Angie L. Bookout

Anatomical Profiling of Nuclear Receptor Expression Reveals a Hierarchical Transcriptional Network

In multicellular organisms, the ability to regulate reproduction, development, and nutrient utilization coincided with the evolution of nuclear receptors (NRs), transcription factors that utilize lipophilic ligands to mediate their function. Studying the expression profile of NRs offers a simple, powerful way to obtain highly relational information about their physiologic functions as individual proteins and as a superfamily. We surveyed the expression of all 49 mouse NR mRNAs in 39 tissues, representing diverse anatomical systems. The resulting data set uncovers several NR clades whose patterns of expression indicate their ability to coordinate the transcriptional programs necessary to affect distinct physiologic pathways. Remarkably, this regulatory network divides along the following two physiologic paradigms: (1) reproduction, development, and growth and (2) nutrient uptake, metabolism, and excretion. These data reveal a hierarchical transcriptional circuitry that extends beyond individual tissues to form a meganetwork governing physiology on an organismal scale.

Quantitative real-time PCR protocol for analysis of nuclear receptor signaling pathways

A major goal of the Nuclear Receptor Signaling Atlas (NURSA) is to elucidate the biochemical and physiological roles of nuclear receptors in vivo. Characterizing the tissue expression pattern of individual receptors and their target genes in whole animals under various pharmacological conditions and genotypes is an essential component of this aim. Here we describe a high-throughput quantitative, real-time, reverse-transcription PCR (QPCR) method for the measurement of both the relative level of expression of a particular transcript in a given tissue or cell type, and the relative change in expression of a particular transcript after pharmacologic or genotypic manipulation. This method is provided as a standardized protocol for those in the nuclear receptor field. It is meant to be a simplified, easy to use protocol for the rapid, high-throughput measurement of transcript levels in a large number of samples. A subsequent report will provide validated primer and probe sequence information for the entire mouse and human nuclear receptor superfamily.

Research Resource: Comprehensive Expression Atlas of the Fibroblast Growth Factor System in Adult Mouse

Although members of the fibroblast growth factor (FGF) family and their receptors have well-established roles in embryogenesis, their contributions to adult physiology remain relatively unexplored. Here, we use real-time quantitative PCR to determine the mRNA expression patterns of all 22 FGFs, the seven principal FGF receptors (FGFRs), and the three members of the Klotho family of coreceptors in 39 different mouse tissues. Unsupervised hierarchical cluster analysis of the mRNA expression data reveals that most FGFs and FGFRs fall into two groups the expression of which is enriched in either the central nervous system or reproductive and gastrointestinal tissues. Interestingly, the FGFs that can act as endocrine hormones, including FGF15/19, FGF21, and FGF23, cluster in a third group that does not include any FGFRs, underscoring their roles in signaling between tissues. We further show that the most recently identified Klotho family member, Lactase-like, is highly and selectively expressed in brown adipose tissue and eye and can function as an additional coreceptor for FGF19. This FGF atlas provides an important resource for guiding future studies to elucidate the physiological functions of FGFs in adult animals.

High-throughput real-time quantitative reverse transcription PCR.

Extensive detail on the application of the real‐time quantitative polymerase chain reaction (QPCR) for the analysis of gene expression is provided in this unit. The protocols are designed for high‐throughput, 384‐well‐format instruments, such as the Applied Biosystems 7900HT, but may be modified to suit any real‐time PCR instrument. QPCR primer and probe design and validation are discussed, and three relative quantitation methods are described: the standard curve method, the efficiency‐corrected ΔCt method, and the comparative cycle time, or ΔΔCt method. In addition, a method is provided for absolute quantification of RNA in unknown samples. RNA standards are subjected to RT‐PCR in the same manner as the experimental samples, thus accounting for the reaction efficiencies of both procedures. This protocol describes the production and quantitation of synthetic RNA molecules for real‐time and non‐real‐time RT‐PCR applications.

Prevention of cholesterol gallstone disease by FXR agonists in a mouse model

Cholesterol gallstone disease is characterized by several events, including cholesterol precipitation in bile, increased bile salt hydrophobicity and gallbladder inflammation. Here, we describe the same phenotype in mice lacking the bile acid receptor, FXR. Furthermore, in susceptible wild-type mice that recapitulate human cholesterol gallstone disease, treatment with a synthetic FXR agonist prevented sequelae of the disease. These effects were mediated by FXR-dependent increases in biliary bile salt and phospholipid concentrations, which restored cholesterol solubility and thereby prevented gallstone formation. Taken together, these results indicate that FXR is a promising therapeutic target for treating or preventing cholesterol gallstone disease.

Fibroblast growth factor 21 promotes bone loss by potentiating the effects of peroxisome proliferator-activated receptor γ

The endocrine hormone fibroblast growth factor 21 (FGF21) is a powerful modulator of glucose and lipid metabolism and a promising drug for type 2 diabetes. Here we identify FGF21 as a potent regulator of skeletal homeostasis. Both genetic and pharmacologic FGF21 gain of function lead to a striking decrease in bone mass. In contrast, FGF21 loss of function leads to a reciprocal high-bone-mass phenotype. Mechanistically, FGF21 inhibits osteoblastogenesis and stimulates adipogenesis from bone marrow mesenchymal stem cells by potentiating the activity of peroxisome proliferator-activated receptor γ (PPAR-γ). Consequently, FGF21 deletion prevents the deleterious bone loss side effect of the PPAR-γ agonist rosiglitazone. Therefore, FGF21 is a critical rheostat for bone turnover and a key integrator of bone and energy metabolism. These results reveal that skeletal fragility may be an undesirable consequence of chronic FGF21 administration.

FGF21 regulates metabolism and circadian behavior by acting on the nervous system

Fibroblast growth factor 21 (FGF21) is a hepatokine that acts as a global starvation signal to modulate fuel partitioning and metabolism, and repress growth1; however the site of action of these diverse effects remains unclear. FGF21 signals through a heteromeric cell surface receptor composed of one of three FGF receptors (FGFR1c, 2c, or 3c) in complex with β-Klotho2-4, a single-pass transmembrane protein that is enriched in metabolic tissues5. Here we show that in addition to its known effects on peripheral metabolism, FGF21 increases systemic glucocorticoid levels, suppresses physical activity, and alters circadian behavior, all features of the adaptive starvation response. These effects are mediated through β-Klotho expression in the suprachiasmatic nucleus (SCN) of the hypothalamus and the dorsal vagal complex (DVC) of the hindbrain. Mice lacking the β-Klotho gene (Klb) in these regions are refractory to these effects, as well as those on metabolism, insulin, and growth. These findings demonstrate a crucial role for the nervous system in mediating the diverse physiologic and pharmacologic actions of FGF21.Fibroblast growth factor 21 (FGF21) is a hepatokine that acts as a global starvation signal to modulate fuel partitioning and metabolism and repress growth; however, the site of action of these diverse effects remains unclear. FGF21 signals through a heteromeric cell-surface receptor composed of one of three FGF receptors (FGFR1c, FGFR2c or FGFR3c) in complex with β-Klotho, a single-pass transmembrane protein that is enriched in metabolic tissues. Here we show that in addition to its known effects on peripheral metabolism, FGF21 increases systemic glucocorticoid levels, suppresses physical activity and alters circadian behavior, which are all features of the adaptive starvation response. These effects are mediated through β-Klotho expression in the suprachiasmatic nucleus of the hypothalamus and the dorsal vagal complex of the hindbrain. Mice lacking the gene encoding β-Klotho (Klb) in these regions are refractory to these effects, as well as those on metabolism, insulin and growth. These findings demonstrate a crucial role for the nervous system in mediating the diverse physiologic and pharmacologic actions of FGF21.

Brain SIRT1: Anatomical Distribution and Regulation by Energy Availability

SIRT1 is a nicotinamide adenosine dinucleotide-dependent deacetylase that orchestrates key metabolic adaptations to nutrient deprivation in peripheral tissues. SIRT1 is induced also in the brain by reduced energy intake. However, very little is known about SIRT1 distribution and the biochemical phenotypes of SIRT1-expressing cells in the neuraxis. Unknown are also the brain sites in which SIRT1 is regulated by energy availability and whether these regulations are altered in a genetic model of obesity. To address these issues, we performed in situ hybridization histochemistry analyses and found that Sirt1 mRNA is highly expressed in metabolically relevant sites. These include, but are not limited to, the hypothalamic arcuate, ventromedial, dorsomedial, and paraventricular nuclei and the area postrema and the nucleus of the solitary tract in the hindbrain. Of note, our single-cell reverse transcription-PCR analyses revealed that Sirt1 mRNA is expressed in pro-opiomelanocortin neurons that are critical for normal body weight and glucose homeostasis. We also found that SIRT1 protein levels are restrictedly increased in the hypothalamus in the fasted brain. Of note, we found that this hypothalamic-specific, fasting-induced SIRT1 regulation is altered in leptin-deficient, obese mice. Collectively, our findings establish the distribution of Sirt1 mRNA throughout the neuraxis and suggest a previously unrecognized role of brain SIRT1 in regulating energy homeostasis.

Identification of a hormonal basis for gallbladder filling

The cycle of gallbladder filling and emptying controls the flow of bile into the intestine for digestion. Here we show that fibroblast growth factor-15, a hormone made by the distal small intestine in response to bile acids, is required for gallbladder filling. These studies demonstrate that gallbladder filling is actively regulated by an endocrine pathway and suggest a postprandial timing mechanism that controls gallbladder motility.

FGF21 Acts Centrally to Induce Sympathetic Nerve Activity, Energy Expenditure, and Weight Loss

The mechanism by which pharmacologic administration of the hormone FGF21 increases energy expenditure to cause weight loss in obese animals is unknown. Here we report that FGF21 acts centrally to exert its effects on energy expenditure and body weight in obese mice. Using tissue-specific knockout mice, we show that βKlotho, the obligate coreceptor for FGF21, is required in the nervous system for these effects. FGF21 stimulates sympathetic nerve activity to brown adipose tissue through a mechanism that depends on the neuropeptide corticotropin-releasing factor. Our findings provide an unexpected mechanistic explanation for the strong pharmacologic effects of FGF21 on energy expenditure and weight loss in obese animals.