104
5.6 Conclusion
Although there are no consistent results as to whether MSCs are affected by ageing, of
those studies that did fi nd a relationship, there are again discrepancies in how MSCs are
affected. Some reasons as to why inconsistent results have been obtained are due to
studies using different cut-off points for age groups, and the inclusion of confounders
such as gender, medical history and chronic illness is not accounted for but could all
cause a difference in results. Also, the period of time spent proliferating in culture before
differentiation media is added could affect the differentiation properties of MSCs as they
begin to lose their characteristics when in ex vivo conditions for a long duration. In addi-
tion, the type of growth and differentiation media, characterisation methods, the passage
of cells used and source of MSCs can all contribute to discrepancies in results.
There are various MSC age markers that are thought to be at an increased level in
MSCs from older donors and interfere with the function of MSCs. Some literature has
suggested that age-related changes in the surrounding environment of MSCs can
affect them such as a reduction of proteoglycans and glycosaminoglycans. This
change has been found to reduce viability and proliferation potential of MSCs in vivo
(Bi et al. 2005 ). Zhou et al. investigated whether there are age-related intrinsic factors
affecting MSCs. They found that there was four times as much senescence-associated
β-galactosidase found in MSCs from older than younger donors (Zhou et al. 2008 ).
This is supported by Stolzing et al. ( 2008 ) who also found an increase in senescence-
associated β-galactosidase with age. A positive correlation relating age with levels of
advanced glycation end products (AGEs) has also been suggested by Zhou et al. to
inhibit proliferation by increasing reactive oxygen species production (ROS) and
inducing apoptosis in MSCs. This is also linked to the age-related increase of RAGE,
the receptor for uptake of AGEs (Stolzing et al. 2008 ). Zhou et al. also suggested that
an age-related increase in p53 and its pathway genes, p21 and BAX, may be respon-
sible for a reduction in proliferation ability and osteoblastogenesis. A tumour suppres-
sor (p161NKa) that inhibits G1 cyclin-dependant kinases 4 and 6 prevents the cell
cycle and therefore reduces proliferation (Zindy et al. 1997 ).
This chapter has focused on how ageing affects properties of MSCs: prolifera-
tion, differentiation and also cell surface characterisation. It can be concluded that
there is a mixed view about the effects of ageing in the current literature. It is impor-
tant to identify the relationship between ageing and MSCs to fi nd out whether they
can be used for autologous transplantation of older patients, as the prevalence of
age-related disorders is increasing. Our described protocols for the isolation and
expansion of these cells are applicable to cells from patients of all ages.
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