The splicing factor hnRNPL demonstrates conserved myocardial regulation across species and is altered in heart failure

Heart failure (HF) is highly prevalent. Mechanisms underlying HF remain incompletely understood. Splicing factors (SF), which control pre-mRNA alternative splicing, regulate cardiac structure and function. This study investigated regulation of the splicing factor heterogeneous nuclear ribonucleoprotein-L (hnRNPL) in the failing heart. hnRNPL protein increased in left ventricular tissue from mice with transaortic constriction-induced HF and from HF patients. In left ventricular tissue, hnRNPL was detected predominantly in nuclei. Knockdown of the hnRNPL homolog Smooth in Drosophila induced cardiomyopathy. Computational analysis of predicted mouse and human hnRNPL binding sites suggested hnRNPL-mediated alternative splicing of tropomyosin, which was confirmed in C2C12 myoblasts. These findings identify hnRNPL as a sensor of cardiac dysfunction and suggest that disturbances of hnRNPL affect alternative splicing in HF.

Simultaneous Positron Emission Tomography and Molecular Magnetic Resonance Imaging of Cardiopulmonary Fibrosis in a Mouse Model of Left Ventricular Dysfunction

BACKGROUND

Aging-associated left ventricular dysfunction promotes cardiopulmonary fibrogenic remodeling, Group 2 pulmonary hypertension (PH), and right ventricular failure. At the time of diagnosis, cardiac function has declined, and cardiopulmonary fibrosis has often developed. Here, we sought to develop a molecular positron emission tomography (PET)-magnetic resonance imaging (MRI) protocol to detect both cardiopulmonary fibrosis and fibrotic disease activity in a left ventricular dysfunction model.

METHODS AND RESULTS

Left ventricular dysfunction was induced by transverse aortic constriction (TAC) in 6-month-old senescence-accelerated prone mice, a subset of mice that received sham surgery. Three weeks after surgery, mice underwent simultaneous PET-MRI at 4.7 T. Collagen-targeted PET and fibrogenesis magnetic resonance (MR) probes were intravenously administered. PET signal was computed as myocardium- or lung-to-muscle ratio. Percent signal intensity increase and Δ lung-to-muscle ratio were computed from the pre-/postinjection magnetic resonance images. Elevated allysine in the heart (P=0.02) and lungs (P=0.17) of TAC mice corresponded to an increase in myocardial magnetic resonance imaging percent signal intensity increase (P<0.0001) and Δlung-to-muscle ratio (P<0.0001). Hydroxyproline in the heart (P<0.0001) and lungs (P<0.01) were elevated in TAC mice, which corresponded to an increase in heart (myocardium-to-muscle ratio, P=0.02) and lung (lung-to-muscle ratio, P<0.001) PET measurements. Pressure-volume loop and echocardiography demonstrated adverse left ventricular remodeling, function, and increased right ventricular systolic pressure in TAC mice.

CONCLUSIONS

Administration of collagen-targeted PET and allysine-targeted MR probes led to elevated PET-magnetic resonance imaging signals in the myocardium and lungs of TAC mice. The study demonstrates the potential to detect fibrosis and fibrogenesis in cardiopulmonary disease through a dual molecular PET-magnetic resonance imaging protocol.

Impaired T cell IRE1α/XBP1 signaling directs inflammation in experimental heart failure with preserved ejection fraction

Heart failure with preserved ejection fraction (HFpEF) is a widespread syndrome with limited therapeutic options and poorly understood immune pathophysiology. Using a 2-hit preclinical model of cardiometabolic HFpEF that induces obesity and hypertension, we found that cardiac T cell infiltration and lymphoid expansion occurred concomitantly with cardiac pathology and that diastolic dysfunction, cardiomyocyte hypertrophy, and cardiac phospholamban phosphorylation were T cell dependent. Heart-infiltrating T cells were not restricted to cardiac antigens and were uniquely characterized by impaired activation of the inositol-requiring enzyme 1α/X-box-binding protein 1 (IRE1α/XBP1) arm of the unfolded protein response. Notably, selective ablation of XBP1 in T cells enhanced their persistence in the heart and lymphoid organs of mice with preclinical HFpEF. Furthermore, T cell IRE1α/XBP1 activation was restored after withdrawal of the 2 comorbidities inducing HFpEF, resulting in partial improvement of cardiac pathology. Our results demonstrated that diastolic dysfunction and cardiomyocyte hypertrophy in preclinical HFpEF were T cell dependent and that reversible dysregulation of the T cell IRE1α/XBP1 axis was a T cell signature of HFpEF.

Deficiency of miR-409-3p improves myocardial neovascularization and function through modulation of DNAJB9/p38 MAPK signaling

Angiogenesis is critical for tissue repair following myocardial infarction (MI), which is exacerbated under insulin resistance or diabetes. MicroRNAs are regulators of angiogenesis. We examined the metabolic regulation of miR-409-3p in post-infarct angiogenesis. miR-409-3p was increased in patients with acute coronary syndrome (ACS) and in a mouse model of acute MI. In endothelial cells (ECs), miR-409-3p was induced by palmitate, while vascular endothelial growth factor (VEGF) and fibroblast growth factor (FGF) decreased its expression. Overexpression of miR-409-3p decreased EC proliferation and migration in the presence of palmitate, whereas inhibition had the opposite effects. RNA sequencing (RNA-seq) profiling in ECs identified DNAJ homolog subfamily B member 9 (DNAJB9) as a target of miR-409-3p. Overexpression of miR-409-3p decreased DNAJB9 mRNA and protein expression by 47% and 31% respectively, while enriching DNAJB9 mRNA by 1.9-fold after Argonaute2 microribonucleoprotein immunoprecipitation. These effects were mediated through p38 mitogen-activated protein kinase (MAPK). Ischemia-reperfusion (I/R) injury in EC-specific miR-409-3p knockout (KO) mice (miR-409ECKO) fed a high-fat, high-sucrose diet increased isolectin B4 (53.3%), CD31 (56%), and DNAJB9 (41.5%). The left ventricular ejection fraction (EF) was improved by 28%, and the infarct area was decreased by 33.8% in miR-409ECKO compared with control mice. These findings support an important role of miR-409-3p in the angiogenic EC response to myocardial ischemia.

hnRNPL expression dynamics in the embryo and placenta

Heterogeneous nuclear ribonucleoprotein L (hnRNPL) is a conserved RNA binding protein (RBP) that plays an important role in the alternative splicing of gene transcripts, and thus in the generation of specific protein isoforms. Global deficiency in hnRNPL in mice results in preimplantation embryonic lethality at embryonic day (E) 3.5. To begin to understand the contribution of hnRNPL-regulated pathways in the normal development of the embryo and placenta, we determined hnRNPL expression profile and subcellular localization throughout development. Proteome and Western blot analyses were employed to determine hnRNPL abundance between E3.5 and E17.5. Histological analyses supported that the embryo and implantation site display distinct hnRNPL localization patterns. In the fully developed mouse placenta, nuclear hnRNPL was observed broadly in trophoblasts, whereas within the implantation site a discrete subset of cells showed hnRNPL outside the nucleus. In the first-trimester human placenta, hnRNPL was detected in the undifferentiated cytotrophoblasts, suggesting a role for this factor in trophoblast progenitors. Parallel in vitro studies utilizing Htr8 and Jeg3 cell lines confirmed expression of hnRNPL in cellular models of human trophoblasts. These studies [support] coordinated regulation of hnRNPL during the normal developmental program in the mammalian embryo and placenta.

A nanoparticle probe for the imaging of autophagic flux in live mice via magnetic resonance and near-infrared fluorescence

Autophagy-the lysosomal degradation of cytoplasmic components via their sequestration into double-membraned autophagosomes-has not been detected non-invasively. Here we show that the flux of autophagosomes can be measured via magnetic resonance imaging or serial near-infrared fluorescence imaging of intravenously injected iron oxide nanoparticles decorated with cathepsin-cleavable arginine-rich peptides functionalized with the near-infrared fluorochrome Cy5.5 (the peptides facilitate the uptake of the nanoparticles by early autophagosomes, and are then cleaved by cathepsins in lysosomes). In the heart tissue of live mice, the nanoparticles enabled quantitative measurements of changes in autophagic flux, upregulated genetically, by ischaemia-reperfusion injury or via starvation, or inhibited via the administration of a chemotherapeutic or the antibiotic bafilomycin. In mice receiving doxorubicin, pre-starvation improved cardiac function and overall survival, suggesting that bursts of increased autophagic flux may have cardioprotective effects during chemotherapy. Autophagy-detecting nanoparticle probes may facilitate the further understanding of the roles of autophagy in disease.

Mixed lineage kinase 3 requires a functional CRIB domain for regulation of blood pressure, cardiac hypertrophy, and left ventricular function

Mixed lineage kinase 3 (MLK3) modulates blood pressure and left ventricular function, but the mechanisms governing these effects remain unclear. In the current study, we therefore investigated the role of the MLK3 Cdc42/Rac interactive binding (CRIB) domain in cardiovascular physiology. We examined baseline and left ventricular pressure overload responses in a MLK3 CRIB mutant (MLK3C/C) mouse, which harbors point mutations in the CRIB domain to disrupt MLK3 activation by Cdc42. Male and female MLK3C/C mice displayed increased invasively measured blood pressure compared with wild-type (MLK3+/+) littermate controls. MLK3C/C mice of both sexes also developed left and right ventricular hypertrophy but normal baseline LV function by echocardiography and invasive hemodynamics. In LV tissue from MLK3C/C mice, map3k11 mRNA, which encodes MLK3, and MLK3 protein were reduced by 74 ± 6% and 73 ± 7%, respectively. After 1-wk LV pressure overload with 25-gauge transaortic constriction (TAC), male MLK3C/C mice developed no differences in LV hypertrophy but displayed reduction in the LV systolic indices ejection fraction and dP/dt normalized to instantaneous pressure. JNK activation was also reduced in LV tissue of MLK3C/C TAC mice. TAC induced MLK3 translocation from cytosolic fraction to membrane fraction in LV tissue from MLK3+/+ but not MLK3C/C mice. These findings identify a role of the MLK3 CRIB domain in MLK3 regulation of basal blood pressure and cardiac morphology, and in promoting the compensatory LV response to pressure overload.NEW & NOTEWORTHY Here, we identified that the presence of two discrete point mutations within the Cdc42/Rac interaction and binding domain of the protein MLK3 recapitulates the effects of whole body MLK3 deletion on blood pressure, cardiac hypertrophy, and left ventricular compensation after pressure overload. These findings implicate the CRIB domain, and thus MLK3 activation by this domain, as critical for maintenance of cardiovascular homeostasis.

Abstract P3063: Downregulation Of The T Cell Unfolded Protein Response Precedes T Cell Cardiac Infiltration In Experimental Heart Failure With Preserved Ejection Fraction

Introduction: Diastolic dysfunction in Heart Failure with Preserved Ejection Fraction (HFpEF) is associated with T cell systemic inflammation and downregulation of myocardial unfolded protein response (UPR) genes. The T cell UPR can modulate T cell effector function and immune responses, yet this is largely unexplored in HFpEF.

Hypothesis: We hypothesized T cells contribute to cardiometabolic HFpEF and that metabolic and nitrosative stress-induced alterations of the T cell UPR modulate T cell activation and diastolic function.

Methods: Male C57/BL6 (wild-type, WT) or T cell receptor alpha-deficient ( Tcra-/-) were fed a high-fat diet (HFD) and L-NAME for 1, 3, and 5 weeks, or standard chow (STD). We assessed diastolic function by invasive hemodynamic analyses. Immune cells were characterized in the heart and spleen by flow cytometry, and cardiac pathology was assessed by histology. The UPR gene expression was evaluated in splenic CD4 + T cells over time by qPCR.

Results: Unlike WT mice, Tcra-/- mice fed HFD/L-NAME for 5 weeks did not develop diastolic dysfunction or cardiomyocyte hypertrophy, demonstrating a critical role for T cells in experimental cardiometabolic HFpEF. Indeed, cardiac CD4 + T cells were increased in WT mice fed HFD/L-NAME for 5 weeks compared to STD, concordant with an expansion of splenic CD44 hi CD62l lo interferon-gamma (IFNγ) + effector cells. Strikingly, splenic T cells also experienced downregulation of the UPR proteins activating transcription factor 4 ( Atf4 ), Atf6 , and X box-binding protein 1 ( Xbp1s/u ). We found that the Atf4 arm of the T cell UPR is the earliest responder to HFD/L-NAME, with observed downregulation of Atf4 and its downstream effector C/EBP homologous protein ( Chop ) as early as 3 weeks, prior to onset of diastolic dysfunction, followed by the subsequent downregulation of Atf6 and Xbp1s/u .

Conclusions: T cells contribute to diastolic dysfunction and cardiomyocyte hypertrophy in experimental cardiometabolic HFpEF. Early modulation of T cell Atf4 precedes diastolic dysfunction, enhanced IFNγ + effector T cell activation, and global T cell UPR downregulation. Ongoing studies are focused on understanding the functional consequences of impaired T cell UPR in cardiometabolic HFpEF.

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.

MLK3 mediates impact of PKG1α on cardiac function and controls blood pressure through separate mechanisms

cGMP-dependent protein kinase 1α (PKG1α) promotes left ventricle (LV) compensation after pressure overload. PKG1-activating drugs improve heart failure (HF) outcomes but are limited by vasodilation-induced hypotension. Signaling molecules that mediate PKG1α cardiac therapeutic effects but do not promote PKG1α-induced hypotension could therefore represent improved therapeutic targets. We investigated roles of mixed lineage kinase 3 (MLK3) in mediating PKG1α effects on LV function after pressure overload and in regulating BP. In a transaortic constriction HF model, PKG activation with sildenafil preserved LV function in MLK3+/+ but not MLK3-/- littermates. MLK3 coimmunoprecipitated with PKG1α. MLK3-PKG1α cointeraction decreased in failing LVs. PKG1α phosphorylated MLK3 on Thr277/Ser281 sites required for kinase activation. MLK3-/- mice displayed hypertension and increased arterial stiffness, though PKG stimulation with sildenafil or the soluble guanylate cyclase (sGC) stimulator BAY41-2272 still reduced BP in MLK3-/- mice. MLK3 kinase inhibition with URMC-099 did not affect BP but induced LV dysfunction in mice. These data reveal MLK3 as a PKG1α substrate mediating PKG1α preservation of LV function but not acute PKG1α BP effects. Mechanistically, MLK3 kinase-dependent effects preserved LV function, whereas MLK3 kinase-independent signaling regulated BP. These findings suggest augmenting MLK3 kinase activity could preserve LV function in HF but avoid hypotension from PKG1α activation.

Abstract 116: T Cells Contribute To Diastolic Dysfunction And Cardiac Hypertrophy In A Preclinical Model Of Heart Failure With Preserved Ejection Fraction

Introduction: Heart Failure with Preserved Ejection Fraction (HFpEF) is a prevalent cardiovascular syndrome with no curative therapies, characterized by diastolic dysfunction, preserved systolic function, and decreased expression of unfolded protein response (UPR) genes in the heart. Obesity and hypertension are risk factors for HFpEF and are intimately associated with systemic inflammation. However, the inflammatory mechanisms driving HFpEF remain largely unexplored.

Hypothesis: We hypothesized that nitrosative stress induced by obesity and hypertension programs T cells to infiltrate the heart and drive cardiac pathology in HFpEF.

Methods: Using a recently established model of HFpEF, we modeled obesity and hypertension in male C57/BL6 (wild-type, WT), T cell receptor alpha-deficient ( Tcra-/-), and Nur77-GFP reporter mice for T cell receptor engagement, using a high-fat diet (HFD) and L-NAME for 5 weeks, or standard chow (STD) as controls. Invasive hemodynamic analyses were used to assess cardiac function, and the heart and lymphoid organs were harvested to characterize immune cell populations by flow cytometry, histology, and gene expression of cardiac remodeling.

Results: In WT mice, HFD/L-NAME induced significant cardiac infiltration of T cells alongside the hallmarks of HFpEF. HFD/L-NAME significantly expanded CD62 lo CD44 hi effector T cells in the mediastinal lymph nodes and spleen. Nur77-GFP mice revealed no antigen engagement by T cells in the heart, however, T cells sorted out of the lymphoid organs of HFpEF mice had significantly decreased gene expression of the UPR gene spliced X box-binding protein 1 (XBP1s) compared to controls, suggesting a T cell intrinsic dysregulation of the UPR, and T cell phenotypic changes independent of TCR engagement in the heart. Strikingly, Tcra-/- mice did not develop diastolic dysfunction or cardiomyocyte hypertrophy, demonstrating a novel role for T cells in this experimental model of HFpEF.

Conclusions: We conclude diastolic dysfunction and cardiomyocyte hypertrophy in HFpEF is T cell dependent. Ongoing studies are determining whether the observed intrinsic T cell changes in XBP1s prime T cells for cardiac infiltration and effector function that results in diastolic dysfunction and HFpEF.

Isolevuglandin-Modified Cardiac Proteins Drive CD4+ T-Cell Activation in the Heart and Promote Cardiac Dysfunction

BACKGROUND

Despite the well-established association between T-cell-mediated inflammation and nonischemic heart failure, the specific mechanisms triggering T-cell activation during the progression of heart failure and the antigens involved are poorly understood. We hypothesized that myocardial oxidative stress induces the formation of isolevuglandin (IsoLG)-modified proteins that function as cardiac neoantigens to elicit CD4+ T-cell receptor (TCR) activation and promote heart failure.

METHODS

We used transverse aortic constriction in mice to trigger myocardial oxidative stress and T-cell infiltration. We profiled the TCR repertoire by mRNA sequencing of intramyocardial activated CD4+ T cells in Nur77GFP reporter mice, which transiently express GFP on TCR engagement. We assessed the role of antigen presentation and TCR specificity in the development of cardiac dysfunction using antigen presentation-deficient MhcII-/- mice and TCR transgenic OTII mice that lack specificity for endogenous antigens. We detected IsoLG protein adducts in failing human hearts. We also evaluated the role of reactive oxygen species and IsoLGs in eliciting T-cell immune responses in vivo by treating mice with the antioxidant TEMPOL and the IsoLG scavenger 2-hydroxybenzylamine during transverse aortic constriction, and ex vivo in mechanistic studies of CD4+ T-cell proliferation in response to IsoLG-modified cardiac proteins.

RESULTS

We discovered that TCR antigen recognition increases in the left ventricle as cardiac dysfunction progresses and identified a limited repertoire of activated CD4+ T-cell clonotypes in the left ventricle. Antigen presentation of endogenous antigens was required to develop cardiac dysfunction because MhcII-/- mice reconstituted with CD4+ T cells and OTII mice immunized with their cognate antigen were protected from transverse aortic constriction-induced cardiac dysfunction despite the presence of left ventricle-infiltrated CD4+ T cells. Scavenging IsoLGs with 2-hydroxybenzylamine reduced TCR activation and prevented cardiac dysfunction. Mechanistically, cardiac pressure overload resulted in reactive oxygen species-dependent dendritic cell accumulation of IsoLG protein adducts, which induced robust CD4+ T-cell proliferation.

CONCLUSIONS

Our study demonstrates an important role of reactive oxygen species-induced formation of IsoLG-modified cardiac neoantigens that lead to TCR-dependent CD4+ T-cell activation within the heart.

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.

Sacubitril/Valsartan Improves Left Ventricular Function in Chronic Pressure Overload Independent of Intact Cyclic Guanosine Monophosphate-dependent Protein Kinase I Alpha Signaling

BACKGROUND

Combined angiotensin receptor/neprilysin inhibition with sacubitril/valsartan (Sac/Val) has emerged as a therapy for heart failure. The presumed mechanism of benefit is through prevention of natriuretic peptide degradation, leading to increased cyclic guanosine monophosphate (cGMP)-dependent protein kinase (PKG) signaling. However, the specific requirement of PKG for Sac/Val effects remains untested.

METHODS AND RESULTS

We examined Sac/Val treatment in mice with mutation of the cGMP-dependent protein kinase I (PKGI)α leucine zipper domain, which is required for cGMP-PKGIα antiremodeling actions in vivo. Wild-type (WT) or PKG leucine zipper mutant (LZM) mice were exposed to 56-day left ventricular (LV) pressure overload by moderate (26G) transaortic constriction (TAC). At day 14 after TAC, mice were randomized to vehicle or Sac/Val by oral gavage. TAC induced the same degree of LV pressure overload in WT and LZM mice, which was not affected by Sac/Val. Although LZM mice, but not WT, developed LV dilation after TAC, Sac/Val improved cardiac hypertrophy and LV fractional shortening to the same degree in both the WT and LZM TAC mice.

CONCLUSION

These findings indicate the beneficial effects of Sac/Val on LV structure and function in moderate pressure overload. The unexpected finding that PKGIα mutation does not abolish the Sac/Val effects on cardiac hypertrophy and on LV function suggests that signaling other than natriuretic peptide- cGMP-PKG mediates the therapeutic benefits of neprilysin inhibition in heart failure.

Estrogen Receptor-α Non-Nuclear Signaling Confers Cardioprotection and Is Essential to cGMP-PDE5 Inhibition Efficacy

Using genetically engineered mice lacking estrogen receptor-α non-nuclear signaling, this study demonstrated that estrogen receptor-α non-nuclear signaling activated myocardial cyclic guanosine monophosphate-dependent protein kinase G and conferred protection against cardiac remodeling induced by pressure overload. This pathway was indispensable to the therapeutic efficacy of cyclic guanosine monophosphate-phosphodiesterase 5 inhibition but not to that of soluble guanylate cyclase stimulation. These results might partially explain the equivocal results of phosphodiesterase 5 inhibitor efficacy and also provide the molecular basis for the advantage of using a soluble guanylate cyclase simulator as a new therapeutic option in post-menopausal women. This study also highlighted the need for female-specific therapeutic strategies for heart failure.

Abstract 434: Acidifying Nanoparticle Upregulates Autophagy and Enhances Cardiomyocyte Survival after Chemotherapy

Introduction: Chemotherapy-induced cardiotoxicity remains prevalent and deadly, with no effective therapy to slow the progression to irreversible heart failure, which in the case of doxorubicin (Dox) can reach 50% mortality. Dox impact on cardiomyocytes (CMs) is multifocal, including oxidative stress, lysosome alkalinization, and apoptosis. PLGAs, poly(DL-lactide-co-glycolide), are FDA-approved polymers, form defined nanoparticles (NPs). We hypothesize that PLGA NPs target the lysosomal compartments, restore lysosomal acidity after Dox, and confer cardioprotective effects.

Methods: We synthesized fluorescent PLGA NPs by click chemistry. In H9C2 myocytes exposed to 1-5 μM of Dox +/- 1 mg/ml of PLGA, we measured cell viability (MTT), lysosomal pH (OG-514), mitochondrial membrane potential (JC-1), and autophagy proteins (western blot). We further co-injected C57Bl6 mice with PLGA (10 mg/kg, i.v.) and Dox (15 mg/kg, i.p.), to image apoptosis (Annexin) and autophagy (cathepsin-activatable autophagy probe, ADN, unpublished) after 24 hrs, or 4 mg/kg Dox weekly, 5x, i.p. and echo after 3-4 weeks.

Results: PLGA NPs formulated are of controlled size and valency, emits near-infrared fluorescence (Fig. A). In H9C2s, PLGA significantly improved survival after Dox (Fig. B), acidified lysosomes (Fig. C), did not impact cell energetics (Fig. D), and further restored autophagic flux (Fig. E). Imaging in Dox mice revealed significant apoptosis reduction and autophagy activation (Fig. F-H), and cardiac function recovery (Fig. I).

Conclusions: PLGA NPs may represent a novel class of cardioprotective therapeutics of early chemotherapy stress, and with translational potential.

T-cell recruitment to the heart: friendly guests or unwelcome visitors?

Myocardial inflammation can lead to lethal acute or chronic heart failure (HF). T lymphocytes (T cells), have been reported in the inflamed heart in different etiologies of HF, and more recent studies support that different T-cell subsets play distinct roles in the heart depending on the inflammation-triggering event. T cells follow sequential steps to extravasate into tissues, but their specific recruitment to the heart is determined by several factors. These include differences in T-cell responsiveness to specific chemokines in the heart environment, as well as differences in the expression of adhesion molecules in response to distinct stimuli, which regulate T-cell recruitment to the heart and have consequences in cardiac remodeling and function. This review focuses on recent advances in our understanding of the role T cells play in the heart, including its critical role for host defense to virus and myocardial healing postischemia, and its pathogenic role in chronic ischemic and nonischemic HF. We discuss a variety of mechanisms that contribute to the inflammatory damage to the heart, as well as regulatory mechanisms that limit the magnitude of T-cell-mediated inflammation. We also highlight areas in which further research is needed to understand the role T cells play in the heart and distinguish the findings reported in experimental animal models and how they may translate to clinical observations in the human heart.

Targeted disruption of glycogen synthase kinase-3β in cardiomyocytes attenuates cardiac parasympathetic dysfunction in type 1 diabetic Akita mice

Type 1 diabetic Akita mice develop severe cardiac parasympathetic dysfunction that we have previously demonstrated is due at least in part to an abnormality in the response of the end organ to parasympathetic stimulation. Specifically, we had shown that hypoinsulinemia in the diabetic heart results in attenuation of the G-protein coupled inward rectifying K channel (GIRK) which mediates the negative chronotropic response to parasympathetic stimulation due at least in part to decreased expression of the GIRK1 and GIRK4 subunits of the channel. We further demonstrated that the expression of GIRK1 and GIRK4 is under the control of the Sterol Regulatory element Binding Protein (SREBP-1), which is also decreased in response to hypoinsulinemia. Finally, given that hyperactivity of Glycogen Synthase Kinase (GSK)3β, had been demonstrated in the diabetic heart, we demonstrated that treatment of Akita mice with Li⁺, an inhibitor of GSK3β, increased parasympathetic responsiveness and SREBP-1 levels consistent with the conclusion that GSK3β might regulate IKACh via an effect on SREBP-1. However, inhibitor studies were complicated by lack of specificity for GSK3β. Here we generated an Akita mouse with cardiac specific inducible knockout of GSK3β. Using this mouse, we demonstrate that attenuation of GSK3β expression is associated with an increase in parasympathetic responsiveness measured as an increase in the heart rate response to atropine from 17.3 ± 3.5% (n = 8) prior to 41.2 ± 5.4% (n = 8, P = 0.017), an increase in the duration of carbamylcholine mediated bradycardia from 8.43 ± 1.60 min (n = 7) to 12.71 ± 2.26 min (n = 7, P = 0.028) and an increase in HRV as measured by an increase in the high frequency fraction from 40.78 ± 3.86% to 65.04 ± 5.64 (n = 10, P = 0.005). Furthermore, patch clamp measurements demonstrated a 3-fold increase in acetylcholine stimulated peak IKACh in atrial myocytes from GSK3β deficiency mice compared with control. Finally, western blot analysis of atrial extracts from knockout mice demonstrated increased levels of SREBP-1, GIRK1 and GIRK4 compared with control. Taken together with our prior observations, these data establish a role of increased GSK3β activity in the pathogenesis of parasympathetic dysfunction in type 1 diabetes via the regulation of IKACh and GIRK1/4 expression.

Distinct Phenotypes Induced by Three Degrees of Transverse Aortic Constriction in Mice

Transverse aortic constriction (TAC) is a well-established model of pressure overload-induced cardiac hypertrophy and failure in mice. The degree of constriction “tightness” dictates the TAC severity and is determined by the gauge (G) of needle used. Though many reports use the TAC model, few studies have directly compared the range of resulting phenotypes. In this study adult male mice were randomized to receive TAC surgery with varying degrees of tightness: mild (25G), moderate (26G) or severe (27G) for 4 weeks, alongside sham-operated controls. Weekly echocardiography and terminal haemodynamic measurements determined cardiac remodelling and function. All TAC models induced significant, severity-dependent left ventricular hypertrophy and diastolic dysfunction compared to sham mice. Mice subjected to 26G TAC additionally exhibited mild systolic dysfunction and cardiac fibrosis, whereas mice in the 27G TAC group had more severe systolic and diastolic dysfunction, severe cardiac fibrosis, and were more likely to display features of heart failure, such as elevated plasma BNP. We also observed renal atrophy in 27G TAC mice, in the absence of renal structural, functional or gene expression changes. 25G, 26G and 27G TAC produced different responses in terms of cardiac structure and function. These distinct phenotypes may be useful in different preclinical settings.