Effect of chloroquine on the expression of genes involved in the mosquito immune response to Plasmodium infection

Simultaneous Gene Delivery and Tracking through Preparation of Photo-Luminescent Nanoparticles Based on Graphene Quantum Dots and Chimeric Peptides

Designing suitable nano-carriers for simultaneous gene delivery and tracking is in the research priorities of the molecular medicine. Non-toxic graphene quantum dots (GQDs) with two different (green and red) emission colors are synthesized by Hummer's method and characterized by UV-Vis, Photoluminescence (PL), Fourier Transform Infrared (FTIR) and Raman spectroscopies, Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). The GQDs are conjugated with MPG-2H1 chimeric peptide and plasmid DNA (pDNA) by non-covalent interactions. Following conjugation, the average diameter of the prepared GQDs increased from 80 nm to 280 nm in complex structure, and the ζ-potential of the complex increased (from -36.87 to -2.56 mV). High transfection efficiency of the nano-carrier and results of confocal microscopy demonstrated that our construct can be considered as a nontoxic carrier with dual functions for gene delivery and nuclear targeting.

Hemozoin activates the innate immune system and reduces Plasmodium berghei infection in Anopheles gambiae

BACKGROUND

Malaria is a worldwide infectious disease caused by Plasmodium parasites and transmitted by female Anopheles mosquitoes. The malaria vector mosquito Anopheles can trigger effective mechanisms to control completion of the Plasmodium lifecycle; the mosquito immune response to the parasite involves several pathways which are not yet well characterized. Plasmodium metabolite hemozoin has emerged as a potent immunostimulator of mammalian tissues. In this study, we aim to investigate the role of this parasite's by-product as stimulator of Anopheles gambiae immunity to Plasmodium berghei.

METHODS

Female mosquitoes were inoculated with hemozoin and the Plasmodium infection rate and intensity were measured. Differences between treatments were detected by Zero-inflated models. Microarray transcription analysis was performed to assess gene expression response to hemozoin. Genome-wide analysis results were confirmed by stimulation of Anopheles gambiae tissues and cells with hemozoin and silencing of REL2-F and its negative regulator Caspar.

RESULTS

Gene expression profiles revealed that hemozoin activates several immunity genes, including pattern recognition receptors (PRRs) and antimicrobial peptides (AMPs). Importantly, we found that the Immune deficiency (Imd) pathway Nuclear Factor-kappaB (NF-κB) transcription factor REL2, in its full-length form REL2-F, was induced upon hemozoin treatment.

CONCLUSIONS

We have for the first time shown the impact of hemozoin treatment in Plasmodium infection, reducing both rate and intensity of the infection. We propose that hemozoin boosts the innate immunity in Anopheles, activating key effector genes involved in mosquito resistance to Plasmodium, and this activation is REL2-mediated.

CpG-containing oligodeoxynucleotides increases resistance of Anopheles mosquitoes to Plasmodium infection

Unmethylated CpG dinucleotide motifs in bacterial DNA or in synthetic oligodeoxynucleotides (ODN) are potent stimulators of the vertebrate innate immune system. However, the potential of these DNA species to modulate mosquito immunity have not been explored. In the present study, we investigated the effects of CpG-ODN on the outcome of Plasmodium infection in insects and on the modulation of mosquito immunity to Plasmodium. Anopheles stephensi and Anopheles gambiae mosquitoes inoculated with CpG-ODN showed significant reductions in the prevalence of Plasmodium infection, intensity of Plasmodium infection, and number of eggs produced. Microarrays were used to elucidate the transcriptional profiles of the fat bodies of CpG-ODN-treated mosquitoes. In total, 172 genes were differentially expressed, of which 136 were up-regulated and 36 were down-regulated. The major functional class of CpG-ODN-regulated genes encoded immune response-related proteins (31%). Within this group, genes associated with coagulation/wound healing were the most frequently represented (23%). Knockdown of a transglutaminase gene that was up-regulated by the CpG-ODN and chemical inhibition of the enzyme resulted in a significant increase in Plasmodium infection. Mosquitoes that were treated with CpG-ODNs were found to be less susceptible to Plasmodium infection. Transcriptional profiling of the fat body suggests that protection is associated with coagulation/wound healing. We show for the first time that transglutaminase activity plays a role in the control of Plasmodium infection.

Plasmodium yoelii: correlation of TEP1 with mosquito melanization induced by nitroquine

The antimalarial drug nitroquine is not only an effective antimalarial drug, it is also able to induce the melanization of Plasmodium species. However, the molecular mechanisms of the recognition reaction induced by this drug remain unclear. Silencing of thioester-containing protein-1 (TEP1) significantly compromised the ability of Anopheles gambiae to melanize the Plasmodium, leading to investigation of the involvement of A. stephensi TEP1 in melanization induced by nitroquine. This study shows that (1) binding of AsTEP1 to oocysts, especially melanized oocysts, (2) after ingestion of anti-AsTEP1 antibody, the melanization rate in antibody-treated mosquitoes are significantly lower than in control mosquito (p<0.05). The results suggest that nitroquine is able to induce Plasmodium recognition by TEP1, possibly triggering the resulting melanotic encapsulation. Further elucidation of the molecular mechanisms of mosquito immunity induced by antimalarial drugs will provide theoretical evidence for the use of antimalarial drugs, and a meaningful pathway for the design of novel antimalarial drugs.

Chloroquine mediated modulation of Anopheles gambiae gene expression

BACKGROUND

Plasmodium development in the mosquito is crucial for malaria transmission and depends on the parasite's interaction with a variety of cell types and specific mosquito factors that have both positive and negative effects on infection. Whereas the defensive response of the mosquito contributes to a decrease in parasite numbers during these stages, some components of the blood meal are known to favor infection, potentiating the risk of increased transmission. The presence of the antimalarial drug chloroquine in the mosquito's blood meal has been associated with an increase in Plasmodium infectivity for the mosquito, which is possibly caused by chloroquine interfering with the capacity of the mosquito to defend against the infection.

METHODOLOGY/PRINCIPAL FINDINGS

In this study, we report a detailed survey of the Anopheles gambiae genes that are differentially regulated by the presence of chloroquine in the blood meal, using an A. gambiae cDNA microarray. The effect of chloroquine on transcript abundance was evaluated separately for non-infected and Plasmodium berghei-infected mosquitoes. Chloroquine was found to affect the abundance of transcripts that encode proteins involved in a variety of processes, including immunity, apoptosis, cytoskeleton and the response to oxidative stress. This pattern of differential gene expression may explain the weakened mosquito defense response which accounts for the increased infectivity observed in chloroquine-treated mosquitoes.

CONCLUSIONS/SIGNIFICANCE

The results of the present study suggest that chloroquine can interfere with several putative mosquito mechanisms of defense against Plasmodium at the level of gene expression and highlight the need for a better understanding of the impacts of antimalarial agents on parasite transmission.

Plasmodium yoelii: correlation of up-regulated prophenoloxidase and phenoloxidases with melanization induced by the antimalarial, nitroquine

Although knowledge of the mosquito immune response has recently improved, less is known about the impact of antimalarial drugs on mosquito immunity. In the present study, we found that nitroquine, an effective antimalaria drug, could also induce melanotic encapsulation of Plasmodium by Anopheles stephensi. The melanization rate of the nitroquine treated group was 60.8%. To explore the effect of nitroquine on mosquito immunity, we determined the increase in activity of phenoloxidases (PO) enzyme, the main component of melanotic encapsulation, with nitroquine treatment. Moreover, we cloned prophenoloxidase (PPO) gene, which is accepted as the inactive phenoloxidase form and observed inducible expression of this gene with nitroquine treatment by real-time PCR. Our data implied that up-regulation of PPO gene and PO activity might be correlated with nitroquine. Nevertheless, nitroquine had no effect on the transcription of PPO gene or the activity of PO enzyme in the mosquito fed on a normal blood meal. In our study, we also observed the degenerative effect of 0.1% nitroquine on Plasmodium in the mosquito. This suggests that the degeneration of Plasmodium induced by nitroquine might result in the exposure of pattern-recognition ligands which can active the immune reaction, up-regulate PPO gene expression and PO activity, and induce the melanization.

Effect of chloroquine on gene expression of Plasmodium yoelii nigeriensis during its sporogonic development in the mosquito vector

Background

The anti-malarial chloroquine can modulate the outcome of infection during the Plasmodium sporogonic development, interfering with Plasmodium gene expression and subsequently, with transmission. The present study sets to identify Plasmodium genes that might be regulated by chloroquine in the mosquito vector.

Methods

Differential display RT-PCR (DDRT-PCR) was used to identify genes expressed during the sporogonic cycle that are regulated by exposure to chloroquine. Anopheles stephensi mosquitoes were fed on Plasmodium yoelii nigeriensis-infected mice. Three days post-infection, mosquitoes were fed a non-infectious blood meal from mice treated orally with 50 mg/kg chloroquine. Two differentially expressed Plasmodium transcripts (Pyn_chl091 and Pyn_chl055) were further characterized by DNA sequencing and real-time PCR analysis.

Results

Both transcripts were represented in Plasmodium EST databases, but displayed no homology with any known genes. Pyn_chl091 was upregulated by day 18 post infection when the mosquito had a second blood meal. However, when the effect of chloroquine on that transcript was investigated during the erythrocytic cycle, no significant differences were observed. Although slightly upregulated by chloroquine exposure the expression of Pyn_chl055 was more affected by development, increasing towards the end of the sporogonic cycle. Transcript abundance of Pyn_chl055 was reduced when erythrocytic stages were treated with chloroquine.

Conclusion

Chloroquine increased parasite load in mosquito salivary glands and interferes with the expression of at least two Plasmodium genes. The transcripts identified contain putative signal peptides and transmembrane domains suggesting that these proteins, due to their location, are targets of chloroquine (not as an antimalarial) probably through cell trafficking and recycling.

Plasmodium yoelii: the effect of second blood meal and anti-sporozoite antibodies on development and gene expression in the mosquito vector, Anopheles stephensi

The sporogonic development of the malaria parasite takes place in the mosquito and a wide range of factors modulates it. Among those, the contents of the blood meal can influence the parasite development directly or indirectly through the mosquito response to the infection. We have studied the effect of a second blood meal in previously infected mosquitoes and the effect of anti-sporozoite immune serum on parasite development and mosquito response to the infection. The prevalence and intensity of infection and gene expression of both Plasmodium yoelii and Anopheles stephensi was analyzed. We verified that a second blood meal and its immune status interfere with parasite development and with Plasmodium and mosquito gene expression.