Phosphatidylethanolamine Deficiency in Mammalian Mitochondria Impairs Oxidative Phosphorylation and Alters Mitochondrial Morphology

Edited by Dennis VoelkerPhosphatidylcholine (PC) is a major phospholipid of mitochondria, comprising 40 -50% of both the outer and the inner membranes. However, PC must be imported from its production organelles because mitochondria lack the enzymes essential for PC biosynthesis. In a previous study, we found that StarD7 mediates the intracellular transfer of PC to mitochondria. Therefore, in this study, we analyzed the contribution of StarD7 to the maintenance of mitochondrial phospholipid content and function using siRNA-mediated knockdown and knock-out (KO) of the StarD7 gene in HEPA-1 cells. Real time analysis of respiratory activity demonstrated that the oxygen consumption rate and activity of mitochondrial complexes were impaired in StarD7-KD cells. To confirm these results, we established StarD7-KO HEPA-1 cells by double nicking using CRISPR/Cas9n. As expected, StarD7-KD and -KO cells showed a significant reduction in mitochondrial PC content. The ATP level and growth rate of KO cells were notably lower compared with wild-type cells when cultured in glucose-free galactosecontaining medium to force cells to rely on mitochondrial ATP production. In KO cells, the level of the MTCO1 protein, a primary subunit of complex IV, was reduced without a concomitant decrease in its mRNA, but the level was restored when StarD7-I was overexpressed. StarD7-KO cells showed impaired formation of the mitochondrial supercomplexes and exhibited a disorganized cristae structure, with no changes in optic atrophy 1 protein. These findings indicate that StarD7 plays important roles in maintaining the proper composition of mitochondrial phospholipids as well as mitochondrial function and morphogenesis.

Section: Contsupporting

confidence: 81%

Section: Contsupporting

confidence: 81%

StarD7 Protein Deficiency Adversely Affects the Phosphatidylcholine Composition, Respiratory Activity, and Cristae Structure of Mitochondria

Horibata

Ando

Zhang

et al. 2016

“…In mammalian cells, ablation of PSD is often associated with fragmented/deformed and dysfunctional mitochondria (42,49,50). A knockdown of TgPSD1mt, on the other hand, did not affect the typical lariat shape morphology of the organelle in T. gondii (Fig.…”

Section: Discussionmentioning

confidence: 99%

Phosphatidylethanolamine Synthesis in the Parasite Mitochondrion Is Required for Efficient Growth but Dispensable for Survival of Toxoplasma gondii

Hartmann

Hellmund

Lucius

et al. 2014

Background: Toxoplasma gondii is a common intracellular parasite of diverse host cells. Results:The parasite can produce phosphatidylethanolamine in its mitochondrion, endoplasmic reticulum, and parasitophorous vacuole, which together allow versatile lipid biogenesis. Conclusion: Multiple routes of lipid synthesis ensure parasite survival in discrete nutrient milieus. Significance: T. gondii offers an instructive model to study membrane biology of parasitic protists.

“…The non-bilayer forming phospholipids PE and CL are required for full activity of the respiratory chain, which generates the membrane potential across the inner membrane (52,55,(57)(58)(59). Thus, we wondered whether the respiratory chain complexes were present and functional in PC-deficient mitochondria.…”

Section: Depletion Of Pc Impairs Protein Transport Into the Innermentioning

confidence: 99%

“…First, binding of preproteins to the TOM complex is disturbed in PE-and CL-deficient mitochondria (49,50). Second, the activity of the respiratory chain complexes, in particular of the cytochrome c oxidase (complex IV), is decreased in mitochondria with reduced PE or CL content (57)(58)(59). Consequently, the membrane potential is decreased, which leads to reduced protein translocation via TIM23 or TIM22 translocases (52,55,57).…”

mentioning

confidence: 99%

Phosphatidylcholine Affects Inner Membrane Protein Translocases of Mitochondria

Schuler¹,

Bartolomeo

Mårtensson

et al. 2016

Two protein translocases transport precursor proteins into or across the inner mitochondrial membrane. The presequence translocase (TIM23 complex) sorts precursor proteins with a cleavable presequence either into the matrix or into the inner membrane. The carrier translocase (TIM22 complex) inserts multispanning proteins into the inner membrane. Both protein import pathways depend on the presence of a membrane potential, which is generated by the activity of the respiratory chain. The non-bilayer-forming phospholipids cardiolipin and phosphatidylethanolamine are required for the activity of the respiratory chain and therefore to maintain the membrane potential for protein import. Depletion of cardiolipin further affects the stability of the TIM23 complex. The role of bilayer-forming phospholipids like phosphatidylcholine (PC) in protein transport into the inner membrane and the matrix is unknown. Here, we report that import of presequence-containing precursors and carrier proteins is impaired in PC-deficient mitochondria. Surprisingly, depletion of PC does not affect stability and activity of respiratory supercomplexes, and the membrane potential is maintained. Instead, the dynamic TIM23 complex is destabilized when the PC levels are reduced, whereas the TIM22 complex remains intact. Our analysis further revealed that initial precursor binding to the TIM23 complex is impaired in PC-deficient mitochondria. We conclude that reduced PC levels differentially affect the TIM22 and TIM23 complexes in mitochondrial protein transport.Mitochondria fulfill essential functions for the survival of the cell like energy conversion to produce ATP, synthesis of amino acids, lipids, and heme, as well as the generation of iron-sulfur clusters. They contain about 1000 proteins in yeast and 1500 proteins in humans (1, 2). More than 99% of the mitochondrial proteins are synthesized as precursors on cytosolic ribosomes. Mitochondria contain a sophisticated system of protein translocases to import precursor proteins (3-9). The translocase of the outer membrane (TOM 3 complex) forms the general entry gate for most precursor proteins. After passage of the TOM channel, distinct protein translocases sort the preproteins into the different subcompartments: the outer and inner membrane as well as the two aqueous compartments, the matrix and intermembrane space.The majority of mitochondrial proteins are sorted into the inner membrane and the matrix. Two inner membrane-bound protein complexes mediate protein import. The presequence translocase (also termed TIM23 complex) transports precursor proteins with a cleavable presequence into the inner membrane and the matrix, whereas the carrier translocase (also termed TIM22 complex) inserts proteins with multiple transmembrane segments into the inner membrane (3-9). The membrane potential across the inner membrane provides the driving force for both protein import pathways and is generated by the activity of the respiratory chain. Presequence-containing preproteins are directly transferred from the ...