2.4 Determination of mitochondrial DNA copy number
The mitochondrial DNA copy number (mtDNA CN) was calculated through real-time quantitative polymerase chain reaction (qPCR) using the PRISM® 7900HT Fast Real-Time PCR System (Applied Biosystems, Foster City, CA, USA). The primer sequences (Cosmogenetech, Daejeon, Korea) used are described in supplementary methods. The mtDNA CN was calculated with adjustments to the standard curve of a calibrator, which contained exactly one copy of mtDNA and one copy of nuclear DNA.