The Effect of Pulsed Electromagnetic Field (PEMF) Pre-treated Mesenchymal Stem Cells on the Regeneration of Crush - Injured Rat Mental Nerve

Abstract

1. Purpose Peripheral nerve injury is often encountered in clinical situations, and cell therapy is a promising regeneration technique. For this purpose, cells must be rapidly expandable, easily harvestable, and immunologically tolerable. Mesenchymal Stem Cells (MSCs), which satisfy these conditions, are a new tool in the regeneration of damaged peripheral nerves. Another non-cellular approach for the injured peripheral nerve regeneration, Pulsed Electromagnetic Field (PEMF), has been suggested. Past in vitro application of PEMF to MSCs increased cell proliferation and growth factor release, and it specifically induced MSC differentiation into Schwann-like cells. Also, PEMF in vivo helps in the regeneration of damaged peripheral nerve, motor, and sensory neurons. The aim of present study was to evaluate the effect of PEMF on the proliferation and growth factor release of MSCs and to evaluate the effect pf PEMF pre-treated MSCs (PMSCs) on peripheral nerve regeneration.

2. Methods MSCs were harvested from the long bones of five-week-old Sprague Dawley rats (200 - 250g) and primary cultured. The effect of PEMF pre-treatment (50 Hz, 0.1 mT, 1 hour/day) on MSCs was evaluated by cell proliferation assay and the change of S100, GFAP, BDNF, and NGF mRNA expression. Cell survival was observed for two weeks by injecting the DiI-labeled MSCs into the injured nerve. Animal surgery was carried out in four groups: Sham, PBS, the MSC-injected group, and the PEMF pre-treated MSCs (PMSCs) -injected group. Crush injury was performed on the left mental nerve using a needle holder with a width of 3 mm for one minute. MSCs and PEMF pre-treated MSCs (PMSCs) (1x106) were suspended in 5 μL PBS and injected into the injury-induced nerve using a Hamilton syringe. Functional recovery of the nerve was carried out by measuring the gap and difference scores at pre-surgery and 1 and 2 weeks post-surgery. Axonal regeneration was evaluated with histomorphometric analysis and retrograde labeling of the trigeminal ganglion (TG).

3. Results The PEMF pre-treated MSCs (PMSCs) group showed higher cell proliferation and growth factor expression than the MSC group. In the mental nerve sensory test, the PMSC injection group showed faster recovery than the untreated MSC injection group. Also, the PEMF pre-treated MSCs (PMSCs) exhibited significantly higher myelinated axon count and density than the MSC and PBS groups. Furthermore, using TG retrograde labeling, a greater number of dyed neurons was counted in the PEMF pre-treated MSCs (PMSCs) group compared to the MSC group.

4. Conclusion PEMF pretreatment on MSCs (PMSCs) in vitro increased not only the growth rate of the cells, but also the expression of nerve growth factors. Moreover, when these PEMF pre-treated MSCs (PMSCs) were injected into an injured nerve, they were more effective in regeneration than untreated MSCs. This suggests that PEMF pre-treated MSCs (PMSCs) are an enhanced strategic tool in cell therapy for recovery of injured nerves.