Arachidonoyl-phosphatidylcholine oscillates during the cell cycle and counteracts proliferation by suppressing Akt membrane binding. Proc Natl Acad Sci U S A. 2013;110:2546-2551. [PMID: 23359699 DOI: 10.1073/pnas.1216182110]

Zeb1 mediates EMT/plasticity-associated ferroptosis sensitivity in cancer cells by regulating lipogenic enzyme expression and phospholipid composition

Therapy resistance and metastasis, the most fatal steps in cancer, are often triggered by a (partial) activation of the epithelial-mesenchymal transition (EMT) programme. A mesenchymal phenotype predisposes to ferroptosis, a cell death pathway exerted by an iron and oxygen-radical-mediated peroxidation of phospholipids containing polyunsaturated fatty acids. We here show that various forms of EMT activation, including TGFβ stimulation and acquired therapy resistance, increase ferroptosis susceptibility in cancer cells, which depends on the EMT transcription factor Zeb1. We demonstrate that Zeb1 increases the ratio of phospholipids containing pro-ferroptotic polyunsaturated fatty acids over cyto-protective monounsaturated fatty acids by modulating the differential expression of the underlying crucial enzymes stearoyl-Co-A desaturase 1 (SCD), fatty acid synthase (FASN), fatty acid desaturase 2 (FADS2), elongation of very long-chain fatty acid 5 (ELOVL5) and long-chain acyl-CoA synthetase 4 (ACSL4). Pharmacological inhibition of selected lipogenic enzymes (SCD and FADS2) allows the manipulation of ferroptosis sensitivity preferentially in high-Zeb1-expressing cancer cells. Our data are of potential translational relevance and suggest a combination of ferroptosis activators and SCD inhibitors for the treatment of aggressive cancers expressing high Zeb1.

Iron(III)-salophene catalyzes redox cycles that induce phospholipid peroxidation and deplete cancer cells of ferroptosis-protecting cofactors

Ferroptosis, a lipid peroxidation-driven cell death program kept in check by glutathione peroxidase 4 and endogenous redox cycles, promises access to novel strategies for treating therapy-resistant cancers. Chlorido [N,N'-disalicylidene-1,2-phenylenediamine]iron (III) complexes (SCs) have potent anti-cancer properties by inducing ferroptosis, apoptosis, or necroptosis through still poorly understood molecular mechanisms. Here, we show that SCs preferentially induce ferroptosis over other cell death programs in triple-negative breast cancer cells (LC50 ≥ 0.07 μM) and are particularly effective against cell lines with acquired invasiveness, chemo- or radioresistance. Redox lipidomics reveals that initiation of cell death is associated with extensive (hydroper)oxidation of arachidonic acid and adrenic acid in membrane phospholipids, specifically phosphatidylethanolamines and phosphatidylinositols, with SCs outperforming established ferroptosis inducers. Mechanistically, SCs effectively catalyze one-electron transfer reactions, likely via a redox cycle involving the reduction of Fe(III) to Fe(II) species and reversible formation of oxo-bridged dimeric complexes, as supported by cyclic voltammetry. As a result, SCs can use hydrogen peroxide to generate organic radicals but not hydroxyl radicals and oxidize membrane phospholipids and (membrane-)protective factors such as NADPH, which is depleted from cells. We conclude that SCs catalyze specific redox reactions that drive membrane peroxidation while interfering with the ability of cells, including therapy-resistant cancer cells, to detoxify phospholipid hydroperoxides.

PM2.5-induced cellular senescence drives brown adipose tissue impairment in middle-aged mice

Airborne fine particulate matter (PM2.5) exposure is closely associated with metabolic disturbance, in which brown adipose tissue (BAT) is one of the main contributing organs. However, knowledge of the phenotype and mechanism of PM2.5 exposure-impaired BAT is quite limited. In the study, male C57BL/6 mice at three different life phases (young, adult, and middle-aged) were simultaneously exposed to concentrated ambient PM2.5 or filtered air for 8 weeks using a whole-body inhalational exposure system. H&E staining and high-resolution respirometry were used to assess the size of adipocytes and mitochondrial function. Transcriptomics was performed to determine the differentially expressed genes in BAT. Quantitative RT-PCR, immunohistochemistry staining, and immunoblots were performed to verify the transcriptomics and explore the mechanism for BAT mitochondrial dysfunction. Firstly, PM2.5 exposure caused altered BAT morphology and mitochondrial dysfunction in middle-aged but not young or adult mice. Furthermore, PM2.5 exposure increased cellular senescence in BAT of middle-aged mice, accompanied by cell cycle arrest, impaired DNA replication, and inhibited AKT signaling pathway. Moreover, PM2.5 exposure disrupted apoptosis and autophagy homeostasis in BAT of middle-aged mice. Therefore, BAT in middle-aged mice was more vulnerable to PM2.5 exposure, and the cellular senescence-initiated apoptosis, autophagy, and mitochondrial dysfunction may be the mechanism of PM2.5 exposure-induced BAT impairment.

Cannabigerol-A useful agent restoring the muscular phospholipids milieu in obese and insulin-resistant Wistar rats?

Numerous strategies have been proposed to minimize obesity-associated health effects, among which phytocannabinoids appear to be effective and safe compounds. In particular, cannabigerol (CBG) emerges as a potent modulator of the composition of membrane phospholipids (PLs), which plays a critical role in the development of insulin resistance. Therefore, here we consider the role of CBG treatment on the composition of PLs fraction with particular emphasis on phospholipid subclasses (e.g., phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylserine (PS), and phosphatidylinositol (PI)) in the red gastrocnemius muscle of Wistar rats fed the standard or high-fat, high-sucrose (HFHS) diet. The intramuscular PLs content was determined by gas-liquid chromatography and based on the composition of individual FAs, we assessed the stearoyl-CoA desaturase 1 (SCD1) index as well as the activity of n-3 and n-6 polyunsaturated fatty acids (PUFAs) pathways. Expression of various proteins engaged in the inflammatory pathway, FAs elongation, and desaturation processes was measured using Western blotting. Our research has demonstrated the important association of obesity with alterations in the composition of muscular PLs, which was significantly improved by CBG supplementation, enriching the lipid pools in n-3 PUFAs and decreasing the content of arachidonic acid (AA), which in turn influenced the activity of PUFAs pathways in various PLs subclasses. CBG also inhibited the local inflammation development and profoundly reduced the SCD1 activity. Collectively, restoring the PLs homeostasis of the myocyte membrane by CBG indicates its new potential medical application in the treatment of obesity-related metabolic disorders.

Regulation and targeting of SREBP-1 in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is an increasing burden on global public health and is associated with enhanced lipogenesis, fatty acid uptake, and lipid metabolic reprogramming. De novo lipogenesis is under the control of the transcription factor sterol regulatory element-binding protein 1 (SREBP-1) and essentially contributes to HCC progression. Here, we summarize the current knowledge on the regulation of SREBP-1 isoforms in HCC based on cellular, animal, and clinical data. Specifically, we (i) address the overarching mechanisms for regulating SREBP-1 transcription, proteolytic processing, nuclear stability, and transactivation and (ii) critically discuss their impact on HCC, taking into account (iii) insights from pharmacological approaches. Emphasis is placed on cross-talk with the phosphatidylinositol-3-kinase (PI3K)-protein kinase B (Akt)-mechanistic target of rapamycin (mTOR) axis, AMP-activated protein kinase (AMPK), protein kinase A (PKA), and other kinases that directly phosphorylate SREBP-1; transcription factors, such as liver X receptor (LXR), peroxisome proliferator-activated receptors (PPARs), proliferator-activated receptor γ co-activator 1 (PGC-1), signal transducers and activators of transcription (STATs), and Myc; epigenetic mechanisms; post-translational modifications of SREBP-1; and SREBP-1-regulatory metabolites such as oxysterols and polyunsaturated fatty acids. By carefully scrutinizing the role of SREBP-1 in HCC development, progression, metastasis, and therapy resistance, we shed light on the potential of SREBP-1-targeting strategies in HCC prevention and treatment.

The role of phospholipids in drug delivery formulations - Recent advances presented at the Researcher's Day 2023 Conference of the Phospholipid Research Center Heidelberg

This Focus on Meetings contribution summarizes recent advances in the research on phospholipids and their applications for drug delivery and analytical purposes that have been presented at the hybrid Researcher's Day 2023 Conference of the Phospholipid Research Center (PRC), held on July 3-5, 2023, in Bad Dürkheim, Germany. The PRC is a non-profit organization focused on expanding and sharing scientific and technological knowledge of phospholipids in pharmaceutical and other applications. This is accomplished by, e.g., funding doctoral and postdoctoral research projects. The progress made with these projects is presented at the Researcher's Day Conference every two years. Four main topics were presented and discussed in various lectures: (1) formulation of phospholipid-based nanocarriers, (2) therapeutic applications of phospholipids and phospholipid-based nanocarriers, (3) phospholipids as excipients in oral, dermal, and parenteral dosage forms, and (4) interactions of phospholipids and phospholipid-based vesicles in biological environment and their use as analytical platforms.

Reducing the metabolic burden of rRNA synthesis promotes healthy longevity in Caenorhabditis elegans

Ribosome biogenesis is initiated by RNA polymerase I (Pol I)-mediated synthesis of pre-ribosomal RNA (pre-rRNA). Pol I activity was previously linked to longevity, but the underlying mechanisms were not studied beyond effects on nucleolar structure and protein translation. Here we use multi-omics and functional tests to show that curtailment of Pol I activity remodels the lipidome and preserves mitochondrial function to promote longevity in Caenorhabditis elegans. Reduced pre-rRNA synthesis improves energy homeostasis and metabolic plasticity also in human primary cells. Conversely, the enhancement of pre-rRNA synthesis boosts growth and neuromuscular performance of young nematodes at the cost of accelerated metabolic decline, mitochondrial stress and premature aging. Moreover, restriction of Pol I activity extends lifespan more potently than direct repression of protein synthesis, and confers geroprotection even when initiated late in life, showcasing this intervention as an effective longevity and metabolic health treatment not limited by aging.

Browning of Mammary Fat Suppresses Pubertal Mammary Gland Development of Mice via Elevation of Serum Phosphatidylcholine and Inhibition of PI3K/Akt Pathway

Mammary fat plays a profound role in the postnatal development of mammary glands. However, the specific types (white, brown, or beige) of adipocytes in mammary fat and their potential regulatory effects on modulating mammary gland development remain poorly understood. This study aimed to investigate the role of the browning of mammary fat on pubertal mammary gland development and explore the underlying mechanisms. Thus, the mammary gland development and the serum lipid profile were evaluated in mice treated with CL316243, a β3-adrenoceptor agonist, to induce mammary fat browning. In addition, the proliferation of HC11 cells co-cultured with brown adipocytes or treated with the altered serum lipid metabolite was determined. Our results showed that the browning of mammary fat by injection of CL316243 suppressed the pubertal development of mice mammary glands, accompanied by the significant elevation of serum dioleoylphosphocholine (DOPC). In addition, the proliferation of HC11 was repressed when co-cultured with brown adipocytes or treated with DOPC. Furthermore, DOPC suppressed the activation of the PI3K/Akt pathway, while the DOPC-inhibited HC11 proliferation was reversed by SC79, an Akt activator, suggesting the involvement of the PI3K/Akt pathway in the DOPC-inhibited proliferation of HC11. Together, the browning of mammary fat suppressed the development of the pubertal mammary gland, which was associated with the elevated serum DOPC and the inhibition of the PI3K/Akt pathway.

α-Tocopherol-13'-Carboxychromanol Induces Cell Cycle Arrest and Cell Death by Inhibiting the SREBP1-SCD1 Axis and Causing Imbalance in Lipid Desaturation

α-Tocopherol-13'-carboxychromanol (α-T-13'-COOH) is an endogenously formed bioactive α-tocopherol metabolite that limits inflammation and has been proposed to exert lipid metabolism-regulatory, pro-apoptotic, and anti-tumoral properties at micromolar concentrations. The mechanisms underlying these cell stress-associated responses are, however, poorly understood. Here, we show that the induction of G₀/G₁ cell cycle arrest and apoptosis in macrophages triggered by α-T-13'-COOH is associated with the suppressed proteolytic activation of the lipid anabolic transcription factor sterol regulatory element-binding protein (SREBP)1 and with decreased cellular levels of stearoyl-CoA desaturase (SCD)1. In turn, the fatty acid composition of neutral lipids and phospholipids shifts from monounsaturated to saturated fatty acids, and the concentration of the stress-preventive, pro-survival lipokine 1,2-dioleoyl-sn-glycero-3-phospho-(1'-myo-inositol) [PI(18:1/18:1)] decreases. The selective inhibition of SCD1 mimics the pro-apoptotic and anti-proliferative activity of α-T-13'-COOH, and the provision of the SCD1 product oleic acid (C18:1) prevents α-T-13'-COOH-induced apoptosis. We conclude that micromolar concentrations of α-T-13'-COOH trigger cell death and likely also cell cycle arrest by suppressing the SREBP1-SCD1 axis and depleting cells of monounsaturated fatty acids and PI(18:1/18:1).

Enantioselective toxicity effect and mechanism of hexaconazole enantiomers to human breast cancer cells

The toxicity effects of chiral pesticides on living organisms have attracted an increasing public attention. This study aims to investigate the toxicity effect and mechanism of hexaconazole (HEX) to human breast cancer cell (MCF-7) at enantiomer levels. HEX exposure obviously inhibited cells activities in a dose-dependent manner. Under the conditions of VIP >1 and p < 0.05, a total of 255 and 177 differential metabolites (DMs), 17 and 15 amino acid- and lipid-related metabolic pathways were disturbed after (+)-HEX and (-)-HEX exposure, respectively. HEX exposure may affect cell membrane function, signal transduction, and cell differentiation. We further investigated the mechanism of enantioselective differences by using molecular docking which showed that CYP17A1 was the main enzyme that leading to endocrine disrupting effects with the binding energy of -6.30 and -6.08 kcal/mol compared to CYP19A1 enzyme which were -5.81 and -5.93 kcal/mol for (+)-HEX and (-)-HEX, respectively. The docking results explained the reasons why (+)-HEX achieved higher cytotoxicity and induced more seriously metabolic profiles than its antipode. These findings could provide a new insight to understand the enantioselective cytotoxicity effect and mechanism of HEX and will be conducive to assessing its risk to human health at enantiomer levels.

Untargeted Lipidomics of Erythrocytes under Simulated Microgravity Conditions

Lipidomics and metabolomics are nowadays widely used to provide promising insights into the pathophysiology of cellular stress disorders. Our study expands, with the use of a hyphenated ion mobility mass spectrometric platform, the understanding of the cellular processes and stress due to microgravity. By lipid profiling of human erythrocytes, we annotated complex lipids such as oxidized phosphocholines, phosphocholines bearing arachidonic in their moiety, as well as sphingomyelins and hexosyl ceramides associated with microgravity conditions. Overall, our findings give an insight into the molecular alterations and identify erythrocyte lipidomics signatures associated with microgravity conditions. If the present results are confirmed in future studies, they may help to develop suitable treatments for astronauts after return to Earth.

Multi-omics analysis revealed the role of CYP1A2 in the induction of mechanical allodynia in type 1 diabetes

Background: Mechanical allodynia (MA) is one of the leading clinical symptoms of painful diabetic peripheral neuropathy (PDPN), which is a primary reason for non-traumatic amputations, foot ulceration, and gait abnormalities in patients with diabetes. However, the pathogenic mechanisms of MA have not yet been fully elucidated, and there is no effective treatment. This study aims to study the potential pathogenetic mechanisms of MA and to provide targets for the therapy of MA. Methods: A single intraperitoneal injection of streptozotocin induced type 1 diabetes in rat models. Subsequently, rats were divided into the control group, the diabetic group without MA, and the diabetic group with MA based on weekly behavioral assays. The differentially expressed lipids in the sciatic nerve of each group were detected using untargeted lipidomics, and the differentially expressed genes in the sciatic nerve of each group were detected by transcriptomics. The pathogenesis of MA was predicted using integrated analysis and validated by immunofluorescence staining and transmission electron microscopy. Results: Untargeted lipidomics revealed the accumulation of a more severe lipid in MA rats. Transcriptomics results suggested that differentially expressed genes in MA rats were primarily related to lipid droplets and myelin sheath. Integrated analysis results indicated that the downregulation of Cytochrome P450 1A2 (CYP1A2) expression was closely linked to lipid metabolism disorders. Immunofluorescence staining demonstrated that down-regulation of CYP1A2 expression occurred in MA rats. Transmission electron microscopy results showed that more severe lipid droplet accumulation and myelin sheath degeneration occurred in MA rats. Conclusion: Our findings imply that the downregulation of CYP1A2 expression leads to disorders of lipid metabolism and further leads to lipid droplet accumulation and myelin sheath degeneration, which might ultimately lead to the development of MA. Therefore, our study contributes to promoting the understanding of the molecular mechanisms of MA and providing potential targets for the clinical treatment of MA.

Formulating elafibranor and obeticholic acid with phospholipids decreases drug-induced association of SPARC to extracellular vesicles from LX-2 human hepatic stellate cells

Chronic hepatic diseases often compromise liver function and are directly responsible for up to two million yearly deaths world-wide. There are yet no treatment options to solve this global medical need. Experimental drugs elafibranor (Ela) and obeticholic acid (OA) appeared promising in numerous earlier studies, but they recently struggled to show significant benefits in patients. Little is known on the drugs' impact on hepatic stellate cells (HSCs), key players in liver fibrogenesis. We recently reported a beneficial effect of polyenylphosphatidylcholines (PPCs)-rich formulations in reverting fibrogenic features of HSCs, including differences in their extracellular vesicles (EVs). Here, we newly formulated Ela and OA in PPC liposomes and evaluated their performance on the LX-2 (human HSC) cell line through our rigorous methods of EV-analysis, now expanded to include lipidomics. We show that direct treatments with Ela and OA increase EV-associated secreted protein acidic and cysteine rich (SPARC), a matricellular protein overexpressed in fibrogenesis. However, our results suggest that this potentially damaging drugs' action to HSCs could be mitigated when delivering them with lipid-based formulations, most notably with a PPC-rich phospholipid inducing specific changes in the cellular and EV phospholipid composition. Thus, EV analysis substantially deepens evaluations of drug performances and delivery strategies.

Lpcat3 deficiency promotes palmitic acid-induced 3T3-L1 mature adipocyte inflammation through enhanced ROS generation

Phosphatidylcholines (PCs) are major phospholipids in the mammalian cell membrane. Structural remodeling of PCs is associated with many biological processes. Lysophosphatidylcholine acyltransferase 3 (Lpcat3), which catalyzes the incorporation of polyunsaturated fatty acyl chains into the sn-2 site of PCs, plays an important role in maintaining plasma membrane fluidity. Adipose tissue is one of the main distribution organs of Lpcat3, while the relationship between Lpcat3 and adipose tissue dysfunction during overexpansion remains unknown. In this study, we reveal that both polyunsaturated PC content and Lpcat3 expression are increased in abdominal adipose tissues of high-fat diet-fed mice when compared with chow-diet-fed mice, indicating that Lpcat3 is involved in adipose tissue overexpansion and dysfunction. Our experiments in 3T3-L1 adipocytes show that inhibition of Lpcat3 does not change triglyceride accumulation but increases palmitic acid-induced inflammation and lipolysis. Conversely, Lpcat3 overexpression exhibits anti-inflammatory and anti-lipolytic effects. Furthermore, mechanistic studies demonstrate that Lpcat3 deficiency promotes reactive oxygen species (ROS) generation by increasing NOX enzyme activity by facilitating the translocation of NOX4 to lipid rafts, thereby aggregating 3T3-L1 adipocyte inflammation induced by palmitic acid. Moreover, overexpression of Lpcat3 exhibits the opposite effects. These findings suggest that Lpcat3 protects adipocytes from inflammation during adipose tissue overexpansion by reducing ROS generation. In conclusion, our study demonstrates that Lpcat3 deficiency promotes palmitic acid-induced inflammation in 3T3-L1 adipocytes by enhancing ROS generation.

PI(18:1/18:1) is a SCD1-derived lipokine that limits stress signaling

Cytotoxic stress activates stress-activated kinases, initiates adaptive mechanisms, including the unfolded protein response (UPR) and autophagy, and induces programmed cell death. Fatty acid unsaturation, controlled by stearoyl-CoA desaturase (SCD)1, prevents cytotoxic stress but the mechanisms are diffuse. Here, we show that 1,2-dioleoyl-sn-glycero-3-phospho-(1’-myo-inositol) [PI(18:1/18:1)] is a SCD1-derived signaling lipid, which inhibits p38 mitogen-activated protein kinase activation, counteracts UPR, endoplasmic reticulum-associated protein degradation, and apoptosis, regulates autophagy, and maintains cell morphology and proliferation. SCD1 expression and the cellular PI(18:1/18:1) proportion decrease during the onset of cell death, thereby repressing protein phosphatase 2 A and enhancing stress signaling. This counter-regulation applies to mechanistically diverse death-inducing conditions and is found in multiple human and mouse cell lines and tissues of Scd1-defective mice. PI(18:1/18:1) ratios reflect stress tolerance in tumorigenesis, chemoresistance, infection, high-fat diet, and immune aging. Together, PI(18:1/18:1) is a lipokine that links fatty acid unsaturation with stress responses, and its depletion evokes stress signaling.

Fatty acid unsaturation by stearoyl-CoA desaturase 1 (SCD1) protects against cellular stress through unclear mechanisms. Here the authors show 1,2-dioleoyl-sn-glycero-3-phospho-(1’-myo-inositol) is an SCD1-derived signaling lipid that regulates stress-adaption, protects against cell death and promotes proliferation.

Patterns of Alpha-Linolenic Acid Incorporation into Phospholipids in H4IIE Cells

Alpha linolenic acid (ALA) is an 18-carbon essential fatty acid found in plant-based foods and oils. While much attention has been placed on conversion of ALA to long chain polyunsaturated fatty acids, alternative routes of ALA metabolism exist and may lead to formation of other bioactive metabolites of ALA. The current study employed a non-targeted metabolomics approach to profile ALA metabolites that are significantly upregulated by ALA treatment. H4IIE hepatoma cells (n=3 samples per time point) were treated with 60 μM ALA or vehicle for 0, 0.25, 0.5, 1, 2, 3, 4, 6, 8, and 12 hours. Samples were then extracted with methanol and analyzed using high-performance liquid chromatography/quadrupole time-of-flight mass spectrometry. We observed selective changes in ALA incorporation into phospholipid classes and subclasses over the 12 hours following ALA treatment. While levels of specific molecular species of ALA-containing phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, and lysophospholipids were elevated with ALA treatment, others were not affected. Of the phospholipids that were increased, some [e.g. PC(18:3/18:1), PC(18:3/18:4), PE(18:3/18:2), PE(18:3/18:3)] were elevated almost immediately after exposure to ALA, while others (e.g. PE(18:1/18:3) PA(18:3/22:6), and PA(18:3/18:2)] were not elevated until several hours after ALA treatment. Overall, these results suggest that ALA incorporation into phospholipids is selective and support a metabolic hierarchy for ALA incorporation into specific phospholipids. Given the functionality of phospholipids based on their fatty acid composition, future studies will need to investigate the implications of ALA incorporation into specific phospholipids on cell function.

The differences of the impact of a lipid and protein corona on the colloidal stability, toxicity, and degradation behavior of iron oxide nanoparticles

AIM

In this study, the influence of a serum albumin (SA) and human plasma (HP) derived protein- and lipid molecule corona on the toxicity and biodegradability of different iron oxide nanoparticles (IONP) was investigated.

METHODS

IONP were synthesized and physicochemically characterized regarding size, charge, and colloidal stability. The adsorbed proteins were quantified and separated by gel electrophoresis. Adsorbed lipids were profiled by ultraperformance liquid chromatography-ESI-tandem mass spectrometry. The biocompatibility was investigated using isolated erythrocytes and a shell-less hen's egg model. The biodegradability was assessed by iron release studies in artificial body fluids.

RESULTS

The adsorption patterns of proteins and lipids varied depending on the surface characteristics of the IONP like charge and hydrophobicity. The biomolecule corona modified IONP displayed favorable colloidal stability and toxicological profile compared to IONP without biomolecule coronas, reducing erythrocyte aggregation and hemolysis in vitro as well as the corresponding effects ex ovo/in vivo. The coronas decreased the degradation speed of all tested IONP compared to bare particles, but, whereas all IONP degraded at the same rate for the SA corona, substantial differences were evident for IONP with HP-derived corona depending on the lipid adsorption profile.

CONCLUSION

In this study the impact of the proteins and lipids in the biomolecule corona on the entire IONP application cycle from the injection process to the degradation was demonstrated.

Remodeling glycerophospholipids affects obesity-related insulin signaling in skeletal muscle

It has long been known that fatty acids can either adversely or positively affect insulin signaling in skeletal muscle, depending on chain length or saturation, and can therefore be primary drivers of systemic insulin sensitivity. However, the detailed mechanisms linking fatty acids to insulin signaling in skeletal muscle have been elusive. In this issue of the JCI, Ferrara et al. suggest a model whereby membrane lipid remodeling mediates skeletal muscle insulin sensitivity. The authors demonstrate that membrane glycerophospholipid fatty acid remodeling by lysophosphatidylcholine acyltransferase 3 (LPCAT3) in skeletal muscle from subjects with obesity was induced, suppressing insulin signaling and glucose tolerance. Loss or gain of LPCAT3 function in mouse models showed that Lpcat3 was both required and sufficient for high-fat diet-induced muscle insulin resistance. These results suggest that the physiochemical properties of muscle cell membranes may drive insulin sensitivity and, therefore, systemic glucose intolerance.

Lysophospholipid acylation modulates plasma membrane lipid organization and insulin sensitivity in skeletal muscle

Aberrant lipid metabolism promotes the development of skeletal muscle insulin resistance, but the exact identity of lipid-mediated mechanisms relevant to human obesity remains unclear. A comprehensive lipidomic analysis of primary myocytes from individuals who were insulin-sensitive and lean (LN) or insulin-resistant with obesity (OB) revealed several species of lysophospholipids (lyso-PLs) that were differentially abundant. These changes coincided with greater expression of lysophosphatidylcholine acyltransferase 3 (LPCAT3), an enzyme involved in phospholipid transacylation (Lands cycle). Strikingly, mice with skeletal muscle-specific knockout of LPCAT3 (LPCAT3-MKO) exhibited greater muscle lysophosphatidylcholine/phosphatidylcholine, concomitant with improved skeletal muscle insulin sensitivity. Conversely, skeletal muscle-specific overexpression of LPCAT3 (LPCAT3-MKI) promoted glucose intolerance. The absence of LPCAT3 reduced phospholipid packing of cellular membranes and increased plasma membrane lipid clustering, suggesting that LPCAT3 affects insulin receptor phosphorylation by modulating plasma membrane lipid organization. In conclusion, obesity accelerates the skeletal muscle Lands cycle, whose consequence might induce the disruption of plasma membrane organization that suppresses muscle insulin action.

Tnfaip2/exoc3-driven lipid metabolism is essential for stem cell differentiation and organ homeostasis

Lipid metabolism influences stem cell maintenance and differentiation but genetic factors that control these processes remain to be delineated. Here, we identify Tnfaip2 as an inhibitor of reprogramming of mouse fibroblasts into induced pluripotent stem cells. Tnfaip2 knockout impairs differentiation of embryonic stem cells (ESCs), and knockdown of the planarian para-ortholog, Smed-exoc3, abrogates in vivo tissue homeostasis and regeneration-processes that are driven by somatic stem cells. When stimulated to differentiate, Tnfaip2-deficient ESCs fail to induce synthesis of cellular triacylglycerol (TAG) and lipid droplets (LD) coinciding with reduced expression of vimentin (Vim)-a known inducer of LD formation. Smed-exoc3 depletion also causes a strong reduction of TAGs in planarians. The study shows that Tnfaip2 acts epistatically with and upstream of Vim in impairing cellular reprogramming. Supplementing palmitic acid (PA) and palmitoyl-L-carnitine (the mobilized form of PA) restores the differentiation capacity of Tnfaip2-deficient ESCs and organ maintenance in Smed-exoc3-depleted planarians. Together, these results identify a novel role of Tnfaip2 and exoc3 in controlling lipid metabolism, which is essential for ESC differentiation and planarian organ maintenance.

The Phospholipid Research Center: Current Research in Phospholipids and Their Use in Drug Delivery

This review summarizes the research on phospholipids and their use for drug delivery related to the Phospholipid Research Center Heidelberg (PRC). The focus is on projects that have been approved by the PRC since 2017 and are currently still ongoing or have recently been completed. The different projects cover all facets of phospholipid research, from basic to applied research, including the use of phospholipids in different administration forms such as liposomes, mixed micelles, emulsions, and extrudates, up to industrial application-oriented research. These projects also include all routes of administration, namely parenteral, oral, and topical. With this review we would like to highlight possible future research directions, including a short introduction into the world of phospholipids.

Loss of metabolic plasticity underlies metformin toxicity in aged Caenorhabditis elegans

Current clinical trials are testing the life-extending benefits of the diabetes drug metformin in healthy individuals without diabetes. However, the metabolic response of a non-diabetic cohort to metformin treatment has not been studied. Here, we show in C. elegans and human primary cells that metformin shortens lifespan when provided in late life, contrary to its positive effects in young organisms. We find that metformin exacerbates ageing-associated mitochondrial dysfunction, causing respiratory failure. Age-related failure to induce glycolysis and activate the dietary-restriction-like mobilization of lipid reserves in response to metformin result in lethal ATP exhaustion in metformin-treated aged worms and late-passage human cells, which can be rescued by ectopic stabilization of cellular ATP content. Metformin toxicity is alleviated in worms harbouring disruptions in insulin-receptor signalling, which show enhanced resilience to mitochondrial distortions at old age. Together, our data show that metformin induces deleterious changes of conserved metabolic pathways in late life, which could bring into question its benefits for older individuals without diabetes.

Role of Patatin-Like Phospholipase Domain-Containing 3 Gene for Hepatic Lipid Content and Insulin Resistance in Diabetes

OBJECTIVE

The rs738409(G) single nucleotide polymorphism (SNP) in the patatin-like phospholipase domain-containing 3 (PNPLA3) gene associates with increased risk and progression of nonalcoholic fatty liver disease (NAFLD). As the recently described severe insulin-resistant diabetes (SIRD) cluster specifically relates to NAFLD, this study examined whether this SNP differently associates with hepatic lipid content (hepatocellular lipids [HCL]) and insulin sensitivity in recent-onset diabetes.

RESEARCH DESIGN AND METHODS

A total of 917 participants in the German Diabetes Study (GDS) underwent genotyping, hyperinsulinemic-euglycemic clamps with stable isotopic tracer dilution, and MRS.

RESULTS

The G allele associated positively with HCL (β = 0.36, P < 0.01), independent of age, sex, and BMI across the whole cohort, but not in the individual clusters. Those with SIRD exhibited lowest whole-body insulin sensitivity compared with those with severe insulin-deficient (SIDD), moderate obesity-related (MOD), moderate age-related (MARD), and severe autoimmune diabetes (SAID) clusters (all P < 0.001). Interestingly, the SIRD group presented with higher prevalence of the rs738409(G) SNP compared with other clusters and the glucose-tolerant control group (P < 0.05). HCL was higher in the SIRD group (median 13.6% [1st quartile 5.8; 3rd quartile 19.1] compared with the MOD (6.4 % [2.1; 12.4], P < 0.05), MARD (3.0% [1.0; 7.9], P < 0.001), SAID (0.4% [0.0; 1.5], P < 0.001), and glucose-tolerant (0.9% [0.4; 4.9), P < 0.001) group. Although the PNPLA3 polymorphism did not directly associate with whole-body insulin sensitivity in SIRD, the G-allele carriers had higher circulating free fatty acid concentrations and greater adipose tissue insulin resistance compared with noncarriers (both P < 0.001).

CONCLUSIONS

Members of the SIRD cluster are more frequently carriers of the rs738409(G) variant. The SNP-associated adipose tissue insulin resistance and excessive lipolysis may contribute to their NAFLD.

Elaidate, a trans fatty acid, suppresses insulin signaling for glucose uptake in a manner distinct from that of stearate

The dietary intake of elaidate (elaidic acid), a trans-fatty acid, is associated with the development of various diseases. Since elaidate is a C18 unsaturated fatty acid with a steric structure similar to that of a C18 saturated fatty acid (stearate), we previously revealed that insulin-dependent glucose uptake was impaired in adipocytes exposed to elaidate prior to and during differentiation similar to stearate. However, it is still unknown whether the mechanism of impairment of insulin-dependent glucose uptake due to elaidate is similar to that of stearate. Here, we indicate that persistent exposure to elaidate has particular effects on insulin signaling and GLUT4 dynamics. Insulin-induced accumulation of Akt at the plasma membrane (PM) and elevations of phosphorylated Akt and AS160 levels in whole cells were suppressed in adipocytes persistently exposed to 50 μM elaidate. Interestingly, persistent exposure to the same concentration of stearate has no effect on the phosphorylated Akt and AS160 levels. When cells were exposed to these fatty acids, elaidate suppressed insulin-induced fusion, but not translocation, of GLUT4 storage vesicles in the PM, whereas stearate did not suppress the fusion and translocation of GLUT4 storage, indicating that elaidate has suppressive effects on the accumulation of Akt and fusion of GLUT4 storage vesicles and that both elaidate and stearate vary in the mechanisms by which they impair insulin-dependent glucose uptake.

Metabolic implication of tigecycline as an efficacious second-line treatment for sorafenib-resistant hepatocellular carcinoma

Sorafenib represents the current standard of care for patients with advanced-stage hepatocellular carcinoma (HCC). However, acquired drug resistance occurs frequently during therapy and is accompanied by rapid tumor regrowth after sorafenib therapy termination. To identify the mechanism of this therapy-limiting growth resumption, we established robust sorafenib resistance HCC cell models that exhibited mitochondrial dysfunction and chemotherapeutic crossresistance. We found a rapid relapse of tumor cell proliferation after sorafenib withdrawal, which was caused by renewal of mitochondrial structures alongside a metabolic switch toward high electron transport system (ETS) activity. The translation-inhibiting antibiotic tigecycline impaired the biogenesis of mitochondrial DNA-encoded ETS subunits and limited the electron acceptor turnover required for glutamine oxidation. Thereby, tigecycline prevented the tumor relapse in vitro and in murine xenografts in vivo. These results offer a promising second-line therapeutic approach for advanced-stage HCC patients with progressive disease undergoing sorafenib therapy or treatment interruption due to severe adverse events.

Phospholipid profiling enables to discriminate tumor- and non-tumor-derived human colon epithelial cells: Phospholipidome similarities and differences in colon cancer cell lines and in patient-derived cell samples

Identification of changes of phospholipid (PL) composition occurring during colorectal cancer (CRC) development may help us to better understand their roles in CRC cells. Here, we used LC-MS/MS-based PL profiling of cell lines derived from normal colon mucosa, or isolated at distinct stages of CRC development, in order to study alterations of PL species potentially linked with cell transformation. We found that a detailed evaluation of phosphatidylinositol (PI) and phosphatidylserine (PS) classes allowed us to cluster the studied epithelial cell lines according to their origin: i) cells originally derived from normal colon tissue (NCM460, FHC); ii) cell lines derived from colon adenoma or less advanced differentiating adenocarcinoma cells (AA/C1, HT-29); or, iii) cells obtained by in vitro transformation of adenoma cells and advanced colon adenocarcinoma cells (HCT-116, AA/C1/SB10, SW480, SW620). Although we tentatively identified several PS and PI species contributing to cell line clustering, full PI and PS profiles appeared to be a key to the successful cell line discrimination. In parallel, we compared PL composition of primary epithelial (EpCAM-positive) cells, isolated from tumor and adjacent non-tumor tissues of colon cancer patients, with PL profiles of cell lines derived from normal colon mucosa (NCM460) and from colon adenocarcinoma (HCT-116, SW480) cells, respectively. In general, higher total levels of all PL classes were observed in tumor cells. The overall PL profiles of the cell lines, when compared with the respective patient-derived cells, exhibited similarities. Nevertheless, there were also some notable differences in levels of individual PL species. This indicated that epithelial cell lines, derived either from normal colon tissue or from CRC cells, could be employed as models for functional lipidomic analyses of colon cells, albeit with some caution. The biological significance of the observed PL deregulation, or their potential links with specific CRC stages, deserve further investigation.

Integration of lipidomics and metabolomics for in-depth understanding of cellular mechanism and disease progression

Mass spectrometry (MS)-based omics technologies are now widely used to profile small molecules in multiple matrices to confer comprehensive snapshots of cellular metabolic phenotypes. The metabolomes of cells, tissues, and organisms comprise a variety of molecules including lipids, amino acids, sugars, organic acids, and so on. Metabolomics mainly focus on the hydrophilic classes, while lipidomics has emerged as an independent omics owing to the complexities of the organismal lipidomes. The potential roles of lipids and small metabolites in disease pathogenesis have been widely investigated in various human diseases, but system-level understanding is largely lacking, which could be partly attributed to the insufficiency in terms of metabolite coverage and quantitation accuracy in current analytical technologies. While scientists are continuously striving to develop high-coverage omics approaches, integration of metabolomics and lipidomics is becoming an emerging approach to mechanistic investigation. Integration of metabolome and lipidome offers a complete atlas of the metabolic landscape, enabling comprehensive network analysis to identify critical metabolic drivers in disease pathology, facilitating the study of interconnection between lipids and other metabolites in disease progression. In this review, we summarize omics-based findings on the roles of lipids and metabolites in the pathogenesis of selected major diseases threatening public health. We also discuss the advantages of integrating lipidomics and metabolomics for in-depth understanding of molecular mechanism in disease pathogenesis.

Aneuploidy-inducing gene knockdowns overlap with cancer mutations and identify Orp3 as a B-cell lymphoma suppressor

Aneuploidy can instigate tumorigenesis. However, mutations in genes that control chromosome segregation are rare in human tumors as these mutations reduce cell fitness. Screening experiments indicate that the knockdown of multiple classes of genes that are not directly involved in chromosome segregation can lead to aneuploidy induction. The possible contribution of these genes to cancer formation remains yet to be defined. Here we identified gene knockdowns that lead to an increase in aneuploidy in checkpoint-deficient human cancer cells. Computational analysis revealed that the identified genes overlap with recurrent mutations in human cancers. The knockdown of the three strongest selected candidate genes (ORP3, GJB3, and RXFP1) enhances the malignant transformation of human fibroblasts in culture. Furthermore, the knockout of Orp3 results in an aberrant expansion of lymphoid progenitor cells and a high penetrance formation of chromosomal instable, pauci-clonal B-cell lymphoma in aging mice. At pre-tumorous stages, lymphoid cells from the animals exhibit deregulated phospholipid metabolism and an aberrant induction of proliferation regulating pathways associating with increased aneuploidy in hematopoietic progenitor cells. Together, these results support the concept that aneuploidy-inducing gene deficiencies contribute to cellular transformation and carcinogenesis involving the deregulation of various molecular processes such as lipid metabolism, proliferation, and cell survival.

Fatty Liver Due to Increased de novo Lipogenesis: Alterations in the Hepatic Peroxisomal Proteome

In non-alcoholic fatty liver disease (NAFLD) caused by ectopic lipid accumulation, lipotoxicity is a crucial molecular risk factor. Mechanisms to eliminate lipid overflow can prevent the liver from functional complications. This may involve increased secretion of lipids or metabolic adaptation to ß-oxidation in lipid-degrading organelles such as mitochondria and peroxisomes. In addition to dietary factors, increased plasma fatty acid levels may be due to increased triglyceride synthesis, lipolysis, as well as de novo lipid synthesis (DNL) in the liver. In the present study, we investigated the impact of fatty liver caused by elevated DNL, in a transgenic mouse model with liver-specific overexpression of human sterol regulatory element-binding protein-1c (alb-SREBP-1c), on hepatic gene expression, on plasma lipids and especially on the proteome of peroxisomes by omics analyses, and we interpreted the results with knowledge-based analyses. In summary, the increased hepatic DNL is accompanied by marginal gene expression changes but massive changes in peroxisomal proteome. Furthermore, plasma phosphatidylcholine (PC) as well as lysoPC species were altered. Based on these observations, it can be speculated that the plasticity of organelles and their functionality may be directly affected by lipid overflow.

A lipidomic workflow capable of resolving sn- and C[double bond, length as m-dash]C location isomers of phosphatidylcholines

As a major class of mammalian lipids, phosphatidylcholines (PCs) often contain mixtures of structural isomers, resulting from different lipogenesis pathways. Profiling PCs at the isomer level, however, remains challenging in lipidomic settings, especially for characterizing the positions of fatty acyls on the glycerol backbone (sn-positions) and the locations of carbon-carbon double bonds (C[double bond, length as m-dash]Cs) in unsaturated acyl chains. In this work, we have developed a workflow for profiling PCs down to sn- and C[double bond, length as m-dash]C locations at high coverage and sensitivity. This capability is enabled by radical-directed fragmentation, forming sn-1 specific fragment ions upon collision-induced dissociation (CID) of bicarbonate anion adducts of PCs ([M + HCO₃]^-) inside a mass spectrometer. This new tandem mass spectrometry (MS/MS) method can be simply incorporated into liquid chromatography by employing ammonium bicarbonate in the mobile phase without any instrument modification needed. It is also compatible with the online Paternò-Büchì reaction and subsequent MS/MS for the assignment of C[double bond, length as m-dash]C locations in sn-1 fatty acyl chains of unsaturated PCs. The analytical performance of the workflow is manifested by identification of 82 distinct PC molecular species from the polar extract of bovine liver, including quantification of 19 pairs of sn-isomers. Finally, we demonstrate that five pairs of PC sn-isomers show significant compositional changes in tissue samples of human breast cancer relative to controls, suggesting a potential for monitoring PC sn-isomers for biomedical applications.

A role for phosphatidylcholine and phosphatidylethanolamine in hepatic insulin signaling

Phosphatidylethanolamine N-methyltransferase (PEMT) is an important enzyme in hepatic phosphatidylcholine (PC) biosynthesis. Pemt^-/- mice fed a high-fat diet are protected from obesity and whole-body insulin resistance. However, Pemt^-/- mice develop severe nonalcoholic steatohepatitis (NASH). Because NASH is often associated with hepatic insulin resistance, we investigated whether the increased insulin sensitivity in Pemt^-/- mice was restricted to nonhepatic tissues or whether the liver was also insulin sensitive. Strikingly, the livers of Pemt^-/- mice compared with those of Pemt^+/+ mice were not insulin resistant, despite elevated levels of hepatic triacylglycerols and diacylglycerols, as well as increased hepatic inflammation and fibrosis. Endogenous glucose production was lower in Pemt^-/- mice under both basal and hyperinsulinemic conditions. Experiments in primary hepatocytes and hepatoma cells revealed improved insulin signaling in the absence of PEMT, which was not due to changes in diacylglycerols, ceramides, or gangliosides. On the other hand, the phospholipid composition in hepatocytes seems critically important for insulin signaling such that lowering the PC:phosphatidylethanolamine (PE) ratio improves insulin signaling. Thus, treatments to reduce the PC:PE ratio in liver may protect against the development of hepatic insulin resistance.-Van der Veen, J. N., Lingrell, S., McCloskey, N., LeBlond, N. D., Galleguillos, D., Zhao, Y. Y., Curtis, J. M., Sipione, S., Fullerton, M. D., Vance, D. E., Jacobs, R. L. A role for phosphatidylcholine and phosphatidylethanolamine in hepatic insulin signaling.

Metabolomics of Green-Tea Catechins on Vascular-Endothelial-Growth-Factor-Stimulated Human-Endothelial-Cell Survival

Neovascularization causes serious oculopathy related to upregulation of vascular-endothelial-growth factor (VEGF) causing new capillary growth via endothelial cells. Green-tea-extract (GTE) constituents possess antiangiogenesis properties. We used VEGF to induce human umbilical-vein endothelial cells (HUVECs) and applied GTE, epigallocatechin gallate (EGCG), and mixtures of different compositions of purified catechins (M1 and M2) to evaluate their efficacies of inhibition and their underlying mechanisms using cell-cycle analysis and untargeted metabolomics techniques. GTE, EGCG, M1, and M2 induced HUVEC apoptosis by 22.1 ± 2, 20.0 ± 0.7, 50.7 ± 8.5, and 69.8 ± 4.1%, respectively. GTE exerted a broad, balanced metabolomics spectrum, involving suppression of the biosynthesis of cellular building blocks and oxidative-phosphorylation metabolites as well as promotion of the biosynthesis of membrane lipids and growth factors. M2 mainly induced mechanisms associated with energy and biosynthesis suppression. Therefore, GTE exerted mechanisms involving both promotion and suppression activities, whereas purified catechins induced extensive apoptosis. GTE could be a more promising antineovascularization remedy for ocular treatment.

Phospholipid Remodeling in Physiology and Disease

Phospholipids are major constituents of biological membranes. The fatty acyl chain composition of phospholipids determines the biophysical properties of membranes and thereby affects their impact on biological processes. The composition of fatty acyl chains is also actively regulated through a deacylation and reacylation pathway called Lands' cycle. Recent studies of mouse genetic models have demonstrated that lysophosphatidylcholine acyltransferases (LPCATs), which catalyze the incorporation of fatty acyl chains into the sn-2 site of phosphatidylcholine, play important roles in pathophysiology. Two LPCAT family members, LPCAT1 and LPCAT3, have been particularly well studied. LPCAT1 is crucial for proper lung function due to its role in pulmonary surfactant biosynthesis. LPCAT3 maintains systemic lipid homeostasis by regulating lipid absorption in intestine, lipoprotein secretion, and de novo lipogenesis in liver. Mounting evidence also suggests that changes in LPCAT activity may be potentially involved in pathological conditions, including nonalcoholic fatty liver disease, atherosclerosis, viral infections, and cancer. Pharmacological manipulation of LPCAT activity and membrane phospholipid composition may provide new therapeutic options for these conditions.

Liver X receptors in lipid signalling and membrane homeostasis

Liver X receptors α and β (LXRα and LXRβ) are nuclear receptors with pivotal roles in the transcriptional control of lipid metabolism. Transcriptional activity of LXRs is induced in response to elevated cellular levels of cholesterol. LXRs bind to and regulate the expression of genes that encode proteins involved in cholesterol absorption, transport, efflux, excretion and conversion to bile acids. The coordinated, tissue-specific actions of the LXR pathway maintain systemic cholesterol homeostasis and regulate immune and inflammatory responses. LXRs also regulate fatty acid metabolism by controlling the lipogenic transcription factor sterol regulatory element-binding protein 1c and regulate genes that encode proteins involved in fatty acid elongation and desaturation. LXRs exert important effects on the metabolism of phospholipids, which, along with cholesterol, are major constituents of cellular membranes. LXR activation preferentially drives the incorporation of polyunsaturated fatty acids into phospholipids by inducing transcription of the remodelling enzyme lysophosphatidylcholine acyltransferase 3. The ability of the LXR pathway to couple cellular sterol levels with the saturation of fatty acids in membrane phospholipids has implications for several physiological processes, including lipoprotein production, dietary lipid absorption and intestinal stem cell proliferation. Understanding how LXRs regulate membrane composition and function might provide new therapeutic insight into diseases associated with dysregulated lipid metabolism, including atherosclerosis, diabetes mellitus and cancer.

Cytochrome c is an oxidative stress-activated plasmalogenase that cleaves plasmenylcholine and plasmenylethanolamine at the sn-1 vinyl ether linkage

Plasmalogens are phospholipids critical for cell function and signaling that contain a vinyl ether linkage at the sn-1 position and are highly enriched in arachidonic acid (AA) at the sn-2 position. However, the enzyme(s) responsible for the cleavage of the vinyl ether linkage in plasmalogens has remained elusive. Herein, we report that cytochrome c, in the presence of either cardiolipin (CL), O₂ and H₂O₂, or oxidized CL and O₂, catalyzes the oxidation of the plasmalogen vinyl ether linkage, promoting its hydrolytic cleavage and resultant production of 2-AA-lysolipids and highly reactive α-hydroxy fatty aldehydes. Using stable isotope labeling in synergy with strategic chemical derivatizations and high-mass-accuracy MS, we deduced the chemical mechanism underlying this long sought-after reaction. Specifically, labeling with either ¹⁸O₂ or H₂¹⁸O, but not with H₂¹⁸O₂, resulted in M + 2 isotopologues of the α-hydroxyaldehyde, whereas reactions with both ¹⁸O₂ and H₂¹⁸O identified the M + 4 isotopologue. Furthermore, incorporation of ¹⁸O from ¹⁸O₂ was predominantly located at the α-carbon. In contrast, reactions with H₂¹⁸O yielded ¹⁸O linked to the aldehyde carbon. Importantly, no significant labeling of 2-AA-lysolipids with ¹⁸O₂, H₂¹⁸O, or H₂¹⁸O₂ was present. Intriguingly, phosphatidylinositol phosphates (PIP₂ and PIP₃) effectively substituted for cardiolipin. Moreover, cytochrome c released from myocardial mitochondria subjected to oxidative stress cleaved plasmenylcholine in membrane bilayers, and this was blocked with a specific mAb against cytochrome c Collectively, these results identify the first plasmalogenase in biology, reveal the production of previously unanticipated signaling lipids by cytochrome c, and present new perspectives on cellular signaling during oxidative stress.

Phospholipid Remodeling and Cholesterol Availability Regulate Intestinal Stemness and Tumorigenesis

Adequate availability of cellular building blocks, including lipids, is a prerequisite for cellular proliferation, but excess dietary lipids are linked to increased cancer risk. Despite these connections, specific regulatory relationships between membrane composition, intestinal stem cell (ISC) proliferation, and tumorigenesis are unclear. We reveal an unexpected link between membrane phospholipid remodeling and cholesterol biosynthesis and demonstrate that cholesterol itself acts as a mitogen for ISCs. Inhibition of the phospholipid-remodeling enzyme Lpcat3 increases membrane saturation and stimulates cholesterol biosynthesis, thereby driving ISC proliferation. Pharmacologic inhibition of cholesterol synthesis normalizes crypt hyperproliferation in Lpcat3-deficient organoids and mice. Conversely, increasing cellular cholesterol content stimulates crypt organoid growth, and providing excess dietary cholesterol or driving endogenous cholesterol synthesis through SREBP-2 expression promotes ISC proliferation in vivo. Finally, disruption of Lpcat3-dependent phospholipid and cholesterol homeostasis dramatically enhances tumor formation in Apc^min mice. These findings identify a critical dietary-responsive phospholipid-cholesterol axis regulating ISC proliferation and tumorigenesis.

Colon Ascendens Stent Peritonitis (CASP) Induces Excessive Inflammation and Systemic Metabolic Dysfunction in a Septic Rat Model

The colon ascendens stent peritonitis (CASP) surgery induces a leakage of gut contents, causing polymicrobial sepsis related to post-operative multiple organ failure and death in surgical patient. To evaluate the effects of CASP on multiple organs, we analyzed the systemic metabolic consequences in liver, kidney, lung, and heart of rats after CASP by employing a combination of metabolomics, clinical chemistry, and biological assays. We found that CASP surgery after 18 h resulted in striking elevations of lipid, amino acids, acetate, choline, PC, and GPC in rat liver together with significant depletion of glucose and glycogen. Marked elevations of organic acids including lactate, acetate, and creatine and amino acids accompanied by decline of glucose, betaine, TMAO, choline metabolites (PC and GPC) nucleotides, and a range of organic osmolytes such as myo-inositol are observed in the kidney of 18 h post-operative rat. Furthermore, 18 h post-operative rats exhibited accumulations of lipid, amino acids, and depletions of taurine, myo-inositol, choline, PC, and GPC and some nucleotides including uridine, inosine, and adenosine in the lung. In addition, significant elevations of some amino acids, uracil, betaine, and choline metabolites, together with depletion of inosine-5'-monophosphate, were only observed in the heart of 18 h post-operative rats. These results provide new insights into pathological consequences of CASP surgery, which are important for timely prognosis of sepsis.

Acetyl-CoA carboxylase 1 regulates endothelial cell migration by shifting the phospholipid composition

The enzyme acetyl-CoA carboxylase (ACC) plays a crucial role in fatty acid metabolism. In recent years, ACC has been recognized as a promising drug target for treating different diseases. However, the role of ACC in vascular endothelial cells (ECs) has been neglected so far. To characterize the role of ACC, we used the ACC inhibitor, soraphen A, as a chemical tool, and also a gene silencing approach. We found that ACC1 was the predominant isoform in human umbilical vein ECs as well as in human microvascular ECs and that soraphen A reduced the levels of malonyl-CoA. We revealed that ACC inhibition shifted the lipid composition of EC membranes. Accordingly, membrane fluidity, filopodia formation, and migratory capacity were reduced. The antimigratory action of soraphen A depended on an increase in the cellular proportion of PUFAs and, most importantly, on a decreased level of phosphatidylglycerol. Our study provides a causal link between ACC, membrane lipid composition, and cell migration in ECs. Soraphen A represents a useful chemical tool to investigate the role of fatty acid metabolism in ECs and ACC inhibition offers a new and valuable therapeutic perspective for the treatment of EC migration-related diseases.

Targeting de novo lipogenesis as a novel approach in anti-cancer therapy

Background:

Although altered membrane physiology has been discussed within the context of cancer, targeting membrane characteristics by drugs being an attractive therapeutic strategy has received little attention so far.

Methods:

Various acetyl-CoA carboxylase 1 (ACC1), and fatty acid synthase (FASN) inhibitors (like Soraphen A and Cerulenin) as well as genetic knockdown approaches were employed to study the effects of disturbed phospholipid composition on membrane properties and its functional impact on cancer progression. By using state-of-the-art methodologies such as LC-MS/MS, optical tweezers measurements of giant plasma membrane vesicles and fluorescence recovery after photobleaching analysis, membrane characteristics were examined. Confocal laser scanning microscopy, proximity ligation assays, immunoblotting as well as migration, invasion and proliferation experiments unravelled the functional relevance of membrane properties in vitro and in vivo.

Results:

By disturbing the deformability and lateral fluidity of cellular membranes, the dimerisation, localisation and recycling of cancer-relevant transmembrane receptors is compromised. Consequently, impaired activation of growth factor receptor signalling cascades results in abrogated tumour growth and metastasis in different in vitro and in vivo models.

Conclusions:

This study highlights the field of membrane properties as a promising druggable cellular target representing an innovative strategy for development of anti-cancer agents.

Do lipids shape the eukaryotic cell cycle?

Successful passage through the cell cycle presents a number of structural challenges to the cell. Inceptive studies carried out in the last five years have produced clear evidence of modulations in the lipid profile (sometimes referred to as the lipidome) of eukaryotes as a function of the cell cycle. This mounting body of evidence indicates that lipids play key roles in the structural transformations seen across the cycle. The accumulation of this evidence coincides with a revolution in our understanding of how lipid composition regulates a plethora of biological processes ranging from protein activity through to cellular signalling and membrane compartmentalisation. In this review, we discuss evidence from biological, chemical and physical studies of the lipid fraction across the cell cycle that demonstrate that lipids are well-developed cellular components at the heart of the biological machinery responsible for managing progress through the cell cycle. Furthermore, we discuss the mechanisms by which this careful control is exercised.

Effects of the dietary carbohydrate-fat ratio on plasma phosphatidylcholine profiles in human and mouse

Phosphatidylcholines (PCs), a major class of human plasma phospholipids, are composed of highly diverse fatty acids. Because the dietary carbohydrate-fat ratio alters the hepatic fatty acid metabolism, plasma fatty acids that bind PCs, which are secreted as lipoproteins from the liver, may be affected by long-term consumption of a high-carbohydrate diet or a high-fat diet. Therefore, in this study, we profiled the plasma PC species comprehensively in formulated dieting conditions to identify those phospholipid molecules that reflect the dietary carbohydrate-fat ratio. C57BL6J mice were fed diets containing different amounts of fat for 8 weeks, and plasma PC species were analyzed under fasting conditions using liquid chromatography-mass spectrometry. In addition, a cross-sectional study of 78 middle-aged Japanese men, who participated in health checkups, was conducted. Nutrient intakes were estimated by a brief self-administered diet-history questionnaire. The plasma PC profiles changed depending on the dietary carbohydrate-fat ratio. Especially, PC (16:0/16:1) and PC (16:0/18:1) levels increased as the dietary carbohydrate-fat ratio increased in human and mouse, suggesting that these PC species reflected the increase in de novo lipogenesis and might become useful biomarkers of the dietary carbohydrate-fat ratio. Since these PCs act as ligands for peroxisome proliferator-activated receptor α, PC species reflecting the dietary carbohydrate-fat ratio may influence metabolism of glucose and lipids.

Vitamin A regulates Akt signaling through the phospholipid fatty acid composition

Protein kinases, including the serine/threonine kinase Akt, mediate manifold bioactivities of vitamin A, although the mechanisms behind the sustained kinase activation are diffuse. To investigate the role of cellular lipids as targetable factors in Akt signaling, we combined mass spectrometry-based lipidomics with immunologic detection of Akt (Ser473) phosphorylation. A screening campaign revealed retinol (vitamin A alcohol) and all-trans retinoic acid (vitamin A acid) (RA) as hits that time-dependently (≥24 h) deplete phosphatidylcholine-bound polyunsaturated fatty acids (PUFA-PCs) from NIH-3T3 mouse fibroblasts while inducing Akt activation (EC₅₀ ≈ 0.1-1 µM). Other mitogenic and stress-regulated kinases were hardly affected. Organized in a coregulated phospholipid subcluster, PUFA-PCs compensated for the RA-induced loss of cellular PUFA-PCs and diminished Akt activation when supplemented. The counter-regulation of phospholipids and Akt by RA was mimicked by knockdown of lysophosphatidylcholine acyltransferase-3 or the selective retinoid X receptor (RXR) agonist bexarotene and prevented by the selective RXR antagonist Hx531. Treatment of mice with retinol decreased the tissue ratio of PUFA-PC and enhanced basal Akt activation preferentially in brain, which was attributed to astrocytes in dissociated cortical cultures. Together, our findings show that RA regulates the long-term activation of Akt by changes in the phospholipid composition.-Pein, H., Koeberle, S. C., Voelkel, M., Schneider, F., Rossi, A., Thürmer, M., Loeser, K., Sautebin, L., Morrison, H., Werz, O., Koeberle, A. Vitamin A regulates Akt signaling through the phospholipid fatty acid composition.

Miscibility Transition Temperature Scales with Growth Temperature in a Zebrafish Cell Line

Cells can alter the lipid content of their plasma membranes upon changes in their environment to maintain and adjust membrane function. Recent work suggests that some membrane functions arise because cellular plasma membranes are poised close to a miscibility transition under growth conditions. Here we report experiments utilizing giant plasma membrane vesicles (GPMVs) to explore how membrane transition temperature varies with growth temperature in a zebrafish cell line (ZF4) that can be adapted for growth between 20 and 32°C. We find that GPMV transition temperatures adjust to be 16.7 ± 1.2°C below growth temperature for four growth temperatures investigated and that adjustment occurs over roughly 2 days when temperature is abruptly lowered from 28 to 20°C. We also find that GPMVs have slightly different lipidomes when isolated from cells adapted for growth at 28 and 20°C. Similar to past work in vesicles derived from mammalian cells, fluctuating domains are observed in ZF4-derived GPMVs, consistent with their having critical membrane compositions. Taken together, these experimental results suggest that cells in culture biologically tune their membrane composition in a way that maintains specific proximity to a critical miscibility transition.

Cyclin-dependent kinase activity enhances phosphatidylcholine biosynthesis in Arabidopsis by repressing phosphatidic acid phosphohydrolase activity

Coordination of endomembrane biogenesis with cell cycle progression is considered to be important in maintaining cell function during growth and development. We previously showed that the disruption of PHOSPHATIDIC ACID PHOSPHOHYDROLASE (PAH) activity in Arabidopsis thaliana stimulates biosynthesis of the major phospholipid phosphatidylcholine (PC) and causes expansion of the endoplasmic reticulum. Here we show that PC biosynthesis is repressed by disruption of the core cell cycle regulator CYCLIN-DEPENDENT KINASE A;1 (CDKA;1) and that this repression is reliant on PAH. Furthermore, we show that cyclin-dependent kinases (CDKs) phosphorylate PAH1 at serine 162, which reduces both its activity and membrane association. Expression of a CDK-insensitive version of PAH1 with a serine 162 to alanine substitution represses PC biosynthesis and also reduces the rate of cell division in early leaf development. Together our findings reveal a physiologically important mechanism that couples the rate of phospholipid biosynthesis and endomembrane biogenesis to cell cycle progression in Arabidopsis.

Visualization of sphingolipids and phospholipids in the fundic gland mucosa of human stomach using imaging mass spectrometry

AIM: To analyze the lipid distribution in gastric mucosae.

METHODS: Imaging mass spectrometry (MS) is a useful tool to survey the distribution of biomolecules in surgical specimens. Here we used the imaging MS apparatus named iMScope to identify the dominant molecules present in the human gastric mucosa near the fundic glands. Five gastric specimens were subjected to iMScope analysis. These specimens were also analyzed by immunohistochemistry using MUC5AC, H(+)-K(+)-ATPaseβ Claudin18 antibodies.

RESULTS: Three major molecules with m/z 725.5, 780.5, and 782.5 detected in the gastric mucosa were identified as sphingomyelin (SM) (d18:1/16:0), phosphatidylcholine (PC) (16:0/18:2), and PC (16:0/18:1), respectively, through MS/MS analyses. Using immunohistological staining, SM (d18:1/16:0) signals were mainly co-localized with the foveolar epithelium marker MUC5AC. In contrast, PC (16:0/18:2) signals were observed in the region testing positive for the fundic gland marker H(+)-K(+)-ATPaseβ. PC (16:0/18:1) signals were uniformly distributed throughout the mucosa.

CONCLUSION: Our basic data will contribute to the studies of lipid species in physical and pathological conditions of the human stomach.

Lipid unsaturation and organelle dynamics

The number of double bonds (=unsaturation) in the acyl chains of phospholipids (PL) influences the physical properties of cellular membranes. Here, we discuss disparate molecular processes, including vesicle budding, ion channel opening, and lipoprotein formation, which are greatly facilitated by PL polyunsaturation in membranes. Experimental and computer-based approaches for the structure and dynamics of PL suggest a common cause for these effects: the ability of the polyunsaturated acyl chain of PL to extend or bent along the membrane normal according to various constraints, thereby enabling a third dimension of motion in a structure that is essentially a 2D fluid.