MEK/ERK and p38 MAPK regulate chondrogenesis of rat bone marrow mesenchymal stem cells through delicate interaction with TGF-beta1/Smads pathway.
OBJECTIVE
This study was carried out to reveal functions and mechanisms of MEK/ERK and p38 pathways in chondrogenesis of rat bone marrow mesenchymal stem cells (BMSCs), and to investigate further any interactions between the mitogen-activated protein kinase (MAPK) and transforming growth factor-beta1 (TGF-beta1)/Smads pathway in the process.


METHODS
Chondrogenic differentiation of rat BMSCs was initiated in micromass culture, in the presence of TGF-beta1, for 2 weeks. ERK1/2 and p38 kinase activities were investigated by Western Blot analysis. Specific MAPK inhibitors PD98059 and SB20350 were employed to investigate regulatory effects of MEK/ERK and p38 signals on gene expression of chondrocyte-specific markers, and TGF-beta1 downstream pathways of Smad2/3.


RESULTS
ERK1/2 was phosphorylated in a rapid but transient manner, whereas p38 was activated in a slow and sustained way. The two MAPK subtypes played opposing roles in mediating transcription of cartilage-specific genes for Col2alpha and aggrecan. TGF-beta1-stimulated gene expression of chondrogenic regulators, Sox9, Runx2 and Ihh, was also affected by activity of PD98059 and SB203580, to different degrees. However, influences of MAPK inhibitors on gene expression were relatively minor when not treated with TGF-beta1. In addition, gene transcription of Smad2/3 was significantly upregulated by TGF-beta1, but was regulated more subtly by treatment with MAPK inhibitors.


CONCLUSIONS
MAPK subtypes seemed to regulate chondrogenesis with a delicate balance, interacting with the TGF-beta1/Smads signalling pathway.
Li
J
J
State Key Laboratory of Oral Diseases, West China College of Stomatology, West China Hospital of Stomatology, Sichuan University, Chengdu, China.
Zhao
Z
Z
Liu
J
J
Huang
N
N
Long
D
D
Wang
J
J
Li
X
X
Liu
Y
Y
D053674:Aggrecans / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D001853:Bone Marrow / Q000378:metabolism; D002454:Cell Differentiation; D019902:Chondrocytes / Q000166:cytology / Q000378:metabolism; D020219:Chondrogenesis / Q000502:physiology*; D015870:Gene Expression; D007093:Imidazoles; D059630:Mesenchymal Stem Cells / Q000378:metabolism*; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D011725:Pyridines; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction; D051899:Smad2 Protein; D053773:Transforming Growth Factor beta1 / Q000378:metabolism* / Q000494:pharmacology*; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism* / Q000494:pharmacology
D053674:Aggrecans; D007093:Imidazoles; D011725:Pyridines; C497782:SMAD2 protein, human; D051899:Smad2 Protein; D053773:Transforming Growth Factor beta1; D048051:p38 Mitogen-Activated Protein Kinases; D020929:Mitogen-Activated Protein Kinase Kinases; C093642:SB 203580