μ-Slide Chemotaxis: a new chamber for long-term chemotaxis studies

A microphysiological system reveals neutrophil contact-dependent attenuation of pancreatic tumor progression by CXCR2 inhibition-based immunotherapy

Cancer cells recruit neutrophils from the bloodstream into the tumor tissue, where these immune cells promote the progression of numerous solid tumors. Studies in mice suggest that blocking neutrophil recruitment to tumors by inhibition of neutrophil chemokine receptor CXCR2 could be a potential immunotherapy for pancreatic cancer. Yet, the mechanisms by which neutrophils promote tumor progression in humans, as well as how CXCR2 inhibition could potentially serve as a cancer therapy, remain elusive. In this study, we developed a human cell-based microphysiological system to quantify neutrophil-tumor spheroid interactions in both "separated" and "contact" scenarios. We found that neutrophils promote the invasion of tumor spheroids through the secretion of soluble factors and direct contact with cancer cells. However, they promote the proliferation of tumor spheroids solely through direct contact. Interestingly, treatment with AZD-5069, a CXCR2 inhibitor, attenuates invasion and proliferation of tumor spheroids by blocking direct contact with neutrophils. Our findings also show that CXCR2 inhibition reduces neutrophil migration toward tumor spheroids. These results shed new light on the tumor-promoting mechanisms of human neutrophils and the tumor-suppressive mechanisms of CXCR2 inhibition in pancreatic cancer and may aid in the design and optimization of novel immunotherapeutic strategies based on neutrophils.

Neutrophil-specific expression of JAK2-V617F or CALRmut induces distinct inflammatory profiles in myeloproliferative neoplasia

BACKGROUND

Neutrophils play a crucial role in inflammation and in the increased thrombotic risk in myeloproliferative neoplasms (MPNs). We have investigated how neutrophil-specific expression of JAK2-V617F or CALRdel re-programs the functions of neutrophils.

METHODS

Ly6G-Cre JAK2-V617F and Ly6G-Cre CALRdel mice were generated. MPN parameters as blood counts, splenomegaly and bone marrow histology were compared to wild-type mice. Megakaryocyte differentiation was investigated using lineage-negative bone marrow cells upon in vitro incubation with TPO/IL-1β. Cytokine concentrations in serum of mice were determined by Mouse Cytokine Array. IL-1α expression in various hematopoietic cell populations was determined by intracellular FACS analysis. RNA-seq to analyse gene expression of inflammatory cytokines was performed in isolated neutrophils from JAK2-V617F and CALR-mutated mice and patients. Bioenergetics of neutrophils were recorded on a Seahorse extracellular flux analyzer. Cell motility of neutrophils was monitored in vitro (time lapse microscopy), and in vivo (two-photon microscopy) upon creating an inflammatory environment. Cell adhesion to integrins, E-selectin and P-selection was investigated in-vitro. Statistical analysis was carried out using GraphPad Prism. Data are shown as mean ± SEM. Unpaired, two-tailed t-tests were applied.

RESULTS

Strikingly, neutrophil-specific expression of JAK2-V617F, but not CALRdel, was sufficient to induce pro-inflammatory cytokines including IL-1 in serum of mice. RNA-seq analysis in neutrophils from JAK2-V617F mice and patients revealed a distinct inflammatory chemokine signature which was not expressed in CALR-mutant neutrophils. In addition, IL-1 response genes were significantly enriched in neutrophils of JAK2-V617F patients as compared to CALR-mutant patients. Thus, JAK2-V617F positive neutrophils, but not CALR-mutant neutrophils, are pathogenic drivers of inflammation in MPN. In line with this, expression of JAK2-V617F or CALRdel elicited a significant difference in the metabolic phenotype of neutrophils, suggesting a stronger inflammatory activity of JAK2-V617F cells. Furthermore, JAK2-V617F, but not CALRdel, induced a VLA4 integrin-mediated adhesive phenotype in neutrophils. This resulted in reduced neutrophil migration in vitro and in an inflamed vessel. This mechanism may contribute to the increased thrombotic risk of JAK2-V617F patients compared to CALR-mutant individuals.

CONCLUSIONS

Taken together, our findings highlight genotype-specific differences in MPN-neutrophils that have implications for the differential pathophysiology of JAK2-V617F versus CALR-mutant disease.

Methods and computational tools to study eukaryotic cell migration in vitro

Cellular movement is essential for many vital biological functions where it plays a pivotal role both at the single cell level, such as during division or differentiation, and at the macroscopic level within tissues, where coordinated migration is crucial for proper morphogenesis. It also has an impact on various pathological processes, one for all, cancer spreading. Cell migration is a complex phenomenon and diverse experimental methods have been developed aimed at dissecting and analysing its distinct facets independently. In parallel, corresponding analytical procedures and tools have been devised to gain deep insight and interpret experimental results. Here we review established experimental techniques designed to investigate specific aspects of cell migration and present a broad collection of historical as well as cutting-edge computational tools used in quantitative analysis of cell motion.

STIM1-dependent store-operated calcium entry mediates sex differences in macrophage chemotaxis and monocyte recruitment

Infiltration of monocyte-derived cells to sites of infection and injury is greater in males than in females, due in part, to increased chemotaxis, the process of directed cell movement toward a chemical signal. The mechanisms governing sexual dimorphism in chemotaxis are not known. We hypothesized a role for the store-operated calcium entry (SOCE) pathway in regulating chemotaxis by modulating leading and trailing edge membrane dynamics. We measured the chemotactic response of bone marrow-derived macrophages migrating toward complement component 5a (C5a). Chemotactic ability was dependent on sex and inflammatory phenotype (M0, M1, and M2), and correlated with SOCE. Notably, females exhibited a significantly lower magnitude of SOCE than males. When we knocked out the SOCE gene, stromal interaction molecule 1 (STIM1), it eliminated SOCE and equalized chemotaxis across both sexes. Analysis of membrane dynamics at the leading and trailing edges showed that STIM1 influences chemotaxis by facilitating retraction of the trailing edge. Using BTP2 to pharmacologically inhibit SOCE mirrored the effects of STIM1 knockout, demonstrating a central role of STIM/Orai-mediated calcium signaling. Importantly, by monitoring the recruitment of adoptively transferred monocytes in an in vivo model of peritonitis, we show that increased infiltration of male monocytes during infection is dependent on STIM1. These data support a model in which STIM1-dependent SOCE is necessary and sufficient for mediating the sex difference in monocyte recruitment and macrophage chemotactic ability by regulating trailing edge dynamics.

VC-resist glioblastoma cell state: vessel co-option as a key driver of chemoradiation resistance

Glioblastoma (GBM) is a highly lethal type of cancer. GBM recurrence following chemoradiation is typically attributed to the regrowth of invasive and resistant cells. Therefore, there is a pressing need to gain a deeper understanding of the mechanisms underlying GBM resistance to chemoradiation and its ability to infiltrate. Using a combination of transcriptomic, proteomic, and phosphoproteomic analyses, longitudinal imaging, organotypic cultures, functional assays, animal studies, and clinical data analyses, we demonstrate that chemoradiation and brain vasculature induce cell transition to a functional state named VC-Resist (vessel co-opting and resistant cell state). This cell state is midway along the transcriptomic axis between proneural and mesenchymal GBM cells and is closer to the AC/MES1-like state. VC-Resist GBM cells are highly vessel co-opting, allowing significant infiltration into the surrounding brain tissue and homing to the perivascular niche, which in turn induces even more VC-Resist transition. The molecular and functional characteristics of this FGFR1-YAP1-dependent GBM cell state, including resistance to DNA damage, enrichment in the G2M phase, and induction of senescence/stemness pathways, contribute to its enhanced resistance to chemoradiation. These findings demonstrate how vessel co-option, perivascular niche, and GBM cell plasticity jointly drive resistance to therapy during GBM recurrence.

Rat primary cortical cell tri-culture to study effects of amyloid-beta on microglia function

Introduction

The etiology and progression of sporadic Alzheimer's Disease (AD) have been studied for decades. One proposed mechanism is that amyloid-beta (Aβ) proteins induce neuroinflammation, synapse loss, and neuronal cell death. Microglia play an especially important role in Aβ clearance, and alterations in microglial function due to aging or disease may result in Aβ accumulation and deleterious effects on neuronal function. However, studying these complex factors in vivo , where numerous confounding processes exist, is challenging, and until recently, in vitro models have not allowed sustained culture of microglia, astrocytes and neurons in the same culture. Here, we employ a tri-culture model of rat primary neurons, astrocytes, and microglia and compare it to co-culture (neurons and astrocytes) and mono-culture enriched for microglia to study microglial function (i.e., motility and Aβ clearance) and proteomic response to exogenous Aβ.

Methods

We established cortical co-culture (neurons and astrocytes), tri-culture (neurons, astrocytes, and microglia), and mono-culture (microglia) from perinatal rat pups. On days in vitro (DIV) 7 - 14, the cultures were exposed to fluorescently-labeled Aβ (FITC-Aβ) particles for varying durations. Images were analyzed to determine the number of FITC-Aβ particles after specific lengths of exposure. A group of cells were stained for βIII-tubulin, GFAP, and Iba1 for morphological analysis via quantitative fluorescence microscopy. Cytokine profiles from conditioned media were obtained. Live-cell imaging with images acquired every 5 minutes for 4 hours was employed to extract microglia motility parameters (e.g., Euclidean distance, migration speed, directionality ratio).

Results and discussion

FITC-Aβ particles were more effectively cleared in the tri-culture compared to the co-culture. This was attributed to microglia engulfing FITC-Aβ particles, as confirmed via epifluorescence and confocal microscopy. Adding FITC-Aβ significantly increased the size of microglia, but had no significant effect on neuronal surface coverage or astrocyte size. Analysis of the cytokine profile upon FITC-Aβ addition revealed a significant increase in proinflammatory cytokines (TNF-α, IL-1α, IL-1β, IL-6) in tri-culture, but not co-culture. In addition, Aβ addition altered microglia motility marked by swarming-like motion with decreased Euclidean distance yet unaltered speed. These results highlight the importance of cell-cell communication in microglia function (e.g., motility and Aβ clearance) and the utility of the tri-culture model to further investigate microglia dysfunction in AD.

Oncogenic KRAS, Mucin 4, and Activin A-Mediated Fibroblast Activation Cooperate for PanIN Initiation

Over 90% of patients with pancreatic ductal adenocarcinoma (PDAC) have oncogenic KRAS mutations. Nevertheless, mutated KRAS alone is insufficient to initiate pancreatic intraepithelial neoplasia (PanIN), the precursor of PDAC. The identities of the other factors/events required to drive PanIN formation remain elusive. Here, optic-clear 3D histology is used to analyze entire pancreases of 2-week-old Pdx1-Cre; LSL-KrasG12D/+ (KC) mice to detect the earliest emergence of PanIN and observed that the occurrence is independent of physical location. Instead, it is found that the earliest PanINs overexpress Muc4 and associate with αSMA+ fibroblasts in both transgenic mice and human specimens. Mechanistically, KrasG12D/+ pancreatic cells upregulate Muc4 through genetic alterations to increase proliferation and fibroblast recruitments via Activin A secretion and consequently enhance cell transformation for PanIN formation. Inhibition of Activin A signaling using Follistatin (FST) diminishes early PanIN-associated fibroblast recruitment, effectively curtailing PanIN initiation and growth in KC mice. These findings emphasize the vital role of interactions between oncogenic KrasG12D/+ -driven genetic alterations and induced microenvironmental changes in PanIN initiation, suggesting potential avenues for early PDAC diagnostic and management approaches.

HAPLN1 matrikine: a bone marrow homing factor linked to poor outcomes in patients with MM

The bone marrow (BM) microenvironment is critical for dissemination, growth, and survival of multiple myeloma (MM) cells. Homing of myeloma cells to the BM niche is a crucial step in MM dissemination, but the mechanisms involved are incompletely understood. In particular, any role of matrikines, neofunctional peptides derived from extracellular matrix proteins, remains unknown. Here, we report that a matrikine derived from hyaluronan and proteoglycan link protein 1 (HAPLN1) induces MM cell adhesion to the BM stromal components, such as fibronectin, endothelial cells, and stromal cells and, furthermore, induces their chemotactic and chemokinetic migration. In a mouse xenograft model, we show that MM cells preferentially home to HAPLN1 matrikine-conditioned BM. The transcription factor STAT1 is activated by HAPLN1 matrikine and is necessary to induce MM cell adhesion, migration, migration-related genes, and BM homing. STAT1 activation is mediated by interferon beta (IFN-β), which is induced by NF-κB after stimulation by HAPLN1 matrikine. Finally, we also provide evidence that higher levels of HAPLN1 in BM samples correlate with poorer progression-free survival of patients with newly diagnosed MM. These data reveal that a matrikine present in the BM microenvironment acts as a chemoattractant, plays an important role in BM homing of MM cells via NF-κB-IFN-β-STAT1 signaling, and may help identify patients with poor outcomes. This study also provides a mechanistic rationale for targeting HAPLN1 matrikine in MM therapy.

CXCL17 binds efficaciously to glycosaminoglycans with the potential to modulate chemokine signaling

Introduction

CXCL17 is a mucosally secreted protein, and the most recently identified human chemokine, an assignment based on protein fold prediction and chemotactic activity for leukocytes. However, these credentials have been the subject of much recent discussion and no experimental evidence has been presented regarding the definitive structure of CXCL17. In this study, we evaluated the structural and chemoattractant credentials of CXCL17 to better characterize this molecule, and gain deeper insights into its functional role as a glycosaminoglycan (GAG) binding protein.

Methods

In the absence of structural information, in silico modeling techniques assessed the likelihood of CXCL17 adopting a chemokine fold. Recombinant CXCL17 was synthesized in mammalian and prokaryotic systems. Modified Boyden chamber and real-time chemotaxis assays assessed the ability of CXCL17 to promote chemotaxis of murine splenocytes, human neutrophils, and CXCR1 transfectants. The efficacy of CXCL17 binding to GAGs was quantified with solid-phase assays and bio-layer interferometry techniques.

Results

All modeling efforts failed to support classification of CXCL17 as a chemokine based on its predicted conformation. Recombinant CXCL17 was observed to dimerize as a function of concentration, a characteristic of several chemokines. Contrary to a previous report, CXCL17 was not chemotactic for murine splenocytes, although it was a low-potency chemoattractant for human neutrophils at micromolar concentrations, several orders of magnitude higher than those required for CXCL8. As anticipated owing to its highly basic nature, CXCL17 bound to GAGs robustly, with key C-terminal motifs implicated in this process. While inactive via CXCR1, CXCL17 was found to inhibit CXCR1-mediated chemotaxis of transfectants to CXCL8 in a dose-dependent manner.

Discussion

In summary, despite finding little evidence for chemokine-like structure and function, CXCL17 readily bound GAGs, and could modulate chemotactic responses to another chemokine in vitro. We postulate that such modulation is a consequence of superior GAG binding, and that C-terminal fragments of CXCL17 may serve as prototypic inhibitors of chemokine function.

Biocompatible High-Resolution 3D-Printed Microfluidic Devices: Integrated Cell Chemotaxis Demonstration

We demonstrate a method to effectively 3D print microfluidic devices with high-resolution features using a biocompatible resin based on avobenzone as the UV absorber. Our method relies on spectrally shaping the 3D printer source spectrum so that it is fully overlapped by avobenzone's absorption spectrum. Complete overlap is essential to effectively limit the optical penetration depth, which is required to achieve high out-of-plane resolution. We demonstrate the high resolution in practice by 3D printing 15 μm square pillars in a microfluidic chamber, where the pillars are separated by 7.7 μm and are printed with 5 μm layers. Furthermore, we show reliable membrane valves and pumps using the biocompatible resin. Valves are tested to 1,000,000 actuations with no observable degradation in performance. Finally, we create a concentration gradient generation (CG) component and utilize it in two device designs for cell chemotaxis studies. The first design relies on an external dual syringe pump to generate source and sink flows to supply the CG channel, while the second is a complete integrated device incorporating on-chip pumps, valves, and reservoirs. Both device types are seeded with adherent cells that are subjected to a chemoattractant CG, and both show clear evidence of chemotactic cellular migration. Moreover, the integrated device demonstrates cellular migration comparable to the external syringe pump device. This demonstration illustrates the effectiveness of our integrated chemotactic assay approach and high-resolution biocompatible resin 3D printing fabrication process. In addition, our 3D printing process has been tuned for rapid fabrication, as printing times for the two device designs are, respectively, 8 and 15 min.

Cells in the polyaneuploid cancer cell (PACC) state have increased metastatic potential

Although metastasis is the leading cause of cancer deaths, it is quite rare at the cellular level. Only a rare subset of cancer cells (~ 1 in 1.5 billion) can complete the entire metastatic cascade: invasion, intravasation, survival in the circulation, extravasation, and colonization (i.e. are metastasis competent). We propose that cells engaging a Polyaneuploid Cancer Cell (PACC) phenotype are metastasis competent. Cells in the PACC state are enlarged, endocycling (i.e. non-dividing) cells with increased genomic content that form in response to stress. Single-cell tracking using time lapse microscopy reveals that PACC state cells have increased motility. Additionally, cells in the PACC state exhibit increased capacity for environment-sensing and directional migration in chemotactic environments, predicting successful invasion. Magnetic Twisting Cytometry and Atomic Force Microscopy reveal that cells in the PACC state display hyper-elastic properties like increased peripheral deformability and maintained peri-nuclear cortical integrity that predict successful intravasation and extravasation. Furthermore, four orthogonal methods reveal that cells in the PACC state have increased expression of vimentin, a hyper-elastic biomolecule known to modulate biomechanical properties and induce mesenchymal-like motility. Taken together, these data indicate that cells in the PACC state have increased metastatic potential and are worthy of further in vivo analysis.

Ras-Related Protein Rab5a Regulates Complement C5a Receptor Trafficking, Chemotaxis, and Chemokine Secretion in Human Macrophages

Complement activation and Rab GTPase trafficking are commonly observed in inflammatory responses. Recruitment of innate immune cells to sites of infection or injury and secretion of inflammatory chemokines are promoted by complement component 5a (C5a) that activates the cell surface protein C5a receptor1 (C5aR1). Persistent activation can lead to a myriad of inflammatory and autoimmune diseases. Here, we demonstrate that the mechanism of C5a induced chemotaxis of human monocyte-derived macrophages (HMDMs) and their secretion of inflammatory chemokines are controlled by Rab5a. We find that C5a activation of the G protein coupled receptor C5aR1 expressed on the surface of HMDMs, recruits β-arrestin2 via Rab5a trafficking, then activates downstream phosphatidylinositol 3-kinase (PI3K)/Akt signaling that culminates in chemotaxis and secretion of pro-inflammatory chemokines from HMDMs. High-resolution lattice light-sheet microscopy on live cells showed that C5a activates C5aR1-GFP internalization and colocalization with Rab5a-tdTomato but not with dominant negative mutant Rab5a-S34N-tdTomato in HEK293 cells. We found that Rab5a is significantly upregulated in differentiated HMDMs and internalization of C5aR1 is dependent on Rab5a. Interestingly, while knockdown of Rab5a inhibited C5aR1-mediated Akt phosphorylation, it did not affect C5aR1-mediated ERK1/2 phosphorylation or intracellular calcium mobilization in HMDMs. Functional analysis using transwell migration and µ-slide chemotaxis assays indicated that Rab5a regulates C5a-induced chemotaxis of HMDMs. Further, C5aR1 was found to mediate interaction of Rab5a with β-arrestin2 but not with G proteins in HMDMs. Furthermore, C5a-induced secretion of pro-inflammatory chemokines (CCL2, CCL3) from HMDMs was attenuated by Rab5a or β-arrestin2 knockdown or by pharmacological inhibition with a C5aR1 antagonist or a PI3K inhibitor. These findings reveal a C5a-C5aR1-β-arrestin2-Rab5a-PI3K signaling pathway that regulates chemotaxis and pro-inflammatory chemokine secretion in HMDMs and suggests new ways of selectively modulating C5a-induced inflammatory outputs.

Multi-feature-Based Robust Cell Tracking

Cell tracking algorithms have been used to extract cell counts and motility information from time-lapse images of migrating cells. However, these algorithms often fail when the collected images have cells with spatially and temporally varying features, such as morphology, position, and signal-to-noise ratio. Consequently, state-of-the-art algorithms are not robust or reliable because they require manual inputs to overcome the cell feature changes. To address these issues, we present a fully automated, adaptive, and robust feature-based cell tracking algorithm for the accurate detection and tracking of cells in time-lapse images. Our algorithm tackles measurement limitations twofold. First, we use Hessian filtering and adaptive thresholding to detect the cells in images, overcoming spatial feature variations among the existing cells without manually changing the input thresholds. Second, cell feature parameters are measured, including position, diameter, mean intensity, area, and orientation, and these parameters are simultaneously used to accurately track the cells between subsequent frames, even under poor temporal resolution. Our technique achieved a minimum of 92% detection and tracking accuracy, compared to 16% from Mosaic and Trackmate. Our improved method allows for extended tracking and characterization of heterogeneous cell behavior that are of particular interest for intravital imaging users.

Alcam-a and Pdgfr-α are essential for the development of sclerotome-derived stromal cells that support hematopoiesis

Mesenchymal stromal cells are essential components of hematopoietic stem and progenitor cell (HSPC) niches, regulating HSPC proliferation and fates. Their developmental origins are largely unknown. In zebrafish, we previously found that the stromal cells of the caudal hematopoietic tissue (CHT), a niche functionally homologous to the mammalian fetal liver, arise from the ventral part of caudal somites. We have now found that this ventral domain is the sclerotome, and that two markers of mammalian mesenchymal stem/stromal cells, Alcam and Pdgfr-α, are distinctively expressed there and instrumental for the emergence and migration of stromal cell progenitors, which in turn conditions the proper assembly of the vascular component of the CHT niche. Furthermore, we find that trunk somites are similarly dependent on Alcam and Pdgfr-α to produce mesenchymal cells that foster HSPC emergence from the aorta. Thus the sclerotome contributes essential stromal cells for each of the key steps of developmental hematopoiesis.

Granulocyte concentrate splitting does not affect phenotype and function

BACKGROUND

More granulocyte concentrates (GCs) could be produced for more patients from the same donor if apheresis bags were split and stored for longer periods of time. Hence, we tested the hypothesis that splitting and extension of storage of GCs do not impair granulocyte function or viability.

STUDY DESIGN AND METHODS

Granulocyte apheresis concentrates were produced using modified fluid gelatin as a separation enhancer, split into two portions, and stored for 24 and 48 h. Granulocyte function, represented by cell migration, reactive oxygen species (ROS) production, and neutrophil extracellular trap formation (NETosis), was measured by live-cell imaging. ROS production, adhesive surface protein expression, and viability were measured by flow cytometry.

RESULTS

Splitting had no effect on any of the tested parameters. After 24 h of storage, live-cell imaging showed no significant difference in migration, time to maximum ROS production, time to half-maximum NETosis, viability, or CD11b expression, but ROS production induced by phorbol 12-myristate 13-acetate (PMA) decreased from an initial median fluorescence intensity of 1775-590 artificial units. After 48 h, PMA-induced ROS production, viability, and migration declined, as reflected by decreases in median total distance (119 vs. 63.5 μm) and median Euclidean distance (30.75 vs. 14.3 μm).

CONCLUSION

Splitting GC products has no effect on granulocyte viability or function, but extended storage >24 h does compromise granulocyte function. The findings confirm that GCs should be transfused within 24 h of collection. Longer storage cannot be recommended.

Analysis of Chemotactic Property of CCN2/CTGF in Intramembranous Osteogenesis

Chemotaxis is a directed migration of cells in response to a gradient of extracellular molecules called chemoattractants. Development, growth, remodeling, and fracture healing of bones are advanced through intramembranous osteogenesis. Chemotaxis of preosteoblasts toward future bone formation sites observed in the early stage of intramembranous osteogenesis is a critical cellular process for normal bone formation. However, molecular biological mechanisms of the chemotaxis of preosteoblasts are not fully understood. We have recently clarified, for the first time, the critical role of the cellular communication network factor 2 (CCN2)/connective tissue growth factor (CTGF)-integrin α5-Ras axis for chemotaxis of preosteoblasts during new bone formation through intramembranous osteogenesis. In this chapter, we describe in detail the procedures of the in vivo and in vitro assays to investigate the chemotactic property of CCN2/CTGF and its underlying molecular biological mechanisms during intramembranous osteogenesis.

Axon pathfinding and targeting: (R)evolution of insights from in vitro assays

Investigating axonal behaviors while neurons are connecting with each other has been a challenge since the early studies on nervous system development. While molecule-driven axon pathfinding has been theorized by observing neurons at different developmental stages in vivo, direct observation and measurements of axon guidance behaviors required the invention of in vitro systems enabling to test the impact of molecules or cellular extracts on axons growing in vitro. With time, the development of novel in vivo approaches has confirmed the mechanisms highlighted in culture and has led in vitro systems to be adapted for cellular processes that are still inaccessible in intact organisms. We here review the evolution of these in vitro assays, which started with crucial contributions from the Bonhoeffer lab.

Assessing cell migration in hydrogels: An overview of relevant materials and methods

Cell migration is essential in numerous living processes, including embryonic development, wound healing, immune responses, and cancer metastasis. From individual cells to collectively migrating epithelial sheets, the locomotion of cells is tightly regulated by multiple structural, chemical, and biological factors. However, the high complexity of this process limits the understanding of the influence of each factor. Recent advances in materials science, tissue engineering, and microtechnology have expanded the toolbox and allowed the development of biomimetic in vitro assays to investigate the mechanisms of cell migration. Particularly, three-dimensional (3D) hydrogels have demonstrated a superior ability to mimic the extracellular environment. They are therefore well suited to studying cell migration in a physiologically relevant and more straightforward manner than in vivo approaches. A myriad of synthetic and naturally derived hydrogels with heterogeneous characteristics and functional properties have been reported. The extensive portfolio of available hydrogels with different mechanical and biological properties can trigger distinct biological responses in cells affecting their locomotion dynamics in 3D. Herein, we describe the most relevant hydrogels and their associated physico-chemical characteristics typically employed to study cell migration, including established cell migration assays and tracking methods. We aim to give the reader insight into existing literature and practical details necessary for performing cell migration studies in 3D environments.

Patterning ECM microstructure to investigate 3D cellular dynamics under multiplexed mechanochemical guidance

Background: Biochemical and biophysical factors jointly regulate the cellular dynamics in many physiological processes. It is therefore imperative to include multiplexed microenvironment cues when employing {in vitro} cell-based assays to model physiological processes. Methods: To meet this need, we have developed a modular platform of 3D cell culture, Modular Control of Microenvironment for Cell Migration and Culture Assay (MC33A), that incorporates directed chemical and mechanical cues in the forms of chemotaxis and contact guidance, respectively. Taking advantage of the functionalities of MC33A, we study the migration and morphology of breast cancer cells in 3D engineered extracellular matrix (ECM) following a serum gradient for chemotaxis. Results: We show that when chemotaxis is facilitated by contact guidance in the same direction as the serum gradient, cells demonstrate dimensional-reduction in their motility and highly elongated ellipsoidal shape. When the direction of ECM alignment diverges from the direction of serum gradient, chemotactic motion is significantly suppressed, and cells are generally more protrusive and rounded in their morphology. Conclusions: These examples demonstrate MC33A as a powerful tool for engineering complex microenvironments of cells that will advance the state-of-the-art of cell-based analysis in drug development, regenerative medicine, and other research areas in bioengineering.

Microfluidic evidence of synergistic effects between mesenchymal stromal cell-derived biochemical factors and biomechanical forces to control endothelial cell function

A functional vascular system is a prerequisite for bone repair as disturbed angiogenesis often causes non-union. Paracrine factors released from human bone marrow derived mesenchymal stromal cells (BMSCs) have angiogenic effects on endothelial cells. However, whether these paracrine factors participate in blood flow dynamics within bone capillaries remains poorly understood. Here, we used two different microfluidic designs to investigate critical steps during angiogenesis and found pronounced effects of endothelial cell proliferation as well as chemotactic and mechanotactic migration induced by BMSC conditioned medium (CM). The application of BMSC-CM in dynamic cultures demonstrates that bioactive factors in combination with fluidic flow-induced biomechanical signals significantly enhanced endothelial cell migration. Transcriptional analyses of endothelial cells demonstrate the induction of a unique gene expression profile related to tricarboxylic acid cycle and energy metabolism by the combination of BMSC-CM factors and shear stress, which opens an interesting avenue to explore during fracture healing. Our results stress the importance of in vivo - like microenvironments simultaneously including biochemical, biomechanical and oxygen levels when investigating key events during vessel repair. STATEMENT OF SIGNIFICANCE: Our results demonstrate the importance of recapitulating in vivo - like microenvironments when investigating key events during vessel repair. Endothelial cells exhibit enhanced angiogenesis characteristics when simultaneous exposing them to hMSC-CM, mechanical forces and biochemical signals simultaneously. The improved angiogenesis may not only result from the direct effect of growth factors, but also by reprogramming of endothelial cell metabolism. Moreover, with this model we demonstrated a synergistic impact of mechanical forces and biochemical factors on endothelial cell behavior and the expression of genes involved in the TCA cycle and energy metabolism, which opens an interesting new avenue to stimulate angiogenesis during fracture healing.

Loss of α6β4 Integrin-Mediated Hemidesmosomes Promotes Prostate Epithelial Cell Migration by Stimulating Focal Adhesion Dynamics

Epithelial cell adhesion is mediated by actin cytoskeleton-linked focal adhesions (FAs) and intermediate filament-associated hemidesmosomes (HDs). HDs are formed by α6β4-integrins and mediate stable anchoring to the extracellular matrix (ECM) while FAs containing β1-integrins regulate cell migration. Loss of HDs has been reported in various cancers such as prostate cancer where it correlates with increased invasive migration. Here we have studied cell migration properties and FA dynamics in genetically engineered prostate epithelial cell lines with intact or disrupted HDs. Disruption of HDs by depleting α6- or β4-integrin expression promoted collective cell migration and modulated migratory activity. Dynamic analysis of fluorescent protein-tagged FA marker proteins revealed faster FA assembly and disassembly kinetics in HD-depleted cells. FRAP analysis showed that loss of HDs correlated with faster diffusion rates of focal adhesion kinase (FAK) and vinculin in and out of FAs. These data suggest that loss of α6β4-mediated HDs promote cell migration and FA assembly dynamics by influencing the molecular diffusion rates of FAK.

Cell Trafficking at the Intersection of the Tumor-Immune Compartments

Migration is an essential cellular process that regulates human organ development and homeostasis as well as disease initiation and progression. In cancer, immune and tumor cell migration is strongly associated with immune cell infiltration, immune escape, and tumor cell metastasis, which ultimately account for more than 90% of cancer deaths. The biophysics and molecular regulation of the migration of cancer and immune cells have been extensively studied separately. However, accumulating evidence indicates that, in the tumor microenvironment, the motilities of immune and cancer cells are highly interdependent via secreted factors such as cytokines and chemokines. Tumor and immune cells constantly express these soluble factors, which produce a tightly intertwined regulatory network for these cells' respective migration. A mechanistic understanding of the reciprocal regulation of soluble factor-mediated cell migration can provide critical information for the development of new biomarkers of tumor progression and of tumor response to immuno-oncological treatments. We review the biophysical andbiomolecular basis for the migration of immune and tumor cells and their associated reciprocal regulatory network. We also describe ongoing attempts to translate this knowledge into the clinic.

Periostin in lymph node pre-metastatic niches governs lymphatic endothelial cell functions and metastatic colonization

Although lymph node (LN) metastasis is an important prognostic parameter in cervical cancer, the tissue remodeling at a pre-metastatic state is poorly documented in LNs. We here identified periostin (POSTN) as a component of non-metastatic LNs by applying proteomic analyses and computerized image quantifications on LNs of patients with cervical cancer. We provide evidence for remarkable modifications of POSTN and lymphatic vessel distributions and densities in non-metastatic sentinel and metastatic human LNs, when compared to distant non-metastatic LNs. POSTN deposition at a pre-metastatic stage was demonstrated in a pre-clinical murine model (the ear sponge assay). Its expression by fibroblastic LN cells was assessed by in situ hybridization and in vitro cultures. In vitro, POSTN promoted lymphatic endothelial cell functions and tumor cell proliferation. Accordingly, the in vivo injection of recombinant POSTN together with VEGF-C boosted the lymphangiogenic response, while the metastatic potential of tumor cells was drastically reduced using a POSTN blocking antibody. This translational study also supports the existence of an unprecedented dialog “in cascade”, between the primary tumor and the first pelvic nodal relay in early cervical cancer, and subsequently from pelvic LN to para-aortic LNs in locally advanced cervical cancers. Collectively, this work highlights the association of POSTN deposition with lymphangiogenesis in LNs, and provides evidence for a key contribution of POSTN in promoting VEGF-C driven lymphangiogenesis and the seeding of metastatic cells.

PD-LI promotes rear retraction during persistent cell migration by altering integrin β4 dynamics

Although the immune checkpoint function of PD-L1 has dominated its study, we report that PD-L1 has an unanticipated intrinsic function in promoting the dynamics of persistent cell migration. PD-L1 concentrates at the rear of migrating carcinoma cells where it facilitates retraction, resulting in the formation of PD-L1-containing retraction fibers and migrasomes. PD-L1 promotes retraction by interacting with and localizing the β4 integrin to the rear enabling this integrin to stimulate contractility. This mechanism involves the ability of PD-L1 to maintain cell polarity and lower membrane tension at the cell rear compared with the leading edge that promotes the localized interaction of PD-L1 and the β4 integrin. This interaction enables the β4 integrin to engage the actin cytoskeleton and promote RhoA-mediated contractility. The implications of these findings with respect to cell-autonomous functions of PD-L1 and cancer biology are significant.

Three-dimensional cancer cell migration directed by dual mechanochemical guidance

Directed cell migration guided by external cues plays a central role in many physiological and pathophysiological processes. The microenvironment of cells often simultaneously contains various cues and the motility response of cells to multiplexed guidance is poorly understood. Here we combine experiments and mathematical models to study the three-dimensional migration of breast cancer cells in the presence of both contact guidance and a chemoattractant gradient. We find that the chemotaxis of cells is complicated by the presence of contact guidance as the microstructure of extracellular matrix (ECM) vary spatially. In the presence of dual guidance, the impact of ECM alignment is determined externally by the coherence of ECM fibers and internally by cell mechanosensing Rho/Rock pathways. When contact guidance is parallel to the chemical gradient, coherent ECM fibers significantly increase the efficiency of chemotaxis. When contact guidance is perpendicular to the chemical gradient, cells exploit the ECM disorder to locate paths for chemotaxis. Our results underscore the importance of fully characterizing the cancer cell microenvironment in order to better understand invasion and metastasis.

Integrative lymph node-mimicking models created with biomaterials and computational tools to study the immune system

The lymph node (LN) is a vital organ of the lymphatic and immune system that enables timely detection, response, and clearance of harmful substances from the body. Each LN comprises of distinct substructures, which host a plethora of immune cell types working in tandem to coordinate complex innate and adaptive immune responses. An improved understanding of LN biology could facilitate treatment in LN-associated pathologies and immunotherapeutic interventions, yet at present, animal models, which often have poor physiological relevance, are the most popular experimental platforms. Emerging biomaterial engineering offers powerful alternatives, with the potential to circumvent limitations of animal models, for in-depth characterization and engineering of the lymphatic and adaptive immune system. In addition, mathematical and computational approaches, particularly in the current age of big data research, are reliable tools to verify and complement biomaterial works. In this review, we first discuss the importance of lymph node in immunity protection followed by recent advances using biomaterials to create in vitro/vivo LN-mimicking models to recreate the lymphoid tissue microstructure and microenvironment, as well as to describe the related immuno-functionality for biological investigation. We also explore the great potential of mathematical and computational models to serve as in silico supports. Furthermore, we suggest how both in vitro/vivo and in silico approaches can be integrated to strengthen basic patho-biological research, translational drug screening and clinical personalized therapies. We hope that this review will promote synergistic collaborations to accelerate progress of LN-mimicking systems to enhance understanding of immuno-complexity.

Rhinovirus infection of bronchial epithelium induces specific bronchial smooth muscle cell migration of severe asthmatic patients

BACKGROUND

Patients with severe asthma show an increase in both exacerbation frequency and bronchial smooth muscle (BSM) mass. Rhinovirus (RV) infection of the bronchial epithelium (BE) is the main trigger of asthma exacerbations. Histological analysis of biopsies shows that a close connection between BE and hypertrophic BSM is a criterion for severity of asthma.

OBJECTIVE

We hypothesized that RV infection of BE specifically increases asthmatic BSM cell migration.

METHODS

Serum samples, biopsies or BSM cells were obtained from 86 patients with severe asthma and 31 non-asthmatic subjects. BE cells from non-asthmatic subjects were cultured in an air-liquid interface and exposed to RV-16. Migration of BSM cells was assessed in response to BE supernatant using chemotaxis assays. Chemokine concentrations were analyzed by transcriptomics and ELISAs. Immunocytochemistry, western blotting and flow cytometry were used to quantify CXCR3 isoform distribution. CXCR3 downstream signaling pathways were assessed by calcium imaging and western blots.

RESULTS

BSM cells from severe asthmatic patients specifically migrated toward RV-infected BE, whereas those from non-asthmatic subjects did not. This specific migration is driven by BE CXCL10, which was increased in vitro in response to RV infection as well as in vivo in serum from exacerbating patients with severe asthma. The mechanism is related to both decreased expression and activation of the CXCR3-B-specific isoform in severe asthmatic BSM cells.

CONCLUSION

We have demonstrated a novel mechanism of BSM remodeling in severe asthmatic patients following RV exacerbation. This study highlights the CXCL10/CXCR3-A axis as a potential therapeutic target in severe asthma.

The ADAM9/UBN2/AKR1C3 axis promotes resistance to androgen-deprivation in prostate cancer

Metastatic and castration-resistant disease is a fatal manifestation of prostate cancer (PCa). The mechanism through which resistance to androgen deprivation in PCa is developed remains largely unknown. Our understanding of the tumor microenvironment (TME) and key signaling pathways between tumors and their TME is currently changing in light of the generation of new knowledge with regard to cancer progression. A disintegrin and metalloproteinase domain-containing protein 9 (ADAM9) is a membranous bridge forming cell-cell and cell-matrix connections that regulate tumor aggressiveness and metastasis. However, it is not known whether ADAM9 expressed in the TME contributes to the CRPC phenotype. In this study, we aimed to investigate the expression patterns of ADAM9 in prostate cancer-associated fibroblasts (CAFs). We also intended to elucidate the effects of both stromal cell- and cancer cell-derived ADAM9 on the progression of CRPC and the implicated molecular pathways. By using both clinical specimens and cell lines, we herein showed that unlike the membrane anchored ADAM9 overexpressed by both PCa cells and prostate CAFs, the secreted isoform of ADAM9 (sADAM9) was strongly detected in CAFs, but rarely in tumor cells, and that could be a serum marker for PCa patients. We demonstrated that functionally sADAM9 are characterized as chemoattractant for the directed movement of androgen-independent PCa cells through integrin downstream FAK/AKT pathway, supporting that elevated sADAM9 by prostate CAFs could be responsible for the promotion of CRPC metastasis. Moreover, by stimulating PCa cells with sADAM9, we found that ubinuclein-2 (UBN2) expression was increased. A positive correlation of ADAM9 and UBN2 expression was observed in androgen receptor-expressing PCa cell lines and further confirmed in clinical PCa specimens. Using a genetic modification approach, we identified UBN2 as a downstream target gene of ADAM9 that is critical for the survival of androgen-dependent PCa cells in response to androgen deprivation, through the induction and effect of the aldo-keto reductase family 1 member C3 (AKR1C3). Collectively, our results reveal a novel action of ADAM9 on the transition of androgen-dependent PCa cells into an androgen-independent manner through the UBN2/AKR1C3 axis; the aforementioned action could contribute to the clinically-observed acquired androgen-deprivation therapy resistance.

Spatial determinates of effector and memory CD8+ T cell fates

The lymph node plays a critical role in mounting an adaptive immune response to infection, clearance of foreign pathogens, and cancer immunosurveillance. Within this complex structure, intranodal migration is vital for CD8⁺ T cell activation and differentiation. Combining tissue clearing and volumetric light sheet fluorescent microscopy of intact lymph nodes has allowed us to explore the spatial regulation of T cell fates. This has determined that short-lived effector (T_SLEC ) are imprinted in peripheral lymph node interfollicular regions, due to CXCR3 migration. In contrast, stem-like memory cell (T_SCM ) differentiation is determined in the T cell paracortex. Here, we detail the inflammatory and chemokine regulators of spatially restricted T cell differentiation, with a focus on how to promote T_SCM . We propose a default pathway for T_SCM differentiation due to CCR7-directed segregation of precursors away from the inflammatory effector niche. Although volumetric imaging has revealed the consequences of intranodal migration, we still lack knowledge of how this is orchestrated within a complex chemokine environment. Toward this goal, we highlight the potential of combining microfluidic chambers with pre-determined complexity and subcellular resolution microscopy.

"Viscotaxis"- directed migration of mesenchymal stem cells in response to loss modulus gradient

Directed cell migration plays a crucial role in physiological and pathological conditions. One important mechanical cue, known to influence cell migration, is the gradient of substrate elastic modulus (E). However, the cellular microenvironment is viscoelastic and hence the elastic property alone is not sufficient to define its material characteristics. To bridge this gap, in this study, we investigated the influence of the gradient of viscous property of the substrate, as defined by loss modulus (G^″) on cell migration. We cultured human mesenchymal stem cells (hMSCs) on a collagen-coated polyacrylamide gel with constant storage modulus (G^') but with a gradient in the loss modulus (G^″). We found hMSCs to migrate from high to low loss modulus. We have termed this form of directional cellular migration as "Viscotaxis". We hypothesize that the high loss modulus regime deforms more due to creep in the long timescale when subjected to cellular traction. Such differential deformation drives the observed Viscotaxis. To verify our hypothesis, we disrupted the actomyosin contractility with myosin inhibitor blebbistatin and ROCK inhibitor Y27632, and found the directional migration to disappear. Further, such time-dependent creep of the high loss material should lead to lower traction, shorter lifetime of the focal adhesions, and dynamic cell morphology, which was indeed found to be the case. Together, findings in this paper highlight the importance of considering the viscous modulus while preparing stiffness-based substrates for the field of tissue engineering. STATEMENT OF SIGNIFICANCE: While the effect of substrate elastic modulus has been investigated extensively in the context of cell biology, the role of substrate viscoelasticity is poorly understood. This omission is surprising as our body is not elastic, but viscoelastic. Hence, the role of viscoelasticity needs to be investigated at depth in various cellular contexts. One such important context is cell migration. Cell migration is important in morphogenesis, immune response, wound healing, and cancer, to name a few. While it is known that cells migrate when presented with a substrate with a rigidity gradient, cellular behavior in response to viscoelastic gradient has never been investigated. The findings of this paper not only reveal a completely novel cellular taxis or directed migration, it also improves our understanding of cell mechanics significantly.

Exosomal miR-19a and IBSP cooperate to induce osteolytic bone metastasis of estrogen receptor-positive breast cancer

Bone metastasis is an incurable complication of breast cancer. In advanced stages, patients with estrogen-positive tumors experience a significantly higher incidence of bone metastasis (>87%) compared to estrogen-negative patients (<56%). To understand the mechanism of this bone-tropism of ER+ tumor, and to identify liquid biopsy biomarkers for patients with high risk of bone metastasis, the secreted extracellular vesicles and cytokines from bone-tropic breast cancer cells are examined in this study. Both exosomal miR-19a and Integrin-Binding Sialoprotein (IBSP) are found to be significantly upregulated and secreted from bone-tropic ER+ breast cancer cells, increasing their levels in the circulation of patients. IBSP is found to attract osteoclast cells and create an osteoclast-enriched environment in the bone, assisting the delivery of exosomal miR-19a to osteoclast to induce osteoclastogenesis. Our findings reveal a mechanism by which ER+ breast cancer cells create a microenvironment favorable for colonization in the bone. These two secreted factors can also serve as effective biomarkers for ER+ breast cancer to predict their risks of bone metastasis. Furthermore, our screening of a natural compound library identifies chlorogenic acid as a potent inhibitor for IBSP-receptor binding to suppress bone metastasis of ER+ tumor, suggesting its preventive use for bone recurrence in ER+ patients.

Human Platelet Lysate-Loaded Poly(ethylene glycol) Hydrogels Induce Stem Cell Chemotaxis In Vitro

Platelet lysates (PL) contain a selection of proteins and growth factors (GFs) that are known to mediate cell activity. Many of these biomolecules have been identified as chemoattractants with the capacity to induce cell migration. In order to effectively deliver and retain these biomolecules to the site of injury, a scaffold containing PL could be an option. We use poly(ethylene glycol) (PEG) hydrogels consisting of 90 vol % PL to investigate their migratory potential on human mesenchymal stem cells (hMSCs). Cells exposed to these hydrogels were tracked, resulting in cell trajectories and detailed migratory parameters (velocity, Euclidean distance, directness, and forward migration index). Volumetric swelling ratios, hydrogel mechanical properties, and the release kinetics of proteins and GFs from hydrogels were also assessed. Furthermore, hMSC spheroids were encapsulated within the hydrogels to qualitatively assess cell invasion by means of sprouting and disintegration of the spheroid. Cell spheroids encapsulated within the PL-PEG gels exhibited initial outgrowths and eventually colonized the 3D matrix successfully. Results from this study confirmed that hMSCs exhibit directional migration toward the PL-loaded hydrogel with increased velocity and directness, compared to the controls. Overall, the incorporation of PL renders the PEG hydrogel bioactive. This study demonstrates the capacity of PL-loaded hydrogel constructs to attract stem cells for endogenous tissue engineering purposes.

The influence of extracellular tissue on neutrophil function and its possible linkage to inflammatory diseases

BACKGROUND

Migration, production of reactive oxygen species (ROS), release of myeloperoxidase (MPO), and NETosis are functional immunological reactions of elementary importance for polymorphonuclear neutrophils (PMN). Unregulated inflammatory response of PMN within tissues plays a key role in the pathophysiology of several diseases. However, little is known about the behavior of PMN after migration through blood vessel walls. Therefore, we investigated the influence of the extracellular matrix (ECM) on PMN function.

MATERIALS AND METHODS

We established an in vitro chemotaxis model of type I and III collagen, fibrin, and herbal agarose tissues using µ-slide chemotaxis devices and N-formylmethionine-leucyl-phenylalanine (fMLP). PMN within the matrices were assessed with a fluorescent time-lapse microscope for live-cell imaging.

RESULTS

PMN function was obviously influenced by the ECM. Type III collagen had an inhibitory effect on PMN migration regarding track length, direction, and targeting. Type III collagen also had an accelerating effect on neutrophil ROS production. Agarose had an inhibitory effect on MPO release and fibrin a retarding effect on NETosis.

CONCLUSION

Because of the high abundance of type III collagen in lung and skin matrices, the interaction of PMN with the respective matrix could be an important mechanism in the pathophysiology of acute respiratory distress syndrome and pyoderma gangrenosum.

Nanoparticles Interfere with Chemotaxis: An Example of Nanoparticles as Molecular "Knockouts" at the Cellular Level

Engineered colloidal nanoparticles show great promise in biomedical applications. While much of the work of assessing nanoparticle impact on living systems has been focused on the direct interactions of nanoparticles with cells/organisms, indirect effects via the extracellular matrix have been observed and may provide deeper insight into nanoparticle fate and effects in living systems. In particular, the large surface area of colloidal nanoparticles may sequester molecules from the biological milieu, make these molecules less bioavailable, and therefore function indirectly as "molecular knockouts" to exert effects at the cellular level and beyond. In this paper, the hypothesis that molecules that control cellular behavior (in this case, chemoattract molecules that promote migration of a human monocytic cell line, THP-1) will be less bioavailable in the presence of appropriately functionalized nanoparticles, and therefore the cellular behavior will be altered, was investigated. Three-dimensional chemotaxis assays for the characterization and comparison of THP-1 cell migration upon exposure to a gradient of monocyte chemoattractant protein-1 (MCP-1), with and without gold nanoparticles with four different surface chemistries, were performed. By time-lapse microscopy, characteristic parameters for chemotaxis, along with velocity and directionality of the cells, were quantified. Anionic poly(sodium 4-styrenesulfonate)-coated gold nanoparticles were found to significantly reduce THP-1 chemotaxis. Enzyme-linked immunosorbent assay results show adsorption of MCP-1 on the poly(sodium 4-styrenesulfonate)-coated gold nanoparticle surface, supporting the hypothesis that adsorption of chemoattractants to nanoparticle surfaces interferes with chemotaxis. Free anionic sulfonated polyelectrolytes also interfered with cell migrational behavior, showing that nanoparticles can also act as carriers of chemotactic-interfering molecules.

New insights into spatio-temporal dynamics of mesenchymal progenitor cell ingress during peri-implant wound healing: Provided by intravital imaging

Surface topography drives the success of orthopedic and dental implants placed in bone, by directing the biology occurring at the tissue-implant interface. Over the last few decades, striking advancements have been made in the development of novel implant surfaces that enhance bone anchorage to their surfaces through contact osteogenesis: the combination of the two phenomena of recruitment and migration of mesenchymal progenitor cells to the implant surface, and their differentiation into bone-forming cells. While the latter is generally understood, the mechanisms and dynamics underlying the migration and recruitment of such progenitor cells into the wound site have garnered little attention. To address this deficit, we surgically inserted metallic implants with two different surface topographies into the skulls of mice, and then employed real-time spatiotemporal microscopic monitoring of the peri-implant tissue healing to track the ingress of cells. Our results show that nano-topographically complex, in comparison to relatively smooth, implant surfaces profoundly affect recruitment of both endothelial cells, which are essential for angiogenesis, and the mesenchymal progenitor cells that give rise to the reparative tissue stroma. The latter appear concomitantly in the wound site with endothelial cells, from the vascularized areas of the periosteum, and demonstrate a proliferative "bloom" that diminishes with time, although some of these cells differentiate into important stromal cells, pericytes and osteocytes, of the reparative wound. In separate experiments we show, using trajectory plots, that the directionality of migration for both endothelial and perivascular cells can be explained by implant surface dependent release of local cytokine gradients from platelets that would become activated on the implant surfaces during initial blood contact. These findings provide new biological insights into the earliest stages of wound healing, and have broad implications in the application of putative nano-topographically complex biomaterials in many tissue types.

Triple-Negative Breast Cancer Cells Recruit Neutrophils by Secreting TGF-β and CXCR2 Ligands

Tumor associated neutrophils (TANs) are frequently detected in triple-negative breast cancer (TNBC). Recent studies also reveal the importance of neutrophils in promoting tumor progression and metastasis during breast cancer. However, the mechanisms regulating neutrophil trafficking to breast tumors are less clear. We sought to determine whether neutrophil trafficking to breast tumors is determined directly by the malignant potential of cancer cells. We found that tumor conditioned media (TCM) harvested from highly aggressive, metastatic TNBC cells induced a polarized morphology and robust neutrophil migration, while TCM derived from poorly aggressive estrogen receptor positive (ER+) breast cancer cells had no activity. In a three-dimensional (3D) type-I collagen matrix, neutrophils migrated toward TCM from aggressive breast cancer cells with increased velocity and directionality. Moreover, in a neutrophil-tumor spheroid co-culture system, neutrophils migrated with increased directionality towards spheroids generated from TNBC cells compared to ER+ cells. Based on these findings, we next sought to characterize the active factors secreted by TNBC cell lines. We found that TCM-induced neutrophil migration is dependent on tumor-derived chemokines, and screening TCM elution fractions based on their ability to induce polarized neutrophil morphology revealed the molecular weight of the active factors to be around 12 kDa. TCM from TNBC cell lines contained copious amounts of GRO (CXCL1/2/3) chemokines and TGF-β cytokines compared to ER+ cell-derived TCM. TCM activity was inhibited by simultaneously blocking receptors specific to GRO chemokines and TGF-β, while the activity remained intact in the presence of either single receptor inhibitor. Together, our findings establish a direct link between the malignant potential of breast cancer cells and their ability to induce neutrophil migration. Our study also uncovers a novel coordinated function of TGF-β and GRO chemokines responsible for guiding neutrophil trafficking to the breast tumor.

A Novel Small Molecule, LCG-N25, Inhibits Oral Streptococcal Biofilm

Dental caries is a chronic oral infectious disease caused by cariogenic biofilm adhered on the tooth surface. Our previous study demonstrated that a repurposed natural compound napabucasin (NAP) showed good antimicrobial activity against oral streptococcal biofilms. The current study designed a novel small molecule, namely LCG-N25, using NAP as a lead compound, and aimed to investigate its potential as an antimicrobial agent in the control of dental caries. LCG-N25 was designed and synthesized with reference to the structure of NAP. The minimal inhibitory concentrations and the minimal bactericidal concentrations of LCG-N25 against Streptococcus mutans, Streptococcus sanguinis, and Streptococcus gordonii were evaluated by microdilution method. The antimicrobial activity of LCG-N25 was further evaluated by crystal violet staining, colony forming units counting, biofilm metabolism assay, dead/live fluorescent staining, and scanning electron microscopy. The effect of LCG-N25 on the extracellular polysaccharides of biofilms was determined by both anthrone-sulfuric acid method and fluorescent staining. The microbial composition of streptococcal biofilms after LCG-N25 treatment was further visualized and quantified by fluorescence in situ hybridization. Besides, the cytotoxicity of LCG-N25 was evaluated by Cell Counting Kit-8 assay, and repeated exposure of S. mutans to LCG-N25 treatment was performed to assess if this novel compound could induce drug resistance of this cariogenic bacterium. We found that LCG-N25 exhibited a good antibacterial activity, low-cytotoxicity, and did not induce drug resistance of cariogenic S. mutans. These findings suggest that LCG-N25 may represent a promising antimicrobial agent that can be used as an adjuvant to the management of dental caries.

The actin-regulatory protein Hem-1 is essential for alveolar macrophage development

Hematopoietic protein-1 (Hem-1) is a hematopoietic cell–specific actin-regulatory protein. Loss-of-function (LOF) variants in the NCKAP1L gene encoding Hem-1 have recently been found to result in primary immunodeficiency disease (PID) in humans, characterized by recurring respiratory infections, asthma, and high mortality. However, the mechanisms of how Hem-1 variants result in PID are not known. In this study, we generated constitutive and myeloid cell–specific Nckap1l-KO mice to dissect the importance of Hem-1 in lung immunity. We found that Hem-1–deficient mice accumulated excessive surfactant and cell debris in airways (pulmonary alveolar proteinosis) due to impaired development of alveolar macrophages (AMs) and reduced expression of the AM differentiation factor Pparg. Residual Hem-1–deficient AMs shifted to a proinflammatory phenotype, and Hem-1–deficient neutrophils and monocytes failed to migrate normally. Myeloid cell–specific Hem-1–deficient mice exhibited increased morbidity following influenza A virus or Streptococcus pneumoniae challenge. These results provide potential mechanisms for how LOF variants in Hem-1 result in recurring respiratory diseases.

Suppressive Role of Bam32/DAPP1 in Chemokine-Induced Neutrophil Recruitment

Bam32 (B cell adaptor molecule of 32 kDa) functions in the immune responses of various leukocytes. However, the role of neutrophil Bam32 in inflammation is entirely unknown. Here, we determined the role of Bam32 in chemokine CXCL2-induced neutrophil chemotaxis in three mouse models of neutrophil recruitment. By using intravital microscopy in the mouse cremaster muscle, we found that transmigrated neutrophil number, neutrophil chemotaxis velocity, and total neutrophil chemotaxis distance were increased in Bam32^−/− mice when compared with wild-type (WT) mice. In CXCL2-induced mouse peritonitis, the total emigrated neutrophils were increased in Bam32^−/− mice at 2 but not 4 h. The CXCL2-induced chemotaxis distance and migration velocity of isolated Bam32^−/− neutrophils in vitro were increased. We examined the activation of small GTPases Rac1, Rac2, and Rap1; the levels of phospho-Akt2 and total Akt2; and their crosstalk with Bam32 in neutrophils. The deficiency of Bam32 suppressed Rap1 activation without changing the activation of Rac1 and Rac2. The pharmacological inhibition of Rap1 by geranylgeranyltransferase I inhibitor (GGTI298) increased WT neutrophil chemotaxis. In addition, the deficiency of Bam32, as well as the inhibition of Rap1 activation, increased the levels of CXCL2-induced Akt1/2 phosphorylation at Thr308/309 in neutrophils. The inhibition of Akt by SH-5 attenuated CXCL2-induced adhesion and emigration in Bam32^−/− mice. Together, our results reveal that Bam32 has a suppressive role in chemokine-induced neutrophil chemotaxis by regulating Rap1 activation and that this role of Bam32 in chemokine-induced neutrophil recruitment relies on the activation of PI3K effector Akt.

Senescent Tumor Cells Build a Cytokine Shield in Colorectal Cancer

Cellular senescence can either support or inhibit cancer progression. Here, it is shown that intratumoral infiltration of CD8+ T cells is negatively associated with the proportion of senescent tumor cells in colorectal cancer (CRC). Gene expression analysis reveals increased expression of C-X-C motif chemokine ligand 12 (CXCL12) and colony stimulating factor 1 (CSF1) in senescent tumor cells. Senescent tumor cells inhibit CD8+ T cell infiltration by secreting a high concentration of CXCL12, which induces a loss of CXCR4 in T cells that result in impaired directional migration. CSF1 from senescent tumor cells enhance monocyte differentiation into M2 macrophages, which inhibit CD8+ T cell activation. Neutralization of CXCL12/CSF1 increases the effect of anti-PD1 antibody in allograft tumors. Furthermore, inhibition of CXCL12 from senescent tumor cells enhances T cell infiltration and results in reducing the number and size of tumors in azoxymethane (AOM)/dextran sulfate sodium (DSS)-induced CRC. These findings suggest senescent tumor cells generate a cytokine barrier protecting nonsenescent tumor cells from immune attack and provide a new target for overcoming the immunotherapy resistance of CRC.

Connective tissue growth factor promotes chemotaxis of preosteoblasts through integrin α5 and Ras during tensile force-induced intramembranous osteogenesis

In vertebrates, new bone formation via intramembranous osteogenesis is a critical biological event for development, remodeling, and fracture healing of bones. Chemotaxis of osteoblast lineage cells is an essential cellular process in new bone formation. Connective tissue growth factor (CTGF) is known to exert chemotactic properties on various cells; however, details of CTGF function in the chemotaxis of osteoblast lineage cells and underlying molecular biological mechanisms have not been clarified. The aim of the present study was to evaluate the chemotactic properties of CTGF and its underlying mechanisms during active bone formation through intramembranous osteogenesis. In our mouse tensile force-induced bone formation model, preosteoblasts were aggregated at the osteogenic front of calvarial bones. CTGF was expressed at the osteogenic front, and functional inhibition of CTGF using a neutralizing antibody suppressed the aggregation of preosteoblasts. In vitro experiments using μ-slide chemotaxis chambers showed that a gradient of CTGF induced chemotaxis of preosteoblastic MC3T3-E1 cells, while a neutralizing integrin α5 antibody and a Ras inhibitor inhibited the CTGF-induced chemotaxis of MC3T3-E1 cells. These findings suggest that the CTGF-integrin α5-Ras axis is an essential molecular mechanism to promote chemotaxis of preosteoblasts during new bone formation through intramembranous osteogenesis.

How Have Leukocyte In Vitro Chemotaxis Assays Shaped Our Ideas about Macrophage Migration?

Simple Summary

The migration of immune cells is vital during inflammatory responses. Macrophages, which are a subset of immune cells, are unique in the ways they migrate because they can switch between different mechanism of migration. This crucial feature of macrophage migration has been underappreciated in the literature because technologies used to study macrophage migration were not able to efficiently detect those subtle differences between macrophages and other immune cells. This review article describes popular technologies used to study macrophage migration and critically assesses their advantages and disadvantages in macrophage migration studies.

Abstract

Macrophage chemotaxis is crucial during both onset and resolution of inflammation and unique among all leukocytes. Macrophages are able to switch between amoeboid and mesenchymal migration to optimise their migration through 3D environments. This subtle migration phenotype has been underappreciated in the literature, with macrophages often being grouped and discussed together with other leukocytes, possibly due to the limitations of current chemotaxis assays. Transwell assays were originally designed in the 1960s but despite their long-known limitations, they are still one of the most popular methods of studying macrophage migration. This review aims to critically evaluate transwell assays, and other popular chemotaxis assays, comparing their advantages and limitations in macrophage migration studies.

Repurposing Napabucasin as an Antimicrobial Agent against Oral Streptococcal Biofilms

Objectives

Disruption of microbial biofilms is an effective way to control dental caries. Drug resistance and side effects of the existing antimicrobials necessitate the development of novel antibacterial agents. The current study was aimed at investigating the antibacterial activities of the repurposed natural compound napabucasin against oral streptococci.

Methods

The minimum inhibitory concentration, minimum bactericidal concentration, minimum biofilm inhibition concentration, and minimum biofilm reduction concentration of Streptococcus mutans, Streptococcus gordonii, and Streptococcus sanguinis were examined by a microdilution method. Cytotoxicity of napabucasin against human oral keratinocytes, human gingival epithelia, and macrophage RAW264.7 was evaluated by CCK8 assays. The dead/live bacterium and exopolysaccharide in the napabucasin-treated multispecies biofilms were evaluated by confocal laser scanning microscopy. Microbial composition within the napabucasin-treated biofilms was further visualized by fluorescent in situ hybridization and qPCR. And the cariogenicity of napabucasin-treated biofilms was evaluated by transverse microradiography.

Results

Napabucasin exhibited good antimicrobial activity against oral streptococcal planktonic cultures and biofilms but with lessened cytotoxicity as compared to chlorhexidine. Napabucasin reduced the cariogenic S. mutans and increased the proportion of the commensal S. gordonii in the multispecies biofilms. More importantly, napabucasin significantly reduced the demineralization capability of biofilms on tooth enamels.

Conclusion

Napabucasin shows lessened cytotoxicity and comparable antimicrobial effects to chlorhexidine. Repurposing napabucasin may represent a promising adjuvant for the management of dental caries.

Supramolecular nanomotors with "pH taxis" for active drug delivery in the tumor microenvironment

Self-propelled nanomotors demonstrating autonomous motion in biologically relevant fuel are currently being studied to overcome the use of external physical or chemical stimuli as precise delivery agents. In this context, the tumor microenvironment (TME) with slightly acidic pH is used for developing cargo-releasing artificial systems triggered by such conditions. However, there is still a need for fabrication of smart nanomotors that can sense the acidic pH prevalent in the TME rather than using an external fuel source for selective activation and thereafter migrating towards tumors for active drug delivery. Herein, supramolecular assembly-based nanomotors are fabricated by in-situ grown CaCO3 nanoparticles and studied for their motility behaviour in endogenously generated acidic pH by HeLa cells and further exploited as an active delivery vehicle for DOX molecules to the cells for their anticancer efficacy. The nanomotors are activated in slightly acidic pH showcasing "pH taxis" towards tumor cells without the need for any sophisticated/complicated technologies or an external fuel source for active and targeted delivery of drugs.

Hypoxia directed migration of human naïve monocytes is associated with an attenuation of cytokine release: indications for a key role of CCL26

Background

Numerous tissue-derived factors have been postulated to be involved in tissue migration of circulating monocytes. The aim of this study was to evaluate whether a defined hypoxic gradient can induce directed migration of naïve human monocytes and to identify responsible autocrine/paracrine factors.

Methods

Monocytes were isolated from peripheral blood mononuclear cells, transferred into chemotaxis chambers and subjected to a defined oxygen gradient with or without the addition of CCL26. Cell migration was recorded and secretome analyses were performed.

Results

Cell migration recordings revealed directed migration of monocytes towards the source of hypoxia. Analysis of the monocyte secretome demonstrated a reduced secretion of 70% (19/27) of the analyzed cytokines under hypoxic conditions. The most down-regulated factors were CCL26 (− 99%), CCL1 (− 95%), CX3CL1 (− 95%), CCL17 (− 85%) and XCL1 (− 83%). Administration of recombinant CCL26 abolished the hypoxia-induced directed migration of human monocytes, while the addition of CCL26 under normoxic conditions resulted in a repulsion of monocytes from the source of CCL26.

Conclusions

Hypoxia induces directed migration of human monocytes in-vitro. Autocrine/paracrine released CCL26 is involved in the hypoxia-mediated monocyte migration and may represent a target molecule for the modulation of monocyte migration in-vivo.

PD1 blockade enhances K+ channel activity, Ca2+ signaling, and migratory ability in cytotoxic T lymphocytes of patients with head and neck cancer

BACKGROUND

Immunotherapy has emerged as a promising treatment modality for head and neck squamous cell carcinoma (HNSCC). Pembrolizumab, an anti-programmed death 1 antibody, is an immunotherapy agent currently approved for metastatic HNSCC and curative intent clinical trials. Although clinical responses to pembrolizumab are promising, many patients fail to respond. However, it is well known that T cell cytotoxicity and chemotaxis are critically important in the elimination of HNSCC tumors. These functions depend on ion channel activity and downstream Ca2+ fluxing abilities, which are defective in patients with HNSCC. The purpose of this study was to elucidate the effects of pembrolizumab on potassium (K+) channel (KCa3.1 and Kv1.3) activity, Ca2+ fluxes, and chemotaxis in the cytotoxic T cells of patients with HNSCC and to determine their correlation with treatment response.

METHODS

Functional studies were conducted in CD8+ peripheral blood T cells (PBTs) and tumor infiltrating lymphocytes (TILs) from patients with HNSCC treated with pembrolizumab. Untreated patients with HNSCC were used as controls. The ion channel activity of CD8+ T cells was measured by patch-clamp electrophysiology; single-cell Ca2+ fluxing abilities were measured by live microscopy. Chemotaxis experiments were conducted in a three-dimensional collagen matrix. Pembrolizumab patients were stratified as responders or non-responders based on pathological response (percent of viable tumor remaining at resection; responders: ≤80% viable tumor; non-responders: >80% viable tumor).

RESULTS

Pembrolizumab increased K+ channel activity and Ca2+ fluxes in TILs independently of treatment response. However, in PBTs from responder patients there was an increased KCa3.1 activity immediately after pembrolizumab treatment that was accompanied by a characteristic increase in Kv1.3 and Ca2+ fluxes as compared with PBTs from non-responder patients. The effects on Kv1.3 and Ca2+ were prolonged and persisted after tumor resection. Chemotaxis was also improved in responder patients' PBTs. Unlike non-responders' PBTs, pembrolizumab increased their ability to chemotax in a tumor-like, adenosine-rich microenvironment immediately after treatment, and additionally they maintained an efficient chemotaxis after tumor resection.

CONCLUSIONS

Pembrolizumab enhanced K+ channel activity, Ca2+ fluxes and chemotaxis of CD8+ T cells in patients with HNSCC, with a unique pattern of response in responder patients that is conducive to the heightened functionality of their cytotoxic T cells.

Fibronectin-Expressing Mesenchymal Tumor Cells Promote Breast Cancer Metastasis

Simple Summary

For cancer to metastasize, tumor cells must not only invade the local tissue but must also grow and proliferate once they arrive. Tumor cell heterogeneity, the presence of multiple types of cancer cells within a tumor, can increase cell proliferation and invasion through cooperative interactions, increasing the potential for metastasis. We recently found that pro-invasion cancer cells express the protein fibronectin and increase metastasis for pro-growth cancer cells. We investigated this interaction by analyzing these two cell types’ migration and survival, both alone and in co-cultures. We find that pro-invasion cells have a protective effect on pro-growth cells, which otherwise die after two days in nutrient-starved conditions. Further, we find that adding soluble fibronectin to pro-growth cells in culture was sufficient to improve survival. However, their survival was higher for co-culturing conditions. These studies highlight the importance of cancer cell heterogeneity and the role of fibronectin in metastasis.

Abstract

Tumor metastasis is connected to epithelial-mesenchymal heterogeneity (EMH) and the extracellular matrix (ECM) within the tumor microenvironment. Mesenchymal-like fibronectin (FN) expressing tumor cells enhance metastasis within tumors that have EMH. However, the secondary tumors are primarily composed of the FN null population. Interestingly, during tumor cell dissemination, the invasive front has more mesenchymal-like characteristics, although the outgrowths of metastatic colonies consist of a more epithelial-like population of cells. We hypothesize that soluble FN provided by mesenchymal-like tumor cells plays a role in supporting the survival of the more epithelial-like tumor cells within the metastatic niche in a paracrine manner. Furthermore, due to a lower rate of proliferation, the mesenchymal-like tumor cells become a minority population within the metastatic niche. In this study, we utilized a multi-parametric cell-tracking algorithm and immunoblotting to evaluate the effect of EMH on the growth and invasion of an isogenic cell series within a 3D collagen network using a microfluidic platform. Using the MCF10A progression series, we demonstrated that co-culture with FN-expressing MCF10CA1h cells significantly enhanced the survival of the more epithelial MCF10CA1a cells, with a two-fold increase in the population after 5 days in co-culture, whereas the population of the MCF10CA1a cells began to decrease after 2.5 days when cultured alone (p < 0.001). However, co-culture did not significantly alter the rate of proliferation for the more mesenchymal MCF10CA1h cells. Epithelial tumor cells not only showed prolonged survival, but migrated significantly longer distances (350 µm compared with 150 µm, respectively, p < 0.01) and with greater velocity magnitude (4.5 µm/h compared with 2.1 µm/h, respectively, p < 0.001) under co-culture conditions and in response to exogenously administered FN. Genetic depletion of FN from the MCF10CA1h cells resulted in a loss of survival and migration capacity of the epithelial and mesenchymal populations. These data suggest that mesenchymal tumor cells may function to support the survival and outgrowth of more epithelial tumor cells within the metastatic niche and that inhibition of FN production may provide a valuable target for treating metastatic disease.

Morphological and Motility Features of the Stable Bleb-Driven Monopodial Form of Entamoeba and Its Importance in Encystation

Entamoeba histolytica and its reptilian counterpart and encystation model Entamoeba invadens formed a polarized monopodial morphology when treated with pentoxifylline. This morphology was propelled by retrograde flow of the cell surface resulting from a cyclic sol-gel conversion of cytoplasm and a stable bleb at the leading edge. Pentoxifylline treatment switched the unpolarized, adherent trophozoites to the nonadherent, stable bleb-driven form and altered the motility pattern from slow and random to fast, directionally persistent, and highly chemotactic. Interestingly, exogenously added adenosine produced multiple protrusions and random motility, an opposite phenotype to that of pentoxifylline. Thus, pentoxifylline, an adenosine antagonist, may be inducing the monopodial morphology by preventing lateral protrusions and restricting the leading edge to one site. The polarized form of E. invadens was aggregation competent, and time-lapse microscopy of encystation revealed its appearance during early hours, mediating the cell aggregation by directional cell migration. The addition of purine nucleotides to in vitro encystation culture prevented the formation of polarized morphology and inhibited the cell aggregation and, thus, the encystation, which further showed the importance of the polarized form in the Entamoeba life cycle. Cell polarity and motility are essential in the pathogenesis of Entamoeba parasites, and the stable bleb-driven polarized morphology of Entamoeba may also be important in invasive amoebiasis.