Microglial lipid droplet accumulation in tauopathy brain is regulated by neuronal AMPK

Lipid droplets: Emerging therapeutic targets for age-related metabolic diseases

Lipids metabolism is crucial in regulating aging and metabolic diseases. Lipid droplets (LDs) are dynamic, complex organelles responsible for the storage and release of neutral lipids, essential for maintaining lipid homeostasis and energy metabolism. Aging accelerates the accumulation of LDs, functional deterioration, and metabolic disorders, thereby inducing age-related metabolic diseases (ARMDs). This review examines published datasets on the association between LDs and ARMDs, focusing on the structure and function of LDs, their interactions with other organelles, and associated proteins. Furthermore, we explore the potential mechanisms by which LDs mediate the onset of ARMDs, including Alzheimer's disease (AD), sarcopenia, metabolic cardiomyopathy, non-alcoholic fatty liver disease (NAFLD), and cancer. Lastly, we discuss intervention strategies aimed at targeting LDs to improve outcomes in ARMDs, including exercise, dietary, and pharmacological interventions.

Alzheimer's disease protective allele of Clusterin modulates neuronal excitability through lipid-droplet-mediated neuron-glia communication

BACKGROUND

Genome-wide association studies (GWAS) of Alzheimer's disease (AD) have identified a plethora of risk loci. However, the disease variants/genes and the underlying mechanisms have not been extensively studied.

METHODS

Bulk ATAC-seq was performed in induced pluripotent stem cells (iPSCs) differentiated various brain cell types to identify allele-specific open chromatin (ASoC) SNPs. CRISPR-Cas9 editing generated isogenic pairs, which were then differentiated into glutamatergic neurons (iGlut). Transcriptomic analysis and functional studies of iGlut co-cultured with mouse astrocytes assessed neuronal excitability and lipid droplet formation.

RESULTS

We identified a putative causal SNP of CLU that impacted neuronal chromatin accessibility to transcription-factor(s), with the AD protective allele upregulating neuronal CLU and promoting neuron excitability. And, neuronal CLU facilitated neuron-to-glia lipid transfer and astrocytic lipid droplet formation coupled with reactive oxygen species (ROS) accumulation. These changes caused astrocytes to uptake less glutamate thereby altering neuron excitability.

CONCLUSIONS

For a strong AD-associated locus near Clusterin (CLU), we connected an AD protective allele to a role of neuronal CLU in promoting neuron excitability through lipid-mediated neuron-glia communication. Our study provides insights into how CLU confers resilience to AD through neuron-glia interactions.

Neuroinflammation in Alzheimer disease

Increasing evidence points to a pivotal role of immune processes in the pathogenesis of Alzheimer disease, which is the most prevalent neurodegenerative and dementia-causing disease of our time. Multiple lines of information provided by experimental, epidemiological, neuropathological and genetic studies suggest a pathological role for innate and adaptive immune activation in this disease. Here, we review the cell types and pathological mechanisms involved in disease development as well as the influence of genetics and lifestyle factors. Given the decade-long preclinical stage of Alzheimer disease, these mechanisms and their interactions are driving forces behind the spread and progression of the disease. The identification of treatment opportunities will require a precise understanding of the cells and mechanisms involved as well as a clear definition of their temporal and topographical nature. We will also discuss new therapeutic strategies for targeting neuroinflammation, which are now entering the clinic and showing promise for patients.

Aging and neurodegeneration: when systemic dysregulations affect brain macrophage heterogeneity

Microglia, the major population of brain resident macrophages, differentiate from yolk sac progenitors in the embryo and play multiple nonimmune roles in brain organization throughout development and life. Various microglia subtypes have been described by transcriptomic and proteomic signatures, involved metabolic pathways, morphology, intracellular complexity, time of residency, and ontogeny, both in development and in disease settings. Such macrophage heterogeneity increases with aging or neurodegeneration. Monocytes' infiltration and differentiation into monocyte-derived macrophages (MDMs) in the brain contribute to this diversity. Microbiota's role in brain diseases has been recently highlighted, revealing how microbial signals, such as metabolites, influence microglia and MDMs. In this brief review, we describe how these signals can influence microglia through their sensome and shape MDMs from their development in the bone marrow to their differentiation in the brain. Monocytes could then be a crucial player in the constitution of a dysbiotic gut-brain axis in neurodegenerative diseases and aging.

Illuminating life processes by vibrational probes

Vibration of chemical bonds can serve as imaging contrast. Vibrational probes, synergized with major advances in chemical bond imaging instruments, have recently flourished and proven valuable in illuminating life processes. Here, we review how the development of vibrational probes with optimal biocompatibility, enhanced sensitivity, multichromatic colors and diverse functionality has extended chemical bond imaging beyond the prevalent label-free paradigm into various novel applications such as imaging metabolites, metabolic imaging, drug imaging, super-multiplex imaging, vibrational profiling and vibrational sensing. These advancements in vibrational probes have greatly facilitated understanding living systems, a new field of vibrational chemical biology.

Advanced vibrational microscopes for life science

Providing molecular fingerprint information, vibrational spectroscopic imaging opens a new window to decipher the function of biomolecules in living systems. While classic vibrational microscopes based on spontaneous Raman scattering or mid-infrared absorption offer rich insights into sample composition, they have very small cross sections or poor spatial resolution. Nonlinear vibrational microscopy, based on coherent Raman scattering or optical photothermal detection of vibrational absorption, overcomes these barriers and enables high-speed and high-sensitivity imaging of chemical bonds in live cells and tissues. Here, we introduce various modalities, including their principles, strengths, weaknesses and data mining methods to the life sciences community. We further provide a guide for prospective users and an outlook on future technological advances.

The role of fatty acid metabolism on B cells and B cell-related autoimmune diseases

Fatty acid metabolism plays a critical role in regulating immune cell function, including B cells, which are central to humoral immunity and the pathogenesis of autoimmune diseases. Emerging evidence suggests that fatty acid metabolism influences B cell development, activation, differentiation, and antibody production, thereby impacting B cell-related autoimmune diseases such as systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), and multiple sclerosis (MS). In this review, we discuss the mechanisms by which fatty acid metabolism modulates B cell biology, including energy provision, membrane composition, and signaling pathways. We highlight how alterations in fatty acid synthesis, oxidation, and uptake affect B cell function and contribute to autoimmune pathogenesis. Additionally, we explore the therapeutic potential of targeting fatty acid metabolism in B cells to treat autoimmune diseases. Understanding the interplay between fatty acid metabolism and B cell immunity may provide novel insights into the development of precision therapies for B cell-mediated autoimmune disorders.

GRAMD1B is a regulator of lipid homeostasis, autophagic flux and phosphorylated tau

Lipid dyshomeostasis and tau pathology are present in frontotemporal lobar degeneration (FTLD) and Alzheimer's disease (AD). However, the relationship between lipid dyshomeostasis and tau pathology remains unclear. We report that GRAM Domain Containing 1B (GRAMD1B), a nonvesicular cholesterol transporter, is increased in excitatory neurons of human neural organoids (HNOs) with the MAPT R406W mutation. Human FTLD, AD cases, and PS19 tau mice also have increased GRAMD1B expression. We show that overexpression of GRAMD1B increases levels of free cholesterol, lipid droplets, and impairs autophagy flux. Modulating GRAMD1B in iPSC-derived neurons also alters key autophagy-related components such as PI3K, phospho-AKT, and p62, as well as phosphorylated tau, and CDK5R1. Blocking GRAMD1B function decreases free cholesterol and lipid droplets. Knocking down GRAMD1B additionally reduces phosphorylated tau, and CDK5R1 expression. Our findings elucidate the role of GRAMD1B in the nervous system and highlight its relevance to FTLD and AD.

Cancer Cell Line Classification Using Raman Spectroscopy of Cancer-Derived Exosomes and Machine Learning

Liquid biopsies are an emerging, noninvasive tool for cancer diagnostics, utilizing biological fluids for molecular profiling. Nevertheless, the current methods often lack the sensitivity and specificity necessary for early detection and real-time monitoring. This work explores an advanced approach to improving liquid biopsy techniques through machine learning analysis of the Raman spectra measured to classify distinct exosome solutions by their cancer origin. This was accomplished by conducting principal component analysis (PCA) of the Raman spectra of exosomes from three cancer cell lines (COLO205, A375, and LNCaP) to extract chemically significant features. This reduced set of features was then utilized to train a linear discriminant analysis (LDA) classifier to predict the source of the exosomes. Furthermore, we investigated differences in the lipid composition in these exosomes by their spectra. This spectral similarity analysis revealed differences in lipid profiles between the different cancer cell lines as well as identified the predominant lipids across all exosomes. Our PCA-LDA framework achieved 93.3% overall accuracy and F1 scores of 98.2%, 91.1%, and 91.0% for COLO205, A375, and LNCaP, respectively. Our results from spectral similarity analysis were also shown to support previous findings of lipid dynamics due to cancer pathology and pertaining to exosome function and structure. These findings underscore the benefits of enhancing Raman spectroscopy analysis with machine learning, laying the groundwork for the development of early noninvasive cancer diagnostics and personalized treatment strategies. This work potentially establishes the foundation for refining the classification model and optimizing exosome extraction and detection from clinical samples for clinical translation.

Hexokinase 2 promotes ISGylation of Acyl-CoA synthetase long-chain family member 4 in sepsis-induced microglia cells

Metabolic reprogramming is often observed in sepsis-associated microglial cells. However, little is known about the aberrant metabolic genes involved in neuroinflammation and lipid accumulation in microglial cells of sepsis-associated encephalopathy (SAE). Here, we show that hexokinase 2 (HK2) is upregulated and strongly associated with the inflammatory response and lipid metabolism in lipopolysaccharide-induced BV2 cells. Downregulation of HK2 lowered the activation of NOD-like receptor signaling family pyrin domain containing 3, both in BV2 cells and in the hippocampus of cecal ligation and puncture-induced male septic mice. Moreover, the inhibition of HK2 promoted lipid droplet reduction. Mechanistically, HK2 knockdown in microglial cells reduced the ISGylation of Acyl-CoA Synthetase Long-chain Family Member 4 (ACSL4) by interferon-stimulated gene 15 (ISG15). Notably, siISG15 effectively down-regulated the expression of ACSL4 in lipopolysaccharide-induced BV2 cells. Our findings provide new mechanistic insights into HK2 in microglial cells through regulation of ACSL4 ISGylation, suggesting a promising therapeutic strategy for treating SAE by targeting HK2. Our findings suggest that HK2 modulates ISGylation of ACSL4 in sepsis-induced microglial cells, indicating that therapeutic targeting of HK2 may constitute a promising strategy for SAE.

Do microglia metabolize fructose in Alzheimer's disease?

Alzheimer's disease (AD) is an age-associated neurodegenerative disorder with a complex etiology. While emerging AD therapeutics can slow cognitive decline, they may worsen dementia in certain groups of individuals. Therefore, alternative treatments are much needed. Microglia, the brain resident macrophages, have the potential to be novel therapeutic targets as they regulate many facets of AD, including lipid droplet (LD) accumulation, amyloid beta (Aβ) clearance, and neuroinflammation. To carry out such functions, microglia undergo phenotypic changes, which are linked to shifts in metabolism and substrate utilization. While homeostatic microglia are driven by oxidative phosphorylation (OXPHOS) and glycolysis, in aging and AD, microglia shift further towards glycolysis. Interestingly, this "metabolic reprogramming" may be linked to an increase in fructose metabolism. In the brain, microglia predominantly express the fructose transporter SLC2A5 (GLUT5), and enzymes involved in fructolysis and endogenous fructose production, with their expression being upregulated in aging and disease. Here, we review evidence for fructose uptake, breakdown, and production in microglia. We also evaluate emerging literature targeting fructose metabolism in the brain and periphery to assess its ability to modulate microglial function in AD. The ability of microglia to transport and utilize fructose, coupled with the well-established role of fructose in metabolic dysfunction, supports the notion that microglial fructose metabolism may be a novel potential therapeutic target for AD.

Bibliometric analysis and visualization of lipid droplets in the central nervous system: research hotspots and Frontiers (2000-2024)

Objective

The aim of this study is to conduct bibliometric analysis and visualization of the research progress of lipid droplets in the central nervous system in detail using CiteSpace, VOSviewer, and to explore the current research status, hotspots, and research trends, with a view to providing a basis for future research.

Methods

This study utilized the Web of Science database to search for 1,066 relevant publications on lipid droplets in the central nervous system from 2000 to 2024. Bibliometric analysis was conducted using CiteSpace and VOSviewer software, producing metrics such as annual publication trends, contributions by countries, institutions, and authors, keyword co-occurrences, and reference co-citation networks. The literature of 25 years or so was explored visually to identify the important areas of lipid droplets in neurological research.

Results

Miguel Lopez is the largest contributor to the relevant literature with 10 publications. The United States, China, Johns Hopkins University, the University of Cambridge, and Zhejiang University are the top contributors in terms of publication volume in this research area. Current research emphasizes the mechanisms of lipid droplets in oxidative stress, neuroinflammation, and related degenerative diseases, with a particular focus on Alzheimer's Disease.

Conclusion

Our analysis suggests enhancing collaboration among countries, institutions, and authors in clinical and basic research on brain lipid droplets.

5-Methylcytosine Methylation-Linked Hippo Pathway Molecular Interactions Regulate Lipid Metabolism

5-methylcytosine (5mC) is a common form of DNA methylation, essentially acting as an epigenetic modification that regulates gene expression by affecting the binding of transcription factors to DNA or by recruiting proteins that make it difficult to recognize and transcribe genes. 5mC methylation is present in eukaryotes in a variety of places, such as in CpG islands, within gene bodies, and in regions of repetitive sequences, whereas in prokaryotic organisms, it is mainly present in genomic DNA. The Hippo pathway is a highly conserved signal transduction pathway, which is extremely important in cell proliferation and death, controlling the size of tissues and organs and regulating cell differentiation, in addition to its important regulatory roles in lipid synthesis, transport, and catabolism. Lipid metabolism is an important part of various metabolic pathways in the human body, and problems in lipid metabolism are related to abnormalities in key enzymes, related proteins, epigenetic inheritance, and certain specific amino acids, which are the key factors affecting its proper regulation. In this article, we will introduce the molecular mechanisms of 5mC methylation and the Hippo signaling pathway, and the possibility of their co-regulation of lipid metabolism, with the aim of providing new ideas for further research and novel therapeutic modalities for lipid metabolism and a reference for the development and exploration of related research.

Exosomes enriched with miR-124-3p show therapeutic potential in a new microfluidic triculture model that recapitulates neuron-glia crosstalk in Alzheimer's disease

Background

Alzheimer's disease (AD), a complex neurodegenerative disease associated with ageing, is the leading cause of dementia. Few people with early AD are eligible for the novel Food and Drug Administration (FDA)-approved drug treatments. Accordingly, new tools and early diagnosis markers are required to predict subtypes, individual stages, and the most suitable personalized treatment. We previously demonstrated that the regulation of microRNA (miR)-124 is crucial for proper neuronal function and microglia reshaping in human AD cell models.

Objective

The aim of this study was to develop an efficient miR-124-3p-loaded exosome strategy and validate its therapeutic potential in using a multi-compartment microfluidic device of neuron-glia that recapitulates age-AD pathological features.

Methods and results

Using cortical microglia from mouse pups, separated from glial mixed cultures and maintained for 2 days in vitro (stressed microglia), we tested the effects of SH-SY5Y-derived exosomes loaded with miR-124-3p mimic either by their direct transfection with Exo-Fect™ (ET124) or by their isolation from the secretome of miR-124 transfected cells (CT124). ET124 revealed better delivery effciency and higher potent effects in improving the stressed microglia status than CT124. Tricultures of human SH-SY5Y neuroblastoma cells (SH-WT) were established in the presence of the human microglia cell line (HMC3) and immortalized human astrocytes (IM-HA) in tricompartmentalized microfluidic devices. Replacement of SH-WT cells with those transfected with APP695 (SH-SWE) in the tricultures and addition of low doses of hydrogen peroxide were used to simulate late-onset AD. The system mimicked AD-associated neurodegeneration and neuroinflammation processes. Notably, ET124 exhibited neuroprotective properties across the three cell types in the AD model by preventing neuronal apoptosis and neurite deficits, redirecting microglial profiles towards a steady state, and attenuating the inflammatory and miRNA fingerprints associated with astrocyte reactivity.

Conclusion

To the best of our knowledge, this is the first study supporting the neuro- and immunoprotective properties of miR-124-engineered exosomes in a microfluidic triculture platform, recapitulating age-related susceptibility to AD. Our system offers potential to develop personalized medicines in AD patient subtypes.

Redox regulation: mechanisms, biology and therapeutic targets in diseases

Redox signaling acts as a critical mediator in the dynamic interactions between organisms and their external environment, profoundly influencing both the onset and progression of various diseases. Under physiological conditions, oxidative free radicals generated by the mitochondrial oxidative respiratory chain, endoplasmic reticulum, and NADPH oxidases can be effectively neutralized by NRF2-mediated antioxidant responses. These responses elevate the synthesis of superoxide dismutase (SOD), catalase, as well as key molecules like nicotinamide adenine dinucleotide phosphate (NADPH) and glutathione (GSH), thereby maintaining cellular redox homeostasis. Disruption of this finely tuned equilibrium is closely linked to the pathogenesis of a wide range of diseases. Recent advances have broadened our understanding of the molecular mechanisms underpinning this dysregulation, highlighting the pivotal roles of genomic instability, epigenetic modifications, protein degradation, and metabolic reprogramming. These findings provide a foundation for exploring redox regulation as a mechanistic basis for improving therapeutic strategies. While antioxidant-based therapies have shown early promise in conditions where oxidative stress plays a primary pathological role, their efficacy in diseases characterized by complex, multifactorial etiologies remains controversial. A deeper, context-specific understanding of redox signaling, particularly the roles of redox-sensitive proteins, is critical for designing targeted therapies aimed at re-establishing redox balance. Emerging small molecule inhibitors that target specific cysteine residues in redox-sensitive proteins have demonstrated promising preclinical outcomes, setting the stage for forthcoming clinical trials. In this review, we summarize our current understanding of the intricate relationship between oxidative stress and disease pathogenesis and also discuss how these insights can be leveraged to optimize therapeutic strategies in clinical practice.

The circular RNA circbabo(5,6,7,8S) regulates lipid metabolism and neuronal integrity via TGF-β/ROS/JNK/SREBP signaling axis in Drosophila

BACKGROUND

Lipid droplets (LDs) are dynamic cytoplasmic lipid-storing organelles that play a pivotal role in maintaining cellular energy balance, lipid homeostasis, and metabolic signaling. Dysregulation of lipid metabolism, particularly excessive lipogenesis, contributes to the abnormal accumulation of LDs in the nervous system, which is associated with several neurodegenerative diseases. Circular RNAs (circRNAs) are a new class of non-coding and regulatory RNAs that are widely expressed in eukaryotes. However, only a subset has been functionally characterized. Here, we identified and functionally characterized a new circular RNA circbabo(5,6,7,8S) that regulates lipogenesis and neuronal integrity in Drosophila melanogaster.

RESULTS

circbabo(5,6,7,8S) is derived from the babo locus which encodes the type I receptor for transforming growth factor β (TGF-β). Depletion of circbabo(5,6,7,8S) in flies causes elevated lipid droplet accumulation, progressive photoreceptor cell loss and shortened lifespan, phenotypes that are rescued by restoring circbabo(5,6,7,8S) expression. In addition, RNA-seq and epistasis analyses reveal that these abnormalities are caused by aberrant activation of the SREBP signaling pathway. Furthermore, circbabo(5,6,7,8S)-depleted tissues display enhanced activation of the TGF-β signaling pathway and compromised mitochondrial function, resulting in upregulation of reactive oxygen species (ROS). Moreover, we provide evidence that circbabo(5,6,7,8S) encodes the protein circbabo(5,6,7,8S)-p, which inhibits TGF-β signaling by interfering with the assembly of babo/put receptor heterodimer complex. Lastly, we show that dysregulation of the ROS/JNK/SREBP signaling cascade is responsible for the LD accumulation, neurodegeneration, and shortened lifespan phenotypes elicited by circbabo(5,6,7,8S) depletion.

CONCLUSIONS

Our study demonstrates the physiological role of the protein-coding circRNA circbabo(5,6,7,8S) in regulating lipid metabolism and neuronal integrity.

Lipids: Emerging Players of Microglial Biology

Lipids are small molecule immunomodulators that play critical roles in maintaining cellular health and function. Microglia, the resident immune cells of the central nervous system, regulate lipid metabolism both in the extracellular environment and within intracellular compartments through various mechanisms. For instance, glycerophospholipids and fatty acids interact with protein receptors on the microglial surface, such as the Triggering Receptor Expressed on Myeloid Cells 2, influencing cellular functions like phagocytosis and migration. Moreover, cholesterol is essential not only for microglial survival but, along with other lipids such as fatty acids, is crucial for the formation, function, and accumulation of lipid droplets, which modulate microglial activity in inflammatory diseases. Other lipids, including acylcarnitines and ceramides, participate in various signaling pathways within microglia. Despite the complexity of the microglial lipidome, only a few studies have investigated the effects of specific lipid classes on microglial biology. In this review, we focus on major lipid classes and their roles in modulating microglial function. We also discuss novel analytical techniques for characterizing the microglial lipidome and highlight gaps in current knowledge, suggesting new directions for future research on microglial lipid biology.

Lipid Metabolic Heterogeneity during Early Embryogenesis Revealed by Hyper-3D Stimulated Raman Imaging

Studying embryogenesis is fundamental to understanding developmental biology and reproductive medicine. Its process requires precise spatiotemporal regulations in which lipid metabolism plays a crucial role. However, the spatial dynamics of lipid species at the subcellular level remains obscure due to technical limitations. To address this challenge, we developed a hyperspectral 3D imaging and analysis method based on stimulated Raman scattering microscopy (hyper-3D SRS) to quantitatively assess lipid profiles in individual embryos through submicrometer resolution (x-y), 3D optical sectioning (z), and chemical bond-selective (Ω) imaging. Using hyper-3D SRS, individual lipid droplets (LDs) in single cells were identified and quantified. Our findings revealed that the LD profiles within a single embryo are not uniform, even as early as the 2-cell stage. Notably, we also discovered a dynamic relationship between the LD size and unsaturation degree as embryos develop, indicating diverse lipid metabolism during early development. Furthermore, abnormal LDs were observed in oocytes of a progeria mouse model, suggesting that LDs could serve as a potential biomarker for assessing oocyte/embryo quality. Overall, our results highlight the potential of hyper-3D SRS as a noninvasive method for studying lipid content, composition, and subcellular distribution in embryos. This technique provides valuable insights into lipid metabolism during embryonic development and has the potential for clinical applications in evaluating oocyte/embryo quality.

Lipidome disruption in Alzheimer's disease brain: detection, pathological mechanisms, and therapeutic implications

Alzheimer's disease (AD) is among the most devastating neurodegenerative disorders with limited treatment options. Emerging evidence points to the involvement of lipid dysregulation in the development of AD. Nevertheless, the precise lipidomic landscape and the mechanistic roles of lipids in disease pathology remain poorly understood. This review aims to highlight the significance of lipidomics and lipid-targeting approaches in the diagnosis and treatment of AD. We summarized the connection between lipid dysregulation in the human brain and AD at both genetic and lipid species levels. We briefly introduced lipidomics technologies and discussed potential challenges and areas of future advancements in the lipidomics field for AD research. To elucidate the central role of lipids in converging multiple pathological aspects of AD, we reviewed the current knowledge on the interplay between lipids and major AD features, including amyloid beta, tau, and neuroinflammation. Finally, we assessed the progresses and obstacles in lipid-based therapeutics and proposed potential strategies for leveraging lipidomics in the treatment of AD.

Lipid droplets in central nervous system and functional profiles of brain cells containing lipid droplets in various diseases

Lipid droplets (LDs), serving as the convergence point of energy metabolism and multiple signaling pathways, have garnered increasing attention in recent years. Different cell types within the central nervous system (CNS) can regulate energy metabolism to generate or degrade LDs in response to diverse pathological stimuli. This article provides a comprehensive review on the composition of LDs in CNS, their generation and degradation processes, their interaction mechanisms with mitochondria, the distribution among different cell types, and the roles played by these cells-particularly microglia and astrocytes-in various prevalent neurological disorders. Additionally, we also emphasize the paradoxical role of LDs in post-cerebral ischemia inflammation and explore potential underlying mechanisms, aiming to identify novel therapeutic targets for this disease.

Exploring the link between dystrophic microglia and the spread of Alzheimer's neuropathology

Genetics and other data modalities indicate that microglia play a critical role in Alzheimer's disease progression, but details of the disease-driving influence of microglia are poorly understood. Microglial cells can be parsed into subtypes based on their histological appearance. One subtype of microglia, termed dystrophic microglia, is characterized structurally by fragmented processes and cytoplasmic decay, and their presence has been associated with ageing and neurodegeneration. Recent studies suggest that the interaction between tau proteins and amyloid-β might induce dystrophic changes in microglia, potentially linking amyloid-β and tau pathologies to their effects on these microglia. We developed a study of human brains to test the hypothesis that dystrophic microglia are involved in Alzheimer's disease progression. We speculated that if their presence is unique to Alzheimer's disease neuropathological change, they would be substantially more common in Alzheimer's disease neuropathological change than in neurodegenerative diseases characterized by other proteinopathies, e.g. α-synuclein or transactive response (TAR) DNA-binding protein 43 kDa (TDP-43) pathology. Our analyses used histologically stained sections from five human brain regions of 64 individuals across six disease states, from healthy controls to advanced Alzheimer's disease stages, including comparative conditions such as Lewy body disease and limbic-predominant age-related TDP-43 encephalopathy neuropathological change. Using stereological sampling and digital pathology, we assessed populations of ramified, hypertrophic and dystrophic microglia. We found a significant increase in dystrophic microglia in areas affected early by Alzheimer's disease neuropathological change, suggesting a disease-specific role in neuropathology. Mediation analysis and structural equation modelling suggest that dystrophic microglia might impact the regional spread of Alzheimer's disease neuropathological change. In the mediation model, tau was found to be the initiating factor leading to the development of dystrophic microglia, which was then associated with the spread of amyloid-β and tau. These results suggest that a loss of the protective role of microglia could contribute to the spread of Alzheimer's disease neuropathological change and indicate that further research into preserving microglial function might be warranted.

NG-497 Alleviates Microglia-Mediated Neuroinflammation in a MTNR1A-Dependent Manner

Microglia-mediated neuroinflammation plays a crucial role in multiple neurological diseases. We have previously found that Atglistatin, the mouse Adipose Triglyceride Lipase (ATGL) inhibitor, could promote lipid droplets (LDs) accumulation and suppress LPS-induced neuroinflammation in mouse microglia. However, Atglistatin was species-selective, which limited its use in clinical settings. Here, we found that NG-497, a previously identified human ATGL inhibitor, significantly increased LDs accumulation and inhibited LPS-induced pro-inflammatory responses in human microglia. Moreover, NG-497 also protected human neurons against neurotoxic cytokines in a humanized in vitro model of neuroinflammation. However, the anti-inflammatory capacity of NG-497 was independent of its effect on ATGL. Instead, we revealed that NG-497 alleviated microglia-mediated neuroinflammation through elevating the protein level of melatonin receptor 1A (MTNR1A). Therefore, in this study, we uncovered a novel MTNR1A-targeting compound, which exhibited anti-inflammatory and neuroprotective effect, highlighting its potential in the treatment of neuroinflammation. Moreover, the MTNRs agonist, Ramelteon, exerts comparable anti-inflammation effects with NG-497.

Mitochondria-Associated Endoplasmic Reticulum Membranes in Microglia: One Contact Site to Rule Them all

Microglia, the resident immune cells of the central nervous system (CNS), play a crucial role in maintaining tissue homeostasis by monitoring and responding to environmental changes through processes such as phagocytosis, cytokine production or synapse remodeling. Their dynamic nature and diverse functions are supported by the regulation of multiple metabolic pathways, enabling microglia to efficiently adapt to fluctuating signals. A key aspect of this regulation occurs at mitochondria-associated ER membranes (MAM), specialized contact sites between the ER and mitochondria. These structures facilitate the exchange of calcium, lipids, and metabolites and serve as metabolic and signaling hubs. This review synthesizes current research on how MAM influence microglial physiology, with an emphasis on their role in immunometabolism, offering new insights into the integration of metabolic and immune functions in the CNS and its impact in the context of neurodegeneration.

Blockage of ATGL-mediated breakdown of lipid droplets in microglia alleviates neuroinflammatory and behavioural responses to lipopolysaccharides

Lipid droplets (LD) are triglyceride storing organelles that have emerged as an important component of cellular inflammatory responses. LD lipolysis via adipose triglyceride lipase (ATGL), the enzyme that catalyses the rate-limiting step of triglyceride lipolysis, regulates inflammation in peripheral immune and non-immune cells. ATGL elicits both pro- and anti-inflammatory responses in the periphery in a cell-type dependent manner. The present study determined the impact of ATGL inhibition and microglia-specific ATGL genetic loss-of-function on acute inflammatory and behavioural responses to pro-inflammatory insult. First, we evaluated the impact of lipolysis inhibition on lipopolysaccharide (LPS)-induced expression and secretion of cytokines and phagocytosis in mouse primary microglia cultures. Lipase inhibitors (ORlistat and ATGListatin) and LPS led to LD accumulation in microglia. Pan-lipase inhibition with ORlistat alleviated LPS-induced expression of IL-1β and IL-6. Specific inhibition of ATGL had a similar action on CCL2, IL-1β and IL-6 expression in both neonatal and adult microglia cultures. CCL2 and IL-6 secretion were also reduced by ATGListatin or knockdown of ATGL. ATGListatin increased phagocytosis in neonatal cultures independently from LPS treatment. Second, targeted and untargeted lipid profiling revealed that ATGListatin reduced LPS-induced generation of pro-inflammatory prostanoids and modulated ceramide species in neonatal microglia. Finally, the role of microglial ATGL in neuroinflammation was assessed using a novel microglia-specific and inducible ATGL knockout mouse model. Loss of microglial ATGL in adult male mice dampened LPS-induced expression of IL-6 and IL-1β and microglial density. LPS-induced sickness- and anxiety-like behaviours were also reduced in male mice with loss of ATGL in microglia. Together, our results demonstrate potent anti-inflammatory effects produced by pharmacological or genetic inhibition of ATGL-mediated triglyceride lipolysis and thereby propose that supressing microglial LD lipolysis has beneficial actions in acute neuroinflammatory conditions.

TREM1-Microglia crosstalk: Neurocognitive disorders

Neurocognitive Disorders (NCDs) primarily affect cognitive functions, including learning, memory, perception, and problem-solving. They predominantly arise as pathological sequelae of central nervous system (CNS) disorders. Emerging evidence suggests that microglial inflammatory activation within the hippocampus underlies the pathogenesis of cognitive impairment. Triggering receptor expressed on myeloid cells 1 (TREM1), a pattern-recognition receptor on microglia, becomes upregulated in response to injury and synergistically amplifies inflammatory responses mediated by other pattern-recognition receptors, leading to uncontrolled inflammation. While TREM1 is lowly expressed in the resting state, its upregulation upon exposure to injurious inflammatory stimuli promotes microglial activation and contributes to the development of NCDs. Consequently, TREM1 may serve as a critical receptor in microglia-mediated inflammation. This article reviews the current understanding of TREM1 and its role in NCDs pathogenesis.

Lipid metabolism: Novel approaches for managing idiopathic epilepsy

Epilepsy is a common neurological condition characterized by abnormal neuronal activity, often leading to cellular damage and death. There is evidence to suggest that lipid imbalances resulting in cellular death play a key role in the development of epilepsy, including changes in triglycerides, cholesterol, sphingolipids, phospholipids, lipid droplets, and bile acids (BAs). Disrupted lipid metabolism acts as a crucial pathological mechanism in epilepsy, potentially linked to processes such as cellular ferroptosis, lipophagy, and immune modulation of gut microbiota (thus influencing the gut-brain axis). Understanding these mechanisms could open up new avenues for epilepsy treatment. This study investigates the association between disturbances in lipid metabolism and the onset of epilepsy.

Identification of tauopathy-associated lipid signatures in Alzheimer's disease mouse brain using label-free chemical imaging

There is cumulative evidence that lipid metabolism plays a key role in the pathogenesis of various neurodegenerative disorders including Alzheimer's disease (AD). Visualising lipid content in a non-destructive label-free manner can aid in elucidating the AD phenotypes towards a better understanding of the disease. In this study, we combined multiple optical molecular-specific methods, Fourier transform infrared (FTIR) spectroscopic imaging, synchrotron radiation-infrared (SR-IR) microscopy, Raman and stimulated Raman scattering (SRS) microscopy, and optical-photothermal infrared (O-PTIR) microscopy with multivariate data analysis, to investigate the biochemistry of brain hippocampus in situ using a mouse model of tauopathy (rTg4510). We observed a significant difference in the morphology and lipid content between transgenic (TG) and wild type (WT) samples. Immunohistochemical staining revealed some degree of microglia co-localisation with elevated lipids in the brain. These results provide new evidence of tauopathy-related dysfunction in a preclinical study at a subcellular level.

Tau is required for glial lipid droplet formation and resistance to neuronal oxidative stress

The accumulation of reactive oxygen species (ROS) is a common feature of tauopathies, defined by Tau accumulations in neurons and glia. High ROS in neurons causes lipid production and the export of toxic peroxidated lipids (LPOs). Glia uptake these LPOs and incorporate them into lipid droplets (LDs) for storage and catabolism. We found that overexpressing Tau in glia disrupts LDs in flies and rat neuron-astrocyte co-cultures, sensitizing the glia to toxic, neuronal LPOs. Using a new fly tau loss-of-function allele and RNA-mediated interference, we found that endogenous Tau is required for glial LD formation and protection against neuronal LPOs. Similarly, endogenous Tau is required in rat astrocytes and human oligodendrocyte-like cells for LD formation and the breakdown of LPOs. Behaviorally, flies lacking glial Tau have decreased lifespans and motor defects that are rescuable by administering the antioxidant N-acetylcysteine amide. Overall, this work provides insights into the important role that Tau has in glia to mitigate ROS in the brain.

Distribution of lipid droplets in hippocampal neurons and microglia: impact of diabetes and exercise

Neuroinflammation, aging, and neurodegenerative disorders are associated with excessive accumulation of neutral lipids in lipid droplets (LDs) in microglia. Type 2 diabetes mellitus (T2DM) may cause neuroinflammation and is a risk factor for neurodegenerative disorders. Here, we show that hippocampal pyramidal neurons contain smaller, more abundant LDs than their neighboring microglia. The density of LDs varied between pyramidal cells in adjacent subregions, with CA3 neurons containing more LDs than CA1 neurons. Within the CA3 region, a gradual increase in the LD content along the pyramidal layer from the hilus toward CA2 was observed. Interestingly, the high neuronal LD content correlated with less ramified microglial morphotypes. Using the db/db model of T2DM, we demonstrated that diabetes increased the number of LDs per microglial cell without affecting the neuronal LD density. High-intensity interval exercise induced smaller changes in the number of LDs in microglia but was not sufficient to counteract the diabetes-induced changes in LD accumulation. The changes observed in response to T2DM may contribute to the cerebral effects of T2DM and provide a mechanistic link between T2DM and neurodegenerative disorders.

Neuronal lipid droplets play a conserved and sex-biased role in maintaining whole-body energy homeostasis

Lipids are essential for neuron development and physiology. Yet, the central hubs that coordinate lipid supply and demand in neurons remain unclear. Here, we combine invertebrate and vertebrate models to establish the presence and functional significance of neuronal lipid droplets (LD) in vivo. We find that LD are normally present in neurons in a non-uniform distribution across the brain, and demonstrate triglyceride metabolism enzymes and lipid droplet-associated proteins control neuronal LD formation through both canonical and recently-discovered pathways. Appropriate LD regulation in neurons has conserved and male-biased effects on whole-body energy homeostasis across flies and mice, specifically neurons that couple environmental cues with energy homeostasis. Mechanistically, LD-derived lipids support neuron function by providing phospholipids to sustain mitochondrial and endoplasmic reticulum homeostasis. Together, our work identifies a conserved role for LD as the organelle that coordinates lipid management in neurons, with implications for our understanding of mechanisms that preserve neuronal lipid homeostasis and function in health and disease.

Neuronal AMPK regulates lipid transport to microglia

In neurodegeneration, neurons release lipids that accumulate in glial lipid droplets (LDs). But what controls lipid transport and how does this affect glia? A recent study by Li et al. discovered that the loss of neuronal AMP-activated protein kinase (AMPK) activity promotes lipid efflux, which drives a proinflammatory state in microglia.

The Neurolipid Atlas: a lipidomics resource for neurodegenerative diseases uncovers cholesterol as a regulator of astrocyte reactivity impaired by ApoE4

Lipid changes in the brain have been implicated in many neurodegenerative diseases including Alzheimer's Disease (AD), Parkinson's disease and Amyotrophic Lateral Sclerosis. To facilitate comparative lipidomic research across brain-diseases we established a data commons named the Neurolipid Atlas, that we have pre-populated with novel human, mouse and isogenic induced pluripotent stem cell (iPSC)-derived lipidomics data for different brain diseases. We show that iPSC-derived neurons, microglia and astrocytes display distinct lipid profiles that recapitulate in vivo lipotypes. Leveraging multiple datasets, we show that the AD risk gene ApoE4 drives cholesterol ester (CE) accumulation in human astrocytes recapitulating CE accumulation measured in the human AD brain. Multi-omic interrogation of iPSC-derived astrocytes revealed that cholesterol plays a major role in astrocyte interferon-dependent pathways such as the immunoproteasome and major histocompatibility complex (MHC) class I antigen presentation. We show that through enhanced cholesterol esterification ApoE4 suppresses immune activation of astrocytes. Our novel data commons, available at neurolipidatlas.com, provides a user-friendly tool and knowledge base for a better understanding of lipid dyshomeostasis in neurodegenerative diseases.