[Abstract unavailable

Recent studies have demonstrated the importance of cellular extrinsic factors in the aging of adult stem cells. However, the effects of an aged cell–extrinsic environment on mesenchymal stem cell (MSC) aging and the factors involved remain unclear. In the current study, we examine the effects of old rat serum (ORS) on the aging of MSCs, and explore the effects and mechanisms of Wnt/β-catenin signaling on MSC aging induced by ORS treatment. Senescence-associated changes in the cells are examined with SA-β-galactosidase staining and ROS staining. The proliferation ability is detected by MTT assay. The surviving and apoptotic cells are determined using AO/EB staining. The results suggest that ORS promotes MSC senescence and reduces the proliferation and survival of cells. The immunofluorescence staining shows that the expression of β-catenin increases in MSCs of old rats. To identify the effects of Wnt/β-catenin signaling on MSC aging induced with ORS, the expression of β-catenin, GSK-3β, and c-myc are detected. The results show that the Wnt/β-catenin signaling in the cells is activated after ORS treatment. Then we examine the aging, proliferation, and survival of MSCs after modulating Wnt/β-catenin signaling. The results indicate that the senescence and dysfunction of MSCs in the medium containing ORS is reversed by the Wnt/β-catenin signaling inhibitor DKK1 or by β-catenin siRNA. Moreover, the expression of γ-H2A.X, a molecular marker of DNA damage response, p16INK4a, p53, and p21 is increased in senescent MSCs induced with ORS, and is also reversed by DKK1 or by β-catenin siRNA. In summary, our study indicates the Wnt/β-catenin signaling may play a critical role in MSC aging induced by the serum of aged animals and suggests that the DNA damage response and p53/p21 pathway may be the main mediators of MSC aging induced by excessive activation of Wnt/β-catenin signaling.

Wild soybean is a typical short-day plant that begins flowering when the days are shorter than its critical photoperiod. Soybean was domesticated in the temperate region of East Asia at the relatively high latitude, and the breeding and release of soybean varieties have historically centered on mid-and high-latitude temperate regions. Low-latitude areas with tropical and subtropical climates were previously considered unsuitable for soybean production because most temperate soybean varieties exhibited precocious flowering and early maturity and suffered from low yields. The discovery and introduction of the long juvenile trait into soybean varieties in the 1970s (Hartwig and Kiihl, 1979) fundamentally changed global soybean production in a way that has had an enormous influence on commodity markets. This trait delays flowering and thereby ensures sufficient vegetative growth prior to the developmental transition to reproductive growth. The long juvenile trait thus solved the early maturation and low yield problems that had hitherto prevented economically viable soybean production in lowlatitude regions (Destro et al., 2001). The United States and Brazil pioneered the introduction of the long juvenile trait in low-latitude soybean breeding programs. Brazil has expanded its soybean production enormously, from 1 million hectares in 1970 (Brown, 2004) to over 33 million hectares in 2016 (http:// gain.fas.usda.gov/Recent%20GAIN%20Publications/Oilseeds %20and%20Products%20Update_Brasilia_Brazil_12-1-2016. pdf).