Critical Involvement of Extracellular ATP Acting on P2RX7 Purinergic Receptors in Photoreceptor Cell Death

Abstract

Stressed cells release ATP, which participates in neurodegenerative processes through the specific ligation of P2RX7 purinergic receptors. Here, we demonstrate that extracellular ATP and the more specific P2RX7 agonist, 2'- and 3'-O-(4-benzoylbenzoyl)-ATP, both induce photoreceptor cell death when added to primary retinal cell cultures or when injected into the eyes from wild-type mice, but not into the eyes from P2RX7(-/-) mice. Photoreceptor cell death was accompanied by the activation of caspase-8 and -9, translocation of apoptosis-inducing factor from mitochondria to nuclei, and TUNEL-detectable chromatin fragmentation. All hallmarks of photoreceptor apoptosis were prevented by premedication or co-application of Brilliant Blue G, a selective P2RX7 antagonist that is already approved for the staining of internal limiting membranes during ocular surgery. ATP release is up-regulated by nutrient starvation in primary retinal cell cultures and seems to be an initializing event that triggers primary and/or secondary cell death via the positive feedback loop on P2RX7. Our results encourage the potential application of Brilliant Blue G as a novel neuroprotective agent in retinal diseases or similar neurodegenerative pathologies linked to excessive extracellular ATP.

Deregulation of ocular nucleotide homeostasis in patients with diabetic retinopathy

“…High concentrations of ATP are known to accelerate apoptosis of photoreceptor cells via ligation of ATP-specific P2X7 receptors [16,39] and in addition, mediate neurodegeneration, gliosis, neovascularization, inflammation, and vascular leakage [12,25]. In felines and rodents, intravitreal administration of ATP induced photoreceptor degeneration, retinal neural remodeling, and Müller cell gliosis, with most of these pathological changes continuing out to 12 weeks postinjection [40].…”

Nucleotides in the Eye: Focus on Functional Aspects and Therapeutic Perspectives

“…Inherited retinal diseases cause increased extracellular ATP levels that may lead to photoreceptor apoptosis. Selective photoreceptor apoptosis mediated by P2X7 receptors (Notomi et al, 2011) occurred after intravitreal injection of ATP in murine retina (Puthussery and Fletcher, 2009;Notomi et al, 2011). In contrast, intraocular injections of Brilliant Blue G, a selective P2X7 receptor antagonist, reduced ATP-induced photoreceptor apoptosis (Notomi et al, 2011).…”

“…Selective photoreceptor apoptosis mediated by P2X7 receptors (Notomi et al, 2011) occurred after intravitreal injection of ATP in murine retina (Puthussery and Fletcher, 2009;Notomi et al, 2011). In contrast, intraocular injections of Brilliant Blue G, a selective P2X7 receptor antagonist, reduced ATP-induced photoreceptor apoptosis (Notomi et al, 2011). Interestingly, P2X7 receptor-mediated photoreceptor apoptosis was reported in BALBCrd mice, a retinitis pigmentosa model (Franke et al, 2005), as upregulated expression of P2X7 receptor, and peak photoreceptor apoptosis occurred at the same time between P20 and P40.…”

Predicting Visual Outcome following Surgery for Idiopathic Macular Holes

“…In a rat model of subretinal injection, BBG did not cause any detectable toxic effects on retinal cells, whereas ICG and trypan blue caused retinal degeneration [31]. Moreover, the BBG dye acts as a P2RX7 antagonist and can mediate neuroprotective effects on retinal neurons [32,33]. As the favourable effects of BBG dye use in MH surgery on visual outcomes have been confirmed in several comparative studies [34,35], the benefits of BBG use should be evaluated in an RCT.…”