Age-Related Differences Between Unrestricted Somatic Stem Cells from Cord Blood and Bone Marrow Derived Mesenchymal Stroma Cells.

During the past years haematopoietic stem cells from unrelated umbilical cord blood have been increasingly used for treatment of leukaemia and genetic diseases. Human cord blood also contains a non-haematopoietic, adherently growing, CD45 negative, Oct4, nanog and Sox2 negative cell population with intrinsic multipotent differentiation potential, described as Unrestricted Somatic Stem Cells (USSC) (Kögler et al. 2004, Kögler et al. 2005, Kögler et al. 2006, Sensken et al. 2007, Liedtke et al. 2007, Liedtke et al.2008, Greschat et al. 2008, Ghodsizad A et al. 2008, Trapp et al. 2008). USSC can be cultivated GMP-grade reaching 1×10⁹ cells in Passage 4–5 (correlating to 26,5 – 28 cumulative population doublings) without losing multipotency. To better understand and characterise USSC, we carried out in vitro studies concerning age-related changes in USSC-lines from human cord blood and in mesenchymal stroma cells derived from human bone marrow (BM-MSC). Telomerase activity and telomeres are involved in cell proliferation as well as the regulation of cell senescence (Lansdorp 2008). In this study 7 USSC-lines and 9 BM-MSC were analyzed for proliferation and senescence at different population doublings (PD). In vitro USSC have a higher proliferation capacity and accordingly a comparably more extended lifespan than BM-MSC. They undergo about 35 to 45 CPD whereas mean level of CPD from BM-MSC reaches 25. Telomere length of 12 USSC, 5 BM-MSC and 5 clonal populations of USSC were calculated after several PD and telomerase activity was measured. Mean terminal restriction fragment’s (TRF’s) length calculated from USSC after 31 CPD averages 9.7 kbp whereas mean telomere length from BM-MSC decreases already after 20 CPD to 7.9 kbp. After 47 CPD in clonal USSC populations mean TRF’s length is 6.1 kbp. Telomerase activity was analysed with RT-PCR and real time PCR. In contrast to previous publications telomerase activity was detected neither in BM-MSC (Parsch et al.) 2003 nor in USSCs (Manca et al. 2008). The percentage of senescent cells after the same number of CPD is significantly higher in BM-MSC than in USSC. About 80% of senescence was observed in BM-MSC but only 10% senescence in USSCs after 26 CPD. Wnt signalling is mandatory for self-renewal, cell proliferation and differentiation of haematopoietic stem cells (Reya et al. 2003). In primitive MSC populations Wnt signalling regulates mesenchymal lineage specification (Etheridge et al. 2004). For analysing the role of Wnt pathway in USSC development quantitative PCR Arrays have been carried out profiling the expression of 84 genes related to Wnt-mediated signal transduction. 8 different USSC populations have been analysed. In all USSCs factors essential for canonical and also non-canonical Wnt-signalling are present. Poor proliferating USSC with high adipogenic differentiation potential show a stronger expression of Wnt-signalling inhibitors like SFRP1, DKK1 and CXXC4. Based on age-related characteristics, USSC from cord blood are a much better source for regeneration compared to their adult MSC counterpart from bone marrow.