inflammatory responses, and energy homeostasis. In this review, we provided up-to-date and comprehensive knowledge about the roles of Sirtuins in adipose tissue remodeling, focusing on the fate of adipocytes, lipid mobilization, adipose tissue inflammation and fibrosis, and browning of adipose tissue, and we summarized the clinical trials of Sirtuin activators and inhibitors in treating metabolic diseases, which might shed light on new therapeutic strategies for obesity and its associated metabolic diseases.

Fibroblast growth factor 21 and dietary interventions: what we know and what we need to know next

Dietary interventions include the change of dietary styles, such as fasting and dietary or nutrient restrictions; or the addition of plant-derived compounds (such as polyphenols known as curcumin, resveratrol, or anthocyanin, or other nutraceuticals) into the diet. During the past a few decades, large number of studies have demonstrated therapeutic activities of these dietary interventions on metabolic and other diseases in human subjects or various animal models. Mechanisms underlying those versatile therapeutic activities, however, remain largely unclear. Interestingly, recent studies have shown that fibroblast growth factor 21 (FGF21), a liver-derived hormone or hepatokine, mediates metabolic beneficial effects of certain dietary polyphenols as well as protein restriction. Here I have briefly summarized functions of FGF21, highlighted related dietary interventions, and presented literature discussions on role of FGF21 in mediating function of dietary polyphenol intervention and protein restriction. This is followed by presenting my perspective view, with the involvement of gut microbiota. It is anticipated that further breakthroughs in this field in the near future will facilitate conceptual merge of classical medicine and modern medicine.

MCAD activation by empagliflozin promotes fatty acid oxidation and reduces lipid deposition in NASH

Medium-chain acyl-CoA dehydrogenase (MCAD) is one of the significant enzymes involved in the β-oxidation of mitochondrial fatty acids. MCAD deficiency affects the β-oxidation of fatty acid and leads to lipid deposition in multiple organs, but little is known about its importance in nonalcoholic steatohepatitis (NASH). Empagliflozin is revealed to effectively improve NASH by increasing research, whereas the specific mechanism still has to be explored. Human liver tissues of patients with or without NASH were obtained for proteomic analysis to screen proteins of interest. db/db mice were given empagliflozin by gavage for 8 weeks. The expression of MCAD and signaling molecules involved in hepatic lipid metabolism was evaluated in human liver, mice and HL7702 cells. We found that the MCAD levels in the liver were significantly reduced in NASH patients compared to patients without NASH. Protein-protein interaction network analysis showed that MCAD was highly correlated with forkhead box A2 (FOXA2) and protein kinase AMP-activated catalytic subunit alpha (PRKAA). AMPK/FOXA2/MCAD signaling pathway was detected to be inhibited in the liver of NASH patients. Decreased expression of MCAD was also observed in the livers of db/db mice and hepatocyte treated with palmitic acid and glucose. Of note, empagliflozin could upregulate MCAD expression by activating AMPK/FOXA2 signaling pathway, reduce lipid deposition and improve NASH in vivo and in vitro. This research demonstrated that MCAD is a key player of hepatic lipid deposition and its targeting partially corrects NASH. MCAD thus may be a potential therapeutic target for the treatment of NASH.

Glucagon-like peptide 1 and fibroblast growth factor-21 in non-alcoholic steatohepatitis: An experimental to clinical perspective

Non-alcoholic steatohepatitis (NASH) is a progressive form of Non-alcoholic fatty liver disease (NAFLD), which slowly progresses toward cirrhosis and finally leads to the development of hepatocellular carcinoma. Obesity, insulin resistance, type 2 diabetes mellitus and the metabolic syndrome are major risk factors contributing to NAFLD. Targeting these risk factors is a rational option for inhibiting NASH progression. In addition, NASH could be treated with therapies that target the metabolic abnormalities causing disease pathogenesis (such as de novo lipogenesis and insulin resistance) as well with medications targeting downstream processes such as cellular damage, apoptosis, inflammation, and fibrosis. Glucagon-like peptide (GLP-1), is an incretin hormone dysregulated in both experimental and clinical NASH, which triggers many signaling pathways including fibroblast growth factor (FGF) that augments NASH pathogenesis. Growing evidence indicates that GLP-1 in concert with FGF-21 plays crucial roles in the conservation of glucose and lipid homeostasis in metabolic disorders. In line, GLP-1 stimulation improves hepatic ballooning, steatosis, and fibrosis in NASH. A recent clinical trial on NASH patients showed that the upregulation of FGF-21 decreases liver fibrosis and hepatic steatosis, thus improving the pathogenesis of NASH. Hence, therapeutic targeting of the GLP-1/FGF axis could be therapeutically beneficial for the remission of NASH. This review outlines the significance of the GLP-1/FGF-21 axis in experimental and clinical NASH and highlights the activity of modulators targeting this axis as potential salutary agents for the treatment of NASH.

Dietary carbohydrates: Pathogenesis and potential therapeutic targets to obesity-associated metabolic syndrome

Metabolic syndrome (MetS) is a common feature in obesity, comprising a cluster of abnormalities including abdominal fat accumulation, hyperglycemia, hyperinsulinemia, dyslipidemia, and hypertension, leading to diabetes and cardiovascular diseases (CVD). Intake of carbohydrates (CHO), particularly a sugary diet that rapidly increases blood glucose, triglycerides, and blood pressure levels is the predominant determining factor of MetS. Complex CHO, on the other hand, are a stable source of energy taking a longer time to digest. In particular, resistant starch (RS) or soluble fiber is an excellent source of prebiotics, which alter the gut microbial composition, which in turn improves metabolic control. Altering maternal CHO intake during pregnancy may result in the child developing MetS. Furthermore, lifestyle factors such as physical inactivity in combination with dietary habits may synergistically influence gene expression by modulating genetic and epigenetic regulators transforming childhood obesity into adolescent metabolic disorders. This review summarizes the common pathophysiology of MetS in connection with the nature of CHO, intrauterine nutrition, genetic predisposition, lifestyle factors, and advanced treatment approaches; it also emphasizes how dietary CHO may act as a key element in the pathogenesis and future therapeutic targets of obesity and MetS.

Salvia-Nelumbinis naturalis improves lipid metabolism of NAFLD by regulating the SIRT1/AMPK signaling pathway

Background

Salvia-Nelumbinis naturalis (SNN), the extract of Chinese herbal medicine, has shown effects on NAFLD. This study aims to explore the underlying mechanism of SNN for regulating the lipid metabolism disorder in NAFLD based on the SIRT1/AMPK signaling pathway.

Methods

Male C57BL/6J mice fed with a high-fat diet (HFD) were used to establish the NAFLD model. Dynamic changes of mice including body weight, liver weight, serological biochemical indexes, liver histopathological changes, and protein level of AMPK and SIRT1 were monitored. After18 weeks, SNN treatment was administrated to the NAFLD mice for another 4 weeks. Besides the aforementioned indices, TC and TG of liver tissues were also measured. Western blot and quantitative RT-PCR were used to detect the expression and/or activation of SIRT1 and AMPK, as well as the molecules associated with lipid synthesis and β-oxidation. Furthermore, AML12 cells with lipid accumulation induced by fatty acids were treated with LZG and EX527 (SIRT1 inhibitor) or Compound C (AMPK inhibitor ) to confirm the potential pharmacological mechanism.

Results

Dynamic observation found the mice induced by HFD with gradually increased body and liver weight, elevated serum cholesterol, hepatic lipid accumulation, and liver injury. After 16 weeks, these indicators have shown obvious changes. Additionally, the hepatic level of SIRT1 and AMPK activation was identified gradually decreased with NAFLD progress. The mice with SNN administration had lower body weight, liver weight, and serum level of LDL-c and ALT than those of the NAFLD model. Hepatosteatosis and hepatic TG content in the liver tissues of the SNN group were significantly reduced. When compared with control mice, the NAFLD mice had significantly decreased hepatic expression of SIRT1, p-AMPK, p-ACC, ACOX1, and increased total Acetylated-lysine, SUV39H2, and SREBP-1c. The administration of SNN reversed the expression of these molecules. In vitro experiments showed the effect of SNN in ameliorating hepatosteatosis and regulating the expression of lipid metabolism-related genes in AML12 cells, which were diminished by EX527 or Compound C co-incubation.

Conclusions

Taken together, the SIRT1/AMPK signaling pathway, involved in hepatic lipid synthesis and degradation, plays a pivotal role in the pathogenesis of NAFLD development. The regulation of SIRT1/AMPK signaling greatly contributes to the underlying therapeutic mechanism of SNN for NAFLD.

Enhanced mitochondrial activity reshapes a gut microbiota profile that delays NASH progression

BACKGROUND AND AIMS

Recent studies suggest that mitochondrial dysfunction promotes progression to NASH by aggravating the gut-liver status. However, the underlying mechanism remains unclear. Herein, we hypothesized that enhanced mitochondrial activity might reshape a specific microbiota signature that, when transferred to germ-free (GF) mice, could delay NASH progression.

APPROACH AND RESULTS

Wild-type and methylation-controlled J protein knockout (MCJ-KO) mice were fed for 6 weeks with either control or a choline-deficient, L-amino acid-defined, high-fat diet (CDA-HFD). One mouse of each group acted as a donor of cecal microbiota to GF mice, who also underwent the CDA-HFD model for 3 weeks. Hepatic injury, intestinal barrier, gut microbiome, and the associated fecal metabolome were then studied. Following 6 weeks of CDA-HFD, the absence of methylation-controlled J protein, an inhibitor of mitochondrial complex I activity, reduced hepatic injury and improved gut-liver axis in an aggressive NASH dietary model. This effect was transferred to GF mice through cecal microbiota transplantation. We suggest that the specific microbiota profile of MCJ-KO, characterized by an increase in the fecal relative abundance of Dorea and Oscillospira genera and a reduction in AF12, Allboaculum, and [Ruminococcus], exerted protective actions through enhancing short-chain fatty acids, nicotinamide adenine dinucleotide (NAD⁺ ) metabolism, and sirtuin activity, subsequently increasing fatty acid oxidation in GF mice. Importantly, we identified Dorea genus as one of the main modulators of this microbiota-dependent protective phenotype.

CONCLUSIONS

Overall, we provide evidence for the relevance of mitochondria-microbiota interplay during NASH and that targeting it could be a valuable therapeutic approach.

Ketone Bodies and SIRT1, Synergic Epigenetic Regulators for Metabolic Health: A Narrative Review

Ketone bodies (KBs) and Sirtuin-1 (SIRT1) have received increasing attention over the past two decades given their pivotal function in a variety of biological contexts, including transcriptional regulation, cell cycle progression, inflammation, metabolism, neurological and cardiovascular physiology, and cancer. As a consequence, the modulation of KBs and SIRT1 is considered a promising therapeutic option for many diseases. The direct regulation of gene expression can occur in vivo through histone modifications mediated by both SIRT1 and KBs during fasting or low-carbohydrate diets, and dietary metabolites may contribute to epigenetic regulation, leading to greater genomic plasticity. In this review, we provide an updated overview of the epigenetic interactions between KBs and SIRT1, with a particular glance at their central, synergistic roles for metabolic health.

New developments in the biology of fibroblast growth factors

The fibroblast growth factor (FGF) family is composed of 18 secreted signaling proteins consisting of canonical FGFs and endocrine FGFs that activate four receptor tyrosine kinases (FGFRs 1-4) and four intracellular proteins (intracellular FGFs or iFGFs) that primarily function to regulate the activity of voltage-gated sodium channels and other molecules. The canonical FGFs, endocrine FGFs, and iFGFs have been reviewed extensively by us and others. In this review, we briefly summarize past reviews and then focus on new developments in the FGF field since our last review in 2015. Some of the highlights in the past 6 years include the use of optogenetic tools, viral vectors, and inducible transgenes to experimentally modulate FGF signaling, the clinical use of small molecule FGFR inhibitors, an expanded understanding of endocrine FGF signaling, functions for FGF signaling in stem cell pluripotency and differentiation, roles for FGF signaling in tissue homeostasis and regeneration, a continuing elaboration of mechanisms of FGF signaling in development, and an expanding appreciation of roles for FGF signaling in neuropsychiatric diseases. This article is categorized under: Cardiovascular Diseases > Molecular and Cellular Physiology Neurological Diseases > Molecular and Cellular Physiology Congenital Diseases > Stem Cells and Development Cancer > Stem Cells and Development.

11β-HSD1 Inhibitor Alleviates Non-Alcoholic Fatty Liver Disease by Activating the AMPK/SIRT1 Signaling Pathway

We investigated the effect of an 11β-HSD1 inhibitor (H8) on hepatic steatosis and its mechanism of action. Although H8, a curcumin derivative, has been shown to alleviate insulin resistance, its effect on non-alcoholic fatty liver disease (NAFLD) remains unknown. Rats were fed a high-fat diet (HFD) for 8 weeks, intraperitoneally injected with streptozotocin (STZ) to induce NAFLD, and, then, treated with H8 (3 or 6 mg/kg/day) or curcumin (6 mg/kg/day) for 4 weeks, to evaluate the effects of H8 on NAFLD. H8 significantly alleviated HFD+STZ-induced lipid accumulation, fibrosis, and inflammation as well as improved liver function. Moreover, 11β-HSD1 overexpression was established by transfecting animals and HepG2 cells with lentivirus, carrying the 11β-HSD1 gene, to confirm that H8 improved NAFLD, by reducing 11β-HSD1. An AMP-activated protein kinase (AMPK) inhibitor (Compound C, 10 μM for 2 h) was used to confirm that H8 increased AMPK, by inhibiting 11β-HSD1, thereby restoring lipid metabolic homeostasis. A silencing-related enzyme 1 (SIRT1) inhibitor (EX572, 10 μM for 4 h) and a SIRT1 activator (SRT1720, 1 μM for 4 h) were used to confirm that H8 exerted anti-inflammatory effects, by elevating SIRT1 expression. Our findings demonstrate that H8 alleviates hepatic steatosis, by inhibiting 11β-HSD1, which activates the AMPK/SIRT1 signaling pathway.

Adipose-derived stem cells alleviate liver injury induced by type 1 diabetes mellitus by inhibiting mitochondrial stress and attenuating inflammation

Background

Type 1 diabetes mellitus (T1D) is a worldwide health priority due to autoimmune destruction and is associated with an increased risk of multiorgan complications. Among these complications, effective interventions for liver injury, which can progress to liver fibrosis and hepatocellular carcinoma, are lacking. Although stem cell injection has a therapeutic effect on T1D, whether it can cure liver injury and the underlying mechanisms need further investigation.

Methods

Sprague–Dawley rats with streptozotocin (STZ)-induced T1D were treated with adipose-derived stem cell (ADSC) or PBS via the tail vein formed the ADSC group or STZ group. Body weights and blood glucose levels were examined weekly for 6 weeks. RNA-seq and PCR array were used to detect the difference in gene expression of the livers between groups.

Results

In this study, we found that ADSCs injection alleviated hepatic oxidative stress and injury and improved liver function in rats with T1D; potential mechanisms included cytokine activity, energy metabolism and immune regulation were potentially involved, as determined by RNA-seq. Moreover, ADSC treatment altered the fibroblast growth factor 21 (FGF21) and transforming growth factor β (TGF-β) levels in T1D rat livers, implying its repair capacity. Disordered intracellular energy metabolism, which is closely related to mitochondrial stress and dysfunction, was inhibited by ADSC treatment. PCR array and ingenuity pathway analyses suggested that the ADSC-induced suppression of mitochondrial stress is related to decreased necroptosis and apoptosis. Moreover, mitochondria-related alterations caused liver inflammation, resulting in liver injury involving the T lymphocyte-mediated immune response.

Conclusions

Overall, these results improve our understanding of the curative effect of ADSCs on T1D complications: ADSCs attenuate liver injury by inhibiting mitochondrial stress (apoptosis and dysfunctional energy metabolism) and alleviating inflammation (inflammasome expression and immune disorder). These results are important for early intervention in liver injury and for delaying the development of liver lesions in patients with T1D.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-02760-z.

Hepatocyte-specific fibroblast growth factor 21 overexpression ameliorates high-fat diet-induced obesity and liver steatosis in mice

Fibroblast growth factor (FGF) 21 is an endocrine growth factor mainly secreted by the liver in response to a ketogenic diet and alcohol consumption. FGF21 signaling requires co-receptor β-klotho (KLB) co-acting with FGF receptors, which has pleiotropic metabolic effects, including induced hepatic fatty acid oxidation and ketogenesis, in human and animal models of obesity. We examined the hepatocyte-specific enhancer/promoter of FGF21 expression plasmids in high-fat diet-fed mice for 12 weeks. Hydrodynamic injection for FGF21 delivery every 6 weeks sustained high circulating levels of FGF21, resulting in marked reductions in body weight, epididymal fat mass, insulin resistance, and liver steatosis. FGF21-induced lipolysis in the adipose tissue enabled the liver to be flooded with fat-derived FFAs. The hepatic expression of Glut2 and Bdh1 was upregulated, whereas that of gluconeogenesis-related genes, G6p and Pepck, and lipogenesis-related genes, Srebp-1 and Srebp-2, was significantly suppressed. FGF21 induced the phosphorylation of AMPK at Thr172 and Raptor at ser792 and suppressed that of mTOR at ser2448, which downregulated mTORC1 signaling and reduced IRS-1 phosphorylation at ser1101. Finally, in the skeletal muscle, FGF21 increased Glut4 and Mct2, a membrane protein that acts as a carrier for ketone bodies. Enzymes for ketone body catabolism (Scot) and citrate cycle (Cs, Idh3a), and a marker of regenerating muscle (myogenin) were also upregulated via increased KLB expression. Thus, FGF21-induced lipolysis was continuously induced by a high-fat diet and fat-derived FFAs might cause liver damage. Hepatic fatty acid oxidation and ketone body synthesis may act as hepatic FFAs' disposal mechanisms and contribute to improved liver steatosis. Liver-derived ketone bodies might be used for energy in the skeletal muscle. The potential FGF21-related crosstalk between the liver and extraliver organs is a promising strategy to prevent and treat metabolic syndrome-related nonalcoholic steatohepatitis.

Aging exaggerates acute-on-chronic alcohol-induced liver injury in mice and humans by inhibiting neutrophilic sirtuin 1-C/EBPα-miRNA-223 axis

BACKGROUND AND AIMS

Aging exacerbates liver neutrophil infiltration and alcohol-associated liver disease (ALD) in mice and humans, but the underlying mechanisms remain obscure. This study aimed to examine the effect of aging and alcohol consumption on neutrophilic Sirtuin 1 (SIRT1) and microRNA-223 (miR-223), and their contribution to ALD pathogeneses.

APPROACH AND RESULTS

Young and aged myeloid-specific Sirt1 knockout mice were subjected to chronic-plus-binge ethanol feeding. Blood samples from healthy controls and patients with chronic alcohol drinking who presented with acute intoxication were analyzed. Neutrophilic Sirt1 and miR-223 expression were down-regulated in aged mice compared with young mice. Deletion of the Sirt1 gene in myeloid cells including neutrophils exacerbated chronic-plus-binge ethanol-induced liver injury and inflammation and down-regulated neutrophilic miR-223 expression. Immunoprecipitation experiments revealed that SIRT1 promoted C/EBPα deacetylation by directly interacting with C/EBPα, a key transcription factor that controls miR-223 biogenesis, and subsequently elevated miR-223 expression in neutrophils. Importantly, down-regulation of SIRT1 and miR-223 expression was also observed in circulating neutrophils from middle-aged and elderly subjects compared with those from young individuals. Chronic alcohol users with acute intoxication had a reduction in neutrophilic SIRT1 expression in young and middle-aged patients, with a greater reduction in the latter group. The neutrophilic SIRT1 expression correlated with neutrophilic miR-223 and serum alanine transaminase levels in those patients.

CONCLUSIONS

Aging increases the susceptibility of alcohol-induced liver injury in mice and humans through the down-regulation of the neutrophilic SIRT1-C/EBPα-miR-223 axis, which could be a therapeutic target for the prevention and/or treatment of ALD.

SIRT1 selectively exerts the metabolic protective effects of hepatocyte nicotinamide phosphoribosyltransferase

Calorie restriction abates aging and cardiometabolic disease by activating metabolic signaling pathways, including nicotinamide adenine dinucleotide (NAD⁺) biosynthesis and salvage. Nicotinamide phosphoribosyltransferase (NAMPT) is rate-limiting in NAD⁺ salvage, yet hepatocyte NAMPT actions during fasting and metabolic duress remain unclear. We demonstrate that hepatocyte NAMPT is upregulated in fasting mice, and in isolated hepatocytes subjected to nutrient withdrawal. Mice lacking hepatocyte NAMPT exhibit defective FGF21 activation and thermal regulation during fasting, and are sensitized to diet-induced glucose intolerance. Hepatocyte NAMPT overexpression induced FGF21 and adipose browning, improved glucose homeostasis, and attenuated dyslipidemia in obese mice. Hepatocyte SIRT1 deletion reversed hepatocyte NAMPT effects on dark-cycle thermogenesis, and hepatic FGF21 expression, but SIRT1 was dispensable for NAMPT insulin-sensitizing, anti-dyslipidemic, and light-cycle thermogenic effects. Hepatocyte NAMPT thus conveys key aspects of the fasting response, which selectively dissociate through hepatocyte SIRT1. Modulating hepatocyte NAD⁺ is thus a potential mechanism through which to attenuate fasting-responsive disease.

Histone Deacetylases as Modulators of the Crosstalk Between Skeletal Muscle and Other Organs

Skeletal muscle plays a major role in controlling body mass and metabolism: it is the most abundant tissue of the body and a major source of humoral factors; in addition, it is primarily responsible for glucose uptake and storage, as well as for protein metabolism. Muscle acts as a metabolic hub, in a crosstalk with other organs and tissues, such as the liver, the brain, and fat tissue. Cytokines, adipokines, and myokines are pivotal mediators of such crosstalk. Many of these circulating factors modulate histone deacetylase (HDAC) expression and/or activity. HDACs form a numerous family of enzymes, divided into four classes based on their homology to their orthologs in yeast. Eleven family members are considered classic HDACs, with a highly conserved deacetylase domain, and fall into Classes I, II, and IV, while class III members are named Sirtuins and are structurally and mechanistically distinct from the members of the other classes. HDACs are key regulators of skeletal muscle metabolism, both in physiological conditions and following metabolic stress, participating in the highly dynamic adaptative responses of the muscle to external stimuli. In turn, HDAC expression and activity are closely regulated by the metabolic demands of the skeletal muscle. For instance, NAD+ levels link Class III (Sirtuin) enzymatic activity to the energy status of the cell, and starvation or exercise affect Class II HDAC stability and intracellular localization. SUMOylation or phosphorylation of Class II HDACs are modulated by circulating factors, thus establishing a bidirectional link between HDAC activity and endocrine, paracrine, and autocrine factors. Indeed, besides being targets of adipo-myokines, HDACs affect the synthesis of myokines by skeletal muscle, altering the composition of the humoral milieu and ultimately contributing to the muscle functioning as an endocrine organ. In this review, we discuss recent findings on the interplay between HDACs and circulating factors, in relation to skeletal muscle metabolism and its adaptative response to energy demand. We believe that enhancing knowledge on the specific functions of HDACs may have clinical implications leading to the use of improved HDAC inhibitors for the treatment of metabolic syndromes or aging.

Overexpression of G protein-coupled receptor 40 protects obesity-induced cardiomyopathy through the SIRT1/LKB1/AMPK pathway

Obesity has become a serious global public health problem, and cardiomyopathy caused by obesity has been paid more and more attention in recent years. As an important protein involved in glucose and lipid metabolism, G protein-coupled receptor 40 (GPR40) exerts cardioprotective effects in some disease models. The aim of this study was to explore whether GPR40 plays a protective role in obesity-induced cardiomyopathy. We established an obesity model by feeding rats with a high-fat diet, and H9c2 cells were stimulated with palmitic acid to mimic high-fat stimulation. Overexpression of GPR40 was achieved by infection with lentivirus or cDNA plasmids. Obesity-induced cardiac injury models exhibit cardiac dysfunction, myocardial hypertrophy and collagen accumulation, accompanied by increased inflammation, oxidative stress and apoptosis. However, GPR40 overexpression attenuated these alterations. Its anti-inflammatory effect may be through inhibiting the nuclear factor-κB pathway, and the anti-oxidative stress may be through activating the nuclear transcription factor erythroid 2-related factor 2 pathway. For the mechanism of GPR40 against obese cardiomyopathy, GPR40 overexpression not only activated the sirtuin 1 (SIRT1)- liver kinase B1 (LKB1)- AMP-activated protein kinase (AMPK) pathway, but also enhanced the binding of SIRT1 to LKB1. The anti-fibrotic, anti-inflammatory, anti-oxidative stress and anti-apoptotic effects of GPR40 overexpression were inhibited by SIRT1 small interfering RNA. In conclusion, GPR40 overexpression protects against obesity-induced cardiac injury in rats, possibly through the SIRT1- LKB1- AMPK pathway.

FGF21 alleviates acute liver injury by inducing the SIRT1-autophagy signalling pathway

Liver injury can lead to different hepatic diseases, which are the mainly causes of high global mortality and morbidity. Autophagy and Sirtuin type 1 (SIRT1) have been shown protective effects in response to liver injury. Previous studies have showed that Fibroblast growth factor 21 (FGF21) could alleviate acute liver injury (ALI), but the mechanism remains unclear. Here, we verified the relationship among FGF21, autophagy and SIRT1 in carbon tetrachloride (CCl₄)‐induced ALI. We established CCl₄‐induced ALI models in C57BL/6 mice and the L02 cell line. The results showed that FGF21 was robustly induced in response to stress during the development of ALI. After exogenous FGF21 treatment in ALI models, liver damage in ALI mice was significantly reduced, as well as serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels. Consistently, FGF21 also greatly reduced the levels of ALT, AST, pro‐inflammatory cytokines interleukin 6 (IL6) and tumour necrosis factor‐alpha (TNFα) in ALI cell lines. Mechanistically, exogenous FGF21 treatment efficiently upregulated the expression of autophagy marker microtubule‐associated protein light chain‐3 beta (LC3 II) and autophagy key molecule coiled‐coil myosin‐like BCL2‐interacting protein (Beclin1), which was accompanied by alleviating hepatotoxicity in CCl₄‐treated wild‐type mice. Then, we examined how FGF21 induced autophagy expression and found that SIRT1 was also upregulated by FGF21 treatment. To further verify our results, we constructed an anti‐SIRT1 lentit‐RNAi to inhibit SIRT1 expression in mice and L02 cells, which reversed the protective effect of FGF21 on ALI. In summary, these results indicate that FGF21 alleviates ALI by enhancing SIRT1‐mediated autophagy.

SIRT1 and Autophagy: Implications in Endocrine Disorders

Autophagy is a cellular process involved in the selective degradation and recycling of dysfunctional intracellular components. It plays a crucial role in maintaining cellular homeostasis and survival by removing damaged and harmful proteins, lipids, and organelles. SIRT1, an NAD⁺-dependent multifunctional enzyme, is a key regulator of the autophagy process. Through its deacetylase activity, SIRT1 participates in the regulation of different steps of autophagy, from initiation to degradation. The levels and function of SIRT1 are also regulated by the autophagy process. Dysregulation in SIRT1-mediated autophagy hinders the proper functioning of the endocrine system, contributing to the onset and progression of endocrine disorders. This review provides an overview of the crosstalk between SIRT1 and autophagy and their implications in obesity, type-2 diabetes mellitus, diabetic cardiomyopathy, and hepatic steatosis.

In Obese Patients With Type 2 Diabetes, Mast Cells in Omental Adipose Tissue Decrease the Surface Expression of CD45, CD117, CD203c, and FcϵRI

The paradigm of mast cells in type 2 diabetes is changing. Although they were first considered deleterious inflammatory cells, now they seem to be important players driving adipose tissue homeostasis. Here we have employed a flow cytometry-based approach for measuring the surface expression of 4 proteins (CD45, CD117, CD203c, and FcϵRI) on mast cells of omental (o-WAT) and subcutaneous white adipose tissue (s-WAT) in a cohort of 96 patients with morbid obesity. The cohort was split into three groups: non-T2D, pre-T2D, and T2D. Noteworthy, patients with T2D have a mild condition (HbA1c <7%). In o-WAT, mast cells of patients with T2D have a decrease in the surface expression of CD45 (p=0.0013), CD117 (p=0.0066), CD203c (p=0.0025), and FcϵRI (p=0.043). Besides, in s-WAT, the decrease was seen only in CD117 (p=0.046). These results indicate that T2D affects more to mast cells in o-WAT than in s-WAT. The decrease in these four proteins has serious effects on mast cell function. CD117 is critical for mast cell survival, while CD45 and FcϵRI are important for mast cell activation. Additionally, CD203c is only present on the cell surface after granule release. Taking together these observations, we suggest that mast cells in o-WAT of patients with T2D have a decreased survival, activation capacity, and secretory function.

Inhibition of ATG3 ameliorates liver steatosis by increasing mitochondrial function

BACKGROUND & AIMS

Autophagy-related gene 3 (ATG3) is an enzyme mainly known for its actions in the LC3 lipidation process, which is essential for autophagy. Whether ATG3 plays a role in lipid metabolism or contributes to non-alcoholic fatty liver disease (NAFLD) remains unknown.

METHODS

By performing proteomic analysis on livers from mice with genetic manipulation of hepatic p63, a regulator of fatty acid metabolism, we identified ATG3 as a new target downstream of p63. ATG3 was evaluated in liver samples from patients with NAFLD. Further, genetic manipulation of ATG3 was performed in human hepatocyte cell lines, primary hepatocytes and in the livers of mice.

RESULTS

ATG3 expression is induced in the liver of animal models and patients with NAFLD (both steatosis and non-alcoholic steatohepatitis) compared with those without liver disease. Moreover, genetic knockdown of ATG3 in mice and human hepatocytes ameliorates p63- and diet-induced steatosis, while its overexpression increases the lipid load in hepatocytes. The inhibition of hepatic ATG3 improves fatty acid metabolism by reducing c-Jun N-terminal protein kinase 1 (JNK1), which increases sirtuin 1 (SIRT1), carnitine palmitoyltransferase 1a (CPT1a), and mitochondrial function. Hepatic knockdown of SIRT1 and CPT1a blunts the effects of ATG3 on mitochondrial activity. Unexpectedly, these effects are independent of an autophagic action.

CONCLUSIONS

Collectively, these findings indicate that ATG3 is a novel protein implicated in the development of steatosis.

LAY SUMMARY

We show that autophagy-related gene 3 (ATG3) contributes to the progression of non-alcoholic fatty liver disease in humans and mice. Hepatic knockdown of ATG3 ameliorates the development of NAFLD by stimulating mitochondrial function. Thus, ATG3 is an important factor implicated in steatosis.