Alteration Analysis of Bone Marrow Mesenchymal Stromal Cells from De Novo Acute Myeloid Leukemia Patients at Diagnosis.

Bone marrow (BM)-derived mesenchymal stromal cells (MSCs) frequently display alterations in several hematologic disorders, such as acute lymphoid leukemia, acute myeloid leukemia (AML), and myelodysplastic syndromes. In acute leukemias, it is not clear whether MSC alterations contribute to the development of the malignant clone or whether they are simply the effect of tumor expansion on the microenvironment. We extensively investigated the characteristics of MSCs isolated from the BM of patients with de novo AML at diagnosis (L-MSCs) in terms of phenotype (gene and protein expression, apoptosis and senescence levels, DNA double-strand break formation) and functions (proliferation and clonogenic potentials, normal and leukemic hematopoiesis-supporting activity). We found that L-MSCs show reduced proliferation capacity and increased apoptosis levels compared with MSCs from healthy controls. Longer population doubling time in L-MSCs was not related to the AML characteristics at diagnosis (French-American-British type, cytogenetics, or tumor burden), but was related to patient age and independently associated with poorer patient outcome, as was cytogenetic prognostic feature. Analyzing, among others, the expression of 93 genes, we found that proliferative deficiency of L-MSCs was associated with a perivascular feature at the expense of the osteo-chondroblastic lineage with lower expression of several niche factors, such as KITLG, THPO, and ANGPT1 genes, the cell adhesion molecule VCAM1, and the developmental/embryonic genes, BMI1 and DICER1. L-MSC proliferative capacity was correlated positively with CXCL12, THPO, and ANGPT1 expression and negatively with JAG1 expression. Anyway, these changes did not affect their in vitro capacity to support normal hematopoiesis and to modify leukemic cell behavior (protection from apoptosis and quiescence induction). Our findings indicate that BM-derived MSCs from patients with newly diagnosed AML display phenotypic and functional alterations such as proliferative deficiency that could be attributed to tumor progression, but does not seem to play a special role in the leukemic process.

Oncogenic STAT5 signaling promotes oxidative stress in chronic myeloid leukemia cells by repressing antioxidant defenses.

STAT5 transcription factors are frequently activated in hematopoietic neoplasms and are targets of various tyrosine kinase oncogenes. Evidences for a crosstalk between STAT5 and reactive oxygen species (ROS) metabolism have recently emerged but mechanisms involved in STAT5-mediated regulation of ROS still remain elusive. We demonstrate that sustained activation of STAT5 induced by Bcr-Abl in chronic myeloid leukemia (CML) cells promotes ROS production by repressing expression of two antioxidant enzymes, catalase and glutaredoxin-1(Glrx1). Downregulation of catalase and Glrx1 expression was also observed in primary cells from CML patients. Catalase was shown not only to reduce ROS levels but also, to induce quiescence in Bcr-Abl-positive leukemia cells. Furthermore, reduction of STAT5 phosphorylation and upregulation of catalase and Glrx1 were also evidenced in leukemia cells co-cultured with bone marrow stromal cells to mimic a leukemic niche. This caused downregulation of ROS levels and enhancement of leukemic cell quiescence. These data support a role of persistent STAT5 signaling in the regulation of ROS production in myeloid leukemias and highlight the repression of antioxidant defenses as an important regulatory mechanism.

In Vitro Synthesis, Delivery, and Bioavailability of Exogenous mRNA in Gene Transfer Mediated by PiggyBac Transposition.

Nowadays, nonviral gene transfer is currently of great importance for introducing exogenous genes into genomes and for ensuring that transgene expression is suitable for therapeutic and bioproduction purposes. The piggyBac transposon-based system is particularly interesting since it is easy to engineer and has a large cargo capacity, up to 100 kb. In its setup, the system requires only the piggyBac transposase protein and the transgene delineated by the two piggyBac-specific inverted terminal repeats. Usually the source of transposase is carried by a DNA plasmid. However, the principal drawback of this method is the lasting presence of the transposase, due to episomal persistence or possible integration of the transposase gene vector into the cell's genome. This can lead to genotoxic effects such as multiple genomic integration events and remobilization of the transposon vector once it has been integrated. One alternative to improve the safety of the system is to deliver the transposase as in vitro-synthesized messenger RNA in order to define a very narrow expression window during which a one-shot transposition process would occur. Issues that can be encountered when working on mRNA cell transfer are related to the quality of the synthetic mRNA, the system used to introduce mRNA into the cells and the bioavailability of the mRNA molecules. Here we describe a method to produce mRNA, verify its quality, determine which transfecting reagents can be used and how this mRNA is available to promote the transposition process in HeLa cells. Additionally, we illustrate this method in stromal mesenchymal cell lines in order to support hematopoiesis.