Hydrodynamic delivery of FGF21 gene alleviates obesity and fatty liver in mice fed a high-fat diet

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

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

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

In situ combinatorial synthesis of degradable branched lipidoids for systemic delivery of mRNA therapeutics and gene editors

The ionizable lipidoid is a key component of lipid nanoparticles (LNPs). Degradable lipidoids containing extended alkyl branches have received tremendous attention, yet their optimization and investigation are underappreciated. Here, we devise an in situ construction method for the combinatorial synthesis of degradable branched (DB) lipidoids. We find that appending branch tails to inefficacious lipidoids via degradable linkers boosts mRNA delivery efficiency up to three orders of magnitude. Combinatorial screening and systematic investigation of two libraries of DB-lipidoids reveal important structural criteria that govern their in vivo potency. The lead DB-LNP demonstrates robust delivery of mRNA therapeutics and gene editors into the liver. In a diet-induced obese mouse model, we show that repeated administration of DB-LNP encapsulating mRNA encoding human fibroblast growth factor 21 alleviates obesity and fatty liver. Together, we offer a construction strategy for high-throughput and cost-efficient synthesis of DB-lipidoids. This study provides insights into branched lipidoids for efficient mRNA delivery.

Fibroblast growth factor 21 alleviates unilateral ureteral obstruction-induced renal fibrosis by inhibiting Wnt/β-catenin signaling pathway

Fibroblast growth factor 21 (FGF21) is a key regulator of energy metabolism. Recent studies suggested that serum FGF21 levels increase with declining renal function. However, the link between FGF21 and kidney diseases and the direct effect of FGF21 in renal fibrosis remains unclear. In this study, FGF21 was upregulated in unilateral ureteral obstruction (UUO)-induced renal fibrosis and cellular fibrosis induced by transforming growth factor-β, and renal expression of FGF21 was positively correlated with fibrosis markers. Additionally, FGF21 was regulated by Wnt/β-catenin signaling pathway. The knockdown and overexpression of FGF21 in mouse tubular epithelial cells demonstrated that FGF21 alleviates renal fibrosis by inhibiting the Wnt/β-catenin signaling pathway. To investigate the effect of FGF21 on renal fibrosis in vivo, we established an overexpression model by injecting the plasmid in mice and found that FGF21 overexpression relieved UUO-induced renal fibrosis and renal inflammatory response. Taken together, FGF21 is upregulated with the activation of Wnt/β-catenin signaling pathway and alleviates renal fibrosis by inhibiting the activation of Wnt/β-catenin signaling pathway in a negative feedback mode. These results provide a new understanding for the source of elevated serum FGF21 in patients with chronic kidney disease and prove that FGF21 is a direct inhibitor of the progression of renal fibrosis, thus providing novel therapeutic intervention insights for renal fibrosis.

Adipokines, Hepatokines and Myokines: Focus on Their Role and Molecular Mechanisms in Adipose Tissue Inflammation

Chronic low-grade inflammation in adipose tissue (AT) is a hallmark of obesity and contributes to various metabolic disorders, such as type 2 diabetes and cardiovascular diseases. Inflammation in ATs is characterized by macrophage infiltration and the activation of inflammatory pathways mediated by NF-κB, JNK, and NLRP3 inflammasomes. Adipokines, hepatokines and myokines - proteins secreted from AT, the liver and skeletal muscle play regulatory roles in AT inflammation via endocrine, paracrine, and autocrine pathways. For example, obesity is associated with elevated levels of pro-inflammatory adipokines (e.g., leptin, resistin, chemerin, progranulin, RBP4, WISP1, FABP4, PAI-1, Follistatin-like1, MCP-1, SPARC, SPARCL1, and SAA) and reduced levels of anti-inflammatory adipokines such as adiponectin, omentin, ZAG, SFRP5, CTRP3, vaspin, and IL-10. Moreover, some hepatokines (Fetuin A, DPP4, FGF21, GDF15, and MANF) and myokines (irisin, IL-6, and DEL-1) also play pro- or anti-inflammatory roles in AT inflammation. This review aims to provide an updated understanding of these organokines and their role in AT inflammation and related metabolic abnormalities. It serves to highlight the molecular mechanisms underlying the effects of these organokines and their clinical significance. Insights into the roles and mechanisms of these organokines could provide novel and potential therapeutic targets for obesity-induced inflammation.

Liver-Specific Nonviral Gene Delivery of Fibroblast Growth Factor 21 Protein Expression in Mice Regulates Body Mass and White/Brown Fat Respiration

Viral-mediated in vivo gene delivery methods currently dominate among therapeutic strategies within the clinical and experimental settings, albeit with well documented limitations arising from immunologic constraints. In this study, we demonstrate the utility of nonviral hepatotropic in vivo gene delivery of unpackaged expression constructs, including one encoding fibroblast growth factor 21 (FGF21). FGF21 is an important hepatokine whose expression positively correlates with therapeutic outcomes across various animal models of obesity. Our data demonstrate that FGF21 expression can be restored into the livers of immunocompetent FGF21 knockout mice for at least 2 weeks after a single injection with an FGF21 expression plasmid. In wild-type C57BL6/J mice, in vivo transfection with an FGF21-expressing plasmid induced weight loss, decreased adiposity, and activated thermogenesis in white fat within 2 weeks. Furthermore, in vivo FGF21 gene delivery protected C57BL6/J mice against diet-induced obesity by decreasing adiposity and increasing uncoupling protein 1-dependent thermogenesis in brown fat and by boosting respiratory capacity in subcutaneous and perigonadal white fat. Together, the data illustrate a facile and effective methodology for delivering prolonged protein expression specifically to the liver. We contend that this method will find utility in basic science research as a practical means to enhance in vivo studies characterizing liver protein function. We further believe our data provide a rationale for further exploring the potential clinical utility of nonviral gene therapy in mouse models of disease. SIGNIFICANCE STATEMENT: This study presents a valuable method for nonviral gene delivery in mice that improves upon existing techniques. The data provide a rationale for further exploring the potential clinical utility of nonviral gene therapy in mouse models of disease and will likely enhance in vivo studies characterizing liver protein function.

Effective and safe delivery of GLP-1AR and FGF-21 plasmids using amino-functionalized dual-mesoporous silica nanoparticles in vitro and in vivo

Nanomaterials have attracted increased attention because of their excellent drug-carrying capacity. However, these nanomaterials are rarely used in the treatment of metabolic diseases. Liraglutide, a glucagon-like peptide-1 receptor agonist, has been widely used in the treatment of type 2 diabetes mellitus (T2DM). Furthermore, fibroblast growth factor 21 (FGF-21) has been found to improve glucose metabolism and insulin resistance (IR). To investigate whether these two molecules have synergistic effects in vivo, we developed a novel drug delivery system using amino-functionalized and embedded dual-mesoporous silica nanoparticles (N-EDMSNs) to simultaneously carry liraglutide and FGF-21, and observed their biological effects. The resultant N-EDMSNs possessed unique hierarchical porous structures consisting of open large pores (>10 nm) and small mesopores (~2.5 nm) in the silica framework, highly positively charged surfaces and good disperisity in aqueous solution. We found that N-EDMSNs had a high loading capacity for exogenous genes and low toxicity to Hepa1-6 cells. Moreover, N-EDMSNs can simultaneously carry FGF-21 plasmids and liraglutide and successfully transfect them into Hepa1-6 cells. The transfection efficiency of N-EDMSNs was higher than that of Lipofectamine 2000 in vitro. In mice experiments, N-EDMSNs/pFGF21 treatment resulted in higher FGF-21 expression in the liver than pFGF21 treatment with hydrodynamic delivery. Compared with both pFGF21 and liraglutide, N-EDMSNs/pFGF21/Lira treatment significantly reduced the food intake, body weight, and blood glucose; increased the energy expenditure and improved hepatic IR in high-fat diet (HFD)-fed mice. Our results demonstrated that the biological effects of N-EDMSNs/pFGF21/Lira complexes were better than those of pFGF21 combined with liraglutide in vivo.

Dietary intake of bioactive ingredients impacts liver and adipose tissue transcriptomes in a porcine model of prepubertal early obesity

Global prevalence of obesity has increased to epidemic proportions over the past 40 years, with childhood obesity reaching alarming rates. In this study, we determined changes in liver and adipose tissue transcriptomes of a porcine model for prepubertal early obesity induced by a high-calorie diet and supplemented with bioactive ingredients. A total of 43 nine-weeks-old animals distributed in four pens were fed with four different dietary treatments for 10 weeks: a conventional diet; a western-type diet; and a western-type diet with Bifidobacterium breve and rice hydrolysate, either adding or not omega-3 fatty acids. Animals fed a western-type diet increased body weight and total fat content and exhibited elevated serum concentrations of cholesterol, whereas animals supplemented with bioactive ingredients showed lower body weight gain and tended to accumulate less fat. An RNA-seq experiment was performed with a total of 20 animals (five per group). Differential expression analyses revealed an increase in lipogenesis, cholesterogenesis and inflammatory processes in animals on the western-type diet while the supplementation with bioactive ingredients induced fatty acid oxidation and cholesterol catabolism, and decreased adipogenesis and inflammation. These results reveal molecular mechanisms underlying the beneficial effects of bioactive ingredient supplementation in an obese pig model.

Uric acid induced hepatocytes lipid accumulation through regulation of miR-149-5p/FGF21 axis

BACKGROUND

Hyperuricemia is a major risk for non-alcoholic fatty liver disease. However, the mechanisms for this phenomenon are not fully understood. This study aimed to investigate whether microRNAs mediated the pathogenic effects of uric acid on non-alcoholic fatty liver disease.

METHODS

Microarray was used to determine the hepatic miRNA expression profiles of male C57BL/6 mice fed on standard chow diet, high fat diet (HFD), and HFD combined with uric acid-lowering therapy by allopurinol. We validated the expression of the most significant differentially expressed microRNAs and explored its role and downstream target in uric acid-induced hepatocytes lipid accumulation.

RESULTS

Microarray analysis and subsequent validation showed that miR-149-5p was significantly up-regulated in the livers of HFD-fed mice, while the expression was down-regulated by allopurinol therapy. MiR-149-5p expression was also significantly up-regulated in uric acid-stimulated hepatocytes. Over-expression of miR-149-5p significantly aggregated uric acid-induced triglyceride accumulation in hepatocytes, while inhibiting miR-149-5p ameliorated the triglyceride accumulation. Luciferase report assay confirmed that FGF21 is a target gene of miR-149-5p. Silencing FGF21 abolished the ameliorative effects of miR-149-5p inhibitor on uric acid-induced hepatocytes lipid accumulation, while overexpression of FGF21 prevented the lipid accumulation induced by miR-149-5p mimics.

CONCLUSIONS

Uric acid significantly up-regulated the expression of miR-149-5p in hepatocytes and induced hepatocytes lipid accumulation via regulation of miR-149-5p/FGF21 axis.

Controlling Obesity and Metabolic Diseases by Hydrodynamic Delivery of a Fusion Gene of Exendin-4 and α1 Antitrypsin

Obesity and associated metabolic comorbidities represent a growing public health problem. In this study, we demonstrate the use of a newly created fusion gene of exendin-4 and α1-antitrypsin to control obesity and obesity-associated metabolic disorders including insulin resistance, fatty liver and hyperglycemia. The fusion gene encodes a protein with exendin-4 peptide placed at the N-terminus of human α-1 antitrypsin, and is named EAT. Hydrodynamic transfer of the EAT gene to mice prevents high-fat diet-induced obesity, insulin resistance and fatty liver development. In diet-induced obese mice, expression of EAT gene induces weight loss, improves glucose homeostasis, and attenuates hepatic steatosis. In ob/ob mice, EAT gene transfer suppresses body weight gain, maintains metabolic homeostasis, and completely blocks fatty liver development. Six-month overexpression of the EAT fusion gene in healthy mice does not lead to any detectable toxicity. Mechanistic study reveals that the resulting metabolic benefits are achieved by a reduced food take and down-regulation of transcription of pivotal genes responsible for lipogenesis and lipid droplet formation in the liver and chronic inflammation in visceral fat. These results validate the feasibility of gene therapy in preventing and restoring metabolic homeostasis under diverse pathologic conditions, and provide evidence in support of a new strategy to control obesity and related metabolic diseases.

Dietary Methionine Restriction Reduces Inflammation Independent of FGF21 Action

OBJECTIVE

Methionine restriction (MR) decreases inflammation and improves markers of metabolic disease in rodents. MR also increases hepatic and circulating concentrations of fibroblast growth factor 21 (FGF21). Emerging evidence has suggested that FGF21 exerts anti-inflammatory effects. The purpose of this study was to determine the role of FGF21 in mediating the MR-induced reduction in inflammation.

METHODS

Wild-type and Fgf21^-/- mice were fed a high-fat (HF) control or HF-MR diet for 8 weeks. In a separate experiment, mice were fed a HF diet (HFD) for 10 weeks. Vehicle or recombinant FGF21 (13.6 µg/d) was administered via osmotic minipump for an additional 2 weeks. Inflammation and metabolic parameters were measured.

RESULTS

Fgf21^-/- mice were more susceptible to HFD-induced inflammation, and MR reduced inflammation in white adipose tissue (WAT) and liver of Fgf21^-/- mice. MR downregulated activity of signal transducer and activator of transcription 3 in WAT of both genotypes. FGF21 administration reduced hepatic lipids and blood glucose concentrations. However, there was little effect of FGF21 on inflammatory gene expression in liver or adipose tissue or circulating cytokines.

CONCLUSIONS

MR reduces inflammation independent of FGF21 action. Endogenous FGF21 is important to protect against the development of HFD-induced inflammation in liver and WAT, yet administration of low-dose FGF21 has little effect on markers of inflammation.

Sleeve gastrectomy attenuates high fat diet-induced non-alcoholic fatty liver disease

Background

A high-fat diet (HFD) is known to lead to obesity, and contributes to the progression of non-alcoholic fatty liver disease. The objective of this study was to evaluate the effects of sleeve gastrectomy (SG) on the progression of HFD-induced hepatic steatosis.

Methods

Fifteen 4-week-old, male Wistar rats were randomly assigned into three groups: NC, HFD + SHAM and HFD + SG. Their body weight, glucose-lipid metabolism, inflammation indices, hepatic steatosis and fibroblast growth factor 21 (FGF21) levels were measured.

Results

Postoperatively, body weights in the HFD + SHAM and HFD + SG group rats decreased during the first week. Thereafter, HFD + SG rats regained their body weight. Differences in insulin, homeostasis model assessment of insulin resistance, triglyceride, free fatty acid, tumor necrosis factor-α and monocyte chemotactic protein-1 levels were statistically significant across the three groups (all P < 0.05). Interestingly, FGF21 levels in the HFD + SG group were markedly lower than in the HFD + SHAM group (P = 0.015), however, there were no differences in the NC group. Hematoxylin and eosin staining demonstrated that more vacuoles were present in the HFD + SHAM liver when compared to the HFD + SG liver. Oil-red O staining showed less red dots in the HFD + SG liver.

Conclusions

Despite eating, surgical re-routing of the gut may prevent weight accumulation, regulate glucose-lipid metabolism and insulin sensitivity, control a chronic inflammatory state, change the secretion pattern of FGF21 and alleviate the severity of fatty liver.

Enhanced expression and distinctive characterization of a long-acting FGF21 and its potential to alleviate nonalcoholic steatohepatitis

We have previously constructed a novel polypeptide, PsTag, that should be useful in the development of biologics with properties comparable to those achievable by PEGylation, but with potentially less side effects. However, the low fermentation yields of polypeptide fusion proteins may limit the application of this technology. We suspected that when polypeptide fusion protein was expressed in E. coli, the corresponding 8 tRNAs were needed to transport a large number of repetitive 5 amino acids to the ribosomes and thus, resulting in a relative deficiency of these tRNAs. PsTag600-FGF21, a long-acting FGF21 fusion protein, was used as a model for studying the effects of these non-rare tRNAs on the efficiency of heterologous protein production in E. coli. To further enhance the expression level and facilitate purification, secretory expressions of PsTag600-FGF21 were achieved by fusion with three signal peptides. Meanwhile, a comparison of several distinctive characterizations was carried out between PsTag600-FGF21 and PEG20K-FGF21. We investigated the protective effects of PsTag600-FGF21 in a nonalcoholic steatohepatitis model induced by methionine- and choline-deficient diet. Our results showed that the provision of 8 tRNAs and secretory expression remarkably increased the expression levels of PsTag fusion protein, meanwhile there were no significant effects on E. coli growth states. PsTag600-FGF21 had a larger hydrodynamic volume, a higher affinity and a longer plasma half-life than PEG20K-FGF21, while avoiding vacuole formation in mice. In NASH mice, administration of PsTag600-FGF21 reduced hepatic steatosis, fibrosis and inflammation. Therefore, PsTag600-FGF21 with higher expression level may be further developed for potentially application in clinics.

Dietary capsaicin and antibiotics act synergistically to reduce non-alcoholic fatty liver disease induced by high fat diet in mice

The prevalence of non-alcoholic fatty liver disease is increasing rapidly worldwide. However, effective strategies for combating high-fat diet (HFD) induced obesity, fatty liver and metabolic disorder are still limited, and outcomes remain poor. In the present study, we evaluated the combined actions of dietary capsaicin and antibiotics on HFD-induced physiological abnormalities in mice. C57BL/6 male mice were fed with HFD (60% calories from fat) for 17 weeks, and the resultant pathophysiological effects were examined. Antibiotic treatment markedly attenuated gut inflammation and leakiness induced by HFD, whereas capsaicin showed limited effects on the gut. However, dietary capsaicin significantly increased PPAR-α expression in adipose tissue, while antibiotics had no such effect. Animals treated with a combination of capsaicin and antibiotics had the smallest body weight gain and fat pad index, as well as the lowest hepatic fat accumulation. Combination treatment also maximally improved insulin responsiveness, as indicated by insulin tolerance tests. These results suggest the co-treatment of capsaicin and antibiotics, a novel combination strategy, would play synergistically to attenuate the HFD-induced obesity, fatty liver and metabolic disorder.

Translational Advances of Hydrofection by Hydrodynamic Injection

Hydrodynamic gene delivery has proven to be a safe and efficient procedure for gene transfer, able to mediate, in murine model, therapeutic levels of proteins encoded by the transfected gene. In different disease models and targeting distinct organs, it has been demonstrated to revert the pathologic symptoms and signs. The therapeutic potential of hydrofection led different groups to work on the clinical translation of the procedure. In order to prevent the hemodynamic side effects derived from the rapid injection of a large volume, the conditions had to be moderated to make them compatible with its use in mid-size animal models such as rat, hamster and rabbit and large animals as dog, pig and primates. Despite the different approaches performed to adapt the conditions of gene delivery, the results obtained in any of these mid-size and large animals have been poorer than those obtained in murine model. Among these different strategies to reduce the volume employed, the most effective one has been to exclude the vasculature of the target organ and inject the solution directly. This procedure has permitted, by catheterization and surgical procedures in large animals, achieving protein expression levels in tissue close to those achieved in gold standard models. These promising results and the possibility of employing these strategies to transfer gene constructs able to edit genes, such as CRISPR, have renewed the clinical interest of this procedure of gene transfer. In order to translate the hydrodynamic gene delivery to human use, it is demanding the standardization of the procedure conditions and the molecular parameters of evaluation in order to be able to compare the results and establish a homogeneous manner of expressing the data obtained, as ‘classic’ drugs.

Fibroblast Growth Factor 21-Metabolic Role in Mice and Men

Since its identification in 2000, the interest of scientists in the hepatokine fibroblast growth factor (FGF) 21 has tremendously grown, and still remains high, due to a wealth of very robust data documenting this factor's favorable effects on glucose and lipid metabolism in mice. For more than ten years now, intense in vivo and ex vivo experimentation addressed the physiological functions of FGF21 in humans as well as its pathophysiological role and pharmacological effects in human metabolic disease. This work produced a comprehensive collection of data revealing overlaps in FGF21 expression and function but also significant differences between mice and humans that have to be considered before translation from bench to bedside can be successful. This review summarizes what is known about FGF21 in mice and humans with a special focus on this factor's role in glucose and lipid metabolism and in metabolic diseases, such as obesity and type 2 diabetes mellitus. We highlight the discrepancies between mice and humans and try to decipher their underlying reasons.

In vivo direct reprogramming of liver cells to insulin producing cells by virus-free overexpression of defined factors

Direct reprogramming of autologous cells from diabetes patients to insulin producing cells is a new method for pancreatic cell replacement therapy. At present, transdifferentiation among mature cells is achieved mainly by introducing foreign genes into the starting tissue with viral vector, but there are potentical safety problems. In the present study, we delivered plasmids carrying Pdx1, Neurog3 and MafA genes (PNM) into mouse hepatocytes by hydrodynamics tail vein injection, investigated islet β cells markers in transfected cells from protein and mRNA level, and then observed the long-term control of blood glucose in diabetic mice. We found that hepatocytes could be directly reprogrammed into insulin-producing cells after PNM gene transfection by non-viral hydrodynamics injection, and fasting blood glucose was reduced to normal, and lasted until 100 days after transfection. Intraperitoneal glucose tolerance test (IPGTT) showed that glucose regulation ability was improved gradually and the serum insulin level approached to the level of normal mice with time. Insulin-positive cells were found in the liver tissue, and the expression of various islet β-cell-specific genes were detected at the mRNA level, including islet mature marker gene Ucn3. In conclusion, we provide a new approach for the treatment of diabetes by in vivo direct reprogramming of liver cells to insulin producing cells through non-viral methods.

Type I neuregulin1α is a novel local mediator to suppress hepatic gluconeogenesis in mice

Neuregulin1 is an epidermal growth factor (EGF)-like domain-containing protein that has multiple isoforms and functions as a local mediator in the control of various cellular functions. Here we show that type I isoform of neuregulin1 with an α-type EGF-like domain (Nrg1α) is the major isoform in mouse liver and regulates hepatic glucose production. Forced expression of Nrg1α in mouse liver enhanced systemic glucose disposal and decreased hepatic glucose production with reduced fasting blood glucose levels. Nuclear forkhead box protein O1 (FoxO1) and its downstream targets, PEPCK and G6Pase, were suppressed in liver and isolated hepatocytes by Nrg1α overexpression. In contrast, silencing of Nrg1α enhanced glucose production with increased PEPCK and G6Pase expressions in cAMP/dexamethasone-stimulated hepatocytes. Mechanistically, the recombinant α-type EGF-like domain of NRG1α (rNRG1α) stimulated the ERBB3 signalling pathway in hepatocytes, resulting in decreased nuclear FoxO1 accumulation via activation of both the AKT and ERK pathways. In addition, acute treatment with rNRG1α also suppressed elevation of blood glucose levels after both glucose and pyruvate challenge. Although a liver-specific deletion of Nrg1 gene in mice showed little effect on systemic glucose metabolism, these results suggest that NRG1α have a novel regulatory function in hepatic gluconeogenesis by regulating the ERBB3-AKT/ERK-FoxO1 cascade.

IL-38 alleviates concanavalin A-induced liver injury in mice

Interleukin (IL)-38 is a poorly characterized cytokine of the IL-1 family with anti-inflammatory activity. The role of IL-38 in liver injury remains unknown. We have investigated the potential effect of hydrodynamic-based gene delivery to express human IL-38 in mice with concanavalin A (Con A)-induced liver injury. Transfer of plasmid DNA encoding IL-38 significantly reduced hepatic toxicity and serum levels of aspartate aminotransferase and alanine aminotransferase compared with administration of a control plasmid. Moreover, IL-38 expression dramatically reduced serum levels of several pro-inflammatory cytokines, such as tumor necrosis factor-α, interferon-γ, IL-6, IL-17, and IL-22, but not levels of the anti-inflammatory cytokine IL-10. These results suggest that in vivo expression of human IL-38 in mice has hepatoprotective effects against Con A-induced liver injury by inhibition of inflammatory cytokine production.

A Fibroblast Growth Factor 21-Pregnane X Receptor Pathway Downregulates Hepatic CYP3A4 in Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) alters drug response. We previously reported that NAFLD is associated with reduced in vivo CYP3A drug-metabolism activity and hepatic CYP3A4 expression in humans as well as mouse and human hepatoma models of the disease. Here, we investigated the role of the lipid- and glucose-modulating hormone fibroblast growth factor 21 (FGF21) in the molecular mechanism regulating CYP3A4 expression in NAFLD. In human subjects, mouse and cellular NAFLD models with lower CYP3A4 expression, circulating FGF21, or hepatic FGF21 mRNA levels were elevated. Administration of recombinant FGF21 or transient hepatic overexpression of FGF21 resulted in reduced liver CYP3A4 luciferase reporter activity in mice and decreased CYP3A4 mRNA expression and activity in cultured Huh7 hepatoma cells. Blocking canonical FGF21 signaling by pharmacological inhibition of MEK1 kinase in Huh7 cells caused de-repression of CYP3A4 mRNA expression with FGF21 treatment. Mice with high-fat diet-induced simple hepatic steatosis and lipid-loaded Huh7 cells had reduced nuclear localization of the pregnane X receptor (PXR), a key transcriptional regulator of CYP3A4 Furthermore, decreased nuclear PXR was observed in mouse liver and Huh7 cells after FGF21 treatment or FGF21 overexpression. Decreased PXR binding to the CYP3A4 proximal promoter was found in FGF21-treated Huh7 cells. An FGF21-PXR signaling pathway may be involved in decreased hepatic CYP3A4 metabolic activity in NAFLD.

Genetic fusion of human FGF21 to a synthetic polypeptide improves pharmacokinetics and pharmacodynamics in a mouse model of obesity

BACKGROUND AND PURPOSE

Chemical conjugation of therapeutic proteins with polyethylene glycol (PEG) is an established strategy to extend their biological half-life (t1/2 ) to a clinically useful range. We developed a novel uncharged and unstructured recombinant polypeptide composed of five amino acids (P, S, T, A and G), named PsTag, as another approach to extend the t1/2 of human FGF21, with increased hydrodynamic radius.

EXPERIMENTAL APPROACH

Human FGF21 was fused with PsTag polymers of differing lengths (200 - 600 residues). Three fusion proteins and native FGF21 were produced in Escherichia coli. The biophysical characteristics, metabolic stability, immunogenicity and pharmacokinetics in were assessed in first. In lean and diet-induced obese (DIO) mice, effects on body weight, oral glucose tolerance tests and levels of relevant hormones and metabolites were studied.

KEY RESULTS

Fusion proteins were solubly expressed in E. coli and prolonged the t1/2 from 0.34h up to 12.9 h in mice. Fusion proteins were also biodegradable, thus avoiding vacuole formation, while lacking immunogenicity in mice. In DIO mice, administration of PsTag fused to FGF21 reduced body weight, blood glucose and lipids levels and reversed hepatic steatosis.

CONCLUSIONS AND IMPLICATIONS

The novel recombinant polypeptide, PsTag, should be useful in the development of biological drugs with properties comparable to those achievable by PEGylation, but with potentially less side effects. In mice, fusion of FGF21 to PsTag prolonged and potentiated pharmacological effects of native FGF21, and may offer greater therapeutic effects in treatment of obesity.

NS5ATP6 modulates intracellular triglyceride content through FGF21 and independently of SIRT1 and SREBP1

The prevalence of nonalcoholic fatty liver disease (NAFLD) is rising strikingly in Western countries and China. The molecular biological mechanism of NAFLD remains unclear, with no effective therapies developed so far. Fibroblast growth factor 21 (FGF21) is a recently discovered hormone, with safe lipid lowering effects. FGF21 analogs are being developed for clinical application. Here we demonstrated that a novel gene, NS5ATP6, modulated intracellular triglyceride (TG) content independently of sirtuin1 (SIRT1) and sterol regulatory element binding protein 1 (SREBP1) in HepG2 cells. Interestingly, NS5ATP6 regulated FGF21 expression both at the mRNA and protein levels. The modulatory effects of NS5ATP6 on intracellular TG content depended upon FGF21. Further studies revealed that NS5ATP6 decreased the promoter activity of FGF21. In addition, NS5ATP6 regulated the expression of miR-577, which directly targeted and regulated FGF21. Therefore, miR-577 might be involved in NS5ATP6 regulation of FGF21 at the post-transcriptional level. In conclusion, NS5ATP6 regulates the intracellular TG level via FGF21, and independently of SIRT1 and SREBP1.

Dual Outcomes of Rosiglitazone Treatment on Fatty Liver

In previous studies, it has been reported that rosiglitazone has opposing effects on nonalcoholic fatty liver disease. The purpose of the current study is to test the hypothesis that such opposing effects are related to different levels of peroxisome proliferator-activated receptor gamma (PPAR-γ) in the liver. Using a gene transfer approach and mice fed a high-fat diet (HFD) as an animal model, we demonstrate that mice with low levels of PPAR-γ expression in the liver are resistant to HFD-induced development of fatty liver when treated with rosiglitazone. Conversely, rosiglitazone treatment actually exacerbates liver steatosis in obese mice that have a higher level of PPAR-γ. Mechanistic studies show that an elevated hepatic PPAR-γ level is associated with an increased expression of genes responsible for lipid metabolism in the liver, particularly Cd36, Fabp4, and Mgat1. The concurrent transfer of these three genes into the mouse liver fully recapitulates the phenotypic change induced by the overexpression of PPAR-γ. These results provide evidence in support of the importance of PPAR-γ in the liver when rosiglitazone is considered for the treatment of fatty liver disease. Clinically, our results suggest the necessity of verifying PPAR-γ levels in the liver when rosiglitazone is considered as a treatment option, and indicate that the direct use of rosiglitazone for treatment of nonalcoholic fatty liver may not be desirable when the patient's PPAR-γ level in the liver is significantly elevated.

Plasma-activated air mediates plasmid DNA delivery in vivo

Plasma-activated air (PAA) provides a noncontact DNA transfer platform. In the current study, PAA was used for the delivery of plasmid DNA in a 3D human skin model, as well as in vivo. Delivery of plasmid DNA encoding luciferase to recellularized dermal constructs was enhanced, resulting in a fourfold increase in luciferase expression over 120 hours compared to injection only (P < 0.05). Delivery of plasmid DNA encoding green fluorescent protein (GFP) was confirmed in the epidermal layers of the construct. In vivo experiments were performed in BALB/c mice, with skin as the delivery target. PAA exposure significantly enhanced luciferase expression levels 460-fold in exposed sites compared to levels obtained from the injection of plasmid DNA alone (P < 0.001). Expression levels were enhanced when the plasma reactor was positioned more distant from the injection site. Delivery of plasmid DNA encoding GFP to mouse skin was confirmed by immunostaining, where a 3-minute exposure at a 10 mm distance displayed delivery distribution deep within the dermal layers compared to an exposure at 3 mm where GFP expression was localized within the epidermis. Our findings suggest PAA-mediated delivery warrants further exploration as an alternative approach for DNA transfer for skin targets.

IL-15/sIL-15Rα gene transfer induces weight loss and improves glucose homeostasis in obese mice

Obesity and its associated metabolic problems are a major public health issue. The objective of the current study is to investigate the therapeutic effects of interleukin 15/soluble interleukin 15 receptor-α (IL-15/sIL-15Rα) on high-fat diet-induced obesity and obesity-associated metabolic disorders. We demonstrate that the multiple hydrodynamic delivery of 2 μg IL-15/sIL-15Rα plasmid results in numerous beneficial effects, including a reduction of body weight and fat mass, an alleviation of fatty liver, an improvement in glucose homeostasis and insulin sensitivity in obese mice. These effects are accompanied by a suppressed expression of genes involved in lipid accumulation and lipogenesis, including Pparγ, Cd36, Fabp4, Mgat1, Scd-1 and Fas, and elevated mRNA levels of genes involved in adaptive thermogenesis and fatty acid β-oxidation, such as Ucp1, Ucp3, Pgc-1α, Pgc-1β, Pparα, Pparδ, Cpt1-α and Cpt1-β in obese animals. These results suggest that the overexpression of the Il-15/sIl-15Rα gene is an effective approach in treating diet-induced obesity and its associated metabolic complications.

Brown adipose tissue: a potential target in the fight against obesity and the metabolic syndrome

BAT (brown adipose tissue) is the main site of thermogenesis in mammals. It is essential to ensure thermoregulation in newborns. It is also found in (some) adult humans. Its capacity to oxidize fatty acids and glucose without ATP production contributes to energy expenditure and glucose homoeostasis. Brown fat activation has thus emerged as an attractive therapeutic target for the treatment of obesity and the metabolic syndrome. In the present review, we integrate the recent advances on the metabolic role of BAT and its relation with other tissues as well as its potential contribution to fighting obesity and the metabolic syndrome.

Activated air produced by shielded sliding discharge plasma mediates plasmid DNA delivery to mammalian cells

Cold plasma is emerging as a potential method for medical applications. The current study assessed the efficacy of a novel cold plasma reactor based on shielded sliding discharge producing cathode-directed streamers generated in ambient air for the delivery of plasmid DNA. Experiments were performed with mouse melanoma cells (B16F10) and human keratinocyte cells (HaCaT) inoculated with plasmid DNA encoding luciferase. Quantitative results measured over a 72-h period displayed luciferase expression levels as high as 5-fold greater in cells exposed to plasma-activated air (PAA) than levels obtained from the inoculation of plasmid DNA alone (P < 0.05, P < 0.01). No effect on cell viability was observed. Delivery of plasmid encoding GFP to HaCaT cells seeded on polycaprolactone (PCL) scaffolds was confirmed by immunostaining. The use of cold plasma for DNA delivery is attractive as it provides a non-viral, non-invasive method where the electrode or the plasma itself never directly contacts the exposed site. The current device design provides localized DNA transfer using a novel technology. Our report suggests PAA warrants further exploration as an alternative or supplemental approach for DNA transfer.

High-fat diet-induced adiposity, adipose inflammation, hepatic steatosis and hyperinsulinemia in outbred CD-1 mice

High-fat diet (HFD) has been applied to a variety of inbred mouse strains to induce obesity and obesity related metabolic complications. In this study, we determined HFD induced development of metabolic disorders on outbred female CD-1 mice in a time dependent manner. Compared to mice on regular chow, HFD-fed CD-1 mice gradually gained more fat mass and consequently exhibited accelerated body weight gain, which was associated with adipocyte hypertrophy and up-regulated expression of adipose inflammatory chemokines and cytokines such as Mcp-1 and Tnf-α. Increased fat accumulation in white adipose tissue subsequently led to ectopic fat deposition in brown adipose tissue, giving rise to whitening of brown adipose tissue without altering plasma level of triglyceride. Ectopic fat deposition was also observed in the liver, which was associated with elevated expression of key genes involved in hepatic lipid sequestration, including Ppar-γ2, Cd36 and Mgat1. Notably, adipose chronic inflammation and ectopic lipid deposition in the liver and brown fat were accompanied by glucose intolerance and insulin resistance, which was correlated with hyperinsulinemia and pancreatic islet hypertrophy. Collectively, these results demonstrate sequentially the events that HFD induces physiological changes leading to metabolic disorders in an outbred mouse model more closely resembling heterogeneity of the human population.

Cold Exposure Improves the Anti-diabetic Effect of T0901317 in Streptozotocin-Induced Diabetic Mice

Activation of liver X receptors (LXRs) can improve glucose tolerance in insulin-independent diabetes, however, whether similar effects can be achieved in insulin-dependent diabetes remains unclear. Here, we evaluated the anti-diabetic activity of T0901317, a potent agonist of LXRs, in diabetic mice induced by streptozotocin, and our data demonstrate that T0901317 is most effective when combined with cold treatment of animals. Treatment with T0901317 improved glucose tolerance of diabetic mice, which was associated with repressed expression of key genes involved in hepatic gluconeogenesis such as Pepck and G6p. Combined treatment by T0901317 and cold exposure reduced transcription of gluconeogenic genes to similar levels. Intriguingly, combined treatment greatly increased expression of Ucp1, Cidea, Dio2, and Elvol3 predominantly in the inguinal white adipose tissue, consequently leading to browning of this fat pad, and resulting in further improvement of glucose tolerance which was associated with increased protein levels of UCP1 and GLUT4. Collectively, these results suggest that browning of white adipose tissue via cold exposure in combination with activation of liver X receptors is an alternative and effective strategy to manage insulin-dependent diabetes.

Hydrodynamic delivery

Hydrodynamic delivery (HD) is a broadly used procedure for DNA and RNA delivery in rodents, serving as a powerful tool for gene/protein drug discovery, gene function analysis, target validation, and identification of elements in regulating gene expression in vivo. HD involves a pressurized injection of a large volume of solution into a vasculature. New procedures are being developed to satisfy the need for a safe and efficient gene delivery in clinic. Here, we summarize the fundamentals of HD, its applications, and future perspectives for clinical use.

Chlorogenic acid improves high fat diet-induced hepatic steatosis and insulin resistance in mice

PURPOSE

Chlorogenic acid (CGA), the most abundant component in coffee, has exhibited many biological activities. The objective of this study is to assess preventive and therapeutic effects of CGA on obesity and obesity-related liver steatosis and insulin resistance.

METHODS

Two sets of experiments were conducted. In set 1, 6-week old C57BL/6 mice were fed a regular chow or high-fat diet (HFD) for 15 weeks with twice intra-peritoneal (IP) injection of CGA (100 mg/kg) or DMSO (carrier solution) per week. In set 2, obese mice (average 50 g) were treated by CGA (100 mg/kg, IP, twice weekly) or DMSO for 6 weeks. Body weight, body composition and food intake were monitored. Blood glucose, insulin and lipid levels were measured at end of the study. Hepatic lipid accumulation and glucose homeostasis were evaluated. Additionally, genes involved in lipid metabolism and inflammation were analyzed by real time PCR.

RESULTS

CGA significantly blocked the development of diet-induced obesity but did not affect body weight in obese mice. CGA treatment curbed HFD-induced hepatic steatosis and insulin resistance. Quantitative PCR analysis shows that CGA treatment suppressed hepatic expression of Pparγ, Cd36, Fabp4, and Mgat1 gene. CGA treatment also attenuated inflammation in the liver and white adipose tissue accompanied by a decrease in mRNA levels of macrophage marker genes including F4/80, Cd68, Cd11b, Cd11c, and Tnfα, Mcp-1 and Ccr2 encoding inflammatory proteins.

CONCLUSION

Our study provides direct evidence in support of CGA as a potent compound in preventing diet-induced obesity and obesity-related metabolic syndrome. Our results suggest that drinking coffee is beneficial in maintaining metabolic homeostasis when on a high fat diet.

Chlorogenic acid improves high fat diet-induced hepatic steatosis and insulin resistance in mice

PURPOSE

Chlorogenic acid (CGA), the most abundant component in coffee, has exhibited many biological activities. The objective of this study is to assess preventive and therapeutic effects of CGA on obesity and obesity-related liver steatosis and insulin resistance.

METHODS

Two sets of experiments were conducted. In set 1, 6-week old C57BL/6 mice were fed a regular chow or high-fat diet (HFD) for 15 weeks with twice intra-peritoneal (IP) injection of CGA (100 mg/kg) or DMSO (carrier solution) per week. In set 2, obese mice (average 50 g) were treated by CGA (100 mg/kg, IP, twice weekly) or DMSO for 6 weeks. Body weight, body composition and food intake were monitored. Blood glucose, insulin and lipid levels were measured at end of the study. Hepatic lipid accumulation and glucose homeostasis were evaluated. Additionally, genes involved in lipid metabolism and inflammation were analyzed by real time PCR.

RESULTS

CGA significantly blocked the development of diet-induced obesity but did not affect body weight in obese mice. CGA treatment curbed HFD-induced hepatic steatosis and insulin resistance. Quantitative PCR analysis shows that CGA treatment suppressed hepatic expression of Pparγ, Cd36, Fabp4, and Mgat1 gene. CGA treatment also attenuated inflammation in the liver and white adipose tissue accompanied by a decrease in mRNA levels of macrophage marker genes including F4/80, Cd68, Cd11b, Cd11c, and Tnfα, Mcp-1 and Ccr2 encoding inflammatory proteins.

CONCLUSION

Our study provides direct evidence in support of CGA as a potent compound in preventing diet-induced obesity and obesity-related metabolic syndrome. Our results suggest that drinking coffee is beneficial in maintaining metabolic homeostasis when on a high fat diet.