Chemogenetic Approaches to Explore the Functions of Free Fatty Acid Receptor 2

Building on the development and use of DREADD forms of muscarinic acetylcholine receptors a conceptually similar form of FFA2 has been produced. Because the described FFA2 antagonists have high affinity at human FFA2 but are essentially inactive at mouse and rat orthologues of the receptor, the FFA2-DREADD was generated from human FFA2. This FFA2-DREADD is activated by sorbic acid but not by SCFAs and blocked by FFA2 antagonists. Sorbic acid is a full agonist at the FFA2-DREADD and signalling mechanisms are identical to those produced by SCFAs at wild-type FFA2. Generation of a ‘knock-in’ transgenic mouse line in which the FFA2-DREADD replaced mouse FFA2 has allowed analysis of specific effects of FFA2 in both in vivo and ex vivo settings. Additional novel and selective activators of the FFA2-DREADD have been identified. Short-chain fatty acids are generated in large amounts by the intestinal microbiota. They activate both the closely related G protein-coupled receptors free fatty acid receptor 2 (FFA2) and free fatty acid receptor 3 (FFA3) that are considered therapeutic targets in diseases of immuno-metabolism. Limited and species-selective small-molecule pharmacology has restricted our understanding of the distinct roles of these receptors. Replacement of mouse FFA2 with a designer receptor exclusively activated by designer drug form of human FFA2 (hFFA2-DREADD) has allowed definition of specific roles of FFA2 in pharmacological and physiological studies conducted both ex vivo and in vivo, whilst overlay of murine disease models offers opportunities for therapeutic validation prior to human studies. Similar approaches can potentially be used to define roles of other poorly characterised receptors. Short-chain fatty acids are generated in large amounts by the intestinal microbiota. They activate both the closely related G protein-coupled receptors free fatty acid receptor 2 (FFA2) and free fatty acid receptor 3 (FFA3) that are considered therapeutic targets in diseases of immuno-metabolism. Limited and species-selective small-molecule pharmacology has restricted our understanding of the distinct roles of these receptors. Replacement of mouse FFA2 with a designer receptor exclusively activated by designer drug form of human FFA2 (hFFA2-DREADD) has allowed definition of specific roles of FFA2 in pharmacological and physiological studies conducted both ex vivo and in vivo, whilst overlay of murine disease models offers opportunities for therapeutic validation prior to human studies. Similar approaches can potentially be used to define roles of other poorly characterised receptors. a chemical species that binds to a receptor and activates it, eliciting a biological response. a chemical species that binds to a receptor, preventing activation by an agonist. a G protein-coupled receptor in which alteration of one of more amino acids in the orthosteric binding pocket results in reduction or elimination of the potency and binding of the endogenous agonist and, in parallel, enhancement of potency (usually from a negligible level) to one or more synthetic small molecules. a DNA sequence incorporated into a cDNA or DNA such that when transcribed and translated, the encoded protein has an additional amino acid sequence that can be easily detected, usually with one or more highly characterised antibodies. a member of the group of GPCRs that responds to short-chain fatty acids including acetate and propionate. a further member of the group of GPCRs that responds to short-chain fatty acids. an incretin (able to promote the release of insulin) hormone produced and released from subsets of enteroendocrine cells in the lower gut in response to stimulation by various mediators including SCFAs. integral membrane protein able to transmit a signal across the cell membrane in response to an external stimulus, to activate (usually) heterotrimeric guanine nucleotide-binding proteins (G proteins). It is characterised by a conserved structure comprising seven helical membrane-spanning domains, an extracellular N terminus, three external loops, three internal loops, and an internal C-terminal domain. Subdivided into classes based upon structural relatedness. in this context an epitope tag sequence that encodes the amino acid sequence Tyr-Pro-Tyr-Asp-Val-Pro-Asp-Tyr-Ala. ligands that are able to only effect a subset of signalling pathways that are controlled by the endogenous agonist(s) of the receptor in question. a family of five related GPCRs whose endogenous ligand is acetylcholine. an effect of a pharmacological ligand that is produced by means other than interacting with the protein or proteins that it is best understood to regulate. an effect of a pharmacological ligand that is produced by interaction with the protein that the ligand is best understood to be able to regulate. a further enteroendocrine hormone released in the lower gut in response to stimulation by various mediators including SCFAs. the concept that an allosteric ligand will differ in the extent of co-operativity it is able to generate when using different orthosteric agonists. an older and now less used term that is synonymous with DREADD. a group of molecules containing a carboxylic acid and one and five carbon atoms.