APOL1 C-Terminal Variants May Trigger Kidney Disease through Interference with APOL3 Control of Actomyosin

The C-terminal variants G1 and G2 of apolipoprotein L1 (APOL1) confer human resistance to the sleeping sickness parasite Trypanosoma rhodesiense, but they also increase the risk of kidney disease. APOL1 and APOL3 are death-promoting proteins that are partially associated with the endoplasmic reticulum and Golgi membranes. We report that in podocytes, either APOL1 C-terminal helix truncation (APOL1Δ) or APOL3 deletion (APOL3KO) induces similar actomyosin reorganization linked to the inhibition of phosphatidylinositol-4-phosphate [PI(4)P] synthesis by the Golgi PI(4)-kinase IIIB (PI4KB). Both APOL1 and APOL3 can form K+ channels, but only APOL3 exhibits Ca2+-dependent binding of high affinity to neuronal calcium sensor-1 (NCS-1), promoting NCS-1-PI4KB interaction and stimulating PI4KB activity. Alteration of the APOL1 C-terminal helix triggers APOL1 unfolding and increased binding to APOL3, affecting APOL3-NCS-1 interaction. Since the podocytes of G1 and G2 patients exhibit an APOL1Δ or APOL3KO-like phenotype, APOL1 C-terminal variants may induce kidney disease by preventing APOL3 from activating PI4KB, with consecutive actomyosin reorganization of podocytes.info:eu-repo/semantics/publishe

Thymus‐derived regulatory T cells restrain pro‐inflammatory Th1 responses by downregulating CD

The severity and intensity of autoimmune disease in Immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) patients and in scurfy mice emphasizes the critical role played by thymus-derived regulatory T cells (tTregs) in maintaining peripheral immune tolerance. However, although tTregs are critical to prevent lethal autoimmunity and excessive inflammatory responses, their suppressive mechanism remains elusive. Here we demonstrate that tTregs selectively inhibit CD27/CD70-dependent Th1 priming, while leaving the IL-12-dependent pathway unaffected. Immunized mice depleted of tTregs showed an increased response of IFN-γ-secreting CD4+ T cells that was strictly reliant on a functional CD27/CD70 pathway. In vitro studies revealed that tTregs downregulate CD70 from the plasma membrane of dendritic cells (DCs) in a CD27-dependent manner. CD70 downregulation required contact between Tregs and DCs and resulted in endocytosis of CD27 and CD70 into the DC. These findings reveal a novel mechanism by which tTregs can maintain tolerance or prevent excessive, proinflammatory Th1 responsesin pressSCOPUS: ar.jFLWINinfo:eu-repo/semantics/publishe

Brucella: Molecular Microbiology and Genomics

Brucella Quorum Sensing: Much More Than Sensing QuorumMatthieu Terwagne, Sophie Uzureau, and Jean-Jacques LetessonQuorum sensing is a regulatory system that allows bacteria to coordinate gene expression according to the local population density. Recently, we demonstrated that the virulence of the facultative intracellular bacteria Brucella depends on quorum sensing. Similar to other Gram negative bacteria, Brucellaquorum sensing utilizes the production and detection of N-acyl homoserine lactone as a signal. However, in Brucella, N-acyl homoserine lactone could serve to monitor the confinement state, a situation in which a single bacterium enclosed in a vacuole can be the quorum. Here, we present a current review covering the intricacies of quorum sensing in Brucella, highlighting the abilities of quorum sensing to influence both Brucella virulence and metabolism.0info:eu-repo/semantics/publishe

Mutations of the Quorum Sensing-Dependent Regulator VjbR Lead to Drastic Surface Modifications in Brucella melitensis▿

Successful establishment of infection by bacterial pathogens requires fine-tuning of virulence-related genes. Quorum sensing (QS) is a global regulation process based on the synthesis of, detection of, and response to small diffusible molecules, called N-acyl-homoserine lactones (AHL), in gram-negative bacteria. In numerous species, QS has been shown to regulate genes involved in the establishment of pathogenic interactions with the host. Brucella melitensis produces N-dodecanoyl homoserine lactones (C12-HSL), which down regulate the expression of flagellar genes and of the virB operon (encoding a type IV secretion system), both of which encode surface virulence factors. A QS-related regulator, called VjbR, was identified as a transcriptional activator of these genes. We hypothesized that VjbR mediates the C12-HSL effects described above. vjbR alleles mutated in the region coding for the AHL binding domain were constructed to test this hypothesis. These alleles expressed in trans in a ΔvjbR background behave as constitutive regulators both in vitro and in a cellular model of infection. Interestingly, the resulting B. melitensis strains, unable to respond to AHLs, aggregate spontaneously in liquid culture. Preliminary characterization of these strains showed altered expression of some outer membrane proteins and overproduction of a matrix-forming exopolysaccharide, suggesting for the first time that B. melitensis could form biofilms. Together, these results indicate that QS through VjbR is a major regulatory system of important cell surface structures of Brucella and as such plays a key role in host-pathogen interactions

Apolipoproteins L control cell death triggered by TLR3/TRIF signaling in dendritic cells.

Apolipoproteins L (ApoLs) are Bcl-2-like proteins expressed under inflammatory conditions in myeloid and endothelial cells. We found that Toll-like receptor (TLR) stimuli, particularly the viral mimetic poly(I:C), specifically induce ApoLs7/11 sub-families in murine CD8α(+)  dendritic cells (DCs). This induction requires the TLR3/TRIF signaling pathway and is dependent on IFN-β in all ApoLs sub-families except for ApoL7c. Poly(I:C) treatment of DCs is also associated with induction of both cell death and autophagy. ApoLs expression is related to promotion of DC death by poly(I:C), as ApoLs7/11 knock-down increases DC survival and ApoLs7 are associated with the anti-apoptotic protein Bcl-xL. Similarly, in human monocyte-derived DCs poly(I:C) induces both cell death and the expression of ApoLs, principally ApoL3. Finally, the BH3-like peptide of ApoLs appears to be involved in the DC death-promoting activity. We would like to propose that ApoLs are involved in cell death linked to activation of DCs by viral stimuli. This article is protected by copyright. All rights reserved.FLWINSCOPUS: ar.jinfo:eu-repo/semantics/publishe

The two-component system PrlS/PrlR of <em>Brucella melitensis</em> is required for persistence in mice and appears to respond to ionic strength

International audienceBacterial adaptation to environmental conditions is essential to ensure a maximal fitness in front of several stresses. In this context, two-component systems (TCS) represent a predominant signal transduction mechanism allowing stimuli sensing to mount an appropriate response. As facultative intracellular pathogens, Brucella spp. are facing various environmental conditions and an adequate response will warrant a successful infection process. Recently, bioinformatics analysis of Brucella genomes predicted a set of 15 bona fide TCS pairs among which some were previously investigated. In this report, we characterized a new TCS locus called prlS/R for probable proline sensor/regulator. It encodes a hybrid histidine kinase (PlrS) with a peculiar Na+/solute symporter N-terminal domain and a transcriptional regulator (belonging to the luxR family) (PrlR). In vitro, Brucella spp. with a functional PrlR/S system trigger the formation of bacterial aggregates that seems to be an adaptive response to a hypersaline environment while a prlS/R mutant does not. We identified the ionic strength as a possible signal sensed by this TCS. Finally, this work correlates the absence of functional PrlR/S system with the lack of hypersaline-induced aggregation in peculiar marine Brucella spp

Apoliporotein L3 interferes with endothelial tube formation via regulation of ERK1/2, FAK and Akt signaling pathway.

Endothelial cells are main actors in vascular homeostasis as they regulate vascular pressure and permeability as well as hemostasis and inflammation. Disturbed stimuli delivered to and by endothelial cells correlate with the so-called endothelial dysfunction and disrupt this homeostasis. As constituents of the inner layer of blood vessels, endothelial cells are also involved in angiogenesis. Apolipoprotein Ls (APOL) comprise a family of newly discovered apolipoproteins with yet poorly understood function, and are suggested to be involved in inflammatory processes and cell death mechanisms. Here we investigate the role of APOLs in endothelial cells stimulated with factors known to be involved in atherogenesis and their possible contribution to endothelial dysfunction with an emphasis on inflammation driven-angiogenesis in vitro.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Global Analysis of Quorum Sensing Targets in the Intracellular Pathogen <i>Brucella melitensis</i> 16 M

Many pathogenic bacteria use a regulatory process termed quorum sensing (QS) to produce and detect small diffusible molecules to synchronize gene expression within a population. In Gram-negative bacteria, the detection of, and response to, these molecules depends on transcriptional regulators belonging to the LuxR family. Such a system has been discovered in the intracellular pathogen <i>Brucella melitensis</i>, a Gram-negative bacterium responsible for brucellosis, a worldwide zoonosis that remains a serious public health concern in countries were the disease is endemic. Genes encoding two LuxR-type regulators, VjbR and BabR, have been identified in the genome of <i>B. melitensis</i> 16 M. A Δ<i>vjbR</i> mutant is highly attenuated in all experimental models of infection tested, suggesting a crucial role for QS in the virulence of <i>Brucella</i>. At present, no function has been attributed to BabR. The experiments described in this report indicate that 5% of the genes in the <i>B. melitensis</i> 16 M genome are regulated by VjbR and/or BabR, suggesting that QS is a global regulatory system in this bacterium. The overlap between BabR and VjbR targets suggest a cross-talk between these two regulators. Our results also demonstrate that VjbR and BabR regulate many genes and/or proteins involved in stress response, metabolism, and virulence, including those potentially involved in the adaptation of <i>Brucella</i> to the oxidative, pH, and nutritional stresses encountered within the host. These findings highlight the involvement of QS as a major regulatory system in <i>Brucella</i> and lead us to suggest that this regulatory system could participate in the spatial and sequential adaptation of <i>Brucella</i> strains to the host environment