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Dynamic increase in extracellular ATP accelerates photoreceptor cell apoptosis via ligation of P2RX7 in subretinal hemorrhage.

ABSTRACT: Photoreceptor degeneration is the most critical cause of visual impairment in age-related macular degeneration (AMD). In neovascular form of AMD, severe photoreceptor loss develops with subretinal hemorrhage due to choroidal neovascularization (CNV), growth of abnormal blood vessels from choroidal circulation. However, the detailed mechanisms of this process remain elusive. Here we demonstrate that neovascular AMD with subretinal hemorrhage accompanies a significant increase in extracellular ATP, and that extracellular ATP initiates neurodegenerative processes through specific ligation of Purinergic receptor P2X, ligand-gated ion channel, 7 (P2RX7; P2X7 receptor). Increased extracellular ATP levels were found in the vitreous samples of AMD patients with subretinal hemorrhage compared to control vitreous samples. Extravascular blood induced a massive release of ATP and photoreceptor cell apoptosis in co-culture with primary retinal cells. Photoreceptor cell apoptosis accompanied mitochondrial apoptotic pathways, namely activation of caspase-9 and translocation of apoptosis-inducing factor (AIF) from mitochondria to nuclei, as well as TUNEL-detectable DNA fragmentation. These hallmarks of photoreceptor cell apoptosis were prevented by brilliant blue G (BBG), a selective P2RX7 antagonist, which is an approved adjuvant in ocular surgery. Finally, in a mouse model of subretinal hemorrhage, photoreceptor cells degenerated through BBG-inhibitable apoptosis, suggesting that ligation of P2RX7 by extracellular ATP may accelerate photoreceptor cell apoptosis in AMD with subretinal hemorrhage. Our results indicate a novel mechanism that could involve neuronal cell death not only in AMD but also in hemorrhagic disorders in the CNS and encourage the potential application of BBG as a neuroprotective therapy.

SUBMITTER: Notomi S

PROVIDER: S-EPMC3540091 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:PurposeWe report a case of old submacular hemorrhage (SMH) due to polypoidal choroidal vasculopathy (PCV). Subretinal endoscopic surgery (SES) was performed, which improved visual function. In addition, we show the intraoperative findings of subretinal aberrant PCV vessels as seen under endoscopic observation, which cannot be observed by microscopic surgery.ObservationsA 71-year-old Japanese man presented with an old dehemoglobinized SMH due to PCV in his left eye. At the time of presentation, three weeks had already passed after the onset of the patient's symptoms, and the best-corrected visual acuity (BCVA) was 20/200. SES was performed to remove the SMH and treat the subretinal PCV lesions. After creating retinal detachment using a 38-gauge cannula, three subretinal 25-gauge trocars were inserted from the sclera to the subretinal space. Then, SES was performed under ophthalmic endoscopic observation with continued subretinal irrigation for maintaining the retinal detachment. After removal of the SMH, subretinal polyp-shaped nodular vascular lesions (polyps) and a branching vascular network, which is located inside the retinal pigmented epithelium, were identified. The sites that presumably originated from the aberrant vessels of the PCV and the associated polyps were coagulated using endodiathermy. After the subretinal procedure, the retina was flattened with fluid/air exchange, and silicone oil (SO) was injected into the vitreous cavity. The SMH completely disappeared after surgery. Although at one-month follow-up BCVA (20/250) was slightly worse than that before surgery, there was an improvement in postoperative retinal sensitivity in the macula compared to that before surgery. At the three-month follow-up, the SO was removed. The BCVA was 20/200 one month after SO removal. No postoperative complications occurred. Additional treatment was not required, including anti-vascular endothelial growth factor therapy, for PCV progression or SMH recurrence in the left eye till the final visit two years after surgery.Conclusion and importanceSES could effectively remove the old SMH, and the activity of PCV was suppressed by intraoperative subretinal coagulation. The retinal sensitivity of the macula improved after the SES. In addition, we observed subretinal polyps and a branching vascular network located internal to the retinal pigmented epithelium under intraoperative subretinal endoscopic observation. SES is a good surgical option for the removal of old SMH or treatment of subretinal lesions.

Project description:IntroductionThe peptide mastoparan 7 (MST7) triggered in human erythrocytes (rbcs) the release of ATP and swelling. Since swelling is a well-known inducer of ATP release, and extracellular (ATPe), interacting with P (purinergic) receptors, can affect cell volume (Vr), we explored the dynamic regulation between Vr and ATPe.Methods and treatmentsWe made a quantitative assessment of MST7-dependent kinetics of Vr and of [ATPe], both in the absence and presence of blockers of ATP efflux, swelling and P receptors.ResultsIn rbcs 10 ?M MST7 promoted acute, strongly correlated changes in [ATPe] and Vr. Whereas MST7 induced increases of 10% in Vr and 190 nM in [ATPe], blocking swelling in a hyperosmotic medium + MST7 reduced [ATPe] by 40%. Pre-incubation of rbcs with 10 ?M of either carbenoxolone or probenecid, two inhibitors of the ATP conduit pannexin 1, reduced [ATPe] by 40-50% and swelling by 40-60%, while in the presence of 80 U/mL apyrase, an ATPe scavenger, cell swelling was prevented. While exposure to 10 ?M NF110, a blocker of ATP-P2X receptors mediating sodium influx, reduced [ATPe] by 48%, and swelling by 80%, incubation of cells in sodium free medium reduced swelling by 92%.Analysis and discussionResults were analyzed by means of a mathematical model where ATPe kinetics and Vr kinetics were mutually regulated. Model dependent fit to experimental data showed that, upon MST7 exposure, ATP efflux required a fast 1960-fold increase of ATP permeability, mediated by two kinetically different conduits, both of which were activated by swelling and inactivated by time. Both experimental and theoretical results suggest that, following MST7 exposure, ATP is released via two conduits, one of which is mediated by pannexin 1. The accumulated ATPe activates P2X receptors, followed by sodium influx, resulting in cell swelling, which in turn further activates ATP release. Thus swelling and P2X receptors constitute essential components of a positive feedback loop underlying ATP-induced ATP release of rbcs.

Project description:Vectors based on the adeno-associated virus (AAV) are currently the preferred tools for delivering genes to photoreceptors (PR) in small and large animals. AAVs have been applied successfully in various models of PR dystrophies. However, unknown barriers still limit AAV's efficient application in several forms of severe PR degenerations due to insufficient transgene expression and/or treated cells at the time of injection. Optimizations of PR gene therapy strategies will likely benefit from the identification of the cellular factors that influence PR transduction. Interestingly, recent studies have shown that the AAV transduction profile of PRs differs significantly between neonatal and adult mouse retinas after subretinal injection. This phenomenon may provide clues to identify host factors that influence the efficiency of AAV-mediated PR transduction. This study demonstrates that rod outer segments are critical modulators of efficient AAV-mediated rod transduction. During retinal development, rod transduction correlated temporally and spatially with the differentiation order of PRs when vectors were introduced subretinally but not when introduced intravitreally. All subretinally injected vectors had an initial preference to transduce cones in the absence of formed rod outer segments and then displayed a preference for rods as the cells matured, independently of the expression cassette or AAV serotype. Consistent with this observation, altered development of rod outer segments was associated with a strong reduction of rod transduction and an increase in the percentage of transduced cones by 2- to 2.8-fold. A similar increase of cone transduction was observed in the adult retinal degeneration 1 (rd1) retina compared to wild-type mice. These results suggest that the loss of rod outer segments in diseased retinas could markedly affect gene transfer efficiency of AAV vectors by limiting the ability of AAVs to infect dying rods efficiently. This information could be exploited for the development of more efficient AAV-based PR gene delivery procedures.

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Dynamic increase in extracellular ATP accelerates photoreceptor cell apoptosis via ligation of P2RX7 in subretinal hemorrhage.

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