Overexpression of CERKL Protects Retinal Pigment Epithelium Mitochondria from Oxidative Stress Effects.

Rocío García-Arroyo,Serena Mirra,Aleix Gavaldà-Navarro,Gemma Marfany,Francesc Villarroya

doi:10.3390/antiox10122018

Abstract

The precise function of CERKL, a Retinitis Pigmentosa (RP) causative gene, is not yet fully understood. There is evidence that CERKL is involved in the regulation of autophagy, stress granules, and mitochondrial metabolism, and it is considered a gene that is resilient against oxidative stress in the retina. Mutations in most RP genes affect photoreceptors, but retinal pigment epithelium (RPE) cells may be also altered. Here, we aimed to analyze the effect of CERKL overexpression and depletion in vivo and in vitro, focusing on the state of the mitochondrial network under oxidative stress conditions. Our work indicates that the depletion of CERKL increases the vulnerability of RPE mitochondria, which show a shorter size and altered shape, particularly upon sodium arsenite treatment. CERKL-depleted cells have dysfunctional mitochondrial respiration particularly upon oxidative stress conditions. The overexpression of two human CERKL isoforms (558 aa and 419 aa), which display different protein domains, shows that a pool of CERKL localizes at mitochondria in RPE cells and that CERKL protects the mitochondrial network—both in size and shape—against oxidative stress. Our results support CERKL being a resilient gene that regulates the mitochondrial network in RPE as in retinal neurons and suggest that RPE cell alteration contributes to particular phenotypic traits in patients carrying CERKL mutations.

Highlights

Retinitis pigmentosa (RP) comprises a genetically heterogenous group of retinal degenerative diseases characterized by night blindness and progressive loss of vision due to photoreceptor degeneration
To assess whether endogenous CERKL colocalizes with mitochondria in murine retinal pigment epithelium (RPE), we performed immunofluorescence of retinal cryosections from WT/WT mice with the mitochondrial marker COX-IV and two different in-house antibodies against peptides encoded by exon
As CERKL is proposed as a resilience gene against oxidative stress in mammalian retina, and its depletion in KD/KO mice causes retinal degeneration, we investigated if KD/KO

Summary

Introduction

Retinitis pigmentosa (RP) comprises a genetically heterogenous group of retinal degenerative diseases characterized by night blindness and progressive loss of vision due to photoreceptor degeneration. CERKL expression is highly complex, with more than 20 transcripts and several alternative promoters in human and mouse tissues [4,5]. This transcriptional complexity results in at least four CERKL isoforms displaying different protein domains [6]. CERKL isoforms have a dynamic subcellular localization and multiple functions: they act as a shuttle from the cytoplasm to the nucleus; are able to bind sphingolipids [7]; interact with antioxidant enzymes [8]; and regulate autophagy, and mitochondrial dynamics and metabolism [9,10]. CERKL has been described as a RNA binding protein that localizes in polysomes, mRNA compact particles, stress granules

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