Type VII collagen (Col VII) is renowned as the major component of anchoring fibrils.
1 It is essential for epithelium-to-stroma anchorage in skin, mucosa, and cornea.
2,3 Although predominantly expressed in skin, Col VII is estimated to comprise a mere 0.001% of the total skin collagen content.
4 Yet, the relevance of such levels of Col VII expression is clinically evidenced in severe dystrophic epidermolysis bullosa, in which patients lack functional Col VII (i.e., anchoring fibrils). Their skin blisters readily at small amounts of friction, damaging their epithelial basement membranes at each event. Such repetitive wounding is accompanied by severe and extensive scar formation, mutilating deformations, and recurrent infections. Patients succumb to skin cancer or sepsis often before age 35.
5,6 Extraocular manifestations are well documented, and encompass mainly corneal and conjunctival (both surface ectoderm) erosions accompanied by scar formation, symblepharon, pannus, and so forth.
6 Intraocular manifestations are mentioned only in rare case reports, where no clinical or histological abnormalities are found,
7 or are limited to lens (also surface ectoderm) sclerosis.
7–9 Interestingly, however, retinal COL7A1 gene expression was recently established (FANTOM5 consortium
10). Moreover, its protein product was demonstrated at the vitreoretinal junction
11,12 and inner layers of the normal retina,
12,13 although no anchoring fibrils were visualized. Anchoring fibrils, however, are reported to be far more numerous at basement membrane zones of mechanically strained tissues.
2,14,15 To investigate the characteristics of intraocular Col VII further, we explored the accommodation system. We observed COL7A1 expression at the pigmented and nonpigmented ciliary epithelia, and Col VII protein at the ciliary body and zonules.