The Effect Of Xiyangcen On MuRF1Expression In A Rat Model Of Denervated Skeletal Muscle Atrophy

Background:Skeletal muscle is the target organ of the peripheral nervous system. Skeletal muscle fibers are highly adaptable to changes in neuromuscular transmission, atrophying in response to denervation and skeletal muscle atrophy induced by denervation is irreversible. Decreases in protein synthesis and increases in protein degradation both have been shown to contribute to muscle protein loss due to disuse, and recent work has delineated elements of both synthetic and proteolytic processes underlying muscle atrophy. It is also becoming evident that ubiquitin-proteasome system (UPS) is involved in muscle proteolysis during atrophy. Several ubiquitin ligases catalyze the transfer of ubiquitin from a carrier protein to UPS substrates, thereby targeting these proteins for degradation by the26S proteasome with a chain of ubiquitin molecules. E3ubiquitin ligases are the key enzyme of these ubiquitin ligases.Although many genes were up-regulated in a single rat model of atrophy, only a small subset was universal in all atrophy models. Bondine et al found that Muscle RING Finger1(MuRF1) was markedly induced in myotubes during atrophy by transcript profiling. Jennifer et al discovered MuRFl expression was upregulated12-to22-fold3days after rat disuse atrophy induced by denervation. The expression of MuRF1maintained high level after7days and returned toward basal levels after14days. Cohen et al observed that atrophying muscles show a loss of myosin-binding protein C (MyBP-C)(3days),myosin light chains1and2(MyLCl and MyLC2) from the myofibril(7-10days) and myosin heavy chain (MyHC)(10days),which selective loss requires MuRF1. Whereas muscle proteolysis would be reduced when the MuRF-1zinc finger structure damaged and mice deficient in MuRF1were found to be resistant to atrophy. These studies surprisingly demonstrate that MuRF-1plays an important role in muscle atrophy and is a potential drug targets for the treatment of muscle atrophy.Chinese medicine Xiyangcen has the effect of bone reinforcement and its main active component is ginsenoside. Recent findings indicate that ginsenoside can retard skeletal muscle atrophy induced by denervation and it is still unclear about the mechanism. Since MuRF-1participates in the degradation of skeletal muscle. Xiyangcen maybe delay skeletal muscle atrophy by affecting MuRF-1expression. This study is to clarify this issue.Objective:To investigate the effect and mechanism of Xiyangcen on MuRF1expression in a rat model of denervated skeletal muscle atrophy.Methods:Fifty-four adult female Wistar rats were randomly divided into three groups:false nerve group (group A, n=6), the denervated gastrocnemius model group (group B, n=24), Xiyangcen treatment group (group C, n=24). The rats in group A is only exposed the sciatic nerve without treatment and recorded as Od. The rats in group B, C rats were cut off the right sciatic nerve and two ends of sciatic nerve were sutured in the muscle membrane after inverted180°. Then the rats in group B were given saline3ml/d by gastric lavage. The rats in group C were given Xiyangcen8pills/d, which dissolved in3ml saline. The rats were killed2、7、14、28d after operation respectively and the right gastrocnemius muscle were retained. The morphological changes of the gastrocnemius muscle tissue were observed with HE staining. The expression of MuRF-1mRNA was detected by Real-time-PCR. The level of MuRF-1protein was determined by Western blot method.Result:(1)Histological analysis of gastrocnemius tissue:The muscle fibers in the false nerve group were integrity. The muscle fibers in the denervated group became thin and the changes are more apparent with the prolonged denervation. Compared with the denervated group, the pathological changes of muscle fibers attenuated in Xiyangcen treatment group.(2) Image analysis of Real-time PCR:Compared with the false nerve group, the expression of MuRF-1mRNA in the denervated group was significantly higher than that of false nerve group at each time point (P<0.05). It reached a peak at2days after the denervation, and then it declined slowly and returned the normal level after28days. The levels of MuRF-1mRNA in Xiyangcen treatment group were significantly lower than those of the denervated group at each time point (P<0.05).(3) Image analysis of western blot:Compared with the false nerve group, the expression of MuRF-1protein in the denervated group was significantly higher than that of false nerve group at each time point (P<0.05). It reached a peak at2days after the denervation, and then it declined slowly and returned the normal level after28days. The levels of MuRF-1protein in Xiyangcen treatment group were significantly lower than those of the denervated group at each time point (P<0.05).Conclusion:MuRF-1showed increased expression in a rat model of denervated skeletal muscle atrophy and Xiyangcen can ameliorate skeletal muscle atrophy by decreasing the expression of MuRF-1.