Interactive endothelial phenotype maintenance and osteogenic differentiation of adipose tissue stromal vascular fraction SSEA-4+ -derived cells

Bone formation relies on complex processes that require well-orchestrated interactions between several cell types, such as bone-forming cells (osteoblasts, OBs) and endothelial cells (ECs). Their co-culture has been proved relevant to mimicking specific features of the bone niche. Here we propose the co-culture of microvascular-like ECs and pre-OBs, both derived from the SSEA-4+ cell subpopulation from the stromal vascular fraction of human adipose tissue (SSEA-4+ hASCs), to define the conditions in which cells synergistically communicate to support the full differentiation of pre-OBs and maintenance of the EC phenotype. Co-cultures of different ratios of the two cell types were established and maintained for up to 21 days in standard endothelial maintenance (ENDO) and osteogenic differentiation (OST) media, as well as in a mixture of these (MIX). The osteogenic maturation of pre-OBs (ALP activity, OPN and OCN expression, calcium deposition), the evolution of EC numbers (CD31+ cells) and maintenance of the endothelial phenotype (CD31 and vWF expression, LDL uptake) were assessed throughout the culture time as a function of cell ratio and culture media. The results obtained demonstrate that EC number has a significant effect on the osteogenic differentiation of pre-OBs, depending on the medium used. While in ENDO medium the osteogenic differentiation was not observed, in the OST and MIX media it was attained at similar levels, except for the co-culture with a higher number of ECs in MIX medium. These findings demonstrate that the use of SSEA-4+ hASCs as a single-cell source is promising to attain 3D bone-like models with the potential to promote vascularized bone tissue regeneration.