Chicken apolipoprotein A-I: cDNA sequence, tissue expression and evolution

Proteomics alterations in chicken jejunum caused by 24 h fasting

The small intestine is the longest part of the chicken (Gallus gallus) gastrointestinal system that is specialized for nutrient absorption. It is known that decrease in intestinal villi area or height in early age can cause a reduction in essential nutrient intake, which may lead to delayed growth and consequently poorer performance of broiler chickens. The small intestinal absorptive surface is known to be affected by various factors, among others things the nutritional state. In our experiment, we aimed to investigate the possible protein expression alterations that lie behind the villus area and height decrease caused by feed deprivation. A total of 24 chickens were divided into three groups, namely ad libitum fed, fasted for 24 h, fasted for 24 h then refed for 2 h. The morphometric parameters were also measured in the duodenum, jejunum and ileum tissue sections using image analysis. Differential proteome analyses from jejunum samples were performed using two-dimensional difference gel electrophoresis followed by tryptic digestion and protein identification by matrix-assisted laser desorption/ionization mass spectrometry. Overall 541 protein spots were detected after 2D. Among them, eleven showed 1.5-fold or higher significant difference in expression and were successfully identified. In response to 24 h fasting, the expression of nine proteins was higher and that of two proteins was lower compared to the ad libitum fed group. The functions of the differentially expressed proteins indicate that the 24 h fasting mainly affects the expression of structural proteins, and proteins involved in lipid transport, general stress response, and intestinal defense.

Isolation and characterization of some novel genes of the apolipoprotein A-I family in Japanese eel, Anguilla japonica

Apolipoproteins such as apolipoprotein (apo) A-I, apoA-IV, and apoE are lipid binding proteins synthesized mainly in the liver and the intestine and play an important role in the transfer of exogenous or endogenous lipids through the circulatory system. To investigate the mechanism of lipid transport in fish, we have isolated some novel genes of the apoA-I family, apoIA-I (apoA-I isoform) 1–11, from Japanese eel by PCR amplification. Some of the isolated genes of apoIA-I corresponded to 28kDa-1 cDNAs which had already been deposited into the database and encoded an apolipoprotein with molecular weight of 28 kDa in the LDL, whereas others seemed to be novel genes. The structural organization of all apoIA-Is consisted of four exons separated by three introns. ApoIA-I10 had a total length of 3232 bp, whereas other genes except for apoIA-I9 ranged from 1280 to 1441 bp. The sequences of apoIA-Is at the exon-intron junctions were mostly consistent with the consensus sequence (GT/AG) at exon-intron boundaries, whereas the sequences of 3′ splice acceptor in intron 1 of apoIA-I1-7 were (AC) but not (AG). The deduced amino acid sequences of all apoIA-Is contained a putative signal peptide and a propeptide of 17 and 5 amino acid residues, respectively. The mature proteins of apoIA-I1-3, 7, and 8 consisted of 237 amino acids, whereas those of apoIA-I4-6 consisted of 239 amino acids. The mature apoIA-I10 sequence showed 65% identity to amino acid sequence of apoIA-I11 which was associated with an apolipoprotein with molecular weight of 23 kDa in the VLDL. All these mature apoIA-I sequences satisfied the common structural features depicted for the exchangeable apolipoproteins such as apoA-I, apoA-IV, and apoE but apoIA-I11 lacked internal repeats 7, 8, and 9 when compared with other members of apoA-I family. Phylogenetic analysis showed that these novel apoIA-Is isolated from Japanese eel were much closer to apoA-I than apoA-IV and apoE, suggesting new members of the apoA-I family.

Homologue of mammalian apolipoprotein A-II in non-mammalian vertebrates

Although apolipoprotein with molecular weight 14 kDa (apo-14 kDa) is associated with fish plasma high-density lipoproteins (HDLs), it remains to be determined whether apo-14 kDa is the homologue of mammalian apoA-II. We have obtained the full cDNA sequences that encode Japanese eel and rainbow trout apo-14 kDa. Homologues of Japanese eel apo-14 kDa sequence could be found in 14 fish species deposited in the DDBJ/EMBL/GenBank or TGI database. Fish apo-14 kDa lacks propeptide and contains more internal repeats than mammalian apoA-II. Nevertheless, phylogenetic analysis allowed fish apo-14 kDa to be the homologue of mammalian apoA-II. In addition, in silico cloning of the TGI, Ensembl, or NCBI database revealed apoA-IIs in dog, chicken, green anole lizard, and African clawed frog whose sequences had not so far been available, suggesting both apoA-I and apoA-II as fundamental constituents of vertebrate HDLs.

Apolipoprotein AI and apolipoprotein E mRNA expression in peripheral white blood cells from patients with orthotopic liver transplantation

BACKGROUND

Apolipoprotein AI/apolipoprotein E (apo-AI/apo-E) ratio change and its induction in non-hepatic tissues have been reported during liver development, regeneration, and several pathophysiologic states. The clinical implication of such changes is unclear, but these could reflect recovery and/or severity of liver damage.

METHODS AND RESULTS

Using RT-PCR we analysed the mRNA expression of apo-AI and apo-E in peripheral white blood cells (PWBC) of patients with different liver diseases who underwent orthotopic liver transplantation (OLT) and compared its expression with the lipid profile and liver function tests. We found that patients showed higher levels of apo-AI mRNA without detection of apo-E mRNA on PWBC at the preoperative day, compared with healthy volunteers (HV). We found an apo-AI/apo-E mRNA ratio of 2.7 during the anhepatic stage, followed by a decrease to 1.3, 0.95, and 0.55 at days 30, 60, and 90, respectively. At the last time point, the apo-AI/apo-E ratio was similar to HV. At day 3 post-OLT, the lowest levels of high-density lipoprotein (HDL)-cholesterol (17 mg/dl; P<0.05) and the highest levels of aspartate aminotransferase, total bilirubin and alkaline phosphatase (77.5 IU/l, 37.9 g/dl, 177.8 IU/l, respectively; P<0.05) were detected.

CONCLUSION

These results indicate that changes of HDL-cholesterol and apo-AI/apo-E mRNA ratio could be a good indicator of liver damage and/or hepatic functional recovery post-OLT.

Expression of apolipoprotein AI mRNA in peripheral white blood cells of patients with alcoholic liver disease

Because (i) changes in plasma and liver mRNA of apolipoprotein (apo) AI have been observed in patients with alcoholic liver disease, (ii) apo AI mRNA can be induced in non-hepatic tissues, and (iii) apolipoproteins expression is influenced by plasma colloid osmotic pressure (P(CO)) and viscosity (eta), we analyzed the Apo AI mRNA expression in the peripheral white blood cells (PWBC), P(CO), and eta in control volunteers (C), patients with liver cirrhosis (LC), and cirrhotic patients with superimposed alcoholic hepatitis (LC+AH). We found that apo AI mRNA is expressed in the PWBC in 20% of C and it is induced 1.5 fold in 66.6% of LC and 1.95 fold in 85% of LC+AH. A significant decrease of P(CO) in LC and LC + AH (14.8 +/- 2.4 and 16.2 +/- 2.4 mm Hg, respectively) compared to C (27.9 +/- 2 mm Hg) was observed. By contrast, eta was mildly increased from 1.7389 +/- 0.07 in C to 1.8022 +/- 0.154 in LC and 1.9030 +/- 0.177 in LC+AH. No significant correlation was found between P(CO) and eta with apo AI mRNA but with lipid profile. In conclusion, apo AI mRNA expression in PWBC is associated to liver disease severity and could be an indirect indicator of alcoholic liver damage.

The ontogenic transcription of complement component C3 and Apolipoprotein A-I tRNA in Atlantic cod (Gadus morhua L.)--a role in development and homeostasis?

The complement system is important both in the innate and adaptive immune response, with C3 as the central protein of all three activation pathways. Apolipoprotein A-I (ApoLP A-I), a high-density lipoprotein (HDL), has been shown to have a regulatory role in the complement system by inhibiting the formation of the membrane attack complex (MAC). Complement has been associated with apoptotic functions, which are important in the immune response and are involved in organ formation and homeostasis. mRNA probes for cod C3 and ApoLP A-I were synthesized and in situ hybridisation used to monitor the ontogenic development of cod from fertilised eggs until 57 days after hatching. Both C3 and ApoLP A-I transcription was detected in the central nervous system (CNS), eye, kidney, liver, muscle, intestines, skin and chondrocytes at different stages of development. Using TUNEL staining, apoptotic cells were identified within the same areas from 4 to 57 days posthatching. The present findings may suggest a role for C3 and ApoLP A-I during larval development and a possible role in the homeostasis of various organs in cod.

The Antarctic toothfish (Dissostichus mawsoni) lacks plasma albumin and utilises high density lipoprotein as its major palmitate binding protein

Plasma from the Antarctic toothfish, Dissostichus mawsoni, a member of the advanced teleost Nototheniidae family, was analysed. Agarose gel electrophoresis showed a major diffuse anionic protein that bound [14C]palmitic acid but not 63Ni2+, and two more cationic proteins that bound 63Ni2+ but not palmitate. Oil Red O staining following cellulose acetate electrophoresis indicated that the palmitate binding protein was a lipoprotein. Two-dimensional electrophoresis showed that this palmitate binding band was composed of three proteins with M(r) of 11, 30, and 42 kDa, without any trace of material at approximately 65 kDa, the mass of albumin. N-terminal sequencing of the palmitate binding band gave a major sequence of DAAQPSQELR-, indicating a high degree of homology to apolipoprotein A-I (apo-AI), the major apolipoprotein of high density lipoprotein (HDL). N-terminal sequencing of the major nickel binding band produced a sequence with no homology to albumin. When ultracentrifugation was used to isolate the lipoproteins from Antarctic toothfish plasma, the palmitate binding protein was found solely in the lipoprotein fraction. In competitive binding experiments, added human albumin did not prevent palmitate binding to toothfish HDL. In conclusion, there is no evidence for albumin in Antarctic toothfish plasma and HDL assumes the role of fatty acid transport.

High density lipoprotein (HDL), and not albumin, is the major palmitate binding protein in New Zealand long-finned (Anguilla dieffenbachii) and short-finned eel (Anguilla australis schmidtii) plasma

Plasma from two members of the teleost Anguillidae family, the New Zealand long-finned (Anguilla dieffenbachii) and short-finned eels (Anguilla australis schmidtii), were examined. Agarose gel electrophoresis showed both species had a major anionic diffuse protein band migrating at approximately the same position as human albumin, and autoradiography showed this protein bound [14C]palmitic acid, but not 63Ni2+. Cellulose acetate electrophoresis followed by Oil Red O staining suggested that this band was a lipoprotein. Two-dimensional electrophoresis of plasma showed the absence of a significant albumin band at approx. 65 kDa, and that the palmitate binding band appeared to be composed of at least three proteins, with the major protein running at 30 kDa. N-Terminal sequencing of the palmitate binding band indicated major sequences of DAPAPP(S)QLED- for long-finned eel and DAPAPPSQLEHV- for short-finned eel, confirming their identities as apo-AI, the major apolipoprotein of high density lipoprotein (HDL). When ultracentrifugation was used to separate the lipoproteins of each species, the anionic palmitate binding protein was found solely in the lipoprotein fractions. There was no evidence of albumin in plasma from either eel, and it appears that in its absence HDL takes on the role of fatty acid transport.

Cloning, characterisation and expression of the apolipoprotein A-I gene in the sea bream (Sparus aurata)

A full length cDNA clone representing apolipoprotein A-I was isolated from a sea bream (Sparus aurata) liver library. The clone encodes a 261 amino acid protein which shows highest amino acid identity (38%) with salmon apolipoprotein A-I. Northern blot analysis showed strong expression of a 1.4 kb transcript in liver with lower expression in intestine. Expression of apolipoprotein A-I in intestine was markedly reduced by treatment with triiodothyronine (T3).

Both apolipoprotein E and A-I genes are present in a nonmammalian vertebrate and are highly expressed during embryonic development

Apolipoprotein E (apoE) is associated with several classes of plasma lipoproteins and mediates uptake of lipoproteins through its ability to interact with specific cell surface receptors. Besides its role in cardiovascular diseases, accumulating evidence has suggested that apoE could play a role in neurodegenerative diseases, such as Alzheimer disease. In vertebrates, apoA-I is the major protein of high-density lipoprotein. ApoA-I may play an important role in regulating the cholesterol content of peripheral tissues through the reverse cholesterol transport pathway. We have isolated cDNA clones that code for apoE and apoA-I from a zebrafish embryo library. Analysis of the deduced amino acid sequences showed the presence of a region enriched in basic amino acids in zebrafish apoE similar to the lipoprotein receptor-binding region of human apoE. We demonstrated by whole-mount in situ hybridization that apoE and apoA-I genes are highly expressed in the yolk syncytial layer, an extraembryonic structure implicated in embryonic and larval nutrition. ApoE transcripts were also observed in the deep cell layer during blastula stage, in numerous ectodermal derivatives after gastrulation, and after 3 days of development in a limited number of cells both in brain and in the eyes. Our data indicate that apoE can be found in a nonmammalian vertebrate and that the duplication events, from which apoE and apoA-I genes arose, occurred before the divergence of the tetrapod and teleost ancestors. Zebrafish can be used as a simple and useful model for studying the role of apolipoproteins in embryonic and larval nutrition and of apoE in brain morphogenesis and regeneration.

Apolipoprotein CII from chicken (Gallus domesticus). The amino-terminal domain is different from corresponding domains in mammals

The amino acid sequence of chicken apolipoprotein CII (apoCII) was determined from cDNA sequencing and from partial protein sequencing. The chicken sequence showed an overall identity of around 30% to all the other previously known apoCII sequences. Comparison of the carboxyl-terminal domain (residues 51-79, human numbering) showed at least 50% identity between species. By limiting the region to residues 51-70 the similarity was remarkably high, about 85%. This is in concert with the previous opinion that residues in the region 56-76 are directly engaged in binding to lipoprotein lipase and in activation of this enzyme. In contrast, in the amino-terminal end up to residue 50 (human numbering) less than 24% of the amino acid residues in chicken apoCII were identical to residues of any of the other species. In addition, chicken apoCII is four residues longer than human apoCII (83 versus 79 residues), probably due to an extension at the amino-terminal end. Although the sequence was completely different in the amino-terminal domain, the structures necessary for binding to lipid appear to be present in chicken apoCII. Secondary structure prediction showed that the amino-terminal domain could form two amphipathic alpha-helices in almost similar areas of the sequence as was previously predicted for human apoCII.

Secretion and processing of apolipoprotein A-I in the avian sciatic nerve during development

Apolipoprotein A-I (apo A-I), a major apolipoprotein synthesized by liver and intestine to facilitate transport of plasma lipids as lipoproteins, has been detected also in the avian sciatic nerve. The mRNA and protein levels of apo A-I have been shown to increase during the period of rapid myelination (LeBlanc et al.: J Cell Biol 109:1245-1256, 1989). In order to assess the synthesis of apo A-I protein and the processing of apo A-I isoforms during development, endoneurial slices of avian sciatic nerves from chicks during active myelination at 15 and 17 days embryonic and 1 day posthatch age were incubated with [35]S-methionine. The incubations were fractionated into secreted and intracellular fractions, and incorporation of the label was assessed for apo A-I protein. The pattern of labeling of Po protein, as a marker of myelination, was also determined in the intracellular and compact myelin fractions. Methionine incorporation into Po protein was highest in the intracellular compartment at the 15-day embryonic stage and decreased thereafter, with a corresponding increase in the myelin fraction. During these developmental periods, the levels of nascent apo A-I increased in both the secreted and intracellular fractions. The synthesis of apo A-I specifically increases in the secreted fraction compared with total protein synthesis. The processing of the pro-apo A-I is also developmentally regulated. In the intracellular compartment, there are approximately equal proportions of the acidic and basic isoforms. However, with increasing age, a higher proportion of the apo A-I is secreted as acidic isoforms. It is concluded that the secretion and processing of apo A-I is developmentally regulated in the chick sciatic nerve, in parallel with the process of active myelination.

Lipoprotein and apoprotein profile of Japanese quail

The present study delineated the lipoprotein and apoprotein distribution in Japanese quail. Quail lipoprotein was composed of three fractions: VLDL, d < 1.020; LDL, 1.020 < d < 1.081; HDL, 1.081 < d < 1.210. When animals were fed the cholesterol-free diet, HDL was the predominant form, LDL intermediate, VLDL and chylomicron were smallest in amount. Feeding of cholesterol induced a marked change in the lipoprotein profile: VLDL or chylomicron predominated over HDL and LDL. An apoprotein of 26 kD (molecular weight) was the major protein moiety comprising more than 50% of total apoprotein in the entire density range of lipoprotein class. Amino acid composition of 26 kD protein was similar to hen, rat and human apo A-I. N-Terminal 36 amino acid sequence of 26 kD protein showed 92% homology to chicken apo A-I and 11% homology to human apo A-1. The 26 kD protein did not react with the antibody raised against human apo A-I. These observation showed that the 26 kD protein was partially identical to apo A-I.

Characterization of the mouse apolipoprotein Apoa-1/Apoc-3 gene locus: genomic, mRNA, and protein sequences with comparisons to other species

In this report we present the genomic, cDNA, and predicted protein sequences for mouse apolipoproteins A-I and CIII, as well as sequence comparisons with other species. The genes for these apolipoproteins are within 2.5 kb of each other and convergently transcribed. The almost 9 kb of genomic sequence presented extends from 1298 bp 5' to the apolipoprotein A-I (Apoa-1) gene to 1249 bp 5' to the apolipoprotein CIII (Apoc-3) gene. The mouse Apoa-1 gene is 1.76 kb in length with four exons and three introns. The 5' flanking region contains TATA and CCAAT box sequences, an interferon responsive element homology, and potential binding sites for transcription factors CTF/NF1 and HNF4. Translation of the cDNA predicts that the mouse Apoa-1 primary transcript is 264 amino acids. The mouse Apoc-3 gene is 2.2 kb in length and also consists of four exons and three introns. The 5' flanking region contains TATA and CCAAT box sequences, RXR-1 and ARP-1 binding sites, and potential binding sites for transcription factors HNF4, NFkB, AP-1, and CTF/NF1. Translation of the cDNA predicts that the mouse Apoc-3 primary transcript is 99 amino acids. The clustering and genomic organization of the mouse Apoa-1 and Apoc-3 genes are similar to those of the rat and human genes. Significant sequence homologies between species exist for the proximal promoter and exonic regions of each gene, but not for the intronic or intergenic regions.(ABSTRACT TRUNCATED AT 250 WORDS)

The salmon gene encoding apolipoprotein A-I: cDNA sequence, tissue expression and evolution

A cDNA encoding an apolipoprotein (Apo) has been isolated from the Atlantic salmon (Salmo salar) and sequenced. It encodes a peptide of 258 amino acids (aa), including a signal peptide of 18 aa, with 5'- and 3'-untranslated regions of the mRNA of 12 and 329 nucleotides, respectively. The protein has structural features in common with other Apo's of human and avian origin, including conserved sequences in the signal peptide and a series of internal repeats of 22 aa. The sequence has been identified as salmon Apo A-I (sApoA-I), and has 23% aa identity with human ApoA-I. Northern-blot analysis using the sApoA-I cDNA probe against total RNA prepared from several salmon tissues detects the expression of this gene in liver, intestine and muscle. A phylogenetic analysis reveals that the mammalian ApoA-I, ApoA-IV and Apo-E aa sequences are more closely related to each other than any of them are to sApoA-I. This suggests that the duplication events, from which A-I, A-IV and E arose, occurred after the divergence of the tetrapod and teleost ancestors.

Isolation, characterization and sequencing of the chicken apolipoprotein-AI-encoding gene

The chicken ApoAI gene has been isolated and characterized. This gene contains three introns: the first is situated after nucleotide (nt) 41 in the 5'-untranslated region of the gene, the second interrupts the codon specifying the Gly-10 of the prepeptide, and the third disrupts the codon for Asp42 in the mature ApoAI protein. The chicken ApoAI gene has 62.6% sequence similarity with the human and 65.0% similarity with the rat gene. Intron-exon organization of the chicken gene is similar to that of human and rat ApoAI genes. Two different transcriptional start points (tsp), only 2 nt apart from each other, have been obtained for the chicken ApoAI gene. The 5'-flanking sequence of the gene contains TAAATA (TATA-like box) and CCACAT (CCAAT-like box) sequences, which are located 21 bp and 96 bp upstream from the tsp, respectively. This gene's sequence and structural organization provide a basis for future studies of the regulation of chicken ApoAI gene expression.

The apolipoprotein A-I gene is actively expressed in the rapidly myelinating avian peripheral nerve

The expression of the apolipoprotein A-I (apo A-I) gene was investigated in the myelinating sciatic nerve. Hybridization analysis with an apo A-I cDNA probe obtained from a cDNA library of mRNA isolated from rapidly myelinating chick sciatic nerve indicated that apo A-I coding transcripts increase during development in the chick sciatic nerve in parallel with the increase of myelin lamellae. Substantial apo A-I-like immunoreactivity in chick sciatic nerve homogenates was detected by Western blotting. The amount of antigen increased from the 15-d embryonic stage to 1 d posthatch and then decreased. Two subcellular fractions corresponding to the cytoplasmic compartments were particularly enriched in apo A-I. apo A-I immunoreactivity was also found in highly purified myelin preparations. Immunohistochemical staining provided further evidence for the presence of apo A-I in the endoneurial compartment of the sciatic nerve. Electron microscopic examination of these fractions after negative staining showed the presence of spherical and disc-shaped particles resembling high density lipoproteins. The presence of apo A-I, cholesterol esters, phospholipids, and triacylglycerols in ultracentrifugal fractions corresponding to serum lipoproteins and the behavior of apo A-I on nondenaturing gradient gels implied that apo A-I was associated with lipid. Studies with short-term organ cultures of sciatic nerves from 1-d chicks strengthened the evidence for local synthesis and secretion of apo A-I and apo A-I-containing lipoproteins by this tissue. These results establish that the apo A-I gene is actively expressed in developing sciatic nerve during the period of rapid myelination. These findings support the hypothesis that apo A-I synthesized within the nerve participates in the local transport of lipids used in myelin biosynthesis.

Effects of phospholipids on the conformation of chicken high density lipoprotein

Apolipoprotein A-I (apo-A-I), the major protein component of chicken high density lipoprotein (HDL), was isolated by hydrophobic interaction chromatography from the lipoprotein fraction of plasma. The apo-A-I was identified from its amino acid composition and molecular weight (by electrophoresis). The isolated protein contained 15% lipid, in the form of neutral lipids and free fatty acids, as compared with 50% lipid, including phospholipid, in intact HDL. The conformation of the isolated protein, as determined from the circular dichroism spectrum, was essentially that of the protein in intact chicken HDL, and similar to that of human HDL. The addition of phospholipid had little effect on the spectrum of this protein. Total delipidation of the protein by extraction with ethanol-diethyl ether mixtures removed the residual lipid, thereby producing an apoprotein with decreased helical structure. The secondary structure of this apoprotein could be restored by the addition of phospholipid.