Lipopolysaccharide inhibits GPR120 expression in macrophages via Toll-like receptor 4 and p38 MAPK activation

The Effects and Mechanisms of n-3 and n-6 Polyunsaturated Fatty Acids in the Central Nervous System

The brain is rich in fatty acids (FAs), with polyunsaturated fatty acids (PUFAs), such as docosahexaenoic acid (C22:6n-3, DHA) and arachidonic acid (C20:4n-6, ARA), and the former predominantly stored in the form of phosphatidylcholine, phosphatidyl ethanolamine (PE, diacyl and plasma phospholipid proform), and phosphatidylserine (PS), while the latter is mainly found in ethanolamine phosphoglycerides (EPG) and contributes to constitute most of phosphoglycerides. When required by the body, PUFAs are liberated from membrane phospholipids (either directly or via their metabolites, which are generated by a series of enzymatic reactions) to participate in various cerebral physiological processes. PUFAs and their derivatives play crucial roles in modulating numerous bodily functions, including neuronal signal transmission, neurogenesis, neuroinflammation, and glucose uptake in the brain, thereby sustaining fundamental brain function. Although PUFAs have been implicated in a spectrum of neurological disorders, including acute brain injury (TBI), multiple sclerosis (MS), and neurodegenerative diseases, their role in conditions such as depression, Alzheimer's disease (AD), and Parkinson's disease (PD) is particularly noteworthy. These disorders are closely linked to critical brain functions, including cognition, memory, and inflammatory processes. Given the substantial body of research elucidating the involvement of PUFAs in the pathogenesis and progression of these diseases, this review will specifically concentrate on their impact within these contexts.

Biased agonism at free-fatty acid receptor-4 (FFA4/GPR120)

Free-fatty acid receptor-4 (FFA4), previously known as GPR120, is a G protein-coupled receptor (GPCR) activated by medium-to-long chain free fatty acids (FFAs), including saturated, monounsaturated, and polyunsaturated fats, many of which (e.g., omega-3 fatty acids) are critical contributors to human health and disease. FFA4 is widely expressed across human tissues, and its activation supports a range of physiological functions, including the release of gastrointestinal incretin hormones like glucagon-like peptide-1 (GLP-1), regulation of pancreatic hormone secretion, peripheral glucose uptake, adipose regulation, and anti-inflammatory responses in macrophages. Due to its pivotal role in energy metabolism and inflammation, FFA4 has emerged as a major target in drug discovery. Historically, FFA4 signaling was linked to the Gαq/11 family of intracellular heterotrimeric G proteins, which mediate its GLP-1 releasing effects. However, emerging evidence indicates that FFA4 can signal through other Gα proteins in various cellular contexts. Notably, its anti-inflammatory effects are also dependent on interactions with β-arrestin proteins, further broadening the receptor's signaling versatility. This review explores the concept of biased agonism at FFA4, emphasizing how this receptor selectively signals through distinct transduction pathways, including Gα proteins and β-arrestins. We also examine the key structural elements of FFA4 that govern its interactions with different signaling partners, the elucidation of which has laid the groundwork for the development of biased agonists aimed at selectively modulating these FFA4-mediated pathways for therapeutic application.

Long Chain Fatty Acids as Modulators of Immune Cells Function: Contribution of FFA1 and FFA4 Receptors

Long-chain fatty acids are molecules that act as metabolic intermediates and constituents of membranes; however, their novel role as signaling molecules in immune function has also been demonstrated. The presence of free fatty acid (FFA) receptors on immune cells has contributed to the understanding of this new role of long-chain fatty acids (LCFAs) in immune function, showing their role as anti-inflammatory or pro-inflammatory molecules and elucidating their intracellular mechanisms. The FFA1 and FFA4 receptors, also known as GPR40 and GPR120, respectively, have been described in macrophages and neutrophils, two key cells mediating innate immune response. Ligands of the FFA1 and FFA4 receptors induce the release of a myriad of cytokines through well-defined intracellular signaling pathways. In this review, we discuss the cellular responses and intracellular mechanisms activated by LCFAs, such as oleic acid, linoleic acid, palmitic acid, docosahexaenoic acid (DHA), and eicosapentaenoic acid (EPA), in T-cells, macrophages, and neutrophils, as well as the role of the FFA1 and FFA4 receptors in immune cells.

Development of Free Fatty Acid Receptor 4 (FFA4/GPR120) Agonists in Health Science

Till the 21^st century, fatty acids were considered as merely building blocks for triglycerides, phospholipids, or cholesteryl esters. However, the discovery of G protein-coupled receptors (GPCRs) for free fatty acids at the beginning of the 21^st century challenged that idea and paved way for a new field of research, merged into the field of receptor pharmacology for intercellular lipid mediators. Among the GPCRs for free fatty acids, free fatty acid receptor 4 (FFA4, also known as GPR120) recognizes long-chain polyunsaturated fatty acids such as DHA and EPA. It is significant in drug discovery because it regulates obesity-induced metaflammation and GLP-1 secretion. Our study reviews information on newly developed FFA4 agonists and their application in pathophysiologic studies and drug discovery. It also offers a potency comparison of the FFA4 agonists in an AP-TGF-α shedding assay.

Differential DNA methylation profile in infants born small-for-gestational-age: association with markers of adiposity and insulin resistance from birth to age 24 months

INTRODUCTION

Prenatal growth restraint followed by rapid postnatal weight gain increases lifelong diabetes risk. Epigenetic dysregulation in critical windows could exert long-term effects on metabolism and confer such risk.

RESEARCH DESIGN AND METHODS

We conducted a genome-wide DNA methylation profiling in peripheral blood from infants born appropriate-for-gestational-age (AGA, n=30) or small-for-gestational-age (SGA, n=21, with postnatal catch-up) at age 12 months, to identify new genes that may predispose to metabolic dysfunction. Candidate genes were validated by bisulfite pyrosequencing in the entire cohort. All infants were followed since birth; cord blood methylation profiling was previously reported. Endocrine-metabolic variables and body composition (dual-energy X-ray absorptiometry) were assessed at birth and at 12 and 24 months.

RESULTS

GPR120 (cg14582356, cg01272400, cg23654127, cg03629447), NKX6.1 (cg22598426, cg07688460, cg17444738, cg12076463, cg10457539), CPT1A (cg14073497, cg00941258, cg12778395) and IGFBP 4 (cg15471812) genes were hypermethylated (GPR120, NKX6.1 were also hypermethylated in cord blood), whereas CHGA (cg13332653, cg15480367, cg05700406), FABP5 (cg00696973, cg10563714, cg16128701), CTRP1 (cg19231170, cg19472078, cg0164309, cg07162665, cg17758081, cg18996910, cg06709009), GAS6 (N/A), ONECUT1 (cg14217069, cg02061705, cg26158897, cg06657050, cg15446043) and SLC2A8 (cg20758474, cg19021975, cg11312566, cg12281690, cg04016166, cg03804985) genes were hypomethylated in SGA infants. These genes were related to β-cell development and function, inflammation, and glucose and lipid metabolism and associated with body mass index, body composition, and markers of insulin resistance at 12 and 24 months.

CONCLUSION

In conclusion, at 12 months, abnormal methylation of GPR120 and NKX6.1 persists and new epigenetic marks further involved in adipogenesis and energy homeostasis arise in SGA infants. These abnormalities may contribute to metabolic dysfunction and diabetes risk later in life.

Characterization of Free Fatty Acid Receptor 4 and Its Involvement in Nutritional Control and Immune Response in Pacific Oysters (Crassostrea gigas)

Free fatty acid receptor 4 (FFAR4) has various physiological functions, including energy regulation and immunological homeostasis. We examined the only FFAR4 homologue in the Pacific oyster Crassostrea gigas (CgFFAR4), which functions as a sensor of long-chain fatty acids. CgFFAR4 is 1098 bp long and contains a seven-transmembrane G protein-coupled receptor domain. CgFFAR4 expression was high in the hepatopancreas, but it was downregulated after fasting, indicating that it plays an essential role in food digestion. Lipopolysaccharide stimulation downregulated CgFFAR4 level, probably as an immune response of the animal. Reduced glycogen level alongside decreased insulin receptor, insulin receptor substrate, and C. gigas glycogen synthase transcription levels after CgFFAR4 knockdown revealed that CgFFAR4 was involved in the regulation of fatty acid and glycogen levels via the insulin pathway. Accordingly, this is the first study on an invertebrate FFAR and provides new insights into the role of this receptor in immune response and nutritional control.

The GPR120 Agonist TUG-891 Inhibits the Motility and Phagocytosis of Mouse Alveolar Macrophages

Movement and phagocytosis characterize the fundamental actions of macrophages. Although it is known that the free fatty acid receptor GPR120 is expressed in macrophages and regulates cytokine expression to exert anti-inflammatory activities, the effects of GPR120 activation on the motility and phagocytosis of macrophages are not clear. In this study, mouse alveolar macrophages (AM) were stimulated with the GPR120 agonist TUG-891, and the changes in cell motility, intracellular Ca²⁺ concentration ([Ca²⁺]i), and the ability of phagocytosis were measured. Mouse AM in controls exhibited active movement in vitro, and TUG-891 significantly restrained AM movement. Meanwhile, TUG-891 stimulated a quick increase in [Ca²⁺]i in AM, which was blocked separately by the Gq protein inhibitor YM-254890, the phospholipase C (PLC) inhibitor U73122, or depletion of endoplasmic reticulum (ER) Ca²⁺ store by thapsigargin. The inhibition of AM movement by TUG-891 was eliminated by YM-254890, U73122, thapsigargin, and chelation of cytosolic Ca²⁺ by BAPTA. Moreover, TUG-891 inhibited AM phagocytosis of fluorescent microspheres, which was also blocked by YM-254890, U73122, thapsigargin, and BAPTA. In conclusion, GPR120 activation in mouse AM increases [Ca²⁺]i but inhibits the motility and phagocytosis via Gq protein/PLC-mediated Ca²⁺ release from ER Ca²⁺ store.