Effects of exogenous recombinant human basic fibroblast growth factor on the healing of muscles in rats after deep tissue injury of pressure ulcers

Objective To investigate the effect of exogenous recombinant human basic fibroblast growth factor (rhbFGF) on the healing of muscles in rats after deep tissue injury of pressure ulcers. Methods Forty-eight SD rats were randomly divided into normal control group, injury control group, post injury day (PID) 4 group, PID 7 group, PID 14 group, PID 21 group according to the random number table, with 8 rats in each group. The rats in normal control group did not receive any treatment, whereas the rats in the latter 5 groups were established the deep tissue injury of pressure ulcer model on both sides of the gracilis muscle on the hind limb. The rats in injury control group did not receive any treatment after injury, while the rats in the latter 4 groups were given subcutaneous injection of 0.1 mL rhbFGF to the left gracilis in a dosage of 100 μg/mL immediately after injury, and an equal volume of normal saline (NS) was injected to right gracilis, once every other day. The rats in injury control group were sacrificed immediately after injury, and the rats in normal control group were sacrificed at the same time point. The rats in the other 4 groups were sacrificed on PID 4, 7, 14, 21, and the gracilis muscles on both sides were harvested respectively. The morphology of the gracilis muscle was examined after HE staining. The expression of myogenin in the tissues was detected by immunofluorescence method. The levels of muscle structural proteins myosin heavy chain (MyHC), phosphorylated protein kinase B (Akt), and phosphorylated mammalian target of rapamycin (mTOR) were determined by Western blotting. Data were processed with one-way analysis of variance and LSD test. Results (1) In normal control group, the nuclei of graciles cells were in uniform size, and they were closely arranged with clear structure, and there were no significant infiltration of inflammatory cells. In injury control group, the nuclei of graciles cells showed signs of pyknosis, dissolution, fracture and structural disorder. Swelling of muscle cells, inflammation infiltration, structural disorder and other pathological signs of injury phenomena in graciles of PID 4 group, PID 7 group, PID 14 group, PID 21 group after rhbFGF treatment were milder compared with those after NS treatment. In addition, the numbers of regenerated myocytes in graciles of PID 4 group, PID 7 group, PID 14 group, PID 21 group after rhbFGF treatment were higher than those after NS treatment. (2) The numbers of graciles myogenin positive cells in normal control group and injury control group were respectively 28±17 and 42±28. The numbers of graciles myogenin positive cells in PID 4 group, PID 7 group, PID 14 group after NS treatment were 100±50, 196±87, 460±110 respectively, while the numbers of graciles myogenin positive cells in PID 4 group, PID 7 group, PID 14 group after rhbFGF treatment were 174±34, 717±182, 613±122 respectively, and the numbers of graciles myogenin positive cells after rhbFGF treatment were significantly higher than those after NS treatment in each group(P 0.05). The expressions of phosphorylated Akt and phosphorylated mTOR in graciles of normal control group were low, and the expression of phosphorylated Akt in graciles increased in injury control group, while the expression of phosphorylated mTOR in graciles decreased in injury control group. The expressions of phosphorylated Akt and phosphorylated mTOR in graciles of PID 4 group, PID 7 group, PID 14 group, PID 21 group after treatment with rhbFGF showed a trend of elevation in the beginning but declined afterwards. The expressions of phosphorylated Akt and phosphorylated mTOR in graciles of PID 4 group after rhbFGF treatment were significantly lower than those after NS treatment (P<0.05 or P<0.01). The expressions of phosphorylated Akt and phosphorylated mTOR in graciles of PID 7 group, PID 14 group, PID 21 group after rhbFGF treatment were significantly higher than those after NS treatment (P<0.05 or P<0.01). Conclusions Exogenous rhbFGF may effectively facilitate the healing of muscle structure and accelerate the regeneration of muscles in rats after deep tissue injury of pressure ulcers, and its mechanism may be related to the improvement of the expression of myogenin and enhancement of the expression of protein of muscle growth-related signaling pathways. Key words: Muscle development; Fibroblast growth factor 2; Myosin heavy chains; Pressure ulcer; Deep tissue injury; Protein kinase B; Mammalian target of rapamycin