Starvation and overcrowding: culture conditions and DNA damage in embryonic stem cells.

Human embryonic stem cells (hESCs) are characterised by their self-renewal capacity and pluripotency, and therefore offer huge possibilities for regenerative medicine and drug testing amongst other. However, we (Spits et al., Nature biotech 26:1361, 2008) and others (Maitra et al., Nature genetics 37:1099, 2005) have uncovered genomic instability during long-term culture in hESCs, casting doubt on the safety of these cells in cell therapy. An improved understanding of the effect of culture conditions on hESCs might contribute to the preservation of genomic integrity, and thus safeguard their scientific and clinical value.
In high-density cultures, fewer nutrients are present per cell, possibly leading to a shortage of substrates for nucleotide synthesis. A lack of nucleotides could then lead to stalled replication forks, causing an increase in double-stranded DNA breaks (DSBs) and intra- and inter-chromosomal rearrangements. To confirm this hypothesis, we plated 3 different hESC lines (VUB07, VUB14 and VUB31) in 4 different densities and found a significant increase (pOur preliminary data indicate a correlation between culture density and the occurrence of DNA breaks and segmental aberrations in hESC in culture. Bearing in mind that we find these differences after 1 passage of 5 days, the long-term effect of culture density could have a strong impact on the genetic stability of hESC cultures.