The TMEM189 gene encodes plasmanylethanolamine desaturase which introduces the characteristic vinyl ether double bond into plasmalogens

Ferroptosis contributes to the progression of female-specific neoplasms, from breast cancer to gynecological malignancies in a manner regulated by non-coding RNAs: Mechanistic implications

Ferroptosis, a recently identified type of non-apoptotic cell death, triggers the elimination of cells in the presence of lipid peroxidation and in an iron-dependent manner. Indeed, ferroptosis-stimulating factors have the ability of suppressing antioxidant capacity, leading to the accumulation of reactive oxygen species (ROS) and the subsequent oxidative death of the cells. Ferroptosis is involved in the pathophysiological basis of different maladies, such as multiple cancers, among which female-oriented malignancies have attracted much attention in recent years. In this context, it has also been unveiled that non-coding RNA transcripts, including microRNAs, long non-coding RNAs, and circular RNAs have regulatory interconnections with the ferroptotic flux, which controls the pathogenic development of diseases. Furthermore, the potential of employing these RNA transcripts as therapeutic targets during the onset of female-specific neoplasms to modulate ferroptosis has become a research hotspot; however, the molecular mechanisms and functional alterations of ferroptosis still require further investigation. The current review comprehensively highlights ferroptosis and its association with non-coding RNAs with a focus on how this crosstalk affects the pathogenesis of female-oriented malignancies, from breast cancer to ovarian, cervical, and endometrial neoplasms, suggesting novel therapeutic targets to decelerate and even block the expansion and development of these tumors.

Interorganelle phospholipid communication, a house not so divided

The presence of membrane-bound organelles with specific functions is one of the main hallmarks of eukaryotic cells. Organelle membranes are composed of specific lipids that govern their function and interorganelle communication. Discoveries in cell biology using imaging and omic technologies have revealed the mechanisms that drive membrane remodeling, organelle contact sites, and metabolite exchange. The interplay between multiple organelles and their interdependence is emerging as the next frontier for discovery using 3D reconstruction of volume electron microscopy (vEM) datasets. We discuss recent findings on the links between organelles that underlie common functions and cellular pathways. Specifically, we focus on the metabolism of ether glycerophospholipids that mediate organelle dynamics and their communication with each other, and the new imaging techniques that are powering these discoveries.

Blockage of TMEM189 induces G2/M arrest and inhibits the growth of breast tumors

Cancer is the major cause of premature death in humans worldwide, demanding more efficient therapeutics. Aberrant cell proliferation resulting from the loss of cell cycle regulation is the major hallmark of cancer, so targeting cell cycle is a promising strategy to combat cancer. However, the molecular mechanism underlying the dysregulation of cell cycle of cancer cells remains poorly understood. TMEM189, a newly identified protein, plays roles in the biosynthesis of ethanolamine plasmalogen and the regulation of autophagy. Here, we demonstrated that the expression level of TMEM189 was negatively correlated with the survival rate of the cancer patients. TMEM189 deficiency significantly suppresses the cancer cell proliferation and migration, and causes cell cycle G2/M arrest both in vitro and in vivo. Furthermore, TMEM189 depletion suppressed the growth of breast tumors in vivo. Taken together, our work indicated that TMEM189 promotes cancer progression by regulating cell cycle G2/M transition, suggesting that it is a promising target in cancer therapy.

The presence of plasmenyl ether lipids in Capsaspora owczarzaki suggests a premetazoan origin of plasmalogen biosynthesis in animals

Plasmalogens are glycerophospholipids with a vinyl ether bond, rather than an ester bond, at sn-1 position. These lipids were described in anaerobic bacteria, myxobacteria, animals and some protists, but not in plants or fungi. Anaerobic and aerobic organisms synthesize plasmalogens differently. The aerobic pathway requires oxygen in the last step, which is catalyzed by PEDS1. CarF and TMEM189 were recently identified as the PEDS1 from myxobacteria and mammals, which could be of valuable use in exploring the distribution of this pathway in eukaryotes. We show the presence of plasmalogens in Capsaspora owczarzaki, one of the closest unicellular relatives of animals. This is the first report of plasmalogens in non-metazoan opisthokontas. Analysis of its genome revealed the presence of enzymes of the aerobic pathway. In a broad BLAST search, we found PEDS1 homologs in Opisthokonta and some genera of Amoebozoa and Excavata, consistent with the restricted distribution of plasmalogens reported in eukaryotes. Within Opisthokonta, PEDS1 is limited to Filasterea (Capsaspora and Pigoraptor), Metazoa and a small group of fungi comprising three genera of ascomycetes. A phylogenetic analysis of PEDS1 traced the acquisition of plasmalogen synthesis in animals to a filasterean ancestor and suggested independent acquisition events for Amoebozoa, Excavata and Ascomycetes.

Upregulated selenoprotein I during lipopolysaccharide-induced B cell activation promotes lipidomic changes and is required for effective differentiation into IgM-secreting plasma B cells

The mechanisms driving metabolic reprogramming during B cell activation are unclear, particularly roles for enzymatic pathways involved in lipid remodeling. We found that murine B cell activation with lipopolysaccharide (LPS) led to a 1.6-fold increase in total lipids that included higher levels of phosphatidylethanolamine (PE) and plasmenyl PE. Selenoprotein I (SELENOI) is an ethanolamine phospholipid transferase involved in the synthesis of both PE and plasmenyl PE, and SELENOI expression was also upregulated during activation. Selenoi knockout (KO) B cells exhibited decreased levels of plasmenyl PE, which plays an important antioxidant role. Lipid peroxidation was measured and found to increase ∼2-fold in KO vs. wild-type (WT) B cells. Cell death was not impacted by KO in LPS-treated B cells and proliferation was only slightly reduced, but differentiation into CD138 + Blimp-1+ plasma B cells was decreased ∼2-fold. This led to examination of B cell receptors important for differentiation that recognize the ligand B cell activating factor, and levels of TACI (transmembrane activator, calcium-modulator, and cytophilin ligand interactor) (CD267) were significantly decreased on KO B cells compared with WT control cells. Vaccination with ovalbumin/adjuvant led to decreased ovalbumin-specific immunoglobulin M (IgM) levels in sera of KO mice compared with WT mice. Real-time polymerase chain reaction analyses revealed a decreased switch from surface to secreted IgM in spleens of KO mice induced by vaccination or LP-BM5 retrovirus infection. Overall, these findings detail the lipidomic response of B cells to LPS activation and reveal the importance of upregulated SELENOI for promoting differentiation into IgM-secreting plasma B cells.

Temperature effects on plasmalogen profile and quality characteristics in Pacific oyster (Crassostrea gigas) during depuration

The quality of Pacific oyster (Crassostrea gigas) can be affected by many factors during depuration, in which temperature is the major element. In this study, we aim to determine the quality and plasmalogen changes in C. gigas depurated at different temperatures. The quality was significantly affected by temperature, represented by varying survival rate, glycogen content, total antioxidant capacity, alkaline phosphatase activity between control and stressed groups. Targeted MS analysis demonstrated that plasmalogen profile was significantly changed during depuration with PUFA-containing plasmalogen species being most affected by temperature. Proteomics analysis and gene expression assay further verified that plasmalogen metabolism is regulated by temperature, specifically, the plasmalogen synthesis enzyme EPT1 was significantly downregulated by high temperature and four plasmalogen-related genes (GPDH, PEDS, Pex11, and PLD1) were transcriptionally regulated. The positive correlations between the plasmalogen level and quality characteristics suggested plasmalogen could be regarded as a quality indicator of oysters during depuration.

Selenoprotein I is indispensable for ether lipid homeostasis and proper myelination

Selenoprotein I (SELENOI) catalyzes the final reaction of the CDP-ethanolamine branch of the Kennedy pathway, generating the phospholipids phosphatidylethanolamine (PE) and plasmenyl-PE. Plasmenyl-PE is a key component of myelin and is characterized by a vinyl ether bond that preferentially reacts with oxidants, thus serves as a sacrificial antioxidant. In humans, multiple loss-of-function mutations in genes affecting plasmenyl-PE metabolism have been implicated in hereditary spastic paraplegia, including SELENOI. Herein, we developed a mouse model of nervous system-restricted SELENOI deficiency that circumvents embryonic lethality caused by constitutive deletion and recapitulates phenotypic features of hereditary spastic paraplegia. Resulting mice exhibited pronounced alterations in brain lipid composition, which coincided with motor deficits and neuropathology including hypomyelination, elevated reactive gliosis, and microcephaly. Further studies revealed increased lipid peroxidation in oligodendrocyte lineage cells and disrupted oligodendrocyte maturation both in vivo and in vitro. Altogether, these findings detail a critical role for SELENOI-derived plasmenyl-PE in myelination that is of paramount importance for neurodevelopment.

The ceramide transport protein CERT is involved in alkylacylglycerol transfer from the ER to the Golgi for the biosynthesis of ether phospholipid

Ether phospholipids are synthesized by a series of enzymes localized in peroxisomes, the endoplasmic reticulum (ER), and the Golgi apparatus. During this process, the lipid intermediate alkylacylglycerol (AAG) synthesized in the ER is transferred from the site of its synthesis to the Golgi apparatus. In this study, we determined whether ceramide transport protein (CERT) is a candidate for AAG transfer. A lipid transfer assay revealed that CERT can mediate AAG transfer between phospholipid liposomes. AAG transport activity was markedly inhibited by the CERT inhibitor HPA-12 and reduced when the lipid transport domain of CERT was deleted. Suppression of CERT in HEK293 cells resulted in increased levels of plasmanyl-PC, which is synthesized by the ER-residing choline/ethanolamine phosphotransferase 1 (CEPT1). The mRNA levels and enzymatic activity of plasmanyl-PC synthesizing enzymes were not increased in CERT-deficient cells, indicating that the increase in plasmanyl-PC results from AAG accumulation in the ER. Re-introduction of CERT into CERT-deficient cells caused a decrease in plasmanyl-PC. Taken together, our findings suggest for the first time that CERT is involved in the transfer of AAG from the ER to the Golgi apparatus and plays a role in the biosynthesis of ether phospholipids.

From TgO/GABA-AT, GABA, and T-263 Mutant to Conception of Toxoplasma

Toxoplasma gondii causes morbidity, mortality, and disseminates widely via cat sexual stages. Here, we find T. gondii ornithine aminotransferase (OAT) is conserved across phyla. We solve TgO/GABA-AT structures with bound inactivators at 1.55 Å and identify an inactivator selective for TgO/GABA-AT over human OAT and GABA-AT. However, abrogating TgO/GABA-AT genetically does not diminish replication, virulence, cyst-formation, or eliminate cat's oocyst shedding. Increased sporozoite/merozoite TgO/GABA-AT expression led to our study of a mutagenized clone with oocyst formation blocked, arresting after forming male and female gametes, with "Rosetta stone"-like mutations in genes expressed in merozoites. Mutations are similar to those in organisms from plants to mammals, causing defects in conception and zygote formation, affecting merozoite capacitation, pH/ionicity/sodium-GABA concentrations, drawing attention to cyclic AMP/PKA, and genes enhancing energy or substrate formation in TgO/GABA-AT-related-pathways. These candidates potentially influence merozoite's capacity to make gametes that fuse to become zygotes, thereby contaminating environments and causing disease.

Ether-lipids and cellular signaling: A differential role of alkyl- and alkenyl-ether-lipids?

Ether-lipids (EL) are specific lipids bearing a characteristic sn-1 ether bond. Depending on the ether or vinyl-ether nature of this bond, they are present as alkyl- or alkenyl-EL, respectively. Among EL, alkenyl-EL, also referred as plasmalogens in the literature, attract most of the scientific interest as they are the predominant EL species in eukaryotic cells, thus less is known about alkyl-EL. EL have been implicated in various signaling pathways and alterations in their quantity are frequently observed in pathologies such as neurodegenerative and cardiovascular diseases or cancer. However, it remains unknown whether both alkyl- and alkenyl-EL play the same roles in these processes. This review summarizes the roles and mechanisms of action of EL in cellular signaling and tries to discriminate between alkyl- and alkenyl-EL. We also focus on the involvement of EL-mediated alterations of cellular signaling in diseases and discuss the potential interest for EL in therapy.

Integration of transcriptomics and metabolomics analysis for unveiling the toxicological profile in the liver of mice exposed to uranium in drinking water

Uranium is a contaminate in the underground water in many regions of the world, which poses health risks to the local populations through drinking water. Although the health hazards of natural uranium have been concerned for decades, the controversies about its detrimental effects continue at present since it is still unclear how uranium interacts with molecular regulatory networks to generate toxicity. Here, we integrate transcriptomic and metabolomic methods to unveil the molecular mechanism of lipid metabolism disorder induced by uranium. Following exposure to uranium in drinking water for twenty-eight days, aberrant lipid metabolism and lipogenesis were found in the liver, accompanied with aggravated lipid peroxidation and an increase in dead cells. Multi-omics analysis reveals that uranium can promote the biosynthesis of unsaturated fatty acids through dysregulating the metabolism of arachidonic acid (AA), linoleic acid, and glycerophospholipid. Most notably, the disordered metabolism of polyunsaturated fatty acids (PUFAs) like AA may contribute to lipid peroxidation induced by uranium, which in turn triggers ferroptosis in hepatocytes. Our findings highlight disorder of lipid metabolism as an essential toxicological mechanism of uranium in the liver, offering insight into the health risks of uranium in drinking water.

TMEM189 as a target gene of MiR-499a-5p regulates breast cancer progression through the ferroptosis pathway

MicroRNA (miR)-499a-5p has been reported to regulate the progression of various tumours. However, the role of miR-499a-5p in breast cancer is unclear. The purpose of this study was to investigate the role and mechanism of miR-499a-5p in breast cancer. The growth effect of miR-499a-5p on breast cancer cells was investigated by the CCK-8 assay, wound healing assay and Transwell invasion assay. The luciferase activity assay was used to verify the downstream targets of miR-499a-5p. The levels of GSH, MDA, and ROS were detected by kits. Quantitative real-time PCR and Western blot were used to determine the expression levels of TMEM189, COX-2, GPX4, and other related genes in cells. miR-499a-5p was down-regulated in MDA-MB-231 cells and was shown to reduced the viability, migration and invasion of MDA-MB-231 cells. Further studies revealed that TMEM189 is a target of miR-499a-5p. miR-499a-5p inhibited breast cancer cell growth by downregulating TMEM189. Furthermore, the down-regulation of TMEM189 promotes ferroptosis in breast cancer cells. The low expression of TMEM189 inhibited the development of breast cancer through the ferroptosis pathway. We have demonstrated for the first time that miR-499a-5p inhibits breast cancer progression by targeting the TMEM189-mediated ferroptosis pathway.

Systematic crosstalk in plasmalogen and diacyl lipid biosynthesis for their differential yet concerted molecular functions in the cell

Plasmalogen is a major phospholipid of mammalian cell membranes. Recently it is becoming evident that the sn-1 vinyl-ether linkage in plasmalogen, contrasting to the ester linkage in the counterpart diacyl glycerophospholipid, yields differential molecular characteristics for these lipids especially related to hydrocarbon-chain order, so as to concertedly regulate biological membrane processes. A role played by NMR in gaining information in this respect, ranging from molecular to tissue levels, draws particular attention. We note here that a broad range of enzymes in de novo synthesis pathway of plasmalogen commonly constitute that of diacyl glycerophospholipid. This fact forms the basis for systematic crosstalk that not only controls a quantitative balance between these lipids, but also senses a defect causing loss of lipid in either pathway for compensation by increase of the counterpart lipid. However, this inherent counterbalancing mechanism paradoxically amplifies imbalance in differential effects of these lipids in a diseased state on membrane processes. While sharing of enzymes has been recognized, it is now possible to overview the crosstalk with growing information for specific enzymes involved. The overview provides a fundamental clue to consider cell and tissue type-dependent schemes in regulating membrane processes by plasmalogen and diacyl glycerophospholipid in health and disease.

Targeting Nrf2 for ferroptosis-based therapy: Implications for overcoming ferroptosis evasion and therapy resistance in cancer

Ferroptosis is a newly discovered form of programmed cell death caused by redox-active iron-mediated lipid peroxidation. Ferroptosis exhibits a unique morphological phenotype resulting from oxidative damage to membrane lipids. Ferroptosis induction has been shown to be effective in treating human cancers that rely on lipid peroxidation repair pathways. Nuclear factor erythroid 2-related factor 2 (Nrf2) can control the regulatory pathways of ferroptosis, which involve genes associated with glutathione biosynthesis, antioxidant responses, and lipid and iron metabolism. Resistant cancer cells often utilize Nrf2 stabilization by Keap1 inactivation or other somatic alterations in the genes from the Nrf2 pathway, which can confer resistance to ferroptosis induction and other therapies. However, pharmacological inactivation of the Nrf2 pathway can sensitize cancer cells to ferroptosis induction. Inducing lipid peroxidation and ferroptosis through regulating the Nrf2 pathway is a promising strategy for enhancing the anticancer effects of chemotherapy and radiation therapy in therapy-resistant human cancers. Despite promising preliminary studies, clinical trials in human cancer therapy have not yet been realized. A deeper understanding of their exact processes and efficacies in various cancers remains unsolved. Therefore, this article aims to summarize the regulatory mechanisms of ferroptosis, their modulation by Nrf2, and the potential of targeting Nrf2 for ferroptosis-based cancer therapy.

Metabolome-Based Genome-Wide Association Study of Duck Meat Leads to Novel Genetic and Biochemical Insights

Meat is among the most consumed foods worldwide and has a unique flavor and high nutrient density in the human diet. However, the genetic and biochemical bases of meat nutrition and flavor are poorly understood. Here, 3431 metabolites and 702 volatiles in 423 skeletal muscle samples are profiled from a gradient consanguinity segregating population generated by Pekin duck × Liancheng duck crosses using metabolomic approaches. The authors identified 2862 metabolome-based genome-wide association studies (mGWAS) signals and 48 candidate genes potentially modulating metabolite and volatile levels, 79.2% of which are regulated by cis-regulatory elements. The level of plasmalogen is significantly associated with TMEM189 encoding plasmanylethanolamine desaturase 1. The levels of 2-pyrrolidone and glycerophospholipids are regulated by the gene expression of AOX1 and ACBD5, which further affects the levels of volatiles, 2-pyrrolidone and decanal, respectively. Genetic variations in GADL1 and CARNMT2 determine the levels of 49 metabolites including L-carnosine and anserine. This study provides novel insights into the genetic and biochemical basis of skeletal muscle metabolism and constitutes a valuable resource for the precise improvement of meat nutrition and flavor.

Ether lipids and a peroxisomal riddle in sperm

Sperm are terminally differentiated cells that lack most of the membranous organelles, resulting in a high abundance of ether glycerolipids found across different species. Ether lipids include plasmalogens, platelet activating factor, GPI-anchors and seminolipid. These lipids play important roles in sperm function and performance, and thus are of special interest as potential fertility markers and therapeutic targets. In the present article, we first review the existing knowledge on the relevance of the different types of ether lipids for sperm production, maturation and function. To further understand ether-lipid metabolism in sperm, we then query available proteomic data from highly purified sperm, and produce a map of metabolic steps retained in these cells. Our analysis pinpoints the presence of a truncated ether lipid biosynthetic pathway that would be competent for the production of precursors through the initial peroxisomal core steps, but devoid of subsequent microsomal enzymes responsible for the final synthesis of all complex ether-lipids. Despite the widely accepted notion that sperm lack peroxisomes, the thorough analysis of published data conducted herein identifies nearly 70% of all known peroxisomal resident proteins as part of the sperm proteome. In view of this, we highlight open questions related to lipid metabolism and possible peroxisomal functions in sperm. We propose a repurposed role for the truncated peroxisomal ether-lipid pathway in detoxification of products from oxidative stress, which is known to critically influence sperm function. The likely presence of a peroxisomal-derived remnant compartment that could act as a sink for toxic fatty alcohols and fatty aldehydes generated by mitochondrial activity is discussed. With this perspective, our review provides a comprehensive metabolic map associated with ether-lipids and peroxisomal-related functions in sperm and offers new insights into potentially relevant antioxidant mechanisms that warrant further research.

Engineering membrane architecture for biotechnological applications

Cellular membranes, predominantly described as a dynamic bilayer, are composed of different lipids, transmembrane proteins, and carbohydrates. Most research on biological membranes focuses on the identification, characterization, and mechanistic aspects of their different components. These studies provide a fundamental understanding of membrane structure, function, and dynamics, establishing a basis for the development of membrane engineering strategies. To date, approaches in this field concentrate on membrane adaptation to harsh conditions during industrial fermentation, which can be caused by temperature, osmotic, or organic solvent stress. With advances in the field of metabolic engineering and synthetic biology, recent breakthroughs include proof of concept microbial production of essential medicines, such as cannabinoids and vinblastine. However, long pathways, low yields, and host adaptation continue to pose challenges to the efficient scale up production of many important compounds. The lipid bilayer is profoundly linked to the activity of heterologous membrane-bound enzymes and transport of metabolites. Therefore, strategies for improving enzyme performance, facilitating pathway reconstruction, and enabling storage of products to increase the yields directly involve cellular membranes. At the forefront of membrane engineering research are re-emerging approaches in lipid research and synthetic biology that manipulate membrane size and composition and target lipid profiles across species. This review summarizes engineering strategies applied to cellular membranes and discusses the challenges and future perspectives, particularly with regards to their applications in host engineering and bioproduction.

Alterations in ether lipid metabolism and the consequences for the mouse lipidome

Alkylglycerol monooxygenase (AGMO) and plasmanylethanolamine desaturase (PEDS1) are enzymes involved in ether lipid metabolism. While AGMO degrades plasmanyl lipids by oxidative cleavage of the ether bond, PEDS1 exclusively synthesizes a specific subclass of ether lipids, the plasmalogens, by introducing a vinyl ether double bond into plasmanylethanolamine phospholipids. Ether lipids are characterized by an ether linkage at the sn-1 position of the glycerol backbone and they are found in membranes of different cell types. Decreased plasmalogen levels have been associated with neurological diseases like Alzheimer's disease. Agmo-deficient mice do not present an obvious phenotype under unchallenged conditions. In contrast, Peds1 knockout mice display a growth phenotype. To investigate the molecular consequences of Agmo and Peds1 deficiency on the mouse lipidome, five tissues from each mouse model were isolated and subjected to high resolution mass spectrometry allowing the characterization of up to 2013 lipid species from 42 lipid subclasses. Agmo knockout mice moderately accumulated plasmanyl and plasmenyl lipid species. Peds1-deficient mice manifested striking changes characterized by a strong reduction of plasmenyl lipids and a concomitant massive accumulation of plasmanyl lipids resulting in increased total ether lipid levels in the analyzed tissues except for the class of phosphatidylethanolamines where total levels remained remarkably constant also in Peds1 knockout mice. The rate-limiting enzyme in ether lipid metabolism, FAR1, was not upregulated in Peds1-deficient mice, indicating that the selective loss of plasmalogens is not sufficient to activate the feedback mechanism observed in total ether lipid deficiency.

Epithelial-Mesenchymal Plasticity: Implications for Ferroptosis Vulnerability and Cancer Therapy

Cancers polarized to a mesenchymal or poorly differentiated state can often evade cell death induced by conventional therapies. The epithelial-mesenchymal transition is involved in lipid metabolism and increases polyunsaturated fatty acid levels in cancer cells, contributing to chemo- and radio-resistance. Altered metabolism in cancer enables invasion and metastasis but is prone to lipid peroxidation under oxidative stress. Cancers with mesenchymal rather than epithelial signatures are highly vulnerable to ferroptosis. Therapy-resistant persister cancer cells show a high mesenchymal cell state and dependence on the lipid peroxidase pathway, which can respond more sensitively to ferroptosis inducers. Cancer cells may survive under specific metabolic and oxidative stress conditions, and targeting this unique defense system can selectively kill only cancer cells. Therefore, this article summarizes the core regulatory mechanisms of ferroptosis in cancer, the relationship between ferroptosis and epithelial-mesenchymal plasticity, and the implications of epithelial-mesenchymal transition for ferroptosis-based cancer therapy.

The origin of long-chain fatty acids required for de novo ether lipid/plasmalogen synthesis

Peroxisomes are single-membrane bounded organelles, that in humans play a dual role in lipid metabolism, including the degradation of very long-chain fatty acids and the synthesis of ether lipids/plasmalogens. The first step in de novo ether lipid synthesis is mediated by the peroxisomal enzyme glyceronephosphate O-acyltransferase, which has a strict substrate specificity reacting only with the long-chain acyl-CoAs. The aim of this study was to determine the origin of these long-chain acyl-CoAs. To this end, we developed a sensitive method for the measurement of de novo ether phospholipid synthesis in cells and, by CRISPR/Cas9 genome editing, generated a series of HeLa cell lines with deficiencies of proteins involved in peroxisomal biogenesis, beta-oxidation, ether lipid synthesis, or metabolite transport. Our results show that the long-chain acyl-CoAs required for the first step of ether lipid synthesis can be imported from the cytosol by the peroxisomal ABCD proteins, in particular ABCD3. Furthermore, we show that these acyl-CoAs can be produced intraperoxisomally by chain shortening of CoA esters of very long-chain fatty acids via beta-oxidation. Our results demonstrate that peroxisomal beta-oxidation and ether lipid synthesis are intimately connected and that the peroxisomal ABC transporters play a crucial role in de novo ether lipid synthesis.

TMEM164 is an acyltransferase that forms ferroptotic C20:4 ether phospholipids

Ferroptosis is an iron-dependent form of cell death driven by oxidation of polyunsaturated fatty acid (PUFA) phospholipids. Large-scale genetic screens have uncovered a specialized role for PUFA ether phospholipids (ePLs) in promoting ferroptosis. Understanding of the enzymes involved in PUFA-ePL production, however, remains incomplete. Here we show, using a combination of pathway mining of genetic dependency maps, AlphaFold-guided structure predictions and targeted lipidomics, that the uncharacterized transmembrane protein TMEM164-the genetic ablation of which has been shown to protect cells from ferroptosis-is a cysteine active center enzyme that selectively transfers C20:4 acyl chains from phosphatidylcholine to lyso-ePLs to produce PUFA ePLs. Genetic deletion of TMEM164 across a set of ferroptosis-sensitive cancer cell lines caused selective reductions in C20:4 ePLs with minimal effects on C20:4 diacyl PLs, and this lipid profile produced a variable range of protection from ferroptosis, supportive of an important but contextualized role for C20:4 ePLs in this form of cell death.

Regulation of plasmalogen biosynthesis in mammalian cells and tissues

Plasmalogens are a unique family of cellular glycerophospholipids that contain a vinyl-ether bond. Synthesis of plasmalogens is initiated in peroxisomes and completed in the endoplasmic reticulum. The absence of plasmalogens in several organs of patients with deficiency in peroxisome biogenesis suggests that de novo synthesis of plasmalogens contributes significantly to plasmalogen homeostasis in humans. Plasmalogen biosynthesis is spatiotemporally regulated by a feedback mechanism that senses the amount of plasmalogens in the inner leaflet of the plasma membrane and regulates the stability of fatty acyl-CoA reductase 1 (FAR1), the rate-limiting enzyme for plasmalogen biosynthesis. Dysregulation of plasmalogen synthesis impairs cholesterol synthesis in cells and brain, resulting in the reduced expression of genes such as mRNA encoding myelin basic protein, a phenotype found in the cerebellum of plasmalogen-deficient mice. In this review, we summarize the current knowledge of molecular mechanisms underlying the regulation of plasmalogen biosynthesis and the link between plasmalogen homeostasis and cholesterol biosynthesis, and address the pathogenesis of impaired plasmalogen homeostasis in rodent and humans.

A tale of two lipids: Lipid unsaturation commands ferroptosis sensitivity

Membrane lipids play important roles in the regulation of cell fate, including the execution of ferroptosis. Ferroptosis is a non-apoptotic cell death mechanism defined by iron-dependent membrane lipid peroxidation. Phospholipids containing polyunsaturated fatty acids (PUFAs) are highly vulnerable to peroxidation and are essential for ferroptosis execution. By contrast, the incorporation of less oxidizable monounsaturated fatty acids (MUFAs) in membrane phospholipids protects cells from ferroptosis. The enzymes and pathways that govern PUFA and MUFA metabolism therefore play a critical role in determining cellular sensitivity to ferroptosis. Here, we review three lipid metabolic processes-fatty acid biosynthesis, ether lipid biosynthesis, and phospholipid remodeling-that can govern ferroptosis sensitivity by regulating the balance of PUFAs and MUFAs in membrane phospholipids.

Lipid metabolism alterations and ferroptosis in cancer: Paving the way for solving cancer resistance

Cancer often perturbs lipid metabolism, which leads to the alteration of metabolism intermediates, contributing to their deregulated growth and metastasis. Alteration of lipid metabolism shifting to contain more polyunsaturated fatty acids (PUFAs) in membrane phospholipids (PLs) also leads to cancer therapy resistance. High amounts of PL-PUFAs render cancer cells more vulnerable to lipid peroxidation (LPO), predisposing them towards ferroptosis, a new form of iron-dependent oxidative regulated cell death. The commitment of cancer undergoing ferroptotic cell death depends on the adaptive lipidome remodeling, LPO patterns, and LPO scavenging ability in heterogeneous cancer cells. Ferroptosis is receiving attention in cancer research as treating cancers, altering membrane lipid homeostasis, and refractory from conventional therapies. Therefore, a better understanding of the molecular underpinning of lipid metabolism alterations may provide new opportunities for solving cancer resistance. This review intends to understand altered lipid metabolism in cancers and discuss lipid composition and metabolic processes associated with ferroptosis induction in cancers.

Mouse Models to Study Peroxisomal Functions and Disorders: Overview, Caveats, and Recommendations

During the last three decades many mouse lines were created or identified that are deficient in one or more peroxisomal functions. Different methodologies were applied to obtain global, hypomorph, cell type selective, inducible, and knockin mice. Whereas some models closely mimic pathologies in patients, others strongly deviate or no human counterpart has been reported. Often, mice, apparently endowed with a stronger transcriptional adaptation, have to be challenged with dietary additions or restrictions in order to trigger phenotypic changes. Depending on the inactivated peroxisomal protein, several approaches can be taken to validate the loss-of-function. Here, an overview is given of the available mouse models and their most important characteristics.

Plasmalogens in bacteria, sixty years on

The presence of plasmalogens in bacteria has been known for 60 years. The recent discovery of two genes encoding reductases that convert diacyl lipids to 1-alk-1'-enyl 2-acyl lipids has confirmed the derivation of plasmalogens from the corresponding diacyl lipids in bacteria. These genes are widely distributed in anaerobic and in some facultatively anaerobic bacteria. Plasmalogens evolved very early in the history of life on earth. Their persistence during eons of evolution suggests that they play a fundamental role in living organism. The phase behavior of plasmalogens and their conformation in membranes is discussed.

Plasmalogens and platelet-activating factor roles in chronic inflammatory diseases

Fatty acids and phospholipid molecules are essential for determining the structure and function of cell membranes, and they hence participate in many biological processes. Platelet activating factor (PAF) and its precursor plasmalogen, which represent two subclasses of ether phospholipids, have attracted increasing research attention recently due to their association with multiple chronic inflammatory, neurodegenerative, and metabolic disorders. These pathophysiological conditions commonly involve inflammatory processes linked to an excess presence of PAF and/or decreased levels of plasmalogens. However, the molecular mechanisms underlying the roles of plasmalogens in inflammation have remained largely elusive. While anti-inflammatory responses most likely involve the plasmalogen signal pathway; pro-inflammatory responses recruit arachidonic acid, a precursor of pro-inflammatory lipid mediators which is released from membrane phospholipids, notably derived from the hydrolysis of plasmalogens. Plasmalogens per se are vital membrane phospholipids in humans. Changes in their homeostatic levels may alter cell membrane properties, thus affecting key signaling pathways that mediate inflammatory cascades and immune responses. The plasmalogen analogs of PAF are also potentially important, considering that anti-PAF activity has strong anti-inflammatory effects. Plasmalogen replacement therapy was further identified as a promising anti-inflammatory strategy allowing for the relief of pathological hallmarks in patients affected by chronic diseases with an inflammatory component. The aim of this Short Review is to highlight the emerging roles and implications of plasmalogens in chronic inflammatory disorders, along with the promising outcomes of plasmalogen replacement therapy for the treatment of various PAF-related chronic inflammatory pathologies.

Molecular insights into peroxisome homeostasis and peroxisome biogenesis disorders

Peroxisomes are single-membrane organelles essential for cell metabolism including the β-oxidation of fatty acids, synthesis of etherlipid plasmalogens, and redox homeostasis. Investigations into peroxisome biogenesis and the human peroxisome biogenesis disorders (PBDs) have identified 14 PEX genes encoding peroxins involved in peroxisome biogenesis and the mutation of PEX genes is responsible for the PBDs. Many recent findings have further advanced our understanding of the biology, physiology, and consequences of a functional deficit of peroxisomes. In this Review, we discuss cell defense mechanisms that counteract oxidative stress by 1) a proapoptotic Bcl-2 factor BAK-mediated release to the cytosol of H₂O₂-degrading catalase from peroxisomes and 2) peroxisomal import suppression of catalase by Ser232-phosphorylation of Pex14, a docking protein for the Pex5-PTS1 complex. With respect to peroxisome division, the important issue of how the energy-rich GTP is produced and supplied for the division process was recently addressed by the discovery of a nucleoside diphosphate kinase-like protein, termed DYNAMO1 in a lower eukaryote, which has a mammalian homologue NME3. In regard to the mechanisms underlying the pathogenesis of PBDs, a new PBD model mouse defective in Pex14 manifests a dysregulated brain-derived neurotrophic factor (BDNF)-TrkB pathway, an important signaling pathway for cerebellar morphogenesis. Communications between peroxisomes and other organelles are also addressed.

Selenoprotein I (selenoi) as a critical enzyme in the central nervous system

Selenoprotein I (selenoi) is a unique selenocysteine (Sec)-containing protein widely expressed throughout the body. Selenoi belongs to two different protein families: the selenoproteins that are characterized by a redox reactive Sec residue and the lipid phosphotransferases that contain the highly conserved cytidine diphosphate (CDP)-alcohol phosphotransferase motif. Selenoi catalyzes the third reaction of the CDP-ethanolamine branch of the Kennedy pathway within the endoplasmic reticulum membrane. This is not a redox reaction and does not directly involve the Sec residue, making selenoi quite distinct among selenoproteins. Selenoi is also unique among lipid phosphotransferases as the only family member containing a Sec residue near its C-terminus that serves an unknown function. The reaction catalyzed by selenoi involves the transfer of the ethanolamine phosphate group from CDP-ethanolamine to one of two lipid donors, 1,2-diacylglycerol (DAG) or 1-alkyl-2-acylglycerol (AAG), to produce PE or plasmanyl PE, respectively. Plasmanyl PE is subsequently converted to plasmenyl PE by plasmanylethanolamine desaturase. Both PE and plasmenyl PE are critical phospholipids in the central nervous system (CNS), as demonstrated through clinical studies involving SELENOI mutations as well as studies in cell lines and mice. Deletion of SELENOI in mice is embryonic lethal, while loss-of-function mutations in the human SELENOI gene have been found in rare cases leading to a form of hereditary spastic paraplegia (HSP). HSP is an upper motor disease characterized by spasticity of the lower limbs, which is often manifested with other symptoms such as impaired vision/hearing, ataxia, cognitive/intellectual impairment, and seizures. This article will summarize the current understanding of selenoi as a metabolic enzyme and discuss its role in the CNS physiology and pathophysiology.

Cooperation effects of radiation and ferroptosis on tumor suppression and radiation injury

Ferroptosis is a kind of oxidative stress-dependent cell death characterized by iron accumulation and lipid peroxidation. It can work in conjunction with radiation to increase reactive oxygen species (ROS) generation and disrupt the antioxidant system, suppressing tumor progression. Radiation can induce ferroptosis by creating ROS, depleting glutathione, activating genes linked to DNA damage and increasing the expression of acyl-CoA synthetase long-chain family member 4 (ACSL4) in tumor cells. Furthermore, ferroptosis can enhance radiosensitivity by causing an iron overload, destruction of the antioxidant system, and lipid peroxidation. Radiation can also cause ferroptosis in normal cells, resulting in radiation injury. The role of ferroptosis in radiation-induced lung, intestinal, skin, and hematological injuries have been studied. In this review, we summarize the potential mechanisms linking ferroptosis, oxidative stress and radiation; analyze the function of ferroptosis in tumor suppression and radiation injury; and discuss the potential of ferroptosis regulation to improve radiotherapy efficacy and reduce adverse effects.

Dysfunctional peroxisomal lipid metabolisms and their ocular manifestations

Retina is rich in lipids and dyslipidemia causes retinal dysfunction and eye diseases. In retina, lipids are not only important membrane component in cells and organelles but also fuel substrates for energy production. However, our current knowledge of lipid processing in the retina are very limited. Peroxisomes play a critical role in lipid homeostasis and genetic disorders with peroxisomal dysfunction have different types of ocular complications. In this review, we focus on the role of peroxisomes in lipid metabolism, including degradation and detoxification of very-long-chain fatty acids, branched-chain fatty acids, dicarboxylic acids, reactive oxygen/nitrogen species, glyoxylate, and amino acids, as well as biosynthesis of docosahexaenoic acid, plasmalogen and bile acids. We also discuss the potential contributions of peroxisomal pathways to eye health and summarize the reported cases of ocular symptoms in patients with peroxisomal disorders, corresponding to each disrupted peroxisomal pathway. We also review the cross-talk between peroxisomes and other organelles such as lysosomes, endoplasmic reticulum and mitochondria.

Ether lipid deficiency disrupts lipid homeostasis leading to ferroptosis sensitivity

Ferroptosis is an iron-dependent form of regulated cell death associated with uncontrolled membrane lipid peroxidation and destruction. Previously, we showed that dietary dihomo-gamma-linolenic acid (DGLA; 20: 3(n-6)) triggers ferroptosis in the germ cells of the model organism, Caenorhabditis elegans. We also demonstrated that ether lipid-deficient mutant strains are sensitive to DGLA-induced ferroptosis, suggesting a protective role for ether lipids. The vinyl ether bond unique to plasmalogen lipids has been hypothesized to function as an antioxidant, but this has not been tested in animal models. In this study, we used C. elegans mutants to test the hypothesis that the vinyl ether bond in plasmalogens acts as an antioxidant to protect against germ cell ferroptosis as well as to protect from whole-body tert-butyl hydroperoxide (TBHP)-induced oxidative stress. We found no role for plasmalogens in either process. Instead, we demonstrate that ether lipid-deficiency disrupts lipid homeostasis in C. elegans, leading to altered ratios of saturated and monounsaturated fatty acid (MUFA) content in cellular membranes. We demonstrate that ferroptosis sensitivity in both wild type and ether-lipid deficient mutants can be rescued in several ways that change the relative abundance of saturated fats, MUFAs and specific polyunsaturated fatty acids (PUFAs). Specifically, we reduced ferroptosis sensitivity by (1) using mutant strains unable to synthesize DGLA, (2) using a strain carrying a gain-of-function mutation in the transcriptional mediator MDT-15, or (3) by dietary supplementation of MUFAs. Furthermore, our studies reveal important differences in how dietary lipids influence germ cell ferroptosis versus whole-body peroxide-induced oxidative stress. These studies highlight a potentially beneficial role for endogenous and dietary MUFAs in the prevention of ferroptosis.

Regulation of plasmalogen metabolism and traffic in mammals: The fog begins to lift

Due to their unique chemical structure, plasmalogens do not only exhibit distinct biophysical and biochemical features, but require specialized pathways of biosynthesis and metabolization. Recently, major advances have been made in our understanding of these processes, for example by the attribution of the gene encoding the enzyme, which catalyzes the final desaturation step in plasmalogen biosynthesis, or by the identification of cytochrome C as plasmalogenase, which allows for the degradation of plasmalogens. Also, models have been presented that plausibly explain the maintenance of adequate cellular levels of plasmalogens. However, despite the progress, many aspects around the questions of how plasmalogen metabolism is regulated and how plasmalogens are distributed among organs and tissues in more complex organisms like mammals, remain unresolved. Here, we summarize and interpret current evidence on the regulation of the enzymes involved in plasmalogen biosynthesis and degradation as well as the turnover of plasmalogens. Finally, we focus on plasmalogen traffic across the mammalian body - a topic of major importance, when considering plasmalogen replacement therapies in human disorders, where deficiencies in these lipids have been reported. These involve not only inborn errors in plasmalogen metabolism, but also more common diseases including Alzheimer's disease and neurodevelopmental disorders.

Ether lipid transfer across the blood-brain and placental barriers does not improve by inactivation of the most abundant ABC transporters

Phospholipid transport from the periphery to the brain is an understudied topic. When certain lipid species are deficient due to impaired synthesis, though, transfer across the blood-brain barrier is essential for replenishing lipids in the brain. For example, the deficiency in plasmalogens, the most abundant ether lipids in mammals, has detrimental effects on the brain, which is a major issue in inherited peroxisomal disorders but also contributes to more common disorders like Alzheimer's disease. Oral administration of alkylglycerols like batyl alcohol, which carry a pre-formed ether bond, enables replenishment of ether lipids in various peripheral tissues. However, plasmalogen deficiency in the brain cannot be overcome by this approach. Here, we tried to increase cerebral plasmalogen uptake by modulating the efflux transport across the blood-brain barrier. We hypothesized, based on previous literature, that at least some ether lipid species readily enter endothelial cells of the barrier through the transporter MFSD2A but are re-exported by ATP-binding cassette (ABC) transporters. By crossbreeding Mdr1a^-/-/Mdr1b^-/-/Bcrp^-/- and ether lipid-deficient Gnpat^-/- mice as well as pharmacological inhibition with MK-571 to inactivate the major ABC transporters at the blood-brain barrier, we evaluated the potential of combined ABC transporter inhibition and oral batyl alcohol administration for the treatment of plasmalogen deficiency. We found that even in the absence of the most abundant ABC transporters, batyl alcohol supplementation did not restore plasmalogen levels in the brain, despite the presence of a wide spectrum of ether lipid subspecies in the plasma as demonstrated by lipidomic analysis. Surprisingly, batyl alcohol treatment of pregnant Gnpat^+/- dams had beneficial effects on the plasmalogen levels of Gnpat^-/- offspring with defective ether lipid biosynthesis, independently of ABC transporter status at the placental barrier. Our results underline the autonomy of brain lipid homeostasis and indicate that peripheral supplementation of ether lipids is not sufficient to supply the brain with larger amounts of plasmalogens. Yet, the findings suggest that alkylglycerol treatment during pregnancy may pose a viable option to ameliorate some of the severe developmental defects of inborn ether lipid deficiency.

Serine ether glycerophospholipids: Decrements in the frontal cortex associated with mild cognitive impairment and Alzheimer's disease

Ether glycerophospholipids (GPL) are involved in membrane fluidity and fusion. Vinyl-ether GPL are also conjectured to provide antioxidant capacity in the brain. The roles of these lipids in the processes involved in the development of dementia are not understood but choline and ethanolamine vinyl-ether GPL (i.e., plasmalogens) are decreased in the brains of subjects with dementia. In contrast, serine ether and vinyl-ether GPL have not been investigated in human brain. We therefore undertook an evaluation of these lipids, utilizing high-resolution mass spectrometry (HR-MS), in tissues from control and dementia subjects that we had previously characterized in-depth. We can report for the first time that a number of serine ether GPL and a more limited number of serine plasmalogens are present in human frontal cortex. In addition, we found that some of these frontal cortex lipids are decreased in Mild Cognitive Impairment (MCI), early-onset Alzheimer's disease (EOAD), and late-onset AD (LOAD). In contrast no alterations in serine ether GPL were monitored in the frontal cortex of donors with schizophrenia, demonstrating disease specificity. These data suggest that further studies of the roles of ether GPL, including serine ether GPL, in brain function are worthy of undertaking.

ATP8B2-Mediated Asymmetric Distribution of Plasmalogens Regulates Plasmalogen Homeostasis and Plays a Role in Intracellular Signaling

Plasmalogens are a subclass of glycerophospholipid containing vinyl-ether bond at the sn-1 position of glycerol backbone. Ethanolamine-containing plasmalogens (plasmalogens) are major constituents of cellular membranes in mammalian cells and de novo synthesis of plasmalogens largely contributes to the homeostasis of plasmalogens. Plasmalogen biosynthesis is regulated by a feedback mechanism that senses the plasmalogen level in the inner leaflet of the plasma membrane and regulates the stability of fatty acyl-CoA reductase 1 (Far1), a rate-limiting enzyme for plasmalogen biosynthesis. However, the molecular mechanism underlying the localization of plasmalogens in cytoplasmic leaflet of plasma membrane remains unknown. To address this issue, we attempted to identify a potential transporter of plasmalogens from the outer to the inner leaflet of plasma membrane by focusing on phospholipid flippases, type-IV P-type adenosine triphosphatases (P4-ATPase), localized in the plasma membranes. We herein show that knockdown of ATP8B2 belonging to the class-1 P4-ATPase enhances localization of plasmalogens but not phosphatidylethanolamine in the extracellular leaflet and impairs plasmalogen-dependent degradation of Far1. Furthermore, phosphorylation of protein kinase B (AKT) is downregulated by lowering the expression of ATP8B2, which leads to suppression of cell growth. Taken together, these results suggest that enrichment of plasmalogens in the cytoplasmic leaflet of plasma membranes is mediated by ATP8B2 and this asymmetric distribution of plasmalogens is required for sensing plasmalogens as well as phosphorylation of AKT.

Plasmalogens and Photooxidative Stress Signaling in Myxobacteria, and How it Unmasked CarF/TMEM189 as the Δ1'-Desaturase PEDS1 for Human Plasmalogen Biosynthesis

Plasmalogens are glycerophospholipids with a hallmark sn-1 vinyl ether bond that endows them with unique physical-chemical properties. They have proposed biological roles in membrane organization, fluidity, signaling, and antioxidative functions, and abnormal plasmalogen levels correlate with various human pathologies, including cancer and Alzheimer’s disease. The presence of plasmalogens in animals and in anaerobic bacteria, but not in plants and fungi, is well-documented. However, their occurrence in the obligately aerobic myxobacteria, exceptional among aerobic bacteria, is often overlooked. Tellingly, discovery of the key desaturase indispensable for vinyl ether bond formation, and therefore fundamental in plasmalogen biogenesis, emerged from delving into how the soil myxobacterium Myxococcus xanthus responds to light. A recent pioneering study unmasked myxobacterial CarF and its human ortholog TMEM189 as the long-sought plasmanylethanolamine desaturase (PEDS1), thus opening a crucial door to study plasmalogen biogenesis, functions, and roles in disease. The findings demonstrated the broad evolutionary sweep of the enzyme and also firmly established a specific signaling role for plasmalogens in a photooxidative stress response. Here, we will recount our take on this fascinating story and its implications, and review the current state of knowledge on plasmalogens, their biosynthesis and functions in the aerobic myxobacteria.

Tricky Isomers—The Evolution of Analytical Strategies to Characterize Plasmalogens and Plasmanyl Ether Lipids

Typically, glycerophospholipids are represented with two esterified fatty acids. However, by up to 20%, a significant proportion of this lipid class carries an ether-linked fatty alcohol side chain at the sn-1 position, generally referred to as ether lipids, which shape their specific physicochemical properties. Among those, plasmalogens represent a distinct subgroup characterized by an sn-1 vinyl-ether double bond. The total loss of ether lipids in severe peroxisomal defects such as rhizomelic chondrodysplasia punctata indicates their crucial contribution to diverse cellular functions. An aberrant ether lipid metabolism has also been reported in multifactorial conditions including Alzheimer’s disease. Understanding the underlying pathological implications is hampered by the still unclear exact functional spectrum of ether lipids, especially in regard to the differentiation between the individual contributions of plasmalogens (plasmenyl lipids) and their non-vinyl-ether lipid (plasmanyl) counterparts. A primary reason for this is that exact identification and quantification of plasmalogens and other ether lipids poses a challenging and usually labor-intensive task. Diverse analytical methods for the detection of plasmalogens have been developed. Liquid chromatography–tandem mass spectrometry is increasingly used to resolve complex lipid mixtures, and with optimized parameters and specialized fragmentation strategies, discrimination between ethers and plasmalogens is feasible. In this review, we recapitulate historic and current methodologies for the recognition and quantification of these important lipids and will discuss developments in this field that can contribute to the characterization of plasmalogens in high structural detail.

Pharmacokinetics, Mass Balance, Excretion, and Tissue Distribution of Plasmalogen Precursor PPI-1011

PPI-1011 is a synthetic plasmalogen precursor in development as a treatment for multiple plasmalogen-deficiency disorders. Previous work has demonstrated the ability of PPI-1011 to augment plasmalogens and its effects in vitro and in vivo, however, the precise uptake and distribution across tissues in vivo has not been investigated. The purpose of this study was to evaluate the pharmacokinetics, mass balance, and excretion of [¹⁴C]PPI-1011 following a single oral administration at 100 mg/kg in Sprague-Dawley rats. Further tissue distribution was examined using quantitative whole-body autoradiography after both single and repeat daily doses at 100 mg/kg/day. Non-compartmental analysis showed that following a single dose, PPI-1011 exhibited peak levels between 6 and 12 h but also a long half-life with mean t_1/2 of 40 h. Mass balance showed that over 50% of the compound-associated radioactivity was absorbed by the body, while approximately 40% was excreted in the feces, 2.5% in the urine, and 10% in expired air within the first 24 h. Quantitative whole-body autoradiography following a single dose showed uptake to nearly all tissues, with the greatest initial uptake in the intestines, liver, and adipose tissue, which decreased time-dependently throughout 168 h post-dose. Following 15 consecutive daily doses, uptake was significantly higher across the entire body at 24 h compared to single dose and remained high out to 96 h where 75% of the initially-absorbed compound-associated radioactivity was still present. The adipose tissue remained particularly high, suggesting a possible reserve of either plasmalogens or alkyl diacylglycerols that the body can pull from for plasmalogen biosynthesis. Uptake to the brain was also definitively confirmed, proving PPI-1011’s ability to cross the blood-brain barrier. In conclusion, our results suggest that oral administration of PPI-1011 results in high uptake across the body, and that repeated dosing over time represents a viable therapeutic strategy for treating plasmalogen deficiencies.

TMEM189 negatively regulates the stability of ULK1 protein and cell autophagy

ULK1 is crucial for initiating autophagosome formation and its activity is tightly regulated by post-translational modifications and protein-protein interactions. In the present study, we demonstrate that TMEM189 (Transmembrane protein 189), also known as plasmanylethanolamine desaturase 1 (PEDS1), negatively regulates the proteostasis of ULK1 and autophagy activity. In TMEM189-overexpressed cells, the formation of autophagesome is impaired, while TMEM189 knockdown increases cell autophagy. Further investigation reveals that TMEM189 interacts with and increases the instability of ULK1, as well as decreases its kinase activities. The TMEM189 N-terminal domain is required for the interaction with ULK1. Additionally, TMEM189 overexpression can disrupt the interaction between ULK1 and TRAF6, profoundly impairs K63-linked polyubiquitination of ULK1 and self-association, leading to the decrease of ULK1 stability. Moreover, in vitro and in vivo experiments suggest that TMEM189 deficiency results in the inhibition of tumorigenicity of gastric cancer. Our findings provide a new insight into the molecular regulation of autophagy and laboratory evidence for investigating the physiological and pathological roles of TMEM189.

Ferroptosis at the intersection of lipid metabolism and cellular signaling

Ferroptosis, a newly emerged form of regulated necrotic cell death, has been demonstrated to play an important role in multiple diseases including cancer, neurodegeneration, and ischemic organ injury. Mounting evidence also suggests its potential physiological function in tumor suppression and immunity. The execution of ferroptosis is driven by iron-dependent phospholipid peroxidation. As such, the metabolism of biological lipids regulates ferroptosis via controlling phospholipid peroxidation, as well as various other cellular processes relevant to phospholipid peroxidation. In this review, we provide a comprehensive analysis by focusing on how lipid metabolism impacts the initiation, propagation, and termination of phospholipid peroxidation; how multiple signal transduction pathways communicate with ferroptosis via modulating lipid metabolism; and how such intimate cross talk of ferroptosis with lipid metabolism and related signaling pathways can be exploited for the development of rational therapeutic strategies.

Essential role of a conserved aspartate for the enzymatic activity of plasmanylethanolamine desaturase

Plasmalogens are an abundant class of glycerophospholipids in the mammalian body, with special occurrence in the brain and in immune cell membranes. Plasmanylethanolamine desaturase (PEDS1) is the final enzyme of plasmalogen biosynthesis, which introduces the characteristic 1-O-alk-1′-enyl double bond. The recent sequence identification of PEDS1 as transmembrane protein 189 showed that its protein sequence is related to a special class of plant desaturases (FAD4), with whom it shares a motif of 8 conserved histidines, which are essential for the enzymatic activity. In the present work, we wanted to gain more insight into the sequence–function relationship of this enzyme and mutated to alanine additional 28 amino acid residues of murine plasmanylethanolamine desaturase including those 20 residues, which are also totally conserved—in addition to the eight-histidine-motif—among the animal PEDS1 and plant FAD4 plant desaturases. We measured the enzymatic activity by transient transfection of tagged murine PEDS1 expression clones to a PEDS1-deficient human HAP1 cell line by monitoring of labeled plasmalogens formed from supplemented 1-O-pyrenedecyl-sn-glycerol in relation to recombinant protein expression. Surprisingly, only a single mutation, namely aspartate 100, led to a total loss of PEDS1 activity. The second strongest impact on enzymatic activity had mutation of phenylalanine 118, leaving only 6% residual activity. A structural model obtained by homology modelling to available structures of stearoyl-CoA reductase predicted that this aspartate 100 residue interacts with histidine 96, and phenylalanine 118 interacts with histidine 187, both being essential histidines assumed to be involved in the coordination of the di-metal center of the enzyme.

Integrative Analysis of the Inflammatory Bowel Disease Serum Metabolome Improves Our Understanding of Genetic Etiology and Points to Novel Putative Therapeutic Targets

BACKGROUND & AIMS

Polygenic and environmental factors are underlying causes of inflammatory bowel disease (IBD). We hypothesized that integration of the genetic loci controlling a metabolite's abundance, with known IBD genetic susceptibility loci, may help resolve metabolic drivers of IBD.

METHODS

We measured the levels of 1300 metabolites in the serum of 484 patients with ulcerative colitis (UC) and 464 patients with Crohn's disease (CD) and 365 controls. Differential metabolite abundance was determined for disease status, subtype, clinical and endoscopic disease activity, as well as IBD phenotype including disease behavior, location, and extent. To inform on the genetic basis underlying metabolic diversity, we integrated metabolite and genomic data. Genetic colocalization and Mendelian randomization analyses were performed using known IBD risk loci to explore whether any metabolite was causally associated with IBD.

RESULTS

We found 173 genetically controlled metabolites (metabolite quantitative trait loci, 9 novel) within 63 non-overlapping loci (7 novel). Furthermore, several metabolites significantly associated with IBD disease status and activity as defined using clinical and endoscopic indexes. This constitutes a resource for biomarker discovery and IBD biology insights. Using this resource, we show that a novel metabolite quantitative trait locus for serum butyrate levels containing ACADS was not supported as causal for IBD; replicate the association of serum omega-6 containing lipids with the fatty acid desaturase 1/2 locus and identify these metabolites as causal for CD through Mendelian randomization; and validate a novel association of serum plasmalogen and TMEM229B, which was predicted as causal for CD.

CONCLUSIONS

An exploratory analysis combining genetics and unbiased serum metabolome surveys can reveal novel biomarkers of disease activity and potential mediators of pathology in IBD.

Ferroptosis: Redox Imbalance and Hematological Tumorigenesis

Ferroptosis is a novel characterized form of cell death featured with iron-dependent lipid peroxidation, which is distinct from any known programmed cell death in the biological processes and morphological characteristics. Recent evidence points out that ferroptosis is correlated with numerous metabolic pathways, including iron homeostasis, lipid metabolism, and redox homeostasis, associating with the occurrence and treatment of hematological malignancies, such as multiple myeloma, leukemia, and lymphoma. Nowadays, utilizing ferroptosis as the target to prevent and treat hematological malignancies has become an active and challenging topic of research, and the regulatory network and physiological function of ferroptosis also need to be further elucidated. This review will summarize the recent progress in the molecular regulation of ferroptosis and the physiological roles and therapeutic potential of ferroptosis as the target in hematological malignancies.

Peroxisomal Stress Response and Inter-Organelle Communication in Cellular Homeostasis and Aging

Peroxisomes are key regulators of cellular and metabolic homeostasis. These organelles play important roles in redox metabolism, the oxidation of very-long-chain fatty acids (VLCFAs), and the biosynthesis of ether phospholipids. Given the essential role of peroxisomes in cellular homeostasis, peroxisomal dysfunction has been linked to various pathological conditions, tissue functional decline, and aging. In the past few decades, a variety of cellular signaling and metabolic changes have been reported to be associated with defective peroxisomes, suggesting that many cellular processes and functions depend on peroxisomes. Peroxisomes communicate with other subcellular organelles, such as the nucleus, mitochondria, endoplasmic reticulum (ER), and lysosomes. These inter-organelle communications are highly linked to the key mechanisms by which cells surveil defective peroxisomes and mount adaptive responses to protect them from damages. In this review, we highlight the major cellular changes that accompany peroxisomal dysfunction and peroxisomal inter-organelle communication through membrane contact sites, metabolic signaling, and retrograde signaling. We also discuss the age-related decline of peroxisomal protein import and its role in animal aging and age-related diseases. Unlike other organelle stress response pathways, such as the unfolded protein response (UPR) in the ER and mitochondria, the cellular signaling pathways that mediate stress responses to malfunctioning peroxisomes have not been systematically studied and investigated. Here, we coin these signaling pathways as "peroxisomal stress response pathways". Understanding peroxisomal stress response pathways and how peroxisomes communicate with other organelles are important and emerging areas of peroxisome research.

Interplay between cardiolipin and plasmalogens in Barth syndrome

Barth syndrome (BTHS) is a rare inherited metabolic disease resulting from mutations in the gene of the enzyme tafazzin, which catalyzes the acyl chain remodeling of the mitochondrial-specific lipid cardiolipin (CL). Tissue samples of individuals with BTHS present abnormalities in the level and the molecular species of CL. In addition, in tissues of a tafazzin knockdown mouse as well as in cells derived from BTHS patients it has been shown that plasmalogens, a subclass of glycerophospholipids, also have abnormal levels. Likewise, administration of a plasmalogen precursor to cells derived from BTHS patients led to an increase in plasmalogen and to some extent CL levels. These results indicate an interplay between CL and plasmalogens in BTHS. This interdependence is supported by the concomitant loss in these lipids in different pathological conditions. However, currently the molecular mechanism linking CL and plasmalogens is not fully understood. Here, a review of the evidence showing the linkage between the levels of CL and plasmalogens is presented. In addition, putative mechanisms that might play a role in this interplay are proposed. Finally, the opportunity of therapeutic approaches based on the regulation of plasmalogens as new therapies for the treatment of BTHS is discussed.

Research progress on the occurrence and therapeutic mechanism of ferroptosis in NSCLC

Ferroptosis refers to a novel way of cell death, inconsistent with the conventional concept of apoptosis and necrosis. It shows a close association with iron metabolism and oxidative damage, as marked by the significant increase of reactive oxygen species, the decreases of mitochondrial volume, and the thickening of membrane density. Recent studies confirmed that ferroptosis is closely associated with the occurrence, development, and therapy of the tumors. As impacted by the high levels of reactive oxygen species and lipid peroxides in lung cancer tissues, it is suggested that ferroptosis is more likely to occur in lung cancer tissues, which may act as a novel approach for non-small cell lung cancer (NSCLC) therapy. In the present study, the research achievements in recent years on the regulating mechanism of ferroptosis and its effect on the occurrence and the therapy of lung cancer are reviewed.