Abstract P200: Endothelial Estrogen Receptor Alpha Does Not Protect Female Mice Against Western Diet Induced Vascular Stiffness

Background: Women with obesity, insulin resistance and type 2 diabetes mellitus (T2D) lose the cardiovascular disease protection normally afforded by female sex hormones, but the underlying mechanism(s) remain unknown. Increases in vascular stiffness occur with aging, but conditions of insulin resistance such as obesity and T2D are characterized by accelerated development of this phenomenon. Under physiological conditions, vascular estrogen signaling via estrogen receptor alpha (ERα) increases endothelial bioavailable nitric oxide which decreases stiffness. Nevertheless, in conditions of insulin resistance, the effects of ERα signaling may be deleterious.

Methods: We used a novel rodent model lacking ERα in the endothelial cells (ECERαKO). The genomic region encompassing exon 3 of the ERα gene was flanked by loxP sites. ECERαKO mice were generated by crossing ERα doubled floxed mice with Cad-Cre+ mice (VE-Cadherin promoter driving expression of Cre-recombinase). Female ECERαKO mice and littermates were fed a high fructose/high sucrose (Western diet - WD) for 8 weeks. The WD diet consisted of 60% fat and 20% sucrose. At the end of the intervention period, mice underwent in vivo and ex vivo assessment of vascular stiffness.

Results: The absence of EC ERα did not impact whole body insulin sensitivity (examined by HOMA-IR). Females lacking the endothelial specific ERα had less vascular stiffness when assessed in vivo via aortic pulse wave velocity than the littermates fed with a WD (3.43 ± 0.184 m/s vs. 4.080 ± 0.172 m/s, p<0.05). Similarly, ex vivo evaluation of aortic endothelial cell stiffness using atomic force microscopy (AFM) revealed increased stiffness in the females with intact EC ERα when compared with ECERαKO females (1.91 ± 0.60 kPa vs. 13.09 ± 2.61 kPa ) (p<0.05). Resistant vessel (femoral artery) also revealed less stiffness (decreased modulus of elasticity) in ECERαKO mice fed a WD.

Conclusion: Endothelial ERα does not protect females from vascular stiffness induced by a WD. Indeed, the present data suggest a predisposition toward protection of rodent lacking ERα in conditions of insulin resistance.

Abstract 64: Conditional Knockout of Activin Like Kinase-1 (ALK-1) Leads to Heart Failure Without Maladaptive Remodeling

Activin like kinase 1 (ALK1) mediates signaling via the TGFb family of ligands. ALK1 activity promotes endothelial proliferation and migration. Reduced ALK1 activity is associated with arteriovenous malformations. No studies have examined the effect of global ALK1 deletion on indices of cardiac remodeling. We hypothesized that reduced levels of ALK1 promote maladaptive cardiac remodeling. Methods: We employed an ALK1 conditional knockout mice (cKO) harboring the ROSA26-CreER knock-in allele whereby a single dose of intraperitoneal tamoxifen triggered ubiquitous Cre recombinase mediated excision of floxed ALK1 alleles. Tamoxifen treated wild-type (WT-Tam; n=5) and vehicle treated ALK1-cKO mice (cKO-Veh; n=5) served as controls for tamoxifen treated ALK1-cKO mice (cKO-Tam; n=15). Results: ALK1 cKO-Tam mice demonstrated reduced 14-day survival compared to cKO-Veh controls (33% vs 100%, respectively, p<0.01). Seven days after treatment, ALK1 cKO mice began to exhibit reduced left ventricular (LV) fractional shortening, progressive LV dilation, and gastrointestinal bleeding. After 14 days total body mass was reduced, but LV and lung mass increased in cKO-Tam not cKO-Veh mice. Peak LV systolic pressure, contractility, and arterial elastance were reduced, but LV end-diastolic pressure and stroke volume increased in cKO-Tam, not cKO-Veh mice. LV ALK1 mRNA and protein levels were reduced in cKO-Tam, not cKO-Veh mice. LV levels of other TGFb-family ligands and receptors (ALK5, TBRII, BMPRII, Endoglin, BMP7, BMP9, and TGFB1) were unchanged between groups. Cardiomyocyte area and LV levels of BNP were increased in cKO-Tam mice, but LV levels of b-MHC, SerCA, and calcineurin were unchanged. No increase in cardiac fibrosis Type I collagen, CTGF, or PAI-1 levels were observed between groups. No differences were observed for any variable studied between cKO-Veh and WT-Tam mice. Conclusion: Global deletion of ALK1 is associated with the development of high output heart failure without maladaptive remodeling. Future studies exploring the functional role of ALK1 in cardiac remodeling are required.

Abstract 178: Blocking the Acetylcholine Activated Inward Rectifier Potassium Current but not the Rapid Delayed Rectifier Potassium Current Restores Sinus Rhythm in the Chronically Fibrillating Sheep Heart

Background: The acetylcholine activated inward rectifier potassium current (IKACh) was shown to be constitutively active in chronic atrial fibrillation. Its blockade has been proposed to be a possible antifibrillatory pharmacotherapy. We therefore tested the hypothesis that blocking IKACh with the bee venom peptide tertiapin, or the small molecule chloroquine, terminates chronic AF in the sheep heart.

Methods and Results: We tested our hypothesis using biochemistry, electrophysiology and molecular modeling. In patch clamp, the IC50 of IKACh block by tertiapin, and chloroquine was 60 nM, and 710 nM respectively, while dofetilde, a currently used class III antiarrhythmic, did not block the current. On the other hand, dofetilide and chloroquine blocked the rapid delayed rectifier potassium current (IKr) with an IC50 of 50nM, and 2.3 microM respectively, while tertiapine had no effects. Furthermore, molecular modeling indicated that 1 chloroquine molecule blocks the intracellular ion permeation vestibule of the tetrameric Kir3.1, a molecular correlate of IKACh, by interacting with amino acids important for the channel’s rectification. Dofetilide did not interact with Kir3.1. In vitro fluorescence measurements of chloroquine titration into the purified Kir3.1 intracellular domain protein confirmed the computational results and indicated that chloroquine directly binds Kir3.1 with a stoichiometry of 1 chloroquine molecule per Kir3.1 tetramer. Finally, optical mapping of the chronically fibrillating sheep atria showed that while tertiapine, chloroquine, and dofetilide slowed down chronic AF and prolonged the action potential, only tertiapine and chloroquine (the IKACh blockers) restored normal sinus rhythm.

Conclusions: IKACh could be a more powerful anti atrial fibrillation target compared to IKr. Pharmacological blockade of IKACh with a peptide, or a small molecule similar to chloroquine could terminate chronic AF and restore normal sinus rhythm.

Abstract 171: T Cell Mediated Immune Responses Regulate Cardiac Remodeling and Survival in Pressure Overload Induced Heart Failure

Background: Clinical data support that inflammation and the improper regulation of the immune response are intimately associated with Heart Failure (HF), however, the type of immune response involved and whether it regulates cardiac remodeling remains largely unexplored. We hypothesize that T cell mediated immune responses and their recruitment into the heart influence cardiac remodeling and contribute to the pathogenesis of pressure overload induced HF.

Methods and Results: Using quantitative flow cytometry we found that T cells infiltrated the heart as Wild-type mice (WT) developed systolic dysfunction and LV hypertrophy in response to transverse aortic constriction (TAC) (p<0.01 TAC vs Sham). Real time imaging demonstrated that T cells from TAC mice adhered to activated heart endothelial cells in higher numbers than T cells from Sham mice under physiological flow conditions in vitro (P<0.05) indicating a systemic T cell activation to pressure overload induced by TAC. Similarly, circulating T cells from patients with HF adhered more to activated human umbilical vein endothelial cells (HUVEC) than T cells from healthy volunteers. Based on these findings, we performed similar TAC studies in T cell deficient mice (TCRα -/- ). In contrast with WT TAC mice, TCRα -/- had preserved LV systolic and diastolic function (p<0.01) determined by echocardiography and hemodynamic studies, reduced LV fibrosis (p<0.001) and TGFβ1, collagen Iα and αSMA gene expression (p<0.05), and reduced LV hypertrophy and gene expression of ANP and BNP (p<0.05), but unaltered expression of SerCA. Remarkably, TCRα -/- had improved survival after 4 weeks of TAC [100%(16/16) TCRα -/- vs 73.7%(14/19) WT, p=0.023]. Ongoing studies will determine the mechanisms regulating T cell recruitment into the heart, the type of T cell response involved and its contribution to pathological remodeling of the heart.

Conclusion: Our studies demonstrate that T cell immune responses and their recruitment into the LV contribute to the pathogenesis of pressure overload induced HF by mechanisms involving T cell regulation of cardiac hypertrophy and fibrosis, and open a window to develop novel therapeutic strategies to improve the structural, functional and molecular deficits of the failing heart.

Abstract 187: Identification of Cardiac-specific Downstream Substrates of Protein Kinase G I as Potential Novel Anti Cardiac Remodeling Targets

We recently reported that mutation of the cGMP-dependent Protein Kinase G I alpha (PKGIα) N-terminal leucine zipper (LZ) domain (in the PKGIα LZ mutant, or LZM, mouse) accelerates LV remodeling and heart failure after TAC, and prevents the anti-remodeling effect of sildenafil. We therefore hypothesized that PKGIα attenuates remodeling by regulating cardiac signaling pathways that are dependent on substrate interactions mediated by its LZ domain. As a first step to identifying cardiac proteins downstream of PKGIα, we screened myocardial lysates for PKGIα LZ domain-interacting proteins.

Our previous work revealed a requirement for the PKGIα LZ domain for the activation of anti-remodeling myocardial JNK activity after LV pressure overload. MLK3 is an MAPKKK that contains an LZ domain and activates JNK. We now demonstrate, by immunoprecipitation, that MLK 3 interacts with the PKGIα LZ domain in myocardial lysates. We show further that 8-Br-cGMP induces MLK3 phosphorylation on Threonine 277 and Serine 281 in WT, but not LZM myocardial lysates. And, in 293 cells transfected with FLAG-MLK3, 8Br-cGMP induced PKGIα-MLK3 co-precipitation, and increased phosphorylation of MLK3 on Thr277/Ser281. Co-transfection of MLK3 and PKGIα also induced MLK3 phosphorylation at the same sites. We next examined the cardiovascular effect of MLK3 deletion in vivo. Male 8 week old MLK3 -/- mice display basal bi-ventricular hypertrophy compared with littermate controls (LV/Tibia length 42.8 + 0.6 mg/cm in WT, 52.9 + 1.8 in MLK3 -/-; P <0.01; RV/TL 10.8 + 0.1 mg/cm in WT, 13.3 + 0.3 in MLK3 -/-; P <0.01; n= 7 WT, 5 MLK3 -/-). By 14-16 weeks of age, LVH progressed in the MLK3 -/- mice (LV/TL 47.7 + 1.3 mg/cm in WT, 59.8 + 7.5 in MLK3-/-; n= 6 WT, 9 MLK3-.-; P <0.01). Arterial blood pressure was modestly increased, though still normal, in the MLK3 -/- mice (SBP 93 + 1 in WT, 113 + 1 in MLK3 -/-). And, 14-16 week MLK3 -/- mice have impaired LV diastolic function (tau 3.2 + 0.1 ms WT, 3.7 + 0.1 MLK3-/-; P 0.06).

Our studies reveal a previously unknown function of MLK3 as a myocardial PKGIα effector and inhibitor of LVH. Together these results support the strategy of exploring LZ-dependent PKGIα substrates in the myocardium to identify novel therapeutic targets for cardiac remodeling.

Steroid receptor coactivator 3 is a coactivator for myocardin, the regulator of smooth muscle transcription and differentiation

Abnormal proliferation of vascular smooth muscle cells (VSMCs) constitutes a key event in atherosclerosis, neointimal hyperplasia, and the response to vascular injury. Estrogen receptor alpha (ERalpha) mediates the protective effects of estrogen in injured blood vessels and regulates ligand-dependent gene expression in vascular cells. However, the molecular mechanisms mediating ERalpha-dependent VSMC gene expression and VSMC proliferation after vascular injury are not well defined. Here, we report that the ER coactivator steroid receptor coactivator 3 (SRC3) is also a coactivator for the major VSMC transcription factor myocardin, which is required for VSMC differentiation to the nonproliferative, contractile state. The N terminus of SRC3, which contains a basic helix-loop-helix/Per-ARNT-Sim protein-protein interaction domain, binds the C-terminal activation domain of myocardin and enhances myocardin-mediated transcriptional activation of VSMC-specific, CArG-containing promoters, including the VSMC-specific genes SM22 and myosin heavy chain. Suppression of endogenous SRC3 expression by specific small interfering RNA attenuates myocardin transcriptional activation in cultured cells. The SRC3-myocardin interaction identifies a site of convergence for nuclear hormone receptor-mediated and VSMC-specific gene regulation and suggests a possible mechanism for the vascular protective effects of estrogen on vascular injury.

The Women's Health Initiative could not have detected cardioprotective effects of starting hormone therapy during the menopausal transition

The Women's Health Initiative (WHI) randomized controlled trial failed to show cardioprotection by estrogen plus progestin treatment of postmenopausal women. But by design, the WHI population was 10-fold underpowered to show cardioprotection of women starting hormone treatment during the menopausal transition. Thus, observational studies that showed cardioprotection in such women remain the only applicable clinical guide to this issue. Randomized controlled trials are urgently needed to test cardioprotection in women starting treatment during the menopausal transition.

The relationship between nonorganic signs and centralization of symptoms in the prediction of return to work for patients with low back pain

BACKGROUND AND PURPOSE

The purpose of this study was to assess the relationship between the nonorganic signs (Waddell scores) of patients with low back pain, their response to repetitive end-range lumbar spine test movements (centralization of symptoms), and the rate of return to work at a 6-month follow-up.

SUBJECTS

Patients were assessed at five locations of the Canadian Back Institute. A consecutive sample of 126 patients with low back pain, with or without referred leg pain, was selected and reviewed.

METHODS

Physical therapists assessed patients' responses to repetitive test movements (centralization), as described by McKenzie, and tested the patients for nonorganic signs (Waddell scores). Therapists completed a data sheet that classified patients as either those who centralize their symptoms or those who do not centralize their symptoms and recorded their Waddell scores. Although the patients were classified at assessment, they remained in treatment. All patients followed a structured Canadian Back Institute protocol of active exercise, regardless of centralization status or Waddell score.

RESULTS

The inability to centralize symptoms indicated a decreased likelihood of returning to work, regardless of the Waddell score. A high Waddell score predicted a poor chance of returning to work, regardless of the patients' ability to centralize symptoms.

CONCLUSION AND DISCUSSION

A high Waddell score appears to be the best predictor of outcome, as indicated by return to work.