Up-Regulation of NLRP3 in the Sclera Correlates with Myopia Progression in a Form-Deprivation Myopia Mouse Model.

BACKGROUND

NOD-, LRR-, and pyrin domain-containing protein 3 (NLRP3) is a common inflammatory factor that induces inflammation by increasing the expression of related cytokines. Although the NLRP3 inflammasome has been implicated in many ophthalmic diseases, its role in myopia is largely unknown. The aim of this study was to explore the relationship between myopia progression and the NLRP3 pathway.

METHODS

A form-deprivation myopia (FDM) mouse model was used. Different degrees of myopic shift were achieved via monocular form deprivation with 0-, 2-, and 4-week covering, and by 4-week covering followed by 1-week uncovering (the blank, FDM2, FDM4, and FDM5 groups, respectively) in both wild-type and NLRP3 (-/-) C57BL/6J mice. Axial length and refractive power were measured to assess the specific degree of myopic shift. The protein levels of NLRP3 and of related cytokines in the sclera were evaluated by Western blotting and immunohistochemistry. Collagen I and matrix metalloproteinase-2 (MMP-2), which affect extracellular matrix (ECM) remodeling of the sclera, were also examined to clarify the possible underlying mechanism.

RESULTS

In wild-type mice, the FDM4 group had the most significant myopic shift. Both the increase in refractive power and the elongation in axial length were significantly different between the experimental and control eyes in the FDM2 group. The protein levels of NLRP3, caspase-1, IL-1β, and IL-18 were significantly up-regulated in the FDM4 group compared to the other groups. The myopic shift was reversed and there was less up-regulation of cytokines in the FDM5 group compared to the FDM4 group. MMP-2 expression showed similar trends to NLRP3, while collagen I expression was inversely correlated. Similar results were found in NLRP3 -/- mice, although there was less myopic shift and less obvious changes in cytokine expression in the treatment groups as compared to the wild-type mice. In the blank group, no significant differences were found in refraction and axial length between wild-type mice and NLRP3 -/- mice of the same age.

CONCLUSIONS

NLRP3 activation in the sclera could be involved in myopia progression in the FDM mouse model. Activation of the NLRP3 pathway up-regulated MMP-2 expression, which in turn affected collagen I and caused scleral ECM remodeling, eventually affecting myopic shift.