Glucocorticoid Causes Iron Accumulation in Liver by Up-Regulating Expression of Iron Regulatory Protein 1 Gene Through GR and STAT5

Iron regulatory protein-1 (IRP-1) is a central factor in the regulation of iron metabolism. Stress causes elevated glucocorticoid secretion and is also associated with iron accumulation in liver; however, the relation between these two processes is not known. Whether glucocorticoids alter the expression of liver IRP-1 and if this contributes to the iron accumulation is presently investigated. Administration (i.v.) of corticosterone daily to rats for 7 days resulted in the upregulation of IRP-1 and transferrin receptor-1 and accumulation of iron in liver. However, expression of ferritin was decreased. The effects of corticosterone were reduced by the prior administration of glucocorticoid antagonist, RU486 to the rats. Similarly, in vitro studies using HL7702 liver cells showed that hydrocortisone increases the expression of IRP-1 while decreasing ferritin. It is also observed that Stat-5 phosphorylation is enhanced in HL7702 cells by hydrocortisone. The electrophoretic mobility shift assays revealed that the binding of glucocorticoid receptor and phospho-STAT5 to the promoter region of IRP-1 gene was enhanced in rats of stress group. Combination of both RU486 and STAT5 inhibitor, PIAS resulted in a stronger reduction of IRP-1 expression than when these inhibitors were used separately. These results strongly implicate glucocorticoid receptor and STAT5 in stress-induced up-regulation of IRP-1, which subsequently enhances transferrin receptor-1 expression and down-regulates ferritin, causing iron accumulation in the liver.     

Effects of Dietary Polychlorinated Biphenyls and Protein Level on Liver and Serum Lipid Metabolism of Rats

The effects of polychlorinated biphenyls (PCB) and dietary protein level on the liver and serum lipid metabolism of rats were studied. Rats were fed an experimental diet containing 7 or 30% casein with or without 0.1 % PCB for 24 days. Dietary PCB increased the level of triglyceride, phospholipid and cholesterol in the liver. The accumulation of triglyceride and cholesterol in liver was markedly increased with a low protein diet. The incorporation of injected ³H₂O into liver cholesterol was increased by PCB, but not affected by the dietary level of protein. The incorporation of the tracer into liver fatty acids was not increased by PCB intake. Dietary PCB also raised serum cholesterol and phospholipid, while PCB decreased triglyceride level, especially in rats on low protein diet. In addition, PCB intake clearly raised serum high density lipoprotein and diminished very low density lipoprotein. In the low protein group, PCB markedly repressed the incorporation of ³H₂O into serum lipids. The results suggest that the hepatic lipids accumulation by the addition of 0.1 % PCB to a low protein diet might be mainly ascribed to a repression in the transport of triglyceride from liver to blood. KEY WORDS: PCB, dietary protein, liver lipids, serum lipoprotein.     

Pattern Formation in the Arabidopsis Embryo Revealed by Position-Specific Lipid Transfer Protein Gene Expression

During Arabidopsis embryogenesis, the zygote divides asymmetrically in the future apical-basal axis; however, a radial axis is initiated only within the eight-celled embryo. Mutations in the GNOM, KNOLLE, and KEULE genes affect these processes: gnom zygotes tend to divide symmetrically; knolle embryos lack oriented cell divisions that initiate protoderm formation; and in keule embryos, an outer cell layer is present that consists of abnormally enlarged cells from early development. Pattern formation along the two axes is reflected by the position-specific expression of the Arabidopsis lipid transfer protein (AtLTP1) gene. In wild-type embryos, the AtLTP1 gene is expressed in the protoderm and initially in all protodermal cells; later, AtLTP1 expression is confined to the cotyledons and the upper end of the hypocotyl. Analysis of AtLTP1 expression in gnom, knolle, and keule embryos showed that gnom embryos also can have no or reversed apical-basal polarity, whereas radial polarity is unaffected. knolle embryos initially lack but eventually form a radial pattern, and keule embryos are affected in protoderm cell morphology rather than in the establishment of the radial pattern.     

大米蛋白调控成熟期大鼠LDLR基因及蛋白表达

为了探讨大米蛋白对成熟期大鼠胆固醇代谢调控因子一低密度脂蛋白受体（low—densitv lipoprotein receptor．LDLR）的调控作用,以18周龄雄性Wistar成熟期大鼠为研究对象,应用大米蛋白及酪蛋白为食物蛋白源,饲喂无胆固醇及富含胆固醇饲料,经18日自由摄食后,测定实验鼠血浆总胆固醇、血浆高密度胆固醇水平及肝脏LDLR基因及蛋白表达水平。对照酪蛋白,大米蛋白均能显著降低大鼠血浆总胆固醇、血浆非高密度胆固醇水平及动脉粥样硬化指数,并且,显著刺激肝脏LDL基因及蛋白表达水平。实验结果表明,大米蛋白降低成熟期大鼠血浆胆固醇水平的作用功效与膳食胆固醇添加与否无关,大米蛋白降胆固醇的作用机制之一是能够有效刺激LDLR的表达,从而抑制LDL—C的转运入血。     

Pre-Slaughter Stress Affects Ryanodine Receptor Protein Gene Expression and the Water-Holding Capacity in Fillets of the Nile Tilapia

Current study evaluated the effect of pre-slaughter stress on serum cortisol levels, pH, colorimetry, water-holding capacity (WHC) and gene expression of ryanodine receptors (RyR1 and RyR3) in the Nile tilapia. A 3x4 factorial scheme experiment was conducted comprising three densities (100, 200, 400 kg/m³) with four transportation times (60, 120, 180, and 240 minutes).Transportation times alone reduced cortisol levels up to 180 minutes, followed by increased WHC and mRNA expression, RyR1 and RyR3 (200 kg/m³ density). No effect of density x transportation time interacted on the evaluated parameters. Results provided the first evidence that pre-slaughter stress affected ryanodine gene expression receptors and, consequently, the water-holding capacity in tilapia fillets.     

高脂饮食对小鼠脂质代谢和leptin基因表达水平的影响

目的建立高脂饮食诱导小鼠肥胖模型,分析高脂饲料对小鼠脂质代谢和leptin基因表达水平的影响。方法用高脂饲料饲喂小鼠,每周定时称重和断尾采血一次,分别测定血清中血糖、胆固醇、甘油三酯、胰岛素和leptin的浓度;5周后,分离、称重小鼠体脂并提取腹部脂肪组织RNA,半定量RT-PCR分析leptin基因表达水平。结果从第2周开始,实验组小鼠体重明显高于对照组小鼠,4周后,体重差异显著（P〈0．05）;血清中血糖、胆固醇、甘油三酯、胰岛素和leptin的含量随体重增加明显增高,4周后,差异显著（P〈0．05）;实验组体脂含量明显高于对照组（P〈0．05）,半定量RT-PCR分析表明,肥胖小鼠脂肪组织leptin基因表达水平高于对照组（P〈0．05）。结论高脂饮食诱导可建立小鼠肥胖模型,并能够引起高胰岛素和高leptin血症,为进一步研究肥胖的发病机制奠定基础。     

Myelin Proteolipid Protein Gene Expression in Jimpy and Jimpymsd Mice

Proteolipid protein (PLP) gene expression was studied in the dysmyelinating mouse mutant jimpy(msd) (jpmsd; myelin synthesis deficient) and compared with that in wild-type mice and the allelic mutant, jimpy (jp). Southern analyses of genomic DNA from jpmsd mice revealed no major rearrangements of the PLP gene relative to the wild-type mouse PLP gene. PLP-specific mRNA levels were significantly reduced in these mutant mice, although both the 3.2- and 2.4-kilobase PLP-specific mRNAs were seen. Also, no size differences in either PLP or DM20 mRNAs were found by S1 nuclease assays of brain RNA from either jpmsd or wild-type mice. Both PLP and DM20 protein were detectable at low levels in jpmsd brain homogenates, and these proteins comigrated with PLP and DM20 protein from normal mice. Western analyses showed an altered PLP:DM20 ratio in jpmsd mice relative to wild-type mice; DM20 levels exceeded PLP levels. It is surprising that a similar pattern of expression was seen in normal mice at less than 10 days of age: DM20 protein expression preceding PLP expression. Thus, jpmsd mice are capable of synthesizing normal PLP and DM20 protein; however, the PLP gene defect has affected the normal developmental pattern of expression for these two proteins.     

自噬在肝脏蛋白质和脂质代谢中的作用

自噬是一个通过降解细胞组分如细胞器和蛋白质等以维持细胞存活和功能的重要的溶酶体途径。肝脏作为新陈代谢的中枢器官,肝脏高度依赖于自噬以发挥正常功能并防止疾病发展。肝细胞自噬的改变参与肝损伤,脂肪肝等肝病的病理变化,以自噬为靶点寻求治疗各种肝病的方法已成为热点研究领域,但自噬在肝脏蛋白质和脂质代谢中的作用极其机制尚不清楚。本文对自噬在肝脏蛋白质和脂质代谢中的作用的最新进展进行综述。     

祛湿化瘀方通过调节AMPK活性改善高脂饮食诱导的实验性脂肪肝肝脏脂肪代谢

目的：研究祛湿化瘀方对高脂饮食诱导的大鼠脂肪肝AMPK蛋白活性及其相关脂肪代谢靶蛋白活性的影响,以探讨该方防治实验性脂肪肝的作用机制。方法：采用高脂饲料饮食诱导大鼠脂肪肝模型,造模大鼠给予高脂饮食4周后,按随机数字表随机分为模型组及祛湿化瘀方组,分别灌胃给予饮用水及中药祛湿化瘀方4周。实验8周末取材后观察：1）肝组织三酰甘油（Triglyceride,TG）、游离脂肪酸（Free Fatty Acid,FFA）含量,2）肝组织病理变化（HE染色、油红染色）,3）肝组织腺苷酸活化的蛋白激酶（AMP-Activated K inase,AMPK）及磷酸化AMPK、肝组织总蛋白及核蛋白固醇调节元件结合蛋白-1 c（Sterol Regulatory Element Binding Protein-1 c、SREBP-1 c）、肝组织总蛋白及核蛋白碳水化合物反应元件结合蛋白（Carbohydrate Response Element Binding Protein、ChREBP）含量、肝组织乙酰辅酶A羧化酶（Acety1 CoA Carboxylase,ACCa-se）及磷酸化ACC蛋白含量,4）肝组织AMPKα1、AMPKα2、SREBP-1、ACCα、SREBP-1 c及ChREBP基因表达水平。结果：1）模型组肝组织TG、FFA含量显著升高,肝组织出现明显大泡样脂肪变性;模型组肝组织AMPK蛋白磷酸化水平降低、核蛋白SREBP-1与ChREBP表达增加、ACC蛋白磷酸化水平降低蛋白活性升高。2）祛湿化瘀方组肝组织TG、FFA含量较模型组显著降低,肝组织炎症及脂肪变性程度减轻;祛湿化瘀方能显著升高肝组织AMPK、ACC蛋白磷酸化水平、降低核蛋白SREBP-1及ChREBP含量。结论：祛湿化瘀方通过调节AMPK活性及其相关靶蛋白活性改善高脂饮食诱导的大鼠脂肪肝肝脂肪代谢,这可能是该方有效防治实验性脂肪肝的重要作用机制之一。     

Effects of Puerarin on Lipid Accumulation and Metabolism in High-Fat Diet-Fed Mice

In order to investigate the mechanisms by which puerarin from kudzu root extract regulates lipid metabolism, fifty mice were randomly assigned to five groups: normal diet, high-fat diet (HFD), and HFD containing 0.2%, 0.4% or 0.8% puerarin for 12 weeks. Body weight, intraperitioneal adipose tissue (IPAT) weight, serum biochemical parameters, and hepatic and feces lipids were measured. Activity and mRNA and protein expressions of hepatic lipid metabolism-related enzymes were analyzed. Compared with HFD, 0.4% and 0.8% puerarin significantly decreased body and IPAT weight. There was a significant decrease in the serum and hepatic concentrations of total cholesterol, triglycerides and leptin in mice fed the 0.4% and 0.8% puerarin diets compared with HFD. Fatty acid synthase activity was suppressed in mice fed the 0.4% and 0.8% puerarin diets, while the activities of AMP-activated protein kinase (AMPK), carnitine acyltransferase (CAT) and hormone-sensitive lipase (HSL) were increased. mRNA expression of peroxisome proliferator-activated receptor γ 2 (PPARγ 2) was down-regulated in liver of mice fed the 0.8% diet compared with HFD, while mRNA expression of CAT and HSL was considerably up-regulated by 0.4% and 0.8% puerarin diets. The protein expression of PPARγ2 in liver was decreased and those of p-AMPK, HSL and p-HSL were increased in mice fed 0.4% and 0.8% puerarin diets. These results suggest that > 0.4% puerarin influenced the activity, mRNA and protein levels of hepatic lipid metabolism-related enzymes, decreasing serum and liver lipids, body weight gain and fat accumulation. Puerarin might be beneficial to prevent lifestyle-related diseases.     

RNA Interference Silencing of a Major Lipid Droplet Protein Affects Lipid Droplet Size in Chlamydomonas reinhardtii

Eukaryotic cells store oils in the chemical form of triacylglycerols in distinct organelles, often called lipid droplets. These dynamic storage compartments have been intensely studied in the context of human health and also in plants as a source of vegetable oils for human consumption and for chemical or biofuel feedstocks. Many microalgae accumulate oils, particularly under conditions limiting to growth, and thus have gained renewed attention as a potentially sustainable feedstock for biofuel production. However, little is currently known at the cellular or molecular levels with regard to oil accumulation in microalgae, and the structural proteins and enzymes involved in the biogenesis, maintenance, and degradation of algal oil storage compartments are not well studied. Focusing on the model green alga Chlamydomonas reinhardtii, the accumulation of triacylglycerols and the formation of lipid droplets during nitrogen deprivation were investigated. Mass spectrometry identified 259 proteins in a lipid droplet-enriched fraction, among them a major protein, tentatively designated major lipid droplet protein (MLDP). This protein is specific to the green algal lineage of photosynthetic organisms. Repression of MLDP gene expression using an RNA interference approach led to increased lipid droplet size, but no change in triacylglycerol content or metabolism was observed.Triacylglycerols (TAGs) are stored in lipid droplets which are subcellular structures in specialized cells ubiquitous to eukaryotes but have more recently also been identified in some prokaryotes (26). In plants and animals, lipid droplets are surrounded by cytosol and are believed to bud off the endoplasmic reticulum (ER) (15, 26). While traditionally considered merely as storage compartments, recent studies suggest that lipid droplets in animals play important additional roles in lipid homeostasis and protein storage (8). In oilseed plants, TAG accumulated in seeds is used as a reservoir of energy and membrane lipid building blocks to support rapid growth after germination (15). Many green algae are capable of accumulating large amounts of TAG in lipid droplets, particularly as a result of abiotic stresses, such as nutrient deprivation or high-light exposure. Although TAG metabolism in algae has not yet been extensively studied at the biochemical or molecular level, it is proposed that TAG turnover contributes primarily to the assembly of membrane lipids to facilitate rapid cell division after the cessation of nutrient limitation (14, 38).The general structure of lipid droplets is conserved in different species with a globular neutral lipid core enclosed by a membrane lipid monolayer (26). In addition, specific proteins are associated with lipid droplets and play important roles in lipid droplet structure and function. A number of recent proteomic studies of lipid droplets from different animals and tissues (8, 40), Saccharomyces cerevisiae (4), and plants (16, 17) have revealed that the lipid droplet-associated proteins of these organisms are quite distinct. For example, the abundant lipid droplet proteins in animals—the so-called “PAT” family of proteins comprised of perilipin, adipose differentiation-related protein (ADRP), and TIP47 (21)—have no apparent orthologs in the desiccating seed plant Arabidopsis thaliana; conversely, the oleosins which coat the oil bodies of Arabidopsis and many other seed plants are not found in animals (26). Reverse genetic studies of these proteins have helped to elucidate the role of A. thaliana oleosins in regulating lipid droplet size and preventing droplet fusion (35, 36) or that of mouse adipocyte perilipin in regulating lipolytic activity at the lipid droplet surface (37). Moreover, recent genomewide RNAi screens in Drosophila cells implicated 1.5 to 3.0% of all genes as directly or indirectly involved in lipid droplet formation and/or regulation and resulted in the identification of a new role for the Arf1-COPI vesicular transport machinery in regulating droplet morphology and lipid utilization (7, 12). In contrast, few molecular details are known about algal lipid droplet biogenesis although many TAG-rich algal species have been described (14).Our efforts to identify proteins related to the PAT protein family or oleosins in the Chlamydomonas reinhardtii genome (24) or genomes of other green algal and diatom species, including Thalassiosira pseudonana, Volvox carteri, and Chlorella sp. NC64A, revealed no putative algal orthologs. In order to identify both potentially novel and conserved proteins which function in algal lipid droplet biogenesis, we studied the accumulation of TAG in lipid droplets of nitrogen-limited C. reinhardtii cells and identified candidate lipid droplet-associated proteins by mass spectrometry.     

Dietary Protein Quality and Liver Arginase Activity of Rats

The arginase activity of the liver of rats was measured after they had been maintained for 11 or 12 days on diets containing natural proteins (casein or gluten) or amino acid mixtures of various tryptophan levels.

Specific activity or total arginase activity increased with the increasing protein quality. Liver arginase activity of the casein group was significantly higher than that of the gluten group in every case for 27-, 61-, and 158-day-old rats. In the case of amino acid diets, the arginase increased with the increments of tryptophan levels up to the “tentative” minimum requirement in the diet. Moreover, these alterations in arginase activity varied inversely with the urinary urea excretion.

From the results, it was assumed that the total activity of liver arginase is not necessarily determined only by the metabolic needs for urea biosynthesis.