Abstract
A human bone marrow-derived mesenchymal stromal cell (MSCs) and cord blood-derived CD34+ stem cell co-culture system was set up in order to evaluate the proliferative and differentiative effects induced by MSCs on CD34+ stem cells, and the reciprocal influences on gene expression profiles. After 10 days of co-culture, non-adherent (SN-fraction) and adherent (AD-fraction) CD34+ stem cells were collected and analysed separately. In the presence of MSCs, a significant increase in CD34+ cell number was observed (fold increase = 14.68), mostly in the SN-fraction (fold increase = 13.20). This was combined with a significant increase in CD34+ cell differentiation towards the BFU-E colonies and with a decrease in the CFU-GM. These observations were confirmed by microarray analysis. Through gene set enrichment analysis (GSEA), we noted a significant enrichment in genes involved in heme metabolism (e.g. LAMP2, CLCN3, BMP2K), mitotic spindle formation and proliferation (e.g. PALLD, SOS1, CCNA1) and TGF-beta signalling (e.g. ID1) and a down-modulation of genes participating in myeloid and lymphoid differentiation (e.g. PCGF2) in the co-cultured CD34+ stem cells. On the other hand, a significant enrichment in genes involved in oxygen-level response (e.g. TNFAIP3, SLC2A3, KLF6) and angiogenesis (e.g. VEGFA, IGF1, ID1) was found in the co-cultured MSCs. Taken together, our results suggest that MSCs can exert a priming effect on CD34+ stem cells, regulating their proliferation and erythroid differentiation. In turn, CD34+ stem cells seem to be able to polarise the BM-niche towards the vascular compartment by modulating molecular pathways related to hypoxia and angiogenesis.
Highlights
Haematopoiesis is a continuous blood cell production process occurring in the bone marrow niche (BM-niche) through the orchestrated proliferation, self-renewal and differentiation of haematopoietic stem cells (HSCs) [1,2].The mesenchymal stem/stromal cells (MSCs) play an essential role in the quiescence, proliferation and differentiation of HSCs [3,4,5]
A 13.20-fold increase in the number of CD34+ cells was observed with the sorted SN-fraction, while no statistically significant difference was found with the sorted AD-fraction
Since the increase was mainly observed in the SN-fraction, we supposed that the inductive proliferative effects of mesenchymal stromal cell (MSCs) on HSCs could be mediated by MSCs-derived molecules
Summary
The mesenchymal stem/stromal cells (MSCs) play an essential role in the quiescence, proliferation and differentiation of HSCs [3,4,5]. They are spatially associated with HSCs, adrenergic nerve fibres and arteriolar vasculature and constitute a structurally unique niche made of MSC-HSC pairings, tightly regulated by local input and long-distance cues [6,7,8,9,10]. In a xenogenic transplantation model, MSCs favour the haematopoietic engraftment by an increased expression of SDF-1 and osteopontin and, when injected locally, they co-localised around blood vessels in the subendosteal region of mice femurs, restoring BM-niche function even when the stroma is damaged [14]
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