Phosphatidylethanolamine -Methyltransferase Knockout Modulates Metabolic Changes in Aging Mice.

Phospholipid metabolism, including phosphatidylcholine (PC) biosynthesis, is crucial for various biological functions and is associated with longevity. Phosphatidylethanolamine -methyltransferase (PEMT) is a protein that catalyzes the biosynthesis of PC, the levels of which change in various organs such as the brain and kidneys during aging. However, the role of PEMT for systemic PC supply is not fully understood.

Global analysis of protein arginine methylation.

Quantitative information about the levels and dynamics of post-translational modifications (PTMs) is critical for an understanding of cellular functions. Protein arginine methylation (ArgMet) is an important subclass of PTMs and is involved in a plethora of (patho)physiological processes. However, because of the lack of methods for global analysis of ArgMet, the link between ArgMet levels, dynamics, and (patho)physiology remains largely unknown.

Metabolomic Profiles of Mouse Tissues Reveal an Interplay between Aging and Energy Metabolism.

Energy metabolism, including alterations in energy intake and expenditure, is closely related to aging and longevity. Metabolomics studies have recently unraveled changes in metabolite composition in plasma and tissues during aging and have provided critical information to elucidate the molecular basis of the aging process. However, the metabolic changes in tissues responsible for food intake and lipid storage have remained unexplored.

Tissue-Specific Landscape of Metabolic Dysregulation during Ageing.

The dysregulation of cellular metabolism is a hallmark of ageing. To understand the metabolic changes that occur as a consequence of the ageing process and to find biomarkers for age-related diseases, we conducted metabolomic analyses of the brain, heart, kidney, liver, lung and spleen in young (9-10 weeks) and old (96-104 weeks) wild-type mice [mixed genetic background of 129/J and C57BL/6] using NMR spectroscopy. We found differences in the metabolic fingerprints of all tissues and distinguished several metabolites to be altered in most tissues, suggesting that they may be universal biomarkers of ageing.

Lysosomal acid lipase regulates VLDL synthesis and insulin sensitivity in mice.

Aims/hypothesis: Lysosomal acid lipase (LAL) hydrolyses cholesteryl esters and triacylglycerols (TG) within lysosomes to mobilise NEFA and cholesterol. Since LAL-deficient (Lal (-/-) ) mice suffer from progressive loss of adipose tissue and severe accumulation of lipids in hepatic lysosomes, we hypothesised that LAL deficiency triggers alternative energy pathway(s).

Methods: We studied metabolic adaptations in Lal (-/-) mice.

Brain cortical cholesterol metabolism is highly affected by human APP overexpression in mice.

Processing of the amyloid precursor protein (APP) and amyloid beta (Aβ) has been for decades in the center of Alzheimer's disease (AD) research. Beside many other variables, lipids, especially cholesterol and its derivatives, are discussed to contribute to AD pathogenesis. Several studies show that cholesterol affects APP metabolism.

Neuroinflammation and related neuropathologies in APPSL mice: further value of this in vivo model of Alzheimer's disease.

Background: Beyond cognitive decline, Alzheimer's disease (AD) is characterized by numerous neuropathological changes in the brain. Although animal models generally do not fully reflect the broad spectrum of disease-specific alterations, the APPSL mouse model is well known to display early plaque formation and to exhibit spatial learning and memory deficits. However, important neuropathological features, such as neuroinflammation and lipid peroxidation, and their progression over age, have not yet been described in this AD mouse model.

Impact of ApoB-100 expression on cognition and brain pathology in wild-type and hAPPsl mice.

During their lifetime, people are commonly exposed to several vascular risk factors that may affect brain ageing and cognitive function. In the last few years, increasing evidence suggests that pathological plasma lipid profiles contribute to the pathogenesis of late-onset Alzheimer's disease. Importantly, hypercholesterolemia, especially elevated low-density lipoprotein cholesterol values, that is, increased apolipoprotein B-100 (ApoB-100) levels, represents an independent risk factor.

Metabolic link between phosphatidylethanolamine and triacylglycerol metabolism in the yeast Saccharomyces cerevisiae.

In the yeast Saccharomyces cerevisiae triacylglycerols (TAG) are synthesized by the acyl-CoA dependent acyltransferases Dga1p, Are1p, Are2p and the acyl-CoA independent phospholipid:diacylglycerol acyltransferase (PDAT) Lro1p which uses phosphatidylethanolamine (PE) as a preferred acyl donor. In the present study we investigated a possible link between TAG and PE metabolism by analyzing the contribution of the four different PE biosynthetic pathways to TAG formation, namely de novo PE synthesis via Psd1p and Psd2p, the CDP-ethanolamine (CDP-Etn) pathway and lyso-PE acylation by Ale1p. In cells grown on the non-fermentable carbon source lactate supplemented with 5mM ethanolamine (Etn) the CDP-Etn pathway contributed most to the cellular TAG level, whereas mutations in the other pathways displayed only minor effects.

Sequential synthesis and methylation of phosphatidylethanolamine promote lipid droplet biosynthesis and stability in tissue culture and in vivo.

Triacylglycerols are stored in eukaryotic cells within lipid droplets (LD). The LD core is enwrapped by a phospholipid monolayer with phosphatidylcholine (PC), the major phospholipid, and phosphatidylethanolamine (PE), a minor component. We demonstrate that the onset of LD formation is characterized by a change in cellular PC, PE, and phosphatidylserine (PS).

Oleate inhibits steryl ester synthesis and causes liposensitivity in yeast.

In the yeast Saccharomyces cerevisiae, neutral lipids can be synthesized by four acyltransferases, namely Dga1p and Lro1p producing triacylglycerols (TAG) and Are1p and Are2p forming steryl esters (SE). TAG and SE are stored in an organelle called lipid particles/droplet. Growth of yeast cells on oleate-supplemented media strongly induced proliferation of lipid particles and specifically the synthesis of TAG, which serve as the major pool for the excess of fatty acids.

Compound heterozygosity (G71R/R140H) in the lecithin:cholesterol acyltransferase (LCAT) gene results in an intermediate phenotype between LCAT-deficiency and fish-eye disease.

The esterification of free cholesterol (FC) in plasma, catalyzed by the enzyme lecithin:cholesterol acyltransferase (LCAT; EC 2.3.1.

Endothelial lipase releases saturated and unsaturated fatty acids of high density lipoprotein phosphatidylcholine.

We assessed the ability of endothelial lipase (EL) to hydrolyze the sn-1 and sn-2 fatty acids (FAs) from HDL phosphatidylcholine. For this purpose, reconstituted discoidal HDLs (rHDLs) that contained free cholesterol, apolipoprotein A-I, and either 1-palmitoyl-2-oleoylphosphatidylcholine, 1-palmitoyl-2-linoleoylphosphatidylcholine, or 1-palmitoyl-2-arachidonylphosphatidylcholine were incubated with EL- and control (LacZ)-conditioned media. Gas chromatography analysis of the reaction mixtures revealed that both the sn-1 (16:0) and sn-2 (18:1, 18:2, and 20:4) FAs were liberated by EL.

Defective uptake of triglyceride-associated fatty acids in adipose tissue causes the SREBP-1c-mediated induction of lipogenesis.

Lipoprotein lipase (LPL) is the only known enzyme in the capillary endothelium of peripheral tissues that hydrolizes plasma triglycerides and provides fatty acids (FAs) for their subsequent tissue uptake. Previously, we demonstrated that mice that express LPL exclusively in muscle develop essentially normal fat mass despite the absence of LPL and the deprivation of nutritionally derived FAs in adipose tissue (AT). Using this mouse model, we now investigated the metabolic response to LPL deficiency in AT that enables maintenance of normal AT mass.

Myocardial dysfunction and male mortality in peroxisome proliferator-activated receptor alpha knockout mice overexpressing lipoprotein lipase in muscle.

Free fatty acids (FFA) are liberated from triglyceride-rich lipoproteins by lipoprotein lipase (LPL) and are considered to be a principal energy source for the heart. The peroxisome proliferator-activated receptor alpha (PPARalpha) is a key regulator of FFA catabolism. To investigate its role in cardiac muscle metabolism, transgenic mice overexpressing LPL in skeletal and cardiac muscle were bred on a PPARalpha knockout background.

Intracellular distribution and mobilization of unesterified cholesterol in adipocytes: triglyceride droplets are surrounded by cholesterol-rich ER-like surface layer structures.

In addition to their central role in triglyceride storage, fat cells are a primary depot of unesterified cholesterol (FC) in the body. In comparison, peripheral cells contain very little FC. This difference in adipocytes versus peripheral tissues is inconsistent with the current theory of cholesterol homeostasis.

Origin and function of epoxyeicosatrienoic acids in vascular endothelial cells: more than just endothelium-derived hyperpolarizing factor?

1. In addition to their contribution to endothelium-derived hyperpolarization, our understanding of the physiological function of epoxyeicosatrienoic acids (EET) within the vascular wall and the actual enzymes involved in the formation of the EET in endothelial cells is very limited. In the present study, the expression of potential cytochrome P450 (CYP) mono/epoxygenases was assessed in endothelial cells isolated from porcine and bovine aortas as well as in the human umbilical vein-derived cell lines EA.

Metabolism of Lp(a): assembly and excretion.

Lp(a) is one of the most atherogenic lipoproteins, and we know much more about the pathophysiology of Lp(a) than about its physiological function and metabolism. From our previous investigations and the new results reported here, we propose the following model of Lp(a) metabolism: apo(a) is biosynthesized in liver cells and the size of the isoform determines its rate of synthesis and excretion. Specific kringle-4 domains in apo(a), mainly T-6 and T-7, bind in a first step to circulating LDL, followed by the stabilization of the newly formed Lp(a) complex by a disulfide bridge.

LDL-mediated interaction of Lp[a] with HepG2 cells: a novel fluorescence microscopy approach.

We studied the topography of Lp[a]-LDL-cell interactions by means of fluorescence microscopy, using fluorescence-labeled lipoproteins. In contrast to known methods which are based on noncovalent labeling of lipoproteins by positively charged amphiphiles, the protein moiety of LDL and Lp[a] was covalently labeled with either BODIP-succinimide-ester (green) or rhodamine X iodoacetamide (red). The interaction of the fluorescent lipoproteins with cultured HepG2 cells was studied using a confocal laser scanning fluorescence microscope.

Urinary excretion of apo(a) fragments. Role in apo(a) catabolism.

The biosynthesis and assembly of lipoprotein(a) [Lp(a)], a marker for atherosclerotic disease, appears to be well understood. However, information is lacking concerning the mode and site of Lp(a) catabolism. Apo(a) is reported to be excreted into the urine.

Molecular characterization of quail apolipoprotein very-low-density lipoprotein II: disulphide-bond-mediated dimerization is not essential for inhibition of lipoprotein lipase.

As part of the avian reproductive effort, large quantities of triglyceride-rich very-low-density lipoprotein (VLDL) particles are transported by receptor-mediated endocytosis into the female germ cells. Although the oocytes are surrounded by a layer of granulosa cells harbouring high levels of active lipoprotein lipase, non-lipolysed VLDL is transported into the yolk. This is because VLDL particles from laying chickens are protected from lipolysis by apolipoprotein (apo)-VLDL-II, a potent dimeric lipoprotein lipase inhibitor [Schneider, Carroll, Severson and Nimpf (1990) J.

A single G to A nucleotide transition in exon IV of the lecithin: cholesterol acyltransferase (LCAT) gene results in an Arg140 to His substitution and causes LCAT-deficiency.

We have characterized the molecular defect causing lecithin:cholesterol acyltransferase (LCAT)-deficiency (LCAT-D) in the LCAT gene in three siblings of Austrian descent. The patients presented with typical symptoms including corneal opacity, hemolytic anemia, and kidney dysfunction. LCAT activities in the plasma of these three patients were undetectable.

A double labeling procedure for lipoproteins: independent visualization of dual ligand-receptor interaction with colloidal gold- and 125I-labeled ligands.

The analysis of multiple ligand binding to a single receptor molecule poses a methodological challenge. The chicken oocyte 95-kDa receptor for the uptake of the two major yolk lipoprotein precursors very low-density lipoprotein (VLDL) and vitellogenin (VTG) is such a multipotent transport receptor. Here we describe methods for rapid independent and simultaneous analysis of VLDL and VTG binding to this receptor, termed VLDL/VTG receptor.

Chicken yolk contains bona fide high density lipoprotein particles.

Lipoproteins, the major nutrient source for developing embryos in egg-laying species, are thought to be transported from the circulation of the hen to the yolk of growing oocytes. In order to fully understand the contribution of the different lipoprotein species to oocyte growth, yolk formation, and embryo development, we have started to elucidate the relationships between the high density lipoproteins (HDL) in serum with the hitherto uncharacterized yolk HDL fraction. Immunoblotting with antibodies against apolipoprotein (apo) A-I, the major protein moiety of circulating HDL, revealed, for the first time, significant amounts of this protein in yolk.