Ultrastructural analysis of damage to nuclear fiber cell membranes in advanced age-related cataracts from India

Abstract

The primary goal was to characterize the structural alterations that occur at the fiber cell interfaces in nuclei of fully opaque cataracts removed by extracapsular cataract surgery in India. The dark yellow to brunescent nuclei, ages 38-78 years, were probably representative of advanced age-related nuclear cataracts. Thick tissue slices were fixed, en bloc stained and embedded for transmission electron microscopy. Stained thin sections contained well-preserved membranes and junctions, although the complex cellular topology often made it necessary to tilt the grid extensively to visualize the membranes. Damage to the fiber cell membranes was noted in all regions of the nucleus. The most important damage occurred within undulating membrane junctions where the loss of membrane segments was common. These membrane breaks were not sites of fusion as membrane edges were detected and cytoplasm appeared to be in contact with extracellular space, which was enlarged in many regions. Dense deposits of protein-like material were frequently observed within the extracellular space and appeared to be similar to protein in the adjacent cytoplasm. The deposits were often 20-50 nm thick, variable in length and located on specific sites on plasma membranes and between clusters of cells or cell processes. In addition, low density regions were seen within the extracellular space, especially within highly undulating membranes where spaces about 100 nm in diameter were observed. The membrane damage was more extensive and extracellular spaces were larger than in aged transparent donor lenses. Because high and low density regions contribute equally to the fluctuations in refractive index, the changes in density due to the observed damage near membranes are likely to produce significant light scattering based on theoretical analysis. The dimensions of the fluctuations in the range 20-100 nm imply that the scattering is probably similar to that of small particles that would increase high-angle scattering visible in the slit lamp. Such damage to membranes would be expected to contribute to the total opacification of the nucleus as the cataract matures. The main sources of the fluctuations appear to be the degradation of membranes and adjacent cytoplasmic proteins, as well as the redistribution of proteins and fragments.

Analysis of nuclear fiber cell cytoplasmic texture in advanced cataractous lenses from Indian subjects using Debye–Bueche theory

“…The fundamental goal then is to demonstrate that all advanced cataracts of the common type, i.e., age-related nuclear, have similar features and accumulate evidence for the hypothesis regarding the loss and/or redistribution of cytoplasmic protein. A large body of biochemical evidence points to modifications of the crystallins (Zigler, 1994;Lampi et al, 1998;Ma et al, 1998;Hanson et al, 2000;Truscott, 2005) and some ultrastructural evidence supports the redistribution of cytoplasmic material, most likely soluble crystallins and crystallin fragments, through damaged membranes into extracellular spaces where deposits are formed (Costello et al, 1992;Costello et al, 2007a). Biochemical results support the hypothesis that aggregation of crystallins is favored by oxidation, deamidation and truncation leading to conformational changes that promote crystallin insolubility and cataract (Hanson et al, 2000).…”

Lipids and the ocular lens

“…Costello et al ( 15 ) speculate that dihydrosphingomyelin could laterally associate with AQPO arrays producing stable curved membranes. Glycby guest, on April 29, 2019 www.jlr.org Downloaded from…”

Optical properties of the lens: an explanation for the zones of discontinuity

“…The fibre cell organisation in the nucleus of the lens is less organised than in the cortical regions (Taylor et al, 1996;Al-Ghoul and Costello, 1997;Shestopalov and Bassnett, 2000) with structural features that can increase the proportion of scattered light (Jedziniak et al, 1975;Costello et al, 2007;Costello et al, 2008). This was simulated by superimposing random oscillations (Park and Miller, 1988) in the central regions and is depicted diagrammatically in Fig.…”

“…Changes in fibre cell membranes with age and cataract, such as breaks in membranes, enlargements of the extracellular space between membranes and protein-like deposits within the extracellular space (Costello et al, 2008) also scatter light. It is notable, that these changes were found in normal control lenses indicating that the process is age-related and may predispose to nuclear cataract rather than being specifically associated with the disease process (Costello et al, 2008). These changes are therefore physiological, as are the zones of discontinuity.…”

“…0:1 mm that add a minor fluctuation to the coordinates of the function R(x,y,z). The fluctuations were higher in the axial regions and declined with distance away from the axis, simulating decreased scatter with distance from the centre of the lens based on morphological findings (Taylor et al, 1996;Al-Ghoul and Costello, 1997;Costello et al, 2007;Costello et al, 2008;Shestopalov and Bassnett, 2000).…”