PKC isozymes in the enhanced regrowth of retinal neurites after optic nerve injury.

ABSTRACT

PURPOSE: To establish an in vitro model of axonal regeneration from mammalian retinal ganglion cells and to evaluate the role of PKC isozymes in promoting such retinal axon regeneration. METHODS: Postnatal day-3 mice were subjected to optic nerve crush, and then retinal ganglion cells (RGCs) were used for culture 5 days later. RGCs were selected using anti-Thy 1.2-coated magnetic beads and plated onto a merosin substrate. Changes in axonal localization of PKC and axonal regeneration were examined in cultured RGCs by immunofluorescence. Changes in PKC isozyme mRNA levels were determined by semiquantitative reverse transcription-polymerase chain reaction (RT-PCR). The role of PKC in RGC neurite outgrowth was examined by treatment with activators or pharmacological inhibitors of PKC activity. RESULTS: RGCs subjected to optic nerve crush injury demonstrated more rapid neurite outgrowth in vitro when compared with RGCs isolated from naïve retina. The neurites of these injury-conditioned RGCs showed both an increased rate of extension and enhanced PKC localization in culture. Injury-conditioned RGCs had elevated PKC isozyme mRNA levels, which probably contributed to the increased level of PKC protein in injury-conditioned RGC axons. Pharmacological activation of PKC enhanced neurite growth, whereas inhibition of PKC suppressed neurite growth in both the conditioned and naïve RGCs. CONCLUSIONS: RGCs actively respond to axonal injury by regulating expression of genes that promote neurite outgrowth. PKC-alpha and -beta isozymes are among the growth-associated proteins that are upregulated after injury. Results of pharmacological manipulation of PKC activity support the argument that increased PKC levels enhance neurite regrowth after axonal injury.