αB Crystallin Chaperone Peptide (mini Cry) Inhibits Senescence in RPE cells by Modulating Mitochondrial Biogenesis and Fission Proteins

Abstract

Purpose : Oxidative stress in the retinal pigment epithelium (RPE) can induce mitochondrial damage and dysfunction and is likely a causative factor in age-related macular degeneration (AMD) pathogenesis. The relevance of RPE senescence to AMD progression is a topic of interest. We characterized senescence in human (h) RPE and investigate the effect of αB Crystallin chaperone peptide (mini Cry) in controlling senescence by regulating mitochondrial function.

Methods : Senescence was induced in hRPE in two ways. First, subconfluent RPE cells were treated with 0.2 µg/mL doxorubicin (DOX) for 3 h in medium containing 0.5% FBS, which was replaced with fresh medium containing 10% FBS. Cells were maintained for 6 days, with the culture medium replaced every 48 h. 75 µg/mL mini Cry or scrambled peptide was present in the culture medium throughout the experiment. Second, subconfluent RPE cells were treated with 500 μM H₂O₂ alone or with 75 μg/mL mini Cry or a scrambled peptide for 2 h. The H₂O₂ treatment was repeated the next day. Cells were maintained in 10% FBS medium for 4 days. Senescence biomarkers (senescence-associated beta-galactosidase [SA-βgal], p21^CIP1, p16^INK4a) and mitochondrial proteins (FIS1, DRP1, MFN2, PGC1-α, mTFA) were analyzed in control and experimental groups.

Results : Increased senescence (SA-βgal staining) was observed with DOX- or H₂O₂-induced senescence. Mini Cry treatment resulted in a significant decrease in SA-βgal positive cells, while a scrambled peptide had no effect. The mRNA and protein levels of p21^CIP1 and p16^INK4a increased 2-3 fold after DOX or H₂O₂ treatment, and mini Cry co-treatment suppressed these levels to unstressed controls levels.
The mitochondrial biogenesis proteins PGC-1 and mTFA increased 1.5 -2.5 fold with senescence inducers and mini Cry reduced their expression significantly. Mitochondrial fission proteins (FIS1, DRP1) increased in response to senescence-induction, while the mitochondrial fusion protein (MFN2) did not change. Mini Cry abolished the increased expression of the fission proteins.

Conclusions : Mini Cry significantly impairs stress-induced senescence by modulating mitochondrial biogenesis and fission proteins in RPE. Future studies in vivo may better define the role of senescence in AMD and the therapeutic potential of mini Cry.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.