Journal of Lipid Research最新文献

Plasma high-density lipoprotein (HDL), originally studied for its role in lipid transport, is now appreciated to have wide-ranging biological functions that become defective during disease. While >200 lipids have collectively been detected in HDL, published HDL lipidomic analyses in different diseases have commonly been targeted to prespecified subsets of lipids. Here, we report the results of untargeted lipidomic analysis of HDL isolated from 101 subjects referred for computed tomographic coronary imaging for whom multiple additional clinical and lipoprotein metadata were measured. Unsupervised clustering of the total HDL lipidome revealed that the subjects fell into one of two discrete groups, herein referred to as HDL "metabotypes." Patients in metabotype 1 were likelier to be female and tended to have a less atherogenic lipoprotein profile, higher HDL cholesterol efflux capacity (CEC), and lower-grade non-calcified burden on coronary imaging than metabotype 2 counterparts. Specific lipids were relatively enriched in metabotype 1 HDL. Linear modeling revealed that several of these lipids were positively associated with CEC, statin use, HDL size, and HDL particle number, and positively correlated with HDL apolipoprotein A-1, suggesting that they may be informative HDL biomarkers. Taken together, we posit a novel, clinically relevant categorization for HDL revealed by systems biology.

The ability of high-density lipoprotein (HDL) to promote cellular cholesterol efflux is a more robust predictor of cardiovascular disease protection than HDL-cholesterol levels in plasma. Previously, we found that lipidated HDL containing both apolipoprotein A-I (APOA1) and A-II (APOA2) promotes cholesterol efflux via the ATP-binding cassette transporter (ABCA1). In the current study, we directly added purified, lipid-free APOA2 to human plasma and found a dose-dependent increase in whole plasma cholesterol efflux capacity. APOA2 likewise increased the cholesterol efflux capacity of isolated HDL with the maximum effect occurring when equal masses of APOA1 and APOA2 coexisted on the particles. Follow-up experiments with reconstituted HDL corroborated that the presence of both APOA1 and APOA2 were necessary for the increased efflux. Using limited proteolysis and chemical cross-linking mass spectrometry, we found that APOA2 induced a conformational change in the N- and C-terminal helices of APOA1. Using reconstituted HDL with APOA1 deletion mutants, we further showed that APOA2 lost its ability to stimulate ABCA1 efflux to HDL if the C-terminal domain of APOA1 was absent, but retained this ability when the N-terminal domain was absent. Based on these findings, we propose a model in which APOA2 displaces the C-terminal helix of APOA1 from the HDL surface which can then interact with ABCA1-much like it does in lipid-poor APOA1. These findings suggest APOA2 may be a novel therapeutic target given this ability to open a large, high-capacity pool of HDL particles to enhance ABCA1-mediated cholesterol efflux.

De novo lipogenesis (DNL) has been implicated in the development and progression of liver steatosis. Hepatic DNL is strongly influenced by dietary macronutrient composition with diets high in carbohydrate increasing DNL while diets high in fat decrease DNL. The enzymes in the core DNL pathway have been well characterized; however, less is known about other liver proteins that play accessory or regulatory roles. In the current study, we associate measured rates of hepatic DNL and fat content with liver proteomic analysis in mice to identify known and unknown proteins that may have a role in DNL. Male mice were fed either a standard chow diet, a semipurified high starch or high-fat diet. Both semipurified diets resulted in increased body weight, fat mass, and liver triglyceride content compared to chow controls, and hepatic DNL was increased in the high starch and decreased in high fat-fed mice. Proteomic analysis identified novel proteins associated with DNL that are involved in taurine metabolism, suggesting a link between these pathways. There was no relationship between proteins that associated with DNL and those associated with liver triglyceride content. Further analysis identified proteins that are differentially regulated when comparing a nonpurified chow diet to either of the semipurified diets, which provide a set of proteins that are influenced by dietary complexity. Finally, we compared the liver proteome between 4- and 30-week diet-fed mice and found remarkable similarity suggesting that metabolic remodeling of the liver occurs rapidly in response to differing dietary components. Together, these findings highlight novel proteins associated with hepatic DNL independently of liver fat content and suggest rapid liver metabolic remodeling in response to dietary composition changes.

Cellular metabolism is a complex process involving the consumption and production of metabolites, as well as the regulation of enzyme synthesis and activity. Modeling of metabolic processes is important to understand the underlying mechanisms, with a wide range of applications in metabolic engineering and health sciences. Cybernetic modeling is a powerful technique that accounts for unknown intricate regulatory mechanisms in complex cellular processes. It models regulation as goal-oriented, where the levels and activities of enzymes are modulated by the cybernetic control variables to achieve the cybernetic objective. This study used cybernetic model to study the enzyme competition between arachidonic acid (AA) and eicosapentaenoic acid (EPA) metabolism in murine macrophages. AA and EPA compete for the shared enzyme cyclooxygenase. Upon external stimuli, AA produces proinflammatory 2-series prostaglandins and EPA metabolizes to antiinflammatory 3-series prostaglandins, where proinflammatory and antiinflammatory responses are necessary for homeostasis. The cybernetic model adequately captured the experimental data for control and EPA-supplemented conditions. The model is validated by performing an F-test, conducting leave-one-out-metabolite cross-validation, and predicting an unseen experimental condition. The cybernetic variables provide insights into the competition between AA and EPA for the cyclooxygenase enzyme. Predictions from our model suggest that the system undergoes a switch from a predominantly proinflammatory state in the control to an antiinflammatory state with EPA-supplementation. The model can also be used to analytically determine the AA and EPA concentrations required for the switch to occur. The quantitative outcomes enhance understanding of proinflammatory and antiinflammatory metabolism in RAW 264.7 macrophages.

In mammalian cells, glycerolipids are mainly synthesized using acyl-CoA-dependent mechanisms. The acyl-CoA-independent transfer of fatty acids between lipids, designated as transacylation reaction, represents an additional mechanism for lipid remodeling and synthesis pathways. Here, we demonstrate that human and mouse phospholipase A2 group IVD (PLA2G4D) catalyzes transacylase reactions using both phospholipids and acylglycerols as substrates. In the presence of monoglycerol and diacylglycerol (MAG and DAG), purified PLA2G4D generates DAG and triacylglycerol, respectively. The enzyme also transfers fatty acids between phospholipids and from phospholipids to acylglycerols. Overexpression of PLA2G4D in COS7 cells enhances the incorporation of polyunsaturated fatty acids into triacylglycerol stores and induces the accumulation of lysophospholipids. In the presence of exogenously added MAG, the enzyme strongly increases cellular DAG formation, while MAG levels are decreased. PLA2G4D is not or poorly detectable in commonly used cell lines. It is expressed in keratinocytes, where it is strongly upregulated by proinflammatory cytokines. Pla2g4d-deficient mouse keratinocytes exhibit complex lipidomic changes in response to cytokine treatment, indicating that PLA2G4D is involved in the remodeling of the lipidome under inflammatory conditions. Transcriptomic analysis revealed that PLA2G4D modulates fundamental biological processes including cell proliferation, differentiation, and signaling. Together, our observations demonstrate that PLA2G4D has broad substrate specificity for fatty acid donor and acceptor lipids, allowing the acyl-CoA-independent synthesis of both phospholipids and acylglycerols. Loss-of-function studies indicate that PLA2G4D affects metabolic and signaling pathways in keratinocytes, which is associated with complex lipidomic and transcriptomic alterations.

Accumulating evidence has revealed that chronic unresolved inflammation can cause significant tissue damage and can be a key mediator of advanced heart failure (HF). Resolvin (Rv) D2, a member of specialized pro-resolving lipid mediators (SPMs), plays a protective role in various diseases by facilitating resolution. However, whether RvD2 participates in the pathogenesis of HF is still unclear. Our study demonstrated that RvD2 treatment mitigated cardiac remodeling and improved cardiac function in HF mice induced by pressure overload. The absence of G protein-coupled receptor 18 (GPR18), an endogenous receptor for RvD2, abolished the beneficial effects of RvD2 on HF. Additionally, RvD2 inhibited inflammatory responses and Ly6C^high macrophage polarization during both early and late inflammatory stages involved in HF. Further investigation revealed that bone marrow transplantation from Gpr18 deficient mice into WT mice blocked the protective effects of RvD2 in HF mice. Moreover, Gpr18 deficiency impeded RvD2's capacity to downregulate inflammatory responses and Ly6C^high macrophage polarization. Consistent with experiments in vivo, RvD2 treatment in bone marrow-derived macrophages (BMDMs) reduced inflammatory responses through its receptor GPR18. Mechanistically, RvD2 suppressed the phosphorylation of STAT1 and NF-κB p65, and the effects of RvD2 were reversed by the application of STAT1 or NF-κB p65 agonists in BMDMs. In conclusion, RvD2/GPR18 axis improved cardiac remodeling and function in pressure overload-induced HF mice by modulating macrophage phenotype via STAT1 and NF-κB p65 pathways. Our findings underscore the anti-inflammatory potential of RvD2/GPR18 axis, suggesting that RvD2/GPR18 axis may be a potential strategy for the treatment of HF.

Lipotoxicity refers to the harmful effects of excess fatty acids on metabolic health, and it can vary depending on the type of fatty acids involved. Saturated and unsaturated fatty acids exhibit distinct effects, though the precise mechanisms behind these differences remain unclear. Here, we investigated the lipotoxicity of palmitic acid (PA), a saturated fatty acid, compared with oleic acid (OA), a monounsaturated fatty acid, in the hepatic cell line HuH7. Our results demonstrated that PA, unlike OA, induces lipotoxicity, endoplasmic reticulum (ER) stress, and autophagy inhibition. Compared with OA, PA treatment leads to less lipid droplet (LD) accumulation and a significant reduction in the mRNA and protein level of diacylglycerol acyltransferase 1 (DGAT1), a key enzyme of triacylglycerol synthesis. Using modulators of ER stress and autophagy, we established that DGAT1 downregulation by PA is closely linked to these cellular pathways. Notably, the ER stress inhibitor 4-phenylbutyrate can suppress PA-induced DGAT1 downregulation. Furthermore, knockdown of DGAT1 by siRNA or with A922500, a specific DGAT1 inhibitor, resulted in cell death, even with OA. Both PA and OA increased the oxygen consumption rate; however, the increase associated with PA was only partially coupled to ATP synthesis. Importantly, treatment with GW7647 a specific PPARα agonist mitigated the lipotoxic effects of PA, restoring PA-induced ER stress, autophagy block, and DGAT1 suppression. In conclusion, our study highlights the crucial role of DGAT1 in PA-induced lipotoxicity, broadening the knowledge of the mechanisms underlying hepatic lipotoxicity and providing the basis for potential therapeutic interventions.

Compound lipids comprise a diverse group of metabolites present in living systems, and metabolic- and environmentally-driven structural distinctions across this family are increasingly linked to biological function. However, methods for deconvoluting these often isobaric lipid species are lacking or require specialized instrumentation. Notably, acyl-chain diversity within cells may be influenced by nutritional states, metabolic dysregulation, or genetic alterations. Therefore, a reliable, validated method of quantifying structurally similar even-, odd-, and branched-chain acyl groups within intact compound lipids will be invaluable for gaining molecular insights into their biological functions. Here we demonstrate the chromatographic resolution of isobaric lipids containing distinct combinations of straight-chain and branched-chain acyl groups via ultra-high-pressure liquid chromatography (UHPLC)-mass spectrometry (MS) using a C30 liquid chromatography column. Using metabolically engineered adipocytes lacking branched-keto acid dehydrogenase A (Bckdha), we validate this approach through a combination of fatty acid supplementation and metabolic tracing using monomethyl branched-chain fatty acids and valine. We observe the resolution of numerous isobaric triacylglycerols and other compound lipids, demonstrating the resolving utility of this method. This approach adds to the toolbox for laboratories to quantify and characterize acyl chain diversity across the lipidome.

Steroid hormones are biologically active factors in human milk (HM) that influence the physical and mental development of infants. Critically, maternal psychosocial stress has been associated with changes in HM steroid composition. This work aimed to characterize the steroid hormone profile of HM and pasteurized donor human milk (DHM) and assess the interplay between maternal physical and psychosocial status, the HM steroid profile, and infant outcomes. A targeted ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method was developed to quantify sixteen steroid hormones in HM samples. HM samples from mothers of term infants (N = 42) and preterm infants (N = 35) were collected at (i) recovery of birth weight or achievement of complete enteral nutrition, respectively, and (ii) 6 months later as well as DHM samples (N = 19) from 11 donors. The physical and psychosocial status of mothers and infant neurodevelopment and temperament were assessed through structured interviews and validated questionnaires. Fourteen steroids were detected in HM/DHM samples, with cortisol, 20β-dihydrocortisol, dehydroepiandrosterone, pregnenolone, and cortisone being present in > 48% of samples. Pregnenolone, 17α-OH-progesterone, and dehydroepiandrosterone are reported for the first time in HM. Whereas milk cortisol levels were not directly related to maternal physical and psychosocial status nor with infant development, cortisone, and pregnenolone correlated positively with maternal weight gain during pregnancy and were associated with maternal well-being and infant growth. The pasteurization process may have a detrimental effect on the steroid hormone levels in HM, which might influence the development of receptors.