A new aspect of the molecular pathogenesis of paroxysmal nocturnal hemoglobinuria

U2AF1 and EZH2 mutations are associated with nonimmune hemolytic anemia in myelodysplastic syndromes

Hemolysis is a well-recognized but poorly characterized phenomenon in a subset of patients with myelodysplastic syndromes (MDS). Its pathobiological basis seems to underpin a nonimmune etiology whose clinical significance has not been adequately characterized. Hemolysis in MDS is often attributed to either ineffective intramedullary erythropoiesis or acquired hemoglobinopathies and red blood cell (RBC) membrane defects. These heterogeneous processes have not been associated with specific genetic subsets of the disease. We aimed to describe the prevalence of hemolysis among patients with MDS, their baseline characteristics, molecular features, and resulting impact on outcomes. We considered baseline serum haptoglobin <10 mg/dL a surrogate marker for intravascular hemolysis. Among 519 patients, 10% had hemolysis. The baseline characteristics were similar among both groups. Only 13% of patients with hemolysis were Coombs-positive, suggesting that hemolysis in MDS is largely not immune-mediated. Inferior survival trends were observed among lower-risk patients with MDS undergoing hemolysis. Decreased response rates to erythropoiesis-stimulating agents (ESA) and higher responses to hypomethylating agents (HMA) were also observed in the hemolysis group. U2AF1 and EZH2 hotspot mutations were more prevalent among those undergoing hemolysis (P < .05). U2AF1 mutations were observed in 30% of patients with hemolysis and occurred almost exclusively at the S34 hotspot. Somatic mutations encoding splicing factors may affect erythrocyte membrane components, biochemical properties, and RBC metabolic function, which underpin the development of atypical clones from erythroid precursors in MDS presenting with hemolysis. Future studies will explore the contribution of altered splicing to the development of acquired hemoglobinopathies.

WT1 in disease: shifting the epithelial-mesenchymal balance

WT1 is a versatile gene that controls transitions between the mesenchymal and epithelial state of cells in a tissue-context dependent manner. As such, WT1 is indispensable for normal development of many organs and tissues. Uncontrolled epithelial to mesenchymal transition (EMT) is a hallmark of a diverse array of pathologies and disturbance of mesenchymal to epithelial transition (MET) has been associated with a number of developmental abnormalities. It is therefore not surprising that WT1 has been linked to many of these. Here we review the role of WT1 in proper control of the mesenchymal-epithelial balance of cells and discuss how far these roles can explain the role of WT1 in a variety of disease states.

Low concentration of serum haptoglobin has impact on understanding complex pathophysiology in patients with acquired bone marrow failure syndromes

To clarify whether measurement of serum haptoglobin (Hp) has impact on understanding pathophysiology in bone marrow failure (BMF) syndromes, we investigated concentrations of serum Hp by nephelometric procedure in 156 Japanese patients with BMF, including 54 aplastic anemia (AA), 50 paroxysmal nocturnal hemoglobinuria (PNH), and 52 myelodysplastic syndromes (MDS) patients. The frequencies with low concentrations of serum Hp (<42 mg/dL) in PNH patients (98.0%) were significantly higher than those in AA (27.8%; P < 0.0001) and MDS (38.5%; P < 0.0001) patients. In AA patients, white blood cell (WBC), absolute neutrophil, and platelet counts were significantly decreased in the group (n = 15) with low concentrations of serum Hp than in that (n = 39) with normal concentrations of it, and WBC counts were positively correlated with concentrations of serum Hp, suggesting that WBC counts may affect the concentrations. In MDS patients, hemoglobin concentrations and serum iron were significantly decreased and increased, respectively, in the group (n = 20) with low concentrations of serum Hp than in that (n = 32) with normal concentrations of it, and the values of serum iron were inversely correlated with concentrations of serum Hp, suggesting that ineffective erythropoiesis may affect the concentrations. Several AA and MDS patients with low concentrations of serum Hp had Coombs-negative autoimmune hemolytic anemia determined by immunoradiometric assay. In conclusion, several factors in conjunction with pathophysiology contribute to decrease of serum Hp in BMF.

Isolating human islets of Langerhans causes loss of decay accelerating factor (CD55) on beta-cells

It has previously been reported that human decay accelerating factor (DAF; CD55) is not expressed on cells isolated from human islets. We have investigated if this absence is caused by the islet isolation procedure and/or the single cell isolation technique. We focused on loss of DAF expression on beta-cells within the intact islet and on isolated individual beta-cells. We established that DAF was expressed in islets and on beta-cells prior to isolation by in situ analysis in the intact pancreas. In situ immunohistochemistry (IHC) was used to examine DAF expression on human pancreatic islets and isolated islets. A reverse transcriptase-polymerase chain reaction (RT-PCR) specific for human DAF mRNA was developed to measure mRNA levels in situ in islets within the intact pancreas, isolated islets, and purified beta-cells. beta-Cells were purified by fluorescence-activated cell sorting. DAF protein expression on these purified cells was measured using flow cytometry. Expression of DAF protein was present on the islets, including beta-cells within the human pancreas; however, comparative data from IHC and flow cytometry revealed the absence of DAF protein on beta-cells in both isolated islets and single cell preparations. Furthermore, compared to mRNA levels detected by in situ RT-PCR in the intact pancreas and in human HEK 293 cells, isolated islets, and purified human beta-cells showed downregulation of DAF mRNA. mRNA was detectable in both of these preparations by RT-PCR; levels were lower following both the islet isolation process (53%) and single cell preparation (a further 62%) compared to HEK 293 controls. Human islet allotransplantation might be more successful if either de novo transfer of DAF onto the isolated islets or novel techniques for islet isolation preserving DAF could be developed.

Neutropenia due to parvovirus B19 infections in patients with paroxysmal nocturnal hemoglobinuria. Blood transfusion and natural infection cases

Two patients with paroxysmal nocturnal hemoglobinuria (PNH) and parvovirus B19 (PVB19) infection are reported. One was infected by PVB19-contaminated blood transfusion, whereas the other had become infected naturally. Both patients completely recovered after transient pancytopenia, but showed severe and intermediate neutropenia (0.216 and 0.768 x 10(9)/l, respectively) at the nadirs of aplastic crises. In the literature, PNH cases also showed neutropenia (0 and 0.54 x 10(9)/l) at aplastic crises. When patients with PNH are infected by PVB19, they may show severe neutropenia and mild thrombocytopenia in addition to severe reticulocytopenia. Therefore, these patients might have to be treated with granulocyte colony-stimulating factor to be able to recover from severe neutropenia.

High frequency of several PIG-A mutations in patients with aplastic anemia and myelodysplastic syndrome

To clarify some characteristics of phosphatidylinositol glycan-class A gene (PIG-A) mutations in aplastic anemia (AA) and myelodysplastic syndrome (MDS) patients compared with those in paroxysmal nocturnal hemoglobinuria (PNH) patients, we investigated PIG-A mutations in CD59- granulocytes and CD48- monocytes from seven AA, eight MDS, and 11 PNH Japanese patients. The most frequent base or type abnormalities of the PIG-A gene in AA and MDS patients were base substitutions or missense mutations, respectively, and deletions or frameshift mutations, respectively, in PNH patients. Several PIG-A mutations, most of which were statistically minor, were found in glycosylphosphatidylinositol-negative cells from all AA and MDS patients but not from all PNH patients. However, the common PIG-A mutations during the clinical course between CD59- granulocytes and/or CD48- monocytes from each AA or MDS patient, except for Case 5, were not found. PIG-A mutations were different between the granulocytes and monocytes from five AA and five MDS patients. Our results indicate that there were some characteristics of PIG-A mutations in AA and MDS patients compared with PNH patients and that several minor PNH clones in these patients occurred at random during the clinical course. This partly explains the transformation of AA or MDS to PNH at intervals.

C4b-binding protein binds to necrotic cells and DNA, limiting DNA release and inhibiting complement activation

After cell death, via apoptosis or necrosis, the uptake of dead cells by neighboring cells or phagocytes prevents the release of intracellular content. An array of molecules, including initiation molecules of the complement system, are involved in marking dead cells for uptake. After binding of these molecules, complement activation takes place, which when uncontrolled might result in a proinflammatory state. In the current study we demonstrate that complement inhibitor, C4b-binding protein (C4BP), binds strongly to necrotic cells, irrespective of the cell type used or the method of induction. After binding of the C4BP-protein S (PS) complex to necrotic cells via PS-phosphatidylserine and C4BP-DNA interactions, C4BP-PS inhibits complement activation on these cells. C4BP binds DNA via a patch of positively charged amino acids, mainly on the second complement control domain of the C4BP alpha-chain (affinity constant: 190 nM). Furthermore, C4BP limits DNA release from necrotic cells and inhibits DNA-mediated complement activation in solution. The C4BP-necrotic cell interaction also occurs in vivo as necrotic areas of arteriosclerotic plaques and of various cancers stain strongly positive for C4BP. This study describes a novel mechanism in which C4BP limits the inflammatory potential of necrotic cells.