Mechanisms regulating thrombus stabilization remain largely unknown. Here, we report that loss of any 1 of the Gas6 receptors (Gas6-Rs), i.e., Tyro3, Axl, or Mer, or delivery of a soluble extracellular domain of Axl that traps Gas6 protects mice against life-threatening thrombosis. Loss of a Gas6-R does not prevent initial platelet aggregation but impairs subsequent stabilization of platelet aggregates, at least in part by reducing “outside-in” signaling and platelet granule secretion. Gas6, through its receptors, activates PI3K and Akt and stimulates tyrosine phosphorylation of the β3 integrin, thereby amplifying outside-in signaling via αIIbβ3. Blocking the Gas6-R–αIIbβ3 integrin cross-talk might be a novel approach to the reduction of thrombosis.
Anne Angelillo-Scherrer, Laurent Burnier, Nathalie Flores, Pierre Savi, Maria DeMol, Paul Schaeffer, Jean-Marc Herbert, Greg Lemke, Stephen P. Goff, Glenn K. Matsushima, H. Shelton Earp, Christian Vesin, Marc F. Hoylaerts, Stéphane Plaisance, Désiré Collen, Edward M. Conway, Bernhard Wehrle-Haller, Peter Carmeliet
B cell chronic lymphocytic leukemia (B-CLL) is a neoplastic disorder characterized by accumulation of B lymphocytes due to uncontrolled growth and resistance to apoptosis. Analysis of B cells freshly isolated from 40 patients with chronic lymphocytic leukemia demonstrated that the Src kinase Lyn, the switch molecule that couples the B cell receptor to downstream signaling, displays anomalous properties. Lyn is remarkably overexpressed at the protein level in leukemic cells as compared with normal B lymphocytes, with a substantial aliquot of the kinase anomalously present in the cytosol. Whereas in normal B lymphocytes Lyn activation is dependent on B cell–receptor stimulation, in resting malignant cells, the constitutive activity of the kinase accounts for high basal protein tyrosine phosphorylation and low responsiveness to IgM ligation. Addition of the Lyn inhibitors PP2 and SU6656 to leukemic cell cultures restores cell apoptosis, and treatment of malignant cells with drugs that induce cell apoptosis decreases both activity and amount of the tyrosine kinase. These findings suggest a direct correlation between high basal Lyn activity and defects in the induction of apoptosis in leukemic cells. They also support a critical role for Lyn in B-CLL pathogenesis and identify this tyrosine kinase as a potential therapeutic target.
Antonella Contri, Anna Maria Brunati, Livio Trentin, Anna Cabrelle, Marta Miorin, Luca Cesaro, Lorenzo A. Pinna, Renato Zambello, Gianpietro Semenzato, Arianna Donella-Deana
Intravenous Ig (IVIg) mediates protection from the effects of immune thrombocytopenic purpura (ITP) as well as numerous other autoimmune states; however, the active antibodies within IVIg are unknown. There is some evidence that antibodies specific for a cell-associated antigen on erythrocytes are responsible, at least in part, for the therapeutic effect of IVIg in ITP. Yet whether an IVIg directed to a soluble antigen can likewise be beneficial in ITP or other autoimmune diseases is also unknown. A murine model of ITP was used to determine the effectiveness of IgG specific to soluble antigens in treating immune thrombocytopenic purpura. Mice experimentally treated with soluble OVA + anti-OVA versus mice treated with OVA conjugated to rbcs (OVA-rbcs) + anti-OVA were compared. In both situations, mice were protected from ITP. Both these experimental therapeutic regimes acted in a complement-independent fashion and both also blocked reticuloendothelial function. In contrast to OVA-rbcs + anti-OVA, soluble OVA + anti-OVA (as well as IVIg) did not have any effect on thrombocytopenia in mice lacking the inhibitory receptor FcγRIIB (FcγRIIB–/– mice). Similarly, antibodies reactive with the endogenous soluble antigens albumin and transferrin also ameliorated ITP in an FcγRIIB-dependent manner. Finally, broadening the significance of these experiments was the finding that anti-albumin was protective in a K/BxN serum–induced arthritis model. We conclude that IgG antibodies directed to soluble antigens ameliorated 2 disparate IVIg-treatable autoimmune diseases.
Vinayakumar Siragam, Davor Brinc, Andrew R. Crow, Seng Song, John Freedman, Alan H. Lazarus
Hemoglobin (Hb) A production during red blood cell development is coordinated to minimize the deleterious effects of free α- and β-Hb subunits, which are unstable and cytotoxic. The α-Hb–stabilizing protein (AHSP) is an erythroid protein that specifically binds α-Hb and prevents its precipitation in vitro, which suggests that it may function to limit free α-Hb toxicities in vivo. We investigated this possibility through gene ablation and biochemical studies. AHSP–/– erythrocytes contained hemoglobin precipitates and were short-lived. In hematopoietic tissues, erythroid precursors were elevated in number but exhibited increased apoptosis. Consistent with unstable α-Hb, AHSP–/– erythrocytes contained increased ROS and evidence of oxidative damage. Moreover, purified recombinant AHSP inhibited ROS production by α-Hb in solution. Finally, loss of AHSP worsened the phenotype of β-thalassemia, a common inherited anemia characterized by excess free α-Hb. Together, the data support a model in which AHSP binds α-Hb transiently to stabilize its conformation and render it biochemically inert prior to Hb A assembly. This function is essential for normal erythropoiesis and, to a greater extent, in β-thalassemia. Our findings raise the possibility that altered AHSP expression levels could modulate the severity of β-thalassemia in humans.
Yi Kong, Suiping Zhou, Anthony J. Kihm, Anne M. Katein, Xiang Yu, David A. Gell, Joel P. Mackay, Kazuhiko Adachi, Linda Foster-Brown, Calvert S. Louden, Andrew J. Gow, Mitchell J. Weiss
Transplantation of genetically corrected autologous hematopoietic stem cells is an attractive approach for the cure of sickle-cell disease and β-thalassemia. Here, we infected human cord blood cells with a self-inactivating lentiviral vector encoding an anti-sickling βA-T87Q-globin transgene and analyzed the transduced progeny produced over a 6-month period after transplantation of the infected cells directly into sublethally irradiated NOD/LtSz-scid/scid mice. Approximately half of the human erythroid and myeloid progenitors regenerated in the mice containing the transgene, and erythroid cells derived in vitro from these in vivo–regenerated cells produced high levels of βA-T87Q-globin protein. Linker-mediated PCR analysis identified multiple transgene-positive clones in all mice analyzed with 2.1 ± 0.1 integrated proviral copies per cell. Genomic sequencing of vector-containing fragments showed that 86% of the proviral inserts had occurred within genes, including several genes implicated in human leukemia. These findings indicate effective transduction of very primitive human cord blood cells with a candidate therapeutic lentiviral vector resulting in the long-term and robust, erythroid-specific production of therapeutically relevant levels of β-globin protein. However, the frequency of proviral integration within genes that regulate hematopoiesis points to a need for additional safety modifications.
Suzan Imren, Mary E. Fabry, Karen A. Westerman, Robert Pawliuk, Patrick Tang, Patricia M. Rosten, Ronald L. Nagel, Philippe Leboulch, Connie J. Eaves, R. Keith Humphries
Myelodysplasia is a hematological disease in which genomic abnormalities accumulate in a hematopoietic stem cell leading to severe pancytopenia, multilineage differentiation impairment, and bone marrow (BM) apoptosis. Mortality in the disease results from pancytopenia or transformation to acute myeloid leukemia. There are frequent cytogenetic abnormalities, including deletions of chromosomes 5, 7, or both. Recurring chromosomal translocations in myelodysplasia are rare, but the most frequent are the t(3;3)(q21;q26) and the inv(3)(q21q26), which lead to the inappropriate activation of the EVI1 gene located at 3q26. To better understand the role of EVI1 in this disease, we have generated a murine model of EVI1-positive myelodysplasia by BM infection and transplantation. We find that EVI1 induces a fatal disease of several stages that is characterized by severe pancytopenia. The disease does not progress to acute myeloid leukemia. Comparison of in vitro and in vivo results suggests that EVI1 acts at two levels. The immediate effects of EVI1 are hyperproliferation of BM cells and downregulation of EpoR and c-Mpl, which are important for terminal erythroid differentiation and platelet formation. These defects are not fatal, and the mice survive for about 10 months with compensated hematopoiesis. Over this time, compensation fails, and the mice succumb to fatal peripheral cytopenia.
Silvia Buonamici, Donglan Li, Yiqing Chi, Rui Zhao, Xuerong Wang, Larry Brace, Hongyu Ni, Yogen Saunthararajah, Giuseppina Nucifora
Paris-Trousseau syndrome (PTS; also known as Jacobsen syndrome) is characterized by several congenital anomalies including a dysmegakaryopoiesis with two morphologically distinct populations of megakaryocytes (MKs). PTS patients harbor deletions on the long arm of chromosome 11, including the FLI1 gene, which encodes a transcription factor essential for megakaryopoiesis. We show here that lentivirus-mediated overexpression of FLI1 in patient CD34+ cells restores the megakaryopoiesis in vitro, indicating that FLI1 hemizygous deletion contributes to the PTS hematopoietic defects. FISH analysis on pre-mRNA and single-cell RT-PCR revealed that FLI1 expression is mainly monoallelic in CD41+CD42– progenitors, while it is predominantly biallelic in the other stages of megakaryopoiesis. In PTS cells, the hemizygous deletion of FLI1 generates a subpopulation of CD41+CD42– cells completely lacking FLI1 transcription. We propose that the absence of FLI1 expression in these CD41+CD42– cells might prevent their differentiation, which could explain the segregation of the PTS MKs into two subpopulations: one normal and one composed of small immature MKs undergoing a massive lysis, presumably originating from either FLI1+ or FLI1– CD41+CD42– cells, respectively. Thus, we point to the role of transient monoallelic expression of a gene essential for differentiation in the genesis of human haploinsufficiency-associated disease and suggest that such a mechanism may be involved in the pathogenesis of other congenital or acquired genetic diseases.
Hana Raslova, Emiko Komura, Jean Pierre Le Couédic, Frederic Larbret, Najet Debili, Jean Feunteun, Olivier Danos, Olivier Albagli, William Vainchenker, Rémi Favier
Small molecule inhibitors, such as imatinib, are effective therapies for tyrosine kinase fusions BCR-ABL–TEL-PDGFβR–mediated human leukemias, but resistance may develop. The unique fusion junctions of these molecules are attractive candidates for molecularly targeted therapeutic intervention using RNA interference (RNAi), which is mediated by small interfering RNA (siRNA). We developed a retroviral system for stable expression of siRNA directed to the unique fusion junction sequence of TEL-PDGFβR in transformed hematopoietic cells. Stable expression of the siRNA resulted in approximately 90% inhibition of TEL-PDGFβR expression and its downstream effectors, including PI3K and mammalian target of rapamycin (mTOR). Expression of TEL-PDGFβR–specific siRNA (TPsiRNA) significantly attenuated the proliferation of TEL-PDGFβR–transformed Ba/F3 cells or disease latency and penetrance in mice induced by intravenous injection of these Ba/F3 cells. Although a 90% reduction in TEL-PDGFβR expression was insufficient to induce cell death, stable siRNA expression sensitized transformed cells to the PDGFβR inhibitor imatinib or to the mTOR inhibitor rapamycin. TPsiRNA also inhibited an imatinib-resistant TEL-PDGFβR mutant, and the inhibition was enhanced by siRNA in combination with PKC412, another PDGFβR inhibitor. Although siRNA delivery in vivo is a challenging problem, stable expression of siRNA, which targets oncogenic fusion genes, may potentiate the effects of conventional therapy for hematologic malignancies.
Jing Chen, Nathan R. Wall, Kerry Kocher, Nicole Duclos, Doriano Fabbro, Donna Neuberg, James D. Griffin, Yang Shi, D. Gary Gilliland
The leukocyte integrin αMβ2/Mac-1 appears to support the inflammatory response through multiple ligands, but local engagement of fibrin(ogen) may be particularly important for leukocyte function. To define the biological significance of fibrin(ogen)-αMβ2 interaction in vivo, gene-targeted mice were generated in which the αMβ2-binding motif within the fibrinogen γ chain (N390RLSIGE396) was converted to a series of alanine residues. Mice carrying the Fibγ390–396A allele maintained normal levels of fibrinogen, retained normal clotting function, supported platelet aggregation, and never developed spontaneous hemorrhagic events. However, the mutant fibrinogen failed to support αMβ2-mediated adhesion of primary neutrophils, macrophages, and αMβ2-expressing cell lines. The elimination of the αMβ2-binding motif on fibrin(ogen) severely compromised the inflammatory response in vivo as evidenced by a dramatic impediment in leukocyte clearance of Staphylococcus aureus inoculated into the peritoneal cavity. This defect in bacterial clearance was due not to diminished leukocyte trafficking but rather to a failure to fully implement antimicrobial functions. These studies definitively demonstrate that fibrin(ogen) is a physiologically relevant ligand for αMβ2, integrin engagement of fibrin(ogen) is critical to leukocyte function and innate immunity in vivo, and the biological importance of fibrinogen in regulating the inflammatory response can be appreciated outside of any alteration in clotting function.
Matthew J. Flick, XinLi Du, David P. Witte, Markéta Jiroušková, Dmitry A. Soloviev, Steven J. Busuttil, Edward F. Plow, Jay L. Degen
Hypoferremia is a common response to systemic infections or generalized inflammatory disorders. In mouse models, the development of hypoferremia during inflammation requires hepcidin, an iron regulatory peptide hormone produced in the liver, but the inflammatory signals that regulate hepcidin are largely unknown. Our studies in human liver cell cultures, mice, and human volunteers indicate that IL-6 is the necessary and sufficient cytokine for the induction of hepcidin during inflammation and that the IL-6–hepcidin axis is responsible for the hypoferremia of inflammation.
Elizabeta Nemeth, Seth Rivera, Victoria Gabayan, Charlotte Keller, Sarah Taudorf, Bente K. Pedersen, Tomas Ganz