Tumor necrosis factor-α-induced insulin resistance in 3T3-L1 adipocytes is accompanied by a loss of insulin receptor substrate-1 and GLUT4 expression without a loss of insulin receptor-mediated signal transduction

A number of studies have demonstrated that tumor necrosis factor-α (TNF-α) is associated with profound insulin resistance in adipocytes and may also play a critical role in the insulin resistance of obesity and non- insulin-dependent diabetes mellitus. Reports on the mechanism of TNF-α action have been somewhat contradictory. GLUT4 down-regulation has been implicated as a possible cause of insulin resistance as has been the reduced kinase function of the insulin receptor. Here we examine the effects of tumor necrosis factor on the protein components thought to be involved in insulin- stimulated glucose transport in adipocytes, namely the insulin receptor, its major substrate IRS-1, and the insulin responsive glucose transporter GLUT4. Prolonged exposure (72-96 h) of 3T3-L1 adipocytes to TNF-α causes a substantial reduction (\u3e 80%) in IRS-1 and GLUT4 mRNA and protein as well as a lesser reduction (\u3e50%) in the amount of the insulin receptor. Nevertheless, the remaining proteins appear to be biochemically indistinguishable from those in untreated adipocytes. Both the insulin receptor and IRS-1 are tyrosine-phosphorylated to the same extent in response to acute insulin stimulation following cellular TNF-α exposure. Furthermore, the ability of the insulin receptor to phosphorylate exogenous substrate in the test tube is also normal following its isolation from TNF-α-treated cells. These results are confirmed by the reduced but obvious level of insulin-dependent glucose transport and GLUT4 translocation observed in TNF- α-treated adipocytes. We conclude that the insulin resistance of glucose transport in 3T3-L1 adipocytes exposed to TNF-α for 72-96 h results from a reduced amount in requisite proteins involved in insulin action. These results are consistent with earlier studies indicating that TNF-α reduces the transcriptional activity of the GLUT4 gene in murine adipocytes, and reduced mRNA transcription of a number of relevant genes may be the general mechanism by which TNF-α causes insulin resistance in adipocytes

The expression and regulation of STATs during 3T3-L1 adipocyte differentiation

STATs (Signal Transducers and Activators of Transcription) comprise a family of transcription factors that reside in the cytoplasm of resting cells. In response to a variety of stimuli, STATs become tyrosine- phosphorylated and translocate to the nucleus where they mediate transcriptional regulation. We have used the 3T3-L1 murine cell line to examine the expression of STAT proteins as a function of their differentiation into adipocytes. The expression of STATs 1, 3, and 5, but not of STAT 6, is markedly elevated in adipocytes as compared with their fibroblast precursors. Exposure of 3T3-L1 preadipocytes to tumor necrosis factor α (TNFα) blocks their differentiation into adipocytes. Therefore, we examined STAT expression as a function of differentiation in the presence of this cytokine. The expression of STATs 1 and 5 is markedly attenuated in the presence of TNFα, whereas STAT 3 expression is unaffected by this treatment. Only STAT 1 is down-regulated by TNFα in fully differentiated cells. Thus, although the expression of STATs 1, 3, and 5 is markedly enhanced upon differentiation, only STAT 5 expression is tightly correlated with the adipocyte phenotype. These data suggest that STAT 5, and possibly STAT 1, could be potential inducers of tissue-specific genes, which contribute to the development and maintenance of the adipocyte phenotype

Expression and compartmentalization of caveolin in adipose cells: Coordinate regulation with and structural segregation from GLUT4

Native rat adipocytes and the mouse adipocyte cell line, 3T3-L1, possess transport vesicles of apparently uniform composition and size which translocate the tissue-specific glucose transporter isoform, GLUT4, from an intracellular pool to the cell surface in an insulin-sensitive fashion. Caveolin, the presumed structural protein of caveolae, has also been proposed to function in vesicular transport. Thus, we studied the expression and subcellular distribution of caveolin in adipocytes. We found that rat fat cells express the highest level of caveolin protein of any tissue studied, and caveolin is also expressed at high levels in cardiac muscle, another tissue possessing insulin responsive GLUT4 translocation. Both proteins are absent from 3T3-L1 fibroblasts and undergo a dramatic coordinate increase in expression upon differentiation of these cells into adipocytes. However, unlike GLUT4 in rat adipocytes not exposed to insulin, the majority of caveolin is present in the plasma membrane. In native rat adipocytes, intracellular GLUT4 and caveolin reside in vesicles practically indistinguishable by their size and buoyant density in sucrose gradients, and both proteins show insulin-dependent translocation to the cell surface. However, by immunoadsorption of GLUT4-containing vesicles with anti-GLUT4 antibody, we show that these vesicles have no detectable caveolin, and therefore, this protein is present in a distinct vesicle population. Thus, caveolin has no direct structural relation to the organization of the intracellular glucose transporting machinery in fat cells

Session 3: To What Extent Should Libraries Be Permitted to Engage in Mass Digitization of Published Works, and for What Purposes?

Transcript of a symposium held at Columbia University about the legality of libraries digitizing published works and the purposes and potential consequences of libraries doing this. Focuses on section 108 of the copyright law as it pertains to mass digitization

The supersymmetric sigma model and the geometry of the Weyl-Kac character formula

Field theoretic and geometric ideas are used to construct a chiral supersymmetric field theory whose ground state is a specified irreducible representation of a centrally extended loop group. The character index of the associated supercharge (an appropriate Dirac operator on $LG/T$) is the Weyl-K\v{a}c character formula which we compute explicitly by the steepest descent approximation.Comment: 40 page

Exact N=2 Landau-Ginzburg Flows

We find exactly solvable N=2-supersymmetric flows whose infrared fixed points are the N=2 minimal models. The exact S-matrices and the Casimir energy (a c-function) are determined along the entire renormalization group trajectory. The c-function runs from c=3 (asymptotically) in the UV to the N=2 minimal model values of the central charge in the IR, leading us to interpret these theories as the Landau-Ginzburg models with superpotential $X^{k+2}$. Consideration of the elliptic genus gives further support for this interpretation. We also find an integrable model in this hierarchy which has spontaneously-broken supersymmetry and superpotential $X$, and a series of integrable models with (0,2) supersymmetry. The flows exhibit interesting behavior in the UV, including a relation to the N=2 super sine-Gordon model. We speculate about the relation between the kinetic term and the cigar target-space metric.Comment: 24 pages, BUHEP-93-17, RU-93-2

Caveolins/caveolae protect adipocytes from fatty acid-mediated lipotoxicity

Mice and humans lacking functional caveolae are dyslipidemic and have reduced fat stores and smaller fat cells. To test the role of caveolins/caveolae in maintaining lipid stores and adipocyte integrity, we compared lipolysis in caveolin-1 (Cav1)-null fat cells to that in cells reconstituted for caveolae by caveolin-1 re-expression. We find that the Cav1-null cells have a modestly enhanced rate of lipolysis and reduced cellular integrity compared with reconstituted cells as determined by the release of lipid metabolites and lactic dehydrogenase, respectively, into the media. There are no apparent differences in the levels of lipolytic enzymes or hormonally stimulated phosphorylation events in the two cell lines. In addition, acute fasting, which dramatically raises circulating fatty acid levels in vivo, causes a significant upregulation of caveolar protein constituents. These results are consistent with the hypothesis that caveolae protect fat cells from the lipotoxic effects of elevated levels fatty acids, which are weak detergents at physiological pH, by virtue of the property of caveolae to form detergentresistant membrane domains

Cavin1; a regulator of lung function and macrophage phenotype.

Caveolae are cell membrane invaginations that are highly abundant in adipose tissue, endothelial cells and the lung. The formation of caveolae is dependent on the expression of various structural proteins that serve as scaffolding for these membrane invaginations. Cavin1 is a newly identified structural protein whose deficiency in mice leads to loss of caveolae formation and to development of a lipodystrophic phenotype. In this study, we sought to investigate the functional role of Cavin1 in the lung. Cavin1 deficient mice possessed dramatically altered distal lung morphology and exhibited significant physiological alterations, notably, increased lung elastance. The changes in distal lung architecture were associated with hypercellularity and the accumulation of lung macrophages. The increases in lung macrophages occurred without changes to circulating numbers of mononuclear cells and without evidence for increased proliferation. However, the increases in lung macrophages were associated with higher levels of macrophage chemotactic factors CXCL2 and CCL2 in BAL fluid from Cavin1-/- mice suggesting a possible mechanism by which these cells accumulate. In addition, lung macrophages from Cavin1-/- mice were larger and displayed measurable differences in gene expression when compared to macrophages from wild-type mice. Interestingly, macrophages were also increased in adipose tissue but not in liver, kidney or skeletal muscle from Cavin1-/- mice, and similar tissue specificity for macrophage accumulation was observed in lungs and adipose tissue from Caveolin1-/- mice. In conclusion, this study demonstrates an important role for Cavin1 in lung homeostasis and suggests that caveolae structural proteins are necessary for regulating macrophage number and phenotype in the lung

Structure and Phase transitions of Yukawa balls

In this review, an overview of structural properties and phase transitions in finite spherical dusty (complex) plasma crystals -- so-called Yukawa balls -- is given. These novel kinds of Wigner crystals can be directly analyzed experimentally with video cameras. The experiments clearly reveal a shell structure and allow to determine the shell populations, to observe metastable states and transitions between configurations as well as phase transitions. The experimental observations of the static properties are well explained by a rather simple theoretical model which treats the dust particles as being confined by a parabolic potential and interacting via an isotropic Yukawa pair potential. The excitation properties of the Yukawa balls such as normal modes and the dynamic behavior, including the time-dependent formation of the crystal requires, in addition, to include the effect of friction between the dust particles and the neutral gas. Aside from first-principle molecular dynamics and Monte Carlo simulations several analytical approaches are reviewed which include shell models and a continuum theory. A summary of recent results and theory-experiment comparisons is given and questions for future research activities are outlined.Comment: Invited review, submitted to Contrib. Plasmas Physic

Caveolae, Fenestrae and Transendothelial Channels Retain PV1 on the Surface of Endothelial Cells

PV1 protein is an essential component of stomatal and fenestral diaphragms, which are formed at the plasma membrane of endothelial cells (ECs), on structures such as caveolae, fenestrae and transendothelial channels. Knockout of PV1 in mice results in in utero and perinatal mortality. To be able to interpret the complex PV1 knockout phenotype, it is critical to determine whether the formation of diaphragms is the only cellular role of PV1. We addressed this question by measuring the effect of complete and partial removal of structures capable of forming diaphragms on PV1 protein level. Removal of caveolae in mice by knocking out caveolin-1 or cavin-1 resulted in a dramatic reduction of PV1 protein level in lungs but not kidneys. The magnitude of PV1 reduction correlated with the abundance of structures capable of forming diaphragms in the microvasculature of these organs. The absence of caveolae in the lung ECs did not affect the transcription or translation of PV1, but it caused a sharp increase in PV1 protein internalization rate via a clathrin- and dynamin-independent pathway followed by degradation in lysosomes. Thus, PV1 is retained on the cell surface of ECs by structures capable of forming diaphragms, but undergoes rapid internalization and degradation in the absence of these structures, suggesting that formation of diaphragms is the only role of PV1