Altered mitochondrial function in type 2 granular corneal dystrophy

Type 2 granular corneal dystrophy (GCD2) is caused by point mutation R124H in the transforming growth factor-βinduced gene (TGFBI) and is characterized by age-dependent progression of corneal deposits. Mitochondrial features in heterozygous GCD2 and normal corneal tissues was evaluated using electron microscopy. Primary corneal fibroblasts of homozygous and normal corneas were cultured to passage 4 or 8. Keratocytes of normal corneal tissue are narrow, and details of their intracellular organelles are difficult to distinguish. Keratocytes of heterozygous GCD2 tissues exhibited many degenerative mitochondria. MitoTracker and cytochrome c staining demonstrated increased mitochondrial activity in mutated cells at early passages. Decreases in depolarized mitochondria, cellular proliferation, and expression of complexes I to V and increases in apoptotic change were observed in late-passage mutant fibroblasts. PGC-1α, ANT-1, p-Akt, and p-mTOR but not NF-κB expression demonstrated a passage-dependent decrease in all cells. Increased passage- or mutation-related intracellular reactive oxygen species and delayed proliferation of methanethiosulfonate (MTS) were recovered using application of antioxidant butylated hydroxyanisole. Mitochondrial features and function were altered in mutated GCD2 keratocytes, in particular in older cells. Alteration of mitochondrial function is critical for understanding the pathogenesis of GCD2.