Mice with cardiomyocyte-specific disruption of the endothelin-1 gene are resistant to hyperthyroid cardiac hypertrophy

Abstract

Endothelin 1 (ET-1), a potent vasoconstrictor peptide expressed by endothelium, is also produced in the heart in response to a variety of stresses. It induces hypertrophy in cultured cardiac myocytes but only at concentrations far greater than those found in plasma. We tested whether ET-1 generated by cardiac myocytes in vivo is a local signal for cardiac hypertrophy. To avoid the perinatal lethality seen in systemic ET-1-null mice, we used the Cre͞loxP system to generate mice with cardiac myocyte-specific disruption of the ET-1 gene. We used the ␣-myosin heavy chain promoter to drive expression of Cre and were able to obtain 75% reduction in ET-1 mRNA in cardiac myocytes isolated from these mice at baseline and after stimulation, in vivo, for 24 h with tri-iodothyronine (T3). Necropsy measurements of cardiac mass indexed for body weight showed a 57% reduction in cardiac hypertrophy in response to 16 days of exogenous T3 in mice homozygous for the disrupted ET-1 allele compared to siblings with an intact ET-1 gene. Moreover, in vivo MRI showed only a 3% increase in left ventricular mass indexed for body weight in mice with the disrupted allele after 3 weeks of T3 treatment versus a 27% increase in mice with an intact ET-1 gene. A reduced hypertrophic response was confirmed by planimetry of cardiac myocytes. We conclude that ET-1, produced locally by cardiac myocytes, and acting in a paracrine͞autocrine manner, is an important signal for myocardial hypertrophy that facilitates the response to thyroid hormone. C ardiac hypertrophy is characterized by an increase in myocardiocyte size and is accompanied by qualitative and quantitative changes in gene expression, protein synthesis, and physiological performance (1). Cardiac hypertrophy helps to maintain cardiac output in the presence of increased demand or afterload, yet it is one of the most important predisposing risk factors for sudden death and the development of heart failure in human populations. A greater understanding of hypertrophy, and the capacity to regulate it in human disease, could have profound clinical implications.Many ligand͞receptor systems, with their specific and interwoven downstream signaling pathways, have been implicated in cardiomyocyte hypertrophy in both cell culture and intact animals (reviewed in ref.2). These include the peptide endothelin 1 (ET-1) and its receptors ET A and ET B on the cell surface of cardiomyocytes. Several lines of evidence suggest that ET-1 functions in a paracrine͞autocrine manner in cardiac hypertrophy. In cell cultures of cardiomyocytes, ET-1 induces hypertrophy as assessed by cell size, increased myofibrillogenesis, and transcriptional changes associated with cardiac hypertrophy such as expression of atrial natriuretic factor (3, 4). Of note, in these studies the concentrations of ET-1 required to produce hypertrophy were 10 Ϫ7 to 10 Ϫ9 M, far greater than those encountered in plasma (10 Ϫ12 to 10 Ϫ13 M) (5). Although cardiac synthesis of ET-1 is negligible under normal circumstances, conditions that stimulate...

Requirement of Nuclear Factor-κB in Angiotensin II– and Isoproterenol-Induced Cardiac Hypertrophy In Vivo

“…6 Less IB␣⌬N protein is detected in heart tissue extracts from ⌬N MHC compared with ⌬N ubi mice because of up to 70% nonmyocytes in whole-heart extracts ( Figure 1C). 6 In addition, Cre MHC mice exhibit mosaicism of Cre recombinase expression, which is estimated to be present in Ϸ70% of cardiomyocytes (described elsewhere, 17 data not shown). Furthermore, recombination was confirmed in isolated cardiomyocytes from ⌬N MHC mice ( Figure 1D).…”

Endothelin-2 deficiency causes growth retardation, hypothermia, and emphysema in mice

“…Although cardiomyocyte-specific ET-1 mediates cardiac hypertrophy induced by thyroid hormone (8), the ET A receptor is not necessary for either basal cardiac function or stress-induced response to angiotensin II or isoproterenol (9). Collecting duct-specific inactivation of ET-1 (10), ET A receptor (11), ET B receptor (12), as well as both ET A and ET B receptors (13) revealed the importance of the ET system in maintaining blood pressure and regulating sodium excretion.…”

Low Blood Pressure in Endothelial Cell–Specific Endothelin 1 Knockout Mice

“…12 We also generated a mouse strain in which exon 2 of ET-1 is deleted by Cre-mediated recombination of ET-1 flox (ET-1 dlox/ϩ ) to confirm the null phenotype of deletion of the gene segment flanked by loxP sites ("flox"ed). Using the ET-1 flox/flox mouse strain, we previously reported cardiomyocyte-specific ET-1 knockout mice with a cardiac ␣-myosin heavy chain (␣-MHC)-Cre transgene 13 that exhibit a diminished hypertrophic response to thyroid hormone. Renal collecting duct-specific ET-1 knockout mice were also created 14,15 that exhibit salt retention and hypertension.…”