A malaria protein factor induces IL-4 production by dendritic cells via PI3K-Akt-NF-κB signaling independent of MyD88/TRIF and promotes Th2 response

The Mechanism of Delayed Ischemic Preconditioning in Alleviating Acute Ischemia/Reperfusion Renal Injury through Treg Mediated by Immature CD11c+ Dendritic Cells

Introduction

Renal ischemia-reperfusion injury (IRI) is one of the major causes of acute kidney injury, and its mechanism is complex involving multiple factors, while delayed ischemic preconditioning (DIPC) has a protective effect on the above process. In our previous study, we found that DIPC can exert its protection on renal IRI by inhibiting the maturation of dendritic cells (DCs), but the mechanism has not been clarified. This study aimed to investigate the protective mechanism of DIPC on renal IRI in mice through Treg mediated by immature DCs (imDCs).

Methods

The IRI mice model, DIPC treatment, and conditional CD11c⁺ DCs (CD11c-DTR) knockout mice were used to perform our study. The maturation and differentiation of DCs and Treg cells in the kidney and spleen were analyzed by flow cytometry. HE staining was used to evaluate the pathology of the kidney tissue. The level of creatinine (Cr), oxidative stress factors (SOD, MDA), and inflammatory factors (TNF-α, IL-10, IL-4) were also measured. Then, imDCs were co-cultured with HK-2 cells, and apoptosis was analyzed with flow cytometry and PI-Hoechst 33,342 fluorescence staining to assess the apoptosis rate of HK-2 cells under hypoxic-reoxygenated (H/R) conditions.

Results

DIPC could decrease renal Cr levels, alleviate pathological renal damage, and reduce oxidative stress and inflammation caused by IRI. Moreover, DIPC could decrease the number of mature DCs (mDCs) and increase Treg lymphocyte infiltration in the kidney tissue, while the reduction of DCs reversed this process. In addition, our in vitro experiment found that in the H/R model, the apoptosis of HK-2 cells decreased which were co-cultured with imDCs.

Conclusion

DIPC can regulate the differentiation of DCs into imDCs, thus affecting the differentiation level and distribution of Treg cells to exert its protective effect on renal IRI.

Innate/Inflammatory Bioregulation of Surfactant Protein D Alleviates Rat Osteoarthritis by Inhibiting Toll-Like Receptor 4 Signaling

Osteoarthritis (OA) is a deteriorating disease of cartilage tissues mainly characterized as low-grade inflammation of the joint. Innate immune molecule surfactant protein D (SP-D) is a member of collectin family of collagenous Ca²⁺-dependent defense lectins and plays a vital role in the inflammatory and innate immune responses. The present study investigated the SP-D-mediated innate/inflammatory bioregulation in OA and explored the underlying molecular mechanism. Transcriptome analysis revealed that SP-D regulated genes were strongly enriched in the inflammatory response, immune response, cellular response to lipopolysaccharide (LPS), PI3K-Akt signaling, Toll-like receptor (TLR) signaling, and extracellular matrix (ECM)-receptor interaction pathways. Knockdown of the SP-D gene by the recombinant adeno-associated virus promoted the macrophage specific markers of CD68, F4/80 and TLR4 in the articular cartilage in vivo. SP-D alleviated the infiltration of synovial macrophages and neutrophils, and inhibited TLR4, TNF-α and the phosphorylation of PI3K, Akt and NF-κB p65 in cartilage. SP-D suppressed cartilage degeneration, inflammatory and immune responses in the rat OA model, whilst TAK-242 strengthened this improvement. In in vitro conditions, SP-D pre-treatment inhibited LPS-induced overproduction of inflammation-correlated cytokines such as IL-1β and TNF-α, and suppressed the overexpression of TLR4, MD-2 and NLRP3. SP-D prevented the LPS-induced degradation of ECM by down-regulating MMP-13 and up-regulating collagen II. Blocking of TLR4 by TAK-242 further enhanced these manifestations. We also demonstrated that SP-D binds to the TLR4/MD-2 complex to suppress TLR4-mediated PI3K/Akt and NF-κB signaling activation in chondrocytes. Taken together, these findings indicate that SP-D has chondroprotective properties dependent on TLR4-mediated PI3K/Akt and NF-κB signaling and that SP-D has an optimal bioregulatory effect on the inflammatory and innate responses in OA.

Malaria-induced bacteremia as a consequence of multiple parasite survival strategies

Globally, malaria continues to be an enormous public health burden, with concomitant parasite-induced damage to the gastrointestinal (GI) barrier resulting in bacteremia-associated morbidity and mortality in both adults and children. Infected red blood cells sequester in and can occlude the GI microvasculature, ultimately leading to disruption of the tight and adherens junctions that would normally serve as a physical barrier to translocating enteric bacteria. Mast cell (MC) activation and translocation to the GI during malaria intensifies damage to the physical barrier and weakens the immunological barrier through the release of enzymes and factors that alter the host response to escaped enteric bacteria. In this context, activated MCs release Th2 cytokines, promoting a balanced Th1/Th2 response that increases local and systemic allergic inflammation while protecting the host from overwhelming Th1-mediated immunopathology. Beyond the mammalian host, recent studies in both the lab and field have revealed an association between a Th2-skewed host response and success of parasite transmission to mosquitoes, biology that is evocative of parasite manipulation of the mammalian host. Collectively, these observations suggest that malaria-induced bacteremia may be, in part, an unintended consequence of a Th2-shifted host response that promotes parasite survival and transmission. Future directions of this work include defining the factors and mechanisms that precede the development of bacteremia, which will enable the development of biomarkers to simplify diagnostics, the identification of therapeutic targets to improve patient outcomes and better understanding of the consequences of clinical interventions to transmission blocking strategies.

Lessons Learned for Pathogenesis, Immunology, and Disease of Erythrocytic Parasites: Plasmodium and Babesia

Malaria caused by Plasmodium species and transmitted by Anopheles mosquitoes affects large human populations, while Ixodes ticks transmit Babesia species and cause babesiosis. Babesiosis in animals has been known as an economic drain, and human disease has also emerged as a serious healthcare problem in the last 20–30 years. There is limited literature available regarding pathogenesis, immunity, and disease caused by Babesia spp. with their genomes sequenced only in the last decade. Therefore, using previous studies on Plasmodium as the foundation, we have compared similarities and differences in the pathogenesis of Babesia and host immune responses. Sexual life cycles of these two hemoparasites in their respective vectors are quite similar. An adult Anopheles female can take blood meal several times in its life such that it can both acquire and transmit Plasmodia to hosts. Since each tick stage takes blood meal only once, transstadial horizontal transmission from larva to nymph or nymph to adult is essential for the release of Babesia into the host. The initiation of the asexual cycle of these parasites is different because Plasmodium sporozoites need to infect hepatocytes before egressed merozoites can infect erythrocytes, while Babesia sporozoites are known to enter the erythrocytic cycle directly. Plasmodium metabolism, as determined by its two- to threefold larger genome than different Babesia, is more complex. Plasmodium replication occurs in parasitophorous vacuole (PV) within the host cells, and a relatively large number of merozoites are released from each infected RBC after schizogony. The Babesia erythrocytic cycle lacks both PV and schizogony. Cytoadherence that allows the sequestration of Plasmodia, primarily P. falciparum in different organs facilitated by prominent adhesins, has not been documented for Babesia yet. Inflammatory immune responses contribute to the severity of malaria and babesiosis. Antibodies appear to play only a minor role in the resolution of these diseases; however, cellular and innate immunity are critical for the clearance of both pathogens. Inflammatory immune responses affect the severity of both diseases. Macrophages facilitate the resolution of both infections and also offer cross-protection against related protozoa. Although the immunosuppression of adaptive immune responses by these parasites does not seem to affect their own clearance, it significantly exacerbates diseases caused by coinfecting bacteria during coinfections.

Particulate matter 2.5 triggers airway inflammation and bronchial hyperresponsiveness in mice by activating the SIRT2-p65 pathway

Exposure to particulate matter 2.5 (PM2.5) potentially triggers airway inflammation by activating nuclear factor-κB (NF-κB). Sirtuin 2 (SIRT2) is a key modulator in inflammation. However, the function and specific mechanisms of SIRT2 in PM2.5-induced airway inflammation are largely understudied. Therefore, this work investigated the mechanisms of SIRT2 in regulating the phosphorylation and acetylation of p65 influenced by PM2.5-induced airway inflammation and bronchial hyperresponsiveness. Results revealed that PM2.5 exposure lowered the expression and activity of SIRT2 in bronchial tissues. Subsequently, SIRT2 impairment promoted the phosphorylation and acetylation of p65 and activated the NF-κB signaling pathway. The activation of p65 triggered airway inflammation, increment of mucus secretion by goblet cells, and acceleration of tracheal stenosis. Meanwhile, p65 phosphorylation and acetylation, airway inflammation, and bronchial hyperresponsiveness were deteriorated in SIRT2 knockout mice exposed to PM2.5. Triptolide (a specific p65 inhibitor) reversed p65 activation and ameliorated PM2.5-induced airway inflammation and bronchial hyperresponsiveness. Our findings provide novel insights into the molecular mechanisms underlying the toxicity of PM2.5 exposure. Triptolide inhibition of p65 phosphorylation and acetylation could be an effective therapeutic approach in averting PM2.5-induced airway inflammation and bronchial hyperresponsiveness.

Histamine Ingestion by Anopheles stephensi Alters Important Vector Transmission Behaviors and Infection Success with Diverse Plasmodium Species

An estimated 229 million people worldwide were impacted by malaria in 2019. The vectors of malaria parasites (Plasmodium spp.) are Anopheles mosquitoes, making their behavior, infection success, and ultimately transmission of great importance. Individuals with severe malaria can exhibit significantly increased blood concentrations of histamine, an allergic mediator in humans and an important insect neuromodulator, potentially delivered to mosquitoes during blood-feeding. To determine whether ingested histamine could alter Anopheles stephensi biology, we provisioned histamine at normal blood levels and at levels consistent with severe malaria and monitored blood-feeding behavior, flight activity, antennal and retinal responses to host stimuli and lifespan of adult female Anopheles stephensi. To determine the effects of ingested histamine on parasite infection success, we quantified midgut oocysts and salivary gland sporozoites in mosquitoes infected with Plasmodium yoelii and Plasmodium falciparum. Our data show that provisioning An. stephensi with histamine at levels consistent with severe malaria can enhance mosquito behaviors and parasite infection success in a manner that would be expected to amplify parasite transmission to and from human hosts. Such knowledge could be used to connect clinical interventions by reducing elevated histamine to mitigate human disease pathology with the delivery of novel lures for improved malaria control.

IL-4Rα signaling by CD8α+ dendritic cells contributes to cerebral malaria by enhancing inflammatory, Th1, and cytotoxic CD8+ T cell responses

Persistent high levels of proinflammatory and Th1 responses contribute to cerebral malaria (CM). Suppression of inflammatory responses and promotion of Th2 responses prevent pathogenesis. IL-4 commonly promotes Th2 responses and inhibits inflammatory and Th1 responses. Therefore, IL-4 is widely considered as a beneficial cytokine via its Th2-promoting role that is predicted to provide protection against severe malaria by inhibiting inflammatory responses. However, IL-4 may also induce inflammatory responses, as the result of IL-4 action depends on the timing and levels of its production and the tissue environment in which it is produced. Recently, we showed that dendritic cells (DCs) produce IL-4 early during malaria infection in response to a parasite protein and that this IL-4 response may contribute to severe malaria. However, the mechanism by which IL-4 produced by DCs contributing to lethal malaria is unknown. Using Plasmodium berghei ANKA-infected C57BL/6 mice, a CM model, we show here that mice lacking IL-4Rα only in CD8α+ DCs are protected against CM pathogenesis and survive, whereas WT mice develop CM and die. Compared with WT mice, mice lacking IL-4Rα in CD11c+ or CD8α+ DCs showed reduced inflammatory responses leading to decreased Th1 and cytotoxic CD8+ T cell responses, lower infiltration of CD8+ T cells to the brain, and negligible brain pathology. The novel results presented here reveal a paradoxical role of IL-4Rα signaling in CM pathogenesis that promotes CD8α+ DC-mediated inflammatory responses that generate damaging Th1 and cytotoxic CD8+ T cell responses.

Toll-like receptor 4, Toll-like receptor 7 and Toll-like receptor 9 agonists enhance immune responses against blood-stage Plasmodium chabaudi infection in BALB/c mice

BACKGROUND

Toll-like receptor (TLR) signals play vital roles during the blood-stage of malaria infections. However, the roles of TLR agonists in the regulation of immune responses and the development of protective immunity to malaria remain poorly understood.

METHOD

BALB/c mice were pre-treated with TLR4, TLR7 and TLR9 agonists, followed by infection with Plasmodium chabaudi. After infection, splenic dendritic cells (DCs), Th1 cells and programmed death-1 (PD-1) expressed on Th1 cells, as well as regulatory T cells (Tregs) were analyzed by flow cytometry. The levels of IFN-γ, TNF-α, TGF-β and IL-10 in splenocytes and IgG1 and IgG2a in serum were measured by ELISA.

RESULT

Administration of TLR4, TLR7 and TLR9 agonists prior to infection improved disease outcomes. All TLR agonists promoted DC activation, and the proportions of Th1 cells increased. In TLR4, TLR7 and TLR9 agonist treated groups the levels of pro-inflammatory cytokines IFN-γ and TNF-α were elevated, and IgG1 and IgG2a serum levels were also significantly increased. TLR4, TLR7 and TLR9 agonists diminished the activation of Tregs and down-regulated the anti-inflammatory cytokines TGF-β and IL-10. Finally, PD-1 expressed on Th1 cells were decreased in TLR4, TLR7 and TLR9 agonist treated groups compared with control groups.

CONCLUSION

TLR4, TLR7 and TLR9 agonists activated DC-mediated innate immune responses and adaptive immune response, which against the blood-stage of Plasmodium and might be applied to malaria protection and treatment.

Expression and role of miR-338-3p in peripheral blood and placenta of patients with pregnancy-induced hypertension

The present study aimed to investigate the role of miR-338-3p in pregnancy-induced hypertension (PIH), and its effects on human trophoblast cells in vitro. Quantitative real-time PCR was used to detect miR-338-3p expression. Human trophoblast HTR8/SVneo cells were transfected with miR-338-3p mimics. Effects of miR-338-3p on cell proliferation, invasion and metastasis, and anoikis resistance were detected by CCK-8 assay, Transwell chamber assay, flow cytometry and western blot analysis, respectively. Bioinformatics analysis was performed to predict the target of miR-338-3p, and the results were confirmed by dual luciferase reporter assay. The expression level of miR-338-3p was significantly upregulated in the peripheral blood and placenta of PIH patients. CCK-8 assay showed that miR-338-3p mimics inhibited the proliferation of HTR8/SVneo cells at indicated time points. Flow cytometry showed that miR-338-3p transfection significantly increased the Ki-67 expression in the HTR8/SVneo cells, indicating enhanced cell proliferation. Transwell chamber assay and western blot analysis showed that the invasion and metastatic abilities of the HTR8/SVneo cells were significantly decreased in the miR-338-3p transfection group, as well as expression levels of MMP-2 and MMP-9. Bioinformatics analysis and dual luciferase reporter assay indicated that AKT3 is a target gene of miR-338-3p. Our results suggest that miR-338-3p is significantly increased in the peripheral blood and placenta of PIH patients, which is correlated with the disease development. miR-338-3p inhibits proliferation, invasion and metastasis, and apoptosis resistance of human trophoblast cells by targeting AKT3.

Simvastatin improves cerebrovascular injury caused by ischemia‑reperfusion through NF‑κB‑mediated apoptosis via MyD88/TRIF signaling

Cerebrovascular injury is the most prevalent human cerebrovascular disease and frequently results in ischemic stroke. Simvastatin may be a potential therapeutic agent for the treatment of patients with cerebrovascular injury. The present study aimed to investigate the efficacy of and the potential mechanisms regulated by simvastatin in a rat model of ischemia-reperfusion (I/R)-induced cerebrovascular injury. Cerebrovascular injury model rats were established and were subsequently treated with simvastatin or a vehicle control following I/R injury. Cell damage, neurological functions and neuronal apoptosis were examined, as well as the nuclear factor (NF)-κB-mediated myeloid differentiation primary response protein 88 (MyD88)/toll-interleukin-1 receptor domain-containing adapter molecule 1 (TRIF) signaling pathway following simvastatin treatment. The results of the present study demonstrated that simvastatin treatment led to a reduction in cell damage, improvement of neurological functions and decreased neuronal apoptosis compared with vehicle-treated I/R model rats, 14 days post-treatment. In addition, simvastatin treatment reduced cerebral water content and blood-brain barrier disruption in cerebrovascular injury induced by I/R. The results also revealed that simvastatin treatment inhibited neuronal apoptosis via the NF-κB-mediated MyD88/TRIF signaling pathway. In conclusion, simvastatin treatment may reduce I/R-induced neuronal apoptosis via inhibition of the NF-κB-mediated MyD88/TRIF signaling pathway.