Determination of Oxidative Stress Markers in the Aqueous Humor and Corneal Tissues of Patients With Congenital Hereditary Endothelial Dystrophy

Experimental Oxidative Stress Breaks Down the Barrier Function of the Corneal Endothelium

Purpose: The fluid pump and barrier functions of the corneal endothelium maintain stromal deturgescence required for corneal transparency. The effect of oxidative stress, a hallmark of Fuchs endothelial corneal dystrophy (FECD), on the endothelial barrier function has been investigated. Methods: The endothelium of porcine corneas ex vivo was exposed to (1) membrane permeable oxidants (H₂O₂, 100 μM, 1 h; tert-butyl-hydroperoxide, 100 μM, 1 h), or (2) ultraviolet A (UVA) with photosensitizers for 15 min, riboflavin (50 μM) or tryptophan (Trp) (100 μM). The effects on the apical junction complex were analyzed by (1) immunostaining the perijunctional actomyosin ring (PAMR) and ZO-1 and (2) assessment of paracellular flux of fluorescein isothiocyanate (FITC)-avidin across cultured endothelial cells grown on biotinylated-gelatin film. The extent of oxidative stress was quantified by changes in intracellular reactive oxygen species (ROS) and mitochondrial membrane potential (MMP) in addition to lipid peroxidation and release of lactate dehydrogenase (LDH). Results: Both methods of oxidative stress led to the disruption of PAMR and ZO-1 concurrent with changes in ROS levels, depolarization of MMP, increased lipid peroxidation, elevated LDH release, and increased permeability of FITC-avidin. The effects of direct oxidants were opposed by SB-203580 [p38 mitogen-activating protein (MAP) kinase inhibitor; 10 μM]. The damage by UVA+photosensitizers was blocked by extracellular catalase (10,000 U/mL). Conclusions: (1) Acute oxidative stress breaks down the barrier function through destruction of PAMR in a p38 MAP kinase-dependent manner. (2) UVA+photosensitizers elicit the breakdown of PAMR via type I reactions, involving H₂O₂ release. (3) Blocking the oxidative stress prevents loss of barrier function, which could be helpful in the therapeutics of FECD.

Whole exome sequencing identified FAM149A as a plausible causative gene for congenital hereditary endothelial dystrophy, affecting Nrf2-Antioxidant signaling upon oxidative stress

BACKGROUND

Congenital hereditary endothelial dystrophy (CHED) is a rare genetic disease of the corneal endothelium with a very early onset of bilateral corneal edema due to degeneration and dysfunction of the corneal endothelium. Currently SLC4A11 is the only established causative gene for CHED, but not all these reported CHED patients could be explained by SLC4A11 deficiency, indicating that the genetic predisposition of CHED still requires further exploration.

METHODS

Trio-based whole-exome sequencing was performed on a CHED patient and his unaffected parents. The GATK2 and an in-house bioinformatics pipeline were applied for variant analyses, following the 2015 American College of Medical Genetics and Genomics (ACMG) guidelines. Potential pathogenic variants were further validated by Sanger sequencing. The expression profiles of FAM149A in cell line, murine tissues or human corneal endothelia were determined by RT-qPCR. Small interfering RNA was used to knock down the expression of FAM149A in vitro. Cell viability was detected by a CCK-8 assay. ROS and 8-OHdG were examined by fluorometric analysis. The nuclear translocation of NRF2 was determined by western blotting.

RESULTS

We identified a homozygous mutation (NM_015398.3: c.991A > G; p.R331G) in the FAM149A gene that related to the phenotype of CHED. FAM149A was found to be highly expressed in corneal endothelium, and up-regulated upon oxidative stress. Further functional investigations demonstrated that deficiency in FAM149A impaired Nrf2-antioxidant signaling, rendering cells more vulnerable to oxidative stress. Consistently, the expression of FAM149A was significantly reduced in patients with corneal endothelium dysfunction.

CONCLUSION

This study demonstrated, for the first time, FAM149A as a plausible causative gene for CHED etiology, offering new insight for future investigation targeting CHED.