Decreased Integrity, Content, and Increased Transcript Level of Mitochondrial DNA Are Associated with Keratoconus

Oxidative stress may play an important role in the pathogenesis of keratoconus (KC). Mitochondrial DNA (mtDNA) is involved in mitochondrial function, and the mtDNA content, integrity, and transcript level may affect the generation of reactive oxygen species (ROS) and be involved in the pathogenesis of KC. We designed a case-control study to research the relationship between KC and mtDNA integrity, content and transcription. One-hundred ninety-eight KC corneas and 106 normal corneas from Chinese patients were studied. Quantitative real-time PCR was used to measure the relative mtDNA content, transcript levels of mtDNA and related genes. Long-extension PCR was used to detect mtDNA damage. ROS, mitochondrial membrane potential and ATP were measured by respective assay kit, and Mito-Tracker Green was used to label the mitochondria. The relative mtDNA content of KC corneas was significantly lower than that of normal corneas (P = 9.19x10(-24)), possibly due to decreased expression of the mitochondrial transcription factor A (TFAM) gene (P = 3.26x10(-3)). In contrast, the transcript levels of mtDNA genes were significantly increased in KC corneas compared with normal corneas (NADH dehydrogenase subunit 1 [ND1]: P = 1.79x10(-3); cytochrome c oxidase subunit 1 [COX1]: P = 1.54x10(-3); NADH dehydrogenase subunit 1, [ND6]: P = 4.62x10(-3)). The latter may be the result of increased expression levels of mtDNA transcription-related genes mitochondrial RNA polymerase (POLRMT) (P = 2.55x10(-4)) and transcription factor B2 mitochondrial (TFB2M) (P = 7.88x10(-5)). KC corneas also had increased mtDNA damage (P = 3.63x10(-10)), higher ROS levels, and lower mitochondrial membrane potential and ATP levels compared with normal corneas. Decreased integrity, content and increased transcript level of mtDNA are associated with KC. These changes may affect the generation of ROS and play a role in the pathogenesis of KC.