On the crawling of animal cells

"Find Me" and "Eat Me" signals: tools to drive phagocytic processes for modulating antitumor immunity

Phagocytosis, a vital defense mechanism, involves the recognition and elimination of foreign substances by cells. Phagocytes, such as neutrophils and macrophages, rapidly respond to invaders; macrophages are especially important in later stages of the immune response. They detect "find me" signals to locate apoptotic cells and migrate toward them. Apoptotic cells then send "eat me" signals that are recognized by phagocytes via specific receptors. "Find me" and "eat me" signals can be strategically harnessed to modulate antitumor immunity in support of cancer therapy. These signals, such as calreticulin and phosphatidylserine, mediate potent pro-phagocytic effects, thereby promoting the engulfment of dying cells or their remnants by macrophages, neutrophils, and dendritic cells and inducing tumor cell death. This review summarizes the phagocytic "find me" and "eat me" signals, including their concepts, signaling mechanisms, involved ligands, and functions. Furthermore, we delineate the relationships between "find me" and "eat me" signaling molecules and tumors, especially the roles of these molecules in tumor initiation, progression, diagnosis, and patient prognosis. The interplay of these signals with tumor biology is elucidated, and specific approaches to modulate "find me" and "eat me" signals and enhance antitumor immunity are explored. Additionally, novel therapeutic strategies that combine "find me" and "eat me" signals to better bridge innate and adaptive immunity in the treatment of cancer patients are discussed.

The Role of TPM3 in Protecting Cardiomyocyte from Hypoxia-Induced Injury via Cytoskeleton Stabilization

Ischemic heart disease (IHD) remains a major global health concern, with ischemia-reperfusion injury exacerbating myocardial damage despite therapeutic interventions. In this study, we investigated the role of tropomyosin 3 (TPM3) in protecting cardiomyocytes against hypoxia-induced injury and oxidative stress. Using the AC16 and H9c2 cell lines, we established a chemical hypoxia model by treating cells with cobalt chloride (CoCl2) to simulate low-oxygen conditions. We found that CoCl2 treatment significantly upregulated the expression of hypoxia-inducible factor 1 alpha (HIF-1α) in cardiomyocytes, indicating the successful induction of hypoxia. Subsequent morphological and biochemical analyses revealed that hypoxia altered cardiomyocyte morphology disrupted the cytoskeleton, and caused cellular damage, accompanied by increased lactate dehydrogenase (LDH) release and malondialdehyde (MDA) levels, and decreased superoxide dismutase (SOD) activity, indicative of oxidative stress. Lentivirus-mediated TPM3 overexpression attenuated hypoxia-induced morphological changes, cellular damage, and oxidative stress imbalance, while TPM3 knockdown exacerbated these effects. Furthermore, treatment with the HDAC1 inhibitor MGCD0103 partially reversed the exacerbation of hypoxia-induced injury caused by TPM3 knockdown. Protein-protein interaction (PPI) network and functional enrichment analysis suggested that TPM3 may modulate cardiac muscle development, contraction, and adrenergic signaling pathways. In conclusion, our findings highlight the therapeutic potential of TPM3 modulation in mitigating hypoxia-associated cardiac injury, suggesting a promising avenue for the treatment of ischemic heart disease and other hypoxia-related cardiac pathologies.

Computational simulation of applying mechanical vibration to mesenchymal stem cell for mechanical modulation toward bone tissue engineering

Evaluation of cell response to mechanical stimuli at in vitro conditions is known as one of the important issues for modulating cell behavior. Mechanical stimuli, including mechanical vibration and oscillatory fluid flow, act as important biophysical signals for the mechanical modulation of stem cells. In the present study, mesenchymal stem cell (MSC) consists of cytoplasm, nucleus, actin, and microtubule. Also, integrin and primary cilium were considered as mechanoreceptors. In this study, the combined effect of vibration and oscillatory fluid flow on the cell and its components were investigated using numerical modeling. The results of the FEM and FSI model showed that the cell response (stress and strain values) at the frequency of 30 H z mechanical vibration has the highest value. The achieved results on shear stress caused by the fluid flow on the cell showed that the cell experiences shear stress in the range of 0 . 1 - 10 Pa . Mechanoreceptors that bind separately to the cell surface, can be highly stimulated by hydrodynamic pressure and, therefore, can play a role in the mechanical modulation of MSCs at in vitro conditions. The results of this research can be effective in future studies to optimize the conditions of mechanical stimuli applied to the cell culture medium and to determine the mechanisms involved in mechanotransduction.

A Multipole Magnetoactive Elastomer for Vibration-Driven Locomotion

Smart materials such as magnetoactive elastomers (MAEs) combine elastic and magnetic properties that can be significantly changed in response to a magnetic field and therefore offer enormous potential for applications in both scientific research and engineering. When such an elastomer contains microsized hard magnetic particles, it can become an elastic magnet once magnetized in a strong magnetic field. This article studies a multipole MAE with the aim of utilizing it as an actuation element of vibration-driven locomotion robots. The elastomer beam has three magnetic poles overall with the same poles at the ends and possesses silicone bristles protruding from its underside. The quasi-static bending of the multipole elastomer in a uniform magnetic field is investigated experimentally. The theoretical model exploits the magnetic torque to describe the field-induced bending shapes. The unidirectional locomotion of the elastomeric bristle-bot is realized in two prototype designs using magnetic actuation of either an external or an integrated source of an alternating magnetic field. The motion principle is based on cyclic interplay of asymmetric friction and inertia forces caused by field-induced bending vibrations of the elastomer. The locomotion behavior of both prototypes shows a strong resonant dependency of the advancing speed on the frequency of applied magnetic actuation.

Phosphorylation/dephosphorylation of PTP-PEST at Serine 39 is crucial for cell migration

We investigated the molecular details of the role of protein tyrosine phosphatase (PTP)-PEST in cell migration. PTP-PEST knockout mouse embryonic fibroblasts (KO MEFs) and MEF cells expressing a dominant-negative mutant of PTP-PEST showed significant suppression of cell migration compared to MEF cells expressing wild-type PTP-PEST (WT MEFs). Moreover, MEF cells harbouring a constitutively active mutant of PTP-PEST (S39A MEFs) showed a marked decrease in cell migration. In addition, MEF cells with no PTP-PEST or little PTP activity rapidly adhered to fibronectin and made many focal adhesions compared to WT MEF cells. In contrast, S39A MEF cells showed weak adhesion to fibronectin and formed a few focal adhesions. Furthermore, investigating the subcellular localization showed that Ser39-phosphorylated PTP-PEST was favourably situated in the adherent area of the pseudopodia. Therefore, we propose that suppression of PTP-PEST enzyme activity due to Ser39-phosphorylation in pseudopodia and at the leading edge of migrating cells induces rapid and good adherence to the extracellular matrix. Thus, suppression of PTP activity by Ser39-phosphorylation is critical for cell migration. Three amino acid substitutions in human PTP-PEST have been previously reported to alter PTP activity. These amino acid substitutions in mouse PTP-PEST altered the migration of MEF cells in a positive correlation.

A Scribble/Cdep/Rac pathway controls follower-cell crawling and cluster cohesion during collective border-cell migration

Collective cell movements drive normal development and metastasis. Drosophila border cells move as a cluster of 6-10 cells, where the role of the Rac GTPase in migration was first established. In border cells, as in most migratory cells, Rac stimulates leading-edge protrusion. Upstream Rac regulators in leaders have been identified; however, the regulation and function of Rac in follower border cells is unknown. Here, we show that all border cells require Rac, which promotes follower-cell motility and is important for cluster compactness and movement. We identify a Rac guanine nucleotide exchange factor, Cdep, which also regulates follower-cell movement and cluster cohesion. Scribble, Discs large, and Lethal giant larvae localize Cdep basolaterally and share phenotypes with Cdep. Relocalization of Cdep::GFP partially rescues Scribble knockdown, suggesting that Cdep is a major downstream effector of basolateral proteins. Thus, a Scrib/Cdep/Rac pathway promotes cell crawling and coordinated, collective migration in vivo.

Motor-Driven Restructuring of Cytoskeleton Composites Leads to Tunable Time-Varying Elasticity

The composite cytoskeleton, comprising interacting networks of semiflexible actin and rigid microtubules, generates forces and restructures by using motor proteins such as myosins to enable key processes including cell motility and mitosis. Yet, how motor-driven activity alters the mechanics of cytoskeleton composites remains an open challenge. Here, we perform optical tweezers microrheology and confocal imaging of composites with varying actin-tubulin molar percentages (25-75, 50-50, and 75-25), driven by light-activated myosin II motors, to show that motor activity increases the elastic plateau modulus by over 2 orders of magnitude by active restructuring of both actin and microtubules that persists for hours after motor activation has ceased. Nonlinear microrheology measurements show that motor-driven restructuring increases the force response and stiffness and suppresses actin bending. The 50-50 composite exhibits the most dramatic mechanical response to motor activity due to the synergistic effects of added stiffness from the microtubules and sufficient motor substrate for pronounced activity.

Electrical Stimulation and Conductive Polymers as a Powerful Toolbox for Tailoring Cell Behaviour in vitro

Electrical stimulation (ES) is a well-known method for guiding the behaviour of nerve cells in in vitro systems based on the response of these cells to an electric field. From this perspective, understanding how the electrochemical stimulus can be tuned for the design of a desired cell response is of great importance. Most biomedical studies propose the application of an electrical potential to cell culture arrays while examining the cell response regarding viability, morphology, and gene expression. Conversely, various studies failed to evaluate how the fine physicochemical properties of the materials used for cell culture influence the observed behaviours. Among the various materials used for culturing cells under ES, conductive polymers (CPs) are widely used either in pristine form or in addition to other polymers. CPs themselves do not possess the optimal surface for cell compatibility because of their hydrophobic nature, which leads to poor protein adhesion and, hence, poor bioactivity. Therefore, understanding how to tailor the chemical properties on the material surface will determine the obtention of improved ES platforms. Moreover, the structure of the material, either in a thin film or in porous electrospun scaffolds, also affects the biochemical response and needs to be considered. In this review, we examine how materials based on CPs influence cell behaviour under ES, and we compile the various ES setups and physicochemical properties that affect cell behaviour. This review concerns the culture of various cell types, such as neurons, fibroblasts, osteoblasts, and Schwann cells, and it also covers studies on stem cells prone to ES. To understand the mechanistic behaviour of these devices, we also examine studies presenting a more detailed biomolecular level of interaction. This review aims to guide the design of future ES setups regarding the influence of material properties and electrochemical conditions on the behaviour of in vitro cell studies.

Quantification of the mesh structure of bundled actin filaments

Biopolymer networks are essential for a wide variety of cellular functions. The biopolymer actin is known to self-assemble into a variety of spatial structures in response to physiological and physical mechanisms. So far, the mechanics of networks of single actin filaments and bundles has previously been described. However, the spatial structure of actin bundles remains poorly understood. Here, we investigate this question by bundling actin filaments with systematically varied concentrations of known physical bundling agents (MgCl2 and PEG) and physiological bundling agents (α-actinin and fascin). We image bundled actin networks with confocal microscopy and perform analysis to describe their mesh size and the nearest-distance distribution, which we call "mesh structure". We find that the mesh size ξ scales universally with actin concentration as ξ ∼ [actin]-1/2. However, the dependence of ξ on the concentration of the bundling agent depends on the agent used. Finally, we find that nearest-distance distributions are best fit by Weibull and Gamma distributions. A complete understanding of the mesh structure of biopolymer networks leads to a more mechanistic understanding of the structure of the cytoskeleton, and can be exploited to design filters with variable porosity for microfluidic devices.

Actuators based on a controlled particle-matrix interaction in magnetic hybrid materials for applications in locomotion and manipulation systems

The paper deals with the investigation of magneto-sensitive elastomers (MSE) and their application in technical actuator systems. MSE consist of an elastic matrix containing suspended magnetically soft and/or hard particles. Additionally, they can also contain silicone oil, graphite particles, thermoplastic components, etc., in various concentrations in order to tune specific properties such as viscosity, conductivity and thermoelasticity, respectively. The focuses of investigations are the beneficial properties of MSE in prototypes for locomotion and manipulation purposes that possess an integrated sensor function. The research follows the principle of a model-based design, i.e. the working steps are ideation, mathematical modelling, material characterization as well as building first functional models (prototypes). The developed apedal (without legs) and non-wheeled locomotion systems use the interplay between material deformations and the mechanical motion in connection with the issues of control and stability. Non-linear friction phenomena lead to a monotonous forward motion of the systems. The aim of this study is the design of such mechanical structures, which reduce the control costs. The investigations deal with the movement and control of ‘intelligent’ mechanisms, for which the magnetically field-controlled particle-matrix interactions provide an appropriate approach. The presented grippers enclose partially gripped objects, which is an advantage for handling sensitive objects. Form-fit grippers with adaptable contour at the contact area enable a uniform pressure distribution on the surface of gripped objects. Furthermore, with the possibility of active shape adaptation, objects with significantly differing geometries can be gripped. To realise the desired active shape adaptation, the effect of field-induced plasticity of MSE is used. The first developed prototypes mainly confirm the functional principles as such without direct application. For this, besides the ability of locomotion and manipulation itself, further technological possibilities have to be added to the systems. The first steps are therefore being taken towards integrated MSE based adaptive sensor systems.

The interplay of membrane cholesterol and substrate on vascular smooth muscle biomechanics

Cardiovascular disease (CVD) remains the primary cause of death worldwide. Specifically, atherosclerosis is a CVD characterized as a slow progressing chronic inflammatory disease. During atherosclerosis, vascular walls accumulate cholesterol and cause fatty streak formation. The progressive changes in vascular wall stiffness exert alternating mechanical cues on vascular smooth muscle cells (VSMCs). The detachment of VSMCs in the media layer of the vessel and migration toward the intima is a critical step in atherosclerosis. VSMC phenotypic switching is a complicated process that modifies VSMC structure and biomechanical function. These changes affect the expression and function of cell adhesion molecules, thus impacting VSMC migration. Accumulating evidence has shown cholesterol is capable of regulating cellular migration, proliferation, and spreading. However, the interaction and coordinated effects of both cellular cholesterol and the extracellular matrix (ECM) stiffness/composition on VSMC biomechanics remains to be elucidated.

NRAS mutant E132K identified in young-onset sporadic colorectal cancer and the canonical mutants G12D and Q61K affect distinct oncogenic phenotypes

Recent data show a global increase in colorectal cancer (CRC) cases among younger demographics, which portends poorer prognosis. The cause of rising incidence is uncertain, and its mutational landscape remains largely unexplored, including those in genes of the epidermal growth factor receptor pathway. Among these are NRAS mutants where there is paucity of functional studies compared to KRAS. Here, the novel NRAS mutant E132K, identified in three tumor samples from Filipino young-onset, sporadic colorectal cancer patients, was investigated for its effects on different cancer hallmarks, alongside the NRAS canonical mutants G12D and Q61K which are yet poorly characterized in the context of CRC. The novel NRAS mutant E132K and the canonical G12D and Q61K mutants show resistance to apoptosis, cytoskeletal reorganization, and loss of adhesion. In contrast to activating KRAS mutations, including the analogous KRAS G12D and Q61K mutations, all three NRAS mutants have no apparent effect on cell proliferation and motility. The results highlight the need to characterize isoform- and mutation-specific oncogenic phenotypes which can have repercussions in disease management and choice of therapeutic intervention. Further analyses of young-onset versus late-onset CRC datasets are necessary to qualify NRAS E132K as a biomarker for the young-onset subtype.

High expression of OSR1 as a predictive biomarker for poor prognosis and lymph node metastasis in breast cancer

PURPOSE

Oxidative stress-responsive kinase 1 (OSR1) plays a crucial role in regulating diverse cellular pathophysiologic functions, including ion homeostasis, development, differentiation, angiogenesis, invasive migration, and metastasis. Regardless, the clinical significance of OSR1 in breast cancer is scarce. The current study was conducted to evaluate the effect of OSR1 on the prognosis of patients with breast cancer with a long-term follow-up.

METHODS

OSR1 expression in formalin-fixed and paraffin-embedded tissue specimens was analyzed. These specimens were collected from 551 evaluable breast cancer cases by immunohistochemistry (IHC). OSR1 expression was dichotomized based on the H-score in IHC. The effects of OSR1 levels on the clinicopathological attributes and survival prediction in patients with breast cancer were explored.

RESULTS

Among 551 specimens, 183 (33.2%) exhibited high expression of OSR1 in tumor cells. High OSR1 levels were markedly correlated with histologic grade (P = 0.035), ER (P < 0.001) and PgR (P = 0.043) expression, lymph node involvement (P < 0.001), TNM stage (P < 0.001), and axillary surgery procedures (P = 0.003). Univariate analysis results indicate that patients with high OSR1 expression had significantly poor overall survival (P < 0.001), distant disease-free survival (P < 0.001), and breast cancer-specific survival (P < 0.001). Multivariable Cox regression analyses suggest that OSR1 expression was an independent predictive marker of poor prognosis and lymph node metastasis (HR 3.224, 95% CI 1.182-8.702, P = 0.023) in patients with breast cancer.

CONCLUSIONS

Our findings indicate that OSR1 is a significantly independent prognosis index for patients with breast cancer with respect to distant disease-free survival, overall survival, and breast cancer-specific survival. High OSR1 expression caused an increase in deaths specifically attributed to breast cancer and was related to increased lymph node metastasis. However, the precise cellular mechanisms for OSR1 in breast cancer require further research.

Cofilin1-driven actin dynamics controls migration of thymocytes and is essential for positive selection in the thymus

Actin dynamics is essential for T-cell development. We show here that cofilin1 is the key molecule for controlling actin filament turnover in this process. Mice with specific depletion of cofilin1 in thymocytes showed increased steady-state levels of actin filaments, and associated alterations in the pattern of thymocyte migration and adhesion. Our data suggest that cofilin1 is controlling oscillatory F-actin changes, a parameter that influences the migration pattern in a 3-D environment. In a collagen matrix, cofilin1 controls the speed and resting intervals of migrating thymocytes. Cofilin1 was not involved in thymocyte proliferation, cell survival, apoptosis or surface receptor trafficking. However, in cofilin1 mutant mice, impaired adhesion and migration resulted in a specific block of thymocyte differentiation from CD4/CD8 double-positive thymocytes towards CD4 and CD8 single-positive cells. Our data suggest that tuning of the dwelling time of thymocytes in the thymic niches is tightly controlled by cofilin1 and essential for positive selection during T-cell differentiation. We describe a novel role of cofilin1 in the physiological context of migration-dependent cell differentiation.

Nitric Oxide and Hydrogen Sulfide Regulation of Ischemic Vascular Growth and Remodeling

Ischemic vascular remodeling occurs in response to stenosis or arterial occlusion leading to a change in blood flow and tissue perfusion. Altered blood flow elicits a cascade of molecular and cellular physiological responses leading to vascular remodeling of the macro- and micro-circulation. Although cellular mechanisms of vascular remodeling such as arteriogenesis and angiogenesis have been studied, therapeutic approaches in these areas have had limited success due to the complexity and heterogeneous constellation of molecular signaling events regulating these processes. Understanding central molecular players of vascular remodeling should lead to a deeper understanding of this response and aid in the development of novel therapeutic strategies. Hydrogen sulfide (H₂ S) and nitric oxide (NO) are gaseous signaling molecules that are critically involved in regulating fundamental biochemical and molecular responses necessary for vascular growth and remodeling. This review examines how NO and H₂ S regulate pathophysiological mechanisms of angiogenesis and arteriogenesis, along with important chemical and experimental considerations revealed thus far. The importance of NO and H₂ S bioavailability, their synthesis enzymes and cofactors, and genetic variations associated with cardiovascular risk factors suggest that they serve as pivotal regulators of vascular remodeling responses. © 2019 American Physiological Society. Compr Physiol 9:1213-1247, 2019.

Contribution of frustules and mucilage trails to the mobility of diatom Navicula sp

The secreted mucilage trails of the diatom Navicula sp. in the process of motility were studied by scanning electron microscopy (SEM), transmission electron microscope (TEM), atomic force microscopy (AFM) and Raman spectra etc. Contrary to previous studies, force measurement was taken directly on the mucilage trails of live cells using the method of in situ force mapping by AFM. The retraction force curve presented an increased tip-substrate peak and a small saw-tooth pattern tip-mucilage peak. Especially, same measurements on various substrates with different surface energy revealed that the mucilage trails actually functioned as a medium increasing the adhesive force between the diatom and substrates, which is crucial to diatom’s adhesion and locomotion. In addition, the mechanical properties of mucilage trails were quite different from mucilage strands in the maximum adhesive force and the maximum polymer extension length. Raman spectra indicated the difference in compositions that both of the two kinds of mucilages had proteins and polysaccharide, but the mucilage strands contained some other components with C=O, —CH₂— and —CH₃ asymmetric and symmetric stretches. This research hammers out more precise information about mucilage trails which would be useful in terms of diatom motility and biofouling prevention.

Axon formation, extension, and navigation: only a neuroscience phenomenon?

Understanding how neurons form, extend, and navigate their finger-like axonal and dendritic processes is crucial for developing therapeutics for the diseased and damaged brain. Although less well appreciated, many other types of cells also send out similar finger-like projections. Indeed, unlike neuronal specific phenomena such as synapse formation or synaptic transmission, an important issue for thought is that this critical long-standing question of how a cellular process like an axon or dendrite forms and extends is not primarily a neuroscience problem but a cell biological problem. In that case, the use of simple cellular processes - such as the bristle cell process of Drosophila - can aid in the fight to answer these critical questions. Specifically, determining how a model cellular process is generated can provide a framework for manipulations of all types of membranous process-containing cells, including different types of neurons.

Room-Temperature Ionic Liquids and Biomembranes: Setting the Stage for Applications in Pharmacology, Biomedicine, and Bionanotechnology

Empirical evidence and conceptual elaboration reveal and rationalize the remarkable affinity of organic ionic liquids for biomembranes. Cations of the so-called room-temperature ionic liquids (RTILs), in particular, are readily absorbed into the lipid fraction of biomembranes, causing a variety of observable biological effects, including generic cytotoxicity, broad antibacterial potential, and anticancer activity. Chemical physics analysis of model systems made of phospholipid bilayers, RTIL ions, and water confirm and partially explain this evidence, quantifying the mild destabilizing effect of RTILs on the structural, dynamic, and thermodynamic properties of lipids in biomembranes. Our Feature Article presents a brief introduction to these systems and to their roles in biophysics and biotechnology, summarizing recent experimental and computational results on their properties. More importantly, it highlights the many developments in pharmacology, biomedicine, and bionanotechnology expected from the current research effort on this topic. To anticipate future developments, we speculate on (i) potential applications of (magnetic) RTILs to affect and control the rheology of cells and biological tissues, of great relevance for diagnostics and (ii) the use of RTILs to improve the durability, reliability, and output of biomimetic photovoltaic devices.

Histone Deacetylase 1 Inhibition Protects Against Hypoxia-Induced Swelling in H9c2 Cardiomyocytes Through Regulating Cell Stiffness

BACKGROUND

The process of cardiomyocyte swelling involves changes of biomechanical properties and profiles of cellular genes. Although many genes have been proved to regulate cell edema of cardiomyocyte, the mechanisms involved in this event, as well as the biomechanical properties of swelling cell, remain unknown.Methods and Results:Whether histone deacetylase 1 (HDAC1) inhibition protects against hypoxia-induced H9c2 cardiomyocyte swelling is examined in this study. Hypoxia-induced changes in the biomechanical properties and cytoskeletal structure that are relevant to cell swelling were also determined. H9c2 cells were treated under a chemical hypoxia situation (cobalt chloride) with HDAC1 inhibition (chemical inhibitor or siRNA) for 5 h, followed by in vitro biological and mechanical characterization. The results showed that expression of HDAC1 instead of HDAC4 was upregulated by chemical hypoxia. HDAC1 inhibition protects H9c2 cells against chemical hypoxia-induced hypoxic injury and cell swelling. HDAC1 inhibition improved cell viability, decreased lactate dehydrogenase leakage, cell apoptosis, malondialdehyde concentration, cell volume, and particles on the cell surface, and increased superoxide dismutase activity. Moreover, chemical hypoxia induced a decrease of Young's modulus, accompanied by alterations in the integrity of acetylated histone and organization of the cytoskeletal network. HDAC1 inhibition significantly reversed these processes.

CONCLUSIONS

Based on the ideal physical model, HDAC1 inhibition protects against hypoxia-induced swelling in H9c2 cardiomyocytes through enhancing cell stiffness. Overall, HDAC1 is a potential therapeutic target for myocardial edema.

Elasticity-based polymer sorting in active fluids: a Brownian dynamics study

While the dynamics of polymer chains in equilibrium media is well understood by now, the polymer dynamics in active non-equilibrium environments can be very different.

Microsphere-Based Hierarchically Juxtapositioned Biphasic Scaffolds Prepared from Poly(Lactic-co-Glycolic Acid) and Nanohydroxyapatite for Osteochondral Tissue Engineering

This study aims to prepare biphasic osteochondral scaffolds based on seamless joining of sintered polymer and polymer/ceramic microspheres for co-culture of chondrocytes and bone marrow stem cells (BMSCs). Poly(lactide-co-glycolide) (PLGA) microspheres and 10% nanohydroxyapatite (nHAP)-incorporated PLGA (PGA/nHAP) microspheres were prepared through the oil-in-water precipitation method. Virgin (V) and composite (C) scaffolds were prepared from 250⁻500 µm PLGA and PLGA/nHAP microspheres, respectively, while osteochondral (OC) scaffolds were fabricated through the combination of V and C scaffolds. Physico-chemical properties of scaffolds were characterized through microscopic-spectroscopic evaluations. The effect of nHAP in scaffolds was investigated through thermogravimetric analysis and mechanical testing, while surface hydrophobicity was tested through contact angle measurements. Rabbit chondrocytes and BMSCs were used for cell culture, and cell morphology and proliferation were determined from SEM and DNA assays. Alizarin red and Alcian blue stains were used to identify the in vitro bone and cartilage tissue-specific regeneration, while cetylpyridinium chloride was used to quantitatively estimate calcium in mineralized bone. For co-culture in OC scaffolds, BMSCs were first seeded in the bone part of the scaffold and cultured in osteogenic medium, followed by seeding chondrocytes in the cartilage part, and cultured in chondrocyte medium. High cell viability was confirmed from the Live/Dead assays. Actin cytoskeleton organization obtained by DAPI-phalloidin staining revealed proper organization of chondrocytes and BMSCs in OC scaffolds. Immunofluorescent staining of bone (type I collagen and osteocalcin (OCN)) and cartilage marker proteins (type II collagen (COL II)) confirmed cellular behavior of osteoblasts and chondrocytes in vitro. Using an ectopic osteochondral defect model by subcutaneous implantation of co-cultured OC scaffolds in nude mice confirmed cell proliferation and tissue development from gross view and SEM observation. IF staining of OCN and COL II in the bone and cartilage parts of OC scaffolds and tissue-specific histological analysis exhibited a time-dependent tissue re-modeling and confirmed the potential application of the biphasic scaffold in osteochondral tissue engineering.

Prediction of traction forces of motile cells

When crawling on a flat substrate, living cells exert forces on it via adhesive contacts, enabling them to build up tension within their cytoskeleton and to change shape. The measurement of these forces has been made possible by traction force microscopy (TFM), a technique which has allowed us to obtain time-resolved traction force maps during cell migration. This cell 'footprint' is, however, not sufficient to understand the details of the mechanics of migration, that is how cytoskeletal elements (respectively, adhesion complexes) are put under tension and reinforce or deform (respectively, mature and/or unbind) as a result. In a recent paper, we have validated a rheological model of actomyosin linking tension, deformation and myosin activity. Here, we complement this model with tentative models of the mechanics of adhesion and explore how closely these models can predict the traction forces that we recover from experimental measurements during cell migration. The resulting mathematical problem is a PDE set on the experimentally observed domain, which we solve using a finite-element approach. The four parameters of the model can then be adjusted by comparison with experimental results on a single frame of an experiment, and then used to test the predictive power of the model for following frames and other experiments. It is found that the basic pattern of traction forces is robustly predicted by the model and fixed parameters as a function of current geometry only.

Amelioration of Neutrophil Membrane Function Underlies Granulocyte-Colony Stimulating Factor Action in Glycogen Storage Disease 1b

Glycogen storage disease (GSD) 1b is a metabolic disorder characterized by a deficiency of glucose 6-phosphate transporter and neutrophil alterations, which are reduced in number and functionally impaired. The present study aimed at investigating neutrophil dysfunction correlating submembrane and cytoskeletal changes at different ages with or without granulocyte-colony stimulating factor (G-CSF) treatment. GSD1b neutrophils showed reduced expression and diffused localization of focal adhesion kinase (FAK) and actin. No abnormalities were observed in GSD1a patient neutrophils. Gelsolin was also slightly reduced in neutrophils of GSD1b patients. When patients were treated for at least 3 months with G-CSF, the neutrophil number and the expression of FAK and actin were significantly increased. Granulocyte colony-stimulating factor treatment was similarly effective when performed in 1 year old patients. FAK auto- and IL-8-mediated phosphorylations were already affected as early as 1 year of age. G-CSF treatment also improved this alteration. Our data suggest that neutrophil dysfunction in GSD1b patients might be related to functional impairment and disorganization of proteins of the sub-membrane apparatus, and that G-CSF treatment counteracts neutropenia and prevents the progressive alterations of neutrophil sub-membrane proteins.

A simple and efficient method for generating high-quality recombinant Mical enzyme for in vitro assays

We have recently identified a new family of multidomain oxidoreductase (redox) enzymes, the MICALs, that directly regulate the actin cytoskeletal elements necessary for the morphology, motility, and trajectory of cells. Our genetic assays reveal that Mical is both necessary and sufficient for actin organization and cellular effects in vivo and our biochemical assays with purified Mical protein reveal that Mical utilizes its redox activity to directly disassemble actin filaments. These results identify Mical proteins as novel actin disassembly factors and uncover a redox signaling mechanism that directly regulates the actin cytoskeleton. These results have also set the stage for in-depth characterization of the Mical enzyme. However, it has been difficult to obtain sufficient amounts of highly-pure Mical protein to conduct further biochemical, structural, imaging, catalytic, and other high-precision studies. Herein, we describe a means for expressing high levels of soluble recombinant Mical protein in bacteria. Likewise, we have designed a new purification strategy that enables the rapid and efficient purification of milligram quantities of highly-pure and >99% active Mical protein. This new strategy for generating large amounts of highly-pure and active Mical protein will aid research objectives designed to characterize the biochemical, enzymology, and structural biology of Mical and its effects on actin filament dynamics.

Mechanics of Vascular Smooth Muscle

Vascular smooth muscle (VSM; see Table 1 for a list of abbreviations) is a heterogeneous biomaterial comprised of cells and extracellular matrix. By surrounding tubes of endothelial cells, VSM forms a regulated network, the vasculature, through which oxygenated blood supplies specialized organs, permitting the development of large multicellular organisms. VSM cells, the engine of the vasculature, house a set of regulated nanomotors that permit rapid stress-development, sustained stress-maintenance and vessel constriction. Viscoelastic materials within, surrounding and attached to VSM cells, comprised largely of polymeric proteins with complex mechanical characteristics, assist the engine with countering loads imposed by the heart pump, and with control of relengthening after constriction. The complexity of this smart material can be reduced by classical mechanical studies combined with circuit modeling using spring and dashpot elements. Evaluation of the mechanical characteristics of VSM requires a more complete understanding of the mechanics and regulation of its biochemical parts, and ultimately, an understanding of how these parts work together to form the machinery of the vascular tree. Current molecular studies provide detailed mechanical data about single polymeric molecules, revealing viscoelasticity and plasticity at the protein domain level, the unique biological slip-catch bond, and a regulated two-step actomyosin power stroke. At the tissue level, new insight into acutely dynamic stress-strain behavior reveals smooth muscle to exhibit adaptive plasticity. At its core, physiology aims to describe the complex interactions of molecular systems, clarifying structure-function relationships and regulation of biological machines. The intent of this review is to provide a comprehensive presentation of one biomachine, VSM.

L-Plastin S-glutathionylation promotes reduced binding to β-actin and affects neutrophil functions

Posttranslational modifications (PTMs) of cytoskeleton proteins due to oxidative stress associated with several pathological conditions often lead to alterations in cell function. The current study evaluates the effect of nitric oxide (DETA-NO)-induced oxidative stress-related S-glutathionylation of cytoskeleton proteins in human PMNs. By using in vitro and genetic approaches, we showed that S-glutathionylation of L-plastin (LPL) and β-actin promotes reduced chemotaxis, polarization, bactericidal activity, and phagocytosis. We identified Cys-206, Cys-283, and Cys-460as S-thiolated residues in the β-actin-binding domain of LPL, where cys-460 had the maximum score. Site-directed mutagenesis of LPL Cys-460 further confirmed the role in the redox regulation of LPL. S-Thiolation diminished binding as well as the bundling activity of LPL. The presence of S-thiolated LPL was detected in neutrophils from both diabetic patients and db/db mice with impaired PMN functions. Thus, enhanced nitroxidative stress may results in LPL S-glutathionylation leading to impaired chemotaxis, polarization, and bactericidal activity of human PMNs, providing a mechanistic basis for their impaired functions in diabetes mellitus.

Reversibility and Viscoelastic Properties of Micropillar Supported and Oriented Magnesium Bundled F-Actin

Filamentous actin is one of the most important cytoskeletal elements. Not only is it responsible for the elastic properties of many cell types, but it also plays a vital role in cellular adhesion and motility. Understanding the bundling kinetics of actin filaments is important in the formation of various cytoskeletal structures, such as filopodia and stress fibers. Utilizing a unique pillar-structured microfluidic device, we investigated the time dependence of bundling kinetics of pillar supported free-standing actin filaments. Microparticles attached to the filaments allowed the measurement of thermal motion, and we found that bundling takes place at lower concentrations than previously found in 3-dimensional actin gels, i.e. actin filaments formed bundles in the presence of 5-12 mM of magnesium chloride in a time-dependent manner. The filaments also displayed long term stability for up to hours after removing the magnesium ions from the buffer, which suggests that there is an extensive hysteresis between cation induced crosslinking and decrosslinking.

An Atomic Force Microscope Study Revealed Two Mechanisms in the Effect of Anticancer Drugs on Rate-Dependent Young's Modulus of Human Prostate Cancer Cells

Mechanical properties of cells have been recognized as a biomarker for cellular cytoskeletal organization. As chemical treatments lead to cell cytoskeletal rearrangements, thereby, modifications of cellular mechanical properties, investigating cellular mechanical property variations provides insightful knowledge to effects of chemical treatments on cancer cells. In this study, the effects of eight different anticancer drugs on the mechanical properties of human prostate cancer cell (PC-3) are investigated using a recently developed control-based nanoindentation measurement (CNM) protocol on atomic force microscope (AFM). The CNM protocol overcomes the limits of other existing methods to in-liquid nanoindentation measurement of live cells on AFM, particularly for measuring mechanical properties of live cells. The Young's modulus of PC-3 cells treated by the eight drugs was measured by varying force loading rates over three orders of magnitude, and compared to the values of the control. The results showed that the Young's modulus of the PC-3 cells increased substantially by the eight drugs tested, and became much more pronounced as the force load rate increased. Moreover, two distinct trends were clearly expressed, where under the treatment of Disulfiram, paclitaxel, and MK-2206, the exponent coefficient of the frequency- modulus function remained almost unchanged, while with Celebrex, BAY, Totamine, TPA, and Vaproic acid, the exponential rate was significantly increased.

Unidirectional cell crawling model guided by extracellular cues

Cell migration is a highly regulated and complex cellular process to maintain proper homeostasis for various biological processes. Extracellular environment was identified as the main affecting factors determining the direction of cell crawling. It was observed experimentally that the cell prefers migrating to the area with denser or stiffer array of microposts. In this article, an integrated unidirectional cell crawling model was developed to investigate the spatiotemporal dynamics of unidirectional cell migration, which incorporates the dominating intracellular biochemical processes, biomechanical processes and the properties of extracellular micropost arrays. The interpost spacing and the stiffness of microposts are taken into account, respectively, to study the mechanism of unidirectional cell locomotion and the guidance of extracellular influence cues on the direction of unidirectional cell crawling. The model can explain adequately the unidirectional crawling phenomena observed in experiments such as "spatiotaxis" and "durotaxis," which allows us to obtain further insights into cell migration.

Zebrafish heart development is regulated via glutaredoxin 2 dependent migration and survival of neural crest cells

Glutaredoxin 2 is a vertebrate specific oxidoreductase of the thioredoxin family of proteins modulating the intracellular thiol pool. Thereby, glutaredoxin 2 is important for specific redox signaling and regulates embryonic development of brain and vasculature via reversible oxidative posttranslational thiol modifications. Here, we describe that glutaredoxin 2 is also required for successful heart formation. Knock-down of glutaredoxin 2 in zebrafish embryos inhibits the invasion of cardiac neural crest cells into the primary heart field. This leads to impaired heart looping and subsequent obstructed blood flow. Glutaredoxin 2 specificity of the observed phenotype was confirmed by rescue experiments. Active site variants of glutaredoxin 2 revealed that the (de)-glutathionylation activity is required for proper heart formation. Our data suggest that actin might be one target during glutaredoxin 2 regulated cardiac neural crest cell migration and embryonic heart development. In summary, this work represents further evidence for the general importance of redox signaling in embryonic development and highlights additionally the importance of glutaredoxin 2 during embryogenesis.

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Reversible redox regulation, S-glutathionylation, regulates heart formation.

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Glutaredoxin 2 controls migration of neural crest cells.

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Loss of glutaredoxin 2 impairs heart looping and subsequently heart functionality.

Micro and Nano-Scale Technologies for Cell Mechanics

Cell mechanics is a multidisciplinary field that bridges cell biology, fundamental mechanics, and micro and nanotechnology, which synergize to help us better understand the intricacies and the complex nature of cells in their native environment. With recent advances in nanotechnology, microfabrication methods and micro-electro-mechanical-systems (MEMS), we are now well situated to tap into the complex micro world of cells. The field that brings biology and MEMS together is known as Biological MEMS (BioMEMS). BioMEMS take advantage of systematic design and fabrication methods to create platforms that allow us to study cells like never before. These new technologies have been rapidly advancing the study of cell mechanics. This review article provides a succinct overview of cell mechanics and comprehensively surveys micro and nano-scale technologies that have been specifically developed for and are relevant to the mechanics of cells. Here we focus on micro and nano-scale technologies, and their applications in biology and medicine, including imaging, single cell analysis, cancer cell mechanics, organ-on-a-chip systems, pathogen detection, implantable devices, neuroscience and neurophysiology. We also provide a perspective on the future directions and challenges of technologies that relate to the mechanics of cells.

Correlation of cytokine levels and microglial cell infiltration during retinal degeneration in RCS rats

Microglial cells, which are immunocompetent cells, are involved in all diseases of the central nervous system. During their activation in various diseases, a variety of soluble factors are released. In the present study, the correlation between cytokine levels and microglial cell migration in the course of retinal degeneration of Royal College of Surgeons (RCS) rats was evaluated. MFG-E8 and CD11b were used to confirm the microglial cells. In the retina of RCS rats, the mRNA expression of seven genes (MFG-E8 and its integrins αυ and ß5, CD11b and the cytokines TNF-α, IL-1ß, and MCP-1) formed almost similar bimodal peak distributions, which were centred at P7 and P45 to P60. In contrast, in rdy rats, which comprised the control group, a unimodal peak distribution centred at P14 was observed. The gene expression accompanied the activation and migration of microglial cells from the inner to the outer layer of the retina during the process of degeneration. Principal component analysis and discriminant function analysis revealed that the expression of these seven genes, especially TNF-α and CD11b, positively correlated with retinal degeneration and microglial activity during retinal degeneration in RCS rats, but not in the control rats. Furthermore, linear regression analysis demonstrated a significant correlation between the expression of these genes and the activation of microglial cells in the dystrophic retina. Our findings suggest that the suppression of microglial cells and the blockade of their cytotoxic effects may constitute a novel therapeutic strategy for treating photoreceptor death in various retinal disorders.

The influence of physical and physiological cues on atomic force microscopy-based cell stiffness assessment

Atomic force microscopy provides a novel technique for differentiating the mechanical properties of various cell types. Cell elasticity is abundantly used to represent the structural strength of cells in different conditions. In this study, we are interested in whether physical or physiological cues affect cell elasticity in Atomic force microscopy (AFM)-based assessments. The physical cues include the geometry of the AFM tips, the indenting force and the operating temperature of the AFM. All of these cues show a significant influence on the cell elasticity assessment. Sharp AFM tips create a two-fold increase in the value of the effective Young's modulus (E(eff)) relative to that of the blunt tips. Higher indenting force at the same loading rate generates higher estimated cell elasticity. Increasing the operation temperature of the AFM leads to decreases in the cell stiffness because the structure of actin filaments becomes disorganized. The physiological cues include the presence of fetal bovine serum or extracellular matrix-coated surfaces, the culture passage number, and the culture density. Both fetal bovine serum and the extracellular matrix are critical for cells to maintain the integrity of actin filaments and consequently exhibit higher elasticity. Unlike primary cells, mouse kidney progenitor cells can be passaged and maintain their morphology and elasticity for a very long period without a senescence phenotype. Finally, cell elasticity increases with increasing culture density only in MDCK epithelial cells. In summary, for researchers who use AFM to assess cell elasticity, our results provide basic and significant information about the suitable selection of physical and physiological cues.

Expression of Tau40 induces activation of cultured rat microglial cells

Accumulation of microtubule-associated protein tau has been observed in the brain of aging and tauopathies. Tau was observed in microglia, but its role is not illustrated. By immunofluorescence staining and the fractal dimension value assay in the present study, we observed that microglia were activated in the brains of rats and mice during aging, simultaneously, the immunoreactivities of total tau and the phosphorylated tau were significantly enhanced in the activated microglia. Furtherly by transient transfection of tau40 (human 2N/4R tau) into the cultured rat microglia, we demonstrated that expression of tau40 increased the level of Iba1, indicating activation of microglia. Moreover, expression of tau40 significantly enhanced the membranous localization of the phosphorylated tau at Ser396 in microglia possibly by a mechanism involving protein phosphatase 2A, extracellular signal-regulated kinase and glycogen synthase kinase-3β. It was also found that expression of tau40 promoted microglial migration and phagocytosis, but not proliferation. And we observed increased secretion of several cytokines, including interleukin (IL)-1β, IL-6, IL-10, tumor necrosis factor-α and nitric oxide after the expression of tau40. These data suggest a novel role of human 2N/4R tau in microglial activation.

Geometric control of cell migration

Morphological polarization involving changes in cell shape and redistribution of cellular signaling machinery, initiate the migration of mammalian cells. Golgi complex typically localizes in front of the nucleus, and this frontwards polarization has been proposed to be involved in directional migration. However, the sequence of events remains unresolved. Does Golgi polarization precede directional migration or vice-versa? We address this question by constraining cells to specific areas and shapes then tracking their motile behavior and the spatio-temporal distribution of Golgi apparatus upon release. Results show that while the position of the Golgi complex depends on the cell geometry, the subcellular localization of the Golgi complex does not define the cell's leading edge. Cells constrained within elongated geometries exhibit polarized extension of lamellipodia and upon release, migrate preferentially along the long axis of the cell. Minimally constrained cells released from larger areas however, exhibit retarded migration regardless of lamellipodia protrusion activity.

Biallelic SEMA3A defects cause a novel type of syndromic short stature

Chromosomal microarray testing is commonly used to identify disease causing de novo copy number variants in patients with developmental delay and multiple congenital anomalies. In such a patient we now observed an 150 kb deletion on chromosome 7q21.11 affecting the first exon of the axon guidance molecule gene SEMA3A (sema domain, immunoglobulin domain (Ig), short basic domain, secreted, (semaphorin) 3A). This deletion was inherited from the healthy father, but considering the function of SEMA3A and phenotypic similarity to the knock-out mice, we still assumed a pathogenic relevance and tested for a recessive second defect. Sequencing of SEMA3A in the patient indeed revealed the de novo in-frame mutation p.Phe316_Lys317delinsThrSerSerAsnGlu. Cloning of the mutated allele in combination with two informative SNPs confirmed compound heterozygosity in the patient. While the altered protein structure was predicted to be benign, aberrant splicing resulting in a premature stop codon was proven by RT-PCR to occur in about half of the transcripts from this allele. Expression profiling in human fetal and adult cDNA panels, confirmed a high expression of SEMA3A in all brain regions as well as in adult and fetal heart and fetal skeletal muscle. Normal intellectual development in the patient was surprising but may be explained by the remaining 20% of SEMA3A expression level demonstrated by quantitative RT-PCR. We therefore report a novel autosomal recessive syndrome characterized by postnatal short stature with relative macrocephaly, camptodactyly, septal heart defect and several minor anomalies caused by biallelic mutations in SEMA3A.

Cloning, overexpression, purification and crystallization of the CRN12 coiled-coil domain from Leishmania donovani

Leishmania donovani coronin CRN12 is an actin-binding protein which consists of two domains: an N-terminal WD repeat domain and a C-terminal coiled-coil domain. The coiled-coil domain is 53 residues in length. Helix-helix interactions in general and coiled coils in particular are ubiquitous in the structure of proteins and play a significant role in the association among proteins, including supramolecular assemblies and transmembrane receptors that mediate cellular signalling, transport and actin dynamics. The L. donovani coronin CRN12 coiled-coil domain (5.8 kDa) was cloned, overexpressed, purified to homogeneity and the N-terminal 6×His tag was successfully removed by thrombin cleavage. Crystals of recombinant L. donovani coronin CRN12 coiled-coil domain were grown by vapour diffusion using a hanging-drop setup. Diffraction-quality crystals were obtained and data extending to 2.46 Å resolution were collected at 100 K on BM14, ESRF, Grenoble, France. The crystal belonged to the monoclinic space group C2, with unit-cell parameters a = 118.0, b = 50.6, c = 46.0 Å, β = 111.0°. Matthews coefficient (VM) calculations suggested the presence of 4-6 molecules in the asymmetric unit, corresponding to a solvent content of ∼33-55%, and are consistent with self-rotation function calculations.

Crawling of a driven adherent membrane

We discuss motions of an elastic N × M membrane model whose constituents can bind reversibly with strength ε to adhesive sites of a flat substrate. One of the edges of the membrane ("front") is driven in one direction at rate constant p by N stochastically treadmilling short parallel lines ("cortex"). The main conclusions derived from Monte Carlo studies of this model are the following: (a) Since the polymerizing cortex pushes only the leading edge of the membrane, the major part of the membranes is dragged behind. Therefore, the locomotion of the membrane can be described by frictional sliding processes which are asymmetrically distributed between front and rear of the membrane. A signature of this asymmetry is the difference between the life times of adhesion bonds at front and rear, τ(1) and τ(M), respectively, where τ(1) ≫ τ(M). (b) There are four characteristic times for the membrane motion: The first time, T(0) ~ τ(M) ~ e(aε), is the resting time where the displacement of the membrane is practically zero. The second time, T(p) ~ τ(1) ~ M, is the friction time which characterizes the time between two consecutive ruptures of adhesion bonds at the front, and which signalizes the onset of drift ("protrusion") at the leading edge. The third time, T(r) ~ M(γ(ε)) (γ > 1), characterizes the "retraction" of the trailing edge, which is the retarded response to the pulling leading edge. The fourth time, T(L) ~ M(2), is the growth time for fluctuation of the end-to-end distance. (c) The separation of time scales, T(r)/T(p) ~ M(γ(ε) - 1), leads to stretched fluctuations of the end-to-end distance, which are considered as stochastic cycles of protrusion and retraction on the time scale of T(L). (d) The drift velocity v obeys anomalous scaling, v/p~f(p(1/γ(ε))M), where f(z) ~ const. for small drag pM ≪ 1, and f(z) ~ z(-γ(ε)) for pM ≫ 1, which implies v~M(-γ(ε)). These results may also turn out to be useful for the (more difficult) problem of understanding the protrusion-retraction cycle of crawling biological cells. We compare our model and our results to previous two-particle theories for membrane protrusion and to known stochastic friction models.

The tandem PH domain-containing protein 2 (TAPP2) regulates chemokine-induced cytoskeletal reorganization and malignant B cell migration

The intracellular signaling processes controlling malignant B cell migration and tissue localization remain largely undefined. Tandem PH domain-containing proteins TAPP1 and TAPP2 are adaptor proteins that specifically bind to phosphatidylinositol-3,4-bisphosphate, or PI(3,4)P2, a product of phosphoinositide 3-kinases (PI3K). While PI3K enzymes have a number of functions in cell biology, including cell migration, the functions of PI(3,4)P2 and its binding proteins are not well understood. Previously we found that TAPP2 is highly expressed in primary leukemic B cells that have strong migratory capacity. Here we find that SDF-1-dependent migration of human malignant B cells requires both PI3K signaling and TAPP2. Migration in a transwell assay is significantly impaired by pan-PI3K and isoform-selective PI3K inhibitors, or by TAPP2 shRNA knockdown (KD). Strikingly, TAPP2 KD in combination with PI3K inhibitor treatment nearly abolished the migration response, suggesting that TAPP2 may contribute some functions independent of the PI3K pathway. In microfluidic chamber cell tracking assays, TAPP2 KD cells show reduction in percentage of migrating cells, migration velocity and directionality. TAPP2 KD led to alterations in chemokine-induced rearrangement of the actin cytoskeleton and failure to form polarized morphology. TAPP2 co-localized with the stable F-actin-binding protein utrophin, with both molecules reciprocally localizing against F-actin accumulated at the leading edge upon SDF-1 stimulation. In TAPP2 KD cells, Rac was over-activated and localized to multiple membrane protrusions, suggesting that TAPP2 may act in concert with utrophin and stable F-actin to spatially restrict Rac activation and reduce formation of multiple membrane protrusions. TAPP2 function in cell migration is also apparent in the more complex context of B cell migration into stromal cell layers – a process that is only partially dependent on PI3K and SDF-1. In summary, this study identified TAPP2 as a novel regulator of malignant B cell migration and a potential therapeutic intervention target.

Asymmetry between pushing and pulling for crawling cells

Eukaryotic cells possess motility mechanisms allowing them not only to self-propel but also to exert forces on obstacles (to push) and to carry cargoes (to pull). To study the inherent asymmetry between active pushing and pulling we model a crawling acto-myosin cell extract as a one-dimensional layer of active gel subjected to external forces. We show that pushing is controlled by protrusion and that the macroscopic signature of the protrusion dominated motility mechanism is concavity of the force-velocity relation. In contrast, pulling is driven by protrusion only at small values of the pulling force and it is replaced by contraction when the pulling force is sufficiently large. This leads to more complex convex-concave structure of the force-velocity relation; in particular, competition between protrusion and contraction can produce negative mobility in a biologically relevant range. The model illustrates active readjustment of the force generating machinery in response to changes in the dipole structure of external forces. The possibility of switching between complementary active mechanisms implies that if necessary "pushers" can replace "pullers" and vice versa.

Molecular physiology of SPAK and OSR1: two Ste20-related protein kinases regulating ion transport

SPAK (Ste20-related proline alanine rich kinase) and OSR1 (oxidative stress responsive kinase) are members of the germinal center kinase VI subfamily of the mammalian Ste20 (Sterile20)-related protein kinase family. Although there are 30 enzymes in this protein kinase family, their conservation across the fungi, plant, and animal kingdom confirms their evolutionary importance. Already, a large volume of work has accumulated on the tissue distribution, binding partners, signaling cascades, and physiological roles of mammalian SPAK and OSR1 in multiple organ systems. After reviewing this basic information, we will examine newer studies that demonstrate the pathophysiological consequences to SPAK and/or OSR1 disruption, discuss the development and analysis of genetically engineered mouse models, and address the possible role these serine/threonine kinases might have in cancer proliferation and migration.

Intrinsic migratory properties of cultured Schwann cells based on single-cell migration assay

The migration of Schwann cells is critical for development of peripheral nervous system and is essential for regeneration and remyelination after nerve injury. Although several factors have been identified to regulate Schwann cell migration, intrinsic migratory properties of Schwann cells remain elusive. In this study, based on time-lapse imaging of single isolated Schwann cells, we examined the intrinsic migratory properties of Schwann cells and the molecular cytoskeletal machinery of soma translocation during migration. We found that cultured Schwann cells displayed three motile phenotypes, which could transform into each other spontaneously during their migration. Local disruption of F-actin polymerization at leading front by a Cytochalasin D or Latrunculin A gradient induced collapse of leading front, and then inhibited soma translocation. Moreover, in migrating Schwann cells, myosin II activity displayed a polarized distribution, with the leading process exhibiting higher expression than the soma and trailing process. Decreasing this front-to-rear difference of myosin II activity by frontal application of a ML-7 or BDM (myosin II inhibitors) gradient induced the collapse of leading front and reversed soma translocation, whereas, increasing this front-to-rear difference of myosin II activity by rear application of a ML-7 or BDM gradient or frontal application of a Caly (myosin II activator) gradient accelerated soma translocation. Taken together, these results suggest that during migration, Schwann cells display malleable motile phenotypes and the extension of leading front dependent on F-actin polymerization pulls soma forward translocation mediated by myosin II activity.