Lipids and synaptic functions

Reduction of eEF2 kinase alleviates the learning and memory impairment caused by acrylamide

BACKGROUND

The impact of acrylamide (ACR) on learning and memory has garnered considerable attention. However, the targets and mechanisms are still unclear.

RESULTS

Elongation factor 2 (eEF2) was significantly upregulated in the results of serum proteomics. Results from in vitro and in vivo experiments indicated a notable upregulation of Eukaryotic elongation factor 2 kinase (eEF2K), the sole kinase responsible for eEF2 phosphorylation, following exposure to ACR (P < 0.05). Subsequent in vitro experiments using eEF2K siRNA and in vivo experiments with eEF2K-knockout mice demonstrated significant improvements in abnormal indicators related to ACR-induced learning and memory deficits (P < 0.05). Proteomic analysis of the hippocampus revealed Lpcat1 as a crucial downstream protein regulated by eEF2K. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses indicated that eEF2K may play a role in the process of ACR-induced learning and memory impairment by affecting ether lipid metabolism.

CONCLUSIONS

In summary, eEF2K as a pivotal treatment target in the mechanisms underlying ACR-induced learning and memory impairment, and studies have shown that it provides robust evidence for potential clinical interventions targeting ACR-induced impairments.

Effect of aerobic exercise on brain metabolite profiles in the mouse models of methamphetamine addiction: LC-MS-based metabolomics study

Methamphetamine (MA) abuse is recognized as a brain disorder, and physical activity has clear benefits for MA use disorders. The specific mechanisms by which physical activity alleviates MA use disorders are currently not fully understood. Based on this, the present study used untargeted metabolomics using liquid chromatography-mass spectrometry (LC-MS) to analyze the metabolic changes induced by MA in the brains of mice by exercise intervention. It was found that after 2 weeks of treadmill training, aerobic exercise modulated MA-induced brain metabolic disorders, in which 129 metabolites existed that were significantly differentiated in response to MA induction, and 32 metabolites were significantly affected by exercise. These differential metabolites were mainly enriched in glycerophospholipid metabolism, steroid hormone biosynthesis and degradation, and renin-angiotensin system pathways. To our knowledge, this study is the first to use LC-MS to investigate the effects of aerobic exercise on MA-induced brain metabolic profiling. The findings of this study provide new insights into exercise therapy using MA.

Amygdala activity and amygdala-hippocampus connectivity: Metabolic diseases, dementia, and neuropsychiatric issues

With rapid aging of the population worldwide, the number of people with dementia is dramatically increasing. Some studies have emphasized that metabolic syndrome, which includes obesity and diabetes, leads to increased risks of dementia and cognitive decline. Factors such as insulin resistance, hyperglycemia, high blood pressure, dyslipidemia, and central obesity in metabolic syndrome are associated with synaptic failure, neuroinflammation, and imbalanced neurotransmitter levels, leading to the progression of dementia. Due to the positive correlation between diabetes and dementia, some studies have called it "type 3 diabetes". Recently, the number of patients with cognitive decline due to metabolic imbalances has considerably increased. In addition, recent studies have reported that neuropsychiatric issues such as anxiety, depressive behavior, and impaired attention are common factors in patients with metabolic disease and those with dementia. In the central nervous system (CNS), the amygdala is a central region that regulates emotional memory, mood disorders, anxiety, attention, and cognitive function. The connectivity of the amygdala with other brain regions, such as the hippocampus, and the activity of the amygdala contribute to diverse neuropathological and neuropsychiatric issues. Thus, this review summarizes the significant consequences of the critical roles of amygdala connectivity in both metabolic syndromes and dementia. Further studies on amygdala function in metabolic imbalance-related dementia are needed to treat neuropsychiatric problems in patients with this type of dementia.

The Niemann-Pick type diseases – A synopsis of inborn errors in sphingolipid and cholesterol metabolism

Disturbances of lipid homeostasis in cells provoke human diseases. The elucidation of the underlying mechanisms and the development of efficient therapies represent formidable challenges for biomedical research. Exemplary cases are two rare, autosomal recessive, and ultimately fatal lysosomal diseases historically named "Niemann-Pick" honoring the physicians, whose pioneering observations led to their discovery. Acid sphingomyelinase deficiency (ASMD) and Niemann-Pick type C disease (NPCD) are caused by specific variants of the sphingomyelin phosphodiesterase 1 (SMPD1) and NPC intracellular cholesterol transporter 1 (NPC1) or NPC intracellular cholesterol transporter 2 (NPC2) genes that perturb homeostasis of two key membrane components, sphingomyelin and cholesterol, respectively. Patients with severe forms of these diseases present visceral and neurologic symptoms and succumb to premature death. This synopsis traces the tortuous discovery of the Niemann-Pick diseases, highlights important advances with respect to genetic culprits and cellular mechanisms, and exposes efforts to improve diagnosis and to explore new therapeutic approaches.

Computational Advances of Protein/Neurotransmitter-membrane Interactions Involved in Vesicle Fusion and Neurotransmitter Release

Vesicle fusion is of crucial importance to neuronal communication at neuron terminals. The exquisite but complex fusion machinery for neurotransmitter release is tightly controlled and regulated by protein/neurotransmitter-membrane interactions. Computational 'microscopies', in particular molecular dynamics simulations and related techniques, have provided notable insight into the physiological process over the past decades, and have made enormous contributions to fields such as neurology, pharmacology and pathophysiology. Here we review the computational advances of protein/neurotransmitter-membrane interactions related to presynaptic vesicle-membrane fusion and neurotransmitter release, and outline the in silico challenges ahead for understanding this important physiological process.

Norethindrone causes cellular and hepatic injury in zebrafish by compromising the metabolic processes associated with antioxidant defence: Insights from metabolomics

Progestins, such as norethindrone (NET), have been increasingly detected in aquatic environments due to their extensive use for medical applications. While NET is notorious for its endocrine disrupting effects, it has been recently shown to cause cellular damage, suggesting its potential impacts on the body defence of organisms. Hence, we examined the histological features and antioxidant defence of zebrafish (Danio rerio) after exposing to NET (50 ng/L and 500 ng/L) for 72 days, followed by analysing its metabolome to explore whether NET disturbs the metabolic processes responsible for antioxidant defence. While acute mortality was not triggered, we found that antioxidant defence was substantially weakened by NET at 500 ng/L (i.e. reduced SOD and GSH levels) and hence liver injury was inflicted (i.e. elevated ALT and MDA levels), as manifested by vacuolization of liver tissues and reduced number of normal cells in the liver. Metabolomic analysis showed that the metabolic processes responsible for antioxidant defence were disrupted by NET (e.g. upregulation of nervonyl carnitine and chenodeoxycholic acid 3-sulfate; downregulation of homolanthionine and acevaltrate) and these changes can undermine antioxidant defence by suppressing Nrf2-ARE and NF-κB pathways that contribute to the synthesis of SOD and GSH. This study demonstrates how NET can compromise the body defence of aquatic organisms via metabolic disruption, suggesting that the impacts of progestins on their fitness are more detrimental than previously thought.

Saturated free fatty acids and association with memory formation

Polyunsaturated free fatty acids (FFAs) such as arachidonic acid, released by phospholipase activity on membrane phospholipids, have long been considered beneficial for learning and memory and are known modulators of neurotransmission and synaptic plasticity. However, the precise nature of other FFA and phospholipid changes in specific areas of the brain during learning is unknown. Here, using a targeted lipidomics approach to characterise FFAs and phospholipids across the rat brain, we demonstrated that the highest concentrations of these analytes were found in areas of the brain classically involved in fear learning and memory, such as the amygdala. Auditory fear conditioning led to an increase in saturated (particularly myristic and palmitic acids) and to a lesser extent unsaturated FFAs (predominantly arachidonic acid) in the amygdala and prefrontal cortex. Both fear conditioning and changes in FFA required activation of NMDA receptors. These results suggest a role for saturated FFAs in memory acquisition.

DIP2A is involved in SOD-mediated antioxidative reactions in murine brain

Autism spectrum disorders (ASDs) are highly associated with oxidative stress. We have recently shown that Disconnected-interacting protein homolog 2 A (DIP2A) functions in ASD pathophysiology by regulating cortactin acetylation for spine development and synaptic transmission. However, its role is not fully understood in the context of its abundant expression in mitochondria. In this paper, we found that DIP2A was involved in superoxide dismutase (SOD)-mediated antioxidative reactions. In mice, DIP2A knockout inhibited SOD activity and increased reactive oxygen species (ROS) levels in the cerebral cortex. In vitro gain-of-function experiments further confirmed the positive role of DIP2A in scavenging ROS upon oxidative stress. Moreover, DIP2A knockout caused irregular mitochondrial morphology in the cerebral cortex and impaired mitochondrial metabolism with an over consumption of lipids for energy supply. Taken together, these results revealed unrecognized functions of DIP2A in antioxidative protection, providing another possible explanation for DIP2A-mediated ASD pathophysiology.

Glia-Derived Extracellular Vesicles: Role in Central Nervous System Communication in Health and Disease

Glial cells are crucial for the maintenance of correct neuronal functionality in a physiological state and intervene to restore the equilibrium when environmental or pathological conditions challenge central nervous system homeostasis. The communication between glial cells and neurons is essential and extracellular vesicles (EVs) take part in this function by transporting a plethora of molecules with the capacity to influence the function of the recipient cells. EVs, including exosomes and microvesicles, are a heterogeneous group of biogenetically distinct double membrane-enclosed vesicles. Once released from the cell, these two types of vesicles are difficult to discern, thus we will call them with the general term of EVs. This review is focused on the EVs secreted by astrocytes, oligodendrocytes and microglia, aiming to shed light on their influence on neurons and on the overall homeostasis of the central nervous system functions. We collect evidence on neuroprotective and homeostatic effects of glial EVs, including neuronal plasticity. On the other hand, current knowledge of the detrimental effects of the EVs in pathological conditions is addressed. Finally, we propose directions for future studies and we evaluate the potential of EVs as a therapeutic treatment for neurological disorders.

Creating Asymmetric Phospholipid Vesicles via Exchange With Lipid-Coated Silica Nanoparticles

Recently, effort has been placed into fabricating model free-floating asymmetric lipid membranes, such as asymmetric vesicles. Here, we report on the use of lipid-coated silica nanoparticles to exchange lipids with initially symmetric vesicles to generate composition-controlled asymmetric vesicles. Our method relies on the simple and natural exchange of lipids between membranes through an aqueous medium. Using a selected temperature, time, and ratio of lipid-coated silica nanoparticles to vesicles, we produced a desired highly asymmetric leaflet composition. At this point, the silica nanoparticles were removed by centrifugation, leaving the asymmetric vesicles in solution. In the present work, the asymmetric vesicles were composed of isotopically distinct dipalmitoylphosphatidylcholine lipids. Lipid asymmetry was detected by both small-angle neutron scattering (SANS) and proton nuclear magnetic resonance (¹H NMR). The rate at which the membrane homogenizes at 75 °C was also assessed.

Involvement of Lipids in Alzheimer's Disease Pathology and Potential Therapies

Lipids constitute the bulk of the dry mass of the brain and have been associated with healthy function as well as the most common pathological conditions of the brain. Demographic factors, genetics, and lifestyles are the major factors that influence lipid metabolism and are also the key components of lipid disruption in Alzheimer's disease (AD). Additionally, the most common genetic risk factor of AD, APOE ϵ4 genotype, is involved in lipid transport and metabolism. We propose that lipids are at the center of Alzheimer's disease pathology based on their involvement in the blood-brain barrier function, amyloid precursor protein (APP) processing, myelination, membrane remodeling, receptor signaling, inflammation, oxidation, and energy balance. Under healthy conditions, lipid homeostasis bestows a balanced cellular environment that enables the proper functioning of brain cells. However, under pathological conditions, dyshomeostasis of brain lipid composition can result in disturbed BBB, abnormal processing of APP, dysfunction in endocytosis/exocytosis/autophagocytosis, altered myelination, disturbed signaling, unbalanced energy metabolism, and enhanced inflammation. These lipid disturbances may contribute to abnormalities in brain function that are the hallmark of AD. The wide variance of lipid disturbances associated with brain function suggest that AD pathology may present as a complex interaction between several metabolic pathways that are augmented by risk factors such as age, genetics, and lifestyles. Herewith, we examine factors that influence brain lipid composition, review the association of lipids with all known facets of AD pathology, and offer pointers for potential therapies that target lipid pathways.

Lipids in the Physiopathology of Hereditary Spastic Paraplegias

Hereditary spastic paraplegias (HSP) are a group of neurodegenerative diseases sharing spasticity in lower limbs as common symptom. There is a large clinical variability in the presentation of patients, partly underlined by the large genetic heterogeneity, with more than 60 genes responsible for HSP. Despite this large heterogeneity, the proteins with known function are supposed to be involved in a limited number of cellular compartments such as shaping of the endoplasmic reticulum or endolysosomal function. Yet, it is difficult to understand why alteration of such different cellular compartments can lead to degeneration of the axons of cortical motor neurons. A common feature that has emerged over the last decade is the alteration of lipid metabolism in this group of pathologies. This was first revealed by the identification of mutations in genes encoding proteins that have or are supposed to have enzymatic activities on lipid substrates. However, it also appears that mutations in genes affecting endoplasmic reticulum, mitochondria, or endolysosome function can lead to changes in lipid distribution or metabolism. The aim of this review is to discuss the role of lipid metabolism alterations in the physiopathology of HSP, to evaluate how such alterations contribute to neurodegenerative phenotypes, and to understand how this knowledge can help develop therapeutic strategy for HSP.

Glia-Derived Extracellular Vesicles: Role in Central Nervous System Communication in Health and Disease

Glial cells are crucial for the maintenance of correct neuronal functionality in a physiological state and intervene to restore the equilibrium when environmental or pathological conditions challenge central nervous system homeostasis. The communication between glial cells and neurons is essential and extracellular vesicles (EVs) take part in this function by transporting a plethora of molecules with the capacity to influence the function of the recipient cells. EVs, including exosomes and microvesicles, are a heterogeneous group of biogenetically distinct double membrane-enclosed vesicles. Once released from the cell, these two types of vesicles are difficult to discern, thus we will call them with the general term of EVs. This review is focused on the EVs secreted by astrocytes, oligodendrocytes and microglia, aiming to shed light on their influence on neurons and on the overall homeostasis of the central nervous system functions. We collect evidence on neuroprotective and homeostatic effects of glial EVs, including neuronal plasticity. On the other hand, current knowledge of the detrimental effects of the EVs in pathological conditions is addressed. Finally, we propose directions for future studies and we evaluate the potential of EVs as a therapeutic treatment for neurological disorders.

Presynaptic disorders: a clinical and pathophysiological approach focused on the synaptic vesicle

The aim of this report is to present a tentative clinical and pathophysiological approach to diseases affecting the neuronal presynaptic terminal, with a major focus on synaptic vesicles (SVs). Diseases are classified depending on which step of the neurobiology of the SV is predominantly affected: (1) biogenesis of vesicle precursors in the neuronal soma; (2) transport along the axon; (3) vesicle cycle at the presynaptic terminal (exocytosis-endocytosis cycle, with the main purpose of neurotransmitter release). Given that SVs have been defined as individual organelles, we highlight the link between the biological processes disturbed by genetic mutations and the clinical presentation of these disorders. The great majority of diseases may present as epileptic encephalopathies, intellectual disability (syndromic or nonsyndromic) with/without autism spectrum disorder (and other neuropsychiatric symptoms), and movement disorders. These symptoms may overlap and present in patients as a combination of clinical signs that results in the spectrum of the synaptopathies. A small number of diseases may also exhibit neuromuscular signs. In general, SV disorders tend to be severe, early encephalopathies that interfere with neurodevelopment. As a consequence, developmental delay and intellectual disability are constant in almost all the defects described. Considering that some of these diseases might mimic other neurometabolic conditions (and in particular treatable disorders), an initial extensive metabolic workup should always be considered. Further knowledge into pathophysiological mechanisms and biomarkers, as well as descriptions of new presynaptic disorders, will probably take place in the near future.