Abstract
Purpose:
To examine the neuroprotective and regenerative effects of taurine-conjugated ursodeoxycholic acid (TUDCA), an anti-endoplasmic reticulum stress agent, in rat retinas exposed to high glucose.
Methods:
All of the procedures were performed in accordance with the ARVO Statement for the Use of Animals in Ophthalmic and Vision Research. Retinas isolated from 6 adult male SD rats were cultured in normal-glucose (NG) or high-glucose (HG) media. TUDCA or neurotrophin-4 (NT-4) was added to the HG medium. After 7 days, the number of regenerating neurites was counted. The explants were cryosectioned and stained by TUNEL and immunostained for p-c-Jun and p-JNK. Statistical analyses were performed with Mann-Whitney U tests.
Results:
In the HG group, the percentage of TUNEL-positive cells in the ganglion cell layer (GCL) was 32.7±11.7% and in the NG group it was 18.8±7.3% (P=0.0002). In the HG group supplemented with TUDCA (HG+TUDCA), the percentage of TUNEL-positive cells was 19.8±7.0% and that supplemented by NT-4 (HG+NT-4) was 19.9±6.4% (P=0.0396, P=0.0367, respectively). In the HG group, the percentage of p-c-Jun- and p-JNK-positive cells in the GCL was 27.9±12.5% and 18.6±5.2%, and both were significantly higher than those in the NG group at 12.1±5.8% (P=0.003) and 13.2±10.4% (P=0.005). In the both groups, the percentage of p-c-Jun-positive (8.7±6.4% and 7.2±5.6%) and p-JNK-positive cells (7.5±2.2% and 7.6±3.6%) were significantly lower than in the HG group (27.9±12.5% and 18.6±5.2%; P=0.0006, P=0.0003, P<0.0001, P<0.0001, respectively). In the HG group, the number of regenerating neurites was significantly fewer than in the NG groups (70.4±45.1/mm2 vs. 140.6±63.1/mm2; P<0.0001). In the HG+TUDCA and HG+NT-4 groups, the number of neurites was significantly higher than in the HG group (130.5±59.2/mm2 vs. 70.2±45.1/mm2, 254.7±74.0/mm2 vs. 70.2±45.1/mm2; P=0.0002, P<0.0001, respectively). In the HG+NT-4 group, the number of neurites was significantly higher than that in the HG+TUDCA group (P=0.00004).
Conclusions:
The neuroprotective effects of TUDCA and NT-4 are similar and are correlated with the suppression of p-c-Jun and p-JNK expression. The stronger regenerative effect of NT-4 than TUDCA shows that not only the suppression of endoplasmic reticulum stress but also other molecular mechanisms may be involved in the regenerative effect of NT-4.
Keywords: 615 neuroprotection •
687 regeneration •
694 retinal culture