The effect of citrate/cis‐aconitate on oxidative metabolism during transformation of Trypanosoma brucei

Abstract

Monomorphic bloodstream forms of Trypanosoma brucei, grown in the mammal, are deficient in aconitase and 2-oxoglutarate dehydrogenase and they do not respire in the presence of the substrates citrate, cis-aconitate, succinate, proline or 2-oxoglutarate. When grown in vitro low levels of aconitase, succinate oxidase and proline oxidase are detected.Addition of citratelcis-aconitate at 37 "C to bloodstream forms leads to the formation of aconitase and proline oxidase. Most cells undergo an 'abortive' transformation to non-dividing procyclic-like cells while some cells adapt to the presence of the citric acid cycle intermediates and continue to multiply as bloodstream forms.At 27°C and in the presence of citratelcis-aconitate bloodstream forms transform synchronously to dividing procyclic cells. Within 72 h the rate of respiration with proline, succinate and 2-oxoglutarate becomes similar to that in established procyclic cells while the rate of glucose oxidation decreases.The possible role of citric acid cycle intermediates in determining whether a trypanosome will retain the properties of a bloodstream trypomastigote or differentiate to a procyclic trypomastigote is discussed.The parasitic protozoan, Trypanosoma brucei, undergoes a series of differentiation steps during its cyclical development in the mammalian host and the arthropod vector, the tsetse fly [l]. Differentiation of bloodstream forms to procyclic cells, a process called transformation, is initiated in the mammal by the transition of dividing slender forms to intermediate and non-dividing stumpy forms, giving rise to a pleomorphic population. After uptake with the blood meal into the midgut of the fly, cells with stumpy morphology are considered to transform most readily to dividing procyclic cells.Transformation of pleomorphic as well as monomorphic populations of rodent-adapted strains which have a uniform slender morphology [2] can be studied in various in vitro systems [3 -91. Synchronous transformation requires two external signals, a temperature change from 37°C to 27°C and the addition of cis-aconitate and/or citrate as inducers Some of the complex morphological, ultrastructural and metabolic changes which characterize transformation have been studied in detail. First, the repression of the synthesis of the variant surface glycoprotein (VSG) in the coated bloodstream forms is an early event which is followed by coat [lo-131. release to form coatless procyclic cells [7, 8, 111. Second, transformation involves profound changes in energy metabolism [14-161. In bloodstream forms glucose is degraded solely by glycolysis to form two mol pyruvate/mol glucose. Reducing equivalents are transferred to oxygen via a unique mitochondrial glycerol-3-phosphate oxidase [17,18]. The promitochondrion lacks a functional citric acid cycle as well as a cytochrome-linked respiratory chain. Stumpy forms contain some mitochondrial enzymes, such as 2-oxoglutarate dehydrogenase and proline oxidase [19]. During transformation to procyclic cells a functional respiratory ...

Non‐cytochrome mediated mitochondrial ATP production in bloodstream form Trypanosoma brucei brucei

“…In either case this does not exclude the possibility that mitochondrial ATP generation may play an important role in mitochondrial development itself during differentiation from bloodstream to procyclic forms. It is known that the Krebs cycle intermediates citrate and cis-aconitate enhance this transition (Overath et al, 1986) which supports this hypothesis. In addition, the ability of transitional cells to survive without glucose may be of value to the parasite when ingested by the vector since these cells are in a glucose-poor environment prior to complete biochemical transformation.…”

“…Evidence of some Krebs cycle enzymes has been found in intermediate/short stumpy forms (Durieux et al, 1991) and a key enzyme, 2-oxoglutarate dehydrogenase, may even be regulated between long slender and transitional forms (Overath et al, 1986;and unpublished observations). We observed that transitional bloodstream form mitochondria accumulated rhodamine 123 whereas long slender forms did not under the conditions we used (Bienen et al 1991).…”

Mitochondrial Development during Life Cycle Differentiation of African Trypanosomes: Evidence for a Kinetoplast-dependent Differentiation Control Point

“…This does not, however, exclude possible interorganellar regulation at the protein level or as the cells move to becoming established procyclic forms. This may be significant because the transition to forms with fully active cytochrome-dependent respiration can take some time in vitro (ϳ72 h; Overath et al, 1986) In both mammalian and yeast cells with mitochondrial dysfunction a number of nuclear transcripts show altered expression (Poyton and McEwen, 1996). This is best studied in yeast where cells with either mitochondrial DNA damage (rho Ϫ ) or the absence of a mitochondrial genome (rho 0 ) modulate a retrograde signaling pathway by which nuclear transcript levels are regulated (Parikh et al, 1987;Sekito et al, 2000).…”

Different trans RNA splicing events in bloodstream and procyclic Trypanosoma brucei

“…1B [20]. After 48 hr, the medium is changed to PCF medium supplemented with cis-aconitate and citrate, and the BSFgrowth temperature of 37°C is dropped to the PCF-growth temperature of 26°C [21]. …”