Abnormal fiber end migration in Royal College of Surgeons rats during posterior subcapsular cataract formation

[摘要] Purpose: Prior structural studies ofposterior subcapsular cataract (PSC) development in Royal College ofSurgeons (RCS) rats suggest that migration of basal fiber ends wasdisrupted, ultimately resulting in a PSC. Therefore the goal of thisstudy was to assess the overall migration patterns as well as changesto the structure and cytoskeleton of basal fiber ends during PSCdevelopment. Methods: Lenses from 48 RCS dystrophicrats (RCS/Lav) and 24 genetically matched control animals (RCS-rdy+/Lav)from 2 to 8 weeks old were examined. Equatorial diameters were measuredand suture patterns were photographed immediately followingenucleation/dissection. Right eye lenses were fixed and processed tovisualize the actin cytoskeleton via laser scanning confocal microcopy(LSCM), left eye lenses were decapsulated, fixed and processed forscanning electron microscopy (SEM). Scaled 3D-computer assisteddrawings (CADs) and animations were constructed from the data to depictthe changes in suture patterns and fiber end architecture. Results: At 2 weeks, dystrophic lensesdisplayed an inverted Y suture on the posterior, and by 3 weeks mostlenses had at least one sub-branch. Additional sub-branches wereobserved with time, opacities being visible as early as 4 weeks andprogressing into PSC plaques by 6 weeks. Control lenses displayedinverted Y sutures at all ages and were transparent. SEM of dystrophiclenses revealed fiber ends with normal size, shape, arrangement, andfilopodia at 2 weeks; scattered areas of dome-shaped fiber ends andsmall filopodia were present at 3 weeks. At 4 weeks the irregularlyarranged domed fiber ends had extremely long filopodia with ‘boutons’at their tips. By 6 weeks all fiber ends within plaques displayedrounded or domed basal membranes and lacked filopodial extensions.Control lenses at all time points had comparable ultrastructure to the2 week old dystrophic lenses. F-actin arrangement within the basalmembrane complex (BMC) of control lenses showed the expected peripheralpattern of labeling at all ages. Dystrophic RCS lenses at 2 weeks werecomparable to controls, however by 3–4 weeks they displayed scatteredfoci of F-actin within the BMC. At all time points thereafter, F-actinwas rearranged into a ‘rosette’ pattern of prominent foci at cellvertices. Conclusions: The data are consistentwith the hypothesis that migration of basal fiber ends is altered in atwo stage process wherein initially, migration patterns undergo a rapidshift resulting in abnormal suture sub-branch formation. Subsequentcytological alterations are consistent with an eventual cessation ofmigration, precluding proper targeting of basal ends to their suturaldestinations and leading to cataract plaque formation.

[学科分类] 生物化学/生物物理