Immediate-early gene responses to different cardiac loads in the ejecting rabbit left ventricle

Engineered heart tissue: Design considerations and the state of the art

Originally developed more than 20 years ago, engineered heart tissue (EHT) has become an important tool in cardiovascular research for applications such as disease modeling and drug screening. Innovations in biomaterials, stem cell biology, and bioengineering, among other fields, have enabled EHT technologies to recapitulate many aspects of cardiac physiology and pathophysiology. While initial EHT designs were inspired by the isolated-trabecula culture system, current designs encompass a variety of formats, each of which have unique strengths and limitations. In this review, we describe the most common EHT formats, and then systematically evaluate each aspect of their design, emphasizing the rational selection of components for each application.

In vivo effects of 17β-estradiol on cardiac Na(+)/K(+)-ATPase expression and activity in rat heart

In this study the in vivo effects of estradiol in regulating Na(+)/K(+)-ATPase function in rat heart was studied. Adult male Wistar rats were treated with estradiol (40μg/kg, i.p.) and after 24h the animals were sacrificed and the heart excised. Following estradiol administration, cardiac Na(+)/K(+)-ATPase activity, expression of the α1 subunit, and phosphorylation of the α1 subunit were significantly increased. These animals also had significantly decreased levels of digoxin-like immunoreactive factor(s). Na(+) levels were also significantly reduced but to a level that was still within the normal physiological range, highlighting the ability of the Na(+)/K(+)-ATPase to balance the ionic composition following treatment with estradiol. Estradiol treated rats also showed increased phosphorylation of protein kinase B (Akt), and extracellular-signal-regulated kinase 1/2 (ERK1/2). We therefore suggest a role for Akt and/or ERK1/2 in estradiol-mediated regulation of cardiac Na(+)/K(+)-ATPase expression and activity in rat heart.

Lack of JunD Promotes Pressure Overload–Induced Apoptosis, Hypertrophic Growth, and Angiogenesis in the Heart

Background— The Jun family of activator protein 1 (AP-1) transcription factors (c-Jun, JunB, and JunD) is involved in fundamental biological processes such as proliferation, apoptosis, tumor angiogenesis, and hypertrophy. The role of individual AP-1 transcription factors in the stressed heart is not clear. In the present study we analyzed the role of JunD in survival, hypertrophy, and angiogenesis in the pressure-overloaded mouse heart after thoracic aortic constriction.

Methods and Results— Mice lacking JunD (knockout [KO]) showed increased mortality and enhanced cardiomyocyte apoptosis and fibrosis associated with increased levels of hypoxia-induced factor-1α, vascular endothelial growth factor (VEGF), p53, and Bax protein and reduced levels of Bcl-2 protein after 7 days of severe pressure overload compared with wild-type (WT) siblings. Cardiomyocyte hypertrophy in surviving KO mice was enhanced compared with that in WT mice. Chronic moderate pressure overload for 12 weeks caused enhanced left ventricular hypertrophy in KO mice, and survival and interstitial fibrosis were comparable with WT mice. Cardiac function, 12 weeks after operation, was comparable among shams and pressure-overloaded mice of both genotypes. In addition, KO mice exposed to chronic pressure overload showed higher cardiac capillary density associated with increased protein levels of VEGF.

Conclusions— Thus, JunD limits cardiomyocyte hypertrophy and protects the pressure-overloaded heart from cardiac apoptosis. These beneficial effects of JunD, however, are associated with antiangiogenic properties.

Direct, autocrine and paracrine effects of cyclic stretch on growth of myocytes and fibroblasts isolated from neonatal rat ventricles

Several studies have demonstrated that static stretch of cardiomyocytes induces cardiomyocyte hypertrophy. We investigated the effects of cyclic stretch, a more physiological stimulus, on protein synthesis and DNA synthesis of rat ventricular cardiomyocytes and cardiofibroblasts. Further-more, we investigated whether these effects are caused by autocrine mechanisms. In addition, we studied the paracrine influences of stretched cardiofibroblasts on cardiomyocyte growth. Short-term cyclic stretch (0-24 h) of cardiomyocytes induced a growth response indicative of cardiomyocyte hypertrophy, given the fact that increased rates of protein synthesis and DNA synthesis were accompanied by an elevated release of atrial natriuretic peptide into the culture medium. In cardiofibroblasts, short-term cyclic stretch also induced a growth response as indicated by an increased rate of protein synthesis and DNA synthesis. Furthermore, incubation of stationary cardiofibroblasts with conditioned medium derived from stretched cardiofibroblasts revealed an autocrine effect of stretch as illustrated by an increased rate of protein synthesis in stationary cardiofibroblasts. In analogy, there was an autocrine effect of stretch on stationary cardiomyocytes incubated with conditioned medium derived from stretched cardiomyocytes. Moreover, we observed a paracrine effect of the conditioned medium derived from stretched cardiofibroblasts on stationary cardiomyocytes. Thus, short-term cyclic stretch of cardiomyocytes and cardiofibroblasts induces growth responses that are the result of direct, autocrine, and paracrine effects. These autocrine/paracrine effects of stretch are most probably due to release of factors from stretched cells.

The trabecula culture system: a novel technique to study contractile parameters over a multiday time period

In the intact heart, various triggers induce alterations in gene expression that impact on contractile function. Because changes in gene expression reflect altered protein expression patterns after 12-48 h, we developed a system in which intact twitching cardiac trabeculae can be studied for multiday periods. Right ventricular trabeculae from pentobarbital sodium anesthetized rabbits were mounted in a sterile, closed muscle chamber. Over the first 48 h, developed force (Fdev) did not significantly change: 102.3 and 98.9% of the initial Fdev was observed after 24 and 48 h, respectively (n = 8). Also, neither diastolic force, time from peak to 50% relaxation (RT50), nor protein synthesis measured by a [3H]leucine incorporation assay changed significantly over time. Contractile response after > 48 h to an increase in extracellular calcium concentration (1.8 to 2.5 mM; Fdev increased 43.5%, n = 2) or to 1 microM isoproterenol (Fdev increased 138.6% and RT50 decreased 34.9%, n = 2) was similar to those observed in freshly dissected preparations. In conclusion, this system can investigate contractile function of multicellular preparations under well-defined physiological conditions after events that alter gene and consequent protein expression.

The AT4 receptor agonist [Nle1]-angiotensin IV reduces mechanically induced immediate-early gene expression in the isolated rabbit heart

Angiotensin II (ANG II), acting principally at the AT1 receptor, modulates mechanically-induced cardiac growth. The ANG II metabolite Angiotensin IV (ANG IV) has been shown to inhibit ANG II-induced mRNA and protein synthesis in chick cardiomyocytes. This effect did not involve the AT1 receptor, but was likely an action at the AT4 receptor. To determine if ANG IV also modulates a mechanically-induced cardiac growth response, we studied the effects of two AT4 receptor ligands, [Nle1]-ANG IV and [divalinal]-ANG IV, on mechanically-induced immediate-early gene expression (c-fos, egr-1, and c-jun) in the buffer perfused (30 degrees C), ejecting, isolated rabbit heart. Mechanical load alone (high systolic pressure and high end-diastolic volume) induced approximately 23-, 49- and 5-fold increases in c-fos, egr-1 and c-jun mRNA (in comparison to control hearts). Perfusion with [Nle1]-ANG IV (10[-10] mol/l) reduced the mechanically-induced expression of c-/fos and egr-1 by 42% and 48%, respectively (P < 0.05). Mechanically-induced c-jun expression was not significantly reduced. Perfusion with [divalinal]-ANG IV (10[-8] mol/l) had no effect on mechanically-induced immediate-early gene expression. We conclude that AT4 receptor agonism influences mechanical immediate-early gene expression, and propose the hypothesis that AT1 and AT4 receptors initiate opposing effects on mechanically-induced immediate-early gene expression in the isolated rabbit left ventricle.