Biomedical subjects

D Bradley Welling

Publications and source records attributed to D Bradley Welling.

13 recordsLinked to original sources

PubMed2006

Regulation of the neurofibromatosis 2 gene promoter expression during embryonic development.

Mutations in the Neurofibromatosis 2 (NF2) gene are associated with predisposition to vestibular schwannomas, spinal schwannomas, meningiomas, and ependymomas. Presently, how NF2 is expressed during embryonic development and in the tissues affected by neurofibromatosis type 2 (NF2) has not been well defined. To examine NF2 expression in vivo, we generated transgenic mice carrying a 2.4-kb NF2 promoter driving beta-galactosidase (beta-gal) with a nuclear localization signal. Whole-mount embryo staining revealed that the NF2 promoter directed beta-gal expression as early as embryonic day E5.5. Strong expression was detected at E6.5 in the embryonic ectoderm containing many mitotic cells. beta-gal staining was also found in parts of embryonic endoderm and mesoderm. The beta-gal staining pattern in the embryonic tissues was corroborated by in situ hybridization analysis of endogenous Nf2 RNA expression. Importantly, we observed strong NF2 promoter activity in the developing brain and in sites containing migrating cells including the neural tube closure, branchial arches, dorsal aorta, and paraaortic splanchnopleura. Furthermore, we noted a transient change of NF2 promoter activity during neural crest cell migration. While little beta-gal activity was detected in premigratory neural crest cells at the dorsal ridge region of the neural fold, significant activity was seen in the neural crest cells already migrating away from the dorsal neural tube. In addition, we detected considerable NF2 promoter activity in various NF2-affected tissues such as acoustic ganglion, trigeminal ganglion, spinal ganglia, optic chiasma, the ependymal cell-containing tela choroidea, and the pigmented epithelium of the retina. The NF2 promoter expression pattern during embryogenesis suggests a specific regulation of the NF2 gene during neural crest cell migration and further supports the role of merlin in cell adhesion, motility, and proliferation during development.

Animals↗

PubMed2006

The molecular biology of vestibular schwannomas: dissecting the pathogenic process at the molecular level.

OBJECTIVE: The goal of this article was to review concisely what is currently known about the tumorigenesis of vestibular schwannomas. BACKGROUND: Recent advances in molecular biology have led to a better understanding of the cause of vestibular schwannomas. Mutations in the neurofibromatosis type 2 tumor suppressor gene (NF2) have been identified in these tumors. In addition, the interactions of merlin, the protein product of the NF2 gene, and other cellular proteins are beginning to give us a better idea of NF2 function and the pathogenesis of vestibular schwannomas. METHODS: Review of the relevant basic science studies at our institution as well as the basic science and clinical literature. RESULTS: The clinical characteristics of vestibular schwannomas and neurofibromatosis type 2 syndromes are reviewed and related to alterations in the NF2 gene. Studies demonstrating our current understanding of tumor developmental pathways are highlighted. In addition, methods of clinical and genetic screening for neurofibromatosis type 2 disease are outlined. Avenues for the development of potential future research and therapies are discussed. CONCLUSION: Great strides have been made to identify why vestibular schwannomas develop at the molecular level. Continued research is needed to find targeted therapies with which to treat these tumors.

Alternative Splicing↗

PubMed2006

Cyclin D(1) and D(3) expression in vestibular schwannomas.

OBJECTIVES: The G1 regulators of the cell cycle, cyclin D(1) and D(3), have been implicated in the regulation of Schwann cell proliferation and differentiation. The purpose of this study is to evaluate cyclin D(1) and D(3) protein expression and the corresponding clinical characteristics of vestibular schwannomas. STUDY DESIGN AND METHODS: Tissue sections of 15 sporadic vestibular schwannomas were prepared. Immunohistochemical analysis of the vestibular schwannomas was performed with anticyclin D(1) and anticyclin D(3) antibodies. The immunoreactivity was evaluated in comparison with adjacent vestibular nerves. Tissue sections of breast carcinoma and prostate carcinoma were used as positive controls for cyclin D(1) and D(3) staining, respectively. Patient demographics, tumor characteristics, and cyclin D expression were reviewed, and statistical analysis was performed. RESULTS: While the breast carcinoma control expressed abundant cyclin D(1) protein, none of the 15 vestibular schwannomas showed detectable cyclin D(1) staining. In contrast, seven of 15 vestibular schwannomas stained positive for the cyclin D(3) protein. Cyclin D(3) staining was taken up in the nucleus of schwannoma tumor cells in greater proportion than Schwann cells of adjacent vestibular nerve. Although sample size was small, no significant difference in the average age of presentation, tumor size, and male to female ratios for the cyclin D(3)(+) or cyclin D(3)(-) groups was found. CONCLUSION: The Cyclin D(1) protein does not appear to play a prominent role in promoting cell cycle progression in vestibular schwannomas. In contrast, cyclin D(3) expression was seen in nearly half of the tumors examined, suggesting that it may have a growth-promoting role in some schwannomas. Further studies are needed to define its cellular mechanism.

Antibodies, Neoplasm↗

PubMed2006

Growth of benign and malignant schwannoma xenografts in severe combined immunodeficiency mice.

OBJECTIVES: Models for the development of new treatment options in vestibular schwannoma (VS) treatment are lacking. The purpose of this study is to establish a quantifiable human VS xenograft model in mice. STUDY DESIGN AND METHODS: Both rat malignant schwannoma cells (KE-F11 and RT4) and human malignant schwannoma (HMS-97) cells were implanted near the sciatic nerve in the thigh of severe combined immunodeficiency (SCID) mice. Additionally, human benign VS specimens were implanted in another set of SCID mice. Three-dimensional tumor volumes were calculated from magnetic resonance images over the next 6 months. RESULTS: Mice implanted with malignant schwannoma cells developed visible tumors within 2 weeks. Imaging using a 4.7-tesla magnetic resonance imaging and immunohistopathologic examination identified solid tumors in all KE-F11 and HMS-97 xenografts, whereas RT4 xenografts consistently developed cystic schwannomas. VS xenografts demonstrated variability in their growth rates similar to human VS. The majority of VS xenografts did not grow but persisted throughout the study, whereas two of 15 xenografts grew significantly. Histopathologic examination and immunohistochemistry confirmed that VS xenografts retained their original microscopic and immunohistochemical characteristics after prolonged implantation. CONCLUSIONS: This study describes the first animal model for cystic schwannomas. Also, we demonstrate the use of high-field magnetic resonance imaging to quantify VS xenograft growth over time. The VS xenografts represent a model complimentary to Nf2 transgenic and knockout mice for translational VS research.

Animals↗

PubMed2006

Leaving a lasting impression: ear mold impressions as middle ear foreign bodies.

OBJECTIVES: We describe a series of otologic complications from impression material used to make hearing aid molds. METHODS: We examined a retrospective case series of patients presenting to a tertiary care academic medical center. RESULTS: The presentation, clinical course, and treatment outcomes of 6 patients with complications related to ear molds are discussed. These patients had preexisting abnormalities in their aural anatomy, including tympanic membrane perforations, retraction pockets, and mastoidectomy cavities. CONCLUSIONS: Although the majority of patients who have ear canal impressions taken experience no adverse outcomes, hearing aid dispensers should perform a thorough history-taking and physical examination to discern those with abnormal anatomy at risk for complications. These patients may benefit from evaluation in conjunction with an otolaryngologist.

Aged↗

PubMed2005

Current concepts in the evaluation and treatment of neurofibromatosis type II.

This article presents the current diagnostic and treatment options for the hereditary disease neurofibromatosis type II, reviews clinical presentation and diagnosis, highlights indications for and methods of clinical and genetic screening, discusses treatment approaches for surgery and stereotactic radiation, and summarizes potential future therapeutic avenues.

Decompression, Surgical↗

PubMed2005

Facial nerve monitoring parameters as a predictor of postoperative facial nerve outcomes after vestibular schwannoma resection.

OBJECTIVE: To evaluate whether the intraoperative stimulus threshold and response amplitude measurements from facial electromyography can predict facial nerve function at 1 year after vestibular schwannoma resection. STUDY DESIGN: Prospective study. SETTING: Tertiary academic center. PATIENTS: Seventy-four consecutive vestibular schwannoma patients. INTERVENTION: The minimal stimulus intensity (in milliamperes) and electromyographic response amplitude (in microvolts) were recorded during stimulation applied to the proximal facial nerve after vestibular schwannoma removal. MAIN OUTCOME MEASURE: Facial nerve outcomes at 1 year were evaluated using the House-Brackmann scale. Analysis was then performed to evaluate whether these electrophysiologic recordings and tumor size could predict facial nerve functional outcomes. RESULTS: Of the 74 patients, 66 of 74 (89%) had House-Brackmann Grade I or II facial nerve function and 8 of 74 (11%) had House-Brackmann Grade III-VI function at 1 year after surgery. If standards were set for intraoperative minimal stimulus intensity of 0.05 mA or less and response amplitude of 240 microV or greater, the authors were able to predict a House-Brackmann Grade I or II outcome in 56 of 66 (85%) patients at 1 year after surgery. With these same electrophysiologic parameters, only 1 of 8 (12%) House-Brackmann Grade III-VI patients also met this standard and thus gave a false-positive result. Logistic regression analysis of the data showed that both a stimulus threshold of 0.05 mA or less and a response amplitude of 240 microV or greater predicted a House-Brackmann Grade I or II outcome with a 98% probability. However, stimulus threshold or response amplitude alone had a much lower probability of the same result. In addition, although tumor size was found to independently predict facial nerve outcomes at 1 year, it did not improve the ability to predict facial nerve function over a model using stimulus intensity and amplitude alone. CONCLUSION: Individually, minimal stimulus intensity or response amplitude was less successful in predicting long-term postoperative facial nerve function. However, if both parameters are considered together, the study demonstrates that they are good prognostic indicators for facial nerve function at 1 year after surgery.

Adult↗

PubMed2005

Angiofibrolipoma of the ear canal.

OBJECTIVES/HYPOTHESIS: Described is the first reported case of an angiofibrolipoma of the ear canal in a patient who presented with right-sided conductive hearing loss and a medial canal stenosis. STUDY DESIGN: Case report. RESULTS/CONCLUSION: This variant of lipoma contains mature adipocytes, blood vessels, and dense collagenous tissue. The physical examination can be misleading, and the diagnosis requires histopathological examination. The patient was treated with complete surgical excision, tympanoplasty, canalplasty, and skin grafting to the external auditory canal. His pure-tone average improved from 37 to 11 dB, and his air-bone gap was closed completely. The lipoma has not recurred in the 6-month period following surgery.

Adult↗

PubMed2003

Predictive factors in pediatric stapedectomy.

OBJECTIVE/HYPOTHESIS: The objective of the study was to investigate predictive factors in the postoperative hearing outcomes in pediatric stapedectomy. STUDY DESIGN: Retrospective case series. The study was performed in a tertiary academic otological practice. METHODS: The outcome of 66 stapedectomies in children 17 years of age and younger were analyzed according to the 1995 American Academy of Otolaryngology-Head and Neck Surgery Committee on Hearing and Equilibrium guidelines. Factors evaluated included patient age, underlying diagnosis (tympanosclerosis, otosclerosis, congenital fixation), type of footplate graft and type of prosthesis used, associated ossicular abnormalities, and revision surgery. RESULTS: The mean postoperative air-bone gap following stapedectomy in children with tympanosclerotic footplate fixation (24.9 dB [+/-11 dB]) was significantly worse than in patients with an underlying diagnosis of congenital stapes fixation (15.7 dB [+/-9 dB]) or otosclerosis (13.1 dB [+/-3 dB]) (P =.024). Revision stapedectomy was also associated with a poorer outcome, but patient age and prosthesis and graft type did not contribute to the outcome in a statistically significant manner. CONCLUSIONS: Pediatric patients with stapes fixation resulting from tympanosclerosis showed poorer outcomes from stapedectomy than patients with congenital or otosclerotic fixation. Outcomes for congenital or otosclerosis fixation more nearly matched the outcomes in the literature for adult series.

Adolescent↗

PubMed2002

Multiple transcription initiation sites, alternative splicing, and differential polyadenylation contribute to the complexity of human neurofibromatosis 2 transcripts.

Northern blot analysis has shown that the human neurofibromatosis type 2 (NF2) cDNA hybridizes to multiple RNA species. To examine whether these hybridizing RNA species represent NF2 transcripts, we cloned the complete NF2 cDNA by a combination of techniques: 5' and 3' rapid amplification of cDNA ends, RT-PCR, and searching and sequencing the NF2-related cDNA clones from the IMAGE consortium. We showed that human NF2 transcripts initiate at multiple positions. Analogous to those reported previously, NF2 transcripts undergo alternative splicing in the coding exons. We isolated eight alternatively spliced NF2 cDNA isoforms, including one that contains a new exon termed exon 2', which potentially could encode proteins of different sizes. We assembled the overlapping cDNA fragments, and the longest NF2 cDNA, containing all 17 exons, consists of 6067 nucleotides, which is consistent with the size of the major RNA species hybridized to the NF2 probe. The cDNA has a 425-nucleotide 5' untranslated region upstream from the ATG start codon, and a long 3' untranslated region of 3869 nucleotides. We also isolated two shorter NF2 cDNAs that were terminated by different polyadenylation signal sequences, which indicates that differential usage of multiple polyadenylation sites also contributes to the complexity of human NF2 transcripts. By reference to the transcription initiation site mapped, we analyzed the 5' flanking sequence of the human NF2 gene. Transient transfection analysis in human 293 kidney, SK-N-AS neuroblastoma, and NT2/D1 teratocarcinoma cells with NF2 promoter-luciferase chimeric constructs revealed a core promoter region extending 400 base pairs from the major transcription initiation site. Although multiple regions are required for full promoter activity, a site-directed mutagenesis experiment identified a GC-rich sequence (position -58 to -46), which could be bound by transcription factor Sp1, as a positive cis-acting regulatory element. Cotransfection studies in Drosophila melanogaster SL2 cells showed that Sp1 could activate the NF2 promoter through the GC-rich sequence.

Alternative Splicing↗

PubMed2002

Virtual temporal bone dissection: an interactive surgical simulator.

OBJECTIVE: Our goal was to integrate current and emerging technology in virtual systems to provide a temporal bone dissection simulator that allows the user interactivity and realism similar to the cadaver laboratory. STUDY DESIGN: Iterative design and validation of a virtual environment for simulating temporal bone dissection. SETTING: University otolaryngology training program with interdisciplinary interaction in a high-performance computer facility. RESULTS: The system provides visual, force feedback (haptic), and aural interfaces. Unlike previous "fly through" virtual systems, this environment provides a richer emulation of surgical experience. CONCLUSION: The system provides a high level of functional utility and, through initial evaluations, demonstrates promise in adding to traditional training methods. SIGNIFICANCE: The system provides an environment to learn temporal bone surgery in a way similar to the experience with cadaver material where the subject is able to interact with the data without constraints (nondeterministic). Eventually, it may provide the "front end" to a large repository of various temporal bone pathologies that can be accessed through the Internet.

Algorithms↗

PubMed2002

Retinoblastoma-cyclin-dependent kinase pathway deregulation in vestibular schwannomas.

OBJECTIVES: The purpose of the study was to identify genes of the retinoblastoma protein (pRb)-cyclin-dependent kinase (CDK) pathway that are deregulated in vestibular schwannomas when compared with normal vestibular nerve tissues. STUDY DESIGN: Expression profiles in eight vestibular schwannomas (four sporadic tumors, one neurofibromatosis type 2 tumor, and three cystic tumors) and a paired normal vestibular nerve from one of the eight patients were chosen. Genes examined included the retinoblastoma susceptibility gene (Rb-1); cyclins D1, D2, A, and E; the CDK inhibitors p18, p19, and p27; CDK2 and CDK6; transcription factors E2F-4, E2F-5, and DP-1; and the neurofibromatosis type 2 gene. METHODS: Total RNA samples were extracted from normal vestibular nerve and vestibular schwannoma tissues and used to generate radiolabeled complementary DNA (cDNA) samples. Labeled cDNA probes were then hybridized to cDNA microarray filters. The hybridization signal was captured and quantified. Differential gene expression profiles between the normal vestibular nerve and vestibular schwannoma were compared. Real-time polymerase chain reaction and immunohistochemistry were used to further confirm the cDNA microarray data. RESULTS: Among genes in the pRb-CDK pathway, CDK2 was substantially underexpressed in seven of the eight vestibular schwannoma tumors examined. Quantitative RNA expression analysis using real-time polymerase chain reaction also showed consistent downregulation of CDK2 in the tumors. Anti-CDK2 antibody stained predominantly in the vestibular nerve and ganglion cells but only weakly in the vestibular schwannoma tissues. CONCLUSIONS: The pRb-CDK pathway was altered in all vestibular schwannoma tumors examined, with CDK2 significantly downregulated in seven of the eight tumors. Further investigation into the regulatory mechanisms governing CDK2 expression may lead to a better understanding of vestibular schwannoma tumorigenesis.

Adult↗

PubMed2002

cDNA microarray analysis of vestibular schwannomas.

BACKGROUND: Vestibular schwannomas are known to harbor mutations in the neurofibromatosis type 2 tumor suppressor gene, but the mechanism of the neurofibromatosis type 2 tumor suppressor gene action is not well understood. Identification of genes differentially expressed in normal and diseased tissues through the use of a large-scale, cDNA microarray approach may lead to increased understanding of pathways that lead to tumor formation. OBJECTIVE: The objectives of this study were to evaluate the gene expression profiles in vestibular schwannomas in comparison with normal vestibular nerve tissues and to identify pathways that may be altered in schwannomas. METHODS: Total RNA was extracted from one normal vestibular nerve and seven vestibular schwannomas. The normal vestibular nerve was from one of the seven patients with small vestibular schwannomas. Radiolabeled cDNA was synthesized and hybridized to cDNA microarray filters that contained 25,920 known genes or expressed sequence tags. Expression profiles were imaged and analyzed. Selected genes that showed three-fold or greater difference in the intensity between the normal nerve and the schwannomas were further examined by real-time polymerase chain reaction and by immunohistochemical staining. RESULTS: Forty-two genes (0.2%) were upregulated 3-fold or more in at least 5 of the 7 tumors when the filter images were compared with a normal adjacent vestibular nerve. Among them, osteonectin, an angiogenesis mediator, and RhoB GTPase, which is important in cell signaling, were significantly upregulated in 5 of 7 tumors. Among genes that were downregulated, an apoptosis-related LUCA-15 gene was highly underexpressed in 6 of 7 schwannomas when compared with the normal nerve. Also, ezrin, a relative of the NF2 protein, was significantly downregulated in 5 of 7 tumors. Real-time PCR and immunohistochemistry data support the cDNA microarray findings. CONCLUSION: Our cDNA microarray analysis of schwannomas suggested several interesting and potentially important tumorigenesis pathways associated with vestibular schwannoma formation. Further in vivo study is necessary to define the roles of these identified genes and their potential relationships with the neurofibromatosis type 2 tumor suppressor gene.

Adult↗