Spontaneous high density lipoprotein deficiency syndrome associated with a Z-linked mutation in chickens

Cholesterol accumulation in ovarian follicles causes ovulation defects in Abca1a -/- Japanese medaka (Oryzias latipes)

ATP-binding cassette A1 (ABCA1) is a membrane protein, which exports excess cellular cholesterol to generate HDL to reduce the risk of the onset of cardiovascular diseases (CVD). In addition, ABCA1 exerts pleiotropic effects on such as inflammation, tissue repair, and cell proliferation and migration. In this study, we explored the novel physiological roles of ABCA1 using Japanese medaka (Oryzias latipes), a small teleost fish. Three Abca1 genes were found in the medaka genome. ABCA1A and ABCA1C exported cholesterol to generate nascent HDL as human ABCA1 when expressed in HEK293 cells. To investigate their physiological roles, each Abca1-deficient fish was generated using the CRISPR-Cas9 system. Abca1a ^-/- female medaka was found to be infertile, while Abca1b ^-/- and Abca1c ^-/- female medaka were fertile. In vitro ovarian follicle culture suggested that Abca1a deficiency causes ovulation defects. In the ovary, ABCA1A was expressed in theca cells, an outermost layer of the ovarian follicle. Total cholesterol content of Abca1a ^-/- ovary was significantly higher than that of the wild-type, while estrogen and progestin contents were compatible with those of the wild-type. Furthermore, cholesterol loading to the wild-type follicles caused ovulation defects. These results suggest that ABCA1A in theca cells regulates cholesterol content in the ovarian follicles and its deficiency inhibits successful ovulation through cholesterol accumulation in the ovarian follicle.

A novel method for screening a vertebrate transcriptome for genes involved in carotenoid binding and metabolism

Carotenoid-based colour signals are widespread in the animal kingdom and common textbook examples of sexually selected traits. Carotenoid pigments must be obtained through the diet as all animals lack the enzymatic machinery necessary to synthesize them from scratch. Once ingested, carotenoids are metabolized, stored, transported and deposited, and some or all of these processes may be limiting for signal production and thus subjected to social or sexual selection on phenotypic coloration. Very little is known about which genes and physiological pathways are involved in carotenoid pigmentation which is unfortunate, as genetic information would allow us to investigate the biochemical consequences of sexual selection. In this study, we present a transcriptome-screening technique and apply it to a carotenoid-signalling bird species, the southern red bishop Euplectes orix, to uncover the gene(s) responsible for the conversion of dietary β-carotene (orange) to canthaxanthin (bright red). The transcriptome, extracted from the liver of a male entering his breeding moult, is expressed within bacterial cells genetically modified to synthesize beta-carotene. Effects of expressed E. orix proteins on the structure or amount of β-carotene are initially detected by eye (based on colour change) and subsequently confirmed by high-performance liquid chromatography. Here, we demonstrate the validity of the technique and provide a list of candidate genes involved in the carotenoid pigmentation pathway. We believe that this method could be applied to other species and tissues and that this may help researchers uncover the genetic basis of carotenoid coloration in vertebrates.

ABCA1 and atherosclerosis

ATP binding cassette transporter A1 (ABCA1) mediates the cellular efflux of phospholipids and cholesterol to lipid-poor apolipoprotein A1 (apoA1) and plays a significant role in high density lipoprotein (HDL) metabolism. ABCA1's role in the causation of Tangier disease, characterized by absent HDL and premature atherosclerosis, has implicated this transporter and its regulators liver-X-receptoralpha (LXRalpha) and peroxisome proliferator activated receptorgamma (PPARgamma) as new candidates potentially influencing the progression of atherosclerosis. In addition to lipid regulation, these genes are involved in apoptosis and inflammation, processes thought to be central to atherosclerotic plaque progression. A Medline-based review of the literature was carried out. Tangier disease and human heterozygotes with ABCA1 mutations provide good evidence that ABCA1 is a major candidate influencing atherosclerosis. Animal and in vitro experiments suggest that ABCA1 not only mediates cholesterol and phospholipid efflux, but is also involved in the regulation of apoptosis and inflammation. The complex and beneficial interactions between apoA1 and ABCA1 seem to be pivotal for cholesterol efflux. The expression of the ABCA1 is tightly regulated. Furthermore the plaque microenvironment could potentially promote ABCA1 protein degradation thus compromising cholesterol efflux. PPAR-LXR-ABCA1 interactions are integral to cholesterol homeostasis and these nuclear receptors have proven anti-inflammatory and anti-matrix metalloproteinase activity. Therapeutic manipulation of the ABCA1 transporter is feasible using PPAR and LXR agonists. PPAR agonists like glitazones and ABCA1 protein stabilization could potentially modify the clinical progression of atherosclerotic lesions.

Production and growth related disorders and other metabolic diseases of poultry – A review

In humans, metabolic complaints may be associated with a failure in one of the body hormone or enzyme systems, a storage disease related to lack of metabolism of secretory products because of the lack of production of a specific enzyme, or the breakdown or reduced activity of some metabolic function. Some of these disorders also occur in poultry, as do other important conditions such as those associated with increased metabolism, rapid growth or high egg production that result in the failure of a body system because of the increased work-load on an organ or system. These make up the largest group of poultry diseases classified as metabolic disorders and cause more economic loss than infectious agents. Poultry metabolic diseases occur primarily in two body systems: (1) cardiovascular ailments, which in broiler chickens and turkeys are responsible for a major portion of the flock mortality; (2) musculoskeletal disorders, which account for less mortality, but in broilers and turkeys slow down growth (thereby reducing profit), and cause lameness, which remains a major welfare concern. In addition, conditions such as osteoporosis and hypocalcaemia in table-egg chickens reduce egg production and can kill.

ABCA1-deficient mice: insights into the role of monocyte lipid efflux in HDL formation and inflammation

Studies with ATP-binding cassette transporter (ABCA1)-deficient mice have been critical in demonstrating the relation between ABCA1 expression, cellular lipid efflux, and HDL metabolism. The phenotype of the ABCA1-deficient mouse parallels the phenotype observed in human Tangier disease, including substantial reductions in both apolipoprotein B and apolipoprotein AI with confounding affects on atherosclerosis.

ABCA1 is essential for efficient basolateral cholesterol efflux during the absorption of dietary cholesterol in chickens

The ATP-binding cassette transporter A1 (ABCA1) participates in the efflux of cholesterol from cells. It remains unclear whether ABCA1 functions to efflux cholesterol across the basolateral or apical membrane of the intestine. We used a chicken model of ABCA1 dysfunction, the Wisconsin hypoalpha mutant (WHAM) chicken, to address this issue. After an oral gavage of radioactive cholesterol, the percentage appearing in the bloodstream was reduced by 79% in the WHAM chicken along with a 97% reduction in the amount of tracer in high density lipoprotein. In contrast, the percentage of radioactive cholesterol absorbed from the lumen into the intestine was not affected by the ABCA1 mutation. Liver X receptor (LXR) agonists have been inferred to decrease cholesterol absorption through activation of ABCA1 expression. However, the LXR agonist T0901317 decreased cholesterol absorption equally in both wild type and WHAM chickens, indicating that the effect of LXR activation on cholesterol absorption is independent of ABCA1. The ABCA1 mutation resulted in accumulation of radioactive cholesterol ester in the intestine and the liver of the WHAM chicken (5.0- and 4.4-fold, respectively), whereas biliary lipid concentrations were unaltered by the WHAM mutation. In summary, ABCA1 regulates the efflux of cholesterol from the basolateral but not apical membrane in the intestine and the liver.

Identification and functional analysis of a naturally occurring E89K mutation in the ABCA1 gene of the WHAM chicken

The Wisconsin hypoalpha mutant (WHAM) chicken has a >90% reduction in plasma HDL due to hypercatabolism by the kidney of lipid-poor apoA-I. The WHAM chickens have a recessive white skin phenotype caused by a single-gene mutation that maps to the chicken Z-chromosome. This corresponds to human 9q31.1, a chromosomal segment that contains the ATP-binding cassette protein-1 (ABCA1) gene, which is mutated in Tangier Disease and familial hypoalphalipoproteinemia. Complete sequencing of the WHAM ABCA1 cDNA identified a missense mutation near the N-terminus of the protein (E89K). The substitution of this evolutionary conserved glutamate residue for lysine in the mouse ABCA1 transporter leads to complete loss of function, resulting principally from defective intracellular trafficking and very little ABCA1 reaching the plasma membrane. The WHAM chicken is a naturally occurring animal model for Tangier Disease.

Species-specific polymorphism in the promoter of the apolipoprotein A-I gene: restoration of human transcriptional efficiency by substitution at positions -189, -144 and -48 bp

Previous studies indicate that species-specific differences in apolipoprotein A-I (apo A-I) expression could be largely explained by cis-acting factors located within or near the 5' flanking region (-231 to +223 bp, where +1 is the start site of transcription). In the present studies, we have localized 7 sites within the (-231 to -15 bp) region of the African green monkey apo A-I gene that differ from the human apo A-I gene 5' flanking region. To identify which of the 7 polymorphic sites were essential for the species-specific differences in apo A-I gene expression, mutated promoter constructs were transfected into HepG2 cells and reporter gene expression was measured. Each of the 7 sites within a defined 5' flanking region of the human gene was individually mutated to the African green nucleotide sequence found at that position. Three of the sites (-189, -144 and -48) were found to raise the human apo A-I promoter activity to approx. 60-65% of the African green promoter. While double mutations (-144/-48 bp and -189/-144 bp), restored the human apo A-I promoter activity to 100% of that found with the African green monkey promoter. Additional studies revealed similar DNA: protein interactions with DNA probes from either human or African green monkey and HepG2 cell nuclear extract. In conclusion, these studies demonstrate that double and triple nucleotide substitutions within the human apo A-I promoter are sufficient to restore gene expression in HepG2 cells to levels seen with the African green monkey promoter. These data suggest that sites -189, -144 and -48 bp are involved in significantly altering the binding affinity of a nuclear factor determining the species-specific level of apo A-I gene transcription.

Chicken genome mapping: a new era in avian genetics

More than 460 loci representing either expressed or anonymous sequences have been mapped on to the first comprehensive molecular genetic linkage map of the chicken genome. Here, we review the current status of poultry genome mapping and discuss some of the new opportunities this provides.

Hypercatabolism of lipoprotein-free apolipoprotein A-I in HDL-deficient mutant chickens

The Wisconsin Hypoalpha Mutant (WHAM) chicken has a sex-linked mutation associated with a 90% reduction in high-density lipoprotein (HDL) cholesterol and apolipoprotein A-I (apoA-I). In the present studies, we did not detect a defect in apoA-I synthesis or secretion in liver or intestine. We tested the hypothesis that apoA-I is not binding properly to lipoprotein particles and is undergoing hypercatabolism. We therefore studied the in vivo turnover of lipid-free 125I-apoA-I. Its turnover was fourfold faster in WHAM chickens than in normal chickens. The 125I-apoA-I equilibrated more slowly with HDL in the WHAM chickens, and these animals had a much larger steady-state pool of lipid-free apoA-I than did control chickens. To determine the tissue sites of degradation of apoA- I, the tissue distribution of 125I-tyramine cellobiose apoA-I was assessed. The liver and kidneys were the major sites of apoA-I degradation, but in the WHAM chickens, the kidney made a twofold larger contribution to apoA-I degradation than in normal chickens. Total plasma phospholipid levels are reduced by 44% to 78% in the WHAM chickens. A phospholipid deficit might explain the elevated lipid-free apoA-I pool and, secondarily, the HDL deficiency of the WHAM chickens.

Compositional changes and apoprotein A-I metabolism of plasma high density lipoprotein in estrogenized chicks

The effect of estrogen on compositional changes, apolipoprotein (apo) A-I metabolism and the morphology of plasma high density lipoprotein (HDL) were investigated in chicks. The administration of 17 beta-estradiol (25 mg/kg body weight) to growing male chicks (8-week-old) markedly reduced the concentrations of plasma HDL components, except for triglyceride (TG). At the same time, levels of TG, total cholesterol (TC) and phospholipid (PL) in plasma were greatly elevated. The respective values for TG, TC, PL and protein in HDL were 13.9, 89.3, 154.1 and 231.7 (mg/dL) in the control, and 39.0, 35.1, 113.8 and 160.0 (mg/dL) in chicks upon estrogen treatment for one day. In vivo kinetic studies showed that the fractional catabolic rate of HDL apo A-I was significantly higher (p less than 0.05) in estrogen-treated chicks than in control birds, indicating an increased efficiency of HDL removal in the former. The production rate of HDL apo A-I also was significantly lower (p less than 0.05) in estrogen-treated chicks. Sodium dodecyl sulfate-acrylamide gel electrophoresis followed by laser scanning densitometry of HDL apolipoproteins in estrogen-treated chicks revealed a reduction of apo A-I and the occurrence of new apolipoproteins which had been absent in HDL of untreated birds. The HDL particles showed that the mean particle size of HDL became larger upon estrogen treatment. Particles with diameters between 70 and 123 A were predominant in HDL of control chicks, while particles with diameters between 97 and 143 A were most abundant in HDL of estrogen-treated chicks.