Fibroblast growth factor-21 is required for weight loss induced by the glucagon-like peptide-1 receptor agonist liraglutide in male mice fed high carbohydrate diets.

OBJECTIVE: Glucagon-like peptide-1 receptor (GLP-1R) agonists (GLP-1RA) and fibroblast growth factor-21 (FGF21) confer similar metabolic benefits. GLP-1RA induce FGF21, leading us to investigate mechanisms engaged by the GLP-1RA liraglutide to increase FGF21 levels and the metabolic relevance of liraglutide-induced FGF21. METHODS: Circulating FGF21 levels were measured in fasted male C57BL/6J, neuronal GLP-1R knockout, ß-cell GLP-1R knockout, and liver peroxisome proliferator-activated receptor alpha knockout mice treated acutely with liraglutide. To test the metabolic relevance of liver FGF21 in response to liraglutide, chow-fed control and liver Fgf21 knockout (LivFgf21-/-) mice were treated with vehicle or liraglutide in metabolic chambers. Body weight and composition, food intake, and energy expenditure were measured. Since FGF21 reduces carbohydrate intake, we measured body weight in mice fed matched diets with low- (LC) or high-carbohydrate (HC) content and in mice fed a high-fat, high-sugar (HFHS) diet. This was done in control and LivFgf21-/- mice and in mice lacking neuronal ß-klotho (Klb) expression to disrupt brain FGF21 signaling. RESULTS: Liraglutide increases FGF21 levels independently of decreased food intake via neuronal GLP-1R activation. Lack of liver Fgf21 expression confers resistance to liraglutide-induced weight loss due to attenuated reduction of food intake in chow-fed mice. Liraglutide-induced weight loss was impaired in LivFgf21-/- mice when fed HC and HFHS diets but not when fed a LC diet. Loss of neuronal Klb also attenuated liraglutide-induced weight loss in mice fed HC or HFHS diets. CONCLUSIONS: Our findings support a novel role for a GLP-1R-FGF21 axis in regulating body weight in a dietary carbohydrate-dependent manner.

Liver Fibroblast Growth Factor 21 (FGF21) is Required for the Full Anorectic Effect of the Glucagon-Like Peptide-1 Receptor Agonist Liraglutide in Male Mice fed High Carbohydrate Diets.

Glucagon-like peptide-1 receptor (GLP-1R) agonists and fibroblast growth factor 21 (FGF21) confer similar metabolic benefits. Studies report that GLP-1RA induce FGF21. Here, we investigated the mechanisms engaged by the GLP-1R agonist liraglutide to increase FGF21 levels and the metabolic relevance of liraglutide-induced FGF21. We show that liraglutide increases FGF21 levels via neuronal GLP-1R activation. We also demonstrate that lack of liver Fgf21 expression confers partial resistance to liraglutide-induced weight loss. Since FGF21 reduces carbohydrate intake, we tested whether the contribution of FGF21 to liraglutide-induced weight loss is dependent on dietary carbohydrate content. In control and liver Fgf21 knockout (Liv Fgf21 -/- ) mice fed calorically matched diets with low- (LC) or high-carbohydrate (HC) content, we found that only HC-fed Liv Fgf21 -/- mice were resistant to liraglutide-induced weight loss. Similarly, liraglutide-induced weight loss was partially impaired in Liv Fgf21 -/- mice fed a high-fat, high-sugar (HFHS) diet. Lastly, we show that loss of neuronal ß-klotho expression also diminishes liraglutide-induced weight loss in mice fed a HC or HFHS diet, indicating that FGF21 mediates liraglutide-induced weight loss via neuronal FGF21 action. Our findings support a novel role for a GLP-1R-FGF21 axis in regulating body weight in the presence of high dietary carbohydrate content.

Pharmacological FGF21 signals to glutamatergic neurons to enhance leptin action and lower body weight during obesity.

OBJECTIVE: Fibroblast growth factor 21 (FGF21) is a peripherally-derived endocrine hormone that acts on the central nervous system (CNS) to regulate whole body energy homeostasis. Pharmacological administration of FGF21 promotes weight loss in obese animal models and human subjects with obesity. However, the central targets mediating these effects are incompletely defined. METHODS: To explore the mechanism for FGF21's effects to lower body weight, we pharmacologically administer FGF21 to genetic animal models lacking the obligate FGF21 co-receptor, ß-klotho (KLB), in either glutamatergic (Vglut2-Cre) or GABAergic (Vgat-Cre) neurons. In addition, we abolish FGF21 signaling to leptin receptor (LepR-Cre) positive cells. Finally, we examine the synergistic effects of FGF21 and leptin to lower body weight and explore the importance of physiological leptin levels in FGF21-mediated regulation of body weight. RESULTS: Here we show that FGF21 signaling to glutamatergic neurons is required for FGF21 to modulate energy expenditure and promote weight loss. In addition, we demonstrate that FGF21 signals to leptin receptor-expressing cells to regulate body weight, and that central leptin signaling is required for FGF21 to fully stimulate body weight loss during obesity. Interestingly, co-administration of FGF21 and leptin synergistically leads to robust weight loss. CONCLUSIONS: These data reveal an important endocrine crosstalk between liver- and adipose-derived signals which integrate in the CNS to modulate energy homeostasis and body weight regulation.

Central FGF21 production regulates memory but not peripheral metabolism.

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. Using a 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 enhance spatial memory.

Tany-Seq: Integrated Analysis of the Mouse Tanycyte Transcriptome.

The ability to maintain energy homeostasis is necessary for survival. Recently, an emerging role for ependymogial cells, which line the third ventricle in the hypothalamus in the regulation of energy homeostasis, has been appreciated. These cells are called tanycytes and are physically at the interface of brain communication with peripheral organs and have been proposed to mediate the transport of circulating hormones from the third ventricle into the parenchyma of the hypothalamus. Despite the important role tanycytes have been proposed to play in mediating communication from the periphery to the brain, we understand very little about the ontology and function of these cells due to their limited abundance and lack of ability to genetically target this cell population reliably. To overcome these hurdles, we integrated existing hypothalamic single cell RNA sequencing data, focusing on tanycytes, to allow for more in-depth characterization of tanycytic cell types and their putative functions. Overall, we expect this dataset to serve as a resource for the research community.

Conditional gene targeting using UCP1-Cre mice directly targets the central nervous system beyond thermogenic adipose tissues.

OBJECTIVE: Uncoupling protein 1 (UCP1) is a mitochondrial protein critical for adaptive thermogenesis in adipose tissues, and it is typically believed to be restricted to thermogenic adipose tissues. UCP1-Cre transgenic mice are utilized in numerous studies to provide "brown adipose-specific" conditional gene targeting. Here, we examined the distribution of Cre and UCP1 throughout the body in UCP1-Cre reporter mice. METHODS: UCP1-Cre mice crossed to Ai14-tdTomato and Ai9-tdTomato reporter mice were used to explore the tissue distribution of Cre recombinase and Ucp1 mRNA in various tissues. UCP1-Cre mice were independently infected with either a Cre-dependent PHP.eB-tdTomato virus or a Cre-dependent AAV-tdTomato virus to determine whether and where UCP1 is actively expressed in the adult central nervous system. In situ analysis of the deposited single cell RNA sequencing data was used to evaluate Ucp1 expression in the hypothalamus. RESULTS: As expected, Ucp1 expression was detected in both brown and inguinal adipose tissues. Ucp1 expression was also detected in the kidney, adrenal glands, thymus, and hypothalamus. Consistent with detectable Ucp1 expression, tdTomato expression was also observed in brown adipose tissue, inguinal white adipose tissue, kidney, adrenal glands, and hypothalamus of both male and female UCP1-Cre; Ai14-tdTomato and UCP1-Cre; Ai9-tdTomato mice by fluorescent imaging and qPCR. Critically, expression of tdTomato, and thus UCP1, within the central nervous system was observed in regions of the brain critical for the regulation of energy homeostasis, including the ventromedial hypothalamus (VMH). CONCLUSIONS: TdTomato expression in UCP1-Cre; tdTomato mice is not restricted to thermogenic adipose tissues. TdTomato was also expressed in the kidneys, adrenal glands, and throughout the brain, including brain regions and cell types that are critical for multiple aspects of central regulation of energy homeostasis. Collectively, these data have important implications for the utility of UCP1-Cre mice as genetic tools to investigate gene function specifically in brown adipose tissue.

A phase I trial of low-dose inhaled carbon monoxide in sepsis-induced ARDS.

BACKGROUND: Acute respiratory distress syndrome (ARDS) is a prevalent disease with significant mortality for which no effective pharmacologic therapy exists. Low-dose inhaled carbon monoxide (iCO) confers cytoprotection in preclinical models of sepsis and ARDS. METHODS: We conducted a phase I dose escalation trial to assess feasibility and safety of low-dose iCO administration in patients with sepsis-induced ARDS. Twelve participants were randomized to iCO or placebo air 2:1 in two cohorts. Four subjects each were administered iCO (100 ppm in cohort 1 or 200 ppm in cohort 2) or placebo for 90 minutes for up to 5 consecutive days. Primary outcomes included the incidence of carboxyhemoglobin (COHb) level ≥10%, prespecified administration-associated adverse events (AEs), and severe adverse events (SAEs). Secondary endpoints included the accuracy of the Coburn-Forster-Kane (CFK) equation to predict COHb levels, biomarker levels, and clinical outcomes. RESULTS: No participants exceeded a COHb level of 10%, and there were no administration-associated AEs or study-related SAEs. CO-treated participants had a significant increase in COHb (3.48% ± 0.7% [cohort 1]; 4.9% ± 0.28% [cohort 2]) compared with placebo-treated subjects (1.97% ± 0.39%). The CFK equation was highly accurate at predicting COHb levels, particularly in cohort 2 (R2 = 0.9205; P < 0.0001). Circulating mitochondrial DNA levels were reduced in iCO-treated participants compared with placebo-treated subjects. CONCLUSION: Precise administration of low-dose iCO is feasible, well-tolerated, and appears to be safe in patients with sepsis-induced ARDS. Excellent agreement between predicted and observed COHb should ensure that COHb levels remain in the target range during future efficacy trials. TRIAL REGISTRATION: ClinicalTrials.gov NCT02425579. FUNDING: NIH grants P01HL108801, KL2TR002385, K08HL130557, and K08GM102695.