Original ArticleGenetic Enhancement of Ventricular Contractility Protects against Pressure-Overload-Induced Cardiac Dysfunction
Introduction
The β1-adrenergic receptor (AR) is the predominant AR-subtype mediating inotropic and chronotropic responses to sympathoadrenergic stimulation of the heart. Although the α1-ARs also mediate a positive inotropic response [1], [2], [3] in the healthy heart this effect is weak compared to that of the β1-AR.
Recently, we showed that transgenic (TG) mice with up to a 170-fold increase in cardiac α1A-ARs did not develop myocardial hypertrophy and showed markedly enhanced inotropy but not lusitropy [4]. The lack of hypertrophy in this TG model was surprising, given that evidence from numerous studies has implicated α1A-AR-activation in the pathogenesis of hypertrophy [5], [6], [7], [8], [9], [10]. Nevertheless, this conclusion was largely based on studies of isolated cardiomyocytes of the rat, a species that may be atypical, since, in contrast to those of virtually all other mammals, including humans and the mouse, they show a 5~10-fold higher level of cardiac α1-AR density [11]. Consistent with this interpretation, differences in α1-AR signalling pathways in cultured rat versus mouse cardiomyocytes have been demonstrated [12], [13]. On the other hand, given that the TG mice display increased expression of atrial natriuretic factor (ANF) [4], it is also possible that even though hypertrophy is not overtly manifested in these mice, their hypertrophic signalling is nonetheless sensitized. If this is the case, these mice should develop more marked hypertrophy in response to pathological stimuli, such as pressure-overload. Alternatively, resistance of the α1A-AR TG model to hypertrophy-development may be due to the restraining influences of an inhibitory pathway. For example, using cultured rat cardiomyocytes, Schafer et al. [14] described cross-talk between β1- and α1-ARs in which concomitant activation of the former suppresses α1-AR-mediated hypertrophic signalling. This raises the question: does this inhibitory cross-talk account for the absence of hypertrophy in the α1A-AR TG mice? More importantly, given that increased cardiac work, such as that associated with pressure-overload, leads to a functional deterioration that can progress to heart failure, the α1A-AR TG mice provide a convenient model to test if enhanced inotropic drive preserves ventricular function in disease states or with chronic β-blockade.
Here, we show that development of pressure-overload hypertrophy is neither enhanced nor impaired in the α1A-AR TG animals, and that contrary to the extant in vitro data in the rat [14] the present in vivo study in the mouse provides no evidence for cross-talk between β1-ARs and α1A-AR-coupled signalling pathways. Importantly, enhanced inotropy by the α1A-AR preserves cardiac function in the face of pressure-overload, with a consequent reduction in heart failure development and related death.
Section snippets
Animals, surgery and drug treatment
A1A2 TG line with 66-fold overexpression of the rat α1A-AR, on a FVB/N genetic background, was used at three to four months of age [4]. All experimental procedures were approved by animal ethics committees. Animals were genotyped, anesthetized with a mixture of ketamine/xylazine/atropine (100/20/1.2 mg/kg, respectively, i.p.), as described previously [4], [15], [16], and then subjected to either a 60% transverse aorta constriction (TAC) or a sham-operation. Cardiac function was evaluated at 7
Phenotype assessment
Absence of hypertrophy in the TG mice was evident from the lack of change in echocardiographic LV mass or in LV weight compared with the NTG littermates (Table 1). Micromanometry showed similar arterial pressures and heart rates in both groups. The hypercontractile phenotype, previously documented in the A1A1 α1A-AR TG line with 170-fold transgene expression [4], was also apparent in the A1A2 line. Thus, the TG mice had significantly smaller LVDs, higher FS and WTI, a steeper slope of aortic
Discussion
In the present study, we have made the following major observations. First, the enhanced inotropy of α1A-AR TG mice is well maintained during pressure-overload, and contributes to better LV contractile function. Second, failure of α1A-AR TG mice to develop hypertrophy is not due to a global defect in their hypertrophic machinery, since they maintain a normal ability to develop pressure-overload hypertrophy comparable to that in NTG mice. Third, β1-AR inhibition of α1A-AR-mediated hypertrophy,
Acknowledgments
Supported in part by grants from the National Heart Foundation, Australia and National Health and Medical Research Council, Australia. We are grateful to Dr. Susan Steinberg for advice on the evaluation of α1A-AR signalling pathways and Dr. Jörg Heierhorst and Bryony Mearns for assistance with some of the signalling studies.
References (38)
- et al.
α- and β-adrenergic stimulation induces distinct patterns of immediate early gene expression in neonatal rat myocardial cells. fos/jun expression is associated with sarcomere assembly; Egr-1 induction is primarily an α1-mediated response
J. Biol. Chem.
(1990) - et al.
Selective activation of α1A-adrenergic receptors in neonatal cardiac myocytes is sufficient to cause hypertrophy and differential regulation of α1-adrenergic receptor subtype mRNAs
J. Mol. Cell Cardiol.
(1998) - et al.
α1-Adrenergic receptor subtype mRNAs are differentially regulated by α1-adrenergic and other hypertrophic stimuli in cardiac myocytes in culture and in vivo. Repression of α1B and α1D but induction of α1C
J. Biol. Chem.
(1996) - et al.
The α1-adrenoceptor subtype- and protein kinase C isoform- dependence of norepinephrine's actions in cardiomyocytes
J. Mol. Cell Cardiol.
(2000) - et al.
The MEKK-JNK pathway is stimulated by α1-adrenergic receptor and ras activation and is associated with in vitro and in vivo cardiac hypertrophy
J. Biol. Chem.
(1997) - et al.
β-Adrenoceptor stimulation attenuates the hypertrophic effect of α-adrenoceptor stimulation in adult rat ventricular cardiomyocytes
J. Am. Coll. Cardiol.
(2001) - et al.
Transgenic mice with cardiac overexpression of α1B-adrenergic receptors. In vivo α1-adrenergic receptor-mediated regulation of β-adrenergic signaling
J. Biol. Chem.
(1997) - et al.
Regulation of myocardial βARK1 expression in catecholamine-induced cardiac hypertrophy in transgenic mice overexpressing α1B-adrenergic receptors
J. Am. Coll. Cardiol.
(2001) - et al.
Hypotension, autonomic failure, and cardiac hypertrophy in transgenic mice overexpressing the α1B-adrenergic receptor
J. Biol. Chem.
(2001) - et al.
MEK1/2-MRK1/2 mediates α1-adrenergic receptor-stimulated hypertrophy in adult rat ventricular myocytes
J. Mol. Cell. Cardiol.
(2001)
Transgenic approaches to 5define the functional role of dual site phospholamban phosphorylation
J. Biol. Chem.
Myocardial α1-adrenoceptor: inotropic effect and physiologic and pathologic implications
Life Sci.
Role of Ca2+-independent PKC in α1-adrenoceptor-mediated inotropic responses of neonatal rat hearts
Am. J. Physiol.
WB4101- and CEC-sensitive positive inotropic actions of phenylephrine in rat cardiac muscle
Am. J. Physiol.
Targeted α1A-adrenergic receptor overexpression induces enhanced cardiac contractility but not hypertrophy
Circ. Res.
Norepinephrine-stimulated hypertrophy of cultured rat myocardial cells is an α1 adrenergic response
J. Clin. Invest.
Adrenergic and muscarinic receptors in the human heart
Pharmacol. Rev.
Autonomous and growth factor-induced hypertrophy in cultured neonatal mouse cardiac myocytes. Comparison with rat
Circ. Res.
Coupling function of endogenous α1- and β-adrenergic receptors in mouse cardiomyocytes
Circ. Res.
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