Effects of Akt/mTOR/p70S6K Signaling Pathway Regulation on Neuron Remodeling Caused by Translocation Repair

Abstract

Peripheral nerve injury repair has been considered a difficult problem in the field of trauma for a long time. Conventional surgical methods are not applicable in some special types of nerve injury, prompting scholars to seek to develop more effective nerve translocation repair technologies. The purpose of this study was to explore the functional state of neurons in injured lower limbs after translocation repair, with a view to preliminarily clarify the molecular mechanisms underlying this process. Eighteen Sprague-Dawley rats were divided into the normal, tibial nerve in situ repair, and common peroneal nerve transposition repair tibial nerve groups. Nerve function assessment and immunohistochemical staining of neurofilament 200 (NF-200), protein kinase B (Akt), mammalian target of rapamycin (mTOR), and ribosomal protein S6 kinase (p70S6K) in the dorsal root ganglia were performed at 12 weeks after surgery. Tibial nerve function and neuroelectrophysiological analysis, osmic acid staining, muscle strength testing, and muscle fiber staining showed that the nerve translocation repair could restore the function of the recipient nerve to a certain extent; however, the repair was not as efficient as the in situ repair. Immunohistochemical staining showed that the translocation repair resulted in changes in the microstructure of neuronal cell bodies, and the expressions of Akt, mTOR, and p70S6K in the three dorsal root ganglia groups were significantly different (p < 0.05). This study demonstrates that the nerve translocation repair technology sets up a new reflex loop, with the corresponding neuroskeletal adjustments, in which, donor neurons dominate the recipient nerves. This indicates that nerve translocation repair technology can lead to neuronal remodeling and is important as a supplementary treatment for a peripheral nerve injury. Furthermore, the Akt/mTOR/p70S6K signaling pathway may be involved in the formation of the new neural reflex loop created as a result of the translocation repair.

Keywords: dorsal root ganglion; peripheral nerve injury; remodeling; signaling pathway; translocation repair.

FIGURE 1

Nerve distribution. (a) Ligature suture point on the proximal stump of the common peroneal nerve; (b) ligature suture point on the distal stump of the common peroneal nerve and (c) ligature suture point on the proximal stump of the tibial nerve.

FIGURE 2

The first row shows the morphology of the right hind paw of a rat from each of the three groups. It can be seen that the toes of the rat in the N group were naturally separated with full plantar muscles. In the TN-TN group, the five-toed curling deformity was mild, and the plantar muscles were slightly atrophied. The five-toe curling deformity was obvious, and the plantar muscles were obviously atrophied in the PN-TN group. The second row shows the TFIs of PT-TN and TN-TN group. *P < 0.05.

FIGURE 3

Nerve conduction velocity was significantly different between pairs, with the highest in the N group and the lowest in the PN-TN group. The TN-TN group had the largest amplitude, which was significantly higher than that of the other two groups. *P < 0.05 vs. other groups.

FIGURE 4

Osmic acid staining. The myelinated nerve fibers in the N group were evenly distributed and the axon area was significantly larger than those of the other two groups. Both the TN-TN group and the PN-TN group had different degrees of fiber invasion and unevenly distributed myelinated nerve fibers. Scale bar: 25 μm.

FIGURE 5

The first row shows the appearance of the right gastrocnemius muscle in each group. The gastrocnemius muscles in the N group were large while gastrocnemius atrophy was significant in the PT-TN group. The second row shows the muscle wet weights and strengths. Consistent with the appearance of the muscles, the muscle status of the N group was the best and that of the PN-TN group was the worst. *P < 0.05 vs. other groups.

FIGURE 6

Morphology of muscle fibers. The muscle fibers in group N were distinctly angular and closely arranged. In the TN-TN and PN-TN groups, oval-shaped muscle fibers could be seen and the gap between the muscle fibers was widened. The muscle fiber diameter of the N group was significantly larger than those of the other two groups. The Gomori staining was normal and there were no signs of mitochondrial disease. Scale bar: 100 μm.

FIGURE 7

DRG morphology and immunohistochemical staining. Yellow-brown staining represents NF-200 positive cells. Scale bar: 20 μm.

FIGURE 8

Expression of Akt/mTOR/p70S6K in the DRG. Yellow-brown staining represents protein expression, with a more intense color representing higher expression levels. Scale bar: 20 μm.