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Frontiers in Immunology 2023Macrophages are essential for the proper inflammatory and reparative processes that lead to regeneration of skeletal muscle after injury. Recent studies have...
Macrophages are essential for the proper inflammatory and reparative processes that lead to regeneration of skeletal muscle after injury. Recent studies have demonstrated close links between the function of activated macrophages and their cellular metabolism. Sterol regulatory element-binding protein 1 (SREBP1) is a key regulator of lipid metabolism and has been shown to affect the activated states of macrophages. However, its role in tissue repair and regeneration is poorly understood. Here we show that systemic deletion of , encoding SREBP1, or macrophage-specific deletion of , encoding SREBP1a, delays resolution of inflammation and impairs skeletal muscle regeneration after injury. deficiency impairs mitochondrial function in macrophages and suppresses the accumulation of macrophages at sites of muscle injury. Lipidomic analyses showed the reduction of major phospholipid species in muscle myeloid cells. Moreover, diet supplementation with eicosapentaenoic acid restored the accumulation of macrophages and their mitochondrial gene expression and improved muscle regeneration. Collectively, our results demonstrate that SREBP1 in macrophages is essential for repair and regeneration of skeletal muscle after injury and suggest that SREBP1-mediated fatty acid metabolism and phospholipid remodeling are critical for proper macrophage function in tissue repair.
Topics: Macrophages; Muscle, Skeletal; Phospholipids; Regeneration; Sterol Regulatory Element Binding Protein 1; Animals; Mice
PubMed: 38259495
DOI: 10.3389/fimmu.2023.1251784 -
Biochimica Et Biophysica Acta.... Jul 2022Adenosine triphosphate-binding cassette transporter subfamily A member 7 (ABCA7) performs incompletely understood biochemical functions that affect pathogenesis of...
Adenosine triphosphate-binding cassette transporter subfamily A member 7 (ABCA7) performs incompletely understood biochemical functions that affect pathogenesis of Alzheimer's disease. ABCA7 is most similar in primary structure to ABCA1, the protein that mediates cell lipid efflux and formation of high-density lipoprotein (HDL). Lipid metabolic labeling/tracer efflux assays were employed to investigate lipid efflux in BHK-ABCA7(low expression), BHK-ABCA7(high expression) and BHK-ABCA1 cells. Shotgun lipid mass spectrometry was used to determine lipid composition of HDL synthesized by BHK-ABCA7 and BHK-ABCA1 cells. BHK-ABCA7(low) cells exhibited significant efflux only of choline-phospholipid and phosphatidylinositol. BHK-ABCA7(high) cells had significant cholesterol and choline-phospholipid efflux to apolipoprotein (apo) A-I, apo E, the 18A peptide, HDL, plasma and cerebrospinal fluid and significant efflux of sphingosine-lipid, serine-lipid (which is composed of phosphatidylserine and phosphatidylethanolamine in BHK cells) and phosphatidylinositol to apo A-I. In efflux assays to apo A-I, after adjustment to choline-phospholipid, ABCA7-mediated efflux removed ~4 times more serine-lipid and phosphatidylinositol than ABCA1-mediated efflux, while ABCA1-mediated efflux removed ~3 times more cholesterol than ABCA7-mediated efflux. Shotgun lipidomic analysis revealed that ABCA7-HDL had ~20 mol% less phosphatidylcholine and 3-5 times more serine-lipid and phosphatidylinositol than ABCA1-HDL, while ABCA1-HDL contained only ~6 mol% (or ~1.1 times) more cholesterol than ABCA7-HDL. The discrepancy between the tracer efflux assays and shotgun lipidomics with respect to cholesterol may be explained by an underestimate of ABCA7-mediated cholesterol efflux in the former approach. Overall, these results suggest that ABCA7 lacks specificity for phosphatidylcholine and releases significantly but not dramatically less cholesterol in comparison with ABCA1.
Topics: ATP-Binding Cassette Transporters; Apolipoprotein A-I; Cholesterol; Choline; Lipoproteins, HDL; Phosphatidylcholines; Phosphatidylinositols; Phospholipids; Serine
PubMed: 35381375
DOI: 10.1016/j.bbalip.2022.159157 -
Biochimica Et Biophysica Acta. Proteins... May 2019Alpha synuclein (αS) is a ~14 kDa intrinsically disordered protein. Decades of research have increased our knowledge on αS yet its physiological function remains... (Review)
Review
Alpha synuclein (αS) is a ~14 kDa intrinsically disordered protein. Decades of research have increased our knowledge on αS yet its physiological function remains largely elusive. The conversion of monomeric αS into oligomers and amyloid fibrils is believed to play a central role of the pathology of Parkinson's disease (PD). It is becoming increasingly clear that the interactions of αS with cellular membranes are important for both αS's functional and pathogenic actions. Therefore, understanding interactions of αS with membranes seems critical to uncover functional or pathological mechanisms. This review summarizes our current knowledge of how physicochemical properties of phospholipid membranes affect the binding and aggregation of αS species and gives an overview of how post-translational modifications and point mutations in αS affect phospholipid membrane binding and protein aggregation. We discuss the disruptive effects resulting from the interaction of αS aggregate species with membranes and highlight current approaches and hypotheses that seek to understand the pathogenic and/or protective role of αS in PD.
Topics: Amyloid; Animals; Cell Membrane; Humans; Lipid Bilayers; Parkinson Disease; Phospholipids; Protein Aggregation, Pathological; alpha-Synuclein
PubMed: 30315896
DOI: 10.1016/j.bbapap.2018.10.006 -
Biochemistry Dec 2021The G-protein-gated inwardly rectifying potassium channel 4 (Kir3.4) subunit forms functional tetramers. Previous studies have established that phosphatidylinositol...
The G-protein-gated inwardly rectifying potassium channel 4 (Kir3.4) subunit forms functional tetramers. Previous studies have established that phosphatidylinositol 4,5-bisphosphate (PI(4,5)P) is required for Kir3.4 function. However, the binding preferences of Kir3.4 for the headgroup and acyl chains of phosphorylated phosphatidylinositides (PIPs) and other lipids are not well understood. Here, the interactions between full-length, human Kir3.4 and lipids are characterized using native mass spectrometry (MS) in conjunction with a soluble fluorescent lipid-binding assay. Kir3.4 displays binding preferences for PIPs, and, in some cases, the degree of binding is influenced by the type of acyl chains. The interactions between Kir3.4 and PIPs are weaker in comparison to full-length, human Kir3.2. The binding of PI(4,5)P modified with a fluorophore to Kir3.2 can be enhanced by other lipids, such as phosphatidylcholine. Introduction of S143T, a mutation that enhances Kir3.4 activity, results in an overall reduction in the channel binding PIPs. In contrast, the D223N mutant of Kir3.4 that mimics the sodium-bound state exhibited stronger binding for PI(4,5)P, particularly for those with 18:0-20:4 acyl chains. Taken together, these results provide additional insight into the interaction between Kir3.4 and lipids that are important for channel function.
Topics: Amino Acid Substitution; Binding Sites; Binding, Competitive; Boron Compounds; Fluorescent Dyes; G Protein-Coupled Inwardly-Rectifying Potassium Channels; Humans; Models, Molecular; Phosphatidylinositols; Phospholipids; Point Mutation; Protein Binding; Protein Structure, Quaternary; Recombinant Proteins; Spectrometry, Mass, Electrospray Ionization
PubMed: 34846128
DOI: 10.1021/acs.biochem.1c00615 -
Current Eye Research Feb 2021: The amount of membrane-bound α-crystallin increases significantly with age and cataract formation, accompanied by a corresponding decline in the level of...
: The amount of membrane-bound α-crystallin increases significantly with age and cataract formation, accompanied by a corresponding decline in the level of α-crystallin in the lens cytoplasm. The purpose of this research is to evaluate the binding affinity of α-crystallin to the phospholipid membranes as well as the physical properties of the membranes after α-crystallin binding. : The continuous wave and saturation recovery electron paramagnetic resonance (EPR) methods were used to obtain the information about the binding affinity and the physical properties of the membrane. In this approach, the cholesterol analog spin label CSL was incorporated in the membrane and the binding of α-crystallin to the membrane was monitored by this spin label. Small uni-lamellar vesicles were prepared from 1-palmitoyl-2-oleoylphosphatidylcholine (POPC) with 1% of CSL. The measured membrane properties included the mobility parameter, fluidity, and the oxygen transport parameter. : The binding affinity ( ) of α-crystallin with the POPC membrane was estimated to be 4.9 ± 2.4 µM. The profiles of mobility parameter showed that mobility parameter decreased with an increase in the binding of α-crystallin. The profiles of spin-lattice relaxation rate showed that the spin-lattice relaxation rate decreased with an increase in binding. These results show that the binding of α-crystallin makes the membrane more immobilized near the head group region of the phospholipids. Furthermore, the profiles of the oxygen transport parameter indicated that the oxygen transport parameter decreased with an increase of binding, indicating the binding of α-crystallin forms a barrier for the passage of non-polar molecules which supports the barrier hypothesis. : The binding of α-crystallin to the membrane alters the physical properties of the membranes, and this plays a significant role in modulating the integrity of the membranes. EPR techniques are useful in studying α-crystallin membrane interactions.
Topics: Cataract; Electron Spin Resonance Spectroscopy; Humans; Lens, Crystalline; Phospholipids; Spin Labels; alpha-Crystallins
PubMed: 32564617
DOI: 10.1080/02713683.2020.1786131 -
Current Opinion in Structural Biology Aug 2018Covalently circularized nanodiscs (cNDs) represent a significant advance in the durability and applicability of nanodisc technology. The new cNDs demonstrate higher size... (Review)
Review
Covalently circularized nanodiscs (cNDs) represent a significant advance in the durability and applicability of nanodisc technology. The new cNDs demonstrate higher size homogeneity and improved stability compared with that of non-circularized forms. Moreover, cNDs can be prepared at various defined sizes up to 80-nm diameter. The large cNDs can house much larger membrane proteins and their complexes than was previously possible with the conventional nanodiscs. In order to experience the full advantages of covalent circularization, high quality circularized scaffold protein and nanodisc samples are needed. Here, we give a concise overview and discuss the technical challenges that needed to be overcome in order to obtain high quality preparations. Furthermore, we review some potential new applications for the cNDs.
Topics: Lipid Bilayers; Membrane Proteins; Nanostructures; Nanotechnology; Phospholipids; Protein Binding; Protein Multimerization
PubMed: 29677570
DOI: 10.1016/j.sbi.2018.03.014 -
Cell Chemical Biology Jul 2022Phospholipids are ligands for nuclear hormone receptors (NRs) that regulate transcriptional programs relevant to normal physiology and disease. Here, we demonstrate that...
Phospholipids are ligands for nuclear hormone receptors (NRs) that regulate transcriptional programs relevant to normal physiology and disease. Here, we demonstrate that mimicking phospholipid-NR interactions is a robust strategy to improve agonists of liver receptor homolog-1 (LRH-1), a therapeutic target for colitis. Conventional LRH-1 modulators only partially occupy the binding pocket, leaving vacant a region important for phospholipid binding and allostery. Therefore, we constructed a set of molecules with elements of natural phospholipids appended to a synthetic LRH-1 agonist. We show that the phospholipid-mimicking groups interact with the targeted residues in crystal structures and improve binding affinity, LRH-1 transcriptional activity, and conformational changes at a key allosteric site. The best phospholipid mimetic markedly improves colonic histopathology and disease-related weight loss in a murine T cell transfer model of colitis. This evidence of in vivo efficacy for an LRH-1 modulator in colitis represents a leap forward in agonist development.
Topics: Animals; Colitis; Ligands; Mice; Phospholipids; Receptors, Cytoplasmic and Nuclear
PubMed: 35316658
DOI: 10.1016/j.chembiol.2022.03.001 -
Emerging Topics in Life Sciences Mar 2023Eukaryotic pathogens with an intracellular parasitic lifestyle are shielded from extracellular threats during replication and growth. In addition to many nutrients,... (Review)
Review
Eukaryotic pathogens with an intracellular parasitic lifestyle are shielded from extracellular threats during replication and growth. In addition to many nutrients, parasites scavenge host cell lipids to establish complex membrane structures inside their host cells. To counteract the disturbance of the host cell plasma membrane they have evolved strategies to regulate phospholipid asymmetry. In this review, the function and importance of lipid asymmetry in the interactions of intracellular protozoan parasites with the target and immune cells of the host are highlighted. The malaria parasite Plasmodium infects red blood cells and extensively refurbishes these terminally differentiated cells. Cholesterol depletion and an altered intracellular calcium ion homeostasis can lead to disruption in erythrocyte membrane asymmetry and increased exposure of phosphatidylserine (PS). Binding to the PS receptor on monocytes and macrophages results in phagocytosis and destruction of infected erythrocytes. Leishmania parasites display apoptotic mimicry by actively enhancing PS exposure on their surface to trigger increased infection of macrophages. In extracellular Toxoplasma gondii a P4-type ATPase/CDC50 co-chaperone pair functions as a flippase important for exocytosis of specialised secretory organelles. Identification and functional analysis of parasite lipid-translocating proteins, i.e. flippases, floppases, and scramblases, will be central for the recognition of the molecular mechanisms of parasite/host interactions. Ultimately, a better understanding of parasitic diseases, host immunity, and immune escape by parasites require more research on the dynamics of phospholipid bilayers of parasites and the infected host cell.
Topics: Animals; Host-Parasite Interactions; Phospholipids; Parasites; Toxoplasma; Eukaryota
PubMed: 36820809
DOI: 10.1042/ETLS20220089 -
Nature Aug 2020Stimulation of the metabotropic GABA receptor by γ-aminobutyric acid (GABA) results in prolonged inhibition of neurotransmission, which is central to brain physiology....
Stimulation of the metabotropic GABA receptor by γ-aminobutyric acid (GABA) results in prolonged inhibition of neurotransmission, which is central to brain physiology. GABA belongs to family C of the G-protein-coupled receptors, which operate as dimers to transform synaptic neurotransmitter signals into a cellular response through the binding and activation of heterotrimeric G proteins. However, GABA is unique in its function as an obligate heterodimer in which agonist binding and G-protein activation take place on distinct subunits. Here we present cryo-electron microscopy structures of heterodimeric and homodimeric full-length GABA receptors. Complemented by cellular signalling assays and atomistic simulations, these structures reveal that extracellular loop 2 (ECL2) of GABA has an essential role in relaying structural transitions by ordering the linker that connects the extracellular ligand-binding domain to the transmembrane region. Furthermore, the ECL2 of each of the subunits of GABA caps and interacts with the hydrophilic head of a phospholipid that occupies the extracellular half of the transmembrane domain, thereby providing a potentially crucial link between ligand binding and the receptor core that engages G proteins. These results provide a starting framework through which to decipher the mechanistic modes of signal transduction mediated by GABA dimers, and have important implications for rational drug design that targets these receptors.
Topics: Binding Sites; Cell Membrane; Cryoelectron Microscopy; GABA-B Receptor Antagonists; Humans; Hydrophobic and Hydrophilic Interactions; Ligands; Models, Molecular; Phospholipids; Protein Domains; Protein Multimerization; Protein Subunits; Receptors, GABA-B; Receptors, Glutamate; Signal Transduction; Structure-Activity Relationship
PubMed: 32580208
DOI: 10.1038/s41586-020-2469-4 -
Molecular Cell Jun 2022Phospholipase A2, group VII (PLA2G7) is widely recognized as a secreted, lipoprotein-associated PLA2 in plasma that converts phospholipid platelet-activating factor...
Phospholipase A2, group VII (PLA2G7) is widely recognized as a secreted, lipoprotein-associated PLA2 in plasma that converts phospholipid platelet-activating factor (PAF) to a biologically inactive product Lyso-PAF during inflammatory response. We report that intracellular PLA2G7 is selectively important for cell proliferation and tumor growth potential of melanoma cells expressing mutant NRAS, but not cells expressing BRAF V600E. Mechanistically, PLA2G7 signals through its product Lyso-PAF to contribute to RAF1 activation by mutant NRAS, which is bypassed by BRAF V600E. Intracellular Lyso-PAF promotes p21-activated kinase 2 (PAK2) activation by binding to its catalytic domain and altering ATP kinetics, while PAK2 significantly contributes to S338-phosphorylation of RAF1 in addition to PAK1. Furthermore, the PLA2G7-PAK2 axis is also required for full activation of RAF1 in cells stimulated by epidermal growth factor (EGF) or cancer cells expressing mutant KRAS. Thus, PLA2G7 and Lyso-PAF exhibit intracellular signaling functions as key elements of RAS-RAF1 signaling.
Topics: Phospholipases A2; Phospholipids; Platelet Activating Factor; Proto-Oncogene Proteins B-raf
PubMed: 35417664
DOI: 10.1016/j.molcel.2022.03.026