Identification of an IL-6 response element in the human LCAT promoter

Effect of Short-Chain Fatty Acids and Polyunsaturated Fatty Acids on Metabolites in H460 Lung Cancer Cells

Lung cancer is the most common primary malignant lung tumor. However, the etiology of lung cancer is still unclear. Fatty acids include short-chain fatty acids (SCFAs) and polyunsaturated fatty acids (PUFAs) as essential components of lipids. SCFAs can enter the nucleus of cancer cells, inhibit histone deacetylase activity, and upregulate histone acetylation and crotonylation. Meanwhile, PUFAs can inhibit lung cancer cells. Moreover, they also play an essential role in inhibiting migration and invasion. However, the mechanisms and different effects of SCFAs and PUFAs on lung cancer remain unclear. Sodium acetate, butyrate, linoleic acid, and linolenic acid were selected to treat H460 lung cancer cells. Through untargeted metabonomics, it was observed that the differential metabolites were concentrated in energy metabolites, phospholipids, and bile acids. Then, targeted metabonomics was conducted for these three target types. Three LC-MS/MS methods were established for 71 compounds, including energy metabolites, phospholipids, and bile acids. The subsequent methodology validation results were used to verify the validity of the method. The targeted metabonomics results show that, in H460 lung cancer cells incubated with linolenic acid and linoleic acid, while the content of PCs increased significantly, the content of Lyso PCs decreased significantly. This demonstrates that there are significant changes in LCAT content before and after administration. Through subsequent WB and RT-PCR experiments, the result was verified. We demonstrated a substantial metabolic disparity between the dosing and control groups, further verifying the reliability of the method.

High-Density Lipoprotein Modifications: A Pathological Consequence or Cause of Disease Progression?

High-density lipoprotein (HDL) is well-known for its cardioprotective effects, as it possesses anti-inflammatory, anti-oxidative, anti-thrombotic, and cytoprotective properties. Traditionally, studies and therapeutic approaches have focused on raising HDL cholesterol levels. Recently, it became evident that, not HDL cholesterol, but HDL composition and functionality, is probably a more fruitful target. In disorders, such as chronic kidney disease or cardiovascular diseases, it has been observed that HDL is modified and becomes dysfunctional. There are different modification that can occur, such as serum amyloid, an enrichment and oxidation, carbamylation, and glycation of key proteins. Additionally, the composition of HDL can be affected by changes to enzymes such as cholesterol ester transfer protein (CETP), lecithin-cholesterol acyltransferase (LCAT), and phospholipid transfer protein (PLTP) or by modification to other important components. This review will highlight some main modifications to HDL and discuss whether these modifications are purely a consequential result of pathology or are actually involved in the pathology itself and have a causal role. Therefore, HDL composition may present a molecular target for the amelioration of certain diseases, but more information is needed to determine to what extent HDL modifications play a causal role in disease development.

Allele-specific enhancers mediate associations between LCAT and ABCA1 polymorphisms and HDL metabolism

For most complex traits, the majority of SNPs identified through genome-wide association studies (GWAS) reside within noncoding regions that have no known function. However, these regions are enriched for the regulatory enhancers specific to the cells relevant to the specific trait. Indeed, many of the GWAS loci that have been functionally characterized lie within enhancers that regulate expression levels of key genes. In order to identify polymorphisms with potential allele-specific regulatory effects, we developed a bioinformatics pipeline that harnesses epigenetic signatures as well as transcription factor (TF) binding motifs to identify putative enhancers containing a SNP with potential allele-specific TF binding in linkage disequilibrium (LD) with a GWAS-identified SNP. We applied the approach to GWAS findings for blood lipids, revealing 7 putative enhancers harboring associated SNPs, 3 of which lie within the introns of LCAT and ABCA1, genes that play crucial roles in cholesterol biogenesis and lipoprotein metabolism. All 3 enhancers demonstrated allele-specific in vitro regulatory activity in liver-derived cell lines. We demonstrated that these putative enhancers are in close physical proximity to the promoters of their respective genes, in situ, likely through chromatin looping. In addition, the associated alleles altered the likelihood of transcription activator STAT3 binding. Our results demonstrate that through our approach, the LD blocks that contain GWAS signals, often hundreds of kilobases in size with multiple SNPs serving as statistical proxies to the true functional site, can provide an experimentally testable hypothesis for the underlying regulatory mechanism linking genetic variants to complex traits.

Lecithin:Cholesterol Acyltransferase Activation by Sulfhydryl-Reactive Small Molecules: Role of Cysteine-31

Lecithin:cholesterol acyltransferase (LCAT) catalyzes plasma cholesteryl ester formation and is defective in familial lecithin:cholesterol acyltransferase deficiency (FLD), an autosomal recessive disorder characterized by low high-density lipoprotein, anemia, and renal disease. This study aimed to investigate the mechanism by which compound A [3-(5-(ethylthio)-1,3,4-thiadiazol-2-ylthio)pyrazine-2-carbonitrile], a small heterocyclic amine, activates LCAT. The effect of compound A on LCAT was tested in human plasma and with recombinant LCAT. Mass spectrometry and nuclear magnetic resonance were used to determine compound A adduct formation with LCAT. Molecular modeling was performed to gain insight into the effects of compound A on LCAT structure and activity. Compound A increased LCAT activity in a subset (three of nine) of LCAT mutations to levels comparable to FLD heterozygotes. The site-directed mutation LCAT-Cys31Gly prevented activation by compound A. Substitution of Cys31 with charged residues (Glu, Arg, and Lys) decreased LCAT activity, whereas bulky hydrophobic groups (Trp, Leu, Phe, and Met) increased activity up to 3-fold (P < 0.005). Mass spectrometry of a tryptic digestion of LCAT incubated with compound A revealed a +103.017 m/z adduct on Cys31, consistent with the addition of a single hydrophobic cyanopyrazine ring. Molecular modeling identified potential interactions of compound A near Cys31 and structural changes correlating with enhanced activity. Functional groups important for LCAT activation by compound A were identified by testing compound A derivatives. Finally, sulfhydryl-reactive β-lactams were developed as a new class of LCAT activators. In conclusion, compound A activates LCAT, including some FLD mutations, by forming a hydrophobic adduct with Cys31, thus providing a mechanistic rationale for the design of future LCAT activators.

DYRK1A overexpression decreases plasma lecithin:cholesterol acyltransferase activity and apolipoprotein A-I levels

BACKGROUND AND AIMS

Down syndrome is caused by trisomy of all or part of human chromosome 21. Individuals with Down syndrome present some metabolic abnormalities involving lipoproteins, notably lower high-density lipoprotein levels associated with altered lecithin:cholesterol acyltransferase activity and apolipoprotein A-I levels. DYRK1A is a kinase overexpressed in Down syndrome that can activate the STAT3 pathway, which is involved in lecithin:cholesterol acyltransferase expression. Therefore, we characterized the role of DYRK1A overexpression on lecithin:cholesterol acyltransferase activity and expression in mouse models.

METHODS

Effects of Dyrk1a overexpression were examined in mice overexpressing Dyrk1a by ELISA, chemical analyses and Western blotting.

RESULTS

Overexpression of DYRK1A decreased plasma lecithin:cholesterol acyltransferase activity and hepatic STAT3 activation, which was associated with activation of SHP2, a tyrosine phosphatase. Although hepatic apolipoprotein E and D levels were increased in mice overexpressing DYRK1A, decreased plasma lecithin:cholesterol acyltransferase activity was associated with decreased hepatic and plasma apolipoprotein A-I levels. High-density lipoprotein-cholesterol levels were also decreased in plasma despite similar total cholesterol and non-high-density lipoprotein-cholesterol levels.

CONCLUSIONS

We identified the role of DYRK1A overexpression on altered lipoprotein metabolism.

Sensing of transcription factor binding via cyanine dye pair fluorescence lifetime changes

We designed and synthesized sensors for imaging transcription factor-DNA interactions using a complementary pair of 21-base pair long oligonucleotides (ODNs) carrying two internucleoside phosphate-linked cyanine fluorophores that can either engage in Förster's resonance energy transfer (FRET) with fluorescence emission or assemble into a ground state quenched dimer with short fluorescence lifetimes (FL). Cyanine fluorophores were linked to ODNs within the NF-κB binding site. These sensors were tested in the presence of recombinant p50 and p65 NF-κB proteins or constitutively NF-κB activating HeLa cell lysates. By using a coherent light excitation source we followed changes in fluorescence lifetime of the donor (Cy5.5) at the donor's excitation and emission light wavelengths, as well as the acceptor (800CW or Cy7 cyanine fluorophores) in FRET mode. We observed increases in the donor lifetime in both emitting (0.08-0.15 ns) and non-emitting quenched (0.21 ns) sensors in response to protein binding. The measurements of lifetimes in FRET mode in quenched pair-carrying ODN duplex sensors showed significant differences in FL of the acceptor cyanine fluorophore between NF-κB-containing and NF-κB-free samples but not in control sensors with ODN sequences that have decreased binding affinity to NF-κB. We anticipate that the observed effects will be instrumental for developing sensors enabling non-invasive imaging in cells that undergo activation of NF-κB.

Exercise-associated generation of PPARγ ligands activates PPARγ signaling events and upregulates genes related to lipid metabolism

The aim of the present study was to test the hypotheses that exercise is associated with generation of peroxisome proliferator-activated receptor-γ (PPARγ) ligands in the plasma and that this may activate PPARγ signaling within circulating monocytes, thus providing a mechanism to underpin the exercise-induced antiatherogenic benefits observed in previous studies. A cohort of healthy individuals undertook an 8-wk exercise-training program; samples were obtained before (Pre) and after (Post) standardized submaximal exercise bouts (45 min of cycling at 70% of maximal O2 uptake, determined at baseline) at weeks 0, 4, and 8. Addition of plasma samples to PPARγ response element (PPRE)-luciferase reporter gene assays showed increased PPARγ activity following standardized exercise bouts (Post/Pre = 1.23 ± 0.10 at week 0, P < 0.05), suggesting that PPARγ ligands were generated during exercise. However, increases in PPARγ/PPRE-luciferase activity in response to the same standardized exercise bout were blunted during the training program (Post/Pre = 1.18 ± 0.14 and 1.10 ± 0.10 at weeks 4 and 8, respectively, P > 0.05 for both), suggesting that the relative intensity of the exercise may affect PPARγ ligand generation. In untrained individuals, specific transient increases in monocyte expression of PPARγ-regulated genes were observed within 1.5–3 h of exercise (1.7 ± 0.4, 2.6 ± 0.4, and 1.4 ± 0.1 fold for CD36, liver X receptor-α, and ATP-binding cassette subfamily A member 1, respectively, P < 0.05), with expression returning to basal levels within 24 h. In contrast, by the end of the exercise program, expression at the protein level of PPARγ target genes had undergone sustained increases that were not associated with an individual exercise bout (e.g., week 8 Pre/ week 0 Pre = 2.79 ± 0.61 for CD36, P < 0.05). Exercise is known to upregulate PPARγ-controlled genes to induce beneficial effects in skeletal muscle (e.g., mitochondrial biogenesis and aerobic respiration). We suggest that parallel exercise-induced benefits may occur in monocytes, as monocyte PPARγ activation has been linked to beneficial antidiabetic effects (e.g., exercise-induced upregulation of monocytic PPARγ-controlled genes is associated with reverse cholesterol transport and anti-inflammatory effects). Thus, exercise-triggered monocyte PPARγ activation may constitute an additional rationale for prescribing exercise to type 2 diabetes patients.

Lecithin cholesterol acyltransferase: an anti- or pro-atherogenic factor?

Lecithin cholesterol acyl transferase (LCAT) is a plasma enzyme that esterifies cholesterol and raises high-density lipoprotein cholesterol, but its role in atherosclerosis is not clearly established. Studies of various animal models have yielded conflicting results, but studies done in rabbits and non-human primates, which more closely simulate human lipoprotein metabolism, indicate that LCAT is likely atheroprotective. Although suggestive, there are also no biomarker studies that mechanistically link LCAT with cardiovascular disease. Imaging studies of patients with LCAT deficiency have also not yielded a clear answer to the role of LCAT in atherosclerosis. Recombinant LCAT, however, is currently being developed as a therapeutic product for enzyme replacement therapy of patients with genetic disorders of LCAT for the prevention and/or treatment of renal disease, but it may also have value for the treatment of acute coronary syndrome.

Molecular characterization, expression profile and association analysis with carcass traits of porcine LCAT gene

The lecithin cholesterol acyltransferase gene (LCAT) plays an important role in lipoprotein metabolism, especially in the process termed 'reverse cholesterol transport'. In this study, we obtained the 1,434 bp mRNA sequence of porcine LCAT including the full coding region and encoding a protein of 472 amino acids. The sequence was deposited into the GenBank under the accession no. EU717835. The genomic sequence of this gene which contains six exons and five introns, is 3,712 bp in length (GQ379050). Bioinformatic analysis of the 5' regulatory region has revealed that some transcription factor Sp1, AP-1, AP-2 and NF-kappaB were represented in this region. Tissue expression analysis showed that the porcine LCAT gene is ubiquitously expressed in all examined tissues. Phylogenetic tree was constructed by aligning the amino acid sequences of different species. Moreover, we found a single nucleotide polymorphism (SNP, C/G266) in intron 1 of the LCAT gene and association analysis showed that it was significantly associated with ratio of lean to fat (P < 0.05), caul fat weight (P < 0.01), leaf fat weight (P < 0.05), carcass length (P < 0.05) and bone percentage (P < 0.05). Our study will lay the groundwork for the further investigations on the detailed physiological function of LCAT in pig models.

Long-Term Change in Cholesterol in Relation to Inflammation-Sensitive Plasma Proteins: A Longitudinal Study

PURPOSE

The nature of the relationship between inflammation and elevated serum lipid levels is incompletely understood. This longitudinal study explores whether elevated levels of inflammation-sensitive plasma proteins (ISPs) are a risk factor for developing increased cholesterol and triglyceride levels.

METHODS

Five ISPs (fibrinogen, orosomucoid, alpha1-antitrypsin, haptoglobin, and ceruloplasmin) were measured in a population-based cohort of nondiabetic healthy men aged 38 to 50 years at baseline. Subjects were reexamined after a mean of 6.2 years. The development of hypercholesterolemia (cholesterol>or=6.5 mmol/L [>or=251 mg/dL]) and hypertriglyceridemia (triglycerides>or=2.3 mmol/L [>or=204 mg/dL]) during follow-up was studied in relation to the number of elevated levels of ISPs (i.e., in the top quartile).

RESULTS

Of men with initially normal cholesterol levels (<6.5 mmol/L; n=2224), proportions of men with no, one, two, and three or more elevated ISP levels at baseline who developed hypercholesterolemia were 12%, 13%, 16%, and 20%, respectively (p for trend=0.0002). This relationship remained significant after adjustments for cholesterol level at baseline and other confounding factors. The relationship between ISP levels and future hypertriglyceridemia was attenuated and nonsignificant after adjustments for confounding factors.

CONCLUSION

In apparently healthy men with initially normal cholesterol levels, elevated ISP levels are a risk factor for development of hypercholesterolemia.

Convergence of genes implicated in Alzheimer's disease on the cerebral cholesterol shuttle: APP, cholesterol, lipoproteins, and atherosclerosis

Polymorphic genes associated with Alzheimer's disease (see ) delineate a clearly defined pathway related to cerebral and peripheral cholesterol and lipoprotein homoeostasis. They include all of the key components of a glia/neurone cholesterol shuttle including cholesterol binding lipoproteins APOA1, APOA4, APOC1, APOC2, APOC3, APOD, APOE and LPA, cholesterol transporters ABCA1, ABCA2, lipoprotein receptors LDLR, LRP1, LRP8 and VLDLR, and the cholesterol metabolising enzymes CYP46A1 and CH25H, whose oxysterol products activate the liver X receptor NR1H2 and are metabolised to esters by SOAT1. LIPA metabolises cholesterol esters, which are transported by the cholesteryl ester transport protein CETP. The transcription factor SREBF1 controls the expression of most enzymes of cholesterol synthesis. APP is involved in this shuttle as it metabolises cholesterol to 7-betahydroxycholesterol, a substrate of SOAT1 and HSD11B1, binds to APOE and is tethered to LRP1 via APPB1, APBB2 and APBB3 at the cytoplasmic domain and via LRPAP1 at the extracellular domain. APP cleavage products are also able to prevent cholesterol binding to APOE. BACE cleaves both APP and LRP1. Gamma-secretase (PSEN1, PSEN2, NCSTN) cleaves LRP1 and LRP8 as well as APP and their degradation products control transcription factor TFCP2, which regulates thymidylate synthase (TS) and GSK3B expression. GSK3B is known to phosphorylate the microtubule protein tau (MAPT). Dysfunction of this cascade, carved out by genes implicated in Alzheimer's disease, may play a major role in its pathology. Many other genes associated with Alzheimer's disease affect cholesterol or lipoprotein function and/or have also been implicated in atherosclerosis, a feature of Alzheimer's disease, and this duality may well explain the close links between vascular and cerebral pathology in Alzheimer's disease. The definition of many of these genes as risk factors is highly contested. However, when polymorphic susceptibility genes belong to the same signaling pathway, the risk associated with multigenic disease is better related to the integrated effects of multiple polymorphisms of genes within the same pathway than to variants in any single gene [Wu, X., Gu, J., Grossman, H.B., Amos, C.I., Etzel, C., Huang, M., Zhang, Q., Millikan, R.E., Lerner, S., Dinney, C.P., Spitz, M.R., 2006. Bladder cancer predisposition: a multigenic approach to DNA-repair and cell-cycle-control genes. Am. J. Hum. Genet. 78, 464-479.]. Thus, the fact that Alzheimer's disease susceptibility genes converge on a clearly defined signaling network has important implications for genetic association studies.

High density lipoproteins in the intersection of diabetes mellitus, inflammation and cardiovascular disease

PURPOSE OF REVIEW

Low HDL-cholesterol, diabetes mellitus and elevated C-reactive protein as well as various inflammatory diseases are risk factors for coronary heart disease. Both diabetes mellitus and inflammation decrease HDL-cholesterol. We summarize recent findings on the mechanisms underlying low HDL-cholesterol in diabetes and inflammation, as well as on novel functions of HDL that may protect not only from atherosclerosis but also from diabetes mellitus and inflammation-induced organ damage.

RECENT FINDINGS

Elevated levels of non-esterified fatty acids and disturbed insulin action contribute to low HDL-cholesterol in diabetes mellitus by modifying lipolysis, apolipoprotein A-I production, as well as the activities of adenosine triphosphate-binding cassette transporter A1 and lipid transfer. Inflammation causes low HDL-cholesterol by increasing the activities of endothelial lipase and soluble phospholipase A2 and by replacing apolipoprotein A-I in HDL with serum amyloid A. HDL and lysosphingolipids therein have been identified as activators of the protein kinase Akt, which in turn is a regulator of apoptosis in beta-cells, endothelial cells, and smooth muscle cells, as well as a regulator of nitric oxide production and adhesion molecule expression in endothelial cells.

SUMMARY

The protective properties of HDL in cytokine production, lipid oxidation, cholesterol efflux and reverse cholesterol transport make HDL a protective agent in inflammation-induced organ damage including diabetes mellitus. However, inflammation and diabetes cause a decrease in HDL-cholesterol concentrations and impair HDL function, placing HDL into the centre of a vicious cycle that may escalate into diabetes mellitus, inflammation-induced organ damage and atherosclerosis.