Endothelin-1 Mediated Decrease in Mitochondrial Gene Expression and Bioenergetics Contribute to Neurodegeneration of Retinal Ganglion Cells

Abstract

Endothelin-1 (ET-1) is a vasoactive peptide that is elevated in aqueous humor as well as circulation of primary open angle glaucoma (POAG) patients. ET-1 has been shown to promote degeneration of optic nerve axons and apoptosis of retinal ganglion cells (RGCs), however, the precise mechanisms are still largely unknown. In this study, RNA-seq analysis was used to assess changes in ET-1 mediated gene expression in primary RGCs, which revealed that 23 out of 156 differentially expressed genes (DEGs) had known or predicted mitochondrial function, of which oxidative phosphorylation emerged as the topmost enriched pathway. ET-1 treatment significantly decreased protein expression of key mitochondrial genes including cytochrome C oxidase copper chaperone (COX17) and ATP Synthase, H + transporting, Mitochondrial Fo Complex (ATP5H) in primary RGCs and in vivo following intravitreal ET-1 injection in rats. A Seahorse ATP rate assay revealed a significant decrease in the rate of mitochondrial ATP production following ET-1 treatment. IOP elevation in Brown Norway rats showed a trend towards decreased expression of ATP5H. Our results demonstrate that ET-1 produced a decrease in expression of vital components of mitochondrial electron transport chain, which compromise bioenergetics and suggest a mechanism by which ET-1 promotes neurodegeneration of RGCs in glaucoma. Glaucoma is an optic neuropathy with an approximate prevalence of 60.5 million people worldwide and is projected to reach 111 million by 2040 1,2 .The disease is commonly associated with elevated intraocular pressure (IOP), accompanied by optic nerve degeneration and loss of retinal ganglion cells (RGCs) 3,4. RGC death via apoptosis is a culminating event in the pathophysiology of glaucoma, stemming from optic nerve axonal injury, leading to visual field loss. Elevated IOP is a major risk factor in primary open-angle-glaucoma and current therapeutic approaches are aimed at lowering IOP with medications, laser treatment, or surgery 5,6. However in some patients, the progression of the disease continues to occur slowly 7 despite lowering IOP, hence there is a compelling need for neuroprotection of RGCs and optic nerve axons and as an additional therapeutic modality. The molecular changes occurring specifically in the RGCs, during the progression of glaucoma, contributing to neurodegeneration, are still poorly understood; hence identifying new therapeutic targets could provide more efficacious neuroprotective treatments. ET-1 is a 21 amino acid vasoactive peptide that acts through two G-protein coupled receptors namely, ET A and ET B receptors, to produce diverse effects in various ocular tissues 8-11. A growing body of evidence suggests that endothelins and their receptors are major contributors to neuronal damage in glaucoma 11-16. The role of endothelins in glaucomatous neurodegeneration has been the subject of several review articles 12,17,18. However, the detailed cellular and molecular mechanisms that contribute to ET-1 mediated-neurodegeneration are not

The Neurovascular Unit in Glaucomatous Neurodegeneration

“…ET-1 receptor activation on astrocytes promotes their proliferation (Lau et al, 2006). Moreover, ET-1 reduces expression of RGC mitochondrial oxidase enzymes, implicating a role for ET-1 in RGC bioenergetics (Chaphalkar et al, 2020). The effect of ET-1 on RGCs and other cell types directly is beyond the scope of this review, but reviewed well in Shoshani et al (2012).…”

Endocrine Dysfunction in Open Angle Glaucoma

“…This occurs without a rise in intraocular pressure. Ischaemia most likely plays a part in the pathogenesis, as well as a possible direct proapoptotic effect due to mitochondrial dysfunction in retinal ganglion cells [38]. It is not known how relevant this factor is in the clinical context.…”

“…Dies geschieht ohne Anstieg des Augeninnendrucks. Pathogenetisch spielen hierbei am ehesten eine Ischämie sowie eine mögliche direkte proapoptotische Wirkung durch eine mitochondriale Dysfunktion in retinalen Ganglienzellen eine Rolle [38]. Wie relevant dieser Faktor im klinischen Kontext ist, ist unbekannt.…”

Hepatic Knockdown of Endothelin Type A Receptor (ETAR) Ameliorates Hepatic Insulin Resistance and Hyperglycemia Through Suppressing p66Shc-Mediated Mitochondrial Fragmentation in High-Fat Diet-Fed Mice

“… 16 , 17 There is evidence that mitochondrial dysfunction is involved in ET1-mediated cellular injuries. 18 , 19 ET1 restrains the key genes expression of mitochondrial electron transport chain and consequent bioenergetics in retinal ganglion cells (RGCs). 18 A recent study indicates ET1 promotes vasoconstriction by increasing mitochondrial fission, which plays a major role in the pathogenesis of hypertension.…”

“… 18 , 19 ET1 restrains the key genes expression of mitochondrial electron transport chain and consequent bioenergetics in retinal ganglion cells (RGCs). 18 A recent study indicates ET1 promotes vasoconstriction by increasing mitochondrial fission, which plays a major role in the pathogenesis of hypertension. 19 However, whether and how mitochondrial fragmentation participates in the regulation of ET1/ETAR signaling on metabolism abnormalities has yet to be clarified.…”