Azacitidine Treatment in High Risk Myelodysplastic Patients in Complete Haematological Remission Reverts Mesenchymal Stem Cells to a Normal Phenotype

Introduction. Myelodysplastic syndromes (MDSs) are a heterogeneous group of clonal hematopoietic stem cell (HSC) malignancies that are characterized by ineffective bone marrow hematopoiesis, peripheral blood cytopenias, and a substantial risk for progression to acute myeloid leukemia. Mesenchymal stem cells (MSCs) isolated from bone marrow of patients affected by myelodysplastic syndromes (MDS) play a critical role in myelodysplastic microenvironment showing altered structural epigenetic and functional features. Methods. In this work we evaluated the effect of azacitidine treatment on MSC-MDS. In particular, we analyzed MSC-MDS from 24 high-risk patients at diagnosis and after azacitidine treatment, studying their morphology, proliferative potential, cell cycle activity and their capacity to support haematopoiesis. Results. MDS-MSCs at diagnosis appeared larger and flattened, achieved confluence at a significantly lower rate than donors and displayed reduced proliferative capacity. In particular 40% of samples were unable to expand. This reduced proliferative capacity of MSC-MDS at diagnosis suggested changes in the cell cycle activity. Therefore we studied the gene expression profiles of 37 regulatory genes, observing CDKN2B up-regulation in MDS-MSCs (8 times higher than donors). Notably, after azacitidine treatment MDS-MSCs of patients who reached complete haematological remission (MDS-MSCs-CR) reverted to the typical BM-MSC morphology and recovered a proliferative potential similar to normal BM-MSC achieving confluence at a significantly higher rate. Molecular analysis on MDS-MSC-CR revealed a significant reduction in the expression level of CDKN2B showing correlation between cell cycle progression and expression level of this gene. Moreover, to study the long-term hematopoietic maintaining ability, MDS-MSCs at diagnosis were cultured with CD133+ cells, and they showed a decreased ability to support the growth of myeloid and erythroid progenitors. Conversely, MSC-MDS-CR showed an increased capacity to support haematopoiesis similar to healthy donors. Conclusion. We showed that MDS-MSCs at diagnosis were structurally and functionally altered while MSC-MDS-CR after azacitidine revert to a normal phenotype. It has been supposed that healthy MSCs adopt MDS-MSCs like molecular features when exposed to haematopoietic MDS cells. Our results may confirm these data suggesting that myelodysplastic cells can alter bone marrow microenvironment interacting with MSC and affecting their normal role and functionality.