Transcriptional repressor E4-binding protein 4 (E4BP4) regulates metabolic hormone fibroblast growth factor 21 (FGF21) during circadian cycles and feeding

Circadian clock communication during homeostasis and ageing

Maintaining homeostasis is essential for continued health, and the progressive decay of homeostatic processes is a hallmark of ageing. Daily environmental rhythms threaten homeostasis, and circadian clocks have evolved to execute physiological processes in a manner that anticipates, and thus mitigates, their effects on the organism. Clocks are active in almost all cell types; their rhythmicity and functional output are determined by a combination of tissue-intrinsic and systemic inputs. Numerous inputs for a specific tissue are produced by the activity of circadian clocks of other tissues or cell types, generating a form of crosstalk known as clock communication. In mammals, the central clock in the hypothalamus integrates signals from external light-dark cycles to align peripheral clocks elsewhere in the body. This regulation is complemented by a tissue-specific milieu of external, systemic and niche inputs that modulate and cooperate with the cellular circadian clock machinery of a tissue to tailor its functional output. These mechanisms of clock communication decay during ageing, and growing evidence suggests that this decline might drive ageing-related morbidities. Dietary, behavioural and pharmacological interventions may offer the possibility to overcome these changes and in turn improve healthspan.

Nfil3 contributes to renal fibrosis by activating fibroblasts through directly promoting the expression of Spp1

The activation of fibroblasts into myofibroblasts and the expansion of myofibroblasts are key processes contributing to renal fibrosis; however, the precise underlying mechanisms remain largely unclear. In this study, we found that nuclear factor, interleukin 3 regulated (Nfil3), a basic leucine zipper transcription factor, was significantly upregulated in fibroblasts in kidney tissues from mouse models of unilateral ureteral obstruction (UUO)-induced renal fibrosis and kidney biopsies from patients with renal fibrosis. Conditional knockout of Nfil3 in fibroblasts (Nfil3flox/floxS100a4Cre) and global knockout of Nfil3 reduced UUO-induced accumulation of myofibroblasts and the severity of renal fibrosis in mice, whereas ectopic expression of Nfil3 in fibroblasts activated renal interstitial fibroblasts and initiated renal fibrosis. Overexpression of Nfil3 significantly induced the expression of secreted phosphoprotein 1 (Spp1). Mechanistically, Nfil3 mediated the upregulation of Spp1 in renal fibroblasts by interacting with a conserved sequence in the promoter of Spp1 to regulate its transcription. Furthermore, transforming growth factor beta 1 (Tgfb1) was found to induce the upregulation of Nfil3 in renal fibroblasts. Knockdown of Nfil3 attenuated Tgfb1-induced expression of extracellular matrix proteins and the proliferation of fibroblasts by downregulating Spp1. Altogether, these results suggest that Nfil3 plays an important role in the activation and expansion of fibroblasts, thereby contributing to renal fibrosis.

The time is now: accounting for time-of-day effects to improve reproducibility and translation of metabolism research

The constant expansion of the field of metabolic research has led to more nuanced and sophisticated understanding of the complex mechanisms that underlie metabolic functions and diseases. Collaborations with scientists of various fields such as neuroscience, immunology and drug discovery have further enhanced the ability to probe the role of metabolism in physiological processes. However, many behaviours, endocrine and biochemical processes, and the expression of genes, proteins and metabolites have daily ~24-h biological rhythms and thus peak only at specific times of the day. This daily variation can lead to incorrect interpretations, lack of reproducibility across laboratories and challenges in translating preclinical studies to humans. In this Review, we discuss the biological, environmental and experimental factors affecting circadian rhythms in rodents, which can in turn alter their metabolic pathways and the outcomes of experiments. We recommend that these variables be duly considered and suggest best practices for designing, analysing and reporting metabolic experiments in a circadian context.

OPN-Mediated Crosstalk Between Hepatocyte E4BP4 and Hepatic Stellate Cells Promotes MASH-Associated Liver Fibrosis

Stressed hepatocytes promote liver fibrosis through communications with hepatic stellate cells (HSCs) during chronic liver injury. However, intra-hepatocyte players that facilitate such cell-to-cell communications are largely undefined. It is previously reported that hepatocyte E4BP4 is potently induced by ER stress and hepatocyte deletion of E4bp4 protects mice from high-fat diet-induced liver steatosis. Here how hepatocyte E4bp4 deficiency impacts the activation of HSCs and the progression toward MASH-associated liver fibrosis is examined. Hepatic E4BP4 is increased in mouse models of NASH diet- or CCl4-induced liver fibrosis. Hepatocyte-specific E4bp4 deletion protected mice against NASH diet-induced liver injury, inflammation, and fibrosis without impacting liver steatosis. Hepatocyte E4BP4 overexpression activated HSCs in a medium transfer experiment, whereas hepatocyte E4bp4 depletion did the opposite. RNA-Seq analysis identified the pro-fibrogenic factor OPN as a critical target of E4BP4 within hepatocytes. Antibody neutralization or shRNA depletion of Opn abrogated hepatocyte E4BP4-induced HSC activation. E4BP4 interacted with and stabilized YAP, an established activator of OPN. Loss of hepatic Yap blocked OPN induction in the liver of Ad-E4bp4-injected mice. Hepatocyte E4BP4 induces OPN via YAP to activate HSCs and promote liver fibrosis during diet-induced MASH. Inhibition of the hepatocyte E4BP4-OPN pathway could offer a novel therapeutic avenue for treating MASLD/MASH.

Fibroblast growth factor 21

Fibroblast growth factor 21 (FGF21) belongs to the FGF19 subfamily and acts systemically, playing a key role in inter-organ crosstalk. Ranging from metabolism, reproduction, and immunity, FGF21 is a pleiotropic hormone which contributes to various physiological processes. Although most of its production across species stems from hepatic tissues, expression of FGF21 in mice has also been identified in adipose tissue, thymus, heart, pancreas, and skeletal muscle. Elevated FGF21 levels are affiliated with various diseases and conditions, such as obesity, type 2 diabetes, preeclampsia, as well as cancer. Murine knockout models are viable and show modest weight gain, while overexpression and gain-of-function models display resistance to weight gain, altered bone volume, and enhanced immunity. In addition, FGF21-based therapies are at the forefront of biopharmaceutical strategies aimed at treating metabolic dysfunction-associated steatotic liver disease.

Circadian patterns of growth factor receptor-dependent signaling and implications for carcinogenesis

Several different signaling pathways that regulate cell proliferation and differentiation are initiated by binding of ligands to cell-surface and membrane-bound enzyme-linked receptors, such as receptor tyrosine kinases and serine-threonine kinases. They prompt phosphorylation of tyrosine and serine-threonine residues and initiate downstream signaling pathways and priming of intracellular molecules that convey the signal in the cytoplasm and nucleus, with transcriptional activation of specific genes enriching cell growth and survival-related cascades. These cell processes are rhythmically driven by molecular clockworks endowed in every cell type and when deregulated play a crucial role in cancer onset and progression. Growth factors and their matching receptor-dependent signaling are frequently overexpressed and/or dysregulated in many cancer types. In this review we focus on the interplay between biological clocks and Growth Factor Receptor-dependent signaling in the context of carcinogenesis.

Structural basis for specific DNA sequence recognition by the transcription factor NFIL3

The CCAAT/enhancer-binding proteins (C/EBPs) constitute a family of pivotal transcription factors involved in tissue development, cellular function, proliferation, and differentiation. NFIL3, as one of them, plays an important role in regulating immune cell differentiation, circadian clock system, and neural regeneration, yet its specific DNA recognition mechanism remains enigmatic. In this study, we showed by the ITC binding experiments that NFIL3 prefers to bind to the TTACGTAA DNA motif. Our structural studies revealed that the α-helical NFIL3 bZIP domain dimerizes through its leucine zipper region, and binds to DNA via its basic region. The two basic regions of the NFIL3 bZIP dimer were pushed apart upon binding to DNA, facilitating the snug accommodation of the two basic regions within the major grooves of the DNA. Remarkably, our binding and structural data also revealed that both NFIL3 and C/EBPα/β demonstrate a shared preference for the TTACGTAA sequence. Furthermore, our study revealed that disease-associated mutations within the NFIL3 bZIP domain result in either reduction or complete disruption of its DNA binding ability. These discoveries not only provide valuable insights into the DNA binding mechanisms of NFIL3 but also elucidate the causal role of NFIL3 mutations in disease pathogenesis.

Circadian Regulation of Endocrine Fibroblast Growth Factors on Systemic Energy Metabolism

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

A pan-cancer characterization of immune-related NFIL3 identifies potential predictive biomarker

Background: Nuclear factor interleukin 3 (NFIL3) mainly focuses on the regulation of the circadian rhythm and immune system. However, the potential role of NFIL3 in human cancers has not been studied extensively. Methods: We retrieved original data from the TCGA, TARGET, and GTEx datasets via the UCSC Xena browser (http://genome.ucsc.edu/) and integrated them using R version 3.6.4. NFIL3 expression was assessed using resources such as UCSC, GEPIA (http://gepia.cancer-pku.cn/), Kaplan-Meier Plotter (KM Plotter; https://kmplot.com/), and the Human Protein Atlas (HPA; https://www.proteinatlas.org/) databases. To investigate the prognostic implications of NFIL3, we utilized GEPIA, Kaplan-Meier Plotter, and PrognoScan (http://www.abren.net/PrognoScan/) datasets. For a comprehensive analysis across multiple cancer types, we employed pan-cancer data from UCSC, examining associations between NFIL3 expression and genomic heterogeneity, tumor mutational burden (TMB), microsatellite instability (MSI), tumor purity, and neoantigens. Furthermore, we explored the relationships between NFIL3 expression and the infiltration of immune cells and the expression of immune checkpoint genes. In the context of ovarian cancer, we validated the expression and functional relevance of NFIL3. Cell Counting Kit 8 (CCK8) assays were conducted to assess cell proliferation, while scratch and transwell assays were employed to evaluate cell migration capabilities. We further examined the interaction between NFIL3 and the p53 signaling pathway through quantitative real-time polymerase chain reaction (qRT-PCR), Western blot analysis, immunofluorescence confocal, and Coimmunoprecipitation (Co-IP) assays. Results: In general, NFIL3 expression in cancerous tissues exhibited diminished levels when compared to normal tissue samples. Notably, NFIL3 expression demonstrated a robust correlation with several pivotal aspects, including prognosis, immune cell infiltration, immune checkpoint-related genes, TMB, MSI, tumor purity, and the presence of neoantigens. Experimental investigations involving scratch assays, transwell assays, and assessments of cell proliferation in ovarian cancer cells have provided indications that NFIL3 may exert influence over cell migration and proliferation processes. Moreover, a substantial association between NFIL3 and the p53 signaling pathway was discerned through Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis, with subsequent validation through qRT-PCR, Western blot analysis, immunofluorescence confocal, and co-immunoprecipitation (Co-IP) assays. Conclusions: Therefore, we concluded NFIL3 may serve as a possible prognostic and immunological pan-cancer biomarker.

Protein Restriction in Metabolic Health: Lessons from Rodent Models

Consumption of protein-rich diets and supplements has been increasingly advocated by individuals seeking to optimize metabolic health and mitigate the effects of aging. Protein intake is postulated to support muscle mass retention and enhance longevity, underscoring its perceived benefits in age-related metabolic regulation. However, emerging evidence presents a paradox; while moderate protein consumption contributes to health maintenance, an excessive intake is associated with an elevated risk of chronic diseases, notably obesity and diabetes. Furthermore, recent studies suggest that reducing the ratio of protein intake to macronutrients improves metabolic parameters and extends lifespan. The aim of this study is to review the current evidence concerning the metabolic effects of protein-restricted diets and their potential mechanisms. Utilizing rodent models, investigations have revealed that protein-restricted diets exert a notable influence over food intake and energy consumption, ultimately leading to body weight loss, depending on the degree of dietary protein restriction. These phenotypic alterations are primarily mediated by the FGF21 signaling pathway, whose activation is likely regulated by ATF4 and the circadian clock. The evidence suggests that protein-restricted diets as an alternative approach to calorie-restricted regimes, particularly in overweight or obese adults. However, more research is needed to determine the optimal level of restriction, duration, and long-term effects of such interventions.

Novel Roles for the Transcriptional Repressor E4BP4 in Both Cardiac Physiology and Pathophysiology

Circadian clocks temporally orchestrate biological processes critical for cellular/organ function. For example, the cardiomyocyte circadian clock modulates cardiac metabolism, signaling, and electrophysiology over the course of the day, such that, disruption of the clock leads to age-onset cardiomyopathy (through unknown mechanisms). Here, we report that genetic disruption of the cardiomyocyte clock results in chronic induction of the transcriptional repressor E4BP4. Importantly, E4BP4 deletion prevents age-onset cardiomyopathy following clock disruption. These studies also indicate that E4BP4 regulates both cardiac metabolism (eg, fatty acid oxidation) and electrophysiology (eg, QT interval). Collectively, these studies reveal that E4BP4 is a novel regulator of both cardiac physiology and pathophysiology.

A new border for circadian rhythm gene NFIL3 in diverse fields of cancer

The circadian rhythm disorder and abnormal expression of rhythm genes are related to many diseases, especially cancer. Rhythm gene NFIL3 is involved in energy metabolism and immune cell differentiation, and its aberrant expression is associated with metabolic diseases and inflammation. Previously, numerous studies have shown that aberrant NFIL3 expression is associated with tumorigenesis, progression, and chemotherapy resistance. For instance, NFIL3 performs as a nuclear transcription factor, impacts cell proliferation, represses apoptosis, and promotes cancer cell invasion and metastasis by regulating the transcription of target genes. In addition, NFIL3 expressed in cancer cells influences the type and proportion of infiltrated immune cells in the tumor microenvironment. Increased expression of NFIL3 induces the chemotherapy and immunotherapy resistance in cancer. In this review, we summarized the pathological functions of NFIL3 in tumorigenesis, cancer development, and treatment. The rhythm gene NFIL3 can be used as a promising target in cancer therapy in the future.

FOXO1 represses PPARα-Mediated induction of FGF21 gene expression

Fibroblast growth factor 21 (FGF21) has emerged as a metabolic regulator that exerts potent anti-diabetic and lipid-lowering effects in animal models of obesity and type 2 diabetes, showing a protective role in fatty liver disease and hepatocellular carcinoma progression. Hepatic expression of FGF21 is regulated by PPARα and is induced by fasting. Ablation of FoxO1 in liver has been shown to increase FGF21 expression in hyperglycemia. To better understand the role of FOXO1 in the regulation of FGF21 expression we have modified HepG2 human hepatoma cells to overexpress FoxO1 and PPARα. Here we show that FoxO1 represses PPARα-mediated FGF21 induction, and that the repression acts on the FGF21 gene promoter without affecting other PPARα target genes. Additionally, we demonstrate that FoxO1 physically interacts with PPARα and that FoxO1/3/4 depletion in skeletal muscle contributes to increased Fgf21 tissue levels. Taken together, these data indicate that FOXO1 is a PPARα-interacting protein that antagonizes PPARα activity on the FGF21 promoter. Because other PPARα target genes remained unaffected, these results suggest a highly specific mechanism implicated in FGF21 regulation. We conclude that FGF21 can be specifically modulated by FOXO1 in a PPARα-dependent manner.

Delayed feeding of a high-sucrose diet led to increased body weight by affecting the circadian rhythm of body temperature and hepatic lipid-metabolism genes in rats

Skipping breakfast is an irregular feeding behavior, typically in young people. In our previous study, we established a 4 h-delayed feeding protocol for rats as a breakfast-skipping model and showed that the 4 h-delayed feeding of a high-fat diet led to body weight gain in rats. Excess sucrose induces metabolic syndrome and fatty liver. Recently, excess sucrose intake has received increased attention. Young people generally consume more sugar than adults do. In the present study, we investigated whether a 4 h-delayed feeding promoted high-sucrose diet-induced abnormalities in lipid metabolism, such as fatty liver and obesity in rats. The 4 h-delayed feeding rats showed increased body weight gain, although it did not induce fatty liver and hyperlipidemia compared to normal feeding rats. Serum insulin concentration during the feeding period was higher than in the control rats, suggesting that slight insulin resistance was induced by the 4 h-delayed feeding. The surge in body temperature was also delayed by 4 h in response to the 4 h-delayed feeding. This delay would result in less energy expenditure to increase body weight. The oscillations of hepatic lipid and glucose metabolism-related gene expression were delayed by almost 2-4 h, and the clock genes were delayed by approximately 2 h. The 4 h-delayed feeding induced weight gain by affecting body temperature, insulin resistance, and circadian oscillation of lipid metabolism-related genes in rats fed a high-sucrose diet, suggesting that a high sucrose intake with breakfast skipping leads to obesity.

Hepatic metabolism gene expression and gut microbes in offspring, subjected to in-utero PFOS exposure and postnatal diet challenges

We examined the changes in hepatic metabolic gene expression and gut microbiota of offspring exposed to PFOS in-utero. At GD17.5, our data showed that PFOS exposure decreased fetal bodyweights and hepatic metabolic gene expressions but increased relative liver mass and lipid accumulation. At PND21, in-utero high-dose PFOS-exposed offspring exhibited significantly greater bodyweight (catch-up-growth), associated with significant induction of hepatic metabolic gene expression. In addition, 16SrRNA-sequencing of the cecal samples revealed an increase in carbohydrate catabolism but a reduction in microbial polysaccharide synthesis and short-chain fatty acid (SCFA) metabolism. From PND21-80, a postnatal diet-challenge for the offspring was conducted. At PND80 under a normal diet, in-utero high-dose PFOS-exposed offspring maintained the growth "catch-up" effect. In contrast, in a high-fat-diet, the bodyweight of in-utero high-dose PFOS-exposed adult offspring were significantly lesser than the corresponding low-dose and control groups. Even though in the high-fat-diet, the in-utero PFOS-exposed adult offspring showed significant upregulation of hepatic metabolic genes, the lower bodyweight suggests that they had difficulty utilizing high-fat nutrients. Noteworthy, the metagenomic data showed a significant reduction in the biosynthesis of microbial polysaccharides, vitamin B, and SCFAs in the PFOS-exposed adult offspring. Furthermore, the observed effects were significantly reduced in the PFOS-exposed adult offspring with the high-fat diet but supplemented with sucrose. Our study demonstrated that in-utero PFOS exposure caused inefficient fat metabolism and increased the risk of hepatic steatosis in offspring.

Hepatic FGF21: Its Emerging Role in Inter-Organ Crosstalk and Cancers

Fibroblast growth factor (FGF) 21 is one of the FGF members with special endocrine properties. In the last twenty years, it has attracted intense research and development for its physiological functions that respond to dietary manipulation, pharmacological benefits of improving the macronutrient metabolism, and clinical values as a biomarker of various human diseases. Generally, FGF21 can be produced by major metabolic organs, but only the subgroup from the liver shows canonical endocrine properties, which emphasizes the special value of delineating the unique secretory and functional characteristics of hepatic FGF21. There has been a growth in literature to address the extra-hepatic activities of FGF21, and many striking findings have therefore been published. Yet, they are fragmented and scattered, and controversies are raised from divergent findings. For this reason, there is a need for a systematic and critical evaluation of current research in this aspect. In this review, we focus on the current knowledge about the molecular biology of endocrine FGF21, especially present details on the regulation of circulating levels of FGF21. We also emphasize its emerging roles in inter-organ crosstalk and cancer development.

The biological clock enhancer nobiletin ameliorates steatosis in genetically obese mice by restoring aberrant hepatic circadian rhythm

Nonalcoholic fatty liver disease (NAFLD) is associated with disruption of homeostatic lipid metabolism, but underlying processes are poorly understood. One possible mechanism is impairment in hepatic circadian rhythm, which regulates key lipogenic mediators in the liver and whose circadian oscillation is diminished in obesity. Nobiletin enhances biological rhythms by activating RAR-related orphan receptor nuclear receptor, protecting against metabolic syndrome in a clock-dependent manner. The effect of nobiletin in NAFLD is unclear. In this study, we investigate the clock-enhancing effects of nobiletin in genetically obese (db/db) PER2::LUCIFERASE reporter mice with fatty liver. We report microarray expression data suggesting hepatic circadian signaling is impaired in db/db mice with profound hepatic steatosis. Circadian PER2 activity, as assessed by mRNA and luciferase assay, was significantly diminished in liver of db/db PER2::LUCIFERASE reporter mice. Continuous animal monitoring systems and constant dark studies suggest the primary circadian defect in db/db mice lies within peripheral hepatic oscillators and not behavioral rhythms or the master clock. In vitro, nobiletin restored PER2 amplitude in lipid-laden PER2::LUCIFERASE reporter macrophages. In vivo, nobiletin dramatically upregulated core clock gene expression, hepatic PER2 activity, and ameliorated steatosis in db/db PER2::LUCIFERASE reporter mice. Mechanistically, nobiletin reduced serum insulin levels, decreased hepatic Srebp1c, Acaca1, Tnfα, and Fgf21 expression, but did not improve Plin2, Plin5, or Cpt1, suggesting nobiletin attenuates steatosis in db/db mice via downregulation of hepatic lipid accumulation. These data suggest restoring endogenous rhythm with nobiletin resolves steatosis in obesity, proposing that hypothesis that targeting the biological clock may be an attractive therapeutic strategy for NAFLD.NEW & NOTEWORTHY NAFLD is the most common chronic liver disease, but underlying mechanisms are unclear. We show here that genetically obese (db/db) mice with fatty liver have impaired hepatic circadian rhythm. Hepatic Per2 expression and PER2 reporter activity are diminished in db/db PER2::LUCIFERASE mice. The biological clock-enhancer nobiletin restores hepatic PER2 in db/db PER2::LUCIFERASE mice, resolving steatosis via downregulation of Srebp1c. These studies suggest targeting the circadian clock may be beneficial strategy in NAFLD.

New insight into ischemic stroke: Circadian rhythm in post-stroke angiogenesis

The circadian rhythm is an endogenous clock system that coordinates and optimizes various physiological and pathophysiological processes, which accord with the master and the peripheral clock. Increasing evidence indicates that endogenous circadian rhythm disruption is involved in the lesion volume and recovery of ischemic stroke. As a critical recovery mechanism in post-stroke, angiogenesis reestablishes the regional blood supply and enhances cognitive and behavioral abilities, which is mainly composed of the following processes: endothelial cell proliferation, migration, and pericyte recruitment. The available evidence revealed that the circadian governs many aspects of angiogenesis. This study reviews the mechanism by which circadian rhythms regulate the process of angiogenesis and its contribution to functional recovery in post-stroke at the aspects of the molecular level. A comprehensive understanding of the circadian clock regulating angiogenesis in post-stroke is expected to develop new strategies for the treatment of cerebral infarction.

Hepatic Hedgehog Signaling Participates in the Crosstalk between Liver and Adipose Tissue in Mice by Regulating FGF21

The Hedgehog signaling pathway regulates many processes during embryogenesis and the homeostasis of adult organs. Recent data suggest that central metabolic processes and signaling cascades in the liver are controlled by the Hedgehog pathway and that changes in hepatic Hedgehog activity also affect peripheral tissues, such as the reproductive organs in females. Here, we show that hepatocyte-specific deletion of the Hedgehog pathway is associated with the dramatic expansion of adipose tissue in mice, the overall phenotype of which does not correspond to the classical outcome of insulin resistance-associated diabetes type 2 obesity. Rather, we show that alterations in the Hedgehog signaling pathway in the liver lead to a metabolic phenotype that is resembling metabolically healthy obesity. Mechanistically, we identified an indirect influence on the hepatic secretion of the fibroblast growth factor 21, which is regulated by a series of signaling cascades that are directly transcriptionally linked to the activity of the Hedgehog transcription factor GLI1. The results of this study impressively show that the metabolic balance of the entire organism is maintained via the activity of morphogenic signaling pathways, such as the Hedgehog cascade. Obviously, several pathways are orchestrated to facilitate liver metabolic status to peripheral organs, such as adipose tissue.

Establishment of H3K9-methylated heterochromatin and its functions in tissue differentiation and maintenance

Heterochromatin is characterized by dimethylated or trimethylated histone H3 Lys9 (H3K9me2 or H3K9me3, respectively) and is found at transposable elements, satellite repeats and genes, where it ensures their transcriptional silencing. The histone methyltransferases (HMTs) that methylate H3K9 — in mammals Suppressor of variegation 3–9 homologue 1 (SUV39H1), SUV39H2, SET domain bifurcated 1 (SETDB1), SETDB2, G9A and G9A-like protein (GLP) — and the ‘readers’ of H3K9me2 or H3K9me3 are highly conserved and show considerable redundancy. Despite their redundancy, genetic ablation or mistargeting of an individual H3K9 methyltransferase can correlate with impaired cell differentiation, loss of tissue identity, premature aging and/or cancer. In this Review, we discuss recent advances in understanding the roles of the known H3K9-specific HMTs in ensuring transcriptional homeostasis during tissue differentiation in mammals. We examine the effects of H3K9-methylation-dependent gene repression in haematopoiesis, muscle differentiation and neurogenesis in mammals, and compare them with mechanistic insights obtained from the study of model organisms, notably Caenorhabditis elegans and Drosophila melanogaster. In all these organisms, H3K9-specific HMTs have both unique and redundant roles that ensure the maintenance of tissue integrity by restricting the binding of transcription factors to lineage-specific promoters and enhancer elements.

Histone H3 Lys9 (H3K9)-methylated heterochromatin ensures transcriptional silencing of repetitive elements and genes, and its deregulation leads to impaired cell and tissue identity, premature aging and cancer. Recent studies in mammals clarified the roles H3K9-specific histone methyltransferases in ensuring transcriptional homeostasis during tissue differentiation.

Spatial distribution of beta-klotho mRNA in the mouse hypothalamus, hippocampal region, subiculum, and amygdala

Beta-klotho (KLB) is a co-receptor required for endocrine fibroblast growth factor (FGF) 15/19 and FGF21 signaling in the brain. Klb is prominent within the hypothalamus, which is consistent with its metabolic functions, but diverse roles for Klb are now emerging. Central Klb expression is low but discrete and may govern FGF-targeted sites. However, given its low expression, it is unclear if Klb mRNA is more widespread. We performed in situ hybridization to label Klb mRNA to generate spatial maps capturing the distribution and level of Klb within the mouse hypothalamus, hippocampal region, subiculum, and amygdala. Semi-quantitative analysis revealed that Klb-labeled cells may express low, medium, or high levels of Klb mRNA. Hypothalamic Klb hybridization was heterogeneous and varied rostrocaudally within the same region. Most Klb-labeled cells were found in the lateral hypothalamic zone, but the periventricular hypothalamic region, including the suprachiasmatic nucleus, contained the greatest proportion of cells expressing medium or high Klb levels. We also found heterogeneous Klb hybridization in the amygdala and subiculum, where Klb was especially distinct within the central amygdalar nucleus and ventral subiculum, respectively. By contrast, Klb-labeled cells in the hippocampal region only expressed low levels of Klb and were typically found in the pyramidal layer of Ammon's horn or dentate gyrus. The Klb-labeled regions identified in this study are consistent with reported roles of Klb in metabolism, taste preference, and neuroprotection. However, additional identified sites, including within the hypothalamus and amygdala, may suggest novel roles for FGF15/19 or FGF21 signaling. The central expression of beta-klotho (Klb) is essential for the physiological actions of endocrine fibroblast growth factors. Klb mRNA was widely expressed throughout the hypothalamus, hippocampus, and amygdala. However, the level of Klb expression varied between cells and contributed to a distinctive pattern of distribution within each brain structure. This article is protected by copyright. All rights reserved.

Fibroblast Growth Factor 21 Facilitates the Homeostatic Control of Feeding Behavior

Fibroblast growth factor 21 (FGF21) is a stress hormone that is released from the liver in response to nutritional and metabolic challenges. In addition to its well-described effects on systemic metabolism, a growing body of literature now supports the notion that FGF21 also acts via the central nervous system to control feeding behavior. Here we review the current understanding of FGF21 as a hormone regulating feeding behavior in rodents, non-human primates, and humans. First, we examine the nutritional contexts that induce FGF21 secretion. Initial reports describing FGF21 as a 'starvation hormone' have now been further refined. FGF21 is now better understood as an endocrine mediator of the intracellular stress response to various nutritional manipulations, including excess sugars and alcohol, caloric deficits, a ketogenic diet, and amino acid restriction. We discuss FGF21's effects on energy intake and macronutrient choice, together with our current understanding of the underlying neural mechanisms. We argue that the behavioral effects of FGF21 function primarily to maintain systemic macronutrient homeostasis, and in particular to maintain an adequate supply of protein and amino acids for use by the cells.

Circadian Clock and Liver Cancer

Simple Summary

The circadian coordination of metabolism is tightly regulated, and its alteration can trigger several diseases, including liver steatohepatitis and cancer. Many factors (such as diet and jet lag) shape both the liver molecular clock and the circadian transcription/translation of genes related to different metabolic pathways. Here, we summarize our current knowledge about the molecular mechanisms that control this circadian regulation of liver metabolism.

Abstract

Circadian clocks control several homeostatic processes in mammals through internal molecular mechanisms. Chronic perturbation of circadian rhythms is associated with metabolic diseases and increased cancer risk, including liver cancer. The hepatic physiology follows a daily rhythm, driven by clock genes that control the expression of several proteins involved in distinct metabolic pathways. Alteration of the liver clock results in metabolic disorders, such as non-alcoholic fatty liver diseases (NAFLD) and impaired glucose metabolism, that can trigger the activation of oncogenic pathways, inducing spontaneous hepatocarcinoma (HCC). In this review, we provide an overview of the role of the liver clock in the metabolic and oncogenic changes that lead to HCC and discuss new potentially useful targets for prevention and management of HCC.

Delayed Meal Timing, a Breakfast Skipping Model, Increased Hepatic Lipid Accumulation and Adipose Tissue Weight by Disintegrating Circadian Oscillation in Rats Fed a High-Cholesterol Diet

Background: To investigate whether shifted timing of eating, breakfast skipping, induces alterations in the circadian clock and abnormal lipid metabolism, we have established a delayed meal timing (DMT) protocol for rats, which started eating food 4 h delay. In the present study, control and DMT rats were fed a high-cholesterol diet during zeitgeber time (ZT) 12-24 and ZT 16-4, respectively. The DMT protocol increased the hepatic lipids and epididymal adipose tissue weight without changes in food intake and body weight. The surge in body temperature was delayed by 4 h in the DMT group, suggesting that energy expenditure was decreased in response to DMT. The peaks of the diurnal rhythm of serum non-esterified fatty acids and insulin were delayed by 2 and 4 h due to DMT, respectively. The oscillation peaks of hepatic de novo fatty acid synthesis gene expression was delayed by 4 h in response to DMT, whereas the peak of hepatic clock genes were 2 h delayed or not by DMT. Although metabolic oscillation is considered to be controlled by clock genes, the disintegration rhythms between the clock genes and lipid metabolism-related genes were not observed in rats fed a high-fat diet in our previous study. These data suggest that the circadian rhythm of de novo fatty acid metabolism is regulated by timing of eating, but is not directly controlled by clock genes. The present study suggests that breakfast skipping would complicate fatty liver and body fat accumulation.

Circadian clocks regulate cardiac arrhythmia susceptibility, repolarization, and ion channels

Daily changes in the incidence of sudden cardiac death (SCD) reveal an interaction between environmental rhythms and internal circadian rhythms. Circadian rhythms are physiological rhythms that alter physiology to anticipate daily changes in the environment. They reflect coordinated activity of cellular circadian clocks that exist throughout the body. This review provides an overview of the state of the field by summarizing the results of several different transgenic mouse models that disrupt the function of circadian clocks throughout the body, in cardiomyocytes, or in adult cardiomyocytes. These studies identify important roles for circadian clocks in regulating heart rate, ventricular repolarization, arrhythmogenesis, and the functional expression of cardiac ion channels. They highlight a new dimension in the regulation of cardiac excitability and represent initial forays into understanding the complexities of how time impacts the functional regulation of ion channels, cardiac excitability, and time of day changes in the incidence of SCD.

Contributions of white and brown adipose tissues to the circadian regulation of energy metabolism

The term energy metabolism comprises the entirety of chemical processes associated with uptake, conversion, storage, and breakdown of nutrients. All these must be tightly regulated in time and space to ensure metabolic homeostasis in an environment characterized by cycles such as the succession of day and night. Most organisms evolved endogenous circadian clocks to achieve this goal. In mammals, a ubiquitous network of cellular clocks is coordinated by a pacemaker residing in the hypothalamic suprachiasmatic nucleus. Adipocytes harbor their own circadian clocks, and large aspects of adipose physiology are regulated in a circadian manner through transcriptional regulation of clock-controlled genes. White adipose tissue (WAT) stores energy in the form of triglycerides at times of high energy levels that then serve as fuel in times of need. It also functions as an endocrine organ, releasing factors in a circadian manner to regulate food intake and energy turnover in other tissues. Brown adipose tissue (BAT) produces heat through nonshivering thermogenesis, a process also controlled by the circadian clock. We here review how WAT and BAT contribute to the circadian regulation of energy metabolism. We describe how adipose rhythms are regulated by the interplay of systemic signals and local clocks and summarize how adipose-originating circadian factors feed-back on metabolic homeostasis. The role of adipose tissue in the circadian control of metabolism becomes increasingly clear as circadian disruption leads to alterations in adipose tissue regulation, promoting obesity and its sequelae. Stabilizing adipose tissue rhythms, in turn, may help to combat disrupted energy homeostasis and obesity.

Regulation of diurnal energy balance by mitokines

The mammalian system of energy balance regulation is intrinsically rhythmic with diurnal oscillations of behavioral and metabolic traits according to the 24 h day/night cycle, driven by cellular circadian clocks and synchronized by environmental or internal cues such as metabolites and hormones associated with feeding rhythms. Mitochondria are crucial organelles for cellular energy generation and their biology is largely under the control of the circadian system. Whether mitochondrial status might also feed-back on the circadian system, possibly via mitokines that are induced by mitochondrial stress as endocrine-acting molecules, remains poorly understood. Here, we describe our current understanding of the diurnal regulation of systemic energy balance, with focus on fibroblast growth factor 21 (FGF21) and growth differentiation factor 15 (GDF15), two well-known endocrine-acting metabolic mediators. FGF21 shows a diurnal oscillation and directly affects the output of the brain master clock. Moreover, recent data demonstrated that mitochondrial stress-induced GDF15 promotes a day-time restricted anorexia and systemic metabolic remodeling as shown in UCP1-transgenic mice, where both FGF21 and GDF15 are induced as myomitokines. In this mouse model of slightly uncoupled skeletal muscle mitochondria GDF15 proved responsible for an increased metabolic flexibility and a number of beneficial metabolic adaptations. However, the molecular mechanisms underlying energy balance regulation by mitokines are just starting to emerge, and more data on diurnal patterns in mouse and man are required. This will open new perspectives into the diurnal nature of mitokines and action both in health and disease.

Hepatic metabolic regulation by nuclear factor E4BP4

Discovered as a b-ZIP transcription repressor 30 years ago, E4 promoter-binding protein 4 (E4BP4) has been shown to play critical roles in immunity, circadian rhythms, and cancer progression. Recent research has highlighted E4BP4 as a novel regulator of metabolisms in various tissues. In this review, we focus on the function and mechanisms of hepatic E4BP4 in regulating lipid and glucose homeostasis, bile metabolism, as well as xenobiotic metabolism. Finally, E4BP4-specific targets will be discussed for the prevention and treatment of metabolic disorders.

A Comparison of Gene Expression Changes in the Blood of Individuals Consuming Diets Supplemented with Olives, Nuts or Long-Chain Omega-3 Fatty Acids

Background: The Mediterranean diet, which is rich in olive oil, nuts, and fish, is considered healthy and may reduce the risk of chronic diseases. Methods: Here, we compared the transcriptome from the blood of subjects with diets supplemented with olives, nuts, or long-chain omega-3 fatty acids and identified the genes differentially expressed. The dietary genes obtained were subjected to network analysis to determine the main pathways, as well as the transcription factors and microRNA interaction networks to elucidate their regulation. Finally, a gene-associated disease interaction network was performed. Results: We identified several genes whose expression is altered after the intake of components of the Mediterranean diets compared to controls. These genes were associated with infection and inflammation. Transcription factors and miRNAs were identified as potential regulators of the dietary genes. Interestingly, caspase 1 and sialophorin are differentially expressed in the opposite direction after the intake of supplements compared to Alzheimer’s disease patients. In addition, ten transcription factors were identified that regulated gene expression in supplemented diets, mild cognitive impairment, and Alzheimer’s disease. Conclusions: We identified genes whose expression is altered after the intake of the supplements as well as the transcription factors and miRNAs involved in their regulation. These genes are associated with schizophrenia, neoplasms, and rheumatic arthritis, suggesting that the Mediterranean diet may be beneficial in reducing these diseases. In addition, the results suggest that the Mediterranean diet may also be beneficial in reducing the risk of dementia.

Advances in non-invasive biomarkers for the diagnosis and monitoring of non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is now the most common chronic liver disease in the United States, affecting approximately 1 out of every 4 Americans. NAFLD is a spectrum of disorders including simple steatosis, characterized by the presence of hepatic steatosis with minimal inflammation, and nonalcoholic steatohepatitis (NASH), characterized by the presence of hepatic steatosis with lobular inflammation, ballooning with or without peri-sinusoidal fibrosis. NASH may lead to progressive fibrosis, and therefore, Individuals with NASH and, in particular, hepatic fibrosis are at increased risk for both liver- and cardiovascular-related outcomes compared to those with steatosis alone. New treatments for NASH and hepatic fibrosis are emerging, so now, more than ever, it is important to identify individuals with more advanced disease who may be candidates for therapy. Noninvasive methods to accurately diagnosis, risk stratify, and monitor both NASH and fibrosis are critically needed. Moreover, since clinically relevant outcomes, such as developing end stage liver disease or liver cancer, take many years to develop, reliable surrogate markers of outcome measures are needed to identify and evaluate potential therapies. In this review, we discuss methods to noninvasively diagnosis and monitor both NASH and fibrosis.

Diagnostic and interventional circulating biomarkers in nonalcoholic steatohepatitis

INTRODUCTION

In the setting of the obesity epidemic, nonalcoholic fatty liver disease (NAFLD) has become one of the most prevalent forms of chronic liver disease worldwide. Approximately 25% of adults globally have NAFLD which includes those with NAFL, or simple steatosis, and individuals with nonalcoholic steatohepatitis (NASH) where inflammation, hepatocyte injury and potentially hepatic fibrosis are found in conjunction with steatosis. Individuals with NASH, particularly those with hepatic fibrosis, have higher rates of liver-related and overall mortality, making this distinction of significant clinical importance. One of the core challenges in current clinical practice is identifying this subset of individuals with NASH without the use of liver biopsy, the gold standard for both diagnostics and staging disease severity. Identifying noninvasive biomarkers, an accurately measured and reproducible parameter, would aide in identifying patients eligible for NASH pharmacotherapy clinical trials and to help tailor intensity of monitoring required.

METHODS RESULTS AND CONCLUSIONS

In this review, we highlight both the currently available and novel diagnostic and interventional circulating biomarkers under investigation for NASH, underscoring their accuracy and limitations relevant to our patient population and current clinical practice.

Prospects of circadian clock in joint cartilage development

Altering the food intake, exercise, and sleep patterns have a great influence on the homeostasis of the biological clock. This leads to accelerated aging of the articular cartilage, susceptibility to arthropathy and other aspects. Deficiency or overexpression of certain circadian clock-related genes accelerates the cartilage deterioration and leads to phenotypic variation in different joints. The process of joint cartilage development includes the formation of joint site, interzone, joint cavitation, epiphyseal ossification center, and cartilage maturation. The mechanism by which, biological clock regulates the cell-cycle, growth, metabolism, and other biological processes of chondrocytes is poorly understood. Here, we summarized the interaction between biological clock proteins and developmental pathways in chondrogenesis and provided the evidence from other tissues that further predicts the molecular patterns of these protein-protein networks in activation, proliferation, and differentiation. The purpose of this review is to gain deeper understanding of the evolution of cartilage and its irreversibility seen in damage and aging.

Alcohol and Liver Clock Disruption Increase Small Droplet Macrosteatosis, Alter Lipid Metabolism and Clock Gene mRNA Rhythms, and Remodel the Triglyceride Lipidome in Mouse Liver

Heavy alcohol drinking dysregulates lipid metabolism, promoting hepatic steatosis – the first stage of alcohol-related liver disease (ALD). The molecular circadian clock plays a major role in synchronizing daily rhythms in behavior and metabolism and clock disruption can cause pathology, including liver disease. Previous studies indicate that alcohol consumption alters liver clock function, but the impact alcohol or clock disruption, or both have on the temporal control of hepatic lipid metabolism and injury remains unclear. Here, we undertook studies to determine whether genetic disruption of the liver clock exacerbates alterations in lipid metabolism and worsens steatosis in alcohol-fed mice. To address this question, male liver-specific Bmal1 knockout (LKO) and flox/flox (Fl/Fl) control mice were fed a control or alcohol-containing diet for 5 weeks. Alcohol significantly dampened diurnal rhythms of mRNA levels in clock genes Bmal1 and Dbp, phase advanced Nr1d1/REV-ERBα, and induced arrhythmicity in Clock, Noct, and Nfil3/E4BP4, with further disruption in livers of LKO mice. Alcohol-fed LKO mice exhibited higher plasma triglyceride (TG) and different time-of-day patterns of hepatic TG and macrosteatosis, with elevated levels of small droplet macrosteatosis compared to alcohol-fed Fl/Fl mice. Diurnal rhythms in mRNA levels of lipid metabolism transcription factors (Srebf1, Nr1h2, and Ppara) were significantly altered by alcohol and clock disruption. Alcohol and/or clock disruption significantly altered diurnal rhythms in mRNA levels of fatty acid (FA) synthesis and oxidation (Acaca/b, Mlycd, Cpt1a, Fasn, Elovl5/6, and Fads1/2), TG turnover (Gpat1, Agpat1/2, Lpin1/2, Dgat2, and Pnpla2/3), and lipid droplet (Plin2/5, Lipe, Mgll, and Abdh5) genes, along with protein abundances of p-ACC, MCD, and FASN. Lipidomics analyses showed that alcohol, clock disruption, or both significantly altered FA saturation and remodeled the FA composition of the hepatic TG pool, with higher percentages of several long and very long chain FA in livers of alcohol-fed LKO mice. In conclusion, these results show that the liver clock is important for maintaining temporal control of hepatic lipid metabolism and that disrupting the liver clock exacerbates alcohol-related hepatic steatosis.

Hepatic E4BP4 induction promotes lipid accumulation by suppressing AMPK signaling in response to chemical or diet-induced ER stress

Prolonged ER stress has been known to be one of the major drivers of impaired lipid homeostasis during the pathogenesis of non-alcoholic liver disease (NAFLD). However, the downstream mediators of ER stress pathway in promoting lipid accumulation remain poorly understood. Here, we present data showing the b-ZIP transcription factor E4BP4 in both the hepatocytes and the mouse liver is potently induced by the chemical ER stress inducer tunicamycin or by high-fat, low-methionine, and choline-deficient (HFLMCD) diet. We showed that such an induction is partially dependent on CHOP, a known mediator of ER stress and requires the E-box element of the E4bp4 promoter. Tunicamycin promotes the lipid droplet formation and alters lipid metabolic gene expression in primary mouse hepatocytes from E4bp4^flox/flox but not E4bp4 liver-specific KO (E4bp4-LKO) mice. Compared with E4bp4^flox/flox mice, E4bp4-LKO female mice exhibit reduced liver lipid accumulation and partially improved liver function after 10-week HFLMCD diet feeding. Mechanistically, we observed elevated AMPK activity and the AMPKβ1 abundance in the liver of E4bp4-LKO mice. We have evidence supporting that E4BP4 may suppress the AMPK activity via promoting the AMPKβ1 ubiquitination and degradation. Furthermore, acute depletion of the Ampkβ1 subunit restores lipid droplet formation in E4bp4-LKO primary mouse hepatocytes. Our study highlighted hepatic E4BP4 as a key factor linking ER stress and lipid accumulation in the liver. Targeting E4BP4 in the liver may be a novel therapeutic avenue for treating NAFLD.

A role for alternative splicing in circadian control of exocytosis and glucose homeostasis

The circadian clock is encoded by a negative transcriptional feedback loop that coordinates physiology and behavior through molecular programs that remain incompletely understood. Here, we reveal rhythmic genome-wide alternative splicing (AS) of pre-mRNAs encoding regulators of peptidergic secretion within pancreatic β cells that are perturbed in Clock-/- and Bmal1-/- β-cell lines. We show that the RNA-binding protein THRAP3 (thyroid hormone receptor-associated protein 3) regulates circadian clock-dependent AS by binding to exons at coding sequences flanking exons that are more frequently skipped in clock mutant β cells, including transcripts encoding Cask (calcium/calmodulin-dependent serine protein kinase) and Madd (MAP kinase-activating death domain). Depletion of THRAP3 restores expression of the long isoforms of Cask and Madd, and mimicking exon skipping in these transcripts through antisense oligonucleotide delivery in wild-type islets reduces glucose-stimulated insulin secretion. Finally, we identify shared networks of alternatively spliced exocytic genes from islets of rodent models of diet-induced obesity that significantly overlap with clock mutants. Our results establish a role for pre-mRNA alternative splicing in β-cell function across the sleep/wake cycle.

Circadian blueprint of metabolic pathways in the brain

The circadian clock is an endogenous, time-tracking system that directs multiple metabolic and physiological functions required for homeostasis. The master or central clock located within the suprachiasmatic nucleus in the hypothalamus governs peripheral clocks present in all systemic tissues, contributing to their alignment and ultimately to temporal coordination of physiology. Accumulating evidence reveals the presence of additional clocks in the brain and suggests the possibility that circadian circuits may feed back to these from the periphery. Here, we highlight recent advances in the communications between clocks and discuss how they relate to circadian physiology and metabolism.

Functional D-box sequences reset the circadian clock and drive mRNA rhythms

The circadian clock drives gene expression rhythms, leading to daily changes in physiology and behavior. In mammals, Albumin D-site-Binding Protein (DBP) rhythmically activates transcription of various genes through a DNA cis-element, D-box. The DBP-dependent transactivation is repressed by competitive binding of E4BP4 to the D-box. Despite the elaborate regulation, physiological roles of the D-box in the circadian clockwork are still elusive. Here we identified 1490 genomic regions recognized commonly by DBP and E4BP4 in the mouse liver. We comprehensively defined functional D-box sequences using an improved bioinformatics method, MOCCS2. In RNA-Seq analysis of E4bp4-knockout and wild type liver, we showed the importance of E4BP4-mediated circadian repression in gene expression rhythms. In addition to the circadian control, we found that environmental stimuli caused acute induction of E4BP4 protein, evoking phase-dependent phase shifts of cellular circadian rhythms and resetting the clock. Collectively, D-box-mediated transcriptional regulation plays pivotal roles in input and output in the circadian clock system.

Berberine stimulates fibroblast growth factor 21 by modulating the molecular clock component brain and muscle Arnt-like 1 in brown adipose tissue

Fibroblast growth factor 21 (FGF21), a member of the FGF subfamily that acts through the FGF receptor 1 with the co-receptor β-Klotho, functions as an important metabolic regulator of peripheral glucose tolerance and lipid homeostasis in an endocrine or autocrine and/or paracrine manner. Previous studies showed that FGF21 ameliorated and prevented the development of metabolic disorders, such as obesity and diabetes mellitus. In the present study, we demonstrated that berberine, a naturally occurring compound, stimulated FGF21 expression in brown adipose tissue (BAT). Furthermore, the up-regulated expression of FGF21 in brown adipocytes in response to berberine was due, at least in part, to the activation of the AMP-activated protein kinase pathway. We also found that berberine reversed high-fat diet-induced obesity concomitant with its regulation of the expression of Fgf21 and the core clock component brain and muscle Arnt-like 1 (Bmal1) in BAT. Berberine significantly up-regulated the gene expression and production of FGF21 in a dose-dependent manner in C3H10T1/2 brown adipocytes. Furthermore, the knockdown of Bmal1 prevented the up-regulated expression of FGF21 in response to berberine in C3H10T1/2 brown adipocytes, suggesting that Bmal1 links the regulatory mechanisms of FGF21 in response to berberine. The present results suggest that berberine stimulates the expression of FGF21 by modulating molecular clock Bmal1 in BAT, which may, in turn, attenuate diet-induced obesity. They also indicate the potential of berberine as a therapeutic agent for obesity and obesity-associated metabolic disorders related to circadian misalignments.

Circulating FGF21 Levels in Human Health and Metabolic Disease

Human fibroblast growth factor 21 (FGF21) is primarily produced and secreted by the liver as a hepatokine. This hormone circulates to its target tissues (e. g., brain, adipose tissue), which requires two components, one of the preferred FGF receptor isoforms (FGFR1c and FGFR3c) and the co-factor beta-Klotho (KLB) to trigger downstream signaling pathways. Although targeting FGF21 signaling in humans by analogues and receptor agonists results in beneficial effects, e. g., improvements in plasma lipids and decreased body weight, it failed to recapitulate the improvements in glucose handling shown for many mouse models. FGF21's role and metabolic effects in mice and its therapeutic potential have extensively been reviewed elsewhere. In this review we focus on circulating FGF21 levels in humans and their associations with disease and clinical parameters, focusing primarily on obesity and obesity-associated diseases such as type-2 diabetes. We provide a comprehensive overview on human circulating FGF21 levels under normal physiology and metabolic disease. We discuss the emerging field of inactivating FGF21 in human blood by fibroblast activation protein (FAP) and its potential clinical implications.

Circadian protein CLK suppresses transforming growth factor-β expression in peripheral B cells of nurses with day-night shift rotation

BACKGROUND AND AIMS

The mechanism of dysfunction of regulatory B cells is unclear. The circadian locomotor output cycles kaput (CLK) regulates immune responses. CLK expression can be increased by alteration of the circadian rhythm. This study tests a hypothesis that alteration of the circadian rhythm, such as engaging the day-night shift rotation (DNSR), interferes with the expression of transforming growth factor (TGF)-β in B cells (TGFbB cell).

METHODS

Peripheral blood samples were collected from DNSR nurses and persons with the regular circadian clock life style (RC). The frequency of TGFbB cells in the blood samples was assessed by flow cytometry. The expression of TGF-beta in B cells was assessed with real time RT-PCR.

RESULTS

We observed that the frequency of peripheral TGFbB cells was less in DNSR nurses as compared to RC subjects. The expression of CLK and histone deacetylase 11 in peripheral B cells was higher, the TGF-β expression was lower, in peripheral B cells of DNSR nurses. Over-expression of CLK repressed the expression of TGF-β in B cells, which was mediated by HDAC11.

CONCLUSIONS

The CLK expression in peripheral B cells is higher in DNSR nurses, which suppresses the expression of TGF-β in B cells. To regulate the expression of CLK during the circadian clock alteration needs to be further investigated.

Hepatic c-Jun regulates glucose metabolism via FGF21 and modulates body temperature through the neural signals

Objective

c-Jun, a prominent member of the activator protein 1 (AP-1) family, is involved in various physiology processes such as cell death and survival. However, a role of hepatic c-Jun in the whole-body metabolism is poorly understood.

Methods

We generated liver-specific c-Jun knock-out (c-jun^△li) mice to investigate the effect of hepatic c-Jun on the whole-body physiology, particularly in blood glucose and body temperature. Primary hepatocytes were also used to explore a direct regulation of c-Jun in gluconeogenesis.

Results

c-jun^△li mice showed higher hepatic gluconeogenic capacity compared with control mice, and similar results were obtained in vitro. In addition, fibroblast growth factor 21 (FGF21) expression was directly inhibited by c-Jun knockdown and adenovirus-mediated hepatic FGF21 over-expression blocked the effect of c-Jun on gluconeogenesis in c-jun^△li mice. Interestingly, c-jun^△li mice also exhibited higher body temperature, with induced thermogenesis and uncoupling protein 1 (UCP1) expression in brown adipose tissue (BAT). Furthermore, the body temperature became comparable between c-jun^△li and control mice at thermoneutral temperature (30 °C). Moreover, the activity of sympathetic nervous system (SNS) was increased in c-jun^△li mice and the higher body temperature was inhibited by beta-adrenergic receptor blocker injection. Finally, the activated SNS and increased body temperature in c-jun^△li mice was most likely caused by the signals from the brain and hepatic vagus nerve, as the expression of c-Fos (the molecular marker of neuronal activation) was changed in several brain areas controlling body temperature and body temperature was decreased by selective hepatic vagotomy.

Conclusions

These data demonstrate a novel function of hepatic c-Jun in the regulation of gluconeogenesis and body temperature via FGF21 and neural signals. Our results also provide novel insights into the organ crosstalk in the regulation of the whole-body physiology.

•

Liver-specific inactivation of c-Jun increased gluconeogenesis via decreasing FGF21 expression.

•

Liver-specific inactivation of c-Jun increased body temperature by promoting thermogenesis in BAT.

•

Hepatic c-Jun modulates body temperature via regulating sympathetic nervous system activity and vagus nerve.

Requirement for NF-κB in maintenance of molecular and behavioral circadian rhythms in mice

The mammalian circadian clock is encoded by an autoregulatory transcription feedback loop that drives rhythmic behavior and gene expression in the brain and peripheral tissues. Transcriptomic analyses indicate cell type-specific effects of circadian cycles on rhythmic physiology, although how clock cycles respond to environmental stimuli remains incompletely understood. Here, we show that activation of the inducible transcription factor NF-κB in response to inflammatory stimuli leads to marked inhibition of clock repressors, including the Period, Cryptochrome, and Rev-erb genes, within the negative limb. Furthermore, activation of NF-κB relocalizes the clock components CLOCK/BMAL1 genome-wide to sites convergent with those bound by NF-κB, marked by acetylated H3K27, and enriched in RNA polymerase II. Abrogation of NF-κB during adulthood alters the expression of clock repressors, disrupts clock-controlled gene cycles, and impairs rhythmic activity behavior, revealing a role for NF-κB in both unstimulated and activated conditions. Together, these data highlight NF-κB-mediated transcriptional repression of the clock feedback limb as a cause of circadian disruption in response to inflammation.

Delayed first active-phase meal, a breakfast-skipping model, led to increased body weight and shifted the circadian oscillation of the hepatic clock and lipid metabolism-related genes in rats fed a high-fat diet

The circadian clock is closely related to human health, such as metabolic syndrome and cardiovascular disease. Our previous study revealed that irregular feeding induced abnormal lipid metabolism with disruption of the hepatic circadian clock. We hypothesized that breakfast skipping induces lipid abnormalities, such as adiposity, by altering the hepatic circadian oscillation of clock and lipid metabolism-related genes. Here, we established a delayed first active-phase meal (DFAM) protocol as a breakfast-skipping model. Briefly, rats were fed a high-fat diet during zeitgeber time (ZT) 12-24 in a control group and ZT 16-4 in the DFAM group. The DFAM group showed increased body weight gain and perirenal adipose tissue weight without a change in total food intake. The circadian oscillations of hepatic clock and de novo fatty acid synthesis genes were delayed by 2-4 h because of DFAM. The peaks of serum insulin, a synchronizer for the liver clock, bile acids, and non-esterified fatty acid (NEFA) were delayed by 4-6 h because of DFAM. Moreover, DFAM delayed the surge in body temperature by 4 h and may have contributed to the increase in body weight gain and adipose tissue weight because of decreased energy expenditure. These data indicated a potential molecular mechanism by which breakfast skipping induces abnormal lipid metabolism, which is related to the altered circadian oscillation of hepatic gene expression. The results also suggested that the delayed peaks of serum NEFA, bile acids, and insulin entrain the circadian rhythm of hepatic clock and lipid metabolism-related genes.

Validation of Housekeeping Genes as Reference for Reverse-Transcription-qPCR Analysis in Busulfan-Injured Microvascular Endothelial Cells

Endothelial cells (ECs) could express some important cytokines and signal molecules which play a key role in normal hematopoiesis and repopulation. Busulfan-induced vascular endothelial injury is an important feature after hematopoietic stem cell transplantation (HSCT). But the molecular mechanism of how the injured ECs affect hematopoietic reconstruction is still unknown. It is possibly through modulation of the change of some gene expression. RT-qPCR is one of the most popular methods used to accurately determine gene expression levels, based on stable reference gene (RG) selection from housekeeping genes. So our aim is to select stable RGs for more accurate measures of mRNA levels during Busulfan-induced vascular endothelial injury. In this study, 14 RGs were selected to investigate their expression stability in ECs during 72 hours of EC injury treated with Busulfan. Our results revealed extreme variation in RG stability compared by five statistical algorithms. ywhaz and alas1 were recognized as the two idlest RGs on account of the final ranking, while the two most usually used RGs (gapdh and actb) were not the most stable RGs. Next, these data were verified by testing signalling pathway genes ctnnb1, robo4, and notch1 based on the above four genes ywha, alas1, gapdh, and actb. It shows that the normalization of mRNA expression data using unstable RGs greatly affects gene fold change, which means the reliability of the biological conclusions is questionable. Based on the best RGs used, we also found that robo4 is significantly overexpressed in Busulfan-impaired ECs. In conclusion, our data reaffirms the importance of RGs selection for the valid analysis of gene expression in Busulfan-impaired ECs. And it also provides very useful guidance and basis for more accurate differential expression gene screening and future expanding biomolecule study of different drugs such as cyclophosphamide and fludarabine-injured ECs.

Spontaneous pulmonary hypertension in genetic mouse models of natural killer cell deficiency

Natural killer (NK) cells are cytotoxic innate lymphoid cells with an established role in the regulation of vascular structure in pregnancy and cancer. Impaired NK cell function has been identified in patients with pulmonary arterial hypertension (PAH), a disease of obstructive vascular remodeling in the lungs, as well as in multiple rodent models of disease. However, the precise contribution of NK cell impairment to the initiation and progression of PAH remains unknown. Here, we report the development of spontaneous pulmonary hypertension in two independent genetic models of NK cell dysfunction, including Nfil3^−/− mice, which are deficient in NK cells due to the absence of the NFIL3 transcription factor, and Ncr1-Gfp mice, which lack the NK activating receptor NKp46. Mouse models of NK insufficiency exhibited increased right ventricular systolic pressure and muscularization of the pulmonary arteries in the absence of elevated left ventricular end-diastolic pressure, indicating that the development of pulmonary hypertension was not secondary to left heart dysfunction. In cases of severe NK cell impairment or loss, a subset of mice failed to develop pulmonary hypertension and instead exhibited reduced systemic blood pressure, demonstrating an extension of vascular abnormalities beyond the pulmonary circulation into the systemic vasculature. In both mouse models, the development of PAH was linked to elevated interleukin-23 production, whereas systemic hypotension in Ncr1-Gfp mice was accompanied by a loss of angiopoietin-2. Together, these results support an important role for NK cells in the regulation of pulmonary and systemic vascular function and the pathogenesis of PAH.

E4BP4 facilitates glucocorticoid sensitivity of human bronchial epithelial cells via down-regulation of glucocorticoid receptor-beta

It has recently been recognized that a subset of asthma patients suffer from glucocorticoid (GC) insensitivity, and glucocorticoid receptor-β (GR-β) is associated with corticosteroid resistance, but the underlying mechanisms remain unknown. Here we demonstrated that Interleukin-17A induced glucocorticoid sensitivity in human bronchial epithelial cells (16HBE) is enhanced, which is depend on E4 promoter-binding protein 4 (E4BP4) mediated GR-β expression. Our data show that the expression of E4BP4 is significantly up-regulated in 16HBE cells, and the depletion of E4BP4 dramatically decreased glucocorticoid sensitivity in IL-17A induced 16HBE cells. Mechanistic studies revealed that E4BP4 plays a crucial role in Interleukin-17A induced glucocorticoid sensitivity in 16HBE cells via down-regulating GR-β, which is probably mediated by PI3K/Akt activation. Collectively, we can draw the conclusion that E4BP4 contribute to enhance the GCs sensitivity, which may offer a new strategy for therapeutic intervention for GC-insensitive asthma.

NFIL3 is a negative regulator of hepatic gluconeogenesis

OBJECTIVE

Nuclear factor interleukin-3 regulated (NFIL3) has been known as an important transcriptional regulator of the development and the differentiation of immune cells. Although expression of NFIL3 is regulated by nutritional cues in the liver, the role of NFIL3 in the glucose metabolism has not been extensively studied. Thus, we wanted to explore the potential role of NFIL3 in the control of hepatic glucose metabolism.

MATERIALS/METHODS

Mouse primary hepatocytes were cultured to perform western blot analysis, Q-PCR and chromatin immunoprecipitation assay. 293T cells were cultured to perform luciferase assay. Male C57BL/6 mice (fed a normal chow diet or high fat diet for 27weeks) as well as ob/ob mice were used for experiments with adenoviral delivery.

RESULTS

We observed that NFIL3 reduced glucose production in hepatocytes by reducing expression of gluconeogenic gene transcription. The repression by NFIL3 required its basic leucine zipper DNA binding domain, and it competed with CREB onto the binding of cAMP response element in the gluconeogenic promoters. The protein levels of hepatic NFIL3 were decreased in the mouse models of genetic- and diet-induced obesity and insulin resistance, and ectopic expression of NFIL3 in the livers of insulin resistant mice ameliorated hyperglycemia and glucose intolerance, with concomitant reduction in expression of hepatic gluconeogenic genes. Finally, we witnessed that knockdown of NFIL3 in the livers of normal chow-fed mice promoted elevations in the glucose levels and expression of hepatic gluconeogenic genes.

CONCLUSIONS

In this study, we showed that NFIL3 functions as an important regulator of glucose homeostasis in the liver by limiting CREB-mediated hepatic gluconeogenesis. Thus, enhancement of hepatic NFIL3 activity in insulin resistant state could be potentially beneficial in relieving glycemic symptoms in the metabolic diseases.

Induction of fibroblast growth factor 21 does not require activation of the hepatic X-box binding protein 1 in mice

Objective

Fibroblast growth factor 21 (FGF21), a key regulator of the metabolic response to fasting, is highly induced by endoplasmic reticulum (ER) stress. The X-box binding protein 1 (Xbp1) is one of several ER stress proteins that has been shown to directly activate the FGF21 promoter. We aimed to determine whether hepatic Xbp1 is required for induction of hepatic FGF21 in vivo.

Methods

Mice bearing a hepatocyte-specific deletion of Xbp1 (Xbp1^LKO) were subjected to fasting, pharmacologic ER stress, or a ketogenic diet, all potent stimuli of Fgf21 expression.

Results

Hepatocyte-specific Xbp1 knockout mice demonstrated normal induction of FGF21 in response to fasting or pharmacologic ER stress and enhanced induction of FGF21 in response to a ketogenic diet. Consistent with preserved induction of FGF21, Xbp1^LKO mice exhibited normal induction of FGF21 target genes and normal ketogenesis in response to fasting or a ketogenic diet.

Conclusion

Hepatic Xbp1 is not required for induction of FGF21 under physiologic or pathophysiologic conditions in vivo.

•

Deletion of hepatic Xbp1 in mice allows for normal induction of FGF21 upon fasting.

•

ER stress induces FGF21 independently of hepatic Xbp1.

•

Mice lacking hepatic Xbp1 show enhanced FGF21 induction when fed a ketogenic diet.

•

Hepatic Xbp1 is not required for induction of FGF21 in vivo.