Retinal ganglion cell mitophagy in ageing and glaucoma

• Applicant: Dr. Katharina Bell
• Subject Area: Ophthalmology
• Term: from 2017 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 398447997

Glaucoma is a leading cause of irreversible vision loss and blindness. This heterogeneous neurodegenerative disease is characterised by progressive retinal ganglion cell (RGC) death, optic nerve degeneration and progressive visual field loss. Elevated intraocular pressure (IOP) is the only risk factor that can be treated. Although other risk factors such as advancing age or neuroinflammatory processes have been recognised, there still is the urgent need to understand disease pathogenesis in greater detail to implement further therapeutic approaches. Recent studies found that mitochondrial damage and dysfunction play an important role in glaucoma and neuroinflammatory processes, although the mechanisms are not understood. RGCs show a high mitochondrial density which accumulate at the optic nerve head in glaucoma patients. Defective mitochondria are eliminated from cells via mitophagy. Boya et al. not only show that autophagy in the retina decreases with age but also that mitophagy, a selective autophagy pathway, plays an essential role in development and differentiation of RGCs and that retinas from autophagy-deficient animals display reduced number of differentiated RGCs. Studies promoting autophagy with rapamycin showed increased RGC survival after axonal damage. As mitochondrial damage and changes have been demonstrated in advancing age and glaucoma, there is a need to investigate the relevance of mitophagy in glaucoma. A recent paper published in Science demonstrates that nicotinamide, a mitophagy inducer, has neuroprotective functions for RGCs when delivered as dietary supplement in a spontaneous glaucoma animal model. Mitophagy was not analysed but treatment was associated with improved mitochondrial health suggesting better turnover. We hypothesis that amelioration of glaucoma is possible by modulating ageing-defective mitophagy. In the proposed experiments the effect of ageing on RGC mitophagy will be analysed by isolating RGC and whole retinae from young and aged mice and stressing these with glaucoma relevant stress factors (e.g. hypoxia, growth factor deprivation or hydrogen peroxide) after inducing (with carbonyl cyanide m-chlorophenyl hydrazine, actinomycin A and oligomycin A or nicotinamide) or inhibiting mitophagy (using cyclosporin A or FK866) in vitro. Mitophagy and autophagy analysis via immunostaining and FACS methods and mitochondrial biogenesis and protein analysis will be performed. Also RGC viability and ROS levels will be determined. Using autophagy deficient Ambra1+/- mice, mitophagy deficient NIX mice and wildtype, two different glaucoma models (optic nerve crush as a severe damage and IOP increase as a milder form of damage) will be used to understand the consequences of autophagy and mitophagy downregulation on RGC survival in young and aged animals. Additionally the neuroprotective effect of nicotinamide will be analysed in greater detail using aged Ambra1+/-, NIX and wildtype mice and both proposed glaucoma models.

• DFG Programme: Research Fellowships
• International Connection: Spain
• Host: Professorin Patricia Boya, Ph.D.