Abstract 015: Increased 20-HETE Levels Contribute to Impaired Glucose Metabolism and Type 2 Diabetes in Cyp4a14 Knockout Mice Fed on High Fat Diet

20-HETE (20-Hydroxyeicosatetraenoic acid) is a cytochrome P450 ω-hydroxylase metabolite of arachidonic acid that promotes endothelial dysfunction, microvascular remodeling and hypertension. Previous studies have shown that urinary 20-HETE levels correlate with BMI and plasma insulin levels. However, there is no direct evidence for the role of 20-HETE in the regulation of glucose metabolism, obesity and type 2 diabetes mellitus. In this study we examined the effect of 20-SOLA (2,5,8,11,14,17-hexaoxanonadecan-19-yl-20-hydroxyeicosa-6(Z),15(Z)-dienoate), a water-soluble 20-HETE antagonist, on blood pressure, weight gain and blood glucose in Cyp4a14 knockout (Cyp4a14-/-) mice fed high-fat diet (HFD). The Cyp4a14-/- male mice exhibit high vascular 20-HETE levels and display 20-HETE-dependent hypertension. There was no difference in weight gain and fasting blood glucose between Cyp4a14-/- and wild type (WT) on regular chow. When subjected to HFD for 15 weeks, a significant increase in weight was observed in Cyp4a14-/- as compared to WT mice (56.5±3.45 vs. 30.2±0.7g, p<0.05). Administration of 20-SOLA (10mg/kg/day in drinking water) significantly attenuated the weight gain (28.7±1.47g, p<0.05) and normalized blood pressure in Cyp4a14-/- mice on HFD (116±0.3 vs. 172.7±4.6mmHg, p<0.05). HFD fed Cyp4a14-/- mice exhibited hyperglycemia as opposed to normal glucose levels in WT on a HFD (154±1.9 vs. 96.3±3.0 mg/dL, p<0.05). 20-SOLA prevented the HFD-induced hyperglycemia in Cyp4a14-/- mice (91±8mg/dL, p<0.05). Plasma insulin levels were markedly high in Cyp4a14-/- mice vs. WT on HFD (2.66±0.7 vs. 0.58±0.18ng/mL, p<0.05); corrected by the treatment with 20-SOLA (0.69±0.09 ng/mL, p<0.05). Importantly, glucose and insulin tolerance tests showed impaired glucose homeostasis and insulin resistance in Cyp4a14-/- mice on HFD; ameliorated by treatment with 20-SOLA. This novel finding that blockade of 20-HETE actions by 20-SOLA prevents HFD-induced obesity and restores glucose homeostasis in Cyp4a14-/- mice suggests that 20-HETE contributes to obesity, hyperglycemia and insulin resistance in HFD induced metabolic disorder. The molecular mechanisms underlying 20-HETE mediated metabolic dysfunction are being currently explored.

Dexamethasone promotes hypertension by allele-specific regulation of the human angiotensinogen gene

The human angiotensinogen (hAGT) gene has polymorphisms in its 2.5-kb promoter that form two haplotype (Hap) blocks: -6A/G (-1670A/G, -1562C/T, and -1561T/C) and -217A/G (-532T/C, -793A/G, -1074T/C, and -1178G/A). Hap -6A/-217A is associated with human hypertension, whereas Hap -6G/-217G reduces cardiovascular risk. Hap -6A/-217A has increased promoter activity with enhanced transcription factor binding, including to the glucocorticoid receptor (GR). Glucocorticoid therapy frequently causes hypertension, the mechanisms for which are incompletely understood. We have engineered double transgenic (TG) mice containing the human renin gene with either Hap of the hAGT gene and examined the physiological significance of glucocorticoid-mediated allele-specific regulation of the hAGT gene. We have also studied the consequential effects on the renin angiotensin system and blood pressure. TG mice with Hap -6A and -6G were treated with and without a low dose of a GR agonist, dexamethasone (2.5 μg/ml), for 72 h. We found greater chromatin-GR binding with increased GR agonist-induced hAGT expression in liver and renal tissues of Hap -6A mice. Additionally, dexamethasone treatment increased circulating hAGT and angiotensin II levels in Hap -6A mice, as compared with -6G mice. Importantly, GR agonist significantly increased blood pressure and redox markers in TG mice with Hap-6A of the hAGT gene. Taken together, our results show, for the first time, that glucocorticoids affect hAGT expression in a haplotype-dependent fashion with SNPs in Hap -6A favoring agonist-induced GR binding. This leads to increased expression of the hAGT, up-regulation of the renin angiotensin system, and increased blood pressure and oxidative stress in Hap -6A mice.

Abstract 047: 20-SOLA, A Novel Water-soluble 20-HETE Antagonist, Elicits Natriuresis And Abrogates Hypertension In Cyp4a14 Knockout Mice

20-HETE (20-hydroxyeicosatetraenoic acid) is a cytochrome P450 (CYP) 4A-derived arachidonate metabolite. In the vasculature, 20-HETE increases smooth muscle contraction, endothelial dysfunction/activation and sensitivity to constrictor stimuli; all of which contribute to hypertension. In renal tubules, 20-HETE inhibits ion transport and has pro-natriuretic functions in salt-sensitive models of hypertension. The pro-natriuretic effect of 20-HETE has not been reported in mouse models of 20-HETE-dependent hypertension. The CYP4a14 knockout (KO) male mice exhibit androgen-dependent upregulation of Cyp4a12, the sole 20-HETE synthase in mice, and display 20-HETE-dependent hypertension; female KO mice show no increase in Cyp412-20-HETE and are normotensive. We examined the effect of 20-SOLA (2,5,8,11,14,17-hexaoxanonadecan-19-yl-20-hydroxyeicosa-6(Z),15(Z)-dienoate), a water-soluble 20-HETE antagonist, and determined its effect on blood pressure (BP) and natriuresis in the KO mice. Administration of 20-SOLA (10mg/kg/day in drinking water) normalized BP in male KO mice; a significant reduction was observed on day 4 (146±1 vs153±2 mmHg in untreated littermates) reaching BP of the normotensive female KO mice (124±1 and 126±1 mmHg for treated and untreated, respectively) at day 10 of treatment (124±1 vs. 153±2 mmHg in untreated male KO; p<0.05). 20-SOLA decreased vascular reactivity to phenylephrine in male KO renal microvessels by 7-fold (EC50: 1.58±0.23 vs 0.22±0.03 μM). Moreover, treatment with 20-SOLA increased urine output in KO male mice as compared to untreated littermates (1.25±0.04 vs. 1.06±0.04 mL; p<0.05). The urine output to water intake ratio was significantly elevated in 20-SOLA-treated KO vs. untreated (0.25±0.01 vs. 0.19±0.01, p<0.05). Importantly, treatment with 20-SOLA increased urinary sodium excretion in the KO male mice (12.33±0.44 vs. 8.33±0.63 μmol/gr BW/24Hrs; p<0.05). These results suggest that 20-HETE has an anti-natriuretic effect in the kidneys of KO mice and that antagonism of 20-HETE’s action using 20-SOLA elicited natriuresis concurrent with reduction in blood pressure. The potential vascular and tubular mechanisms underlying 20-HETE anti-natriuretic action are being currently explored.

Abstract 101: The Role of MicroRNAs in the Regulation of Human Aldosterone Synthase Gene Expression

The human aldosterone synthase ( hCYP11B2 ) gene encodes a key enzyme for the biosynthesis of aldosterone which is part of the renin-angiotensin-aldosterone system. Molecular variants in this gene have been associated with essential hypertension. MicroRNAs (miRNAs) are a family of small, noncoding RNAs that bind to the 3’-untranslated region (3’UTR) of the gene and regulate its expression. Our main objective in this study was to investigate whether miRNAs bind at the polymorphic sites present in the 3’UTR of hCYP11B2 gene and modulate its expression.

Previous studies have suggested that -344T/C (rs1799998) polymorphism in the hCYP11B2 promoter is associated with hypertension. Here, we compared nucleotide sequences of the promoter and 3’UTR of hCYP11B2 gene from hypertensive and normotensive subjects and found that rs1799998 is in linkage disequilibrium with 735G/A (rs28491316). Thus, variant -344T almost always occurs with variant 735G; whereas variant -344C almost always occurs with variant 735A. Bioinformatic algorithms of the full-length 3’UTR for miRNAs revealed that hsa-miR-766 was possibly binding at the 735G allele. To examine if this miRNA regulates hCYP11B2 gene expression, reporter constructs were made where luciferase gene was attached to 1.4 kb of hCYP11B2 3’UTR containing either 735G, or 735A and co-transfected into HEK293 cells with either pre-miR-766 or anti-pre-miR-766. Our results showed that pre-miR-766 reduced luciferase activity in a dose dependent manner in the presence of 735G allele. There was a significant decrease (65+2%) in the luciferase activity with pre-miR-766 (50 nM) in the presence of 735G allele, whereas it was insignificant (4+5%) in the presence of 735A allele. In H295R cells that express hCYP11B2 gene, pre-miR-766 (50nM) reduced luciferase activity by 81+1% in the presence of 735G allele. We also showed that transfection of pre-mir-766 reduced hCYP11B2 mRNA level by about 23.6% in H295R cells. In corroboration with these results, anti-pre-miR-766 did not decrease luciferase activity in presence of either allele in both cell cultures.

Our results suggest that hCYP11B2 gene expression may be regulated by differential binding of miR-766 at 735G/A polymorphism present in its 3’UTR.

Abstract 239: MicroRNAs hsa-miR-584 and hsa-miR-31 Regulate Expression of Human Angiotensnogen Gene

Background: Hypertension is a risk factor for stroke, myocardial infarction, and congestive heart failure. A single nucleotide polymorphism (SNP) (rs7079) in 3’UTR of human angiotensinogen (hAGT) gene is associated with elevated blood pressure. We have used TargetScan V6.0, miRanda miRNA prediction algorithms and found that two microRNAs hsa-miR-584 and hsa-miR-31 may bind differentially to rs7079 and alter the expression of hAGT gene.

METHODS: The effect of hsa-miR-584 and hsa-miR-31 miRNAs on endogenous AGT expression levels in Hep3B cells were studied by transfection of individual miRNA mimics followed by quantitative real time PCR (Q-RT-PCR) of the hAGT gene. In addition, the 600 bp 3’UTR of hAGT gene containing either rs7079C or rs7079A was PCR amplified and cloned in to the multiple cloning site of pMIR-REPORT™ miRNA Expression Vector containing luciferase gene. These reporter constructs were then co-transfected with either miRNA mimics or inhibitors to study the effect of miRNAs on luciferase activity in Hep3B cells since these cells express hAGT gene. These experiments were also performed in HEK293 cells which do not express the hAGT gene.

Results: Q-RT-PCR showed that hsa-miR-584 and hsa-miR-31 mimics at 50nM concentration reduced endogenous hAGT mRNA levels by 38% and 30% respectively compared to the mock (without any microRNA) or negative control (which does not have any binding site for eukaryotic 3’UTRs) in Hep3B cells. Furthermore hsa-miR-584 and hsa-miR-31 showed 40% and 25% reduced luciferase activity of the construct containing rs7079 C allele. On the other hand these miRNAs did not affect the luciferase activity in the presence of rs7079 A. When dose dependent anti miRNA inhibitors were transfected along with miRNA mimics, these mimics abolished the microRNA induced down-regulation of luciferase activity.

Conclusion: hsa-miR-584 and hsa-miR-31 miRNAs bind strongly to the hAGT 3’UTR containing rs7079 C allele as compared to rs7079 A allele and may down regulate the expression of AGT gene containing rs7079 C allele. This may be one of the possible mechanism involved in association of rs7079 A allele with human hypertension.

Transgenic mice with -6A haplotype of the human angiotensinogen gene have increased blood pressure compared with -6G haplotype

Hypertension is a serious risk factor for cardiovascular disease, and the angiotensinogen (AGT) gene locus is associated with human essential hypertension. The human AGT (hAGT) gene has an A/G polymorphism at -6, and the -6A allele is associated with increased blood pressure. However, transgenic mice containing 1.2 kb of the promoter with -6A of the hAGT gene show neither increased plasma AGT level nor increased blood pressure compared with -6G. We have found that the hAGT gene has three additional SNPs (A/G at -1670, C/G at -1562, and T/G at -1561). Variants -1670A, -1562C, and -1561T almost always occur with -6A, and variants -1670G, -1562G, and -1561G almost always occur with -6G. Therefore, the hAGT gene may be subdivided into either -6A or -6G haplotypes. We show that these polymorphisms affect the binding of HNF-1α and glucocorticoid receptor to the promoter, and a reporter construct containing a 1.8-kb hAGT gene promoter with -6A haplotype has 4-fold increased glucocorticoid-induced promoter activity as compared with -6G haplotype. In order to understand the physiological significance of these haplotypes in an in vivo situation, we have generated double transgenic mice containing either the -6A or -6G haplotype of the hAGT gene and the human renin gene. Our ChIP assay shows that HNF-1α and glucocorticoid receptor have stronger affinity for the chromatin obtained from the liver of transgenic mice containing -6A haplotype. Our studies also show that transgenic mice containing -6A haplotype have increased plasma AGT level and increased blood pressure as compared with -6G haplotype. Our studies explain the molecular mechanism involved in association of the -6A allele of the hAGT gene with hypertension.