GEP analysis validates high risk MDS and acute myeloid leukemia post MDS mice models and highlights novel dysregulated pathways

International audienceBACKGROUND:In spite of the recent discovery of genetic mutations in most myelodysplasic (MDS) patients, the pathophysiology of these disorders still remains poorly understood, and only few in vivo models are available to help unravel the disease.METHODS:We performed global specific gene expression profiling and functional pathway analysis in purified Sca1+ cells of two MDS transgenic mouse models that mimic human high-risk MDS (HR-MDS) and acute myeloid leukemia (AML) post MDS, with NRASD12 and BCL2 transgenes under the control of different promoters MRP8NRASD12/tethBCL-2 or MRP8[NRASD12/hBCL-2], respectively.RESULTS:Analysis of dysregulated genes that were unique to the diseased HR-MDS and AML post MDS mice and not their founder mice pointed first to pathways that had previously been reported in MDS patients, including DNA replication/damage/repair, cell cycle, apoptosis, immune responses, and canonical Wnt pathways, further validating these models at the gene expression level. Interestingly, pathways not previously reported in MDS were discovered. These included dysregulated genes of noncanonical Wnt pathways and energy and lipid metabolisms. These dysregulated genes were not only confirmed in a different independent set of BM and spleen Sca1+ cells from the MDS mice but also in MDS CD34+ BM patient samples.CONCLUSIONS:These two MDS models may thus provide useful preclinical models to target pathways previously identified in MDS patients and to unravel novel pathways highlighted by this study

BCL-2 Inhibitor ABT-737 effectively targets leukemia-initiating cells with differential regulation of relevant genes leading to extended survival in a NRAS/BCL-2 mouse model of high risk-myelodysplastic syndrome

During transformation, myelodysplastic syndromes (MDS) are characterized by reducing apoptosis of bone marrow (BM) precursors. Mouse models of high risk (HR)-MDS and acute myelogenous leukemia (AML) post-MDS using mutant NRAS and overexpression of human BCL-2, known to be poor prognostic indicators of the human diseases, were created. We have reported the efficacy of the BCL-2 inhibitor, ABT-737, on the AML post-MDS model; here, we report that this BCL-2 inhibitor also significantly extended survival of the HR-MDS mouse model, with reductions of BM blasts and lineage negative/Sca1+/KIT+ (LSK) cells. Secondary transplants showed increased survival in treated compared to untreated mice. Unlike the AML model, BCL-2 expression and RAS activity decreased following treatment and the RAS:BCL-2 complex remained in the plasma membrane. Exon-specific gene expression profiling (GEP) of HR-MDS mice showed 1952 differentially regulated genes upon treatment, including genes important for the regulation of stem cells, differentiation, proliferation, oxidative phosphorylation, mitochondrial function, and apoptosis; relevant in human disease. Spliceosome genes, found to be abnormal in MDS patients and downregulated in our HR-MDS model, such as Rsrc1 and Wbp4, were upregulated by the treatment, as were genes involved in epigenetic regulation, such as DNMT3A and B, upregulated upon disease progression and downregulated upon treatment

Exploration of Disease Markers under Translational Medicine Model

Disease markers are defined as the biomarkers with specific characteristics during the general physical, pathological or therapeutic process, the detection of which can inform the progression of present biological process of organisms. However, the exploration of disease markers is complicated and difficult, and only a few markers can be used in clinical practice and there is no significant difference in the mortality of cancers before and after biomarker exploration. Translational medicine focuses on breaking the blockage between basic medicine and clinical practice. In addition, it also establishes an effective association between researchers engaged on basic scientific discovery and clinical physicians well informed of patients' requirements, and gives particular attentions on how to translate the basic molecular biological research to the most effective and appropriate methods for the diagnosis, treatment and prevention of diseases, hoping to translate basic research into the new therapeutic methods in clinic. Therefore, this study mainly summarized the exploration of disease markers under translational medicine model so as to provide a basis for the translation of basic research results into clinical application

Alternative effects of RAS and RAF oncogenes on the proliferation and apoptosis of factor-dependent FDC-P1 cells

Despite the fact that RAF-1 lies immediately downstream of p21RAS in the MAP kinase-signalling cascade, recent evidence in non-haematopoietic environments suggest that RAS and RAF can transduce signals through alternative pathways specific to a particular cell type. Since mutational activation of RAS occurs at high frequency in human leukaemia, we have investigated the contribution of signalling from mutant RAF in mediating the transforming effects of the N-RAS oncogene in the growth factor-dependent cell line, FDC-P1. Independent activation of N-RAS extended the period of exponential growth leading to an increased saturating density under optimal growth conditions. Under conditions of growth factor withdrawal, cells expressing mutant RAS, but not control cells, demonstrated protection against apoptotic death. Although RAF promoted cell proliferation in a similar manner to that observed in FDCP-RAS cells, expression of mutant RAF was not as effective at protecting these cells against apoptotic death following growth factor withdrawal. The results suggest that RAS utilises RAF-dependent signals in promoting the proliferation of FDC-P1 cells but the anti-apoptotic effects of this oncogene are mediated through a RAF- and BCL-2-independent pathway

Mutant N-RAS induces erythroid lineage dysplasia in human CD34+ Cells

RAS mutations arise at high frequency (20–40%) in both acute myeloid leukemia and myelodysplastic syndrome (which is considered to be a manifestation of preleukemic disease). In each case, mutations arise predominantly at the N-RAS locus. These observations suggest a fundamental role for this oncogene in leukemogenesis. However, despite its obvious significance, little is known of how this key oncogene may subvert the process of hematopoiesis in human cells. Using CD34+ progenitor cells, we have modeled the preleukemic state by infecting these cells with amphotropic retrovirus expressing mutant N-RAS together with the selectable marker gene lacZ. Expression of the lacZ gene product, β-galactosidase, allows direct identification and study of N-RAS–expressing cells by incubating infected cultures with a fluorogenic substrate for β-galactosidase, which gives rise to a fluorescent signal within the infected cells. By using multiparameter flow cytometry, we have studied the ability of CD34+ cells expressing mutant N-RAS to undergo erythroid differentiation induced by erythropoietin. By this means, we have found that erythroid progenitor cells expressing mutant N-RAS exhibit a proliferative defect resulting in an increased cell doubling time and a decrease in the proportion of cells in S + G2M phase of the cell cycle. This is linked to a slowing in the rate of differentiation as determined by comparative cell-surface marker analysis and ultimate failure of the differentiation program at the late-erythroblast stage of development. The dyserythropoiesis was also linked to an increased tendency of the RAS-expressing cells to undergo programmed cell death during their differentiation program. This erythroid lineage dysplasia recapitulates one of the most common features of myelodysplastic syndrome, and for the first time provides a causative link between mutational activation of N-RAS and the pathogenesis of preleukemia