Inflammasomes in Host Defense and Autoimmunity

Inflammasomes are large multi-protein complexes that control host defense and inflammation during infections with pathogens. Their clinical importance however reaches beyond infectious disease, since dysregulated inflammasome activity has also been linked to many auto-inflammatory disorders. This article gives a short overview on the basics of inflammasome signaling, their activation mechanisms and their role in autoimmunity

Noncanonical inflammasomes: caspase-11 activation and effector mechanisms

Inflammasomes are cytosolic, multiprotein complexes assembled by members of the NOD-like receptor (NLR) and PYHIN protein families in response to pathogen-associated molecular patterns (PAMPs) and danger signals, and serve as activation platforms for caspase-1. Recently, a new noncanonical inflammasome pathway has been described that activates caspase-11, an understudied pro-inflammatory caspase. Despite new insights into the signaling events that control caspase-11 activation, a number of unanswered questions remain..

ASC filament formation serves as a signal amplification mechanism for inflammasomes

A hallmark of inflammasome activation is the ASC speck, a micrometre-sized structure formed by the inflammasome adaptor protein ASC (apoptosis-associated speck-like protein containing a CARD), which consists of a pyrin domain (PYD) and a caspase recruitment domain (CARD). Here we show that assembly of the ASC speck involves oligomerization of ASC(PYD) into filaments and cross-linking of these filaments by ASC(CARD). ASC mutants with a non-functional CARD only assemble filaments but not specks, and moreover disrupt endogenous specks in primary macrophages. Systematic site-directed mutagenesis of ASC(PYD) is used to identify oligomerization-deficient ASC mutants and demonstrate that ASC speck formation is required for efficient processing of IL-1β, but dispensable for gasdermin-D cleavage and pyroptosis induction. Our results suggest that the oligomerization of ASC creates a multitude of potential caspase-1 activation sites, thus serving as a signal amplification mechanism for inflammasome-mediated cytokine production

Die Partei "Öffentliche Angelegenheiten"

Die Diplomarbeit beschäftigt sich mit der tschechischen politischen Partei „Öffentliche Angelegenheiten“ (Věci Veřejné (VV)). Es wird untersucht, ob sich die Partei nach genau festgelegten Kriterien, so wie sie die politikwissenschaftliche Disziplin versteht, als eine populistische Partei bezeichnen lässt. Im Weiteren wird der Frage nachgegangen, inwieweit die VV einen typischen populistischen Akteur der ostmitteleuropäischen Politik darstellt. Im theoretischen Teil wird zunächst auf das Phänomen des „politischen Populismus“ eingegangen. Ausgehend von einer Darstellung der historischen Entwicklung populistischer Parteien und der Reflexion über Populismusforschung, widmet sich die Arbeit der Festlegung von wissenschaftlichen Kriterien für populistische politische Akteure. Dabei werden auch Fragen der gesellschaftlichen Voraussetzungen für populistische Mobilisierung, sowie das komplizierte Verhältnis zwischen Populismus und Ideologie und Populismus und Demokratie mit einbezogen. Im zweiten Teil der Arbeit wird dann auf die Spezifika des ostmitteleuropäischen Populismus eingegangen, darüber hinaus werden auch eigene ausgewählte populistische Akteure der Region dargestellt. Im analytischen Teil wird zuerst die Partei „Öffentliche Angelegenheiten“ kurz vorgestellt, die Basisinformationen über die VV beinhalten sowie die bisherige politische Entwicklung, als auch die internen Organisations- und Entscheidungsstrukturen der Partei. Im Weiteren widmet sich die Arbeit anhand der im ersten Teil festgelegten Kriterien der Analyse der VV als einer populistischen Partei. Anschließend wird auch die Frage beantwortet, inwieweit die Partei den spezifischen Charakteristiken der ostmitteleuropäischen Populisten entspricht. Das Ziel der Diplomarbeit liegt also in der Analyse der VV als einen typischen Darsteller des ostmitteleuropäischen politischen Populismus.This thesis deals with the Czech political party “Public Affairs“ (Věci Veřejné (VV)). It attempts to analyze this party with the help of political populism concept. The main focus is on answering the question if VV could be marked according to clearly defined rules as a populist party. Furthermore, thesis continues with exploring the extent to which VV could be considered as a typical populist actor of Central–Eastern European politics. The theoretical part of the work is dedicated to phenomenon “political populism”. At first it maps the historical development of populist parties, as well as it summarizes research done so far on this topic. The main point of the theoretical part is then to develop clear definition criteria of populist parties, as they are defined in political science. In this context the subject of searching social causes of populist actors’ emergence and success cannot be forgotten, as well as complicated relationship between populism and ideology and populism and democracy. The second part of the work concentrates on the specifics of Central–Eastern European populism. Thereafter several populist parties from this region will be briefly introduced. The analytical part starts with describing “Věci Veřejné”. At first it focuses on the development of this party on the Czech political scene, secondly on its internal organizational and decision-making mechanisms. The main topic of the analytical part is analyzing to which content VV could be marked according to the criteria described in the first chapter as a typical Central-Eastern European populist party, which is the main goal of this thesis

Innate Immune Recognition of Francisella Tularensis: Activation of Type-I Interferons and the Inflammasome

Francisella tularensis is an intracellular pathogen that can cause severe disease in a wide range of mammalian hosts. Primarily residing in host macrophages, F. tularensis escapes phagosomal degradation, and replicates in the macrophage cytosol. The macrophage uses a series of pattern recognition receptors to detect conserved microbial molecules from invading pathogens, and initiates an appropriate host response. In the cytosol, F. tularensis is recognized by the inflammasome, a multiprotein complex responsible for the activation of the cysteine protease caspase-1. Caspase-1 activation leads to processing and release of proinflammatory cytokines and host cell death. Here we review recent work on the molecular mechanisms of inflammasome activation by F. tularensis, and its consequences both in vitro and in vivo. Finally, we discuss the coordination between the inflammasome and other cytosolic host responses, and the evidence for F. tularensis virulence factors that suppress inflammasome activation

Protective Anti-V Antibodies Inhibit Pseudomonas and Yersinia Translocon Assembly within Host Membranes

Pathogenic Yersinia species and Pseudomonas aeruginosa share a similar type III secretion/translocation system. The translocation system consists of 3 secreted proteins, YopB/PopB, YopD/PopD, and LcrV/PcrV; the latter is known to be a protective antigen. In an in vitro assay, the translocation system causes the lysis of erythrocytes infected with wild-type (wt) P. aeruginosa. wt Y. enterocolitica is not hemolytic, but a multiknockout mutant deprived of all the effectors and of YopN (ΔHOPEMN) is hemolytic. In the presence of antibodies against PcrV and Y. pestis LcrV, the hemolytic activity of P. aeruginosa was inhibited. Similarly, the hemolytic activity of ΔHOPEMN was inhibited in the presence of anti-LcrV antibodies. The assembly of the translocon, composed of PopB/D and YopB/D proteins, was disturbed in immunoprotected erythrocyte membranes, mimicking the phenotypes of V knockout mutants. Thus, protective antibodies against the V antigens of Yersinia species and P. aeruginosa act at the level of the formation of the translocon pore in membranes of infected host cells by blocking the function of LcrV/PcrV. The hemolysis assay could be adapted for high-throughput screening of anti-infectious compounds that specifically target the type III transloco

GSDMD membrane pore formation constitutes the mechanism of pyroptotic cell death

Pyroptosis is a lytic type of cell death that is initiated by inflammatory caspases. These caspases are activated within multi-protein inflammasome complexes that assemble in response to pathogens and endogenous danger signals. Pyroptotic cell death has been proposed to proceed via the formation of a plasma membrane pore, but the underlying molecular mechanism has remained unclear. Recently, gasdermin D (GSDMD), a member of the ill-characterized gasdermin protein family, was identified as a caspase substrate and an essential mediator of pyroptosis. GSDMD is thus a candidate for pyroptotic pore formation. Here, we characterize GSDMD function in live cells and in vitro We show that the N-terminal fragment of caspase-1-cleaved GSDMD rapidly targets the membrane fraction of macrophages and that it induces the formation of a plasma membrane pore. In vitro, the N-terminal fragment of caspase-1-cleaved recombinant GSDMD tightly binds liposomes and forms large permeability pores. Visualization of liposome-inserted GSDMD at nanometer resolution by cryo-electron and atomic force microscopy shows circular pores with variable ring diameters around 20 nm. Overall, these data demonstrate that GSDMD is the direct and final executor of pyroptotic cell death