Molecular and Cellular Mechanisms of Aging in Hematopoietic Stem Cells and Their Niches

Aging drives the genetic and epigenetic changes that result in a decline in hematopoietic stem cell (HSC) functioning. Such changes lead to aging-related hematopoietic/immune impairments and hematopoietic disorders. Understanding how such changes are initiated and how they progress will help in the development of medications that could improve the quality life for the elderly and to treat and possibly prevent aging-related hematopoietic diseases. Here, we review the most recent advances in research into HSC aging and discuss the role of HSC-intrinsic events, as well as those that relate to the aging bone marrow niche microenvironment in the overall processes of HSC aging. In addition, we discuss the potential mechanisms by which HSC aging is regulated

Role of TET dioxygenases in the regulation of both normal and pathological hematopoiesis

The family of ten-eleven translocation dioxygenases (TETs) consists of TET1, TET2, and TET3. Although all TETs are expressed in hematopoietic tissues, only TET2 is commonly found to be mutated in age-related clonal hematopoiesis and hematopoietic malignancies. TET2 mutation causes abnormal epigenetic landscape changes and results in multiple stages of lineage commitment/differentiation defects as well as genetic instability in hematopoietic stem/progenitor cells (HSPCs). TET2 mutations are founder mutations (first hits) in approximately 40–50% of cases of TET2-mutant (TET2MT) hematopoietic malignancies and are later hits in the remaining cases. In both situations, TET2MT collaborates with co-occurring mutations to promote malignant transformation. In TET2MT tumor cells, TET1 and TET3 partially compensate for TET2 activity and contribute to the pathogenesis of TET2MT hematopoietic malignancies. Here we summarize the most recent research on TETs in regulating of both normal and pathogenic hematopoiesis. We review the concomitant mutations and aberrant signals in TET2MT malignancies. We also discuss the molecular mechanisms by which concomitant mutations and aberrant signals determine lineage commitment in HSPCs and the identity of hematopoietic malignancies. Finally, we discuss potential strategies to treat TET2MT hematopoietic malignancies, including reverting the methylation state of TET2 target genes and targeting the concomitant mutations and aberrant signals

Proteomic analysis of maize grain development using iTRAQ reveals temporal programs of diverse metabolic processes

Total proteins identified in maize grains (XLSX 745 kb

Tak1 is Required for the Survival of Hematopoietic Cells and Hepatocytes in Mice

Transforming growth factor beta-activated kinase 1 (TAK1), a member of the MAPKKK family, is a key mediator of proinflammatory and stress signals. Activation of TAK1 by proinflammatory cytokines and T and B cell receptors induces the nuclear localization of nuclear factor kappaB (NF-kappaB) and the activation of c-Jun N-terminal kinase (JNK)/AP1 and P38, which play important roles in mediating inflammation, immune responses, T and B cell activation, and epithelial cell survival. Here, we report that TAK1 is critical for the survival of both hematopoietic cells and hepatocytes. Deletion of TAK1 results in bone marrow (BM) and liver failure in mice due to the massive apoptotic death of hematopoietic cells and hepatocytes. Hematopoietic stem cells and progenitors were among those hematopoietic cells affected by TAK1 deletion-induced cell death. This apoptotic cell death is autonomous, as demonstrated by reciprocal BM transplantation. Deletion of TAK1 resulted in the inactivation of both JNK and NF-kappaB signaling, as well as the down-regulation of expression of prosurvival genes

Pathogenic Role of mTORC1 and mTORC2 in Pulmonary Hypertension.

Concentric lung vascular wall thickening due to enhanced proliferation of pulmonary arterial smooth muscle cells is an important pathological cause for the elevated pulmonary vascular resistance reported in patients with pulmonary arterial hypertension. We identified a differential role of mammalian target of rapamycin (mTOR) complex 1 and complex 2, two functionally distinct mTOR complexes, in the development of pulmonary hypertension (PH). Inhibition of mTOR complex 1 attenuated the development of PH; however, inhibition of mTOR complex 2 caused spontaneous PH, potentially due to up-regulation of platelet-derived growth factor receptors in pulmonary arterial smooth muscle cells, and compromised the therapeutic effect of the mTOR inhibitors on PH. In addition, we describe a promising therapeutic strategy using combination treatment with the mTOR inhibitors and the platelet-derived growth factor receptor inhibitors on PH and right ventricular hypertrophy. The data from this study provide an important mechanism-based perspective for developing novel therapies for patients with pulmonary arterial hypertension and right heart failure

Ripk3 signaling regulates HSCs during stress and represses radiation-induced leukemia in mice

Receptor-interacting protein kinase 3 (Ripk3) is one of the critical mediators of inflammatory cytokine-stimulated signaling. Here we show that Ripk3 signaling selectively regulates both the number and the function of hematopoietic stem cells (HSCs) during stress conditions. Ripk3 signaling is not required for normal homeostatic hematopoiesis. However, in response to serial transplantation, inactivation of Ripk3 signaling prevents stress-induced HSC exhaustion and functional HSC attenuation, while in response to fractionated low doses of ionizing radiation (IR), inactivation of Ripk3 signaling accelerates leukemia/lymphoma development. In both situations, Ripk3 signaling is primarily stimulated by tumor necrosis factor-α. Activated Ripk3 signaling promotes the elimination of HSCs during serial transplantation and pre-leukemia stem cells (pre-LSCs) during fractionated IR by inducing Mlkl-dependent necroptosis. Activated Ripk3 signaling also attenuates HSC functioning and represses a pre-LSC-to-LSC transformation by promoting Mlkl-independent senescence. Furthermore, we demonstrate that Ripk3 signaling induces senescence in HSCs and pre-LSCs by attenuating ISR-mediated mitochondrial quality control

TAK1 and TBK1 are Differentially Required by GMP- and LMPP-like Leukemia Stem Cells

Acute myeloid leukemia (AML) encompasses a diverse group of cancers that originate in the blood-forming tissues of the bone marrow. Aside from the M3 subtype (PML-RARA+), AML carries a 5-year survival rate of 28% for patients 20+ years of age. AML is the most common cancer of the hematopoietic system and is slightly more common in biological males; the average age at diagnosis is 68 years. Standard frontline treatment for AML is a 2-phase regimen of intensive chemotherapy (CTx) employing daunorubicin and cytarabine. Despite 60-70% of patients achieving complete remission (CR), at least half of CR-achieving patients experience relapse within 3 years from their diagnosis. Additionally, 30-40% of patients present with refractory AML, experiencing little to no benefit from frontline treatment. AML relapses when a pool of undetectable, CTx-resistant leukemia stem cells (LSCs) survives & proliferates after frontline CTx [1]. Notably, the poor performance status of many AML patients precludes use of the standard CTx regimen; while reduced-intensity CTx still offers therapeutic benefit, it is less effective at killing LSCs and, as a result, relapse is more likely. Goardon, et al. determined that AML patients harbor two types of LSCs: granulocyte-macrophage progenitor (GMP)-like LSCs and FLT3+ lymphoid-primed multipotential progenitor (LMPP)-like LSCs [2]. Eradication of both types of LSCs is necessary to maintain CR in AML. Our group and others have established that ~40% of AML patients express upregulated Toll-like receptor (TLR) signaling (TLR+). TLR+ disease is associated with specific genetic abnormalities, such as MLL rearrangements (MLL-r+), and is inversely associated with prognosis (Figure 1) [3,4]. TLR+ AML represents a challenging, treatment-sparse subset of an already difficult-to-treat disease. To study TLR+ AML, we utilize an MLL-r+ model using the MLL-AF9 oncogene. We have also demonstrated that both GMP- and LMPP-like LSCs require TLR-associated Ser/Thr protein kinases for their survival [5-7]. Specifically, GMP-like LSCs require TAK1 and LMPP-like LSCs require TBK1. The loss of either Tak1 or Tbk1 ablates the corresponding LSC pool and enriches for the opposite LSC pool in vitro and in vivo. Recently, our group determined that the genetic loss of Tak1 sensitizes mouse AML cells to TBK1 blockade in vitro. Strikingly, the loss of Tbk1 also seems to extend overall survival (OS) despite causing extramedullary AML. While mice given Tbk1NULL AML cells develop a subcutaneous tumor of AML cells (chloroma) near the pelvis, they survive longer than mice given control (Tbk1WT) AML cells. The clinical significance is unknown, but these data support our impression that the loss of Tbk1 forces AML cells to differentiate; this should be therapeutically favorable, as inducing the differentiation of AML cells is an effective treatment strategy. Theoretically, chloromas may form in Tbk1NULL AML due to the enrichment of GMP-like LSCs, which express higher levels of chemokine receptors. We hypothesize that the differentiation & eradication of LSCs can be induced by blocking TAK1/TBK1 in combination with standard CTx (and possibly targeted agents like Mylotarg®, Venclexta®, and/or Xospata®). We propose TAK1/TBK1 parallel blockade as augmentation to standard CTx, ideally allowing for a dose-reduction of CTx & promoting improved patient outcomes

Sensitizing Leukemia Stem Cells to NF-κB Inhibitor Treatment in Vivo by Inactivation of Both TNF and IL-1 Signaling

We previously reported that autocrine TNF-α (TNF) is responsible for JNK pathway activation in a subset of acute myeloid leukemia (AML) patient samples, providing a survival/proliferation signaling parallel to NF-κB in AML stem cells (LSCs). In this study, we report that most TNF-expressing AML cells (LCs) also express another pro-inflammatory cytokine, IL1β, which acts in a parallel manner. TNF was produced primarily by LSCs and leukemic progenitors (LPs), whereas IL1β was mainly produced by partially differentiated leukemic blasts (LBs). IL1β also stimulates an NF-κB-independent pro-survival and proliferation signal through activation of the JNK pathway. We determined that co-inhibition of signaling stimulated by both TNF and IL1β synergizes with NF-κB inhibition in eliminating LSCs both ex vivo and in vivo. Our studies show that such treatments are most effective in M4/5 subtypes of AML

FAK Mediates a Compensatory Survival Signal Parallel to PI3K-AKT in PTEN-Null T-ALL Cells

SummaryMutations and inactivation of phosphatase and tensin homolog deleted from chromosome 10 (PTEN) are observed in 15%–25% of cases of human T cell acute lymphoblastic leukemia (T-ALL). Pten deletion induces myeloproliferative disorders (MPDs), acute myeloid leukemia (AML), and/or T-ALL in mice. Previous studies attributed Pten-loss-related hematopoietic defects and leukemogenesis to excessive activation of phosphatidylinositol 3-kinase (PI3K)/AKT/mTOR signaling. Although inhibition of this signal dramatically suppresses the growth of PTEN-null T-ALL cells in vitro, treatment with inhibitors of this pathway does not cause a complete remission in vivo. Here, we report that focal adhesion kinase (Fak), a protein substrate of Pten, also contributes to T-ALL development in Pten-null mice. Inactivation of the FAK signaling pathway by either genetic or pharmacologic methods significantly sensitizes both murine and human PTEN-null T-ALL cells to PI3K/AKT/mTOR inhibition when cultured in vitro on feeder layer cells or a matrix and in vivo