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Atsushi Mikami

Publications and source records attributed to Atsushi Mikami.

10 recordsLinked to original sources
PubMed2007

Expression patterns of LIS1, dynein and their interaction partners dynactin, NudE, NudEL and NudC in human gliomas suggest roles in invasion and proliferation.

Diffusely infiltrating gliomas are the most common type of primary intracranial neoplasm in humans. One of the major obstacles to the effective treatment of these tumors is their highly infiltrative growth. However, mechanisms controlling their migration and proliferation are poorly understood. Glioma cells resemble neural progenitors, and we hypothesize that gliomas recapitulate the capacity of migration and proliferation of progenitors that takes place during brain development. Based on recent evidence implicating cytoplasmic dynein and its regulatory proteins in neural progenitor migration and division, we conducted immunohistochemical evaluation of surgically resected human glioma samples for the presence and distribution of these proteins. We examined expression of LIS1, the gene responsible for type I lissencephaly, cytoplasmic dynein and the dynein- and LIS1-interacting factors dynactin, NudE/NudEL and NudC, which play significant roles in neural progenitor cell behavior. We found that each of these proteins is expressed in all histological types and grades of human neuroectodermal tumors examined. Immunohistochemical analysis revealed that the levels of expression varied from cell to cell within each tumor, ranging from very high to undetectable. This stands in contrast to the low levels of diffuse staining seen in non-neoplastic brain tissue. Of particular interest, we noted tumor cells infiltrating the white matter and tumor cells undergoing cell division amongst the cells with notably high expression levels. These findings are compatible with the idea that LIS1 and its interacting proteins play a role in glioma migration and proliferation analogous to their role during brain development.

1-Alkyl-2-acetylglycerophosphocholine Esterase↗
PubMed2006

Treatment with granulocyte colony-stimulating factor ameliorates chronic heart failure.

Chronic heart failure remains a leading cause of mortality. Although granulocyte colony-stimulating factor (G-CSF) is reported to have a beneficial affect on postinfarction cardiac remodeling and dysfunction when administered before the onset of or at the acute stage of myocardial infarction (MI), its effect on established heart failure is unknown. We show here that subcutaneous administration of G-CSF greatly improves the function of murine hearts failing due to a large, healed MI. G-CSF changed the geometry of the infarct scar from elongated and thin to short and thick, induced hypertrophy among surviving cardiomyocytes, and reduced myocardial fibrosis. Expression of G-CSF receptor was confirmed in failing hearts and was upregulated by G-CSF treatment. G-CSF treatment also led to activation of signal transducer and activator of transcription-3 and induction of GATA-4 and various sarcomeric proteins such as myosin heavy chain, troponin I and desmin. Expression of metalloproteinase-2 and -9 was also increased in G-CSF-treated hearts, while that of tumor necrosis factor-alpha, angiotensin II type 1 receptor (AT1) and transforming growth factor-beta1 was reduced. Although activation of Akt was noted in G-CSF-treated hearts, vessel density was unchanged, and apoptosis was too rare to exert a meaningful effect. No bone marrow-derived cardiomyocytes or vascular cells were detected in the failing hearts of green fluorescent protein chimeric mice. Finally, beneficial effects of G-CSF on cardiac function were found persisting long after discontinuing the treatment (2 weeks). Collectively, these findings suggest G-CSF administration could be an effective approach to treating chronic heart failure following a large MI.

Animals↗
PubMed2006

A therapeutic dose of the lipophilic statin pitavastatin enhances oxidant-induced apoptosis in human vascular smooth muscle cells.

We examined effects of a physiologic concentration of pitavastatin (0.01 micromol/L) on oxidant-induced apoptosis in cultured human vascular smooth muscle cells (VSMCs). Apoptosis was induced in VSMCs by hydrogen peroxide (H2O2, 300 micromol/L), as evidenced by in situ nick end-labeling and scanning electron microscopy. This apoptotic response was accompanied by increased activation of mitogen-activated protein kinases (MAPKs--ie, increases in the phosphorylated forms of extracellular signal-regulated kinase (p-ERK), c-Jun N-terminal kinase (p-JNK), and p38 MAPK (p-p38 MAPK). Although pitavastatin alone did not induce VSMC death, pretreatment with pitavastatin significantly enhanced H2O2-induced apoptosis and prolonged activation of JNK and p38 MAPK (for up to 24 h) but not ERK. Expression of MAPK phosphatase-1 (MKP-1) also was upregulated by H2O2, but this was not affected by pitavastatin. The apoptosis accelerating effect was observed also in simvastatin but not in pravastatin. Treating VSMCs with mevalonate, farnesyl pyrophosphate, or geranylgeranyl pyrophosphate completely blocked the statin-induced enhancement of VSMC apoptosis, suggesting that protein prenylation is critically involved. It thus appears that pitavastatin enhances H2O2-induced VSMC apoptosis, at least in part, via increases in MAPK activation and protein prenylation, but independently of MKP-1 expression, which consequently results in reduction of VSMC population.

Apoptosis↗
PubMed2005

Long range allosteric control of cytoplasmic dynein ATPase activity by the stalk and C-terminal domains.

The dynein motor domain consists of a ring of six AAA domains with a protruding microtubule-binding stalk and a C-terminal domain of unknown function. To understand how conformational information is communicated within this complex structure, we produced a series of recombinant and proteolytic rat motor domain fragments, which we analyzed enzymatically. A recombinant 210-kDa half-motor domain fragment surprisingly exhibited a 6-fold higher steady state ATPase activity than a 380-kDa complete motor domain fragment. The increased ATPase activity was associated with a complete loss of sensitivity to inhibition by vanadate and an approximately 100-fold increase in the rate of ADP release. The time course of product release was discovered to be biphasic, and each phase was stimulated approximately 1000-fold by microtubule binding to the 380-kDa motor domain. Both the half-motor and full motor domain fragments were remarkably resistant to tryptic proteolysis, exhibiting either two or three major cleavage sites. Cleavage near the C terminus of the 380-kDa motor domain released a 32-kDa fragment and abolished sensitivity to vanadate. Cleavage at this site was insensitive to ATP or 5'-adenylyl-beta,gamma-imidodiphosphate but was blocked by ADP-AlF3 or ADP-vanadate. Based on these data, we proposed a model for long range allosteric control of product release at AAA1 and AAA3 through the microtubule-binding stalk and the C-terminal domain, the latter of which may interact with AAA1 to close the motor domain ring in a cross-bridge cycle-dependent manner.

Adenosine Diphosphate↗
PubMed2005

Postinfarction gene therapy against transforming growth factor-beta signal modulates infarct tissue dynamics and attenuates left ventricular remodeling and heart failure.

BACKGROUND: Fibrosis and progressive failure are prominent pathophysiological features of hearts after myocardial infarction (MI). We examined the effects of inhibiting transforming growth factor-beta (TGF-beta) signaling on post-MI cardiac fibrosis and ventricular remodeling and function. METHODS AND RESULTS: MI was induced in mice by left coronary artery ligation. An adenovirus harboring soluble TGF-beta type II receptor (Ad.CAG-sTbetaRII), a competitive inhibitor of TGF-beta, was then injected into the hindlimb muscles on day 3 after MI (control, Ad.CAG-LacZ). Post-MI survival was significantly improved among sTbetaRII-treated mice (96% versus control at 71%), which also showed a significant attenuation of ventricular dilatation and improved function 4 weeks after MI. At the same time, histological analysis showed reduced fibrous tissue formation. Although MI size did not differ in the 2 groups, MI thickness was greater and circumference was smaller in the sTbetaRII-treated group; within the infarcted area, alpha-smooth muscle actin-positive cells were abundant, which might have contributed to infarct contraction. Apoptosis among myofibroblasts in granulation tissue during the subacute stage (10 days after MI) was less frequent in the sTbetaRII-treated group, and sTbetaRII directly inhibited Fas-induced apoptosis in cultured myofibroblasts. Finally, treatment of MI-bearing mice with sTbetaRII was ineffective if started during the chronic stage (4 weeks after MI). CONCLUSIONS: Postinfarction gene therapy aimed at suppressing TGF-beta signaling mitigates cardiac remodeling by affecting cardiac fibrosis and infarct tissue dynamics (apoptosis inhibition and infarct contraction). This suggests that such therapy may represent a new approach to the treatment of post-MI heart failure, applicable during the subacute stage.

Animals↗
PubMed2004

Critical roles for the Fas/Fas ligand system in postinfarction ventricular remodeling and heart failure.

In myocardial infarction (MI), granulation tissue cells disappear via apoptosis to complete a final scarring with scanty cells. Blockade of this apoptosis was reported to improve post-MI ventricular remodeling and heart failure. However, the molecular biological mechanisms for the apoptosis are unknown. Fas and Fas ligand were overexpressed in the granulation tissue at the subacute stage of MI (1 week after MI) in mice, where apoptosis frequently occurred. In mice lacking functioning Fas (lpr strain) and in those lacking Fas ligand (gld strain), apoptotic rate of granulation tissue cells was significantly fewer compared with that of genetically controlled mice, and post-MI ventricular remodeling and dysfunction were greatly attenuated. Mice were transfected with adenovirus encoding soluble Fas (sFas), a competitive inhibitor of Fas ligand, on the third day of MI. The treatment resulted in suppression of granulation tissue cell apoptosis and produced a thick, cell-rich infarct scar containing rich vessels and bundles of smooth muscle cells with a contractile phenotype at the chronic stage (4 weeks after MI). This accompanied not only alleviation of heart failure but also survival improvement. However, the sFas gene delivery during scar tissue phase was ineffective, suggesting that beneficial effects of the sFas gene therapy owes to inhibition of granulation tissue cell apoptosis. The Fas/Fas ligand interaction plays a critical role for granulation tissue cell apoptosis after MI. Blockade of this apoptosis by interfering with the Fas/Fas ligand interaction may become one of the therapeutic strategies against chronic heart failure after large MI.

Adenoviridae↗
PubMed2004

Expression of vascular endothelial growth factor and its receptors Flk-1 and Flt-1 during the regeneration of autotransplanted adrenal cortex in the adrenalectomized rat.

PURPOSE: Autotransplantation of the adrenal cortex may be a therapeutic alternative in the future. For successful adrenal transplantation revascularization is necessary. It is possible that vascular endothelial growth factor (VEGF), which is a potent angiogenic peptide, may have some roles in adrenal transplantation through 2 its receptors, kinase insert domain-containing region (Flk-1) and fms-like tyrosine kinase (Flt-1). Therefore, we studied sequential changes in expression of VEGF, Flk-1 and Flt-1 in regenerated adrenal. MATERIALS AND METHODS: Eight to 9-week-old male Wistar rats underwent bilateral adrenalectomy and immediate adrenal capsular autotransplantation. The expression of VEGF, Flk-1 and Flt-1 was analyzed by immunohistochemistry and reverse-transcriptase-polymerase chain reaction. RESULTS: Angiogenesis was observed in the remodeling of adrenal sinusoidal endothelium during adrenal regeneration. Reverse transcriptase-polymerase chain reaction and immunohistochemistry showed that VEGF expression increased in grafted tissue with time after transplantation and its Flk-1 receptor, which localized to endothelial cells, increased transiently during the regeneration process. Immunostaining for Flt-1 receptor was identified in adrenocortical cells and its intensity gradually increased during adrenal regeneration. CONCLUSIONS: During adrenal gland regeneration VEGF and its receptors Flk-1 and Flt-1 are thought to be involved in neovascularization.

Adrenal Cortex↗
PubMed2002

Molecular structure of cytoplasmic dynein 2 and its distribution in neuronal and ciliated cells.

Cytoplasmic dynein is involved in a wide variety of cellular functions. In addition to the initially characterized form (MAP 1C/dynein 1), a second form of cytoplasmic dynein (dynein 2) has been identified and implicated in intraflagellar transport (IFT) in lower eukaryotes and in Golgi organization in vertebrates. In the current study, the primary structure of the full-length dynein 2 heavy chain (HC) was determined from cDNA sequence. The dynein 1 and dynein 2 sequences were similar within the motor region, and around the light intermediate chain (LIC)-binding site within the N-terminal stem region. The dynein 2 HC co-immunoprecipitated with LIC3, a homologue of dynein 1 LICs. Dynein 2 mRNA was abundant in the ependymal layer of the neural tube and in the olfactory epithelium. Antibodies to dynein 2 HC, LIC3 and a component of IFT particles strongly stained the ependymal layer lining the lateral ventricles. Both dynein 2 HC and LIC3 staining was also observed associated with connecting cilia in the retina and within primary cilia of non-neuronal cultured cells. These data support a specific role for dynein 2 in the generation and maintenance of cilia.

Animals↗
PubMed2002

A requirement for cytoplasmic dynein and dynactin in intermediate filament network assembly and organization.

We present evidence that vimentin intermediate filament (IF) motility in vivo is associated with cytoplasmic dynein. Immunofluorescence reveals that subunits of dynein and dynactin are associated with all structural forms of vimentin in baby hamster kidney-21 cells. This relationship is also supported by the presence of numerous components of dynein and dynactin in IF-enriched cytoskeletal preparations. Overexpression of dynamitin biases IF motility toward the cell surface, leading to a perinuclear clearance of IFs and their redistribution to the cell surface. IF-enriched cytoskeletal preparations from dynamitin-overexpressing cells contain decreased amounts of dynein, actin-related protein-1, and p150Glued relative to controls. In contrast, the amount of dynamitin is unaltered in these preparations, indicating that it is involved in linking vimentin cargo to dynactin. The results demonstrate that dynein and dynactin are required for the normal organization of vimentin IF networks in vivo. These results together with those of previous studies also suggest that a balance among the microtubule (MT) minus and plus end-directed motors, cytoplasmic dynein, and kinesin are required for the assembly and maintenance of type III IF networks in interphase cells. Furthermore, these motors are to a large extent responsible for the long recognized relationships between vimentin IFs and MTs.

Animals↗