Mfn2-dependent fusion pathway of PE-enriched micron-sized vesicles.

Mitofusins (Mfn1 and Mfn2) are the mitochondrial outer-membrane fusion proteins in mammals and belong to the dynamin superfamily of multidomain GTPases. Recent structural studies of truncated variants lacking alpha helical transmembrane domains suggested that Mfns dimerize to promote the approximation and the fusion of the mitochondrial outer membranes upon the hydrolysis of guanine 5'-triphosphate disodium salt (GTP). However, next to the presence of GTP, the fusion activity seems to require multiple regulatory factors that control the dynamics and kinetics of mitochondrial fusion through the formation of Mfn1-Mfn2 heterodimers. Here, we purified and reconstituted the full-length murine Mfn2 protein into giant unilamellar vesicles (GUVs) with different lipid compositions. The incubation with GTP resulted in the fusion of Mfn2-GUVs. High-speed video-microscopy showed that the Mfn2-dependent membrane fusion pathway progressed through a zipper mechanism where the formation and growth of an adhesion patch eventually led to the formation of a membrane opening at the rim of the septum. The presence of physiological concentration (up to 30 mol%) of dioleoyl-phosphatidylethanolamine (DOPE) was shown to be a requisite to observe GTP-induced Mfn2-dependent fusion. Our observations show that Mfn2 alone can promote the fusion of micron-sized DOPE-enriched vesicles without the requirement of regulatory cofactors, such as membrane curvature, or the assistance of other proteins.

Comparing the metabolic signatures of obesity defined by waist circumference, waist-hip ratio, or BMI.

OBJECTIVE: Measuring obesity is crucial for assessing health risks and developing effective prevention and treatment strategies. The most common methods used to measure obesity include BMI, waist circumference, and waist-hip ratio. This study aimed to determine the metabolic signatures associated with each measure of obesity in the Qatari population. METHODS: Metabolomics profiling was conducted to identify, quantify, and characterize metabolites in serum samples from the study participants. Inverse rank normalization, principal component analysis, and orthogonal partial least square-discriminant analysis were used to analyze the metabolomics data. RESULTS: This study revealed significant differences in metabolites associated with obesity based on different measurements. In men, phosphatidylcholine and phosphatidylethanolamine metabolites were significantly enriched in individuals classified as having obesity based on the waist-hip ratio. In women, significant changes were observed in leucine, isoleucine, and valine metabolism metabolites. Unique metabolites were found in the different categorization groups that could serve as biomarkers for assessing many obesity-related disorders. CONCLUSIONS: This study identified unique metabolic signatures associated with obesity based on different measurements in the Qatari population. These findings contribute to a better understanding of the molecular pathways involved in obesity and may have implications for developing personalized prevention and treatment strategies.

Phosphatidylethanolamines link ferroptosis and autophagy during appressorium formation of rice blast fungus.

A cell death pathway, ferroptosis, occurs in conidial cells and is critical for formation and function of the infection structure, the appressorium, in the rice blast fungus Magnaporthe oryzae. In this study, we identified an orthologous lysophosphatidic acid acyltransferase (Lpaat) acting at upstream of phosphatidylethanolamines (PEs) biosynthesis and which is required for such fungal ferroptosis and pathogenicity. Two PE species, DOPE and SLPE, that depend on Lpaat function for production were sufficient for induction of lipid peroxidation and the consequent ferroptosis, thus positively regulating fungal pathogenicity. On the other hand, both DOPE and SLPE positively regulated autophagy. Loss of the LPAAT gene led to a decrease in the lipidated form of the autophagy protein Atg8, which is probably responsible for the autophagy defect of the lpaatΔ mutant. GFP-Lpaat was mostly localized on the membrane of lipid droplets (LDs) that were stained by the fluorescent dye monodansylpentane (MDH), suggesting that LDs serve as a source of lipids for membrane PE biosynthesis and probably as a membrane source of autophagosome. Overall, our results reveal novel intracellular membrane-bound organelle dynamics based on Lpaat-mediated lipid metabolism, providing a temporal and spatial link of ferroptosis and autophagy.

Serum lipid metabolism characteristics and potential biomarkers in patients with unilateral sudden sensorineural hearing loss.

BACKGROUND: Glycerophospholipids (GPLs) are essential for cell membrane structure and function. Sphingomyelin and its metabolites regulate cell growth, apoptosis, and stress responses. This study aimed to investigate lipid metabolism in patients experiencing sudden sensorineural hearing loss across all frequencies (AF-SSNHL). METHODS: The study included 60 patients diagnosed with unilateral AF-SSNHL, among whom 30 patients had a level of hearing improvement ≥ 15 dB after 6 months of follow-up. A propensity score-matched (2:1) control group was used. Liquid chromatography‒mass spectrometry based untargeted lipidomics analysis combined with multivariate statistics was performed to investigate the lipids change. The "lipidome" R package and weighted gene co-expression network analysis (WGCNA) were utilised to assess the lipids' structural features and the association between lipids and hearing. RESULTS: Lipidomics successfully differentiated the AF-SSNHL group from the control group, identifying 17 risk factors, mainly including phosphatidylcholine (PC), phosphatidylethanolamine (PE), and related metabolites. The ratios of lysophosphatidylcholine/PC, lysophosphatidylethanolamine/PE, and lysodimethylphosphatidylethanolamine/PE were upregulated, while some glycerophospholipid (GPL)-plasmalogens were downregulated in the AF-SSNHL group, indicating abnormal metabolism of GPLs. Trihexosylceramide (d34:1), PE (18:1e_22:5), and sphingomyelin (d40:3) were significantly different between responders and nonresponders, and positively correlated with hearing improvement. Additionally, the results of the WGCNA also suggested that partial GPL-plasmalogens were positively associated with hearing improvement. CONCLUSION: AF-SSNHL patients exhibited abnormally high blood lipids and pronounced GPLs metabolic abnormalities. Sphingolipids and GPL-plasmalogens had an association with the level of hearing improvement. By understanding the lipid changes, clinicians may be able to predict the prognosis of hearing recovery and personalize treatment approaches.

Development and validation of a plasmalogen score as an independent modifiable marker of metabolic health: population based observational studies and a placebo-controlled cross-over study.

BACKGROUND: Decreased levels of circulating ethanolamine plasmalogens [PE(P)], and a concurrent increase in phosphatidylethanolamine (PE) are consistently reported in various cardiometabolic conditions. Here we devised, a plasmalogen score (Pls Score) that mirrors a metabolic signal that encompasses the levels of PE(P) and PE and captures the natural variation in circulating plasmalogens and perturbations in their metabolism associated with disease, diet, and lifestyle. METHODS: We utilised, plasma lipidomes from the Australian Obesity, Diabetes and Lifestyle study (AusDiab; n = 10,339, 55% women) a nationwide cohort, to devise the Pls Score and validated this in the Busselton Health Study (BHS; n = 4,492, 56% women, serum lipidome) and in a placebo-controlled crossover trial involving Shark Liver Oil (SLO) supplementation (n = 10, 100% men). We examined the association of the Pls Score with cardiometabolic risk factors, type 2 diabetes mellitus (T2DM), cardiovascular disease and all-cause mortality (over 17 years). FINDINGS: In a model, adjusted for age, sex and BMI, individuals in the top quintile of the Pls Score (Q5) relative to Q1 had an OR of 0.31 (95% CI 0.21-0.43), 0.39 (95% CI 0.25-0.61) and 0.42 (95% CI 0.30-0.57) for prevalent T2DM, incident T2DM and prevalent cardiovascular disease respectively, and a 34% lower mortality risk (HR = 0.66; 95% CI 0.56-0.78). Significant associations between diet and lifestyle habits and Pls Score exist and these were validated through dietary supplementation of SLO that resulted in a marked change in the Pls Score. INTERPRETATION: The Pls Score as a measure that captures the natural variation in circulating plasmalogens, was not only inversely related to cardiometabolic risk and all-cause mortality but also associate with diet and lifestyle. Our results support the potential utility of the Pls Score as a biomarker for metabolic health and its responsiveness to dietary interventions. Further research is warranted to explore the underlying mechanisms and optimise the practical implementation of the Pls Score in clinical and population settings. FUNDING: National Health and Medical Research Council (NHMRC grant 233200), National Health and Medical Research Council of Australia (Project grant APP1101320), Health Promotion Foundation of Western Australia, and National Health and Medical Research Council of Australia Senior Research Fellowship (#1042095).

Structural basis of lipid head group entry to the Kennedy pathway by FLVCR1.

Phosphatidylcholine and phosphatidylethanolamine, the two most abundant phospholipids in mammalian cells, are synthesized de novo by the Kennedy pathway from choline and ethanolamine, respectively1-6. Despite the essential roles of these lipids, the mechanisms that enable the cellular uptake of choline and ethanolamine remain unknown. Here we show that the protein encoded by FLVCR1, whose mutation leads to the neurodegenerative syndrome posterior column ataxia and retinitis pigmentosa7-9, transports extracellular choline and ethanolamine into cells for phosphorylation by downstream kinases to initiate the Kennedy pathway. Structures of FLVCR1 in the presence of choline and ethanolamine reveal that both metabolites bind to a common binding site comprising aromatic and polar residues. Despite binding to a common site, FLVCR1 interacts in different ways with the larger quaternary amine of choline in and with the primary amine of ethanolamine. Structure-guided mutagenesis identified residues that are crucial for the transport of ethanolamine, but dispensable for choline transport, enabling functional separation of the entry points into the two branches of the Kennedy pathway. Altogether, these studies reveal how FLVCR1 is a high-affinity metabolite transporter that serves as the common origin for phospholipid biosynthesis by two branches of the Kennedy pathway.

The complete assembly of human LAT1-4F2hc complex provides insights into its regulation, function and localisation.

The LAT1-4F2hc complex (SLC7A5-SLC3A2) facilitates uptake of essential amino acids, hormones and drugs. Its dysfunction is associated with many cancers and immune/neurological disorders. Here, we apply native mass spectrometry (MS)-based approaches to provide evidence of super-dimer formation (LAT1-4F2hc)2. When combined with lipidomics, and site-directed mutagenesis, we discover four endogenous phosphatidylethanolamine (PE) molecules at the interface and C-terminus of both LAT1 subunits. We find that interfacial PE binding is regulated by 4F2hc-R183 and is critical for regulation of palmitoylation on neighbouring LAT1-C187. Combining native MS with mass photometry (MP), we reveal that super-dimerization is sensitive to pH, and modulated by complex N-glycans on the 4F2hc subunit. We further validate the dynamic assemblies of LAT1-4F2hc on plasma membrane and in the lysosome. Together our results link PTM and lipid binding with regulation and localisation of the LAT1-4F2hc super-dimer.

Circulating perturbation of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) is associated to cardiac remodeling and NLRP3 inflammasome in cardiovascular patients with insulin resistance risk.

Lipidome perturbation occurring during meta-inflammation is associated to left ventricle (LV) remodeling though the activation of the NLRP3 inflammasome, a key regulator of chronic inflammation in obesity-related disorders. Little is known about phosphatidylcholine (PC) and phosphatidylethanolamine (PE) as DAMP-induced NLRP3 inflammasome. Our study is aimed to evaluate if a systemic reduction of PC/PE molar ratio can affect NLRP3 plasma levels in cardiovascular disease (CVD) patients with insulin resistance (IR) risk. Forty patients from IRCCS Policlinico San Donato were enrolled, and their blood samples were drawn before heart surgery. LV geometry measurements were evaluated by echocardiography and clinical data associated to IR risk were collected. PC and PE were quantified by ESI-MS/MS. Circulating NLRP3 was quantified by an ELISA assay. Our results have shown that CVD patients with IR risk presented systemic lipid impairment of PC and PE species and their ratio in plasma was inversely associated to NLRP3 levels. Interestingly, CVD patients with IR risk presented LV changes directly associated to increased levels of NLRP3 and a decrease in PC/PE ratio in plasma, highlighting the systemic effect of meta-inflammation in cardiac response. In summary, PC and PE can be considered bioactive mediators associated to both the NLRP3 and LV changes in CVD patients with IR risk.

Comparative study of melasma in patients before and after treatment based on lipomics.

BACKGROUND: Skin barrier alterations play a crucial function in melasma development. Past researches have demonstrated variations in lipid content between the epidermis of melasma lesions and normal tissues, along with the varied expression of lipid-related genes in melasma. This study aimed to analyze the lipidome profiles of skin surface lipids (SSL) in patients with melasma before and after treatment to understand associated abnormalities. METHODS: Melasma was treated with tranexamic acid orally and hydroquinone cream topically. Disease was assessed using the Melasma Area and Severity Index (MASI), and the impact to life was evaluated with Melasma Quality of Life (MELASQoL) score. Epidermal melanin particles were observed using reflection confocal microscopy (RCM), whereas epidermal pigment and blood vessel morphology were observed using dermoscopy, and SSL samples were collected. Specific information regarding alterations in lipid composition was obtained through multivariate analysis of the liquid chromatography-mass spectrometry data. RESULTS: After treatment, patients with melasma exhibited decreased MASI and MELASQoL scores (P < 0.001); RCM revealed reduced melanin content in the lesions, and dermoscopy revealed fewer blood vessels. Fifteen lipid subclasses and 382 lipid molecules were identified using lipidomic assays. The expression levels of total lipids, phosphatidylcholine, and phosphatidylethanolamine in the melasma lesions decreased after treatment (P < 0.05). CONCLUSION: This study revealed alterations in the SSL composition after effective melasma treatment, suggesting a compensatory role for lipids in melasma barrier function. The mechanism involving SSL and the lipid barrier, which influences melasma's occurrence, needs further elucidation.

Distinctive Lipid Characteristics of Colorectal Cancer Revealed through Non-targeted Lipidomics Analysis of Tongue Coating.

The metabolites and microbiota in tongue coating display distinct characteristics in certain digestive disorders, yet their relationship with colorectal cancer (CRC) remains unexplored. Here, we employed liquid chromatography coupled with tandem mass spectrometry to analyze the lipid composition of tongue coating using a nontargeted approach in 30 individuals with colorectal adenomas (CRA), 32 with CRC, and 30 healthy controls (HC). We identified 21 tongue coating lipids that effectively distinguished CRC from HC (AUC = 0.89), and 9 lipids that differentiated CRC from CRA (AUC = 0.9). Furthermore, we observed significant alterations in the tongue coating lipid composition in the CRC group compared to HC/CRA groups. As the adenoma-cancer sequence progressed, there was an increase in long-chain unsaturated triglycerides (TG) levels and a decrease in phosphatidylethanolamine plasmalogen (PE-P) levels. Furthermore, we noted a positive correlation between N-acyl ornithine (NAOrn), sphingomyelin (SM), and ceramide phosphoethanolamine (PE-Cer), potentially produced by members of the Bacteroidetes phylum. The levels of inflammatory lipid metabolite 12-HETE showed a decreasing trend with colorectal tumor progression, indicating the potential involvement of tongue coating microbiota and tumor immune regulation in early CRC development. Our findings highlight the potential utility of tongue coating lipid analysis as a noninvasive tool for CRC diagnosis.

Colon microbiota and metabolite potential impact on tail fat deposition of Altay sheep.

Tail fat deposition of Altay sheep not only increased the cost of feeding but also reduced the economic value of meat. Currently, because artificial tail removal and gene modification methods cannot solve this problem, it is maybe to consider reducing tail fat deposition from the path of intestinal microbiota and metabolite. We measured body weight and tail fat weight, collected the serum for hormone detection by enzyme-linked immunosorbent assay, and collected colon contents to 16S rRNA sequence and liquid chromotography with mass spectrometry detection to obtain colon microbiota and metabolite information, from 12 3-month-old and 6-month-old Altay sheep. Subsequently, we analyzed the correlation between colon microbiota and tail fat weight, hormones, and metabolites, respectively. We identified that the tail fat deposition of Altay sheep increased significantly with the increase of age and body weight, and the main microbiota that changed were Verrucomicrobia, Cyanobacteria, Akkermansia, Bacteroides, Phocaeicola, Escherichia-Shigella, and Clostridium_sensu_stricto_1. The results indicated that the diversities of metabolites in the colon contents of 3-months old and 6-months old were mainly reflected in phosphocholine (PC) and phosphatidylethanolamine (PE) in the lipid metabolism pathway. The correlations analyzed showed that Verrucomicrobia, Chlamydiae, Akkermansia, Ruminococcaceae_UCG-005, Bacteroides, and Phocaeicola were negatively correlated with tail fat deposition. Verrucomicrobia, Akkermansia, and Bacteroides were negatively correlated with growth hormone (GH). Verrucomicrobia was positively correlated with L-a-lysophosphatidylserine and PE(18:1(9Z)/0:0). Our results showed that tail fat deposition of Altay sheep was probably correlated with the abundance of Verrucomicrobia, Akkermansia, Bacteroides of colon microbiota, PC, PE of metabolites, and GH of serum. IMPORTANCE: Excessive tail fat deposition of Altay sheep caused great economic losses, and the current research results could not solve this problem well. Now, our research speculates that the tail fat deposition of Aletay sheep may be related to the abundance of Verrucomicrobia, Akkermansia, Bacteroides, metabolites phosphocholine, phosphatidylethanolamine, and growth hormone of serum. Further investigation of the interaction mechanism between these microbiota or metabolites and tail fat deposition is helpful in reducing tail fat deposition of Altay sheep and increasing the economic benefits of breeding farms.

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.

Sedentary behavior in mice induces metabolic inflexibility by suppressing skeletal muscle pyruvate metabolism.

Carbohydrates and lipids provide the majority of substrates to fuel mitochondrial oxidative phosphorylation. Metabolic inflexibility, defined as an impaired ability to switch between these fuels, is implicated in a number of metabolic diseases. Here, we explore the mechanism by which physical inactivity promotes metabolic inflexibility in skeletal muscle. We developed a mouse model of sedentariness, small mouse cage (SMC), that, unlike other classic models of disuse in mice, faithfully recapitulated metabolic responses that occur in humans. Bioenergetic phenotyping of skeletal muscle mitochondria displayed metabolic inflexibility induced by physical inactivity, demonstrated by a reduction in pyruvate-stimulated respiration (JO2) in the absence of a change in palmitate-stimulated JO2. Pyruvate resistance in these mitochondria was likely driven by a decrease in phosphatidylethanolamine (PE) abundance in the mitochondrial membrane. Reduction in mitochondrial PE by heterozygous deletion of phosphatidylserine decarboxylase (PSD) was sufficient to induce metabolic inflexibility measured at the whole-body level, as well as at the level of skeletal muscle mitochondria. Low mitochondrial PE in C2C12 myotubes was sufficient to increase glucose flux toward lactate. We further implicate that resistance to pyruvate metabolism is due to attenuated mitochondrial entry via mitochondrial pyruvate carrier (MPC). These findings suggest a mechanism by which mitochondrial PE directly regulates MPC activity to modulate metabolic flexibility in mice.

The unusual substrate specificity of Escherichia coli cardiolipin synthase C does not require the product of the transcriptionally engaged ymdB gene.

Polycistronic transcription and translation of ymdB-clsC have been thought to be required for full activity of ClsC. The authentic initiation codon of the clsC gene is present within the open reading frame of the upstream located ymdB gene. ClsC translated from authentic initiation codon drives cardiolipin (CL) synthesis without transcriptionally paired YmdB. YmdB is not necessary for the substrate specificity of ClsC utilizing phosphatidylethanolamine (PE) as a co-substrate.

The phospholipids cardiolipin and phosphatidylethanolamine differentially regulate MDC biogenesis.

Cells utilize multiple mechanisms to maintain mitochondrial homeostasis. We recently characterized a pathway that remodels mitochondria in response to metabolic alterations and protein overload stress. This remodeling occurs via the formation of large membranous structures from the mitochondrial outer membrane called mitochondrial-derived compartments (MDCs), which are eventually released from mitochondria and degraded. Here, we conducted a microscopy-based screen in budding yeast to identify factors that regulate MDC formation. We found that two phospholipids, cardiolipin (CL) and phosphatidylethanolamine (PE), differentially regulate MDC biogenesis. CL depletion impairs MDC biogenesis, whereas blocking mitochondrial PE production leads to constitutive MDC formation. Additionally, in response to metabolic MDC activators, cellular and mitochondrial PE declines, and overexpressing mitochondrial PE synthesis enzymes suppress MDC biogenesis. Altogether, our data indicate a requirement for CL in MDC biogenesis and suggest that PE depletion may stimulate MDC formation downstream of MDC-inducing metabolic stress.

DGAT2 inhibition blocks SREBP-1 cleavage and improves hepatic steatosis by increasing phosphatidylethanolamine in the ER.

Diacylglycerol acyltransferase 2 (DGAT2) catalyzes the final step of triglyceride (TG) synthesis. DGAT2 deletion in mice lowers liver TGs, and DGAT2 inhibitors are under investigation for the treatment of fatty liver disease. Here, we show that DGAT2 inhibition also suppressed SREBP-1 cleavage, reduced fatty acid synthesis, and lowered TG accumulation and secretion from liver. DGAT2 inhibition increased phosphatidylethanolamine (PE) levels in the endoplasmic reticulum (ER) and inhibited SREBP-1 cleavage, while DGAT2 overexpression lowered ER PE concentrations and increased SREBP-1 cleavage in vivo. ER enrichment with PE blocked SREBP-1 cleavage independent of Insigs, which are ER proteins that normally retain SREBPs in the ER. Thus, inhibition of DGAT2 shunted diacylglycerol into phospholipid synthesis, increasing the PE content of the ER, resulting in reduced SREBP-1 cleavage and less hepatic steatosis. This study reveals a new mechanism that regulates SREBP-1 activation and lipogenesis that is independent of sterols and SREBP-2 in liver.

NAPE-PLD in the ventral tegmental area regulates reward events, feeding and energy homeostasis.

The N-acyl phosphatidylethanolamine-specific phospholipase D (NAPE-PLD) catalyzes the production of N-acylethanolamines (NAEs), a family of endogenous bioactive lipids, which are involved in various biological processes ranging from neuronal functions to energy homeostasis and feeding behaviors. Reward-dependent behaviors depend on dopamine (DA) transmission between the ventral tegmental area (VTA) and the nucleus accumbens (NAc), which conveys reward-values and scales reinforced behaviors. However, whether and how NAPE-PLD may contribute to the regulation of feeding and reward-dependent behaviors has not yet been investigated. This biological question is of paramount importance since NAEs are altered in obesity and metabolic disorders. Here, we show that transcriptomic meta-analysis highlights a potential role for NAPE-PLD within the VTA→NAc circuit. Using brain-specific invalidation approaches, we report that the integrity of NAPE-PLD is required for the proper homeostasis of NAEs within the midbrain VTA and it affects food-reward behaviors. Moreover, region-specific knock-down of NAPE-PLD in the VTA enhanced food-reward seeking and reinforced behaviors, which were associated with increased in vivo DA release dynamics in response to both food- and non-food-related rewards together with heightened tropism towards food consumption. Furthermore, midbrain knock-down of NAPE-PLD, which increased energy expenditure and adapted nutrient partitioning, elicited a relative protection against high-fat diet-mediated body fat gain and obesity-associated metabolic features. In conclusion, these findings reveal a new key role of VTA NAPE-PLD in shaping DA-dependent events, feeding behaviors and energy homeostasis, thus providing new insights on the regulation of body metabolism.

Cryo-EM structure of human sphingomyelin synthase and its mechanistic implications for sphingomyelin synthesis.

Sphingomyelin (SM) has key roles in modulating mammalian membrane properties and serves as an important pool for bioactive molecules. SM biosynthesis is mediated by the sphingomyelin synthase (SMS) family, comprising SMS1, SMS2 and SMS-related (SMSr) members. Although SMS1 and SMS2 exhibit SMS activity, SMSr possesses ceramide phosphoethanolamine synthase activity. Here we determined the cryo-electron microscopic structures of human SMSr in complexes with ceramide, diacylglycerol/phosphoethanolamine and ceramide/phosphoethanolamine (CPE). The structures revealed a hexameric arrangement with a reaction chamber located between the transmembrane helices. Within this structure, a catalytic pentad E-H/D-H-D was identified, situated at the interface between the lipophilic and hydrophilic segments of the reaction chamber. Additionally, the study unveiled the two-step synthesis process catalyzed by SMSr, involving PE-PLC (phosphatidylethanolamine-phospholipase C) hydrolysis and the subsequent transfer of the phosphoethanolamine moiety to ceramide. This research provides insights into the catalytic mechanism of SMSr and expands our understanding of sphingolipid metabolism.

Phosphatidylethanolamine (18:2e/18:2) may inhibit adipose tissue wasting in patients with cancer cachexia by increasing lysophosphatidic acid receptor 6.

BACKGROUND: Cancer associated cachexia is characterized by the significant loss of adipose tissue, leading to devastating weight loss and muscle wasting in the majority of cancer patients. The effects and underlying mechanisms of degradation metabolites on adipocytes in cachectic patients remain poorly understood. To address this knowledge gap, we conducted a comprehensive study combining lipidomic analysis of subcutaneous and visceral adipose tissue with transcriptomics data from the database to investigate the mechanisms of lipid regulation in adipocytes. METHODS: We collected subcutaneous and visceral adipose tissue samples from cachectic and noncachectic cancer patients. Lipidomic analysis was performed to identify differentially expressed lipids in both types of adipose tissue. Additionally, transcriptomics data from the GEO database were analyzed to explore gene expression patterns in adipocytes. Bioinformatics analysis was employed to determine the enrichment of differentially expressed genes in specific pathways. Furthermore, molecular docking studies were conducted to predict potential protein targets of specific lipids, with a focus on the PI3K-Akt signaling pathway. Western blot analysis was used to validate protein levels of the identified target gene, lysophosphatidic acid receptor 6 (LPAR6), in subcutaneous and visceral adipose tissue from cachectic and noncachectic patients. RESULTS: Significant lipid differences in subcutaneous and visceral adipose tissue between cachectic and noncachectic patients were identified by multivariate statistical analysis. Cachectic patients exhibited elevated Ceramides levels and reduced CerG2GNAc1 levels (P < 0.05). A total of 10 shared lipids correlated with weight loss and IL-6 levels, enriched in Sphingolipid metabolism, GPI-anchor biosynthesis, and Glyceropholipid metabolism pathways. LPAR6 expression was significantly elevated in both adipose tissues of cachectic patients (P < 0.05). Molecular docking analysis indicated strong binding of Phosphatidylethanolamine (PE) (18:2e/18:2) to LPAR6. CONCLUSIONS: Our findings suggest that specific lipids, including PE(18:2e/18:2), may mitigate adipose tissue wasting in cachexia by modulating the expression of LPAR6 through the PI3K-Akt signaling pathway. The identification of these potential targets and mechanisms provides a foundation for future investigations and therapeutic strategies to combat cachexia. By understanding the underlying lipid regulation in adipocytes, we aim to develop targeted interventions to ameliorate the devastating impact of cachexia on patient outcomes and quality of life. Nevertheless, further studies and validation are warranted to fully elucidate the intricate mechanisms involved and translate these findings into effective clinical interventions.

Strikingly High Activity of 15-Lipoxygenase Towards Di-Polyunsaturated Arachidonoyl/Adrenoyl-Phosphatidylethanolamines Generates Peroxidation Signals of Ferroptotic Cell Death.

The vast majority of membrane phospholipids (PLs) include two asymmetrically positioned fatty acyls: oxidizable polyunsaturated fatty acids (PUFA) attached predominantly at the sn2 position, and non-oxidizable saturated/monounsaturated acids (SFA/MUFA) localized at the sn1 position. The peroxidation of PUFA-PLs, particularly sn2-arachidonoyl(AA)- and sn2-adrenoyl(AdA)-containing phosphatidylethanolamines (PE), has been associated with the execution of ferroptosis, a program of regulated cell death. There is a minor subpopulation (≈1-2 mol %) of doubly PUFA-acylated phospholipids (di-PUFA-PLs) whose role in ferroptosis remains enigmatic. Here we report that 15-lipoxygenase (15LOX) exhibits unexpectedly high pro-ferroptotic peroxidation activity towards di-PUFA-PEs. We revealed that peroxidation of several molecular species of di-PUFA-PEs occurred early in ferroptosis. Ferrostatin-1, a typical ferroptosis inhibitor, effectively prevented peroxidation of di-PUFA-PEs. Furthermore, co-incubation of cells with di-AA-PE and 15LOX produced PUFA-PE peroxidation and induced ferroptotic death. The decreased contents of di-PUFA-PEs in ACSL4 KO A375 cells was associated with lower levels of di-PUFA-PE peroxidation and enhanced resistance to ferroptosis. Thus, di-PUFA-PE species are newly identified phospholipid peroxidation substrates and regulators of ferroptosis, representing a promising therapeutic target for many diseases related to ferroptotic death.