Biomedical subjects

Sun Hee Yim

Publications and source records attributed to Sun Hee Yim.

6 recordsLinked to original sources

PubMed2006

Disruption of the Arnt gene in endothelial cells causes hepatic vascular defects and partial embryonic lethality in mice.

Vascular endothelial cells (ECs) play a critical role in angiogenesis and organogenesis, especially in embryonic liver development. Hypoxia-inducible transcription factors (Hifs) are a key trigger of hypoxic signals, a primary stimulus of angiogenesis. The aryl hydrocarbon receptor nuclear translocator (Arnt), also called Hif-1beta, serves as an obligate heterodimerization partner of Hif-1alpha and Hif-2alpha. Using Cre-Lox technology, the mouse Arnt gene was specifically disrupted in endothelial cells. The resulting mice, designated ArntDeltaEC, developed impaired hepatic vasculature, liver necrosis, and degenerative lesions in cardiac myocytes at the late embryonic stage (E16.5-E18.5), leading to approximately 90% neonatal lethality. Low serum glucose, downregulation of glucose transporter-1 and glucose-6-phosphatase mRNA, and hepatocyte proliferation were observed in ArntDeltaEC embryos. Magnetic resonance imaging on E16.5 embryonic livers revealed that ArntDeltaEC mice had a significant volume of avascular region. ArntDeltaEC mice that survived to the adult stage were fertile, showed normal behavioral activity, but had smaller livers with mild portal fibrosis, dilated blood vessels, abnormal collagen accumulation, and remarkable iron deposition. ArntDeltaEC mice had reduced adiposity, impaired serum lipid homeostasis, and a higher respiratory exchange ratio, indicating they utilized relatively more carbohydrates than their ArntF/F counterparts. In conclusion, endothelial Arnt plays a pivotal role in embryonic liver development. Adult ArntDeltaEC mice carrying embryonic hepatic defects developed what was possibly an early stage of cirrhosis with consequences of limited oxygen availability and altered lipid metabolism.

Animals↗

PubMed2005

Role of hepatocyte nuclear factor 4alpha in control of blood coagulation factor gene expression.

Hepatocyte nuclear factor 4alpha (HNF4alpha) plays an important role in the maintenance of many liver-specific functions. Liver-specific HNF4alpha-null mice were used to determine whether hepatic HNF4alpha regulates blood coagulation in vivo. These mice exhibited reduced expression of hepatic coagulation factors V, IX, XI, XII, and XIIIB and a prolonged activated partial thromboplastin time but not prothrombin time. Promoter analysis of the mouse FXII and FXIIIB genes was performed to determine whether HNF4alpha directly regulates the genes encoding these coagulation factors. Sequence analysis revealed the presence of one and two HNF4alpha binding sites in the mouse FXII and FXIIIB genes, respectively. Using transient transfection and electrophoretic mobility shift analyses with the mouse FXII and FXIIIB promoters, it was established that the high levels of promoter activity were dependent on HNF4alpha binding sites and the expression of HNF4alpha. In conclusion, HNF4alpha has a critical role in blood coagulation homeostasis by directing transcription of the FXII and XIIIB genes.

Animals↗

PubMed2005

Regulation of bile acid biosynthesis by hepatocyte nuclear factor 4alpha.

Hepatocyte nuclear factor 4alpha (HNF4alpha) regulates many genes that are preferentially expressed in liver. Mice lacking hepatic expression of HNF4alpha (HNF4alphaDeltaL) exhibited markedly increased levels of serum bile acids (BAs) compared with HNF4alpha-floxed (HNF4alphaF/F) mice. The expression of genes involved in the hydroxylation and side chain beta-oxidation of cholesterol, including oxysterol 7alpha-hydroxylase, sterol 12alpha-hydroxylase (CYP8B1), and sterol carrier protein x, was markedly decreased in HNF4alphaDeltaL mice. Cholesterol 7alpha-hydroxylase mRNA and protein were diminished only during the dark cycle in HNF4alphaDeltaL mice, whereas expression in the light cycle was not different between HNF4alphaDeltaL and HNF4alphaF/F mice. Because CYP8B1 expression was reduced in HNF4alphaDeltaL mice, it was studied in more detail. In agreement with the mRNA levels, CYP8B1 enzyme activity was absent in HNF4alphaDeltaL mice. An HNF4alpha binding site was found in the mouse Cyp8b1 promoter that was able to direct HNF4alpha-dependent transcription. Surprisingly, cholic acid-derived BAs, produced as a result of CYP8B1 activity, were still observed in the serum and gallbladder of these mice. These studies reveal that HNF4alpha plays a central role in BA homeostasis by regulation of genes involved in BA biosynthesis, including hydroxylation and side chain beta-oxidation of cholesterol in vivo.

Animals↗

PubMed2004

Disruption of hepatic C/EBPalpha results in impaired glucose tolerance and age-dependent hepatosteatosis.

C/EBPalpha is highly expressed in liver and regulates many genes that are preferentially expressed in liver. Because C/EBPalpha-null mice die soon after birth, it is impossible to analyze the function of C/EBPalpha in the adult with this model. To address the function of C/EBPalpha in adult hepatocytes, liver-specific C/EBPalpha-null mice were produced using a floxed C/EBPalpha allele and the albumin-Cre transgene. Unlike whole body C/EBPalpha-null mice, mice lacking hepatic C/EBPalpha expression did not exhibit hypoglycemia, nor did they show reduced hepatic glycogen in adult. Expression of liver glycogen synthase, phosphoenolpyruvate carboxykinase, and glucose-6-phosphatase remained at normal levels. However, these mice exhibited impaired glucose tolerance due in part to reduced expression of hepatic glucokinase, and hyperammonemia from reduced expression of hepatic carbamoyl phosphate synthase-I. These mice also had reduced serum cholesterol and steatotic livers that was exacerbated with aging. This phenotype could be explained by increased expression of hepatic lipoprotein lipase and reduced expression of microsomal triglyceride transfer protein, apolipoproteins B100, and A-IV. These data demonstrate that hepatic C/EBPalpha is critical for ammonia detoxification and glucose and lipid homeostasis in adult mice.

Aging↗

PubMed2002

The aryl hydrocarbon receptor (AhR) and its nuclear translocator (Arnt) are dispensable for normal mammary gland development but are required for fertility.

The aryl hydrocarbon receptor (AhR) and its nuclear translocator (Arnt) are transcription factors that play a role in the detection of and adaptation to environmental signals. AhR-null mice are viable but show impaired lactation. Deletion of the Arnt gene from the mouse genome results in embryonic lethality. To determine the role of Arnt in mammary development and function, we inactivated the Arnt gene in mammary epithelium using Cre-loxP recombination. Inactivation of the Arnt gene during pregnancy did not disrupt alveolar development or the ability of dams to nurse their litters. In contrast, dams in which the Arnt gene had been inactivated during puberty and in ovaries were subfertile, exhibited retarded mammary development, and impaired mammary function. To distinguish defects autonomous to mammary epithelium from indirect effects controlled by ovarian hormones, we transplanted Arnt-null and AhR-null mammary epithelium into wild-type mice and evaluated development after one pregnancy. Normal mammary structures were observed in the absence of Arnt and AhR, demonstrating that neither transcription factor is necessary for mammary development.

Animals↗

PubMedDate not supplied

Microarray analysis using amplified mRNA from laser capture microdissection of microscopic hepatocellular precancerous lesions and frozen hepatocellular carcinomas reveals unique and consistent gene expression profiles.

The indirect labeling cDNA microarray technique was used to evaluate gene expression profiles of pure cell populations from frozen sections of carcinomas and adenomas harvested from precancerous hepatocellular lesions by using laser capture microdissection (LCM). The levels of differentially expressed genes were investigated using a cDNA microarray with 9,984 features with only 2 ug of two-round amplified aRNA, equivalent to 35 cells from LCM-adenomas and frozen samples of carcinomas from simian virus 40 (SV40) large T antigen transgenic rats. A total of 855 genes were identified as being 3-fold or more differentially expressed in carcinomas or adenomas as compared to normal tissue controls. Among these 855 genes, 71 genes were differentially expressed in both carcinomas and adenomas. Commonly up-regulated genes in both carcinoma and adenomas were 28 while 41 of the 71 genes were commonly down-regulated. Two genes, Igh1 (immunoglobulin heavy chain 1(Serum IgG2a), Image clone ID: 875880) and EST clone (AI893585, Image clone ID: 596604) were more than 7-fold up-regulated in carcinomas and 6-fold down-regulated in adenomas. In Cy5 and Cy3 reciprocal experiments for screening out false positive signals, the amplified carcinomas showed higher Pearson Correlation Coefficient values (-0.94 and -0.92) than the LCM-amplified adenoma samples (-0.79 and -0.84). LCM-amplified samples provided higher signal intensities over backgrounds and a greater average of Cy5:Cy3 ratios. Expression levels of mRNAs from selected genes, determined by using traditional dot blot analysis, revealed that 36 of 40 tested expression profiles were consistent with the microarray data. Thus, amplified aRNA harvested from homogeneous cell types using LCM can be applied to study gene expression profiles by use of microarray analysis.

Animals↗