Gene Expression of Acetylcholine Receptor Subunits and Myogenic Regulatory Factors Following Peripheral Nerve Injury

Peripheral nerve lesions cause impairment to both sensory and motor function. Motor functional recovery correlates with the gene expression of specific nicotinic acetylcholine receptor (nAChR) subunits and myogenic regulatory factors (MRF) which stabilize the neuromuscular junction. Sensory functional recovery correlates with the gene expression of Growth Associated Protein-43 (GAP-43) in the dorsal root ganglion (DRG), which affects axon growth. Understanding the gene expression of nAChR, MRF, and GAP-43 is critical in predicting motor and sensory recovery following nerve injury and repair. The goals of this study were to document the gene expression of nAChr, MRF, and GAP-43 following nerve injury.

Forty-five rats underwent left tibial nerve transection with the right tibial nerve as control. The gastrocnemius, L4 DRG, and L5 DRG were harvested, at different time points up to 1 year after nerve transection, and the following measurements made: 1) muscle mass (percentage of control); 2) gene expression of nAChR subunits (alpha, beta, gamma, delta, epsilon); 3) MRF (MyoD, Myogenin, and MRF 4); GAP-43. RNA extraction was performed followed by real time RT-PCR for gene expression analysis.

1. Significant muscle atrophy was observed following nerve injury. Muscle mass decreased 60% at 1 week, 80% at 1 month, and plateaued at 13% of control after 2 months. 2. nAChR subunits were significant4ly upregulated following nerve injury with each returning to normal levels at specific time points. Gene expression of the alpha-subunit returned to normal levels at 1 month following nerve injury. 3. MRF was also significantly upregulated following nerve injury, returning to normal levels at specific time points. Gene expression of MRF 4 demonstrated a pattern similar to that of the nAChR alpha-subunit. 4. Gene expression of GAP-43 was upregulated following nerve injury and remained elevated at 3 months.

Gene expressions of most nAChR subunits, MRF, and GAP-43 were upregulated within 1 month after nerve injury, suggesting that the first month following nerve injury is critical for delayed nerve repair. A similar pattern of gene expression in the nAChR alpha subunit and MRF 4 suggests that MRF 4 may mediate expression of the alpha subunit, thereby affecting neuromuscular junction stability. The significant upregulation of nAChr subunits and MRF correlate with a significant decrease in muscle mass. Documentation of the pattern of gene expression of nAChR subunits, MRF, and GAP-43 provides the potential for the development of gene therapies to facilitate functional recovery following nerve injury and repair.