Initial stages of cell-matrix adhesion can be mediated and modulated by cell-surface hyaluronan

Influence of Controlled Chirality on the Crystallization of Maleimide-Functionalized 3,4-Ethylenedioxythiophene (EDOT-MA) Monomers

Conjugated poly(alkoxythiophenes) such as poly(3,4-ethylenedioxythiophene) (PEDOT) have attracted considerable interest for use in a variety of applications such as biomedical devices, energy storage, and chemical sensing. Functionalized versions of the 3,4-ethylenedioxythiophene (EDOT) monomer make it possible to create polymers with properties tailored for specific applications. The maleimide functional group shows particular promise due to the wide variety of chemical modifications that it can undergo. Here, we examine the role that control of the chirality of the maleimide (MA) substituent has on the crystal structure and crystallization of the EDOT-MA monomer. We describe a method for the synthesis of a homochiral (S) variant of EDOT-MA and compare its crystallography, morphology, and thermal properties to that of the (R,S) EDOT-MA racemic compound. The conformation of the EDOT-MA molecule was substantially different, with the molecules adopting an "L" shape in the homochiral crystal, while in the racemic crystals, they were more colinear. The thermal stability of the homochiral crystals (Tm = 128.6 °C) was slightly higher than the racemic ones (Tm = 102.8 °C). We expect these results to be important in better understanding the solid-state assembly of the corresponding polymers prepared from these monomers.

Basic and clinical study of the effect of exogenous hyaluronic acid on the quality of acellular dermal matrix combined with thin intermediate split thickness skin graft

BACKGROUND

To promote wound recovery in the recipient region, we studied the impact of exogenous hyaluronic acid (HA) on acellular dermal matrix (ADM) paired with thin intermediate-thickness skin transplant.

METHODS

This study contains animal and clinical experiments. 50 Japanese big ear rabbits were separated into HA1, HA2, PADM, TS, and NS groups. Clinical part included 50 scar patients dividing into 5 groups (TS + HA + ADM 1, TS + ADM2, TS, TS + ADM and normal skin (NS)).

RESULTS

In the animal trial, after 56 days, the grafts contracted least in the HA2 group; HA2 had the highest microvascular density (MVD), HA concentration, and collagen I and III expression. In clinical work, ADM > HA + ADM2 > HA + ADM1 > TS > NS; Type I and III collagen: HA + ADM1 and HA + ADM2 were higher than ADM; HA content: TS > HA + ADM1 > HA + ADM 2 > ADM.

CONCLUSIONS

ADM, exogenous hyaluronic acid mixed with thin skin autograft has better biomechanical qualities and therapeutic impact than acellular dermal matrix alone, and the reconstructive result is near to self-thick skin autograft in all indexes.

The extracellular matrix mechanics in the vasculature

Mechanical stimuli from the extracellular matrix (ECM) modulate vascular differentiation, morphogenesis and dysfunction of the vasculature. With innovation in measurements, we can better characterize vascular microenvironment mechanics in health and disease. Recent advances in material sciences and stem cell biology enable us to accurately recapitulate the complex and dynamic ECM mechanical microenvironment for in vitro studies. These biomimetic approaches help us understand the signaling pathways in disease pathologies, identify therapeutic targets, build tissue replacement and activate tissue regeneration. This Review analyzes how ECM mechanics regulate vascular homeostasis and dysfunction. We highlight approaches to examine ECM mechanics at tissue and cellular levels, focusing on how mechanical interactions between cells and the ECM regulate vascular phenotype, especially under certain pathological conditions. Finally, we explore the development of biomaterials to emulate, measure and alter the physical microenvironment of pathological ECM to understand cell-ECM mechanical interactions toward the development of therapeutics.

Concentration Dependent Effect of Quaternary Amines on the Adhesion of U251-MG Cells

Cationic gels have seen increasing interest in recent years for 2D cell cultivation since they may represent an alternative to the well-known RGD-peptide motif functionalized gels. However, few hydrogel systems with adjustable cationic strength have been fabricated and investigated so far. In this work, eight gels with defined concentrations of cationic groups, two of which also contained the RGD peptide, were prepared from three well-defined, soluble precursor copolymers with thiol-functionalities and PEGDA3500 as a crosslinker via thiol-ene chemistry. Live/dead stainings of U-251-MG cells on the hydrogels with different concentrations of the cationic motif were made after 3 days and 7 days of cultivation. The results show a high dependence of the number of adhesive cells and their morphology, cluster versus spread cells, on the concentration of cationic groups in the gel. This effect was more pronounced when the gels were not further dialyzed before usage. In addition, a synergistic effect of the two motifs, cationic group and RGD peptide, could be demonstrated, which together induce stronger cell adhesion than either motif alone.

Correlation of cell mechanics with the resistance to malignant transformation in naked mole rat fibroblasts

Naked mole rats (NMRs) demonstrate exceptional longevity and resistance to cancer. Using a biochemical approach, it was previously shown that the treatment of mouse fibroblast cells with RasV12 oncogene and SV40 Large T antigen (viral oncoprotein) led to malignant transformations of cells. In contrast, NMR fibroblasts were resistant to malignant transformations upon this treatment. Here we demonstrate that atomic force microscopy (AFM) can provide information which is in agreement with the above finding, and further, adds unique information about the physical properties of cells that is impossible to obtain by other existing techniques. AFM indentation data were collected from individual cells and subsequently processed through the brush model to obtain information about the mechanics of the cell body (absolute values of the effective Young's moduli). Furthermore, information about the physical properties of the pericellular layer surrounding the cells was obtained. We found a statistically significant decrease in the rigidity of mouse cells after the treatment, whereas there was no significant change found in the rigidity of NMR cells upon the treatment. We also found that the treatment caused a substantial increase in a long part of the pericellular layer in NMR cells only (the long brush was defined as having a size of >10 microns). The mouse cells and smaller brush did not show statistically significant changes upon treatment. The observed change in cell mechanics is in agreement with the frequently observed decrease in cell rigidity during progression towards cancer. The change in the pericellular layer due to the malignant transformation of fibroblast cells has practically not been studied, though it was shown that the removal of part of the pericellular layer of NMR fibroblasts made the cells susceptible to malignant transformation. Although it is plausible to speculate that the observed increase in the long part of the brush layer of NMR cells might help cells to resist malignant transformations, the significance of the observed change in the pericellular layer is yet to be understood. As of now, we can conclude that changes in cell mechanics might be used as an indication of the resistance of NMR cells to malignant transformations.

The cell surface hyaluronidase TMEM2 plays an essential role in mouse neural crest cell development and survival

Hyaluronan (HA) is a major extracellular matrix component whose tissue levels are dynamically regulated during embryonic development. Although the synthesis of HA has been shown to exert a substantial influence on embryonic morphogenesis, the functional importance of the catabolic aspect of HA turnover is poorly understood. Here, we demonstrate that the transmembrane hyaluronidase TMEM2 plays an essential role in neural crest development and the morphogenesis of neural crest derivatives, as evidenced by the presence of severe craniofacial abnormalities in Wnt1-Cre–mediated Tmem2 knockout (Tmem2^CKO) mice. Neural crest cells (NCCs) are a migratory population of cells that gives rise to diverse cell lineages, including the craniofacial complex, the peripheral nervous system, and part of the heart. Analysis of Tmem2 expression during NCC formation and migration reveals that Tmem2 is expressed at the site of NCC delamination and in emigrating Sox9-positive NCCs. In Tmem2^CKO embryos, the number of NCCs emigrating from the neural tube is greatly reduced. Furthermore, linage tracing reveals that the number of NCCs traversing the ventral migration pathway and the number of post-migratory neural crest derivatives are both significantly reduced in a Tmem2^CKO background. In vitro studies using Tmem2-depleted mouse O9-1 neural crest cells demonstrate that Tmem2 expression is essential for the ability of these cells to form focal adhesions on and to migrate into HA-containing substrates. Additionally, we show that Tmem2-deficient NCCs exhibit increased apoptotic cell death in NCC-derived tissues, an observation that is corroborated by in vitro experiments using O9-1 cells. Collectively, our data demonstrate that TMEM2-mediated HA degradation plays an essential role in normal neural crest development. This study reveals the hitherto unrecognized functional importance of HA degradation in embryonic development and highlights the pivotal role of Tmem2 in the developmental process.

As a major component of the extracellular matrix, hyaluronan is particularly abundant in the extracellular matrix of embryonic tissues, where its expression is dynamically regulated during tissue morphogenetic processes. Tissue levels of hyaluronan are regulated not only by its synthesis but also by its degradation. Curiously, however, mice lacking known hyaluronidase molecules, including HYAL1 and HYAL2, exhibit minimal embryonic phenotypes. As a result, our understanding of the role of the catabolic aspect of hyaluronan metabolism in embryonic development is quite limited. Here, we show that TMEM2, a recently identified hyaluronidase that degrades hyaluronan on the cell surface, plays a critical role in the development of neural crest cells and their derivatives. Our analyses of Tmem2 conditional knockout mice, Tmem2 knock-in reporter mice, and in vitro cell cultures demonstrate that TMEM2 is essential for generating a tissue environment needed for efficient migration of neural crest cells from the neural tube. Our paper reveals for the first time that the degradation of hyaluronan plays a specific regulatory role in embryonic morphogenesis, and that dysregulation of hyaluronan degradation leads to severe developmental defects.

Inhibitor of Hyaluronic Acid Synthesis 4-Methylumbelliferone Suppresses the Secretory Processes That Ensure the Invasion of Neutrophils into Tissues and Induce Inflammation

Integrin-dependent adhesion of neutrophils to tissue, accompanied by the development of neutrophil-induced inflammation, occurs both in the focus of infection and in the absence of infection in metabolic disorders such as reperfusion after ischemia, diabetes mellitus, or the development of pneumonia in patients with cystic fibrosis or viral diseases. Hyaluronic acid (HA) plays an important role in the recruitment of neutrophils to tissues. 4-methylumbilliferon (4-MU), an inhibitor of HA synthesis, is used to treat inflammation, but its mechanism of action is unknown. We studied the effect of 4-MU on neutrophil adhesion and concomitant secretion using adhesion to fibronectin as a model for integrin-dependent adhesion. 4-MU reduced the spreading of neutrophils on the substrate and the concomitant secretion of granule proteins, including pro-inflammatory components. 4-MU also selectively blocked adhesion-induced release of the free amino acid hydroxylysine, a product of lysyl hydroxylase, which can influence cell invasion by modifying the extracellular matrix. Finally, 4-MU inhibited the formation of cytonemes, the extracellular membrane secretory structures containing the pro-inflammatory bactericides of the primary granules. The anti-inflammatory effect of 4-MU may be associated with the suppression of secretory processes that ensure the neutrophil invasion and initiate inflammation. We suggest that HA, due to the peculiarities of its synthesis, can promote the release of secretory carriers from the cell and 4-MU can block this process.

Biomimetic polypyrrole/hyaluronic acid electrodes integrated with hyaluronidase inhibitors offer persistent electroactivity and resistance to cell binding

Conductive polymers, including polypyrrole (PPy), have garnered much attention as bioelectrodes because of their high conductivity, low interfacial resistance, environmental stability, and biocompatibility. In particular, the introduction of high-molecular weight...

Physics and Physiology of Cell Spreading in Two and Three Dimensions

Cells spread on surfaces and within three-dimensional (3-D) matrixes as they grow, divide, and move. Both chemical and physical signals orchestrate spreading during normal development, wound healing, and pathological states such as fibrosis and tumor growth. Diverse molecular mechanisms drive different forms of cell spreading. This article discusses mechanisms by which cells spread in 2-D and 3-D and illustrates new directions in studies of this aspect of cell function.

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 cell surface hyaluronidase TMEM2 regulates cell adhesion and migration via degradation of hyaluronan at focal adhesion sites

The extracellular matrix (ECM) plays an important role in maintaining tissue homeostasis and poses a significant physical barrier to in vivo cell migration. Accordingly, as a means of enhancing tissue invasion, tumor cells use matrix metalloproteinases to degrade ECM proteins. However, the in vivo ECM is comprised not only of proteins but also of a variety of nonprotein components. Hyaluronan (HA), one of the most abundant nonprotein components of the interstitial ECM, forms a gel-like antiadhesive barrier that is impenetrable to particulate matter and cells. Mechanisms by which tumor cells penetrate the HA barrier have not been addressed. Here, we demonstrate that transmembrane protein 2 (TMEM2), the only known transmembrane hyaluronidase, is the predominant mediator of contact-dependent HA degradation and subsequent integrin-mediated cell–substrate adhesion. We show that a variety of tumor cells are able to eliminate substrate-bound HA in a tightly localized pattern corresponding to the distribution of focal adhesions (FAs) and stress fibers. This FA-targeted HA degradation is mediated by TMEM2, which itself is localized at site of FAs. TMEM2 depletion inhibits the ability of tumor cells to attach and migrate in an HA-rich environment. Importantly, TMEM2 directly binds at least two integrins via interaction between extracellular domains. Our findings demonstrate a critical role for TMEM2-mediated HA degradation in the adhesion and migration of cells on HA-rich ECM substrates and provide novel insight into the early phase of FA formation.

Behaviour of Vascular Smooth Muscle Cells on Amine Plasma-Coated Materials with Various Chemical Structures and Morphologies

Amine-coated biodegradable materials based on synthetic polymers have a great potential for tissue remodeling and regeneration because of their excellent processability and bioactivity. In the present study, we have investigated the influence of various chemical compositions of amine plasma polymer (PP) coatings and the influence of the substrate morphology, represented by polystyrene culture dishes and polycaprolactone nanofibers (PCL NFs), on the behavior of vascular smooth muscle cells (VSMCs). Although all amine-PP coatings improved the initial adhesion of VSMCs, 7-day long cultivation revealed a clear preference for the coating containing about 15 at.% of nitrogen (CPA-33). The CPA-33 coating demonstrated the ideal combination of good water stability, a sufficient amine group content, and favorable surface wettability and morphology. The nanostructured morphology of amine-PP-coated PCL NFs successfully slowed the proliferation rate of VSMCs, which is essential in preventing restenosis of vascular replacements in vivo. At the same time, CPA-33-coated PCL NFs supported the continuous proliferation of VSMCs during 7-day long cultivation, with no significant increase in cytokine secretion by RAW 264.7 macrophages. The CPA-33 coating deposited on biodegradable PCL NFs therefore seems to be a promising material for manufacturing small-diameter vascular grafts, which are still lacking on the current market.

Enhancement of Intracellular Calcium Ion Mobilization by Moderately but Not Highly Positive Material Surface Charges

Electrostatic forces at the cell interface affect the nature of cell adhesion and function; but there is still limited knowledge about the impact of positive or negative surface charges on cell-material interactions in regenerative medicine. Titanium surfaces with a variety of zeta potentials between −90 mV and +50 mV were generated by functionalizing them with amino polymers, extracellular matrix proteins/peptide motifs and polyelectrolyte multilayers. A significant enhancement of intracellular calcium mobilization was achieved on surfaces with a moderately positive (+1 to +10 mV) compared with a negative zeta potential (−90 to −3 mV). Dramatic losses of cell activity (membrane integrity, viability, proliferation, calcium mobilization) were observed on surfaces with a highly positive zeta potential (+50 mV). This systematic study indicates that cells do not prefer positive charges in general, merely moderately positive ones. The cell behavior of MG-63s could be correlated with the materials’ zeta potential; but not with water contact angle or surface free energy. Our findings present new insights and provide an essential knowledge for future applications in dental and orthopedic surgery.

Adhesive Properties of the Hyaluronan Pericellular Coat in Hyaluronan Synthases Overexpressing Mesenchymal Stem Cells

Hyaluronan (HA), a natural component of the extracellular matrix, is supposed to have a regulatory function in the stem cell niche. Bone marrow-derived human mesenchymal stem cells (hMSCs) are known to express all three hyaluronan synthases (HASes), which are responsible for HA production. HA is extruded into the extracellular matrix, but also stays bound to the plasma membrane forming a pericellular coat, which plays a key role during early cell adhesion. Since HAS isoenzymes, HAS1, HAS2 and HAS3, produce HA with different molecular weights, a difference in their role for cell adhesion is expected. Here, we transduced the immortalized hMSC cell line SCP1 to constitutively express eGFP-tagged HASes (SCP1-HAS-eGFP) by lentiviral gene transfer. The overexpression of the HAS-eGFP was shown on RNA and protein levels, HA was determined by ELISA and the stained HA-coat was analyzed using confocal microscopy. Time-lapse microscopy, spreading assay and single cell force spectroscopy using atomic force microscopy were applied to characterize adhesion of the different HAS transduced SCP1 cells. We showed in this study that HAS3 overexpressing cells formed the thickest pericellular coat compared with control or HAS1 and HAS2 transduced cells. Furthermore, SCP1-HAS3-eGFP displayed faster and stronger adhesion compared to cells overexpressing the other synthases or control cells. We conclude that overexpression of HASes in hMSCs differentially modulates their initial adhesive interactions with the substrate. This observation might be helpful in regenerative medicine goals.

Roles of hyaluronan in cardiovascular and nervous system disorders

Hyaluronan is a widely occurring extracellular matrix molecule, which is not only a supporting structural component, but also an active regulator of cellular functions. The chemophysical and biological properties of hyaluronan are greatly affected by its molecular size and several hyaluronan-binding proteins, making hyaluronan a fascinating molecule with great functional diversity. This review summarizes our current understanding of the roles of hyaluronan in cardiovascular and nervous system disorders, such as atherosclerosis, myocardial infarction, and stroke, with the aim to provide a foundation for future research and clinical trials.

ADAMTS9-Regulated Pericellular Matrix Dynamics Governs Focal Adhesion-Dependent Smooth Muscle Differentiation

Focal adhesions anchor cells to extracellular matrix (ECM) and direct assembly of a pre-stressed actin cytoskeleton. They act as a cellular sensor and regulator, linking ECM to the nucleus. Here, we identify proteolytic turnover of the anti-adhesive proteoglycan versican as a requirement for maintenance of smooth muscle cell (SMC) focal adhesions. Using conditional deletion in mice, we show that ADAMTS9, a secreted metalloprotease, is required for myometrial activation during late gestation and for parturition. Through knockdown of ADAMTS9 in uterine SMC, and manipulation of pericellular versican via knockdown or proteolysis, we demonstrate that regulated pericellular matrix dynamics is essential for focal adhesion maintenance. By influencing focal adhesion formation, pericellular versican acts upstream of cytoskeletal assembly and SMC differentiation. Thus, pericellular versican proteolysis by ADAMTS9 balances pro- and anti-adhesive forces to maintain an SMC phenotype, providing a concrete example of the dynamic reciprocity of cells and their ECM.

Biomaterial substrate modifications that influence cell-material interactions to prime cellular responses to nonviral gene delivery

IMPACT STATEMENT

This review summarizes how biomaterial substrate modifications (e.g. chemical modifications like natural coatings, ligands, or functional side groups, and/or physical modifications such as topography or stiffness) can prime the cellular response to nonviral gene delivery (e.g. affecting integrin binding and focal adhesion formation, cytoskeletal remodeling, endocytic mechanisms, and intracellular trafficking), to aid in improving gene delivery for applications where a cell-material interface might exist (e.g. tissue engineering scaffolds, medical implants and devices, sensors and diagnostics, wound dressings).

Tuning RGD Motif and Hyaluronan Density to Study Integrin Binding

Well-controlled surfaces with immobilized substrates enable novel approaches to investigate specific aspects of biological processes related to cell adhesion or motility. A subset of integrins, cellular transmembrane glycoproteins, recognize the evolutionarily conserved tripeptide sequence RGD, and anchor cells to their surrounding proteins as well as mediate bidirectional signaling. In this study, the main question was how co-presentation of hyaluronan (HA), an essential component of the extracellular matrix (ECM), and the RGD motif affect integrin binding. We report a method to prepare self-assembled monolayers on gold surfaces, co-presenting the cell adhesive RGD motif and small HA molecules, to investigate integrin containing proteoliposome binding. This technique enables an independent adjustment of the RGD motif and HA density while maintaining a passivating background: Layer formation and subsequent interactions with α_IIbβ₃ integrins, which are reconstituted in liposomes, was monitored by label-free quartz crystal microbalance with dissipation monitoring (QCM-D). Exceeding a critical RGD motif density of 40% results in enhanced binding of proteoliposomes. Co-presentation studies with varying HA and constant RGD motif density demonstrate that marginal amounts of HA are sufficient to prevent integrin binding. These findings are of specific importance in relation to cancer cell microenvironments, which show highly enriched HA in the surrounding ECM to reduce adhesion properties.

Cell Dynamics in the Correct Control of Bone Metabolism Using Natural Treatments

The present study was undertaken in order to assess the efficacy of a commercial product containing calcium and silicon (Osteosil-Calcium®) on cell metabolism. MG-63 osteblast-like cells were cultured in the presence of three different drug concentrations (10, 5 and 2.5 μg/mL). Either serum-free culture and standard culture with serum were investigated. Morpho-functional tests (MTT and ALP), scanning electron microscopy (SEM), microanalysis (EDAX) and time-lapse video microscopy were performed. Cell actin cytoskeletal modification with fluorescence phalloidin staining was also tested. Our data show the in vitro functional efficacy of Osteosil-Calcium® on MG63 cell viability and ALP production. This study demonstrates its positive effect on the metabolism of the single cell and suggests wider uses of this drug in health protection and or in Regenerative Medicine therapies which are currently applied to the elderly

Restricted cell functions on micropillars are alleviated by surface-nanocoating with amino groups

The topographical and chemical surface features of biomaterials are sensed by the cells, affecting their physiology at the interface. When placed on titanium, we recently discovered osteoblasts attempted caveolae-mediated phagocytosis of the sharp-edged microstructures. This active, energy-consuming process resulted in decreased osteoblastic cell functions (e.g. secretion of extracellular matrix proteins). However, chemical modification with plasma polymerized allylamine (PPAAm) was able to amplify osteoblast adhesion and spreading, resulting in better implant osseointegration in vivo In the present in vitro study, we analyzed whether this plasma polymer nanocoating is able to attenuate the microtopography-induced changes of osteoblast physiology. On PPAAm, we found cells showed a higher cell interaction with the geometrical micropillars by 30 min, and a less distinct reduction in the mRNA expression of collagen type I, osteocalcin and fibronectin after 24 h of cell growth. Interestingly, the cells were more active and sensitive on PPAAm-coated micropillars, and react with a substantial Ca²⁺ ion mobilization after stimulation with ATP. These results highlight that it is important for osteoblasts to establish cell surface contact for them to perform their functions.

AFM Indentation Analysis of Cells to Study Cell Mechanics and Pericellular Coat

Atomic force microscopy (AFM) indentation analysis of cells is a unique method of measuring stiffness of the cell body and physical properties of its pericellular coat. These cell parameters correlate with cells of abnormality and diseases. Viable biological cells can be studied with this method directly in a culture dish with no special preparation. Here we describe a step-by-step method to analyze the AFM force-indentation curves to derive cell mechanics (the modulus of elasticity of the cell body) and the parameters of the pericellular coat (density and the thickness of the coat layer). Technical details, potential difficulties, and points of special attention are described.

Imaging of Soft and Biological Samples Using AFM Ringing Mode

Ringing mode of atomic force microscopy (AFM) enables imaging the surfaces of biological samples, cells, tissue, biopolymers, etc. to obtain unique information, such as the size of molecules pulled by the AFM probe from the sample surface, heights of the sample at different load forces, etc. (up to eight different imaging channels can be recorded simultaneously, which is in addition to five channels already available in other rival modes). The imaging can be done in both air (gases) and liquid (buffers). In addition, the images obtained in ringing mode do not have several common artifacts and can be collected up to 20× faster compared to the rival imaging modes. Here we describe a step-by-step approach to collect images in ringing mode applied to biological and soft materials in general. Technical details, potential difficulties, and points of special attention are described.

Multiphoton Fabrication of Fibronectin-Functionalized Protein Micropatterns: Stiffness-Induced Maturation of Cell-Matrix Adhesions in Human Mesenchymal Stem Cells

Cell-matrix adhesions are important structures governing the interactions between cells and their microenvironment at the cell-matrix interface. The focal complex (FC) and focal adhesion (FA) have been substantially investigated in conventional planar culture systems using fibroblasts as an in vitro model. However, the formation of more mature types of cell-matrix adhesion in human mesenchymal stem cells (hMSCs), including fibrillar adhesion (FBA) and 3D matrix adhesion (3DMA), have not been fully elucidated. Here we investigate the niche factor(s) that influence(s) the maturation of FBA and 3DMA by using multiphoton fabrication-based micropatterning. First, the bovine serum albumin (BSA)-made protein micropatterns were functionalized by incorporating various concentrations of fibronectin (FN) in fabrication solution. The amount of cross-linked FN is positively correlated with the initial concentration of FN in the reaction liquid, as verified by immunofluorescence staining. On the other hand, the anisotropic FN-functionalized micropatterns were fabricated by varying the length (i.e., in-plane stiffness) and height (i.e., bending stiffness) of micropatterns, respectively. Finally, hMSCs were cultured on these micropatterns for 2 h and 1 day to determine the formation of FBA and 3DMA, respectively, using immunofluorescence staining. Results demonstrated that FN-functionalized micropatterns with high anisotropy in x-y dimension benefit FBA maturation. Furthermore, niche factors such as higher bending and in-plane stiffness and the presence of abundant fibronectin have a positive effect on the maturation of FN-based cell-matrix adhesion. These findings could provide some new perspectives on designing platforms for further cell niche study and rationalizing scaffold design for tissue engineering.

Pericellular Brush and Mechanics of Guinea Pig Fibroblast Cells Studied with AFM

The atomic force microscopy (AFM) indentation method combined with the brush model can be used to separate the mechanical response of the cell body from deformation of the pericellular layer surrounding biological cells. Although self-consistency of the brush model to derive the elastic modulus of the cell body has been demonstrated, the model ability to characterize the pericellular layer has not been explicitly verified. Here we demonstrate it by using enzymatic removal of hyaluronic content of the pericellular brush for guinea pig fibroblast cells. The effect of this removal is clearly seen in the AFM force-separation curves associated with the pericellular brush layer. We further extend the brush model for brushes larger than the height of the AFM probe, which seems to be the case for fibroblast cells. In addition, we demonstrate that an extension of the brush model (i.e., double-brush model) is capable of detecting the hierarchical structure of the pericellular brush, which, for example, may consist of the pericellular coat and the membrane corrugation (microridges and microvilli). It allows us to quantitatively segregate the large soft polysaccharide pericellular coat from a relatively rigid and dense membrane corrugation layer. This was verified by comparison of the parameters of the membrane corrugation layer derived from the force curves collected on untreated cells (when this corrugation membrane part is hidden inside the pericellular brush layer) and on treated cells after the enzymatic removal of the pericellular coat part (when the corrugations are exposed to the AFM probe). We conclude that the brush model is capable of not only measuring the mechanics of the cell body but also the parameters of the pericellular brush layer, including quantitative characterization of the pericellular layer structure.

Compartmentalized microfluidic perfusion system to culture human induced pluripotent stem cell aggregates

Microfluidic perfusion systems enable small-volume cell cultures under precisely controlled microenvironments, and are typically developed for cell-based high-throughput screening. However, most such systems are designed to manipulate dissociated single cells, not cell aggregates, and are thus unsuitable to induce differentiation in human induced pluripotent stem cells (hiPSCs), which is conventionally achieved by using cell aggregates to increase cell-cell interactions. We have now developed a compartmentalized microfluidic perfusion system with large flow channels to load, culture, and observe cell aggregates. Homogeneously sized cell aggregates to be loaded into the device were prepared by shredding flat hiPSC colonies into squares. These aggregates were then seeded into microchambers coated with fibronectin and bovine serum albumin (BSA) to establish adherent and floating cultures, respectively, both of which are frequently used to differentiate hiPSCs. However, the number of aggregates loaded in fibronectin-coated microchambers was much lower than in BSA-coated microchambers, suggesting that fibronectin traps cell aggregates before they reach the chambers. Accordingly, hiPSCs that reached the microchambers subsequently adhered. In contrast, BSA-coated microchambers did not allow cell aggregates to adhere, but were sufficiently deep to prevent cell aggregates from flowing out during perfusion of media. Immunostaining for markers of undifferentiated cells showed that cultures on both fibronectin- and BSA-coated microchambers were successfully established. Notably, we found that floating aggregates eventually adhered to surfaces coated with BSA upon differentiation, and that differentiation depends on the initial size of aggregates. Collectively, these results suggest that the microfluidic system is suitable for manipulating hiPSC aggregates in compartmentalized microchambers.

Abrogated Cell Contact Guidance on Amino-Functionalized Microgrooves

Topographical and chemical features of biomaterial surfaces affect the cell physiology at the interface and are promising tools for the improvement of implants. The dominance of the surface topography on cell behavior is often accentuated. Striated surfaces induce an alignment of cells and their intracellular adhesion-mediated components. Recently, it could be demonstrated that a chemical modification via plasma polymerized allylamine was not only able to boost osteoblast cell adhesion and spreading but also override the cell alignment on stochastically machined titanium. In order to discern what kind of chemical surface modifications let the cell forget the underlying surface structure, we used an approach on geometric microgrooves produced by deep reactive ion etching (DRIE). In this study, we systematically investigated the surface modification by (i) methyl-, carboxyl-, and amino functionalization created via plasma polymerization processes, (ii) coating with the extracellular matrix protein collagen-I or immobilization of the integrin adhesion peptide sequence Arg-Gly-Asp (RGD), and (iii) treatment with an atmospheric pressure plasma jet operating with argon/oxygen gas (Ar/O₂). Interestingly, only the amino functionalization, which presented positive charges at the surface, was able to chemically disguise the microgrooves and therefore to interrupt the microtopography induced contact guidance of the osteoblastic cells MG-63. However, the RGD peptide coating revealed enhanced cell spreading as well, with fine, actin-containing protrusions. The Ar/O₂-functionalization demonstrated the best topography handling, e.g. cells closely attached even to features such as the sidewalls of the groove steps. In the end, the amino functionalization is unique in abrogating the cell contact guidance.

AFM study shows prominent physical changes in elasticity and pericellular layer in human acute leukemic cells due to inadequate cell-cell communication

Biomechanical properties of single cells in vitro or ex vivo and their pericellular interfaces have recently attracted a lot of attention as a potential biophysical (and possibly prognostic) marker of various diseases and cell abnormalities. At the same time, the influence of the cell environment on the biomechanical properties of cells is not well studied. Here we use atomic force microscopy to demonstrate that cell-cell communication can have a profound effect on both cell elasticity and its pericellular coat. A human pre-B p190^BCR/ABL acute lymphoblastic leukemia cell line (ALL3) was used in this study. Assuming that cell-cell communication is inversely proportional to the distance between cells, we study ALL3 cells in vitro growing at different cell densities. ALL3 cells demonstrate a clear density dependent behavior. These cells grow very well if started at a relatively high cell density (HD, >2 × 10⁵ cells ml^-1) and are poised to grow at low cell density (LD, <1 × 10⁴ cells ml^-1). Here we observe ∼6× increase in the elastic (Young's) modulus of the cell body and ∼3.6× decrease in the pericellular brush length of LD cells compared to HD ALL3 cells. The difference observed in the elastic modulus is much larger than typically reported for pathologically transformed cells. Thus, cell-cell communication must be taken into account when studying biomechanics of cells, in particular, correlating cell phenotype and its biophysical properties.

The extracellular matrix in cancer progression: Role of hyalectan proteoglycans and ADAMTS enzymes

Remodelling of the extracellular matrix (ECM) has emerged as a key factor in cancer progression. Proteoglycans, including versican and other hyalectans, represent major structural elements of the ECM where they interact with other important molecules, including the glycosaminoglycan hyaluronan and the CD44 cell surface receptor. The hyalectan proteoglycans are regulated through cleavage by the proteolytic actions of A Disintegrin-like And Metalloproteinase domain with Thrombospondin-1 motif (ADAMTS) family members. Alteration in the balance between hyalectan proteoglycans and ADAMTS enzymes has been proposed to be a crucial factor in cancer progression either in a positive or negative manner depending on the context. Further complexity arises due to the formation of bioactive cleavage products, such as versikine, which may also play a role, and non-enzymatic functions for ADAMTS proteins. This research is providing fresh insights into cancer biology and opportunities for the development of new diagnostic and treatment strategies.

Hyaluronic Acid--an "Old" Molecule with "New" Functions: Biosynthesis and Depolymerization of Hyaluronic Acid in Bacteria and Vertebrate Tissues Including during Carcinogenesis

Hyaluronic acid is an evolutionarily ancient molecule commonly found in vertebrate tissues and capsules of some bacteria. Here we review modern data regarding structure, properties, and biological functions of hyaluronic acid in mammals and Streptococcus spp. bacteria. Various aspects of biogenesis and degradation of hyaluronic acid are discussed, biosynthesis and degradation metabolic pathways for glycosaminoglycan together with involved enzymes are described, and vertebrate and bacterial hyaluronan synthase genes are characterized. Special attention is given to the mechanisms underlying the biological action of hyaluronic acid as well as the interaction between polysaccharide and various proteins. In addition, all known signaling pathways involving hyaluronic acid are outlined. Impaired hyaluronic acid metabolism, changes in biopolymer molecular weight, hyaluronidase activity, and enzyme isoforms often accompany carcinogenesis. The interaction between cells and hyaluronic acid from extracellular matrix that may be important during malignant change is discussed. An expected role for high molecular weight hyaluronic acid in resistance of naked mole rat to oncologic diseases and the protective role of hyaluronic acid in bacteria are discussed.

Biophysical differences between chronic myelogenous leukemic quiescent and proliferating stem/progenitor cells

The treatment of chronic myeloid leukemia (CML), a clonal myeloproliferative disorder has improved recently, but most patients have not yet been cured. Some patients develop resistance to the available tyrosine kinase treatments. Persistence of residual quiescent CML stem cells (LSCs) that later resume proliferation is another common cause of recurrence or relapse of CML. Eradication of quiescent LSCs is a promising approach to prevent recurrence of CML. Here we report on new biophysical differences between quiescent and proliferating CD34+ LSCs, and speculate how this information could be of use to eradicate quiescent LSCs. Using AFM measurements on cells collected from four untreated CML patients, substantial differences are observed between quiescent and proliferating cells in the elastic modulus, pericellular brush length and its grafting density at the single cell level. The higher pericellular brush densities of quiescent LSCs are common for all samples. The significance of these observations is discussed.

Load Rate and Temperature Dependent Mechanical Properties of the Cortical Neuron and Its Pericellular Layer Measured by Atomic Force Microscopy

When studying the mechanical properties of cells by an indentation technique, it is important to take into account the nontrivial pericellular interface (or pericellular "brush") which includes a pericellular coating and corrugation of the pericellular membrane (microvilli and microridges). Here we use atomic force microscopy (AFM) to study the mechanics of cortical neurons taking into account the presence of the above pericellular brush surrounding cell soma. We perform a systematic study of the mechanical properties of both the brush layer and the underlying neuron soma and demonstrate that the brush layer is likely responsible for the low elastic modulus (<1 kPa) typically reported for cortical neurons. When the contribution of the pericellular brush is excluded, the average elastic modulus of the cortical neuron soma is found to be 3-4 times larger than previously reported values measured under similar physiological conditions. We also demonstrate that the underlying soma behaves as a nonviscous elastic material over the indentation rates studied (1-10 μm/s). As a result, it seems that the brush layer is responsible for the previously reported viscoelastic response measured for the neuronal cell body as a whole, within these indentation rates. Due to of the similarities between the macroscopic brain mechanics and the effective modulus of the pericellular brush, we speculate that the pericellular brush layer might play an important role in defining the macroscopic mechanical properties of the brain.

Synthesis and Characterization of Calcium Tartrate Dihydrate Nanoparticles

Calcium tartrate finds various applications. In the present study, calcium tartrate nanoparticles were synthesized by wet chemical method using surfactant mediated approach. The powder XRD pattern revealed the typical broadening of peaks indicating the nanostructured nature. The average crystallite size was calculated by applying the Scherrer's formula to powder XRD pattern and was found in the range of 22.8–23.9 nm. The particle size and morphology of the synthesized nanoparticles was confirmed by using transmission electron microscopy (TEM). FTIR spectroscopy was used to confirm the presence of various functional groups. From TGA, it was found that calcium tartrate nanoparticles remained stable up to 120°C and were having two water molecules associated with them. The results are compared with the bulk crystalline materials available in the literature.

Hyaluronan synthase 3 (HAS3) overexpression downregulates MV3 melanoma cell proliferation, migration and adhesion

Malignant skin melanoma is one of the most deadly human cancers. Extracellular matrix (ECM) influences the growth of malignant tumors by modulating tumor cells adhesion and migration. Hyaluronan is an essential component of the ECM, and its amount is altered in many tumors, suggesting an important role for hyaluronan in tumorigenesis. Nonetheless its role in melanomagenesis is not understood. In this study we produced a MV3 melanoma cell line with inducible expression of the hyaluronan synthase 3 (HAS3) and studied its effect on the behavior of the melanoma cells. HAS3 overexpression expanded the cell surface hyaluronan coat and decreased melanoma cell adhesion, migration and proliferation by cell cycle arrest at G1/G0. Melanoma cell migration was restored by removal of cell surface hyaluronan by Streptomyces hyaluronidase and by receptor blocking with hyaluronan oligosaccharides, while the effect on cell proliferation was receptor independent. Overexpression of HAS3 decreased ERK1/2 phosphorylation suggesting that inhibition of MAP-kinase signaling was responsible for these suppressive effects on the malignant phenotype of MV3 melanoma cells.

Towards early detection of cervical cancer: Fractal dimension of AFM images of human cervical epithelial cells at different stages of progression to cancer

We used AFM HarmoniX modality to analyse the surface of individual human cervical epithelial cells at three stages of progression to cancer, normal, immortal (pre-malignant) and carcinoma cells. Primary cells from 6 normal strains, 6 cancer, and 6 immortalized lines (derived by plasmid DNA-HPV-16 transfection of cells from 6 healthy individuals) were tested. This cell model allowed for good control of the cell phenotype down to the single cell level, which is impractical to attain in clinical screening tests (ex-vivo). AFM maps of physical (nonspecific) adhesion are collected on fixed dried cells. We show that a surface parameter called fractal dimension can be used to segregate normal from both immortal pre-malignant and malignant cells with sensitivity and specificity of more than 99%. The reported method of analysis can be directly applied to cells collected in liquid cytology screening tests and identified as abnormal with regular optical methods to increase sensitivity.

FROM THE CLINICAL EDITOR

Despite cervical smear screening, sometimes it is very difficult to differentiate cancers cells from pre-malignant cells. By using AFM to analyze the surface properties of human cervical epithelial cells, the authors were able to accurately identify normal from abnormal cells. This method could augment existing protocols to increase diagnostic accuracy.

Synovial fluid hyaluronan mediates MSC attachment to cartilage, a potential novel mechanism contributing to cartilage repair in osteoarthritis using knee joint distraction

Objectives

Knee joint distraction (KJD) is a novel, but poorly understood, treatment for osteoarthritis (OA) associated with remarkable ‘spontaneous’ cartilage repair in which resident synovial fluid (SF) multipotential mesenchymal stromal cells (MSCs) may play a role. We hypothesised that SF hyaluronic acid (HA) inhibited the initial interaction between MSCs and cartilage, a key first step to integration, and postulate that KJD environment favoured MSC/cartilage interactions.

Methods

Attachment of dual-labelled SF-MSCs were assessed in a novel in vitro human cartilage model using OA and rheumatoid arthritic (RA) SF. SF was digested with hyaluronidase (hyase) and its effect on adhesion was observed using confocal microscopy. MRI and microscopy were used to image autologous dual-labelled MSCs in an in vivo canine model of KJD. SF-HA was investigated using gel electrophoresis and densitometry.

Results

Osteoarthritic-synovial fluid (OA-SF) and purified high molecular weight (MW) HA inhibited SF-MSC adhesion to plastic, while hyase treatment of OA-SF but not RA-SF significantly increased MSC adhesion to cartilage (3.7-fold, p<0.05) These differences were linked to the SF mediated HA-coat which was larger in OA-SF than in RA-SF. OA-SF contained >9 MDa HA and this correlated with increases in adhesion (r=0.880). In the canine KJD model, MSC adhesion to cartilage was evident and also dependent on HA MW.

Conclusions

These findings highlight an unappreciated role of SF-HA on MSC interactions and provide proof of concept that endogenous SF-MSCs are capable of adhering to cartilage in a favourable biochemical and biomechanical environment in OA distracted joints, offering novel one-stage strategies towards joint repair.

Optical anisotropy reveals molecular order in a mouse enthesis

Entheses are specialized biological structures that functionally anchor tendons to bones. The complexity, mechanical characteristics and properties of the entheses, particularly those related to exercise, mechanical load and pathologies, have been extensively analyzed; however, the macromolecular organization of the enthesis fibers, as assessed by polarization microscopy, has not yet been investigated. Morphological and optical anisotropy characteristics, such as birefringence, linear dichroism (LD) and differential interference contrast (DIC-PLM) properties, are thus analyzed in this study of a healthy adult mouse calcaneal tendon-bone enthesis. The molecular and supramolecular order of collagen and GAGs was determined for the collagen bundles of this enthesis. Based on a birefringence plot pattern as well as on metachromasy and linear dichroism after toluidine blue staining at pH 4.0, a similarity between the calcaneal tendon-bone enthesis and cartilage during ossification may be assumed. This similarity is assumed to favor the adequacy of this enthesis to support a compressive load. Considering that the collagen-proteoglycan complexes and the enthesis fibers themselves have a chiral nature, these structures could be acting via reciprocal signaling with the cellular environment of the enthesis.

Hyaluronan Controls the Deposition of Fibronectin and Collagen and Modulates TGF-β1 Induction of Lung Myofibroblasts

The contribution of hyaluronan-dependent pericellular matrix to TGF-β1-driven induction and maintenance of myofibroblasts is not understood. Hyaluronan is an extracellular matrix (ECM) glycosaminoglycan important in cell adhesion, proliferation and migration, and is implicated in myofibroblast formation and maintenance. Reduced turnover of hyaluronan has been linked to differentiation of myofibroblasts and potentiation of lung fibrosis. Fibronectin is a fibril forming adhesive glycoprotein that is also upregulated following induction with TGF-β1. Although they are known to bind each other, the interplay between hyaluronan and fibronectin in the pericellular matrix during myofibroblast induction and matrix assembly is not clear. This study addresses the role of hyaluronan and its interaction with fibrillar matrix components during myofibroblast formation. Hyaluronan and fibronectin were increased and co-localized in the ECM following myofibroblast induction by TGF-β1. Inhibition of hyaluronan synthesis in TGF-β1-induced lung myofibroblasts over a 4day period with 4-methyl umbelliferone (4-MU) further enhanced myofibroblast morphology, caused increased deposition of fibronectin and type I collagen in the ECM, and increased expression of alpha-smooth muscle actin and hyaluronan synthase 2 (HAS2) mRNA. Hyaluronan oligosaccharides or hyaluronidase treatment, which more effectively disrupted the pericellular matrix, had similar effects. CD44 and β1 integrins co-localized in the cell membrane and along some stress fibers. However, CD44 and hyaluronan were specifically excluded from focal adhesions, and associated primarily with cortical actin. Time-lapse imaging of the immediate effects of hyaluronidase digestion showed that hyaluronan matrix primarily mediates attachment of membrane and cortical actin between focal contacts, suggesting that surface adhesion through hyaluronan and CD44 is distinct from focal adhesion through β1 integrins and fibronectin. Fluorescein-labeled hyaluronan bound regularly along fibronectin fibers and co-localized more with β1 integrin and less with CD44. Therefore, the hyaluronan matrix can interfere with the assembly of fibrillar ECM components, and this interplay regulates the degree of myofibroblast formation. These data also suggest that adhesion through hyaluronan matrix impacts cytoskeletal organization, and is potentially part of a clutch mechanism that regulates stick and slip of myofibroblasts by affecting the adhesion to and organization of fibronectin and collagen.

Aging of plasma-polymerized allylamine nanofilms and the maintenance of their cell adhesion capacity

The long-term stability and γ-sterilisability of bioactive layers is the precondition for the application of implants. Thus, aging processes of a microwave deposited, plasma polymerized allylamine nanofilm (PPAAm) with positively charged amino groups were evaluated concerning physicochemical characteristics and cell adhesion capacity over the course of one year. XPS, FT-IR, surface free energy, and water contact angle measurements elucidated not only the oxidation of the PPAAm film due to atmospheric oxygen reacting with surface free radicals but also the influence of atmospheric moisture during sample storage in ambient air. Surprisingly, within 7 days 70% of the primary amino groups are lost and mostly converted into amides. A positive zeta-potential was verified for half a year and longer. Increasing polar surface groups and a water contact angle shift from 60° to 40° are further indications of altered surface properties. Nevertheless, MG-63 human osteoblastic cells adhered and spread out considerably on aged and additionally γ-sterilized PPAAm layers deposited on polished titanium alloys (Ti-6Al-4V_P). These cell-relevant characteristics were highly significant over the whole period of one year and may not be related to the existence of primary amino groups. Rather, the oxidation products, the chemical amide group, that is, seem to support the attachment of osteoblasts at all times up to one year.

The effect of tenocyte/hyaluronic acid therapy on the early recovery of healing Achilles tendon in rats

The aim of this study was to explore the potential for a better recovery outcome for the Achilles tendon at an early healing stage when a mixed biomaterial-tenocyte injection is used. The experimental animals underwent single limb Achilles tendon transection followed by suturing repair. A solution of either hyaluronic acid with or without tenocytes or normal saline was randomly chosen to be injected around the injury site after surgery. To obtain the comprehensive recovery condition of the rats on different management protocols, the animals were evaluated histologically, mechanically, and functionally. A significant difference in the recovery condition was found in the injured tendon injected with the hyaluronic acid solution with tenocytes compared with the other groups. Tendon stiffness and the locomotion abilities of the rats with healing Achilles tendons were improved in the hyaluronic acid with tenocyte transplantation group. The acceleration of the inflammatory phase in rats with the hyaluronic acid with tenocyte injections might be the major reason for the better functional outcomes.

Peeping into human renal calcium oxalate stone matrix: characterization of novel proteins involved in the intricate mechanism of urolithiasis

BACKGROUND

The increasing number of patients suffering from urolithiasis represents one of the major challenges which nephrologists face worldwide today. For enhancing therapeutic outcomes of this disease, the pathogenic basis for the formation of renal stones is the need of hour. Proteins are found as major component in human renal stone matrix and are considered to have a potential role in crystal-membrane interaction, crystal growth and stone formation but their role in urolithiasis still remains obscure.

METHODS

Proteins were isolated from the matrix of human CaOx containing kidney stones. Proteins having MW>3 kDa were subjected to anion exchange chromatography followed by molecular-sieve chromatography. The effect of these purified proteins was tested against CaOx nucleation and growth and on oxalate injured Madin-Darby Canine Kidney (MDCK) renal epithelial cells for their activity. Proteins were identified by Matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF MS) followed by database search with MASCOT server. In silico molecular interaction studies with CaOx crystals were also investigated.

RESULTS

Five proteins were identified from the matrix of calcium oxalate kidney stones by MALDI-TOF MS followed by database search with MASCOT server with the competence to control the stone formation process. Out of which two proteins were promoters, two were inhibitors and one protein had a dual activity of both inhibition and promotion towards CaOx nucleation and growth. Further molecular modelling calculations revealed the mode of interaction of these proteins with CaOx at the molecular level.

CONCLUSIONS

We identified and characterized Ethanolamine-phosphate cytidylyltransferase, Ras GTPase-activating-like protein, UDP-glucose:glycoprotein glucosyltransferase 2, RIMS-binding protein 3A, Macrophage-capping protein as novel proteins from the matrix of human calcium oxalate stone which play a critical role in kidney stone formation. Thus, these proteins having potential to modulate calcium oxalate crystallization will throw light on understanding and controlling urolithiasis in humans.