Proline hydroxylation of CREB-regulated transcriptional coactivator 2 controls hepatic glucose metabolism.

Prolyl hydroxylase domain (PHD) enzymes change HIF activity according to oxygen signal; whether it is regulated by other physiological conditions remains largely unknown. Here, we report that PHD3 is induced by fasting and regulates hepatic gluconeogenesis through interaction and hydroxylation of CRTC2. Pro129 and Pro615 hydroxylation of CRTC2 following PHD3 activation is necessary for its association with cAMP-response element binding protein (CREB) and nuclear translocation, and enhanced binding to promoters of gluconeogenic genes by fasting or forskolin. CRTC2 hydroxylation-stimulated gluconeogenic gene expression is independent of SIK-mediated phosphorylation of CRTC2. Liver-specific knockout of PHD3 (PHD3 LKO) or prolyl hydroxylase-deficient knockin mice (PHD3 KI) show attenuated fasting gluconeogenic genes, glycemia, and hepatic capacity to produce glucose during fasting or fed with high-fat, high-sucrose diet. Importantly, Pro615 hydroxylation of CRTC2 by PHD3 is increased in livers of fasted mice, diet-induced insulin resistance or genetically obese ob/ob mice, and humans with diabetes. These findings increase our understanding of molecular mechanisms linking protein hydroxylation to gluconeogenesis and may offer therapeutic potential for treating excessive gluconeogenesis, hyperglycemia, and type 2 diabetes.

Intrahepatic osteopontin signaling by CREBZF defines a checkpoint for steatosis-to-NASH progression.

BACKGROUND AND AIMS: NASH has emerged as a leading cause of chronic liver disease. However, the mechanisms that govern NASH fibrosis remain largely unknown. CREBZF is a CREB/ATF bZIP transcription factor that causes hepatic steatosis and metabolic defects in obesity. APPROACH AND RESULTS: Here, we show that CREBZF is a key mechanism of liver fibrosis checkpoint that promotes hepatocyte injury and exacerbates diet-induced NASH in mice. CREBZF deficiency attenuated liver injury, fibrosis, and inflammation in diet-induced mouse models of NASH. CREBZF increases HSC activation and fibrosis in a hepatocyte-autonomous manner by stimulating an extracellular matrix protein osteopontin, a key regulator of fibrosis. The inhibition of miR-6964-3p mediates CREBZF-induced production and secretion of osteopontin in hepatocytes. Adeno-associated virus -mediated rescue of osteopontin restored HSC activation, liver fibrosis, and NASH progression in CREBZF-deficient mice. Importantly, expression levels of CREBZF are increased in livers of diet-induced NASH mouse models and humans with NASH. CONCLUSIONS: Osteopontin signaling by CREBZF represents a previously unrecognized intrahepatic mechanism that triggers liver fibrosis and contributes to the severity of NASH.

Activating Adenosine Monophosphate-Activated Protein Kinase Mediates Fibroblast Growth Factor 1 Protection From Nonalcoholic Fatty Liver Disease in Mice.

BACKGROUND AND AIMS: Fibroblast growth factor (FGF) 1 demonstrated protection against nonalcoholic fatty liver disease (NAFLD) in type 2 diabetic and obese mice by an uncertain mechanism. This study investigated the therapeutic activity and mechanism of a nonmitogenic FGF1 variant carrying 3 substitutions of heparin-binding sites (FGF1△HBS ) against NAFLD. APPROACH AND RESULTS: FGF1△HBS administration was effective in 9-month-old diabetic mice carrying a homozygous mutation in the leptin receptor gene (db/db) with NAFLD; liver weight, lipid deposition, and inflammation declined and liver injury decreased. FGF1△HBS reduced oxidative stress by stimulating nuclear translocation of nuclear erythroid 2 p45-related factor 2 (Nrf2) and elevation of antioxidant protein expression. FGF1△HBS also inhibited activity and/or expression of lipogenic genes, coincident with phosphorylation of adenosine monophosphate-activated protein kinase (AMPK) and its substrates. Mechanistic studies on palmitate exposed hepatic cells demonstrated that NAFLD-like oxidative damage and lipid accumulation could be reversed by FGF1△HBS . In palmitate-treated hepatic cells, small interfering RNA (siRNA) knockdown of Nrf2 abolished only FGF1△HBS antioxidative actions but not improvement of lipid metabolism. In contrast, AMPK inhibition by pharmacological agent or siRNA abolished FGF1△HBS benefits on both oxidative stress and lipid metabolism that were FGF receptor (FGFR) 4 dependent. Further support of these in vitro findings is that liver-specific AMPK knockout abolished therapeutic effects of FGF1△HBS against high-fat/high-sucrose diet-induced hepatic steatosis. Moreover, FGF1△HBS improved high-fat/high-cholesterol diet-induced steatohepatitis and fibrosis in apolipoprotein E knockout mice. CONCLUSIONS: These findings indicate that FGF1△HBS is effective for preventing and reversing liver steatosis and steatohepatitis and acts by activation of AMPK through hepatocyte FGFR4.

Pulse-Modulation Eddy Current Evaluation of Interlaminar Corrosion in Stratified Conductors: Semi-Analytical Modeling and Experiments.

Interlaminar corrosion (ILC) poses a severe threat to stratified conductors which are broadly employed in engineering fields including aerospace, energy, etc. Therefore, for the pressing concern regarding the safety and integrity of stratified conductors, it is imperative to non-intrusively and quantitatively interrogate ILC via non-destructive evaluation techniques. In this paper, pulse-modulation eddy current (PMEC) for imaging and assessment of ILC is intensively investigated through theoretical simulations and experiments. A semi-analytical model of PMEC evaluation of ILC occurring at the interlayer of two conductor layers is established based on the extended truncated region eigenfunction expansion (ETREE) along with the efficient algorithm for the numerical computation of eigenvalues for reflection coefficients of the stratified conductor under inspection. Based on theoretical investigation, PMEC evaluation of ILC in testing samples are further scrutinized by using the PMEC imaging system built up for the experimental study. The theoretical and experimental results have revealed the feasibility of PMEC for imaging and evaluation of ILC in stratified conductors.

CREBZF as a Key Regulator of STAT3 Pathway in the Control of Liver Regeneration in Mice.

BACKGROUND AND AIMS: STAT3, a member of the signal transducer and activator of transcription (STAT) family, is strongly associated with liver injury, inflammation, regeneration, and hepatocellular carcinoma development. However, the signals that regulate STAT3 activity are not completely understood. APPROACH AND RESULTS: Here we characterize CREB/ATF bZIP transcription factor CREBZF as a critical regulator of STAT3 in the hepatocyte to repress liver regeneration. We show that CREBZF deficiency stimulates the expression of the cyclin gene family and enhances liver regeneration after partial hepatectomy. Flow cytometry analysis reveals that CREBZF regulates cell cycle progression during liver regeneration in a hepatocyte-autonomous manner. Similar results were observed in another model of liver regeneration induced by intraperitoneal injection of carbon tetrachloride (CCl4 ). Mechanistically, CREBZF potently associates with the linker domain of STAT3 and represses its dimerization and transcriptional activity in vivo and in vitro. Importantly, hepatectomy-induced hyperactivation of cyclin D1 and liver regeneration in CREBZF liver-specific knockout mice was reversed by selective STAT3 inhibitor cucurbitacin I. In contrast, adeno-associated virus-mediated overexpression of CREBZF in the liver inhibits the expression of the cyclin gene family and attenuates liver regeneration in CCl4 -treated mice. CONCLUSIONS: These results characterize CREBZF as a coregulator of STAT3 to inhibit regenerative capacity, which may represent an essential cellular signal to maintain liver mass homeostasis. Therapeutic approaches to inhibit CREBZF may benefit the compromised liver during liver transplantation.

The ER-localized Ca2+-binding protein calreticulin couples ER stress to autophagy by associating with microtubule-associated protein 1A/1B light chain 3.

Autophagy is of key importance for eliminating aggregated proteins during the maintenance of cellular proteostasis in response to endoplasmic reticulum (ER) stress. However, the upstream signaling that mediates autophagy activation in response to ER stress is incompletely understood. In this study, in vivo and in vitro approaches were utilized that include gain- and loss-of-function assays and mouse livers and human cell lines with tunicamycin-induced pharmacological ER stress. We report that calreticulin, a quality control chaperone that binds to misfolded glycoproteins for refolding in the ER, is induced under ER stress. Calreticulin overexpression stimulated the formation of autophagosomes and increased autophagic flux. Interestingly, calreticulin was sufficient for attenuating ER stress in tunicamycin- or thapsigargin-treated HeLa cells, whereas lentivirus-mediated shRNA calreticulin knockdown exacerbated ER stress. Mechanistically, we noted that calreticulin induces autophagy by interacting with microtubule-associated protein 1A/1B-light chain 3 (LC3). Confocal microscopy revealed that the colocalization of calreticulin and LC3 at the autophagosome was enhanced under ER stress conditions. Importantly, a conserved LC3-interacting region was necessary for calreticulin-mediated stimulation of autophagy and for reducing ER stress. These findings indicate a calreticulin-based mechanism that couples ER stress to autophagy activation, which, in turn, attenuates cellular stress, likely by alleviating the formation of aberrantly folded proteins. Pharmacological or genetic approaches that activate calreticulin-autophagy signaling may have potential for managing ER stress and related cellular disorders.

Characteristics Regarding Lift-Off Intersection of Pulse-Modulation Eddy Current Signals for Evaluation of Hidden Thickness Loss in Cladded Conductors.

The cladded conductor is broadly utilized in engineering fields, such as aerospace, energy, and petrochemical; however, it is vulnerable to thickness loss occurring in the clad layer and nonconductive protection coating due to abrasive and corrosive environments. Such a flaw severely undermines the integrity and safety of the mechanical structures. Therefore, evaluating the thickness loss hidden inside cladded conductors via reliable nondestructive evaluation techniques is imperative. This paper intensively investigates the pulse-modulation eddy current technique (PMEC) for the assessment of thickness loss in a cladded conductor. An analytical model of the ferrite-cored probe is established for analyzing PMEC signals and characteristics of lift-off intersection (LOI) in testing signals. Experiments are conducted for evaluation of the thickness loss in cladded conductors. An inverse scheme based on LOI for estimation of the thickness-loss depth is proposed and further verified. Through simulations and experiments, it is found that the influences of the thickness loss in the clad layer and protective coating on the PMEC signals can be decoupled in virtue of the LOI characteristics. Based on LOI, the hidden thickness loss can be efficiently evaluated without much of a reduction in accuracy by using the PMEC probe for dedicated inspection of the cladded conductor.

Macrophage CREBZF Orchestrates Inflammatory Response to Potentiate Insulin Resistance and Type 2 Diabetes.

Chronic adipose tissue inflammation accompanied by macrophage accumulation and activation is implicated in the pathogenesis of insulin resistance and type 2 diabetes in humans. The transcriptional coregulator CREBZF is a key factor in hepatic metabolism, yet its role in modulating adipose tissue inflammation and type 2 diabetes remains elusive. The present study demonstrates that overnutrition-induced CREBZF links adipose tissue macrophage (ATM) proinflammatory activation to insulin resistance. CREBZF deficiency in macrophages, not in neutrophils, attenuates macrophage infiltration in adipose, proinflammatory activation, and hyperglycemia in diet-induced insulin-resistant mice. The coculture assays show that macrophage CREBZF deficiency improves insulin sensitivity in primary adipocytes and adipose tissue. Mechanistically, CREBZF competitively inhibits the binding of IκBα to p65, resulting in enhanced NF-κB activity. In addition, bromocriptine is identified as a small molecule inhibitor of CREBZF in macrophages, which suppresses the proinflammatory phenotype and improves metabolic dysfunction. Furthermore, CREBZF is highly expressed in ATM of obese humans and mice, which is positively correlated with proinflammatory genes and insulin resistance in humans. This study identifies a previously unknown role of CREBZF coupling ATM activation to systemic insulin resistance and type 2 diabetes.

Induced degradation of lineage-specific oncoproteins drives the therapeutic vulnerability of small cell lung cancer to PARP inhibitors.

Although BRCA1/2 mutations are not commonly found in small cell lung cancer (SCLC), a substantial fraction of SCLC shows clinically relevant response to PARP inhibitors (PARPis). However, the underlying mechanism(s) of PARPi sensitivity in SCLC is poorly understood. We performed quantitative proteomic analyses and identified proteomic changes that signify PARPi responses in SCLC cells. We found that the vulnerability of SCLC to PARPi could be explained by the degradation of lineage-specific oncoproteins (e.g., ASCL1). PARPi-induced activation of the E3 ligase HUWE1 mediated the ubiquitin-proteasome system (UPS)-dependent ASCL1 degradation. Although PARPi induced a general DNA damage response in SCLC cells, this signal generated a cell-specific response in ASCL1 degradation, leading to the identification of HUWE1 expression as a predictive biomarker for PARPi. Combining PARPi with agents targeting these pathways markedly improved therapeutic response in SCLC. The degradation of lineage-specific oncoproteins therefore represents a previously unidentified mechanism for PARPi efficacy in SCLC.

Time-Frequency Characteristics and Evolution Law of Acoustic Emission Signals during the Deformation and Failure of Deformed Coal.

The research on the time-frequency characteristics and evolution law of acoustic emission (AE) signals during deformed coal failure is more conducive to understand the damage mechanism of coal. In this study, the experiments of AE monitoring during the intact and deformed coal failure were first conducted under loading axial stress and unloading confining stress conditions. Based on the evolution characteristics of volume strain and AE event rate, the damage process of coal was divided into three stages: nonfracture development stage, stable development stage of fracture, and unstable development stage of fracture. The distribution and evolution of AE waveform time-frequency properties under different damage processes were then analyzed and discussed. Besides, the evolution of the average value of different time-frequency parameters per 200 s for the intact coal and per 25 s for the deformed coal was discussed. The results show that the amplitude of most AE events stabilizes in 40-50 dB during the intact and deformed coal failure. The average amplitude of the deformed coal has an approximate positive correlation with the loading stress. The percentage of AE events with longer duration and rise time increases suddenly before the peak stress for the intact coal and after the peak stress for the deformed coal, which corresponds to the abrupt increase property of the average duration and rise time. For the frequency properties, the peak frequency and frequency centroid of the intact coal are distributed within 50-125 and 75-150 kHz, with those of the deformed coal located within 20-120 and 80-130 kHz, respectively. The average peak frequency and frequency centroid of the intact coal show an upward trend except for the initial fracture closure stage, while the average peak frequency and average frequency centroid of the deformed coal present a downward trend before the peak stress and have a smaller growth after the peak stress. According to the above-mentioned analysis, the sudden increase of the average duration and rise time, the lower average peak frequency, and the lower frequency centroid can be regarded as the precursor for the instability and failure of deformed coal. This research can provide a new idea and theoretical guidance for the early warning of outbursts.

Nimbolide targets RNF114 to induce the trapping of PARP1 and synthetic lethality in BRCA-mutated cancer.

Recent studies have pointed to PARP1 trapping as a key determinant of the anticancer effects of PARP1 inhibitors (PARPi). We identified RNF114, as a PARylation-dependent, E3 ubiquitin ligase involved in DNA damage response. Upon sensing genotoxicity, RNF114 was recruited, in a PAR-dependent manner, to DNA lesions, where it targeted PARP1 for degradation. The blockade of this pathway interfered with the removal of PARP1 from DNA lesions, leading to profound PARP1 trapping. We showed that a natural product, nimbolide, inhibited the E3 ligase activity of RNF114 and thus caused PARP1 trapping. However, unlike conventional PARPi, nimbolide treatment induced the trapping of both PARP1 and PARylation-dependent DNA repair factors. Nimbolide showed synthetic lethality with BRCA mutations, and it overcame intrinsic and acquired resistance to PARPi, both in vitro and in vivo. These results point to the exciting possibility of targeting the RNF114-PARP1 pathway for the treatment of homologous recombination-deficient cancers.

Sodium Butyrate Supplementation Inhibits Hepatic Steatosis by Stimulating Liver Kinase B1 and Insulin-Induced Gene.

BACKGROUND AND AIMS: Butyric acid is an intestinal microbiota-produced short-chain fatty acid, which exerts salutary effects on alleviating nonalcoholic fatty liver disease (NAFLD). However, the underlying mechanism of butyrate on regulating hepatic lipid metabolism is largely unexplored. METHODS: A mouse model of NAFLD was induced with high-fat diet feeding, and sodium butyrate (NaB) intervention was initiated at the eighth week and lasted for 8 weeks. Hepatic steatosis was evaluated and metabolic pathways concerning lipid homeostasis were analyzed. RESULTS: Here, we report that administration of NaB by gavage once daily for 8 weeks causes an augmentation of insulin-induced gene (Insig) activity and inhibition of lipogenic gene in mice fed with high-fat diet. Mechanistically, NaB is sufficient to enhance the interaction between Insig and its upstream kinase AMP-activated protein kinase (AMPK). The stimulatory effects of NaB on Insig-1 activity are abolished in AMPKα1/α2 double knockout (AMPK-/-) mouse primary hepatocytes. Moreover, AMPK activation by NaB is mediated by LKB1, as evidenced by the observations showing NaB-mediated induction of phosphorylation of AMPK, and its downstream target acetyl-CoA carboxylase is diminished in LKB1-/- mouse embryonic fibroblasts. CONCLUSIONS: These studies indicate that NaB serves as a negative regulator of hepatic lipogenesis in NAFLD and that NaB attenuates hepatic steatosis and improves lipid profile and liver function largely through the activation of LKB1-AMPK-Insig signaling pathway. Therefore, NaB has therapeutic potential for treating NAFLD and related metabolic diseases.

The Effects of B1344, a Novel Fibroblast Growth Factor 21 Analog, on Nonalcoholic Steatohepatitis in Nonhuman Primates.

Nonalcoholic steatohepatitis has emerged as a major cause of liver diseases with no effective therapies. Here, we evaluate the efficacies and pharmacokinetics of B1344, a long-acting polyethylene glycolylated (PEGylated) fibroblast growth factor 21 analog, in a nongenetically modified nonhuman primate species that underwent liver biopsy and demonstrate the potential for efficacies in humans. B1344 is sufficient to selectively activate signaling from the ßKlotho/FGFR1c receptor complex. In cynomolgus monkeys with nonalcoholic fatty liver disease (NAFLD), administration of B1344 via subcutaneous injection for 11 weeks caused a profound reduction of hepatic steatosis, inflammation, and fibrosis, along with amelioration of liver injury and hepatocyte death, as evidenced by liver biopsy specimen and biochemical analysis. Moreover, improvement of metabolic parameters was observed in the monkeys, including reduction of body weight and improvement of lipid profiles and glycemic control. To determine the role of B1344 in the progression of murine NAFLD independent of obesity, B1344 was administered to mice fed a methionine- and choline-deficient diet. Consistently, B1344 administration prevented the mice from lipotoxicity damage and nonalcoholic steatohepatitis in a dose-dependent manner. These results provide preclinical validation for an innovative therapeutic approach to NAFLD and support further clinical testing of B1344 for treating nonalcoholic steatohepatitis and other metabolic diseases in humans.

Thrombospondin 1 improves hepatic steatosis in diet-induced insulin-resistant mice and is associated with hepatic fat content in humans.

BACKGROUND: Nonalcoholic fatty liver disease (NAFLD) is associated with altered production of secreted proteins. Increased understanding of secreted proteins could lead to improved prediction and treatment of NAFLD. Here, we aimed to discover novel secreted proteins in humans that are associated with hepatic fat content using unbiased proteomic profiling strategy, and how the identified Thbs1 modulates lipid metabolism and hepatic steatosis. METHOD: NAFLD patients were enrolled and treated with lifestyle intervention. Patients who underwent liver biopsy were enrolled for analyzing the correlation between circulating Thbs1 and liver steatosis. Mice were fed on high-fat, high-sucrose diet and treated with recombinant Thbs1. Primary hepatocytes isolated from CD36 knockout (CD36-/-) mice and their wild-type littermates (controls) were treated with glucose plus insulin for 24 h together with or without recombinant Thbs1. FINDING: Serum Thbs1 levels are increased in participants with NAFLD and positively associated with liver steatosis grades. Improvement of liver steatosis after lifestyle intervention was accompanied with significant reduction of serum Thbs1 levels. Pharmacological administration of recombinant human Thbs1 attenuates hepatic steatosis in diet-induced obese mice. Treatment with Thbs1 protein or stably overexpression of Thbs1 causes a significant reduction of lipid accumulation in primary hepatocytes or HepG2 cells exposed to high glucose plus insulin, suggesting that Thbs1 regulates lipid metabolism in a hepatocyte-autonomous manner. Mechanistically, Thbs1 inhibits cleavage and processing of SREBP-1, leading to a reduction of target lipogenic gene expression and hepatic steatosis. Inhibitory effects of Thbs1 on lipogenesis and triglyceride accumulation are abrogated in CD36 deficient primary hepatocytes exposed to high glucose plus insulin. Interestingly, beneficial effects of Thbs1 on lipid accumulation are observed in primary hepatocytes treated with a Thbs1 nonapeptide mimetic ABT-526. INTERPRETATION: Thbs1 is a biomarker for NAFLD in humans, and pharmacological and genetic approaches for the modulation of Thbs1 activity may have the therapeutic potential for treating hepatic steatosis. FUND: A full list of funding bodies that contributed to this study can be found in the Funding Sources section.

The Circadian Protein Period2 Suppresses mTORC1 Activity via Recruiting Tsc1 to mTORC1 Complex.

Although emerging evidence indicates an important role of the circadian clock in modulating the diurnal oscillation of mammalian target of rapamycin complex 1 (mTORC1) signaling, the underlying molecular mechanism remains elusive. Here we show that Period2 (Per2), a core clock protein, functions as a scaffold protein to tether tuberous sclerosis complex 1 (Tsc1), Raptor, and mTOR together to specifically suppress the activity of mTORC1 complex. Due to the loss of its inhibition of mTORC1, Per2 deficiency significantly enhances protein synthesis and cell proliferation but reduces autophagy. Furthermore, we find that the glucagon-Creb/Crtc2 signaling cascade induces Per2 expression, which mediates the suppression of mTORC1 in mouse liver during fasting. Our study not only uncovers a novel role of Per2 in regulating the mTORC1 pathway, but also sheds new light on the mechanism of fasting inhibition on mTORC1 in the liver.

Post-translational regulation of lipogenesis via AMPK-dependent phosphorylation of insulin-induced gene.

Insulin-induced gene (Insig) negatively regulates SREBP-mediated de novo fatty acid synthesis in the liver. However, the upstream regulation of Insig is incompletely understood. Here we report that AMPK interacts with and mediates phosphorylation of Insig. Thr222 phosphorylation following AMPK activation is required for protein stabilization of Insig-1, inhibition of cleavage and processing of SREBP-1, and lipogenic gene expression in response to metformin or A769662. AMPK-dependent phosphorylation ablates Insig's interaction with E3 ubiquitin ligase gp78 and represses its ubiquitination and degradation, whereas AMPK deficiency shows opposite effects. Interestingly, activation of AMPK by metformin causes an augmentation of Insig stability and reduction of lipogenic gene expression, and leads to the attenuation of hepatic steatosis in HFHS diet-fed mice. Moreover, hepatic overexpression of Insig-1 rescues hepatic steatosis in liver-specific AMPKα2 knockout mice fed with HFHS diet. These findings uncover a novel effector of AMPK. Targeting Insig may have the therapeutic potential for treating fatty liver disease and related disorders.

Indole-3-propionic acid inhibits gut dysbiosis and endotoxin leakage to attenuate steatohepatitis in rats.

Microbial metabolites have emerged as critical components that mediate the metabolic effects of the gut microbiota. Here, we show that indole-3-propionic acid (IPA), a tryptophan metabolite produced by gut bacteria, is a potent anti-non-alcoholic steatohepatitis (NASH) microbial metabolite. Here, we demonstrate that administration of IPA modulates the microbiota composition in the gut and inhibits microbial dysbiosis in rats fed a high-fat diet. IPA induces the expression of tight junction proteins, such as ZO-1 and Occludin, and maintains intestinal epithelium homeostasis, leading to a reduction in plasma endotoxin levels. Interestingly, IPA inhibits NF-κB signaling and reduces the levels of proinflammatory cytokines, such as TNFα, IL-1ß, and IL-6, in response to endotoxin in macrophages to repress hepatic inflammation and liver injury. Moreover, IPA is sufficient to inhibit the expression of fibrogenic and collagen genes and attenuate diet-induced NASH phenotypes. The beneficial effects of IPA on the liver are likely mediated through inhibiting the production of endotoxin in the gut. These findings suggest a protective role of IPA in the control of metabolism and uncover the gut microbiome and liver cross-talk in regulating the intestinal microenvironment and liver pathology via a novel dietary nutrient metabolite. IPA may provide a new therapeutic strategy for treating NASH.

Berberine attenuates hepatic steatosis and enhances energy expenditure in mice by inducing autophagy and fibroblast growth factor 21.

BACKGROUND AND PURPOSE: Berberine, a compound from rhizome coptidis, is traditionally used to treat gastrointestinal infections, such as bacterial diarrhoea. Recently, berberine was shown to have hypoglycaemic and hypolipidaemic effects. We investigated the mechanisms by which berberine regulates hepatic lipid metabolism and energy expenditure in mice. EXPERIMENTAL APPROACH: Liver-specific SIRT1 knockout mice and their wild-type littermates were fed a high-fat, high-sucrose (HFHS) diet and treated with berberine by i.p. injection for five weeks. Mouse primary hepatocytes and human HepG2 cells were treated with berberine and then subjected to immunoblotting analysis and Oil Red O staining. KEY RESULTS: Berberine attenuated hepatic steatosis and controlled energy balance in mice by inducing autophagy and FGF21. These beneficial effects of berberine on autophagy and hepatic steatosis were abolished by a deficiency of the nutrient sensor SIRT1 in the liver of HFHS diet-fed obese mice and in mouse primary hepatocytes. SIRT1 is essential for berberine to potentiate autophagy and inhibit lipid storage in mouse livers in response to fasting. Mechanistically, the berberine stimulates SIRT1 deacetylation activity and induces autophagy in an autophagy protein 5-dependent manner. Moreover, the administration of berberine was shown to promote hepatic gene expression and circulating levels of FGF21 and ketone bodies in mice in a SIRT1-dependent manner. CONCLUSIONS AND IMPLICATIONS: Berberine acts in the liver to regulate lipid utilization and maintain whole-body energy metabolism by mediating autophagy and FGF21 activation. Hence, it has therapeutic potential for treating metabolic defects under nutritional overload, such as fatty liver diseases, type 2 diabetes and obesity.

Hepatic ATF6 Increases Fatty Acid Oxidation to Attenuate Hepatic Steatosis in Mice Through Peroxisome Proliferator-Activated Receptor α.

The endoplasmic reticulum quality control protein activating transcription factor 6 (ATF6) has emerged as a novel metabolic regulator. Here, we show that adenovirus-mediated overexpression of the dominant-negative form of ATF6 (dnATF6) increases susceptibility to develop hepatic steatosis in diet-induced insulin-resistant mice and fasted mice. Overexpression of dnATF6 or small interfering RNA-mediated knockdown of ATF6 decreases the transcriptional activity of peroxisome proliferator-activated receptor α (PPARα)/retinoid X receptor complex, and inhibits oxygen consumption rates in hepatocytes, possibly through inhibition of the binding of PPARα to the promoter of its target gene. Intriguingly, ATF6 physically interacts with PPARα, enhances the transcriptional activity of PPARα, and triggers activation of PPARα downstream targets, such as CPT1α and MCAD, in hepatocytes. Furthermore, hepatic overexpression of the active form of ATF6 promotes hepatic fatty acid oxidation and protects against hepatic steatosis in diet-induced insulin-resistant mice. These data delineate the mechanism by which ATF6 controls the activity of PPARα and hepatic mitochondria fatty acid oxidation. Therefore, strategies to activate ATF6 could be used as an alternative avenue to improve liver function and treat hepatic steatosis in obesity.