Resumo

During WD it is important that myelin debris are effectively removed from axonal environment, in order to improve axon regeneration. Schwann cells (SC) and macrophages (MŲ) play a crucial role during WD, for both cellular types are able to engulf myelin debris. Galectin-3 is expressed in SC and MŲ after lesion and some studies have correlated its expression with the success of myelin phagocytosis after injury. Recently, our group reported that sciatic nerve regeneration was accelerated in gal-3-/- mice, although the reasons for the rapid axonal regeneration remains unclear. It is feasible to suppose that an accelerated axon regeneration could be a consequence of faster axon degeneration so, our main objective, in the present study, was to clarify the role of gal-3 during sciatic nerve WD by comparing gal-3-/- and wild-type animals. For this, we adopted two models of nerve degeneration: in vivo and in vitro degeneration. We analysed the nerve transverse semithin sections at 4, 7 and 21 days after in vivo degeneration and 7 days after in vitro degeneration. For in vivo degeneration we measured the degenerating index (D.I.) which indicates the presence of myelin ovoids plus fibers under degeneration. We observed that WD and myelin removal were faster in gal-3-/- than wild-type mice (D.I.: 4 days: 163.3 ± 35.1 x 110 ± 44; 1 week: 68.5 ± 27.7 x 161.7 ± 60.2; 3 weeks: 29 ± 10.4 x 94.6 ± 5.0, respectively). Furthermore, 1 week after in vitro degeneration the gal-3-/- nerves appeared more degenerated with more disintegrated fibers and myelin debris than wild-type nerves. These morphological findings led us to search differences between gal-3-/- and wild type WD. We also looked for TLR-4 expression, by immunohistochemistry, since it has been reported that mice lacking this protein display a delayed WD and myelin removal. Our results showed that nerves from gal-3-/- animals were more immunostained for TLR-4 than wild-type nerves. We also measured the release of nitrite from nerve explants by Griess reaction because nitric oxide is describe as a powerful oxidant capable to dissolute myelin sheath. We observed that gal-3-/- nerves released more nitrite than wild-type nerves (15µM ± 8.2 x 12.2µM ± 8). In conclusion, gal-3-/- animals showed faster WD and myelin phagocytosis after sciatic nerve injury. These could be explained, at least, by the higher release of nitric oxide, accelerating myelin destruction, and TLR-4 overexpression, which could enable SC and MŲ to efficiently clean up myelin debris from nerve environment.