The mitochondrial regulator PGC1α is induced by cGMP-PKG signaling and mediates the protective effects of phosphodiesterase 5 inhibition in heart failure

Phosphodiesterase 5 inhibition (PDE5i) activates cGMP-dependent protein kinase (PKG) and ameliorates heart failure; however, its impact on cardiac mitochondrial regulation has not been fully determined. Here, we investigated the role of the mitochondrial regulator peroxisome proliferator-activated receptor γ co-activator-1α (PGC1α) in the PDE5i-conferred cardioprotection, utilizing PGC1α null mice. In PGC1α^+/+ hearts exposed to 7 weeks of pressure overload by transverse aortic constriction, chronic treatment with the PDE5 inhibitor sildenafil improved cardiac function and remodeling, with improved mitochondrial respiration and upregulation of PGC1α mRNA in the myocardium. By contrast, PDE5i-elicited benefits were abrogated in PGC1α^-/- hearts. In cultured cardiomyocytes, PKG overexpression induced PGC1α, while inhibition of the transcription factor CREB abrogated the PGC1α induction. Together, these results suggest that the PKG-PGC1α axis plays a pivotal role in the therapeutic efficacy of PDE5i in heart failure.

CRD-733, a Novel PDE9 (Phosphodiesterase 9) Inhibitor, Reverses Pressure Overload-Induced Heart Failure

BACKGROUND

Augmentation of NP (natriuretic peptide) receptor and cyclic guanosine monophosphate (cGMP) signaling has emerged as a therapeutic strategy in heart failure (HF). cGMP-specific PDE9 (phosphodiesterase 9) inhibition increases cGMP signaling and attenuates stress-induced hypertrophic heart disease in preclinical studies. A novel cGMP-specific PDE9 inhibitor, CRD-733, is currently being advanced in human clinical studies. Here, we explore the effects of chronic PDE9 inhibition with CRD-733 in the mouse transverse aortic constriction pressure overload HF model.

METHODS

Adult male C57BL/6J mice were subjected to transverse aortic constriction and developed significant left ventricular (LV) hypertrophy after 7 days (P<0.001). Mice then received daily treatment with CRD-733 (600 mg/kg per day; n=10) or vehicle (n=17), alongside sham-operated controls (n=10).

RESULTS

CRD-733 treatment reversed existing LV hypertrophy compared with vehicle (P<0.001), significantly improved LV ejection fraction (P=0.009), and attenuated left atrial dilation (P<0.001), as assessed by serial echocardiography. CRD-733 prevented elevations in LV end diastolic pressures (P=0.037) compared with vehicle, while lung weights, a surrogate for pulmonary edema, were reduced to sham levels. Chronic CRD-733 treatment increased plasma cGMP levels compared with vehicle (P<0.001), alongside increased phosphorylation of Ser²⁷³ of cardiac myosin binding protein-C, a cGMP-dependent protein kinase I phosphorylation site.

CONCLUSIONS

The PDE9 inhibitor, CRD-733, improves key hallmarks of HF including LV hypertrophy, LV dysfunction, left atrial dilation, and pulmonary edema after pressure overload in the mouse transverse aortic constriction HF model. Additionally, elevated plasma cGMP may be used as a biomarker of target engagement. These findings support future investigation into the therapeutic potential of CRD-733 in human HF.

PDE5 inhibitor efficacy is estrogen dependent in female heart disease

Inhibition of cGMP-specific phosphodiesterase 5 (PDE5) ameliorates pathological cardiac remodeling and has been gaining attention as a potential therapy for heart failure. Despite promising results in males, the efficacy of the PDE5 inhibitor sildenafil in female cardiac pathologies has not been determined and might be affected by estrogen levels, given the hormone's involvement in cGMP synthesis. Here, we determined that the heart-protective effect of sildenafil in female mice depends on the presence of estrogen via a mechanism that involves myocyte eNOS-dependent cGMP synthesis and the cGMP-dependent protein kinase Iα (PKGIα). Sildenafil treatment failed to exert antiremodeling properties in female pathological hearts from Gαq-overexpressing or pressure-overloaded mice after ovary removal; however, estrogen replacement restored the effectiveness of sildenafil in these animals. In females, sildenafil-elicited myocardial PKG activity required estrogen, which stimulated tonic cardiomyocyte cGMP synthesis via an eNOS/soluble guanylate cyclase pathway. In contrast, eNOS activation, cGMP synthesis, and sildenafil efficacy were not estrogen dependent in male hearts. Estrogen and sildenafil had no impact on pressure-overloaded hearts from animals expressing dysfunctional PKGIα, indicating that PKGIα mediates antiremodeling effects. These results support the importance of sex differences in the use of PDE5 inhibitors for treating heart disease and the critical role of estrogen status when these agents are used in females.

Steroid-sensitive gene 1 is a novel cyclic GMP-dependent protein kinase I substrate in vascular smooth muscle cells

NO, via its second messenger cGMP, activates protein kinase GI (PKGI) to induce vascular smooth muscle cell relaxation. The mechanisms by which PKGI kinase activity regulates cardiovascular function remain incompletely understood. Therefore, to identify novel protein kinase G substrates in vascular cells, a λ phage coronary artery smooth muscle cell library was constructed and screened for phosphorylation by PKGI. The screen identified steroid-sensitive gene 1 (SSG1), which harbors several predicted PKGI phosphorylation sites. We observed direct and cGMP-regulated interaction between PKGI and SSG1. In cultured vascular smooth muscle cells, both the NO donor S-nitrosocysteine and atrial natriuretic peptide induced SSG1 phosphorylation, and mutation of SSG1 at each of the two predicted PKGI phosphorylation sites completely abolished its basal phosphorylation by PKGI. We detected high SSG1 expression in cardiovascular tissues. Finally, we found that activation of PKGI with cGMP regulated SSG1 intracellular distribution.

Mutation of the protein kinase I alpha leucine zipper domain produces hypertension and progressive left ventricular hypertrophy: a novel mouse model of age-dependent hypertensive heart disease

Hypertensive heart disease causes significant mortality in older patients, yet there is an incomplete understanding of molecular mechanisms that regulate age-dependent hypertensive left ventricular hypertrophy (LVH). Therefore, we tested the hypothesis that the cGMP-dependent protein kinase G I alpha (PKGIα) attenuates hypertensive LVH by evaluating the cardiac phenotype in mice with selective mutations of the PKGIα leucine zipper domain. These leucine zipper mutant (LZM) mice develop basal hypertension. Compared with wild-type controls, 8-month-old adult LZM mice developed increased left ventricular end-diastolic pressure but without frank LVH. In advanced age (15 months), the LZM mice developed overt pathological LVH. These findings reveal a role of PKGIα in normally attenuating hypertensive LVH. Therefore, mutation of the PKGIα LZ domain produces a clinically relevant model for hypertensive heart disease of aging.

Protein kinase g iα inhibits pressure overload-induced cardiac remodeling and is required for the cardioprotective effect of sildenafil in vivo

BACKGROUND

Cyclic GMP (cGMP) signaling attenuates cardiac remodeling, but it is unclear which cGMP effectors mediate these effects and thus might serve as novel therapeutic targets. Therefore, we tested whether the cGMP downstream effector, cGMP-dependent protein kinase G Iα (PKGIα), attenuates pressure overload-induced remodeling in vivo.

METHODS AND RESULTS

The effect of transaortic constriction (TAC)-induced left ventricular (LV) pressure overload was examined in mice with selective mutations in the PKGIα leucine zipper interaction domain. Compared with wild-type littermate controls, in response to TAC, these Leucine Zipper Mutant (LZM) mice developed significant LV systolic and diastolic dysfunction by 48 hours (n=6 WT sham, 6 WT TAC, 5 LZM sham, 9 LZM TAC). In response to 7-day TAC, the LZM mice developed increased pathologic hypertrophy compared with controls (n=5 WT sham, 4 LZM sham, 8 WT TAC, 11 LZM TAC). In WT mice, but not in LZM mice, phosphodiesterase 5 (PDE5) inhibition with sildenafil (Sil) significantly inhibited TAC-induced cardiac hypertrophy and LV systolic dysfunction in WT mice, but this was abolished in the LZM mice (n=3 WT sham, 4 LZM sham, 3 WT TAC vehicle, 6 LZM TAC vehicle, 4 WT TAC Sil, 6 LZM TAC Sil). And in response to prolonged, 21-day TAC (n=8 WT sham, 7 LZM sham, 21 WT TAC, 15 LZM TAC), the LZM mice developed markedly accelerated mortality and congestive heart failure. TAC induced activation of JNK, which inhibits cardiac remodeling in vivo, in WT, but not in LZM, hearts, identifying a novel signaling pathway activated by PKGIα in the heart in response to LV pressure overload.

CONCLUSIONS

These findings reveal direct roles for PKGIα in attenuating pressure overload-induced remodeling in vivo and as a required effector for the cardioprotective effects of sildenafil.

Direct binding and regulation of RhoA protein by cyclic GMP-dependent protein kinase Iα

Vascular smooth muscle cell (VSMC) tone is regulated by the state of myosin light chain (MLC) phosphorylation, which is in turn regulated by the balance between MLC kinase and MLC phosphatase (MLCP) activities. RhoA activates Rho kinase, which phosphorylates the regulatory subunit of MLC phosphatase, thereby inhibiting MLC phosphatase activity and increasing contraction and vascular tone. Nitric oxide is an important mediator of VSMC relaxation and vasodilation, which acts by increasing cyclic GMP (cGMP) levels in VSMC, thereby activating cGMP-dependent protein kinase Iα (PKGIα). PKGI is known to phosphorylate Rho kinase, preventing Rho-mediated inhibition of MLC phosphatase, promoting vasorelaxation, although the molecular mechanisms that mediate this are unclear. Here we identify RhoA as a target of activated PKGIα and show further that PKGIα binds directly to RhoA, inhibiting its activation and translocation. In protein pulldown and immunoprecipitation experiments, binding of RhoA and PKGIα was demonstrated via a direct interaction between the amino terminus of RhoA (residues 1-44), containing the switch I domain of RhoA, and the amino terminus of PKGIα (residues 1-59), which includes a leucine zipper heptad repeat motif. Affinity assays using cGMP-immobilized agarose showed that only activated PKGIα binds RhoA, and a leucine zipper mutant PKGIα was unable to bind RhoA even if activated. Furthermore, a catalytically inactive mutant of PKGIα bound RhoA but did not prevent RhoA activation and translocation. Collectively, these results support that RhoA is a PKGIα target and that direct binding of activated PKGIα to RhoA is central to cGMP-mediated inhibition of the VSMC Rho kinase contractile pathway.

Abstract 104: Protein Kinase GIα Functions in the Cardiac Myocyte as a Tonic Inhibitor of Pathologic Cardiac Hypertrophy In Vivo

Objectives: We and others previously demonstrated that activation of the NO-cGMP-Protein Kinase G (PKG) pathway inhibits cardiac hypertrophy and remodeling in vivo. However, it remains untested whether PKG specifically in the cardiac myocyte (CM) mediates these effects. We therefore tested the hypothesis that PKGIα inhibits pathologic cardiac hypertrophy through a specific role in the CM.

Methods and Results: We created and characterized mice with CM-restricted excision of PKGIα. Mice were generated in which the PKGI exon 1 (specific for the Iα isoform) was flanked by loxP sites. We crossed these PKGIα fl/fl mice with αMHC-Cre mice which constitutively express Cre recombinase selectively in the CM. The resultant PKGIα fl/fl / αMHC-Cre+/- mice were compared with PKGIα fl/fl / αMHC-Cre-/- littermate controls (termed PKG CMKO and Ctrl, respectively). By age 3 months (n=5 per genotype), male PKG CMKO mice developed atrial and LV hypertrophy compared with Ctrl littermates PKG CMKO atrial weight/tibia length 0.33 ± 0.03 mg/mm vs 0.22 ± .01 in Ctrl, P <0.05; PKG CMKO LV/TL 5.0 ± 0.2 mg/mm vs 4.1 ± 0.4 in Ctrl, P <0.05). LV CM cross sectional area also increased in the 3 month old PKG CMKO mice (9445 ± 282 pixels PKG CMKO vs 8273 ± 213 in Ctrl, n>400 cells/genotype, 5 hearts per genotype; P <0.001). The systolic index end systolic elastance was decreased in 3 month old PKG CMKO mice (PKG CMKO 3.1 ± 0.4 mmHg/μ l vs 6.1 ± 1.0 in Ctrl-; P <0.05). Importantly, blood pressure did not differ between genotypes. By age 6 months, PKG CMKO mice developed early mortality (3 of 4 PKG CMKO males died at 6 months of age vs 0 of 4 Ctrl males). Total heart and atrial weights of male mice (n=3 PKG CMKO , 4 Ctrl) increased in PKG CMKO mice (heart weight/tibia length 10.8 ± 1.7 mg/mm in PKG CMKO vs 7.1 ± 0.6 in Ctrl; P <0.05; atrial weight/tibia length 2.3 ± 1.1 mg/mm in PKG CMKO vs 0.30 ± 0.1 Ctrl, P <0.05). LV fractional shortening percentage, recorded at 6 months age, trended lower in the PKG CMKO mice as well (35 ± 3% PKG CMKO vs 44 ± 4% Ctrl, P 0.09).

Conclusions: These data provide the first evidence that PKGIα functions in the CM as a tonic inhibitor of age-dependent pathologic hypertrophy, supporting further study of PKGIα as a therapeutic target in the prevention and treatment of LV remodeling and congestive heart failure.

Endothelial dysfunction and systemic hypertension by selective cGMP-dependent protein kinase I inhibition using novel cell-penetrating peptide delivered in vivo

BACKGROUND AND OBJECTIVE

Nitric oxide (NO) and related nitrovasodilators regulate blood pressure by activation of soluble guanylate cyclase, elevation of cyclic guanosine monophosphate (cGMP), and activation of cGMP-dependent protein kinase (cGPK). Despite the progress of our understanding of the NO/cGMP mediated vasorelaxation, partly through conventional cGPK knock-out mice, the role of cGPK remains unclear. In particular, the downstream target(s) of the kinase are not well defined. We hypothesized that highly selective inhibitors of cGPK delivered in vivo in adult may elucidate the role of the kinase in vasorelaxation and regulation of blood pressure.

METHODS AND RESULTS

We have adopted a newly developed method of TAT-mediated protein transduction to study NO/cGMP signaling pathways in mice. In vitro, TAT-cGPK inhibitor peptide blocked autophosphorylation of the kinase. The effect of cGPK inhibition on murine blood pressure (BP) was investigated by continuous infusion of 100 μg of the inhibitor into the internal jugular vein over 72 hours. In 8 animals infused with the inhibitor, the mean BP increased by 38 ± 24/31 ± 30 mm Hg (from 108 ± 14/92 ± 19 to 145 ± 13/123 ± 19 mm Hg) whereas in 8 animals injected with either saline (4) or TAT-green fluorescent protein (4), the BP remained the same (from 117 ± 21/101 ± 26 to 119 ± 22/96 ± 30 mm Hg); P=0.001. Ex vivo, using vascular ring assays, NO-dependent relaxation in murine aortas harvested from animals administered with TAT-cGPK inhibitor was inhibited by 25% (sham 76 ± 11%, inhibitor 51 ± 13%).

CONCLUSION

We demonstrated that highly specific peptide inhibitor of cGPK induced adult murine hypertension through inhibition of nitric oxide mediated relaxation.

Reduced endoglin activity limits cardiac fibrosis and improves survival in heart failure

BACKGROUND

Heart failure is a major cause of morbidity and mortality worldwide. The ubiquitously expressed cytokine transforming growth factor-β1 (TGFβ1) promotes cardiac fibrosis, an important component of progressive heart failure. Membrane-associated endoglin is a coreceptor for TGFβ1 signaling and has been studied in vascular remodeling and preeclampsia. We hypothesized that reduced endoglin expression may limit cardiac fibrosis in heart failure.

METHODS AND RESULTS

We first report that endoglin expression is increased in the left ventricle of human subjects with heart failure and determined that endoglin is required for TGFβ1 signaling in human cardiac fibroblasts using neutralizing antibodies and an siRNA approach. We further identified that reduced endoglin expression attenuates cardiac fibrosis, preserves left ventricular function, and improves survival in a mouse model of pressure-overload-induced heart failure. Prior studies have shown that the extracellular domain of endoglin can be cleaved and released into the circulation as soluble endoglin, which disrupts TGFβ1 signaling in endothelium. We now demonstrate that soluble endoglin limits TGFβ1 signaling and type I collagen synthesis in cardiac fibroblasts and further show that soluble endoglin treatment attenuates cardiac fibrosis in an in vivo model of heart failure.

CONCLUSION

Our results identify endoglin as a critical component of TGFβ1 signaling in the cardiac fibroblast and show that targeting endoglin attenuates cardiac fibrosis, thereby providing a potentially novel therapeutic approach for individuals with heart failure.

Abstract 1: Opposing Roles for Endoglin and Soluble Endoglin in Cardiac Remodeling and Heart Failure

Transforming growth factor beta-1 (TGFb1) promotes cardiac fibrosis. The transmembrane co-receptor Endoglin (Eng; CD105) facilitates TGFb1 signaling via SMAD effector proteins. In contrast, a circulating form of soluble endoglin (sEng) inhibits TGFb1 signaling in vascular endothelium. We recently reported that increased sEng levels in human serum correlate with clinical indices of heart failure severity. Therefore, we tested the hypothesis that Eng and sEng mediate opposing effects on cardiac fibrosis in heart failure. In male, wild-type mice (WT), Eng expression increased in the left ventricle (LV) after 2, 4, and 10 weeks of thoracic aortic constriction (TAC) accompanied by progressive LV fibrosis and hypertrophy. In contrast to WT mice, Eng haploinsufficient (Eng +/− ) mice had preserved LV function (FS%: 78±4 vs 22±16, Eng +/− vs WT, p<0.01) and improved survival [88%(7/8) vs 50%(4/8), Eng +/− vs WT, p<0.001) after 10 weeks of TAC. Reduced LV fibrosis was observed in Eng +/− mice, while LV mass, cardiomyocyte hypertrophy, and calcineurin, SerCA, and bMHC expression were comparable to WT after TAC. Capillary density was significantly higher in Eng +/− mice after TAC compared to WT. LV SMAD phosphorylation (pSMAD) after TAC was studied and a preferential increase was observed in pSMAD1/5/8 expression in Eng +/− mice as compared to WT mice, in which cardiac pSmad2/3 expression was increased. The dependence of TGFb1 induced collagen synthesis on Eng expression was tested in vitro using human cardiac fibroblasts (hCF). Neutralizing antibodies and siRNA against Eng each attenuated TGFb1 induced collagen synthesis. In contrast, conditioned media from cells transfected with an adenovirus over-expressing sEng attenuated pSMAD2/3 expression and TGFb1 induced collagen synthesis in hCF. Treatment of hCF with recombinant sEng blocked TGFb1 induced collagen synthesis in a dose-dependent manner, confirming an inhibitory role of sEng. These results indicate that Eng and sEng mediate opposite effects on TGFb1 induced collagen synthesis. Reduced Eng expression uncouples cardiac fibrosis from cardiomyocyte hypertrophy, promotes SMAD1/5/8-signaling, and enhances angiogenesis. Eng may represent a novel therapeutic target to improve survival in heart failure.

Aldosterone regulates vascular gene transcription via oxidative stress-dependent and -independent pathways

OBJECTIVE

Aldosterone (Aldo) antagonism prevents cardiovascular mortality by unclear mechanisms. Aldo binds to the mineralocorticoid receptor (MR), a ligand-activated transcription factor, which is expressed in human vascular cells. Here we define the early Aldo-regulated vascular transcriptome and investigate the mechanisms of gene regulation by Aldo in the vasculature that may contribute to vascular disease.

METHODS AND RESULTS

Gene expression profiling of Aldo-treated mouse aortas identified 72 genes regulated by Aldo. These genes are overrepresented in Gene Ontology categories involved in vascular function and disease. Quantitative reverse transcription-polymerase chain reaction was used to confirm and further explore mechanisms of vascular gene regulation by Aldo. Aldo-regulated vascular gene expression was inhibited by actinomycin D and MR antagonists supporting a transcriptional MR-dependent mechanism. Aldo regulation of a subset of genes was enhanced in the setting of vascular endothelial denudation and blocked by the free radical scavenger Tempol, supporting synergy between Aldo and vascular injury that is oxidative stress dependent. In the aortic arch, a region predisposed to atherosclerosis, the injury-enhanced genes also demonstrated enhanced expression compared with the descending aorta, both at baseline and after Aldo exposure. Furthermore, the clinically beneficial MR antagonist spironolactone inhibited expression of the identified genes in aortic tissue from humans with atherosclerosis.

CONCLUSIONS

This study defines the Aldo-regulated vascular transcriptome and characterizes a subset of proatherogenic genes with enhanced Aldo-stimulated, oxidative stress-dependent expression in the setting of vascular injury and in areas predisposed to atherosclerosis. Inhibition of MR regulation of these genes may play a role in the protective effects of Aldo antagonists in patients with vascular disease, and these pathways may provide novel drug targets to prevent atherosclerosis in humans.

Elevated Soluble fms-Like Tyrosine Kinase-1 Levels in Acute Coronary Occlusion

Objective—

Early recognition of an acute coronary occlusion (ACO) improves clinical outcomes. Soluble fms-like tyrosine kinase-1 (sFLT1) is an endothelium-derived protein induced by hypoxia. We tested whether sFLT1 levels are elevated in ACO.

Methods and Results—

Serum sFLT1 levels were measured by enzyme-linked immunosorbent assay in patients with ST-segment elevations and angiographically confirmed ACO, unstable angina/non ST-segment elevation myocardial infarction, and 2 control groups. To further explore sFLT1 release, a mouse model of ACO and in vitro human coronary artery endothelial cell injury were used. sFLT1 levels were increased in ACO compared with unstable angina/non-ST-elevation myocardial infarction, catheterized controls, or healthy volunteers (200.7±15.5 versus 70.7±44.0 versus 10.2±4.0 versus 11.7±1.7 pg/mL respectively, P <0.001 versus ACO). At presentation, all ACO patients had elevated sFLT1 levels (>15 pg/mL, 99th percentile in controls), whereas 57% had levels of the MB isoform of creatine kinase levels >10 ng/mL ( P <0.01) and 85% had ultrasensitive troponin I levels >0.05 ng/mL ( P <0.05). Within 60 minutes after symptom onset, sFLT1 was more sensitive than the MB isoform of creatine kinase or ultrasensitive troponin I for ACO (100% versus 20% versus 20% respectively; P ≤0.01 for each). Within 60 minutes of ACO in mice, sFLT1 levels were elevated. Hypoxia and thrombin increased sFLT1 levels within 15 minutes in human coronary artery endothelial cells.

Conclusion—

sFLT1 levels may be an early indicator of endothelial hypoxia in ACO.

Usefulness of soluble endoglin as a noninvasive measure of left ventricular filling pressure in heart failure

Progressive left ventricular (LV) dysfunction induces expression of the cytokine transforming growth factor-β1. Endoglin (CD105) is a transforming growth factor-β1 co-receptor that is released into the circulation as soluble endoglin (sEng). The objective of the present study was to assess the serum levels of sEng in patients with heart failure and to identify the predictive value of sEng for detecting elevated left ventricular end-diastolic pressures (LVEDPs). We measured the sEng levels in 82 consecutive patients with suspected LV dysfunction referred for determination of left heart filling pressures using cardiac catheterization. Among these subjects, the sEng levels correlated with the LVEDP (R = 0.689; p <0.0001), irrespective of the LV ejection fraction. Using a receiving operating characteristic curve, the sEng levels predicted an LVEDP of ≥16 mm Hg with an area under the curve of 0.85, exceeding the measured area under the curves for both atrial and brain natriuretic peptide, currently used biomarkers for heart failure diagnosis (atrial natriuretic peptide 0.68 and brain natriuretic peptide 0.65; p <0.01 vs sEng). In 10 subjects receiving medical therapy guided by invasive hemodynamic monitoring for heart failure, decreased a pulmonary capillary wedge pressure was associated with a reduced sEng level (R = 0.75, p = 0.008). Finally, compared to 25 healthy controls, the sEng levels were elevated in subjects with suspected LV dysfunction (3,589 ± 588 vs 4,257 ± 966 pg/ml, respectively, p <0.005) and correlated directly with the New York Heart Association class (R = 0.501, p<0.001). In conclusion, circulating levels of sEng are elevated in patients with increased LVEDP and New York Heart Association class, irrespective of the LV ejection fraction. sEng levels also decreased in association with a reduced cardiac filling pressure after diuresis. These findings have identified circulating sEng as a sensitive measure of elevated left heart filling pressures.

Placental growth factor mediates aldosterone-dependent vascular injury in mice

In clinical trials, aldosterone antagonists reduce cardiovascular ischemia and mortality by unknown mechanisms. Aldosterone is a steroid hormone that signals through renal mineralocorticoid receptors (MRs) to regulate blood pressure. MRs are expressed and regulate gene transcription in human vascular cells, suggesting that aldosterone might have direct vascular effects. Using gene expression profiling, we identify the pro-proliferative VEGF family member placental growth factor (PGF) as an aldosterone-regulated vascular MR target gene in mice and humans. Aldosterone-activated vascular MR stimulated Pgf gene transcription and increased PGF protein expression and secretion in the mouse vasculature. In mouse vessels with endothelial damage and human vessels from patients with atherosclerosis, aldosterone enhanced expression of PGF and its receptor, FMS-like tyrosine kinase 1 (Flt1). In atherosclerotic human vessels, MR antagonists inhibited PGF expression. In vivo, aldosterone infusion augmented vascular remodeling in mouse carotids following wire injury, an effect that was lost in Pgf-/- mice. In summary, we have identified PGF as what we believe to be a novel downstream target of vascular MR that mediates aldosterone augmentation of vascular injury. These findings suggest a non-renal mechanism for the vascular protective effects of aldosterone antagonists in humans and support targeting the vascular aldosterone/MR/PGF/Flt1 pathway as a therapeutic strategy for ischemic cardiovascular disease.

Role of toll-like receptor 4 in intimal foam cell accumulation in apolipoprotein E-deficient mice

OBJECTIVE

Atherosclerosis encompasses a conspicuously maladaptive inflammatory response that might involve innate immunity. Here, we compared the role of Toll-like receptor 4 (TLR4) with that of TLR2 in intimal foam cell accumulation and inflammation in apolipoprotein E (ApoE) knockout (KO) mice in vivo and determined potential mechanisms of upstream activation and downstream action.

METHODS AND RESULTS

We measured lipid accumulation and gene expression in the lesion-prone lesser curvature of the aortic arch. TLR4 deficiency reduced intimal lipid by ≈75% in ApoE KO mice, despite unaltered total serum cholesterol and triglyceride levels, whereas TLR2 deficiency reduced it by ≈45%. TLR4 deficiency prevented the increased interleukin-1α (IL-1α) and monocyte chemoattractant protein-1 mRNA levels seen within lesional tissue, and it also lowered serum IL-1α levels. Smooth muscle cells (SMC) were present within the intima of the lesser curvature of the aortic arch at this early lesion stage, and they enveloped and permeated nascent lesions, which consisted of focal clusters of foam cells. Cholesterol enrichment of SMC in vitro stimulated acyl-coenzyme A:cholesterol acyltransferase-1 mRNA expression, cytoplasmic cholesterol ester accumulation, and monocyte chemoattractant protein-1 mRNA and protein expression in a TLR4-dependent manner.

CONCLUSIONS

TLR4 contributes to early-stage intimal foam cell accumulation at lesion-prone aortic sites in ApoE KO mice, as does TLR2 to a lesser extent. Intimal SMC surround and penetrate early lesions, where TLR4 signaling within them may influence lesion progression.

Renal actions of RGS2 control blood pressure

G protein-coupled receptors (GPCRs) have key roles in cardiovascular regulation and are important targets for the treatment of hypertension. GTPase-activating proteins, such as RGS2, modulate downstream signaling by GPCRs. RGS2 displays regulatory selectivity for the Gαq subclass of G proteins, and mice lacking RGS2 develop hypertension through incompletely understood mechanisms. Using total body RGS2-deficient mice, we used a kidney crosstransplantation strategy to examine separately the contributions of RGS2 actions in the kidney from those in extrarenal tissues with regard to BP regulation. Loss of renal RGS2 was sufficient to cause hypertension, whereas the absence of RGS2 from all extrarenal tissues including the peripheral vasculature did not significantly alter BP. Accordingly, these results suggest that RGS2 acts within the kidney to modulate BP and prevent hypertension. These data support a critical role for the renal epithelium and/or vasculature as the final determinants of the intra-arterial pressure in hypertension.

Rapid progress for non-nuclear estrogen receptor signaling

Estrogen receptors are best known as ligand-activated transcription factors that regulate vascular cell gene expression. For many years now, a rapid signaling pathway mediated by cell membrane-associated estrogen receptors also has been recognized, but the physiological relevance of this pathway has remained unclear. In this issue of the JCI, Chambliss et al. provide new data to indicate that activation of non-nuclear estrogen receptor signaling regulates processes central to cardiovascular health and disease. These investigators show that an estrogen-dendrimer conjugate (EDC), which activates estrogen receptors but remains non-nuclear, stimulates vascular EC migration in vitro and protects against vascular injury in vivo. They show further that the vascular benefits of EDC in vivo occur selectively in the vasculature, without stimulating the uterus or enhancing growth of breast cancer xenografts. Taken together, these findings indicate that activation of non-nuclear estrogen receptor signaling regulates vascular events of physiological relevance and suggest that translation of these findings into clinically relevant therapeutic interventions is a logical next goal.

Little ROCK is a ROCK1 pseudogene expressed in human smooth muscle cells

Background

Sequencing of the human genome has identified numerous chromosome copy number additions and subtractions that include stable partial gene duplications and pseudogenes that when not properly annotated can interfere with genetic analysis. As an example of this problem, an evolutionary chromosome event in the primate ancestral chromosome 18 produced a partial duplication and inversion of rho-associated protein kinase 1 (ROCK1 -18q11.1, 33 exons) in the subtelomeric region of the p arm of chromosome 18 detectable only in humans. ROCK1 and the partial gene copy, which the gene databases also currently call ROCK1, include non-unique single nucleotide polymorphisms (SNPs).

Results

Here, we characterize this partial gene copy of the human ROCK1, termed Little ROCK, located at 18p11.32. Little ROCK includes five exons, four of which share 99% identity with the terminal four exons of ROCK1 and one of which is unique to Little ROCK. In human while ROCK1 is expressed in many organs, Little ROCK expression is restricted to vascular smooth muscle cell (VSMC) lines and organs rich in smooth muscle. The single nucleotide polymorphism database (dbSNP) lists multiple variants contained in the region shared by ROCK1 and Little ROCK. Using gene and cDNA sequence analysis we clarified the origins of two non-synonymous SNPs annotated in the genome to actually be fixed differences between the ROCK1 and the Little ROCK gene sequences. Two additional coding SNPs were valid polymorphisms selectively within Little ROCK. Little ROCK-Green Fluorescent fusion proteins were highly unstable and degraded by the ubiquitin-proteasome system in vitro.

Conclusion

In this report we have characterized Little ROCK (ROCK1P1), a human expressed pseudogene derived from partial duplication of ROCK1. The large number of pseudogenes in the human genome creates significant genetic diversity. Our findings emphasize the importance of taking into consideration pseudogenes in all candidate gene and genome-wide association studies, as well as the need for complete annotation of human pseudogenome.

Application of gene network analysis techniques identifies AXIN1/PDIA2 and endoglin haplotypes associated with bicuspid aortic valve

Bicuspid Aortic Valve (BAV) is a highly heritable congenital heart defect. The low frequency of BAV (1% of general population) limits our ability to perform genome-wide association studies. We present the application of four a priori SNP selection techniques, reducing the multiple-testing penalty by restricting analysis to SNPs relevant to BAV in a genome-wide SNP dataset from a cohort of 68 BAV probands and 830 control subjects. Two knowledge-based approaches, CANDID and STRING, were used to systematically identify BAV genes, and their SNPs, from the published literature, microarray expression studies and a genome scan. We additionally tested Functionally Interpolating SNPs (fitSNPs) present on the array; the fourth consisted of SNPs selected by Random Forests, a machine learning approach. These approaches reduced the multiple testing penalty by lowering the fraction of the genome probed to 0.19% of the total, while increasing the likelihood of studying SNPs within relevant BAV genes and pathways. Three loci were identified by CANDID, STRING, and fitSNPS. A haplotype within the AXIN1-PDIA2 locus (p-value of 2.926x10(-06)) and a haplotype within the Endoglin gene (p-value of 5.881x10(-04)) were found to be strongly associated with BAV. The Random Forests approach identified a SNP on chromosome 3 in association with BAV (p-value 5.061x10(-06)). The results presented here support an important role for genetic variants in BAV and provide support for additional studies in well-powered cohorts. Further, these studies demonstrate that leveraging existing expression and genomic data in the context of GWAS studies can identify biologically relevant genes and pathways associated with a congenital heart defect.

Estrogen actions in the cardiovascular system

This brief review summarizes the current state of the field for estrogen receptor actions in the cardiovascular system and the cardiovascular effects of hormone replacement therapy (HRT). It is organized into three parts: a short Introduction and overview of the current view of how estrogen works on blood vessels; a summary of the current status of clinical information regarding HRT and cardiovascular effects; and an update on state-of-the-art mouse models of estrogen action using estrogen receptor knockout mice.

cGMP-dependent protein kinase I is crucial for angiogenesis and postnatal vasculogenesis

Background

Endothelium-derived nitric oxide plays an important role for the bone marrow microenvironment. Since several important effects of nitric oxide are mediated by cGMP-dependent pathways, we investigated the role of the cGMP downstream effector cGMP-dependent protein kinase I (cGKI) on postnatal neovascularization.

Methodology/Principal Findings

In a disc neovascularization model, cGKI^−/− mice showed an impaired neovascularization as compared to their wild-type (WT) littermates. Infusion of WT, but not cGKI^−/− bone marrow progenitors rescued the impaired ingrowth of new vessels in cGKI-deficient mice. Bone marrow progenitors from cGKI^−/− mice showed reduced proliferation and survival rates. In addition, we used cGKIα leucine zipper mutant (LZM) mice as model for cGKI deficiency. LZM mice harbor a mutation in the cGKIα leucine zipper that prevents interaction with downstream signaling molecules. Consistently, LZM mice exhibited reduced numbers of vasculogenic progenitors and impaired neovascularization following hindlimb ischemia compared to WT mice.

Conclusions/Significance

Our findings demonstrate that the cGMP-cGKI pathway is critical for postnatal neovascularization and establish a new role for cGKI in vasculogenesis, which is mediated by bone marrow-derived progenitors.

Regulator of G protein signaling 2 mediates cardiac compensation to pressure overload and antihypertrophic effects of PDE5 inhibition in mice

The heart initially compensates for hypertension-mediated pressure overload by enhancing its contractile force and developing hypertrophy without dilation. Gq protein-coupled receptor pathways become activated and can depress function, leading to cardiac failure. Initial adaptation mechanisms to reduce cardiac damage during such stimulation remain largely unknown. Here we have shown that this initial adaptation requires regulator of G protein signaling 2 (RGS2). Mice lacking RGS2 had a normal basal cardiac phenotype, yet responded rapidly to pressure overload, with increased myocardial Gq signaling, marked cardiac hypertrophy and failure, and early mortality. Swimming exercise, which is not accompanied by Gq activation, induced a normal cardiac response, while Rgs2 deletion in Galphaq-overexpressing hearts exacerbated hypertrophy and dilation. In vascular smooth muscle, RGS2 is activated by cGMP-dependent protein kinase (PKG), suppressing Gq-stimulated vascular contraction. In normal mice, but not Rgs2-/- mice, PKG activation by the chronic inhibition of cGMP-selective phosphodiesterase 5 (PDE5) suppressed maladaptive cardiac hypertrophy, inhibiting Gq-coupled stimuli. Importantly, PKG was similarly activated by PDE5 inhibition in myocardium from both genotypes, but PKG plasma membrane translocation was more transient in Rgs2-/- myocytes than in controls and was unaffected by PDE5 inhibition. Thus, RGS2 is required for early myocardial compensation to pressure overload and mediates the initial antihypertrophic and cardioprotective effects of PDE5 inhibitors.

Differential regulation of the inducible nitric oxide synthase gene by estrogen receptors 1 and 2

Estrogen has both rapid and longer term direct effects on cardiovascular tissues mediated by the two estrogen receptors, ESR1 and ESR2. Previous work identified that estrogen regulates the expression of inducible nitric oxide synthase (NOS2A) in vascular smooth muscle cells (VSMC). ESR2 knockout mice have vascular dysfunction due to dysregulation of NOS2A expression and these mice are hypertensive (Zhu et al. Science 2002 295 505-508). Here, we report studies to examine the differential regulation of NOS2A gene expression by ESR1 and 2. Immunoblotting and RT-PCR studies revealed that different VSMC lines expressed different levels of ESR1 and ESR2 protein and mRNA. VSMC from different vascular beds were studied, including aortic VSMC expressing ESR1 and radial (Rad) VSMC expressing ESR2. E(2) inhibited NO production and NOS2A protein expression in aortic VSMC. Human NOS2A promoter-reporter studies revealed suppression of NOS2A reporter activity by E(2) in aortic VSMC, and stimulation of NOS2A reporter activity by E(2) in Rad arterial VSMC. In heterologous expression studies of COS-7 cells lacking endogenous ER, E(2) treatment of COS-7 cells did not alter NOS2A reporter activity in the presence of ESR1, while reporter activity increased 2.3-fold in the presence of ESR2. Similar experiments in COS-7 cells using the selective estrogen receptor modulator raloxifene showed that raloxifene caused a reduction in NOS2A reporter activity with ESR1 coexpression and an increase with ESR2 coexpression. Rat VSMC expressing ESR2 but not ESR1 also showed increased NOS2A reporter activity with E(2) treatment, an effect lost when ESR1 was introduced into the cells. Taken together, these data support that hNOS2A transcription is regulated positively by ESR2 and negatively by ESR1 in VSMC, supporting differential actions of these two estrogen receptors on a physiologically relevant gene in VSMC.

Rapid recruitment of temporally distinct vascular gene sets by estrogen

Cardiovascular disease is the leading cause of mortality for both men and women in developed countries. The sex steroid hormone estrogen is required for normal vascular physiology. Estrogen functions by binding to intracellular estrogen receptors (ER), ERalpha and ERbeta, ligand-activated transcription factors that are expressed in both vascular endothelial and smooth muscle cells. We recently demonstrated that long-term (8 d) estrogen treatment in vivo in mice recruits distinct vascular gene sets mediated by ERalpha and ERbeta and that the promoters from these gene sets are enriched for binding sites of specific transcription factors, leading to the hypothesis that estrogen initiates a cascade of early transcriptional events that modulate gene expression in the vasculature. Here we test this hypothesis using gene expression profiling to examine initial transcriptional events (2-8 h) mediated by estrogen in blood vessels. Our data reveal that 1) estrogen regulates temporally distinct cascades of vascular gene expression, 2) initially, estrogen-mediated vascular gene repression predominates, 3) the earliest estrogen-recruited gene program is enriched in vascular transcription factors that can interact with binding sites present in estrogen-regulated vascular genes recruited subsequently, and 4) estrogen-regulated genes recruited next have specific functions, including lipid metabolism and cellular growth and proliferation that are potentially important for estrogen's known vascular functions. In summary, estrogen directly and rapidly recruits specific transcriptional factors that then propagate distinct cascades of gene expression. These data define the temporal recruitment of specific vascular genes by estrogen and enable further analysis of the mechanisms by which estrogen directly regulates vascular function.

Probing the interaction between the coiled coil leucine zipper of cGMP-dependent protein kinase Ialpha and the C terminus of the myosin binding subunit of the myosin light chain phosphatase

Nitric oxide and nitrovasodilators induce vascular smooth muscle cell relaxation in part by cGMP-dependent protein kinase I (PKG-Ialpha)-mediated activation of myosin phosphatase (MLCP). Mechanistically it has been proposed that protein-protein interactions between the N-terminal leucine zipper (LZ) domain of PKG-Ialpha ((PKG-Ialpha(1-59)) and the LZ and/or coiled coil (CC) domain of the myosin binding subunit (MBS) of MLCP are localized in the C terminus of MBS. Although recent studies have supported these interactions, the critical amino acids responsible for these interactions have not been identified. Here we present structural and biophysical data identifying that the LZ domain of PKG-Ialpha(1-59) interacts with a well defined 42-residue CC motif (MBS(CT42)) within the C terminus of MBS. Using glutathione S-transferase pulldown experiments, chemical cross-linking, size exclusion chromatography, circular dichroism, and isothermal titration calorimetry we identified a weak dimer-dimer interaction between PKG-Ialpha(1-59) and this C-terminal CC domain of MBS. The K(d) of this non-covalent complex is 178.0+/-1.5 microm. Furthermore our (1)H-(15)N heteronuclear single quantum correlation NMR data illustrate that this interaction is mediated by several PKG-Ialpha residues that are on the a, d, e, and g hydrophobic and electrostatic interface of the C-terminal heptad layers 2, 4, and 5 of PKG-Ialpha. Taken together these data support a role for the LZ domain of PKG-Ialpha and the CC domain of MBS in this requisite contractile complex.

Variation in estrogen-related genes associated with cardiovascular phenotypes and circulating estradiol, testosterone, and dehydroepiandrosterone sulfate levels

BACKGROUND

Younger age at the onset of menopause and lower circulating levels of estrogen are risk factors for cardiovascular disease. Several studies have detected associations between variations in genes encoding estrogen receptors alpha (ESR1) and beta (ESR2), and enzyme aromatase (CYP19A1), which regulates the estrogen to testosterone ratio, and cardiovascular phenotypes in the Framingham Heart Study. To explore potential mechanisms by which these gene variants may contribute to cardiovascular disease, we tested the hypothesis that the polymorphisms were associated with endogenous steroid hormone levels.

METHODS

Multiple regression analysis was used to assess the relation between reported polymorphisms and total serum estradiol, testosterone, and dehydroepiandrosterone sulfate levels in 834 men and 687 women who attended the third and fourth Framingham Heart Study examination cycles.

RESULTS

In men, significant associations were detected between CYP19A1 polymorphisms and estradiol and testosterone levels, and the estradiol to testosterone ratio (P ranges 0.0005-0.01). Specifically, carriers of common haplotype rs700518[G]-(TTTA)(n) [L]-rs726547[C] had higher estradiol levels (5% per copy; P = 0.0004), lower testosterone levels (17% per copy; P = 0.036), and a higher estradiol to testosterone ratio (24% per copy; P < 0.0001) compared with the rs700518[A]-(TTTA)(n) [S]-rs726547[C] carriers. In addition, postmenopausal carriers of the ESR2 (CA)(n) long allele and rs1256031 [C] allele had moderately higher estradiol levels (P < or = 0.03). No significant associations with the ESR1 variants were detected.

CONCLUSIONS

Our findings suggest that variations in CYP19A1 correlate with steroid hormone levels in men. Knowledge that a specific carrier status may predispose to altered steroid hormone levels may lead to targeted intervention strategies to reduce health risks in genetically susceptible individuals.

17 Beta-estradiol differentially affects left ventricular and cardiomyocyte hypertrophy following myocardial infarction and pressure overload

BACKGROUND

We have shown previously that 17beta-estradiol (E2) increases left ventricular (LV) and cardiomyocyte hypertrophy after myocardial infarction (MI). However, E2 decreases hypertrophy in pressure overload models. We hypothesized that the effect of estrogen on cardiac hypertrophy was dependent on the type of hypertrophic stimulus.

METHODS AND RESULTS

Ovariectomized wild-type female mice (n = 192) were given vehicle or E2 treatment followed by coronary ligation (MI), transverse aortic constriction (TAC), or sham operation. Signaling pathway activation was studied at 3, 24, and 48 hours, whereas echocardiography and hemodynamic studies were performed at 14 days. MI induced early but transient activation of p38 and p42/44 MAPK pathways, whereas TAC induced sustained activation of both pathways. E2 had no effect on these pathways, but increased Stat3 activation after MI while decreasing Stat3 activation after TAC. MI caused LV dilation and decreased fractional shortening (FS) that were unaltered by E2. TAC caused LV dilation, reduced FS, and increased LV mass, but in this model, E2 improved these parameters. After MI, E2 led to increases in myocyte cross-sectional area, atrial natriuretic peptide (ANP) and beta-myosin heavy chain (MHC) gene expression, but E2 diminished TAC-induced increases ANP and beta-MHC gene expression.

CONCLUSIONS

These data demonstrate that the effects of E2 on LV and myocyte remodeling depend on the nature of the hypertrophic stimulus. The opposing influence of E2 on hypertrophy in these models may, in part, result from differential effects of E2 on Stat3 activation. Further work will be necessary to explore this and other potential mechanisms by which estrogen affects hypertrophy in these models.

Functional mineralocorticoid receptors in human vascular endothelial cells regulate intercellular adhesion molecule-1 expression and promote leukocyte adhesion

In clinical trials, aldosterone antagonists decrease cardiovascular mortality and ischemia by unknown mechanisms. The steroid hormone aldosterone acts by binding to the mineralocorticoid receptor (MR), a ligand-activated transcription factor. In humans, aldosterone causes MR-dependent endothelial cell (EC) dysfunction and in animal models, aldosterone increases vascular macrophage infiltration and atherosclerosis. MR antagonists inhibit these effects without changing blood pressure, suggesting a direct role for vascular MR in EC function and atherosclerosis. Whether human vascular ECs express functional MR is not known. Here, we show that human coronary artery and aortic ECs express MR mRNA and protein and that EC MR mediates aldosterone-dependent gene transcription. Human ECs also express the enzyme 11-beta-hydroxysteroid dehydrogenase-2 (11betaHSD2), and inhibition of 11betaHSD2 in aortic ECs enhances gene transactivation by cortisol, supporting that EC 11betaHSD2 is functional. Furthermore, aldosterone stimulates transcription of the proatherogenic leukocyte-EC adhesion molecule intercellular adhesion molecule (ICAM)1 gene and protein expression on human coronary artery ECs, an effect inhibited by the MR antagonist spironolactone and by MR knock down with small interfering RNA. Cell adhesion assays demonstrate that aldosterone promotes leukocyte-EC adhesion, an effect that is inhibited by spironolactone and ICAM1 blocking antibody, supporting that aldosterone induction of EC ICAM1 surface expression via MR mediates leukocyte-EC adhesion. These data show that aldosterone activates endogenous EC MR and proatherogenic gene expression in clinically important human ECs. These studies describe a novel mechanism by which aldosterone may influence ischemic cardiovascular events and support a new explanation for the decrease in ischemic events in patients treated with aldosterone antagonists.

High blood pressure arising from a defect in vascular function

Hypertension, a major cardiovascular risk factor and cause of mortality worldwide, is thought to arise from primary renal abnormalities. However, the etiology of most cases of hypertension remains unexplained. Vascular tone, an important determinant of blood pressure, is regulated by nitric oxide, which causes vascular relaxation by increasing intracellular cGMP and activating cGMP-dependent protein kinase I (PKGI). Here we show that mice with a selective mutation in the N-terminal protein interaction domain of PKGIalpha display inherited vascular smooth muscle cell abnormalities of contraction, abnormal relaxation of large and resistance blood vessels, and increased systemic blood pressure. Renal function studies and responses to changes in dietary sodium in the PKGIalpha mutant mice are normal. These data reveal that PKGIalpha is required for normal VSMC physiology and support the idea that high blood pressure can arise from a primary abnormality of vascular smooth muscle cell contractile regulation, suggesting a new approach to the diagnosis and therapy of hypertension and cardiovascular diseases.

Estrogen Receptors α and β Mediate Distinct Pathways of Vascular Gene Expression, Including Genes Involved in Mitochondrial Electron Transport and Generation of Reactive Oxygen Species

Estrogen plays an important role in the regulation of vascular tone and in the pathophysiology of cardiovascular disease. Physiological effects of estrogen are mediated through estrogen receptors alpha (ERalpha) and beta (ERbeta), which are both expressed in vascular smooth muscle and endothelial cells. However, the molecular pathways mediating estrogen effects in blood vessels are not well defined. We have performed gene expression profiling in the mouse aorta to identify comprehensive gene sets the expression of which is regulated by long-term (1 wk) estrogen treatment. The ER subtype dependence of the alterations in gene expression was characterized by parallel gene expression profiling experiments in ERalpha-deficient [ERalpha knockout (ERalphaKO)] and ERbeta-deficient (ERbetaKO) mice. Importantly, these data revealed that ERalpha- and ERbeta-dependent pathways regulate distinct and largely nonoverlapping sets of genes. Whereas ERalpha is essential for most of the estrogen-mediated increase in gene expression in wild-type aortas, ERbeta mediates the large majority (nearly 90%) of estrogen-mediated decreases in gene expression. Biological functions of the estrogen-regulated genes include extracellular matrix synthesis, in addition to electron transport in the mitochondrion and reactive oxygen species pathways. Of note, the estrogen/ERbeta pathway mediates down-regulation of mRNAs for nuclear-encoded subunits in each of the major complexes of the mitochondrial respiratory chain. Several estrogen-regulated genes also encode transcription factors. Computational analysis of promoters from coexpressed genes revealed overrepresentation of binding sites for such factors, lending support for an estrogen-regulatory transcriptional network in the vasculature. Overall, these findings provide a foundation for understanding the molecular basis for estrogen effects on vasculature gene expression.

Mineralocorticoid Receptor Activation Promotes Vascular Cell Calcification

OBJECTIVE

Clinical studies demonstrate that mineralocorticoid receptor (MR) antagonism improves outcomes in cardiovascular patients and that vascular calcification correlates with adverse cardiac events. We have recently demonstrated that human vascular smooth muscle cells (VSMCs) express functional MRs that, in response to aldosterone, modulate expression of osteogenic genes including alkaline phosphatase (ALP) and bone morphogenetic protein-2 (BMP2). This study examines the effects of MR activation by aldosterone on the process of in vitro vascular calcification.

METHODS AND RESULTS

Using immunoblotting and adenoviral promoter-reporter assays, we demonstrated that calcifying vascular cells (CVCs), an in vitro model of vascular calcification, express MRs that mediate both aldosterone- and cortisol-stimulated gene transcription. In this model, aldosterone stimulated ALP activity, an early marker of osteoblastic differentiation, as well as mineralization. Aldosterone antagonism with spironolactone abolished both effects implicating CVC MRs in the mechanism of aldosterone-stimulated vascular calcification. Inhibition of BMP2 signaling by overexpression of dominant negative BMP2 receptor did not attenuate aldosterone-induced osteoblastic differentiation.

CONCLUSIONS

Aldosterone activation of MR promotes osteoblastic differentiation and mineralization of VSMCs independent of BMP2 signaling. These data provide a mechanistic link between hormone-mediated VSMC MR activation and vascular calcification, two processes associated with increased risk of cardiovascular ischemic events in humans.

Age-related changes in echocardiographic measurements: association with variation in the estrogen receptor-alpha gene

Left ventricular (LV) mass and other LV measures have been shown to be heritable. In this study we hypothesized that functional variation in the gene coding for estrogen receptor-alpha (ESR1), known for mediating the effect of estrogens on myocardium, is associated with age-related changes in LV structure. Four genetic markers (ESR1 TA repeat; rs2077647, or +30T>C; rs2234693, or PvuII; and rs9340799, or XbaI) were genotyped in 847 unrelated individuals (488 women) from the Framingham Offspring Study, who attended 2 examination cycles 16 years apart (mean ages at first examination: 43+/-9 years; at follow-up: 59+/-9 years). ANCOVA was used to assess the association of polymorphisms and their haplotypes with cross-sectional measurements and longitudinal changes in LV mass, wall thickness, end-diastolic and end-systolic internal diameter, and fractional shortening after adjustment for factors known to influence these variables. Changes over time were detected for all of the LV measurements (P ranging from <0.0001 to 0.02), except for fractional shortening in men. The SS genotype of the ESR1 TA repeat polymorphism in the promoter region was associated with longitudinal changes in LV mass and LV wall thickness (P ranging from 0.0006 to 0.01). Moreover, the TA[S]-+30[T]-PvuII[T]-XbaI[A] haplotype (frequency: 47.5%) was associated with greater LV changes as compared with the TA[L]-+30[C]-PvuII[C]-XbaI[G] haplotype (frequency: 31.8%). Our results are consistent with the hypothesis that common ESR1 polymorphisms are significantly associated with age-related changes in LV structure. Understanding the mechanisms predisposing to unfavorable LV remodeling of the heart with advancing age may aid in the discovery of new therapeutic targets for the prevention of heart failure.

Complex actions of sex steroids in adipose tissue, the cardiovascular system, and brain: Insights from basic science and clinical studies

Recent publications describing the results of the Women's Health Initiative (WHI) and other studies reporting the impact of hormone therapy on aging women have spurred reexamination of the broad use of estrogens and progestins during the postmenopausal years. Here, we review the complex pharmacology of these hormones, the diverse and sometimes opposite effects that result from the use of different estrogenic and progestinic compounds, given via different delivery routes in different concentrations and treatment sequence, and to women of different ages and health status. We examine our new and growing appreciation of the role of estrogens in the immune system and the inflammatory response, and we pose the concept that estrogen's interface with this system may be at the core of some of the effects on multiple physiological systems, such as the adipose/metabolic system, the cardiovascular system, and the central nervous system. We compare and contrast clinical and basic science studies as we focus on the actions of estrogens in these systems because the untoward effects of hormone therapy reported in the WHI were not expected. The broad interpretation and publicity of the results of the WHI have resulted in a general condemnation of all hormone replacement in postmenopausal women. In fact, careful review of the extensive literature suggests that data resulting from the WHI and other recent studies should be interpreted within the narrow context of the study design. We argue that these results should encourage us to perform new studies that take advantage of a dialogue between basic scientists and clinician scientists to ensure appropriate design, incorporation of current knowledge, and proper interpretation of results. Only then will we have a better understanding of what hormonal compounds should be used in which populations of women and at what stages of menopausal/postmenopausal life.

Estrogen Receptor α Gene Variation Is Associated With Risk of Myocardial Infarction in More Than Seven Thousand Men From Five Cohorts

Understanding the mechanisms by which estrogens affect cardiovascular disease risk, including the role of variation in the gene for estrogen receptor alpha (ESR1), may be key to new treatment strategies. We investigated whether the CC genotype at ESR1 c.454-397T>C is associated with increased risk among men. Study of more than 7000 whites in 5 cohorts from 4 countries provided evidence that genotype CC, present in roughly 20% of individuals, is a risk factor for nonfatal acute myocardial infarction (odds ratio=1.44; P<0.0001), after adjustment for established cardiovascular risk factors. After exclusion of younger subjects from 2 cohorts, because of age interaction, the odds ratio increased (to 1.63).

Variation in estrogen-related genes and cross-sectional and longitudinal blood pressure in the Framingham Heart Study

OBJECTIVE

To examine the association between variation in estrogen-related genes and cross-sectional and longitudinal blood pressure in men and women.

DESIGN

In 1780 unrelated members of the community-based Framingham Heart Study offspring cohort, systolic blood pressure and diastolic blood pressure were measured over a total of six examination cycles encompassing 24 years of follow-up. Multivariate regression analyses were used to assess the relation between untreated cross-sectional and longitudinal blood pressure and polymorphisms at the estrogen receptor-alpha (ESR1), estrogen receptor-beta (ESR2), aromatase (CYP19A1), and nuclear receptor coactivator 1 (NCOA1) genes after adjustment for common risk factors.

RESULTS

In men, systolic blood pressure and pulse pressure (systolic blood pressure minus diastolic blood pressure) were associated with two polymorphisms in ESR1, while pulse pressure was also associated with variations in NCOA1 and CYP19A1. Polymorphisms in ESR1, CYP19A1, and NCOA1 were associated with diastolic blood pressure in women.

CONCLUSIONS

Although the underlying relations between genes involved in estrogen action and hypertension remain to be completely understood, our findings provide suggestive evidence of gender-specific contributions of estrogen-related genes to blood pressure variation. As no correction for multiple testing was performed in the analyses, we view these results as suggestive and not definitive. Further studies are warranted to confirm these results using a comprehensive set of polymorphisms in order to shed more light on the involvement of estrogen in blood pressure regulation.

Cyclic GMP-dependent protein kinase Ialpha inhibits thrombin receptor-mediated calcium mobilization in vascular smooth muscle cells

Vascular smooth muscle contractile state is regulated by intracellular calcium levels. Nitric oxide causes vascular relaxation by stimulating production of cyclic GMP, which activates type I cGMP-dependent protein kinase (PKGI) in vascular smooth muscle cells (VSMC), inhibiting agonist-induced intracellular Ca2+ mobilization ([Ca2+]i). The relative roles of the two PKGI isozymes, PKGIalpha and PKGIbeta, in cyclic GMP-mediated inhibition of [Ca2+]i in VSMCs are unclear. Here we have investigated the ability of PKGI isoforms to inhibit [Ca2+]i in response to VSMC activation. Stable Chinese hamster ovary cell lines expressing PKGIalpha or PKGIbeta were created, and the ability of PKGI isoforms to inhibit [Ca2+]i in response to thrombin receptor stimulation was examined. In Chinese hamster ovary cells stably expressing PKGIalpha or PKGIbeta, 8-Br-cGMP activation suppressed [Ca2+]i by thrombin receptor activation peptide (TRAP) by 98 +/- 1 versus 42 +/- 5%, respectively (p <0.002). Immunoblotting studies of cultured human VSMC cells from multiple sites using PKGIalpha- and PKGIbeta-specific antibodies showed PKGIalpha is the predominant VSMC PKGI isoform. [Ca2+]i following thrombin receptor stimulation was examined in the absence or presence of cyclic GMP in human coronary VSMC cells (Co403). 8-Br-cGMP significantly inhibited TRAP-induced [Ca2+]i in Co403, causing a 4-fold increase in the EC50 for [Ca2+]i. In the absence of 8-Br-cGMP, suppression of PKGIalpha levels by RNA interference (RNAi) led to a significantly greater TRAP-stimulated rise in [Ca2+]i as compared with control RNAi-treated Co403 cells. In the presence of 8-Br-cGMP, the suppression of PKGIalpha expression by RNAi led to the complete loss of cGMP-mediated inhibition of [Ca2+]i. Adenoviral overexpression of PKGIbeta in Co403 cells was unable to alter TRAP-stimulated Ca2+ mobilization either before or after suppression of PKGIalpha expression by RNAi. These results support that PKGIalpha is the principal cGMP-dependent protein kinase isoform mediating inhibition of VSMC activation by the nitric oxide/cyclic GMP pathway.

Sex-specific association between estrogen receptor-alpha gene variation and measures of adiposity: the Framingham Heart Study

BACKGROUND

Polymorphisms in estrogen receptor-alpha (ESR1) may be associated with variation in body mass index and waist circumference. However, most prior studies have been limited by sample size and power.

METHODS

DNA from 1763 unrelated men and women (mean age, 56 yr) from the Framingham Heart Study offspring cohort was genotyped for four ESR1 polymorphisms: T30C (rs2077647) in exon 1, PvuII (rs2234693), and XbaI (rs 9340799) in intron 1, and C1335G (rs 1801132) in exon 4.

RESULTS

Men homozygous for the PvuII C allele (frequency, 0.45) had lower waist circumference (99.3 cm), compared with TT homozygous men (99.8 cm) and heterozygotes (100.6 cm) (P < 0.004). Similar results were obtained with XbaI, which lies in the same linkage disequilibrium block. C1335G also demonstrated a gender-specific association: men with CG or GG genotypes had lower mean body mass index, 27.7 and 27.9 kg/m2 respectively, compared with 28.6 kg/m2 among the CC homozygotes (P < 0.01). No significant associations were seen with T30C, nor were associations observed among women.

CONCLUSIONS

Polymorphisms in ESR1 are associated with measures of adiposity in men. These associations further support the hypothesis that the intron 1 region of ESR1 influences phenotypes important for cardiovascular risk.

Association of estrogen receptor beta gene polymorphisms with left ventricular mass and wall thickness in women

BACKGROUND

Left ventricular (LV) hypertrophy is a significant risk factor for cardiovascular disease. Given sex-based differences in cardiac structure and remodeling, we hypothesized that variation in estrogen pathway genes might be associated with alteration of LV structure.

METHODS

We studied 1249 unrelated individuals, 547 men and 702 women (mean age 59 years) from the Framingham Heart Study. Eight single nucleotide polymorphisms in the genes for estrogen receptor alpha and estrogen receptor beta (ESR2) were tested for association with 5 LV measures: LV mass (LVM), LV wall thickness (LVWT), LV internal diameter at end-diastole and end-systole, and fractional shortening. Sex-specific multiple regression analyses were performed adjusting for age, weight, height, systolic and diastolic blood pressure, hypertension treatment, diabetes, and in women, menopausal status.

RESULTS

In men, there was no evidence of association between the estrogen pathway polymorphisms tested and LV structure or function. In women, however, two polymorphisms, ESR2 rs1256031 and ESR2 rs1256059, in linkage disequilibrium with one another, were associated with LVM and LVWT (P = .0007 to .03); the association was most pronounced in those women with hypertension (P = .0006 to .01). The association did not appear to be explained by variation in blood pressure, plasma lipoprotein levels, or hyperglycemia.

CONCLUSIONS

The ESR2 polymorphisms are associated with LV structural differences in women with hypertension in a community-based population. These data are consistent with the hypothesis that genetic factors may mediate part of the observed sex-based differences in LV structure and remodeling.

Modulator Recognition Factor 1, an AT-Rich Interaction Domain Family Member, Is a Novel Corepressor for Estrogen Receptor α

Cardiovascular tissues are important targets of estrogen action. Vascular cells express the two known estrogen receptors (ERs), ERalpha and ERbeta, ligand-activated transcription factors that regulate gene transcription through interactions with both coactivator and corepressor molecules. To isolate ERalpha coregulators in vascular cells, we performed a yeast two-hybrid screen for ERalpha-interacting proteins using a human aorta library. Here we report the identification of modulator recognition factor 1 (MRF1) as an ERalpha-interacting corepressor protein. Full-length MRF1 binds to both the N terminus and the C terminus of ERalpha. ERalpha and MRF1 coimmunoprecipitate in an estradiol-independent manner, and recombinant ERalpha binds to both full-length and COOH-terminal MRF1 in the absence of estradiol. MRF1 also interacts in a ligand-dependent manner with thyroid receptor alpha, retinoid X receptor alpha, and androgen receptor, and in a ligand-independent manner with ERbeta and the retinoic acid receptor. MRF1 RNA is highly expressed in aorta, heart, skeletal muscle, and liver. MRF1 has intrinsic repressor activity in an in vitro GAL reporter assay. Transient transfection studies show that MRF1 represses transcription by ERalpha activated by estradiol in a dose-dependent manner, as well as by the selective ER modulators 4-hydroxy-tamoxifen and raloxifene. MRF1 repression is not influenced by pharmacological inhibition of histone deacetylase. These data identify MRF1 as a repressor of ERalpha-mediated transcriptional activation and support a role for MRF1 in regulating ER-dependent gene expression in cardiovascular and other cells.

Estrogen receptor alpha gene variation and the risk of stroke

BACKGROUND AND PURPOSE

Estrogen receptor alpha (ESR1) gene variation is associated with a range of important estrogen-dependent characteristics, including responses of lipid profile and atherosclerotic severity to hormone replacement therapy, coronary heart disease risk, and migraine. The roles that reproductive steroids play in cerebrovascular pathophysiology and ischemia are an important area of investigation. Given that there is a significantly higher risk of myocardial infarction among men with the CC genotype (PP of PvuII) of c.454-397T>C (rs2234693), we asked whether this genotype is associated with a higher risk of stroke.

METHODS

Relative risk of stroke by genotype was determined in 2709 participants of the Second Northwick Park Heart Study, white males with a mean baseline age 56 years and follow up 10.5 years.

RESULTS

Compared with participants with the ESR1 c.454-397CT or TT genotype, those with the CC genotype had a relative risk of stroke of 1.92 (95% confidence interval, 1.06 to 3.48, P=0.03) after adjustment for age, primary care practice; additional adjustment for body mass index, serum cholesterol and triglyceride levels, hypertension, diabetes, and smoking status. Exclusion of stroke cases with coronary heart disease gave results that were essentially unchanged.

CONCLUSIONS

In this study, subjects with the common ESR1 c.454-397CC genotype have a substantial increase in risk of stroke. In another publication, other ESR1 variation was associated with migraine. We thus hypothesize that estrogen receptor variation may provide a basis for the established relationship among estrogens, migraine, and stroke.

Tobacco smoking, estrogen receptor alpha gene variation and small low density lipoprotein level

High levels of small low density lipoprotein (LDL) particles are a major risk factor for cardiovascular morbidity and mortality. Both estrogens and smoking, with known anti-estrogenic effects, alter the atherogenic lipid profile. We tested for a role of interaction between smoking and estrogen receptor alpha gene (ESR1) variation in association with plasma concentration of atherogenic small LDL particles and LDL particle size. We studied 1727 unrelated subjects, 854 women and 873 men, mean age 51 years (SD 10), from the population-based Framingham Heart Study. After covariate adjustment, women who smoked and had the common ESR1 c.454-397 TT genotype (in 30% of women, T was present on both chromosomes at position 397 prior to the start of exon 2) had >1.7-fold higher levels of small LDL particles than women with the alternative genotypes (P-value for smoking-genotype interaction was 0.001). Similar results were obtained for three other ESR1 variants including c.454-351A > G, in the same linkage disequilibrium block. A similar substantial gender-specific result was also evident with a fifth variant, in a separate linkage disequilibrium block, in exon 4 (P = 0.003). Women who smoked and had specific, common ESR1 genotypes had a substantially higher plasma concentration of atherogenic small LDL particles. Significant results revealed a dose-dependent effect of smoking and were evident in both pre- and postmenopausal women. The reported association has the potential to explain the risks associated with estrogen use in certain women and a recent report of association between an ESR1 haplotype comprised of c.454-397 T and c.454-351 A alleles with increased myocardial infarction and ischaemic heart disease, independent of the standard, established cardiovascular risk factors.

Estrogen receptor-alpha variants are associated with lipoprotein size distribution and particle levels in women: the Framingham Heart Study

Plasma lipid profile is affected by endogenous estrogen levels and hormone replacement therapy (HRT). As plasma lipid concentrations have a significant heritable basis and the effects of both endogenous estrogen and use of HRT are mediated by estrogen receptors, we sought to investigate the relationships between polymorphisms in estrogen receptor-alpha (ESR1) and plasma lipid and lipoprotein concentrations. We analyzed data from 854 women (mean age 52+/-10 years) from the Framingham Heart Study. A TA repeat in the promoter region, c.30T>C in exon 1, c.454-397T>C, and c.454-351A>G in intron 1, all in linkage disequilibrium (LD), were significantly associated with low-density lipoprotein (LDL) particle size and concentration of small LDL particles. Women with the c.454-397C allele had larger LDL particle size (21.09+/-0.02 nm versus 21.01+/-0.03 nm, p=0.021) concurrent with lower small LDL particle concentration (0.47+/-0.02 mmol/L versus 0.58+/-0.03 mmol/L, p=0.008). Moreover, the TA[L]-c.30C-c.454-397C-c.454-351G haplotype (frequency, 32%) was associated with lower small LDL particle concentrations (-0.06+/-0.03 mmol/L change associated with each copy of this haplotype, p=0.011) when compared to the TA[S]-c.30T-c.454-397T-c.454-351A haplotype (frequency, 46%), where L and S are long and short TA repeats. Our results suggest that common ESR1 polymorphisms have a significant effect on lipoprotein metabolism in women.

In hypertension, the kidney is not always the heart of the matter

Blood pressure abnormalities are thought to originate from intrinsic changes in the kidney, a concept that has been largely unchallenged for more than 4 decades. However, recent molecular, cellular, and transgenic mouse studies support an alternative hypothesis: primary abnormalities in vascular cell function can also directly cause abnormalities of blood pressure. In this issue of the JCI, Crowley and coworkers describe the application of an elegant cross-renal transplant model to type 1A angiotensin (AT(1A)) receptor-deficient mice and their wild-type littermates to explore the relative contributions of renal and extrarenal tissues to the low blood pressure seen in the AT(1A) receptor-deficient animals. Their studies further support the emerging paradigm that primary abnormalities of the vasculature can make unique, nonredundant contributions to blood pressure regulation; the findings have potentially important implications for the ways we diagnose and treat blood pressure diseases in humans.