Effects of low-intensity pulsed ultrasound on fracture healing and caveolin-1 gene expression in the radius defects of rabbits / 复旦学报（医学版）

ABSTRACT

Objective To explore the effect of low-intensity pulsed ultrasound (LIPUS) on long bone fracture healing and to examine caveolin-1 gene expression in the radius defects of rabbits.Methods A total of 24 New Zealand rabbits with 3-mm bone defects at lower 1/3 in both radii were randomly assigned to 4 groups (n=6).Daily LIPUS treatment was performed to the right fracture sites at a intensity of 30 mW/cm2 for 20 minutes,while the left sites received sham treatment with power off.To assess the effects of LIPUS on bone defects,X-ray imaging and hematoxylin-eosin staining were applied 7,14,21,28 days after the surgery.Additionally,the immunohistochemical staining was used to determine the subcllular localization of caveolin-1 and semi-quantify the caveolin-1 level,qPCR was performed to detect the mRNA level of caveolin-1,gene Col2a1 and Col10a1,and osteocalcin.Results On day 14,the radiological score of the right radii and mineralized callus area were significantly higher than that of the left ones,both of them were elevated with time flied.Histological examination suggested that the differentiation and apoptosis of chondrocytes along with the formation and bridging of the bone trabeculas appeared earlier in the right radius defects.The immunohistochemical staining showed that on day 7 and 14,the level of caveolin-1 increased with the proliferation and differentiation of condrocytes,and was significantly higher in callus tissues on the right sites.On day 21 and 28,the mesenchymal stem cells migrated to the surface of cartilage matrix started to differentiate into osteoblasts,the level of caveolin-1 decreased,and was significantly lower on the right sites.The result of qPCR indicated that compared with the left sites the caveolin-1 gene expression on the right sites was significantly higher on day 7,while significantly lower on day 21.The mRNA expression levels of Col2a1,Col10a1 and osteocalcin on the right sites were significantly higher on day 7 and 14,but they were significantly lower on day 21 and 28,except for Col10a1 on day 28.Conclusions Advancing endochondral ossification is considered to be a crucial mechanism during long bone fracture healing promoted by LIPUS.The caveolin-1 gene expression first increased in the chondrocytes then decreased in the mesenchymal stem cells during the process.