VPS4A Mutations in Humans Cause Syndromic Congenital Dyserythropoietic Anemia due to Cytokinesis and Trafficking Defects.

The Congenital Dyserythropoietic Anemia (CDA) Registry was established with the goal to facilitate investigations of natural history, biology, and molecular pathogenetic mechanisms of CDA. Three unrelated individuals enrolled in the registry had a syndrome characterized by CDA and severe neurodevelopmental delay. They were found to have missense mutations in VPS4A, a gene coding for an ATPase that regulates the ESCRT-III machinery in a variety of cellular processes including cell division, endosomal vesicle trafficking, and viral budding. Bone marrow studies showed binucleated erythroblasts and erythroblasts with cytoplasmic bridges indicating abnormal cytokinesis and abscission. Circulating red blood cells were found to retain transferrin receptor (CD71) in their membrane, demonstrating that VPS4A is critical for normal reticulocyte maturation. Using proband-derived induced pluripotent stem cells (iPSCs), we have successfully modeled the hematologic aspects of this syndrome in vitro, recapitulating their dyserythropoietic phenotype. Our findings demonstrate that VPS4A mutations cause cytokinesis and trafficking defects leading to a human disease with detrimental effects to erythropoiesis and neurodevelopment.

Neutrophils Derived from Genetically Modified Human Induced Pluripotent Stem Cells Circulate and Phagocytose Bacteria In Vivo.

Bacterial and fungal infections are a major cause of morbidity and mortality in neutropenic patients. Donor-derived neutrophil transfusions have been used for prophylaxis or treatment for infection in neutropenic patients. However, the short half-life and the limited availability of large numbers of donor-derived neutrophils for transfusion remain a significant hurdle in the implementation of neutrophil transfusion therapy. Here, we investigate the in vitro and in vivo activity of neutrophils generated from human induced pluripotent stem cells (iPSC), a potentially unlimited resource to produce neutrophils for transfusion. Phenotypic analysis of iPSC-derived neutrophils reveal reactive oxygen species production at similar or slightly higher than normal peripheral blood neutrophils, but have an ∼50%-70% reduced Escherichia coli phagocytosis and phorbol 12-myristate 13-acetate induced formation of neutrophil extracellular traps (NET). Signaling of granulocytic precursors identified impaired AKT activation, but not ERK or STAT3, in agonist-stimulated iPSC-derived neutrophils. Expression of a constitutively activated AKT in iPSC-derived neutrophils restores most phagocytic activity and NET formation. In a model of bacterial induced peritonitis in immunodeficient mice, iPSC-derived neutrophils, with or without corrected AKT activation, migrate similarly to the peritoneal fluid as peripheral blood neutrophils, whereas the expression of activated AKT significantly improves their phagocytic activity in vivo. Stem Cells Translational Medicine 2019;8:557-567.

Pathogenesis of ELANE-mutant severe neutropenia revealed by induced pluripotent stem cells.

Severe congenital neutropenia (SCN) is often associated with inherited heterozygous point mutations in ELANE, which encodes neutrophil elastase (NE). However, a lack of appropriate models to recapitulate SCN has substantially hampered the understanding of the genetic etiology and pathobiology of this disease. To this end, we generated both normal and SCN patient-derived induced pluripotent stem cells (iPSCs), and performed genome editing and differentiation protocols that recapitulate the major features of granulopoiesis. Pathogenesis of ELANE point mutations was the result of promyelocyte death and differentiation arrest, and was associated with NE mislocalization and activation of the unfolded protein response/ER stress (UPR/ER stress). Similarly, high-dose G-CSF (or downstream signaling through AKT/BCL2) rescues the dysgranulopoietic defect in SCN patient-derived iPSCs through C/EBPß-dependent emergency granulopoiesis. In contrast, sivelestat, an NE-specific small-molecule inhibitor, corrected dysgranulopoiesis by restoring normal intracellular NE localization in primary granules; ameliorating UPR/ER stress; increasing expression of CEBPA, but not CEBPB; and promoting promyelocyte survival and differentiation. Together, these data suggest that SCN disease pathogenesis includes NE mislocalization, which in turn triggers dysfunctional survival signaling and UPR/ER stress. This paradigm has the potential to be clinically exploited to achieve therapeutic responses using lower doses of G-CSF combined with targeting to correct NE mislocalization.