Turnover of glycosomes during life-cycle differentiation ofTrypanosoma brucei

Abstract

Protozoan Kinetoplastida, a group that comprises the pathogenic Trypanosoma brucei, compartmentalize several metabolic systems such as the major part of the glycolytic pathway, in multiple peroxisome-like organelles, designated glycosomes. Trypanosomes have a complicated life cycle, involving two major, distinct stages living in the mammalian bloodstream and several stages inhabiting different body parts of the tsetse fly. Previous studies on non-differentiating trypanosomes have shown that the metabolism and enzymatic contents of glycosomes in bloodstream-form and cultured procyclic cells, representative of the stage living in the insect's midgut, differ considerably. In this study, the morphology of glycosomes and their position relative to the lysosome were followed, as were the levels of some glycosomal enzymes and markers for other subcellular compartments, during the differentiation from bloodstream-form to procyclic trypanosomes. Our studies revealed a small tendency of glycosomes to associate with the lysosome when a population of long-slender bloodstream forms differentiated into short-stumpy forms which are pre-adapted to live in the fly. The same phenomenon was observed during the short-stumpy to procyclic transformation, but then the process was fast and many more glycosomes were associated with the dramatically enlarged degradation organelle. The observations suggested an efficient glycosome turnover involving autophagy. Changes observed in the levels of marker enzymes are consistent with the notion that, during differentiation, glycosomes with enzymatic contents specific for the old life-cycle stage are degraded and new glycosomes with different contents are synthesized, causing that the metabolic repertoire of trypanosomes is, at each stage, optimally adapted to the environmental conditions encountered.

Glycerol 3-Phosphate Alters Trypanosoma brucei Hexokinase Activity in Response to Environmental Change

“…During differentiation, glycosomes co-localize with lysosomes, which occurs quickly (and involves a high percentage of glycosomes) during the transition from short stumpy form parasites (the mammalian blood form pre-adapted for life in the insect) to PF parasites (10). This process resembles pexophagy, the mechanism for peroxisome turnover in methylotrophic yeast that occurs when nutritional conditions change (23).…”

“…Changes in glycosome content occur through glycosomal autophagy (10). During differentiation, glycosomes co-localize with lysosomes, which occurs quickly (and involves a high percentage of glycosomes) during the transition from short stumpy form parasites (the mammalian blood form pre-adapted for life in the insect) to PF parasites (10).…”

“…Because of this dynamic metabolism, PF parasites can grow normally in the near absence of glucose. However, complete elimination of nutrients by incubation in PBS triggers association of glycosomes with the acidic (pH 4.8 (20)) lysosomal compartment in PF cells, a process similar to pexophagy in yeast (10).…”

“…For example, as the parasite transits from the short stumpy form (which is found in mammalian blood and is pre-adapted for life in the tsetse fly vec-tor), glycosomes fuse with lysosomes (10). A process similar to pexophagy, which is the autophagy of peroxisomes in response to metabolic changes found in yeast, has been implicated in the turnover of glycosomal components.…”

Rapamycin inhibits trypanosome cell growth by preventing TOR complex 2 formation

“…Autophagy is not well studied in T. brucei and no molecular markers have been described so far, although it was suggested to be involved in differentiation processes including glycosomes turnover (17). However, TORC1-mediated regulation of autophagy in other eukaryotes is well known.…”