Extracellular matrix and integrin signalling: the shape of things to come. Biochem J. 1999;339:481-488. [PMID: 10215583 DOI: 10.1042/0264-6021:3390481]

Layer-by-layer assembly of nanofilms to control cell functions

Control of cell functions by layer-by-layer assembly has a great challenge in tissue engineering and biomedical applications. We summarize current hot approaches in this review.

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

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

Relevance of meniscal cell regional phenotype to tissue engineering

PURPOSE

Meniscus contains heterogeneous populations of cells that have not been fully characterized. Cell phenotype is often lost during culture; however, culture expansion is typically required for tissue engineering. We examined and compared cell-surface molecule expression levels on human meniscus cells from the vascular and avascular regions and articular chondrocytes while documenting changes during culture-induced dedifferentiation.

MATERIALS AND METHODS

Expressions of 16 different surface molecules were examined by flow cytometry after monolayer culture for 24 h, 1 week, and 2 weeks. Menisci were also immunostained to document the spatial distributions of selected surface molecules.

RESULTS

Meniscus cells and chondrocytes exhibited several similarities in surface molecule profiles with dynamic changes during culture. A greater percentage of meniscal cells were positive for CD14, CD26, CD49c, and CD49f compared to articular chondrocytes. Initially, more meniscal cells from the vascular region were positive for CD90 compared to cells from the avascular region or chondrocytes. Cells from the vascular region also expressed higher levels of CD166 and CD271 compared to cells from the avascular region. CD90, CD166, and CD271-positive cells were predominately perivascular in location. However, CD166-positive cells were also located in the superficial layer and in the adjacent synovial and adipose tissue.

CONCLUSIONS

These surface marker profiles provide a target phenotype for differentiation of progenitors in tissue engineering. The spatial location of progenitor cells in meniscus is consistent with higher regenerative capacity of the vascular region, while the surface progenitor subpopulations have potential to be utilized in tears created in the avascular region.

Recent Advances in Biosensing With Photonic Crystal Surfaces: A Review

Photonic crystal surfaces that are designed to function as wavelength-selective optical resonators have become a widely adopted platform for label-free biosensing, and for enhancement of the output of photon-emitting tags used throughout life science research and in vitro diagnostics. While some applications, such as analysis of drug-protein interactions, require extremely high resolution and the ability to accurately correct for measurement artifacts, others require sensitivity that is high enough for detection of disease biomarkers in serum with concentrations less than 1 pg/ml. As the analysis of cells becomes increasingly important for studying the behavior of stem cells, cancer cells, and biofilms under a variety of conditions, approaches that enable high resolution imaging of live cells without cytotoxic stains or photobleachable fluorescent dyes are providing new tools to biologists who seek to observe individual cells over extended time periods. This paper will review several recent advances in photonic crystal biosensor detection instrumentation and device structures that are being applied towards direct detection of small molecules in the context of high throughput drug screening, photonic crystal fluorescence enhancement as utilized for high sensitivity multiplexed cancer biomarker detection, and label-free high resolution imaging of cells and individual nanoparticles as a new tool for life science research and single-molecule diagnostics.

Coupled Simulation of Heart Valves: Applications to Clinical Practice

The last few decades have seen great advances in the understanding of heart valves, and consequently, in the development of novel treatment modalities and surgical procedures for valves afflicted by disease. This is due in part to the profound advancements in computing technology and noninvasive medical imaging techniques that have made it possible to numerically model the complex heart valve systems characterized by distinct features at different length scales and various interacting processes. In this article, we highlight the importance of explicitly coupling these multiple scales and diverse processes to accurately simulate the true behavior of the heart valves, in health and disease. We examine some of the computational modeling studies that have a direct consequence on clinical practice.

Extracellular matrix, gap junctions, and retinal vascular homeostasis in diabetic retinopathy

The vascular basement membrane (BM) contains extracellular matrix (ECM) proteins that assemble in a highly organized manner to form a supportive substratum for cell attachment facilitating myriad functions that are vital to cell survival and overall retinal homeostasis. The BM provides a microenvironment in which bidirectional signaling through integrins regulates cell attachment, turnover, and functionality. In diabetic retinopathy, the BM undergoes profound structural and functional changes, and recent studies have brought to light the implications of such changes. Thickened vascular BM in the retinal capillaries actively participate in the development and progression of characteristic changes associated with diabetic retinopathy. High glucose (HG)-induced compromised cell-cell communication via gap junctions (GJ) in retinal vascular cells may disrupt homeostasis in the retinal microenvironment. In this review, the role of altered ECM synthesis, compromised GJ activity, and disturbed retinal homeostasis in the development of retinal vascular lesions in diabetic retinopathy are discussed.

Enalapril stimulates collagen biosynthesis through prolidase-dependent mechanism in cultured fibroblasts

The mechanism of a lower incidence of dermatological manifestations in patients treated with enalapril compared to patients treated with other ACE-inhibitors, e.g., captopril, is not known. The finding that prolidase plays an important role in collagen biosynthesis and that some angiotensin-converting enzyme inhibitors affect prolidase activity led us to evaluate its effect on collagen biosynthesis in cultured human skin fibroblasts. Since insulin-like growth factor (IGF-I) and transforming growth factor beta 1 (TGF-β1) are the most potent stimulators of both collagen biosynthesis and prolidase activity, and prolidase is regulated by β₁ integrin signaling, the effect of enalapril and enalaprilat on IGF-IR, TGF-β1, and β₁ integrin receptor expressions was evaluated. Cells were treated with milimolar concentrations (0.3 and 0.5 mM) of enalapril and enalaprilat for 24 h. The activity of prolidase was determined by colorimetic assay. Collagen biosynthesis was evaluated by radiometric assay. Expression of signaling proteins was evaluated using Western blot. It was found that enalapril- and enalaprilat-dependent increase in prolidase activity and expression was accompanied by parallel increase in collagen biosynthesis. The exposure of the cells to 0.5 mM enalapril and enalaprilat contributed to increase in IGF-IR and α₂β₁ integrin receptor as well as TGF-β1 and NF-κB p65 expressions. Enalapril- and enalaprilat-dependent increase of collagen biosynthesis in fibroblasts results from increase of prolidase activity and expression, which may undergo through activation of α₂β₁ integrin and IGF-IR signaling as well as upregulation of TGF-β1 and NF-κB p65, the inhibitor of collagen gene expression.

Differential vital staining of normal fibroblasts and melanoma cells by an anionic conjugated polyelectrolyte

Molecular probes for imaging of live cells are of great interest for studying biological and pathological processes. The anionic luminescent conjugated polythiophene (LCP) polythiophene acetic acid (PTAA), has previously been used for vital staining of cultured fibroblasts as well as transformed cells with results indicating differential staining due to cell phenotype. Herein, we investigated the behavior of PTAA in two normal and five transformed cells lines. PTAA fluorescence in normal cells appeared in a peripheral punctated pattern whereas the probe was more concentrated in a one-sided perinuclear localization in the five transformed cell lines. In fibroblasts, PTAA fluorescence was initially associated with fibronectin and after 24 h partially localized to lysosomes. The uptake and intracellular target in malignant melanoma cells was more ambiguous and the intracellular target of PTAA in melanoma cells is still elusive. PTAA was well tolerated by both fibroblasts and melanoma cells, and microscopic analysis as well as viability assays showed no signs of negative influence on growth. Stained cells maintained their proliferation rate for at least 12 generations. Although the probe itself was nontoxic, photoinduced cellular toxicity was observed in both cell lines upon irradiation directly after staining. However, no cytotoxicity was detected when the cells were irradiated 24 h after staining, indicating that the photoinduced toxicity is dependent on the cellular location of the probe. Overall, these studies certified PTAA as a useful agent for vital staining of cells, and that PTAA can potentially be used to study cancer-related biological and pathological processes.

Canonical Wnt signalling regulates epithelial patterning by modulating levels of laminins in zebrafish appendages

The patterning and morphogenesis of body appendages – such as limbs and fins – is orchestrated by the activities of several developmental pathways. Wnt signalling is essential for the induction of limbs. However, it is unclear whether a canonical Wnt signalling gradient exists and regulates the patterning of epithelium in vertebrate appendages. Using an evolutionarily old appendage – the median fin in zebrafish – as a model, we show that the fin epithelium exhibits graded changes in cellular morphology along the proximo-distal axis. This epithelial pattern is strictly correlated with the gradient of canonical Wnt signalling activity. By combining genetic analyses with cellular imaging, we show that canonical Wnt signalling regulates epithelial cell morphology by modulating the levels of laminins, which are extracellular matrix components. We have unravelled a hitherto unknown mechanism involved in epithelial patterning, which is also conserved in the pectoral fins – evolutionarily recent appendages that are homologous to tetrapod limbs.

Highlighted article: In the zebrafish fin, a Wnt gradient dictates the expression of laminin α5, which signals via integrin α3 to control epithelial cell morphology.

Targeted delivery of extracellular matrix protected against neurologic defects after focal ischemia reperfusion in rats

Ischemic stroke is one of the leading causes of morbidity and mortality worldwide and characterized by defective angiogenesis. The functional sequences (RGDs, GRGDSPASSPISC) derived from fibronectin have been confirmed to augment angiogenesis in vivo and in vitro. However, delivery of peptides into the brain parenchyma has been hampered by the presence of the blood-brain barrier (BBB). We fused RGDs with penetratin (Antp) derived from Drosophila antennapedia homeodomain protein to improve the penetration of peptides through BBB into ischemic hemisphere. We found Antp-RGDs successfully not only penetrate the SH-SY5Y cells but also penetrated through BBB into ischemic hemisphere by intraperitoneal injection. In addition, application of Antp-RGDs to the focal cerebral ischemic reperfusion injury in rats resulted in the reduction of cerebral ischemic volume and the improvement of neurologic score according to the 21-point score. We further demonstrated that activation of phosphorylation-extracellular-signal related kinase 1/2 (p-ERK 1/2) and upregulation of gene VEGF resulted from post-treatment with Antp-RGDs 2 hours after reperfusion onset might at least partly contribute to the benefic changes after focal cerebral ischemic reperfusion injury in rats. Our data suggested that Antp-RGDs may serve as an attractive therapeutic intervention for treating ischemic stroke.

Liver bioengineering: from the stage of liver decellularized matrix to the multiple cellular actors and bioreactor special effects

Liver bioengineering has been a field of intense research and popular excitement in the past decades. It experiences great interest since the introduction of whole liver acellular scaffolds generated by perfusion decellularization (1-3). Nevertheless, the different strategies developed so far have failed to generate hepatic tissue in vitro bioequivalent to native liver tissue. Even notable novel strategies that rely on iPSC-derived liver progenitor cells potential to self-organize in association with endothelial cells in hepatic organoids are lacking critical components of the native tissue (e.g., bile ducts, functional vascular network, hepatic microarchitecture, etc) (4). Hence, it is vital to understand the strengths and short comes of our current strategies in this quest to re-create liver organogenesis in vitro. To shed some light into these issues, this review describes the different actors that play crucial roles in liver organogenesis and highlights the steps still missing to successfully generate whole livers and hepatic organoids in vitro for multiple applications.

Involvement of ILK/ERK1/2 and ILK/p38 pathways in mediating the enhanced osteoblast differentiation by micro/nanotopography

The hierarchical micro/nanotextured topography (MNT) on titanium (Ti) implant surface significantly enhances osteoblast differentiation. We have demonstrated that integrin-linked kinase (ILK) is a key underlying signal molecule and β-catenin is one of its downstream mediators in MNT-regulated osteoblast behavior. Here we propose that mitogen-activated protein kinases (MAPKs), including extracellular signal-regulated kinase 1/2 (ERK1/2), p38 and c-Jun NH2-terminal kinase (JNK), are other mediators downstream of ILK, and this study aims to confirm this. Firstly, the levels of ILK and MAPK activity in MG63 cells on MNT are examined by Western blot analysis. The ILK, ERK1/2 and p38 signals are significantly up-regulated by MNT, whereas the JNK activity is undetectable by Western blot. The MG63 cell morphology, proliferation and differentiation are studied in the absence and presence of the MAPK subgroup inhibitors to confirm their roles in cell functions on the Ti surface. The MAPK subgroup inhibitors obviously change the cell shape and depress cell proliferation. Blocking the ERK1/2 or p38 signaling, but not the JNK signaling, significantly down-regulates the cell osteogenesis-related gene expression, ALP production, collagen secretion and matrix mineralization. Afterwards, the ILK expression is down-regulated using ILK-specific siRNA (ILKsi) and then the MAPK activity is determined. ILKsi significantly attenuates the phosphorylated ERK1/2 and p38 levels on MNT, explicitly demonstrating that the ERK1/2 and p38 signalings are downstream effectors of ILK. In conclusion, these data demonstrate that both ILK/ERK1/2 and ILK/p38 pathways are involved in the mechanisms mediating the enhanced osteoblast differentiation by biomaterial surface topography, hopefully directing the biomaterial modification and biofunctionalization.

Longissimus dorsi transcriptome analysis of purebred and crossbred Iberian pigs differing in muscle characteristics

BACKGROUND

The two main genetic types in Iberian pig production show important phenotypic differences in growth, fattening and tissue composition since early developmental stages. The objective of this work was the evaluation of muscle transcriptome profile in piglets of both genetic types, in order to identify genes, pathways and regulatory factors responsible for their phenotypic differences. Contemporary families coming from pure Iberian pigs (IB) or from crossing with Duroc boars (DU×IB) were generated. Piglets (14 from each genetic type) were slaughtered at weaning (28 days) and longissimus dorsi was sampled for composition and gene expression studies. RNA was obtained and hybridized to Affymetrix Porcine Genechip expression arrays.

RESULTS

Loin muscle chemical composition showed significant differences between genetic types in intramuscular fat content (6.1% vs. 4.3% in IB and DUxIB animals, respectively, P = 0.009) and in saturated (P = 0.019) and monounsaturated fatty acid proportions (P = 0.044). The statistical analysis of gene expression data allowed the identification of 256 differentially expressed (DE) genes between genetic types (FDR < 0.10), 102 upregulated in IB and 154 upregulated in DU×IB. Transcript differences were validated for a subset of DE genes by qPCR. We observed alteration in biological functions related to extracellular matrix function and organization, cellular adhesion, muscle growth, lipid metabolism and proteolysis. Candidate genes with known effects on muscle growth were found among the DE genes upregulated in DU×IB. Genes related to lipid metabolism and proteolysis were found among those upregulated in IB. Regulatory factors (RF) potentially involved in the expression differences were identified by calculating the regulatory impact factors. Twenty-nine RF were found, some of them with known relationship with tissue development (MSTN, SIX4, IRX3), adipogenesis (CEBPD, PPARGC1B), or extracellular matrix processes (MAX, MXI1). Correlation among the expression of these RF and DE genes show relevant differences between genetic types.

CONCLUSION

These results provide valuable information about genetic mechanisms determining the phenotypic differences on growth and meat quality between the genetic types studied, mainly related to the development and function of the extracellular matrix and also to some metabolic processes as proteolysis and lipid metabolism. Transcription factors and regulatory mechanisms are proposed for these altered biological functions.

Role of integrin alpha4 in drug resistance of leukemia

Chemotherapeutic drug resistance in acute lymphoblastic leukemia (ALL) is a significant problem, resulting in poor responsiveness to first-line treatment or relapse after transient remission. Classical anti-leukemic drugs are non-specific cell cycle poisons; some more modern drugs target oncogenic pathways in leukemia cells, although in ALL these do not play a very significant role. By contrast, the molecular interactions between microenvironment and leukemia cells are often neglected in the design of novel therapies against drug resistant leukemia. It was shown however, that chemotherapy resistance is promoted in part through cell–cell contact of leukemia cells with bone marrow (BM) stromal cells, also called cell adhesion-mediated drug resistance (CAM-DR). Incomplete response to chemotherapy results in persistence of resistant clones with or without detectable minimal residual disease (MRD). Approaches for how to address CAM-DR and MRD remain elusive. Specifically, studies using anti-functional antibodies and genetic models have identified integrin alpha4 as a critical molecule regulating BM homing and active retention of normal and leukemic cells. Pre-clinical evidence has been provided that interference with alpha4-mediated adhesion of ALL cells can sensitize them to chemotherapy and thus facilitate eradication of ALL cells in an MRD setting. To this end, Andreeff and colleagues recently provided evidence of stroma-induced and alpha4-mediated nuclear factor-κB signaling in leukemia cells, disruption of which depletes leukemia cells of strong survival signals. We here review the available evidence supporting the targeting of alpha4 as a novel strategy for treatment of drug resistant leukemia.

Micro- and nanotopography with extracellular matrix coating modulate human corneal endothelial cell behavior

The human corneal endothelium plays an important role in maintaining corneal transparency. Human corneal endothelial cells have limited regenerative capability in vivo. Consequently, endothelial dysfunction can occur following corneal endothelial trauma or inherited diseases. To restore endothelial function, corneal transplantation is needed. However, there is a worldwide shortage of donor corneas, motivating the development of a tissue-engineered graft alternative using cultivated endothelial cells. To induce in vitro cell proliferation, much effort has been made to improve culture conditions and to mimic the native extracellular microenvironment. We incorporated topographical and biochemical cues in our in vitro culture of human corneal endothelial cell line B4G12 (HCEC-B4G12) and hypothesized that manipulation of the extracellular environment can modulate cell proliferation, morphometry and phenotype. The topographies tested were nanopillars, microwells and micropillars on polydimethylsiloxane, while the biochemical factors were extracellular matrix protein coatings of fibronectin-collagen I (FC), FNC® coating mix (FNC) and laminin-chondroitin sulfate (LC). Cellular morphometry, Na(+)/K(+)-ATPase and zona occludens 1 (ZO-1) gene and protein expression were analyzed 3days after cells had formed a confluent monolayer. The cell circularity on all patterns and coatings was above 0.78. On all coatings, cell area was the lowest on micropillars. The coefficient of variation (CV) of the cell area was the lowest on nanopillars with an LC coating. With an FC coating, micropillars induced a better cellular outcome as the cells had the greatest circularity, smallest cell area and highest Na(+)/K(+)-ATPase and ZO-1 gene and protein expression. With the LC coating, HCECs grown on nanopillars resulted in the lowest CV of the cell area and the highest ZO-1 gene expression. Thus, HCEC-B4G12 morphometry and phenotype can be improved using different topographical and biochemical cues.

A screen of suitable inducers for germline differentiation of chicken embryonic stem cells

Differentiation of germ cells from embryonic stem cells in vitro could have great application for treating infertility and provide an excellent model for uncovering molecular mechanisms of germline generation. In this study, we aim to screen the suitable inducers that may prove the efficiency of driving chicken embryonic stem cells (ES cells) toward germ cells. The male ES cells were separeted into different groups: single retinoic acid (RA) treatment, co-cultured with sertoli cell feeder with RA induction, cultured on matrix proteins (fibronectin, laminin and collagen) with RA treatment, cultured on fibronectin with sertoli cell feeder and RA induction, and single bone morphogenetic protein 4 (BMP4) treatment. Quantitative RT-PCR and immunoourescence were performed to characterize the ES cells differentiation process. The results showed that spermatogonial stem cells (SSCs)-like were not detected in single RA and RA with collagen groups, but were observed in the other groups. The expression of ES specific genes (Nanog and Sox2) was decreased while SSCs marker genes (Dazl, Stra8, integrin α6, integrinβ1 and C-kit) was remarkably increased. The multiple comparsion results showed that the expression of SSCs marker genes in RA with sertoli cells group was significantly higher than the other groups(P<0.05). Collectively, our results suggested that chicken ES cells possess the potency to differentiate into SSCs-like cells in vitro through RA, matrix proteins, sertoli cells and BMP4 induction, of which co-cultured with sertoli cell feeder with RA induction was proved to be the best.

Bone regeneration potential of stem cells derived from periodontal ligament or gingival tissue sources encapsulated in RGD-modified alginate scaffold

Mesenchymal stem cells (MSCs) provide an advantageous alternative therapeutic option for bone regeneration in comparison to current treatment modalities. However, delivering MSCs to the defect site while maintaining a high MSC survival rate is still a critical challenge in MSC-mediated bone regeneration. Here, we tested the bone regeneration capacity of periodontal ligament stem cells (PDLSCs) and gingival mesenchymal stem cells (GMSCs) encapsulated in a novel RGD- (arginine-glycine-aspartic acid tripeptide) coupled alginate microencapsulation system in vitro and in vivo. Five-millimeter-diameter critical-size calvarial defects were created in immunocompromised mice and PDLSCs and GMSCs encapsulated in RGD-modified alginate microspheres were transplanted into the defect sites. New bone formation was assessed using microcomputed tomography and histological analyses 8 weeks after transplantation. Results confirmed that our microencapsulation system significantly enhanced MSC viability and osteogenic differentiation in vitro compared with non-RGD-containing alginate hydrogel microspheres with larger diameters. Results confirmed that PDLSCs were able to repair the calvarial defects by promoting the formation of mineralized tissue, while GMSCs showed significantly lower osteogenic differentiation capability. Further, results revealed that RGD-coupled alginate scaffold facilitated the differentiation of oral MSCs toward an osteoblast lineage in vitro and in vivo, as assessed by expression of osteogenic markers Runx2, ALP, and osteocalcin. In conclusion, these results for the first time demonstrated that MSCs derived from orofacial tissue encapsulated in RGD-modified alginate scaffold show promise for craniofacial bone regeneration. This treatment modality has many potential dental and orthopedic applications.

UVC inhibits collagen biosynthesis through up-regulation of NF-κB p65 signaling in cultured fibroblasts

The effects of UVC on collagen biosynthesis, prolidase activity, expression of α₂β₁ integrin, IGF-I receptor, FAK, MAP-kinases (ERK1 and ERK2) and the transcription factor NF-κB p65 were evaluated in human dermal fibroblasts. Confluent fibroblasts were treated with UVC light at a rates of 30 and 60 J/m(2). It was found that UVC-dependent decrease in collagen biosynthesis was not accompanied by parallel decrease in prolidase activity and expression. Since insulin-like growth factor receptor (IGF-IR) and α₂β₁ integrin signaling are the most potent regulators of collagen biosynthesis, the effect of UVC on IGF-IR and α₂β₁ integrin receptor expressions were evaluated. It was found that the exposure of the cells to UVC contributed to decrease in α₂β₁ integrin receptor and FAK expression and to an increase in IGF-IR and pERK1, pERK2 expressions. It was accompanied by an increase in the expression of NF-κB p65, the known inhibitor of collagen gene expression. The data suggest that UVC-dependent decrease of collagen biosynthesis in cultured human skin fibroblasts results from decrease in α₂β₁ integrin receptor signaling and activation of NF-κB p65, that is responsible for down-regulation of collagen gene expression.

Involvement of CD137 ligand signaling in neural stem cell death

CD137 is a member of the tumor necrosis factor/nerve growth factor receptor superfamily. Interaction of CD137 with its ligand (CD137L) affects the apoptosis, proliferation and differentiation of immune cells. Interestingly, the CD137 receptor/ligand system involves the bi-directional transduction of signals. The expression of CD137 and its ligand is not restricted to immune organs, but can also be detected in a wide variety of tissues such as the brain, kidney, lung and heart. However, its role in brain is largely unknown. This study was performed to determine the role of CD137L reverse signaling in the apoptosis of neural stem cells. We identified the expression of CD137 and its ligand in C17.2 neural stem cells derived from mouse embryonic cerebellum. We found that the activation of CD137L reverse signaling by CD137 resulted in a decrease in cell adhesion to the fibronectin-coated culture basement, thus causing detachment-induced cell death. Furthermore, we showed that the cell death induced by CD137 was completely ameliorated by integrin activators and caspase inhibitors. Therefore we suggest that CD137L reverse signaling exerts a pro-apoptotic effect by suppressing integrin-mediated survival signals in neural stem cells.

Photonic crystal enhanced microscopy for imaging of live cell adhesion

A form of microscopy that utilizes a photonic crystal biosensor surface as a substrate for cell attachment enables label-free, quantitative, submicron resolution, time-resolved imaging of cell-surface interactions without cytotoxic staining agents or temporally-unstable fluorophores. Other forms of microscopy do not provide this direct measurement of live cell-surface attachment localization and strength that includes unique, dynamic morphological signatures critical to the investigation of important biological phenomena such as stem cell differentiation, chemotaxis, apoptosis, and metastasis. Here, we introduce Photonic Crystal Enhanced Microscopy (PCEM), and apply it to the study of murine dental stem cells to image the evolution of cell attachment and morphology during chemotaxis and drug-induced apoptosis. PCEM provides rich, dynamic information about the evolution of cell-surface attachment profiles over biologically relevant time-scales. Critically, this method retains the ability to monitor cell behavior with spatial resolution sufficient for observing both attachment footprints of filopodial extensions and intracellular attachment strength gradients.

Characterization of white shrimp Litopenaeus vannamei integrin β and its role in immunomodulation by dsRNA-mediated gene silencing

The full sequence of white shrimp Litopenaeus vannamei integrin β (LV-B) is 2879bp which encodes 787 amino acids (aa) of the open reading frame (ORF). The mature protein (764 aa) contains (1) an extracellular domain (ED) of 692 aa, (2) a transmembrane domain (TD) of 23 aa, and (3) a cytoplasmic domain (CD) of 49 aa. The cloned LV-B grouped together with crayfish Pacifastacus leniusculus integrin β (PL-B1), but was far away from vertebrate integrin β1, β3, β5, β6, β7, and β8, and another L. vannamei integrin β (LV). A Southern blot analysis indicated that the cloned LV-B was a single copy of genomic DNA. LV-B mRNA was expressed in all tissues, and was highly expressed in haemocytes. LV-B was downregulated in shrimp 24 and 96h after having received white spot syndrome virus (WSSV). LV-B expression by haemocytes of shrimp was higher in the postmoult (A and B) stage, and lower in the premoult (D2/D3) stage. LV-B expression was significantly higher by shrimp reared in 2.5‰ and 5‰ salinities. Shrimp injected with integrin β dsRNA showed gene silencing of integrin β after 36h. LV-B-silenced shrimp showed decreased hyaline cells (HCs), granular cells (GCs, including semi-granular cells), the total haemocyte count (THC), respiratory bursts (RBs), and lysozyme activity, but showed increased RB/HC, superoxide dismutase (SOD) activity/HC, and the phenoloxidase (PO) activity/GC. LV-B-silenced shrimp showed upregulated expressions of lipopolysaccharide- and β-glucan-binding protein (LGBP), peroxinectin (PX), prophenoloxidase I (proPO I), proPO II, proPO-activating enzyme (ppA), α2-macroglobulin (α2-M), cytMnSOD, mtMnSOD, and heat shock protein 70 (HSP70). It was concluded that integrin β plays important roles in proPO activation, phagocytosis, and the antioxidant system for immunomodulation in shrimp.

Spatial patterning of endothelium modulates cell morphology, adhesiveness and transcriptional signature

Microscale and nanoscale structures can spatially pattern endothelial cells (ECs) into parallel-aligned organization, mimicking their cellular alignment in blood vessels exposed to laminar shear stress. However, the effects of spatial patterning on the function and global transcriptome of ECs are incompletely characterized. We used both parallel-aligned micropatterned and nanopatterned biomaterials to evaluate the effects of spatial patterning on the phenotype of ECs, based on gene expression profiling, functional characterization of monocyte adhesion, and quantification of cellular morphology. We demonstrate that both micropatterned and aligned nanofibrillar biomaterials could effectively guide EC organization along the direction of the micropatterned channels or nanofibrils, respectively. The ability of ECs to sense spatial patterning cues were abrogated in the presence of cytoskeletal disruption agents. Moreover, both micropatterned and aligned nanofibrillar substrates promoted an athero-resistant EC phenotype by reducing endothelial adhesiveness for monocytes and platelets, as well as by downregulating the expression of adhesion proteins and chemokines. We further found that micropatterned ECs have a transcriptional signature that is unique from non-patterned ECs, as well as from ECs aligned by shear stress. These findings highlight the importance of spatial patterning cues in guiding EC organization and function, which may have clinical relevance in the development of vascular grafts that promote patency.

The advantages of three-dimensional culture in a collagen hydrogel for stem cell differentiation

We evaluated the advantages of three-dimensional (3D) culture in a collagen hydrogel for stem cell differentiation, including the morphology of differentiated cells, differentiation efficiency of stem cells from aged rat and cells after passaging and freeze/thawing. Rat mesenchymal stem cells (MSCs) from young and aged rats, and MSCs after passaging and freeze/thawing were induced to differentiate into osteoblasts in 3D and 2D cultures, and histological studies were performed. Differentiation efficiency was evaluated by markers of osteoblastic differentiation including Runx2 and osterix gene expressions, osteocalcin secretion and calcium deposition. MSCs were stained positive for alkaline phosphatase in 3D and 2D cultures. However, the morphology of differentiated cells in 3D culture, which was different from that in 2D culture, was similar to that of osteoblasts in vivo. Markers of osteoblastic differentiation in MSCs from aged rats in 3D culture were higher than those in MSCs from young rats in 2D culture. Markers of osteoblastic differentiation in MSCs after passaging and freeze/thawing in 3D culture were higher than those in nonpassaged MSCs in 2D culture. These results indicate that 3D culture in a collagen hydrogel has advantages for the differentiation of MSCs into osteoblasts with a similar phenotype to that of in vivo, when using even MSCs from aged donors or after passaging and freeze/thawing.

Bit1 in anoikis resistance and tumor metastasis

Epithelial cells and most adherent normal cells rely on adhesion-dependent, integrin-mediated survival signals from the extracellular matrix (ECM) to survive. When these cells are deprived of adhesion to the ECM, they undergo a specific form of apoptosis termed "anoikis." In contrast, malignant cells have attained mechanisms to enable them to survive in the absence of adhesion and are considered anchorage-independent. This review will focus on the biological function of the Bcl2-inhibitor of transcription (Bit1) protein in the anoikis process, the underlying molecular mechanism of Bit1 apoptotic function, and its role in tumor metastasis.

Survival and structural evaluations of three-dimensional tissues fabricated by the hierarchical cell manipulation technique

Mouse L929 fibroblasts and normal human dermal fibroblasts (NHDFs) were constructed into three-dimensional (3-D) multilayered tissues by directly coating them with nano-films consisting of fibronectin (FN) and gelatin (G) onto the surface of the cell layer using layer-by-layer assembly. The one-, two- and five-layered (1L, 2L and 5L) tissues were cultured for 1 month in order to evaluate their long-term survival and structural changes. L929 cells in the 3-D tissues showed excessive proliferation throughout the culture period, regardless of the starting layer number. The cross-sectional images stained with hematoxylin and eosin revealed heterogeneous and random increases in the thickness of their layered structures, probably due to the immortalized property of L929 fibroblasts. On the other hand, NHDFs, which are primary cells, showed high stability in their amount of DNA in the multilayered structures, and their thicknesses were completely maintained even after 1 month of incubation. To evaluate the living cell density in each layer of 5L tissues during the culture period, 5L NHDFs were fluorescently labeled with LIVE/DEAD reagent and analyzed by confocal laser scanning microscopy. Although the upper layers did not show any dead cells, the bottom layers showed pieces of dead cell nuclei depending on culture time. However, the living cell densities in all layers were almost the same, even after 1 month of culture, suggesting that the 5L structures were completely filled with living cells. These findings from the multilayered tissue constructs will provide important information not only for the construction of 3-D engineered tissues in tissue engineering but also on 3-D cell culture in biological science generally.

Simplified microenvironments and reduced cell culture size influence the cell differentiation outcome in cellular microarrays

Cellular microarrays present a promising tool for multiplex evaluation of the signalling effect of substrate-immobilized factors on cellular differentiation. In this paper, we compare the early myoblast-to-osteoblast cell commitment steps in response to a growth factor stimulus using standard well plate differentiation assays or cellular microarrays. Our results show that restraints on the cell culture size, inherent to cellular microarrays, impair the differentiation outcome. Also, while cells growing on spots with immobilised BMP-2 are early biased towards the osteoblast fate, longer periods of cell culturing in the microarrays result in cell proliferation and blockage of osteoblast differentiation. The results presented here raise concerns about the efficiency of cell differentiation when the cell culture dimensions are reduced to a simplified microspot environment. Also, these results suggest that further efforts should be devoted to increasing the complexity of the microspots composition, aiming to replace signalling cues missing in this system.

Extracellular matrix protein adsorption to phosphate-functionalized gels from serum promotes osteogenic differentiation of human mesenchymal stem cells

One of the primary goals for tissue engineering is to induce new tissue formation by stimulating specific cell function. Human mesenchymal stem cells (hMSCs) are a particularly important cell type that has been widely studied for differentiation down the osteogenic (bone) lineage, and we recently found that simple phosphate functional groups incorporated into poly(ethylene glycol) (PEG) hydrogels could induce osteogenesis without using differentiation medium by unknown mechanisms. Here, we aimed to determine whether direct or indirect cell/materials interactions were responsible for directing hMSCs down the osteogenic lineage on phosphate (PO(4))-functionalized PEG hydrogels. Our results indicated that serum components adsorbed onto PO(4)-PEG hydrogels from medium in a presoaking step were sufficient for attachment and spreading of hMSCs, even when seeded in serum-free conditions. Blocking antibodies for collagen and fibronectin (targeted to the hydrogel), as well as β1 and β3 integrin blocking antibodies (targeted to the cells), each reduced attachment of hMSCs to PO(4)-PEG hydrogels, suggesting that integrin-mediated interactions between cells and adsorbed matrix components facilitate attachment and spreading. Outside-in signaling, and not merely shape change, was found to be required for osteogenesis, as alkaline phosphatase activity and expression of CBFA1, osteopontin and collagen-1 were each significantly down regulated upon inhibition of focal adhesion kinase phosphorylation even though the focal adhesion structure or cell shape was unchanged. Our results demonstrate that complex function (i.e. osteogenic differentiation) can be controlled using simple functionalization strategies, such as incorporation of PO(4), but that the role of these materials may be due to more complex influences than has previously been appreciated.

The role of Ras-ERK-IL-1β signaling pathway in upregulation of elastin expression by human coronary artery smooth muscle cells cultured in 3D scaffolds

Incorporation of endogenous elastin, a key structural component of the vascular extracellular matrix (ECM), is an important requirement for engineered vascular tissues. In addition to providing elastic recoil of the tissue, elastin influences cell function and promotes cell signaling by interacting with specific cell surface receptors. Although progress has been made in understanding the mechanisms of in vivo elastin expression and incorporation into fibers, it is notably absent from engineered vessels. Recently we showed that the three-dimensional (3D) scaffold topography was able to upregulate elastin synthesis by human coronary artery smooth muscle cells (HCASMC). The present study was undertaken to explore the molecular mechanisms responsible for 3D scaffold-induced elastin gene transcription. Here, we show several lines of evidence that signal transduction pathway leading to elastin gene expression by HCASMC cultured in synthetic 3D scaffolds to be strikingly different from two-dimensional (2D) surfaces. In 3D scaffolds, α5β1 integrin engagement by HCASMC was significantly reduced and the putative focal adhesion kinase (FAK) was poorly phosphorylated concomitant with FAK and protein tyrosine kinase Pyk2 downregulation. FAK-associated adhesion proteins vinculin and paxillin were also significantly downregulated by the 3D scaffold topography. Furthermore, contrary to 2D cultures, HCASMC cultured on 3D scaffolds had no Rho activation suggesting pliability of the elastomeric synthetic scaffold. Elastin expression in 3D cultures followed Ras-ERK1/2 signal transduction pathway and was further dependent on endogenously expressed interleukin-1β (IL-1β). Blocking of ERK1/2 activation using a pharmacologic inhibitor reduced both elastin and IL-1β gene expressions in 3D cultures. Transient transfection of IL-1β using siRNA, however, did not affect ERK1/2 activation but downregulated elastin gene expression suggesting that endogenous IL-1β acts downstream from ERK1/2. Taken together, results of the present study provide evidence that endogenous IL-1β play a role in elastin gene upregulation and, that this upregulation is mediated by the Ras-ERK1/2 pathway in 3D cultures.

Ameloblastin regulates cell attachment and proliferation through RhoA and p27

The matrix adhesion protein ameloblastin (AMBN) is one of the unique components of the mineralizing matrix of bones and teeth. Here we focused on two types of cells expressing AMBN - mouse dental follicle cells (mDF) and mouse periodontal ligament cells (mPDL) - to decipher AMBN function in developing dental, periodontal, and bone tissues. To test AMBN function, cell culture dishes of mDF and mPDL were exposed to either full-length or C-terminal (amino acids 137-407) recombinant Ambn protein. Alternatively, cells were subjected to transient transfection using an Ambn-small hairpin (sh) RNA vector. Our cell culture studies documented that dishes coated with full-length AMBN promoted the attachment of mPDL and mDF cells as early as 1 h after seeding. In order to identify potential intermediaries that might aid the effect of AMBN on adhesion, RhoA expression levels in AMBN-coated and uncoated control dishes were assessed. These studies indicated that AMBN induced RhoA expression 4 h after seeding, especially in mPDL cells. After 4 h of culture, the cell cycle inhibitor p27 was also up-regulated. In addition, exogenous AMBN and its C-terminal fragment reduced the proliferation of mDF and mPDL. Finally, transient transfection of mDF and mPDL cells with the Ambn-shRNA vector resulted in the down-regulation of p27 in mPDL cells. Together, these data indicate that AMBN affects cell adhesion via RhoA and cell cycle progression through p27.

aV integrins and TGF-β-induced EMT: a circle of regulation

Transforming growth factor-β (TGF-β) has roles in embryonic development, the prevention of inappropriate inflammation and tumour suppression. However, TGF-β signalling also regulates pathological epithelial-to-mesenchymal transition (EMT), inducing or progressing a number of diseases ranging from inflammatory disorders, to fibrosis and cancer. However, TGF-β signalling does not proceed linearly but rather induces a complex network of cascades that mutually influence each other and cross-talk with other pathways to successfully induce EMT. Particularly, there is substantial evidence for cross-talk between αV integrins and TGF-β during EMT, and anti-integrin therapeutics are under development as treatments for TGF-β-related disorders. However, TGF-β's complex signalling network makes the development of therapeutics to block TGF-β-mediated pathology challenging. Moreover, despite our current understanding of integrins and TGF-β function during EMT, the precise mechanism of their role during physiological versus pathological EMT is not fully understood. This review focuses on the circle of regulation between αV integrin and TGF-β signalling during TGF-β induced EMT, which pose as a significant driver to many known TGF-β-mediated disorders.

AT14A mediates the cell wall-plasma membrane-cytoskeleton continuum in Arabidopsis thaliana cells

AT14A has a small domain that has sequence similarities to integrins from animals. Integrins serve as a transmembrane linker between the extracellular matrix and the cytoskeleton, which play critical roles in a variety of biological processes. Because the function of AT14A is unknown, Arabidopsis thaliana AT14A, which is a transmembrane receptor for cell adhesion molecules and a middle member of the cell wall-plasma membrane-cytoskeleton continuum in plants, has been described. AT14A, co-expressed with green fluorescent protein (GFP), was found to localize mainly to the plasma membrane. The mutant Arabidopsis at14a-1 cells exhibit various phenotypes with cell shape, cell cluster size, thickness, and cellulose content of cell wall, the adhesion between cells, and the adhesion of plasma membrane to cell wall varied by plasmolysis. Using direct staining of filamentous actin and indirect immunofluorescence staining of microtubules, cortical actin filaments and microtubules arrays were significantly altered in cells, either where AT14A was absent or over-expressed. It is concluded that AT14A may be a substantial middle member of the cell wall-plasma membrane-cytoskeleton continuum and play an important role in the continuum by regulating cell wall and cortical cytoskeleton organization.

Differential response of arterial and venous endothelial cells to extracellular matrix is modulated by oxygen

Binding of endothelial cell (EC) integrins to extracellular-matrix (ECM) components is one of the key events to trigger intracellular signaling that will ultimately result in proper vascular development. Even within one tissue, the endothelial phenotype differs between arteries and veins. Here, we tested the hypothesis that anchorage dependent processes, such as proliferation, viability, survival and actin organization of venous (VEC) and arterial EC (AEC) differently depend on ECM proteins. Moreover,because of different oxygen tension in AEC and VEC, we tested oxygen as a co-modulator of ECM effects. Primary human placental VEC and AEC were grown in collagens I and IV, fibronectin, laminin, gelatin and uncoated plates and exposed to 12 and 21% oxygen. Our main findings revealed that VEC are more sensitive than AEC to changes in the ECM composition. Proliferation and survival of VEC, in contrast to AEC, were profoundly increased by the presence of collagen I and fibronectin when compared with gelatin or uncoated plates. These effects were reversed by inhibition of focal adhesion kinase (Fak) and modulated by oxygen. VEC were more susceptible to the oxygen dependent ECM effects than AEC. However, no differential ECM effect on actin organization was observed between the two cell types. These data provide first evidence that AEC and VEC from the same vascular loop respond differently to ECM and oxygen in a Fak-dependent manner.

Layer-by-layer assembly through weak interactions and their biomedical applications

The surface design and control of substrates with nanometer- or micrometer-sized polymer films are of considerable interest for both fundamental and applied studies in the biomedical field because of the required surface properties. The layer-by-layer (LbL) technique was discovered in 1991 by Decher and co-workers for the fabrication of polymer multilayers constructed mainly through electrostatic interaction. The scope and applicability of this LbL assembly has been extended by introducing molecularly regular conformations of polymers or proteins by employing, for the first time, weak interactions such as van der Waals interactions and biological recognition. Since these weak interactions are the sum of the attractive or repulsive forces between parts of the same molecule, they allow macromolecules to be easily arranged into the most stable conformation in a LbL film. By applying this characteristic feature, the template polymerization of stereoregular polymers, stereoregular control of surface biological properties, drastic morphological control of biodegradable nano materials, and the development of three-dimensional cellular multilayers as a tissue model were successfully achieved. It is expected that LbL assembly using weak interactions will promote further interest into fundamental and applied studies on the design of surface chemistry in the biomedical field.

Adhesive proteins linked with focal adhesion kinase regulate neurite outgrowth of PC12 cells

Adhesive proteins existing in the extracellular matrix (ECM) play important roles in the regulation of neuronal cell behavior, including cell adhesion, motility and neurite outgrowth. Herein we show the effects of a series of adhesive proteins on the neurite outgrowth of PC12 cells and elucidate that this is closely related to the activation of focal adhesion kinase (FAK). For this we prepared culture substrates by coating tissue culture plastic with either collagen (Col), fibronectin (FN) or laminin (LN) and investigated the neurite outgrowth behavior. The results demonstrated that neurite outgrowth was highly dependent on the particular type of adhesive protein. While neurite number was comparable on all the coated surfaces, the length of neurites was greater on the FN- and LN-coated ones (greatest on the LN-coated one). In particular, FAK expression was highly up-regulated in the FN- and LN-coated surfaces, as revealed by Western blot analysis. A knock-down experiment further supported the idea that neurite outgrowth was largely suppressed in cells transfected with a FAK knock-down gene. Taken together, the neurite outgrowth of PC12 cells was greatly affected by adhesive proteins of the ECM, particularly FN and LN, and this is considered to be closely related to FAK intracellular signaling. This study may be useful in the consideration and design of nerve guidance and three-dimensional scaffolds which are appropriate to promote neuronal growth and nerve tissue regeneration.

Spatial arrangement of polycaprolactone/collagen nanofiber scaffolds regulates the wound healing related behaviors of human adipose stromal cells

A sufficient cell source and minimal invasiveness in obtaining human adipose stromal cells (hASCs) hold great promise for their utilization in wound repair. However, little is known about how cell-residing microenvironments regulate the cellular response. In this study we explored the effects of polycaprolactone (PCL)/collagen nanofibers with distinct spatial arrangements (aligned and random) on phenotypic expression of hASCs in vitro. Elongated cell morphology, higher proliferation, and faster migration rate were observed for hASCs cultured on the aligned nanofibers, showing that hASCs could detect the nanofiber spatial arrangement and then distinctively respond. This study on the expression of extracellular matrix (ECM) related genes in hASCs revealed higher synthesis capacity for critical ECM molecules including tropoelastin, collagen I, and matrix metalloproteinase (MMP)-1 on the aligned nanofibers. Integrins α(5), β(1), β(3), β(6,) and transforming growth factor (TGF)-β(1) were differentially regulated by PCL/collagen nanofiber arrangements. Our results indicate that fiber orientation-induced phenotypic change of hASCs may be regulated by integrins and TGF-β signaling synergistically. These findings demonstrate the potential application of hASCs and aligned PCL/collagen nanofibers for accelerated wound repair.

Intervertebral disk tissue engineering using biphasic silk composite scaffolds

Scaffolds composed of synthetic, natural, and hybrid materials have been investigated as options to restore intervertebral disk (IVD) tissue function. These systems fall short of the lamellar features of the native annulus fibrosus (AF) tissue or focus only on the nucleus pulposus (NP) tissue. However, successful regeneration of the entire IVD requires a combination approach to restore functions of both the AF and NP. To address this need, a biphasic biomaterial structure was generated by using silk protein for the AF and fibrin/hyaluronic acid (HA) gels for the NP. Two cell types, porcine AF cells and chondrocytes, were utilized. For the AF tissue, two types of scaffold morphologies, lamellar and porous, were studied with the porous system serving as a control. Toroidal scaffolds formed out of the lamellar, and porous silk materials were used to generate structures with an outer diameter of 8 mm, inner diameter of 3.5 mm, and a height of 3 mm (the interlamellar distance in the lamellar scaffold was 150-250 μm, and the average pore sizes in the porous scaffolds were 100-250 μm). The scaffolds were seeded with porcine AF cells to form AF tissue, whereas porcine chondrocytes were encapsulated in fibrin/HA hydrogels for the NP tissue and embedded in the center of the toroidal disk. Histology, biochemical assays, and gene expression indicated that the lamellar scaffolds supported AF-like tissue over 2 weeks. Porcine chondrocytes formed the NP phenotype within the hydrogel after 4 weeks of culture with the AF tissue that had been previously cultured for 2 weeks, for a total of 6 weeks of cultivation. This biphasic scaffold simulating in combination of both AF and NP tissues was effective in the formation of the total IVD in vitro.

Modulation of fibroblast inflammatory response by surface modification of a perfluorinated ionomer

An ideal surface for implantable glucose sensors would be able to evade the events leading to chronic inflammation and fibrosis, thereby extending its utility in an in vivo environment. Nafion™, a perfluorinated ionomer, is the membrane material preferred for in situ glucose sensors. Unfortunately, the surface properties of Nafion™ promote random protein adsorption and eventual foreign body encapsulation, thus leading to loss of glucose signal over time. Details of the techniques to render Nafion™ nonprotein fouling are given in a previous article [T. I. Valdes et al., Biomaterials 29, 1356 (2008)]. Once random protein adsorption is prevented, a biologically active peptide can be covalently bonded to the treated Nafion™ to induce cellular adhesion. Cellular responses to these novel decorated Nafion™ surfaces are detailed here, including cell viability, cell spreading, and type I collagen synthesis. Normal human dermal fibroblasts (NHDFs) were cultured on control and modified Nafion™ surfaces. Findings indicate that Nafion™ modified with 10% 2-hydroxyethyl methacrylate and 90% tetraglyme created a nonfouling surface that was subsequently decorated with the YRGDS peptide. NHDFs were shown to have exhibited decreased type I collagen production in comparison to NHDF cells on unmodified Nafion™ surfaces. Here, the authors report evidence that proves that optimizing conditions to prevent protein adsorption and enhance cellular adhesion may eliminate fibrous encapsulation of an implant.