Cigarette Smoke Extract Causes Injury in Primary Retinal Ganglion Cells via Apoptosis and Autophagy

Aims: To investigate whether tobacco smoke directly injures retinal ganglion cells (RGCs) and to evaluate the mechanisms of cell death. Methods: Primary rat RGCs were harvested from 3- or 4-day-old newborn rats and exposed to cigarette smoke extract (CSE). Cell viability was determined by adenosine 5ˊ-triphosphate (ATP) assay. Apoptosis was evaluated by terminal deoxynucleotidyl transferase (TdT)-mediated deoxyuridine triphosphate (dUTP) nick-end labeling (TUNEL) and real-time reverse transcription polymerase chain reaction (RT-PCR) for Bcl-2 family. Autophagy was also assessed by Western immunoblots for light chain (LC) 3B. Results: When the primary RGCs were exposed to CSE for 2 h, cell viability decreased in a dose-dependent manner, as measured by ATP assay. In the presence of 0.05% CSE, the RGC viability was 77.68% ± 7.60% compared to the control cells; in the presence of 1.0% CSE, viability was 47.48% ± 2.56% of the control cells. As determined by TUNEL, CSE increased the apoptotic RGCs in a dose-dependent manner. In the presence of 0.05% CSE, the apoptosis was 26.55% ± 1.97% of the control cells; in the presence of 2.5% CSE, it was 41.07% ± 3.75% of the control cells. When apoptosis was evaluated using real-time RT-PCR, exposure to 0.05% CSE resulted in significantly increased expression of Bad, Bax, Bcl-2, and Bcl-XL mRNA. When autophagy was assessed by Western immunoblots, exposure to 0.05% CSE significantly increased the expression of LC3B II. Conclusions: Our data suggest that CSE directly injures primary RGCs, and both cell death mechanisms of apoptosis and autophagy seem to be related to this CSE-induced RGC damage.