Contribution of autophagy to ocular hypertension and neurodegeneration in the DBA/2J spontaneous glaucoma mouse model

Abstract

Glaucoma is a progressive optic neuropathy characterized by axonal degeneration and retinal ganglion cells loss. Several factors have been postulated to play a role in glaucoma, elevated intraocular pressure (IOP) being the best well-known causative factor. The mechanisms leading to ocular hypertension and glaucoma are still not fully understood. An increasing number of evidence indicates a role of autophagy in the pathophysiological process of ocular hypertension and glaucoma. However, while all of the studies agree that autophagy is induced in RGCs in response to injury, autophagy was found to either protect or promote cell death depending on the experimental model used. In order to gain more insight into both, the role of autophagy in the pathogenesis of glaucoma and the effect of chronic IOP elevation in the autophagy pathway, we have investigated here for the first time autophagy in the iridocorneal angle region, retinal ganglion cell bodies, and ON axons in the spontaneous ocular hypertensive DBA/2J mouse glaucoma model and in the transgenic DBA/2J::GFP-LC3 mice, generated in our laboratory. Our results indicate decreased autophagic flux in the outflow pathway cells in the DBA/2J mice, characterized by increased levels of LC3-II and p62 together with a decrease in the lysosomal marker LAMP1, evaluated by western blot and immunofluorescence. Elevated presence of autophagic vacuoles in the DBA/2J and, in particular, in the DBA/2J::GFP-LC3 mice was also observed. Expression of the GFP-LC3 transgene was associated to higher cumulative IOP in the DBA/2J background. In addition to higher elevation in IOP, DBA/2J::GFP-LC3 were characterized by further RGCs and exacerbated axonal degeneration compared to DBA/2J. This was accompanied by the notable high presence of autophagic figures within degenerating axons. These results strongly suggest overactivation of autophagy as a potential cellular mechanism leading to ON degeneration in the chronic hypertensive DBA/2J mice.

Retinal Ganglion Cells With a Glaucoma OPTN(E50K) Mutation Exhibit Neurodegenerative Phenotypes when Derived from Three-Dimensional Retinal Organoids

“…The age-related loss of RGCs in glaucoma is characteristic of the loss of neurons found in many neurodegenerative diseases ( Chu, 2019 , Edens et al., 2016 , Gupta and Yucel, 2007 , Hartwick, 2001 , Hirt et al., 2018 , Lai et al., 2017 , Mancino et al., 2018 , Moloudizargari et al., 2017 , Nixon, 2013 , Wostyn et al., 2019 ). In this context, RGCs differentiate normally during early retinogenesis, with degeneration associated with age and disease progression.…”

Tau Abnormalities and Autophagic Defects in Neurodegenerative Disorders; A Feed-forward Cycle

“…Fine-tuning of autophagy is essential for normal neuronal development and functions such as synaptic transmission and memory formation [54]. Overactivation of autophagy can disrupt these processes and can also contribute to cell death under some disease conditions [71][72][73][74][75]. Further understanding of the regulatory mechanisms of neuronal autophagy and their disruption under pathological conditions will lead to a therapeutic application in the future.…”

The Role of Autophagy in Glaucomatous Optic Neuropathy

“…Another drawback of many publications is the lack of autophagic flux assay that limits the correct interpretation of the data (Klionsky et al, 2016). It must also be considered that several studies used in vitro and in vivo models expressing GFP-LC3, this can form aggregates that are often indistinguishable from autophagosomes by fluorescence microscopy and may also alter the physiological autophagosome turnover (Kuma et al, 2007;Hirt et al, 2018). Moreover, the available drugs modulating autophagy affect multiple pathways, making the isolation and interpretation of autophagy in the different experimental settings difficult.…”

“…More recently, Hirt and colleagues monitored autophagy in the iridocorneal angle region and retina of DBA/2J and transgenic DBA/2J:GFP-LC3 mice; in both strains decreased LAMP1 and upregulation of LC3II and p62 were reported in the angle region, while decreased levels of all three proteins were shown in the RGC bodies, suggesting an overall slowed autophagic flux (Hirt et al, 2018).…”