Plasma FGF21 concentrations, adipose fibroblast growth factor receptor-1 and β-klotho expression decrease with fasting in northern elephant seals

Biological and pharmacological functions of the FGF19- and FGF21-coreceptor beta klotho

Beta klotho (KLB) is a fundamental component in fibroblast growth factor receptor (FGFR) signaling as it serves as an obligatory coreceptor for the endocrine hormones fibroblast growth factor 19 (FGF19) and fibroblast growth factor 21 (FGF21). Through the development of FGF19- and FGF21 mimetics, KLB has emerged as a promising drug target for treating various metabolic diseases, such as type 2 diabetes (T2D), non-alcoholic fatty liver disease (NAFLD), and cardiovascular disease. While rodent studies have significantly increased our understanding of KLB function, current clinical trials that test the safety and efficacy of KLB-targeting drugs raise many new scientific questions about human KLB biology. Although most KLB-targeting drugs can modulate disease activity in humans, individual patient responses differ substantially. In addition, species-specific differences in KLB tissue distribution may explain why the glucose-lowering effects that were observed in preclinical studies are not fully replicated in clinical trials. Besides, the long-term efficacy of KLB-targeting drugs might be limited by various pathophysiological conditions known to reduce the expression of KLB. Moreover, FGF19/FGF21 administration in humans is also associated with gastrointestinal side effects, which are currently unexplained. A better understanding of human KLB biology could help to improve the efficacy and safety of existing or novel KLB/FGFR-targeting drugs. In this review, we provide a comprehensive overview of the current understanding of KLB biology, including genetic variants and their phenotypic associations, transcriptional regulation, protein structure, tissue distribution, subcellular localization, and function. In addition, we will highlight recent developments regarding the safety and efficacy of KLB-targeting drugs in clinical trials. These insights may direct the development and testing of existing and future KLB-targeting drugs.

Fasting decreases plasma FGF21 in obese subjects and the expression of FGF21 receptors in adipose tissue in both lean and obese subjects

Fibroblast growth factor 21 (FGF21) is a metabolic regulator of energy and lipid metabolism. FGF21 is highly expressed in liver while FGF21 receptors (beta-klotho (KLB) and FGFR1c) are highly expressed in white adipose tissues (WATs). Plasma FGF21 has been shown to be increased after 7–10 days of fasting but oppositely plasma FGF21 is also increased in obesity. The aim of this study was to measure the effect of 60 h of fasting on plasma FGF21 levels in obese and lean subjects and to determine the gene expression of KLB and FGFR1c in the subcutaneous WAT before, during and after 60 h of fasting. Eight obese (BMI >30 kg/m2) and seven lean subjects (BMI <25 kg/m2) were fasted for 60 h and blood samples were taken at time 0 and after 12, 36 and 60 h of fasting. A biopsy from the subcutaneous WAT was taken at time 0, 12 and 60 h of fasting. FGF21 was measured in plasma by an ELISA and mRNA expression of KLB and FGFR1c was measured in WAT by quantitative PCR (qPCR). The fast significantly decreased plasma FGF21 in obese subjects while no change in plasma FGF21 was observed in lean subjects. Interestingly, KLB was significantly decreased in WAT in response to fasting in both lean and obese subjects indicating a potential important adaptive regulation of KLB in response to fasting.

Highly selective and sensitive measurement of active forms of FGF21 using novel immunocapture enrichment with LC–MS/MS

Aim: Recombinant FGF21 analogs are under wide ranging investigations as a potential therapeutic agent for Type 2 diabetes, as well as other metabolic disorders. The endogenous FGF21 is often used as a surrogate pharmacodynamic(PD) biomarker to assess drug efficacy and safety. Results & methodology: Immunocapture was performed using a monoclonal antibody which had been generated to bind to specific domain of native FGF21 as the capture reagent. After immunocapture, enzymatic digestion was performed and a native FGF21-specific tryptic peptide was monitored using LC–MS/MS by selective reaction monitoring. Conclusion: We have successfully developed and validated a bioanalytical assay which provides the specificity to differentiate the endogenous FGF21 from the recombinant therapeutic agent which has nearly identical sequence to the endogenous molecule.

Identification of new susceptibility loci for type 2 diabetes and shared etiological pathways with coronary heart disease

To evaluate the shared genetic etiology of type 2 diabetes (T2D) and coronary heart disease (CHD), we conducted a genome-wide, multi-ancestry study of genetic variation for both diseases in up to 265,678 subjects for T2D and 260,365 subjects for CHD. We identify 16 previously unreported loci for T2D and 1 locus for CHD, including a new T2D association at a missense variant in HLA-DRB5 (odds ratio (OR) = 1.29). We show that genetically mediated increase in T2D risk also confers higher CHD risk. Joint T2D-CHD analysis identified eight variants-two of which are coding-where T2D and CHD associations appear to colocalize, including a new joint T2D-CHD association at the CCDC92 locus that also replicated for T2D. The variants associated with both outcomes implicate new pathways as well as targets of existing drugs, including icosapent ethyl and adipocyte fatty-acid-binding protein.

The effects of metformin on fibroblast growth factor 19, 21 and fibroblast growth factor receptor 1 in high-fat diet and streptozotocin induced diabetic rats

To understand metformin's effects on fibroblast growth factors (FGFs) and fibroblast growth factor receptor 1 (FGFR1), we investigated circulating fibroblast growth factor-19 (FGF19), FGF21 levels, and FGFR1 in type 2 diabetes mellitus (T2DM). In addition, protein kinase B (Akt) signaling pathway was detected to explain the possible mechanisms. T2DM was induced by feeding rats with high-fat diet for 11 weeks, followed by a low dose of streptozotocin (STZ, 30-35 mg/kg, intraperitoneally). Control rats (Con) were fed on a normal chow; diabetic rats (DM) were fed on high-fat diet supplemented with or without metformin (METF) for 12 weeks (500 mg·kg^-1·d^-1). Biochemical parameters were detected at the end of 24th weeks. FGFR1 expression and protein kinase B (Akt) phosphorylation in the pancreas and visceral adipose tissues were detected using either Western blot (WB) or immunohistochemistry (IHC). Serum FGF19 and FGF21 were measured using enzyme-linked immune sorbent assay (ELISA). Metformin treated DM rats showed improved glucose, lipid and bile acid metabolism. Besides, significantly decreased FGF19 and increased FGF21 were observed in DM+METF rats. DM rats showed significantly increased FGFR1 both in the pancreas and visceral adipose tissues. While in DM+METF rats, FGFR1 was almost remained at a normal level in the pancreas and increased in the visceral adipose tissue compared to that in DM rats. Besides, metformin treatment restores Akt phosphorylation in both tissues. The altered glucose and lipid profiles by metformin treatment may be associated with the increased circulating FGF21 and tissue-specific expressions of FGFR1.

Feeding a Modified Fish Diet to Bottlenose Dolphins Leads to an Increase in Serum Adiponectin and Sphingolipids

Feeding a modified fish diet has been suggested to improve insulin sensitivity in bottlenose dolphins; however, insulin sensitivity was not directly measured. Since demonstrating an improvement in insulin sensitivity is technically difficult in dolphins, we postulated that directional changes in the hormone axis: fibroblast growth factor 21 (FGF21)/Adiponectin/Ceramide (Cer), could provide further support to this hypothesis. We measured 2-h post-prandial serum FGF21, total adiponectin, percent unmodified adiponectin, ceramide, and sphingosine levels from dolphins fed a diet rich in heptadecanoic acid (C17:0) over 24 weeks. Serum FGF21 was quantified by ELISA with an observed range of 129-1599 pg/ml, but did not significantly change over the 24-week study period. Total adiponectin levels (mean ± SD) significantly increased from 776 ± 400 pmol/ml at week 0 to 1196 ± 467 pmol/ml at week 24. The percent unmodified adiponectin levels (mean ± SD) decreased from 23.8 ± 6.0% at week 0 to 15.2 ± 5.2% at week 24. Interestingly, although FGF21 levels did not change, there was a good correlation between FGF21 and total adiponectin (ρ = 0.788, P < 0.001). We quantified the abundances of serum ceramides and sphingosines (SPH) because adiponectin has a defined role in sphingolipid metabolism through adiponectin receptor-mediated activation of ceramidases. The most abundant ceramide in dolphin sera was Cer 24:1 comprising 49% of the ceramides measured. Significant reductions were observed in the unsaturated Cer 18:1, Cer 20:1, and Cer 24:1, whereas significant increases were observed in saturated Cer 22:0, Cer 24:0, and Cer 26:0. However, total serum ceramides did not change. Significant elevations were detected for total sphingosine, dihydrosphingosine, sphingosine-1-phosphate, and dihydrosphingosine-1-phosphate. Proteomic analysis of the serum proteins revealed few changes in serum proteins over the study period. In conclusion, shifting the dolphin diet to fishes rich in odd chain saturated fatty acids, such as C17:0, resulted in increased serum levels of the insulin sensitizing hormone adiponectin and serum SPH consistent with an insulin-sensitizing phenotype. It is still unclear whether FGF21 plays a role in the regulation of adiponectin in dolphins, similar to that shown in laboratory animal models.