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

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.

Genetic dissection of non-syndromic retinitis pigmentosa

“…[ 150 ] It has a complex expression due to alternative splicing (>20 transcripts expressing in various tissues). [ 151 ] Its expression has been identified in various body tissues (brain, kidney, and lung) with the highest expression in the retina (four isoforms, having 419, 463, 532 and 558 amino acids are known to be expressed in the retina). [ 152 153 ] It is expressed mostly in the photoreceptors and the retinal ganglion cells.…”

“…There are studies on the expression of genetic variants of CERKL also in RPE, but its function in the RPE cells is unknown. [ 151 ]…”

“…It is known to cause ARRP (RP26) and also CORD. [ 151 ] It was identified first in a Spanish family having RP and was considered as one of the most prevalent genes for ARRP or CORD in the Spanish cohort. [ 152 155 ] In CERKL , 39 variants have been identified for IRDs and p.Arg257Stop is the most prevalent variant of CERKL .…”

“…[ 150 156 ] Variants result in increased oxidative stress and eventually lead to retinal degeneration. [ 151 ]…”

Oxidative Stress as a Main Contributor of Retinal Degenerative Diseases

“…Redox modifications also regulate gene expression, transcription factors and epigenetic pathways [5]. Changes in the expression of some genes can also modify the oxidative stress effects [6]. Under physiological conditions, there is a cellular balance between RNOS formation and removal as the organism has its own defence system to neutralise or catalyse RNOS and to repair damage from enzymatic antioxidants such as copper-zinc and manganese superoxide dismutases, catalase, peroxiredoxin, glutathione peroxidase, and glutathione reductase.…”