Search

Although microRNA-7 (miRNA-7) is known to regulate proliferation of cancer cells by targeting Epidermal growth factor receptor (EGFR/ERBB) family, less is known about its role in cardiac physiology. Transgenic (Tg) mouse with cardiomyocyte-specific overexpression of miRNA-7 was generated to determine its role in cardiac physiology and pathology. Echocardiography on the miRNA-7 Tg mice showed cardiac dilation instead of age-associated physiological cardiac hypertrophy observed in non-Tg control mice. Subjecting miRNA-7 Tg mice to transverse aortic constriction (TAC) resulted in cardiac dilation associated with increased fibrosis bypassing the adaptive cardiac hypertrophic response to TAC. miRNA-7 expression in cardiomyocytes resulted in significant loss of ERBB2 expression with no changes in ERBB1 (EGFR). Cardiac proteomics in the miRNA-7 Tg mice showed significant reduction in mitochondrial membrane structural proteins compared to NTg reflecting role of miRNA-7 beyond the regulation of EGFR/ERRB in mediating cardiac dilation. Consistently, electron microscopy showed that miRNA-7 Tg hearts had disorganized rounded mitochondria that was associated with mitochondrial dysfunction. These findings show that expression of miRNA-7 in the cardiomyocytes results in cardiac dilation instead of adaptive hypertrophic response during aging or to TAC providing insights on yet to be understood role of miRNA-7 in cardiac function., (© 2021. The Author(s).)

Background: Preeclampsia increases the risk of heart disease. Defects in the protease corin, including the variant T555I/Q568P found in approximately 12% of blacks, have been associated with preeclampsia and cardiac hypertrophy. The objective of this study was to investigate the role of corin and the T555I/Q568P variant in preeclampsia-associated cardiac alterations using genetically modified mouse models., Methods: Virgin wild-type (WT) and corin knockout mice with or without a cardiac WT corin or T555I/Q568P variant transgene were mated at 3 or 6 months of age. Age- and genotype-matched virgin mice were used as controls. Cardiac morphology and function were assessed at gestational day 18.5 or 28 days postpartum by histologic and echocardiographic analyses., Results: Pregnant corin knockout mice at gestational day 18.5 developed cardiac hypertrophy. Such a pregnancy-associated phenotype was not found in WT or corin knockout mice with a cardiac WT corin transgene. Pregnant corin knockout mice with a cardiac T555I/Q568P variant transgene developed cardiac hypertrophy similar to that in pregnant corin knockout mice. The cardiac hypertrophy persisted postpartum in corin knockout mice and was worse if the mice were mated at 6 instead of 3 months of age. There was no hypertrophy-associated decrease in cardiac function in pregnant corin knockout mice., Conclusions: In mice, corin deficiency causes cardiac hypertrophy during pregnancy. Replacement of cardiac WT corin, but not the T555I/Q568P variant found in blacks, rescues this phenotype, indicating a local antihypertrophic function of corin in the heart. Corin deficiency may represent an underlying mechanism in preeclampsia-associated cardiomyopathies., (Copyright © 2018 Canadian Cardiovascular Society. Published by Elsevier Inc. All rights reserved.)

The role of α₁-adrenergic receptors (ARs) in the regulation of cardiac hypertrophy is still unclear, because transgenic mice demonstrated hypertrophy or the lack of it despite high receptor overexpression. To further address the role of the α₁-ARs in cardiac hypertrophy, we analyzed unique transgenic mice that overexpress constitutively active mutation (CAM) α₁A-ARs or CAM α₁B-ARs under the regulation of large fragments of their native promoters. These constitutively active receptors are expressed in all tissues that endogenously express their wild-type counterparts as opposed to only myocyte-targeted transgenic mice. In this study, we discovered that CAM α₁A-AR mice in vivo have cardiac hypertrophy independent of changes in blood pressure, corroborating earlier studies, but in contrast to myocyte-targeted α₁A-AR mice. We also found cardiac hypertrophy in CAM α₁B-AR mice, in agreement with previous studies, but hypertrophy only developed in older mice. We also discovered unique α₁-AR-mediated hypertrophic signaling that was AR subtype-specific with CAM α₁A-AR mice secreting atrial naturietic factor and interleukin-6 (IL-6), whereas CAM α₁B-AR mice expressed activated nuclear factor-κB (NF-κB). These particular hypertrophic signals were blocked when the other AR subtype was coactivated. We also discovered that crossbreeding the two CAM models (double CAM α₁A/B-AR) inhibited the development of hypertrophy and was reversible with single receptor activation, suggesting that coactivation of the receptors can lead to novel antagonistic signal transduction. This was confirmed by demonstrating antagonistic signals that were even lower than normal controls in the double CAM α₁A/B-AR mice for p38, NF-κB, and the IL-6/glycoprotein 130/signal transducer and activator of transcription 3 pathway. Because α₁A/B double knockout mice fail to develop hypertrophy in response to IL-6, our results suggest that IL-6 is a major mediator of α₁A-AR cardiac hypertrophy.

Activation of cardiac phosphoinositide 3-kinase α (PI3Kα) by growth factors, such as insulin, or activation of PI3Kγ downstream of heterotrimeric guanine nucleotide-binding protein (G protein)-coupled receptors stimulates the activity of the kinase Akt, which phosphorylates and inhibits glycogen synthase kinase-3 (GSK-3). We found that PI3Kγ inhibited GSK-3 independently of the insulin-PI3Kα-Akt axis. Although insulin treatment activated Akt in PI3Kγ knockout mice, phosphorylation of GSK-3 was decreased compared to control mice. GSK-3 is activated when dephosphorylated by the protein phosphatase 2A (PP2A), which is activated when methylated by the PP2A methyltransferase PPMT-1. PI3Kγ knockout mice showed increased activity of PPMT-1 and PP2A and enhanced nuclear export of the GSK-3 substrate NFATc3. GSK-3 inhibits cardiac hypertrophy, and the hearts of PI3Kγ knockout mice were smaller compared to those of wild-type mice. Cardiac overexpression of a catalytically inactive PI3Kγ (PI3Kγ(inact)) transgene in PI3Kγ knockout mice reduced the activities of PPMT-1 and PP2A and increased phosphorylation of GSK-3. Furthermore, PI3Kγ knockout mice expressing the PI3Kγ(inact) transgene had larger hearts than wild-type or PI3Kγ knockout mice. Our studies show that a kinase-independent function of PI3Kγ could directly inhibit GSK-3 function by preventing the PP2A-PPMT-1 interaction and that this inhibition of GSK-3 was independent of Akt.

For over a century, there has been intense debate as to the reason why some cardiac stresses are pathological and others are physiological. One long-standing theory is that physiological overloads such as exercise are intermittent, while pathological overloads such as hypertension are chronic. In this study, we hypothesized that the nature of the stress on the heart, rather than its duration, is the key determinant of the maladaptive phenotype. To test this, we applied intermittent pressure overload on the hearts of mice and tested the roles of duration and nature of the stress on the development of cardiac failure. Despite a mild hypertrophic response, preserved systolic function, and a favorable fetal gene expression profile, hearts exposed to intermittent pressure overload displayed pathological features. Importantly, intermittent pressure overload caused diastolic dysfunction, altered beta-adrenergic receptor (betaAR) function, and vascular rarefaction before the development of cardiac hypertrophy, which were largely normalized by preventing the recruitment of PI3K by betaAR kinase 1 to ligand-activated receptors. Thus stress-induced activation of pathogenic signaling pathways, not the duration of stress or the hypertrophic growth per se, is the molecular trigger of cardiac dysfunction.

Cardiac stress consistently activates c-Jun NH(2)-terminal kinase (JNK) pathways, however the role of different members of the JNK family is unclear. In this study, we applied pressure overload (TAC) in mice with selective deletion of the three JNK genes (Jnk1(-/-), Jnk2(-/-), and Jnk3(-/-)). Following TAC, all three JNK knockout mouse lines developed cardiac hypertrophy similar to wild-type mice (WT), but only JNK1(-/-) mice displayed a significant reduction in fractional shortening after 3 and 7 days of pressure overload, associated with a significant increase in terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling staining and marked inflammatory infiltrate. After the acute deterioration stage, JNK1(-/-) mice underwent a slow recovery followed by a steady progression of cardiac dysfunction, becoming indistinguishable from WT after 12 weeks of TAC. These data suggest that JNK1 plays a protective role in response to pressure overload, preventing the early deterioration in cardiac function following an acute increase in afterload.

The G protein-coupled receptor (GPCR) kinase beta-adrenergic receptor (beta-AR) kinase-1 (beta-ARK1) is elevated during heart failure; however, its role is not fully understood. Beta-ARK1 contains several domains that are capable of protein-protein interactions that may play critical roles in the regulation of GPCR signaling. In this study, we developed a novel line of transgenic mice that express an amino-terminal peptide of beta-ARK1 that is comprised of amino acid residues 50-145 (beta-ARKnt) in the heart to determine whether this domain has any functional significance in vivo. Surprisingly, the beta-ARKnt transgenic mice presented with cardiac hypertrophy. Our data suggest that the phenotype was driven via an enhanced beta-AR system, as beta-ARKnt mice had elevated cardiac beta-AR density. Moreover, administration of a beta-AR antagonist reversed hypertrophy in these mice. Interestingly, signaling through the beta-AR in response to agonist stimulation was not enhanced in these mice. Thus the amino terminus of beta-ARK1 appears to be critical for normal beta-AR regulation in vivo, which further supports the hypothesis that beta-ARK1 plays a key role in normal and compromised cardiac GPCR signaling.

Cardiac myocytes respond to biomechanical stress by initiating cellular processes that lead to hypertrophy. Although cardiac hypertrophy is a response to increased stress on the heart, it is also associated with elevated plasma catecholamine levels and an increase in cardiac morbidity and mortality. Understanding the cellular signals that initiate the hypertrophic response is of critical importance in identifying pathways that mediate the hypertrophic heart's maladaptive deterioration to cardiac failure. Here we present data demonstrating an important role for G protein-coupled receptors in the induction of in vivo cardiac hypertrophy and the activation of signaling pathways, such as the mitogen activated protein kinase and phosphoinositide-3 kinase pathways.

Background: A long-standing hypothesis has been that hypertrophy is compensatory and by normalizing wall stress acts to maintain normal cardiac function. Epidemiological data, however, have shown that cardiac hypertrophy is associated with increased mortality, thus casting doubt on the validity of this hypothesis., Methods and Results: To determine whether cardiac hypertrophy is necessary to preserve cardiac function, we used 2 genetically altered mouse models that have an attenuated hypertrophic response to 8 weeks of pressure overload. End-systolic wall stress (sigma(es)) obtained by sonomicrometry after 1 week of pressure overload showed complete normalization of sigma(es) in pressure-overloaded wild-type mice (287+/-39 versus sham, 254+/-34 g/cm2), whereas the blunted hypertrophic response in the transgenic mice was inadequate to normalize sigma(es) (415+/-81 g/cm2, P<0.05). Remarkably, despite inadequate normalization of sigma(es), cardiac function as measured by serial echocardiography showed little deterioration in either of the pressure-overloaded genetic models with blunted hypertrophy. In contrast, wild-type mice with similar pressure overload showed a significant increase in chamber dimensions and progressive deterioration in cardiac function. Analysis of downstream signaling pathways in the late stages of pressure overload suggests that phosphoinositide 3-kinase may play a pivotal role in the transition from hypertrophy to heart failure., Conclusions: These data suggest that under conditions of pressure overload, the development of cardiac hypertrophy and normalization of wall stress may not be necessary to preserve cardiac function, as previously hypothesized.

Activation of phosphoinositide 3-kinases is coupled to both phosphotyrosine/growth factor and G protein-coupled receptors. We explored the role of phosphoinositide 3-kinase activation in myocardium during in vivo pressure overload hypertrophy in mice. Cytosolic extracts from wild type hypertrophied hearts showed a selective increase in the phosphoinositide 3-kinase gamma isoform. To address the role of G protein-coupled receptor-mediated activation of phosphoinositide 3-kinase, we used transgenic mice with cardiac-specific overexpression of a Gbetagamma sequestering peptide. Extracts from hypertrophied transgenic hearts showed complete loss of phosphoinositide 3-kinase activation, indicating a Gbetagamma-dependent process. To determine the class of G proteins that contribute Gbetagamma dimers for in vivo phosphoinositide 3-kinase activation, two strategies were used: 1) transgenic mice with cardiac-specific overexpression of a G(q) inhibitor peptide and 2) pertussis toxin treatment prior to pressure overload in wild type mice. Pressure overloaded G(q) inhibitor transgenic mice showed a complete absence of phosphoinositide 3-kinase activation, whereas pretreatment with pertussis toxin showed robust phosphoinositide 3-kinase activation. Taken together, these data demonstrate that activation of the phosphoinositide 3-kinase during in vivo pressure overload hypertrophy is Gbetagamma-dependent and the Gbetagamma dimers arise from stimulation of G(q)-coupled receptors.