Expression data of murine model of cardiac hypertrophy
ABSTRACT: An initial cellular change in the pathogenesis of heart failure is cardiomyocyte hypertrophy, characterized by increased cell size, enhanced protein synthesis and reactivation of fetal genes. In addition to mechanical stresses, several neurohumoral factors have been identified as potent hypertrophic agents, including angiotensin II, endothelin, and catecholamines. We used microarrays to study the gene expression during cardiac hypertrophy. Overall design: Balb/c mice (6-8w) were treated with TAC, ATII infusion, and myocardial infarction. TAC model: The transverse aorta (TAC) was constricted at the upper left sternal border by ligation with a 7-silk surgical thread and 27-gauge needle, which was removed thereafter. Sham-operated controls underwent an identical procedure without TAC. At 1 week and 1month after the procedure, LV was harvested. Ang II model.: Ang II was dissolved in 0.9% NaCl at concentrations sufficient to allow an infusion rate of 2.0 mg/kg/day, known to produce hypertension and cardiac hypertrophy. Control mice received a vehicle (saline) via an osmotic minipump. At 1 week after the procedure, LV was harvested. MI model: The proximal portion of the left coronary artery was ligated using an 8-0 nylon thread. Myocardial ischemia was confirmed by the discoloration of the heart and typical ECG changes. After 30 min occlusion, the left coronary artery was reperfused by loosening the ligature. In sham-operated mice (SHAM), the pericardium was opened, but the coronary artery was not ligated. At 1 day, 1week, and 1 month after the procedure, LV was harvested.
Project description:An initial cellular change in the pathogenesis of heart failure is cardiomyocyte hypertrophy, characterized by increased cell size, enhanced protein synthesis and reactivation of fetal genes. In addition to mechanical stresses, several neurohumoral factors have been identified as potent hypertrophic agents, including angiotensin II, endothelin, and catecholamines. We used microarrays to study the gene expression during cardiac hypertrophy. Balb/c mice (6-8w) were treated with TAC, ATII infusion, and myocardial infarction. TAC model: The transverse aorta (TAC) was constricted at the upper left sternal border by ligation with a 7-silk surgical thread and 27-gauge needle, which was removed thereafter. Sham-operated controls underwent an identical procedure without TAC. At 1 week and 1month after the procedure, LV was harvested. Ang II model.: Ang II was dissolved in 0.9% NaCl at concentrations sufficient to allow an infusion rate of 2.0 mg/kg/day, known to produce hypertension and cardiac hypertrophy. Control mice received a vehicle (saline) via an osmotic minipump. At 1 week after the procedure, LV was harvested. MI model: The proximal portion of the left coronary artery was ligated using an 8-0 nylon thread. Myocardial ischemia was confirmed by the discoloration of the heart and typical ECG changes. After 30 min occlusion, the left coronary artery was reperfused by loosening the ligature. In sham-operated mice (SHAM), the pericardium was opened, but the coronary artery was not ligated. At 1 day, 1week, and 1 month after the procedure, LV was harvested.
Project description:Ablating insulin receptors in cardiomyocytes causes subendocardial fibrosis and left ventricular (LV) dysfunction after 4 wk of transverse aortic constriction (TAC). To determine whether these maladaptive responses are precipitated by coronary vascular dysfunction, we studied mice with cardiomyocyte-restricted knock out of insulin receptors (CIRKO) and wild-type (WT) TAC mice before the onset of overt LV dysfunction. Two weeks of TAC produced comparable increases (P < 0.05 vs. respective sham) in heart weight/body weight (mg/g) in WT-TAC (8.03 ± 1.14, P < 0.05 vs. respective sham) and CIRKO-TAC (7.76 ± 1.25, P < 0.05 vs. respective sham) vs. WT-sham (5.64 ± 0.11) and CIRKO-sham (4.64 ± 0.10) mice. In addition, 2 wk of TAC were associated with similar LV geometry and function (echocardiography) and interstitial fibrosis (picrosirius red staining) in CIRKO and WT mice. Responses to acetylcholine (ACh), N(G)-monomethyl-L-arginine (l-NMMA), and sodium nitroprusside (SNP) were measured in coronary arteries that were precontracted to achieve ?70% of maximal tension development using the thromboxane A(2) receptor mimetic U-46619 (?3 × 10(-6) M). ACh-evoked vasorelaxation was absent in WT-TAC but was present in CIRKO-TAC albeit reduced relative to sham-operated animals. l-NMMA-evoked tension development was similar in vessels from CIRKO-TAC mice but was lower (P < 0.05) in WT-TAC animals vs. the respective sham-operated groups, and SNP-evoked vasorelaxation was similar among all mice. Thus estimates of stimulated and basal endothelial nitric oxide release were better preserved in CIRKO vs. WT mice in response to 2 wk of TAC. These findings indicate that maladaptive LV remodeling previously observed in CIRKO-TAC mice is not precipitated by coronary artery dysfunction, because CIRKO mice exhibit compensatory mechanisms (e.g., increased eNOS transcript and protein) to maintain coronary endothelial function in the setting of pressure overload.
Project description:Cyclic GMP (cGMP) signaling attenuates cardiac remodeling, but it is unclear which cGMP effectors mediate these effects and thus might serve as novel therapeutic targets. Therefore, we tested whether the cGMP downstream effector, cGMP-dependent protein kinase G I? (PKGI?), attenuates pressure overload-induced remodeling in vivo.The effect of transaortic constriction (TAC)-induced left ventricular (LV) pressure overload was examined in mice with selective mutations in the PKGI? leucine zipper interaction domain. Compared with wild-type littermate controls, in response to TAC, these Leucine Zipper Mutant (LZM) mice developed significant LV systolic and diastolic dysfunction by 48 hours (n=6 WT sham, 6 WT TAC, 5 LZM sham, 9 LZM TAC). In response to 7-day TAC, the LZM mice developed increased pathologic hypertrophy compared with controls (n=5 WT sham, 4 LZM sham, 8 WT TAC, 11 LZM TAC). In WT mice, but not in LZM mice, phosphodiesterase 5 (PDE5) inhibition with sildenafil (Sil) significantly inhibited TAC-induced cardiac hypertrophy and LV systolic dysfunction in WT mice, but this was abolished in the LZM mice (n=3 WT sham, 4 LZM sham, 3 WT TAC vehicle, 6 LZM TAC vehicle, 4 WT TAC Sil, 6 LZM TAC Sil). And in response to prolonged, 21-day TAC (n=8 WT sham, 7 LZM sham, 21 WT TAC, 15 LZM TAC), the LZM mice developed markedly accelerated mortality and congestive heart failure. TAC induced activation of JNK, which inhibits cardiac remodeling in vivo, in WT, but not in LZM, hearts, identifying a novel signaling pathway activated by PKGI? in the heart in response to LV pressure overload.These findings reveal direct roles for PKGI? in attenuating pressure overload-induced remodeling in vivo and as a required effector for the cardioprotective effects of sildenafil.
Project description:Recent data suggest adiponectin, an adipocyte-derived hormone, affects development of heart failure in response to hypertension. Severe short-term pressure overload [1-3 wk of transverse aortic constriction (TAC)] in adiponectin(-/-) mice causes greater left ventricle (LV) hypertrophy than in wild-type (WT) mice, but conflicting results are reported regarding LV remodeling, with either increased or decreased LV end diastolic volume compared with WT mice. Here we assessed the effects of prolonged TAC on LV hypertrophy and remodeling. WT and adiponectin(-/-) mice were subjected to TAC and maintained for 6 wk. Regardless of strain, TAC induced similar LV hypertrophy ( approximately 70%) and upregulation of mRNA for heart failure marker genes. However, LV chamber size was dramatically different, with classic LV dilation in WT TAC mice but concentric LV hypertrophy in adiponectin(-/-) mice. LV end diastolic and systolic volumes were lower and ejection fraction higher in adiponectin(-/-) TAC mice compared with WT, indicating that adiponectin deletion prevented LV remodeling and deterioration in systolic function. The activities of marker enzymes of mitochondrial oxidative capacity were reduced in WT TAC mice by approximately 35%, whereas enzyme activities were maintained at sham levels in adiponectin(-/-) TAC mice. In conclusion, in WT mice, long-term pressure overload caused dilated LV hypertrophy accompanied by decreased activity of mitochondrial oxidative enzymes. Although adiponectin deletion did not affect LV hypertrophy, it prevented LV chamber remodeling and preserved mitochondrial oxidative capacity, suggesting that adiponectin plays a permissive role in mediating changes in cardiac structure and metabolism in response to pressure overload.
Project description:In mice, transverse aortic constriction (TAC) is variably characterized as a model of pressure overload-induced hypertrophy (left ventricular [LV] hypertrophy, or LVH) or heart failure (HF). While commonly used, variability in the TAC model is poorly defined. The objectives of this study were to characterize the variability in the TAC model and to define a simple, noninvasive method of prospectively identifying mice with HF versus compensated LVH after TAC.Eight-week-old male C57BL/6J mice underwent TAC or sham and then echocardiography at 3 weeks post-TAC. A group of sham and TAC mice were euthanized after the 3-week echocardiogram, while the remainder underwent repeat echocardiography and were euthanized at 9 weeks post-TAC. The presence of TAC was assessed with two-dimensional echocardiography, anatomic aortic m-mode and color flow, and pulsed-wave Doppler examination of the transverse aorta (TA) and by LV systolic pressure (LVP). Trans-TAC pressure gradient was assessed invasively in a subset of mice. HF was defined as lung/body weight>upper limit in sham-operated mice.As compared with sham, TAC mice had higher TA velocity, LVP and LV weight, and lower ejection fraction (EF) at 3 or 9 weeks post-TAC. Only a subset of TAC mice (28%) developed HF. As compared with compensated LVH, HF mice were characterized by similar TA velocity and higher percent TA stenosis, but lower LVP, higher LV weight, larger LV cavity, lower EF and stress-corrected midwall fiber shortening, and more fibrosis. Both EF and LV mass measured by echocardiography at 3 weeks post-TAC were predictive of the presence of HF at 3 or 9 weeks post-TAC.In wild-type mice, TAC produces a variable cardiac phenotype. Marked abnormalities in LV mass and EF at echocardiography 3 weeks post-TAC identify mice with HF at autopsy. These data are relevant to appropriate design and interpretation of murine studies.
Project description:Left ventricular hypertrophy (LVH) is associated with electric remodeling and increased arrhythmia risk, although the underlying mechanisms are poorly understood. In the experiments here, functional voltage-gated (Kv) and inwardly rectifying (Kir) K(+) channel remodeling was examined in a mouse model of pressure overload-induced LVH, produced by transverse aortic constriction (TAC). Action potential durations (APDs) at 90% repolarization in TAC LV myocytes and QT(c) intervals in TAC mice were prolonged. Mean whole-cell membrane capacitance (C(m)) was higher, and I(to,f), I(K,slow), I(ss), and I(K1) densities were lower in TAC, than in sham, LV myocytes. Although the primary determinant of the reduced current densities is the increase in C(m), I(K,slow) amplitudes were decreased and I(ss) amplitudes were increased in TAC LV cells. Further experiments revealed regional differences in the effects of LVH. Cellular hypertrophy and increased I(ss) amplitudes were more pronounced in TAC endocardial LV cells, whereas I(K,slow) amplitudes were selectively reduced in TAC epicardial LV cells. Consistent with the similarities in I(to,f) and I(K1) amplitudes, Kv4.2, Kv4.3, and KChIP2 (I(to,f)), as well as Kir2.1 and Kir2.2 (I(K1)), transcript and protein expression levels were similar in TAC and sham LV. Unexpectedly, expression of I(K,slow) channel subunits Kv1.5 and Kv2.1 was increased in TAC LV. Biochemical experiments also demonstrated that, although total protein was unaltered, cell surface expression of TASK1 was increased in TAC LV. Functional changes in repolarizing K(+) currents with LVH, therefore, result from distinct cellular (cardiomyocyte enlargement) and molecular (alterations in the numbers of functional channels) mechanisms.
Project description:BACKGROUND:Ventricular remodeling increases the propensity of ventricular tachyarrhythmias and sudden death in patients. We studied the mechanism underlying these fatal arrhythmias, electrical and structural cardiac remodeling, as well as arrhythmogeneity during early, compensated hypertrophy in a rat model of chronic pressure overload. METHODS:Twenty-six Wistar rats were subjected to transverse aortic constriction (TAC) (n?=?13) or sham operation (n?=?13). Four weeks postoperative, echo- and electrocardiography was performed. Epicardial (208 or 455 sites) and transmural (30 sites) ventricular activation mapping was performed on Langendorff perfused hearts. Subsequently, hearts were processed for (immuno)histological and molecular analyses. RESULTS:TAC rats showed significant hypertrophy with preserved left ventricular (LV) function. Epicardial conduction velocity (CV) was similar, but more dispersed in TAC. Transmural CV was slowed in TAC (37.6?±?2.9?cm s(-1)) compared to sham (58.5?±?3.9?cm s(-1); P?<?0.01). Sustained polymorphic ventricular tachycardias were induced from LV in 8/13 TAC and in 0/13 sham rats. During VT, electrical activation patterns showed variable sites of earliest epicardial activation and altering sites of functional conduction block. Wandering epicardial reentrant activation was sporadically observed. Collagen deposition was significantly higher in TAC compared to sham, but not different between arrhythmogenic and non-arrhythmogenic TAC animals. Connexin43 (Cx43) expression was heterogeneous with a higher prevalence of non-phosphorylated Cx43 in arrhythmogenic TAC animals. CONCLUSION:In TAC rats with compensated cardiac hypertrophy, dispersion of conduction correlated to arrhythmogenesis, an increased heterogeneity of Cx43, and a partial substitution with non-phosphorylated Cx43. These alterations may result in the increased vulnerability to polymorphic VTs.
Project description:RATIONALE:The role of interleukin (IL)-6 in the pathogenesis of cardiac myocyte hypertrophy remains controversial. OBJECTIVE:To conclusively determine whether IL-6 signaling is essential for the development of pressure overload-induced left ventricular (LV) hypertrophy and to elucidate the underlying molecular pathways. METHODS AND RESULTS:Wild-type and IL-6 knockout (IL-6(-/-)) mice underwent sham surgery or transverse aortic constriction (TAC) to induce pressure overload. Serial echocardiograms and terminal hemodynamic studies revealed attenuated LV hypertrophy and superior preservation of LV function in IL-6(-/-) mice after TAC. The extents of LV remodeling, fibrosis, and apoptosis were reduced in IL-6(-/-) hearts after TAC. Transcriptional and protein assays of myocardial tissue identified Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) and signal transducer and activator of transcription 3 (STAT3) activation as important underlying mechanisms during cardiac hypertrophy induced by TAC. The involvement of these pathways in myocyte hypertrophy was verified in isolated cardiac myocytes from wild-type and IL-6(-/-) mice exposed to prohypertrophy agents. Furthermore, overexpression of CaMKII in H9c2 cells increased STAT3 phosphorylation, and exposure of H9c2 cells to IL-6 resulted in STAT3 activation that was attenuated by CaMKII inhibition. Together, these results identify the importance of CaMKII-dependent activation of STAT3 during cardiac myocyte hypertrophy via IL-6 signaling. CONCLUSIONS:Genetic deletion of IL-6 attenuates TAC-induced LV hypertrophy and dysfunction, indicating a critical role played by IL-6 in the pathogenesis of LV hypertrophy in response to pressure overload. CaMKII plays an important role in IL-6-induced STAT3 activation and consequent cardiac myocyte hypertrophy. These findings may have significant therapeutic implications for LV hypertrophy and failure in patients with hypertension.
Project description:Animal models of pressure overload are valuable for understanding hypertensive heart disease. We characterised a surgical model of pressure overload-induced hypertrophy in C57BL/6J mice produced by suprarenal aortic constriction (SAC). Compared to sham controls, at one week post-SAC systolic blood pressure was significantly elevated and left ventricular (LV) hypertrophy was evident by a 50% increase in the LV weight-to-tibia length ratio due to cardiomyocyte hypertrophy. As a result, LV end-diastolic wall thickness-to-chamber radius (h/R) ratio increased, consistent with the development of concentric hypertrophy. LV wall thickening was not sufficient to normalise LV wall stress, which also increased, resulting in LV systolic dysfunction with reductions in ejection fraction and fractional shortening, but no evidence of heart failure. Pathological LV remodelling was evident by the re-expression of fetal genes and coronary artery perivascular fibrosis, with ischaemia indicated by enhanced cardiomyocyte Hif1a expression. The expression of stem cell factor receptor, c-Kit, was low basally in cardiomyocytes and did not change following the development of robust hypertrophy, suggesting there is no role for cardiomyocyte c-Kit signalling in pathological LV remodelling following pressure overload.
Project description:BACKGROUND:To better understand reverse left ventricular (LV) remodeling, we developed a murine model wherein mice develop LV remodeling after transverse aortic constriction (TAC) and a small apical myocardial infarct (MI) and undergo reverse LV remodeling after removal of the aortic band. METHODS AND RESULTS:Mice studied were subjected to sham (n=6) surgery or TAC+MI (n=12). Two weeks post-TAC+MI, 1 group underwent debanding (referred to as heart failure debanding [HF-DB] mice; n=6), whereas the aortic band remained in a second group (heart failure [HF] group; n=6). LV remodeling was evaluated by 2D echocardiography at 1 day, 2 weeks and 6 weeks post-TAC+MI. The hearts were analyzed by transcriptional profiling at 4 and 6 weeks and histologically at 6 weeks. Debanding normalized LV volumes, LV mass, and cardiac myocyte hypertrophy at 6 weeks in HF-DB mice, with no difference in myofibrillar collagen in the HF and HF-DB mice. LV ejection fraction and radial strain improved after debanding; however, both remained decreased in the HF-DB mice relative to sham and were not different from HF mice at 6 weeks. Hemodynamic unloading in the HF-DB mice was accompanied by a 35% normalization of the HF genes at 2 weeks and 80% of the HF genes at 4 weeks. CONCLUSIONS:Hemodynamic unloading of a pathophysiologically relevant mouse model of HF results in normalization of LV structure, incomplete recovery of LV function, and incomplete reversal of the HF transcriptional program. The HF-DB mouse model may provide novel insights into mechanisms of reverse LV remodeling.