Abstract
Abstract: :
Purpose:To characterize the previously described (Marsili et al., Exp. Eye Res. 79, 595–612, 2004) unusual pattern of fibrils in a narrow band of adult nuclear fiber cells of the OXYS strain of rats. Methods:Lenses from OXYS rats, which have an inherently high level of oxidative stress, and normal control Wistar rats were Vibratome sectioned fresh, immersion fixed and prepared for light and electron microscopy. Histological sections were stained for up to 20 hrs with Congo Red. Results:Electron microscopy revealed a region 400–500 µm from the capsule of OXYS lenses containing fiber cells with cytoplasm composed of a complex tangle of fibrils that were similar in many ways to amyloid fibrils. Two types of patterns were observed. For some fiber cells the entire cytoplasm appeared to be replaced by the fibrillar network surrounded by typical plasma membrane. In other fiber cells a localized region of cytoplasm displayed the fibril pattern that blended into normal appearing cytoplasm predominated by closely packed 16–20 nm alpha–crystallin spheres. Again typical plasma membranes surrounded the cells and did not appear structurally to be involved in the formation of the fibrils. Some of the localized domains appeared to have a nucleation center from which fibrils emanate. Linear fibrils found at the interface with normal cytoplasm were particularly interesting. They were often up to 200 nm in length and composed of a linear string of 16–20 nm diameter beads. A stain excluding region connecting the beads suggests a mode of formation from alpha–crystallin spheres. Fibril interiors excluded heavy metal stain; however, fibril surfaces and interfibril spaces stain like typical hydrophilic proteins. Fibrils were often straight for short distances but were more commonly curved. Fibril diameters varied over a narrow range with most around 7–8 nm and fibrils were frequently branched. True amyloid fibrils are usually straight and not branched. Moreover, histological sections showed no indication of Congo Red staining or birefringence. Conclusions:These morphological observations suggest that the fibrils are formed from crystallins modified by oxidative damage. Similar in appearance to amyloid fibrils, the fibrils probably result from the alignment of hydrophobic domains of modified alpha–crystallin spheres producing stain excluding interiors.
Keywords: cataract • microscopy: electron microscopy • image processing