Molecular Cardiology
Calcineurin Splicing Variant Calcineurin A1 Improves
Cardiac Function After Myocardial Infarction Without
Inducing Hypertrophy
Leanne E. Felkin, PhD; Takuya Narita, MD, PhD*; Rene ´e Germack, PhD*;
Yasunori Shintani, MD, PhD*; Kunihiko Takahashi, MD, PhD*; Padmini Sarathchandra, PhD;
Marina M. Lo ´pez-Olan ˜eta, MLT; Jesu ´s M. Go ´mez-Salinero, BS; Ken Suzuki, MD, PhD;
Paul J.R. Barton, PhD; Nadia Rosenthal, PhD; Enrique Lara-Pezzi, PhD
Background—Calcineurin is a calcium-regulated phosphatase that plays a major role in cardiac hypertrophy. We
previously described that alternative splicing of the calcineurin A (CnA) gene generates the CnA1 isoform, with a
unique C-terminal region that is different from the autoinhibitory domain present in all other CnA isoforms. In skeletal
muscle, CnA1 is necessary for myoblast proliferation and stimulates regeneration, reducing fibrosis and accelerating
the resolution of inflammation. Its role in the heart is currently unknown.
Methods and Results—We generated transgenic mice overexpressing CnA1 in postnatal cardiomyocytes under the control of
the -myosin heavy chain promoter. In contrast to previous studies using an artificially truncated calcineurin, CnA1
overexpression did not induce cardiac hypertrophy. Moreover, transgenic mice showed improved cardiac function and
reduced scar formation after myocardial infarction, with reduced neutrophil and macrophage infiltration and decreased
expression of proinflammatory cytokines. Immunoprecipitation and Western blot analysis showed interaction of CnA1 with
the mTOR complex 2 and activation of the Akt/SGK cardioprotective pathway in a PI3K-independent manner. In addition,
gene expression profiling revealed that CnA1 activated the transcription factor ATF4 downstream of the Akt/mTOR
pathway to promote the amino acid biosynthesis program, to reduce protein catabolism, and to induce the antifibrotic and
antiinflammatory factor growth differentiation factor 15, which protects the heart through Akt activation.
Conclusions—Calcineurin A1 shows a unique mode of action that improves cardiac function after myocardial infarction,
activating different cardioprotective pathways without inducing maladaptive hypertrophy. These features make CnA1
an attractive candidate for the development of future therapeutic approaches. (Circulation. 2011;123:2838-2847.)
Key Words: amino acids
calcineurin
mice, transgenic
myocardial infarction
signal transduction
C
alcineurin is a calcium-dependent serine/threonine phos-
phatase that regulates a wide variety of physiological
and pathological processes.
1
Calcineurin links changes in
intracellular calcium to gene transcription by dephosphory-
lating the transcription factor nuclear factor of activated T
cells (NFAT), among others, and inducing its translocation to
the nucleus.
1
It is composed of a catalytic subunit (CnA) and
a regulatory subunit (CnB). Three different CnA isoforms are
found in mammals: CnA and CnA, which are ubiquitously
expressed, and CnA, restricted to brain and testis. They
share a common structure, including a phosphatase domain,
CnB-binding region, calmodulin-binding region, and
C-terminal autoinhibitory domain. In its inactive state, the
catalytic site in CnA is blocked by this autoinhibitory domain.
In response to raised intracellular calcium, CnB and calmod-
ulin activate CnA by inducing a conformational change that
displaces the autoinhibitory domain and exposes the catalytic
site. Artificial removal of the autoinhibitory domain renders
CnA constitutively active and results in full NFAT activation.
Clinical Perspective on p 2847
In the heart, calcineurin participates in both cardiac devel-
opment and disease. Calcineurin plays a central role in the
development of maladaptive but not physiological hypertro-
phy.
2
Transgenic mice overexpressing an artificially trun-
cated, constitutively active form of CnA that lacks the
Received August 30, 2010; accepted April 4, 2011.
From the Heart Science Centre, National Heart and Lung Institute, Imperial College London, London, UK (L.E.F., R.G., P.S., K.S., P.J.R.B., N.R.,
E.L.-P.); Translational Cardiovascular Therapeutics, William Harvey Research Institute, Barts and The London School of Medicine and Dentistry, Queen
Mary University of London, UK (T.N., Y.S., K.T., K.S.); Mouse Biology Unit, European Molecular Biology Laboratory, Rome, Italy (N.R.);
Cardiovascular Development Biology Department, Centro Nacional de Investigaciones Cardiovasculares, Madrid, Spain (M.M.L.-O., J.M.G.-S., E.L.-P.);
and NIHR Cardiovascular Biomedical Research Unit, Royal Brompton and Harefield NHS Foundation Trust, London, UK (P.J.R.B.).
*Drs Narita, Germack, Shintani, and Takahashi contributed equally to this article.
The online-only Data Supplement is available with this article at http://circ.ahajournals.org/cgi/content/full/CIRCULATIONAHA.110.012211/DC1.
Correspondence to Enrique Lara-Pezzi, Cardiovascular Development Biology Department, Centro Nacional de Investigaciones Cardiovasculares,
Melchor Ferna ´ndez Almagro 3, 28029 Madrid, Spain. E-mail elara@cnic.es
© 2011 American Heart Association, Inc.
Circulation is available at http://circ.ahajournals.org DOI: 10.1161/CIRCULATIONAHA.110.012211
2838
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