Mitochondrial Complex I Defect Induces ROS Release and Degeneration in Trabecular Meshwork Cells of POAG Patients: Protection by Antioxidants

Abstract

There is growing evidence that oxidative stress contributes to the progression of primary open-angle glaucoma (POAG), a leading cause of irreversible blindness worldwide. The authors provide evidence that mitochondrial dysfunction is a possible mechanism for the loss of trabecular meshwork (TM) cells in persons with POAG. TM from patients with POAG (GTM) and age-matched subjects without disease (NTM) were obtained by standard surgical trabeculectomy. Primary TM cultures were treated with one of the following mitochondrial respiratory chain inhibitors: rotenone (ROT, complex I inhibitor), thenoyltrifluoroacetone (TTFA, complex II inhibitor), myxothiazol or antimycin A (MYX, AM-complex III inhibitors); mitochondrial permeability transition (MPT) inhibitor cyclosporine A (CsA); and antioxidants vitamin E (Vit E) or N-acetylcysteine (NAC). Mitochondrial function was determined by changes in mitochondrial membrane potential (DeltaPsim) and adenosine triphosphate (ATP) production with the fluorescent probes 5,5',6,6'-tetrachloro-1,1'3,3'-tetraethylbenzimid azolocarbocyanine iodide (JC-1) and a luciferin/luciferase-based ATP assay, respectively. Reactive oxygen species (ROS) level, determined by H(2)-DCF-DA, and cell death, measured by lactate dehydrogenase activity and Annexin V-FITC labeling, were also examined. GTM cells have higher endogenous ROS levels, lower ATP levels, and decreased Delta Psi m and they are more sensitive to mitochondrial complex I inhibition than their normal counterparts. ROT induces a further increase in ROS production, the release of cytochrome c, and decreases in ATP level and Delta Psi m in GTM cells, eventually leading to apoptosis. Complex II and III inhibition had little effect on the cells. Antioxidants protect against ROT-induced death by inhibiting ROS generation and cytochrome c release. The authors propose that a mitochondrial complex I defect is associated with the degeneration of TM cells in patients with POAG, and antioxidants and MPT inhibitors can reduce the progression of this condition.