Tissue-Specific Distribution of Coenzyme Q10 in Medaka (Oryzias latipes): Implications for Antioxidant Systems in Relation to Vitamin E, Cholesterol, and Mitochondrial DNA Content

Coenzyme Q10 (CoQ10) is an essential lipid-soluble antioxidant and a key component of the mitochondrial electron transport chain, playing critical roles in cellular redox homeostasis and energy metabolism. Although organ-specific differences in CoQ10 levels have been reported in humans, the mechanisms underlying tissue-specific regulation of CoQ10 remain poorly understood. Moreover, species differences in the predominant CoQ isoform limit the suitability of conventional rodent models for studying human CoQ10 metabolism, aging, and disease.In this study, we aimed to explore factors contributing to organ-specific CoQ10 levels and to establish fundamental reference data for medaka (Oryzias latipes), a vertebrate model that endogenously synthesizes CoQ10. CoQ10 concentrations in multiple organs were quantified by high-performance liquid chromatography. Levels of vitamin E and free cholesterol were also measured. Mitochondrial DNA (mtDNA) content was assessed as an index of mitochondrial abundance, and expression of CoQ10 biosynthetic enzymes, the CoQ-binding protein prosaposin (Psap), and 3-hydroxy-3-methylglutaryl-CoA reductase was analyzed by RT-qPCR.CoQ10 was detected in all organs examined, with the highest levels observed in the heart and liver, followed by the kidney and brain, and lower levels in skeletal muscle and the digestive tract. No significant sex-dependent differences were observed. CoQ10 levels were positively associated with PDSS2 expression and mtDNA content, while Psap expression showed strong positive correlations with multiple CoQ-related genes.These findings provide insight into factors associated with tissue-specific CoQ10 distribution and support medaka as a physiologically relevant model for investigating CoQ10 metabolism, oxidative stress, aging, and disease.