Abstract
Purpose :
Glycogen Synthase Kinase 3 alpha (GSK3α) and beta (GSK3β) kinases are key regulators of cell survival and death pathways. GSK3 inhibition has been a therapeutic approach for neurodegenerative disorders such as Alzheimer’s and Parkinson’s disease. In the retina, drug inhibition of GSK3 showed promising beneficial effects under pathological conditions. In our study, we aimed at deciphering the neuroprotective mechanism of GSK3 inhibition using mouse genetic models and identifying other therapeutic factors for new treatment.
Methods :
Conditional mouse lines were generated using αPax6-Cre with retinal specific deletion of either isozyme of Gsk3 (Gsk3α/Gsk3β). Photoreceptor degeneration was induced in vivo using MNU, and ex vivo on retinal explant culture. RNA-Seq analysis was performed on control and MNU-injected mice carrying only one allele of Gsk3α (Gsk3αf+βff α-Cre) expressed in the retina. Recombinant protein Osteopontin (OPN) was injected intra-vitreally or added to explant culture medium. Cell death was assessed with TUNEL assay.
Results :
GSK3 is significantly inactivated during photoreceptor degeneration. Such inhibition was mimicked using mouse models with partial deletion of either Gsk3. In these models, induced-photoreceptor cell death ex vivo and in vivo following MNU injection was significantly decreased compared to controls. RNA-Seq analysis showed that most downregulated genes belonged to the phototransduction cascade. Upregulated genes identified were mostly related to inflammatory response and cell chemotaxis including secreted factors such as Spp1 and Fgf2. Increased transcriptomic and proteomic expression of both was confirmed between Gsk3αf+βff α-Cre and Gsk3αf+βff mice under degenerative and physiological condition. Immunostaining showed that OPN (Spp1) expression is limited to ganglion cells in WT and induced in Müller cells under different degenerative conditions. OPN treatment results in increased photoreceptor survival in ex vivo and in vivo degeneration model in WT mice. Interestingly, FGF2 expression was increased following OPN treatment.
Conclusions :
Our work strongly suggests that the neuroprotective effects of GSK3 inhibition might be mediated by increased expression of OPN in Muller cells, triggering upregulation of FGF2 in photoreceptors. Such a feedback loop could be critical to modulate inflammatory response following retinal injury and sustain photoreceptor survival.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.