Multi-component lipid emulsions, rather than soy-oil emulsions, prevent cholestasis by an unknown mechanism. Here, we quantified liver function, bile acid pools, and gut microbial and metabolite profiles in premature, parenterally fed pigs given a soy-oil lipid emulsion, Intralipid (IL); a multi component lipid emulsion, SMOFlipid (SMOF); a novel emulsion with a modified fatty-acid composition (EXP); or a control enteral diet (ENT) for 22 days. We assayed serum cholestasis markers; measured total bile acid levels in plasma, liver, and gut contents; and analyzed colonic bacterial 16S rRNA gene sequences and metabolomic profiles. Serum cholestasis markers (i.e. bilirubin, bile acids, and g-glutamyl transferase) were highest in IL-fed pigs and normalized in those given SMOF, EXP, or ENT. Gut bile acid pools were lowest in the IL treatment and were increased in the SMOF and EXP treatments and comparable to ENT. Multiple bile acids, especially their conjugated forms, were higher in the colon contents of SMOF and EXP than in IL pigs. Colonic microbial communities of SMOF and EXP pigs had lower relative abundance of several Gram-positive anaerobes, including Clostridrium XIVa, and higher abundance of Enterobacteriaceae than those of IL and ENT pigs. Differences in lipid and microbial-derived compounds were also observed in colon metabolite profiles. These results indicate that multi-component lipid emulsions prevent cholestasis and restore enterohepatic bile flow in association with gut microbial and metabolomic changes. We conclude that sustained bile flow induced by multi-component lipid emulsions likely exerts a dominant effect in reducing bile acid–sensitive, Gram-positive bacteria.

The levels and composition of sphingolipids and related metabolites are altered in aging and common disorders such as diabetes and cancers, as well as in neurodegenerative, cardiovascular, and respiratory diseases. Changes in sphingolipids have been implicated as being an essential step in mitochondria-driven cell death. However, little is known about the precise sphingolipid composition and modulation in mitochondria or related organelles. Here, we used LC–MS/MS to analyze the presence of key components of the ceramide metabolic pathway in vivo and in vitro in purified endoplasmic reticulum (ER), mitochondria-associated membranes (MAM), and mitochondria. Specifically, we analyzed the sphingolipids in the three pathways that generate ceramide: sphinganine in the de novo ceramide pathway, sphingomyelin in the breakdown pathway, and sphingosine in the salvage pathway. We observed sphingolipid profiles in mouse liver, mouse brain, and a human glioma cell line (U251). We analyzed the quantitative and qualitative changes of these sphingolipids during staurosporine (STS)-induced apoptosis in U251 cells. Ceramide, especially C16-ceramide, levels increased during early apoptosis possibly through a conversion from mitochondrial sphinganine and sphingomyelin, but sphingosine and lactosyl- and glucosyl-ceramide levels were unaffected. We also found that ceramide generation is enhanced in mitochondria when sphingomyelin levels are decreased in the MAM. This decrease was associated with an increase in acid sphingomyelinase (ASM) activity in MAM. We conclude that meaningful sphingolipid modifications occur in MAM, the mitochondria, and ER during the early phases of apoptosis.

Vitamin A aldehyde covalently bound to opsin protein is embedded in a phospholipid-rich membrane that supports photon absorption and phototransduction in photoreceptor cell outer segments. Following absorption of a photon, the 11-cis-retinal chromophore of visual pigment in photoreceptor cells isomerizes to all-trans-retinal. To maintain photosensitivity 11-cis-retinal must be replaced. At the same time, however, all-trans-retinal has to be handled so as to prevent nonspecific aldehyde activity. Some molecules of retinaldehyde upon release from opsin are efficiently reduced to retinol. Other molecules are released into the lipid phase of the disc membrane where they form a conjugate (N-retinylidene-PE, NRPE) through a Schiff base linkage with phosphatidylethanolamine (PE). The reversible formation of NRPE serves as a transient sink for retinaldehyde that is intended to return retinaldehyde to the visual cycle. However, if instead of hydrolyzing to PE and retinaldehyde, NRPE reacts with a second molecule of retinaldehyde a synthetic pathway is initiated that leads to the formation of multiple species of unwanted bisretinoid fluorophores. We report on recently identified members of the bisretinoid family some of which differ with respect to the acyl chains associated with the glycerol backbone. We discuss processing of the lipid moieties of these fluorophores in lysosomes of retinal pigment epithelial (RPE) cells, their fluorescence characters and new findings related to light and iron-associated oxidation of bisretinoids.

7 May 2020

Withdrawn by Author.

Ankylosing Spondylitis (AS) is a common, inflammatory rheumatic disease, which primarily affects the axial skeleton and is associated with sacroiliitis, uveitis and enthesitis. Unlike other autoimmune rheumatic diseases, such as rheumatoid arthritis or systemic lupus erythematosus, autoantibodies have not yet been reported to be a feature of AS. We therefore wished to determine if plasma from patients with AS contained autoantibodies and if so, characterize and quantify this response in comparison to patients with Rheumatoid Arthritis (RA) and healthy controls. Two high-density nucleic acid programmable protein arrays expressing a total of 3498 proteins were screened with plasma from 25 patients with AS, 17 with RA and 25 healthy controls. Autoantigens identified were subjected to Ingenuity Pathway Analysis in order to determine patterns of signalling cascades or tissue origin. 44% of patients with Ankylosing Spondylitis demonstrated a broad autoantibody response, as compared to 33% of patients with RA and only 8% of healthy controls. Individuals with AS demonstrated autoantibody responses to shared autoantigens, and 60% of autoantigens identified in the AS cohort were restricted to that group. The AS patients autoantibody responses were targeted towards connective, skeletal and muscular tissue, unlike those of RA patients or healthy controls. Thus, patients with AS show evidence of systemic humoral autoimmunity and multispecific autoantibody production. Nucleic Acid Programmable Protein Arrays constitute a powerful tool to study autoimmune diseases.

In quantitative proteomics work, the differences in expression of many separate proteins are routinely examined to test for significant differences between treatments. This leads to the multiple hypothesis testing problem: when many separate tests are performed many will be significant by chance and be false positive results. Statistical methods such as the false discovery rate (FDR) method that deal with this problem have been disseminated for more than one decade. However a survey of proteomics journals shows that such tests are not widely implemented in one commonly used technique, quantitative proteomics using two-dimensional electrophoresis (2-DE). We outline a selection of multiple hypothesis testing methods, including some that are well known and some lesser known, and present a simple strategy for their use by the experimental scientist in quantitative proteomics work generally. The strategy focuses on the desirability of simultaneous use of several different methods, the choice and emphasis dependent on research priorities and the results in hand. This approach is demonstrated using case scenarios with experimental and simulated model data.

Electrospray ionization is today the most widely used ionization technique in chemical and bio-chemical analysis. Interfaced with a mass spectrometer it allows to investigate the molecular composition of liquid samples. With electrospray a large variety of chemical substances can be ionized. There is no limitation in mass which enables even the investigation of large non-covalent protein complexes. Its high ionization efficiency profoundly changed bio-molecular sciences because proteins can be identified and quantified on trace amounts in a high throughput fashion. This review article focusses mainly on the exploration of the underlying ionization mechanism. Some ionization characteristics are discussed which are related to this mechanism. Typical spectra of peptides, proteins and non-covalent complexes are shown and the quantitative character of spectra is highlighted. Finally the possibilities and limitations in measuring the association constant of bivalent non-covalent complexes are described.

Protein tyrosine kinases (PTKs) play key roles in cellular signal transduction, cell cycle regulation, cell division, and cell differentiation. Dysregulation of PTK-activated pathways, often by receptor overexpression, gene amplification, or genetic mutation, is a causal factor underlying numerous cancers. In this study, we have developed a parallel reaction monitoring (PRM)-based assay for quantitative profiling of 83 PTKs. The assay detects 308 proteotypic peptides from 54 receptor tyrosine kinases and 29 nonreceptor tyrosine kinases in a single run. Quantitative comparisons were based on the labeled reference peptide method. We implemented the assay in four cell models: 1) a comparison of proliferating versus epidermal growth factor (EGF)-stimulated A431 cells, 2) a comparison of SW480Null (mutant APC) and SW480APC (APC restored) colon tumor cell lines, and 3) a comparison of 10 colorectal cancer cell lines with different genomic abnormalities, and 4) lung cancer cell lines with either susceptibility (11-18) or acquired resistance (11-18R) to the epidermal growth factor receptor tyrosine kinase inhibitor erlotinib. We observed distinct PTK expression changes that were induced by stimuli, genomic features or drug resistance, which were consistent with previous reports. However, most of the measured expression differences were novel observations. For example, acquired resistance to erlotinib in the 11-18 cell model was associated not only with previously reported upregulation of MET, but also with upregulation of FLK2 and downregulation of LYN and PTK7. Immunoblot analyses and shotgun proteomics data were highly consistent with PRM data. Multiplexed PRM assays provide a targeted, systems-level profiling approach to evaluate cancer-related proteotypes and adaptations. Data are available through Proteome eXchange Accession PXD002706.

Stimulating brown adipose tissue (BAT) activity represents a promising therapy for overcoming metabolic diseases. mTORC2 is important for regulating BAT metabolism, but its downstream targets have not been fully characterized. In this study, we apply proteomics and phosphoproteomics to investigate the downstream effectors of mTORC2 in brown adipocytes. We compare wild-type controls to isogenic cells with an induced knockout of the mTORC2 subunit RICTOR (Rictor-iKO) by stimulating each with insulin for a 30-minute time course. In Rictor-iKO cells, we identify decreases to the abundance of glycolytic and de novo lipogenesis enzymes, and increases to mitochondrial proteins as well as a set of proteins known to increase upon interferon stimulation. We also observe significant differences to basal phosphorylation due to chronic RICTOR loss including decreased phosphorylation of the lipid droplet protein perilipin-1 in Rictor-iKO cells, suggesting that RICTOR could be involved with regulating basal lipolysis or droplet dynamics. Finally, we observe mild dampening of acute insulin signaling response in Rictor-iKO cells, and a subset of AKT substrates exhibiting statistically significant dependence on RICTOR.

Accumulation and propagation of hyperphosphorylated tau (p-tau) is a common neuropathological hallmark associated with neurodegeneration of Alzheimer's disease (AD), frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17), and related tauopathies. Extracellular vesicles, specifically exosomes, have recently been demonstrated to participate in mediating tau propagation in brain. Exosomes produced by human induced pluripotent stem cell (iPSC)-derived neurons expressing mutant Tau (mTau), containing the P301L and V337M Tau mutations of FTDP-17, possess the ability to propagate p-tau pathology after injection into mouse brain.  To gain an understanding of the mTau exosome cargo involved in tau pathogenesis, these pathogenic exosomes were analyzed by proteomics and bioinformatics. The data showed that mTau expression dysregulates the exosome proteome to result in (1) proteins uniquely present only in mTau, and not control exosomes, (2) the absence of proteins in mTau exosomes, uniquely present in control exosomes, and (3) shared proteins which were significantly up-regulated or down-regulated in mTau compared to control exosomes. Notably, mTau exosomes (not control exosomes) contain ANP32A (also known as I1PP2A), an endogenous inhibitor of the PP2A phosphatase which regulates the phosphorylation state of p-tau.  Several of the mTau exosome-specific proteins have been shown to participate in AD mechanisms involving lysosomes, inflammation, secretases, and related processes.  Furthermore, the mTau exosomes lacked a substantial portion of proteins present in control exosomes involved in pathways of localization, vesicle transport, and protein binding functions. The shared proteins present in both mTau and control exosomes represented exosome functions of vesicle-mediated transport, exocytosis, and secretion processes. These data illustrate mTau as a dynamic regulator of the biogenesis of exosomes to result in acquisition, deletion, and up- or down-regulation of protein cargo to result in pathogenic mTau exosomes capable of in vivo propagation of p-tau neuropathology in mouse brain. 

1 July 2008 , Number 9

Oil people call them pipe dreams: plans to transport energy across vast distances to places where it is needed most. That need is clear in Pakistan and India, but can the obstacles be overcome at this time of high prices, to turn the recurring dreams into reality?

1 January 2007 , Number 2

For all the cynicism it has evoked, the United States’ Iraq Study Group report might still lead to a regional diplomatic process, which could ease Iran and the US into negotiations. A grand bargain is very unlikely, but with Washington at the table, there might be enough advantage for both sides in a gradual process to halt the current slide towards a deeper confrontation.

7 May 2020 , Volume 96, Number 3

7 May 2020 , Volume 96, Number 3

7 May 2020 , Volume 96, Number 3

A fundamental feature of the eukaryotic cell membrane is the asymmetric arrangement of lipids in its two leaflets. A cell invests significant energy to maintain this asymmetry and uses it to regulate important biological processes, such as apoptosis and vesiculation. The dynamic coupling of the inner or cytoplasmic and outer or exofacial leaflets is a challenging open question in membrane biology. Here, we combined fluorescence lifetime imaging microscopy (FLIM) with imaging total internal reflection fluorescence correlation spectroscopy (ITIR-FCS) to differentiate the dynamics and organization of the two leaflets of live mammalian cells. We characterized the biophysical properties of fluorescent analogs of phosphatidylcholine, sphingomyelin, and phosphatidylserine in the plasma membrane of two mammalian cell lines (CHO-K1 and RBL-2H3). Because of their specific transverse membrane distribution, these probes allowed leaflet-specific investigation of the plasma membrane. We compared the results of the two methods having different temporal and spatial resolution. Fluorescence lifetimes of fluorescent lipid analogs were in ranges characteristic for the liquid ordered phase in the outer leaflet and for the liquid disordered phase in the inner leaflet. The observation of a more fluid inner leaflet was supported by free diffusion in the inner leaflet, with high average diffusion coefficients. The liquid ordered phase in the outer leaflet was accompanied by slower diffusion and diffusion with intermittent transient trapping. Our results show that the combination of FLIM and ITIR-FCS with specific fluorescent lipid analogs is a powerful tool for investigating lateral and transbilayer characteristics of plasma membrane in live cell lines.

APOA5 is a low-abundance exchangeable apolipoprotein that plays critical roles in human triglyceride (TG) metabolism. Indeed, aberrations in the plasma concentration or structure of APOA5 are linked to hypertriglyceridemia, hyperchylomicronemia, myocardial infarction risk, obesity, and coronary artery disease. While it has been successfully produced at low yield in bacteria, the resulting protein had limitations for structure-function studies due to its low solubility under physiological buffer conditions. We hypothesized that the yield and solubility of recombinant APOA5 could be increased by: i) engineering a fusion protein construct in a codon optimized expression vector, ii) optimizing an efficient refolding protocol, and iii) screening buffer systems at physiological pH. The result was a high-yield (25 mg/l) bacterial expression system that produces lipid-free APOA5 soluble at concentrations of up to 10 mg/ml at a pH of 7.8 in bicarbonate buffers. Physical characterization of lipid-free APOA5 indicated that it exists as an array of multimers in solution, and far UV circular dichroism analyses show differences in total α-helicity between acidic and neutral pH buffering conditions. The protein was functional in that it bound and emulsified multilamellar dimyristoyl-phosphatidylcholine vesicles and could inhibit postprandial plasma TG accumulation when injected into C57BL/6J mice orally gavaged with Intralipid.

Xanthophyllomyces dendrorhous is a basidiomycete yeast known as a natural producer of astaxanthin, a carotenoid of commercial interest because of its antioxidant properties. Recent studies indicated that X. dendrorhous has a functional SREBP pathway involved in the regulation of isoprenoid compound biosynthesis, which includes ergosterol and carotenoids. SREBP is a major regulator of sterol metabolism and homeostasis in mammals; characterization in fungi also provides information about its role in the hypoxia adaptation response and virulence. SREBP protease processing is required to activate SREBP pathway functions in fungi. Here, we identified and described the STP1 gene, which encodes a metallopeptidase of the M50 family involved in the proteolytic activation of the transcription factor Sre1 of the SREBP pathway, in X. dendrorhous. We assessed STP1 function in stp1 strains derived from the wild-type and a mutant of ergosterol biosynthesis that overproduces carotenoids and sterols. Bioinformatic analysis of the deduced protein predicted the presence of characteristic features identified in homologs from mammals and fungi. The stp1 mutation decreased yeast growth in the presence of azole drugs and reduced transcript levels of Sre1-dependent genes. This mutation also negatively affected the carotenoid- and sterol-overproducing phenotype. Western blot analysis demonstrated that Sre1 was activated in the yeast ergosterol biosynthesis mutant and that the stp1 mutation introduced in this strain prevented Sre1 proteolytic activation. Overall, our results demonstrate that STP1 encodes a metallopeptidase involved in proteolytic activation of Sre1 in X. dendrorhous, contributing to our understanding of fungal SREBP pathways.

Ceramides (Cers) with ultralong (~32-carbon) chains and -esterified linoleic acid, composing a subclass called omega-O-acylceramides (acylCers), are indispensable components of the skin barrier. Normal barriers typically contain acylCer concentrations of ~10 mol%; diminished concentrations, along with altered or missing long periodicity lamellar phase (LPP), and increased permeability accompany an array of skin disorders, including atopic dermatitis, psoriasis, and ichthyoses. We developed model membranes to investigate the effects of the acylCer structure and concentration on skin lipid organization and permeability. The model membrane systems contained six to nine Cer subclasses as well as fatty acids, cholesterol, and cholesterol sulfate; acylCer content—namely, acylCers containing sphingosine (Cer EOS), dihydrosphingosine (Cer EOdS), and phytosphingosine (Cer EOP) ranged from zero to 30 mol%. Systems with normal physiologic concentrations of acylCer mixture mimicked the permeability and nanostructure of human skin lipids (with regard to LPP, chain order, and lateral packing). The models also showed that the sphingoid base in acylCer significantly affects the membrane architecture and permeability and that Cer EOP, notably, is a weaker barrier component than Cer EOS and Cer EOdS. Membranes with diminished or missing acylCers displayed some of the hallmarks of diseased skin lipid barriers (i.e., lack of LPP, less ordered lipids, less orthorhombic chain packing, and increased permeability). These results could inform the rational design of new and improved strategies for the barrier-targeted treatment of skin diseases.

We previously described the expression of CD36 and LPL by breast cancer (BC) cells and tissues and the growth-promoting effect of VLDL observed only in the presence of LPL. We now report a model in which LPL is bound to a heparan sulfate proteoglycan motif on the BC cell surface and acts in concert with the VLDL receptor to internalize VLDLs via receptor-mediated endocytosis. We also demonstrate that gene-expression programs for lipid synthesis versus uptake respond robustly to triglyceride-rich lipoprotein availability. The literature emphasizes de novo FA synthesis and exogenous free FA uptake using CD36 as paramount mechanisms for lipid acquisition by cancer cells. We find that the uptake of intact lipoproteins is also an important mechanism for lipid acquisition and that the relative reliance on lipid synthesis versus uptake varies among BC cell lines and in response to VLDL availability. This metabolic plasticity has important implications for the development of therapies aimed at the lipid dependence of many types of cancer, in that the inhibition of FA synthesis may elicit compensatory upregulation of lipid uptake. Moreover, the mechanism that we have elucidated provides a direct connection between dietary fat and tumor biology.­.

Nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH) are emerging as leading causes of liver disease worldwide and have been recognized as one of the major unmet medical needs of the 21st century. Our recent translational studies in mouse models, human cell lines, and well-characterized patient cohorts have identified serine/threonine kinase (STK)25 as a protein that coats intrahepatocellular lipid droplets (LDs) and critically regulates liver lipid homeostasis and progression of NAFLD/NASH. Here, we studied the mechanism-of-action of STK25 in steatotic liver by relative quantification of the hepatic LD-associated phosphoproteome from high-fat diet-fed Stk25 knockout mice compared with their wild-type littermates. We observed a total of 131 proteins and 60 phosphoproteins that were differentially represented in STK25-deficient livers. Most notably, a number of proteins involved in peroxisomal function, ubiquitination-mediated proteolysis, and antioxidant defense were coordinately regulated in Stk25^–/– versus wild-type livers. We confirmed attenuated peroxisomal biogenesis and protection against oxidative and ER stress in STK25-deficient human liver cells, demonstrating the hepatocyte-autonomous manner of STK25’s action. In summary, our results suggest that regulation of peroxisomal function and metabolic stress response may be important molecular mechanisms by which STK25 controls the development and progression of NAFLD/NASH.

Phospholipases A₂ (PLA₂s) catalyze hydrolysis of the sn-2 substituent from glycerophospholipids to yield a free fatty acid (i.e., arachidonic acid), which can be metabolized to pro- or anti-inflammatory eicosanoids. Macrophages modulate inflammatory responses and are affected by Ca²⁺-independent phospholipase A₂ (PLA₂)β (iPLA₂β). Here, we assessed the link between iPLA₂β-derived lipids (iDLs) and macrophage polarization. Macrophages from WT and KO (iPLA₂β–/–) mice were classically M1 pro-inflammatory phenotype activated or alternatively M2 anti-inflammatory phenotype activated, and eicosanoid production was determined by ultra-performance LC ESI-MS/MS. As a genotypic control, we performed similar analyses on macrophages from RIP.iPLA₂β.Tg mice with selective iPLA₂β overexpression in β-cells. Compared with WT, generation of select pro-inflammatory prostaglandins (PGs) was lower in iPLA₂β^–/–, and that of a specialized pro-resolving lipid mediator (SPM), resolvin D2, was higher; both changes are consistent with the M2 phenotype. Conversely, macrophages from RIP.iPLA₂β.Tg mice exhibited an opposite landscape, one associated with the M1 phenotype: namely, increased production of pro-inflammatory eicosanoids (6-keto PGF₁α, PGE₂, leukotriene B₄) and decreased ability to generate resolvin D2. These changes were not linked with secretory PLA₂ or cytosolic PLA₂α or with leakage of the transgene. Thus, we report previously unidentified links between select iPLA₂β-derived eicosanoids, an SPM, and macrophage polarization. Importantly, our findings reveal for the first time that β-cell iPLA₂β-derived signaling can predispose macrophage responses. These findings suggest that iDLs play critical roles in macrophage polarization, and we posit that they could be targeted therapeutically to counter inflammation-based disorders.

Elevated levels of triglyceride-rich lipoproteins (TRLs), both fasting and postprandial, are associated with increased risk for atherosclerosis. However, guidelines for treatment are defined solely by fasting lipid levels, even though postprandial lipids may be more informative. In the postprandial state, circulating lipids consist of dietary fat transported from the intestine in chylomicrons (CMs; containing ApoB48) and fat transported from the liver in VLDL (containing ApoB100). Research into the roles of endogenous versus dietary fat has been hindered because of the difficulty in separating these particles by ultracentrifugation. CM fractions have considerable contamination from VLDL (purity, 10%). To separate CMs from VLDL, we produced polyclonal antibodies against ApoB100 and generated immunoaffinity columns. TRLs isolated by ultracentrifugation of plasma were applied to these columns, and highly purified CMs were collected (purity, 90–94%). Overall eight healthy unmedicated adult volunteers (BMI, 27.2 ± 1.4 kg/m²; fasting triacylglycerol, 102.6 ± 19.5 mg/dl) participated in a feeding study, which contained an oral stable-isotope tracer (1-¹³C acetate). We then used this technique on plasma samples freshly collected during an 8 h human feeding study from a subset of four subjects. We analyzed fractionated lipoproteins by Western blot, isolated and derivatized triacylglycerols, and calculated fractional de novo lipogenesis. The results demonstrated effective separation of postprandial lipoproteins and substantially improved purity compared with ultracentrifugation protocols, using the immunoaffinity method. This method can be used to better delineate the role of dietary sugar and fat on postprandial lipids in cardiovascular risk and explore the potential role of CM remnants in atherosclerosis.

Whether HDL is associated with dementia risk is unclear. In addition to apoA1, other apolipoproteins are found in HDL, creating subspecies of HDL that may have distinct metabolic properties. We measured apoA1, apoC3, and apoJ levels in plasma and apoA1 levels in HDL that contains or lacks apoE, apoJ, or apoC3 using a modified sandwich ELISA in a case-cohort study nested within the Ginkgo Evaluation of Memory Study. We included 995 randomly selected participants and 521 participants who developed dementia during a mean of 5.1 years of follow-up. The level of total apoA1 was not significantly related to dementia risk, regardless of the coexistence of apoC3, apoJ, or apoE. Higher levels of total plasma apoC3 were associated with better cognitive function at baseline (difference in Modified Mini-Mental State Examination scores tertile 3 vs. tertile 1: 0.60; 95% CI: 0.23, 0.98) and a lower dementia risk (adjusted hazard ratio tertile 3 vs. tertile 1: 0.73; 95% CI: 0.55, 0.96). Plasma concentrations of apoA1 in HDL and its apolipoprotein-defined subspecies were not associated with cognitive function at baseline or with the risk of dementia during follow-up. Similar studies in other populations are required to better understand the association between apoC3 and Alzheimer’s disease pathology.

Zinc metallopeptidase STE24 (ZMPSTE24) is essential for the conversion of farnesyl–prelamin A to mature lamin A, a key component of the nuclear lamina. In the absence of ZMPSTE24, farnesyl–prelamin A accumulates in the nucleus and exerts toxicity, causing a variety of disease phenotypes. By ~4 months of age, both male and female Zmpste24^–/– mice manifest a near-complete loss of adipose tissue, but it has never been clear whether this phenotype is a direct consequence of farnesyl–prelamin A toxicity in adipocytes. To address this question, we generated a conditional knockout Zmpste24 allele and used it to create adipocyte-specific Zmpste24–knockout mice. To boost farnesyl–prelamin A levels, we bred in the "prelamin A–only" Lmna allele. Gene expression, immunoblotting, and immunohistochemistry experiments revealed that adipose tissue in these mice had decreased Zmpste24 expression along with strikingly increased accumulation of prelamin A. In male mice, Zmpste24 deficiency in adipocytes was accompanied by modest changes in adipose stores (an 11% decrease in body weight, a 23% decrease in body fat mass, and significantly smaller gonadal and inguinal white adipose depots). No changes in adipose stores were detected in female mice, likely because prelamin A expression in adipose tissue is lower in female mice. Zmpste24 deficiency in adipocytes did not alter the number of macrophages in adipose tissue, nor did it alter plasma levels of glucose, triglycerides, or fatty acids. We conclude that ZMPSTE24 deficiency in adipocytes, and the accompanying accumulation of farnesyl–prelamin A, reduces adipose tissue stores, but only modestly and only in male mice.

Angiopoietin-like protein 3 (ANGPTL3) inhibits lipid clearance and is a promising target for managing cardiovascular disease. Here we investigated the effects of a high-sugar (high-fructose) diet on circulating ANGPTL3 concentrations in rhesus macaques. Plasma ANGPTL3 concentrations increased ~30% to 40% after 1 and 3 months of a high-fructose diet (both P < 0.001 vs. baseline). During fructose-induced metabolic dysregulation, plasma ANGPTL3 concentrations were positively correlated with circulating indices of insulin resistance [assessed with fasting insulin and the homeostatic model assessment of insulin resistance (HOMA-IR)], hypertriglyceridemia, adiposity (assessed as leptin), and systemic inflammation [C-reactive peptide (CRP)] and negatively correlated with plasma levels of the insulin-sensitizing hormone adropin. Multiple regression analyses identified a strong association between circulating APOC3 and ANGPTL3 concentrations. Higher baseline plasma levels of both ANGPTL3 and APOC3 were associated with an increased risk for fructose-induced insulin resistance. Fish oil previously shown to prevent insulin resistance and hypertriglyceridemia in this model prevented increases of ANGPTL3 without affecting systemic inflammation (increased plasma CRP and interleukin-6 concentrations). ANGPTL3 RNAi lowered plasma concentrations of ANGPTL3, triglycerides (TGs), VLDL-C, APOC3, and APOE. These decreases were consistent with a reduced risk of atherosclerosis. In summary, dietary sugar-induced increases of circulating ANGPTL3 concentrations after metabolic dysregulation correlated positively with leptin levels, HOMA-IR, and dyslipidemia. Targeting ANGPTL3 expression with RNAi inhibited dyslipidemia by lowering plasma TGs, VLDL-C, APOC3, and APOE levels in rhesus macaques.

Atherosclerosis-related CVD causes nearly 20 million deaths annually. Most patients are treated after plaques develop, so therapies must regress existing lesions. Current therapies reduce plaque volume, but targeting all apoB-containing lipoproteins with intensive combinations that include alirocumab or evinacumab, monoclonal antibodies against cholesterol-regulating proprotein convertase subtilisin/kexin type 9 and angiopoietin-like protein 3, may provide more benefit. We investigated the effect of such lipid-lowering interventions on atherosclerosis in APOE*3-Leiden.CETP mice, a well-established model for hyperlipidemia. Mice were fed a Western-type diet for 13 weeks and thereafter matched into a baseline group (euthanized at 13 weeks) and five groups that received diet alone (control) or with treatment [atorvastatin; atorvastatin and alirocumab; atorvastatin and evinacumab; or atorvastatin, alirocumab, and evinacumab (triple therapy)] for 25 weeks. We measured effects on cholesterol levels, plaque composition and morphology, monocyte adherence, and macrophage proliferation. All interventions reduced plasma total cholesterol (37% with atorvastatin to 80% with triple treatment; all P < 0.001). Triple treatment decreased non-HDL-C to 1.0 mmol/l (91% difference from control; P < 0.001). Atorvastatin reduced atherosclerosis progression by 28% versus control (P < 0.001); double treatment completely blocked progression and diminished lesion severity. Triple treatment regressed lesion size versus baseline in the thoracic aorta by 50% and the aortic root by 36% (both P < 0.05 vs. baseline), decreased macrophage accumulation through reduced proliferation, and abated lesion severity. Thus, high-intensive cholesterol-lowering triple treatment targeting all apoB-containing lipoproteins regresses atherosclerotic lesion area and improves lesion composition in mice, making it a promising potential approach for treating atherosclerosis.

apoB exists as apoB100 and apoB48, which are mainly found in hepatic VLDLs and intestinal chylomicrons, respectively. Elevated plasma levels of apoB-containing lipoproteins (Blps) contribute to coronary artery disease, diabetes, and other cardiometabolic conditions. Studying the mechanisms that drive the assembly, intracellular trafficking, secretion, and function of Blps remains challenging. Our understanding of the intracellular and intraorganism trafficking of Blps can be greatly enhanced, however, with the availability of fusion proteins that can help visualize Blp transport within cells and between tissues. We designed three plasmids expressing human apoB fluorescent fusion proteins: apoB48-GFP, apoB100-GFP, and apoB48-mCherry. In Cos-7 cells, transiently expressed fluorescent apoB proteins colocalized with calnexin and were only secreted if cells were cotransfected with microsomal triglyceride transfer protein. The secreted apoB-fusion proteins retained the fluorescent protein and were secreted as lipoproteins with flotation densities similar to plasma HDL and LDL. In a rat hepatoma McA-RH7777 cell line, the human apoB100 fusion protein was secreted as VLDL- and LDL-sized particles, and the apoB48 fusion proteins were secreted as LDL- and HDL-sized particles. To monitor lipoprotein trafficking in vivo, the apoB48-mCherry construct was transiently expressed in zebrafish larvae and was detected throughout the liver. These experiments show that the addition of fluorescent proteins to the C terminus of apoB does not disrupt their assembly, localization, secretion, or endocytosis. The availability of fluorescently labeled apoB proteins will facilitate the exploration of the assembly, degradation, and transport of Blps and help to identify novel compounds that interfere with these processes via high-throughput screening.

The composition-function relationship of HDL particles and its effects on the mechanisms driving coronary heart disease (CHD) is poorly understood. We tested the hypothesis that the functionality of HDL particles is significantly influenced by their lipid composition. Using a novel 3D-separation method, we isolated five different-sized HDL subpopulations from CHD patients who had low preβ-1 functionality (low-F) (ABCA1-dependent cholesterol-efflux normalized for preβ-1 concentration) and controls who had either low-F or high preβ-1 functionality (high-F). Molecular numbers of apoA-I, apoA-II, and eight major lipid classes were determined in each subpopulation by LC-MS. The average number of lipid molecules decreased from 422 in the large spherical α-1 particles to 57 in the small discoid preβ-1 particles. With decreasing particle size, the relative concentration of free cholesterol (FC) decreased in α-mobility but not in preβ-1 particles. Preβ-1 particles contained more lipids than predicted; 30% of which were neutral lipids (cholesteryl ester and triglyceride), indicating that these particles were mainly remodeled from larger particles not newly synthesized. There were significant correlations between HDL-particle functionality and the concentrations of several lipids. Unexpectedly, the phospholipid:FC ratio was significantly correlated with large-HDL-particle functionality but not with preβ-1 functionality. There was significant positive correlation between particle functionality and total lipids in high-F controls, indicating that the lipid-binding capacity of apoA-I plays a major role in the cholesterol efflux capacity of HDL particles. Functionality and lipid composition of HDL particles are significantly correlated and probably both are influenced by the lipid-binding capacity of apoA-I.

Diets high in calories can be used to model metabolic diseases, including obesity and its associated comorbidities, in animals. Drosophila melanogaster fed high-sugar diets (HSDs) exhibit complications of human obesity including hyperglycemia, hyperlipidemia, insulin resistance, cardiomyopathy, increased susceptibility to infection, and reduced longevity. We hypothesize that lipid storage in the high-sugar-fed fly’s fat body (FB) reaches a maximum capacity, resulting in the accumulation of toxic lipids in other tissues or lipotoxicity. We took two approaches to characterize tissue-specific lipotoxicity. Ultra-HPLC-MS/MS and MALDI-MS imaging enabled spatial and temporal localization of lipid species in the FB, heart, and hemolymph. Substituent chain length was diet dependent, with fewer odd chain esterified FAs on HSDs in all sample types. By contrast, dietary effects on double bond content differed among organs, consistent with a model where some substituent pools are shared and others are spatially restricted. Both di- and triglycerides increased on HSDs in all sample types, similar to observations in obese humans. Interestingly, there were dramatic effects of sugar feeding on lipid ethers, which have not been previously associated with lipotoxicity. Taken together, we have identified candidate endocrine mechanisms and molecular targets that may be involved in metabolic disease and lipotoxicity.

The hydrolysis of triglycerides in triglyceride-rich lipoproteins by LPL is critical for the delivery of triglyceride-derived fatty acids to tissues, including heart, skeletal muscle, and adipose tissues. Physiologically active LPL is normally bound to the endothelial cell protein glycosylphosphatidylinositol-anchored high-density lipoprotein binding protein 1 (GPIHBP1), which transports LPL across endothelial cells, anchors LPL to the vascular wall, and stabilizes LPL activity. Disruption of LPL-GPIHBP1 binding significantly alters triglyceride metabolism and lipid partitioning. In this study, we modified the NanoLuc® Binary Technology split-luciferase system to develop a novel assay that monitors the binding of LPL to GPIHBP1 on endothelial cells in real time. We validated the specificity and sensitivity of the assay using endothelial lipase and a mutant version of LPL and found that this assay reliably and specifically detected the interaction between LPL and GPIHBP1. We then interrogated various endogenous and exogenous inhibitors of LPL-mediated lipolysis for their ability to disrupt the binding of LPL to GPIHBP1. We found that angiopoietin-like (ANGPTL)4 and ANGPTL3-ANGPTL8 complexes disrupted the interactions of LPL and GPIHBP1, whereas the exogenous LPL blockers we tested (tyloxapol, poloxamer-407, and tetrahydrolipstatin) did not. We also found that chylomicrons could dissociate LPL from GPIHBP1 and found evidence that this dissociation was mediated in part by the fatty acids produced by lipolysis. These results demonstrate the ability of this assay to monitor LPL-GPIHBP1 binding and to probe how various agents influence this important complex.

CVD is the leading cause of death worldwide, and genetic investigations into the human lipidome may provide insight into CVD risk. The aim of this study was to estimate the heritability of circulating lipid species and their genetic correlation with CVD traits. Targeted lipidomic profiling was performed on 4,492 participants from the Busselton Family Heart Study to quantify the major fatty acids of 596 lipid species from 33 classes. We estimated narrow-sense heritabilities of lipid species/classes and their genetic correlations with eight CVD traits: BMI, HDL-C, LDL-C, triglycerides, total cholesterol, waist-hip ratio, systolic blood pressure, and diastolic blood pressure. We report heritabilities and genetic correlations of new lipid species/subclasses, including acylcarnitine (AC), ubiquinone, sulfatide, and oxidized cholesteryl esters. Over 99% of lipid species were significantly heritable (h²: 0.06–0.50) and all lipid classes were significantly heritable (h²: 0.14–0.50). The monohexosylceramide and AC classes had the highest median heritabilities (h² = 0.43). The largest genetic correlation was between clinical triglycerides and total diacylglycerol (r_g = 0.88). We observed novel positive genetic correlations between clinical triglycerides and phosphatidylglycerol species (r_g: 0.64–0.82), and HDL-C and alkenylphosphatidylcholine species (r_g: 0.45–0.74). Overall, 51% of the 4,768 lipid species-CVD trait genetic correlations were statistically significant after correction for multiple comparisons. This is the largest lipidomic study to address the heritability of lipids and their genetic correlation with CVD traits. Future work includes identifying putative causal genetic variants for lipid species and CVD using genome-wide SNP and whole-genome sequencing data.

Myelin is a unique lipid-rich membrane structure that accelerates neurotransmission and supports neuronal function. Sphingolipids are critical myelin components. Yet sphingolipid content and synthesis have not been well characterized in oligodendrocytes, the myelin-producing cells of the CNS. Here, using quantitative real-time PCR, LC-MS/MS-based lipid analysis, and biochemical assays, we examined sphingolipid synthesis during the peak period of myelination in the postnatal rat brain. Importantly, we characterized sphingolipid production in isolated oligodendrocytes. We analyzed sphingolipid distribution and levels of critical enzymes and regulators in the sphingolipid biosynthetic pathway, with focus on the serine palmitoyltransferase (SPT) complex, the rate-limiting step in this pathway. During myelination, levels of the major SPT subunits increased and oligodendrocyte maturation was accompanied by extensive alterations in the composition of the SPT complex. These included changes in the relative levels of two alternative catalytic subunits, SPTLC2 and -3, in the relative levels of isoforms of the small subunits, ssSPTa and -b, and in the isoform distribution of the SPT regulators, the ORMDLs. Myelination progression was accompanied by distinct changes in both the nature of the sphingoid backbone and the N-acyl chains incorporated into sphingolipids. We conclude that the distribution of these changes among sphingolipid family members is indicative of a selective channeling of the ceramide backbone toward specific downstream metabolic pathways during myelination. Our findings provide insights into myelin production in oligodendrocytes and suggest how dysregulation of the biosynthesis of this highly specialized membrane could contribute to demyelinating diseases.

Alcoholic liver disease (ALD) is the most prevalent type of chronic liver disease with significant morbidity and mortality worldwide. ALD begins with simple hepatic steatosis and progresses to alcoholic steatohepatitis, fibrosis, and cirrhosis. The severity of hepatic steatosis is highly associated with the development of later stages of ALD. This review explores the disturbances of alcohol-induced hepatic lipid metabolism through altered hepatic lipid uptake, de novo lipid synthesis, fatty acid oxidation, hepatic lipid export, and lipid droplet formation and catabolism. In addition, we review emerging data on the contributions of genetics and bioactive lipid metabolism in alcohol-induced hepatic lipid accumulation.

The formation and properties of liquid-ordered (Lo) lipid domains (rafts) in the plasma membrane are still poorly understood. This limits our ability to manipulate ordered lipid domain-dependent biological functions. Giant plasma membrane vesicles (GPMVs) undergo large-scale phase separations into coexisting Lo and liquid-disordered lipid domains. However, large-scale phase separation in GPMVs detected by light microscopy is observed only at low temperatures. Comparing Förster resonance energy transfer-detected versus light microscopy-detected domain formation, we found that nanodomains, domains of nanometer size, persist at temperatures up to 20°C higher than large-scale phases, up to physiologic temperature. The persistence of nanodomains at higher temperatures is consistent with previously reported theoretical calculations. To investigate the sensitivity of nanodomains to lipid composition, GPMVs were prepared from mammalian cells in which sterol, phospholipid, or sphingolipid composition in the plasma membrane outer leaflet had been altered by cyclodextrin-catalyzed lipid exchange. Lipid substitutions that stabilize or destabilize ordered domain formation in artificial lipid vesicles had a similar effect on the thermal stability of nanodomains and large-scale phase separation in GPMVs, with nanodomains persisting at higher temperatures than large-scale phases for a wide range of lipid compositions. This indicates that it is likely that plasma membrane nanodomains can form under physiologic conditions more readily than large-scale phase separation. We also conclude that membrane lipid substitutions carried out in intact cells are able to modulate the propensity of plasma membranes to form ordered domains. This implies lipid substitutions can be used to alter biological processes dependent upon ordered domains.

Acne is one of the most common dermatological conditions, but the details of its pathology are unclear, and current management regimens often have adverse effects. Cutibacterium acnes is known as a major acne-associated bacterium that derives energy from lipase-mediated sebum lipid degradation. C. acnes is commensal, but lipase activity has been observed to differ among C. acnes types. For example, higher populations of the type IA strains are present in acne lesions with higher lipase activity. In the present study, we examined a conserved lipase in types IB and II that was truncated in type IA C. acnes strains. Closed, blocked, and open structures of C. acnes ATCC11828 lipases were elucidated by X-ray crystallography at 1.6–2.4 Å. The closed crystal structure, which is the most common form in aqueous solution, revealed that a hydrophobic lid domain shields the active site. By comparing closed, blocked, and open structures, we found that the lid domain-opening mechanisms of C. acnes lipases (_CAlipases) involve the lid-opening residues, Phe-179 and Phe-211. To the best of our knowledge, this is the first structure-function study of _CAlipases, which may help to shed light on the mechanisms involved in acne development and may aid in future drug design.

Lipid rafts regulate the initiation of cellular metabolic and signaling pathways by organizing the pathway components in ordered microdomains on the cell surface. Cellular responses regulated by lipid rafts range from physiological to pathological, and the success of a therapeutic approach targeting "pathological" lipid rafts depends on the ability of a remedial agent to recognize them and disrupt pathological lipid rafts without affecting normal raft-dependent cellular functions. In this article, concluding the Thematic Review Series on Biology of Lipid Rafts, we review current experimental therapies targeting pathological lipid rafts, including examples of inflammarafts and clusters of apoptotic signaling molecule-enriched rafts. The corrective approaches include regulation of cholesterol and sphingolipid metabolism and membrane trafficking by using HDL and its mimetics, LXR agonists, ABCA1 overexpression, and cyclodextrins, as well as a more targeted intervention with apoA-I binding protein. Among others, we highlight the design of antagonists that target inflammatory receptors only in their activated form of homo- or heterodimers, when receptor dimerization occurs in pathological lipid rafts. Other therapies aim to promote raft-dependent physiological functions, such as augmenting caveolae-dependent tissue repair. The overview of this highly dynamic field will provide readers with a view on the emerging concept of targeting lipid rafts as a therapeutic strategy.

Cellular membranes are not homogenous mixtures of proteins; rather, they are segregated into microdomains on the basis of preferential association between specific lipids and proteins. These microdomains, called lipid rafts, are well known for their role in receptor signaling on the plasma membrane (PM) and are essential to such cellular functions as signal transduction and spatial organization of the PM. A number of disease states, including atherosclerosis and other cardiovascular disorders, may be caused by dysfunctional maintenance of lipid rafts. Lipid rafts do not occur only in the PM but also have been found in intracellular membranes and extracellular vesicles (EVs). Here, we focus on discussing newly discovered functions of lipid rafts and microdomains in intracellular membranes, including lipid and protein trafficking from the ER, Golgi bodies, and endosomes to the PM, and we examine lipid raft involvement in the production and composition of EVs. Because lipid rafts are small and transient, visualization remains challenging. Future work with advanced techniques will continue to expand our knowledge about the roles of lipid rafts in cellular functioning.

Lipid rafts are highly ordered regions of the plasma membrane that are enriched in cholesterol and sphingolipids and play important roles in many cells. In hematopoietic stem and progenitor cells (HSPCs), lipid rafts house receptors critical for normal hematopoiesis. Lipid rafts also can bind and sequester kinases that induce negative feedback pathways to limit proliferative cytokine receptor cycling back to the cell membrane. Modulation of lipid rafts occurs through an array of mechanisms, with optimal cholesterol efflux one of the major regulators. As such, cholesterol homeostasis also regulates hematopoiesis. Increased lipid raft content, which occurs in response to changes in cholesterol efflux in the membrane, can result in prolonged receptor occupancy in the cell membrane and enhanced signaling. In addition, certain diseases, like diabetes, may contribute to lipid raft formation and affect cholesterol retention in rafts. In this review, we explore the role of lipid raft-related mechanisms in hematopoiesis and CVD (specifically, atherosclerosis) and discuss how defective cholesterol efflux pathways in HSPCs contribute to expansion of lipid rafts, thereby promoting myelopoiesis and thrombopoiesis. We also discuss the utility of cholesterol acceptors in contributing to lipid raft regulation and disruption, and highlight the potential to manipulate these pathways for therapeutic gain in CVD as well as other disorders with aberrant hematopoiesis.

Activation of microglia and astrocytes secondary to inflammatory processes contributes to the development and perpetuation of pain with a neuropathic phenotype. This pain state presents as a chronic debilitating condition and affects a large population of patients with conditions like rheumatoid arthritis and diabetes, or after surgery, trauma, or chemotherapy. Here, we review the regulation of lipid rafts in glial cells and the role they play as a key component of neuroinflammatory sensitization of central pain signaling pathways. In this context, we introduce the concept of an inflammaraft (i-raft), enlarged lipid rafts harboring activated receptors and adaptor molecules and serving as an organizing platform to initiate inflammatory signaling and the cellular response. Characteristics of the inflammaraft include increased relative abundance of lipid rafts in inflammatory cells, increased content of cholesterol per raft, and increased levels of inflammatory receptors, such as toll-like receptor (TLR)4, adaptor molecules, ion channels, and enzymes in lipid rafts. This inflammaraft motif serves an important role in the membrane assembly of protein complexes, for example, TLR4 dimerization. Operating within this framework, we demonstrate the involvement of inflammatory receptors, redox molecules, and ion channels in the inflammaraft formation and the regulation of cholesterol and sphingolipid metabolism in the inflammaraft maintenance and disruption. Strategies for targeting inflammarafts, without affecting the integrity of lipid rafts in noninflammatory cells, may lead to developing novel therapies for neuropathic pain states and other neuroinflammatory conditions.

Lipid rafts are small, dynamic membrane areas characterized by the clustering of selected membrane lipids as the result of the spontaneous separation of glycolipids, sphingolipids, and cholesterol in a liquid-ordered phase. The exact dynamics underlying phase separation of membrane lipids in the complex biological membranes are still not fully understood. Nevertheless, alterations in the membrane lipid composition affect the lateral organization of molecules belonging to lipid rafts. Neural lipid rafts are found in brain cells, including neurons, astrocytes, and microglia, and are characterized by a high enrichment of specific lipids depending on the cell type. These lipid rafts seem to organize and determine the function of multiprotein complexes involved in several aspects of signal transduction, thus regulating the homeostasis of the brain. The progressive decline of brain performance along with physiological aging is at least in part associated with alterations in the composition and structure of neural lipid rafts. In addition, neurodegenerative conditions, such as lysosomal storage disorders, multiple sclerosis, and Parkinson’s, Huntington’s, and Alzheimer’s diseases, are frequently characterized by dysregulated lipid metabolism, which in turn affects the structure of lipid rafts. Several events underlying the pathogenesis of these diseases appear to depend on the altered composition of lipid rafts. Thus, the structure and function of lipid rafts play a central role in the pathogenesis of many common neurodegenerative diseases.

Cholesterol/sphingolipid-rich membrane domains, known as lipid rafts or membrane rafts, play a critical role in the compartmentalization of signaling pathways. Physical segregation of proteins in lipid rafts may modulate the accessibility of proteins to regulatory or effector molecules. Thus, lipid rafts serve as sorting platforms and hubs for signal transduction proteins. Cancer cells contain higher levels of intracellular cholesterol and lipid rafts than their normal non-tumorigenic counterparts. Many signal transduction processes involved in cancer development (insulin-like growth factor system and phosphatidylinositol 3-kinase-AKT) and metastasis [cluster of differentiation (CD)44] are dependent on or modulated by lipid rafts. Additional proteins playing an important role in several malignant cancers (e.g., transmembrane glycoprotein mucin 1) are also being detected in association with lipid rafts, suggesting a major role of lipid rafts in tumor progression. Conversely, lipid rafts also serve as scaffolds for the recruitment and clustering of Fas/CD95 death receptors and downstream signaling molecules leading to cell death-promoting raft platforms. The partition of death receptors and downstream signaling molecules in aggregated lipid rafts has led to the formation of the so-called cluster of apoptotic signaling molecule-enriched rafts, or CASMER, which leads to apoptosis amplification and can be pharmacologically modulated. These death-promoting rafts can be viewed as a linchpin from which apoptotic signals are launched. In this review, we discuss the involvement of lipid rafts in major signaling processes in cancer cells, including cell survival, cell death, and metastasis, and we consider the potential of lipid raft modulation as a promising target in cancer therapy.

Lipid rafts, solid regions of the plasma membrane enriched in cholesterol and glycosphingolipids, are essential parts of a cell. Functionally, lipid rafts present a platform that facilitates interaction of cells with the outside world. However, the unique properties of lipid rafts required to fulfill this function at the same time make them susceptible to exploitation by pathogens. Many steps of pathogen interaction with host cells, and sometimes all steps within the entire lifecycle of various pathogens, rely on host lipid rafts. Such steps as binding of pathogens to the host cells, invasion of intracellular parasites into the cell, the intracellular dwelling of parasites, microbial assembly and exit from the host cell, and microbe transfer from one cell to another all involve lipid rafts. Interaction also includes modification of lipid rafts in host cells, inflicted by pathogens from both inside and outside the cell, through contact or remotely, to advance pathogen replication, to utilize cellular resources, and/or to mitigate immune response. Here, we provide a systematic overview of how and why pathogens interact with and exploit host lipid rafts, as well as the consequences of this interaction for the host, locally and systemically, and for the microbe. We also raise the possibility of modulation of lipid rafts as a therapeutic approach against a variety of infectious agents.

Lipid rafts are organized plasma membrane microdomains, which provide a distinct level of regulation of cellular metabolism and response to extracellular stimuli, affecting a diverse range of physiologic and pathologic processes. This Thematic Review Series focuses on Biology of Lipid Rafts rather than on their composition or structure. The aim is to provide an overview of ideas on how lipid rafts are involved in regulation of different pathways and how they interact with other layers of metabolic regulation. Articles in the series will review the involvement of lipid rafts in regulation of hematopoiesis, production of extracellular vesicles, host interaction with infection, and the development and progression of cancer, neuroinflammation, and neurodegeneration, as well as the current outlook on therapeutic targeting of lipid rafts.