title: Ethambutol induces impaired autophagic flux and apoptosis in the rat retina.
abstract: Ethambutol (EMB), an effective first-line antituberculosis agent, can cause serious visual impairment or irreversible vision loss in a significant number of patients. However, the mechanism underlying this ocular cytotoxicity remains to be elucidated. In this study, we found that there were statistically significant dose- and time-dependent increases in the number of cytoplasmic vacuoles and the level of cell death in EMB-treated RGC-5 cells (retinal ganglion cells). The protein kinase C (PKC)δ inhibitor rottlerin markedly reduced the EMB-induced activation of caspase-3 and the subsequent apoptosis of RGC-5 cells. Western blot analysis revealed that the expression levels of class III PI3K, Beclin-1, p62 and LC3-II were upregulated, and LC3 immunostaining results showed activation of the early phase and inhibition of the late stage of autophagy in retinas of the EMB-intraperitoneal (IP)-injected rat model. We further demonstrated that exposure to EMB induces autophagosome accumulation, which results from the impaired autophagic flux that is mediated by a PKCδ-dependent pathway, inhibits the PI3K/Akt/mTOR signaling pathway and leads to apoptotic death in retina neuronal cells. These results indicate that autophagy dysregulation in retinal neuronal cells might play a substantial role in EMB-induced optic neuroretinopathy.
authors.affiliation: Department of Molecular Biology and Human Genetics, Tzu Chi University, Hualien 97002, Taiwan sphophdoc1688@gms.tcu.edu.tw rktsai@tzuchi.com.tw.
authors.forename: Shun-Ping
authors.initials: SP
authors.lastname: Huang
authors.affiliation: Department of Molecular Biology and Human Genetics, Tzu Chi University, Hualien 97002, Taiwan.
authors.forename: Jia-Ying
authors.initials: JY
authors.lastname: Chien
authors.affiliation: Institute of Eye Research, Buddhist Tzu Chi General Hospital, Hualien 97002, Taiwan Institute of Medical Sciences, Tzu Chi University, Hualien 97002, Taiwan sphophdoc1688@gms.tcu.edu.tw rktsai@tzuchi.com.tw.
authors.forename: Rong-Kung
authors.initials: RK
authors.lastname: Tsai
mesh_terms: D000098:Acetophenones / Q000494:pharmacology; D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D001343:Autophagy / Q000187:drug effects*; D001578:Benzopyrans / Q000494:pharmacology; D015415:Biomarkers / Q000378:metabolism; D053148:Caspase 3 / Q000378:metabolism; D053179:Caspase 7 / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D004977:Ethambutol / Q000494:pharmacology*; D005074:Evoked Potentials, Visual / Q000187:drug effects; D006801:Humans; D020287:In Situ Nick-End Labeling; D008247:Lysosomes / Q000187:drug effects / Q000378:metabolism; D008297:Male; D008954:Models, Biological; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D051745:Protein Kinase C-delta / Q000378:metabolism; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D017208:Rats, Wistar; D012160:Retina / Q000166:cytology* / Q000187:drug effects* / Q000201:enzymology / Q000502:physiology; D012165:Retinal Ganglion Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism; D015854:Up-Regulation / Q000187:drug effects; D014617:Vacuoles / Q000187:drug effects / Q000378:metabolism
chemical_list: D000098:Acetophenones; D001578:Benzopyrans; D015415:Biomarkers; D053148:Caspase 3; D053179:Caspase 7; D004977:Ethambutol; D019869:Phosphatidylinositol 3-Kinases; D051745:Protein Kinase C-delta; D047428:Protein Kinase Inhibitors; D058570:TOR Serine-Threonine Kinases; C085746:rottlerin
keywords: Apoptosis; Autophagy; Ethambutol; Optic neuroretinopathy; Rottlerin