Metabolic signaling of ceramides through the FPR2 receptor inhibits adipocyte thermogenesis.
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| Title: | Metabolic signaling of ceramides through the FPR2 receptor inhibits adipocyte thermogenesis. |
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| Authors: | Lin, Hui, Ma, Chuanshun, Cai, Kui, Guo, Lulu, Wang, Xuemei, Lv, Lin, Zhang, Chao, Lin, Jun, Zhang, Daolai, Ye, Chuan, Wang, Tengwei, Huang, Shenming, Han, Jifei, Zhang, Zihao, Gao, Junyan, Zhang, Mingxiang, Pu, Zhao, Li, Fengyang, Guo, Yongyuan, Zhou, Xiaojun |
| Source: | Science. 5/1/2025, Vol. 388 Issue 6746, p1-19. 19p. |
| Subjects: | Ceramides, Fat cells, Body temperature regulation, G protein coupled receptors, Electron microscopy |
| Abstract: | Ceramides play a central role in human health and disease, yet their role as systemic signaling molecules remain poorly understood. In this work, we identify formyl peptide receptor 2 (FPR2) as a membrane receptor that specifically binds long-chain ceramides (C14 to C20). In brown and beige adipocytes, C16:0 ceramide binding to FPR2 inhibits thermogenesis through Gi cyclic adenosine monophosphate signaling pathways, an effect that is reversed in the absence of FPR2. We present three cryo–electron microscopy structures of FPR2 in complex with Gi trimers bound to C16:0, C18:0, and C20:0 ceramides. The hydrophobic tails are deeply embedded in the orthosteric ligand pocket, which has a limited amount of plasticity. Modification of the ceramide binding motif in closely related receptors, such as FPR1 or FPR3, converts them from inactive to active ceramide receptors. Our findings provide a structural basis for adipocyte thermogenesis mediated by FPR2. Editor's summary: Lipids are crucial molecules for membrane structure and energy storage, but they are also key signaling molecules within and between cells. Lin et al. investigated the cell surface G protein–coupled receptor FPR2, which is expressed highly in adipocytes, and found that it responds specifically to ceramide lipids with a saturated acyl chain and a length of 20 or fewer carbons. Experiments in mice showed that such lipids are inhibitory for thermogenesis in brown adipose tissue and can lead to detrimental metabolic outcomes in mice fed a high-fat diet. The authors also determined cryo–electron microscopy structures of FPR2 bound to ceramides that revealed the molecular basis for lipid recognition. —Michael A. Funk INTRODUCTION: Ceramides, comprising a conserved sphingosine base amide linked to a fatty acid chain of variable carbon lengths, are essential cell membrane lipids and metabolic messengers. The increased endogenous ceramides levels are associated with pathological development in various chronic diseases, including but not limited to type 2 diabetes mellitus, obesity, hepatic steatosis, and autoimmune diseases. Historically, ceramide research has focused predominantly on intracellular mechanisms, leaving receptor-mediated transmembrane signaling less explored. RATIONALE: Recent studies have identified ceramide as a key mediator of interorgan effects that may involve transmembrane signaling. However, whether there are specific membrane receptors that sense ceramides is unknown. Moreover, the signaling mechanisms by which ceramides regulate cells in target tissues, such as adipocytes, remain unclear. We observed that the exogenous application of C16:0 ceramide inhibited fat thermogenesis and decreased intracellular cyclic adenosine monophosphate (cAMP) levels. We therefore hypothesized that a Gi-coupled receptor mediates the acute effects of ceramide in adipose tissue. Unbiased screening of receptors associated with Gi signaling was performed to identify ceramide receptors in adipocytes. RESULTS: By screening the top 60 G protein–coupled receptors (GPCRs) expressed in adipocytes, we determined that formyl peptide receptor 2 (FPR2), a class A GPCR, is the Gi-coupled ceramide receptor in adipocytes. Fluorescein arsenical hairpin–bioluminescence resonance energy transfer (FlAsH-BRET) sensor assays, activity measurements, and radioligand binding assays revealed a direct interaction between ceramides and FPR2. Further functional characterization of FPR2 deficiency in adipocyte-specific Fpr2–conditional knockout mice indicated that the ceramide-FPR2-Gi signaling axis plays a central role in the ceramide-induced reduction in adipose thermogenesis. Additionally, FPR2 recognizes only specific types of ceramides, and receptors that are phylogenetically related to FPR2, such as FPR1 or FPR3, are not activated by ceramides. To reveal the underlying mechanisms, we solved the structures of the C16:0-FPR2-Gi1, C18:0-FPR2-Gi1, and C20:0-FPR2-Gi1 complexes through cryo–electron microscopy (cryo-EM). The structures revealed that ceramides bind within the orthosteric ligand pocket of FPR2. The H1023.29F178ECL2 hydrophobic motif and the E89ECL1T177ECL2D2817.32 polar motif of FPR2 were found to be essential for the recognition of the C=C double bond of the fatty acid chain and the carboxylated sphingoid group of ceramides. Most notably, the back mutants FPR1-G89ECL1E and FPR3-A1985.35L-H2055.42R converted these two receptors from inactive to active in response to ceramide stimulation. CONCLUSION: Our results revealed that FPR2, a Gi-coupled ceramide receptor, mediates the inhibitory effect on adipocyte thermogenesis by sensing ceramide and decreasing intracellular cAMP levels. Structural analysis revealed key features of FPR2, including a hydrophobic ligand-binding pocket and polar interaction motifs, that enable the selective recognition of ceramides, particularly C16:0, C18:0, and C20:0, while excluding very-long-chain or unsaturated ceramides. The identification of FPR2 as a selective ceramide receptor not only provides a foundation for developing targeted therapies for obesity and related metabolic disorders associated with elevated plasma ceramide levels but also suggests that the interaction of ceramides with membrane receptors may play important roles in ceramide biology. Membrane receptor FPR2 senses ceramides to regulate adipogenic thermogenesis.: Ceramide-activated FPR2 in adipocytes stimulates Gi signaling and inhibits adipose thermogenesis. The adipocyte-specific Fpr2–conditional knockout mice abolish the inhibitory effects of ceramides. Structural analysis through cryo-EM revealed that FPR2 specifically recognized the C=C double bond and the carboxylated sphingoid group of the ceramide through the H1023.29F178ECL2 and E89ECL1T177ECL2D2817.32 motifs, respectively. Single-letter abbreviations for the amino acid residues referenced throughout this study are as follows: H, His; F, Phe; E, Glu; T, Thr; D, Asp; A, Ala; L, Leu; R, Arg; G, Gly. [ABSTRACT FROM AUTHOR] |
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| Database: | Psychology and Behavioral Sciences Collection |
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| Abstract: | Ceramides play a central role in human health and disease, yet their role as systemic signaling molecules remain poorly understood. In this work, we identify formyl peptide receptor 2 (FPR2) as a membrane receptor that specifically binds long-chain ceramides (C14 to C20). In brown and beige adipocytes, C16:0 ceramide binding to FPR2 inhibits thermogenesis through Gi cyclic adenosine monophosphate signaling pathways, an effect that is reversed in the absence of FPR2. We present three cryo–electron microscopy structures of FPR2 in complex with Gi trimers bound to C16:0, C18:0, and C20:0 ceramides. The hydrophobic tails are deeply embedded in the orthosteric ligand pocket, which has a limited amount of plasticity. Modification of the ceramide binding motif in closely related receptors, such as FPR1 or FPR3, converts them from inactive to active ceramide receptors. Our findings provide a structural basis for adipocyte thermogenesis mediated by FPR2. Editor's summary: Lipids are crucial molecules for membrane structure and energy storage, but they are also key signaling molecules within and between cells. Lin et al. investigated the cell surface G protein–coupled receptor FPR2, which is expressed highly in adipocytes, and found that it responds specifically to ceramide lipids with a saturated acyl chain and a length of 20 or fewer carbons. Experiments in mice showed that such lipids are inhibitory for thermogenesis in brown adipose tissue and can lead to detrimental metabolic outcomes in mice fed a high-fat diet. The authors also determined cryo–electron microscopy structures of FPR2 bound to ceramides that revealed the molecular basis for lipid recognition. —Michael A. Funk INTRODUCTION: Ceramides, comprising a conserved sphingosine base amide linked to a fatty acid chain of variable carbon lengths, are essential cell membrane lipids and metabolic messengers. The increased endogenous ceramides levels are associated with pathological development in various chronic diseases, including but not limited to type 2 diabetes mellitus, obesity, hepatic steatosis, and autoimmune diseases. Historically, ceramide research has focused predominantly on intracellular mechanisms, leaving receptor-mediated transmembrane signaling less explored. RATIONALE: Recent studies have identified ceramide as a key mediator of interorgan effects that may involve transmembrane signaling. However, whether there are specific membrane receptors that sense ceramides is unknown. Moreover, the signaling mechanisms by which ceramides regulate cells in target tissues, such as adipocytes, remain unclear. We observed that the exogenous application of C16:0 ceramide inhibited fat thermogenesis and decreased intracellular cyclic adenosine monophosphate (cAMP) levels. We therefore hypothesized that a Gi-coupled receptor mediates the acute effects of ceramide in adipose tissue. Unbiased screening of receptors associated with Gi signaling was performed to identify ceramide receptors in adipocytes. RESULTS: By screening the top 60 G protein–coupled receptors (GPCRs) expressed in adipocytes, we determined that formyl peptide receptor 2 (FPR2), a class A GPCR, is the Gi-coupled ceramide receptor in adipocytes. Fluorescein arsenical hairpin–bioluminescence resonance energy transfer (FlAsH-BRET) sensor assays, activity measurements, and radioligand binding assays revealed a direct interaction between ceramides and FPR2. Further functional characterization of FPR2 deficiency in adipocyte-specific Fpr2–conditional knockout mice indicated that the ceramide-FPR2-Gi signaling axis plays a central role in the ceramide-induced reduction in adipose thermogenesis. Additionally, FPR2 recognizes only specific types of ceramides, and receptors that are phylogenetically related to FPR2, such as FPR1 or FPR3, are not activated by ceramides. To reveal the underlying mechanisms, we solved the structures of the C16:0-FPR2-Gi1, C18:0-FPR2-Gi1, and C20:0-FPR2-Gi1 complexes through cryo–electron microscopy (cryo-EM). The structures revealed that ceramides bind within the orthosteric ligand pocket of FPR2. The H1023.29F178ECL2 hydrophobic motif and the E89ECL1T177ECL2D2817.32 polar motif of FPR2 were found to be essential for the recognition of the C=C double bond of the fatty acid chain and the carboxylated sphingoid group of ceramides. Most notably, the back mutants FPR1-G89ECL1E and FPR3-A1985.35L-H2055.42R converted these two receptors from inactive to active in response to ceramide stimulation. CONCLUSION: Our results revealed that FPR2, a Gi-coupled ceramide receptor, mediates the inhibitory effect on adipocyte thermogenesis by sensing ceramide and decreasing intracellular cAMP levels. Structural analysis revealed key features of FPR2, including a hydrophobic ligand-binding pocket and polar interaction motifs, that enable the selective recognition of ceramides, particularly C16:0, C18:0, and C20:0, while excluding very-long-chain or unsaturated ceramides. The identification of FPR2 as a selective ceramide receptor not only provides a foundation for developing targeted therapies for obesity and related metabolic disorders associated with elevated plasma ceramide levels but also suggests that the interaction of ceramides with membrane receptors may play important roles in ceramide biology. Membrane receptor FPR2 senses ceramides to regulate adipogenic thermogenesis.: Ceramide-activated FPR2 in adipocytes stimulates Gi signaling and inhibits adipose thermogenesis. The adipocyte-specific Fpr2–conditional knockout mice abolish the inhibitory effects of ceramides. Structural analysis through cryo-EM revealed that FPR2 specifically recognized the C=C double bond and the carboxylated sphingoid group of the ceramide through the H1023.29F178ECL2 and E89ECL1T177ECL2D2817.32 motifs, respectively. Single-letter abbreviations for the amino acid residues referenced throughout this study are as follows: H, His; F, Phe; E, Glu; T, Thr; D, Asp; A, Ala; L, Leu; R, Arg; G, Gly. [ABSTRACT FROM AUTHOR] |
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| ISSN: | 00368075 |
| DOI: | 10.1126/science.ado4188 |
