Recombinant human insulin-like growth factor-1 promotes hyperplasia of muscle fibers of urethral rhabdosphincter in rats by activating satellite cells in situ

Abstract

Objective To observe the activation of satellite cells of urethral rhabdosphincter of Sprague-Dawley (SD) rats after local injetion of human recombinant insulin-like growth factor-1. Methods 20 male SD rats were randomly divided into four groups: control group, and low, medium, and high-dose group (n=5 in each group). Recombinant human insulinlikegrowth factor-1 (rhIGF-1) in doses of 20, 50, 100 μg/μl was locally injected into the urethral wall of rats in low, medium, and high-dose rhIGF-1 group, and the same volume of saline was given to rats in control group. After 4 weeks, the rats were sacrificed. The newly formed myofibers were determined by hematoxylin-eosin (HE) staining and the activation of satellite cells were detected by immunohistochemical staining with satellite cell specific anti-c-Met antibody and anti-pax7 antibody. Results HE staining showed the number of newly formed muscle fibers in control group, 20 μg/μl group, 50 μg/μl group and 100 μg/μl group were (0.82±0.75), (1.33±0.62), (2.00±0.74), (2.67±0.98), respectively; immunofluorescence staining showed the number of pax7 positive muscle fibers were (27.00±2.65), (37.87±9.46), (61.83±11.66), (64.27±9.28), respectively; the mean fluorescence intensity of c-Met were (7.41±2.00), (15.39±4.96), (21.60±4.26), (24.04±3.13), respectively. Compared with control group, new muscle fibers increased significantly in 50 μg/μland 100 μg/μl group (P values were 0.004 and 0.000, respectively). The number of pax7 positive cells also increased significantly in these two groups (P values were 0.000 and 0.000, respectively). However, there was no significant difference between 20 μg/μl group and control group in the number of new muscle fibers and pax7 positive cells (P=0.487 and 0.425, respectively). The mean fluorescence intensity of c-Met in three treated groups were higher than that in control group (P=0.000, 0.000 and 0.000, respectively). Conclusion Local injection of human recombinant insulin-like growth factor-1 in urethral wall activates muscle satellite cells, promoting it to proliferate and differentiate into new muscle fibers, causing the hypertrophy of urethral rhabdosphincter of SD rats. Key words: Recombinant insulin-like growth factor-1; Skeletal muscle satellite cells; Urethral rhabdosphincter