Hypoxia Differentially Modulates the Genomic Stability of Clinical-Grade ADSCs and BM-MSCs in Long-Term Culture

Long-term cultures under hypoxic conditions have been demonstrated to maintain the phenotype of mesenchymal stromal/stem cells (MSCs) and to prevent the emergence of senescence. According to several studies, hypoxia has frequently been reported to drive genomic instability in cancer cells and in MSCs by hindering the DNA damage response and DNA repair. Thus, we evaluated the occurrence of DNA damage and repair events during the ex vivo expansion of clinical-grade adipose-derived stromal cells (ADSCs) and bone marrow (BM)-derived MSCs cultured with platelet lysate under 21% (normoxia) or 1% (hypoxia) O-2 conditions. Hypoxia did not impair cell survival after DNA damage, regardless of MSC origin. However, ADSCs, unlike BM-MSCs, displayed altered gamma H2AX signaling and increased ubiquitylated gamma H2AX levels under hypoxic conditions, indicating an impaired resolution of DNA damage-induced foci. Moreover, hypoxia specifically promoted BM-MSC DNA integrity, with increased Ku80, TP53BP1, BRCA1, and RAD51 expression levels and more efficient nonhomologous end joining and homologous recombination repair. We further observed that hypoxia favored mtDNA stability and maintenance of differentiation potential after genotoxic stress. We conclude that long-term cultures under 1% O-2 were more suitable for BM-MSCs as suggested by improved genomic stability compared with ADSCs.