Basal membrane complex architecture is disrupted during posterior subcapsular cataract formation in Royal College of...

Previous studies detailing the development of posterior subcapsular cataracts (PSC) in Royal College of Surgeons (RCS) rats have shown that aberrant fiber-end migration underlies the structural compromise. This investigation was conducted to examine the distribution of select basal membrane complex (BMC) components and to assess the intravitreal levels of specific cytokines during PSC formation.

Lenses from 52 RCS dystrophic rats (RCS/Lav) and 28 genetically matched control animals (RCS-rdy(+)/Lav) from 2 to 8 weeks old were used. After enucleation, vitreous was collected for eventual cytokine level analyses; lenses were then removed and processed for immunocytochemical localization of actin, cadherin, β integrin, vinculin, and cell nuclei.

At 2-3 weeks postnatal, dystrophic lenses showed normal BMC distribution of actin, cadherin, and vinculin; however β integrin distribution was altered as compared to controls. By 4-6 weeks of age, F-actin was visible as bright foci arranged in a "rosette" pattern around fiber-end profiles. Concurrently, vinculin was rearranged into a diffuse pattern within the BMC. Cadherin delineated the fiber ends in dystrophic lenses until 5 weeks postnatal, after which it displayed diffuse cytoplasmic staining with more definitive labeling at the BMC periphery. β integrin was initially distributed as punctuate spots at 2-3 weeks postnatal; however, by 4-6 weeks it was co-localized with F-actin around the periphery of fiber ends. The distribution of F-actin, cadherin, and β integrin components did not undergo further changes after 6 weeks of age; however, vinculin was present predominantly at the periphery of the BMC in 7-8-week-old dystrophic lenses. Intravitreal cytokine levels were assessed for interleukin (IL)-1α, IL-4, IL-6, IL-8, tumor necrosis factor (TNF), and interferon (IFN)-γ. Levels of IL-1α, IL-4, TNF, and IFN-γ demonstrated a similar pattern, with concentrations increasing from 2 to 6 weeks postnatal and then decreasing slightly up to 8 weeks of age. IL-4 and TNF had the highest average concentrations, with peaks of 148.00 pg/ml and 34.20 pg/ml, respectively.

The data indicate that defined rearrangements of normal BMC architecture precede and characterize the structural changes that culminate in the PSC. These are consistent with modifications of adhesion mechanics involving cell-cell attachment, cell-matrix adhesion, and timely fiber-end detachment. Further, the results suggest that pro-inflammatory cytokines are potential initiating factors in aberrant fiber-end migration and subsequent PSC formation.