The chromatin remodeler CHD8 governs hematopoietic stem/progenitor survival by regulating ATM-mediated P53 protein stability.

The Chd8 gene encodes a member of the chromodomain helicase DNA-binding (CHD) family of SNF2H-like adenosine triphosphate (ATP)-dependent chromatin remodeler, the mutations of which define a subtype of autism spectrum disorders. Increasing evidence from recent studies indicates that ATP-dependent chromatin-remodeling genes are involved in the control of crucial gene-expression programs in hematopoietic stem/progenitor cell (HSPC) regulation. In this study, we identified CHD8 as a specific and essential regulator of normal hematopoiesis. Loss of Chd8 leads to severe anemia, pancytopenia, bone marrow failure, and engraftment failure related to a drastic depletion of HSPCs. CHD8 forms a complex with ATM and its deficiency increases chromatin accessibility and drives genomic instability in HSPCs causing an activation of ATM kinase that further stabilizes P53 protein by phosphorylation and leads to increased HSPC apoptosis. Deletion of P53 rescues the apoptotic defects of HSPCs and restores overall hematopoiesis in Chd8-/- mice. Our findings demonstrate that chromatin organization by CHD8 is uniquely necessary for the maintenance of hematopoiesis by integrating the ATM-P53-mediated survival of HSPCs.

Immunodeficiency and bone marrow failure with mosaic and germline TLR8 gain of function.

Inborn errors of immunity (IEI) are a genetically heterogeneous group of disorders with a broad clinical spectrum. Identification of molecular and functional bases of these disorders is important for diagnosis, treatment, and an understanding of the human immune response. We identified 6 unrelated males with neutropenia, infections, lymphoproliferation, humoral immune defects, and in some cases bone marrow failure associated with 3 different variants in the X-linked gene TLR8, encoding the endosomal Toll-like receptor 8 (TLR8). Interestingly, 5 patients had somatic variants in TLR8 with <30% mosaicism, suggesting a dominant mechanism responsible for the clinical phenotype. Mosaicism was also detected in skin-derived fibroblasts in 3 patients, demonstrating that mutations were not limited to the hematopoietic compartment. All patients had refractory chronic neutropenia, and 3 patients underwent allogeneic hematopoietic cell transplantation. All variants conferred gain of function to TLR8 protein, and immune phenotyping demonstrated a proinflammatory phenotype with activated T cells and elevated serum cytokines associated with impaired B-cell maturation. Differentiation of myeloid cells from patient-derived induced pluripotent stem cells demonstrated increased responsiveness to TLR8. Together, these findings demonstrate that gain-of-function variants in TLR8 lead to a novel childhood-onset IEI with lymphoproliferation, neutropenia, infectious susceptibility, B- and T-cell defects, and in some cases, bone marrow failure. Somatic mosaicism is a prominent molecular mechanism of this new disease.

Gene therapy restores the transcriptional program of hematopoietic stem cells in Fanconi anemia.

Clinical trials have shown that lentiviral-mediated gene therapy can ameliorate bone marrow failure (BMF) in nonconditioned Fanconi anemia (FA) patients resulting from the proliferative advantage of corrected FA hematopoietic stem and progenitor cells (HSPC). However, it is not yet known if gene therapy can revert affected molecular pathways in diseased HSPC. Single-cell RNA sequencing was performed in chimeric populations of corrected and uncorrected HSPC co-existing in the BM of gene therapy-treated FA patients. Our study demonstrates that gene therapy reverts the transcriptional signature of FA HSPC, which then resemble the transcriptional program of healthy donor HSPC. This includes a down-regulated expression of TGF-ß and p21, typically up-regulated in FA HSPC, and upregulation of DNA damage response and telomere maintenance pathways. Our results show for the first time the potential of gene therapy to rescue defects in the HSPC transcriptional program from patients with inherited diseases; in this case, in FA characterized by BMF and cancer predisposition.

NLRP1 inflammasome activation induces pyroptosis of hematopoietic progenitor cells.

Cytopenias are key prognostic indicators of life-threatening infection, contributing to immunosuppression and mortality. Here we define a role for Caspase-1-dependent death, known as pyroptosis, in infection-induced cytopenias by studying inflammasome activation in hematopoietic progenitor cells. The NLRP1a inflammasome is expressed in hematopoietic progenitor cells and its activation triggers their pyroptotic death. Active NLRP1a induced a lethal systemic inflammatory disease that was driven by Caspase-1 and IL-1ß but was independent of apoptosis-associated speck-like protein containing a CARD (ASC) and ameliorated by IL-18. Surprisingly, in the absence of IL-1ß-driven inflammation, active NLRP1a triggered pyroptosis of hematopoietic progenitor cells resulting in leukopenia at steady state. During periods of hematopoietic stress induced by chemotherapy or lymphocytic choriomeningitis virus (LCMV) infection, active NLRP1a caused prolonged cytopenia, bone marrow hypoplasia, and immunosuppression. Conversely, NLRP1-deficient mice showed enhanced recovery from chemotherapy and LCMV infection, demonstrating that NLRP1 acts as a cellular sentinel to alert Caspase-1 to hematopoietic and infectious stress.

Hematogone Hyperplasia Masquerading as Acute Lymphoblastic Leukemia With Concurrent Hypercupremia.

Alterations in copper homeostasis is an uncommon cause for hematologic alterations frequently presenting with dysplastic features in the bone marrow. Most of these alterations have been documented in adult patients with copper deficiency. Rare cases show hematogone hyperplasia in these patients. Effects of mild copper excess have not been documented in literature. We are describing a pediatric patient who presented with pancytopenia associated with hypercupraemia (excess of copper). Bone marrow examination showed hematogone hyperplasia. Interestingly, correction of serum copper levels with zinc therapy lead to complete improvement in pancytopenia. Hematogones had also reduced in subsequent marrow biopsy after therapy.

Tmem30a Plays Critical Roles in Ensuring the Survival of Hematopoietic Cells and Leukemia Cells in Mice.

The fundamental structure of eukaryotic cell plasma membrane is the phospholipid bilayer, which contains four major phospholipids. These phospholipids are asymmetrically distributed between the outer and inner leaflets. P4-ATPase flippase complexes play essential roles in ensuring this asymmetry. We found that conditional deletion of Tmem30a, the ß subunit of P4-ATPase flippase complex, caused pancytopenia in mice. Tmem30a deficiency resulted in depletion of lineage-committed blood cells in the peripheral blood, spleen, and bone marrow. Ablation of Tmem30a also caused the depletion of hematopoietic stem cells (HSCs). HSC RNA sequencing results revealed that multiple biological processes and signal pathways were involved in the event, including mammalian target of rapamycin signaling, genes for HSC stemness, and genes responding to interferons. Our results also revealed that targeting Tmem30a signaling had therapeutic utility in BCR/ABL1-induced chronic myeloid leukemia.

A Tie2-Notch1 signaling axis regulates regeneration of the endothelial bone marrow niche.

Loss-of-function studies have determined that Notch signaling is essential for hematopoietic and endothelial development. By deleting a single allele of the Notch1 transcriptional activation domain we generated viable, post-natal mice exhibiting hypomorphic Notch signaling. These heterozygous mice, which lack only one copy of the transcriptional activation domain, appear normal and have no endothelial or hematopoietic phenotype, apart from an inherent, cell-autonomous defect in T-cell lineage development. Following chemotherapy, these hypomorphs exhibited severe pancytopenia, weight loss and morbidity. This phenotype was confirmed in an endothelial-specific, loss-of-function Notch1 model system. Ang1, secreted by hematopoietic progenitors after damage, activated endothelial Tie2 signaling, which in turn enhanced expression of Notch ligands and potentiated Notch1 receptor activation. In our heterozygous, hypomorphic model system, the mutant protein that lacks the Notch1 transcriptional activation domain accumulated in endothelial cells and interfered with optimal activity of the wildtype Notch1 transcriptional complex. Failure of the hypomorphic mutant to efficiently drive transcription of key gene targets such as Hes1 and Myc prolonged apoptosis and limited regeneration of the bone marrow niche. Thus, basal Notch1 signaling is sufficient for niche development, but robust Notch activity is required for regeneration of the bone marrow endothelial niche and hematopoietic recovery.

Demonstration of IgG Subclass (IgG1 and IgG3) in Immuno-Related Hemocytopenia.

BACKGROUND: Immuno-related hemocytopenia (IRH) is defined as idiopathic cytopenia of undetermined significance (ICUS) patients with autoantibodies. In our previous studies, we found that IgG1 levels were increased in IRH patients and might cause the destruction of hematopoietic cells. METHODS: In this study, we analyzed IgG subclasses in 30 IRH patients (male:female = 13:17, median age 32 years, range 18 - 56), 15 IRH remission patients (IRH-R) (male:female = 6:9, median age 34, range 20 - 52) and 20 normal controls (male:female = 8:12, median age 27, range 24 - 36) by Cytometric Bead Array, Flow Cytometry and Immunohistochemical staining. RESULTS: Levels of IgG1/IgG3 in the bone marrow supernatant of IRH patents, as well as the proportion of CD5+ B lymphocytes and Th2 cells (CD3+CD8-IL-4+) were higher than those of IRH-R patients and normal controls, and IgG1 levels had a positive correlation with the proportion of Th2 cells. In IRH patients, IgG1 and IgG3 were positive on nucleated erythrocytes and granulocytes, which were negative in IRH-R patients and healthy controls and had inverse correlations with hematopoietic function. Using immunohistochemical staining, IgG1 were also detected on bone marrow biopsies of IRH patients. CONCLUSIONS: The results indicated that IgG1 and IgG3 autoantibodies in IRH patients might play a key role in the IRH pathogenesis and in the abnormal immune function of IRH patients.

Conditional TRF1 knockout in the hematopoietic compartment leads to bone marrow failure and recapitulates clinical features of dyskeratosis congenita.

TRF1 is part of the shelterin complex, which binds telomeres and it is essential for their protection. Ablation of TRF1 induces sister telomere fusions and aberrant numbers of telomeric signals associated with telomere fragility. Dyskeratosis congenita is characterized by a mucocutaneous triad, bone marrow failure (BMF), and presence of short telomeres because of mutations in telomerase. A subset of patients, however, show mutations in the shelterin component TIN2, a TRF1-interacting protein, presenting a more severe phenotype and presence of very short telomeres despite normal telomerase activity. Allelic variations in TRF1 have been found associated with BMF. To address a possible role for TRF1 dysfunction in BMF, here we generated a mouse model with conditional TRF1 deletion in the hematopoietic system. Chronic TRF1 deletion results in increased DNA damage and cellular senescence, but not increased apoptosis, in BM progenitor cells, leading to severe aplasia. Importantly, increased compensatory proliferation of BM stem cells is associated with rapid telomere shortening and further increase in senescent cells in vivo, providing a mechanism for the very short telomeres of human patients with mutations in the shelterin TIN2. Together, these results represent proof of principle that mutations in TRF1 lead to the main clinical features of BMF.

Diagnosis of immune pathophysiology in patients with bone marrow failure.

Differential diagnosis of pancytopenia with bone marrow (BM) hypoplasia represented by aplastic anemia (AA) is often challenging for physicians, because no laboratory tests have been established, until recently, to distinguish immune-mediated BM failure, which includes acquired AA (aAA) and a subset of low-risk myelodysplastic syndrome (MDS), from non-immune BM failure, which is primarily caused by genetic abnormalities in hematopoietic stem cells (HSCs). HSCs of healthy individuals often undergo somatic mutations, and some acquire phenotypic changes that allow them to escape immune attack against themselves. Once an immune attack against HSCs occurs, HSCs that undergo somatic mutations survive the immune attack and continue to produce their progenies with the same genetic or phenotypic changes. The presence of mature blood cells derived from mutated HSCs in the peripheral blood serves as evidence of the immune-mediated destruction of HSCs. Glycosylphosphatidylinositol-anchored protein-deficient (GPI[-]) blood cells and HLA class I allele-lacking (HLA[-]) leukocytes are two major aberrant cell types that represent the immune mechanism underlying BM failure. This review focuses on the importance of identifying immune mechanisms using laboratory markers, including GPI(-) cells and HLA(-) leukocytes, in the management of BM failure.

A mouse model of hereditary folate malabsorption: deletion of the PCFT gene leads to systemic folate deficiency.

The human proton coupled folate transporter (PCFT) is involved in low pH-dependent intestinal folate transport. In this report, we describe a new murine model of the hereditary folate malabsorption syndrome that we developed through targeted disruption of the first 3 coding exons of the murine homolog of the PCFT gene. By 4 weeks of age, PCFT-deficient (PCFT(-/-)) mice developed severe macrocytic normochromic anemia and pancytopenia. Immature erythroblasts accumulated in the bone marrow and spleen of PCFT(-/-) mice and failed to differentiate further, showing an increased rate of apoptosis in intermediate erythroblasts and reduced release of reticulocytes. In response to the inefficient hematologic development, the serum of the PCFT(-/-) animals contained elevated concentrations of erythropoietin, soluble transferrin receptor (sCD71), and thrombopoietin. In vivo folate uptake experiments demonstrated a systemic folate deficiency caused by disruption of PCFT-mediated intestinal folate uptake, thus confirming in vivo a critical and nonredundant role of the PCFT protein in intestinal folate transport and erythropoiesis. The PCFT-deficient mouse serves as a model for the hereditary folate malabsorption syndrome and is the most accurate animal model of folate deficiency anemia described to date that closely captures the spectrum of pathology typical of this disease.

Increased frequency of bone marrow T follicular helper cells in patients with immune-related pancytopenia.

Immune-related pancytopenia (IRP) is one kind of bone marrow failure diseases which is related to autoantibodies. Autoantibodies have been detected on the membrane of various bone marrow (BM) hemopoietic cells by BM mononuclear-cell-Coombs test or flow cytometric analysis. There are autoantibodies in the BM supernatant of IRP patients, which can target several antigens on hematopoietic cells membranes by western blot. T follicular helper (Tfh) cells are the true helper cells for Ab responses, which represent one of the most numerous and important subsets of effector T cells. Dysregulation of Tfh cell function or expression of Tfh cell-associated molecules could contribute to the pathogenesis of autoimmune diseases. Currently, there are no studies regarding the role of Tfh cells in IRP patients. The percentages of Tfh cells, Tfh-related molecules ICOS, CD40L, IL-21, and Bcl-6 in BM were investigated in 90 patients with IRP, and 25 healthy controls. We observed that there exist increased quantity and hyperfunction of Tfh cells in IRP, and the results were correlated with patient characteristics. It was indicated that dysregulated Tfh cells might be involved in the pathogenesis of IRP and that inhibition of Tfh cells effector molecules might provide opportunities for new therapeutic approaches to IRP and even other human autoimmune diseases.

[Changes of transcription factors Bcl-6, Foxp3 and RORγt in CD4(+) cells in bone marrow of immuno-related hematocytopenia].

OBJECTIVE: To evaluate the possible mechanism of transcription factors B cell lymphoma 6 (Bcl-6) , forkhead/winged helix transcription factor 3 (Foxp3) and retinoic acid related orphan receptor (RORγt) in CD4(+) T cells for immuno-related hematocytopenia (IRH). METHODS: CD4(+) T cells were harvested from 40 IRH patients, 38 aplastic anemia subjects and 25 normal controls and separated by magnetic activated cell sorting (MACS). Then the expressions of transcription factors of Foxp3, RORγ and Bcl-6 in CD4(+) T cells were measured by real time fluorescent quantitative-polymerase chain reaction (QRT-PCR). RESULTS: Auto-antibody was detected on CD34(+) cells (67.5% (27/40) ), CD15(+) cells (65.0% (26/40)), GlyA(+) cells (75.0% (30/40) ), auto-antibody involving three, two or one myeloid cell were detected in 27.5% (11/40), 52.5% (21/40), 20.0% (8/40) of IRH patients. Compensatory increase of Foxp3 mRNA was found in IRH (0.124 (0.073-0.198) vs 0.071 (0.046-0.118), P < 0.05). The expression of Bcl-6 was higher (2.243 (0.854-4.544) vs 1.211 (0.131-2.816), P < 0.05). Compared to aplastic anemia, the expression of RORγt was lower in IRH (0.133 (0.068-0.189) vs 0.290 (0.138-0.480), P < 0.01) and the ratio of Treg/Th17 shifted to Th17 in patients with aplastic anemia (Foxp3/RORγt ratio,0.500 (0.240-0.795) vs 0.975 (0.483-1.416), P < 0.01). CONCLUSION: As one kind of bone marrow failures caused by autoantibody to bone marrow cells, IRH may occur due to a high expression of Bcl-6 in CD4(+) T cells, its immunopathogenesis is different from that of aplastic anemia.

Haploinsufficiency of the essential gene Rps12 causes defects in erythropoiesis and hematopoietic stem cell maintenance.

Ribosomal protein (Rp) gene haploinsufficiency can result in Diamond-Blackfan Anemia (DBA), characterized by defective erythropoiesis and skeletal defects. Some mouse Rp mutations recapitulate DBA phenotypes, although others lack erythropoietic or skeletal defects. We generated a conditional knockout mouse to partially delete Rps12. Homozygous Rps12 deletion resulted in embryonic lethality. Mice inheriting the Rps12KO/+ genotype had growth and morphological defects, pancytopenia, and impaired erythropoiesis. A striking reduction in hematopoietic stem cells (HSCs) and progenitors in the bone marrow (BM) was associated with decreased ability to repopulate the blood system after competitive and non-competitive BM transplantation. Rps12KO/+ lost HSC quiescence, experienced ERK and MTOR activation, and increased global translation in HSC and progenitors. Post-natal heterozygous deletion of Rps12 in hematopoietic cells using Tal1-Cre-ERT also resulted in pancytopenia with decreased HSC numbers. However, post-natal Cre-ERT induction led to reduced translation in HSCs and progenitors, suggesting that this is the most direct consequence of Rps12 haploinsufficiency in hematopoietic cells. Thus, RpS12 has a strong requirement in HSC function, in addition to erythropoiesis.

Irisin protected hemopoietic stem cells and improved outcome of severe bone marrow failure.

Acquired aplastic anemia (AA) is a bone marrow failure (BMF) disease, characterized by fatty bone marrow (BM) and BM hypocellularity resulted from auto-immune dysregulated T cells-mediated destruction of BM haemopoietic stem cells (HPSC). The objective of this study was to investigate potential therapeutic effect of irisin, a molecule involved in adipose tissue transition, on AA mouse model. Our results showed that the concentration of irisin in serum was lower in AA patients than in healthy controls, suggesting a role of irisin in the pathogenesis of AA. In the AA mice, irisin administration prolonged the survival rate, prevented or attenuated peripheral pancytopenia, and preserved HPSC in the BM. Moreover, irisin also markedly reduced BM adipogenesis. In vitro results showed that irisin increased both cell proliferation and colony numbers of HPSC. Furthermore, our results demonstrated that irisin upregulated the expression of mitochondrial ATPase Inhibitory Factor 1 (IF1) in HPSC, inhibited the activation of mitochondrial fission protein (DRP1) and enhanced aerobic glycolysis. Taken together, our findings indicate novel roles of irisin in the pathogenesis of AA, and in the protection of HPSC through stimulation of proliferation and regulation of mitochondria function, which provides a proof-of-concept for the application of irisin in AA therapy.

Induction of elastin expression in vascular endothelial cells relates to hepatoportal sclerosis in idiopathic portal hypertension: possible link to serum anti-endothelial cell antibodies.

Hepatoportal sclerosis accompanied by dense elastic fibre deposition is generally regarded as the primary lesion in the development of idiopathic portal hypertension (IPH). This study was performed to clarify the mechanism of elastic fibre deposition in the peripheral portal tracts of IPH liver in relation to serum anti-endothelial cell antibodies (AECA). In-vitro experiments were performed using human dermal microvascular endothelial cells (HMVEC) and patients' sera. The presence of serum AECA was assayed by a cell-based enzyme-linked immunosorbent assay (ELISA) using HMVEC. Immunohistochemical analysis of elastin was performed using liver tissue sections of IPH patients. IPH sera contained one or more AECA that could bind to the vascular endothelial cells of the peripheral portal tracts of the liver. When the value of AECA greater than the mean ± 2 standard deviations of healthy controls was regarded as positive, the positive detection rate of either immunoglobulin (Ig)G, IgA or IgM AECA in IPH sera was 30% (10 of 33 cases). IPH sera induced the expression of elastin in HMVEC, which appeared to be associated with the presence of AECA. Apoptosis was also induced in HMVEC by the stimulation with IPH sera. In vivo, elastin expression was observed in the endothelial cells of the peripheral portal tracts of IPH livers in a proportion of cases. The disease pathogenesis of IPH seems to be heterogeneous, and this study elucidated a possible contribution of the induction of elastin expression in the portal vessels to hepatoportal sclerosis of IPH, which might be linked to serum AECA as a causative factor.

[Preliminary study of autoantigens on the membrane of erythropoietic cells of the patients with BMMNC-Coomb's test(+) hemocytopenia].

OBJECTIVE: To observe the relationship between erythropoietin receptor (EPOR) and autoantibodies-IgG/IgM (auto-Ab) on the membrane of erythropoietic cells of the patients with bone marrow mononuclear cells (BMMNC)-Coomb's test(+) hemocytopenia (immunorelated pancytopenia (IRP)) and explore the probable autoantigens of auto-Ab in IRP. METHODS: A total of 46 newly diagnosed IRP patients (15 with auto-Ab on erythropoietic cells and 31 without) and 18 healthy controls were enrolled. The EPOR expressions on their nuclear erythrocytes were tested with flow cytometry (FCM) to observe the relationship between EPOR and auto-Ab. EPOR mRNA was detected by reverse transcription (RT)-PCR. Stat5 and P-Stat5 proteins in nucleated erythrocytes were measured by Western blot. EPOR expressions on nucleated erythrocytes membrane were re-tested after stripping autoantibodies with glycine buffer. RESULTS: (1) EPOR of auto-Ab(+) group (1.6% ± 0.9%)was significantly lower than that of auto-Ab(-) group (4.6% ± 4.1%, P < 0.01)and the latter was significantly higher than that of normal controls (2.3% ± 1.8%, P < 0.05). EPOR of IRP patients was inversely correlated with their auto-Ab (r = -0.543, P = 0.000). (2) EPOR mRNA of auto-Ab(+) group (0.68 ± 0.14)was significantly higher than that of auto-Ab(-) group (0.55 ± 0.12, P < 0.01) and normal controls (0.58 ± 0.12, P < 0.05). (3) Protein Stat5 of auto-Ab(+) group (1.45 ± 0.94) was significantly higher than that of normal controls (0.54 ± 0.36, P < 0.05). While P-Stat5 of auto-Ab(+) group (0.42 ± 0.18)was significantly lower than that of normal controls (0.85 ± 0.38, P < 0.05). (4) EPOR expression increased significantly after auto-Ab stripping. CONCLUSIONS: The auto-Ab of some IRP patients blocks or competitively inhibits EPOR on the membrane of erythropoietic cells. And EPOR may be one of autoantigens in IRP.