Aberrant Lipid Metabolism in the Forebrain Niche Suppresses Adult Neural Stem Cell Proliferation in an Animal Model of Alzheimer's Disease

Lipid droplets in the nervous system: involvement in cell metabolic homeostasis

Lipid droplets serve as primary storage organelles for neutral lipids in neurons, glial cells, and other cells in the nervous system. Lipid droplet formation begins with the synthesis of neutral lipids in the endoplasmic reticulum. Previously, lipid droplets were recognized for their role in maintaining lipid metabolism and energy homeostasis; however, recent research has shown that lipid droplets are highly adaptive organelles with diverse functions in the nervous system. In addition to their role in regulating cell metabolism, lipid droplets play a protective role in various cellular stress responses. Furthermore, lipid droplets exhibit specific functions in neurons and glial cells. Dysregulation of lipid droplet formation leads to cellular dysfunction, metabolic abnormalities, and nervous system diseases. This review aims to provide an overview of the role of lipid droplets in the nervous system, covering topics such as biogenesis, cellular specificity, and functions. Additionally, it will explore the association between lipid droplets and neurodegenerative disorders. Understanding the involvement of lipid droplets in cell metabolic homeostasis related to the nervous system is crucial to determine the underlying causes and in exploring potential therapeutic approaches for these diseases.

Lipid remodeling in context of cellular senescence

Cellular senescence is a response that irreversibly arrests stressed cells thus providing a potent tumor suppressor mechanism. In parallel, senescent cells exhibit an immunogenic secretome called SASP (senescence-associated secretory phenotype) that impairs tissue homeostasis and is involved in numerous age-related diseases. Senescence establishment is achieved through the unfolding of a profound transcriptional reprogramming together with morphological changes. These alterations are accompanied by important metabolic adaptations characterized by biosynthetic pathways reshuffling and lipid remodeling. In this mini-review we highlight the intricate links between lipid metabolism and the senescence program and we discuss the potential interventions on lipid pathways that can alleviate the senescence burden.

New insights in lipid metabolism: potential therapeutic targets for the treatment of Alzheimer's disease

Alzheimer's disease (AD) is increasingly recognized as being intertwined with the dysregulation of lipid metabolism. Lipids are a significant class of nutrients vital to all organisms, playing crucial roles in cellular structure, energy storage, and signaling. Alterations in the levels of various lipids in AD brains and dysregulation of lipid pathways and transportation have been implicated in AD pathogenesis. Clinically, evidence for a high-fat diet firmly links disrupted lipid metabolism to the pathogenesis and progression of AD, although contradictory findings warrant further exploration. In view of the significance of various lipids in brain physiology, the discovery of complex and diverse mechanisms that connect lipid metabolism with AD-related pathophysiology will bring new hope for patients with AD, underscoring the importance of lipid metabolism in AD pathophysiology, and promising targets for therapeutic intervention. Specifically, cholesterol, sphingolipids, and fatty acids have been shown to influence amyloid-beta (Aβ) accumulation and tau hyperphosphorylation, which are hallmarks of AD pathology. Recent studies have highlighted the potential therapeutic targets within lipid metabolism, such as enhancing apolipoprotein E lipidation, activating liver X receptors and retinoid X receptors, and modulating peroxisome proliferator-activated receptors. Ongoing clinical trials are investigating the efficacy of these strategies, including the use of ketogenic diets, statin therapy, and novel compounds like NE3107. The implications of these findings suggest that targeting lipid metabolism could offer new avenues for the treatment and management of AD. By concentrating on alterations in lipid metabolism within the central nervous system and their contribution to AD development, this review aims to shed light on novel research directions and treatment approaches for combating AD, offering hope for the development of more effective management strategies.

Multiciliated ependymal cells: an update on biology and pathology in the adult brain

Mature multiciliated ependymal cells line the cerebral ventricles where they form a partial barrier between the cerebrospinal fluid (CSF) and brain parenchyma and regulate local CSF microcirculation through coordinated ciliary beating. Although the ependyma is a highly specialized brain interface with barrier, trophic, and perhaps even regenerative capacity, it remains a misfit in the canon of glial neurobiology. We provide an update to seminal reviews in the field by conducting a scoping review of the post-2010 mature multiciliated ependymal cell literature. We delineate how recent findings have either called into question or substantiated classical views of the ependymal cell. Beyond this synthesis, we document the basic methodologies and study characteristics used to describe multiciliated ependymal cells since 1980. Our review serves as a comprehensive resource for future investigations of mature multiciliated ependymal cells.

Development of BODIPY-based fluorescent probes for imaging Aβ aggregates and lipid droplet viscosity

Alzheimer's disease (AD), gradually recognized as an untreatable neurodegenerative disorder, has been considered to be closely associated with Aβ plaques, which consist of β-amyloid protein (Aβ) and is one of the crucial pathological features of AD. There are no obvious symptoms in the initial phase of AD, and thus the therapeutic interventions are important for early diagnosis of AD. Moreover, recent researches have indicated that lipid droplets might serve as a potential ancillary biomarker, and its viscosity changes are closely associated to the pathological process of AD. Herein, two newly fluorescent probes 5QSZ and BQSZ have been developed and synthesized for identifying Aβ aggregates and detecting the viscosity of lipid droplet. After selectively binding to Aβ aggregates, 5QSZ and BQSZ exhibited linear and obvious fluorescence enhancements (32.58 and 36.70 folds), moderate affinity (Kd = 268.0 and 148.6 nM) and low detection limits (30.11 and 65.37 nM) in aqueous solutions. Further fluorescence staining of 5QSZ on brain tissue sections of APP/PS1 transgenic mouse exhibited the higher selectivity of 5QSZ towards Aβ aggregates locating at the core of the plaques. Furthermore, 5QSZ and BQSZ displayed strong linear fluorescence emission enhancements towards viscosity changes and would be utilized to monitor variation in cellular viscosity induced by LPS or monensin. These two probes were non-cytotoxic and showed good localization in lipid droplets. Therefore, 5QSZ and BQSZ could serve as potential bi-functional fluorescent probes to image Aβ aggregates and monitor the viscosity of lipid droplets, which have significant implications for the early diagnosis and progression of AD.

Exposure to lipid mixture induces intracellular lipid droplet formation and impairs mitochondrial functions in astrocytes

Astrocytes, the predominant glial cells in the central nervous system (CNS), play diverse roles including metabolic support for neurons, provision of neurotrophic factors, facilitation of synaptic neurotransmitter uptake, regulation of ion balance, and involvement in synaptic formation. The accumulation of lipids has been noted in various neurological conditions, yet the response of astrocytes to lipid-rich environments remains unclear. In this study, primary astrocytes isolated from the neonatal rat cortex were exposed to a lipid mixture (LM) comprising cholesterol and various fatty acids to explore their reaction. Our results showed that astrocyte viability remained unchanged following 24 h of 5% or 10% LM treatment. However, exposure to LM for 96 h resulted in reduced cell viability. In addition, LM treatment led to the accumulation of lipid droplets (LDs) in astrocytes, with LD size increasing over prolonged exposure periods. Following 24 h of LM treatment and then 48 h in fresh medium, a significant reduction in intracellular LD size was observed in cultures treated with 5% LM, while no change occurred in cultures exposed to 10% LM. Yet, exposure to 10% LM for 24 h significantly increased the expression of the cholesterol efflux regulatory protein/ATP-binding cassette transporter (ABCA1) gene, responsible for intracellular cholesterol efflux, resulting in reduced cholesterol content within astrocytes. Moreover, LM exposure led to decreased mitochondrial membrane potential (MMP) and increased levels of mature apoptosis-inducing factor (AIF). The smaller LDs were observed to co-localize with microtubule-associated protein 1A/1 B light chain 3 B (LC3) and lysosomal-associated membrane protein-1 (LAMP-1) in LM-treated astrocytes, coinciding with lysosomal acidification. These results indicate that the continuous buildup of LDs in astrocytes residing in lipid-enriched environments may be attributed to disruptions caused by LM in mitochondrial and lysosomal functions. Such disruptions could potentially impede the supportive role of astrocytes in neuronal function.

Emerging Functional Connections Between Metabolism and Epigenetic Remodeling in Neural Differentiation

Stem cells possess extraordinary capacities for self-renewal and differentiation, making them highly valuable in regenerative medicine. Among these, neural stem cells (NSCs) play a fundamental role in neural development and repair processes. NSC characteristics and fate are intricately regulated by the microenvironment and intracellular signaling. Interestingly, metabolism plays a pivotal role in orchestrating the epigenome dynamics during neural differentiation, facilitating the transition from undifferentiated NSC to specialized neuronal and glial cell types. This intricate interplay between metabolism and the epigenome is essential for precisely regulating gene expression patterns and ensuring proper neural development. This review highlights the mechanisms behind metabolic regulation of NSC fate and their connections with epigenetic regulation to shape transcriptional programs of stemness and neural differentiation. A comprehensive understanding of these molecular gears appears fundamental for translational applications in regenerative medicine and personalized therapies for neurological conditions.

Postmortem Fatty Acid Abnormalities in the Cerebellum of Patients with Essential Tremor

Fatty acids play many critical roles in brain function but have not been investigated in essential tremor (ET), a frequent movement disorder suspected to involve cerebellar dysfunction. Here, we report a postmortem comparative analysis of fatty acid profiles by gas chromatography in the cerebellar cortex from ET patients (n = 15), Parkinson's disease (PD) patients (n = 15) and Controls (n = 17). Phosphatidylcholine (PC), phosphatidylethanolamine (PE) and phosphatidylinositol (PI)/ phosphatidylserine (PS) were separated by thin-layer chromatography and analyzed separately. First, the total amounts of fatty acids retrieved from the cerebellar cortex were lower in ET patients compared with PD patients, including monounsaturated (MUFA) and polyunsaturated fatty acids (PUFA). The diagnosis of ET was associated with lower cerebellar levels of saturated fatty acids (SFA) and PUFA (DHA and ARA) in the PE fraction specifically, but with a higher relative content of dihomo-γ-linolenic acid (DGLA; 20:3 ω-6) in the PC fraction. In contrast, a diagnosis of PD was associated with higher absolute concentrations of SFA, MUFA and ω-6 PUFA in the PI + PS fractions. However, relative PI + PS contents of ω-6 PUFA were lower in both PD and ET patients. Finally, linear regression analyses showed that the ω-3:ω-6 PUFA ratio was positively associated with age of death, but inversely associated with insoluble α-synuclein. Although it remains unclear how these FA changes in the cerebellum are implicated in ET or PD pathophysiology, they may be related to an ongoing neurodegenerative process or to dietary intake differences. The present findings provide a window of opportunity for lipid-based therapeutic nutritional intervention.

Plasma lipidomics in early APP/PS1 female mouse model and its relationship with brain: Is it affected by the estrous cycle?

BACKGROUND

Alzheimer's disease (AD) is the most prevalent dementia, showing higher incidence in women. Besides, lipids play an essential role in brain, and they could be dysregulated in neurodegeneration. Specifically, impaired plasma lipid levels could predict early AD diagnosis. This work aims to identify the main plasma lipids altered in early AD female mouse model and evaluate their relationship with brain lipidome. Also, the possible involvement of the estrous cycle in lipid metabolism has been evaluated.

METHODS

Plasma samples of wild-type (n = 10) and APP/PS1 (n = 10) female mice of 5 months of age were collected, processed, and analysed using a lipidomic mass spectrometry-based method. A statistical analysis involving univariate and multivariate approaches was performed to identify significant lipid differences related to AD between groups. Also, cytology tests were conducted to confirm estrous cycle phases.

RESULTS

Three hundred thirty lipids were detected in plasma, 18 of them showed significant differences between groups; specifically, some triacylglycerols, cholesteryl esters, lysophosphatidylcholines, phosphatidylcholines, and ether-linked phosphatidylcholines, increased in early AD; while other phosphatidylcholines, phosphatidylethanolamines, ceramides, and ether-linked phosphatidylethanolamines decreased in early AD. A multivariate approach was developed from some lipid variables, showing high diagnostic indexes (70% sensitivity, 90% specificity, 80% accuracy). From brain and plasma lipidome, some significant correlations were observed, mainly in the glycerophospholipid family. Also, some differences were found in both plasma and brain lipids, according to the estrous cycle phase.

CONCLUSIONS

Therefore, lipid alterations can be identified in plasma at early AD stages in mice females, with a relationship with brain lipid metabolism for most of the lipid subfamilies, suggesting some lipids as potential AD biomarkers. In addition, the estrous cycle monitoring could be relevant in female studies.

Mechanisms of Abnormal Lipid Metabolism in the Pathogenesis of Disease

Lipid metabolism is a critical component in preserving homeostasis and health, and lipids are significant chemicals involved in energy metabolism in living things. With the growing interest in lipid metabolism in recent years, an increasing number of studies have demonstrated the close relationship between abnormalities in lipid metabolism and the development of numerous human diseases, including cancer, cardiovascular, neurological, and endocrine system diseases. Thus, understanding how aberrant lipid metabolism contributes to the development of related diseases and how it works offers a theoretical foundation for treating and preventing related human diseases as well as new avenues for the targeted treatment of related diseases. Therefore, we discuss the processes of aberrant lipid metabolism in various human diseases in this review, including diseases of the cardiovascular system, neurodegenerative diseases, endocrine system diseases (such as obesity and type 2 diabetes mellitus), and other diseases including cancer.

ATG14 and STX18: gatekeepers of lipid droplet degradation and the implications for disease modulation

Lipophagy, a form of autophagy specific to the degradation of lipid droplets (LDs), plays an important role in the maintenance of cellular homeostasis and metabolic processes. A recent study has identified ATG14 (autophagy related 14) as a molecule that targets LDs and marks them for degradation via lipophagy; a process that is inhibited by the binding of STX18 (syntaxin 18) to ATG14 in mammalian cells. The exact mechanism of regulation of lipophagy, and subsequently of cellular LD levels, is still under investigation; however, dysregulation of this process has been linked to a number of disease phenotypes. An imbalance of lipid levels can result in a wide variety of conditions depending on the cell/tissue type in which they occur. In cells of the retinal pigment epithelium, lipid accumulation can result in dry age-related macular degeneration, in hepatocytes it can result in nonalcoholic fatty liver diseases and in neural cells it can result in the pathogenesis of neurodegenerative conditions such as Alzheimer and Parkinson diseases. Based upon its wide range of implications in diseases, modulation of lipophagy is currently being further investigated for its potential as a treatment for a variety of conditions ranging from viral infection to developmental illnesses.

APOE and Alzheimer's disease: Pathologic clues from transgenic Drosophila melanogaster

Alzheimer's disease (AD) is one of the most common forms of neurodegenerative diseases. Apolipoprotein E4 (ApoE4) is the main genetic risk factor in the development of late-onset AD. However, the exact mechanism underlying ApoE4-mediated neurodegeneration remains unclear. We utilized Drosophila melanogaster to examine the neurotoxic effects of various human APOE isoforms when expressed specifically in glial and neural cells. We assessed impacts on mitochondrial dynamics, ER stress, lipid metabolism, and bio-metal ion concentrations in the central nervous system (CNS) of the transgenic flies. Dachshund antibody staining revealed a reduction in the number of Kenyon cells. Behavioral investigations including ethanol tolerance and learning and memory performance demonstrated neuronal dysfunction in APOE4-expressing larvae and adult flies. Transcription level of marf and drp-1 were found to be elevated in APOE4 flies, while atf4, atf6, and xbp-1 s showed down regulation. Enhanced concentrations of triglyceride and cholesterol in the CNS were observed in APOE4 transgenic flies, with especially pronounced effects upon glial-specific expression of the gene. Spectrophotometry of brain homogenate revealed enhanced Fe++ and Zn++ ion levels in conjunction with diminished Cu++ levels upon APOE4 expression. To explore therapeutic strategies, we subjected the flies to heat-shock treatment, aiming to activate heat-shock proteins (HSPs) and assess their potential to mitigate the neurotoxic effects of APOE isoforms. The results showed potential therapeutic benefits for APOE4-expressing flies, hinting at an ability to attenuate memory deterioration. Overall, our findings suggest that APOE4 can alter lipid metabolism, bio metal ion homeostasis, and disrupt the harmonious fission-fusion balance of neuronal and glial mitochondria, ultimately inducing ER stress. These alterations mirror the main clinical manifestations of AD in patients. Therefore, our work underscores the suitability of Drosophila as a fertile model for probing the pathological roles of APOE and furthering our understanding of diverse isoform-specific functions.

Developmental neurotoxicity of PFOA exposure on hiPSC-derived cortical neurons

PFOA is a legacy Per- and Polyfluorinated Substances (PFAS), a group of chemicals widely used in various industrial applications and consumer products. Although there has been a voluntary phase out of PFOA since 2005, it is still widely detected in various water supplies. A growing body of evidence suggests an association between PFOA exposure, particularly during developmental stages, with increased risks of neurodegenerative diseases (NDs). The neurotoxic mechanism of developmental PFOA exposure, however, remains poorly understood. Utilizing human induced-pluripotent stem cell (hiPSC)-derived cortical neurons, we investigated the effect of PFOA exposure prior to differentiation and assessed changes in neuronal characteristics, transcriptome, and neurodegeneration markers mimicking a Developmental Origin of Health and Disease (DoHAD) paradigm. Exposure to PFOA before neuron differentiation resulted in persistent alterations in nuclear morphology, neuronal network, and calcium activity. RNA sequencing analysis further revealed transcriptomic changes aligning with Alzheimer's Disease (AD) after PFOA exposure. These observations were further corroborated by alterations in tau phosphorylation markers, the presence of fibrillar tau, an increase in liquid droplets, and a decrease in RNA translational efficiency characterized using a battery of biochemical assays. Taken together, our results revealed persistent deficits of key neuronal characteristics induced by pre-differentiation PFOA exposure, suggesting impairments in several AD-related pathways that can together contribute to the elevation of AD risk after pre-differentiation PFOA exposure.

Truncated tau interferes with the autophagy and endolysosomal pathway and results in lipid accumulation

The autophagy-lysosomal pathway plays a critical role in the clearance of tau protein aggregates that deposit in the brain in tauopathies, and defects in this system are associated with disease pathogenesis. Here, we report that expression of Tau35, a tauopathy-associated carboxy-terminal fragment of tau, leads to lipid accumulation in cell lines and primary cortical neurons. Our findings suggest that this is likely due to a deleterious block of autophagic clearance and lysosomal degradative capacity by Tau35. Notably, upon induction of autophagy by Torin 1, Tau35 inhibited nuclear translocation of transcription factor EB (TFEB), a key regulator of lysosomal biogenesis. Both cell lines and primary cortical neurons expressing Tau35 also exhibited changes in endosomal protein expression. These findings implicate autophagic and endolysosomal dysfunction as key pathological mechanisms through which disease-associated tau fragments could lead to the development and progression of tauopathy.

Cholesterol Metabolism in Neurodegenerative Diseases

Significance: Cholesterol plays a crucial role in the brain, where it is highly concentrated and tightly regulated to support normal brain functions. It serves as a vital component of cell membranes, ensuring their integrity, and acts as a key regulator of various brain processes. Dysregulation of cholesterol metabolism in the brain has been linked to impaired brain function and the onset of neurodegenerative diseases such as Alzheimer's disease (AD), Parkinson's disease, and Huntington's disease. Recent Advances: A significant advancement has been the identification of astrocyte-derived apoliprotein E as a key regulator of de novo cholesterol biosynthesis in neurons, providing insights into how extracellular signals influence neuronal cholesterol levels. In addition, the development of antibody-based therapies, particularly for AD, presents promising opportunities for therapeutic interventions. Critical Issues: Despite significant research, the association between cholesterol and neurodegenerative diseases remains inconclusive. It is crucial to distinguish between plasma cholesterol and brain cholesterol, as these pools are relatively independent. This differentiation should be considered when evaluating statin-based treatment approaches. Furthermore, assessing not only the total cholesterol content in the brain but also its distribution among different types of brain cells is essential. Future Direction: Establishing a causal link between changes in brain/plasma cholesterol levels and the onset of brain dysfunction/neurodegenerative diseases remains a key objective. In addition, conducting cell-specific analyses of cholesterol homeostasis in various types of brain cells under pathological conditions will enhance our understanding of cholesterol metabolism in neurodegenerative diseases. Manipulating cholesterol levels to restore homeostasis may represent a novel approach for alleviating neurological symptoms.

A fluorescent perilipin 2 knock-in mouse model reveals a high abundance of lipid droplets in the developing and adult brain

Lipid droplets (LDs) are dynamic lipid storage organelles. They are tightly linked to metabolism and can exert protective functions, making them important players in health and disease. Most LD studies in vivo rely on staining methods, providing only a snapshot. We therefore developed a LD-reporter mouse by labelling the endogenous LD coat protein perilipin 2 (PLIN2) with tdTomato, enabling staining-free fluorescent LD visualisation in living and fixed tissues and cells. Here we validate this model under standard and high-fat diet conditions and demonstrate that LDs are highly abundant in various cell types in the healthy brain, including neurons, astrocytes, ependymal cells, neural stem/progenitor cells and microglia. Furthermore, we also show that LDs are abundant during brain development and can be visualized using live imaging of embryonic slices. Taken together, our tdTom-Plin2 mouse serves as a novel tool to study LDs and their dynamics under both physiological and diseased conditions in all tissues expressing Plin2.

Protein Tyrosine Phosphatase 1B (PTP1B): A Comprehensive Review of Its Role in Pathogenesis of Human Diseases

Overexpression of protein tyrosine phosphatase 1B (PTP1B) disrupts signaling pathways and results in numerous human diseases. In particular, its involvement has been well documented in the pathogenesis of metabolic disorders (diabetes mellitus type I and type II, fatty liver disease, and obesity); neurodegenerative diseases (Alzheimer's disease, Parkinson's disease); major depressive disorder; calcific aortic valve disease; as well as several cancer types. Given this multitude of therapeutic applications, shortly after identification of PTP1B and its role, the pursuit to introduce safe and selective enzyme inhibitors began. Regrettably, efforts undertaken so far have proved unsuccessful, since all proposed PTP1B inhibitors failed, or are yet to complete, clinical trials. Intending to aid introduction of the new generation of PTP1B inhibitors, this work collects and organizes the current state of the art. In particular, this review intends to elucidate intricate relations between numerous diseases associated with the overexpression of PTP1B, as we believe that it is of the utmost significance to establish and follow a brand-new holistic approach in the treatment of interconnected conditions. With this in mind, this comprehensive review aims to validate the PTP1B enzyme as a promising molecular target, and to reinforce future research in this direction.

Metabolic differences in MSTN and FGF5 dual-gene edited sheep muscle cells during myogenesis

Dynamic metabolic reprogramming occurs at different stages of myogenesis and contributes to the fate determination of skeletal muscle satellite cells (MuSCs). Accumulating evidence suggests that mutations in myostatin (MSTN) have a vital role in regulating muscle energy metabolism. Here, we explored the metabolic reprogramming in MuSCs and myotube cells in MSTN and FGF5 dual-gene edited sheep models prepared previously, and also focused on the metabolic alterations during myogenic differentiation of MuSCs. Our study revealed that the pathways of nucleotide metabolism, pantothenate and CoA biosynthesis were weakened, while the unsaturated fatty acids biosynthesis were strengthened during myogenic differentiation of sheep MuSCs. The MSTN and FGF5 dual-gene editing mainly inhibited nucleotide metabolism and biosynthesis of unsaturated fatty acids in sheep MuSCs, reduced the number of lipid droplets in per satellite cell, and promoted the pentose phosphate pathway, and the interconversion of pentose and glucuronate. The MSTN and FGF5 dual-gene editing also resulted in the inhibition of nucleotide metabolism and TCA cycle pathway in differentiated myotube cells. The differential metabolites we identified can be characterized as biomarkers of different cellular states, and providing a new reference for MSTN and FGF5 dual-gene editing in regulation of muscle development. It may also provide a reference for the development of muscle regeneration drugs targeting biomarkers.

Lipid Droplets and Neurodegeneration

Energy metabolism in the brain has been considered one of the critical research areas of neuroscience for ages. One of the most vital parts of brain metabolism cascades is lipid metabolism, and fatty acid plays a crucial role in this process. The fatty acid breakdown process in mitochondria undergoes through a conserved pathway known as β-oxidation where acetyl-CoA and shorter fatty acid chains are produced along with a significant amount of energy molecule. Further, the complete breakdown of fatty acids occurs when they enter the mitochondrial oxidative phosphorylation. Cells store energy as neutral lipids in organelles known as Lipid Droplets (LDs) to prepare for variations in the availability of nutrients. Fatty acids are liberated by lipid droplets and are transported to various cellular compartments for membrane biogenesis or as an energy source. Current research shows that LDs are important in inflammation, metabolic illness, and cellular communication. Lipid droplet biology in peripheral organs like the liver and heart has been well investigated, while the brain's LDs have received less attention. Recently, there has been increased awareness of the existence and role of these dynamic organelles in the central nervous system, mainly connected to neurodegeneration. In this review, we discussed the role of beta-oxidation and lipid droplet formation in the oxidative phosphorylation process, which directly affects neurodegeneration through various pathways.

α-Synuclein Overexpression and the Microbiome Shape the Gut and Brain Metabolome in Mice

Pathological forms of the protein α-synuclein contribute to a family of disorders termed synucleinopathies, which includes Parkinson's disease (PD). Most cases of PD are believed to arise from gene-environment interactions. Microbiome composition is altered in PD, and gut bacteria are causal to symptoms and pathology in animal models. To explore how the microbiome may impact PD-associated genetic risks, we quantitatively profiled nearly 630 metabolites from 26 biochemical classes in the gut, plasma, and brain of α-synuclein-overexpressing (ASO) mice with or without microbiota. We observe tissue-specific changes driven by genotype, microbiome, and their interaction. Many differentially expressed metabolites in ASO mice are also dysregulated in human PD patients, including amine oxides, bile acids and indoles. Notably, levels of the microbial metabolite trimethylamine N-oxide (TMAO) strongly correlate from the gut to the plasma to the brain, identifying a product of gene-environment interactions that may influence PD-like outcomes in mice. TMAO is elevated in the blood and cerebral spinal fluid of PD patients. These findings uncover broad metabolomic changes that are influenced by the intersection of host genetics and the microbiome in a mouse model of PD.

Interplay of CD36, autophagy, and lipid metabolism: insights into cancer progression

CD36, a scavenger receptor B2 that is dynamically distributed between cell membranes and organelle membranes, plays a crucial role in regulating lipid metabolism. Abnormal CD36 activity has been linked to a range of metabolic disorders, such as obesity, nonalcoholic fatty liver disease, insulin resistance and cardiovascular disease. CD36 undergoes various modifications, including palmitoylation, glycosylation, and ubiquitination, which greatly affect its binding affinity to various ligands, thereby triggering and influencing various biological effects. In the context of tumors, CD36 interacts with autophagy to jointly regulate tumorigenesis, mainly by influencing the tumor microenvironment. The central role of CD36 in cellular lipid homeostasis and recent molecular insights into CD36 in tumor development indicate the applicability of CD36 as a therapeutic target for cancer treatment. Here, we discuss the diverse posttranslational modifications of CD36 and their respective roles in lipid metabolism. Additionally, we delve into recent research findings on CD36 in tumors, outlining ongoing drug development efforts targeting CD36 and potential strategies for future development and highlighting the interplay between CD36 and autophagy in the context of cancer. Our aim is to provide a comprehensive understanding of the function of CD36 in both physiological and pathological processes, facilitating a more in-depth analysis of cancer progression and a better development and application of CD36-targeting drugs for tumor therapy in the near future.

Emerging functions of the mitochondria-ER-lipid droplet three-way junction in coordinating lipid transfer, metabolism, and storage in cells

Over the past two decades, we have witnessed a growing appreciation for the importance of membrane contact sites (CS) in facilitating direct communication between organelles. CS are tiny regions where the membranes of two organelles meet but do not fuse and allow the transfer of metabolites between organelles, playing crucial roles in the coordination of cellular metabolic activities. The significant advancements in imaging techniques and molecular and cell biology research have revealed that CS are more complex than what originally thought, and as they are extremely dynamic, they can remodel their shape, composition, and functions in accordance with metabolic and environmental changes and can occur between more than two organelles. Here, we describe how recent studies led to the identification of a three-way mitochondria-ER-lipid droplet CS and discuss the emerging functions of these contacts in maintaining lipid storage, homeostasis, and balance. We also summarize the properties and functions of key protein components localized at the mitochondria-ER-lipid droplet interface, with a special focus on lipid transfer proteins. Understanding tripartite CS is essential for unraveling the complexities of inter-organelle communication and cooperation within cells.

Gut microbiota-host lipid crosstalk in Alzheimer's disease: implications for disease progression and therapeutics

Trillions of intestinal bacteria in the human body undergo dynamic transformations in response to physiological and pathological changes. Alterations in their composition and metabolites collectively contribute to the progression of Alzheimer's disease. The role of gut microbiota in Alzheimer's disease is diverse and complex, evidence suggests lipid metabolism may be one of the potential pathways. However, the mechanisms that gut microbiota mediate lipid metabolism in Alzheimer's disease pathology remain unclear, necessitating further investigation for clarification. This review highlights the current understanding of how gut microbiota disrupts lipid metabolism and discusses the implications of these discoveries in guiding strategies for the prevention or treatment of Alzheimer's disease based on existing data.

Central inhibition of stearoyl-CoA desaturase has minimal effects on the peripheral metabolic symptoms of the 3xTg Alzheimer's disease mouse model

Evidence from genetic and epidemiological studies point to lipid metabolism defects in both the brain and periphery being at the core of Alzheimer's disease (AD) pathogenesis. Previously, we reported that central inhibition of the rate-limiting enzyme in monounsaturated fatty acid synthesis, stearoyl-CoA desaturase (SCD), improves brain structure and function in the 3xTg mouse model of AD (3xTg-AD). Here, we tested whether these beneficial central effects involve recovery of peripheral metabolic defects, such as fat accumulation and glucose and insulin handling. As early as 3 months of age, 3xTg-AD mice exhibited peripheral phenotypes including increased body weight and visceral and subcutaneous white adipose tissue as well as diabetic-like peripheral gluco-regulatory abnormalities. We found that intracerebral infusion of an SCD inhibitor that normalizes brain fatty acid desaturation, synapse loss and learning and memory deficits in middle-aged memory-impaired 3xTg-AD mice did not affect these peripheral phenotypes. This suggests that the beneficial effects of central SCD inhibition on cognitive function are not mediated by recovery of peripheral metabolic abnormalities. Given the widespread side-effects of systemically administered SCD inhibitors, these data suggest that selective inhibition of SCD in the brain may represent a clinically safer and more effective strategy for AD.

The cell biology of APOE in the brain

Apolipoprotein E (APOE) traffics lipids in the central nervous system. The E4 variant of APOE is a major genetic risk factor for Alzheimer's disease (AD) and a multitude of other neurodegenerative diseases, yet the molecular mechanisms by which APOE4 drives disease are still unclear. A growing collection of studies in iPSC models, knock-in mice, and human postmortem brain tissue have demonstrated that APOE4 expression in astrocytes and microglia is associated with the accumulation of cytoplasmic lipid droplets, defects in endolysosomal trafficking, impaired mitochondrial metabolism, upregulation of innate immune pathways, and a transition into a reactive state. In this review, we collate these developments and suggest testable mechanistic hypotheses that could explain common APOE4 phenotypes.

APOE traffics to astrocyte lipid droplets and modulates triglyceride saturation and droplet size

The E4 variant of APOE strongly predisposes individuals to late-onset Alzheimer's disease. We demonstrate that in response to lipogenesis, apolipoprotein E (APOE) in astrocytes can avoid translocation into the endoplasmic reticulum (ER) lumen and traffic to lipid droplets (LDs) via membrane bridges at ER-LD contacts. APOE knockdown promotes fewer, larger LDs after a fatty acid pulse, which contain more unsaturated triglyceride after fatty acid pulse-chase. This LD size phenotype was rescued by chimeric APOE that targets only LDs. Like APOE depletion, APOE4-expressing astrocytes form a small number of large LDs enriched in unsaturated triglyceride. Additionally, the LDs in APOE4 cells exhibit impaired turnover and increased sensitivity to lipid peroxidation. Our data indicate that APOE plays a previously unrecognized role as an LD surface protein that regulates LD size and composition. APOE4 causes aberrant LD composition and morphology. Our study contributes to accumulating evidence that APOE4 astrocytes with large, unsaturated LDs are sensitized to lipid peroxidation, which could contribute to Alzheimer's disease risk.

ATG5 (autophagy related 5) in microglia controls hippocampal neurogenesis in Alzheimer disease

Macroautophagy/autophagy is the intracellular degradation process of cytoplasmic content and damaged organelles. Autophagy is strongly associated with the progression of Alzheimer disease (AD). Microglia are brain-resident macrophages, and recent studies indicate that autophagy in microglia protects neurons from neurodegeneration. Postnatal neurogenesis, the generation of new neurons from adult neural stem cells (NSCs), is impaired in AD patients as well as in AD animal models. However, the extent to which microglial autophagy influences adult NSCs and neurogenesis in AD animal models has not been studied. Here, we showed that conditional knock out (cKO) of Atg5 (autophagy related 5) in microglia inhibited postnatal neurogenesis in the dentate gyrus (DG) of the hippocampus, but not in the subventricular zone (SVZ) of a 5×FAD mouse model. Interestingly, the protection of neurogenesis by Atg5 in microglia was only observed in female AD mice. To confirm the roles of autophagy in microglia for postnatal hippocampal neurogenesis, we generated additional cKO mice to delete autophagy essential genes Rb1cc1 or Atg14 in microglia. However, these rb1cc1 cKO and atg14 cKO mice did not exhibit neurogenesis defects in the context of a female AD mouse model. Last, we used the CSF1R antagonist to deplete ATG5-deficient microglia and this intervention restored neurogenesis in the hippocampus of 5×FAD mice. These results indicate that microglial ATG5 is essential to maintain postnatal hippocampal neurogenesis in a mouse model of AD. Our findings further support the notion that ATG5 in microglia supports NSC health and may prevent neurodegeneration.Abbreviations: 5×FAD: familial Alzheimer disease; Aβ: β-amyloid; AD: Alzheimer disease; AIF1: allograft inflammatory factor 1; ATG: autophagy related; BrdU: 5-bromo-2'-deoxyuridine; CA: Cornu Ammonis; cKO: conditional knock out; CSF1R: colony stimulating factor 1 receptor; Ctrl: control; DCX: doublecortin; DG: dentate gyrus; GFAP: glial fibrillary acidic protein; GZ: granular zone; H&E: hematoxylin and eosin; IF: immunofluorescence; LD: lipid droplet; LDAM: lipid droplets accumulated microglia; LPS: lipopolysaccharides; MAP1LC3B/LC3: microtubule-associated protein 1 light chain 3 beta; NSCs: neural stem cells; RB1CC1: RB1-inducible coiled-coil 1; SOX2: SRY (sex determining region Y)-box 2; SGZ: subgranular zone; SVZ: subventricular zone; WT: wild type.

Integrative brain omics approach reveals key role for sn-1 lysophosphatidylethanolamine in Alzheimer's dementia

The biology of individual lipid species and their relevance in Alzheimer's disease (AD) remains incompletely understood. We utilized non-targeted mass spectrometry to examine brain lipids variations across 316 post-mortem brains from participants in the Religious Orders Study (ROS) or Rush Memory and Aging Project (MAP) cohorts classified as either control, asymptomatic AD (AAD), or symptomatic AD (SAD) and integrated the lipidomics data with untargeted proteomic characterization on the same individuals. Lipid enrichment analysis and analysis of variance identified significantly lower abundance of lysophosphatidylethanolamine (LPE) and lysophosphatidylcholine (LPC) species in SAD than controls or AAD. Lipid-protein co-expression network analyses revealed that lipid modules consisting of LPE and LPC exhibited a significant association to protein modules associated with MAPK/metabolism, post-synaptic density, and Cell-ECM interaction pathways and were associated with better antemortem cognition and with neuropathological changes seen in AD. Particularly, LPE 22:6 [sn-1] levels are significantly decreased across AD cases (SAD) and show the most influence on protein changes compared to other lysophospholipid species. LPE 22:6 may be a lipid signature for AD and could be leveraged as potential therapeutic or dietary targets for AD.

The role of ApoE in fatty acid transport from neurons to astrocytes under ischemia/hypoxia conditions

BACKGROUND

The aim of this study was to investigate whether ischemia/hypoxia conditions induce fatty acid transport from neurons to astrocytes and whether this mechanism is affected by ApoE isoforms.

METHODS AND RESULTS

A neonatal rat model of hypoxic-ischemic brain damage was established. Excessive accumulation of lipid droplets and upregulation of ApoE expression occurred in the hippocampus and cerebral cortex after hypoxia-ischemia, which implied the occurrence of abnormal fatty acid metabolism. Lipid peroxidation was induced in an oxygen-glucose deprivation and reperfusion (OGDR) model of ApoE-/- primary neurons. The number of BODIPY 558/568 C12-positive particles (fatty acid markers) transferred from neurons to astrocytes was significantly increased with the addition of human recombinant ApoE compared with that in the OGDR group, which significantly increased the efficiency of fatty acid transport from neurons to astrocytes and neuronal viability. However, ApoE4 was found to be associated with lower efficiency in fatty acid transport and less protective effects in OGDR-induced neuronal cell death than both ApoE2 and ApoE3. COG133, an ApoE-mimetic peptide, partially compensated for the adverse effects of ApoE4. FABP5 and SOD1 gene and protein expression levels were upregulated in astrocytes treated with BODIPY 558/568 C12 particles.

CONCLUSIONS

In conclusion, ApoE plays an important role in mediating the transport of fatty acids from neurons to astrocytes under ischemia/hypoxia conditions, and this transport mechanism is ApoE isoform dependent. ApoE4 has a low transfer efficiency and may be a potential target for the clinical treatment of neonatal hypoxic-ischemic encephalopathy.

Novel insights into brain lipid metabolism in Alzheimer's disease: Oligodendrocytes and white matter abnormalities

Alzheimer's disease (AD) is the most common cause of dementia. A genome-wide association study has shown that several AD risk genes are involved in lipid metabolism. Additionally, epidemiological studies have indicated that the levels of several lipid species are altered in the AD brain. Therefore, lipid metabolism is likely changed in the AD brain, and these alterations might be associated with an exacerbation of AD pathology. Oligodendrocytes are glial cells that produce the myelin sheath, which is a lipid-rich insulator. Dysfunctions of the myelin sheath have been linked to white matter abnormalities observed in the AD brain. Here, we review the lipid composition and metabolism in the brain and myelin and the association between lipidic alterations and AD pathology. We also present the abnormalities in oligodendrocyte lineage cells and white matter observed in AD. Additionally, we discuss metabolic disorders, including obesity, as AD risk factors and the effects of obesity and dietary intake of lipids on the brain.

Brain areas lipidomics in female transgenic mouse model of Alzheimer's disease

Lipids are the major component of the brain with important structural and functional properties. Lipid disruption could play a relevant role in Alzheimer's disease (AD). Some brain lipidomic studies showed significant differences compared to controls, but few studies have focused on different brain areas related to AD. Furthermore, AD is more prevalent in females, but there is a lack of studies focusing on this sex. This work aims to perform a lipidomic study in selected brain areas (cerebellum, amygdala, hippocampus, entire cortex) from wild-type (WT, n = 10) and APPswe/PS1dE9 transgenic (TG, n = 10) female mice of 5 months of age, as a model of early AD, to identify alterations in lipid composition. A lipidomic mass spectrometry-based method was optimized and applied to brain tissue. As result, some lipids showed statistically significant differences between mice groups in cerebellum (n = 68), amygdala (n = 49), hippocampus (n = 48), and the cortex (n = 22). In addition, some lipids (n = 15) from the glycerolipid, phospholipid, and sphingolipid families were statistically significant in several brain areas simultaneously between WT and TG. A selection of lipid variables was made to develop a multivariate approach to assess their discriminant potential, showing high diagnostic indexes, especially in cerebellum and amygdala (sensitivity 70-100%, sensibility 80-100%).

Single-cell mapping of lipid metabolites using an infrared probe in human-derived model systems

Understanding metabolic heterogeneity is the key to uncovering the underlying mechanisms of metabolic-related diseases. Current metabolic imaging studies suffer from limitations including low resolution and specificity, and the model systems utilized often lack human relevance. Here, we present a single-cell metabolic imaging platform to enable direct imaging of lipid metabolism with high specificity in various human-derived 2D and 3D culture systems. Through the incorporation of an azide-tagged infrared probe, selective detection of newly synthesized lipids in cells and tissue became possible, while simultaneous fluorescence imaging enabled cell-type identification in complex tissues. In proof-of-concept experiments, newly synthesized lipids were directly visualized in human-relevant model systems among different cell types, mutation status, differentiation stages, and over time. We identified upregulated lipid metabolism in progranulin-knockdown human induced pluripotent stem cells and in their differentiated microglia cells. Furthermore, we observed that neurons in brain organoids exhibited a significantly lower lipid metabolism compared to astrocytes.

Isolation and Lipidomic Profiling of Neuronal Lipid Droplets: Unveiling the Lipid Landscape for insights into Neurodegenerative Disorders

Recent advances have expanded the role of lipid droplets (LDs) beyond passive lipid storage, implicating their involvement in various metabolic processes across mammalian tissues. Neuronal LDs, long debated in existence, have been identified in several neural structures, raising questions about their contribution to neurodegenerative disorders. Elucidating the specific chemical makeup of these organelles within neurons is critical for understanding their implication in neural pathologies. This study outlines an improved methodology to stimulate and isolate mature LDs from cultured primary neurons, offering insights into their unique lipid-protein composition. Integrating this method with high-throughput techniques may unveil disease-specific alterations in lipid metabolism, providing avenues for potential therapeutic interventions.

Lead exposure induced lipid metabolism disorders by regulating the lipophagy process in microglia

Environmental lead (Pb) pollution is a worldwide public health problem and causes various diseases, especially neurodegenerative diseases. It is increasingly recognized that microglia-mediated neuroinflammation plays a crucial role in lead neurotoxicity, but the underlying mechanisms remain to be further explored. Recent studies indicated that cell metabolism, especially lipid metabolism, regulates many microglial functions, including cytokine secretion and phagocytosis. Whether lipid metabolism is involved in Pb-induced neuroinflammation is still unknown. In the current studies, we investigated the effects of Pb on microglial lipid metabolism by utilizing lipidomics. Histochemistry staining and oxygen consumption rate (OCR) were used to validate lipidomics results. Fenofibrate (FEN), a peroxisome proliferator-activated receptor-α (PPAR-α) agonist, was applied to investigate whether lipid metabolism regulation mitigated Pb's neuroinflammatory response. Microglial autophagic proteins were detected to investigate the role of lipophagy in Pb's effect on lipid metabolism. Our results showed that Pb exposure increased concentrations of various lipid metabolites and induced lipid metabolism disorders, especially in fatty acid metabolism. Pb caused lipid droplet (LD) accumulation and slightly enhanced fatty acid oxidation (FAO) in microglia. FEN pretreatment markedly inhibited Pb's effects on LDs and further mitigated Pb-induced inflammatory response by reducing pro-cytokines' expression and enhancing phagocytosis function. FEN intervention also inhibited Pb's neurotoxicity by improving cognition-related behaviors. Pb exposure induced an abnormal increase of autophagic proteins, but the FEN addition partially neutralized Pb's effects on autophagy. Our data indicate that the Pb-induced neuroinflammation is regulated by fatty acid metabolism via the lipophagy process. Therapies focusing on lipid metabolism regulation are powerful tactics in Pb toxicity prevention and treatment.

Association of serum oleic acid level with depression in American adults: a cross-sectional study

BACKGROUND

As the most abundant fatty acid in plasma, oleic acid has been found to be associated with multiple neurological diseases; however, results from studies of the relationship between oleic acid and depression are inconsistent.

METHODS

This cross-sectional study analyzed 4,459 adults from the National Health and Nutrition Examination Survey 2011-2014. The following covariates were adjusted in multivariable logistic regression models: age, sex, race/ethnicity, education level, marital status, body mass index, physical activity, smoking status, alcohol status, metabolic syndrome, omega-3 polyunsaturated fatty acids, and total cholesterol.

RESULTS

Serum oleic acid levels were positively associated with depression. After adjusting for all covariates, for every 1 mmol/L increase in oleic acid levels, the prevalence of depression increased by 40% (unadjusted OR: 1.35, 95%CI: 1.16-1.57; adjusted OR: 1.40, 95% CI: 1.03-1.90).

CONCLUSIONS

Our study suggests that oleic acid may play a role in depression. Further research is needed to investigate the potential benefits of changing oleic acid levels for the treatment and prevention of depression.

Lipid droplets in Zika neuroinfection: Potential targets for intervention?

Lipid droplets (LD) are evolutionarily conserved lipid-enriched organelles with a diverse array of cell- and stimulus-regulated proteins. Accumulating evidence demonstrates that intracellular pathogens exploit LD as energy sources, replication sites, and part of the mechanisms of immune evasion. Nevertheless, LD can also favor the host as part of the immune and inflammatory response to pathogens. The functions of LD in the central nervous system have gained great interest due to their presence in various cell types in the brain and for their suggested involvement in neurodevelopment and neurodegenerative diseases. Only recently have the roles of LD in neuroinfections begun to be explored. Recent findings reveal that lipid remodelling and increased LD biogenesis play important roles for Zika virus (ZIKV) replication and pathogenesis in neural cells. Moreover, blocking LD formation by targeting DGAT-1 in vivo inhibited virus replication and inflammation in the brain. Therefore, targeting lipid metabolism and LD biogenesis may represent potential strategies for anti-ZIKV treatment development. Here, we review the progress in understanding LD functions in the central nervous system in the context of the host response to Zika infection.

Adipose transplantation improves olfactory function and neurogenesis via PKCα-involved lipid metabolism in Seipin Knockout mice

BACKGROUND

Lipodystrophy-associated metabolic disorders caused by Seipin deficiency lead to not only severe lipodystrophy but also neurological disorders. However, the underlying mechanism of Seipin deficiency-induced neuropathy is not well elucidated, and the possible restorative strategy needs to be explored.

METHODS

In the present study, we used Seipin knockout (KO) mice, combined with transcriptome analysis, mass spectrometry imaging, neurobehavior test, and cellular and molecular assay to investigate the systemic lipid metabolic abnormalities in lipodystrophic mice model and their effects on adult neurogenesis in the subventricular zone (SVZ) and olfactory function. After subcutaneous adipose tissue (AT) transplantation, metabolic and neurological function was measured in Seipin KO mice to clarify whether restoring lipid metabolic homeostasis would improve neurobehavior.

RESULTS

It was found that Seipin KO mice presented the ectopic accumulation of lipids in the lateral ventricle, accompanied by decreased neurogenesis in adult SVZ, diminished new neuron formation in the olfactory bulb, and impaired olfactory-related memory. Transcriptome analysis showed that the differentially expressed genes (DEGs) in SVZ of adult Seipin KO mice were significantly enriched in lipid metabolism. Mass spectrometry imaging showed that the levels of glycerophospholipid and diglyceride (DG) were significantly increased. Furthermore, we found that AT transplantation rescued the abnormality of peripheral metabolism in Seipin KO mice and ameliorated the ectopic lipid accumulation, concomitant with restoration of the SVZ neurogenesis and olfactory function. Mechanistically, PKCα expression was up-regulated in SVZ tissues of Seipin KO mice, which may be a potential mediator between lipid dysregulation and neurological disorder. DG analogue (Dic8) can up-regulate PKCα and inhibit the proliferation and differentiation of neural stem cells (NSCs) in vitro, while PKCα inhibitor can block this effect.

CONCLUSION

This study demonstrates that Seipin deficiency can lead to systemic lipid disorder with concomitant SVZ neurogenesis and impaired olfactory memory. However, AT restores lipid homeostasis and neurogenesis. PKCα is a key mediator mediating Seipin KO-induced abnormal lipid metabolism and impaired neurogenesis in the SVZ, and inhibition of PKCα can restore the impaired neurogenesis. This work reveals the underlying mechanism of Seipin deficiency-induced neurological dysfunction and provides new ideas for the treatment of neurological dysfunction caused by metabolic disorders.

Fatty acid metabolism changes in association with neurobehavioral deficits in animal models of fetal alcohol spectrum disorders

Fetal alcohol spectrum disorders (FASD) show behavioral problems due to prenatal alcohol exposure (PAE). A previous study reports changes in gene expressions linked to fatty acid (FA) metabolism in the cerebral cortex of the PAE mouse model. We find an increase of palmitic acid and arachidonic acid in phospholipid in the cerebral cortex of PAE at postnatal day 30. The increase of palmitic acid is consistent with increase of the producing enzyme, Fasn (fatty acid synthase). Decrease of 26:6 FA is also consistent with the increase of the enzyme which uses 26:6 as a substrate for making very long chain FAs, Elovl4 (elongation of very long chain fatty acids protein 4). However, there is no increase in the elongated products. Rather, lipid droplets (LDs) accumulated in the brain. Although FA-associated metabolic measurements are not affected by PAE, the abundance of FA-related gut microbiota is altered. This suggests that the gut microbiome could serve as a tool to facilitate uncovering the brain pathophysiology of FASD and a potential target to mitigate neurobehavioral problems.

The regulatory role of lipophagy in central nervous system diseases

Lipid droplets (LDs) are the organelles for storing neutral lipids, which are broken down when energy is insufficient. It has been suggested that excessive accumulation of LDs can affect cellular function, which is important to coordinate homeostasis of lipids in vivo. Lysosomes play an important role in the degradation of lipids, and the process of selective autophagy of LDs through lysosomes is known as lipophagy. Dysregulation of lipid metabolism has recently been associated with a variety of central nervous system (CNS) diseases, but the specific regulatory mechanisms of lipophagy in these diseases remain to be elucidated. This review summarizes various forms of lipophagy and discusses the role that lipophagy plays in the development of CNS diseases in order to reveal the related mechanisms and potential therapeutic targets for these diseases.

The Lipid Invasion Model: Growing Evidence for This New Explanation of Alzheimer's Disease

The Lipid Invasion Model (LIM) is a new hypothesis for Alzheimer's disease (AD) which argues that AD is a result of external lipid invasion to the brain, following damage to the blood-brain barrier (BBB). The LIM provides a comprehensive explanation of the observed neuropathologies associated with the disease, including the lipid irregularities first described by Alois Alzheimer himself, and accounts for the wide range of risk factors now identified with AD, all of which are also associated with damage to the BBB. This article summarizes the main arguments of the LIM, and new evidence and arguments in support of it. The LIM incorporates and extends the amyloid hypothesis, the current main explanation of the disease, but argues that the greatest cause of late-onset AD is not amyloid-β (Aβ) but bad cholesterol and free fatty acids, let into the brain by a damaged BBB. It suggests that the focus on Aβ is the reason why we have made so little progress in treating the disease in the last 30 years. As well as offering new perspectives for further research into the diagnosis, prevention, and treatment of AD, based on protecting and repairing the BBB, the LIM provides potential new insights into other neurodegenerative diseases such as Parkinson's disease and amyotrophic lateral sclerosis/motor neuron disease.

The Janus-Faced Role of Lipid Droplets in Aging: Insights from the Cellular Perspective

It is widely accepted that nine hallmarks-including mitochondrial dysfunction, epigenetic alterations, and loss of proteostasis-exist that describe the cellular aging process. Adding to this, a well-described cell organelle in the metabolic context, namely, lipid droplets, also accumulates with increasing age, which can be regarded as a further aging-associated process. Independently of their essential role as fat stores, lipid droplets are also able to control cell integrity by mitigating lipotoxic and proteotoxic insults. As we will show in this review, numerous longevity interventions (such as mTOR inhibition) also lead to strong accumulation of lipid droplets in Saccharomyces cerevisiae, Caenorhabditis elegans, Drosophila melanogaster, and mammalian cells, just to name a few examples. In mammals, due to the variety of different cell types and tissues, the role of lipid droplets during the aging process is much more complex. Using selected diseases associated with aging, such as Alzheimer's disease, Parkinson's disease, type II diabetes, and cardiovascular disease, we show that lipid droplets are "Janus"-faced. In an early phase of the disease, lipid droplets mitigate the toxicity of lipid peroxidation and protein aggregates, but in a later phase of the disease, a strong accumulation of lipid droplets can cause problems for cells and tissues.

A Perspective on the Link between Mitochondria-Associated Membranes (MAMs) and Lipid Droplets Metabolism in Neurodegenerative Diseases

Mitochondria interact with the endoplasmic reticulum (ER) through contacts called mitochondria-associated membranes (MAMs), which control several processes, such as the ER stress response, mitochondrial and ER dynamics, inflammation, apoptosis, and autophagy. MAMs represent an important platform for transport of non-vesicular phospholipids and cholesterol. Therefore, this region is highly enriched in proteins involved in lipid metabolism, including the enzymes that catalyze esterification of cholesterol into cholesteryl esters (CE) and synthesis of triacylglycerols (TAG) from fatty acids (FAs), which are then stored in lipid droplets (LDs). LDs, through contact with other organelles, prevent the toxic consequences of accumulation of unesterified (free) lipids, including lipotoxicity and oxidative stress, and serve as lipid reservoirs that can be used under multiple metabolic and physiological conditions. The LDs break down by autophagy releases of stored lipids for energy production and synthesis of membrane components and other macromolecules. Pathological lipid deposition and autophagy disruption have both been reported to occur in several neurodegenerative diseases, supporting that lipid metabolism alterations are major players in neurodegeneration. In this review, we discuss the current understanding of MAMs structure and function, focusing on their roles in lipid metabolism and the importance of autophagy in LDs metabolism, as well as the changes that occur in neurogenerative diseases.

Systematic review of brain and blood lipidomics in Alzheimer's disease mouse models

Alzheimer's disease (AD) diagnosis is based on invasive and expensive biomarkers. Regarding AD pathophysiological mechanisms, there is evidence of a link between AD and aberrant lipid homeostasis. Alterations in lipid composition have been observed in blood and brain samples, and transgenic mouse models represent a promising approach. Nevertheless, there is great variability among studies in mice for the determination of different types of lipids in targeted and untargeted methods. It could be explained by the different variables (model, age, sex, analytical technique), and experimental conditions used. The aim of this work is to review the studies on lipid alteration in brain tissue and blood samples from AD mouse models, focusing on different experimental parameters. As result, great disparity has been observed among the reviewed studies. Brain studies showed an increase in gangliosides, sphingomyelins, lysophospholipids and monounsaturated fatty acids and a decrease in sulfatides. In contrast, blood studies showed an increase in phosphoglycerides, sterols, diacylglycerols, triacylglycerols and polyunsaturated fatty acids, and a decrease in phospholipids, lysophospholipids and monounsaturated fatty acids. Thus, lipids are closely related to AD, and a consensus on lipidomics studies could be used as a diagnostic tool and providing insight into the mechanisms involved in AD.

Lipid metabolism and Alzheimer's disease: clinical evidence, mechanistic link and therapeutic promise

Alzheimer's disease (AD) is an age-associated neurodegenerative disorder with multifactorial etiology, intersecting genetic and environmental risk factors, and a lack of disease-modifying therapeutics. While the abnormal accumulation of lipids was described in the very first report of AD neuropathology, it was not until recent decades that lipid dyshomeostasis became a focus of AD research. Clinically, lipidomic and metabolomic studies have consistently shown alterations in the levels of various lipid classes emerging in early stages of AD brains. Mechanistically, decades of discovery research have revealed multifaceted interactions between lipid metabolism and key AD pathogenic mechanisms including amyloidogenesis, bioenergetic deficit, oxidative stress, neuroinflammation, and myelin degeneration. In the present review, converging evidence defining lipid dyshomeostasis in AD is summarized, followed by discussions on mechanisms by which lipid metabolism contributes to pathogenesis and modifies disease risk. Furthermore, lipid-targeting therapeutic strategies, and the modification of their efficacy by disease stage, ApoE status, and metabolic and vascular profiles, are reviewed.

Implications of Hypothalamic Neural Stem Cells on Aging and Obesity-Associated Cardiovascular Diseases

The hypothalamus, one of the major regulatory centers in the brain, controls various homeostatic processes, and hypothalamic neural stem cells (htNSCs) have been observed to interfere with hypothalamic mechanisms regulating aging. NSCs play a pivotal role in the repair and regeneration of brain cells during neurodegenerative diseases and rejuvenate the brain tissue microenvironment. The hypothalamus was recently observed to be involved in neuroinflammation mediated by cellular senescence. Cellular senescence, or systemic aging, is characterized by a progressive irreversible state of cell cycle arrest that causes physiological dysregulation in the body and it is evident in many neuroinflammatory conditions, including obesity. Upregulation of neuroinflammation and oxidative stress due to senescence has the potential to alter the functioning of NSCs. Various studies have substantiated the chances of obesity inducing accelerated aging. Therefore, it is essential to explore the potential effects of htNSC dysregulation in obesity and underlying pathways to develop strategies to address obesity-induced comorbidities associated with brain aging. This review will summarize hypothalamic neurogenesis associated with obesity and prospective NSC-based regenerative therapy for the treatment of obesity-induced cardiovascular conditions.

Early postnatal defects in neurogenesis in the 3xTg mouse model of Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder leading to dementia. The hippocampus, which is one of the sites where neural stem cells reside and new neurons are born, exhibits the most significant neuronal loss in AD. A decline in adult neurogenesis has been described in several animal models of AD. However, the age at which this defect first appears remains unknown. To determine at which stage, from birth to adulthood, the neurogenic deficits are found in AD, we used the triple transgenic mouse model of AD (3xTg). We show that defects in neurogenesis are present as early as postnatal stages, well before the onset of any neuropathology or behavioral deficits. We also show that 3xTg mice have significantly fewer neural stem/progenitor cells, with reduced proliferation and decreased numbers of newborn neurons at postnatal stages, consistent with reduced volumes of hippocampal structures. To determine whether there are early changes in the molecular signatures of neural stem/progenitor cells, we perform bulk RNA-seq on cells sorted directly from the hippocampus. We show significant changes in the gene expression profiles at one month of age, including genes of the Notch and Wnt pathways. These findings reveal impairments in neurogenesis very early in the 3xTg AD model, which provides new opportunities for early diagnosis and therapeutic interventions to prevent neurodegeneration in AD.

Mechanisms of abnormal adult hippocampal neurogenesis in Alzheimer's disease

Alzheimer's disease (AD) is a degenerative disease of the central nervous system, the most common type of dementia in old age, which causes progressive loss of cognitive functions such as thoughts, memory, reasoning, behavioral abilities and social skills, affecting the daily life of patients. The dentate gyrus of the hippocampus is a key area for learning and memory functions, and an important site of adult hippocampal neurogenesis (AHN) in normal mammals. AHN mainly consists of the proliferation, differentiation, survival and maturation of newborn neurons and occurs throughout adulthood, but the level of AHN decreases with age. In AD, the AHN will be affected to different degrees at different times, and its exact molecular mechanisms are increasingly elucidated. In this review, we summarize the changes of AHN in AD and its alteration mechanism, which will help lay the foundation for further research on the pathogenesis and diagnostic and therapeutic approaches of AD.

Repair of airway epithelia requires metabolic rewiring towards fatty acid oxidation

Epithelial tissues provide front-line barriers shielding the organism from invading pathogens and harmful substances. In the airway epithelium, the combined action of multiciliated and secretory cells sustains the mucociliary escalator required for clearance of microbes and particles from the airways. Defects in components of mucociliary clearance or barrier integrity are associated with recurring infections and chronic inflammation. The timely and balanced differentiation of basal cells into mature epithelial cell subsets is therefore tightly controlled. While different growth factors regulating progenitor cell proliferation have been described, little is known about the role of metabolism in these regenerative processes. Here we show that basal cell differentiation correlates with a shift in cellular metabolism from glycolysis to fatty acid oxidation (FAO). We demonstrate both in vitro and in vivo that pharmacological and genetic impairment of FAO blocks the development of fully differentiated airway epithelial cells, compromising the repair of airway epithelia. Mechanistically, FAO links to the hexosamine biosynthesis pathway to support protein glycosylation in airway epithelial cells. Our findings unveil the metabolic network underpinning the differentiation of airway epithelia and identify novel targets for intervention to promote lung repair.

Emerging Links between Nonalcoholic Fatty Liver Disease and Neurodegeneration

The association between liver and brain health has gained attention as biomarkers of liver function have been revealed to predict neurodegeneration. The liver is a central regulator in metabolic homeostasis. However, in nonalcoholic fatty liver disease (NAFLD), homeostasis is disrupted which can result in extrahepatic organ pathologies. Emerging literature provides insight into the mechanisms behind the liver-brain health axis. These include the increased production of liver-derived factors that promote insulin resistance and loss of neuroprotective factors under conditions of NAFLD that increase insulin resistance in the central nervous system. In addition, elevated proinflammatory cytokines linked to NAFLD negatively impact the blood-brain barrier and increase neuroinflammation. Furthermore, exacerbated dyslipidemia associated with NAFLD and hepatic dysfunction can promote altered brain bioenergetics and oxidative stress. In this review, we summarize the current knowledge of the crosstalk between liver and brain as it relates to the pathophysiology between NAFLD and neurodegeneration, with an emphasis on Alzheimer's disease. We also highlight knowledge gaps and future areas for investigation to strengthen the potential link between NAFLD and neurodegeneration.

TRPV1 regulates ApoE4-disrupted intracellular lipid homeostasis and decreases synaptic phagocytosis by microglia

Although the ε4 allele of the apolipoprotein E (ApoE4) gene has been established as a genetic risk factor for many neurodegenerative diseases, including Alzheimer's disease, the mechanism of action remains poorly understood. Transient receptor potential vanilloid 1 (TRPV1) was reported to regulate autophagy to protect against foam cell formation in atherosclerosis. Here, we show that ApoE4 leads to lipid metabolism dysregulation in microglia, resulting in enhanced MHC-II-dependent antigen presentation and T-cell activation. Lipid accumulation and inflammatory reactions were accelerated in microglia isolated from TRPV1^flox/flox; Cx3cr1^cre-ApoE4 mice. We showed that metabolic boosting by treatment with the TRPV1 agonist capsaicin rescued lipid metabolic impairments in ApoE4 neurons and defects in autophagy caused by disruption of the AKT-mTOR pathway. TRPV1 activation with capsaicin reversed ApoE4-induced microglial immune dysfunction and neuronal autophagy impairment. Capsaicin rescued memory impairment, tau pathology, and neuronal autophagy in ApoE4 mice. Activation of TRPV1 decreased microglial phagocytosis of synapses in ApoE4 mice. TRPV1 gene deficiency exacerbated recognition memory impairment and tau pathology in ApoE4 mice. Our study suggests that TRPV1 regulation of lipid metabolism could be a therapeutic approach to alleviate the consequences of the ApoE4 allele.