The pleomorphic cholesterol sensing motifs of transmembrane proteins.

Millions of years of phylogenetic evolution have shaped the crosstalk between sterols and membrane-embedded proteins. This lengthy process, which began before the appearance of eukaryotic cells, has sculpted the two types of molecules to cover a wide spectrum of structural interconnectedness, ranging from rapid touch-and-go hits of low-affinity between surfaces to stronger lock-and-key type structural contacts. The former usually involve relatively loose contacts between linear amino acid sequences on the membrane-exposed transmembrane domains of the protein, readily accessible to the sterols as they briefly visit clefts between adjacent transmembrane segments while in rapid exchange with the bulk lipid bilayer.

Cognitive synaptopathy: synaptic and dendritic spine dysfunction in age-related cognitive disorders.

Cognitive impairment is a leading component of several neurodegenerative and neurodevelopmental diseases, profoundly impacting on the individual, the family, and society at large. Cognitive pathologies are driven by a multiplicity of factors, from genetic mutations and genetic risk factors, neurotransmitter-associated dysfunction, abnormal connectomics at the level of local neuronal circuits and broader brain networks, to environmental influences able to modulate some of the endogenous factors. Otherwise healthy older adults can be expected to experience some degree of mild cognitive impairment, some of which fall into the category of subjective cognitive deficits in clinical practice, while many neurodevelopmental and neurodegenerative diseases course with more profound alterations of cognition, particularly within the spectrum of the dementias.

A supervised graph-based deep learning algorithm to detect and quantify clustered particles.

Considerable efforts are currently being devoted to characterizing the topography of membrane-embedded proteins using combinations of biophysical and numerical analytical approaches. In this work, we present an end-to-end (, human intervention-independent) algorithm consisting of two concatenated binary Graph Neural Network (GNNs) classifiers with the aim of detecting and quantifying dynamic clustering of particles. As the algorithm only needs simulated data to train the GNNs, it is parameter-independent.

Carlos Gutiérrez-Merino: Synergy of Theory and Experimentation in Biological Membrane Research.

Professor Carlos Gutiérrez-Merino, a prominent scientist working in the complex realm of biological membranes, has made significant theoretical and experimental contributions to the field. Contemporaneous with the development of the fluid-mosaic model of Singer and Nicolson, the Förster resonance energy transfer (FRET) approach has become an invaluable tool for studying molecular interactions in membranes, providing structural insights on a scale of 1-10 nm and remaining important alongside evolving perspectives on membrane structures. In the last few decades, Gutiérrez-Merino's work has covered multiple facets in the field of FRET, with his contributions producing significant advances in quantitative membrane biology.

Modulation of a rapid neurotransmitter receptor-ion channel by membrane lipids.

Membrane lipids modulate the proteins embedded in the bilayer matrix by two non-exclusive mechanisms: direct or indirect. The latter comprise those effects mediated by the physicochemical state of the membrane bilayer, whereas direct modulation entails the more specific regulatory effects transduced via recognition sites on the target membrane protein. The nicotinic acetylcholine receptor (nAChR), the paradigm member of the pentameric ligand-gated ion channel (pLGIC) superfamily of rapid neurotransmitter receptors, is modulated by both mechanisms.

Insulin resistance induced by long-term hyperinsulinemia abolishes the effects of acute insulin exposure on cell-surface nicotinic acetylcholine receptor levels and actin cytoskeleton morphology.

Using CHO-K1/A5 cells, a clonal cell line that robustly expresses adult muscle-type nicotinic acetylcholine receptor (nAChR), we explored whether insulin resistance in these mammalian cells affects cell-surface expression of the nAChR, its endocytic internalization, and actin cytoskeleton integrity. Acute nanomolar insulin stimulation resulted in a slow increase in nAChR cell-surface levels, reaching maximum levels at ∼1 h. Long periods of insulin incubation caused CHO-K1/A5 cells to become insulin resistant, as previously observed with several other cell types.

Therapeutic Strategies Aimed at Improving Neuroplasticity in Alzheimer Disease.

Alzheimer disease (AD) is the most prevalent form of dementia among elderly people. Owing to its varied and multicausal etiopathology, intervention strategies have been highly diverse. Despite ongoing advances in the field, efficient therapies to mitigate AD symptoms or delay their progression are still of limited scope.

Nicotinic Acetylcholine Receptor Dysfunction in Addiction and in Some Neurodegenerative and Neuropsychiatric Diseases.

The cholinergic system plays an essential role in brain development, physiology, and pathophysiology. Herein, we review how specific alterations in this system, through genetic mutations or abnormal receptor function, can lead to aberrant neural circuitry that triggers disease. The review focuses on the nicotinic acetylcholine receptor (nAChR) and its role in addiction and in neurodegenerative and neuropsychiatric diseases and epilepsy.

Apolipoprotein E4 heterologous expression, purification under non-denaturing conditions, and effects on neuronal clonal cell lines.

The ε4 allele of the apolipoprotein E gene (APOE4) constitutes the main genetic risk factor for late-onset Alzheimer disease (AD). High amounts of pure apolipoprotein E4 (ApoE4), in a rapid and reproducible fashion, could be of value for studying its pathophysiological roles in AD. The aim of the present work was to optimize a preparative method to obtain highly purified recombinant ApoE4 (rApoE4) with full biological activity.

Structure and function meet at the nicotinic acetylcholine receptor-lipid interface.

The nicotinic acetylcholine receptor (nAChR) is a transmembrane protein that mediates fast intercellular communication in response to the endogenous neurotransmitter acetylcholine. It is the best characterized and archetypal molecule in the superfamily of pentameric ligand-gated ion channels (pLGICs). As a typical transmembrane macromolecule, it interacts extensively with its vicinal lipid microenvironment.

Role of cholesterol-recognition motifs in the infectivity of SARS-CoV-2 variants.

The presence of linear amino acid motifs with the capacity to recognize the neutral lipid cholesterol, known as Cholesterol Recognition/interaction Amino acid Consensus sequence (CRAC), and its inverse or mirror image, CARC, has recently been reported in the primary sequence of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike S homotrimeric glycoprotein. These motifs also occur in the two other pathogenic coronaviruses, SARS-CoV, and Middle-East respiratory syndrome CoV (MERS-CoV), most conspicuously in the transmembrane domain, the fusion peptide, the amino-terminal domain, and the receptor binding domain of SARS-CoV-2 S protein. Here we analyze the presence of cholesterol-recognition motifs in these key regions of the spike glycoprotein in the pathogenic CoVs.

Fluorescence microscopy imaging of a neurotransmitter receptor and its cell membrane lipid milieu.

Hampered by the diffraction phenomenon, as expressed in 1873 by Abbe, applications of optical microscopy to image biological structures were for a long time limited to resolutions above the ∼200 nm barrier and restricted to the observation of stained specimens. The introduction of fluorescence was a game changer, and since its inception it became the gold standard technique in biological microscopy. The plasma membrane is a tenuous envelope of 4 nm-10 nm in thickness surrounding the cell.

Mapping the Nicotinic Acetylcholine Receptor Nanocluster Topography at the Cell Membrane with STED and STORM Nanoscopies.

The cell-surface topography and density of nicotinic acetylcholine receptors (nAChRs) play a key functional role in the synapse. Here we employ in parallel two labeling and two super-resolution microscopy strategies to characterize the distribution of this receptor at the plasma membrane of the mammalian clonal cell line CHO-K1/A5. Cells were interrogated with two targeted techniques (confocal microscopy and stimulated emission depletion (STED) nanoscopy) and single-molecule nanoscopy (stochastic optical reconstruction microscopy, STORM) using the same fluorophore, Alexa Fluor 647, tagged onto either α-bungarotoxin (BTX) or the monoclonal antibody mAb35.

Interactions between the Nicotinic and Endocannabinoid Receptors at the Plasma Membrane.

Compartmentalization, together with transbilayer and lateral asymmetries, provide the structural foundation for functional specializations at the cell surface, including the active role of the lipid microenvironment in the modulation of membrane-bound proteins. The chemical synapse, the site where neurotransmitter-coded signals are decoded by neurotransmitter receptors, adds another layer of complexity to the plasma membrane architectural intricacy, mainly due to the need to accommodate a sizeable number of molecules in a minute subcellular compartment with dimensions barely reaching the micrometer. In this review, we discuss how nature has developed suitable adjustments to accommodate different types of membrane-bound receptors and scaffolding proteins via membrane microdomains, and how this "effort-sharing" mechanism has evolved to optimize crosstalk, separation, or coupling, where/when appropriate.

The synaptic lipidome in health and disease.

Adequate homeostasis of lipid, protein and carbohydrate metabolism is essential for cells to perform highly specific tasks in our organism, and the brain, with its uniquely high energetic requirements, posesses singular characteristics. Some of these are related to its extraordinary dotation of synapses, the specialized subcelluar structures where signal transmission between neurons occurs in the central nervous system. The post-synaptic compartment of excitatory synapses, the dendritic spine, harbors key molecules involved in neurotransmission tightly packed within a minute volume of a few femtoliters.

Fluorescence Studies of Nicotinic Acetylcholine Receptor and Its Associated Lipid Milieu: The Influence of Erwin London's Methodological Approaches.

Erwin London dedicated considerable effort to understanding lipid interactions with membrane-resident proteins and how these interactions shaped the formation and maintenance of lipid phases and domains. In this endeavor, he developed ad hoc techniques that greatly contributed to advancements in the field. We have employed and/or modified/extended some of his methodological approaches and applied them to investigate lipid interaction with the nicotinic acetylcholine receptor (nAChR) protein, the paradigm member of the superfamily of rapid pentameric ligand-gated ion channels (pLGIC).

The constellation of cholesterol-dependent processes associated with SARS-CoV-2 infection.

The role of cholesterol in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and other coronavirus-host cell interactions is currently being discussed in the context of two main scenarios: i) the presence of the neutral lipid in cholesterol-rich lipid domains involved in different steps of the viral infection and ii) the alteration of metabolic pathways by the virus over the course of infection. Cholesterol-enriched lipid domains have been reported to occur in the lipid envelope membrane of the virus, in the host-cell plasma membrane, as well as in endosomal and other intracellular membrane cellular compartments. These membrane subdomains, whose chemical and physical properties distinguish them from the bulk lipid bilayer, have been purported to participate in diverse phenomena, from virus-host cell fusion to intracellular trafficking and exit of the virions from the infected cell.

COVID-19 and neurological sequelae: Vitamin D as a possible neuroprotective and/or neuroreparative agent.

SARS-CoV-2, the etiological agent of the current COVID-19 pandemic, belongs to a broad family of coronaviruses that also affect humans. SARS-CoV-2 infection usually leads to bilateral atypical pneumonia with significant impairment of respiratory function. However, the infectious capacity of SARS-CoV-2 is not limited to the respiratory system, but may also affect other vital organs such as the brain.

Dendritic spine membrane proteome and its alterations in autistic spectrum disorder.

Dendritic spines are small protrusions stemming from the dendritic shaft that constitute the primary specialization for receiving and processing excitatory neurotransmission in brain synapses. The disruption of dendritic spine function in several neurological and neuropsychiatric diseases leads to severe information-processing deficits with impairments in neuronal connectivity and plasticity. Spine dysregulation is usually accompanied by morphological alterations to spine shape, size and/or number that may occur at early pathophysiological stages and not necessarily be reflected in clinical manifestations.

Fluorescence sensors for imaging membrane lipid domains and cholesterol.

Lipid membrane domains are supramolecular lateral heterogeneities of biological membranes. Of nanoscopic dimensions, they constitute specialized hubs used by the cell as transient signaling platforms for a great variety of biologically important mechanisms. Their property to form and dissolve in the bulk lipid bilayer endow them with the ability to engage in highly dynamic processes, and temporarily recruit subpopulations of membrane proteins in reduced nanometric compartments that can coalesce to form larger mesoscale assemblies.

Nanoscale Sub-Compartmentalization of the Dendritic Spine Compartment.

Compartmentalization of the membrane is essential for cells to perform highly specific tasks and spatially constrained biochemical functions in topographically defined areas. These membrane lateral heterogeneities range from nanoscopic dimensions, often involving only a few molecular constituents, to micron-sized mesoscopic domains resulting from the coalescence of nanodomains. Short-lived domains lasting for a few milliseconds coexist with more stable platforms lasting from minutes to days.

Dysregulation of Neuronal Nicotinic Acetylcholine Receptor-Cholesterol Crosstalk in Autism Spectrum Disorder.

Autism spectrum disorder (ASD) is a set of complex neurodevelopmental diseases that include impaired social interaction, delayed and disordered language, repetitive or stereotypic behavior, restricted range of interests, and altered sensory processing. The underlying causes of the core symptoms remain unclear, as are the factors that trigger their onset. Given the complexity and heterogeneity of the clinical phenotypes, a constellation of genetic, epigenetic, environmental, and immunological factors may be involved.

A deep learning-based approach to model anomalous diffusion of membrane proteins: the case of the nicotinic acetylcholine receptor.

We present a concatenated deep-learning multiple neural network system for the analysis of single-molecule trajectories. We apply this machine learning-based analysis to characterize the translational diffusion of the nicotinic acetylcholine receptor at the plasma membrane, experimentally interrogated using superresolution optical microscopy. The receptor protein displays a heterogeneous diffusion behavior that goes beyond the ensemble level, with individual trajectories exhibiting more than one diffusive state, requiring the optimization of the neural networks through a hyperparameter analysis for different numbers of steps and durations, especially for short trajectories (<50 steps) where the accuracy of the models is most sensitive to localization errors.

Morphological and biochemical repercussions of infection in a 3D human brain neurospheres model.

Background: Toxoplasmosis is caused by the parasite that can infect the central nervous system (CNS), promoting neuroinflammation, neuronal loss, neurotransmitter imbalance and behavioral alterations. infection is also related to neuropsychiatric disorders such as schizophrenia. The pathogenicity and inflammatory response in rodents are different to the case of humans, compromising the correlation between the behavioral alterations and physiological modifications observed in the disease.

Homomeric and Heteromeric α7 Nicotinic Acetylcholine Receptors in Health and Some Central Nervous System Diseases.

Nicotinic acetylcholine receptors (nAChRs) are pentameric ligand-gated ion channels involved in the modulation of essential brain functions such as memory, learning, and attention. Homomeric α7 nAChR, formed exclusively by five identical α7 subunits, is involved in rapid synaptic transmission, whereas the heteromeric oligomers composed of α7 in combination with β subunits display metabotropic properties and operate in slower time frames. At the cellular level, the activation of nAChRs allows the entry of Na and Ca; the two cations depolarize the membrane and trigger diverse cellular signals, depending on the type of nAChR pentamer and neurons involved, the location of the intervening cells, and the networks of which these neuronal cells form part.