Baclofen Protects Primary Rat Retinal Ganglion Cells from Chemical Hypoxia-Induced Apoptosis Through the Akt and PERK Pathways

Retinal ganglion cells (RGCs) consume large quantities of energy to convert light information into a neuronal signal, which makes them highly susceptible to hypoxic injury. This study aimed to investigate the potential protection by baclofen, a GABA(B) receptor agonist of RGCs against hypoxia-induced apoptosis. Cobalt chloride (CoCl(2)) was applied to mimic hypoxia. Primary rat RGCs were subjected to CoCl(2) with or without baclofen treatment, and RNA interference techniques were used to knock down the GABA(B)2 gene in the primary RGCs. The viability and apoptosis of RGCs were assessed using cell viability and terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) assays, Hoechst staining, and flow cytometry. The expression of cleaved caspase-3, bcl-2, bax, Akt, phospho-Akt, protein kinase RNA (PKR)-like ER kinase (PERK), phospho-PERK, eIF2α, phospho-eIF2α, ATF-4 and CCAAT/enhancer-binding protein homologous protein (CHOP) were measured using western blotting. GABA(B)2 mRNA expression was determined using quantitative real-time polymerase chain reaction (qRT-PCR) analysis. Our study revealed that CoCl(2) significantly induced RGC apoptosis and that baclofen reversed these effects. CoCl(2)-induced reduction of Akt activity was also reversed by baclofen. Baclofen prevented the activation of the PERK pathway and the increase in CHOP expression induced by CoCl(2). Knockdown of GABA(B)2 and the inactivation of the Akt pathway by inhibitors reduced the protective effect of baclofen on CoCl(2)-treated RGCs. Taken together, these results demonstrate that baclofen protects RGCs from CoCl(2)-induced apoptosis by increasing Akt activity and by suppressing the PERK pathway and CHOP activation.