LIM kinase/cofilin dysregulation promotes macrothrombocytopenia in severe von Willebrand disease-type 2B

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Abstract

von Willebrand disease type 2B (VWD-type 2B) is characterized by gain-of-function mutations of von Willebrand factor (vWF) that enhance its binding to platelet glycoprotein Ibα and alter the protein’s multimeric structure. Patients with VWD-type 2B display variable extents of bleeding associated with macrothrombocytopenia and sometimes with thrombopathy. Here, we addressed the molecular mechanism underlying the severe macrothrombocytopenia both in a knockin murine model for VWD-type 2B by introducing the p.V1316M mutation in the murine Vwf gene and in a patient bearing this mutation. We provide evidence of a profound defect in megakaryocyte (MK) function since: (a) the extent of proplatelet formation was drastically decreased in 2B MKs, with thick proplatelet extensions and large swellings; and (b) 2B MKs presented actin disorganization that was controlled by upregulation of the RhoA/LIM kinase (LIMK)/cofilin pathway. In vitro and in vivo inhibition of the LIMK/cofilin signaling pathway rescued actin turnover and restored normal proplatelet formation, platelet count, and platelet size. These data indicate, to our knowledge for the first time, that the severe macrothrombocytopenia in VWD-type 2B p.V1316M is due to an MK dysfunction that originates from a constitutive activation of the RhoA/LIMK/cofilin pathway and actin disorganization. This suggests a potentially new function of vWF during platelet formation that involves regulation of actin dynamics.

Authors

Alexandre Kauskot, Sonia Poirault-Chassac, Frédéric Adam, Vincent Muczynski, Gabriel Aymé, Caterina Casari, Jean-Claude Bordet, Christelle Soukaseum, Chantal Rothschild, Valérie Proulle, Audrey Pietrzyk-Nivau, Eliane Berrou, Olivier D. Christophe, Jean-Philippe Rosa, Peter J. Lenting, Marijke Bryckaert, Cécile V. Denis, Dominique Baruch

Circumventing furin enhances factor VIII biological activity and ameliorates bleeding phenotypes in hemophilia models

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Abstract

Processing by the proprotein convertase furin is believed to be critical for the biological activity of multiple proteins involved in hemostasis, including coagulation factor VIII (FVIII). This belief prompted the retention of the furin recognition motif (amino acids 1645–1648) in the design of B-domain–deleted FVIII (FVIII-BDD) products in current clinical use and in the drug development pipeline, as well as in experimental FVIII gene therapy strategies. Here, we report that processing by furin is in fact deleterious to FVIII-BDD secretion and procoagulant activity. Inhibition of furin increases the secretion and decreases the intracellular retention of FVIII-BDD protein in mammalian cells. Our new variant (FVIII-ΔF), in which this recognition motif is removed, efficiently circumvents furin. FVIII-ΔF demonstrates increased recombinant protein yields, enhanced clotting activity, and higher circulating FVIII levels after adeno-associated viral vector–based liver gene therapy in a murine model of severe hemophilia A (HA) compared with FVIII-BDD. Moreover, we observed an amelioration of the bleeding phenotype in severe HA dogs with sustained therapeutic FVIII levels after FVIII-ΔF gene therapy at a lower vector dose than previously employed in this model. The immunogenicity of FVIII-ΔF did not differ from that of FVIII-BDD as a protein or a gene therapeutic. Thus, contrary to previous suppositions, FVIII variants that can avoid furin processing are likely to have enhanced translational potential for HA therapy.

Authors

Joshua I. Siner, Benjamin J. Samelson-Jones, Julie M. Crudele, Robert A. French, Benjamin J. Lee, Shanzhen Zhou, Elizabeth Merricks, Robin Raymer, Timothy C. Nichols, Rodney M. Camire, Valder R. Arruda

A xenograft model of macrophage activation syndrome amenable to anti-CD33 and anti–IL-6R treatment

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Abstract

Transgenic expression of key myelosupportive human cytokines in immune-deficient mice corrects for the lack of cross-species activities of stem cell factor (SCF), IL-3, and GM-CSF. When engrafted with human umbilical cord blood (UCB), these triple-transgenic mice produce BM and spleen grafts with much higher myeloid composition, relative to nontransgenic controls. Shortly after engraftment with UCB, these mice develop a severe, fatal macrophage activation syndrome (MAS) characterized by a progressive drop in rbc numbers, increased reticulocyte counts, decreased rbc half-life, progressive cytopenias, and evidence of chronic inflammation, including elevated human IL-6. The BM becomes strikingly hypocellular, and spleens are significantly enlarged with evidence of extramedullary hematopoiesis and activated macrophages engaged in hemophagocytosis. This manifestation of MAS does not respond to lymphocyte-suppressive therapies such as steroids, i.v. immunoglobulin, or antibody-mediated ablation of human B and T cells, demonstrating a lymphocyte-independent mechanism of action. In contrast, elimination of human myeloid cells using gemtuzumab ozogamicin (anti-CD33) completely reversed the disease. Additionally, the IL-6R antibody tocilizumab delayed progression and prolonged lifespan. This new model of MAS provides an opportunity for investigation of the mechanisms driving this disease and for the testing of directed therapies in a humanized mouse.

Authors

Mark Wunderlich, Courtney Stockman, Mahima Devarajan, Navin Ravishankar, Christina Sexton, Ashish R. Kumar, Benjamin Mizukawa, James C. Mulloy

Platelet integrin α6β1 controls lung metastasis through direct binding to cancer cell–derived ADAM9

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Abstract

Metastatic dissemination of cancer cells, which accounts for 90% of cancer mortality, is the ultimate hallmark of malignancy. Growing evidence suggests that blood platelets have a predominant role in tumor metastasis; however, the molecular mechanisms involved remain elusive. Here, we demonstrate that genetic deficiency of integrin α6β1 on platelets markedly decreases experimental and spontaneous lung metastasis. In vitro and in vivo assays reveal that human and mouse platelet α6β1 supports platelet adhesion to various types of cancer cells. Using a knockdown approach, we identified ADAM9 as the major counter receptor of α6β1 on both human and mouse tumor cells. Static and flow-based adhesion assays of platelets binding to DC-9, a recombinant protein covering the disintegrin-cysteine domain of ADAM9, demonstrated that this receptor directly binds to platelet α6β1. In vivo studies showed that the interplay between platelet α6β1 and tumor cell–expressed ADAM9 promotes efficient lung metastasis. The integrin α6β1–dependent platelet-tumor cell interaction induces platelet activation and favors the extravasation process of tumor cells. Finally, we demonstrate that a pharmacological approach targeting α6β1 efficiently impairs tumor metastasis through a platelet-dependent mechanism. Our study reveals a mechanism by which platelets promote tumor metastasis and suggests that integrin α6β1 represents a promising target for antimetastatic therapies.

Authors

Elmina Mammadova-Bach, Paola Zigrino, Camille Brucker, Catherine Bourdon, Monique Freund, Adèle De Arcangelis, Scott I. Abrams, Gertaud Orend, Christian Gachet, Pierre Henri Mangin

Increased mitochondrial DNA deletions and copy number in transfusion-dependent thalassemia

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Abstract

BACKGROUND. Iron overload is the primary cause of morbidity in transfusion-dependent thalassemia. Increase in iron causes mitochondrial dysfunction under experimental conditions, but the occurrence and significance of mitochondrial damage is not understood in patients with thalassemia.

METHODS. Mitochondrial DNA (mtDNA) to nuclear DNA copy number (Mt/N) and frequency of the common 4977-bp mitochondrial deletion (ΔmtDNA⁴⁹⁷⁷) were quantified using a quantitative PCR assay on whole blood samples from 38 subjects with thalassemia who were receiving regular transfusions.

RESULTS. Compared with healthy controls, Mt/N and ΔmtDNA⁴⁹⁷⁷ frequency were elevated in thalassemia (P = 0.038 and P < 0.001, respectively). ΔmtDNA⁴⁹⁷⁷ was increased in the presence of either liver iron concentration > 15 mg/g dry-weight or splenectomy, with the highest levels observed in subjects who had both risk factors (P = 0.003). Myocardial iron (MRI T2* < 20 ms) was present in 0%, 22%, and 46% of subjects with ΔmtDNA⁴⁹⁷⁷ frequency < 20, 20–40, and > 40/1 × 10⁷ mtDNA, respectively (P = 0.025). Subjects with Mt/N values below the group median had significantly lower Matsuda insulin sensitivity index (5.76 ± 0.53) compared with the high Mt/N group (9.11 ± 0.95, P = 0.008).

CONCLUSION. Individuals with transfusion-dependent thalassemia demonstrate age-related increase in mtDNA damage in leukocytes. These changes are markedly amplified by splenectomy and are associated with extrahepatic iron deposition. Elevated mtDNA damage in blood cells may predict the risk of iron-associated organ damage in thalassemia.

FUNDING. This project was supported by Children’s Hospital & Research Center Oakland Institutional Research Award and by the National Center for Advancing Translational Sciences, NIH, through UCSF-CTSI grant UL1 TR000004.

Authors

Ashutosh Lal, Esteban Gomez, Cassandra Calloway

Protective and detrimental effects of neuroectodermal cell–derived tissue factor in mouse models of stroke

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Abstract

Within the CNS, a dysregulated hemostatic response contributes to both hemorrhagic and ischemic strokes. Tissue factor (TF), the primary initiator of the extrinsic coagulation cascade, plays an essential role in hemostasis and also contributes to thrombosis. Using both genetic and pharmacologic approaches, we characterized the contribution of neuroectodermal (NE) cell TF to the pathophysiology of stroke. We used mice with various levels of TF expression and found that astrocyte TF activity reduced to ~5% of WT levels was still sufficient to maintain hemostasis after hemorrhagic stroke but was also low enough to attenuate inflammation, reduce damage to the blood-brain barrier, and improve outcomes following ischemic stroke. Pharmacologic inhibition of TF during the reperfusion phase of ischemic stroke attenuated neuronal damage, improved behavioral deficit, and prevented mortality of mice. Our data demonstrate that NE cell TF limits bleeding complications associated with the transition from ischemic to hemorrhagic stroke and also contributes to the reperfusion injury after ischemic stroke. The high level of TF expression in the CNS is likely the result of selective pressure to limit intracerebral hemorrhage (ICH) after traumatic brain injury but, in the modern era, poses the additional risk of increased ischemia-reperfusion injury after ischemic stroke.

Authors

Shaobin Wang, Brandi Reeves, Erica M. Sparkenbaugh, Janice Russell, Zbigniew Soltys, Hua Zhang, James E. Faber, Nigel S. Key, Daniel Kirchhofer, D. Neil Granger, Nigel Mackman, Rafal Pawlinski

The MEK inhibitor trametinib separates murine graft-versus-host disease from graft-versus-tumor effects

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Abstract

The efficacy of allogeneic hematopoietic stem cell transplantation for hematologic malignancies is limited by the difficulty in suppressing graft-versus-host disease (GVHD) without compromising graft-versus-tumor (GVT) effects. We previously showed that RAS/MEK/ERK signaling depends on memory differentiation in human T cells, which confers susceptibility to selective inhibition of naive T cells. Actually, antineoplastic MEK inhibitors selectively suppress alloreactive T cells, sparing virus-specific T cells in vitro. Here, we show that trametinib, a MEK inhibitor clinically approved for melanoma, suppresses GVHD safely without affecting GVT effects in vivo. Trametinib prolonged survival of GVHD mice and attenuated GVHD symptoms and pathology in the gut and skin. It inhibited ERK1/2 phosphorylation and expansion of donor T cells, sparing Tregs and B cells. Although high-dose trametinib inhibited myeloid cell engraftment, low-dose trametinib suppressed GVHD without severe adverse events. Notably, trametinib facilitated the survival of mice transplanted with allogeneic T cells and P815 tumor cells with no residual P815 cells observed in the livers and spleens, whereas tacrolimus resulted in P815 expansion. These results confirm that trametinib selectively suppresses GVHD-inducing T cells while sparing antitumor T cells in vivo, which makes it a promising candidate for translational studies aimed at preventing or treating GVHD.

Authors

Hidekazu Itamura, Takero Shindo, Isao Tawara, Yasushi Kubota, Ryusho Kariya, Seiji Okada, Krishna V. Komanduri, Shinya Kimura

A clinical measure of DNA methylation predicts outcome in de novo acute myeloid leukemia

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Abstract

BACKGROUND. Variable response to chemotherapy in acute myeloid leukemia (AML) represents a major treatment challenge. Clinical and genetic features incompletely predict outcome. The value of clinical epigenetic assays for risk classification has not been extensively explored. We assess the prognostic implications of a clinical assay for multilocus DNA methylation on adult patients with de novo AML.

METHODS. We performed multilocus DNA methylation assessment using xMELP on samples and calculated a methylation statistic (M-score) for 166 patients from UPENN with de novo AML who received induction chemotherapy. The association of M-score with complete remission (CR) and overall survival (OS) was evaluated. The optimal M-score cut-point for identifying groups with differing survival was used to define a binary M-score classifier. This classifier was validated in an independent cohort of 383 patients from the Eastern Cooperative Oncology Group Trial 1900 (E1900; NCT00049517).

RESULTS. A higher mean M-score was associated with death and failure to achieve CR. Multivariable analysis confirmed that a higher M-score was associated with death (P = 0.011) and failure to achieve CR (P = 0.034). Median survival was 26.6 months versus 10.6 months for low and high M-score groups. The ability of the M-score to perform as a classifier was confirmed in patients ≤ 60 years with intermediate cytogenetics and patients who achieved CR, as well as in the E1900 validation cohort.

CONCLUSION. The M-score represents a valid binary prognostic classifier for patients with de novo AML. The xMELP assay and associated M-score can be used for prognosis and should be further investigated for clinical decision making in AML patients.

Authors

Marlise R. Luskin, Phyllis A. Gimotty, Catherine Smith, Alison W. Loren, Maria E. Figueroa, Jenna Harrison, Zhuoxin Sun, Martin S. Tallman, Elisabeth M. Paietta, Mark R. Litzow, Ari M. Melnick, Ross L. Levine, Hugo F. Fernandez, Selina M. Luger, Martin Carroll, Stephen R. Master, Gerald B.W. Wertheim

Histone deacetylase inhibitor panobinostat induces calcineurin degradation in multiple myeloma

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Abstract

Multiple myeloma (MM) is a relapsed and refractory disease, one that highlights the need for developing new molecular therapies for overcoming of drug resistance. Addition of panobinostat, a histone deacetylase (HDAC) inhibitor, to bortezomib and dexamethasone improved progression-free survival (PFS) in relapsed and refractory MM patients. Here, we demonstrate how calcineurin, when inhibited by immunosuppressive drugs like FK506, is involved in myeloma cell growth and targeted by panobinostat. mRNA expression of PPP3CA, a catalytic subunit of calcineurin, was high in advanced patients. Panobinostat degraded PPP3CA, a degradation that should have been induced by inhibition of the chaperone function of heat shock protein 90 (HSP90). Cotreatment with HDAC inhibitors and FK506 led to an enhanced antimyeloma effect with a greater PPP3CA reduction compared with HDAC inhibitors alone both in vitro and in vivo. In addition, this combination treatment efficiently blocked osteoclast formation, which results in osteolytic lesions. The poor response and short PFS duration observed in the bortezomib-containing therapies of patients with high PPP3CA suggested its relevance to bortezomib resistance. Moreover, bortezomib and HDAC inhibitors synergistically suppressed MM cell viability through PPP3CA inhibition. Our findings underscore the usefulness of calcineurin-targeted therapy in MM patients, including patients who are resistant to bortezomib.

Authors

Yoichi Imai, Eri Ohta, Shu Takeda, Satoko Sunamura, Mariko Ishibashi, Hideto Tamura, Yan-hua Wang, Atsuko Deguchi, Junji Tanaka, Yoshiro Maru, Toshiko Motoji

Nonhematopoietic Nrf2 dominantly impedes adult progression of sickle cell anemia in mice

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Abstract

The prevention of organ damage and early death in young adults is a major clinical concern in sickle cell disease (SCD). However, mechanisms that control adult progression of SCD during the transition from adolescence are poorly defined with no cognate prophylaxis. Here, we demonstrate in a longitudinal cohort of homozygous SCD (SS) mice a link between intravascular hemolysis, vascular inflammation, lung injury, and early death. Prophylactic Nrf2 activation in young SS mice stabilized intravascular hemolysis, reversed vascular inflammation, and attenuated lung edema in adulthood. Enhanced Nrf2 activation in endothelial cells in vitro concurred with the dramatic effect on vascular inflammation in the mice. BM chimeric SS mice lacking Nrf2 expression in nonhematopoietic tissues were created to dissect the role of nonerythroid Nrf2 in SCD progression. The SS chimeras developed severe intravascular hemolysis despite having erythroid Nrf2. In addition, they developed premature vascular inflammation and pulmonary edema and died younger than donor littermates with intact nonhematopoietic Nrf2. Our results reveal a dominant protective role for nonhematopoietic Nrf2 against tissue damage in both erythroid and nonerythroid tissues in SCD. Furthermore, we show that prophylactic augmentation of Nrf2-coordinated cytoprotection effectively impedes onset of the severe adult phenotype of SCD in mice.

Authors

Samit Ghosh, Chibueze A. Ihunnah, Rimi Hazra, Aisha L. Walker, Jason M. Hansen, David R. Archer, Amma T. Owusu-Ansah, Solomon F. Ofori-Acquah