Protein Synthesis In Heart Muscle Research Articles

Insulin Promotes Mitochondrial Respiration and Survival through PI3K/AKT/GSK3 Pathway in Human Embryonic Stem Cells.

SummaryInsulin is an essential growth factor for the survival and self-renewal of human embryonic stem cells (hESCs). Although it is best known as the principal hormone promoting glycolysis in somatic cells, insulin's roles in hESC energy metabolism remain unclear. In this report, we demonstrate that insulin is essential to sustain hESC mitochondrial respiration that is rapidly decreased upon insulin removal. Insulin-dependent mitochondrial respiration is stem cell specific, and mainly relies on pyruvate and glutamine, while glucose suppresses excessive oxidative phosphorylation. Pharmacologic and genetic manipulations reveal that continuous insulin signal sustains mitochondrial respiration through PI3K/AKT activation and downstream GSK3 inhibition. We further show that insulin acts through GSK3 inhibition to suppress caspase activation and rescue cell survival. This study uncovers a critical role of the AKT/GSK3 pathway in the regulation of mitochondrial respiration and cell survival, highlighting insulin as an essential factor for accurate assessment of mitochondrial respiration in hESCs.

Histostereologic analysis of the parenchyma and stroma of the atrophied myocardium in starvation

The reduced functional load during starvation or protein deficiency leads to reduced protein synthesis in heart muscle [11-13, 15]. Inhibition of protein metabolism associated with interruption of the supply of structural material with the food causes delay in the renewal of contractile proteins, and the unsynchronized changes in the ultrastructural organization of cardiomyocytes are connected with this [3, 4]. The principal structural manifestation of inhibition of protein synthesis when the functional load is reduced is atrophy of the myocardium [2, 6, 9]. Quantitative morphological investigations of the myocardium during starvation have revealed considerable changes in the architectonics of the cardiomyocytes during their atrophy [3, 7]. However, the character and direction of relations between the parenchyma and connective tissue in heart muscle during starvation have not been adequately studied.

The regulation of protein synthesis in heart muscle under normal conditions and in the adriamycin-cardiomyopathy.

The regulation of cardiac protein synthesis, in particular messenger-RNA (mRNA) and polyribosome metabolism, has been investigated in normal rat heart muscle and in the adriamycin-cardiomyopathy by using newly developed methods for the isolation, characterization and in-vitro translation of cardiac polyribosomes and mRNA. The obtained data allow the following conclusions: 1. Normal heart muscle has a high content of polyribosomes (865 micrograms/g) and of mRNA (20-60 micrograms/g), and thus a high rate of protein synthesis. 2. The level of cardiac polyribosomes and mRNA is strictly age-dependent and much higher in young animals (2-3 x). This corresponds to a higher cardiac protein synthesis rate in young animals with a growing heart muscle, and shows that the protein-synthetic reserves of heart muscle decrease sharply with age. 3. Withdrawal of food for 1-3 days results in a pronounced decrease (-50% to -70%) of cardiac polyribosomes and mRNA, demonstrating that the cardiac protein synthesis reacts very sensitively to conditions of starving. 4. The cardiac polyribosomes and mRNA are unevenly distributed in the myocyte. The bulk of these substances is present in the cardiac microsomes, and much less is found in nuclei, myofibrils, mitochondria and in the post-microsomal fraction (=cell-sap) of the cardiac muscle. This shows that the major intracellular site of cardiac protein synthesis is the microsomal fraction of the myocyte. 5. A pool of untranslated mRNA was demonstrated to be present in the cell-sap of the myocyte. This mRNA is to some extent translatable in-vitro and appears to represent mRNA sub-pools with two functions: a) mRNA which is partially broken down or in the process of being broken down, and b) intact mRNA which could have a "reserve-function", e.g., by being utilized to increase cardiac protein synthesis under certain conditions. 6. A method of quantitating small amounts of cardiac mRNA (25-50 ng) has been developed which makes it possible to estimate the mRNA content of cardiac biopsies. 7. These methods were utilized to study the relevance of changes in RNA- and protein synthesis in the development of the adriamycin-cardiomyopathy. It appears that severe decreases in cardiac mRNA and polyribosome levels are a key factor in the pathogenesis of the adriamycin-cardiomyopathy. These decreases are probably caused by the direct binding of adriamycin to cardiac DNA and lead themselves to a persisting decrease in cardiac protein synthesis which in view of the short half-lives of the cardiac contractile proteins (5-12 days) causes a gradual loss of cardiac structure and function.

Effect of insulin on protein synthesis in skeletal muscle of an isolated perfused preparation of rat hemicorpus.

A method for perfusion in vitro of a preparation of rat hemicorpus was developed for study of the metabolism of skeletal muscle. The preparation was stable during perfusion, as indicated by maintenance of ATP concentration, perfusion pressure, and oxygen consumption for up to 90 min. The perfused hemicorpus provided the following advantages for study of protein synthesis in skeletal muscle: (a) hormones and substrates reached the muscle cells through an intact capillary bed, and (b) the preparation included the psoas muscle, which was sufficiently large to allow measurements of intermediates in the pathway of protein synthesis and was readily homogenized for preparation of ribosomes and ribosomal subunits. Perfusion of psoas muscle from fasted rats with buffer containing glucose and insulin reduced the concentration of ribosomal subunits and increased phenylalanine incorporation as compared to perfusion with buffer containing glucose alone. In addition, the hormone increased glucose uptake from the perfusate and inhibited release of free fatty acids from the preparation. When the muscle was perfused with buffer that contained glucose and palmitate, the concentration of ribosomal subunits and phenylalanine incorporation were unchanged. Since fatty acid is known to stimulate protein synthesis in heart muscle, these results indicated that rates of protein synthesis in heart, but not in skeletal, muscle would be maintained during fasting or in diabetic animals by increased plasma concentration of fatty acid.

Regulation of Protein Synthesis in Heart Muscle: I. EFFECT OF AMINO ACID LEVELS ON PROTEIN SYNTHESIS

Protein synthesis in heart muscle has been studied in the isolated rat heart perfused with buffer containing glucose and various amino acid mixtures. The rate of synthesis was evaluated by measuring incorporation of 14C-phenylalanine into whole heart protein and myosin. Protein degradation was estimated by measuring the fall in the specific activity of the free phenylalanine pool and the release of phenylalanine from the heart. 14C-Phenylalanine was suitable for these studies since it equilibrated rapidly with an intracellular pool of stable size and was not converted to other amino acids. Participation of the intracellular free amino acid pool as an intermediate in the pathway of protein synthesis was established. Synthesis of whole heart protein and myosin was increased about 40% when amino acid levels were increased from 1 to 5 times normal plasma levels. A group of 12 amino acids substituted for the complete mixture in producing this effect. Protein degradation appeared to occur at about twice the rate of protein synthesis during perfusion with normal plasma levels of amino acid. When perfusate levels of amino acid were raised, cellular levels of 12 amino acids increased. In general, intracellular amino acid levels reached stable values within 30 min. These studies indicated that protein synthesis in heart muscle could be stimulated by raising perfusate amino acid levels above those normally found in rat plasma. Although net uptake of isoleucine and leucine was observed, suggesting that these amino acids were used as oxidative substrate, the increased rate of synthesis appeared to be due to a direct effect on the pathway of protein synthesis rather than an indirect effect mediated by changes in energy levels of the cell.

Effect of Overload and Hyperbaric Oxygen on Protein Synthesis in Heart Muscle.

s1 May 1967Effect of Overload and Hyperbaric Oxygen on Protein Synthesis in Heart Muscle.Sidney S. Schreiber, M.D., F.A.C.P., Marcus A. Rothschild, M.D., F.A.C.P., Murray Oratz, Ph.D.Sidney S. Schreiber, M.D., F.A.C.P.Search for more papers by this author, Marcus A. Rothschild, M.D., F.A.C.P.Search for more papers by this author, Murray Oratz, Ph.D.Search for more papers by this authorAuthor, Article, and Disclosure Informationhttps://doi.org/10.7326/0003-4819-66-5-1038_2 SectionsAboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinkedInRedditEmail ExcerptProlonged increase in left ventricle contractile action resulting from aortic hypertension or increased cardiac output is associated with hypertrophy and increased protein synthesis, but the mechanism stimulating synthesis is unclear. Using14C-labeled lysine, protein synthesis was measured in the perfused guinea pig heart. Increased fluid load or elevation of aortic pressure without increased load resulted in increased ventricular contractile action and increased14C-lysine incorporation into ventricle protein after 3 hr. Protein synthesis was also augmented in the absence of ventricular overload with increase in direct coronary perfusion. Because of the possible effect of oxygen availability due to increased coronary flow... This content is PDF only. To continue reading please click on the PDF icon. Author, Article, and Disclosure InformationAffiliations: New York, New York PreviousarticleNextarticle Advertisement FiguresReferencesRelatedDetails Metrics 1 May 1967Volume 66, Issue 5Page: 1038-1038KeywordsGuinea pigsHeartHyperbaric oxygenHypertensionLeft ventricleLysineMyocardiumOxygenProtein synthesisProteins ePublished: 1 December 2008 Issue Published: 1 May 1967 PDF downloadLoading ...