Wnt11 in regulation of physiological and pathological cardiac growth.

Wnt11 regulates early cardiac development and left ventricular compaction in the heart, but it is not known how Wnt11 regulates postnatal cardiac maturation and response to cardiac stress in the adult heart. We studied cell proliferation/maturation in postnatal and adolescent Wnt11 deficient (Wnt11-/-) heart and subjected adult mice with partial (Wnt11+/-) and complete Wnt11 (Wnt11-/-) deficiency to cardiac pressure overload. In addition, we subjected primary cardiomyocytes to recombinant Wnt proteins to study their effect on cardiomyocyte growth. Wnt11 deficiency did not affect cardiomyocyte proliferation or maturation in the postnatal or adolescent heart. However, Wnt11 deficiency led to enlarged heart phenotype that was not accompanied by significant hypertrophy of individual cardiomyocytes. Analysis of stressed adult hearts from wild-type mice showed a progressive decrease in Wnt11 expression in response to pressure overload. When studied in experimental cardiac pressure overload, Wnt11 deficiency did not exacerbate cardiac hypertrophy or remodeling and cardiac function remained identical between the genotypes. When subjecting cardiomyocytes to hypertrophic stimulus, the presence of recombinant Wnt11 together with Wnt5a reduced protein synthesis. In conclusion, Wnt11 deficiency does not affect postnatal cardiomyocyte proliferation but leads to cardiac growth. Interestingly, Wnt11 deficiency alone does not substantially modulate hypertrophic response to pressure overload in vivo. Wnt11 may require cooperation with other noncanonical Wnt proteins to regulate hypertrophic response under stress.

MiR-185-5p regulates the development of myocardial fibrosis.

BACKGROUND: Cardiac fibrosis stiffens the ventricular wall, predisposes to cardiac arrhythmias and contributes to the development of heart failure. In the present study, our aim was to identify novel miRNAs that regulate the development of cardiac fibrosis and could serve as potential therapeutic targets for myocardial fibrosis. METHODS AND RESULTS: Analysis for cardiac samples from sudden cardiac death victims with extensive myocardial fibrosis as the primary cause of death identified dysregulation of miR-185-5p. Analysis of resident cardiac cells from mice subjected to experimental cardiac fibrosis model showed induction of miR-185-5p expression specifically in cardiac fibroblasts. In vitro, augmenting miR-185-5p induced collagen production and profibrotic activation in cardiac fibroblasts, whereas inhibition of miR-185-5p attenuated collagen production. In vivo, targeting miR-185-5p in mice abolished pressure overload induced cardiac interstitial fibrosis. Mechanistically, miR-185-5p targets apelin receptor and inhibits the anti-fibrotic effects of apelin. Finally, analysis of left ventricular tissue from patients with severe cardiomyopathy showed an increase in miR-185-5p expression together with pro-fibrotic TGF-ß1 and collagen I. CONCLUSIONS: Our data show that miR-185-5p targets apelin receptor and promotes myocardial fibrosis.

GSK3ß Serine 389 Phosphorylation Modulates Cardiomyocyte Hypertrophy and Ischemic Injury.

Prior studies show that glycogen synthase kinase 3ß (GSK3ß) contributes to cardiac ischemic injury and cardiac hypertrophy. GSK3ß is constitutionally active and phosphorylation of GSK3ß at serine 9 (S9) inactivates the kinase and promotes cellular growth. GSK3ß is also phosphorylated at serine 389 (S389), but the significance of this phosphorylation in the heart is not known. We analyzed GSK3ß S389 phosphorylation in diseased hearts and utilized overexpression of GSK3ß carrying ser→ala mutations at S9 (S9A) and S389 (S389A) to study the biological function of constitutively active GSK3ß in primary cardiomyocytes. We found that phosphorylation of GSK3ß at S389 was increased in left ventricular samples from patients with dilated cardiomyopathy and ischemic cardiomyopathy, and in hearts of mice subjected to thoracic aortic constriction. Overexpression of either GSK3ß S9A or S389A reduced the viability of cardiomyocytes subjected to hypoxia-reoxygenation. Overexpression of double GSK3ß mutant (S9A/S389A) further reduced cardiomyocyte viability. Determination of protein synthesis showed that overexpression of GSK3ß S389A or GSK3ß S9A/S389A increased both basal and agonist-induced cardiomyocyte growth. Mechanistically, GSK3ß S389A mutation was associated with activation of mTOR complex 1 signaling. In conclusion, our data suggest that phosphorylation of GSK3ß at S389 enhances cardiomyocyte survival and protects from cardiomyocyte hypertrophy.

Characterization of apela, a novel endogenous ligand of apelin receptor, in the adult heart.

The G protein-coupled apelin receptor regulates important processes of the cardiovascular homeostasis, including cardiac development, cardiac contractility, and vascular tone. Most recently, a novel endogenous peptide ligand for the apelin receptor was identified in zebrafish, and it was named apela/elabela/toddler. The peptide was originally considered as an exclusively embryonic regulator, and so far its function in the adult organism remains elusive. We show here that apela is predominantly expressed in the non-cardiomyocyte fraction in the adult rodent heart. We also provide evidence that apela binds to apelin receptors in the heart. Using isolated adult rat hearts, we demonstrate, that just like the fellow receptor agonist apelin, apela increases cardiac contractility and induces coronary vasodilation already in the nanomolar level. The inotropic effect, as revealed by Western blot analysis, is accompanied by a significant increase in extracellular signal-regulated kinase (ERK) 1/2 phosphorylation. Pharmacological inhibition of ERK1/2 activation markedly attenuates the apela-induced inotropy. Analysis of samples from infarcted mouse hearts showed that expression of both apela and apelin receptor is induced in failing mouse hearts and correlate with left ventricular ejection fraction. Hence, we conclude that apela is present in the adult heart, is upregulated in post-infarction cardiac remodeling, and increases cardiac contractility in an ERK1/2-dependent manner.