Human adipose mesenchymal stromal cells growing into PCL-nHA electrospun scaffolds undergo hypoxia adaptive ultrastructural changes

Human Adipose-Derived Mesenchymal Stem/Stromal Cells (hAD-MSCs) have great potential for tissue regeneration. Since transplanted hAD-MSCs are likely to be placed in a hypoxic environment, culturing the cells under hypoxic conditions might improve their post-transplantation survival and regenerative performance. The combination of hAD-MSCs and PCL-nHA nanofibers synergically improves the contribution of both components for osteoblast differentiation. In this work, we hypothesized that this biomaterial constitutes a hypoxic environment for hAD-MSCs. We studied the cellular re-arrangement and the subcellular ultrastructure by Transmission Electron Microscopy (TEM) of hAD-MSCs grown into PCL-nHA nanofibers, and we compared them with the same cells grown in two-dimensional cultures, over tissue culture-treated plastic, or glass coverslips. Among the most evident changes, PCL-nHA grown cells showed enlarged mitochondria, and accumulation of glycogen granules, consistent with a hypoxic environment. We observed a 3.5 upregulation (p = 0.0379) of Hypoxia Inducible Factor (HIF)-1A gene expression in PCL-nHA grown cells. This work evidences for the first time intra-cellular changes in three-dimensional compared to two-dimensional cultures, which are adaptive responses of the cells to an environment more closely resembling that of the in vivo niche after transplantation, thus PCL-nHA nanofibers are adequate for hAD-MSCs pre-conditioning.