La lipolyse est une réaction enzymatique qui influence négativement les qualités organoleptiques et technologiques du lait. La lipolyse spontanée (LS) correspond à la part de la lipolyse qui dépend de l’animal et du système d’élevage. La LS résulte de l’action de la lipoprotéine lipase (LPL) et de ses cofacteurs sur les globules gras (GG). L’objectif de la thèse a été de comprendre les variations de LS à l’échelle zootechnique et à l’échelle du lait. Les vaches (VL) ont pu être classées en 2 groupes selon leur phénotype : « susceptible » et « non susceptible » à la LS, confirmant l’importance de l’effet individu. Chez les VL susceptibles, nous avons confirmé un effet de la race/génétique, de la parité, du stade physiologique, du moment de la traite, de la fréquence de traite et de l’alimentation.La LS était plus élevée dans les laits issus de la traite du soir, chez les VL Holstein, génotypées KK au locus de DGAT-1. Elle l’était également en fin de lactation et en début de lactation uniquement chez les multipares hautes productrices. Un bilan énergétique négatif pourrait expliquer ces variations. L’augmentation de la fréquence de traite, la restriction alimentaire, l’alimentation à base d’ensilage de maïs comparé à l’herbe conservée/fraîche et la supplémentation lipidique ont également augmenté la LS. Le mécanisme d’action implique probablement une inhibition de la LS par la protéose peptone 5. La membrane des GG semblerait avoir un rôle crucial dans le maintien de l’intégrité du GG, l’interaction avec la LPL et l’équilibre des cofacteurs. L’impact des facteurs zootechniq / Lipolysis is an enzymatic reaction which leads to off-flavor in milk and impairs technological properties of milk. Spontaneous lipolysis (SL) is the fraction of lipolysis which depends on cows and breeding systems. SP corresponds to the hydrolysis of milk fat in milk fat globules (MFG) by the lipoprotein lipase (LPL) and its cofactors. The aim of the PhD was to understand SL variations at both zootechnical and biochemical levels. Cows were sorted in two groups according their phenotype: “susceptible” and “non-susceptible” to SL, confirming the strong impact of the individual effect. Among cows “susceptible” to SL, we confirmed the effects of breed/genetics, parity, physiological stage, milking moment, milking frequency and feeding systems. SL was higher in evening milks of Holstein cows and of cows having the KK genotype at the DGAT-1 locus. SL was higher in late lactation and, in early lactation only for high merit multiparous cows, probably in relation to negative energy balanceAn increase in milking frequency, feeding restriction, maize silage based diets compared to fresh grass and conserved grass based diets and lipid supplementation enhanced SL. At a biochemical level, LS might be inhibited by proteose peptone 5. The MFG membrane might play an important role on MFG integrity, LPL and MFG interactions, and cofactors balance. The impact of zootechnical and biochemical factors on SL is still difficult to hierarchize

Le paludisme est causé par un parasite appelé Plasmodium falciparum, transmis lors de la piqûre d'un moustique. Au stade sanguin, ce parasite unicellulaire, de forme ovoïde, envahit les globules rouges, s'y multiplie avant d'être libéré pour une nouvelle invasion à la fin d'un cycle de 48 heures. Ce travail de thèse porte sur le mouvement du parasite au cours du processus d'invasion. L'étape préalable à la pénétration du parasite dans sa cellule hôte est le mouvement de réorientation permettant de mettre en contact son complexe apical avec la membrane de la cellule hôte. Afin de comprendre comment le parasite génère les mouvements nécessaires à cette réorientation sans l'aide de flagelle, de cil ou de déformation, notre approche est d'observer et de décrire le mouvement des parasites sur un substrat rigide, au travers d'une analyse détaillée des trajectoires du parasite. Nous observons que le parasite explore tous les degrés de liberté qui lui sont accessibles compte tenu de son attachement au substrat: translation et rotation dans le plan et réorientation de sa partie apicale. Nous avons identifié trois types de mouvement: confiné, dirigé et circulaire. Nous caractérisons ces trajectoires et mouvements en utilisant une analyse de corrélation et en discutant les mécanismes possibles à l'origine de ces trajectoires particulières. Enfin, nous examinons le rôle des constituants du cytosquelette sur le mouvement du parasite, en affectant spécifiquement les filaments d'actine et les microtubules. Les conséquences de la polymérisation de ces structures sur le mouvement du parasites sont discutées. / Malaria is caused by a parasite called Plasmodium falciparum, transmitted via mosquito's bites. At the blood stage, these unicellular ovoidal parasites invade red blood cells (RBCs), multiply and are released at the end of a 48h cycle, ready for new invasions. This work is focused on the motion of the parasite during the invasion process. To penetrate into the host cell, the parasite reorient its apical part towards the RBC membrane. For this purpose, the parasite generates different movements that allow him to find the correct position to form a specific junction to invade the cell. To understand how the parasite is able to move and reorient without the aid of cilia, flagella or deformations, we performed a detailed analysis of the parasite trajectories and orientation on rigid substrate. We observe that the substrate-attached parasite explores all degrees of freedom with in-plane rotation, translation and flipping. Three types of motion have been identified: confined, directed circular . We characterize these trajectories and motions using correlation analysis and we discuss the possible mechanisms that could explain these peculiar trajectories. Finally, to determine the role of the cytoskeleton components in the parasite motion, specific structures such as the actin filaments and the microtubules have been specifically affected. We will describe and discuss the consequences of depolymerizing or stabilizing these structures.

ABSTRACT Effects of Milk Processing on the Milk Fat Globule Membrane Constituents Xiomara E. Elías-Argote The milk fat globule membrane (MFGM) is avidly studied by many groups of scientists around the world due to its unprecedented nutritional and functional properties; however, limited research has been performed on the effects of milk processing on the chemical changes of the MFGM. Thus, this study highlights the changes that lipids and proteins undergo from the time milk leaves cow’s udders. Cooling (4 °C) was included along with subsequent pasteurization by different traditional thermal processes and cold pasteurization by pulse light ultra violet treatment. Cooling milk to 4 °C had a measureable effect on the MFGM composition, resulting in protein alterations, particularly to butyrophilin and adipophilin. Thermal treatments disturbed the native structures of molecules and increased the adsorption of milk and whey proteins on the globules, especially a-lactalbumin and b-lactoglobulin. As the heat intensity increased, the aggregation of fat globules became more pronounced due to protein interactions. Intrinsic MFGM proteins also varied in relative abundance during the processing steps. The concentrations of polar lipids did not change during processing, with the exception of phosphatidylserine, which decreased during the cooling and thermal treatments. Cold pasteurization (UV treatment) had a minimal effect on fat globules and MFGM proteins. Since the MFGM promises to deliver nutritional effects and more when included in food products, currently HTST pasteurization was shown to be the best method to process milk and obtain MFGM isolates for further supplementation.

Milk fat globule membrane surrounds the fat droplets of milk. It is a biopolymer containing primarily membrane glycoproteins and polar lipids which contribute to its properties as a possible neutraceutical. The aims of the studies were to determine if dietary milk fat globule membrane: (1) confers protection against colon carcinogenesis; and (2) promotes gut mucosal integrity while decreasing inflammation compared to diets containing corn oil or anhydrous milk fat. Aim 1. Three dietary treatments differing only in the fat source were formulated: (1) AIN-76A, corn oil; (2) AIN-76A, anhydrous milk fat; and (3) AIN-76A, 50% milk fat globule membrane, 50% anhydrous milk fat. Each diet was formulated to contain 50 g/kg diet of fat and to be identical in macro and micro nutrient content. To assess protection against colon carcinogenesis, male, weanling Fischer-344 rats were randomly assigned to one of the three dietary treatments. Animals were injected with 1,2-dimethylhydrazine once per week at weeks 3 and 4. After 13 weeks animals were sacrificed, colons were removed, and aberrant crypt foci were counted by microscopy. Rats fed the milk fat globule membrane diet (n = 16) had significantly fewer aberrant crypt foci (20.9 ± 5.7) compared to rats fed corn oil (n = 17) or anhydrous milk fat (n = 16) diets (31.3 ± 9.5 and 29.8 ± 11.4 respectively; P < 0.05). Aim 2. Male BALB/c mice were randomly assigned to one of two diets: AIN- 76A, corn oil or AIN-76A, 50% milk fat globule membrane, 50% anhydrous milk fat. After 5 weeks mice were injected with saline vehicle control or lipopolysaccharide and gavaged with dextran-FITC. To assess gut mucosal integrity and inflammation, serum samples were assayed for dextran-FITC 24 and 48 hours after gavage, and a panel of 16 cytokine concentrations was analyzed. Serum concentrations of IL-6, IL-10, IL-17, MCP-1, IFNγ, and TNFα decreased and gut permeability decreased 45% in lipopolysaccharide challenged mice fed milk fat globule membrane diet compared to control diet at 24 hours (P < 0.05). Overall, the results of these aims suggest that diets containing milk fat globule membrane are protective against colon carcinogenesis, inhibit the inflammatory response, and protect against gastrointestinal stress.

Dans la partie "adhésion", nous avons montré que la dynamique d'adhésion<br />de vésicules induite par des ligands spécifiques était gouvernée soit par la diffusion<br />de ligands dans la membrane, soit par le temps de réaction entre le ligand et le<br />récepteur, dépendant de la préparation chimique des surfaces. Au contraire, les<br />premières étapes de l'adhésion de cellules semblent être contrôlées par la<br />dissipation visqueuse à l'intérieur de la cellule.<br />Dans la partie "tubes de membrane", nous avons étudié la formation et<br />l'élongation de tubes de membrane. Tout d'abord, en formant des tubes à partir de<br />vésicules adhérées, nous avons montré que l'élongation des tubes s'accompagne<br />d'un étirement élastique de la membrane. Ensuite, en analysant expérimentalement<br />et théoriquement l'interaction et la coalescence de deux tubes membranaires, nous<br />avons proposé une méthode pour déterminer la rigidité de courbure de vésicules<br />lipidiques. Enfin, nous avons revisité la description mécanique de tubes extraits de<br />globules rouges et nous avons mis en évidence un comportement rhéofluidifiant de<br />la membrane durant l'élongation, indiquant l'influence du squelette de spectrine.

Several analytical mean field models are presented for the class of stimuli responsive polymers that are driven by the lower critical solution temperature (LCST) transition. For solutions above the polymer crossover concentration, a hybrid model combines lattice-fluid excluded volume and van-der-Waals interactions with a combinatorial approach for the statistics of hydrogen bonding, hydration, and ionic bonding. This approach yields models for the LCST of both neutral polymers and lightly charged polyelectrolytes in aqueous salt solution. The results are shown to be in semi-quantitative agreement with experimental data for the cloud point of polyethylene oxide (PEO) in aqueous solution with various salts, and some aspects of the lyotropic series are reproduced. Results for lightly charged polyelectrolytes are compared to and shown to be in qualitative agreement with aspects of experimentally observed behavior. Finally, a framework is established for extension of these models to further aspects of the lyotropic series and polyelectrolyte behavior. At the nanoscale, lattice fluid (LF) and scaled particle theory (SPT) approaches are employed to model the LCST-related coil-globule-transition (CGT) of isolated polymer chains in highly dilute solution. The predicted CGT behavior semi-quantitatively correlates with experimental results for several polymer-solvent systems and over a range of pressures. Both the LF and SPT models exhibit a heating induced coil-to-globule transition (HCGT) temperature that increases with pressure until it merges with a cooling induced coil-to-globule transition (CCGT). The point at which the CCGT and HCGT meet is a hypercritical point that also corresponds to a merging of the lower critical and upper critical solution temperatures. Theoretical results are discussed in terms of a generalized polymer/solvent phase diagram that possesses three hypercritical points. Within the lattice model, a dimensionless transition temperature [author gives mathematical symbol] is given for a long chain simply by the equation [author gives mathematical equation], where [part of the equation] is the bulk solvent occupied volume fraction at the transition temperature. Furthermore, there is a critical value of the ratio of polymer to solvent S-L characteristic temperature below which no HCGT transition is predicted for an infinite chain. / text

Les vésicules sont des bicouches fermées de molécules tensioactives, remplies de liquide, à l'intérieur d'un autre liquide. Leur taille peut être comprise entre dix et 100 microns : elles sont alors dites géantes. Nous nous intéressons à la dynamique de deux de ces objets dans un cisaillement simple, c'est à dire l'écoulement d'un liquide situé entre deux plaques planes se translatant l'une par rapport à l'autre à vitesse et distance constante. Nous commençons par une étude asymptotique, pour des vésicules quasi-sphériques en interaction lointaine. Nous utilisons ensuite un code de calcul basé sur la méthode des éléments de frontière pour étudier le cas de vésicules moins sphériques et plus proches, et comparons les résultats obtenus avec des expériences. Nous présentons enfin comment cette étude peut être utilisée pour prédire certaines propriétés de diffusion d'une suspension de vésicules, dans le régime semi-dilué, où seul le détail des interactions à deux corps est considéré.

Video files: Some images may require stereoscopic glasses / Fat in milk and cream is present as tiny droplets, which are each enveloped in a thin membrane, called the milk fat globule membrane (MFGM). The MFGM can easily be damaged by factors such as pumping the milk and applying other forms of agitation. MFGM damage is believed to reduce processing efficiency and compromise the quality of manufactured products. A comprehensive review of the literature showed that our understanding of changes occurring in the MFGM post secretion of the fat globule by the mammary secretory cell is still rudimentary. Furthermore, it was found that a fundamental understanding of MFGM damage in raw milk is lacking. Hence, this study sought to develop analytical techniques for studying the MFGM. Fluorescent probes were identified that associated with the MFGM (bovine, ovine, human) in one of two ways: either by embedding in the phospholipid bilayer (lipophilic probe) or by binding to carbohydrate moieties of glycosylated chains in the glycocalyx (lectin probes). The use of these probes, in combination with either conventional fluorescence microscopy or confocal laser scanning microscopy, allowed 2-D images and 3-D images of fat globules to be made. Application of water-soluble lipophilic probes and the lectin wheat germ agglutinin (WGA) directly to milk allowed the staining of the MFGM in its native environment. Variable distribution patterns of the probes in the MFGM were observed, which suggests that the MFGM of fat globules in harvested milk is structurally and chemically heterogeneous both within and among globules from the same species and between species, and even among fat globules within the milk of an individual animal. Furthermore, the binding behaviour of WGA to the MFGM of native fat globules (in bovine milk) and washed fat globules (in model systems) following heat treatment implicated β-lactoglobulin, α-lactalbumin, immunoglobulin M and/or the glycosylated proteins Periodic acid Schiff 6/7 in the disappearance of fat globule aggregation upon elevated heat treatment of milk. The results of the current study showed that the use of membrane-specific fluorescent probes, particularly in combination with confocal laser scanning microscopy, has significant potential for providing real time structural and chemical information about the MFGM in matrices such as harvested milk and milk products. In addition to the fluorescence microscopy techniques, development of other techniques was also conducted. Flow cytometry was shown to have significant potential for the quantitative determination of various properties of fat globules and their membranes. Although no suitable sample preparation technique could be developed in this study, atomic force microscopy is believed to have significant potential for studying structural and physical properties of the MFGM. Selective harvesting of individual fat globules was shown to be possible by using a micromanipulator. In future work, this technique is expected to be used in combination with fluorescence microscopy, or atomic force microscopy. The present study has shown that the development and application of novel analytical techniques has advanced, and in the future will further advance, understanding of the MFGM.

La microcirculation sanguine est un système constitué de réseaux complexesde vaisseaux sanguins de diamètres micrométriques. C’est le lieu privilégié deséchanges de gaz et de nutriments entre le sang et les tissus.Les écoulements dans ces réseaux sont gouvernés par les propriétés des constituantsdu sang c’est-à-dire des cellules en suspension dans du plasma et plus particulièrementdes globules rouges qui sont les cellules majoritaires dans le sang.Selon les conditions de l’écoulement, les globules rouges, qui sont des particulesdéformables, peuvent présenter différents types de formes et de dynamiques quiinfluencent la rhéologie de la suspension. Les interactions hydrodynamiques entreglobules rouges et avec les parois dans les vaisseaux confinés influencent égalementles écoulements à travers des phénomènes de diffusion mais aussi de structurationdes globules au sein de la suspension. Il a notamment été montré que des couchesde plasma dépourvues de globules rouges près des parois des vaisseaux sanguins induisentune diminution de la viscosité effective de la suspension lorsqu’on diminuele diamètre du vaisseau. Par ailleurs, des structurations en file ont également étéobservées dans la microcirculation sanguine avec des conséquences probables surla rhéologie. Au cours de ces travaux de thèse, nous avons investigué les propriétésrhéologiques de suspensions de globules rouges en micro-écoulement grâce à uneméthode de rhéométrie microfluidique. Nous avons focalisé notre attention sur larelation entre la rhéologie et la structuration de la suspension dans un canal, liéeau confinement ainsi qu’aux régimes dynamiques des globules en écoulement.Dans certains cas pathologiques comme la drépanocytose où les propriétés desglobules rouges peuvent être modifiées, les écoulements dans la microcirculationpeuvent être perturbés et conduire à des crises vaso-occlusives dont les mécanismesphysiques restent mal compris. Nous avons exploré la dynamique de formationd’occlusions et leurs évolutions dans des réseaux de canaux micrométriques modèlesavec des suspensions de globules rouges dont les propriétés ont été modifiées,révélant ainsi une dynamique complexe où l’adhésion et des effets d’obstructionsinterviennent. / Blood microcirculation consists in blood flowing in complex microvessel networks.Gas and nutrient exchanges between blood and tissues occur in these networks.Microcirculatory blood flows are governed by the properties of blood components,mainly red blood cells suspended in plasma. Red blood cells are deformableparticles which can exibit different shapes and motion dynamics that influence therheology. Hydrodynamic interactions between red blood cells and with walls of theconfined channels lead to diffusion and structuration in the suspension that alsoaffects the rheology. Plasma cell-free layers near walls observed in the microcirculationinduce a decrease of the effective viscosity with decreasing vessel diameter.Other types of structuration like layering of red blood cells have been observed inthe microcirculation with possible rheological consequences. In the present work,we investigated the rheology of confined red blood cell suspensions and focusedon the link between rheology and structuration of the suspension thanks to amicrofluidic viscosimeter.The sickle cell disease which modifies the properties of red blood cells leadsto flow disorders with the formation of occlusions in the narrow capillaries ofthe microcirculation. We explored the formation and the evolution of occlusionsin simplified networks of microchannels when properties of red blood cells aremodified, revealing complex dynamics where adhesion and jamming effect occur.

Blood is a complex suspension of deformable particles, red blood cells, which exhibits a sophisticated dynamics when flowing in the microvasculature. Most of these complex phenomena, non-linear rheology, structuration of the suspension, heterogeneities of the hematocrit distribution, are directly connected to the rich microscopic dynamics of individual red blood cells, and their hydrodynamics interactions. We investigate a few aspects of the dynamics of red blood cells and giant vesicles - a simple model for RBCs. A study on the dynamics of very deflated vesicles, with shapes similar to those of red blood cells, shows that these objects which haven't received a lot of attention so far can exhibit richer than expected dynamics. We then mainly focus on the still unexplored problem of hydrodynamic interactions between vesicles or red blood cells and their consequences at the scale of the suspension. An experimental study of the interaction of two identical vesicles in shear flow shows that there is a net repulsion between the cells that leads to an increase of the distance between vesicles in a suspension. Scaling arguments are proposed for this interaction and a comparison with numerical results is performed and a quantitative estimation of a shear induced diffusion coefficient obtained by averaging the results for pair interactions is found. Finally, we investigate the diffusion of a cloud of red blood cells in Poiseuille flow in order to directly determine diffusion coefficients. The experiment shows that the cloud widens when traveling along the channel with a power law behaviour indicating sub-diffusion. This effect is confirmed by a theoretical analysis of a few limit cases. / Blood is a complex suspension of deformable particles, red blood cells, which exhibits a sophisticated dynamics when flowing in the microvasculature. Most of these complex phenomena, non-linear rheology, structuration of the suspension, heterogeneities of the hematocrit distribution, are directly connected to the rich microscopic dynamics of individual red blood cells, and their hydrodynamics interactions. We investigate a few aspects of the dynamics of red blood cells and giant vesicles - a simple model for RBCs. A study on the dynamics of very deflated vesicles, with shapes similar to those of red blood cells, shows that these objects which haven't received a lot of attention so far can exhibit richer than expected dynamics. We then mainly focus on the still unexplored problem of hydrodynamic interactions between vesicles or red blood cells and their consequences at the scale of the suspension. An experimental study of the interaction of two identical vesicles in shear flow shows that there is a net repulsion between the cells that leads to an increase of the distance between vesicles in a suspension. Scaling arguments are proposed for this interaction and a comparison with numerical results is performed and a quantitative estimation of a shear induced diffusion coefficient obtained by averaging the results for pair interactions is found. Finally, we investigate the diffusion of a cloud of red blood cells in Poiseuille flow in order to directly determine diffusion coefficients. The experiment shows that the cloud widens when traveling along the channel with a power law behaviour indicating sub-diffusion. This effect is confirmed by a theoretical analysis of a few limit cases.