Serpin overexpression in Plasmodium-infected midgut cells

Summary The design of effective, vector-based malaria transmission blocking strategies relies on a thorough understanding of the molecular and cellular interactions that occur during the parasite sporogonic cycle in the mosquito. During Plasmodium berghei invasion, transcription from the SRPN10 locus, encoding four serine protease inhibitors of the ovalbumin family, is strongly induced in the mosquito midgut. Herein we demonstrate that intense induction as well as redistribution of SRPN10 occurs specifically in the parasite-invaded midgut epithelial cells. Quantitative analysis establishes that in response to epithelial invasion, SRPN10 translocates from the nucleus to the cytoplasm and this is followed by strong SRPN10 overexpression. The invaded cells exhibit signs of apoptosis, suggesting a link between this type of intracellular serpin and epithelial damage. The SRPN10 gene products constitute a novel, robust and cell-autonomous marker of midgut invasion by ookinetes. The SRPN10 dynamics at the subcellular level confirm and further elaborate the 'time bomb' model of P. berghei invasion in both Anopheles stephensi and Anopheles gambiae. In contrast, this syndrome of responses is not elicited by mutant P. berghei ookinetes lacking the major ookinete surface proteins, P28 and P25. Molecular markers with defined expression patterns, in combination with mutant parasite strains, will facilitate dissection of the molecular mechanisms underlying vector competence and development of effective transmission blocking strategies

Mosquito immune responses and compatibility between Plasmodium parasites and anopheline mosquitoes

<p>Abstract</p> <p>Background</p> <p>Functional screens based on dsRNA-mediated gene silencing identified several <it>Anopheles gambiae </it>genes that limit <it>Plasmodium berghei </it>infection. However, some of the genes identified in these screens have no effect on the human malaria parasite <it>Plasmodium falciparum</it>; raising the question of whether different mosquito effector genes mediate anti-parasitic responses to different <it>Plasmodium </it>species.</p> <p>Results</p> <p>Four new <it>An. gambiae </it>(G3) genes were identified that, when silenced, have a different effect on <it>P. berghei </it>(Anka 2.34) and <it>P. falciparum </it>(3D7) infections. Orthologs of these genes, as well as <it>LRIM1 </it>and <it>CTL4</it>, were also silenced in <it>An. stephensi </it>(Nijmegen Sda500) females infected with <it>P. yoelii </it>(17XNL). For five of the six genes tested, silencing had the same effect on infection in the <it>P. falciparum-An. gambiae </it>and <it>P. yoelii-An. stephensi </it>parasite-vector combinations. Although silencing <it>LRIM1 </it>or <it>CTL4 </it>has no effect in <it>An. stephensi </it>females infected with <it>P. yoelii</it>, when <it>An. gambiae </it>is infected with the same parasite, silencing these genes has a dramatic effect. In <it>An. gambiae </it>(G3), TEP1, LRIM1 or LRIM2 silencing reverts lysis and melanization of <it>P. yoelii</it>, while <it>CTL4 </it>silencing enhances melanization.</p> <p>Conclusion</p> <p>There is a broad spectrum of compatibility, the extent to which the mosquito immune system limits infection, between different <it>Plasmodium </it>strains and particular mosquito strains that is mediated by TEP1/LRIM1 activation. The interactions between highly compatible animal models of malaria, such as <it>P. yoelii </it>(17XNL)-<it>An. stephensi </it>(Nijmegen Sda500), is more similar to that of <it>P. falciparum </it>(3D7)-<it>An. gambiae </it>(G3).</p

Genetic susceptibility to systemic lupus erythematosus protects against cerebral malaria in mice.

Plasmodium falciparum has exerted tremendous selective pressure on genes that improve survival in severe malarial infections. Systemic lupus erythematosus (SLE) is an autoimmune disease that is six to eight times more prevalent in women of African descent than in women of European descent. Here we provide evidence that a genetic susceptibility to SLE protects against cerebral malaria. Mice that are prone to SLE because of a deficiency in FcγRIIB or overexpression of Toll-like receptor 7 are protected from death caused by cerebral malaria. Protection appears to be by immune mechanisms that allow SLE-prone mice better to control their overall inflammatory responses to parasite infections. These findings suggest that the high prevalence of SLE in women of African descent living outside of Africa may result from the inheritance of genes that are beneficial in the immune control of cerebral malaria but that, in the absence of malaria, contribute to autoimmune disease

The Anopheles gambiae Oxidation Resistance 1 (OXR1) Gene Regulates Expression of Enzymes That Detoxify Reactive Oxygen Species

OXR1 is an ancient gene, present in all eukaryotes examined so far that confers protection from oxidative stress by an unknown mechanism. The most highly conserved region of the gene is the carboxyl-terminal TLDc domain, which has been shown to be sufficient to prevent oxidative damage.OXR1 has a complex genomic structure in the mosquito A. gambiae, and we confirm that multiple splice forms are expressed in adult females. Our studies revealed that OXR1 regulates the basal levels of catalase (CAT) and glutathione peroxidase (Gpx) expression, two enzymes involved in detoxification of hydrogen peroxide, giving new insight into the mechanism of action of OXR1. Gene silencing experiments indicate that the Jun Kinase (JNK) gene acts upstream of OXR1 and also regulates expression of CAT and GPx. Both OXR1 and JNK genes are required for adult female mosquitoes to survive chronic oxidative stress. OXR1 silencing decreases P. berghei oocyst formation. Unexpectedly, JNK silencing has the opposite effect and enhances Plasmodium infection in the mosquito, suggesting that JNK may also mediate some, yet to be defined, antiparasitic response.The JNK pathway regulates OXR1 expression and OXR1, in turn, regulates expression of enzymes that detoxify reactive oxygen species (ROS) in Anopheles gambiae. OXR1 silencing decreases Plasmodium infection in the mosquito, while JNK silencing has the opposite effect and enhances infection

The JAK-STAT Pathway Controls Plasmodium vivax Load in Early Stages of Anopheles aquasalis Infection

Malaria affects 300 million people worldwide every year and 450,000 in Brazil. In coastal areas of Brazil, the main malaria vector is Anopheles aquasalis, and Plasmodium vivax is responsible for the majority of malaria cases in the Americas. Insects possess a powerful immune system to combat infections. Three pathways control the insect immune response: Toll, IMD, and JAK-STAT. Here we analyze the immune role of the A. aquasalis JAK-STAT pathway after P. vivax infection. Three genes, the transcription factor Signal Transducers and Activators of Transcription (STAT), the regulatory Protein Inhibitors of Activated STAT (PIAS) and the Nitric Oxide Synthase enzyme (NOS) were characterized. Expression of STAT and PIAS was higher in males than females and in eggs and first instar larvae when compared to larvae and pupae. RNA levels for STAT and PIAS increased 24 and 36 hours (h) after P. vivax challenge. NOS transcription increased 36 h post infection (hpi) while this protein was already detected in some midgut epithelial cells 24 hpi. Imunocytochemistry experiments using specific antibodies showed that in non-infected insects STAT and PIAS were found mostly in the fat body, while in infected mosquitoes the proteins were found in other body tissues. The knockdown of STAT by RNAi increased the number of oocysts in the midgut of A. aquasalis. This is the first clear evidence for the involvement of a specific immune pathway in the interaction of the Brazilian malaria vector A. aquasalis with P. vivax, delineating a potential target for the future development of disease controlling strategies

An Epithelial Serine Protease, AgESP, Is Required for Plasmodium Invasion in the Mosquito Anopheles gambiae

Background: Plasmodium parasites need to cross the midgut and salivary gland epithelia to complete their life cycle in the mosquito. However, our understanding of the molecular mechanism and the mosquito genes that participate in this process is still very limited. Methodology/Principal Findings: We identified an Anopheles gambiae epithelial serine protease (AgESP) that is constitutively expressed in the submicrovillar region of mosquito midgut epithelial cells and in the basal side of the salivary glands that is critical for Plasmodium parasites to cross these two epithelial barriers. AgESP silencing greatly reduces Plasmodium berghei and Plasmodium falciparum midgut invasion and prevents the transcriptional activation of gelsolin, a key regulator of actin remodeling and a reported Plasmodium agonist. AgESP expression is highly induced in midgut cells invaded by Plasmodium, suggesting that this protease also participates in the apoptotic response to invasion. In salivary gland epithelial cells, AgESP is localized on the basal side–the surface with which sporozoites interact. AgESP expression in the salivary gland is also induced in response to P. berghei and P. falciparum sporozoite invasion, and AgESP silencing significantly reduces the number of sporozoites that invade this organ. Conclusion: Our findings indicate that AgESP is required for Plasmodium parasites to effectively traverse the midgut and salivary gland epithelial barriers. Plasmodium parasites need to modify the actin cytoskeleton of mosquito epithelial cells t

Apolipophorin-III Mediates Antiplasmodial Epithelial Responses in Anopheles gambiae (G3) Mosquitoes

Apolipophorin-III (ApoLp-III) is known to play an important role in lipid transport and innate immunity in lepidopteran insects. However, there is no evidence of involvement of ApoLp-IIIs in the immune responses of dipteran insects such as Drosophila and mosquitoes.We report the molecular and functional characterization of An. gambiae apolipophorin-III (AgApoLp-III). Mosquito ApoLp-IIIs have diverged extensively from those of lepidopteran insects; however, the predicted tertiary structure of AgApoLp-III is similar to that of Manduca sexta (tobacco hornworm). We found that AgApoLp-III mRNA expression is strongly induced in the midgut of An. gambiae (G3 strain) mosquitoes in response to Plasmodium berghei infection. Furthermore, immunofluorescence stainings revealed that high levels of AgApoLp-III protein accumulate in the cytoplasm of Plasmodium-invaded cells and AgApoLp-III silencing increases the intensity of P. berghei infection by five fold.There are broad differences in the midgut epithelial responses to Plasmodium invasion between An. gambiae strains. In the G3 strain of An. gambiae AgApoLp-III participates in midgut epithelial defense responses that limit Plasmodium infection

Molecular characterization of a blood-meal induced trypsin from the mosquito Aedes aegypti.

Adult and laIval midgut trypsins from the mosquito Aedes aegypli were isolated using benzamidine affinity chromatography. The cDNA of the late trypsin induced by the blood meal was isolated using an anti-trypsin monoclonal antibody, cloned and sequenced. The 862 bp sequence codes for a 257 amino acid protein, which is presumably a trypsin precursor, since the sequence of purified mosquito trypsin begins at residue 26, immediately following an arginine residue in the precursor. The amino terminal 25 amino acids in the precursor are composed of a putative 15 amino acid signal peptide and a 10 amino acid activation peptide. The activation peptide in the mosquito is different from that of vertebrate trypsinogens and suggests that activation takes place by tryptic cleavage. The deduced amino acid sequence is homologous to that of other trypsins in those residues around the catalytic triad, and in several residues which are found only in trypsins. However, the sequence of the specificity pocket in mosquito trypsin, KESPC, differs from that found in other trypsins, KDSC. The Asp is thought to bind the basic residue of the substrate, and the Glu in the mosquito trypsin may serve the same role. The changes in trypsin protein and mRNA levels following a blood meal indicate that an important component of the regulation of trypsin synthesis is at the transcriptional level. A genomic clone of "late trypsin" was isolated, mapped, and 1.2 kb of the upstream regulatory region were sequenced. The gene has no introns within the coding region. A TAT A box consensus sequence (TAT AAA) was found at position -31 from the 5' end of the mature mRNA. A cluster of five repeat sequences homologous to the GCN4 DNA binding site was found within 200 nucleotides upstream of the cap site. GCN4 is required for derepression mediated control of general amino acid biosynthesis in response to amino acid starvation in yeast. This suggests that a similar protein might regulate expression of the late trypsin gene in the mosquito. Southern blot analysis of genomic DNA suggests that the regions flanking the late trypsin coding region are polymorphic