Loss of the nutrient receptor Tas1R3 reduces atherosclerotic plaque accumulation and hepatic steatosis in ApoE-/- mice

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.

Effect of T1R3 Taste Receptor Gene Deletion on Dextran Sulfate Sodium-Induced Colitis in Mice

Taste receptor type 1 member 3 (T1R3) recognize umami or sweet tastes and also contributes type 2 immunity and autophagy in small intestine and muscle cells, respectively. Since imbalance of type 1 and type 2 immunity and autophagy affect intestinal bowel disease (IBD), we hypothesized that T1R3 have a potential role in the incidence and progression of colitis. In the present study, we investigated whether genetic deletion of T1R3 impacted aggravation of DSS-induced colitis in mice. We found that T1R3-KO mice showed reduction in colon damage, including reduced inflammation and colon shrinking relative to those of WT mice following DSS treatment. mRNA expression of tight junction components, particularly claudin1 was significantly lower in T1R3-KO mice with trend to lower inflammation related gene mRNA expression in colon. Other parameters, such as response to microbial stimuli in splenic lymphocytes and peritoneal macrophages, gut microbiota composition, and expression of autophagy-related proteins, were similar between WT and KO mice. Together, these results indicated that deletion of T1R3 has a minor role in intestinal inflammation induced by DSS-induced acute colitis in mice.

Sucralose, a Non-nutritive Artificial Sweetener Exacerbates High Fat Diet-Induced Hepatic Steatosis Through Taste Receptor Type 1 Member 3

Non-alcoholic fatty liver disease (NAFLD) is the most common chronic liver disease globally, and it is strongly associated with obesity. To combat obesity, artificial sweeteners are often used to replace natural sugars, and sucralose is one of the most extensively used sweeteners. It was known that sucralose exerted effects on lipid metabolism dysregulation, and hepatic inflammation; however, the effects of sucralose on hepatic steatosis were still obscure. In this study, we found that supplements of sucralose enhanced high-fat-diet (HFD)-induced hepatic steatosis. In addition, treatment of sucralose increased reactive oxygen species (ROS) generation and induced endoplasmic reticulum (ER) stress in HepG2 cells. Pretreatment of ROS or ER stress inhibitors reversed the effects of sucralose on lipogenesis. Furthermore, pretreatment of taste receptor type 1 membrane 3 (T1R3) inhibitor or T1R3 knockdown reversed sucralose-induced lipogenesis in HepG2 cells. Taken together, sucralose might activate T1R3 to generate ROS and promote ER stress and lipogenesis, and further accelerate to the development of hepatic steatosis.