Targeting signaling pathways in heart failure by gene transfer

Cardiac remodeling and failure: from molecules to man (Part III)

Given the lack of a unified theory of heart failure, future research efforts will be required to unify and synthesize our current understanding of the multiple mechanisms that control remodeling in the failing heart. Matrix remodeling and the associated activation of inflammatory cytokines and MMPs have emerged as key pathways in the development of heart failure. As such, attempts to understand the integrated control of ECM homeostasis with the bioactivation of inflammatory cytokines may be of particular relevance to the development of effective anti-remodeling approaches. Notably, the implantation of isolated populations of cells in failing myocardium has a profound and consistent anti-remodeling effect that limits the progression to CHF. These observations were consistently identified in numerous studies using diverse experimental animal models and varied cell types. Accordingly, multicenter clinical trials are underway, and the preliminary data in patients with CHF are encouraging. Despite the enormous promise of cell transplantation to restore and regenerate failing myocardium, the mechanisms underlying these profound biological effects are not understood. An improved understanding of the myocardial response to cell implantation, particularly on parameters of matrix remodeling, may help unify our current understanding of the progression of heart failure and optimize the development of this technique for its evolving therapeutic use. The following review outlines recent advances in medical and surgical approaches to control the remodeling process that underlies the progression of heart failure.

Alterations in early action potential repolarization causes localized failure of sarcoplasmic reticulum Ca2+ release

Depressed contractility of failing myocytes involves a decreased rate of rise of the Ca2+ transient. Synchronization of Ca2+ release from the junctional sarcoplasmic reticulum (SR) is responsible for the rapid rise of the normal Ca2+ transient. This study examined the idea that spatially and temporally dyssynchronous SR Ca2+ release slows the rise of the cytosolic Ca2+ transient in failing feline myocytes. Left ventricular hypertrophy (LVH) with and without heart failure (HF) was induced in felines by constricting the ascending aorta. Ca2+ transients were measured in ventricular myocytes using confocal line scan imaging. Ca2+ transients were induced by field stimulation, square wave voltage steps, or action potential (AP) voltage clamp. SR Ca2+ release was significantly less well spatially and temporally synchronized in field-stimulated HF versus control or LVH myocytes. Surprisingly, depolarization of HF cells to potentials where Ca2+ currents (ICa) were maximal resynchronized SR Ca2+ release. Correspondingly, decreases in the amplitude of ICa desynchronized SR Ca2+ release in control, LVH, and HF myocytes to the same extent. HF myocytes had significant loss of phase 1 AP repolarization and smaller ICa density, which should both reduce Ca2+ influx. When normal myocytes were voltage clamped with HF AP profiles SR Ca2+ release was desynchronized. SR Ca2+ release becomes dyssynchronized in failing feline ventricular myocytes because of reductions in Ca2+ influx induced in part by alterations in early repolarization of the AP. Therefore, therapies that restore normal early repolarization should improve the contractility of the failing heart.

Cardiovascular Gene Therapy: Angiogenesis and Beyond

Recent advances in understanding the mechanisms of disease have produced many new targets for gene therapy. However, it has been difficult to convert these new insights into clinically useful applications. In the field of cardiovascular medicine, most clinical studies of gene therapy have focused on angiogenesis as a treatment for ischemia. Initial enthusiasm was supported by small, uncontrolled, phase 1 trials. However, several large efficacy studies have recently been published that have not shown clinically significant improvement, and a few well-publicized complications of gene therapy have cast a pall over the entire field. In this review, we will summarize specific technical aspects of cardiovascular gene therapy, examine the recent series of clinical studies, and explore the direction of future work for the principal cardiovascular diseases.