scholarly journals Regulation of the Human Cholesterol 7α-Hydroxylase Gene (CYP7A1) by Thyroid Hormone in Transgenic Mice

Endocrinology ◽  
2004 ◽  
Vol 145 (2) ◽  
pp. 574-581 ◽  
Author(s):  
Victor A. B. Drover ◽  
Luis B. Agellon
Keyword(s):  
Thyroid Hormone ◽  
Transgenic Mice ◽  
Bile Acids ◽  
Biosynthetic Pathway ◽  
Cultured Cells ◽  
Gene Promoter ◽  
Mrna Abundance ◽  
In Vivo Model ◽  
Hydroxylase Gene

Abstract Thyroid hormones exert significant changes in the metabolism of bile acids. However, in humans, the effect of thyroid hormone on cholesterol 7α-hydroxylase (cyp7a), the rate- controlling enzyme in the classical bile acid biosynthetic pathway, remains poorly understood and has been difficult to study directly in vivo. Previous studies from our laboratory have shown that the activity of the human cholesterol 7α-hydroxylase gene promoter is repressed by T3 in cultured cells. Accordingly, we hypothesized that T3 would negatively regulate human CYP7A1 gene expression in vivo. We tested this hypothesis by inducing hypo- and hyperthyroidism in transgenic mice expressing the human CYP7A1 gene. Hypothyroidism did not affect the abundance of human cyp7a mRNA in transgenic mice. In hyperthyroid male mice, human cyp7a mRNA abundance was decreased. No significant change in cyp7a mRNA abundance was observed in hyperthyroid female mice. Gender differences in the amount of cholesterol and bile acids in gallbladder bile were also observed. The data indicate that thyroid hormone can repress the human CYP7A1 gene in transgenic mice, but this effect is dependent on gender in this in vivo model.

scholarly journals Cholesterol and bile acids regulate cholesterol 7 alpha-hydroxylase expression at the transcriptional level in culture and in transgenic mice.

1994 ◽  
Vol 14 (4) ◽  
pp. 2809-2821 ◽  
Author(s):  
M I Ramirez ◽  
D Karaoglu ◽  
D Haro ◽  
C Barillas ◽  
R Bashirzadeh ◽  
...  
Keyword(s):  
Tissue Culture ◽  
Transgenic Mice ◽  
Bile Acids ◽  
Transcriptional Activation ◽  
Fusion Gene ◽  
Proximal Promoter ◽  
Transcriptional Level ◽  
Endogenous Gene ◽  
Hydroxylase Gene

Cholesterol 7 alpha-hydroxylase (7 alpha-hydroxylase) is the rate-limiting enzyme in bile acid biosynthesis. It is subject to a feedback control, whereby high levels of bile acids suppress its activity, and cholesterol exerts a positive control. It has been suggested that posttranscriptional control plays a major part in that regulation. We have studied the mechanisms by which cholesterol and bile acids regulate expression of the 7 alpha-hydroxylase gene and found it to be solely at the transcriptional level by using two different approaches. First, using a tissue culture system, we localized a liver-specific enhancer located 7 kb upstream of the transcriptional initiation site. We also showed that low-density lipoprotein mediates transcriptional activation of chimeric genes, containing either the 7 alpha-hydroxylase or the albumin enhancer in front of the 7 alpha-hydroxylase proximal promoter, to the same extent as the in vivo cholesterol-mediated regulation of 7 alpha-hydroxylase mRNA. In a second approach, using transgenic mice, we have found that expression of an albumin enhancer-7 alpha-hydroxylase-lacZ fusion gene is restricted to the liver and is regulated by cholesterol and bile acids in a manner quantitatively similar to that of the endogenous gene. We also found, that a liver-specific enhancer is necessary for expression of the rat 7 alpha-hydroxylase gene, in agreement with the tissue culture experiments. Together, these results demonstrate that cholesterol and bile acids regulate the expression of the 7 alpha-hydroxylase gene solely at the transcriptional level.

scholarly journals Cholesterol and bile acids regulate cholesterol 7 alpha-hydroxylase expression at the transcriptional level in culture and in transgenic mice

1994 ◽  
Vol 14 (4) ◽  
pp. 2809-2821
Author(s):  
M I Ramirez ◽  
D Karaoglu ◽  
D Haro ◽  
C Barillas ◽  
R Bashirzadeh ◽  
...  
Keyword(s):  
Tissue Culture ◽  
Transgenic Mice ◽  
Bile Acids ◽  
Transcriptional Activation ◽  
Fusion Gene ◽  
Proximal Promoter ◽  
Transcriptional Level ◽  
Endogenous Gene ◽  
Hydroxylase Gene

Cholesterol 7 alpha-hydroxylase (7 alpha-hydroxylase) is the rate-limiting enzyme in bile acid biosynthesis. It is subject to a feedback control, whereby high levels of bile acids suppress its activity, and cholesterol exerts a positive control. It has been suggested that posttranscriptional control plays a major part in that regulation. We have studied the mechanisms by which cholesterol and bile acids regulate expression of the 7 alpha-hydroxylase gene and found it to be solely at the transcriptional level by using two different approaches. First, using a tissue culture system, we localized a liver-specific enhancer located 7 kb upstream of the transcriptional initiation site. We also showed that low-density lipoprotein mediates transcriptional activation of chimeric genes, containing either the 7 alpha-hydroxylase or the albumin enhancer in front of the 7 alpha-hydroxylase proximal promoter, to the same extent as the in vivo cholesterol-mediated regulation of 7 alpha-hydroxylase mRNA. In a second approach, using transgenic mice, we have found that expression of an albumin enhancer-7 alpha-hydroxylase-lacZ fusion gene is restricted to the liver and is regulated by cholesterol and bile acids in a manner quantitatively similar to that of the endogenous gene. We also found, that a liver-specific enhancer is necessary for expression of the rat 7 alpha-hydroxylase gene, in agreement with the tissue culture experiments. Together, these results demonstrate that cholesterol and bile acids regulate the expression of the 7 alpha-hydroxylase gene solely at the transcriptional level.

scholarly journals The TRH Gene Is Regulated by Thyroid Hormone at the Level of Transcription in Vivo

2010 ◽  
Vol 31 (1) ◽  
pp. 136-136
Author(s):  
Michelle L. Sugrue ◽  
Kristen R. Vella ◽  
Crystal Morales ◽  
Marisol E. Lopez ◽  
Anthony N. Hollenberg
Keyword(s):  
Thyroid Hormone ◽  
Genomic Region ◽  
Model System ◽  
Model Systems ◽  
In Vivo Model ◽  
Pituitary Thyroid Axis ◽  
Thyroid Axis ◽  
Normal Production

ABSTRACT The expression of the TRH gene in the paraventricular nucleus (PVH) of the hypothalamus is required for the normal production of thyroid hormone (TH) in rodents and humans. In addition, the regulation of TRH mRNA expression by TH, specifically in the PVH, ensures tight control of the set point of the hypothalamic-pituitary-thyroid axis. Although many studies have assumed that the regulation of TRH expression by TH is at the level of transcription, there is little data available to demonstrate this. We used two in vivo model systems to show this. In the first model system, we developed an in situ hybridization (ISH) assay directed against TRH heteronuclear RNA to measure TRH transcription directly in vivo. We show that in the euthyroid state, TRH transcription is present both in the PVH and anterior/lateral hypothalamus. In the hypothyroid state, transcription is activated in the PVH only and can be shut off within 5 h by TH. In the second model system, we employed transgenic mice that express the Cre recombinase under the control of the genomic region containing the TRH gene. Remarkably, TH regulates Cre expression in these mice in the PVH only. Taken together, these data affirm that TH regulates TRH at the level of transcription in the PVH only and that genomic elements surrounding the TRH gene mediate its regulation by T3. Thus, it should be possible to identify the elements within the TRH locus that mediate its regulation by T3 using in vivo approaches.

scholarly journals The Thyrotropin-Releasing Hormone Gene Is Regulated by Thyroid Hormone at the Level of Transcription in Vivo

Endocrinology ◽  
2010 ◽  
Vol 151 (2) ◽  
pp. 793-801 ◽  
Author(s):  
Michelle L. Sugrue ◽  
Kristen R. Vella ◽  
Crystal Morales ◽  
Marisol E. Lopez ◽  
Anthony N. Hollenberg
Keyword(s):  
Thyroid Hormone ◽  
Genomic Region ◽  
Model System ◽  
Model Systems ◽  
In Vivo Model ◽  
Pituitary Thyroid Axis ◽  
Thyroid Axis ◽  
Normal Production

The expression of the TRH gene in the paraventricular nucleus (PVH) of the hypothalamus is required for the normal production of thyroid hormone (TH) in rodents and humans. In addition, the regulation of TRH mRNA expression by TH, specifically in the PVH, ensures tight control of the set point of the hypothalamic-pituitary-thyroid axis. Although many studies have assumed that the regulation of TRH expression by TH is at the level of transcription, there is little data available to demonstrate this. We used two in vivo model systems to show this. In the first model system, we developed an in situ hybridization (ISH) assay directed against TRH heteronuclear RNA to measure TRH transcription directly in vivo. We show that in the euthyroid state, TRH transcription is present both in the PVH and anterior/lateral hypothalamus. In the hypothyroid state, transcription is activated in the PVH only and can be shut off within 5 h by TH. In the second model system, we employed transgenic mice that express the Cre recombinase under the control of the genomic region containing the TRH gene. Remarkably, TH regulates Cre expression in these mice in the PVH only. Taken together, these data affirm that TH regulates TRH at the level of transcription in the PVH only and that genomic elements surrounding the TRH gene mediate its regulation by T3. Thus, it should be possible to identify the elements within the TRH locus that mediate its regulation by T3 using in vivo approaches.

scholarly journals Tissue Deiodinase Activity during Prolonged Critical Illness: Effects of Exogenous Thyrotropin-Releasing Hormone and Its Combination with Growth Hormone-Releasing Peptide-2

Endocrinology ◽  
2005 ◽  
Vol 146 (12) ◽  
pp. 5604-5611 ◽  
Author(s):  
Yves Debaveye ◽  
Björn Ellger ◽  
Liese Mebis ◽  
Erik Van Herck ◽  
Willy Coopmans ◽  
...  
Keyword(s):  
Critical Illness ◽  
Thyroid Hormone ◽  
In Vivo Model ◽  
Joint Control ◽  
Hormone Metabolism ◽  
Thyroid Hormone Metabolism ◽  
Tsh Secretion ◽  
Underlying Mechanisms ◽  
To Receive

Prolonged critical illness is characterized by reduced pulsatile TSH secretion, causing reduced thyroid hormone release and profound changes in thyroid hormone metabolism, resulting in low circulating T3 and elevated rT3 levels. To further unravel the underlying mechanisms, we investigated the effects of exogenous TRH and GH-releasing peptide-2 (GHRP-2) in an in vivo model of prolonged critical illness. Burn-injured, parenterally fed rabbits were randomized to receive 4-d treatment with saline, 60 μg/kg·h GHRP-2, 60 μg/kg·h TRH, or 60 μg/kg·h TRH plus 60 μg/kg·h GHRP-2 started on d 4 of the illness (n = 8/group). The activities of the deiodinase 1 (D1), D2, and D3 in snap-frozen liver, kidney, and muscle as well as their impact on circulating thyroid hormone levels were studied. Compared with healthy controls, hepatic D1 activity in the saline-treated, ill animals was significantly down-regulated (P = 0.02), and D3 activity tended to be up-regulated (P = 0.06). Infusion of TRH and TRH plus GHRP-2 restored the catalytic activity of D1 (P = 0.02) and increased T3 levels back within physiological range (P = 0.008). D3 activity was normalized by all three interventions, but only addition of GHRP-2 to TRH prevented the rise in rT3 seen with TRH alone (P = 0.02). Liver D1 and D3 activity were correlated (respectively, positively and negatively) with the changes in circulating T3 (r = 0.84 and r = −0.65) and the T3/rT3 ratio (r = 0.71 and r = −0.60). We conclude that D1 activity during critical illness is suppressed and related to the alterations within the thyrotropic axis, whereas D3 activity tends to be increased and under the joint control of the somatotropic and thyrotropic axes.

scholarly journals A Novel Platform to Test In Vivo Single Gene Dependencies in t(8,21) and t(15,17) AML Confirms Zeb2 as Leukemia Target

Cancers ◽  
2020 ◽  
Vol 12 (12) ◽  
pp. 3768
Author(s):  
Giulia De Conti ◽  
Alicja M. Gruszka ◽  
Debora Valli ◽  
Andrea Umberto Cammarata ◽  
Matteo Righi ◽  
...  
Keyword(s):  
Transgenic Mice ◽  
Fluorescent Protein ◽  
Constitutive Expression ◽  
Model Systems ◽  
Leukemic Cells ◽  
Tamoxifen Treatment ◽  
Selection Marker ◽  
In Vivo Model ◽  
Hematopoietic Stem

The increased usage of high-throughput technologies in cancer research, including genetic and drug screens, generates large sets of candidate targets that need to be functionally validated for their roles in tumor development. Thus, reliable and robust in vivo model systems are needed to perform reverse genetic experiments. Ideally, these models should allow for a conditional silencing of the target and an unambiguous identification of engineered cancer cells. Here, we present a platform consisting of: (i) t(8;21) and t(15;17) driven acute myeloid leukemia (AML) transgenic mice with constitutive expression of green fluorescent protein (GFP) and inducible expression of Cre recombinase, and (ii) REX, a modified pSico lentiviral vector for inducible shRNA expression and red fluorescent protein (RFP) as a selection marker. In this system, leukemic cells from transgenic mice are transduced with REX, flow sorted, and transplanted into syngeneic hosts. Gene interference is induced in established tumors by tamoxifen treatment. Dual-color cell fluorescence guides the in vivo identification of shRNA interfered AML cells, monitoring engraftment and disease progression. We tested the platform by inducing knockdown of Zeb2, a gene upregulated by AML1-ETO and PML-RARα oncogenes in pre-leukemic hematopoietic stem cell compartment, and observed a significant delay in leukemia onset. This proves the power and utility of the platform and confirms Zeb2 contribution to the pathogenesis of AML.

scholarly journals Endothelial-specific gene expression directed by the tie gene promoter in vivo

Blood ◽  
1995 ◽  
Vol 86 (5) ◽  
pp. 1828-1835 ◽  
Author(s):  
J Korhonen ◽  
I Lahtinen ◽  
M Halmekyto ◽  
L Alhonen ◽  
J Janne ◽  
...  
Keyword(s):  
Endothelial Cells ◽  
Transgenic Mice ◽  
Reporter Gene ◽  
Promoter Activity ◽  
Cultured Cells ◽  
Luciferase Reporter ◽  
Specific Gene ◽  
Luciferase Reporter Gene ◽  
Human And Mouse

The tie gene encodes a receptor tyrosine kinase that is expressed in the endothelium of blood vessels, particularly during embryonic development and angiogenesis in adults. We have cloned and characterized the mouse tie gene and isolated the human and mouse tie promoters. The promoter activities of human and mouse tie were analyzed using luciferase reporter gene constructs in transfected cell lines and beta-galactosidase constructs in transgenic mice. In transfection assays of cultured cells, both human and mouse promoter DNA fragments showed activity that was not restricted to endothelial cells. In contrast, in transgenic mice both promoters directed expression of the reporter gene to endothelial cells undergoing vasculogenesis and angiogenesis. In adult mice, tie promoter activity in lung and many vessels of the kidney was as high as in the vessels of the corresponding embryonic tissues, whereas in the heart, brain and liver, tie promoter activity was downregulated and restricted to coronaries, cusps, capillaries, and arteries. Our results show that the endothelial cell-type specificity of the tie promoter in vivo can be transferred to heterologous genes by using relatively short promoter fragments. The tie promoter, thus, has useful properties for potential gene therapy.

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