Integrative Physiology Reversibility of Adverse, Calcineurin-Dependent Cardiac Remodeling

Rationale: Studies to dissect the role of calcineurin in pathological cardiac remodeling have relied heavily on murine models, in which genetic gain-and loss-of-function manipulations are initiated at or before birth. However, the great majority of clinical cardiac pathology occurs in adults. Yet nothing is known about the effects of calcineurin when its activation commences in adulthood. Furthermore, despite the fact that ventricular hypertrophy is a well-established risk factor for heart failure, the relative pace and progression of these 2 major phenotypic features of heart disease are unknown. Finally, even though therapeutic interventions in adults are designed to slow, arrest, or reverse disease pathogenesis, little is known about the capacity for spontaneous reversibility of calcineurin-dependent pathological remodeling. Objective: We set out to address these 3 questions by studying mice engineered to harbor in cardiomyocytes a constitutively active calcineurin transgene driven by a tetracycline-responsive promoter element. to determine the natural history of disease pathogenesis, and to determine when, if ever, these events are reversible. Activation of the calcineurin transgene in adult mice triggered rapid and robust cardiac growth with features characteristic of pathological hypertrophy. Concentric hypertrophy preceded the development of systolic dysfunction, fetal gene activation, fibrosis, and clinical heart failure. Furthermore, cardiac hypertrophy reversed spontaneously when calcineurin activity was turned off, and expression of fetal genes reverted to baseline. Fibrosis, a prominent feature of pathological cardiac remodeling, manifested partial reversibility. Conclusions: Together, these data establish and define the deleterious effects of calcineurin signaling in the adult heart and reveal that calcineurin-dependent hypertrophy with concentric geometry precedes systolic dysfunction and heart failure. Furthermore, these findings demonstrate that during much of the disease process, calcineurin-dependent remodeling remains reversible. S trong epidemiological evidence links left ventricular hypertrophy with adverse cardiovascular events, including heart failure and death. 1– 4 Consistent with this, current therapies that improve clinical outcomes are often associated with regression of ventricular hypertrophy. 5–7 However, whereas significant strides have been made recently in elucidating the molecular circuitry governing pathological cardiac remodeling, 8 few therapies in clinical use target hypertrophic growth mechanisms directly. Calcineurin is a cytoplasmic protein phosphatase implicated in the pathogenesis of cardiac hypertrophy and heart failure. 9 Calcineurin dephosphorylates transcription factors of the NFAT (nuclear factor of activated T cells) family, resulting in their translocation to the nucleus and triggering of a complex transcriptional program. 10 Calcineurin also targets other proteins to activate nontranscriptional signaling cascades. Consistent with widespread involvement in …