Normal cardiac function in mice with supraphysiological cardiac creatine levels

Abstract

DO. Normal cardiac function in mice with supraphysiological cardiac creatine levels. Am J Physiol Heart Circ Physiol 306: H373-H381, 2014. First published November 22, 2013; doi:10.1152/ajpheart.00411.2013.-Creatine and phosphocreatine levels are decreased in heart failure, and reductions in myocellular phosphocreatine levels predict the severity of the disease and portend adverse outcomes. Previous studies of transgenic mouse models with increased creatine content higher than two times baseline showed the development of heart failure and shortened lifespan. Given phosphocreatine's role in buffering ATP content, we tested the hypothesis whether elevated cardiac creatine content would alter cardiac function under normal physiological conditions. Here, we report the creation of transgenic mice that overexpress the human creatine transporter (CrT) in cardiac muscle under the control of the ␣-myosin heavy chain promoter. Cardiac transgene expression was quantified by qRT-PCR, and human CrT protein expression was documented on Western blots and immunohistochemistry using a specific anti-CrT antibody. High-energy phosphate metabolites and cardiac function were measured in transgenic animals and compared with age-matched, wild-type controls. Adult transgenic animals showed increases of 5.7-and 4.7-fold in the content of creatine and free ADP, respectively. Phosphocreatine and ATP levels were two times as high in young transgenic animals but declined to control levels by the time the animals reached 8 wk of age. Transgenic mice appeared to be healthy and had normal life spans. Cardiac morphometry, conscious echocardiography, and pressure-volume loop studies demonstrated mild hypertrophy but normal function. Based on our characterization of the human CrT protein expression, creatine and phosphocreatine content, and cardiac morphometry and function, these transgenic mice provide an in vivo model for examining the therapeutic value of elevated creatine content for cardiac pathologies. cardiac failure; creatine transporter; energy metabolism; phosphocreatins A HALLMARK OF CARDIAC FAILURE is a marked disturbance of energy metabolism. In this condition, the manner in which ATP is buffered and transferred, via the creatine kinase (CK) system, from the mitochondria to utilization sites, is profoundly altered (26). In the early stages of heart failure, myocardial creatine (Cr) and phosphocreatine (PCr) are reduced by as much as 70%, whereas a slow and progressive ATP loss of up to 30 -40% is observed at the latter stages of the disease (4,28,39,45). Moreover, the PCr-to-ATP ratio decreases, and this decrease is a better predictor of overall and cardiovascular-related mortality than traditional indexes such as ejection fraction or New York Heart Association symptomatology (27). These deficits in high-energy metabolites are accompanied by decreases in the activity and expression levels of the CKs in the myocardium (22, 38). Recent reports elegantly illustrated that increased CK function has a protective effect in murine models of ...

Role of Creatine in the Heart: Health and Disease

“…Moreover, they found that such an increase in intracellular creatine caused downregulation of the cellular enzyme enolase, which supposedly decreased glycolytic activity of the cardiomyocytes [ 40 ]. However, a different group later used the same transporter over-expression to obtain a large increase in intracellular creatine, but did not find any adverse effect of this increase [ 42 ]. In an interesting study, Zervou et al [ 43 ] compared wildtype mice, mice overexpressing the creatine transporter that showed a moderate increase in creatine, and mice overexpressing the transporter that showed a large creatine increase (average creatine content was 81 nmol/mg protein in wildtype animals, 123 and 220 in the other two groups, respectively).…”

Augmentation of Creatine in the Heart

“…These mice were also shown to have impaired glycolytic capacity as a result of reduced enolase expression [67]. Recently, a second mouse model of CrT overexpression (CrT-OE Duke) has been described with normal cardiac function and only mild hypertrophy despite creatine levels up to 5.7-fold higher than controls [68]. Notably, PCr levels are elevated at 2 and 4 weeks, but return to normal by 8 weeks of age while creatine levels continue to increase throughout.…”

“…Furthermore, only 4% of cardiomyocytes appear to express the transgene. Several factors may contribute to these differences, for example, the Oxford mouse over-expresses rabbit CrT using an MLC2v promoter on a C57BL/6J background [23]; whereas the Duke mouse is human CrT using αMHC promoter on an FVB background [68].…”

Modulation of CT1 Function: From Klotho Protein to Ammonia and Beyond

“…Supra-normal myocardial creatine and phosphocreatine concentrations thus might lead to energetic impairment, probably due to the fact that the myocardium is incapable of keeping the augmented creatine pool adequately phosphorylated. On the other hand, Santacruz et al ( 38 ) found no cardiac damage in mice with supraphysiological cardiac creatine levels. Adult transgenic animals showed an increase of 5.7-fold in the content of myocardial creatine, yet cardiac morphometry, echocardiography, and pressure–volume loop analyses demonstrated mild hypertrophy but normal function.…”