The Role of Vinculin in the Regulation of the Mechanical Properties of Cells

Compliant substrates mitigate the senescence associated phenotype of stress induced mesenchymal stromal cells

Mesenchymal stromal cells (MSCs) are a promising cell population for musculoskeletal cell-based therapies due to their multipotent differentiation capacity and complex secretome. Cells from younger donors are mechanosensitive, evidenced by changes in cell morphology, adhesivity, and differentiation as a function of substrate stiffness in both two- and three-dimensional culture. However, MSCs from older individuals exhibit reduced differentiation potential and increased senescence, limiting their potential for autologous use. While substrate stiffness is known to modulate cell phenotype, the influence of the mechanical environment on senescent MSCs is poorly described. To address this question, we cultured irradiation induced premature senescent MSCs on polyacrylamide hydrogels and assessed expression of senescent markers, cell morphology, and secretion of inflammatory cytokines. Compared to cells on tissue culture plastic, senescent MSCs exhibited decreased markers of the senescence associated secretory phenotype (SASP) when cultured on 50 kPa gels, yet common markers of senescence (e.g., p21, CDKN2A, CDKN1A) were unaffected. These effects were muted in a physiologically relevant heterotypic mix of healthy and senescent MSCs. Conditioned media from senescent MSCs on compliant substrates increased osteoblast mineralization compared to conditioned media from cells on TCP. Mixed populations of senescent and healthy cells induced similar levels of osteoblast mineralization compared to healthy MSCs, further indicating an attenuation of the senescent phenotype in heterotypic populations. These data indicate that senescent MSCs exhibit a decrease in senescent phenotype when cultured on compliant substrates, which may be leveraged to improve autologous cell therapies for older donors.

pH-regulated single cell migration

Over the last two decades, extra- and intracellular pH have emerged as fundamental regulators of cell motility. Fundamental physiological and pathological processes relying on appropriate cell migration, such as embryonic development, wound healing, and a proper immune defense on the one hand, and autoimmune diseases, metastatic cancer, and the progression of certain parasitic diseases on the other, depend on surrounding pH. In addition, migrating single cells create their own localized pH nanodomains at their surface and in the cytosol. By this means, the migrating cells locally modulate their adhesion to, and the re-arrangement and digestion of, the extracellular matrix. At the same time, the cytosolic nanodomains tune cytoskeletal dynamics along the direction of movement resulting in concerted lamellipodia protrusion and rear end retraction. Extracellular pH gradients as found in wounds, inflamed tissues, or the periphery of tumors stimulate directed cell migration, and long-term exposure to acidic conditions can engender a more migratory and invasive phenotype persisting for hours up to several generations of cells after they have left the acidic milieu. In the present review, the different variants of pH-dependent single cell migration are described. The underlying pH-dependent molecular mechanisms such as conformational changes of adhesion molecules, matrix protease activity, actin (de-)polymerization, and signaling events are explained, and molecular pH sensors stimulated by H+ signaling are presented.

Confinement primes cells for faster migration by polarizing active mitochondria

Mechanical cues in the tumor microenvironment interplay with internal cellular processes to control cancer cell migration. Microscale pores present in tumor tissue confer varying degrees of confinement on migrating cells, increasing matrix contact and inducing cytoskeletal rearrangement. Previously, we observed that increased collagen matrix contact significantly increased cell migration speed and cell-induced strains within the matrix. However, the effects of this confinement on future cell migration are not fully understood. Here, we use a collagen microtrack platform to determine the effect of confinement on priming MDA-MB-231 cancer cells for fast migration. We show that migration through a confined track results in increased speed and accumulation of migratory machinery, including actin and active mitochondria, in the front of migrating breast cancer cells. By designing microtracks that allow cells to first navigate a region of high confinement, then a region of low confinement, we assessed whether migration in high confinement changes future migratory behavior. Indeed, cells maintain their speed attained in high confinement even after exiting to a region of low confinement, indicating that cells maintain memory of previous matrix cues to fuel fast migration. Active mitochondria maintain their location at the front of the cell even after cells leave high confinement. Furthermore, knocking out vinculin to disrupt focal adhesions disrupts active mitochondrial localization and disrupts the fast migration seen upon release from confinement. Together, these data suggest that active mitochondrial localization in confinement may facilitate fast migration post-confinement. By better understanding how confinement contributes to future cancer cell migration, we can identify potential therapeutic targets to inhibit breast cancer metastasis.

Development of a Ratiometric Tension Sensor Exclusively Responding to Integrin Tension Magnitude in Live Cells

Integrin tensions are critical for cell mechanotransduction. By converting force to fluorescence, molecular tension sensors image integrin tensions in live cells with a high resolution. However, the fluorescence signal intensity results collectively from integrin tension magnitude, tension dwell time, integrin density, sensor accessibility, and so forth, making it highly challenging to specifically monitor the molecular force level of integrin tensions. Here, a ratiometric tension sensor (RTS) was developed to exclusively monitor the integrin tension magnitude. The RTS consists of two tension-sensing units that are coupled in series and always subject to the same integrin tension. These two units are activated by tension to fluoresce in separate spectra and with different activation rates. The ratio of their activation probabilities, reported by fluorescence ratiometric measurement, is solely determined by the local integrin tension magnitude. RTS responded sensitively to the variation of integrin tension magnitude in platelets and focal adhesions due to different cell plating times, actomyosin inhibition, or vinculin knockout. At last, RTS confirmed that integrin tension magnitude in platelets and focal adhesions decreases monotonically with the substrate rigidity, verifying the rigidity dependence of integrin tensions in live cells and suggesting that integrin tension magnitude could be a key biomechanical factor in cell rigidity sensing.

Meldonium Inhibits Cell Motility and Wound-Healing in Trabecular Meshwork Cells and Scleral Fibroblasts: Possible Applications in Glaucoma

Meldonium (MID) is a synthetic drug designed to decrease the availability of L-carnitine-a main player in mitochondrial energy generation-thus modulating the cell pathways of energy metabolism. Its clinical effects are mostly evident in blood vessels during ischemic events, when the hyperproduction of endogenous carnitine enhances cell metabolic activities, leading to increased oxidative stress and apoptosis. MID has shown vaso-protective effects in model systems of endothelial dysfunction induced by high glucose or by hypertension. By stimulating the endothelial nitric oxide synthetase (eNOS) via PI3 and Akt kinase, it has shown beneficial effects on the microcirculation and blood perfusion. Elevated intraocular pressure (IOP) and endothelial dysfunction are major risk factors for glaucoma development and progression, and IOP remains the main target for its pharmacological treatment. IOP is maintained through the filtration efficiency of the trabecular meshwork (TM), a porous tissue derived from the neuroectoderm. Therefore, given the effects of MID on blood vessels and endothelial cells, we investigated the effects of the topical instillation of MID eye drops on the IOP of normotensive rats and on the cell metabolism and motility of human TM cells in vitro. Results show a significant dose-dependent decrease in the IOP upon topic treatment and a decrease in TM cell motility in the wound-healing assay, correlating with an enhanced expression of vinculin localized in focal adhesion plaques. Motility inhibition was also evident on scleral fibroblasts in vitro. These results may encourage a further exploration of MID eye drops in glaucoma treatment.

Vinculin transmits high-level integrin tensions that are dispensable for focal adhesion formation

Focal adhesions (FAs) transmit force and mediate mechanotransduction between cells and the matrix. Previous studies revealed that integrin-transmitted force is critical to regulate FA formation. As vinculin is a prominent FA protein implicated in integrin tension transmission, this work studies the relation among integrin tensions (force), vinculin (protein), and FA formation (structure) by integrin tension manipulation, force visualization and vinculin knockout (KO). Two DNA-based integrin tension tools are adopted: tension gauge tether (TGT) and integrative tension sensor (ITS), with TGT restricting integrin tensions under a designed Ttol (tension tolerance) value and ITS visualizing integrin tensions above the Ttol value by fluorescence. Results show that large FAs (area >1 μm2) were formed on the TGT surface with Ttol of 54 pN but not on those with lower Ttol values. Time-series analysis of FA formation shows that focal complexes (area <0.5 μm2) appeared on all TGT surfaces 20 min after cell plating, but only matured to large FAs on TGT with Ttol of 54 pN. Next, we tested FA formation in vinculin KO cells on TGT surfaces. Surprisingly, the Ttol value of TGT required for large FA formation is drastically decreased to 23 pN. To explore the cause, we visualized integrin tensions in both wild-type and vinculin KO cells using ITS. The results showed that integrin tensions in FAs of wild-type cells frequently activate ITS with Ttol of 54 pN. With vinculin KO, however, integrin tensions in FAs became lower and unable to activate 54 pN ITS. Force signal intensities of integrin tensions reported by 33 and 43 pN ITS were also significantly reduced with vinculin KO, suggesting that vinculin is essential to transmit high-level integrin tensions and involved in transmitting intermediate-level integrin tensions in FAs. However, the high-level integrin tensions transmitted by vinculin are not required by FA formation.

Mechanical Properties of Colorectal Cancer Cells Determined by Dynamic Atomic Force Microscopy: A Novel Biomarker

Simple Summary

Colorectal cancer (CRC) is presently the third-most abundant and the second-most lethal cancer worldwide. Thus, there is a real and urgent need to investigate the processes behind the appearance, development, and proliferation of CRC cells. Several biochemical pathways have been investigated to understand their role in oncogene activation and tumor-suppressor gene inhibition. Despite the research increase in biochemistry, there is still a need to better understand the biophysical cues that drive the activation of signaling pathways relevant to mechanotransduction and cell transformation. The elucidation of these biological processes may help to hinder oncogenic mechanisms and to find biomarkers that could be used to design more personalized therapeutic strategies.

Abstract

Colorectal cancer (CRC) has been addressed in the framework of molecular, cellular biology, and biochemical traits. A new approach to studying CRC is focused on the relationship between biochemical pathways and biophysical cues, which may contribute to disease understanding and therapy development. Herein, we investigated the mechanical properties of CRC cells, namely, HCT116, HCT15, and SW620, using static and dynamic methodologies by atomic force microscopy (AFM). The static method quantifies Young’s modulus; the dynamic method allows the determination of elasticity, viscosity, and fluidity. AFM results were correlated with confocal laser scanning microscopy and cell migration assay data. The SW620 metastatic cells presented the highest Young’s and storage moduli, with a defined cortical actin ring with distributed F-actin filaments, scarce vinculin expression, abundant total focal adhesions (FAK), and no filopodia formation, which could explain the lessened migratory behavior. In contrast, HCT15 cells presented lower Young’s and storage moduli, high cortical tubulin, less cortical F-actin and less FAK, and more filopodia formation, probably explaining the higher migratory behavior. HCT116 cells presented Young’s and storage moduli values in between the other cell lines, high cortical F-actin expression, intermediate levels of total FAK, and abundant filopodia formation, possibly explaining the highest migratory behavior.

Adhesion strength and anti-tumor agents regulate vinculin of breast cancer cells

The onset and progression of cancer are strongly associated with the dissipation of adhesion forces between cancer cells, thus facilitating their incessant attachment and detachment from the extracellular matrix (ECM) to move toward metastasis. During this process, cancer cells undergo mechanical stresses and respond to these stresses with membrane deformation while inducing protrusions to invade the surrounding tissues. Cellular response to mechanical forces is inherently related to the reorganization of the cytoskeleton, the dissipation of cell–cell junctions, and the adhesion to the surrounding ECM. Moreover, the role of focal adhesion proteins, and particularly the role of vinculin in cell attachment and detachment during migration, is critical, indicating the tight cell–ECM junctions, which favor or inhibit the metastatic cascade. The biomechanical analysis of these sequences of events may elucidate the tumor progression and the potential of cancer cells for migration and metastasis. In this work, we focused on the evaluation of the spreading rate and the estimation of the adhesion strength between breast cancer cells and ECM prior to and post-treatment with anti-tumor agents. Specifically, different tamoxifen concentrations were used for ER⁺ breast cancer cells, while even concentrations of trastuzumab and pertuzumab were used for HER2⁺ cells. Analysis of cell stiffness indicated an increased elastic Young’s modulus post-treatment in both MCF-7 and SKBR-3 cells. The results showed that the post-treatment spreading rate was significantly decreased in both types of breast cancer, suggesting a lower metastatic potential. Additionally, treated cells required greater adhesion forces to detach from the ECM, thus preventing detachment events of cancer cells from the ECM, and therefore, the probability of cell motility, migration, and metastasis was confined. Furthermore, post-detachment and post-treatment vinculin levels were increased, indicating tighter cell–ECM junctions, hence limiting the probability of cell detachment and, therefore, cell motility and migration.

Molecular Mechanisms of the Convergent Adaptation of Bathypelagic and Abyssopelagic Fishes

Harsh environments provide opportunities to study how different species adapt, at the molecular level, to similar environmental stressors. High hydrostatic pressure, low temperature, and absence of sunlight in the deep-sea environment are challenging conditions for gene expression, cell morphology and vision. Adaptation of fish to this environment appears independently in at least 22 orders of fish, but it remains uncertain whether these adaptations represent convergent evolution. In this study, we performed comparative genomic analysis of 80 fish species to determine genetic evidences for adaptations to the deep-sea environment. The 80 fishes were divided into six groups according to their order. Positive selection and convergent evolutionary analysis were performed and functional enrichment analysis of candidate genes was performed. Positively selected genes (pik3ca, pik3cg, vcl and sphk2) were identified to be associated with the cytoskeletal response to mechanical forces and gene expression. Consistent signs of molecular convergence genes (grk1, ednrb, and nox1) in dark vision, skin color, and bone rarefaction were revealed. Functional assays of Grk1 showed that the convergent sites improved dark vision in deep-sea fish. By identifying candidate genes and functional profiles potentially involved in cold, dark, and high-pressure responses, the results of this study further enrich the understanding of fish adaptations to deep-sea environments.

Efficient deformation mechanisms enable invasive cancer cells to migrate faster in 3D collagen networks

Cancer cell migration is a widely studied topic but has been very often limited to two dimensional motion on various substrates. Indeed, less is known about cancer cell migration in 3D fibrous-extracellular matrix (ECM) including variations of the microenvironment. Here we used 3D time lapse imaging on a confocal microscope and a phase correlation method to follow fiber deformations, as well as cell morphology and live actin distribution during the migration of cancer cells. Different collagen concentrations together with three bladder cancer cell lines were used to investigate the role of the metastatic potential on 3D cell migration characteristics. We found that grade-3 cells (T24 and J82) are characterized by a great diversity of shapes in comparison with grade-2 cells (RT112). Moreover, grade-3 cells with the highest metastatic potential (J82) showed the highest values of migration speeds and diffusivities at low collagen concentration and the greatest sensitivity to collagen concentration. Our results also suggested that the small shape fluctuations of J82 cells are the signature of larger migration velocities. Moreover, the displacement fields generated by J82 cells showed significantly higher fiber displacements as compared to T24 and RT112 cells, regardless of collagen concentration. The analysis of cell movements enhanced the fact that bladder cancer cells were able to exhibit different phenotypes (mesenchymal, amoeboid). Furthermore, the analysis of spatio-temporal migration mechanisms showed that cancer cells are able to push or pull on collagen fibers, therefore producing efficient local collagen deformations in the vicinity of cells. Our results also revealed that dense actin regions are correlated with the largest displacement fields, and this correlation is enhanced for the most invasive J82 cancer cells. Therefore this work opens up new routes to understand cancer cell migration in soft biological networks.

The Central Role of the F-Actin Surface in Myosin Force Generation

Actin is one of the most abundant and versatile proteins in eukaryotic cells. As discussed in many contributions to this Special Issue, its transition from a monomeric G-actin to a filamentous F-actin form plays a critical role in a variety of cellular processes, including control of cell shape and cell motility. Once polymerized from G-actin, F-actin forms the central core of muscle-thin filaments and acts as molecular tracks for myosin-based motor activity. The ATP-dependent cross-bridge cycle of myosin attachment and detachment drives the sliding of myosin thick filaments past thin filaments in muscle and the translocation of cargo in somatic cells. The variation in actin function is dependent on the variation in muscle and non-muscle myosin isoform behavior as well as interactions with a plethora of additional actin-binding proteins. Extensive work has been devoted to defining the kinetics of actin-based force generation powered by the ATPase activity of myosin. In addition, over the past decade, cryo-electron microscopy has revealed the atomic-evel details of the binding of myosin isoforms on the F-actin surface. Most accounts of the structural interactions between myosin and actin are described from the perspective of the myosin molecule. Here, we discuss myosin-binding to actin as viewed from the actin surface. We then describe conserved structural features of actin required for the binding of all or most myosin isoforms while also noting specific interactions unique to myosin isoforms.

The EBV-Encoded Oncoprotein, LMP1, Recruits and Transforms Fibroblasts via an ERK-MAPK-Dependent Mechanism

Latent membrane protein 1 (LMP1), the major oncoprotein encoded by Epstein–Barr virus (EBV), is expressed at widely variable levels in undifferentiated nasopharyngeal carcinoma (NPC) biopsies, fueling intense debate in the field as to the importance of this oncogenic protein in disease pathogenesis. LMP1-positive NPCs are reportedly more aggressive, and in a similar vein, the presence of cancer-associated fibroblasts (CAFs) surrounding “nests” of tumour cells in NPC serve as indicators of poor prognosis. However, there is currently no evidence linking LMP1 expression and the presence of CAFs in NPC. In this study, we demonstrate the ability of LMP1 to recruit fibroblasts in vitro in an ERK-MAPK-dependent mechanism, along with enhanced viability, invasiveness and transformation to a myofibroblast-like phenotype. Taken together, these findings support a putative role for LMP1 in recruiting CAFs to the tumour microenvironment in NPC, ultimately contributing to metastatic disease.

Vinculin-mediated axon growth requires interaction with actin but not talin in mouse neocortical neurons

The actin-binding protein vinculin is a major constituent of focal adhesion, but its role in neuronal development is poorly understood. We found that vinculin deletion in mouse neocortical neurons attenuated axon growth both in vitro and in vivo. Using functional mutants, we found that expression of a constitutively active vinculin significantly enhanced axon growth while the head-neck domain had an inhibitory effect. Interestingly, we found that vinculin-talin interaction was dispensable for axon growth and neuronal migration. Strikingly, expression of the tail domain delayed migration, increased branching, and stunted axon. Inhibition of the Arp2/3 complex or abolishing the tail domain interaction with actin completely reversed the branching phenotype caused by tail domain expression without affecting axon length. Super-resolution microscopy showed increased mobility of actin in tail domain expressing neurons. Our results provide novel insights into the role of vinculin and its functional domains in regulating neuronal migration and axon growth.

The Diminishing Returns of Mechanical Loading and Potential Mechanisms that Desensitize Osteocytes

Adaptation to mechanical loading is critical to maintaining bone mass and offers therapeutic potential to preventing age-related bone loss and osteoporosis. However, increasing the duration of loading is met with "diminishing returns" as the anabolic response quickly becomes saturated. As a result, the anabolic response to daily activities and repetitive bouts of loading is limited by the underlying mechanisms that desensitize and render bone unresponsive at the cellular level. Osteocytes are the primary cells that respond to skeletal loading and facilitate the overall anabolic response. Although many of osteocytes' signaling mechanisms activated in response to loading are considered anabolic in nature, several of them can also render osteocytes insensitive to further stimuli and thereby creating a negative feedback loop that limits osteocytes' overall response. The purpose of this review is to examine the potential mechanisms that may contribute to the loss of mechanosensitivity. In particular, we examined the inactivation/desensitization of ion channels and signaling molecules along with the potential role of endocytosis and cytoskeletal reorganization. The significance in defining the negative feedback loop is the potential to identify unique targets for enabling osteocytes to maintain their sensitivity. In doing so, we can begin to cultivate new strategies that capitalize on the anabolic nature of daily activities that repeatedly load the skeleton.

Biomarkers of tumor invasiveness in proteomics (Review)

Over the past two decades, quantitative proteomics has emerged as an important tool for deciphering the complex molecular events involved in cancers. The number of references involving studies on the cancer metastatic process has doubled since 2010, while the last 5 years have seen the development of novel technologies combining deep proteome coverage capabilities with quantitative consistency and accuracy. To highlight key findings within this huge amount of information, the present review identified a list of tumor invasive biomarkers based on both the literature and data collected on a biocollection of experimental cell lines, tumor models of increasing invasiveness and tumor samples from patients with colorectal or breast cancer. Crossing these different data sources led to 76 proteins of interest out of 1,245 mentioned in the literature. Information on these proteins can potentially be translated into clinical prospects, since they represent potential targets for the development and evaluation of innovative therapies, alone or in combination. Herein, a systematical review of the biology of each of these proteins, including their specific subcellular/extracellular or multiple localizations is presented. Finally, as an important advantage of quantitative proteomics is the ability to provide data on all these molecules simultaneously in cell pellets, body fluids or paraffin‑embedded sections of tumors/invaded tissues, the significance of some of their interconnections is discussed.

Tuning of Titanium Microfiber Scaffold with UV-Photofunctionalization for Enhanced Osteoblast Affinity and Function

Titanium (Ti) is an osteoconductive material that is routinely used as a bulk implant to fix and restore bones and teeth. This study explored the effective use of Ti as a bone engineering scaffold. Challenges to overcome were: (1) difficult liquid/cell infiltration into Ti microfiber scaffolds due to the hydrophobic nature of Ti; and (2) difficult cell attachment on thin and curved Ti microfibers. A recent discovery of UV-photofunctionalization of Ti prompted us to examine its effect on Ti microfiber scaffolds. Scaffolds in disk form were made by weaving grade 4 pure Ti microfibers (125 µm diameter) and half of them were acid-etched to roughen the surface. Some of the scaffolds with original or acid-etched surfaces were further treated by UV light before cell culture. Ti microfiber scaffolds, regardless of the surface type, were hydrophobic and did not allow glycerol/water liquid to infiltrate, whereas, after UV treatment, the scaffolds became hydrophilic and immediately absorbed the liquid. Osteogenic cells from two different origins, derived from the femoral and mandibular bone marrow of rats, were cultured on the scaffolds. The number of cells attached to scaffolds during the early stage of culture within 24 h was 3–10 times greater when the scaffolds were treated with UV. The development of cytoplasmic projections and cytoskeletal, as well as the expression of focal adhesion protein, were exclusively observed on UV-treated scaffolds. Osteoblastic functional phenotypes, such as alkaline phosphatase activity and calcium mineralization, were 2–15 times greater on UV-treated scaffolds, with more pronounced enhancement on acid-etched scaffolds compared to that on the original scaffolds. These effects of UV treatment were associated with a significant reduction in atomic carbon on the Ti microfiber surfaces. In conclusion, UV treatment of Ti microfiber scaffolds tunes their physicochemical properties and effectively enhances the attachment and function of osteoblasts, proposing a new strategy for bone engineering.

Surface Charge-Mediated Cell-Surface Interaction on Piezoelectric Materials

Cell-material interactions play an essential role in the development of scaffold-based tissue engineering strategies. Cell therapies are still limited in treating injuries when severe damage causes irreversible loss of muscle cells. Electroactive biomaterials and, in particular, piezoelectric materials offer new opportunities for skeletal muscle tissue engineering since these materials have demonstrated suitable electroactive microenvironments for tissue development. In this study, the influence of the surface charge of piezoelectric poly(vinylidene fluoride) (PVDF) on cell adhesion was investigated. The cytoskeletal organization of C2C12 myoblast cells grown on different PVDF samples was studied by immunofluorescence staining, and the interactions between single live cells and PVDF were analyzed using an atomic force microscopy (AFM) technique termed single-cell force spectroscopy. It was demonstrated that C2C12 myoblast cells seeded on samples with net surface charge present a more elongated morphology, this effect being dependent on the surface charge but independent of the poling direction (negative or positive surface charge). It was further shown that the cell deadhesion forces of individual C2C12 cells were higher on PVDF samples with an overall negative surface charge (8.92 ± 0.45 nN) compared to those on nonpoled substrates (zero overall surface charge) (4.06 ± 0.20 nN). These findings explicitly demonstrate that the polarization/surface charge is an important parameter to determine cell fate as it affects C2C12 cell adhesion, which in turn will influence cell behavior, namely, cell proliferation and differentiation.

Skin Protein Profile after Major Weight Loss and Its Role in Body Contouring Surgery

Chronic inflammation during morbid obesity significantly alters cutaneous tissue. Large weight loss achieved after bariatric surgery minimizes or halts damage caused by metabolic syndrome, but further deteriorates the clinical condition of skin. Postbariatric skin flaccidity produces major difficulties to plastic surgery. In this study, we analyzed differences in protein composition of the skin between patients with morbid obesity and those after large weight loss and established correlations between differentially expressed proteins and clinical characteristics of postbariatric skin tissue, to improve body contouring surgery techniques.

The cell adhesion molecule IGPR-1 is activated by and regulates responses of endothelial cells to shear stress

Vascular endothelial cells respond to blood flow-induced shear stress. However, the mechanisms through which endothelial cells transduce mechanical signals to cellular responses remain poorly understood. In this report, using tensile-force assays, immunofluorescence and atomic force microscopy, we demonstrate that immunoglobulin and proline-rich receptor-1 (IGPR-1) responds to mechanical stimulation and increases the stiffness of endothelial cells. We observed that IGPR-1 is activated by shear stress and tensile force and that flow shear stress-mediated IGPR-1 activation modulates remodeling of endothelial cells. We found that under static conditions, IGPR-1 is present at the cell-cell contacts; however, under shear stress, it redistributes along the cell borders into the flow direction. IGPR-1 activation stimulated actin stress fiber assembly and cross-linking with vinculin. Moreover, we noted that IGPR-1 stabilizes cell-cell junctions of endothelial cells as determined by staining of cells with ZO1. Mechanistically, shear stress stimulated activation of AKT Ser/Thr kinase 1 (AKT1), leading to phosphorylation of IGPR-1 at Ser-220. Inhibition of this phosphorylation prevented shear stress-induced actin fiber assembly and endothelial cell remodeling. Our findings indicate that IGPR-1 is an important player in endothelial cell mechanosensing, insights that have important implications for the pathogenesis of common maladies, including ischemic heart diseases and inflammation.

Migrating Myofibroblastic Iliotibial Band-Derived Fibroblasts Represent a Promising Cell Source for Ligament Reconstruction

The iliotibial band (ITB) is a suitable scaffold for anterior cruciate ligament (ACL) reconstruction, providing a sufficient mechanical resistance to loading. Hence, ITB-derived fibroblasts attract interest for ligament tissue engineering but have so far not been characterized. This present study aimed at characterizing ITB fibroblasts before, during, and after emigration from cadaveric ITB explants to decipher the emigration behavior and to utilize their migratory capacity for seeding biomaterials. ITB and, for comparison, ACL tissues were assessed for the content of alpha smooth muscle actin (αSMA) expressing fibroblasts and degeneration. The cell survival and αSMA expression were monitored in explants used for cell isolation, monolayer, self-assembled ITB spheroids, and spheroids seeded in polyglycolic acid (PGA) scaffolds. The protein expression profile of targets typically expressed by ligamentocytes (collagen types I-III, elastin, lubricin, decorin, aggrecan, fibronectin, tenascin C, CD44, β1-integrins, vimentin, F-actin, αSMA, and vascular endothelial growth factor A [VEGFA]) was compared between ITB and ACL fibroblasts. A donor- and age-dependent differing percentage of αSMA positive cells could be detected, which was similar in ITB and ACL tissues despite the grade of degeneration being significantly higher in the ACL due to harvesting them from OA knees. ITB fibroblasts survived for several months in an explant culture, continuously forming monolayers with VEGFA and an increased αSMA expression. They shared their expression profile with ACL fibroblasts. αSMA decreased during the monolayer to spheroid/scaffold transition. Using self-assembled spheroids, the migratory capacity of reversible myofibroblastic ITB cells can be utilized for colonizing biomaterials for ACL tissue engineering and to support ligament healing.

Impaired osteoblastic behavior and function on saliva-contaminated titanium and its restoration by UV treatment

The objective of this study was to examine behavior and function of osteoblasts on saliva-contaminated titanium and its potential improvement after UV light treatment. Acid-etched titanium disks were contaminated with human saliva. Osteoblasts derived from rat femur were cultured on contaminated and clean titanium disks. Contaminated disks further treated with UV light were also tested. The number of attached cells, the degree of cell spreading, and the expression of adhesion protein were significantly decreased on saliva-contaminated surfaces compared with clean surfaces. The gene expression of osteocalcin was also downregulated on contaminated surfaces, whereas ALP activity and mineralization were not significantly influenced. The impaired functions on contaminated surfaces were significantly increased if the surfaces were further treated with UV and even outperformed the ones on clean titanium surfaces. XPS analysis revealed that the atomic percentage of carbon and nitrogen detected on contaminated surfaces were substantially decreased after UV treatment. These results suggest that osteoblastic behavior and function were compromised on titanium surfaces contaminated with saliva. The compromised functions no longer happened if the surfaces were further treated with UV light, providing the basis to understand the effect of biological contamination on osseointegration and to explore UV treatment as a decontaminating technology.

Live cell imaging reveals focal adhesions mechanoresponses in mammary epithelial cells under sustained equibiaxial stress

Mechanical stimuli play a key role in many cell functions such as proliferation, differentiation and migration. In the mammary gland, mechanical signals such as the distension of mammary epithelial cells due to udder filling are proposed to be directly involved during lactation and involution. However, the evolution of focal adhesions -specialized multiprotein complexes that mechanically connect cells with the extracellular matrix- during the mammary gland development, as well as the influence of the mechanical stimuli involved, remains unclear. Here we present the use of an equibiaxial stretching device for exerting a sustained normal strain to mammary epithelial cells while quantitatively assessing cell responses by fluorescence imaging techniques. Using this approach, we explored changes in focal adhesion dynamics in HC11 mammary cells in response to a mechanical sustained stress, which resembles the physiological stimuli. We studied the relationship between a global stress and focal adhesion assembly/disassembly, observing an enhanced persistency of focal adhesions under strain as well as an increase in their size. At a molecular level, we evaluated the mechanoresponses of vinculin and zyxin, two focal adhesion proteins postulated as mechanosensors, observing an increment in vinculin molecular tension and a slower zyxin dynamics while increasing the applied normal strain.

Substrate stiffness regulated migration and invasion ability of adenoid cystic carcinoma cells via RhoA/ROCK pathway

OBJECTIVES

Human salivary adenoid cystic carcinoma (SACC) is one of the most common malignant tumours of the salivary gland and has strong migratory and invasive ability, which often lead to poor prognosis and lower survival rate. Tumour tissue tends to stiffen during solid tumour progression. This study aimed to investigate the influence of various substrate stiffness on the migration and invasion of SACC.

METHODS

Salivary adenoid cystic carcinoma cell line ACC2 cells were cultured on polydimethylsiloxane substrates (PDMS) with varying stiffness for investigating the effects of substrate stiffness on the activities of MMPs and TIMPs. The underlying mechanism was also explored.

RESULTS

When ACC2 cells were cultured on various stiffness of PDMS, the expressions of matrix metalloproteinases 2 (MMP2), MMP9, MMP14, RhoA, Rac1, Rho-associated protein kinase 1 (ROCK1) and ROCK2 were up-regulated with increasing substrate stiffness, whereas that of tissue inhibitor of matrix metalloproteinase 1 (TIMP1), TIMP2 and TIMP4 were down-regulated with increasing substrate stiffness.

CONCLUSIONS

Our results showed that substrate stiffness regulated the activities of MMPs and TIMPs and then modulate migratory and invasive ability of ACC2 cells via RhoA/ROCK pathway. This work indicate that matrix stiffness played an important role in progression of SACC, which not only can help understand the strong invasive ability of SACC, but also suggested that therapeutically targeting matrix stiffness may help reduce migration and invasion of SACC and improve effective therapies.

Diverse patterns of molecular changes in the mechano-responsiveness of focal adhesions

Focal adhesions anchor contractile actin fibers with the extracellular matrix, sense the generated tension and respond to it by changing their morphology and composition. Here we ask how this mechanosensing is enabled at the protein-network level, given the modular assembly and multitasking of focal adhesions. To address this, we applied a sensitive 4-color live cell imaging approach, enabling monitoring patterns of molecular changes in single focal adhesions. Co-imaging zyxin, FAK, vinculin and paxillin revealed heterogeneities in their responses to Rho-associated kinase (ROCK)-mediated perturbations of actomyosin contractility. These responses were rather weakly correlated between the proteins, reflecting diverse compositional changes in different focal adhesions. This diversity is partially attributable to the location of focal adhesions, their area, molecular content and previous contractility perturbations, suggesting that integration of multiple local cues shapes differentially focal adhesion mechano-responsiveness. Importantly, the compositional changes upon ROCK perturbations exhibited distinct paths in different focal adhesions. Moreover, the protein exhibiting the strongest response to ROCK perturbations varied among different focal adhesions. The diversity in response patterns is plausibly enabled by the modular mode of focal adhesions assembly and can provide them the needed flexibility to perform multiple tasks by combining optimally a common set of multifunctional components.

Upregulation of osteogenesis of mesenchymal stem cells with virus-based thin films

A major aim of tissue engineering is to develop biomimetic scaffolding materials that can guide the proliferation, self-renewal and differentiation of multipotent stem cells into specific lineages. Cellular functions can be controlled by the interactions between cells and biomaterials. Therefore, the surface chemistry and topography of support materials play a pivotal role in modulating cell behaviors at many stages of cell growth and development. Due to their highly ordered structure and programmable surface chemistries, which provide unique topography as biomaterials, viral nanoparticles have been utilized as building blocks for targeted cell growth and differentiation. This review article discusses the fabrication of two-dimensional virus-based thin film on substrates and highlights the study of the effect of chemical and physical cues introduced by plant virus nanoparticle thin films on the promotion of osteogenic differentiation of BMSCs.

Why we need mechanics to understand animal regeneration

Mechanical forces are an important contributor to cell fate specification and cell migration during embryonic development in animals. Similarities between embryogenesis and regeneration, particularly with regards to pattern formation and large-scale tissue movements, suggest similarly important roles for physical forces during regeneration. While the influence of the mechanical environment on stem cell differentiation in vitro is being actively exploited in the fields of tissue engineering and regenerative medicine, comparatively little is known about the role of stresses and strains acting during animal regeneration. In this review, we summarize published work on the role of physical principles and mechanical forces in animal regeneration. Novel experimental techniques aimed at addressing the role of mechanics in embryogenesis have greatly enhanced our understanding at scales from the subcellular to the macroscopic - we believe the time is ripe for the field of regeneration to similarly leverage the tools of the mechanobiological research community.

Plasma membrane expression of ZNF185 is a prognostic factor in pancreatic ductal carcinoma

Pancreatic ductal carcinoma (PDC) is one of the major causes of cancer-associated mortality globally due to its high potential for distant metastasis. To understand hematogenous metastasis, the molecular expression profiles of weak metastatic PDC cell subline BxPC-3 and highly liver-metastatic cell subline LM-BxPC-3 were compared, and zinc finger protein 185 (ZNF185) was identified as a molecule that is upregulated in LM-BxPC-3 cells. The aim of the present study was to evaluate the clinicopathological significance of ZNF185 in PDC. Using immunohistochemistry, ZNF185 expression was investigated in 182 patients with PDC, in association with numerous clinicopathological variables. The expression profile of ZNF185 was also characterized using xenograft models. In contrast to parent BxPC-3 cells in subcutaneous transplanted tumor foci, which only expressed ZNF185 on their plasma membrane (m)ZNF185, LM-BxPC-3 cells in liver-metastatic foci that were formed subsequent to transplantation all expressed cytoplasmic (c)ZNF185. Additionally, 51% of the cells at the periphery of the tumor foci expressed mZNF185. Expression of cZNF185, and of mZNF185 and cZNF185 combined was identified in 93 and 39% of clinical patients with PDC, respectively. Patients with mZNF185-negative and -positive PDC exhibited a median survival time of 30.2 months and 21.3 months, respectively. Multivariate analysis indicated that the expression of mZNF185 is closely associated with a shorter overall survival time. Increased marked venous invasion was more prevalent in patients who were mZNF185-positive, as compared with patients who were mZNF185-negative. These data suggest that the expression of mZNF185 is an independent and unfavorable prognosticator in patients with PDC. The results suggested that the amount and subcellular location of ZNF185 are correlated with the position of the cancer cells expressing it within the nests. Additionally, the subcellular location of ZNF185 may be important to its biological function.

β-Lapachone Inhibits Lung Metastasis of Colorectal Cancer by Inducing Apoptosis of CT26 Cells

Background: β-Lapachone is a quinone-containing compound found in red lapacho (Tabebuia impetiginosa, syn. T avellanedae) trees. Lapacho has been used in traditional medicine by several South and Central American indigenous people to treat various types of cancer. The purpose of this study was to investigate the antimetastatic properties of β-lapachone and the underlying mechanisms using colon cancer cells. Methods: This research used metastatic murine colon cancer cell lines, colon 26 (CT26) and colon 38 (MC38). A WST assay, annexin V assay, cell cycle analysis, wound healing assay, invasion assay, western blot analysis, and real-time reverse transcription–polymerase chain reaction were performed to examine the effects of β-lapachone on metastatic phenotypes and molecular mechanisms. The effect of β-lapachone on lung metastasis was assessed in a mouse experimental metastasis model. Results: We found that the inhibition of proliferation of the colon cancer cell lines by β-lapachone was due to the induction of apoptosis and cell cycle arrest. β-Lapachone induced the apoptosis of CT26 cells through caspase-3, -8, and -9 activation; poly(ADP-ribose) polymerase cleavage; and downregulation of the Bcl-2 family in a dose- and time-dependent manner. In addition, a low concentration of β-lapachone decreased the cell migration and invasion by decreasing the expression of matrix metalloproteinases-2 and -9, and increased the expression of tissue inhibitors of metalloproteinases-1 and -2. Moreover, β-lapachone treatment regulated the expression of epithelial-mesenchymal transition markers such as E- and N-cadherin, vimentin, β-catenin, and Snail in CT26 cells. In the mouse experimental metastasis model, β-lapachone significantly inhibited the lung metastasis of CT26 cells. Conclusions: Our results demonstrated the inhibitory effect of β-lapachone on colorectal lung metastasis. This compound may be useful for developing therapeutic agents to treat metastatic cancer.

Deregulation of focal adhesion formation and cytoskeletal tension due to loss of A-type lamins

The nuclear lamina mechanically integrates the nucleus with the cytoskeleton and extracellular environment and regulates gene expression. These functions are exerted through direct and indirect interactions with the lamina's major constituent proteins, the A-type lamins, which are encoded by the LMNA gene. Using quantitative stable isotope labeling-based shotgun proteomics we have analyzed the proteome of human dermal fibroblasts in which we have depleted A-type lamins by means of a sustained siRNA-mediated LMNA knockdown. Gene ontology analysis revealed that the largest fraction of differentially produced proteins was involved in actin cytoskeleton organization, in particular proteins involved in focal adhesion dynamics, such as actin-related protein 2 and 3 (ACTR2/3), subunits of the ARP2/3 complex, and fascin actin-bundling protein 1 (FSCN1). Functional validation using quantitative immunofluorescence showed a significant reduction in the size of focal adhesion points in A-type lamin depleted cells, which correlated with a reduction in early cell adhesion capacity and an increased cell motility. At the same time, loss of A-type lamins led to more pronounced stress fibers and higher traction forces. This phenotype could not be mimicked or reversed by experimental modulation of the STAT3-IL6 pathway, but it was partly recapitulated by chemical inhibition of the ARP2/3 complex. Thus, our data suggest that the loss of A-type lamins perturbs the balance between focal adhesions and cytoskeletal tension. This imbalance may contribute to mechanosensing defects observed in certain laminopathies.

Low-magnitude, high-frequency vibration promotes the adhesion and the osteogenic differentiation of bone marrow-derived mesenchymal stem cells cultured on a hydroxyapatite-coated surface: The direct role of Wnt/β-catenin signaling pathway activation

The positive effect of low-magnitude, high‑frequency (LMHF) vibration on implant osseointegration has been demonstrated; however, the underlying cellular and molecular mechanisms remain unknown. The aim of this study was to explore the effect of LMHF vibration on the adhesion and the osteogenic differentiation of bone marrow-derived mesenchymal stem cells (BMSCs) cultured on hydroxyapatite (HA)-coated surfaces in an in vitro model as well as to elucidate the molecular mechanism responsible for the effects of LMHF vibration on osteogenesis. LMHF vibration resulted in the increased expression of fibronectin, which was measured by immunostaining and RT-qPCR. Stimulation of BMSCs by LMHF vibration resulted in the rearrangement of the actin cytoskeleton with more prominent F-actin. Moreover, the expression of β1 integrin, vinculin and paxillin was notably increased following LMHF stimulation. Scanning electron microscope observations revealed that there were higher cell numbers and more extracellular matrix attached to the HA-coated surface in the LMHF group. Alkaline phosphatase activity as well as the expression of osteogenic-specific genes, namely Runx2, osterix, collagen I and osteocalcin, were significantly elevated in the LMHF group. In addition, the protein expression of Wnt10B, β-catenin, Runx2 and osterix was increased following exposure to LMHF vibration. Taken together, the findings of this study indicate that LMHF vibration promotes the adhesion and the osteogenic differentiation of BMSCs on HA-coated surfaces in vitro, and LMHF vibration may directly induce osteogenesis by activating the Wnt/β‑catenin signaling pathway. These data suggest that LMHF vibration enhances the osseointegration of bone to a HA-coated implant, and provide a scientific foundation for improving bone-implant osseointegration through the application of LMHF vibration.

Vinculin Regulates Directionality and Cell Polarity in 2D, 3D Matrix and 3D Microtrack Migration

During metastasis, cells can use proteolytic activity to form tube-like "microtracks" within the extracellular matrix (ECM). Using these microtracks, cells can migrate unimpeded through the stroma. To investigate the molecular mechanisms of microtrack migration, we developed an in vitro 3D micromolded collagen platform. When in microtracks, cells tend to migrate unidirectionally. Since focal adhesions are the primary mechanism by which cells interact with the ECM, we examined the roles of several focal adhesion molecules in driving unidirectional motion. Vinculin knockdown results in the repeated reversal of migration direction compared with control cells. Tracking the position of the Golgi centroid relative to the position of the nucleus centroid reveals that vinculin knockdown disrupts cell polarity in microtracks. Vinculin also directs migration on 2D substrates and in 3D uniform collagen matrices, indicated by reduced speed, shorter net displacement and decreased directionality in vinculin-deficient cells. In addition, vinculin is necessary for Focal Adhesion Kinase (FAK) activation in 3D as vinculin knockdown results in reduced FAK activation in both 3D uniform collagen matrices and microtracks, but not on 2D substrates, and accordingly, FAK inhibition halts cell migration in 3D microtracks. Together, these data indicate that vinculin plays a key role in polarization during migration.

Differentiated localizations of phosphorylated focal adhesion kinase in endothelial cells of rat splenic sinus

The splenic sinus endothelium adhering via adherens junctions and tight junctions regulates the passage of blood cells through the splenic cord. Focal adhesion kinase (FAK) regulates the focal adhesion complex in the basal part of endothelial cells and is an integrated component of cell-cell adhesion, depending on its phosphorylation status. The objectives of this study are to assess the localization of FAK phosphorylated at tyrosine residues and the related proteins of integrin β5, talin, paxillin, p130Cas, vinculin, RhoA, Rac1, Rac2, Cdc42 and VE-cadherin, in the sinus endothelial cells of rat spleen and to examine the roles of FAK in regulating endothelial adhesion and the passage of blood cells. Immunofluorescence microscopy of tissue cryosections revealed that FAK was localized in the entire circumference of sinus endothelial cells and FAK phosphorylated at Try397 residue (pFAKy397) and pFAKy576 were precisely localized in the adherens junctions of the endothelial cells, whereas pFAKy925 was localized in the basal part of the endothelial cells. Paxillin and vinculin were prominently localized in the basal part of the endothelial cells. Integrin β5, talin and p130Cas were colocalized with FAK in the entire circumference of sinus endothelial cells. RhoA, Rac2 and Cdc42 were localized in the entire circumference of sinus endothelial cells close to FAK, stress fibers and cortical actin filaments. Immunogold electron microscopy revealed that pFAKy397 and pFAKy576 were colocalized with VE-cadherin, RhoA, Rac2 and Cdc42 in the adherens junctions of the endothelial cells. Possible functional roles of FAK in splenic sinus endothelial cells are also discussed.

Signaling of extracellular matrices for tissue regeneration and therapeutics

Cells receive important regulatory signals from their extracellular matrix (ECM) and the physical property of the ECM regulates important cellular behaviors like cell proliferation, migration and differentiation. A large part of tissue formation and regeneration depends on cellular interaction with its ECM. A comprehensive understanding of the mechanistic biochemical pathway of the ECM components is necessary for the design of a biomaterial scaffold for tissue engineering. Depending on the type of tissue, the ECM requirement might be different and this would influence its downstream intracellular cell signaling. Here, we reviewed the ECM and its signaling pathway by discussing: 1) classification of the ECM into hard, elastic and soft tissue based on its physical properties, 2) proliferation and differentiation control of the ECM, 3) roles of membrane receptor and its intracellular regulation factor, 4) ECM remodeling via inside-out signaling. By providing a comprehensive overview of the ECM's role in mechanotransduction and the self-regulatory effect of cells back on the ECM, we hope to provide a better insight of the physical and biochemical cues from the ECM. A sound understanding on the in vivo ECM has implication on the choice of materials and surface coating of biomimetic scaffolds used for tissue regeneration and therapeutics in a cell-free scaffold.

Smad2/3-Regulated Expression of DLX2 Is Associated with Radiation-Induced Epithelial-Mesenchymal Transition and Radioresistance of A549 and MDA-MB-231 Human Cancer Cell Lines

The control of radioresistance and metastatic potential of surviving cancer cells is important for improving cancer eradication by radiotheraphy. The distal-less homeobox2 (DLX2) gene encodes for a homeobox transcription factor involved in morphogenesis and its deregulation was found in human solid tumors and hematologic malignancies. Here we investigated the role of DLX2 in association with radiation-induced epithelial to mesenchymal transition (EMT) and stem cell-like properties and its regulation by Smad2/3 signaling in irradiated A549 and MDA-MB-231 human cancer cell lines. In irradiated A549 and MDA-MB-231 cells, EMT was induced as demonstrated by EMT marker expression, phosphorylation of Smad2/3, and migratory and invasive ability. Also, irradiated A549 and MDA-MB-231 cells showed increased cancer stem cells (CSCs) marker. Interestingly, DLX2 was overexpressed upon irradiation. Therefore, we examined the role of DLX2 in radiation-induced EMT and radioresistance. The overexpression of DLX2 alone induced EMT, migration and invasion, and CSC marker expression. The reduced colony-forming ability in irradiated cells was partially restored by DLX2 overexpression. On the other hand, the depletion of DLX2 using si-RNA abolished radiation-induced EMT, CSC marker expression, and phosphorylation of Smad2/3 in irradiated A549 and MDA-MB-231 cells. Also, depletion of DLX2 increased the radiation sensitivity in both cell lines. Moreover, knockdown of Smad2/3, a key activator of TGF-β1 pathway, abrogated the radiation-induced DLX2 expression, indicating that radiation-induced DLX2 expression is dependent on Smad2/3 signaling. These results demonstrated that DLX2 plays a crucial role in radioresistance, radiation-induced EMT and CSC marker expression, and the expression of DLX2 is regulated by Smad2/3 signaling in A549 and MDA-MB-231 cell lines.

The Src non-receptor tyrosine kinase paradigm: New insights into mammalian Sertoli cell biology

Src kinases are non-receptor tyrosine kinases that phosphorylate diverse substrates, which control processes such as cell proliferation, differentiation and survival; cell adhesion; and cell motility. c-Src, the prototypical member of this protein family, is widely expressed by several organs that include the testis. In the seminiferous epithelium of the adult rat testis, c-Src is highest at the tubule lumen during the release of mature spermatids. Other studies show that testosterone regulates spermatid adhesion to Sertoli cells via c-Src, indicating Src phosphorylates key substrates that prompt the disassembly of Sertoli cell-spermatid junctions. A more recent in vitro study reveals that c-Src participates in the internalization of proteins that constitute the blood-testis barrier, which is present between Sertoli cells, suggesting a similar mechanism of junction disassembly is at play during spermiation. In this review, we discuss recent findings on c-Src, with an emphasis on its role in spermatogenesis in the mammalian testis.

Virus Nanoparticles Mediated Osteogenic Differentiation of Bone Derived Mesenchymal Stem Cells

There are few methodologies that allow manipulating a biomaterial surface at nanometer scale, which controllably influence different cellular functions. In this study, virus nanoparticles with different structural features are selected to prepare 2D substrates with defined nanoscale topographies and the cellular responses are investigated. It is demonstrated that the viral nanoparticle based substrates could accelerate and enhance osteogenesis of bone derived mesenchymal stem cells as indicated by the upregulation of osteogenic markers, including bone morphogenetic protein-2, osteocalcin, and osteopontin, at both gene and protein expression levels. Moreover, alkaline phosphatase activity and calcium mineralization, both indicators for a -successful bone formation, are also increased in cells grown on these nanoscale possessed substrates. These discoveries and developments present a new paradigm for nanoscale engineering of a biomaterial surface.

The pH-sensing receptor OGR1 improves barrier function of epithelial cells and inhibits migration in an acidic environment

The pH-sensing receptor ovarian cancer G protein-coupled receptor 1 (OGR1; GPR68) is expressed in the gut. Inflammatory bowel disease is typically associated with a decrease in local pH, which may lead to altered epithelial barrier function and subsequent gastrointestinal repair involving epithelial cell adhesion and migration. As the mechanisms underlying the response to pH changes are not well understood, we have investigated OGR1-mediated, pH-dependent signaling pathways in intestinal epithelial cells. Caco-2 cells stably overexpressing OGR1 were created and validated as tools to study OGR1 signaling. Barrier function, migration, and proliferation were measured using electric cell-substrate impedance-sensing technology. Localization of the tight junction proteins zonula occludens protein 1 and occludin and the rearrangement of cytoskeletal actin were examined by confocal microscopy. Paracellular permeability and protein and gene expression analysis using DNA microarrays were performed on filter-grown Caco-2 monolayers. We report that an acidic pH shift from pH 7.8 to 6.6 improved barrier function and stimulated reorganization of filamentous actin with prominent basal stress fiber formation. Cell migration and proliferation during in vitro wound healing were inhibited. Gene expression analysis revealed significant upregulation of genes related to cytoskeleton remodeling, cell adhesion, and growth factor signaling. We conclude that acidic extracellular pH can have a signaling function and impact the physiology of intestinal epithelial cells. The deconstruction of OGR1-dependent signaling may aid our understanding of mucosal inflammation mechanisms.

Phosphorylation and turnover of paxillin in focal contacts is controlled by force and defines the dynamic state of the adhesion site

Micro-environmental clues are critical to cell behavior. One of the key elements of migration is the generation and response to forces. Up to now there is no definitive concept on how the generation and responses to cellular forces influence cell behavior. Here, we show that phosphorylation of paxillin is a crucial event in the response to exogenous forces. Application of force induced growth of adhesion sites and this phenomenon was accompanied by a downregulation of Src family kinase activity, which in turn led to a decrease in the phosphorylation of paxillin at the tyrosine residues Y31 and Y118. The force-dependent growth of adhesion sites is mediated by a decrease in the turnover-rate of paxillin in focal contacts. This turnover critically depended on the phosphorylation state of paxillin at Y31/118. Paxillin is an important regulator in the control of the aggregate state of the whole adhesion site since the turnover of other adhesion site proteins such as vinculin is influenced by the phosphorylation state of paxillin as well. Taken together these data suggest that SFK dependent phosphorylation of paxillin is a crucial event in the regulation of adhesion site function in response to force.

PMP22 is critical for actin-mediated cellular functions and for establishing lipid rafts

Haploinsufficiency of peripheral myelin protein 22 (PMP22) causes hereditary neuropathy with liability to pressure palsies, a peripheral nerve lesion induced by minimal trauma or compression. As PMP22 is localized to cholesterol-enriched membrane domains that are closely linked with the underlying actin network, we asked whether the myelin instability associated with PMP22 deficiency could be mediated by involvement of the protein in actin-dependent cellular functions and/or lipid raft integrity. In peripheral nerves and cells from mice with PMP22 deletion, we assessed the organization of filamentous actin (F-actin), and actin-dependent cellular functions. Using in vitro models, we discovered that, in the absence of PMP22, the migration and adhesion capacity of Schwann cells and fibroblasts are similarly impaired. Furthermore, PMP22-deficient Schwann cells produce shortened myelin internodes, and display compressed axial cell length and collapsed lamellipodia. During early postnatal development, F-actin-enriched Schmidt-Lanterman incisures do not form properly in nerves from PMP22(-/-) mice, and the expression and localization of molecules associated with uncompacted myelin domains and lipid rafts, including flotillin-1, cholesterol, and GM1 ganglioside, are altered. In addition, we identified changes in the levels and distribution of cholesterol and ApoE when PMP22 is absent. Significantly, cholesterol supplementation of the culture medium corrects the elongation and migration deficits of PMP22(-/-) Schwann cells, suggesting that the observed functional impairments are directly linked with cholesterol deficiency of the plasma membrane. Our findings support a novel role for PMP22 in the linkage of the actin cytoskeleton with the plasma membrane, likely through regulating the cholesterol content of lipid rafts.

Changes in integrin αv, vinculin and connexin43 in the medial prefrontal cortex in rats under single-prolonged stress

Post‑traumatic stress disorder (PTSD) is a stress‑accociated mental disorder that occurs as a result of exposure to a traumatic event, with characteristic symptoms, including intrusive memories, hyperarousal and avoidance. The medial prefrontal cortex (mPFC) is known to be significantly involved in emotional adjustment, particularly introspection, inhibition of the amygdala and emotional memory. Previous structural neuroimaging studies have revealed that the mPFC of PTSD patients was significantly smaller when compared with that of controls and their emotional adjustment function was weakened. However, the mechanisms that cause such atrophy remain to be elucidated. The aim of the present study was to elucidate the possible mechanisms involved in apoptosis induced by single‑prolonged stress (SPS) in the mPFC of PTSD rats. SPS is an animal model reflective of PTSD. Of the proposed animal models of PTSD, SPS is one that has been shown to be reliably reproducible in patients with PTSD. Wistar rats were sacrificed at 1, 4, 7 and 14 days after exposure to SPS. Apoptotic cells were assessed using electron microscopy and the TUNEL method. Expression of integrin αv, vinculin and connexin43 were detected using immunohistochemistry, western blotting and reverse transcription polymerase chain reaction. The present results demonstrated that apoptotic cells significantly increased in the mPFC of SPS rats, accompanied with changes in expression of integrin αv, vinculin and connexin43. The present results indicated that SPS‑induced apoptosis in the mPFC of PTSD rats and the mitochondrial pathway were involved in the process of SPS‑induced apoptosis.

LPA-mediated migration of ovarian cancer cells involves translocalization of Gαi2 to invadopodia and association with Src and β-pix

Lysophosphatidic acid (LPA) plays a critical role in the migration and invasion of ovarian cancer cells. However, the downstream spatiotemporal signaling events involving specific G protein(s) underlying this process are largely unknown. In this report, we demonstrate that LPA signaling causes the translocation of Gαi2 into the invadopodia leading to its interaction with the tyrosine kinase Src and the Rac/CDC42-specific guanine nucleotide exchange factor, β-pix. Our results establish that Gαi2 activates Rac1 through a p130Cas-dependent pathway in ovarian cancer cells. Moreover, our report reveals that knockdown of Gαi2 leads to loss of β-pix and active-Rac association in the invadopodia. We also show that knockdown of Gαi2 leads to the complete loss of translocation to p130Cas to focal adhesions. Finally, when Gαi2 is knocked down, this led to the total distribution of Src being shifted primarily from invadopodia and the leading edge of the cells to the perinuclear region, suggesting that Src is inactive in the absence of Gαi2. Overall, our report provides tantalizing evidence that Gαi2 is a critical signaling component of a large signaling complex in the invadopodia that if disrupted could serve as an excellent target for therapy in ovarian and potentially other cancers.

Non-metastatic 2 (NME2)-mediated suppression of lung cancer metastasis involves transcriptional regulation of key cell adhesion factor vinculin

Tumor metastasis refers to spread of a tumor from site of its origin to distant organs and causes majority of cancer deaths. Although >30 metastasis suppressor genes (MSGs) that negatively regulate metastasis have been identified so far, two issues are poorly understood: first, which MSGs oppose metastasis in a tumor type, and second, which molecular function of MSG controls metastasis. Herein, integrative analyses of tumor-transcriptomes (n = 382), survival data (n = 530) and lymph node metastases (n = 100) in lung cancer patients identified non-metastatic 2 (NME2) as a key MSG from a pool of >30 metastasis suppressors. Subsequently, we generated a promoter-wide binding map for NME2 using chromatin immunoprecipitation with promoter microarrays (ChIP-chip), and transcriptome profiling. We discovered novel targets of NME2 which are involved in focal adhesion signaling. Importantly, we detected binding of NME2 in promoter of focal adhesion factor, vinculin. Reduced expression of NME2 led to enhanced transcription of vinculin. In comparison, NME1, a close homolog of NME2, did not bind to vinculin promoter nor regulate its expression. In line, enhanced metastasis of NME2-depleted lung cancer cells was found in zebrafish and nude mice tumor models. The metastatic potential of NME2-depleted cells was remarkably diminished upon selective RNA-i-mediated silencing of vinculin. Together, we demonstrate that reduced NME2 levels lead to transcriptional de-repression of vinculin and regulate lung cancer metastasis.

Rho-associated protein kinase modulates neurite extension by regulating microtubule remodeling and vinculin distribution

Rho-associated protein kinase is an essential regulator of cytoskeletal dynamics during the process of neurite extension. However, whether Rho kinase regulates microtubule remodeling or the distribution of adhesive proteins to mediate neurite outgrowth remains unclear. By specifically modulating Rho kinase activity with pharmacological agents, we studied the morpho-dynamics of neurite outgrowth. We found that lysophosphatidic acid, an activator of Rho kinase, inhibited neurite outgrowth, which could be reversed by Y-27632, an inhibitor of Rho kinase. Meanwhile, reorganization of microtubules was noticed during these processes, as indicated by their significant changes in the soma and growth cone. In addition, exposure to lysophosphatidic acid led to a decreased membrane distribution of vinculin, a focal adhesion protein in neurons, whereas Y-27632 recruited vinculin to the membrane. Taken together, our data suggest that Rho kinase regulates rat hippocampal neurite growth and microtubule formation via a mechanism associated with the redistribution of vinculin.

The fundamental role of mechanical properties in the progression of cancer disease and inflammation

The role of mechanical properties in cancer disease and inflammation is still underinvestigated and even ignored in many oncological and immunological reviews. In particular, eight classical hallmarks of cancer have been proposed, but they still ignore the mechanics behind the processes that facilitate cancer progression. To define the malignant transformation of neoplasms and finally reveal the functional pathway that enables cancer cells to promote cancer progression, these classical hallmarks of cancer require the inclusion of specific mechanical properties of cancer cells and their microenvironment such as the extracellular matrix as well as embedded cells such as fibroblasts, macrophages or endothelial cells. Thus, this review will present current cancer research from a biophysical point of view and will therefore focus on novel physical aspects and biophysical methods to investigate the aggressiveness of cancer cells and the process of inflammation. As cancer or immune cells are embedded in a certain microenvironment such as the extracellular matrix, the mechanical properties of this microenvironment cannot be neglected, and alterations of the microenvironment may have an impact on the mechanical properties of the cancer or immune cells. Here, it is highlighted how biophysical approaches, both experimental and theoretical, have an impact on the classical hallmarks of cancer and inflammation. It is even pointed out how these biophysical approaches contribute to the understanding of the regulation of cancer disease and inflammatory responses after tissue injury through physical microenvironmental property sensing mechanisms. The recognized physical signals are transduced into biochemical signaling events that guide cellular responses, such as malignant tumor progression, after the transition of cancer cells from an epithelial to a mesenchymal phenotype or an inflammatory response due to tissue injury. Moreover, cell adaptation to mechanical alterations, in particular the understanding of mechano-coupling and mechano-regulating functions in cell invasion, appears as an important step in cancer progression and inflammatory response to injuries. This may lead to novel insights into cancer disease and inflammatory diseases and will overcome classical views on cancer and inflammation. In addition, this review will discuss how the physics of cancer and inflammation can help to reveal whether cancer cells will invade connective tissue and metastasize or how leukocytes extravasate and migrate through the tissue. In this review, the physical concepts of cancer progression, including the tissue basement membrane a cancer cell is crossing, its invasion and transendothelial migration as well as the basic physical concepts of inflammatory processes and the cellular responses to the mechanical stress of the microenvironment such as external forces and matrix stiffness, are presented and discussed. In conclusion, this review will finally show how physical measurements can improve classical approaches that investigate cancer and inflammatory diseases, and how these physical insights can be integrated into classical tumor biological approaches.