NMDA enhances stretching-induced differentiation of osteoblasts through the ERK1/2 signaling pathway.
Activation of the excitatory neurotransmitter N-methyl-d-aspartate (NMDA) and stretching both increase Ca(2+) influx in osteoblastic cells. We postulated that NMDA would enhance the osteoblastic cell's response to stretching. The goal of this study was to investigate, in the presence of the neurotransmitter NMDA, the effect of mechanical loading on osteoblast's stage of differentiation and the mitogen-activated protein kinase (MAPK) signaling pathway associated with it. Rat primary osteoblastic cells were subjected to cyclic, equibiaxial stretch for 48 h in the presence or absence of NMDA. Pretreatment with 0.5 mM NMDA significantly enhanced the stretching magnitude-dependent increase in osteogenesis markers. MK801, an antagonist of NMDA receptors, abolished those responses. To further study the mechanism of this response, osteoblastic cells were stretched for 5, 15, or 60 min in the absence of NMDA. Cyclic stretch induced a rapid increase in extracellular signal-regulated kinase ERK1/2 phosphorylation with the peak at 15 min, but no changes were noted in p38 and JNK pathway signaling. NMDA could enhance ERK1/2 phosphorylation stimulated by stretching. U0126, an inhibitor of ERK1/2, blocked the increase in osteogenesis markers. In conclusion, the current study demonstrates that there is a synergistic effect between mechanical stimulation and NMDA in osteoblasts. ERK1/2 signaling may be the common pathway in the increased response to stretching in the presence of NMDA in osteoblastic cells.
Department of Endocrine and Metabolic Diseases, Ruijin Hospital, Shanghai Jiaotong University School of Medicine, Shanghai, PR China. shirleylee1220@sjtu.edu.cn
Jie-Li
JL
Li
Bin
B
Cui
Li
L
Qi
Xiao-Ying
XY
Li
Lian-Fu
LF
Deng
Guang
G
Ning
Jian-Min
JM
Liu
D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D002454:Cell Differentiation; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology*; D020935:MAP Kinase Signaling System; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism*; D008954:Models, Biological; D016202:N-Methylaspartate / Q000494:pharmacology*; D010006:Osteoblasts / Q000378:metabolism*; D015675:Osteocalcin / Q000378:metabolism; D010766:Phosphorylation; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction
D018690:Excitatory Amino Acid Agonists; D015675:Osteocalcin; D016202:N-Methylaspartate; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D000469:Alkaline Phosphatase