Cell density triggers slender to stumpy differentiation of Trypanosoma brucei bloodstream forms in culture

110

African sleeping sickness is a disease caused by Trypanosoma brucei. T. brucei proliferate rapidly in the mammalian bloodstream as long, slender forms, but at higher population densities they transform into nondividing, short, stumpy forms. This is thought to be a mechanism adopted by T. brucei to establish a stable hostparasite relationship and to allow a transition into the insect stage of its life cycle. Earlier studies have suggested a role for cAMP in mediating this transformation. In this study, using membranepermeable nucleotide analogs, we show that it is not the cAMP analogs themselves but rather the hydrolyzed products of membrane-permeable cAMP analogs that prevent proliferation of T. brucei. The metabolic products are more potent than the cAMP analogs, and hydrolysis-resistant cAMP analogs are not antiproliferative. We further show that the antiproliferative effect of these membrane-permeable adenosine analogs is caused by transformation into forms resembling short, stumpy bloodstream forms. These data suggest that the slender-to-stumpy transformation of T. brucei may not be mediated directly by cAMP and also raise the possibility of using such adenosine analogs as antitrypanosomal drugs.adenosine ͉ EPACs ͉ phosphodiesterases ͉ trypanosomes

Section: Discussionmentioning

confidence: 99%

Hydrolysis products of cAMP analogs cause transformation ofTrypanosoma bruceifrom slender to stumpy-like forms

Laxman¹,

Riechers²,

Sadı́lek

et al. 2006

110

“…The slender cells have an intrinsic growth rate r t , where t is time after inoculation and, when a slender cell divides, there is a probability, f, that one daughter cell will differentiate to a stumpy cell. This rate of differentiation increases as the total number of parasites increases (33,34). The slender cells are also able to switch VSG.…”

Section: T Rypanosomes Switch Antigens Primarily By Duplication Ofmentioning

confidence: 98%

“…Factors known to exert significant influence on the course of infection include the density-dependent, parasite-triggered differentiation to the nondividing short stumpy stage (33,34), density-dependent general growth interference between trypanosomes (37) (which is likely to include any indirect immune system effects, such as reported in model host infections; ref. 38), and the VSG-specific antibody responses.…”

Section: T Rypanosomes Switch Antigens Primarily By Duplication Ofmentioning

confidence: 99%

“…There is another VSGtriggered immune response, which activates macrophages to yield trypanocidal agents (38), but it is not known whether this response kills trypanosomes variant-specifically. Because this response is mainly extravascular (43), and order is not influenced by trypanosomes in that compartment (17,39), it is unlikely to (37), switching between variants and the density-dependent variables of differentiation to the nonproliferating stumpy stage (33), immune response onset (46,47), and removal of variants. The simulation began with 1,000 trypanosomes (akin to natural transmissions from tsetse) and involved a computationally feasible archive of 30 VSGs; the output provides a sample of events rather than simulating an entire infection.…”

Section: T Rypanosomes Switch Antigens Primarily By Duplication Ofmentioning

confidence: 99%

See 1 more Smart Citation

Parasite-intrinsic factors can explain ordered progression of trypanosome antigenic variation

Lythgoe

Morrison

Read

et al. 2007

Pathogens often persist during infection because of antigenic variation in which they evade immunity by switching between distinct surface antigen variants. A central question is how ordered appearance of variants, an important determinant of chronicity, is achieved. Theories suggest that it results directly from a complex pattern of transition connectivity between variants or indirectly from effects such as immune cross-reactivity or differential variant growth rates. Using a mathematical model based only on known infection variables, we show that order in trypanosome infections can be explained more parsimoniously by a simpler combination of two key parasite-intrinsic factors: differential activation rates of parasite variant surface glycoprotein (VSG) genes and densitydependent parasite differentiation. The model outcomes concur with empirical evidence that several variants are expressed simultaneously and that parasitaemia peaks correlate with VSG genes within distinct activation probability groups. Our findings provide a possible explanation for the enormity of the recently sequenced VSG silent archive and have important implications for field transmission.mathematical model ͉ Typanosoma brucei ͉ variant surface glycoprotein ͉ switching ͉ hierarchy

“…A process related to cell density seems to be responsible for triggering the slender to stumpy differentiation in bloodstream forms of T. brucei in culture (5). The signal responsible for cell cycle arrest in the G 1 ͞G 0 phase that induces a quick and efficient differentiation is mediated by a low molecular weight factor termed SIF (Stumpy Induction Factor).…”

mentioning

confidence: 99%

Cloning and characterization of a cAMP-specific phosphodiesterase (TbPDE2B) from Trypanosoma brucei

Rascón

Soderling

Schaefer

et al. 2002

Here we report the cloning, expression, and characterization of a cAMP-specific phosphodiesterase (PDE) from Trypanosoma brucei (TbPDE2B). Using a bioinformatic approach, two different expressed sequence tag clones were identified and used to isolate the complete sequence of two identical PDE genes arranged in tandem. Each gene consists of 2,793 bases that predict a protein of 930 aa with a molecular mass of 103.2 kDa. Two GAF (for cGMP binding and stimulated PDEs, Anabaena adenylyl cyclases, and Escherichia coli FhlA) domains, similar to those contained in many signaling molecules including mammalian PDE2, PDE5, PDE6, PDE10, and PDE11, were located N-terminal to a consensus PDE catalytic domain. The catalytic domain is homologous to the catalytic domain of all 11 mammalian PDEs, the Dictyostelium discoideum RegA, and a probable PDE from Caenorhabditis elegans. It is most similar to the T. brucei PDE2A (89% identity). TbPDE2B has substrate specificity for cAMP with a K m of 2.4 M. cGMP is not hydrolyzed by TbPDE2B nor does this cyclic nucleotide modulate cAMP PDE activity. The nonselective PDE inhibitors 3-isobutyl-1-methylxanthine, papaverine and pentoxifyline are poor inhibitors of TbPDE2B. Similarly, PDE inhibitors selective for the mammalian PDE families 2, 3, 5, and 6 (erythro-9-[3-(2-hydroxynonyl)]-adenine, enoximone, zaprinast, and sildenafil) were also unable to inhibit this enzyme. However, dipyridamole was a reasonably good inhibitor of this enzyme with an IC50 of 27 M. cAMP plays key roles in cell growth and differentiation in this parasite, and PDEs are responsible for the hydrolysis of this important second messenger. Therefore, parasite PDEs, including this one, have the potential to be attractive targets for selective drug design.inhibitors ͉ GAF domain