Search

Metabolic functions of the hepatic hormone fibroblast growth factor 21 (FGF21) have been recognized for more than a decade in studying the responses of human subjects and rodent models to nutritional stresses such as fasting, high-fat diet or ketogenic diet consumption, and ethanol intake. Our interest in the beneficial metabolic effects of FGF21 has risen due to its potential ability to serve as a therapeutic agent for various metabolic disorders, including type 2 diabetes, obesity, and fatty liver diseases, as well as its potential to act as a diagnostic or prognostic biomarker for metabolic and other disorders. Here, we briefly review the FGF21 gene and protein structures, its expression pattern, and cellular signaling cascades that mediate FGF21 production and function. We mainly focus on discussing experimental and clinical literature pertaining to FGF21 as a therapeutic agent. Furthermore, we present several lines of investigation, including a few studies conducted by our team, suggesting that FGF21 expression and function can be regulated by dietary polyphenol interventions. Finally, we discuss the literature debating FGF21 as a potential biomarker in various disorders. [ABSTRACT FROM AUTHOR]

β-cat/TCF, formed by β-cat and a TCF family member, serves as the effector of the developmental canonical Wnt signaling cascade. β-cat/TCFs can also function as effectors of metabolic hormones or growth factors during adulthood. We have demonstrated recently that liver-specific expression of dominant-negative TCF7L2 (TCF7L2DN) led to impaired glucose disposal in both male and female mice. Increased hepatic lipogenesis, however, was observed in male but not in female mice. Our further investigations on such LTCFDN transgenic mouse model revealed the role of estradiol (E2) in stimulating β-cat/TCF activity. E2 reconstitution in WT mice with ovariectomy (OVX) restored the resistance of female mice to HFD induced body weight gain, insulin intolerance and elevation of hepatic lipogenic gene expression. Such beneficial effects of E2 reconstitution, however, were absent in LTCFDN female mice. To identify downstream metabolic effector/s of Wnt signaling in regulating hepatic lipogenesis, we assessed metabolic hormone expression in LTCFDN and WT littermates. Curiously, hepatic but not adipose tissue FGF-21 level was reduced in male LTCFDN mice. We then directly assessed the effect of E2 on hepatic FGF-21 expression. In WT mice on LFD diet, OVX leads to reduced hepatic FGF-21 mRNA and protein levels, associated with reduced circulating FGF-21 hormone level. These reduction was associated with reduced hepatic β-cat S675 phosphorylation, TCF7 and TCF7L2 expression. In WT mice on HFD, OVX also reduced hepatic FGF-21 mRNA and circulating FGF-21 hormone levels. Such reduction was also restored with E2 reconstitution. Our study hence identified that FGF-21 is likely among the downstream effectors of E2-Wnt signaling cascade in hepatic lipid homeostasis. Disclosure: W. Shao: None. Y. Badakhshi: None. T. Jin: None. Funding: Canadian Institutes of Health Research (PJT159735) [ABSTRACT FROM AUTHOR]

The metabolic hormone FGF-21 is mainly produced and released from the liver in response to nutritional stresses such as starvation, alcohol or ketogenic diet consumption. Body weight lowering and insulin signaling sensitization effects of FGF-21 and its analogues have been demonstrated in animal models or in human subjects. We show here that hepatic FGF-21 mRNA and FGF-21 protein levels were reduced in male LTCFDN, a transgenic mouse line in which canonical Wnt signaling cascade is functionally attenuated due to the expression of dominant negative transcription factor TCF7L2 in the liver, and the reduction is not associated with reduced expression of PPARα, a key transactivator of FGF-21. Furthermore, starvation-induced plasma FGF-21 elevation was also attenuated in male LTCFDN mice. Utilizing mouse primary hepatocytes, we found that FGF-21 mRNA and FGF-21 protein expression can be increased by Wnt-3a or LiCl treatment. Two evolutionarily conserved TCF binding motifs (TCFB) were then located within the mouse FGF-21 gene promoter. Luciferase and ChIP results suggest that one of them is responsible for β-cat/TCF mediated activation on FGF-21 transcription.It has been shown recently that in mouse brain tanycytes, FGF-21 secretion can be induced by palmitate treatment. We found that in mouse primary hepatocytes, palmitate but not oleate treatment increased expression of the Wnt target gene Ccnd1, which encodes cyclin D1. Our observations hence suggest that Wnt signaling cascade is involved in hepatic FGF-21 production and secretion, and the positive regulation is likely independent of fibrate/PPARα-mediated induction. Investigations on this novel hepatic signaling axis will strengthen our knowledge on the physiologically significant hormone FGF-21, leading to novel therapeutic avenues in treating impaired metabolism. Disclosure: Y. Badakhshi: None. W. Shao: None. L. Tian: None. T. Jin: None. Funding: Canadian Institutes of Health Research (PJT159735) [ABSTRACT FROM AUTHOR]

Background: Dietary polyphenols including anthocyanins target multiple organs.Objective: We aimed to assess the involvement of glucagon-like peptide 1 (GLP-1), leptin, insulin and fibroblast growth factor 21 (FGF21) in mediating metabolic beneficial effects of purified anthocyanin cyanidin-3-glucoside (Cy3G).Methods: Intestinal proglucagon gene (Gcg; encoding GLP-1) and liver Fgf21 expression were assessed in 6-wk-old male C57BL-6J mice fed a low-fat-diet (LFD; 10% of energy from fat), alone or with 1.6 mg Cy3G/L in drinking water for 3 wk [experiment (Exp.) 1; n = 5/group]. Similar mice were fed the LFD or a high-fat diet (HFD; 60% energy from fat) with or without Cy3G for 20 wk. Half of the mice administered Cy3G also received 4 broad-spectrum antibiotics (ABs) in drinking water between weeks 11 and 14, for a total of 6 groups (n = 8/group). Metabolic tolerance tests were conducted between weeks 2 and 16. Relevant hormone gene expression and plasma hormone concentrations were assessed mainly at the end of 20 wk (Exp. 2).Results: In Exp. 1, Cy3G administration increased ileal but not colonic Gcg level by 2-fold (P < 0.05). In Exp. 2, Cy3G attenuated HFD-induced body-weight gain (20.3% at week 16), and improved glucose tolerance (26.5% at week 15) but not insulin tolerance. Although Cy3G had no effect on glucose tolerance in LFD mice, LFD/Cy3G/AB mice showed better glucose tolerance than LFD/Cy3G mice (23%). In contrast, HFD/Cy3G/AB mice showed worse glucose tolerance compared with HFD/Cy3G mice (15%). Beneficial effects of Cy3G in HFD mice were not associated with changes in plasma leptin, insulin or GLP-1 concentrations. However, Cy3G increased hepatic Fgf21 expression in mice in Exp. 1 by 4-fold and attenuated Fgf21 overexpression in HFD mice (Exp. 2, 22%), associated with increased expression of genes that encode FGFR1 and β-klotho (>3-fold, P < 0.05).Conclusions: Dietary Cy3G may reduce body weight and exert metabolic homeostatic effects in mice via changes in hepatic FGF21. [ABSTRACT FROM AUTHOR]

The bipartite transcription factor β-catenin (β-cat)/T cell factor (TCF), formed by free β-cat and a given TCF family member, serves as the effector of the developmental Wnt signaling cascade. β-cat/TCFs also serve as effectors of certain peptide hormones or growth factors during adulthood. We reported that liver-specific expression of dominant-negative Transcription factor 7 like 2 (TCF7L2DN) led to impaired glucose disposal. Here we show that, in this LTCFDN transgenic mouse model, serum and hepatic lipid contents were elevated in male but not in female mice. In hepatocytes, TCF7L2DN adenovirus infection led to stimulated expression of genes that encode lipogenic transcription factors and lipogenic enzymes, while estradiol (E2) treatment attenuated the stimulation, associated with Wnt-target gene activation. Mechanistically, this E2-mediated activation can be attributed to elevated β-cat Ser675 phosphorylation and TCF expression. In wild-type female mice, ovariectomy (OVX) plus high-fat diet (HFD) challenge impaired glucose disposal and insulin tolerance, associated with increased hepatic lipogenic transcription factor sterol regulatory element-binding protein 1-c (SREBP-1c) expression. In wild-type mice with OVX, E2 reconstitution attenuated HFD-induced metabolic defects. Some of the attenuation effects, including insulin intolerance, elevated liver-weight gain, and hepatic SREBP-1c expression, were not affected by E2 reconstitution in HFD-fed LTCFDN mice with OVX. Finally, the effects of E2 in hepatocytes on β-cat/TCF activation can be attenuated by the G-protein-coupled estrogen receptor (GPER) antagonist G15. Our study thus expanded the scope of functions of the Wnt pathway effector β-cat/TCF, as it can also mediate hepatic functions of E2 during adulthood. This study also enriches our mechanistic understanding of gender differences in the risk and pathophysiology of metabolic diseases. [ABSTRACT FROM AUTHOR]

microRNA (miRNA) activity and regulation are of increasing interest as new therapeutic targets. Traditional approaches to assess miRNA levels in cells rely on RNA sequencing or quantitative PCR. While useful, these approaches are based on RNA extraction and cannot be applied in real-time to observe miRNA activity with single-cell resolution. We developed a green fluorescence protein (GFP)-based reporter system that allows for a direct, real-time readout of changes in miRNA activity in live cells. The miRNA activity reporter (MiRAR) consists of GFP fused to a 3′ untranslated region containing specific miRNA binding sites, resulting in miRNA activity-dependent GFP expression. Using qPCR, we verified the inverse relationship of GFP fluorescence and miRNA levels. We demonstrated that this novel optogenetic reporter system quantifies cellular levels of the tumor suppressor miRNA let-7 in real-time in single Human embryonic kidney 293 (HEK 293) cells. Our data shows that the MiRAR can be applied to detect changes in miRNA levels upon disruption of miRNA degradation pathways. We further show that the reporter could be adapted to monitor another disease-relevant miRNA, miR-122. With trivial modifications, this approach could be applied across the miRNome for quantification of many specific miRNA in cell cultures, tissues, or transgenic animal models. [ABSTRACT FROM AUTHOR]