Hematopoiesis-supportive function of growth-arrested human adipose-tissue stromal cells under physiological hypoxia

Ex vivo expansion of hematopoietic progenitors is considered as an attractive tool to increase the number of stem and progenitor cells (HSPCs) for cell therapy. The efficacy of ex vivo expansion is strongly depends on the feeder cell activity to mimic hematopoietic microenvironment. Here we demonstrated, that combination of mitomycin C-induced growth arrest and tissue-related O₂ (physiological hypoxia) modulated stromal capacity of adipose tissue derived stromal cells (ASCs). Growth arrest did not affect viability, stromal phenotype and multilineage potential of ASCs permanently expanded at tissue-related O₂. Meanwhile, the PCR analysis revealed an up-regulation of genes, encoded molecules of cell-cell (ICAM1, HCAM/CD44) and cell-matrix adhesion (ITGs), extracellular matrix production (COLs) and remodeling (MMPs, HAS1) in growth-arrested ASCs at physiological hypoxia in comparison with ambient O₂ (20%). The number of ICAM-1 positive ASCs was increased under low O₂ as well. These alterations contributed into the ex vivo expansion of cord blood HSPCs providing the preferential production of primitive HSPCs. The number of cobblestone area forming cell (CAFC) colonies was 1.5-fold higher at physiological hypoxia (p < 0.05). CAFCs considered as long-term culture-initiating cells (LTC-IC) known to support long-term hematopoiesis restoration in vivo. The presented data may be applicable in the development of upscale protocols of HSPC expansion.