Dnmt3a-mutated clonal hematopoiesis promotes osteoporosis.

Osteoporosis is caused by an imbalance of osteoclasts and osteoblasts, occurring in close proximity to hematopoietic cells in the bone marrow. Recurrent somatic mutations that lead to an expanded population of mutant blood cells is termed clonal hematopoiesis of indeterminate potential (CHIP). Analyzing exome sequencing data from the UK Biobank, we found CHIP to be associated with increased incident osteoporosis diagnoses and decreased bone mineral density. In murine models, hematopoietic-specific mutations in Dnmt3a, the most commonly mutated gene in CHIP, decreased bone mass via increased osteoclastogenesis. Dnmt3a-/- demethylation opened chromatin and altered activity of inflammatory transcription factors. Bone loss was driven by proinflammatory cytokines, including Irf3-NF-κB-mediated IL-20 expression from Dnmt3a mutant macrophages. Increased osteoclastogenesis due to the Dnmt3a mutations was ameliorated by alendronate or IL-20 neutralization. These results demonstrate a novel source of osteoporosis-inducing inflammation.

Incident adverse events following therapy for acute promyelocytic leukemia.

The use of all-trans retinoic acid (ATRA) combined with arsenic trioxide (ATO) with or without cytotoxic chemotherapy is highly effective in acute promyelocytic leukemia (APL) but incident chronic adverse events (AEs) after initiation of therapy are not well understood. We retrospectively analyzed adult patients with newly diagnosed APL from 2004 through 2014 to identify incident AEs following treatment and contributing risk factors. Cardiac and neurologic AEs were more common and characterized in detail. Cardiac AEs such as the development of coronary artery disease (CAD), arrhythmias, and heart failure had a cumulative incidence of 6.4% (CI95 1.8-11.1%), 2.9% (CI95 0.0-6.4%), 5.8% (CI95 1.2-10.3%) at 4 years from diagnosis, respectively. In multivariate analyses of factors influencing heart failure, the presence of clinical or radiographic CAD (HR 4.25; P = 0.011) or troponin elevation prior to completion of therapy (HR 8.86; P = 0.0018) were associated with increased heart failure incidence, but not anthracycline use or dose. Neurological AEs were common following therapy; at 4 years, the cumulative incidence of vision changes was 12.4% (CI95 6.0-18.7%), peripheral neuropathy 10.3% (CI95 4.5-16.1%), and memory or cognitive change 7.6% (CI95 2.5-12.7%). We did not identify any association between specific therapies and the development of cardiac and neurologic AEs. APL is a highly curable leukemia; further efforts are needed to address incident chronic AEs, with particular focus on cardiac and neurological care.

Interferon-α signaling promotes embryonic HSC maturation.

In the developing mouse embryo, the first hematopoietic stem cells (HSCs) arise in the aorta-gonad-mesonephros (AGM) and mature as they transit through the fetal liver (FL). Compared with FL and adult HSCs, AGM HSCs have reduced repopulation potential in irradiated adult transplant recipients but mechanisms underlying this deficiency in AGM HSCs are poorly understood. By co-expression gene network analysis, we deduced that AGM HSCs show lower levels of interferon-α (IFN-α)/Jak-Stat1-associated gene expression than FL HSCs. Treatment of AGM HSCs with IFN-α enhanced long-term hematopoietic engraftment and donor chimerism. Conversely, IFN-α receptor-deficient AGMs (Ifnαr1(-/-)), had significantly reduced donor chimerism. We identify adenine-thymine-rich interactive domain-3a (Arid3a), a factor essential for FL and B lymphopoiesis, as a key transcriptional co-regulator of IFN-α/Stat1 signaling. Arid3a occupies the genomic loci of Stat1 as well as several IFN-α effector genes, acting to regulate their expression. Accordingly, Arid3a(-/-) AGM HSCs had significantly reduced transplant potential, which was rescued by IFN-α treatment. Our results implicate the inflammatory IFN-α/Jak-Stat pathway in the developmental maturation of embryonic HSCs, whose manipulation may lead to increased potency of reprogrammed HSCs for transplantation.

Pure White Cell Aplasia and Necrotizing Myositis.

Pure white cell aplasia (PWCA) is a rare hematologic disorder characterized by the absence of neutrophil lineages in the bone marrow with intact megakaryopoiesis and erythropoiesis. PWCA has been associated with autoimmune, drug-induced, and viral exposures. Here, we report a case of a 74-year-old female who presented with severe proximal weakness without pain and was found to have PWCA with nonspecific inflammatory necrotizing myositis and acute liver injury on biopsies. These findings were associated with a recent course of azithromycin and her daily use of a statin. Myositis improved on prednisone but PWCA persisted. With intravenous immunoglobulin and granulocyte-colony stimulating factor therapies, her symptoms and neutrophil counts improved and were sustained for months.

Flow-induced protein kinase A-CREB pathway acts via BMP signaling to promote HSC emergence.

Fluid shear stress promotes the emergence of hematopoietic stem cells (HSCs) in the aorta-gonad-mesonephros (AGM) of the developing mouse embryo. We determined that the AGM is enriched for expression of targets of protein kinase A (PKA)-cAMP response element-binding protein (CREB), a pathway activated by fluid shear stress. By analyzing CREB genomic occupancy from chromatin-immunoprecipitation sequencing (ChIP-seq) data, we identified the bone morphogenetic protein (BMP) pathway as a potential regulator of CREB. By chemical modulation of the PKA-CREB and BMP pathways in isolated AGM VE-cadherin(+) cells from mid-gestation embryos, we demonstrate that PKA-CREB regulates hematopoietic engraftment and clonogenicity of hematopoietic progenitors, and is dependent on secreted BMP ligands through the type I BMP receptor. Finally, we observed blunting of this signaling axis using Ncx1-null embryos, which lack a heartbeat and intravascular flow. Collectively, we have identified a novel PKA-CREB-BMP signaling pathway downstream of shear stress that regulates HSC emergence in the AGM via the endothelial-to-hematopoietic transition.

Signaling axis involving Hedgehog, Notch, and Scl promotes the embryonic endothelial-to-hematopoietic transition.

During development, the hematopoietic lineage transits through hemogenic endothelium, but the signaling pathways effecting this transition are incompletely characterized. Although the Hedgehog (Hh) pathway is hypothesized to play a role in patterning blood formation, early embryonic lethality of mice lacking Hh signaling precludes such analysis. To determine a role for Hh signaling in patterning of hemogenic endothelium, we assessed the effect of altered Hh signaling in differentiating mouse ES cells, cultured mouse embryos, and developing zebrafish embryos. In differentiating mouse ES cells and mouse yolk sac cultures, addition of Indian Hh ligand increased hematopoietic progenitors, whereas chemical inhibition of Hh signaling reduced hematopoietic progenitors without affecting primitive streak mesoderm formation. In the setting of Hh inhibition, induction of either Notch signaling or overexpression of Stem cell leukemia (Scl)/T-cell acute lymphocytic leukemia protein 1 rescued hemogenic vascular-endothelial cadherin(+) cells and hematopoietic progenitor formation. Together, our results reveal that Scl overexpression is sufficient to rescue the developmental defects caused by blocking the Hh and Notch pathways, and inform our understanding of the embryonic endothelial-to-hematopoietic transition.

Application of induced pluripotent stem cells to hematologic disease.

Induced pluripotent stem cells (iPSC) were first generated from somatic cells via the transduction of four 'Yamanaka' factors, Oct4, Sox2, Klf4 and c-Myc. Because iPSC are similar to embryonic stem cells (ESC) and can be differentiated into any cell type of choice, iPSC have the potential to become a platform for personalized medicine by allowing a patient's own cells to become a source of therapeutic tissue. This review describes the main challenges in iPSC technology by focusing on its application to hematologic diseases. The explosive interest in improving iPSC technology has generated numerous genetic and chemical methods for iPSC derivation, but these methods must be evaluated comparatively for their safety and efficacy because there are risks of genetic abnormalities and oncogenesis. Competent iPSC will need to be selected carefully based on physical, genetic and functional criteria, and differentiated efficiently into hematopoietic stem cells via modulation of several signaling pathways before they prove valuable in the clinic.

Dopamine neurons derived from embryonic stem cells efficiently induce behavioral recovery in a Parkinsonian rat model.

To test the in vivo effect of a high yield of dopaminergic (DA) neurons (90% of total neurons) which had been generated from a genetically modified mouse embryonic stem cell line, N2, the cells were transplanted into a rat model of Parkinson's disease (PD). The PD animals grafted with N2-derived cells showed significant behavior improvements compared with sham controls from 2 weeks posttransplantation, whereas animals with naïve D3-derived cells ( approximately 28% DA neurons of total neurons) showed only a modest recovery. Furthermore, hyperactivity observed in the subthalamic nucleus, pedunculopontine nucleus, and substantia nigra pars reticulata of PD rat models was dramatically reduced by the grafting of N2-derived cells. The number of DA neurons in the striatum which originated from N2 grafting was much higher compared to that from D3 grafting, and the neurons efficiently released DA in the brain, showing a good correlation with behavioral recovery.