The Promotive Effects of PTHrP on the Union of Femoral Shaft Fracture in a Mouse Model

Abstract

In order to explore the effects of PTH-related peptide on fracture healing in mice, the intervention effects and mechanism of action of PTH-related peptide on femoral shaft fracture models in mice of different genotypes were analysed to obtain a new approach for promoting the healing fractures clinically. A total of 32 8-week old PTH-related peptide wild-type and PTH-related peptide gene knockout heterozygous (PTH-related peptide +/-) mice were selected as the test system and standard femoral shaft fracture mouse models were constructed by intramedullary wire fixation. After model construction, all mice were randomly divided into the wild type control, the PTH-related peptide +/- control, the wild type treated and the PTH-related peptide +/- treated groups, with 8 mice in each group. Mice in both treated groups were administered with 80 μg/kg/day of PTH-related peptide (1-34) subcutaneously and the control groups received subcutaneous injections of saline. After 2 weeks, all mice were sacrificed and the fractured right femur of each mouse in each group was taken for X-ray examination and micro-CT scan to observe the union of the fracture. Next, the formed callus tissues were paraffin-embedded and stained to analyse and compare the bone formation changes of osteoblasts in the fracture sites of mice. Compared to the wild-type group, the saline-treated mice in the PTH-related peptide +/- group had clear fracture lines with callus volume and bone mineral density significantly reduced; after PTH-related peptide treatment, the fractures in the PTH-related peptide +/- group were tightly connected and a large number of osseous calluses were formed; in addition, the density of the callus was higher, which was significantly different from those in the control group (p<0.05). Compared to the wild-type group, the area of cartilage callus of the saline-treated PTH-related peptide +/- group increased by 97 % (p<0.05); after PTH-related peptide administration, the total callus area and osseous callus area increased significantly, while the area of cartilage osseous significantly decreased compared to the control group and after PTH-related peptide administration, the number of osteoblasts and the percent positive area of collagen I in mice were significantly increased compared to the control group. In conclusion, endogenous PTH-related peptide deficiency could lead to delayed healing of fracture, which could be compensated by PTH-related peptide administration, thereby accelerating the formation of calluses and promoting fracture healing in mice.