Darrabie MD, Arciniegas AJ, Mishra R, Bowles DE, Jacobs DO, Santacruz L. AMPK and substrate availability regulate creatine transport in cultured cardiomyocytes. Am J Physiol Endocrinol Metab 300: E870 -E876, 2011. First published March 1, 2011; doi:10.1152/ajpendo.00554.2010.-Profound alterations in myocellular creatine and phosphocreatine levels are observed during human heart failure. To maintain its intracellular creatine stores, cardiomyocytes depend upon a cell membrane creatine transporter whose regulation is not clearly understood. Creatine transport capacity in the intact heart is modulated by substrate availability, and it is reduced in the failing myocardium, likely adding to the energy imbalance that characterizes heart failure. AMPK, a key regulator of cellular energy homeostasis, acts by switching off energy-consuming pathways in favor of processes that generate energy. Our objective was to determine the effects of substrate availability and AMPK activation on creatine transport in cardiomyocytes. We studied creatine transport in rat neonatal cardiomyocytes and HL-1 cardiac cells expressing the human creatine transporter cultured in the presence of varying creatine concentrations and the AMPK activator 5-aminoimidazole-4-carboxamide-1--D-ribonucleoside (AICAR). Transport was enhanced in cardiomyocytes following incubation in creatine-depleted medium or AICAR. The changes in transport were due to alterations in Vmax that correlated with changes in total and cell surface creatine transporter protein content. Our results suggest a positive role for AMPK in creatine transport modulation for cardiomyocytes in culture. myocardial creatine content; cardiac energy metabolism; adenosine 5=-monophosphate-activated protein kinase; cardiac failure CREATINE (Cr) and its phosphorylated form phosphocreatine (PCr), together with creatine kinases (CK), comprise a system that helps maintain ATP stores in cardiac and skeletal myocytes (23). During cardiac hypertrophy and heart failure, the myocardium exhibits marked changes in energy metabolism, including changes in substrate utilization, as well as in the content of high-energy metabolites. The PCr/ATP ratio decreases (9,19
The molecular differences between ischemic (IF) and non-ischemic (NIF) heart failure are poorly defined. A better understanding of the molecular differences between these two heart failure etiologies may lead to the development of more effective heart failure therapeutics. In this study extensive proteomic and phosphoproteomic profiles of myocardial tissue from patients diagnosed with IF or NIF were assembled and compared.Proteins extracted from left ventricular sections were proteolyzed and phosphopeptides were enriched using titanium dioxide resin. Gel- and label-free nanoscale capillary liquid chromatography coupled to high resolution accuracy mass tandem mass spectrometry allowed for the quantification of 4,436 peptides (corresponding to 450 proteins) and 823 phosphopeptides (corresponding to 400 proteins) from the unenriched and phospho-enriched fractions, respectively.Protein abundance did not distinguish NIF from IF. In contrast, 37 peptides (corresponding to 26 proteins) exhibited a ≥2-fold alteration in phosphorylation state (p<0.05) when comparing IF and NIF. The degree of protein phosphorylation at these 37 sites was specifically dependent upon the heart failure etiology examined. Proteins exhibiting phosphorylation alterations were grouped into functional categories: transcriptional activation/RNA processing; cytoskeleton structure/function; molecular chaperones; cell adhesion/signaling; apoptosis; and energetic/metabolism.Phosphoproteomic analysis demonstrated profound post-translational differences in proteins that are involved in multiple cellular processes between different heart failure phenotypes. Understanding the roles these phosphorylation alterations play in the development of NIF and IF has the potential to generate etiology-specific heart failure therapeutics, which could be more effective than current therapeutics in addressing the growing concern of heart failure.
Heart failure is a common complication of doxorubicin (DOX) therapy. Previous studies have shown that DOX adversely impacts cardiac energy metabolism, and the ensuing energy deficiencies antedate clinical manifestations of cardiac toxicity. Brief exposure of cultured cardiomyocytes to DOX significantly decreases creatine transport, which is the cell's sole source of creatine. We present the results of a study performed to determine if physiological creatine supplementation (5 mmol/L) could protect cardiomyocytes in culture from cellular injury resulting from exposure to therapeutic levels of DOX. Creatine supplementation significantly decreased cytotoxicity, apoptosis, and reactive oxygen species production caused by DOX. The protective effect was specific to creatine and depended on its transport into the cell.
Creatine (Cr), phosphocreatine (PCr), and creatine kinases (CK) comprise an energy shuttle linking ATP production in mitochondria with cellular consumption sites. Myocytes cannot synthesize Cr: these cells depend on uptake across the cell membrane by a specialized creatine transporter (CrT) to maintain intracellular Cr levels. Hypoxia interferes with energy metabolism, including the activity of the creatine energy shuttle, and therefore affects intracellular ATP and PCr levels. Here, we report that exposing cultured cardiomyocytes to low oxygen levels rapidly diminishes Cr transport by decreasing V max and K m. Pharmacological activation of AMP‐activated kinase (AMPK) abrogated the reduction in Cr transport caused by hypoxia. Cr supplementation increases ATP and PCr content in cardiomyocytes subjected to hypoxia, while also significantly augmenting the cellular adaptive response to hypoxia mediated by HIF‐1 activation. Our results indicate that: (1) hypoxia reduces Cr transport in cardiomyocytes in culture, (2) the cytoprotective effects of Cr supplementation are related to enhanced adaptive physiological responses to hypoxia mediated by HIF‐1, and (3) Cr supplementation increases the cellular ATP and PCr content in RNCMs exposed to hypoxia.
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