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A. Joy, K. J. Al-Ghoul; Abnormal Fiber End Migration Leads to Posterior Subcapsular Cataract (PSC) Formation in Royal College of Surgeons (RCS) Rats. Invest. Ophthalmol. Vis. Sci. 2010;51(13):2628.
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© ARVO (1962-2015); The Authors (2016-present)
Evaluation of posterior fiber ends of RCS rat lenses reveals distinct structural and cytoskeletal changes as early as 3wks post natal that lead to PSC formation. These include multiple suture sub-branches, altered fiber end morphology and associated BMC changes. The objective of this study was to detail fiber end changes that precede and culminate in a PSC in RCS rats.
A total of 35 RCS rats (2-6wk old), were euthanized, lenses removed and photographed. All OD lenses were processed for laser scanning confocal microscopy (LSCM) to localize BMC components, and all OS lenses for scanning electron microscopy (SEM) to evaluate fiber end morphology.
At 2wks, lenses displayed the typical inverted-Y suture pattern on the posterior, and by 3wks most lenses had at least one sub-branch. Additional sub-branches were observed with time, opacities being visible as early as 4wks and progressing into PSC plaques by 6wks. SEM revealed fiber ends with normal size, shape, arrangement and filopodia at 2wks, scattered areas of dome-shaped fiber ends and small filopodia at 3wks, and irregularly arranged dome-shaped ends at 4wks. Filopodia at 4wks were extremely long and had ‘boutons’ at their tips. Extensive membrane blebbing and cell separation were also seen at this age. LSCM showed normal distribution of cadherin, vinculin and β-integrin at 2- 3wks. F-actin although normal at 2wks, was visible as scattered bright foci at 3wks, which increased in incidence by 4wks. The BMC at 5wks was distinct with F-actin rearranged as a ‘rosette’ pattern with bright foci at the vertices. At all ages, cadherin delineated the fiber ends and integrin was arranged as plaques within the ends throughout the BMC. Integrin labeling was present at both peri-sutural and sutural regions, which is contrary to that seen in normal rat lenses.
The initial changes to fiber ends (2-4wks) are accompanied by minor changes to the BMC indicating that migration of the ends continues, albeit misdirected, resulting in abnormal suture sub-branches. Between 4-6 wks, the changes are more extreme and are accompanied by distinct rearrangements of normal BMC architecture. The data suggest that a modification of adhesion mechanics at the BMC, specifically, cell-cell attachment, cell-matrix adhesion and timely fiber end detachment, are consistent with a cessation of fiber end migration in RCS rat lenses.
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