Low mitochondrial DNA copy number in peripheral blood mononuclear cells is associated with future mortality risk: a long-term follow-up study from Japan.

ABSTRACT

OBJECTIVES: The mitochondrial DNA (mtDNA) is unique and circular with multiple copies of the genome. The lower mtDNA copy number (mtDNA-CN) in leukocytes is associated with the risk of all-cause mortality. However, its long-term association is unknown. Thus, the study examined the association between mtDNA-CN and the risk of all-cause mortality in a long-term follow-up study in the Japanese population. DESIGN: This longitudinal study included the study cohort from an annual, population-based health checkup in the town of Yakumo, Hokkaido, Japan. SETTING AND PARTICIPANTS: 814 participants (baseline age range 38-80 years, mean 56.3 years) were included in this study in 1990. They were followed-up regarding mortality for about 30 years (median 28.1 years) till 2019. MEASURES: The genomic DNA was extracted from peripheral blood mononuclear cells and the mtDNA-CN was measured using real-time polymerase chain reaction. The level of the mtDNA-CN was divided into tertiles (low, middle, and high). The participants were categorized based on their age into middle-aged (<60 years old) or old-aged (≥60 years old). Survival analysis was performed for tertile of mtDNA-CN and compared using the log-rank test. Univariate and multivariable Cox proportional hazard regression analyses were performed to assess the association between mtDNA-CN and all-cause mortality. The model adjusted with age, sex, body mass index, systolic blood pressure, smoking habit, alcohol consumption, exercise habit, and education level. RESULTS: The low levels of mtDNA-CN resulted in a significant decrease in cumulative survival rate (P < 0.05). The risk of mortality was significantly higher in the middle-aged cohort when mtDNA-CN levels were low (hazard ratios [95% confidence intervals] 1.98 [1.10-3.56]). CONCLUSION: This study demonstrated that leukocyte mtDNA-CN is associated with future mortality risk. Our study findings may lead to further research on the early prediction of mortality and its underlying mechanisms.