Inhibiting the activation of MAPK (ERK1/2) in stressed Müller cells prevents photoreceptor degeneration
Shaoxue Zeng, Ting Zhang, Yingying Chen, Joshua A. Chu‐Tan, Kaiyu Jin, Sora Lee, Michelle Yam, Michele C. Madigan, Nilisha Fernando, Adrian V. Cioanca, Fanfan Zhou, Meidong Zhu, Junjun Zhang, Riccardo Natoli, Xiaohui Fan, Ling Zhu, Mark C. Gillies
Abstract
Rationale: Mller cells play an essential role in maintaining the health of retinal photoreceptors. Dysfunction of stressed Mller cells often results in photoreceptor degeneration. However, how these cells communicate under stress and the signalling pathways involved remain unclear. In this study, we inhibited the MAPK (ERK1/2) signalling, mainly activated in Mller cells, evaluated the protective effects on the photoreceptors and further explored the signalling communication between stressed Mller cells and degenerating photoreceptors. Methods: We evaluated the changes of MAPK (ERK1/2) signalling and its downstream targets in human retinal explants treated with PD98059, a specific phosphorylated ERK1/2 inhibitor, by western blot and immunostaining. We further assessed photoreceptor degeneration by TUNEL staining and outer nuclear layer thickness. We also injected PD98059 into the eyes of mice exposed to photo-oxidative stress. We evaluated the protective effects on photoreceptor degeneration by optical coherence tomography (OCT) and electroretinography (ERG). The crosstalk between Mller cells and photoreceptors was further dissected based on the changes of transcription factors by RNA sequencing and protein profiles of multiple signalling pathways. Results: We found that MAPK (ERK1/2) signalling was mainly activated in Mller cells under stress, both ex vivo and in vivo. PD98059 inhibited the phosphorylation of ERK1/2, reduced expression of the gliotic marker glial fibrillary acidic protein (GFAP) in Mller cells and increased levels of the neuroprotective factor, interphotoreceptor retinoid-binding protein (IRBP) in photoreceptors. Inhibition of pERK1/2 also reduced retinal photo-oxidative damage in mice retinas assessed by OCT and ERG. We also identified that the JAK/STAT3 signalling pathway might mediate signalling transduction from Mller cells to photoreceptors. Conclusion: MAPK (ERK1/2) deactivation through chemical inhibition, mainly in stressed Mller cells, can alleviate gliosis in Mller cells and restore the expression of IRBP in photoreceptors, which appears to prevent retinal degeneration. Our findings suggested a new way to prevent photoreceptor degeneration by manipulating the stress response in Mller cells.