Phosphatidylserine synthase plays an essential role in glia and affects development, as well as the maintenance of neuronal function

Pss knockdown in the midgut causes growth retardation in Drosophila similar to that in human LMHD

BACKGROUND

Phosphatidylserine synthase (PSS), localized in the mitochondrial membrane, synthesizes phosphatidylserine. In humans, mutations in Pss lead to Lenz-Majewski hyperostotic dwarfism, a disorder affecting growth and development. The effects of Pss mutations on the growth of Drosophila melanogaster are not fully known. Hence, this study was conducted to investigate the effects of Pss knockdown on the growth and development of D. melanogaster.

RESULTS

Enterocyte (EC)-specific Pss knockdown resulted in reduced cell size in the gut via reduced Akt signaling. EC-specific Pss knockdown was associated with a decrease in gut size, a change in gut pH, and reduced food intake. These abnormalities affected normal nutrient metabolism in larvae, leading to decreased secretion of Drosophila insulin-like peptides. Consequently, the reduced systemic Akt signaling at the organismal level resulted not only in impaired gut growth but also in abnormal organismal growth and development.

CONCLUSION

These findings highlight the significant role of the Pss gene in the growth and development of D. melanogaster.

Distinct systemic impacts of Aβ42 and Tau revealed by whole-organism snRNA-seq

Both neuronal and peripheral tissues become disrupted in Alzheimer's disease (AD). However, a comprehensive understanding of how AD impacts different tissues across the whole organism is lacking. Using Drosophila, we generated an AD Fly Cell Atlas (AD-FCA) based on whole-organism single-nucleus transcriptomes of 219 cell types from flies expressing AD-associated proteins, either human amyloid-β 42 peptide (Aβ42) or Tau, in neurons. We found that Aβ42 primarily affects the nervous system, including sensory neurons, while Tau induces accelerated aging in peripheral tissues. We identified a neuronal cluster enriched in Aβ42 flies, which has high lactate dehydrogenase (LDH) expression. This LDH-high cluster is conserved in 5XFAD mouse and human AD datasets. We found a conserved defect in fat metabolism from both fly and mouse tauopathy models. The AD-FCA offers new insights into how Aβ42 or Tau systemically and differentially affects a whole organism and provides a valuable resource for understanding brain-body communication in neurodegeneration.

Epigenetic and Metabolic Landscape of Dementia with Lewy Bodies

BACKGROUND

Lewy body diseases, including dementia with Lewy bodies (DLB), are characterized by α-synuclein accumulation, leading to dementia. Previous studies suggest distinct epigenetic and metabolomic profiles in DLB.

OBJECTIVE

This study aims to identify diagnostic biomarkers by analyzing the methylome and metabolome in the Brodmann area 7 of postmortem brain tissues from DLB patients and control subjects using multiomics approaches.

METHODS

Methylation analysis was performed using the Illumina EPIC array, and metabolomics profiling was conducted via 1H nuclear magnetic resonance (NMR) and direct injection/liquid chromatography coupled with mass spectrometry. Differential methylation and metabolite analysis were conducted, followed by pathway enrichment to explore biological relevance.

RESULTS

We identified 3478 significantly differentially methylated cytosines, mostly hypermethylated, enriched in CpG islands near transcription start sites. Pathway enrichment analysis showed significant pathways, primarily linked to olfactory and synaptic functions. Metabolomics profiling identified 15 significantly altered metabolites, with Phosphatidylethanolamine (PE) Biosynthesis being the most affected pathway. Key correlations between differentially methylated cytosines and metabolites, particularly in the PE Biosynthesis pathway involving PTDSS1 and PCYT2 genes, were observed.

CONCLUSIONS

Notably, sex-specific differences were found, with females exhibiting more epigenetic and metabolomic changes than males. Increased hypermethylation, linked to transcriptional silencing, and disruptions in PE biosynthesis suggest a role in synaptic dysfunction and olfactory deficits. In addition, α-aminoadipic acid was strongly associated with vascular functions, hinting at a possible overlap between vascular health and DLB. This study provides new insights into DLB mechanisms and potential therapeutic targets. © 2024 International Parkinson and Movement Disorder Society.

Proteomic analysis across aged tissues reveals distinct signatures and the crucial involvement of midgut barrier function in the regulation of aging

The process of aging is a natural phenomenon characterized by gradual deterioration in biological functions and systemic homeostasis, which can be modulated by both genetic and environmental factors. Numerous investigations conducted on model organisms, including nematodes, flies, and mice, have elucidated several pivotal aging pathways, such as insulin signaling and AMPK signaling. However, it remains uncertain whether the regulation of the aging process is uniform or diverse across different tissues and whether manipulating the same aging factor can result in consistent outcomes in various tissues. In this study, we utilize the Drosophila organism to investigate tissue-specific proteome signatures during the aging process. Although distinct proteins undergo changes in aged tissues, certain common altered functional networks are constituently identified across different tissues, including the decline of the mitochondrial ribosomal network, autophagic network, and anti-ROS defense networks. Furthermore, downregulation of insulin receptor (InR) in the midguts, muscle, and central nervous system (CNS) of flies leads to a significant extension in fly lifespans. Notably, despite manipulating the same aging gene InR, diverse alterations in proteins are observed across different tissues. Importantly, knockdown of InR in the midguts leads to a distinct proteome compared with other tissues, resulting in enhanced actin nucleation and glutathione metabolism, while attenuating age-related elevation of serine proteases. Consequently, knockdown of InR results in rejuvenation of the integrity of the midgut barrier and augmentation of anti-ROS defense capabilities. Our findings suggest that the barrier function of the midgut plays a pivotal role in defending against aging, underscoring the paramount importance of maintaining optimal gut physiology to effectively delay the aging process. Moreover, when considering age-related changes across various tissues, it is more reasonable to identify functional networks rather than focusing solely on individual proteins.

Differential functions of phosphatidylinositol 4-kinases in neurotransmission and synaptic development

Phosphoinositides, such as PI(4,5)P2, are known to function as structural components of membranes, signalling molecules, markers of membrane identity, mediators of protein recruitment and regulators of neurotransmission and synaptic development. Phosphatidylinositol 4-kinases (PI4Ks) synthesize PI4P, which are precursors for PI(4,5)P2, but may also have independent functions. The roles of PI4Ks in neurotransmission and synaptic development have not been studied in detail. Previous studies on PI4KII and PI4KIIIβ at the Drosophila larval neuromuscular junction have suggested that PI4KII and PI4KIIIβ enzymes may serve redundant roles, where single PI4K mutants yielded mild or no synaptic phenotypes. However, the precise synaptic functions (neurotransmission and synaptic growth) of these PI4Ks have not been thoroughly studied. Here, we used PI4KII and PI4KIIIβ null mutants and presynaptic-specific knockdowns of these PI4Ks to investigate their roles in neurotransmission and synaptic growth. We found that PI4KII and PI4KIIIβ appear to have non-overlapping functions. Specifically, glial PI4KII functions to restrain synaptic growth, whereas presynaptic PI4KIIIβ promotes synaptic growth. Furthermore, loss of PI4KIIIβ or presynaptic PI4KII impairs neurotransmission. The data presented in this study uncover new roles for PI4K enzymes in neurotransmission and synaptic growth.

Dietary "Beigeing" Fat Contains More Phosphatidylserine and Enhances Mitochondrial Function while Counteracting Obesity

Activation of mitochondrial function and heat production in adipose tissue by the modification of dietary fat is a promising strategy against obesity. However, as an important source of lipids for ketogenic and daily diets, the function of fats extracted from different adipose tissue sites was largely unknown. In this study, we illustrated the function of fats extracted from adipose tissues with different "beigeing" properties in the ketogenic diet and identified lipid profiles of fats that facilitate energy expenditure. We found that the anti-obesity effect of ketogenic diets was potentiated by using "beigeing" fat [porcine subcutaneous adipose tissue (SAT)] as a major energy-providing ingredient. Through lipidomic analyses, phosphatidylserine (PS) was identified as a functional lipid activating thermogenesis in adipose tissue. Moreover, in vivo studies showed that PS induces adipose tissue thermogenesis and alleviates diet-induced obesity in mice. In vitro studies showed that PS promotes UCP1 expression and lipolysis of adipocytes. Mechanistically, PS promoted mitochondrial function in adipocytes via the ADCY3-cAMP-PKA-PGC1α pathway. In addition, PS-PGC1a binding may affect the stability of the PGC1α protein, which further augments PS-induced thermogenesis. These results demonstrated the efficacy of dietary SAT fats in diminishing lipid accumulation and the underlying molecular mechanism of PS in enhancing UCP1 expression and mitochondrial function. Thus, our findings suggest that as dietary fat, "beigeing" fat provides more beneficial lipids that contribute to the improvement of mitochondrial function, including PS, which may become a novel, nonpharmacological therapy to increase energy expenditure and counteract obesity and its related diseases.

Loss of function of phosphatidylserine synthase causes muscle atrophy in Drosophila

Maintenance of appropriate muscle mass is crucial for physical activity and metabolism. Aging and various pathological conditions can cause sarcopenia, a condition characterized by muscle mass decline. Although sarcopenia has been actively studied, the mechanisms underlying muscle atrophy are not well understood. Thus, we aimed to investigate the role of Phosphatidylserine synthase (Pss) in muscle development and homeostasis in Drosophila. The results showed that muscle-specific Pss knockdown decreased exercise capacity and produced sarcopenic phenotypes. In addition, it increased the apoptosis rate because of the elevated reactive oxygen species production resulting from mitochondrial dysfunction. Moreover, the autophagy rate increased due to increased FoxO activity caused by reduced Akt activity. Collectively, these findings demonstrate that enhanced apoptosis and autophagy rates resulting from muscle-specific Pss knockdown jointly contribute to sarcopenia development, highlighting the key role of the PSS pathway in muscle health.

Lipid organization and turnover in the plasma membrane of human differentiating neural progenitor cells revealed by time-of-flight secondary ion mass spectrometry imaging

Membrane lipids have been known to influence multiple signalling and cellular processes. Dysregulation of lipids at the neuronal membrane is connected to a significant alteration of the brain function and morphology, leading to brain diseases and neurodegeneration. Understanding the lipid composition and turnover of neuronal membrane will provide a significant insight into the molecular events underlying the regulatory effects of these biomolecules in a neuronal system. In this study, we aimed to characterize the composition and turnover of the plasma membrane lipids in human neural progenitor cells (NPCs) at an early differentiation stage into midbrain neurons using ToF-SIMS imaging. Lipid composition of the native plasma membrane was explored, followed by an examination of the lipid turnover using different isotopically labelled lipid precursors, including 13C-choline, 13C-lauric acid, 15N-linoleic, and 13C-stearic. Our results showed that differentiating NPCs contain a high abundance of ceramides, glycerophosphoserines, neutral glycosphingolipids, diradylglycerols, and glycerophosphocholines at the plasma membrane. In addition, different precursors were found to incorporate into different membrane lipids which are specific for the short- or long-carbon chains, and the unsaturation or saturation stage of the precursors. The lipid structure of neuronal membrane reflects the differentiation status of NPCs, and it can be altered significantly using a particular lipid precursor. Our study illustrates a potential of ToF-SIMS imaging to study native plasma membrane lipids and elucidate complex cellular processes by providing molecular -rich information at a single cell level.

Cdk8/CDK19 promotes mitochondrial fission through Drp1 phosphorylation and can phenotypically suppress pink1 deficiency in Drosophila

Cdk8 in Drosophila is the orthologue of vertebrate CDK8 and CDK19. These proteins have been shown to modulate transcriptional control by RNA polymerase II. We found that neuronal loss of Cdk8 severely reduces fly lifespan and causes bang sensitivity. Remarkably, these defects can be rescued by expression of human CDK19, found in the cytoplasm of neurons, suggesting a non-nuclear function of CDK19/Cdk8. Here we show that Cdk8 plays a critical role in the cytoplasm, with its loss causing elongated mitochondria in both muscles and neurons. We find that endogenous GFP-tagged Cdk8 can be found in both the cytoplasm and nucleus. We show that Cdk8 promotes the phosphorylation of Drp1 at S616, a protein required for mitochondrial fission. Interestingly, Pink1, a mitochondrial kinase implicated in Parkinson's disease, also phosphorylates Drp1 at the same residue. Indeed, overexpression of Cdk8 significantly suppresses the phenotypes observed in flies with low levels of Pink1, including elevated levels of ROS, mitochondrial dysmorphology, and behavioral defects. In summary, we propose that Pink1 and Cdk8 perform similar functions to promote Drp1-mediated fission.

A humoral stress response protects Drosophila tissues from antimicrobial peptides

7An efficient immune system must provide protection against a broad range of pathogens without causing excessive collateral tissue damage. While immune effectors have been well characterized, we know less about the resilience mechanisms protecting the host from its own immune response. Antimicrobial peptides (AMPs) are small, cationic peptides that contribute to innate defenses by targeting negatively charged membranes of microbes. While protective against pathogens, AMPs can be cytotoxic to host cells. Here, we reveal that a family of stress-induced proteins, the Turandots, protect the Drosophila respiratory system from AMPs, increasing resilience to stress. Flies lacking Turandot genes are susceptible to environmental stresses due to AMP-induced tracheal apoptosis. Turandot proteins bind to host cell membranes and mask negatively charged phospholipids, protecting them from cationic pore-forming AMPs. Collectively, these data demonstrate that Turandot stress proteins mitigate AMP cytotoxicity to host tissues and therefore improve their efficacy.

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.

Per- and Polyfluoroalkyl Substances: Impacts on Morphology, Behavior and Lipid Levels in Zebrafish Embryos

The presence of per- and polyfluoroalkyl substances (PFASs) in aquatic environments is often persistent and widespread. Understanding the potential adverse effects from this group of chemicals on aquatic communities allows for better hazard characterization. This study examines impacts on zebrafish (Danio rerio) embryo physiology, behavior, and lipid levels from exposure to perfluorooctanoic acid (PFOA), perfluorohexane sulfonate (PFHxS), and heptadecafluorooctanesulfonic acid (PFOS). Embryos were exposed to lethal and sublethal levels of each chemical and monitored for alterations in physiological malformations, mortality, lipid levels, and behavior (only PFOA and PFHxS). The predicted 50% lethal concentrations for 120 hpf embryos were 528.6 ppm PFOA, 14.28 ppm PFHxS, and 2.14 ppm PFOS. Spine curvature and the inability of the 120 hpf embryos to maintain a dorsal-up orientation was significantly increased at 10.2 ppm PFHxS and 1.9 ppm PFOS exposure. All measured 120 hpf embryo behaviors were significantly altered starting at the lowest levels tested, 188 ppm PFOA and 6.4 ppm PFHxS. Lipid levels decreased at the highest PFAS levels tested (375 PFOA ppm, 14.4 PFHxS ppm, 2.42 ppm PFOS). In general, the PFAS chemicals, at the levels examined in this study, increased morphological deformities, embryo activity, and startle response time, as well as decreased lipid levels in 120 hpf zebrafish embryos.

Not So Rare: Diseases Based on Mutant Proteins Controlling Endoplasmic Reticulum-Mitochondria Contact (MERC) Tethering

Mitochondria-endoplasmic reticulum contacts (MERCs), also called endoplasmic reticulum (ER)-mitochondria contact sites (ERMCS), are the membrane domains, where these two organelles exchange lipids, Ca2+ ions, and reactive oxygen species. This crosstalk is a major determinant of cell metabolism, since it allows the ER to control mitochondrial oxidative phosphorylation and the Krebs cycle, while conversely, it allows the mitochondria to provide sufficient ATP to control ER proteostasis. MERC metabolic signaling is under the control of tethers and a multitude of regulatory proteins. Many of these proteins have recently been discovered to give rise to rare diseases if their genes are mutated. Surprisingly, these diseases share important hallmarks and cause neurological defects, sometimes paired with, or replaced by skeletal muscle deficiency. Typical symptoms include developmental delay, intellectual disability, facial dysmorphism and ophthalmologic defects. Seizures, epilepsy, deafness, ataxia, or peripheral neuropathy can also occur upon mutation of a MERC protein. Given that most MERC tethers and regulatory proteins have secondary functions, some MERC protein-based diseases do not fit into this categorization. Typically, however, the proteins affected in those diseases have dominant functions unrelated to their roles in MERCs tethering or their regulation. We are discussing avenues to pharmacologically target genetic diseases leading to MERC defects, based on our novel insight that MERC defects lead to common characteristics in rare diseases. These shared characteristics of MERCs disorders raise the hope that they may allow for similar treatment options.

Cholesterol is required for activity-dependent synaptic growth

Changes in cholesterol content of neuronal membranes occur during development and brain aging. Little is known about whether synaptic activity regulates cholesterol levels in neuronal membranes and whether these changes affect neuronal development and function. We generated transgenic flies that express the cholesterol-binding D4H domain of perfringolysin O toxin and found increased levels of cholesterol in presynaptic terminals of Drosophila larval neuromuscular junctions following increased synaptic activity. Reduced cholesterol impaired synaptic growth and largely prevented activity-dependent synaptic growth. Presynaptic knockdown of adenylyl cyclase phenocopied the impaired synaptic growth caused by reducing cholesterol. Furthermore, the effects of knocking down adenylyl cyclase and reducing cholesterol were not additive, suggesting that they function in the same pathway. Increasing cAMP levels using a dunce mutant with reduced phosphodiesterase activity failed to rescue this impaired synaptic growth, suggesting that cholesterol functions downstream of cAMP. We used a protein kinase A (PKA) sensor to show that reducing cholesterol levels reduced presynaptic PKA activity. Collectively, our results demonstrate that enhanced synaptic activity increased cholesterol levels in presynaptic terminals and that these changes likely activate the cAMP-PKA pathway during activity-dependent growth.

Mitochondrial phospholipid metabolism in health and disease

Studies of rare human genetic disorders of mitochondrial phospholipid metabolism have highlighted the crucial role that membrane phospholipids play in mitochondrial bioenergetics and human health. The phospholipid composition of mitochondrial membranes is highly conserved from yeast to humans, with each class of phospholipid performing a specific function in the assembly and activity of various mitochondrial membrane proteins, including the oxidative phosphorylation complexes. Recent studies have uncovered novel roles of cardiolipin and phosphatidylethanolamine, two crucial mitochondrial phospholipids, in organismal physiology. Studies on inter-organellar and intramitochondrial phospholipid transport have significantly advanced our understanding of the mechanisms that maintain mitochondrial phospholipid homeostasis. Here, we discuss these recent advances in the function and transport of mitochondrial phospholipids while describing their biochemical and biophysical properties and biosynthetic pathways. Additionally, we highlight the roles of mitochondrial phospholipids in human health by describing the various genetic diseases caused by disruptions in their biosynthesis and discuss advances in therapeutic strategies for Barth syndrome, the best-studied disorder of mitochondrial phospholipid metabolism.

Very-long-chain fatty acids induce glial-derived sphingosine-1-phosphate synthesis, secretion, and neuroinflammation

VLCFAs (very-long-chain fatty acids) are the most abundant fatty acids in myelin. Hence, during demyelination or aging, glia are exposed to higher levels of VLCFA than normal. We report that glia convert these VLCFA into sphingosine-1-phosphate (S1P) via a glial-specific S1P pathway. Excess S1P causes neuroinflammation, NF-κB activation, and macrophage infiltration into the CNS. Suppressing the function of S1P in fly glia or neurons, or administration of Fingolimod, an S1P receptor antagonist, strongly attenuates the phenotypes caused by excess VLCFAs. In contrast, elevating the VLCFA levels in glia and immune cells exacerbates these phenotypes. Elevated VLCFA and S1P are also toxic in vertebrates based on a mouse model of multiple sclerosis (MS), experimental autoimmune encephalomyelitis (EAE). Indeed, reducing VLCFA with bezafibrate ameliorates the phenotypes. Moreover, simultaneous use of bezafibrate and fingolimod synergizes to improve EAE, suggesting that lowering VLCFA and S1P is a treatment avenue for MS.

Identification of potential biomarkers for diagnosis of syphilis from the cerebrospinal fluid based on untargeted metabolomic analysis

The infection rate of syphilis continues to rise globally, and the difficulty in diagnosis of neurosyphilis promptly needs to be resolved. More specific and sensitive diagnostic markers for latent syphilis and neurosyphilis should be found. Here the metabolic profiles of 88 cerebrospinal fluid samples from syphilis patients and controls were analyzed by LC/MS-based untargeted metabolomics. In total, 272 metabolites based on 3937 features obtained in ESI- mode and 252 metabolites based on 3799 features in ESI+ mode were identified. The experimental process was evaluated by principal component analysis, partial least squares discriminant analysis, and hierarchical cluster analysis. A clear separation between latent syphilis and neurosyphilis was found. Levels of lipid and linoleic acid metabolites, such as 9-oxo-octadecadienoic acid and 9,10,13-trihydroxyoctadecenoic acid, were increased in syphilis patients. In patients with neurosyphilis, significant changes in levels of 5-hydroxy-L-tryptophan (5-HTP) and acetyl-N-formyl-5-methoxykynurenamine (AFMK) in the tryptophan-kynurenine pathway were also detected. Only one metabolite, theophylline, differed significantly between symptomatic and asymptomatic neurosyphilis patients. Additionally, KEGG analysis revealed significant enrichment of tryptophan metabolism pathways, indicating a high correlation between tryptophan metabolism and syphilis symptoms. Levels of linoleic acid metabolites, 5-HTP, AFMK and theophylline were significantly altered in different patients. The role of these differential metabolites in the development of syphilis is worthy of further exploration. Our results may promote the development of biomarkers for diagnosis of latent syphilis from neurosyphilis, and for that of asymptomatic neurosyphilis from symptomatic neurosyphilis in the future.

Phosphatidylserine in the Nervous System: Cytoplasmic Regulator of the AKT and PKC Signaling Pathways and Extracellular "Eat-Me" Signal in Microglial Phagocytosis

Phosphatidylserine (PtdSer) is an important anionic phospholipid found in eukaryotic cells and has been proven to serve as a beneficial factor in the treatment of neurodegenerative diseases. PtdSer resides in the inner leaflet of the plasma membrane, where it is involved in regulating the AKT and PKC signaling pathways; however, it becomes exposed to the extracellular leaflet during neurodevelopmental processes and neurodegenerative diseases, participating in microglia-mediated synaptic and neuronal phagocytosis. In this paper, we review several characteristics of PtdSer, including the synthesis and translocation of PtdSer, the functions of cytoplasmic and exposed PtdSer, and different PtdSer-detection materials used to further understand the role of PtdSer in the nervous system.

Pivotal roles for membrane phospholipids in axonal degeneration

Membrane phospholipids are critical components of several signaling pathways. Maintained in a variety of asymmetric distributions, their trafficking across the membrane can be induced by intra-, extra-, and intercellular events. A familiar example is the externalization of phosphatidylserine from the inner leaflet to the outer leaflet in apoptosis, inducing phagocytosis of the soma. Recently, it has been recognized that phospholipids in the axonal membrane may be a signal for axonal degeneration, regeneration, or other processes. This review focuses on key recent developments and areas for ongoing investigations. KEY FACTS: Phosphatidylserine externalization propagates along an axon after axonal injury and is delayed in the Wallerian degeneration slow (Wld^S) mutant. The ATP8A2 flippase mutant has spontaneous axonal degeneration. Microdomains of axonal degeneration in spheroid bodies have differential externalization of phosphatidylserine and phosphatidylethanolamine. Phospholipid trafficking could represent a mechanism for coordinated axonal degeneration and elimination, i.e. axoptosis, analogous to apoptosis of the cell body.