LKB1 and AMPK maintain epithelial cell polarity under energetic stress

LKB1 is mutated in both familial and spontaneous tumors, and acts as a master kinase that activates the PAR-1 polarity kinase and the adenosine 5′monophosphate–activated kinase (AMPK). This has led to the hypothesis that LKB1 acts as a tumor suppressor because it is required to maintain cell polarity and growth control through PAR-1 and AMPK, respectively. However, the genetic analysis of LKB1–AMPK signaling in vertebrates has been complicated by the existence of multiple redundant AMPK subunits. We describe the identification of mutations in the single Drosophila melanogaster AMPK catalytic subunit AMPKα. Surprisingly, ampkα mutant epithelial cells lose their polarity and overproliferate under energetic stress. LKB1 is required in vivo for AMPK activation, and lkb1 mutations cause similar energetic stress–dependent phenotypes to ampkα mutations. Furthermore, lkb1 phenotypes are rescued by a phosphomimetic version of AMPKα. Thus, LKB1 signals through AMPK to coordinate epithelial polarity and proliferation with cellular energy status, and this might underlie the tumor suppressor function of LKB1

Altered Metabolism and Persistent Starvation Behaviors Caused by Reduced AMPK Function in Drosophila

Organisms must utilize multiple mechanisms to maintain energetic homeostasis in the face of limited nutrient availability. One mechanism involves activation of the heterotrimeric AMP-activated protein kinase (AMPK), a cell-autonomous sensor to energetic changes regulated by ATP to AMP ratios. We examined the phenotypic consequences of reduced AMPK function, both through RNAi knockdown of the gamma subunit (AMPKγ) and through expression of a dominant negative alpha (AMPKα) variant in Drosophila melanogaster. Reduced AMPK signaling leads to hypersensitivity to starvation conditions as measured by lifespan and locomotor activity. Locomotor levels in flies with reduced AMPK function were lower during unstressed conditions, but starvation-induced hyperactivity, an adaptive response to encourage foraging, was significantly higher than in wild type. Unexpectedly, total dietary intake was greater in animals with reduced AMPK function yet total triglyceride levels were lower. AMPK mutant animals displayed starvation-like lipid accumulation patterns in metabolically key liver-like cells, oenocytes, even under fed conditions, consistent with a persistent starved state. Measurements of O2 consumption reveal that metabolic rates are greater in animals with reduced AMPK function. Lastly, rapamycin treatment tempers the starvation sensitivity and lethality associated with reduced AMPK function. Collectively, these results are consistent with models that AMPK shifts energy usage away from expenditures into a conservation mode during nutrient-limited conditions at a cellular level. The highly conserved AMPK subunits throughout the Metazoa, suggest such findings may provide significant insight for pharmaceutical strategies to manipulate AMPK function in humans

ITERATIVE RECEPTANCE METHOD FOR DETERMINING HARMONIC RESPONSE OF STRUCTURES WITH SYMMETRICAL NONLINEARITIES

Although there are several techniques available for the harmonic vibration analysis of non-linear systems, the application of these methods to multi-degree of freedom systems is rather limited. In this study a new method (the Iterative Receptance Method—IRM) is developed for the harmonic vibration analysis of non-linear multi-degree of freedom systems with non-linear stiffness and damping forces. Different kinds of non-linearities are covered by expressing non-linear spring and damping forces as polynomials in displacements and velocities, respectively. Quasilinear receptance matrix of a non-linear system for a given level of external forcing is determined by using the receptance matrix of the linear part of the system and a matrix representing the non-linearity in the system. An iterative algorithm is employed in the numerical solution. The iterative receptance method is also modified for an efficient dynamic analysis of structures with local non-linearities. The application of the method is demonstrated by numerical examples, and the results are found to be quite encouraging for the application of the method to practical structures with large degrees of freedom

Analytical modeling of the machine tool spindle dynamics under operational conditions

Chatter is an important problem in machining operations, and can be avoided by utilizing stability diagrams which are generated using frequency response functions (FRF) at the tool tip. In general, tool point FRF is obtained experimentally or analytically for the idle state of the machine. However, during high speed cutting operations, gyroscopic effects and changes of contact stiffness and damping at the interfaces as well as the changes in the bearing properties may lead to variations in the tool point FRF. Thus, stability diagrams obtained using the idle state FRFs may not provide accurate predictions in such cases. Spindle, holder and tool can be modeled analytically; however variations under operational conditions must be included in order to have accurate predictions. In authors previous works Timoshenko beam model was employed and subassembly FRFs were coupled by using receptance coupling method. In this paper, extension of the model to the prediction of operational FRFs is presented. In order to include the rotational effects on the system dynamics, gyroscopic terms are added to the Timoshenko beam model. Variations of the bearing parameters are included by structural modification techniques. Thus, for various spindle speeds, and holder and tool combinations, the tool point FRFs can be predicted and used in stability diagrams

The use of noise measurements in machining stability analysis

Self-excited vibrations, namely chatter, is one of the most important problems in machining operations. Under certain conditions, the cutting system becomes unstable as a result of the dynamic interaction between the process and the structures. As a result of this dynamic interaction between the cutting tool and the work material, a high level noise is generated in addition to the very poor machined part surface quality. Chatter models used for the generation of the stability diagrams need the frequency response function (FRF) at the tool work interface point in addition to the material constants. Although high level noise generated in chatter is undesirable in a production facility, it creates a unique opportunity for the chatter tests. The frequency spectrum can be used to identify the chatter and the source when combined with the modal data. Considering the practical difficulties of placing a sensor in the cutting zone, the importance of this very inexpensive and reliable way of chatter identification and measurement can be understood much better. In this paper, the experimental verification, by using noise measurements, of the stability diagrams obtained from recently developed chatter and structural dynamics models for milling will be demonstrated with example applications. The comparison between the modeled and measured FRFs, the correlation of the modal frequencies with the predicted and the measured chatter frequencies by using the noise measurements will also be presented

Analytical modeling of asymmetric multi-segment rotor - bearing systems with Timoshenko beam model including gyroscopic moments

In this study, analytical modeling and an analysis approach for asymmetric multi-segment rotor bearing systems are presented. Timoshenko beam model which includes the effect of gyroscopic moments is employed for modeling rotor segments. Instead of applying FEM, sub-segment Frequency Response Functions (FRFs) are obtained analytically, and sub-segment FRFs obtained are coupled by using receptance coupling method. Bearing properties are included into system dynamics by employing structural modification techniques. The proposed analytical model is verified by using FEM approach. It is shown that using analytical model and receptance coupling, compared with FEM, reduces computational time drastically without losing accuracy

A study of three bacteria isolated from marine sediment and description of Micromonospora globispora sp. nov.

19 páginas, 2 figuras, 4 tablasDuring a study looking for the isolation of new actinobacteria strains with potential for antibiotic production from deep marine sediment, three strains were collected with a morphology similar to the one described for the Micromonospora genus. A polyphasic study was designed to determine the taxonomic affiliation of the strains S2901T, S2903, and S2904. All the strains showed chemotaxonomic properties in line with their classification in the genus Micromonospora, meso-diaminopimelic acid in the wall peptidoglycan, a tetrahydrogenated menaquinone with nine isoprene units as major respiratory quinone, iso-C15:0 and iso-C16:0 as major fatty acids and diphosphatidylglycerol, phosphatidylethanolamine and phosphatidylinositol as major polar lipids. The 16S rRNA gene sequences of strain S2901T, S2903, and S2904 showed the highest similarity (99.2%) with the type strain of Micromonospora halophytica DSM 43171T, forming an independent branch in the phylogenetic gene tree. Their independent position was confirmed with gyrB gene and MLSA phylogenies. Whole genome sequences confirmed by digital DNA-DNA hybridization analysis that the isolates should be assigned to a new species within the genus Micromonospora for which the name Micromonospora globispora sp. nov. (S2901T, S2903 and S2904) is proposed.This project was supported by Ondokuz Mayis University (project PYO. FEN. 1901.12.014) and the School of Biology (Newcastle University).Peer reviewe

Robustness Analysis of Intentional Mistuning Patterns in Randomly Mistuned Bladed Disk Assemblies

It is known that bladed disks, which are usually designed as cyclically symmetric structures, undergo considerable amount of forced response amplitude magnification due to the phenomenon called mistuning. Mistuning is inevitable for any cyclically symmetric bladed disk assembly since it is caused by manufacturing tolerances, material properties and operational wear. Since reducing the level of mistuning beyond certain limits is not possible with the current technology, the attempts are rather made to reduce or control the forced response magnification, where intentional mistuning is an alternative., Intentional Mistuning. is to mistune a cyclically symmetric bladed disk with a pre-defined pattern. However, because of the fact that some uncontrolled variation is still unavoidable, it is vital to evaluate any intentional mistuning pattern together with a certain amount of random mistuning. The aim of this study is to statistically compare the robustness of intentional mistuning patterns such as harmonic, linear and pseudo harmonic, with different levels of random mistuning applied on top. Therefore, intentional mistuning patterns will be evaluated without disregarding the effect of uncertainties already present in the system. Two sample bladed disk models are used to gather information on model dependence. Reduced order models of the sample bladed disks are built for this study to reduce computation time. Monte Carlo simulations with selected intentional and random mistuning pairs are then performed under pre-defined excitations to compare the performance of the intentional mistuning patterns applied

A closed-form approach for identification of dynamical contact parameters in spindle-holder-tool assemblies

Accurate identification of contact dynamics is very crucial in predicting the dynamic behavior and chatter stability of spindle-tool assemblies in machining centers. it is well known that the stability lobe diagrams used for predicting regenerative chatter vibrations can be obtained from the tool point frequency response function (FRF) of the system. As previously shown by the authors, contact dynamics at the spindle-holder and holder-tool interfaces as well as the dynamics of bearings affect the tool point FRF considerably. Contact stiffness and damping values alter the frequencies and peak values of dominant vibration modes, respectively. Fast and accurate identification of contact dynamics in spindle-tool assemblies has become an important issue in the recent years. In this paper, a new method for identifying contact dynamics in spindle-holder-tool assemblies from experimental measurements is presented. The elastic receptance coupling equations are employed in a simple manner and closed-form expressions are obtained for the stiffness and damping parameters of the joint of interest. Although this study focuses on the contact dynamics at the spindle-holder and holder-tool interfaces of the assembly, the identification approach proposed in this paper might as well be used for identifying the dynamical parameters of bearings, spindle-holder interface and as well as other critical joints. After presenting the mathematical theory, an analytical case study is given for demonstration of the identification approach. Experimental verification is provided for identification of the dynamical contact parameters at the holder-tool interface of a spindle-holder-tool assembly