Long‐lasting accumulation of hemopexin in permanently transected peripheral nerves and its down‐regulation during regeneration

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Abstract
We have previously demonstrated that hemopexin is present in the intact sciatic nerve and is overproduced in the distal stump after nerve transection (Swerts et al.: J Biol Chem 267:10596–10600, 1992). To get further insight into the function of this hemoprotein in nervous tissue, we have documented long‐term changes in hemopexin levels in permanently degenerated (transected) and regenerting (crush‐lesioned) sciatic nerves of adult rats, using immunochemical techniques. As early as a couple of days after nerve transection, the amount of hemopexin was raised in the distal stump and at the end of the proximal stump. Similarly, after a crush lesion hemopexin was rapidly increased at the injury site and in the distal part of the nerve. Subsequently, in transected nerves the level of hemopexin rose steadily and remained elevated, representing, three months after injury, over 20 times the amount found in intact contralateral nerves. In contrast, in crush‐lesioned nerves, hemopexin level declined progressively in a proximodistal direction and returned to basal values 2 months after injury, together with axonal regeneration. This long‐term increase in hemopexin in permanently degenerated nerves and its progressive return to normal levels during nerve regeneration suggests that hemopexin content could be regulated negatively, directly or indirectly, by growing axons. In turn, these results support the idea that hemopexin could be involved in the process of Wallerian degeneration and/or in nerve repair.