Detection of FGF15 in plasma by stable isotope standards and capture by anti-peptide antibodies and targeted mass spectrometry

Hepatic FXR-FGF4 is required for bile acid homeostasis via an FGFR4-LRH-1 signal node under cholestatic stress

Bile acid (BA) homeostasis is vital for various physiological processes, whereas its disruption underlies cholestasis. The farnesoid X receptor (FXR) is a master regulator of BA homeostasis via the ileal fibroblast growth factor (FGF)15/19 endocrine pathway, responding to postprandial or abnormal transintestinal BA flux. However, the de novo paracrine signal mediator of hepatic FXR, which governs the extent of BA synthesis within the liver in non-postprandial or intrahepatic cholestatic conditions, remains unknown. We identified hepatic Fgf4 as a direct FXR target that paracrinally signals to downregulate Cyp7a1 and Cyp8b1. The effect of FXR-FGF4 is mediated by an uncharted intracellular FGF receptor 4 (FGFR4)-LRH-1 signaling node. This liver-centric pathway acts as a first-line checkpoint for intrahepatic and transhepatic BA flux upstream of the peripheral FXR-FGF15/19 pathway, which together constitutes an integral hepatoenteric control mechanism that fine-tunes BA homeostasis, counteracting cholestasis and hepatobiliary damage. Our findings shed light on potential therapeutic strategies for cholestatic diseases.

Mass spectrometry-based targeted proteomics for analysis of protein mutations

Cancers are caused by accumulated DNA mutations. This recognition of the central role of mutations in cancer and recent advances in next-generation sequencing, has initiated the massive screening of clinical samples and the identification of 1000s of cancer-associated gene mutations. However, proteomic analysis of the expressed mutation products lags far behind genomic (transcriptomic) analysis. With comprehensive global proteomics analysis, only a small percentage of single nucleotide variants detected by DNA and RNA sequencing have been observed as single amino acid variants due to current technical limitations. Proteomic analysis of mutations is important with the potential to advance cancer biomarker development and the discovery of new therapeutic targets for more effective disease treatment. Targeted proteomics using selected reaction monitoring (also known as multiple reaction monitoring) and parallel reaction monitoring, has emerged as a powerful tool with significant advantages over global proteomics for analysis of protein mutations in terms of detection sensitivity, quantitation accuracy and overall practicality (e.g., reliable identification and the scale of quantification). Herein we review recent advances in the targeted proteomics technology for enhancing detection sensitivity and multiplexing capability and highlight its broad biomedical applications for analysis of protein mutations in human bodily fluids, tissues, and cell lines. Furthermore, we review recent applications of top-down proteomics for analysis of protein mutations. Unlike the commonly used bottom-up proteomics which requires digestion of proteins into peptides, top-down proteomics directly analyzes intact proteins for more precise characterization of mutation isoforms. Finally, general perspectives on the potential of achieving both high sensitivity and high sample throughput for large-scale targeted detection and quantification of important protein mutations are discussed.

A genetic model for in vivo proximity labelling of the mammalian secretome

Organ functions are highly specialized and interdependent. Secreted factors regulate organ development and mediate homeostasis through serum trafficking and inter-organ communication. Enzyme-catalysed proximity labelling enables the identification of proteins within a specific cellular compartment. Here, we report a BirA*G3 mouse strain that enables CRE-dependent promiscuous biotinylation of proteins trafficking through the endoplasmic reticulum. When broadly activated throughout the mouse, widespread labelling of proteins was observed within the secretory pathway. Streptavidin affinity purification and peptide mapping by quantitative mass spectrometry (MS) proteomics revealed organ-specific secretory profiles and serum trafficking. As expected, secretory proteomes were highly enriched for signal peptide-containing proteins, highlighting both conventional and non-conventional secretory processes, and ectodomain shedding. Lower-abundance proteins with hormone-like properties were recovered and validated using orthogonal approaches. Hepatocyte-specific activation of BirA*G3 highlighted liver-specific biotinylated secretome profiles. The BirA*G3 mouse model demonstrates enhanced labelling efficiency and tissue specificity over viral transduction approaches and will facilitate a deeper understanding of secretory protein interplay in development, and in healthy and diseased adult states.

Feeding activates FGF15-SHP-TFEB-mediated lipophagy in the gut

Lysosome‐mediated macroautophagy, including lipophagy, is activated under nutrient deprivation but is repressed after feeding. We show that, unexpectedly, feeding activates intestinal autophagy/lipophagy in a manner dependent on both the orphan nuclear receptor, small heterodimer partner (SHP/NR0B2), and the gut hormone, fibroblast growth factor‐15/19 (FGF15/19). Furthermore, postprandial intestinal triglycerides (TGs) and apolipoprotein‐B48 (ApoB48), the TG‐rich chylomicron marker, were elevated in SHP‐knockout and FGF15‐knockout mice. Genomic analyses of the mouse intestine indicated that SHP partners with the key lysosomal activator, transcription factor‐EB (TFEB) to upregulate the transcription of autophagy/lipolysis network genes after feeding. FGF19 treatment activated lipophagy, reducing TG and ApoB48 levels in HT29 intestinal cells, which was dependent on TFEB. Mechanistically, feeding‐induced FGF15/19 signaling increased the nuclear localization of TFEB and SHP via PKC beta/zeta‐mediated phosphorylation, leading to increased transcription of the TFEB/SHP target lipophagy genes, Ulk1 and Atgl. Collectively, these results demonstrate that paradoxically after feeding, FGF15/19‐activated SHP and TFEB activate gut lipophagy, limiting postprandial TGs. As excess postprandial lipids cause dyslipidemia and obesity, the FGF15/19‐SHP‐TFEB axis that reduces intestinal TGs via lipophagic activation provides promising therapeutic targets for obesity‐associated metabolic disease.

Molecular Basis of Bile Acid-FXR-FGF15/19 Signaling Axis

Bile acids (BAs) are a group of amphiphilic molecules consisting of a rigid steroid core attached to a hydroxyl group with a varying number, position, and orientation, and a hydrophilic side chain. While BAs act as detergents to solubilize lipophilic nutrients in the small intestine during digestion and absorption, they also act as hormones. Farnesoid X receptor (FXR) is a nuclear receptor that forms a heterodimer with retinoid X receptor α (RXRα), is activated by BAs in the enterohepatic circulation reabsorbed via transporters in the ileum and the colon, and plays a critical role in regulating gene expression involved in cholesterol, BA, and lipid metabolism in the liver. The FXR/RXRα heterodimer also exists in the distal ileum and regulates production of fibroblast growth factor (FGF) 15/FGF19, a hormone traveling via the enterohepatic circulation that activates hepatic FGF receptor 4 (FGFR4)-β-klotho receptor complex and regulates gene expression involved in cholesterol, BA, and lipid metabolism, as well as those regulating cell proliferation. Agonists for FXR and analogs for FGF15/19 are currently recognized as a promising therapeutic target for metabolic syndrome and cholestatic diseases.

Fibroblast growth factor 15/19 expression, regulation, and function: An overview

Since the discovery of fibroblast growth factor (FGF)-19 over 20 years ago, our understanding of the peptide and its role in human biology has moved forward significantly. A member of a superfamily of paracrine growth factors regulating embryonic development, FGF19 is unique in that it is a dietary-responsive endocrine hormone linked with bile acid homeostasis, glucose and lipid metabolism, energy expenditure, and protein synthesis during the fed to fasted state. FGF19 achieves this through targeting multiple tissues and signaling pathways within those tissues. The diverse functional capabilities of FGF19 is due to the unique structural characteristics of the protein and its receptor binding in various cell types. This review will cover the current literature on the protein FGF19, its target receptors, and the biological pathways they target through unique signaling cascades.

Discovery of farnesoid X receptor and its role in bile acid metabolism

In 1995, the nuclear hormone orphan receptor farnesoid X receptor (FXR, NR1H4) was identified as a farnesol receptor expressed mainly in liver, kidney, and adrenal gland of rats. In 1999, bile acids were identified as endogenous FXR ligands. Subsequently, FXR target genes involved in the regulation of hepatic bile acid synthesis, secretion, and intestinal re-absorption were identified. FXR signaling was proposed as a mechanism of feedback regulation of the rate-limiting enzyme for bile acid synthesis, cholesterol 7⍺-hydroxylase (CYP7A1). The primary bile acids synthesized in the liver are transformed to secondary bile acids by the gut microbiota. The gut-to-liver axis plays a critical role in the regulation of bile acid synthesis, composition and circulating bile acid pool size, which in turn regulates glucose, lipid, and energy metabolism. Dysregulation of bile acid metabolism and FXR signaling in the gut-to-liver axis contributes to metabolic diseases including obesity, diabetes, and non-alcoholic fatty liver disease. This review will cover the discovery of FXR as a bile acid sensor in the regulation of bile acid metabolism and as a metabolic regulator of lipid, glucose, and energy homeostasis. It will also provide an update of FXR functions in the gut-to-liver axis and the drug therapies targeting bile acids and FXR for the treatment of liver metabolic diseases.

A SISCAPA-based approach for detection of SARS-CoV-2 viral antigens from clinical samples

SARS-CoV-2, a novel human coronavirus, has created a global disease burden infecting > 100 million humans in just over a year. RT-PCR is currently the predominant method of diagnosing this viral infection although a variety of tests to detect viral antigens have also been developed. In this study, we adopted a SISCAPA-based enrichment approach using anti-peptide antibodies generated against peptides from the nucleocapsid protein of SARS-CoV-2. We developed a targeted workflow in which nasopharyngeal swab samples were digested followed by enrichment of viral peptides using the anti-peptide antibodies and targeted parallel reaction monitoring (PRM) analysis using a high-resolution mass spectrometer. This workflow was applied to 41 RT-PCR-confirmed clinical SARS-CoV-2 positive nasopharyngeal swab samples and 30 negative samples. The workflow employed was highly specific as none of the target peptides were detected in negative samples. Further, the detected peptides showed a positive correlation with the viral loads as measured by RT-PCR Ct values. The SISCAPA-based platform described in the current study can serve as an alternative method for SARS-CoV-2 viral detection and can also be applied for detecting other microbial pathogens directly from clinical samples.

Modulating effects of capsaicin on glucose homeostasis and the underlying mechanism

Abnormal glucose homeostasis is linked to a variety of metabolic syndromes, such as insulin resistance, obesity, type-2 diabetes mellitus, hypertension and cardiovascular diseases. Maintenance of normal glucose homeostasis is important for the body to keep normal biological functions. As the major bioactive ingredient in chili peppers responsible for the pungent flavor, capsaicin has been reported to effectively improve glucose homeostasis with low cytotoxicity. In this review, the modulating effects of capsaicin on glucose homeostasis in cell models, animal models and human trials are summarized through both TRPV1 dependent and TRPV1 independent pathways. The relevant molecular mechanisms underlying its regulatory effects are also evaluated. Understanding the effects and mechanisms of capsaicin on glucose metabolism could provide theoretical evidence for its application in the food and pharmaceutical industries.

Fibroblast Growth Factor 21 Response in a Preclinical Alcohol Model of Acute-on-Chronic Liver Injury

BACKGROUND AND AIMS

Fibroblast growth factor (FGF) 21 has recently been shown to play a potential role in bile acid metabolism. We aimed to investigate the FGF21 response in an ethanol-induced acute-on-chronic liver injury (ACLI) model in Abcb4-/- mice with deficiency of the hepatobiliary phospholipid transporter.

METHODS

Total RNA was extracted from wild-type (WT, C57BL/6J) and Abcb4-/- (KO) mice, which were either fed a control diet (WT-Cont and KO-Cont groups; n = 28/group) or ethanol diet, followed by an acute ethanol binge (WT-EtOH and KO-EtOH groups; n = 28/group). A total of 58 human subjects were recruited into the study, including patients with alcohol-associated liver disease (AALD; n = 31) and healthy controls (n = 27). The hepatic and ileal expressions of genes involved in bile acid metabolism, plasma FGF levels, and bile acid and its precursors 7α- and 27-hydroxycholesterol (7α- and 27-OHC) concentrations were determined. Primary mouse hepatocytes were isolated for cell culture experiments.

RESULTS

Alcohol feeding significantly induced plasma FGF21 and decreased hepatic Cyp7a1 levels. Hepatic expression levels of Fibroblast growth factor receptor 1 (Fgfr1), Fgfr4, Farnesoid X-activated receptor (Fxr), and Small heterodimer partner (Shp) and plasma FGF15/FGF19 levels did not differ with alcohol challenge. Exogenous FGF21 treatment suppressed Cyp7a1 in a dose-dependent manner in vitro. AALD patients showed markedly higher FGF21 and lower 7α-OHC plasma levels while FGF19 did not differ.

CONCLUSIONS

The simultaneous upregulation of FGF21 and downregulation of Cyp7a1 expressions upon chronic plus binge alcohol feeding together with the invariant plasma FGF15 and hepatic Shp and Fxr levels suggest the presence of a direct regulatory mechanism of FGF21 on bile acid homeostasis through inhibition of CYP7A1 by an FGF15-independent pathway in this ACLI model. Lay Summary: Alcohol challenge results in the upregulation of FGF21 and repression of Cyp7a1 expressions while circulating FGF15 and hepatic Shp and Fxr levels remain constant both in healthy and pre-injured livers, suggesting the presence of an alternative FGF15-independent regulatory mechanism of FGF21 on bile acid homeostasis through the inhibition of Cyp7a1.

Intestinal FGF15/19 physiologically repress hepatic lipogenesis in the late fed-state by activating SHP and DNMT3A

Hepatic lipogenesis is normally tightly regulated but is aberrantly elevated in obesity. Fibroblast Growth Factor-15/19 (mouse FGF15, human FGF19) are bile acid-induced late fed-state gut hormones that decrease hepatic lipid levels by unclear mechanisms. We show that FGF15/19 and FGF15/19-activated Small Heterodimer Partner (SHP/NR0B2) have a role in transcriptional repression of lipogenesis. Comparative genomic analyses reveal that most of the SHP cistrome, including lipogenic genes repressed by FGF19, have overlapping CpG islands. FGF19 treatment or SHP overexpression in mice inhibits lipogenesis in a DNA methyltransferase-3a (DNMT3A)-dependent manner. FGF19-mediated activation of SHP via phosphorylation recruits DNMT3A to lipogenic genes, leading to epigenetic repression via DNA methylation. In non-alcoholic fatty liver disease (NAFLD) patients and obese mice, occupancy of SHP and DNMT3A and DNA methylation at lipogenic genes are low, with elevated gene expression. In conclusion, FGF15/19 represses hepatic lipogenesis by activating SHP and DNMT3A physiologically, which is likely dysregulated in NAFLD.

Hepatic lipogenesis is a tightly regulated process, which is elevated in obesity. Here the authors report that FGF15/19, bile acid-induced gut hormones, repress lipogenic genes in the late fed-state by activating small heterodimer partner (SHP) and promoting SHP-dependent recruitment of DNA methyltransferase DNMT3A to lipogenic genes.

FGF15/19 is required for adipose tissue plasticity in response to thermogenic adaptations

Objective

To determine the role of enterokine FGF15/19 in adipose tissue thermogenic adaptations.

Methods

Circulating FGF19 and gene expression (qRT-PCR) levels were assessed in subcutaneous adipose tissue from obese human patients. Effects of experimentally increased FGF15 and FGF19 levels in vivo were determined in mice using adenoviral and adeno-associated vectors. Adipose tissues were characterized in FGF15-null mice under distinct cold-related thermogenic challenges. The analyses spanned metabolic profiling, tissue characterization, histology, gene expression, and immunoblot assays.

Results

In humans, FGF19 levels are directly associated with UCP1 gene expression in subcutaneous adipose tissue. Experimental increases in FGF15 or FGF19 induced white fat browning in mice as demonstrated by the appearance of multilocular beige cells and markers indicative of a beige phenotype, including increased UCP1 protein levels. Mice lacking FGF15 showed markedly impaired white adipose tissue browning and a mild reduction in parameters indicative of BAT activity in response to cold-induced environmental thermogenic challenges. This was concomitant with signs of altered systemic metabolism, such as reduced glucose tolerance and impaired cold-induced insulin sensitization.

Conclusions

Enterokine FGF15/19 is a key factor required for adipose tissue plasticity in response to thermogenic adaptations.

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Circulating FGF19 levels correlate positively with signs of fat browning in humans.

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Adaptive adipose tissue browning in response to cold is impaired in mice lacking FGF15.

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Experimentally induced increase in FGF15 or FGF19 promotes fat browning in mice.

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FGF15/19 signaling is required for thermogenic challenge-induced plasticity of adipose tissue.

Bile acid receptors FXR and TGR5 signaling in fatty liver diseases and therapy

Bile acid synthesis is the most significant pathway for catabolism of cholesterol and for maintenance of whole body cholesterol homeostasis. Bile acids are physiological detergents that absorb, distribute, metabolize, and excrete nutrients, drugs, and xenobiotics. Bile acids also are signal molecules and metabolic integrators that activate nuclear farnesoid X receptor (FXR) and membrane Takeda G protein-coupled receptor 5 (TGR5; i.e., G protein-coupled bile acid receptor 1) to regulate glucose, lipid, and energy metabolism. The gut-to-liver axis plays a critical role in the transformation of primary bile acids to secondary bile acids, in the regulation of bile acid synthesis to maintain composition within the bile acid pool, and in the regulation of metabolic homeostasis to prevent hyperglycemia, dyslipidemia, obesity, and diabetes. High-fat and high-calorie diets, dysbiosis, alcohol, drugs, and disruption of sleep and circadian rhythms cause metabolic diseases, including alcoholic and nonalcoholic fatty liver diseases, obesity, diabetes, and cardiovascular disease. Bile acid-based drugs that target bile acid receptors are being developed for the treatment of metabolic diseases of the liver.

Nidufexor (LMB763), a Novel FXR Modulator for the Treatment of Nonalcoholic Steatohepatitis

Farnesoid X receptor (FXR) agonists are emerging as important potential therapeutics for the treatment of nonalcoholic steatohepatitis (NASH) patients, as they exert positive effects on multiple aspects of the disease. FXR agonists reduce lipid accumulation in the liver, hepatocellular inflammation, hepatic injury, and fibrosis. While there are currently no approved therapies for NASH, the bile acid-derived FXR agonist obeticholic acid (OCA; 6-ethyl chenodeoxycholic acid) has shown promise in clinical studies. Previously, we described the discovery of tropifexor (LJN452), the most potent non-bile acid FXR agonist currently in clinical investigation. Here, we report the discovery of a novel chemical series of non-bile acid FXR agonists based on a tricyclic dihydrochromenopyrazole core from which emerged nidufexor (LMB763), a compound with partial FXR agonistic activity in vitro and FXR-dependent gene modulation in vivo. Nidufexor has advanced to Phase 2 human clinical trials in patients with NASH and diabetic nephropathy.

Systematic assessment of antibody selectivity in plasma based on a resource of enrichment profiles

There is a strong need for procedures that enable context and application dependent validation of antibodies. Here, we applied a magnetic bead assisted workflow and immunoprecipitation mass spectrometry (IP-MS/MS) to assess antibody selectivity for the detection of proteins in human plasma. A resource was built on 414 IP experiments using 157 antibodies (targeting 120 unique proteins) in assays with heat-treated or untreated EDTA plasma. For each protein we determined their antibody related degrees of enrichment using z-scores and their frequencies of identification across all IP assays. Out of 1,313 unique endogenous proteins, 426 proteins (33%) were detected in >20% of IPs, and these background components were mainly comprised of proteins from the complement system. For 45% (70/157) of the tested antibodies, the expected target proteins were enriched (z-score ≥ 3). Among these 70 antibodies, 59 (84%) co-enriched other proteins beside the intended target and mainly due to sequence homology or protein abundance. We also detected protein interactions in plasma, and for IGFBP2 confirmed these using several antibodies and sandwich immunoassays. The protein enrichment data with plasma provide a very useful and yet lacking resource for the assessment of antibody selectivity. Our insights will contribute to a more informed use of affinity reagents for plasma proteomics assays.

Metabolic Messengers: fibroblast growth factor 15/19

Fibroblast growth factor (FGF) 15 in mice and its human orthologue FGF19 (together denoted FGF15/19) are gut hormones that control homeostasis of bile acids and glucose during the transition from the fed to the fasted state. Apart from its central role in the regulation of bile acid homeostasis, FGF15/19 is now recognized as a transversal metabolic coordinator at the crossroads of the gut, liver, brain and white adipose tissue. Dysregulation of FGF15/19 signalling may contribute to the pathogenesis of several diseases affecting the gut-liver axis and to metabolic diseases. Here, we provide an overview of current knowledge of the physiological roles of the enterokine FGF15/19 and highlight commonalities and differences between the two orthologues. We also discuss the putative therapeutic potential in areas of unmet medical need-such has cholestatic liver diseases and non-alcoholic steatohepatitis, for which FGF19 is being tested in ongoing clinical trials-as well as the possibility of using FGF19 for the treatment of obesity and type II diabetes.

Phosphorylation of hepatic farnesoid X receptor by FGF19 signaling-activated Src maintains cholesterol levels and protects from atherosclerosis

The bile acid (BA) nuclear receptor, farnesoid X receptor (FXR/NR1H4), maintains metabolic homeostasis by transcriptional control of numerous genes, including an intestinal hormone, fibroblast growth factor-19 (FGF19; FGF15 in mice). Besides activation by BAs, the gene-regulatory function of FXR is also modulated by hormone or nutrient signaling-induced post-translational modifications. Recently, phosphorylation at Tyr-67 by the FGF15/19 signaling-activated nonreceptor tyrosine kinase Src was shown to be important for FXR function in BA homeostasis. Here, we examined the role of this FXR phosphorylation in cholesterol regulation. In both hepatic FXR-knockout and FXR-knockdown mice, reconstitution of FXR expression up-regulated cholesterol transport genes for its biliary excretion, including scavenger receptor class B member 1 (Scarb1) and ABC subfamily G member 8 (Abcg5/8), decreased hepatic and plasma cholesterol levels, and increased biliary and fecal cholesterol levels. Of note, these sterol-lowering effects were blunted by substitution of Phe for Tyr-67 in FXR. Moreover, consistent with Src's role in phosphorylating FXR, Src knockdown impaired cholesterol regulation in mice. In hypercholesterolemic apolipoprotein E-deficient mice, expression of FXR, but not Y67F-FXR, ameliorated atherosclerosis, whereas Src down-regulation exacerbated it. Feeding or treatment with an FXR agonist induced Abcg5/8 and Scarb1 expression in WT, but not FGF15-knockout, mice. Furthermore, FGF19 treatment increased occupancy of FXR at Abcg5/8 and Scarb1, expression of these genes, and cholesterol efflux from hepatocytes. These FGF19-mediated effects were blunted by the Y67F-FXR substitution or Src down-regulation or inhibition. We conclude that phosphorylation of hepatic FXR by FGF15/19-induced Src maintains cholesterol homeostasis and protects against atherosclerosis.

Transgenerational impact of maternal obesogenic diet on offspring bile acid homeostasis and nonalcoholic fatty liver disease

Studies show maternal obesity is a risk factor for metabolic syndrome and nonalcoholic fatty liver disease (NAFLD) in offspring. Here we evaluated potential mechanisms underlying these phenotypes. Female C57Bl6 mice were fed chow or an obesogenic high-fat/high-sucrose (HF/HS) diet with subsequent mating of F1 and F2 female offspring to lean males to develop F2 and F3 generations, respectively. Offspring were fed chow or fibrogenic (high transfat, cholesterol, fructose) diets, and histopathological, metabolic changes, and bile acid (BA) homeostasis was evaluated. Chow-fed F1 offspring from maternal HF/HS lineages (HF/HS) developed periportal fibrosis and inflammation with aging, without differences in hepatic steatosis but increased BA pool size and shifts in BA composition. F1, but not F2 or F3, offspring from HF/HS showed increased steatosis on a fibrogenic diet, yet inflammation and fibrosis were paradoxically decreased in F1 offspring, a trend continued in F2 and F3 offspring. HF/HS feeding leads to increased periportal fibrosis and inflammation in chow-fed offspring without increased hepatic steatosis. By contrast, fibrogenic diet-fed F1 offspring from HF/HS dams exhibited worse hepatic steatosis but decreased inflammation and fibrosis. These findings highlight complex adaptations in NAFLD phenotypes with maternal diet.

Small Heterodimer Partner and Fibroblast Growth Factor 19 Inhibit Expression of NPC1L1 in Mouse Intestine and Cholesterol Absorption

BACKGROUND & AIMS

The nuclear receptor subfamily 0 group B member 2 (NR0B2, also called SHP) is expressed at high levels in the liver and intestine. Postprandial fibroblast growth factor 19 (human FGF19, mouse FGF15) signaling increases the transcriptional activity of SHP. We studied the functions of SHP and FGF19 in the intestines of mice, including their regulation of expression of the cholesterol transporter NPC1L1 )NPC1-like intracellular cholesterol transporter 1) and cholesterol absorption.

METHODS

We performed histologic and biochemical analyses of intestinal tissues from C57BL/6 and SHP-knockout mice and performed RNA-sequencing analyses to identify genes regulated by SHP. The effects of fasting and refeeding on intestinal expression of NPC1L1 were examined in C57BL/6, SHP-knockout, and FGF15-knockout mice. Mice were given FGF19 daily for 1 week; fractional cholesterol absorption, cholesterol and bile acid (BA) levels, and composition of BAs were measured. Intestinal organoids were generated from C57BL/6 and SHP-knockout mice, and cholesterol uptake was measured. Luciferase reporter assays were performed with HT29 cells.

RESULTS

We found that the genes that regulate lipid and ion transport in intestine, including NPC1L1, were up-regulated and that cholesterol absorption was increased in SHP-knockout mice compared with C57BL/6 mice. Expression of NPC1L1 was reduced in C57BL/6 mice after refeeding after fasting but not in SHP-knockout or FGF15-knockout mice. SHP-knockout mice had altered BA composition compared with C57BL/6 mice. FGF19 injection reduced expression of NPC1L1, decreased cholesterol absorption, and increased levels of hydrophilic BAs, including tauro-α- and -β-muricholic acids; these changes were not observed in SHP-knockout mice. SREBF2 (sterol regulatory element binding transcription factor 2), which regulates cholesterol, activated transcription of NPC1L1. FGF19 signaling led to phosphorylation of SHP, which inhibited SREBF2 activity.

CONCLUSIONS

Postprandial FGF19 and SHP inhibit SREBF2, which leads to repression of intestinal NPC1L1 expression and cholesterol absorption. Strategies to increase FGF19 signaling to activate SHP might be developed for treatment of hypercholesterolemia.

Potential of Intestine-Selective FXR Modulation for Treatment of Metabolic Disease

Farnesoid X receptor controls bile acid metabolism, both in the liver and intestine. This potent nuclear receptor not only maintains homeostasis of its own ligands, i.e., bile acids, but also regulates glucose and lipid metabolism as well as the immune system. These findings have led to substantial interest for FXR as a therapeutic target and to the recent approval of an FXR agonist for treating primary biliary cholangitis as well as ongoing clinical trials for other liver diseases. Given that FXR biology is complex, including moderate expression in tissues outside of the enterohepatic circulation, temporal expression of isoforms, posttranscriptional modifications, and the existence of several other bile acid-responsive receptors such as TGR5, clinical application of FXR modulators warrants thorough understanding of its actions. Recent findings have demonstrated remarkable physiological effects of targeting FXR specifically in the intestine (iFXR), thereby avoiding systemic release of modulators. These include local effects such as improvement of intestinal barrier function and intestinal cholesterol turnover, as well as systemic effects such as improvements in glucose homeostasis, insulin sensitivity, and nonalcoholic fatty liver disease (NAFLD). Intriguingly, metabolic improvements have been observed with both an iFXR agonist that leads to production of enteric Fgf15 and increased energy expenditure in adipose tissues and antagonists by reducing systemic ceramide levels and hepatic glucose production. Here we review the recent findings on the role of intestinal FXR and its targeting in metabolic disease.

Fibroblast Growth Factor 15/19: From Basic Functions to Therapeutic Perspectives

Discovered 20 years ago, fibroblast growth factor (FGF)19, and its mouse ortholog FGF15, were the first members of a new subfamily of FGFs able to act as hormones. During fetal life, FGF15/19 is involved in organogenesis, affecting the development of the ear, eye, heart, and brain. At adulthood, FGF15/19 is mainly produced by the ileum, acting on the liver to repress hepatic bile acid synthesis and promote postprandial nutrient partitioning. In rodents, pharmacologic doses of FGF19 induce the same antiobesity and antidiabetic actions as FGF21, with these metabolic effects being partly mediated by the brain. However, activation of hepatocyte proliferation by FGF19 has long been a challenge to its therapeutic use. Recently, genetic reengineering of the molecule has resolved this issue. Despite a global overlap in expression pattern and function, murine FGF15 and human FGF19 exhibit several differences in terms of regulation, molecular structure, signaling, and biological properties. As most of the knowledge originates from the use of FGF19 in murine models, differences between mice and humans in the biology of FGF15/19 have to be considered for a successful translation from bench to bedside. This review summarizes the basic knowledge concerning FGF15/19 in mice and humans, with a special focus on regulation of production, morphogenic properties, hepatocyte growth, bile acid homeostasis, as well as actions on glucose, lipid, and energy homeostasis. Moreover, implications and therapeutic perspectives concerning FGF19 in human diseases (including obesity, type 2 diabetes, hepatic steatosis, biliary disorders, and cancer) are also discussed.

Postprandial FGF19-induced phosphorylation by Src is critical for FXR function in bile acid homeostasis

Farnesoid-X-Receptor (FXR) plays a central role in maintaining bile acid (BA) homeostasis by transcriptional control of numerous enterohepatic genes, including intestinal FGF19, a hormone that strongly represses hepatic BA synthesis. How activation of the FGF19 receptor at the membrane is transmitted to the nucleus for transcriptional regulation of BA levels and whether FGF19 signaling posttranslationally modulates FXR function remain largely unknown. Here we show that FXR is phosphorylated at Y67 by non-receptor tyrosine kinase, Src, in response to postprandial FGF19, which is critical for its nuclear localization and transcriptional regulation of BA levels. Liver-specific expression of phospho-defective Y67F-FXR or Src downregulation in mice results in impaired homeostatic responses to acute BA feeding, and exacerbates cholestatic pathologies upon drug-induced hepatobiliary insults. Also, the hepatic FGF19-Src-FXR pathway is defective in primary biliary cirrhosis (PBC) patients. This study identifies Src-mediated FXR phosphorylation as a potential therapeutic target and biomarker for BA-related enterohepatic diseases.

FXR plays an important role in bile acid homeostasis by transcriptionally modulating several enterohepatic genes, including intestinal FGF19, that repress hepatic bile acid synthesis. Here the authors show that postprandial FGF19 regulates FXR transcriptional activity via its action on the tyrosine kinase Src, which phosphorylates FXR.

Development of an automated, interference-free, 2D-LC–MS/MS assay for quantification of a therapeutic mAb in human sera

Aim: Hybrid LC–MS/MS assays are increasingly used to quantitate proteins in biological matrices. These assays involve analyte enrichment at the protein level. Although suitability has been demonstrated, they are limited by the lack of appropriate affinity reagents and may suffer from interferences caused by binding proteins or antibodies. Results: An online stable isotope standards and capture by anti-peptide antibodies assay was developed, which involves tryptic digestion of a therapeutic monoclonal antibody in human serum to destroy interfering proteins followed by enrichment using high affinity peptide antibodies. The assay was validated and compared with a standard ligand-binding assay currently used for quantification. Conclusion: The data show that the stable isotope standards and capture by anti-peptide antibodies-2D-LC–MS/MS assay can be used as an alternative method for measurement of monoclonal antibodies in clinical samples.

The portal-drained viscera release fibroblast growth factor 19 in humans

Fibroblast growth factor 19 (FGF19) is an ileum‐derived endrocrine factor that is produced in response to transepithelial bile salt flux. FGF19 represses bile salt synthesis in the liver. Despite the general assumption that FGF19 signals to the liver via portal blood, no human data are available to support this notion. The aim was to study portal FGF19 levels, and determined bile salt and FGF19 fluxes across visceral organs in humans. Bile salt and FGF19 levels were assessed in arterial, portal, and hepatic venous blood collected from fasted patients who underwent partial liver resection for colorectal liver metastases (n = 30). Fluxes across the portal‐drained viscera (PDV), liver, and splanchnic area were calculated. Portal bile salt levels (7.8 [5.0–12.4] μmol/L) were higher than levels in arterial (2.7 [1.7–5.5] μmol/L, P < 0.0001) and hepatic venous blood (3.4 [2.5–6.5] μmol/L, P < 0.0001). Bile salts released by the PDV (+1.2 [+0.7–+2.0] mmol kg⁻¹ h⁻¹, P < 0.0001) were largely taken up by the liver (−1.0 [−1.8 to −0.4] mmol kg⁻¹ h⁻¹, P < 0.0001). Portal levels of FGF19 (161 ± 78 pg/mL) were higher than arterial levels (135 ± 65 pg/mL, P = 0.046). A net release of FGF19 by the PDV (+4.0 [+2.1 to +9.9] ng kg⁻¹ h⁻¹, P < 0.0001) was calculated. There was no significant flux of FGF19 across the liver (−0.2 [−3.7 to +7.4] ng kg⁻¹ h⁻¹, P = 0.93). In conclusion, FGF19 levels in human portal blood are higher than in arterial blood. FGF19 is released by the portal‐drained viscera under fasted steady state conditions.

FGF19, FGF21, and an FGFR1/β-Klotho-Activating Antibody Act on the Nervous System to Regulate Body Weight and Glycemia

Despite the different physiologic functions of FGF19 and FGF21 as hormonal regulators of fed and fasted metabolism, their pharmacologic administration causes similar increases in energy expenditure, weight loss, and enhanced insulin sensitivity in obese animals. Here, in genetic loss-of-function studies of the shared co-receptor β-Klotho, we show that these pharmacologic effects are mediated through a common, tissue-specific pathway. Surprisingly, FGF19 and FGF21 actions in liver and adipose tissue are not required for their longer-term weight loss and glycemic effects. In contrast, β-Klotho in neurons is essential for both FGF19 and FGF21 to cause weight loss and lower glucose and insulin levels. We further show an FGF21 mimetic antibody that activates the FGF receptor 1/β-Klotho complex also requires neuronal β-Klotho for its metabolic effects. These studies highlight the importance of the nervous system in mediating the beneficial weight loss and glycemic effects of endocrine FGF drugs.

Bile Acid Signaling Pathways from the Enterohepatic Circulation to the Central Nervous System

Bile acids are best known as detergents involved in the digestion of lipids. In addition, new data in the last decade have shown that bile acids also function as gut hormones capable of influencing metabolic processes via receptors such as FXR (farnesoid X receptor) and TGR5 (Takeda G protein-coupled receptor 5). These effects of bile acids are not restricted to the gastrointestinal tract, but can affect different tissues throughout the organism. It is still unclear whether these effects also involve signaling of bile acids to the central nervous system (CNS). Bile acid signaling to the CNS encompasses both direct and indirect pathways. Bile acids can act directly in the brain via central FXR and TGR5 signaling. In addition, there are two indirect pathways that involve intermediate agents released upon interaction with bile acids receptors in the gut. Activation of intestinal FXR and TGR5 receptors can result in the release of fibroblast growth factor 19 (FGF19) and glucagon-like peptide 1 (GLP-1), both capable of signaling to the CNS. We conclude that when plasma bile acids levels are high all three pathways may contribute in signal transmission to the CNS. However, under normal physiological circumstances, the indirect pathway involving GLP-1 may evoke the most substantial effect in the brain.

Beneficial effects of bile acid receptor agonists in pulmonary disease models

INTRODUCTION

Bile acids act as steroid hormones, controlling lipid, glucose and energy metabolism, as well as inflammation and fibrosis. Their actions are implemented through activation of nuclear (FXR, VDR, PXR) and membrane G protein-coupled (TGR5, S1PR2) receptors. Areas covered: This review discusses the potential of FXR and TGR5 as therapeutic targets in the treatment of pulmonary disorders linked to metabolism and/or inflammation. Obeticholic acid (OCA) is the most clinically advanced bile acid-derived agonist for FXR-mediated anti-inflammatory and anti-fibrotic effects. It therefore represents an attractive pharmacological approach for the treatment of lung conditions characterized by vascular and endothelial dysfunctions. Expert opinion: Inflammation, vascular remodeling and fibrotic processes characterize the progression of pulmonary arterial hypertension (PAH) and idiopathic pulmonary fibrosis (IPF). These processes are only partially targeted by the available therapeutic options and still represent a relevant medical need. The results hereby summarized demonstrate OCA efficacy in preventing experimental lung disorders, i.e. monocrotaline-induced PAH and bleomycin-induced fibrosis, by abating proinflammatory and vascular remodeling progression. TGR5 is also expressed in the lung, and targeting the TGR5 pathway, using the TGR5 agonist INT-777 or the dual FXR/TGR5 agonist INT-767, could also contribute to the treatment of pulmonary disorders mediated by inflammation and fibrosis.

Bile acids, FGF15/19 and liver regeneration: From mechanisms to clinical applications

The liver has an extraordinary regenerative capacity rapidly triggered upon injury or resection. This response is intrinsically adjusted in its initiation and termination, a property termed the "hepatostat". Several molecules have been involved in liver regeneration, and among them bile acids may play a central role. Intrahepatic levels of bile acids rapidly increase after resection. Through the activation of farnesoid X receptor (FXR), bile acids regulate their hepatic metabolism and also promote hepatocellular proliferation. FXR is also expressed in enterocytes, where bile acids stimulate the expression of fibroblast growth factor 15/19 (FGF15/19), which is released to the portal blood. Through the activation of FGFR4 on hepatocytes FGF15/19 regulates bile acids synthesis and finely tunes liver regeneration as part of the "hepatostat". Here we review the experimental evidences supporting the relevance of the FXR-FGF15/19-FGFR4 axis in liver regeneration and discuss potential therapeutic applications of FGF15/19 in the prevention of liver failure. This article is part of a Special Issue entitled: Cholangiocytes in Health and Disease edited by Jesus Banales, Marco Marzioni, Nicholas LaRusso and Peter Jansen.

Bile acid receptors link nutrient sensing to metabolic regulation

Non-alcoholic fatty liver disease (NAFLD) is a common liver disease in Western populations. Non-alcoholic steatohepatitis (NASH) is a more debilitating form of NAFLD characterized by hepatocellular injury and inflammation, which significantly increase the risk of end-stage liver and cardiovascular diseases. Unfortunately, there are no available drug therapies for NASH. Bile acids are physiological detergent molecules that are synthesized from cholesterol exclusively in the hepatocytes. Bile acids circulate between the liver and intestine, where they are required for cholesterol solubilization in the bile and dietary fat emulsification in the gut. Bile acids also act as signaling molecules that regulate metabolic homeostasis and inflammatory processes. Many of these effects are mediated by the bile acid-activated nuclear receptor farnesoid X receptor (FXR) and the G protein-coupled receptor TGR5. Nutrient signaling regulates hepatic bile acid synthesis and circulating plasma bile acid concentrations, which in turn control metabolic homeostasis. The FXR agonist obeticholic acid has had beneficial effects on NASH in recent clinical trials. Preclinical studies have suggested that the TGR5 agonist and the FXR/TGR5 dual agonist are also potential therapies for metabolic liver diseases. Extensive studies in the past few decades have significantly improved our understanding of the metabolic regulatory function of bile acids, which has provided the molecular basis for developing promising bile acid-based therapeutic agents for NASH treatment.

Matrix metalloproteinase processing of PTHrP yields a selective regulator of osteogenesis, PTHrP1-17

Parathyroid hormone-related protein (PTHrP) is a critical regulator of bone resorption and augments osteolysis in skeletal malignancies. Here we report that the mature PTHrP_1-36 hormone is processed by matrix metalloproteinases to yield a stable product, PTHrP_1-17. PTHrP_1-17 retains the ability to signal through PTH1R to induce calcium flux and ERK phosphorylation but not cyclic AMP production or CREB phosphorylation. Notably, PTHrP_1-17 promotes osteoblast migration and mineralization in vitro, and systemic administration of PTHrP_1-17 augments ectopic bone formation in vivo. Further, in contrast to PTHrP_1-36, PTHrP_1-17 does not affect osteoclast formation/function in vitro or in vivo. Finally, immunoprecipitation-mass spectrometry analyses using PTHrP_1-17-specific antibodies establish that PTHrP_1-17 is indeed generated by cancer cells. Thus, matrix metalloproteinase-directed processing of PTHrP disables the osteolytic functions of the mature hormone to promote osteogenesis, indicating important roles for this circuit in bone remodelling in normal and disease contexts.

Roles of Ileal ASBT and OSTα-OSTβ in Regulating Bile Acid Signaling

BACKGROUND

In addition to their classical role as detergents, bile acids function as signaling molecules to regulate gastrointestinal physiology, carbohydrate and lipid metabolism, and energy expenditure. The pharmacodynamic potential of bile acids is dependent in part on the tight pharmacokinetic control of their concentration and metabolism, properties governed by their hepatic synthesis, enterohepatic cycling, and biotransformation via host and gut microbiota-catalyzed pathways. Key Messages: By altering the normal cycling and compartmentalization of bile acids, changes in hepatobiliary or intestinal transport can affect signaling and lead to the retention of cytotoxic hydrophobic bile acids and cell injury. This review discusses advances in our understanding of the intestinal transporters that maintain the enterohepatic cycling of bile acids, signaling via bile acid-activated nuclear and G protein receptors, and mechanisms of bile acid-induced cell injury.

CONCLUSIONS

Dysregulated expression of the Asbt and Ostα-Ostβ alters bile acid signaling via the gut-liver farnesoid X receptor-fibroblast growth factor 15/19 axis and may contribute to other bile acid-regulated metabolic and cell injury pathways.

Chronic Over-expression of Fibroblast Growth Factor 21 Increases Bile Acid Biosynthesis by Opposing FGF15/19 Action

Pharmacological doses of fibroblast growth factor (FGF) 21 effectively normalize glucose, lipid and energy homeostasis in multiple animal models with many benefits translating to obese humans with type 2 diabetes. However, a role for FGF21 in the regulation of bile acid metabolism has not been reported. Herein, we demonstrate AAV-mediated FGF21 overexpression in mice increases liver expression of the key bile acid producing enzyme, Cyp7a1, resulting in an increased bile acid pool. Furthermore, in cholecystectomized mice, FGF21-mediated bile acid pool increase led to increased transit of bile acids into colon. We elucidate that the mechanism of FGF21 induced bile acid changes is mainly through antagonizing FGF15/19 function on liver βKlotho/FGFR4 receptor complex; thus inhibiting FGF15/19-mediated suppression of Cyp7a1 expression. In conclusion, these data reveal a previously unidentified role for FGF21 on bile acid metabolism and may be relevant to understand the effects of FGF21 analogs in clinical studies.

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Chronic FGF21 overexpression in mice leads to increases in bile acid production and bile acid pool.

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FGF21 mediates the bile acid changes at least in part through antagonizing FGF15/19 function.

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Cross-talk between FGF molecules may be a regulatory mechanism for their function.

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Effects of FGF21 on bile acid metabolism may be relevant to understand FGF21 clinical observations.

Pharmacological doses of FGF21 effectively normalize glucose, lipid and energy homeostasis in multiple animal models, and several FGF21 analogs are being evaluated in the clinic as potential therapies for type 2 diabetes. However, a role for FGF21 in the regulation of bile acid metabolism has not been reported. In the present study, we revealed a link between chronic FGF21 overexpression to increases in bile acid synthesis in mice and uncovered a new cross-talk mechanism between FGF molecules. These findings may highlight an importance aspect of FGF21's pharmacology for future clinical study considerations.

Advances in targeted proteomics and applications to biomedical research

Targeted proteomics technique has emerged as a powerful protein quantification tool in systems biology, biomedical research, and increasing for clinical applications. The most widely used targeted proteomics approach, selected reaction monitoring (SRM), also known as multiple reaction monitoring (MRM), can be used for quantification of cellular signaling networks and preclinical verification of candidate protein biomarkers. As an extension to our previous review on advances in SRM sensitivity (Shi et al., Proteomics, 12, 1074-1092, 2012) herein we review recent advances in the method and technology for further enhancing SRM sensitivity (from 2012 to present), and highlighting its broad biomedical applications in human bodily fluids, tissue and cell lines. Furthermore, we also review two recently introduced targeted proteomics approaches, parallel reaction monitoring (PRM) and data-independent acquisition (DIA) with targeted data extraction on fast scanning high-resolution accurate-mass (HR/AM) instruments. Such HR/AM targeted quantification with monitoring all target product ions addresses SRM limitations effectively in specificity and multiplexing; whereas when compared to SRM, PRM and DIA are still in the infancy with a limited number of applications. Thus, for HR/AM targeted quantification we focus our discussion on method development, data processing and analysis, and its advantages and limitations in targeted proteomics. Finally, general perspectives on the potential of achieving both high sensitivity and high sample throughput for large-scale quantification of hundreds of target proteins are discussed.

Overexpression of β-Klotho in Adipose Tissue Sensitizes Male Mice to Endogenous FGF21 and Provides Protection From Diet-Induced Obesity

The endocrine hormone fibroblast growth factor 21 (FGF21) is induced in the adaptive response to nutrient deprivation, where it serves to regulate the integrated response to fasting via its primary receptor complex, FGF receptor 1 coupled with the cofactor β-klotho (KLB) in target tissues. Curiously, endogenous FGF21 levels are also elevated in preclinical models of obesity and in obese/diabetic individuals. In addition to higher FGF21 levels, reduced KLB expression in liver and adipose tissue has been noted in these same individuals, suggesting that obesity may represent an FGF21 resistant state. To explore the contribution of tissue-specific KLB levels to endogenous FGF21 activity, in both fasting and high-fat diet feeding conditions, we generated animals overexpressing KLB in liver (LKLBOE) or adipose (ATKLBOE). Supportive of tissue-specific partitioning of FGF21 action, after chronic high-fat feeding, ATKLBOE mice gained significantly less weight than WT. Reduced weight gain was associated with elevated caloric expenditure, accompanied by a reduced respiratory exchange ratio and lower plasma free fatty acids levels, suggestive of augmented lipid metabolism. In contrast, LKLBOE had no effect on body weight but did reduce plasma cholesterol. The metabolic response to fasting was enhanced in LKLBOE mice, evidenced by increased ketone production, whereas no changes in this were noted in ATKLBOE mice. Taken together, these data provide further support that specific effects of FGF21 are mediated via engagement of distinct target organs. Furthermore, enhancing KLB expression in adipose may sensitize to endogenous FGF21, thus representing a novel strategy to combat metabolic disease.

Bcl2 is a critical regulator of bile acid homeostasis by dictating Shp and lncRNA H19 function

Bile acid (BA) metabolism is tightly controlled by nuclear receptor signaling to coordinate regulation of BA synthetic enzymes and transporters. Here we reveal a molecular cascade consisting of the antiapoptotic protein BCL2, nuclear receptor Shp, and long non-coding RNA (lncRNA) H19 to maintain BA homeostasis. Bcl2 was overexpressed in liver of C57BL/6J mice using adenovirus mediated gene delivery for two weeks. Hepatic overexpression of Bcl2 caused drastic accumulation of serum BA and bilirubin levels and dysregulated BA synthetic enzymes and transporters. Bcl2 reactivation triggered severe liver injury, fibrosis and inflammation, which were accompanied by a significant induction of H19. Bcl2 induced rapid SHP protein degradation via the activation of caspase-8 pathway. The induction of H19 in Bcl2 overexpressed mice was contributed by a direct loss of Shp transcriptional repression. H19 knockdown or Shp re-expression largely rescued Bcl2-induced liver injury. Strikingly different than Shp, the expression of Bcl2 and H19 was hardly detectable in adult liver but was markedly increased in fibrotic/cirrhotic human and mouse liver. We demonstrated for the first time a detrimental effect of Bcl2 and H19 associated with cholestatic liver fibrosis and an indispensable role of Shp to maintain normal liver function.

Pharmacology of bile acid receptors: Evolution of bile acids from simple detergents to complex signaling molecules

For many years, bile acids were thought to only function as detergents which solubilize fats and facilitate the uptake of fat-soluble vitamins in the intestine. Many early observations; however, demonstrated that bile acids regulate more complex processes, such as bile acids synthesis and immune cell function through activation of signal transduction pathways. These studies were the first to suggest that receptors may exist for bile acids. Ultimately, seminal studies by many investigators led to the discovery of several bile acid-activated receptors including the farnesoid X receptor, the vitamin D receptor, the pregnane X receptor, TGR5, α5 β1 integrin, and sphingosine-1-phosphate receptor 2. Several of these receptors are expressed outside of the gastrointestinal system, indicating that bile acids may have diverse functions throughout the body. Characterization of the functions of these receptors over the last two decades has identified many important roles for these receptors in regulation of bile acid synthesis, transport, and detoxification; regulation of glucose utilization; regulation of fatty acid synthesis and oxidation; regulation of immune cell function; regulation of energy expenditure; and regulation of neural processes such as gastric motility. Through these many functions, bile acids regulate many aspects of digestion ranging from uptake of essential vitamins to proper utilization of nutrients. Accordingly, within a short time period, bile acids moved beyond simple detergents and into the realm of complex signaling molecules. Because of the important processes that bile acids regulate through activation of receptors, drugs that target these receptors are under development for the treatment of several diseases, including cholestatic liver disease and metabolic syndrome. In this review, we will describe the various bile acid receptors, the signal transduction pathways activated by these receptors, and briefly discuss the physiological processes that these receptors regulate.

Therapeutic potential of the endocrine fibroblast growth factors FGF19, FGF21 and FGF23

The endocrine fibroblast growth factors (FGFs), FGF19, FGF21 and FGF23, are critical for maintaining whole-body homeostasis, with roles in bile acid, glucose and lipid metabolism, modulation of vitamin D and phosphate homeostasis and metabolic adaptation during fasting. Given these functions, the endocrine FGFs have therapeutic potential in a wide array of chronic human diseases, including obesity, type 2 diabetes, cancer, and kidney and cardiovascular disease. However, the safety and feasibility of chronic endocrine FGF administration has been challenged, and FGF analogues and mimetics are now being investigated. Here, we discuss current knowledge of the complex biology of the endocrine FGFs and assess how this may be harnessed therapeutically.

Role of Proteomics in the Development of Personalized Medicine

Advances in proteomic technologies have made import contribution to the development of personalized medicine by facilitating detection of protein biomarkers, proteomics-based molecular diagnostics, as well as protein biochips and pharmacoproteomics. Application of nanobiotechnology in proteomics, nanoproteomics, has further enhanced applications in personalized medicine. Proteomics-based molecular diagnostics will have an important role in the diagnosis of certain conditions and understanding the pathomechanism of disease. Proteomics will be a good bridge between diagnostics and therapeutics; the integration of these will be important for advancing personalized medicine. Use of proteomic biomarkers and combination of pharmacoproteomics with pharmacogenomics will enable stratification of clinical trials and improve monitoring of patients for development of personalized therapies. Proteomics is an important component of several interacting technologies used for development of personalized medicine, which is depicted graphically. Finally, cancer is a good example of applications of proteomic technologies for personalized management of cancer.

Antibodies as means for selective mass spectrometry

For protein analysis of biological samples, two major strategies are used today; mass spectrometry (MS) and antibody-based methods. Each strategy offers advantages and drawbacks. However, combining the two using an immunoenrichment step with MS analysis brings together the benefits of each method resulting in increased sensitivity, faster analysis and possibility of higher degrees of multiplexing. The immunoenrichment can be performed either on protein or peptide level and quantification standards can be added in order to enable determination of the absolute protein concentration in the sample. The combination of immunoenrichment and MS holds great promise for the future in both proteomics and clinical diagnostics. This review describes different setups of immunoenrichment coupled to mass spectrometry and how these can be utilized in various applications.

FXR Primes the Liver for Intestinal FGF15 Signaling by Transient Induction of β-Klotho

The bile acid (BA)-sensing nuclear receptor, farnesoid X receptor (FXR), regulates postprandial metabolic responses, including inhibition of BA synthesis, by inducing the intestinal hormone, fibroblast growth factor (FGF)15 (FGF19 in human). In this study, we tested a novel hypothesis that FXR not only induces intestinal FGF15 but also primes the liver for effectively responding to the signal by transcriptional induction of the obligate coreceptor for FGF15, β-Klotho (βKL). Activation of FXR by a synthetic agonist, GW4064, in mice increased occupancy of FXR and its DNA-binding partner, retinoid X receptor-α, at FGF15-signaling component genes, particularly βKL, and induced expression of these genes. Interestingly, mRNA levels of Fgfr4, the FGF15 receptor, were not increased by GW4064, but protein levels increased as a result of βKL-dependent increased protein stability. Both FGF receptor 4 and βKL protein levels were substantially decreased in FXR-knockout (KO) mice, and FGF19 signaling, monitored by phosphorylated ERK, was blunted in FXR-KO mice, FXR-KO mouse hepatocytes, and FXR-down-regulated human hepatocytes. Overexpression of βKL in FXR-lacking hepatocytes partially restored FGF19 signaling and inhibition by FGF19 of Cyp7a1, which encodes the rate-limiting BA biosynthetic enzyme. In mice, transient inductions of intestinal Fgf15 and hepatic βKL were temporally correlated after GW4064 treatment, and pretreatment of hepatocytes with GW4064 before FGF19 treatment enhanced FGF19 signaling, which was abolished by transcriptional inhibition or βKL down-regulation. This study identifies FXR as a gut-liver metabolic coordinator for FGF15/19 action that orchestrates transient induction of hepatic βKL and intestinal Fgf15/19 in a temporally correlated manner.

Metabolic roles of endocrine fibroblast growth factors

Considerable effort is currently being devoted to understanding the physiological and pharmacological action of the endocrine fibroblast growth factors (FGFs). These three proteins (FGF15/19, FGF21 and FGF23) act in a tissue-specific manner through a membrane-complex consisting of an FGF-receptor and α/βKlotho. FGF15/19 is produced in the intestine and regulates postprandial liver metabolism and gallbladder filling. FGF21 is largely liver-derived and co-ordinates adaptive changes in response to nutritional and physiological stresses. FGF23 signals from the bone to the kidney to maintain phosphate homeostasis. In pharmacological settings, FGF15/19, FGF21, and the prototypical FGF1, potentially represent novel treatments for obesity and diabetes. This review summarises the recent advances in our understanding of the biology of these important metabolic regulators.

Metabolic fibroblast growth factors (FGFs): Mediators of energy homeostasis

The metabolic fibroblast growth factors (FGFs), FGF1, FGF15/19, and FGF21 differ from classic FGFs in that they modulate energy homeostasis in response to fluctuating nutrient availability. These unique mediators of metabolism regulate a number of physiological processes which contribute to their potent pharmacological properties. Administration of pharmacological doses of these FGFs causes weight loss, increases energy expenditure, and improves carbohydrate and lipid metabolism in obese animal models. However, many questions remain regarding the precise molecular and physiological mechanisms governing the effects of individual metabolic FGFs. Here we review the metabolic actions of FGF1, FGF15/19, and FGF21 while providing insights into their pharmacological effects by examining known biological functions.