Academic Appointments

Honors & Awards

  • Fellow, American Surgical Association (2013-present)
  • President, Society of University Surgeons (2012-2013)
  • Chair, Publications Committee, Society of University Surgeons (2008-2010)
  • Faculty Scholarship, Robert L and Mary Ellenburg Foundation (2008-2011)
  • Wound Care Management Award, American College of Surgeons (2008-2010)
  • Faculty Research Fellow, American College of Surgeons (2002-2004)
  • Resident Research Scholarship, American College of Surgeons (1996-1998)

Professional Education

  • BA, Northwestern University, biological sciences (1985)
  • MD, Northwestern Univ Med School, medicine (1994)
  • PhD, Univ of Illinois Coll of Med, molecular genetics (1993)

Community and International Work

  • Hospital de la Familia, Nuevo Progresso, Guatemala


    medical care in Guatemala

    Populations Served

    low income Guatemalans



    Ongoing Project


    Opportunities for Student Involvement


Research & Scholarship

Current Research and Scholarly Interests

We are broadly interested in understanding the response to injury by studying the cellular responses to stress. Many of the molecular pathways involved in the response to injury have protective or regenerative functions. The ultimate goal of these studies is to better understand how organisms heal and repair injury with an eye towards applying this knowledge in regenerative medicine strategies.

We are currently examining the role of a cellular stress response in wound healing. Another project looks at the role of the matricellular protein, Del1, in the skeletal pathology. And finally, we are interested in the molecular control of genes important in fracture healing.

Clinical Trials

  • Cyberknife Radiosurgery for Locally Advanced Pancreatic Cancer Not Recruiting

    The purpose of the trial is to test the efficacy of combining conventional chemoradiotherapy with radiosurgery for locally advanced pancreas cancer.

    Stanford is currently not accepting patients for this trial. For more information, please contact Stanford Cancer Clinical Trials Office, (650) 498 - 7061.

    View full details

  • Trilogy Stereotactic Body Radiotherapy for Pancreatic Cancer Not Recruiting

    This study will assess the efficacy of treating locally advanced pancreatic cancer using Stereotactic Body Radiotherapy (using Trilogy) and Gemcitabine

    Stanford is currently not accepting patients for this trial. For more information, please contact Jeff Kim, (650) 498 - 7703.

    View full details

  • Evaluation of Stereotactic Radiosurgery For Liver Malignancies Not Recruiting

    This study is intended to establish the practicality of treating cancer in the liver with precisely administered single fractions of high-energy radiation using a radiosurgical (cross-firing) technique. A second purpose is to establish a safe dose for such therapy. Finally, the efficacy of radiosurgical ablation of liver tumors, in terms of radiographic response, will be measured.

    Stanford is currently not accepting patients for this trial. For more information, please contact Jeff Kim, (650) 498 - 7703.

    View full details


2017-18 Courses

Stanford Advisees


All Publications

  • Laboratory Models for the Study of Normal and Pathologic Wound Healing. Plastic and reconstructive surgery Boyko, T. V., Longaker, M. T., Yang, G. P. 2017; 139 (3): 654-662


    Current knowledge of wound healing is based on studies using various in vitro and in vivo wound models. In vitro models allow for biological examination of specific cell types involved in wound healing. In vivo models generally provide the full spectrum of biological responses required for wound healing, including inflammation and angiogenesis, and provide cell-cell interactions not seen in vitro. In this review, the authors aim to delineate the most relevant wound healing models currently available and to discuss their strengths and limitations in their approximation of the human wound healing processes to aid scientists in choosing the most appropriate wound healing models for designing, testing, and validating their experiments.

    View details for DOI 10.1097/PRS.0000000000003077

    View details for PubMedID 28234843

  • Hernia Mesh Repair and Global Surgery-Reply. JAMA surgery Forrester, J. D., Forrester, J. A., Yang, G. P. 2016

    View details for DOI 10.1001/jamasurg.2016.3497

    View details for PubMedID 27732714

  • Enhancing Local Resources in Low- and Middle-Income Countries Through Education. JAMA surgery Yang, G. P., Wren, S. M. 2016

    View details for DOI 10.1001/jamasurg.2016.3365

    View details for PubMedID 27706484

  • Surgical Mesh Should Be Made Affordable to Low- and Middle-Income Countries JAMA SURGERY Forrester, J. D., Forrester, J. A., Yang, G. P. 2016; 151 (6): 499-500

    View details for DOI 10.1001/jamasurg.2015.5456

    View details for Web of Science ID 000377932700005

    View details for PubMedID 26934533

  • Del1 Knockout Mice Developed More Severe Osteoarthritis Associated with Increased Susceptibility of Chondrocytes to Apoptosis. PloS one Wang, Z., Tran, M. C., Bhatia, N. J., Hsing, A. W., Chen, C., LaRussa, M. F., Fattakhov, E., Rashidi, V., Jang, K. Y., Choo, K. J., Nie, X., Mathy, J. A., Longaker, M. T., Dauskardt, R. H., Helms, J. A., Yang, G. P. 2016; 11 (8)


    We identified significant expression of the matricellular protein, DEL1, in hypertrophic and mature cartilage during development. We hypothesized that this tissue-specific expression indicated a biological role for DEL1 in cartilage biology.Del1 KO and WT mice had cartilage thickness evaluated by histomorphometry. Additional mice underwent medial meniscectomy to induce osteoarthritis, and were assayed at 1 week for apoptosis by TUNEL staining and at 8 weeks for histology and OA scoring. In vitro proliferation and apoptosis assays were performed on primary chondrocytes.Deletion of the Del1 gene led to decreased amounts of cartilage in the ears and knee joints in mice with otherwise normal skeletal morphology. Destabilization of the knee led to more severe OA compared to controls. In vitro, DEL1 blocked apoptosis in chondrocytes.Osteoarthritis is among the most prevalent diseases worldwide and increasing in incidence as our population ages. Initiation begins with an injury resulting in the release of inflammatory mediators. Excessive production of inflammatory mediators results in apoptosis of chondrocytes. Because of the limited ability of chondrocytes to regenerate, articular cartilage deteriorates leading to the clinical symptoms including severe pain and decreased mobility. No treatments effectively block the progression of OA. We propose that direct modulation of chondrocyte apoptosis is a key variable in the etiology of OA, and therapies aimed at preventing this important step represent a new class of regenerative medicine targets.

    View details for DOI 10.1371/journal.pone.0160684

    View details for PubMedID 27505251

    View details for PubMedCentralID PMC4978450

  • A distinct regulatory region of the Bmp5 locus activates gene expression following adult bone fracture or soft tissue injury. Bone Guenther, C. A., Wang, Z., Li, E., Tran, M. C., Logan, C. Y., Nusse, R., Pantalena-Filho, L., Yang, G. P., Kingsley, D. M. 2015; 77: 31-41


    Bone morphogenetic proteins (BMPs) are key signaling molecules required for normal development of bones and other tissues. Previous studies have shown that null mutations in the mouse Bmp5 gene alter the size, shape and number of multiple bone and cartilage structures during development. Bmp5 mutations also delay healing of rib fractures in adult mutants, suggesting that the same signals used to pattern embryonic bone and cartilage are also reused during skeletal regeneration and repair. Despite intense interest in BMPs as agents for stimulating bone formation in clinical applications, little is known about the regulatory elements that control developmental or injury-induced BMP expression. To compare the DNA sequences that activate gene expression during embryonic bone formation and following acute injuries in adult animals, we assayed regions surrounding the Bmp5 gene for their ability to stimulate lacZ reporter gene expression in transgenic mice. Multiple genomic fragments, distributed across the Bmp5 locus, collectively coordinate expression in discrete anatomic domains during normal development, including in embryonic ribs. In contrast, a distinct regulatory region activated expression following rib fracture in adult animals. The same injury control region triggered gene expression in mesenchymal cells following tibia fracture, in migrating keratinocytes following dorsal skin wounding, and in regenerating epithelial cells following lung injury. The Bmp5 gene thus contains an "injury response" control region that is distinct from embryonic enhancers, and that is activated by multiple types of injury in adult animals.

    View details for DOI 10.1016/j.bone.2015.04.010

    View details for PubMedID 25886903

  • Moisturizing different racial skin types. The Journal of clinical and aesthetic dermatology Wan, D. C., Wong, V. W., Longaker, M. T., Yang, G. P., Wei, F. 2014; 7 (6): 25-32


    The skin is a complex organ involved in thermoregulation, gas exchange, protection against pathogens, and barrier function to maintain proper hydration. When dry, the ability for skin to execute these tasks becomes impaired. Dry skin affects almost everyone as we age, but it is also dependent on external factors, such as dry climate, colder temperatures, and repeated washing. In addition, increasing evidence has shown racial variability in the physiological properties of skin, which directly impacts water content of the stratum corneum and sensitivity to exogenously applied agents. A multitude of products have been developed to treat dry skin, and as a group, moisturizers have been designed to either impart or restore hydration in the stratum corneum. Given the large number of moisturizers presently available, depending on individual components, several different mechanisms may be employed to promote skin hydration. As there exists dramatic racial variability in skin properties, certain moisturizers may thus be more effective in some and less effective in others to treat the common condition of dry skin.

    View details for PubMedID 25013536

  • 2013 Society of University Surgeons Presidential Address: Reassessing the Halstedian residency. Surgery Yang, G. P. 2013; 154 (2): 137-142

    View details for DOI 10.1016/j.surg.2013.03.017

    View details for PubMedID 23889943

  • The angiogenic factor Dell prevents apoptosis of endothelial cells through integrin binding SURGERY Wang, Z., Kundu, R. K., Longaker, M. T., Quertermous, T., Yang, G. P. 2012; 151 (2): 296-305


    Del1 is a secreted protein that is expressed in the endothelium during development and can stimulate angiogenesis through integrin binding and signaling. We were interested in the specific effects of del1 on endothelial cell biology to gain insight into its biologic role during angiogenesis.Primary endothelial cells were treated with a variety of inducers of apoptosis and anoikis followed by assays for numbers of apoptotic cells, and harvest of total protein for immunoblot analysis.Del1 prevented endothelial cell apoptosis in response to TNFα/IFNγ, etoposide, and anoikis, but had no effect on proliferation. The anti-apoptotic effect was mediated specifically through binding of integrin αvβ3 by the RGD motif. FAK/ERK and Akt signaling were both necessary to mediate the anti-apoptotic effect of Del1 with the exception of anoikis, which required only Akt activation.Del1 has been previously shown to promote vascular smooth muscle cell adhesion, migration, and proliferation. We demonstrate here that Del1 prevented apoptosis of endothelial cells in cell culture through integrin binding without any effect on proliferation.

    View details for DOI 10.1016/j.surg.2011.07.013

    View details for Web of Science ID 000299607800019

    View details for PubMedID 21893328

  • Unfolded Protein Response Regulation in Keloid Cells JOURNAL OF SURGICAL RESEARCH Butler, P. D., Wang, Z., Ly, D. P., Longaker, M. T., Koong, A. C., Yang, G. P. 2011; 167 (1): 151-157


    Keloids are a common form of pathologic wound healing characterized by excessive production of extracellular matrix. The unfolded protein response (UPR) is a cellular response to hypoxia, a component of the wound microenvironment, capable of protecting cells from the effects of over-accumulation of misfolded proteins. Since keloids have hypersecretion of extracellular matrix, we hypothesized that keloid fibroblasts (KFs) may have enhanced activation of the UPR compared with normal fibroblasts (NFs).KFs and NFs were placed in a hypoxia chamber for 0, 24, and 48h. We also used tunicamycin to specifically up-regulate the UPR. UPR activation was assayed by PCR for xbp-1 splicing and by immunoblotting with specific antibodies for the three UPR transducers. Nuclear localization of XBP-1 protein in KFs was confirmed by immunofluorescence.There is increased activation of XBP-1 protein in KFs compared with NFs following exposure to hypoxia. Pancreatic ER kinase (PERK) and ATF-6, two other pathways activated by the UPR, show comparable activation between KFs and NFs. We confirmed that there is enhanced activation of XBP-1 by demonstrating increased nuclear localization of XBP-1 using immunofluorescence.In contrast to our initial hypothesis that keloids would have broad activation of the UPR, we demonstrate here that there is a specific up-regulation of one facet of the UPR response. This may represent a specific molecular defect in KFs compared with NFs, and also suggests modulation of the UPR can be used in wound healing therapy.

    View details for DOI 10.1016/j.jss.2009.04.036

    View details for Web of Science ID 000288744100029

    View details for PubMedID 19631342

  • Comparative Healing of Rat Fascia Following Incision with Three Surgical Instruments JOURNAL OF SURGICAL RESEARCH Chang, E. I., Carlson, G. A., Vose, J. G., Huang, E. J., Yang, G. P. 2011; 167 (1): E47-E54


    Incisional hernia and fascial dehiscence are associated with significant postoperative morbidity. Electrosurgical devices using pulsed radiofrequency energy and a novel electrode design markedly reduce thermal injury during cutting and coagulation while maintaining equal surgical performance. In this study, we examine fascial healing dynamics in a rat model following incision with a pulsed radiofrequency energy device (PRE), a conventional electrosurgical device, and a standard "cold" scalpel. We hypothesize that incisions made with the pulsed radiofrequency energy device will result in a superior fascial healing profile compared with conventional electrosurgery.Full thickness surgical incisions were created in rat fascia using a commercially available PRE device, conventional electrosurgery, and a scalpel. Harvested fascial specimens were analyzed for burst strength testing and healing-associated histologic characteristics at d 7, 14, 21, and 42.PRE incisions were fully healed by 6 wk with normal tissue architecture. By all measures, wounds created by the PRE device were comparable to those made with the standard scalpel. Compared with PRE, conventional electrosurgery incisions exhibited a larger zone of tissue injury (68% greater in Coag mode, P < 0.0001; 46% greater in Cut mode, P < 0.001), an increased inflammatory response and a less favorable wound architecture. In the immediate postoperative period (1 wk), burst strength testing demonstrated that PRE fascial wounds were significantly stronger than those made by electrosurgery in Coag mode (318%, P = 0.001).The favorable fascial healing profile of the PRE device suggests that it is a promising new surgical technology. The early improved strength of wounds made with this device is of particular interest, as wound dehiscence is of greatest concern early in the healing process.

    View details for DOI 10.1016/j.jss.2010.12.019

    View details for Web of Science ID 000288744100007

    View details for PubMedID 21324486

  • Engineered epidermal growth factor mutants with faster binding on-rates correlate with enhanced receptor activation FEBS LETTERS Lahti, J. L., Lui, B. H., Beck, S. E., Lee, S. S., Ly, D. P., Longaker, M. T., Yang, G. P., Cochran, J. R. 2011; 585 (8): 1135-1139


    Receptor tyrosine kinases (RTKs) regulate critical cell signaling pathways, yet the properties of their cognate ligands that influence receptor activation are not fully understood. There is great interest in parsing these complex ligand-receptor relationships using engineered proteins with altered binding properties. Here we focus on the interaction between two engineered epidermal growth factor (EGF) mutants and the EGF receptor (EGFR), a model member of the RTK superfamily. We found that EGF mutants with faster kinetic on-rates stimulate increased EGFR activation compared to wild-type EGF. These findings support previous predictions that faster association rates correlate with enhanced receptor activity.

    View details for DOI 10.1016/j.febslet.2011.03.044

    View details for Web of Science ID 000289505400004

    View details for PubMedID 21439278

    View details for PubMedCentralID PMC3118396



    We performed a Phase I dose-escalation study to explore the feasibility and safety of treating primary and metastatic liver tumors with single-fraction stereotactic body radiotherapy (SBRT).Between February 2004 and February 2008, 26 patients were treated for 40 identifiable lesions. Nineteen patients had hepatic metastases, 5 had intrahepatic cholangiocarcinomas, and 2 had recurrent hepatocellular carcinomas. The prescribed radiation dose was escalated from 18 to 30 Gy at 4-Gy increments with a planned maximum dose of 30 Gy. Cumulative incidence functions accounted for competing risks to estimate local failure (LF) incidence over time under the competing risk of death.All patients tolerated the single-fraction SBRT well without developing a dose-limiting toxicity. Nine acute Grade 1 toxicities, one acute Grade 2 toxicity, and two late Grade 2 gastrointestinal toxicities were observed. After a median of 17 months follow-up (range, 2-55 months), the cumulative risk of LF at 12 months was 23%. Fifteen patients have died: 11 treated for liver metastases and 4 with primary liver tumors died. The median survival was 28.6 months, and the 2-year actuarial overall survival was 50.4%.It is feasible and safe to deliver single-fraction, high-dose SBRT to primary or metastatic liver malignancies measuring ≤5 cm. Moreover, single-fraction SBRT for liver lesions demonstrated promising local tumor control with minimal acute and long-term toxicity. Single-fraction SBRT appears to be a viable nonsurgical option, but further studies are warranted to evaluate both control rates and impact on quality of life.

    View details for DOI 10.1016/j.ijrobp.2009.08.020

    View details for Web of Science ID 000282147000026

    View details for PubMedID 20350791

  • Human melanoma-initiating cells express neural crest nerve growth factor receptor CD271 NATURE Boiko, A. D., Razorenova, O. V., van de Rijn, M., Swetter, S. M., Johnson, D. L., Ly, D. P., Butler, P. D., Yang, G. P., Joshua, B., Kaplan, M. J., Longaker, M. T., Weissman, I. L. 2010; 466 (7302): 133-U155


    The question of whether tumorigenic cancer stem cells exist in human melanomas has arisen in the last few years. Here we show that in melanomas, tumour stem cells (MTSCs, for melanoma tumour stem cells) can be isolated prospectively as a highly enriched CD271(+) MTSC population using a process that maximizes viable cell transplantation. The tumours sampled in this study were taken from a broad spectrum of sites and stages. High-viability cells isolated by fluorescence-activated cell sorting and re-suspended in a matrigel vehicle were implanted into T-, B- and natural-killer-deficient Rag2(-/-)gammac(-/-) mice. The CD271(+) subset of cells was the tumour-initiating population in 90% (nine out of ten) of melanomas tested. Transplantation of isolated CD271(+) melanoma cells into engrafted human skin or bone in Rag2(-/-)gammac(-/-) mice resulted in melanoma; however, melanoma did not develop after transplantation of isolated CD271(-) cells. We also show that in mice, tumours derived from transplanted human CD271(+) melanoma cells were capable of metastatsis in vivo. CD271(+) melanoma cells lacked expression of TYR, MART1 and MAGE in 86%, 69% and 68% of melanoma patients, respectively, which helps to explain why T-cell therapies directed at these antigens usually result in only temporary tumour shrinkage.

    View details for DOI 10.1038/nature09161

    View details for Web of Science ID 000279343800049

    View details for PubMedID 20596026

    View details for PubMedCentralID PMC2898751

  • Cell Permeant Peptide Analogues of the Small Heat Shock Protein, HSP20, Reduce TGF-beta 1-Induced CTGF Expression in Keloid Fibroblasts JOURNAL OF INVESTIGATIVE DERMATOLOGY Lopes, L. B., Furnish, E. J., Komalavilas, P., Flynn, C. R., Ashby, P., Hansen, A., Ly, D. P., Yang, G. P., Longaker, M. T., Panitch, A., Brophy, C. M. 2009; 129 (3): 590-598


    A growing body of evidence suggests the involvement of connective tissue growth factor (CTGF) in the development and maintenance of fibrosis and excessive scarring. As the expression of this protein requires an intact actin cytoskeleton, disruption of the cytoskeleton represents an attractive strategy to decrease CTGF expression and, consequently, excessive scarring. The small heat-shock-related protein (HSP20), when phosphorylated by cyclic nucleotide signaling cascades, displaces phospho-cofilin from the 14-3-3 scaffolding protein leading to activation of cofilin as an actin-depolymerizing protein. In the present study, we evaluated the effect of AZX100, a phosphopeptide analogue of HSP20, on transforming growth factor-beta-1 (TGF-beta1)-induced CTGF and collagen expression in human keloid fibroblasts. We also examined the effect of AZX100 on scar formation in vivo in dermal wounds in a Siberian hamster model. AZX100 decreased the expression of CTGF and type I collagen induced by TGF-beta1, endothelin, and lysophosphatidic acid. Treatment with AZX100 decreased stress fiber formation and altered the morphology of human dermal keloid fibroblasts. In vivo, AZX100 significantly improved collagen organization in a Siberian hamster scarring model. Taken together, these results suggest the potential use of AZX100 as a strategy to prevent excessive scarring and fibrotic disorders.

    View details for DOI 10.1038/jid.2008.264

    View details for Web of Science ID 000263569500011

    View details for PubMedID 18787533

  • The Role of Tumor Cell-Derived Connective Tissue Growth Factor (CTGF/CCN2) in Pancreatic Tumor Growth CANCER RESEARCH Bennewith, K. L., Huang, X., Ham, C. M., Graves, E. E., Erler, J. T., Kambham, N., Feazell, J., Yang, G. P., Koong, A., Giaccia, A. J. 2009; 69 (3): 775-784


    Pancreatic cancer is highly aggressive and refractory to existing therapies. Connective tissue growth factor (CTGF/CCN2) is a fibrosis-related gene that is thought to play a role in pancreatic tumor progression. However, CCN2 can be expressed in a variety of cell types, and the contribution of CCN2 derived from either tumor cells or stromal cells as it affects the growth of pancreatic tumors is unknown. Using genetic inhibition of CCN2, we have discovered that CCN2 derived from tumor cells is a critical regulator of pancreatic tumor growth. Pancreatic tumor cells derived from CCN2 shRNA-expressing clones showed dramatically reduced growth in soft agar and when implanted s.c. We also observed a role for CCN2 in the growth of pancreatic tumors implanted orthotopically, with tumor volume measurements obtained by positron emission tomography imaging. Mechanistically, CCN2 protects cells from hypoxia-mediated apoptosis, providing an in vivo selection for tumor cells that express high levels of CCN2. We found that CCN2 expression and secretion was increased in hypoxic pancreatic tumor cells in vitro, and we observed colocalization of CCN2 and hypoxia in pancreatic tumor xenografts and clinical pancreatic adenocarcinomas. Furthermore, we found increased CCN2 staining in clinical pancreatic tumor tissue relative to stromal cells surrounding the tumor, supporting our assertion that tumor cell-derived CCN2 is important for pancreatic tumor growth. Taken together, these data improve our understanding of the mechanisms responsible for pancreatic tumor growth and progression, and also indicate that CCN2 produced by tumor cells represents a viable therapeutic target for the treatment of pancreatic cancer.

    View details for DOI 10.1158/0008-5472.CAN-08-0987

    View details for Web of Science ID 000263048700010

    View details for PubMedID 19179545

    View details for PubMedCentralID PMC2747032

  • Gemcitabine chemotherapy and single-fraction stereotactic body radiotherapy for locally advanced pancreatic cancer INTERNATIONAL JOURNAL OF RADIATION ONCOLOGY BIOLOGY PHYSICS Schellenberg, D., Goodman, K. A., Lee, F., Chang, S., Kuo, T., Ford, J. M., Fisher, G. A., Quon, A., Desser, T. S., Norton, J., Greco, R., Yang, G. P., Koong, A. C. 2008; 72 (3): 678-686


    Fractionated radiotherapy and chemotherapy for locally advanced pancreatic cancer achieves only modest local control. This prospective trial evaluated the efficacy of a single fraction of 25 Gy stereotactic body radiotherapy (SBRT) delivered between Cycle 1 and 2 of gemcitabine chemotherapy.A total of 16 patients with locally advanced, nonmetastatic, pancreatic adenocarcinoma received gemcitabine with SBRT delivered 2 weeks after completion of the first cycle. Gemcitabine was resumed 2 weeks after SBRT and was continued until progression or dose-limiting toxicity. The gross tumor volume, with a 2-3-mm margin, was treated in a single 25-Gy fraction by Cyberknife. Patients were evaluated at 4-6 weeks, 10-12 weeks, and every 3 months after SBRT.All 16 patients completed SBRT. A median of four cycles (range one to nine) of chemotherapy was delivered. Three patients (19%) developed local disease progression at 14, 16, and 21 months after SBRT. The median survival was 11.4 months, with 50% of patients alive at 1 year. Patients with normal carbohydrate antigen (CA)19-9 levels either at diagnosis or after Cyberknife SBRT had longer survival (p <0.01). Acute gastrointestinal toxicity was mild, with 2 cases of Grade 2 (13%) and 1 of Grade 3 (6%) toxicity. Late gastrointestinal toxicity was more common, with five ulcers (Grade 2), one duodenal stenosis (Grade 3), and one duodenal perforation (Grade 4). A trend toward increased duodenal volumes radiated was observed in those experiencing late effects (p = 0.13).SBRT with gemcitabine resulted in comparable survival to conventional chemoradiotherapy and good local control. However, the rate of duodenal ulcer development was significant.

    View details for DOI 10.1016/j.ijrobp.2008.01.051

    View details for Web of Science ID 000259894300008

    View details for PubMedID 18395362

  • Increased rate of hair regrowth in mice with constitutive overexpression of Del 1 JOURNAL OF SURGICAL RESEARCH Hsu, G. P., Mathy, J. A., Wang, Z., Xia, W., Sakamoto, G., Kundu, R., Longaker, M. T., Quertermous, T., Yang, G. P. 2008; 146 (1): 73-80


    Developmental endothelial locus (Del)1 is a secreted extracellular matrix-associated protein that stimulates angiogenesis through integrin binding and is implicated in vasculogenesis. We hypothesized that increased expression of an angiogenic factor would lead to enhanced wound healing.Transgenic mice had Del1 cloned behind a keratin 14 promoter (K14-Del1) to drive constitutive expression in basal keratinocytes. Transgenic animals and wild-type litter mates underwent excisional wounding or depilation, and tissues were harvested at various time points. Wound healing and hair regrowth were assessed by photography, histology, and immunohistochemistry. For injection experiments, purified Del1 protein was injected in the flanks of wild-type mice with carrier on the contralateral flank as a control. Del1 expression during hair development was performed using transgenic mice with a LacZ cassette introduced downstream from the native promoter.K14-Del1 animals appeared normal and healed excisional wounds normally but demonstrated an increased rate of hair regrowth after wound healing. Using depilation experiments to specifically address hair follicle growth, we found increased hair regrowth was independent of wounding. This was confirmed by injection of purified Del1 protein. During normal hair anagenesis, Del1 is expressed in the root of the hair follicle.Constitutive expression of Del1 in skin does not affect skin vascularity or improve wound healing. Surprisingly, we found the primary effect of constitutive Del1 expression in the basal keratinocytes was increased hair growth following induction of anagenesis. During normal hair anagenesis, we see expression of Del1 in the root of the hair follicle suggesting it may function there to stimulate hair growth.

    View details for DOI 10.1016/j.jss.2007.02.024

    View details for Web of Science ID 000254798700011

    View details for PubMedID 17764695

  • Current progress in keloid research and treatment JOURNAL OF THE AMERICAN COLLEGE OF SURGEONS Butler, P. D., Longaker, M. T., Yang, G. P. 2008; 206 (4): 731-741
  • Use of organotypic coculture to study keloid biology 17th Annual Meeting of the Society-for-Black-Academic-Surgeons Butler, P. D., Ly, D. P., Longaker, M. T., Yang, G. P. EXCERPTA MEDICA INC-ELSEVIER SCIENCE INC. 2008: 144–48


    Keloids are pathologic scars afflicting a large segment of our population and for which there is no definitive therapy. The lack of an animal model for keloid formation has hampered study. We developed an in vitro organotypic skin model to simulate normal keloid biology, which may allow us to study keloid formation without an animal model.Normal (NFs) and keloid (KFs) human fibroblasts were cultured in a collagen matrix to create a 3-dimensional dermal structure. Normal human keratinocytes (NKs) were cultured as a second layer on top and exposed to an air-fluid interface to allow differentiation into a mature keratinocyte layer. The organotypic skin was maintained for 28 days in Dulbecco's modified eagle medium with 10% fetal calf serum. Samples were collected, processed, sectioned, stained with hematoxylin and eosin, and then measured for qualitative analysis. alpha-smooth-muscle actin was also evaluated by immunoblotting.KF/NK organotypic skin showed increased collagen deposition, based on significantly denser collagen staining, with increased dermal thickness compared with NF/NK organotypic skin. We saw increased contracture in the KF/NK construct, and this correlated with increased organization of alpha-smooth-muscle actin fibers in the dermal layer of KF/NK organotypic skin compared with NF/NK skin.We have shown that coculture of KFs with keloid keratinocytes leads to an increased collagen production and dermal contracture compared with NFs and NKs, consistent with known keloid behavior. Given the lack of an animal model, we believe that organotypic skin culture can serve as a surrogate to study keloid formation.

    View details for DOI 10.1016/j.amjsurg.2007.10.003

    View details for Web of Science ID 000252598400002

    View details for PubMedID 18070722

  • Increased CCN2 transcription in keloid fibroblasts requires cooperativity between AP-1 and SMAD binding sites ANNALS OF SURGERY Xia, W., Kong, W., Wang, Z., Phan, T., Lim, I. J., Longaker, M. T., Yang, G. P. 2007; 246 (5): 886-895


    We examined the transcriptional response to serum stimulation as an in vitro model of wound healing in keloid fibroblasts to identify molecular mechanisms leading to their aberrant growth.Keloids are proliferative dermal growths representing a pathologic wound healing response. Although several groups have shown increased expression of profibrotic factors in keloids, there is little known about why they are expressed at higher levels than normal.Fibroblasts derived from keloids and normal scar were subjected to serum stimulation as an in vitro model to mimic a component of the wound microenvironment to examine differential gene expression in keloid derived fibroblasts versus normal human fibroblasts. A promoter analysis was performed to identify specific enhancers involved in mediating the differential response of connective tissue growth factor (CTGF, CCN2). Point mutations in the enhancers were performed to confirm their role. Finally, we examined activation of transcription factors known to bind the targeted enhancers.Transcription of CCN2 after serum stimulation was significantly higher in keloid versus normal fibroblasts. Promoter analysis demonstrates the fragment from -625/-140 conferred increased serum responsiveness. Mutational analysis showed an AP-1 and SMAD binding site were both necessary for serum responsiveness. Preventing activation of either transcriptional complex will block CCN2 transcription. Additional experiments suggest that a single complex that includes components of the AP-1 and SMAD binding complexes is responsible for transactivation in response to serum. The key difference between keloid and normal fibroblasts appears to be the degree of activation of c-Jun.We suggest that altered responsiveness to cellular stress, based upon current data using serum stimulation and past data on response to mechanical strain, is a key defect leading to keloid formation.

    View details for DOI 10.1097/SLA.0b013e318070d54f

    View details for Web of Science ID 000250773400028

    View details for PubMedID 17968183

  • Treatment of oesophageal ulcerations using endoscopic transplantation of tissue-engineered autologous oral mucosal epithelial cell sheets in a canine model GUT Yang, G. P., Soetikno, R. M. 2007; 56 (3): 313-314

    View details for DOI 10.1136/gut.2006.100073

    View details for Web of Science ID 000244714700001

    View details for PubMedID 17339239

  • Stereotactic body radiotherapy for unresectable pancreatic cancer 38th San Francisco Radiation Oncology Conference Chang, S. T., Goodman, K. A., Yang, G. R., Koong, A. C. KARGER. 2007: 386–394


    Pancreatic cancer is a devastating disease with few effective treatment modalities. Recent technological advances have made possible the delivery of single-fraction stereotactic body radiotherapy (SBRT) to patients with locally advanced pancreatic tumors. This paper presents experience at Stanford University with SBRT for patients with unresectable pancreatic cancer. Pancreatic tumors of up to 100 cm3 could be treated. Patients achieved greater than 90% local control for the remainder of their lives. Currently, the standard dose for pancreatic tumors treated at this institution is 25 Gy given in a single fraction. Four-dimensional CT and PET scans have been essential for optimal treatment planning. PET-CT scanning may be a more effective method for evaluating tumor response than conventional CT scanning. Adjuvant systemic therapies could be administered in coordination with SBRT. SBRT is an effective method of treating patients resulting in excellent local control. Current research is aimed at defining the optimal method of combining this treatment with other cancer therapies.

    View details for Web of Science ID 000248596600023

    View details for PubMedID 17641521

  • Differential transcriptional responses of keloid and normal keratinocytes to serum stimulation JOURNAL OF SURGICAL RESEARCH Xia, W., Phan, T., Lim, I. J., Longaker, M. T., Yang, G. P. 2006; 135 (1): 156-163


    Keloids are benign tumors that occur only in response to injury, for which there is no effective treatment. We demonstrated previously that keloid keratinocytes (KKs) promote fibroblast proliferation more than normal keratinocytes (NKs) and that transforming growth factor (TGF)-beta is a component of that signal. We used the transcriptional response to serum stimulation to examine how TGF-beta expression is stimulated in KKs.Quiescent KKs and NKs were stimulated using serum; harvested using RNA at 0, 1, 6, 12, and 24 h; and analyzed using quantitative real-time polymerase chain reaction. TGF-beta activity in the conditioned medium was measured with an MLEC/PAI-luciferase assay. Inhibition of ERK1/2, p38 kinase, and JNK pathways was performed with PD98059, SB203580, and SP600125, respectively.Increased transcription of TGF-beta2 occurs within 1 h of serum stimulation in KKs but not in NKs. In contrast, TGF-beta3 transcription was suppressed in KKs compared with NKs. No significant differences were observed in the transcriptional response of TGF-beta1. Increased TGF-beta2 mRNA correlated with increased TGF-beta biological activity in the conditioned medium. Inhibition of the ERK, p38 kinase or JNK signal transduction pathways blocked the transcriptional up-regulation of TGF-beta2, TbetaR1, and TbetaR2 in KKs.KKs produce more TGF-beta2 mRNA than NKs in response to serum stimulation, resulting in increased TGF-beta activity in conditioned medium. Combining these results with our previous data lead us to propose a model of keloid formation characterized by an exaggerated response to cellular stress and abnormal epithelial-mesenchymal signaling promoting keloid formation.

    View details for DOI 10.1016/j.jss.2006.01.031

    View details for Web of Science ID 000240203500023

    View details for PubMedID 16564547

  • Functions of vitamin D, retinoic acid, and dexamethasone in mouse adipose-derived mesenchymal cells TISSUE ENGINEERING Malladi, P., Xu, Y., Yang, G. P., Longaker, M. T. 2006; 12 (7): 2031-2040


    Adipose-derived mesenchymal cells (AMCs) offer great promise for tissue engineering of bone. Previously, 1,25-dihydroxyvitamin D3, retinoic acid (RA), and dexamethasone had been shown to promote osteogenesis in bone marrow-derived mesenchymal cells (BMSCs). To study the osteogenic characteristics of mouse AMCs, we applied these 3 hormones alone and in combination to the AMCs and examined markers of osteogenic differentiation. Interestingly, vitamin D and RA demonstrated a consistent, dose-dependent enhancement of osteogenesis and upregulated osteoblast specific markers including osteopontin and osteocalcin. However, in AMCs, dexamethasone clearly inhibited osteogenic differentiation in a dose dependent fashion and greatly increased the adipogenic marker peroxisome proliferator activated receptor gamma (PPAgamma). In summary, we show in vitro that vitamin D and RA are potential candidates to serve as enhancers of osteogenesis of AMCs and may be incorporated into future cell-based strategies for bone tissue engineering.

    View details for Web of Science ID 000239571800029

    View details for PubMedID 16889531

  • Connective tissue growth factor-specific monoclonal antibody therapy inhibits pancreatic tumor growth and metastasis CANCER RESEARCH Dornhoefer, N., Spong, S., Bennewith, K., Salim, A., Klaus, S., Kambham, N., Wong, C., Kaper, F., Sutphin, P., Nacalumi, R., Hoeckel, M., Le, Q., Longaker, M., Yang, G., Koong, A., Giaccia, A. 2006; 66 (11): 5816-5827


    Pancreatic cancer is highly aggressive and refractory to most existing therapies. Past studies have shown that connective tissue growth factor (CTGF) expression is elevated in human pancreatic adenocarcinomas and some pancreatic cancer cell lines. To address whether and how CTGF influences tumor growth, we generated pancreatic tumor cell lines that overexpress different levels of human CTGF. The effect of CTGF overexpression on cell proliferation was measured in vitro in monolayer culture, suspension culture, or soft agar, and in vivo in tumor xenografts. Although there was no effect of CTGF expression on proliferation in two-dimensional cultures, anchorage-independent growth (AIG) was enhanced. The capacity of CTGF to enhance AIG in vitro was linked to enhanced pancreatic tumor growth in vivo when these cells were implanted s.c. in nude mice. Administration of a neutralizing CTGF-specific monoclonal antibody, FG-3019, had no effect on monolayer cell proliferation, but blocked AIG in soft agar. Consistent with this observation, anti-CTGF treatment of mice bearing established CTGF-expressing tumors abrogated CTGF-dependent tumor growth and inhibited lymph node metastases without any toxicity observed in normal tissue. Together, these studies implicate CTGF as a new target in pancreatic cancer and suggest that inhibition of CTGF with a human monoclonal antibody may control primary and metastatic tumor growth.

    View details for DOI 10.1158/0008-5472.CAN-06-0081

    View details for Web of Science ID 000238003100038

    View details for PubMedID 16740721

  • Gene expression programs in response to hypoxia: Cell type specificity and prognostic significance in human cancers PLOS MEDICINE Chi, J. T., Wang, Z., Nuyten, D. S., Rodriguez, E. H., Schaner, M. E., Salim, A., Wang, Y., Kristensen, G. B., Helland, A., Borresen-Dale, A. L., Giaccia, A., Longaker, M. T., Hastie, T., Yang, G. P., Van de Vijver, M. J., Brown, P. O. 2006; 3 (3): 395-409


    Inadequate oxygen (hypoxia) triggers a multifaceted cellular response that has important roles in normal physiology and in many human diseases. A transcription factor, hypoxia-inducible factor (HIF), plays a central role in the hypoxia response; its activity is regulated by the oxygen-dependent degradation of the HIF-1alpha protein. Despite the ubiquity and importance of hypoxia responses, little is known about the variation in the global transcriptional response to hypoxia among different cell types or how this variation might relate to tissue- and cell-specific diseases.We analyzed the temporal changes in global transcript levels in response to hypoxia in primary renal proximal tubule epithelial cells, breast epithelial cells, smooth muscle cells, and endothelial cells with DNA microarrays. The extent of the transcriptional response to hypoxia was greatest in the renal tubule cells. This heightened response was associated with a uniquely high level of HIF-1alpha RNA in renal cells, and it could be diminished by reducing HIF-1alpha expression via RNA interference. A gene-expression signature of the hypoxia response, derived from our studies of cultured mammary and renal tubular epithelial cells, showed coordinated variation in several human cancers, and was a strong predictor of clinical outcomes in breast and ovarian cancers. In an analysis of a large, published gene-expression dataset from breast cancers, we found that the prognostic information in the hypoxia signature was virtually independent of that provided by the previously reported wound signature and more predictive of outcomes than any of the clinical parameters in current use.The transcriptional response to hypoxia varies among human cells. Some of this variation is traceable to variation in expression of the HIF1A gene. A gene-expression signature of the cellular response to hypoxia is associated with a significantly poorer prognosis in breast and ovarian cancer.

    View details for DOI 10.1371/journal.pmed.0030047

    View details for Web of Science ID 000236897500020

    View details for PubMedID 16417408

  • P38 MAP kinase mediates transforming growth factor-beta 2 transcription in human keloid fibroblasts AMERICAN JOURNAL OF PHYSIOLOGY-REGULATORY INTEGRATIVE AND COMPARATIVE PHYSIOLOGY Xia, W., Longaker, M. T., Yang, G. P. 2006; 290 (3): R501-R508


    Keloids are abnormal fibrous growths of the dermis that develop only in response to wounding and represent a form of benign skin tumor. Previous studies have shown increased protein levels of TGF-beta in keloid tissue, suggesting a strong association with keloid formation leading us to examine mechanisms for why it is more highly expressed in keloids. Here, we use serum stimulation as an in vitro model to mimic a component of the wound microenvironment and examine differential gene expression in keloid human fibroblasts (KFs) vs. normal human fibroblasts (NFs). Transcription of TGF-beta2 was rapid and peaked between 1 and 6 h after serum stimulation in KFs vs. NFs. We confirmed increased TGF-beta activity in the conditioned medium from KFs, but not NFs. Inhibition of second messenger signaling pathways demonstrated that only the p38 MAPK inhibitor SB-203580 could block upregulation of TGF-beta2 following serum stimulation in KFs. Immunoblotting demonstrated that p38 MAPK was phosphorylated within 15 min and was maintained at a high level in KFs but not in NFs. The transcription factors activating transcription factor-2 and Elk-1 are activated by p38 MAPK, and also showed rapid and prolonged phosphorylation kinetics in KFs but not in NFs. In conclusion, increased TGF-beta2 transcription in response to serum stimulation in KFs appears to be mediated by the p38 MAPK pathway. This suggests the mechanism of keloid pathogenesis may be due in part to an inherent difference in how the fibroblasts respond to wounding.

    View details for DOI 10.1152/ajpregu.00472.2005

    View details for Web of Science ID 000235210300003

    View details for PubMedID 16467496

  • Increased transcriptional response to mechanical strain in keloid fibroblasts due to increased focal adhesion complex formation JOURNAL OF CELLULAR PHYSIOLOGY Wang, Z., Fong, K. D., Phan, T. T., Lim, I. J., Longaker, M. T., Yang, G. P. 2006; 206 (2): 510-517


    Clinicians have observed that keloids preferentially form in body areas subject to increased skin tension. We hypothesized a difference exists in the transcriptional response of keloid fibroblasts to mechanical strain compared with normal fibroblasts. Normal and keloid fibroblasts were seeded in a device calibrated to deliver a known level of equibiaxial strain. We examined the transcriptional response of TGF-beta isoforms and collagen Ialpha, genes differentially expressed in keloids. Keloid fibroblasts produced more mRNA for TGF-beta1, TGF-beta2, and collagen Ialpha after mechanical strain compared to normals, and this was correlated with protein production. Inhibiting the major mechanical signal transduction pathway with the ERK inhibitor, U0126, blocked upregulation of gene expression. In addition, keloid fibroblasts formed more focal adhesion complexes as measured by immunofluorescence for focal adhesion kinase, integrin beta1, and vinculin. Finally, there is increased activation of focal adhesion kinase when we detected the phosphorylated form of focal adhesion kinase with immunofluorescence and immunoblotting. In summary, keloid fibroblasts have an exaggerated response to mechanical strain compared to normal fibroblasts leading to increased production of pro-fibrotic growth factors. This may be one molecular mechanism for the development of keloids.

    View details for DOI 10.1002/jcp.20486

    View details for Web of Science ID 000234458300028

    View details for PubMedID 16155910

  • Phase II study to assess the efficacy of conventionally fractionated radiotherapy followed by a stereotactic radiosurgery boost in patients with locally advanced pancreatic cancer INTERNATIONAL JOURNAL OF RADIATION ONCOLOGY BIOLOGY PHYSICS Koong, A. C., Christofferson, E., Le, Q. T., Goodman, K. A., Ho, A., Kuo, T., Ford, J. M., Fisher, G. A., Greco, R., Norton, J., Yang, G. P. 2005; 63 (2): 320-323


    To determine the efficacy of concurrent 5-fluorouracil (5-FU) and intensity-modulated radiotherapy (IMRT) followed by body stereotactic radiosurgery (SRS) in patients with locally advanced pancreatic cancer.In this prospective study, all patients (19) had pathologically confirmed adenocarcinoma and were uniformly staged. Our treatment protocol consisted of 45 Gy IMRT with concurrent 5-FU followed by a 25 Gy SRS boost to the primary tumor.Sixteen patients completed the planned therapy. Two patients experienced Grade 3 toxicity (none had more than Grade 3 toxicity). Fifteen of these 16 patients were free from local progression until death. Median overall survival was 33 weeks.Concurrent IMRT and 5-FU followed by SRS in patients with locally advanced pancreatic cancer results in excellent local control, but does not improve overall survival and is associated with more toxicity than SRS, alone.

    View details for DOI 10.1016/j.ijrobp.2005.07.002

    View details for Web of Science ID 000232083700002

    View details for PubMedID 16168826

  • Complex epithelial-mesenchymal interactions modulate transforming growth factor-beta expression in keloid-derived cells WOUND REPAIR AND REGENERATION Xia, W., Phan, T. T., Lim, I. J., Longaker, M. T., Yang, G. P. 2004; 12 (5): 546-556


    Keloids are proliferative dermal growths representing a pathologic wound healing response. We have previously demonstrated that coculture of fibroblasts derived from either keloid or normal skin have an elevated proliferation rate when cocultured with keloid-derived keratinocytes vs. normal keratinocytes. In these studies, we examined the contribution of transforming growth factor-beta (TGF-beta) to this phenomenon using a two-chamber coculture system. Fibroblast proliferation in coculture was slower with the addition of a pan-TGF-beta neutralizing antibody. Keloid keratinocytes in coculture expressed more TGF-beta1, -beta3, and TGF-beta receptor 1 than normal keratinocytes. Keloid fibroblasts cocultured with keloid keratinocytes expressed more mRNA for TGF-beta1, -beta2, TGF-beta receptor 1, and Smad2. Keloid fibroblasts also produced more type I collagen, connective tissue growth factor, and insulin-like growth factor-II/mannose-6-phosphate receptor when cocultured with keloid keratinocytes vs. normal keratinocytes. Levels of total and activated TGF-beta activity increased when fibroblasts were cocultured with keratinocytes, correlating with the changes in transcriptional activity of TGF-beta. In conclusion, we find a complex paracrine interaction regulates TGF-beta mRNA expression and activation between keratinocytes and fibroblasts. These data suggest that keloid pathogenesis may result from both an increased TGF-beta production and activation by the keloid keratinocyte, and elevated TGF-beta expression, utilization, and signaling in keloid fibroblasts.

    View details for Web of Science ID 000224025400007

    View details for PubMedID 15453837

  • Phase I study of stereotactic radiosurgery in patients with locally advanced pancreatic cancer INTERNATIONAL JOURNAL OF RADIATION ONCOLOGY BIOLOGY PHYSICS Koong, A. C., Le, Q. T., Ho, A., Fong, B., Fisher, G., Cho, C., Ford, J., Poen, J., Gibbs, I. C., Mehta, V. K., Kee, S., Trueblood, W., Yang, G., Bastidas, J. A. 2004; 58 (4): 1017-1021


    To determine the feasibility and toxicity of delivering stereotactic radiosurgery to patients with locally advanced pancreatic cancer.Patients with Eastern Cooperative Oncology Group performance status < or=2 and locally advanced pancreatic cancer were enrolled on this Phase I dose escalation study. Patients received a single fraction of radiosurgery consisting of either 15 Gy, 20 Gy, or 25 Gy to the primary tumor. Acute gastrointestinal toxicity was scored according to the Radiation Therapy Oncology Group criteria. Response to treatment was determined by serial high-resolution computed tomography scanning.Fifteen patients were treated at 3 dose levels (3 patients received 15 Gy, 5 patients received 20 Gy, and 7 patients received 25 Gy). At these doses, no Grade 3 or higher acute gastrointestinal toxicity was observed. This trial was stopped before any dose-limiting toxicity was reached, because the clinical objective of local control was achieved in all 6 evaluable patients treated at 25 Gy.It is feasible to deliver stereotactic radiosurgery to patients with locally advanced pancreatic cancer. The recommended dose to achieve local control without significant acute gastrointestinal toxicity is 25 Gy.

    View details for DOI 10.1016/j.ijrobp.2003.11.004

    View details for Web of Science ID 000220084200001

    View details for PubMedID 15001240

  • From scarless fetal wounds to keloids: Molecular studies in wound healing WOUND REPAIR AND REGENERATION Yang, G. P., Lim, I. J., Phan, T. T., Lorenz, H. P., Longaker, M. T. 2003; 11 (6): 411-418


    Surgical researchers were among the first to describe the different phases of wound healing and the events in tissue repair and regeneration that were taking place during each phase. The understanding of these events has been significantly enhanced in recent years by modern techniques in molecular and cellular biology. In this article, we discuss new findings in scarless fetal repair, angiogenesis in wound healing, and keloid pathogenesis. This serves to highlight the advances that have been made and also how much remains to be understood.

    View details for Web of Science ID 000186779200006

    View details for PubMedID 14617279

  • Tissue engineering and regenerative medicine CLINICS IN PLASTIC SURGERY Jenkins, D. D., Yang, G. P., Lorenz, H. P., Longaker, M. T., Sylvester, K. G. 2003; 30 (4): 581-?


    Regenerative medicine is evolving toward a powerful new paradigm of functional restoration. With the ethical use of gene therapy or through the manipulation of autologous tissues, improved tissue replacements may soon be available. The promise of engineered whole organs, although fraught with technical hurdles, remains on the horizon. As these advances occur, physicians and surgeons of the twenty-first century will possess ever more powerful tools to restore form and function.

    View details for DOI 10.1016/S0094-1298(03)00076-2

    View details for Web of Science ID 000186313400011

    View details for PubMedID 14621306

  • FGF-2 stimulation affects calvarial osteoblast biology: Quantitative analysis of nine genes important for cranial suture biology by real-time reverse transcription polymerase chain reaction PLASTIC AND RECONSTRUCTIVE SURGERY Mathy, J. A., Lenton, K., Nacamuli, R. P., Fong, K. D., Song, H. M., Fang, T. D., Yang, G. P., Longaker, M. T. 2003; 112 (2): 528-539


    Appropriately timed closure of the cranial sutures is a critical factor in normal postnatal morphogenesis of the cranial vault. Suture patency is necessary to permit rapid neonatal expansion of the cerebral hemispheres, and later ossification is important for bony protection of the cerebrum. Premature suture ossification (craniosynostosis) leads to myriad adverse functional and developmental consequences. Several murine studies have implicated dura-derived fibroblast growth factor-2 (FGF-2) paracrine signaling as a critical factor promoting physiologic posterior frontal suture fusion. In this study, the authors used real-time reverse transcription polymerase chain reaction (RT-PCR) to study an in vitro system that models the in vivo stimulation of suture calvarial osteoblasts by dura-derived FGF-2. The authors advocate real-time RT-PCR as a powerful and rapid technique that offers advantages in the highly sensitive, specific, and reproducible analyses of nine genes known to be important in cranial suture biology. The genes studied were growth factors [FGF-2, transforming growth factor (TGF)-beta 1, TGF-beta 2, and TGF-beta 3], growth factor receptors (FGF-R1, FGF-R2, TGF-beta RI, and TGF-beta RII), and a marker of osteoblast differentiation (Co1-I alpha I). These analyses provide a "snapshot" of several important genes involved in suture fusion that is more inclusive and quantitative than that which has been previously reported.

    View details for DOI 10.1097/01.PRS.0000070729.05978.BB

    View details for Web of Science ID 000184532700020

    View details for PubMedID 12900611

  • A spike in parathyroid hormone during neck exploration may cause a false-negative intraoperative assay result ARCHIVES OF SURGERY Yang, G. P., LEVINE, S., Weigel, R. J. 2001; 136 (8): 945-949


    We hypothesize that false-negative results using the rapid intraoperative parathyroid hormone (IOPTH) assay can be caused by spikes in the level of parathyroid hormone that occur during mobilization of the adenoma.Retrospective analysis of a case series.University tertiary care center.Ten consecutive patients with primary hyperparathyroidism.All patients underwent neck exploration with IOPTH monitoring. Using a sampling protocol described in the literature, IOPTH values were checked at the time of incision, during mobilization of the adenoma, and 10 minutes after resection of the adenoma.Patients were evaluated for adequate parathyroid tissue excision as determined by IOPTH levels and examination of ipsilateral glands. All patients had normal serum calcium values documented postoperatively. Parathyroid hormone half-life was calculated assuming first-order kinetic decay.Nine patients had an appropriate decline in IOPTH with a mean +/- SD parathyroid hormone half-life of 3.9 +/- 1.08 minutes. Mobilization of the adenoma resulted in a spike in the IOPTH value, with 1 patient's value increasing from a baseline of 95.5 pg/mL (10.1 pmol/L) to 751 pg/mL (79.1 pmol/L). Another patient who was confirmed to have a solitary adenoma had a false-negative postexcision value. A spike in IOPTH that occurred during neck dissection was not detected by the sampling protocol and explains the false-negative value. A literature review revealed that most protocols check baseline values early in the operation and are at risk for false-negative results due to a spike from mobilization of the adenoma.These data demonstrate that false-negative IOPTH assay findings can result from a spike in parathyroid hormone level during exploration, which may go unrecognized if baseline values are measured during the early stages of mobilization of the adenoma. We have altered our assay protocol and have begun measuring IOPTH at the time of neck incision, at the time the adenoma is completely removed (time zero [t(0)]), and 10 minutes after excision.

    View details for Web of Science ID 000170247100025

    View details for PubMedID 11485536

  • Genomic structure of the promoters of the human estrogen receptor-alpha gene demonstrate changes in chromatin structure induced by AP2 gamma JOURNAL OF BIOLOGICAL CHEMISTRY Schuur, E. R., McPherson, L. A., Yang, G. P., Weigel, R. J. 2001; 276 (18): 15519-15526


    Expression of human estrogen receptor-alpha (ERalpha) involves the activity from several promoters that give rise to alternate untranslated 5' exons. However, the genomic locations of the alternate 5' exons have not been reported previously. We have developed a contig map of the human ERalpha gene that includes all of the known alternate 5' exons. By using S1 nuclease and 5'- rapid amplification of cDNA ends, the cap sites for the alternate ERalpha transcripts E and H were identified. DNase I-hypersensitive sites specific to ERalpha-positive cells were associated with each of the cap sites. A DNase I-hypersensitive site, HS1, was localized to binding sites for AP2 in the untranslated region of exon 1 and was invariably present in the chromatin structure of ERalpha-positive cells. Overexpression of AP2gamma in human mammary epithelial cells generated the HS1-hypersensitive site. The ERalpha promoter was induced by AP2gamma in mammary epithelial cells, and trans-activation was dependent upon the region of the promoter containing the HS1 site. These results demonstrate that AP2gamma trans-activates the ERalpha gene in hormone-responsive tumors by inducing changes in the chromatin structure of the ERalpha promoter. These data are further evidence for a critical role for AP2 in the oncogenesis of hormone-responsive breast cancers.

    View details for Web of Science ID 000168528800131

    View details for PubMedID 11278455

  • Distal emboli as an unusual late complication of a thrombosed arteriovenous hemodialysis graft JOURNAL OF VASCULAR SURGERY Yang, G. P., Lee, W. A., Olcott, C. 2000; 32 (6): 1229-1231


    The creation of an arteriovenous fistula for long-term hemodialysis access is one of the most commonly performed procedures in vascular and transplantation surgery. Prosthetic conduits are frequently prone to failure within their first year of construction, and after one or two revisions, they are left in their thrombosed state as permanent subcutaneous foreign bodies in the extremities. Conventional teaching has regarded these chronically thrombosed grafts to have a benign natural history, and their removal has been considered unnecessary. We describe an unusual late complication of distal thromboemboli from a chronically occluded arteriovenous graft that was implanted 10 years before and appeared as acute hand ischemia.

    View details for DOI 10.1067/mva.2000.109741

    View details for Web of Science ID 000165847400034

    View details for PubMedID 11107099

  • Combining SSH and cDNA microarrays for rapid identification of differentially expressed genes NUCLEIC ACIDS RESEARCH Yang, G. P., Ross, D. T., Kuang, W. W., Brown, P. O., Weigel, R. J. 1999; 27 (6): 1517-1523


    Comparing patterns of gene expression in cell lines and tissues has important applications in a variety of biological systems. In this study we have examined whether the emerging technology of cDNA microarrays will allow a high throughput analysis of expression of cDNA clones generated by suppression subtractive hybridization (SSH). A set of cDNA clones including 332 SSH inserts amplified by PCR was arrayed using robotic printing. The cDNA arrays were hybridized with fluorescent labeled probes prepared from RNA from ER-positive (MCF7 and T47D) and ER-negative (MDA-MB-231 and HBL-100) breast cancer cell lines. Ten clones were identified that were over-expressed by at least a factor of five in the ER-positive cell lines. Northern blot analysis confirmed over-expression of these 10 cDNAs. Sequence analysis identified four of these clones as cytokeratin 19, GATA-3, CD24 and glutathione-S-transferase mu-3. Of the remaining six cDNA clones, four clones matched EST sequences from two different genes and two clones were novel sequences. Flow cytometry and immunofluorescence confirmed that CD24 protein was over-expressed in the ER-positive cell lines. We conclude that SSH and microarray technology can be successfully applied to identify differentially expressed genes. This approach allowed the identification of differentially expressed genes without the need to obtain previously cloned cDNAs.

    View details for Web of Science ID 000079256800016

    View details for PubMedID 10037815