Initial Contribution Of Low-Level-Laser-Therapy To Osteoblastic Cells Undering Tension Stimuli In Vitro And Its Signal Transduction

Orthodontic treatment is related to the forces acting on the teeth and other structures. Within the dentoalveolar systems the principle changes resulting from the forces are seen,but the forces can also influence other structure,such as temporomnadibular and joint area sutures. Both modeling and remodeling are modulated by the interaction of metabolic and mechanical signals. It is important to study the biological response and mechanism of the osteoblast to the mechanical stretching strain because these changes in mechanical stimulus modulate bone mass and architecture mainly through the osteoblast. There are many studies about the late biological responses of osteoblast to stretching stress , but the results are different. In order to understand the initial responses involved in mechnao-transduction,it is necessary for us to examine the effect of stretching mechanical strain.Low level laser(LLL) is a kind of visible light with the wavelength between 600~950 nm,sometimes it is also called weak laser,soft laser,cold laser, and so on. LLL can offer the output power below 250 mW and is characterized by its monochromatism.Furthermore it not only has heat effect,but also biochemical effects, which could not result in irreversible damage to bio-tissue. It just likes the effect obtained by physical factors such as a puncture and moxibustion,so that is called"biostimulation", or"photo-biomodulation". The corresponding therapy is called low-level-laser-therapy (LLLT). There are many areas where LLLT could play an important role on our medical workers. There are many study about the positive effects of LLLT on bone fomation and rebuilding,but there are still several studies confirmed that LLLT has no effect on osteoblast and bone rebuilding.Now, LLLT is still not a widely acceptable therapy, therefore,it is necessary to verify the efficacy to osteoblast of LLLT more experiments.Osteoblastic cells MG-63 were subjected to the mechanical strain by a four-point bending system(ZL01256849.X) at 0.5 Hz. The cells were loaded with tension stress at 3000μstrain and then subjected to LLLT.①The cell cycle, apoptosis of MG-63 were measured by flow cytometry (FCM)and the ALP of MG-63 were measured by spectro photometer.②To investigate the effect of LLLT on mRNA and protein expression of col I and OPN of MG-63 undering tension stimulus in vitro and to detect the effect of LLLT on ECMP and the mechanism of LLLT.③To investigate the changes of intracelluler calcium concentration when osteoblasts undering stretching responded to LLLT.Result:1. The Four-point Bending System can exert a physiologic magnitude tension strain on osteoblastic cells MG-63 in vitro. Before and after physiological stresses,the osteoblast adhesion and growth status are very well, But after loading over physiological level,the cells fell off and even go to death.2. Compared to a control group, stretching strain groups present less G1-stage cells ,more S-stage cells and higher proliferation index (PI,PI=S+G2/ G1+S+G2) (P<0.05). Laser-strain groups present more G2-stage cells than the other two groups(P<0.05). Compared to stretching strain group, the apoptosis rates in laser-strain groups are lower (P<0.05). The expression of ALP in laser-strain groups and stretching strain group are higher than that in control group(P<0.01).and the The expression of ALP in laser-strain groups is higer than that in stretching strain group (P< 0.05).3. With RT-PCR method and western blot ,the expression of collagen I and OPN in laser-strain group and stretching strain group are higher than that in control group(P<0.05).And the expression of collagen I and OPN in laser-strain group are higher than that in stretching strain group(P<0.05).4. Concentration of the intracellular calcium ion in laser-strain groups are higher than that in strain group(P < 0.05) . Concentration of the intracellular calcium ion in laser-strain groups increase gently in stead of'jump'in stretching strain group.In conclusion,LLLT may have a positive effect on MG-63 undering stretching strain in vitro, for instance, promoting proliferation and differentiation and expressing col I and OPN. The intracelluler calcium plays an important role in cell mechaotransduction and responses to LLLT . LLLT could regulate the rhythm of increasing concentration of the intracellular calcium ion and make it gently.These results obtained by this paper can provide a theory supporting for clinical applications of LLLT.