Upregulation of Semaphorin 3A and the associated biochemical and cellular events in a rat model of retinal detachment

Background: Retinal detachment, as a result of injury or disease, is a severe disorder that may ultimately lead to complete blindness. Despite advanced surgical repair techniques, the visual acuity of patients is often limited. We investigated some of the biochemical and morphological alterations following experimental retinal detachment in laboratory animals. Methods: Unilateral retinal detachment was induced in male Wistar rats; contralateral untreated eyes served as a control. Approximately half of the retinal area was detached by a sub-retinal injection of 5 μl Saline. The incidence and extent of the retinal detachment was evaluated using MRI analysis and fundus images. The retinas were collected at intervals of 24 hours, 7, 14 and 28 days following the procedure. Using Western blot and immunohistochemical analysis, the expression levels of Semaphorin3A, Neuropilin1, GAP43 and NF-H were studied. In addition, morphological changes in Müller and microglial cells were examined. TUNEL staining was used to assess apoptosis. Results: We found that theexpression level of Semaphorin3A was up-regulated and reached its peak at two time points: 24 hours and 14 days after surgery. A similar pattern of expression was found for Neuropilin1. TUNEL-positive cells, indicating apoptotic processes, were evident 24 hours post retinal detachment and increased after 7 days. On the other hand, GAP43 expression was up-regulated 14 days after retinal detachment, and further intensified 28 days post-surgery. Microglial cells were activated shortly after detachment and concentrated mostly at the inner plexiform layer. GFAP staining revealed hypertrophy of Müller cells. Conclusions: The biochemical and morphological changes suggest that apoptosis as well as axonal regrowth take place following retinal detachment. Collectively, these findings may explain the limited success following repair surgery in terms of visual acuity and physiological function of the retina. Our study may open a new approach for treatment of early phase retinal detachment, as well as improve post-operative care that may, in turn, improve the functional result of the surgery. In addition, further study is required on several other factors that may affect visual acuity, such as size and location of the detached area and the time lapse between detachment and surgery.