Osteoblast differentiation and mature gene regulation inside femoral head with steroid-induced osteonecrosis in response to mechanical stress stimulation

Abstract

Objective To study dynamic changes of gene expressions and protein synthesis of Runx2 (runt-related transcription factor-2), Osterix, osteocalcin and AJ18 inside the femoral head with steroid-induced osteonecrosis after mechanical stress stimulation in rats. Methods A total of 50 Wistar rats (half male in sex) weighing 250-270 g (mean 260 g) were involved in this study and randomly divided into experimental group (40 rats) and normal group (10 rats). The rats in experimental group were injected with dexamethasone (20 mg/kg) via bilateral gluteus maximus alternatively once a week and then trained on laboratory animal treadmill twice weekly to make rat model of femoral head necrosis. After identifying the successfully induced model by Hematoxylin and eosin stain, glucocorticoid injection was ceased and the experimental group was randomly divided into model control group, 4 weeks, 6 weeks, 8 weeks groups after hormone training stopped. Then, total RNA and total protein were extracted from femoral head for detecting dynamic changes of genes expressions and proteins synthesis of Runx2, Osterix, osteocalcin and A J18 after mechanical stress stimulation inside the femoral head with steroid-induced osteonecrosis by means of real-time quantitative PCR and Western blot assay. Results In 4 weeks, 6 weeks, 8 weeks groups after hormone training stopped, the gene expressions and proteins synthesis of Runx2, Osterix and osteocalein were reduced more significantly compared with model control group, mBNA expression values of Runx2, Osterix and osteoealcin were 0. 1809, 0. 1639, 0. 1374 and 0. 4219, 0. 3026, 0.2652 and 0. 2857, 0.2027, 0. 1583 times of those in model control group. The expressions of Runx2, Osterix and osteocalcin showed a downward trend with time. The mBNA expression and protein synthesis of AJ18 at 4th, 6th and 8th weeks after hormone training stopped were 2.6391,4. 2718 and 5. 3165 times of model control group. Conclusions In addition to hormonal factors, inappropriate mechanical stress inhibits expressions and proteins synthesis of Runx2, Osterix and osteocalcin, while the expression and protein synthesis of AJ18 are upgraded in early steroid-induced femoral head necrosis in rats. Key words: Femur head necrosis; Dexamethasome; Gone expression regulation; Rats; Wistar