De novo synthesis of cardiolipin controls respiratory chain biogenesis in neonatal mouse hearts

Postnatal maturation of the mammalian heart requires a vast increase in respiratory enzymes. The mitochondria-specific lipid cardiolipin (CL) is essential for respiratory chain integrity but has no defined function in heart maturation. Here, we determined how the two steps of CL biogenesis, de novo synthesis and acyl chain remodeling, affect the maturation of cardiac mitochondria in mice. Cardiomyocyte-restricted deletion of the CL synthase Crls1 in late gestation does not affect CL levels at birth but blocks the increase in the tissue concentration of CL observed during normal postnatal maturation. Deletion of Crls1 prevents the postnatal rise in cristae density and in the intramitochondrial concentration of respiratory proteins. This inhibits cardiac development, precipitates heart failure, and causes death by the age of 2 weeks. In contrast, ablation of CL remodeling by cardiomyocyte-restricted deletion of Tafazzin does not disrupt mitochondrial maturation or cardiac development, although it has a similar effect on the CL concentration and profoundly alters the CL species composition. Our data show that CL synthesis, but not CL remodeling, controls expression of the respiratory chain by a mechanism independent of the CL concentration.