Lack of type XVIII collagen results in anterior ocular defects.

Mice lacking type XVIII collagen have defects in the posterior part of the eye, including delayed regression of the hyaloid vasculature and poor outgrowth of the retinal vessels. We report here that these mice also have a fragile iris and develop atrophy of the ciliary body. The irises of Col18a1-/- mice can be seen to adhere to the lens and cornea. After the pupils begin to function, the double layer of epithelial cells separates at the apical cell contacts, leading to defoliation of its posterior pigment epithelial cell layer, and extracellular material begins to accumulate in the basement membrane zones of the iris. In contrast to the iris epithelia, where no clear signs of cellular atrophy were detected, the lack of type XVIII collagen resulted in atrophy of the pigmented epithelial cells of the ciliary body, and there were also ultrastructural abnormalities in the basement membrane zones. These changes did not lead to chronically elevated intraocular pressures, however. Our results indicate that type XVIII collagen is needed for the integrity of the epithelial basement membranes of the iris and the ciliary body and that its gene should therefore be taken into account as a new potential cause of anterior segment disorders in the eye.

Structurally altered basement membranes and hydrocephalus in a type XVIII collagen deficient mouse line.

Type XVIII collagen/endostatin is known to be crucial for the eye, as witnessed by severe eye defects in Knobloch syndrome patients with mutations in this collagen and in Col18a1(-/-) mice. We show here that in a specific C57BL background, 20% of the Col18a1(-/-) mice developed hydrocephalus, and dilation of the brain ventricles was observed by MRI in all of the mutant mice. Significant broadening was observed in the epithelial basement membrane (BM) of the choroid plexuses (CP), its width being 86.4+/-10.52 nm, compared with 61.4+/-6.05 nm in wild-type mice. The CP epithelial cell morphology was balloon-shaped rather than cuboidal, and the microvilli of the apical surface of the CP epithelium contained more vacuoles in the null mice than in the wild-type, as also did the CP epithelial cells, which is suggestive of alterations in cerebrospinal fluid production. Analysis of BMs elsewhere in the body revealed a broadened epidermal BM in the Col18a1(-/-) mice, but this did not result in any apparent functional deficiencies. Moreover, markedly broadened BMs were found in the atrioventricular valves of the heart and in the kidney tubules, whereas the glomerular mesangial matrix of the kidneys was expanded in the mutant mice and serum creatinine levels were elevated, indicating alterations in kidney filtration capacity. We thus suggest that type XVIII collagen is a structurally important constituent of BMs, and that its absence can result in a variety of phenotypic alterations.