Time-Dependent Changes of Cell Proliferation After Laser Photocoagulation in Mouse Chorioretinal Tissue

This study investigated the time course of cell proliferation after laser photocoagulation and analyzed the cell types of proliferating cells.

C57BL/6J mice received unilateral laser photocoagulation. Intraperitoneal bromodeoxyuridine (BrdU) injection was performed, and mice were divided into two groups according to the injection paradigm: group 1 with continuous injection and group 2 with periodic injection. Each group was again divided into four subgroups according to injection period: 0 to 3 days (n = 11), 0 to 7 days (n = 14), 0 to 14 days (n = 6), and 0 to 28 days (n = 6) after laser photocoagulation for group 1; and 0 to 3 days (n = 11), 4 to 7 days (n = 6), 8 to 14 days (n = 6), and 15 to 28 days (n = 6) after laser photocoagulation for group 2. The eyes were examined with immunohistochemistry using anti-BrdU antibody and other various antibodies for identification of proliferating cells. Manual cell counting and flow cytometry were performed for quantification.

In group 1, the number of BrdU+ cells showed marked increase during the first 3 days of laser lesioning, reaching its maximum after 7 days (P < 0.05). Group 2 also demonstrated peak proliferation during the first 3 days, but a significantly reduced number of BrdU+ cells were detected during 4 to 7 days, 8 to 14 days, and 15 to 28 days of laser treatment (P < 0.05). BrdU+ cells colocalized with CD11b, F4/80, iba1, RPE65, CD31, and glial fibrillary acidic protein (GFAP) labeling, and CD11b+, F4/80+, and iba1+ cells constituted the main fraction of BrdU+ cells.

Laser photocoagulation induced cell proliferation mostly during the first 3 days, and many proliferating cells were identified as inflammatory cells, RPE cells, endothelial cells, and Müller cells.