bims-medebr 2024-06-23 papers

bims-medebr

Biomed News

on Metabolism of the developing brain

Issue of 2024–06–23
twenty-six papers selected by
Regina F. Fernández, Johns Hopkins University

Deficient brain GABA metabolism leads to widespread impairments of astrocyte and oligodendrocyte function.
Consequences of a 2-Deoxyglucose Exposure on the ATP Content and the Cytosolic Glucose Metabolism of Cultured Primary Rat Astrocytes.
Exploration of dietary interventions to treat mitochondrial fatty acid disorders in a mouse model.
Characterization of β-Hydroxybutyrate as a Cell Autonomous Fuel for Active Excitatory and Inhibitory Neurons.
mTOR inhibition enhances synaptic and mitochondrial function in Alzheimer's disease in an APOE genotype-dependent manner.
Targeting the sphingolipid rheostat in IDH1 mut glioma alters cholesterol homeostasis and triggers apoptosis via membrane degradation.
Co-registration of MALDI-MSI and histology demonstrates gangliosides co-localize with amyloid beta plaques in Alzheimer's disease.
Exposure to lipid mixture induces intracellular lipid droplet formation and impairs mitochondrial functions in astrocytes.
Arachidonic acid mobilization and peroxidation promote microglial dysfunction in Aβ pathology.
Psychosocial experiences are associated with human brain mitochondrial biology.
Lipidomics and Mass Spectrometry Imaging unveil Alterations in Mice Hippocampus Lipid Composition exposed to Hypoxia.
Do oligodendrocytes regulate axonal glucose uptake and consumption?
PLA2G15 is a Lysosomal BMP Hydrolase with Ester Position Specificity and its Targeting Ameliorates Lysosomal Disease.
H2S prevents the disruption of the blood-brain barrier in rats with prenatal hyperhomocysteinemia.
Beta-Hydroxybutyrate Mitigates Sensorimotor and Cognitive Impairments in a Photothrombosis-Induced Ischemic Stroke in Mice.
Simplification of Dietary Treatment in Pharmacoresistant Epilepsy: Impact of C8 and C10 Fatty Acids on Sirtuins of Neuronal Cells In Vitro.
Astrocytic LRP1 enables mitochondria transfer to neurons and mitigates brain ischemic stroke by suppressing ARF1 lactylation.
Activation of Neurotoxic Astrocytes Due to Mitochondrial Dysfunction Triggered by POLG Mutation.
Cerebral Glucose Metabolism Is a Valuable Predictor of Survival in Patients with Lewy Body Diseases.
Neonatal dysregulation of 2-arachidonoylglycerol induces impaired brain function in adult mice.
Liver as a new target organ in Alzheimer's disease: insight from cholesterol metabolism and its role in amyloid-beta clearance.
Lipid droplets in the nervous system: involvement in cell metabolic homeostasis.
Apolipoprotein E4 interferes with lipid metabolism to exacerbate depression-like behaviors in 5xFAD mice.
Is mitochondrial morphology important for cellular physiology?
Rft1 catalyzes lipid-linked oligosaccharide translocation across the ER membrane.
FABP5-binding lipids regulate autophagy in differentiated SH-SY5Y cells.

Glia. 2024 Jun 20.

Deficient brain GABA metabolism leads to widespread impairments of astrocyte and oligodendrocyte function.

Jens V Andersen, Oana C Marian, Filippa L Qvist, Emil W Westi, Blanca I Aldana, Arne Schousboe, Anthony S Don, Niels H Skotte, Petrine Wellendorph.

  The neurometabolic disorder succinic semialdehyde dehydrogenase (SSADH) deficiency leads to great neurochemical imbalances and severe neurological manifestations. The cause of the disease is loss of function of the enzyme SSADH, leading to impaired metabolism of the principal inhibitory neurotransmitter GABA. Despite the known identity of the enzymatic deficit, the underlying pathology of SSADH deficiency remains unclear. To uncover new mechanisms of the disease, we performed an untargeted integrative analysis of cerebral protein expression, functional metabolism, and lipid composition in a genetic mouse model of SSADH deficiency (ALDH5A1 knockout mice). Our proteomic analysis revealed a clear regional vulnerability, as protein alterations primarily manifested in the hippocampus and cerebral cortex of the ALDH5A1 knockout mice. These regions displayed aberrant expression of proteins linked to amino acid homeostasis, mitochondria, glial function, and myelination. Stable isotope tracing in acutely isolated brain slices demonstrated an overall maintained oxidative metabolism of glucose, but a selective decrease in astrocyte metabolic activity in the cerebral cortex of ALDH5A1 knockout mice. In contrast, an elevated capacity of oxidative glutamine metabolism was observed in the ALDH5A1 knockout brain, which may serve as a neuronal compensation of impaired astrocyte glutamine provision. In addition to reduced expression of critical oligodendrocyte proteins, a severe depletion of myelin-enriched sphingolipids was found in the brains of ALDH5A1 knockout mice, suggesting degeneration of myelin. Altogether, our study highlights that impaired astrocyte and oligodendrocyte function is intimately linked to SSADH deficiency pathology, suggesting that selective targeting of glial cells may hold therapeutic potential in this disease.

Keywords:  SSADH deficiency; brain energy metabolism; glia; glutamate/GABA‐glutamine cycle; myelin

DOI:  https://doi.org/10.1002/glia.24585
Neurochem Res. 2024 Jun 19.

Consequences of a 2-Deoxyglucose Exposure on the ATP Content and the Cytosolic Glucose Metabolism of Cultured Primary Rat Astrocytes.

Antonia Regina Harders, Patrick Watermann, Gabriele Karger, Sadhbh Cynth Denieffe, Alina Weller, Annika Carina Dannemann, Johanna Elisabeth Willker, Yvonne Köhler, Christian Arend, Ralf Dringen.

  The glucose analogue 2-deoxyglucose (2DG) has frequently been used as a tool to study cellular glucose uptake and to inhibit glycolysis. Exposure of primary cultured astrocytes to 2DG caused a time- and concentration-dependent cellular accumulation of 2-deoxyglucose-6-phosphate (2DG6P) that was accompanied by a rapid initial decline in cellular ATP content. Inhibitors of mitochondrial respiration as well as inhibitors of mitochondrial uptake of pyruvate and activated fatty acids accelerated the ATP loss, demonstrating that mitochondrial ATP regeneration contributes to the partial maintenance of the ATP content in 2DG-treated astrocytes. After a 30 min exposure to 10 mM 2DG the specific content of cellular 2DG6P had accumulated to around 150 nmol/mg, while cellular ATP was lowered by 50% to around 16 nmol/mg. Following such a 2DG6P-loading of astrocytes, glycolytic lactate production from applied glucose was severely impaired during the initial 60 min of incubation, but was reestablished during longer incubation concomitant with a loss in cellular 2DG6P content. In contrast to glycolysis, the glucose-dependent NADPH regeneration via the pentose phosphate pathway (PPP) was only weakly affected in 2DG6P-loaded astrocytes and in cells that were coincubated with glucose in the presence of an excess of 2DG. Additionally, in the presence of 2DG PPP-dependent WST1 reduction was found to have doubled compared to hexose-free control incubations, indicating that cellular 2DG6P can serve as substrate for NADPH regeneration by the astrocytic PPP. The data presented provide new insights on the metabolic consequences of a 2DG exposure on the energy and glucose metabolism of astrocytes and demonstrate the reversibility of the inhibitory potential of a 2DG-treatment on the glucose metabolism of cultured astrocytes.

Keywords:  ATP; Astrocytes; Deoxyglucose; Glucose; Glycolysis; Pentose phosphate pathway

DOI:  https://doi.org/10.1007/s11064-024-04192-y
J Nutr Biochem. 2024 Jun 13. pii: S0955-2863(24)00125-6. [Epub ahead of print] 109692

Exploration of dietary interventions to treat mitochondrial fatty acid disorders in a mouse model.

Kaija J Autio, Hennariikka Koivisto, Werner Schmitz, Anna Puronurmi, Heikki Tanila, Alexander J Kastaniotis.

  Mitochondrial fatty acids synthesis (mtFAS) is a conserved metabolic pathway essential for mitochondrial respiration. The best characterized mtFAS product is the medium-chain fatty acid octanoate (C8) used as a substrate in the synthesis of lipoic acid (LA), a cofactor required by several mitochondrial enzyme complexes. In humans, mutations in the mtFAS component enoyl reductase MECR cause childhood-onset neurodegenerative disorder MEPAN. A complete deletion of Mecr in mice is embryonically lethal, while selective deletion of Mecr in cerebellar Purkinje cells causes neurodegeneration in these cells. A fundamental question in the research of mtFAS deficiency is if the defect is amenable to treatment by supplementation with known mtFAS products. Here we used the Purkinje-cell specific mtFAS deficiency neurodegeneration model mice to study if feeding the mice with a medium-chain triacylglycerol-rich formula supplemented with LA could slow down or prevent the neurodegeneration in Purkinje cell-specific Mecr KO mice. Feeding started at the age of 4 weeks and continued until the age of 9 months. The neurological status on the mice was assessed at the age of 3, 6 and 9 months with behavioral tests and the state of the Purkinje cell deterioration in the cerebellum was studied histologically. We showed that feeding the mice with medium chain triacylglycerols and LA affected fatty acid profiles in the cerebellum and plasma but did not prevent the development of neurodegeneration in these mice. Our results indicate that dietary supplementation with medium chain fatty acids and LA alone is not an efficient way to treat mtFAS disorders.

Keywords:  Mitochondrial fatty acid synthesis; lipoic acid; medium chain fatty acid; mouse model; neurodegeneration

DOI:  https://doi.org/10.1016/j.jnutbio.2024.109692
bioRxiv. 2024 Jun 09. pii: 2024.06.08.598077. [Epub ahead of print]

Characterization of β-Hydroxybutyrate as a Cell Autonomous Fuel for Active Excitatory and Inhibitory Neurons.

Kirsten Bredvik, Charmaine Liu, Timothy A Ryan.

The ketogenic diet is an effective treatment for drug-resistant epilepsy, but the therapeutic mechanisms are poorly understood. Although ketones are able to fuel the brain, it is not known whether ketones are directly metabolized by neurons on a time scale sufficiently rapid to fuel the bioenergetic demands of sustained synaptic transmission. Here, we show that nerve terminals can use the ketone β-hydroxybutyrate in a cell- autonomous fashion to support neurotransmission in both excitatory and inhibitory nerve terminals and that this flexibility relies on Ca 2+ dependent upregulation of mitochondrial metabolism. Using a genetically encoded ATP sensor, we show that inhibitory axons fueled by ketones sustain much higher ATP levels under steady state conditions than excitatory axons, but that the kinetics of ATP production following activity are slower when using ketones as fuel compared to lactate/pyruvate for both excitatory and inhibitory neurons.
Significance Statement: The ketogenic diet is a standard treatment for drug resistant epilepsy, but the mechanism of treatment efficacy is largely unknown. Changes to excitatory and inhibitory balance is one hypothesized mechanism. Here, we determine that ATP levels are differentially higher in inhibitory neurons compared to excitatory neurons, suggesting that greater mitochondrial ATP production in inhibitory neurons could be one mechanism mediating therapeutic benefit. Further, our studies of ketone metabolism by synaptic mitochondria should inform management of side effects and risks associated with ketogenic diet treatments. These results provide novel insights that clarify the role of ketones at the cellular level in ketogenic diet treatment for intractable epilepsy and inform the use of ketogenic diets for neurologic and psychiatric conditions more broadly.

DOI: https://doi.org/10.1101/2024.06.08.598077
J Cereb Blood Flow Metab. 2024 Jun 16. 271678X241261942

mTOR inhibition enhances synaptic and mitochondrial function in Alzheimer's disease in an APOE genotype-dependent manner.

Basavaraju G Sanganahalli, Jelena M Mihailovic, Hemendra J Vekaria, Daniel Coman, Andrew T Yackzan, Abeoseh Flemister, Chetan Aware, Kathryn Wenger, W Brad Hubbard, Patrick G Sullivan, Fahmeed Hyder, Ai-Ling Lin.

  Apolipoprotein ε4 (APOE4) carriers develop brain metabolic dysfunctions decades before the onset of Alzheimer's disease (AD). A goal of the study is to identify if rapamycin, an inhibitor for the mammalian target of rapamycin (mTOR) inhibitor, would enhance synaptic and mitochondrial function in asymptomatic mice with human APOE4 gene (E4FAD) before they showed metabolic deficits. A second goal is to determine whether there may be genetic-dependent responses to rapamycin when compared to mice with human APOE3 alleles (E3FAD), a neutral AD genetic risk factor. We fed asymptomatic E4FAD and E3FAD mice with control or rapamycin diets for 16 weeks from starting from 3 months of age. Neuronal mitochondrial oxidative metabolism and excitatory neurotransmission rates were measured using in vivo 1H-[13C] proton-observed carbon-edited magnetic resonance spectroscopy, and isolated mitochondrial bioenergetic measurements using Seahorse. We found that rapamycin enhanced neuronal mitochondrial function, glutamate-glutamine cycling, and TCA cycle rates in the asymptomatic E4FAD mice. In contrast, rapamycin enhances glycolysis, non-neuronal activities, and inhibitory neurotransmission of the E3FAD mice. These findings indicate that rapamycin might be able to mitigate the risk for AD by enhancing brain metabolic functions for cognitively intact APOE4 carriers, and the responses to rapamycin are varied by APOE genotypes. Consideration of precision medicine may be needed for future rapamycin therapeutics.

Keywords:  APOE4; Alzheimer’s disease; Rapamycin; mitochondrial function; synaptic activity

DOI:  https://doi.org/10.1177/0271678X241261942
bioRxiv. 2024 Apr 27. pii: 2024.04.26.591321. [Epub ahead of print]

Targeting the sphingolipid rheostat in IDH1 mut glioma alters cholesterol homeostasis and triggers apoptosis via membrane degradation.

Tyrone Dowdy, Helena Muley Vilamu, Adrian Lita, Aiguo Li, Tomohiro Yamasaki, Lumin Zhang, Raj Chari, Hua Song, Meili Zhang, Wei Zhang, Nicole Briceno, Dionne Davis, Mark R Gilbert, Mioara Larion.

The cross-regulation of metabolism and trafficking is not well understood for the vital sphingolipids and cholesterol constituents of cellular compartments. While reports are starting to surface on how sphingolipids like sphingomyelin (SM) dysregulate cholesterol levels in different cellular compartments (Jiang et al., 2022), limited research is available on the mechanisms driving the relationship between sphingolipids and cholesterol homeostasis, or its biological implications. Previously, we have identified sphingolipid metabolism as a unique vulnerability for IDH1 mut gliomas via a rational drug design. Herein, we show how modulating sphingolipid levels affects cholesterol homeostasis in brain tumors. However, we unexpectedly discovered for the first time that C17 sphingosine and NDMS addition to cancer cells alters cholesterol homeostasis by impacting its cellular synthesis, uptake, and efflux leading to a net decrease in cholesterol levels and inducing apoptosis. Our results reflect a reverse correlation between the levels of sphingosines, NDMS, and unesterified, free cholesterol in the cells. We show that increasing sphingosine and NDMS (a sphingosine analog) levels alter not only the trafficking of cholesterol between membranes but also the efflux and synthesis of cholesterol. We also demonstrate that despite the effort to remove free cholesterol by ABCA1-mediated efflux or by suppressing machinery for the influx (LDLR) and biosynthetic pathway (HMGCR), apoptosis is inevitable for IDH1 mut glioma cells. This is the first study that shows how altering sphingosine levels directly affects cholesterol homeostasis in cancer cells and can be used to manipulate this relationship to induce apoptosis in IDH1 mut gliomas.

DOI: https://doi.org/10.1101/2024.04.26.591321
Acta Neuropathol. 2024 06 19. 147(1): 105

Co-registration of MALDI-MSI and histology demonstrates gangliosides co-localize with amyloid beta plaques in Alzheimer's disease.

Nikita Ollen-Bittle, Shervin Pejhan, Stephen H Pasternak, C Dirk Keene, Qi Zhang, Shawn N Whitehead.

  Alzheimer's disease (AD) is a progressive neurological condition characterized by impaired cognitive function and behavioral alterations. While AD research historically centered around mis-folded proteins, advances in mass spectrometry techniques have triggered increased exploration of the AD lipidome with lipid dysregulation emerging as a critical player in AD pathogenesis. Gangliosides are a class of glycosphingolipids enriched within the central nervous system. Previous work has suggested a shift in a-series gangliosides from complex (GM1) to simple (GM2 and GM3) species may be related to the development of neurodegenerative disease. In addition, complex gangliosides with 20 carbon sphingosine chains have been shown to increase in the aging brain. In this study, we utilized matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI-MSI) to interrogate the in situ relationship of a-series gangliosides with either 18 or 20 carbon sphingosine chains (d18:1 or d20:1, respectively) in the post-mortem human AD brain. Here, we expanded upon previous literature and demonstrated a significant decrease in the GM1 d20:1 to GM1 d18:1 ratio in regions of the dentate gyrus and entorhinal cortex in AD relative to control brain tissue. Then, we demonstrated that the MALDI-MSI profile of GM3 co-localizes with histologically confirmed amyloid beta (Aβ) plaques and found a significant increase in both GM1 and GM3 in proximity to Aβ plaques. Collectively, this study demonstrates a perturbation of the ganglioside profile in AD, and validates a pipeline for MALDI-MSI and classic histological staining in the same tissue sections. This demonstrates feasibility for integrating untargeted mass spectrometry imaging approaches into a digital pathology framework.

Keywords:  Alzheimer’s disease; Digital pathology; Gangliosides; Lipids; MALDI-MSI

DOI:  https://doi.org/10.1007/s00401-024-02759-1
Neurochem Int. 2024 Jun 14. pii: S0197-0186(24)00119-0. [Epub ahead of print]178 105792

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

Yi-Chen Li, Jing-Ting Fu, Shun-Fen Tzeng.

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

Keywords:  Astrocytes; Autophagy; Lipid droplets; Lipid mixture; Mitochondria

DOI:  https://doi.org/10.1016/j.neuint.2024.105792
J Neurosci. 2024 Jun 12. pii: e0202242024. [Epub ahead of print]

Arachidonic acid mobilization and peroxidation promote microglial dysfunction in Aβ pathology.

Da Lin, Andrew Gold, Sarah Kaye, Jeffrey R Atkinson, Marcus Tol, Andrew Sas, Benjamin Segal, Peter Tontonoz, Jiangjiang Zhu, Jie Gao.

Aberrant increase of arachidonic acid (ARA) has long been implicated in the pathology of Alzheimer's disease (AD), while the underlying causal mechanism remains unclear. In this study, we revealed a link between ARA mobilization and microglial dysfunction in Aβ pathology. Lipidomic analysis of primary microglia from AppNL-GF mice showed a marked increase in free ARA and lysophospholipids (LPLs) along with a decrease in ARA-containing phospholipids, suggesting increased ARA release from phospholipids (PLs). To manipulate ARA-containing PLs in microglia, we genetically deleted Lysophosphatidylcholine Acyltransferase 3 (Lpcat3), the main enzyme catalyzing the incorporation of ARA into PLs. Loss of microglial Lpcat3 reduced the levels of ARA-containing phospholipids, free ARA and LPLs, leading to a compensatory increase in monounsaturated fatty acid (MUFA)-containing PLs in both male and female App NL-GF mice. Notably, the reduction of ARA in microglia significantly ameliorated oxidative stress and inflammatory responses while enhancing the phagocytosis of Aβ plaques and promoting the compaction of Aβ deposits. Mechanistically, sc-RNA seq suggested that LPCAT3 deficiency facilitates phagocytosis by facilitating de novo lipid synthesis while protecting microglia from oxidative damage. Collectively, our study reveals a novel mechanistic link between ARA mobilization and microglial dysfunction in AD. Lowering brain ARA levels through pharmacological or dietary interventions may be a potential therapeutic strategy to slow down AD progression.Significance Statement This study revealed a novel mechanistic link between the increase of arachidonic acid and microglial dysfunction in Alzheimer's disease. We discovered that microglia in an AD mouse model show heightened free ARA, pointing to increased ARA release from phospholipids. By targeting Lysophosphatidylcholine Acyltransferase in microglia, we effectively reduced ARA levels, leading to decreased oxidative stress and inflammation, and enhanced clearance of Aβ plaques. This study suggests that lowering brain ARA levels could be a viable approach to slow AD progression.

DOI: https://doi.org/10.1523/JNEUROSCI.0202-24.2024
Proc Natl Acad Sci U S A. 2024 Jul 02. 121(27): e2317673121

Psychosocial experiences are associated with human brain mitochondrial biology.

Caroline Trumpff, Anna S Monzel, Carmen Sandi, Vilas Menon, Hans-Ulrich Klein, Masashi Fujita, Annie Lee, Vladislav A Petyuk, Cheyenne Hurst, Duc M Duong, Nicholas T Seyfried, Aliza P Wingo, Thomas S Wingo, Yanling Wang, Madhav Thambisetty, Luigi Ferrucci, David A Bennett, Philip L De Jager, Martin Picard.

  Psychosocial experiences affect brain health and aging trajectories, but the molecular pathways underlying these associations remain unclear. Normal brain function relies on energy transformation by mitochondria oxidative phosphorylation (OxPhos). Two main lines of evidence position mitochondria both as targets and drivers of psychosocial experiences. On the one hand, chronic stress exposure and mood states may alter multiple aspects of mitochondrial biology; on the other hand, functional variations in mitochondrial OxPhos capacity may alter social behavior, stress reactivity, and mood. But are psychosocial exposures and subjective experiences linked to mitochondrial biology in the human brain? By combining longitudinal antemortem assessments of psychosocial factors with postmortem brain (dorsolateral prefrontal cortex) proteomics in older adults, we find that higher well-being is linked to greater abundance of the mitochondrial OxPhos machinery, whereas higher negative mood is linked to lower OxPhos protein content. Combined, positive and negative psychosocial factors explained 18 to 25% of the variance in the abundance of OxPhos complex I, the primary biochemical entry point that energizes brain mitochondria. Moreover, interrogating mitochondrial psychobiological associations in specific neuronal and nonneuronal brain cells with single-nucleus RNA sequencing (RNA-seq) revealed strong cell-type-specific associations for positive psychosocial experiences and mitochondria in glia but opposite associations in neurons. As a result, these "mind-mitochondria" associations were masked in bulk RNA-seq, highlighting the likely underestimation of true psychobiological effect sizes in bulk brain tissues. Thus, self-reported psychosocial experiences are linked to human brain mitochondrial phenotypes.

Keywords:  mitochondria; proteome; psychosocial factors; single cell RNA-seq; transcriptome

DOI:  https://doi.org/10.1073/pnas.2317673121
J Lipid Res. 2024 Jun 10. pii: S0022-2275(24)00080-4. [Epub ahead of print] 100575

Lipidomics and Mass Spectrometry Imaging unveil Alterations in Mice Hippocampus Lipid Composition exposed to Hypoxia.

Jiayue Gao, Zhiying Guo, Ming Zhao, Xiang Cheng, Xiufang Jiang, Yikun Liu, Wenpeng Zhang, Xiangpei Yue, Xuechao Fei, Yaqun Jiang, Lu Chen, Shaojie Zhang, Tong Zhao, Lingling Zhu.

  Lipids are components of cytomembranes that are involved in various biochemical processes. High-altitude hypoxic environments not only affect the body's energy metabolism, but these environments can also cause abnormal lipid metabolism involved in the hypoxia-induced cognitive impairment. Thus, comprehensive lipidomic profiling of the brain tissue is an essential step toward understanding the mechanism of cognitive impairment induced by hypoxic exposure. In the present study, mice showed reduced new-object recognition and spatial memory when exposed to hypobaric hypoxia for 1 day. Histomorphological staining revealed significant morphological and structural damage to the hippocampal tissue, along with prolonged exposure to hypobaric hypoxia. Dynamic lipidomics of the mouse hippocampus showed a significant shift in both the type and distribution of phospholipids, as verified by spatial lipid mapping. Collectively, these results have provided new insights into the cognitive decline induced by high altitude, in which alterations in lipid metabolism may be an important contributing factor.

Keywords:  LC-MS; MSI; hypobaric hypoxia; lipidome; lipidomics

DOI:  https://doi.org/10.1016/j.jlr.2024.100575
Trends Neurosci. 2024 Jun 11. pii: S0166-2236(24)00115-2. [Epub ahead of print]

Do oligodendrocytes regulate axonal glucose uptake and consumption?

Jessica L Fletcher, Kaylene M Young.

  Neurons have high energy demands. In a recent study, Looser et al. identified oligodendrocyte Kir4.1 as the activity-dependent driver of oligodendrocyte glycolysis that ensures that lactate is supplied to active neurons. Given that oligodendrocyte Kir4.1 also influenced axonal glucose consumption and uptake, oligodendrocytes may play a broader role in neuronal metabolic regulation.

Keywords:  Kir4.1; conduction velocity; lactate; metabolism; potassium; sodium-calcium exchanger (NCX)

DOI:  https://doi.org/10.1016/j.tins.2024.06.001
bioRxiv. 2024 Jun 08. pii: 2024.06.07.597919. [Epub ahead of print]

PLA2G15 is a Lysosomal BMP Hydrolase with Ester Position Specificity and its Targeting Ameliorates Lysosomal Disease.

Kwamina Nyame, Jian Xiong, Arthur Ph de Jong, Hisham N Alsohybe, Matthijs Raaben, Guido Hartmann, Judith A Simcox, Vincent A Blomen, Monther Abu-Remaileh.

Lysosomes catabolize lipids and other biological molecules, a function essential for cellular and organismal homeostasis. Key to lipid catabolism in the lysosome is bis(monoacylglycero)phosphate (BMP), a major lipid constituent of intralysosomal vesicles (ILVs) and a stimulator of lipid-degrading enzymes. BMP levels are altered in a broad spectrum of human conditions, including neurodegenerative diseases. Although BMP synthase was recently discovered, it has long been thought that BMP's unique stereochemistry confers resistance to acid phospholipases, a requirement for its role in the lysosome. Here, we demonstrate that PLA2G15, a major lysosomal phospholipase, efficiently hydrolyzes BMP with primary esters regardless of stereochemistry. Interestingly, we discover that BMP's unique esterification position is what confers resistance to hydrolysis. Purified PLA2G15 catabolizes most BMP species derived from cell and tissue lysosomes under acidic conditions. Furthermore, PLA2G15 catalytic activity against synthesized BMP stereoisomers with primary esters was comparable to its canonical substrates. Conversely, BMP with secondary esters is intrinsically stable in vitro and requires acyl migration for hydrolysis in lysosomes. Consistent with our biochemical data, PLA2G15-deficient tissues and cells accumulate multiple BMP species, a phenotype reversible by supplementing wildtype PLA2G15 but not its catalytically dead mutant. Increasing BMP levels by targeting PLA2G15 reverses the cholesterol accumulation phenotype in Niemann Pick Disease Type C (NPC1) patient fibroblasts and significantly ameliorate disease pathologies in NPC1-deficient mice leading to extended lifespan. Our findings establish the rules that govern the stability of BMP in the lysosome and identify PLA2G15 as a lysosomal BMP hydrolase and as a potential target for modulating BMP levels for therapeutic intervention.

DOI: https://doi.org/10.1101/2024.06.07.597919
J Pharmacol Sci. 2024 Aug;pii: S1347-8613(24)00038-0. [Epub ahead of print]155(4): 131-139

H2S prevents the disruption of the blood-brain barrier in rats with prenatal hyperhomocysteinemia.

A V Yakovlev, A S Detterer, O V Yakovleva, A Hermann, G F Sitdikova.

  Elevation of the homocysteine concentration in the plasma called hyperhomocysteinemia (hHCY) during pregnancy causes a number of pre- and postnatal developmental disorders. The aim of our study was to analyze the effects of H2S donors -NaHS and N-acetylcysteine (NAC) on blood-brain barrier (BBB) permeability in rats with prenatal hHCY. In rats with mild hHCY BBB permeability assessed by Evans Blue extravasation in brain increased markedly throughout life. Administration of NaHS or NAC during pregnancy attenuated hHCY-associated damage and increased endogenous concentrations of sulfides in brain tissues. Acute application of dl-homocysteine thiolactone induced BBB leakage, which was prevented by the NMDA receptor antagonist MK-801 or H2S donors. Rats with hHCY demonstrated high levels of NO metabolite - nitrites and proinflammatory cytokines (IL-1β, TNF-α, IL-6) in brain. Lactate dehydrogenase (LDH) activity in the serum was higher in rats with hHCY. Mitochondrial complex-I activity was lower in brain of hHCY rats. NaHS treatment during pregnancy restored levels of proinflammatory cytokines, nitrites and activity of the respiratory chain complex in brain as well as the LDH activity in serum. Our data suggest that H2S has neuroprotective effects against prenatal hHCY-associated BBB disturbance providing a potential strategy for the prevention of developmental impairments in newborns.

Keywords:  Blood-brain barrier; Hydrogen sulfide; Inflammation; Nitrites; Prenatal hyperhomocysteinemia

DOI:  https://doi.org/10.1016/j.jphs.2024.05.001
Int J Mol Sci. 2024 May 24. pii: 5710. [Epub ahead of print]25(11):

Beta-Hydroxybutyrate Mitigates Sensorimotor and Cognitive Impairments in a Photothrombosis-Induced Ischemic Stroke in Mice.

Artem P Gureev, Irina S Sadovnikova, Ekaterina V Chernyshova, Arina D Tsvetkova, Polina I Babenkova, Veronika V Nesterova, Ekaterina P Krutskikh, Daria E Volodina, Natalia A Samoylova, Nadezda V Andrianova, Denis N Silachev, Egor Y Plotnikov.

  The consequences of stroke include cognitive deficits and sensorimotor disturbances, which are largely related to mitochondrial impairments in the brain. In this work, we have shown that the mimetic of the ketogenic diet beta-hydroxybutyrate (βHB) can improve neurological brain function in stroke. At 3 weeks after photothrombotic stroke, mice receiving βHB with drinking water before and after surgery recovered faster in terms of sensorimotor functions assessed by the string test and static rods and cognitive functions assessed by the Morris water maze. At the same time, the βHB-treated mice had lower expression of some markers of astrocyte activation and inflammation (Gfap, Il-1b, Tnf). We hypothesize that long-term administration of βHB promotes the activation of the nuclear factor erythroid 2-related factor 2/antioxidant response element (Nrf2/ARE) pathway, which leads to increased expression of antioxidant genes targeting mitochondria and genes involved in signaling pathways necessary for the maintenance of synaptic plasticity. βHB partially maintained mitochondrial DNA (mtDNA) integrity during the first days after photothrombosis. However, in the following three weeks, the number of mtDNA damages increased in all experimental groups, which coincided with a decrease in Ogg1 expression, which plays an important role in mtDNA repair. Thus, we can assume that βHB is not only an important metabolite that provides additional energy to brain tissue during recovery from stroke under conditions of mitochondrial damage but also an important signaling molecule that supports neuronal plasticity and reduces neuroinflammation.

Keywords:  ischemia; mitochondria; neuroprotection; oxidative stress; stroke

DOI:  https://doi.org/10.3390/ijms25115710
Nutrients. 2024 May 29. pii: 1678. [Epub ahead of print]16(11):

Simplification of Dietary Treatment in Pharmacoresistant Epilepsy: Impact of C8 and C10 Fatty Acids on Sirtuins of Neuronal Cells In Vitro.

Miriam Rebekka Rühling, Hans Hartmann, Anibh Martin Das.

  Pharmacotherapy is the therapeutic mainstay in epilepsy; however, in about 30% of patients, epileptic seizures are drug-resistant. A ketogenic diet (KD) is an alternative therapeutic option. The mechanisms underlying the anti-seizure effect of a KD are not fully understood. Epileptic seizures lead to an increased energy demand of neurons. An improvement in energy provisions may have a protective effect. C8 and C10 fatty acids have been previously shown to activate mitochondrial function in vitro. This could involve sirtuins (SIRTs) as regulatory elements of energy metabolism. The aim of the present study was to investigate whether ß-hydroxybutyrate (ßHB), C8 fatty acids, C10 fatty acids, or a combination of C8 and C10 (250/250 µM) fatty acids, which all increase under a KD, could up-regulate SIRT1, -3, -4, and -5 in HT22 hippocampal murine neurons in vitro. Cells were incubated for 1 week in the presence of these metabolites. The sirtuins were measured at the enzyme (fluorometrically), protein (Western blot), and gene expression (PCR) levels. In hippocampal cells, the C8, C10, and C8 and C10 incubations led to increases in the sirtuin levels, which were not inferior to a ßHB incubation as the 'gold standard'. This may indicate that both C8 and C10 fatty acids are important for the antiepileptic effect of a KD. A KD may be replaced by nutritional supplements of C8 and C10 fatty acids, which could facilitate the diet.

Keywords:  ketogenic diet; medium-chain fatty acids; pharmacoresistant epilepsy; sirtuins; ß-hydroxybutyrate

DOI:  https://doi.org/10.3390/nu16111678
Cell Metab. 2024 Jun 14. pii: S1550-4131(24)00192-X. [Epub ahead of print]

Astrocytic LRP1 enables mitochondria transfer to neurons and mitigates brain ischemic stroke by suppressing ARF1 lactylation.

Jian Zhou, Lifang Zhang, Jianhua Peng, Xianhui Zhang, Fan Zhang, Yuanyuan Wu, An Huang, Fengling Du, Yuyan Liao, Yijing He, Yuke Xie, Long Gu, Chenghao Kuang, Wei Ou, Maodi Xie, Tianqi Tu, Jinwei Pang, Dingkun Zhang, Kecheng Guo, Yue Feng, Shigang Yin, Yang Cao, Tao Li, Yong Jiang.

  Low-density lipoprotein receptor-related protein-1 (LRP1) is an endocytic/signaling cell-surface receptor that regulates diverse cellular functions, including cell survival, differentiation, and proliferation. LRP1 has been previously implicated in the pathogenesis of neurodegenerative disorders, but there are inconsistencies in its functions. Therefore, whether and how LRP1 maintains brain homeostasis remains to be clarified. Here, we report that astrocytic LRP1 promotes astrocyte-to-neuron mitochondria transfer by reducing lactate production and ADP-ribosylation factor 1 (ARF1) lactylation. In astrocytes, LRP1 suppressed glucose uptake, glycolysis, and lactate production, leading to reduced lactylation of ARF1. Suppression of astrocytic LRP1 reduced mitochondria transfer into damaged neurons and worsened ischemia-reperfusion injury in a mouse model of ischemic stroke. Furthermore, we examined lactate levels in human patients with stroke. Cerebrospinal fluid (CSF) lactate was elevated in stroke patients and inversely correlated with astrocytic mitochondria. These findings reveal a protective role of LRP1 in brain ischemic stroke by enabling mitochondria-mediated astrocyte-neuron crosstalk.

Keywords:  LRP1; astrocytes; ischemic stroke; lactate; mitochondria transfer; neurons

DOI:  https://doi.org/10.1016/j.cmet.2024.05.016
Int J Biol Sci. 2024 ;20(8): 2860-2880

Activation of Neurotoxic Astrocytes Due to Mitochondrial Dysfunction Triggered by POLG Mutation.

Kristina Xiao Liang, Anbin Chen, Atefeh Kianian, Cecilie Katrin Kristiansen, Tsering Yangzom, Jessica Furriol, Lena Elise Høyland, Mathias Ziegler, Torbjørn Kråkenes, Charalampos Tzoulis, Evandro Fei Fang, Gareth John Sullivan, Laurence A Bindoff.

Mitochondrial diseases are associated with neuronal death and mtDNA depletion. Astrocytes respond to injury or stimuli and damage to the central nervous system. Neurodegeneration can cause astrocytes to activate and acquire toxic functions that induce neuronal death. However, astrocyte activation and its impact on neuronal homeostasis in mitochondrial disease remain to be explored. Using patient cells carrying POLG mutations, we generated iPSCs and then differentiated these into astrocytes. POLG astrocytes exhibited mitochondrial dysfunction including loss of mitochondrial membrane potential, energy failure, loss of complex I and IV, disturbed NAD+/NADH metabolism, and mtDNA depletion. Further, POLG derived astrocytes presented an A1-like reactive phenotype with increased proliferation, invasion, upregulation of pathways involved in response to stimulus, immune system process, cell proliferation and cell killing. Under direct and indirect co-culture with neurons, POLG astrocytes manifested a toxic effect leading to the death of neurons. We demonstrate that mitochondrial dysfunction caused by POLG mutations leads not only to intrinsic defects in energy metabolism affecting both neurons and astrocytes, but also to neurotoxic damage driven by astrocytes. These findings reveal a novel role for dysfunctional astrocytes that contribute to the pathogenesis of POLG diseases.

DOI: https://doi.org/10.7150/ijbs.93445
Ann Neurol. 2024 Jun 18.

Cerebral Glucose Metabolism Is a Valuable Predictor of Survival in Patients with Lewy Body Diseases.

Joachim Brumberg, Ganna Blazhenets, Sabrina Bühler, Johannes Fostitsch, Michel Rijntjes, Yilong Ma, David Eidelberg, Cornelius Weiller, Wolfgang H Jost, Lars Frings, Nils Schröter, Philipp T Meyer.

OBJECTIVE: Patients with Lewy body diseases have an increased risk of dementia, which is a significant predictor for survival. Posterior cortical hypometabolism on [18F]fluorodeoxyglucose positron emission tomography (PET) precedes the development of dementia by years. We therefore examined the prognostic value of cerebral glucose metabolism for survival.
METHODS: We enrolled patients diagnosed with Parkinson's disease (PD), Parkinson's disease with dementia, or dementia with Lewy bodies who underwent [18F]fluorodeoxyglucose PET. Regional cerebral metabolism of each patient was analyzed by determining the expression of the PD-related cognitive pattern (Z-score) and by visual PET rating. We analyzed the predictive value of PET for overall survival using Cox regression analyses (age- and sex-corrected) and calculated prognostic indices for the best model.
RESULTS: Glucose metabolism was a significant predictor of survival in 259 included patients (n = 118 events; hazard ratio: 1.4 [1.2-1.6] per Z-score; hazard ratio: 1.8 [1.5-2.2] per visual PET rating score; both p < 0.0001). Risk stratification with visual PET rating scores yielded a median survival of 4.8, 6.8, and 12.9 years for patients with severe, moderate, and mild posterior cortical hypometabolism (median survival not reached for normal cortical metabolism). Stratification into 5 groups based on the prognostic index revealed 10-year survival rates of 94.1%, 78.3%, 34.7%, 0.0%, and 0.0%.
INTERPRETATION: Regional cerebral glucose metabolism is a significant predictor of survival in Lewy body diseases and may allow an earlier survival prediction than the clinical milestone "dementia." Thus, [18F]fluorodeoxyglucose PET may improve the basis for therapy decisions, especially for invasive therapeutic procedures like deep brain stimulation in Parkinson's disease. ANN NEUROL 2024.

DOI: https://doi.org/10.1002/ana.27005
Neuropharmacology. 2024 Jun 15. pii: S0028-3908(24)00214-4. [Epub ahead of print] 110045

Neonatal dysregulation of 2-arachidonoylglycerol induces impaired brain function in adult mice.

Kyung-Jun Boo, Dae Hyun Kim, Eunbi Cho, Dong Hyun Kim, Se Jin Jeon, Chan Young Shin.

  The endocannabinoid system (ECS) regulates neurotransmission linked to synaptic plasticity, cognition, and emotion. While it has been demonstrated that dysregulation of the ECS in adulthood is relevant not only to central nervous system (CNS) disorders such as autism spectrum disorder, cognitive dysfunction, and depression but also to brain function, there are few studies on how dysregulation of the ECS in the neonatal period affects the manifestation and pathophysiology of CNS disorders later in life. In this study, DO34, a diacylglycerol lipase alpha (DAGLα) inhibitor affecting endocannabinoid 2-AG production, was injected into C57BL/6N male mice from postnatal day (PND) 7 to PND 10, inducing dysregulation of the ECS in the neonatal period. Subsequently, we examined whether it affects neuronal function in adulthood through electrophysiological and behavioral evaluation. DO34-injected mice showed significantly decreased cognitive functions, attributed to impairment of hippocampal synaptic plasticity. The findings suggest that regulation of ECS activity in the neonatal period may induce enduring effects on adult brain function.

Keywords:  2-Arachidonoylglycerol; Cognition; Diacylglycerol lipase alpha; Endocannabinoid system; Hippocampus; Neonatal period

DOI:  https://doi.org/10.1016/j.neuropharm.2024.110045
Neural Regen Res. 2025 Mar 01. 20(3): 695-714

Liver as a new target organ in Alzheimer's disease: insight from cholesterol metabolism and its role in amyloid-beta clearance.

Beibei Wu, Yuqing Liu, Hongli Li, Lemei Zhu, Lingfeng Zeng, Zhen Zhang, Weijun Peng.

Alzheimer's disease, the primary cause of dementia, is characterized by neuropathologies, such as amyloid plaques, synaptic and neuronal degeneration, and neurofibrillary tangles. Although amyloid plaques are the primary characteristic of Alzheimer's disease in the central nervous system and peripheral organs, targeting amyloid-beta clearance in the central nervous system has shown limited clinical efficacy in Alzheimer's disease treatment. Metabolic abnormalities are commonly observed in patients with Alzheimer's disease. The liver is the primary peripheral organ involved in amyloid-beta metabolism, playing a crucial role in the pathophysiology of Alzheimer's disease. Notably, impaired cholesterol metabolism in the liver may exacerbate the development of Alzheimer's disease. In this review, we explore the underlying causes of Alzheimer's disease and elucidate the role of the liver in amyloid-beta clearance and cholesterol metabolism. Furthermore, we propose that restoring normal cholesterol metabolism in the liver could represent a promising therapeutic strategy for addressing Alzheimer's disease.

DOI: https://doi.org/10.4103/1673-5374.391305
Neural Regen Res. 2025 Mar 01. 20(3): 740-750

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

Yuchen Zhang, Yiqing Chen, Cheng Zhuang, Jingxuan Qi, Robert Chunhua Zhao, Jiao Wang.

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.

DOI: https://doi.org/10.4103/NRR.NRR-D-23-01401
Animal Model Exp Med. 2024 Jun 19.

Apolipoprotein E4 interferes with lipid metabolism to exacerbate depression-like behaviors in 5xFAD mice.

Yanjv Gong, Mingfeng Li, Min Liu, Xinghan Wu, Yanhong Li, Chuan Qin, Ling Zhang.

   BACKGROUND: Apolipoprotein E4 (ApoE4) allele is the strongest genetic risk factor for late-onset Alzheimer's disease, and it can aggravate depressive symptoms in non-AD patients. However, the impact of ApoE4 on AD-associated depression-like behaviors and its underlying pathogenic mechanisms remain unclear.
METHODS: This study developed a 5xFAD mouse model overexpressing human ApoE4 (E4FAD). Behavioral assessments and synaptic function tests were conducted to explore the effects of ApoE4 on cognition and depression in 5xFAD mice. Changes in peripheral and central lipid metabolism, as well as the levels of serotonin (5-HT) and γ-aminobutyric acid (GABA) neurotransmitters in the prefrontal cortex, were examined. In addition, the protein levels of 24-dehydrocholesterol reductase/glycogen synthase kinase-3 beta/mammalian target of rapamycin (DHCR24/GSK3β/mTOR) and postsynaptic density protein 95/calmodulin-dependent protein kinase II/brain-derived neurotrophic factor (PSD95/CaMK-II/BDNF) were measured to investigate the molecular mechanism underlying the effects of ApoE4 on AD mice.
RESULTS: Compared with 5xFAD mice, E4FAD mice exhibited more severe depression-like behaviors and cognitive impairments. These mice also exhibited increased amyloid-beta deposition in the hippocampus, increased astrocyte numbers, and decreased expression of depression-related neurotransmitters 5-HT and GABA in the prefrontal cortex. Furthermore, lipid metabolism disorders were observed in E4FAD, manifesting as elevated low-density lipoprotein cholesterol and reduced high-density lipoprotein cholesterol in peripheral blood, decreased cholesterol level in the prefrontal cortex, and reduced expression of key enzymes and proteins related to cholesterol synthesis and homeostasis. Abnormal expression of proteins related to the DHCR24/GSK3β/mTOR and PSD95/CaMK-II/BDNF pathways was also observed.
CONCLUSION: This study found that ApoE4 overexpression exacerbates depression-like behaviors in 5xFAD mice and confirmed that ApoE4 reduces cognitive function in these mice. The mechanism may involve the induction of central and peripheral lipid metabolism disorders. Therefore, modulating ApoE expression or function to restore cellular lipid homeostasis may be a promising therapeutic target for AD comorbid with depression. This study also provided a better animal model for studying AD comorbid with depression.

Keywords:  5xFAD mice; Alzheimer's disease; ApoE4 allele; depression like

DOI:  https://doi.org/10.1002/ame2.12446
Trends Endocrinol Metab. 2024 Jun 11. pii: S1043-2760(24)00123-1. [Epub ahead of print]

Is mitochondrial morphology important for cellular physiology?

Timothy Wai.

  Mitochondria are double membrane-bound organelles the network morphology of which in cells is shaped by opposing events of fusion and fission executed by dynamin-like GTPases. Mutations in these genes can perturb the form and functions of mitochondria in cell and animal models of mitochondrial diseases. An expanding array of chemical, mechanical, and genetic stressors can converge on mitochondrial-shaping proteins and disrupt mitochondrial morphology. In recent years, studies aimed at disentangling the multiple roles of mitochondrial-shaping proteins beyond fission or fusion have provided insights into the homeostatic relevance of mitochondrial morphology. Here, I review the pleiotropy of mitochondrial fusion and fission proteins with the aim of understanding whether mitochondrial morphology is important for cell and tissue physiology.

Keywords:  fission and fusion; genetic disease; mitochondrial dynamics; mitochondrial dysfunction; mitochondrial morphology

DOI:  https://doi.org/10.1016/j.tem.2024.05.005
Nat Commun. 2024 Jun 17. 15(1): 5157

Rft1 catalyzes lipid-linked oligosaccharide translocation across the ER membrane.

Shuai Chen, Cai-Xia Pei, Si Xu, Hanjie Li, Yi-Shi Liu, Yicheng Wang, Cheng Jin, Neta Dean, Xiao-Dong Gao.

The eukaryotic asparagine (N)-linked glycan is pre-assembled as a fourteen-sugar oligosaccharide on a lipid carrier in the endoplasmic reticulum (ER). Seven sugars are first added to dolichol pyrophosphate (PP-Dol) on the cytoplasmic face of the ER, generating Man5GlcNAc2-PP-Dol (M5GN2-PP-Dol). M5GN2-PP-Dol is then flipped across the bilayer into the lumen by an ER translocator. Genetic studies identified Rft1 as the M5GN2-PP-Dol flippase in vivo but are at odds with biochemical data suggesting Rft1 is dispensable for flipping in vitro. Thus, the question of whether Rft1 plays a direct or an indirect role during M5GN2-PP-Dol translocation has been controversial for over two decades. We describe a completely reconstituted in vitro assay for M5GN2-PP-Dol translocation and demonstrate that purified Rft1 catalyzes the translocation of M5GN2-PP-Dol across the lipid bilayer. These data, combined with in vitro results demonstrating substrate selectivity and rft1∆ phenotypes, confirm the molecular identity of Rft1 as the M5GN2-PP-Dol ER flippase.

DOI: https://doi.org/10.1038/s41467-024-48999-3
PLoS One. 2024 ;19(6): e0300168

FABP5-binding lipids regulate autophagy in differentiated SH-SY5Y cells.

Alejandro Soto-Avellaneda, Alexandra E Oxford, Fabio Halla, Peyton Vasquez, Emily Oe, Anton D Pugel, Alyssa M Schoenfeld, Matthew C Tillman, André Cuevas, Eric A Ortlund, Brad E Morrison.

The motor features of Parkinson's disease result from loss of dopaminergic neurons in the substantia nigra with autophagy dysfunction being closely linked to this disease. While a large body of work focusing on protein effectors of autophagy has been reported, regulation of autophagy by lipids has garnered far less attention. Therefore, we sought to identify endogenous lipid molecules that act as signaling mediators of autophagy in differentiated SH-SY5Y cells, a commonly used dopaminergic neuron-like cell model. In order to accomplish this goal, we assessed the role of a fatty acid-binding protein (FABP) family member on autophagy due to its function as an intracellular lipid chaperone. We focused specifically upon FABP5 due to its heightened expression in dopaminergic neurons within the substantia nigra and SH-SY5Y cells. Here, we report that knockdown of FABP5 resulted in suppression of autophagy in differentiated SH-SY5Y cells suggesting the possibility of an autophagic role for an interacting lipid. A lipidomic screen of FABP5-interacting lipids uncovered hits that include 5-oxo-eicosatetraenoic acid (5OE) and its precursor metabolite, arachidonic acid (AA). Additionally, other long-chain fatty acids were found to bind FABP5, such as stearic acid (SA), hydroxystearic acid (HSA), and palmitic acid (PA). The addition of 5OE, SA, and HSA but not AA or PA, led to potent inhibition of autophagy in SH-SY5Y cells. To identify potential molecular mechanisms for autophagy inhibition by these lipids, RNA-Seq was performed which revealed both shared and divergent signaling pathways between the lipid-treated groups. These findings suggest a role for these lipids in modulating autophagy through diverse signaling pathways and could represent novel therapeutic targets for Parkinson's disease.

DOI: https://doi.org/10.1371/journal.pone.0300168