FIBROBLAST GROWTH FACTOR 2 EXERTS DIFFERENT UNEXPECTED EFFECTS ON BONE MARROW-DERIVED HUMAN MESENCHYMAL STROMAL CELLS

Bone marrow-derived Mesenchymal stromal cells (BM-MSCs) are fibroblast-like adherent cells that grow as colony forming unit-fibroblasts exhibiting high proliferative potential and ability to differentiate in a variety of tissues, including fat, bone, cartilage, muscle and neural cells. Thus, MSCs are promising cells for clinical use in regenerative medicine and also as immune regulators. Several growth factors are commonly used to in vitro expand MSCs, including fibroblast growth factor-2 (FGF2). In this study, we investigated the effects of FGF2 on BM-MSCs from 17 pediatric patients, cultured in the absence or presence of FGF2 as both heterogeneous bulk populations and colonies derived from single cells isolated since the initial BM mononuclear fraction. FGF2 induced morphologic changes in both bulk and cloned populations with cells showing smaller dimensions, more refractive appearance, reduced adherence to plastic support and reduced adhesion to each other. Both surface and mRNA expression of adhesion molecules such as VCAM1/CD106, ICAM1/CD54 and ALCAM/CD166 were down-regulated in FGF-dependent cultures in comparison to untreated ones, as studied by flow cytometry and quantitative RT-PCR. Moreover, FGF2 induced a significant dose-dependent down-regulation of CD90 expression which was paralleled by significant increase of surface HLA-DR and Class II major histocompatibility complex transactivator (CIITA) mRNA expression, as demonstrated by flow cytometry and RT-PCR, respectively. Despite this effect, FGF2-cultured MSCs were indeed negative for co-stimulatory molecules such as CD40, CD80 and CD86, and along with this, they were unable to stimulate allogeneic CD4+ T cells or allogeneic NK cells. Finally, in terms of differentiation, FGF2-cultured MSCs more easily differentiated towards cartilage than non FGF2-treated cells. These results suggest that FGF2 possess several unexpected activities on BM-MSCs and further studies are needed to understand the molecular pathways involved.