Defective Lipid Research Articles

Lipid droplet analysis in caveolin-deficient adipocytes: alterations in surface phospholipid composition and maturation defects

Caveolins form plasmalemnal invaginated caveolae. They also locate around intracellular lipid droplets but their role in this location remains unclear. By studying primary adipocytes that highly express caveolin-1, we characterized the impact of caveolin-1 deficiency on lipid droplet proteome and lipidome. We identified several missing proteins on the lipid droplet surface of caveolin-deficient adipocytes and showed that the caveolin-1 lipid droplet pool is organized as multi-protein complexes containing cavin-1, with similar dynamics as those found in caveolae. On the lipid side, caveolin deficiency did not qualitatively alter neutral lipids in lipid droplet, but significantly reduced the relative abundance of surface phospholipid species: phosphatidylserine and lysophospholipids. Caveolin-deficient adipocytes can form only small lipid droplets, suggesting that the caveolin-lipid droplet pool might be involved in lipid droplet size regulation. Accordingly, we show that caveolin-1 concentration on adipocyte lipid droplets positively correlated with lipid droplet size in obese rodent models and human adipocytes. Moreover, rescue experiments by caveolin- green fluorescent protein in caveolin-deficient cells exposed to fatty acid overload demonstrated that caveolin-coated lipid droplets were able to grow larger than caveolin-devoid lipid droplets. Altogether, these data demonstrate that the lipid droplet-caveolin pool impacts on phospholipid and protein surface composition of lipid droplets and suggest a functional role on lipid droplet expandability.

The ARF-Like GTPase ARFRP1 Is Essential for Lipid Droplet Growth and Is Involved in the Regulation of Lipolysis

ADP-ribosylation factor (ARF)-related protein 1 (ARFRP1) is a GTPase regulating protein trafficking between intracellular organelles. Here we show that mice lacking Arfrp1 in adipocytes (Arfrp1(ad-/-)) are lipodystrophic due to a defective lipid droplet formation in adipose cells. Ratios of mono-, di-, and triacylglycerol, as well as the fatty acid composition of triglycerides, were unaltered. Lipid droplets of brown adipocytes of Arfrp1(ad-/-) mice were considerably smaller and exhibited ultrastructural alterations, such as a disturbed interaction of small lipid-loaded particles with the larger droplets, suggesting that ARFRP1 mediates the transfer of newly formed small lipid particles to the large storage droplets. SNAP23 (synaptosomal-associated protein of 23 kDa) associated with small lipid droplets of control adipocytes but was located predominantly in the cytosol of Arfrp1(ad-/-) adipocytes, suggesting that lipid droplet growth is defective in Arfrp1(ad-/-) mice. In addition, levels of phosphorylated hormone-sensitive lipase (HSL) were elevated, and association of adipocyte triglyceride lipase (ATGL) with lipid droplets was enhanced in brown adipose tissue from Arfrp1(ad-/-) mice. Accordingly, basal lipolysis was increased after knockdown of Arfrp1 in 3T3-L1 adipocytes. The data indicate that disruption of ARFRP1 prevents the normal enlargement of lipid droplets and produces an activation of lipolysis.

Ichthyosis congenita gravis – eine medizinische und psychosoziale Herausforderung

Harlequin ichthyosis is the most severe congenital keratinizing disorder. It is caused by mutations in the ABCA12 gene leading to defective lipid transport. The infants are born with ectropion, eclabium and fissured plate-like skin. Today these infants can survive with neonatal intensive care and retinoid therapy and need long-term interdisciplinary treatment in order to improve quality of life. However, the outcome in our case is impaired by severe psychomotor developmental delay, which has not yet been associated with Harlequin Ichthyosis.

Dysregulation of lipolysis and lipid metabolism in visceral and subcutaneous adipocytes by high-fat diet: role of ATGL, HSL, and AMPK

This study investigated the molecular mechanisms by which a high-fat diet (HFD) dysregulates lipolysis and lipid metabolism in mouse epididymal (visceral, VC) and inguinal (subcutaneous, SC) adipocytes. Eight-weeks of HFD feeding increased adipose triglyceride lipase (ATGL) content and comparative gene identification-58 (CGI-58) expression, whereas hormone-sensitive lipase (HSL) phosphorylation and perilipin content were severely reduced. Adipocytes from HFD mice elicited increased basal but blunted epinephrine-stimulated lipolysis and increased diacylglycerol content in both fat depots. Consistent with impaired adrenergic receptor signaling, HFD also increased adipose-specific phospholipase A(2) expression in both fat depots. Inhibition of E-prostanoid 3 receptor increased basal lipolysis in control adipocytes but failed to acutely alter the effects of HFD on lipolysis in both fat depots. In HFD visceral adipocytes, activation of adenylyl cyclases by forskolin increased HSL phosphorylation and surpassed the lipolytic response of control cells. However, in HFD subcutaneous adipocytes, forskolin induced lipolysis without detectable HSL phosphorylation, suggesting activation of an alternative lipase in response to HFD-induced suppression of HSL in VC and SC adipocytes. HFD also powerfully inhibited basal, epinephrine-, and forskolin-induced AMP kinase (AMPK) activation as well peroxisome proliferator-activated receptor gamma coactivator-1alpha expression, citrate synthase activity, and palmitate oxidation in both fat depots. In summary, novel evidence is provided that defective adrenergic receptor signaling combined with upregulation of ATGL and suppression of HSL and AMPK signaling mediate HFD-induced alterations in lipolysis and lipid utilization in VC and SC adipocytes, which may play an important role in defective lipid mobilization and metabolism seen in diet-induced obesity.

1H, 13C, and 15N NMR assignments of StnII-R29Q, a defective lipid binding mutant of the sea anemone actinoporin Sticholysin II

Several studies have been made to characterize the molecular properties and activity of Sticholysin II (StnII), a 175 amino acid protein secreted by the sea anemone Stichodactyla helianthus. In particular, the biochemical characterization of different mutants of this protein have been shown to be essential for the rational understanding of its activity. Here we report the nearly complete NMR (15)N, (13)C and (1)H chemical shift assignments, at pH 4.0 and 25 degrees C, of a less hemolytic and defective lipid binding mutant of StnII, the R29Q variant (BMRB no 16362).

Apolipoprotein E knock-out and knock-in mice: atherosclerosis, metabolic syndrome, and beyond

Given the multiple differences between mice and men, it was once thought that mice could not be used to model atherosclerosis, principally a human disease. Apolipoprotein E-deficient (apoEKO) mice have convincingly changed this view, and the ability to model human-like plaques in these mice has provided scientists a platform to study multiple facets of atherogenesis and to explore potential therapeutic interventions. In addition to its well-established role in lipoprotein metabolism, recent observations of reduced adiposity and improved glucose homeostasis in apoEKO mice suggest that apoE may also play a key role in energy metabolism in peripheral organs, including adipose tissue. Finally, along with apoEKO mice, knockin mice expressing human apoE isoforms in place of endogenous mouse apoE have provided insights into how quantitative and qualitative genetic alterations interact with the environment in the pathogenesis of complex human diseases.

Unilateral Atrophy of the Cheek

Lipodystrophies are a set of heterogeneous conditions resulting from defective lipid metabolism and characterized by adipose tissue atrophy. We report on a 54-year-old woman who presented at the Department of Oral and Maxillofacial Surgery with an increasing unilateral atrophy of her left cheek for the past 3 years. The patient's history showed that she had sustained a left zygoma fracture 35 years ago but did not have any other disease. According to the patient's wish, a correction of the left cheek was performed by autologous fat injection, which led to a highly acceptable postoperative result. We compare this treatment with different alternatives.

Deletion of Single Amino Acid E235 Affects the Structure and Lipid Interaction of Human Apolipoprotein A-I C-Terminal Peptides

The C-terminal domain of apolipoprotein (apo) A-I plays an important role in lipid binding. ApoA-I Nichinan, a naturally occurring human apoA-I variant with a deletion of E235 located in the C-terminus, is associated with low high-density lipoprotein (HDL) cholesterolemia. In the present study, a series of variant peptides corresponding to residues 220-241 of human apoA-I were examined to clarify the influences of E235 deletion (DeltaE235) on the structure and lipid interaction of the C-terminal region. NMR studies demonstrated that in trifluoroethanol, apoA-I 220-241/DeltaE235 peptide forms the alpha-helical structure similar to wild-type (WT) peptide. Circular dichroism measurements revealed that the interaction with phospholipid vesicles induced structural changes from random coil to alpha-helix both in apoA-I 220-241 WT and E235A, a variant with a negative charge ablation, peptides. These peptides also showed abilities to form HDL-like particles through microsolubilization of phospholipid vesicles, indicating that the negative charge ablation in E235 has no effect on the lipid interaction. By contrast, neither lipid binding-induced alpha-helix formation nor microsolubilization of vesicles were observed in apoA-I 220-241/DeltaE235 and L230P, a helix-breaking variant, peptides. In addition, fluorescence measurements showed that tryptophan fluorescence intensity of apoA-I 220-241/F225W greatly increased upon lipid binding, while only a little increase was observed for the corresponding DeltaE235 variant. Taken together, these results suggest that the deletion of E235 causes defective lipid binding of apoA-I Nichinan because of the impaired helix-forming ability of the C-terminal residues.

Down-regulation of liver Gal β1, 4GlcNAc α2, 6-sialyltransferase gene by ethanol significantly correlates with alcoholic steatosis in humans

Hepatic steatosis and steatohepatitis are frequent results of long-term ethanol exposure. We have previously demonstrated that long-term ethanol down-regulates Gal βl, 4GlcNAc α2, 6-sialyltransferase (ST6Gal1), leading to defective glycosylation of a number of proteins including apolipoprotein (apo) E and apo J and the appearance of asialoconjugates in the blood of continuously alcohol-fed animals as well as in human alcoholics. In the current study, we have explored the possibility of whether ethanol-induced down-regulation of ST6Gal1 could contribute toward alcoholic steatosis in human alcoholics presumably because of impaired lipid and lipoprotein transport caused by this down-regulation. Real-time quantitative polymerase chain reaction analyses of liver samples from nondrinkers, moderate drinkers, and heavy drinkers as well as from subjects with and without alcoholic liver disease revealed direct evidence that the down-regulation of ST6Gal1 may be due to ethanol per se. The ST6Gal1 messenger RNA level was reduced by as much as 70% in moderate and heavy drinkers as well as in patients with alcoholic liver disease, but was not changed in subjects with liver disease due to causes other than alcohol exposure. Biochemical and histopathologic analysis demonstrated that the liver total cholesterol was increased by more than 30% ( P < .05) and 75% ( P < .01), respectively, in moderate and heavy drinkers compared with nondrinkers, with even more dramatic changes in triglyceride levels. Significantly, there was a strong inverse correlation between ST6Gal1 messenger RNA level and liver lipid deposit (F = 8.68, P < .001) by statistical analysis. Thus, it is suggested that alcohol-mediated down-regulation of hepatic ST6Gal1 gene leads to defective glycosylation of lipid-carrying apolipoproteins such as apo E and apo J, resulting in defective intracellular lipid and lipoprotein transport, which in turn may contribute to alcoholic steatosis.

FDA approves i.v. calcium-channel blocker

The Medicines Company and FDA announced in early August the approval of clevidipine butyrate, or Cleviprex, injectable emulsion for the reduction of blood pressure when oral therapy is not feasible or not desirable. According to the company, the drug, a dihydropyridine derivative, is the first new i.v. antihypertensive treatment for which FDA has approved labeling in 10 years. A spokesperson said the company plans to launch the product in September. The labeling recommends starting clevidipine butyrate treatment at 1–2 mg/hr and increasing the dosage until the desired blood pressure is attained. Reportedly, the desired therapeutic response in most patients occurs at 4–6 mg/hr. There is limited experience with the drug at a dosage of >32 mg/hr. Patients’ blood pressure and heart rate should be monitored continuously during clevidipine butyrate treatment and afterward until vital signs stabilize. Because Cleviprex is an oil-in-water emulsion made with soybean oil and egg yolk phospholipids, patients must not receive the drug product if they are allergic to soybeans, soy products, eggs, or egg products or have a condition involving defective lipid metabolism. In addition, patients with severe aortic stenosis must not receive clevidipine butyrate because the drug’s effect on the cardiovascular system may reduce the amount of oxygen delivered to the heart’s muscular tissue.

Differential Control of the CCAAT/Enhancer-binding Protein β (C/EBPβ) Products Liver-enriched Transcriptional Activating Protein (LAP) and Liver-enriched Transcriptional Inhibitory Protein (LIP) and the Regulation of Gene Expression during the Response to Endoplasmic Reticulum Stress

The accumulation of unfolded proteins in the endoplasmic reticulum (ER) triggers a stress response program that protects cells early in the response and can lead to apoptosis during prolonged stress. The basic leucine zipper transcription factor, CCAAT/enhancer-binding protein beta (C/EBPbeta), is one of the genes with increased expression during ER stress. Translation of the C/EBPbeta mRNA from different initiation codons leads to the synthesis of two transcriptional activators (LAP-1 and -2) and a transcriptional repressor (LIP). The LIP/LAP ratio is a critical factor in C/EBPbeta-mediated gene transcription. It is shown here that the LIP/LAP ratio decreased by 5-fold during the early phase of ER stress and increased by 20-fold during the late phase, mostly because of changes in LIP levels. The early decrease in LIP required degradation via the proteasome pathway and phosphorylation of the translation initiation factor, eIF2alpha. The increased LIP levels during the late phase were due to increased synthesis and increased stability of the protein. It is proposed that regulation of synthesis and degradation rates during ER stress controls the LIP/LAP ratio. The importance of C/EBPbeta in the ER-stress response program was demonstrated using C/EBPbeta-deficient mouse embryonic fibroblasts. It is shown that C/EBPbeta attenuates expression of pro-survival ATF4 target genes in late ER stress and enhances expression of cell death-associated genes downstream of CHOP. The inhibitory effect of LIP on ATF4-induced transcription was demonstrated for the cat-1 amino acid transporter gene. We conclude that regulation of LIP/LAP ratios during ER stress is a novel mechanism for modulating the cellular stress response.

Alzheimer's Risk Factor Also Aids HIV

A study out this week suggests that in addition to predisposing carriers to Alzheimer9s disease, the defective lipid transporter apolipoprotein E4 also hastens the death of people infected with HIV, possibly by allowing the virus easy entry into cells.

Pathogen destruction versus intracellular survival: the role of lipids as phagosomal fate determinants

Phagocytosis is a key component of the innate immune response and of the clearance of apoptotic bodies. Phagosome formation and subsequent maturation require extensive cytoskeletal rearrangement and precisely choreographed vesicular fusion and fission events. The objectives of this review are to highlight the functional importance of lipids in the phagocytic process, to discuss how pathogenic microorganisms can in some cases manipulate host lipid metabolism to either co-opt or disrupt phagosome maturation and promote their own survival, and to describe how defective phagosomal lipid metabolism can result in disease.

An update on molecular aspects of the non‐syndromic ichthyoses

Ichthyosis includes a number of subtypes from congenital severe forms, such as harlequin ichthyosis (HI), to mild non-congenital forms, such as ichthyosis vulgaris. Recently, research into the pathomechanisms of ichthyoses has dramatically advanced and led to the identification of several causative genes and molecules underlying the genetic defects. In most types of ichthyosis, pathogenic mechanisms are associated with defects in skin barrier function. Three major components of the stratum corneum barrier are (i) intercellular lipid layers, (ii) cornified cell envelope and (iii) keratin-filaggrin degradation products. The causative molecules underlying ichthyosis subtypes include ABCA12, lipoxygenase-3, 12R-lipoxygenase, CYP4F2 homolog, ichthyin and steroid sulphatase and all these are thought to be related to the intercellular lipid layers. Transglutaminase 1 has a function in cornified cell envelope formation. Keratins 1, 10 and 2 are involved in the keratin network of suprabasal keratinocytes and filaggrin are essential for formation of keratohyalin granules. In fact, loss of ABCA12 function leads to a defective lipid barrier in the stratum corneum, resulting in the HI phenotype and ABCA12 is a known keratinocyte lipid transporter associated with lipid transport in lamellar granules. Filaggrin gene mutations in ichthyosis vulgaris cause keratohyalin granule deficiency. Information concerning genetic defects and ichthyotic disease pathomechanisms are beneficial to develop effective therapy and provide information for genetic counselling including prenatal diagnosis for families affected by ichthyotic disease.

Stratum Corneum Acidification Is Impaired in Moderately Aged Human and Murine Skin

Aged skin commonly is afflicted by inflammatory skin diseases or xerosis/eczema that could be triggered or exacerbated by impaired epidermal permeability barrier homeostasis. This defect is linked to reduced epidermal lipid synthesis in humans and in mice of advanced age (i.e., >75 years in human or >18-24 months in mice). We now report that barrier defects in moderately aged humans (50-80 years) or analogously aged mice (12-15 months) are linked instead to defective stratum corneum (SC) acidity. In moderately aged mouse epidermis, we find that abnormal acidification, in turn, is linked to decreased Na+/H+ antiporter (NHE1) expression. Decreased NHE1 levels lead to increased SC pH, which results in defective lipid processing and delayed maturation of lamellar membranes, due to suboptimal activation of the pH-sensitive essential, lipid-processing enzyme, beta-glucocerebrosidase. Conversely, impaired SC integrity in moderately aged mice is due to increased pH-dependent activation of serine proteases, leading to premature degradation of corneodesmosomes. These abnormalities were normalized by exogenously acidifying the SC, suggesting a basis for the well-known acidification therapies that are widely used to treat the pathologic xerosis/eczema seen in moderately aged humans.

Defective Lipid Delivery Modulates Glucose Tolerance and Metabolic Response to Diet in Apolipoprotein E–Deficient Mice

Apolipoprotein E (ApoE) regulates plasma lipid levels via modulation of lipolysis and serving as ligand for receptor-mediated clearance of triglyceride (TG)-rich lipoproteins. This study tested the impact of modulating lipid delivery to tissues on insulin responsiveness and diet-induced obesity. ApoE(+/+) and apoE(-/-) mice were placed on high-fat-high-sucrose diabetogenic diet or control diet for 24 weeks. Plasma TG clearance, glucose tolerance, and tissue uptake of dietary fat and glucose were assessed. Plasma TG clearance and lipid uptake by adipose tissue were impaired, whereas glucose tolerance was improved in control diet-fed apoE(-/-) mice compared with apoE(+/+) mice after an oral lipid load. Fat mass was reduced in apoE(-/-) mice compared with apoE(+/+) mice under both dietary conditions. The apoE(-/-) mice exhibited lower body weight and insulin levels than apoE(+/+) mice when fed the diabetogenic diet. Glucose tolerance and uptake by muscle and brown adipose tissue (BAT) was also improved in mice lacking apoE when fed the diabetogenic diet. Indirect calorimetry studies detected no difference in energy expenditure and respiratory quotient between apoE(+/+) and apoE(-/-) mice on control diet. Energy expenditure and uncoupling protein-1 expression in BAT were slightly but not significantly increased in apoE(-/-) mice on diabetogenic diet. These results demonstrated that decreased lipid delivery to insulin-sensitive tissues improves insulin sensitivity and ameliorates diet-induced obesity.

Dynamics and heterogeneity of bovine hippocampal membranes: Role of cholesterol and proteins

The structural and dynamic consequence of alterations in membrane lipid composition (specifically cholesterol) in neuronal membranes is poorly understood. Previous work from our laboratory has established bovine hippocampal membranes as a convenient natural source for studying neuronal receptors. In this paper, we have explored the role of cholesterol and proteins in the dynamics and heterogeneity of bovine hippocampal membranes using fluorescence lifetime distribution analysis of the environment-sensitive fluorescent probe Nile Red incorporated into such membranes by the maximum entropy method (MEM), and time-resolved fluorescence anisotropy measurements. The peak position and the width of the lifetime distribution of Nile Red show a progressive reduction with increasing cholesterol depletion from native hippocampal membranes indicating that the extent of heterogeneity decreases with decrease in membrane cholesterol content. This is accompanied by a concomitant decrease of the fluorescence anisotropy and rotational correlation time. Our results point out that the microenvironment experienced by Nile Red is relatively insensitive to the presence of proteins in hippocampal membranes. Interestingly, Nile Red lifetime distribution in liposomes of lipid extracts is similar to that of native membranes indicating that proteins do not contribute significantly to the high level of heterogeneity observed in native membranes. These results could be relevant in understanding the neuronal diseases characterized by defective membrane lipid metabolism.

The Crucial Step in Ether Phospholipid Biosynthesis: Structural Basis of a Noncanonical Reaction Associated with a Peroxisomal Disorder

Ether phospholipids are essential constituents of eukaryotic cell membranes. Rhizomelic chondrodysplasia punctata type 3 is a severe peroxisomal disorder caused by inborn deficiency of alkyldihydroxyacetonephosphate synthase (ADPS). The enzyme carries out the most characteristic step in ether phospholipid biosynthesis: formation of the ether bond. The crystal structure of ADPS from Dictyostelium discoideum shows a fatty-alcohol molecule bound in a narrow hydrophobic tunnel, specific for aliphatic chains of 16 carbons. Access to the tunnel is controlled by a flexible loop and a gating helix at the protein-membrane interface. Structural and mutagenesis investigations identify a cluster of hydrophilic catalytic residues, including an essential tyrosine, possibly involved in substrate proton abstraction, and the arginine that is mutated in ADPS-deficient patients. We propose that ether bond formation might be orchestrated through a covalent imine intermediate with the flavin, accounting for the noncanonical employment of a flavin cofactor in a nonredox reaction.

Increased lipid rafts and accelerated lipopolysaccharide-induced tumor necrosis factor-α secretion in Abca1-deficient macrophages

Lipid rafts on the cell surface are believed to be very important as platforms for various cellular functions. The aim of this study was to know whether defective lipid efflux may influence lipid rafts on the cell surface and their related cellular functions. We investigated macrophages with defective lipid efflux from ATP binding cassette transporter A1-deficient (Abca1-KO) mice. Lipid rafts were evaluated by the following two novel probes: a biotinylated and protease (subtilisin Carlsberg)-nicked derivative of theta-toxin and a fluorescein ester of polyethylene glycol-derived cholesterol. Lipid rafts in Abca1-KO macrophages were increased, as demonstrated by both probes. Moreover, activities of nuclear factor kappaB, mRNA and intracellular distribution, and secretion of tumor necrosis factor-alpha (TNF-alpha) were examined after stimulation by lipopolysaccharides (LPSs). LPS-induced responses of the activation of nuclear factor kappaB and TNF-alpha were more prompt and accelerated in the Abca1-KO macrophages compared with wild-type macrophages. Modification of lipid rafts by cyclodextrin and nystatin corrected the abnormal response, suggesting an association between the increased lipid rafts and abnormal TNF-alpha secretion. We report here that Abca1-KO macrophages with defective lipid efflux exhibited increased lipid rafts on the cell surface and accelerated TNF-alpha secretion.

Characterization of plasma proteome in biliary atresia

Background Biliary atresia (BA) is a disorder during infancy with unknown etiology in which progression frequently leads to liver cirrhosis. Plasma proteome is characterized in this study. Methods Twelve paired plasma samples from 6 children with BA who received surgical correction at early stage and then liver transplantation at late stage of liver cirrhosis were studied. Plasma samples from 2 subjects without liver disorder were used as normal reference for 2-dimensional gel electrophoresis and for identification of protein spots by mass spectrometric analysis. Plasma samples from another 3 normal subjects (with a total of 5) were used for nephelometric quantification of immunoglobulin kappa light chain in comparison with patients' samples. Results Among the protein spots detected, ranging from 6 to 200 kDa mass with p Is of 3–10, significant up-regulation of immunoglobulin kappa light chain was found at the late stage of BA, which was subsequently confirmed by nephelometric analysis. Conversely, significant decrease of apolipoprotein (Apo) A-I and C-II, haptoglobin α2 and β chain, and transthyretin were detected during the progression of BA. Conclusions Increased immunoglobulin kappa light chain detected in late-stage BA characterizes adverse immune modulation in this disorder. Decreased apolipoproteins, haptoglobin and transthyretin levels might be potential markers of progressive liver injury, fibrosis and defective lipid metabolism in BA.