title: Adult human mesenchymal stem cell differentiation to the osteogenic or adipogenic lineage is regulated by mitogen-activated protein kinase.
abstract: Adult human mesenchymal stem cells are primary, multipotent cells capable of differentiating to osteocytic, chondrocytic, and adipocytic lineages when stimulated under appropriate conditions. To characterize the molecular mechanisms that regulate osteogenic differentiation, we examined the contribution of mitogen-activated protein kinase family members, ERK, JNK, and p38. Treatment of these stem cells with osteogenic supplements resulted in a sustained phase of ERK activation from day 7 to day 11 that coincided with differentiation, before decreasing to basal levels. Activation of JNK occurred much later (day 13 to day 17) in the osteogenic differentiation process. This JNK activation was associated with extracellular matrix synthesis and increased calcium deposition, the two hallmarks of bone formation. Inhibition of ERK activation by PD98059, a specific inhibitor of the ERK signaling pathway, blocked the osteogenic differentiation in a dose-dependent manner, as did transfection with a dominant negative form of MAP kinase kinase (MEK-1). Significantly, the blockage of osteogenic differentiation resulted in the adipogenic differentiation of the stem cells and the expression of adipose-specific mRNAs peroxisome proliferator-activated receptor gamma2, aP2, and lipoprotein lipase. These observations provide a potential mechanism involving MAP kinase activation in osteogenic differentiation of adult stem cells and suggest that commitment of hMSCs into osteogenic or adipogenic lineages is governed by activation or inhibition of ERK, respectively.
authors.affiliation: Osiris Therapeutics Inc., Baltimore, Maryland 21231, USA.
authors.forename: R K
authors.initials: RK
authors.lastname: Jaiswal
authors.forename: N
authors.initials: N
authors.lastname: Jaiswal
authors.forename: S P
authors.initials: SP
authors.lastname: Bruder
authors.forename: G
authors.initials: G
authors.lastname: Mbalaviele
authors.forename: D R
authors.initials: DR
authors.lastname: Marshak
authors.forename: M F
authors.initials: MF
authors.lastname: Pittenger
mesh_terms: D000273:Adipose Tissue / Q000166:cytology*; D000328:Adult; D001483:Base Sequence; D001842:Bone and Bones / Q000166:cytology*; D002454:Cell Differentiation; D019070:Cell Lineage; D017931:DNA Primers; D006801:Humans; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010012:Osteogenesis; D015398:Signal Transduction; D013234:Stem Cells / Q000166:cytology*
chemical_list: D017931:DNA Primers; D020928:Mitogen-Activated Protein Kinases