ΔFosB-induced cataract

PURPOSE. The objective of this study was to investigate a possible relationship between posterior subcapsular cataract (PSC) formation and expression of the transcription factor ΔFosB. METHODS. Western blot analysis was performed on bitransgenic NSE-tTA, TetOp-ΔFosB, and single-Transgenic NSE-tTA control mice to determine the pattern of ΔFosB expression within the eye. Light and scanning electron microscopy and biochemical analyses were also performed. RESULTS. In mice expressing ΔFosB, cataract developed that initially appeared to be posterior subcapsular and gradually matured to involve the entire lens. The enlarged posterior ends of developing secondary fibers curved away from the visual axis to form an elevated opaque posterior plaque. As a result, posterior suture formation did not occur. At a later time, the attenuated posterior capsule overlying the plaque ruptured and the lens nucleus subluxated into the vitreous. Retinal damage was also observed but only from postnatal day 65, a time when extensive lens degeneration had already occurred. ΔFosB expression was observed well before the detection of morphologic change in both the lens and the retina. Within the lens, ΔFosB expression was found in both the epithelium and fibers. The development of cataracts was a direct consequence of ΔFosB expression and was not due to the disruption of an endogenous gene by transgene integration since cataracts could be prevented by silencing expression of ΔFosB by feeding bitransgenic animals doxycycline (Dox). Moreover, cataracts were observed in bitransgenic mice derived from two independent TetOp-ΔFosB founder lines but not in single NSE-tTA transgenic controls. Cataractogenesis was not a consequence of abnormal development, because mice conceived and raised on Dox to prevent expression of ΔFosB also were subject to formation of PSC when expression of ΔFosB was turned on in adult animals by removing Dox. Examination of biochemical parameters indicated that the earliest change observed was the disruption of calcium homeostasis with a significant increase in Ca²⁺ influx, followed by a gradual but marked decrease in protein content. Significant changes in certain metabolic parameters and protein composition were also observed. CONCLUSIONS. The ΔFosB-induced cataract in which the major morphologic early event was the disruption of normal posterior fiber formation, may be a good model for PSC. By identifying ΔFosB-regulated target genes, it should be possible to achieve a better understanding of the molecular mechanisms through which PSC is formed.