Chemokines,inflammation and Trypanosoma cruzi infection

The inflammatory response that follows the infection with Trypanosoma cruzi is essential for host resistance to infection but is also responsible for the diverse pathology observed in Chagas disease. Here, we examine the stimuli and mechanisms underlying chemokine production following infection in vitro and in vivo, and the ability of chemokines to coordinate the influx of inflammatory and immune cells to the site of parasite infection, and to control T. cruzi growth.     

Sugar nucleotide pools of Trypanosoma brucei, Trypanosoma cruzi, and Leishmania major

The cell surface glycoconjugates of trypanosomatid parasites are intimately involved in parasite survival, infectivity, and virulence in their insect vectors and mammalian hosts. Although there is a considerable body of work describing their structure, biosynthesis, and function, little is known about the sugar nucleotide pools that fuel their biosynthesis. In order to identify and quantify parasite sugar nucleotides, we developed an analytical method based on liquid chromatography-electrospray ionization-tandem mass spectrometry using multiple reaction monitoring. This method was applied to the bloodstream and procyclic forms of Trypanosoma brucei, the epimastigote form of T. cruzi, and the promastigote form of Leishmania major. Five sugar nucleotides, GDP-alpha-d-mannose, UDP-alpha-d-N-acetylglucosamine, UDP-alpha-d-glucose, UDP-alpha-galactopyranose, and GDP-beta-l-fucose, were common to all three species; one, UDP-alpha-d-galactofuranose, was common to T. cruzi and L. major; three, UDP-beta-l-rhamnopyranose, UDP-alpha-d-xylose, and UDP-alpha-d-glucuronic acid, were found only in T. cruzi; and one, GDP-alpha-d-arabinopyranose, was found only in L. major. The estimated demands for each monosaccharide suggest that sugar nucleotide pools are turned over at very different rates, from seconds to hours. The sugar nucleotide survey, together with a review of the literature, was used to define the routes to these important metabolites and to annotate relevant genes in the trypanosomatid genomes.     

Sialoglycolipids in Trypanosoma cruzi

Mild oxidation of epimastigote forms of T.cruzi followed by sodium borotritide reduction incorporates radioactivity into glycolipid fractions. Column chromatography on silica gel of the chloroform:methanol (2:1) extract separated two main peaks of radioactivity. Treatment with neuraminidase released 30% and 18% of the radioactivity, respectively. Paper chromatography showed peaks of radioactivity with relative migration to NANA7 of 1.33 in fraction A and 1.33 and 1.51 in fraction B. When unlabeled cells were submitted to a Folch extraction, thin layer chromatography of the upper phase showed at least two components detected with the resorcinol-copper reagent. Enzymatic and mild acid hydrolysis released a sialic acid with a migration relative to NANA of 1.22. These results suggest that a substituted sialic acid is present in glycolipids of the epimastigote form of T.cruzi.     

Serine hydroxymethyltransferase activity in Trypanosoma cruzi, Trypanosoma rangeli and American Leishmania spp

Serine hydroxymethyltransferase (SHMT) was studied in several American trypanosomatids, Trypanosoma cruzi epimastigotes displaying, in contrast with T. rangeli, high enzymatic activity. Several Leishmania spp. members, including L. braziliensis, L. mexicana and L. garnhami promastigotes, under identical assay conditions, showed low enzymatic activity. The T. cruzi and leishmanial enzymes presented several different kinetic properties, and thus apparent Km for THF was 0.30 mM for the trypanosomal SHMT vs 0.60 mM for the leishmanial enzyme, while the apparent Km for serine was 0.40 mM for trypanosomal SHMT vs 0.15 mM for leishmanial enzyme. There were significant variations in the specific activity of SHMT between the several different trypanosomatids strains studied, but the meaning of these results is not clear because they showed no correlation either with taxonomy or infectivity.     

Intermediary metabolism of Trypanosoma cruzi

In this article, Julio Urbino discusses the characteristics o f the intermediary metabolism of Trypanosoma cruzi (the causative agent of Chagas disease), which are responsible for the unusual capacity of this parasite to use carbohydrates or amino acids as carbon and energy sources without drastic changes in its catabolic enzyme levels(1-3). Many, but not all, o f the metabolic capabilities of this organism are shared with Leishmania and the procyclic form o f the African trypanosomes, and the reviewer presents a metabolic model which is also consistent with the information available on these other parasites(2,4).     

The kinetoplast DNA of the Australian trypanosome,Trypanosoma copemani,shares features with Trypanosoma cruzi and Trypanosoma lewisi

Kinetoplast DNA (kDNA) is the mitochondrial genome of trypanosomatids. It consists of a few dozen maxicircles and several thousand minicircles, all catenated topologically to form a two-dimensional DNA network. Minicircles are heterogeneous in size and sequence among species. They present one or several conserved regions that contain three highly conserved sequence blocks. CSB-1 (10?bp sequence) and CSB-2 (8?bp sequence) present lower interspecies homology, while CSB-3 (12?bp sequence) or the Universal Minicircle Sequence is conserved within most trypanosomatids. The Universal Minicircle Sequence is located at the replication origin of the minicircles, and is the binding site for the UMS binding protein, a protein involved in trypanosomatid survival and virulence. Here, we describe the structure and organisation of the kDNA of Trypanosoma copemani, a parasite that has been shown to infect mammalian cells and has been associated with the drastic decline of the endangered Australian marsupial, the woylie (Bettongia penicillata). Deep genomic sequencing showed that T. copemani presents two classes of minicircles that share sequence identity and organisation in the conserved sequence blocks with those of Trypanosoma cruzi and Trypanosoma lewisi. A 19,257?bp partial region of the maxicircle of T. copemani that contained the entire coding region was obtained. Comparative analysis of the T. copemani entire maxicircle coding region with the coding regions of T. cruzi and T. lewisi showed they share 71.05% and 71.28% identity, respectively. The shared features in the maxicircle/minicircle organisation and sequence between T. copemani and T. cruzi/T. lewisi suggest similarities in their process of kDNA replication, and are of significance in understanding the evolution of Australian trypanosomes.     

The gamma-glutamyltranspeptidase of Trypanosoma cruzi

Trypanosoma cruzi epimastigotes show gamma-glutamyltranspeptidase activity which has characteristics significantly different than the mammalian enzyme. The protozoan enzyme is localized in the cytosolic fraction, it has a Km of 1.6 mM and a Vmax of 17.4 nmol/min/mg protein with L-gamma-glutamyl-p-nitroanilide as gamma-glutamyl donor, and an optimun pH range from 7.5 to 8.0. The best amino acid acceptors were L-histidine, L-asparagine, L-aspartate, L-glutamate and L-proline, but L-glutamine was a very poor acceptor. The enzyme was very sensitive to inhibition by 6-diazo-5-oxo-L-norleucine (k2 = 4.0 X 10(5)/M per min) and O-diazo-acetyl-L-serine (k2 = 1.1 X 10(4)/M per min). Phenobarbital (k2 = 8.38/M per min) and L-serine borate (Ki = 34 mM) were poor inhibitors. The activity of the enzyme was not correlated with the logarithmic phase of growth of the parasites and steadily decreases with the age of the cultures.     

Trypanosoma cruzi trans-sialidase and cell invasion

Trypanosoma cruzi does not synthesize sialic acid but does contain a trans-sialidase, an enzyme capable of transferring sialic acid between host glycoconjugates and the parasite. Sialic acids are negatively charged carbohydrates attached to the terminal non-reducing end of glycoproteins and glycolipids, and their presence can dramatically influence many cell-surface recognition processes. Since sialic acids have been implicated in several ligand-receptor interactions, including the interaction of pathogenic viruses, bacteria and protozoans with their hosts, the expression of trans-sialidase and the acquisition of sialic acid by T. cruzi may be relevant to the interaction of the parasite with the host, and consequently may influence the pathobiology of Chagas disease. In this review, Sergio Schenkman and Daniel Eichinger discuss recent data about the structure and function of T. cruzi trans-sialidase.     

Cell signalling and Trypanosoma cruzi invasion

Mammalian cell invasion by the protozoan pathogen Trypanosoma cruzi is critical to its survival in the host. To promote its entry into a wide variety of non-professional phagocytic cells, infective trypomastigotes exploit an arsenal of heterogenous surface glycoproteins, secreted proteases and signalling agonists to actively manipulate multiple host cell signalling pathways. Signals initiated in the parasite upon contact with mammalian cells also function as critical regulators of the invasion process. Whereas the full spectrum of cellular responses modulated by T. cruzi is not yet known, mounting evidence suggests that these pathways impinge on a number of cellular processes, in particular the ubiquitous wound-repair mechanism exploited for lysosome-mediated parasite entry. Furthermore, differential engagement of host cell signalling pathways in a cell type-specific manner and modulation of host cell gene expression by T. cruzi are becoming recognized as essential determinants of infectivity and intracellular survival by this pathogen.