PD98059 inhibits the activation of mitogen-activated protein kinase in stressed Müller cells and protects photoreceptor from degeneration

Abstract

Purpose : Since Müller cell dysfunction under stress may result in photoreceptor degeneration, it is possible that manipulation of molecular signaling in stressed Müller cells may protect photoreceptors. We evaluated the protective effect of PD98059, a mitogen-activated protein kinase (MAPK) inhibitor, on photoreceptors in human retinal explant cultures exposed to photo-oxidative stress.

Methods : Human retinal explants treated with PD98059 were evaluated for changes in MAPK signaling and its downstream targets by Western blot and immunostaining. We also assessed photoreceptor degeneration by TUNEL staining and outer nuclear layer thickness. We also injected the MAPK inhibitor into eyes of mice exposed to photo-oxidative stress. We assessed retinal function by electroretinography and evaluated the photoreceptor degeneration histologically. The crosstalk between Müller cells and photoreceptors was dissected based on the protein profiles of multiple signaling pathways and transcription factors.

Results : MAPK signaling was activated in Müller cells in cultured human retinal explants. PD98059 inhibited phosphorylation of Erk1/2, a key step in MAPK signaling in Müller cells. Inhibition of Erk1/2 reduced the expression of the gliotic marker glial fibrillary acidic protein (GFAP) in Müller cells. Treatment with PD98059 also suppressed Jak/Stat signaling in photoreceptors and thus activated transcription factor OTX2. The level of the neuroprotective factor IRBP was elevated after treatment with PD98059. TUNEL staining in the outer nuclear layer (ONL) was reduced after MAPK inhibition. In vivo studies indicated that PD98059 treatment suppressed MAPK signaling in the Müller cells of mouse retinas exposed to 100K lux light, with reduced expression of GFAP by Müller cells and preservation of photoreceptors.

Conclusions : MAPK deactivation through chemical inhibition in stressed Müller cells can alleviate gliosis and restore the expression of IRBP in photoreceptors which appears to prevent their degeneration. Our findings suggest a new therapeutic target to prevent or treat photoreceptor degeneration.

This is a 2020 ARVO Annual Meeting abstract.