PF541 TRANSCRIPTIONAL ALTERATIONS OF HEMATOPOIETIC STEM CELLS IN MYELODYSPLASTIC SYNDROMES
Authors: T. Ezponda, J.P. Romero, M. Ainciburu, A. Alfonso, A. Vilas, P. San Martín, L. Castro, T. Jiménez, F. López, J. Hernández, A. Molero, J. Montoro, B. Tazón, B. Paiva, M. Díez‐Campelo, D. Valcárcel, J. San Miguel, D. Lara, F. Prósper
Journal: HemaSphere (2019)

Background: Over the last years, great effort has been made in characterizing the molecular pathogenesis of hematological malignancies. In myelodysplastic syndromes (MDS), studies have mainly focused on the analysis of the mutational profiles of hematopoietic progenitors, but the fundamental molecular bases of the disease are still incomplete. It is very possible that, as in other hematological diseases, transcriptional and epigenetic mechanisms also play a relevant role. Aims: In the present work, we aimed to characterize the transcriptional profile of the hematopoietic stem cells (HSCs) of MDS patients and healthy donors in order to identify altered genes and pathways that could contribute to the development and/or maintenance of the disease. Methods: HSCs were isolated from an homogeneous group of 10 untreated MDS patients with multilineage dysplasia as well as from healthy aged donors (median of 70 y/o) as controls, with the use of fluorescence activated cell sorting (FACS) (CD34+, CD38‐, CD90+, CD45RA‐). The transcriptional profiles of these cells were determined using low‐input RNA‐sequencing (MARS‐Seq). All statistical analyses were carried out in the R/Bioconductor programming environment. Functional analyses of differentially expressed genes were carried out using gene ontology, ingenuity pathway analysis and gene set enrichment analysis. Results: Unsupervised clustering of the 5% most variable genes among all samples demonstrated that most MDS specimens clustered separately from healthy controls, indicating that differences in the transcriptome of these cells are able to distinguish healthy and pathological HSCs. An unsupervised principal component analysis showed an expected heterogeneity of MDS patients; nevertheless, most of these patients clustered separately from healthy controls, corroborating our previous finding. To identify altered genes and pathways in HSCs from MDS patients we performed differential gene expression analysis, finding 56 and 45 up and down‐regulated genes (p‐value&lt;0.05, FC&gt;2), respectively. Intriguingly, among such genes, and despite the expected heterogeneity observed in MDS patients, we detected a very homogeneous deregulation of a subset of genes, suggesting common pathological mechanisms among patients. Gene ontology analysis showed that upregulated genes were involved in biological processes such as regulation of RNA processing (non‐sense mediated decay and translation initiation), telomere capping and regulation of megakaryocyte differentiation. Among downregulated genes, we found many genes involved in the response to extrinsic signals, including regulators of angiogenesis, cell‐cell signaling, chemokine‐mediated signaling pathways and chemotaxis. Deregulated genes in MDS included the presence of transcriptional regulators, such as transcription factors and chromatin remodelers, which may be responsible for the transcriptional aberrations observed in these patients. Moreover, we also observed an alteration in the expression of many genes involved in the regulation of cell death, a process known to be altered in the hematopoietic progenitors of this disease. Summary/Conclusion: Altogether, our data points towards the deregulation of the HSC transcriptional profile, affecting relevant processes which may alter intrinsic functions as well as their response to the microenvironment in order to favor their survival in MDS patients.