Biomedical subjects

Yasuhide Okamoto

Publications and source records attributed to Yasuhide Okamoto.

7 recordsLinked to original sources

PubMed2006

Cholesterol granuloma surrounding the endolymphatic sac.

We report a unique case of cholesterol granuloma (CG) surrounding the endolymphatic sac (ES). A 49-year-old man presented with the left side of sensorineural hearing loss, tinnitus, and vertigo. Magnetic resonance and computed tomography imaging revealed a CG surrounding the left ES. The patient initially underwent left transmastoid surgical resection of the tumor. At the time of surgery, brown fluid was aspirated from the tumor, but no other tumors were found. Histopathological examination revealed that the tumor contained cholesterol crystals, confirming the diagnosis of CG. At his 12-month postoperative follow-up, there was no evidence of recurrence. We discuss the radiology, pathology, and surgical removal of CGs surrounding ES.

Audiometry, Pure-Tone↗

PubMed2006

An artificially constructed de novo human chromosome behaves almost identically to its natural counterpart during metaphase and anaphase in living cells.

Human artificial chromosomes (HACs) are promising reagents for the analysis of chromosome function. While HACs are maintained stably, the segregation mechanisms of HACs have not been investigated in detail. To analyze HACs in living cells, we integrated 256 copies of the Lac operator into a precursor yeast artificial chromosome (YAC) containing alpha-satellite DNA and generated green fluorescent protein (GFP)-tagged HACs in HT1080 cells expressing a GFP-Lac repressor fusion protein. Time-lapse analyses of GFP-HACs and host centromeres in living mitotic cells indicated that the HAC was properly aligned at the spindle midzone and that sister chromatids of the HAC separated with the same timing as host chromosomes and moved to the spindle poles with mobility similar to that of the host centromeres. These results indicate that a HAC composed of a multimer of input alpha-satellite YACs retains most of the functions of the centromeres on natural chromosomes. The only difference between the HAC and the host chromosome was that the HAC oscillated more frequently, at higher velocity, across the spindle midzone during metaphase. However, this provides important evidence that an individual HAC has the capacity to maintain tensional balance in the pole-to-pole direction, thereby stabilizing its position around the spindle midzone.

Anaphase↗

PubMed2005

Rapid generation of long synthetic tandem repeats and its application for analysis in human artificial chromosome formation.

Human artificial chromosomes (HACs) provide a unique opportunity to study kinetochore formation and to develop a new generation of vectors with potential in gene therapy. An investigation into the structural and the functional relationship in centromeric tandem repeats in HACs requires the ability to manipulate repeat substructure efficiently. We describe here a new method to rapidly amplify human alphoid tandem repeats of a few hundred base pairs into long DNA arrays up to 120 kb. The method includes rolling-circle amplification (RCA) of repeats in vitro and assembly of the RCA products by in vivo recombination in yeast. The synthetic arrays are competent in HAC formation when transformed into human cells. As short multimers can be easily modified before amplification, this new technique can identify repeat monomer regions critical for kinetochore seeding. The method may have more general application in elucidating the role of other tandem repeats in chromosome organization and dynamics.

Cell Line, Tumor↗

PubMed2005

Permanent threshold shift caused by acute cochlear mitochondrial dysfunction is primarily mediated by degeneration of the lateral wall of the cochlea.

Mitochondrial dysfunction in the cochlea is thought to be an important cause of sensorineural hearing loss. Recently, we have established a novel rat model with acute hearing impairment caused by exposure to the mitochondrial toxin 3-nitropropionic acid (3-NP) to analyze the mechanism of cochlear mitochondrial dysfunction. Both permanent and temporary threshold shifts were observed in this model depending on the amount of 3-NP used to induce hearing impairment. In this study, we demonstrate cochlear morphological changes in the permanent threshold shift model. Marked degeneration was detected in type 2 fibrocytes in the spiral prominence, type 4 fibrocytes in the spiral ligament, marginal cells and intermediate cells in the stria vascularis 3 h after 3-NP administration; these changes were progressive for at least 14 days. Less prominent degeneration was detected in type 1 and type 3 fibrocytes in the spiral ligament. These results indicate that permanent threshold shift caused by acute cochlear mitochondrial dysfunction is primarily mediated by cellular degeneration in the lateral wall of the cochlea, and suggest that therapy of cochlear hearing loss due to acute energy failure may be achieved through protection and regeneration of the cochlear lateral wall.

Acute Disease↗

PubMed2005

[Evaluation of the quality of life in sudden deafness patients by HHIA (hearing Hatidicap Inventory) and questionnaire].

After treatments, several patients with sudden deafness (SD) continued to have symptoms, including hearing loss, tinnitus and dizziness. These unresolved symptoms and their effect on the quality of life (QOL) in SD patients have not been studied. We evaluated QOL using the Hearing handicap inventory (HHIA) and an original questionnaire in SD patients who had been treated more than 6 months prior to the study. Compared to results in bilateral sensorineural hearing were significantly lower in SD patients (p<0.01). In bil SNHL, this score peaked two to 10 years after onset of disease and decreased thereafter. The score peaked more than 10 years after onset of disease in patients with SD. While hearing and test scores were correlated in bil-SNHL, this was not observed in SD. About half of patients were embarrassed by hearing loss and tinnitus after treatment. Among patients who scored more than 44 points on HHIA, all reported hearing loss and tinnitus. When asked about subjective changes in hearing after treatment, 27% believed their hearing had improved, 60% believed there was no change, and 13% believed their hearing had deteriorated. Cases believing deterioration in hearing also had high scores on HHIA. Sequelae of SD may worsen QOL, driving embarrassed patients to visit other medical facilities in to improve their QOL. Even though hearing may not improve after initial treatment in ears affected by SD, informed consent about the clinical course and audiological follow-up should be done.

Adult↗

PubMed2004

A novel animal model of acute cochlear mitochondrial dysfunction.

Acute mitochondrial dysfunction in the cochlea is likely to result in hearing loss as a consequence of local energy shortage, similar to ischemia- or noise-induced hearing loss. To establish an animal model of acute cochlear mitochondrial dysfunction, we applied a mitochondrial toxin, 3-nitropropionic acid (3-NP) in the rat cochlea. Rats treated with 500mM 3-NP exhibited permanent threshold shifts in acoustic brainstem response while the same volume of 300mM 3-NP caused temporary threshold shifts. Histological examination in the permanent threshold shift model revealed severe degeneration of fibrocytes within spiral ligament and spiral limbus, indicating these cells are vulnerable to acute mitochondrial dysfunction. This model represents a novel tool for investigating the pathophysiology of acute cochlear mitochondrial dysfunction.

Animals↗

PubMed2003

Epigenetic assembly of centromeric chromatin at ectopic alpha-satellite sites on human chromosomes.

To investigate the mechanism of chromatin assembly at human centromeres, we isolated cultured human cell lines in which a transfected alpha-satellite (alphoid) YAC was integrated ectopically into the terminal region of host chromosome 16, where it was stably maintained. Centromere activity of the alphoid YAC was suppressed at ectopic locations on the host chromosome, as indicated by the absent or reduced assembly of CENP-A and -C. However, long-term culture in selective medium, or short-term treatment with the histone deacetylase inhibitor Trichostatin A (TSA), promoted the re-assembly of CENPA, -B and -C at the YAC site and the release of minichromosomes containing the YAC integration site. Chromatin immunoprecipitation analyses of the re-formed minichromosome and the alphoid YAC-based stable human artificial chromosome both indicated that CENP-A and CENP-B assembled only on the inserted alphoid array but not on the YAC arms. On the YAC arms at the alphoid YAC integration sites, TSA treatment increased both the acetylation level of histone H3 and the transcriptional level of a marker gene. An increase in the level of transcription was also observed after long-term culture in selective medium. These activities, which are associated with changes in chromatin structure, might reverse the suppressed chromatin state of the YAC at ectopic loci, and thus might be involved in the epigenetic change of silent centromeres on ectopic alphoid loci.

Acetylation↗