Oral Delivery of the P2Y₁₂Receptor Antagonist Ticagrelor Prevents Loss of Photoreceptors in an ABCA4^−/−Mouse Model of Retinal Degeneration

Abstract

Purpose Accumulation of lysosomal waste is linked to neurodegeneration in multiple diseases, and pharmacologic enhancement of lysosomal activity is hypothesized to reduce pathology. An excessive accumulation of lysosomal-associated lipofuscin waste and an elevated lysosomal pH occur in retinal pigment epithelial cells of the ABCA4 −/− mouse model of Stargardt's retinal degeneration. As treatment with the P2Y 12 receptor antagonist ticagrelor was previously shown to lower lysosomal pH and lipofuscin-like autofluorescence in these cells, we asked whether oral delivery of ticagrelor also prevented photoreceptor loss. Methods Moderate light exposure was used to accelerate photoreceptor loss in albino ABCA4 −/− mice as compared to BALB/c controls. Ticagrelor (0.1%–0.15%) was added to mouse chow for between 1 and 10 months. Photoreceptor function was determined with electroretinograms, while cell survival was determined using optical coherence tomography and histology. Results Protection by ticagrelor was demonstrated functionally by using the electroretinogram, as ticagrelor-treated ABCA4 −/− mice had increased a- and b-waves compared to untreated mice. Mice receiving ticagrelor treatment had a thicker outer nuclear layer, as measured with both optical coherence tomography and histologic sections. Ticagrelor decreased expression of LAMP1, implicating enhanced lysosomal function. No signs of retinal bleeding were observed after prolonged treatment with ticagrelor. Conclusions Oral treatment with ticagrelor protected photoreceptors in the ABCA4 −/− mouse, which is consistent with enhanced lysosomal function. As mouse ticagrelor exposure levels were clinically relevant, the drug may be of benefit in preventing the loss of photoreceptors in Stargardt's disease and other neurodegenerations associated with lysosomal dysfunction.

The P2X7 Receptor in Microglial Cells Modulates the Endolysosomal Axis, Autophagy, and Phagocytosis

“…Increased clearance can also be induced by stimulating the cystic-fibrosis transmembrane conductance regulator (CFTR) chloride channel localized to the lysosomal membrane (Liu et al, 2012 ), or by acid nanoparticles transported to the lysosomal lumen (Baltazar et al, 2012 ; Lööv et al, 2015 ). Antagonists targeted to the P2Y 12 receptor were recently shown to lower lysosomal pH and improve clearance; of note, oral delivery of the FDA-approved antagonist ticagrelor (Brilinta) lowered lysosomal pH and was protective in a mouse model of neurodegeneration (Lu et al, 2018 , 2019 ). Whether this drug can cross the blood-brain barrier to reach microglial cells, and whether it will interfere with other microglial functions regulated by the P2Y 12 receptor remains to be determined.…”

Rapid morphologic changes to microglial cells and upregulation of mixed microglial activation state markers induced by P2X7 receptor stimulation and increased intraocular pressure

“…Retinae or isolated microglia were homogenized using TRIzol (Invitrogen). RNA was purified with an RNeasy mini kit (Qiagen, Inc.) and converted to cDNA using a High Capacity cDNA Reverse Transcription Kit (Applied Biosystems); qPCR was performed with Power or PowerUp SYBR green (Applied Biosystems) on the 7300 or Quant Studio 3 Real-Time PCR systems (Applied Biosystems) using standard annealing and elongation protocols, with data analyzed using the delta-delta CT approach as described [ 39 ]. Primers are listed in Table 2 .…”

Impaired cathepsin D in retinal pigment epithelium cells mediates Stargardt disease pathogenesis

“…21 Additionally, Abca4 −/− mice treated with the P2Y 12 receptor antagonist Ticagrelor showed restored lysosomal acidity, reduced autofluorescence, and protection against photoreceptor degeneration. 23,49 Here, we demonstrate that Ticagrelor treatment in RPE cells derived from two STGD1 patients efficiently reduces lysosomal pH (Figure 6C). Importantly, the re-acidification of lysosomes of STGD1 RPE cells treated with Ticagrelor had significant positive outcomes: (i) immature CatD aggregates were reduced to near normal levels (Figure 6D,E), and (ii) proper CatD protein maturation restored CatD proteolytic activity to normal levels (Figure 6F).…”

“…Pharmacological therapies targeting the re‐acidification of lysosomes were tested in models for neurodegenerative diseases and lysosomal storage disorders to reduce pathologies associated with waste material buildup 48 . Particularly in the RPE, manipulation of cytoplasmic cAMP levels by pharmacological means has been effective in lowering lysosomal pH 21,23,49 . Abca4 −/− mice fed with Ticagrelor, a P2Y 12 receptor antagonist, restored lysosomal acidity and reduced RPE autofluorescence 23 .…”