Increased Lipolysis and Energy Expenditure in a Mouse Model with Severely Impaired Glucagon Secretion

10.1371/journal.pone.0026671PLoS ONE610

Loss of BCAA Catabolism during Carcinogenesis Enhances mTORC1 Activity and Promotes Tumor Development and Progression

Tumors display profound changes in cellular metabolism, yet how these changes aid the development and growth of tumors is not fully understood. Here we use a multi-omic approach to examine liver carcinogenesis and regeneration, and find that progressive loss of branched-chain amino acid (BCAA) catabolism promotes tumor development and growth. In human hepatocellular carcinomas and animal models of liver cancer, suppression of BCAA catabolic enzyme expression led to BCAA accumulation in tumors, though this was not observed in regenerating liver tissues. The degree of enzyme suppression strongly correlated with tumor aggressiveness, and was an independent predictor of clinical outcome. Moreover, modulating BCAA accumulation regulated cancer cell proliferation in vitro, and tumor burden and overall survival in vivo. Dietary BCAA intake in humans also correlated with cancer mortality risk. In summary, loss of BCAA catabolism in tumors confers functional advantages, which could be exploited by therapeutic interventions in certain cancers

Measuring intracellular pH in the heart using hyperpolarized carbon dioxide and bicarbonate: a 13C and 31P magnetic resonance spectroscopy study

AIMS: Technological limitations have restricted in vivo assessment of intracellular pH (pH(i)) in the myocardium. The aim of this study was to evaluate the potential of hyperpolarized [1-(13)C]pyruvate, coupled with (13)C magnetic resonance spectroscopy (MRS), to measure pH(i) in the healthy and diseased heart. METHODS AND RESULTS: Hyperpolarized [1-(13)C]pyruvate was infused into isolated rat hearts before and immediately after ischaemia, and the formation of (13)CO(2) and H(13)CO(3)(-) was monitored using (13)C MRS. The HCO(3)(-)/CO(2) ratio was used in the Henderson-Hasselbalch equation to estimate pH(i). We tested the validity of this approach by comparing (13)C-based pH(i) measurements with (31)P MRS measurements of pH(i). There was good agreement between the pH(i) measured using (13)C and (31)P MRS in control hearts, being 7.12 +/- 0.10 and 7.07 +/- 0.02, respectively. In reperfused hearts, (13)C and (31)P measurements of pH(i) also agreed, although (13)C equilibration limited observation of myocardial recovery from acidosis. In hearts pre-treated with the carbonic anhydrase (CA) inhibitor, 6-ethoxyzolamide, the (13)C measurement underestimated the (31)P-measured pH(i) by 0.80 pH units. Mathematical modelling predicted that the validity of measuring pH(i) from the H(13)CO(3)(-)/(13)CO(2) ratio depended on CA activity, and may give an incorrect measure of pH(i) under conditions in which CA was inhibited, such as in acidosis. Hyperpolarized [1-(13)C]pyruvate was also infused into healthy living rats, where in vivo pH(i) from the H(13)CO(3)(-)/(13)CO(2) ratio was measured to be 7.20 +/- 0.03. CONCLUSION: Metabolically generated (13)CO(2) and H(13)CO(3)(-) can be used as a marker of cardiac pH(i) in vivo, provided that CA activity is at normal levels

Neuronal Calcium Sensor Synaptotagmin-9 Is Not Involved in the Regulation of Glucose Homeostasis or Insulin Secretion

BACKGROUND:Insulin secretion is a complex and highly regulated process. It is well established that cytoplasmic calcium is a key regulator of insulin secretion, but how elevated intracellular calcium triggers insulin granule exocytosis remains unclear, and we have only begun to define the identities of proteins that are responsible for sensing calcium changes and for transmitting the calcium signal to release machineries. Synaptotagmins are primarily expressed in brain and endocrine cells and exhibit diverse calcium binding properties. Synaptotagmin-1, -2 and -9 are calcium sensors for fast neurotransmitter release in respective brain regions, while synaptotagmin-7 is a positive regulator of calcium-dependent insulin release. Unlike the three neuronal calcium sensors, whose deletion abolished fast neurotransmitter release, synaptotagmin-7 deletion resulted in only partial loss of calcium-dependent insulin secretion, thus suggesting that other calcium-sensors must participate in the regulation of insulin secretion. Of the other synaptotagmin isoforms that are present in pancreatic islets, the neuronal calcium sensor synaptotagmin-9 is expressed at the highest level after synaptotagmin-7. METHODOLOGY/PRINCIPAL FINDINGS:In this study we tested whether synaptotagmin-9 participates in the regulation of glucose-stimulated insulin release by using pancreas-specific synaptotagmin-9 knockout (p-S9X) mice. Deletion of synaptotagmin-9 in the pancreas resulted in no changes in glucose homeostasis or body weight. Glucose tolerance, and insulin secretion in vivo and from isolated islets were not affected in the p-S9X mice. Single-cell capacitance measurements showed no difference in insulin granule exocytosis between p-S9X and control mice. CONCLUSIONS:Thus, synaptotagmin-9, although a major calcium sensor in the brain, is not involved in the regulation of glucose-stimulated insulin release from pancreatic β-cells

Reduced Body Weight and Increased Energy Expenditure in Transgenic Mice Over-Expressing Soluble Leptin Receptor

studies have shown that OBRe expression is inversely correlated to body weight and leptin levels. However, it is not clear whether OBRe plays an active role, either in collaboration with leptin or independently, in the maintenance of body weight.To investigate the function of OBRe in the regulation of energy homeostasis, we generated transgenic mice that express OBRe under the control of human serum amyloid P (hSAP) component gene promoter. The transgene led to approximately doubling of OBRe in circulation in the transgenic mice than in wild type control mice. Transgenic mice exhibited lower body weight at 4 weeks of age, and slower rate of weight gain when compared with control mice. Furthermore, transgenic mice had lower body fat content. Indirect calorimetry revealed that transgenic mice had reduced food intake, increased basal metabolic rate, and increased lipid oxidation, which could account for the differences in body weight and body fat content. Transgenic mice also showed higher total circulating leptin, with the majority of it being in the bound form, while the amount of free leptin is comparable between transgenic and control mice.These results are consistent with the role of OBRe as a leptin binding protein in regulating leptin's bioavailability and activity

Studies on secretion from the chromaffin cells of the adrenal medulla

This thesis describes metabolic changes occurring in chromaffin cells when secreting catecholamine (principally adrenaline), and the factors involved in maintaining the rate of secretion. In perfused pig adrenal glands, 31p nuclear magnetic resonance showed that nucleotide stored with catecholamine in the secretory vesicles (chromaffin granules) of the chromaffin cell was distinguishable from cytoplasmic nucleotide. Intragranular pH was 5.52 ± 0.15 (± SD, n=8) in ischaemic glands and rose (+ 0.22 ± 0.16 (± SD, n=6)) on recovery of cytoplasmic ATP during perfusion. This suggests that catecholamine accumulation by the granules is not driven by an ATP-generated pH gradient in intact tissue, as cytoplasmic ATP did not reduce intragranular pH. Perfused cortex-free ox adrenal medulla consumed 0.51 ± 0.19 (± SD, n=8) μmole 02/min/g wet weight after 210-230 minutes of perfusion, and this rose 30% during 4 minute O.lmM acetylcholine stimulations. This enhancement correlated with secretion but depended on the mode of stimulation, indicating that ATP consumption in secretion itself was an inadequate explanation. The proton-translocating Mg-ATPase of the chromaffin granule may hydrolyse ATP at its uncoupled rate on entering the plasma membrane during secretion by exocytosis. 1.4 ± 0.9 (± SD, n=12) moles of catecholamine were secreted per mole of enhanced oxygen consumption over 16 minutes. From this ratio, the oxygen consumption enhancement is shown to be much larger than that predicted from uncoupled proton pumping. Ouabain-sensitive oxygen consumption rose from < 6% to 18 ± 8% (± SD, n=4) during prolonged acetylcholine stimulation in the absence of calcium, suggesting that Na,K-ATPase was not responsible for all of the oxygen consumption enhancement. On continuous stimulation, secretion showed a biphasic decline in both pig and ox. A decline was also observed on intermittent stimulation. Cell death, potential-sensitive calcium gating and acetylcholine receptor desensitisation were only minor contributors. Little recovery occurred on resting the tissue for 2-3 hours between stimulations. The results are explained in terms of depletion of a pool of chromaffin granules adjacent to the plasma membrane.</p