Sox-9 facilitates differentiation of adipose tissue-derived stem cells into a chondrocyte-like phenotype in vitro

The purpose of this study is to test whether ectopic expression of Sox-9 can induce adipose tissue-derived stem cells (ASCs) to function as real nucleus pulposus (NP) cells in vitro. Adenoviral vectors expressing Sox-9 were reported to infect the chondroblastic and human disc cells, which resulted in increased Sox-9 and type II collagen production. ASCs were isolated from rat inguinal adipose pad, characterized, and transduced in vitro with a retroviral vector encoding the Sox-9 gene. Sox-9-engineered ASCs (ASCs/Sox-9) were induced for the chondrocyte-like cell differentiation by 3D cultured in alginate beads and TGF-β3 for 2 weeks. Expression of exogenous Sox-9 protein was detected. Type II collagen and Aggrecan gene expressions of induced ASCs/Sox-9 were measured using real-time PCR; proteoglycans expressions were measured by checking the glycosaminoglycan content and type II collagen production by enzyme-linked immunosorbent assay. Isolated ASCs were CD 29⁺/ CD44⁺/C-Kit^-/Lin^-/CD34^-/CD45 ^-. ASCs/Sox-9 expressed marked increase in exogenous Sox-9 protein. After induction, type II collagen gene expression was sevenfold higher in mRNA levels, with an approximately twofold increase in protein levels of ASCs/Sox-9 compared to ASCs. Type II collagen and proteoglycan productions were significantly increased in the ASCs/Sox-9 compared to the ASCs. In addition, co-culture of induced ASCs/Sox-9 with matured NP cells resulted in enhanced increase in proteoglycan and type II collagen production. Constitutive retroviral expression of Sox-9 could efficiently induce ASCs differentiation into chondrocyte-like cells. This novel approach may provide a practicable system for a simple and rapid differentiation of ASCs into chondrocyte-like cells which may be potentially used as a stem cell-based therapeutic tool for the treatment of degenerative disc diseases.