Abstract
In adult mammals, axon regeneration is limited within the lesion site after injury to the optic nerve. Changes in the microenvironment of lesion sites play an important role in retinal ganglion cells (RGCs) axon regeneration along with other intrinsic factors. In this study, the effect of the lesion site on the microenvironment and axon growth was evaluated using a refined optic nerve crush (ONC) injury model, in which the injury range was extended compared to classical injury. The number of regenerated axons labeled anterogradely with cholera toxin B fragment (CTB) was significantly increased in the long-range crush injury (LI) group compared to the ONC group at distances of 500, 1000 and 1500 µm from the initial site of the injury. These data confirmed that RGC axons can regenerate inside the lesion site. Immunofluorescence and proteomic analysis showed that the microenvironment at the lesion site was highly heterogeneous. The levels of myelin-associated inhibitors, chondroitin-sulfate proteoglycans (CSPGs) and other axon growth inhibitors decreased inside the lesion site compared to the posterior segment of the optic nerve lesion site. The expression of multiple lysosome-related enzymes, metabolic inhibitors including cholesterol esterase, cathepsin B, D, Z and arylsulfatase B (ARSB) were significantly increased inside the lesion site for the LI group compared to the normal optic nerves. Our results suggest that the model of long range optic nerve injury is more useful towards understanding the lesion microenvironment and the endogenous regeneration of RGCs. Also, we showed that myelin and neurocan (a CSPG) are differently expressed in the optic nerve between the interior and posterior lesion sites and may explain why axons cannot reach the brain through the lesion site.