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

Emerging roles of SIRT1 in fatty liver diseases

Fatty liver diseases, which are commonly associated with high-fat/calorie diet, heavy alcohol consumption and/or other metabolic disorder causes, lead to serious medical concerns worldwide in recent years. It has been demonstrated that metabolic homeostasis disruption is most likely to be responsible for this global epidemic. Sirtuins are a group of conserved nicotinamide adenine dinucleotide (NAD⁺) dependent histone and/or protein deacetylases belonging to the silent information regulator 2 (Sir2) family. Among seven mammalian sirtuins, sirtuin 1 (SIRT 1) is the most extensively studied one and is involved in both alcoholic and nonalcoholic fatty liver diseases. SIRT1 plays beneficial roles in regulating hepatic lipid metabolism, controlling hepatic oxidative stress and mediating hepatic inflammation through deacetylating some transcriptional regulators against the progression of fatty liver diseases. Here we summarize the latest advances of the biological roles of SIRT1 in regulating lipid metabolism, oxidative stress and inflammation in the liver, and discuss the potential of SIRT1 as a therapeutic target for treating alcoholic and nonalcoholic fatty liver diseases.

Targeting NAD+ in Metabolic Disease: New Insights Into an Old Molecule

Nicotinamide adenine dinucleotide (NAD+) is an established cofactor for enzymes serving cellular metabolic reactions. More recent research identified NAD+ as a signaling molecule and substrate for sirtuins and poly-adenosine 5'-diphosphate polymerases; enzymes that regulate protein deacetylation and DNA repair, and translate changes in energy status into metabolic adaptations. Deranged NAD+ homeostasis and concurrent alterations in mitochondrial function are intrinsic in metabolic disorders, such as type 2 diabetes, nonalcoholic fatty liver, and age-related diseases. Contemporary NAD+ precursors show promise as nutraceuticals to restore target tissue NAD+ and have demonstrated the ability to improve mitochondrial function and sirtuin-dependent signaling. This review discusses the accumulating evidence for targeting NAD+ metabolism in metabolic disease, maps the different strategies for NAD+ boosting, and addresses the challenges and open questions in the field. The health potential of targeting NAD+ homeostasis will inform clinical study design to identify nutraceutical approaches for combating metabolic disease and the unwanted effects of aging.

Hepatocyte-specific sirtuin 6 deletion predisposes to nonalcoholic steatohepatitis by up-regulation of Bach1, an Nrf2 repressor

Sirtuin (Sirt)6 has been implicated in negative regulation of inflammation and lipid metabolism, although its function in the progression from simple steatosis to nonalcoholic steatohepatitis (NASH) remains to be defined. To explore the role of hepatocyte Sirt6 in NASH development, we generated hepatocyte-specific Sirt6-knockout (KO) mice that were fed a high-fat and high-fructose (HFHF) diet for 16 wk. HFHF-fed KO mice had increased hepatic steatosis and inflammation and aggravated glucose intolerance and insulin resistance compared with wild-type mice. HFHF-induced liver fibrosis and oxidative stress and related gene expression were significantly elevated in KO mice. In the livers of KO mice, nuclear factor erythroid 2-related factor 2 (Nrf2) was down-regulated; conversely, BTB domain and CNC homolog 1 (Bach1), a nuclear repressor of Nrf2, were up-regulated. We discovered that Sirt6, which interacts with Bach1 under basal condition, induces its detachment from the antioxidant response element (ARE) region of heme oxygenase 1 promoter. Furthermore, we found that Sirt6 promotes Nrf2 binding to ARE in response to oxidative stimuli, which leads to the expression of phase II/antioxidant enzymes. Finally, we showed that HFHF-induced steatosis, inflammation, and fibrosis were ameliorated by adenoviral Sirt6 overexpression. Sirt6 may be a useful therapeutic target for amelioration of NASH by curbing inflammation and oxidative stress.-Ka, S.-O, Bang, I. H., Bae, E. J., Park, B.-H. Hepatocyte-specific sirtuin 6 deletion predisposes to nonalcoholic steatohepatitis by up-regulation of Bach1, an Nrf2 repressor.

Scopolin ameliorates high-fat diet induced hepatic steatosis in mice: potential involvement of SIRT1-mediated signaling cascades in the liver

The present study aimed to investigate whether scopolin exhibits beneficial effects on high-fat diet (HFD)-induced hepatic steatosis in mice. The involvement of sirtuin 1 (SIRT1) as a molecular target for scopolin was also explored. Scopolin decreased the Km of SIRT1 for p53 and nicotinamide adenine dinucleotide without altering Vmax in a cell-free system. Scopolin alleviated oleic acid-induced lipid accumulation and downregulation of SIRT1 activity in HepG2 cells, and these beneficial effects of scopolin were abolished in the presence of SIRT1 inhibitor. Mice administered 0.02% scopolin for 8 weeks exhibited improved phenotypes of HFD-induced hepatic steatosis along with increased hepatic SIRT1 activity and protein expression. Scopolin resulted in increased deacetylation of sterol regulatory element-binding protein 1c with subsequent downregulation of lipogenic genes, and enhanced deacetylation of protein peroxisome proliferator-activated receptor-γ coactivator 1α with upregulation of fatty acid oxidation genes in livers. Scopolin also enhanced deacetylation of nuclear factor-kappa enhancer binding protein and liver kinase B1 (LKB1), facilitating LKB1/AMP-activated protein kinase signaling cascades. Scopolin attenuated hepatic steatosis through activation of SIRT1-mediated signaling cascades, a potent regulator of lipid homeostasis. Increased hepatic SIRT1 activity and protein expression appeared to be associated with these beneficial effects of scopolin.

Link Between ER-Stress, PPAR-Alpha Activation, and BET Inhibition in Relation to Apolipoprotein A-I Transcription in HepG2 Cells

Activating transcription factor peroxisome proliferator-activated receptor alpha (PPARα) may increase apoA-I transcription. Furthermore, Bromodomain and Extra-Terminal domain (BET) protein inhibitors increase, whereas Endoplasmic Reticulum (ER) stress decreases apoA-I transcription. We examined possible links between these processes as related to apoA-I transcription in HepG2 cells. JQ1(+), thapsigargin, and GW7647 were used to induce, respectively BET inhibition, ER-stress, and PPARα activation. Expression of ER-stress markers (CHOP, XBP1s) was analyzed by western blotting. PPARα, KEAP1 (marker for BET inhibition), and apoA-I mRNAs were measured using qPCR. ER-stress and BET inhibition both decreased PPARα mRNA expression and activity, but did not interfere with each other, as ER-stress did not change KEAP1 and JQ1(+) did not influence ER-stress marker production. Interestingly, PPARα activation and BET-inhibition diminished ER-stress marker production and rescued apoA-I transcription during existing ER-stress. We conclude that the ER-stress mediated reduction in apoA-I transcription could be partly mediated via the inhibition of PPARα mRNA expression and activity. In addition, BET inhibition increased apoA-I transcription, even if PPARα production and activity were decreased. Finally, both BET inhibition and PPARα activation ameliorate the apoA-I lowering effect of ER-stress and are therefore interesting targets to elevate apoA-I transcription. J. Cell. Biochem. 118:2161-2167, 2017. © 2016 Wiley Periodicals, Inc.

Metabolic role of fibroblast growth factor 21 in liver, adipose and nervous system tissues

The hepatokine fibroblast growth factor 21 (FGF21) is a novel polypeptide ligand, which is involved in glucose and lipid metabolism, and contributes significantly to lowering body weight and enhancing insulin sensitivity. A large number of pre-clinical and clinical results demonstrate that FGF21 is a potential drug target for treating obesity and type 2 diabetes mellitus. In the present review, the tissue specific actions and molecular mechanisms of FGF21 are discussed with a focus on the liver, adipose tissue and nervous system, as well as investigating the outcomes of clinical trials of FGF21, with the aim of interpreting and delineating the complexity physiology of FGF21.

Optimized Analysis of In Vivo and In Vitro Hepatic Steatosis

Establishing a system of procedures to qualitatively and quantitatively characterize in vivo and in vitro hepatic steatosis is important for metabolic study in the liver. Here, numerous assays are described to comprehensively measure the phenotype and parameters of hepatic steatosis in mouse and hepatocyte models. Combining the physiological, histological, and biochemical methods, this system can be used to assess the progress of hepatic steatosis. In vivo, the measurements of body weight and nuclear magnetic resonance (NMR) provide a general understanding of mice in a non-invasive manner. Hematoxylin and Eosin (H&E) and Oil Red O staining determine the histological morphology and lipid deposition of liver tissue under nutrient overload conditions, such as high-fat diet feeding. Next, the total lipid contents are isolated by chloroform/methanol extraction, which are followed by a biochemical analysis for triglyceride and cholesterol. Moreover, mouse primary hepatocytes are treated with high glucose plus insulin to stimulate lipid accumulation, an efficient in vitro model to mimic diet-induced hyperglycemia and hyperinsulinemia in vivo. Then, the lipid deposition is measured by Oil Red O staining and chloroform/methanol extraction. Oil Red O staining determines intuitive hepatic steatotic phenotypes, while the lipid extraction analysis determines the parameters that can be analyzed statistically. The present protocols are of interest to scientists in the fields of fatty liver diseases, insulin resistance, and type 2 diabetes.

Aging aggravates alcoholic liver injury and fibrosis in mice by downregulating sirtuin 1 expression

BACKGROUND & AIMS

Aging is known to exacerbate the progression of alcoholic liver disease (ALD), but the underlying mechanisms remain obscure. The aim of this study was to use a chronic plus binge ethanol feeding model in mice to evaluate the effects of aging on alcohol-induced liver injury.

METHODS

C57BL/6 mice were subjected to short-term (10days) ethanol plus one binge or long-term (8weeks) ethanol plus multiple binges of ethanol. Liver injury and fibrosis were determined. Hepatic stellate cells (HSCs) were isolated and used in in vitro studies.

RESULTS

Middle-aged (12-14months) and old-aged (>16months) mice were more susceptible to liver injury, inflammation, and oxidative stress induced by short-term plus one binge or long-term plus multiple binges of ethanol feeding when compared to young (8-12weeks) mice. Long-term plus multiple binges of ethanol feeding induced greater liver fibrosis in middle-aged mice than that in young mice. Hepatic expression of sirtuin 1 (SIRT1) protein was downregulated in the middle-aged mice compared to young mice. Restoration of SIRT1 expression via the administration of adenovirus-SIRT1 vector ameliorated short-term plus binge ethanol-induced liver injury and fibrosis in middle-aged mice. HSCs isolated from middle-aged mice expressed lower levels of SIRT1 protein and were more susceptible to spontaneous activation in in vitro culture than those from young mice. Overexpression of SIRT1 reduced activation of HSCs from middle-aged mice in vitro with downregulation of PDGFR-α and c-Myc, while deletion of SIRT1 activated HSCs isolated from young mice in vitro. Finally, HSC-specific SIRT1 knockout mice were more susceptible to long-term chronic-plus-multiple binges of ethanol-induced liver fibrosis with upregulation of PDGFR-α expression.

CONCLUSIONS

Aging exacerbates ALD in mice through the downregulation of SIRT1 in hepatocytes and HSCs. Activation of SIRT1 may serve as a novel target for the treatment of ALD.

LAY SUMMARY

Aged mice are more susceptible to alcohol-induced liver injury and fibrosis, which is, at least in part, due to lower levels of sirtuin 1 protein in hepatocytes and hepatic stellate cells. Our findings suggest that sirtuin 1 activators may have beneficial effects for the treatment of alcoholic liver disease in aged patients.

Fibroblast growth factor 21 night watch: advances and uncertainties in the field

Fibroblast growth factor (FGF) 21 belongs to a hormone-like subgroup within the FGF superfamily. The members of this subfamily, FGF19, FGF21 and FGF23, are characterized by their reduced binding affinity for heparin that enables them to be transported in the circulation and function in an endocrine manner. It is likely that FGF21 also acts in an autocrine and paracrine fashion, as multiple organs can produce this protein and its plasma concentration seems to be below the level necessary to induce a pharmacological effect. FGF21 signals via FGF receptors, but for efficient receptor engagement it requires a cofactor, membrane-spanning βKlotho (KLB). The regulation of glucose uptake in adipocytes was the initial biological activity ascribed to FGF21, but this hormone is now recognized to stimulate many other pathways in vitro and display multiple pharmacological effects in metabolically compromised animals and humans. Understanding of the precise physiology of FGF21 and its potential medicinal role has evolved exponentially over the last decade, yet numerous aspects remain to be defined and others are a source of debate. Here we provide a historical overview of the advances in FGF21 biology focusing on the uncertainties in the mechanism of action as well as the differing viewpoints relating to this intriguing protein.

β-Caryophyllene protects against alcoholic steatohepatitis by attenuating inflammation and metabolic dysregulation in mice

BACKGROUND AND AIMS

β-Caryophyllene (BCP) is a plant-derived FDA approved food additive with anti-inflammatory properties. Some of its beneficial effects in vivo are reported to involve activation of cannabinoid CB₂ receptors that are predominantly expressed in immune cells. Here, we evaluated the translational potential of BCP using a well-established model of chronic and binge alcohol-induced liver injury.

METHODS

In this study, we investigated the effects of BCP on liver injury induced by chronic plus binge alcohol feeding in mice in vivo by using biochemical assays, real-time PCR and histology analyses. Serum and hepatic BCP levels were also determined by GC/MS.

RESULTS

Chronic treatment with BCP alleviated the chronic and binge alcohol-induced liver injury and inflammation by attenuating the pro-inflammatory phenotypic `M1` switch of Kupffer cells and by decreasing the expression of vascular adhesion molecules intercellular adhesion molecule 1, E-Selectin and P-Selectin, as well as the neutrophil infiltration. It also beneficially influenced hepatic metabolic dysregulation (steatosis, protein hyperacetylation and PPAR-α signalling). These protective effects of BCP against alcohol-induced liver injury were attenuated in CB₂ receptor knockout mice, indicating that the beneficial effects of this natural product in liver injury involve activation of these receptors. Following acute or chronic administration, BCP was detectable both in the serum and liver tissue homogenates but not in the brain.

CONCLUSIONS

Given the safety of BCP in humans, this food additive has a high translational potential in treating or preventing hepatic injury associated with oxidative stress, inflammation and steatosis.

LINKED ARTICLES

This article is part of a themed section on Inventing New Therapies Without Reinventing the Wheel: The Power of Drug Repurposing. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.2/issuetoc.

Antidiabetic Effect of Brain-Derived Neurotrophic Factor and Its Association with Inflammation in Type 2 Diabetes Mellitus

Brain-derived neurotrophic factor (BDNF) is a neurotrophin, which plays an important role in the central nervous system, and systemic or peripheral inflammatory conditions, such as acute coronary syndrome and type 2 diabetes mellitus (T2DM). BDNF is also expressed in several nonneuronal tissues, and platelets are the major source of peripheral BDNF. Here, we reviewed the potential role of BDNF in platelet reactivity in T2DM and its association with selected inflammatory and platelet activation mediators. Besides that, we focused on adipocytokines such as leptin, resistin, and adiponectin which are considered to take part in inflammation and both lipid and glucose metabolism in diabetic patients as previous studies showed the relation between adipocytokines and BDNF. We also reviewed the evidences of the antidiabetic effect of BDNF and the association with circulating inflammatory cytokines in T2DM.

The transcription cofactor CRTC1 protects from aberrant hepatic lipid accumulation

Nonalcoholic fatty liver disease (NAFLD) is a rapidly emerging global health-problem. NAFLD encompasses a range of conditions associated with hepatic steatosis, aberrant accumulation of fat in hepatocytes. Although obesity and metabolic syndrome are considered to have a strong association with NAFLD, genetic factors that predispose liver to NAFLD and molecular mechanisms by which excess hepatic lipid develops remain largely unknown. We report that the transcription cofactor CRTC1 confers broad spectrum protection against hepatic steatosis development. CRTC1 directly interferes with the expression of genes regulated by lipogenic transcription factors, most prominently liver x receptor α (LXRα). Accordingly, Crtc1 deficient mice develop spontaneous hepatic steatosis in young age. As a cyclic AMP effector, CRTC1 mediates anti-steatotic effects of calorie restriction (CR). Notably, CRTC1 also mediates anti-lipogenic effects of bile acid signaling, whereas it is negatively regulated by miR-34a, a pathogenic microRNA upregulated in a broad spectrum of NAFLD. These patterns of gene function and regulation of CRTC1 are distinct from other CR-responsive proteins, highlighting critical protective roles that CRTC1 selectively plays against NAFLD development, which in turn provides novel opportunities for selectively targeting beneficial therapeutic effects of CR.

Lycium barbarum polysaccharide attenuates high-fat diet-induced hepatic steatosis by up-regulating SIRT1 expression and deacetylase activity

In this study, we aimed to investigate the protective effects and underlying mechanism of Lycium barbarum polysaccharide (LBP) on high-fat-induced nonalcoholic fatty liver disease (NAFLD). Recently, sirtuin 1 (SIRT1) has been shown to play an important role in the regulation of hepatocellular lipid metabolism. Here, we demonstrated that LBP up-regulates SIRT1 deacetylase activity and protein expression by enhancing the NAD⁺/NADH ratio. Subsequently, LBP promoted LKB1 deacetylation and AMPK phosphorylation via SIRT1-dependent signalling. We also found that LBP increases acetyl-CoA carboxylase (ACC) phosphorylation and adipose triglyceride lipase (ATGL) protein expression and decreases fatty acid synthase (FAS) by activating the SIRT1/LKB1/AMPK pathway in vitro and in vivo. However, SIRT1 small interfering RNA (siRNA)-mediated knockdown reversed the LBP-mediated effects on ACC, FAS and ATGL. Moreover, LBP elevated carnitine palmitoyltransferase-1 alpha (CPT-1α) expression by suppressing malonyl-CoA accumulation. Taken together, our data indicate that LBP plays a vital role in the regulation of hepatic lipid metabolism and that pharmacological activation of SIRT1 by LBP may be a strategy for the prevention of NAFLD.

Inactivation of Sirt1 in mouse livers protects against endotoxemic liver injury by acetylating and activating NF-κB

Sirtuin 1 (Sirt1) is a deacetylase that regulates many cellular processes in the liver, and so far its role in endotoxemic liver injury is elusive. So we conditionally inactivate Sirt1 in murine hepatocytes to determine its role in d-galactosamine (GalN)/lipopolysaccharide (LPS)-induced liver damage, which is a well-established experimental model mimicking septic liver injury and fulminant hepatitis. Ablation of Sirt1 shows remarkable protection against GalN/LPS-induced liver injury, which is a result of enhanced NF-κB response because knockdown of RelA/p65 negates the protective effect of Sirt1 knockout. Mechanistically, NF-κB p65 is maintained in a hyperacetylated, DNA-binding competent state in tumor necrosis factor-α (TNF-α)-challenged albumin-Cre⁺ (AlbCre⁺) hepatocytes. Transfection of hepatocytes with a recombinant acetylated p65 expression construct replicates the protection afforded by Sirt1 knockout. Transfection of AlbCre⁺ hepatocytes with a recombinant wild-type Sirt1 construct, rather than a deacetylase-defective one, compromises NF-κB activation and resensitizes hepatocytes to TNF-α-induced apoptosis. Taken together, our results demonstrate that Sirt1 deacetylates p65 and compromises NF-κB activity in hepatocytes when confronted with LPS/TNF-α stimulation, leading to increased susceptibility to endotoxemic injury. These findings identify a possible protein effector to maneuver the hepatic NF-κB signaling pathway under inflammatory circumstances and a feasible way to increase hepatocellular resistance to endotoxin/TNF-α toxicity.

Heme-Regulated eIF2α Kinase Modulates Hepatic FGF21 and Is Activated by PPARβ/δ Deficiency

Fibroblast growth factor 21 (FGF21), a peptide hormone with pleiotropic effects on carbohydrate and lipid metabolism, is considered a target for the treatment of diabetes. We investigated the role of peroxisome proliferator-activated receptor (PPAR) β/δ deficiency in hepatic FGF21 regulation. Increased Fgf21 expression was observed in the livers of PPARβ/δ-null mice and in mouse primary hepatocytes when this receptor was knocked down by small interfering RNA (siRNA). Increased Fgf21 was associated with enhanced protein levels in the heme-regulated eukaryotic translation initiation factor 2α (eIF2α) kinase (HRI). This increase caused enhanced levels of phosphorylated eIF2α and activating transcription factor (ATF) 4, which is essential for Fgf21-induced expression. siRNA analysis demonstrated that HRI regulates Fgf21 expression in primary hepatocytes. Enhanced Fgf21 expression attenuated tunicamycin-induced endoplasmic reticulum stress, as demonstrated by using a neutralizing antibody against FGF21. Of note, increased Fgf21 expression in mice fed a high-fat diet or hepatocytes exposed to palmitate was accompanied by reduced PPARβ/δ and activation of the HRI-eIF2α-ATF4 pathway. Moreover, pharmacological activation of HRI increased Fgf21 expression and reduced lipid-induced hepatic steatosis and glucose intolerance, but these effects were not observed in Fgf21-null mice. Overall, these findings suggest that HRI is a potential target for regulating hepatic FGF21 levels.

FGF21 activates AMPK signaling: impact on metabolic regulation and the aging process

Fibroblast growth factor 21 (FGF21) has a significant role in the regulation of energy metabolism, e.g., in the control of systemic glucose and lipid metabolism. For instance, FGF21 enhances insulin sensitivity, increases glucose uptake, and thus can decrease serum hyperglycemia, while it also increases lipid oxidation and inhibits lipogenesis. AMP-activated protein kinase (AMPK) is a tissue energy sensor involved in maintaining the energy balance and tissue integrity. It is known that AMPK signaling generates an energy metabolic profile which displays a remarkable overlap with that of FGF21. There is convincing evidence that endocrine FGF21 signaling activates the AMPK pathway, either directly through FGFR1/β-klotho signaling or indirectly by stimulating the secretion of adiponectin and corticosteroids, which consequently can activate AMPK signaling in their target tissues. By activating AMPK, FGF21 can promote a healthy aging process and thus extend mammalian lifespan. We will examine the signaling mechanisms through which FGF21 can activate the AMPK pathway and then discuss the significance of the close connection between FGF21 and AMPK signaling in the control of metabolic disorders and the aging process.

Hepatic Fasting-Induced PPARα Activity Does Not Depend on Essential Fatty Acids

The liver plays a central role in the regulation of fatty acid metabolism, which is highly sensitive to transcriptional responses to nutrients and hormones. Transcription factors involved in this process include nuclear hormone receptors. One such receptor, PPARα, which is highly expressed in the liver and activated by a variety of fatty acids, is a critical regulator of hepatic fatty acid catabolism during fasting. The present study compared the influence of dietary fatty acids and fasting on hepatic PPARα-dependent responses. Pparα^−/− male mice and their wild-type controls were fed diets containing different fatty acids for 10 weeks prior to being subjected to fasting or normal feeding. In line with the role of PPARα in sensing dietary fatty acids, changes in chronic dietary fat consumption influenced liver damage during fasting. The changes were particularly marked in mice fed diets lacking essential fatty acids. However, fasting, rather than specific dietary fatty acids, induced acute PPARα activity in the liver. Taken together, the data imply that the potent signalling involved in triggering PPARα activity during fasting does not rely on essential fatty acid-derived ligand.

Promising therapies for treatment of nonalcoholic steatohepatitis

INTRODUCTION

Non-alcoholic fatty liver disease (NAFLD) has become the most common etiology for abnormal aminotransferase levels and chronic liver disease. Its growing prevalence is largely linked to the presence of metabolic syndrome, particularly diabetes and insulin resistance. It is estimated that 60-80% of the type 2 diabetic population has NAFLD. NAFLD encompasses a range of conditions ranging from simple steatosis to non-alcoholic steatohepatitis (NASH). A subset of patients with hepatic steatosis progress to NASH, while 15-20% of patients with NASH develop cirrhosis. This progression is thought to be multifactorial, and there are currently no FDA-approved medications for the treatment of NASH.

AREAS COVERED

We review drugs currently in Phase II and III clinical trials for treatment of NAFLD and NASH, including their mechanisms of action, relationship to the pathophysiology of NASH, and rationale for their development.

EXPERT OPINION

The treatment of NASH is complex and necessitates targeting a number of different pathways. Combination therapy, preferably tailored toward the disease stage and severity, will be needed to achieve maximum therapeutic effect. With multiple agents currently being developed, there may soon be an ability to effectively slow or even reverse the disease process in many NAFLD/NASH patients.

Fibroblast growth factor 21 deficiency exacerbates chronic alcohol-induced hepatic steatosis and injury

Fibroblast growth factor 21 (FGF21) is a hepatokine that regulates glucose and lipid metabolism in the liver. We sought to determine the role of FGF21 in hepatic steatosis in mice exposed to chronic alcohol treatment and to discern underlying mechanisms. Male FGF21 knockout (FGF21 KO) and control (WT) mice were divided into groups that were fed either the Lieber DeCarli diet containing 5% alcohol or an isocaloric (control) diet for 4 weeks. One group of WT mice exposed to alcohol received recombinant human FGF21 (rhFGF21) in the last 5 days. Liver steatosis and inflammation were assessed. Primary mouse hepatocytes and AML-12 cells were incubated with metformin or rhFGF21. Hepatic genes and the products involved in in situ lipogenesis and fatty acid β-oxidation were analyzed. Alcohol exposure increased circulating levels and hepatic expression of FGF21. FGF21 depletion exacerbated alcohol-induced hepatic steatosis and liver injury, which was associated with increased activation of genes involved in lipogenesis mediated by SREBP1c and decreased expression of genes involved in fatty acid β-oxidation mediated by PGC1α. rhFGF21 administration reduced alcohol-induced hepatic steatosis and inflammation in WT mice. These results reveal that alcohol-induced FGF21 expression is a hepatic adaptive response to lipid dysregulation. Targeting FGF21 signaling could be a novel treatment approach for alcoholic steatohepatitis.

Fibroblast growth factor 21 improves hepatic insulin sensitivity by inhibiting mammalian target of rapamycin complex 1 in mice

Among the 22 fibroblast growth factors (FGFs), FGF21 has now emerged as a key metabolic regulator. However, the mechanism whereby FGF21 mediates its metabolic actions per se remains largely unknown. Here, we show that FGF21 represses mammalian target of rapamycin complex 1 (mTORC1) and improves insulin sensitivity and glycogen storage in a hepatocyte-autonomous manner. Administration of FGF21 in mice inhibits mTORC1 in the liver, whereas FGF21-deficient mice display pronounced insulin-stimulated mTORC1 activation and exacerbated hepatic insulin resistance (IR). FGF21 inhibits insulin- or nutrient-stimulated activation of mTORC1 to enhance phosphorylation of Akt in HepG2 cells at both normal and IR condition. TSC1 deficiency abrogates FGF21-mediated inhibition of mTORC1 and augmentation of insulin signaling and glycogen synthesis. Strikingly, hepatic βKlotho knockdown or hepatic hyperactivation of mTORC1/ribosomal protein S6 kinase 1 abrogates hepatic insulin-sensitizing and glycemic-control effects of FGF21 in diet-induced insulin-resistant mice. Moreover, FGF21 improves methionine- and choline-deficient diet-induced steatohepatitis.

CONCLUSIONS

FGF21 acts as an inhibitor of mTORC1 to control hepatic insulin action and maintain glucose homeostasis, and mTORC1 inhibition by FGF21 has the therapeutic potential for treating IR and type 2 diabetes. (Hepatology 2016;64:425-438).

Emerging Liver-Kidney Interactions in Nonalcoholic Fatty Liver Disease

Mounting evidence connects non-alcoholic fatty liver disease (NAFLD) to chronic kidney disease (CKD). We review emerging mechanistic links between NAFLD and CKD, including altered activation of angiotensin converting enzyme (ACE)-2, nutrient/energy sensors sirtuin-1 and AMP-activated kinase, as well as impaired antioxidant defense mediated by nuclear factor erythroid 2-related factor-2 (Nrf2). Dietary fructose excess may also contribute to NAFLD and CKD. NAFLD affects renal injury through lipoprotein dysmetabolism and altered secretion of the hepatokines fibroblast growth factor-21, fetuin-A, insulin-like growth factor-1, and syndecan-1. CKD may mutually aggravate NAFLD and associated metabolic disturbances through altered intestinal barrier function and microbiota composition, the accumulation of uremic toxic metabolites, and alterations in pre-receptor glucocorticoid metabolism. We conclude by discussing the implications of these findings for the treatment of NAFLD and CKD.

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.

Expression of fibroblast growth factor 21 in patients with biliary atresia

Fibroblast growth factor 21 is a critical circulating adipokine involving in metabolic disorders and various liver diseases. This study was performed to investigate whether FGF21 is also associated with the pathophysiology of biliary atresia. Serum FGF21 levels were measured in 57 BA patients and 20 age matched healthy controls. We also examined hepatic FGF21 mRNA expression and FGF21 protein levels in liver tissues obtained from 15 BA patients undergoing liver transplantation and 5 cases of pediatric donation after cardiac death donor without liver diseases by RT-PCR and Western blotting. Patients with BA showed significantly higher serum FGF21 levels than those without BA (554.7pg/mL [83-2300] vs. 124.5pg/mL [66-270], P<0.05). Patients with BA also had significantly higher FGF21 mRNA and protein levels in hepatic tissues than control subjects. Serum FGF21 expression increased corresponding to the severity of liver fibrosis. Furthermore, serum FGF21 levels dropped significantly in BA patients within 6months after liver transplantation and approached baseline in healthy controls (P>0.05). In vivo, FXR knockout could significantly abrogate cholestasis induced FGF21 expression. FGF21 levels in serum and liver tissue increased significantly in BA patients. In vivo, cholestasis could induce FGF21 expression in FXR dependent manner.

The Effects of High Fat Diet and Resveratrol on Mitochondrial Activity of Brown Adipocytes

BACKGROUND

Resveratrol (RSV) is a polyphenolic phytoalexin that has many effects on metabolic diseases such as diabetes and obesity. Given the importance of brown adipose tissue (BAT) for energy expenditure, we investigated the effects of RSV on brown adipocytes.

METHODS

For the in vitro study, interscapular BAT was isolated from 7-week-old male Sprague Dawley rats. For the in vivo study, 7-week-old male Otsuka Long Evans Tokushima Fatty (OLETF) rats were divided into four groups and treated for 27 weeks with: standard diet (SD); SD+RSV (10 mg/kg body weight, daily); high fat diet (HFD); HFD+RSV. RSV was provided via oral gavage once daily during the in vivo experiments.

RESULTS

RSV treatment of primary cultured brown preadipocytes promoted mitochondrial activity, along with over-expression of estrogen receptor α (ER-α). In OLETF rats, both HFD and RSV treatment increased the weight of BAT and the differentiation of BAT. However, only RSV increased the mitochondrial activity and ER-α expression of BAT in the HFD-fed group. Finally, RSV improved the insulin sensitivity of OLETF rats by increasing the mitochondrial activity of BAT, despite having no effects on white adipocytes and muscles in either diet group.

CONCLUSION

RSV could improve insulin resistance, which might be associated with mitochondrial activity of brown adipocyte. Further studies evaluating the activity of RSV for both the differentiation and mitochondrial activity of BAT could be helpful in investigating the effects of RSV on metabolic parameters.

Roles of FGFs As Paracrine or Endocrine Signals in Liver Development, Health, and Disease

The liver plays important roles in multiple processes including metabolism, the immune system, and detoxification and also has a unique capacity for regeneration. FGFs are growth factors that have diverse functions in development, health, and disease. The FGF family now comprises 22 members. Several FGFs have been shown to play roles as paracrine signals in liver development, health, and disease. FGF8 and FGF10 are involved in embryonic liver development, FGF7 and FGF9 in repair in response to liver injury, and FGF5, FGF8, FGF9, FGF17, and FGF18 in the development and progression of hepatocellular carcinoma. In contrast, FGF15/19 and FGF21 are endocrine signals. FGF15/19, which is produced in the ileum, is a negative regulator of bile acid metabolism and a stimulator of gallbladder filling. FGF15/19 is a postprandial, insulin-independent activator of hepatic protein and glycogen synthesis. It is also required for hepatocellular carcinoma and liver regeneration. FGF21 is a hepatokine produced in the liver. FGF21 regulates glucose and lipid metabolism in white adipose tissue. Serum FGF21 levels are elevated in non-alcoholic fatty liver. FGF21 also protects against non-alcoholic fatty liver. These findings provide new insights into the roles of FGFs in the liver and potential therapeutic strategies for hepatic disorders.

Fibroblast Growth Factor 21 As an Emerging Therapeutic Target for Type 2 Diabetes Mellitus

Fibroblast growth factor (FGF) 21 is a distinctive member of the FGF family that functions as an endocrine factor. It is expressed predominantly in the liver, but is also found in adipose tissue and the pancreas. Pharmacological studies have shown that FGF21 normalizes glucose and lipid homeostasis, thereby preventing the development of metabolic disorders, such as obesity and diabetes. Despite growing evidence for the therapeutic potential of FGF21, paradoxical increases of FGF21 in different disease conditions point to the existence of FGF21 resistance. In this review, we give a critical appraisal of recent advances in the understanding of the regulation of FGF21 production under various physiological conditions, its antidiabetic actions, and the clinical implications. We also discuss recent preclinical and clinical trials using engineered FGF21 analogs in the management of diabetes, as well as the potential side effects of FGF21 therapy.

The Role of Clinical Proteomics, Lipidomics, and Genomics in the Diagnosis of Alzheimer's Disease

The early diagnosis of Alzheimer’s disease (AD) has become important to the reversal and treatment of neurodegeneration, which may be relevant to premature brain aging that is associated with chronic disease progression. Clinical proteomics allows the detection of various proteins in fluids such as the urine, plasma, and cerebrospinal fluid for the diagnosis of AD. Interest in lipidomics has accelerated with plasma testing for various lipid biomarkers that may with clinical proteomics provide a more reproducible diagnosis for early brain aging that is connected to other chronic diseases. The combination of proteomics with lipidomics may decrease the biological variability between studies and provide reproducible results that detect a community’s susceptibility to AD. The diagnosis of chronic disease associated with AD that now involves genomics may provide increased sensitivity to avoid inadvertent errors related to plasma versus cerebrospinal fluid testing by proteomics and lipidomics that identify new disease biomarkers in body fluids, cells, and tissues. The diagnosis of AD by various plasma biomarkers with clinical proteomics may now require the involvement of lipidomics and genomics to provide interpretation of proteomic results from various laboratories around the world.

Fibroblast Growth Factor 21 Mediates Glycemic Regulation by Hepatic JNK

The cJun NH2-terminal kinase (JNK)-signaling pathway is implicated in metabolic syndrome, including dysregulated blood glucose concentration and insulin resistance. Fibroblast growth factor 21 (FGF21) is a target of the hepatic JNK-signaling pathway and may contribute to the regulation of glycemia. To test the role of FGF21, we established mice with selective ablation of the Fgf21 gene in hepatocytes. FGF21 deficiency in the liver caused marked loss of FGF21 protein circulating in the blood. Moreover, the protective effects of hepatic JNK deficiency to suppress metabolic syndrome in high-fat diet-fed mice were not observed in mice with hepatocyte-specific FGF21 deficiency, including reduced blood glucose concentration and reduced intolerance to glucose and insulin. Furthermore, we show that JNK contributes to the regulation of hepatic FGF21 expression during fasting/feeding cycles. These data demonstrate that the hepatokine FGF21 is a key mediator of JNK-regulated metabolic syndrome.

Protective role of silent information regulator 1 against hepatic ischemia: effects on oxidative stress injury, inflammatory response, and MAPKs

OBJECTIVE

Previous studies have verified that silent information regulator 1 (SIRT1), a class III histone deacetylase, protects against ischemia reperfusion (IR) injury (IRI) in some organs. In this study, we examined whether SIRT1 could protect against hepatic IRI and explored the potential mechanisms.

RESEARCH DESIGN AND METHODS

We examined whether SIRT1 could protect against hepatic IRI in vivo and in vitro using hepatic-specific SIRT1(-/-) mice, SIRT1 siRNA-transfected hepatocytes and SIRT1(+/+) hepatocytes.

RESULTS

The expression and activity of SIRT1 were significantly reduced during reperfusion compared with that observed in the control group. Hepatic-specific SIRT1(-/-) mice exhibited significant increase of hepatic damage markers and augment of oxidative stress and inflammatory response compared with control mice. In vitro studies demonstrated similar results. Furthermore, SIRT1 upregulation protects against hepatic IRI, through the overexpression of p-JNK, p-p38MAPK, and p-ERK. The protection of SIRT1 can be effectively reversed by the inhibitors of p38MAPK, JNK, and ERK.

CONCLUSION

The activation of SIRT1 significantly inhibits the oxidative stress and inflammatory response during hepatic IRI, which can be developed as a novel method to protect against hepatic IRI.

The emerging role of fibroblast growth factor 21 in diabetic nephropathy

Diabetic nephropathy (DN), an important cause of end-stage renal diseases, brings about great social and economic burden. Due to the variable pathological changes and clinical course, the prognosis of DN is very difficult to predict. DN is also usually associated with enhanced genomic damage and cellular injury. Fibroblast growth factor 21 (FGF21), a nutritionally regulated hormone secreted mainly by the liver, plays a critical role in metabolism. Administration of FGF21 decreases blood glucose, triglyceride, and cholesterol levels, and improves insulin sensitivity, which is closely associated with the development and progression of glomerular diseases. In addition, FGF21 level was associated with renal function. However, the precise role of FGF21 in DN remains unclear. This review will give a comprehensive understanding of the underlying role of FGF21 and its possible interaction with other molecules in DN.

Acetylation of lysine 109 modulates pregnane X receptor DNA binding and transcriptional activity

Pregnane X receptor (PXR) is a major transcriptional regulator of xenobiotic metabolism and transport pathways in the liver and intestines, which are critical for protecting organisms against potentially harmful xenobiotic and endobiotic compounds. Inadvertent activation of drug metabolism pathways through PXR is known to contribute to drug resistance, adverse drug-drug interactions, and drug toxicity in humans. In both humans and rodents, PXR has been implicated in non-alcoholic fatty liver disease, diabetes, obesity, inflammatory bowel disease, and cancer. Because of PXR's important functions, it has been a therapeutic target of interest for a long time. More recent mechanistic studies have shown that PXR is modulated by multiple PTMs. Herein we provide the first investigation of the role of acetylation in modulating PXR activity. Through LC-MS/MS analysis, we identified lysine 109 (K109) in the hinge as PXR's major acetylation site. Using various biochemical and cell-based assays, we show that PXR's acetylation status and transcriptional activity are modulated by E1A binding protein (p300) and sirtuin 1 (SIRT1). Based on analysis of acetylation site mutants, we found that acetylation at K109 represses PXR transcriptional activity. The mechanism involves loss of RXRα dimerization and reduced binding to cognate DNA response elements. This mechanism may represent a promising therapeutic target using modulators of PXR acetylation levels. This article is part of a Special Issue entitled: Xenobiotic nuclear receptors: New Tricks for An Old Dog, edited by Dr. Wen Xie.

Dietary and pharmacological modification of the insulin/IGF-1 system: exploiting the full repertoire against cancer

As more and more links between cancer and metabolism are discovered, new approaches to treat cancer using these mechanisms are considered. Dietary restriction of either calories or macronutrients has shown great potential in animal studies to both reduce the incidence and growth of cancer, and to act synergistically with other treatment strategies. These studies have also shown that dietary restriction simultaneously targets many of the molecular pathways that are targeted individually by anticancer drugs. The insulin/insulin-like growth factor-1 (IGF-1) system has thereby emerged as a key regulator of cancer growth pathways. Although lowering of insulin levels with diet or drugs such as metformin and diazoxide seems generally beneficial, some practitioners also utilize strategic elevations of insulin levels in combination with chemotherapeutic drugs. This indicates a broad spectrum of possibilities for modulating the insulin/IGF-1 system in cancer treatment. With a specific focus on dietary restriction, insulin administration and the insulin-lowering drug diazoxide, such modifications of the insulin/IGF-1 system are the topic of this review. Although preclinical data are promising, we point out that insulin regulation and the metabolic response to a certain diet often differ between mice and humans. Thus, the need for collecting more human data has to be emphasized.

Fibroblast Growth Factor 21 Protects against Atherosclerosis via Fine-Tuning the Multiorgan Crosstalk

Fibroblast growth factor 21 (FGF21) is a metabolic hormone with pleiotropic effects on energy metabolism and insulin sensitivity. Besides its antiobese and antidiabetic activity, FGF21 also possesses the protective effects against atherosclerosis. Circulating levels of FGF21 are elevated in patients with atherosclerosis, macrovascular and microvascular complications of diabetes, possibly due to a compensatory upregulation. In apolipoprotein E-deficient mice, formation of atherosclerotic plaques is exacerbated by genetic depletion of FGF21, but is attenuated upon replenishment with recombinant FGF21. However, the blood vessel is not the direct target of FGF21, and the antiatherosclerotic activity of FGF21 is attributed to its actions in adipose tissues and liver. In adipocytes, FGF21 promotes secretion of adiponectin, which in turn acts directly on blood vessels to reduce endothelial dysfunction, inhibit proliferation of smooth muscle cells and block conversion of macrophages to foam cells. Furthermore, FGF21 suppresses cholesterol biosynthesis and attenuates hypercholesterolemia by inhibiting the transcription factor sterol regulatory element-binding protein-2 in hepatocytes. The effects of FGF21 on elevation of adiponectin and reduction of hypercholesterolemia are also observed in a phase-1b clinical trial in patients with obesity and diabetes. Therefore, FGF21 exerts its protection against atherosclerosis by fine-tuning the interorgan crosstalk between liver, brain, adipose tissue, and blood vessels.

Non-alcoholic steatohepatitis: emerging molecular targets and therapeutic strategies

Non-alcoholic fatty liver disease - the most common chronic liver disease - encompasses a histological spectrum ranging from simple steatosis to non-alcoholic steatohepatitis (NASH). Over the next decade, NASH is projected to be the most common indication for liver transplantation. The absence of an effective pharmacological therapy for NASH is a major incentive for research into novel therapeutic approaches for this condition. The current focus areas for research include the modulation of nuclear transcription factors; agents that target lipotoxicity and oxidative stress; and the modulation of cellular energy homeostasis, metabolism and the inflammatory response. Strategies to enhance resolution of inflammation and fibrosis also show promise to reverse the advanced stages of liver disease.

Lactate induces FGF21 expression in adipocytes through a p38-MAPK pathway

FGF21 (fibroblast growth factor 21), first described as a main fasting-responsive molecule in the liver, has been shown to act as a true metabolic regulator in additional tissues, including muscle and adipose tissues. In the present study, we found that the expression and secretion of FGF21 was very rapidly increased following lactate exposure in adipocytes. Using different pharmacological and knockout mice models, we demonstrated that lactate regulates Fgf21 expression through a NADH/NAD-independent pathway, but requires active p38-MAPK (mitogen activated protein kinase) signalling. We also demonstrated that this effect is not restricted to lactate as additional metabolites including pyruvate and ketone bodies also activated the FGF21 stress response. FGF21 release by adipose cells in response to an excess of intermediate metabolites may represent a physiological mechanism by which the sensing of environmental metabolic conditions results in the release of FGF21 to improve metabolic adaptations.

Autophagy in Ischemic Livers: A Critical Role of Sirtuin 1/Mitofusin 2 Axis in Autophagy Induction

No-flow ischemia occurs during cardiac arrest, hemorrhagic shock, liver resection and transplantation. Recovery of blood flow and normal physiological pH, however, irreversibly injures the liver and other tissues. Although the liver has the powerful machinery for mitochondrial quality control, a process called mitophagy, mitochondrial dysfunction and subsequent cell death occur after reperfusion. Growing evidence indicates that reperfusion impairs mitophagy, leading to mitochondrial dysfunction, defective oxidative phosphorylation, accumulation of toxic metabolites, energy loss and ultimately cell death. The importance of acetylation/deacetylation cycle in the mitochondria and mitophagy has recently gained attention. Emerging data suggest that sirtuins, enzymes deacetylating a variety of target proteins in cellular metabolism, survival and longevity, may also act as an autophagy modulator. This review highlights recent advances of our understanding of a mechanistic correlation between sirtuin 1, mitophagy and ischemic liver injury.

SIRT1 and insulin resistance

Sirtuin 1 (SIRT1) is a prototype mammalian NAD(+)-dependent protein deacetylase that has emerged as a key metabolic sensor in various metabolic tissues. Growing evidence suggests that SIRT1 regulates glucose and lipid metabolism through its deacetylase activity. In this review, we have summarized the recent progress in SIRT1 research with a particular focus on the role of SIRT1 in insulin resistance at different metabolic tissues. Recent data indicate that activated SIRT1 improves the insulin sensitivity of liver, skeletal muscle and adipose tissues and protects the function and cell mass of pancreatic β-cells. These findings suggest that SIRT1 might be a new therapeutic target for the prevention of disease related to insulin resistance, such as metabolic syndrome and type 2 diabetes mellitus.

Fenofibrate Induces Ketone Body Production in Melanoma and Glioblastoma Cells

Ketone bodies [beta-hydroxybutyrate (bHB) and acetoacetate] are mainly produced in the liver during prolonged fasting or starvation. bHB is a very efficient energy substrate for sustaining ATP production in peripheral tissues; importantly, its consumption is preferred over glucose. However, the majority of malignant cells, particularly cancer cells of neuroectodermal origin such as glioblastoma, are not able to use ketone bodies as a source of energy. Here, we report a novel observation that fenofibrate, a synthetic peroxisome proliferator-activated receptor alpha (PPARa) agonist, induces bHB production in melanoma and glioblastoma cells, as well as in neurospheres composed of non-transformed cells. Unexpectedly, this effect is not dependent on PPARa activity or its expression level. The fenofibrate-induced ketogenesis is accompanied by growth arrest and downregulation of transketolase, but the NADP/NADPH and GSH/GSSG ratios remain unaffected. Our results reveal a new, intriguing aspect of cancer cell biology and highlight the benefits of fenofibrate as a supplement to both canonical and dietary (ketogenic) therapeutic approaches against glioblastoma.

Practical prospects for boosting hepatic production of the "pro-longevity" hormone FGF21

Fibroblast growth factor-21 (FGF21), produced mainly in hepatocytes and adipocytes, promotes leanness, insulin sensitivity, and vascular health while down-regulating hepatic IGF-I production. Transgenic mice overexpressing FGF21 enjoy a marked increase in median and maximal longevity comparable to that evoked by calorie restriction - but without a reduction in food intake. Transcriptional factors which promote hepatic FGF21 expression include PPARα, ATF4, STAT5, and FXR; hence, fibrate drugs, elevated lipolysis, moderate-protein vegan diets, growth hormone, and bile acids may have potential to increase FGF21 synthesis. Sirt1 activity is required for optimal responsiveness of FGF21 to PPARα, and Sirt1 activators can boost FGF21 transcription. Conversely, histone deacetylase 3 (HDAC3) inhibits PPARα's transcriptional impact on FGF21, and type 1 deacetylase inhibitors such as butyrate therefore increase FGF21 expression. Glucagon-like peptide-1 (GLP-1) increases hepatic expression of both PPARα and Sirt1; acarbose, which increases intestinal GLP-1 secretion, also increases FGF21 and lifespan in mice. Glucagon stimulates hepatic production of FGF21 by increasing the expression of the Nur77 transcription factor; increased glucagon secretion can be evoked by supplemental glycine administered during post-absorptive metabolism. The aryl hydrocarbon receptor (AhR) has also been reported recently to promote FGF21 transcription. Bilirubin is known to be an agonist for this receptor, and this may rationalize a recent report that heme oxygenase-1 induction in the liver boosts FGF21 expression. There is reason to suspect that phycocyanorubin, a bilirubin homolog that is a metabolite of the major phycobilin in spirulina, may share bilirubin's agonist activity for AhR, and perhaps likewise promote FGF21 induction. In the future, regimens featuring a plant-based diet, nutraceuticals, and safe drugs may make it feasible to achieve physiologically significant increases in FGF21 that promote metabolic health, leanness, and longevity.

Mouse models of metabolic liver injury

Metabolic liver injury is one of the fastest growing health problems worldwide. Alcoholic and non-alcoholic fatty livers have been shown to be associated with progression to end-stage liver diseases, as well as to liver cancers, in humans. More importantly, there are no validated therapies for these disorders, therefore intensive research is required in this area. This review of standard operation procedures focuses on the experimental models of fatty liver disease in the mouse. Firstly, use of these experimental models might improve understanding of underlying mechanisms, and secondly this might help to test potential therapeutic options. This article includes, besides a short historic background, an insight into the pathobiochemical mechanisms and detailed experimental procedures as well as the practical implementation of these models.

Understanding the Physiology of FGF21

Fibroblast growth factor 21 (FGF21) is a peptide hormone that is synthesized by several organs and regulates energy homeostasis. Excitement surrounding this relatively recently identified hormone is based on the documented metabolic beneficial effects of FGF21, which include weight loss and improved glycemia. The biology of FGF21 is intrinsically complicated owing to its diverse metabolic functions in multiple target organs and its ability to act as an autocrine, paracrine, and endocrine factor. In the liver, FGF21 plays an important role in the regulation of fatty acid oxidation both in the fasted state and in mice consuming a high-fat, low-carbohydrate ketogenic diet. FGF21 also regulates fatty acid metabolism in mice consuming a diet that promotes hepatic lipotoxicity. In white adipose tissue (WAT), FGF21 regulates aspects of glucose metabolism, and in susceptible WAT depots, it can cause browning. This peptide is highly expressed in the pancreas, where it appears to play an anti-inflammatory role in experimental pancreatitis. It also has an anti-inflammatory role in cardiac muscle. Although typically not expressed in skeletal muscle, FGF21 is induced in situations of muscle stress, particularly mitochondrial myopathies. FGF21 has been proposed as a novel therapeutic for metabolic complications such as diabetes and fatty liver disease. This review aims to interpret and delineate the ever-expanding complexity of FGF21 physiology.

FGF21 Revolutions: Recent Advances Illuminating FGF21 Biology and Medicinal Properties

The biology of fibroblast growth factor 21 (FGF21) has evolved through its first decade at a revolutionary pace with dramatic refinements in this relatively short span of time. This field is poised now with a deeper understanding of its specific physiological role, pathological ramifications for its inappropriate function, and a much-enriched context of the complex hormonal network in which it serves to regulate metabolism. As a derivative of these discoveries, the application of FGF21 as a medicinal agent has emerged with structurally optimized protein-based analogs being preclinically explored in multiple species, and, more recently, through clinical studies. These novel findings set a foundation for ongoing inquiries that structure future research into this intriguing protein.

Hepatocyte β-Klotho regulates lipid homeostasis but not body weight in mice

β-Klotho (β-Kl), a transmembrane protein expressed in the liver, pancreas, adipose tissues, and brain, is essential for feedback suppression of hepatic bile acid synthesis. Because bile acid is a key regulator of lipid and energy metabolism, we hypothesized potential and tissue-specific roles of β-Kl in regulating plasma lipid levels and body weight. By crossing β-kl(-/-) mice with newly developed hepatocyte-specific β-kl transgenic (Tg) mice, we generated mice expressing β-kl solely in hepatocytes (β-kl(-/-)/Tg). Gene expression, metabolomic, and in vivo flux analyses consistently revealed that plasma level of cholesterol, which is over-excreted into feces as bile acids in β-kl(-/-), is maintained in β-kl(-/-) mice by enhanced de novo cholesterogenesis. No compensatory increase in lipogenesis was observed, despite markedly decreased plasma triglyceride. Along with enhanced bile acid synthesis, these lipid dysregulations in β-kl(-/-) were completely reversed in β-kl(-/-)/Tg mice. In contrast, reduced body weight and resistance to diet-induced obesity in β-kl(-/-) mice were not reversed by hepatocyte-specific restoration of β-Kl expression. We conclude that β-Kl in hepatocytes is necessary and sufficient for lipid homeostasis, whereas nonhepatic β-Kl regulates energy metabolism. We further demonstrate that in a condition with excessive cholesterol disposal, a robust compensatory mechanism maintains cholesterol levels but not triglyceride levels in mice.

Acarbose: safe and effective for lowering postprandial hyperglycaemia and improving cardiovascular outcomes

α-Glucosidase inhibitors (AGIs) are a class of oral glucose-lowering drugs used exclusively for treatment or prevention of type 2 diabetes mellitus. AGIs act by altering the intestinal absorption of carbohydrates through inhibition of their conversion into simple sugars (monosaccharides) and thus decrease the bioavailability of carbohydrates in the body, significantly lowering blood glucose levels. The three AGIs used in clinical practice are acarbose, voglibose and miglitol. This review will focus on the cardiovascular properties of acarbose. The current available data suggest that AGIs (particularly acarbose) may be safe and effective for the treatment of prediabetes and diabetes.

HDAC5-mTORC1 Interaction in Differential Regulation of Ghrelin and Nucleobindin 2 (NUCB2)/Nesfatin-1

Sodium valporate (VPA), a broad-spectrum inhibitor of histone deacetylases (HDACs), increased ghrelin whereas decreased nesfatin-1 in mice fed normal chow diet or high-fat diet. Alterations in ghrelin and nucleobindin 2/nesfatin-1 were mediated by HDAC5 but not HDAC4. Activation of mTORC1 significantly attenuated the effect of VPA on ghrelin and nesfatin-1 levels. HDAC5 coimmunoprecipitated with raptor. Inhibition of HDAC5 by VPA, trichostatin A, or siHDAC5 markedly increased acetylation of raptor Lys840 and subsequent phosphorylation of raptor Ser792, resulting in suppression of mTORC1 signaling. A raptor mutant lacking the Lys840 acetylation site showed a decrement in phosphorylation of raptor Ser792 and subsequent increase in mTORC1 signaling. These alterations were associated with reciprocal changes in ghrelin and nucleobindin 2/nesfatin-1 expression. These findings reveal HDAC5-mTORC1 signaling as a novel mechanism in the differential regulation of gastric ghrelin and nesfatin-1.