In vitro -induced differentiation of MPCs from different tissue sources. (a-d) Chondrogenic differentiation evaluated after 21 days in micropellet culture. (a) Immunohistochemical analysis of cartilage markers (COL2 and AGN) and alcian blue (AB) and picrosirius (PS) staining in pellet cultures of MPCs. (d) Expression of COL2, a specific marker for chondrogenesis, measured in differentiated MPC cultures compared with day 0 (D0) cultures, determined by quantitative RT-PCR with GAPDH as an internal control. (b-e) Osteogenic differentiation of MPCs assessed after 21-day culture in osteogenic medium. (b) All MPCs tested exhibited ALP activity and produced a mineralized matrix stained with alizarin red. T-MPCs displayed less alizarin red staining compared with BM-MPCs, M-MPCs, and DP-MPCs. (e) Significant upregulation of the expression of osteocalcin (OC), an osteoblast-specific gene, compared with undifferentiated MPCs was observed after osteogenic induction of BM-MPCs, T-MPCs, M-MPCs, and DP-MPCs compared with D0 cultures. (c-f) Adipogenic differentiation of MPCs cultured in adipogenic medium for 21 days. (c) All MPCs tested exhibited lipid-containing intracellular vacuoles that stained with oil red O at the end of the differentiation period. (f) MPCs cultured in adipogenic medium upregulated the expression of adipocyte-specific genes (PPAR-γ and LPL) compared with MPCs at D0. Quantitative RT-PCR data represent the mean ± SD in three independent experiments. *P ≤ 0.05, versus D0; **P ≤ 0.05, versus BM-MPCs.