Regular Research Articles
Identification and characterization of LPLAT7 as an sn-1-specific lysophospholipid acyltransferase
The main fatty acids at the sn-1 position of phospholipids (PLs) are saturated or monounsaturated fatty acids such as palmitic acid (C16:0), stearic acid (C18:0), and oleic acid (C18:1) and are constantly replaced, like unsaturated fatty acids at the sn-2 position. However, little is known about the molecular mechanism underlying the replacement of fatty acids at the sn-1 position, i.e., the sn-1 remodeling. Previously, we established a method to evaluate the incorporation of fatty acids into the sn-1 position of lysophospholipids (lyso-PLs).Adaptations of the 3T3-L1 adipocyte lipidome to defective ether lipid catabolism upon Agmo knockdown
Little is known about the physiological role of alkylglycerol monooxygenase (AGMO), the only enzyme capable of cleaving the 1-O-alkyl ether bond of ether lipids. Expression and enzymatic activity of this enzyme can be detected in a variety of tissues including adipose tissue. This labile lipolytic membrane-bound protein uses tetrahydrobiopterin as a cofactor, and mice with reduced tetrahydrobiopterin levels have alterations in body fat distribution and blood lipid concentrations. In addition, manipulation of AGMO in macrophages led to significant changes in the cellular lipidome, and alkylglycerolipids, the preferred substrates of AGMO, were shown to accumulate in mature adipocytes.Isomeric lipid signatures reveal compartmentalized fatty acid metabolism in cancer
The cellular energy and biomass demands of cancer drive a complex dynamic between uptake of extracellular FAs and their de novo synthesis. Given that oxidation of de novo synthesized FAs for energy would result in net-energy loss, there is an implication that FAs from these two sources must have distinct metabolic fates; however, hitherto, all FAs have been considered part of a common pool. To probe potential metabolic partitioning of cellular FAs, cancer cells were supplemented with stable isotope-labeled FAs.The SARS-CoV2 envelope differs from host cells, exposes procoagulant lipids, and is disrupted in vivo by oral rinses
The lipid envelope of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is an essential component of the virus; however, its molecular composition is undetermined. Addressing this knowledge gap could support the design of antiviral agents as well as further our understanding of viral-host protein interactions, infectivity, pathogenicity, and innate immune system clearance. Lipidomics revealed that the virus envelope comprised mainly phospholipids (PLs), with some cholesterol and sphingolipids, and with cholesterol/phospholipid ratio similar to lysosomes.Determination of tissue contributions to the circulating lipid pool in cold exposure via systematic assessment of lipid profiles
Plasma lipid levels are altered in chronic conditions such as type 2 diabetes and cardiovascular disease as well as during acute stresses such as fasting and cold exposure. Advances in MS-based lipidomics have uncovered a complex plasma lipidome of more than 500 lipids that serve functional roles, including as energy substrates and signaling molecules. This plasma lipid pool is maintained through regulation of tissue production, secretion, and uptake. A major challenge in understanding the lipidome complexity is establishing the tissues of origin and uptake for various plasma lipids, which is valuable for determining lipid functions.Impact of pasteurization on the self-assembly of human milk lipids during digestion
Human milk is critical for the survival and development of infants. This source of nutrition contains components that protect against infections while stimulating immune maturation. In cases where the mother's own milk is unavailable, pasteurized donor milk is the preferred option. Although pasteurization has been shown to have minimal impact on the lipid and FA composition before digestion, no correlation has been made between the impact of pasteurization on the FFA composition and the self-assembly of lipids during digestion, which could act as delivery mechanisms for poorly water-soluble components.KIAA1363 affects retinyl ester turnover in cultured murine and human hepatic stellate cells
Large quantities of vitamin A are stored as retinyl esters (REs) in specialized liver cells, the hepatic stellate cells (HSCs). To date, the enzymes controlling RE degradation in HSCs are poorly understood. In this study, we identified KIAA1363 (also annotated as arylacetamide deacetylase 1 or neutral cholesterol ester hydrolase 1) as a novel RE hydrolase. We show that KIAA1363 is expressed in the liver, mainly in HSCs, and exhibits RE hydrolase activity at neutral pH. Accordingly, addition of the KIAA1363-specific inhibitor JW480 largely reduced RE hydrolase activity in lysates of cultured murine and human HSCs.Apolipoprotein F concentration, activity, and the properties of LDL controlling ApoF activation in hyperlipidemic plasma
Apolipoprotein F (ApoF) modulates lipoprotein metabolism by selectively inhibiting cholesteryl ester transfer protein activity on LDL. This ApoF activity requires that it is bound to LDL. How hyperlipidemia alters total plasma ApoF and its binding to LDL are poorly understood. In this study, total plasma ApoF and LDL-bound ApoF were quantified by ELISA (n = 200). Plasma ApoF was increased 31% in hypercholesterolemic plasma but decreased 20% in hypertriglyceridemia. However, in donors with combined hypercholesterolemia and hypertriglyceridemia, the elevated triglyceride ameliorated the rise in ApoF caused by hypercholesterolemia alone.Mass spectrometry imaging of phosphatidylcholine metabolism in lungs administered with therapeutic surfactants and isotopic tracers
Mass spectrometry imaging (MSI) visualizes molecular distributions throughout tissues but is blind to dynamic metabolic processes. Here, MSI with high mass resolution together with multiple stable isotope labeling provided spatial analyses of phosphatidylcholine (PC) metabolism in mouse lungs. Dysregulated surfactant metabolism is central to many respiratory diseases. Metabolism and turnover of therapeutic pulmonary surfactants were imaged from distributions of intact and metabolic products of an added tracer, universally 13C-labeled dipalmitoyl PC (U13C-DPPC).Lipid remodeling in response to methionine stress in MDA-MBA-468 triple-negative breast cancer cells
Methionine (Met) is an essential amino acid and critical precursor to the cellular methyl donor S-adenosylmethionine. Unlike nontransformed cells, cancer cells have a unique metabolic requirement for Met and are unable to proliferate in growth media where Met is replaced with its metabolic precursor, homocysteine. This metabolic vulnerability is common among cancer cells regardless of tissue origin and is known as “methionine dependence”, “methionine stress sensitivity”, or the Hoffman effect. The response of lipids to Met stress, however, is not well-understood.Octanoate is differentially metabolized in liver and muscle and fails to rescue cardiomyopathy in CPT2 deficiency
Long-chain fatty acid oxidation is frequently impaired in primary and systemic metabolic diseases affecting the heart; thus, therapeutically increasing reliance on normally minor energetic substrates, such as ketones and medium-chain fatty acids, could benefit cardiac health. However, the molecular fundamentals of this therapy are not fully known. Here, we explored the ability of octanoate, an eight-carbon medium-chain fatty acid known as an unregulated mitochondrial energetic substrate, to ameliorate cardiac hypertrophy in long-chain fatty acid oxidation-deficient hearts because of carnitine palmitoyltransferase 2 deletion (Cpt2M−/−).Endothelial ether lipids link the vasculature to blood pressure, behavior, and neurodegeneration
Vascular disease contributes to neurodegeneration, which is associated with decreased blood pressure in older humans. Plasmalogens, ether phospholipids produced by peroxisomes, are decreased in Alzheimer's disease, Parkinson's disease, and other neurodegenerative disorders. However, the mechanistic links between ether phospholipids, blood pressure, and neurodegeneration are not fully understood. Here, we show that endothelium-derived ether phospholipids affect blood pressure, behavior, and neurodegeneration in mice.Monomeric bile acids modulate the ATPase activity of detergent-solubilized ABCB4/MDR3
ABCB4, also called multidrug-resistant protein 3 (MDR3), is an ATP binding cassette transporter located in the canalicular membrane of hepatocytes that specifically translocates phosphatidylcholine (PC) lipids from the cytoplasmic to the extracellular leaflet. Due to the harsh detergent effect of bile acids, PC lipids provided by ABCB4 are extracted into the bile. While it is well known that bile acids are the major extractor of PC lipids from the membrane into bile, it is unknown whether only PC lipid extraction is improved or whether bile acids also have a direct effect on ABCB4.Shark liver oil supplementation enriches endogenous plasmalogens and reduces markers of dyslipidemia and inflammation
Plasmalogens are membrane glycerophospholipids with diverse biological functions. Reduced plasmalogen levels have been observed in metabolic diseases; hence, increasing their levels might be beneficial in ameliorating these conditions. Shark liver oil (SLO) is a rich source of alkylglycerols that can be metabolized into plasmalogens. This study was designed to evaluate the impact of SLO supplementation on endogenous plasmalogen levels in individuals with features of metabolic disease. In this randomized, double-blind, placebo-controlled cross-over study, the participants (10 overweight or obese males) received 4-g Alkyrol® (purified SLO) or placebo (methylcellulose) per day for 3 weeks followed by a 3-week washout phase and were then crossed over to 3 weeks of the alternate placebo/Alkyrol® treatment.Apolipoprotein A-I modulates HDL particle size in the absence of apolipoprotein A-II
Human high-density lipoproteins (HDLs) are a complex mixture of structurally related nanoparticles that perform distinct physiological functions. We previously showed that human HDL containing apolipoprotein A-I (APOA1) but not apolipoprotein A-II (APOA2), designated LpA-I, is composed primarily of two discretely sized populations. Here, we isolated these particles directly from human plasma by antibody affinity chromatography, separated them by high-resolution size-exclusion chromatography and performed a deep molecular characterization of each species.Differential contributions of choline phosphotransferases CPT1 and CEPT1 to the biosynthesis of choline phospholipids
Choline phospholipids (PLs) such as phosphatidylcholine (PC) and 1-alkyl-2-acyl-sn-glycerophosphocholine are important components for cell membranes and also serve as a source of several lipid mediators. These lipids are biosynthesized in mammals in the final step of the CDP-choline pathway by the choline phosphotransferases choline phosphotransferase 1 (CPT1) and choline/ethanolamine phosphotransferase 1 (CEPT1). However, the contributions of these enzymes to the de novo biosynthesis of lipids remain unknown.Nonalcoholic fatty liver disease stratification by liver lipidomics
Nonalcoholic fatty liver disease (NAFLD) is a common metabolic dysfunction leading to hepatic steatosis. However, NAFLD's global impact on the liver lipidome is poorly understood. Using high-resolution shotgun mass spectrometry, we quantified the molar abundance of 316 species from 22 major lipid classes in liver biopsies of 365 patients, including nonsteatotic patients with normal or excessive weight, patients diagnosed with NAFL (nonalcoholic fatty liver) or NASH (nonalcoholic steatohepatitis), and patients bearing common mutations of NAFLD-related protein factors.Platelets induce free and phospholipid-esterified 12-hydroxyeicosatetraenoic acid generation in colon cancer cells by delivering 12-lipoxygenase
Platelets promote tumor metastasis by inducing promalignant phenotypes in cancer cells and directly contributing to cancer-related thrombotic complications. Platelet-derived extracellular vesicles (EVs) can promote epithelial-mesenchymal transition (EMT) in cancer cells, which confers high-grade malignancy. 12S-hydroxyeicosatetraenoic acid (12-HETE) generated by platelet-type 12-lipoxygenase (12-LOX) is considered a key modulator of cancer metastasis through unknown mechanisms. In platelets, 12-HETE can be esterified into plasma membrane phospholipids (PLs), which drive thrombosis.The maternal blood lipidome is indicative of the pathogenesis of severe preeclampsia
Preeclampsia is a pregnancy-specific syndrome characterized by hypertension and proteinuria after 20 weeks of gestation. However, it is not well understood what lipids are involved in the development of this condition, and even less is known how these lipids mediate its formation. To reveal the relationship between lipids and preeclampsia, we conducted lipidomic profiling of maternal sera of 44 severe preeclamptic and 20 healthy pregnant women from a multiethnic cohort in Hawaii. Correlation network analysis showed that oxidized phospholipids have increased intercorrelations and connections in preeclampsia, whereas other lipids, including triacylglycerols, have reduced network correlations and connections.Vitamin D deficiency promotes accumulation of bioactive lipids and increased endocannabinoid tone in zebrafish
Vitamin D is well known for its traditional role in bone mineral homeostasis; however, recent evidence suggests that vitamin D also plays a significant role in metabolic control. This study served to investigate putative linkages between vitamin D deficiency (VDD) and metabolic disruption of bioactive lipids by MS imaging. Our approach employed infrared-matrix-assisted laser desorption electrospray ionization MS imaging for lipid metabolite profiling in 6-month-old zebrafish fed either a VDD or a vitamin D-sufficient (VDS) diet.Amodiaquine promotes testosterone production and de novo synthesis of cholesterol and triglycerides in Leydig cells
Testosterone is a hormone essential for male reproductive function. It is produced primarily by Leydig cells in the testicle through activation of steroidogenic acute regulatory protein and a series of steroidogenic enzymes, including a cytochrome P450 side-chain cleavage enzyme (cytochome P450 family 11 subfamily A member 1), 17α-hydroxylase (cytochrome P450 family 17 subfamily A member 1), and 3β-hydroxysteroid dehydrogenase. These steroidogenic enzymes are mainly regulated at the transcriptional level, and their expression is increased by the nuclear receptor 4A1.Hepatic deletion of Mboat7 (LPIAT1) causes activation of SREBP-1c and fatty liver
Genetic variants that increase the risk of fatty liver disease and cirrhosis have recently been identified in the proximity of membrane-bound O-acyltransferase domain-containing 7 (MBOAT7). To elucidate the link between these variants and fatty liver disease, we characterized Mboat7 liver-specific KO mice (Mboat7 LSKO). Chow-fed Mboat7 LSKO mice developed fatty livers and associated liver injury. Lipidomic analysis of liver using MS revealed a pronounced reduction in 20-carbon PUFA content in phosphatidylinositols (PIs) but not in other phospholipids.Lipid signature of advanced human carotid atherosclerosis assessed by mass spectrometry imaging
Carotid atherosclerosis is a risk factor for ischemic stroke, one of the main causes of mortality and disability worldwide. The disease is characterized by plaques, heterogeneous deposits of lipids, and necrotic debris in the vascular wall, which grow gradually and may remain asymptomatic for decades. However, at some point a plaque can evolve to a high-risk plaque phenotype, which may trigger a cerebrovascular event. Lipids play a key role in the development and progression of atherosclerosis, but the nature of their involvement is not fully understood.Deletion of lysophosphatidylcholine acyltransferase 3 in myeloid cells worsens hepatic steatosis after a high-fat diet
Recent studies have highlighted an important role for lysophosphatidylcholine acyltransferase 3 (LPCAT3) in controlling the PUFA composition of cell membranes in the liver and intestine. In these organs, LPCAT3 critically supports cell-membrane-associated processes such as lipid absorption or lipoprotein secretion. However, the role of LPCAT3 in macrophages remains controversial. Here, we investigated LPCAT3's role in macrophages both in vitro and in vivo in mice with atherosclerosis and obesity.
