doi: 10.1161/hh1101.092004
© 2001 American Heart Association, Inc.
Letter to the Editor |
Overwhelming Evidence of the Beneficial Effects of SERCA Gene Transfer in Heart Failure
Harvard Medical School, Massachusetts General Hospital, Cardiovascular Research Center, Charlestown, Mass, hajjar@cvrc.mgh.harvard.edu
Imperial College, London, UK
To the Editor:
We read with great interest the work by O’Donnell et al1 on the possible toxic effect of the sarcoplasmic reticulum Ca2+ ATPase pump in neonatal cardiac myocytes. Because gene transfer of SERCA2a is being currently considered as a modality for the treatment of heart failure,2 the work by O’Donnell et al has the potential of raising concern about such a strategy. However, a number of limitations in this study preclude any definitive conclusions regarding the toxicity of overexpressing SERCA. The authors demonstrated the expression of the noncardiac isoform SERCA1 in embryonic and neonatal cardiac myocytes in their studies. These cardiomyocytes have a poorly developed sarcoplasmic reticulum and do not represent functionally the adult heart. In addition, the expression of the SERCA1 isoform may result in abnormal intracellular trafficking, which results in irregular calcium signaling. Although the authors state that cytotoxic effects observed with SERCA1 overexpression are "slightly" higher than with the empty or reporter viruses, no statistical significance is shown. The apoptosis index, which is unusually high in this study compared with other published studies,3 is not reportedly different between SERCA1 overexpression or GFP overexpression. The conclusions drawn in this study are in direct contrast to those validated by numerous experimental results showing that overexpression of the cardiac isoform, SERCA2a, improves contractility both in vivo and in vitro without detrimental effects.4 5 6 Most importantly, a recent study by Davia et al7 showed that overexpression of SERCA2a in adult rabbit cardiac myocytes has protective effects in contrast to ß-agonism and prolongs survival in these adult cardiomyocytes. In addition, the exogenous expression of SERCA2a by either transgenesis or adenovirus has ranged from 1.13- to 2-fold,4 8 9 pointing toward an endogenous regulation of SERCA2a levels in cardiac cells. Although the study by O’Donnell et al1 describes cytotoxic effects of recombinant adenoviruses in embryonic and neonatal cardiac myocytes, there is very little evidence that exogenously increasing SR ATPase activity has detrimental effects. On the contrary, there is ample evidence that expression of the cardiac isoform, SERCA2a, not only rescues contractile function in failing hearts but has protective effects.
References
1.
O’Donnell
JM, Sumbilla CM, Ma H, Farrance IKG, Cavagna M, Klein MG, Inesi G.
Tight control of exogenous SERCA expression is required to obtain
acceleration of calcium transients with minimal cytotoxic effects in
cardiac myocytes. Circ Res. 2001;88:415–421.
2.
Hajjar RJ, del
Monte F, Matsui T, Rosenzweig A. Prospects for gene therapy for heart
failure. Circ Res. 2000;86:616–621.
3.
Matsui T, Li L, del
Monte F, Fukui Y, Franke TF, Hajjar RJ, Rosenzweig A. Adenoviral gene
transfer of activated phosphatidylinositol 3'-kinase and Akt
inhibits apoptosis of hypoxic cardiomyocytes in
vitro. Circulation. 1999;100:2373–2379.
4.
Hajjar RJ, Kang JX,
Gwathmey JK, Rosenzweig A. Physiological effects of
adenoviral gene transfer of sarcoplasmic reticulum calcium ATPase in
isolated rat myocytes.
Circulation. 1997;95:423–429.
5.
Miyamoto MI,
del Monte F, Schmidt U, DiSalvo TS, Kang ZB, Matsui T, Guerrero JL,
Gwathmey JK, Rosenzweig A, Hajjar RJ. Adenoviral gene transfer of
SERCA2a improves left-ventricular function in aortic-banded
rats in transition to heart failure. Proc
Natl Acad Sci
USA. 2000;97:793–798.
6.
del Monte F,
Harding SE, Schmidt U, Matsui T, Kang ZB, Dec GW, Gwathmey JK,
Rosenzweig A, Hajjar RJ. Restoration of contractile function in
isolated cardiomyocytes from failing human hearts by gene
transfer of SERCA2a.
Circulation. 1999;100:2308–2311.
7. Davia K, Bernobich E, Ranu HR, del Monte F, Terracciano CM, MacLeod KT, Adamson DL, Chaudhri B, Hajjar RJ, Harding SE. SERCA2a overexpression decreases the incidence of aftercontractions in adult rabbit ventricular myocytes. J Mol Cell Cardiol. 2001;33:1005–1115.[Medline] [Order article via Infotrieve]
8. He H, Giordano FJ, Hilal-Dandan R, Choi DJ, Rockman HA, McDonough PM, Bluhm WF, Meyer M, Sayen MR, Swanson E, Dillmann WH. Overexpression of the rat sarcoplasmic reticulum Ca2+ ATPase gene in the heart of transgenic mice accelerates calcium transients and cardiac relaxation. J Clin Invest. 1997;100:380–389.[Medline] [Order article via Infotrieve]
9.
Baker DL, Hashimoto
K, Grupp IL, Ji Y, Reed T, Loukianov E, Grupp G, Bhagwhat A, Hoit B,
Walsh R, Marbán E, Periasamy M. Targeted overexpression of the
sarcoplasmic reticulum Ca2+-ATPase increases
cardiac contractility in transgenic mouse hearts.
Circ Res. 1998;83:1205–1214.
Response
Biochemistry and Molecular Biology, University of Maryland School of Medicine, Baltimore, Md, ginesi@umaryland.edu
I am gratified for the interest elicited by our study.R1 With it, we did not mean to raise obstacles to laudable attempts to develop SERCA gene transfer modalities for the treatment of heart failure.R2 Our laboratory has for a long time generated basic information, including the original description of cardiac SERCA,R3 leading to the present interest regarding its role in heart failure. In our experiments, we use embryo or neonatal hearts to obtain reliable myocyte cultures that are suited to quantitative and statistical measurements, including accurate determination of catalytic turnover in various isoforms.R4 In these preparations, we showed sarcoplasmic reticulum development by confocal microscopy, and we did indeed find that a 2-fold increase in SERCA expression level improves Ca2+ signaling. This effect was demonstrated with complementary Ca2+ indicators to yield kinetic as well as stoichiometric measurements.R5 We prefer not to culture adult myocytes because of their low survival rate, which precludes meaningful statistics on the effects of experimental perturbations on survival. An advantageous switch to the SERCA1 isoform has been demonstrated not only in our experimentsR4 but also in transgenic animals.R6 It is important to recognize that, in transgenic animals, regulation by untranslated regions and occurrence of compensatory mechanisms allow safe levels of expression in surviving animals. Our concern is related to establishment of conditions for both safe and effective exogenous gene transfer by means of viral vectors, which is likely the method to be used in failing hearts. We have made careful efforts to restrict the viral titer to avoid cytotoxic effectsR1 and to use cell-specific promoters to limit expression to cardiac muscle.R7 Certainly one would not want cytotoxic expression of exogenous SERCA in smooth muscle, endothelium, and even liver cells (in addition to cardiac myocytes), which would be obtained by nondiscriminative use of strong and constitutive promoters. We hope that this information will help the development of safe and effective methods of gene transfer.
References
1. O’Donnell JM, Sumbilla CM, Ma H, Farrance IKG, Cavagna M, Klein MG, Inesi G. Tight control of exogenous SERCA expression is required to obtain acceleration of calcium transients with minimal toxic effects in cardiac myocytes. Circ Res. 2001;88:415–421.
2. Hajjar RJ, del Monte F, Matsui T, Rosenzweig A. Prospects for gene therapy for heart failure. Circ Res. 2000;86:616–621.
3. Inesi G, Ebashi S, Watanabe S. Preparation of vesicular relaxing factor from bovine heart tissue. Am J Physiol. 1964;14:167–222.
4.
Sumbilla C,
Cavagna M, Zhong L, Ma H, Lewis D, Farrance IK, Inesi G. Comparison of
SERCA1 and SERCA2a expressed in COS-1 cells and cardiac myocytes.
Am J Physiol. 1999;277:H2381–H2391.
5. Cavagna M, O’Donnell JM, Sumbilla C, Inesi G. Exogenous Ca2+-ATPase isoform effects on Ca2+ transients of embryonic chicken and neonatal rat cardiac myocytes. J Physiol. 2000;528(pt 1):53–63.
6.
Loukianov E, Ji Y,
Grupp IL, Kirkpatrick DL, Baker DL, Loukianova T, Grupp G, Lytton J,
Walsh RA, Periasamy M. Enhanced myocardial
contractility and increased
Ca2+ transport function in transgenic hearts
expressing the fast-twitch skeletal muscle sarcoplasmic reticulum
Ca2+ ATPase.
Circ Res. 1998;83:889–897.
7. Inesi G, Lewis D, Sumbilla C, Nandi A, Huff KW, Rogers TB, Johns DC, Kessler CP, Ordhal CP. Cell specific promoter in adenovirus vector for transgenic expression of SERCA1 ATPase in cardiac myocytes. Am J Physiol. 1998;43:C645–C653.
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