Retinal ganglion cell mitophagy in ageing and glaucoma
Final Report Abstract
This project aimed to better understand the role of autophagy and mitophagy deficiency following retinal ganglion cell (RGC) axonal damage in the context of glaucoma and ageing. Autophagy is an intracellular degradation and recycling pathway of cytoplasmic contents and shows a generalised decline with ageing. Glaucoma is an age-related disease and RGCs, being post-mitotic cells, are especially dependant on adequate energy supply through oxidative phosphorylation. Increased mtDNA mutations however, also found in glaucoma patients, lead to increased oxidative stress and reduced ATP production. In general, damaged mitochondria are cleared via the specific autophagy pathway for mitochondria, namely mitophagy. Studies point towards autophagy and mitophagy being dysregulated in glaucoma over and above the decline observed in ageing. Genetic changes in the p16 locus, which is involved in ageing, predispose to rare forms of glaucoma. Additionally, genetic changes link mitophagy dysregulation to elevated glaucoma risk. It is as yet however not known whether boosting autophagy and mitophagy could be one way of rescuing RGCs from glaucoma damage. In order to analyse the effect of autophagy and mitophagy deficiency on RGCs in the context of ageing and glaucoma related damage, optic nerve crush (ONC) studies using young (5 months) and older (13 months) Ambra1+/+ and Ambra1+/gt mice were performed. AMBRA1 (autophagy/beclin-1 regulator 1) plays a role in the initiation of the autophagy process and is a relevant mitophagy receptor, making the mouse a valuable model for analysing autophagy and mitophagy deficiency. We found increased RGC vulnerability after ONC in the older heterozygote animals, whereas no difference between wildtype and heterozygotes could be found in the younger mice. Proteomics and qPCR analysis pointed towards altered oxidative stress response mechanisms and altered mitophagy response after damage in the old heterozygote Ambra1+/gt mice. These results are the first to demonstrate an age-related change in RGC damage due to autophagy and mitophagy deficiency. More research should be performed to understand the compensation mechanisms in younger ages and how these could be boosted with older age. Boosting mitophagy could be one promising therapeutic target. Analysing primary RGCs in vitro we found that they can be rescued from oxidative stress by incubation with the known mitophagy inducer DFP. Using RGCs isolated from mito-QC receptor mice, we demonstrated that reduction of apoptosis by DFP was accompanied with increased mitophagy, underlining the importance of boosting mitophagy to be of value in RGC neuroprotection. However, in two optic nerve crush experiments inducing mitophagy with either nicotinamide or with CORM-A1 we could not find neuroprotection of RGCs. This was against our proposed hypothesis and should be reanalysed in greater detail. Possibly we were missing the therapeutic opportunity by performing the experiments with young rather than aged animals. In addition, the ONC model induces a large insult, and a dramatic loss of cells, therefore less invasive and more physiological models should be considered as well. In general, however, the results showed for the first time, the relevance for autophagy and mitophagy deficiency for RGCs even in early ageing. This is an important finding, as the risk for glaucoma is increased from middle-aged onwards and has been linked to autophagy/mitophagy deficiency. Finding therapeutic options to address this deficiency could help reduce RGC vulnerability towards glaucoma related stress factors and therefore increase patient outcomes.
Publications
- “The mito-QC Reporter for Quantitative Mitophagy Assessment in Primary Retinal Ganglion Cells and Experimental Glaucoma Models”, Int J Mol Sci 2020 Mar 10;21(5)
I Risognol, B Villarejo-Zori, P Teresak, E Sierra-Filardi, X Pereiro, N Rodriguey- Muela, E Vecino, HLA Veira, K Bell, P Boya
(See online at https://doi.org/10.3390/ijms21051882) - „Age related retinal ganglion cell susceptibility in context of autophagy deficiency”. Cell Death Discov. 2020, Apr. 17; 6:21
K. Bell, I Rosignol, E Sierra-Filardi, N Rodriguez-Muela, C Schmelter, F Cecconi, F Grus, P Boya
(See online at https://doi.org/10.1038/s41420-020-0257-4)
