Gene expression during long-term culture of mesenchymal stem cells obtained from patients with amyotrophic lateral sclerosis

Ex-vivo expansion of bone marrow (BM)-derived mesenchymal stem cells (MSCs) before clinical use for amyotrophic lateral sclerosis (ALS) patients is essential but occasionally results in cellular senescence as well as decrease of differentiation potential. In this study, we analyzed the genes that are up- or down-regulated by the long-term culture of MSCs from the BM of ALS patients using microarray and real-time RT-PCR. Among the analyzed genes, 878 (cluster 11) including RUNX2, SMO, IHH, GPNMB, HGF, COL10A1 and WNT3 were continually downregulated during long-term culture, whereas 732 (cluster 14) including PCGF5, HHIP and SERPINB2 were continually up-regulated. A gene ontology (GO) analysis revealed that genes related to cell differentiation (GO:0030154), growth factor activity (GO:0008201) and ossification (GO:0001503) belonged to cluster 11. Genes related to cell morphogenesis (GO:0000902) and protein tyrosine phosphatase activity (GO:0004725) belonged to cluster 14. When we also analyzed DNA methylation in RUNX2 using methylation-specific PCR, the -3.8 kb and -3.0 kb CpG island shores adjacent to the promoter of RUNX2 DNA became hypermethylated upon successive subculture. These results suggest that the decrease in RUNX2 mRNA observed during the long-term culture of MSCs may be at least partially related to the hypermethylation of the RUNX2 CpG island shores.