Proliferation of Mouse Retinal Müller Cells in Response to Methylnitrosourea-Induced Retinotoxic Stress

Abstract

Single intraperitoneal injection of methylnitrosourea (MNU) induces in mice the loss of retinal photoreceptors as a nonlinear dose response (Tronov et al. 2015). DNA repair was the putative mechanism for causing a threshold of DNA alkylation in retina cells. Photoreceptor degeneration can stimulate Muller glial cells to transdifferentiate into photoreceptor-like cells in adult mouse retina treated with MNU (Wan et al., 2008). In this paper, we evaluated Muller cell proliferative response to different doses of MNU and compared the response to DNA damage and repair in suspensions of retinal and Muller cells using a comet assay and BrdU (thymidine analogue) as a marker of proliferation. MNU administration in the dose ≤ 40 mg/kg did not result in the activation of Muller cell proliferation in 3 days after the treatment. By this time point, no DNA damage after this dose was observed. For MNU doses that exceed 50 mg/kg, TUNEL-detected death of retinal photoreceptors increased more than 10-fold in the proliferating pool of Muller cells. DNA breaks (single- and double-strand breaks and AP sites) were observed. The results are discussed within the framework of the concept of misbalance of excision repair that results in formation of cytotoxic intermediates in DNA initiated death of photoreceptors followed by activation of Muller retinal cells.