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Critical Role of Striatin in Blood Pressure and Vascular Responses to Dietary Sodium Intake. - Hypertension
Striatin is a protein regulator of vesicular trafficking in neurons that also binds caveolin-1 and Ca(2+)-calmodulin and could activate endothelial nitric oxide synthase. We have shown that striatin colocalizes with the mineralocorticoid receptor and that mineralocorticoid receptor activation increases striatin levels in vascular cells. To test whether striatin is a regulator of vascular function, wild-type and heterozygous striatin-deficient mice (Strn(+/-)) were randomized in crossover intervention to restricted (0.03%) and liberal sodium (1.6%) diets for 7 days on each diet, and blood pressure and aortic vascular function were measured. Compared with wild-type, sodium restriction significantly reduced blood pressure in Strn(+/-). On liberal salt intake, phenylephrine and high KCl caused a greater vascular contraction in Strn(+/-) than wild-type, and endothelium removal, nitric oxide synthase inhibitor L-NAME, and guanylate cyclase inhibitor ODQ enhanced phenylephrine contraction to a smaller extent in Strn(+/-) than wild-type. On liberal salt, acetylcholine relaxation was less in Strn(+/-) than in wild-type, and endothelium removal, L-NAME, and ODQ blocked acetylcholine relaxation, suggesting changes in endothelial NO-cGMP. On liberal salt, endothelial nitric oxide synthase mRNA expression and the ratio of endothelial nitric oxide synthase activator pAkt/total Akt were decreased in Strn(+/-) versus wild-type. Vascular relaxation to NO donor sodium nitroprusside was not different among groups. Thus, striatin deficiency is associated with salt sensitivity of blood pressure, enhanced vasoconstriction, and decreased vascular relaxation, suggesting a critical role for striatin, through modulation of endothelial NO-cGMP, in regulation of vascular function and BP during changes in sodium intake.Â© 2015 American Heart Association, Inc.
Variants in striatin gene are associated with salt-sensitive blood pressure in mice and humans. - Hypertension
Striatin is a novel protein that interacts with steroid receptors and modifies rapid, nongenomic activity in vitro. We tested the hypothesis that striatin would in turn affect mineralocorticoid receptor function and consequently sodium, water, and blood pressure homeostasis in an animal model. We evaluated salt sensitivity of blood pressure in novel striatin heterozygote knockout mice. Compared with wild type, striatin heterozygote exhibited a significant increase in blood pressure when sodium intake was increased from restricted (0.03%) to liberal (1.6%) sodium. Furthermore, renal expression of mineralocorticoid receptor and its genomic downstream targets serum/glucocorticoid-regulated kinase 1, and epithelial sodium channel was increased in striatin heterozygote versus wild-type mice on liberal sodium intake while the pAkt/Akt ratio, readout of mineralocorticoid receptor's rapid, nongenomic pathway, was reduced. To determine the potential clinical relevance of these findings, we tested the association between single nucleotide polymorphic variants of striatin gene and salt sensitivity of blood pressure in 366 white hypertensive subjects. HapMap-derived tagging single nucleotide polymorphisms identified an association of rs2540923 with salt sensitivity of blood pressure (odds ratio, 6.25; 95% confidence interval, 1.7-20; P=0.01). These data provide the first in vivo evidence in humans and rodents that associates striatin with markers of mineralocorticoid receptor activity. The data also support the hypothesis that the rapid, nongenomic mineralocorticoid receptor pathway (mediated via striatin) has a role in modulating the interaction between salt intake and blood pressure.Â© 2014 American Heart Association, Inc.
Dissociation of hyperglycemia from altered vascular contraction and relaxation mechanisms in caveolin-1 null mice. - The Journal of pharmacology and experimental therapeutics
Hyperglycemia and endothelial dysfunction are associated with hypertension, but the specific causality and genetic underpinning are unclear. Caveolin-1 (cav-1) is a plasmalemmal anchoring protein and modulator of vascular function and glucose homeostasis. Cav-1 gene variants are associated with reduced insulin sensitivity in hypertensive individuals, and cav-1(-/-) mice show endothelial dysfunction, hyperglycemia, and increased blood pressure (BP). On the other hand, insulin-sensitizing therapy with metformin may inadequately control hyperglycemia while affecting the vascular outcome in certain patients with diabetes. To test whether the pressor and vascular changes in cav-1 deficiency states are related to hyperglycemia and to assess the vascular mechanisms of metformin under these conditions, wild-type (WT) and cav-1(-/-) mice were treated with either placebo or metformin (400 mg/kg daily for 21 days). BP and fasting blood glucose were in cav-1(-/-) > WT and did not change with metformin. Phenylephrine (Phe)- and KCl-induced aortic contraction was in cav-1(-/-) < WT; endothelium removal, the nitric-oxide synthase (NOS) blocker L-NAME (N(Ï‰)-nitro-L-arginine methyl ester), or soluble guanylate cyclase (sGC) inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) enhanced Phe contraction, and metformin blunted this effect. Acetylcholine-induced relaxation was in cav-1(-/-) > WT, abolished by endothelium removal, L-NAME or ODQ, and reduced with metformin. Nitric oxide donor sodium nitroprusside was more potent in inducing relaxation in cav-1(-/-) than in WT, and metformin reversed this effect. Aortic eNOS, AMPK, and sGC were in cav-1(-/-) > WT, and metformin decreased total and phosphorylated eNOS and AMPK in cav-1(-/-). Thus, metformin inhibits both vascular contraction and NO-cGMP-dependent relaxation but does not affect BP or blood glucose in cav-1(-/-) mice, suggesting dissociation of hyperglycemia from altered vascular function in cav-1-deficiency states.
Human interventions to characterize novel relationships between the renin-angiotensin-aldosterone system and parathyroid hormone. - Hypertension
Observational studies in primary hyperaldosteronism suggest a positive relationship between aldosterone and parathyroid hormone (PTH); however, interventions to better characterize the physiological relationship between the renin-angiotensin-aldosterone system (RAAS) and PTH are needed. We evaluated the effect of individual RAAS components on PTH using 4 interventions in humans without primary hyperaldosteronism. PTH was measured before and after study (1) low-dose angiotensin II (Ang II) infusion (1 ng/kg per minute) and captopril administration (25 mgÃ—1); study (2) high-dose Ang II infusion (3 ng/kg per minute); study (3) blinded crossover randomization to aldosterone infusion (0.7 Âµg/kg per hour) and vehicle; and study (4) blinded randomization to spironolactone (50 mg/daily) or placebo for 6 weeks. Infusion of Ang II at 1 ng/kg per minute acutely increased aldosterone (+148%) and PTH (+10.3%), whereas Ang II at 3 ng/kg per minute induced larger incremental changes in aldosterone (+241%) and PTH (+36%; P<0.01). Captopril acutely decreased aldosterone (-12%) and PTH (-9.7%; P<0.01). In contrast, aldosterone infusion robustly raised serum aldosterone (+892%) without modifying PTH. However, spironolactone therapy during 6 weeks modestly lowered PTH when compared with placebo (P<0.05). In vitro studies revealed the presence of Ang II type I and mineralocorticoid receptor mRNA and protein expression in normal and adenomatous human parathyroid tissues. We observed novel pleiotropic relationships between RAAS components and the regulation of PTH in individuals without primary hyperaldosteronism: the acute modulation of PTH by the RAAS seems to be mediated by Ang II, whereas the long-term influence of the RAAS on PTH may involve aldosterone. Future studies to evaluate the impact of RAAS inhibitors in treating PTH-mediated disorders are warranted.
Direct renin inhibition modulates insulin resistance in caveolin-1-deficient mice. - Metabolism: clinical and experimental
To test the hypothesis that aliskiren improves the metabolic phenotype in a genetic mouse model of the metabolic syndrome (the caveolin-1 (cav-1) knock out (KO) mouse).Eleven-week-old cav-1 KO and genetically matched wild-type (WT) mice were randomized to three treatment groups: placebo (n=8/group), amlodipine (6 mg/kg/day, n=18/ group), and aliskiren (50 mg/kg/day, n=18/ group). After three weeks of treatment, all treatment groups were assessed for several measures of insulin resistance (fasting insulin and glucose, HOMA-IR, and the response to an intraperitoneal glucose tolerance test (ipGTT)) as well as for triglyceride levels and the blood pressure response to treatment.Treatment with aliskiren did not affect the ipGTT response but significantly lowered the HOMA-IR and insulin levels in cav-1 KO mice. However, treatment with amlodipine significantly degraded the ipGTT response, as well as the HOMA-IR and insulin levels in the cav-1 KO mice. Aliskiren also significantly lowered triglyceride levels in the cav-1 KO but not in the WT mice. Moreover, aliskiren treatment had a significantly greater effect on blood pressure readings in the cav-1 KO vs. WT mice, and was marginally more effective than amlodipine.Our results support the hypothesis that aliskiren reduces insulin resistance as indicated by improved HOMA-IR in cav-1 KO mice whereas amlodipine treatment resulted in changes consistent with increased insulin resistance. In addition, aliskiren was substantially more effective in lowering blood pressure in the cav-1 KO mouse model than in WT mice and marginally more effective than amlodipine.Copyright Â© 2013 Elsevier Inc. All rights reserved.
Lysine-specific demethylase 1: an epigenetic regulator of salt-sensitive hypertension. - American journal of hypertension
Hypertension (HTN) represents a complex heritable disease in which environmental factors may directly affect gene function via epigenetic mechanisms. The aim of this study was to test the hypothesis that dietary salt influences the activity of a histone-modifying enzyme, lysine-specific demethylase 1 (LSD-1), which in turn is associated with salt-sensitivity of blood pressure (BP).Animal and human studies were performed. Salt-sensitivity of LSD-1 expression was assessed in wild-type (WT) and LSD-1 heterozygote knockout (LSD-1(+/-)) mice. Clinical relevance was tested by multivariate associations between single-nuclear polymorphisms (SNPs) in the LSD-1 gene and salt-sensitivity of BP, with control of dietary sodium, in a primary African-American hypertensive cohort and two replication hypertensive cohorts (Caucasian and Mexican-American).LSD-1 expression was modified by dietary salt in WT mice with lower levels associated with liberal salt intake. LSD-1(+/-) mice expressed lower LSD-1 protein levels than WT mice in kidney tissue. Similar to LSD-1(+/-) mice, African-American minor allele carriers of two LSD-1 SNPs displayed greater change in systolic BP (SBP) in response to change from low to liberal salt diet (rs671357, P = 0.01; rs587168, P = 0.005). This association was replicated in the Hispanic (rs587168, P = 0.04) but not the Caucasian cohort. Exploratory analyses demonstrated decreased serum aldosterone concentrations in African-American minor allele carriers similar to findings in the LSD-1(+/-) mice, decreased Î±-EnaC expression in LSD-1(+/-) mice, and impaired renovascular responsiveness to salt loading in minor allele carriers.The results of this translational research study support a role for LSD-1 in the pathogenesis of salt-sensitive HTN.
Identification of a novel cell death receptor mediating IGFBP-3-induced anti-tumor effects in breast and prostate cancer. - The Journal of biological chemistry
Insulin-like growth factor-binding protein-3 (IGFBP-3), a major regulator of endocrine actions of IGFs, is a p53-regulated potent apoptotic factor and is significantly suppressed in a variety of cancers. Recent epidemiologic studies suggest that IGFBP-3 contributes to cancer risk protection in a variety of cancers, and a polymorphic variation of IGFBP-3 influences cancer risk, although other studies vary in their conclusions. Some antiproliferative actions of IGFBP-3 have been reported to be independent of IGFs, but the precise biochemical/molecular mechanisms of IGF-independent, antiproliferative actions of IGFBP-3 are largely unknown. Here we report a new cell death receptor, IGFBP-3R, that is a single-span membrane protein and binds specifically to IGFBP-3 but not other IGFBP species. Expression analysis of IGFBP-3 and IGFBP-3R indicates that the IGFBP-3/IGFBP-3R axis is impaired in breast and prostate cancer. We also provide evidence for anti-tumor effect of IGFBP-3R in vivo using prostate and breast cancer xenografts in athymic nude mice. Further in vitro studies demonstrate that IGFBP-3R mediates IGFBP-3-induced caspase-8-dependent apoptosis in various cancer cells. Knockdown of IGFBP-3R attenuated IGFBP-3-induced caspase activities and apoptosis, whereas overexpression of IGFBP-3R enhanced IGFBP-3 biological effects. IGFBP-3R physically interacts and activates caspase-8, and knockdown of caspase-8 expression or activity inhibited IGFBP-3/IGFBP-3R-induced apoptosis. Here, we propose that IGFBP-3R represents a novel cell death receptor and is essential for the IGFBP-3-induced apoptosis and tumor suppression. Thus, the IGFBP-3/IGFBP-3R axis may provide therapeutic and prognostic value for the treatment of cancer.
Mapping the UDP-glucuronic acid binding site in UDP-glucuronosyltransferase-1A10 by homology-based modeling: confirmation with biochemical evidence. - Biochemistry
The UDP-glucuronosyltransferase (UGT) isozyme system is critical for protecting the body against endogenous and exogenous chemicals by linking glucuronic acid donated by UDP-glucuronic acid to a lipophilic acceptor substrate. UGTs convert metabolites, dietary constituents, and environmental toxicants to highly excretable glucuronides. Because of difficulties associated with purifying endoplasmic reticulum-bound UGTs for structural studies, we carried out homology-based computer modeling to aid analysis. The search found structural homology in Escherichia coli UDP-galactose 4-epimerase. Consistent with predicted similarities involving the common UDP moiety in substrate/inhibitor, UDP-glucose and UDP-hexanol amine caused competitive inhibition by Lineweaver-Burk plots. Among predicted binding sites N292, K314, K315, and K404 in UGT1A10, two informative sets of mutants K314R/Q/A/E/G and K404R/E had null activities or 2.7-fold higher/50% less activity, respectively. Scatchard analysis of binding data of the affinity ligand, 5-azidouridine-[beta- (32)P]diphosphoglucuronic acid, to purified UGT1A10-His or UGT1A7-His revealed high- and low-affinity binding sites. 2-Nitro-5-thiocyanobenzoic acid-digested UGT1A10-His bound with the radiolabeled affinity ligand revealed an 11.3 and 14.3 kDa peptide associated with K314 and K404, respectively, in a discontinuous SDS-PAGE system. Similar treatment of 1A10His-K314A bound with the ligand lacked both peptides; 1A10-HisK404R- and 1A10-HisK404E showed 1.3-fold greater and 50% less label in the 14.3 kDa peptide, respectively, compared to 1A10-His without affecting the 11.3 kDa peptide. Scatchard analysis of binding data of the affinity ligand to 1A10His-K404R and -K404E showed a 6-fold reduction and a large increase in K d, respectively. Our results indicate that K314 and K404 are required UDP-glcA binding sites in 1A10, that K404 controls activity and high-affinity sites, and that K314 and K404 are strictly conserved in 70 aligned UGTs, except for S321, equivalent to K314, in UGT2B15 and 2B17 and I321 in the inactive UGT8, which suggests UGT2B15 and 2B17 contain suboptimal activity. Hence our data strongly support UDP-glcA binding to K314 and K404 in UGT1A10.
Phosphorylation of a UDP-glucuronosyltransferase regulates substrate specificity. - Proceedings of the National Academy of Sciences of the United States of America
UDP-glucuronosyltransferase (UGT) isozymes catalyze detoxification of numerous chemical toxins present in our daily diet and environment by conjugation to glucuronic acid. The special properties and enzymatic mechanism(s) that enable endoplasmic reticulum-bound UGT isozymes to convert innumerable structurally diverse lipophiles to excretable glucuronides are unknown. Inhibition of cellular UGT1A7 and UGT1A10 activities and of [33P]orthophosphate incorporation into immunoprecipitable proteins after exposure to curcumin or calphostin-C indicated that the isozymes are phosphorylated. Furthermore, inhibition of UGT phosphorylation and activity by treatment with PKCepsilon-specific inhibitor peptide supported PKC involvement. Co-immunoprecipitation, colocalization by means of immunofluorescence, and cross-linking studies of PKCepsilon and UGT1A7His revealed that the proteins reside within 11.4 angstroms of each other. Moreover, mutation of three PKC sites in each UGT isozyme demonstrated that T73A/G and T202A/G caused null activity, whereas S432G-UGT1A7 caused a major shift of its pH-8.5 optimum to 6.4 with new substrate selections, including 17beta-estradiol. S432G-UGT1A10 exhibited a minor pH shift without substrate alterations. PKCepsilon involvement was confirmed by the demonstration that PKCepsilon overexpression enhanced activity of UGT1A7 but not of its S432 mutant and the conversion of 17beta-[14C]estradiol by S432G-UGT1A7 but not by UGT1A7. Consistent with these observations, treatment of UGT1A7-transfected cells with PKCepsilon-specific inhibitor peptide or general PKC inhibitors increased 17beta-estradiol catalysis between 5- and 11-fold, with parallel decreases in phosphoserine-432. Here, we report a mechanism involving PKC-mediated phosphorylation of UGT such that phosphoserine/threonine regulates substrate specificity in response to chemical exposures, which possibly confers survival benefit.
Statin Use and Adrenal Aldosterone Production in Hypertensive and Diabetic Subjects. - Circulation
Statins substantially reduce cardiovascular mortality and appear to have beneficial effects independent of their lipid-lowering properties. We evaluated the hypothesis that statin use may modulate the secretion of aldosterone, a well-known contributor to cardiovascular disease.We measured adrenal hormones in 2 intervention studies. In study 1 in hypertensive subjects, aldosterone was analyzed at baseline and after angiotensin II stimulation on both high- and low-sodium diets (1122 observations, 15% on statins for >3 months). Statin users had 33% lower aldosterone levels in adjusted models (P<0.001). Cortisol was not modified by statins. In secondary analyses, the lowest aldosterone levels were seen with lipophilic statins and with higher doses. Statin users had lower blood pressure and reduced salt sensitivity of blood pressure (both P<0.001). In study 2, aldosterone was measured in diabetic patients on a high-sodium diet, before and after angiotensin II stimulation (143 observations, 79% statin users). Again, statin users had 26% lower aldosterone levels (P=0.006), particularly those using lipophilic statins. Ex vivo studies in rat adrenal glomerulosa cells confirmed that lipophilic statins acutely inhibited aldosterone, but not corticosterone, in response to different secretagogues.Statin use among hypertensive and diabetic subjects was associated with lower aldosterone secretion in response to angiotensin II and a low-sodium diet in 2 human intervention studies. This effect appeared to be most pronounced with lipophilic statins and higher doses. Future studies to evaluate whether aldosterone inhibition may partially explain the robust cardioprotective effects of statins are warranted.Â© 2015 American Heart Association, Inc.
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