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Cell Reports Sep 2022Mitochondria are dynamic organelles essential for cell survival whose structural and functional integrity rely on selective and regulated transport of lipids from/to the...
Mitochondria are dynamic organelles essential for cell survival whose structural and functional integrity rely on selective and regulated transport of lipids from/to the endoplasmic reticulum (ER) and across the mitochondrial intermembrane space. As they are not connected by vesicular transport, the exchange of lipids between ER and mitochondria occurs at membrane contact sites. However, the mechanisms and proteins involved in these processes are only beginning to emerge. Here, we show that the main physiological localization of the lipid transfer proteins ORP5 and ORP8 is at mitochondria-associated ER membrane (MAM) subdomains, physically linked to the mitochondrial intermembrane space bridging (MIB)/mitochondrial contact sites and cristae junction organizing system (MICOS) complexes that bridge the two mitochondrial membranes. We also show that ORP5/ORP8 mediate non-vesicular transport of phosphatidylserine (PS) lipids from the ER to mitochondria by cooperating with the MIB/MICOS complexes. Overall our study reveals a physical and functional link between ER-mitochondria contacts involved in lipid transfer and intra-mitochondrial membrane contacts maintained by the MIB/MICOS complexes.
Topics: Endoplasmic Reticulum; Mitochondria; Mitochondrial Membranes; Mitochondrial Proteins; Phosphatidylserines
PubMed: 36130504
DOI: 10.1016/j.celrep.2022.111364 -
The EMBO Journal Jul 2023The mature mammalian brain connectome emerges during development via the extension and pruning of neuronal connections. Glial cells have been identified as key players...
The mature mammalian brain connectome emerges during development via the extension and pruning of neuronal connections. Glial cells have been identified as key players in the phagocytic elimination of neuronal synapses and projections. Recently, phosphatidylserine has been identified as neuronal "eat-me" signal that guides elimination of unnecessary input sources, but the associated transduction systems involved in such pruning are yet to be described. Here, we identified Xk-related protein 8 (Xkr8), a phospholipid scramblase, as a key factor for the pruning of axons in the developing mammalian brain. We found that mouse Xkr8 is highly expressed immediately after birth and required for phosphatidylserine exposure in the hippocampus. Mice lacking Xkr8 showed excess excitatory nerve terminals, increased density of cortico-cortical and cortico-spinal projections, aberrant electrophysiological profiles of hippocampal neurons, and global brain hyperconnectivity. These data identify phospholipid scrambling by Xkr8 as a central process in the labeling and discrimination of developing neuronal projections for pruning in the mammalian brain.
Topics: Animals; Mice; Phospholipid Transfer Proteins; Apoptosis Regulatory Proteins; Apoptosis; Phosphatidylserines; Axons; Neuronal Plasticity; Mammals; Membrane Proteins
PubMed: 37211968
DOI: 10.15252/embj.2022111790 -
Trends in Biochemical Sciences Sep 2017Nature repeatedly repurposes, in that molecules that serve as metabolites, energy depots, or polymer subunits are at the same time used to deliver signals within and... (Review)
Review
Nature repeatedly repurposes, in that molecules that serve as metabolites, energy depots, or polymer subunits are at the same time used to deliver signals within and between cells. The preeminent example of this repurposing is ATP, which functions as a building block for nucleic acids, an energy source for enzymatic reactions, a phosphate donor to regulate intracellular signaling, and a neurotransmitter to control the activity of neurons. A series of recent studies now consolidates the view that phosphatidylserine (PtdSer), a common phospholipid constituent of membrane bilayers, is similarly repurposed for use as a signal between cells and that the ligands and receptors of the Tyro3/Axl/Mer (TAM) family of receptor tyrosine kinases (RTKs) are prominent transducers of this signal.
Topics: Animals; Humans; Ligands; Phosphatidylserines; Receptor Protein-Tyrosine Kinases; Signal Transduction
PubMed: 28734578
DOI: 10.1016/j.tibs.2017.06.004 -
Advanced Drug Delivery Reviews Apr 2016Clearance of apoptotic debris is a vital role of the innate immune system. Drawing upon principles of apoptotic clearance, convenient delivery vehicles including... (Review)
Review
Clearance of apoptotic debris is a vital role of the innate immune system. Drawing upon principles of apoptotic clearance, convenient delivery vehicles including intrinsic anti-inflammatory characteristics and specificity to immune cells can be engineered to aid in drug delivery. In this article, we examine the use of phosphatidylserine (PtdSer), the well-known "eat-me" signal, in nanoparticle-based therapeutics making them highly desirable "meals" for phagocytic immune cells. Use of PtdSer facilitates engulfment of nanoparticles allowing for imaging and therapy in various pathologies and may result in immunomodulation. Furthermore, we discuss the targeting of the macrophages and other cells at sites of inflammation in disease. A thorough understanding of the immunobiology of "eat-me" signals is requisite for the successful application of "eat-me"-bearing materials in biomedical applications.
Topics: Animals; Diagnostic Imaging; Drug Carriers; Drug Therapy; Humans; Immunity, Innate; Pharmaceutical Preparations; Phosphatidylserines
PubMed: 26826436
DOI: 10.1016/j.addr.2016.01.009 -
Trends in Cell Biology Mar 2017Positive-strand RNA viruses are the largest group of RNA viruses on Earth and cellular membranes are critical for all aspects of their life cycle, from entry and... (Review)
Review
Positive-strand RNA viruses are the largest group of RNA viruses on Earth and cellular membranes are critical for all aspects of their life cycle, from entry and replication to exit. In particular, membranes serve as platforms for replication and as carriers to transmit these viruses to other cells, the latter either as an envelope surrounding a single virus or as the vesicle containing a population of viruses. Notably, many animal and human viruses appear to induce and exploit phosphatidylinositol 4-phosphate/cholesterol-enriched membranes for replication, whereas many plant and insect-vectored animal viruses utilize phosphatidylethanolamine/cholesterol-enriched membranes for the same purpose; and phosphatidylserine-enriched membrane carriers are widely used by both single and populations of viruses for transmission. Here I discuss the implications for viral pathogenesis and therapeutic development of this remarkable convergence on specific membrane lipid blueprints for replication and transmission.
Topics: Animals; Extracellular Vesicles; Humans; Lipids; Phosphatidylinositol Phosphates; Phosphatidylserines; Virus Diseases; Virus Replication
PubMed: 27838086
DOI: 10.1016/j.tcb.2016.09.011 -
Cellular & Molecular Biology Letters Jul 2023The dynamics of phosphatidylserine in the plasma membrane is a tightly regulated feature of eukaryotic cells. Phosphatidylserine (PS) is found preferentially in the...
BACKGROUND
The dynamics of phosphatidylserine in the plasma membrane is a tightly regulated feature of eukaryotic cells. Phosphatidylserine (PS) is found preferentially in the inner leaflet of the plasma membrane. Disruption of this asymmetry leads to the exposure of phosphatidylserine on the cell surface and is associated with cell death, synaptic pruning, blood clotting and other cellular processes. Due to the role of phosphatidylserine in widespread cellular functions, an efficient phosphatidylserine probe is needed to study them. Currently, a few different phosphatidylserine labelling tools are available; however, these labels have unfavourable signal-to-noise ratios and are difficult to use in tissues due to limited permeability. Their application in living tissue requires injection procedures that damage the tissue and release damage-associated molecular patterns, which in turn stimulates phosphatidylserine exposure.
METHODS
For this reason, we developed a novel genetically encoded phosphatidylserine probe based on the C2 domain of the lactadherin (MFG-E8) protein, suitable for labelling exposed phosphatidylserine in various research models. We tested the C2 probe specificity to phosphatidylserine on hybrid bilayer lipid membranes by observing surface plasmon resonance angle shift. Then, we analysed purified fused C2 proteins on different cell culture lines or engineered AAVs encoding C2 probes on tissue cultures after apoptosis induction. For in vivo experiments, neurotropic AAVs were intravenously injected into perinatal mice, and after 2 weeks, brain slices were collected to observe C2-SNAP expression.
RESULTS
The biophysical analysis revealed the high specificity of the C2 probe for phosphatidylserine. The fused recombinant C2 proteins were suitable for labelling phosphatidylserine on the surface of apoptotic cells in various cell lines. We engineered AAVs and validated them in organotypic brain tissue cultures for non-invasive delivery of the genetically encoded C2 probe and showed that these probes were expressed in the brain in vivo after intravenous AAV delivery to mice.
CONCLUSIONS
We have demonstrated that the developed genetically encoded PS biosensor can be utilised in a variety of assays as a two-component system of C2 and C2m2 fusion proteins. This system allows for precise quantification and PS visualisation at directly specified threshold levels, enabling the evaluation of PS exposure in both physiological and cell death processes.
Topics: Animals; Mice; Phosphatidylserines; Cell Membrane; Lipid Bilayers; Biosensing Techniques; Cell Line
PubMed: 37501184
DOI: 10.1186/s11658-023-00472-7 -
Cell Communication and Signaling : CCS Oct 2019Phosphatidylserine (PtdSer), an essential constituent of eukaryotic membranes, is the most abundant anionic phospholipid in the eukaryotic cell accounting for up to 10%... (Review)
Review
Phosphatidylserine (PtdSer), an essential constituent of eukaryotic membranes, is the most abundant anionic phospholipid in the eukaryotic cell accounting for up to 10% of the total cellular lipid. Much of what is known about PtdSer is the role exofacial PtdSer plays in apoptosis and blood clotting. However, PtdSer is generally not externally exposed in healthy cells and plays a vital role in several intracellular signaling pathways, though relatively little is known about the precise subcellular localization, transmembrane topology and intracellular dynamics of PtdSer within the cell. The recent development of new, genetically-encoded probes able to detect phosphatidylserine is leading to a more in-depth understanding of the biology of this phospholipid. This review aims to give an overview of recent developments in our understanding of the role of PtdSer in intracellular signaling events derived from the use of these recently developed methods of phosphatidylserine detection.
Topics: Animals; Cells; Humans; Intracellular Space; Phosphatidylserines
PubMed: 31615534
DOI: 10.1186/s12964-019-0438-z -
FEBS Letters Jan 2015Phospholipid scramblase activity is involved in the collapse of phospholipid (PL) asymmetry at the plasma membrane leading to externalization of phosphatidylserine. This... (Review)
Review
Phospholipid scramblase activity is involved in the collapse of phospholipid (PL) asymmetry at the plasma membrane leading to externalization of phosphatidylserine. This activity is crucial for initiation of the blood coagulation cascade and for recognition/elimination of apoptotic cells by macrophages. Efforts to identify gene products associated with this activity led to the characterization of PL scramblase (PLSCR) and XKR family members which contribute to phosphatidylserine exposure in response to apoptotic stimuli. Meanwhile, TMEM16 family members were identified to externalize phosphatidylserine in response to elevated calcium in Scott syndrome platelets, which is critical for activation of the coagulation cascade. Herein, we report their mechanisms of gene regulation, molecular functions independent of their scrambling activity, and their potential roles in pathogenic conditions.
Topics: Animals; Apoptosis; Blood Coagulation Disorders; Blood Platelets; Cell Membrane; Humans; Phosphatidylserines; Phospholipid Transfer Proteins
PubMed: 25479087
DOI: 10.1016/j.febslet.2014.11.036 -
Biochimica Et Biophysica Acta Apr 2015Ras proteins assemble into transient nanoclusters on the plasma membrane. Nanoclusters are the sites of Ras effector recruitment and activation and are therefore... (Review)
Review
Ras proteins assemble into transient nanoclusters on the plasma membrane. Nanoclusters are the sites of Ras effector recruitment and activation and are therefore essential for signal transmission. The dynamics of nanocluster formation and disassembly result in interesting emergent properties including high-fidelity signal transmission. More recently the lipid structure of Ras nanoclusters has been reported and shown to contribute to isoform-specific Ras signaling. In addition specific lipids play critical roles in mediating the formation, stability and dynamics of Ras nanoclusters. In consequence the spatiotemporal organization of these lipids has emerged as important and novel regulators of Ras function. This article is part of a Special Issue entitled: Nanoscale membrane organisation and signalling.
Topics: Animals; Cell Membrane; Humans; Lipids; Nanoparticles; Phosphatidylserines; Signal Transduction; ras Proteins
PubMed: 25234412
DOI: 10.1016/j.bbamcr.2014.09.008 -
Bioarchitecture 2014Loss of plasma membrane asymmetry is a hallmark of apoptosis, but lipid bilayer asymmetry and loss of asymmetry can contribute to numerous cellular functions and... (Review)
Review
Loss of plasma membrane asymmetry is a hallmark of apoptosis, but lipid bilayer asymmetry and loss of asymmetry can contribute to numerous cellular functions and responses that are independent of programmed cell death. Exofacial exposure of phosphatidylserine occurs in lymphocytes and mast cells after antigenic stimulation and in the absence of apoptosis, suggesting that there is a functional requirement for phosphatidylserine exposure in immunocytes. In this review we examine current ideas as to the nature of this functional role in mast cell activation. Mechanistically, there is controversy as to the candidate proteins responsible for phosphatidylserine translocation from the internal to external leaflet, and here we review the candidacies of mast cell PLSCR1 and TMEM16F. Finally we examine the potential relationship between functionally important mast cell membrane perturbations and phosphatidylserine exposure during activation.
Topics: Apoptosis; Cell Membrane; Humans; Lipids; Mast Cells; Phosphatidylserines
PubMed: 25759911
DOI: 10.1080/19490992.2014.995516