Involvement of the vagus nerve and hepatic gene expression in serum adiponectin concentrations in mice

Several humoral factors, such as adiponectin and urate, have been suggested to affect metabolic syndromes. Previously, we reported a reduction in blood adiponectin concentrations after a high-fructose diet partially via the vagus nerve in rats. Although a lithogenic diet (LD), i.e., supplementation of a normal control diet (CT) with 0.6% cholesterol and 0.2% sodium cholate, reduced blood adiponectin concentrations, the involvement of the vagus nerve in this mechanism remains unclear. To estimate the involvement of the vagus nerve in the regulation of blood adiponectin concentrations using an LD, male imprinting control region mice that had been vagotomized (HVx) or only laparotomized (Sham) were administered a CT or an LD for 10 weeks. Serum adiponectin concentrations in the Sham-LD, HVx-CT, and HVx-LD groups were reduced by half compared with the Sham-CT group. The hepatic mRNA levels of fibroblast growth factor 21 (Fgf21), which reportedly stimulates adiponectin secretion from white adipose tissue, were lower in the LD groups compared with the CT groups. HepG2 hepatoma cells showed that various bile acids reduced the mRNA expression of FGF21. Moreover, the LD increased serum urate concentrations and reduced hepatic expressions of the acyl-CoA oxidase 1 (Acox1) mRNA and glucokinase, suggesting insufficient regeneration of ATP from AMP. In conclusion, serum adiponectin concentration may be regulated via the vagus nerve in normal mice, whereas a reduction of hepatic Fgf21 mRNA by bile acids may also lower serum adiponectin levels. Moreover, the LD may promote hepatic AMP accumulation and subsequently increase the serum urate concentration in mice. (AU)

Involvement of the vagus nerve and hepatic gene expression in serum adiponectin concentrations in mice.

Several humoral factors, such as adiponectin and urate, have been suggested to affect metabolic syndromes. Previously, we reported a reduction in blood adiponectin concentrations after a high-fructose diet partially via the vagus nerve in rats. Although a lithogenic diet (LD), i.e., supplementation of a normal control diet (CT) with 0.6% cholesterol and 0.2% sodium cholate, reduced blood adiponectin concentrations, the involvement of the vagus nerve in this mechanism remains unclear. To estimate the involvement of the vagus nerve in the regulation of blood adiponectin concentrations using an LD, male imprinting control region mice that had been vagotomized (HVx) or only laparotomized (Sham) were administered a CT or an LD for 10 weeks. Serum adiponectin concentrations in the Sham-LD, HVx-CT, and HVx-LD groups were reduced by half compared with the Sham-CT group. The hepatic mRNA levels of fibroblast growth factor 21 (Fgf21), which reportedly stimulates adiponectin secretion from white adipose tissue, were lower in the LD groups compared with the CT groups. HepG2 hepatoma cells showed that various bile acids reduced the mRNA expression of FGF21. Moreover, the LD increased serum urate concentrations and reduced hepatic expressions of the acyl-CoA oxidase 1 (Acox1) mRNA and glucokinase, suggesting insufficient regeneration of ATP from AMP. In conclusion, serum adiponectin concentration may be regulated via the vagus nerve in normal mice, whereas a reduction of hepatic Fgf21 mRNA by bile acids may also lower serum adiponectin levels. Moreover, the LD may promote hepatic AMP accumulation and subsequently increase the serum urate concentration in mice.

Emerging roles of brain tanycytes in regulating blood-hypothalamus barrier plasticity and energy homeostasis.

Seasonal changes in food intake and adiposity in many animal species are triggered by changes in the photoperiod. These latter changes are faithfully transduced into a biochemical signal by melatonin secreted by the pineal gland. Seasonal variations, encoded by melatonin, are integrated by third ventricular tanycytes of the mediobasal hypothalamus through the detection of the thyroid-stimulating hormone (TSH) released from the pars tuberalis. The mediobasal hypothalamus is a critical brain region that maintains energy homeostasis by acting as an interface between the neural networks of the central nervous system and the periphery to control metabolic functions, including ingestive behavior, energy homeostasis, and reproduction. Among the cells involved in the regulation of energy balance and the blood-hypothalamus barrier (BHB) plasticity are tanycytes. Increasing evidence suggests that anterior pituitary hormones, specifically TSH, traditionally considered to have unitary functions in targeting single endocrine sites, display actions on multiple somatic tissues and central neurons. Notably, modulation of tanycytic TSH receptors seems critical for BHB plasticity in relation to energy homeostasis, but this needs to be proven.

CRISPR-Cas9-based genome-wide screening identified novel targets for treating sorafenib-resistant hepatocellular carcinoma: a cross-talk between FGF21 and the NRF2 pathway.

The treatment of hepatocellular carcinoma (HCC) has been dominated by multikinase inhibitors for more than a decade. However, drug resistance can severely restrict the efficacy of these drugs. Using CRISPR/CAS9 genome library screening, we evaluated Kelch-like ECH-associated protein 1 (KEAP1) as a key regulator of sorafenib's susceptibility in HCC. We also investigated whether KEAP1's knockdown can stabilize nuclear factor (erythroid-derived 2)-like 2 (NRF2) protein levels that led to sorafenib's resistance, including an NRF2 inhibitor that can synergize with sorafenib to abolish HCC's growth in vitro and in vivo. Furthermore, we clarified that fibroblast growth factor 21 (FGF21) is an important downstream regulator of NRF2 in HCC. Intriguingly, we observed that FGF21 bound to NRF2 through the C-terminus of FGF21, thereby stabilizing NRF2 by reducing its ubiquitination and generating a positive feedback loop in sorafenib-resistant HCC. These findings, therefore, propose that targeting FGF21 is a promising strategy to combat HCC sorafenib's resistance.

Bupleuri radix extract ameliorates impaired lipid metabolism in high-fat diet-induced obese mice via gut microbia-mediated regulation of FGF21 signaling pathway.

BACKGROUND: Obesity and its comorbidities are associated with abnormal lipid metabolism and gut microbiota dysbiosis. Bupleuri Radix is a medicinal plant used in traditional Chinese medicine with the prevention and treatment of obesity-related diseases. In this study, we aim to validate the regulation of Bupleuri Radix Extract (BupE) on lipid metabolism in obese mice, and try to find out the potential active components and reveal the underlying mechanisms. METHODS: Ingredients in BupE, their circulating metabolites in mice and fecal biotransformation products were analyzed by ultra-performance liquid chromatography coupled to quadrupole time-of-flight mass spectrometry (UPLC/Q-TOF-MS). Western blotting, RT-PCR and ELISA were used for tests of objective genes and proteins. 16 s rRNA sequencing was performed to examine intestinal bacteria composition and microbes' functional changes were predicted with PICRUSt software. An absolute quantification method was set up via the construction of recombinant plasmid for the assays of intestinal flora. Specific microbial strains were cultured in anaerobic conditions and oral administrated to mice for intestinal mono-colonization. RESULTS: BupE attenuated obesity, liver steatosis, and dyslipidemia in HFD-fed mice by up-regulating the expression of FGF21 in liver and white adipose tissue (WAT) as well as the downstream proteins of FGF21 signal pathway including ß-klotho, GLUT1 and PGC-1α, etc. UPLC/Q-TOF-MS fingerprints showed no compounds from BupE or their metabolites or biotransformation products were detected in rodent serum samples. High-throughput pyrosequencing data indicated that BupE reversed obesity-induced constructional and functional alterations of intestinal flora. Two bacterial strains, Bacteroides acidifaciens (B. acidifaciens) and Ruminococcus gnavus (R. gnavus), were separated and identified from the feces of obese mice and by intestinal mono-colonization they were verified to intervene in the anti-obesity effects of BupE on mice. CONCLUSION: These data suggest that BupE protects against diet-induced obesity and counteracts metabolic syndrome features consistent with a mechanism involving the gut-liver axis that boosts hepatic FGF21 secretion and consequent down-stream proteins expression relating to lipid metabolism. And in this gut-liver axis, intestinal microbes such as B.acidifaciens and R.gnavus play an indispensable role.

Baseline HOMA IR and Circulating FGF21 Levels Predict NAFLD Improvement in Patients Undergoing a Low Carbohydrate Dietary Intervention for Weight Loss: A Prospective Observational Pilot Study.

BACKGROUND: Non-alcoholic fatty liver disease (NAFLD) is a major cause of liver disease. Very low-calorie ketogenic diets (VLCKD) represent a feasible treatment as they induce profound weight loss and insulin resistance (IR) improvement. Despite the recognized benefits on NAFLD deriving from pharmacological administration of fibroblast growth factor 21 (FGF21), whose endogenous counterpart is a marker of liver injury, little is known about its physiology in humans. AIM: To identify predictors of NAFLD improvement as reflected by the reduction of the non-invasive screening tool hepatic steatosis index (HSI) in obese patients undergoing a weight loss program. METHODS: Sixty-five obese patients underwent a 90-day dietary program consisting of a VLCKD followed by a hypocaloric low carbohydrate diet (LCD). Anthropometric parameters, body composition, and blood and urine chemistry were assessed. RESULTS: Unlike most parameters improving mainly during the VLCKD, the deepest HSI change was observed after the LCD (p = 0.02 and p < 0.0001, respectively). Baseline HOMA-IR and serum FGF21 were found to be positive (R = 0.414, p = 0009) and negative (R = 0.364, p = 0.04) independent predictors of HSI reduction, respectively. CONCLUSIONS: We suggest that patients with IR and NAFLD derive greater benefit from a VLCKD, and we propose a possible role of human FGF21 in mediating NAFLD amelioration following nutritional manipulation.

Dietary Supplementation with Dunaliella Tertiolecta Prevents Whitening of Brown Fat and Controls Diet-Induced Obesity at Thermoneutrality in Mice.

We investigated the effect of evodiamine-containing microalga Dunaliella tertiolecta (DT) on the prevention of diet-induced obesity in a thermoneutral C57BL/6J male (30 °C). It attenuates the activity of brown adipose tissue (BAT), which accelerates diet-induced obesity. Nine-week-old mice were fed a high-fat diet supplemented with 10 g (Low group) or 25 g (High group) DT powder per kg food for 12 weeks. Compared to control mice without DT supplementation, body weight gain was significantly reduced in the High group with no difference in food intake. Tissue analyses indicated maintenance of multilocular morphology in BAT and reduced fat deposition in liver in DT-supplemented mice. Molecular analysis showed a significant decrease in mammalian target of rapamycin-ribosomal S6 protein kinase signaling pathway in white adipose tissue and upregulation in mRNA expression of brown fat-associated genes including fibroblast growth factor-21 (Fgf21) and uncoupling protein 1 (Ucp1) in BAT in the High group compared to the control. In the experiments using C3H10T1/2 adipocytes, DT extract upregulated mRNA expression of brown fat-associated genes in dose-dependent and time-dependent manners, accompanied by a significant increase in secreted FGF21 levels. Our data show the ability of DT as a nutraceutical to prevent brown fat attenuation and diet-induced obesity in vivo.

Ethyl acetate extract of sappanwood alleviates experimental atherosclerosis in rats through changes in FGF21 and SREBP-2 expression.

Sappanwood extract shows promising effects against atherosclerosis. The fibroblast growth factor 21 (FGF21) and sterol regulatory element-binding protein 2 (SREBP2) are involved in atherosclerosis development. This study aimed to examine whether sappanwood ethyl acetate extract (SEAE) alleviates experimental atherosclerosis in rats through FGF21/SREBP-2 signaling. Rats were randomized to six groups (n=10/group): blank control, model, simvastatin (positive control, 4.2 mg/kg/d), and SEAE high-, medium-, and low-dose (2.30, 1.15, and 0.575 g/kg/d, respectively). The high-fat- and vitamin D3-induced rodent model of atherosclerosis was created (except in the blank control group). Aorta and liver underwent histopathologic examination. SREPB-2 and FGF21 expression levels were examined by real-time RT-PCR and western blot. Compared with the blank control group, the model group showed aortic and hepatic histopathology compatible with the development of atherosclerosis due to a high-fat diet. In addition, total cholesterol, triglycerides, and low-density lipoprotein cholesterol (LDL-C) were elevated (all P<0.05). SREBP2 expression was high, and FGF21 expression was low (both P<0.05). Compared with the model group, SEAE alleviated the changes in liver and aorta by histopathology and decreased total cholesterol, triglycerides, and LDL-C (all P<0.05), especially in the medium-, and high-dose groups. In addition, medium-dose SEAE increased FGF21 levels (mRNA: +296%; protein: +69%; P<0.05) and decreased SREBP2 levels (mRNA: -44%; protein: -77%; P<0.05). Simvastatin, as the positive control, had similar effects to those of SEAE. In conclusion, SEAE improves lipid metabolism and alleviates atherosclerosis through changes in FGF21 and SREBP-2 expression levels.

Ishige okamurae Extract Ameliorates the Hyperglycemia and Body Weight Gain of db/db Mice through Regulation of the PI3K/Akt Pathway and Thermogenic Factors by FGF21.

Type 2 diabetes mellitus and related metabolic disorders, such as dyslipidemia, present increasing challenges to health worldwide, as a result of urbanization, the increasing prevalence of obesity, poor lifestyle, and other stress-related factors. Ishige okamurae extract (IOE) is known to be effective at lowering blood glucose and ameliorating metabolic disease. However, detailed mechanisms for these effects have yet to be elucidated. Here, we show that IOE ameliorates substrate (IRS)/ phosphatidylinositol 3-kinase (PI3K)/Akt pathway and increasing glucose transporter 4 (GLUT4) expression in skeletal muscle and white adipose tissue (WAT). We also demonstrate that IOE increases the expression of fibroblast growth factor (FGF)21, a regulator of glucose and energy metabolism in muscle and WAT. In addition, IOE administration increased peroxisome proliferator-activated receptor γ coactivator 1α expression, which regulates expression of the key thermogenic molecule uncoupling protein 1 in WAT. Thus, the effects of IOE to ameliorate hyperglycemia and adiposity may be mediated through FGF21 activating insulin signaling and increasing the expression of GLUT4 and pro-thermogenic factors.

Activation of AK005401 aggravates acute ischemia/reperfusion mediated hippocampal injury by directly targeting YY1/FGF21.

Ischemia exerts a negative impact on mitochondrial function, which ultimately results in neuronal damage via alterations in gene transcription and protein expression. Long non- coding RNAs (LncRNAs) play pivotal roles in the regulation of target protein expression and gene transcription. In the present study, we observed the effect of an unclassical LncRNA AK005401on ischemia/reperfusion (I/R) ischemia-mediated hippocampal injury and investigated the regulatory role of fibroblast growth factor 21 (FGF21) and Yin Yang 1 (YY1). C57Black/6 mice were subjected to I/R using the bilateral common carotid clip reperfusion method, and AK005401 siRNA oligos were administered via intracerebroventricular injection. HT22 cells were used to establish a model of oxygen-glucose deprivation/reoxygenation (OGD/R). We observed pathological morphology and mitochondrial structure. Neuronal apoptosis was evident. Cell activity, cell respiration, FGF21, YY1, and antioxidant capacity were evaluated. I/R or OGD/R significantly increased the expressions of AK005401and YY1 and decreased FGF21expression, which further attenuated the activation of PI3K/Akt, promoted reactive oxygen species (ROS) generation, and then caused mitochondria dysfunction and cell apoptosis, which were reversed by AK005401 siRNA oligos and were aggravated by overexpression of AK005401 and YY1. We conclude that AK005401/YY1/FGF21 signaling pathway has an important role in I/R-mediated hippocampal injury.

KLB, encoding ß-Klotho, is mutated in patients with congenital hypogonadotropic hypogonadism.

Congenital hypogonadotropic hypogonadism (CHH) is a rare genetic form of isolated gonadotropin-releasing hormone (GnRH) deficiency caused by mutations in > 30 genes. Fibroblast growth factor receptor 1 (FGFR1) is the most frequently mutated gene in CHH and is implicated in GnRH neuron development and maintenance. We note that a CHH FGFR1 mutation (p.L342S) decreases signaling of the metabolic regulator FGF21 by impairing the association of FGFR1 with ß-Klotho (KLB), the obligate co-receptor for FGF21. We thus hypothesized that the metabolic FGF21/KLB/FGFR1 pathway is involved in CHH Genetic screening of 334 CHH patients identified seven heterozygous loss-of-function KLB mutations in 13 patients (4%). Most patients with KLB mutations (9/13) exhibited metabolic defects. In mice, lack of Klb led to delayed puberty, altered estrous cyclicity, and subfertility due to a hypothalamic defect associated with inability of GnRH neurons to release GnRH in response to FGF21. Peripheral FGF21 administration could indeed reach GnRH neurons through circumventricular organs in the hypothalamus. We conclude that FGF21/KLB/FGFR1 signaling plays an essential role in GnRH biology, potentially linking metabolism with reproduction.

Circulating FGF21 in humans is potently induced by short term overfeeding of carbohydrates.

OBJECTIVE: Fibroblast-growth factor 21 (FGF21) is thought to be important in metabolic regulation. Recently, low protein diets have been shown to increase circulating FGF21 levels. However, when energy contribution from dietary protein is lowered, other macronutrients, such as carbohydrates, must be increased to meet eucaloric balance. This raises the possibility that intake of a diet rich in carbohydrates may induce an increase in plasma FGF21 levels per se. Here we studied the role of dietary carbohydrates on the levels of circulating FGF21 and concomitant physiologic effects by feeding healthy men a carbohydrate rich diet without reducing protein intake. METHODS: A diet enriched in carbohydrates (80 E% carbohydrate; CHO) and a eucaloric control diet (CON) were provided to nine healthy men for three days. The energy intake during the CHO diet was increased (+75% energy) to ensure similar dietary protein intake in CHO and CON. To control for the effect of caloric surplus, we similarly overfed (+75% energy) the same subjects for three days with a fat-rich diet (78 E% fat; FAT), consisting of primarily unsaturated fatty acids. The three diets were provided in random order. RESULTS: After CHO, plasma FGF21 concentration increased 8-fold compared to CON (329 ± 99 vs. 39 ± 9 pg ml-1, p < 0.05). In contrast, after FAT only a non-significant tendency (p = 0.073) to an increase in plasma FGF21 concentration was found. The increase in FGF21 concentration after CHO correlated closely (r = 0.88, p < 0.01) with increased leg glucose uptake (62%, p < 0.05) and increased hepatic glucose production (17%, p < 0.01), indicating increased glucose turnover. Plasma fatty acid (FA) concentration was decreased by 68% (p < 0.01), supported by reduced subcutaneous adipose tissue HSL Ser660 phosphorylation (p < 0.01) and perilipin 1 protein content (p < 0.01), pointing to a suppression of adipose tissue lipolysis. Concomitantly, a 146% increase in the plasma marker of hepatic de novo lipogenesis C16:1 n-7 FA (p < 0.01) was observed together with 101% increased plasma TG concentration (p < 0.001) in association with CHO intake and increased plasma FGF21 concentration. CONCLUSION: Excess dietary carbohydrate, but not fat, led to markedly increased FGF21 secretion in humans, notably without protein restriction, and affected glucose and lipid homeostais.

Upregulation of rat liver PPARα-FGF21 signaling by a docosahexaenoic acid and thyroid hormone combined protocol.

Prevention of ischemia-reperfusion liver injury is achieved by a combined omega-3 and thyroid hormone (T3 ) protocol, which may involve peroxisome-proliferator activated receptor-α (PPAR-α)-fibroblast growth factor 21 (FGF21) signaling supporting energy requirements. Combined docosahexaenoic acid (DHA; daily doses of 300 mg/kg for 3 days) plus 0.05 mg T3 /kg given to fed rats elicited higher hepatic DHA contents and serum T3 levels, increased PPAR-α mRNA and its DNA binding, with higher mRNA expression of the PPAR-α target genes for carnitine-palmitoyl transferase 1α, acyl-CoA oxidase, and 3-hydroxyl-3-methylglutaryl-CoA synthase 2, effects that were mimicked by 0.1 mg T3 /kg given alone or by the PPAR-α agonist WY-14632. Under these conditions, the mRNA expression of retinoic X receptor-α (RXR-α) is also increased, with concomitant elevation of the hepatic mRNA and protein FGF21 levels and those of serum FGF21. It is concluded that PPAR-α-FGF21 induction by DHA combined with T3 may involve ligand activation of PPAR-α by DHA and enhanced expression of PPAR-α by T3 , with consequent upregulation of the FGF21 that is controlled by PPAR-α. Considering the beneficial effects of PPAR-α-FGF21 signaling on carbohydrate and lipid metabolism, further investigations are required to clarify its potential therapeutic applications in human metabolic disorders. © 2016 BioFactors, 42(6):638-646, 2016.

The modulating effect of Persea americana fruit extract on the level of expression of fatty acid synthase complex, lipoprotein lipase, fibroblast growth factor-21 and leptin--A biochemical study in rats subjected to experimental hyperlipidemia and obesity.

BACKGROUND: Obesity is a multifactorial disorder which is closely associated with hyperlipidemia. Avocados are edible fruits traditionally consumed for various health benefits including body weight reduction. HYPOTHESIS/PURPOSE: To determine the hypolipidemic and anti-obesity effect of hydro-alcoholic fruit extract of avocado (HFEA) in rats fed with high fat diet (HFD). STUDY DESIGN: Male Sprague Dawley rats were divided into four groups. Groups 1 and 2 rats were fed with normal diet. Groups 3 and 4 rats were fed with HFD for 14 weeks. In addition, Groups 2 and 4 rats were co-administered with 100 mg/kg body weight of HFEA from 3rd week onwards. METHODS: The HFEA was subjected to HPLC to quantify the major phytonutrients. Body mass index (BMI), adiposity index (ADI), total fat pad mass (TFP), blood lipid levels were determined in all the groups of rats. The mRNA expression of fatty acid synthase (FASN), lipoprotein lipase (LPL), fibroblast growth factor 21 (FGF21) and leptin was also assessed. RESULTS: HFEA was found to contain flavonoids: rutin-141.79, quercetin-5.25, luteolin-165, phenolic compounds: gallic acid-198.57, ellagic acid-238.22, vanillic acid-4.79 and phytosterols: betasitosterol-70, stigmasterol-12.5 (mg/100 g). HFEA reduced BMI, ADI, TFP, blood cholesterol, triglycerides, and LDL in rats fed with HFD. Serum leptin was found reduced in HFEA co-administered rats. The mRNA expression of FASN, LPL, and leptin in subcutaneous and visceral adipose tissue was found to be significantly reduced in HFEA co-administered rats. The gene expression of fibroblast growth factor-21 (FGF21) was found to be significantly increased in HFEA treated rats when compared to HFD control rats. CONCLUSION: The hypolipidemic effect of HFEA may be partly due to its modulating effect on endogenous fat synthesis and adiponectin formation through the transcription factor FGF21. The results also show that avocado fruit extract has profound influence on leptin activity, which controls satiety and hunger to regulate the food intake.

Dihydromyricetin improves glucose and lipid metabolism and exerts anti-inflammatory effects in nonalcoholic fatty liver disease: A randomized controlled trial.

Ampelopsis grossedentata, a medicinal and edible plant, has been widely used in China for hundreds of years, and dihydromyricetin is the main active ingredient responsible for its various biological actions. We investigated the effects of dihydromyricetin on glucose and lipid metabolism, inflammatory mediators and several biomarkers in nonalcoholic fatty liver disease. In a double-blind clinical trial, sixty adult nonalcoholic fatty liver disease patients were randomly assigned to receive either two dihydromyricetin or two placebo capsules (150 mg) twice daily for three months. The serum levels of alanine, aspartate aminotransferase, γ-glutamyl transpeptidase, glucose, low-density lipoprotein-cholesterol and apolipoprotein B, and the homeostasis model assessment of insulin resistance (HOMA-IR) index were significantly decreased in the dihydromyricetin group compared with the placebo group. In the dihydromyricetin group, the serum levels of tumor necrosis factor-alpha, cytokeratin-18 fragment and fibroblast growth factor 21 were decreased, whereas the levels of serum adiponectin were increased at the end of the study. We conclude that dihydromyricetin supplementation improves glucose and lipid metabolism as well as various biochemical parameters in patients with nonalcoholic fatty liver disease, and the therapeutic effects of dihydromyricetin are likely attributable to improved insulin resistance and decreases in the serum levels of tumor necrosis factor-alpha, cytokeratin-18, and fibroblast growth factor 21.

Skeletal muscle increases FGF21 expression in mitochondrial disorders to compensate for energy metabolic insufficiency by activating the mTOR-YY1-PGC1α pathway.

Fibroblast growth factor 21 (FGF21) is a growth factor with pleiotropic effects on regulating lipid and glucose metabolism. Its expression is increased in skeletal muscle of mice and humans with mitochondrial disorders. However, the effects of FGF21 on skeletal muscle in response to mitochondrial respiratory chain deficiency are largely unknown. Here we demonstrate that the increased expression of FGF21 is a compensatory response to respiratory chain deficiency. The mRNA and protein levels of FGF21 were robustly raised in skeletal muscle from patients with mitochondrial myopathy or MELAS. The mammalian target of rapamycin (mTOR) phosphorylation levels and its downstream targets, Yin Yang 1 (YY1) and peroxisome proliferator-activated receptor γ, coactivator 1α (PGC-1α), were increased by FGF21 treatment in C2C12 myoblasts. Activation of the mTOR-YY1-PGC1α pathway by FGF21 in myoblasts regulated energy homeostasis as demonstrated by significant increases in intracellular ATP synthesis, oxygen consumption rate, activity of citrate synthase, glycolysis, mitochondrial DNA copy number, and induction of the expression of key energy metabolic genes. The effects of FGF21 on mitochondrial function required phosphoinositide 3-kinase (PI3K), which activates mTOR. Inhibition of PI3K, mTOR, YY1, and PGC-1α activities attenuated the stimulating effects of FGF21 on intracellular ATP levels and mitochondrial gene expression. Our findings revealed that mitochondrial respiratory chain deficiency elicited a compensatory response in skeletal muscle by increasing the FGF21 expression levels in muscle, which resulted in enhanced mitochondrial function through an mTOR-YY1-PGC1α-dependent pathway in skeletal muscle.

Artemisia scoparia extract attenuates non-alcoholic fatty liver disease in diet-induced obesity mice by enhancing hepatic insulin and AMPK signaling independently of FGF21 pathway.

OBJECTIVE: Nonalcoholic fatty liver disease (NAFLD) is a common liver disease which has no standard treatment. In this regard, we sought to evaluate the effects of extracts of Artemisia santolinaefolia (SANT) and Artemisia scoparia (SCO) on hepatic lipid deposition and cellular signaling in a diet-induced obesity (DIO) animal model. MATERIALS/METHODS: DIO C57/B6J mice were randomly divided into three groups, i.e. HFD, SANT and SCO. Both extracts were incorporated into HFD at a concentration of 0.5% (w/w). Fasting plasma glucose, insulin, adiponectin, and FGF21 concentrations were measured. RESULTS: At the end of the 4-week intervention, liver tissues were collected for analysis of insulin, AMPK, and FGF21 signaling. SANT and SCO supplementation significantly increased plasma adiponectin levels when compared with the HFD mice (P<0.001). Fasting insulin levels were significantly lower in the SCO than HFD mice, but not in SANT group. Hepatic H&E staining showed fewer lipid droplets in the SCO group than in the other two groups. Cellular signaling data demonstrated that SCO significantly increased liver IRS-2 content, phosphorylation of IRS-1, IR ß, Akt1 and Akt2, AMPK α1 and AMPK activity and significantly reduced PTP 1B abundance when compared with the HFD group. SCO also significantly decreased fatty acid synthase (FAS), HMG-CoA Reductase (HMGR), and Sterol regulatory element-binding protein 1c (SREBP1c), but not Carnitine palmitoyltransferase I (CPT-1) when compared with HFD group. Neither SANT nor SCO significantly altered plasma FGF21 concentrations and liver FGF21 signaling. CONCLUSION: This study suggests that SCO may attenuate liver lipid accumulation in DIO mice. Contributing mechanisms were postulated to include promotion of adiponectin expression, inhibition of hepatic lipogenesis, and/or enhanced insulin and AMPK signaling independent of FGF21 pathway.