Denervation of muscle results in a rapid and programmed loss of muscle size and function known as muscular atrophy. It is generally considered that muscle function is irretrievable after prolonged denervation (6 to 12 months) despite re-acquisition of innervation. This prolonged denervation results in a decrease in the number of muscle stem cells, which is detrimental to restoring muscle regeneration after innervation. Previous studies suggested that muscular atrophy is the result of protein homeostasis deficiency, and some studies have suggested that this process is related to the apoptosis of muscle cells. The mechanism of apoptosis is still unclear, and the molecular mechanism controlling the imbalance of protein synthesis and degradation pathways in denervation muscle atrophy remains to be explored. Many studies have explored the inhibition of muscle atrophy: resveratrol has anti-aging effects and can relieve metabolic disorders, and it can significantly prevent muscle atrophy after denervation in mice; NF-κB targeted drugs have been used in the treatment of denervation muscular atrophy to delay muscle atrophy, inhibiting apoptosis by inhibiting the classical NF-κB signaling pathway; In the study of Schilling et al., denervated muscular atrophy treated by injection of the allogenic ADSC, showed a decrease in inflammatory factors and achieve delay muscular atrophy. The treatment we have chosen is also intended to delay muscle atrophy by promoting the regeneration of muscle stem cells and acting anti-inflammation.
Human adipose stem cells have low immunoantigenicity, due to their great commercial value, hADSC has been applied in animal experiments to expand their clinical adaptability[20, 21]. We selected hADSC for injection and further explored it based on Schilling's study. After analyzed by two-way ANOVA, it was found that the hADSC group delayed muscle atrophy was manifested in muscle wet weight and muscle fiber area in 4 weeks after surgery. This may suggest that hADSC needs a certain period time to play a role in the muscle, which is consistent with Schilling's view that ADSC needs to overcome the trauma of injection and take a period of time to show its regenerative effect. The results of our study also showed that the effect of the hADSC group and the combined group was similar, which also suggested that hADSC might be the key factor in the treatment, while PRP injection had little effect on the results.
Platelet-rich plasma (PRP) is a useful treatment method used in orthopedics, oral surgery, plastic surgery, dermatology and other medical fields[22–25]. PRP is an autoserum containing a high concentration of platelets and growth factors. α particles in platelets are responsible for promoting stem cell regeneration and soft tissue remodeling. PRP particles contain many basic growth factors, such as platelet-derived growth factor, vascular endothelial growth factor, epithelial growth factor, transforming growth factor, insulin-like growth factor, etc.[26, 27]. These growth factors are also thought to induce cell proliferation, angiogenesis, and chemotaxis, and also contain serotonin, dopamine, histamine, adenosine, and calcium, all of which increase cell membrane permeability. Studies have shown that platelet-rich plasma can promote the recovery of arthritis models induced by pro-inflammatory cytokines with the assistance of collagen protein, showing certain anti-inflammatory ability. A study by Bendinelli et al. showed that platelet-rich plasma may exert an anti-inflammatory effect on human chondrocytes through the mechanism of NF-κB inhibition by HGF. Previous studies have found that ADSCs can inhibit denervation muscular atrophy by inhibiting inflammatory response. Therefore, we wanted to inhibit denervation atrophy by injecting PRP, and play the role of PRP in inhibiting inflammation and promoting cell regeneration. Meanwhile, PRP has a variety of growth factors, which can induce the proliferation of stem cells. We also hope that PRP can delay muscle atrophy by inducing the proliferation of muscle stem cells. In our results, the walking analysis showed that sciatic nerve function had not been restored, eliminating the impact of nerve regeneration on muscle. The wet weight of the gastrocnemius muscle in the PRP injection group increased 4 weeks after operation compared with that in the PBS group and the difference was statistically significant. However, there was no increase in the area of single muscle fiber, which may indicate that PRP injection may not delay the atrophy of muscle fiber to achieve weight increase, but may increase the weight of other tissues, or some substances may not be fully metabolized after PRP injection. But the specific reasons may need further research.
Our study has several limitations. First, we just observed four weeks, the long-term prognosis is unclear. If we want to understand the long-term outcome, the trial period can be extended. Finally, we only carried out animal experiments and did not explore the mechanism further. Future studies are needed to unravel these limitations.
In conclusion, hADSCs injection may delay muscular atrophy after sciatic nerve injury in rats, and PRP injection has little effect on delaying muscular atrophy after sciatic nerve injury in rats.