Novel sterol metabolic network of Trypanosoma brucei procyclic and bloodstream forms

Trypanosoma brucei is the protozoan parasite that causes African trypanosomiasis, a neglected disease of people and animals. Co-metabolite analysis, labelling studies using [methyl- ²H ₃]- methionine and substrate/product specificities of the cloned 24-SMT (sterol C24-methyltransferase) and 14-SDM (sterol C14- demethylase) from T. brucei afforded an uncommon sterol metabolic network that proceeds from lanosterol and 31- norlanosterol to ETO [ergosta-5,7,25(27)-trien-3β-ol], 24-DTO [dimethyl ergosta-5,7,25(27)-trienol] and ergosterol [ergosta- 5,7,22(23)-trienol]. To assess the possible carbon sources of ergosterol biosynthesis, specifically ¹³C-labelled specimens of lanosterol, acetate, leucine and glucose were administered to T. brucei and the ¹³C distributions found were in accord with the operation of the acetate-mevalonate pathway, with leucine as an alternative precursor, to ergostenols in either the insect or bloodstream form. In searching for metabolic signatures of procyclic cells, we observed that the ¹³C-labelling treatments induce fluctuations between the acetyl-CoA (mitochondrial) and sterol (cytosolic) synthetic pathways detected by the progressive increase in ¹³C-ergosterol production (control <[2- ¹³C]leucine<[2- ¹³C]acetate<[1- ¹³C]glucose) and corresponding depletion of cholesta-5,7,24-trienol. We conclude that anabolic fluxes originating in mitochondrial metabolism constitute a flexible part of sterol synthesis that is further fluctuated in the cytosol, yielding distinct sterol profiles in relation to cell demands on growth.