The Effect Of Tensile Strains On The Rat Chongdrocyte Proliferation And HIF-1a Expression In Vitro

Objectives:To investigate the effect of tensile strains on the proliferation and hypoxia inducible factor-la(HIF-la)expression of spheno-occipital synchondrosis(SOS)chondrocytes cultured in vitro.Methods:The primary chondrocytes separated from the SOS of SD rats’ skull base were cultured and a finite cell line was established in vitro.Dynamic tensile strains of different magnitudes(0,1000μ,3000μ,5000μ strain),as well as different durations(0,0.5,2,6h)were exerted to second generations of cultured chondrocytes using a four-point bending system.Morphological changes of chondrocytes were observed with inversted phase contrast microscope;index of cellular proliferation was calculated using the DNA content at different phase of cell cycle counted with flow cytometry;The expression of genes(HIF1-a、VEGF、SOX9、Collagen Ⅱ、Runx 2、Collagen X)were evaluated by Real-time PCR;Western blot was used to detect and quantify the expression of proteins((HIF1-a、VEGF、SOX9、Collagen Ⅱ).Results:1.Compared with control group(0μ strain),stimulated by tensile strains,the cells stretched and the intercellular gap widened with the increase of strains;the proliferation of chondrocytes of experimental groups were significantly increased(P<0.05),with a peak increment at 1000μ strain.The expression of HIF-1a、Runx 2、SOX9、Collagen Ⅱ genes and proteins were also significantly increased under the 1000μ strain,then,decreased gradually while the strain was increased;The expression of VEGF,Collagen X genes were gragually increased with the increase of tensile strain,and reached the peak at 3000tμ strain,decreased at 5000μ strain.2.The same tensile strain(1000 u strain,0.5Hz)were applied to chondrocytes for different time,as the extension of time,the cells stretched,wider intercellular gap length ered observed;The proliferation of chondrocytes dereased at first,rise again over time;The expression of HIF1-a,Runx2,SOX9,CollagenⅡ,VEGF,Collagen X genes increased and then dereased over time,and the expression reached the peak at the point of 2h,the proteins expression change of HIF-1a,SOX9,Collagen Ⅱ,VEGF was same as gene expression.Conclusions:There are different effect on the proliferation and expression of HIF-1a under different tensile strain.In this study,1000μ strain increased the proliferation and expression of HIF-1a mostly.There are different effect on the proliferation and expression of HIF-1a under the same tensile strain but different time,short or long time go against the effect.HIF-1a may participate in tensile strain on the adjustment of the chondrocytes proliferation,differentiation,and the mechanism is worth further study.