Disease-causing mutations associated with bestrophinopathies promote apoptosis in retinal pigment epithelium cells

Impaired Bestrophin Channel Activity in an iPSC-RPE Model of Best Vitelliform Macular Dystrophy (BVMD) from an Early Onset Patient Carrying the P77S Dominant Mutation

Best Vitelliform Macular dystrophy (BVMD) is the most prevalent of the distinctive retinal dystrophies caused by mutations in the BEST1 gene. This gene, which encodes for a homopentameric calcium-activated ion channel, is crucial for the homeostasis and function of the retinal pigment epithelia (RPE), the cell type responsible for recycling the visual pigments generated by photoreceptor cells. In BVMD patients, mutations in this gene induce functional problems in the RPE cell layer with an accumulation of lipofucsin that evolves into cell death and loss of sight. In this work, we employ iPSC-RPE cells derived from a patient with the p.Pro77Ser dominant mutation to determine the correlation between this variant and the ocular phenotype. To this purpose, gene and protein expression and localization are evaluated in iPSC-RPE cells along with functional assays like phagocytosis and anion channel activity. Our cell model shows no differences in gene expression, protein expression/localization, or phagocytosis capacity, but presents an increased chloride entrance, indicating that the p.Pro77Ser variant might be a gain-of-function mutation. We hypothesize that this variant disturbs the neck region of the BEST1 channel, affecting channel function but maintaining cell homeostasis in the short term. This data shed new light on the different phenotypes of dominant mutations in BEST1, and emphasize the importance of understanding its molecular mechanisms. Furthermore, the data widen the knowledge of this pathology and open the door for a better diagnosis and prognosis of the disease.

Procyanidin protects human retinal pigment epithelial cells from high glucose by inhibiting autophagy

PURPOSE

The damage of hyperglycemia to the retinal pigment epithelial (RPE) cells is a critical event in diabetic retinopathy (DR). Procyanidin (PC), a kind of polyphenol compounds, has shown to be effective in preventing and treating diabetes as well as its complications, in which autophagy disorder is involved in the pathological mechanism. However, it remains unclear whether PC can play a protective role in DR by regulating the autophagy of RPE. Here, the effect of PC on RPE under high glucose conditions and the role of autophagy were investigated.

MATERIALS AND METHODS

The cell viability of ARPE-19, a human RPE cell line, was detected by cell counting kit-8 (CCK-8) and the apoptosis rate was measured by flow cytometry. The protein expressions of apoptosis markers, including Bax, Bcl-2, and Caspase-3, as well as autophagy markers including LC3, p62, p53, and mTOR were detected by Western blotting. Autophagic flux in ARPE-19 cells was detected by transfection with Ad-mCherry-GFP-LC3B.

RESULTS

Under high glucose conditions, the viability of ARPE-19 was decreased and the apoptosis rate increased, the protein expressions of Bax, Caspase-3, LC3-II/LC3-I, and p-p53 were all increased and the expressions of Bcl-2, p62, and p-mTOR decreased, and autophagic flux was increased compared with that of the controls. Treatment with PC weakened all these changes caused by high glucose. When rapamycin (RPM), an autophagy agonist was added, the cell viability of ARPE-19 by PC treatment was decreased while the apoptosis was increased.

CONCLUSIONS

Our findings indicate that through the p53/mTOR autophagy pathway, PC may protect RPE cells from high glucose-induced injury.

The best course of action

An 11-year-old girl noted gradual visual loss in the right eye for 1 year with subfoveal yellow deposits in both eyes. Optical coherence tomography, electro-oculogram and electroretinogram was in-keeping with Best Disease. This disorder is discussed.