An essential role for cardiolipin in the stability and function of the mitochondrial calcium uniporter

Calcium uptake by the mitochondrial calcium uniporter coordi-nates cytosolic signaling events with mitochondrial bioenergetics. During the past decade all protein components of the mitochon-drial calcium uniporter have been identified, including MCU, the pore-forming subunit. However, the specific lipid requirements, if any, for the function and formation of this channel complex are currently not known. Here we utilize yeast, which lacks the mito-chondrial calcium uniporter, as a model system to address this problem. We use heterologous expression to functionally recon-stitute human uniporter machinery both in wild-type yeast as well as in mutants defective in the biosynthesis of phosphatidyletha-nolamine, phosphatidylcholine, or cardiolipin (CL). We uncover a specific requirement of CL for in vivo reconstituted MCU stability and activity. The CL requirement of MCU is evolutionarily con-served with loss of CL triggering rapid turnover of MCU homologs and impaired calcium transport. Furthermore, we observe reduced abundance and activity of endogenous MCU in mammalian cellular models of Barth syndrome, which is characterized by a partial loss of CL. MCU abundance is also decreased in the cardiac tissue of Barth syndrome patients. Our work raises the hypothesis that im-paired mitochondrial calcium transport contributes to the patho-genesis of Barth syndrome, and more generally, showcases the utility of yeast phospholipid mutants in dissecting the phospho-lipid requirements of ion channel complexes.