Differential expression of GAP‐43 and neurofilament during peripheral nerve regeneration through bio‐artificial conduits

Nerve conduits are promising alternatives for repairing nerve gaps; they provide a close microenvironment that supports nerve regeneration. In this sense, histological analysis of axonal growth is a determinant to achieve successful nerve regeneration. To evaluate this process, the most‐used immunohistochemical markers are neurofilament (NF), β‐III tubulin and, infrequently, GAP‐43. However, GAP‐43 expression in long‐term nerve regeneration models is still poorly understood. In this study we analysed GAP‐43 expression and its correlation with NF and S‐100, using three tissue‐engineering approaches with different regeneration profiles. A 10 mm gap was created in the sciatic nerve of 12 rats and repaired using collagen conduits or collagen conduits filled with fibrin–agarose hydrogels or with hydrogels containing autologous adipose‐derived mesenchymal stem cells (ADMSCs). After 12 weeks the conduits were harvested for histological analysis. Our results confirm the long‐term expression of GAP‐43 in all groups. The expression of GAP‐43 and NF was significantly higher in the group with ADMSCs. Interestingly, GAP‐43 was observed in immature, newly formed axons and NF in thicker and mature axons. These proteins were not co‐expressed, demonstrating their differential expression in newly formed nerve fascicles. Our descriptive and quantitative histological analysis of GAP‐43 and NFL allowed us to determine, with high accuracy, the heterogenic population of axons at different stages of maturation in three tissue‐engineering approaches. Finally, to perform a complete assessment of axonal regeneration, the quantitative immunohistochemical evaluation of both GAP‐43 and NF could be a useful quality control in tissue engineering. Copyright © 2014 John Wiley & Sons, Ltd.