In particular, p53 mainly mediates prosenescence signals that are derived via oncogene activation, telomere dysfunction, DNA damage, and reactive oxygen species 
In particular, p53 mainly mediates prosenescence signals that are derived via oncogene activation, telomere dysfunction, DNA damage, and reactive oxygen species . dickkopf-1 (an antagonist of the Wnt coreceptor) and -catenin siRNA transfection promotes senescence in MSCs. Interestingly, the magnitude of the response to enhanced Wnt3a/-catenin signaling appears to depend on the senescent state during extended culture, particularly after multiple passages. These results suggest that Wnt3a signaling might be a predominant factor that could be used to overcome senescence in long-term cultured MSCs by directly intervening in the proliferative capacity and MSC senescence. The functional role of Wnt3a/-catenin signaling in hedging cellular senescence may allow the development of new approaches for stem cell-based therapies. Introduction Adult mesenchymal stem cells (MSCs) can be easily isolated, self-renew, and differentiate into a range of mesenchymal tissues both Oxacillin sodium monohydrate (Methicillin) in vivo and in vitro [1C3]. Therefore, they are considered an attractive candidate for the development of cell-based therapeutics . Prolonged passaging of the in vitro culture environment is a prerequisite for acquiring a suitable number of MSCs for cell therapeutics. However, the process may adversely affect the physiological properties of MSCs, such as stemness, proliferation, and differentiation potency. MSCs that are maintained in vitro for a long periods of time develop cellular senescence, which consequently limits the number of cell doublings . Although cellular senescence is caused by various factors, senescent cells display a number of common characteristics that make them easily distinguishable from growing cells . Generally, senescence triggers morphological transformations that result in enlarged, flattened, and multinucleated cells. Given the role of tumor suppressors and cell cycle regulators in cancer cells, p53-p16-Rb signaling is used as a biomarker to identify senescent cells [7,8]. In particular, p53 mainly mediates prosenescence signals that are derived via oncogene activation, telomere dysfunction, DNA damage, and reactive oxygen species . Another commonly used indicator is senescence-associated -galactosidase (SA–gal) activity . Increasing lysosomal biogenesis Oxacillin sodium monohydrate (Methicillin) in senescent cells is accompanied by the upregulation of SA–gal activity at pH 6.0 . Several studies report that canonical Wnt signaling keeps stem cells in a self-renewing and undifferentiated state [12C14], although the intensity of Wnt signaling can lead to different or even opposite biological functions [15,16]. MSCs express a number of Wnt ligands (including Wnt2, Wnt4, Wnt5a, Wnt11, and Oxacillin sodium monohydrate (Methicillin) Wnt16), Wnt receptors, and Wnt inhibitors . Because senescence is thought to limit the proliferative lifespan of many human stem cell populations, Wnt signaling and senescence in MSCs should be coordinated with each other . Some studies suggest that canonical Wnt signals delay senescence through the coordinated and combined effects of multiple pathways, including -catenin activation, c-myc expression, and the inactivation of the senescence-associated heterochromatin foci (SAHF) assembly pathway [12,19,20]. Although efforts to explore the interrelationship between Wnt signaling and cellular senescence are underway, to what extent Wnt/-catenin signaling contributes to the development of senescence in MSCs remains largely unknown. In this study, we investigate the feasibility of Rabbit polyclonal to IRF9 Wnt/-catenin signaling as regulator of the progression of senescence during extended MSC culturing. Materials and Methods Cell culture The MSCs used in this study were donated by MEDIPOST Co., Ltd. (Seongnam, Korea). Umbilical cord blood was collected from the umbilical vein after neonatal delivery and obtaining informed consent from all Oxacillin sodium monohydrate (Methicillin) mothers. Umbilical cord blood-derived mesenchymal stem cells (UCB-MSCs) were separated, as previously described , and maintained in -minimum essential media (-MEM; Gibco) supplemented with 10% heat-inactivated fetal bovine serum (FBS;.