Effect of neurotrophic factors on neuronal apoptosis and neurite regeneration in cultured rat retinas exposed to high glucose

The purpose of this study was to investigate the effect of brain-derived neurotrophic factor (BDNF), neurotrophin-4 (NT-4), and citicoline on neuronal apoptosis and neurite regeneration in cultured rat retinas exposed to high glucose (HG). The retinas of six adult Sprague-Dawley rats were studied. After the rats were euthanized, the retinas were isolated and cultured in serum-free medium. One group of explants was cultured in normal glucose (NG) and another group in HG medium (HGM). BDNF, NT-4, or citicoline were added to the HGM. After 7 days, the number of regenerating neurites was counted. Then, the explants were fixed, cryosectioned, and stained by TdT-dUTP terminal nick-end labeling (TUNEL), and also immunostained for the active-forms of caspase-3 and -9. The numbers of TUNEL-positive and caspase-3 and -9-immunopositive cells in the ganglion cell layer (GCL) were significantly higher, and the number of regenerating neurites was significantly lower in retinas cultured in HGM than in NG medium. Retinas incubated in HGM supplemented with BDNF, NT-4, or citicoline had significantly lower numbers of TUNEL-positive and caspase-3 and -9-immunopositive cells in the GCL, and the numbers of regenerating neurites were significantly higher than in HGM without these factors. We conclude that the increase in the number of apoptotic cells and decrease the number of regenerating neurites in the HGM indicate that HG is toxic to RGCs. The decrease in the number of apoptotic cells in the HGM containing BDNF, NT-4, or citicoline is correlated with the suppression of the caspase-9 and -3 activities.