Abstract
Abstract: :
Purpose: Using the genetic mouse model, we have demonstrated that lack of intrinsic Bcl–2–support growth mechanisms in neurons and induction of reactive astrocytes after injury are the two essential elements resulting in optic nerve regenerative failure in adult mammals. Ideally, a therapeutic strategy should be accomplished by manipulating Bcl–2 expression and reactive astrocytes through pharmaceutical approaches. Thus, in this study, we examined the effect of lithium, a neuroprotective agent that induces Bcl–2 expression in the adult retina, and gliotoxin, a glutamate analogue that selectively kills astrocytes, on optic nerve regeneration in adult mice. Methods: Optic nerve crush procedure was carried out in adult mice, and a gelform soaked with 10 mg/ml of gliotoxin, L–alpha–aminoadipate, or saline as control was applied to the injury site. Thereafter, the mice were divided into two groups: one group received a diet containing lithium (3.5mg/kg), and the other group received control diet. Levels of Bcl–2 expression in the retina were determined by quantitative RT–PCR and immunostain, and the efficacy of gliotoxin was examined by immunofluorescence labeling of astrocyte marker, glial fibrillary acidic protein (GFAP). Optic nerve regeneration was assessed 8 days after injury, using immunohistochemistry and anterograde axon tracing. Results: Mice received a diet containing lithium expressed Bcl–2 in the ganglion cell layer compared with those received a control diet. In addition, application of gliotoxin efficiently ablated astrocytes and generated a GFAP–free tract along the optic nerve. Administration of gliotoxin or lithium alone did not promote optic nerve regeneration. However, application of lithium and gliotoxin simultaneously induced robust optic nerve regeneration over long distances. Conclusions: Activating Bcl–2–supported growth mechanism and suppressing the activity of reactive astrocytes are essential for optic nerve regeneration in adult mammals. The data suggest a potential therapeutic strategy for inducing optic nerve regeneration by concurrent application of lithium and gliotoxin.
Keywords: regeneration • retinal glia • ganglion cells