Distinct amino acid–sensing mTOR pathways regulate skeletal myogenesis

Signaling through the mammalian target of rapamycin (mTOR) in response to amino acid availability controls many cellular and developmental processes. mTOR is a master regulator of myogenic differentiation, but the pathways mediating amino acid signals in this process are not known. Here we examine the Rag GTPases and the class III phosphoinositide 3-kinase (PI3K) Vps34, two mediators of amino acid signals upstream of mTOR complex 1 (mTORC1) in cell growth regulation, for their potential involvement in myogenesis. We find that, although both Rag and Vps34 mediate amino acid activation of mTORC1 in C2C12 myoblasts, they have opposing functions in myogenic differentiation. Knockdown of RagA/B enhances, whereas overexpression of active RagB/C mutants impairs, differentiation, and this inhibitory function of Rag is mediated by mTORC1 suppression of the IRS1-PI3K-Akt pathway. On the other hand, Vps34 is required for myogenic differentiation. Amino acids activate a Vps34-phospholipase D1 (PLD1) pathway that controls the production of insulin-like growth factor II, an autocrine inducer of differentiation, through the Igf2 muscle enhancer. The product of PLD, phosphatidic acid, activates the enhancer in a rapamycin-sensitive but mTOR kinase–independent manner. Our results uncover amino acid–sensing mechanisms controlling the homeostasis of myogenesis and underline the versatility and context dependence of mTOR signaling.     

Decreased mitochondrial OGG1 expression is linked to mitochondrial defects and delayed hepatoma cell growth

Many solid tumor cells exhibit mitochondrial respiratory impairment; however, the mechanisms of such impairment in cancer development remain unclear. Here, we demonstrate that SNU human hepatoma cells with declined mitochondrial respiratory activity showed decreased expression of mitochondrial 8-oxoguanine DNA glycosylase/lyase (mtOGG1), a mitochondrial DNA repair enzyme; similar results were obtained with human hepatocellular carcinoma tissues. Among several OGG1-2 variants with a mitochondrial-targeting sequence (OGG1-2a, -2b, -2c, -2d, and -2e), OGG1-2a was the major mitochondrial isoform in all examined hepatoma cells. Interestingly, hepatoma cells with low mtOGG1 levels showed delayed cell growth and increased intracellular reactive oxygen species (ROS) levels. Knockdown of OGG1-2 isoforms in Chang-L cells, which have active mitochondrial respiration with high mtOGG1 levels, significantly decreased cellular respiration and cell growth, and increased intracellular ROS. Overexpression of OGG1-2a in SNU423 cells, which have low mtOGG1 levels, effectively recovered cellular respiration and cell growth activities, and decreased intracellular ROS. Taken together, our results suggest that mtOGG1 plays an important role in maintaining mitochondrial respiration, thereby contributing to cell growth of hepatoma cells.     

The biomechanical effect of the collar of a femoral stem on total hip arthroplasty

To investigate the biomechanical effect of collars, finite element analyses are carried out through two hip joints that are implanted using collared and collarless stems, respectively, and an intact hip joint model. For the analyses, the sacrum, coxal bone, and the cancellous and cortical bones of a femur are modelled using finite elements based on X-ray computed tomographic images taken from a 27-year-old woman. From the results, it is found that a collar with perfect calcar contact prevents stem subsidence and decreases the proximal–lateral gap and the lateral stem tilting. Therefore, it can impart reasonable biomechanical stability for total hip arthroplasty. However, its low load transmission ability and increased stem tilting effect due to the imperfect contact between the collar and the calcar are found to be serious problems that need to be solved. Results of clinical follow-up are presented for supporting the computational results.     

Induction of the Differentiation of HL-60 Promyelocytic Leukemia Cells by l-Ascorbic Acid

The present study was undertaken to examine the effect of l-ascorbic acid (LAA) on the growth of HL-60 promyelocytic leukemia cells, besides induction of apoptosis. LAA (≥10^-4?M) was found to markedly inhibit the proliferation of HL-60 in liquid culture and clonogenicity in semisolid culture. Moreover, LAA-treated HL-60 showed activity to produce chemiluminescence and expressed CD 66b cell surface antigens, indicating that LAA induces the differentiation of HL-60 mainly into granulocytes. The results are supported by morphological changes of LAA-treated HL-60 into segmented neutrophils. Therefore, the inhibitory effect of LAA on the growth of HL-60 cells seems to arise from the induction of differentiation. To assess the potential role of LAA, cells were exposed to oxygen radical scavengers in the absence or presence of LAA. Catalase abolished and superoxide dismutase promoted LAA-induced differentiation of HL-60. Thus, H²O² produced as a result of LAA treatment seems to play a major role in induction of HL-60 differentiation.     

Gender-dependent expression of pancreatic proteins in streptozotocin-induced diabetic rats

To elucidate gender-dependent protein regulation and molecular abnormalities in streptozotocin (STZ)-induced diabetes, we compared differentially expressed pancreatic proteins between male and female diabetic rats and their healthy controls using a 2-DE-based proteomic approach. In animal experiments, we found that females exposed to STZ displayed greater susceptibility towards diabetes development due to lower insulin secretion and severe β-cell damage. It was also accompanied with more impaired regulation of sex hormones, lower glucose tolerance, and higher blood glucose levels compared to male diabetic rats. Among 748 detected protein spots ranging in mass from 6 to 240 kDa between pH 3 and 10, a total of 42 proteins showed significant sexually-dimorphic regulation patterns between male and female diabetic rats. Proteomic data revealed that male and female rats displayed prominent gender-dimorphic differential regulation of pancreatic proteins involved in glycolysis, the citric acid cycle, amino acid synthesis, lipid metabolism, insulin biosynthesis, β-cell regeneration, cell signaling, as well as antioxidative and cellular stress defense. In conclusion, the current proteomic study revealed that severely impaired protein regulation in the pancreas, at least in part, is responsible for increased susceptibility of female rats to STZ-induced diabetes.     

Stress response of plant H+-PPase-expressing transgenic Escherichia coli and Saccharomyces cerevisiae: a potentially useful mechanism for the development of stress-tolerant organisms

The simple proton-translocating inorganic pyrophosphatase (H⁺-PPase) found in plants and protists is an evolutionally conserved, essential enzyme that catalyzes the hydrolysis of pyrophosphate (PPi). Little is known about the functional contribution of H⁺-PPase to the cellular response to abiotic stresses, except its high salinity and drought stress. To investigate the role of H⁺-PPase during response to cellular stress, we isolated the cDNA of Arabidopsis thaliana H⁺-PPase (AVP1) and Oryza sativa H⁺-PPase (OVP1) and constructed transgenic Saccharomyces cerevisiae and Escherichia coli lines that express AVP1 and OVP1. In S. cerevisiae, the expression of a chimeric derivative of the AVP1 and OVP1 alleviated the phenotype associated with ipp2-deficient cells in the presence of high salinity (NaCl) and metal stressors (Cd, Mn, and Zn). In E. coli, AVP1 and OVP1 overexpression conferred enhanced tolerance to abiotic stresses, including heat shock and H₂O₂, as well as NaCl, Cd, Mn, Zn, Ca, and Al. Interestingly, AVP1 and OVP1 overexpression resulted in hypersensitivity to menadione and cobalt. These results demonstrate the cellular capacity of AVP1- and OVP1-expressing transgenic yeast and E. coli in response to physiological, abiotic stresses. Moreover, our results suggest new ways of engineering stress-tolerant plants that are capable of responding to climate change. Here, we provide an outline of an experimental system to examine the alternative roles of plant H⁺-PPase.     

A frequency monitoring system development for wide-area power grid protection

There have been recent research activities on GPS-based FNET to prevent wide-area blackouts by monitoring frequency deviation. This paper introduces a system for monitoring regional frequencies in power grid developed as an advanced research project for intelligent wide-area protective relaying in South Korea. The system is implemented by modeling an actual 345 kV transmission system of South Korea using EMTP-RV and by measuring voltages and currents at five regions. The frequencies are estimated using our previous proposed method, a frequency estimation algorithm with gain compensation. The monitoring system implemented is used to examine frequency propagation effects and various fault conditions. Simulation results showed that the proposed system could achieve good performance regarding the frequency monitoring under both steady states and dynamic fault conditions.     

Enlarged Cavum Septum Pellucidum as a Neurodevelopmental Marker in Adolescent-Onset Opiate Dependence

Objective

Adolescent-onset exposure to highly addictive substances such as opiates may induce far-reaching deleterious effects on later mental and physical health. However, little is known about the neurodevelopmental basis for adolescent-onset opiate dependence. Here we examined whether having an abnormally large cavum septum pellucidum (CSP), a putative marker of limbic structural maldevelopment, is associated with opiate dependence particularly beginning in adolescence.

Method

The overall length of the CSP and the prevalence of abnormal enlargement of the CSP were assessed and compared in 65 opiate-dependent subjects (41 adolescent-onset opiate users and 24 adult-onset opiate users) and 67 healthy subjects.

Results

Opiate-dependent subjects showed a greater prevalence of abnormal CSP enlargement relative to healthy subjects (odds ratio [OR]=3.64, p=0.034). The overall CSP length of adolescent-onset opiate-dependent subjects was greater, as compared not only with healthy subjects (F_1,104=11.03, p=0.001) but also with those who began opiate use during adulthood (F_1,61=4.43, p=0.039).

Conclusions

The current findings provide the first evidence that abnormal CSP enlargement, which reflects limbic system dysgenesis of neurodevelopmental origin, may be linked to later development of opiate dependence. In addition, a greater CSP length, which indicates more severe limbic abnormalities, appears to confer higher risk for earlier onset of opiate use.