Altered Mitochondrial Base Excision Repair and Mitochondrial DNA Instability in Peripheral Leukocytes of Patients with MASLD

Metabolic dysfunction-associated steatotic liver disease (MASLD) is a multifactorial metabolic disorder that is strongly associated with mitochondrial dysfunction and oxidative stress, which may potentially compromise the integrity of mitochondrial DNA (mtDNA). However, the role of the base excision repair (BER) pathway—the main mechanism responsible for repairing oxidative lesions in mitochondria—and maintaining mtDNA stability in MASLD remains poorly understood. Here, we analyzed total mRNA expression levels of key BER components in whole-blood samples, along with mitochondrial protein levels of the selected components. Additionally, we assessed the mtDNA copy number and the damage of mtDNA and nuclear DNA in peripheral leukocytes from MASLD patients and healthy controls. We found that MASLD patients differed from controls in mtDNA and nuclear DNA damage, mtDNA copy number, and selected BER-related markers. However, because the MASLD and control groups also differed substantially in age and BMI, these molecular differences should be interpreted as potentially being associated with age- and BMI-related metabolic status rather than attributable to MASLD alone. While several BER-related genes were downregulated at the mRNA level, the corresponding mitochondrial protein levels were not consistently decreased in MASLD (ProteomeXchange: PXD075974), indicating a discordance between transcriptional and protein-level regulation. These results suggest that altered mitochondrial BER and mtDNA instability in peripheral leukocytes may reflect the combined influence of MASLD, aging, obesity, and broader metabolic dysfunction.