Retinal BMI1 Expression Preserves Photoreceptors in Sodium-Iodate-Induced Oxidative Stress Models

Abstract

Dry age-related macular degeneration (AMD) is a leading cause of vision loss in individuals over 50, yet no approved therapies exist for early or intermediate stages of the disease. Oxidative stress is a central driver of retinal degeneration in AMD, and sodium iodate (NaIO₃)-induced injury serves as a well-characterized model of oxidative damage to the retinal pigment epithelium (RPE) and photoreceptors. BMI1, a poly-comb group protein involved in DNA repair, mitochondrial function, and cellular renewal, has emerged as a promising therapeutic target for retinal neuroprotection. We evaluated the efficacy of AAV-mediated BMI1 gene delivery in murine models using two administration routes: subretinal (SR) and suprachoroidal (SC). AAV5.BMI1 (1 × 10⁹ vg/eye) was delivered SR in Balb/c mice and evaluated at 4 and 15 weeks post-injection. AAV8.BMI1 (5 × 10⁹ or 1 × 10¹⁰ vg/eye) was administered SC in C57BL/6 mice and assessed at 4 weeks. Control groups received BSS or AAV8.stuffer. Following NaIO₃ exposure, retinal structure and function were analyzed by optical coherence tomography (OCT), electroretinography (ERG), histology, and molecular assays. SC delivery of AAV8.BMI1 achieved the highest levels of retinal BMI1 expression with no evidence of local or systemic toxicity. Treated eyes showed dose-dependent preservation of outer nuclear layer (ONL) thickness and significantly improved ERG responses indicating structural and functional protection. These findings support SC AAV.BMI1 gene therapy as a promising, minimally invasive, and translatable approach for early intervention in intermediate AMD.

Keywords: AAV gene therapy; BMI1; age-related macular degeneration; retina; retinal pigment epithelium; sodium iodate.

Figure 1

Sodium iodate induces severe retinal degeneration in mice. (A) Representative OCT images 4 weeks post-injection with BSS or NaIO₃ (40 mg/kg, IV), demonstrating disruption of outer retinal layers in treated animals. GCL, ganglion cell layer; IPL, inner plexiform layer; INL, inner nuclear layer; OPL, outer plexiform layer; ONL, outer nuclear layer; ELM, external limiting membrane; IS/OS, inner/outer segments; RPE, retinal pigment epithelium. (B) Quantification of ONL thickness 1500 µm from the optic nerve (n = 10 eyes/group). (C) ERG recordings demonstrating complete loss of scotopic a-wave, photopic b-wave, and c-wave amplitudes in NaIO₃-treated animals (n = 10 eyes/group). Data are presented as mean ± SD. *** p < 0.001; **** p < 0.0001.

Figure 2

AAV-mediated BMI1 gene therapy induces durable, dose-dependent expression in murine retina and RPE. (A) BMI1 mRNA levels in RPE at 4, 8, and 14 weeks following subretinal AAV5.BMI1 (1 × 10⁹ vg/eye) delivery (n = 5 per group). (B) BMI1 protein levels in retina and RPE measured by MSD assay 4 weeks after suprachoroidal AAV8.BMI1 delivery at 5 × 10⁹ or 1 × 10¹⁰ vg/eye (n = 5 per group). (C) BMI1 mRNA expression in microdissected retina and RPE following high-dose suprachoroidal AAV8.BMI1 (1 × 10¹⁰ vg/eye) administration (n = 5 per group). Data are presented as mean ± SD. * p < 0.05; ** p < 0.01; *** p < 0.001; and **** p < 0.0001.

Figure 3

AAV-delivered BMI1 protects against NaIO₃-induced retinal damage. (A) Rhodopsin immunofluorescence (green) in retinas of BSS or AAV5.BMI1-SR-treated Balb/c mice (50 mg/kg NaIO₃, IP; n = 7), showing ONL preservation in treated mice. Magnification (20×). (B) H&E staining of retinal cross-sections following AAV5.BMI1 or control treatment reveals preservation of retinal layers in BMI1-treated mice. Magnification (20×). (C) BMI1 immunohistochemical staining (brown) in C57BL/6 mice shows robust nuclear BMI1 expression in the ONL following AAV8.BMI1 treatment (40 mg/kg NaIO₃, IV; n = 5). Magnification (20×). (D) Representative ONL measurements from H&E-stained retinas. (E) Quantification of ONL thickness from baseline (1500 µm from optic nerve) shows significant ONL preservation in AAV8.BMI1-treated animals. (F) Total ONL thickness is significantly increased in AAV8.BMI1-treated eyes compared with controls. Data are presented as mean ± SD, ** p < 0.01; *** p < 0.001; n = 5 per group.

Figure 4

AAV8.BMI1 preserves retinal function following NaIO₃-induced oxidative stress. Representative ERG traces recorded at baseline and 4 weeks post-NaIO₃ injection in mice treated with BSS, AAV8.stuffer, or AAV8.BMI1 at two doses. Quantification of scotopic a-wave and photopic b-wave amplitudes demonstrates significant functional preservation in animals receiving 1 × 10¹⁰ vg/eye AAV8.BMI1 (n = 5 per group). Data are shown as mean ± SD. * p < 0.05.