Biomedical subjects

Akira Katsumi

Publications and source records attributed to Akira Katsumi.

9 recordsLinked to original sources

PubMed2006

High titer of ADAMTS13 inhibitor associated with thrombotic microangiopathy of the gut and skeletal muscle after allogeneic hematopoietic stem cell transplantation.

Transplantation-associated thrombotic microangiopathy (TMA) is one of the main complications after hematopoietic stem cell transplantation (HSCT). At the time of onset of gut TMA, a patient developed a high titer of an inhibitor of the non-immunoglobulin G type to ADAMTS13, which physiologically hydrolyzes von Willebrand factor to control spontaneous intravascular thrombus formation. The patient developed symptoms of myositis, a disorder that has occasionally been reported to manifest after HSCT and to resemble some idiopathic autoimmune diseases. However, a muscle biopsy specimen presented pathologic findings of TMA, including microvascular platelet thrombus formation, without inflammatory lymphocyte infiltration. ADAMTS13 activities returned to normal after steroid treatment, and the improvement of TMA symptoms followed. This patient appears to represent a rare case of post-HSCT TMA associated with the development of an ADAMTS13 inhibitor.

ADAM Proteins↗

PubMed2006

Recurrent intramural hematoma of the small intestine in a severe hemophilia A patient with a high titer of factor VIII inhibitor: a case report and review of the literature.

A 17-year-old man with severe hemophilia A (factor VIII <1%) developed intermittent left upper quadrant pain. He had a high titer of factor VIII inhibitor (1024 Bethesda units/mL) and was diagnosed with intramural hematoma of the jejunum. He was managed conservatively with activated prothrombin complex concentrate (APCC), resulting in the resolution of symptoms. He developed recurrent intramural hematoma of the small intestine over the next 54 months, and was successfully treated with APCC. This case highlights a rare clinical manifestation in hemophilia patients, and also indicates the effectiveness of APCC instead of exploratory surgery for intramural hematoma. Cases of intramural hematoma of the gastrointestinal tract among hemophilia patients are also reviewed.

Adolescent↗

PubMed2006

Establishment of a stroma-dependent human acute myelomonocytic leukemia cell line, NAMO-2, with FLT3 tandem duplication.

We have established a stroma-dependent myelomonocytic cell line, NAMO-2, with FLT3 internal tandem duplication (FLT3/ITD). Leukemia cells from a patient with acute myelomonocytic leukemia were administered to form subcutaneous tumors in nude mice, which were maintained successively, although we failed to establish continuously growing cells from the original leukemia cell culture. In the cultures of cells from subcutaneous tumors, there were stroma cells that had originated from the nude mice and showed continuous growth. The leukemia cells showed continuous growth dependent on this stroma, and this cell line was named NAMO-2. Detection of FLT3/ITD by the reverse transcriptase polymerase chain reaction (PCR) and genomic PCR showed that NAMO-2 was homozygous for FLT3/ITD. Constitutive activation of FLT3 was detected by Western blotting, and the phosphorylation of Akt, MEK, and STAT5 was also observed. FLT3 kinase inhibitor AG1296 specifically inhibited cell growth. NAMO-2 provides a useful tool to analyze adherence-dependent survival signaling of leukemia with FLT3/ITD and a model for the screening of FLT3 kinase inhibitors.

Animals↗

PubMed2005

Identification of amino acid residues essential for heparin binding by the A1 domain of human von Willebrand factor.

Platelet adhesion is mediated by von Willebrand factor (VWF) that binds platelet glycoprotein Ib (GPIb). Previous observations suggested that heparin competitively inhibits the binding of VWF to GPIb and may down-regulate platelet adhesion. We performed charged-to-alanine scanning mutagenesis of domain A1 and studied dose-dependent binding to heparin-Sepharose beads. Mutations at Lys1362 and Arg1395, at which the GPIb binding was markedly decreased, showed 41% and 42% binding, respectively. Clustered mutations in the segments 1332KDRKR1336 and 1405KKKK1408, which have been proposed as heparin binding sequences, showed 72% and 52% binding, respectively. However, single alanine substitutions within these clusters showed normal binding. Our findings suggest that heparin may inhibit the binding of VWF to GPIb by interacting with GPIb binding and interpret why some hemorrhagic complications of heparin therapy are not predictable based on techniques for monitoring the conventional anticoagulant effects of heparin.

Amino Acid Substitution↗

PubMed2005

Integrin activation and matrix binding mediate cellular responses to mechanical stretch.

Mechanical tension is a critical determinant of cell growth, differentiation, apoptosis, migration, and development. Integrins have been implicated in sensing force but little is known about how forces are transduced to biochemical signals. We now show that mechanical strain stimulates conformational activation of integrin alphavbeta3 in NIH3T3 cells. Integrin activation is mediated by phosphoinositol 3-kinase and is followed by an increase in integrin binding to extracellular matrix proteins. Mechanical stretch stimulation of JNK was dependent on new integrin binding to extracellular matrix. These data define a molecular mechanism for the role of integrins in mechanotransduction.

Animals↗

PubMed2005

Rho-kinase and myosin II activities are required for cell type and environment specific migration.

Cell migration is important in the development of atherosclerotic lesions. Macrophages and smooth muscle cells migrate into the subendothelial space of arteries, leading to plaque formation. Long-term inhibition of the activity of Rho-kinase induces a regression of atherosclerotic coronary lesions, probably by preventing migration of macrophages and smooth muscle cells. Previous reports concerning the effect of Rho-kinase inhibitors on cell migration are contradictory, however. We examined here the cell type specificity of Rho-kinase inhibitors and found that migration of endothelial cells, macrophages, and smooth muscle cells was inhibited by treatment with Rho-kinase inhibitors in a dose-dependent fashion in a three-dimensional migration assay, whereas that of fibroblasts and epithelial cells was not inhibited. Myosin II inhibitor prevented cell migration in a manner similar to Rho-kinase inhibitors. In contrast, in a two-dimensional migration assay, cell migration was not inhibited by Rho-kinase or myosin II inhibitors for any of the cell types examined. Taken together, these results indicate that Rho-kinase inhibitors suppress migration of specific cell types under specific conditions through the regulation of myosin II activity. Our findings suggest that Rho-kinase is the therapeutic target of atherosclerosis accompanied with invasion by leukocytes and smooth muscle cells.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗

PubMed2004

Targeted disruption of mouse ortholog of the human MYH9 responsible for macrothrombocytopenia with different organ involvement: hematological, nephrological, and otological studies of heterozygous KO mice.

Among three different isoforms of non-muscle myosin heavy chains (NMMHCs), only NMMHCA is associated with inherited human disease, called MYH9 disorders, characterized by macrothrombocytopenia and characteristic granulocyte inclusions. Here targeted gene disruption was performed to understand fundamental as well as pathological role of the gene for NMMHCA, MYH9. Heterozygous intercrosses yielded no homozygous animals among 552 births, suggesting that MYH9 expression is required for embryonic development. In contrast, MYH9+/- mice were viable and fertile without gross anatomical, hematological, and nephrological abnormalities. Immunofluorescence analysis also showed the normal cytoplasmic distribution of NMMHCA. We further measured the auditory brainstem response and found two of six MYH9+/- mice had hearing losses, whereas the remaining four were comparable to wild-type mice. Such observation may parallel the diverse expression of Alport's manifestations of human individuals with MYH9 disorders and suggest the limited requirement of the gene for maintenance and function of specific organs.

Animals↗

PubMed2004

Integrins in mechanotransduction.

Mechanical forces are crucial to the regulation of cell and tissue morphology and function. At the cellular level, forces influence cytoskeletal organization, gene expression, proliferation, and survival. Integrin-mediated adhesions are intrinsically mechanosensitive and a large body of data implicates integrins in sensing mechanical forces. We review the relationship between integrins and mechanical forces, the role of integrins in cellular responses to stretch and fluid flow, and propose that some of these events are mechanistically related.

Animals↗

PubMed2002

Effects of cell tension on the small GTPase Rac.

Cells in the body are subjected to mechanical stresses such as tension, compression, and shear stress. These mechanical stresses play important roles in both physiological and pathological processes; however, mechanisms transducing mechanical stresses into biochemical signals remain elusive. Here, we demonstrated that equibiaxial stretch inhibited lamellipodia formation through deactivation of Rac. Nearly maximal effects on Rac activity were obtained with 10% strain. GAP-resistant, constitutively active V12Rac reversed this inhibition, supporting a critical role for Rac inhibition in the response to stretch. In contrast, activation of endogenous Rac with a constitutively active nucleotide exchange factor did not, suggesting that regulation of GAP activity most likely mediates the inhibition. Uniaxial stretch suppressed lamellipodia along the sides lengthened by stretch and increased it at the adjacent ends. A fluorescence assay for localized Rac showed comparable changes in activity along the sides versus the ends after uniaxial stretch. Blocking polarization of Rac activity by expressing V12Rac prevented subsequent alignment of actin stress fibers. Treatment with Y-27632 or ML-7 that inhibits myosin phosphorylation and contractility increased lamellipodia through Rac activation and decreased cell polarization. We hypothesize that regulation of Rac activity by tension may be important for motility, polarization, and directionality of cell movement.

Amides↗