Regulation of cell function by extracellular matrix

A review on regulation of cell cycle by extracellular matrix

The extracellular matrix (ECM) is a network of structural proteins, glycoproteins and proteoglycans that assists independent cells in aggregating and forming highly organized functional structures. ECM serves numerous purposes and is an essential component of tissue structure and functions. Initially, the role of ECM was considered to be confined to passive functions like providing mechanical strength and structural identity to tissues, serving as barriers and platforms for cells. The doors to understanding ECM's proper role in tissue functioning opened with the discovery of cellular receptors, integrins to which ECM components binds and influences cellular activities. Understanding and utilizing ECM's potential to control cellular function has become a topic of much interest in recent decades, providing different outlooks to study processes involved in developmental programs, wound healing and tumour progression. On another front, the regulatory mechanisms operating to prevent errors in the cell cycle have been topics of a titanic amount of studies. This is expected as many diseases, most infamously cancer, are associated with defects in their functioning. This review focuses on how ECM, through different methods, influences the progression of the somatic cell cycle and provides deeper insights into molecular mechanisms of functional communication between adhesion complex, signalling pathways and cell cycle machinery.

Association of MMP-2 and MMP-9 Polymorphisms with Diabetes and Pathogenesis of Diabetic Complications

Type 2 diabetes mellitus (T2D) affects millions of people around the world, and its complications have serious health consequences. In addition to external factors, the causes of morbidity and increased risk were also sought in the variability of the human genome. A phenomenon that can answer these questions is the occurrence of single-nucleotide polymorphisms (SNP). They constitute a field for research into genetic determinants responsible for the increase in the risk of the discussed metabolic disease. This article presents the outline of two enzymes: metalloproteinases 2 and 9 (MMP-2, MMP-9), their biological activity and the effect caused by differences in individual alleles in the population, as well as the reports on the importance of these DNA sequence variations in the occurrence of diabetes mellitus type 2 and associated conditions. The results of the conducted research indicate a relationship between two MMP-2 polymorphisms (rs243865, rs243866) and two MMP-9 polymorphisms (rs3918242, rs17576) and the presence of T2D. This could offer a promising possibility to use them as predictive and diagnostic markers. However, due to the low number of reports, more research is needed to clearly confirm the link between these SNPs and diabetes.

Three-dimensional pore network characterization of reconstructed extracellular matrix

The extracellular matrix (ECM) has a fiber network that provides physical scaffolds to cells and plays important roles by regulating cellular functions. Some previous works characterized the mechanical and geometrical properties of the ECM fiber network using reconstituted collagen-I. However, the characterization of the porous structure of reconstituted collagen-I has been limited to the pore diameter measurement, and pore network extraction has not been applied to reconstituted collagen-I despite the importance of pore interconnectivity. Here, we aim to show the importance of characterizing the pore network of reconstituted collagen-I by comparing the pore networks of structures that have different fiber alignments. We show that the fiber alignment significantly changes the pore throat area but not the pore diameter. Also, we demonstrate that larger pore throats are directed in the direction of the fiber alignment, which may help in understanding the enhanced cell migration when fibers are aligned.

Bioprinting Approaches to Engineering Vascularized 3D Cardiac Tissues

PURPOSE OF REVIEW

3D bioprinting technologies hold significant promise for the generation of engineered cardiac tissue and translational applications in medicine. To generate a clinically relevant sized tissue, the provisioning of a perfusable vascular network that provides nutrients to cells in the tissue is a major challenge. This review summarizes the recent vascularization strategies for engineering 3D cardiac tissues.

RECENT FINDINGS

Considerable steps towards the generation of macroscopic sizes for engineered cardiac tissue with efficient vascular networks have been made within the past few years. Achieving a compact tissue with enough cardiomyocytes to provide functionality remains a challenging task. Achieving perfusion in engineered constructs with media that contain oxygen and nutrients at a clinically relevant tissue sizes remains the next frontier in tissue engineering. The provisioning of a functional vasculature is necessary for maintaining a high cell viability and functionality in engineered cardiac tissues. Several recent studies have shown the ability to generate tissues up to a centimeter scale with a perfusable vascular network. Future challenges include improving cell density and tissue size. This requires the close collaboration of a multidisciplinary teams of investigators to overcome complex challenges in order to achieve success.

A Spontaneous 3D Bone-On-a-Chip for Bone Metastasis Study of Breast Cancer Cells

Bone metastasis occurs at ≈70% frequency in metastatic breast cancer. The mechanisms used by tumors to hijack the skeleton, promote bone metastases, and confer therapeutic resistance are poorly understood. This has led to the development of various bone models to investigate the interactions between cancer cells and host bone marrow cells and related physiological changes. However, it is challenging to perform bone studies due to the difficulty in periodic sampling. Herein, a bone-on-a-chip (BC) is reported for spontaneous growth of a 3D, mineralized, collagenous bone tissue. Mature osteoblastic tissue of up to 85 µm thickness containing heavily mineralized collagen fibers naturally formed in 720 h without the aid of differentiation agents. Moreover, co-culture of metastatic breast cancer cells is examined with osteoblastic tissues. The new bone-on-a-chip design not only increases experimental throughput by miniaturization, but also maximizes the chances of cancer cell interaction with bone matrix of a concentrated surface area and facilitates easy, frequent observation. As a result, unique hallmarks of breast cancer bone colonization, previously confirmed only in vivo, are observed. The spontaneous 3D BC keeps the promise as a physiologically relevant model for the in vitro study of breast cancer bone metastasis.

The Tubulointerstitial Pathophysiology of Progressive Kidney Disease

Accumulating evidence suggests that the central locus for the progression of CKD is the renal proximal tubule. As injured tubular epithelial cells dedifferentiate in attempted repair, they stimulate inflammation and recruit myofibroblasts. At the same time, tissue loss stimulates remnant nephron hypertrophy. Increased tubular transport workload eventually exceeds the energy-generating capacity of the hypertrophied nephrons, leading to anerobic metabolism, acidosis, hypoxia, endoplasmic reticulum stress, and the induction of additional inflammatory and fibrogenic responses. The result is a vicious cycle of injury, misdirected repair, maladaptive responses, and more nephron loss. Therapy that might be advantageous at one phase of this progression pathway could be deleterious during other phases. Thus, interrupting this downward spiral requires narrowly targeted approaches that promote healing and adequate function without generating further entry into the progression cycle.

Epigalloccatechin-3-gallate inhibits ocular neovascularization and vascular permeability in human retinal pigment epithelial and human retinal microvascular endothelial cells via suppression of MMP-9 and VEGF activation

Epigalloccatechin-3-gallate (EGCG) is the main polyphenol component of green tea (leaves of Camellia sinensis). EGCG is known for its antioxidant, anti-inflammatory, antiviral, and anti-carcinogenic properties. Here, we identify EGCG as a new inhibitor of ocular angiogenesis and its vascular permeability. Matrix metalloproteinases (MMPs) and vascular endothelial growth factor (VEGF) play a key role in the processes of extracellular matrix (ECM) remodeling and microvascular permeability during angiogenesis. We investigated the inhibitory effects of EGCG on ocular neovascularization and vascular permeability using the retina oriented cells and animal models induced by VEGF and alkaline burn. EGCG treatment significantly decreased mRNA and protein expression levels of MMP-9 in the presence of 12-O-tetradecanoylphorbol-13-acetate (TPA) and tumor necrosis factor alpha (TNF-α) in human retinal pigment epithelial cells (HRPECs). EGCG also effectively protected ARPE-19 cells from cell death and attenuated mRNA expressions of key angiogenic factors (MMP-9, VEGF, VEGF Receptor-2) by inhibiting generation of reactive oxygen species (ROS). EGCG significantly inhibited proliferation, vascular permeability, and tube formation in VEGF-induced human retinal microvascular endothelial cells (HRMECs). Furthermore, EGCG significantly reduced vascular leakage and permeability by blood-retinal barrier breakdown in VEGF-induced animal models. In addition, EGCG effectively limited upregulation of MMP-9 and platelet endothelial cell adhesion molecule (PECAM/CD31) on corneal neovascularization (CNV) induced by alkaline burn. Our data suggest that MMP-9 and VEGF are key therapeutic targets of EGCG for treatment and prevention of ocular angiogenic diseases such as age-related macular degeneration, diabetic retinopathy, and corneal neovascularization.

Endothelialization approaches for viable engineered tissues

One of the main limitation in obtaining thick, 3-dimensional viable engineered constructs is the inability to provide a sufficient and functional blood vessel system essential for the in vitro survival and the in vivo integration of the construct. Different strategies have been proposed to simulate the ingrowth of new blood vessels into engineered tissue, such as the use of growth factors, fabrication scaffold technologies, in vivo prevascularization and cell-based strategies, and it has been demonstrated that endothelial cells play a central role in the neovascularization process and in the control of blood vessel function. In particular, different "environmental" settings (origin, presence of supporting cells, biomaterial surface, presence of hemodynamic forces) strongly influence endothelial cell function, angiogenic potential and the in vivo formation of durable vessels. This review provides an overview of the different techniques developed so far for the vascularization of tissue-engineered constructs (with their advantages and pitfalls), focusing the attention on the recent development in the cell-based vascularization strategy and the in vivo applications.

MG63 osteoblast-like cells exhibit different behavior when grown on electrospun collagen matrix versus electrospun gelatin matrix

Electrospinning is a simple and efficient method of fabricating a non-woven polymeric nanofiber matrix. However, using fluorinated alcohols as a solvent for the electrospinning of proteins often results in protein denaturation. TEM and circular dichroism analysis indicated a massive loss of triple-helical collagen from an electrospun collagen (EC) matrix, and the random coils were similar to those found in gelatin. Nevertheless, from mechanical testing we found the Young's modulus and ultimate tensile stresses of EC matrices were significantly higher than electrospun gelatin (EG) matrices because matrix stiffness can affect many cell behaviors such as cell adhesion, proliferation and differentiation. We hypothesize that the difference of matrix stiffness between EC and EG will affect intracellular signaling through the mechano-transducers Rho kinase (ROCK) and focal adhesion kinase (FAK) and subsequently regulates the osteogenic phenotype of MG63 osteoblast-like cells. From the results, we found there was no significant difference between the EC and EG matrices with respect to either cell attachment or proliferation rate. However, the gene expression levels of OPN, type I collagen, ALP, and OCN were significantly higher in MG63 osteoblast-like cells grown on the EC than in those grown on the EG. In addition, the phosphorylation levels of Y397-FAK, ERK1/2, BSP, and OPN proteins, as well as ALP activity, were also higher on the EC than on the EG. We further inhibited ROCK activation with Y27632 during differentiation to investigate its effects on matrix-mediated osteogenic differentiation. Results showed the extent of mineralization was decreased with inhibition after induction. Moreover, there is no significant difference between EC and EG. From the results of the protein levels of phosphorylated Y397-FAK, ERK1/2, BSP and OPN, ALP activity and mineral deposition, we speculate that the mechanism that influences the osteogenic differentiation of MG63 osteoblast-like cells on EC and EG is matrix stiffness and via ROCK-FAK-ERK1/2.

Characterizations of chondrocyte attachment and proliferation on electrospun biodegradable scaffolds of PLLA and PBSA for use in cartilage tissue engineering

The influence of physical characteristics of electrospun three-dimensional (3D) fibrous scaffolds based on polybutylene succinate-co-adipate (PBSA) and poly l-lactic acid (PLLA) on the culture of primary human chondrocytes (PHCs) in terms of cell attachment, proliferation, and re-differentiation was investigated. Physical characteristics assessed for two polymers electrospun at two different delivery rates (PBSA-3, PBSA-16, PLLA-3, and PLLA-16) including average fiber diameter, average pore diameter, porosity, and contact angle. Results demonstrated that 3D fibrous scaffolds are better for PHCs' attachment than two-dimensional (2D) casting films made of the same polymeric materials. It was also found that 3D fibrous scaffolds are appropriate architecture for the proliferation of PHCs than 2D casting films and dependent upon the polymer used. Histological analysis revealed that a significant amount of PHC was found to be growing only within layers of PLLA fibrous scaffolds. The mitochondrial ribonucleic acid (mRNA) expression of both aggrecan and type II collagen by PHCs cultured in tissue culture polystyrene for 28 days decreased significantly. The mRNA expression of both aggrecan and type II collagen by PHCs cultured in PBSA scaffolds increased from 14 to 28 days, whereas only mRNA expression of aggrecan cultured in both PLLA scaffolds increased from 14 to 28 days.

The thrombogenicity of human umbilical vein endothelial cell seeded collagen modules

Modular tissue-engineered constructs are assembled from sub-mm sized cylindrical collagen gel modules which are covered with a surface layer of human umbilical vein endothelial cells (HUVEC). The resulting construct is permeated by a network of interconnected endothelial cell lined channels to facilitate blood perfusion and nutrient delivery. This design strategy relies critically on the endothelial cells' layer behaving in a non-thrombogenic manner on the module surface and the objective here was to characterize this thrombogenicity. HUVEC prolonged clotting times in whole blood-module mixtures, and enabled slightly heparinized whole blood perfusion of an assembled modular construct in vitro with no increase in platelet loss compared to background levels. Flow cytometry and scanning electron microscopy indicated that HUVEC seeded modules reduced platelet activation and deposition but not leukocyte activation, compared to collagen only modules. Plasma recalcification times on non-stimulated HUVEC were longer compared to stimulated HUVEC but not different than that on collagen only module films and were not prolonged by incubation with a tissue factor blocking antibody. Together these data suggest that a functional non-thrombogenic layer of EC was generated on the module surface and that this layer should be sufficient to maintain continuous blood flow through an engineered modular tissue. In/ex vivo studies are warranted to confirm this conclusion.

Design of a new stretching apparatus and the effects of cyclic strain and substratum on mouse lung epithelial-12 cells

The pulmonary epithelium is exposed to mechanical strains during normal breathing or mechanical ventilation. While important for the regulation of cellular processes, excessive strains damage epithelial cells. To investigate the effects of strain on the epithelium, we developed a stretching device to apply equi-biaxial strains to cells cultured on elastic membranes. Following device validation, we exposed a murine epithelial cell line (MLE-12) to 30 min of cyclic stretch with 0, 25, 50, 75 and 100% change in surface area on pronectin or type I collagen coated membranes. Following stretch, we assessed cell viability using fluorescent immunocytochemisty and surfactant secretion using [(3)H] labeled phosphatidylcholine (PC). Cell injury increased with increasing strain with cells on pronectin showing more injury than on type I collagen. Stretching had no effect on surfactant secretion on either substratum suggesting MLE-12 cells are a poor model for stretch-induced surfactant secretion. The cells grown on pronectin, however, demonstrated a 3-fold increase in surfactant secretion compared to those grown on type I collagen at all strains. This suggests that, while this cell line does not demonstrate stretch-induced surfactant secretion, the underlying extracellular matrix plays a crucial factor in both cell death and signal transduction in response to strain.

The influence of biomaterials on endothelial cell thrombogenicity

Driven by tissue engineering and regenerative medicine, endothelial cells are being used in combination with biomaterials in a number of applications for the purpose of improving blood compatibility and host integration. Endothelialized vascular grafts are beginning to be used clinically with some success in some centers, while endothelial seeding is being explored as a means of creating a vasculature within engineered tissues. The underlying assumption of this strategy is that when cultured on artificial biomaterials, a confluent layer of endothelial cells maintain their non-thrombogenic phenotype. In this review the existing knowledge base of endothelial cell thrombogenicity cultured on a number of different biomaterials is summarized. The importance of selecting appropriate endpoint measures that are most reflective of overall surface thrombogenicity is the focus of this review. Endothelial cells inhibit thrombosis through three interconnected regulatory systems (1) the coagulation cascade, (2) the cellular components of the blood such as leukocytes and platelets and (3) the complement cascade, and also through effects on fibrinolysis and vascular tone, the latter which influences blood flow. Thus, in order to demonstrate the thrombogenic benefit of seeding a biomaterial with EC, the conditions under which EC surfaces are more likely to exhibit lower thrombogenicity than unseeded biomaterial surfaces need to be consistent with the experimental context. The endpoints selected should be appropriate for the dominant thrombotic process that occurs under the given experimental conditions.

Extended-Term Culture of Bone Cells in a Compartmentalized Bioreactor

A specialized bioreactor is used to grow mineralizing, collagenous tissue up to 150 microm thick from an inoculum of isolated murine (mouse calvaria MC3T3-E1, American Type Culture Collection (ATCC) CRL-2593) or human (hFOB 1.19 ATCC CRL-11372) fetal osteoblasts over uninterrupted culture periods longer than 120 days (4 months). Proliferation and phenotypic progression of an osteogenic-cell monolayer into a tissue consisting of 6 or more cell layers of mature osteoblasts in the bioreactor was compared with cell performance in conventional tissue-culture polystyrene (TCPS) controls. Cells in the bioreactor basically matched results obtained in TCPS over a 15-day culture interval, but loss of insoluble extracellular matrix and an approximate doubling of apoptosis rates in TCPS after 30 days indicated that progressive instability of cultures maintained in TCPS with periodic refeeding but without subculture. In contrast, stable cultures were maintained in the bioreactor for more than 120 days, suggesting that extended-term tissue maintenance is feasible with little or no special technique. Transmission electron microscopy ultramorphology of tissue derived from hFOB 1.19 recovered from the bioreactor after only 15 days of culture showed evidence of osteocytic-like processes and gap junctions between cells like those observed in vivo, in addition to elaboration of the usual osteoblastic markers such as alkaline phosphatase activity and mineralization (alizarin red). Thus, the bioreactor design based on the principle of simultaneous growth and dialysis was shown to create an extraordinarily stable peri-cellular environment that better simulates the in vivo condition than conventional tissue culture. The bioreactor shows promise as a tool for the in vitro study of osteogenesis and osteopathology.

Injectable cartilage tissue engineering

Cartilage is the tissue that lines the surface of bones in articulating joints, allowing painless joint movement. Cartilage loss is an increasingly significant problem, particularly with the ageing of active baby boomers, with few efficacious treatments available at present. Tissue engineering is a field that has evolved over recent years to combat tissue loss by providing a living tissue equivalent or substitute that can mimic the properties of the lost tissue. The general strategy of tissue engineering is to place cells on a biomaterial scaffold that is designed to promote cell function and form new tissue. This review describes the status of materials that are available as injectable scaffolds for tissue engineering and the numerous cell types that can be applied to cartilage repair, including cells derived from cartilage and stem cells. The current state of injectable cartilage tissue engineering and the hurdles that remain for widespread clinical application are discussed.

Matrix metalloproteinases and mesangial remodeling in light chain-related glomerular damage

BACKGROUND

Matrix metalloproteinases (MMPs) belong to the zinc endopeptidase subgroup of the metalloproteinase superfamily and are primarily involved in extracellular matrix (ECM) remodeling. Alterations of the mesangial ECM in AL-amyloidosis (AL-Am) and light chain deposition disease (LCDD) are crucial in their pathogeneses as two divergent entities.

METHODS

Protein expression patterns of five MMPs (MMP-1, 2, 3, 7, and 9) in renal tissues obtained from autopsies and kidney biopsies, and cultured human mesangial cells (HMCs) treated with light chains obtained from the urines of patients with AL-Am and LCDD were analyzed. MMP mRNA expressions were determined in glomeruli following laser capture microdissection and selective MMP microarray. Zymography was used to assess MMP activity.

RESULTS

The average glomerular MMP expression was 6 times greater in AL-Am than LCDD and negative control renal tissues with different expression profiles: MMP-1, 7 > 9 > 3 > 2, MMP-1 > 2, 9 > 3 > 7, and MMP-2, 3, 7 > 9 > 1, respectively. Microdissected glomeruli and HMCs treated with light chains expressed higher levels of MMP mRNA and proteins in AL-Am than LCDD. Zymography was used to assess activity demonstrating increased MMP-2 in AL-Am.

CONCLUSION

Altered expressions of MMPs play a key role in the pathogenesis of AL-Am and LCDD. MMPs were more highly expressed in AL-Am compared to LCDD.

Expression of {beta}1 integrin receptors during rat pancreas development--sites and dynamics

The integrin receptors link to extracellular matrix proteins and exert a dynamic role in development by providing the physical basis for cell adhesion and controlling cell growth. In the present study, we examined changes in the expression of beta1 integrins and its associated alpha-subunits to islet cell development in the rat pancreas. A significant increase in protein expression of integrin alpha3, alpha6, and beta1 was observed from fetal to postnatal life. High mRNA levels of these integrin subunits was detected at embryonic d 18 and dropped significantly after birth with relatively low expression throughout postnatal life. Integrins alpha3, alpha5, alpha6, and beta1 were expressed in a cell-specific manner in the pancreas with high integrin immunoreactivity in duct and islet regions during fetal life, and a progressive increase later into postnatal life. The coexpression with islet and putative islet precursor markers during fetal and postnatal development suggest a role for these integrin subunits in differentiation and maturation of islets. Functional studies in vitro showed that anti-beta1 antibody treatment inhibited islet cell adhesion to extracellular matrices and disrupted islet architecture. Blockade of beta1 integrin receptor and knockdown beta1 mRNA resulted in a decrease in the expression of insulin mRNA and increased islet cell death. These results suggest that progression in islet cell development is accompanied by and dependent upon cell adhesion via beta1 integrin and its respective alpha-subunits and suggest that the beta1 family of integrins may play a critical role in islet cell architecture, development, integrity, and function.

Low-molecular-weight peptides derived from extracellular matrix as chemoattractants for primary endothelial cells

The development of synthetic and naturally occurring scaffolds for tissue engineering applications has included strategies to promote attachment of specific cell types, control the rate of scaffold degradation, encourage angiogenesis, or otherwise modulate the host response. We have reported that bioscaffolds developed from porcine small intestinal submucosa (SIS) facilitate the constructive remodeling of tissues and recruit marrow-derived cells that persist long after the acute inflammatory stages have resolved. We have not yet determined which cells are recruited, the eventual fate of these cells, or via what mechanisms the events occur. We now have analyzed various molecular weight fractions of acid-hydrolyzed SIS by both functional and morphologic methods and have determined that fraction 4 (5 to 16 kDa) possesses chemoattractant activity for primary murine adult liver, heart, and kidney endothelial cells in vitro. Addition of fraction 4 to Matrigel plugs promoted in vivo vascularization when the plugs were implanted subcutaneously in mice. These results indicate that small-molecular-weight peptides derived from the degradation of porcine SIS are biologically active in the recruitment of murine endothelial cells in vitro and in vivo.

Melanoma cell migration to type IV collagen requires activation of NF-kappaB

Chemotaxis is the consequence of environmental factors engaging their receptors to initiate signaling cascades. However, the biochemical mechanisms controlling this phenomenon are not clear. We employed an in vitro modified Boyden 48-well chemotaxis migration system to characterize the role of signal transducers in type IV collagen (CIV) induced A2058 human melanoma cell migration. Using specific pharmacological inhibitors and a series of dominant-negative and constitutively active signaling proteins, we show that Ras and Rac GTPases, PI-3K, and PKC participate in cell migration mediated by beta1 integrins. Collagen also induces a time- dependent degradation of IkappaB-alpha and an increase in nuclear translocation of NF-kappaB which is dependent on PKC pathway. More importantly, collagen-stimulated melanoma cell migration directly correlated with an increase in NF-kappaB transactivation. Furthermore, CIV induced an increase in beta1 integrin mRNA levels. Specific NF-kappaB inhibitors Helenalin and SN-50 inhibited melanoma cell migration to collagen, indicating a novel requirement for NF-kappaB transactivation in cell chemotaxis mediated by beta1 integrin signals. These results describe signal transduction events that are initiated by type IV collagen through beta1 integrins and demonstrate an important role for NF-kappaB in regulating melanoma chemotaxis.

Fibronectin: an interesting vocal fold protein

A great deal of information is accruing regarding the function of the extracellular matrix. Once thought to be simply a structural entity to surround cells, it is now known to do much more. Fibronectin in particular has received specific attention. Fibronectin is a ubiquitous glycoprotein found most abundantly in the extracellular matrix of regenerating, healing, and embryonic tissue. Vast evidence supports the fact that fibronectin participates in many diverse functions throughout the body that are relevant to vocal fold biology. This article introduces the structure of fibronectin and its isoforms and provides an introduction to some of the many functions it plays. It also reviews the evidence about fibronectin's place in vocal folds and vocal fold pathology. It discusses fibronectin's presence in vocal nodules, vocal polyps, vocal scarring, and Reinke's edema, and reviews the data on its role in mucosal wave impairment. Lastly, it discusses preliminary microarray data that show gene expression for fibronectin to be upregulated in true vocal folds when compared to false vocal folds.

[Ca2+]i as a potential downregulator of alpha2beta1-integrin-mediated A2058 tumor cell migration to type IV collagen

We have investigated cellular Ca2+ regulation during A2058 human melanoma cell chemotaxis to type IV collagen (CIV). We have identified alpha2beta1-integrin as the primary mediator of A2058 cell response to CIV in vitro. Integrin ligation initiated a characteristic intracellular Ca2+ concentration ([Ca2+]i) response consisting of an internal release and a receptor-mediated Ca2+ entry. Thapsigargin (TG) pretreatment drained overlapping and CIV-inducible internal Ca2+ stores while initiating a store-operated Ca2+ release (SOCR). CIV-mediated Ca2+ entry was additive to TG-SOCR, suggesting an independent signaling mechanism. Similarly, ionophore application in a basal medium containing Ca2+ initiated a sustained influx. Elevated [Ca2+]i from TG-SOCR or ionophore significantly attenuated cell migration to CIV by recruiting the Ca2+/calcineurin-mediated signaling pathway. Furthermore, low [Ca2+]i induced by EGTA application in the presence of ionophore fully restored cell motility to CIV. Together, these results suggest that [Ca2+]i signaling accompanying A2058 cell response to alpha2beta1-integrin ligation is neither necessary nor sufficient and that elevated [Ca2+]i downregulates cell motility via a calcineurin-mediated mechanism in A2058 cell chemotaxis to CIV.

Extracellular Matrix Globules in Renal Oncocytoma

Extracellular hyaline globules resulting from abnormal accumulation of matrix components have been described in several pathological conditions, including renal tumors. We studied 16 renal oncocytomas and observed these bodies in 11 of them. In these tumors, they showed a homogeneous texture as well as roundish, smooth contours, and were easily detected in hematoxylin-eosin sections in five cases. PAS staining greatly facilitated the identification of globules in the remaining six cases, where they were fewer in number. Immunohistochemically, they appeared to be composed primarily of basement membrane material, being strongly reactive to antibodies for type IV collagen, laminin, and heparan sulphate proteoglycan. In addition, a weak immunoreactivity for type I and type III collagen, and fibronectin was observed in some cases, whereas no globule stained for tenascin. We also analyzed 89 renal cell carcinomas, and found somewhat similar bodies in 10 of them. However, they were more scanty in the latter tumors, and displayed a more irregular configuration with granular or smudged contours. We conclude that, although the mere presence of extracellular hyaline globules does not justify a distinction between renal oncocytoma and renal cell carcinoma, the detection of a large number of well-demarcated, roundish extracellular bodies with smooth contours suggests renal oncocytoma.

Extracellular lipid-mediated signaling in tumor-cell activation and pseudopod protrusion

We have pioneered an in vitro pseudopod-generation model wherein suspended tumor cells are stimulated to form pseudopods into glass micropipettes in response to soluble collagen type IV (CIV). Pertussis toxin and removing intracellular calcium were found previously to be inhibitory to that process. We now extend those observations to dissect the roles of transmembrane calcium influx and circulating fatty acids on pseudopod extension. Removal of fatty acids from BSA in basal media resulted in abrogation of pseudopod formation, while reconstitution of free fatty acids restored cell pseudopod protrusion. We thus hypothesized that fatty acids may provide necessary pseudopod stimulatory signals. Addition of lysophosphatidic acid (LPA) to the fatty acid-free CIV solution or in an opposite pipette without CIV permitted approximately 50% pseudopod recovery in all pipette directions in a dose-dependent fashion. Thapsigargin (TG), an agent that releases internal calcium stores and causes opening of store-operated calcium channels, restored pseudopod protrusion up to 80% in CIV with fatty acid-free albumin. [Ca(2+)](i) release was non-additive when cells were stimulated by TG and LPA, suggesting overlapping [Ca(2+)](i) stores. The combination of TG and LPA in fatty acid-free albumin fully restored the pseudopod response to CIV. Addition of EGTA to chelate stimulatory media calcium blocked the pseudopod response to CIV in the presence of fatty acids. This indicates that pseudopod protrusion requires transmembrane calcium entry. Thus, extracellular lipids and calcium mobilization are required to complement CIV in pseudopod protrusion from suspended cells.

Use of green fluorescent protein-conjugated beta-actin as a novel molecular marker for in vitro tumor cell chemotaxis assay

To study the dynamics of actin cytoskeleton rearrangement in living cells, an eukaryotic expression vector expressing a beta-actin-GFP fusion protein was generated. The expression construct when transfected into NIH3T3 fibroblast, A2058 human melanoma and 293T human embryonic kidney carcinoma cell lines expressed beta-actin-GFP fusion protein, which colocalized with endogenous cellular actin as determined by histoimmunofluorescence staining. The beta-actin-GFP was also observed to be reorganized in response to treatments with the chemoattractant type IV collagen. Cells extended pseudopodial protrusions and altered the morphology of their cortical structure in response to type IV collagen stimulation. More importantly, beta-actin-GFP accumulated in areas undergoing these dynamic cytoskeleton changes, indicating that beta-actin-GFP could participate in actin polymerization. Although ectopic expression of beta-actin-GFP lead to minor side effects on cell proliferation, these studies suggest that this strategy provides an alternative to the invasive techniques currently used to study actin dynamics and permits real-time visualization of actin rearrangements in response to environmental cues.

Characterization of integrin expression in islets isolated from hamster, canine, porcine, and human pancreas

The reasons for the failure of clinical islet transplantation remain obscure. Islet isolation, however, exposes the islet to variety of cellular stresses, including disruption of the cell-matrix relationship, an event associated with apoptosis. The cell-matrix relationship is characterized by an interaction between cell surface integrin receptors and matrix molecules of the surrounding basement membrane (BM). The purpose of this study was to characterize integrin expression and the distribution of the peri-insular BM in human, porcine, canine, and hamster pancreas, and after routine islet isolation. Whereas islets in the porcine pancreas do not have a demonstrable BM, islets in the human, canine, and hamster pancreas have an almost continuous BM with very little direct exocrine to endocrine cell-cell contact. After islet isolation, the BM was destroyed, only to be reestablished during the period of culture. In the pancreas of all four species, integrin alpha3 was expressed only on islet cells, and integrin alpha5 was present on islet cells as well as on acinar, centroacinar, and duct cells. Integrin alphaV was detected only in human and canine pancreas. Integrin beta1 was demonstrated only in the human pancreas. In isolated islets, integrin alpha3, alpha5, and alphaV expression decreased during the culture period and the intensity of the staining was observed to be coincident with the distribution of the BM. In summary, this is the first report of integrin expression in hamster, canine, porcine, and human islets. After islet isolation, the altered islet cell-matrix relationship is reflected both in the decrease in integrin expression and in the destruction of the peri-insular BM. These profound changes will need to be considered as the process of islet isolation for transplantation is refined. (J Histochem Cytochem 47:499-506, 1999)

Basic fibroblast growth factor release by human coronary artery endothelial cells is enhanced by matrix proteins, 17beta-estradiol, and a PKC signaling pathway

Endothelial cell function is regulated by interactions among cells, the extracellular matrix (ECM), and soluble mediators. We investigated this interaction by examining the effect of 17beta-estradiol (E2) on release of basic fibroblast growth factor (FGF-2) by human coronary artery endothelial cells (HCAEC) cultured on ECM proteins. After estrogen-depleted HCAEC were treated with E2 for 2 h, the conditioned media and cell layers were evaluated by immunoblot or ELISA for FGF-2. Release of FGF-2 into conditioned media was enhanced 10-fold compared to that on plastic and a further 2.4-fold by E2. As FGF-2 release from cells into the media increases, there is a corresponding decrease in the cellular content of FGF-2. By ELISA, FGF-2 release increased 406, 179, and 262%, on type IV collagen, laminin, or fibronectin, respectively. HCAEC cultured on type I collagen did not show E2-enhanced FGF-2 release by ELISA or immunoblot analysis. No changes were noted in HCAEC release of lactate dehydrogenase, tested as a control protein for cellular integrity. The estrogen receptor antagonist ICI182,780 blocked E2-induced, but not basal, FGF-2 release. Increased FGF-2 release occurred via a cycloheximide-insensitive pathway. Neither brefeldin-A nor genistein inhibited E2 enhancement of FGF-2 release by HCAEC cultured on fibronectin. However, the protein kinase C inhibitor calphostin C inhibited the E2-augmented FGF-2 release. These data show that E2 enhances FGF-2 release by HCAEC cultured on basement membrane proteins in the absence of wounding. This action requires the estrogen receptor and PKC activity, but does not require new protein synthesis, endoplasmic reticulum-to-Golgi-mediated secretion, or protein tyrosine phosphorylation. E2-enhanced FGF-2 release could contribute to the cardioprotective effects of estrogen.

Overproduction of urokinase-type plasminogen activator is regulated by phospholipase D- and protein kinase C-dependent pathways in murine mammary adenocarcinoma cells

Urokinase-type plasminogen activator (uPA) initiates a proteolytic cascade with which invasive cells eliminate barriers to movement. The signaling pathways regulating uPA production in tumor cells remain unclear. We first studied the effects of n-butanol, a phospholipase D (PLD) and protein kinase C (PKC) inhibitor, on the production of uPA in murine mammary adenocarcinoma cells. Tumor cell monolayers treated during 24 h with 0.3% v/v n-butanol, secreted 45-50% less uPA to the culture medium than control monolayers (P < 0.001) as determined by radial caseinolysis, zymography and western blot. This inhibition occurred also with 5-h treatments and remained up to 5 h after the removal of the alcohol. Treatment with the phorbol ester PMA or with EGF, strongly increased uPA production (P < 0.001). Interestingly, a mild inhibition of uPA production was observed when PMA stimulation was assayed in cotreatments with n-butanol. In contrast EGF was unable to reverse the inhibition induced by n-butanol. H7 significantly inhibited uPA activity (P < 0.001) secreted to the culture media. Furthermore, phosphatidic acid significantly stimulated uPA production meanwhile propranolol, which blocks phosphatidic acid availability, reduced it, suggesting a main regulatory role for this intermediary metabolite. These results suggest for the first time that uPA production is regulated by PLD and PKC signal transduction pathways in murine mammary adenocarcinoma cells.

Tunica media remodeling in mesenteric arteries of hypertensive rats

BACKGROUND

The tunica media of the vascular wall is a composite material comprised of smooth muscle cells and fibrous and nonfibrous matrix proteins.

METHODS

Using morphometric techniques, this study quantifies the cell and matrix composition of normotensive (Wistar-Kyoto) and spontaneously hypertensive rat mesenteric arteries.

RESULTS

The data show that the superior mesenteric artery (SMA) and small mesenteric arteries are different in matrix composition, cell-to-matrix ratio, and cellular dense body content. Compared with normotensive arteries, hypertensive arteries have less basement membrane but more collagen and extracellular matrix ground substance. SMA from hypertensive rats has about 30% less elastin than does normotensive artery. In contrast, the elastin content of small arteries of both strains was about the same and was less than 4% of the matrix area. Except in hypertensive SMA, membrane dense bodies occupy 7-10% of the cell area and more than 10 times the area occupied by cytoplasmic dense bodies. In contrast, cells from hypertensive SMA have about half the membrane dense body area of the normotensive cells. A decreased proportion of dense bodies in the hypertensive SMA is consistent with the "partial detachment" of these cells from the matrix.

CONCLUSIONS

These results are consistent with both cellular and matrix "remodeling" in diseased vessels in response to continuous, long-term elevated blood pressure.

Physiological principles for surgical correction of detrusor dysfunction

Urinary incontinence may be the result of various forms of detrusor overactivity. Several surgical therapies have been devised, but with the exception of procedures to relieve urethral obstruction, none abolishes the overactivity or restores normal micturition. In general, ablative neurosurgery is considered only in patients with chronic neurologic disease. Bladder augmentation is useful in selected patients. The indications for urinary diversion in patients with detrusor overactivity and urge incontinence are quite limited.

Plasminogen activators augment endothelial cell organization in vitro by two distinct pathways

Endothelial cell differentiation into capillary structures is a complex process that requires the concerted effects of several extracellular matrix proteases, including plasminogen activators. Here, the role of tissue-type plasminogen activator (tPA) and urokinase-type plasminogen activator (uPA) was evaluated in an in vitro model of endothelial morphogenesis involving organization of human umbilical vein endothelial cells into tubular structures when they are cultured on the basement membrane preparation, Matrigel. Both uPA and tPA were detected in HUVEC cultures on Matrigel, and inhibitors of plasminogen activators or of serine proteases decreased the extent of the tube network formed by the cells. The decrease resulting from serine protease inhibitors was additive to that from matrix metalloproteinase inhibitors which have previously been shown to decrease tube formation in this model, suggesting that the two classes of proteases modulate tube formation by distinct mechanisms. Plasminogen activator inhibitor (PAI)-1 decreased tube formation by 50% when added up to 4.5 h after the initiation of an 18 h assay and caused 25% inhibition when added 9.5 h after culture initiation, indicating that the effects of plasminogen activators are not limited to an early event in the differentiation process. Steady-state expression of mRNA for uPA increased during the first several hours of culture on Matrigel, further supporting a role for PA activity throughout the process of tube formation. These findings suggested that PAs may affect multiple events during tube-forming activity. A fucosylated peptide comprising the amino-terminal domain of uPA that binds to the uPA receptor (uPAR) but lacking proteolytic activity enhanced tube formation. In contrast, a defucosylated form of the same peptide had no effect. Since fucosylation of this fragment has been shown to be essential in other models of cell stimulation by uPA-uPAR interaction, these data support the hypothesis that uPA enhances endothelial morphogenesis both through proteolytic activity and via uPAR occupancy. Plasminogen activators could facilitate angiogenesis in vivo.

Inhibition of proteoglycan synthesis induces an increase in follicle stimulating hormone (FSH)-stimulated estradiol production by immature rat Sertoli cells

In order to define the possible involvement of proteoglycans (PG) in the regulation of Sertoli cell functions, we have examined the effect of para-nitrophenyl-beta-D-xyloside (PNPX), a specific inhibitor of PG synthesis, on follicle stimulating hormone (FSH)-dependent estradiol production by immature rat Sertoli cells. Addition of PNPX to the culture medium induced a dose-dependent inhibition of 35S-labeled PG synthesis in Sertoli cells both in the medium and the cell layer. Simultaneously there was a drastic increase in 35S-labeled secreted glycosaminoglycans. By 1 mM PNPX, syntheses of chondroitin sulfate proteoglycans released into culture medium and of heparan sulfate proteoglycans associated with the cell layer were 35% of values from untreated cells. Simultaneously, PNPX induced a twofold (mean of seven experiments, range 17-250%) enhancement of FSH (100 ng/ml)-stimulated estradiol production. In each individual experiment, there was an inverse relationship between the amplitude of PNPX-induced increase in FSH responsiveness and the FSH capability to stimulate basal estradiol production in cultured rat Sertoli cells. The effect of PNPX on FSH-stimulated aromatase activity was not mimicked by para-nitrophenyl-beta-D-galactoside, a structural analog of PNPX that has no effect on PG synthesis. The (Bu)2cAMP-stimulated estradiol synthesis was not modified in the presence of PNPX. Moreover, PNPX enhancement of FSH-stimulated estradiol synthesis disappeared when Sertoli cells were cultured in the presence of 1-methyl-3-isobutylxanthine, an inhibitor of phosphodiesterase activity. These findings suggest that inhibition of PG synthesis under PNPX conditions did not affect signal transduction steps distal to cAMP but rather decreased the phosphodiesterase activity in Sertoli cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Balance between matrix synthesis and degradation: a determinant of glomerulosclerosis

In glomerular health and disease, the balance between extracellular matrix (ECM) protein synthesis and degradation determines the amount of matrix that accumulates locally. While cell and whole animal regulation of ECM synthesis has been the subject of ongoing study, attention has become focused on proteases that degrade matrix components only recently. Two major ECM protease systems have been defined. The plasminogen activators (PAs) are serine proteases that have matrix-degrading capability and also activate plasminogen to plasmin. Plasmin not only degrades ECM proteins, but also may activate members of the matrix metalloproteinase (MMP) family which comprise the second major matrix-degrading system. Specific biological antagonists of both the PAs and the MMPs tightly regulate proteolysis by these enzymes. All of these enzymes and inhibitors have been detected in the kidney, and their expression may be altered to facilitate ECM accumulation in conditions associated with matrix expansion, such as glomerulosclerosis. Work is in progress to determine how these systems are regulated in the kidney and to further define their contribution to the sclerotic process.

Separation of a 170-K delayed-implantation-associated protein with inhibitory activity on trophoblast outgrowth and RNA synthesis by mouse embryo

PROBLEM

To screen the uterine protein responsible for embryonic dormancy associated with delayed implantation.

METHOD

Uterine protein extracts and sera from mice in which delayed implantation had been induced and those from pregnant mice were separated by three steps of chromatography and SDS-PAGE by monitoring an inhibitory activity on trophoblast outgrowth. The presence of the separated protein in the uterine luminal fluid was assessed. Effect of the protein on cell proliferation and RNA synthesis by blastocysts were assessed.

RESULTS

A 170-K protein was found in the uterine tissue as well as uterine luminal fluid associated with delayed implantation. The 170-K protein suppressed RNA synthesis by approximately 50% and cell proliferation in blastocysts.

CONCLUSION

A 170-K protein is secreted into the uterine lumen during delayed implantation period. The ability of 170-K protein to suppress RNA synthesis and cell proliferation may play a role in regulation of embryonic dormancy associated with delayed implantation.

Cellular biology of glomerulosclerosis

The burgeoning literature on glomerulosclerosis makes frequent review of the literature necessary. At this stage, the key processes involved have surely been defined. It is now appropriate to make deductions about possible therapies and to plan experiments and trials.

Extracellular matrix alters epithelial differentiation

Extracellular matrix (ECM) induces and maintains the differentiation of epithelial cells, not by totally altering their state of differentiation, but by activating overt differentiation. Recent studies of cultured mammary cells provide an elegant molecular analysis of this kind of progressive cell differentiation. Other studies show that ECM can not only activate and enhance a differentiated state, but can even alter it in bringing about transformation of epithelium to mesenchyme.