Paracrine Factors Released by Osteoblasts Provide Strong Platelet Engraftment Properties

Abstract

Ex vivo expansion of hematopoietic stem cell (HSCs) and progenitors may one day overcome the slow platelet engraftment kinetics associated with umbilical cord blood transplantation. Serumfree medium conditioned with osteoblasts (i.e., osteoblast-conditioned medium [OCM]) derived from mesenchymal stromal cells (MSC) was previously shown to increase cell growth and raise the levels of human platelets in mice transplanted with OCM-expanded progenitors. Herein, we characterized the cellular and molecular mechanisms responsible for these osteoblast-derived properties. Limiting dilution transplantation assays revealed that osteoblasts secrete soluble factors that synergize with exogenously added cytokines to promote the production of progenitors with short-term platelet engraftment activities, and to a lesser extent with long-term platelet engraftment activities. OCM also modulated the expression repertoire of cell-surface receptors implicated in the trafficking of HSC and progenitors to the bone marrow. Furthermore, OCM contains growth factors with prosurvival and proliferation activities that synergized with stem cell factor. Insulin-like growth factor (IGF)-2 was found to be present at higher levels in OCM than in control medium conditioned with MSC. Inhibition of the IGF-1 receptor, which conveys IGF-2 0 intracellular signaling, largely abolished the growth-promoting activity of OCM on immature CD34 + subsets and progenitors in OCM cultures. Finally, IGF-1R effects appear to be mediated in part by the coactivator β-catenin. In summary, these results provide new insights into the paracrine regulatory activities of osteoblasts on HSC, and how these can be used to modulate the engraftment properties of human HSC and progenitors expanded in culture. STEM CELLS 2019;37:345-356 SIGNIFICANCE STATEMENTOsteoblasts are one of many different cell type implicated in the regulation of hematopoiesis through various mechanism including the release of paracrine factors such as growth factors, chemokines and extracellular matrix proteins. It has been shown that these factors strongly modulate the growth of umbilical cord blood stem and progenitor cells through activation of insulin-like growth factor-1 receptor and subsequent activation of the transcriptional activation complex β-catenin/TCF. Osteoblasts also modulated the expression repertoire of cell-surface receptors implicated in the homing of progenitors to the bone marrow. Altogether, these properties significantly enhanced the platelet engrafting activity of progenitors produced in cultures.

The Role of Insulin-Like Growth Factor-2 on the Cellular Viability and Differentiation to the Osteogenic Lineage and Mineralization of Stem Cells Cultured on Deproteinized Bovine Bone Mineral

“…IGF-2 also acted as an important mitogen regarding liver repopulation in animal model [21]. IGF-2 was reported to be at higher level in the osteoblast-conditioned medium when compared with the control medium conditioned with the stem cells [22]. The expression of IGF-2 in developing osteophyte was strongly associated with a degree of osteogenesis, with the highest expression in active osteoblasts [23].…”

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“…While ex vivo expansion of HSC and progenitors is not currently feasible, it is an active area of research. In a recent article in Stem Cells , Abu‐Khader et al explore the mechanisms of action of MSC‐derived osteoblast conditioned media (OCM) to increase engraftment potential of ex vivo produced progenitor cells . They had previously shown that OCM could increase expansion and engraftment of UCB CD34+, and used these studies as a foundation to gain further understanding of the molecular mechanisms behind their findings .…”

“…One method to enhance their therapeutic potential is by stimulating these responses before cell administration by some pretreatment strategy that is specific to the mechanism of healing. In our second featured article, Abu‐Khader et al used conditioned medium from MSC‐derived osteoblasts to pre‐condition umbilical cord blood progenitor cells for enhanced platelet engraftment after transplant . In a related article, Abreu et al pre‐treated MSC with bronchoalveolar lavage fluid or serum from a murine model of allergic asthma to promote MSC anti‐inflammatory properties .…”

Dynamic secretome of bone marrow-derived stromal cells reveals a cardioprotective biochemical cocktail

“…paracrine signaling | secretome | secretion dynamics | paracrine dynamics | cell-cell communication S ecreted diffusive molecular factors are critical for intercellular communication enabling complex multicellular behaviors (1)(2)(3). Not surprisingly, therefore, secretion of various ligands is highly controlled, frequently dynamic in nature, and, like other cellular phenotypes, dependent on the biological context (4,5).…”

“…Surprisingly, these cells, like other adult stem cell types, do not appear to directly integrate into the damaged tissue, but rather rapidly and completely clear from the site of MI (myocardial infarction) (10,17,18). This paradoxical finding has led to an increasing speculation that transient paracrine signaling is the principal mechanism accounting for BMSC function (1), explaining the survival and rescue of target tissues, including the heart (16,18).…”