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

Isolation, characterization, proteome, miRNAome, and the embryotrophic effects of chicken egg yolk nanovesicles (vitellovesicles)

Egg yolk constitutes about a third of the structure of the chicken egg however, the molecular structure and physiological effects of egg yolk-derived lipid membranous vesicles are not clearly understood. In this study, for the first record, the egg yolk nanovesicles (vitellovesicles, VVs) were isolated, characterized, and used as a supplement for porcine embryo culture. Yolks of ten freshly oviposited eggs were filtered and ultracentrifuged at 100,000 × g for 3 h to obtain a pellet. Cryogenic transmission electron microscopy and nanoparticle tracking analysis of the pellet revealed bilipid membranous vesicles. Protein contents of the pellet were analyzed using tandem mass spectrometry and the miRNA content was also profiled through BGISEQ-500 sequencer. VVs were supplemented with the in vitro culture medium of day-7 hatched parthenogenetic blastocysts. After 2 days of blastocyst culture, the embryonic cell count was increased in VVs supplemented embryos in comparison to the non-supplemented embryos. TUNEL assay showed that apoptotic cells were increased in control groups when compared with the VVs supplemented group. Reduced glutathione was increased by 2.5 folds in the VVs supplemented group while reactive oxygen species were increased by 5.3 folds in control groups. Quantitative PCR analysis showed that VVs significantly increased the expression of lipid metabolism-associated genes (monoglyceride lipase and lipase E), anti-apoptotic gene (BCL2), and superoxide dismutase, while significantly reducing apoptotic gene (BAX). Culturing embryos on Matrigel basement membrane matrix indicated that VVs significantly enhanced embryo attachment and embryonic stem cell outgrowths compared to the non-supplemented group. This considers the first report to characterize the molecular bioactive cargo contents of egg yolk nanovesicles to show their embryotrophic effect on mammalian embryos. This effect might be attributed to the protein and miRNA cargo contents of VVs. VVs can be used for the formulation of in vitro culture medium for mammalian embryos including humans.

Integrative analysis of transcriptomic data related to the liver of laying hens: from physiological basics to newly identified functions

Background

At sexual maturity, the liver of laying hens undergoes many metabolic changes to support vitellogenesis. In published transcriptomic approaches, hundreds of genes were reported to be overexpressed in laying hens and functional gene annotation using gene ontology tools have essentially revealed an enrichment in lipid and protein metabolisms. We reanalyzed some data from a previously published article comparing 38-week old versus 10-week old hens to give a more integrative view of the functions stimulated in the liver at sexual maturity and to move beyond current physiological knowledge. Functions were defined based on information available in Uniprot database and published literature.

Results

Of the 516 genes previously shown to be overexpressed in the liver of laying hens, 475 were intracellular (1.23–50.72 fold changes), while only 36 were predicted to be secreted (1.35–66.93 fold changes) and 5 had no related information on their cellular location. Besides lipogenesis and protein metabolism, we demonstrated that the liver of laying hens overexpresses several clock genes (which supports the circadian control of liver metabolic functions) and was likely to be involved in a liver/brain/liver circuit (neurotransmitter transport), in thyroid and steroid hormones metabolisms. Many genes were associated with anatomical structure development, organ homeostasis but also regulation of blood pressure. As expected, several secreted proteins are incorporated in yolky follicles but we also evidenced that some proteins are likely participating in fertilization (ZP1, MFGE8, LINC00954, OVOCH1) and in thyroid hormone maturation (CPQ). We also proposed that secreted proteins (PHOSPHO1, FGF23, BMP7 but also vitamin-binding proteins) may contribute to the development of peripheral organs including the formation of medullar bones to provide labile calcium for eggshell formation. Thirteen genes are uniquely found in chicken/bird but not in human species, which strengthens that some of these genes may be specifically related to avian reproduction.

Conclusions

This study gives additional hypotheses on some molecular actors and mechanisms that are involved in basic physiological function of the liver at sexual maturity of hen. It also revealed some additional functions that accompany reproductive capacities of laying hens, and that are usually underestimated when using classical gene ontology approaches.

iTRAQ-based quantitative proteomic analysis provides insights into strong broodiness in Muscovy duck (Cairina moschata) combined with metabolomics analysis

Much attention has been paid to the broodiness of the Muscovy duck, but the molecular mechanism of broodiness remains largely unknown. In this study, the ovary tissues of Muscovy ducks during the broody and laying periods were used to investigate differentially expressed proteins (DEPs) by the iTRAQ-based proteomics approach. A total of 335 DEPs were identified, including 139 up-regulated and 196 down-regulated proteins. Six proteins (APOV1, GAL, SAA, GNB5, VLDLR and CDK1) with higher changes in expression were selected, and these proteins are mainly involved in the pathways related to reproductive performance, such as Oocyte meiosis, and PI3K-Akt signaling pathway. Steroid biosynthesis was the most significantly enriched pathway by KEGG pathway enriched analysis. The qRT-PCR analysis was applied to verify the proteomic analysis. Meanwhile, metabolomics analysis found that several important differentially expressed metabolites (DEMs) (7-dehydrodesmosterol, 25-Hydroxyvitamin D3, 7-Dehydrocholesterol, Pregnanolone, Allopregnanolone and estrogen) that were also mainly involved in Steroid biosynthesis, Steroid hormone biosynthesis and Metabolic pathways. Crucially, the changes in the abundance of these metabolites are closely related to the changes in the protein abundance of proteins identified in the same pathway, and it is always the upstream key enzymes that influence the production of downstream metabolites.

The physiology of lipid storage and use in reptiles

Lipid metabolism is central to understanding whole-animal energetics. Reptiles store most excess energy in lipid form, mobilise those lipids when needed to meet energetic demands, and invest lipids in eggs to provide the primary source of energy to developing embryos. Here, I review the mechanisms by which non-avian reptiles store, transport, and use lipids. Many aspects of lipid absorption, transport, and storage appear to be similar to birds, including the hepatic synthesis of lipids from glucose substrates, the transport of triglycerides in lipoproteins, and the storage of lipids in adipose tissue, although adipose tissue in non-avian reptiles is usually concentrated in abdominal fat bodies or the tail. Seasonal changes in fat stores suggest that lipid storage is primarily for reproduction in most species, rather than for maintenance during aphagic periods. The effects of fasting on plasma lipid metabolites can differ from mammals and birds due to the ability of non-avian reptiles to reduce their metabolism drastically during extended fasts. The effect of fasting on levels of plasma ketones is species specific: β-hydroxybutyrate concentration may rise or fall during fasting. I also describe the process by which the bulk of lipids are deposited into oocytes during vitellogenesis. Although this process is sometimes ascribed to vitellogenin-based transport in reptiles, the majority of lipid deposition occurs via triglycerides packaged in very-low-density lipoproteins (VLDLs), based on physiological, histological, biochemical, comparative, and genomic evidence. I also discuss the evidence for non-avian reptiles using 'yolk-targeted' VLDLs during vitellogenesis. The major physiological states - feeding, fasting, and vitellogenesis - have different effects on plasma lipid metabolites, and I discuss the possibilities and potential problems of using plasma metabolites to diagnose feeding condition in non-avian reptiles.

A novel estrogen-regulated avian apolipoprotein

In search for yet uncharacterized proteins involved in lipid metabolism of the chicken, we have isolated a hitherto unknown protein from the serum lipoprotein fraction with a buoyant density of ≤1.063 g/ml. Data obtained by protein microsequencing and molecular cloning of cDNA defined a 537 bp cDNA encoding a precursor molecule of 178 residues. As determined by SDS-PAGE, the major circulating form of the protein, which we designate apolipoprotein-VLDL-IV (Apo-IV), has an apparent M_r of approximately 17 kDa. Northern Blot analysis of different tissues of laying hens revealed Apo-IV expression mainly in the liver and small intestine, compatible with an involvement of the protein in lipoprotein metabolism. To further investigate the biology of Apo-IV, we raised an antibody against a GST-Apo-IV fusion protein, which allowed the detection of the 17-kDa protein in rooster plasma, whereas in laying hens it was detectable only in the isolated ≤1.063 g/ml density lipoprotein fraction. Interestingly, estrogen treatment of roosters caused a reduction of Apo-IV in the liver and in the circulation to levels similar to those in mature hens. Furthermore, the antibody crossreacted with a 17-kDa protein in quail plasma, indicating conservation of Apo-IV in avian species. In search for mammalian counterparts of Apo-IV, alignment of the sequence of the novel chicken protein with those of different mammalian apolipoproteins revealed stretches with limited similarity to regions of ApoC-IV and possibly with ApoE from various mammalian species. These data suggest that Apo-IV is a newly identified avian apolipoprotein.

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Apo-VLDL-IV (Apo-IV) is a newly identified avian apolipoprotein.

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Apo-IV expression is suppressed by estrogen.

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Apo-IV containing VLDL particles are excluded from uptake into yolk.

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Apo-IV has limited similarity to mammalian ApoC-IV.

Sensitivity of expression of perivitelline membrane glycoprotein ZP1 mRNA in the liver of Japanese quail (Coturnix japonica) to estrogenic compounds

Avian perivitelline membrane protein, ZP1, is synthesized and secreted by the liver with the stimulation of estrogens. In the present study, we measured the expression of ZP1 gene in the liver of immature male quail treated with various estrogenic compounds and in the liver of male quail embryos that were developed in the fertilized eggs laid by mother quail injected with various estrogenic compounds during vitellogenesis. Total RNA extracted from the liver was reverse-transcribed and cDNA was subjected to real-time PCR. Both diethylstilbestrol and ethinyl estradiol caused significant effect on the increase in mRNA in immature male quail. In contrast, diethylstilbestrol administered via the route of maternal injection was not effective for induction of embryonic mRNA, although the effect of ethinyl estradiol administered via the same route was prominent. These results showed that direct administration of estrogenic compounds, diethylstilbestrol and ethinyl estradiol, stimulates the induction of ZP1 gene, but the rate of accumulation of these compounds in the yolk is different during vitellogenesis. The present studies suggest that although ZP1 gene is a sensitive biomarker to evaluate the effects of endocrine disruptors, the route of administration is an important factor to compare the effectiveness.

Cloning and expression of the genes associated with lipid metabolism in Tsaiya ducks

Sterol regulatory element binding protein 1 (SREBP1) drives the expression of several lipogenic genes, whereas SREBP2 dictates the expression of every gene involved in cholesterolgenesis in mammals. In the current study, we cloned the cDNA fragments for SREBP1, SREBP2, fatty acid synthase (FAS), 3-hydroxy-3-methylglutaryl-CoA reductase (HMG-CoA reductase), and very low density apolipoprotein-II (apoVLDL-II), the genes associated with lipid metabolism. Fifteen ducks immediately before the first egg was laid (18 wk old) and 15 ducks from the same population at an egg production rate of 80% were killed. Total RNA was extracted from liver and used to amplify the targeted genes by reverse transcription-PCR and screening of a cDNA library. The sequence data showed that Tsaiya duck SREBP1, SREBP2, FAS, and HMG-CoA reductase were highly homologous to that of chicken. Tsaiya duck SREBP1 mRNA was expressed in adipose tissue, cardiac muscle, skeletal muscle, liver, and ovary. The SREBP2 mRNA concentration was highest in liver and ovary. Concentrations of FAS and HMG-CoA reductase mRNA were high in liver and lower in other tissues. The apoVLDL-II mRNA was specifically expressed in the liver. The differences between mRNA concentrations of SREBP1, SREBP2, and FAS in the livers of laying and prelay ducks were not significant. However, the concentrations of hepatic HMG-CoA reductase and apoVLDL-II mRNA were higher in the laying ducks than in prelay ducks. Therefore, laying may affect particular aspects of lipid metabolism, especially biochemical pathways that involved apoVLDL-II and HMG-CoA reductase.

Lipoprotein receptors in extraembryonic tissues of the chicken

Yolk is the major source of nutrients for the developing chicken embryo, but molecular details of the delivery mechanisms are largely unknown. During oogenesis in the chicken, the main yolk components vitellogenin and very low density lipoprotein (VLDL) are taken up into the oocytes via a member of the low density lipoprotein receptor gene family termed LR8 (Bujo, H., Hermann, M., Kaderli, M. O., Jacobsen, L., Sugawara, S., Nimpf, J., Yamamoto, T., and Schneider, W. J. (1994) EMBO J. 13, 5165-5175). This endocytosis is accompanied by partial degradation of the yolk precursor protein moieties; however, fragmentation does not abolish binding of VLDL to LR8. The receptor exists in two isoforms that differ by a so-called O-linked sugar domain; the shorter form (LR8-) is the major form in oocytes, and the longer protein (LR8+) predominates in somatic cells. Here we show that both LR8 isoforms are expressed at ratios that vary with embryonic age in the extraembryonic yolk sac, which mobilizes yolk for utilization by the embryo, and in the allantois, the embryo's catabolic sink. Stored yolk VLDL interacts with LR8 localized on the surface of the yolk sac endodermal endothelial cells (EEC), is internalized, and degraded, as demonstrated by the catabolism of fluorescently labeled VLDL in cultured EEC. Addition to the incubation medium of the 39-kDa receptor-associated protein, which inhibits all known LR8/ligand interactions, blocks the uptake of VLDL by EEC. The levels of endogenous receptor-associated protein correspond to those of LR8+ but not LR8-, suggesting that it may play a role in the modulation of surface presentation of LR8+. Importantly, EEC express significant levels of microsomal triglyceride transfer protein and protein disulfide isomerase, key components required for lipoprotein synthesis. Because the apolipoprotein pattern of VLDL isolated from the yolk sac-efferent omphalomesenteric vein is very different from that of yolk VLDL, these data strongly suggest that embryo plasma VLDL is resynthesized in the EEC. LR8 is a key mediator of a two-step pathway, which affects the uptake of VLDL from the yolk sac and the subsequent delivery of its components to the growing embryo.

Effect of divergent selection for total plasma phosphorus on plasma and yolk very low density lipoproteins and plasma concentrations of selected hormones in laying Japanese quail

Japanese quail lines were divergently selected over 32 generations for laying hen plasma yolk precursor, as measured by total plasma phosphorus (TPP). The high (HP) and low (LP) lines were developed from a randombred control population (R1) that was maintained without conscious selection. The purpose of the present study was to characterize the composition of very low density lipoproteins (VLDL) in laying Japanese quail hens (VLDLy) and the concentration of selected hormones in laying hens from the HP, LP, and R1 lines. The changes in TPP because of genetic selection in the Japanese quail lines were associated with large alterations in plasma VLDLy concentration (HP > R1 > LP), but only minor changes in lipid composition and size (HP > LP = R1; P< or =0.01) of plasma VLDLy particles. Basal plasma levels of hormones associated with reproduction and lipid metabolism were also different among lines, with luteinizing hormone (LH) ranking HP >R1 = LP and triiodothyronine (T3), thyroxine (T4), and 17beta-estradiol ranking HP > R1 > LP (P< or =0.05). The results suggest possible increased rates of hepatic lipogenesis, hepatic VLDLy assembly and secretion, and plasma VLDLy concentration in association with increases in concentrations of plasma LH, T3, T4, and 17beta-estradiol. Concentrations of total lipids in yolk VLDL were not different among lines, and only minor line differences in the concentration of different classes of yolk VLDL neutral lipids were detected. The data indicate a preferential uptake of a specific plasma VLDLy subpopulation into rapidly growing ovarian follicles, resulting in a constant composition of yolk VLDL of laid eggs among lines of Japanese quail with large differences in plasma VLDLy concentration.

Select 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitors vary in their ability to reduce egg yolk cholesterol levels in laying hens through alteration of hepatic cholesterol biosynthesis and plasma VLDL composition

The inability to markedly attenuate cholesterol levels in chicken eggs has led to speculation that cholesterol is essential for yolk formation and that egg production would cease when yolk cholesterol deposition was inadequate for embryonic survival. However, this critical level hypothesis remains unproven. Here, we determine the relative responsiveness of laying hens to three select inhibitors of 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGR), the rate-limiting enzyme of cholesterol biosynthesis. A control diet, either alone or supplemented with one of two dietary levels (0.03 or 0.06%) of atorvastatin, lovastatin, or simvastatin, was fed to White Leghorn hens for 5 wk. Liver cholesterol concentrations (mg/g tissue) were decreased (P </= 0.05) by each HMGR inhibitor; however, total liver cholesterol (mg) did not differ among treatments. Microsomal hepatic HMGR activities were increased one- to twofold in all HMGR inhibitor-treated groups, while HMGR mRNA levels were unaffected. Diameters of plasma VLDL particles, the main cholesterol-carrying yolk precursor macromolecules, were reduced (P </= 0.05) only in hens fed 0.06% atorvastatin, and the particles contained 38% less total cholesterol (P </= 0.05) than controls. Plasma total cholesterol concentrations were lowered (P </= 0.05) by both doses of atorvastatin (-56, -63%) and simvastatin (-36,-45%). Egg cholesterol contents were maximally reduced by 46% (P </= 0.05), 7% (P > 0.05), and 22% (P </= 0.05) in hens fed the 0.06% level of atorvastatin, lovastatin, and simvastatin, respectively, while overall egg production [-19% (P </= 0.05), +4% (P > 0.05), and -3% (P > 0.05)], was much less affected. We concluded that cholesterol per se may not be an obligatory component for yolk formation in chickens and, as such, may be amenable to further pharmacological manipulation

The VLDL receptor: an LDL receptor relative with eight ligand binding repeats, LR8

The discovery in 1992 of a member of the low density lipoprotein receptor (LDLR) family with eight ligand binding repeats (LR8) has raised more questions than have been answered to date. Here, we summarize the current status of knowledge about this intriguing molecule, generally termed VLDL receptor, at the molecular biological, cell biological, and physiological levels. On one hand, the wealth of reports concerning the role(s) of this receptor in lipoprotein metabolism in mammalian systems has revealed partially conflicting details, particularly in regards to its natural ligand(s) and site of action. On the other hand, molecular genetic and biochemical studies in the chicken have clearly demonstrated the multiple roles of LR8 in the physiology and reproduction of egg-laying species, and have generated insights into the evolutionary aspects of the LDLR gene family.