The cytoprotective peptide humanin protects RPE cells from oxidative stress by modulating mitochondrial bioenergetics and delayed RPE senescence

Abstract

Purpose: Humanin (HN) is a 24-amino acid peptide expressed from an open reading frame within the mitochondrial 16S ribosomal RNA. HN has been reported to have cytoprotective, metabolic, anti-inflammatory and anti-fibrilogenic properties in multiple cell cultures and in various animal models. Hence, we investigated the effects of HN in oxidative stress-induced RPE cell death, particularly with respect to mitochondrial bioenergetics and induction of senescence.

Methods: Localization of HN and its receptors in RPE cells and polarized RPE monolayers was studied by confocal microscopy. To study the protective effect of HN, primary hRPE cells were treated with 150 µM tert-Butyl hydroperoxide (tBH) in the absence/presence of varying doses of HN (0.5-10 µg/ml) for 24 h. Mitochondrial respiration was measured in RPE cells using the XF96 analyzer. Effects of HN on RPE cell death, reactive oxygen species (ROS) formation and oxidative stress-induced senescence were studied by TUNEL assay, MitoSox staining and SA-β-Gal staining, respectively.

Results: Our studies showed prominent cytoplasmic expression of HN and its receptors in non-polarized and polarized RPE cells. In the cytoplasm, HN co-localized with mitochondria. Primary hRPE cells treated with 150 µM tBH for 24 h showed marked cell death and a significant decrease in mitochondrial bioenergetics; HN co-treatment inhibited mitochondrial ROS formation and significantly restored mitochondrial respiration. The decrease in mitochondrial function, namely, basal mitochondrial oxygen consumption rates, ATP turnover, reserve capacity and proton leak, was prevented by HN co-treatment. HN protected RPE cells from oxidative stress-induced cell death by STAT3 phosphorylation and inhibiting caspase-3 activation. HN co-treatment resulted in a delay of tBH-induced senescence in RPE cells.

Conclusions: HN protects RPE cells from oxidant injury by attenuating cell death and restoring mitochondrial function. HN also delays RPE senescence. Our data suggest a potential role for HN therapy in the prevention and treatment of retinal degeneration.