Stroke induced by middle cerebral artery occlusion (MCAO) causes long-term formation of new striatal neurons from stem/progenitor cells in the subventricular zone (SVZ). We explored whether MCAO ...leads to hypoxia, changes in vessel density, and angiogenesis in the ipsilateral SVZ and adjacent striatum, and determined the relation between the migrating neuroblasts and the vasculature.
Adult rats were subjected to 2 hours of MCAO. Hypoxia was studied by injecting Hypoxyprobe-1 during MCAO or 6 weeks later. Vessel density and length was estimated using stereology. New cells were labeled with 5'-bromo-2'deoxyuridine (BrdU) during weeks 1 and 2 or 7 and 8 after MCAO, and angiogenesis was assessed immunohistochemically with antibodies against BrdU and endothelial cell markers. Distance from neuroblasts to nearest vessel was measured using confocal microscopy.
The ischemic insult caused transient hypoxia and early, low-grade angiogenesis, but no damage or increase of vascular density in the SVZ. Angiogenesis was detected during the first 2 weeks in the dorsomedial striatum adjacent to the SVZ, which also showed long-lasting increase of vascularization. At 2, 6, and 16 weeks after MCAO, the majority of neuroblasts migrated through this area toward the damage, closely associated with blood vessels.
The vasculature plays an important role for long-term striatal neurogenesis after stroke. During several months, neuroblasts migrate close to blood vessels through an area exhibiting early vascular remodeling and persistently increased vessel density. Optimizing vascularization should be an important strategy to promote neurogenesis and repair after stroke.
Hematopoietic stem cells (HSCs) are maintained in hypoxic niches in endosteal regions of bones. Here we demonstrate that Cripto and its receptor GRP78 are important regulators of HSCs in the niche. ...Flow cytometry analyses revealed two distinct subpopulations of CD34
−KSL cells based on the expression of GRP78, and these populations showed different reconstitution potential in transplantation assays. GRP78
+HSCs mainly reside in the endosteal area, are more hypoxic, and exhibit a lower mitochondrial potential, and their HSC capacity was maintained in vitro by Cripto through induction of higher glycolytic activity. Additionally, HIF-1α KO mice have decreased numbers of GRP78
+HSCs and reduced expression of Cripto in the endosteal niche. Furthermore, blocking GRP78 induced a movement of HSCs from the endosteal to the central marrow area. These data suggest that Cripto/GRP78 signaling is an important pathway that regulates HSC quiescence and maintains HSCs in hypoxia as an intermediary of HIF-1α.
► Cripto is highly expressed in HSCs and can maintain their function ex vivo ► Cripto regulates HSCs through the receptor GRP78 on the GRP78
+ subset of HSCs ► GRP78
+HSCs are endosteal, more hypoxic, and have high glycolytic activity ► Cripto regulates HSC quiescence and metabolism as an intermediary of HIF-1α
•Germline (GL) gain-of-function (GOF) SAMD9/SAMD9L mutations cause different syndromes with a predisposition to myeloid neoplasms in the young.•Primary somatic compensation mutations in the blood are ...very frequent in patients with GL GOF SAMD9/SAMD9L-related diseases.•GL loss-of-function SAMD9/SAMD9L mutations are commonly found in myeloid neoplasms in older patients.•The heterogeneity of the different SAMD9/SAMD9L mutations complicates their classification as benign or pathogenic.
SAMD9 and SAMD9L are two interferon-regulated genes located adjacent to each other on chromosome 7q21.2. Germline gain-of-function (GL GOF) mutations in SAMD9/SAMD9L are the genetic cause of MIRAGE syndrome, ataxia-pancytopenia (ATXPC) syndrome, myeloid leukemia syndrome with monosomy 7 (MLSM7), refractory cytopenia of childhood (RCC), transient monosomy 7 in children, SAMD9L-associated autoinflammatory disease (SAAD), and a proportion of inherited aplastic anemia and bone marrow failure syndromes. The myeloid neoplasms associated with GL GOF SAMD9/SAMD9L mutations have been included in the World Health Organization (WHO) 2022 classification. The discovery of SAMD9/SAMD9L-related diseases has revealed some interesting pathobiological mechanisms, such as a high rate of primary somatic compensation, with one of the mechanisms being (transient) monosomy 7 a mechanism also described as “adaption by aneuploidy.” The somatic compensation in the blood can complicate the diagnosis of SAMD9/SAMD9L-related disease when relying on hematopoietic tissues for diagnosis. Recently, GL loss-of function (LOF) mutations have been identified in older individuals with myeloid malignancies in accordance with a mouse model of SAMD9L loss that develops a myelodysplastic syndrome (MDS)-like disease late in life. The discovery of SAMD9/SAMD9L-associated syndromes has resulted in a deeper understanding of the genetics and biology of diseases/syndromes that were previously oblivious and thought to be unrelated to each other. Besides giving an overview of the literature, this review wants to also provide some practical guidance for the classification of SAMD9/SAMD9L variants that is complicated by the nonrecurrent nature of these mutations but also by the fact that both GL GOF, as well as loss-of-function mutations, have been identified.
Conditional knockout mice are commonly used to study the function of specific genes in hematopoiesis. Different promoters that drive Cre expression have been utilized, with the interferon-inducible ...Mx1-Cre still being the most commonly used “deleter strain” in experimental hematology. However, different pitfalls associated with this system could lead to misinterpretation in functional studies. We present here two of these issues related to the use of Mx1-Cre: first, a high spontaneous recombination rate when applying commonly used techniques in experimental hematology, and second, undesired short-term consequences of the use of polyinosinic:polycytidylic acid, including changes in cellular phenotypes that, however, resolve within days. Our studies emphasize therefore that proper controls are crucial when modeling gene deletion using the Mx1-Cre transgene.
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•Common research methods induce uncontrolled activation of the Mx1-Cre system•The leakiness of the Mx1-Cre system can result in misinterpretation of results•pIpC alters the phenotype of HSPCs that resolves by day 8•pIpC has limited effects on the proliferation of HSPCs
In this article, Cammenga, Velasco-Hernandez, and colleagues describe technical issues associated with the Mx1-Cre model in hematopoiesis, including a high level of spontaneous activation induced by multiple experimental procedures. These pitfalls can lead to misinterpretation of results so proper controls are needed to avoid these problems.
Hypoxia is emerging as an important characteristic of the hematopoietic stem cell (HSC) niche, but the molecular mechanisms contributing to quiescence, self-renewal, and survival remain elusive. ...Vascular endothelial growth factor A (VEGFA) is a key regulator of angiogenesis and hematopoiesis. Its expression is commonly regulated by hypoxia-inducible factors (HIF) that are functionally induced in low-oxygen conditions and that activate transcription by binding to hypoxia-response elements (HRE). Vegfa is indispensable for HSC survival, mediated by a cell-intrinsic, autocrine mechanism. We hypothesized that a hypoxic HSC microenvironment is required for maintenance or up-regulation of Vegfa expression in HSCs and therefore crucial for HSC survival. We have tested this hypothesis in the mouse model Vegfaδ/δ, where the HRE in the Vegfa promoter is mutated, preventing HIF binding. Vegfa expression was reduced in highly purified HSCs from Vegfaδ/δ mice, showing that HSCs reside in hypoxic areas. Loss of hypoxia-regulated Vegfa expression increases the numbers of phenotypically defined hematopoietic stem and progenitor cells. However, HSC function was clearly impaired when assessed in competitive transplantation assays. Our data provide further evidence that HSCs reside in a hypoxic microenvironment and demonstrate a novel way in which the hypoxic niche affects HSC fate, via the hypoxia-VEGFA axis.
Objective Recent evidence suggests that hematopoietic stem cells (HSCs) in the bone marrow (BM) are located in areas where the environment is hypoxic. Although previous studies have demonstrated ...positive effects by hypoxia, its role in HSC maintenance has not been fully elucidated, neither has the molecular mechanisms been delineated. Here, we have investigated the consequence of in vitro incubation of HSCs in hypoxia prior to transplantation and analyzed the role of hypoxia-inducible factor (HIF)−1α. Materials and Methods HSC and progenitor populations isolated from mouse BM were cultured in 20% or 1% O2 , and analyzed for effects on cell cycle, expression of cyclin-dependent kinase inhibitors genes, and reconstituting ability to lethally irradiated mice. The involvement of HIF-1α was studied using methods of protein stabilization and gene silencing. Results When long-term FLT3− CD34− Lin− Sca-1+ c-Kit+ (LSK) cells were cultured in hypoxia, cell numbers were significantly reduced in comparison to normoxia. This was due to a decrease in proliferation and more cells accumulating in G0 . Moreover, the proportion of HSCs with long-term engraftment potential was increased. Whereas expression of the cyclin-dependent kinase inhibitor genes p21cip1 , p27Kip1 , and p57Kip2 increased in LSK cells by hypoxia, only p21cip1 was upregulated in FLT3− CD34− LSK cells. We could demonstrate that expression of p27Kip1 and p57Kip2 was dependent of HIF-1α. Surprisingly, overexpression of constitutively active HIF-1α or treatment with the HIF stabilizer agent FG-4497 led to a reduction in HSC reconstituting ability. Conclusions Our results imply that hypoxia, in part via HIF-1α, maintains HSCs by decreasing proliferation and favoring quiescence.
Relapse of acute myeloid leukemia (AML) remains a significant clinical challenge due to limited therapeutic options and poor prognosis. Leukemic stem cells (LSCs) are the cellular units responsible ...for relapse in AML, and strategies that target LSCs are thus critical. One proposed potential strategy to this end is to break the quiescent state of LSCs, thereby sensitizing LSCs to conventional cytostatics. The hypoxia-inducible factor (HIF) pathway is a main driver of cellular quiescence and a potential therapeutic target, with precedence from both solid cancers and leukemias. Here, we used a conditional knockout Hif-1α mouse model together with a standard chemotherapy regimen to evaluate LSC targeting in AML. Contrary to expectation, our studies revealed that Hif-1α-deleted-leukemias displayed a faster disease progression after chemotherapy. Our studies thereby challenge the general notion of cancer stem cell sensitization by inhibition of the HIF pathway, and warrant caution when applying HIF inhibition in combination with chemotherapy in AML.
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•Deletion of Hif-1α accelerates the progression of chemotherapy-treated MLL-AF9-AML•Deletion of Hif-1α does not decrease LSC frequency after chemotherapy•Chemotherapy targets more mature cells indicated by transcriptional analysis•Hif-1α deletion affects few transcriptional pathways in AML cells
In this article, Bryder, Velasco-Hernandez and colleagues show that the combination of chemotherapy and Hif-1α deletion in a murine model of MLL-AF9-AML leads to a faster progression of the disease without altering LSCs frequency. Single-cell transcriptional analysis indicates that Hif-1α deletion leads to few transcriptional modifications.
Germline mutations in the SAMD9 and SAMD9L genes, located in tandem on chromosome 7, are associated with a clinical spectrum of disorders including the MIRAGE syndrome, ataxia-pancytopenia syndrome ...and myelodysplasia and leukemia syndrome with monosomy 7 syndrome. Germline gain-of-function mutations increase SAMD9 or SAMD9L's normal antiproliferative effect. This causes pancytopenia and generally restricted growth and/or specific organ hypoplasia in non-hematopoietic tissues. In blood cells, additional somatic aberrations that reverse the germline mutation's effect, and give rise to the clonal expansion of cells with reduced or no antiproliferative effect of SAMD9 or SAMD9L include complete or partial chromosome 7 loss or loss-of-function mutations in SAMD9 or SAMD9L. Furthermore, the complete or partial loss of chromosome 7q may cause myelodysplastic syndrome in these patients. SAMD9 mutations appear to associate with a more severe disease phenotype, including intrauterine growth restriction, developmental delay and hypoplasia of adrenal glands, testes, ovaries or thymus, and most reported patients died in infancy or early childhood due to infections, anemia and/or hemorrhages. SAMD9L mutations have been reported in a few families with balance problems and nystagmus due to cerebellar atrophy, and may lead to similar hematological disease as seen in SAMD9 mutation carriers, from early childhood to adult years. We review the clinical features of these syndromes, discuss the underlying biology, and interpret the genetic findings in some of the affected family members. We provide expert-based recommendations regarding diagnosis, follow-up, and treatment of mutation carriers.
Fms-related tyrosine kinase 3 (FLT3) receptor serves as a prognostic marker and therapeutic target in acute myeloid leukemia (AML). Approximately one-third of AML patients carry mutation in FLT3, ...associated with unfavourable prognosis and high relapse rate. The multitargeted kinase inhibitor midostaurin (PKC412) in combination with standard chemotherapy (daunorubicin and cytarabine) was recently shown to increase overall survival of AML patients. For that reason, PKC412 has been approved for treatment of AML patients with FLT3-mutation. PKC412 synergizes with standard chemotherapy, but the mechanism involved is not fully understood and the risk of relapse is still highly problematic.
By utilizing the unique nature of mass cytometry for single cell multiparameter analysis, we have explored the proteomic effect and intracellular signaling response in individual leukemic cells with internal tandem duplication of FLT3 (FLT3-ITD) after midostaurin treatment in combination with daunorubicin or cytarabine.
We have identified a synergistic inhibition of intracellular signaling proteins after PKC412 treatment in combination with daunorubicin. In contrast, cytarabine antagonized phosphorylation inhibition of PKC412. Moreover, we found elevated levels of FLT3 surface expression after cytarabine treatment. Interestingly, the surface localization of FLT3 receptor increased in vivo on the blast cell population of two AML patients during day 3 of induction therapy (daunorubicin; once/day from day 1-3 and cytarabine; twice/day from day 1-7). We found FLT3 receptor expression to correlate with intracellular cytarabine (AraC) response. AML cell line cultured with AraC with or without PKC412 had an antagonizing phosphorylation inhibition of pAKT (p = 0.042 and 0.0261, respectively) and pERK1/2 (0.0134 and 0.0096, respectively) in FLT3
compared to FLT3
expressing cell populations.
Our study provides insights into how conventional chemotherapy affects protein phosphorylation of vital signaling proteins in human leukemia cells. The results presented here support further investigation of novel strategies to treat FLT3-mutated AML patients with PKC412 in combination with chemotherapy agents and the potential development of novel treatment strategies.
The acute myelogenous leukemia–1 (AML1)–ETO fusion protein is generated by the t(8;21), which is found in 40% of AMLs of the French-American-British M2 subtype. AML1-ETO interferes with the function ...of the AML1 (RUNX1, CBFA2) transcription factor in a dominant-negative fashion and represses transcription by binding its consensus DNA–binding site and via protein-protein interactions with other transcription factors. AML1 activity is critical for the development of definitive hematopoiesis, and haploinsufficiency of AML1 has been linked to a propensity to develop AML. Murine experiments suggest that AML1-ETO expression may not be sufficient for leukemogenesis; however, like the BCR-ABL isoforms, the cellular background in which these fusion proteins are expressed may be critical to the phenotype observed. Retroviral gene transfer was used to examine the effect of AML1-ETO on the in vitro behavior of human hematopoietic stem and progenitor cells. Following transduction of CD34+ cells, stem and progenitor cells were quantified in clonogenic assays, cytokine-driven expansion cultures, and long-term stromal cocultures. Expression of AML1-ETO inhibited colony formation by committed progenitors, but enhanced the growth of stem cells (cobblestone area-forming cells), resulting in a profound survival advantage of transduced over nontransduced cells. AML1-ETO–expressing cells retained progenitor activity and continued to express CD34 throughout the 5-week long-term culture. Thus, AML1-ETO enhances the self-renewal of pluripotent stem cells, the physiological target of many acute myeloid leukemias.
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