Bidirectional extracellular matrix signaling during tissue morphogenesis

Looking both ways: Electroactive biomaterials with bidirectional implications for dynamic cell-material crosstalk

Cells exist in natural, dynamic microenvironmental niches that facilitate biological responses to external physicochemical cues such as mechanical and electrical stimuli. For excitable cells, exogenous electrical cues are of interest due to their ability to stimulate or regulate cellular behavior via cascade signaling involving ion channels, gap junctions, and integrin receptors across the membrane. In recent years, conductive biomaterials have been demonstrated to influence or record these electrosensitive biological processes whereby the primary design criterion is to achieve seamless cell-material integration. As such, currently available bioelectronic materials are predominantly engineered toward achieving high-performing devices while maintaining the ability to recapitulate the local excitable cell/tissue microenvironment. However, such reports rarely address the dynamic signal coupling or exchange that occurs at the biotic-abiotic interface, as well as the distinction between the ionic transport involved in natural biological process and the electronic (or mixed ionic/electronic) conduction commonly responsible for bioelectronic systems. In this review, we highlight current literature reports that offer platforms capable of bidirectional signal exchange at the biotic-abiotic interface with excitable cell types, along with the design criteria for such biomaterials. Furthermore, insights on current materials not yet explored for biointerfacing or bioelectronics that have potential for bidirectional applications are also provided. Finally, we offer perspectives aimed at bringing attention to the coupling of the signals delivered by synthetic material to natural biological conduction mechanisms, areas of improvement regarding characterizing biotic-abiotic crosstalk, as well as the dynamic nature of this exchange, to be taken into consideration for material/device design consideration for next-generation bioelectronic systems.

Squishy matters - Corneal mechanobiology in health and disease

The cornea, as a dynamic and responsive tissue, constantly interacts with mechanical forces in order to maintain its structural integrity, barrier function, transparency and refractive power. Cells within the cornea sense and respond to various mechanical forces that fundamentally regulate their morphology and fate in development, homeostasis and pathophysiology. Corneal cells also dynamically regulate their extracellular matrix (ECM) with ensuing cell-ECM crosstalk as the matrix serves as a dynamic signaling reservoir providing biophysical and biochemical cues to corneal cells. Here we provide an overview of mechanotransduction signaling pathways then delve into the recent advances in corneal mechanobiology, focusing on the interplay between mechanical forces and responses of the corneal epithelial, stromal, and endothelial cells. We also identify species-specific differences in corneal biomechanics and mechanotransduction to facilitate identification of optimal animal models to study corneal wound healing, disease, and novel therapeutic interventions. Finally, we identify key knowledge gaps and therapeutic opportunities in corneal mechanobiology that are pressing for the research community to address especially pertinent within the domains of limbal stem cell deficiency, keratoconus and Fuchs' endothelial corneal dystrophy. By furthering our understanding corneal mechanobiology, we can contextualize discoveries regarding corneal diseases as well as innovative treatments for them.

The Impact of the Cellular Environment and Aging on Modeling Alzheimer's Disease in 3D Cell Culture Models

Creating a cellular model of Alzheimer's disease (AD) that accurately recapitulates disease pathology has been a longstanding challenge. Recent studies showed that human AD neural cells, integrated into three-dimensional (3D) hydrogel matrix, display key features of AD neuropathology. Like in the human brain, the extracellular matrix (ECM) plays a critical role in determining the rate of neuropathogenesis in hydrogel-based 3D cellular models. Aging, the greatest risk factor for AD, significantly alters brain ECM properties. Therefore, it is important to understand how age-associated changes in ECM affect accumulation of pathogenic molecules, neuroinflammation, and neurodegeneration in AD patients and in vitro models. In this review, mechanistic hypotheses is presented to address the impact of the ECM properties and their changes with aging on AD and AD-related dementias. Altered ECM characteristics in aged brains, including matrix stiffness, pore size, and composition, will contribute to disease pathogenesis by modulating the accumulation, propagation, and spreading of pathogenic molecules of AD. Emerging hydrogel-based disease models with differing ECM properties provide an exciting opportunity to study the impact of brain ECM aging on AD pathogenesis, providing novel mechanistic insights. Understanding the role of ECM aging in AD pathogenesis should also improve modeling AD in 3D hydrogel systems.

Biology of cancer; from cellular and molecular mechanisms to developmental processes and adaptation

Cancer research has been largely focused on the cellular and molecular levels of investigation. Recent data show that not only the cell but also the extracellular matrix plays a major role in the progression of malignancy. In this way, the cells and the extracellular matrix create a specific local microenvironment that supports malignant development. At the same time, cancer implies a systemic evolution which is closely related to developmental processes and adaptation. Consequently, there is currently a real gap between the local investigation of cancer at the microenvironmental level, and the pathophysiological approach to cancer as a systemic disease. In fact, the cells and the matrix are not only complementary structures but also interdependent components that act synergistically. Such relationships lead to cell-matrix integration, a supracellular form of biological organization that supports tissue development. The emergence of this supracellular level of organization, as a structure, leads to the emergence of the supracellular control of proliferation, as a supracellular function. In humans, proliferation is generally involved in developmental processes and adaptation. These processes suppose a specific configuration at the systemic level, which generates high-order guidance for local supracellular control of proliferation. In conclusion, the supracellular control of proliferation act as an interface between the downstream level of cell division and differentiation, and upstream level of developmental processes and adaptation. Understanding these processes and their disorders is useful not only to complete the big picture of malignancy as a systemic disease, but also to open new treatment perspectives in the form of etiopathogenic (supracellular or informational) therapies.

Transcriptome analysis reveals hepatotoxicity in zebrafish induced by cyhalofop‑butyl

Cyhalofop‑butyl is a highly effective aryloxyphenoxypropionate herbicide and widely used for weed control in paddy fields. With the increasing residue of cyhalofop‑butyl, it poses a threat to the survival of aquatic organisms. Here, we investigated the effect of cyhalofop‑butyl on zebrafish to explore its potential hepatotoxic mechanism. The results showed that cyhalofop‑butyl induced hepatocyte degeneration, vacuolation and necrosis of larvae after embryonic exposure for 4 days and caused liver atrophy after 5 days. Meanwhile, the activities of enzymes related to liver function were significantly increased by 0.2 mg/L cyhalofop‑butyl and higher, such as alanine transaminase (ALT) and aspartate transaminase (AST). And the contents of triglyceride (TG) involved in lipid metabolism were significantly decreased by 0.4 mg/L cyhalofop-buty. The expression of genes related to liver development was also significantly down-regulated. Furthermore, transcriptome results showed that the pathways involved in metabolism, immune system and endocrine system were significantly impacted, which may be related to hepatoxicity. To sum up, the present study demonstrated the hepatoxicity caused by cyhalofop-buty and its underlying mechanism. The results may provide new insights for the risk of cyhalofop‑butyl to aquatic organisms and new horizons for the pathogenesis of hepatotoxicity.

Chondrogenic differentiation of mesenchymal stem cells through cartilage matrix-inspired surface coatings

The stem cell niche comprises soluble molecules and extracellular matrix components which provide chemical and mechanical cues that determine the differentiation of stem cells. Here, the effect of polyelectrolyte multilayer (PEM) composition and terminal layer fabricated with layer-by-layer technique (LBL) pairing either hyaluronan [in its native (nHA) and oxidized form (oHA)] or chondroitin sulfate (CS) with type I collagen (Col I) is investigated on chondrogenic differentiation of human umbilical mesenchymal stem cells (hUC-MSCs). Physical studies performed to investigate the establishment and structure of the surface coatings show that PEM composed of HA and Col I show a dominance of nHA or oHA with considerably lesser organization of Col I fibrils. In contrast, distinguished fibrilized Col I is found in nCS-containing PEM. Generally, Col I-terminated PEM promote the adhesion, migration, and growth of hUC-MSCs more than GAG-terminated surfaces due to the presence of fibrillar Col I but show a lower degree of differentiation towards the chondrogenic lineage. Notably, the Col I/nHA PEM not only supports adhesion and growth of hUC-MSCs but also significantly promotes cartilage-associated gene and protein expression as found by histochemical and molecular biology studies, which is not seen on the Col I/oHA PEM. This is related to ligation of HA to the cell receptor CD44 followed by activation of ERK/Sox9 and noncanonical TGF-β signaling-p38 pathways that depends on the molecular weight of HA as found by immune histochemical and western blotting. Hence, surface coatings on scaffolds and other implants by PEM composed of nHA and Col I may be useful for programming MSC towards cartilage regeneration.

Roles of Chondroitin Sulfate Proteoglycans as Regulators of Skeletal Development

The extracellular matrix (ECM) is critically important for most cellular processes including differentiation, morphogenesis, growth, survival and regeneration. The interplay between cells and the ECM often involves bidirectional signaling between ECM components and small molecules, i.e., growth factors, morphogens, hormones, etc., that regulate critical life processes. The ECM provides biochemical and contextual information by binding, storing, and releasing the bioactive signaling molecules, and/or mechanical information that signals from the cell membrane integrins through the cytoskeleton to the nucleus, thereby influencing cell phenotypes. Using these dynamic, reciprocal processes, cells can also remodel and reshape the ECM by degrading and re-assembling it, thereby sculpting their environments. In this review, we summarize the role of chondroitin sulfate proteoglycans as regulators of cell and tissue development using the skeletal growth plate model, with an emphasis on use of naturally occurring, or created mutants to decipher the role of proteoglycan components in signaling paradigms.

Metabolic labeling of secreted matrix to investigate cell-material interactions in tissue engineering and mechanobiology

Re-creating features of the native extracellular matrix (ECM) with engineered biomaterials has become a valuable tool to probe the influence of ECM properties on cellular functions (e.g., differentiation) and toward the engineering of tissues. However, characterization of newly secreted (nascent) matrix and turnover, which are important in the context of cells interacting with these biomaterials, has been limited by a lack of tools. We developed a protocol to visualize and quantify the spatiotemporal evolution of newly synthesized and deposited matrix by cells that are either cultured atop (2D) or embedded within (3D) biomaterial systems (e.g., hydrogels, fibrous matrices). This technique relies on the incorporation of a noncanonical amino acid (azidohomoalanine) into proteins as they are synthesized. Deposited nascent ECM components are then visualized with fluorescent cyclooctynes via copper-free cycloaddition for spatiotemporal analysis or modified with cleavable biotin probes for identification. Here we describe the preparation of hyaluronic acid hydrogels through ultraviolet or visible light induced cross-linking for 2D and 3D cell culture, as well as the fluorescent labeling of nascent ECM deposited by cells during culture. We also provide protocols for secondary immunofluorescence of specific ECM components and ImageJ-based ECM quantification methods. Hyaluronic acid polymer synthesis takes 2 weeks to complete, and hydrogel formation for 2D or 3D cell culture is performed in 2-3 h. Lastly, we detail the identification of nascent proteins, including enrichment, preparation and analysis with mass spectrometry, which can be completed in 10 d.

Preservation of the naïve features of mesenchymal stromal cells in vitro: Comparison of cell- and bone-derived decellularized extracellular matrix

The fate and behavior of bone marrow mesenchymal stem/stromal cells (BM-MSC) is bidirectionally influenced by their microenvironment, the stem cell niche, where a magnitude of biochemical and physical cues communicate in an extremely orchestrated way. It is known that simplified 2D in vitro systems for BM-MSC culture do not represent their naïve physiological environment. Here, we developed four different 2D cell-based decellularized matrices (dECM) and a 3D decellularized human trabecular-bone scaffold (dBone) to evaluate BM-MSC behavior. The obtained cell-derived matrices provided a reliable tool for cell shape-based analyses of typical features associated with osteogenic differentiation at high-throughput level. On the other hand, exploratory proteomics analysis identified native bone-specific proteins selectively expressed in dBone but not in dECM models. Together with its architectural complexity, the physico-chemical properties of dBone triggered the upregulation of stemness associated genes and niche-related protein expression, proving in vitro conservation of the naïve features of BM-MSC.

Cumulus Extracellular Matrix Is an Important Part of Oocyte Microenvironment in Ovarian Follicles: Its Remodeling and Proteolytic Degradation

The extracellular matrix (ECM) is an essential structure with biological activities. It has been shown that the ECM influences gene expression via cytoskeletal components and the gene expression is dependent upon cell interactions with molecules and hormones. The development of ovarian follicles is a hormone dependent process. The surge in the luteinizing hormone triggers ovulatory changes in oocyte microenvironment. In this review, we discuss how proteolytic cleavage affects formation of cumulus ECM following hormonal stimulation; in particular, how the specific proteasome inhibitor MG132 affects gonadotropin-induced cytoskeletal structure, the organization of cumulus ECM, steroidogenesis, and nuclear maturation. We found that after the inhibition of proteolytic cleavage, gonadotropin-stimulated oocyte-cumulus complexes (OCCs) were without any signs of cumulus expansion; they remained compact with preserved cytoskeletal F-actin-rich transzonal projections through the oocyte investments. Concomitantly, a significant decrease was detected in progesterone secretion and in the expression of gonadotropin-stimulated cumulus expansion-related transcripts, such as HAS2 and TNFAIP6. In agreement, the covalent binding between hyaluronan and the heavy chains of serum-derived the inter-alpha-trypsin inhibitor, essential for the organization of cumulus ECM, was missing.

Changes in the Transcriptome and Proteome of Cartilage in Microtia

ABSTRACT

Congenital microtia is a severe physiological defect and is among the most common craniofacial defects. It is characterized by severe auricle dysplasia, external auditory canal atresia or stenosis, and middle ear malformation, though inner ear development is mostly normal with some hearing occurring through bone conduction. Auricular reconstruction is the only treatment for congenital microtia. In this study, the authors integrated messenger ribonucleic acid and mass spectrometry data of cartilage obtained from the affected and unaffected sides of 16 unilateral microtia patients who had undergone ear reconstruction surgery. The authors next performed functional analyses to investigate differences in the proteome of the affected and unaffected ears to elicit molecular pathways involved in microtia pathogenesis. The authors collected 16 pairs samples. Proteomic and transcriptomic analyses identified 47 genes that were differentially expressed in affected and unaffected cartilage. Integrated pathway analysis implicated the involvement of genes related to cell adhesion, extracellular matrix organization, and cell migration in disease progression. Through the integration of gene and protein expression data in human primary chondrocytes, the authors identified molecular markers of microtia progression that were replicated across independent datasets and that have translational potential.

Effects of biophysical cues of 3D hydrogels on mesenchymal stem cells differentiation

For stem cell research, three-dimensional (3D) hydrogels are increasingly recognized as more physiological systems than two-dimensional culture plates due to bidirectional and 3D interaction of stem cells and surrounding matrix. Among various stem cells, mesenchymal stem cells (MSCs) are one of the most widely applied from bench to bedside. In 3D hydrogels, MSCs are allowed to actively remodel the surrounding matrix through proteolytic degradation and cell-exerted force, which highly resembles in vivo situation. Notably, factors affecting hydrogel modifiability including matrix viscoelasticity and matrix degradability have been found to regulate adhesion, morphology, and fate decision of MSCs. In addition, MSCs within 3D hydrogels have been found to employ multiple mechanotransduction mechanisms including not only the classic integrin-actomyosin cytoskeleton system but also ion channels, microtubule cytoskeleton, and self-secreted proteinaceous matrix. This review summarizes the effects of biophysical cues on MSCs differentiation in 3D hydrogels and underlying mechanobiology in a hope to update our readers' understanding of stem cell biology and guide tissue engineering.

Interaction between extracellular cancer matrix and stromal breast cells

INTRODUCTION

Stromal-epithelial interactions are fundamental for normal organ development and there is a multitude of evidence that the different components of the microenvironment are also necessary for the maintenance and promotion of the "tumor organ". Deregulated tumor associated extracellular matrix (tECM) is a hallmark of cancer, causing an alteration in the amount and composition of the different components (i.e. proteins, proteoglycans, glycoproteins and polysaccharids) of the ECM. As epithelial-stromal interactions are reciprocal, it is possible that tECM itself is able to initiate tumor development. We therefore established a mouse model to examine the influence of tECM of murine breast cancer on developing breast tissue in mice.

MATERIALS AND METHODS

Breast cancer was established in 5 BALB/c mice by subcutaneous injection of 1×106 4T1 cells in 100μl PBS into the left mammary fat pad. The mammary fat pad including the primary tumor was excised after two weeks, decellularised and labelled as tumor extracellular matrix (tECM). Tumor ECM of 4T1 tumors was implanted into the 4th inguinal mammary fat pad of BALB/c mice (n = 5) aged 5 days. After 12 weeks the fourth mammary fat pad including the primary tumor was excised. Tissue was used for paraffin embedding and mouse breast cancer PCR array. Murine breast cancer tissue (BCT) and normal murine breast tissue (BT) served as control.

RESULTS

Gene array analysis of 84 breast cancer-specific transcripts revealed that the mammary gland cells which were exposed to tumor ECM (tECM-BT) showed a similarly high overexpression for 22 genes as apparent for breast cancer tissue (BCT). The corresponding scatter plot showed a high agreement in the expression of the examined genes between the mammary gland cells which were exposed to tumor ECM and the breast cancer tissue.

DISCUSSION

Our results clearly demonstrate that the tECM is able to shift the gene expression pattern of murine mammary epithelial cells towards that of carcinoma, indicating a role in breast cancer initiation. These data underlines that the acellular component of the tumor (ECM) can lead to a transformation of mammary gland tissue cells. These data show for the first time that the interaction of normal breast tissue cells with tumor ECM leads to an exchange of information and a consecutive overexpression of tumor-specific genes.

Esophageal Cancer Development: Crucial Clues Arising from the Extracellular Matrix

In the last years, the extracellular matrix (ECM) has been reported as playing a relevant role in esophageal cancer (EC) development, with this compartment being related to several aspects of EC genesis and progression. This sounds very interesting due to the complexity of this highly incident and lethal tumor, which takes the sixth position in mortality among all tumor types worldwide. The well-established increase in ECM stiffness, which is able to trigger mechanotransduction signaling, is capable of regulating several malignant behaviors by converting alteration in ECM mechanics into cytoplasmatic biochemical signals. In this sense, it has been shown that some molecules play a key role in these events, particularly the different collagen isoforms, as well as enzymes related to its turnover, such as lysyl oxidase (LOX) and matrix metalloproteinases (MMPs). In fact, MMPs are not only involved in ECM stiffness, but also in other events related to ECM homeostasis, which includes ECM remodeling. Therefore, the crucial role of distinct MMPs isoform has already been reported, especially MMP-2, -3, -7, and -9, along EC development, thus strongly associating these proteins with the control of important cellular events during tumor progression, particularly in the process of invasion during metastasis establishment. In addition, by distinct mechanisms, a vast diversity of glycoproteins and proteoglycans, such as laminin, fibronectin, tenascin C, galectin, dermatan sulfate, and hyaluronic acid exert remarkable effects in esophageal malignant cells due to the activation of oncogenic signaling pathways mainly involved in cytoskeleton alterations during adhesion and migration processes. Finally, the wide spectrum of interactions potentially mediated by ECM may represent a singular intervention scenario in esophageal carcinogenesis natural history and, due to the scarce knowledge on the cellular and molecular mechanisms involved in EC development, the growing body of evidence on ECM’s role along esophageal carcinogenesis might provide a solid base to improve its management in the future.

Multi-cell ECM compaction is predictable via superposition of nonlinear cell dynamics linearized in augmented state space

Cells interacting through an extracellular matrix (ECM) exhibit emergent behaviors resulting from collective intercellular interaction. In wound healing and tissue development, characteristic compaction of ECM gel is induced by multiple cells that generate tensions in the ECM fibers and coordinate their actions with other cells. Computational prediction of collective cell-ECM interaction based on first principles is highly complex especially as the number of cells increase. Here, we introduce a computationally-efficient method for predicting nonlinear behaviors of multiple cells interacting mechanically through a 3-D ECM fiber network. The key enabling technique is superposition of single cell computational models to predict multicellular behaviors. While cell-ECM interactions are highly nonlinear, they can be linearized accurately with a unique method, termed Dual-Faceted Linearization. This method recasts the original nonlinear dynamics in an augmented space where the system behaves more linearly. The independent state variables are augmented by combining auxiliary variables that inform nonlinear elements involved in the system. This computational method involves a) expressing the original nonlinear state equations with two sets of linear dynamic equations b) reducing the order of the augmented linear system via principal component analysis and c) superposing individual single cell-ECM dynamics to predict collective behaviors of multiple cells. The method is computationally efficient compared to original nonlinear dynamic simulation and accurate compared to traditional Taylor expansion linearization. Furthermore, we reproduce reported experimental results of multi-cell induced ECM compaction.

Collective behaviors of multiple cells interacting through an ECM are prohibitively complex to predict with a mechanistic computational model due to its highly nonlinear dynamics and high dimensional space. We introduce a methodology where nonlinear dynamics of single cells are superposed to predict collective multi-cellular behaviors through a developed linearization method. We represent nonlinear single cell dynamics with linear state equations by augmenting the independent state variables with a set of auxiliary variables. We then transform the linear augmented state equations to a low-dimensional latent model and superpose the linear latent models of individual cells to predict collective behaviors that emerge from multi-cellular interactions. The method successfully reproduced experimental results of cell-induced ECM compaction.

Local nascent protein deposition and remodelling guide mesenchymal stromal cell mechanosensing and fate in three-dimensional hydrogels

Hydrogels serve as valuable tools for studying cell-extracellular matrix interactions in three-dimensional environments that recapitulate aspects of native extracellular matrix. However, the impact of early protein deposition on cell behaviour within hydrogels has largely been overlooked. Using a bio-orthogonal labelling technique, we visualized nascent proteins within a day of culture across a range of hydrogels. In two engineered hydrogels of interest in three-dimensional mechanobiology studies-proteolytically degradable covalently crosslinked hyaluronic acid and dynamic viscoelastic hyaluronic acid hydrogels-mesenchymal stromal cell spreading, YAP/TAZ nuclear translocation and osteogenic differentiation were observed with culture. However, inhibition of cellular adhesion to nascent proteins or reduction in nascent protein remodelling reduced mesenchymal stromal cell spreading and nuclear translocation of YAP/TAZ, resulting in a shift towards adipogenic differentiation. Our findings emphasize the role of nascent proteins in the cellular perception of engineered materials and have implications for in vitro cell signalling studies and application to tissue repair.

Initiating Events in Direct Cardiomyocyte Reprogramming

Direct reprogramming of fibroblasts into cardiomyocyte-like cells (iCM) holds great potential for heart regeneration and disease modeling and may lead to future therapeutic applications. Currently, application of this technology is limited by our lack of understanding of the molecular mechanisms that drive direct iCM reprogramming. Using a quantitative mass spectrometry-based proteomic approach, we identified the temporal global changes in protein abundance that occur during initial phases of iCM reprogramming. Collectively, our results show systematic and temporally distinct alterations in levels of specific functional classes of proteins during the initiating steps of reprogramming including extracellular matrix proteins, translation factors, and chromatin-binding proteins. We have constructed protein relational networks associated with the initial transition of a fibroblast into an iCM. These findings demonstrate the presence of an orchestrated series of temporal steps associated with dynamic changes in protein abundance in a defined group of protein pathways during the initiating events of direct reprogramming.

Evaluation of the developmental toxicity of 2,7-dibromocarbazole to zebrafish based on transcriptomics assay

Polyhalogenated carbazoles (PHCZs), which have the similar structure of dioxin, have been reported ubiquitous in the environments and drawn wide concerns. However, their potential ecological and health risks are still poorly understood. Here, wildtype zebrafish embryos were used to evaluate the environmental risks of 2,7-dibromocarbazole (2,7-DBCZ), 3,6-dibromocarbazole (3,6-DBCZ), and 3,6-dichlorocarbazole (3,6-DCCZ). 2,7-DBCZ was the most toxic compound with the 96-h LC₅₀ value of 581.8 ± 29.3 μg·L^-1 and the EC₅₀ value of 201.5 ± 6.5 μg·L^-1 for pericardial edema. The teratogenic effects of 2,7-DBCZ were tested using transgenic zebrafish larvae. The transcriptomic analysis revealed that 90 genes in zebrafish expressed differently after exposure to 2,7-DBCZ, and many pathways were related to aryl hydrocarbon receptor (AhR) activation. The qRT-PCR also showed that expression levels of AhR1 and CYP1 A in zebrafish were significantly up-regulated after exposure to 2,7-DBCZ. In conclusion, 2,7-DBCZ exhibited more potent toxicity and cardiac teratogenic effects, and presented developmental toxicity partially consistent with AhR activation. Our results will be of great help to the risk assessment and regulation-making of PHCZs. Meanwhile, further studies should be promoted to illustrate the potential mechanism between PHCZs and AhR in the near future.

The adhesion receptor GPR56 is activated by extracellular matrix collagen III to improve β-cell function

AIMS

G-protein coupled receptor 56 (GPR56) is the most abundant islet-expressed G-protein coupled receptor, suggesting a potential role in islet function. This study evaluated islet expression of GPR56 and its endogenous ligand collagen III, and their effects on β-cell function.

METHODS

GPR56 and collagen III expression in mouse and human pancreas sections was determined by fluorescence immunohistochemistry. Effects of collagen III on β-cell proliferation, apoptosis, intracellular calcium ([Ca2+]i) and insulin secretion were determined by cellular BrdU incorporation, caspase 3/7 activities, microfluorimetry and radioimmunoassay, respectively. The role of GPR56 in islet vascularisation and innervation was evaluated by immunohistochemical staining for CD31 and TUJ1, respectively, in pancreases from wildtype (WT) and Gpr56-/- mice, and the requirement of GPR56 for normal glucose homeostasis was determined by glucose tolerance tests in WT and Gpr56-/- mice.

RESULTS

Immunostaining of mouse and human pancreases revealed that GPR56 was expressed by islet β-cells while collagen III was confined to the peri-islet basement membrane and islet capillaries. Collagen III protected β-cells from cytokine-induced apoptosis, triggered increases in [Ca2+]i and potentiated glucose-induced insulin secretion from WT islets but not from Gpr56-/- islets. Deletion of GPR56 did not affect glucose-induced insulin secretion in vitro and it did not impair glucose tolerance in adult mice. GPR56 was not required for normal islet vascularisation or innervation.

CONCLUSION

We have demonstrated that collagen III improves islet function by increasing insulin secretion and protecting against apoptosis. Our data suggest that collagen III may be effective in optimising islet function to improve islet transplantation outcomes, and GPR56 may be a target for the treatment of type 2 diabetes.

Design of synthetic extracellular matrices for probing breast cancer cell growth using robust cyctocompatible nucleophilic thiol-yne addition chemistry

Controlled, three-dimensional (3D) cell culture systems are of growing interest for both tissue regeneration and disease, including cancer, enabling hypothesis testing about the effects of microenvironment cues on a variety of cellular processes, including aspects of disease progression. In this work, we encapsulate and culture in three dimensions different cancer cell lines in a synthetic extracellular matrix (ECM), using mild and efficient chemistry. Specifically, harnessing the nucleophilic addition of thiols to activated alkynes, we have created hydrogel-based materials with multifunctional poly(ethylene glycol) (PEG) and select biomimetic peptides. These materials have definable, controlled mechanical properties (G' = 4-10 kPa) and enable facile incorporation of pendant peptides for cell adhesion, relevant for mimicking soft tissues, where polymer architecture allows tuning of matrix degradation. These matrices rapidly formed in the presence of sensitive breast cancer cells (MCF-7) for successful encapsulation with high cell viability, greatly improved relative to that observed with the more widely used radically-initiated thiol-ene crosslinking chemistry. Furthermore, controlled matrix degradation by both bulk and local mechanisms, ester hydrolysis of the polymer network and cell-driven enzymatic hydrolysis of cell-degradable peptide, allowed cell proliferation and the formation of cell clusters within these thiol-yne hydrogels. These studies demonstrate the importance of chemistry in ECM mimics and the potential thiol-yne chemistry has as a crosslinking reaction for the encapsulation and culture of cells, including those sensitive to radical crosslinking pathways.

Applications of Cardiac Extracellular Matrix in Tissue Engineering and Regenerative Medicine

The role of the cardiac extracellular matrix (cECM) in providing biophysical and biochemical cues to the cells housed within during disease and development has become increasingly apparent. These signals have been shown to influence many fundamental cardiac cell behaviors including contractility, proliferation, migration, and differentiation. Consequently, alterations to cell phenotype result in directed remodeling of the cECM. This bidirectional communication means that the cECM can be envisioned as a medium for information storage. As a result, the reprogramming of the cECM is increasingly being employed in tissue engineering and regenerative medicine as a method with which to treat disease. In this chapter, an overview of the composition and structure of the cECM as well as its role in cardiac development and disease will be provided. Additionally, therapeutic modulation of cECM for cardiac regeneration as well as bottom-up and top-down approaches to ECM-based cardiac tissue engineering is discussed. Finally, lingering questions regarding the role of cECM in tissue engineering and regenerative medicine are offered as a catalyst for future research.

TM4SF5 promotes metastatic behavior of cells in 3D extracellular matrix gels by reducing dependency on environmental cues

Transmembrane 4 L six family member 5 (TM4SF5) is highly expressed in hepatocellular carcinoma tissues and enhances migration in two-dimensional environments. Here, we investigated how TM4SF5 is involved in diverse pro-metastatic phenotypes in in vivo-like three-dimensional (3D) extracellular matrix gels. TM4SF5-positive cells aggressively formed invasive foci in 3D Matrigel, depending on TM4SF5-mediated signaling activity, cytoskeletal organization, and matrix metallopeptidase (MMP) 2-mediated extracellular remodeling, whereas TM4SF5-null cells did not. The TM4SF5-null cells did, however, form invasive foci in 3D Matrigel following inhibition of Rho-associated protein kinase or addition of collagen I, suggesting that collagen I compensated for TM4SF5 expression. Similarly, TM4SF5-positive cells expressing vascular endothelial-cadherin formed network-like vasculogenic mimicry in 3D Matrigel and collagen I mixture gels, whereas TM4SF5-negative cells in the mixture gels displayed the network structures only upon further treatment with epidermal growth factor. The foci formation also required MMP2-mediated remodeling of the extracellular matrix. Co-cultures exhibited TM4SF5-positive or cancer-associated fibroblasts at the outward edges of TM4SF5-null cell clusters. Compared with TM4SF5-null cells, TM4SF5-positive cells in 3D collagen gels showed a more invasive outgrowth with dramatic invadopodia. These observations suggest that TM4SF5 plays roles in the promotion of diverse metastatic properties with fewer environmental requirements than TM4SF5-negative cells.

Endogenous and Exogenous Stem/Progenitor Cells in the Lung and Their Role in the Pathogenesis and Treatment of Pediatric Lung Disease

The lung is a complex organ with a vast surface area whose main function is to release cellular waste to be exhaled and to replenish the supply of oxygen to the tissues of the body. The conduction of air from the external environment is not without risks, and the lung contains many specialized epithelial cell subtypes that are protecting the lung from foreign material and injury. Specialized cell subtypes are produced during lung development in the fetus as well as postnatally and injury to them due to genetic disease, premature birth, or postnatal environmental injury may lead to devastating disease. Chronic diseases, such as bronchopulmonary dysplasia, cystic fibrosis, and pulmonary arterial hypertension, contribute significantly to morbidity and mortality worldwide, yet successful interventions are often limited. Stem/progenitor cells have emerged as a potentially new preventative or therapeutic option. They are generally defined by the ability to undergo self-renewal and give rise to more differentiated cells. They are important in the early development of embryonic structures and organ differentiation in utero. Postnatally, they function in continued growth, maintenance, and regeneration. Clinically, the immunomodulatory properties of some classes of stem/progenitor cells avoid the major obstacle of immunological rejection seen in organ transplantation and other cell therapies. This review highlights some known human progenitor/stem cells and the most recent advances in stem cell therapies both in vivo and in vitro to prevent and treat pediatric lung disease.

Review of the cellular and biological principles of distraction osteogenesis: An in vivo bioreactor tissue engineering model

Distraction osteogenesis (DO) is a widely used technique in plastic and orthopaedic surgery. During the process, mechanical force is applied to fractured bone to enhance the regenerative processes and induce new bone formation. Although there is an abundance of literature on the clinical process of DO, there is a distinct lack of focus on the underlying biological principles governing this process. DO follows the basic premises of tissue engineering. The mechanical stress stimulates mesenchymal stem cell differentiation down an osteoblastic lineage on a matrix background. The aim of this review is to give an overview of the current knowledge of the molecular mechanism governing this process.

Hydrogel patterning by diffusion through the matrix and subsequent light-triggered chemical immobilization

A novel approach to hyaluronic acid (HA) hydrogel with a chemical gradient of the matrix-linked bisphosphonate (BP) groups is presented. The method consists of two steps, including initial generation of physical gradient patterns of BPs by diffusion of BP acrylamide reagent into HA matrix carrying thiol groups and subsequent chemical immobilization of the BP groups by UV light-triggered thiol-ene addition reaction. This gradient hydrogel permits spatial three-dimensional regulation of secondary interactions of different molecules with the polymer matrix. In particular, graded amounts of cytochrome c (cyt c) were reversibly absorbed in the hydrogel, thus enabling the subsequent spatially controlled release of the therapeutic protein. The obtained patterned hydrogel acts also as a unique reactor in which peroxidase-catalyzed oxidation of a substrate is determined by spatial position of the enzyme (cyt c) in the matrix resulting in a range of product concentrations. As an example, matrix template-assisted oxidation of 3,3',5,5'-tetarmethylbenzydine (TMB) in the presence of H2O2 occurs simultaneously at different rates within the gradient hydrogel. Moreover, calcium binding to the gradient HABP hydrogel reflects the pattern of immobilized BP groups eventually leading to the graded biomineralization of the matrix. This approach opens new possibilities for use of hydrogels as dynamic models for biologic three-dimensional structures such as extracellular matrix.

Extracellular matrix signaling in morphogenesis and repair

The extracellular matrix (ECM) is critically important for many cellular processes including growth, differentiation, survival, and morphogenesis. Cells remodel and reshape the ECM by degrading and reassembling it, playing an active role in sculpting their surrounding environment and directing their own phenotypes. Both mechanical and biochemical molecules influence ECM dynamics in multiple ways; by releasing small bioactive signaling molecules, releasing growth factors stored within the ECM, eliciting structural changes to matrix proteins which expose cryptic sites and by degrading matrix proteins directly. The dynamic reciprocal communication between cells and the ECM plays a fundamental roll in tissue development, homeostasis, and wound healing.

Mapping of mechanical strains and stresses around quiescent engineered three-dimensional epithelial tissues

Understanding how physical signals guide biological processes requires qualitative and quantitative knowledge of the mechanical forces generated and sensed by cells in a physiologically realistic three-dimensional (3D) context. Here, we used computational modeling and engineered epithelial tissues of precise geometry to define the experimental parameters that are required to measure directly the mechanical stress profile of 3D tissues embedded within native type I collagen. We found that to calculate the stresses accurately in these settings, we had to account for mechanical heterogeneities within the matrix, which we visualized and quantified using confocal reflectance and atomic force microscopy. Using this technique, we were able to obtain traction forces at the epithelium-matrix interface, and to resolve and quantify patterns of mechanical stress throughout the surrounding matrix. We discovered that whereas single cells generate tension by contracting and pulling on the matrix, the contraction of multicellular tissues can also push against the matrix, causing emergent compression. Furthermore, tissue geometry defines the spatial distribution of mechanical stress across the epithelium, which communicates mechanically over distances spanning hundreds of micrometers. Spatially resolved mechanical maps can provide insight into the types and magnitudes of physical parameters that are sensed and interpreted by multicellular tissues during normal and pathological processes.

Involvement of matrix metalloproteinase-2 in the development of renal interstitial fibrosis in mouse obstructive nephropathy

Renal fibrosis is a common finding in progressive renal diseases. Matrix metalloproteinases (MMPs) are involved in epithelial-to-mesenchymal transition (EMT). We investigated the role of MMP-2 and the effect of inhibition of MMPs on the development of renal fibrosis. Renal fibrosis was induced in MMP-2 wild-type (MMP-2⁺/⁺) mice by unilateral ureteral obstruction (UUO). Renal histopathology, EMT-associated molecules, and activity of MMP-2 and MMP-9 were examined during the development of interstitial fibrosis. UUO-renal fibrosis was also induced in MMP-2 deficient (MMP-2⁻/⁻) and MMP-2⁺/⁺ mice treated with minocycline (inhibitor of MMPs). In MMP-2⁺/⁺ mice, MMP-2 and MMP-9 were expressed in damaged tubules, and their activities increased in a time-dependent manner after UUO. Interstitial fibrosis was noted at day 14, with deposition of types III and I collagens and expression of markers of mesenchymal cells (S100A4, vimentin, α-smooth muscle actin, and heat shock protein-47) in damaged tubular epithelial cells, together with F4/80+ macrophage infiltration. Fibrotic kidneys expressed EMT-associated molecules (ILK, TGF-β1, Smad, Wnt, β-catenin, and Snail). In contrast, the kidneys of MMP-2⁻/⁻ mice and minocycline-treated MMP-2⁺/⁺ mice showed amelioration of renal fibrosis with reduced expression of markers of mesenchymal cells in tubular epithelial cells, inhibition of upregulated EMT-associated molecules, and suppression of macrophage infiltration. The results suggested that MMP-2 have a pathogenic role in renal interstitial fibrosis, possibly through the induction of EMT and macrophage infiltration. Inhibition of MMPs may be beneficial therapeutically in renal fibrosis.

The contribution of cellular mechanotransduction to cardiomyocyte form and function

Myocardial development is regulated by an elegantly choreographed ensemble of signaling events mediated by a multitude of intermediates that take a variety of forms. Cellular differentiation and maturation are a subset of vertically integrated processes that extend over several spatial and temporal scales to create a well-defined collective of cells that are able to function cooperatively and reliably at the organ level. Early efforts to understand the molecular mechanisms of cardiomyocyte fate determination focused primarily on genetic and chemical mediators of this process. However, increasing evidence suggests that mechanical interactions between the extracellular matrix (ECM) and cell surface receptors as well as physical interactions between neighboring cells play important roles in regulating the signaling pathways controlling the developmental processes of the heart. Interdisciplinary efforts have made it apparent that the influence of the ECM on cellular behavior occurs through a multitude of physical mechanisms, such as ECM boundary conditions, elasticity, and the propagation of mechanical signals to intracellular compartments, such as the nucleus. In addition to experimental studies, a number of mathematical models have been developed that attempt to capture the interplay between cells and their local microenvironment and the influence these interactions have on cellular self-assembly and functional behavior. Nevertheless, many questions remain unanswered concerning the mechanism through which physical interactions between cardiomyocytes and their environment are translated into biochemical cellular responses and how these signaling modalities can be utilized in vitro to fabricate myocardial tissue constructs from stem cell-derived cardiomyocytes that more faithfully represent their in vivo counterpart. These studies represent a broad effort to characterize biological form as a conduit for information transfer that spans the nanometer length scale of proteins to the meter length scale of the patient and may yield new insights into the contribution of mechanotransduction into heart development and disease.

Spatial anisotropies and temporal fluctuations in extracellular matrix network texture during early embryogenesis

Early stages of vertebrate embryogenesis are characterized by a remarkable series of shape changes. The resulting morphological complexity is driven by molecular, cellular, and tissue-scale biophysical alterations. Operating at the cellular level, extracellular matrix (ECM) networks facilitate cell motility. At the tissue level, ECM networks provide material properties required to accommodate the large-scale deformations and forces that shape amniote embryos. In other words, the primordial biomaterial from which reptilian, avian, and mammalian embryos are molded is a dynamic composite comprised of cells and ECM. Despite its central importance during early morphogenesis we know little about the intrinsic micrometer-scale surface properties of primordial ECM networks. Here we computed, using avian embryos, five textural properties of fluorescently tagged ECM networks — (a) inertia, (b) correlation, (c) uniformity, (d) homogeneity, and (e) entropy. We analyzed fibronectin and fibrillin-2 as examples of fibrous ECM constituents. Our quantitative data demonstrated differences in the surface texture between the fibronectin and fibrillin-2 network in Day 1 (gastrulating) embryos, with the fibronectin network being relatively coarse compared to the fibrillin-2 network. Stage-specific regional anisotropy in fibronectin texture was also discovered. Relatively smooth fibronectin texture was exhibited in medial regions adjoining the primitive streak (PS) compared with the fibronectin network investing the lateral plate mesoderm (LPM), at embryonic stage 5. However, the texture differences had changed by embryonic stage 6, with the LPM fibronectin network exhibiting a relatively smooth texture compared with the medial PS-oriented network. Our data identify, and partially characterize, stage-specific regional anisotropy of fibronectin texture within tissues of a warm-blooded embryo. The data suggest that changes in ECM textural properties reflect orderly time-dependent rearrangements of a primordial biomaterial. We conclude that the ECM microenvironment changes markedly in time and space during the most important period of amniote morphogenesis—as determined by fluctuating textural properties.

Role of epimorphin in bile duct formation of rat liver epithelial stem-like cells: involvement of small G protein RhoA and C/EBPβ

Epimorphin/syntaxin 2 is a high conserved and very abundant protein involved in epithelial morphogenesis in various organs. We have shown recently that epimorphin (EPM), a protein exclusively expressed on the surface of hepatic stellate cells and myofibroblasts of the liver, induces bile duct formation of hepatic stem-like cells (WB-F344 cells) in a putative biophysical way. Therefore, the aim of this study was to present some of the molecular mechanisms by which EPM mediates bile duct formation. We established a biliary differentiation model by co-culture of EPM-overexpressed mesenchymal cells (PT67(EPM)) with WB-F344 cells. Here, we showed that EPM could promote WB-F344 cells differentiation into bile duct-like structures. Biliary differentiation markers were also elevated by EPM including Yp, Cx43, aquaporin-1, CK19, and gamma glutamyl transpeptidase (GGT). Moreover, the signaling pathway of EPM was analyzed by focal adhesion kinase (FAK), extracellular regulated kinase 1/2 (ERK1/2), and RhoA Western blot. Also, a dominant negative (DN) RhoA-WB-F344 cell line (WB(RhoA-DN)) was constructed. We found that the levels of phosphorylation (p) of FAK and ERK1/2 were up-regulated by EPM. Most importantly, we also showed that RhoA is necessary for EPM-induced activation of FAK and ERK1/2 and bile duct formation. In addition, a dual luciferase-reporter assay and CHIP assay was performed to reveal that EPM regulates GGT IV and GGT V expression differentially, possibly mediated by C/EBPβ. Taken together, these data demonstrated that EPM regulates bile duct formation of WB-F344 cells through effects on RhoA and C/EBPβ, implicating a dual aspect of this morphoregulator in bile duct epithelial morphogenesis.

Enterolobium contortisiliquum trypsin inhibitor (EcTI), a plant proteinase inhibitor, decreases in vitro cell adhesion and invasion by inhibition of Src protein-focal adhesion kinase (FAK) signaling pathways

Tumor cell invasion is vital for cancer progression and metastasis. Adhesion, migration, and degradation of the extracellular matrix are important events involved in the establishment of cancer cells at a new site, and therefore molecular targets are sought to inhibit such processes. The effect of a plant proteinase inhibitor, Enterolobium contortisiliquum trypsin inhibitor (EcTI), on the adhesion, migration, and invasion of gastric cancer cells was the focus of this study. EcTI showed no effect on the proliferation of gastric cancer cells or fibroblasts but inhibited the adhesion, migration, and cell invasion of gastric cancer cells; however, EcTI had no effect upon the adhesion of fibroblasts. EcTI was shown to decrease the expression and disrupt the cellular organization of molecules involved in the formation and maturation of invadopodia, such as integrin β1, cortactin, neuronal Wiskott-Aldrich syndrome protein, membrane type 1 metalloprotease, and metalloproteinase-2. Moreover, gastric cancer cells treated with EcTI presented a significant decrease in intracellular phosphorylated Src and focal adhesion kinase, integrin-dependent cell signaling components. Together, these results indicate that EcTI inhibits the invasion of gastric cancer cells through alterations in integrin-dependent cell signaling pathways.

Structure and epitope distribution of heparan sulfate is disrupted in experimental lung hypoplasia: a glycobiological epigenetic cause for malformation?

BACKGROUND

Heparan sulfate (HS) is present on the surface of virtually all mammalian cells and is a major component of the extracellular matrix (ECM), where it plays a pivotal role in cell-cell and cell-matrix cross-talk through its large interactome. Disruption of HS biosynthesis in mice results in neonatal death as a consequence of malformed lungs, indicating that HS is crucial for airway morphogenesis. Neonatal mortality (~50%) in newborns with congenital diaphragmatic hernia (CDH) is principally associated with lung hypoplasia and pulmonary hypertension. Given the importance of HS for lung morphogenesis, we investigated developmental changes in HS structure in normal and hypoplastic lungs using the nitrofen rat model of CDH and semi-synthetic bacteriophage ('phage) display antibodies, which identify distinct HS structures.

RESULTS

The pulmonary pattern of elaborated HS structures is developmentally regulated. For example, the HS4E4V epitope is highly expressed in sub-epithelial mesenchyme of E15.5 - E17.5 lungs and at a lower level in more distal mesenchyme. However, by E19.5, this epitope is expressed similarly throughout the lung mesenchyme.We also reveal abnormalities in HS fine structure and spatiotemporal distribution of HS epitopes in hypoplastic CDH lungs. These changes involve structures recognised by key growth factors, FGF2 and FGF9. For example, the EV3C3V epitope, which was abnormally distributed in the mesenchyme of hypoplastic lungs, is recognised by FGF2.

CONCLUSIONS

The observed spatiotemporal changes in HS structure during normal lung development will likely reflect altered activities of many HS-binding proteins regulating lung morphogenesis. Abnormalities in HS structure and distribution in hypoplastic lungs can be expected to perturb HS:protein interactions, ECM microenvironments and crucial epithelial-mesenchyme communication, which may contribute to lung dysmorphogenesis. Indeed, a number of epitopes correlate with structures recognised by FGFs, suggesting a functional consequence of the observed changes in HS in these lungs. These results identify a novel, significant molecular defect in hypoplastic lungs and reveals HS as a potential contributor to hypoplastic lung development in CDH. Finally, these results afford the prospect that HS-mimetic therapeutics could repair defective signalling in hypoplastic lungs, improve lung growth, and reduce CDH mortality.

Circulating bone morphogenetic protein 1-3 isoform increases renal fibrosis

Bone morphogenetic proteins (BMPs) participate in organ regeneration through autocrine and paracrine actions, but the existence and effects of these proteins in the systemic circulation is unknown. Using liquid chromatography-mass spectrometry, we identified BMP6, GDF15, and the BMP1-3 isoform of the Bmp1 gene in plasma samples from healthy volunteers and patients with CKD. We isolated the endogenous BMP1-3 protein and demonstrated that it circulates as an active enzyme, evidenced by its ability to cleave dentin matrix protein-1 in vitro. In rats with CKD, administration of recombinant BMP1-3 increased renal fibrosis and reduced survival. In contrast, administration of a BMP1-3-neutralizing antibody reduced renal fibrosis, preserved renal function, and increased survival. In addition, treating with the neutralizing antibody was associated with low plasma levels of TGFβ1 and connective tissue growth factor. In HEK293 cells and remnant kidneys, BMP1-3 increased the transcription of collagen type I, TGFβ1, β-catenin, and BMP7 via a BMP- and Wnt-independent mechanism that involved signaling through an integrin β1 subunit. The profibrotic effect of BMP1-3 may, in part, be a result of the accompanied decrease in decorin (DCN) expression. Taken together, inhibition of circulating BMP1-3 reduces renal fibrosis, suggesting that this pathway may be a therapeutic target for CKD.

Disruption of reelin signaling alters mammary gland morphogenesis

Reelin signaling is required for appropriate cell migration and ductal patterning during mammary gland morphogenesis. Dab1, an intracellular adaptor protein activated in response to reelin signaling, is expressed in the developing mammary bud and in luminal epithelial cells in the adult gland. Reelin protein is expressed in a complementary pattern, first in the epithelium overlying the mammary bud during embryogenesis and then in the myoepithelium and periductal stroma in the adult. Deletion in mouse of either reelin or Dab1 induced alterations in the development of the ductal network, including significant retardation in ductal elongation, decreased terminal branching, and thickening and disorganization of the luminal wall. At later stages, some mutant glands overcame these early delays, but went on to exhibit enlarged and chaotic ductal morphologies and decreased terminal branching: these phenotypes are suggestive of a role for reelin in spatial patterning or structural organization of the mammary epithelium. Isolated mammary epithelial cells exhibited decreased migration in response to exogenous reelin in vitro, a response that required Dab1. These observations highlight a role for reelin signaling in the directed migration of mammary epithelial cells driving ductal elongation into the mammary fat pad and provide the first evidence that reelin signaling may be crucial for regulating the migration and organization of non-neural tissues.

A role for specific collagen motifs during wound healing and inflammatory response of fibroblasts in the teleost fish gilthead seabream

Specific sites and sequences in collagen to which cells can attach, either directly or through protein intermediaries, were identified using Toolkits of 63-amino acid triple-helical peptides and specific shorter GXX'GEX″ motifs, which have different intrinsic affinity for integrins that mediate cell adhesion and migration. We have previously reported that collagen type I (COL-I) was able to prime in vitro the respiratory burst and induce a specific set of immune- and extracellular matrix-related molecules in phagocytes of the teleost fish gilthead seabream (Sparus aurata L.). It was also suggested that COL-I would provide an intermediate signal during the early inflammatory response in gilthead seabream. Since fibroblasts are highly involved in the initiation of wound repair and regeneration processes, in the present study SAF-1 cells (gilthead seabream fibroblasts) were used to identify the binding motifs in collagen by end-point and real-time cell adhesion assays using the collagen peptides and Toolkits. We identified the collagen motifs involved in the early magnesium-dependent adhesion of these cells. Furthermore, we found that peptides containing the GFOGER and GLOGEN motifs (where O is hydroxyproline) present high affinity for SAF-1 adhesion, expressed as both cell number and surface covering, while in cell suspensions, these motifs were also able to induce the expression of the genes encoding the proinflammatory molecules interleukin-1β and cyclooxygenase-2. These data suggest that specific collagen motifs are involved in the regulation of the inflammatory and healing responses of teleost fish.

Dynamic Electromechanical Hydrogel Matrices for Stem Cell Culture

Hydrogels have numerous biomedical applications including synthetic matrices for cell culture and tissue engineering. Here we report the development of hydrogel based multifunctional matrices that not only provide three-dimensional structural support to the embedded cells but also can simultaneously provide potentially beneficial dynamic mechanical and electrical cues to the cells. A unique aspect of these matrices is that they undergo reversible, anisotropic bending dynamics in an electric field. The direction and magnitude of this bending can be tuned through the hydrogel crosslink density while maintaining the same electric potential gradient, allowing control over the mechanical strain imparted to the cells in a three-dimensional environment. The conceptual design of these hydrogels was motivated through theoretical modeling of the osmotic pressure changes occurring at the gel-solution interfaces in an electric field. These electro-mechanical matrices support survival, proliferation, and differentiation of stem cells. Thus, these new three-dimensional in vitro synthetic matrices, which mimic multiple aspects of the native cellular environment, take us one step closer to in vivo systems.

BIOMIMETIC GRADIENT HYDROGELS FOR TISSUE ENGINEERING

During tissue morphogenesis and homeostasis, cells experience various signals in their environments, including gradients of physical and chemical cues. Spatial and temporal gradients regulate various cell behaviours such as proliferation, migration, and differentiation during development, inflammation, wound healing, and cancer. One of the goals of functional tissue engineering is to create microenvironments that mimic the cellular and tissue complexity found in vivo by incorporating physical, chemical, temporal, and spatial gradients within engineered three-dimensional (3D) scaffolds. Hydrogels are ideal materials for 3D tissue scaffolds that mimic the extracellular matrix (ECM). Various techniques from material science, microscale engineering, and microfluidics are used to synthesise biomimetic hydrogels with encapsulated cells and tailored microenvironments. In particular, a host of methods exist to incorporate micrometer to centimetre scale chemical and physical gradients within hydrogels to mimic the cellular cues found in vivo. In this review, we draw on specific biological examples to motivate hydrogel gradients as tools for studying cell-material interactions. We provide a brief overview of techniques to generate gradient hydrogels and showcase their use to study particular cell behaviours in two-dimensional (2D) and 3D environments. We conclude by summarizing the current and future trends in gradient hydrogels and cell-material interactions in context with the long-term goals of tissue engineering.

Reconstructing the differentiation niche of embryonic stem cells using biomaterials

The biochemical cues and topographical architecture of the extracellular environment extensively influence ES cell fate. The microenvironment surrounding the developing embryo presents these instructive cues in a complex and interactive manner in order to guide cell fate decisions. Current stem cell research aims to reconstruct this multifaceted embryonic niche to recapitulate development in vitro. This review focuses on 2D and 3D differentiation niches created from natural and synthetic biomaterials to guide the differentiation of ES cells toward specific lineages. Biomaterials engineered to present specific physical constraints are also reviewed for their role in differentiation.

Synergistic induction of bone formation by hOP-1, hTGF-beta3 and inhibition by zoledronate in macroporous coral-derived hydroxyapatites

Thirty coral-derived calcium carbonate-based macroporous constructs with limited hydrothermal conversion to hydroxyapatite (7% HA/CC) were implanted in the rectus abdominis of three adult non-human primate Papio ursinus to investigate the intrinsic induction of bone formation. Macroporous constructs with 125 microg human recombinant osteogenic protein-1 (hOP-1) or 125 microg human recombinant transforming growth factor-beta(3) (hTGF-beta(3)) were also implanted. The potential synergistic interaction between morphogens was tested by implanting binary applications of hOP-1 and hTGF-beta(3) 5:1 by weight, respectively. To evaluate the role of osteoclastic activity on the implanted macroporous surfaces, coral-derived constructs were pre-loaded with 0.24 mg of bisphosphonate zoledronate (Zometa). To correlate the morphology of tissue induction with osteogenic gene expression and activation, harvested specimens on day 90 were analyzed for changes in OP-1 and TGF-beta(3) mRNA synthesis by quantitative real-time polymerase chain reaction (qRT-PCR). The induction of bone formation in 7% HA/CC solo correlated with OP-1 expression. Massive bone induction formed by binary applications of the recombinant morphogens. Single applications of hOP-1 and hTGF-beta(3) also resulted in substantial bone formation, not comparable however to synergistic binary applications. Zoledronate-treated macroporous constructs showed limited bone formation and in two specimens bone formation was altogether absent; qRT-PCR showed a prominent reduction of OP-1 gene expression whilst TGF-beta(3) expression was far greater than OP-1. The lack of bone formation by zoledronate-treated specimens indicates that osteoclastic activity on the implanted coral-derived constructs is critical for the spontaneous induction of bone formation. Indirectly, zoledronate-treated samples showing lack of OP-1 gene expression and absent or very limited bone formation by induction confirm that the spontaneous induction of bone formation by coral-derived macroporous constructs is initiated by secreted BMPs/OPs, in context the OP-1 isoform.