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Neural Engineering

Neuromodulation: Peripheral Nerve Stimulation

Skeletal muscle reprogramming enhances reinnervation after peripheral nerve injury

Thursday, October 24, 2024
4:30 PM – 4:45 PM EST
Location: Room 315

Introduction: Peripheral Nerve Injuries (PNI) affect more than 20 million Americans and severely impact the quality of life by causing long-term disability. The onset of PNI is characterized by nerve degeneration distal to the nerve injury resulting in long periods of skeletal muscle denervation, leading to muscle atrophy and ultimately inability of the muscle to “accept” innervation. We hypothesize that reprogramming the skeletal muscle to an embryonic-like state may preserve its reinnervation capability following PNI. Previous work in our lab has shown that the transcription factor NANOG can rejuvenate skeletal muscle by increasing the number of Pax7+ satellite cells and embryonic myosin heavy chain (eMYHC) in muscle fibers in vivo. These results prompted us to hypothesize that NANOG might reprogram skeletal muscle and improve functional recovery after PNI.

Materials and

Methods: To study the effect of NANOG on skeletal muscle innervation, we generated a mouse model (Col1a1-tetO-Nanog, in the ROSA26 locus, hereafter referred to as N+) in which NANOG expression can be induced upon exposure to doxycycline (Dox) using the slow-release polymer, Elvax for a period of 2 weeks. Elvax implantation was accompanied by sciatic nerve transection and end-to-end repair in both N+ and wild type (WT). WT served as controls. Functional recovery and reinnervation was analyzed using needle electromyography (EMG) recordings, and muscle force was assessed using a force transducer. Molecular level changes in muscle and nerve were assessed by RNA-sequencing, RT-PCR, Western blots and immunohistochemistry.

Results, Conclusions, and Discussions: NANOG expression in the muscle dedifferentiated it to an early-development like state as seen by expression of eMYHC (Fig. A), and induced transcriptional changes to enhance structural integrity of the skeletal muscleand rejuvenate the muscle. In a sciatic nerve transection model, muscle specific NANOG expression led to increased overlap of muscular acetylcholine receptors (AChRs) with neurofilament and synaptic vesicles, indicating efficient synapse formation (Fig. A). The functional recovery after PNI was monitored by measuring toe-spread reflex, which showed significant and consistent improvements in the toe-spread reflex of N+ mice after week 5 post injury (Fig. B). EMG recordings demonstrated that N+ mice elicited almost 3x increase in EMG amplitude as compared to WT mice at 5wks and 16wks post nerve injury, suggesting that improved reinnervation may be the result of re-engineering the muscle to a permissible state (Fig. C). Interestingly, we found that NANOG expression in the muscle prevented atrophy and resulted in increased isometric force production as compared to WT animals (Fig. D). To conclude, while most PNI research focuses on decreasing the time needed for axons to reach their targets, such as artificial nerve scaffolds, our objective is to increase the period during which muscle can be reinnervated and regain full recovery of motor function. In this study, we show that re-engineering the muscle to an embryonic-like state by ectopic NANOG expression can improve functional outcomes after PNI.

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