Macrophage-Associated Gelatinase Degrades Basement Membrane at the Optic Fissure Margins During Normal Ocular Development in Mice

Basement membrane degradation and macrophage aggregation at the optic fissure margins are crucial to optic fissure closure during normal murine eye development. Basement membrane degradation is also an essential step in cancer development, and matrix metalloproteinases (MMPs) play an important role. In this study, we investigated MMP alteration at the degrading basement membrane of optic fissure margins in mice and attempted to clarify the relationship between MMP activity and macrophages. Serial coronal frozen sections of eyes from BALB/c fetuses were prepared and gelatinase activity was examined using in situ zymography techniques. The frozen sections were immunohistochemically stained with anti-F4/80, anti-MMP 2, and anti-MMP 9 antibodies. Serial coronal paraffin sections were also immunohistochemically stained with anti-type IV collagen and anti-F4/80, and basement membrane disintegration and macrophage aggregation at the optic fissure margins were examined. The basement membrane of optic fissure margins was rapidly degraded during gestational days (GDs) 12.0 to 12.5. Meanwhile, gelatinase activity at F4/80-positive macrophages significantly increased during GDs 11.5 to 12.0 and declined thereafter; some of those were also positive for MMP2. The number of macrophages was also increased and decreased at nearly the same time. Intramacrophage MMPs may be responsible for basement membrane degradation at the optic fissure margins during normal eye development in mice.