Postnatal developmental dynamics of mitochondrial complex I in mouse tissues

Although the content of mitochondrial enzymes in different tissues can vary greatly, understanding the regulation behind these differences has been hampered by a lack of quantitative knowledge in relation to postnatal development. Here we report a quantitative analysis of developing brain, heart, kidneys, and muscle tissue of C57BL/6J mice, focusing on the content of mitochondrial complex I, a key component of the respiratory chain. We found that in all tissues except kidneys, complex I content gradually increases after birth, reaching a plateau level at around 25 days. Complex I content in muscles does not change significantly until <i>postnatal day 7</i>-<i>10</i>, and then also increases. The greatest increment was found in kidneys, where a 16-fold increase in complex I level after birth was observed. We also found that content of complex I in all postnatal tissues, but muscle, is higher in males than in females. These baseline dynamics of this key mitochondrial flavoprotein serve as a reference for evaluating genetic influences on development and provide a standard for assessing mitochondrial complex I function during postnatal growth.<b>NEW & NOTEWORTHY</b> Mitochondrial complex I is a key enzyme of mammalian oxidative phosphorylation. Here, we provide the first quantitative map of mitochondrial complex I maturation in postnatal mouse tissues. Complex I content rises after birth with striking tissue- and sex-specific patterns, including a dramatic 16-fold increase in kidney. These findings establish a baseline for developmental bioenergetics and a reference for evaluating genetic or disease-related mitochondrial dysfunction.