Search for nucleon decay via n→ν[over ¯]π0 and p→ν[over ¯]π+ in Super-Kamiokande.

We present the results of searches for nucleon decay via n→ν[over ¯]π0 and p→ν[over ¯]π+ using data from a combined 172.8 kt·yr exposure of Super-Kamiokande-I,-II, and-III. We set lower limits on the partial lifetime for each of these modes: τn→ν[over ¯]π0>1.1×10(33) years and τp→ν[over ¯]π+>3.9×10(32) years at a 90% confidence level.

Search for dinucleon decay into kaons in Super-Kamiokande.

A search for the dinucleon decay pp → K+ K+ has been performed using 91.6 kton·yr data from Super-Kamiokande-I. This decay provides a sensitive probe of the R-parity-violating parameter λ112''. A boosted decision tree analysis found no signal candidates in the data. The expected background was 0.28±0.19 atmospheric neutrino induced events and the estimated signal detection efficiency was 12.6%±3.2%. A lower limit of 1.7×10(32) years has been placed on the partial lifetime of the decay O16 → C14K+ K+ at 90% C.L. A corresponding upper limit of 7.8×10(-9) has been placed on the parameter λ112''.

Evidence for the appearance of atmospheric tau neutrinos in super-Kamiokande.

Super-Kamiokande atmospheric neutrino data were fit with an unbinned maximum likelihood method to search for the appearance of tau leptons resulting from the interactions of oscillation-generated tau neutrinos in the detector. Relative to the expectation of unity, the tau normalization is found to be 1.42 ± 0.35(stat)(-0.12)(+0.14)(syst) excluding the no-tau-appearance hypothesis, for which the normalization would be zero, at the 3.8σ level. We estimate that 180.1 ± 44.3(stat)(-15.2)(+17.8) (syst) tau leptons were produced in the 22.5 kton fiducial volume of the detector by tau neutrinos during the 2806 day running period. In future analyses, this large sample of selected tau events will allow the study of charged current tau neutrino interaction physics with oscillation produced tau neutrinos.

Search for differences in oscillation parameters for atmospheric neutrinos and antineutrinos at Super-Kamiokande.

We present a search for differences in the oscillations of antineutrinos and neutrinos in the Super-Kamiokande-I, -II, and -III atmospheric neutrino sample. Under a two-flavor disappearance model with separate mixing parameters between neutrinos and antineutrinos, we find no evidence for a difference in oscillation parameters. Best-fit antineutrino mixing is found to be at (Δm2,sin2 2θ)=(2.0×10(-3) eV2, 1.0) and is consistent with the overall Super-K measurement.

Continuous expression of Bcl-xL protein during megakaryopoiesis is post-translationally regulated by thrombopoietin-mediated Akt activation, which prevents the cleavage of Bcl-xL.

BACKGROUND: One of the important biological activities of thrombopoietin (TPO) is to prevent the apoptosis of megakaryocytes. As the antiapoptotic protein Bcl-xL, which has been proven to be indispensable for erythroid differentiation, is also abundantly expressed in megakaryocytes, it is assumed that Bcl-xL plays an important role in megakaryopoiesis. OBJECTIVES: We investigated the expression of Bcl-xL during megakaryopoiesis and the underlying regulatory mechanism. METHODS AND RESULTS: In stem cell-derived megakaryocytes, expression of Bcl-xL increased in the early and mid-stages of the differentiation. Both in vitro in cell culture and in vivo in an animal model, expression of Bcl-xL protein was maintained until the platelet-producing stage. TPO depletion caused significant decrease in Bcl-xL protein level without affecting its mRNA in both megakaryocytes and TPO-dependent megakaryocytic UT-7/TPO cells, suggesting that Bcl-xL protein level in TPO-dependent cells is post-translationally regulated. In agreement with this finding, we recognized the appearance of a 12-kD fragment of Bcl-xL upon TPO depletion. This cleavage of Bcl-xL was inhibited by a caspase-3-specific inhibitor. Furthermore, pretreatment of UT-7/TPO with a phosphatidylinositol 3-kinase (PI3 K) inhibitor resulted in the cleavage of Bcl-xL even in the presence of TPO. We thus hypothesized that PI3 K inhibits the activation of caspase-3 and consequent cleavage of Bcl-xL. To prove this, we prepared UT-7/TPO cells transfected with constitutively active Akt-1. When TPO was depleted, the transfectant was significantly less liable to caspase-3 activation and Bcl-xL cleavage. CONCLUSIONS: Bcl-xL protein is expressed throughout megakaryopoiesis until platelets are produced, and its expression level is at least in part post-translationally regulated through TPO-mediated Akt activation.

Characterization of a patient with glycoprotein (GP) VI deficiency possessing neither anti-GPVI autoantibody nor genetic aberration.

BACKGROUND: There have been only seven reported cases of glycoprotein (GP) VI deficiency. However, the pathogenesis of this disorder has not been well-elucidated. OBJECTIVES: We characterized a novel patient with GPVI deficiency and used these platelets to investigate the role of GPVI in normal hemostasis. PATIENT: A 31-year-old female with immune thrombocytopenic purpura who had been suffering from mild bleeding diathesis even after recovery from thrombocytopenia. RESULTS AND CONCLUSION: The patient's platelets did not aggregate in response to either convulxin or collagen-related peptide. Immunoblotting revealed complete absence of the GPVI molecule, whereas a significantly reduced but substantial amount of Fc receptor (FcR) gamma-chain was expressed. Platelet stimulation with convulxin did not induce tyrosine-phosphorylation of FcR gamma-chain, indicating a defect in GPVI-mediated signaling. Concerning the underlying pathogenesis, we found normal level of GPVI-mRNA expression, no aberration of the sequence of the entire coding region of GPVI, and presence of degraded GPVI in her plasma. However, no anti-GPVI autoantibody was detected either by the binding assay to GPVI-Fc2 fusion protein or by immunoblotting/immunoprecipitation using the patient's immunoglobulin. We thus consider that either a short-time exposure to anti-GPVI autoantibody or a continuous exposure to low titers of the autoantibody has resulted in persistent GPVI deficiency. Under high shear flow, the patient's platelets could not form large aggregates, although initial platelet attachment was obviously observed. These results suggest that GPVI deficiency in this patient resulted in defective platelet thrombi development, manifesting as bleeding diathesis. Furthermore, our observations indicate that coordination of GPVI with integrin alpha2beta1 is essential for physiological platelet thrombus formation.

Enhanced expression of CD71, transferrin receptor, on immature reticulocytes in patients with paroxysmal nocturnal hemoglobinuria.

Erythroid cells in the marrow express CD71, transferrin receptor, and reticulocytes released from the marrow lose their expression during maturation. The immature reticulocyte fraction, the proportion of reticulocytes with the highest content of RNA, has been determined by hematology analysis. In the present study, we examined CD71 expression on immature reticulocytes by flow cytometry (FCM) in paroxysmal nocturnal hemoglobinuria (PNH) patients with reticulocytosis. We modified 'reticulocyte-gated FCM' to multi-color FCM, i.e. RNA/CD71, RNA-CD59 or CD59/CD71/CD45. In PNH, in addition to the increased number of immature reticulocytes (%CD71-positive), a more immature phenotype in regard to both CD71 intensity and RNA content levels was demonstrated. In seven PNH patients studied, %CD71-positive reticulocytes were significantly increased at 32.2 +/- 11.9% (n = 10, normal 10.4 +/- 3.5%, P = 0.002). RNA content levels (assessed by mean fluorescence index, MFI) in CD71-positive reticulocytes were significantly increased at 812.0 +/- 215.2 MFI in PNH (n = 10, normal 508 +/- 86.1 MFI, P = 0.002). These data indicate that stimulated erythropoietic conditions induce the release of more immature reticulocytes to the peripheral blood than ordinary erythropoietic conditions. CD71 intensity on immature reticulocytes was well correlated with their RNA content levels, indicating the usefulness of CD71 as an immature reticulocyte marker.

The pro-apoptotic BH3-only protein Bim regulates cell cycle progression of hematopoietic progenitors during megakaryopoiesis.

SUMMARY BACKGROUND: The pro-apoptotic BH3-only protein Bim is recognized as a pivotal regulator of apoptosis induced by the depletion of cytokines. In the present study, we examined the role of Bim in megakaryopoiesis. METHODS: Megakaryocyte (MK) progenitors obtained from bim knockout (KO) mice were analyzed in vitro for liability to apoptosis after the depletion of cytokines, ability to differentiate into MKs and proliferation/cell cycle progression in response to thrombopoietin (TPO). The production of platelets in vitro was evaluated by assaying the formation of proplatelets in MKs. Megakaryopoiesis in vivo was observed in a mouse model of thrombocytopenia induced by injecting fluorouracil (5-FU). RESULTS: Bim-deficient CD34-/c-kit+/Sca-1+/Lineage- stem cells and MKs were highly resistant to apoptosis induced by cytokine depletion, suggesting that Bim is involved in the apoptotic process in both stem cells and MKs. As bim KO mice exhibited splenomegaly and thrombocytopenia, splenectomized mice were used for experiments in vivo. Platelet recovery after 5-FU-induced thrombocytopenia was significantly delayed in bim KO mice. Corresponding with this, numbers of MKs in the recovery phase bone marrow were significantly reduced in bim KO mice. Culture of c-kit+/Lineage- progenitors with TPO revealed that Bim-deficient cells poorly proliferate and differentiate into CD41+ cells in comparison with wild-type (WT) cells. However, once differentiated into MKs, these cells matured normally. Furthermore, cell cycle analyses demonstrated that transition from the G1 to the S phase was delayed in Bim-deficient stem cells. CONCLUSIONS: In the present study, we demonstrated that Bim plays a pivotal role in the regulation of cell cycle progression in hepatopoietic progenitors during megakaryopiesis.

Caspase activation is involved in early megakaryocyte differentiation but not in platelet production from megakaryocytes.

To elucidate whether caspase activation is involved in megakaryopoiesis, we characterized megakaryocytes (MKs) in vav-bcl-2 transgenic (Tg) mice, in which Bcl-2 is overexpressed in hematopoietic cells. To exclude the effect of splenomegaly in Tg mice on megakaryopoiesis, splenectomy was performed. After splenectomy, basal platelet counts in peripheral blood were not significantly different between Tg and wild-type (WT) mice. However, when experimental thrombocytopenia was induced by injecting 5-fluorouracil into splenectomized mice, overshoot of platelet counts during the recovery phase was hardly observed in Tg mice. Analyses of MK ploidy during the recovery phase showed that MKs less than 16 N ploidy were significantly decreased in Tg mice, suggesting that MK supply from progenitors is impaired. Supporting this, differentiation of CD34-/c-kit+/Sca-1+/Lineage- stem cells into MKs was significantly hampered in Tg mice, whereas megakaryocyte-erythroid progenitors (MEPs) normally differentiated into MKs. It suggests that differentiation into MKs is impaired in Tg mice before the stage of MEP. Furthermore, MK colony formation in WT cells was dose-dependently inhibited in the presence of a caspase inhibitor. Contrary, Bcl-2-overexpressing MKs showed normal ability for in vitro platelet production. We thus believe that caspase activation is involved in the differentiation of progenitors into megakaryocytic lineage but not in platelet production.