Lipid rafts and neurodegeneration: structural and functional roles in physiologic aging and neurodegenerative diseases

Quantitation of F-actin in cytoskeletal reorganization: Context, methodology and implications

The actin cytoskeleton is involved in a large number of cellular signaling events in addition to providing structural integrity to the cell. Actin polymerization is a key event during cellular signaling. Although the role of actin cytoskeleton in cellular processes such as trafficking and motility has been extensively studied, the reorganization of the actin cytoskeleton upon signaling has been rarely explored due to lack of suitable assays. Keeping in mind this lacuna, we developed a confocal microscopy based approach that relies on high magnification imaging of cellular F-actin, followed by image reconstruction using commercially available software. In this review, we discuss the context and relevance of actin quantitation, followed by a detailed hands-on approach of the methodology involved with specific points on troubleshooting and useful precautions. In the latter part of the review, we elucidate the method by discussing applications of actin quantitation from our work in several important problems in contemporary membrane biology ranging from pathogen entry into host cells, to GPCR signaling and membrane-cytoskeleton interaction. We envision that future discovery of cell-permeable novel fluorescent probes, in combination with genetically encoded actin-binding reporters, would allow real-time visualization of actin cytoskeleton dynamics to gain deeper insights into active cellular processes in health and disease.

Regulation of cellular and systemic sphingolipid homeostasis

One hundred and fifty years ago, Johann Thudichum described sphingolipids as unusual "Sphinx-like" lipids from the brain. Today, we know that thousands of sphingolipid molecules mediate many essential functions in embryonic development and normal physiology. In addition, sphingolipid metabolism and signalling pathways are dysregulated in a wide range of pathologies, and therapeutic agents that target sphingolipids are now used to treat several human diseases. However, our understanding of sphingolipid regulation at cellular and organismal levels and their functions in developmental, physiological and pathological settings is rudimentary. In this Review, we discuss recent advances in sphingolipid pathways in different organelles, how secreted sphingolipid mediators modulate physiology and disease, progress in sphingolipid-targeted therapeutic and diagnostic research, and the trans-cellular sphingolipid metabolic networks between microbiota and mammals. Advances in sphingolipid biology have led to a deeper understanding of mammalian physiology and may lead to progress in the management of many diseases.

Age-Related Effects of Inhalational Anesthetics in B4galnt1-Null and Cuprizone-Treated Mice: Clinically Relevant Insights into Demyelinating Diseases

Anesthetics are essential agents that are frequently used in clinical practice to induce a reversible loss of consciousness and sensation by depressing the central nervous system. The inhalational anesthetics isoflurane and sevoflurane are preferred due to their rapid induction and recovery times and ease of administration. Despite their widespread use, the exact molecular mechanisms by which these anesthetics induce anesthesia are not yet fully understood. In this study, the age-dependent effects of inhalational anesthetics on two demyelination models were investigated: congenital (B4galnt1-null) and chemically induced (cuprizone). Various motor and cognitive tests were used to determine sensitivity to isoflurane and sevoflurane anesthesia. B4galnt1-null mice, which exhibit severe motor deficits due to defects in ganglioside synthesis, showed significant impairments in motor coordination and balance in all motor tests, which were exacerbated by both anesthetics. Cuprizone-treated mice, which mimic the demyelination in B4galnt1-null mice, also showed altered, age-dependent sensitivity to anesthesia. The study showed that older mice exhibited more pronounced deficits, with B4galnt1-null mice showing the greatest susceptibility to sevoflurane. These differential responses to anesthetics suggest that age and underlying myelin pathology significantly influence anesthetic effects.

Polar Lipids Supplementation Enhances Basal Excitatory Synaptic Transmission in Primary Cortical Neuron

SCOPE

Polar lipids, such as gangliosides and phospholipids, are fundamental structural components that play critical roles in the development and maturation of neurons in the brain. Recent evidence has demonstrated that dietary intakes of polar lipids in early life are associated with improved cognitive outcomes during infancy and adolescence. However, the specific mechanisms through which these lipids impact cognition remain unclear.

METHODS AND RESULTS

This study examines the direct physiological impact of polar lipid supplementation, in the form of buttermilk powder, on primary cortical neuron growth and maturation. The changes are measured with postsynaptic current response recordings, immunohistochemical examination of functional synapse localization and numbers, and the biochemical quantification of receptors responsible for neuronal synaptic neurotransmission. Chronic exposure to polar lipids increases primary mouse cortical neuron basal excitatory synapse response strength attributed to enhanced dendritic complexity and an altered expression of the excitatory α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor subunit 2 (GluR2).

CONCLUSION

The present finding suggests that dietary polar lipids improve human cognition through an enhancement of neuronal maturation and/or function.

Dysregulated lipid metabolism networks modulate T-cell function in people with relapsing-remitting multiple sclerosis

Altered cholesterol, oxysterol, sphingolipid, and fatty acid concentrations are reported in blood, cerebrospinal fluid, and brain tissue of people with relapsing-remitting multiple sclerosis (RRMS) and are linked to disease progression and treatment responses. CD4 + T cells are pathogenic in RRMS, and defective T-cell function could be mediated in part by liver X receptors (LXRs)-nuclear receptors that regulate lipid homeostasis and immunity. RNA-sequencing and pathway analysis identified that genes within the 'lipid metabolism' and 'signalling of nuclear receptors' pathways were dysregulated in CD4 + T cells isolated from RRMS patients compared with healthy donors. While LXRB and genes associated with cholesterol metabolism were upregulated, other T-cell LXR-target genes, including genes involved in cellular lipid uptake (inducible degrader of the LDL receptor, IDOL), and the rate-limiting enzyme for glycosphingolipid biosynthesis (UDP-glucosylceramide synthase, UGCG) were downregulated in T cells from patients with RRMS compared to healthy donors. Correspondingly, plasma membrane glycosphingolipids were reduced, and cholesterol levels increased in RRMS CD4 + T cells, an effect partially recapitulated in healthy T cells by in vitro culture with T-cell receptor stimulation in the presence of serum from RRMS patients. Notably, stimulation with LXR-agonist GW3965 normalized membrane cholesterol levels, and reduced proliferation and IL17 cytokine production in RRMS CD4 + T-cells. Thus, LXR-mediated lipid metabolism pathways were dysregulated in T cells from patients with RRMS and could contribute to RRMS pathogenesis. Therapies that modify lipid metabolism could help restore immune cell function.

The impact of volatile anesthetics and propofol on phosphatidylinositol 4,5-bisphosphate signaling

Phosphatidylinositol 4,5-bisphosphate (PIP2), as well as other anionic phospholipids, play a pivotal role in various cellular processes, including ion channel regulation, receptor trafficking, and intracellular signaling pathways. The binding of volatile anesthetics and propofol to PIP2 leads to alterations in PIP2-mediated signaling causing modulation of ion channels such as ɣ-aminobutyric acid type A (GABAA) receptors, voltage-gated calcium channels, and potassium channels through various mechanisms. Additionally, the interaction between anionic phospholipids and G protein-coupled receptors plays a critical role in various anesthetic pathways, with these anesthetic-induced changes impacting PIP2 levels which cause cascading effects on receptor trafficking, including GABAA receptor internalization. This comprehensive review of various mechanisms of interaction provides insights into the intricate interplay between PIP2 signaling and anesthetic-induced changes, shedding light on the molecular mechanisms underlying anesthesia.

Identification of z-axis filopodia in growth cones using super-resolution microscopy

A growth cone is a highly motile tip of an extending axon that is crucial for neural network formation. Three-dimensional-structured illumination microscopy, a type of super-resolution light microscopy with a resolution that overcomes the optical diffraction limitation (ca. 200 nm) of conventional light microscopy, is well suited for studying the molecular dynamics of intracellular events. Using this technique, we discovered a novel type of filopodia distributed along the z-axis ("z-filopodia") within the growth cone. Z-filopodia were typically oriented in the direction of axon growth, not attached to the substratum, protruded spontaneously without microtubule invasion, and had a lifetime that was considerably shorter than that of conventional filopodia. Z-filopodia formation and dynamics were regulated by actin-regulatory proteins, such as vasodilator-stimulated phosphoprotein, fascin, and cofilin. Chromophore-assisted laser inactivation of cofilin induced the rapid turnover of z-filopodia. An axon guidance receptor, neuropilin-1, was concentrated in z-filopodia and was transported together with them, whereas its ligand, semaphorin-3A, was selectively bound to them. Membrane domains associated with z-filopodia were also specialized and resembled those of lipid rafts, and their behaviors were closely related to those of neuropilin-1. The results suggest that z-filopodia have unique turnover properties, and unlike xy-filopodia, do not function as force-generating structures for axon extension.

Modulation of Lipid Dynamics in the β-Amyloid Aggregates Induced Membrane Fragmentation

Nonspecific membrane disruption is considered a plausible mechanism for the cytotoxicity induced by β-amyloid (Aβ) aggregates. In scenarios of high local Aβ concentrations, a two-step membrane fragmentation model has been proposed. Initially, membrane-embedded Aβ oligomeric aggregates form, followed by membrane fragmentation. However, the key molecular-level interactions between Aβ oligomeric aggregates and lipids that drive the second-stage membrane fragmentation remain unclear. This study monitors the time-dependent changes in lipid dynamics and water accessibility of model liposomes during Aβ-induced membrane fragmentation. Our results indicate that lipid dynamics on the nanosecond to microsecond time scale undergo rapid acceleration upon initial incubation with membrane-incorporated Aβ oligomeric aggregates, followed by a slow deceleration process. Concurrently, lipid headgroups become less accessible to water. Both observations suggest a carpet-like mechanism of membrane disruption for the Aβ-induced membrane fragmentation process.

Brain cholesterol and Alzheimer's disease: challenges and opportunities in probe and drug development

Cholesterol homeostasis is impaired in Alzheimer's disease; however, attempts to modulate brain cholesterol biology have not translated into tangible clinical benefits for patients to date. Several recent milestone developments have substantially improved our understanding of how excess neuronal cholesterol contributes to the pathophysiology of Alzheimer's disease. Indeed, neuronal cholesterol was linked to the formation of amyloid-β and neurofibrillary tangles through molecular pathways that were recently delineated in mechanistic studies. Furthermore, remarkable advances in translational molecular imaging have now made it possible to probe cholesterol metabolism in the living human brain with PET, which is an important prerequisite for future clinical trials that target the brain cholesterol machinery in Alzheimer's disease patients-with the ultimate aim being to develop disease-modifying treatments. This work summarizes current concepts of how the biosynthesis, transport and clearance of brain cholesterol are affected in Alzheimer's disease. Further, current strategies to reverse these alterations by pharmacotherapy are critically discussed in the wake of emerging translational research tools that support the assessment of brain cholesterol biology not only in animal models but also in patients with Alzheimer's disease.

Unraveling the link between neuropathy target esterase NTE/SWS, lysosomal storage diseases, inflammation, abnormal fatty acid metabolism, and leaky brain barrier

Mutations in Drosophila Swiss cheese (SWS) gene or its vertebrate orthologue neuropathy target esterase (NTE) lead to progressive neuronal degeneration in flies and humans. Despite its enzymatic function as a phospholipase is well established, the molecular mechanism responsible for maintaining nervous system integrity remains unclear. In this study, we found that NTE/SWS is present in surface glia that forms the blood-brain barrier (BBB) and that NTE/SWS is important to maintain its structure and permeability. Importantly, BBB glia-specific expression of Drosophila NTE/SWS or human NTE in the sws mutant background fully rescues surface glial organization and partially restores BBB integrity, suggesting a conserved function of NTE/SWS. Interestingly, sws mutant glia showed abnormal organization of plasma membrane domains and tight junction rafts accompanied by the accumulation of lipid droplets, lysosomes, and multilamellar bodies. Since the observed cellular phenotypes closely resemble the characteristics described in a group of metabolic disorders known as lysosomal storage diseases (LSDs), our data established a novel connection between NTE/SWS and these conditions. We found that mutants with defective BBB exhibit elevated levels of fatty acids, which are precursors of eicosanoids and are involved in the inflammatory response. Also, as a consequence of a permeable BBB, several innate immunity factors are upregulated in an age-dependent manner, while BBB glia-specific expression of NTE/SWS normalizes inflammatory response. Treatment with anti-inflammatory agents prevents the abnormal architecture of the BBB, suggesting that inflammation contributes to the maintenance of a healthy brain barrier. Considering the link between a malfunctioning BBB and various neurodegenerative diseases, gaining a deeper understanding of the molecular mechanisms causing inflammation due to a defective BBB could help to promote the use of anti-inflammatory therapies for age-related neurodegeneration.

Aβ peptide enhances GluA1 internalization via lipid rafts in Alzheimer's-related hippocampal LTP dysfunction

Amyloid β (Aβ) is a central contributor to neuronal damage and cognitive impairment in Alzheimer's disease (AD). Aβ disrupts AMPA receptor-mediated synaptic plasticity, a key factor in early AD progression. Numerous studies propose that Aβ oligomers hinder synaptic plasticity, particularly long-term potentiation (LTP), by disrupting GluA1 (encoded by GRIA1) function, although the precise mechanism remains unclear. In this study, we demonstrate that Aβ mediates the accumulation of GM1 ganglioside in lipid raft domains of cultured cells, and GluA1 exhibits preferential localization in lipid rafts via direct binding to GM1. Aβ enhances the raft localization of GluA1 by increasing GM1 in these areas. Additionally, chemical LTP stimulation induces lipid raft-dependent GluA1 internalization in Aβ-treated neurons, resulting in reduced cell surface and postsynaptic expression of GluA1. Consistent with this, disrupting lipid rafts and GluA1 localization in rafts rescues Aβ-mediated suppression of hippocampal LTP. These findings unveil a novel functional deficit in GluA1 trafficking induced by Aβ, providing new insights into the mechanism underlying AD-associated cognitive dysfunction.

Serotonin Signaling through Lipid Membranes

Serotonin (5-HT) is a vital modulatory neurotransmitter responsible for regulating most behaviors in the brain. An inefficient 5-HT synaptic function is often linked to various mental disorders. Primarily, membrane proteins controlling the expression and activity of 5-HT synthesis, storage, release, receptor activation, and inactivation are critical to 5-HT signaling in synaptic and extra-synaptic sites. Moreover, these signals represent information transmission across membranes. Although the lipid membrane environment is often viewed as fairly stable, emerging research suggests significant functional lipid-protein interactions with many synaptic 5-HT proteins. These protein-lipid interactions extend to almost all the primary lipid classes that form the plasma membrane. Collectively, these lipid classes and lipid-protein interactions affect 5-HT synaptic efficacy at the synapse. The highly dynamic lipid composition of synaptic membranes suggests that these lipids and their interactions with proteins may contribute to the plasticity of the 5-HT synapse. Therefore, this broader protein-lipid model of the 5-HT synapse necessitates a reconsideration of 5-HT's role in various associated mental disorders.

Methodological Pitfalls of Investigating Lipid Rafts in the Brain: What Are We Still Missing?

The purpose of this review is to succinctly examine the methodologies used in lipid raft research in the brain and to highlight the drawbacks of some investigative approaches. Lipid rafts are biochemically and biophysically different from the bulk membrane. A specific lipid environment within membrane domains provides a harbor for distinct raftophilic proteins, all of which in concert create a specialized platform orchestrating various cellular processes. Studying lipid rafts has proved to be arduous due to their elusive nature, mobility, and constant dynamic reorganization to meet the cellular needs. Studying neuronal lipid rafts is particularly cumbersome due to the immensely complex regional molecular architecture of the central nervous system. Biochemical fractionation, performed with or without detergents, is still the most widely used method to isolate lipid rafts. However, the differences in solubilization when various detergents are used has exposed a dire need to find more reliable methods to study particular rafts. Biochemical methods need to be complemented with other approaches such as live-cell microscopy, imaging mass spectrometry, and the development of specific non-invasive fluorescent probes to obtain a more complete image of raft dynamics and to study the spatio-temporal expression of rafts in live cells.

Lipid Peroxidation Drives Liquid-Liquid Phase Separation and Disrupts Raft Protein Partitioning in Biological Membranes

The peroxidation of membrane lipids by free radicals contributes to aging, numerous diseases, and ferroptosis, an iron-dependent form of cell death. Peroxidation changes the structure and physicochemical properties of lipids, leading to bilayer thinning, altered fluidity, and increased permeability of membranes in model systems. Whether and how lipid peroxidation impacts the lateral organization of proteins and lipids in biological membranes, however, remains poorly understood. Here, we employ cell-derived giant plasma membrane vesicles (GPMVs) as a model to investigate the impact of lipid peroxidation on ordered membrane domains, often termed membrane rafts. We show that lipid peroxidation induced by the Fenton reaction dramatically enhances the phase separation propensity of GPMVs into coexisting liquid-ordered (Lo) and liquid-disordered (Ld) domains and increases the relative abundance of the disordered phase. Peroxidation also leads to preferential accumulation of peroxidized lipids and 4-hydroxynonenal (4-HNE) adducts in the disordered phase, decreased lipid packing in both Lo and Ld domains, and translocation of multiple classes of raft proteins out of ordered domains. These findings indicate that the peroxidation of plasma membrane lipids disturbs many aspects of membrane rafts, including their stability, abundance, packing, and protein and lipid composition. We propose that these disruptions contribute to the pathological consequences of lipid peroxidation during aging and disease and thus serve as potential targets for therapeutic intervention.

Amyloid-β Pathology Is the Common Nominator Proteinopathy of the Primate Brain Aging

Senile plaques, mainly diffuse, and cerebral amyloid-β (Aβ) angiopathy are prevalent in the aging brain of non-human primates, from lemurs to non-human Hominidae. Aβ but not hyper-phosphorylated tau (HPtau) pathology is the common nominator proteinopathy of non-human primate brain aging. The abundance of Aβ in the aging primate brain is well tolerated, and the impact on cognitive functions is usually limited to particular tasks. In contrast, human brain aging is characterized by the early appearance of HPtau pathology, mainly forming neurofibrillary tangles, dystrophic neurites of neuritic plaques, and neuropil threads, preceding Aβ deposits by several decades and by its severity progressing from selected nuclei of the brain stem, entorhinal cortex, and hippocampus to the limbic system, neocortex, and other brain regions. Neurofibrillary tangles correlate with cognitive impairment and dementia in advanced cases. Aβ pathology is linked in humans to altered membrane protein and lipid composition, particularly involving lipid rafts. Although similar membrane alterations are unknown in non-human primates, membrane senescence is postulated to cause the activated β-amyloidogenic pathway, and Aβ pathology is the prevailing signature of non-human and human primate brain aging.

First-in-human single-dose study of nizubaglustat, a dual inhibitor of ceramide glucosyltransferase and non-lysosomal glucosylceramidase: Safety, tolerability, pharmacokinetics, and pharmacodynamics of single ascending and multiple doses in healthy adults

Nizubaglustat is a novel, orally available, brain penetrant, potent, and selective dual inhibitor of ceramide glucosyltranferase and non-lysosomal neutral glucosylceramidase (NLGase), which is currently under development for the treatment of subjects with neurological manifestations in primary and secondary gangliosidoses. The objectives of this first-in-human study were to evaluate the safety and tolerability, pharmacokinetics, and pharmacodynamics (PD) of single oral doses of nizubaglustat after single (1, 3, and 9 mg) and multiple oral doses (9 mg once per day (QD) over 14 days) in healthy adults. Nizubaglustat was rapidly absorbed and systemic exposure was dose-proportional. Steady-state was achieved after three days of QD multiple dosing with minimal accumulation. Renal clearance accounted for around 15% of nizubaglustat elimination. Following multiple dosing, plasma concentrations of glucosylceramide (GlcCer), lactosylceramide (LacCer), and monosialodihexosylganglioside (GM3) decreased to a nadir at Day 10. PD target engagement of GCS inhibition was shown by a median decrease from baseline of plasma concentrations of GlcCer, LacCer, and GM3 ganglioside by 70%, 50%, and 48%, respectively. NLGase inhibition was also manifested by increased concentrations of GlcCer in cerebrospinal fluid from Day 1 to Day 14. Nizubaglustat was safe and well-tolerated at all doses tested. Consistent with the high selectivity, and the absence of intestinal disaccharidases inhibition, no cases of diarrhea were reported. No decreased appetite or weight loss was noted. Only treatment-emergent adverse events with preferred terms belonging to the system organ class skin and subcutaneous disorders of mild intensity were reported as drug-related in the nizubaglustat arm, in line with the pharmacological mechanism targeting glucosylceramide metabolism. Taken together, these data support QD dosing of nizubaglustat and its ongoing development in patients with primary and secondary forms of gangliosidoses.

Metabolic Syndrome: A Narrative Review from the Oxidative Stress to the Management of Related Diseases

Metabolic syndrome (MS) is a growing disorder affecting thousands of people worldwide, especially in industrialised countries, increasing mortality. Oxidative stress, hyperglycaemia, insulin resistance, inflammation, dysbiosis, abdominal obesity, atherogenic dyslipidaemia and hypertension are important factors linked to MS clusters of different pathologies, such as diabesity, cardiovascular diseases and neurological disorders. All biochemical changes observed in MS, such as dysregulation in the glucose and lipid metabolism, immune response, endothelial cell function and intestinal microbiota, promote pathological bridges between metabolic syndrome, diabesity and cardiovascular and neurodegenerative disorders. This review aims to summarise metabolic syndrome's involvement in diabesity and highlight the link between MS and cardiovascular and neurological diseases. A better understanding of MS could promote a novel strategic approach to reduce MS comorbidities.

Are There Lipid Membrane-Domain Subtypes in Neurons with Different Roles in Calcium Signaling?

Lipid membrane nanodomains or lipid rafts are 10-200 nm diameter size cholesterol- and sphingolipid-enriched domains of the plasma membrane, gathering many proteins with different roles. Isolation and characterization of plasma membrane proteins by differential centrifugation and proteomic studies have revealed a remarkable diversity of proteins in these domains. The limited size of the lipid membrane nanodomain challenges the simple possibility that all of them can coexist within the same lipid membrane domain. As caveolin-1, flotillin isoforms and gangliosides are currently used as neuronal lipid membrane nanodomain markers, we first analyzed the structural features of these components forming nanodomains at the plasma membrane since they are relevant for building supramolecular complexes constituted by these molecular signatures. Among the proteins associated with neuronal lipid membrane nanodomains, there are a large number of proteins that play major roles in calcium signaling, such as ionotropic and metabotropic receptors for neurotransmitters, calcium channels, and calcium pumps. This review highlights a large variation between the calcium signaling proteins that have been reported to be associated with isolated caveolin-1 and flotillin-lipid membrane nanodomains. Since these calcium signaling proteins are scattered in different locations of the neuronal plasma membrane, i.e., in presynapses, postsynapses, axonal or dendritic trees, or in the neuronal soma, our analysis suggests that different lipid membrane-domain subtypes should exist in neurons. Furthermore, we conclude that classification of lipid membrane domains by their content in calcium signaling proteins sheds light on the roles of these domains for neuronal activities that are dependent upon the intracellular calcium concentration. Some examples described in this review include the synaptic and metabolic activity, secretion of neurotransmitters and neuromodulators, neuronal excitability (long-term potentiation and long-term depression), axonal and dendritic growth but also neuronal cell survival and death.

Reexamining the Causes and Effects of Cholesterol Deposition in the Brains of Patients with Alzheimer's Disease

Alzheimer's disease (AD) is a degenerative disease of the central nervous system. Numerous studies have shown that imbalances in cholesterol homeostasis in the brains of AD patients precede the onset of clinical symptoms. In addition, cholesterol deposition has been observed in the brains of AD patients even though peripheral cholesterol does not enter the brain through the blood‒brain barrier (BBB). Studies have demonstrated that cholesterol metabolism in the brain is associated with many pathological conditions, such as amyloid beta (Aβ) production, Tau protein phosphorylation, oxidative stress, and inflammation. In 2022, some scholars put forward a new hypothesis of AD: the disease involves lipid invasion and its exacerbation of the abnormal metabolism of cholesterol in the brain. In this review, by discussing the latest research progress, the causes and effects of cholesterol retention in the brains of AD patients are analyzed and discussed. Additionally, the possible mechanism through which AD may be improved by targeting cholesterol is described. Finally, we propose that improving the impairments in cholesterol removal observed in the brains of AD patients, instead of further reducing the already impaired cholesterol synthesis in the brain, may be the key to preventing cholesterol deposition and improving the corresponding pathological symptoms.

CDP-choline to promote remyelination in multiple sclerosis: the need for a clinical trial

Multiple sclerosis is a multifactorial chronic inflammatory disease of the central nervous system that leads to demyelination and neuronal cell death, resulting in functional disability. Remyelination is the natural repair process of demyelination, but it is often incomplete or fails in multiple sclerosis. Available therapies reduce the inflammatory state and prevent clinical relapses. However, therapeutic approaches to increase myelin repair in humans are not yet available. The substance cytidine-5'-diphosphocholine, CDP-choline, is ubiquitously present in eukaryotic cells and plays a crucial role in the synthesis of cellular phospholipids. Regenerative properties have been shown in various animal models of diseases of the central nervous system. We have already shown that the compound CDP-choline improves myelin regeneration in two animal models of multiple sclerosis. However, the results from the animal models have not yet been studied in patients with multiple sclerosis. In this review, we summarise the beneficial effects of CDP-choline on biolipid metabolism and turnover with regard to inflammatory and regenerative processes. We also explain changes in phospholipid and sphingolipid homeostasis in multiple sclerosis and suggest a possible therapeutic link to CDP-choline.

Neuro-HIV-New insights into pathogenesis and emerging therapeutic targets

HIV-associated neurocognitive disorders (HAND) is a term describing a complex set of cognitive impairments accompanying HIV infection. Successful antiretroviral therapy (ART) reduces the most severe forms of HAND, but milder forms affect over 50% of people living with HIV (PLWH). Pathogenesis of HAND in the ART era remains unknown. A variety of pathogenic factors, such as persistent HIV replication in the brain reservoir, HIV proteins released from infected brain cells, HIV-induced neuroinflammation, and some components of ART, have been implicated in driving HAND pathogenesis in ART-treated individuals. Here, we propose another factor-impairment of cholesterol homeostasis and lipid rafts by HIV-1 protein Nef-as a possible contributor to HAND pathogenesis. These effects of Nef on cholesterol may also underlie the effects of other pathogenic factors that constitute the multifactorial nature of HAND pathogenesis. The proposed Nef- and cholesterol-focused mechanism may provide a long-sought unified explanation of HAND pathogenesis that takes into account all contributing factors. Evidence for the impairment by Nef of cellular cholesterol balance, potential effects of this impairment on brain cells, and opportunities to therapeutically target this element of HAND pathogenesis are discussed.

The Ying and Yang of Ganglioside Function in Cancer

The plethora of information about the expression of cancer cell-associated gangliosides, their role(s) in signal transduction, and their potential usefulness in the development of cancer treatments makes this an appropriate time to review these enigmatic glycosphingolipids. Evidence, reflecting the work of many, indicates that (1) expression of specific gangliosides, not generally found in high concentrations in most normal human cells, can be linked to certain types of cancer. (2) Gangliosides can affect the ability of cells to interact either directly or indirectly with growth factor receptors, thereby changing such things as a cell's mobility, rate of proliferation, and metastatic ability. (3) Anti-ganglioside antibodies have been tested, with some success, as potential treatments for certain cancers. (4) Cancer-associated gangliosides shed into the circulation can (a) affect immune cell responsiveness either positively or negatively, (b) be considered as diagnostic markers, and (c) be used to look for recurrence. (5) Cancer registries enable investigators to evaluate data from sufficient numbers of patients to obtain information about potential therapies. Despite advances that have been made, a discussion of possible approaches to identifying additional treatment strategies to inhibit metastasis, responsible for the majority of deaths of cancer patients, as well as for treating therapy-resistant tumors, is included.

Lipid rafts mediate multilineage differentiation of human dental pulp-derived stem cells (DPSCs)

Cell outer membranes contain glycosphingolipids and protein receptors, which are integrated into glycoprotein domains, known as lipid rafts, which are involved in a variety of cellular processes, including receptor-mediated signal transduction and cellular differentiation process. In this study, we analyzed the lipidic composition of human Dental Pulp-Derived Stem Cells (DPSCs), and the role of lipid rafts during the multilineage differentiation process. The relative quantification of lipid metabolites in the organic fraction of DPSCs, performed by Nuclear Magnetic Resonance (NMR) spectroscopy, showed that mono-unsaturated fatty acids (MUFAs) were the most representative species in the total pool of acyl chains, compared to polyunsatured fatty acids (PUFAs). In addition, the stimulation of DPSCs with different culture media induces a multilineage differentiation process, determining changes in the gangliosides pattern. To understand the functional role of lipid rafts during multilineage differentiation, DPSCs were pretreated with a typical lipid raft affecting agent (MβCD). Subsequently, DPSCs were inducted to differentiate into osteoblast, chondroblast and adipoblast cells with specific media. We observed that raft-affecting agent MβCD prevented AKT activation and the expression of lineage-specific mRNA such as OSX, PPARγ2, and SOX9 during multilineage differentiation. Moreover, this compound significantly prevented the tri-lineage differentiation induced by specific stimuli, indicating that lipid raft integrity is essential for DPSCs differentiation. These results suggest that lipid rafts alteration may affect the signaling pathway activated, preventing multilineage differentiation.

Role of rafts in neurological disorders

INTRODUCTION

Rafts are protein-lipid structural nanodomains involved in efficient signal transduction and the modulation of physiological processes of the cell plasma membrane. Raft disruption in the nervous system has been associated with a wide range of disorders.

DEVELOPMENT

We review the concept of rafts, the nervous system processes in which they are involved, and their role in diseases such as Parkinson's disease, Alzheimer disease, and Huntington disease.

CONCLUSIONS

Based on the available evidence, preservation and/or reconstitution of rafts is a promising treatment strategy for a wide range of neurological disorders.

Potential therapeutic effect of olfactory ensheathing cells in neurological diseases: neurodegenerative diseases and peripheral nerve injuries

Neurological diseases are destructive, mainly characterized by the failure of endogenous repair, the inability to recover tissue damage, resulting in the increasing loss of cognitive and physical function. Although some clinical drugs can alleviate the progression of these diseases, but they lack therapeutic effect in repairing tissue injury and rebuilding neurological function. More and more studies have shown that cell therapy has made good achievements in the application of nerve injury. Olfactory ensheathing cells (OECs) are a special type of glial cells, which have been proved to play an important role as an alternative therapy for neurological diseases, opening up a new way for the treatment of neurological problems. The functional mechanisms of OECs in the treatment of neurological diseases include neuroprotection, immune regulation, axon regeneration, improvement of nerve injury microenvironment and myelin regeneration, which also include secreted bioactive factors. Therefore, it is of great significance to better understand the mechanism of OECs promoting functional improvement, and to recognize the implementation of these treatments and the effective simulation of nerve injury disorders. In this review, we discuss the function of OECs and their application value in the treatment of neurological diseases, and position OECs as a potential candidate strategy for the treatment of nervous system diseases.

Developing a Blood Cell-Based Diagnostic Test for Myalgic Encephalomyelitis/Chronic Fatigue Syndrome Using Peripheral Blood Mononuclear Cells

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is characterized by debilitating fatigue that profoundly impacts patients' lives. Diagnosis of ME/CFS remains challenging, with most patients relying on self-report, questionnaires, and subjective measures to receive a diagnosis, and many never receiving a clear diagnosis at all. In this study, a single-cell Raman platform and artificial intelligence are utilized to analyze blood cells from 98 human subjects, including 61 ME/CFS patients of varying disease severity and 37 healthy and disease controls. These results demonstrate that Raman profiles of blood cells can distinguish between healthy individuals, disease controls, and ME/CFS patients with high accuracy (91%), and can further differentiate between mild, moderate, and severe ME/CFS patients (84%). Additionally, specific Raman peaks that correlate with ME/CFS phenotypes and have the potential to provide insights into biological changes and support the development of new therapeutics are identified. This study presents a promising approach for aiding in the diagnosis and management of ME/CFS and can be extended to other unexplained chronic diseases such as long COVID and post-treatment Lyme disease syndrome, which share many of the same symptoms as ME/CFS.

Robust homeostasis of cellular cholesterol is a consequence of endogenous antithetic integral control

Although cholesterol is essential for cellular viability and proliferation, it is highly toxic in excess. The concentration of cellular cholesterol must therefore be maintained within tight tolerances, and is thought to be subject to a stringent form of homeostasis known as Robust Perfect Adaptation (RPA). While much is known about the cellular signalling interactions involved in cholesterol regulation, the specific chemical reaction network structures that might be responsible for the robust homeostatic regulation of cellular cholesterol have been entirely unclear until now. In particular, the molecular mechanisms responsible for sensing excess whole-cell cholesterol levels have not been identified previously, and no mathematical models to date have been able to capture an integral control implementation that could impose RPA on cellular cholesterol. Here we provide a detailed mathematical description of cholesterol regulation pathways in terms of biochemical reactions, based on an extensive review of experimental and clinical literature. We are able to decompose the associated chemical reaction network structures into several independent subnetworks, one of which is responsible for conferring RPA on several intracellular forms of cholesterol. Remarkably, our analysis reveals that RPA in the cholesterol concentration in the endoplasmic reticulum (ER) is almost certainly due to a well-characterised control strategy known as antithetic integral control which, in this case, involves the high-affinity binding of a multi-molecular transcription factor complex with cholesterol molecules that are excluded from the ER membrane. Our model provides a detailed framework for exploring the necessary biochemical conditions for robust homeostatic control of essential and tightly regulated cellular molecules such as cholesterol.

Lipid peroxidation drives liquid-liquid phase separation and disrupts raft protein partitioning in biological membranes

The peroxidation of membrane lipids by free radicals contributes to aging, numerous diseases, and ferroptosis, an iron-dependent form of cell death. Peroxidation changes the structure, conformation and physicochemical properties of lipids, leading to major membrane alterations including bilayer thinning, altered fluidity, and increased permeability. Whether and how lipid peroxidation impacts the lateral organization of proteins and lipids in biological membranes, however, remains poorly understood. Here, we employ cell-derived giant plasma membrane vesicles (GPMVs) as a model to investigate the impact of lipid peroxidation on ordered membrane domains, often termed membrane rafts. We show that lipid peroxidation induced by the Fenton reaction dramatically enhances phase separation propensity of GPMVs into co-existing liquid ordered (raft) and liquid disordered (non-raft) domains and increases the relative abundance of the disordered, non-raft phase. Peroxidation also leads to preferential accumulation of peroxidized lipids and 4-hydroxynonenal (4-HNE) adducts in the disordered phase, decreased lipid packing in both raft and non-raft domains, and translocation of multiple classes of proteins out of rafts. These findings indicate that peroxidation of plasma membrane lipids disturbs many aspects of membrane rafts, including their stability, abundance, packing, and protein and lipid composition. We propose that these disruptions contribute to the pathological consequences of lipid peroxidation during aging and disease, and thus serve as potential targets for therapeutic intervention.

The Influence of Lipid Microdomain Heterogeneity on Protein-Protein Interactions: Proteomic Analysis of Co-Immunoprecipitated Binding Partners of P450 1A2 and P450 3A in Rat Liver Microsomes

Liver cytochrome P450s (CYPs) of the endoplasmic reticulum (ER) are involved in the metabolism of exogenous and endogenous chemicals. The ER is not uniform, but possesses ordered lipid microdomains containing higher levels of saturated fatty acids, sphingomyelin, and cholesterol and disordered regions containing higher levels of polyunsaturated fatty acid chains. The various forms of drug-metabolizing P450s partition to either the ordered or disordered lipid microdomains with different degrees of specificity. P450s readily form complexes with ER-resident proteins, including other forms of P450. This study aims to ascertain whether lipid microdomain localization influences protein-P450 interactions in rat liver microsomes. Thus, liver microsomes were co-immunoprecipitated with CYP1A2-specific and CYP3A-specific antibodies, and the co-immunoprecipitating proteins were identified by liquid chromatography mass spectrometry proteomic analysis. These two P450s preferentially partition to ordered and disordered microdomains, respectively. More than 100 proteins were co-immunoprecipitated with each P450. Segregation of proteins into different microdomains did not preclude their interaction. However, CYP3A interacted broadly with proteins from ordered microdomains, whereas CYP1A2 reacted with a limited subset of these proteins. This is consistent with the concept of lipid raft heterogeneity and may indicate that CYP1A2 is targeted to a specific type of lipid raft. Although many of the interacting proteins for both P450s were other-drug metabolizing enzymes, other interactions were also evident. The consistent CYP3A binding partners were predominantly involved in phase I/II drug metabolism; however, CYP1A2 interacted not only with xenobiotic metabolizing enzymes, but also with enzymes involved in diverse cellular responses such as ER stress and protein folding. SIGNIFICANCE STATEMENT: This work describes the protein interactomes in rat liver microsomes of two important cytochromes P450s (CYP1A2 and CYP3A) in drug metabolism and describes the relationship of the interacting proteins to lipid microdomain distribution.

Uncovering the Lipid Web: Discovering the Multifaceted Roles of Lipids in Human Diseases and Therapeutic Opportunities

Lipids, characterized by their hydrophobic nature, encompass a wide range of molecules with distinct properties and functions [...].

Alterations of Oligodendrocyte and Myelin Energy Metabolism in Multiple Sclerosis

Multiple sclerosis (MS) is a complex autoimmune disease of the central nervous system (CNS), characterized by demyelination and neurodegeneration. Oligodendrocytes play a vital role in maintaining the integrity of myelin, the protective sheath around nerve fibres essential for efficient signal transmission. However, in MS, oligodendrocytes become dysfunctional, leading to myelin damage and axonal degeneration. Emerging evidence suggests that metabolic changes, including mitochondrial dysfunction and alterations in glucose and lipid metabolism, contribute significantly to the pathogenesis of MS. Mitochondrial dysfunction is observed in both immune cells and oligodendrocytes within the CNS of MS patients. Impaired mitochondrial function leads to energy deficits, affecting crucial processes such as impulse transmission and axonal transport, ultimately contributing to neurodegeneration. Moreover, mitochondrial dysfunction is linked to the generation of reactive oxygen species (ROS), exacerbating myelin damage and inflammation. Altered glucose metabolism affects the energy supply required for oligodendrocyte function and myelin synthesis. Dysregulated lipid metabolism results in changes to the composition of myelin, affecting its stability and integrity. Importantly, low levels of polyunsaturated fatty acids in MS are associated with upregulated lipid metabolism and enhanced glucose catabolism. Understanding the intricate relationship between these mechanisms is crucial for developing targeted therapies to preserve myelin and promote neurological recovery in individuals with MS. Addressing these metabolic aspects may offer new insights into potential therapeutic strategies to halt disease progression and improve the quality of life for MS patients.

Molecular and biophysical features of hippocampal "lipid rafts aging" are modified by dietary n-3 long-chain polyunsaturated fatty acids

"Lipid raft aging" in nerve cells represents an early event in the development of aging-related neurodegenerative diseases, such as Alzheimer's disease. Lipid rafts are key elements in synaptic plasticity, and their modification with aging alters interactions and distribution of signaling molecules, such as glutamate receptors and ion channels involved in memory formation, eventually leading to cognitive decline. In the present study, we have analyzed, in vivo, the effects of dietary supplementation of n-3 LCPUFA on the lipid structure, membrane microviscosity, domain organization, and partitioning of ionotropic and metabotropic glutamate receptors in hippocampal lipid raffs in female mice. The results revealed several lipid signatures of "lipid rafts aging" in old mice fed control diets, consisting in depletion of n-3 LCPUFA, membrane unsaturation, along with increased levels of saturates, plasmalogens, and sterol esters, as well as altered lipid relevant indexes. These changes were paralleled by increased microviscosity and changes in the raft/non-raft (R/NR) distribution of AMPA-R and mGluR5. Administration of the n-3 LCPUFA diet caused the partial reversion of fatty acid alterations found in aged mice and returned membrane microviscosity to values found in young animals. Paralleling these findings, lipid rafts accumulated mGluR5, NMDA-R, and ASIC2, and increased their R/NR proportions, which collectively indicate changes in synaptic plasticity. Unexpectedly, this diet also modified the lipidome and dimension of lipid rafts, as well as the domain redistribution of glutamate receptors and acid-sensing ion channels involved in hippocampal synaptic plasticity, likely modulating functionality of lipid rafts in memory formation and reluctance to age-associated cognitive decline.

Exploring the Role of Anionic Lipid Nanodomains in the Membrane Disruption and Protein Folding of Human Islet Amyloid Polypeptide Oligomers on Lipid Membrane Surfaces Using Multiscale Molecular Dynamics Simulations

The aggregation of human Islet Amyloid Polypeptide (hIAPP) on cell membranes is linked to amyloid diseases. However, the physio-chemical mechanisms of how these hIAPP aggregates trigger membrane damage are unclear. Using coarse-grained and all-atom molecular dynamics simulations, we investigated the role of lipid nanodomains in the presence or absence of anionic lipids, phosphatidylserine (PS), and a ganglioside (GM1), in the membrane disruption and protein folding behaviors of hIAPP aggregates on phase-separated raft membranes. Our raft membranes contain liquid-ordered (Lo), liquid-disordered (Ld), mixed Lo/Ld (Lod), PS-cluster, and GM1-cluster nanosized domains. We observed that hIAPP aggregates bound to the Lod domain in the absence of anionic lipids, but also to the GM1-cluster- and PS-cluster-containing domains, with stronger affinity in the presence of anionic lipids. We discovered that L16 and I26 are the lipid anchoring residues of hIAPP binding to the Lod and PS-cluster domains. Finally, significant lipid acyl chain order disruption in the annular lipid shells surrounding the membrane-bound hIAPP aggregates and protein folding, particularly beta-sheet formation, in larger protein aggregates were evident. We propose that the interactions of hIAPP and both non-anionic and anionic lipid nanodomains represent key molecular events of membrane damage associated with the pathogenesis of amyloid diseases.

Compromised Myelin and Axonal Molecular Organization Following Adult-Onset Sulfatide Depletion

3-O-sulfogalactosylceramide, or sulfatide, is a prominent myelin glycosphingolipid reduced in the normal appearing white matter (NAWM) in Multiple Sclerosis (MS), indicating that sulfatide reduction precedes demyelination. Using a mouse model that is constitutively depleted of sulfatide, we previously demonstrated that sulfatide is essential during development for the establishment and maintenance of myelin and axonal integrity and for the stable tethering of certain myelin proteins in the sheath. Here, using an adult-onset depletion model of sulfatide, we employ a combination of ultrastructural, immunohistochemical and biochemical approaches to analyze the consequence of sulfatide depletion from the adult CNS. Our findings show a progressive loss of axonal protein domain organization, which is accompanied by axonal degeneration, with myelin sparing. Similar to our previous work, we also observe differential myelin protein anchoring stabilities that are both sulfatide dependent and independent. Most notably, stable anchoring of neurofascin155, a myelin paranodal protein that binds the axonal paranodal complex of contactin/Caspr1, requires sulfatide. Together, our findings show that adult-onset sulfatide depletion, independent of demyelination, is sufficient to trigger progressive axonal degeneration. Although the pathologic mechanism is unknown, we propose that sulfatide is required for maintaining myelin organization and subsequent myelin-axon interactions and disruptions in these interactions results in compromised axon structure and function.

Lipid domain boundary triggers membrane damage and protein folding of human islet amyloid polypeptide in the early pathogenesis of amyloid diseases

The misfolding and self-aggregation of human Islet Amyloid Polypeptide (hIAPP) are linked to the onset of type 2 diabetes (T2D). However, the mechanism of how the disordered hIAPP aggregates trigger membrane damage leading to the loss of Islet cells in T2D is unknown. Using coarse-grained (CG) and all-atom (AA) molecular dynamics simulations, we have investigated the membrane-disruption behaviors of hIAPP oligomers on the phase-separated lipid nanodomains that mimic the highly heterogeneous lipid raft structures of cell membranes. Our results revealed that hIAPP oligomers preferentially bind to the liquid-ordered and liquid-disordered domain boundary around two hydrophobic residues at L16 and I26, and lipid acyl chain order disruption and beta-sheet formation occur upon hIAPP binding to the membrane surface. We propose that the lipid order disruption and surface-induced beta-sheet formation on the lipid domain boundary represent the early molecular events of membrane damage associated with the early pathogenesis of T2D.

Olfactory ensheathing cells and neuropathic pain

Damage to the nervous system can lead to functional impairment, including sensory and motor functions. Importantly, neuropathic pain (NPP) can be induced after nerve injury, which seriously affects the quality of life of patients. Therefore, the repair of nerve damage and the treatment of pain are particularly important. However, the current treatment of NPP is very weak, which promotes researchers to find new methods and directions for treatment. Recently, cell transplantation technology has received great attention and has become a hot spot for the treatment of nerve injury and pain. Olfactory ensheathing cells (OECs) are a kind of glial cells with the characteristics of lifelong survival in the nervous system and continuous division and renewal. They also secrete a variety of neurotrophic factors, bridge the fibers at both ends of the injured nerve, change the local injury microenvironment, and promote axon regeneration and other biological functions. Different studies have revealed that the transplantation of OECs can repair damaged nerves and exert analgesic effect. Some progress has been made in the effect of OECs transplantation in inhibiting NPP. Therefore, in this paper, we provided a comprehensive overview of the biology of OECs, described the possible pathogenesis of NPP. Moreover, we discussed on the therapeutic effect of OECs transplantation on central nervous system injury and NPP, and prospected some possible problems of OECs transplantation as pain treatment. To provide some valuable information for the treatment of pain by OECs transplantation in the future.

HIPPOCAMPAL GANGLIOSIDE COMPOSITION IS ALTERED BY METFORMIN AND LIRAGLUTIDE TREATMENT IN A HIGH-FAT HIGH-SUGAR DIET RAT MODEL

Insulin resistance has many deleterious effects on the central nervous system, including the initiation and potentiation of neurodegeneration. While the pathogenesis of Alzheimer's disease has been extensively researched with many insights into the effects of amyloids and neurofibrillary tangles, the connection between the two pathogenic entities has not yet been fully elucidated. Gangliosides are commonly found in neuronal membranes and myelin, specifically in lipid rafts that have been linked to pathological amyloidogenesis. In this study, 64 Sprague Dawley rats with equal sex distribution were separated into four sex-specific groups, as follows: control group on standard diet; group on high-fat, high-sugar diet (HFHSD); group on HFHSD treated with metformin; and group on HFHSD treated with liraglutide. Free-floating immunohistochemistry of the rat hippocampi was performed to analyze group-specific and sex-specific changes in the composition of the four most common gangliosides found in neuronal membranes and myelin sheaths, GM1, GD1a, GD1b and GT1b. The groups on HFHSD showed glucose tolerance impairment and body weight increase at the end of the experiment, whereas the groups treated with pharmacotherapeutics had better insulin sensitivity and decreases in body weight by the end of the experiment. Most changes were observed for GM1 and GD1b. Positive immunoreactivity for GM1 was observed in the male group treated with liraglutide in regions where it is not physiologically found. The changes observed following HFHSD and liraglutide treatment were suggestive of ganglioside restructuring that might have implications on pathological amyloidogenesis. Metformin treatment did not significantly alter the hippocampal ganglioside composition in either sex.

Myeloid masquerade: Microglial transcriptional signatures in retinal development and disease

Microglia are dynamic guardians of neural tissue and the resident immune cells of the central nervous system (CNS). The disease-associated microglial signature (DAM), also known as the microglial neurodegenerative phenotype (MGnD), has gained significant attention in recent years as a fundamental microglial response common to various neurodegenerative disease pathologies. Interestingly, this signature shares many features in common with developmental microglia, suggesting the existence of recycled gene programs which play a role both in early neural circuit formation as well as in response to aging and disease. In addition, recent advances in single cell RNA sequencing have revealed significant heterogeneity within the original DAM signature, with contributions from both yolk sac-derived microglia as well as bone marrow-derived macrophages. In this review, we examine the role of the DAM signature in retinal development and disease, highlighting crosstalk between resident microglia and infiltrating monocytes which may critically contribute to the underlying mechanisms of age-related neurodegeneration.

Milk fat globule membrane concentrate as a nutritional supplement prevents age-related cognitive decline in old rats: A lipidomic study of synaptosomes

Aging is associated with a decline in cognitive abilities, mainly in memory and executive functioning. A similar but premature deterioration in cognitive capacities is the hallmark of mild cognitive impairment, Alzeimer's disease and dementia. The biochemical mechanisms that cause these neurodegenerative disorders are poorly understood. However, some evidence suggests that insufficient dietary intakes of some phospholipids could impact on brain function and increase the risk of future cognitive impairment and dementia. We evaluated the cognitive and biochemical effects of supplementation with a milk fat globule membrane (MFGM) concentrate in aged rats. We observed that, compared to control animals, MFGM supplemented rats showed enhanced spatial working memory, but both groups exhibited similar reference spatial learning and emotional memory abilities. No significant differences between BDNF levels in the hippocampus and frontal cortex of treated rats as compared to controls were found. The nootropic effects observed were accompanied by significant changes in the lipid composition of synaptic membranes. MFGM supplementation increased the levels of EPA and DHA acids as well as the plasmalogens content in the synaptosomes isolated from the hippocampus (Synapt-HP) and the frontal cortex (Synapt-FC). In addition enhanced levels of phosphatidyl serine (PS), particularly PS(18:1/18:1), and phosphatidyl inositol (PI) molecular species were observed in Synapt-HP and Synapt-FC of treated animals.Lipidomic analysis also revealed greater concentration of phosphatidyl ethanolamine (PE) molecular species containing very long-chain fatty acids and PE plasmenyls in Synapt-HP as well as an increase of the SM content in Synapt-FC from the MFGM group. Although further studies are needed to confirm the underlying mechanism (individual or synergistic), these results suggest that MFGM supplementation could be employed as a dietary implement to restore the proper cerebral concentration of some bioactive lipids and prevent or slow the progression of age-related cognitive impairment.

Simulation toolkits at the molecular scale for trans-scale thermal signaling

Thermogenesis is a physiological activity of releasing heat that originates from intracellular biochemical reactions. Recent experimental studies discovered that externally applied heat changes intracellular signaling locally, resulting in global changes in cell morphology and signaling. Therefore, we hypothesize an inevitable contribution of thermogenesis in modulating biological system functions throughout the spatial scales from molecules to individual organisms. One key issue examining the hypothesis, namely, the "trans-scale thermal signaling," resides at the molecular scale on the amount of heat released via individual reactions and by which mechanism the heat is employed for cellular function operations. This review introduces atomistic simulation tool kits for studying the mechanisms of thermal signaling processes at the molecular scale that even state-of-the-art experimental methodologies of today are hardly accessible. We consider biological processes and biomolecules as potential heat sources in cells, such as ATP/GTP hydrolysis and multiple biopolymer complex formation and disassembly. Microscopic heat release could be related to mesoscopic processes via thermal conductivity and thermal conductance. Additionally, theoretical simulations to estimate these thermal properties in biological membranes and proteins are introduced. Finally, we envisage the future direction of this research field.

Rethinking purinergic concepts and updating the emerging role of P2X7 and P2X4 in amyotrophic lateral sclerosis

The topic of the present review regards the ubiquitous and phylogenetically most ancient prototype of intercellular signaling, the one mediated by extracellular nucleosides and nucleotides, bearing a strong influence on pathophysiological processes in the nervous system. Not by chance, purine and pyrimidine molecules are the most prevalent and ubiquitous chemical messengers in the animal and plant kingdoms, operating through a large plethora of purinergic metabolizing enzymes, P1 and P2 receptors, nucleoside and nucleotide channels and transporters. Because ectonucleotidases degrade the agonists of P2 receptors while simultaneously generate the agonists for P1 receptors, and because several agonists, or antagonists, simultaneously bind and activate, or inhibit, more than one receptor subtype, it follows that an all-inclusive "purinergic network" perspective should be better considered when looking at purinergic actions. This becomes particularly crucial during pathological conditions as for instance amyotrophic lateral sclerosis, where the contribution of purinergic signaling has been demonstrated to differ according to each target cell phenotype and stage of disease progression. Here we will present some newly updated results about P2X7 and P2X4 as the most thoroughly investigated P2 receptors in amyotrophic lateral sclerosis, being aware that the comprehension of their actions is still in progress, and that the purinergic rationale for studying this disease must be however wide-ranging and all-inclusive. This article is part of the Special Issue on 'Purinergic Signaling: 50 years'.

Multi-Omic analyses characterize the ceramide/sphingomyelin pathway as a therapeutic target in Alzheimer's disease

Dysregulation of sphingomyelin and ceramide metabolism have been implicated in Alzheimer's disease. Genome-wide and transcriptome-wide association studies have identified various genes and genetic variants in lipid metabolism that are associated with Alzheimer's disease. However, the molecular mechanisms of sphingomyelin and ceramide disruption remain to be determined. We focus on the sphingolipid pathway and carry out multi-omics analyses to identify central and peripheral metabolic changes in Alzheimer's patients, correlating them to imaging features. Our multi-omics approach is based on (a) 2114 human post-mortem brain transcriptomics to identify differentially expressed genes; (b) in silico metabolic flux analysis on context-specific metabolic networks identified differential reaction fluxes; (c) multimodal neuroimaging analysis on 1576 participants to associate genetic variants in sphingomyelin pathway with Alzheimer's disease pathogenesis; (d) plasma metabolomic and lipidomic analysis to identify associations of lipid species with dysregulation in Alzheimer's; and (e) metabolite genome-wide association studies to define receptors within the pathway as a potential drug target. We validate our hypothesis in amyloidogenic APP/PS1 mice and show prolonged exposure to fingolimod alleviated synaptic plasticity and cognitive impairment in mice. Our integrative multi-omics approach identifies potential targets in the sphingomyelin pathway and suggests modulators of S1P metabolism as possible candidates for Alzheimer's disease treatment.

Cholesterol as a key player in amyloid β-mediated toxicity in Alzheimer’s disease

Alzheimer’s disease (AD) is a neurodegenerative disorder that is one of the most devastating and widespread diseases worldwide, mainly affecting the aging population. One of the key factors contributing to AD-related neurotoxicity is the production and aggregation of amyloid β (Aβ). Many studies have shown the ability of Aβ to bind to the cell membrane and disrupt its structure, leading to cell death. Because amyloid damage affects different parts of the brain differently, it seems likely that not only Aβ but also the nature of the membrane interface with which the amyloid interacts, helps determine the final neurotoxic effect. Because cholesterol is the dominant component of the plasma membrane, it plays an important role in Aβ-induced toxicity. Elevated cholesterol levels and their regulation by statins have been shown to be important factors influencing the progression of neurodegeneration. However, data from many studies have shown that cholesterol has both neuroprotective and aggravating effects in relation to the development of AD. In this review, we attempt to summarize recent findings on the role of cholesterol in Aβ toxicity mediated by membrane binding in the pathogenesis of AD and to consider it in the broader context of the lipid composition of cell membranes.

Deciphering the relationship between caveolae-mediated intracellular transport and signalling events

The caveolae-mediated transport across polarized epithelial cell barriers has been largely deciphered in the last decades and is considered the second essential intracellular transfer mechanism, after the clathrin-dependent endocytosis. The basic cell biology knowledge was supplemented recently, with the molecular mechanisms beyond caveolae generation implying the key contribution of the lipid-binding proteins (the structural protein Caveolin and the adapter protein Cavin), along with the bulb coat stabilizing molecules PACSIN-2 and Eps15 homology domain protein-2. The current attention is focused also on caveolae architecture (such as the bulb coat, the neck, the membrane funnel inside the bulb, and the associated receptors), and their specific tasks during the intracellular transport of various cargoes. Here, we resume the present understanding of the assembly, detachment, and internalization of caveolae from the plasma membrane lipid raft domains, and give an updated view on transcytosis and endocytosis, the two itineraries of cargoes transport via caveolae. The review adds novel data on the signalling molecules regulating caveolae intracellular routes and on the transport dysregulation in diseases. The therapeutic possibilities offered by exploitation of Caveolin-1 expression and caveolae trafficking, and the urgent issues to be uncovered conclude the review.

Trained Immunity and HIV Infection

Findings that certain infections induce immunity not only against the causing agent, but also against an unrelated pathogen have intrigued investigators for many years. Recently, underlying mechanisms of this phenomenon have started to come to light. It was found that the key cells responsible for heterologous protection are innate immune cells such as natural killer cells (NKs), dendritic cells, and monocytes/macrophages. These cells are 'primed' by initial infection, allowing them to provide enhanced response to subsequent infection by the same or unrelated agent. This phenomenon of innate immune memory was termed 'trained immunity'. The proposed mechanism for trained immunity involves activation by the first stimulus of metabolic pathways that lead to epigenetic changes, which maintain the cell in a "trained" state, allowing enhanced responses to a subsequent stimulus. Innate immune memory can lead either to enhanced responses or to suppression of subsequent responses ('tolerance'), depending on the strength and length of the initial stimulation of the immune cells. In the context of HIV infection, innate memory induced by infection is not well understood. In this Hypothesis and Theory article, we discuss evidence for HIV-induced trained immunity in human monocytes, its possible mechanisms, and implications for HIV-associated co-morbidities.

Lipid Signaling During Gamete Maturation

Cell lipids are differentially distributed in distinct organelles and within the leaflets of the bilayer. They can further form laterally defined sub-domains within membranes with important signaling functions. This molecular and spatial complexity offers optimal platforms for signaling with the associated challenge of dissecting these pathways especially that lipid metabolism tends to be highly interconnected. Lipid signaling has historically been implicated in gamete function, however the detailed signaling pathways involved remain obscure. In this review we focus on oocyte and sperm maturation in an effort to consolidate current knowledge of the role of lipid signaling and set the stage for future directions.

Sphingolipid Players in Multiple Sclerosis: Their Influence on the Initiation and Course of the Disease

Sphingolipids (SLs) play a significant role in the nervous system, as major components of the myelin sheath, contributors to lipid raft formation that organize intracellular processes, as well as active mediators of transport, signaling and the survival of neurons and glial cells. Alterations in SL metabolism and content are observed in the course of central nervous system diseases, including multiple sclerosis (MS). In this review, we summarize the current evidence from studies on SLs (particularly gangliosides), which may shed new light upon processes underlying the MS background. The relevant aspects of these studies include alterations of the SL profile in MS, the role of antibodies against SLs and complexes of SL-ligand-invariant NKT cells in the autoimmune response as the core pathomechanism in MS. The contribution of lipid-raft-associated SLs and SL-laden extracellular vesicles to the disease etiology is also discussed. These findings may have diagnostic implications, with SLs and anti-SL antibodies as potential markers of MS activity and progression. Intriguing prospects of novel therapeutic options in MS are associated with SL potential for myelin repair and neuroprotective effects, which have not been yet addressed by the available treatment strategies. Overall, all these concepts are promising and encourage the further development of SL-based studies in the field of MS.

Fatty Acid Metabolism and T Cells in Multiple Sclerosis

Cellular metabolic remodeling is intrinsically linked to the development, activation, differentiation, function, and survival of T cells. T cells transition from a catabolic, naïve state to an anabolic effector state upon T cell activation. Subsequently, specialization of T cells into T helper (Th) subsets, including regulatory T cells (Treg), requires fine-tuning of metabolic programs that better support and optimize T cell functions for that particular environment. Increasingly, studies have shown that changes in nutrient availability at both the cellular and organismal level during disease states can alter T cell function, highlighting the importance of better characterizing metabolic-immune axes in both physiological and disease settings. In support of these data, a growing body of evidence is emerging that shows specific lipid species are capable of altering the inflammatory functional phenotypes of T cells. In this review we summarize the metabolic programs shown to support naïve and effector T cells, and those driving Th subsets. We then discuss changes to lipid profiles in patients with multiple sclerosis, and focus on how the presence of specific lipid species can alter cellular metabolism and function of T cells.

CB2R Activation Regulates TFEB-Mediated Autophagy and Affects Lipid Metabolism and Inflammation of Astrocytes in POCD

Evidence suggests that the accumulation of lipid drots (LDs) accelerates damage to mitochondria and increases the release of inflammatory factors. These have been implicated as a mechanism underlying neurodegenerative diseases or tumors and aging-related diseases such as postoperative cognitive dysfunction (POCD), nevertheless, accumulation of lipid droplets has not been extensively studied in the central nervous system (CNS). Here, we found that after surgery, there was activation of astrocytes and lipid accumulation in the hippocampus. However, cannabinoid receptor type II (CB2R) activation significantly reduced lipid accumulation in astrocytes and change the expression of genes related to lipid metabolism. CB2R reduces the release of the inflammatory factors interleukin-1 beta (IL-1β) and interleukin 6 (IL-6) in peripheral serum and simultaneously improves cognitive ability in mice with POCD. Further research on mechanisms indicates that CB2R activation promotes the nuclear entry of the bHLH-leucine zipper transcription factor, the transcription factor EB (TFEB), and which is a master transcription factor of the autophagy–lysosomal pathway, also reduces TFEB-S211 phosphorylation. When CB2R promotes TFEB into the nucleus, TFEB binds at two sites within promoter region of PGC1α, promoting PGC1α transcription and accelerating downstream lipid metabolism. The aforementioned process leads to autophagy activation and decreases cellular lipid content. This study uncovers a new mechanism allowing CB2R to regulate lipid metabolism and inflammation in POCD.

Targeting Lipid Rafts as a Rapid Screening Strategy for Potential Antiadipogenic Polyphenols along with the Structure-Activity Relationship and Mechanism Elucidation

Obesity is a global public health problem that endangers human health, and a rapid search for compounds with antiadipogenic activity could provide solutions to overcome this problem. Polyphenols are potential antiadipogenic compounds, but the screening strategy, structure-activity relationship (SAR), and elucidation of their mechanisms of action remain poorly understood because of the high diversity of polyphenols. Lipid rafts, enriched with sphingolipids and cholesterol, are considered a potential target of polyphenols for the regulation of cellular processes and diseases. Here, a novel rapid screening active polyphenol strategy that targets the lipid rafts using molecular dynamic simulation was developed and validated by 3T3-L1 preadipocyte assay. The screening strategy is high-throughput, inexpensive, reagent-free, and effort saving. In addition, the SAR and mechanisms of action mediating the differentiation-inhibition of the preadipocyte by polyphenols were well elucidated by utilizing multiple technologies, such as "raft-like liposomes" systems, giant plasma membrane vesicles, noninvasive lipid raft probes, and ultrahigh-resolution microscopy. High inhibitory-activity polyphenols could penetrate deeper into the hydrophobic lipid center, in an inverted V-shaped manner or by insertion of galloyl groups into rafts, thus disrupting the ordered domain of lipid rafts. In contrast, the medium and low inhibitory-activity polyphenols could only localize on the surface of lipid rafts, exerting slight and the weakest interference with a lipid raft structure, respectively. The combined use of reliable technologies could yield new knowledge on the SAR and the molecular mechanisms of polyphenols.