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(Circulation Research. 2001;89:343.)
© 2001 American Heart Association, Inc.

Integrative Physiology

Targeted _1A-Adrenergic Receptor Overexpression Induces Enhanced Cardiac Contractility but not Hypertrophy

Fang Lin, W. Andrew Owens, Songhai Chen, Mary E. Stevens, Scott Kesteven, Jane F. Arthur, Elizabeth A. Woodcock, Michael P. Feneley, Robert M. Graham

From the Victor Chang Cardiac Research Institute (F.L., W.A.O., S.C., S.K., M.P.F., R.M.G.) and Cardiology Department (S.K., M.P.F., R.M.G.), St Vincent’s Hospital, Darlinghurst, New South Wales, Australia; Faculty of Medicine (M.P.F., R.M.G.), The University of New South Wales, Kensington, New South Wales, Australia; Bayer Corp (M.E.S.), Berkeley, Calif; and Baker Medical Research Institute (J.F.A., E.A.W.), Prahran, Victoria, Australia.

Correspondence to Robert M. Graham, Molecular Cardiology Unit, Victor Chang Cardiac Research Institute, 384 Victoria St, Darlinghurst 2010, New South Wales, Australia. E-mail b.graham{at}victorchang.unsw.edu.au

	Abstract

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Activation of the _1A-adrenergic receptor (_1A-AR)/Gq pathway has been implicated as a critical trigger for the development of cardiac hypertrophy. However, direct evidence from in vivo studies is still lacking. To address this issue, transgenic mice with cardiac-targeted overexpression of the _1A-AR (4- to 170-fold) were generated, using the rodent -myosin heavy chain promoter. Heterozygous animals displayed marked enhancement of cardiac contractility, evident from increases in dP/dt_max (80%, P<0.0001), dP/dt_max/LVP_inst (76%, P<0.001), dP/dt_max:dP/dt_min (104%, P<0.0001), and fractional shortening (33%, P<0.05). Moreover, changes in the dP/dt_max–end-diastolic volume relationship provided load-independent evidence of a primary increase in contractility. Blood pressure and heart rate were largely unchanged, and there was a small increase in (-)norepinephrine-stimulated, but not basal, phospholipase C activity. Increased contractility was directly related to the level of receptor overexpression and could be completely reversed by acute _1A- but not ß-AR blockade. Despite the robust changes in contractility, transgenic animals displayed no morphological, histological, or echocardiographic evidence of left ventricular hypertrophy. In addition, apart from an increase in atrial natriuretic factor mRNA, expression of other hypertrophy-associated genes was unchanged. To our knowledge, these data provide the first in vivo evidence for an inotropic action of the _1A-AR.

Key Words: cardiac hemodynamics • phospholipase C activity • dP/dt • receptor signaling

	Introduction

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Sympathetic control of cardiac function is mediated predominately by ß₁-adrenergic receptors (ß₁-ARs) acting via Gs and the adenylyl cyclase–protein kinase A pathway. Additionally, the heart contains ₁-ARs that may also mediate increases in contractility, as well as changes in the electrophysiological properties and metabolic responses of the myocardium.¹ All three ₁-AR subtypes (_1A, _1B, and _1D) have been identified in heart and isolated cardiomyocytes at the mRNA level, although only _1A- and _1B-ARs appear to be expressed as functional proteins in a variety of mammalian species ranging from the mouse to humans.^1–3

Acutely, cardiac ₁-AR activation results in polyphosphoinositide hydrolysis that is predominantly Gq-mediated and induces positive inotropic effects due to either an increase in cytosolic free Ca²⁺ levels or to increased responsiveness of the myofilaments to Ca²⁺.^1,3 Cardiac ₁-AR stimulation also leads to activation of the Na⁺-H⁺ exchanger and, as a result, activation of the Na⁺-Ca²⁺ exchanger, as well as Na⁺,K⁺-ATPase activation.^1,3 Responses to ₁-AR activation and expression of the various subtypes are developmentally regulated and show marked species and regional myocardial differences. Nonetheless, there is currently little evidence that cardiac ₁-ARs play a major functional role under normal physiological conditions.¹ In pathological settings, cardiac ₁-ARs may function in a compensatory fashion to maintain cardiac inotropy when the ß-AR system is downregulated and uncoupled.³ On the other hand, cardiac ₁-ARs, particularly of the _1A subtype, have also been implicated as primary mediators of cardiac hypertrophy and malignant arrhythmias.^4–7 Thus, chronic exposure of cardiomyocytes to ₁-AR agonists result in hypertrophy and is associated with a specific pattern of gene expression, most notably the induction of the ventricular-embryonic atrial natriuretic factor (ANF) gene, and the constitutively expressed myosin light chain-2 (MLC-2) gene, as well as the accumulation and assembly of contractile proteins into sarcomeric units.^1,4 The signaling pathways mediating hypertrophic responses to ₁-AR stimulation have not been fully elucidated. However, ANF gene expression and the morphological features of hypertrophy are generally thought to require Gq-mediated phospholipase C (PLC) activation.⁴ Not surprisingly, therefore, targeted overexpression of Gq in the myocardium results in marked induction of hypertrophic gene markers as well as contractile impairment, cardiac decompensation, and biventricular failure.⁸ Others have shown that the ₁-AR hypertrophic response involves activation of members of the mitogen-activated protein kinase superfamily, as well as the PI-3-kinase/mTOR/p70^S6k pathway.^9,10

Although both the _1A and _1B subtypes have been reported to induce myocyte growth and hypertrophy, most studies favor the _1A-AR as the dominant subtype.^1,4–6 This conclusion, however, is based largely on studies of rat heart or neonatal rat cardiomyocytes, a species that shows the most abundant expression of myocardial ₁-AR (amounting to 50% of the total adrenergic receptor pool) and robust ₁-AR–mediated inotropic responses.^1,3 By contrast, in human myocardium, ₁-ARs account for only 15% to 20% of the total adrenergic receptor pool.¹ Interestingly, cardiac-targeted overexpression of either the wild-type _1B-AR or a constitutively active mutant, in the mouse, a species that like humans shows very low levels of cardiac ₁-AR expression,³ produces little, if any, hypertrophy, and either no change in contractility or impairment, rather than enhanced cardiac function,^7,11–13 an effect due to promiscuous interaction with Gi and inhibition of the adenylyl cyclase pathway and to upregulation of G protein receptor–coupled kinase-2.¹² Given the lack of in vivo data on the role of cardiac _1A-ARs, we elected in the present study to develop a mouse line with targeted overexpression of this ₁ subtype. Based on studies of five independent lines thus developed, we report that cardiac overexpression of the _1A-AR results neither in cardiac hypertrophy nor in cardiac impairment. Rather, these animals demonstrate a marked increases in cardiac contractility that is directly related to the level of receptor overexpression and can be completely abolished by acute _1A-AR blockade.

	Materials and Methods

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Generation of Transgenic Mice
Transgenic mice expressing the wild-type rat _1A-AR under the control of the rat -myosin heavy chain (MHC) promoter were generated using standard methodologies. Five transgenic lines were established and bred with FVB/N. Litter sizes and postnatal development were indistinguishable from those of wild-type animals. Heterozygous animals from at least the third generation, and at the ages indicated, were used for all studies, with their nontransgenic littermates (NTLs) serving as controls. All studies were performed with approval of the Lawrence Berkeley National Laboratory and St Vincent’s Hospital Institutional Review Board/Animal Ethics Committee. Supplementary information regarding the generation of the transgenic mice, details of the methodologies involved in their biochemical, morphometric and histological characterization, and details of other methodologies is available at www.circresaha.org.

Echocardiography
Studies were performed on mice anesthetized with 2.5% avertin (0.01 mL/g) (Aldrich Chemical Company, Inc), using a Hewlett-Packard Sonos 5500 ultrasonograph equipped with a 12-MHz phased-array transducer.

Hemodynamic Studies
Hemodynamics were determined by micromanometry using a 1.4F pressure transducer in mice anesthetized with xylazine (20 mg/kg) and ketamine (100 mg/kg). dP/dt_max–end-diastolic volume relationships¹⁴ were determined in additional mice (n=6 per group) by sonomicrometry during inferior vena caval occlusion.

Statistical Analysis
Data are presented as mean±1 SEM. The number of mice used is indicated. All hemodynamic, echocardiographic, and ECG recordings and subsequent data analyses were performed without knowledge of the mouse genotype. Statistical analyses were performed using paired and unpaired Student’s t tests and ANOVA. Comparison of the dP/dt_max–end-diastolic volume relationships was made by multiple linear regression analysis.¹⁵ Receptor binding data were analyzed using the curve-fitting program PRISM. For comparisons of data fit to a one- or two-site model, the F test was used. In all analyses, a value of P<0.05 was considered significant.

An expanded Materials and Methods section can be found in the online data supplement available at http://www.circresaha.org.

	Results

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Production of Transgenic Mice
Transgenic mice were generated using the rat -MHC promoter to allow cardiac-restricted _1A-AR overexpression. The transgene was detected by polymerase chain reaction (PCR) and Southern blot analysis (data not shown). Five founder mice, designated A1A1 to A1A5, produced transgenic offspring at the expected mendelian frequency. Copy number in the different transgenic lines ranged from 5 to 70.

Transgene Expression
Expression (Northern blot analysis) was abundant in heart but absent in lung, liver, spleen, kidney, and brain (data not shown). Overexpression of _1A-AR protein was confirmed by Western blotting using a monoclonal antibody against a 1D4 C-terminal epitope (Figure 1A). A single 68-kDa species was detected in the cardiac membranes of all transgenic lines but not in those of their NTLs (Figure 1B), indicating that the receptor protein underwent appropriate posttranslational modification and was fully glycosylated. This was further demonstrated by immunofluorescence staining of ventricular cryosections using a polyclonal antibody against the endogenous C-tail of the _1A-AR. Labeling was clearly evident throughout the ventricles of transgenic mice but not in the ventricles of the NTLs, where the expression level of the endogenous _1A-AR is too low to be detected. In the transgenic animals, only surface cardiomyocyte labeling was evident (Figure 1C), confirming that the transgenic receptor protein was expressed appropriately on the cell membrane.

View larger version (29K): [in this window] [in a new window]   Figure 1. Generation of transgenic mice and 1A transgene expression. A, Schematic representation of the transgene construct, which consisted of the rat -MHC promoter, a cDNA for wild-type 1A-AR containing a 1D4 epitope, and an SV40 intron and polyadenylation signal. The region of the 5` MHC promoter used as probe for Southern blot analysis is underlined. B, Western blot analysis showing that an antibody against the C-terminal 1D4 epitope tag detected the expressed transgene, but not the endogenously expressed 68-kDa receptor. In the blot shown, equal amounts of protein were used for each line. In addition, studies in which larger amounts of protein were used, the 68-kDa receptor species was readily apparent even for the A1A5 line (data not shown). C, Immunofluorescence detection of receptor expression showing membrane staining (arrows). Frozen sections (6 µm) of ventricles from a 2-month-old NTL and TG animal of the A1A1 line were incubated with a goat polyclonal antibody against the C-tail of the wild-type 1AAR and then an FITC-conjugated secondary antibody. D, 1A-AR expression determined from equilibrium radioligand binding studies, using [3H]prazosin and membranes prepared from the hearts (10 to 20 per group) of NTLs and their TG counterparts of the A1A1–A1A5 lines. Numbers in parentheses indicate fold increase over the NTL values.

By radioligand binding assays analysis, the NTLs expressed on average 17±0.5 fmol/mg protein (n=10) of endogenous ₁-AR. These levels are similar to those reported by others^3,16 in the mouse (5 to 18 fmol/mg), of which 25% are of the _1A and 75% of the _1B subtype,¹⁶ and in humans (12 fmol/mg), but are markedly lower than those found in rat cardiac membranes (90 fmol/mg).³ In transgenic cardiac membranes, _1A-AR expression was increased by 170- and 148-fold to 2976±30 and 1958±230 fmol/mg protein in the A1A1 and A1A4 lines, respectively. The remaining transgenic lines, A1A2, A1A3, and A1A5, demonstrated 66-, 112- and 4-fold receptor overexpression, respectively (Figure 1D). Competition radioligand binding studies were also used to show that the cardiac ₁-ARs in the transgenic animals were predominantly of the _1A subtype (see the Table in the online data supplement available at www.circresaha.org).

Receptor-Mediated PLC Activation
As shown in Figure 2A, basal total [³H]inositol phosphates were not significantly different in left ventricular (LV) strips from the transgenic animals and their NTLs. In the transgenic tissues, (-)norepinephrine stimulation resulted in a small but significant increase in total [³H]inositol phosphates, to a level significantly above the basal value (P<0.05) and also significantly above that observed with (-)norepinephrine stimulation of the NTL tissue (P<0.05). The increases in total [³H]inositol phosphates with (-)norepinephrine stimulation were due to increases in the 1- (or 3-) and 4-isomers of inositol monophosphate, with smaller increases in inositol-1,4-bisphosphate. However, inositol-1,4,5-trisphosphate levels were unchanged (Figure 2A).

View larger version (17K): [in this window] [in a new window]   Figure 2. Inositol phosphate and adenylyl cyclase responses. A, LV strips were isolated and labeled with [3H]myo-inositol and subsequently incubated with LiCl (10 mmol/L) and (±)propranolol (1 µmol/L), in the absence (white bars) or presence (black bars) of (-)norepinephrine (100 µmol/L) for 20 minutes. [3H]Inositol phosphates were extracted and quantitated as detailed in Materials and Methods. *P<0.05 compared with the (-)norepinephrine response in the NTLs; #P<0.05 compared with the TG response in the absence of (-)norepinephrine. InsPs indicates total inositol phosphates; 1/3IP1, inositol-(1 or 3)-monophosphate; 4IP1, inositol-4-monophosphate; 1,4 IP2, inositol-1,4-bisphosphate; and 1,4,5IP3, inositol-1,4,5-trisphosphate. B, LV strips were incubated in the absence (white bars) or presence of isoproterenol (100 µmol/L) (black bars) or phenylephrine (100 µmol/L) (hatched bars) for 5 minutes. cAMP was extracted and determined as detailed in Materials and Methods. *P<0.05 vs response in the absence of isoproterenol.

Hypertrophy Assessment
As shown in Table 1, although transgenic animals of the A1A1 line and their NTL controls showed the expected age-related increases (by 10% to 20%) in body weight, cardiac biventricular weight, and tibial length, neither these parameters nor the ratios of biventricular weight to body weight or biventricular weight to tibial length differed between the transgenic animals and their NTLs. In agreement with these gross morphology findings, cardiomyocyte cross-sectional area was also not significantly different in the transgenic animals as compared with their NTL controls (Table 1).

View this table: [in this window] [in a new window]   Table 1.  Morphometric Analysis of Transgenic (TG) Animals and Their Nontransgenic Littermates (NTLs)

Consistent with the known regulation of ANF transcription by a phenylephrine (ie, ₁-AR) response element,¹⁷ compared with the NTLs, ANF mRNA expression was increased by 7.3- and 4.2-fold in the A1A1 and A1A4 lines, which have 170- and 148-fold _1A-AR overexpression, respectively, but not in the A1A5 line, which overexpresses the _1A-AR by only 4-fold (Figure 3). However, expression of other hypertrophy-associated genes, including MLC-2v, - and ß-MHC, SERCA2a, and -skeletal actin, as well as phospholamban (PLB), was unaltered (Figure 3).

View larger version (44K): [in this window] [in a new window]   Figure 3. Analysis of cardiac gene expression. A, Expression of ANF, MLC-2v, -MHC, ß-MHC, ß-skeletal actin, SERCA2a, PLB, and GAPDH mRNA was determined by Northern blot analysis using RNA isolated from the ventricles of 2-month-old NTLs and their TG counterparts. B, Hybridization signals were quantified using a PhosphoImager, normalized for GAPDH expression, and presented as fold increase over that in the NTL controls. C, Expression of PLB, or its Ser16 (S16) or Thr17 (T17) phosphorylated forms, SERCA2a, troponin I, MLC, the Na+-Ca2+ exchanger, or the Na+-H+ antiporter (NHE1), was determined by Western blot analysis. The results shown are representative of the findings with cardiac homogenates from six 2-month-old TG animals of the A1A1 line and six NTLs.

Echocardiographic and Hemodynamic Assessments
Echocardiographic evaluation of the A1A1 _1A transgenics showed enhanced LV emptying observed in the 2D mode and virtual apposition of the LV posterior and anterior walls in the M-mode images (Figure 4B). Quantitatively, this was evidenced by a 33% increase (P<0.05) in fractional shortening, which was associated with a 72% decrease in LV internal dimension at end-systole and a lesser (8%) decrease in LV internal dimension at end-diastole (Table 2). Because dP/dt_max should decrease as a function of reduced LV end-diastolic volume,¹⁴ the fact that dP/dt_max increased in the transgenic animals (Table 3), despite a reduction in end-diastolic LV chamber dimension, indicates enhancement of contractility in these animals. This was further demonstrated by a significant leftward/upward shift (P<0.001) of the dP/dt_max–end-diastolic volume relationship in A1A1 transgenic animals (slope 252 792±41 207 mm Hg · s^-1 · mL^-1; intercept 0.012±0.004 mL; r²=0.93±0.02) as compared with their NTLs (slope 137 059±37 012 mm Hg · s^-1 · mL^-1; intercept 0.03±0.01 mL; r²=0.94±0.02). Cardiac output was not significantly different in the _1A transgenic animals. The finding of an increased ratio of wall thickness to chamber radius (h/r) and an increased ratio of LV mass to LV internal dimension at end-diastole, but no change in LV mass, is compatible with the reduced LV chamber size being due to markedly enhanced adrenergic drive in the _1A transgenics (Table 2).

View larger version (42K): [in this window] [in a new window]   Figure 4. Micromanometry and echocardiography. A, Representative LV pressure and dP/dt traces from NTL and TG animals of the A1A1 line. Note that the initial tracing for each parameter is shown at a slower recording speed to indicate the resolution of the data. B, Representative 2D short-axis image (dotted circles show the outlines of the LV cavities at end-systole) and M-mode echocardiographic tracings (upper arrows show the anterior and lower arrows the posterior LV walls at end-systole). Echocardiography was performed on anesthetized NTL and TG (A1A1) animals at 8 to 12 weeks of age, as described in Materials and Methods.

View this table: [in this window] [in a new window]   Table 2.  M-Mode Echocardiographic Measurements

View this table: [in this window] [in a new window]   Table 3.  Hemodynamics of Transgenic (TG) Animals and Their Nontransgenic Littermates (NTLs)

By micromanometry, neither systolic nor diastolic aortic pressure was altered in the _1A transgenics, whereas heart rate was 16% higher in the A1A1 line but not in the A1A5 line (Table 3). Consistent with enhanced LV fractional shortening on echocardiography, enhanced contractility was demonstrated by increased LV dP/dt_max and by increased dP/dt_max normalized for instantaneous pressure (by 80% and 76%, respectively, P<0.001) in the A1A1 _1A transgenics (Figure 4A) but not in the A1A5 line. LV dP/dt_min was not significantly different from that in the NTLs in either line. As a result, the ratio of dP/dt_max to dP/dt_min was doubled from 0.93 in the NTLs to 1.9 in the _1A transgenics with 170-fold receptor overexpression (Table 3). Similar increases in LV dP/dt_max and the ratio of dP/dt_max to dP/dt_min were observed in the A1A2, A1A3, and A1A4 transgenics (data not shown). Although absolute LV dP/dt_min values were unaltered, the finding that the time constant of isovolumic relaxation () was prolonged by 40% in the A1A1 line indicates impaired relaxation (Table 3). LV end-diastolic pressure was significantly lower in the A1A1 transgenics, consistent with echocardiographic evidence of a lower end-diastolic volume in this line.

Mechanism of Enhanced Contractility
We next investigated the possibility that the hypercontractile phenotype of the _1A transgenics was due to promiscuous interaction with the cardiac ß-AR/Gs/adenylyl cyclase pathway. These studies revealed that ß-AR density (56.5±0.5 fmol/mg, _1A transgenics; 58.7±2.4 fmol/mg, NTLs) and both basal and maximal (-)isoproterenol-stimulated cAMP generation (Figure 2B) were unaltered in the _1A transgenics. Also, activation of LV strips with the ₁-agonist phenylephrine (in the presence of the ß-antagonist (±) propranolol) failed to increase cAMP generation in either the _1A transgenics or their NTLs (Figure 2B). These in vitro findings were also confirmed in in vivo studies, in which the ß-AR agonist (-)isoproterenol was administered to 2-month-old animals of the A1A1 line, both before and after complete ß-AR blockade with (±)propranolol. As expected, administration of isoproterenol to NTL controls produced a marked increase in dP/dt_max from 8037±805 to 14 424±842 mm Hg/s (P<0.0001) and a slight increase in dP/dt_min from -7721±568 to -9086±755 mm Hg/s (P<0.05), effects that were completely inhibited by (±)propranolol (Figure 5A). By contrast, ß-AR stimulation was unable to increase the already enhanced contractility of the _1A-AR transgenics, and both dP/dt_max and dP/dt_min remained unaltered in these animals with induction of ß-blockade (Figure 5A).

View larger version (16K): [in this window] [in a new window]   Figure 5. Cardiac responses to adrenergic receptor activation and blockade. The studies in panels A and B were performed on separate groups (n=8 per group) of 8- to 10-week-old NTL controls (|BU) and their TG (|B7) counterparts of the A1A1 line. A, Effect of ß-AR stimulation on the rate of pressure development (+dP/dt) and decay (-dP/dt) was determined by infusion of isoproterenol (Iso, 0.32 ng · g-1 · min-1) for the times indicated by the bars. At the time indicated, the animals were subjected to ß-AR blockade with (±)propranolol (100 ng/g) given as an intravenous bolus. #P<0.05, **P<0.01, TG versus NTL; *P<0.001 for Iso response versus baseline in the NTLs. B, Effect of 1A-specific blockade with KMD-3213 (100 µmol/L; 0.1 µL · g–1 · min–1) on +dP/dt and -dP/dt in NTL controls ( and TG animals (). *P<0.001, NTL versus TG.

The specificity of the _1A-transgenic cardiac phenotype and its dependence on _1A-AR signaling was evaluated by producing selective _1A-AR blockade with KMD-3213. As shown in Figure 5B, infusion of KMD-3213 to _1A transgenics caused a gradual decline in dP/dt_max over 3 minutes, to values not significantly different from those in NTLs. By contrast, neither cardiac contractility (Figure 5B) nor blood pressure or heart rate (data not shown) was significantly altered with administration of KMD-3213 to the NTL controls.

Finally, we also evaluated if expression of various receptor-coupled effectors or contractile proteins was altered in the _1A transgenics. As shown in Figure 3C, neither total PLB expression nor that of two phosphorylated PLB species was altered in the _1A transgenics. Similarly, expression of SERCA2a, troponin I, MLC, the Na⁺-Ca²⁺ exchanger, and NHE1 was also unchanged.

	Discussion

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The novelty of this work lies in the following. First, to our knowledge, this is the first study to specifically show an inotropic action of the _1A-AR in vivo. Second, the dissociation of inotropy from hypertrophy indicates that these two receptor-coupled responses are mediated by distinct signaling pathways. Third, it demonstrates that despite the _1A- and _1B-ARs both being Gq-coupled, their downstream-activated pathways differ. This is evident from the finding that only cardiac-targeted overexpression of the _1A-AR results in enhanced contractility. Fourth, it demonstrates that receptor-linked PLC activation, per se, does not mediate enhanced cardiac contractility. Thus, receptor-linked inotropy and PLC activation are clearly uncoupled in the _1A- versus _1B-AR overexpressors. Fifth, it questions the role of the cardiac _1A-AR as a mediator of hypertrophy, a conclusion based entirely on in vivo studies of the rat and in vitro studies of rat cardiac tissue and cardiomyocytes.^1,3–6 Sixth, as a corollary, and given that human myocardium, like that of the mouse, but unlike that of the rat, expresses only very low levels of ₁-ARs, it also questions the relevance of the rat as a model of human cardiac hypertrophy.

Previous studies of cardiac-targeted ₁-AR-overexpression, involving the wild-type _1B subtype or a constitutively active mutant, demonstrated either no change or impairment of cardiac contractility.^11–13,18 In contrast, as shown here, _1A-AR overexpression markedly enhances contractility. This was evidenced by (1) increased echocardiographic fractional shortening with a decrease in LV dimension at both end-diastole and end-systole; (2) increased dP/dt_max, which could not be further augmented by ß-AR stimulation, and increased dP/dt_max normalized for instantaneous LV pressure despite decreased baseline end-diastolic volume; and (3) a significant leftward/upward shift of the relationship between dP/dt_max and end-diastolic volume, a load-independent index of contractility.¹⁴

Although dP/dt_max was markedly increased in the _1A-transgenic animals, dP/dt_min, a measure of cardiac relaxation, was unchanged. As a result, the ratio of dP/dt_max to dP/dt_min doubled in the transgenic animals, a finding not observed in _1B-AR, PLB knockout, or ß₂-AR models of enhanced cardiac contractility.^13,19,20 In contrast, in animals with genetically induced hypertrophic cardiomyopathy, an increase in this ratio has been noted,²¹ suggesting a relative disparity between contraction and relaxation phenomena. In keeping with this interpretation, the time constant of isovolumic relaxation () was prolonged in the _1A transgenics. Further studies in older animals are currently being undertaken to explore the mechanism of this altered relaxation and to ascertain if, long term, it results in cardiac dysfunction. It is of interest, however, that preliminary hemodynamic studies of 12-month-old _1A transgenics of the A1A1 and A1A4 lines demonstrate persistence of both the hypercontractile phenotype and lack of hypertrophy.

Several lines of evidence indicate that the _1A-transgenic phenotype is due to receptor overexpression and not to indirect effects, resulting, for example, from promiscuous G protein or effector coupling or to crosstalk with other signaling pathways. Thus, the enhanced contractility is directly related to overexpression of the _1A-AR and can be eliminated by acute _1A-specific receptor blockade. Moreover, the enhanced contractility is not associated with a change in ß-AR density or either basal or (-) isoproterenol-stimulated adenylyl cyclase activity and is unaltered by maximal ß-AR blockade. Because ß-AR stimulation increases both the rate of cardiac contraction and relaxation, the finding that dP/dt_min is not increased in the _1A transgenics also argues against crosstalk with ß-ARs in this model. Finally, in contrast to ß-AR activation, stimulation with the ₁-agonist phenylephrine does not increase cAMP generation (Figure 3B).

The _1A-AR–coupled signaling pathway mediating increased contractility in the transgenic animals is currently unclear, given that expression of a variety of receptor-coupled effectors and contractile proteins is unaltered in the _1A transgenics (Figure 3). Consideration of this question must take into account the unchanged or impaired contractility observed in mice with cardiac-targeted overexpression of the wild-type _1B-AR or a constitutively active mutant, despite both an increase in basal PLC activity^7,11,12 and a more marked increase in (-)norepinephrine-stimulated activity (230% increase in total inositol phosphates),⁷ than that observed in the _1A transgenics (+101%). Moreover, neither the _1A (Figure 2) nor the _1B overexpressors⁷ showed changes in inositol-1,4,5-trisphoshate (IP₃). Thus, it is unlikely that inositol phosphates are primarily responsible for the contractile phenotype observed in the _1A transgenics. In any case, concentrations of cardiac IP₃ receptors are low and are not localized primarily to Ca²⁺ stores, responses to IP₃ are slow and weak, and the Ca²⁺ so generated does not contribute to Ca²⁺-induced Ca²⁺ release.⁷ Thus, IP₃ liberated by ₁-AR activation of PLC is unlikely to be an important regulator of intracellular Ca²⁺ concentration under physiological conditions.

Other possible candidates for the increased contractility include the transient outward K⁺ current (I_to) and the Na⁺-H⁺ exchanger, which are inhibited and activated, respectively, by ₁-AR–stimulated protein kinase C (PKC) activation.¹ Suppression of I_to prolongs action potential duration and increases cystolic calcium transients, whereas activation of the Na⁺-H⁺ exchanger results in cystolic alkalization and sensitization of the myofilaments to intracellular Ca²⁺. However, the activator of PKC, sn-1,2-diacylglycerol (DAG), is generated in equimolar amounts to inositol phosphates as a result of PLC-mediated cleavage of inositol phospholipids. Thus, DAG release and consequent PKC activation would be expected to be lower for the _1A than the _1B transgenics. Subtype-specific differences in receptor signaling may, therefore, depend on activation of different PKC isoforms by the two ₁-ARs.²² It is also of note in this regard, that in addition to interaction with the Gq/PLCß pathway, the _1B but not the _1A-AR couples via the high-molecular-weight G protein Gh to PLC.²³

In addition to activation of the Na⁺-H⁺ exchanger, phosphorylation of regulatory myosin light chains (RLCs) also results in an increased rate of force generation due to sensitization of the myofilaments to Ca²⁺, as well as enhanced myofibrillar organization,^24–26 and transgenic mice in which the wild-type RLCs are replaced by a mutant protein that is resistant to phosphorylation develop biventricular dilation and a decrease in dobutamine-stimulated dP/dt_max.²⁴ Phosphorylation of RLCs is catalyzed by myosin light chain kinase, Rho kinase, and PKC. Because these enzymes are all activated by ₁-AR stimulation,^24,25 enhanced RLC phosphorylation may contribute to the hypercontractile phenotype observed in the _1A transgenics.

Despite compelling evidence to implicate the _1A-AR/Gq pathway in cardiac hypertrophy and hypertrophic gene induction,^1,3–6 the _1A transgenics failed to develop hypertrophy. It is also of interest in this regard, that studies both in cultured rat cardiomyocytes and in the intact rat^5,6 indicate that expression of the _1A-AR, but not _1B-AR or _1D-AR, is itself increased by ₁-AR and other hypertrophic stimuli, including aortic banding.⁵ Failure of the _1A transgenics to develop hypertrophy is, thus, quite surprising and contrasts with the marked hypertrophy and remodeling observed in mice with cardiac overexpression of Gq⁸ or other Gq-coupled receptors, such as the angiotensin II type I receptor.²⁷ To resolve this paradox, species differences in cardiac _1A-AR signaling, in the transcriptional regulation of the _1A-AR or both, must be invoked. Interestingly, it has been reported recently that expression of the mouse _1A-AR does not increase with hypertrophy in vivo,^18,28 indicating very different regulation of _1A gene expression in mouse, as compared with rat, cardiomyocytes. Nevertheless, in the present study, given that expression of the _1A transgene was sustained because it was under the control of a heterologous promoter, and that enhanced _1A-AR signaling persisted, altered transcriptional regulation of the mouse _1A-AR gene cannot account for the failure to induce hypertrophy.

In keeping with the lack of hypertrophy observed here in vivo in adult _1A-transgenic animals, Deng et al²⁹ have also found that neonatal mouse cardiomyocytes are resistant to ₁-AR–stimulated hypertrophy, despite displaying intact ß-AR–mediated and T₃-activated hypertrophic responses. Thus, our studies, as well as those of others, indicated that cardiac _1A-AR–coupled hypertrophic pathways present in the rat may not be present in the mouse. Nonetheless, the finding of enhanced cardiac contractility and increased ANF mRNA expression indicate that _1A-AR–coupled signaling is intact in the mouse and, importantly, that the pathway mediating receptor-coupled inotropic responses is preserved.

In summary, the cardiac _1A transgenic model developed in the present study questions the role of the _1A-AR as a mediator of cardiac hypertrophy while demonstrating mediation of an unexpectedly robust increase in contractility. This potentially provides unique opportunities for understanding biochemical pathways relevant to these two responses, pathways that may also be important for the regulation of cardiac function in humans.

	Acknowledgments

 
This work was supported in part by grants (9938388, 970982, and 980199) from the National Health and Medical Research Council of Australia (R.M.G.), a Postgraduate Medical Research Scholarship (PM97S0254) from the National Heart Foundation, Australia (F.L.), and a Royal Australasian College of Surgeons/Royal College of Surgeons of England Research Exchange Fellowship and National Heart Foundation, Australia Postgraduate Medical Research Scholarship (W.A.O.).

Received December 15, 2000; accepted July 12, 2001.

	References

Top Abstract Introduction Materials and Methods Results Discussion References

 
1. Hwa J, De Young MB, Perez DM, Graham RM. Autonomic control of myocardium: -adrenoceptor mechanisms. In: Burnstock G, ed; Shepherd J, Vatner SF, volume eds. The Autonomic Nervous System, Volume VIII, The Nervous Control of the Heart. Cambridge, Mass: Harvard University Press; 1996.

2. Graham RM, Perez DM, Hwa J, Piascik MT. ₁-Adrenergic receptor subtypes: molecular structure, function, and signaling. Circ Res. . 1996; 78: 737–749.

3. Brodde OE, Michel MC. Adrenergic and muscarinic receptors in the human heart. Pharmacol Rev. . 1999; 51: 651–690.

4. Knowlton KU, Michel MC, Itani M, Shubeita HE, Ishihara K, Brown JH, Chien KR. The _1A-adrenergic receptor subtype mediates biochemical, molecular, and morphologic features of cultured myocardial cell hypertrophy. J Biol Chem. . 1993; 268: 15374–15380.

5. Rokosh DG, Stewart AF, Chang KC, Bailey BA, Karliner JS, Camacho SA, Long CS, Simpson PC. ₁-Adrenergic receptor subtype mRNAs are differentially regulated by _1A-adrenergic and other hypertrophic stimuli in cardiac myocytes in culture and in vivo: repression of _1B and _1D but induction of _1C. J Biol Chem. . 1996; 271: 5839–5843.

6. Autelitano DJ, Woodcock EA. Selective activation of _1A-adrenergic receptors in neonatal cardiac myocytes is sufficient to cause hypertrophy and differential regulation of ₁-adrenergic receptor subtype mRNAs. J Mol Cell Cardiol. . 1998; 30: 1515–1523.

7. Harrison SN, Autelitano DJ, Wang BH, Milano C, Du XJ, Woodcock EA. Reduced reperfusion-induced Ins(1,4,5)P₃ generation and arrhythmias in hearts expressing constitutively active _1B-adrenergic receptors. Circ Res. . 1998; 83: 1232–1240.

8. D’Angelo DD, Sakata Y, Lorenz JN, Boivin GP, Walsh RA, Liggett SB, Dorn GW II. Transgenic G q overexpression induces cardiac contractile failure in mice. Proc Natl Acad Sci USA. . 1997; 94: 8121–8126.

9. Glennon PE, Kaddoura S, Sale EM, Sale GJ, Fuller SJ, Sugden PH. Depletion of mitogen-activated protein kinase using an antisense oligodeoxynucleotide approach downregulates the phenylephrine-induced hypertrophic response in rat cardiac myocytes. Circ Res. . 1996; 78: 954–961.

10. Boluyt MO, Zheng JS, Younes A, Long X, O’Neill L, Silverman H, Lakatta EG, Crow MT. Rapamycin inhibits ₁-adrenergic receptor-stimulated cardiac myocyte hypertrophy but not activation of hypertrophy-associated genes. Evidence for involvement of p70 S6 kinase. Circ Res. . 1997; 81: 176–186.

11. Milano CA, Dolber PC, Rockman HA, Bond RA, Venable ME, Allen LF, Lefkowitz RJ. Myocardial expression of a constitutively active _1B-adrenergic receptor in transgenic mice induces cardiac hypertrophy. Proc Natl Acad Sci USA. . 1994; 91: 10109–10113.

12. Akhter SA, Milano CA, Shotwell KF, Cho MC, Rockman HA, Lefkowitz RJ, Koch WJ. Transgenic mice with cardiac overexpression of _1B-adrenergic receptors: in vivo ₁-adrenergic receptor-mediated regulation of ß-adrenergic signaling. J Biol Chem. . 1997; 272: 21253–21259.

13. Grupp IL, Lorenz JN, Walsh RA, Boivin GP, Rindt H. Overexpression of _1B-adrenergic receptor induces left ventricular dysfunction in the absence of hypertrophy. Am J Physiol. . 1998; 275: H1338–H1350.

14. Little WC, Cheng C-P, Mumma M, Igarashi Y, Vinten-Johansen J, Johnson WE. Comparisons of measures of left ventricular contractile performance derived from pressure-volume loops in conscious dogs. Circulation. . 1989; 80: 1378–1387.

15. Karunanithi MK, Young JA, Kalnins W, Kesteven S, Feneley MP. Response of the intact canine left ventricle to increased afterload and increased coronary perfusion pressure in the presence of coronary flow autoregulation. Circulation. . 1999; 100: 1562–1568.

16. Cavalli A, Lattion AL, Hummler E, Nenniger M, Pedrazzini T, Aubert JF, Michel MC, Yang M, Lembo G, Vecchione C, Mostardini M, Schmidt A, Beermann F, Cotecchia S. Decreased blood pressure response in mice deficient of the _1B-adrenergic receptor. Proc Natl Acad Sci USA. . 1997; 94: 11589–11594.

17. Ardati A, Nemer M. A nuclear pathway for ₁-adrenergic receptor signaling in cardiac cells. EMBO J. . 1993; 12: 5131–5139.

18. Wang BH, Du XJ, Autelitano DJ, Milano CA, Woodcock EA. Adverse effects of constitutively active _1B-adrenergic receptors after pressure overload in mouse hearts. Am J Physiol Heart Circ Physiol. . 2000; 279: H1079–H1086.

19. Luo W, Grupp IL, Harrer J, Ponniah S, Grupp G, Duffy JJ, Doetschman T, Kranias EG. Targeted ablation of the phospholamban gene is associated with markedly enhanced myocardial contractility and loss of ß-agonist stimulation. Circ Res. . 1994; 75: 401–409.

20. Milano CA, Allen LF, Rockman HA, Dolber PC, McMinn TR, Chien KR, Johnson TD, Bond RA, Lefkowitz RJ. Enhanced myocardial function in transgenic mice overexpressing the ß₂-adrenergic receptor. Science. . 1994; 264: 582–586.

21. Georgakopoulos D, Christe ME, Giewat M, Seidman CM, Seidman JG, Kass DA. The pathogenesis of familial hypertrophic cardiomyopathy: early and evolving effects from an -cardiac myosin heavy chain missense mutation. Nat Med. . 1999; 5: 327–330.

22. Deng X-F, Rokosh DG, Simpson PC. ₁-Adrenergic receptor subtypes activate different PKC isoforms in mouse heart. Circulation. . 1999; 100 (suppl I): I-566. Abstract.

23. Chen S, Lin F, Iismaa S, Lee KN, Birckbichler PJ, Graham RM. ₁-adrenergic receptor signaling via Gh is subtype specific and independent of its transglutaminase activity. J Biol Chem. . 1996; 271: 32385–32391.

24. Sanbe A, Fewell JG, Gulick J, Osinska H, Lorenz J, Hall DG, Murray LA, Kimball TR, Witt SA, Robbins J. Abnormal cardiac structure and function in mice expressing nonphosphorylatable cardiac regulatory myosin light chain 2. J Biol Chem. . 1999; 274: 21085–21094.

25. Hoshijima M, Sah VP, Wang Y, Chien KR, Brown JH. The low molecular weight GTPase Rho regulates myofibril formation and organization in neonatal rat ventricular myocytes: involvement of Rho kinase. J Biol Chem. . 1998; 273: 7725–7730.

26. Aoki H, Sadoshima J, Izumo S. Myosin light chain kinase mediates sarcomere organization during cardiac hypertrophy in vitro. Nat Med. . 2000; 6: 183–188.

27. Paradis P, Dali-Youcef N, Paradis FW, Thibault G, Nemer M. Overexpression of angiotensin II type I receptor in cardiomyocytes induces cardiac hypertrophy and remodeling. Proc Natl Acad Sci USA. . 2000; 97: 931–936.

28. Snyder LD, Rokosh G, Simpson PC. An _1C-adrenergic receptor/ß-galactosidase reporter mouse for cardiac hypertrophic signaling. Circulation. . 1999; 100 (suppl I): I-553. Abstract.

29. Deng X-F, Rokosh DG, Simpson PC. Autonomous and growth factor-induced hypertrophy in cultured neonatal mouse cardiac myocytes. Circ Res. . 2000; 87: 781–788.

30. Matsubara H, Takaki M, Yasuhara S, Araki J, Suga H. Logistic time constant of isovolumic relaxation pressure-time curve in the canine left ventricle. Better alternative to exponential time constant. Circulation. . 1995; 92: 2318–2326.

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