Long-term exercise stabilizes atherosclerotic plaque in apolipoprotein-E deficient mice

PURPOSE: Exercise is known to reduce cardiovascular mortality. However, the precise mechanisms are still unknown. Because atherosclerotic plaque destabilization and rupture leads to dramatic cardiovascular events, stabilization of plaque might be regarded as an important goal of an exercise preventive therapy. The present study examined the plaque-stabilizing effect of long-term exercise in experimental atherosclerosis using apolipoprotein E-deficient mice (ApoE(-/-)). METHODS: ApoE(-/-) mice were subjected to 6 months of swimming exercise. A group of sedentary animals were used as controls. Morphometry and characteristics of atherosclerotic plaque stability were assessed in aortic sinus by immunohistochemistry. Aortic levels of total protein kinase Akt (protein kinase B), phosphorylated Akt at Ser(473) (p-Akt), total endothelial nitric oxide synthase (eNOS), and phosphorylated eNOS at Ser(1177) (p-eNOS) were assessed by Western blotting. RESULTS: Exercised mice developed a more stable plaque phenotype as shown by decreased macrophage and increased smooth muscle cell content. Protein expressions of Akt, p-Akt, eNOS, and p-eNOS were not modulated by exercise. CONCLUSIONS: Long-term exercise promotes plaque stability in ApoE(-/-) mice. The Akt-mediated eNOS phosphorylation pathway seems not to be the primary molecular mechanism.

Energy transfer mechanism and Auger effect in Er3+ coupled silicon nanoparticle samples

We report a spectroscopic study about the energy transfer mechanism among silicon nanoparticles (Si-np), both amorphous and crystalline, and Er ions in a silicon dioxide matrix. From infrared spectroscopic analysis, we have determined that the physics of the transfer mechanism does not depend on the Si-np nature, finding a fast (< 200 ns) energy transfer in both cases, while the amorphous nanoclusters reveal a larger transfer efficiency than the nanocrystals. Moreover, the detailed spectroscopic results in the visible range here reported are essential to understand the physics behind the sensitization effect, whose knowledge assumes a crucial role to enhance the transfer rate and possibly employing the material in optical amplifier devices. Joining the experimental data, performed with pulsed and continuous-wave excitation, we develop a model in which the internal intraband recombination within Si-np is competitive with the transfer process via an Auger electron"recycling" effect. Posing a different light on some detrimental mechanism such as Auger processes, our findings clearly recast the role of Si-np in the sensitization scheme, where they are able to excite very efficiently ions in close proximity to their surface. (C) 2010 American Institute of Physics.

"In vitro" study of the molecular mechanism of the "E.Coli" Hsp 70/Hsp40/NEF chaperone system and its interactions with ?-sinuclein

SUMMARY Under stressful conditions, mutant or post-translationally modified proteins may spontaneously misfold and form toxie species, which may further assemble into a continuum of increasingly large and insoluble toxic oligomers that may further condense into less toxic, compact amyloids in the cell Intracellular accumulation of aggregated proteins is a common denominator of several neurodegenerative diseases. To cope with the cytotoxicity induced by abnormal, aggregated proteins, cells have evolved various defence mechanisms among which, the molecular chaperones Hsp70. Hsp70 (DnaK in E. coii) is an ATPase chaperone involved in many physiological processes in the cell, such as assisting de novo protein folding, dissociating native protein oligomers and serving as pulling motors in the import of polypeptides into organelles. In addition, Hsp70 chaperones can actively solubilize and reactivate stable protein aggregates, such as heat- or mutation-induced aggregates. Hsp70 requires the cooperation of two other co-chaperones: Hsp40 and NEF (Nucleotide exchange factor) to fulfil its unfolding activity. In the first experimental section of this thesis (Chapter II), we studied by biochemical analysis the in vitro interaction between recombinant human aggregated α-synuclein (a-Syn oligomers) mimicking toxic a-Syn oligomers species in PD brains, with a model Hsp70/Hsp40 chaperone system (the E. coii DnaK/DnaJ/GrpE). We found that chaperone-mediated unfolding of two denatured model enzymes were strongly affected by α-Syn oligomers but, remarkably, not by monomers. This in vitro observed dysfunction of the Hsp70 chaperone system resulted from the sequestration of the Hsp40 proteins by the oligomeric α-synuclein species. In the second experimental part (Chapter III), we performed in vitro biochemical analysis of the co-chaperone function of three E. coii Hsp40s proteins (DnaJ, CbpA and DjlA) in the ATP-fuelled DnaK-mediated refolding of a model DnaK chaperone substrate into its native state. Hsp40s activities were compared using dose-response approaches in two types of in vitro assays: refolding of heat-denatured G6PDH and DnaK-mediated ATPase activity. We also observed that the disaggregation efficiency of Hsp70 does not directly correlate with Hsp40 binding affinity. Besides, we found that these E. coii Hsp40s confer substrate specificity to DnaK, CbpA being more effective in the DnaK-mediated disaggregation of large G6PDH aggregates than DnaJ under certain conditions. Sensibilisées par différents stress ou mutations, certaines protéines fonctionnelles de la cellule peuvent spontanément se convertir en formes inactives, mal pliées, enrichies en feuillets bêta, et exposant des surfaces hydrophobes favorisant l'agrégation. Cherchant à se stabiliser, les surfaces hydrophobes peuvent s'associer aux régions hydrophobes d'autres protéines mal pliées, formant des agrégats protéiques stables: les amyloïdes. Le dépôt intracellulaire de protéines agrégées est un dénominateur commun à de nombreuses maladies neurodégénératives. Afin de contrer la cytotoxicité induite par les protéines agrégées, les cellules ont développé plusieurs mécanismes de défense, parmi lesquels, les chaperonnes moléculaires Hsp70. Hsp70 nécessite la collaboration de deux autres co-chaperonnes : Hsp40 et NEF pour accomplir son activité de désagrégation. Hsp70 (DnaK, chez E. coli) est impliquée par ailleurs dans d'autres fonctions physiologiques telles que l'assistanat de protéines néosynthétisées à la sortie du ribosome, ou le transport transmembranaire de polypeptides. Par ailleurs, les chaperonnes Hsp70 peuvent également solubiliser et réactiver des protéines agrégées à la suite d'un stress ou d'une mutation. Dans la première partie expérimentale de cette thèse (Chapter II), nous avons étudié in vitro l'interaction entre les oligomères d'a-synucleine, responsables entre autres, de la maladie de Parkinson, et le système chaperon Hsp70/Hsp40 (système Escherichia coli DnaK/DnaJ/GrpE). Nous avons démontré que contrairement aux monomères, les oligomères d'a-synucleine inhibaient le système chaperon lors du repliement de protéines agrégées. Cette dysfonction du système chaperon résulte de la séquestration des chaperonnes Hsp40 par les oligomères d'a-synucleine. La deuxième partie expérimentale (Chapitre III) est consacrée à une étude in vitro de la fonction co-chaperonne de trois Hsp40 d'is. coli (DnaJ, CbpA, et DjlA) lors de la désagrégation par DnaK d'une protéine pré-agrégée. Leurs activités ont été comparées par le biais d'une approche dose-réponse au niveau de deux analyses enzymatiques: le repliement de la protéine agrégée et l'activité ATPase de DnaK. Par ailleurs, nous avons mis en évidence que l'efficacité de désagrégation d'Hsp70 et l'affinité des chaperonnes Hsp40 vis-à-vis de leur substrat n'étaient pas corrélées positivement. Nous avons également montré que ces trois chaperonnes Hsp40 étaient directement impliquées dans la spécificité des fonctions accomplies par les chaperonnes Hsp70. En effet, DnaK en présence de CbpA assure la désagrégation de large agrégats protéiques avec une efficacité nettement plus accrue qu'en présence de DnaJ.

Iowa Interstate Rest Area Stabilization Ponds, September 1979

This report is presented in two parts . P a r t I takes a new look at the design of rest area stabilization ponds after nearly 10 years' experience with some of the existing ponds and in the light of new design standards issued by Iowa DEQ. The Iowa DOT is embarking on improvements t o the ponds a t some of the r e s t areas. These improvements may include installation of drainage tile around the ponds to lower the water table below the pond bottom, sealing of the ponds with bentonite clay to reduce the infiltration to limits recently established by Iowa DEQ, and the enlargement of the ponds installation of aeration equipment t o increase the pond capacity. As the Iowa DOT embarks on this improvement program, it behooves them t o make only the improvements that are absolutely necessary to achieve waste water treatment goals. These ponds are subject to an extremely seasonal load and thus the ordinary standards used for pond design are not appropriate. Thus, Part I of the report presents a rationale for design and operation of the ponds which is deemed appropriate for t h e i r unique seasonally loaded character. Part I1 of the report looks a t the feasibility of using wind power for the aeration of the ponds, if and when aeration is deemed necessary.

Influence of the driving mechanism on the response of systems with athermal dynamics: The example of the random-field Ising model

We investigate the influence of the driving mechanism on the hysteretic response of systems with athermal dynamics. In the framework of local mean-field theory at finite temperature (but neglecting thermally activated processes), we compare the rate-independent hysteresis loops obtained in the random field Ising model when controlling either the external magnetic field H or the extensive magnetization M. Two distinct behaviors are observed, depending on disorder strength. At large disorder, the H-driven and M-driven protocols yield identical hysteresis loops in the thermodynamic limit. At low disorder, when the H-driven magnetization curve is discontinuous (due to the presence of a macroscopic avalanche), the M-driven loop is reentrant while the induced field exhibits strong intermittent fluctuations and is only weakly self-averaging. The relevance of these results to the experimental observations in ferromagnetic materials, shape memory alloys, and other disordered systems is discussed.

AMP-activated protein kinase mediates glucocorticoid-induced metabolic changes: a novel mechanism in Cushing's syndrome.

Chronic exposure to glucocorticoid hormones, resulting from either drug treatment or Cushing's syndrome, results in insulin resistance, central obesity, and symptoms similar to the metabolic syndrome. We hypothesized that the major metabolic effects of corticosteroids are mediated by changes in the key metabolic enzyme adenosine monophosphate-activated protein kinase (AMPK) activity. Activation of AMPK is known to stimulate appetite in the hypothalamus and stimulate catabolic processes in the periphery. We assessed AMPK activity and the expression of several metabolic enzymes in the hypothalamus, liver, adipose tissue, and heart of a rat glucocorticoid-excess model as well as in in vitro studies using primary human adipose and primary rat hypothalamic cell cultures, and a human hepatoma cell line treated with dexamethasone and metformin. Glucocorticoid treatment inhibited AMPK activity in rat adipose tissue and heart, while stimulating it in the liver and hypothalamus. Similar data were observed in vitro in the primary adipose and hypothalamic cells and in the liver cell line. Metformin, a known AMPK regulator, prevented the corticosteroid-induced effects on AMPK in human adipocytes and rat hypothalamic neurons. Our data suggest that glucocorticoid-induced changes in AMPK constitute a novel mechanism that could explain the increase in appetite, the deposition of lipids in visceral adipose and hepatic tissue, as well as the cardiac changes that are all characteristic of glucocorticoid excess. Our data suggest that metformin treatment could be effective in preventing the metabolic complications of chronic glucocorticoid excess.

Role of the GNOM gene in Arabidopsis apical-basal patterning--From mutant phenotype to cellular mechanism of protein action.

How the apical-basal axis of polarity is established in embryogenesis is still a mystery in plant development. This axis appeared specifically compromised by mutations in the Arabidopsis GNOM gene. Surprisingly, GNOM encodes an ARF guanine-nucleotide exchange factor (ARF-GEF) that regulates the formation of vesicles in membrane trafficking. In-depth functional analysis of GNOM and its closest relative, GNOM-LIKE 1 (GNL1), has provided a mechanistic explanation for the development-specific role of a seemingly mundane trafficking regulator. The current model proposes that GNOM is specifically involved in the endosomal recycling of the auxin-efflux carrier PIN1 to the basal plasma membrane in provascular cells, which in turn is required for the accumulation of the plant hormone auxin at the future root pole through polar auxin transport. Thus, the analysis of GNOM highlights the importance of cell-biological processes for a mechanistic understanding of development.

Noise-Driven Mechanism for Pattern Formation

We extend the mechanism for noise-induced phase transitions proposed by Ibañes et al. [Phys. Rev. Lett. 87, 020601 (2001)] to pattern formation phenomena. In contrast with known mechanisms for pure noise-induced pattern formation, this mechanism is not driven by a short-time instability amplified by collective effects. The phenomenon is analyzed by means of a modulated mean field approximation and numerical simulations.

Interactions between cells and functionalized nanoparticles

In this present thesis Superparamagnetic Iron Oxide Nanoparticles (SPIONs) with 9 nm in diameter were selected as nanocarriers in order to study their potential application as drug delivery systems. Therefore the aim of the study was to demonstrate the proof of concept by establishing an efficient system of drug delivery, which would be a valuable tool in biomedical applications, such as the treatement of cancer, by reducing the side effects due to administration of a high concentration of therapeutic agents. As demonstrated in a previous study, the uptake of SPIONs by tumoral human cells was enhanced by the presence of amino groups on their surface. The stabilization of SPIONs were then performed and optimized by the coating of poly(vinylalcohol) and poly(vinylalcohol/vinylamine). Such nanoparticles were known as aminoPVA-SPIONs. The toxicity and the inflammatory reaction of aminoPVA-SPIONs were evaluated in order to establish their potentiel use in the human body. The results demonstrated that the human cells were able to invaginate aminoPVA-SPIONS without revealing any toxicity and inflammatory reaction. The analysis by transmission electron microscopy (TEM), scanning electron microscopy (SEM), cryo-TEM, confocal microscopy and histological staining (i.e. Prussian Blue) showed that the iron oxide core of SPIONs were located in the cytoplasm of cells and concentrated in vesicles. The evaluation of the mechanism of uptake of aminoPVA-SPIONs revealed that their uptake by monolayer cell culture was performed via an active mechanism, which was achieved by a clathrin-mediated endocytosis. Consequently, it was suggested that aminoPVA-SPIONs were good candidates as nanocarriers in drug delivery systems, which were able to reach the cytoplasm of cells. Their incubation with three-dimensional models mimicing tissues, such as differentiated rat brain cell-derived aggregates and spheroids, revealed that aminoPVA-SPIONs were able to invade into deep cell layers according to the stage of growth of these models. In the view of these promising results, drug-SPIONs were prepared by the functionalization of aminoPVA-SPIONs via a biological labile chemical bond by one of these three antineoplastic agents, which are widely used in clinical practice: 5-fluorourdine (Fur) (an antimetabolite), or camptothecin (CPT) (a topoisomerase inhibitor) or doxorubicin (DOX) (an anthracycline which interfere with DNA). The results shown that drug-SPIONs were internalized by human melanoma cells, as it was expected due the previous results with aminoPVA-SPIONs, and in addition they were active as anticancer agents, suggesting the efficient release of the drug from the drug-SPIONs. The results with CPT-SPIONs were the most promising, whereas DOX- SPIONs did not demonstrate a prononced activity of DOX. In conclusion, the results demonstrated that functionalized iron oxide nanoparticles are a promising tool in order to deliver therapeutic agents. - Dans le cadre de ce travail de thèse, les nanoparticules superparamagnétiques d'oxyde de fer (SPIONs) ayant un diamètre de 9 nm ont été choisies, afin d'étudier leur éventuelle utilisation dans un système de délivrance d'agents thérapeutiques. Ainsi le but de la thèse est de démontrer la faisabilité de fabriquer un système efficace de délivrance d'agents thérapeutiques, qui serait un outil intéressant dans le cadre d'une utilisation biomédicale, par exemple lors du traitement du cancer, qui pourrait réduire les effets secondaires provoqués par le dosage trop élevé de médicaments. Comme il a été démontré dans une précédente étude, l'invagination des SPIONs par des cellules humaines cancéreuses est améliorée par la présence de groupes fonctionnels amino à leur surface. La stabilisation des SPIONs est ainsi effectuée et optimisée par l'enrobage de poly(vinylalcool) et de (poly(vinylalcool/vinylamine), qui sont connues sous le nom de aminoPVA-SPIONs. La toxicité et la réaction inflammatoire des aminoPVA-SPIONs ont été évaluées dans le but de déterminer leur potentielle utilisation dans le corps humain. Les résultats démontrèrent que les cellules humaines sont capables d'invaginer les aminoPVAS-SPIONs sans induire une réaction toxique ou inflammatoire. L'analyse par la microscopie électronique en transmission électronique (TEM), la microscopie électronique à balayage (SEM), le cryo-microscopie électronique (SEM), la microscopie confocale et la coloration histologique (par ex, le bleu de Prusse) a montré que l'oxyde de fer des SPIONs est localisé dans le cytoplasme des cellules et est concentré dans des vesicules. L'évaluation du méchanisme d'invagination des aminoPVA-SPIONs ont révélé que leur invagination par des monocultures de cellules est effectué par un méchanisme actif, contrôlé par une endocytose induite par les clathrins. Par conséquent, les aminoPVA-SPIONs sont de bons candidats en tant que transporteurs (nanocamers) dans un système de délivrance d'agents thérapeuthique, capable d'atteindre le cytoplasme des cellules. Leur incubation avec des modèles tridimenstionnels imitant les tissues, tels que les aggrégats de cellules de cerveau différenciées et les sphéroïdes, a montré que les aminoPVA-SPIONs sont capable de pénétrer dans les couches profondes des modèles, selon l'état d'avancement de leur croissance. En vue de ces résultats prometteurs, les drug-SPIONs ont été préparés en fonctionalisant les aminoPVA-SPIONs par le biai d'une liaison chimique labile par un des trois agents thérapeutiques, déjà utilisé en pratique : 5-fluorourdine (Fur) (un antimétabolite), or camptothecin (CPT) (un inhibiteur de la topoisomerase) or doxorubicin (DOX) (un anthracycline qui interfère avec le DNA). Les résultats ont montré que les drug-SPIONs sont capable d'être internalisés par les mélanomes, comme il a été attendu d'après les résultats obtenus précédemment avec les aminoPVA-SPIONs, et de plus, les drug-SPIONs sont actifs, ce qui suggère un relargage efficace de l'agent thérapeutique du drug-SPIONs. Les résultats obtenus avec les CPT-SPIONs sont les plus prometteurs, tandis que ceux avec les DOX-SPIONs, ce n'est pas le cas, dont l'activité thérapeutique de DOX n'a pas été aussi efficace. En conclusion, les résultats ont pu démontrer que les nanoparticules d'oxyde de fer fonctionnalisées sont un outil prometteur dans la délivrance d'agents thérapeutiques.

Bacterial-induced protection against allergy through a novel multi-component immunoregulatory mechanism

Airborne microbial products have been reported to promote immune responses that suppress asthma, yet how these beneficial effects take place remains controversial and poorly understood. We have found that pulmonary exposure with the bacterium Escherichia coli leads to a suppression of allergic airway inflammation, characterized by reduced airway-hyperresponsiveness, eosinophilia and cytokine production by T cells in the lung. This immune modulation was neither mediated by the induction of a Th1 response nor regulatory T cells; was dependent on TLR-4 but did not involve TLR-desensitization. Dendritic cell migration to the draining lymph nodes and subsequent activation of T cells was unaffected by prior exposure to E.coli indicating that the immunomodulation was limited to the lung environment. In non-treated control mice ovalbumin was primarily presented by airway CD11b+ CD11c+ DCs expressing high levels of MHC class II molecules whilst the DCs in E.coli-treated mice displayed a less activated phenotype and had impaired antigen presentation capacity. Consequently, in situ Th2 cytokine production by ovalbuminspecific effector T cells recruited to the airways was significantly reduced. The suppression of airways hyper responsiveness was mediated through the recruitment of IL-17-producing gd-T cells; however, the suppression of dendritic cells and T cells was mediated through a distinct mechanism that could not be overcome by the local administration of activated dendritic cells, or by the in vivo administration of TNF-alpha. Taken together, these data reveal a novel multi-component immunoregulatory pathway that acts to protect the airways from allergic inflammation.

Regulation of Nav1.7 and Nav1.8 voltage-gated sodium channels by Nedd4-2 and β-subunits and its implication in neuropathic pain

In mammals, the presence of excitable cells in muscles, heart and nervous system is crucial and allows fast conduction of numerous biological information over long distances through the generation of action potentials (AP). Voltage-gated sodium channels (Navs) are key players in the generation and propagation of AP as they are responsible for the rising phase of the AP. Navs are heteromeric proteins composed of a large pore-forming a-subunit (Nav) and smaller ß-auxiliary subunits. There are ten genes encoding for Navl.l to Nav1.9 and NaX channels, each possessing its own specific biophysical properties. The excitable cells express differential combinations of Navs isoforms, generating a distinct electrophysiological signature. Noteworthy, only when anchored at the membrane are Navs functional and are participating in sodium conductance. In addition to the intrinsic properties of Navs, numerous regulatory proteins influence the sodium current. Some proteins will enhance stabilization of membrane Navs while others will favour internalization. Maintaining equilibrium between the two is of crucial importance for controlling cellular excitability. The E3 ubiquitin ligase Nedd4-2 is a well-characterized enzyme that negatively regulates the turnover of many membrane proteins including Navs. On the other hand, ß-subunits are known since long to stabilize Navs membrane anchoring. Peripheral neuropathic pain is a disabling condition resulting from nerve injury. It is characterized by the dysregulation of Navs expressed in dorsal root ganglion (DRG) sensory neurons as highlighted in different animal models of neuropathic pain. Among Navs, Nav1.7 and Nav1.8 are abundantly and specifically expressed in DRG sensory neurons and have been recurrently incriminated in nociception and neuropathic pain development. Using the spared nerve injury (SNI) experimental model of neuropathic pain in mice, I observed a specific reduction of Nedd4-2 in DRG sensory neurons. This decrease subsequently led to an upregulation of Nav1.7 and Nav1.8 protein and current, in the axon and the DRG neurons, respectively, and was sufficient to generate neuropathic pain-associated hyperexcitability. Knocking out Nedd4-2 specifically in nociceptive neurons led to the same increase of Nav1.7 and Nav1.8 concomitantly with an increased thermal sensitivity in mice. Conversely, rescuing Nedd4-2 downregulation using viral vector transfer attenuated neuropathic pain mechanical hypersensitivity. This study demonstrates the significant role of Nedd4-2 in regulating cellular excitability in vivo and its involvement in neuropathic pain development. The role of ß-subunits in neuropathic pain was already demonstrated in our research group. Because of their stabilization role, the increase of ßl, ß2 and ß3 subunits in DRGs after SNI led to increased Navs anchored at the membrane. Here, I report a novel mechanism of regulation of a-subunits by ß- subunits in vitro; ßl and ß3-subunits modulate the glycosylation pattern of Nav1.7, which might account for stabilization of its membrane expression. This opens new perspectives for investigation Navs state of glycosylation in ß-subunits dependent diseases, such as in neuropathic pain. - Chez les mammifères, la présence de cellules excitables dans les muscles, le coeur et le système nerveux est cruciale; elle permet la conduction rapide de nombreuses informations sur de longues distances grâce à la génération de potentiels d'action (PA). Les canaux sodiques voltage-dépendants (Navs) sont des participants importants dans la génération et la propagation des PA car ils sont responsables de la phase initiale de dépolarisation du PA. Les Navs sont des protéines hétéromériques composées d'une grande sous-unité a (formant le pore du canal) et de petites sous-unités ß accompagnatrices. Il existe dix gènes qui codent pour les canaux sodiques, du Nav 1.1 au Nav 1.9 ainsi que NaX, chacun possédant des propriétés biophysiques spécifiques. Les cellules excitables expriment différentes combinaisons des différents isoformes de Navs, qui engendrent une signature électrophysiologique distincte. Les Navs ne sont fonctionnels et ne participent à la conductibilité du Na+, que s'ils sont ancrés à la membrane plasmique. En plus des propriétés intrinsèques des Navs, de nombreuses protéines régulatrices influencent également le courant sodique. Certaines protéines vont favoriser l'ancrage et la stabilisation des Navs exprimés à la membrane, alors que d'autres vont plutôt favoriser leur internalisation. Maintenir l'équilibre des deux processus est crucial pour contrôler l'excitabilité cellulaire. Dans ce contexte, Nedd4-2, de la famille des E3 ubiquitin ligase, est une enzyme bien caractérisée qui régule l'internalisation de nombreuses protéines, notamment celle des Navs. Inversement, les sous-unités ß sont connues depuis longtemps pour stabiliser l'ancrage des Navs à la membrane. La douleur neuropathique périphérique est une condition débilitante résultant d'une atteinte à un nerf. Elle est caractérisée par la dérégulation des Navs exprimés dans les neurones sensoriels du ganglion spinal (DRG). Ceci a été démontré à de multiples occasions dans divers modèles animaux de douleur neuropathique. Parmi les Navs, Nav1.7 et Nav1.8 sont abondamment et spécifiquement exprimés dans les neurones sensoriels des DRG et ont été impliqués de façon récurrente dans le développement de la douleur neuropathique. En utilisant le modèle animal de douleur neuropathique d'épargne du nerf sural (spared nerve injury, SNI) chez la souris, j'ai observé une réduction spécifique des Nedd4-2 dans les neurones sensoriels du DRG. Cette diminution avait pour conséquence l'augmentation de l'expression des protéines et des courants de Nav 1.7 et Nav 1.8, respectivement dans l'axone et les neurones du DRG, et était donc suffisante pour créer l'hyperexcitabilité associée à la douleur neuropathique. L'invalidation pour le gène codant pour Nedd4-2 dans une lignée de souris génétiquement modifiées a conduit à de similaires augmentations de Nav1.7 et Nav1.8, parallèlement à une augmentation à la sensibilité thermique. A l'opposé, rétablir une expression normale de Nedd4-2 en utilisant un vecteur viral a eu pour effet de contrecarrer le développement de l'hypersensibilité mécanique lié à ce modèle de douleur neuropathique. Cette étude démontre le rôle important de Nedd4-2 dans la régulation de l'excitabilité cellulaire in vivo et son implication dans le développement des douleurs neuropathiques. Le rôle des sous-unités ß dans les douleurs neuropathiques a déjà été démontré dans notre groupe de recherche. A cause de leur rôle stabilisateur, l'augmentation des sous-unités ßl, ß2 et ß3 dans les DRG après SNI, conduit à une augmentation des Navs ancrés à la membrane. Dans mon travail de thèse, j'ai observé un nouveau mécanisme de régulation des sous-unités a par les sous-unités ß in vitro. Les sous-unités ßl et ß3 régulent l'état de glycosylation du canal Nav1.7, et stabilisent son expression membranaire. Ceci ouvre de nouvelles perspectives dans l'investigation de l'état de glycosylation des Navs dans des maladies impliquant les sous-unités ß, notamment les douleurs neuropathiques.

Stabilization of soil hydraulic properties under a long term no-till system

The area under the no-tillage system (NT) has been increasing over the last few years. Some authors indicate that stabilization of soil physical properties is reached after some years under NT while other authors debate this. The objective of this study was to determine the effect of the last crop in the rotation sequence (1st year: maize, 2nd year: soybean, 3rd year: wheat/soybean) on soil pore configuration and hydraulic properties in two different soils (site 1: loam, site 2: sandy loam) from the Argentinean Pampas region under long-term NT treatments in order to determine if stabilization of soil physical properties is reached apart from a specific time in the crop sequence. In addition, we compared two procedures for evaluating water-conducting macroporosities, and evaluated the efficiency of the pedotransfer function ROSETTA in estimating the parameters of the van Genuchten-Mualem (VGM) model in these soils. Soil pore configuration and hydraulic properties were not stable and changed according to the crop sequence and the last crop grown in both sites. For both sites, saturated hydraulic conductivity, K0, water-conducting macroporosity, εma, and flow-weighted mean pore radius, R0ma, increased from the 1st to the 2nd year of the crop sequence, and this was attributed to the creation of water-conducting macropores by the maize roots. The VGM model adequately described the water retention curve (WRC) for these soils, but not the hydraulic conductivity (K) vs tension (h) curve. The ROSETTA function failed in the estimation of these parameters. In summary, mean values of K0 ranged from 0.74 to 3.88 cm h-1. In studies on NT effects on soil physical properties, the crop effect must be considered.

Intramolecular coupling as a mechanism for a liquid-liquid phase transition

We study a model for water with a tunable intramolecular interaction Js, using mean-field theory and off-lattice Monte Carlo simulations. For all Js>~0, the model displays a temperature of maximum density. For a finite intramolecular interaction Js>0, our calculations support the presence of a liquid-liquid phase transition with a possible liquid-liquid critical point for water, likely preempted by inevitable freezing. For J=0, the liquid-liquid critical point disappears at T=0.

Optimization of Soil Stabilization with Class C Fly Ash, January 1987

Previous Iowa DOT sponsored research has shown that some Class C fly ashes are ementitious (because calcium is combined as calcium aluminates) while other Class C ashes containing similar amounts of elemental calcium are not (1). Fly ashes from modern power plants in Iowa contain significant amounts of calcium in their glassy phases, regardless of their cementitious properties. The present research was based on these findings and on the hyphothesis that: attack of the amorphous phase of high calcium fly ash could be initiated with trace additives, thus making calcium available for formation of useful calcium-silicate cements. Phase I research was devoted to finding potential additives through a screening process; the likely chemicals were tested with fly ashes representative of the cementitious and non-cementitious ashes available in the state. Ammonium phosphate, a fertilizer, was found to produce 3,600 psi cement with cementitious Neal #4 fly ash; this strength is roughly equivalent to that of portland cement, but at about one-third the cost. Neal #2 fly ash, a slightly cementitious Class C, was found to respond best with ammonium nitrate; through the additive, a near-zero strength material was transformed into a 1,200 psi cement. The second research phase was directed to optimimizing trace additive concentrations, defining the behavior of the resulting cements, evaluating more comprehensively the fly ashes available in Iowa, and explaining the cement formation mechanisms of the most promising trace additives. X-ray diffraction data demonstrate that both amorphous and crystalline hydrates of chemically enhanced fly ash differ from those of unaltered fly ash hydrates. Calciumaluminum- silicate hydrates were formed, rather than the expected (and hypothesized) calcium-silicate hydrates. These new reaction products explain the observed strength enhancement. The final phase concentrated on laboratory application of the chemically-enhanced fly ash cements to road base stabilization. Emphasis was placed on use of marginal aggregates, such as limestone crusher fines and unprocessed blow sand. The nature of the chemically modified fly ash cements led to an evaluation of fine grained soil stabilization where a wide range of materials, defined by plasticity index, could be stabilized. Parameters used for evaluation included strength, compaction requirements, set time, and frost resistance.