Cell migration: fibroblasts find a new way to get ahead

The Potential of Eight Plasma Proteins as Biomarkers in Redefining Leptospirosis Diagnosis

Leptospirosis, a notifiable endemic disease in Malaysia, has higher mortality rates than regional dengue fever. Diverse clinical symptoms and limited diagnostic methods complicate leptospirosis diagnosis. The demand for accurate biomarker-based diagnostics is increasing. This study investigated the plasma proteome of leptospirosis patients with leptospiraemia and seroconversion compared with dengue patients and healthy subjects using isobaric tags for relative and absolute quantitation (iTRAQ)-mass spectrometry (MS). The iTRAQ analysis identified a total of 450 proteins, which were refined to a list of 290 proteins through a series of exclusion criteria. Differential expression in the plasma proteome of leptospirosis patients compared to the control groups identified 11 proteins, which are apolipoprotein A-II (APOA2), C-reactive protein (CRP), fermitin family homolog 3 (FERMT3), leucine-rich alpha-2-glycoprotein 1 (LRG1), lipopolysaccharide-binding protein (LBP), myosin-9 (MYH9), platelet basic protein (PPBP), platelet factor 4 (PF4), profilin-1 (PFN1), serum amyloid A-1 protein (SAA1), and thrombospondin-1 (THBS1). Following a study on a verification cohort, a panel of eight plasma protein biomarkers was identified for potential leptospirosis diagnosis: CRP, LRG1, LBP, MYH9, PPBP, PF4, SAA1, and THBS1. In conclusion, a panel of eight protein biomarkers offers a promising approach for leptospirosis diagnosis, addressing the limitations of the "one disease, one biomarker" concept.

Matrix Resistance Toward Proteolytic Cleavage Controls Contractility-Dependent Migration Modes During Angiogenic Sprouting

Tissue homeostasis and disease states rely on the formation of new blood vessels through angiogenic sprouting, which is tightly regulated by the properties of the surrounding extracellular matrix. While physical cues, such as matrix stiffness or degradability, have evolved as major regulators of cell function in tissue microenvironments, it remains unknown whether and how physical cues regulate endothelial cell migration during angiogenesis. To investigate this, a biomimetic model of angiogenic sprouting inside a tunable synthetic hydrogel is created. It is shown that endothelial cells sense the resistance of the surrounding matrix toward proteolytic cleavage and respond by adjusting their migration phenotype. The resistance cells encounter is impacted by the number of covalent matrix crosslinks, crosslink degradability, and the proteolytic activity of cells. When matrix resistance is high, cells switch from a collective to an actomyosin contractility-dependent single cellular migration mode. This switch in collectivity is accompanied by a major reorganization of the actin cytoskeleton, where stress fibers are no longer visible, and F-actin aggregates in large punctate clusters. Matrix resistance is identified as a previously unknown regulator of angiogenic sprouting and, thus, provides a mechanism by which the physical properties of the matrix impact cell migration modes through cytoskeletal remodeling.

Centella triterpenes cream as a potential drug for the treatment of hypertrophic scar through inhibiting the phosphorylation of STAT3: A network pharmacology analysis and in vitro experiments

BACKGROUND

Hypertrophic scars (HS) often affect the normal function and appearance of the skin and bring adverse effects to the body and mind of patients, being a challenge in the fields of burns and plastic surgery as well as rehabilitation. Despite significant efficacy of centella triterpenes cream for treating HS clinically, its pharmacodynamics and molecular targets are still unclear. Therefore, the network pharmacology analysis combined with in vitro cell molecular biology experiments was used to explore the mechanism and targets of centella triterpenes cream treating HS in this study.

METHODS

First, target genes of asiaticoside (AC) were obtained from the databases including the Comparative Toxicogenomics Database, similarity ensemble approach, SwissTargetPrediction and TargetNet, and HS targets were acquired from the databases like Disgenet, GeneCards, and Online Mendelian Inheritance in Man. The common targets of AC-HS were obtained through plotting a Venn diagram. Subsequently, STRING 11.0 was employed for analyzing the protein-protein interaction (PPI) network of the common targets, and cytoscape 3.9.0 for analyzing the connectivity of PPI and plotting the network diagram of "drug-component-target". Additionally, a modified tissue culture method was applied to separate primary normal fibroblasts (NFs) in human skin and hypertrophic scar fibroblasts (HSFs). HSFs after 24-h AC treatment were subjected to MTT assay to detect cell viability, scratch assay to assess cell migration ability, and western blot to test the protein expression levels of STAT3, p-STAT3, transforming growth factor-β1 (TGF-β1), collagen I (COL 1), fibronectin 1 (FN1), and alpha-smooth muscle actin (α-SMA).

RESULTS

In network pharmacology analysis, 134 pharmacodynamic targets of AC and 2333 HS targets were obtained after retrieving the database, 50 AC-HS common targets were obtained by a Venn diagram, and a total of 178 edges and 13 core genes such as JUN and STAT3 were acquired by PPI analysis. In vitro experiments showed that the phosphorylation level of STAT3 (p-STAT3) was increased in HSFs. In addition to reducing p-STAT3 in HSFs, AC significantly inhibited the cell viability and migration of HSFs and downregulated the protein levels of TGF-β1, COL 1, FN 1, and α-SMA.

CONCLUSION

STAT3 can be activated in HS. AC may exert its pharmacological effects of inhibiting TGF-β1 signal transduction and regulating extracellular matrix remodeling in HS by inhibiting STAT3 phosphorylation. However, the specific molecular mechanism of AC remains to be verified through further experiments.

Comparison of three in vitro keratinocytes-fibroblasts wound healing models commonly used in pharmaceutical research

OBJECTIVES

Several common wound healing models have been used to evaluate wound healing agents and formulations, namely: conditioned media (CM), transwell co-cultures (TWCC) and co-cultures (CC) in a monolayer. However, no study has been conducted to compare the relevance of these models in the keratinocytes and fibroblasts interaction physiologically. Therefore, this study aimed to compare these models based on cell migration and proliferation, and matrix metalloproteinase (MMP) expression.

METHODS

Cell migration was analysed by scratch assay and MMP-7, while cell proliferation was analysed by (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) tetrazolium reduction assay.

KEY FINDINGS

Increased cell migration was observed in CM and TWCC models, while varied results were obtained in CC. Cell migration was increased due to upregulation of MMP-7 in CM and TWCC models, while it was downregulated in CC, which might have hindered migration of both cells in monolayers.

CONCLUSIONS

CM and TWCC are more suitable than CC for wound healing research and for evaluating wound healing agents or formulations, as they can better simulate the layered tissue constructs and paracrine interactions in the physiological environment.

Collective cell migration driven by filopodia-New insights from the social behavior of myotubes

Collective migration is a key process that is critical during development, as well as in physiological and pathophysiological processes including tissue repair, wound healing and cancer. Studies in genetic model organisms have made important contributions to our current understanding of the mechanisms that shape cells into different tissues during morphogenesis. Recent advances in high-resolution and live-cell-imaging techniques provided new insights into the social behavior of cells based on careful visual observations within the context of a living tissue. In this review, we will compare Drosophila testis nascent myotube migration with established in vivo model systems, elucidate similarities, new features and principles in collective cell migration.

Excitable networks controlling cell migration during development and disease

The directed movements of individual, groups, or sheets of cells at specific times in particular locations bring about form and complexity to developing organisms. Cells move by extending protrusions, such as macropinosomes, pseudopods, lamellipods, filopods, or blebs. Although many of the cytoskeletal components within these structures are known, less is known about the mechanisms that determine their location, number, and characteristics. Recent evidence suggests that control may be exerted by a signal transduction excitable network whose components and activities, including Ras, PI3K, TorC2, and phosphoinositides, self-organize on the plasma membrane and propagate in waves. The waves drive the various types of protrusions, which in turn, determine the modes of cell migration. Acute perturbations at specific points in the network produce abrupt shifts in protrusion type, including transitions from pseudopods to filopods or lamellipods. These observations have also contributed to a delineation of the signal transduction network, including candidate fast positive and delayed negative feedback loops. The network contains many oncogenes and tumor suppressors, and other molecules which have recently been implicated in developmental and metabolic abnormalities. Thus, the concept of signal transduction network excitability in cell migration can be used to understand disease states and morphological changes occurring in development.

Colloidal crystals of compliant microgel beads to study cell migration and mechanosensitivity in 3D

Tissues are defined not only by their biochemical composition, but also by their distinct mechanical properties. It is now widely accepted that cells sense their mechanical environment and respond to it. However, studying the effects of mechanics in in vitro 3D environments is challenging since current 3D hydrogel assays convolve mechanics with gel porosity and adhesion. Here, we present novel colloidal crystals as modular 3D scaffolds where these parameters are principally decoupled by using monodisperse, protein-coated PAAm microgel beads as building blocks, so that variable stiffness regions can be achieved within one 3D colloidal crystal. Characterization of the colloidal crystal and oxygen diffusion simulations suggested the suitability of the scaffold to support cell survival and growth. This was confirmed by live-cell imaging and fibroblast culture over a period of four days. Moreover, we demonstrate unambiguous durotactic fibroblast migration and mechanosensitive neurite outgrowth of dorsal root ganglion neurons in 3D. This modular approach of assembling 3D scaffolds from mechanically and biochemically well-defined building blocks allows the spatial patterning of stiffness decoupled from porosity and adhesion sites in principle and provides a platform to investigate mechanosensitivity in 3D environments approximating tissues in vitro.

Substance P enhances cellular migration and inhibits senescence in human dermal fibroblasts under hyperglycemic conditions

Diabetes induces cellular dysfunction in dermal fibroblasts, such as impairment in migration, which is a major cause of chronic wound. Here, we demonstrated that the migration of human dermal fibroblasts was impaired under a high glucose culture condition. Substance P (SP) rescued the impaired migration of the fibroblasts. The activity of Rac1, Rho-associated kinase (ROCK), and Src was required for SP-mediated rescue of fibroblast migration. SP activated Rac1 and Src, whereas, NSC23766, a Rac1 inhibitor, and PP1 and PP2, Src inhibitors, inhibited SP-mediated enhancement of fibroblast migration. Y-27632, a ROCK inhibitor, inhibited the SP-mediated rescue of fibroblast migration. Senescence-associated β-galactosidase activity increased in human dermal fibroblasts cultured in a high glucose environment, but SP inhibited the β-galactosidase activity of the fibroblasts. These results suggest that SP promotes the migration of human dermal fibroblasts in diabetic-condition-mimicking cultures via the activity of Rac1, ROCK, and Src, and inhibits fibroblast senescence in hyperglycemic cultures.

The focal adhesion scaffold protein Hic-5 regulates vimentin organization in fibroblasts

Focal adhesion (FA)-stimulated reorganization of the F-actin cytoskeleton regulates cellular size, shape, and mechanical properties. However, FA cross-talk with the intermediate filament cytoskeleton is poorly understood. Genetic ablation of the FA-associated scaffold protein Hic-5 in mouse cancer-associated fibroblasts (CAFs) promoted a dramatic collapse of the vimentin network, which was rescued following EGFP-Hic-5 expression. Vimentin collapse correlated with a loss of detergent-soluble vimentin filament precursors and decreased vimentin S72/S82 phosphorylation. Additionally, fluorescence recovery after photobleaching analysis indicated impaired vimentin dynamics. Microtubule (MT)-associated EB1 tracking and Western blotting of MT posttranslational modifications indicated no change in MT dynamics that could explain the vimentin collapse. However, pharmacological inhibition of the RhoGTPase Cdc42 in Hic-5 knockout CAFs rescued the vimentin collapse, while pan-formin inhibition with SMIFH2 promoted vimentin collapse in Hic-5 heterozygous CAFs. Our results reveal novel regulation of vimentin organization/dynamics by the FA scaffold protein Hic-5 via modulation of RhoGTPases and downstream formin activity.

Sticking to a plan: adhesion and signaling control spatial organization of cells within migrating collectives

Collective cell migration is required in a vast array of biological phenomena, including organogenesis and embryonic development. The mechanisms that underlie collective cell migration not only involve the morphogenetic changes associated with single cell migration, but also require the maintenance of cell-cell junctions during movement. Additionally, cell shape changes and polarity must be coordinated in a multicellular manner in order to preserve directional movement in the migrating cohort, and often relates to multiple functions of common signaling pathways. In this review, we summarize the current understanding of the mechanisms underlying higher order tissue organization during migration, with particular focus on the interplay between cell adhesion and signaling that we propose can be tuned to support different types of collective movements.

The Biophysics of 3D Cell Migration

Three-dimensional (3D) cell culture systems have gained increasing interest not only for 3D migration studies but also for their use in drug screening, tissue engineering, and ex vivo modeling of metastatic behavior in the field of cancer biology and morphogenesis in the field of developmental biology. The goal of studying cells in a 3D context is to attempt to more faithfully recapitulate the physiological microenvironment of tissues, including mechanical and structural parameters that we envision will reveal more predictive data for development programs and disease states. In this review, we discuss the pros and cons of several well-characterized 3D cell culture systems for performing 3D migration studies. We discuss the intracellular and extracellular signaling mechanisms that govern cell migration. We also describe the mathematical models and relevant assumptions that can be used to describe 3D cell movement.

Nanoscale localization of proteins within focal adhesions indicates discrete functional assemblies with selective force-dependence

Focal adhesions (FAs) are subcellular regions at the micrometer scale that link the cell to the surrounding microenvironment and control vital cell functions. However, the spatial architecture of FAs remains unclear at the nanometer scale. We used two-color and three-color super-resolution stimulated emission depletion microscopy to determine the spatial distributions and co-localization of endogenous FA components in fibroblasts. Our data indicate that adhesion proteins inside, but not outside, FAs are organized into nanometer size units of multi-protein assemblies. The loss of contractile force reduced the nanoscale co-localization between different types of proteins, while it increased this co-localization between markers of the same type. This suggests that actomyosin-dependent force exerts a nonrandom, specific, control of the localization of adhesion proteins within cell-matrix adhesions. These observations are consistent with the possibility that proteins in cell-matrix adhesions are assembled in nanoscale particles, and that force regulates the localization of the proteins therein in a protein-specific manner. This detailed knowledge of how the organization of FA components at the nanometer scale is linked to the capacity of the cells to generate contractile forces expands our understanding of cell adhesion in health and disease.

Distinct biological events generated by ECM proteolysis by two homologous collagenases

It is well established that the expression profiles of multiple and possibly redundant matrix-remodeling proteases (e.g., collagenases) differ strongly in health, disease, and development. Although enzymatic redundancy might be inferred from their close similarity in structure, their in vivo activity can lead to extremely diverse tissue-remodeling outcomes. We observed that proteolysis of collagen-rich natural extracellular matrix (ECM), performed uniquely by individual homologous proteases, leads to distinct events that eventually affect overall ECM morphology, viscoelastic properties, and molecular composition. We revealed striking differences in the motility and signaling patterns, morphology, and gene-expression profiles of cells interacting with natural collagen-rich ECM degraded by different collagenases. Thus, in contrast to previous notions, matrix-remodeling systems are not redundant and give rise to precise ECM-cell crosstalk. Because ECM proteolysis is an abundant biochemical process that is critical for tissue homoeostasis, these results improve our fundamental understanding its complexity and its impact on cell behavior.

Follistatin-like 1 promotes cardiac fibroblast activation and protects the heart from rupture

Follistatin‐like 1 (Fstl1) is a secreted protein that is acutely induced in heart following myocardial infarction (MI). In this study, we investigated cell type‐specific regulation of Fstl1 and its function in a murine model of MI. Fstl1 was robustly expressed in fibroblasts and myofibroblasts in the infarcted area compared to cardiac myocytes. The conditional ablation of Fstl1 in S100a4‐expressing fibroblast lineage cells (Fstl1‐cfKO mice) led to a reduction in injury‐induced Fstl1 expression and increased mortality due to cardiac rupture during the acute phase. Cardiac rupture was associated with a diminished number of myofibroblasts and decreased expression of extracellular matrix proteins. The infarcts of Fstl1‐cfKO mice displayed weaker birefringence, indicative of thin and loosely packed collagen. Mechanistically, the migratory and proliferative capabilities of cardiac fibroblasts were attenuated by endogenous Fstl1 ablation. The activation of cardiac fibroblasts by Fstl1 was mediated by ERK1/2 but not Smad2/3 signaling. This study reveals that Fstl1 is essential for the acute repair of the infarcted myocardium and that stimulation of early fibroblast activation is a novel function of Fstl1.

Linking immune responses with fibrosis in allergic eye disease

PURPOSE OF REVIEW

Here, we explore an emerging theme in the literature, which is the role of dendritic cells in the causation of fibrosis. To fully appreciate this pathway to disease, we also review the most recent literature regarding dendritic cell biology as it pertains to ocular surface tissues. On the basis of this information, we propose a unifying hypothesis for how dendritic cells may cause conjunctival fibrosis in the allergy setting.

RECENT FINDINGS

Work in models of airway remodeling and liver fibrosis has pointed to a potentially central role for dendritic cells in the pathobiology of fibrosis. Indeed, these cells are recognized as the most potent antigen-presenting cells, and as such activate T lymphocytes that are profibrotic under certain conditions. However, recent findings suggest a more direct role for dendritic cells, which opens up the possibility that a similar pathway may be relevant in the causation of conjunctival fibrosis, particularly in allergic eye disease.

SUMMARY

Conjunctival fibrosis is a serious clinical concern and is associated with chronic inflammation of the ocular surface tissue, such as in allergic eye disease. Dendritic cells are required in mediating allergic disease by activating pathologic T lymphocytes. Recent findings pointing to a central role for dendritic cell in fibrosis may, however, mean that these cells could also be contributing directly to conjunctival fibrosis. If so, furthering our understanding of dendritic cells could lead to the identification of novel and more effective therapeutic strategies to treat this disease.

Pérez L, San Martín N, Gálvez BG. Membrane Blebbing Is Required for Mesenchymal Precursor Migration

Mesenchymal precursors (MPs) present some advantageous features, such as differentiation and migration, which make them promising candidates for cell therapy. A better understanding of MP migration characteristics would aid the development of cell delivery protocols. Traditionally, cell migration is thought to occur only through the formation of lamellipodia. More recently, contractility-driven bleb formation has emerged as an alternative mechanism of motility. Here we report that MPs derived from different tissues present spontaneously dynamic cytoplasmic projections in sub-confluent culture, which appear as a combination of lamellipodia with blebs in the leading edge. Upon initial seeding, however, only bleb structures could be observed. Immunofluorescence revealed the presence of pERM, RhoA and F-actin during the blebbing process. Results from migration assays in the presence of blebbistatin, a myosin II inhibitor, showed that bleb formation correlated with migratory capacity, suggesting a functional role for blebs in migration. Bleb formation might be a useful mechanism to improve cell migration in cellular therapy protocols.

Lamellipodia and Membrane Blebs Drive Efficient Electrotactic Migration of Rat Walker Carcinosarcoma Cells WC 256

The endogenous electric field (EF) may provide an important signal for directional cell migration during wound healing, embryonic development and cancer metastasis but the mechanism of cell electrotaxis is poorly understood. Additionally, there is no research addressing the question on the difference in electrotactic motility of cells representing various strategies of cell movement—specifically blebbing vs. lamellipodial migration. In the current study we constructed a unique experimental model which allowed for the investigation of electrotactic movement of cells of the same origin but representing different modes of cell migration: weakly adherent, spontaneously blebbing (BC) and lamellipodia forming (LC) WC256 cells. We report that both BC and LC sublines show robust cathodal migration in a physiological EF (1–3 V/cm). The directionality of cell movement was completely reversible upon reversing the field polarity. However, the full reversal of cell direction after the change of EF polarity was much faster in the case of BC (10 minutes) than LC cells (30 minutes). We also investigated the distinct requirements for Rac, Cdc42 and Rho pathways and intracellular Ca²⁺ in electrotaxis of WC256 sublines forming different types of cell protrusions. It was found that Rac1 is required for directional movement of LC to a much greater extent than for BC, but Cdc42 and RhoA are more crucial for BC than for LC cells. The inhibition of ROCK did not affect electrotaxis of LC in contrast to BC cells. The results also showed that intracellular Ca²⁺ is essential only for the electrotactic reaction of BC cells. Moreover, inhibition of MLCK and myosin II did not affect the electrotaxis of LC in contrast to BC cells. In conclusion, our results revealed that both lamellipodia and membrane blebs can efficiently drive electrotactic migration of WC 256 carcinosarcoma cells, however directional migration is mediated by different signalling pathways.

Investigation of the Viability, Adhesion, and Migration of Human Fibroblasts in a Hyaluronic Acid/Gelatin Microgel-Reinforced Composite Hydrogel for Vocal Fold Tissue Regeneration

The potential use of a novel scaffold biomaterial consisting of cross-linked hyaluronic acid (HA)-gelatin (Ge) composite microgels is investigated for use in treating vocal fold injury and scarring. Cell adhesion integrins and kinematics of cell motion are investigated in 2D and 3D culture conditions, respectively. Human vocal fold fibroblast (hVFF) cells are seeded on HA-Ge microgels attached to a HA hydrogel thin film. The results show that hVFF cells establish effective adhesion to HA-Ge microgels through the ubiquitous expression of β1 integrin in the cell membrane. The microgels are then encapsulated in a 3D HA hydrogel for the study of cell migration. The cells within the HA-Ge microgel-reinforced composite hydrogel (MRCH) scaffold have an average motility speed of 0.24 ± 0.08 μm min(-1) . The recorded microscopic images reveal features that are presumably associated with lobopodial and lamellipodial cell migration modes within the MRCH scaffold. Average cell speed during lobopodial migration is greater than that during lamellipodial migration. The cells move faster in the MRCH than in the HA-Ge gel without microgels. These findings support the hypothesis that HA-Ge MRCH promotes cell adhesion and migration; thereby they constitute a promising biomaterial for vocal fold repair.

RhoA Ambivalently Controls Prominent Myofibroblast Characteritics by Involving Distinct Signaling Routes

Introduction

RhoA has been shown to be beneficial in cardiac disease models when overexpressed in cardiomyocytes, whereas its role in cardiac fibroblasts (CF) is still poorly understood. During cardiac remodeling CF undergo a transition towards a myofibroblast phenotype thereby showing an increased proliferation and migration rate. Both processes involve the remodeling of the cytoskeleton. Since RhoA is known to be a major regulator of the cytoskeleton, we analyzed its role in CF and its effect on myofibroblast characteristics in 2 D and 3D models.

Results

Downregulation of RhoA was shown to strongly affect the actin cytoskeleton. It decreased the myofibroblast marker α-sm-actin, but increased certain fibrosis-associated factors like TGF-β and collagens. Also, the detailed analysis of CTGF expression demonstrated that the outcome of RhoA signaling strongly depends on the involved stimulus. Furthermore, we show that proliferation of myofibroblasts rely on RhoA and tubulin acetylation. In assays accessing three different types of migration, we demonstrate that RhoA/ROCK/Dia1 are important for 2D migration and the repression of RhoA and Dia1 signaling accelerates 3D migration. Finally, we show that a downregulation of RhoA in CF impacts the viscoelastic and contractile properties of engineered tissues.

Conclusion

RhoA positively and negatively influences myofibroblast characteristics by differential signaling cascades and depending on environmental conditions. These include gene expression, migration and proliferation. Reduction of RhoA leads to an increased viscoelasticity and a decrease in contractile force in engineered cardiac tissue.

Microtubule-Mediated Inositol Lipid Signaling Plays Critical Roles in Regulation of Blebbing

Cells migrate by extending pseudopods such as lamellipodia and blebs. Although the signals leading to lamellipodia extension have been extensively investigated, those for bleb extension remain unclear. Here, we investigated signals for blebbing in Dictyostelium cells using a newly developed assay to induce blebbing. When cells were cut into two pieces with a microneedle, the anucleate fragments vigorously extended blebs. This assay enabled us to induce blebbing reproducibly, and analyses of knockout mutants and specific inhibitors identified candidate molecules that regulate blebbing. Blebs were also induced in anucleate fragments of leukocytes, indicating that this assay is generally applicable to animal cells. After cutting, microtubules in the anucleate fragments promptly depolymerized, followed by the extension of blebs. Furthermore, when intact cells were treated with a microtubule inhibitor, they frequently extended blebs. The depolymerization of microtubules induced the delocalization of inositol lipid phosphatidylinositol 3,4,5-trisphosphate from the cell membrane. PI3 kinase-null cells frequently extended blebs, whereas PTEN-null cells extended fewer blebs. From these observations, we propose a model in which microtubules play a critical role in bleb regulation via inositol lipid metabolism.

Fibroblast Migration in 3D is Controlled by Haptotaxis in a Non-muscle Myosin II-Dependent Manner

Cell migration in 3D is a key process in many physiological and pathological processes. Although valuable knowledge has been accumulated through analysis of various 2D models, some of these insights are not directly applicable to migration in 3D. In this study, we have confined biomimetic hydrogels within microfluidic platforms in the presence of a chemoattractant (platelet-derived growth factor-BB). We have characterized the migratory responses of human fibroblasts within them, particularly focusing on the role of non-muscle myosin II. Our results indicate a prominent role for myosin II in the integration of chemotactic and haptotactic migratory responses of fibroblasts in 3D confined environments.

Distinct signaling mechanisms regulate migration in unconfined versus confined spaces

α4β1 integrin promotes migration of fibroblast-like cells in confined environment by enhancing myosin IIA via Rac1 inhibition, whereas unconfined migration requires Rac1 and myosin IIB.

Using a microchannel assay, we demonstrate that cells adopt distinct signaling strategies to modulate cell migration in different physical microenvironments. We studied α4β1 integrin–mediated signaling, which regulates cell migration pertinent to embryonic development, leukocyte trafficking, and melanoma invasion. We show that α4β1 integrin promotes cell migration through both unconfined and confined spaces. However, unlike unconfined (2D) migration, which depends on enhanced Rac1 activity achieved by preventing α4/paxillin binding, confined migration requires myosin II–driven contractility, which is increased when Rac1 is inhibited by α4/paxillin binding. This Rac1–myosin II cross talk mechanism also controls migration of fibroblast-like cells lacking α4β1 integrin, in which Rac1 and myosin II modulate unconfined and confined migration, respectively. We further demonstrate the distinct roles of myosin II isoforms, MIIA and MIIB, which are primarily required for confined and unconfined migration, respectively. This work provides a paradigm for the plasticity of cells migrating through different physical microenvironments.

WIP regulates persistence of cell migration and ruffle formation in both mesenchymal and amoeboid modes of motility

The spatial distribution of signals downstream from receptor tyrosine kinases (RTKs) or G-protein coupled receptors (GPCR) regulates fundamental cellular processes that control cell migration and growth. Both pathways rely significantly on actin cytoskeleton reorganization mediated by nucleation-promoting factors such as the WASP-(Wiskott-Aldrich Syndrome Protein) family. WIP (WASP Interacting Protein) is essential for the formation of a class of polarised actin microdomain, namely dorsal ruffles, downstream of the RTK for PDGF (platelet-derived growth factor) but the underlying mechanism is poorly understood. Using lentivirally-reconstituted WIP-deficient murine fibroblasts we define the requirement for WIP interaction with N-WASP (neural WASP) and Nck for efficient dorsal ruffle formation and of WIP-Nck binding for fibroblast chemotaxis towards PDGF-AA. The formation of both circular dorsal ruffles in PDGF-AA-stimulated primary fibroblasts and lamellipodia in CXCL13-treated B lymphocytes are also compromised by WIP-deficiency. We provide data to show that a WIP-Nck signalling complex interacts with RTK to promote polarised actin remodelling in fibroblasts and provide the first evidence for WIP involvement in the control of migratory persistence in both mesenchymal (fibroblast) and amoeboid (B lymphocytes) motility.

Actin stress fibre subtypes in mesenchymal-migrating cells

Mesenchymal cell migration is important for embryogenesis and tissue regeneration. In addition, it has been implicated in pathological conditions such as the dissemination of cancer cells. A characteristic of mesenchymal-migrating cells is the presence of actin stress fibres, which are thought to mediate myosin II-based contractility in close cooperation with associated focal adhesions. Myosin II-based contractility regulates various cellular activities, which occur in a spatial and temporal manner to achieve directional cell migration. These myosin II-based activities involve the maturation of integrin-based adhesions, generation of traction forces, establishment of the front-to-back polarity axis, retraction of the trailing edge, extracellular matrix remodelling and mechanotransduction. Growing evidence suggests that actin stress fibre subtypes, namely dorsal stress fibres, transverse arcs and ventral stress fibres, could provide this spatial and temporal myosin II-based activity. Consistent with their functional differences, recent studies have demonstrated that the molecular composition of actin stress fibre subtypes differ significantly. This present review focuses on the current view of the molecular composition of actin stress fibre subtypes and how these fibre subtypes regulate mesenchymal cell migration.

Cellular and molecular mechanisms controlling the migration of melanocytes and melanoma cells

During embryonic development in vertebrates, the neural crest-derived melanoblasts migrate along the dorsolateral axis and cross the basal membrane separating the dermis from the epidermis to reach their final location in the interfollicular epidermis and epidermal hair follicles. Neoplastic transformation converts melanocytes into highly invasive and metastatic melanoma cells. In vitro, these cells extend various types of protrusions and adopt two interconvertible modes of migration, mesenchymal and amoeboid, driven by different signalling molecules. In this review, we describe the major contributions of natural mouse mutants, mouse models generated by genetic engineering and in vitro culture systems, to identification of the genes, signalling pathways and mechanisms regulating the migration of normal and pathological cells of the melanocyte lineage, at both the cellular and molecular levels.