Nitric oxide leads to cytoskeletal reorganization in the retinal pigment epithelium under oxidative stress

Abstract

Light is a risk factor for various eye diseases, including age-related macular degeneration (AMD) and retinitis pigmentosa (RP). We aim to understand how cytoskeletal proteins in the retinal pigment epithetlium (RPE) respond to oxidative stress, including light and how these responses affect apoptotic signaling. Previously, proteomic analysis revealed that the expression levels of vimentin and serine/threonine protein phosphatase 2A (PP2A) are significantly increased when mice are exposed under continuous light for 7 days compared to a condition of 12 hrs light/dark cycling exposure using retina degeneration 1 (rd1) model. When melatonin is administered to animals while they are exposed to continuous light, the levels of vimentin and PP2A return to a normal level. Vimentin is a substrate of PP2A that directly binds to vimentin and dephosphorylates it. The current study shows that upregulation of PP2Ac (catalytic subunit) phosphorylation negatively correlates with vimentin phosphorylation under stress condition. Stabilization of vimentin appears to be achieved by decreased PP2Ac phosphorylation by nitric oxide induction. We tested our hypothesis that site-specific modifications of PP2Ac may drive cytoskeletal reorganization by vimentin dephosphorylation through nitric oxide signaling. We speculate that nitric oxide determines protein nitration under stress conditions. Our results demonstrate that PP2A and vimentin are modulated by nitric oxide as a key element involved in cytoskeletal signaling. The current study suggests that external stress enhances nitric oxide to regulate PP2Ac and vimentin phosphorylation, thereby stabilizing or destabilizing vimentin. Phosphorylation may result in depolymerization of vimentin, leading to nonfilamentous particle formation. We propose that a stabilized vimentin might act as an anti-apoptotic molecule when cells are under oxidative stress.

Altered Cytoskeleton as a Mitochondrial Decay Signature in the Retinal Pigment Epithelium

“…Our unbiased proteomic approach demonstrated that actin, tubulin, and vimentin filaments were changed dramatically in the RPE and retina under oxidative environment [2, 3, 6]. Oxidants disrupt barrier integrity and cell junction to initiate the RPE pathogenesis through a blood-retina barrier degeneration mechansim.…”

“…Balance between actin filaments, intermediate filaments, and microtubules regulates RPE cytoskeleton, mitochondrial morphology as well as mitochondrial traffic. Vimentin phosphorylations induce disassembly of intermediate filaments in vitro [6, 19]. Melatonin is synthesized nocturnally to protect the retina and a potential therapy for retinal diseases.…”

“…Vimentin is involed in light-induced cytoskeleton changes in the retina and the RPE through PP2A and nitric oxide mechanism [6]. N-terminus of vimentin molecule is responsible for intermediate filament interaction with mitochondria.…”

“…ARPE-19 cells were cultured as reported previously [1,4,6,7]. Confluent RPE cells were treated with intense light (7,000 lux, 1 hr) or tert-butyl hydroperoxide (or H 2 O 2 ) as oxidative stress (100-200 μM, 24 hrs) in serum free media.…”

Prohibitin as the Molecular Binding Switch in the Retinal Pigment Epithelium

“…Prohibitin is involved in cell cycle regulation and apoptosis 6 by interacting with the retinoblastoma tumor suppressor protein Rb [7]. Prohibitin plays a major role in C-Raf activation for epithelial cell adhesion and migration [8]. Oxidative stress-induced implications during mitochondrial biogenesis, disruption of mitochondria-nuclear communication, and damage to the mitochondrial DNA (mtDNA) lead to the development of diabetic retinopathy (DR) [10,11,12].…”