Regular Paper

Acta Neuropathologica

, Volume 89, Issue 3, pp 219-226

First online:

Axonal regeneration into chronically denervated distal stump

2. Active expression of type I collagen mRNA in epineurium
  • J. SiironenAffiliated withDepartment of Pathology, University of TurkuCentral University Hospital of Turku
  • , V. VuorinenAffiliated withDepartment of Neurosurgery, University of Helsinki
  • , H. S. TaskinenAffiliated withDepartment of Pathology, University of TurkuCentral University Hospital of Turku
  • , M. RöyttäAffiliated withDepartment of Pathology, University of TurkuCentral University Hospital of Turku

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Abstract

During the first 2 weeks after an injury to peripheral nerve, endoneurial cells proliferate and express integrin β1 and mRNA for collagen types I and III. Clinical results for surgical repair within this time are clearly better than those obtained after delayed (months after original injury) surgery. The question of whether this is due to changes in the proliferative capacity of endoneurial cells or to changes in expression of mRNA for collagen types I and III or integrin β1 was studied using rats. The left common peroneal nerve was transected and allowed to degenerate for 3 and 6 months. After these times, the tibial nerve of the same animals were transected, and the fresh proximal stump of the transected tibial nerve was sutured into the chronically denervated distal stump of the common peroneal nerve. At 3 and 6 weeks after the reoperation, samples were collected from the distal stump for morphometry, immunohistochemistry and in situ hybridization. Proliferating cells and Schwann cells were identified by immunohistochemistry. These cells increased markedly in number during the axonal reinnervation. In situ hybridization revealed that in the epineurium and perineurium, which were fibrotic, especially type I but also type III collagen mRNA were highly expressed. The amount of type I collagen mRNA in the endoneurium seemed to increase with progressing axonal reinnervation. Immunostaining for integrin β1 was negative in these distal stumps. In the present study the proliferation of endoneurial cells and expression of type I collagen mRNA in the endoneurium were similar to those found after immediate regeneration of transected peripheral nerve. However, the failure of endoneurial fibroblasts to express the integrin β1 subunit may indicate an advanced degeneration of the denervated distal stump. Moreover, clear expression of type I and III collagen mRNA in epineurial fibroblasts indicates scarring at the region of the transection and may play a role in prohibitting full structural recovery of the injured peripheral nerve.

Key words

Delayed regeneration Type I collagen Type III collagen mRNA Schwann cell proliferation