Retinitis pigmentosa (RP) exhibits complex genetic heterogeneity, and the downstream pathogenic mechanisms underlying different etiologies remain unclear. This study aimed to explore the differential mechanisms by which the metabolite uridine and its receptor P2Y6R regulate microglial activation and photoreceptor apoptosis in different RP animal models.

① Uridine content in the retina was measured using ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) in rd1 mice (aged 28 d, weighing 13 to 18 g, n=3), rd10 mice (aged 45 d, weighing 20 to 25 g, n=3) and age-matched C57 BL/6J control mice (n=3/group), as well as RCS rats (aged 60 d, weighing 200 to 250 g, n=4) and age-matched RCS-rdy control rats (n=4). Retinal pyrimidine metabolites were analyzed using ultra performance liquid chromatography-high resolution mass spectrometry (UPLC-HRMS) at various disease stages in rd10 mice (aged 18 d, weighing 7 to 10 g; aged 25 d, weighing 11 to 15 g; aged 45 d; n=5), with age-matched C57 BL/6J mice serving as controls (n=5). ② Five-week-old C57 BL/6J mice received unilateral subretinal injection of uridine (100 mmol/L, 2 μL), with contralateral eyes injected with PBS as controls. After 7 d, electroretinography (ERG), outer nuclear layer (ONL) thickness analysis, immunofluorescence staining, and TUNEL assay were performed (n=3). ③ RT-qPCR was used to detect mRNA expression of P2Y receptor family members (P2ry1, P2ry2, P2ry4, P2ry6, P2ry12) in the retina of C57 BL/6J mice following subretinal injection of uridine or PBS (n=3). ④ The P2Y6R inhibitor MRS2578 (3 mg/kg per day) or vehicle (corn oil containing 0. 6% dimethyl sulfoxide) was administered to rd10 mice (aged 14 d, weighing 7 to 10 g, n=3) and RCS rats (aged 15 d, weighing 25 to 30 g, n=3) prior to degeneration onset. ERG, ONL thickness, photoreceptor apoptosis, and microglial number and morphology were evaluated. ⑤ RT-qPCR was performed to detect the expression of uridine synthesis and metabolism-related enzymes (Upp1, Upp2, Uck1, Uck2) in the retina of 45-day-old rd10 and C57 BL/6J mice (n=3).

① Compared with age-matched C57 BL/6J control mice, retinal uridine content was significantly elevated in rd1 and rd10 mice (P<0. 05), whereas no significant change was observed in RCS rats compared with age-matched RCS-rdy control rats. Retinal uridine levels in rd10 mice progressively increased with disease progression compared with age-matched C57 BL/6J control mice (P<0. 0001). ② Subretinal injection of uridine in C57 BL/6J mice resulted in significant reductions in a-wave and b-wave amplitudes (P<0. 05), ONL thinning (P<0. 0001), increased microglial activation (P<0. 01) with migration toward the ONL, and increased TUNEL-positive cells (P<0. 01). ③ After uridine injection, the mRNA expression of P2ry6 was upregulated in the retina of C57 BL/6J mice (P<0. 05). ④ Compared with the vehicle-treated group, MRS2578 treatment significantly improved the amplitudes of the a-wave and b-wave (P<0. 05), increased the ONL thickness, reduced the number of TUNEL-positive cells (P<0. 05), and promoted the reversal of microglia from an amoeboid-activated state to a resting, ramified state in rd10 mice. In contrast, in RCS rats, MRS2578 treatment failed to significantly inhibit microglial activation or delay retinal degeneration compared with vehicle-treated controls. ⑤ Compared with age-matched C57 BL/6J control mice, rd10 mice exhibited upregulated expression of Upp1 (P<0. 05), Upp2 (P<0. 01), and Uck1 (P<0. 01) in the retina, with decreased UMP and uracil levels.

The uridine-P2Y6R signaling axis exacerbates retinal degeneration through microglial activation in the rd10 mouse model of primary photoreceptor degeneration, whereas this mechanism is absent in the RCS rat model of primary retinal pigment epithelial dysfunction. These findings reveal the heterogeneity of retinal degeneration mechanisms across different etiological backgrounds, suggesting that targeting the uridine-P2Y6R axis may represent a potential therapeutic strategy for specific RP subtypes.

To investigate the potential therapeutic targets and underlying molecular mechanisms of Z-ligustilide (Z-LIG) in treating retinitis pigmentosa (RP).

By integrating multiple databases, such as GeneCards and TargetNet, common targets for RP and Z-LIG were identified. Protein-protein interaction (PPI) network analysis of the targets was conducted using the STRING database and analyzed in Cytoscape to identify core targets. The DAVID database was employed for the functional enrichment analysis of Gene Ontology (GO) and the pathway enrichment analysis of Kyoto Encyclopedia of Genes and Genomes (KEGG) for the core targets. The PubChem database was accessed for molecular docking verification to validate the binding affinity between Z-LIG and the core targets. Finally, male rd10 mice were randomly divided into a control group (n=5) and a Z-LIG treatment group (n=5). The protective effect of Z-LIG on the visual function in rd10 mice was verified through visual electrophysiology and behavioral tests. Western blotting and RT-qPCR were utilized to investigate the molecular mechanism of action.

A total of 66 shared targets between RP and Z-LIG were identified through the screening process. PPI network analysis identified 55 key targets. GO enrichment analysis yielded 623 terms, which covering 3 dimensions, including cellular component (CC), molecular function (MF), and biological process (BP), such as inflammatory response. KEGG pathway enrichment analysis further concentrated 124 terms, which were enriched in the PI3K-Akt signaling pathway. Molecular docking suggested that Z-LIG could specifically bind with high affinity to RP-related core targets (such as EGFR and STAT3) via hydrogen bonds. In animal experiments, compared to the control group, the rd10 mice from the Z-LIG group showed a greater preference for the dark environment in the light/dark transition test (P<0.05), exhibited significantly higher amplitudes of A-wave and B-wave in electroretinogram (ERG) (P<0.05), greater number of outer nuclear layers, with fewer apoptotic cells and less microglial activation (P<0.05), demonstrated obviously reduced protein levels of p-PI3K/PI3K and p-AKT/AKT in the retina (P<0.05), and had notably down-regulated mRNA levels of pro-inflammatory cytokines IL-1β and IL-6 (P<0.05).

Z-LIG may exert a protective effect on the retina of rd10 mice by inhibiting the activation of the PI3K/AKT-inflammatory axis, thereby delaying retinal degeneration.

To explore the differences in therapeutic efficacy and possible mechanism of different routes of administration of fullerene nanoparticles in the treatment of radiation retinopathy.

Eight-week-old adult male SD rats were randomly divided into blank group (Control), irradiation group (X-Ray), irradiation+vitreous cavity administration group [X+F (IVT)], irradiation+ocular surface administration group [X+F (OS)], and irradiation+intravenous administration group [X+F (IV)], with 5 rats in each group. The blank group was not treated, the irradiation groups exposed to X-ray irradiation to establish the model, and fullerenol nanoparticles were given to the treatment groups through different routes after irradiation. At 7, 14, and 28 d after modeling, body weight and fundus changes were measured to evaluate drug safety, retinal optical coherence tomography (OCT) was used to observe the change in retinal tissue structure, and electroretinography (ERG) was applied for oscillatory potentials (OPs) to evaluate visual function. CD31 immunofluorescence staining was carried out to evaluate retinal endothelial vascular status, and in vivo imaging was utilized to evaluate the accumulation of fullerenol nanoparticles in the eyes.

The growth curves of body weight demonstrated that fullerenol nanoparticles did not affect the growth and development of rats, with no statistical difference between the treatment groups and the control group. Irradiation resulted in a significant reduction in visual function, decreased amplitudes of a-wave and b-wave, and declined OPs (P<0.01), and significantly increased thicknesses of the ganglion cell layer (GCL) and the inner nuclear layer (INL) in the retinas, as evidenced by OCT (P<0.01), along with a notably absent presence of CD31-positive cells (P<0.01). Notably, the X+F (IVT) group obtained significantly improved visual function after intravitreal administration, effectively maintained thickness of the GCL and INL, and prevention against the loss of CD31-positive cells (P<0.01). However, no such effective results were observed in the irradiated groups receiving intravenous either ocular surface administration. In vivo imaging revealed that intravitreal administration maintained high ocular accumulation of fullerene for 96 h, while ocular surface administration sustained these concentrations for only 12 h. Intravenous administration, in contrast, only led to a predominant drug distribution in vascular-rich areas, but reduced ocular accumulation.

Fullerene nanoparticles possess a therapeutic effect on radiation retinopathy, and the intravitreal administration route demonstrates better efficacy than ocular surface and intravenous administration.