Influence of Slc11a1 on the outcome of Salmonella enterica serovar Enteritidis infection in mice is associated with Th polarization

The SLC transporter in nutrient and metabolic sensing, regulation, and drug development

The prevalence of metabolic diseases is growing worldwide. Accumulating evidence suggests that solute carrier (SLC) transporters contribute to the etiology of various metabolic diseases. Consistent with metabolic characteristics, the top five organs in which SLC transporters are highly expressed are the kidney, brain, liver, gut, and heart. We aim to understand the molecular mechanisms of important SLC transporter-mediated physiological processes and their potentials as drug targets. SLC transporters serve as ‘metabolic gate’ of cells and mediate the transport of a wide range of essential nutrients and metabolites such as glucose, amino acids, vitamins, neurotransmitters, and inorganic/metal ions. Gene-modified animal models have demonstrated that SLC transporters participate in many important physiological functions including nutrient supply, metabolic transformation, energy homeostasis, tissue development, oxidative stress, host defense, and neurological regulation. Furthermore, the human genomic studies have identified that SLC transporters are susceptible or causative genes in various diseases like cancer, metabolic disease, cardiovascular disease, immunological disorders, and neurological dysfunction. Importantly, a number of SLC transporters have been successfully targeted for drug developments. This review will focus on the current understanding of SLCs in regulating physiology, nutrient sensing and uptake, and risk of diseases.

Enterobacteria and host resistance to infection

Enterobacteriaceae are a large family of Gram-negative, non-spore-forming bacteria. Although many species exist as part of the natural flora of animals including humans, some members are associated with both intestinal and extraintestinal diseases. In this review, we focus on members of this family that have important roles in human disease: Salmonella, Escherichia, Shigella, and Yersinia, providing a brief overview of the disease caused by these bacteria, highlighting the contribution of animal models to our understanding of their pathogenesis and of host genetic determinants involved in susceptibility or resistance to infection.

Solute carrier protein family 11 member 1 (Slc11a1) activation efficiently inhibits Leishmania donovani survival in host macrophages

Visceral leishmaniasis (kala-azar), a life threatening disease caused by L. donovani, is a latent threat to more than 147 million people living in disease endemic South East Asia region of the Indian subcontinent. The therapeutic option to control leishmanial infections are very limited, and at present comprise only two drugs, an antifungal amphotericin B and an antitumor miltefosine, which are also highly vulnerable for parasitic resistance. Therefore, identification and development of alternate control measures is an exigent requirement to control leishmanial infections. In this study, we report that functionally induced expression of solute carrier protein family 11 member 1 (Slc11a1), a transmembrane divalent cationic transporter recruited on the surface of phagolysosomes after phagocytosis of parasites, effectively inhibits Leishmania donovani growth in host macrophages. Further, the increased Slc11a1 functionality also resulted in increased production of NOx, TNF-α and IL-12 by activated macrophages. The findings of this study signify the importance of interplay between Slc11a1 expression and macrophages activation that can be effectively used to control of Leishmania growth and survival.

Genetic dissection of the ity3 locus identifies a role for ncf2 co-expression modules and suggests selp as a candidate gene underlying the ity3.2 locus

Typhoid fever and salmonellosis, which are caused by Salmonella typhi and typhimurium, respectively, are responsible for significant morbidity and mortality in both developed and developing countries. We model typhoid fever using mice infected with Salmonella typhimurium, which results in a systemic disease, whereby the outcome of infection is variable in different inbred strains of mice. This model recapitulates several clinical aspects of the human disease and allows the study of the host response to Salmonella typhimurium infection in vivo. Previous work in our laboratory has identified three loci (Ity, Ity2, and Ity3) in the wild-derived MOLF/Ei mice influencing survival after infection with Salmonella typhimurium. Fine mapping of the Ity3 locus indicated that two sub-loci contribute collectively to the susceptibility of B6.MOLF-Ity/Ity3 congenic mice to Salmonella infection. In the current paper, we provided further evidence supporting a role for Ncf2 (neutrophil cytosolic factor 2 a subunit of NADPH oxidase) as the gene underlying the Ity3.1 sub-locus. Gene expression profiling indicated that the Ity3.1 sub-locus defined a global gene expression signature with networks articulated around Ncf2. Furthermore, based on differential expression and complementation analysis using Selp (selectin-P) knock-out mice, Selp was identified as a strong candidate gene for the Ity3.2 sub-locus.

Fine-mapping and phenotypic analysis of the Ity3 Salmonella susceptibility locus identify a complex genetic structure

Experimental animal models of Salmonella infections have been widely used to identify genes important in the host immune response to infection. Using an F2 cross between the classical inbred strain C57BL/6J and the wild derived strain MOLF/Ei, we have previously identified Ity3 (Immunity to Typhimurium locus 3) as a locus contributing to the early susceptibility of MOLF/Ei mice to infection with Salmonella Typhimurium. We have also established a congenic strain (B6.MOLF-Ity/Ity3) with the MOLF/Ei Ity3 donor segment on a C57BL/6J background. The current study was designed to fine map and characterize functionally the Ity3 locus. We generated 12 recombinant sub-congenic strains that were characterized for susceptibility to infection, bacterial load in target organs, cytokine profile and anti-microbial mechanisms. These analyses showed that the impact of the Ity3 locus on survival and bacterial burden was stronger in male mice compared to female mice. Fine mapping of Ity3 indicated that two subloci contribute collectively to the susceptibility of B6.MOLF-Ity/Ity3 congenic mice to Salmonella infection. The Ity3.1 sublocus controls NADPH oxidase activity and is characterized by decreased ROS production, reduced inflammatory cytokine response and increased bacterial burden, thereby supporting a role for Ncf2 (neutrophil cytosolic factor 2 a subunit of NADPH oxidase) as the gene underlying this sublocus. The Ity3.2 sub-locus is characterized by a hyperresponsive inflammatory cytokine phenotype after exposure to Salmonella. Overall, this research provides support to the combined action of hormonal influences and complex genetic factors within the Ity3 locus in the innate immune response to Salmonella infection in wild-derived MOLF/Ei mice.

Functional validation of the genetic architecture of Salmonella Enteritidis persistence in 129S6 mice

The Gram-negative bacteria, Salmonella, cause a broad spectrum of clinical diseases in humans, ranging from asymptomatic carriage to life-threatening sepsis. We have designed an experimental model to study the contribution of genetic factors to the persistence of Salmonella Enteritidis during the late phase of infection in 129S6/SvEvTac and C57BL/6J mice. C57BL/6J mice cleared the bacteria from their reticuloendothelial system within a period of 42 days, whereas the 129S6 mice still presented a high bacterial load. Using this model, we have identified ten Salmonella Enteritidis susceptibility loci (Ses1, Ses1.1, and Ses3-Ses10) associated with bacterial persistence in target organs of 129S6/SvEvTac mice using a two-locus epistasis QTL linkage mapping approach. Significant statistical interactions were detected between Ses1 on chromosome 1 and Ses5 on chromosome 7 and between Ses1 and Ses4 on chromosome X. In this study, we functionally validated the genetic architecture of Salmonella persistence in 129S6 mice using single- (129S6.B6-Ses1.2 that combines Ses1 and Ses1.1 loci, 129S6.B6-Ses4, and 129S6.B6-Ses5) and double-congenic mice (129S6.B6-Ses1.2/Ses4 and 129S6.B6-Ses1.2/Ses5). These experiments demonstrate functional interactions between Ses1.2 and Ses4 or Ses5 that improve Salmonella Enteritidis clearance, validating the critical role played by gene-gene interactions in the contribution to bacterial clearance heritability. Improved bacterial clearance in double-congenic mice could be explained by the impact of Ses4 and Ses5 in combination with Ses1.2 on TH polarization since a TH2 bias (decreased Ifng and increased Il4 mRNA levels and reduced IgG2a immunoglobulins in the serum) was observed in 129S6.B6-Ses1.2/Ses5 mice and a TH17 (high Il17 expression) bias in 129S6.B6-Ses1.2/Ses4.

Salmonella's long-term relationship with its host

Host-adapted strains of Salmonella enterica cause systemic infections and have the ability to persist systemically for long periods of time and pose significant public-health problems. Multidrug-resistant S. enterica serovar Typhi (S. Typhi) and nontyphoidal Salmonella (NTS) are on the increase and are often associated with HIV infection. Chronically infected hosts are often asymptomatic and transmit disease to naïve hosts via fecal shedding of bacteria, thereby serving as a critical reservoir for disease. Salmonella utilizes multiple ways to evade and modulate host innate and adaptive immune responses in order to persist in the presence of a robust immune response. Survival in macrophages and modulation of immune cells migration allow Salmonella to evade various immune responses. The ability of Salmonella to persist depends on a balance between immune responses that lead to the clearance of the pathogen and avoidance of damage to host tissues.

Macrophage activation and differentiation signals regulate schlafen-4 gene expression: evidence for Schlafen-4 as a modulator of myelopoiesis

BACKGROUND

The ten mouse and six human members of the Schlafen (Slfn) gene family all contain an AAA domain. Little is known of their function, but previous studies suggest roles in immune cell development. In this report, we assessed Slfn regulation and function in macrophages, which are key cellular regulators of innate immunity.

METHODOLOGY/PRINCIPAL FINDINGS

Multiple members of the Slfn family were up-regulated in mouse bone marrow-derived macrophages (BMM) by the Toll-like Receptor (TLR)4 agonist lipopolysaccharide (LPS), the TLR3 agonist Poly(I∶C), and in disease-affected joints in the collagen-induced model of rheumatoid arthritis. Of these, the most inducible was Slfn4. TLR agonists that signal exclusively through the MyD88 adaptor protein had more modest effects on Slfn4 mRNA levels, thus implicating MyD88-independent signalling and autocrine interferon (IFN)-β in inducible expression. This was supported by the substantial reduction in basal and LPS-induced Slfn4 mRNA expression in IFNAR-1⁻/⁻ BMM. LPS causes growth arrest in macrophages, and other Slfn family genes have been implicated in growth control. Slfn4 mRNA levels were repressed during macrophage colony-stimulating factor (CSF-1)-mediated differentiation of bone marrow progenitors into BMM. To determine the role of Slfn4 in vivo, we over-expressed the gene specifically in macrophages in mice using a csf1r promoter-driven binary expression system. Transgenic over-expression of Slfn4 in myeloid cells did not alter macrophage colony formation or proliferation in vitro. Monocyte numbers, as well as inflammatory macrophages recruited to the peritoneal cavity, were reduced in transgenic mice that specifically over-expressed Slfn4, while macrophage numbers and hematopoietic activity were increased in the livers and spleens.

CONCLUSIONS

Slfn4 mRNA levels were up-regulated during macrophage activation but down-regulated during differentiation. Constitutive Slfn4 expression in the myeloid lineage in vivo perturbs myelopoiesis. We hypothesise that the down-regulation of Slfn4 gene expression during macrophage differentiation is a necessary step in development of this lineage.

Defining the immune response to Ehrlichia species using murine models

Pathogenic bacteria belonging to the family Anaplasmataceae include species of the genera Ehrlichia and Anaplasma. Ehrlichia chaffeensis, first known as the causative agent of human monocytic ehrlichiosis, also infects several vertebrate hosts including white-tailed deer, dogs, coyotes and goats. E. chaffeensis is transmitted from the bite of an infected hard tick, such as Amblyomma americanum. E. chaffeensis and other tick-transmitted pathogens have adapted to both the tick and vertebrate host cell environments. Although E. chaffeensis persists in both vertebrate and tick hosts for long periods of time, little is known about that process. Immunological studies will be valuable in assessing how the pathogen persists in nature in both vertebrate and invertebrate hosts. Understanding the host immune response to the pathogen originating from dual host backgrounds is also important to develop effective methods of diagnosis, control and treatment. In this paper, we provide our perspective of the current understanding of the immune response against E. chaffeensis in relation to other related Anaplasmataceae pathogens.

Toll-like receptors and cytokines in immune responses to persistent mycobacterial and Salmonella infections

Bacterial persistence is of major concern worldwide in the control of a number of bacterial infections. The carriers who are asymptomatic act as reservoirs of the bacteria. Knowledge of the host response, of the persistence process, and of the potential of biological mediators as diagnostic markers is essential towards development of prophylactic and treatment modalities for these diseases. Immune mechanisms related to recognition and elimination of the bacteria play pivotal roles in the control of bacterial infections. The majority of the studies on bacterial infections detail the immune mechanisms in the active phase of infection, and reports on the immune status in carriers are scanty. The present review describes the role of recognition molecules (TLRs) and the immune mediators (cytokines) in bacterial persistence. It appears that the TLR-mediated induction of cytokine profiles differs in active infection and bacterial persistence, with an active Th1 response being beneficial for the clearance of a high load of bacteria and at the same time conducive for the persistence of low bacterial load. Immunomodulation aiming at stimulation of the immune responses should be carried out with care as it could give rise to a carrier state in individuals with low load of the bacteria.

Subcellular localization of the Schlafen protein family

Although the first members of the Schlafen gene family were first described almost 10 years ago, the precise molecular/biochemical functions of the proteins they encode still remain largely unknown. Roles in cell growth, haematopoietic cell differentiation, and T cell development/maturation have, with some experimental support, been postulated, but none have been conclusively verified. Here, we have determined the subcellular localization of Schlafens 1, 2, 4, 5, 8, and 9, representing all three of the murine subgroups. We show that the proteins from subgroups I and II localize to the cytoplasm, while the longer forms in subgroup III localize exclusively to the nuclear compartment. We also demonstrate upregulation of Schlafen2 upon differentiation of haematopoietic cells and show this endogenous protein localizes to the cytoplasm. Thus, we propose the different subgroups of Schlafen proteins are likely to have functionally distinct roles, reflecting their differing localizations within the cell.

Genetics-squared: combining host and pathogen genetics in the analysis of innate immunity and bacterial virulence

The interaction of bacterial pathogens with their hosts' innate immune systems can be extremely complex and is often difficult to disentangle experimentally. Using mouse models of bacterial infections, several laboratories have successfully applied genetic approaches to identify novel host genes required for innate immune defense. In addition, a variety of creative bacterial genetic schemes have been developed to identify key bacterial genes involved in triggering or evading host immunity. In cases where both the host and pathogen are amenable to genetic manipulation, a combination of host and pathogen genetic approaches can be used. Focusing on bacterial infections of mice, this review summarizes the benefits and limitations of applying genetic analysis to the study of host-pathogen interactions. In particular, we consider how prokaryotic and eukaryotic genetic strategies can be combined, or "squared," to yield new insights in host-pathogen biology.

Molecular genetic analysis of two loci (Ity2 and Ity3) involved in the host response to infection with Salmonella typhimurium using congenic mice and expression profiling

Numerous genes have been identified to date that contribute to the host response to systemic Salmonella Typhimurium infection in mice. We have previously identified two loci, Ity2 and Ity3, that control survival to Salmonella infection in the wild-derived inbred MOLF/Ei mouse using a (C57BL/6J x MOLF/Ei)F(2)cross. We validated the existence of these two loci by creating congenic mice carrying each quantitative trait locus (QTL) in isolation. Subcongenic mice generated for each locus allowed us to define the critical intervals underlying Ity2 and Ity3. Furthermore, expression profiling was carried out with the aim of identifying differentially expressed genes within the critical intervals as potential candidate genes. Genomewide expression arrays were used to interrogate expression differences in the Ity2 congenics, leading to the identification of a new candidate gene (Havcr2, hepatitis A virus cellular receptor 2). Interval-specific oligonucleotide arrays were created for Ity3, identifying one potential candidate gene (Chi3l1, chitinase 3-like 1) to be pursued further. The combination of the use of congenics in QTL confirmation and fine mapping and in the identification of candidate genes by expression profiling has been successful and represents a step toward quantitative gene(s) identification.

Slc11a1, formerly Nramp1, is expressed in dendritic cells and influences major histocompatibility complex class II expression and antigen-presenting cell function

Solute carrier family 11 member a1 (Slc11a1; formerly Nramp1) encodes a late endosomal/lysosomal protein/divalent cation transporter that regulates iron homeostasis in macrophages. During macrophage activation, Slc11a1 has multiple pleiotropic effects on gene regulation and function, including gamma interferon-induced class II expression and antigen-presenting cell function. The wild-type allele at Slc11a1 has been associated with a bias in Th1 cell function in vivo, which is beneficial in resistance to infection against intracellular macrophage pathogens but detrimental in contributing to development of type 1 diabetes. The extent to which this depends on macrophage versus dendritic cell (DC) function is not known. Here we show that Slc11a1 is expressed in late endosomes and/or lysosomes of CD11c(+) DCs. DCs from mutant and congenic wild-type mice upregulate interleukin-12 (IL-12) and IL-10 mRNA in response to lipopolysaccharide (LPS) stimulation, but the ratio of IL-10 to IL-12 is higher in unstimulated DCs and DCs stimulated for 15 h with LPS from mutant mice than from wild-type mice. DCs from wild-type mice upregulate major histocompatibility complex class II in response to LPS more efficiently than DCs from mutant mice. Unstimulated DCs from wild-type and mutant mice present ovalbumin (OVA) peptide with an efficiency equivalent to that of an OVA-specific CD4 T-cell line, but DCs from wild-type mice are more efficient at processing and presenting OVA or Leishmania activator of cell kinase (LACK) protein to OVA- and LACK-specific T cells. These data indicate that wild-type Slc11a1 expressed in DCs may play a role both in determining resistance to infectious disease and in susceptibility to autoimmune disease such as type 1 diabetes.

Structure of GrlR and the implication of its EDED motif in mediating the regulation of type III secretion system in EHEC

Enterohemorrhagic Escherichia coli (EHEC) is a common cause of severe hemorrhagic colitis. EHEC's virulence is dependent upon a type III secretion system (TTSS) encoded by 41 genes. These genes are organized in several operons clustered in the locus of enterocyte effacement. Most of the locus of enterocyte effacement genes, including grlA and grlR, are positively regulated by Ler, and Ler expression is positively and negatively modulated by GrlA and GrlR, respectively. However, the molecular basis for the GrlA and GrlR activity is still elusive. We have determined the crystal structure of GrlR at 1.9 A resolution. It consists of a typical beta-barrel fold with eight beta-strands containing an internal hydrophobic cavity and a plug-like loop on one side of the barrel. Strong hydrophobic interactions between the two beta-barrels maintain the dimeric architecture of GrlR. Furthermore, a unique surface-exposed EDED (Glu-Asp-Glu-Asp) motif is identified to be critical for GrlA-GrlR interaction and for the repressive activity of GrlR. This study contributes a novel molecular insight into the mechanism of GrlR function.

Slc11a1 (formerly NRAMP1) gene modulates both acute inflammatory reactions and pristane-induced arthritis in mice

Mice selected for the maximum acute inflammatory reaction (AIRmax) are highly susceptible to pristane-induced arthritis (PIA), whereas mice selected for the minimum response (AIRmin) are resistant. These lines show distinct patterns of leukocyte infiltration and R and S allele frequency disequilibrium of the solute carrier family 11a member 1 (Slc11a1) gene. In order to study the interactions of the Slc11a1 R and S alleles with the inflammation modulating Quantitative Trait Loci (QTL) during PIA development, homozygous AIRmax(RR), AIRmax(SS), AIRmin(RR) and AIRmin(SS) lines were produced by genotype-assisted breedings. These mice received two intraperitoneal injections of 0.5 ml pristane at 60-day intervals, and the subsequent development of arthritis was assessed for 210 days. Cytokine-secreting cell profiles were investigated using enzyme-linked immunospot. Arthritis incidence in AIRmax(RR) mice reached 29%, whereas PIA incidence in AIRmax(SS) mice was 70% by day 180. AIRmin(RR) mice were resistant, whereas 13.3% of AIRmin(SS) mice became arthritic. The presence of the defective S allele also increased arthritis severity, although acute inflammation was higher in mice bearing the R allele. A predominant Th0/Th2-type response in Slc11a1(SS) mice was observed. These results indicate that Slc11a1 is a strong candidate for the QTL modulating acute inflammation and for PIA.

Caspase-1-mediated activation of interleukin-1beta (IL-1beta) and IL-18 contributes to innate immune defenses against Salmonella enterica serovar Typhimurium infection

Caspase-1 (Casp-1) mediates the processing of the proinflammatory cytokines interleukin-1beta (IL-1beta) and IL-18 to their mature forms. Casp-1-deficient mice succumb more rapidly to Salmonella challenge than do wild-type animals. Both Casp-1 substrates, IL-18 and IL-1beta, are relevant for control of Salmonella enterica serovar Typhimurium. We used IL-18-/- and IL-1beta-/- mice in addition to administration of recombinant IL-18 to Casp-1-/- mice to demonstrate that IL-18 is important for resistance to the systemic infection but not for resistance to the intestinal phase of the infection. This suggests that IL-1beta is critical for the intestinal phase of the disease. Thus, we show that Casp-1 is essential for host innate immune defense against S. enterica serovar Typhimurium and that Casp-1 substrates are required at distinct times and anatomical sites.