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3.3 Tactics to Overcome Ageing
The advanced knowledge of how stem cells from aged donors will behave sets the
scene for how to overcome the discussed diffi culties in ex vivo culturing. There are
known important genetic factors that infl uence cellular division, as discussed above.
In a recent study (Lee et al. 2009 ), the authors introduced wild-type p53-inducible
phosphatase-1 (Wip1) in culturing hMSCs, and it was found to lower p16INK4A
expression leading to p38 mitogen-activated protein kinase (MAPK) inactivation.
This successfully delayed cell growth arrest in prolonged culture. However, it failed
to induce senescent MSCs back into a replicative cell cycle. This study does suggest
that induction of p16-related senescence is an irreversible step in stem cell fate.
Simpler methods to help promote proliferative capacity in cells from older
donors include the use of antioxidants in culture, as described by Ko et al. ( 2011 ) or
using low oxygen tension (Fehrer et al. 2007 ). Cell density in culture has an impact
on replicative capacity (Colter et al. 2009 ). hMSCs were shown proliferate at a
greater rate if plated at reduced cellular densities of 1.5 or 3.0 cells/cm^2. In addition,
single cell-derived MSC clones were able to be expanded up to 50 PDs in serial
passages of low cellular density, whereas growth was seen to be a plateau after 15
passages when cultured at higher cellular densities (Colter et al. 2009 ).
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