Pax7 is a paired box transcription factor expressed by all satellite cells which are critically required for muscle regeneration and growth. The absolute requirements of Pax7 in the maintenance of the satellite cell pool are widely acknowledged. However the mechanisms by which Pax7 executes muscle regeneration or contributes to satellite cell homeostasis remain elusive. We performed cell and molecular analysis of Pax7 null satellite cells to investigate muscle stem cell function. Through genome wide studies, we found that genes involved in cell cell interactions, regulation of migration, control of lipid metabolism and inhibition of myogenic differentiation were significantly perturbed in Pax7 null satellite cells. Analysis of satellite cells in vitro showed that Pax7 null satellite cells undergo precocious myogenic differentiation and have perturbed expression of genes involved in the Notch signaling pathway. We showed that Notch 1 is a novel Pax7 target gene and by using a genetic approach we demonstrated that ectopic expression of the constitutively active intracellular domain of Notch1 (NICD1) in Pax7 null satellite cells is sufficient to maintain the satellite cell pool as well as to restore their proliferation. Instead of differentiating into myogenic cells and in the absence of a myogenic cue, NICD1 Pax7 null satellite cells become a source of ectopic brown fat within muscles and give rise to brown adipocytes both in vivo and in vitro. In conclusion we showed that Notch 1 partially rescues Pax7 deficient satellite cells loss and proliferation. Additionally we provide the first evidence that Notch signalling contributes to satellite cell fate by inhibiting terminal myogenic differentiation and inducing brown adipogenesis.

The preadipocyte is crucial for healthy adipose tissue (AT) remodeling, and insulin resistance in these cells may contribute to AT dysfunction. Chronic exposure to insulin and high glucose induces insulin resistance in the 3T3-L1 mouse adipocyte cell line in vitro, however, whether this occurs in human preadipocytes is not known. To investigate this, human preadipocytes were isolated from subcutaneous AT obtained from 6 female patients undergoing elective surgery (Research Ethics Board-approved). Human preadipocytes were incubated in 5 mM glucose or 25 mM glucose in the presence or absence of 0.6 nM insulin for 48 hours, followed by acute 100 nM insulin stimulation. 25 mM glucose + 0.6 nM insulin inhibited insulin-stimulated tyrosine phosphorylation of IR-β (77%) and IRS-1 (81%) compared to NG (p<0.01), however, insulin-stimulated Ser473 Akt phosphorylation was not affected. 25 mM glucose and/or 0.6 nM insulin did not significantly change levels of pro-inflammatory adipokines. 25 mM glucose and/or 0.6 nM, prior to and/or during 14 days of adipogenic induction, did not affect levels of adipogenic markers or intracellular triglyceride accumulation.

Iron is an essential micronutrient that plays a role in essential processes in all living organisms. Because iron deficiency anemia is the number one human nutritional deficiency worldwide, research has been focused on studying biofortification, a method of plant breeding focused on increasing the nutrient content of the grain. In order to effectively implement this strategy, research to understand the molecular mechanisms surrounding iron uptake and maintenance within plants is necessary. A major goal of this work lies in exploring iron signaling in Arabidopsis thaliana and further characterization of the yellowstripe1-like1yellowstripe1-like3 (ysl1ysl3) double mutant plant. As shown here, iron signaling in arabidopsis appears to be regulated by a long distance signal derived in the shoots. The ysl1ysl3 double mutant is a plant shown to have severe mis-regulation of iron regulated genes. Here, I show ysl1ysl3 mutant plants are unable to respond to iron deficiency properly and lose signaling ability. It has been proposed that these defects are due to iron accumulation in the shoots but that appears untrue suggesting alternative functions for YSL1 and YSL3 in iron signaling. Another goal of the work included here seeks to elucidate alternative roles for ZmYS1 in maize outside of primary acquisition of iron from the soil. Here, ZmYS1 expression is shown via promoter::GUS analysis expressing throughout the shoot in many cell-types consistent with a role in the movement of iron between leaf tissues. Interestingly, expression in germinating seeds suggests ZmYS1 may also play a role in remobilization of stored iron in developing embryos.

No description available.

<p>High density lipoprotein (HDL) is an independent risk factor for thedevelopment of coronary heart disease. HDL mediated reverse cholesterol transport is a key element responsible for the cardioprotective effects of HDL. In addition HDL exerts other atheroprotective effects in vascular cells. The HDL receptor, scavenger receptor class I type B (SR-BI) derives the process of reverse cholesterol transport, mediates HDL signaling in the vasculature and protects against atherosclerosis. However, the exact atheroprotective mechanisms of HDL and SR-BI are not clearly understood.This thesis starts by characterizing a model of occlusive coronary arteryatherosclerosis, the SR-BI/apolipoprotein E double knockout mice and tests the effectsof phenolic rich pomegranate extract on disease progression. Coronary artery disease in these mice starts at three weeks of age and progresses rapidly leading to sudden death within three to five weeks. The administration of pomegranate extract reduced the extent of coronary artery atherosclerosis possibly via mechanisms that involved alterations in lipid metabolism and reduced inflammation and oxidative stress.The next two chapters aimed to gain better understanding of the atheroprotectiveactions of HDL and SR-BI. Increased macrophage apoptosis is a key event in the development of atherosclerotic plaques. HDL signaling via SR-BI reduced macrophage apoptosis while the lack of macrophage SR-BI was associated with increased macrophage apoptosis and necrotic core areas, features of plaque instability. Next HDL and SR-BI effects on macrophage migration, a key event in atherosclerotic plaque regression, are described. HDL stimulated the migration of macrophages in a manner that was dependent on SR-BI, its adaptor protein, PDZK1, and the G-protein coupled receptor, sphingosine-1-phosphate receptor 1. SR-BI mediated macrophage migration may suggest a potential role of SR-BI in atherosclerotic plaque regression.To expand our view of HDL effects on macrophages we have used proteomics as an approach. HDL treatment of macrophages altered the expression of multiple proteins.Validation experiment confirmed changes in interesting and particularly relevant protein targets in HDL mediated protection against macrophage apoptosis and inflammation and in HDL induced macrophage migration. Follow up experiments will determine their involvement in HDL and SR-BI mediated signaling. Overall this work represents a milestone in understanding the atheroprotective effects of HDL and SR-BI in macrophages.</p> / Doctor of Philosophy (PhD)

The innate immune system depends for its effectiveness on the function of specialized pattern recognition receptors which enable it to target pathogens for destruction on the basis of conserved molecular patterns such as flagellin or lipopolysaccharide (LPS). Specifically, LPS is recognized by the Toll-like receptor 4 (TLR4), activating a signaling pathway which triggers the production of both pro- and anti-inflammatory mediators. Very low doses of LPS, however, preferentially induce pro-inflammatory cytokines, which can lead to persistent low-grade inflammation, a contributing factor in a host of chronic diseases. The mild pro-inflammatory skewing induced by super-low-dose LPS also potentiates the inflammatory response to later challenge with a higher dose of LPS in a phenomenon known as the "Shwartzman reaction" or "endotoxin priming". We investigated the mechanisms involved in pro-inflammatory skewing by super-low-dose LPS in THP-1 cells and found it to be governed by a regulatory circuit of competitive inhibition between glycogen synthase kinase 3 (GSK3) and Akt, which promote the activity of the transcription factors FoxO1 and CREB, respectively. Super-low-dose LPS mildly activated FoxO1 and pro-inflammatory gene transcription without inducing anti-inflammatory genes or activating CREB, and this pro-inflammatory skewing could be abolished by inhibition of GSK3 or direct activation of CREB. We then examined the dynamics of the LPS response at various different dosages in murine bone-marrow-derived macrophages (BMDM). The pro-inflammatory cytokine IL-12 was most strongly induced by intermediate LPS dosages, with very low or high doses inducing less robust IL-12 production. Knockout of the inhibitory TLR4 pathway molecules Lyn or IRAK-M resulted in sustained induction of IL-12 by high doses of LPS. By activating CREB, we were able to reduce inflammation in WT BMDM, and saw that this corresponded with increased phosphorylation of CREB. Overall, we are confident that this subnetwork is an important switch regulating the resolution of inflammation in response to TLR4 stimulation. Furthermore, we propose that endotoxin priming is an example of the generalized capacity of all signaling networks to recall prior states, and that an appreciation for the history and context of exposure to stimuli is critical for the understanding of signaling behavior. / Ph. D.

No description available.

Most existing studies of receptor signaling are qualitative, which can lead scientists to misinterpret or overlook key information about the extent and timing of key events. To overcome these shortcomings, we have applied quantitative approaches to characterize receptor activation and signaling events. Most signaling studies focus on events occurring at a particular level in the system (e.g., on the membrane, at the level of phosphorylation of intracellular signaling molecules, or at the level of transcription). Instead, we are interested in taking a longitudinal view of signaling by achieving a quantitative understanding of a single signaling pathway from initial stimulation of the receptor by its growth factor (GF) ligand, through to gene expression, and functional cellular responses. As a model system for our studies, we used the growth factor receptor tyrosine kinase, REarranged during Transfection (RET), which requires a ligand and a glycosylphosphatidylinositol-anchored co-receptor for activation. RET mediates the response of cells to members of the glial cell-line derived neurotrophic factor (GDNF) family of neurotrophins, which are important in the development and maintenance of a subset of neuronal cells as well as in other cell types and tissues. We have characterized the molecular mechanisms of RET activation and signaling by pursuing the following four aims: 1) We developed a sensitive and robust luciferase reporter gene assay for RET signaling. 2) We characterized the dynamic relationship between receptor activation and downstream signaling events, including gene transcription and translation of three target genes. 3) We used the reporter gene assay, and other detection approaches, to test and quantify crosstalk between RET and other GF receptors. 4) We developed a FRET reporter system to enable monitoring of the assembly of the activated RET receptor complex on cells, as a means to distinguish between ligand-induced oligomerization and pre-associated oligomer mechanisms. Through these four aims, we have established new methods to quantitatively elucidate mechanisms of GF receptor activation, new insights into how signals are propagated from the receptor to the nucleus and into a functional response, and have established crosstalk between RET and other GF receptor pathways.

京都大学 / 0048 / 新制・課程博士 / 博士(医科学) / 甲第21025号 / 医科博第86号 / 新制||医科||6(附属図書館) / 京都大学大学院医学研究科医科学専攻 / (主査)教授 斎藤 通紀, 教授 渡邊 直樹, 教授 岩井 一宏 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

Yes / Ca2+ release from the Golgi apparatus regulates key functions of the organelle, including vesicle trafficking. However, the signaling pathways that control this form of Ca2+ release are poorly understood and evidence of discrete Golgi Ca2+ release events is lacking. Here, we identified the Golgi apparatus as the source of prolonged Ca2+ release events that originate from the nuclear ‘poles’ of primary cardiac cells. Once initiated, Golgi Ca2+ release was unaffected by global depletion of sarcoplasmic reticulum Ca2+, and disruption of the Golgi apparatus abolished Golgi Ca2+ release without affecting sarcoplasmic reticulum function, suggesting functional and anatomical independence of Golgi and sarcoplasmic reticulum Ca2+ stores. Maximal activation of β1-adrenoceptors had only a small stimulating effect on Golgi Ca2+ release. However, inhibition of phosphodiesterase (PDE) 3 or 4, or downregulation of PDE 3 and 4 in heart failure markedly potentiated β1-adrenergic stimulation of Golgi Ca2+ release, consistent with compartmentalization of cAMP signaling within the Golgi apparatus microenvironment. β1-adrenergic stimulation of Golgi Ca2+ release involved activation of both Epac and PKA signaling pathways and CaMKII. Interventions that stimulated Golgi Ca2+ release induced trafficking of vascular growth factor receptor-1 (VEGFR-1) from the Golgi apparatus to the surface membrane. These data establish the Golgi apparatus as a juxtanuclear focal point for Ca2+ and β1-adrenergic signaling, which functions independently from the sarcoplasmic reticulum and the global Ca2+ transients that underlie the primary contractile function of the cell.