Humanin G (HNG) protects age-related macular degeneration (AMD) transmitochondrial ARPE-19 cybrids from mitochondrial and cellular damage

Sonali Nashine,M Cristina Kenney,Anthony B Nesburn,Baruch D Kuppermann,Marilyn Chwa,Pinchas Cohen,Stephanie Lu

doi:10.1038/cddis.2017.348

Abstract

Age-related macular degeneration (AMD) ranks third among the leading causes of visual impairment with a blindness prevalence rate of 8.7%. Despite several treatment regimens, such as anti-angiogenic drugs, laser therapy, and vitamin supplementation, being available for wet AMD, to date there are no FDA-approved therapies for dry AMD. Substantial evidence implicates mitochondrial damage and retinal pigment epithelium (RPE) cell death in the pathogenesis of AMD. However, the effects of AMD mitochondria and Humanin G (HNG), a more potent variant of the mitochondrial-derived peptide (MDP) Humanin, on retinal cell survival have not been elucidated. In this study, we characterized mitochondrial and cellular damage in transmitochondrial cybrid cell lines that contain identical nuclei but possess mitochondria from either AMD or age-matched normal (Older-normal (NL)) subjects. AMD cybrids showed (1) reduced levels of cell viability, lower mtDNA copy numbers, and downregulation of mitochondrial replication/transcription genes and antioxidant enzyme genes; and (2) elevated levels of genes related to apoptosis, autophagy and ER-stress along with increased mtDNA fragmentation and higher susceptibility to amyloid-β-induced toxicity compared to NL cybrids. In AMD cybrids, HNG protected the AMD mitochondria, reduced pro-apoptosis gene and protein levels, upregulated gp130 (a component of the HN receptor complex), and increased the protection against amyloid-β-induced damage. In summary, in cybrids, damaged AMD mitochondria mediate cell death that can be reversed by HNG treatment. Our results also provide evidence of Humanin playing a pivotal role in protecting cells with AMD mitochondria. In the future, it may be possible that AMD patient’s blood samples containing damaged mitochondria may be useful as biomarkers for this condition. In conclusion, HNG may be a potential therapeutic target for treatment of dry AMD, a debilitating eye disease that currently has no available treatment. Further studies are needed to establish HNG as a viable mitochondria-targeting therapy for dry AMD.

Highlights

Early Age-related macular degeneration (AMD) manifests with formation of drusen deposits between the retinal pigment epithelium (RPE) and Bruch’s membrane
Analyses of the 503-2484 bps mtDNA regions showed 120% higher numbers of mtDNA lesions in AMD cybrids (2.2 ± 0.34 a.u.) compared to normal (1 ± 0.32 a.u., P = 0.04) (Figure 1e). These results suggest that mitochondria from AMD patients have significantly higher levels of mtDNA damage with impaired replication and transcription
Since all cybrids have identical nuclei, these results suggest that AMD mitochondria may mediate cell death/stress by upregulation of nuclear-encoded apoptosis, autophagy, and ER stress genes and downregulation of antioxidant genes

Summary

Introduction

Early AMD manifests with formation of drusen deposits between the retinal pigment epithelium (RPE) and Bruch’s membrane. Retina is one of the highest energy demanding and oxygenconsuming tissues of the human body, relying on oxidative mitochondrial metabolism for ATP formation.[5] Mitochondrial. MtDNA is susceptible to oxidative damage because of its poor DNA repair capacity. Any mtDNA damage causes perturbations in energy metabolism, leading to oxidative stress, depletion of antioxidants and eventual RPE cell death. A large body of literature has linked mitochondrial dysfunction and resulting RPE cell death to the development and progression of AMD, glaucoma, diabetic retinopathy.[7,8,9,10,11,12]

Methods

Results

Conclusion