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    • It has been suggested that similarly to

    2018-11-08

    It has been suggested that similarly to embryonic stem smo inhibitor (ESCs), stemness-related properties of some stromal stem/progenitor cells are supported by regulatory networks of transcription factors OCT4, SOX2 and NANOG (Greco et al., 2007; Ng and Surani, 2011; Park et al., 2012; Riekstina et al., 2009). When over-expressed, these factors reprogram differentiated cells to an embryonic-like state designated as pluripotent stem cells. These reprogrammed cells exhibit the morphology and growth characteristics of ESCs and express ESC marker genes (Takahashi et al., 2007). Stromal cells with stem/progenitor-like properties can be found in a diverse range of tissues and organs (Parekkadan and Milwid, 2010). White adipose tissue is considered as a rich source of stromal cells due to its simple harvesting methods and high numbers of isolated cells (Gimble et al., 2007). Growth kinetics, immunogenic characteristics, in vitro differentiation potential, senescence ratio and angiogenic activity of adipose tissue derived stromal cells (ADSCs) (also known as adipose-derived “mesenchymal stem cells”) are comparable with stromal cells obtained from other sources; however, several differences have been reported (De Ugarte et al., 2003; Izadpanah et al., 2006; Noel et al., 2008; Wagner et al., 2005; Winter et al., 2003). Purification of homogenous functionally relevant stem/progenitor cells from adipose tissue is still a challenge. Widely used methods of ADSC isolation include separation of adipose tissue stromal vascular fraction, followed by sorting according to the immunophenotype guidelines suggested by the International Society for Cellular Therapy, and selection of a plastic adherent population (Dominici et al., 2006). It has become clear that this method yields highly heterogeneous populations with only a fraction of cells with stem/progenitor characteristics (Gimble et al., 2010; Madonna et al., 2009; Tallone et al., 2011). Heterogeneity of initial populations may result in unpredictable effects and non-reproducible results, and therefore it remains one of the key problems in the field. Numerous clinical applications of stromal cell populations isolated from different tissues rely on the migration and homing of therapeutic cells in the site of injury or inflammation (Chamberlain et al., 2007). Also, it has been suggested that inflammatory conditions result in activation and directional movement of endogenous cells to the sites of injury where they participate in the processes of tissue regeneration. Signals of inflammation are partly mediated by chemokines. These signaling molecules act via binding to their seven-transmembrane receptors belonging to the G-protein coupled receptor (GPCR) family. Chemokines and their receptors play essential roles in the immune system by regulating mobilization and migration of several cell types including neutrophils and B- and T-lymphocytes (Bendall, 2005). Also, chemokines are associated with a variety of other cellular functions including proliferation, differentiation and establishment of cellular polarity. Several data also indicate that chemokines have cell type and concentration dependent anti- and pro-apoptotic effects (Vlahakis et al., 2002). Twenty chemokine receptors and approximately 50 chemokines are identified in humans. Bone marrow derived stromal cells (BMSCs) express several chemokine receptors (CCR1, CCR4, CCR6, CCR7, CCR9, CCR10, CXCR4, CXCR5, CXCR6, CX3CR1), and respective chemokines induce migration of BMSCs in vitro (Fox et al., 2007; Honczarenko et al., 2006; Ruster et al., 2006; Sordi et al., 2005; Von Luttichau et al., 2005; Wynn et al., 2004). Data concerning chemokine system in ADSCs are very limited. It has been demonstrated that ADSCs are chemotactic in vitro, but, compared to BMSCs, ADSCs express a smaller subset of chemokine receptors (CCR1, CCR7, CXCR4, CXCR5 and CXCR6) (Baek et al., 2011). Here we analyze the entire repertoire of chemokine receptors in human ADSCs, peripheral blood mononuclear cells and dermal fibroblasts, and show that CCR1 is one of the few chemokine receptors highly expressed in ADSCs. Interestingly, expression of CCR1 in different pools of ADSCs positively correlates with the expression levels of the stem cell marker genes SOX2, OCT4 and NANOG, whereas exposure of ADSCs to CCL5, a ligand for CCR1, stimulates proliferation of CCR1+ cells accompanied with increased expression of SOX2, OCT4 and NANOG. Our results also show that CCR1 is an active receptor in ADSCs, and signaling via the CCL5/CCR1 axis triggers not only migration of cells but also activation of ERK and AKT kinases as well as NFκB signaling pathway.