Expression Of The Associated Proteins In Death Receptor Pathway In Steroid-induced Juvenile Rabbit Model Of Avascular Necrosis Of Femoral Head

ObjectiveTo detect the expressions of Fas, TNFR1, DR3and caspase-8in the tissue of the femoralhead, as well as to explore the main receptor pathway to regulate the apoptosis insteroid-induced juvenile rabbit model of avascular necrosis of femoral head.MethodsForty New Zealand rabbits with2-month-old age were selected, including20male and20female, weighing1.3to1.8kg. They were randomly divided into two groups: the steroidinjection group(SIG)(n=30) and the control group(CG)(n=10). Prednisolone acetate of7.5mg/kg(0.3ml/kg) was injected into each rabbit for the SIG and equal volume saline forthe CG twice a week for eight weeks. X-ray and CT examination were performed at the4thand8thweek after the first injection. All experimental animals were sacrificed after the8thweek, their bilateral femoral head cartilages were collected for histopathological andRT-PCR examination. According to imaging and histopathology results, the SIG wasfurther divided into the disease group(DG) and the non-disease group(NDG). The RT-PCRmethod was used to detect the expressions of Fas, caspase-8, DR3, TNFR1in the femoralheads of DG, NDG, CG and compare the differences among the three groups.Results1.In SIG(n=30), only26rabbits survived in the end. According to imaging and histopatho-logy results,6experimental animals were identified having positive avascular necrosis, theincidence was23.08%(6/26).2.In the SIG, the bone mineral density of femoral heads was increased evenly and thenormal bone texture disappeared. The osteoepiphysis of the femoral heads in the SIG wassmaller and the hip clearance was wider than in the CG. The height of epiphysis in the SIGwas also decreased compared to that in the CG.3.The bone trabeculae became sparser and thinner, some of them were fractured andirregular in SIG. The DG(n=6) appeared osteocyte karyopyknosis, deformation andmargination in bone lacunae, increased empty lacunae, while the NDG(n=20) and CG(n=10) only appeared few lacunae vacancies. At the end of the8thweek, there werestatistical differences at proportion of bone trabeculae between DG/NDG and CG (q=27.35,25.42, P<0.01); the empty lacunae rate of the DG had an extreme difference with that ofany other group (q=10.77,12.53, P<0.01).4.The expression levels of Fas in DG, NDG and CG were (161.58±29.79),(110.89±10.39)and (92.77±14.07). Significant difference was found between DG and CG (t=4.21,P<0.01), but not between NDG and CG (t=2.10, P>0.05). The expression levels of DR3inDG, NDG and CG were (105.43±4.78),(103.12±8.71),(94.55±8.14). The differencebetween the two groups was not statistically significant (t=0.58,1.69,1.54, P>0.05). Theexpression levels of TNFR1in DG, NDG and CG were (118.39±15.25),(103.59±10.4),(93.76±9.49). The difference between the DG and CG was statistically significant (t=2.94,P<0.01). The expression levels of caspase-8in DG, NDG and CG were (153.42±27.56),(115.03±17.1),(92.48±16.43). Significant difference was found between DG and CG(t=3.86, P<0.01).5. The linear regression analysis results showed: under the joint action of Fas, DR3,TNFR1, only the Fas could significantly predict caspase-8, and its regression equation reg-ression got significant effect and could explain68.1%of the variance; while the regressioneffects the DR3and TNFR1to caspase-8were not significant, indicating that the Fas wasthe main influence factor to caspase-8.Conclusion Fas-mediated death receptor pathway might play a major role in theregulation of avascular necrosis.