McCulloch, Andrew D.

Heart failure with preserved ejection fraction (HFpEF), a major public health problem that is rising in prevalence, is associated with high morbidity and mortality and is considered to be the greatest unmet need in cardiovascular medicine today because of a general lack of effective treatments. To address this challenging syndrome, the National Heart, Lung, and Blood Institute convened a working group made up of experts in HFpEF and novel research methodologies to discuss research gaps and to prioritize research directions over the next decade. Here, we summarize the discussion of the working group, followed by key recommendations for future research priorities. There was uniform recognition that HFpEF is a highly integrated, multiorgan, systemic disorder requiring a multipronged investigative approach in both humans and animal models to improve understanding of mechanisms and treatment of HFpEF. It was recognized that advances in the understanding of basic mechanisms and the roles of inflammation, macrovascular and microvascular dysfunction, fibrosis, and tissue remodeling are needed and ideally would be obtained from (1) improved animal models, including large animal models, which incorporate the effects of aging and associated comorbid conditions; (2) repositories of deeply phenotyped physiological data and human tissue, made accessible to researchers to enhance collaboration and research advances; and (3) novel research methods that take advantage of computational advances and multiscale modeling for the analysis of complex, high-density data across multiple domains. The working group emphasized the need for interactions among basic, translational, clinical, and epidemiological scientists and across organ systems and cell types, leveraging different areas or research focus, and between research centers. A network of collaborative centers to accelerate basic, translational, and clinical research of pathobiological mechanisms and treatment strategies in HFpEF was discussed as an example of a strategy to advance research progress. This resource would facilitate comprehensive, deep phenotyping of a multicenter HFpEF patient cohort with standardized protocols and a robust biorepository. The research priorities outlined in this document are meant to stimulate scientific advances in HFpEF by providing a road map for future collaborative investigations among a diverse group of scientists across multiple domains.

Key points Mutations in the caveolae scaffolding protein, caveolin‐3 (Cav3), have been linked to the long QT type 9 inherited arrhythmia syndrome (LQT9) and the cause of underlying action potential duration prolongation is incompletely understood. In the present study, we show that LQT9 Cav3 mutations, F97C and S141R, cause mutation‐specific gain of function effects on Cav1.2‐encoded L‐type Ca2+ channels responsible for ICa,L and also cause loss of function effects on heterologously expressed Kv4.2 and Kv4.3 channels responsible for Ito. A computational model of the human ventricular myocyte action potential suggests that the major ionic current change causing action potential duration prolongation in the presence of Cav3‐F97C is the slowly inactivating ICa,L but, for Cav3‐S141R, both increased ICa,L and increased late Na+ current contribute equally to action potential duration prolongation. Overall, the LQT9 Cav3‐F97C and Cav3‐S141R mutations differentially impact multiple ionic currents, highlighting the complexity of Cav3 regulation of cardiac excitability and suggesting mutation‐specific therapeutic approaches. AbstractMutations in the CAV3 gene encoding caveolin‐3 (Cav3), a scaffolding protein integral to caveolae in cardiomyocytes, have been associated with the congenital long‐QT syndrome (LQT9). Initial studies demonstrated that LQT9‐associated Cav3 mutations, F97C and S141R, increase late sodium current as a potential mechanism to prolong action potential duration (APD) and cause LQT9. Whether these Cav3 LQT9 mutations impact other caveolae related ion channels remains unknown. We used the whole‐cell, patch clamp technique to characterize the effect of Cav3‐F97C and Cav3‐S141R mutations on heterologously expressed Cav1.2+Cavβ2cN4 channels, as well as Kv4.2 and Kv4.3 channels, in HEK 293 cells. Expression of Cav3‐S141R increased ICa,L density without changes in gating properties, whereas expression of Cav3‐F97C reduced Ca2+‐dependent inactivation of ICa,L without changing current density. The Cav3‐F97C mutation reduced current density and altered the kinetics of IKv4.2 and IKv4.3 and also slowed recovery from inactivation. Cav3‐S141R decreased current density and also slowed activation kinetics and recovery from inactivation of IKv4.2 but had no effect on IKv4.3. Using the O'Hara–Rudy computational model of the human ventricular myocyte action potential, the Cav3 mutation‐induced changes in Ito are predicted to have negligible effect on APD, whereas blunted Ca2+‐dependent inactivation of ICa,L by Cav3‐F97C is predicted to be primarily responsible for APD prolongation, although increased ICa,L and late INa by Cav3‐S141R contribute equally to APD prolongation. Thus, LQT9 Cav3‐associated mutations, F97C and S141R, produce mutation‐specific changes in multiple ionic currents leading to different primary causes of APD prolongation, which suggests the use of mutation‐specific therapeutic approaches in the future.

The National Heart, Lung, and Blood Institute (NHLBI) convened a workshop of cardiologists, cardiac electrophysiologists, cell biophysicists, and computational modelers on August 20 and 21, 2007, in Washington, DC, to advise the NHLBI on new research directions needed to develop integrative approaches to elucidate human cardiac function. The workshop strove to identify limitations in the use of data from nonhuman animal species for elucidation of human electromechanical function/activity and to identify what specific information on ion channel kinetics, calcium handling, and dynamic changes in the intracellular/extracellular milieu is needed from human cardiac tissues to develop more robust computational models of human cardiac electromechanical activity. This article summarizes the workshop discussions and recommendations on the following topics: (1) limitations of animal models and differences from human electrophysiology, (2) modeling ion channel structure/function in the context of whole-cell electrophysiology, (3) excitation–contraction coupling and regulatory pathways, (4) whole-heart simulations of human electromechanical activity, and (5) what human data are currently needed and how to obtain them. The recommendations can be found on the NHLBI Web site at http://www.nhlbi.nih.gov/meetings/workshops/electro.htm.