Effects of HO-1 on the Integrity of Retinal Pigment Epithelial Cells in Regulating Axial Elongation in Experimental Myopia

Purpose: The study aimed to explore the potential involvement of the heme oxygenase-1 (HO-1) protein in myopic axial elongation. Tight junctions (TJs) form the structural basis of retinal pigment epithelium (RPE) barrier functions. Although oxidative stress contributes to myopia, it remains unclear how HO-1 influences TJ integrity in RPE cells. Methods: Guinea pigs aged 2 to 3 weeks underwent bilateral lens-induced myopization (LIM) and received intraperitoneal injections (i.p.) of the HO-1 activators hemin 50 mg/kg, with or without inhibitor ZnPP 50 mg/kg. Ocular biometry, optical coherence tomography, and fundus photography were performed. Transmission electron microscopy (TEM) and confocal microscopy were used to assess TJ changes in myopic guinea pigs. ARPE19 cell cultures were treated with NaIO3 or ZnPP that regulated HO-1 expression. TJ integrity was examined by anti-zonula occludens 1 (ZO-1) and antioccludin staining of cultured cells, flatmount RPE tissues, and average length from the TEM pictures. Western blot analysis was used to evaluate protein expression levels. Results: Eyes subjected to LIM and LIM + hemin + ZnPP (i.p.) treatment exhibited significantly greater axial elongation than those in the control group (0.71 ± 0.03 mm and 0.68 ± 0.04 mm vs. 0.49 ± 0.06 mm, respectively), accompanied by increased HO-1 protein expression during the study period. No significant differences in axial length or refractive error were observed between the LIM and LIM + hemin + ZnPP (i.p.) groups. In contrast, eyes in the LIM + hemin (i.p.) group showed the greatest axial elongation (0.81 ± 0.04 mm), whereas eyes treated with LIM + ZnPP (i.p.) demonstrated inhibition of HO-1 overexpression and a marked attenuation of axial elongation (0.54 ± 0.05 mm). ZnPP treatment also preserved TJ integrity and mitigated retinal and choroidal thinning. Mechanistically, TJ structures were compromised in association with elevated HO-1 expression but were rescued by the HO-1 inhibitor ZnPP. Immunofluorescence analysis identified RPE cells as the primary site of HO-1 activation. Moreover, HO-1 overexpression resulted in downregulation of the TJ proteins ZO-1 and occludin, a finding that was further confirmed by Western blot analysis. Conclusions: Higher expression of HO-1 caused axial elongation and the development of refraction errors in guinea pigs. TJs were destroyed with myopia development and higher HO-1 expression. ZnPP, as an HO-1 inhibitor, may alleviate myopia development and TJ destruction in guinea pigs and RPE cells.