Functional and Molecular Alterations of Bone Marrow Mesenchymal Stem and Progenitor Cells in Patients with Myelodysplastic Syndrome with Ring Sideroblast

Myelodysplastic Syndrome with Ring Sideroblast (MDS-RS), a clonal hematopoietic cell neoplasm, is low risk MDS, characterized by anemia, hyperplastic ineffective erythropoiesis and marrow ring sideroblasts. Mouse studies have shown that bone marrow niche, including endothelial cells, osteoblasts, adipocytes and mesenchymal stem cells (MSCs), contribute to progression of various hematological disorders. However, in vivo contribution of the different bone marrow stromal cells to the progression of MDS-RS in patients remains largely unknown.

To investigate this, we have phenotypically, molecularly and functionally characterized the BM native stromal cell subsets including MSCs freshly isolated by multi-color fluorescence activated cell sorting (FACS) from bone marrow of MDS-RS patients and age-matched healthy donors. We found: 1) the MDS-RS MSCs, estimated by colony forming unit-fibroblast (CFU-F), shared similar immunophenotype with normal MSCs (CD45^-CD235a^-CD31^-CD44^-, most of which were CD271⁺CD146⁺CD106⁺); 2) the frequency of CFU-Fs was significantly increased in the phenotypically defined MSCs of MDS-RS bone marrow compared to that of age-matched healthy controls (p=0.005); 3) multi-lineage differentiation assay revealed impaired osteogenic differentiation potential, but enhanced adipogenic differentiation potential of MDS-RS MSCs; 4) FACS analysis showed increased frequency of the adhesion receptor integrin α4 (ITGA4) in the CD44^- MSCs from MDS-RS bone marrow (p=0.013); 5) Correspondingly, RNA-sequencing of the freshly isolated bone marrow MSCs and endothelial cells revealed altered gene expression profile of these cells in MDS-RS patients. Among those, ITGA4, ITGA11, ITGAE and ITGB1 are upregulated in the MDS-RS MSCs, indicating potential abnormal adhesive interaction of the MSCs with hematopoietic stem cells in the patients. In addition, the cell cycling gene KI67 is upregulated whereas cell cycle negative regulators, like CDKN1A and CDKN1C are downregulated in the MDS-RS MSCs, which is consistent with their increased CFU-F activity. Interestingly, we detected abnormal expression of hematopoietic growth factors such as downregulation of ANGPTL4 in the MDS-RS MSCs and upregulation of ANGPT1 in the MDS-RS endothelial cells. The functional relationship between the stromal cell alterations and the abnormal hematopoiesis as well as the underlying molecular mechanisms are currently under investigation.

Taken together, our data provide new evidence for phenotypic, functional and molecular alterations of bone marrow mesenchymal cells in MDS-RS patients. The molecular pathways mediating bone marrow niche alteration could be potential therapeutic targets for new treatment of MDS-RS.