The Glia-Neuron Lactate Shuttle and Elevated ROS Promote Lipid Synthesis in Neurons and Lipid Droplet Accumulation in Glia via APOE/D

Metabolic reprogramming: a new option for the treatment of spinal cord injury

Spinal cord injuries impose a notably economic burden on society, mainly because of the severe after-effects they cause. Despite the ongoing development of various therapies for spinal cord injuries, their effectiveness remains unsatisfactory. However, a deeper understanding of metabolism has opened up a new therapeutic opportunity in the form of metabolic reprogramming. In this review, we explore the metabolic changes that occur during spinal cord injuries, their consequences, and the therapeutic tools available for metabolic reprogramming. Normal spinal cord metabolism is characterized by independent cellular metabolism and intercellular metabolic coupling. However, spinal cord injury results in metabolic disorders that include disturbances in glucose metabolism, lipid metabolism, and mitochondrial dysfunction. These metabolic disturbances lead to corresponding pathological changes, including the failure of axonal regeneration, the accumulation of scarring, and the activation of microglia. To rescue spinal cord injury at the metabolic level, potential metabolic reprogramming approaches have emerged, including replenishing metabolic substrates, reconstituting metabolic couplings, and targeting mitochondrial therapies to alter cell fate. The available evidence suggests that metabolic reprogramming holds great promise as a next-generation approach for the treatment of spinal cord injury. To further advance the metabolic treatment of the spinal cord injury, future efforts should focus on a deeper understanding of neurometabolism, the development of more advanced metabolomics technologies, and the design of highly effective metabolic interventions.

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.

Probiotic therapy modulates the brain-gut-liver microbiota axis in a mouse model of traumatic brain injury

The interplay between gut microbiota and host health is crucial for maintaining the overall health of the body and brain, and it is even more crucial how changes in the bacterial profile can influence the aftermath of traumatic brain injury (TBI). We studied the effects of probiotic treatment after TBI to identify potential changes in hepatic lipid species relevant to brain function. Bioinformatic analysis of the gut microbiota indicated a significant increase in the Firmicutes/Bacteroidetes ratio in the probiotic-treated TBI group compared to sham and untreated TBI groups. Although strong correlations between gut bacteria and hepatic lipids were found in sham mice, TBI disrupted these links, and probiotic treatment did not fully restore them. Probiotic treatment influenced systemic glucose metabolism, suggesting altered metabolic regulation. Behavioral tests confirmed memory improvement in probiotic-treated TBI mice. While TBI reduced hippocampal mRNA expression of CaMKII and CREB, probiotics reversed these effects yet did not alter BDNF mRNA levels. Elevated pro-inflammatory markers TNF-α and IL1-β in TBI mice were not significantly affected by probiotic treatment, pointing to different mechanisms underlying the probiotic benefits. In summary, our study suggests that TBI induces dysbiosis, alters hepatic lipid profiles, and preemptive administration of Lactobacillus helveticus and Bifidobacterium longum probiotics can counter neuroplasticity deficits and memory impairment. Altogether, these findings highlight the potential of probiotics for attenuating TBI's detrimental cognitive and metabolic effects through gut microbiome modulation and hepatic lipidomic alteration, laying the groundwork for probiotics as a potential TBI therapy.

Isoform- and cell-state-specific APOE homeostasis and function

Apolipoprotein E is the major lipid transporter in the brain and an important player in neuron-astrocyte metabolic coupling. It ensures the survival of neurons under stressful conditions and hyperactivity by nourishing and detoxifying them. Apolipoprotein E polymorphism, combined with environmental stresses and/or age-related alterations, influences the risk of developing late-onset Alzheimer's disease. In this review, we discuss our current knowledge of how apolipoprotein E homeostasis, i.e. its synthesis, secretion, degradation, and lipidation, is affected in Alzheimer's disease.

TRIM21-mediated ubiquitination of PLIN2 regulates neuronal lipid droplet accumulation after acute spinal cord injury

To investigate the changes in neuronal lipid droplet (LD) accumulation and lipid metabolism after acute spinal cord injury (SCI), we established a rat model of compressive SCI. Oil Red O staining, BODIPY 493/503 staining, and 4-hydroxynonenal immunofluorescence staining were performed to determine overall LD accumulation, neuronal LD accumulation, and lipid peroxidation. Lipidomics was conducted to identify the lipid components in the local SCI microenvironment. We focused on the expression and regulation of perilipin 2 (PLIN2) and knocked down PLIN2 in vivo by intrathecal injection of adeno-associated virus 9-synapsin-short-hairpin RNA-PLIN2 (AAV9-SYN-shPlin2). Motor function was assessed using the Basso-Beattie-Bresnahan score. Proteins that interacted with PLIN2 were screened by immunoprecipitation (IP) and qualitative shotgun proteomics, and confirmed by co-IP. A ubiquitination assay was performed to validate whether ubiquitination was involved in PLIN2 degradation. Oil Red O staining indicated that LDs steadily accumulated after SCI. Fluorescent staining indicated the accumulation of LDs in neurons with increased lipid peroxidation. Lipidomics revealed significant changes in lipid components after SCI. PLIN2 expression significantly increased following SCI, and knockdown of PLIN2 using AAV9-SYN-Plin2 reduced neuronal LD accumulation. This intervention improved the neuronal survival and motor function of injured rats. IP and qualitative shotgun proteomics identified tripartite motif-containing protein 21 (TRIM21) as a direct binding protein of PLIN2, and this interaction was confirmed by co-IP in vitro and immunofluorescence staining in vivo. By manipulating TRIM21 expression, we found it was negatively correlated with PLIN2 expression. In conclusion, PLIN2 is involved in neuronal LD accumulation following SCI. TRIM21 mediated the ubiquitination and degradation of PLIN2 in neurons. Inhibition of PLIN2 enhanced the recovery of motor function after SCI.

Metabolic reprogramming of the inflammatory response in the nervous system: the crossover between inflammation and metabolism

Metabolism is a fundamental process by which biochemicals are broken down to produce energy (catabolism) or used to build macromolecules (anabolism). Metabolism has received renewed attention as a mechanism that generates molecules that modulate multiple cellular responses. This was first identified in cancer cells as the Warburg effect, but it is also present in immunocompetent cells. Studies have revealed a bidirectional influence of cellular metabolism and immune cell function, highlighting the significance of metabolic reprogramming in immune cell activation and effector functions. Metabolic processes such as glycolysis, oxidative phosphorylation, and fatty acid oxidation have been shown to undergo dynamic changes during immune cell response, facilitating the energetic and biosynthetic demands. This review aims to provide a better understanding of the metabolic reprogramming that occurs in different immune cells upon activation, with a special focus on central nervous system disorders. Understanding the metabolic changes of the immune response not only provides insights into the fundamental mechanisms that regulate immune cell function but also opens new approaches for therapeutic strategies aimed at manipulating the immune system.

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.

HIV-TAT dysregulates microglial lipid metabolism through SREBP2/miR-124 axis: Implication of lipid droplet accumulation microglia in NeuroHIV

Chronic HIV infection can dysregulate lipid/cholesterol metabolism in the peripheral system, contributing to the higher incidences of diabetes and atherosclerosis in HIV (+) individuals. Recently, accumulating evidence indicate that HIV proteins can also dysregulate lipid/cholesterol metabolism in the brain and such dysregulation could be linked with the pathogenesis of HIV-associated neurological disorders (HAND)/NeuroHIV. To further characterize the association between lipid/cholesterol metabolism and HAND, we employed HIV-inducible transactivator of transcription (iTAT) and control mice to compare their brain lipid profiles. Our results reveal that HIV-iTAT mice possess dysregulated lipid profiles and have increased numbers of lipid droplets (LDs) accumulation microglia (LDAM) in the brains. HIV protein TAT can upregulate LDs formation through enhancing the lipid/cholesterol synthesis in vitro. Mechanistically, HIV-TAT increases the expression of sterol regulatory element-binding protein 2 (SREBP2) through microRNA-124 downregulation. Cholesterol synthesis inhibition can block HIV-TAT-mediated NLRP3 inflammasome activation and microglial activation in vitro as well as mitigate aging-related behavioral impairment and memory deficiency in HIV-iTAT mice. Taken together, our results indicate an inherent role of lipid metabolism and LDAM in the pathogenesis of NeuroHIV (immunometabolism). These findings suggest that LDAM reversal through modulating lipid/cholesterol metabolism could be a novel therapeutic target for ameliorating NeuroHIV symptoms in chronic HIV (+) individuals.

Inhibition of sterol O-acyltransferase 1 blocks Zika virus infection in cell lines and cerebral organoids

Viruses depend on host metabolic pathways and flaviviruses are specifically linked to lipid metabolism. During dengue virus infection lipid droplets are degraded to fuel replication and Zika virus (ZIKV) infection depends on triglyceride biosynthesis. Here, we systematically investigated the neutral lipid-synthesizing enzymes diacylglycerol O-acyltransferases (DGAT) and the sterol O-acyltransferase (SOAT) 1 in orthoflavivirus infection. Downregulation of DGAT1 and SOAT1 compromises ZIKV infection in hepatoma cells but only SOAT1 and not DGAT inhibitor treatment reduces ZIKV infection. DGAT1 interacts with the ZIKV capsid protein, indicating that protein interaction might be required for ZIKV replication. Importantly, inhibition of SOAT1 severely impairs ZIKV infection in neural cell culture models and cerebral organoids. SOAT1 inhibitor treatment decreases extracellular viral RNA and E protein level and lowers the specific infectivity of virions, indicating that ZIKV morphogenesis is compromised, likely due to accumulation of free cholesterol. Our findings provide insights into the importance of cholesterol and cholesterol ester balance for efficient ZIKV replication and implicate SOAT1 as an antiviral target.

The Astrocyte: Metabolic Hub of the Brain

Astrocytic metabolism has taken center stage. Interposed between the neuron and the vasculature, astrocytes exert control over the fluxes of energy and building blocks required for neuronal activity and plasticity. They are also key to local detoxification and waste recycling. Whereas neurons are metabolically rigid, astrocytes can switch between different metabolic profiles according to local demand and the nutritional state of the organism. Their metabolic state even seems to be instructive for peripheral nutrient mobilization and has been implicated in information processing and behavior. Here, we summarize recent progress in our understanding of astrocytic metabolism and its effects on metabolic homeostasis and cognition.

Dominant missense variants in SREBF2 are associated with complex dermatological, neurological, and skeletal abnormalities

PURPOSE

We identified 2 individuals with de novo variants in SREBF2 that disrupt a conserved site 1 protease (S1P) cleavage motif required for processing SREBP2 into its mature transcription factor. These individuals exhibit complex phenotypic manifestations that partially overlap with sterol regulatory element binding proteins (SREBP) pathway-related disease phenotypes, but SREBF2-related disease has not been previously reported. Thus, we set out to assess the effects of SREBF2 variants on SREBP pathway activation.

METHODS

We undertook ultrastructure and gene expression analyses using fibroblasts from an affected individual and utilized a fly model of lipid droplet (LD) formation to investigate the consequences of SREBF2 variants on SREBP pathway function.

RESULTS

We observed reduced LD formation, endoplasmic reticulum expansion, accumulation of aberrant lysosomes, and deficits in SREBP2 target gene expression in fibroblasts from an affected individual, indicating that the SREBF2 variant inhibits SREBP pathway activation. Using our fly model, we discovered that SREBF2 variants fail to induce LD production and act in a dominant-negative manner, which can be rescued by overexpression of S1P.

CONCLUSION

Taken together, these data reveal a mechanism by which SREBF2 pathogenic variants that disrupt the S1P cleavage motif cause disease via dominant-negative antagonism of S1P, limiting the cleavage of S1P targets, including SREBP1 and SREBP2.

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.

Glucose uptake in pigment glia suppresses tau-induced inflammation and photoreceptor degeneration in Drosophila

Brain inflammation contributes to the pathogenesis of neurodegenerative diseases such as Alzheimer's disease (AD). Glucose hypometabolism and glial activation are pathological features seen in AD brains; however, the connection between the two is not fully understood. Using a Drosophila model of AD, we identified that glucose metabolism in glia plays a critical role in neuroinflammation under disease conditions. Expression of human tau in the retinal cells, including photoreceptor neurons and pigment glia, causes photoreceptor degeneration accompanied by inclusion formation and swelling of lamina glial cells. We found that inclusions are formed by glial phagocytosis, and swelling of the laminal cortex correlates with the expression of antimicrobial peptides (AMPs). Co-expression of human glucose transporter 3 ( GLUT3 ) with tau in the retina does not affect tau levels but suppresses these inflammatory responses and photoreceptor degeneration. We also found that expression of GLUT3 , specifically in the pigment glia, is sufficient to suppress inflammatory phenotypes and mitigate photoreceptor degeneration in the tau-expressing retina. Our results suggest that glial glucose metabolism contributes to inflammatory responses and neurodegeneration in tauopathy.

Highlights

Tau expression in the fly retina induces glial activationPigment glial cells mediate inflammatory phenotypes in the degenerating retinaEnhanced glucose uptake in the pigment glia suppresses inflammation and photoreceptor neurodegeneration caused by tau expression.

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

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 remain largely unknown. For a strong AD-associated locus near Clusterin ( CLU ), we tied an AD protective allele to a role of neuronal CLU in promoting neuron excitability through lipid-mediated neuron-glia communication. We identified a putative causal SNP of CLU that impacts neuron-specific chromatin accessibility to transcription-factor(s), with the AD protective allele upregulating neuronal CLU and promoting neuron excitability. Transcriptomic analysis and functional studies in induced pluripotent stem cell (iPSC)-derived neurons co-cultured with mouse astrocytes show that neuronal CLU facilitates neuron-to-glia lipid transfer and astrocytic lipid droplet formation coupled with reactive oxygen species (ROS) accumulation. These changes cause astrocytes to uptake less glutamate thereby altering neuron excitability. Our study provides insights into how CLU confers resilience to AD through neuron-glia interactions.

Selenoprotein H mediates low selenium-related cognitive decline through impaired oligodendrocyte myelination with disrupted hippocampal lipid metabolism in female mice

Low selenium levels are closely associated with reduced cognitive performance and lipid dysregulation, yet the mechanism of action remains unclear. The physiological function of selenium is primarily mediated by selenoproteins. Selenoprotein H (SELENOH), as one of the selenium-containing proteins, has an unelucidated role in regulating cognitive status and lipid metabolism. In this study, we established a Selenoh gene knockout (HKO) mouse model to investigate whether Selenoh mediates the impact of selenium on cognitive function. We found that HKO mice showed a significant decline in cognition compared with the wild-type (HWT) littermates, and were not affected by deficient or excessive selenium, while no differences in anxiety and depression behavior were observed. HKO mice showed reduced myelin basic protein expression in hippocampal oligodendrocytes, with decreased glycolipid levels and increased phospholipid and sphingolipid levels in the hippocampus. Furthermore, the high-fat diet (HFD) exerted no effect on cognition and limited impact on the gene profile in the hippocampus of HKO mice. Compared with those of HWT mice, the myelination pathways in the hippocampus of HKO mice were downregulated as revealed by RNA-seq, which was further confirmed by the reduced expression levels of myelin-related proteins. Finally, HKO increased the expression of hippocampal fatty acid transporter (FATP) 4, and HFD increased the FATP4 expression in HWT mice but not in HKO mice. In summary, our study demonstrated that HKO induced cognitive decline by impairing myelination in oligodendrocytes with disrupted hippocampal lipid metabolism, which provided a novel viewpoint on the selenoprotein-mediated neurodegenerative diseases of selenium.

Hypercholesterolemia and the Increased Risk of Vascular Dementia: a Cholesterol Perspective

PURPOSE OF REVIEW

Vascular dementia (VaD) is the second most prevalent type of dementia after Alzheimer's disease.Hypercholesterolemia may increase the risk of dementia, but the association between cholesterol and cognitive function is very complex. From the perspective of peripheral and brain cholesterol, we review the relationship between hypercholesterolemia and increased risk of VaD and how the use of lipid-lowering therapies affects cognition.

RECENT FINDINGS

Epidemiologic studies show since 1980, non-HDL-C levels of individuals has increased rapidly in Asian countries.The study has suggested that vascular risk factors increase the risk of VaD, such as disordered lipid metabolism. Dyslipidemia has been found to interact with chronic cerebral hypoperfusion to promote inflammation resulting in cognitive dysfunction in the brain.Hypercholesterolemia may be a risk factor for VaD. Inflammation could potentially serve as a link between hypercholesterolemia and VaD. Additionally, the potential impact of lipid-lowering therapy on cognitive function is also worth considering. Finding strategies to prevent and treat VaD is critical given the aging of the population to lessen the load on society. Currently, controlling underlying vascular risk factors is considered one of the most effective methods of preventing VaD. Understanding the relationship between abnormal cholesterol levels and VaD, as well as discovering potential serum biomarkers, is important for the early prevention and treatment of VaD.

Unleashing metabolic power for axonal regeneration

Axon regeneration requires the mobilization of intracellular resources, including proteins, lipids, and nucleotides. After injury, neurons need to adapt their metabolism to meet the biosynthetic demands needed to achieve axonal regeneration. However, the exact contribution of cellular metabolism to this process remains elusive. Insights into the metabolic characteristics of proliferative cells may illuminate similar mechanisms operating in axon regeneration; therefore, unraveling previously unappreciated roles of metabolic adaptation is critical to achieving neuron regrowth, which is connected to the therapeutic strategies for neurological conditions necessitating nerve repairs, such as spinal cord injury and stroke. Here, we outline the metabolic role in axon regeneration and discuss factors enhancing nerve regrowth, highlighting potential novel metabolic treatments for restoring nerve function.

Altering heparan sulfate suppresses cell abnormalities and neuron loss in Drosophila presenilin model of Alzheimer Disease

We examined the function of heparan-sulfate-modified proteoglycans (HSPGs) in pathways affecting Alzheimer disease (AD)-related cell pathology in human cell lines and mouse astrocytes. Mechanisms of HSPG influences on presenilin-dependent cell loss were evaluated in Drosophila using knockdown of the presenilin homolog, Psn, together with partial loss-of-function of sulfateless (sfl), a gene specifically affecting HS sulfation. HSPG modulation of autophagy, mitochondrial function, and lipid metabolism were shown to be conserved in human cell lines, Drosophila, and mouse astrocytes. RNA interference (RNAi) of Ndst1 reduced intracellular lipid levels in wild-type mouse astrocytes or those expressing humanized variants of APOE, APOE3, and APOE4. Neuron-directed knockdown of Psn in Drosophila produced apoptosis and cell loss in the brain, phenotypes suppressed by reductions in sfl expression. Abnormalities in mitochondria, liposomes, and autophagosome-derived structures in animals with Psn knockdown were also rescued by reduction of sfl. These findings support the direct involvement of HSPGs in AD pathogenesis.

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.

Multiple Roles of Apolipoprotein E4 in Oxidative Lipid Metabolism and Ferroptosis During the Pathogenesis of Alzheimer's Disease

Alzheimer's disease (AD) is the most prevalent neurodegenerative disease worldwide and has a great socio-economic impact. Modified oxidative lipid metabolism and dysregulated iron homeostasis have been implicated in the pathogenesis of this disorder, but the detailed pathophysiological mechanisms still remain unclear. Apolipoprotein E (APOE) is a lipid-binding protein that occurs in large quantities in human blood plasma, and a polymorphism of the APOE gene locus has been identified as risk factors for AD. The human genome involves three major APOE alleles (APOE2, APOE3, APOE4), which encode for three subtly distinct apolipoprotein E isoforms (APOE2, APOE3, APOE4). The canonic function of these apolipoproteins is lipid transport in blood and brain, but APOE4 allele carriers have a much higher risk for AD. In fact, about 60% of clinically diagnosed AD patients carry at least one APOE4 allele in their genomes. Although the APOE4 protein has been implicated in pathophysiological key processes of AD, such as extracellular beta-amyloid (Aβ) aggregation, mitochondrial dysfunction, neuroinflammation, formation of neurofibrillary tangles, modified oxidative lipid metabolism, and ferroptotic cell death, the underlying molecular mechanisms are still not well understood. As for all mammalian cells, iron plays a crucial role in neuronal functions and dysregulation of iron homeostasis has also been implicated in the pathogenesis of AD. Imbalances in iron homeostasis and impairment of the hydroperoxy lipid-reducing capacity induce cellular dysfunction leading to neuronal ferroptosis. In this review, we summarize the current knowledge on APOE4-related oxidative lipid metabolism and the potential role of ferroptosis in the pathogenesis of AD. Pharmacological interference with these processes might offer innovative strategies for therapeutic interventions.

Chronic sub-lethal exposure to clothianidin triggers organismal and sub-organismal-level health hazards in a non-target organism, Drosophila melanogaster

Neonicotinoids are among the most widely used systemic pesticides across the world. These chemicals have gathered significant attention for their potential adverse impacts on non-target organisms. Clothianidin is a novel neonicotinoid pesticide, employed globally to control sucking and chewing types of pests. In nature, various non-target organisms can be exposed to this chemical through contaminated food, water, and air. Nonetheless, extensive investigations demonstrating the sub-lethal impacts of clothianidin on non-target entities are limited. Hence, the present study was aimed to unravel the chronic sub-lethal impacts (LC50 0.74 μg/mL) of clothianidin on a non-target organism, Drosophila melanogaster. The study parameters involved multiple tiers of life ranging from organismal level to the sub-cellular level. 1st instar larvae were exposed to the six sub-lethal concentrations viz. 0.05, 0.06, 0.07, 0.08, 0.09, and 0.1 μg/mL of clothianidin till their 3rd larval instar. Investigations involving organismal level have revealed clothianidin-induced significant reduction in the developmental duration, life span, phototaxis, and physical activities of the treated individuals. Interestingly, the tested compound has also altered the compound eye morphology of treated flies. Study was extended to the tissue and cellular levels where reduced cell viability in gut, brain, and fat body was apparent. Additionally, increased ROS production, nuclear disorganization, and higher lipid deposition were evident in gut of exposed individuals. Study was further extended to the sub-cellular level where chronic exposure to clothianidin up-regulated the major oxidative stress markers such as lipid peroxidation, protein carbonylation, HSP-70, SOD, catalase, GSH, and thioredoxin reductase. Furthermore, the activities of detoxifying enzymes such as CYP4501A1 and GST were also altered. Chronic exposure to clothianidin also triggered DNA fragmentation in treated larvae. In essence, results of this multi-level study depict the ROS-mediated toxicity of clothianidin on a non-target organism, D. melanogaster.

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.

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.

Association between abnormal lipid metabolism and Alzheimer's disease: New research has revealed significant findings on the APOE4 genotype in microglia

APOE4 is widely recognized as a genetic risk factor for Alzheimer's disease (AD), implicated in 60-80% of all AD cases. Recent research suggests that microglia carrying the APOE4 genotype display abnormal lipid metabolism and accumulate lipid droplets, which may exacerbate the pathology of AD. Microglia play a critical role in immune surveillance within the central nervous system and are responsible for removing harmful particles and preserving neuronal function. The APOE4 genotype causes abnormal lipid metabolism in microglia, resulting in excessive accumulation of lipid droplets. This accumulation not only impairs the phagocytic and clearance capabilities of microglia but also disrupts their interactions with neurons, resulting in disorganization and neurodegenerative alterations at the neuronal network level. In addition, the presence of APOE4 modifies the metabolic landscape of microglia, particularly affecting purinergic signaling and lipid metabolism, thereby exacerbating the pathological processes of AD. In conclusion, the accumulation of lipid droplets and abnormal lipid metabolism may be critical mechanisms in the progression of AD in microglia carrying the APOE4 genotype.

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

The accumulation of lipid droplets (LDs) in aging and Alzheimer's disease brains is considered a pathological phenomenon with unresolved cellular and molecular mechanisms. Utilizing stimulated Raman scattering (SRS) microscopy, we observed significant in situ LD accumulation in microglia of tauopathy mouse brains. SRS imaging, combined with deuterium oxide (D2O) labeling, revealed heightened lipogenesis and impaired lipid turnover within LDs in tauopathy fly brains and human neurons derived from induced pluripotent stem cells (iPSCs). Transfer of unsaturated lipids from tauopathy iPSC neurons to microglia induced LD accumulation, oxidative stress, inflammation, and impaired phagocytosis. Neuronal AMP-activated protein kinase (AMPK) inhibits lipogenesis and promotes lipophagy in neurons, thereby reducing lipid flux to microglia. AMPK depletion in prodromal tauopathy mice increased LD accumulation, exacerbated pro-inflammatory microgliosis, and promoted neuropathology. Our findings provide direct evidence of native, aberrant LD accumulation in tauopathy brains and underscore the critical role of AMPK in regulating brain lipid homeostasis.

Senescent glia link mitochondrial dysfunction and lipid accumulation

Senescence is a cellular state linked to ageing and age-onset disease across many mammalian species1,2. Acutely, senescent cells promote wound healing3,4 and prevent tumour formation5; but they are also pro-inflammatory, thus chronically exacerbate tissue decline. Whereas senescent cells are active targets for anti-ageing therapy6-11, why these cells form in vivo, how they affect tissue ageing and the effect of their elimination remain unclear12,13. Here we identify naturally occurring senescent glia in ageing Drosophila brains and decipher their origin and influence. Using Activator protein 1 (AP1) activity to screen for senescence14,15, we determine that senescent glia can appear in response to neuronal mitochondrial dysfunction. In turn, senescent glia promote lipid accumulation in non-senescent glia; similar effects are seen in senescent human fibroblasts in culture. Targeting AP1 activity in senescent glia mitigates senescence biomarkers, extends fly lifespan and health span, and prevents lipid accumulation. However, these benefits come at the cost of increased oxidative damage in the brain, and neuronal mitochondrial function remains poor. Altogether, our results map the trajectory of naturally occurring senescent glia in vivo and indicate that these cells link key ageing phenomena: mitochondrial dysfunction and lipid accumulation.

Role of nerve growth factor on cognitive impairment in patients with Alzheimer's disease carrying apolipoprotein E ε4

AIMS

To investigate the roles of neurotrophic factors on cognition in patients with Alzheimer's disease (AD) carrying Apolipoprotein E (APOE) ε4.

METHODS

Totals of 173 patients with AD were divided into APOE ε4 carrier and non-carrier groups, and their demographics, cognition, and neurotrophic factors in cerebrospinal fluid (CSF) were compared. Multiple linear regression analyses were performed to assess correlations among APOE ε4, neurotrophic factors and cognition. Mediation analyses were conducted to assess the sequential associations among APOE ε4, nerve growth factor (NGF), and cognition.

RESULTS

Global cognition and multiple domains were impaired in the APOE ε4 carrier group (all p < 0.05). NGF level in the APOE ε4 carrier group was lower than that in the non-carrier group (p = 0.016). NGF level showed significant correlations with both global and multiple domains cognitions. Specifically, NGF mediated the association between APOE ε4 and Animal Fluency Test score (β, -0.45; 95% CI [-0.96, -0.07]; p < 0.001) and Trail Making Test-A (time) (β, 0.15; 95% CI [0.01, 0.33]; p < 0.001).

CONCLUSION

APOE ε4 is associated with cognitive impairment, and those carrying APOE ε4 have decreased NGF level in CSF. Declined NGF level is correlated with compromised cognition. NGF mediates APOE ε4-associated cognitive impairment.

An important role for triglyceride in regulating spermatogenesis

Drosophila is a powerful model to study how lipids affect spermatogenesis. Yet, the contribution of neutral lipids, a major lipid group which resides in organelles called lipid droplets (LD), to sperm development is largely unknown. Emerging evidence suggests LD are present in the testis and that loss of neutral lipid- and LD-associated genes causes subfertility; however, key regulators of testis neutral lipids and LD remain unclear. Here, we show LD are present in early-stage somatic and germline cells within the Drosophila testis. We identified a role for triglyceride lipase brummer (bmm) in regulating testis LD, and found that whole-body loss of bmm leads to defects in sperm development. Importantly, these represent cell-autonomous roles for bmm in regulating testis LD and spermatogenesis. Because lipidomic analysis of bmm mutants revealed excess triglyceride accumulation, and spermatogenic defects in bmm mutants were rescued by genetically blocking triglyceride synthesis, our data suggest that bmm-mediated regulation of triglyceride influences sperm development. This identifies triglyceride as an important neutral lipid that contributes to Drosophila sperm development, and reveals a key role for bmm in regulating testis triglyceride levels during spermatogenesis.

Alzheimer's disease risk allele of PICALM causes detrimental lipid droplets in microglia

Despite genome-wide association studies of late-onset Alzheimer's disease (LOAD) having identified many genetic risk loci1-6, the underlying disease mechanisms remain largely unknown. Determining causal disease variants and their LOAD-relevant cellular phenotypes has been a challenge. Leveraging our approach for identifying functional GWAS risk variants showing allele-specific open chromatin (ASoC)7, we systematically identified putative causal LOAD risk variants in human induced pluripotent stem cells (iPSC)-derived neurons, astrocytes, and microglia (MG) and linked PICALM risk allele to a previously unappreciated MG-specific role of PICALM in lipid droplet (LD) accumulation. ASoC mapping uncovered functional risk variants for 26 LOAD risk loci, mostly MG-specific. At the MG-specific PICALM locus, the LOAD risk allele of rs10792832 reduced transcription factor (PU.1) binding and PICALM expression, impairing the uptake of amyloid beta (Aβ) and myelin debris. Interestingly, MG with PICALM risk allele showed transcriptional enrichment of pathways for cholesterol synthesis and LD formation. Genetic and pharmacological perturbations of MG further established a causal link between the reduced PICALM expression, LD accumulation, and phagocytosis deficits. Our work elucidates the selective LOAD vulnerability in microglia for the PICALM locus through detrimental LD accumulation, providing a neurobiological basis that can be exploited for developing novel clinical interventions.

Loss of dihydroceramide desaturase drives neurodegeneration by disrupting endoplasmic reticulum and lipid droplet homeostasis in glial cells

Dihydroceramide desaturases convert dihydroceramides to ceramides, the precursors of all complex sphingolipids. Reduction of DEGS1 dihydroceramide desaturase function causes pediatric neurodegenerative disorder hypomyelinating leukodystrophy-18 (HLD-18). We discovered that infertile crescent (ifc), the Drosophila DEGS1 homolog, is expressed primarily in glial cells to promote CNS development by guarding against neurodegeneration. Loss of ifc causes massive dihydroceramide accumulation and severe morphological defects in cortex glia, including endoplasmic reticulum (ER) expansion, failure of neuronal ensheathment, and lipid droplet depletion. RNAi knockdown of the upstream ceramide synthase schlank in glia of ifc mutants rescues ER expansion, suggesting dihydroceramide accumulation in the ER drives this phenotype. RNAi knockdown of ifc in glia but not neurons drives neuronal cell death, suggesting that ifc function in glia promotes neuronal survival. Our work identifies glia as the primary site of disease progression in HLD-18 and may inform on juvenile forms of ALS, which also feature elevated dihydroceramide levels.

Molecular and cellular organization of odorant binding protein genes in Drosophila

Chemosensation is important for the survival and reproduction of animals. The odorant binding proteins (OBPs) are thought to be involved in chemosensation together with chemosensory receptors. While OBPs were initially considered to deliver hydrophobic odorants to olfactory receptors in the aqueous lymph solution, recent studies suggest more complex roles in various organs. Here, we use GAL4 transgenes to systematically analyze the expression patterns of all 52 members of the Obp gene family and 3 related chemosensory protein genes in adult Drosophila, focusing on chemosensory organs such as the antenna, maxillary palp, pharynx, and labellum, and other organs such as the brain, ventral nerve cord, leg, wing, and intestine. The OBPs were observed to express in diverse organs and in multiple cell types, suggesting that these proteins can indeed carry out diverse functional roles. Also, we constructed 10 labellar-expressing Obp mutants, and obtained behavioral evidence that these OBPs may be involved in bitter sensing. The resources we constructed should be useful for future Drosophila OBP gene family research.

The Intersection of cerebral cholesterol metabolism and Alzheimer's disease: Mechanisms and therapeutic prospects

Alzheimer's disease (AD) is a common neurodegenerative disease in the elderly, the exact pathogenesis of which remains incompletely understood, and effective preventive and therapeutic drugs are currently lacking. Cholesterol plays a vital role in cell membrane formation and neurotransmitter synthesis, and its abnormal metabolism is associated with the onset of AD. With the continuous advancement of imaging techniques and molecular biology methods, researchers can more accurately explore the relationship between cholesterol metabolism and AD. Elevated cholesterol levels may lead to vascular dysfunction, thereby affecting neuronal function. Additionally, abnormal cholesterol metabolism may affect the metabolism of β-amyloid protein, thereby promoting the onset of AD. Brain cholesterol levels are regulated by multiple factors. This review aims to deepen the understanding of the subtle relationship between cholesterol homeostasis and AD, and to introduce the latest advances in cholesterol-regulating AD treatment strategies, thereby inspiring readers to contemplate deeply on this complex relationship. Although there are still many unresolved important issues regarding the risk of brain cholesterol and AD, and some studies may have opposite conclusions, further research is needed to enrich our understanding. However, these findings are expected to deepen our understanding of the pathogenesis of AD and provide important insights for the future development of AD treatment strategies targeting brain cholesterol homeostasis.

Does glial lipid dysregulation alter sleep in Alzheimer's and Parkinson's disease?

In this opinion article, we discuss potential connections between sleep disturbances observed in Alzheimer's disease (AD) and Parkinson's disease (PD) and the dysregulation of lipids in the brain. Research using Drosophila has highlighted the role of glial-mediated lipid metabolism in sleep and diurnal rhythms. Relevant to AD, the formation of lipid droplets in glia, which occurs in response to elevated neuronal reactive oxygen species (ROS), is required for sleep. In disease models, this process is disrupted, arguing a connection to sleep dysregulation. Relevant to PD, the degradation of neuronally synthesized glucosylceramides by glia requires glucocerebrosidase (GBA, a PD-associated risk factor) and this regulates sleep. Loss of GBA in glia causes an accumulation of glucosylceramides and neurodegeneration. Overall, research primarily using Drosophila has highlighted how dysregulation of glial lipid metabolism may underlie sleep disturbances in neurodegenerative diseases.

Abnormal Morphology and Synaptogenic Signaling in Astrocytes Following Prenatal Opioid Exposure

In recent decades, there has been a dramatic rise in the rates of children being born after in utero exposure to drugs of abuse, particularly opioids. Opioids have been shown to have detrimental effects on neurons and glia in the central nervous system (CNS), but the impact of prenatal opioid exposure (POE) on still-developing synaptic circuitry is largely unknown. Astrocytes exert a powerful influence on synaptic development, secreting factors to either promote or inhibit synapse formation and neuronal maturation in the developing CNS. Here, we investigated the effects of the partial µ-opioid receptor agonist buprenorphine on astrocyte synaptogenic signaling and morphological development in cortical cell culture. Acute buprenorphine treatment had no effect on the excitatory synapse number in astrocyte-free neuron cultures. In conditions where neurons shared culture media with astrocytes, buprenorphine attenuated the synaptogenic capabilities of astrocyte-secreted factors. Neurons cultured from drug-naïve mice showed no change in synapses when treated with factors secreted by astrocytes from POE mice. However, this same treatment was synaptogenic when applied to neurons from POE mice, indicating a complex neuroadaptive response in the event of impaired astrocyte signaling. In addition to promoting morphological and connectivity changes in neurons, POE exerted a strong influence on astrocyte development, disrupting their structural maturation and promoting the accumulation of lipid droplets (LDs), suggestive of a maladaptive stress response in the developing CNS.

Brain energy metabolism: A roadmap for future research

Although we have learned much about how the brain fuels its functions over the last decades, there remains much still to discover in an organ that is so complex. This article lays out major gaps in our knowledge of interrelationships between brain metabolism and brain function, including biochemical, cellular, and subcellular aspects of functional metabolism and its imaging in adult brain, as well as during development, aging, and disease. The focus is on unknowns in metabolism of major brain substrates and associated transporters, the roles of insulin and of lipid droplets, the emerging role of metabolism in microglia, mysteries about the major brain cofactor and signaling molecule NAD+, as well as unsolved problems underlying brain metabolism in pathologies such as traumatic brain injury, epilepsy, and metabolic downregulation during hibernation. It describes our current level of understanding of these facets of brain energy metabolism as well as a roadmap for future research.

Astrocytic HILPDA promotes lipid droplets generation to drive cognitive dysfunction in mice with sepsis-associated encephalopathy

AIMS

Sepsis-associated encephalopathy (SAE) is manifested as a spectrum of disturbed cerebral function ranging from mild delirium to coma. However, the pathogenesis of SAE has not been clearly elucidated. Astrocytes play important roles in maintaining the function and metabolism of the brain. Most recently, it has been demonstrated that disorders of lipid metabolism, especially lipid droplets (LDs) dyshomeostasis, are involved in a variety of neurodegenerative diseases. The aim of this study was to investigate whether LDs are involved in the underlying mechanism of SAE.

METHODS

The open field test, Y-maze test, and contextual fear conditioning test (CFCT) were used to test cognitive function in SAE mice. Lipidomics was utilized to investigate alterations in hippocampal lipid metabolism in SAE mice. Western blotting and immunofluorescence labeling were applied for the observation of related proteins.

RESULTS

In the current study, we found that SAE mice showed severe cognitive dysfunction, including spatial working and contextual memory. Meanwhile, we demonstrated that lipid metabolism was widely dysregulated in the hippocampus by using lipidomic analysis. Furthermore, western blotting and immunofluorescence confirmed that LDs accumulation in hippocampal astrocytes was involved in the pathological process of cognitive dysfunction in SAE mice. We verified that LDs can be inhibited by specifically suppress hypoxia-inducible lipid droplet-associated protein (HILPDA) in astrocytes. Meanwhile, cognitive dysfunction in SAE was ameliorated by reducing A1 astrocyte activation and inhibiting presynaptic membrane transmitter release.

CONCLUSION

The accumulation of astrocytic lipid droplets plays a crucial role in the pathological process of SAE. HILPDA is an attractive therapeutic target for lipid metabolism regulation and cognitive improvement in septic patients.

Bromocriptine protects perilesional spinal cord neurons from lipotoxicity after spinal cord injury

Recent studies have revealed that lipid droplets accumulate in neurons after brain injury and evoke lipotoxicity, damaging the neurons. However, how lipids are metabolized by spinal cord neurons after spinal cord injury remains unclear. Herein, we investigated lipid metabolism by spinal cord neurons after spinal cord injury and identified lipid-lowering compounds to treat spinal cord injury. We found that lipid droplets accumulated in perilesional spinal cord neurons after spinal cord injury in mice. Lipid droplet accumulation could be induced by myelin debris in HT22 cells. Myelin debris degradation by phospholipase led to massive free fatty acid production, which increased lipid droplet synthesis, β-oxidation, and oxidative phosphorylation. Excessive oxidative phosphorylation increased reactive oxygen species generation, which led to increased lipid peroxidation and HT22 cell apoptosis. Bromocriptine was identified as a lipid-lowering compound that inhibited phosphorylation of cytosolic phospholipase A2 by reducing the phosphorylation of extracellular signal-regulated kinases 1/2 in the mitogen-activated protein kinase pathway, thereby inhibiting myelin debris degradation by cytosolic phospholipase A2 and alleviating lipid droplet accumulation in myelin debris-treated HT22 cells. Motor function, lipid droplet accumulation in spinal cord neurons and neuronal survival were all improved in bromocriptine-treated mice after spinal cord injury. The results suggest that bromocriptine can protect neurons from lipotoxic damage after spinal cord injury via the extracellular signal-regulated kinases 1/2-cytosolic phospholipase A2 pathway.

Glial metabolism versatility regulates mushroom body-driven behavioral output in Drosophila

Providing metabolic support to neurons is now recognized as a major function of glial cells that is conserved from invertebrates to vertebrates. However, research in this field has focused for more than two decades on the relevance of lactate and glial glycolysis for neuronal energy metabolism, while overlooking many other facets of glial metabolism and their impact on neuronal physiology, circuit activity, and behavior. Here, we review recent work that has unveiled new features of glial metabolism, especially in Drosophila, in the modulation of behavioral traits involving the mushroom bodies (MBs). These recent findings reveal that spatially and biochemically distinct modes of glucose-derived neuronal fueling are implemented within the MB in a memory type-specific manner. In addition, cortex glia are endowed with several antioxidant functions, whereas astrocytes can serve as pro-oxidant agents that are beneficial to redox signaling underlying long-term memory. Finally, glial fatty acid oxidation seems to play a dual fail-safe role: first, as a mode of energy production upon glucose shortage, and, second, as a factor underlying the clearance of excessive oxidative load during sleep. Altogether, these integrated studies performed in Drosophila indicate that glial metabolism has a deterministic role on behavior.

Obesity during preclinical Alzheimer's disease development exacerbates brain metabolic decline

Alzheimer's disease (AD) is the most common form of dementia. Obesity in middle age increases AD risk and severity, which is alarming given that obesity prevalence peaks at middle age and obesity rates are accelerating worldwide. Midlife, but not late-life obesity increases AD risk, suggesting that this interaction is specific to preclinical AD. AD pathology begins in middle age, with accumulation of amyloid beta (Aβ), hyperphosphorylated tau, metabolic decline, and neuroinflammation occurring decades before cognitive symptoms appear. We used a transcriptomic discovery approach in young adult (6.5 months old) male and female TgF344-AD rats that overexpress mutant human amyloid precursor protein and presenilin-1 and wild-type (WT) controls to determine whether inducing obesity with a high-fat/high-sugar "Western" diet during preclinical AD increases brain metabolic dysfunction in dorsal hippocampus (dHC), a brain region vulnerable to the effects of obesity and early AD. Analyses of dHC gene expression data showed dysregulated mitochondrial and neurotransmission pathways, and up-regulated genes involved in cholesterol synthesis. Western diet amplified the number of genes that were different between AD and WT rats and added pathways involved in noradrenergic signaling, dysregulated inhibition of cholesterol synthesis, and decreased intracellular lipid transporters. Importantly, the Western diet impaired dHC-dependent spatial working memory in AD but not WT rats, confirming that the dietary intervention accelerated cognitive decline. To examine later consequences of early transcriptional dysregulation, we measured dHC monoamine levels in older (13 months old) AD and WT rats of both sexes after long-term chow or Western diet consumption. Norepinephrine (NE) abundance was significantly decreased in AD rats, NE turnover was increased, and the Western diet attenuated the AD-induced increases in turnover. Collectively, these findings indicate obesity during prodromal AD impairs memory, potentiates AD-induced metabolic decline likely leading to an overproduction of cholesterol, and interferes with compensatory increases in NE transmission.

The alpha-ketoacid dehydrogenase complexes of Drosophila melanogaster

The conserved family of alpha-ketoacid dehydrogenase complexes (AKDHCs) catalyze essential reactions in central metabolism and their dysregulation is implicated in several human diseases. Drosophila melanogaster provides an excellent model system to study the genetics and functions of these complexes. However, a systematic account of Drosophila AKDHCs and their composition has been lacking. Here, I identify and classify the genes encoding all Drosophila AKDHC subunits, update their functional annotations and integrate this work into the FlyBase database.

Cell non-autonomous control of autophagy and metabolism by glial cells

Glia are the protectors of the nervous system, providing neurons with support and protection from cytotoxic insults. We previously discovered that four astrocyte-like glia can regulate organismal proteostasis and longevity in C. elegans. Expression of the UPRER transcription factor, XBP-1s, in these glia increases stress resistance, and longevity, and activates the UPRER in intestinal cells via neuropeptides. Autophagy, a key regulator of metabolism and aging, has been described as a cell autonomous process. Surprisingly, we find that glial XBP-1s enhances proteostasis and longevity by cell non-autonomously reprogramming organismal lipid metabolism and activating autophagy. Glial XBP-1s regulates the activation of another transcription factor, HLH-30/TFEB, in the intestine. HLH-30 activates intestinal autophagy, increases intestinal lipid catabolism, and upregulates a robust transcriptional program. Our study reveals a novel role for glia in regulating peripheral lipid metabolism, autophagy, and organellar health through peripheral activation of HLH-30 and autophagy.

Glia-derived secretory fatty acid binding protein Obp44a regulates lipid storage and efflux in the developing Drosophila brain

Glia derived secretory factors play diverse roles in supporting the development, physiology, and stress responses of the central nervous system (CNS). Through transcriptomics and imaging analyses, we have identified Obp44a as one of the most abundantly produced secretory proteins from Drosophila CNS glia. Protein structure homology modeling and Nuclear Magnetic Resonance (NMR) experiments reveal Obp44a as a fatty acid binding protein (FABP) with a high affinity towards long-chain fatty acids in both native and oxidized forms. Further analyses demonstrate that Obp44a effectively infiltrates the neuropil, traffics between neuron and glia, and is secreted into hemolymph, acting as a lipid chaperone and scavenger to regulate lipid and redox homeostasis in the developing brain. In agreement with this essential role, deficiency of Obp44a leads to anatomical and behavioral deficits in adult animals and elevated oxidized lipid levels. Collectively, our findings unveil the crucial involvement of a noncanonical lipid chaperone to shuttle fatty acids within and outside the brain, as needed to maintain a healthy brain lipid environment. These findings could inspire the design of novel approaches to restore lipid homeostasis that is dysregulated in CNS diseases.

A neuron-glia lipid metabolic cycle couples daily sleep to mitochondrial homeostasis

Sleep is thought to be restorative to brain energy homeostasis, but it is not clear how this is achieved. We show here that Drosophila glia exhibit a daily cycle of glial mitochondrial oxidation and lipid accumulation that is dependent on prior wake and requires the Drosophila APOE orthologs NLaz and GLaz, which mediate neuron-glia lipid transfer. In turn, a full night of sleep is required for glial lipid clearance, mitochondrial oxidative recovery and maximal neuronal mitophagy. Knockdown of neuronal NLaz causes oxidative stress to accumulate in neurons, and the neuronal mitochondrial integrity protein, Drp1, is required for daily glial lipid accumulation. These data suggest that neurons avoid accumulation of oxidative mitochondrial damage during wake by using mitophagy and passing damage to glia in the form of lipids. We propose that a mitochondrial lipid metabolic cycle between neurons and glia reflects a fundamental function of sleep relevant for brain energy homeostasis.

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.

The seminal vesicle is a juvenile hormone-responsive tissue in adult male Drosophila melanogaster

Juvenile hormone (JH) is one of the most essential hormones controlling insect metamorphosis and physiology. While it is well known that JH affects many tissues throughout the insects life cycle, the difference in JH responsiveness and the repertoire of JH-inducible genes among different tissues has not been fully investigated. In this study, we monitored JH responsiveness in vivo using transgenic Drosophila melanogaster flies carrying a JH response element-GFP (JHRE-GFP) construct. Our data highlight the high responsiveness of the epithelial cells within the seminal vesicle, a component of the male reproductive tract, to JH. Specifically, we observe an elevation in the JHRE-GFP signal within the seminal vesicle epithelium upon JH analog administration, while suppression occurs upon knockdown of genes encoding the intracellular JH receptors, Methoprene-tolerant and germ cell-expressed. Starting from published transcriptomic and proteomics datasets, we next identified Lactate dehydrogenase as a JH-response gene expressed in the seminal vesicle epithelium, suggesting insect seminal vesicles undergo metabolic regulation by JH. Together, this study sheds new light on biology of the insect reproductive regulatory system.

Sex-specific changes in protein expression of membrane transporters in the brain cortex of 5xFAD mouse model of Alzheimer's disease

Membrane transporters playing an important role in the passage of drugs, metabolites and nutrients across the membranes of the brain cells have been shown to be involved in pathogenesis of Alzheimer's disease (AD). However, little is known about sex-specific changes in transporter protein expression at the brain in AD. Here, we investigated sex-specific alterations in protein expression of three ATP-binding cassette (ABC) and five solute carriers (SLC) transporters in the prefrontal cortex of a commonly used model of familial AD (FAD), 5xFAD mice. Sensitive liquid chromatography tandem mass spectrometry-based quantitative targeted absolute proteomic analysis was applied for absolute quantification of transporter protein expression. We compared the changes in transporter protein expressions in 7-month-old male and female 5xFAD mice versus sex-matched wild-type mice. The study revealed a significant sex-specific increase in protein expression of ABCC1 (p = 0.007) only in male 5xFAD mice as compared to sex-matched wild-type animals. In addition, the increased protein expression of glucose transporter 1 (p = 0.01), 4F2 cell-surface antigen heavy chain (p = 0.01) and long-chain fatty acid transport protein 1 (p = 0.02) were found only in female 5xFAD mice as compared to sex-matched wild-type animals. Finally, protein expression of alanine/serine/cysteine/threonine transporter 1 was upregulated in both male (p = 0.02) and female (p = 0.002) 5xFAD mice. The study provides important information about sex-specific changes in brain cortical transporter expression in 5xFAD mice, which will facilitate drug development of therapeutic strategies for AD targeting these transporters and drug delivery research.

Whole organism snRNA-seq reveals systemic peripheral changes in Alzheimer's Disease fly models

Peripheral tissues become disrupted in Alzheimer's Disease (AD). However, a comprehensive understanding of how the expression of AD-associated toxic proteins, Aβ42 and Tau, in neurons impacts the periphery is lacking. Using Drosophila, a prime model organism for studying aging and neurodegeneration, we generated the Alzheimer's Disease Fly Cell Atlas (AD-FCA): whole-organism single-nucleus transcriptomes of 219 cell types from adult flies neuronally expressing human Aβ42 or Tau. In-depth analyses and functional data reveal impacts on peripheral sensory neurons by Aβ42 and on various non-neuronal peripheral tissues by Tau, including the gut, fat body, and reproductive system. This novel AD atlas provides valuable insights into potential biomarkers and the intricate interplay between the nervous system and peripheral tissues in response to AD-associated proteins.