Abstract
Purpose :
Congenital or idiopathic retinal degeneration (RD) leads to vision impairment and blindness. The loss of photoreceptors in the outer retina triggers pathophysiological remodeling, a crucial but understudied phenomenon affecting the inner retina, resulting in intrinsic and spontaneous retinal ganglion cell (RGC) hyperactivity, reducing the signal-to-noise ratio (SNR) of remaining light responses, further degrading vision. Inhibition of hyperactivity improves image recognition in-vivo, using strategies that are currently clinically unsuitable. This study aims to uncover new druggable targets and devise therapeutics to block hyperactivity and improve vision in animal models and patients.
Methods :
Rd1 mice (a retinitis pigmentosa model) were crossbred with purinergic 2x isoform 7 (P2X7) knockout mice, generating a double-mutant mouse strain. Gene and protein expression were tested using qRT-PCR, RNA-sequencing, and immunohistochemistry in retinal lysates or fixed eyeballs. Membrane permeability of Yo-Pro dyes was quantified using confocal imaging in whole-mounted living retinas. RGC activity was recorded using multielectrode arrays and patch-clamp electrophysiology.
Results :
Here we show that photoreceptor loss upregulates transmembrane P2X7 receptor in the inner retina. Knocking-out P2X7 in RD mice prevents hyperactivity, while P2X7 overexpression in WT retina increases spontaneous action potential firing. RNA-sequencing indicates RD enhances the expression of membrane depolarization-related genes in a P2X7-dependent manner, including ion channels and transporters such as HCN1, CACNA1h, RYR2/3, and SLC1A2 (figure 1). Patch-clamp recordings following photoreceptor loss reveal robust HCN1-dependent ion current activation in Off-RGCs but not On-RGCs, which was rescued by knocking-out P2X7.
Conclusions :
P2X7 is necessary and sufficient for degeneration-dependent hyperactivity in the inner retina of blind mice. Our results suggest that this effect is achieved through downstream activation of several ion channels and transporters, most significantly HCN1 channels in Off-RGCs. Targeting P2X7 in photoreceptor degeneration could be a viable therapeutic approach to antagonize pathophysiological remodeling, reduce spontaneous hyperactivity, and improve the SNR of light responses.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.