Mg2+ and Ca2+ differentially regulate beta 1 integrin-mediated adhesion of dermal fibroblasts and keratinocytes to various extracellular matrix proteins

ER and SOCE Ca2+ signals are not required for directed cell migration in human microglia

The central nervous system (CNS) is constantly surveilled by microglia, highly motile and dynamic cells deputed to act as the first line of immune defense in the brain and spinal cord. Alterations in the homeostasis of the CNS are detected by microglia that respond by migrating toward the affected area. Understanding the mechanisms controlling directed cell migration of microglia is crucial to dissect their responses to neuroinflammation and injury. We used a combination of pharmacological and genetic approaches to explore the involvement of calcium (Ca2+) signaling in the directed migration of induced pluripotent stem cell (iPSC)-derived microglia challenged with a purinergic stimulus. This approach mimics cues originating from injury of the CNS. Unexpectedly, simultaneous imaging of microglia migration and intracellular Ca2+ changes revealed that this phenomenon does not require Ca2+ signals generated from the endoplasmic reticulum (ER) and store-operated Ca2+ entry (SOCE) pathways. Instead, we find evidence that human microglial chemotaxis to purinergic signals is mediated by cyclic AMP in a Ca2+-independent manner. These results challenge prevailing notions, with important implications in neurological conditions characterized by perturbation in Ca2+ homeostasis.

In Situ Hybridization of circRNAs in Cells and Tissues through BaseScope™ Strategy

Imaging-based approaches are powerful strategies that nowadays have been largely used to gain insight into the function of different types of macromolecules. As for RNA, it is becoming clear how important is its intracellular localization for the control of proper cell differentiation and development and how its perturbation can be linked to several pathological states. This aspect is even more important if one thinks of highly polarized cells such as neurons.In this chapter, we describe in detail an innovative RNA-FISH approach for the detection of circular RNAs (circRNAs), a recently discovered class of noncoding RNAs, which display different subcellular localizations and whose functions still largely remain to be elucidated. The detection of these molecules represents a great challenge, above all because they share most of their sequence with the corresponding linear counterparts, from which they differ only for the back-splicing junction (BSJ) originating from the circularization reaction. This implies the use of RNA-FISH probes capable of specifically binding the BSJ and avoiding the detection of the linear counterpart. This requirement imposes the design of probes on a very small region, which implies the risk of obtaining a low and undetectable signal. The BaseScope™ Assay RNA-FISH technology overpasses this problem since it is based on branched-DNA probes. With this approach it is possible to target a specific region of the RNA, even small such as a splicing junction, and at the same time to obtain a strong and well detectable signal. All this is possible thanks to subsequent series of probes that, starting from the first hybridization to the BSJ, build a branched tree of probes that greatly amplifies the signal. Here we provide a detailed step-by-step protocol of BaseScope™ RNA-FISH on circRNAs coupled with immunofluorescence, both in cells and tissues, and we address difficulties which may arise when using this methodology that depend on cell type, specific permeabilization, image acquisition, and post-acquisition analyses.

An Overview of Scaffolds and Biomaterials for Skin Expansion and Soft Tissue Regeneration: Insights on Zinc and Magnesium as New Potential Key Elements

The utilization of materials in medical implants, serving as substitutes for non-functional biological structures, supporting damaged tissues, or reinforcing active organs, holds significant importance in modern healthcare, positively impacting the quality of life for millions of individuals worldwide. However, certain implants may only be required temporarily to aid in the healing process of diseased or injured tissues and tissue expansion. Biodegradable metals, including zinc (Zn), magnesium (Mg), iron, and others, present a new paradigm in the realm of implant materials. Ongoing research focuses on developing optimized materials that meet medical standards, encompassing controllable corrosion rates, sustained mechanical stability, and favorable biocompatibility. Achieving these objectives involves refining alloy compositions and tailoring processing techniques to carefully control microstructures and mechanical properties. Among the materials under investigation, Mg- and Zn-based biodegradable materials and their alloys demonstrate the ability to provide necessary support during tissue regeneration while gradually degrading over time. Furthermore, as essential elements in the human body, Mg and Zn offer additional benefits, including promoting wound healing, facilitating cell growth, and participating in gene generation while interacting with various vital biological functions. This review provides an overview of the physiological function and significance for human health of Mg and Zn and their usage as implants in tissue regeneration using tissue scaffolds. The scaffold qualities, such as biodegradation, mechanical characteristics, and biocompatibility, are also discussed.

Sustained release of magnesium and zinc ions synergistically accelerates wound healing

Skin wounds are a major medical challenge that threaten human health. Functional hydrogel dressings demonstrate great potential to promote wound healing. In this study, magnesium (Mg) and zinc (Zn) are introduced into methacrylate gelatin (GelMA) hydrogel via low-temperature magnetic stirring and photocuring, and their effects on skin wounds and the underlying mechanisms are investigated. Degradation testing confirmed that the GelMA/Mg/Zn hydrogel released magnesium ions (Mg²⁺) and zinc ions (Zn²⁺) in a sustained manner. The Mg²⁺ and Zn²⁺ not only enhanced the migration of human skin fibroblasts (HSFs) and human immortalized keratinocytes (HaCats), but also promoted the transformation of HSFs into myofibroblasts and accelerated the production and remodeling of extracellular matrix. Moreover, the GelMA/Mg/Zn hydrogel enhanced the healing of full-thickness skin defects in rats via accelerated collagen deposition, angiogenesis and skin wound re-epithelialization. We also identified the mechanisms through which GelMA/Mg/Zn hydrogel promoted wound healing: the Mg²⁺ promoted Zn²⁺ entry into HSFs and increased the concentration of Zn²⁺ in HSFs, which effectively induced HSFs to differentiate into myofibroblasts by activating the STAT3 signaling pathway. The synergistic effect of Mg²⁺ and Zn²⁺ promoted wound healing. In conclusion, our study provides a promising strategy for skin wounds regeneration.

Antibacterial and Cytocompatible pH-Responsive Peptide Hydrogel

A short peptide, FHHF-11, was designed to change stiffness as a function of pH due to changing degree of protonation of histidines. As pH changes in the physiologically relevant range, G' was measured at 0 Pa (pH 6) and 50,000 Pa (pH 8). This peptide-based hydrogel is antimicrobial and cytocompatible with skin cells (fibroblasts). It was demonstrated that the incorporation of unnatural AzAla tryptophan analog residue improves the antimicrobial properties of the hydrogel. The material developed can have a practical application and be a paradigm shift in the approach to wound treatment, and it will improve healing outcomes for millions of patients each year.

Recent Advances in Cell Sheet Engineering: From Fabrication to Clinical Translation

Cell sheet engineering, a scaffold-free tissue fabrication technique, has proven to be an important breakthrough technology in regenerative medicine. Over the past two decades, the field has developed rapidly in terms of investigating fabrication techniques and multipurpose applications in regenerative medicine and biological research. This review highlights the most important achievements in cell sheet engineering to date. We first discuss cell sheet harvesting systems, which have been introduced in temperature-responsive surfaces and other systems to overcome the limitations of conventional cell harvesting methods. In addition, we describe several techniques of cell sheet transfer for preclinical (in vitro and in vivo) and clinical trials. This review also covers cell sheet cryopreservation, which allows short- and long-term storage of cells. Subsequently, we discuss the cell sheet properties of angiogenic cytokines and vasculogenesis. Finally, we discuss updates to various applications, from biological research to clinical translation. We believe that the present review, which shows and compares fundamental technologies and recent advances in cell engineering, can potentially be helpful for new and experienced researchers to promote the further development of tissue engineering in different applications.

Applications of Biodegradable Magnesium-Based Materials in Reconstructive Oral and Maxillofacial Surgery: A Review

Reconstruction of defects in the maxillofacial region following traumatic injuries, craniofacial deformities, defects from tumor removal, or infections in the maxillofacial area represents a major challenge for surgeons. Various materials have been studied for the reconstruction of defects in the maxillofacial area. Biodegradable metals have been widely researched due to their excellent biological properties. Magnesium (Mg) and Mg-based materials have been extensively studied for tissue regeneration procedures due to biodegradability, mechanical characteristics, osteogenic capacity, biocompatibility, and antibacterial properties. The aim of this review was to analyze and discuss the applications of Mg and Mg-based materials in reconstructive oral and maxillofacial surgery in the fields of guided bone regeneration, dental implantology, fixation of facial bone fractures and soft tissue regeneration.

Metallic ion-based graphene oxide functionalized silk fibroin-based dressing promotes wound healing via improved bactericidal outcomes and faster re-epithelization

An ideal wound dressing material should enhance the wound healing process and must avoid bacterial contamination. In this study, the synergistic effect of graphene oxide (GO), silver (Ag) and magnesium (Mg) based silk electrospun nanofibrous film on wound healing was evaluated. It reports the influence of essential elements Mg and Ag during the skin regeneration process. Silver and magnesium nanoparticles were doped in graphene oxide. The goal of the present study was to fabricate an electrospun nanofibrous patch with nanoscale fillers to improve the wound recuperation manner and decrease the recuperation time to forestall microorganism infections and improve cellular behavior. Doping was done to insert Ag2+ and Mg2+ ions in the crystal lattice of GO to overcome the disadvantage of aggregation of Ag and Mg nanoparticles. In this study, Mg and Ag ions doped GO functionalized silk fibroin/PVA dressing material was prepared using the electrospinning technique. It was found that, Mg-GO@NSF/PVA and Ag/Mg-GO@NSF/PVA film possess good cytocompatibility, low hemolytic effect and effective antibacterial and anti-biofilm activities. Furthermore, their improved hydrophilicity and mid-range water vapor transmission rate allow them to be a suitable wound dressing material. The effect of prepared film on wound repair were investigated in excision rat model. It indicates, the wound covered with Ag/Mg-GO@NSF/PVA film showed the highest wound contraction rate and re-epithelization, allowing faster repair of wound sites. In conclusion, the development of metallic ions doped GO based silk fibroin/PVA is a promising approach towards development of antibiotic free wound dressing material. It prevents anti-biofilm formation and also provides adequate therapeutic effects for accelerating wound healing.

The Physico-Chemical Properties and Exploratory Real-Time Cell Analysis of Hydroxyapatite Nanopowders Substituted with Ce, Mg, Sr, and Zn (0.5-5 at.%)

Cation-substituted hydroxyapatite (HA), standalone or as a composite (blended with polymers or metals), is currently regarded as a noteworthy candidate material for bone repair/regeneration either in the form of powders, porous scaffolds or coatings for endo-osseous dental and orthopaedic implants. As a response to the numerous contradictions reported in literature, this work presents, in one study, the physico-chemical properties and the cytocompatibility response of single cation-doped (Ce, Mg, Sr or Zn) HA nanopowders in a wide concentration range (0.5–5 at.%). The modification of composition, morphology, and structure was multiparametrically monitored via energy dispersive X-ray, X-ray photoelectron, Fourier-transform infrared and micro-Raman spectroscopy methods, as well as by transmission electron microscopy and X-ray diffraction. From a compositional point of view, Ce and Sr were well-incorporated in HA, while slight and pronounced deviations were observed for Mg and Zn, respectively. The change of the lattice parameters, crystallite size, and substituting cation occupation factors either in the Ca(I) or Ca(II) sites were further determined. Sr produced the most important HA structural changes. The in vitro biological performance was evaluated by the (i) determination of leached therapeutic cations (by inductively coupled plasma mass spectrometry) and (ii) assessment of cell behaviour by both conventional assays (e.g., proliferation—3-(4,5-dimethyl thiazol-2-yl) 5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium assay; cytotoxicity—lactate dehydrogenase release assay) and, for the first time, real-time cell analysis (RTCA). Three cell lines were employed: fibroblast, osteoblast, and endothelial. When monophasic, the substituted HA supported the cells’ viability and proliferation without signs of toxicity. The RTCA results indicate the excellent adherence of cells. The study strived to offer a perspective on the behaviour of Ce-, Mg-, Sr-, or Zn-substituted HAs and to deliver a well-encompassing viewpoint on their effects. This can be highly important for the future development of such bioceramics, paving the road toward the identification of candidates with highly promising therapeutic effects.

Research status of biodegradable metals designed for oral and maxillofacial applications: A review

The oral and maxillofacial regions have complex anatomical structures and different tissue types, which have vital health and aesthetic functions. Biodegradable metals (BMs) is a promising bioactive materials to treat oral and maxillofacial diseases. This review summarizes the research status and future research directions of BMs for oral and maxillofacial applications. Mg-based BMs and Zn-based BMs for bone fracture fixation systems, and guided bone regeneration (GBR) membranes, are discussed in detail. Zn-based BMs with a moderate degradation rate and superior mechanical properties for GBR membranes show great potential for clinical translation. Fe-based BMs have a relatively low degradation rate and insoluble degradation products, which greatly limit their application and clinical translation. Furthermore, we proposed potential future research directions for BMs in the oral and maxillofacial regions, including 3D printed BM bone scaffolds, surface modification for BMs GBR membranes, and BMs containing hydrogels for cartilage regeneration, soft tissue regeneration, and nerve regeneration. Taken together, the progress made in the development of BMs in oral and maxillofacial regions has laid a foundation for further clinical translation.

An insight into the mechanism of antibacterial activity by magnesium oxide nanoparticles

The exact mechanism behind the antibacterial efficacy of nanoparticles has remained unexplored to date. This study aims to shed light the mechanism adopted using magnesium oxide nanoparticles prepared in ethyl alcohol against gram-negative and gram-positive bacterial cells, and the generation of reactive oxygen species (ROS) is proposed to be the dominant mechanism. This paradigm is supported by the quantification of the hydroxyl radical and superoxide anions produced in the nanoparticle treated and untreated bacterial solutions, and by the reduction of the antibacterial efficiency after the addition of a radical scavenger. The production of free Mg2+ ions from the nanoparticle is supposed to be the causative agent behind this uncontrolled ROS generation, resulting in excessive oxidative stress, which the antioxidants of the bacterial cells are unable to nullify, leading to cell damage. The amount of proteins, carbohydrates and lipids leaked due to the distortion of the cellular membrane is also quantified, and it is observed that their leakage trend varies on the structure of the bacterial cell. FESEM images taken at certain time intervals show the gradual internalization of the nanoparticles, and increasing rupture of bacterial cell membranes, leading to cell necrosis.

A Surface-Tailoring Method for Rapid Non-Thermosensitive Cell-Sheet Engineering via Functional Polymer Coatings

Cell sheet engineering, a technique utilizing a monolayer cell sheet, has recently emerged as a promising technology for scaffold-free tissue engineering. In contrast to conventional tissue-engineering approaches, the cell sheet technology allows cell harvest as a continuous cell sheet with intact extracellular matrix proteins and cell-cell junction, which facilitates cell transplantation without any other artificial biomaterials. A facile, non-thermoresponsive method is demonstrated for a rapid but highly reliable platform for cell-sheet engineering. The developed method exploits the precise modulation of cell-substrate interactions by controlling the surface energy of the substrate via a series of functional polymer coatings to enable prompt cell sheet harvesting within 100 s. The engineered surface can trigger an intrinsic cellular response upon the depletion of divalent cations, leading to spontaneous cell sheet detachment under physiological conditions (pH 7.4 and 37 °C) in a non-thermoresponsive manner. Additionally, the therapeutic potential of the cell sheet is successfully demonstrated by the transplantation of multilayered cell sheets into mouse models of diabetic wounds and ischemia. These findings highlight the ability of the developed surface for non-thermoresponsive cell sheet engineering to serve as a robust platform for regenerative medicine and provide significant breakthroughs in cell sheet technology.

Effect of physical cues of altered extract media from biodegradable magnesium implants on human gingival fibroblasts

Volume stable barrier membranes made of magnesium are very promising in Guided Bone Regeneration (GBR) to treat periodontal bone defects in dentistry due to their excellent biocompatibility and biodegradability. During the degradation process the cells are exposed to the alteration of various parameters, so called physical cues, involving surface alterations due to the formed corrosion layer and medium alterations arising from the dissolved corrosion products. Cell migration of human gingival fibroblasts (HGF), as a crucial parameter for optimal healing process in GBR, has been investigated on magnesium membranes and revealed that medium alterations by dissolved corrosion products have a higher impact on cell migration than surface alterations. However, the effect of each altered medium parameter on cell migration has not been adequately studied, but their roles are crucial to explain the slower migration rate on magnesium surfaces compared to titanium and tissue culture plastic surfaces. Our study investigates the single effect of Mg²⁺, Ca²⁺, H₂ and increased osmolality as well as the effect of magnesium extracts, which contain a dynamic mixture of previous parameters on cell migration, proliferation and viability of HGF. We showed that at 75 mM Mg²⁺ concentration and at 0 mM Ca²⁺, respectively, the cell migration rate is greatly reduced. In complex magnesium extract media, we found that a temporarily increased ratio of Mg²⁺ to Ca²⁺ conditioned a slow HGF migration rate. Based on these findings and the characterization of supernatants from HGF migration assays on Mg membranes, we propose, that the slower migration rate of HGF can be explained by the altered ratio of Mg²⁺ to Ca²⁺, caused by increasing concentrations of Mg²⁺ and decreasing concentrations of Ca²⁺ in the vicinity of the corroding Mg implant, combined with a constantly increased molecular hydrogen concentration in the supernatant. These results are cell type specific and should be checked carefully, if necessary, for Mg implant performance. STATEMENT OF SIGNIFICANCE: The study is providing a systematic approach to explain the main effects of extract medium parameters (physical cues) such as magnesium or calcium ion concentration, osmolality and dissolved molecular hydrogen and CO₂ in cell culture media modified by co-incubating with corroding magnesium implants on the migration rate of human gingival fibroblasts (HGF). This study uncovers for the first time the combinatory effect of slightly increased molecular hydrogen and the change in Mg²⁺/Ca²⁺ ratio on HGF cell migration.

Design of a migration assay for human gingival fibroblasts on biodegradable magnesium surfaces

A novel regenerative approach to Guided Bone Regeneration (GBR) in dental surgery is based on the development of biodegradable and volume stable barrier membranes made of metallic magnesium. Currently used volume stable barrier membranes are made of titanium-reinforced PTFE or titanium-reinforced collagen membranes, both, however, are accompanied by a high incidence of wound dehiscence resulting in membrane exposure, which leads to an increased infection risk. An exposed membrane could also occur directly after insertion due to insufficient soft tissue coverage of the membrane. In both cases, fast wound margin regeneration is required. As a first step of soft-tissue regeneration, gingival fibroblasts need to migrate over the barrier membrane and close the dehiscent wound. Based on this aim, this study investigated the migration behaviour of human gingival fibroblasts on a magnesium surface. Major experimental challenges such as formation of hydrogen bubbles due to initial magnesium corrosion and non-transparent material surfaces have been addressed to allow cell adhesion and to follow cell migration. The designed scratch-based cell migration assay involved vital fluorescent cell staining on a pre-corroded magnesium membrane to simulate invivo wound dehiscence. The assay has been used to compare cell migration on pre-corroded magnesium to titanium surfaces and tissue culture plastic as control substrates. First results of this assay showed that human gingival fibroblasts migrate slower on pre-corroded magnesium compared to plastic and titanium. However, the scratch was finally closed on all materials. Compared to titanium surfaces and tissue culture plastic, the surface roughness and the surface free energy (SFE) could not explain slower cell migration on magnesium surfaces. Immunohistological investigations of cellular structure revealed, that magnesium ions increased focal adhesion at concentration of additionally 75 mM MgCl₂ in cell culture medium. The use of our designed cell migration assay has shown that ionic medium alterations due to magnesium corrosion has a higher impact on the cell migration rate than surface alterations.

STATEMENT OF SIGNIFICANCE

The design of a migration assay on non-transparent magnesium surfaces will add the option to study cell response to surface modifications, coatings and the corrosion process itself under life view conditions.

Integrin-linked kinase and ELMO2 modulate recycling endosomes in keratinocytes

The formation of tight cell-cell junctions is essential in the epidermis for its barrier properties. In this tissue, keratinocytes follow a differentiation program tightly associated with their movement from the innermost basal to the outer suprabasal layers, and with changes in their cell-cell adhesion profile. Intercellular adhesion in keratinocytes is mediated through cell-cell contacts, including E-cadherin-based adherens junctions. Although the mechanisms that mediate E-cadherin delivery to the plasma membrane have been widely studied in simple epithelia, this process is less well understood in the stratified epidermis. In this study, we have investigated the role of Engulfment and Cell Motility 2 (ELMO2) and integrin-linked kinase (ILK) in the positioning of E-cadherin-containing recycling endosomes during establishment of cell-cell contacts in differentiating keratinocytes. We now show that induction of keratinocyte differentiation by Ca²⁺ is accompanied by localization of ELMO2 and ILK to Rab4- and Rab11a-containing recycling endosomes. The positioning of long-loop Rab11a-positive endosomes at areas adjacent to cell-cell contacts is disrupted in ELMO2- or ILK-deficient keratinocytes, and is associated with impaired localization of E-cadherin to cell borders. Our studies show a previously unrecognized role for ELMO2 and ILK in modulation of endosomal positioning, which may play key roles in epidermal sheet maintenance and permeability barrier function.

Extracellular Vesicles Exploit Viral Entry Routes for Cargo Delivery

Extracellular vesicles (EVs) have emerged as crucial mediators of intercellular communication, being involved in a wide array of key biological processes. Eukaryotic cells, and also bacteria, actively release heterogeneous subtypes of EVs into the extracellular space, where their contents reflect their (sub)cellular origin and the physiologic state of the parent cell. Within the past 20 years, presumed subtypes of EVs have been given a rather confusing diversity of names, including exosomes, microvesicles, ectosomes, microparticles, virosomes, virus-like particles, and oncosomes, and these names are variously defined by biogenesis, physical characteristics, or function. The latter category, functions, in particular the transmission of biological signals between cells in vivo and how EVs control biological processes, has garnered much interest. EVs have pathophysiological properties in cancer, neurodegenerative disorders, infectious disease, and cardiovascular disease, highlighting possibilities not only for minimally invasive diagnostic applications but also for therapeutic interventions, like macromolecular drug delivery. Yet, in order to pursue therapies involving EVs and delivering their cargo, a better grasp of EV targeting is needed. Here, we review recent progress in understanding the molecular mechanisms underpinning EV uptake by receptor-ligand interactions with recipient cells, highlighting once again the overlap of EVs and viruses. Despite their highly heterogeneous nature, EVs require common viral entry pathways, and an unanticipated specificity for cargo delivery is being revealed. We discuss the challenges ahead in delineating specific roles for EV-associated ligands and cellular receptors.

Inhibitor encapsulated, self-healable and cytocompatible chitosan multilayer coating on biodegradable Mg alloy: a pH-responsive design

The design of functional biomaterials that respond intelligently to external stimuli has become a rapidly growing area with widespread interest. This work contributes to the development of a feedback-active anticorrosion system with intriguing self-healing ability to protect magnesium (Mg) from biocorrosion. The system was constituted by an inner micro/nano-porous, ceramic-like pre-coating developed readily from the substrate, and an outermost inhibitor (nanosized cerium (Ce) oxides) containing chitosan (CS) multilayers. Here, the pre-coating acted as both an "anchoring" and a "barrier" layer to acquire structural integrity and improved impedance, respectively. Green CS served as cargo for Ce to be entrapped, harnessing Ce-NH₂ complexation chemistry. The coating barrier properties were evaluated by electrochemical impedance spectroscopy. The active corrosion inhibition was assessed by immersion degradation tests with respect to Mg²⁺ release, pH alteration, crack development, and scanning Kelvin potential. To our delight, the coatings effectively protected the substrate from biocorrosion in vitro compared with bare alloys. Putatively, the pH-triggered formation of Ce oxide precipitation, along with the pH-buffering activity and movable swelling capacity of CS macromolecules, should have contributed to restraining the anodic activity and healing the cracks/defects dynamically. Furthermore, the coated substrate had the biocompatibility to elicit better attachment and growth of osteoblasts.

Substrate Stiffness Affects Human Keratinocyte Colony Formation

Restoration of epidermal organization and function in response to a variety of pathophysiological insults is critically dependent on coordinated keratinocyte migration, proliferation, and stratification during the process of wound healing. These processes are mediated by the reconfiguration of both cell-cell (desmosomes, adherens junctions) and cell-matrix (focal adhesions, hemidesmosomes) junctions and the cytoskeletal filament networks that they serve to interconnect. In this study, we investigated the role of substrate elasticity (stiffness) on keratinocyte colony formation in vitro during the process of nascent epithelial sheet formation as triggered by the calcium switch model of keratinocyte culture. Keratinocytes cultured on pepsin digested type I collagen coated soft (nominal E = 1.2 kPa) polyacrylamide gels embedded with fluorescent microspheres exhibited (i) smaller spread contact areas, (ii) increased migration velocities, and (iii) increased rates of colony formation with more cells per colony than did keratinocytes cultured on stiff (nominal E = 24 kPa) polyacrylamide gels. As assessed by tracking of embedded microsphere displacements, keratinocytes cultured on soft substrates generated large local substrate deformations that appeared to recruit adjacent keratinocytes into joining an evolving colony. Together with the observed differences in keratinocyte kinematics and substrate deformations, we developed two ad hoc analyses, termed distance rank (DR) and radius of cooperativity (RC), that help to objectively ascribe what we perceive as increasingly cooperative behavior of keratinocytes cultured on soft versus stiff gels during the process of colony formation. We hypothesize that the differences in keratinocyte colony formation observed in our experiments could be due to cell-cell mechanical signaling generated via local substrate deformations that appear to be correlated with the increased expression of β4 integrin within keratinocytes positioned along the periphery of an evolving cell colony.

Cation type specific cell remodeling regulates attachment strength

Single-molecule experiments indicate that integrin affinity is cation-type-dependent, but in spread cells integrins are engaged in complex focal adhesions (FAs), which can also regulate affinity. To better understand cation-type-dependent adhesion in fully spread cells, we investigated attachment strength by application of external shear. While cell attachment strength is indeed modulated by cations, the regulation of integrin-mediated adhesion is also exceedingly complex, cell specific, and niche dependent. In the presence of magnesium only, fibroblasts and fibrosarcoma cells remodel their cytoskeleton to align in the direction of applied shear in an α5-integrin/fibronectin-dependent manner, which allows them to withstand higher shear. In the presence of calcium or on collagen in modest shear, fibroblasts undergo piecewise detachment but fibrosarcoma cells exhibit increased attachment strength. These data augment the current understanding of force-mediated detachment by suggesting a dynamic interplay in situ between cell adhesion and integrins depending on local niche cation conditions.

Generation of composites for bone tissue-engineering applications consisting of gellan gum hydrogels mineralized with calcium and magnesium phosphate phases by enzymatic means

Mineralization of hydrogels, desirable for bone regeneration applications, may be achieved enzymatically by incorporation of alkaline phosphatase (ALP). ALP-loaded gellan gum (GG) hydrogels were mineralized by incubation in mineralization media containing calcium and/or magnesium glycerophosphate (CaGP, MgGP). Mineralization media with CaGP:MgGP concentrations 0.1:0, 0.075:0.025, 0.05:0.05, 0.025:0.075 and 0:0.1 (all values mol/dm³ , denoted A, B, C, D and E, respectively) were compared. Mineral formation was confirmed by IR and Raman, SEM, ICP-OES, XRD, TEM, SAED, TGA and increases in the the mass fraction of the hydrogel not consisting of water. Ca was incorporated into mineral to a greater extent than Mg in samples mineralized in media A-D. Mg content and amorphicity of mineral formed increased in the order A < B < C < D. Mineral formed in media A and B was calcium-deficient hydroxyapatite (CDHA). Mineral formed in medium C was a combination of CDHA and an amorphous phase. Mineral formed in medium D was an amorphous phase. Mineral formed in medium E was a combination of crystalline and amorphous MgP. Young's moduli and storage moduli decreased in dependence of mineralization medium in the order A > B > C > D, but were significantly higher for samples mineralized in medium E. The attachment and vitality of osteoblastic MC3T3-E1 cells were higher on samples mineralized in media B-E (containing Mg) than in those mineralized in medium A (not containing Mg). All samples underwent degradation and supported the adhesion of RAW 264.7 monocytic cells, and samples mineralized in media A and B supported osteoclast-like cell formation. Copyright © 2014 John Wiley & Sons, Ltd.

A novel glass ionomer cement containing MgCO(3 )apatite induced the increased proliferation and differentiation of human pulp cells in vitro

This study aimed to investigate the in vitro biological response of human dental pulp cells to glass ionomer cement (GIC, Fuji IX GP(®)) containing 2.5% magnesium carbonate apatite (MgCO(3)Ap). MgCO(3)Ap was synthesized by wet method and characterized using FT-IR, XPS, and SEM. Fuji IX GP(®) served as a control. Test and control cements were prepared by encapsulated mixing the powder with Fuji IX-liquid (P/L=3.6:1). Eluates from cements extracted by 1 mL culture medium were collected at day 1, 7 and 14, and used for WST-1 proliferation assay. For ALPase activity, cells were maintained with cements in transwells, harvested and enzyme activity was measured at day 1, 4, 7, 14, and 21. We found a higher cell proliferation and increased ALPase activity by pulp cells in the test group compared to the control. This suggests the potential of GIC containing this novel biological apatite as a restorative material for pulp-dentin regeneration.

Osteoblastic cell response on fluoridated hydroxyapatite coatings: the effect of magnesium incorporation

Magnesium (Mg) ions were incorporated into fluoridated hydroxyapatite (HA) coating by the sol-gel dip-coating method. Mg in the coating was measured by x-ray photoelectron spectroscopy (XPS). The changes of calcium and magnesium concentrations were recorded to monitor the dissolution behavior of the coatings. In vitro cell responses were evaluated using MG63 cells in terms of cell morphology, proliferation and differentiation. The substitution of Mg and F ions into the HA crystal structure was confirmed by XPS. Only a limited amount of Mg can be incorporated into HA lattice. The dissolution test revealed that Mg incorporation increased the solubility of the coating in the tris-buffered saline solution. The highest solubility was achieved at x = 1.5 (Ca((10-x))Mg(x)(PO(4))(6) F(OH). In the cell culture test, well-spread cells were observed on all the coatings. Also, a significantly positive effect of Mg ions on cell proliferation and late differentiation was found at x = 1.5. Mg incorporation stimulates osteoblastic cell responses on fluoridated hydroxyapatite coatings.

Chondrocyte aggregation in suspension culture is GFOGER-GPP- and beta1 integrin-dependent

Isolated chondrocytes form aggregates in suspension culture that maintain chondrocyte phenotype in a physiological pericellular environment. The molecular mechanisms involved in chondrocyte aggregation have not been previously identified. Using this novel suspension culture system, we performed mRNA and protein expression analysis along with immunohistochemistry for potential cell adhesion molecules and extracellular matrix integrin ligands. Inhibition of aggregation assays were performed using specific blocking agents. We found that: (i) direct cell-cell interactions were not involved in chondrocyte aggregation, (ii) chondrocytes in aggregates were surrounded by a matrix rich in collagen II and cartilage oligomeric protein (COMP), (iii) aggregation depends on a beta1-integrin, which binds a triple helical GFOGER sequence found in collagens, (iv) integrin alpha10-subunit is the most highly expressed alpha-subunit among those tested, including alpha5, in aggregating chondrocytes. Taken together, this body of evidence suggests that the main molecular interaction involved in aggregation of phenotypically stable chondrocytes is the alpha10beta1-collagen II interaction.

Divalent cations modulate the integrin-mediated malignant phenotype in pancreatic cancer cells

We have previously demonstrated that pathophysiological shifts in the concentrations of extracellular Mg(2+) and Ca(2+) activate the alpha(2)beta(1) integrin-mediated malignant phenotype on type I collagen in pancreatic cancer cells, as evidenced by increased adhesion, migration and proliferation. In the present study, we examined the integrin and divalent cation specificity of pancreatic cancer cell interactions with other physiologically relevant extracellular matrix proteins, including fibronectin, type IV collagen, laminin and vitronectin. Our results indicate that, like alpha(2)beta(1) integrin-mediated interactions with type I collagen, beta(1) integrin-mediated adhesion to fibronectin, type IV collagen and laminin are promoted by Mg(2+) but not by Ca(2+). On vitronectin, cells attach via alpha(v)beta(5) and beta(1) integrins, and in the presence of either divalent cation. We also demonstrate that, like type I collagen, pancreatic cancer cell migration and proliferation on fibronectin, laminin and type IV collagen is maximal when Mg(2+) is present at concentrations that promote optimal adhesion and Ca(2+) is present at concentrations less than Mg(2+). On vitronectin, Panc-1 cell migration is maximal with decreased Mg(2+) and increased Ca(2+), but the reverse is true for BxPC-3 cells. Both cell lines exhibited maximal proliferation with increased Mg(2+) and decreased Ca(2+), however. Together with evidence indicating that the in vivo local tumor microenvironment contains increased Mg(2+) and decreased Ca(2+), our studies demonstrate that such divalent cation shifts could activate the integrin-mediated malignant phenotype in pancreatic cancer.

Assessment of an Automated Bioreactor to Propagate and Harvest Keratinocytes for Fabrication of Engineered Skin Substitutes

Engineered skin substitutes (ESS) composed of autologous fibroblasts and keratinocytes attached to collagen-glycosaminoglycan (GAG) scaffolds are effective adjuncts in the treatment of massive burns. The Kerator, an automated bioreactor for keratinocyte culture, could hypothetically reduce labor and material requirements, and increase availability of ESS. Human keratinocytes were cultured in the Kerator and also in tissue-culture flasks. It was found that keratinocyte confluence increased exponentially with time in both the Kerator (r2=0.99) and the flasks (r2=0.96). Confluence (mean+/-SEM) of keratinocytes in the flasks (28+/-2.3%) was significantly higher than in the Kerator (18+/-0.93%) at day 4. However, there was no difference in confluence at harvest. The colony forming efficiency (CFE) and population doublings (PD) per day of keratinocytes harvested from the Kerator were 67+/-4.7% and 0.80+/-0.06, respectively, and were not different from the corresponding values for keratinocytes from flasks. ESS fabricated with keratinocytes from the Kerator or from the flasks were comparable in vitro in terms of histological anatomy, cellular viability, and surface hydration. These findings show that there are no differences between keratinocytes from the Kerator and those from the flasks regarding (a) growth to confluence, (b) CFE and growth rate (PD/day), or (c) quality of ESS in vitro, suggesting that the Kerator can automate fabrication of ESS and increase its availability for treatment of skin wounds.

Adhesion and signaling by B cell-derived exosomes: the role of integrins

Exosomes are nanometer-sized vesicles secreted by various cells, with potentially diverse roles in physiology. Although emphasis has been placed on their involvement in immune modulation, their potential for more wide-ranging biological effects has not been appreciated. A common exosome feature is the expression of adhesion molecules, which include the integrin family. We have for the first time addressed the possible function of B cell-derived exosome-integrins by examining adhesive interactions of exosomes (immobilized onto beads) with extracellular matrix (ECM) components and cytokine-treated fibroblasts. Integrin (beta1 and beta2) expression was demonstrated by Western blotting and flow cytometry. Binding studies (with blocking antibodies) demonstrated their function in adhesion to collagen-I, fibronectin, and tumor necrosis factor (TNF)-alpha-activated fibroblasts. Exosome adhesion to TNF-alpha-activated fibroblasts also triggered integrin-dependent changes in cytosolic calcium, measured by single cell imaging. Thus, B cell-derived exosomes express functional integrins, which are capable of mediating anchorage to ECM and cell-surface adhesion molecules, and may be a novel mode of delivering adhesion signals at distances beyond that of direct cell-cell contact during inflammation.

ALS-like skin changes in mice on a chronic low-Ca/Mg high-Al diet

Epidemiologic studies of endemic foci of amyotrophic lateral sclerosis (ALS) have shown low concentrations of Ca/Mg and high concentrations of Al/Mn in the drinking water and garden soil, which may play a causative role in the pathogenesis of endemic ALS. We studied the effects of chronic exposure to a low-Ca/Mg high-Al maltol diet on the skin of experimental animals. In ALS patients, atrophy of the epidermis, edematous changes with separated collagen fibrils and an accumulation of amorphous materials between collagen bundles were regarded as pathognomonic skin changes of ALS. Mice chronically fed a low-Ca/Mg high-Al maltol diet showed neuronal degeneration and loss in the spinal cords and cerebral cortices, as well as skin changes including atrophy, separation of collagen fibrils and accumulation of amorphous materials, similar to the skin changes characteristic of ALS. This is the first report of skin changes in animal models similar to those of ALS. We speculate that environmental factors such as chronic low-Ca/Mg high-Al condition play some causative role in the pathogenesis of Kii-ALS.

Action of FGMgCO3Ap-collagen composite in promoting bone formation

To improve the biological properties of materials as bone substitutes, functionally graded CO3 apatite crystals containing magnesium, FGMgCO3Ap, were synthesized to be mixed with atelocollagen and made into a composite pellet. A radio-labeled cell adhesion experiment showed that the degree of adherence of mouse MC3T3E1 osteoblast-like cells to the FGMgCO3Ap-collagen composite was better than to CO3Ap-collagen and much better than to the Ti plate. When the composites were implanted beneath the periosteum cranii of rats, the FGMgCO3Ap-collagen composite was metabolized faster than the CO3Ap-collagen composite and better formation of new bone and osteoblast arrangement at the interface between the composite and the periosteum cranii was observed. When the composites were implanted into the femur of rabbits, clear bone formation with a higher degree of bone density was observed for the FGMgCO3Ap-collagen composite. These results suggest that the Mg2+ ions taken into the apatite crystals may contribute to the acceleration of osteoblast adhesion to apatites and promote bone formation, cross-talking with osteoblasts at the molecular level.

Influence of donor age and culture conditions on tissue engineering of mucosa autografts

In oral surgery the transplantation of tissue engineered mucosa is used more frequently. The conventional single cell suspension culture method (SCSM) involves murine feeder cells and foetal calf serum. The explant technique (ET) has been used as alternative culture procedure. Aim was to study the efficacy of the ET and the SCSM without feeder cells to grow primary cultures and to test the effects of donor age, of extracellular matrix proteins (ECMP), and of autogenous serum on cell growth in explant cultures. These factors were assessed in cultures of 58 patients overall. In 48 cultures of 12 patients primary cell growth was compared between the ET and the SCSM. Eighteen of 24 cultures were established with the ET whereas only 3 of 24 were established with the SCSM. To test the influence of donor age on cell multiplication, the proliferation rate (DNA synthesis measured by bromodeoxyuridine uptake) and the overall growth (DNA content) was determined in cultures of five young and five old donors. In cultures from old donors (mean age 56 years) proliferation was lower but more sustained relative to the cultures from the young donors (mean age 25 years). In old donors overall in vitro cell growth was only 2/3 of that in young donors. In cultures of 20 donors the influence on cell adhesion and growth of the ECMP fibronectin and laminin was assessed by planimetry. While ECMP augmented explant adhesion, these substances did not enhance keratinocyte growth significantly. Comparing the influence of autogenous and foetal calf serum on cell growth no differences were observed in all cultures of the six donors. In conclusion, the ET without additional ECMP coating and with autogenous instead of foetal calf serum are now used to culture gingival keratinocytes for tissue engineering mucosa grafts. Consequently xenogenous components are avoided, being a considerable advantage.

Divalent cations modulate human colon cancer cell adhesion

BACKGROUND

Iatrogenic tumor implantation within surgical sites can compromise curative cancer surgery. Cancer cell adhesion to extracellular matrix proteins is mediated by diverse matrix receptors, most notably integrins. Divalent cations may modulate integrin-ligand interactions in some cells.

MATERIALS AND METHODS

We studied adhesion of SW620 and Caco-2 human colon cancer cells to collagen I, the dominant collagen of the interstitial matrix, and confirmed our results in primary human colon cancer cells from surgical specimens. Single cell suspensions in either HEPES/NaCl buffer or media supplemented with 0-1 mM Mn2+ or Mg2+, and 0-10 mM Zn2+ or Ca2+ were plated onto collagen-I-precoated dishes for 30 min.

RESULTS

Supplementation of the HEPES/NaCl/BSA buffer with 1 mM Mn2+, Mg2+, Zn2+, or Ca2+ affected adhesion differently. Mn2+ (1 mM) markedly promoted SW620 adhesion vs control (21.17 +/- 0.08-fold). Mg2+ (1 mM) had a similar but lesser effect (14.71 +/- 0.02-fold). However, 1-10 mM Ca2+ inhibited basal cell adhesion by 22.0 +/- 3.1 to 88.0 +/- 7.3 % inhibition. Ca2+ (2.5-10 mM) also inhibited Mn2+-induced adhesion. Zn2+ stimulated basal adhesion slightly at lower concentrations but inhibited Mn2+-stimulated adhesion similarly to Ca2+ at higher concentrations. Results were duplicated in conventional serum containing culture medium supplemented with these cations. Caco-2 cells and primary cancer cells yielded similar results. All results are significant to P < 0.01.

DISCUSSION

Integrin-mediated colon cancer cell adhesion is affected by extracellular divalent cation concentrations. Washing the surgical site with dilute calcium or zinc solutions might diminish perioperative tumor implantation.

Synthesis of functionally graded MgCO3 apatite accelerating osteoblast adhesion

As a means of improving the biological properties of materials for use as bone substitutes, functionally graded carbonate apatite containing Mg, FGMgCO3Ap, was synthesized at 60 degrees C and pH 7.4 using a gradient magnesium supply system. X-ray diffraction analysis of FGMgCO3Ap showed a poorly crystallized apatitic pattern, similar to that of human bone. ESCA analysis clearly showed the negative gradient distribution in Mg1s intensity (atomic concentration) of magnesium from the crystal surface toward the inner core. When the FGMgCO3Ap crystals were mixed with collagen, the resulting FGMgCO3Ap-collagen composite, irradiated with UV light for 4 h, retained their features in the saline solution. After washing away the nonadhesive cells, a cell adhesion assay showed that the optical density of the FGMgCO3Ap-collagen composite was higher than that of the CO3Ap-collagen composite. SEM observation showed that the osteoblast-like cells adhered well to the surface of the FGMgCO3Ap-collagen composite. Staining with hematoxylin-eosin and alizarin red confirmed the existence of a great many more cells and a thicker extracellular matrix layer on the FGMgCO3Ap-collagen composite than on the CO3Ap-collagen composite. This result demonstrated the acceleration effect of magnesium ions on osteoblast adhesion on the FGMgCO3Ap-collagen composite.

Fibrinogen and fibrin are anti-adhesive for keratinocytes: a mechanism for fibrin eschar slough during wound repair

During cutaneous wound repair the epidermis avoids the fibrin-rich clot; rather it migrates down the collagen-rich dermal wound margin and over fibronectin-rich granulation tissue. The mechanism(s) underlying keratinocyte movement in this precise pathway has not been previously addressed. Here we demonstrate that cultured human keratinocytes do not express functional fibrinogen/fibrin receptors, specifically alpha v beta 3. Biologic modifiers known to induce integrin expression or activation did not induce adhesion to fibrin, fibrinogen, or its fragments. Epidermal explant outgrowth and single epidermal cell migration failed to occur on either fibrin or fibrinogen. Surprisingly, fibrin and fibrinogen mixed at physiologic molar ratios with fibronectin abrogated keratinocyte attachment to fibronectin. Keratinocytes transduced with the beta 3 integrin subunit cDNA, expressed alpha v beta 3 on their surface and attached to and spread on fibrinogen and fibrin. beta-gal cDNA-transduced keratinocytes did not demonstrate this activity. Furthermore, beta 3 cDNA-transduced keratinocyte adhesion to fibrin was inhibited by LM609 monoclonal antibody to alpha v beta 3 in a concentration-dependent fashion. From these data, we conclude that normal human keratinocytes cannot interact with fibrinogen and its derivatives due to the lack of alpha v beta 3. Thus, fibrinogen and fibrin are authentic anti-adhesive for keratinocytes. This may be a fundamental reason why the migrating epidermis dissects the fibrin eschar from wounds.

The angiogenic factors Cyr61 and connective tissue growth factor induce adhesive signaling in primary human skin fibroblasts

The angiogenic inducers cysteine-rich angiogenic protein 61 (Cyr61) and connective tissue growth factor (CTGF) are structurally related, extracellular matrix-associated heparin-binding proteins. Both can stimulate chemotaxis and promote proliferation in endothelial cells and fibroblasts in culture and induce neovascularization in vivo. Encoded by inducible immediate early genes, Cyr61 and CTGF are synthesized upon growth factor stimulation in cultured fibroblasts and during cutaneous wound healing in dermal fibroblasts. Recently, we have shown that adhesion of primary human fibroblasts to immobilized Cyr61 is mediated through integrin alpha(6)beta(1) and cell surface heparan sulfate proteoglycans (HSPGs) (Chen, N., Chen, C.-C., and Lau, L.F. (2000) J. Biol. Chem. 275, 24953-24961), providing the first demonstration of an absolute requirement for HSPGs in integrin-mediated cell attachment. We show in this study that CTGF also mediates fibroblast adhesion through the same mechanism and demonstrate that fibroblasts adhesion to immobilized Cyr61 or CTGF induces distinct adhesive signaling responses consistent with their biological activities. Compared with fibroblast adhesion to fibronectin, laminin, or type I collagen, cell adhesion to Cyr61 or CTGF induces 1) more extensive and prolonged formation of filopodia and lamellipodia, concomitant with formation of integrin alpha(6)beta(1)-containing focal complexes localized at leading edges of pseudopods; 2) activation of intracellular signaling molecules including focal adhesion kinase, paxillin, and Rac with similar rapid kinetics; 3) sustained activation of p42/p44 MAPKs lasting for at least 9 h; and 4) prolonged gene expression changes including up-regulation of MMP-1 (collagenase-1) and MMP-3 (stromelysin-1) mRNAs and proteins sustained for at least 24 h. Together, these results establish Cyr61 and CTGF as bona fide adhesive substrates with specific signaling capabilities, provide a molecular basis for their activities in fibroblasts through integrin alpha(6)beta(1) and HSPG-mediated signaling during attachment and indicate that these proteins may function in matrix remodeling through the activation of metalloproteinases during angiogenesis and wound healing.

Adhesion of human skin fibroblasts to Cyr61 is mediated through integrin alpha 6beta 1 and cell surface heparan sulfate proteoglycans

The angiogenic inducer Cyr61 is an extracellular matrix-associated heparin-binding protein that can mediate cell adhesion, stimulate cell migration, and enhance growth factor-stimulated DNA synthesis in both fibroblasts and endothelial cells in culture. In vivo, Cyr61 induces neovascularization and promotes tumor growth. Cyr61 is a prototypic member of a highly conserved family of secreted proteins that includes connective tissue growth factor, nephroblastoma overexpressed, Elm-1/WISP-1, Cop-1/WISP-2, and WISP-3. Encoded by an immediate early gene, Cyr61 synthesis is induced by serum growth factors in cultured fibroblasts and in dermal fibroblasts during cutaneous wound healing. We previously demonstrated that Cyr61 mediates adhesion of vascular endothelial cells and activation-dependent adhesion of blood platelets through direct interaction with integrins alpha(V)beta(3) and alpha(IIb)beta(3), respectively. In this study, we show that the adhesion of primary human skin fibroblasts to Cyr61 is mediated through integrin alpha(6)beta(1) and cell surface heparan sulfate proteoglycans (HSPGs), which most likely serve as co-receptors. Either destruction of cell surface HSPGs or prior occupancy of the Cyr61 heparin-binding site completely blocked cell adhesion to Cyr61. A heparin-binding defective mutant of Cyr61 was unable to mediate fibroblast adhesion through integrin alpha(6)beta(1) but still mediated endothelial cell adhesion through integrin alpha(V)beta(3), indicating that endothelial cell adhesion through integrin alpha(V)beta(3) is independent of the heparin-binding activity of Cyr61. These results identify Cyr61 as a novel adhesive substrate for integrin alpha(6)beta(1) and provide the first demonstration of the requirement for HSPGs in integrin-mediated cell attachment. In addition, these findings suggest that Cyr61 might elicit disparate biological effects in different cell types through interaction with distinct integrin receptors.

Mouse proximal tubular cell-cell adhesion inhibits apoptosis by a cadherin-dependent mechanism

Adhesion of epithelial cells to matrix is known to inhibit apoptosis. However, the role of cell-cell adhesion in mediating cell survival remains uncertain. Primary cultures of mouse proximal tubular (MPT) cells were used to examine the role of cell-cell adhesion in promoting survival. When MPT cells were deprived of both cell-matrix and cell-cell adhesion, they died by apoptosis. However, when incubated in agarose-coated culture dishes (to prevent cell-matrix adhesion) and at high cell density (to allow cell-cell interactions), MPT cells adhered to one another and remained viable. Expression of E-cadherin among suspended, aggregating cells increased with time. A His-Ala-Val (HAV)-containing peptide that inhibits homophilic E-cadherin binding prevented cell-cell aggregation and promoted apoptosis of MPT cells in suspension. By contrast, inhibition of potential beta(1)-integrin-mediated interactions between cells in suspension did not prevent either aggregation or survival of suspended cells. Aggregation of cells in suspension activated phosphatidylinositol 3-kinase (PI3K), an event that was markedly reduced by the presence of the HAV peptide. LY-294002, an inhibitor of PI3K, also inhibited survival of suspended cells. In summary, we provide novel evidence that MPT cells, when deprived of normal cell-matrix interactions, can adhere to one another in a cadherin-dependent fashion and remain viable. Survival of aggregated cells depends on activation of PI3K.

Position-dependent linkages of fibronectin- integrin-cytoskeleton

Position-dependent cycling of integrin interactions with both the cytoskeleton and extracellular matrix (ECM) is essential for cell spreading, migration, and wound healing. Whether there are regional changes in integrin concentration, ligand affinity or cytoskeleton crosslinking of liganded integrins has been unclear. Here, we directly demonstrate a position-dependent binding and release cycle of fibronectin-integrin-cytoskeleton interactions with preferential binding at the front of motile 3T3 fibroblasts and release at the endoplasm-ectoplasm boundary. Polystyrene beads coated with low concentrations of an integrin-binding fragment of fibronectin (fibronectin type III domains 7-10) were 3-4 times more likely to bind to integrins when placed within 0.5 microns vs. 0.5-3 microns from the leading edge. Integrins were not concentrated at the leading edge, nor did anti-integrin antibody-coated beads bind preferentially at the leading edge. However, diffusing liganded integrins attached to the cytoskeleton preferentially at the leading edge. Cytochalasin inhibited edge binding, which suggested that cytoskeleton binding to the integrins could alter the avidity for ligand beads. Further, at the ectoplasm-endoplasm boundary, the velocity of bead movement decreased, diffusive motion increased, and approximately one-third of the beads were released into the medium. We suggest that cytoskeleton linkage of liganded integrins stabilizes integrin-ECM bonds at the front whereas release of cytoskeleton-integrin links weakens integrin-ECM bonds at the back of lamellipodia.

Stricture formation in Crohn's disease: the role of intestinal fibroblasts

OBJECTIVE

To determine whether intestinal fibroblasts in patients with Crohn's disease (CD) have an enhanced capacity to reorganize collagen and thus cause stricture formation.

SUMMARY BACKGROUND DATA

Stricture formation is a characteristic feature of CD that may distinguish it from other forms of inflammatory bowel disease. Methods Fibroblasts were obtained at surgery from the colon and ileum of patients with CD and ulcerative colitis (UC) and control patients. Primary fibroblast cultures were obtained by explant technique. Fibroblast contractile activity was measured using fibroblast-populated collagen lattices (FPCLs), in which the cultured fibroblasts were seeded in free-floating collagen gel matrices that they reorganize and contract. Fibroblast contractile activity was measured as the reduction of surface area (mm2) of collagen gel matrix at 24-hour intervals for 1 week.

RESULTS

Fibroblasts from patients with CD displayed enhanced capacity to contract FPCL when compared to UC and control fibroblasts. This activity was maximal in fibroblasts recovered from strictured regions in CD. Fibroblasts from patients with UC had a contractile capacity similar to that of controls. Hydrocortisone inhibited this in vitro contractile activity in a dose-dependent manner.

CONCLUSIONS

Intestinal fibroblasts in CD possess enhanced capacity for collagen reorganization and contractile activity in vitro. This activity may be responsible for stricture formation in CD.

Detection of soluble alpha1 integrin in human serum

An enzyme-linked immunosorbent assay (ELISA) for the detection and quantitation of soluble alpha1beta1 integrins (salpha1) in human serum samples was developed. Solid phase-bound anti-alpha1 integrin monoclonal antibody (mAb) TS2/7 was used to capture salpha1, and mAb 1B3.1 was used to detect the immobilized integrin. An extract of human placenta (PE) containing 340 ng/mL of VLA-1 molecules served as a positive control, and serum samples from normal donors and patients were assayed. Optimal binding of anti-alpha1 integrin mAb 1B3.1, expressed as specific optical density (OD), was obtained when a 5 microng/mL solution of anti-alpha1 integrin "capture" mAb TS2/7 was immobilized to the wells and the PE was added. Solutions of albumin or collagen, in contrast, did not result in binding, confirming the specificity of the assay for sal. Furthermore, the specific OD of the wells correlated directly with the concentration of PE. A concentration of salpha1 above that of a 1:100 dilution of PE--that is, >3.4 ng/mL of integrin, in which the intra-assay correlation of variance was <5.7%, was found in 5 of 8, 3 of 8, and 6 of 9 serum samples from normal individuals, patients with connective tissue diseases (CTD), and patients with liver diseases (LD), respectively. These results suggest, for the first time, that salpha1 are present in healthy and diseased human serum.

The epidermotropic mycosis fungoides associated alpha1beta1 integrin (VLA-1, CD49a/CD29) is primarily a collagen IV receptor on malignant T cells

Several of the beta1 integrin receptors [very late antigen (VLA) molecules] for extracellular matrix (ECM) proteins are expressed by malignant T cells in cutaneous T-cell lymphoma (CTCL). We evaluated the function of VLA-1, a beta1 integrin specifically expressed in epidermotropic mycosis fungoides (MF), in CD4+ leukemic T cells Jurkat line). We found that Jurkat cells adhere significantly to collagens only after their activation with phorbol 12-myristate 13-acetate (PMA). However, the adhesion to collagen IV (but not to collagen I) of Jurkat cells selected for expressing increased levels of VLA-1 (with unchanged levels of VLA-2, the second collagen integrin receptor) was significantly enhanced relative to that of "VLA-1 low" cells. Monoclonal antibody (mAb) 1B3.1, directed against the collagen binding domain of VLA-1, inhibited adhesion to collagen IV and to collagen I by 36.67%+/-5.25% and 18%+/-4.32%, respectively (p<0.05), whereas the inhibition by anti-VLA-2 mAb PIE6 was comparable on both collagens (25%+/-7.48% and 36.3%+/-0.94%, respectively; p<0.09). Immuno-histochemical studies of skin biopsies from 10 untreated MF patients showed that in all cases at least 10% of the lymphocytes residing in the epidermis are VLA-1+VLA-2-. While not directly applicable to MF, the demonstrated functions of VLA-1 in leukemic Jurkat cells, together with its expression in MF skin, suggest a role for VLA-1 integrins in epidermotropism in a small proportion of leukemic MF cells.

Migration of human keratinocytes in electric fields requires growth factors and extracellular calcium

Currents that leak out of wounds generate electric fields lateral to the wound. These fields induce directional locomotion of human keratinocytes in vitro and may promote wound healing in vivo. We have examined the effects of growth factors and calcium, normally present in culture medium and the wound fluid, on the directional migration of human keratinocytes in culture. In electric fields of physiologic strength (100 mV per mm), keratinocytes migrated directionally towards the cathode at a rate of about 1 microm per min. This directional migration requires several growth factors. In the absence of these growth factors, the cell migration rate decreased but directionality was maintained. Epidermal growth factor alone restored cell migration rates at concentrations as low as 0.2 ng per ml. Insulin at 5-100 microg per ml or bovine pituitary extract at 0.2%-2% vol/vol also stimulated keratinocyte motility but was not sufficient to fully restore the migration rate. Keratinocyte migration in electric fields requires extracellular calcium. Changes in calcium concentrations from 3 microM to 3.3 mM did not significantly change keratinocyte migration rate nor directionality in electric fields; however, addition of the chelator ethyleneglycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid to migration medium reduced, and eventually abolished, keratinocyte motility. Our results show that (i) growth factors and extracellular calcium are required for electric field-induced directional migration of human keratinocytes, and (ii) keratinocytes migrate equally well in low and high calcium media.

Characteristics of cation binding to the I domains of LFA-1 and MAC-1. The LFA-1 I domain contains a Ca2+-binding site

The crystal structures of the I domains of integrins MAC-1 (alphaM beta2; CD11b/CD18) and LFA-1 (alphaL beta2; CD11a/CD18) show that a single conserved cation-binding site is present in each protein. Purified recombinant I domains have intrinsic ligand binding activity, and in several systems this interaction has been demonstrated to be cation-dependent. It has been proposed that the I domain cation-binding site represents a general metal ion-dependent adhesion motif utilized for binding protein ligands. Here we show that the purified recombinant I domain of LFA-1 (alphaLI) binds cations, but with significantly different characteristics compared with the I domain of MAC-1 (alphaMI). Both alphaLI and alphaMI bind 54Mn2+ in a conformation-dependent manner, and in general, cations with charge and size characteristics similar to Mn2+ most effectively inhibit 54Mn2+ binding. Surprisingly, however, physiological levels of Ca2+ (1-2 mM) inhibited 54Mn2+ binding to purified alphaLI, but not to alphaMI. Using 45Ca2+ and 54Mn2+ in direct binding studies, the dissociation constants (KD) for the interactions between these cations and alphaLI were estimated to be 5-6 x 10(-5) and 1-2 x 10(-5) M, respectively. Together with the available structural information, the data suggest differential affinities for Mn2+ and Ca2+ binding to the single conserved site within alphaLI. Antagonism of LFA-1, but not MAC-1, -mediated cell adhesion by Ca2+ may be related to the Ca2+ binding activity of the LFA-1 I domain.

Induction and repression of collagenase-1 by keratinocytes is controlled by distinct components of different extracellular matrix compartments

In all forms of cutaneous wounds, collagenase-1 (matrix metalloproteinase-1 (MMP-1)) is invariably expressed by basal keratinocytes migrating over the dermal matrix. We report that native type I collagen mediates induction of MMP-1 by primary human keratinocytes. Collagen-mediated induction of MMP-1 was rapid, being detected 2 h after plating, and was transcriptionally regulated. As demonstrated by in situ hybridization, only migrating keratinocytes expressed MMP-1, suggesting that contact with collagen is not sufficient to induce MMP-1 expression in keratinocytes; the cells must also be migrating. Upon denaturation, type I collagen lost its ability to induce MMP-1 expression but still supported cell adhesion. Other dermal or wound matrix proteins, such as type III collagen, fibrin, and fibronectin, and a mixture of basement membrane proteins did not induce MMP-1 production. In the presence of collagen, laminin-1 inhibited induction of MMP-1 but laminin-5 did not. Taken together, these observations suggest that as basal keratinocytes migrate from the basal lamina onto the dermal matrix contact with native type I collagen induces MMP-1 expression. In addition, our findings suggest that re-establishment of the basement membrane and, in particular, contact with laminin-1 provides a potent signal to down-regulate MMP-1 production as the epithelium is repaired.

The activity of collagenase-1 is required for keratinocyte migration on a type I collagen matrix

We have shown in a variety of human wounds that collagenase-1 (MMP-1), a matrix metalloproteinase that cleaves fibrillar type I collagen, is invariably expressed by basal keratinocytes migrating across the dermal matrix. Furthermore, we have demonstrated that MMP-1 expression is induced in primary keratinocytes by contact with native type I collagen and not by basement membrane proteins or by other components of the dermal or provisional (wound) matrix. Based on these observations, we hypothesized that the catalytic activity of MMP-1 is necessary for keratinocyte migration on type I collagen. To test this idea, we assessed keratinocyte motility on type I collagen using colony dispersion and colloidal gold migration assays. In both assays, primary human keratinocytes migrated efficiently on collagen. The specificity of MMP-1 in promoting cell movement was demonstrated in four distinct experiments. One, keratinocyte migration was completely blocked by peptide hydroxymates, which are potent inhibitors of the catalytic activity of MMPs. Two, HaCaTs, a line of human keratinocytes that do not express MMP-1 in response to collagen, did not migrate on a type I collagen matrix but moved efficiently on denatured type I collagen (gelatin). EGF, which induces MMP-I production by HaCaT cells, resulted in the ability of these cells to migrate across a type I collagen matrix. Three, keratinocytes did not migrate on mutant type I collagen lacking the collagenase cleavage site, even though this substrate induced MMP-1 expression. Four, cell migration on collagen was completely blocked by recombinant tissue inhibitor of metalloproteinase-1 (TIMP-1) and by affinity-purified anti-MMP-1 antiserum. In addition, the collagen-mediated induction of collagenase-1 and migration of primary keratinocytes on collagen was blocked by antibodies against the alpha2 integrin subunit but not by antibodies against the alpha1 or alpha3 subunits. We propose that interaction of the alpha2beta1 integrin with dermal collagen mediates induction of collagenase-1 in keratinocytes at the onset of healing and that the activity of collagenase-1 is needed to initiate cell movement. Furthermore, we propose that cleavage of dermal collagen provides keratinocytes with a mechanism to maintain their directionality during reepithelialization.

Laminin-alpha2 but not -alpha1-mediated adhesion of human (Duchenne) and murine (mdx) dystrophic myotubes is seriously defective

It has been suggested that alpha-dystroglycan links the dystrophin-associated protein complex and extracellular matrix and that the absence of dystrophin and alpha-dystroglycan in Duchenne muscular dystrophy (DMD) may lead to the breakdown of this linkage. In the present study, myotubes from DMD patients and murine X-linked muscular dystrophic mice (mdx) were used to measure their adhesive force to the physiological laminin-alpha2 substrate, and it was found that the dystrophic myotubes were selectively unable to sustain adhesion. However, normal and dystrophic myotubes attached equally well to the laminin-alpha1 substrate. As far as we know, this is the first experimental evidence that the absence of dystrophin causes the complete loss of a still unknown laminin-alpha2-dependent adhesion force, therefore suggesting that the primary consequence of Duchenne dystrophy consists of the loss of an authentic mechanical linkage at the level of the alpha-dystroglycan/basal lamina interface.