Matrix metalloproteinase-1 localization in the normal human uveoscleral outflow pathway

To determine the distribution of matrix metalloproteinase-1 (MMP-1) in the uveoscleral outflow pathway and other anterior segment tissues of normal human eyes.

Normal human eyes were fixed in methacarn and sectioned and immunostained using a specific polyclonal antibody to MMP-1. Immunoreactivity was visualized using diaminobenzidine. To compare the staining intensity in various tissues, the mean optical density within the ciliary body, mid-iris stroma, iris root, uveal trabecular meshwork, cornea, and sclera was determined using imaging densitometry. To determine the cellular distribution of MMP-1 in ciliary muscle, additional sections were double-immunostained using antibodies to MMP-1 and calponin. These sections were examined by confocal laser scanning microscopy. Specificity of the antibody to MMP-1 in ocular tissues was confirmed by western blot analysis with uveal tract homogenates.

Moderate-to-strong MMP-1 immunoreactivity was observed in ciliary muscle, iris, sclera, corneal endothelium, and ciliary nonpigmented epithelium. Lighter immunoreactivity was observed in corneal epithelium, blood vessels, trabecular meshwork, Schlemm's canal, and associated collector channels. Confocal microscopy showed that ciliary muscle MMP-1 was primarily inside ciliary muscle cells. Densitometry showed that net optical density was approximately fivefold greater in ciliary muscle, iris root, and sclera than in trabecular meshwork.

MMP-1 was prominently identified in regions of the anterior segment of normal human eyes associated with the uveoscleral outflow pathway and in the iris, corneal endothelium, and ciliary nonpigmented epithelium. These data support the hypothesis that MMP-1 activity is involved in regulating uveoscleral outflow facility.