Adrenergic regulation of the vasculature impairs leukocyte interstitial migration and suppresses immune responses.

The sympathetic nervous system (SNS) controls various physiological functions via the neurotransmitter noradrenaline. Activation of the SNS in response to psychological or physical stress is frequently associated with weakened immunity. Here, we investigated how adrenoceptor signaling influences leukocyte behavior. Intravital two-photon imaging after injection of noradrenaline revealed transient inhibition of CD8+ and CD4+ T cell locomotion in tissues. Expression of ß-adrenergic receptor in hematopoietic cells was not required for NA-mediated inhibition of motility. Rather, chemogenetic activation of the SNS or treatment with adrenergic receptor agonists induced vasoconstriction and decreased local blood flow, resulting in abrupt hypoxia that triggered rapid calcium signaling in leukocytes and halted cell motility. Oxygen supplementation reversed these effects. Treatment with adrenergic receptor agonists impaired T cell responses induced in response to viral and parasitic infections, as well as anti-tumor responses. Thus, stimulation of the SNS impairs leukocyte mobility, providing a mechanistic understanding of the link between adrenergic receptors and compromised immunity.

An Optimized and Detailed Step-by-Step Protocol for the Analysis of Neuronal Morphology in Golgi-Stained Fetal Sheep Brain.

Antenatal brain development during the final trimester of human pregnancy is a time when mature neurons become increasingly complex in morphology, through axonal and dendritic outgrowth, dendritic branching, and synaptogenesis, together with myelin production. Characterizing neuronal morphological development over time is of interest to developmental neuroscience and provides the framework to measure gray matter pathology in pregnancy compromise. Neuronal microstructure can be assessed with Golgi staining, which selectively stains a small percentage (1-3%) of neurons and their entire dendritic arbor. Advanced imaging processing and analysis tools can then be employed to quantitate neuronal cytoarchitecture. Traditional Golgi-staining protocols have been optimized, and commercial kits are readily available offering improved speed and sensitivity of Golgi staining to produce consistent results. Golgi-stained tissue is then visualized under light microscopy and image analysis may be completed with several software programs for morphological analysis of neurons, including freeware and commercial products. Each program requires optimization, whether semiautomated or automated, requiring different levels of investigator intervention and interpretation, which is a critical consideration for unbiased analysis. Detailed protocols for fetal ovine brain tissue are lacking, and therefore, we provide a step-by-step workflow of computer software analysis for morphometric quantification of Golgi-stained neurons. Here, we utilized the commonly applied FD Rapid GolgiStain kit (FD NeuroTechnologies) on ovine fetal brains collected at 127 days (0.85) of gestational age for the analysis of CA1 pyramidal neurons in the hippocampus. We describe the step-by-step protocol to retrieve neuronal morphometrics using Imaris imaging software to provide quantification of apical and basal dendrites for measures of dendrite length (µm), branch number, branch order, and Sholl analysis (intersections over radius). We also detail software add-ons for data retrieval of dendritic spines including the number of spines, spine density, and spine classification, which are critical indicators of synaptic function. The assessment of neuronal morphology in the developing brain using Rapid-Golgi and Imaris software is labor-intensive, particularly during the optimization period. The methodology described in this step-by-step description is novel, detailed, and aims to provide a reproducible, working protocol to quantify neuronal cytoarchitecture with simple descriptions that will save time for the next users of these commonly used techniques.

SIDT1 Localizes to Endolysosomes and Mediates Double-Stranded RNA Transport into the Cytoplasm.

dsRNA is a common by-product of viral replication and acts as a potent trigger of antiviral immunity. SIDT1 and SIDT2 are closely related members of the SID-1 transmembrane family. SIDT2 functions as a dsRNA transporter and is required to traffic internalized dsRNA from endocytic compartments into the cytosol for innate immune activation, but the role of SIDT1 in dsRNA transport and in the innate immune response to viral infection is unclear. In this study, we show that Sidt1 expression is upregulated in response to dsRNA and type I IFN exposure and that SIDT1 interacts with SIDT2. Moreover, similar to SIDT2, SIDT1 localizes to the endolysosomal compartment, interacts with the long dsRNA analog poly(I:C), and, when overexpressed, enhances endosomal escape of poly(I:C) in vitro. To elucidate the role of SIDT1 in vivo, we generated SIDT1-deficient mice. Similar to Sidt2-/- mice, SIDT1-deficient mice produced significantly less type I IFN following infection with HSV type 1. In contrast to Sidt2-/- mice, however, SIDT1-deficient animals showed no impairment in survival postinfection with either HSV type 1 or encephalomyocarditis virus. Consistent with this, we observed that, unlike SIDT2, tissue expression of SIDT1 was relatively restricted, suggesting that, whereas SIDT1 can transport extracellular dsRNA into the cytoplasm following endocytosis in vitro, the transport activity of SIDT2 is likely to be functionally dominant in vivo.

NOD1 is required for Helicobacter pylori induction of IL-33 responses in gastric epithelial cells.

Helicobacter pylori (H. pylori) causes chronic inflammation which is a key precursor to gastric carcinogenesis. It has been suggested that H. pylori may limit this immunopathology by inducing the production of interleukin 33 (IL-33) in gastric epithelial cells, thus promoting T helper 2 immune responses. The molecular mechanism underlying IL-33 production in response to H. pylori infection, however, remains unknown. In this study, we demonstrate that H. pylori activates signalling via the pathogen recognition molecule Nucleotide-Binding Oligomerisation Domain-Containing Protein 1 (NOD1) and its adaptor protein receptor-interacting serine-threonine Kinase 2, to promote production of both full-length and processed IL-33 in gastric epithelial cells. Furthermore, IL-33 responses were dependent on the actions of the H. pylori Type IV secretion system, required for activation of the NOD1 pathway, as well as on the Type IV secretion system effector protein, CagA. Importantly, Nod1+/+ mice with chronic H. pylori infection exhibited significantly increased gastric IL-33 and splenic IL-13 responses, but decreased IFN-γ responses, when compared with Nod1-/- animals. Collectively, our data identify NOD1 as an important regulator of mucosal IL-33 responses in H. pylori infection. We suggest that NOD1 may play a role in protection against excessive inflammation.

ß2-Adrenoceptors on tumor cells play a critical role in stress-enhanced metastasis in a mouse model of breast cancer.

Chronic stress accelerates metastasis - the main cause of death in cancer patients - through the activation of ß-adrenoceptors (ßARs). We have previously shown that ß2AR signaling in MDA-MB-231(HM) breast cancer cells, facilitates invadopodia formation and invasion in vitro. However, in the tumor microenvironment where many stromal cells also express ßAR, the role of ß2AR signaling in tumor cells in metastasis is unclear. Therefore, to investigate the contribution of ß2AR signaling in tumor cells to metastasis in vivo, we used RNA interference to generate MDA-MB-231(HM) breast cancer cells that are deficient in ß2AR. ß2AR knockdown in tumor cells reduced the proportion of cells with a mesenchymal-like morphology and, as expected, reduced tumor cell invasion in vitro. Conversely, overexpression of ß2AR in low metastatic MCF-7 breast cancer cells induced an invasive phenotype. Importantly, we found that knockdown of ß2AR in tumor cells significantly reduced the impact of stress on metastasis in vivo. These findings highlight a crucial role for ß2AR tumor cell signaling in the adverse effects of stress on metastasis, and indicate that it may be necessary to block ß2AR on tumor cells to fully control metastatic progression.

ß2-adrenoceptor signaling regulates invadopodia formation to enhance tumor cell invasion.

INTRODUCTION: For efficient metastatic dissemination, tumor cells form invadopodia to degrade and move through three-dimensional extracellular matrix. However, little is known about the conditions that favor invadopodia formation. Here, we investigated the effect of ß-adrenoceptor signaling - which allows cells to respond to stress neurotransmitters - on the formation of invadopodia and examined the effect on tumor cell invasion. METHODS: To characterize the molecular and cellular mechanisms of ß-adrenergic signaling on the invasive properties of breast cancer cells, we used functional cellular assays to quantify invadopodia formation and to evaluate cell invasion in two-dimensional and three-dimensional environments. The functional significance of ß-adrenergic regulation of invadopodia was investigated in an orthotopic mouse model of spontaneous breast cancer metastasis. RESULTS: ß-adrenoceptor activation increased the frequency of invadopodia-positive tumor cells and the number of invadopodia per cell. The effects were selectively mediated by the ß2-adrenoceptor subtype, which signaled through the canonical Src pathway to regulate invadopodia formation. Increased invadopodia occurred at the expense of focal adhesion formation, resulting in a switch to increased tumor cell invasion through three-dimensional extracellular matrix. ß2-adrenoceptor signaling increased invasion of tumor cells from explanted primary tumors through surrounding extracellular matrix, suggesting a possible mechanism for the observed increased spontaneous tumor cell dissemination in vivo. Selective antagonism of ß2-adrenoceptors blocked invadopodia formation, suggesting a pharmacological strategy to prevent tumor cell dissemination. CONCLUSION: These findings provide insight into conditions that control tumor cell invasion by identifying signaling through ß2-adrenoceptors as a regulator of invadopodia formation. These findings suggest novel pharmacological strategies for intervention, by using ß-blockers to target ß2-adrenoceptors to limit tumor cell dissemination and metastasis.

Tropomyosin isoform 3 promotes the formation of filopodia by regulating the recruitment of actin-binding proteins to actin filaments.

Tropomyosins are believed to function in part by stabilizing actin filaments. However, accumulating evidence suggests that fundamental differences in function exist between tropomyosin isoforms, which contributes to the formation of functionally distinct filament populations. We investigated the functions of the high-molecular-weight isoform Tm3 and examined the molecular properties of Tm3-containing actin filament populations. Overexpression of the Tm3 isoform specifically induced the formation of filopodia and changes in actin solubility. We observed alterations in actin-binding protein recruitment to filaments, co-incident with changes in expression levels, which can account for this functional outcome. Tm3-associated filaments recruit active actin depolymerizing factor and are bundled into filopodia by fascin, which is both up-regulated and preferentially associated with Tm3-containing filaments in the Tm3 overexpressing cells. This study provides further insight into the isoform-specific roles of different tropomyosin isoforms. We conclude that variation in the tropomyosin isoform composition of microfilaments provides a mechanism to generate functionally distinct filament populations.

Microscopy Methods for Imaging MIF and Its Interaction Partners.

Fluorescence microscopy has become a powerful tool to investigate proteins in their natural environment. Well-established techniques like widefield and confocal fluorescence microscopy have commonly been used for decades to visualize biomolecules in single cells and tissue sections. Live cell microscopy allows for the investigation of biomolecular trafficking, and other specialized techniques, such as proximity ligation assays (PLA) and fluorescence lifetime imaging microscopy (FLIM), can be used to study interactions between biomolecules of interest. Finally, with the most recent rise of optical super-resolution microscopy, we can investigate target biomolecules in situ with unprecedented detail on the nanometer scale. Here, we discuss various optical microscopy techniques that have successfully been used to image MIF. We highlight applications, advantages, and limitations of each technique. The techniques described here can easily be adapted to investigate other target proteins, their localization, interaction partners, and mechanisms of action.

Tropomyosin isoforms define distinct microfilament populations with different drug susceptibility.

Two tropomyosin isoforms, human Tm5(NM1) and Tm3, were over-expressed in B35 rat neuro-epithelial cells to examine preferential associations between specific actin and tropomyosin isoforms and to determine the role tropomyosin isoforms play in regulating the drug susceptibility of actin filament populations. Immunofluorescence staining and Western blot analysis were used to study the organisation of specific filament populations and their response to treatment with two widely used actin-destabilising drugs, latrunculin A and cytochalasin D. In Tm5(NM1) cells, we observed large stress fibres which showed predominant co-localisation of beta-actin and low-molecular-weight gamma-tropomyosin isoforms. Tm3 cells had an abundance of cellular protrusions which contained both the beta- and gamma-actin isoforms, predominately populated by high-molecular-weight alpha- and beta-tropomyosin isoforms. The stress fibres observed in Tm5(NM1) cells were more resistant to both latrunculin A and cytochalasin D than filaments containing the high-molecular-weight tropomyosins observed in Tm3 cells. Knockdown of the over-expressed Tm5(NM1) isoform with a human-specific Tm5(NM1) siRNA reversed the phenotype and caused a reversal in the observed drug resistance. We conclude that there are preferential associations between specific actin and tropomyosin isoforms, which are cell type specific, but it is the tropomyosin composition of a filament population which determines the susceptibility to actin-targeting drugs.

Macrophage migration inhibitory factor is required for NLRP3 inflammasome activation.

Macrophage migration inhibitory factor (MIF) exerts multiple effects on immune cells, as well as having functions outside the immune system. MIF can promote inflammation through the induction of other cytokines, including TNF, IL-6, and IL-1 family cytokines. Here, we show that inhibition of MIF regulates the release of IL-1α, IL-1ß, and IL-18, not by affecting transcription or translation of these cytokines, but via activation of the NLRP3 inflammasome. MIF is required for the interaction between NLRP3 and the intermediate filament protein vimentin, which is critical for NLRP3 activation. Further, we demonstrate that MIF interacts with NLRP3, indicating a role for MIF in inflammasome activation independent of its role as a cytokine. These data advance our understanding of how MIF regulates inflammation and identify it as a factor critical for NLRP3 inflammasome activation.

Automated analysis of invadopodia dynamics in live cells.

Multiple cell types form specialized protein complexes that are used by the cell to actively degrade the surrounding extracellular matrix. These structures are called podosomes or invadopodia and collectively referred to as invadosomes. Due to their potential importance in both healthy physiology as well as in pathological conditions such as cancer, the characterization of these structures has been of increasing interest. Following early descriptions of invadopodia, assays were developed which labelled the matrix underneath metastatic cancer cells allowing for the assessment of invadopodia activity in motile cells. However, characterization of invadopodia using these methods has traditionally been done manually with time-consuming and potentially biased quantification methods, limiting the number of experiments and the quantity of data that can be analysed. We have developed a system to automate the segmentation, tracking and quantification of invadopodia in time-lapse fluorescence image sets at both the single invadopodia level and whole cell level. We rigorously tested the ability of the method to detect changes in invadopodia formation and dynamics through the use of well-characterized small molecule inhibitors, with known effects on invadopodia. Our results demonstrate the ability of this analysis method to quantify changes in invadopodia formation from live cell imaging data in a high throughput, automated manner.

Unraveling the enigma: progress towards understanding the coronin family of actin regulators.

Coronins are a conserved family of actin cytoskeleton regulators that promote cell motility and modulate other actin-dependent processes. Although these proteins have been known for 20 years, substantial progress has been made in the past 5 years towards their understanding. In this review, we examine this progress, place it into the context of what was already known, and pose several questions that remain to be addressed. In particular, we cover the emerging consensus about the role of Type I coronins in coordinating the function of Arp2/3 complex and ADF/cofilin proteins. This coordination plays an important role in leading-edge actin dynamics and overall cell motility. Finally, we discuss the roles played by the more exotic coronins of the Type II and III classes in cellular processes away from the leading edge.