While the facial skeleton is formed by HOX

While the facial skeleton is formed by HOX negative neural crest buy Calcium Ionophore I (Creuzet et al., 2002), the skeleton, originating from mesoderm-derived progenitor cells, is usually HOX positive in adults (Leucht et al., 2008). In bone regeneration experiments, Leucht et al. revealed that the HOX negative mandibular progenitor cells are favourable in bone repair as compared to the HOX positive tibial progenitor cells (Leucht et al., 2008). In their experiments, HOX negative mandibular progenitor cells started to express HOX genes after transplantation into a tibial bone defect leading to bone repair. In contrast to that, HOX positive tibial progenitor cells transplanted into a mandibular defect failed to regenerate bone. This data is supported by recent findings, suggesting the biological advantages of HOX negative cells isolated from endoral sites (Lohberger et al., 2012). The potency of a HOX negative cell to adapt the HOX code of surrounding cells or tissues therefore seems to be an important feature for regenerative approaches but also for the normal development in the skeleton of the fetus. As HOX genes are able to translocate passively through biological membranes, a technique applying a co-culture method provides several advantages. In the work presented here, USSCs (HOX−) with a restricted adipogenic potential were co-cultured with CDSCs and BMSCs (HOX+) to test if the USSCs are able to adapt a HOX positive expression pattern. Additionally, changes of the lineage-specific cell fate modulated by co-culture were monitored for osteogenic, chondrogenic and adipogenic differentiation in this approach. Finally, following hypotheses were tested:
Material and methods
Results
Discussion Although stromal cell populations can be isolated from numerous human tissues (Fraser et al., 2006; Griffiths et al., 2005; Kogler et al., 2009), their developmental origins remain largely unknown and their characterization is discussed controversially (Bianco, 2011a; Bianco, 2011b). USSCs display a strong similarity to CDSCs and BMSCs in their immunophenotype and their osteogenic and chondrogenic differentiation potential in vitro, but differ in their restricted adipogenic potential (Kluth et al., 2010). In 2010, we were able to distinguish these two functionally distinct neonatal stromal cell populations derived from cord blood additionally on the HOX gene expression pattern (Liedtke et al., 2010). In order to define if the limited adipogenic differentiation potential in USSCs is reflected by the HOX gene expression, co-culture experiments were performed. The hypothesis was pursued that co-culture of USSCs (HOX−) with CDSCs and BMSCs (HOX+) could be sufficient to adapt the HOX expression pattern of a surrounding cell as it was shown before in mice for periosteal progenitor cells (Leucht et al., 2008). For the first time, the results of our study clearly demonstrate in detail that adaption of the HOX code by co-culture is possible in the human system for CB-derived subpopulations. Notably, the adaption of the HOX code attends with a cell fate switch of USSCs gaining an adipogenic differentiation potential. These results imply that the adaptiveness of USSCs to surrounding cells is an important feature when using these cells in therapeutical approaches. In addition the impact of the co-culture on the osteogenic differentiation capacity was tested. Both USSC and CDSC lines can be easily differentiated towards the chondrogenic and osteogenic lineage but can individually differ in the content of proteoglycans in chondrogenesis or in the level of mineralization during osteogenesis. Co-cultured USSCs revealed an adaption to the CDSC line reflected by a lower level of proteoglycans detected at day 21 of chondrogenic differentiation. Co-culture of a CDSCs with lower mineralization than USSCs revealed an adjustment of the USSCs to the mineralization level of the CDSCs. Furthermore, these results were confirmed on transcript level for several osteo/chondro-associated genes.