Preferential and Comprehensive Reconstitution of Severely Damaged Sciatic Nerve Using Murine Skeletal Muscle-Derived Multipotent Stem Cells

Loss of vital functions in the somatic motor and sensory nervous systems can be induced by severe peripheral nerve transection with a long gap following trauma. In such cases, autologous nerve grafts have been used as the gold standard, with the expectation of activation and proliferation of graft-concomitant Schwann cells associated with their paracrine effects. However, there are a limited number of suitable sites available for harvesting of nerve autografts due to the unavoidable sacrifice of other healthy functions. To overcome this problem, the potential of skeletal muscle-derived multipotent stem cells (Sk-MSCs) was examined as a novel alternative cell source for peripheral nerve regeneration. Cultured/expanded Sk-MSCs were injected into severely crushed sciatic nerve corresponding to serious neurotmesis. After 4 weeks, engrafted Sk-MSCs preferentially differentiated into not only Schwann cells, but also perineurial/endoneurial cells, and formed myelin sheath and perineurium/endoneurium, encircling the regenerated axons. Increased vascular formation was also observed, leading to a favorable blood supply and waste product excretion. In addition, engrafted cells expressed key neurotrophic and nerve/vascular growth factor mRNAs; thus, endocrine/paracrine effects for the donor/recipient cells were also expected. Interestingly, skeletal myogenic capacity of expanded Sk-MSCs was clearly diminished in peripheral nerve niche. The same differentiation and tissue reconstitution capacity of Sk-MSCs was sufficiently exerted in the long nerve gap bridging the acellular conduit, which facilitated nerve regeneration/reconnection. These effects represent favorable functional recovery in Sk-MSC-treated mice, as demonstrated by good corduroy walking. We also demonstrated that these differentiation characteristics of the Sk-MSCs were comparable to native peripheral nerve-derived cells, whereas the therapeutic capacities were largely superior in Sk-MSCs. Therefore, Sk-MSCs can be a novel/suitable alternative cell source for healthy nerve autografts.创伤后伴长间隙的重度周围神经横断伤，可引发躯体运动与感觉神经系统的重要功能丧失。此类病例中，自体神经移植（autologous nerve grafts）一直被视作金标准，其核心机制在于激活并增殖移植物伴随的雪旺细胞（Schwann cells），并依托其旁分泌效应发挥治疗作用。然而，由于不可避免地需要牺牲其他健康组织的功能，可用于采集自体神经移植物的合适供区数量极为有限。为解决这一临床难题，本研究探讨了骨骼肌源性多能干细胞（skeletal muscle-derived multipotent stem cells, Sk-MSCs）作为周围神经再生新型替代细胞源的潜力。将培养/扩增后的Sk-MSCs注射至对应严重神经断离伤的重度挤压坐骨神经损伤部位。术后4周，移植的Sk-MSCs不仅优先分化为雪旺细胞，还可分化为神经束膜/内膜细胞（perineurial/endoneurial cells），并形成髓鞘与神经束膜/神经内膜，包裹再生轴突。同时观察到血管生成增加，这有助于建立良好的血液供应并促进代谢废物排出。此外，移植细胞可表达关键神经营养因子及神经/血管生长因子mRNA，因此其对供者/受者细胞的内分泌/旁分泌效应也得到了验证。值得注意的是，扩增后的Sk-MSCs在周围神经微环境中的骨骼肌成肌能力显著减弱。在无细胞导管桥接的长神经间隙模型中，Sk-MSCs同样可充分发挥上述分化与组织重构能力，进而促进神经再生与连接。正如小鼠绳梯样步态（corduroy walking）所证实的那样，Sk-MSCs治疗组小鼠实现了良好的功能恢复。本研究还证实，Sk-MSCs的上述分化特性与天然周围神经源性细胞相当，但其治疗效能显著更优。因此，Sk-MSCs可作为健康自体神经移植的新型、合适的替代细胞源。