[Dynamic changes of landscape pattern and hemeroby in Ximen Island wetland, Zhejiang Province, China].

Abstract: The hemeroby type classification system of Ximen Island wetland of Zhejiang Province was established based on the multiple datasets: SOPT-5 image data with a spatial resolution of 5 m in 2007 and 2010, its wetland land cover and land use status, the National Land Use Classification (on trail), and sea area use classification of marine industry standards as well as remote sensing data features. Meanwhile, the dynamic relationship between the landscape pattern and the degree of hemeroby in Ximen Island was investigated with the landscape indices and hemeroby index (HI) derived from the landscape pattern index and GIS spatial analysis. The results showed that the wetland landscape spatial heterogeneity, fragmentation and dominance index dropped, and the landscape shape index complexity was low. The human disturbance center developed from a dispersion type to a concentration type. The landscape type of the disturbance center was bare land and settlement. The HI rose up from the sea to the land. Settlement, wharf and traffic land had the highest HI. The HI of the mudflat cultivation, mudflats and raft-cultivation dramatically changed. Marine-terrestrial interlaced zone showed a low total HI with unstable characteristics. The number of patches declined of undisturbed, partially disturbed and completely disturbed landscapes. Mean patch areas of partially disturbed and completely disturbed landscapes increased, and that of the undisturbed decreased. Mean shape index of the undisturbed landscape decreased, while the partially disturbed and completely disturbed landscapes showed a trend of shape complication.

The Scap/SREBP pathway is essential for developing diabetic fatty liver and carbohydrate-induced hypertriglyceridemia in animals.

Insulin resistance leads to hypertriglyceridemia and hepatic steatosis and is associated with increased SREBP-1c, a transcription factor that activates fatty acid synthesis. Here, we show that steatosis in insulin-resistant ob/ob mice was abolished by deletion of Scap, an escort protein necessary for generating nuclear isoforms of all three SREBPs. Scap deletion reduced lipid synthesis and prevented fatty livers despite persistent obesity, hyperinsulinemia, and hyperglycemia. Scap deficiency also prevented steatosis in mice fed high-fat diets. Steatosis was also prevented when siRNAs were used to silence Scap in livers of sucrose-fed hamsters, a model of diet-induced steatosis and hypertriglyceridemia. This silencing reduced all three nuclear SREBPs, decreasing lipid biosynthesis and abolishing sucrose-induced hypertriglyceridemia. These results demonstrate that SREBP activation is essential for development of diabetic hepatic steatosis and carbohydrate-induced hypertriglyceridemia, but not insulin resistance. Inhibition of SREBP activation has therapeutic potential for treatment of hypertriglyceridemia and fatty liver disease.

Upregulation of Scavenger Receptor BI by Hepatic Nuclear Factor 4α through a Peroxisome Proliferator-Activated Receptor γ-Dependent Mechanism in Liver.

Hepatic nuclear factor 4α (HNF4α) modulates the transcriptional activation of numerous metabolic genes in liver. In this study, gene-array analysis revealed that HNF4α overexpression increased peroxisome proliferator-activated receptorγ (PPARγ) greatly in cultured rat primary hepatocytes. PPAR-response-element-driven reporter gene expression could be elevated by HNF4α. Bioinformatics analysis revealed a high-affinity HNF4α binding site in the human PPARγ2 promoter and in vitro experiments showed that this promoter could be transactivated by HNF4α. The presence of HNF4α on the promoter was then confirmed by ChIP assay. In vivo, hepatic overexpression of HNF4α decreased cholesterol levels both in plasma and liver and several hepatic genes related to cholesterol metabolism, including scavenger receptor BI (SR-BI), were upregulated. The upregulation of SR-BI by HNF4α could be inhibited by a PPARγ antagonist in vitro. In conclusion, HNF4α regulates cholesterol metabolism in rat by modulating the expression of SR-BI in the liver, in which the upregulation of PPARγ was involved.

Amino acid substitution in NPC1 that abolishes cholesterol binding reproduces phenotype of complete NPC1 deficiency in mice.

Substitution mutations in adjacent amino acids of the N-terminal domain of NPC1, a lysosomal membrane protein, abolish its cholesterol binding activity and impair its ability to export cholesterol from lysosomes of cultured cells lacking npc1 [Kwon HJ, et al. (2009) Cell 137:1213-1224]. Here, we show that the same two mutations (proline-202 and phenylalanine-203, both changed to alanine) reproduce the phenotype of complete NPC1 deficiency when knocked into the mouse npc1 gene by homologous recombination. Homozygous npc1(pf/pf) mice exhibited neurodegeneration beginning at day 49 and died at a median age of 84 d, as previously reported for mice that lack npc1. Liver and other organs of the npc1(pf/pf) mice accumulated excess cholesterol in lysosomes. In liver, mRNAs encoding several lysosomal proteins were elevated, including NPC1 and NPC2 and several digestive enzymes (acid lipase, ß-glucuronidase, and cathepsins B and D). Weekly treatment with hydroxypropyl-ß-cyclodextrin (HPCD) beginning at 7 wk reduced hepatic cholesterol accumulation and diminished the lysosomal mRNAs. We conclude that the cholesterol binding site in the N-terminal domain of NPC1 is essential for cholesterol export from lysosomes in living animals as it is in cultured cells. The HPCD-mediated reduction of excess lysosomal enzymes may contribute to the ability of this drug to delay the progression of NPC disease in mice.

Ghrelin O-acyltransferase (GOAT) is essential for growth hormone-mediated survival of calorie-restricted mice.

Ghrelin O-acyltransferase (GOAT) attaches octanoate to proghrelin, which is processed to ghrelin, an octanoylated peptide hormone that stimulates release of growth hormone (GH) from pituitary cells. Elimination of the gene encoding ghrelin or its receptor produces only mild phenotypes in mice. Thus, the essential function of ghrelin is obscure. Here, we eliminate the Goat gene in mice, thereby eliminating all octanoylated ghrelin from blood. On normal or high fat diets, Goat(-/-) mice grew and maintained the same weights as wild-type (WT) littermates. When subjected to 60% calorie restriction, WT and Goat(-/-) mice both lost 30% of body weight and 75% of body fat within 4 days. In both lines, fasting blood glucose initially declined equally. After 4 days, glucose stabilized in WT mice at 58-76 mg/dL. In Goat(-/-) mice, glucose continued to decline, reaching 12-36 mg/dL on day 7. At this point, WT mice showed normal physical activity, whereas Goat(-/-) mice were moribund. GH rose progressively in calorie-restricted WT mice and less in Goat(-/-) mice. Infusion of either ghrelin or GH normalized blood glucose in Goat(-/-) mice and prevented death. Thus, an essential function of ghrelin in mice is elevation of GH levels during severe calorie restriction, thereby preserving blood glucose and preventing death.

Down-regulation of hepatic HNF4alpha gene expression during hyperinsulinemia via SREBPs.

Mutations in the coding region of hepatocyte nuclear factor 4alpha (HNF4alpha), and its upstream promoter (P2) that drives expression in the pancreas, are known to lead to maturity-onset diabetes of the young 1 (MODY1). HNF4alpha also controls gluconeogenesis and lipid metabolism in the liver, where the proximal promoter (P1) predominates. However, very little is known about the role of hepatic HNF4alpha in diabetes. Here, we examine the expression of hepatic HNF4alpha in two diabetic mouse models, db/db mice (type 2, insulin resistant) and streptozotocin-treated mice (type 1, insulin deficient). We found that the level of HNF4alpha protein and mRNA was decreased in the liver of db/db mice but increased in streptozotocin-treated mice. Because insulin increases the activity of sterol regulatory element-binding proteins (SREBP)-1c and -2, we also examined the effect of SREBPs on hepatic HNF4alpha gene expression and found that, like insulin, ectopic expression of SREBPs decreases the level of hepatic HNF4alpha protein and mRNA both in vitro in primary hepatocytes and in vivo in the liver of C57BL/6 mice. Finally, we use gel shift, chromatin immunoprecipitation, small interfering RNA, and reporter gene analysis to show that SREBP2 binds the human HNF4alpha P1 promoter and negatively regulates its expression. These data indicate that hyperinsulinemia down-regulates HNF4alpha in the liver through the up-regulation of SREBPs, thereby establishing a link between these two critical transcription factor pathways that regulate lipid and glucose metabolism in the liver. These findings also provide new insights into diabetes-associated complications such as fatty liver disease.

AMP-activated protein kinase promotes the differentiation of endothelial progenitor cells.

OBJECTIVE: Endothelial progenitor cells (EPCs) can differentiate into endothelial cells (ECs) and participate in postnatal vasculogenesis, but the mechanism of EPC differentiation remains largely unknown. We investigated the role of AMP-activated protein kinase (AMPK) in EPC differentiation and functions. METHODS AND RESULTS: Vascular endothelial growth factor caused the phosphorylation of AMPK, acetyl-coenzymeA (CoA) carboxylase (ACC), and eNOS in human cord blood-derived EPCs. The expression of EC markers, including VE-cadherin and intercellular adhesion molecule1 (ICAM-1), was also increased but blocked by Compound C, an AMPK inhibitor. AICAR, an AMPK agonist, increased the phosphorylation of ACC and eNOS and the expression of EC markers in a time- and dose-dependent manner, which reinforces the positive effect of AMPK on EPC differentiation. The effects of AICAR could be blocked by treatment with L-NAME, an eNOS inhibitor. Functionally, AICAR increased but Compound C decreased the angiogenesis of EPCs in vitro and in vivo. Furthermore, lovastatin promoted the activation of AMPK and eNOS, the expression of EC markers, tube formation, adhesion, and in vivo vasculogenesis of EPCs, which could be blocked by treatment with Compound C. CONCLUSIONS: The activation of eNOS by AMPK during EPC differentiation provides a novel mechanism for the pleiotropic effects of statins in benefiting the cardiovascular system.

Peroxisome proliferator-activated receptor-delta induces insulin-induced gene-1 and suppresses hepatic lipogenesis in obese diabetic mice.

UNLABELLED: Primary nonalcoholic fatty liver disease is one of the most common forms of chronic liver diseases and is associated with insulin-resistant states such as diabetes and obesity. Recent work has revealed potential implications of peroxisome proliferator-activated receptor-delta (PPARdelta) in lipid homeostasis and insulin resistance. In this study, we examined the effect of PPARdelta on sterol regulatory element-binding protein-1 (SREBP-1), a pivotal transcription factor controlling lipogenesis in hepatocytes. Treatment with GW0742, the PPARdelta agonist, or overexpression of PPARdelta markedly reduced intracellular lipid accumulation. GW0742 and PPARdelta overexpression in hepatocytes induced the expression of insulin-induced gene-1 (Insig-1), an endoplasmic reticulum protein braking SREBP activation, at both the mRNA and the protein levels. PPARdelta inhibited the proteolytic processing of SREBP-1 into the mature active form, thereby suppressing the expression of the lipogenic genes fatty acid synthase, stearyl CoA desaturase-1, and acetyl coenzyme A carboxylase. Our results revealed a direct binding of PPARdelta to a noncanonical peroxisome proliferator responsive element motif upstream of the transcription initiation site of human Insig-1. The disruption of this site diminished the induction of Insig-1, which suggested that Insig-1 is a direct PPARdelta target gene in hepatocytes. Knockdown of endogenous Insig-1 attenuated the suppressive effect of GW0742 on SREBP-1 and its target genes, indicating PPARdelta inhibited SREBP-1 activation via induction of Insig-1. Furthermore, overexpression of PPARdelta by intravenous infection with the PPARdelta adenovirus induced the expression of Insig-1, suppressed SREBP-1 activation, and, consequently, ameliorated hepatic steatosis in obese db/db mice. CONCLUSION: Our study reveals a novel mechanism by which PPARdelta regulates lipogenesis, suggesting potential therapeutic applications of PPARdelta modulators in obesity and type 2 diabetes, as well as related steatotic liver diseases.

Insights into cholesterol efflux in vascular endothelial cells.

Vascular endothelial dysfunction is considered an initial step of atherogenesis, and the complicated cellular events of atherosclerosis begin with focal inflammation leading to foam cell formation and accumulation of cholesterol in the subendothelial space. Of the cells that make up atherosclerotic plaque, vascular endothelial cells (ECs) are the most resistant to cholesterol accumulation. However, ECs express receptors for modified lipoproteins and have the biochemical pathways for sterol synthesis and receptor-mediated endocytosis of lipoproteins. Cholesterol efflux continues even when cellular cholesterol mass is unchanged. Therefore, cholesterol efflux pathways may play an important role in endothelial cholesterol homeostasis. Recent study results suggest that apolipoprotein A-I and high density lipoproteins promote cellular cholesterol efflux through mechanisms depending on ATP-binding cassette transporter A1 in ECs. Caveolae and its structural protein caveolin-1 are abundant in ECs and could be contributors to cholesterol trafficking as well. However, the roles of each pathway in efflux and homeostasis of cellular cholesterol in ECs are still controversial. This article reviews recent progress in the understanding of cholesterol efflux and underlying mechanisms in ECs and proposes a model of efflux of cellular cholesterol. Such a cholesterol efflux pathway could provide insight into the efficient removal of excess cellular cholesterol in preventing atherogenesis.

Oxidized LDL downregulates ATP-binding cassette transporter-1 in human vascular endothelial cells via inhibiting liver X receptor (LXR).

OBJECTIVE: ATP-binding cassette transporter-1 (ABCA1) mediates the active efflux of cholesterol and phospholipids, playing an important role in cholesterol homeostasis and atherogenesis. Oxidized low density lipoprotein (oxLDL) is an atherogenic molecule associated with the vascular endothelial dysfunction and development of atherosclerotic plaque. This report describes the effect of copper-catalyzed oxLDL on the regulation of ABCA1 in human endothelial cells (ECs). METHODS AND RESULTS: oxLDL downregulated ABCA1 at both mRNA and protein levels in a dose-dependent manner. This inhibitory effect of oxLDL was observed with both minimally and extensively oxLDL. Transfection of the ABCA1 promoter luciferase revealed oxLDL to substantially decrease ABCA1 promoter activity at basal conditions and after stimulation by overexpressing the liver X receptor LXRalpha and retinoid X receptor RXRalpha. oxLDL also attenuated LXR activation by blocking LXR ligand binding and interfering with the generation of 27-hydroxycholesterol, an LXR endogenous ligand. Furthermore, oxLDL inhibited exogenous cholesterol- and oxysterol-induced endothelial ABCA1 induction. CONCLUSION: oxLDL downregulated ABCA1 by inhibiting LXR activation in endothelial cells. Such an effect may contribute to endothelial dysfunction and plaque formation.