Right Heart Function in Health and Chronic Disease

Veterans Affairs Med Ctr San Francisco, San Francisco CA

Investigators

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Abstract

? DESCRIPTION (provided by applicant): Failure of the right ventricle (RV) is a prevalent cause of cardiovascular morbidity and mortality, and the leading cause of death in patients with pulmonary hypertension. Moreover, RV failure frequently arises in patients with failure of the left ventricle (LV) and causes markedly worse symptoms and prognosis contrasted with patients with LV failure without RV dysfunction. Despite clinical significance, RV failure is relatively understudied, poorly understood and there i a need for more effective therapies to treat RV failure. We reported that the inotropic response to stimulation of ?1-adrenergic receptors (?1-ARs) is fundamentally different in the RV (negative inotropy) vs. LV (positive inotropy). Importantly, in RV failure, ?1-AR inotropic responses are upregulated and switched from a negative inotropic response in non-failing RV to a robust positive inotropic response in failing RV. This renewal project will build on the following recent observations: * Of the two major cardiac ?1-AR subtypes (?1A & ?1B), the dramatic switch from ?1-AR-mediated negative inotropy in non-failing RV to positive inotropy in failing RV is mediated solely by the ?1A-subtype but not the ?1B-subtype, suggesting that ?1A-subtype signaling is upregulated in failing RV. Consistent with beneficial effects mediated by the ?1A-subtype, in a model of RV failure, treatment for 2 wk. with the ?1A-subtype-specific agonist A61603 has major beneficial effects evidenced by improved in- vivo function, and reduced myocardial injury (evidenced by lower serum cardiac TnI, less myocardial fibrosis, and less ultrastructural cellular damage observed in electron micrographs). * Mechanistically, levels of reactive oxygen species (ROS) are elevated in failing RV, and our preliminary studies show that for failing RV, chronic treatment with A61603 increased levels of superoxide dismutase (SOD) and markedly reduced ROS. * ROS increases expression and activity of two intracellular isoforms of matrix-metalloproteinase-2 (MMP-2): the canonical full-length MMP-2 (FL-MMP-2) and a novel N-terminal truncated isoform (NTT-MMP-2). We reported that FL-MMP-2 impairs myocardial force by causing damage to the myofilaments. In contrast, we found that NTT-MMP-2 impairs myocardial force by impairing Ca2+ handling, without damage to myofilaments. * Chronic treatment with A61603 markedly reduces levels of FL-MMP-2 and NTT-MMP-2. Thus, for failing RV, ?1A-subtype-mediated lowering of FL-MMP-2 and NTT-MMP-2 levels may reduce damage to myofilaments and Ca2+ handling. Consistent with this, we found that for failing RV chronic treatment with A61603 increased myofilament function. 1. Hypothesis: For failing RV, chronic ?1A-subtype stimulation causes reduced ROS, which leads to decreased levels of FL-MMP-2 and NTT-MMP-2, and thereby, to reduced damage to myofilaments and Ca2+ handling. 2. Hypothesis: Chronic therapy with a ?1A-subtype agonist is beneficial in a chronic model of RV failure. Aim 1. Determine the mechanisms for the beneficial effects of ?1A-subtype therapy in RV failure. For failing RV, we will determine if the beneficial effects of ?1A therapy with A61603 involves increased SOD, leading to reduced ROS, which results in lower levels of FL-MMP-2 and NTT-MMP-2, and thereby, reduced damage to myofilaments and Ca2+ handling. Aim 2. Determine if chronic ?1A therapy has a beneficial effect on recovery of RV function in a chronic model of already established RV failure. Using a chronic pulmonary stenosis model of established RV failure, we will chronically treat mice for up to 20 wk. with A61603. We will determine if A61603 induces recovery of RV function and outcomes in chronic RV failure, and determine the mechanisms involved.