Adenosine A₁Receptors Selectively Modulate Oxygen-Induced Retinopathy at the Hyperoxic and Hypoxic Phases by Distinct Cellular Mechanisms

Abstract

PURPOSE.We critically evaluated the role of the adenosine A 1 receptor (A 1 R) in normal development of retinal vasculature and pathogenesis of retinopathy of prematurity (ROP) by using the A 1 R knockout (KO) mice and oxygen-induced retinopathy (OIR) model. METHODS.Mice deficient in A 1 Rs and their wild-type (WT) littermates were examined during normal postnatal development or after being subjected to 75% oxygen from postnatal day (P) 7 to P12 and to room air from P12 to P17 (OIR model of ROP). Retinal vascularization was examined by whole-mount fluorescence and cross-sectional hematoxylin-eosin staining. Cellular proliferation, astrocyte and microglial activation, and tip cell function were determined by isolectin staining and immunohistochemistry. Apoptosis was determined by TUNEL assay.RESULTS. Genetic deletion of the A 1 R did not affect normal retinal vascularization during postnatal development with indistinguishable three-layer vascularization patterns in retina between WT and A 1 R KO mice. In the OIR model, genetic deletion of the A 1 R resulted in stage-specific effects: reduced hyperoxia-induced retinal vaso-obliteration at P12, but reduced avascular area and attenuated hypoxia-induced intraretinal revascularization without affecting intravitreal neovascularization at P17 and reduced avascular areas in retina at P21. These distinct effects of A 1 Rs on OIR were associated with A 1 R control of apoptosis mainly in inner and outer nuclear layers at the vasoobliterative phase (P12) and the growth of endothelium tip cells at the vasoproliferative phase (P17), without modification of cellular proliferation, astrocytic activation, and tissue inflammation.CONCLUSIONS. Adenosine A 1 receptor activity is not required for normal postnatal development of retinal vasculature but selectively controls hyperoxia-induced vaso-obliteration and hypoxia-driven revascularization by distinct cellular mechanisms.

Adenosine receptors and caffeine in retinopathy of prematurity

“…Our characterization of the A 1 R KO and WT mice in normal and OIR model demonstrate that genetic deletion of the A 1 R does not affect normal retinal vascularization during postnatal development since ontogeny of the superficial, deep and intermedial layers of retinal vasculatures is largely indistinguishable between WT and A 1 R KO mice (Zhang et al, 2015). However, in OIR model, A 1 R activity distinctly controls hyperoxia-induced vaso-obliteration at postnatal day (P) 12 and hypoxia-induced revascularization at P17.…”

“…The A 1 R mRNA and ligand binding are detected in developing retina (Brito et al, 2012) and is reduced in retina of OIR model (Zhang et al, 2015). Our characterization of the A 1 R KO and WT mice in normal and OIR model demonstrate that genetic deletion of the A 1 R does not affect normal retinal vascularization during postnatal development since ontogeny of the superficial, deep and intermedial layers of retinal vasculatures is largely indistinguishable between WT and A 1 R KO mice (Zhang et al, 2015).…”

“…At the vaso-proliferative phase (P17), A 1 R KO attenuates hypoxia-induced intra-retinal revascularization without affecting intra-vitreal neovascularization at P17. This effect of A 1 R KO on OIR is associated with the reduced number of endothelium tip cells, without modification of cellular proliferation and astrocytic activation (Zhang et al, 2015). Thus, A 1 R activity is not required for normal postnatal development of retinal vasculatures, but selectively controls hyperoxia-induced vaso-obliteration and hypoxia-driven revascularization by distinct cellular mechanisms.…”

“…Indeed, our preliminary study indicates the protection against pathological angiogenesis at the hypoxic phase (P17) by A 2A R KO and by A 2A R antagonists (KW6002) and by caffeine (non-selective adenosine receptor antagonists). However, detailed analysis indicated that A 1 R KO reduced avascular areas at during the hyperoxic phase (P12) (Zhang et al, 2015). Similarly, A 2A R KO and caffeine was effective in protecting OIR not only at P17, but also at P12 (unpublished data).…”

Aberrant adenosine A2A receptor signaling contributes to neurodegeneration and cognitive impairments in a mouse model of synucleinopathy

“…The TUNEL staining was performed on 30 μm sticking frozen sections using a commercial In Situ Cell Death Detection Kit (Roche Diagnostics, Basel, Switzerland) as we described recently (Zhang et al, 2015). Briefly, hippocampal sections (30 μm) were permeabilized and antigen retrieval by 0.1% sodium citrate buffer solution with 0.1% Triton X-100 for 5 min at 4 °C.…”