Michael T Longaker

Stanford Medicine, Stanford, California, United States

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Publications (556)1854.19 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Fat graft volume retention remains highly unpredictable, but addition of adipose-derived stromal cells (ASCs) to fat grafts has been shown to improve retention. The present study aimed to investigate the mechanisms involved in ASC enhancement of fat grafting. ASCs isolated from human lipoaspirate were labeled with green fluorescent protein (GFP) and luciferase. Fat grafts enhanced with ASCs were injected into the scalp and bioluminescent imaging was performed to follow retention of ASCs within the fat graft. Fat grafts were also explanted at days 1, 5, and 10 post-grafting for ASC extraction and single-cell gene analysis. Finally, CD31 immunohistochemical staining was performed on fat grafts enriched with ASCs. Bioluminescent imaging demonstrated significant reduction in luciferase+ ASCs within fat grafts at five days post-grafting. A similar reduction in viable GFP+ ASCs retrieved from explanted grafts was also noted. Single cell analysis revealed expression of multiple genes/markers related to cell survival and angiogenesis including BMPR2, CD90, CD105, FGF2, CD248, TGFß1, and VEGFA. Genes involved in adipogenesis were not expressed by ASCs. Finally, CD31 staining revealed significantly higher vascular density in fat grafts explanted at day 10 post-grafting. Although ASC survival in the hypoxic graft environment decreases significantly over time, these cells provide multiple angiogenic growth factors. Therefore, improved fat graft volume retention with ASC enrichment may be due to improved graft vascularization.
    Plastic and reconstructive surgery. 12/2014;
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    ABSTRACT: To investigate how epithelial mechanotransduction pathways impact wound repair.
    Annals of surgery. 12/2014; 260(6):1138-46.
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    ABSTRACT: Mesenchymal stem cells (MSCs) show promise for cellular therapy and regenerative medicine. Human adipose-derived stem cells (hASCs) represent an attractive source of seed cells in bone regeneration. How to effectively improve osteogenic differentiation of hASCs in the bone tissue engineering has become a very important question with profound translational implications. Numerous regulatory pathways dominate osteogenic differentiation of hASCs involving transcriptional factors and signaling molecules. However, how these factors combine with each other to regulate hASCs osteogenic differentiation still remains to be illustrated. The highly conserved developmental proteins TWIST play key roles for transcriptional regulation in mesenchymal cell lineages. This study investigates TWIST1 function in hASCs osteogenesis. Our results show that TWIST1 shRNA silencing increased the osteogenic potential of hASCs in vitro and their skeletal regenerative ability when applied in vivo. We demonstrate that the increased osteogenic capacity observed with TWIST1 knockdown in hASCs is mediated through endogenous activation of BMP and ERK/FGF signaling leading, in turn, to upregulation of TAZ, a transcriptional modulator of mesenchymal stem cells differentiation along the osteoblast lineage. Inhibition either of BMP or ERK/FGF signaling suppressed TAZ upregulation and the enhanced osteogenesis in shTWIST1 hASCs. Co-silencing of both TWIST1 and TAZ abrogated the effect elicited by TWIST1 knockdown thus, identifying TAZ as a downstream mediator through which TWIST1 knockdown enhanced osteogenic differentiation in hASCs. Our functional study contributes to a better knowledge of molecular mechanisms governing the osteogenic ability of hASCs, and highlights TWIST1 as a potential target to facilitate in vivo bone healing. This article is protected by copyright. All rights reserved. © 2014 AlphaMed Press.
    Stem Cells 11/2014; · 7.70 Impact Factor
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    ABSTRACT: Wnt signaling is a critical regulator of bone development, but the identity and role of the Wnt-producing cells are still unclear. We addressed these questions through in situ hybridization, lineage tracing, and genetic experiments. First, we surveyed the expression of all 19 Wnt genes and Wnt target gene Axin2 in the neonatal mouse bone by in situ hybridization, and demonstrated-to our knowledge for the first time-that Osterix-expressing cells coexpress Wnt and Axin2. To track the behavior and cell fate of Axin2-expressing osteolineage cells, we performed lineage tracing and showed that they sustain bone formation over the long term. Finally, to examine the role of Wnts produced by Osterix-expressing cells, we inhibited Wnt secretion in vivo, and observed inappropriate differentiation, impaired proliferation, and diminished Wnt signaling response. Therefore, Osterix-expressing cells produce their own Wnts that in turn induce Wnt signaling response, thereby regulating their proliferation and differentiation.
    Proceedings of the National Academy of Sciences of the United States of America. 11/2014;
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    ABSTRACT: In the last decade there has been a rapid expansion in clinical trials using mesenchymal stromal cells (MSCs) from a variety of tissues. However, despite similarities in morphology, immunophenotype and differentiation behavior in vitro, MSCs sourced from distinct tissues do not necessarily have equivalent biological properties. We performed a genome-wide methylation, transcription and in vivo evaluation of MSCs from human bone marrow (BM), white adipose tissue, umbilical cord and skin cultured in humanized media. Surprisingly, only BM-derived MSCs spontaneously formed a bone marrow cavity through a vascularized cartilage intermediate in vivo that was progressively replaced by hematopoietic tissue and bone. Only BM-derived MSCs exhibited a chondrogenic transcriptional program with hypomethylation and increased expression of RUNX3, RUNX2, BGLAP, MMP13 and ITGA10 consistent with a latent and primed skeletal developmental potential. The humanized MSC-derived microenvironment permitted homing and maintenance of long-term murine SLAM(+) hematopoietic stem cells (HSCs) as well as human CD34(+)/CD38(-)/CD90(+)/CD45RA(+) HSCs after cord blood transplantation. These studies underscore the profound differences in developmental potential between MSC sources independent of donor age with implications for their clinical use. We also demonstrate a tractable human niche model for studying homing and engraftment of human hematopoietic cells in normal and neoplastic states. Copyright © 2014 American Society of Hematology.
    Blood 11/2014; · 9.78 Impact Factor
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    ABSTRACT: Wounds, both chronic and acute, continue to be a tremendous socioeconomic burden. As such, technologies drawn from many disciplines within science and engineering are constantly being incorporated into innovative wound healing therapies. While many of these therapies are experimental, they have resulted in new insights into the pathophysiology of wound healing, and in turn the development of more specialized treatments for both normal and abnormal wound healing states. Herein, we review some of the emerging technologies that are currently being developed to aid and improve wound healing after cutaneous injury.
    Regenerative medicine. 11/2014; 9(6):817-830.
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    ABSTRACT: Introduction: Diabetes mellitus is a chronic disease associated with altered bone metabolism that leads to complications including nonunion, malunion and delayed union of fractures. The mechanism(s) leading to impaired fracture healing remains to be elucidated. We hypothesize that there is an imbalance betwen bone formation and resorption in diabetic fracture healing, leading to impaired bone healing. Methods: Bone marrow was isolated from femora of diabetic (db/db) and wild type control mice and cultured in RANKL and MCSF-enriched medium. After one week, assays were fixed for TRAP staining. Closed, bicortical femoral fractures were created in age- and gender-matched diabetic (db/db) and wild type mice. Radiography and mechanical testing were utilized to assess fracture healing. Femora and sera were harvested at different timepoints post fracture for histological, transcriptional and translational analysis. The response to fracture injury in diabetic compared to control mice was analyzed using a Luminex multiplex assay to identify changes in circulating cytokines following femoral fracture. Quantitative PCR was performed to analyze differential gene expression of key osteoclastogenic, osteoblastogenic and adipogenic genes. Furthermore, microarray analysis was performed to identify genes that were differentially expressed in diabetic fracture callus compared to wild-type control. Results: Bone marrow from diabetic mice formed significantly higher numbers of osteoclasts in vitro compared to wild type bone marrow (* p<0.05). Osteoclasts formed from diabetic bone marrow were larger in size and had more nuclei per cell than wild type controls (* p<0.05). Diabetic mice showed delayed callus development on radiographic assessment in vivo. The diabetic fracture group were weaker in comparison to the wild-type control on mechanical testing (* p<0.05). Histological analysis of fracture callus showed an increased deposition of adipocytes within the diabetic callus compared to wild-type callus (* p<0.05). Quantitative PCR identified a significant upregulation in transcription of genes contributing to osteoclastogenesis versus osteoblastogenesis (* p<0.05) in diabetic versus wild-type callus. Notably, there was an upregulation of peroxisome proliferator-activated receptor gamma in diabetic callus, which promotes adipocyte differentiation. Microarray analysis identified multiple further genes that were differentially expressed in diabetic callus versus wild-type control. Conclusions: Fracture healing is impaired in our murine model of diabetes. Our findings illustrate an upregulation of genes related to osteoclast and adipocyte function, with a concomitant reduction of osteoblastogenic gene expression in diabetic mice.
    Plastic and reconstructive surgery. 10/2014; 134(4S-1 Suppl):61-62.
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    ABSTRACT: Introduction Ultrasound assisted liposuction (UAL) is gaining popularity in plastic surgery for permitting easier fat harvest while minimizing trauma and blood loss. However, little has been studied concerning the quality of adipose derived stromal cells (ADSCs) obtained with this method. As the role of ADSCs in cell based therapies is growing dramatically, we studied the regenerative abilities of ADSCs harvested by traditional suction assisted liposuction (SAL) versus UAL. Methods Paired lipoaspirate samples obtained via SAL and UAL from healthy patients were analyzed for their ADSCs yield via Fluorescent Assisted Cell Sorting (FACS) using an established progenitor surface marker profile (CD34+CD31-CD45-). Cells sorted by this profile were then compared for their proliferation capacity using an MTT assay and were grown in culture for differentiation toward adipogenic osteogenic, and angiogenic lineages. Gene expression profiles were compared with qPCR. Cell staining was used to compare adipogenic and osteogneic markers. Tissue regenerative abilities were compared employing an established murine wound-healing model by adding 250k ADSCs obtained via SAL or UAL seeded on a hydrogel scaffold to the wounds controlled with hydrogel alone. Results There was no significant differences in ADSC yield, viability or proliferation between UAL and SAL (*p<.05). Equal adipogenic differentiation capability was demonstrated on Oil Red O staining and by the lack of any significantly different expression of PPAR-gamma or LPL at Day 7 of differentiation (*p>.05). Similarly, Alkaline Phosphatase and Alizarin Red staining demonstrated similar osteogenic differentiation capability that coincided with the non-significantly different expression of oseogenic markers Runx-2, Osteopontin and Osteocalcin (*p>.05). There was a significantly accelerated rate of wound healing comparing each of the cell assisted groups versus hydrogel alone (*p<.05) and no significant difference between SAL and UAL groups (*p>.05). Conclusions UAL represents an equivalently viable way to obtain functional ADSCs for cell-based therapies as compared to traditional SAL. ------------------------- [DD1]Did we do that? If no, kick out
    Plastic and reconstructive surgery. 10/2014; 134(4S-1 Suppl):56-57.
  • Geoffrey C Gurtner, Michael T Longaker
    Plastic and reconstructive surgery. 10/2014; 134(4):664e-6e.
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    ABSTRACT: Introduction Plastic Surgery is among the most competitive specialties, but little is known about the characteristics of programs that are most attractive to successful applicants. This study aimed to understand program characteristics that are most influential to students when ranking plastic surgery programs and to identify changes that programs may make to improve and attract the best students. Methods An anonymous, 21-question, multiple choice and open response online survey of newly matched plastic surgery residents in 2011-2012 and 2012-2013 academic years was conducted. Subjects were queried regarding their personal qualifications, application experiences, and motivations for residency program selection. Results A total of 92 out of 245 matched plastic surgery resident responded for a participation rate of 38%. Applicants with Step I scores greater than 245 received significantly more interviews (*p=.001) and ranked likelihood to be happy and resident benefits as significantly less important (*p<.05), but geographic location as significantly more important (*p=.005). Applicants who had published more than 2 manuscripts received significantly more interviews (*p=.001), and they ranked the presence of a strong research infrastructure, program reputation, and overall strength of training as significantly more important (*p<.05), but plastic surgery months as significantly less important (*p<.05). 42% of applicants completed an away rotation at the program which they matched, and these applicants were significantly more likely to match at their number one ranked program (*p=.001). Overall, applicants identified programs where residents appeared extremely happy as the most positive in influencing their ranking (99%), followed by high reported OR case numbers (96%), presence of a faculty mentorship program (89%), and strong research infrastructure (73%). Of all the disciplines in Plastic Surgery tested, newly matched residents expressed that strength in reconstructive surgery excluding breast was the most attractive to them, followed by Pediatric and Craniofacial Surgery, Microsurgery, Hand Surgery, Breast Surgery, Cosmetic Surgery, and finally Burn Surgery. Conclusions Plastic surgery applicants have differing preferences, but some attributes resonate similarly among applicants, and these trends can guide programs for improvement.
    Plastic and reconstructive surgery. 10/2014; 134(4S-1 Suppl):63-64.
  • Journal of the American College of Surgeons 09/2014; 219(3):S82-S83. · 4.50 Impact Factor
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    ABSTRACT: Chronic wounds are a major source of morbidity for patients and represent a significant health burden. Implementing noninvasive techniques that accelerate healing of these wounds would provide great benefit. Ultrasound appears to be an effective modality for the treatment of chronic wounds in humans. MIST Therapy is a noncontact, low-frequency ultrasound treatment delivered through a saline mist. A variety of mechanisms have been proposed to explain the efficacy of ultrasound therapy, but the underlying molecular and cellular pathways impacted by this technique remain unclear. The in vivo effect of noncontact, low-frequency ultrasound was therefore examined in a humanized excisional wound model.
    Plastic &amp Reconstructive Surgery 09/2014; 134(3):402e-411e. · 3.54 Impact Factor
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    ABSTRACT: Conditions such as congenital anomalies, cancers, and trauma can all result in devastating deficits of bone in the craniofacial skeleton. This can lead to significant alteration in function and appearance that may have significant implications for patients. In addition, large bone defects in this area can pose serious clinical dilemmas, which prove difficult to remedy, even with current gold standard surgical treatments. The craniofacial skeleton is complex and serves important functional demands. The necessity to develop new approaches for craniofacial reconstruction arises from the fact that traditional therapeutic modalities, such as autologous bone grafting, present myriad limitations and carry with them the potential for significant complications. While the optimal bone construct for tissue regeneration remains to be elucidated, much progress has been made in the past decade. Advances in tissue engineering have led to innovative scaffold design, complemented by progress in the understanding of stem cell-based therapy and growth factor enhancement of the healing cascade. This review focuses on the role of biomaterials for craniofacial bone engineering, highlighting key advances in scaffold design and development.
    Journal of dental research. 08/2014;
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    ABSTRACT: Following radiation therapy, skin becomes fibrotic and can present a difficult problem for reconstructive surgeons. There is an increasing belief that fat grafting under irradiated skin can reverse the damage caused by radiation. The present study evaluated the effect of fat grafting on irradiated skin, along with fat graft quality and retention rates in irradiated tissue.
    Plastic and reconstructive surgery. 08/2014; 134(2):249-57.
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    ABSTRACT: Effective skin regeneration therapies require a successful interface between progenitor cells and biocompatible delivery systems. We previously demonstrated the efficiency of a biomimetic pullulan-collagen hydrogel scaffold for improving bone marrow-derived mesenchymal stem cell survival within ischemic skin wounds by creating a "stem cell niche" that enhances regenerative cytokine secretion. Adipose-derived mesenchymal stem cells (ASCs) represent an even more appealing source of stem cells because of their abundance and accessibility, and in this study we explored the utility of ASCs for hydrogel-based therapies. To optimize hydrogel cell seeding, a rapid, capillary force-based approach was developed and compared with previously established cell seeding methods. ASC viability and functionality following capillary hydrogel seeding were then analyzed in vitro and in vivo. In these experiments, ASCs were seeded more efficiently by capillary force than by traditional methods and remained viable and functional in this niche for up to 14 days. Additionally, hydrogel seeding of ASCs resulted in the enhanced expression of multiple stemness and angiogenesis-related genes, including Oct4, Vegf, Mcp-1, and Sdf-1. Moving in vivo, hydrogel delivery improved ASC survival, and application of both murine and human ASC-seeded hydrogels to splinted murine wounds resulted in accelerated wound closure and increased vascularity when compared with control wounds treated with unseeded hydrogels. In conclusion, capillary seeding of ASCs within a pullulan-collagen hydrogel bioscaffold provides a convenient and simple way to deliver therapeutic cells to wound environments. Moreover, ASC-seeded constructs display a significant potential to accelerate wound healing that can be easily translated to a clinical setting.
    Stem cells translational medicine. 07/2014;
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    ABSTRACT: Although fat grafting can address many soft-tissue deficits, results remain inconsistent. In this study, the authors compared physical properties of fat following injection using an automated, low-shear device or the modified Coleman technique.
    Plastic and reconstructive surgery. 07/2014; 134(1):39-46.
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    ABSTRACT: The requirement and influence of the peripheral nervous system on tissue replacement in mammalian appendages remain largely undefined. To explore this question, we have performed genetic lineage tracing and clonal analysis of individual cells of mouse hind limb tissues devoid of nerve supply during regeneration of the digit tip, normal maintenance, and cutaneous wound healing. We show that cellular turnover, replacement, and cellular differentiation from presumed tissue stem/progenitor cells within hind limb tissues remain largely intact independent of nerve and nerve-derived factors. However, regenerated digit tips in the absence of nerves displayed patterning defects in bone and nail matrix. These nerve-dependent phenotypes mimic clinical observations of patients with nerve damage resulting from spinal cord injury and are of significant interest for translational medicine aimed at understanding the effects of nerves on etiologies of human injury.
    Proceedings of the National Academy of Sciences of the United States of America. 06/2014;
  • Derrick C Wan, Michael T Longaker
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    ABSTRACT: Cell-lineage tracing has revealed a complex heterogeneity present in postnatal tissue and adult progenitors. Chau et al. (2014) and Long et al. (2014) provide further evidence for this among adipocytes, and their findings underscore the importance of cellular ontogeny not just for development but also for potential treatment of disease.
    Cell metabolism. 06/2014; 19(6):900-901.
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    ABSTRACT: 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.
    Journal of Clinical and Aesthetic Dermatology 06/2014; 7(6):25-32.
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    ABSTRACT: The mechanism and magnitude by which the mammalian kidney generates and maintains its proximal tubules, distal tubules, and collecting ducts remain controversial. Here, we use long-term in vivo genetic lineage tracing and clonal analysis of individual cells from kidneys undergoing development, maintenance, and regeneration. We show that the adult mammalian kidney undergoes continuous tubulogenesis via expansions of fate-restricted clones. Kidneys recovering from damage undergo tubulogenesis through expansions of clones with segment-specific borders, and renal spheres developing in vitro from individual cells maintain distinct, segment-specific fates. Analysis of mice derived by transfer of color-marked embryonic stem cells (ESCs) into uncolored blastocysts demonstrates that nephrons are polyclonal, developing from expansions of singly fated clones. Finally, we show that adult renal clones are derived from Wnt-responsive precursors, and their tracing in vivo generates tubules that are segment specific. Collectively, these analyses demonstrate that fate-restricted precursors functioning as unipotent progenitors continuously maintain and self-preserve the mouse kidney throughout life.
    Cell reports. 05/2014;

Publication Stats

10k Citations
1,854.19 Total Impact Points

Institutions

  • 2002–2014
    • Stanford Medicine
      • • Division of Plastic and Reconstructive Surgery
      • • Adult Plastic Surgery Clinic
      • • Department of Surgery
      Stanford, California, United States
    • Stanford University
      • • Department of Surgery
      • • Division of Pediatric Cardiology
      • • Division of Plastic and Reconstructive Surgery
      Palo Alto, California, United States
    • University of Utah
      • Huntsman Cancer Institute
      Salt Lake City, UT, United States
  • 2013
    • Ruhr-Universität Bochum
      Bochum, North Rhine-Westphalia, Germany
  • 2012–2013
    • Oregon Health and Science University
      • Department of Surgery
      Portland, Oregon, United States
    • Children's Mercy Hospital
      Kansas City, Missouri, United States
    • Duke University Medical Center
      Durham, North Carolina, United States
  • 1998–2012
    • State University of New York Downstate Medical Center
      • Department of Surgery
      Brooklyn, NY, United States
  • 2011
    • University of Virginia
      • Department of Surgery
      Charlottesville, VA, United States
  • 2010
    • University of Texas Southwestern Medical Center
      • Department of Plastic Surgery
      Dallas, TX, United States
  • 2009
    • The Ohio State University
      • Department of Surgery
      Columbus, OH, United States
    • University of Naples Federico II
      Napoli, Campania, Italy
  • 1999–2008
    • University of California, Los Angeles
      • • Department of Surgery
      • • School of Dentistry
      Los Angeles, California, United States
    • University of Connecticut
      • Department of Surgery
      Mansfield City, CT, United States
  • 1998–2008
    • New York University
      • Institute of Reconstructive Plastic Surgery
      New York City, NY, United States
  • 2007
    • King's College London
      Londinium, England, United Kingdom
    • Massachusetts Institute of Technology
      • Department of Mechanical Engineering
      Cambridge, MA, United States
  • 2006
    • Lucile Packard Children’s Hospital at Stanford
      Palo Alto, California, United States
  • 2005
    • Cedars-Sinai Medical Center
      • Cedars Sinai Medical Center
      Los Angeles, CA, United States
  • 2001–2005
    • National University of Singapore
      • Department of Surgery
      Singapore, Singapore
  • 2004
    • University of Nebraska Medical Center
      • Department of Surgery
      Omaha, Nebraska, United States
  • 2002–2004
    • University of Nebraska at Omaha
      • Department of Surgery
      Omaha, NE, United States
    • Singapore General Hospital
      • Department of Plastic Surgery
      Tumasik, Singapore
  • 2003
    • Nova Southeastern University
      • College of Dental Medicine
      Florida, NY, United States
    • University of Minnesota Twin Cities
      • Department of Surgery
      Minneapolis, MN, United States
    • Fourth Military Medical University
      Xi’an, Liaoning, China
  • 2002–2003
    • Brigham and Women's Hospital
      • • Department of Surgery
      • • Division of Plastic Surgery
      Boston, MA, United States
  • 1990–2003
    • University of California, San Francisco
      • Department of Surgery
      San Francisco, CA, United States
  • 2000
    • American Society of Ophthalmic Plastic and Reconstructive Surgery
      New York City, New York, United States
    • Harbor-UCLA Medical Center
      Torrance, California, United States
    • NYU Langone Medical Center
      • Department of Surgery
      New York City, NY, United States
  • 1995–2000
    • CUNY Graduate Center
      New York City, New York, United States