Reversible cardiac fibrosis and heart failure induced by conditional expression of an antisense mRNA of the mineralocorticoid receptor in cardiomyocytes

Abstract

Cardiac failure is a common feature in the evolution of cardiac disease. Among the determinants of cardiac failure, the reninangiotensin-aldosterone system has a central role, and antagonism of the mineralocorticoid receptor (MR) has been proposed as a therapeutic strategy. In this study, we questioned the role of the MR, not of aldosterone, on heart function, using an inducible and cardiac-specific transgenic mouse model. We have generated a conditional knock-down model by expressing solely in the heart an antisense mRNA directed against the murine MR, a transcription factor with unknown targets in cardiomyocytes. Within 2-3 mo, mice developed severe heart failure and cardiac fibrosis in the absence of hypertension or chronic hyperaldosteronism. Moreover, cardiac failure and fibrosis were fully reversible when MR antisense mRNA expression was subsequently suppressed.C ardiac failure is a major health problem with increasing incidence with aging of the population. Cardiac fibrosis is a marker of cardiac failure and a crucial determinant of myocardial heterogeneity, increasing diastolic stiffness, systolic dysfunction, and the propensity for reentry arrhythmias (1). Animal models are necessary to investigate the mechanisms of appearance and regression of cardiac remodeling and to improve therapeutic strategies. In this paper, we report on a conditional mouse transgenic model in which cardiac fibrosis can be induced and reversed. This was achieved by regulating the expression of the mineralocorticoid receptor (MR) in cardiomyocytes.Studies in both experimental animals and humans have suggested that aldosterone excess may have deleterious effects on cardiac function (2). Recently, the Randomized Aldactone Evaluation Study (RALES) showed that treatment of patients experiencing severe heart failure with spironolactone, an antagonist of the aldosterone receptor (mineralocorticoid receptor) used in the treatment of hypertension, improved both morbidity and mortality (3). These findings have resulted in the recommendation of spironolactone use in the treatment of severe heart failure (4). In RALES, the mechanisms and cellular targets involved in the beneficial effect of spironolactone action are largely unknown. Because MR is expressed in both cardiomyocytes (5) and the kidney (6), it has been difficult to separate the direct effects of signaling through the cardiac MR and indirect effects resulting from actions of the drug on renal MR. MR is a ligand-dependent transcription factor of the steroid receptor superfamily (7). In the kidney, aldosterone binding to MR increases sodium reabsorption and potassium excretion (6). Inactivating mutations of MR result in chronic renal salt wasting, and activating mutation of MR causes hypertension, underscoring the essential role of this pathway in sodium balance and the control of blood pressure (8, 9). In the heart, however, the role of MR in physiologic and pathologic situations has not been defined. A MR knockout mouse model is available (10), but these animals die in the first ...

Mechanisms of Mineralocorticoid Action

“…84 In contrast, a recent study by Beggah et al 85 reported that expression of MR antisense, and thus knockdown of the MR in cardiac myocytes, produced severe cardiac hypertrophy and fibrosis that was made worse with spironolactone treatment. It has been suggested that this response is not a specific effect of loss of MR signaling but was in large part attributable to the overexpression of a foreign protein in the myocytes, given that very similar heart failure and pathology was seen in cardiac myocyte overexpression of green fluorescent protein 86 or an inflammatory response to the use of antisense.…”

Of mice and models: improved animal models for biomedical research

“…Cardiac fibrosis arises after knocking-down the mineralocorticoid receptor (MR) in cardiomyocytes. Surprisingly, restoring the expression of MR protein was sufficient to completely reverse cardiopathy (7). D: brain dysfunction and learning/memory.…”

Local renin-angiotensin systems and their interactions with extra-adrenal corticosteroid production

“…Steroid effects will be mediated via the MR also expressed in the tissue. However, this pattern of events has been called into question by Beggah et al 36 They used mice transgenically altered to produce antisense mRNA against the cardiac MR gene in response to a cardiac promoter-specific signal.That is, the animals were subject to a temporally determined, tissue-specific and reversible MR knockout. Paradoxically, this resulted in responses identical to those described above for mineralocorticoid excess.…”