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Internal Mechanisms (internal + mechanism)
Selected AbstractsDifferential apoptotic response of J774 macrophages to alumina and ultra-high-molecular-weight polyethylene particlesJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 1 2002Alain Petit We recently identified apoptosis in in vitro wear particle-stimulated macrophages. The recent explosion of interest in apoptosis lies in the fact that it is under positive and negative regulation through evolutionary conserved biochemical pathways. It may also be possible to modulate macrophage apoptosis in the treatment of periprosthetic osteolysis. The purpose of this study was to compare the macrophage response to identically sized particles of alumina ceramic (Al2O3) and ultra-high-molecular-weight polyethylene (UHMWPE) in terms of TNF-, release and induction of apoptosis. J774 mouse macrophages were incubated for 0,24 h in the presence of Al2O3 and UHMWPE particles. TNF-, release was measured by ELISA; Poly(ADP-ribose)polymerase (PARP) and caspase-3 expression was analyzed by Western blot; DNA fragmentation (DNA laddering) was visualized on agarose gel containing ethidium bromide. Al2O3 particles induced TNF-, release after 4 h incubation with concentrations reaching 483 and 800 pg/ml after 24 h with 125 and 250 particles/macrophage, respectively (control = 161 pg/ml) (P < 0.05 vs. control). The same concentrations of UHMWPE particles induced a much larger and significant TNF-, release after only 1 h incubation, increasing up to 6250 pg/ml after 24 h (P < 0.05 vs. control). Western blot analysis demonstrated that the active caspase-3 fragment (17 kDa) and the proteolytic PARP fragment (85 kDa) were expressed after 2 h incubation with 125 and 250 Al2O3 particles/macrophage. The active caspase-3 and the PARP fragment had lower expression and appeared after a longer incubation time (8 h) with 125 and 250 UHMWPE particles/macrophage. Finally, DNA fragmentation (DNA laddering) was observed after 16 h with 125 and 250 particles of Al2O3 per macrophage whereas no laddering was induced by UHMWPE particles even after 24 h incubation. This study shows that although both Al2O3 and UHMWPE particles induce TNF-, release, this stimulation was much greater (8,10 times higher) with UHMWPE than A12O3 (P < 0.05 vs. control). As well, the induction of apoptosis, as measured by activation of caspase-3, PARP cleavage and DNA laddering, is different for these two particles, being faster and more important with Al2O3 than UHMWPE. We hypothesize that the ability of Al2O3 to induce macrophage apoptosis may explain the lower TNF-, release observed with these particles and explain the differences seen in osteolysis patterns of ceramic,ceramic (CC) vs. metal,polyethylene (Mpe) articulations. In conclusion, apoptosis may be a major internal mechanism to decrease macrophage activity and may be a desired therapeutic endpoint. The identification of an apoptosis-related pathway in the macrophage response to ceramic particles provides crucial data for a rational approach in the treatment and/or prevention of periprosthetic osteolysis. © 2002 Orthopaedic Research Society. Published by Elsevier Science Ltd. All rights reserved. [source] Influence of isolation on the recovery of pond mesocosms from the application of an insecticide.ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 6 2007Abstract The influence of relative isolation on the ecological recovery of freshwater outdoor mesocosm communities after an acute toxic stress was assessed in a 14-month-long study. A single concentration of deltamethrin was applied to 8 out of 16 outdoor 9-m3 mesocosms to create a rapid decrease of the abundance of arthropods. To discriminate between external and internal recovery mechanisms, four treated and four untreated (control) mesocosms were covered with 1-mm mesh screen lids. The dynamics of planktonic communities were monitored in the four types of ponds. The abundance of many phytoplankton taxa increased after deltamethrin addition, but the magnitude of most increases was relatively small, probably due to low nutrient availability and the survival of rotifers. The greatest impact on zooplankton was seen in Daphniidae and, to a lesser extent, calanoid copepods. Recovery (defined as when statistical analysis failed to detect a difference in the abundance between the deltamethrin-treated ponds and corresponding control ponds for two consecutive sampling dates) of Daphniidae was observed in the water column 105 and 77 d after deltamethrin addition in open and covered mesocosms, respectively, and <42 d for both open and covered ponds at the surface of the sediments. Rotifers did not proliferate, probably because of the survival of predators (e.g., cyclopoid copepods). These results confirm that the recovery of planktonic communities after exposure to a strong temporary chemical stress mostly depends upon internal mechanisms (except for larvae of the insect Chaoborus sp.) and that recovery dynamics are controlled by biotic factors, such as the presence of dormant forms and selective survival of predators. [source] Microstructural deformation mechanisms of unsaturated granular soilsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 5 2002J. A. Gili Abstract A discrete model for unsaturated granular soils has been developed. Three discrete entities have been defined: particles, water menisci and pores. Local interaction forces and water transfer mechanisms have been integrated into a model through the appropriate equilibrium and balance equations. The results of several numerical tests using this model have been described and discussed. Simulations include wetting and drying under load tests, the application of suction cycles and the effect of a deviatoric stress ratio on wetting-induced collapse. The model reacts just as true granular soil samples behave in laboratory tests. The model provides a new insight into the internal mechanisms leading to large-scale features of behaviour such as wetting-induced collapse or the increase in soil strength provided by suction. The paper also stresses that matric suction changes acting on a granular structure are capable of explaining most of the macroscopic features of stress,strain behaviour. Copyright © 2002 John Wiley & Sons, Ltd. [source] Alliance Capability as a Mediator Between Experience and Alliance Performance: An Empirical Investigation into the Alliance Capability Development Process*JOURNAL OF MANAGEMENT STUDIES, Issue 1 2007Koen H. Heimeriks abstract This study centres around the way in which firms can enhance alliance performance through the development of alliance capabilities. Whereas most research has focused on inter-firm antecedents of alliance performance, research on intra-firm antecedents pointing to prior experience and internal mechanisms to foster knowledge transfer has only recently emerged. As little is known about how firms develop alliance capabilities, this study aims to uncover how differences in sources of alliance capabilities explain performance heterogeneity. The data are derived from a detailed survey held among alliance managers and Vice-Presidents of 151 firms. The survey covers over 2600 alliances for the period 1997,2001. This study not only finds that alliance capabilities partially mediate between alliance experience and alliance performance, but also yields novel insights into the micro-level building blocks underlying the process of alliance capability development. [source] Differential sensitivity in the survival of oligodendrocyte cell lines to overexpression of myelin proteolipid protein gene productsJOURNAL OF NEUROSCIENCE RESEARCH, Issue 6 2001Ernesto R. Bongarzone Abstract The proteolipid (PLP) gene encodes at least four proteins, including the classic PLP and DM20, which are important components of the myelin sheath, and the recently identified soma-restricted (sr) isoforms, srPLP and srDM20. The classic PLP and DM20 gene products have been implicated in oligodendrocyte survival by overexpression studies in vitro and in vivo. The classic and sr proteolipids are targeted to different cellular compartments in the oligodendrocyte, suggesting different cellular functions. Accordingly, we examined the effects of in vitro overexpression of the sr-PLP/DM20 isoforms on the survival of stably transfected, conditionally immortalized, oligodendroglial cell lines and compared this to overexpression of the classic and the jimpy-mutated proteolipids. The results indicate that overexpression of either normal or jimpy classic PLP/DM20 resulted in a dramatic reduction in the survival of the oligodendrocyte cell lines at the nonpermissive temperature, but not the COS-7 cell line, a cell line expressing the same oncogene constitutively. Survival of the oligodendrocyte cell lines was significantly less affected when either the sr-PLP/DM20 or the dopamine D-2 receptor, another cell membrane protein, was overexpressed in the cell lines. These results suggest that overexpression of the "classic" PLP or DM20 can compromise the survival of oligodendrocytes whether or not they are mutated. Furthermore, they suggest that the internal mechanisms for normal targeting of the PLP/DM20 isoforms of either the "classic" or the "sr" types influence the oligodendrocyte's ability to survive when these proteolipids are overexpressed. J. Neurosci. Res. 65:485,492, 2001. © 2001 Wiley-Liss, Inc. [source] Efficiency, Performance and Changing Corporate Governance in China's Township,Village Enterprises since the 1990sASIAN-PACIFIC ECONOMIC LITERATURE, Issue 1 2001Russell Smyth This article outlines some of the major challenges facing Chinese township,village enterprises (TVEs) since the 1990s. The authors argue that the internal mechanisms associated with the unique ownership structure of TVEs has allowed them to perform better than state-owned enterprises (SOEs). Since the mid-1990s, debt levels in the TVE sector have increased sharply. Most of the problems of TVEs have been magnified by the close relationship between local governments and enterprises, which was once one of their major strengths. Since the mid-1990s, local governments have come to regard TVEs with high levels of debt as a burden rather than an asset. In response local governments have moved to other, more indirect forms of governance over most TVEs under their control, while retaining direct control over the most successful. These alternative ownership structures include share-holding co-operatives and outright privatisation. [source] Effet de la structure des droits de vote sur la qualité des mécanismes internes de gouvernance: Cas des entreprises canadiennesCANADIAN JOURNAL OF ADMINISTRATIVE SCIENCES, Issue 3 2006Ameur Boujenoui Résumé Le conseil d'administration est considéré comme une des composantes importantes des mécanismes internes de gouvernance d'entreprise. Les recherches dans ce domaine ont porté, entre autres, sur la structure du conseil, sa composition ainsi que sur lesfacteurs qui déterminent celles-ci et plusieurs auteurs font référence à la structure de l'actionnariat. Menée sur un échantillon de 214 entreprises canadiennes cotées en bourse, cette étude explore l'effet de la structure du contrôle des droits de vote sur la qualité des mécanismes internes de gouvernance. Les résultats obtenus indiquent que la concentration du contrôle, l'actionnariat interne et celui des détenteurs de blocs sont reliés négativement à la qualité de ces mécanismes, alors que l'actionnariat des investisseurs institutionnels a un effet positif. Abstract The board of directors is among the most important internal mechanisms of corporate governance. Most studies on board of directors have focused mainly on its structure, composition and factors influencing its composition as well as on the shareholding structure. This paper attempts to supplement past studies on board of directors by reviewing 214 publicly traded Canadian companies and exploring the impact of the structure of voting rights on the quality of internal control mechanisms of governance. Our findings indicate that the concentration of control, the internal and blockholder ownership are negatively related to the quality of those mechanisms, while institutional investors have a positive impact. [source] | |||||||||||||