Neutrophil chemotaxis in a patient with neonatal-onset multisystem inflammatory disease and Muckle-Wells syndrome

A Pro-Inflammatory Signature Constitutively Activated in Monogenic Autoinflammatory Diseases

Autoinflammatory diseases (AIDs) are disorders characterised by recurrent inflammatory episodes in charge of different organs with no apparent involvement of autoantibodies or antigen-specific T lymphocytes. Few common clinical features have been identified among all monogenic AIDs (mAIDs), while the search for a common molecular pattern is still ongoing. The aim of this study was to increase knowledge on the inflammatory pathways in the development of mAIDs in order to identify possible predictive or diagnostic biomarkers for each disease and to develop future preventive and therapeutic strategies. Using protein array-based systems, we evaluated two signalling pathways known to be involved in inflammation and a wide range of inflammatory mediators (pro-inflammatory cytokines and chemokines) in a cohort of 23 patients affected by different mAIDs, as FMF, TRAPS, MKD, Blau syndrome (BS), and NLRP12D. Overall, we observed upregulation of multiple signalling pathway intermediates at protein levels in mAIDs patients’ PBMCs, compared with healthy controls, with significant differences also between patients. FMF, TRAPS, and BS presented also peculiar activations of inflammatory pathways that can distinguish them. MAPK pathway activation, however, seems to be a common feature. The serum level of cytokines and chemokines produced clear differences between patients with distinct diseases, which can help distinguish each autoinflammatory disease. The FMF cytokine production profile appears broader than that of TRAPS, which, in turn, has higher cytokine levels than BS. Our findings suggest an ongoing subclinical inflammation related to the abnormal and constitutive signalling pathways and define an elevated inflammatory cytokine signature. Moreover, the upregulation of Th17-related cytokines emphasises the important role for Th17 and/or Th17-like cells also in monogenic AIDs.

Holding the inflammatory system in check: NLRs keep it cool

Inflammation is a double-edged sword. While short-lived, acute inflammation is essential for the repair and resolution of infection and damage, uncontrolled and unresolved chronic inflammation is central to several diseases, including cancer, autoimmune diseases, allergy, metabolic disease, and cardiovascular disease. This report aims to review the literature regarding several members of the nucleotide-binding domain, leucine-rich repeat-containing receptor (NLR) family of pattern recognition sensors/receptors that serve as checkpoints for inflammation. Understanding the negative regulation of inflammation is highly relevant to the development of therapeutics for inflammatory as well as infectious diseases.

The F-BAR protein PSTPIP1 controls extracellular matrix degradation and filopodia formation in macrophages

PSTPIP1 is a cytoskeletal adaptor and F-BAR protein that has been implicated in autoinflammatory disease, most notably in the PAPA syndrome: pyogenic sterile arthritis, pyoderma gangrenosum, and acne. However, the mechanism by which PSTPIP1 regulates the actin cytoskeleton and contributes to disease pathogenesis remains elusive. Here, we show that endogenous PSTPIP1 negatively regulates macrophage podosome organization and matrix degradation. We identify a novel PSTPIP1-R405C mutation in a patient presenting with aggressive pyoderma gangrenosum. Identification of this mutation reveals that PSTPIP1 regulates the balance of podosomes and filopodia in macrophages. The PSTPIP1-R405C mutation is in the SRC homology 3 (SH3) domain and impairs Wiskott-Aldrich syndrome protein (WASP) binding, but it does not affect interaction with protein-tyrosine phosphatase (PTP)-PEST. Accordingly, WASP inhibition reverses the elevated F-actin content, filopodia formation, and matrix degradation induced by PSTPIP1-R405C. Our results uncover a novel role for PSTPIP1 and WASP in orchestrating different types of actin-based protrusions. Our findings implicate the cytoskeletal regulatory functions of PSTPIP1 in the pathogenesis of pyoderma gangrenosum and suggest that the cytoskeleton is a rational target for therapeutic intervention in autoinflammatory disease.

The role of microtubules in neutrophil polarity and migration in live zebrafish

Microtubules control cell motility by positively regulating polarization in many cell types. However, how microtubules regulate leukocyte migration is not well understood, particularly in living organisms. Here we exploited the zebrafish system to study the role of microtubules in neutrophil migration in vivo. The localization of microtubules was visualized in motile neutrophils using various bioprobes, revealing that, in contrast to what has been seen in studies in vitro, the microtubule organizing center is positioned in front of the nucleus (relative to the direction of migration) in motile neutrophils. Microtubule disassembly impaired attraction of neutrophils to wounds but enhanced the polarity of F-actin dynamics as measured by the distribution of stable and dynamic F-actin. Microtubule depolymerization inhibited polarized phosphoinositol 3-kinase (PI(3)K) activation at the leading edge and induced rapid PI(3)K independent motility. Finally, we show that microtubules exert their effects on neutrophil polarity and motility at least in part by the negative regulation of both Rho and Rac activity. These results provide new insight into the role of microtubules in neutrophil migration in a living vertebrate and show that the motility of these professional migratory cells are subject to distinctly different rules from those established for other cell types.

NLRP3 inflammasome plays a key role in the regulation of intestinal homeostasis

BACKGROUND

Attenuated innate immune responses to the intestinal microbiota have been linked to the pathogenesis of Crohn's disease (CD). Recent genetic studies have revealed that hypofunctional mutations of NLRP3, a member of the NOD-like receptor (NLR) superfamily, are associated with an increased risk of developing CD. NLRP3 is a key component of the inflammasome, an intracellular danger sensor of the innate immune system. When activated, the inflammasome triggers caspase-1-dependent processing of inflammatory mediators, such as IL-1β and IL-18.

METHODS

In the current study we sought to assess the role of the NLRP3 inflammasome in the maintenance of intestinal homeostasis through its regulation of innate protective processes. To investigate this role, Nlrp3(-/-) and wildtype mice were assessed in the dextran sulfate sodium and 2,4,6-trinitrobenzenesulfonic acid models of experimental colitis.

RESULTS

Nlrp3(-/-) mice were found to be more susceptible to experimental colitis, an observation that was associated with reduced IL-1β, reduced antiinflammatory cytokine IL-10, and reduced protective growth factor TGF-β. Macrophages isolated from Nlrp3(-/-) mice failed to respond to bacterial muramyl dipeptide. Furthermore, Nlrp3-deficient neutrophils exhibited reduced chemotaxis and enhanced spontaneous apoptosis, but no change in oxidative burst. Lastly, Nlrp3(-/-) mice displayed altered colonic β-defensin expression, reduced colonic antimicrobial secretions, and a unique intestinal microbiota.

CONCLUSIONS

Our data confirm an essential role for the NLRP3 inflammasome in the regulation of intestinal homeostasis and provide biological insight into disease mechanisms associated with increased risk of CD in individuals with NLRP3 mutations.

The role of inflammatory cytokines and NF-kappaB/MAPK signaling pathways in the evolution of familial Mediterranean fever: current clinical perspectives and potential therapeutic approaches

Familial Mediterranean fever (FMF) is one of the social and health care problems for several populations that is known as a historically endemic disease of inflammatory nature. FMF, albeit a rare disorder, is characterized by recurrent fevers and painful inflammation of various body parts, especially the abdomen, lungs, and joints. FMF is typically characterized by inflammation of the abdominal lining (peritonitis), inflammation of the lining surrounding the lungs (pleurisy), painful, swollen joints (arthralgia and occasionally arthritis), and a characteristic ankle rash, a condition that is referred to as recurrent polyserositis, or familial paroxysmal polyserositis. Moreover, FMF is an inherited inflammatory disorder usually occurring in people of Mediterranean origin - including Sephardic Jews, Arabs, Armenians, and Turks; but it may ostensibly affect any other ethnic group, however, rarely. While there's no cure for this disorder, FMF is typically diagnosed during childhood, and signs and symptoms are treatable - or even preventable - by specialized medical attrition. The inflammatory signaling pathways associated with the evolution of FMF are currently being unraveled has that has therapeutic repercussions. In this review, I recap major concepts associated with the cellular and molecular immunology of FMF, especially shedding light on the likely roles of inflammatory cytokines, the transcription factor nuclear factor (NF)-kappaB, and the superfamily of mitogen-activated protein kinases (MAPKs). Furthermore, I summarize current advances for the clinical treatments available for FMF.

Analysis of neutrophil polarization and chemotaxis

Neutrophil polarization and directed migration (chemotaxis) are critical for the inflammatory response. Neutrophil chemotaxis is achieved by the sensing of narrow gradients of chemoattractant and the subsequent polarization and directed migration toward the chemotactic source. Despite recent progress, the signaling mechanisms that regulate neutrophil polarization during chemotaxis have not been clearly defined. Here, we describe methods to analyze neutrophil polarization and asymmetric redistribution of signaling components induced by chemoattractant using immunofluorescence. Further, methods are described to dissect the role of specific signaling pathways during chemotaxis by the use of murine neutrophils from transgenic mouse models. Finally, methods for time-lapse microscopy and transwell assay for the analysis of neutrophil chemotaxis will also be discussed.

The PCH family member proline-serine-threonine phosphatase-interacting protein 1 targets to the leukocyte uropod and regulates directed cell migration

Pombe Cdc15 homology (PCH) family members have emerged as important regulators of membrane-cytoskeletal interactions. Here we show that PSTPIP1, a PCH family member expressed in hematopoietic cells, regulates the motility of neutrophil-like cells and is a novel component of the leukocyte uropod where it colocalizes with other uropod components, such as type I PIPKIgamma. Furthermore, we show that PSTPIP1 association with the regulator of endocytosis, dynamin 2, and PSTPIP1 expression impairs transferrin uptake and endocytosis. We also show that PSTPIP1 localizes at the rear of neutrophils with a subpopulation of F-actin that is specifically detected by the binding of an F-actin probe that detects a more stable population of actin. Finally, we show that actin polymerization, but not the microtubule network, is necessary for the polarized distribution of PSTPIP1 toward the rear of the cell. Together, our findings demonstrate that PSTPIP1 is a novel component of the leukocyte uropod that regulates endocytosis and cell migration.

Resolution of inflammation by retrograde chemotaxis of neutrophils in transgenic zebrafish

Neutrophil chemotaxis to sites of inflammation is a critical process during normal immune responses to tissue injury and infection and pathological immune responses leading to chronic inflammation. Although progress has been made in understanding the mechanisms that promote neutrophil recruitment to inflamed tissue, the mechanisms that regulate the resolution phase of the inflammatory response have remained relatively elusive. To define the mechanisms that regulate neutrophil-mediated inflammation in vivo, we have developed a novel transgenic zebrafish in which the neutrophils express GFP under control of the myeloperoxidase promoter (zMPO:GFP). Tissue injury induces a robust, inflammatory response, which is characterized by the rapid chemotaxis of neutrophils to the wound site. In vivo time-lapse imaging shows that neutrophils subsequently display directed retrograde chemotaxis back toward the vasculature. These findings implicate retrograde chemotaxis as a novel mechanism that regulates the resolution phase of the inflammatory response. The zMPO:GFP zebrafish provides unique insight into the mechanisms of neutrophil-mediated inflammation and thereby offers opportunities to identify new regulators of the inflammatory response in vivo.