Osteogenic Potential of Adipose-Derived Macrospheroids Cocultured with CD11b+ Monocytes

Among potential cell-based therapies, adipose-derived stem cells (ASCs) have been proposed as a promising source of stem cells for tissue regeneration. Although many recent clinical trials have investigated the use of adipose tissue or ASCs in transplantation, analysis of the microstructures of outgrowing macrosized spheroids (macrospheroids) or three-dimensional coculture of ASC spheroids and monocyte/macrophage lineages has not been performed. The aim of this study was to analyze the microstructures of murine-derived ASC macrospheroids and the growth and osteogenic potential of these macrospheroids in a three-dimensional environment and after calcification induction by coculture with monocytes.

The histologic structures of murine-derived ASC macrospheroids and the expression of marker genes for multipotency within these macrospheroids were analyzed by hematoxylin and eosin staining and in situ hybridization. ASC macrospheroid microstructures were observed by transmission electron microscopy, and cell proliferation in the spheroids was analyzed. Additionally, the growth and osteogenic potential of these macrospheroids were assessed in two-dimensional and three-dimensional environments and after calcification induction by coculture with monocytes.

The expression of Oct3/4, Nanog, and Sox2 was detected even in the deep zone of spheroids, although higher expression was observed at the surface. Cell proliferation was detected within the spheroid centers. Observation of spheroid microstructure revealed extracellular matrix production within the spheroid architecture. Transplantation of a spheroid on the hydroxyapatite disc resulted in three-dimensional cell growth, filling the disc. Coculture of the spheroids with monocytes led to the formation of many osteoclast-like, multinucleated cells, and calcification was observed after 3 weeks of coculture.

ASC spheroids exhibited high capacity for dynamic three-dimensional growth and osteogenic differentiation. Furthermore, ASC spheroids promoted monocyte differentiation into osteoclast-like cells, which may enhance the osteogenic potential of ASC spheroids.