Abstract
Purpose :
TAZ-deficient mice show progressive decrease in corneal endothelial cell (CEnC) density as observed in patients with Fuchs endothelial corneal dystrophy (FECD). The purpose of this study was to expand our understanding of the mechanism of how TAZ or Wwtr1 deficiency leads to CEnC loss by determining ultrastructural characteristics of CEnCs and expression of GRP78 (78 kDa glucose-regulated protein), a well-known endoplasmic reticulum (ER) stress marker, in wildtype (WT), Wwtr1+/- and Wwtr1-/- mice.
Methods :
Ultrathin sections of 3 corneas for each genotype from 2- and 12-month-old age groups were prepared for transmission electron microscopy (TEM). The number of mitochondria was counted in each TEM image at X36,000 magnification. Mitochondria with indistinct cristae and electrolucent areas were considered abnormal, and the percentage of the number of dysfunctional mitochondria/the total number of mitochondria (%) was calculated and compared between genotypes for each age group using a two-way ANOVA. Immunofluorescence staining for GRP78 was performed in 3 corneas for each genotype. The staining intensity was quantitated by calculating corrected total cell fluorescence (CTCF) and compared between genotypes using a Kruskal-Wallis test.
Results :
The CEnCs from Wwtr1-/- mice showed dilated ER and indistinct cristae and electrolucency in mitochondria beginning at 2 months of age. By 12 months of age, the severity had increased with numerous autophagosomes and regional CEnC loss also identified. The percentage of dysfunctional mitochondria (%) was significantly greater in Wwtr1-/- mice versus WT and Wwtr1+/- mice at 2 months of age (31.1 ± 6.1, 39.5 ± 5.0, and 79.0 ± 2.4 for WT, Wwtr1+/- and Wwtr1-/-, respectively; P < 0.0001) and versus WT mice at 12 months of age (45.6 ± 4.7, 59.7 ± 9.9, and 72.9 ± 9.7 for WT, Wwtr1+/- and Wwtr1-/-, respectively; P = 0.0011). Although there was no statistical difference, there was increased staining for GRP78 in CEnCs of TAZ-deficient mice (11481 ± 1079, 18916 ± 6646, and 21025 ± 6845 for WT, Wwtr1+/- and Wwtr1-/-, respectively).
Conclusions :
Wwtr1 deficiency causes ER stress and mitochondrial dysfunction in CEnCs modeling what is observed in the endothelium of FECD patients. This murine model of late-onset FECD can be utilized to study the pathophysiology of and novel treatments for mitochondrial and ER stress in FECD.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.