In vivo and ex vivo evaluation of the responses of rat Müller glia after injury

Retinal ex vivo systems have been widely used to investigate diverse physiological and pathological processes in the retina. Although retinal ex vivo systems are generally considered to approximate in vivo environment of the retina, careful evaluation of how ex vivo conditions affect cellular function is necessary for accurate interpretation of such data. Here we analyzed the responses of retinal Müller glia to photoreceptor injury in vivo and ex vivo to assess the effects of ex vivo culture on the phenotypes of Müller glia in pathological contexts. A rat model of photoreceptor injury was generated by intraperitoneal injection of methyl methanesulfonate (MMS) and retinal ex vivo cultures were prepared 1 or 2 days after MMS treatment. A substantial number of Müller glia die by apoptosis after injury-induced proliferation in vivo, but not ex vivo. While the pattern of Müller glia proliferation was similar between the models, the extent of phagocytic activity, migration, DNA damage response, and neurogenic factor expression varied across the models. These findings reveal previously unrecognized effects of ex vivo culture on Müller glia in disease contexts, highlighting the need for caution when assessing injury-induced phenotypes of Müller glia using retinal ex vivo systems.