Research project P5/29 (Research action P5)
The molecular mechanisms used by parasites to undergo developmental transformations and adapt to their hosts are poorly characterized. We propose to study African trypanosomes (prototype Trypanosoma brucei) as model organisms to investigate these mechanisms. In direct continuation of results obtained during the previous collaborative work (P4/09), we propose to study several aspects of the dialog between the parasite and its hosts, covering the parasite-host and host-parasite interactions, the intracellular signaling pathways and the genetic mechanisms of cellular response to environmental signals.
1. Model system: the cellular differentiation from long slender (LS) to short stumpy (SS) forms
We propose to focus our studies on a model system, which is the cellular differentiation from long slender (LS) to short stumpy (SS) forms. This differentiation seems to depend on activation of the cAMP signaling pathway. The ULB group will analyze this signaling cascade into some detail, in close collaboration with the ITG partner and a laboratory specialized in the field (M. Boshart, MBB).
2. Studies on surface receptors and endocytosis
The work supported by the previous IAP programme has led to new insights into ligand uptake and proteins involved in endocytosis in T. brucei. In particular, we have shown that N-linked glycans containing linear stretches of poly-N-acetyllactosamine (pNAL) are specific to proteins from the endocytic pathway. In collaboration with Dr.D. Nolan (TCD), the ULB group will evaluate the hypothesis that these glycans act as sorting signals for endocytosis by interacting with a specific trypanosomal lectin. In addition, we propose to characterize two additional transmembrane proteins presumably linked to the endocytotic machinery, a putative lectin for high mannose and the surface receptor pESAG1. Ongoing studies by the VUB on the role of high mannose in the binding and uptake of host macromolecules will be pursued. Finally, a main effort will be undertaken by all partners to elucidate the mechanism by which a protein termed SRA confers resistance to lysis by human serum in T. rhodesiense, and a putative receptor possibly involved in the adaptation of T. gambiense to man will be characterized.
3. Studies of metabolic changes during differentiation
In close collaboration with the ULB team and with the help of ITG, the UCL group proposes to study the turnover of glycosomes and glycosomal enzymes during the differentiation of T. brucei, focusing on the LS-SS-Procyclic transformation. Specific questions to be addressed are: (1) Are new glycosomal enzymes induced in a small subset of existing glycosomes that can proliferate? (2) Is the population of glycosomes heterogeneous? (3) Are old, non-proliferating glycosomes degraded by autophagy? (4) Is the turnover of glycosomes under the control of the same signaling pathways as other differentiation-associated changes occurring on the surface and the endocytic pathway ?
4. Trypanosome-macrophage interactions
During the previous IAP program a detailed analysis was made of the possible contribution of the cytokine environment and macrophage activation status in resistance to African trypanosomosis. Collectively, these results showed that trypanosomes can elicit M1 and/or M2 types of macrophages and that the M1/M2 balance may determine the level of resistance to African trypanosome infection. Future studies in this area by the VUB and ULB groups will focus on the following lines of investigations: (1) In view of the increasing evidence for distinctive roles of M1 versus M2 cells in immunomodulation and immunopathology, efforts will be concentrated on a thorough genetical, phenotypical and functional characterization of trypanosome-elicited M1/M2 cells. (2) The involvement of both host and parasite components in the induction and regulation of M1/M2 cells will be further analyzed in depth, and refined.
5. Trypanosome-tsetse fly interactions
Nothing is known so far about the role of salivary gland components in the development of the parasite in the fly and the vertebrate host. Based on progress achieved during our previous IAP collaboration, the ITG proposes to characterize a potential candidate, and to develop new approaches towards the identification of immunomodulating components, with the help of the ULB and VUB partners.
