Sex differences in FGF21-induced changes in hepatic metabolism
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ABSTRACT: To investigate sex-dependent changes in hepatic metabolism in response to fibroblast growth factor-21 (FGF21), we administered FGF21 or vehicle to mice on a high-fat diet then performed gene expression profiling analysis using data obtained from RNA-seq from livers of male and female mice.
Project description:To investigate sex-dependent effects of fibroblast growth factor-21 (FGF21), diet-induced obese male and female wildtype mice were administered two acute doses of FGF21 or saline vehicle. Mice were euthanized, livers collected, and submitted for untargeted metabolomics analysis.
Project description:The cJun NH2-terminal kinase (JNK) signaling pathway in the liver promotes systemic changes in metabolism by regulating PPARa-dependent expression of the hepatokine FGF21. Hepatocyte-specific gene ablation studies demonstrated that the Mapk9 gene (encodes JNK2) plays a key mechanistic role. Mutually exclusive inclusion of exons 7a and 7b yields expression of the isoforms JNK2a and JNK2b. Here we demonstrate that Fgf21 gene expression and metabolic regulation is primarily regulated by the JNK2a isoform. To identify relevant substrates of JNK2a, we performed a quantitative phosphoproteomic study of livers isolated from control mice, mice with JNK-deficiency in hepatocytes, and mice that express only JNK2a or JNK2b in hepatocytes. We identified the JNK substrate RXRa as a protein that exhibited JNK2a-promoted phosphorylation in vivo. RXRa functions as a heterodimeric partner of PPARa and may therefore mediate the effects of JNK2a signaling on Fgf21 expression. To test this hypothesis, we established mice with hepatocyte-specific expression of wild-type or mutated RXRa proteins. We found that the RXRa phosphorylation site Ser260 was required for suppression of Fgf21 gene expression. Collectively, these data establish a JNK-mediated signaling pathway that regulates hepatic Fgf21 expression.
Project description:Fibroblast growth factor 21 (Fgf21) is a liver-derived, fasting-induced hormone with broad effects on growth, nutrient metabolism and insulin sensitivity. Here, we report the discovery of a novel mechanism regulating Fgf21 expression under growth and fasting-feeding. The Sel1LHrd1 complex is the most conserved branch of mammalian endoplasmic reticulum (ER)- associated degradation (ERAD) machinery. Mice with liver-specific deletion of Sel1L exhibit growth retardation with markedly elevated circulating Fgf21, reaching levels close to those in Fgf21 transgenic mice or pharmacological models. Mechanistically, we show that the Sel1LHrd1 ERAD complex controls Fgf21 transcription by regulating the ubiquitination and turnover (and thus nuclear abundance) of ER-resident transcription factor Crebh, while having no effect on the other well-known Fgf21 transcription factor Pparα. Our data reveal a physiologically regulated, inverse correlation between Sel1L-Hrd1 ERAD and Crebh-Fgf21 levels under fasting-feeding and growth. This study not only establishes the importance of Sel1L-Hrd1 ERAD in the liver in the regulation of systemic energy metabolism, but also reveals a novel hepatic “ERADCrebh- Fgf21” axis directly linking ER protein turnover to gene transcription and systemic metabolic regulation.
Project description:Chronic stress leads post-traumatic stress disorder (PTSD) and to metabolic complications, including fatty liver. It is feasible, that stress immediately initiates molecular mechanisms to alter energy metabolism and glucose homeostasis which interfere with hepatic lipid accumulation after stress recovery. We aim to elucidate these molecular mechanisms of long term stress effects on metabolism and focus on physiological adaptation and the role of FGF21, which is protective in hepatic lipid accumulation. Methods FGF21 knockout and control mice were exposed to chronic variable stress (Cvs) and recovered for 3 months to simulate PTSD. We determined in vivo and ex vivo energy metabolism, mitochondrial function by extracellular flux analysis, alterations in DNA modifying enzymes and gene regulation immediately after stress and after the recovery period to determine long term alterations. Results Chronic stress leads to reduced insulin sensitivity and hepatic lipid accumulation with increased fatty acid uptake (FAU), stress-induced lipolysis, and reduction in NAD+/NAD ratio and Sirt activity. Immediately after stress, PPARa and SREBP-1 target genes are differentially regulated and are involved in the development of stress-induced fatty liver. After recovery, insulin sensitivity increases but insulin-induced de novo lipogenesis (DNL) is reduced and FAU is increased. HDAC and MT activity are suppressed, whereas HAT activity increases, linking metabolic adjustments to transcriptional regulators. Thus, key metabolic genes are differentially regulated and secreted proteins indicate the activation of liver disease by Cvs only in FGF21WT. GR binding to the Cd36 promoter is altered. After stress recovery, serum FGF21 is increased and protects against lipid accumulation. FGF21 interacts by attenuating DNL, increasing FAU and HAT activity, and balancing mitochondrial activity. Higher long-term stress-induced activation and binding of GR to the FGF21 promoter may contribute to the prolonged FGF21 release. Conclusions We show that previous stress exposure determines predisposition to fatty liver disease is regulated by FGF21. Immediately after Cvs, altered gene regulation and activity of DNA-modifying enzymes determine the metabolic late effects seen in PTSD. FGF21 functions after chronic stress exposure i) to protect against hepatic lipid accumulation, ii) to maintain mitochondrial capacity, and iii) to mediate in the modulation of DNA-modifying enzymes. These findings highlight the protective role of FGF21 even in stress-induced hepatic lipid accumulation.
Project description:FGF21 is a novel secreted protein with robust anti-diabetic, anti-obesity, and anti-atherogenic activities in preclinical species. In the current study, we investigated the signal transduction pathways downstream of FGF21 following acute administration of the growth factor to mice. Focusing on adipose tissues, we identified FGF21-mediated downstream signaling events and target engagement biomarkers. Specifically, RNA profiling of adipose tissues and phosphoproteomic profiling of adipocytes, following FGF21 treatment revealed several specific changes in gene expression and post-translational modifications, specifically phosphorylation, in several relevant proteins. Affymetrix microarray analysis of white adipose tissues isolated from both C57BL/6 (fed either regular chow or HFD) and db/db mice identified over 150 robust potential RNA transcripts and over 50 potential secreted proteins that were changed greater than 1.5 fold by FGF21 acutely. Phosphoprofiling analysis identified over 130 phosphoproteins that were modulated greater than 1.5 fold by FGF21 in 3T3-L1 adipocytes. Bioinformatic analysis of the combined gene and phosphoprotein profiling data identified a number of known metabolic pathways such as glucose uptake, insulin receptor signaling, Erk/Mapk signaling cascades, and lipid metabolism. Moreover, a number of novel events with hitherto unknown links to FGF21 signaling were observed at both the transcription and protein phosphorylation levels following treatment. We conclude that such a combined "omics" approach can be used not only to identify robust biomarkers for novel therapeutics but can also enhance our understanding of downstream signaling pathways; in the example presented here, novel FGF21-mediated signaling events in adipose tissue have been revealed that warrant further investigation. Three mouse strains (C57BL6 on chow diet, C57BL6 on high fat diet, and db/db on chow diet) were treated with either vehicle, wild-type FGF21, or pegylated FGF21 acutely or for several days and three white adipose tissues (IWAT, EWAT, RPWAT) and brown adipose tissue (BAT) were profiled on custom Affymetrix microarrays. The primary goal was to identify robust and consistent acute target engagement biomarkers of FGF21 activation in white adipose tissues.
Project description:Autophagy is essential for cellular survival and energy homeostasis under nutrient deprivation. Despite the emerging importance of nuclear events in autophagy regulation, epigenetic control of autophagy gene transcription remains unclear. Here, we identify Jumonji-D3 (JMJD3/KDM6B) histone demethylase as a key epigenetic activator of hepatic autophagy. Upon fasting-induced fibroblast growth factor-21 (FGF21) signaling, JMJD3 epigenetically upregulated global autophagy-network genes, including Tfeb, Atg7, Atgl, and Fgf21, through demethylation of histone H3K27-me3, resulting in autophagy-mediated lipid degradation. Mechanistically, phosphorylation of JMJD3 at Thr-1044 by FGF21 signal-activated PKA increased its nuclear localization and interaction with the nuclear receptor PPARto transcriptionally activate autophagy. Chronic administration of FGF21 in obese mice improved defective autophagy and hepatosteatosis in a JMJD3-dependent manner. Remarkably, in non-alcoholic fatty liver disease patients, hepatic expression of JMJD3, ATG7, LC3, and KL were substantially decreased. These findings demonstrate that FGF21-JMJD3 signaling epigenetically links nutrient deprivation with hepatic autophagy and lipid degradation in mammals
Project description:Cancer-associated cachexia (CAC) is a multifactorial, metabolic wasting syndrome that coincides with cancer malignancies of multiple entities. CAC is characterized by progressive loss of muscle mass and adipose tissue and diminishes therapy responsiveness. Here, we show that the expression of FGF21 is induced in livers of tumor-bearing mice with CAC. FGF21 deficiency promotes weight loss, exacerbates adipose tissue wasting and increases systemic inflammation, pointing towards a protective role of FGF21 in CAC. In line, IL6-mediated STAT3 activation induces FGF21 expression in hepatocytes as well as adipocytes. FGF21 promotes anabolic signaling cascades, increases cellular glucose uptake in response to IL6 exposure and counteracts cytokine-mediated glycerol release, thereby opposing adipose tissue loss in CAC. Eventually, we find that FGF21 is increased in cancer patients with clinical CAC. Together, we reveal a protective role for FGF21 in experimental CAC and identify the protein as a potential biomarker in clinical cachexia.
Project description:Fibroblast growth factor 21 (FGF21) is a liver-derived endocrine hormone that functions to regulate energy homeostasis and macronutrient intake. Recently, FGF21 was reported to be produced and secreted from hypothalamic tanycytes, to regulate peripheral lipid metabolism. However, rigorous investigation of FGF21 expression in the brain has yet to be accomplished. Utilizing a novel mouse model that drives CRE recombinase in FGF21-expressing cells, we demonstrate that FGF21 is not expressed in the hypothalamus, but instead is produced from the retrosplenial cortex (RSC), an essential brain region for spatial learning and memory. Furthermore, we find that central FGF21 produced in the RSC enhances spatial memory but does not regulate energy homeostasis or sugar intake. Finally, our data demonstrate that administration of FGF21 prolongs the duration of long-term potentiation in the hippocampus and enhances activation of hippocampal neurons. Thus, endogenous and pharmacological FGF21 appear to function in the hippocampus to strengthen the formation of spatial memory.
Project description:Thyroid hormone (TH) influences metabolic pathways by binding to specific receptors (TRs), which are conditional transcription factors. T3 works through TRs to induce fibroblast growth factor (FGF) 21, a peptide hormone that is usually induced in fasting and influences lipid and carbohydrate metabolism via local hepatic and systemic endocrine effects. While administered TH and FGF21 display overlapping actions, including reductions in serum lipids, current models suggest that these hormones act independently in vivo. Here, we examined mechanisms of TH regulation of FGF21 expression and tested the possibility that FGF21 is required for induction of hepatic TH-responsive genes. We confirm that active TH (T3) and the TRβ selective thyromimetic GC-1 increase FGF21 transcript and peptide levels in mouse liver and that this effect requires TRβ. T3 also induces FGF21 in cultured hepatocytes and this effect involves direct actions of TRβ1, which binds a TRE within intron 2 of FGF21. Gene expression profiles in wild type and FGF21 knockout mice are highly similar indicating that FGF21 is dispensable for the majority of hepatic T3 gene responses. A small subset of genes displays diminished T3 response in the absence of FGF21. However, most of these are not obviously involved in T3-dependent hepatic lipid and carbohydrate metabolic processes. Accordingly, T3-dependent effects upon serum lipids are maintained in the FGF21-/- background. Our findings suggest that T3 regulates genes involved in classical hepatic metabolic responses independently of FGF21.