Prevention of Hepatic Steatosis and Hepatic Insulin Resistance by Knockdown of cAMP Response Element-Binding Protein

SummaryIn patients with poorly controlled type 2 diabetes mellitus (T2DM), hepatic insulin resistance and increased gluconeogenesis contribute to fasting and postprandial hyperglycemia. Since cAMP response element-binding protein (CREB) is a key regulator of gluconeogenic gene expression, we hypothesized that decreasing hepatic CREB expression would reduce fasting hyperglycemia in rodent models of T2DM. In order to test this hypothesis, we used a CREB-specific antisense oligonucleotide (ASO) to knock down CREB expression in liver. CREB ASO treatment dramatically reduced fasting plasma glucose concentrations in ZDF rats, ob/ob mice, and an STZ-treated, high-fat-fed rat model of T2DM. Surprisingly, CREB ASO treatment also decreased plasma cholesterol and triglyceride concentrations, as well as hepatic triglyceride content, due to decreases in hepatic lipogenesis. These results suggest that CREB is an attractive therapeutic target for correcting both hepatic insulin resistance and dyslipidemia associated with nonalcoholic fatty liver disease (NAFLD) and T2DM

Tumor necrosis factor-alpha upregulates 11beta-hydroxysteroid dehydrogenase type 1 expression by CCAAT/enhancer binding protein-beta in HepG2 cells

The enzyme 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) catalyzes the conversion of inactive to active glucocorticoids. 11beta-HSD1 plays a crucial role in the pathogenesis of obesity and controls glucocorticoid actions in inflammation. Several studies have demonstrated that TNF-alpha increases 11beta-HSD1 mRNA and activity in various cell models. Here, we demonstrate that mRNA and activity of 11beta-HSD1 is increased in liver tissue from transgenic mice overexpressing TNF-alpha, indicating that this effect also occurs in vivo. To dissect the molecular mechanism of this increase, we investigated basal and TNF-alpha-induced transcription of the 11beta-HSD1 gene (HSD11B1) in HepG2 cells. We found that TNF-alpha acts via p38 MAPK pathway. Transient transfections with variable lengths of human HSD11B1 promoter revealed highest activity with or without TNF-alpha in the proximal promoter region (-180 to +74). Cotransfection with human CCAAT/enhancer binding protein-alpha (C/EBPalpha) and C/EBPbeta-LAP expression vectors activated the HSD11B1 promoter with the strongest effect within the same region. Gel shift and RNA interference assays revealed the involvement of mainly C/EBPalpha, but also C/EBPbeta, in basal and only of C/EBPbeta in the TNF-alpha-induced HSD11B1 expression. Chromatin immunoprecipitation assay confirmed in vivo the increased abundance of C/EBPbeta on the proximal HSD11B1 promoter upon TNF-alpha treatment. In conclusion, C/EBPalpha and C/EBPbeta control basal transcription, and TNF-alpha upregulates 11beta-HSD1, most likely by p38 MAPK-mediated increased binding of C/EBPbeta to the human HSD11B1 promoter. To our knowledge, this is the first study showing involvement of p38 MAPK in the TNF-alpha-mediated 11beta-HSD1 regulation, and that TNF-alpha stimulates enzyme activity in vivo

Impaired protein stability of 11beta-hydroxysteroid dehydrogenase type 2: a novel mechanism of apparent mineralocorticoid excess

Apparent mineralocorticoid excess (AME) is a severe form of hypertension that is caused by impaired activity of 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD2), which converts biologically active cortisol into inactive cortisone. Mutations in HSD11B2 result in cortisol-induced activation of mineralocorticoid receptors and cause hypertension with hypokalemia, metabolic alkalosis, and suppressed circulating renin and aldosterone concentrations. This study uncovered the first patient with AME who was described in the literature, identified the genetic defect in HSD11B2, and provided evidence for a novel mechanism of reduced 11beta-HSD2 activity. This study identified a cluster of amino acids (335 to 339) in the C-terminus of 11beta-HSD2 that are essential for protein stability. The cluster includes Tyr(338), which is mutated in the index patient, and Arg(335) and Arg(337), previously reported to be mutated in hypertensive patients. It was found that wild-type 11beta-HSD2 is a relatively stable enzyme with a half-life of 21 h, whereas that of Tyr(338)His and Arg(337)His was 3 and 4 h, respectively. Enzymatic activity of Tyr(338)His was partially retained at 26 degrees C or in the presence of the chemical chaperones glycerol and dexamethasone, indicating thermodynamic instability and misfolding. The results provide evidence that the degradation of both misfolded mutant Tyr(338)His and wild-type 11beta-HSD2 occurs through the proteasome pathway. Therefore, impaired 11beta-HSD2 protein stability rather than reduced gene expression or loss of catalytic activity seems to be responsible for the development of hypertension in some individuals with AME

Impaired Protein Stability of 11β-Hydroxysteroid Dehydrogenase Type 2: A Novel Mechanism of Apparent Mineralocorticoid Excess

Apparent mineralocorticoid excess (AME) is a severe form of hypertension that is caused by impaired activity of 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD2), which converts biologically active cortisol into inactive cortisone. Mutations in HSD11B2 result in cortisol-induced activation of mineralocorticoid receptors and cause hypertension with hypokalemia, metabolic alkalosis, and suppressed circulating renin and aldosterone concentrations. This study uncovered the first patient with AME who was described in the literature, identified the genetic defect in HSD11B2, and provided evidence for a novel mechanism of reduced 11beta-HSD2 activity. This study identified a cluster of amino acids (335 to 339) in the C-terminus of 11beta-HSD2 that are essential for protein stability. The cluster includes Tyr(338), which is mutated in the index patient, and Arg(335) and Arg(337), previously reported to be mutated in hypertensive patients. It was found that wild-type 11beta-HSD2 is a relatively stable enzyme with a half-life of 21 h, whereas that of Tyr(338)His and Arg(337)His was 3 and 4 h, respectively. Enzymatic activity of Tyr(338)His was partially retained at 26 degrees C or in the presence of the chemical chaperones glycerol and dexamethasone, indicating thermodynamic instability and misfolding. The results provide evidence that the degradation of both misfolded mutant Tyr(338)His and wild-type 11beta-HSD2 occurs through the proteasome pathway. Therefore, impaired 11beta-HSD2 protein stability rather than reduced gene expression or loss of catalytic activity seems to be responsible for the development of hypertension in some individuals with AME

Tumor necrosis factor-α upregulates 11β-hydroxysteroid dehydrogenase type 1 expression by CCAAT/enhancer binding protein-β in HepG2 cells

The enzyme 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) catalyzes the conversion of inactive to active glucocorticoids. 11beta-HSD1 plays a crucial role in the pathogenesis of obesity and controls glucocorticoid actions in inflammation. Several studies have demonstrated that TNF-alpha increases 11beta-HSD1 mRNA and activity in various cell models. Here, we demonstrate that mRNA and activity of 11beta-HSD1 is increased in liver tissue from transgenic mice overexpressing TNF-alpha, indicating that this effect also occurs in vivo. To dissect the molecular mechanism of this increase, we investigated basal and TNF-alpha-induced transcription of the 11beta-HSD1 gene (HSD11B1) in HepG2 cells. We found that TNF-alpha acts via p38 MAPK pathway. Transient transfections with variable lengths of human HSD11B1 promoter revealed highest activity with or without TNF-alpha in the proximal promoter region (-180 to +74). Cotransfection with human CCAAT/enhancer binding protein-alpha (C/EBPalpha) and C/EBPbeta-LAP expression vectors activated the HSD11B1 promoter with the strongest effect within the same region. Gel shift and RNA interference assays revealed the involvement of mainly C/EBPalpha, but also C/EBPbeta, in basal and only of C/EBPbeta in the TNF-alpha-induced HSD11B1 expression. Chromatin immunoprecipitation assay confirmed in vivo the increased abundance of C/EBPbeta on the proximal HSD11B1 promoter upon TNF-alpha treatment. In conclusion, C/EBPalpha and C/EBPbeta control basal transcription, and TNF-alpha upregulates 11beta-HSD1, most likely by p38 MAPK-mediated increased binding of C/EBPbeta to the human HSD11B1 promoter. To our knowledge, this is the first study showing involvement of p38 MAPK in the TNF-alpha-mediated 11beta-HSD1 regulation, and that TNF-alpha stimulates enzyme activity in vivo

C/EBP beta isoforms control HSD11B2 promoter activity.

<p>(<i>A</i>) HT-29 cells were transfected with the full length human HSD11B2 promoter cloned into pGL3-basic luciferase vector (p4.5 kb-HSD11B2, 400 ng) and a dose response of LAP expressing vector (pCMV-LAP, 6.25 to 400 ng). A schematic representation of the promoter of HSD11B2 is shown on the left side. The transcriptional initiation site is indicated by an arrow (+1). The empty pcDNA3 vector was used to equalize the amount of transfected DNA in every condition and the pCMV-hRL (100 ng) was used as transfection efficiency control. Cells were lysed for luciferase assays 24 h after transfection, and the reading were normalized by renilla activity. (<i>B</i>) HT-29 cells were transfected with the plasmids p4.5 kb-HSD11B2 (400 ng), pRL-CMV (100 ng), pCMV-LAP (50 ng) and an increasing quantity of pCMV-LIP (50 ng to 400 ng). (<i>C</i>) HT-29 cells were transfected with the wild type p4.5 kb-HSD11B2 and p0.2 kb-HSD11B2 constructs or with the C/EBP mutated constructs. (<i>D</i>) HT-29 cells were transfected with the wild type p4.5 kb-HSD11B2 or the C/EBP mutated construct together with increasing concentration of pCMV-LAP.</p

Schematic representation of the insulin pathway and its regulation by sustained insulin stimulation in HT-29.

<p>mRNAs were quantified 24 h after insulin (10⁻⁷ M) treatment using RT² Profiler PCR Arrays PAHS-30C. Up-regulated transcripts are shown in red and down-regulated transcripts are shown in green.</p

Sustained insulin treatment diminished the 11beta-HSD2 expression and activity in HT-29 cells.

<p>(<i>A</i>) 11beta-HSD2 activity was measured by ³H-cortisol/cortisone conversion assay in colonic cell lines 24 h after incubation with insulin (10⁻¹¹–10⁻⁷ M). The activity measured for HCT116 in absence of insulin was set as 100%. (<i>B</i>) Dose-response effect of insulin (10⁻⁹–10⁻⁵ M) on HSD11B2 mRNA (gray bars) and activity (curve) in HT-29 cells treated for 24 h. (<i>C</i>) Time-dependent effect of insulin (10⁻⁷ M) on HSD11B2 mRNA (gray bars) and activity (curve) in HT-29 cells. (<i>D</i>) Time-dependent effect of insulin (10⁻⁷ M) on 11beta-HSD2 protein level.</p

Binding of C/EBP alpha/beta on human HSD11B2 promoter.

<p><i>(A) Nuclear proteins isolated from HT-29 cells bind to identified C/EBP alpha/beta sites.</i>4 µg of nuclear extracts isolated from insulin treated (for the indicated period of time, 10⁻⁷ M) or untreated HT-29 cells were incubated with radiolabeled probe encompassing the consensus C/EBP alpha/beta site in the presence or absence of non-radiolabeled (100×) competitor probe (cons C/EBP alpha/beta or mut C/EBP alpha/beta) (lanes1–7). Arrows indicate C/EBP alpha/beta / DNA shifts (C1, C2, C3) separated from free probe by gel electrophoresis. The complex C3 is formed in presence of radiolabeled −198 C/EBP alpha/beta probe (lanes 14–17) while complex C2 is formed in presence of radiolabeled −4362 C/EBP alpha/beta probe (lane 22–25). <i>(B) Nuclear proteins isolated from HT-29 cells bind to the consensus SP1 site.</i> Nuclear extracts isolated from insulin treated (for the indicated period of time, 10⁻⁷ M) or untreated HT-29 cells were incubated with radiolabeled probe encompassing the consensus SP1 site with and without non-radiolabeled (100X) competitor probe (cons SP1, lane 5or mut SP1, lane 6). The arrow indicates SP1/DNA shifts separated from free probe by gel electrophoresis. The complex intensity increased modestly with insulin treatment. The specific shift was abolished by the cold cons SP1 probe (lane 5) while not affected when mut SP1 probe was used as competitor (lane 6). <i>(C) Chromatin immunoprecipitation (ChIP) analysis of C/EBP alpha and C/EBP beta during insulin stimulation in HT-29 cells.</i> ChIPs were performed from untreated (W/O) and insulin induced (1–24 h) HT-29 cells using antibodies specific for C/EBP alpha (middle panel) and C/EBP beta (bottom panel), a no-antibody control (NO). The precipitated chromatin was analyzed using primers specific for the human HSD11B2 promoter. The DNA fragments were amplified with PCR primers to detect a 210 bp fragment containing the potential −177 and −198 C/EBP sites within the HSD11B2 promoter. Input chromatin is represented in upper panel.</p