Programmed switch in the mitochondrial degradation pathways during human retinal ganglion cell differentiation from stem cells is critical for RGC survival

• Published in: Redox biology Vol. 34; p. 101465
• Main Authors: Das, Arupratan, Bell, Claire M., Berlinicke, Cynthia A., Marsh-Armstrong, Nicholas, Zack, Donald J.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.07.2020; Elsevier
• Subjects: Autophagy; from the Special Issue on Oxidative stress in retina and retinal pigment epithelium in health and disease; Edited by Vera Bonilha; Glaucoma; Human retinal ganglion cells (hRGCs); Mitophagy; Stem cells; Ubiquitine-proteasome system (UPS); Glaucoma; Mitophagy; Autophagy; Human retinal ganglion cells (hRGCs); Stem cells; Ubiquitine-proteasome system (UPS)
• ISSN: 2213-2317; 2213-2317
• DOI: 10.1016/j.redox.2020.101465

Retinal ganglion cell (RGC) degeneration is the root cause for vision loss in glaucoma as well as in other forms of optic neuropathy. A variety of studies have implicated abnormal mitochondrial quality control (MQC) as contributing to RGC damage and degeneration in optic neuropathies. The ability to differentiate human pluripotent stem cells (hPSCs) into RGCs provides an opportunity to study RGC MQC in great detail. Degradation of damaged mitochondria is a critical step of MQC, and here we have used hPSC-derived RGCs (hRGCs) to analyze how altered mitochondrial degradation pathways in hRGCs affect their survival. Using pharmacological methods, we have investigated the role of the proteasomal and endo-lysosomal pathways in degrading damaged mitochondria in hRGCs and their precursor stem cells. We found that upon mitochondrial damage induced by the proton uncoupler carbonyl cyanide m-chlorophenyl hydrazone (CCCP), hRGCs more efficiently degraded mitochondria than did their precursor stem cells. We further identified that for degrading damaged mitochondria, stem cells predominantly use the ubiquitine-proteasome system (UPS) while hRGCs use the endo-lysosomal pathway. UPS inhibition causes apoptosis and cell death in stem cells, while hRGC viability is dependent on the endo-lysosomal pathway but not on the UPS pathway. These findings suggest that manipulation of the endo-lysosomal pathway could be therapeutically relevant for RGC protection in treating optic neuropathies associated with mitophagy defects. Endo-lysosome dependent cell survival is also conserved in other human neurons as we found that differentiated human cerebral cortical neurons also degenerated upon endo-lysosomal inhibition but not with proteasome inhibition. The above graphical abstract represents a summary of the data presented in this work. Our data shows human pluripotent stem cells (hPSCs) predominantly use the ubiquitin-proteasome system (UPS) for maintaining mitochondrial homeostasis. However, during the course of differentiation to human retinal ganglion cells (hRGCs), cellular preference for maintaining mitochondrial homeostasis shifts towards the endo-lysosomal pathway, which becomes essential for hRGC survival. [Display omitted] •Human retinal ganglion cells (hRGCs) degrade damaged mitochondria more efficiently than the origin stem cells.•Human stem cells rely on the ubiquitin proteasome system (UPS) for damaged mitochondrial clearance and survival.•hRGCs rely on the endo-lysosomal pathway for mitochondrial clearance and survival.•Unlike stem cells, proteasomal inhibition did not cause severe cell death for hRGCs.•Transition from the UPS to endo-lysosomal pathway during differentiation was also observed for cerebral cortical neurons.