Background Ectonucleotide pyrophosphatase/phosphodiesterase (ENPP)-1 is a membrane-bound protein that catalyzes the hydrolysis of extracellular nucleoside triphosphates to monophosphate and extracellular inorganic pyrophosphate (ePPi).Mechanical stimulation regulates ENPP-1 expression.This study sought to investigate the changes in ENPP-1 expression after stimulation using cyclic mechanical tension (CMT).Methods Rat end-plate chondrocytes were cultured and subjected to CMT (at 3％,6％,and 9％ elongation) for 20,40,and 60 minutes to observe changes in the expression of ENPP-1.To investigate the pathway,end-plate chondrocytes were exposed to 10 ng/ml of transforming growth factor beta 1 (TGF-β1),TGF-β1 siRNA,or a specific extracellular signalregulated kinase (ERK)1/2 inhibitor,U0126,in addition to CMT.Changes in ENPP-1 expression were measured by reverse transcription PCR (RT-PCR) and West blotting.Results We observed the largest increase in ENPP-1 expression following 3％ elongation CMT stimulation.ENPP-1 expression was also increased when end-plate chondrocytes were exposed to 10 ng/ml of TGF-β1,but decreased after TGF-β31 knockdown with siRNA.ERK1/2 phosphorylation was activated after 3％ elongation for 40 minutes,and the stimulatory effect of TGF-β31 on ENPP-1 mRNA and protein expression was inhibited by the suppression of the ERK1/2 pathway using U0126.Conclusion CMT increases the expression of ENPP-1 in end-plate chondrocytes in a manner likely dependent on TGF-β1 induction by the ERK1/2 signaling pathway.