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Reduced OPA1, Mitochondrial Fragmentation and Increased Susceptibility to Apoptosis in Granular Corneal Dystrophy
Seung-Il Choi1,2, Ga-Hyun Lee1, Jong-Hwan Woo1
1Corneal Dystrophy Research Institute, Yonsei University College of Medicine, Seoul 03722, Republic of Korea.
Abstract:
The progressive degeneration of granular corneal dystrophy type 2 (GCD2) corneal fibroblasts is associated with altered mitochondrial function, but the underlying mechanisms are incompletely understood. We investigated whether an imbalance of mitochondrial dynamics contributes to mitochondrial dysfunction of GCD2 corneal fibroblasts. Transmission electron microscopy revealed several small, structurally abnormal mitochondria with altered cristae morphology in GCD2 corneal fibroblasts. Confocal microscopy showed enhanced mitochondrial fission and fragmented mitochondrial tubular networks. Western blotting revealed higher levels of MFN1, MFN2, and pDRP1 and decreased levels of OPA1 and FIS1 in GCD2. OPA1 reduction by short hairpin RNA (shRNA) resulted in fragmented mitochondrial tubular networks and increased susceptibility to mitochondrial stress-induced apoptosis. A decrease in the mitochondrial biogenesis-related transcription factors NRF1 and PGC1α was observed, while there was an increase in the mitochondrial membrane proteins TOM20 and TIM23. Additionally, reduced levels of mitochondrial DNA (mtDNA) were exhibited in GCD2 corneal fibroblasts. These observations suggest that altered mitochondrial fission/fusion and biogenesis are the critical molecular mechanisms that cause mitochondrial dysfunction contributing to the degeneration of GCD2 corneal fibroblasts.
Insights
Mitochondrial dynamics are altered in granular corneal dystrophy type 2 (GCD2) fibroblasts, showing increased fission and reduced biogenesis. This mitochondrial dysfunction contributes to the degeneration of GCD2 corneal cells.
Area of Science:
- Ophthalmology
- Cell Biology
- Mitochondrial Biology
Background:
- Granular corneal dystrophy type 2 (GCD2) is characterized by progressive corneal fibroblast degeneration.
- Altered mitochondrial function is implicated in GCD2 pathogenesis, but mechanisms remain unclear.
Purpose of the Study:
- To investigate the role of mitochondrial dynamics imbalance in GCD2 corneal fibroblast dysfunction.
- To elucidate the molecular mechanisms underlying mitochondrial dysfunction in GCD2.
Main Methods:
- Transmission electron microscopy (TEM) and confocal microscopy to assess mitochondrial morphology and dynamics.
- Western blotting to quantify key mitochondrial fission/fusion proteins (MFN1, MFN2, pDRP1, OPA1, FIS1) and biogenesis factors (NRF1, PGC1α).
- Short hairpin RNA (shRNA) knockdown of OPA1 and measurement of mitochondrial DNA (mtDNA) levels.
Main Results:
- GCD2 fibroblasts exhibited structurally abnormal mitochondria with altered cristae, enhanced fission, and fragmented networks.
- Increased levels of MFN1, MFN2, pDRP1 and decreased OPA1, FIS1 were observed in GCD2.
- OPA1 reduction exacerbated mitochondrial fragmentation and apoptosis susceptibility.
- Decreased NRF1, PGC1α, and mtDNA levels, alongside increased TOM20 and TIM23, indicated impaired mitochondrial biogenesis.
Conclusions:
- Imbalances in mitochondrial fission/fusion dynamics and impaired biogenesis are critical mechanisms driving mitochondrial dysfunction in GCD2 corneal fibroblasts.
- These molecular alterations contribute significantly to the degenerative processes observed in GCD2.
