Deletion of GPR40 fatty acid receptor gene in mice blocks mercaptoacetate-induced feeding

Expression and structural analysis of taste receptor genes in Iberian and Duroc pigs

BACKGROUND

Taste receptor genes are expressed in sensory cells located in the tongue and influence food preferences, voluntary feed intake, and other relevant traits. Taste perception may differ between livestock breeds that show differences in eating behaviour and between animals that receive different diets or show phenotypic variation in feed intake or related-traits. The objectives of this work were to deepen the understanding of the regulation of the function of taste receptor genes in the circumvallate papillae of obese Iberian pigs in comparison to Duroc pigs, and to characterize their genetic variation and associations with relevant production traits.

RESULTS

We performed a gene expression and structural analysis of ten taste receptor genes in Iberian and Duroc pigs. Gene expression was quantified in the circumvallate papillae of 48 growing Iberian and Duroc pigs maintained under identical management conditions but fed isocaloric diets differing in energy source: either high concentration of fat rich in oleic acid (HO) or carbohydrates (CH); and sacrificed after 47 days of treatment (50.5 kg live weight). Gene expression differed between the two breeds for most of the analyzed genes, with the TAS1R1, TAS1R2, TAS1R3, TAS2R4, TAS2R38, TAS2R39, GPR84, and CD36 genes being overexpressed in Duroc pigs. The diet effect was modulated by breed, with TAS1R1, TAS1R3, and TAS2R4 genes being overexpressed only in Duroc pigs fed the HO diet. Detection of genetic variants (single nucleotide polymorphisms, SNPs) for this panel of genes was performed on muscle RNA-seq data, and three SNPs in the TAS1R1, TAS1R3, and CD36 genes were selected for association studies. All three SNPs were associated with various growth, fattening, tissue fat content, and composition traits. Moreover, the CD36:c.910G/T SNP was associated with oral CD36 gene expression and with differences in the predicted mRNA secondary structure.

CONCLUSIONS

Most taste receptor genes are expressed at lower level in circumvallate papillae from Iberian than Duroc pigs. This aligns with lower overall taste sensitivity, higher feed intake, and obese nature of Iberian pigs. Significant association results were observed for SNPs in the TAS1R1 and TAS1R3 genes with meat quality traits and liver composition, which showed segregation in world-wide distributed breeds, but particularly for a potential causal SNP in the CD36 gene, associated with growth and tissue composition, which segregates in Iberian populations.

Hindbrain glucoregulatory mechanisms: Critical role of catecholamine neurons in the ventrolateral medulla

Glucose is the required metabolic substrate for the brain. Yet the brain stores very little glucose. Therefore, the brain continuously monitors glucose availability to detect hypoglycemia and to mobilize system-wide responses to protect and restore euglycemia. Catecholamine (CA) neurons in the hindbrain are critical elements of the brain's glucoregulatory mechanisms. They project widely throughout the brain and spinal cord, innervating sites controlling behavioral, endocrine and visceral responses. Hence, CA neurons are capable of triggering a rapid, coordinated and multifaceted response to glucose challenge. This article reviews experimental data that has begun to elucidate the importance of CA neurons for glucoregulation, the functions of specific CA subpopulations in the ventrolateral medulla, and the extended circuitry through which they engage other levels of the nervous system to accomplish their essential glucoregulatory task. Hopefully, this review also suggests the vast amount of work yet to be done in this area and the justification for engaging in that effort.

Caralluma fimbriata extract activity involves the 5-HT2c receptor in PWS Snord116 deletion mouse model

INTRODUCTION

In Prader-Willi syndrome (PWS), nonprotein coding small nucleolar (sno) RNAs are involved in the paternally deleted region of chromosome 15q11.2-q13, which is believed to cause the hyperphagic phenotype of PWS. Central to this is SnoRNA116. The supplement Caralluma fimbriata extract (CFE) has been shown to decrease appetite behavior in some individuals with PWS. We therefore investigated the mechanism underpinning the effect of CFE on food intake in the Snord116del mouse. Experiments utilized appetite stimulants which included a 5-hydroxytryptamine (5-HT) 2c receptor antagonist (SB242084), as the 5-HT2cR is implicated in central signaling of satiety.

METHODS

After 9-week chronic CFE treatment (33 mg or 100 mg kg^-1  day^-1 ) or placebo, the 14-week-old Snord116del (SNO) and wild-type mice (n = 72) were rotated through intraperitoneal injections of (a) isotonic saline; (b) 400 mg/kg of 2-deoxyglucose (2DG) (glucose deprivation); (c) 100 mglkg beta-mercaptoacetate (MA), fatty acid signaling; and (d) SB242084 (a selective 5HT2cR antagonist), with 5 days between reagents. Assessments of food intake were from baseline to 4 hr, followed by immunohistochemistry of neural activity utilizing c-Fos, neuropeptide Y, and alpha-melanocyte-stimulating hormone within hypothalamic appetite pathways.

RESULTS

Caralluma fimbriata extract administration decreased food intake more strongly in the SNO100CFE group with significantly stimulated food intake demonstrated during coadministration with SB242084. Though stimulatory deprivation was expected to stimulate food intake, 2DG and MA resulted in lower intake in the snord116del mice compared to the WT animals (p = <0.001). Immunohistochemical mapping of hypothalamic neural activity was consistent with the behavioral studies.

CONCLUSIONS

This study identifies a role for the 5-HT2cR in CFE-induced appetite suppression and significant stimulatory feeding disruptions in the snord116del mouse model.

Grifolic acid induces mitochondrial membrane potential loss and cell death of RAW264.7 macrophages

Grifolic acid is a phenolic compound that was first extracted from the mushroom Albatrellus confluens; it acts as an agonist of the free fatty acid receptor (FFAR4). FFAR4 is expressed in macrophages and mediates the anti‑inflammatory effects of n‑3 unsaturated free fatty acids. In the present study, the effects of grifolic acid on macrophages were observed in mouse RAW264.7 cells. It was demonstrated that grifolic acid (2.5‑20 µmol/l) treatment reduced RAW264.7 cell viability in a dose‑ and time‑dependent manner. The number of apoptotic cells significantly increased following grifolic acid treatment compared with the untreated control cells. Grifolic acid treatment resulted in a significant decrease in cellular adenosine 5'‑triphosphate (ATP) content in RAW264.7 cells. Mitochondrial membrane potential (MMP), as measured by JC‑1 staining, was significantly diminished by grifolic acid treatment in a dose‑ and time‑dependent manner. Treatment with cyclosporine A, a protector of MMP, attenuated grifolic acid‑induced reduction of MMP and viability in RAW264.7 cells. FFAR4 knockdown did not significantly influence grifolic acid‑induced reduction of cell viability, ATP levels or MMP. In conclusion, grifolic acid may induce macrophage cell death by reducing MMP and by inhibiting ATP production probably in an FFAR4‑independent manner.

Fatty acid and mineral receptors as drug targets for gastrointestinal disorders

Nutrient-sensing receptors, including fatty acid receptors (FFA1–FFA4), Ca2+-sensing receptors and Zn2+-sensing receptors, are involved in several biological processes. These receptors are abundantly expressed in the GI tract, where they have been shown to play crucial roles in regulating GI function. This review provides an overview of the GI functions of fatty acid and mineral receptors, including the regulation of gastric and enteroendocrine functions, GI motility, ion transport and cell growth. Recently, several lines of evidence have implicated these receptors as promising therapeutic targets for the treatment of GI disorders, for example, inflammatory bowel disease, colorectal cancer, metabolic syndrome and diarrheal diseases. A future perspective on drug discovery research targeting these receptors is discussed.

Neural Signaling Metabolites May Modulate Energy Use in Hibernation

Despite an epidemic in obesity and metabolic syndrome limited means exist to effect adiposity or metabolic rate other than life style changes. Here we review evidence that neural signaling metabolites may modulate thermoregulatory pathways and offer novel means to fine tune energy use. We extend prior reviews on mechanisms that regulate thermogenesis and energy use in hibernation by focusing primarily on the neural signaling metabolites adenosine, AMP and glutamate.