The lamin A/C Ig-fold undergoes cell density-dependent changes that alter epitope binding

Lamins A/C are nuclear intermediate filament proteins that are involved in diverse cellular mechanical and biochemical functions. Here, we report that recognition of Lamins A/C by a commonly used antibody (JOL-2) that binds the Lamin A/C Ig-fold and other antibodies targeting similar epitopes is highly dependent on cell density, even though Lamin A/Clevels do not change. We propose that the effect is caused by partial unfolding or masking of the C'E and/or EF loops of the Ig-fold in response to cell spreading. Surprisingly, JOL-2 antibody labeling was insensitive to disruption of cytoskeletal filaments or the Linker of Nucleoskeleton and Cytoskeleton (LINC) complex. Furthermore, neither nuclear stiffness nor nucleo-cytoskeletal force transmission changed with cell density. These findings are important for the interpretation of immunofluorescence data for Lamin A/C and also raise the intriguing prospect that the conformational changes may play a role in Lamin A/C mediated cellular function.

WAVE2 Regulates Actin-Dependent Processes Induced by the B Cell Antigen Receptor and Integrins

B cell antigen receptor (BCR) signaling induces actin cytoskeleton remodeling by stimulating actin severing, actin polymerization, and the nucleation of branched actin networks via the Arp2/3 complex. This enables B cells to spread on antigen-bearing surfaces in order to increase antigen encounters and to form an immune synapse (IS) when interacting with antigen-presenting cells (APCs). Although the WASp, N-WASp, and WAVE nucleation-promoting factors activate the Arp2/3 complex, the role of WAVE2 in B cells has not been directly assessed. We now show that both WAVE2 and the Arp2/3 complex localize to the peripheral ring of branched F-actin when B cells spread on immobilized anti-Ig antibodies. The siRNA-mediated depletion of WAVE2 reduced and delayed B cell spreading on immobilized anti-Ig, and this was associated with a thinner peripheral F-actin ring and reduced actin retrograde flow compared to control cells. Depleting WAVE2 also impaired integrin-mediated B cell spreading on fibronectin and the LFA-1-induced formation of actomyosin arcs. Actin retrograde flow amplifies BCR signaling at the IS, and we found that depleting WAVE2 reduced microcluster-based BCR signaling and signal amplification at the IS, as well as B cell activation in response to antigen-bearing cells. Hence, WAVE2 contributes to multiple actin-dependent processes in B lymphocytes.

Atypical peripheral actin band formation via overactivation of RhoA and nonmuscle myosin II in mitofusin 2-deficient cells

Cell spreading and migration play central roles in many physiological and pathophysiological processes. We have previously shown that MFN2 regulates the migration of human neutrophil-like cells via suppressing Rac activation. Here, we show that in mouse embryonic fibroblasts, MFN2 suppresses RhoA activation and supports cell polarization. After initial spreading, the wild-type cells polarize and migrate, whereas the Mfn2-/- cells maintain a circular shape. Increased cytosolic Ca2+ resulting from the loss of Mfn2 is directly responsible for this phenotype, which can be rescued by expressing an artificial tether to bring mitochondria and endoplasmic reticulum to close vicinity. Elevated cytosolic Ca2+ activates Ca2+/calmodulin-dependent protein kinase II, RhoA, and myosin light-chain kinase, causing an overactivation of nonmuscle myosin II, leading to a formation of a prominent F-actin ring at the cell periphery and increased cell contractility. The peripheral actin band alters cell physics and is dependent on substrate rigidity. Our results provide a novel molecular basis to understand how MFN2 regulates distinct signaling pathways in different cells and tissue environments, which is instrumental in understanding and treating MFN2-related diseases.

Cas phosphorylation regulates focal adhesion assembly

Integrin-mediated cell attachment rapidly induces tyrosine kinase signaling. Despite years of research, the role of this signaling in integrin activation and focal adhesion assembly is unclear. We provide evidence that the Src-family kinase (SFK) substrate Cas (Crk-associated substrate, p130Cas, BCAR1) is phosphorylated and associated with its Crk/CrkL effectors in clusters that are precursors of focal adhesions. The initial phospho-Cas clusters contain integrin β1 in its inactive, bent closed, conformation. Later, phospho-Cas and total Cas levels decrease as integrin β1 is activated and core focal adhesion proteins including vinculin, talin, kindlin, and paxillin are recruited. Cas is required for cell spreading and focal adhesion assembly in epithelial and fibroblast cells on collagen and fibronectin. Cas cluster formation requires Cas, Crk/CrkL, SFKs, and Rac1 but not vinculin. Rac1 provides positive feedback onto Cas through reactive oxygen, opposed by negative feedback from the ubiquitin proteasome system. The results suggest a two-step model for focal adhesion assembly in which clusters of phospho-Cas, effectors and inactive integrin β1 grow through positive feedback prior to integrin activation and recruitment of core focal adhesion proteins.

Sculpting Rupture-Free Nuclear Shapes in Fibrous Environments

Cytoskeleton-mediated force transmission regulates nucleus morphology. How nuclei shaping occurs in fibrous in vivo environments remains poorly understood. Here suspended nanofiber networks of precisely tunable (nm-µm) diameters are used to quantify nucleus plasticity in fibrous environments mimicking the natural extracellular matrix. Contrary to the apical cap over the nucleus in cells on 2-dimensional surfaces, the cytoskeleton of cells on fibers displays a uniform actin network caging the nucleus. The role of contractility-driven caging in sculpting nuclear shapes is investigated as cells spread on aligned single fibers, doublets, and multiple fibers of varying diameters. Cell contractility increases with fiber diameter due to increased focal adhesion clustering and density of actin stress fibers, which correlates with increased mechanosensitive transcription factor Yes-associated protein (YAP) translocation to the nucleus. Unexpectedly, large- and small-diameter fiber combinations lead to teardrop-shaped nuclei due to stress fiber anisotropy across the cell. As cells spread on fibers, diameter-dependent nuclear envelope invaginations that run the nucleus's length are formed at fiber contact sites. The sharpest invaginations enriched with heterochromatin clustering and sites of DNA repair are insufficient to trigger nucleus rupture. Overall, the authors quantitate the previously unknown sculpting and adaptability of nuclei to fibrous environments with pathophysiological implications.

Surface Structure of Zirconia Implants: An Integrative Review Comparing Clinical Results with Preclinical and In Vitro Data

Background: The purpose of this review was to analyze and correlate the findings for zirconia implants in clinical, preclinical and in vitro cell studies in relation to surface structure. Methods: Electronic searches were conducted to identify clinical, preclinical and in vitro cell studies on zirconia implant surfaces. The primary outcomes were mean bone loss (MBL) for clinical studies, bone-to-implant contact (BIC) and removal torque (RT) for preclinical studies and cell spreading, cell proliferation and gene expression for cell studies. The secondary outcomes included comparisons of data found for those surfaces that were investigated in all three study types. Results: From 986 screened titles, 40 studies were included for data extraction. In clinical studies, only micro-structured surfaces were investigated. The lowest MBL was reported for sandblasted and subsequently etched surfaces, followed by a sinter and slurry treatment and sandblasted surfaces. For BIC, no clear preference of one surface structure was observable, while RT was slightly higher for micro-structured than smooth surfaces. All cell studies showed that cell spreading and cytoskeletal formation were enhanced on smooth compared with micro-structured surfaces. Conclusions: No correlation was observed for the effect of surface structure of zirconia implants within the results of clinical, preclinical and in vitro cell studies, underlining the need for standardized procedures for human, animal and in vitro studies.

Gradual Stress-Relaxation of Hydrogel Regulates Cell Spreading

There is growing evidence that the mechanical properties of extracellular matrices (ECMs), including elasticity and stress-relaxation, greatly influence the function and form of the residing cells. However, the effects of elasticity and stress-relaxation are often correlated, making the study of the effect of stress-relaxation on cellular behaviors difficult. Here, we designed a hybrid network hydrogel with a controllable stress-relaxation gradient and a constant elasticity. The hydrogel is crosslinked by covalent bonds and dynamic peptide-metal ion coordination interactions. The stress-relaxation gradient is controlled by spatially controlling the coordination and covalent crosslinker ratios. The different parts of the hydrogel exhibit distinct stress-relaxation amplitudes but the have same stress-relaxation timescale. Based on this hydrogel, we investigate the influence of hydrogel stress-relaxation on cell spreading. Our results show that the spreading of cells is suppressed at an increasing stress-relaxation amplitude with a fixed elasticity and stress-relaxation timescale. Our study provides a universal route to tune the stress-relaxation of hydrogels without changing their components and elasticity, which may be valuable for systematic investigations of the stress-relaxation gradient in cell cultures and organoid constructions.

Octa-arginine and Octa-lysine Promote Cell Adhesion through Heparan Sulfate Proteoglycans and Integrins

Octa-arginine (R8) has been extensively studied as a cell-penetrating peptide. R8 binds to diverse transmembrane heparan sulfate proteoglycans (HSPGs), including syndecans, and is internalized by cells. R8 is also reported to bind to integrin β1. In this study, we evaluated the biological activities of R8 and octa-lysine (K8), a peptide similar to R8, with a focus on cell adhesion. R8 and K8 were immobilized on aldehyde-agarose matrices via covalent conjugation, and the effect of these peptides on cell attachment, spreading, and proliferation was examined using human dermal fibroblasts. The results indicated that R8- and K8-matrices mediate cell adhesion mainly via HSPGs. Moreover, R8- and K8-matrices interacted with integrin β1 and promote cell spreading and proliferation. These results are useful for further understanding of the R8-membrane interactions and the cellular uptake mechanisms. In addition, the R8- and K8-matrices may potentially be used as a multi-functional biomaterial to promote cell adhesion, spreading, and proliferation.

Vimentin Intermediate Filaments Mediate Cell Morphology on Viscoelastic Substrates

The ability of cells to take and change shape is a fundamental feature underlying development, wound repair, and tissue maintenance. Central to this process is physical and signaling interactions between the three cytoskeletal polymeric networks: F-actin, microtubules, and intermediate filaments (IFs). Vimentin is an IF protein that is essential to the mechanical resilience of cells and regulates cross-talk among the cytoskeleton, but its role in how cells sense and respond to the surrounding extracellular matrix is largely unclear. To investigate vimentin’s role in substrate sensing, we designed polyacrylamide hydrogels that mimic the elastic and viscoelastic nature of in vivo tissues. Using wild-type and vimentin-null mouse embryonic fibroblasts, we show that vimentin enhances cell spreading on viscoelastic substrates, even though it has little effect in the limit of purely elastic substrates. Our results provide compelling evidence that vimentin modulates how cells sense and respond to their environment and thus plays a key role in cell mechanosensing.

Graphene Enhances Actin Filament Assembly Kinetics and Modulates NIH-3T3 Fibroblast Cell Spreading

Actin plays critical roles in various cellular functions, including cell morphogenesis, differentiation, and movement. The assembly of actin monomers into double-helical filaments is regulated in surrounding microenvironments. Graphene is an attractive nanomaterial that has been used in various biomaterial applications, such as drug delivery cargo and scaffold for cells, due to its unique physical and chemical properties. Although several studies have shown the potential effects of graphene on actin at the cellular level, the direct influence of graphene on actin filament dynamics has not been studied. Here, we investigate the effects of graphene on actin assembly kinetics using spectroscopy and total internal reflection fluorescence microscopy. We demonstrate that graphene enhances the rates of actin filament growth in a concentration-dependent manner. Furthermore, cell morphology and spreading are modulated in mouse embryo fibroblast NIH-3T3 cultured on a graphene surface without significantly affecting cell viability. Taken together, these results suggest that graphene may have a direct impact on actin cytoskeleton remodeling.

Designer DNA Hydrogels Stimulate 3D Cell Invasion by Enhanced Receptor Expression and Membrane Endocytosis

DNA has emerged as one of the smartest biopolymers to bridge the gap between chemical science and biology to design scaffolds like hydrogels by physical entanglement or chemical bonding with remarkable properties. We present here a completely new application of DNA-based hydrogels in terms of their capacity to stimulate membrane endocytosis, leading to enhanced cell spreading and invasion for cells in ex vivo 3D spheroids models. Multiscale simulation studies along with DLS data showed that the hydrogel formation was enhanced at lower temperature and it converts to liquid with increase in temperature. DNA hydrogels induced cell spreading as observed by the increase in cellular area by almost two-fold followed by an increase in the receptor expression, the endocytosis, and the 3D invasion potential of migrating cells. Our first results lay the foundation for upcoming diverse applications of hydrogels to probe and program various cellular and physiological processes that can have lasting applications in stem cell programming and regenerative therapeutics.

Emerging Roles of Pleckstrin-2 Beyond Cell Spreading

Pleckstrin-2 is a member of pleckstrin family with well-defined structural features that was first identified in 1999. Over the past 20 years, our understanding of PLEK2 biology has been limited to cell spreading. Recently, increasing evidences support that PLEK2 plays important roles in other cellular events beyond cell spreading, such as erythropoiesis, tumorigenesis and metastasis. It serves as a potential diagnostic and prognostic biomarker as well as an attractive target for the treatment of cancers. Herein, we summary the protein structure and molecular interactions of pleckstrin-2, with an emphasis on its regulatory roles in tumorigenesis.

Cell spreading behaviors on hybrid nanopillar and nanohole arrays

Although nanopillars (NPs) provide a promising tool for capturing tumor cells, the effect of mixing NPs with other nanopatterns on cell behavior remains to be further studied. In this paper, a method of fabricating silicon nanoscale topographies by combining laser interference lithography with metal assisted chemical etching was introduced to investigate the behaviors and pseudopodia of A549 cells on the topologies. It was found that cells had a limited manner in spreading with small cell areas on the silicon nanopillar (SiNP) arrays, but a good manner in spreading with large cell areas on the silicon nanohole (SiNH) arrays. When on the hybrid SiNP/SiNH arrays, cells had medium cell areas and they arranged orderly along the boundaries of SiNPs and SiNHs, as well as 80% of cells displayed a preference for SiNPs over SiNHs. Furthermore, the lamellipodia and filopodia are dominant in the hybrid SiNP/SiNH and SiNP arrays, respectively, both of them are dominant in the SiNH arrays. In addition, the atomic force acoustic microscopy was also employed to detect the subsurface features of samples. The results suggest that the hybrid SiNP/SiNH arrays have a targeted trap and elongation effect on cells. The findings provide a promising method in designing hybrid nanostructures for efficient tumor cell traps, as well as regulating the cell behaviors and pseudopodia.

Lamin A/C Mechanosensor Drives Tumor Cell Aggressiveness and Adhesion on Substrates With Tissue-Specific Elasticity

Besides its structural properties in the nucleoskeleton, Lamin A/C is a mechanosensor protein involved in perceiving the elasticity of the extracellular matrix. In this study we provide evidence about Lamin A/C-mediated regulation of osteosarcoma cell adhesion and spreading on substrates with tissue-specific elasticities. Our working hypothesis is based on the observation that low-aggressive and bone-resident SaOS-2 osteosarcoma cells express high level of Lamin A/C in comparison to highly metastatic, preferentially to the lung, osteosarcoma 143B cells, thereby suggesting a role for Lamin A/C in tumor cell tropism. Specifically, LMNA gene over-expression in 143B cells induced a reduction in tumor cell aggressiveness in comparison to parental cells, with decreased proliferation rate and reduced migration capability. Furthermore, LMNA reintegration into 143B cells changed the adhesion properties of tumor cells, from a preferential tropism toward the 1.5 kPa PDMS substrate (resembling normal lung parenchyma) to the 28 kPa (resembling pre-mineralized bone osteoid matrix). Our study suggests that Lamin A/C expression could be involved in the organ tropism of tumor cells, thereby providing a rationale for further studies focused on the definition of cancer mechanism of metastatization.

Poly(glycerol sebacate)-co-poly(ethylene glycol)/Gelatin Hybrid Hydrogels as Biocompatible Biomaterials for Cell Proliferation and Spreading

Synthetic polymers have been widely employed to prepare hydrogels for biomedical applications, such as cell culture, drug delivery, and tissue engineering. However, the activity of cells cultured in the synthetic polymer-based hydrogels faces the challenges of limited cell proliferation and spreading compared to cells cultured in natural polymer-based hydrogels. To address this concern, a hybrid hydrogel strategy is demonstrated by incorporating thiolated gelatin (GS) into the norbornene-functionalized poly (glycerol sebacate)-co-polyethylene glycol (Nor_PGS-co-PEG, NPP) network to prepare highly biocompatible NPP/GS_UV hydrogels after the thiol-ene photo-crosslinking reaction. The GS introduces several desirable features (i.e., enhanced water content, enlarged pore size, increased mechanical property, and more cell adhesion sites) to the NPP/GS_UV hydrogels, facilitating the cell proliferation and spreading inside the network. Thus, the highly biocompatible NPP/GS_UV hydrogels are promising materials for cell encapsulation and tissue engineering applications. Taken together, the hybrid hydrogel strategy is demonstrated as a powerful approach to fabricate hydrogels with a highly friendly environment for cell culture, expanding the biomedical applications of hydrogels.

High ligand density drives extensive spreading and motility on soft GelMA gels

In comparison to synthetic hydrogels where ligand density and stiffness can be independently tuned, cell responses are expected to deviate on native biopolymer networks where ligand density and stiffness are coupled. Here we probe the tensional homeostasis of fibroblasts on methacrylated gelatin (GelMA) gels, which are widely used in tissue engineering applications. On 5%-15% GelMA gels which are very soft (10-100's of Pa's in stiffness), fibroblasts were found to spread extensively and assemble prominent stress fibers and focal adhesions. Probing of contractile mechanics using trypsin-induced detachment revealed adhesive drag, but not contractility, was sensitive to GelMA concentration. Contractility-altering drugs blebbistatin and nocodazole, which exhibited opposite effects on focal adhesion size, both led to reduction in adhesive drag and cell rounding. However, cell motility was impacted only in nocodazole-treated cells. Collectively, our experiments suggest that on soft GelMA gels, contractility-independent adhesion clustering mediated by high ligand density can drive cell spreading and motility.

Adhesion of Neurons and Glial Cells with Nanocolumnar TiN Films for Brain-Machine Interfaces

Coupling of cells to biomaterials is a prerequisite for most biomedical applications; e.g., neuroelectrodes can only stimulate brain tissue in vivo if the electric signal is transferred to neurons attached to the electrodes' surface. Besides, cell survival in vitro also depends on the interaction of cells with the underlying substrate materials; in vitro assays such as multielectrode arrays determine cellular behavior by electrical coupling to the adherent cells. In our study, we investigated the interaction of neurons and glial cells with different electrode materials such as TiN and nanocolumnar TiN surfaces in contrast to gold and ITO substrates. Employing single-cell force spectroscopy, we quantified short-term interaction forces between neuron-like cells (SH-SY5Y cells) and glial cells (U-87 MG cells) for the different materials and contact times. Additionally, results were compared to the spreading dynamics of cells for different culture times as a function of the underlying substrate. The adhesion behavior of glial cells was almost independent of the biomaterial and the maximum growth areas were already seen after one day; however, adhesion dynamics of neurons relied on culture material and time. Neurons spread much better on TiN and nanocolumnar TiN and also formed more neurites after three days in culture. Our designed nanocolumnar TiN offers the possibility for building miniaturized microelectrode arrays for impedance spectroscopy without losing detection sensitivity due to a lowered self-impedance of the electrode. Hence, our results show that this biomaterial promotes adhesion and spreading of neurons and glial cells, which are important for many biomedical applications in vitro and in vivo.

The Actin-Disassembly Protein Glia Maturation Factor γ Enhances Actin Remodeling and B Cell Antigen Receptor Signaling at the Immune Synapse

Signaling by the B cell antigen receptor (BCR) initiates actin remodeling. The assembly of branched actin networks that are nucleated by the Arp2/3 complex exert outward force on the plasma membrane, allowing B cells to form membrane protrusions that can scan the surface of antigen-presenting cells (APCs). The resulting Arp2/3 complex-dependent actin retrograde flow promotes the centripetal movement and progressive coalescence of BCR microclusters, which amplifies BCR signaling. Glia maturation factor γ (GMFγ) is an actin disassembly-protein that releases Arp2/3 complex-nucleated actin filaments from actin networks. By doing so, GMFγ could either oppose the actions of the Arp2/3 complex or support Arp2/3 complex-nucleated actin polymerization by contributing to the recycling of actin monomers and Arp2/3 complexes. We now show that reducing the levels of GMFγ in human B cell lines via transfection with a specific siRNA impairs the ability of B cells to spread on antigen-coated surfaces, decreases the velocity of actin retrograde flow, diminishes the coalescence of BCR microclusters into a central cluster at the B cell-APC contact site, and decreases APC-induced BCR signaling. These effects of depleting GMFγ are similar to what occurs when the Arp2/3 complex is inhibited. This suggests that GMFγ cooperates with the Arp2/3 complex to support BCR-induced actin remodeling and amplify BCR signaling at the immune synapse.

Molecular basis for Ras suppressor-1 binding to PINCH-1 in focal adhesion assembly

Ras suppressor-1 (Rsu-1) is a leucine-rich repeat (LRR)-containing protein that is crucial for regulating cell adhesion and is involved in such physiological and pathological processes as focal adhesion assembly and tumor metastasis. Rsu-1 interacts with zinc-finger type multi-LIM domain-containing adaptor protein PINCH-1, known to be involved in the integrin-mediated consensus adhesome, but not with its highly homologous family member PINCH-2. However, the structural basis for and regulatory mechanisms of this specific interaction remain unclear. Here, we determined the crystal structures of Rsu-1 and its complex with the PINCH-1 LIM4-5 domains. Rsu-1 displays an arc-shaped solenoid architecture, with eight LRRs shielded by N- and C-terminal capping modules. We showed that the conserved concave surface of the Rsu-1 LRR domain binds and stabilizes the PINCH-1 LIM5 domain via salt bridge and hydrophobic interactions, while the C-terminal non-LIM region of PINCH-2 sterically disfavors Rsu-1 binding. We also showed that Rsu-1 can be assembled, via PINCH-1-binding, into a heteropentamer complex comprising Rsu-1, PINCH-1, ILK, Parvin, and Kindlin-2, which constitute a major consensus integrin adhesome crucial for focal adhesion assembly. Our mutagenesis and cell biological data emphasize the significance of the Rsu-1/PINCH-1 interaction in focal adhesion assembly and cell spreading, providing crucial molecular insights into Rsu-1-mediated cell adhesion with implications for disease development.

The Wdr1-LIMK-Cofilin Axis Controls B Cell Antigen Receptor-Induced Actin Remodeling and Signaling at the Immune Synapse

When B cells encounter membrane-bound antigens, the formation and coalescence of B cell antigen receptor (BCR) microclusters amplifies BCR signaling. The ability of B cells to probe the surface of antigen-presenting cells (APCs) and respond to APC-bound antigens requires remodeling of the actin cytoskeleton. Initial BCR signaling stimulates actin-related protein (Arp) 2/3 complex-dependent actin polymerization, which drives B cell spreading as well as the centripetal movement and coalescence of BCR microclusters at the B cell-APC synapse. Sustained actin polymerization depends on concomitant actin filament depolymerization, which enables the recycling of actin monomers and Arp2/3 complexes. Cofilin-mediated severing of actin filaments is a rate-limiting step in the morphological changes that occur during immune synapse formation. Hence, regulators of cofilin activity such as WD repeat-containing protein 1 (Wdr1), LIM domain kinase (LIMK), and coactosin-like 1 (Cotl1) may also be essential for actin-dependent processes in B cells. Wdr1 enhances cofilin-mediated actin disassembly. Conversely, Cotl1 competes with cofilin for binding to actin and LIMK phosphorylates cofilin and prevents it from binding to actin filaments. We now show that Wdr1 and LIMK have distinct roles in BCR-induced assembly of the peripheral actin structures that drive B cell spreading, and that cofilin, Wdr1, and LIMK all contribute to the actin-dependent amplification of BCR signaling at the immune synapse. Depleting Cotl1 had no effect on these processes. Thus, the Wdr1-LIMK-cofilin axis is critical for BCR-induced actin remodeling and for B cell responses to APC-bound antigens.

Investigations of Chirality Effects on Undifferentiated State of Mesenchymal Stem Cells Using Soft Nanofibrous Oligopeptide Hydrogels

Soft nanofibrous oligopeptide hydrogels consisting of self-assembled l- and d-form Fmoc-Phe-Phe-Cys networks photo-cross-linked by poly(ethylene glycol)-dimethacrylate, which are referred to as l- and d-gel, respectively, were developed for investigation of chirality effects on the undifferentiated state of mesenchymal stem cells. Encapsulated mesenchymal stem cells in d-gel showed slower growth and less spreading, resulting in higher maintenance of the undifferentiated state, compared to in l-gel. This indicates that d-form peptide materials might be useful as scaffold materials for regenerative medicine using stem cells.

Microfabricated Gaps Reveal the Effect of Geometrical Control in Wound Healing

The geometry (size and shape) of gaps is a key determinant in controlling gap closure during wound healing. However, conventional methods for creating gaps result in un-defined geometries and poorly characterized conditions (cell death factors and cell debris), which can influence the gap closure process. To overcome these limitations, a novel method to create well-defined geometrical gaps is developed. First, smooth muscle cells (SMCs) are seeded in variously shaped micro-containers made out of hyaluronic acid hydrogels. Cell proliferation and cell tension induce fibrous collagen production by SMCs predominantly around the edges of the micro-containers. Upon removal of SMCs, the selectively deposited collagen results in micro-containers with cell-adhesive regions along the edges and walls. Fibroblasts are seeded in these micro-containers, and upon attaching and spreading, they naturally form gaps with different geometries. The rapid proliferation of fibroblasts from the edge results in filling and closure of the gaps. It is demonstrated that gap closure rate as well as closure mechanism is strongly influenced by geometrical features, which points to an important role for cellular tension and cell proliferation in gap closure.

Effect of Cell Spreading on Rosette Formation by Human Pluripotent Stem Cell-Derived Neural Progenitor Cells

Neural rosettes (NPC rosettes) are radially arranged groups of cells surrounding a central lumen that arise stochastically in monolayer cultures of human pluripotent stem cell (hPSC)-derived neural progenitor cells (NPC). Since NPC rosette formation is thought to mimic cell behavior in the early neural tube, these rosettes represent important in vitro models for the study of neural tube morphogenesis. However, using current protocols, NPC rosette formation is not synchronized and results are inconsistent among different hPSC lines, hindering quantitative mechanistic analyses and challenging live cell imaging. Here, we report a rapid and robust protocol to induce rosette formation within 6 h after evenly-sized “colonies” of NPC are generated through physical cutting of uniformly polarized NESTIN⁺/PAX6⁺/PAX3⁺/DACH1⁺ NPC monolayers. These NPC rosettes show apically polarized lumens studded with primary cilia. Using this assay, we demonstrate reduced lumenal size in the absence of PODXL, an important apical determinant recently identified as a candidate gene for juvenile Parkinsonism. Interestingly, time lapse imaging reveals that, in addition to radial organization and apical lumen formation, cells within cut NPC colonies initiate rapid basally-driven spreading. Further, using chemical, genetic and biomechanical tools, we show that NPC rosette morphogenesis requires this basal spreading activity and that spreading is tightly regulated by Rho/ROCK signaling. This robust and quantitative NPC rosette platform provides a sensitive system for the further investigation of cellular and molecular mechanisms underlying NPC rosette morphogenesis.

Cell Type-Specific Adhesion and Migration on Laser-Structured Opaque Surfaces

Cytocompatibility is essential for implant approval. However, initial in vitro screenings mainly include the quantity of adherent immortalized cells and cytotoxicity. Other vital parameters, such as cell migration and an in-depth understanding of the interaction between native tissue cells and implant surfaces, are rarely considered. We investigated different laser-fabricated spike structures using primary and immortalized cell lines of fibroblasts and osteoblasts and included quantification of the cell area, aspect ratio, and focal adhesions. Furthermore, we examined the three-dimensional cell interactions with spike topographies and developed a tailored migration assay for long-term monitoring on opaque materials. While fibroblasts and osteoblasts on small spikes retained their normal morphology, cells on medium and large spikes sank into the structures, affecting the composition of the cytoskeleton and thereby changing cell shape. Up to 14 days, migration appeared stronger on small spikes, probably as a consequence of adequate focal adhesion formation and an intact cytoskeleton, whereas human primary cells revealed differences in comparison to immortalized cell lines. The use of primary cells, analysis of the cell-implant structure interaction as well as cell migration might strengthen the evaluation of cytocompatibility and thereby improve the validity regarding the putative in vivo performance of implant material.

Human Salivary Histatin-1 Promotes Osteogenic Cell Spreading on Both Bio-Inert Substrates and Titanium SLA Surfaces

Promoting cell spreading is crucial to enhance bone healing and implant osteointegration. In this study, we investigated the stimulatory effect of human salivary histatin-1 (Hst-1) on the spreading of osteogenic cells in vitro as well as the potential signaling pathways involved. Osteogenic cells were seeded on bio-inert glass slides with or without the presence of Hst1 in dose-dependent or time-course assays. 1 scrambled and 6 truncated Hst1 variants were also evaluated. Cell spreading was analyzed using a well-established point-counting method. Fluorescent microscopy was adopted to examine the cellular uptake of fluorescently labeled Hst1 (F-Hst1) and also the cell spreading on sandblasted and acid etched titanium surfaces. Signaling inhibitors, such as U0126, SB203580, and pertussis toxin (PTx) were used to identify the potential role of extracellular-signal-regulated kinase, p38 and G protein-coupled receptor pathways, respectively. After 60 min incubation, Hst1 significantly promoted the spreading of osteogenic cells with an optimal concentration of 10 μM, while truncated and scrambled Hst1 did not. F-Hst1 was taken up and localized in the vicinity of the nuclei. U0126 and SB2030580, but not PTx, inhibited the effect of Hst1. 10 μM Hst1 significantly promoted the spreading of osteogenic cells on both bio-inert substrates and titanium SLA surfaces, which involved ERK and p38 signaling. Human salivary histatin-1 might be a promising peptide to enhance bone healing and implant osteointegration in clinic.

Efficacy of Plasma-Polymerized Allylamine Coating of Zirconia after Five Years

Plasma-polymerized allylamine (PPAAm) coatings of titanium enhance the cell behavior of osteoblasts. The purpose of the present study was to evaluate a PPAAm nanolayer on zirconia after a storage period of 5 years. Zirconia specimens were directly coated with PPAAm (ZA0) or stored in aseptic packages at room temperature for 5 years (ZA5). Uncoated zirconia specimens (Zmt) and the micro-structured endosseous surface of a zirconia implant (Z14) served as controls. The elemental compositions of the PPAAm coatings were characterized and the viability, spreading and gene expression of human osteoblastic cells (MG-63) were assessed. The presence of amino groups in the PPAAm layer was significantly decreased after 5 years due to oxidation processes. Cell viability after 24 h was significantly higher on uncoated specimens (Zmt) than on all other surfaces. Cell spreading after 20 min was significantly higher for Zmt = ZA0 > ZA5 > Z14, while, after 24 h, spreading also varied significantly between Zmt > ZA0 > ZA5 > Z14. The expression of the mRNA differentiation markers collagen I and osteocalcin was upregulated on untreated surfaces Z14 and Zmt when compared to the PPAAm specimens. Due to the high biocompatibility of zirconia itself, a PPAAm coating may not additionally improve cell behavior.

Quantitative Phase Imaging of Spreading Fibroblasts Identifies the Role of Focal Adhesion Kinase in the Stabilization of the Cell Rear

Cells attaching to the extracellular matrix spontaneously acquire front-rear polarity. This self-organization process comprises spatial activation of polarity signaling networks and the establishment of a protruding cell front and a non-protruding cell rear. Cell polarization also involves the reorganization of cell mass, notably the nucleus that is positioned at the cell rear. It remains unclear, however, how these processes are regulated. Here, using coherence-controlled holographic microscopy (CCHM) for non-invasive live-cell quantitative phase imaging (QPI), we examined the role of the focal adhesion kinase (FAK) and its interacting partner Rack1 in dry mass distribution in spreading Rat2 fibroblasts. We found that FAK-depleted cells adopt an elongated, bipolar phenotype with a high central body mass that gradually decreases toward the ends of the elongated processes. Further characterization of spreading cells showed that FAK-depleted cells are incapable of forming a stable rear; rather, they form two distally positioned protruding regions. Continuous protrusions at opposite sides results in an elongated cell shape. In contrast, Rack1-depleted cells are round and large with the cell mass sharply dropping from the nuclear area towards the basal side. We propose that FAK and Rack1 act differently yet coordinately to establish front-rear polarity in spreading cells.

Active FHOD1 promotes the formation of functional actin stress fibers

The formin FHOD1 acts as a nucleating, capping and bundling protein of actin filaments. In cells, release from the C-terminal diaphanous autoregulatory domain (DAD) of FHOD1 stimulates the protein into the active form. However, the cellular physiological relevance of active form FHOD1 and the phenotypic regulation by FHOD1 depletion are not completely understood. Here, we show that in contrast with the cytosolic diffused expression of auto-inhibited FHOD1, active FHOD1 by C-terminal truncation was recruited into all three types of actin stress fibers in human osteosarcoma cells. Notably, the recruited active FHOD1 was more incorporated with myosin II than α-actinin, and associated with both naïve and mature focal adhesions. Active FHOD1 displayed faster turnover than actin molecules on ventral stress fibers. Moreover, we witnessed the emergence of active FHOD1 from the cell periphery, which subsequently moved centripetally together with transverse arcs. Furthermore, FHOD1 knockdown resulted in defective maturation of actomyosin bundles and subsequently longer non-contractile dorsal stress fibers, whereas the turnover of both actin and myosin II were maintained normally. Importantly, the loss of FHOD1 led to slower actin centripetal flow, resulting in abnormal cell spreading and migration defects. Taken together, these results reveal a critical role of FHOD1 in temporal- and spatial- control of the morphology and dynamics of functional actin stress fibers during variable cell behavior.

Extracellular Matrix Geometry and Initial Adhesive Position Determine Stress Fiber Network Organization during Cell Spreading

Three-dimensional matrices often contain highly structured adhesive tracks that require cells to turn corners and bridge non-adhesive areas. Here, we investigate these complex processes using micropatterned cell adhesive frames. Spreading kinetics on these matrices depend strongly on initial adhesive position and are predicted by a cellular Potts model (CPM), which reflects a balance between adhesion and intracellular tension. As cells spread, new stress fibers (SFs) assemble periodically and parallel to the leading edge, with spatial intervals of ∼2.5 μm, temporal intervals of ∼15 min, and characteristic lifetimes of ∼50 min. By incorporating these rules into the CPM, we can successfully predict SF network architecture. Moreover, we observe broadly similar behavior when we culture cells on arrays of discrete collagen fibers. Our findings show that ECM geometry and initial cell position strongly determine cell spreading and that cells encode a memory of their spreading history through SF network organization.

Quantitative Correlation of Nanotopography with Cell Spreading via Focal Adhesions Using Adipose-Derived Stem Cells

Nanotopography mimicking extracellular environments reportedly impact cell morphological changes; however, elucidating this relationship has been challenging. To control cellular responses using nanostructures, in this study, the quantitative relationship between nanotopography and cell spreading mediated by focal adhesions (FAs) is demonstrated using adipose-derived stem cells (ASCs). The spreading of ASCs and area of FAs are analyzed for the distribution of filamentous actin and vinculin, respectively, using fluorescent images. FAs require a specific area for adhesion (herein defined as effective contact area [ECA]) to maintain cell attachment on nanopillar arrays. An ECA is the area of FAs supported by nanopillars, multiplying the area fraction (AF) of their top surface. Regarding the spreading of cells, the mean area of ASCs linearly decreases as the mean area of FAs increases. Because the area of FAs is inversely correlated to the AF of the nanopillar arrays, the spreading of cells can be quantitatively correlated with nanotopography. The results provide a conceptual framework for controlling cell behaviors to design artificial substrates for tissue-engineering applications.

Ultrafast Laser Processing of Nanostructured Patterns for the Control of Cell Adhesion and Migration on Titanium Alloy

Femtosecond laser texturing is a promising surface functionalization technology to improve the integration and durability of dental and orthopedic implants. Four different surface topographies were obtained on titanium-6aluminum-4vanadium plates by varying laser processing parameters and strategies: surfaces presenting nanostructures such as laser-induced periodic surface structures (LIPSS) and ‘spikes’, associated or not with more complex multiscale geometries combining micro-pits, nanostructures and stretches of polished areas. After sterilization by heat treatment, LIPSS and spikes were characterized to be highly hydrophobic, whereas the original polished surfaces remained hydrophilic. Human mesenchymal stem cells (hMSCs) grown on simple nanostructured surfaces were found to spread less with an increased motility (velocity, acceleration, tortuosity), while on the complex surfaces, hMSCs decreased their migration when approaching the micro-pits and preferentially positioned their nucleus inside them. Moreover, focal adhesions of hMSCs were notably located on polished zones rather than on neighboring nanostructured areas where the protein adsorption was lower. All these observations indicated that hMSCs were spatially controlled and mechanically strained by the laser-induced topographies. The nanoscale structures influence surface wettability and protein adsorption and thus influence focal adhesions formation and finally induce shape-based mechanical constraints on cells, known to promote osteogenic differentiation.

All-trans retinoic acid and human salivary histatin-1 promote the spreading and osteogenic activities of pre-osteoblasts in vitro

Cell‐based bone tissue engineering techniques utilize both osteogenic cells and biomedical materials, and have emerged as a promising approach for large‐volume bone repair. The success of such techniques is highly dependent on cell adhesion, spreading, and osteogenic activities. In this study, we investigated the effect of co‐administration of all‐trans retinoic acid (ATRA) and human salivary peptide histatin‐1 (Hst1) on the spreading and osteogenic activities of pre‐osteoblasts on bio‐inert glass surfaces. Pre‐osteoblasts (MC3T3‐E1 cell line) were seeded onto bio‐inert glass slides in the presence and absence of ATRA and Hst1. Cell spreading was scored by measuring surface areas of cellular filopodia and lamellipodia using a point‐counting method. The distribution of fluorogenic Hst1 within osteogenic cells was also analyzed. Furthermore, specific inhibitors of retinoic acid receptors α, β, and γ, such as ER‐50891, LE‐135, and MM‐11253, were added to identify the involvement of these receptors. Cell metabolic activity, DNA content, and alkaline phosphatase (ALP) activity were assessed to monitor their effects on osteogenic activities. Short‐term (2 h) co‐administration of 10 μm ATRA and Hst1 to pre‐osteoblasts resulted in significantly higher spreading of pre‐osteoblasts compared to ATRA or Hst1 alone. ER‐50891 and LE‐135 both nullified these effects of ATRA. Co‐administration of ATRA and Hst1 was associated with significantly higher metabolic activity, DNA content, and ALP activity than either ATRA or Hst1 alone. In conclusion, co‐administration of Hst1 with ATRA additively stimulated the spreading and osteogenicity of pre‐osteoblasts on bio‐inert glass surfaces in vitro.

Molecular underpinnings of integrin binding to collagen-mimetic peptides containing vascular Ehlers-Danlos syndrome-associated substitutions

Collagens carry out critical extracellular matrix (ECM) functions by interacting with numerous cell receptors and ECM components. Single glycine substitutions in collagen III, which predominates in vascular walls, result in vascular Ehlers-Danlos syndrome (vEDS), leading to arterial, uterine, and intestinal rupture and an average life expectancy of <50 years. Collagen interactions with integrin α₂β₁ are vital for platelet adhesion and activation; however, how these interactions are impacted by vEDS-associated mutations and by specific amino acid substitutions is unclear. Here, we designed collagen-mimetic peptides (CMPs) with previously reported Gly → Xaa (Xaa = Ala, Arg, or Val) vEDS substitutions within a high-affinity integrin α₂β₁-binding motif, GROGER. We used these peptides to investigate, at atomic-level resolution, how these amino acid substitutions affect the collagen III-integrin α₂β₁ interaction. Using a multitiered approach combining biological adhesion assays, CD, NMR, and molecular dynamics (MD) simulations, we found that these substitutions differentially impede human mesenchymal stem cell spreading and integrin α₂-inserted (α₂I) domain binding to the CMPs and were associated with triple-helix destabilization. Although an Ala substitution locally destabilized hydrogen bonding and enhanced mobility, it did not significantly reduce the CMP-integrin interactions. MD simulations suggested that bulkier Gly → Xaa substitutions differentially disrupt the CMP-α₂I interaction. The Gly → Arg substitution destabilized CMP-α₂I side-chain interactions, and the Gly → Val change broke the essential Mg²⁺ coordination. The relationship between the loss of functional binding and the type of vEDS substitution provides a foundation for developing potential therapies for managing collagen disorders.

Biological Response to Macroporous Chitosan-Agarose Bone Scaffolds Comprising Mg- and Zn-Doped Nano-Hydroxyapatite

Modification of implantable scaffolds with magnesium and zinc for improvement of bone regeneration is a growing trend in the engineering of biomaterials. The aim of this study was to synthesize nano-hydroxyapatite substituted with magnesium (Mg²⁺) (HA-Mg) and zinc (Zn²⁺) (HA-Zn) ions in order to fabricate chitosan-agarose-hydroxyapatite (HA) scaffolds (chit/aga/HA) with improved biocompatibility. Fabricated biomaterials containing Mg²⁺ or Zn²⁺ were tested using osteoblasts and mesenchymal stem cells to determine the effect of incorporated metal ions on cell adhesion, spreading, proliferation, and osteogenic differentiation. The study was conducted in direct contact with the scaffolds (cells were seeded onto the biomaterials) and using fluid extracts of the materials. It demonstrated that incorporation of Mg²⁺ ions into chit/aga/HA structure increased spreading of the osteoblasts, promoted cell proliferation on the scaffold surface, and enhanced osteocalcin production by mesenchymal stem cells. Although biomaterial containing Zn²⁺ did not improve cell proliferation, it did enhance type I collagen production by mesenchymal stem cells and extracellular matrix mineralization as compared to cells cultured in a polystyrene well. Nevertheless, scaffolds made of pure HA gave better results than material with Zn²⁺. Results of the experiments clearly showed that modification of the chit/aga/HA scaffold with Zn²⁺ did not have any positive impact on cell behavior, whereas, incorporation of Mg²⁺ ions into its structure may significantly improve biocompatibility of the resultant material, increasing its potential in biomedical applications.

Vimentin Intermediate Filament Rings Deform the Nucleus During the First Steps of Adhesion

During cell spreading, cells undergo many changes to their architecture and their mechanical properties. Vimentin, as an integral part of the cell architecture, and its mechanical stability must adapt to the new state of the cell. This study focuses on the structures formed by vimentin during the first steps of cell adhesion. Very early, ball-like structures, or "knots," are seen and often vimentin filaments emerge in the shape of rings around the nucleus. Although intermediate filaments are not known to be associated to motor proteins to form contractile systems, these rings can nonetheless strongly deform the cell nucleus. In the first 6 to 12 h of adhesion, these vimentin knots and rings disappear, and the intermediate filament network returns to the state seen before detachment of the cells. As these vimentin structures are very transient in the early steps of cell spreading, they have rarely been described in the literature. However, they can also be seen during mitosis, which is an event that involves partial detachment and re-spreading of the cells. Interestingly, the turnover dynamics of vimentin are reduced in both the knots and rings, compared to vimentin in the lamellipodia. It remains to define how the force is transmitted from the ball-like structures to the rings, and to measure the impact of such strong nuclear deformation on gene expression during cell re-spreading and the rearrangement of the vimentin network.

Integrin Mechano-chemical Signaling Generates Plasma Membrane Nanodomains that Promote Cell Spreading

Glycosylphosphatidylinositol-anchored proteins (GPI-APs) are a major class of lipid-anchored plasma membrane proteins. GPI-APs form nanoclusters generated by cortical acto-myosin activity. While our understanding of the physical principles governing this process is emerging, the molecular machinery and functional relevance of GPI-AP nanoclustering are unknown. Here, we first show that a membrane receptor signaling pathway directs nanocluster formation. Arg-Gly-Asp motif-containing ligands bound to the β1-integrin receptor activate src and focal adhesion kinases, resulting in RhoA signaling. This cascade triggers actin-nucleation via specific formins, which, along with myosin activity, drive the nanoclustering of membrane proteins with actin-binding domains. Concurrently, talin-mediated activation of the mechano-transducer vinculin is required for the coupling of the acto-myosin machinery to inner-leaflet lipids, thereby generating GPI-AP nanoclusters. Second, we show that these nanoclusters are functional; disruption of their formation either in GPI-anchor remodeling mutants or in vinculin mutants impairs cell spreading and migration, hallmarks of integrin function.

Neutrophil Cell Shape Change: Mechanism and Signalling during Cell Spreading and Phagocytosis

Perhaps the most important feature of neutrophils is their ability to rapidly change shape. In the bloodstream, the neutrophils circulate as almost spherical cells, with the ability to deform in order to pass along narrower capillaries. Upon receiving the signal to extravasate, they are able to transform their morphology and flatten onto the endothelium surface. This transition, from a spherical to a flattened morphology, is the first key step which neutrophils undergo before moving out of the blood and into the extravascular tissue space. Once they have migrated through tissues towards sites of infection, neutrophils carry out their primary role-killing infecting microbes by performing phagocytosis and producing toxic reactive oxygen species within the microbe-containing phagosome. Phagocytosis involves the second key morphology change that neutrophils undergo, with the formation of pseudopodia which capture the microbe within an internal vesicle. Both the spherical to flattened stage and the phagocytic capture stage are rapid, each being completed within 100 s. Knowing how these rapid cell shape changes occur in neutrophils is thus fundamental to understanding neutrophil behaviour. This article will discuss advances in our current knowledge of this process, and also identify an important regulated molecular event which may represent an important target for anti-inflammatory therapy.

Biphasic mechanosensitivity of T cell receptor-mediated spreading of lymphocytes

Mechanosensing by T cells through the T cell receptor (TCR) is at the heart of immune recognition. While the mechanobiology of the TCR at the molecular level is increasingly well documented, its link to cell-scale response is poorly understood. Here we explore T cell spreading response as a function of substrate rigidity and show that remarkably, depending on the surface receptors stimulated, the cellular response may be either biphasic or monotonous. When adhering solely via the TCR complex, T cells respond to environmental stiffness in an unusual fashion, attaining maximal spreading on an optimal substrate stiffness comparable to that of professional antigen-presenting cells. However, in the presence of additional ligands for the integrin LFA-1, this biphasic response is abrogated and the cell spreading increases monotonously with stiffness up to a saturation value. This ligand-specific mechanosensing is effected through an actin-polymerization-dependent mechanism. We construct a mesoscale semianalytical model based on force-dependent bond rupture and show that cell-scale biphasic or monotonous behavior emerges from molecular parameters. As the substrate stiffness is increased, there is a competition between increasing effective stiffness of the bonds, which leads to increased cell spreading and increasing bond breakage, which leads to decreased spreading. We hypothesize that the link between actin and the receptors (TCR or LFA-1), rather than the ligand/receptor linkage, is the site of this mechanosensing.

The influence of the stiffness of GelMA substrate on the outgrowth of PC12 cells

Recent studies have shown the importance of cell–substrate interaction on neurone outgrowth, where the Young’s modulus of the matrix plays a crucial role on the neurite length, migration, proliferation, and morphology of neurones. In the present study, PC12 cells were selected as the representative neurone to be cultured on hydrogel substrates with different stiffness to explore the effect of substrate stiffness on the neurone outgrowth. By adjusting the concentration of gelatin methacryloyl (GelMA), the hydrogel substrates with the variation of stiffnesses (indicated by Young’s modulus) from approximately 3–180 KPa were prepared. It is found that the stiffness of GelMA substrates influences neuronal outgrowth, including cell viability, adhesion, spreading, and average neurite length. Our results show a critical range of substrate’s Young’s modulus that support PC12 outgrowth, and modulate the cell characteristics and morphology. The present study provides an insight into the relationship between the stiffness of GelMA hydrogel substrates and PC12 cell outgrowth, and helps the design and optimization of tissue engineering scaffolds for nerve regeneration.

Cell Attachment and Spreading on Carbon Nanotubes Is Facilitated by Integrin Binding

Owing to their exceptional physical, chemical, and mechanical properties, carbon nanotubes (CNTs) have been extensively studied for their effect on cellular behaviors. However, little is known about the process by which cells attach and spread on CNTs and the process for cell attachment and spreading on individual single-walled CNTs has not been studied. Cell adhesion and spreading is essential for cell communication and regulation and the mechanical interaction between cells and the underlying substrate can influence and control cell behavior and function. A limited number of studies have described different adhesion mechanisms, such as cellular process entanglements with multi-walled CNT aggregates or adhesion due to adsorption of serum proteins onto the nanotubes. Here, we hypothesized that cell attachment and spreading to both individual single-walled CNTs and multi-walled CNT aggregates is governed by the same mechanism. Specifically, we suggest that cell attachment and spreading on nanotubes is integrin-dependent and is facilitated by the adsorption of serum and cell-secreted adhesive proteins to the nanotubes.

T Cells on Engineered Substrates: The Impact of TCR Clustering Is Enhanced by LFA-1 Engagement

We created APC-mimetic synthetic substrates to study the impact of ligand clustering on T cell activation and spreading. The substrates exhibit antibodies directed against the TCR-complex in the form of a patterned array of sub micrometric dots surrounded by a fluid supported lipid bilayer (SLB) which may itself be functionalized with another bio-molecule. We show that for T cell adhesion mediated by T cell receptor (TCR) alone, in the patterned, but not in the corresponding homogeneous controls, the TCR, ZAP-70 and actin are present in the form of clusters or patches that co-localize with the ligand-dots. However, global cell scale parameters like cell area and actin distribution are only weakly impacted by ligand clustering. In presence of ICAM-1 - the ligand of the T cell integrin LFA-1 - on the SLB, the TCR is still clustered due to the patterning of its ligands, but now global parameters are also impacted. The actin organization changes to a peripheral ring, resembling the classical actin distribution seen on homogeneous substrates, the patterned membrane topography disappears and the membrane is flat, whereas the cell area increases significantly. These observations taken together point to a possible pivotal role for LFA-1 in amplifying the effect of TCR-clustering. No such effect is evident for co-engagement of CD28, affected via its ligand B7.2. Unlike on ICAM-1, on B7.2 cell spreading and actin organization are similar for homogeneous and patterned substrates. However, TCR and ZAP-70 clusters are still formed in the patterned case. These results indicate complementary role for LFA-1 and CD28 in the regulation and putative coupling of TCR micro-clusters to actin. The engineered substrates presented here clearly have the potential to act as platform for fundamental research in immune cell biology, as well as translational analyses in immunotherapy, for example to screen molecules for their role in T cell adhesion/activation.

The impact of experimental design choices on parameter inference for models of growing cell colonies

To better understand development, repair and disease progression, it is useful to quantify the behaviour of proliferative and motile cell populations as they grow and expand to fill their local environment. Inferring parameters associated with mechanistic models of cell colony growth using quantitative data collected from carefully designed experiments provides a natural means to elucidate the relative contributions of various processes to the growth of the colony. In this work, we explore how experimental design impacts our ability to infer parameters for simple models of the growth of proliferative and motile cell populations. We adopt a Bayesian approach, which allows us to characterize the uncertainty associated with estimates of the model parameters. Our results suggest that experimental designs that incorporate initial spatial heterogeneities in cell positions facilitate parameter inference without the requirement of cell tracking, while designs that involve uniform initial placement of cells require cell tracking for accurate parameter inference. As cell tracking is an experimental bottleneck in many studies of this type, our recommendations for experimental design provide for significant potential time and cost savings in the analysis of cell colony growth.

Dynamics of p14ARF and Focal Adhesion Kinase-Mediated Autophagy in Cancer

It has been widely shown that the focal adhesion kinase (FAK) is involved in nearly every aspect of cancer, from invasion to metastasis to epithelial–mesenchymal transition and maintenance of cancer stem cells. FAK has been shown to interact with p14ARF (alternative reading frame)—a well-established tumor suppressor—and functions in the negative regulation of cancer through both p53-dependent and -independent pathways. Interestingly, both FAK and ARF (human and mouse counterpart) proteins, as well as p53, are involved in autophagy—a process of “self-digestion”—whose main function is the recycling of cellular components and quality control of proteins and organelles. In the last years, an unexpected role of p14ARF in the survival of cancer cells has been underlined in different cellular contexts, suggesting a novel pro-oncogenic function of this protein. In this review, the mechanisms whereby ARF and FAK control autophagy are presented, as well as the role of autophagy in cell migration and spreading. Integrated investigation of these cell functions is extremely important to understand the mechanism of the basis of cell transformation and migration and thus cancer development.

Matching material and cellular timescales maximizes cell spreading on viscoelastic substrates

Recent evidence has shown that, in addition to rigidity, the viscous response of the extracellular matrix (ECM) significantly affects the behavior and function of cells. However, the mechanism behind such mechanosensitivity toward viscoelasticity remains unclear. In this study, we systematically examined the dynamics of motor clutches (i.e., focal adhesions) formed between the cell and a viscoelastic substrate using analytical methods and direct Monte Carlo simulation. Interestingly, we observe that, for low ECM rigidity, maximum cell spreading is achieved at an optimal level of viscosity in which the substrate relaxation time falls between the timescale for clutch binding and its characteristic binding lifetime. That is, viscosity serves to stiffen soft substrates on a timescale faster than the clutch off-rate, which enhances cell-ECM adhesion and cell spreading. On the other hand, for substrates that are stiff, our model predicts that viscosity will not influence cell spreading, since the bound clutches are saturated by the elevated stiffness. The model was tested and validated using experimental measurements on three different material systems and explained the different observed effects of viscosity on each substrate. By capturing the mechanism by which substrate viscoelasticity affects cell spreading across a wide range of material parameters, our analytical model provides a useful tool for designing biomaterials that optimize cellular adhesion and mechanosensing.

Cell adhesion to anosmin via α5β1, α4β1, and α9β1 integrins

Anosmin is an extracellular matrix protein, and genetic defects in anosmin result in human Kallmann syndrome. It functions in neural crest formation, cell adhesion, and neuronal migration. Anosmin consists of multiple domains, and it has been reported to bind heparan sulfate, FGF receptor, and UPA. In this study, we establish cell adhesion/spreading assays for anosmin and use them for antibody inhibition analyses to search for an integrin adhesion receptor. We find that α5β1, α4β1, and α9β1 integrins are needed for effective adhesive receptor function in cell adhesion and cell spreading on anosmin; adhesion is inhibited by both RGD and α4β1 CS1-based peptides. This identification of anosmin-integrin adhesion receptors should facilitate studies of anosmin function in cell and developmental biology.

Regulation of IL-1 signaling through control of focal adhesion assembly

IL-1 signaling is adhesion-restricted in many cell types, but the mechanism that drives it is not defined. We screened for proteins recruited to nascent adhesions in IL-1-treated human fibroblasts with tandem mass tag-mass spectrometry. We used fibronectin bead preparations to enrich 10 actin-associated proteins. There was a 1.2 times log 2-fold enrichment of actin capping protein (ACP) at 30 min after IL-1 stimulation. Knockdown (KD) of ACP by siRNA reduced IL-1-induced ERK activation(by 56%, matrix metalloproteinase-3 (MMP-3) expression by 48%, and MMP-9 expression by 62% (in all reductions, P < 0.01). Confocal or structured illumination microscopy showed that ACP was diffused throughout the cytosol but strongly accumulated at the ruffled border of spreading cells. ACP colocalized with nascent paxillin- and vinculin-containing adhesions at the ruffled border, but not with mature adhesions in the center. ACP KD promoted the formation of large, stable adhesions. Immunoprecipitation and proximity ligation analysis showed that ACP was associated with the IL-1 signal transduction proteins myeloid differentiation factor 88 (MyD88) and IL-1 receptor-associated kinase (IRAK) at the ruffled border of the leading edge. IL-1-induced phospho-ERK and MyD88 or IRAK colocalized at the leading edge. We concluded that ACP is required for recruitment and function of IL-1 signaling complexes in nascent adhesions at the leading edge of the cell.-Wang, Q., Delcorde, J., Tang, T., Downey, G. P., McCulloch, C. A. Regulation of IL-1 signaling through control of focal adhesion assembly.

Mechanics of Cell Mechanosensing in Protrusion and Retraction of Lamellipodium

Lamellipodia (LP), a subcellular structure at cell front, plays a key role in cell spreading and migration. And its mechanosensing function is of crucial importance for cell activities. But the mechanism of the mechanosensing function remains poorly understood. Here we developed a multiscale model to consider its protrusion and retraction processes, and analyzed the forces acted on the key structural components of the LP and the effect of these forces on LP movement. Our results show that raising substrate rigidity increases the force acting on the focal adhesion (FA) and decreases the force on LP actin, thus promoting the maturation of FA while suppressing the detachment of LP actin from the cell membrane. The membrane tension also influences the LP movement, but its effect is opposite to that of the substrate rigidity. It turns out that the substrate rigidity and membrane tension together regulate the dynamics of FAs and the detachment of LP actin, which in turn determine the LP movement. Interestingly, we found that the effect of substrate rigidity and membrane tension on the LP movement both exhibit a biphasic manner. We show that our predictions agree, in general, with the experiments on cell mechanosensing behaviors at both subcellular and cellular levels.

Controlled Interfacial Permeation, Nanostructure Formation, Catalytic Efficiency, Signal Enhancement Capability, and Cell Spreading by Adjusting Photochemical Cross-Linking Degrees of Layer-by-Layer Films

Interfacial properties including permeation, catalytic efficiency, Raman signal enhancement capabilities, and cell spreading efficiencies are important features that determine material functionality and applications. Here, we propose a facile method to adjust the above-mentioned properties by controlling the cross-linking degrees of multilayer using a photoactive molecule. After treating the cross-linked films in basic solutions, films with different cross-linking degrees presented varying residue thicknesses and film morphologies. As a result, these different films possessed distinct molecular loading and release characteristics. In addition, gold nanoparticles (AuNPs) of different morphological traits were generated by redox reactions coupled with diffusion within these films. The AuNP-polyelectrolyte obtained from the polyelectrolyte films of the medium cross-linking degrees displayed the highest catalytic efficiency and signal enhancement capabilities. Furthermore, cells responded to the variation of film cross-linking degrees, and on the films with the highest cross-linking degree, cells adhered with the highest speed. We expect this report to provide a general interfacial material engineering strategy for material designs.

Overexpression of HPV16 E6* Alters β-Integrin and Mitochondrial Dysfunction Pathways in Cervical Cancer Cells

BACKGROUND

High-risk human papillomaviruses (HPV) cause nearly all cases of cervical cancer, as well as many types of oral and anogenital cancer. Alternative splicing increases the capacity of the HPV genome to encode the proteins necessary for successful completion of its infectious life cycle. However, the roles of these splice variants, including E6*, the smaller splice isoform of the E6 oncogene, in carcinogenesis are not clear.

MATERIALS AND METHODS

SiHa (HPV16(+)) and C33A (HPV(-)) cells were transfected with the E6* plasmid, and tandem mass tag-labeled protein levels were quantified by mass spectrometry. Proteomic analyses identified pathways affected by E6* in both HPV(+) and HPV(-) cells, and pathways were validated using in vitro methods.

RESULTS

A total of 4,300 proteins were identified and quantified in lysates of SiHa and C33A cells with and without HPV16 E6* expression. SiHa and C33A cells expressing E6* underwent changes in protein expression affecting integrin signaling and mitochondrial dysfunction pathways, respectively. Subsequent experiments were performed to validate selected E6*-mediated alterations in protein levels.

CONCLUSION

E6* modifies the expression of proteins involved in mitochondrial dysfunction and oxidative phosphorylation in C33A cells, and β-integrin signaling in SiHa cells.

Alteration of transbilayer phospholipid compositions is involved in cell adhesion, cell spreading, and focal adhesion formation

We previously showed that P4-ATPases, ATP10A/ATP8B1, and ATP11A/ATP11C have flippase activities toward phosphatidylcholine (PC), and aminophospholipids [phosphatidylserine (PS) and phosphatidylethanolamine], respectively. Here, we investigate the effect of PC-specific flippases versus aminophospholipid-specific flippases in cell spreading on the extracellular matrix. Expression of PC-flippases, but not PS-flippases, delayed cell adhesion, cell spreading and inhibited formation of focal adhesions. In addition, overexpression of a PS-binding probe that sequesters PS in the cytoplasmic leaflet delayed cell spreading and inhibited formation of focal adhesions. These results suggest that elevation of PC at the cytoplasmic leaflet of the plasma membrane by expression of PC-flippases may reduce the local concentration of PS or phosphoinositides, required for efficient cell adhesion, focal adhesion formation, and cell spreading.