Blood current issue

JAK2 V617F down-modulates MPL

Fleischman, A. G., Tyner, J. W. — 2012-05-17T09:01:20-07:00

Hitting the target in MCL

Crump, M. — 2012-05-17T09:01:20-07:00

Chopped and diced: Dicer1 deletion generates myeloid dysplasia

Barber, D. L. — 2012-05-17T09:01:20-07:00

NHERF-2 silences the silencers

Arbiser, J. L. — 2012-05-17T09:01:20-07:00

Atypical mycobacteria in a patient with HIV and ITP

Jayakar, V., Gharaie, S. — 2012-05-17T09:01:20-07:00

Silent cerebral infarcts: a review on a prevalent and progressive cause of neurologic injury in sickle cell anemia

2012-05-17T09:01:20-07:00

Silent cerebral infarct (SCI) is the most common form of neurologic disease in children with sickle cell anemia (SCA). SCI is defined as abnormal magnetic resonance imaging (MRI) of the brain in the setting of a normal neurologic examination without a history or physical findings associated with an overt stroke. SCI occurs in 27% of this population before their sixth, and 37% by their 14th birthdays. In adults with SCA, the clinical history of SCI is poorly defined, although recent evidence suggests that they too may have ongoing risk of progressive injury. Risk factors for SCI include male sex, lower baseline hemoglobin concentration, higher baseline systolic blood pressure, and previous seizures. Specific morbidity associated with SCI includes a decrement in general intellectual abilities, poor academic achievement, progression to overt stroke, and progressive SCI. In addition, children with previous stroke continue to have both overt strokes and new SCI despite receiving regular blood transfusion therapy for secondary stroke prevention. Studies that only include overt stroke as a measure of CNS injury significantly underestimate the total cerebral injury burden in this population. In this review, we describe the epidemiology, natural history, morbidity, medical management, and potential therapeutic options for SCI in SCA.

Selective CDK4/6 inhibition with tumor responses by PD0332991 in patients with mantle cell lymphoma

2012-05-17T09:01:20-07:00

Mantle cell lymphoma (MCL) carries an unfavorable prognosis and requires new treatment strategies. The associated t(11:14) translocation results in enhanced cyclin D1 expression and cyclin D1–dependent kinase activity to promote cell-cycle progression. A pharmacodynamic study of the selective CDK4/6 inhibitor PD0332991 was conducted in 17 patients with relapsed disease, using 2-deoxy-2-[¹⁸F]fluoro-D-glucose (FDG) and 3-deoxy-3[¹⁸F]fluorothymidine (FLT) positron emission tomography (PET) to study tumor metabolism and proliferation, respectively, in concert with pre- and on-treatment lymph node biopsies to assess retinoblastoma protein (Rb) phosphorylation and markers of proliferation and apoptosis. Substantial reductions in the summed FLT-PET maximal standard uptake value (SUV_max), as well as in Rb phosphorylation and Ki-67 expression, occurred after 3 weeks in most patients, with significant correlations among these end points. Five patients achieved progression-free survival time of > 1 year (range, 14.9-30.1+ months), with 1 complete and 2 partial responses (18% objective response rate; 90% confidence interval, 5%-40%). These patients demonstrated > 70%, > 90%, and ≥ 87.5% reductions in summed FLT SUV_max and expression of phospho-Rb and Ki67, respectively, parameters necessary but not sufficient for long-term disease control. The results of the present study confirm CDK4/6 inhibition by PD0332991 at a well-tolerated dose and schedule and suggest clinical benefit in a subset of MCL patients. This study is registered at www.clinicaltrials.gov under identifier NCT00420056.

Combination of bendamustine, lenalidomide, and dexamethasone (BLD) in patients with relapsed or refractory multiple myeloma is feasible and highly effective: results of phase 1/2 open-label, dose escalation study

2012-05-17T09:01:20-07:00

This multicenter phase 1/2 trial investigated the combination of bendamustine, lenalidomide, and dexamethasone in repeating 4-week cycles as treatment for relapsed refractory multiple myeloma (MM). Phase 1 established maximum tolerated dose (MTD). Phase 2 assessed overall response rate at the MTD. Secondary endpoints included progression-free survival (PFS) and overall survival (OS). A total of 29 evaluable patients were enrolled. Median age was 63 years (range, 38-80 years). Median number of prior therapies was 3 (range, 1-6). MTD was bendamustine 75 mg/m² (days 1 and 2), lenalidomide 10 mg (days 1-21), and dexamethasone 40 mg (weekly) of a 28-day cycle. Partial response rate was 52%, with very good partial response achieved in 24%, and minimal response in an additional 24% of patients. Median follow-up was 13 months; median OS has not been reached. One-year OS is 93% (95% confidence interval [CI], 59%-99%). Median PFS is 6.1 months (95% CI, 3.7-9.4 months) with one-year PFS of 20% (95% CI, 6%-41%). Grade 3/4 adverse events included neutropenia, thrombocytopenia, anemia, hyperglycemia, and fatigue. This first phase 1/2 trial testing bendamustine, lenalidomide, and dexamethasone as treatment of relapsed refractory MM was feasible and highly active. This study is registered at www.clinicaltrials.gov as #NCT01042704.

Phase 2 study of the JAK kinase inhibitor ruxolitinib in patients with refractory leukemias, including postmyeloproliferative neoplasm acute myeloid leukemia

2012-05-17T09:01:20-07:00

We conducted a phase 2 study of ruxolitinib in patients with relapsed/refractory leukemias. Patients with acceptable performance status (0-2), adequate organ function, and no active infection, received ruxolitinib 25 mg orally twice a day for 4 weeks (1 cycle). Response was assessed after every 2 cycles of treatment, and patients who completed 2 cycles were allowed to continue treatment until disease progression. Dose escalation to 50 mg twice daily was permitted in patients demonstrating a benefit. Thirty-eight patients, with a median age of 69 years (range, 45-88), were treated. The median number of prior therapies was 2 (range, 1-6). Twelve patients had JAK2V617F mutation. Patients received a median of 2 cycles of therapy (range, 1-22). Three of 18 patients with postmyeloproliferative neoplasm (MPN) acute myeloid leukemia (AML) showed a significant response; 2 achieved complete remission (CR) and one achieved a CR with insufficient recovery of blood counts (CRi). The responding patients with palpable spleens also had significant reductions in spleen size. Overall, ruxolitinib was very well tolerated with only 4 patients having grade 3 or higher toxicity. Ruxolitinib has modest antileukemic activity as a single agent, particularly in patients with post-MPN AML. The study was registered at www.clinicaltrials.gov as NCT00674479.

MYC+ diffuse large B-cell lymphoma is not salvaged by classical R-ICE or R-DHAP followed by BEAM plus autologous stem cell transplantation

2012-05-17T09:01:20-07:00

Approximately 5-10% of diffuse large B-cell lymphomas (DLBCL) harbor a 8q24/MYC rearrangement (MYC⁺). We determined the prognostic significance of MYC rearrangement in patients with relapsed/refractory DLBCL prospectively treated by R-ICE or R-DHAP followed by high-dose therapy and autologous stem cell transplantation. Twenty-eight (17%) of the 161 patients analyzed presented a MYC⁺ rearrangement, targeted as either simple hit (25%) or complex hits (n=75%) including MYC/BCL2, MYC/BCL6, and MYC/BCL2/BCL6. Results were statistically highly concordant in matched primary and relapsed biopsies (n = 45). Compared to the MYC^– DLBCL patients, the MYC⁺ DLBCL patients presented with a more elevated lactico-deshydrogenase level (P = .0006) and a more advanced age adjusted international prognostic index (P = .0039). The 4-year PFS and OS were significantly lower in the MYC⁺ DLBCL patients than those in the MYC^– DLBCL patients, with rates of 18% vs 42% (P = .0322), and of 29% vs 62% (P = .0113), respectively. Type of treatment, R-DHAP or R-ICE, had no impact on survivals, with 4-year PFS rates of 17% vs 19% and 4-year OS rates of 26% vs 31%. In conclusion, MYC rearrangement is an early event in DLBCL. MYC⁺ DLBCL patients have a significant inferior prognosis than MYC^– DLBCL patients. Their outcome was not influenced by the proposed salvage therapy.

Thrombopoietin receptor down-modulation by JAK2 V617F: restoration of receptor levels by inhibitors of pathologic JAK2 signaling and of proteasomes

2012-05-17T09:01:20-07:00

The constitutively active JAK2 V617F mutant is the major determinant of human myeloproliferative neoplasms (MPNs). We show that coexpression of murine JAK2 V617F and the murine thrombopoietin (Tpo) receptor (TpoR, c-MPL) in hematopoietic cell lines or heterozygous knock-in of JAK2 V617F in mice leads to down-modulation of TpoR levels. Enhanced TpoR ubiquitinylation, proteasomal degradation, reduced recycling, and maturation are induced by the constitutive JAK2 V617F activity. These effects can be prevented in cell lines by JAK2 and proteasome inhibitors. Restoration of TpoR levels by inhibitors could be detected in platelets from JAK2 inhibitor-treated myelofibrosis patients that express the JAK2 V617F mutant, and in platelets from JAK2 V617F knock-in mice that were treated in vivo with JAK2 or proteasome inhibitors. In addition, we show that Tpo can induce both proliferative and antiproliferative effects via TpoR at low and high JAK2 activation levels, respectively, or on expression of JAK2 V617F. The antiproliferative signaling and receptor down-modulation by JAK2 V617F were dependent on signaling via TpoR cytosolic tyrosine 626. We propose that selection against TpoR antiproliferative signaling occurs by TpoR down-modulation and that restoration of down-modulated TpoR levels could become a biomarker for the treatment of MPNs.

Regulation of Th1/Th2 polarization by tissue inhibitor of metalloproteinase-3 via modulating dendritic cells

2012-05-17T09:01:20-07:00

Tissue inhibitor of metalloproteinase-3 (TIMP-3) is one of a family of proteins inhibiting matrix metalloproteinases, which has also been identified as a mediator for checking inflammation. Meanwhile, it is well known that inflammation causes the activation of the immune response. However, it is not clear whether TIMP-3 plays a role in the immune system. In the present study, we demonstrated a novel function of TIMP-3 in Th1/Th2 polarization through its influence on the antigen-presenting cells. First, TIMP-3 was found strikingly up-regulated by IL-4 during the differentiation of human dendritic cells via the p38MAPK pathway. Second, the expression of costimulatory molecule-CD86 was repressed by TIMP-3. Besides, the induction of IL-12 in matured dendritic cells was significantly inhibited in a PI3K-dependent manner. Furthermore, dendritic cells matured in the presence of TIMP-3 could stimulate allogeneic naive T helper (Th) cells to display a prominent Th2 polarization. Importantly, in an autoimmune disorder–primary immune thrombocytopenia, TIMP-3 showed a statistically positive correlation with IL-4 and platelet count, but a negative correlation with IFN- in patient blood samples. Collectively, these in vitro and in vivo data clearly suggested a novel role of TIMP-3 in Th1/Th2 balance in humans.

Comprehensive analysis of unique cases with extraordinary control over HIV replication

2012-05-17T09:01:20-07:00

True long-term nonprogressors (LTNPs)/elite controllers (ECs) maintain durable control over HIV replication without antiretroviral therapy. Herein we describe 4 unique persons who were distinct from conventional LTNPs/ECs in that they had extraordinarily low HIV burdens and comparatively weak immune responses. As a group, typical LTNPs/ECs have unequivocally reactive HIV-1 Western blots, viral loads below the lower threshold of clinical assays, low levels of persistent viral reservoirs, an over-representation of protective HLA alleles, and robust HIV-specific CD8⁺ T-cell responses. The 4 unique cases were distinguished from typical LTNPs/ECs based on weakly reactive Western blots, undetectable plasma viremia by a single copy assay, extremely low to undetectable HIV DNA levels, and difficult to isolate replication-competent virus. All 4 had at least one protective HLA allele and CD8⁺ T-cell responses that were disproportionately high for the low antigen levels but comparatively lower than those of typical LTNPs/ECs. These unique persons exhibit extraordinary suppression over HIV replication, therefore, higher-level control than has been demonstrated in previous studies of LTNPs/ECs. Additional insight into the full spectrum of immune-mediated suppression over HIV replication may enhance our understanding of the associated mechanisms, which should inform the design of efficacious HIV vaccines and immunotherapies.

IL-21 inhibits T cell IL-2 production and impairs Treg homeostasis

2012-05-17T09:01:20-07:00

Modulation of regulatory T cell (Treg) suppression has important implications for vaccine development, the effectiveness of tumor surveillance, and the emergence of autoimmunity. We have previously shown that the cytokine IL-21 can counteract Treg suppression. However, whether this reflects an effect of IL-21 on Treg, conventional T cells, or antigen-presenting cells is not known. Here we have used lymphocyte populations from IL-21R–deficient mice to pinpoint which cell type needs to be targeted by IL-21 for Treg suppression to be overcome. We show that IL-21 counteracts suppression by acting on conventional T cells and that this is associated with inhibition of IL-2 production. Despite the lack of IL-2, conventional T-cell responses proceed unimpaired because IL-21 can substitute for IL-2 as a T cell growth factor. However, IL-21 is unable to substitute for IL-2 in supporting the Treg compartment. Thus, IL-21 signaling in conventional T cells indirectly impacts Treg homeostasis by decreasing IL-2 availability. These data demonstrate that IL-21 and IL-2 can have overlapping roles in promoting conventional T-cell responses but play distinct roles in controlling Treg homeostasis and function. The data also suggest a new paradigm whereby cytokines can promote immunity by inhibiting IL-2.

Maturation-related histone modifications in the PU.1 promoter regulate Th9-cell development

Ramming, A., Druzd, D., Leipe, J., Schulze-Koops, H., Skapenko, A. — 2012-05-17T09:01:20-07:00

Epigenetic histone modifications are thought to underlie the rapid memory immune response to recall antigen that develops after vaccination. However, histone-modification patterns in genes encoding transcription factors regulating cytokine production have not been investigated in either memory and naive T cells or as the immune system matures to understand the differences in cytokine response patterns. In the present study, we analyzed histone modifications in promoter regions of T-bet, GATA-3, PU.1, IRF4, and RORC in neonatal naive T cells and in adult naive and memory CD4 T cells, and found a unique and dynamic histone-modification pattern in the PU.1 promoter that was related to age and the naive/memory status of a T cell. Naive T cells required more intense stimulation to switch the chromatin pattern in the PU.1 promoter from a repressive to permissive state, and therefore to produce IL-9 than did memory T cells. Inhibition of repressive histone methylation by the specific inhibitor 3-deazaneplanocin induced Th9-specific PU.1 expression, even in conditions that would normally yield only Th0 cytokines. Conversely, prevention of histone acetylation by the histone acetyltransferase inhibitor curcumin diminished PU.1 expression after IL-9–inducing stimulation. Our findings identify age- and differentiation-status–related epigenetic modifications of PU.1 as a unique regulator of Th9 memory acquisition and Th9 immunity.

KAP1 regulates gene networks controlling mouse B-lymphoid cell differentiation and function

2012-05-17T09:01:20-07:00

Chromatin remodeling is fundamental for B-cell differentiation. In the present study, we explored the role of KAP1, the cofactor of KRAB-ZFP transcriptional repressors, in this process. B-lymphoid–specific Kap1-KO mice displayed reduced numbers of mature B cells, lower steady-state levels of Abs, and accelerated rates of decay of neutralizing Abs after viral immunization. Transcriptome analyses of Kap1-deleted B splenocytes revealed an up-regulation of PTEN, the enzymatic counteractor of PIK3 signaling, and of genes encoding DNA-damage response factors, cell-cycle regulators, and chemokine receptors. ChIP/seq studies established that KAP1 bound at or close to several of these genes and controlled chromatin status at their promoters. Genome wide, KAP1 binding sites lacked active B cell–specific enhancers and were enriched in repressive histone marks, further supporting a role for this molecule in gene silencing in vivo. Likely responsible for tethering KAP1 to at least some of these targets, a discrete subset of KRAB-ZFPs is enriched in B lymphocytes. Our results therefore reveal the role of KRAB/KAP1–mediated epigenetic regulation in B-cell development and homeostasis.

Multiple myeloma exhibits novel dependence on GLUT4, GLUT8, and GLUT11: implications for glucose transporter-directed therapy

2012-05-17T09:01:20-07:00

Multiple myeloma is one of numerous malignancies characterized by increased glucose consumption, a phenomenon with significant prognostic implications in this disease. Few studies have focused on elucidating the molecular underpinnings of glucose transporter (GLUT) activation in cancer, knowledge that could facilitate identification of promising therapeutic targets. To address this issue, we performed gene expression profiling studies involving myeloma cell lines and primary cells as well as normal lymphocytes to uncover deregulated GLUT family members in myeloma. Our data demonstrate that myeloma cells exhibit reliance on constitutively cell surface-localized GLUT4 for basal glucose consumption, maintenance of Mcl-1 expression, growth, and survival. We also establish that the activities of the enigmatic transporters GLUT8 and GLUT11 are required for proliferation and viability in myeloma, albeit because of functionalities probably distinct from whole-cell glucose supply. As proof of principle regarding the therapeutic potential of GLUT-targeted compounds, we include evidence of the antimyeloma effects elicited against both cell lines and primary cells by the FDA-approved HIV protease inhibitor ritonavir, which exerts a selective off-target inhibitory effect on GLUT4. Our work reveals critical roles for novel GLUT family members and highlights a therapeutic strategy entailing selective GLUT inhibition to specifically target aberrant glucose metabolism in cancer.

ALK+ALCLs induce cutaneous, HMGB-1-dependent IL-8/CXCL8 production by keratinocytes through NF-{kappa}B activation

2012-05-17T09:01:20-07:00

Anaplastic large-cell lymphomas (ALCLs) bearing the t(2;5) translocation (ALK⁺ALCLs) are frequently characterized by skin colonization and associated with a poor prognosis. Using conditional transgenic models of anaplastic lymphoma kinase–positive (ALK⁺) lymphomas and human ALK⁺ALCL cell lines, in the present study, we show that high-mobility-group box-1 (HMGB-1), a proinflammatory cytokine, is released by ALK⁺ cells, and demonstrate extracellular HMGB-1–stimulated secretion of the IL-8 chemokine by HaCaT keratinocytes through the involvement of MMP-9, PAR-2, and the NF-B pathway. Furthermore, we demonstrate that, in vitro, IL-8 is able to induce the invasiveness of ALK⁺ cells, which express the IL-8 receptors CXCR1 and CXCR2. In vitro and in vivo, HMGB-1 inhibition achieved by glycyrrhizin treatment led to a drastic reduction in ALK⁺ cell invasiveness. The pathophysiological relevance of our observations was confirmed by demonstrating that the HMGB-1 and IL-8 receptors are expressed in ALK⁺ALCL biopsies. We have also shown that IL-8 secretion is correlated with leukemic dissemination of ALK⁺ cells in a significant number of patients. The results of the present study demonstrate for the first time a relationship among the pro-inflammatory mediators HMGB-1, MMP-9, PAR-2, and IL-8. We propose that these mediators create a premetastatic niche within the skin, thereby participating in ALK⁺ lymphoma epidermotropism.

RhoH is critical for cell-microenvironment interactions in chronic lymphocytic leukemia in mice and humans

2012-05-17T09:01:20-07:00

Trafficking of B-cell chronic lymphocytic leukemia (CLL) cells to the bone marrow and interaction with supporting stromal cells mediates important survival and proliferation signals. Previous studies have demonstrated that deletion of Rhoh led to a delayed disease onset in a murine model of CLL. Here we assessed the impact of RhoH on homing, migration, and cell-contact dependent interactions of CLL cells. Rhoh^–/– CLL cells exhibited reduced marrow homing and subsequent engraftment. In vitro migration toward the chemokines CXCL12 and CXCL13 and cell-cell interactions between Rhoh^–/– CLL cells and the supporting microenvironment was reduced. In the absence of RhoH the distribution of phosphorylated focal adhesion kinase, a protein known to coordinate activation of the Rho GTPases RhoA and Rac, appeared less polarized in chemokine-stimulated Rhoh^–/– CLL cells, and activation and localization of RhoA and Rac was dysregulated leading to defective integrin function. These findings in the Rhoh^–/– CLL cells were subsequently demonstrated to closely resemble changes in GTPase activation observed in human CLL samples after in vitro and in vivo treatment with lenalidomide, an agent with known influence on microenvironment protection, and suggest that RhoH plays a critical role in prosurvival CLL cell-cell and cell-microenvironment interactions with this agent.

Multilineage dysplasia does not influence prognosis in CEBPA-mutated AML, supporting the WHO proposal to classify these patients as a unique entity

2012-05-17T09:01:20-07:00

In 2008, the World Health Organization introduced CEBPA (encoding the CCAAT/enhancer binding protein)–mutated acute myeloid leukemia (AML) as a provisional entity. However, the classification of CEBPA-mutated AML with multilineage dysplasia (MLD; ≥ 50% dysplastic cells in 2-3 lineages) remains to be clarified. In the present study, we investigated 108 CEBPA-mutated AML patients for the impact of MLD, karyotype, and additional mutations. MLD⁺ patients differed from MLD^– patients only by lower mean WBC counts, not by biologic characteristics, cytogenetic risk profiles, or additional mutations. Survival was better for female patients, patients < 60 years of age, for intermediate versus adverse karyotypes, and, in the case of FLT3-ITD negativity, biallelic versus monoallelic/homozygous CEBPA mutations. In contrast, 2-year overall survival and event-free survival did not differ significantly between MLD⁺ and MLD^– patients. By univariable Cox regression analysis, sex, age, WBC count, and cytogenetic risk category were related to overall survival, but MLD was not. Therefore, because dysplasia is not relevant for this subtype, CEBPA-mutated AML patients should be characterized only according to mutation status, cytogenetic risk group, or additional mutations.

Dicer1 deletion in myeloid-committed progenitors causes neutrophil dysplasia and blocks macrophage/dendritic cell development in mice

2012-05-17T09:01:20-07:00

MicroRNAs (miRNAs) have the potential to regulate cellular differentiation programs; however, miRNA deficiency in primary hematopoietic stem cells (HSCs) results in HSC depletion in mice, leaving the question of whether miRNAs play a role in early-lineage decisions un-answered. To address this issue, we deleted Dicer1, which encodes an essential RNase III enzyme for miRNA biogenesis, in murine CCAAT/enhancer-binding protein α (C/EBPA)–positive myeloid-committed progenitors in vivo. In contrast to the results in HSCs, we found that miRNA depletion affected neither the number of myeloid progenitors nor the percentage of C/EBPA–positive progenitor cells. Analysis of gene-expression profiles from wild-type and Dicer1-deficient granulocyte-macrophage progenitors (GMPs) revealed that 20 miRNA families were active in GMPs. Of the derepressed miRNA targets in Dicer1-null GMPs, 27% are normally exclusively expressed in HSCs or are specific for multipotent progenitors and erythropoiesis, indicating an altered gene-expression landscape. Dicer1-deficient GMPs were defective in myeloid development in vitro and exhibited an increased replating capacity, indicating the regained self-renewal potential of these cells. In mice, Dicer1 deletion blocked monocytic differentiation, depleted macrophages, and caused myeloid dysplasia with morphologic features of Pelger-Huët anomaly. These results provide evidence for a miRNA-controlled switch for a cellular program of self-renewal and expansion toward myeloid differentiation in GMPs.

Phenotype diversity in type 1 Gaucher disease: discovering the genetic basis of Gaucher disease/hematologic malignancy phenotype by individual genome analysis

2012-05-17T09:01:20-07:00

Gaucher disease (GD), an inherited macrophage glycosphingolipidosis, manifests with an extraordinary variety of phenotypes that show imperfect correlation with mutations in the GBA gene. In addition to the classic manifestations, patients suffer from increased susceptibility to hematologic and nonhematologic malignancies. The mechanism(s) underlying malignancy in GD is not known, but is postulated to be secondary to macrophage dysfunction and immune dysregulation arising from lysosomal accumulation of glucocerebroside. However, there is weak correlation between GD/cancer phenotype and the systemic burden of glucocerebroside-laden macrophages. Therefore, we hypothesized that genetic modifier(s) may underlie the GD/cancer phenotype. In the present study, the genetic basis of GD/T-cell acute lymphoblastic lymphoma in 2 affected siblings was deciphered through genomic analysis. GBA gene sequencing revealed homozygosity for a novel mutation, D137N. Whole-exome capture and massively parallel sequencing combined with homozygosity mapping identified a homozygous novel mutation in the MSH6 gene that leads to constitutional mismatch repair deficiency syndrome and increased cancer risk. Enzyme studies demonstrated that the D137N mutation in GBA is a pathogenic mutation, and immunohistochemistry confirmed the absence of the MSH6 protein. Therefore, precise phenotype annotation followed by individual genome analysis has the potential to identify genetic modifiers of GD, facilitate personalized management, and provide novel insights into disease pathophysiology.

Regulation of murine normal and stress-induced erythropoiesis by Desert Hedgehog

2012-05-17T09:01:20-07:00

The function of Hedgehog signaling in hematopoiesis is controversial, with different experimental systems giving opposing results. Here we examined the role of Desert Hedgehog (Dhh) in the regulation of murine erythropoiesis. Dhh is one of 3 mammalian Hedgehog family proteins. Dhh is essential for testis development and Schwann cell function. We show, by analysis of Dhh-deficient mice, that Dhh negatively regulates multiple stages of erythrocyte differentiation. In Dhh-deficient bone marrow, the common myeloid progenitor (CMP) population was increased, but differentiation from CMP to granulocyte/macrophage progenitor was decreased, and the mature granulocyte population was decreased, compared with wild-type (WT). In contrast, differentiation from CMP to megakaryocyte/erythrocyte progenitor was increased, and the megakaryocyte/erythrocyte progenitor population was increased. In addition, we found that erythroblast populations were Dhh-responsive in vitro and ex vivo and that Dhh negatively regulated erythroblast differentiation. In Dhh-deficient spleen and bone marrow, BFU-Es and erythroblast populations were increased compared with WT. During recovery of hematopoiesis after irradiation, and under conditions of stress-induced erythropoiesis, erythrocyte differentiation was accelerated in both spleen and bone marrow of Dhh-deficient mice compared with WT.

t-PA-specific modulation of a human blood-brain barrier model involves plasmin-mediated activation of the Rho kinase pathway in astrocytes

Niego, B., Freeman, R., Puschmann, T. B., Turnley, A. M., Medcalf, R. L. — 2012-05-17T09:01:20-07:00

Tissue-type plasminogen activator (t-PA) can modulate permeability of the neurovascular unit and exacerbate injury in ischemic stroke. We examined the effects of t-PA using in vitro models of the blood-brain barrier. t-PA caused a concentration-dependent increase in permeability. This effect was dependent on plasmin formation and potentiated in the presence of plasminogen. An inactive t-PA variant inhibited the t-PA–mediated increase in permeability, whereas blockade of low-density lipoprotein receptors or exposed lysine residues resulted in similar inhibition, implying a role for both a t-PA receptor, most likely a low-density lipoprotein receptor, and a plasminogen receptor. This effect was selective to t-PA and its close derivative tenecteplase. The truncated t-PA variant reteplase had a minor effect on permeability, whereas urokinase and desmoteplase were ineffective. t-PA also induced marked shape changes in both brain endothelial cells and astrocytes. Changes in astrocyte morphology coincided with increased F-actin staining intensity, larger focal adhesion size, and elevated levels of phosphorylated myosin. Inhibition of Rho kinase blocked these changes and reduced t-PA/plasminogen–mediated increase in permeability. Hence plasmin, generated on the cell surface selectively by t-PA, modulates the astrocytic cytoskeleton, leading to an increase in blood-brain barrier permeability. Blockade of the Rho/Rho kinase pathway may have beneficial consequences during thrombolytic therapy.

Inhibition of factor XI activation attenuates inflammation and coagulopathy while improving the survival of mouse polymicrobial sepsis

2012-05-17T09:01:20-07:00

Severe bacterial sepsis often leads to a systemic procoagulant and proinflammatory condition that can manifest as disseminated intravascular coagulation, septic shock, and multiple organ failure. Because activation of the contact proteases factor XII (FXII), prekallikrein, and factor XI (FXI) can trigger coagulation and inflammatory responses, the contact factors have been considered potential targets for the treatment of sepsis. However, the pathogenic role of contact activation in severe infections has not been well defined. We therefore investigated whether an anticoagulant antibody (14E11) that selectively inhibits prothrombotic FXI activation by activated FXII (FXIIa) modifies the course of bowel perforation-induced peritoneal sepsis in mice. Early anticoagulation with 14E11 suppressed systemic thrombin- antithrombin complex formation, IL-6, and TNF-α levels, and reduced platelet consumption in the circulation and deposition in the blood vessels. Treatment with 14E11 within 12 hours after bowel perforation significantly improved survival compared with vehicle treatment, and the saturating dose did not increase tail bleeding. These data suggest that severe polymicrobial abdominal infection induces prothrombotic FXI activation, to the detriment of the host. Systemic anticoagulation by inhibiting FXI activation or FXIIa procoagulant activity during sepsis may therefore limit the development of disseminated intravascular coagulation without increasing bleeding risks.

von Willebrand factor (VWF) propeptide binding to VWF D'D3 domain attenuates platelet activation and adhesion

2012-05-17T09:01:20-07:00

Noncovalent association between the von Willebrand factor (VWF) propeptide (VWFpp) and mature VWF aids N-terminal multimerization and protein compartmentalization in storage granules. This association is currently thought to dissipate after secretion into blood. In the present study, we examined this proposition by quantifying the affinity and kinetics of VWFpp binding to mature VWF using surface plasmon resonance and by developing novel anti-VWF D'D3 mAbs. Our results show that the only binding site for VWFpp in mature VWF is in its D'D3 domain. At pH 6.2 and 10mM Ca²⁺, conditions mimicking intracellular compartments, VWFpp-VWF binding occurs with high affinity (K_D = 0.2nM, k_off = 8 x 10^–5 s^–1). Significant, albeit weaker, binding (K_D = 25nM, k_off = 4 x 10^–3 s^–1) occurs under physiologic conditions of pH 7.4 and 2.5mM Ca²⁺. This interaction was also observed in human plasma (K_D = 50nM). The addition of recombinant VWFpp in both flow-chamber–based platelet adhesion assays and viscometer-based shear-induced platelet aggregation and activation studies reduced platelet adhesion and activation partially. Anti-D'D3 mAb DD3.1, which blocks VWFpp binding to VWF-D'D3, also abrogated platelet adhesion, as shown by shear-induced platelet aggregation and activation studies. Our data demonstrate that VWFpp binding to mature VWF occurs in the circulation, which can regulate the hemostatic potential of VWF by reducing VWF binding to platelet GpIbα.

Targeting recombinant thrombomodulin fusion protein to red blood cells provides multifaceted thromboprophylaxis

2012-05-17T09:01:20-07:00

Thrombin generates fibrin and activates platelets and endothelium, causing thrombosis and inflammation. Endothelial thrombomodulin (TM) changes thrombin's substrate specificity toward cleavage of plasma protein C into activated protein C (APC), which opposes its thrombotic and inflammatory activities. Endogenous TM activity is suppressed in pathologic conditions, and antithrombotic interventions involving soluble TM are limited by rapid blood clearance. To overcome this problem, we fused TM with a single chain fragment (scFv) of an antibody targeted to red blood cells. scFv/TM catalyzes thrombin-mediated generation of activated protein C and binds to circulating RBCs without apparent damage, thereby prolonging its circulation time and bioavailability orders of magnitude compared with soluble TM. In animal models, a single dose of scFv/TM, but not soluble TM, prevents platelet activation and vascular occlusion by clots. Thus, scFv/TM serves as a prodrug and provides thromboprophylaxis at low doses (0.15 mg/kg) via multifaceted mechanisms inhibiting platelets and coagulation.

Regulation of acute graft-versus-host disease by microRNA-155

2012-05-17T09:01:20-07:00

Acute graft-versus-host disease (aGVHD) remains a major complication of allogeneic hematopoietic stem cell transplant (alloHSCT), underscoring the need to further elucidate its mechanisms and develop novel treatments. Based on recent observations that microRNA-155 (miR-155) is up-regulated during T-cell activation, we hypothesized that miR-155 is involved in the modulation of aGVHD. Here we show that miR-155 expression was up-regulated in T cells from mice developing aGVHD after alloHSCT. Mice receiving miR-155–deficient donor lymphocytes had markedly reduced lethal aGVHD, whereas lethal aGVHD developed rapidly in mice recipients of miR-155 overexpressing T cells. Blocking miR-155 expression using a synthetic anti–miR-155 after alloHSCT decreased aGVHD severity and prolonged survival in mice. Finally, miR-155 up-regulation was shown in specimens from patients with pathologic evidence of intestinal aGVHD. Altogether, our data indicate a role for miR-155 in the regulation of GVHD and point to miR-155 as a novel target for therapeutic intervention in this disease.

NHERF-2 maintains endothelial homeostasis

2012-05-17T09:01:20-07:00

The Na⁺/H⁺ exchanger regulatory factor-2 (NHERF-2) is an integral component of almost all endothelial cells (ECs), yet its endothelial function is not known. Here, we found that NHERF-2, is a key regulator of endothelial homeostasis because NHERF-2–silenced ECs proliferate at a much higher rate even in the absence of mitogens such as VEGF compared with control ECs. We further show that the hyperproliferation phenotype of NHERF-2–silenced EC is because of an accelerated cell cycle that is probably caused by a combination of the following factors: increased cytoplasmic calcium, increased expression of c-Myc, increased expression of cyclin D1, and reduced expression of p27. Using an experimental mouse model of human hemangioma, we found that the endothelial neoplasms derived from NHERF-2–silenced cells were much larger in volume than those derived from control cells. Thus, NHERF-2 is a negative regulator of endothelial proliferation and may have important roles in endothelial homeostasis and vascular modeling.

Human Langerhans cells are immature in melanoma sentinel lymph nodes

2012-05-17T09:01:20-07:00

Response: Breslow thickness and excision interval affect the activation state of Langerhans cells in melanoma sentinel lymph nodes

2012-05-17T09:01:20-07:00

Generation of Th17 from human naive CD4+ T cells preferentially occurs from FOXP3+ Tregs upon costimulation via CD28 or CD5

Ayyoub, M., Raffin, C., Valmori, D. — 2012-05-17T09:01:20-07:00

Response: priming of human naive CD4+ T cells via CD5 costimulation requires IL-6 for optimal Th17 development

2012-05-17T09:01:20-07:00

Genomic loss of patient-specific HLA in acute myeloid leukemia relapse after well-matched unrelated donor HSCT

2012-05-17T09:01:20-07:00