Research : Cardiac Signal Transduction and Cellular Biology Laboratory

Research Directions

Left ventricular hypertrophy is a major risk factor for the development of heart failure, a syndrome of great public heath significance, contributing to 300,000 deaths each year in the U.S. alone. At the cellular level, myocyte hypertrophy is the primary response of the heart to chronic stress. In disease, this non-mitotic growth is accompanied by changes in gene expression, ion fluxes and metabolism that can affect cardiac contractility and induce myocyte apoptosis and interstitial myocardial fibrosis. This pathologic remodeling is the proximate cause of heart failure and the associated morbidity and mortality.

What regulates pathologic cardiac hypertrophy? The Kapiloff Laboratory has a longstanding interest in the signal transduction pathways involved in pathological cardiac remodeling. In particular, we have focused on identifying signaling molecules that might be therapeutically targeted to prevent the pathological cardiac hypertrophy that leads to heart failure. More recently, we have expanded our interests to study similar signaling pathways involved in stroke. We have found that insights relating to myocyte hypertrophy are germane to our understanding of neuronal survival after stroke. Through a robust combination of biochemistry, cell biology, and in vivo physiology, our laboratory strives to push forward the frontiers of basic cardiovascular biology using comprehensive state-of-the art technologies.

mAKAP: Specificity and efficacy in intracellular signal transduction is often conferred by the anchoring and co-localization of key enzymes and their upstream activators and substrate effectors by scaffold proteins. A major focus of our laboratory has been the characterization of multimolecular signaling complexes organized by the scaffold protein mAKAP in myocytes and neurons. We have shown that at the nuclear envelope, mAKAP “signalosomes” transduce cAMP, mitogen-activated protein kinase, Ca2+, and hypoxic signals regulating the transcription factors NFATc, MEF2 and HIF-1α. We have recently characterized a new mAKAP conditional knock-out mouse, showing that mAKAP expression in the heart is required for pathological remodeling. Cardiac myocyte-specific mAKAP knock-out diminished the heart failure induced by long term pressure overload, improving survival. We are continuing to study signaling by mAKAP complexes in vitro, including the ongoing characterization of both past and newly identified mAKAP binding partners. For example, we have been developing live cell imaging tools to study the local regulation of cAMP fluxes by the adenylyl cyclase (AC5) and phosphodiesterase (PDE4D3) bound to mAKAP at the nuclear envelope.

Anchoring Disruptor Therapeutics: Our research into mAKAP complexes has led to the identification of novel targets for the treatment of heart failure. In particular, we have recently discovered that type 3 p90 ribosomal S6 kinase (RSK3) is required for pathological remodeling. In mice subjected to pressure overload, RSK3 knock-out attenuated the induction of both left ventricular hypertrophy and genetic markers of remodeling, without a deleterious effect on cardiac function. RSK3 knock-out also was protective in models of catecholamine toxicity and familial hypertrophic cardiomyopathy. RSK3’s unique N-terminal domain confers high affinity, regulated binding to mAKAP, defining a novel protein-protein interaction that explains the selective binding of that kinase isoform to the scaffold. Remarkably, expression of peptides that disrupt RSK3 anchoring inhibited myocyte hypertrophy in vitro. We are currently developing the use of adeno-associated virus gene therapy to block pathological hypertrophy and the development of heart failure in vivo via expression of the competing peptides.

CIP4: The F-BAR protein CIP4 is a scaffold that regulates membrane deformation and tubulation, organization of the actin cytoskeleton, endocytosis of growth factor receptors, and vesicle trafficking. Little is known about the F-BAR family of membrane-binding proteins in the heart. We have obtained new data showing that CIP4 is a scaffold important for hypertrophic signal transduction. Ongoing studies are defining how CIP4 contributes to myocyte regulation.

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