Residency:Stanford University School of Medicine (06/30/2008) CA
Internship:Stanford University School of Medicine (06/30/2002) CA
Medical Education:Stanford University School of Medicine (06/2001) CA
Fellowship:Hospital for Sick Children (06/30/2010) Canada
Fellowship:Lund Strategic Research Center for Stem Cell Biology and Cell Therapy (06/2009)
Independent Studies (7)
- Directed Reading in Neurosurgery
NSUR 299 (Aut, Win, Spr, Sum)
- Early Clinical Experience in Neurosurgery
NSUR 280 (Aut, Win, Spr, Sum)
- Graduate Research
NSUR 399 (Aut, Win, Spr, Sum)
HUMBIO 194 (Win)
- Medical Scholars Research
NSUR 370 (Aut, Win, Spr, Sum)
- Research in Human Biology
HUMBIO 193 (Aut, Win)
- Undergraduate Research
NSUR 199 (Aut, Win, Spr, Sum)
- Directed Reading in Neurosurgery
Multiplex meta-analysis of medulloblastoma expression studies with external controls.
Pacific Symposium on Biocomputing. Pacific Symposium on Biocomputing
We propose and discuss a method for doing gene expression meta-analysis (multiple datasets) across multiplex measurement modalities measuring the expression of many genes simultaneously (e.g. microarrays and RNAseq) using external control samples and a method of heterogeneity detection to identify and filter on comparable gene expression measurements. We demonstrate this approach on publicly available gene expression datasets from samples of medulloblastoma and normal cerebellar tissue and identify some potential new targets in the treatment of medulloblastoma.
View details for PubMedID 24297537
Roles of PINK1, mTORC2, and mitochondria in preserving brain tumor-forming stem cells in a noncanonical Notch signaling pathway.
Genes & development
2013; 27 (24): 2642-2647
The self-renewal versus differentiation choice of Drosophila and mammalian neural stem cells (NSCs) requires Notch (N) signaling. How N regulates NSC behavior is not well understood. Here we show that canonical N signaling cooperates with a noncanonical N signaling pathway to mediate N-directed NSC regulation. In the noncanonical pathway, N interacts with PTEN-induced kinase 1 (PINK1) to influence mitochondrial function, activating mechanistic target of rapamycin complex 2 (mTORC2)/AKT signaling. Importantly, attenuating noncanonical N signaling preferentially impaired the maintenance of Drosophila and human cancer stem cell-like tumor-forming cells. Our results emphasize the importance of mitochondria to N and NSC biology, with important implications for diseases associated with aberrant N signaling.
View details for DOI 10.1101/gad.225169.113
View details for PubMedID 24352421
Primary surgical management by reduction and fixation of unstable hangman's fractures with discoligamentous instability or combined fractures
JOURNAL OF NEUROSURGERY-SPINE
2013; 19 (5): 569-575
Several controversial issues arise in the management of unstable hangman's fractures. Some surgeons perform external reduction and immobilize the patient's neck in a halo vest, while others perform surgical reduction and internal fixation. The nonsurgical treatments with rigid collar or halo vest immobilization present problems, including nonunion, pseudarthrosis, skull fracture, and scalp laceration and may also fail to achieve anatomical realignment of the local C2-3 kyphosis. With recent advances in surgical technique and technology, surgical intervention is increasingly performed as the primary treatment in high cervical fractures. The outcomes of such surgeries are often superior to those of conservative treatment. The authors propose that surgical intervention as a primary management for hangman's fracture may avoid risks inherent in conservative management when severe circumferential discoligamentous instability is present and may reduce the risk of catastrophic results at the fracture site. The purposes of this study were to assess fracture healing following expedient reduction and surgical fixation and to propose a guideline for treatment of unstable hangman's fractures.From April 2006 to December 2011, the authors treated 105 patients with high cervical fractures. This study included 23 (21.9%) of these patients (15 men and 8 women; mean age 46.4 years) with Type II, IIa, and III hangman's fractures according to the Levine and Edwards classification. The patient's age, sex, mechanism of injury, associated injuries, neurological status, and complications were ascertained. The authors retrospectively assessed the clinical outcome (Neck Disability Index), radiological findings (disc height, translation, and angulation), and bony healing.The average follow-up period was 28.9 months (range 12-63.2 months). The overall average Neck Disability Index score at the time of this study was 6.6 ± 2.3. The average duration of hospitalization was 20.3 days, and fusion was achieved in all cases by 14.8 ± 1.6 weeks after surgery, as demonstrated on dynamic radiographs and cervical 3D CT scans. The mean pretreatment translation was 6.9 ± 3.2 mm, and the mean postoperative translation was 1.6 ± 1.8 mm (mean reduction 5.2 ± 3.1 mm). The initial angulation was 4.7° ± 5.3° and the postoperative angulation was 2.5° ± 1.8° (mean reduction 6.1° ± 5.3°). The preoperative and postoperative values for translation and angulation differed significantly (p < 0.05). The overall C2-3 disc height was 6.7 ± 1.2 mm preoperatively, whereas 3 months after surgery it was 6.4 ± 1.1 mm. These values did not differ significantly (p = 0.0963).The authors observed effective reduction and bony healing in cases of unstable hangman's fractures after fixation, and all patients experienced favorable clinical outcomes with neck pain improvement. The protocols allowed for physiological reconstruction of the fractured deformities and avoided external fixation. The authors suggest that posterior reduction and screw fixation should be used as a primary treatment to promote stability of hangman's fracture in the presence of discoligamentous instability or combined fractures.
View details for DOI 10.3171/2013.8.SPINE12948
View details for Web of Science ID 000325956500006
View details for PubMedID 24033304
Usp16 contributes to somatic stem-cell defects in Down's syndrome.
2013; 501 (7467): 380-384
Down's syndrome results from full or partial trisomy of chromosome 21. However, the consequences of the underlying gene-dosage imbalance on adult tissues remain poorly understood. Here we show that in Ts65Dn mice, which are trisomic for 132 genes homologous to genes on human chromosome 21, triplication of Usp16 reduces the self-renewal of haematopoietic stem cells and the expansion of mammary epithelial cells, neural progenitors and fibroblasts. In addition, Usp16 is associated with decreased ubiquitination of Cdkn2a and accelerated senescence in Ts65Dn fibroblasts. Usp16 can remove ubiquitin from histone H2A on lysine 119, a critical mark for the maintenance of multiple somatic tissues. Downregulation of Usp16, either by mutation of a single normal Usp16 allele or by short interfering RNAs, largely rescues all of these defects. Furthermore, in human tissues overexpression of USP16 reduces the expansion of normal fibroblasts and postnatal neural progenitors, whereas downregulation of USP16 partially rescues the proliferation defects of Down's syndrome fibroblasts. Taken together, these results suggest that USP16 has an important role in antagonizing the self-renewal and/or senescence pathways in Down's syndrome and could serve as an attractive target to ameliorate some of the associated pathologies.
View details for DOI 10.1038/nature12530
View details for PubMedID 24025767
Brain Tumor Stem Cell Multipotency Correlates with Nanog Expression and Extent of Passaging in Human Glioblastoma Xenografts
2013; 4 (5): 792-801
Glioblastoma multiforme (GBM) is the most common primary brain tumor, with a median survival of only 15 months. A subpopulation of cells, the brain tumor stem cells (BTSCs), may be responsible for the malignancy of this disease. Xenografts have proven to be a robust model of human BTSCs, but the effects of long-term passaging have yet to be determined. Here we present a study detailing changes in BTSC multipotency, invasive migration, and proliferation after serial passaging of human GBM xenografts. Immunocytochemistry and tumorsphere formation assays demonstrated the presence of BTSCs in both early generation (EG-BTSCs; less than 15 passages) and late generation (LG-BTSCs; more than 24 passages) xenografts. The EG-BTSCs upregulated expression of lineage markers for neurons and oligodendrocytes upon differentiation, indicating multipotency. In contrast, the LG-BTSCs were restricted to an astrocytic differentiation. Quantitative migration and proliferation assays showed that EG-BTSCs are more migratory and proliferative than LG-BTSCs. However, both populations respond similarly to the chemokine SDF-1 by increasing invasive migration. These differences between the EG- and LG-BTSCs were correlated with a significant decrease in nanog expression as determined by qRT-PCR. Mice implanted intracranially with EG-BTSCs showed shorter survival when compared to LG-BTSCs. Moreover, differentiation prior to implantation of EG-BTSCs, but not LG-BTSCs, led to increased survival. Thus, nanog may identify multipotent BTSCs. Furthermore, limited passaging of xenografts preserves these multipotent BTSCs, which may be an essential underlying feature of GBM lethality.
View details for Web of Science ID 000322580000015
View details for PubMedID 23801022
Application of diffusion tensor tractography in pediatric optic pathway glioma Clinical article
JOURNAL OF NEUROSURGERY-PEDIATRICS
2012; 10 (4): 273-280
Magnetic resonance imaging is commonly used in diagnosis and surveillance for optic pathway glioma (OPG). The authors investigated the role of diffusion tensor (DT) tractography in assessing the location of visual pathway fibers in the presence of tumor.Data in 10 children with OPG were acquired using a 3T MRI generalized autocalibrating parallel acquisitions DT-echo planar imaging sequence (25 isotropic directions with a b value of 1000 seconds/mm(2), slice thickness 3 mm). Fiber tractography was performed, with seed regions placed within the optic chiasm and bilateral nerves on the coronal plane, including the tumor and surrounding normal-appearing tissue. Tracking was performed with a curvature threshold of 30°.For prechiasmatic lesions, fibers either stopped abruptly at the tumor or traversed abnormally dilated nerve segments. Similar findings were seen with chiasmatic lesions, with an additional arrangement in which fibers diverged around the tumor. For each patient, DT tractography provided additional information about visual fiber arrangement in relation to the tumor that was not evident by using conventional MRI methods. Retrospective reconstruction of visual fibers in 1 patient with new postoperative hemianopia revealed an unexpected superior displacement of the optic tract that might have been helpful information had it been applied to preoperative planning or surgical navigation.Optic pathway DT tractography is feasible in patients with OPG and provides new information about the arrangement of visual fibers in relation to tumors that could be incorporated into surgical navigation for tumor biopsy or debulking procedures.
View details for DOI 10.3171/2012.7.PEDS1270
View details for Web of Science ID 000309485300005
The predictive value of serum myeloperoxidase for vasospasm in patients with aneurysmal subarachnoid hemorrhage
2012; 35 (3): 413-419
Vasospasm is a major contributor to morbidity and mortality in aneurysmal subarachnoid hemorrhage (SAH), with inflammation playing a key role in its pathophysiology. Myeloperoxidase (MPO), an inflammatory marker, was examined as a potential marker of vasospasm in patients with SAH. Daily serum samples from patients with aneurysmal SAH were assayed for MPO, and transcranial Doppler (TCDs) and neurological exams were assessed to determine vasospasm. Suspected vasospasm was confirmed by angiography. Peak MPO levels were then compared with timing of onset of vasospasm, based on clinical exams, TCDs and cerebral angiography. Patients with vasospasm had a mean MPO level of 115.5 ng/ml, compared to 59.4 ng/ml in those without vasospasm, 42.0 ng/ml in those with unruptured aneurysms, and 4.3 ng/ml in normal controls. In patients who experienced vasospasm, MPO was elevated above the threshold on the day of, or at any point prior to, vasospasm in 10 of 15 events (66.7%), and on the day of, or within 2 days prior to, vasospasm in 8 of 15 events (53.3%). Elevated serum MPO correlates with clinically evident vasospasm following aneurysmal SAH. The potential utility of MPO as a marker of vasospasm is discussed.
View details for DOI 10.1007/s10143-012-0375-4
View details for Web of Science ID 000305230000023
View details for PubMedID 22370810
A NEUROSURGEON'S GUIDE TO STEM CELLS, CANCER STEM CELLS, AND BRAIN TUMOR STEM CELLS
2009; 65 (2): 237-249
Stem cells and their potential applications have become the forefront of scientific, political, and ethical discourse. Whereas stem cells were long accepted as units of development and evolution, it is now becoming increasingly clear that they are also units of oncogenesis. Although the field of stem cell biology is expanding at an astounding rate, the data attained are not readily translatable for the physicians who may eventually deliver these tools to patients. Herein, we provide a brief review of stem cell and cancer stem cell biology and highlight the scientific and clinical implications of recent findings regarding the presence of cancer-forming stem cells in brain tumors.
View details for DOI 10.1227/01.NEU.0000349921.14519.2A
View details for Web of Science ID 000268523200005
View details for PubMedID 19625901
Wnt-Signaling in Retinal Development and Disease
STEM CELLS AND DEVELOPMENT
2009; 18 (1): 7-15
The Wnt-signaling pathway is a known regulator of stem cell maintenance, cellular proliferation and differentiation, and cancer development in various tissues. Wnt proteins play a central role during various stages of retinal development; retinal field establishment, retinal and hyaloid vasculogenesis, cornea and lens development, eye field formation, and maintenance of retinal stem cell and neuronal specification in many species are Wnt-regulated processes. Uncontrolled Wnt signaling may cause retinal diseases such as familial exudative vitroretinopathy, retinitis pigmentosa, and Norrie's disease, further underscoring the importance of the Wnt-signaling pathway in the retina. This review summarizes major developments and discoveries regarding the role of the Wnt-signaling pathway as it pertains to retinal development and disease.
View details for DOI 10.1089/scd.2008.0169
View details for Web of Science ID 000263313700004
View details for PubMedID 18690791
Supraorbital approach for repair of open anterior skull base fracture Case report
JOURNAL OF NEUROSURGERY-PEDIATRICS
2008; 2 (6): 420-423
To the authors' knowledge, this is the first report of the use of anterior orbitotomy via the supraorbital eyelid crease to repair a dural tear caused by an orbital roof fracture. When transorbital penetrating injuries occur in children, they are commonly caused by accidental falls onto pointed objects. The authors report on their experience with a 7-year-old girl who fell onto a blunt metal rod hanger that penetrated her left eyelid, traversed superior to the eye globe, and penetrated the orbital roof at a depth of 3-4 cm, lacerating the dura mater and entering the cerebrum. An anterior transpalpebral transorbital approach was used to perform the microsurgical anterior skull base and dural repair. The authors advocate the application of this approach to orbital roof fractures because it provides excellent access to the orbital roof, eliminates the need for more invasive craniotomy, results in a small and well-hidden scar in the eye crease, and overall offers a shorter recovery time with less psychological stress to the patient.
View details for DOI 10.3171/PED.2008.2.12.420
View details for Web of Science ID 000261205600010
View details for PubMedID 19035689
Wnt-mediated self-renewal of neural stem/progenitor cells
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2008; 105 (44): 16970-16975
In this work we have uncovered a role for Wnt signaling as an important regulator of stem cell self-renewal in the developing brain. We identified Wnt-responsive cells in the subventricular zone of the developing E14.5 mouse brain. Responding cell populations were enriched for self-renewing stem cells in primary culture, suggesting that Wnt signaling is a hallmark of self-renewing activity in vivo. We also tested whether Wnt signals directly influence neural stem cells. Using inhibitors of the Wnt pathway, we found that Wnt signaling is required for the efficient cloning and expansion of single-cell derived populations that are able to generate new stem cells as well as neurons, astrocytes, and oligodendrocytes. The addition of exogenous Wnt3a protein enhances clonal outgrowth, demonstrating not only a critical role for the Wnt pathway for the regulation of neurogenesis but also its use for the expansion of neural stem cells in cell culture and in tissue engineering.
View details for DOI 10.1073/pnas.0808616105
View details for Web of Science ID 000260913800033
View details for PubMedID 18957545
Stereotactic radiosurgery for a cardiac sarcoma: A case report
TECHNOLOGY IN CANCER RESEARCH & TREATMENT
2008; 7 (5): 363-367
Pulmonary artery intimal sarcoma is an uncommon tumor with a poor prognosis. We report a case of a 75-year-old man with a pulmonary artery sarcoma, recurrent following surgical resection. To palliate symptoms of this recurrence, he underwent CyberKnife stereotactic radiosurgery with a clinical and radiographic response of his treated disease. No acute or sub-acute toxicity was seen until the patient's death due to metastatic disease 10 weeks following treatment. The feasibility and short-term safety of this technique are reviewed, with emphasis on the stereotactic planning considerations, such as mediastinal organ movement and radiation tolerance.
View details for Web of Science ID 000259799000003
View details for PubMedID 18783285
Two-year-old girl with cervicomedullary junction stenosis and an unknown type of skeletal dysplasia
JOURNAL OF NEUROSURGERY-PEDIATRICS
2008; 2 (3): 200-202
The authors present a novel case of skeletal dysplasia in a 2.8-year-old girl. The patient presented with progressive lower cranial nerve palsy and myelopathy due to constriction at the cervicomedullary junction caused by overgrowth of the occipital bone of the foramen magnum and the C-1. She also had prominent bone overgrowth of the superior orbital ridges, resulting in excessive stretching of periorbital skin and an inability to fully close her eyes.
View details for DOI 10.3171/PED/2008/2/9/200
View details for Web of Science ID 000258903800010
View details for PubMedID 18759602
Radiation therapy and CyberKnife radiosurgery in the management of craniopharyngiomas
2008; 24 (5)
Many benign intracranial tumors are amenable to radiotherapy treatment including meningiomas, schwannomas, pituitary tumors, and craniopharyngiomas. The authors present their experience in the treatment of craniopharyngiomas in 16 patients using frameless CyberKnife stereotactic radiosurgery (SRS). The authors discuss the role of radiation therapy in the management of these tumors, and more specifically, the role of CyberKnife SRS.Sixteen patients were treated for residual or recurrent craniopharyngioma between 2000 and 2007 with CyberKnife SRS at Stanford University Medical Center. All patients underwent magnetic resonance imaging and visual and neuroendocrine evaluations before and at regular intervals after SRS. A multisession treatment regimen and a nonisocentric treatment plan for each patient were used with a mean marginal dose of 21.6 Gy and a mean maximal dose of 29.9 Gy.There were adequate clinical data to assess outcomes in 11 of 16 patients. Evaluation of patients between 13 and 71 years of age (mean 34.5 years) with a mean follow-up period of 15.4 months revealed no deterioration in visual or neuroendocrine function. Tumor shrinkage was achieved in 7 of these 11 patients, and tumor control in another 3. One patient had cystic enlargement of the residual tumor.The authors' early experience with the application of CyberKnife SRS to residual or recurrent craniopharyngiomas has been positive; control or shrinkage of the tumor was achieved in 91% of patients, with no visual or neuroendocrine complications. Longer-term follow-up with a larger group of patients is required to fully evaluate the safety and effectiveness of this treatment modality.
View details for DOI 10.3171/FOC/2008/24/5/E4
View details for Web of Science ID 000256374300004
View details for PubMedID 18447743
Intracarotid injection of fluorescence activated cell-sorted CD49d-positive neural stem cells improves targeted cell delivery and behavior after stroke in a mouse stroke model
2008; 39 (4): 1300-1306
Intravascular delivery of neural stem cells (NSCs) after stroke has been limited by the low efficiency of transendothelial migration. Vascular cell adhesion molecule-1 is an endothelial adhesion molecule known to be upregulated early after stroke and is responsible for the firm adhesion of inflammatory cells expressing the surface integrin, CD49d. We hypothesize that enriching for NSCs that express CD49d and injecting them into the carotid artery would improve targeted cell delivery to the injured brain.Mouse NSCs were analyzed for the expression of CD49d by fluorescence activated cell sorting. A CD49d-enriched (CD49d(+)) (>95%) and -depleted (CD49d(-); <5%) NSC population was obtained by cell sorting. C57/Bl6 mice underwent left-sided hypoxia-ischemia surgery and were assigned to receive 3 x 10(5) CD49d(+), CD49d(-) NSCs, or vehicle injection into the left common carotid artery 48 hours after stroke. Behavioral recovery was measured using a rotarod for 2 weeks after cell injection.Fluorescence activated cell sorting analysis revealed 25% CD49d(+) NSCs. In a static adhesion assay, NSCs adhered to vascular cell adhesion molecule-1 in a dose-dependent manner. Significantly more NSCs were found in the cortex, the hippocampus, and the subventricular zone in the ischemic hemisphere in animals receiving CD49d(+) NSCs as compared with CD49d(-) NSCs (P<0.05). Animals treated with CD49d(+) cells showed a significantly better behavioral recovery as compared with CD49d(-) and vehicle-treated animals.We show that enrichment of NSCs by fluorescence activated cell sorting for the surface integrin, CD49d, and intracarotid delivery promotes cell homing to the area of stroke in mice and improves behavioral recovery.
View details for DOI 10.1161/STROKEAHA.107.500470
View details for Web of Science ID 000254632900038
View details for PubMedID 18309158
Hematopoietic stem cell-derived pericytic cells in brain tumor angio-architecture
STEM CELLS AND DEVELOPMENT
2008; 17 (1): 11-18
Bone marrow-derived cells are recruited into tumor vasculature in response to angiogenic signals, and some of the cells within the newly forming tumor vessels are hematopoietic stem cells (HSCs) in origin. Previous studies suggest that bone marrow-derived pericytes are associated with newly formed vessels in tumors. In this study, we used an orthotopic rat glioma model (RT-2/RAG) to examine the contribution of long-term hematopoietic stem cell (LT-HSC)-derived pericytic cells to brain tumor angiogenesis. Mice (RAG-2/KO5.2) were lethally irradiated, and their hematopoietic cells were repopulated by transplantation of double fluorescence-activated cell-sorted LT-HSCs that express green fluorescent protein (GFP+). RT-2/RAG cells were then injected into the striatum of the chimeric mice 6 weeks post-transplantation. The animals were sacrificed 9 days after tumor implantation, and the incorporation and lineage-specific marker expression profile of the GFP+ cells within the growing tumor and tumor periphery were analyzed. LT-HSC-derived GFP+ cells were noted to incorporate onto the surface of tumor vessels within the perivascular space. LT-HSC-derived GFP+ cells express the pericyte progenitor marker, platelet-derived growth factor receptor-beta (PDGFR beta), as well as mature perictyte markers such as nerve/glial antigen 2 proteoglycan (NG2), alpha-smooth muscle actin (alpha SMA), and desmin. These LT-HSC-derived cells may represent a population of progenitor or committed pericytes within the neovascular tree and may play a role in shaping the angio-architecture in the vascular niche of brain tumors.
View details for DOI 10.1089/scd.2007.0117
View details for Web of Science ID 000253628600002
View details for PubMedID 18240955
The effect of bleeding on hematopoietic stem cell cycling and self-renewal
STEM CELLS AND DEVELOPMENT
2007; 16 (5): 707-717
Hematopoietic stem cells (HSCs) divide and give rise to more committed progenitors, which ultimately produce all lineages of blood cells. HSCs can be induced to enter the cell cycle in vitro and in vivo by stimulatory cytokines and in vivo by ablation of bone marrow (BM) cells with irradiation or chemotherapeutic agents. Although it has been postulated that rates of HSC proliferation increase with normal hematopoietic stresses, such as infection or hemorrhage, this hypothesis has never been directly tested. The ability to analyze HSCs prospectively by cell-surface phenotype c-kit(+), Thy1.1(lo), Sca-1(+), Linage(neg/lo) has allowed us to perform a detailed examination of the effects of bleeding on the cell cycle kinetics of HSCs. Our results demonstrate for the first time that HSCs in both the BM and the spleen proliferate and self-renew in response to tail-vein bleeding in mice. This response was suppressed when red blood cells, but not when white blood cells, were transferred after bleeding. Thus, regulators of HSC proliferation can sense and respond to red blood cell levels.
View details for DOI 10.1089/scd.2007.0017
View details for Web of Science ID 000251266900003
View details for PubMedID 17999593
Cyberknife radiosurgery for lesions of the foramen magnum
TECHNOLOGY IN CANCER RESEARCH & TREATMENT
2007; 6 (4): 329-335
The region of the foramen magnum (FM) presents an especially difficult area for therapeutic intervention. Indeed, this location is challenging to access surgically, particularly in the case of intramedullary and anterior lesions. Therefore, the potential for morbidity associated with therapy to the foramen magnum, most frequently in the form of lower cranial nerve deficits, has encouraged the search for methods that can effectively treat lesions of this region while sparing the important neighboring structures. We report our experience in the use of Cyberknife radiosurgery as a treatment option for these lesions. Thirty-five patients (17 men, 18 women; mean age, 51 yr; range, 18-83) with 35 lesions either spanning or approximating the foramen magnum were treated with the CyberKnife radiosurgical system. Histologies were determined either by prior surgery or radiographic criteria and included 25 benign tumors (nine meningiomas, five schwannomas, four neurofibromas, three hemangioblastomas, two ependymomas, one chordomas, and one pilocytic astrocytoma) along with 10 malignant growths (nine metastases and one chondrosarcoma). Twenty-seven (77%) patients presented with at least one sign and/or symptom, while eight (23%) patients were completely asymptomatic. The most common symptoms were headache, limb numbness, and limb/truncal ataxia, all of which were reported by ten (29%) patients. Among cranial neuropathies, CN XII dysfunction was evident in four (11%) patients. The specific fractionation schedule (mean of 1.8 sessions; range, 1-5) was based on the size of the treated lesion. The mean dose utilized was 19 Gy. Radiographic follow-up was obtained for twenty-three (66%) patients. Nine of the twenty-three (39%) were stable in size, ten lesions decreased in size (43%), and four lesions increased in size (17%). In terms of symptom relief, follow-up was collected for twenty-four (69%) patients. Eleven (46%) of these patients experienced no change in their signs or symptoms, while seven (29%) patients experienced improvement. Six (25%) patients witnessed deterioration in their signs and symptoms. Overall, eighteen (75%) patients had their signs and symptoms either stabilize or improve. There were eleven (31%) deaths in our series, eight of which were related to the disease (though not directly related to CyberKnife treatment) and three of which were from unrelated causes. Complications directly related to CyberKnife radiosurgery were noted in four (11%) of the thirty-five patients. These included one case of temporary emesis immediately following treatment, one case of cystic enlargement two months out, and two cases of radiation necrosis (occurring 1.5 yrs and 2.5 yrs out from treatment). Cyberknife radiosurgery can be an effective treatment for many foramen magnum lesions.
View details for Web of Science ID 000249073000010
View details for PubMedID 17668941
Cerebral myiasis associated with angiosarcoma of the scalp: case report.
2007; 61 (1): E167-?
Primary human cerebral myiasis is an exceedingly rare condition and is almost never encountered by physicians in developed countries. The case report summarizes a case of extensive cerebral myiasis in a periurban community in the United States.After a minor motor vehicle accident, police brought a 75-year-old man to the emergency room because he was observed to have a large cranial lesion. Examination revealed a 15 x 17 cm frontal bone defect with eroded frontal dura, exposed cortex, and massive cortical maggot infestation.The patient was empirically treated with intravenous antibiotics for meningitis. Maggots (Phaenicia sericata, or the green bottle fly) were removed by suction, attrition, and gentle contact exposure to a mild bleach solution. Biopsy of the scalp and cranium revealed angiosarcoma, for which operative treatment was refused. The patient was transferred to a skilled nursing facility for palliative care where he died 3 months later.This is the first published case of cerebral myiasis in the United States. Although human cerebral myiasis is rare, conditions do exist in this country that permit myiasis.
View details for PubMedID 17621006
Incorporation of bone marrow-derived Flk-1-expressing CD34+ cells in the endothelium of tumor vessels in the mouse brain
2006; 59 (2): 374-381
Neoangiogenesis is a prerequisite for the full phenotypic expression and growth of a malignant tumor mass. It is believed to be triggered by tissue hypoxia and involves proliferation and sprouting of the preexisting vessels and the recruitment of endothelial progenitor cells from bone marrow.A chimeric mouse model was used to examine the contribution of these progenitor cells to the neovasculature of brain tumor. T-cell knockout (RAG/KO5.2) mice were irradiated lethally, and their bone marrow was repopulated with T-cell depleted green fluorescent protein (GFP)-expressing bone marrow cells. RAG/RT-2 glioma cells were implanted into the striatum of the animals. Neovascular formation at various times of tumor growth was monitored together with the extent of incorporation of GFP+ bone marrow-derived cells within the vascular tree, in particular, cells carrying the endothelial progenitor markers CD34 and Flk-1.The recruitment of GFP+ cells to the growing tumor and their incorporation into the vascular network occurred during the period of increasing vascular density and preceded the expansion of the tumor. The number of marrow-derived cells with endothelial morphology and phenotype was small but significant (4% of all endothelial cells at Day 12); 54% of all tumor vessels contained at least one GFP+ cell.Our results suggest that bone marrow cells are recruited to newly formed and remodeled tumor vessels. Their recruitment may occur in response to signals from a highly proliferating milieu, and their role is to support the neovascular complex and to promote tumor growth.
View details for DOI 10.1227/01.NEU.0000222658.66878.CC
View details for Web of Science ID 000239763800047
View details for PubMedID 16883178
New vessel formation in the central nervous system during tumor growth, vascular malformations, and Moyamoya
CURRENT NEUROVASCULAR RESEARCH
2006; 3 (3): 237-245
In the normal adult brain, blood vessel formation is tightly down-regulated. However, pathologic processes such as brain tumors can increase the proportion of endothelial cells involved in angiogenesis. When this process is initiated, a complex series of timed events result in new vessel formation. In this review, we will describe the process of angiogenesis in the central nervous system. We will discuss the roles of Vascular Endothelial Growth Factor (VEGF), Fibroblast Growth Factor (FGF), Angiopoietins, Platelet Derived Growth Factor (PDGF), and integrins in angiogenesis. We will also look into their significance in disease processes such as neoplasms, arteriovenous malformations (AVM), and Moyamoya disease.
View details for Web of Science ID 000240424200008
View details for PubMedID 16918387
Differential expression of angiopoietin-1 and angiopoietin-2 may enhance recruitment of bone marrow-derived endothelial precursor cells into brain tumors
2005; 27 (8): 801-806
Angiogenesis is necessary for sustained neoplastic development. The angiopoietins Ang-1 and Ang-2 have been implicated in the regulation of this process; recent reports have suggested that a net gain in Ang-2 activity may be an initiating factor for tumor angiogenesis. We examined the recruitment of bone marrow-derived endothelial precursor cells into developing tumor neovasculature, and the spatial relationship between these cells and angiopoietin (Ang-1 and Ang-2) expression.For this study T-cell depleted knockout mice (RAG-2/KO-5.2) were lethally irradiated and their bone marrow was reconstituted by bone marrow cells (BMCs) from transgenic mice (C57BL/Ka-Thy1.1) expressing green fluorescent protein (GFP). Rat glioma cells (RT-2/RAG) were then injected into the transplanted animals to form solid brain tumors. The animals were killed and their brains were analysed using immunohistochemistry and fluorescence-activated cell sorting.We found that BMCs migrated preferentially into the tumor when compared to adjacent healthy brain parenchyma. Furthermore, GFP+/CD34+ cells represented up to 8% of endothelial-like cells within the walls of tumor blood vessels. In the tumor, significant colocalization of Ang-2 with GFP+/CD34+ cells was noted (>80%), but colocalization with Ang-1 never exceeded 20%. In normal tissue directly surrounding the tumor, GFP+/CD34+ cells colocalized strongly with both angiopoietins (>75% and >70% for Ang-1 and Ang-2, respectively).The relative increase in angiopoietin-2 activity in brain tumors may result in the creation of a pro-angiogenic environment that enhances the recruitment of putative bone marrow-derived endothelial precursor cells into the tumor's developing vascular tree.
View details for DOI 10.1179/016164105X49319
View details for Web of Science ID 000233967800004
View details for PubMedID 16354539
Identification of phenotypic neural stem cells in a pediatric astroblastoma
JOURNAL OF NEUROSURGERY
2005; 103 (5): 446-450
The goal of this study was to illustrate the findings of a significant subpopulation of cells within a pediatric astroblastoma that have the specific cell surface phenotype found on known human neural stem cells.Cells with a cell surface marker profile characteristic of human neural stem cells were isolated using fluorescence-activated cell sorting from a mostly nonmitotic astroblastoma removed from the brain of an 11-year-old girl. An unusually high proportion (24%) of the cells were CD133 positive and CD24, CD34, and CD45 negative (CD133(+)CD24(-)CD34(-)CD45(-) cells), the phenotypic antigenic pattern associated with neural stem cells; very few CD133-positive cells were not also CD24, CD34, and CD45 negative. Some cells (12%) were CD34 positive, indicating the presence within the tumor of hematopoietic stem cells. Cells formed cytospheres that resembled neurospheres when seeded into stem cell media and coexpressed beta-tubulin and glial fibrillary acidic protein (GFAP) but did not express the oligodendrocyte marker O4. Cell proliferation was demonstrated by incorporation of bromodeoxyuridine. The cells lost their capacity for self-renewal in vitro after four to six passages, although they continued to coexpress beta-tubulin and GFAP. The cells did not differentiate into neurons or astrocytes when placed in differentiation medium.Although this astroblastoma contained a high proportion of phenotypic neural stemlike cells, the cells had limited proliferative capacity and multipotency. Their role in astroblastoma formation and growth is unknown.
View details for Web of Science ID 000233081900012
View details for PubMedID 16302618
Hematopoietic stem cells give rise to perivascular endothelial-like cells during brain tumor angiogenesis
STEM CELLS AND DEVELOPMENT
2005; 14 (5): 478-486
Bone marrow (BM) cells have recently been shown to give rise to skeletal, hepatic, cardiac, neural, and vascular endothelial tissues. However, it has been shown that this is the result of cell fusion rather than transdifferentiation of hematopoietic stem cells (HSC). For this study, we established a mouse model of brain tumor growth to investigate the differentiation potential of HSC into endothelial cells during brain tumor-induced angiogenesis. Nontransgenic (GFP(neg)) recipient mice were lethally irradiated, and their hematopoietic cells were subsequently repopulated by transplantation of a single green fluorescent protein (GFP)-expressing HSC. Rat glioma (RT-2/RAG) cells were then injected into the striatum of the chimeric mice 6-8 weeks post-transplantation. The animals were sacrificed 3-9 days after tumor implantation, and the mobilization, temporal-spatial distribution, and lineage-specific marker expression profile of the GFP(+) cells within the growing tumor were analyzed. We saw that GFP(+) cells gave rise to elongated, CD34(+)/Flk-1(+) cells that incorporated into the endothelium of tumor blood vessels. However, all GFP(+) cells were also CD45(+), and the presence of CD45 on the HSC-derived endothelial-like cells supports the hypothesis that the hematopoietic cells were recruited into the tumor milieu. The fact that we failed to demonstrate the expression of von Willebrand factor in these cells argues against a true endothelial identity. Nevertheless, the recruitment of HSC-derived endothelial-like cells was an extremely rare event in normal brain parenchyma, and, thus, the permissive influence afforded by the growing tumor appeared to enhance the perivascular tropism and acquisition of an endothelial phenotypes by a population of HSC-derived cells.
View details for Web of Science ID 000233904500003
View details for PubMedID 16305333
alpha(v)beta(3) integrin in central nervous system tumors
2005; 36 (6): 665-669
alpha(v)beta(3) Is an integrin specifically expressed in endothelial cells of newly forming blood vessels. Integrin-mediated angiogenesis is hypothesized to play a central role in the development and the progression of central nervous system neoplasms. Accordingly, it is considered a potential target for antiangiogenic therapy. In the current study, we compare the expression of alpha(v)beta(3) in ependymomas, oligodendrogliomas, pilocytic astrocytomas, medulloblastomas, and vestibular schwannomas (acoustic neuromas). Samples of 5 tumors of each of the 5 tumor types were harvested surgically and frozen. After the pathological diagnosis was confirmed, immunohistochemistry was performed using an anti- alpha(v)beta(3) monoclonal antibody (LM609). The expression of alpha(v)beta(3) was assessed using a 4-tiered (0-3) grading scheme reflecting the percentage of positively staining vessels. All vestibular schwannomas demonstrated strong (grade 3) alpha(v)beta(3) expression. The expression was uniformly prominent in Antoni B regions of the tumors. Of 5 ependymomas, 4 demonstrated uniformly strong alpha(v)beta(3). Oligodendrogliomas, medulloblastomas, and pilocytic astrocytomas demonstrated more variable alpha(v)beta(3). alpha(v)beta(3) may contribute significantly to angiogenesis in vestibular schwannomas and ependymomas. Despite the high vascular density of oligodendrogliomas, pilocytic astrocytomas, and medulloblastomas, these tumors had variable moderate alpha(v)beta(3) expression. This discrepancy suggests temporal and/or regional variability in the angiogenesis in these types of tumor. This study provides the first demonstration of alpha(v)beta(3) expression in vestibular schwannomas, medulloblastomas, and pilocytic astrocytomas.
View details for DOI 10.1016/j.humpath.2005.03.014
View details for Web of Science ID 000230633500010
View details for PubMedID 16021573
Preuss Resident Research Award: bone marrow-derived Flk-1-expressing CD34+ cells contribute to the endothelium of tumor vessels in mouse brain.
2005; 52: 384-388
View details for PubMedID 16626098
Incorporation of naive bone marrow derived cells into the vascular architecture of brain tumor
2004; 11 (8): 699-708
Neovascularization is essential for tumor growth and invasion. Mounting evidence suggests that tumor cells recruit circulating endothelial progenitor cells to promote vasculogenesis to compliment tumor angiogenesis. This study examines the constitutive role of bone marrow-derived cells in this process.Rat glioma cells were implanted into brains of T-cell-depleted knockout mice. At various timepoints after tumor implantation, naïve bone marrow cells from ubiquitous transgenic mice expressing green fluorescent protein (GFP) were infused into these animals. The incorporation of GFP-positive cells into the vascular architecture was visualized by fluorescence confocal microscopy in conjunction with the transcription profiles of vascular endothelial growth factor (VEGF) and angiopoietin-1 and -2 (Ang-1 and Ang-2).Of the cells infused, 8 days after tumor implantation, 0.49% were found exclusively sequestered in the vicinity of tumor vessels. This coincided with a decline in the expression of Ang-1 and a rise in the expression of VEGF and Ang-2. A few of these cells (0.66 of the 0.49%) localized onto the vascular wall. They resembled endothelial cells and expressed vWF.The incorporation of bone marrow-derived unpurified endothelial cells into the tumor vascular bed is both time-limited and infrequent. These cells may play a supportive rather than a constitutive role in tumor neovascularization.
View details for DOI 10.1080/10739680490521005
View details for Web of Science ID 000225641500007
View details for PubMedID 15726837
Telomerase activation and rejuvenation of telomere length in stimulated T cells derived from serially transplanted hematopoietic stem cells
JOURNAL OF EXPERIMENTAL MEDICINE
2002; 196 (11): 1427-1433
Telomeres shorten in hematopoietic cells, including hematopoietic stem cells (HSCs), during aging and after transplantation, despite the presence of readily detectable levels of telomerase in these cells. In T cells, antigenic stimulation has been shown to result in a marked increase in the level of telomerase activity. We now show that stimulation of T cells derived from serially transplanted HSC results in a telomerase-dependent elongation of telomere length to a size similar to that observed in T cells isolated directly from young mice. Southern analysis of telomere length in resting and anti-CD3/CD28 stimulated donor-derived splenic T cells revealed an increase in telomere size by approximately 7 kb for the population as a whole. Stimulation of donor-derived T cells from recipients of HSCs from telomerase-deficient mice did not result in regeneration of telomere length, demonstrating a dependence on telomerase. Furthermore, clonal anti-CD3/CD28 stimulation of donor-derived T cells followed by fluorescent in situ hybridization (FISH) analysis of telomeric signal intensity showed that telomeres had increased in size by approximately 50% for all clonal expansions. Together, these results imply that one role for telomerase in T cells may be to renew or extend replicative potential via the rejuvenation of telomere length.
View details for DOI 10.1084/jem.20021003
View details for Web of Science ID 000179682000004
View details for PubMedID 12461078
Telomere shortening accompanies increased cell cycle activity during serial transplantation of hematopoietic stem cells
JOURNAL OF EXPERIMENTAL MEDICINE
2001; 193 (8): 917-924
Reactivation of telomerase and maintenance of telomere length can lead to the prevention of replicative senescence in some human somatic cells grown in vitro. To investigate whether telomere shortening might also play a role in the limitation of hematopoietic stem cell (HSC) division capacity in vivo, we analyzed telomere length during serial transplantation of murine HSCs. Southern blot analysis of telomere length in donor bone marrow cells revealed extensive shortening ( approximately 7 kb) after just two rounds of HSC transplantation. The number of cycling HSCs increased after transplantation and remained elevated for at least 4 mo, while the frequency of HSCs in the bone marrow was completely regenerated by 2 mo after transplantation. Direct analysis of telomeres in HSCs by fluorescent in situ hybridization during serial transplantation also revealed a reduction in telomere size. Together, these data show that telomeres shorten during division of HSCs in vivo, and are consistent with the hypothesis that telomere shortening may limit the replicative capacity of HSCs.
View details for Web of Science ID 000168199900004
View details for PubMedID 11304552
Cyclophosphamide/granulocyte colony-stimulating factor causes selective mobilization of bone marrow hematopoietic stem cells into the blood after M phase of the cell cycle
2001; 97 (8): 2278-2285
Cytokine-mobilized peripheral blood hematopoietic stem cells (MPB HSC) are widely used for transplantation in the treatment of malignancies, but the mechanism of HSC mobilization is unclear. Although many HSC in bone marrow (BM) cycle rapidly and expand their numbers in response to cytoreductive agents, such as cyclophosphamide (CY), and cytokines, such as granulocyte colony-stimulating factor (G-CSF), MPB HSC are almost all in the G(0) or G(1) phase of the cell cycle. This has raised the question of whether a subset of noncycling BM HSC is selectively released, or whether cycling BM HSC are mobilized after M phase, but before the next S phase of the cell cycle. To distinguish between these possibilities, mice were treated with one dose of CY followed by daily doses of G-CSF, and dividing cells were marked by administration of bromodeoxyuridine (BrdU) during the interval that BM HSC are expanding. After CY and 4 days of G-CSF, 98.5% of the 2n DNA content long-term repopulating MPB (LT)-HSC stained positively for BrdU, and therefore derived from cells that divided during the treatment interval. Next, LT-HSC from mice previously treated with a single dose of CY, which kills cycling cells, and 3 daily doses of G-CSF, were nearly all killed by a second dose of CY, suggesting that CY/G-CSF causes virtually all LT-HSC to cycle. Analysis of cyclin D2 messenger RNA (mRNA) expression and total RNA content of MPB HSC suggests that these cells are mostly in G(1) phase. After CY/G-CSF treatment, virtually all BM LT-HSC enter the cell cycle; some of these HSC then migrate into the blood, specifically after M phase, and are rapidly recruited to particular hematopoietic organs.
View details for Web of Science ID 000168516100011
View details for PubMedID 11290588
Inactivation of a GFP retrovirus occurs at multiple levels in long-term repopulating stem cells and their differentiated progeny
2000; 96 (3): 894-901
Hematopoietic stem cell gene therapy holds promise for the treatment of many hematologic disorders. One major variable that has limited the overall success of gene therapy to date is the lack of sustained gene expression from viral vectors in transduced stem cell populations. To understand the basis for reduced gene expression at a single-cell level, we have used a murine retroviral vector, MFG, that expresses the green fluorescent protein (GFP) to transduce purified populations of long-term self-renewing hematopoietic stem cells (LT-HSC) isolated using the fluorescence-activated cell sorter. Limiting dilution reconstitution of lethally irradiated recipient mice with 100% transduced, GFP(+) LT-HSC showed that silencing of gene expression occurred rapidly in most integration events at the LT-HSC level, irrespective of the initial levels of GFP expression. When inactivation occurred at the LT-HSC level, there was no GFP expression in any hematopoietic lineage clonally derived from silenced LT-HSC. Inactivation downstream of LT-HSC that stably expressed GFP( )in long-term reconstituted animals was restricted primarily to lymphoid cells. These observations suggest at least 2 distinct mechanisms of silencing retrovirally expressed genes in hematopoietic cells.
View details for Web of Science ID 000088394000017
View details for PubMedID 10910902
The role of apoptosis in the regulation of hematopoietic stem cells: Overexpression of BCL-2 increases both their number and repopulation potential
JOURNAL OF EXPERIMENTAL MEDICINE
2000; 191 (2): 253-263
Hematopoietic stem cells (HSC) give rise to cells of all hematopoietic lineages, many of which are short lived. HSC face developmental choices: self-renewal (remain an HSC with long-term multilineage repopulating potential) or differentiation (become an HSC with short-term multilineage repopulating potential and, eventually, a mature cell). There is a large overcapacity of differentiating hematopoietic cells and apoptosis plays a role in regulating their numbers. It is not clear whether apoptosis plays a direct role in regulating HSC numbers. To address this, we have employed a transgenic mouse model that overexpresses BCL-2 in all hematopoietic cells, including HSC: H2K-BCL-2. Cells from H2K-BCL-2 mice have been shown to be protected against a wide variety of apoptosis-inducing challenges. This block in apoptosis affects their HSC compartment. H2K-BCL-2-transgenic mice have increased numbers of HSC in bone marrow (2.4x wild type), but fewer of these cells are in the S/G(2)/M phases of the cell cycle (0.6x wild type). Their HSC have an increased plating efficiency in vitro, engraft at least as well as wild-type HSC in vivo, and have an advantage following competitive reconstitution with wild-type HSC.
View details for Web of Science ID 000084908000006
View details for PubMedID 10637270
In vivo proliferation and cell cycle kinetics of long-term self-renewing hematopoietic stem cells
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
1999; 96 (6): 3120-3125
A rare set of hematopoietic stem cells (HSC) must undergo a massive expansion to produce mature blood cells. The phenotypic isolation of HSC from mice offers the opportunity to determine directly their proliferation kinetics. We analyzed the proliferation and cell cycle kinetics of long-term self-renewing HSC (LT-HSC) in normal adult mice. At any one time, approximately 5% of LT-HSC were in S/G2/M phases of the cell cycle and another 20% were in G1 phase. BrdUrd incorporation was used to determine the rate at which different cohorts of HSC entered the cell cycle over time. About 50% of LT-HSC incorporated BrdUrd by 6 days and >90% incorporated BrdUrd by 30 days. By 6 months, 99% of LT-HSC had incorporated BrdUrd. We calculated that approximately 8% of LT-HSC asynchronously entered the cell cycle per day. Nested reverse transcription-PCR analysis revealed cyclin D2 expression in a high proportion of LT-HSC. Although approximately 75% of LT-HSC are quiescent in G0 at any one time, all HSC are recruited into cycle regularly such that 99% of LT-HSC divide on average every 57 days.
View details for Web of Science ID 000079224500101
View details for PubMedID 10077647
Hematopoietic stem cells: Challenges to expectations
CURRENT OPINION IN IMMUNOLOGY
1997; 9 (2): 216-221
The past year provided a number of challenges to our expectations regarding hematopoietic stem cell (HSC) biology. Evidence has emerged that HSCs arise intraembryonically before they can be detected in the yolk sac. A number of genes that may regulate the formation, self-renewal, or differentiation of HSC have been identified. New markers for purifying HSCs have also been described. Although different groups have attributed different properties to HSCs, it now appears that the differences may be explained by variations in assay conditions rather than by differences in the HSCs themselves. Finally, insights have emerged into the complexity of the regulation of HSC proliferation and adhesion properties.
View details for Web of Science ID A1997WV04000008
View details for PubMedID 9099790
CD90 expression segregates tumor-sphere forming cells in human glioblastoma multiforme
OXFORD UNIV PRESS INC. 2006: 471-471
View details for Web of Science ID 000240877301309
- Lymphoid development from stem cells and the common lymphocyte progenitors COLD SPRING HARBOR LAB PRESS, PUBLICATIONS DEPT. 1999: 1-12