Roles of creatine in the regulation of cardiac protein synthesis

The observation that increased muscular activity leads to muscle hypertrophy is well known, but identification of the biochemical and physiological mechanisms by which this occurs remains an important problem. Experiments have been described (5, 6) which suggest that creatine, an end product of contraction, is involved in the control of contractile protein synthesis in differentiating skeletal muscle cells and may be the chemical signal coupling increased muscular activity and the increased muscular mass. During contraction, the creatine concentration in muscle transiently increases as creatine phosphate is hydrolyzed to regenerate ATP. In isometric contraction in skeletal muscle for example, Edwards and colleagues (3) have found that nearly all of the creatine phosphate is hydrolyzed. In this case, the creatine concentration is increased about twofold, and it is this transient change in creatine concentration which is postulated to lead to increased contractile protein synthesis. If creatine is found in several intracellular compartments, as suggested by Lee and Vissher (7), local changes in concentration may be greater then twofold. A specific effect on contractile protein synthesis seems reasonable in light of the work of Rabinowitz (13) and of Page et al. (11), among others, showing disproportionate accumulation of myofibrillar and mitochondrial proteins in response to work-induced hypertrophy and thyroxin-stimulated growth. Previous experiments (5, 6) have shown that skeletal muscles cells which have differentiated in vitro or in vivo synthesize myosin heavy-chain and actin, the major myofibrillar polypeptides, faster when supplied creatine in vitro. The stimulation is specific for contractile protein synthesis since neither the rate of myosin turnover nor the rates of synthesis of noncontractile protein and DNA are affected by creatine. The experiments reported in this communication were undertaken to test whether creatine selectively stimulates contractile protein synthesis in heart as it does in skeletal muscle.     

A relationship between weight loss during food deprivation and subsequent meal size in the locust, Chortoicetes terminifera

Sizes of meals of 0·5 M sucrose taken by adults of either sex of Chortoicetes terminifera showed a strong positive correlation with the weight loss of the insects during the preceding 24 hr period of food deprivation. The relationship was less marked in males fed water, and there was no relationship in those fed 1·0 M sucrose. Meal size in females fed water was as strongly weight loss dependent as in those fed 0·5 M sucrose, but was less so in those fed 1·0 M sucrose. The results indicated that changes occurring after the completion of gut emptying influence meal size.     

Control of myogenesis in the mouse myogenic C2 cell line by medium composition and by insulin: Characterization of permissive and inducible C2 myoblasts

Using subcloning and manipulations of culture conditions we have isolated from the mouse myogenic cell line C2 a variant cell line that we named inducible. Unlike the progenitor cells that are referred to as permissive, inducible myoblasts differentiate poorly in Dulbecco modified Eagle medium plus fetal calf serum (FCS) and require the presence of insulin at a high concentration (1.6 10(-6) M) or insulin-like growth factor I (IGFI) at a lower concentration (2.5 10(-8) M) to differentiate. Permissive and inducible myoblasts fail to differentiate when grown in MCDB202 medium plus 20% FCS, even after a prolonged arrest in G1 phase. This shows that an arrest in G1 is in itself insufficient to trigger terminal differentiation. Both cell types also exhibit distinct patterns of accumulation of muscle mRNAs corresponding to sarcomeric actins and myosin light chain MLC1A. The possibility that these two cell lines might represent two different stages of the progression of myoblasts toward terminal differentiation is discussed.     

Disease-associated pathophysiologic structures in pediatric rheumatic diseases show characteristics of scale-free networks seen in physiologic systems: implications for pathogenesis and treatment

Background

Tamoxifen (TAM) is a well characterized breast cancer drug and selective estrogen receptor modulator (SERM) which also has been associated with a small increase in risk for uterine cancers. TAM's partial agonist activation of estrogen receptor has been characterized for specific gene promoters but not at the genomic level in vivo.Furthermore, reducing uncertainties associated with cross-species extrapolations of pharmaco- and toxicogenomic data remains a formidable challenge.

Results

A comparative ligand and species analysis approach was conducted to systematically assess the physiological, morphological and uterine gene expression alterations elicited across time by TAM and ethynylestradiol (EE) in immature ovariectomized Sprague-Dawley rats and C57BL/6 mice. Differential gene expression was evaluated using custom cDNA microarrays, and the data was compared to identify conserved and divergent responses. 902 genes were differentially regulated in all four studies, 398 of which exhibit identical temporal expression patterns.

Conclusion

Comparative analysis of EE and TAM differentially expressed gene lists suggest TAM regulates no unique uterine genes that are conserved in the rat and mouse. This demonstrates that the partial agonist activities of TAM extend to molecular targets in regulating only a subset of EE-responsive genes. Ligand-conserved, species-divergent expression of carbonic anhydrase 2 was observed in the microarray data and confirmed by real time PCR. The identification of comparable temporal phenotypic responses linked to related gene expression profiles demonstrates that systematic comparative genomic assessments can elucidate important conserved and divergent mechanisms in rodent estrogen signalling during uterine proliferation.     

Purification and properties of protoporphyrinogen oxidase from an anaerobic bacterium, Desulfovibrio gigas.

Protoporphyrinogen oxidase has been solubilized from plasma membranes of Desulfovibrio gigas. The enzyme was purified to apparent homogeneity with single silver-stained protein bands on isoelectric focusing and sodium dodecyl sulfate-polyacrylamide gels. This protoporphyrinogen oxidase has a molecular weight (Mr) of 148,000 and is composed of three dissimilar subunits of Mrs 12,000, 18,500, and 57,000, which are held together by sulfhydryl bonds. Unlike other protoporphyrinogen oxidases, which use molecular oxygen as an electron acceptor, this enzyme does not couple to oxygen. The protoporphyrinogen oxidase donates electrons to 2,6-dichlorophenol-indophenol but not to NAD+, NADP+, flavin adenine dinucleotide, or flavin mononucleotide. The natural physiological electron acceptor of the protoporphyrinogen oxidase from D. gigas is unknown. By using 2,6-dichlorophenol-indophenol as the electron acceptor, the Km and Vmax values for oxidation of protoporphyrinogen were determined to be 21 microM and 8.38 nmol/min per 70 micrograms of protein, respectively. The catalytic rate constant, Kcat, was calculated to be 17.7 mol of protoporphyrin formed per mole of enzyme per min of incubation, and the Kcat/Km was 0.84. Energies of activation were calculated from Arrhenius plots with 7,429 cal (ca. 31,080 J)/mol per degree below 10 degrees C and 1,455 cal (ca. 6,088, J)/mol per degree above 10 degrees C. Optimum enzyme activity was at 23 degrees C, and inhibition was observed with both N-ethylmaleimide and iodoacetamide.     

Gold nanorods targeted to delta opioid receptor: plasmon-resonant contrast and photothermal agents

Molecularly targeted gold nanorods were investigated for applications in both diagnostic imaging and disease treatment with cellular resolution. The nanorods were tested in two genetically engineered cell lines derived from the human colon carcinoma HCT-116, a model for studying ligand-receptor interactions. One of these lines was modified to express delta opioid receptor (deltaOR) and green fluorescent protein, whereas the other was receptor free and expressed a red fluorescent protein, to serve as the control. Deltorphin, a high-affinity ligand for deltaOR, was stably attached to the gold nanorods through a thiol-terminated linker. In a mixed population of cells, we demonstrated selective imaging and destruction of receptor-expressing cells while sparing those cells that did not express the receptor. The molecularly targeted nanorods can be used as an in vitro ligand-binding and cytotoxic treatment assay platform and could potentially be applied in vivo for diagnostic and therapeutic purposes with endoscopic technology.     

Trees tolerate an extreme heatwave via sustained transpirational cooling and increased leaf thermal tolerance

Heatwaves are likely to increase in frequency and intensity with climate change, which may impair tree function and forest C uptake. However, we have little information regarding the impact of extreme heatwaves on the physiological performance of large trees in the field. Here, we grew Eucalyptus parramattensis trees for 1 year with experimental warming (+3°C) in a field setting, until they were greater than 6 m tall. We withheld irrigation for 1 month to dry the surface soils and then implemented an extreme heatwave treatment of 4 consecutive days with air temperatures exceeding 43°C, while monitoring whole‐canopy exchange of CO₂ and H₂O, leaf temperatures, leaf thermal tolerance, and leaf and branch hydraulic status. The heatwave reduced midday canopy photosynthesis to near zero but transpiration persisted, maintaining canopy cooling. A standard photosynthetic model was unable to capture the observed decoupling between photosynthesis and transpiration at high temperatures, suggesting that climate models may underestimate a moderating feedback of vegetation on heatwave intensity. The heatwave also triggered a rapid increase in leaf thermal tolerance, such that leaf temperatures observed during the heatwave were maintained within the thermal limits of leaf function. All responses were equivalent for trees with a prior history of ambient and warmed (+3°C) temperatures, indicating that climate warming conferred no added tolerance of heatwaves expected in the future. This coordinated physiological response utilizing latent cooling and adjustment of thermal thresholds has implications for tree tolerance of future climate extremes as well as model predictions of future heatwave intensity at landscape and global scales.