MR Activation Research Articles

Switchable Cardiac L Type Ca2+ Channel Transcript by Mineralocorticoid Pathway

Regulation of expression of the ubiquitous L-type Cav1.2 Ca2+ channels (encoded by the CaCNA1C gene) is critically involved in the pathogenesis of serious neurological, retinal, cardiac, vascular and metabolic disorders, in which the mineralocorticoid hormone, aldosterone, via its cognate receptor (MR), plays pivotal, yet elusive, roles. MR-related extrarenal actions can be attributed to Cav1.2 deregulation, notably in cardiac and vascular cells that express this transcriptional factor. However, underlying molecular mechanisms remain unexplained. Here, we show that aldosterone induces expression of the cardiac long N-terminal Cav1.2 isoform (Cav1.2-LNT) through MR transactivation on the most proximal CaCNA1C gene promoter (P1). In cardiomyocytes aldosterone increased in dose-dependent manner Cav1.2-LNT expression at both mRNA and protein levels, correlating with enhanced dose-, time- and MR-dependent P1-promoter activity, through MR recruitment to specific DNA binding elements. The in vivo relevance of this regulation is confirmed in transgenic mice harbouring the luciferase reporter gene under the control of the P1-promoter. Moreover, aldosterone enhanced the functional expression of the Cav1.2-LNT in rat coronary smooth muscle cells increasing vascular tone. These results identify cardiac CaCNA1C gene as a new specific mineralocorticoid target gene, unravelling new insights into the molecular mechanisms associated with MR activation.

Clinical Implications

HomeHypertensionVol. 66, No. 1Clinical Implications Free AccessResearch ArticlePDF/EPUBAboutView PDFView EPUBSections ToolsAdd to favoritesDownload citationsTrack citationsPermissions ShareShare onFacebookTwitterLinked InMendeleyReddit Jump toFree AccessResearch ArticlePDF/EPUBClinical Implications Originally published1 Jul 2015https://doi.org/10.1161/HYPERTENSIONAHA.115.05813Hypertension. 2015;66:2Renal Complement Activation in Preeclampsia (page 117)Download figureDownload PowerPointA growing body of evidence suggests that complement dysregulation plays a role in the pathogenesis of preeclampsia. The kidney is one of the major organs affected in preeclampsia. Penning et al hypothesized that complement activation is involved in the kidney damage in preeclampsia. In this issue, they studied autopsied kidneys from 11 women with preeclampsia, 25 pregnant controls, and 14 nonpregnant controls with hypertension. The samples were immunostained for complement factors and immunoglobulins. All of the kidney sections obtained from the preeclamptic women contained glomerular C4d deposits in a predominantly global staining pattern. Furthermore, preeclampsia was associated with glomerular C1q and IgM, but not with mannose-binding lectin or properdin, indicating classical pathway activation. The results were validated in a soluble fms-like tyrosine kinase-1–induced preeclampsia mouse model. These mice developed excess glomerular C4 deposits and increased levels of circulating activated C3, indicating that preeclampsia-related renal complement activation is initiated by endothelial damage caused by angiogenic dysregulation. The results from this study suggest that inhibiting complement activation could be beneficial for preventing the renal manifestations of preeclampsia. The authors previously found increased classical pathway activation in the placentas of preeclamptic women. Inhibiting excessive complement activation may therefore be a promising therapeutic approach affecting multiple organ systems. However, further investigation is needed to establish the safety of complement inhibition during pregnancy.Mineralocorticoid Blockade and Aortic Stiffness (page 99)Women are normally protected against development of cardiovascular disease, but this protection is lost in conditions of insulin resistance, such as obesity and type 2 diabetes mellitus. Data from our laboratory, and that of others, suggest that consumption of a Western diet, high in fat and refined carbohydrates, and associated heightened tissue renin–angiotensin–aldosterone system activity results in attenuated nitric oxide–mediated vasodilation and increased vascular fibrosis and stiffness. This is consistent with clinical observations that obesity, insulin resistance, and diabetes mellitus are predisposing factors for development of vascular stiffness in both men and women. Our current study indicates that low doses of the mineralocorticoid receptor blocker spironolactone, which does not affect blood pressure, prevent Western diet–induced abnormalities in nitric oxide–mediated vasorelaxation and vascular stiffness in women (Figure). These findings have important clinical implications because vascular stiffness is a powerful predictor for the development of cardiovascular disease. Furthermore, these findings suggest that a strategy to reduce mineralocorticoid receptor signaling may be preventative and therapeutic in protecting against development of vascular disease in women.Download figureDownload PowerPointNeutrophil Gelatinase–Associated Lipocalin Mediates Mineralocorticoids Fibrotic Effects (page 158)Download figureDownload PowerPointMineralocorticoid receptor (MR) antagonists showed benefit in cardiovascular diseases, but their mode of action remains poorly understood. Underlying mechanisms may associate diuretic, antifibrotic, and anti-inflammatory effects. Clinical use of MR antagonists presents some limitations related to their renal potassium sparing effect that favors hyperkalemia in patients with renal dysfunction. Understanding the signaling pathways modulated by aldosterone and MR in cardiovascular diseases is required to identify novel targets and biomarkers of MR activation.In this issue, Tarjus et al report that a novel MR target, neutrophil gelatinase–associated lipocalin (NGAL), has a critical role in high blood pressure and cardiovascular remodeling induced by mineralocorticoid activation: preventing NGAL expression in a murine model blunted cardiovascular extracellular matrix deposition and increased blood pressure. In patients with stage B heart failure, plasma levels of the complex between NGAL and matrix metalloproteinase 9 correlated with fibrosis markers, such as procollagen type I N-terminal peptide. NGAL–matrix metalloproteinase 9 complex levels may be useful as biomarkers of MR activation to select patients prone to MR antagonists and therefore increasing the benefit/risk balance of this therapeutic class.These data also uncover a novel role of NGAL that has been considered until now as a marker of renal injury but may also have a mechanistic role in cardiovascular disease and beyond. NGAL may be a novel therapeutic target in hypertension and extracellular matrix deposition. Previous Back to top Next FiguresReferencesRelatedDetails July 2015Vol 66, Issue 1 Advertisement Article InformationMetrics © 2015 American Heart Association, Inc.https://doi.org/10.1161/HYPERTENSIONAHA.115.05813 Originally publishedJuly 1, 2015 PDF download Advertisement

ToF Performance Evaluation of PET Modules With Digital Silicon Photomultiplier Technology During MR Operation

In 2012, we presented the Hyperion-II $^{\rm D}$ preclinical PET insert which uses Philips Digital Photon Counting’s digital SiPMs and is designed to be operated in a 3-T MRI. In this work we use the same platform equipped with scintillators having dimensions closer to a clinical application. This allows an investigation of the time of flight (ToF) performance of the platform and its behavior during simultaneous MR operation. We employ LYSO crystal arrays of $4\times 4 \times 10~\hbox{mm}^{3}$ coupled to $4 \times 4$ PDPC DPC 3200-22 sensors (DPC) resulting in a one-to-one coupling of crystals to read-out channels. Six sensor stacks are mounted onto a singles processing unit in a $2 \times 3$ arrangement. Two modules are mounted horizontally facing each other on a gantry with a crystal-to-crystal spacing of 217.6 mm (gantry position). A second arrangement places the modules at the maximum distance of approximately 410 mm inside the MR bore (maximum distance position) which brings each module close to the gradient system. The DPCs are cooled down to approximately $5 - {10^ \circ }{\rm C}$ under operation. We disable 20% of the worst cells and use an overvoltage of ${V_{{\rm ov}}} = 2.0~\hbox{V}$ and 2.5 V. To obtain the best time stamps, we use the trigger scheme 1 (first photon trigger), a narrow energy window of $511 \pm 50~\hbox{keV}$ and a minimum required light fraction of the main pixel of more than 65% to reject intercrystal scatter. By using a $^{22}\hbox{Na}$ point source in the isocenter of the modules, the coincidence resolution time (CRT) of the two modules is evaluated inside the MRI system without MR activity and while using highly demanding gradient sequences. Inside the ${{\rm B}_0}$ field without any MR activity at an overvoltage of ${V_{{\rm ov}}} = 2.0~\hbox{V}$ , the energy resolution is 11.45% (FWHM) and the CRT is 250 ps (FWHM). At an overvoltage of ${V_{{\rm ov}}} = 2.5~\hbox{V}$ , the energy resolution is 11.15% (FWHM) and the CRT is 240 ps (FWHM). During a heavy $z$ -gradient sequence (EPI factor: 49, gradient strength: 30 mT/m, slew rate: 192.3 mT/m/ms, TE/TR: 12/25 ms and switching duty cycle: 67%) at the gantry position and an overvoltage of ${V_{{\rm ov}}} = 2.0~\hbox{V}$ , the energy resolution is degraded relatively by 4.1% and the CRT by 25%. Using the same sequence but at the maximum distance position and an overvoltage of ${V_{{\rm ov}}} = 2.5~\hbox{V}$ , we measure a degradation of the energy resolution of 9.2% and a 52% degradation of the CRT. The Hyperion-II $^{\rm D}$ platform proofs to deliver good timing performance and energy resolution inside the MRI system even under highly demanding gradient sequences.

Effect of mineralocorticoid receptor blockade on hippocampal‐dependent memory in adults with obesity

ObjectiveThe hippocampus is crucial for paired-associate learning. Obesity is associated with increased MR activity in peripheral and possibly central tissues, decreased hippocampal size in humans and impaired hippocampal learning in rodents. The MR is expressed in hippocampal neurons and MR blockade improves hippocampal learning in obese animals. We sought to determine whether MR blockade would modulate paired-associate learning in obese men and women.Design and MethodsMen and women ages 20-61 years with BMIs between 30-45 kg/m2 were randomly assigned to placebo (n=11; 7 women) or 50 mg spironolactone daily (n=12; 7 women) for six weeks. At baseline and post treatment, subjects underwent a clinical and hormonal evaluation. They also underwent a computerized task that assesses paired-associate learning and has been shown by functional magnetic resonance imaging to activate the hippocampus.ResultsIn an ANCOVA model that adjusted for baseline paired-associate learning, age, and race, spironolactone treatment was associated with a significant (p=0.043) improvement in hippocampal memory as compared to placebo treatment.ConclusionsOur findings demonstrate, for the first time, that blocking MR with chronic, low-dose spironolactone treatment improves paired-associate learning in obese individuals, suggesting that MR activation contributes to hippocampal memory modulation in humans.

FcRγ-chain, Grb2 and SHP-1 are invovled in mannose receptor (CD206)-mediated signaling in relation to tuberculosis (INC4P.329)

Abstract The mannose receptor (MR, CD206) is highly expressed on human macrophages. It is a major pattern recognition receptor for pathogens, mediates phagocytosis and endocytosis, and regulates inflammatory signaling pathways. We have shown that the MR mediates Mycobacterium tuberculosis (M.tb) phagocytosis by human macrophages which leads to up-regulation of PPARγ expression and a delay in phagosome-lysosome (P-L) fusion. However, the associated receptor-specific downstream signaling molecules are unknown. We assayed for MR-associated proteins by MALDI-TOF and Western blot using a pull down assay with macrophage lysates and phosphorylated and un-phosphorylated MR cytoplasmic tail peptides. We have identified that FcRg-chain interacts with the MR and this interaction is necessary for MR surface exposure on human monocyte-derived macrophages (MDMs). Furthermore, M.tb infection of MDMs leads to phosphorylation of MR tyrosine residues and recruitment of Grb2 which initiates the Rac/Pak/Cdc-42 signaling cascade required for phagocytosis, and activation of MAP kinases and the PI3k/Akt pathway. MR activation also recruits and activates SHP-1. SHP-1 blockade increases M.tb P-L fusion and inflammatory cytokines. In conclusion, we have identified key MR signaling molecules and regulatory pathways which initiate phagocytosis and other immune-related functions in human macrophages.

Human RAD50 makes a functional DNA-binding complex.

The MRE11-RAD50-NBS1 (MRN) complex has several distinct functions in DNA repair including important roles in both non-homologous end-joining (NHEJ) and homologous recombination (HR). The biochemical activities of MR(N) have been well characterized implying specific functional roles for the components. The arrangement of proteins in the complex implies interdependence of their biochemical activities making it difficult to separate specific functions. We obtained purified human RAD50 and observed that it binds ATP, undergoes ATP-dependent conformational changes as well as having ATPase activity. Scanning force microscopy analysis clearly showed that RAD50 binds DNA although not as oligomers. RAD50 alone was not functional in tethering DNA molecules. ATP increased formation of RAD50 multimers which were however globular lacking extended coiled coils, in contrast to the MR complex where ATP induced oligomers have obvious coiled coils protruding from a central domain. These results suggest that MRE11 is important in maintaining the structural arrangement of RAD50 in the protein complex and perhaps has a role in reinforcing proper alignment of the coiled coils in the ATP-bound state.

Quantitative assessment of small bowel motility in patients with Crohn's disease using dynamic MRI.

Assessment of motility alterations by functional magnetic resonance imaging (MRI) contributes to improved evaluation of inflammatory bowel disease. The aim of the study was to quantify motility in inflammatory bowel segments and to compare motility alterations with MR-based parameters for activity of inflammation in Crohn's disease (CD). Thirty consecutive patients with CD underwent bowel MRI which included a dynamic sequence for automatic generation of parametric maps facilitating quantification of bowel motility. Mean motility score (MMS) of small bowel segments with signs of inflammation was measured and compared with MMS of the whole gastrointestinal tract (GI tract). MRI-based score of inflammatory activity and lesion length were correlated with the MMS ratio of inflammatory small bowel lesion and whole GI tract. Inflammatory bowel segments showed a mean value of MMSs of 1080, whereas the whole GI tract showed a mean value of MMSs of 2839 (p < 0.0001). Decrease in motility ranged between 20 and 87% in inflammatory bowel segments compared to the MMS of the whole GI tract. The MMS ratio of an inflammatory small bowel segment and whole GI tract showed negative correlation with MR activity score (r = -0.5921, p = 0.0003) and length of the lesion (r = -0.3495, p = 0.0462). Quantitative assessment of motility alterations by means of motility scoring in small bowel segments affected by CD provides additional information on inflammatory activity.

Duelling receptors: estrogen receptor versus mineralocorticoid receptor in the cardiovascular system.

here are times when investigators pursuing 2 distinctlines of research that address a common topic appeartobeoperatinginaparalleluniverse.Anyonewhohasservedin a grant review process will have pondered the irony of aseriesofgrantapplicationsaddressingthesamequestionbutvia different approaches or biological systems, each con-vincedtheirsisthekeypathwaywhilesteadfastlyignoringallother approaches. This has arguably been true of the workaddressing the role of steroid hormones in cardiovasculardisease,ormorespecificallycardiacfibrosis.Forsomeyears,thebeneficialeffectsofestrogenhavebeenextensivelychar-acterizedwithrespectnotonlytovascularreactivitybutalsofibrosis (1–3). The clinical correlate is of course the relativeprotection against cardiovascular disease in premenopausalwomen that is lost after the menopause. In the parallel uni-verse, a number of groups, including our own, have proveddetailedcharacterizationofthemolecularmechanismsdriv-ingtheproinflammatory,profibroticconsequencesofexcessmineralocorticoid receptor (MR) activation, be it by aldo-steroneorcortisol/corticosterone(reviewedinRef.4).Thesestudies,aswiththoseforestrogen,haveastrongclinicalcon-nection exemplified by the excess adverse consequences ofhyperaldosteronism, where the cardiovascular complica-tions of hypertension are clearly worse for the equivalentrises in blood pressure with hyperaldosteronism than forother causes of hypertension (5). This key role of MR acti-vation is further confirmed by a series of clinical trials thathave demonstrated improved outcomes for cardiac failurewhereanMRantagonistisaddedtoconventionaltherapy(6).The initial report of a pathophysiological role for ad-renalhormonesinvascularinflammationandfibrosiswasmadebyHansSeylein1946,butthisfindingwasnotfullyappreciated until Brilla and Weber in 1992 stimulated in-terestintheroleofaldosteroneincardiacfibrosis(4).Thesubsequent studies not only established a role for activa-tion of the MR, independent of hypertension and hyper-trophy, in cardiovascular inflammation and fibrosis butalso identified MR, activated by aldosterone, deoxycor-ticosterone, or cortisol/corticosterone, as the critical me-diator. More recent studies from our group and othershave dissected the tissue specificity of the response usingtissue-selective MR-null mice with key roles attributed tothe vascular MR (endothelial and smooth muscle cells)together with cardiomyocytes and cells of the monocyte/macrophagelineage(4).Ararelyacknowledgedsubtextinthese various rodent studies is that they are almost inev-itably performed in male animals, with the explanationbeing: “the response is more robust,” blinkered thinkingthat perhaps hides a critical biological significance. Morerecently, recognition has emerged that both experimen-tally and clinically sex-selective differences in the re-sponsestomineralocorticoidexcessandindeedmineralo-corticoid antagonist therapy need to be considered (7).Studiesusingarangeofanimalmodelsofvascularinjuryand/or cardiac fibrosis report exacerbation by aldosteroneand attenuation by estrogen (8), albeit almost never in thesamestudy.Arias-Lozaetal(9)directlyexaminedthisques-tion,findingthatestradiol(E2)actingthroughbothestrogenreceptors (ERs), ER and ER , was able to attenuate aldo-sterone-induced cardiovascular remodeling in salt-treatedrats. Pedram et al (1) have reported a critical role for ER -specific agonists in the prevention of cardiac hypertrophyand progression to cardiac fibrosis in female mice. This

Abstract MP05: Mineralocorticoid And Angiotensin II Type 1 Receptors In The Subfornical Organ Mediate Angiotensin II Hypertension In Rats

Circulating Ang II increases BP through both peripheral and central mechanisms. Activation of both AT 1 R and MR in the CNS plays a critical role in Ang II-induced hypertension. The subfornical organ (SFO) contains both MR and AT 1 R and can relay the signals of circulating Ang II to downstream nuclei such as the PVN. In this study, we evaluated the effect of intra-SFO infusion of AAV-MR-siRNA or AAV-AT 1a R-siRNA on MR or AT 1 R mRNA expression in the SFO and PVN and Ang II induced hypertension as assessed by telemetry. Two week sc infusion of Ang II at 500 ng/kg/min in Wistar rats on regular salt diet increased BP by 60~65 mmHg. This pressor effect of Ang II was largely prevented by AAV-MR-siRNA or AAV-AT 1 R-siRNA in the SFO (Figure). Ang II increased AT 1 R mRNA expression (1.7± 0.4 vs 0.8 ± 0.04 х10 -1 , p&lt;0.05) in the SFO. Both MR- and AT 1 R-siRNA in the SFO prevented this increase (1.1 ± 0.2х10 -1 and 1.0± 0.3х10 -1 ). In contrast, Ang II decreased MR mRNA expression (3.2 ± 0.2 vs. 4.1 ± 0.2х10 -2 , p&lt;0.05) in the SFO. Both MR- and AT 1 R-siRNA further decreased MR mRNA expression (2.7 ± 0.2 х10 -2 and 2.3 ± 0.3 х10 -2 ). In the PVN, Ang II increased AT 1 R mRNA by ~100% and MR mRNA by ~20%. Only AT 1 R-siRNA in the SFO prevented these increases in the PVN. AAV mediated eGFP fluorescence expression was observed in the SFO but not the PVN. These results suggest that circulating Ang II differentially regulates MR and AT 1 R expression in the SFO. Prevention of Ang II induced AT 1 R up-regulation by knockdown of either AT 1 R or MR suggests a MR dependent regulation of AT 1 R in the SFO. MR-AT 1 R signaling in the SFO appears to play a major role in Ang II-induced hypertension in rats. * p&lt;0.05, vs. baseline values; a: p&lt;0.05, vs. AAV-SCM-siRNA

Knockdown of mineralocorticoid or angiotensin II type 1 receptor gene expression in the paraventricular nucleus prevents angiotensin II hypertension in rats.

Circulating Ang II activates an aldosterone-mineralocorticoid receptor (MR) - angiotensin II (Ang II) - angiotensin type 1 receptor (AT1R) pathway in the hypothalamus. To obtain insights into the actual neuronal projections involved, adeno-associated virus carrying small interfering RNA against either AT1aR (AAV-AT1aR-siRNA) or MR (AAV-MR-siRNA) were infused into the paraventricular nucleus (PVN) in Wistar rats. Intra-PVN infusion of AAV-AT1aR-siRNA or AAV-MR-siRNA decreased AT1R or MR expression in the PVN but not in the subfornical organ (SFO) or supraoptic nucleus (SON). Subcutaneous infusion of Ang II at 500ngkg(-1)min(-1) for 2weeks increased mean arterial pressure by 60-70mmHg, and increased AT1R and MR expression in the SFO, SON and PVN. Intra-PVN AT1aR-siRNA prevented the Ang II-induced increase in AT1R but not MR expression in the PVN, and MR-siRNA prevented MR but not AT1R expression in the PVN. The increases in AT1R and MR expression in both the SFO and the SON were not changed by the two AAV-siRNAs. Specific knockdown of AT1R or MR in the PVN by AAV-siRNA each prevented most of the Ang II-induced hypertension. Prevention of the subcutaneous Ang II-induced increase in MR but not the increase in AT1R by knockdown of MR and vice versa suggests an independent regulation of MR and AT1R expression in the PVN. Both AT1R and MR activation in the PVN play a critical role in Ang II-induced hypertension in rats.

Hsp90 Blockers Inhibit Adipocyte Differentiation and Fat Mass Accumulation

Geldanamycin derivatives are benzoquinone ansamycin antibiotics that bind to Hsp90 and alter its function. The alteration of Hsp90 activity limits some cellular hormonal responses by inhibiting nuclear receptors activation. The nuclear receptors activity, such as PPARγ, the mineralocorticoid and glucocorticoid receptors (MR and GR) play a critical role in the conversion of preadipocytes to mature adipocytes. Given the importance of these nuclear receptors for adipogenesis, we investigated the effects of geldanamycin analogues (GA) on adipocyte differentiation and function. We found that early exposure of preadipocyte cells to GA inhibited their conversion into mature adipocytes by inhibiting the adipogenic transcriptional program and lipid droplets accumulation. Furthermore, GA altered the adipokines secretion profile of mature adipocyte. The anti-adipogenic effect of GA was also confirmed in mice fed a high fat diet. Biochemical analysis revealed that anti-adipogenic effects of geldanamycin analogues may result from the simultaneous inhibition of MR, GR and PPARγ activity. Taken together, our observations lead us to propose Hsp90 as a potent target for drug development in the control of obesity and its related metabolic complications.

0298: The early mineralocorticoid receptor antagonism mitigates the metabolic syndrome symptoms and transition to heart failure in the SHHF rat model

Mineralocorticoid Receptor Antagonists (MRA) have proven their cardioprotective effects in individuals with chronic heart failure (CHF) by minimizing the cardiovascular damages caused by the excessive aldosterone production observed in those patients. Metabolic syndrome (MetS) that represents one of the major risk factors for CHF has been also reported to be associated with increased aldosterone levels and MR activation and may contribute in that way to the pathogenesis of HF. Thus, we hypothesized that targeting the MetS by the early antagonism of the MR may prevent or delay the subsequent transition to CHF in a rat model of HF associated or not with a MetS. MRA Eplerenone (100 mg/kg/day) or placebo was administrated to 1.5 month-old obese and lean Spontaneously Hypertensive Heart Failure male rats (SHHF cp/cp and SHHF +/+ respectively) for a period of 11 months. Animal metabolic and cardiac parameters were regularly monitored during the protocol. When compared to the SHHF +/+ , MetS rats induces of mortality of 30% in SHHF cp/cp group that was completely prevented by the preventive treatment with Eplerenone. Indeed, SHHF cp/cp developed over time a massive obesity, dyslipidemia and insulin resistance. Echocardiograms showed an accelerated transition to cardiac dysfunction evidenced by left ventricular hypertrophy (LVH), a decreased relaxation and contractile properties of the myocardium as well as LV dilatation. MRA, prevented rats’ body weight gain (–10%), dyslipidemia (–50%) and enhanced adiponectinemia (+50%). Independently of a blood pressure decrease, cardiac parameters of Eple-SHHF cp/cp rats were preserved compared to SHHF cp/cp : LV diameter (9.9±0.14 vs 11.4±0.13 mm, respectively), LV mass (1760±72 vs 2195±73 mg), ejection fraction (70±1 vs 59±1%), isovolumic relaxation time (30±1 vs 22±1 ms) and E/A ratio (1.7±0.1 vs 3±0.3). Altogether, our data demonstrated that administration of eplerenone at the very early stages of MetS delayed their progression to CHF and prevented mortality. The beneficial cardioprotective effects were obtained via a mechanism independent of blood pressure lowering.

Corticosteroid Receptors, Their Chaperones and Cochaperones: How Do They Modulate Adipogenesis?

It is well known that glucocorticoids and mineralocorticoids are part of the list of hormones that control adipogenesis as well as different aspects of the physiology of the adipose tissue. Their actions are mediated through their binding to the glucocorticoid and the mineralocorticoid receptors (GR and MR, respectively), in complex with heat shock proteins (Hsps) and high molecular weight immunophilins (IMMs). Albeit many aspects of the molecular mechanism of the corticosteroid receptors are not fully elucidated yet, it was not until recently that the first evidences of the functional importance of Hsps and IMMs in the process of adipocyte differentiation have been described. Hsp90 and the high molecular weight IMM FKBP51 modulate GR and MR activity at multiple levels, that is, hormone binding affinity, their subcellular distribution, and the transcriptional status, among other aspects of the NR function. Interestingly, it has recently been described that Hsp90 and FKBP51 also participate in the control of PPARγ`, a key transcription factor in the control of adipogenesis and the maintenance of the adipocyte phenotype. In addition, novel roles have been uncovered for FKBP51 in the organization of the nuclear architecture through its participation in the reorganization of the nuclear lamina and the control of the subnuclear distribution of GR. Thus, the aim of this review is to integrate and discuss the actual understanding of the role of corticosteroid receptors, their chaperones and cochaperones, in the process of adipocyte differentiation.

Corticosterone targets distinct steps of synaptic transmission via concentration specific activation of mineralocorticoid and glucocorticoid receptors

Hippocampal neurons are affected by chronic stress and have a high density of cytoplasmic mineralocorticoid and glucocorticoid receptors (MR and GR). Detailed studies on the genomic effects of the stress hormone corticosterone at physiologically relevant concentrations on different steps in synaptic transmission are limited. In this study, we tried to delineate how activation of MR and GR by different concentrations of corticosterone affects synaptic transmission at various levels. The effect of 3-h corticosterone (25, 50, and 100 nM) treatment on depolarization-mediated calcium influx, vesicular release and properties of miniature excitatory post-synaptic currents (mEPSCs) were studied in cultured hippocampal neurons. Activation of MR with 25 nM corticosterone treatment resulted in enhanced depolarization-mediated calcium influx via a transcription-dependent process and increased frequency of mEPSCs with larger amplitude. On the other hand, activation of GR upon 100 nM corticosterone treatment resulted in increase in the rate of vesicular release via the genomic actions of GR. Furthermore, GR activation led to significant increase in the frequency of mEPSCs with larger amplitude and faster decay. Our studies indicate that differential activation of the dual receptor system of MR and GR by corticosterone targets the steps in synaptic transmission differently.

Respective roles of cortisol, aldosterone and angiotensin II during pathophysiology of atherosclerosis

The involvement of angiotensin II, cortisol and aldosterone in increased cardiovascular risk is well known but their interactions within arterial wall and during atheroma formation are not established. In fact, mild cortisol excess is associated with a higher prevalence of cardiovascular events, increased intima media thickness, a higher frequency of atherosclerotic plaques and increased mortality. Conversely, remission from hypercortisolism is followed by improvement in cardiovascular risk markers as intima-media thickness or arterial distensibility, suggesting a strong link between cortisol excess and adverse vascular remodeling. On the other hand, implication of renin-angiotensin system (RAS) in atheromatous remodeling is well documented. The RAS also includes aldosterone, a mineralocorticoid which secretion is mainly and strongly stimulated by angiotensin II, and which receptor (MR) can also be activated by cortisol given that MR affinity is similar for both aldosterone and cortisol. The role of aldosterone in arterial remodeling is still very controversial. Aldosterone treatment associated with a high salt diet induced not only hypertension but also oxidative stress, collagen synthesis and vascular inflammation. However in models without salt loading or arterial hypertension, such as the treatment with deoxycorticosterone acetate in dogs, no alterations in aortic structure were observed and moreover, the MR blockade with eplerenone did not attenuate atherosclerosis in the aorta of diabetic Apo-E KO mice. It stems that among the different effects and mechanisms described in cell experiments, it is not known which are indeed operating in situ in human vessels and thus, if local cortisol is deleterious or beneficial and, if activation of MR by aldosterone or cortisol is important in vascular remodeling and atherogenesis. RAS blocker treatment would be particularly beneficial in essential hypertensive patients with low plasma renin, to attenuate both angiotensin II and also cortisol up-regulation.

Targeting of 11β‐hydroxysteroid dehydrogenase type 2 (11βHSD2) in the nucleus of the solitary tract (NTS) links salt appetite and hypertension

11βHSD2 catalyses the inactivation of cortisol to cortisone, and thus ensures aldosterone‐specific activation of MR in target tissues. Cre‐lox technology was used to selectively target hsd11b2 expression in the NTS of mice. Telemetry was used to measure blood pressure during which Cre+ and Cre− mice (n=6 per group) had free access to either H2O or H2O and 1.5% NaCl. Cre+ mice were normotensive when given access to water. When offered a choice of water or saline, Cre+ mice had a significant salt preference (68% total fluid intake was NaCl), contrasting with Cre‐mice, which had salt aversion (40% total fluid intake was NaCl). The increased salt intake resulted in significant hypertension, (P=0.0004 active period, P=0.0178 inactive period). In Cre+ mice hypertension occurred over a time period during which balance studies showed that sodium was not retained. When salt‐intake was matched in Cre+ and Cre− mice, only the mice with NTS targeting of hsd11b2 developed a salt induced hypertension.Here we have defined a role of mineralocorticoid receptors in the NTS that unifies the behavioral drive to consume sodium with the long‐term control of blood pressure. These data indicate a primary central component to the hypertension in the Cre+ mice. Funded by British Heart Foundation.

MR or AT1R gene silencing in the PVN markedly attenuates Ang II‐induced hypertension in rats

Functional studies suggest that circulating Ang II activates an aldosterone‐MR‐endogenous ouabain (EO)‐ AT1R pathway in the hypothalamus and thereby causes hypertension. The present study examined whether intra‐PVN infusion of AAV‐MR‐siRNA or AAV‐AT1aR‐siRNA attenuates Ang II‐induced hypertension in rats. Two wks after bilateral intra‐PVN infusion of AAV‐MR‐siRNA (1 μl of 2.5 × 1010 genomic particles / ml), MR mRNA and protein expression in the PVN were reduced by 56% and 31% (P&lt;0.01), compared with rats infused with AAV‐SCM‐siRNA. In 2nd set of rats, 1 week following bilateral intra‐PVN infusion of AAV‐MR‐siRNA, AAV‐AT1aR‐siRNA (1 μl of 2.5 × 1010 genomic particles / ml) or AAV‐SCM‐siRNA, Ang II was infused subcutaneously at 500ng/kg/min. After 2 weeks, AAV‐AT1aR‐siRNA significantly attenuated, whereas AAV‐MR‐siRNA largely prevented the Ang II‐induced hypertension. These results suggest that MR activation in the PVN plays a major role in Ang II‐induced hypertension, and genetic intervention of MR or AT1R production by AAV‐siRNA into specific nuclei provides new insights into the actual pathways of MR‐EO neuromodulation. MAP (mmHg) HR (bpm) AAV‐SCM‐siRNA ( n=5) 113 ± 2 377 ± 8 AAV‐SCM‐siRNA +Ang II ( n=5) 192 ± 7 a 416 ± 15 AAV‐AT1aR‐siRNA+ Ang II ( n=7) 153 ± 8*, Δ 411 ± 12 AAV‐MR‐siRNA + Ang II ( n=7) 121 ± 6 377 ± 12 Data=means± SE. p&lt;0.05, vs. others, p&lt;0.05, vs. AAV‐SCM, p&lt;0.05, vs. AAV‐MR. (Supported by grant # FRN:MOP‐74432 from the Canadian Institutes of Health Research)

Blood Pressure Variability Activates Cardiac Mineralocorticoid Receptor and Induces Cardiac Remodeling in Hypertensive Rats

Hypertensive patients with large blood pressure variability (BPV) have aggravated target organ damage. Because the aldosterone/mineralocorticoid receptor (MR) system is a possible mechanism of hypertensive organ damage, we investigated in spontaneously hypertensive rats (SHRs) whether a specific MR blocker, eplerenone, would prevent BPV-induced aggravation of hypertensive cardiac remodeling. A rat model of a combination of hypertension and large BPV was created by performing bilateral sinoaortic denervation (SAD) in SHRs. SAD increased BPV without changing mean BP. SAD induced perivascular macrophage infiltration and aggravated myocardial fibrosis and cardiac hypertrophy, resulting in LV systolic dysfunction. Immunohistostaining revealed SAD-induced translocation of MRs into the nuclei (ie, MR activation) of the intramyocardial arterial medial cells and cardiac myocytes. SAD increased phosphorylation of p21-activated kinase1 (PAK1), a regulator of MR nuclear translocation. Chronic administration of a subdepressor dose of eplerenone prevented MR translocation, macrophage infiltration, myocardial fibrosis, cardiac hypertrophy, and LV dysfunction, while not affecting BPV. Circulating levels of aldosterone and cortisol were not changed by SAD. Eplerenone inhibited the aggravation of cardiac inflammation and hypertensive cardiac remodeling, and thereby prevented progression of LV dysfunction in SHRs with large BPV. This suggests that the PAK1-MR pathway plays a role in cardiac inflammation and remodeling induced by large BPV superimposed on hypertension, independent of circulating aldosterone.

Oxidative stress-induced glomerular mineralocorticoid receptor activation limits the benefit of salt reduction in Dahl salt-sensitive rats.

BackgroundMineralocorticoid receptor (MR) antagonists attenuate renal injury in salt-sensitive hypertensive rats with low plasma aldosterone levels. We hypothesized that oxidative stress causes MR activation in high-salt-fed Dahl salt-sensitive rats. Furthermore, we determined if MR activation persisted and induced renal injury, even after switching from a high- to a normal-salt diet.Methods and FindingsHigh-salt feeding for 4 weeks increased dihydroethidium fluorescence (DHE, an oxidant production marker), p22phox (a NADPH oxidase subunit) and serum and glucocorticoid-regulated kinase-1 (SGK1, an MR transcript) in glomeruli, compared with normal-salt feeding, and these changes persisted 4 weeks after salt withdrawal. Tempol treatment (0.5 mmol/L) during high-salt feeding abolished the changes in DHE fluorescence, p22phox and SGK1. Dietary salt reduction after a 4-week high-salt diet decreased both blood pressure and proteinuria, but was associated with significantly higher proteinuria than in normal control rats at 4 weeks after salt reduction. Administration of tempol during high-salt feeding, or eplerenone, an MR antagonist (100 mg/kg/day), started after salt reduction, recovered proteinuria to normal levels at 4 weeks after salt reduction. Paraquat, a reactive oxygen species generator, enhanced MR transcriptional activity in cultured rat mesangial cells and mouse podocytes.ConclusionsThese results suggest that oxidative stress plays an important role in glomerular MR activation in Dahl salt-sensitive rats. Persistent MR activation even after reducing salt intake could limit the beneficial effects of salt restriction.

High Salt Intake Down-Regulates Colonic Mineralocorticoid Receptors, Epithelial Sodium Channels and 11β-Hydroxysteroid Dehydrogenase Type 2

Besides the kidneys, the gastrointestinal tract is the principal organ responsible for sodium homeostasis. For sodium transport across the cell membranes the epithelial sodium channel (ENaC) is of pivotal relevance. The ENaC is mainly regulated by mineralocorticoid receptor mediated actions. The MR activation by endogenous 11β-hydroxy-glucocorticoids is modulated by the 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD2). Here we present evidence for intestinal segment specific 11β-HSD2 expression and hypothesize that a high salt intake and/or uninephrectomy (UNX) affects colonic 11β-HSD2, MR and ENaC expression. The 11β-HSD2 activity was measured by means of 3H-corticosterone conversion into 3H-11-dehydrocorticosterone in Sprague Dawley rats on a normal and high salt diet. The activity increased steadily from the ileum to the distal colon by a factor of about 3, an observation in line with the relevance of the distal colon for sodium handling. High salt intake diminished mRNA and protein of 11β-HSD2 by about 50% (p<0.001) and reduced the expression of the MR (p<0.01). The functionally relevant ENaC-β and ENaC-γ expression, a measure of mineralocorticoid action, diminished by more than 50% by high salt intake (p<0.001). The observed changes were present in rats with and without UNX. Thus, colonic epithelial cells appear to contribute to the protective armamentarium of the mammalian body against salt overload, a mechanism not modulated by UNX.