The metabolic phenotype of the failing heart includes a decrease in
phosphocreatine and total
creatine concentration [Cr], potentially contributing to contractile dysfunction. Surprisingly, in 32- week-old mice over-expressing the myocardial
creatine transporter (CrT-OE), we previously demonstrated that elevated [Cr] correlates with left ventricular (LV)
hypertrophy and failure. The aim of this study was to determine the temporal relationship between elevated [Cr] and the onset of cardiac dysfunction and to screen for potential molecular mechanisms. CrT-OE mice were compared with wild-type (WT) littermate controls longitudinally using cine-MRI to measure cardiac function and single-voxel (1)H-MRS to measure [Cr] in vivo at 6, 16, 32, and 52 weeks of age. CrT-OE mice had elevated [Cr] at 6 weeks (mean 1.9-fold), which remained constant throughout life. Despite this increased [Cr],
LV dysfunction was not apparent until 16 weeks and became more pronounced with age. Additionally, LV tissue from 12 to 14 week old CrT-OE mice was compared to WT using 2D difference in-gel electrophoresis (DIGE). These analyses detected a majority of the heart's metabolic
enzymes and identified seven
proteins that were differentially expressed between groups. The most pronounced
protein changes were related to energy metabolism: alpha- and
beta-enolase were selectively decreased (p<0.05), while the remaining
enzymes of glycolysis were unchanged. Consistent with a decrease in
enolase content, its activity was significantly lower in CrT-OE hearts (in WT, 0.59+/-0.02 micromol
ATP produced/microg
protein/min; CrT-OE, 0.31+/-0.06; p<0.01). Additionally, anaerobic
lactate production was decreased in CrT-OE mice (in WT, 102+/-3 micromol/g wet myocardium; CrT-OE, 78+/-13; p=0.02), consistent with decreased glycolytic capacity. Finally, we found that
enolase may be regulated by increased expression of the
beta-enolase repressor
transcription factor, which was significantly increased in CrT-OE hearts. This study demonstrates that chronically increased myocardial [Cr] in the CrT-OE model leads to the development of progressive
hypertrophy and
heart failure, which may be mediated by a compromise in glycolytic capacity at the level of
enolase.