The key transcription factor sterol regulatory element binding protein-1 (SREBP1) plays a central role in milk fat synthesis. SREBP1 stimulates the transcription of genes encoding lipogenic enzymes. The overall objective of these studies was to investigate the mechanisms of SREBP1 regulation by nutrients. In the first study, chromatin immunoprecipitation (ChIP) accompanied with deep-sequencing was employed to investigate the potential sterol regulatory elements (SRE) in the promoter of SREBP1-target genes. The SRE in three known SREBP1-target genes SREBP1, fatty acid synthase (FASN) and stearoyl-CoA desaturase (SCD) were first validated in a bovine mammary epithelial cell line (MacT) and in bovine mammary tissues. At least one or two SRE binding sites in 24 selected lipogenic genes were identified within 50,000 base pair to the 5'-transcription start site through ChIP-seq. The genes closest to the highest enriched peaks were involved in cell integrity, defense or signal transduction whereas lipogenic genes were not among the top enrichment leading to the questions about the success of the ChIP. The second study was conducted to determine the effect of t10, c12-conjugated linoleic acid (CLA) on insulin induced gene-1 (Insig1), an endoplasmic reticulum (ER) protein that anchors SREBP1 and prevents proteolytic activation of SREBP1. MacT cells were treated with increasing levels of t10, c12-CLA. High concentration of t10, c12-CLA inhibited Insig1 degradation therefore decreased SREBP1 maturation. Furthermore, immunoprecipitation (IP) confirmed that t10, c12-CLA reduced Insig1 proteasomal degradation by disrupting the interaction between Insig1 and UBX domain-containing protein 8 (Ubxd8), which is part of a degradation complex that removes Insig1 from the ER. In the third study, three potential regulators of SREBP1 activation and their pathways were investigated in insulin, t10, c12-CLA or glucose treated MacT cells. Insulin-induced mammalian target of rapamycin (mTOR) signaling stimulated lipogenesis via activation of SREBP1 and the stimulatory effect was based on the regulation on cAMP response element binding protein coactivator 2 (CRTC2) phosphorylation, Lipin1 translocation and glycogen synthase kinase-3 (GSK3)-dependent proteasomal degradation. t10, c12-CLA inhibited SREBP1 through AMP-activated protein kinase (AMPK) phosphorylation, a key protein kinase in energy homeostasis. Glucose stabilized the SREBP1 chaperone protein SCAP and facilitated SREBP1 activation. Overall, SREBP1 activation is under specific regulation of t10, c12-CLA and interacts with multiple major cellular signaling pathways in response to hormonal stimulation and nutrient availability. / Ph. D.

Biosynthesis of milk conjugated linoleic acid (CLA), a component of milk fat with demonstrated health benefits, requires a dietary source of PUFA. Even with PUFA supplementation, milk CLA is highly variable. Therefore, this study was aimed at identifying factors responsible for the variations in rumen CLA precursors and milk CLA. Study 1 evaluated the efficiency of CLA production by grazing cows compared to those fed grass silage or fresh grass. Grazing cows were more efficient than those fed grass silage or fresh grass in milk CLA production. About 75% of the variability in milk CLA was related to the differences in PUFA (l8:2n-6 + 18:3n-3) intake and the remainder was related to factors regulating the extent of PUFA biohydrogenation in the rumen. This study demonstrated that PUFA intake is important but it is not the only factor responsible for the observed variation in milk CLA production. Study 2 evaluated the effect of diets differing in rate of starch degradation on rumen PUFA biohydrogenation and milk CLA. Concentrations of ruminal t11-18:1 and milk CLA were greater for barley-based diets than corn-based diets and were not different between rolling and grinding, indicating that factors inherent in the source of starch were responsible for the observed differences and these factors could not be modified by rolling or grinding the grain. Study 3 examined the effect of stage of lactation on persistency of milk t10-18:1, t11-18:1 and CLA for control and test (supplemented with PUFA and monensin) diets from calving to 270 days in milk. Milk concentrations of t11-18:1 and RA remained similar across the lactation length and were greater for the test diet compared to the control. Changes in milk t10-18:1 concentration during lactation appeared to reflect an effect of the degree of rumen fermentation on PUFA biohydrogenating bacteria. Although PUFA intake is important for milk CLA production, only those diets that give rise to increased ruminal t11-18:1 result in greater milk CLA. Concentrations of rumen t11-18:1 is influenced by the amount of PUFA consumed, degree of shift to t10-18:1 and the extent of PUFA biohydrogenation in the rumen. / Animal Science

No description available.

L'objectif principal de cette thèse est d'étudier l'influence du pourcentage de concentré de la ration combiné à la supplémentation lipidique sur les flux duodénaux des parois et des lipides, sur les performances laitières et la composition en acides gras (AG) du lait de chèvre. Dans une deuxième phase, nous étudions les effets induits par l'infusion duodénale de t10,c12-CLA et son interaction avec les facteurs alimentaires décrits ci-dessus sur la production de la matière grasse (MG) du lait de chèvre et son profil en AG. Dans l'étude bibliographique, nous avons quantifié l'influence de l'apport de lipides issus d'oléo-protéagineux, selon la présentation des lipides (graines vs. huiles) et l'origine botanique sur les performances laitières et de la composition du lait. Pour cela, nous avons constitué une base de données compilant les informations issues des recherches conduites uniquement sur des vaches laitières, en raison du faible nombre d'études sur des chèvres. La réponse de la production laitière à l'incorporation de lipides est variable selon le stade de lactation. L'incorporation d'oléo-protéagineux réduit le taux butyreux (TB) du lait, principalement lorsque l'apport se fait sous forme d'huile; parallèlement on observe une augmentation des proportions des AG trans-C18:1 dans le lait. L'origine botanique de l'oléoprotéagineux a moins d'impact sur les performances laitières que sur le profil en AG longs. La partie expérimentale est constituée de deux expérimentations conduites sur des chèvres laitières en milieu de lactation, en vue de relier la composition des flux duodénaux de lipides et le profil en AG du lait. Le dispositif expérimental factoriel 2 x 2 a combiné la proportion de concentré (bas: 45% vs. haut: 65% de la matière sèche de la ration) et l'apport lipidique (Expérimentation 1: témoin sans lipides vs. graines de colza laminées) ou la nature des lipides (Expérimentation 2: graines de colza laminées vs. graines de soja extrudées). Contrairement aux résultats obtenus sur des vaches laitières, les rations riches en concentré, l'apport de lipides, ou la combinaison de l'apport de lipides au sein des rations riches en concentré ne diminuent pas le TB du lait. En revanche, les pourcentages de trans-C18:1 (surtout de t11) et de c9,t11-CLA dans le duodénum et dans le lait sont augmentés par ces facteurs et leur interaction. La nature de la supplémentation lipidique n'a que peu d'impact sur les performances laitières. Les graines de colza augmentent les teneurs des AG trans dans le lait par rapport au soja; toutefois il est difficile de séparer les effets de l'origine des graines de l'effet de la quantité d'AG ingérés. Les flux duodénaux et fécaux des parois sont diminués par les rations riches en concentré, mais non modifiés par l'apport lipidique, probablement parce que les quantités d'AG ingérés n'ont pas été assez élevées et/ou les graines n'ont pas permis une libération des AG assez rapide pour avoir un effet défavorable sur les microbes cellulolytiques du rumen. Les raisons de la différence de réponse entre chèvres et vaches à l'apport lipidique ne sont pas complètement élucidées, mais la différence de sensibilité de la synthèse mammaire de MG à certains AG trans semble être une de ces raisons. Indépendamment du régime, l'infusion duodénale de t10,c12-CLA, un très puissant inhibiteur des enzymes responsables de la synthèse de novo dans la glande mammaire bovine, ne provoque pas des réductions du TB dans le lait de chèvre, malgré un important transfert vers le lait. Par contre, dans les deux espèces, cet AG diminue la capacité de desaturation dans la glande mammaire. Chez les chèvres, l'utilisation de rations riches en concentré et supplémentées en lipides a augmenté la production de lait, de MG, de t11-C18:1 et de c9,t11-CLA. Par ailleurs, le profil en AG du lait de chèvre peut être modulé par l'origine botanique de l'oléoprotéagineux ajouté à la ration.

Novel integrated ozone contactor design and optimization tools which consist of an instrument that measures ozone decay kinetics, a program that performs predictive simulation, and an experimental method to examine mixing characteristics within the ozone contactor, were developed in this study. A multi-channel stopped-flow reactor (MC-SFR) is an instrument that performs automatic, real-time, and continuous analysis of ozone decay kinetics in natural waters. Ozone Contactor Model (OCM) is the software to simulate the performance of full-scale ozone bubble-diffuser contactors in support of current and future regulations regarding pathogen and bromate control in drinking water. The MC-SFR and OCM developed in this study were further applied to simulate Cryptosporidium parvum oocyst log inactivation and bromate formation in Linnwood Water Plant Ozone Facility (LWPOF) at Milwaukee Water Works, Milwaukee, WI and model predictions were verified with experimental results. Three dimensional laser induced fluorescence(3DLIF) allowed real time characterization of mixing conditions in a physical model ozone contactors by capturing fluorescence image emitted from a laser dye (i.e. Rhodamine 6G) using a high speed CCD camera. 3DLIF system was applied to analyze the hydrodynamics of two representative types of ozone contactor: direct discharge side-stream venturi injector (SVI) and multi-chambered fine bubble diffuser (FBD). Experimental results verified the presence of circulative swirling related for low dispersion for SVI reactor and the existence of non-ideal flow including short circuiting and internal recirculation in FBD reactor. Finally, integrated tools were applied to the design of a new ozone contactor under planning stage to assess current design and to recommend the improvement.