Understanding the physiology of heart failure through cellular and in vivo models-towards targeting of complex mechanisms

Abstract

New Findings: • What is the topic of this review? Heart failure is a progressive disease syndrome that, in the early stages, involves subtle tissue and cellullar changes. This review highlights novel imaging techniques that allow quantitative investigation of the underlying pathophysiological mechanisms in vivo. • What advances does it highlight? High-content voltage imaging of the left ventricle showed significant conduction slowing in the mdx mouse model of heart failure, corresponding to selective loss of Na+ channels and dystrophin in the lateral cardiac myocyte membrane. Super-resolution STED imaging after myocardial infarction uncovered proliferative, differential remodelling of individual T-tubules and network properties leading to intracellular Ca2+ release heterogeneity. These techniques reveal potential mechanisms of arrhythmia susceptibility, tissue degeneration and contractile dysfunction. Heart failure (HF) is a complex disease syndrome, which affects physiology at all levels, from the molecule to the whole organism. Following a causative insult, a maladaptive response occurs, which sustains cardiac remodelling and leads to a final common pathway of debilitating HF symptoms. In terms of mechanisms, distinct defects of excitation-contraction coupling compartments and organelles have been identified in cardiac samples of patients and animal models, which include changes in Ca2+ transport proteins and T-tubules. From a physiological standpoint, the source of regulatory intracellular Ca2+ is defined by ~20,000 Ca2+ release units per cardiac myocyte, which jointly modulate contractile force production. We and others have characterized key changes in protein and membrane components of Ca2+ release units during HF in patient samples and transgenic models to gain insight into complex disease mechanisms. While earlier HF studies identified intracellular Ca2+ release as a major cause of contractile dysfunction, electrical dysfunction has gained attention as an important mechanism of HF mortality. In parallel, high-resolution imaging techniques have become instrumental to understand HF mechanisms in the intact cell and tissue environment, supporting translation of novel diagnostic strategies. Indeed, the increased spatial and temporal resolution of different experimental imaging techniques addresses the vastly different scales of HF pathophysiology, to correlate experimental with clinical surrogate markers, and to extend mechanisms to early, often subtle changes in HF. This last goal, in particular, will be essential to translate novel pathophysiological insight back to the growing number of asymptomatic individuals at increased risk for HF development, who may benefit most from early therapeutic interventions. © 2012 The Physiological Society.