The role of adipose-derived stem cells in a self-organizing 3D model with regard to human soft tissue healing.

The clinical phenomenon of inadequate soft tissue healing still remains an important issue. The occurrence of chronic wounds is correlated to the life span, which is still increasing in western countries. Tissue engineering products containing adipose-derived stem cells are discussed as a promising therapeutic approach. Several studies confirmed the value of these cells for soft tissue healing improvement, suggesting a paracrine as well as a direct effect on vessel repair and angiogenesis. In an attempt to figure out specific effects of adipose-derived stem cells on dermal microvascular endothelial cells with respect to the different phases of soft tissue healing, we designed a 3D in vitro model on the basis of spheroids. Basic parameters like spheroid volume, cell numbers, and rate of apoptotic cells were determined in dependence on culture time, on different oxygen conditions and using mono- as well as co-cultures of both cell types. Furthermore we focused on gene expression and protein levels of interleukin-6, interleukin-8, monocyte chemoattractant protein-1, and vascular endothelial growth factor, which are discussed against the background of therapies for chronic wounds. The visualization of α-smooth muscle actin allowed the estimation of the function of adipose-derived stem cells as stabilizer for dermal microvascular endothelial cells. The results of the present 3D model underscore a paracrine effect of adipose-derived stem cells on microvessel repair during early hypoxic conditions, whereas a stabilizing effect occurs during a later phase of soft tissue healing, simultaneously to reoxygenation.