Abstract: Objective: To investigate the protective effects of erythropoietin derived peptide, also known as spiral B surface peptide (HBSP), on kidney and aggregated proteins (Agrin) levels in acute skeletal muscle strain rats. Methods: Forty SPF grade SD male rats were randomly divided into control group, injury group, HBSP group and EPO group, with 10 rats in each group. Acute skeletal muscle strain animal models were established except the control group. After successful modeling, the rats in HBSP group and EPO group were intraperitoneally injected with 60 μg/kg HBSP and 5 000 U/kg recombinant human erythropoietin (rhEPO), and the rats in the control group and the injured group were intraperitoneally injected with 0.9% normal saline. Renal function was monitored with relevant kits; Hematoxylin-eosin staining was used to observe the pathological morphology of kidney tissue and skeletal muscle strain tissue. The apoptosis rate of renal tissue cells was detected by in situ terminal transferase labeling (TUNEL). Western blot and quantitative polymerase chain reaction (Q-PCR) were used to determine the expressions of Agrin and muscular-specific kinase (MuSK) in the injured skeletal muscle of rats in each group. Results: Compared with the control group, the renal function indexes serum creatinine (Cr), urea nitrogen (BUN) and 24 h urinary protein (UP24) levels of rats in injured group were increased (P＜ 0.05), but the levels of BUN, Cr and UP24 of rats in HBSP group were decreased (P＜0.05). Compared with HBSP group, there were no significant differences in the above indexes in EPO group (P＞0.05). In the control group, the muscle fiber structure was intact, the shape and structure of the fiber bundles were normal, and there was no infiltration of red blood cells and inflammatory cells in the interstitium, and no fibrohyperplasia. In the injured group, the muscle tissue showed sparse and irregular arrangement, and the interstitial widened with a large number of inflammatory cells and red blood cell infiltration. Erythrocytes and inflammatory cells were reduced in HBSP group and EPO group, and the transverse and longitudinal lines of muscle were clear. The glomerular structure of the rats in the fibrohyperplasia control group was intact and no lesions were observed. In the injured group, glomerular hypertrophy and significant matrix hyperplasia were observed, as well as the expansion of renal cysts with vacuolar and significant inflammatory infiltration were observed, and the inflammatory infiltration was reduced in the HBSP and EPO groups. Glomerular hypertrophy and hyperplasia were alleviated. The apoptosis rates of kidney cells in control group, injured group, HBSP group and EPO group were (4.05±0.51) %, (26.30±2.05) %, (14.28±1.62) % and (16.03±1.77) %, respectively, and there were significant differences among these groups (P＜0.05). Compared with control group, the levels of Agrin and MuSK in skeletal muscle pulled tissue were significantly decreased (P＜0.05), and those of HBSP group and EPO group were significantly increased compared with injured group (P＜0.05), but there was no significant difference between HBSP group and EPO group (P＞0.05). Conclusion: Erythropoietin derived peptide (HBSP) has obvious intervention effects on renal function injury in rats with acute skeletal muscle strain, and its mechanisms may be related to reducing the apoptosis rate of renal tissue cells and activating Agrin and MuSK expression.

Key words: acute skeletal muscle strain, erythropoietin derived peptide, renal function, aggregated proteins, rats