Functional Recovery of Completely Denervated Muscle: Implications for Innervation of Tissue-Engineered Muscle

Abstract

Tissue-engineered muscle has been proposed as a solution to repair volumetric muscle defects and to restore muscle function. To achieve functional recovery, engineered muscle tissue requires integration of the host nerve. In this study, we investigated whether denervated muscle, which is analogous to tissue-engineered muscle tissue, can be reinnervated and can recover muscle function using an in vivo model of denervation followed by neurotization. The outcomes of this investigation may provide insights on the ability of tissue-engineered muscle to integrate with the host nerve and acquire normal muscle function. Eighty Lewis rats were classified into three groups: a normal control group (n = 16); a denervated group in which sciatic innervations to the gastrocnemius muscle were disrupted (n = 32); and a transplantation group in which the denervated gastrocnemius was repaired with a common peroneal nerve graft into the muscle (n = 32). Neurofunctional behavior, including extensor postural thrust (EPT), withdrawal reflex latency (WRL), and compound muscle action potential (CMAP), as well as histological evaluations using alpha-bungarotoxin and anti-NF-200 were performed at 2, 4, 8, and 12 weeks (n = 8) after surgery. We found that EPT was improved by transplantation of the nerve grafts, but the EPT values in the transplanted animals at 12 weeks postsurgery were still significantly lower than those measured for the normal control group at 4 weeks (EPT, 155.0 -38.9 vs. 26.3 -13.8 g, p < 0.001; WRL, 2.7 -2.30 vs. 8.3 -5.5 s, p = 0.027). In addition, CMAP latency and amplitude significantly improved with time after surgery in the transplantation group ( p < 0.001, one-way analysis of variance), and at 12 weeks postsurgery, CMAP latency and amplitude were not statistically different from normal control values (latency, 0.9 -0.0 vs. 1.3 -0.7 ms, p = 0.164; amplitude, 30.2 -7.0 vs. 46.4 -26.9 mV, p = 0.184). Histologically, regeneration of neuromuscular junctions was seen in the transplantation group. This study indicates that transplanted nerve tissue is able to regenerate neuromuscular junctions within denervated muscle, and thus the muscle can recover partial function. However, the function of the denervated muscle remains in the subnormal range even at 12 weeks after direct nerve transplantation. These results suggest that tissue-engineered muscle, which is similarly denervated, could be innervated and become functional in vivo if it is properly integrated with the host nerve.

Engineered Skeletal Muscle Units for Repair of Volumetric Muscle Loss in the Tibialis Anterior Muscle of a Rat

“…33 Of particular interest is the innervation and formation of neuromuscular junctions, an obstacle to tissue engineering strategies for muscle repair, and a critical step for contractile control of engineered muscle graft tissue. 34 Our immunohistochemical stains show numerous nerve fibers branching from the grafted nerve into our engineered muscle, with individual nerve branches extending throughout the grafted region and terminating at clusters of acetylcholine receptors, demonstrating the in vivo development of neuromuscular junctions within the SMUs.…”

“…34 Past studies in our lab have also demonstrated that reinnervation of the rat medial gastrocnemius muscle after denervation is an extensive process that may require over 3 months before maximum recovery is achieved. 35 Thus, despite the promising innervation and neuromuscular junction formation observed in our SMUs, it is likely that their neuromuscular interfaces had not yet fully matured after only 28 days in vivo.…”

Tissue Engineering and Regenerative Medicine: Recent Innovations and the Transition to Translation

“…36 Investigators have also begun to explore how such tissues can be re-enervated, for example in skeletal muscle preparations, guiding both vascular health as well as neural connectivity to the host. 37 These and other publications support the growing interest and increasing complexity in organ/native ECMbased tissue replacement approaches.…”

Synergizing Engineering and Biology to Treat and Model Skeletal Muscle Injury and Disease

“…The formation of NMJs and improved force generation have been reported for engineered muscles that were implanted around a femoral nerve (123), and motor function in denervated muscle has been recovered through transplantation of a peroneal nerve (124) or stem cell–derived motor neurons (125). Although in vitro coculture of engineered rodent muscle and motor neurons can yield the formation of functional NMJs and enhance force production (74–76, 126), it is not clear that composite muscle–nerve constructs, although more complicated to produce, would add any benefit in vivo compared with the use of muscle-only constructs.…”