Publications by authors named "Jenny Yuan"

18 Publications

  • Page 1 of 1

Next-Generation Surrogate Wnts Support Organoid Growth and Deconvolute Frizzled Pleiotropy In Vivo.

Cell Stem Cell 2020 Nov 19;27(5):840-851.e6. Epub 2020 Aug 19.

Department of Molecular and Cellular Physiology, Department of Structural Biology, Howard Hughes Medical Institute, Stanford University School of Medicine, Stanford, CA 94305, USA. Electronic address:

Modulation of Wnt signaling has untapped potential in regenerative medicine due to its essential functions in stem cell homeostasis. However, Wnt lipidation and Wnt-Frizzled (Fzd) cross-reactivity have hindered translational Wnt applications. Here, we designed and engineered water-soluble, Fzd subtype-specific "next-generation surrogate" (NGS) Wnts that hetero-dimerize Fzd and Lrp6. NGS Wnt supports long-term expansion of multiple different types of organoids, including kidney, colon, hepatocyte, ovarian, and breast. NGS Wnts are superior to Wnt3a conditioned media in organoid expansion and single-cell organoid outgrowth. Administration of Fzd subtype-specific NGS Wnt in vivo reveals that adult intestinal crypt proliferation can be promoted by agonism of Fzd5 and/or Fzd8 receptors, while a broad spectrum of Fzd receptors can induce liver zonation. Thus, NGS Wnts offer a unified organoid expansion protocol and a laboratory "tool kit" for dissecting the functions of Fzd subtypes in stem cell biology.
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http://dx.doi.org/10.1016/j.stem.2020.07.020DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7655723PMC
November 2020

Receptor subtype discrimination using extensive shape complementary designed interfaces.

Nat Struct Mol Biol 2019 06 13;26(6):407-414. Epub 2019 May 13.

Department of Biochemistry, University of Washington, Seattle, WA, USA.

To discriminate between closely related members of a protein family that differ at a limited number of spatially distant positions is a challenge for drug discovery. We describe a combined computational design and experimental selection approach for generating binders targeting functional sites with large, shape complementary interfaces to read out subtle sequence differences for subtype-specific antagonism. Repeat proteins are computationally docked against a functionally relevant region of the target protein surface that varies in the different subtypes, and the interface sequences are optimized for affinity and specificity first computationally and then experimentally. We used this approach to generate a series of human Frizzled (Fz) subtype-selective antagonists with extensive shape complementary interaction surfaces considerably larger than those of repeat proteins selected from random libraries. In vivo administration revealed that Wnt-dependent pericentral liver gene expression involves multiple Fz subtypes, while maintenance of the intestinal crypt stem cell compartment involves only a limited subset.
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http://dx.doi.org/10.1038/s41594-019-0224-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6582999PMC
June 2019

A RECK-WNT7 Receptor-Ligand Interaction Enables Isoform-Specific Regulation of Wnt Bioavailability.

Cell Rep 2018 10;25(2):339-349.e9

Department of Medicine, Division of Hematology, Stanford University School of Medicine, Stanford, CA 94305, USA. Electronic address:

WNT7A and WNT7B control CNS angiogenesis and blood-brain barrier formation by activating endothelial Wnt/β-catenin signaling. The GPI-anchored protein RECK and adhesion G protein-coupled receptor GPR124 critically regulate WNT7-specific signaling in concert with FZD and LRP co-receptors. Here, we demonstrate that primarily the GPR124 ectodomain, but not its transmembrane and intracellular domains, mediates RECK/WNT7-induced canonical Wnt signaling. Moreover, RECK is the predominant binding partner of GPR124 in rat brain blood vessels in situ. WNT7A and WNT7B, but not WNT3A, directly bind to purified recombinant soluble RECK, full-length cell surface RECK, and the GPR124:RECK complex. Chemical cross-linking indicates that RECK and WNT7A associate with 1:1 stoichiometry, which stabilizes short-lived, active, monomeric, hydrophobic WNT7A. In contrast, free WNT7A rapidly converts into inactive, hydrophilic aggregates. Overall, RECK is a selective WNT7 receptor that mediates GPR124/FZD/LRP-dependent canonical Wnt/β-catenin signaling by stabilizing active cell surface WNT7, suggesting isoform-specific regulation of Wnt bioavailability.
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http://dx.doi.org/10.1016/j.celrep.2018.09.045DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6338448PMC
October 2018

Non-equivalence of Wnt and R-spondin ligands during Lgr5 intestinal stem-cell self-renewal.

Nature 2017 05 3;545(7653):238-242. Epub 2017 May 3.

Department of Medicine, Stanford University School of Medicine, Stanford, California 94305, USA.

The canonical Wnt/β-catenin signalling pathway governs diverse developmental, homeostatic and pathological processes. Palmitoylated Wnt ligands engage cell-surface frizzled (FZD) receptors and LRP5 and LRP6 co-receptors, enabling β-catenin nuclear translocation and TCF/LEF-dependent gene transactivation. Mutations in Wnt downstream signalling components have revealed diverse functions thought to be carried out by Wnt ligands themselves. However, redundancy between the 19 mammalian Wnt proteins and 10 FZD receptors and Wnt hydrophobicity have made it difficult to attribute these functions directly to Wnt ligands. For example, individual mutations in Wnt ligands have not revealed homeostatic phenotypes in the intestinal epithelium-an archetypal canonical, Wnt pathway-dependent, rapidly self-renewing tissue, the regeneration of which is fueled by proliferative crypt Lgr5 intestinal stem cells (ISCs). R-spondin ligands (RSPO1-RSPO4) engage distinct LGR4-LGR6, RNF43 and ZNRF3 receptor classes, markedly potentiate canonical Wnt/β-catenin signalling, and induce intestinal organoid growth in vitro and Lgr5 ISCs in vivo. However, the interchangeability, functional cooperation and relative contributions of Wnt versus RSPO ligands to in vivo canonical Wnt signalling and ISC biology remain unknown. Here we identify the functional roles of Wnt and RSPO ligands in the intestinal crypt stem-cell niche. We show that the default fate of Lgr5 ISCs is to differentiate, unless both RSPO and Wnt ligands are present. However, gain-of-function studies using RSPO ligands and a new non-lipidated Wnt analogue reveal that these ligands have qualitatively distinct, non-interchangeable roles in ISCs. Wnt proteins are unable to induce Lgr5 ISC self-renewal, but instead confer a basal competency by maintaining RSPO receptor expression that enables RSPO ligands to actively drive and specify the extent of stem-cell expansion. This functionally non-equivalent yet cooperative interaction between Wnt and RSPO ligands establishes a molecular precedent for regulation of mammalian stem cells by distinct priming and self-renewal factors, with broad implications for precise control of tissue regeneration.
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http://dx.doi.org/10.1038/nature22313DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5641471PMC
May 2017

Gpr124 is essential for blood-brain barrier integrity in central nervous system disease.

Nat Med 2017 Apr 13;23(4):450-460. Epub 2017 Mar 13.

Department of Medicine, Stanford University School of Medicine, Stanford, California, USA.

Although blood-brain barrier (BBB) compromise is central to the etiology of diverse central nervous system (CNS) disorders, endothelial receptor proteins that control BBB function are poorly defined. The endothelial G-protein-coupled receptor (GPCR) Gpr124 has been reported to be required for normal forebrain angiogenesis and BBB function in mouse embryos, but the role of this receptor in adult animals is unknown. Here Gpr124 conditional knockout (CKO) in the endothelia of adult mice did not affect homeostatic BBB integrity, but resulted in BBB disruption and microvascular hemorrhage in mouse models of both ischemic stroke and glioblastoma, accompanied by reduced cerebrovascular canonical Wnt-β-catenin signaling. Constitutive activation of Wnt-β-catenin signaling fully corrected the BBB disruption and hemorrhage defects of Gpr124-CKO mice, with rescue of the endothelial gene tight junction, pericyte coverage and extracellular-matrix deficits. We thus identify Gpr124 as an endothelial GPCR specifically required for endothelial Wnt signaling and BBB integrity under pathological conditions in adult mice. This finding implicates Gpr124 as a potential therapeutic target for human CNS disorders characterized by BBB disruption.
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http://dx.doi.org/10.1038/nm.4309DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5559385PMC
April 2017

Oncogenic transformation of diverse gastrointestinal tissues in primary organoid culture.

Nat Med 2014 Jul 25;20(7):769-77. Epub 2014 May 25.

Department of Medicine, Hematology Division, Stanford University School of Medicine, Stanford, California, USA.

The application of primary organoid cultures containing epithelial and mesenchymal elements to cancer modeling holds promise for combining the accurate multilineage differentiation and physiology of in vivo systems with the facile in vitro manipulation of transformed cell lines. Here we used a single air-liquid interface culture method without modification to engineer oncogenic mutations into primary epithelial and mesenchymal organoids from mouse colon, stomach and pancreas. Pancreatic and gastric organoids exhibited dysplasia as a result of expression of Kras carrying the G12D mutation (Kras(G12D)), p53 loss or both and readily generated adenocarcinoma after in vivo transplantation. In contrast, primary colon organoids required combinatorial Apc, p53, Kras(G12D) and Smad4 mutations for progressive transformation to invasive adenocarcinoma-like histology in vitro and tumorigenicity in vivo, recapitulating multi-hit models of colorectal cancer (CRC), as compared to the more promiscuous transformation of small intestinal organoids. Colon organoid culture functionally validated the microRNA miR-483 as a dominant driver oncogene at the IGF2 (insulin-like growth factor-2) 11p15.5 CRC amplicon, inducing dysplasia in vitro and tumorigenicity in vivo. These studies demonstrate the general utility of a highly tractable primary organoid system for cancer modeling and driver oncogene validation in diverse gastrointestinal tissues.
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http://dx.doi.org/10.1038/nm.3585DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4087144PMC
July 2014

A liver Hif-2α-Irs2 pathway sensitizes hepatic insulin signaling and is modulated by Vegf inhibition.

Nat Med 2013 Oct 15;19(10):1331-1337. Epub 2013 Sep 15.

Division of Hematology, Stanford University School of Medicine, Stanford, California 94305, USA.

Insulin initiates diverse hepatic metabolic responses, including gluconeogenic suppression and induction of glycogen synthesis and lipogenesis. The liver possesses a rich sinusoidal capillary network with a higher degree of hypoxia and lower gluconeogenesis in the perivenous zone as compared to the rest of the organ. Here, we show that diverse vascular endothelial growth factor (VEGF) inhibitors improved glucose tolerance in nondiabetic C57BL/6 and diabetic db/db mice, potentiating hepatic insulin signaling with lower gluconeogenic gene expression, higher glycogen storage and suppressed hepatic glucose production. VEGF inhibition induced hepatic hypoxia through sinusoidal vascular regression and sensitized liver insulin signaling through hypoxia-inducible factor-2α (Hif-2α, encoded by Epas1) stabilization. Notably, liver-specific constitutive activation of HIF-2α, but not HIF-1α, was sufficient to augment hepatic insulin signaling through direct and indirect induction of insulin receptor substrate-2 (Irs2), an essential insulin receptor adaptor protein. Further, liver Irs2 was both necessary and sufficient to mediate Hif-2α and Vegf inhibition effects on glucose tolerance and hepatic insulin signaling. These results demonstrate an unsuspected intersection between Hif-2α-mediated hypoxic signaling and hepatic insulin action through Irs2 induction, which can be co-opted by Vegf inhibitors to modulate glucose metabolism. These studies also indicate distinct roles in hepatic metabolism for Hif-1α, which promotes glycolysis, and Hif-2α, which suppresses gluconeogenesis, and suggest new treatment approaches for type 2 diabetes mellitus.
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http://dx.doi.org/10.1038/nm.3295DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3795838PMC
October 2013

Cross-talk between hypoxia and insulin signaling through Phd3 regulates hepatic glucose and lipid metabolism and ameliorates diabetes.

Nat Med 2013 Oct 15;19(10):1325-30. Epub 2013 Sep 15.

Division of Radiation and Cancer Biology, Department of Radiation Oncology, Center for Clinical Sciences Research, Stanford, California, USA.

Signaling initiated by hypoxia and insulin powerfully alters cellular metabolism. The protein stability of hypoxia-inducible factor-1 alpha (Hif-1α) and Hif-2α is regulated by three prolyl hydroxylase domain-containing protein isoforms (Phd1, Phd2 and Phd3). Insulin receptor substrate-2 (Irs2) is a critical mediator of the anabolic effects of insulin, and its decreased expression contributes to the pathophysiology of insulin resistance and diabetes. Although Hif regulates many metabolic pathways, it is unknown whether the Phd proteins regulate glucose and lipid metabolism in the liver. Here, we show that acute deletion of hepatic Phd3, also known as Egln3, improves insulin sensitivity and ameliorates diabetes by specifically stabilizing Hif-2α, which then increases Irs2 transcription and insulin-stimulated Akt activation. Hif-2α and Irs2 are both necessary for the improved insulin sensitivity, as knockdown of either molecule abrogates the beneficial effects of Phd3 knockout on glucose tolerance and insulin-stimulated Akt phosphorylation. Augmenting levels of Hif-2α through various combinations of Phd gene knockouts did not further improve hepatic metabolism and only added toxicity. Thus, isoform-specific inhibition of Phd3 could be exploited to treat type 2 diabetes without the toxicity that could occur with chronic inhibition of multiple Phd isoforms.
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http://dx.doi.org/10.1038/nm.3294DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4089950PMC
October 2013

Partial proteasome inhibitors induce hair follicle growth by stabilizing β-catenin.

Stem Cells 2014 Jan;32(1):85-92

Program in Epithelial Biology, Stanford University, School of Medicine, Stanford, California, USA.

The activation of tissue stem cells from their quiescent state represents the initial step in the complex process of organ regeneration and tissue repair. While the identity and location of tissue stem cells are becoming known, how key regulators control the balance of activation and quiescence remains mysterious. The vertebrate hair is an ideal model system where hair cycling between growth and resting phases is precisely regulated by morphogen signaling pathways, but how these events are coordinated to promote orderly signaling in a spatial and temporal manner remains unclear. Here, we show that hair cycle timing depends on regulated stability of signaling substrates by the ubiquitin-proteasome system. Topical application of partial proteasomal inhibitors (PaPIs) inhibits epidermal and dermal proteasome activity throughout the hair cycle. PaPIs prevent the destruction of the key anagen signal β-catenin, resulting in more rapid hair growth and dramatically shortened telogen. We show that PaPIs induce excess β-catenin, act similarly to the GSK3β antagonist LiCl, and antagonize Dickopf-related protein-mediated inhibition of anagen. PaPIs thus represent a novel class of hair growth agents that act through transiently modifying the balance of stem cell activation and quiescence pathways.
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http://dx.doi.org/10.1002/stem.1525DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4116182PMC
January 2014

Verbal interactions in Taiwanese group counseling process: a cross-cultural perspective.

Psychol Rep 2012 Oct;111(2):349-63

College of Humanities and Education Chung Yuan Christian University, Taiwan, ROC.

Although group verbal behaviors have been extensively studied, little research has examined how the types and frequencies of interactions vary across cultures. The purpose of this study was to examine verbal interactions in the Taiwanese group counseling process from a cultural perspective. 58 students were recruited from seven colleges of a comprehensive university in Taiwan. They were randomly assigned to one of the following: the Family Reconstruction group, Transactional Analysis group, or Growth group, as well as three Counseling groups. By using the Hill Interaction Matrix-SS (HIM-SS), participants' verbal interactions in the three groups were coded. Personal and Relationship Content verbal interactions were frequently used and the Confrontative and Assertive Work verbal interactions were least used in the group process. Personal, Relationship, Conventional, and Speculative verbal interactions were ranked high, but those of Group, Topics, Confrontative, and Assertive were much less used by both leaders and members. The differences of the verbal interactions and Silence responses between leaders and members in counseling groups were examined; there were no significant differences between the leaders' and members' verbal interactions and Silence. Specific types of verbal interactions influenced by cultural issues were discussed.
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http://dx.doi.org/10.2466/02.07.15.21.PR0.111.5.349-363DOI Listing
October 2012

The HIF signaling pathway in osteoblasts directly modulates erythropoiesis through the production of EPO.

Cell 2012 Mar;149(1):63-74

Division of Radiation and Cancer Biology, Department of Radiation Oncology, Center for Clinical Sciences Research, Stanford University, Stanford, CA 94303-5152, USA.

Osteoblasts are an important component of the hematopoietic microenvironment in bone. However, the mechanisms by which osteoblasts control hematopoiesis remain unknown. We show that augmented HIF signaling in osteoprogenitors results in HSC niche expansion associated with selective expansion of the erythroid lineage. Increased red blood cell production occurred in an EPO-dependent manner with increased EPO expression in bone and suppressed EPO expression in the kidney. In contrast, inactivation of HIF in osteoprogenitors reduced EPO expression in bone. Importantly, augmented HIF activity in osteoprogenitors protected mice from stress-induced anemia. Pharmacologic or genetic inhibition of prolyl hydroxylases1/2/3 in osteoprogenitors elevated EPO expression in bone and increased hematocrit. These data reveal an unexpected role for osteoblasts in the production of EPO and modulation of erythropoiesis. Furthermore, these studies demonstrate a molecular role for osteoblastic PHD/VHL/HIF signaling that can be targeted to elevate both HSCs and erythroid progenitors in the local hematopoietic microenvironment.
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http://dx.doi.org/10.1016/j.cell.2012.01.051DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3408231PMC
March 2012

AXL is an essential factor and therapeutic target for metastatic ovarian cancer.

Cancer Res 2010 Oct 21;70(19):7570-9. Epub 2010 Sep 21.

Division of Radiation and Cancer Biology, Department of Radiation Oncology, Center for Clinical Sciences Research, Stanford University, Stanford, California 94305-5152, USA.

The receptor tyrosine kinase AXL is thought to play a role in metastasis; however, the therapeutic efficacy of an AXL-targeting agent remains largely untested in metastatic disease. In this study, we defined AXL as a therapeutic target for metastatic ovarian cancer. AXL is primarily expressed in metastases and advanced-stage human ovarian tumors but not in normal ovarian epithelium. Genetic inhibition of AXL in human metastatic ovarian tumor cells is sufficient to prevent the initiation of metastatic disease in vivo. Mechanistically, inhibition of AXL signaling in animals with metastatic disease results in decreased invasion and matrix metalloproteinase activity. Most importantly, soluble human AXL receptors that imposed a specific blockade of the GAS6/AXL pathway had a profound inhibitory effect on progression of established metastatic ovarian cancer without normal tissue toxicity. These results offer the first genetic validation of GAS6/AXL targeting as an effective strategy for inhibition of metastatic tumor progression in vivo. Furthermore, this study defines the soluble AXL receptor as a therapeutic candidate agent for treatment of metastatic ovarian cancer, for which current therapies are ineffective.
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http://dx.doi.org/10.1158/0008-5472.CAN-10-1267DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3408227PMC
October 2010

Soluble receptor-mediated selective inhibition of VEGFR and PDGFRbeta signaling during physiologic and tumor angiogenesis.

Proc Natl Acad Sci U S A 2008 Jul 16;105(29):10185-90. Epub 2008 Jul 16.

Division of Hematology, Stanford University School of Medicine, Stanford, CA 94305, USA.

The simultaneous targeting of both endothelial cells and pericytes via inhibition of VEGF receptor (VEGFR) and PDGFbeta receptor (PDGFRbeta) signaling, respectively, has been proposed to enhance the efficacy of antiangiogenic tumor therapy. Clinical and preclinical modeling of combined VEGFR and PDGFRbeta signaling inhibition, however, has used small molecule kinase inhibitors with inherently broad substrate specificities, precluding detailed examination of this hypothesis. Here, adenoviral expression of a soluble VEGFR2/Flk1 ectodomain (Ad Flk1-Fc) in combination with a soluble ectodomain of PDGFRbeta (Ad sPDGFRbeta) allowed highly selective inhibition of these pathways. The activity of Ad sPDGFRbeta was validated in vitro against PDGF-BB and in vivo with near-complete blockade of pericyte recruitment in the angiogenic corpus luteum, resulting in prominent hemorrhage, thus demonstrating an essential function for PDGF signaling during ovarian angiogenesis. Combination therapy with Ad PDGFRbeta and submaximal doses of Ad Flk1-Fc produced modest additive antitumor effects; however, no additivity was observed with maximal VEGF inhibition in numerous s.c. models. Notably, VEGF inhibition via Ad Flk1-Fc was sufficient to strongly suppress tumor endothelial and pericyte content as well as intratumoral PDGF-B mRNA, obscuring additive Ad sPDGFRbeta effects on pericytes or tumor volume. These studies using highly specific soluble receptors suggest that additivity between VEGFR and PDGFRbeta inhibition depends on the strength of VEGF blockade and appears minimal under conditions of maximal VEGF antagonism.
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http://dx.doi.org/10.1073/pnas.0803194105DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2474564PMC
July 2008

VEGF modulates erythropoiesis through regulation of adult hepatic erythropoietin synthesis.

Nat Med 2006 Jul 25;12(7):793-800. Epub 2006 Jun 25.

Division of Hematology, Stanford University School of Medicine, 269 Campus Drive, CCSR 1155, Stanford, California, 94305, USA.

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.
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http://dx.doi.org/10.1038/nm1428DOI Listing
July 2006

Hydrophilic absorbable copolyester exhibiting zero-order drug release.

Pharm Res 2006 Apr 10;23(4):821-34. Epub 2006 Feb 10.

Procedural Implants R&D, Ethicon, a Johnson & Johnson Company, Route 22 West, Somerville, New Jersey 08876-0151, USA.

Purpose: A novel absorbable hydrophilic copolyester developed in our laboratory, amorphous 40/60 poly(ethylene diglycolate-co-glycolide), exhibits outstanding physical properties. Films made from this material appear fully transparent, colorless, soft and slightly elastic, but relatively strong and durable materials so that they can be potentially used as stand-alone devices in various in-vivo medical applications. In this study, in-vitro drug release characteristics of this copolyester were examined.

Methods: High Performance Liquid Chromatography was used to generate release profiles on selected non-steroidal anti-inflammatory agents, NSAIDs. In addition, dielectric relaxation spectroscopy, as well as mid- and near infrared spectroscopy, were used to study specific polymer chain interactions in water and buffer solution as a function of aging time at 37 degrees C.

Results: This copolyester, compression molded into a film, exhibited nearly constant in-vitro release of various hydrophilic and hydrophobic drugs. The release profile showed minimal or, in most cases, no burst effect. The effect was observed with the three NSAIDs that were tested as model compounds; however, this system may prove generally useful for other drug entities. In-vitro hydrolysis conducted at 37 degrees C on this hydrophilic copolyester revealed an unusually long induction period (no hydrolysis for up to 6 days), followed by the relatively rapid hydrolysis. Data from dipole relaxation spectroscopy indicated that the water molecules do not structurally associate with the polymer chains in phosphate buffer during initial hydrolysis period.

Conclusions: The results suggest unique dynamics of water diffusion through the polymer matrix that may play a critical role in achieving controlled release properties. Furthermore, we suspect that the molecular interactions associated with this new synthetic absorbable material may find a critical utility in important medical applications.
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http://dx.doi.org/10.1007/s11095-006-9664-3DOI Listing
April 2006

Essential requirement for Wnt signaling in proliferation of adult small intestine and colon revealed by adenoviral expression of Dickkopf-1.

Proc Natl Acad Sci U S A 2004 Jan 26;101(1):266-71. Epub 2003 Dec 26.

Department of Medicine, Stanford University School of Medicine, Center for Clinical Sciences Research 3100, 269 Campus Drive, Stanford, CA 94305, USA.

Whereas the adult gastrointestinal epithelium undergoes tremendous self-renewal through active proliferation in crypt stem cell compartments, the responsible growth factors regulating this continuous proliferation have not been defined. The exploration of physiologic functions of Wnt proteins in adult organisms has been hampered by functional redundancy and the necessity for conditional inactivation strategies. Dickkopf-1 (Dkk1) is a potent secreted Wnt antagonist that interacts with Wnt coreceptors of the LRP family. To address the contribution of Wnt signaling to gastrointestinal epithelial proliferation, adenoviral expression of Dkk1 was used to achieve stringent, conditional, and reversible Wnt inhibition in adult animals. Adenovirus Dkk1 (Ad Dkk1) treatment of adult mice repressed expression of the Wnt target genes CD44 and EphB2 within 2 days in both small intestine and colon, indicating an extremely broad role for Wnt signaling in the maintenance of adult gastrointestinal gene expression. In parallel, Ad Dkk1 markedly inhibited proliferation in small intestine and colon, accompanied by progressive architectural degeneration with the loss of crypts, villi, and glandular structure by 7 days. Whereas decreased Dkk1 expression at later time points (>10 days) was followed by crypt and villus regeneration, which was consistent with a reversible process, substantial mortality ensued from colitis and systemic infection. These results indicate the efficacy of systemic expression of secreted Wnt antagonists as a general strategy for conditional inactivation of Wnt signaling in adult organisms and illustrate a striking reliance on a single growth factor pathway for the maintenance of the architecture of the adult small intestine and colon.
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http://dx.doi.org/10.1073/pnas.2536800100DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC314174PMC
January 2004

Human epidermal growth factor receptor signaling contributes to tumor growth via angiogenesis in her2/neu-expressing experimental Wilms' tumor.

J Pediatr Surg 2003 Nov;38(11):1569-73

Division of Pediatric Surgery, Columbia University, New York, NY, USA.

Background: The human epidermal growth factor family (HER) members play a significant role in the mesenchymal-to-epithelial transition during renal tubulogenesis. HER misexpression has been linked also to loss of growth control, invasiveness, and promotion of angiogenesis in breast cancers and other human malignant tumors

Methods: The authors screened Wilms' tumor samples and derived cell lines for expression of her2/neu, which was detected in both unfavorable and favorable histology tissues. Xenografts were implanted in mice using her2/neu(+) and her2/neu(-) cell lines and the effect of specific blockade tested using monoclonal anti-her2/neu antibody.

Results: Blocking antibody suppressed tumor growth in her2/neu(+) but not her2/neu(-) experimental Wilms' tumor. In addition, antibody exposure resulted in suppression of tumor angiogenesis but no decrease in tumor cell proliferation in her2/neu(+) xenografts.

Conclusions: Her2/neu contributes to the growth of some Wilms' tumors, and an important mechanism of its action is promotion of angiogenesis.
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http://dx.doi.org/10.1016/s0022-3468(03)00562-1DOI Listing
November 2003

Blockade of her2/neu decreases VEGF expression but does not alter HIF-1 distribution in experimental Wilms tumor.

Oncol Rep 2003 Sep-Oct;10(5):1271-4

Division of Pediatric Surgery, Columbia University, New York, NY, USA.

Her2/neu regulates angiogenesis in human breast cancer, in part by stabilizing hypoxia-inducible factor 1alpha (HIF-1alpha), causing accumulation of the HIF-1 heterodimer and thus increasing expression of the proangiogenic cytokine VEGF. Her2/neu has recently been shown to be overexpressed in a subset of Wilms tumors. Using her2/neu (+) and her2/neu (-) Wilms tumor cell lines, we tested the effect of blocking anti-her2/neu antibody in vitro and in vivo. Blocking antibody did not alter VEGF expression in vitro, but decreased expression of VEGF in her2/neu (+) Wilms tumor xenografts. Tumor suppression was less marked than in parallel experiments using agents directly blocking VEGF. HIF-1alpha immunostaining was not altered in her2/neu (+) xenografts exposed to blocking antibody. These results suggest that her2/neu contributes to Wilms tumor angiogenesis in vivo by regulating VEGF, but other processes may act to rescue HIF-1alpha and thus to support tumor growth in this system.
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April 2004