PURPOSE.
Hypoxia-induced apoptosis is responsible for reduced retinal ganglion cell (RGC) viability in a variety of chronic ocular disorders.
Sirtuin 1 (
SIRT1) plays an important role in preserving cell viability during
hypoxia. We investigated the role of
SIRT1 in sustaining RGC viability in an in vitro model of
hypoxia. METHODS. Staurosphorine-differentiated RGCs (RGC-5) received varying hypoxic concentrations (100-500 μM) of
cobalt chloride (CoCl2) for 24 hours.
Hypoxia-induced cell viability was assessed by WST-1 assay. The role of
SIRT1 in promoting viability was determined indirectly via
sirtinol (
SIRT1 inhibitor).
Hypoxia-induced apoptosis was evaluated by measuring stress-activated
protein kinase/c-
jun N-terminal kinase (SAPK/JNK) and
caspase 3 activity.
Vascular endothelial growth factor (
VEGF) was measured to ascertain the influence of
SIRT1. RESULTS. CoCl2 concentrations greater than 100 μM resulted in significantly reduced RGC viability (P=0.01). CoCl2 treatment increased
SIRT1 levels significantly (P<0.01): 100 (6.5-fold), 200 (6-fold), 300 (3.5-fold), and 400 μM (4.5-fold). Phosphorylated SAPK/JNK increased 36-fold (200 μM CoCl2 concentration), then plateaued at the 300- (25-fold) and 400-μM (27.8-fold) CoCl2 concentrations (P<0.01). CoCl2 and
sirtinol treatment increased
Caspase 3 activity (P<0.05).
VEGF release was significantly higher than control at the 100-μM CoCl2 concentrations (P<0.01).
Sirtinol reduced RGC viability,
SIRT1 levels, and
VEGF release (P<0.01) while having greater effect on SAPK/JNK phosphorylation. CONCLUSIONS.
SIRT1 significantly influences RGC viability.
Sirtinol's effect reflects the interaction
SIRT1 has with apoptotic signaling
proteins. This investigation demonstrated
SIRT1 importance in forestalling the effects of
hypoxia-induced apoptosis.