Scleral macrophages contribute to myopia development via MMP-2 upregulation

Abstract

Purpose : Even though scleral macrophages are present in abundance in human and rodent sclera, nothing is known about their possible contribution to restructuring this tissue during myopia progression. We aimed here to address this question in a form-deprivation myopia (FDM) mouse model.

Methods : Myopia was induced in 3-week-old male wild-type C57BL/6 mice by subjecting them to form deprivation (FD) for 2 weeks. At the end of each treatment period, immunofluorescent staining evaluated the scleral macrophage density along with the MMP-2 expression levels in macrophages in the FD treated right eyes (FD-T). The densities of scleral macrophage were also evaluated in the fellow non-deprived left eyes (FD-F) and the normal control eyes (NC) of age-matched mice. To assess the effect of macrophage-specific Mmp-2 deletion on myopia progression, the FDM development in macrophage-specific Mmp-2 deletion (LysM^CreMmp-2^fl/fl) mice was compared with this process in their Cre-negative littermate control (Mmp-2^fl/fl) mice.

Results : After 2 weeks of FD, the macrophage density along with their MMP-2 expression levels was markedly greater in the posterior region of the scleras of FD-T eyes than in either the FD-F or NC eyes in wild type mice. After 4 weeks of FD, double F4/80 and MMP-2 immunofluorescence showed that both their density and percentage of MMP-2⁺F4/80⁺ cells among the entire F4/80⁺ cell population in the scleras increased in the FD-T eyes of Mmp-2^fl/fl + FD mice, but not in the FD-T eyes of LysM^CreMmp-2^fl/fl + FD mice as compared with respective levels in the FD-F eyes. Furthermore, the FD-induced increases in density and percentage of the MMP-2⁺ F4/80⁺ cells were both suppressed in the LysM^CreMmp-2^fl/fl -FD-T eyes, as compared with Mmp-2^fl/fl-FD-T eyes. After 4 weeks of FD, the myopia induced in the LysM^CreMmp-2^fl/fl) mice was 59% less than that in the Mmp-2^fl/fl mice. Consistent with these differences in refraction, the increase in AL was significantly inhibited in the LysM^CreMmp-2^fl/fl mice, relative to that in Mmp-2^fl/fl mice.

Conclusions : FD-induced increases in scleral macrophage abundance which accompanied MMP-2 upregulation. This association suggests that such increases contribute to the ECM remodeling process underlying myopia progression.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.