Perturbation of phosphatidylethanolamine synthesis affects mitochondrial morphology and cell‐cycle progression in procyclic‐form Trypanosoma brucei

Abstract

SummaryPhosphatidylethanolamine (PE) and phosphatidylcholine (PC) are the two major constituents of eukaryotic cell membranes. In the protist Trypanosoma brucei, PE and PC are synthesized exclusively via the Kennedy pathway. To determine which organelles or processes are most sensitive to a disruption of normal phospholipid levels, the cellular consequences of a decrease in the levels of PE or PC, respectively, were studied following RNAi knockdown of four enzymes of the Kennedy pathway. RNAi against ethanolamine-phosphate cytidylyltransferase (ET) disrupted mitochondrial morphology and ultrastructure. Electron microscopy revealed alterations of inner mitochondrial membrane morphology, defined by a loss of disk-like cristae. Despite the structural changes in the mitochondrion, the cells maintained oxidative phosphorylation. Our results indicate that the inner membrane morphology of T. brucei procyclic forms is highly sensitive to a decrease of PE levels, as a change in the ultrastructure of the mitochondrion is the earliest phenotype observed after RNAi knock-down of ET. Interference with phospholipid synthesis also impaired normal cell-cycle progression. ET RNAi led to an accumulation of multinucleate cells. In contrast, RNAi against choline-/ethanolamine phosphotransferase, which affected PC as well as PE levels, caused a cell division phenotype characterized by non-division of the nucleus and production of zoids.

Formation and function of phosphatidylserine and phosphatidylethanolamine in mammalian cells

“…Convincing in vitro experimental evidence supports a role for PE, a cone-shaped lipid, in membrane fusion since PE has the tendency to form non-lamellar membrane structures and modulates membrane curvature [140][141][142][143]. Consistent with these findings, PE plays an important role in contractile ring disassembly at the cleavage furrow during cytokinesis of mammalian cells [144,145], and a lack of PE inhibits progression of the cell cycle in the parasite T. brucei, probably by impairing membrane fusion [138]. PE also regulates the fusion of mitotic Golgi membranes [146].…”

“…Elimination of both PE and cardiolipin in yeast causes massive fragmentation of mitochondria and loss of mitochondrial membrane potential [137]. Mitochondrial morphology is also altered by depletion of PE in T. brucei although in this organism PE is made entirely by the non-mitochondrial CDP-ethanolamine pathway [138]. Thus, evidence is accumulating that the PE content of mitochondria is crucial for maintaining normal mitochondrial function.…”

“…Moreover, PE is a precursor for the synthesis of anandamide (N-arachidonoylethanolamine), the ligand for cannabinoid receptors in the brain [135,136]. Mitochondria, particularly the inner membranes, are enriched in PE compared to other membranes and a decrease in the mitochondrial content of PE profoundly alters mitochondrial morphology in yeast [137], T. brucei [138] and mammalian cells [139] (Section 5.4). Convincing in vitro experimental evidence supports a role for PE, a cone-shaped lipid, in membrane fusion since PE has the tendency to form non-lamellar membrane structures and modulates membrane curvature [140][141][142][143].…”

The Kennedy pathway—De novo synthesis of phosphatidylethanolamine and phosphatidylcholine

“…This suggests that import of PE into the organelle becomes growth limiting and results in the enhanced formation of respiration-deficient cells (16). The mitochondrial membranes of the parasite Trypanosoma brucei are also highly sensitive to perturbations in the phospholipid metabolism that result in a direct or indirect decrease of PE (21,28).…”

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

“…Reduction of PE synthesis via PSD alters mitochondrial morphology in yeast (52) and Trypanosoma brucei (53), and depletion of PE to Ͻ4% of yeast phospholipids impairs survival (51,54). PE synthesis from PSD is essential in yeast mutants lacking CL synthase, suggesting that CL and PE have overlapping functions (55).…”