FFAR4: A New Player in Cardiometabolic Disease?

G protein-coupled receptors and traditional Chinese medicine: new thinks for the development of traditional Chinese medicine

G protein-coupled receptors (GPCRs) widely exist in vivo and participate in many physiological processes, thus emerging as important targets for drug development. Approximately 30% of the Food and Drug Administration (FDA)-approved drugs target GPCRs. To date, the 'one disease, one target, one molecule' strategy no longer meets the demands of drug development. Meanwhile, small-molecule drugs account for 60% of FDA-approved drugs. Traditional Chinese medicine (TCM) has garnered widespread attention for its unique theoretical system and treatment methods. TCM involves multiple components, targets and pathways. Centered on GPCRs and TCM, this paper discusses the similarities and differences between TCM and GPCRs from the perspectives of syndrome of TCM, the consistency of TCM's multi-component and multi-target approaches and the potential of GPCRs and TCM in the development of novel drugs. A novel strategy, 'simultaneous screening of drugs and targets', was proposed and applied to the study of GPCRs. We combine GPCRs with TCM to facilitate the modernisation of TCM, provide valuable insights into the rational application of TCM and facilitate the research and development of novel drugs. This study offers theoretical support for the modernisation of TCM and introduces novel ideas for development of safe and effective drugs.

Spaceflight induces changes in gene expression profiles linked to insulin and estrogen

Organismal adaptations to spaceflight have been characterized at the molecular level in model organisms, including Drosophila and C. elegans. Here, we extend molecular work to energy metabolism and sex hormone signaling in mice and humans. We found spaceflight induced changes in insulin and estrogen signaling in rodents and humans. Murine changes were most prominent in the liver, where we observed inhibition of insulin and estrogen receptor signaling with concomitant hepatic insulin resistance and steatosis. Based on the metabolic demand, metabolic pathways mediated by insulin and estrogen vary among muscles, specifically between the soleus and extensor digitorum longus. In humans, spaceflight induced changes in insulin and estrogen related genes and pathways. Pathway analysis demonstrated spaceflight induced changes in insulin resistance, estrogen signaling, stress response, and viral infection. These data strongly suggest the need for further research on the metabolic and reproductive endocrinologic effects of space travel, if we are to become a successful interplanetary species.

Current Insights into the Effects of Dietary α-Linolenic Acid Focusing on Alterations of Polyunsaturated Fatty Acid Profiles in Metabolic Syndrome

The plant-derived α-linolenic acid (ALA) is an essential n-3 acid highly susceptible to oxidation, present in oils of flaxseeds, walnuts, canola, perilla, soy, and chia. After ingestion, it can be incorporated in to body lipid pools (particularly triglycerides and phospholipid membranes), and then endogenously metabolized through desaturation, elongation, and peroxisome oxidation to eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), with a very limited efficiency (particularly for DHA), beta-oxidized as an energy source, or directly metabolized to C18-oxilipins. At this moment, data in the literature about the effects of ALA supplementation on metabolic syndrome (MetS) in humans are inconsistent, indicating no effects or some positive effects on all MetS components (abdominal obesity, dyslipidemia, impaired insulin sensitivity and glucoregulation, blood pressure, and liver steatosis). The major effects of ALA on MetS seem to be through its conversion to more potent EPA and DHA, the impact on the n-3/n-6 ratio, and the consecutive effects on the formation of oxylipins and endocannabinoids, inflammation, insulin sensitivity, and insulin secretion, as well as adipocyte and hepatocytes function. It is important to distinguish the direct effects of ALA from the effects of EPA and DHA metabolites. This review summarizes the most recent findings on this topic and discusses the possible mechanisms.

Double knockout of FFAR4 and FGF21 aggravates metabolic disorders in mice

Several investigations have examined the involvement of free fatty acid receptor 4 (FFAR4) in metabolic disorders, but its action remains controversial. To investigate whether endogenous fibroblast growth factor 21 (FGF21)-mediated signaling controls the metabolic status in FFAR4-deficient mice, we generated FFAR4/FGF21 double knockout (DKO) mice. We also evaluated the role of FGF21 on glucose and lipid metabolism in FFAR4 KO mice fed a high-fat diet. Levels of FGF21 were significantly increased in FFAR4-deficient mice and double deletion of FGF21 and FFAR4 led to severe metabolic disorders. Additionally, FFAR4/FGF21 DKO mice displayed metabolic abnormalities that may be caused by decreased energy expenditure. Collectively, this study characterized the effects of endogenous FGF21, which acts as a master feedback regulator in the absence of FFAR4.

Incretins play an important role in FFA4/GPR120 regulation of glucose metabolism by GW-9508

AIMS

To assess the role of GPR120 in glucose metabolism and incretin regulation from enteroendocrine L- and K-cells with determination of the cellular localisation of GPR120 in intestinal tissue and clonal Glucagon-Like Peptide-1 (GLP-1)/Gastric Inhibitory Polypeptide (GIP) cell lines.

MAIN METHODS

Anti-hyperglycaemic, insulinotropic and incretin secreting properties of the GPR120 agonist, GW-9508 were explored in combination with oral and intraperitoneal glucose tolerance tests (GTT) in lean, diabetic and incretin receptor knockout mice. Cellular localisation of GPR120 was assessed by double immunofluorescence.

KEY FINDINGS

Compared to intraperitoneal injection, oral administration of GW-9508 (0.1 μmol/kg body weight) together with glucose reduced the glycaemic excursion by 22-31 % (p < 0.05-p < 0.01) and enhanced glucose-induced insulin release by 30 % (p < 0.01) in normal mice. In high fat fed diabetic mice, orally administered GW-9508 lowered plasma glucose by 17-27 % (p < 0.05-p < 0.01) and augmented insulin release by 22-39 % (p < 0.05-p < 0.001). GW-9508 had no effect on the responses of GLP-1 receptor knockout mice and GIP receptor knockout mice. Consistent with this, oral GW-9508 increased circulating total GLP-1 release by 39-44 % (p < 0.01) and total GIP by 37-47 % (p < 0.01-p < 0.001) after 15 and 30 min in lean NIH Swiss mice. Immunocytochemistry demonstrated GPR120 expression on mouse enteroendocrine L- and K-cells, GLUTag cells and pGIP/Neo STC-1 cells.

SIGNIFICANCE

GPR120 is expressed on intestinal L- and K-cells and stimulates GLP-1/GIP secretory pathways involved in mediating enhanced insulin secretion and improved glucose tolerance, following oral GW-9508. These novel data strongly support the development of potent and selective GPR120 agonists as an effective therapeutic approach for diabetes.

Dissecting the molecular profiling and tumor immune microenvironment of three subtypes of esophageal cancer

BACKGROUND

Great improvements have been made in the prognosis of esophageal cancer (ESCA) with the application of chemotherapy and immunotherapy. However, the majority of cases remain resistant to these regimens. Hence there is an urgent need to characterize the subtypes of ESCA with favorable survival outcome and drug responsiveness.

METHODS

We characterized the malignant cells of ESCA and explored their communication with immune cells using the Cellchat algorithm. The ligand-receptor interaction pairs were then used as inputting information to identify the subtypes of ESCA by unsupervised clustering analysis. Further investigation aimed to dissect the different patterns of tumor immune microenvironment (TIME), tumor mutation burden, immunotherapy responsiveness and drug sensitivity among the various subtypes of ESCA. A nomogram was also constructed to predict the survival rate of ESCA patients by conducting Cox regression and decision curve analysis.

RESULTS

Three subtypes were identified based on the ligand-receptor interaction pairs. Patients in cluster 2 showed a longer survival time and less likelihood of response to immunotherapy compared with cluster 1 or 3. Eight hub genes were screened to construct a prognostic signature, which can stratify patients well into high- and low-risk groups with distinct survival outcomes and drug sensitivities. The nomogram showed quite good performance in predicting patient survival rates of 1 and 3 years.

CONCLUSION

This study characterized the molecular profiling and TIME patterns of three subtypes of ESCA. The relative findings will provide emergent insights for the treatment of ESCA.

Reduced Free Fatty Acid Receptor 4 Gene Expression is Associated With Extreme Obesity and Insulin Resistance in Children

OBJECTIVES

Free fatty acid receptor 4 (FFAR4) is a G-protein-coupled membrane receptor highly expressed in macrophages that triggers anti-inflammatory effects and promotes insulin sensitization. We have previously found significant associations between the FFAR4 rs11187533 single nucleotide polymorphism (SNP) and various obesity comorbidity parameters. We aimed to verify the FFAR4 expression levels in children with obesity and the associated comorbidities.

METHODS

Thirty-eight children with obesity were studied. Clinical and anthropometric evaluation was performed. A venous sample under fasting conditions was obtained. Biochemical study included parameters of metabolic risk. DNA was extracted and genotyped for the rs11187533 FFAR4 SNP. Real-time PCR technique was performed to investigate the gene expression. Relative FFAR4 mRNA levels were determined according to the 2-ΔΔCt method.

RESULTS

Significant differences in FFAR4 expression levels between the CC and CT-TT genotypes of the rs11187533 FFAR4 SNP were observed (P = 0.034). The minor allele T presented higher levels of FFAR4 expression. We found that a loss of FFAR4 expression was associated with extreme obesity (P = 0.032). The lowest FFAR4 expression levels were observed in children who had higher insulin (P = 0.008) and homeostasis model assessment insulin resistance values (P = 0.012) and lower quantitative insulin-sensitivity check index (P = 0.033).

CONCLUSIONS

The underexpression of FFAR4 was associated with extreme obesity and parameters indicative of obesity comorbidities in children. This under expression could be partially influenced by the presence of the C allele rs11187533 FFAR4 SNP.

New Insights in the Control of Fat Homeostasis: The Role of Neurotensin

Neurotensin (NT) is a small peptide with pleiotropic functions, exerting its primary actions by controlling food intake and energy balance. The first evidence of an involvement of NT in metabolism came from studies on the central nervous system and brain circuits, where NT acts as a neurotransmitter, producing different effects in relation to the specific region involved. Moreover, newer interesting chapters on peripheral NT and metabolism have emerged since the first studies on the NT-mediated regulation of gut lipid absorption and fat homeostasis. Intriguingly, NT enhances fat absorption from the gut lumen in the presence of food with a high fat content, and this action may explain the strong association between high circulating levels of pro-NT, the NT stable precursor, and the increased incidence of metabolic disorders, cardiovascular diseases, and cancer observed in large population studies. This review aims to provide a synthetic overview of the main regulatory effects of NT on several biological pathways, particularly those involving energy balance, and will focus on new evidence on the role of NT in controlling fat homeostasis, thus influencing the risk of unfavorable cardio–metabolic outcomes and overall mortality in humans.

Replacing arginine 99 with leucine to study the kinetics of interconnected allosteric interactions between FFAR4 and naturally occurring fatty acids

The long-chain fatty acid receptor FFAR4 is the main G-protein-coupled receptor in the body for detecting long-chain fatty acids. It has been shown that Arg99 may be an important residue for fatty acid recognition and for the activation of hFFAR4, though direct evidence is still lacking. In this study, Arg99 on hFFAR4 was substituted with leucine by genetic manipulation, and a double-layer gold nanoparticle biosensor based on hFFAR4 (Arg99 → Leu) was constructed. The interconnected allosteric interaction between 11 naturally occurring fatty acid ligands and the receptor was determined. The results showed that Arg99 is the key residue on hFFAR4 for the recognition of the carboxyl group on fatty acids. This study offered direct quantitative evidence for the role played by different residues in receptor-ligand recognition and interconnected allosterism, providing a new approach for investigating the mechanisms and kinetics of interconnected receptor-ligand allosterism.

Metabolite G-Protein Coupled Receptors in Cardio-Metabolic Diseases

G protein-coupled receptors (GPCRs) have originally been described as a family of receptors activated by hormones, neurotransmitters, and other mediators. However, in recent years GPCRs have shown to bind endogenous metabolites, which serve functions other than as signaling mediators. These receptors respond to fatty acids, mono- and disaccharides, amino acids, or various intermediates and products of metabolism, including ketone bodies, lactate, succinate, or bile acids. Given that many of these metabolic processes are dysregulated under pathological conditions, including diabetes, dyslipidemia, and obesity, receptors of endogenous metabolites have also been recognized as potential drug targets to prevent and/or treat metabolic and cardiovascular diseases. This review describes G protein-coupled receptors activated by endogenous metabolites and summarizes their physiological, pathophysiological, and potential pharmacological roles.

Identification of Immune-Cell-Related Prognostic Biomarkers of Esophageal Squamous Cell Carcinoma Based on Tumor Microenvironment

Background

Esophageal squamous cell carcinoma (ESCC) is one of the most fatal cancers in the world. The 5-year survival rate of ESCC is <30%. However, few biomarkers can accurately predict the prognosis of patients with ESCC. We aimed to identify potential survival-associated biomarkers for ESCC to improve its poor prognosis.

Methods

ImmuneAI analysis was first used to access the immune cell abundance of ESCC. Then, ESTIMATE analysis was performed to explore the tumor microenvironment (TME), and differential analysis was used for the selection of immune-related differentially expressed genes (DEGs). Weighted gene coexpression network analysis (WGCNA) was used for selecting the candidate DEGs. Least absolute shrinkage and selection operator (LASSO) Cox regression was used to build the immune-cell-associated prognostic model (ICPM). Kaplan–Meier curve of survival analysis was performed to evaluate the efficacy of the ICPM.

Results

Based on the ESTIMATE and ImmuneAI analysis, we obtained 24 immune cells’ abundance. Next, we identified six coexpression module that was associated with the abundance. Then, LASSO regression models were constructed by selecting the genes in the module that is most relevant to immune cells. Two test dataset was used to testify the model, and we finally, obtained a seven-genes survival model that performed an excellent prognostic efficacy.

Conclusion

In the current study, we filtered seven key genes that may be potential prognostic biomarkers of ESCC, and they may be used as new factors to improve the prognosis of cancer.