Trypanosomatid Aquaporins: Roles in Physiology and Drug Response

Current Treatments to Control African Trypanosomiasis and One Health Perspective

Human African Trypanosomiasis (HAT, sleeping sickness) and Animal African Trypanosomiasis (AAT) are neglected tropical diseases generally caused by the same etiological agent, Trypanosoma brucei. Despite important advances in the reduction or disappearance of HAT cases, AAT represents a risky reservoir of the infections. There is a strong need to control AAT, as is claimed by the European Commission in a recent document on the reservation of antimicrobials for human use. Control of AAT is considered part of the One Health approach established by the FAO program against African Trypanosomiasis. Under the umbrella of the One Health concepts, in this work, by analyzing the pharmacological properties of the therapeutic options against Trypanosoma brucei spp., we underline the need for clearer and more defined guidelines in the employment of drugs designed for HAT and AAT. Essential requirements are addressed to meet the challenge of drug use and drug resistance development. This approach shall avoid inter-species cross-resistance phenomena and retain drugs therapeutic activity.

Candidate genes for monitoring hydrogen peroxide resistance in the salmon louse, Lepeophtheirus salmonis

BACKGROUND

Hydrogen peroxide (H₂O₂) is one of the delousing agents used to control sea lice infestations in salmonid aquaculture. However, some Lepeophtheirus salmonis populations have developed resistance towards H₂O₂. An increased gene expression and activity of catalase, an enzyme that breaks down H₂O₂, have been detected in resistant lice, being therefore introduced as a resistance marker in the salmon industry. In the present study the aim was to validate the use of catalase expression as a marker and to identify new candidate genes as additional markers to catalase, related to H₂O₂ resistance in L. salmonis.

METHODS

A sensitive and an H₂O₂ resistant laboratory strain (P0 generation, not exposed to H₂O₂ for several years) were batch crossed to generate a cohort with a wide range of H₂O₂ sensitivities (F2 generation). F2 adult females were then exposed to H₂O₂ to separate sensitive and resistant individuals. Those F2 lice, the P0 lice and field-collected resistant lice (exposed to H₂O₂ in the field) were used in an RNA sequencing study.

RESULTS

Catalase was upregulated in resistant lice exposed to H₂O₂ compared to sensitive lice. This was, however, not the case for unexposed resistant P0 lice. Several other genes were found differentially expressed between sensitive and resistant lice, but most of them seemed to be related to H₂O₂ exposure. However, five genes were consistently up- or downregulated in the resistant lice independent of exposure history. The upregulated genes were: one gene in the DNA polymerase family, one gene encoding a Nesprin-like protein and an unannotated gene encoding a small protein. The downregulated genes encoded endoplasmic reticulum resident protein 29 and an aquaporin (Glp1_v2).

CONCLUSIONS

Catalase expression seems to be induced by H₂O₂ exposure, since it was not upregulated in unexposed resistant lice. This may pose a challenge for its use as a resistance marker. The five new genes associated with resistance are put forward as complementary candidate genes. The most promising was Glp1_v2, an aquaglyceroporin that may serve as a passing channel for H₂O₂. Lower channel number can reduce the influx or distribution of H₂O₂ in the salmon louse, being directly involved in the resistance mechanism.

Drug transporter and oxidative stress gene expression in human macrophages infected with benznidazole-sensitive and naturally benznidazole-resistant Trypanosoma cruzi parasites treated with benznidazole

Background

Chagas disease is a potentially life-threatening disease caused by the protozoan parasite Trypanosoma cruzi. Current therapeutic management is limited to treatment with nitroheterocyclic drugs, such as nifurtimox (NFX) and benznidazole (BZ). Thus, the identification of affordable and readily available drugs to treat resistant parasites is urgently required worldwide. To analyse the effects of BZ on human macrophage gene expression, a quantitative PCR (qPCR) array analysis was performed using drug transporter and oxidative stress pathway genes to compare the gene expression profiles of human differentiated THP-1 macrophage (THP-1 MΦ) cells infected or not with benznidazole-sensitive (CL Brener) and naturally benznidazole-resistant (Colombiana) T. cruzi parasites followed by treatment with BZ.

Results

The gene expression analysis indicated that the expression levels of 62 genes were either up- or downregulated at least 3-fold in the host upon infection with CL Brener and BZ treatment, of which 46 were upregulated and 16 were downregulated. Moreover, the expression level of 32 genes was altered in THP-1 MФ cells infected with Colombiana and treated with BZ, of which 29 were upregulated and 3 were downregulated. Our results revealed that depending on the specific condition, human THP-1 MΦ cells infected with T. cruzi strains with sensitive or resistant phenotypes and treated with BZ expressed high mRNA levels of AQP1, AQP9 and ABCB1 (MDR1) compared to those of the control cells.

Conclusions

Our findings suggest that the proteins encoded by AQP1, AQP9 and ABCB1 may be implicated in benznidazole detoxification. Therefore, studies on gene expression are required to better understand the host response to pathogens and drug treatment integrated with functional and metabolic data to identify potentially novel targets for the treatment of this important and neglected tropical disease.

Electronic supplementary material

The online version of this article (10.1186/s13071-019-3485-9) contains supplementary material, which is available to authorized users.

Phylogenetic and specific sequence analysis of four paralogs in insect Aquaporins

Aquaporins (AQP) are proteins that form channels to facilitate the movement of water across cell membranes in plants, bacteria and animals. Insect AQPs are indispensable for cellular water management under stress, including dehydration and cold. To better understand the biological significance of molecular evolution of gene sequences, followed by structural and functional specialization, the present study used ClustalX2.1, MEGA7.0, Jalview and Mesquite software to build an insect AQP phylogenetic tree and visualize the evolutionary associations among insect AQPs. It was demonstrated that 45 AQPs were classified as four major paralogs with each amino acid sequence containing two conserved NPA (Asp‑Pro‑Ala) motifs located in the center and C‑terminal domains, and other residues conserved within the paralogous groups, however not among them. All these differences in amino acid content may affect the structure, function and classification of the AQPs. The findings provide a basis for further study to understand insect AQPs through sequence comparison, structure and predicted function.

A proteomics approach reveals molecular manipulators of distinct cellular processes in the salivary glands of Glossina m. morsitans in response to Trypanosoma b. brucei infections

Background

Glossina m. morsitans is the primary vector of the Trypanosoma brucei group, one of the causative agents of African trypanosomoses. The parasites undergo metacyclogenesis, i.e. transformation into the mammalian-infective metacyclic trypomastigote (MT) parasites, in the salivary glands (SGs) of the tsetse vector. Since the MT-parasites are largely uncultivable in vitro, information on the molecular processes that facilitate metacyclogenesis is scanty.

Methods

To bridge this knowledge gap, we employed tandem mass spectrometry to investigate protein expression modulations in parasitized (T. b. brucei-infected) and unparasitized SGs of G. m. morsitans. We annotated the identified proteins into gene ontologies and mapped the up- and downregulated proteins within protein-protein interaction (PPI) networks.

Results

We identified 361 host proteins, of which 76.6 % (n = 276) and 22.3 % (n = 81) were up- and downregulated, respectively, in parasitized SGs compared to unparasitized SGs. Whilst 32 proteins were significantly upregulated (> 10-fold), only salivary secreted adenosine was significantly downregulated. Amongst the significantly upregulated proteins, there were proteins associated with blood feeding, immunity, cellular proliferation, homeostasis, cytoskeletal traffic and regulation of protein turnover. The significantly upregulated proteins formed major hubs in the PPI network including key regulators of the Ras/MAPK and Ca²⁺/cAMP signaling pathways, ubiquitin-proteasome system and mitochondrial respiratory chain. Moreover, we identified 158 trypanosome-specific proteins, notable of which were proteins in the families of the GPI-anchored surface glycoproteins, kinetoplastid calpains, peroxiredoxins, retrotransposon host spot multigene and molecular chaperones. Whilst immune-related trypanosome proteins were over-represented, membrane transporters and proteins involved in translation repression (e.g. ribosomal proteins) were under-represented, potentially reminiscent of the growth-arrested MT-parasites.

Conclusions

Our data implicate the significantly upregulated proteins as manipulators of diverse cellular processes in response to T. b. brucei infection, potentially to prepare the MT-parasites for invasion and evasion of the mammalian host immune defences. We discuss potential strategies to exploit our findings in enhancement of trypanosome refractoriness or reduce the vector competence of the tsetse vector.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-016-1714-z) contains supplementary material, which is available to authorized users.

Number and regulation of protozoan aquaporins reflect environmental complexity

Protozoa are a diverse group of unicellular eukaryotes. Evidence has accumulated that protozoan aquaporin water and solute channels (AQP) contribute to adaptation in changing environments. Intracellular protozoan parasites live a well-sheltered life. Plasmodium spp. express a single AQP, Toxoplasma gondii two, while Trypanosoma cruzi and Leishamnia spp. encode up to five AQPs. Their AQPs are thought to import metabolic precursors and simultaneously to dispose of waste and to help parasites survive osmotic stress during transmission to and from the insect vector or during kidney passages. Trypanosoma brucei is a protozoan parasite that swims freely in the human blood. Expression and intracellular localization of the three T. brucei AQPs depend on the stage of differentiation during the life cycle, suggesting distinct roles in energy generation, metabolism, and cell motility. Free-living amoebae are in direct contact with the environment, encountering severe and sudden changes in the availability of nutrition, and in the osmotic conditions due to rainfall or drought. Amoeba proteus expresses a single AQP that is present in the contractile vacuole complex required for osmoregulation, whereas Dictyostelium discoideum expresses four AQPs, of which two are present in the single-celled amoeboidal stage and two more in the later multicellular stages preceding spore formation. The number and regulation of protozoan aquaporins may reflect environmental complexity. We highlight the gated AqpB from D. discoideum as an example of how life in the wild is challenged by a complex AQP structure-function relationship.