Objective: To differentiate rat adipose tissue-derived mesenchymal stem cells (ADSCs) into cells with a nucleus pulposus-like phenotype in vitro,so as to lay a foundation for the cell-based transplantation therapy of degenerated intervertebral discs.Methods: Rat ADSCs were isolated only from the subcutaneous inguinal region and purified by limited dilution.ADSCs of the third passages were analyzed by fluorescence activated cell sorter (FACS) to detect the cell surface markers (Sca-1,CD44,CD45,CD11b).To induce ADSCs towards a nucleus pulposus-like phenotype,ADSCs were immobilized in 3-dimensional alginate hydrogels and cultured in an inducing medium containing transforming growth factor-betal (TGF-β1) under hypoxia (2% O2),while control groups under normoxia (21% O2) in alginate beads in medium with or without the presence of TGF-β1.Semiquantitative reverse transcription polymerase chain reaction (RT-PCR) was carded out to evaluate phenotypic and biosynthetic activities in the process of differentiation.Meanwhile,Alcian blue staining were used to detect the formation of sulfated glycosaminoglycans (GAGs) in the differentiated cells.Results: The purified ADSCs were fibroblast-like and proliferated rapidly in vitro.The flow cytometry showed that ADSCs were positive for Sea-1 and CD44,negative for CD45 and CD11b.The results of RT-PCR manifested that the gene expressions of Sox-9,aggrecan and collagen Ⅱ,which were chondrocyte specific,were upregulated in medium containing TGF-β1 under hypoxia (2% O2).Likewise,gene expression of HIF-la,which was characteristics of intervertebral discs,was also upregulated.Simultaneously,Alcian blue staining exhibited the formation of many GAGs.Conclusions: The approach in our experiment is a simple and effective way to acquire a large quantity of homogenous ADSCs.Rat ADSCs can be differentiated into nucleus pulposus-like cells.ADSCs may replace bone marrow mesenchymal stem cells as a new kind of seed cells in regeneration of degenerated intervertebral discs using cell transplantation therapy.