Creatine Kinase Overexpression Increases in vivo ATP Synthesis in the Failing Mouse Heart
A. Gupta1,2, V. P. Chacko3, Y. Wang4, and R. G. Weiss2,5
Department of Medicine, Division of Cardiology, The Johns Hopkins University, School of Medicine, Baltimore, MD, United States, 2Department of Radiology,
Division of Magnetic Resonance Research, The Johns Hopkins University, Baltimore, MD, United States, 3Department of Radiology,Division of Magnetic Resonance
Research, The Johns Hopkins University School of Medicine, Baltimore, MD, United States, 4Department of Anesthesiology and medicine, University of California,
Los Angeles, CA, United States, 5Department of Medicine, Division of Cardiology, The Johns Hopkins University School of Medicine, Baltimore, MD, United States
1
INTRODUCTION: High ATP delivery rates fuel cardiac contraction and impaired ATP transfer through creatine kinase (CK), the
prime cardiac energy reserve, may limit contractile function in heart failure (HF)1. The rate of ATP synthesis through CK (CK flux) is
reduced in experimental and human HF, but means to augment CK flux in HF are lacking. We hypothesized that failing mouse hearts
overexpressing the predominant M isoform of CK (CK-M) would have enhanced CK flux. We adapted 31P MRS TRiST 2-3 to noninvasively measure in vivo cardiac CK flux in the mouse heart and test the hypothesis that ATP flux is reduced in murine HF.
MATERIALS AND METHODS: Experiments were carried out on
a Bruker Biospec MRI/MRS spectrometer equipped with a
4.7T/40cm Oxford magnet and a 12cm (inner diameter) actively
shielded gradient set, as previously described3. The TRiST method
was adapted2-3 and evaluated in the in vivo mouse heart. The TRiST
cardiac study included 3 image-guided, localized 31P MRS
acquisitions: two with irradiation of γ-ATP at -2.5ppm (TR=1.5s and
TR=6s), and one with control irradiation at +2.5ppm (TR=10s),
which were all acquired on healthy control (n=11), control with 8
weeks after thoracic aorta constriction (TAC, n=10), CK-M overexpressed (n=8) and CK-M over-expressed with TAC (n=7) mouse
hearts. CK flux was calculated as [PCr]x(kf), where kf is the CK
pseudo-first order rate constant. [PCr] and [ATP] were evaluated in
vivo in murine hearts as described previously4.
RESULTS: A representative 1H image and spatially-localized TRiST
31
P spectra are shown in Fig.1. 31P MRS results are summarized in
Table 1. Cardiac CK flux was reduced by ~50% with TAC (Table 1).
Murine cardiac kf and ATP flux, as well as their relative reductions
with TAC (Table 1), agree with values previously reported in normal
(kf=0.32±0.07s-1, ATP flux=3.2±0.09µmol/g/s) and failing
(kf=0.21±0.07s-1, ATP flux=1.6±0.06µmol/g/s) human hearts5.
Importantly, cardiac kf and CK flux in the CK-M over-expressed
control and TAC animals were significantly higher than that in
respective controls (Table 1).
Figure 1: (A) Typical transverse 1H MR image of a mouse thorax with 31P
MR cardiac voxel denoted by white lines (B) 31P MR spectrum with γphosphate of ATP saturation with TR=1.5s, NEX=96, (C) γ-phosphate
ATP saturation with TR=6s, NEX=32, and (D) control saturation
spectrum with TR=10s and NEX=16. PCr; phosphocreatine, β-ATP; βphosphate of adenosine triphosphate
CONCLUSIONS: Despite size and heart rate differences, CK flux is
similar in vivo in murine and human hearts and comparably reduced
in HF. CK-M overexpression, at least in mice, offers the first means
to augment impaired ATP delivery to the failing heart.
REFERENCES: (1) Katz AM. Cardiol Clin 1998;16:633-644.(2) Schär M. et. al.
Mag. Reso. Med. 2010; 63: 1493-1501. (3) Gupta A. et. al. Circ. Cardiovasc. Imaging.
2010. (4) Gupta A. et. al. Am. J. Physiol Heart Circ Physiol. 2009; 297:H59-H64. (5)
Weiss R.G. et. al. PNAS 2005; 102:808-813.
Proc. Intl. Soc. Mag. Reson. Med. 19 (2011)
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Table 1: PCr/ATP, [PCr], [ATP], Kf ATP flux measured by 31PMRS under
in vivo mouse heart (Mean ± S.D.) *P < 0.05 compared to control, $P <
0.05 compared to respective control