Jenny Y.Y. Ooi

Ibrutinib increases the risk of atrial fibrillation, potentially through inhibition of cardiac PI3K-Akt signaling

To the editor: The Bruton’s tyrosine kinase (BTK) inhibitor ibrutinib sets a new standard of care for the treatment of patients with relapsed or refractory chronic lymphocytic leukemia (CLL)[1][1],[2][2] and mantle cell lymphoma (MCL).[3][3] Ibrutinib is generally well tolerated and largely

Pathophysiology of cardiac hypertrophy and heart failure: signaling pathways and novel therapeutic targets

Abstract The onset of heart failure is typically preceded by cardiac hypertrophy, a response of the heart to increased workload, a cardiac insult such as a heart attack or genetic mutation. Cardiac hypertrophy is usually characterized by an increase in cardiomyocyte size and thickening of ventricular walls. Initially, such growth is an adaptive response to maintain cardiac function; however, in settings of sustained stress and as time progresses, these changes become maladaptive and the heart ultimately fails. In this review, we discuss the key features of pathological cardiac hypertrophy and the numerous mediators that have been found to be involved in the pathogenesis of cardiac hypertrophy affecting gene transcription, calcium handling, protein synthesis, metabolism, autophagy, oxidative stress and inflammation. We also discuss new mediators including signaling proteins, microRNAs, long noncoding RNAs and new findings related to the role of calcineurin and calcium-/calmodulin-dependent protein kinases. We also highlight mediators and processes which contribute to the transition from adaptive cardiac remodeling to maladaptive remodeling and heart failure. Treatment strategies for heart failure commonly include diuretics, angiotensin converting enzyme inhibitors, angiotensin II receptor blockers and β-blockers; however, mortality rates remain high. Here, we discuss new therapeutic approaches (e.g., RNA-based therapies, dietary supplementation, small molecules) either entering clinical trials or in preclinical development. Finally, we address the challenges that remain in translating these discoveries to new and approved therapies for heart failure.

Vascular histone deacetylation by pharmacological HDAC inhibition

HDAC inhibitors can regulate gene expression by post-translational modification of histone as well as nonhistone proteins. Often studied at single loci, increased histone acetylation is the paradigmatic mechanism of action. However, little is known of the extent of genome-wide changes in cells stimulated by the hydroxamic acids, TSA and SAHA. In this article, we map vascular chromatin modifications including histone H3 acetylation of lysine 9 and 14 (H3K9/14ac) using chromatin immunoprecipitation (ChIP) coupled with massive parallel sequencing (ChIP-seq). Since acetylation-mediated gene expression is often associated with modification of other lysine residues, we also examined H3K4me3 and H3K9me3 as well as changes in CpG methylation (CpG-seq). RNA sequencing indicates the differential expression of ∼30% of genes, with almost equal numbers being up- and down-regulated. We observed broad deacetylation and gene expression changes conferred by TSA and SAHA mediated by the loss of EP300/CREBBP binding at multiple gene promoters. This study provides an important framework for HDAC inhibitor function in vascular biology and a comprehensive description of genome-wide deacetylation by pharmacological HDAC inhibition.

The small-molecule BGP-15 protects against heart failure and atrial fibrillation in mice

Heart failure (HF) and atrial fibrillation (AF) share common risk factors, frequently coexist and are associated with high mortality. Treatment of HF with AF represents a major unmet need. Here we show that a small molecule, BGP-15, improves cardiac function and reduces arrhythmic episodes in two independent mouse models, which progressively develop HF and AF. In these models, BGP-15 treatment is associated with increased phosphorylation of the insulin-like growth factor 1 receptor (IGF1R), which is depressed in atrial tissue samples from patients with AF. Cardiac-specific IGF1R transgenic overexpression in mice with HF and AF recapitulates the protection observed with BGP-15. We further demonstrate that BGP-15 and IGF1R can provide protection independent of phosphoinositide 3-kinase-Akt and heat-shock protein 70; signalling mediators often defective in the aged and diseased heart. As BGP-15 is safe and well tolerated in humans, this study uncovers a potential therapeutic approach for HF and AF.

Therapeutic silencing of miR-652 restores heart function and attenuates adverse remodeling in a setting of established pathological hypertrophy

Expression of microRNA‐652 (miR‐652) increases in the diseased heart, decreases in a setting of cardioprotection, and is inversely correlated with heart function. The aim of this study was to assess the therapeutic potential of inhibiting miR‐652 in a mouse model with established pathological hypertrophy and cardiac dysfunction due to pressure overload. Mice were subjected to a sham operation or transverse aortic constriction (TAC) for 4 wk to induce hypertrophy and cardiac dysfunction, followed by administration of a locked nucleic acid (LNA)‐antimiR‐652 (miR‐652 inhibitor) or LNA control. Cardiac function was assessed before and 8 wk post‐treatment. Expression of miR‐652 increased in hearts subjected to TAC compared to sham surgery (2.9‐fold), and this was suppressed by ~95% in LNA‐antimiR‐652‐treated TAC mice. Inhibition of miR‐652 improved cardiac function in TAC mice (fractional shortening:29±1% at 4 wk post‐TAC compared to 35±1% post‐treatment) and attenuated cardiac hypertrophy. Improvement in heart function was associated with reduced cardiac fibrosis, less apoptosis and B‐type natriuretic peptide gene expression, and preserved angiogenesis. Mechanistically, we identified Jagged1 (a Notch1 ligand) as a novel direct target of miR‐652. In summary, these studies provide the first evidence that silencing of miR‐652 protects the heart against pathological remodeling and improves heart function.—Bernardo, B. C., Nguyen, S. S., Winbanks, C. E., Gao, X.‐M., Boey, E. J. H., Tham, Y. K., Kiriazis, H., Ooi, J. Y. Y., Porrello, E. R., Igoor, S., Thomas, C. J., Gregorevic, P., Lin, R. C. Y., Du, X.‐J., McMullen, J. R. Therapeutic silencing of miR‐652 restores heart function and attenuates adverse remodeling in a setting of established pathological hypertrophy. FASEB J. 28, 5097–5110 (2014). www.fasebj.org

Silencing of miR-34a Attenuates Cardiac Dysfunction in a Setting of Moderate, but Not Severe, Hypertrophic Cardiomyopathy

Therapeutic inhibition of the miR-34 family (miR-34a,-b,-c), or miR-34a alone, have emerged as promising strategies for the treatment of cardiac pathology. However, before advancing these approaches further for potential entry into the clinic, a more comprehensive assessment of the therapeutic potential of inhibiting miR-34a is required for two key reasons. First, miR-34a has ∼40% fewer predicted targets than the miR-34 family. Hence, in cardiac stress settings in which inhibition of miR-34a provides adequate protection, this approach is likely to result in less potential off-target effects. Secondly, silencing of miR-34a alone may be insufficient in settings of established cardiac pathology. We recently demonstrated that inhibition of the miR-34 family, but not miR-34a alone, provided benefit in a chronic model of myocardial infarction. Inhibition of miR-34 also attenuated cardiac remodeling and improved heart function following pressure overload, however, silencing of miR-34a alone was not examined. The aim of this study was to assess whether inhibition of miR-34a could attenuate cardiac remodeling in a mouse model with pre-existing pathological hypertrophy. Mice were subjected to pressure overload via constriction of the transverse aorta for four weeks and echocardiography was performed to confirm left ventricular hypertrophy and systolic dysfunction. After four weeks of pressure overload (before treatment), two distinct groups of animals became apparent: (1) mice with moderate pathology (fractional shortening decreased ∼20%) and (2) mice with severe pathology (fractional shortening decreased ∼37%). Mice were administered locked nucleic acid (LNA)-antimiR-34a or LNA-control with an eight week follow-up. Inhibition of miR-34a in mice with moderate cardiac pathology attenuated atrial enlargement and maintained cardiac function, but had no significant effect on fetal gene expression or cardiac fibrosis. Inhibition of miR-34a in mice with severe pathology provided no therapeutic benefit. Thus, therapies that inhibit miR-34a alone may have limited potential in settings of established cardiac pathology.

HDAC inhibition attenuates cardiac hypertrophy by acetylation and deacetylation of target genes

Pharmacological histone deacetylase (HDAC) inhibitors attenuate pathological cardiac remodeling and hypertrophic gene expression; yet, the direct histone targets remain poorly characterized. Since the inhibition of HDAC activity is associated with suppressing hypertrophy, we hypothesized histone acetylation would target genes implicated in cardiac remodeling. Trichostatin A (TSA) regulates cardiac gene expression and attenuates transverse aortic constriction (TAC) induced hypertrophy. We used chromatin immunoprecipitation (ChIP) coupled with massive parallel sequencing (ChIP-seq) to map, for the first time, genome-wide histone acetylation changes in a preclinical model of pathological cardiac hypertrophy and attenuation of pathogenesis with TSA. Pressure overload-induced cardiac hypertrophy was associated with histone acetylation of genes implicated in cardiac contraction, collagen deposition, inflammation, and extracellular matrix identified by ChIP-seq. Gene set enrichment analysis identified NF-kappa B (NF-κB) transcription factor activation with load induced hypertrophy. Increased histone acetylation was observed on the promoters of NFκB target genes (Icam1, Vcam1, Il21r, Il6ra, Ticam2, Cxcl10) consistent with gene activation in the hypertrophied heart. Surprisingly, TSA attenuated pressure overload-induced cardiac hypertrophy and the suppression of NFκB target genes by broad histone deacetylation. Our results suggest a mechanism for cardioprotection subject to histone deacetylation as a previously unknown target, implicating the importance of inflammation by pharmacological HDAC inhibition. The results of this study provides a framework for HDAC inhibitor function in the heart and argues the long held views of acetylation is subject to more flexibility than previously thought.

The therapeutic potential of miRNAs regulated in settings of physiological cardiac hypertrophy

Cardiac hypertrophy is broadly defined as an increase in heart mass. Heart enlargement in a setting of cardiac disease is referred to as pathological hypertrophy and often progresses to heart failure. Physiological hypertrophy refers to heart growth in response to postnatal development, exercise training and pregnancy, and is an adaptive response associated with the activation of cardioprotective signaling cascades. miRNAs have emerged as novel therapeutic targets for numerous pathologies, and miRNA-based therapies have already entered clinical trials. The identification of miRNAs differentially regulated during physiological growth may open up new therapeutic approaches for heart failure. In this review, we present information on miRNAs regulated in models of physiological hypertrophy, describe preclinical cardiac disease studies that have successfully targeted miRNAs regulated in settings of physiological growth (miR-34, miR-15, miR-199b, miR-208a and miR-378), and discuss challenges to overcome for the safe entry of miRNA-based therapies into the clinic for heart failure patients.

Identification of miR-34 regulatory networks in settings of disease and antimiR-therapy: Implications for treating cardiac pathology and other diseases

ABSTRACT Expression of the miR-34 family (miR-34a, -34b, -34c) is elevated in settings of heart disease, and inhibition with antimiR-34a/antimiR-34 has emerged as a promising therapeutic strategy. Under chronic cardiac disease settings, targeting the entire miR-34 family is more effective than targeting miR-34a alone. The identification of transcription factor (TF)-miRNA regulatory networks has added complexity to understanding the therapeutic potential of miRNA-based therapies. Here, we sought to determine whether antimiR-34 targets secondary miRNAs via TFs which could contribute to antimiR-34-mediated protection. Using miRNA-Seq we identified differentially regulated miRNAs in hearts from mice with cardiac pathology due to transverse aortic constriction (TAC), and focused on miRNAs which were also regulated by antimiR-34. Two clusters of stress-responsive miRNAs were classified as “pathological” and “cardioprotective,” respectively. Using ChIPBase we identified 45 TF binding sites on the promoters of “pathological” and “cardioprotective” miRNAs, and 5 represented direct targets of miR-34, with the capacity to regulate other miRNAs. Knockdown studies in a cardiomyoblast cell line demonstrated that expression of 2 “pathological” miRNAs (let-7e, miR-31) was regulated by one of the identified TFs. Furthermore, by qPCR we confirmed that expression of let-7e and miR-31 was lower in hearts from antimiR-34 treated TAC mice; this may explain why targeting the entire miR-34 family is more effective than targeting miR-34a alone. Finally, we showed that Acsl4 (a common target of miR-34, let-7e and miR-31) was increased in hearts from TAC antimiR-34 treated mice. In summary, antimiR-34 regulates the expression of other miRNAs and this has implications for drug development.

MicroRNAs differentially regulated in cardiac and skeletal muscle in health and disease: potential drug targets?

The identification of non‐coding RNA species, previously thought of as ‘junk’ DNA, adds a new dimension of complexity to the regulation of DNA, RNA and protein. MicroRNAs are short non‐coding RNA species that control gene expression, are dysregulated in settings of cardiac and skeletal muscle disease and have emerged as promising therapeutic targets. MicroRNAs specifically enriched in cardiac and skeletal muscle are called myomiRs and play an important role in cardiac pathology and skeletal muscle biology. Moreover, microRNA profiles are altered in response to exercise and disease; thus, their potential as therapeutic drug targets is being widely explored. In the cardiovascular field, therapeutic inhibition of microRNAs has been shown to be effective in improving cardiac outcome in preclinical cardiac disease models. MicroRNAs that promote skeletal muscle regeneration are attractive therapeutic targets in muscle wasting conditions where regenerative capacity is compromised.