Age-dependent iris abnormalities in collagen XVIII/endostatin deficient mice with similarities to human pigment dispersion syndrome.
OBJECTIVE
Collagen XVIII is expressed in ocular basement membranes (BMs) and inactivating mutations cause Knobloch syndrome, with several ocular abnormalities. In this study we investigated ocular structures in collagen XVIII/endostatin (Col18a1(-/-))-deficient mice to elucidate the role of this extracellular matrix component in the eye.


METHODS
Eyes of Col18a1(-/-) and control mice were examined by light and transmission electron microscopy, laser scanning ophthalmoscopy, and fluorescence angiography. Immunohistochemical analysis of neuronal, epithelial, and immune cells in the eye was performed with antibodies against established cell markers.


RESULTS
Col18a1(-/-) mice showed a disruption of the posterior iris pigment epithelial (IPE) cell layer with release of melanin granules. The BM of the posterior IPE was attached to the lens and the nonpigmented epithelium of the ciliary body, which was flattened in mutant mice. In aged mutant mice a severe thickening of the stromal iris BM zone was found, and pigmented cells migrated out of the iris and covered the retina along the inner limiting membrane (ILM), sometimes penetrating into the retina. These cells resembled iris clump cells, and immunohistochemistry demonstrated that they were macrophage-like cells. Furthermore, morphologically abnormal retinal vasculature was seen by fluorescence angiography.


CONCLUSIONS
The abnormalities in the iris and ciliary body of Col18a1(-/-) mice demonstrate an important role of collagen XVIII for the function of ocular BMs. The absence of this collagen alters the properties of BMs and leads to severe defects in the iris, showing striking similarities to human pigment dispersion syndrome. In addition, loss of collagen XVIII creates changes that allow clump cells to migrate out of the iris. These cells have not been well characterized previously. In the current study we showed that they are macrophage-like cells and are able to penetrate the ILM in mutant mice. The disease mechanism of human pigment dispersion syndrome is not well understood, but Col18a1(-/-) mice may serve as a model and demonstrate the potential importance of alterations in extracellular matrix components in this disease.
Marneros
Alexander G
AG
Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115, USA. alexander_marneros@hms.harvard.edu
Olsen
Bjorn R
BR
D000375:Aging; D020533:Angiogenesis Inhibitors / Q000172:deficiency / Q000502:physiology*; D000818:Animals; D001485:Basement Membrane / Q000502:physiology / Q000648:ultrastructure; D002924:Ciliary Body / Q000002:abnormalities / Q000378:metabolism / Q000648:ultrastructure; D003094:Collagen / Q000172:deficiency / Q000502:physiology*; D043170:Collagen Type XVIII; D043169:Endostatins; D017889:Exfoliation Syndrome / Q000209:etiology* / Q000378:metabolism / Q000473:pathology; D005109:Extracellular Matrix / Q000502:physiology / Q000648:ultrastructure; D005124:Eye Abnormalities / Q000209:etiology* / Q000378:metabolism / Q000473:pathology; D005260:Female; D005451:Fluorescein Angiography; D019084:Fluorescent Antibody Technique, Indirect; D007498:Iris / Q000002:abnormalities* / Q000473:pathology; D007499:Iris Diseases / Q000209:etiology* / Q000378:metabolism / Q000473:pathology; D008297:Male; D008543:Melanins / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D016253:Microscopy, Immunoelectron; D009887:Ophthalmoscopy; D010446:Peptide Fragments / Q000172:deficiency / Q000502:physiology*; D010857:Pigment Epithelium of Eye / Q000378:metabolism / Q000473:pathology / Q000648:ultrastructure; D014603:Uveal Diseases / Q000209:etiology / Q000378:metabolism / Q000473:pathology
D020533:Angiogenesis Inhibitors; D043170:Collagen Type XVIII; D043169:Endostatins; D008543:Melanins; D010446:Peptide Fragments; D003094:Collagen