The Effect Of HIF-1α On BMP2-induced Chondrogenic And Osteogenic Differentiation

Stem cell-based approaches to cartilage and bone repair have garneredconsiderable attention. Hypoxia inducible factor-1α (HIF-1α), which is thetranscription factor primarily response for mediating the effects of hypoxia,may be important for regulating the osteochondrogenic differentiation ofstem cells. We, therefore, investigated the effects of HIF-1α onBMP2-induced chondrogenic and osteogenic differentiation to furtherexplore the role of the hypoxia pathway in the osteochondrogenicdifferentiation of stem cells. C3H10T1/2cells were induced to undergochondrogenic and osteogenic differentiation by BMP2. Theosteochondrogenic differentiation was monitored using real-timepolymerase chain reaction (COL2A1, aggrecan, COL1A1, and alkalinephosphatase [ALP]) and western blotting (Sox9, COL2A1, Runx2,osteopontin, and osteocalcin). Chondrogenic differentiation was furtherevaluated using Alcian blue staining for sulfated glycosaminoglycans(GAGs). Osteogenic differentiation was also assessed using ALP activityassays and Alizarin red S staining for mineralized matrix. We also detected the effect of HIF-1α on BMP2-induced devolpment of fetal limb explantculture. In addition, we demonstrated the role of HIF-1α inosteochondrogenic differentiation by subcutaneous stem cell implantationin athymic nude mice. The exogenous expression of HIF-1α potentiated theBMP2-induced chondrogenic differentiation of C3H10T1/2cells in vitro,as indicated by the increased expression of chondrogenic markers (Sox9,COL2A1, aggrecan). HIF-1α obviously enhanced GAG secretion duringBMP2-induced chondrogenic differentiation. However, HIF-1α negativelyregulated BMP2-induced osteogenic differentiation, as indicated by adecrease in the expression of Runx2, COL1A1, ALP, osteopontin, andosteocalcin, and decreased matrix mineralization. HIF-1α also inhibitedendochondral ossification during fetal limb explant culture andBMP2-induced osteochondrogenic differentiation in vivo. Thus, our resultsrevealed that HIF-1α, the master transcription factor of the hypoxiapathway, promotes BMP2-induced chondrogenic differentiation but inhibitsosteogenic differentiation and endochondral ossification, therebymaintaining the chondrogenic phenotype.