Gene transfer in eukaryotic cells and organisms suffers from epigenetic effects that result in low or unstable transgene expression and high clonal variability. Use of epigenetic regulators such as matrix attachment regions (MARs) is a promising approach to alleviate such unwanted effects. Dissection of a known MAR allowed the identification of sequence motifs that mediate elevated transgene expression. Bioinformatics analysis implied that these motifs adopt a curved DNA structure that positions nucleosomes and binds specific transcription factors. From these observations, we computed putative MARs from the human genome. Cloning of several predicted MARs indicated that they are much more potent than the previously known element, boosting the expression of recombinant proteins from cultured cells as well as mediating high and sustained expression in mice. Thus we computationally identified potent epigenetic regulators, opening new strategies toward high and stable transgene expression for research, therapeutic production or gene-based therapies.

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 ...