IMMUNOLOCALIZATION OF PROLYL 4-HYDROXYLASE SUBUNITS, ALPHA-SMOOTH MUSCLE ACTIN, AND EXTRACELLULAR-MATRIX COMPONENTS IN HUMAN LENS CAPSULES WITH LENS IMPLANTS

Lens capsules become fibrotic after the extraction of a cataract. To u nderstand this phenomenon, we evaluated the immunolocalization of prol yl 4-hydroxylase (an enzyme involved in procollagen hydroxylation), an d extracellular matrix components and cytoskeletal components in a nor mal human lens capsule and in others with intraocular lenses. Lens cap sules containing intraocular lenses were removed from a patient with p roliferative vitreoretinopathy and three with proliferative diabetic r etinopathy during vitreous surgery. Two circular sections of the anter ior capsules with lens epithelial cells were obtained by anterior caps ulotomy during cataract surgery. In addition, a lens capsular bag was obtained immediately after phacoemulsification. The lens capsules were processed for light microscopic immunohistochemical detection of the alpha and beta subunits of prolyl 4-hydroxylase, extracellular matrix components (including collagen types, laminin and cellular fibronectin ) or cytoskeletal components (such as cytokeratin, vimentin and alpha- smooth muscle actin). Monolayer lens epithelial cells were seen on the inner surface of the normal anterior capsules. Each intraocular lens was found to be fixed in the capsular bag. Light microscopic immunohis tochemistry showed that these proliferating cells expressed vimentin a nd alpha-smooth muscle actin; in contrast, quiescent lens epithelial c ells did not stain for alpha-smooth muscle actin. Marked immunostainin g for subunits of prolyl 4-hydroxylase was detected in lens epithelial cells proliferating on the capsules, while no or only faint prolyl 4- hydroxylase immunoreactivity was detected in quiescent lens epithelial cells immediately after phacoemulsification. Collagen types I, III an d VI and cellular fibronectin were observed diffusely in accumulated c onnective tissue on a capsule with an intraocular lens. Type TV collag en immunoreactivity was seen both in the capsules and in the connectiv e tissue accumulation on the capsules. Collagen V and laminin were det ected in association with cellular proliferation. Collagen VII and VII I and laminin 5 were not seen. We concluded that during wound healing of the lens capsule after cataract extraction, the lens epithelial cel ls that proliferate on the inner surface of the capsule transform it i nto a myofibroblastic phenotype, expressing prolyl 4-hydroxylase and a lpha-smooth muscle actin. These proliferating cells are involved in th e production of collagen on the lens capsule. This results in a postop erative fibrotic process and contraction of the lens capsule. (C) 1998 Academic Press Limited.