Beta interferon-mediated activation of signal transducer and activator of transcription protein 1 interferes with Rickettsia conorii replication in human endothelial cells

Rickettsia rickettsii virulence determinants RARP2 and RapL mitigate IFN- signaling in primary human dermal microvascular endothelial cells

We compared the growth characteristics of a virulent Rickettsia rickettsii strain (Sheila Smith) to an attenuated R. rickettsii stain (Iowa) and a non-pathogenic species (R. montanensis) in primary human dermal microvascular endothelial cells (HDMEC). All replicated in Vero cells, however, only the Sheila Smith strain productively replicated in HDMECs. The Iowa strain showed minimal replication over a 24-h period, while R. montanensis lost viability and induced lysis of the HDMECs via a rapid programmed cell death response. Both the virulent and attenuated R. rickettsii strains, but not R. montanensis, induced an interferon-1 response, although the response was of lesser magnitude and delayed in the Sheila Smith strain. IFN-β secretion correlated with increased host cell lysis, and treatment with anti-IFNAR2 antibody decreased lysis from Iowa-infected but not Sheila Smith-infected cells. Both Sheila Smith- and Iowa-infected cells eventually lysed, although the response from Sheila Smith was delayed and showed characteristics of apoptosis. We, therefore, examined whether reconstitution of the Iowa strain with two recently described putative virulence determinants might enhance survival of Iowa within HDMECs. Reconstitution with RARP2, which is inhibitory to anterograde trafficking through the Golgi apparatus, reduced IFN-β secretion but had no effect on cell lysis. RapL, which proteolytically processes surface exposed autotransporters and enhances replication of Iowa in Guinea pigs, suppressed both IFN-β production and host cell lysis. These findings suggest distinct mechanisms by which virulent spotted fever group rickettsiae may enhance intracellular survival and replication.IMPORTANCEWe examined a naturally occurring non-pathogenic rickettsial species, R. montanensis, a laboratory-attenuated R. rickettsii strain (Iowa), and a fully virulent R. rickettsii strain (Sheila Smith) for growth in human dermal microvascular endothelial cells. The two avirulent strains replicated poorly or not at all. Only the virulent Sheila Smith strain replicated. IFN-β production correlated with the inhibition of R. rickettsii Iowa. Reconstitution of Iowa with either of two recently described putative virulence determinants altered the IFN-β response. A rickettsial ankyrin repeat protein, RARP2, disrupts the trans-Golgi network and inhibits IFN-β secretion. An autotransporter peptidase, RapL, restores proteolytic maturation of outer membrane autotransporters and diminishes the IFN-β response to enhance cell survival and permit replication of the recombinant strain. These studies point the way toward discovery of mechanisms for innate immune response avoidance by virulent rickettsia.

TRIM56-mediated production of type I interferon inhibits intracellular replication of Rickettsia rickettsii

Rickettsia rickettsii (R. rickettsii), the causative agent of Rocky Mountain spotted fever (RMSF), is the most pathogenic member among Rickettsia spp. Previous studies have shown that tripartite motif-containing 56 (TRIM56) E3 ligase-induced ubiquitination of STING is important for cytosolic DNA sensing and type I interferon production to induce anti-DNA viral immunity, but whether it affects intracellular replication of R. rickettsii remains uncharacterized. Here, we investigated the effect of TRIM56 on HeLa and THP-1 cells infected with R. rickettsii. We found that the expression of TRIM56 was upregulated in the R. rickettsii-infected cells, and the overexpression of TRIM56 inhibited the intracellular replication of R. rickettsii, while R. rickettsii replication was enhanced in the TRIM56-silenced host cells with the reduced phosphorylation of IRF3 and STING and the increased production of interferon-β. In addition, the mutation of the TRIM56 E3 ligase catalytic site impairs the inhibitory function against R. rickettsii in HeLa cells. Altogether, our study discovers that TRIM56 is a host restriction factor of R. rickettsii by regulating the cGAS-STING-mediated signaling pathway. This study gives new evidence for the role of TRIM56 in the innate immune response against intracellular bacterial infection and provides new therapeutic targets for RMSF.

IMPORTANCE

Given that Rickettsia rickettsii (R. rickettsii) is the most pathogenic member within the Rickettsia genus and serves as the causative agent of Rocky Mountain spotted fever, there is a growing need to explore host targets. In this study, we examined the impact of host TRIM56 on R. rickettsii infection in HeLa and THP-1 cells. We observed a significant upregulation of TRIM56 expression in R. rickettsii-infected cells. Remarkably, the overexpression of TRIM56 inhibited the intracellular replication of R. rickettsii, while silencing TRIM56 enhanced bacterial replication accompanied by reduced phosphorylation of IRF3 and STING, along with increased interferon-β production. Notably, the mutation of the TRIM56's E3 ligase catalytic site did not impede R. rickettsii replication in HeLa cells. Collectively, our findings provide novel insights into the role of TRIM56 as a host restriction factor against R. rickettsii through the modulation of the cGAS-STING signaling pathway.

Anaphylatoxin signaling activates macrophages to control intracellular Rickettsia proliferation

IMPORTANCE

Pathogenic Rickettsia species are extremely dangerous bacteria that grow within the cytoplasm of host mammalian cells. In most cases, these bacteria are able to overpower the host cell and grow within the protected environment of the cytoplasm. However, a dramatic conflict occurs when Rickettsia encounter innate immune cells; the bacteria can "win" by taking over the host, or the bacteria can "lose" if the host cell efficiently fights the infection. This manuscript examines how the immune complement system is able to detect the presence of Rickettsia and alert nearby cells. Byproducts of complement activation called anaphylatoxins are signals that "activate" innate immune cells to mount an aggressive defensive strategy. This study enhances our collective understanding of the innate immune reaction to intracellular bacteria and will contribute to future efforts at controlling these dangerous infections.

Temporal patterns of gene expression in response to inoculation with a virulent Anaplasma phagocytophilum strain in sheep

The aim of this study was to characterize the gene expression of host immune- and cellular responses to a Norwegian virulent strain of Anaplasma phagocytophilum, the cause of tick-borne fever in sheep. Ten sheep were intravenously inoculated with a live virulent strain of A. phagocytophilum. Clinical-, observational-, hematological data as well as bacterial load, flow cytometric cell count data from peripheral blood mononuclear cells and host's gene expression post infection was analysed. The transcriptomic data were assessed for pre-set time points over the course of 22 days following the inoculation. Briefly, all inoculated sheep responded with clinical signs of infection 3 days post inoculation and onwards with maximum bacterial load observed on day 6, consistent with tick-borne fever. On days, 3-8, the innate immune responses and effector processes such as IFN1 signaling pathways and cytokine mediated signaling pathways were observed. Several pathways associated with the adaptive immune responses, namely T-cell activation, humoral immune responses, B-cell activation, and T- and B-cell differentiation dominated on the days of 8, 10 and 14. Flow-cytometric analysis of the PBMCs showed a reduction in CD4+CD25+ cells on day 10 and 14 post-inoculation and a skewed CD4:CD8 ratio indicating a reduced activation and proliferation of CD4-T-cells. The genes of important co-stimulatory molecules such as CD28 and CD40LG, important in T- and B-cell activation and proliferation, did not significantly change or experienced downregulation throughout the study. The absence of upregulation of several co-stimulatory molecules might be one possible explanation for the low activation and proliferation of CD4-T-cells during A. phagocytophilum infection, indicating a suboptimal CD4-T-cell response. The upregulation of T-BET, EOMES and IFN-γ on days 8-14 post inoculation, indicates a favoured CD4 Th1- and CD8-response. The dynamics and interaction between CD4+CD25+ and co-stimulatory molecules such as CD28, CD80, CD40 and CD40LG during infection with A. phagocytophilum in sheep needs further investigation in the future.

Boutonneuse Fever in Southeastern Romania

Boutonneuse fever (BF) is an eruptive disease and is classified as a spotted fever, which is endemic in the Mediterranean basin (i.e., Marseille fever or Mediterranean spotted fever) and the Black Sea, caused by Rickettsia conorii, with dog ticks being a vector (i.e., Rhipicephalus sanguineus). In Romania, although the first reported outbreak of BF occurred during the summer of 1931 in Constanta, the disease was discovered in 1910. Although the disease has occurred most frequently in the two counties of the Dobruja region (Constanta and Tulcea), a region of the Balkan Peninsula, during the last few years, other counties in southeastern Romania have started to report BF cases. In a period of 9 years, 533 cases were registered in Constanta county, while in a period of 11 years, 339 cases were registered in Bucharest county. In this review, we describe the bacterial tick-borne disease caused by R. conorii in southeastern Romania, focusing on its history and epidemiology, pathophysiology, clinical aspects, diagnosis, treatment and preventive measures in the context of climate changes. Although R. conorii is the principal etiologic agent of BF in southeastern Romania, we should take into consideration that other Rickettsia spp. could be present and involved in disease transmission.

Vascular endothelial cell-specific disruption of the profilin1 gene leads to severe multiorgan pathology and inflammation causing mortality

Actin-binding protein Profilin1 is an important regulator of actin cytoskeletal dynamics in cells and critical for embryonic development in higher eukaryotes. The objective of the present study was to examine the consequence of loss-of-function of Pfn1 in vascular endothelial cells (ECs) in vivo. We utilized a mouse model engineered for tamoxifen-inducible biallelic inactivation of the Pfn1 gene selectively in EC (Pfn1EC-KO). Widespread deletion of EC Pfn1 in adult mice leads to severe health complications presenting overt pathologies (endothelial cell death, infarct, and fibrosis) in major organ systems and evidence for inflammatory infiltrates, ultimately compromising the survival of animals within 3 weeks of gene ablation. Mice deficient in endothelial Pfn1 exhibit selective bias toward the proinflammatory myeloid-derived population of immune cells, a finding further supported by systemic elevation of proinflammatory cytokines. We further show that triggering Pfn1 depletion not only directly upregulates proinflammatory cytokine/chemokine gene expression in EC but also potentiates the paracrine effect of EC on proinflammatory gene expression in macrophages. Consistent with these findings, we provide further evidence for increased activation of Interferon Regulatory Factor 7 (IRF7) and STAT1 in EC when depleted of Pfn1. Collectively, these findings for the first time demonstrate a prominent immunological consequence of loss of endothelial Pfn1 and an indispensable role of endothelial Pfn1 in mammalian survival unlike tolerable phenotypes of Pfn1 loss in other differentiated cell types.

Sensing the Messenger: Potential Roles of Cyclic-di-GMP in Rickettsial Pathogenesis

Pathogenic bacteria causing human rickettsioses, transmitted in nature by arthropod vectors, primarily infect vascular endothelial cells lining the blood vessels, resulting in 'endothelial activation' and onset of innate immune responses. Nucleotide second messengers are long presumed to be the stimulators of type I interferons, of which bacterial cyclic-di-GMP (c-di-GMP) has been implicated in multiple signaling pathways governing communication with other bacteria and host cells, yet its importance in the context of rickettsial interactions with the host has not been investigated. Here, we report that all rickettsial genomes encode a putative diguanylate cyclase pleD, responsible for the synthesis of c-di-GMP. In silico analysis suggests that although the domain architecture of PleD is apparently well-conserved among different rickettsiae, the protein composition and sequences likely vary. Interestingly, cloning and sequencing of the pleD gene from virulent (Sheila Smith) and avirulent (Iowa) strains of R. rickettsii reveals a nonsynonymous substitution, resulting in an amino acid change (methionine to isoleucine) at position 236. Additionally, a previously reported 5-bp insertion in the genomic sequence coding for pleD (NCBI accession: NC_009882) was not present in the sequence of our cloned pleD from R. rickettsii strain Sheila Smith. In vitro infection of HMECs with R. rickettsii (Sheila Smith), but not R. rickettsii (Iowa), resulted in dynamic changes in the levels of pleD up to 24 h post-infection. These findings thus provide the first evidence for the potentially important role(s) of c-di-GMP in the determination of host-cell responses to pathogenic rickettsiae. Further studies into molecular mechanisms through which rickettsial c-di-GMP might regulate pathogen virulence and host responses should uncover the contributions of this versatile bacterial second messenger in disease pathogenesis and immunity to human rickettsioses.

Mediterranean Spotted Fever: Current Knowledge and Recent Advances

Mediterranean spotted fever (MSF) is an emerging tick-borne rickettsiosis of the spotted fever group (SFG), endemic in the Mediterranean basin. By virtue of technological innovations in molecular genetics, it has been determined that the causative agent of MSF is Rickettsia conorii subspecies conorii. The arthropod vector of this bacterium is the brown dog tick Rhipicephalus sanguineus. The true nature of the reservoir of R. conorii conorii has not been completely deciphered yet, although many authors theorize that the canine population, other mammals, and the ticks themselves could potentially contribute as reservoirs. Typical symptoms of MSF include fever, maculopapular rash, and a characteristic eschar (“tache noire”). Atypical clinical features and severe multi-organ complications may also be present. All of these manifestations arise from the disseminated infection of the endothelium by R. conorii conorii. Several methods exist for the diagnosis of MSF. Serological tests are widely used and molecular techniques have become increasingly available. Doxycycline remains the treatment of choice, while preventive measures are focused on modification of human behavior and vector control strategies. The purpose of this review is to summarize the current knowledge on the epidemiology, pathogenesis, clinical features, diagnosis, and treatment of MSF.

Interferon receptor-deficient mice are susceptible to eschar-associated rickettsiosis

Arthropod-borne rickettsial pathogens cause mild and severe human disease worldwide. The tick-borne pathogen Rickettsia parkeri elicits skin lesions (eschars) and disseminated disease in humans; however, inbred mice are generally resistant to infection. We report that intradermal infection of mice lacking both interferon receptors (Ifnar1-/-;Ifngr1-/-) with as few as 10 R. parkeri elicits eschar formation and disseminated, lethal disease. Similar to human infection, eschars exhibited necrosis and inflammation, with bacteria primarily found in leukocytes. Using this model, we find that the actin-based motility factor Sca2 is required for dissemination from the skin to internal organs, and the outer membrane protein OmpB contributes to eschar formation. Immunizing Ifnar1-/-;Ifngr1-/- mice with sca2 and ompB mutant R. parkeri protects against rechallenge, revealing live-attenuated vaccine candidates. Thus, Ifnar1-/-;Ifngr1-/- mice are a tractable model to investigate rickettsiosis, virulence factors, and immunity. Our results further suggest that discrepancies between mouse and human susceptibility may be due to differences in interferon signaling.

Cutaneous Immunoprofiles of Three Spotted Fever Group Rickettsia Cases

Spotted fever group rickettsia (SFGR) can cause mild to fatal illness. The early interaction between the host and rickettsia in skin is largely unknown, and the pathogenesis of severe rickettsiosis remains an important topic. A surveillance of SFGR infection by PCR of blood and skin biopsy specimens followed by sequencing and immunohistochemical (IHC) detection was performed on patients with a recent tick bite between 2013 and 2016. Humoral and cutaneous immunoprofiles were evaluated in different SFGR cases by serum cytokine and chemokine detection, skin IHC staining, and transcriptome sequencing (RNA-seq).

Spotted fever group rickettsia (SFGR) can cause mild to fatal illness. The early interaction between the host and rickettsia in skin is largely unknown, and the pathogenesis of severe rickettsiosis remains an important topic. A surveillance of SFGR infection by PCR of blood and skin biopsy specimens followed by sequencing and immunohistochemical (IHC) detection was performed on patients with a recent tick bite between 2013 and 2016. Humoral and cutaneous immunoprofiles were evaluated in different SFGR cases by serum cytokine and chemokine detection, skin IHC staining, and transcriptome sequencing (RNA-seq). A total of 111 SFGR cases were identified, including 79 “Candidatus Rickettsia tarasevichiae,” 22 Rickettsia raoultii, 8 Rickettsia sibirica, and 2 Rickettsia heilongjiangensis cases. The sensitivity to detect SFGR in skin biopsy specimens (9/24, 37.5%) was significantly higher than that in blood samples (105/2,671, 3.9%) (P < 0.05). As early as 1 day after the tick bite, rickettsiae could be detected in the skin. R. sibirica infection was more severe than “Ca. Rickettsia” and R. raoultii infections. Increased levels of serum interleukin-18 (IL-18), IP10, and monokine induced by gamma interferon (MIG) and decreased levels of IL-2 were observed in febrile patients infected with R. sibirica compared to those infected with “Ca. Rickettsia.” RNA-seq and IHC staining could not discriminate between SFGR-infected and uninfected tick bite skin lesions. However, the type I interferon (IFN) response was differently expressed between R. sibirica and R. raoultii infections at the cutaneous interface. It is concluded that skin biopsy specimens were more reliable for the detection of SFGR infection in human patients although the immunoprofile may be complicated by immunomodulators induced by the tick bite.

Distribution and Ecological Drivers of Spotted Fever Group Rickettsia in Asia

Spotted fever group and related rickettsia (SFGR) are a neglected group of pathogens that belong to the genus Rickettsia. SFGR are zoonotic and are transmitted by arthropod vectors, primarily ticks, fleas and mites to accidental hosts. These emerging and re-emerging infections are widely distributed throughout the world. Land-use change and increasing human-wildlife conflict compound the risk of SFGR infection to local people in endemic areas and travelers to these regions. In this article, we discuss the rickettsial organisms causing spotted fever and related diseases, their arthropod vectors in Asia and the impact of land-use change on their spread.

Diagnosis of spotted fever group Rickettsia infections: the Asian perspective

Spotted fever group rickettsiae (SFG) are a neglected group of bacteria, belonging to the genus Rickettsia, that represent a large number of new and emerging infectious diseases with a worldwide distribution. The diseases are zoonotic and are transmitted by arthropod vectors, mainly ticks, fleas and mites, to hosts such as wild animals. Domesticated animals and humans are accidental hosts. In Asia, local people in endemic areas as well as travellers to these regions are at high risk of infection. In this review we compare SFG molecular and serological diagnostic methods and discuss their limitations. While there is a large range of molecular diagnostics and serological assays, both approaches have limitations and a positive result is dependent on the timing of sample collection. There is an increasing need for less expensive and easy-to-use diagnostic tests. However, despite many tests being available, their lack of suitability for use in resource-limited regions is of concern, as many require technical expertise, expensive equipment and reagents. In addition, many existing diagnostic tests still require rigorous validation in the regions and populations where these tests may be used, in particular to establish coherent and worthwhile cut-offs. It is likely that the best strategy is to use a real-time quantitative polymerase chain reaction (qPCR) and immunofluorescence assay in tandem. If the specimen is collected early enough in the infection there will be no antibodies but there will be a greater chance of a PCR positive result. Conversely, when there are detectable antibodies it is less likely that there will be a positive PCR result. It is therefore extremely important that a complete medical history is provided especially the number of days of fever prior to sample collection. More effort is required to develop and validate SFG diagnostics and those of other rickettsial infections.

Global Transcriptomic Profiling of Pulmonary Gene Expression in an Experimental Murine Model of Rickettsia conorii Infection

Mediterranean spotted fever develops from an infection with Rickettsia conorii, an obligate intracellular, Gram-negative, endotheliotropic, and tick-transmitted bacterial pathogen, and is an acute, febrile illness that can progress to life-threatening complications if not diagnosed and treated early with effective antibiotics. Despite significant morbidity and mortality, little is known about changes in gene expression that determine the host responses during in vivo infection. We have investigated the transcriptional landscape of host lungs as a prominently affected organ system in an established murine model of infection by RNA-sequencing. Ingenuity pathway analysis resulted in the identification of 1332 differentially expressed genes and 292 upstream regulators. Notably, genes encoding for ubiquitin D, aconitate decarboxylase, antimicrobial peptides, calgranulins, cytokines and chemokines, and guanylate binding proteins were highly up-regulated, whereas those involved in hemoglobin biosynthesis and heme homeostasis were significantly down-regulated. Amongst response regulators, nucleotide-binding oligomerization domain-containing protein 2 and killer cell lectin-like receptors were differentially expressed, and gene clustering revealed eukaryotic initiation factor-2, oxidative phosphorylation, and ubiquitination as the predominantly activated biological pathways. Collectively, this first global transcriptomic profiling has identified R. conorii-induced regulation of novel genes and pathways in the host lungs, further in-depth investigation of which will strengthen our understanding of the pathogenesis of human rickettsioses.

A Type I Interferon and IL-10 Induced by Orientia tsutsugamushi Infection Suppresses Antigen-Specific T Cells and Their Memory Responses

Despite the various roles of type I interferon (type I IFN) responses during bacterial infection, its specific effects in vivo have been poorly characterized in scrub typhus caused by Orientia tsutsugamushi infection. Here, we show that type I IFNs are primarily induced via intracellular nucleic acids sensors, including RIG-I/MAVS and cGAS/STING pathways, during O. tsutsugamushi invasion. However, type I IFN signaling did not significantly affect pathogenesis, mortality, or bacterial burden during primary infection in vivo, when assessed in a mice model lacking a receptor for type I IFNs (IFNAR KO). Rather, it significantly impaired the induction of antigen-specific T cells and reduced memory T cell responses. IFNAR KO mice that recovered from primary infection showed stronger antigen-specific T cell responses, especially Th1, and more efficiently controlled bacteremia during secondary infection than wild type mice. Enhanced IL-10 expression by macrophages in the presence of type I IFN signaling might play a significant role in the suppression of antigen-specific T cell responses as neutralization or knock-out (KO) of IL-10 increased T cell responses in vitro. Therefore, induction of the type I IFN/IL-10 axis by O. tsutsugamushi infection might play a significant role in the suppression of T cell responses and contribute to the short longevity of cell-mediated immunity, often observed in scrub typhus patients.

Pathogenesis of Rickettsial Diseases: Pathogenic and Immune Mechanisms of an Endotheliotropic Infection

Obligately intracytosolic rickettsiae that cycle between arthropod and vertebrate hosts cause human diseases with a spectrum of severity, primarily by targeting microvascular endothelial cells, resulting in endothelial dysfunction. Endothelial cells and mononuclear phagocytes have important roles in the intracellular killing of rickettsiae upon activation by the effector molecules of innate and adaptive immunity. In overwhelming infection, immunosuppressive effects contribute to the severity of illness. Rickettsia-host cell interactions involve host cell receptors for rickettsial ligands that mediate cell adhesion and, in some instances, trigger induced phagocytosis. Rickettsiae interact with host cell actin to effect both cellular entry and intracellular actin-based mobility. The interaction of rickettsiae with the host cell also involves rickettsial evasion of host defense mechanisms and exploitation of the intracellular environment. Signal transduction events exemplify these effects. An intriguing frontier is the array of rickettsial noncoding RNA molecules and their potential effects on the pathogenesis and transmission of rickettsial diseases.

Fibroblast growth factor receptor-1 mediates internalization of pathogenic spotted fever rickettsiae into host endothelium

Rickettsial infections continue to cause serious morbidity and mortality in severe human cases around the world. Host cell adhesion and invasion is an essential requisite for intracellular growth, replication, and subsequent dissemination of pathogenic rickettsiae. Heparan sulfate proteoglycans [HSPGs] facilitate the interactions between fibroblast growth factor(s) and their tyrosine kinase receptors resulting in receptor dimerization/activation and have been implicated in bacterial adhesion to target host cells. In the present study, we have investigated the contributions of fibroblast growth factor receptors [FGFRs] in rickettsial entry into the host cells. Inhibition of HSPGs by heparinase and FGFRs by AZD4547 (a selective small-molecule inhibitor) results in significant reduction in rickettsial internalization into cultured human microvascular endothelial cells (ECs), which represent the primary targets of pathogenic rickettsiae during human infections. Administration of AZD4547 during R. conorii infection in a murine model of endothelial-target spotted fever rickettsiosis also diminishes pulmonary rickettsial burden in comparison to mock-treated controls. Silencing of FGFR1 expression using a small interfering RNA also leads to similar inhibition of R. rickettsii invasion into ECs. Consistent with these findings, R. rickettsii infection of ECs also results in phosphorylation of tyrosine 653/654, suggesting activation of FGFR1. Using isobaric tag for relative and absolute quantitation [iTRAQ]-based proteomics approach, we further demonstrate association of β-peptide of rickettsial outer membrane protein OmpA with FGFR1. Mechanistically, FGFR1 binds to caveolin-1 and mediates bacterial entry via caveolin-1 dependent endocytosis. Together, these results identify host cell FGFR1 and rickettsial OmpA as another novel receptor-ligand pair contributing to the internalization of pathogenic rickettsiae into host endothelial cells and the potential application of FGFR-inhibitor drugs as adjunct therapeutics against spotted fever rickettsioses.

Endothelial Cell Proteomic Response to Rickettsia conorii Infection Reveals Activation of the Janus Kinase (JAK)-Signal Transducer and Activator of Transcription (STAT)-Inferferon Stimulated Gene (ISG)15 Pathway and Reprogramming Plasma Membrane Integrin/Cadherin Signaling

Rickettsia conorii is the etiologic agent of Mediterranean spotted fever, a re-emerging infectious disease with significant mortality. This Gram-negative, obligately intracellular pathogen is transmitted via tick bites, resulting in disseminated vascular endothelial cell infection with vascular leakage. In the infected human, Rickettsia conorii infects endothelial cells, stimulating expression of cytokines and pro-coagulant factors. However, the integrated proteomic response of human endothelial cells to R. conorii infection is not known. In this study, we performed quantitative proteomic profiling of primary human umbilical vein endothelial cells (HUVECs) with established R conorii infection versus those stimulated with endotoxin (LPS) alone. We observed differential expression of 55 proteins in HUVEC whole cell lysates. Of these, we observed induction of signal transducer and activator of transcription (STAT)1, MX dynamin-like GTPase (MX1), and ISG15 ubiquitin-like modifier, indicating activation of the JAK-STAT signaling pathway occurs in R. conorii-infected HUVECs. The down-regulated proteins included those involved in the pyrimidine and arginine biosynthetic pathways. A highly specific biotinylated cross-linking enrichment protocol was performed to identify dysregulation of 11 integral plasma membrane proteins that included up-regulated expression of a sodium/potassium transporter and down-regulation of α-actin 1. Analysis of Golgi and soluble Golgi fractions identified up-regulated proteins involved in platelet-endothelial adhesion, phospholipase activity, and IFN activity. Thirty four rickettsial proteins were identified with high confidence in the Golgi, plasma membrane, or secreted protein fractions. The host proteins associated with rickettsial infections indicate activation of interferon-STAT signaling pathways; the disruption of cellular adhesion and alteration of antigen presentation pathways in response to rickettsial infections are distinct from those produced by nonspecific LPS stimulation. These patterns of differentially expressed proteins suggest mechanisms of pathogenesis as well as methods for diagnosis and monitoring Rickettsia infections.

Unmethylated CpG motifs inToxoplasma gondiiDNA induce TLR9- and IFN-β-dependent expression ofα-defensin-5 in intestinal epithelial cells

The gut epithelial barrier is a strategic place to prevent, or at least to limit, parasite dissemination upon oral infection withToxoplasma gondii. Innate immunity to this pathogen results from delicate interactions involving different components of the infecting agent and the host. We herein aimed to examine the molecular mechanism by which protozoan DNA boosts the production ofα-defensin-5 (DEFA-5), the main antimicrobial peptide at the target site of infection. The present study shows that DEFA-5 is rapidly upregulated in intestinal epithelial cells following intracellular Toll-like receptor 9 (TLR9) activation by unmethylated CpG motifs in DNA fromT. gondii(CpG-DNA). Concomitantly, CpG-DNA purified from the pathogen markedly increased TLR9 mRNA expression levels in the Caco-2 cell line. We further verified that DEFA-5 production was dependent on interferon-βreleased from these cells upon treatment with CpG-DNA prepared from tachyzoites. Our results suggest that, in protozoan DNA-stimulated intestinal epithelial cells, the TLR9/interferon-β/DEFA-5 pathway may initiate an innate anti-T. gondiiresponse without the need of parasite invasion. These findings highlight the key role of the gut epithelium in Toxoplasma recognition and amplification of local host defence against this microbe, thereby contributing to gain insight into immunoprotective mechanisms and to improve therapeutic strategies.

Identification of genes whose expression is altered by obesity throughout the arterial tree

We used next-generation RNA sequencing (RNA-Seq) technology on the whole transcriptome to identify genes whose expression is consistently affected by obesity across multiple arteries. Specifically, we examined transcriptional profiles of the iliac artery as well as the feed artery, first, second, and third branch order arterioles in the soleus, gastrocnemius, and diaphragm muscles from obese Otsuka Long-Evans Tokushima Fatty (OLETF) and lean Long-Evans Tokushima Otsuka (LETO) rats. Within the gastrocnemius and soleus muscles, the number of genes differentially expressed with obesity tended to increase with increasing branch order arteriole number (i.e., decreasing size of the artery). This trend was opposite in the diaphragm. We found a total of 15 genes that were consistently upregulated with obesity (MIS18A, CTRB1, FAM151B, FOLR2, PXMP4, OAS1B, SREBF2, KLRA17, SLC25A44, SNX10, SLFN3, MEF2BNB, IRF7, RAD23A, LGALS3BP) and five genes that were consistently downregulated with obesity (C2, GOLGA7, RIN3, PCP4, CYP2E1). A small fraction (∼9%) of the genes affected by obesity was modulated across all arteries examined. In conclusion, the present study identifies a select number of genes (i.e., 20 genes) whose expression is consistently altered throughout the arterial network in response to obesity and provides further insight into the heterogeneous vascular effects of obesity. Although there is no known direct function of the majority of 20 genes related to vascular health, the obesity-associated upregulation of SREBF2, LGALS3BP, IRF7, and FOLR2 across all arteries is suggestive of an unfavorable vascular phenotypic alteration with obesity. These data may serve as an important resource for identifying novel therapeutic targets against obesity-related vascular complications.

Efficacy of IFN-λ1 to protect human airway epithelial cells against human rhinovirus 1B infection

Impaired interferon (IFN) production has been observed in various obstructive respiratory diseases. This contributes to enhanced sensitivity towards viral infections triggering acute exacerbations. To compensate for this impaired host IFN response, there is need to explore new therapeutic strategies, like exogenous administration of IFNs as prophylactic treatment. In the present study, we examined the protective potential of IFN-λ1 and compared it with the previously established protecting effect of IFN-β. A549 cells and human primary bronchial epithelial cells were first treated with either IFN-β (500 IU/ml) or IFN-λ1 (500 ng/ml) for 18 h. For infection, two approaches were adopted: i) Continuous scenario: after pre-treatment, cells were infected immediately for 24 h with human rhinovirus 1B (HRV1B) in IFN-containing medium, or were cultured for another 72 h in IFN-containing medium, and then infected for 24 h with HRV1B, ii) Pre-treatment scenario: IFN-containing medium was replaced after 18 h and cells were infected for 4 h either immediately after pre-treatment or after additional culturing for 72 h in IFN-free medium. The protective effect was evaluated in terms of reduction in the number of viral copies/infectious progeny, and enhanced expression of IFN-stimulated genes (ISGs). In both cell types and in both approaches, IFN-λ1 and IFN-β treatment resulted in pronounced and long-lasting antiviral effects exemplified by significantly reduced viral copy numbers and diminished infectious progeny. This was associated with strong up-regulation of multiple ISGs. However, in contrast to the IFN-β induced expression of ISGs, which decreased over time, expression of ISGs induced by IFN-λ1 was sustained or even increased over time. Here we demonstrate that the protective potential of IFN-λ1 is comparable to IFN-β. Yet, the long-lasting induction of ISGs by IFN-λ1 and most likely less incitement of side effects due to more localized expression of its receptors could make it an even more promising candidate for prophylactic treatment than IFN-β.

Recent molecular insights into rickettsial pathogenesis and immunity

Human infections with arthropod-borne Rickettsia species remain a major global health issue, causing significant morbidity and mortality. Epidemic typhus due to Rickettsia prowazekii has an established reputation as the 'scourge of armies', and as a major determinant of significant 'historical turning points'. No suitable vaccines for human use are currently available to prevent rickettsial diseases. The unique lifestyle features of rickettsiae include obligate intracellular parasitism, intracytoplasmic niche within the host cell, predilection for infection of microvascular endothelium in mammalian hosts, association with arthropods and the tendency for genomic reduction. The fundamental research in the field of Rickettsiology has witnessed significant recent progress in the areas of pathogen adhesion/invasion and host immune responses, as well as the genomics, proteomics, metabolomics, phylogenetics, motility and molecular manipulation of important rickettsial pathogens. The focus of this review article is to capture a snapshot of the latest developments pertaining to the mechanisms of rickettsial pathogenesis and immunity.

Suppressor of cytokine signalling protein SOCS1 and UBP43 regulate the expression of type I interferon-stimulated genes in human microvascular endothelial cells infected with Rickettsia conorii

Rickettsia conorii, the causative agent of Mediterranean spotted fever, preferentially infects human microvascular endothelium and activates pro-inflammatory innate immune responses as evidenced by enhanced expression and secretion of cytokines and chemokines. Our recent studies reveal that human microvascular endothelial cells (HMECs) infected with R. conorii also launch 'antiviral' host defence mechanisms typically governed by type I interferons. To summarize, infected HMECs secrete IFN-β to activate STAT1 in an autocrine/paracrine manner and display increased expression of IFN-stimulated genes, for example ISG15, which in turn activate innate responses to interfere with intracellular replication of rickettsiae. We now present evidence that UBP43 and SOCS1, known negative regulators of JAK/STAT signalling, are also induced in R. conorii-infected HMECs, of which UBP43 but not SOCS1 functions to negatively regulate STAT1 activation. Interestingly, UBP43 induction is almost completely abolished in the presence of IFN-β-neutralizing antibody, implicating an important role for UBP43 as a feedback inhibitor for IFN-β-mediated STAT1 activation. In contrast, SOCS1 expression is only partially affected by IFN-β neutralization, implicating potential involvement of as-yet-unidentified IFN-independent mechanism(s) in SOCS1 induction during R. conorii infection. A number of IFN-stimulated genes, including ISG15, OAS1, MX1, IRF1, IRF9 and TAP1 are also induced in an IFN-β-dependent manner, whereas GBP1 remains unaffected by IFN-β neutralization. Increased STAT1 phosphorylation in HMECs subjected to UBP43 knockdown led to transcriptional activation of OAS1, MX1 and GBP1, confirming the negative regulatory role of UBP43. Although IRF1, IRF9 and TAP1 were induced by IFN-β, siRNA-mediated silencing of UBP43 or SOCS1 did not significantly affect their transcriptional activation. Expression of ISG15 was, however, increased in HMECs transfected with siRNA for UBP43 and SOCS1. Thus, unique regulatory patterns of induced expression of UBP43, SOCS1 and IFN-stimulated genes represent pathogen-specific responses underlying IFN-β-mediated host endothelial signalling during the pathogenesis of spotted fever group rickettsiosis.

The oncolytic activity of Newcastle disease virus in clear cell renal carcinoma cells in normoxic and hypoxic conditions: the interplay between von Hippel-Lindau and interferon-β signaling

Viral-mediated oncolysis is a promising cancer therapeutic approach offering an increased efficacy with less toxicity than the current therapies. The complexity of solid tumor microenvironments includes regions of hypoxia. In these regions, the transcription factor, hypoxia inducible factor (HIF), is active and regulates expression of many genes that contribute to aggressive malignancy, radio-, and chemo-resistance. To investigate the oncolytic efficacy of a highly virulent (velogenic) Newcastle disease virus (NDV) in the presence or absence of HIF-2α, renal cell carcinoma (RCC) cell lines with defective or reconstituted wild-type (wt) von Hippel-Lindau (VHL) activity were used. We show that these RCC cells responded to NDV by producing only interferon (IFN)-β, but not IFN-α, and are associated with increased STAT1 phosphorylation. Restoration of wt VHL expression enhanced NDV-induced IFN-β production, leading to prolonged STAT1 phosphorylation and increased cell death. Hypoxia augmented NDV oncolytic activity regardless of the cells' HIF-2α levels. These results highlight the potential of oncolytic NDV as a potent therapeutic agent in the killing of hypoxic cancer cells.

Rickettsia conorii infection stimulates the expression of ISG15 and ISG15 protease UBP43 in human microvascular endothelial cells

Rickettsia conorii, an obligate intracellular bacterium and the causative agent of Mediterranean spotted fever, preferentially infects microvascular endothelial cells of the mammalian hosts leading to onset of innate immune responses, characterized by the activation of intracellular signaling mechanisms, release of pro-inflammatory cytokines and chemokines, and killing of intracellular rickettsiae. Our recent studies have shown that interferon (IFN)-β, a cytokine traditionally considered to be involved in antiviral immunity, plays an important role in the autocrine/paracrine regulation of host defense mechanisms and control of R. conorii growth in the host endothelial cells. Here, we show that R. conorii infection induces the expression of ISG15 (an interferon-stimulated gene coding a protein of 17kD) and UBP43 (an ISG15-specific protease) at the levels of mRNA and protein and report the evidence of ISGylation of as yet unidentified target proteins in cultured human microvascular endothelium. Infection-induced expression of ISG15 and UBP43 requires intracellular replication of rickettsiae and production of IFN-β, because treatment with tetracycline and presence of an antibody capable of neutralizing IFN-β activity resulted in near complete attenuation of both responses. Inhibition of R. conorii-induced ISG15 by RNA interference results in significant increase in the extent of rickettsial replication, whereas UBP43 knockdown yields a reciprocal inhibitory effect. In tandem, these results demonstrate the stimulation of interferon-β-mediated innate immune mechanisms capable of perturbing the growth and replication of pathogenic rickettsiae and provide first evidence for ISG15-mediated post-translational modification of host cellular proteins during infection with an intracellular bacterium.