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Biomedical subjects

George D Yancopoulos

Publications and source records attributed to George D Yancopoulos.

At least 19 recordsLinked to original sources
PubMed2006

Angiopoietin-2 functions as an autocrine protective factor in stressed endothelial cells.

Angiopoietin (Ang)-2, a context-dependent agonist/antagonist for the vascular-specific Tie2 receptor, is highly expressed by endothelial cells at sites of normal and pathologic angiogenesis. One prevailing model suggests that in these settings, Ang-2 acts as an autocrine Tie2 blocker, inhibiting the stabilizing influence of the Tie2 activator Ang-1, thereby promoting vascular remodeling. However, the effects of endogenous Ang-2 on cells that are actively producing it have not been studied in detail. Here, we demonstrate that Ang-2 expression is rapidly induced in endothelial cells by the transcription factor FOXO1 after inhibition of the phosphatidylinositol 3-kinase/Akt pathway. We employ RNAi and blocking antibodies to show that in this setting, Ang-2 unexpectedly functions as a Tie2 agonist, bolstering Akt activity so as to provide negative feedback on FOXO1-regulated transcription and apoptosis. In addition, we show that Ang-2, like Ang-1, activates Tie2/Akt signaling in vivo, thereby inhibiting the expression of FOXO1 target genes. Consistent with a role for Ang-2 as a Tie2 activator, we demonstrate that Ang-2 inhibits vascular leak. Our data suggests a model in which Ang-2 expression is induced in stressed endothelial cells, where it acts as an autocrine Tie2 agonist and protective factor.

Androstadienes↗
PubMed2006

SIRT4 inhibits glutamate dehydrogenase and opposes the effects of calorie restriction in pancreatic beta cells.

Sir2 is an NAD-dependent deacetylase that connects metabolism with longevity in yeast, flies, and worms. Mammals have seven Sir2 homologs (SIRT1-7). We show that SIRT4 is a mitochondrial enzyme that uses NAD to ADP-ribosylate and downregulate glutamate dehydrogenase (GDH) activity. GDH is known to promote the metabolism of glutamate and glutamine, generating ATP, which promotes insulin secretion. Loss of SIRT4 in insulinoma cells activates GDH, thereby upregulating amino acid-stimulated insulin secretion. A similar effect is observed in pancreatic beta cells from mice deficient in SIRT4 or on the dietary regimen of calorie restriction (CR). Furthermore, GDH from SIRT4-deficient or CR mice is insensitive to phosphodiesterase, an enzyme that cleaves ADP-ribose, suggesting the absence of ADP-ribosylation. These results indicate that SIRT4 functions in beta cell mitochondria to repress the activity of GDH by ADP-ribosylation, thereby downregulating insulin secretion in response to amino acids, effects that are alleviated during CR.

Adenosine Diphosphate Ribose↗
PubMed2006

Cutting edge: IL-23 cross-regulates IL-12 production in T cell-dependent experimental colitis.

Although IL-12 and IL-23 share the common p40 subunit, IL-23, rather than IL-12, seems to drive the pathogenesis of experimental autoimmune encephalomyelitis and arthritis, because IL-23/p19 knockout mice are protected from disease. In contrast, we describe in this study that newly created LacZ knockin mice deficient for IL-23 p19 were highly susceptible for the development of experimental T cell-mediated TNBS colitis and showed even more severe colitis than wild-type mice by endoscopic and histologic criteria. Subsequent studies revealed that dendritic cells from p19-deficient mice produce elevated levels of IL-12, and that IL-23 down-regulates IL-12 expression upon TLR ligation. Finally, in vivo blockade of IL-12 p40 in IL-23-deficient mice rescued mice from lethal colitis. Taken together, our data identify cross-regulation of IL-12 expression by IL-23 as novel key regulatory pathway during initiation of T cell dependent colitis.

Animals↗
PubMed2006

VEGF modulates erythropoiesis through regulation of adult hepatic erythropoietin synthesis.

Vascular endothelial growth factor (VEGF) exerts crucial functions during pathological angiogenesis and normal physiology. We observed increased hematocrit (60-75%) after high-grade inhibition of VEGF by diverse methods, including adenoviral expression of soluble VEGF receptor (VEGFR) ectodomains, recombinant VEGF Trap protein and the VEGFR2-selective antibody DC101. Increased production of red blood cells (erythrocytosis) occurred in both mouse and primate models, and was associated with near-complete neutralization of VEGF corneal micropocket angiogenesis. High-grade inhibition of VEGF induced hepatic synthesis of erythropoietin (Epo, encoded by Epo) >40-fold through a HIF-1alpha-independent mechanism, in parallel with suppression of renal Epo mRNA. Studies using hepatocyte-specific deletion of the Vegfa gene and hepatocyte-endothelial cell cocultures indicated that blockade of VEGF induced hepatic Epo by interfering with homeostatic VEGFR2-dependent paracrine signaling involving interactions between hepatocytes and endothelial cells. These data indicate that VEGF is a previously unsuspected negative regulator of hepatic Epo synthesis and erythropoiesis and suggest that levels of Epo and erythrocytosis could represent noninvasive surrogate markers for stringent blockade of VEGF in vivo.

Animals↗
PubMed2006

Pharmacologic blockade of angiopoietin-2 is efficacious against model hemangiomas in mice.

Hemangioma of infancy is the most common neoplasm of childhood. While hemangiomas are classic examples of angiogenesis, the angiogenic factors responsible for hemangiomas are not fully understood. Previously, we demonstrated that malignant endothelial tumors arise in the setting of autocrine loops involving vascular endothelial growth factor (VEGF) and its major mitogenic receptor vascular endothelial growth factor receptor 2. Hemangiomas of infancy differ from malignant endothelial tumors in that they usually regress, or can be induced to regress by pharmacologic means, suggesting that angiogenesis in hemangiomas differs fundamentally from that of malignant endothelial tumors. Here, we demonstrate constitutive activation of the endothelial tie-2 receptor in human hemangioma of infancy and, using a murine model of hemangioma, bEnd.3 cells; we show that bEnd.3 hemangiomas produce both angiopoietin-2 (ang-2) and its receptor, tie-2, in vivo. We also demonstrate that inhibition of tie-2 signaling with a soluble tie-2 receptor decreases bEnd.3 hemangioma growth in vivo. The efficacy of tie-2 blockade suggests that either tie-2 activation or ang-2 may be required for in vivo growth. To address this issue, we used tie-2-deficient bEnd.3 hemangioma cells, which, surprisingly, were fully proficient in in vivo growth. Previous studies from our laboratory and others have implicated reactive oxygen-generating nox enzymes in the angiogenic switch, so we examined the effect of nox inhibitors on ang-2 production in vitro and on bEnd.3 tumor growth in vivo. We then inhibited ang-2 production pharmacologically using novel inhibitors of nox enzymes and found that this treatment nearly abolished bEnd.3 hemangioma growth in vivo. Signal-transduction blockade targeting ang-2 production may be useful in the treatment of human hemangiomas in vivo.

Angiopoietin-2↗
PubMed2006

Genomic instability and aging-like phenotype in the absence of mammalian SIRT6.

The Sir2 histone deacetylase functions as a chromatin silencer to regulate recombination, genomic stability, and aging in budding yeast. Seven mammalian Sir2 homologs have been identified (SIRT1-SIRT7), and it has been speculated that some may have similar functions to Sir2. Here, we demonstrate that SIRT6 is a nuclear, chromatin-associated protein that promotes resistance to DNA damage and suppresses genomic instability in mouse cells, in association with a role in base excision repair (BER). SIRT6-deficient mice are small and at 2-3 weeks of age develop abnormalities that include profound lymphopenia, loss of subcutaneous fat, lordokyphosis, and severe metabolic defects, eventually dying at about 4 weeks. We conclude that one function of SIRT6 is to promote normal DNA repair, and that SIRT6 loss leads to abnormalities in mice that overlap with aging-associated degenerative processes.

Aging↗
PubMed2006

Peripheral myelin protein 22 is in complex with alpha6beta4 integrin, and its absence alters the Schwann cell basal lamina.

Peripheral myelin protein 22 (PMP22) is a tetraspan membrane glycoprotein, the misexpression of which is associated with hereditary demyelinating neuropathies. Myelinating Schwann cells (SCs) produce the highest levels of PMP22, yet the function of the protein in peripheral nerve biology is unresolved. To investigate the potential roles of PMP22, we engineered a novel knock-out (-/-) mouse line by replacing the first two coding exons of pmp22 with the lacZ reporter. PMP22-deficient mice show strong beta-galactosidase reactivity in peripheral nerves, cartilage, intestines, and lungs, whereas phenotypically they display the characteristics of tomaculous neuropathy. In the absence of PMP22, myelination of peripheral nerves is delayed, and numerous axon-SC profiles show loose basal lamina, suggesting altered interactions of the glial cells with the extracellular matrix. The levels of beta4 integrin, a molecule involved in the linkage between SCs and the basal lamina, are severely reduced in nerves of PMP22-deficient mice. During early stages of myelination, PMP22 and beta4 integrin are coexpressed at the cell surface and can be coimmunoprecipitated together with laminin and alpha6 integrin. In agreement, in clone A colonic carcinoma cells, epitope-tagged PMP22 forms a complex with beta4 integrin. Together, these data indicate that PMP22 is a binding partner in the integrin/laminin complex and is involved in mediating the interaction of SCs with the extracellular environment.

Adenocarcinoma↗
PubMed2006

Resistin-like molecule beta regulates innate colonic function: barrier integrity and inflammation susceptibility.

BACKGROUND: Resistin-like molecule (RELM) beta is a cysteine-rich cytokine expressed in the gastrointestinal tract and implicated in insulin resistance and gastrointestinal nematode immunity; however, its function primarily remains an enigma. OBJECTIVE: We sought to elucidate the function of RELM-beta in the gastrointestinal tract. METHODS: We generated RELM-beta gene-targeted mice and examined colonic epithelial barrier function, gene expression profiles, and susceptibility to acute colonic inflammation. RESULTS: We show that RELM-beta is constitutively expressed in the colon by goblet cells and enterocytes and has a role in homeostasis, as assessed by alterations in colon mRNA transcripts and epithelial barrier function in the absence of RELM-beta. Using acute colonic inflammatory models, we demonstrate that RELM-beta has a central role in the regulation of susceptibility to colonic inflammation. Mechanistic studies identify that RELM-beta regulates expression of type III regenerating gene (REG) (REG3beta and gamma), molecules known to influence nuclear factor kappaB signaling. CONCLUSIONS: These data define a critical role for RELM-beta in the maintenance of colonic barrier function and gastrointestinal innate immunity. CLINICAL IMPLICATIONS: These findings identify RELM-beta as an important molecule in homeostatic gastrointestinal function and colonic inflammation, and as such, these results have implications for a variety of human inflammatory gastrointestinal conditions, including allergic gastroenteropathies.

Animals↗
PubMed2005

Leucine aminopeptidase is not essential for trimming peptides in the cytosol or generating epitopes for MHC class I antigen presentation.

To detect viral infections and tumors, CD8+ T lymphocytes monitor cells for the presence of antigenic peptides bound to MHC class I molecules. The majority of MHC class I-presented peptides are generated from the cleavage of cellular and viral proteins by the ubiquitin-proteasome pathway. Many of the oligopeptides produced by this process are too long to stably bind to MHC class I molecules and require further trimming for presentation. Leucine aminopeptidase (LAP) is an IFN-inducible cytosolic aminopeptidase that can trim precursor peptides to mature epitopes and has been thought to play an important role in Ag presentation. To examine the role of LAP in generating MHC class I peptides in vivo, we generated LAP-deficient mice and LAP-deficient cell lines. These mutant mice and cells are viable and grow normally. The trimming of peptides in LAP-deficient cells is not reduced under basal conditions or after stimulation with IFN. Similarly, there is no reduction in presentation of peptides from precursor or full-length Ag constructs or in the overall supply of peptides from cellular proteins to MHC class I molecules even after stimulation with IFN. After viral infection, LAP-deficient mice generate normal CTL responses to seven epitopes from three different viruses. These data demonstrate that LAP is not an essential enzyme for generating most MHC class I-presented peptides and reveal redundancy in the function of cellular aminopeptidases.

Amino Acid Sequence↗
PubMed2005

Vascular endothelial growth factor trap combined with paclitaxel strikingly inhibits tumor and ascites, prolonging survival in a human ovarian cancer model.

Ovarian cancer is characterized by i.p. carcinomatosis and massive ascites. Vascular endothelial growth factor (VEGF) plays a pivotal role in tumor angiogenesis and vascular leakage leading to ascites. We assessed the efficacy of a soluble decoy receptor (VEGF Trap) combined with paclitaxel, in a mouse model of human ovarian cancer. Tumor burden after VEGF Trap plus paclitaxel was reduced by approximately 98% versus controls. No measurable ascites developed in the treated group. Morphologic studies showed that most residual tumor had degenerative changes. Diaphragmatic and hepatic tumors were not found in the VEGF Trap plus paclitaxel group in contrast to controls, indicating lack of metastasis. In vivo FITC-lectin tumor vessel imaging showed sparse, short, straight vessels in treated mice as compared to controls, in which vessels were numerous, irregular, tortuous, and leaky. In a survival study, all controls underwent euthanasia between 29 and 58 days after tumor cell inoculation (cachexia, extensive ascites, and tumor masses). In the VEGF Trap plus paclitaxel group, mice were ambulating and eating normally with no signs of disease for at least 81 days after tumor cell inoculation, and survival occurred for 129.9 +/- 38.88 days with no further treatment. We conclude that combination therapy with VEGF Trap plus paclitaxel may provide a novel, long-lasting therapeutic strategy for treatment of patients with ovarian cancer associated with ascites.

Analysis of Variance↗
PubMed2005

Angiopoietin 1 causes vessel enlargement, without angiogenic sprouting, during a critical developmental period.

Early in development, endothelial cells proliferate, coalesce, and sprout to form a primitive plexus of undifferentiated microvessels. Subsequently, this plexus remodels into a hierarchical network of different-sized vessels. Although the processes of proliferation and sprouting are well studied and are dependent on the angiogenic growth factor VEGF, the factors involved in subsequent vessel remodeling are poorly understood. Here, we show that angiopoietin 1 can induce circumferential vessel enlargement, specifically on the venous side of the circulation. This action is due to the ability of angiopoietin 1 to promote endothelial cell proliferation in the absence of angiogenic sprouting; vessel growth without sprouting has not been ascribed to other vascular growth factors, nor has specificity for a particular segment of the vasculature. Moreover, angiopoietin 1 potently mediates widespread vessel enlargement only during a brief postnatal period, in particular, prior to the fourth postnatal week, corresponding to stages in which VEGF inhibition causes widespread vessel regression. These findings show that angiopoietin 1 has a potentially unique role among the vascular growth factors by acting to enlarge blood vessels without inducing sprouting, and also define a critical window of vascular plasticity in neonatal development. Finding the key molecular factors that regulate this plasticity may prove crucial to the further development of pro- and anti-angiogenic therapies.

Age Factors↗
PubMed2005

Lhx6 delineates a pathway mediating innate reproductive behaviors from the amygdala to the hypothalamus.

In mammals, innate reproductive and defensive behaviors are mediated by anatomically segregated connections between the amygdala and hypothalamus. This anatomic segregation poses the problem of how the brain integrates activity in these circuits when faced with conflicting stimuli eliciting such mutually exclusive behaviors. Using genetically encoded and conventional axonal tracers, we have found that the transcription factor Lhx6 delineates the reproductive branch of this pathway. Other Lhx proteins mark neurons in amygdalar nuclei implicated in defense. We have traced parallel projections from the posterior medial amygdala, activated by reproductive or defensive olfactory stimuli, respectively, to a point of convergence in the ventromedial hypothalamus. The opposite neurotransmitter phenotypes of these convergent projections suggest a "gate control" mechanism for the inhibition of reproductive behaviors by threatening stimuli. Our data therefore identify a potential neural substrate for integrating the influences of conflicting behavioral cues and a transcription factor family that may contribute to the development of this substrate.

Aggression↗
PubMed2005

Functional characterization of mouse RDH11 as a retinol dehydrogenase involved in dark adaptation in vivo.

We previously cloned mouse RDH11 (mRDH11) as a gene regulated by the transcription factor sterol regulatory element-binding proteins and showed that it is a retinol dehydrogenase expressed in non-ocular tissues such as the liver and testis and in the retina (Kasus-Jacobi, A., Ou, J., Bashmakov, Y. K., Shelton, J. M., Richardson, J. A., Goldstein, J. L., and Brown, M. S. (2003) J. Biol. Chem. 278, 32380-32389). It was proposed to function in the recycling of the visual chromophore 11-cis-retinal after photoisomerization by a bleaching light, a pathway referred to as the visual cycle. In this work, we describe our studies on the ocular function of mRDH11. We created a knockout mouse by replacing the mrdh11 coding sequence with the lacZ reporter gene for expression profiling. 5-Bromo-4-chloro-3-indolyl-beta-D-galactopyranoside (X-Gal) staining demonstrated active transcription of this gene in photoreceptor cells. We show by immunoblot analysis that mRDH11 is associated with retinal membranes purified from a non-outer segment fraction of the retina. No obvious retinal defect was found during development and aging of RDH11-deficient mice. The functional consequences of mRDH11 disruption were investigated by electroretinography. Dark adaptation was delayed by a factor of 2.5-3 compared with wild-type mice. However, the kinetics of 11-cis-retinal recycling during dark adaptation was not affected, suggesting that mRDH11 is not involved in the visual cycle. We propose that mRDH11 disruption affects retinoid metabolism in photoreceptor inner segments and delays the kinetics of dark adaptation through modulation of calcium homeostasis.

Aging↗
PubMed2005

Resistance to diet-induced obesity in mice globally overexpressing OGH/GPB5.

We identified a glycoprotein hormone beta-subunit (OGH, also called GPB5) that, as a heterodimer with the alpha-subunit GPA2, serves as a second ligand for the thyroid-stimulating hormone receptor. Mice in which the OGH gene is deleted (OGH-/-) are indistinguishable from WT littermates in body weight, response to high-fat diet, metabolic parameters, body composition, and insulin tolerance. Mice engineered to transgenically globally overexpress OGH (OGH-TG) develop approximately 2-fold elevations in their basal thyroid levels and weigh slightly less than WT littermates despite increased food intake because of an increase in their metabolic rates. Moreover, when OGH-TG mice are challenged with a high-fat diet, they gain significantly less weight and body fat than their WT littermates. The OGH-TG mice also have reduced blood glucose, insulin, cholesterol, and triglycerides. In contrast to other approaches in which the thyroid axis is activated, OGH-TG mice exhibit only minor changes in heart rate and blood pressure. Our findings suggest that constitutive low-level activation of the thyroid axis (via OGH or other means) may provide a beneficial therapeutic approach for combating diet-induced obesity.

Animals↗
PubMed2005

Absence of the lipid phosphatase SHIP2 confers resistance to dietary obesity.

Genetic ablation of Inppl1, which encodes SHIP2 (SH2-domain containing inositol 5-phosphatase 2), was previously reported to induce severe insulin sensitivity, leading to early postnatal death. In the previous study, the targeting construct left the first eighteen exons encoding Inppl1 intact, generating a Inppl1(EX19-28-/-) mouse, and apparently also deleted a second gene, Phox2a. We report a new SHIP2 knockout (Inppl1(-/-)) targeted to the translation-initiating ATG, which is null for Inppl1 mRNA and protein. Inppl1(-/-) mice are viable, have normal glucose and insulin levels, and normal insulin and glucose tolerances. The Inppl1(-/-) mice are, however, highly resistant to weight gain when placed on a high-fat diet. These results suggest that inhibition of SHIP2 would be useful in the effort to ameliorate diet-induced obesity, but call into question a dominant role of SHIP2 in modulating glucose homeostasis.

Animals↗
PubMed2005

Agouti-related protein-deficient mice display an age-related lean phenotype.

Endogenous modulators of the central melanocortin system, such as the agouti-related protein (AgRP), should hold a pivotal position in the regulation of energy intake and expenditure. Despite this, AgRP-deficient mice were recently reported to exhibit normal food intake, body weight gain, and energy expenditure. Here we demonstrate that 2- to 3-month-old Agrp null mice do in fact exhibit subtle changes in response to feeding challenges (fasting and MCR agonists) but, of more significance and magnitude, exhibit reduced body weight and adiposity after 6 months of age. This age-dependent lean phenotype is correlated with increased metabolic rate, body temperature, and locomotor activity and increased circulating thyroid hormone (T4 and T3) and BAT UCP-1 expression. These results provide further proof of the importance of the AgRP neuronal system in the regulation of energy homeostasis.

Adipose Tissue↗