Studies On The Mechanism Of Promoting Action Of Low Frequency Pulsed Electromagnetic Fields On Bone Formation Through CAMP/PKA And P38 MAPKs Signal Pathway

Osteoporosis is a kind of common bone disease, which is characterized by the decrease of bone mass and the degradation of bone microstructure, and these lead to the increased risk of fracture, eventually. With the coming era of aging in our country, osteoporosis has already become a chronic disease which seriously affects the life quality of middleaged and old people. Numerous studies have shown that low frequency electromagnetic fields can increase bone mineral density and improve biomechanical property of laboratory animals while retard the loss of bone mass and increase the bone mineral deposition. Furthermore, low frequency electromagnetic fields has a series of advantages: non-invasive, little toxic and side effect, easy to use and so on. Through the effect of low frequency electromagnetic fields on the treatment of osteoprosis has been proved, and used in clinical therapeutics, the specific mechanism of it is still not very clear. Our previous research has shown that 50 Hz 0.6m T low frequency pulsed electromagnetic fields can promote the maturation and mineralization of rat calvarial osteoblast. This paper will explore the molecular mechagnism of bone formation stimulated by it from the following aspects, which will provide a reliable theoretical basis for the clinical application of pulsed eletromagnetic fields.Initially, we monitored the changes of osteogenic related fators after pulsed electromagnetic field treatment. The results showed the gene transcription and protein expression changed immediately after treatment, and the expression of protein slightly lagged behind the gene transcription, these signified that pulsed electromagnetic fields has the genomic effects in bone remodeling. However, the alkaline phosphatase achieved maximum activity at 3 hours after pulsed electromagnetic field treatment, the gene transcription of it began to elevate at 6 hours, activity changes prior to genes transcription, these revealed the nongenomic effects is also exsit.Next, we investigated whether c AMP/ PKA signal pathway was involved in the promoting action of low frequency pulsed electromagnetic fields on bone formation. The results exbited the concentration of c AMP rised obviously, the level of phosphorylated PKA also increased and presented a phenomenon of nuclear translocation, these illustrated pulsed electromagnetic fields activates the c AMP/PKA signal pathway. When using DDA and KT5720, the inhibitor of adenylate cyclase and PKA, respectively, the rise of osteogenic indicators such as the activity of alkaline phosphatase, the osteogenic gene transcription and protein expression, the number and area of calcified nodules returned to the control level after pulsed electromagnetic field treatment, these demonstrated that c AMP/PKA signal pathway is necessary for the bone formation advanced by low frequency pulsed electromagnetic fields.Further, we questioned whether MAPKs signal pathway was activated in the process of bone formation stimulated by low frequency pulsed electromagnetic fields. The results suggested the level of phosphorylated p38 was enhanced, while p-ERK1/2 and p-JNK1/2 were not, and the rise of the activity of alkaline phosphatase, the number and area of positive clone of alkaline phosphatase and calcified nodules regressed after pulsed electromagnetic field treatment when using SB202190, an inhibitor of p38. These mean that p38 MAPKs signal pathway is essential for the bone formation boosted by low frequency pulsed electromagnetic fields.Finally, we explored the relationship between the c AMP/PKA signaling pathway and p38 MAPKs signaling pathway in the process of promoting bone formation by electromagnetic field. The results indicated the highly phosphorylated p38 was dephosphorylation significantly after pretreating the rat calvarial osteoblast with DDA and KT5720, and p-PKA did the same when using SB202190. These implied that the “cross talk” really exists between the c AMP/PKA and p38 MAPKs signal pathway.In conclusion, this paper found 50 Hz 0.6m T PEMFs promptes bone formation through c AMP/PKA and p38 signal pathway for the first time. Furthermore, there is a close correlation between them, these are of great significance to reveal the mechanism of low frequence electromagnetic fields for bone formation.