A peripheral lipid sensor GPR120 remotely contributes to suppression of PGD2-microglia-provoked neuroinflammation and neurodegeneration in the mouse hippocampus

Background Neuroinflammation is a key pathological component of neurodegenerative disease and is characterized by microglial activation and the secretion of proinflammatory mediators. We previously reported that a surge in prostaglandin D2 (PGD2) production and PGD2-induced microglial activation could provoke neuroinflammation. We also reported that a lipid sensor GPR120 (free fatty acid receptor 4), which is expressed in intestine, could be activated by polyunsaturated fatty acids (PUFA), thereby mediating secretion of glucagon-like peptide-1 (GLP-1). Dysfunction of GPR120 results in obesity in both mice and humans. Methods To reveal the relationship between PGD2-microglia-provoked neuroinflammation and intestinal PUFA/GPR120 signaling, we investigated neuroinflammation and neuronal function with gene and protein expression, histological, and behavioral analysis in GPR120 knockout (KO) mice. Results In the current study, we discovered notable neuroinflammation (increased PGD2 production and microglial activation) and neurodegeneration (declines in neurogenesis, hippocampal volume, and cognitive function) in GPR120 KO mice. We also found that Hematopoietic–prostaglandin D synthase (H-PGDS) was expressed in microglia, microglia were activated by PGD2, H-PGDS expression was upregulated in GPR120 KO hippocampus, and inhibition of PGD2 production attenuated this neuroinflammation. GPR120 KO mice exhibited reduced intestinal, plasma, and intracerebral GLP-1 contents. Peripheral administration of a GLP-1 analogue, liraglutide, reduced PGD2-microglia-provoked neuroinflammation and further neurodegeneration in GPR120 KO mice. Conclusions Our results suggest that neurological phenotypes in GPR120 KO mice are probably caused by dysfunction of intestinal GPR120. These observations raise the possibility that intestinal GLP-1 secretion, stimulated by intestinal GPR120, may remotely contributed to suppress PGD2-microglia-provoked neuroinflammation in the hippocampus.

Activation of Microbiota Sensing – Free Fatty Acid Receptor 2 Signaling Ameliorates Amyloid-β Induced Neurotoxicity by Modulating Proteolysis-Senescence Axis

Multiple emerging evidence indicates that the gut microbiota contributes to the pathology of Alzheimer’s disease (AD)—a debilitating public health problem in older adults. However, strategies to beneficially modulate gut microbiota and its sensing signaling pathways remain largely unknown. Here, we screened, validated, and established the agonists of free fatty acid receptor 2 (FFAR2) signaling, which senses beneficial signals from short chain fatty acids (SCFAs) produced by microbiota. The abundance of SCFAs, is often low in the gut of older adults with AD. We demonstrated that inhibition of FFAR2 signaling increases amyloid-beta (Aβ) stimulated neuronal toxicity. Thus, we screened FFAR2 agonists using an in-silico library of more than 144,000 natural compounds and selected 15 of them based on binding with FFAR2-agonist active sites. Fenchol (a natural compound commonly present in basil) was recognized as a potential FFAR2 stimulator in neuronal cells and demonstrated protective effects against Aβ-stimulated neurodegeneration in an FFAR2-dependent manner. In addition, Fenchol reduced AD-like phenotypes, such as Aβ-accumulation, and impaired chemotaxis behavior in Caenorhabditis (C.) elegans and mice models, by increasing Aβ-clearance via the promotion of proteolysis and reduced senescence in neuronal cells. These results suggest that the inhibition of FFAR2 signaling promotes Aβ-induced neurodegeneration, while the activation of FFAR2 by Fenchol ameliorates these abnormalities by promoting proteolytic Aβ-clearance and reducing cellular senescence. Thus, stimulation of FFAR2 signaling by Fenchol as a natural compound can be a therapeutic approach to ameliorate AD pathology.

Commensal microbe-derived acetate suppresses NAFLD/NASH development via hepatic FFAR2 signalling in mice

Background Non-alcoholic liver disease (NAFLD) is the hepatic manifestation of metabolic syndrome, and it can progress to non-alcoholic steatohepatitis (NASH). Alterations in the gut microbiome have been implicated in the development of NAFLD/NASH, although the underlying mechanisms remain unclear. Results We found that the consumption of the prebiotic inulin markedly ameliorated the phenotype of NAFLD/NASH, including hepatic steatosis and fibrosis, in mice. Inulin consumption resulted in global changes in the gut microbiome, including concomitant enrichment of the genera Bacteroides and Blautia, and increased concentrations of short-chain fatty acids, particularly acetate, in the gut lumen and portal blood. The consumption of acetate-releasing resistant starch protected against NAFLD development. Colonisation by Bacteroides acidifaciens and Blautia producta in germ-free mice resulted in synergetic effects on acetate production from inulin. Furthermore, the absence of free fatty acid receptor 2 (FFAR2), an acetate receptor, abolished the protective effect of inulin, as indicated by the more severe liver hypertrophy, hypercholesterolaemia and inflammation. These effects can be attributed to an exacerbation of insulin resistance in the liver, but not in muscle or adipose tissue. Conclusion These findings demonstrated that the commensal microbiome–acetate–FFAR2 molecular circuit improves insulin sensitivity in the liver and prevents the development of NAFLD/NASH.

Abstract P389: Free Fatty Acid Receptor 4 Is Necessary For An Adaptive Response Following Heart Failure Induced By Metabolic Syndrome In Mice

Non-resolving inflammation is central to the pathogenesis of heart failure (HF). Heart failure preserved ejection fraction (HFpEF) is a type of HF that is particularly associated with inflammation provoked by metabolic syndrome (MetS). The G-protein coupled receptor, free fatty acid receptor 4 (Ffar4), is a receptor for medium and long chain fatty acids (FA) that regulates metabolism and attenuates inflammation. Ffar4 is expressed in the human heart, and downregulated in heart failure. Furthermore, polymorphisms in Ffar4 have been associated with eccentric remodeling in a patient cohort. Previously, Ffar4 was shown to protect the heart from pathologic stress by attenuating oxidative stress in a mouse model of pressure overload. Here, we tested the hypothesis that Ffar4 would attenuate the development of heart failure using a mouse model of MetS-induced HFpEF. Metabolic syndrome was induced in mice by feeding a high-fat, high-sucrose diet (42% fat, 30% sucrose) to produce obesity and delivering the nitric oxide synthase inhibitor, L-NAME, in the drinking water to induce hypertension. The combined intervention (referred to as HFpEF diet) resulted in mice developing excessive adiposity, glucose intolerance (in males only), and mild hypertension. After 20 weeks on the HFpEF diet, both male and female WT mice, developed diastolic dysfunction (increased E/A and E/e’) and preserved ejection fraction (EF), consistent with clinical HFpEF. In Ffar4KO male mice HFpEF diet induced a greater degree of diastolic dysfunction compared to WT mice, despite equivalent metabolic parameters. Female Ffar4KO mice fed the HFpEF diet had a greater increase in weight gain and adiposity compared to WT female mice. Surprisingly, diastolic function was equivalent between WT and FFAR4KO female mice, suggesting a sex-based difference in FFAR4 cardioprotection. Our data show that Ffar4 attenuates HFpEF secondary to MetS.