Disruption of Parasite hmgb2 Gene Attenuates Plasmodium berghei ANKA Pathogenicity

Babesia microti alleviates disease manifestations caused by Plasmodium berghei ANKA in murine co-infection model of complicated malaria

Malaria remains one of the most significant health issues worldwide, accounting for 2.6% of the total global disease burden, and efforts to eliminate this threat continue. The key focus is to develop an efficient and long-term immunity to this disease via vaccination or therapeutic approach, and innovative strategies would enable us to achieve this target. Previously, using a mouse co-infection disease model, cross-protection was illustrated between Babesia microti and Plasmodium chabaudi. Hence, this study was planned to elucidate the impact of acute B. microti Peabody mjr and Plasmodium berghei ANKA co-infection on the consequence of complicated malaria in the C57BL/6J mouse model of malaria. Furthermore, immune response and pathological features were analyzed, and the course of the disease was compared among experimental groups. Our study established that acute B. microti infection activated immunity which was otherwise suppressed by P. berghei. The immunosuppressive tissue microenvironment was counteracted as evidenced by the enhanced immune cell population in co-infected mice, in contrast to P. berghei-infected control mice. Parasite sequestration in the brain, liver, lung, and spleen of co-infected mice was significantly decreased and tissue injury was ameliorated. Meanwhile, the serum levels of IFN-γ, TNF-α, and IL-12p70 were reduced while the secretion of IL-10 was promoted in co-infected mice. Eventually, co-infected mice showed an extended rate of survival. Hereby, the principal cytokines associated with the severity of malaria by P. berghei infection were TNF-α, IFN-γ, and IL-12p70. Moreover, it was evident from our flow cytometry results that innate immunity is crucial and macrophages are at the frontline of immunity against P. berghei infection. Our study recommended further investigations to shed light on the effects of babesiosis in suppressing malaria with the goal of developing Babesia-based therapy against malaria.

Comparative genomics reveals unique features of two Babesia motasi subspecies: Babesia motasi lintanensis and Babesia motasi hebeiensis

Parasites of the Babesia genus are prevalent worldwide and infect a wide diversity of domestic animals and humans. Herein, using Oxford Nanopore Technology and Illumina sequencing technologies, we sequenced two Babesia sub-species, Babesia motasi lintanensis and Babesia motasi hebeiensis. We identified 3,815 one-to-one ortholog genes that are specific to ovine Babesia spp. Phylogenetic analysis reveals that the two B. motasi subspecies form a distinct clade from other Piroplasma spp. Consistent with their phylogenetic position, comparative genomic analysis reveals that these two ovine Babesia spp. share higher colinearity with Babesia bovis than with Babesia microti. Concerning the speciation date, B. m. lintanensis split from B. m. hebeiensis approximately 17 million years ago. Genes correlated to transcription, translation, protein modification and degradation, as well as differential/specialized gene family expansions in these two subspecies may favor adaptation to vertebrate and tick hosts. The close relationship between B. m. lintanensis and B. m. hebeiensis is underlined by a high degree of genomic synteny. Compositions of most invasion, virulence, development, and gene transcript regulation-related multigene families, including spherical body protein, variant erythrocyte surface antigen, glycosylphosphatidylinositol anchored proteins, and transcription factor Apetala 2 genes, is largely conserved, but in contrast to this conserved situation, we observe major differences in species-specific genes that may be involved in multiple functions in parasite biology. For the first time in Babesia spp., we find abundant fragments of long terminal repeat-retrotransposons in these two species. We provide fundamental information to characterize the genomes of B. m. lintanensis and B. m. hebeiensis, providing insights into the evolution of B. motasi group parasites.

PfHMGB2 has a role in malaria parasite mosquito infection

Differentiation of asexually replicating parasites into gametocytes is critical for successful completion of the sexual phase of the malaria parasite life cycle. Gametes generated from gametocytes fuse to form a zygote which differentiates into ookinetes and oocysts. The sporozoites are formed inside oocysts which migrate to the salivary glands for next cycle of human infection. These morphologically and functionally distinct stages require stage-specific gene expression via specific transcriptional regulators. The capacity of high mobility group box (HMGB) proteins to interact with DNA in a sequence independent manner enables them to regulate higher order chromosome organization and regulation of gene expression. Plasmodium falciparum HMGB2 (PfHMGB2) shows a typical L- shaped predicted structure which is similar to mammalian HMG box proteins and shows very high protein sequence similarity to PyHMGB2 and PbHMGB2. Functional characterization of PfHMGB2 by gene deletion (Pfhmgb2¯) showed that knockout parasites develop normally as asexual stages and undergo gametocytogenesis. Transmission experiments revealed that Pfhmgb2¯ can infect mosquitoes and develop as oocyst stages. However, transmission was reduced compared to wild type (WT) parasites and as a consequence, the salivary gland sporozoites were reduced in number. In summary, we demonstrate that PfHMGB2 has no role in asexual growth and a modest role in sexual phase development and parasite transmission to the mosquito.

A hypometabolic defense strategy against malaria

Hypoglycemia is a clinical hallmark of severe malaria, the often-lethal outcome of Plasmodium falciparum infection. Here, we report that malaria-associated hypoglycemia emerges from a non-canonical resistance mechanism, whereby the infected host reduces glycemia to starve Plasmodium. This hypometabolic response is elicited by labile heme, a byproduct of hemolysis that induces illness-induced anorexia and represses hepatic glucose production. While transient repression of hepatic glucose production prevents unfettered immune-mediated inflammation, organ damage, and anemia, when sustained over time it leads to hypoglycemia, compromising host energy expenditure and adaptive thermoregulation. The latter arrests the development of asexual stages of Plasmodium via a mechanism associated with parasite mitochondrial dysfunction. In response, Plasmodium activates a transcriptional program associated with the reduction of virulence and sexual differentiation toward the generation of transmissible gametocytes. In conclusion, malaria-associated hypoglycemia represents a trade-off of a hypometabolic-based defense strategy that balances parasite virulence versus transmission.

Preparing for Transmission: Gene Regulation in Plasmodium Sporozoites

Plasmodium sporozoites are transmitted to mammals by anopheline mosquitoes and first infect the liver, where they transform into replicative exoerythrocytic forms, which subsequently release thousands of merozoites that invade erythrocytes and initiate the malaria disease. In some species, sporozoites can transform into dormant hypnozoites in the liver, which cause malaria relapses upon reactivation. Transmission from the insect vector to a mammalian host is a critical step of the parasite life cycle, and requires tightly regulated gene expression. Sporozoites are formed inside oocysts in the mosquito midgut and become fully infectious after colonization of the insect salivary glands, where they remain quiescent until transmission. Parasite maturation into infectious sporozoites is associated with reprogramming of the sporozoite transcriptome and proteome, which depends on multiple layers of transcriptional and post-transcriptional regulatory mechanisms. An emerging scheme is that gene expression in Plasmodium sporozoites is controlled by alternating waves of transcription activity and translational repression, which shape the parasite RNA and protein repertoires for successful transition from the mosquito vector to the mammalian host.

A genetically hmgb2 attenuated blood stage P. berghei induces crossed-long live protection

Due to the lack of efficiency to control malaria elicited by sub-unit vaccine preparations, vaccination with live-attenuated Plasmodium parasite as reported 70 years ago with irradiated sporozoites regained recently a significant interest. The complex life cycle of the parasite and the different stages of development between mammal host and anopheles do not help to propose an easy vaccine strategy. In order to achieve a complete long-lasting protection against Plasmodium infection and disease, we considered a genetically attenuated blood stage parasite in the hmgb2 gene coding for the high-mobility-group-box 2 (HMGB2). This Plasmodium protein belongs to the HMGB family and hold as the mammal proteins, a double life since it acts first as a nuclear factor involved in chromatin remodelling and transcription regulation and second, when secreted as an active pro-inflammatory alarmin protein. Even though the number of reports on whole living attenuated blood stage parasites is limited when compared to attenuated sporozoites, the results reported with Plasmodium KO parasites are very encouraging. In this report, we present a novel strategy based on pre-immunization with Δhmgb2PbNK65 parasitized red blood cells that confer long-lasting protection in a murine experimental cerebral malaria model against two highly pathogenic homologous and heterologous parasites.

PfHMGB2 protects yellow catfish (Pelteobagrus fulvidraco) from bacterial infection by promoting phagocytosis and proliferation of PBL

HMGB2, a member of the high mobility group box family, plays an important role in host immune responses. However, the mechanism of action of HMGB2 is not well understood. Herein, a homologue from yellow catfish (Pelteobagrus fulvidraco) was cloned and named PfHMGB2. The deduced amino acid sequence of PfHMGB2 possessed a typical tripartite structure (two DNA binding boxes and an acid tail) and shared 90% identity with the predicted HMGB2 from I. punctatus. The mRNA of PfHMGB2 was widely distributed in all 11 tested tissues in healthy fish bodies and was significantly induced in the liver and head kidney when yellow catfish were injected with inactivated Aeromonas hydrophila. Consistently, PfHMGB2 mRNA could also be induced in yellow catfish peripheral blood leucocytes (PBL) by lipopolysaccharide. The recombinant PfHMGB2 protein was purified from E. coli BL21 (DE3):pET-28a/PfHMGB2 and showed DNA-binding affinity. Moreover, rPfHMGB2 improved the phagocytosis and proliferation activity and upregulated the mRNA expression of the pro-inflammatory cytokine TNFα in yellow catfish PBL. These results indicated that PfHMGB2 could protect yellow catfish from pathogen infection by activating PBL.

Essential role of GEXP15, a specific Protein Phosphatase type 1 partner, in Plasmodium berghei in asexual erythrocytic proliferation and transmission

The essential and distinct functions of Protein Phosphatase type 1 (PP1) catalytic subunit in eukaryotes are exclusively achieved through its interaction with a myriad of regulatory partners. In this work, we report the molecular and functional characterization of Gametocyte EXported Protein 15 (GEXP15), a Plasmodium specific protein, as a regulator of PP1. In vitro interaction studies demonstrated that GEXP15 physically interacts with PP1 through the RVxF binding motif in P. berghei. Functional assays showed that GEXP15 was able to increase PP1 activity and the mutation of the RVxF motif completely abolished this regulation. Immunoprecipitation assays of tagged GEXP15 or PP1 in P. berghei followed by immunoblot or mass spectrometry analyses confirmed their interaction and showed that they are present both in schizont and gametocyte stages in shared protein complexes involved in the spliceosome and proteasome pathways and known to play essential role in parasite development. Phenotypic analysis of viable GEXP15 deficient P. berghei blood parasites showed that they were unable to develop lethal infection in BALB/c mice or to establish experimental cerebral malaria in C57BL/6 mice. Further, although deficient parasites produced gametocytes they did not produce any oocysts/sporozoites indicating a high fitness cost in the mosquito. Global proteomic and phosphoproteomic analyses of GEXP15 deficient schizonts revealed a profound defect with a significant decrease in the abundance and an impact on phosphorylation status of proteins involved in regulation of gene expression or invasion. Moreover, depletion of GEXP15 seemed to impact mainly the abundance of some specific proteins of female gametocytes. Our study provides the first insight into the contribution of a PP1 regulator to Plasmodium virulence and suggests that GEXP15 affects both the asexual and sexual life cycle.

In the absence of an effective vaccine and the emerging resistance to artemisinin combination therapy, malaria is still a significant threat to human health. Increasing our understanding of the specific mechanisms of the biology of Plasmodium is essential to propose new strategies to control this infection. Here, we demonstrated that GEXP15, a specific protein in Plasmodium, was able to interact with the Protein Phosphatase 1 and regulate its activity. We showed that both proteins are implicated in common protein complexes involved in the mRNA splicing and proteasome pathways. We reported that the deletion of GEXP15 leads to a loss of parasite virulence during asexual stages and a total abolishment of the capacity of deficient parasites to develop in the mosquito. We also found that this deletion affects both protein phosphorylation status and significantly decreases the expression of essential proteins in schizont and gametocyte stages. This study characterizes for the first time a novel molecular pathway through the control of PP1 by an essential and specific Plasmodium regulator, which may contribute to the discovery of new therapeutic targets to control malaria.

DNA aptamers for the recognition of HMGB1 from Plasmodium falciparum

Rapid Diagnostic Tests (RDTs) for malaria are restricted to a few biomarkers and antibody-mediated detection. However, the expression of commonly used biomarkers varies geographically and the sensibility of immunodetection can be affected by batch-to-batch differences or limited thermal stability. In this study we aimed to overcome these limitations by identifying a potential biomarker and by developing molecular sensors based on aptamer technology. Using gene expression databases, ribosome profiling analysis, and structural modeling, we find that the High Mobility Group Box 1 protein (HMGB1) of Plasmodium falciparum is highly expressed, structurally stable, and present along all blood-stages of P. falciparum infection. To develop biosensors, we used in vitro evolution techniques to produce DNA aptamers for the recombinantly expressed HMG-box, the conserved domain of HMGB1. An evolutionary approach for evaluating the dynamics of aptamer populations suggested three predominant aptamer motifs. Representatives of the aptamer families were tested for binding parameters to the HMG-box domain using microscale thermophoresis and rapid kinetics. Dissociation constants of the aptamers varied over two orders of magnitude between nano- and micromolar ranges while the aptamer-HMG-box interaction occurred in a few seconds. The specificity of aptamer binding to the HMG-box of P. falciparum compared to its human homolog depended on pH conditions. Altogether, our study proposes HMGB1 as a candidate biomarker and a set of sensing aptamers that can be further developed into rapid diagnostic tests for P. falciparum detection.

Disease Tolerance as an Inherent Component of Immunity

Pathogenic organisms exert a negative impact on host health, revealed by the clinical signs of infectious diseases. Immunity limits the severity of infectious diseases through resistance mechanisms that sense and target pathogens for containment, killing, or expulsion. These resistance mechanisms are viewed as the prevailing function of immunity. Under pathophysiologic conditions, however, immunity arises in response to infections that carry health and fitness costs to the host. Therefore, additional defense mechanisms are required to limit these costs, before immunity becomes operational as well as thereafter to avoid immunopathology. These are tissue damage control mechanisms that adjust the metabolic output of host tissues to different forms of stress and damage associated with infection. Disease tolerance is the term used to define this defense strategy, which does not exert a direct impact on pathogens but is essential to limit the health and fitness costs of infection. Under this argument, we propose that disease tolerance is an inherent component of immunity.

Pre-conditioning with tanshinone IIA attenuates the ischemia/reperfusion injury caused by liver grafts via regulation of HMGB1 in rat Kupffer cells

OBJECTIVE

We have evaluated the protective mechanism of tanshinone IIA in ischemia/reperfusion injury (IRI) induced by liver grafts, revealing novel supplementary immunotherapy for liver transplantation.

METHODS

The tanshinone IIA preconditioning group (TP group) was pretreated with tanshinone IIA via intraperitoneal injection for 1 week before receiving orthotopic liver transplantation with hepatic arterial ischemia for 30min. The sham-operation group (SO group), control graft group (CG group) and IRI group were pretreated with an equivalent volume of normal saline. The IRI group and CG group received orthotopic liver transplantation with or without hepatic arterial ischemia. Rats were sacrificed at each time point, serum was collected for ELISA detection, and Kupffer cells (KCs) were isolated to extract total protein and RNA for western blotting and real-time PCR, respectively.

RESULTS

The levels of TNF-α and IL-4 in the TP group were significantly lower than those of in the IRI group; meanwhile the IL-10 and TGF-β levels were significantly higher than in the IRI group. The protein and mRNA expression levels of HMGB1 were significantly lower in TP group than in the IRI group at each time point. The TLR-4, Myd88, NLRP3 and p-NF-κb p65 expression levels in the TP groups were significantly lower than those in the IRI group, while the PTEN, PI3K and AKT phosphorylation levels in the TP groups were significantly higher than those in the IRI group.

CONCLUSIONS

Tanshinone IIA attenuates IRI caused by liver grafts via down-regulation of the HMGB1-TLR-4/NF-κb pathway in KCs and activation of PTEN/PI3K/AKT pathway, suggesting a potential role for prevention of liver cell IRI during liver transplantation.