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 grey 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 semi-automated 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) 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 labour-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.

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 β-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.

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.

β2-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 β-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 β-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 β-adrenergic regulation of invadopodia was investigated in an orthotopic mouse model of spontaneous breast cancer metastasis.

Results

β-adrenoceptor activation increased the frequency of invadopodia-positive tumor cells and the number of invadopodia per cell. The effects were selectively mediated by the β₂-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. β₂-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 β₂-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 β₂-adrenoceptors as a regulator of invadopodia formation. These findings suggest novel pharmacological strategies for intervention, by using β-blockers to target β₂-adrenoceptors to limit tumor cell dissemination and metastasis.

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.

Abstract B092: Beta-blockade of breast cancer metastasis: Receptor regulation and downstream signaling pathways

Chronic stress accelerates breast cancer metastasis through beta-adrenergic signaling and recent clinical studies found that beta-blockade reduced metastasis in women with breast cancer. However, the specific beta-adrenergic receptor subtype(s) through which stress-responsive neurotransmitters mediates effects on cancer remain unknown. To identify the receptor that transmits beta-adrenergic signaling to primary mammary tumors, we used bioluminescence imaging to longitudinally quantify the effect on metastasis of beta-blockers that selectively inhibit beta1 vs. beta 2 adrenergic receptors in an orthotopic mouse model of breast cancer progression. Non-specific beta-blockade with propranolol reduced metastasis by >90% (p = .03), confirming a key role for beta-adrenergic signaling pathways in stress-enhanced metastasis. Treatment with the beta2-selective antagonist ICI118551 similarly reduced stress-enhanced metastasis to control levels. In contrast, beta-1 selective blockade failed to protect against metastasis. Pharmacological intervention studies and gene expression analyses have started to define the downstream signaling pathways of beta-adrenergic regulation of metastasis. These studies may provide mechanistic explanation for recent clinical findings that not all beta-blockers protect against metastasis and provide a framework for selection of cancer patients who may optimally benefit from beta-blockade.

Citation Format: Ming Gene Chai, Caroline P. Le, Sarah J. Creed, Benjamin A L Finnin, Matthew A. Pimentel, David Shackleford, Andreas Moeller, Izhak Haviv, J. Robert Lane, Erica K. Sloan. Beta-blockade of breast cancer metastasis: Receptor regulation and downstream signaling pathways. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Breast Cancer Research: Genetics, Biology, and Clinical Applications; Oct 3-6, 2013; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2013;11(10 Suppl):Abstract nr B092.

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.

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.