Selective adhesion of macrophages to denatured forms of type I collagen is mediated by scavenger receptors

Macrophages Rapidly Seal off the Punctured Zebrafish Larval Brain through a Vital Honeycomb Network Structure

There is accumulating evidence that macrophages play additional important roles in tissue damage besides their typical phagocytosis. Although the aggregation of macrophages on injured sites has long been observed, few researchers have focused on the role of the overall structure of macrophage aggregation. In this study, we developed a standardized traumatic brain injury (TBI) model in zebrafish larvae to mimic edema and brain tissue spillage symptoms after severe brain trauma. Using time-lapse imaging, we showed that macrophages/microglia in zebrafish larvae responded rapidly and dominated the surface of injured tissue, forming a meaningful honeycomb network structure through their compact aggregation and connection. Disrupting this structure led to fatal edema-like symptoms with severe loss of brain tissue. Using the RNA-Seq, together with the manipulation of in vitro cell lines, we found that collagen IV was indispensable to the formation of honeycomb network structures. Our study thus revealed a novel perspective regarding macrophages forming a protective compact structure with collagen IV. This honeycomb network structure acted as a physical barrier to prevent tissue loss and maintain brain homeostasis after TBI. This study may provide new evidence of macrophages’ function for the rapid protection of brain tissue after brain injury.

Biomaterial Integration in the Joint: Pathological Considerations, Immunomodulation, and the Extracellular Matrix

Defects of articular joints are becoming an increasing societal burden due to a persistent increase in obesity and aging. For some patients suffering from cartilage erosion, joint replacement is the final option to regain proper motion and limit pain. Extensive research has been undertaken to identify novel strategies enabling earlier intervention to promote regeneration and cartilage healing. With the introduction of decellularized extracellular matrix (dECM), researchers have tapped into the potential for increased tissue regeneration by designing biomaterials with inherent biochemical and immunomodulatory signals. Compared to conventional and synthetic materials, dECM-based materials invoke a reduced foreign body response. It is therefore highly beneficial to understand the interplay of how these native tissue-based materials initiate a favorable remodeling process by the immune system. Yet, such an understanding also demands increasing considerations of the pathological environment and remodeling processes, especially for materials designed for early disease intervention. This knowledge would avoid rejection and help predict complications in conditions with inflammatory components such as arthritides. This review outlines general issues facing biomaterial integration and emphasizes the importance of tissue-derived macromolecular components in regulating essential homeostatic, immunological, and pathological processes to increase biomaterial integration for patients suffering from joint degenerative diseases. This article is protected by copyright. All rights reserved.

Tissue engineered bovine saphenous vein extracellular matrix scaffolds produced via antigen removal achieve high in vivo patency rates

Diseases of small diameter blood vessels encompass the largest portion of cardiovascular diseases, with over 4.2 million people undergoing autologous vascular grafting every year. However, approximately one third of patients are ineligible for autologous vascular grafting due to lack of suitable donor vasculature. Acellular extracellular matrix (ECM) scaffolds derived from xenogeneic vascular tissue have potential to serve as ideal biomaterials for production of off-the-shelf vascular grafts capable of eliminating the need for autologous vessel harvest. A modified antigen removal (AR) tissue process, employing aminosulfabetaine-16 (ASB-16) was used to create off-the-shelf small diameter (< 3 mm) vascular graft from bovine saphenous vein ECM scaffolds with significantly reduced antigenic content, while retaining native vascular ECM protein structure and function. Elimination of native tissue antigen content conferred graft-specific adaptive immune avoidance, while retention of native ECM protein macromolecular structure resulted in pro-regenerative cellular infiltration, ECM turnover and innate immune self-recognition in a rabbit subpannicular model. Finally, retention of the delicate vascular basement membrane protein integrity conferred endothelial cell repopulation and 100% patency rate in a rabbit jugular interposition model, comparable only to Autograft implants. Alternatively, the lack of these important basement membrane proteins in otherwise identical scaffolds yielded a patency rate of only 20%. We conclude that acellular antigen removed bovine saphenous vein ECM scaffolds have potential to serve as ideal off-the-shelf small diameter vascular scaffolds with high in vivo patency rates due to their low antigen content, retained native tissue basement membrane integrity and preserved native ECM structure, composition and functional properties. STATEMENT OF SIGNIFICANCE: The use of autologous vessels for the treatment of small diameter vascular diseases is common practice. However, the use of autologous tissue poses significant complications due to tissue harvest and limited availability. Developing an alternative vessel for use for the treatment of small diameter vessel diseases can potentially increase the success rate of autologous vascular grafting by eliminating complications related to the use of autologous vessel and increased availability. This manuscript demonstrates the potential of non-antigenic extracellular matrix (ECM) scaffolds derived from xenogeneic vascular tissue as off-the-shelf vascular grafts for the treatment of small diameter vascular diseases.

Epigenetics in Kawasaki Disease

Kawasaki disease (KD) is a common febrile multisystemic inflammatory illness in children that preferentially affects coronary arteries. Children with KD who develop coronary artery aneurysms have a life-long risk of premature coronary artery disease. Hypothesis of inherent predisposition to KD is supported by epidemiological evidence that suggests increased risk of development of disease in certain ethnicities and in children with a previous history of KD in siblings or parents. However, occurrence of cases in clusters, seasonal variation, and very low risk of recurrence suggests an acquired trigger (such as infections) for the development of illness. Epigenetic mechanisms that modulate gene expression can plausibly explain the link between genetic and acquired predisposing factors in KD. Analysis of epigenetic factors can also be used to derive biomarkers for diagnosis and prognostication in KD. Moreover, epigenetic mechanisms can also help in pharmacogenomics with the development of targeted therapies. In this review, we analysed the available literature on epigenetic factors such as methylation, micro-RNAs, and long non-coding RNAs in KD and discuss how these mechanisms can help us better understand the disease pathogenesis and advance the development of new biomarkers in KD.

Candida albicans/Macrophage Biointerface on Human and Porcine Decellularized Adipose Matrices

Macrophages, cells effective in sensing, internalizing and killing Candida albicans, are intertwined with the extracellular matrix (ECM) through different signals, which include the release of specific cytokines. Due to the importance of these interactions, the employment of in vitro models mimicking a fungal infection scenario is essential to evaluate the ECM effects on the macrophage response. In this work, we have analyzed the effects of human and porcine decellularized adipose matrices (DAMs), obtained by either enzymatic or organic solvent treatment, on the macrophage/Candida albicans interface. The present study has allowed us to detect differences on the activation of macrophages cultured on either human- or porcine-derived DAMs, evidencing changes in the macrophage actin cytoskeleton, such as distinct F-actin-rich membrane structures to surround the pathogen. The macrophage morphological changes observed on these four DAMs are key to understand the defense capability of these cells against this fungal pathogen. This work has contributed to the knowledge of the influence that the extracellular matrix and its components can exert on macrophage metabolism, immunocompetence and capacity to respond to the microenvironment in a possible infection scenario.

Biomechanical Contributions to Macrophage Activation in the Tumor Microenvironment

Alterations in extracellular matrix composition and organization are known to promote tumor growth and metastatic progression in breast cancer through interactions with tumor cells as well as stromal cell populations. Macrophages display a spectrum of behaviors from tumor-suppressive to tumor-promoting, and their function is spatially and temporally dependent upon integrated signals from the tumor microenvironment including, but not limited to, cytokines, metabolites, and hypoxia. Through years of investigation, the specific biochemical cues that recruit and activate tumor-promoting macrophage functions within the tumor microenvironment are becoming clear. In contrast, the impact of biomechanical stimuli on macrophage activation has been largely underappreciated, however there is a growing body of evidence that physical cues from the extracellular matrix can influence macrophage migration and behavior. While the complex, heterogeneous nature of the extracellular matrix and the transient nature of macrophage activation make studying macrophages in their native tumor microenvironment challenging, this review highlights the importance of investigating how the extracellular matrix directly and indirectly impacts tumor-associated macrophage activation. Additionally, recent advances in investigating macrophages in the tumor microenvironment and future directions regarding mechano-immunomodulation in cancer will also be discussed.

Identification of a novel monocytic phenotype in Classic Hodgkin Lymphoma tumor microenvironment

Classic Hodgkin lymphoma (CHL) characteristically shows few malignant cells in a microenvironment comprised of mixed inflammatory cells. Although CHL is associated with a high cure rate, recent studies have associated poor prognosis with absolute monocyte count in peripheral blood and increased monocyte/macrophages in involved lymph nodes. Thus, the role of monocytic infiltration and macrophage differentiation in the tumor microenvironment of CHL may be more relevant than absolute macrophage numbers to defining prognosis in CHL patients and potentially have therapeutic implications. Most studies identify tumor-associated macrophages (TAMs) using markers (e.g., CD68) expressed by macrophages and other mononuclear phagocytes, such as monocytes. In contrast, Class A Scavenger Receptor (SR-A/CD204) is expressed by tissue macrophages but not monocytic precursors. In this study, we examined SR-A expression in CHL (n = 43), and compared its expression with that of other macrophage markers. We confirmed a high prevalence of mononuclear cells that stained with CD68, CD163, and CD14 in CHL lymph nodes. However, SR-A protein expression determined by immunohistochemistry was limited to macrophages localized in sclerotic bands characteristic of nodular sclerosis CHL. In contrast, SR-A protein was readily detectable in lymph nodes with metastatic tumor, extra-nodal CHL, T cell/histiocyte-rich large B cell lymphoma, and resident macrophages in non-malignant tissues, including spleen, lymph node, liver and lung. The results of SR-A protein expression paralleled the expression of SR-A mRNA determined by quantitative RT-PCR. These data provide evidence that tumor-infiltrating monocyte/macrophages in CHL have a unique phenotype that likely depends on the microenvironment of nodal CHL.

Extracellular Matrices to Modulate the Innate Immune Response and Enhance Bone Healing

Extracellular matrices (ECMs) have emerged as promising off-the-shelf products to induce bone regeneration, with the capacity not only to activate osteoprogenitors, but also to influence the immune response. ECMs generated starting from living cells such as mesenchymal stromal cells (MSCs) have the potential to combine advantages of native tissue-derived ECMs (e.g., physiological presentation of multiple regulatory factors) with those of synthetic ECMs (e.g., customization and reproducibility of composition). MSC-derived ECMs could be tailored by enrichment not only in osteogenic cytokines, but also in immunomodulatory factors, to skew the innate immune response toward regenerative processes. After reviewing the different immunoregulatory properties of ECM components, here we propose different approaches to engineer ECMs enriched in factors capable to regulate macrophage polarization, recruit host immune and mesenchymal cells, and stimulate the synthesis of other immunoinstructive cytokines. Finally, we offer a perspective on the possible evolution of the paradigm based on biological and chemico-physical design considerations, and the use of gene editing approaches.

Extracellular Matrix-Based Strategies for Immunomodulatory Biomaterials Engineering

The extracellular matrix (ECM) is a complex and dynamic structural scaffold for cells within tissues and plays an important role in regulating cell function. Recently it has become appreciated that the ECM contains bioactive motifs that can directly modulate immune responses. This review describes strategies for engineering immunomodulatory biomaterials that utilize natural ECM-derived molecules and have the potential to harness the immune system for applications ranging from tissue regeneration to drug delivery. A top-down approach utilizes full-length ECM proteins, including collagen, fibrin, or hyaluronic acid-based materials, as well as matrices derived from decellularized tissue. These materials have the benefit of maintaining natural conformation and structure but are often heterogeneous and encumber precise control. By contrast, a bottom-up approach leverages immunomodulatory domains, such as Arg-Gly-Asp (RGD), matrix metalloproteinase (MMP)-sensitive peptides, or leukocyte-associated immunoglobulin-like receptor-1(LAIR-1) ligands, by incorporating them into synthetic materials. These materials have tunable control over immune cell functions and allow for combinatorial approaches. However, the synthetic approach lacks the full natural context of the original ECM protein. These two approaches provide a broad range of engineering techniques for immunomodulation through material interactions and hold the potential for the development of future therapeutic applications.

Biomaterials: Foreign Bodies or Tuners for the Immune Response?

The perspectives of regenerative medicine are still severely hampered by the host response to biomaterial implantation, despite the robustness of technologies that hold the promise to recover the functionality of damaged organs and tissues. In this scenario, the cellular and molecular events that decide on implant success and tissue regeneration are played at the interface between the foreign body and the host inflammation, determined by innate and adaptive immune responses. To avoid adverse events, rather than the use of inert scaffolds, current state of the art points to the use of immunomodulatory biomaterials and their knowledge-based use to reduce neutrophil activation, and optimize M1 to M2 macrophage polarization, Th1 to Th2 lymphocyte switch, and Treg induction. Despite the fact that the field is still evolving and much remains to be accomplished, recent research breakthroughs have provided a broader insight on the correct choice of biomaterial physicochemical modifications to tune the reaction of the host immune system to implanted biomaterial and to favor integration and healing.

Harnessing macrophage plasticity for tissue regeneration

Macrophages are versatile and plastic effector cells of the immune system, and contribute to diverse immune functions including pathogen or apoptotic cell removal, inflammatory activation and resolution, and tissue healing. Macrophages function as signaling regulators and amplifiers, and influencing their activity is a powerful approach for controlling inflammation or inducing a wound-healing response in regenerative medicine. This review discusses biomaterials-based approaches for altering macrophage activity, approaches for targeting drugs to macrophages, and approaches for delivering macrophages themselves as a therapeutic intervention.

When size matters: differences in demineralized bone matrix particles affect collagen structure, mesenchymal stem cell behavior, and osteogenic potential

Demineralized bone matrix (DBM) is a natural, collagen-based, osteoinductive biomaterial. Nevertheless, there are conflicting reports on the efficacy of this product. The purpose of this study was to evaluate whether DBM collagen structure is affected by particle size and can influence DBM cytocompatibility and osteoinductivity. Sheep cortical bone was ground and particles were divided in three fractions with different sizes, defined as large (L, 1-2 mm), medium (M, 0.5-1 mm), and small (S, <0.5 mm). After demineralization, the chemical-physical analysis clearly showed a particle size-dependent alteration in collagen structure, with DBM-M being altered but not as much as DBM-S. DBM-M displayed a preferable trend in almost all biological characteristics tested, although all DBM particles revealed an optimal cytocompatibility. Subcutaneous implantation of DBM particles into immunocompromised mice resulted in bone induction only for DBM-M. When sheep MSC were seeded onto particles before implantation, all DBM particles were able to induce new bone formation with the best incidence for DBM-M and DBM-S. In conclusion, the collagen alteration in DBM-M is likely the best condition to promote bone induction in vivo. Furthermore, the choice of 0.5-1 mm particles may enable to obtain more efficient and consistent results among different research groups in bone tissue-engineering applications. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1019-1033, 2017.

Production of a Bilayered Self-Assembled Skin Substitute Using a Tissue-Engineered Acellular Dermal Matrix

Our bilayered self-assembled skin substitutes (SASS) are skin substitutes showing a structure and functionality very similar to native human skin. These constructs are used, in life-threatening burn wounds, as permanent autologous grafts for the treatment of such affected patients even though their production is exacting. We thus intended to shorten their current production time to improve their clinical applicability. A self-assembled decellularized dermal matrix (DM) was used. It allowed the production of an autologous skin substitute from patient's cells. The characterization of SASS reconstructed using a decellularized dermal matrix (SASS-DM) was performed by histology, immunofluorescence, transmission electron microscopy, and uniaxial tensile analysis. Using the SASS-DM, it was possible to reduce the standard production time from about 8 to 4 and a half weeks. The structure, cell differentiation, and mechanical properties of the new skin substitutes were shown to be similar to the SASS. The decellularization process had no influence on the final microstructure and mechanical properties of the DM. This model, by enabling the production of a skin substitute in a shorter time frame without compromising its intrinsic tissue properties, represents a promising addition to the currently available burn and wound treatments.

Cleavage of Type I Collagen by Fibroblast Activation Protein-α Enhances Class A Scavenger Receptor Mediated Macrophage Adhesion

Pathophysiological conditions such as fibrosis, inflammation, and tumor progression are associated with modification of the extracellular matrix (ECM). These modifications create ligands that differentially interact with cells to promote responses that drive pathological processes. Within the tumor stroma, fibroblasts are activated and increase the expression of type I collagen. In addition, activated fibroblasts specifically express fibroblast activation protein-α (FAP), a post-prolyl peptidase. Although FAP reportedly cleaves type I collagen and contributes to tumor progression, the specific pathophysiologic role of FAP is not clear. In this study, the possibility that FAP-mediated cleavage of type I collagen modulates macrophage interaction with collagen was examined using macrophage adhesion assays. Our results demonstrate that FAP selectively cleaves type I collagen resulting in increased macrophage adhesion. Increased macrophage adhesion to FAP-cleaved collagen was not affected by inhibiting integrin-mediated interactions, but was abolished in macrophages lacking the class A scavenger receptor (SR-A/CD204). Further, SR-A expressing macrophages localize with activated fibroblasts in breast tumors of MMTV-PyMT mice. Together, these results demonstrate that FAP-cleaved collagen is a substrate for SR-A-dependent macrophage adhesion, and suggest that by modifying the ECM, FAP plays a novel role in mediating communication between activated fibroblasts and macrophages.

Innate Immunity and Biomaterials at the Nexus: Friends or Foes

Biomaterial implants are an established part of medical practice, encompassing a broad range of devices that widely differ in function and structural composition. However, one common property amongst biomaterials is the induction of the foreign body response: an acute sterile inflammatory reaction which overlaps with tissue vascularisation and remodelling and ultimately fibrotic encapsulation of the biomaterial to prevent further interaction with host tissue. Severity and clinical manifestation of the biomaterial-induced foreign body response are different for each biomaterial, with cases of incompatibility often associated with loss of function. However, unravelling the mechanisms that progress to the formation of the fibrotic capsule highlights the tightly intertwined nature of immunological responses to a seemingly noncanonical “antigen.” In this review, we detail the pathways associated with the foreign body response and describe possible mechanisms of immune involvement that can be targeted. We also discuss methods of modulating the immune response by altering the physiochemical surface properties of the biomaterial prior to implantation. Developments in these areas are reliant on reproducible and effective animal models and may allow a “combined” immunomodulatory approach of adapting surface properties of biomaterials, as well as treating key immune pathways to ultimately reduce the negative consequences of biomaterial implantation.

Physical and mechanical regulation of macrophage phenotype and function

Macrophages are tissue-resident immune cells that play a critical role in maintaining homeostasis and fighting infection. In addition, these cells are involved in the progression of many pathologies including cancer and atherosclerosis. In response to a variety of microenvironmental stimuli, macrophages can be polarized to achieve a spectrum of functional phenotypes. This review will discuss some emerging evidence in support of macrophage phenotypic regulation by physical and mechanical cues. As alterations in the physical microenvironment often underlie pathophysiological states, an understanding of their effects on macrophage phenotype and function may help provide mechanistic insights into disease pathogenesis.

Prostaglandins produced during class A scavenger receptor-mediated macrophage adhesion differentially regulate cytokine production

Inflammation is associated with modification of the extracellular environment, changes in cytokine expression, and the accumulation of immune cells. Such modifications create ligands that support SR-A-mediated macrophage adhesion and retention. This may be particularly important in settings, such as atherosclerosis and diabetes, as modified lipoproteins and gluc-collagen are ligands for SR-A. SR-A-mediated adhesion requires the PLA₂-dependent generation of AA and its metabolism by 12/15 LOX. In contrast, the inhibition of the COX-dependent conversion of AA to PG had no effect on SR-A-mediated adhesion. In this study, macrophages were isolated from SR-A^+/+ and SR-A^-/- mice and plated on gluc-collagen to test the hypothesis that COX-derived PGs are produced during SR-A-mediated adhesion and regulate macrophage function. SR-A-mediated binding to gluc-collagen induced a rapid but transient increase in PG production, which required the activation of PLA₂ and Src kinase but not PI3K. SR-A^+/+ macrophages cultured on gluc-collagen for 24 h secreted a similar amount of TNF-α and 2.5-fold more IL-10 than SR-A^-/- macrophages. The inhibition of COX substantially increased TNF-α production but reduced IL-10 levels in SR-A^+/+ macrophages. These effects of COX inhibition were reversed by exogenous PGE₂ and mimicked by specific antagonism of the EP4 receptor. Thus, in addition to the enhancement of macrophage adhesion, SR-A binding to gluc-collagen stimulates PG production, which in turn, differentially regulates the expression of inflammatory cytokines.

Macrophage-like U937 cells recognize collagen fibrils with strain-induced discrete plasticity damage

At its essence, biomechanical injury to soft tissues or tissue products means damage to collagen fibrils. To restore function, damaged collagen must be identified, then repaired or replaced. It is unclear at present what the kernel features of fibrillar damage are, how phagocytic or synthetic cells identify that damage, and how they respond. We recently identified a nanostructural motif characteristic of overloaded collagen fibrils that we have termed discrete plasticity. In this study, we have demonstrated that U937 macrophage-like cells respond specifically to overload-damaged collagen fibrils. Tendons from steer tails were bisected, one half undergoing 15 cycles of subrupture mechanical overload and the other serving as an unloaded control. Both halves were decellularized, producing sterile collagen scaffolds that contained either undamaged collagen fibrils, or fibrils with discrete plasticity damage. Matched-pairs were cultured with U937 cells differentiated to a macrophage-like form directly on the substrate. Morphological responses of the U937 cells to the two substrates-and evidence of collagenolysis by the cells-were assessed using scanning electron microscopy. Enzyme release into medium was quantified for prototypic matrix metalloproteinase-1 (MMP-1) collagenase, and MMP-9 gelatinase. When adherent to damaged collagen fibrils, the cells clustered less, showed ruffled membranes, and frequently spread: increasing their contact area with the damaged substrate. There was clear structural evidence of pericellular enzymolysis of damaged collagen-but not of control collagen. Cells on damaged collagen also released significantly less MMP-9. These results show that U937 macrophage-like cells recognize strain-induced discrete plasticity damage in collagen fibrils: an ability that may be important to their removal or repair.

Lung collagens perpetuate pulmonary fibrosis via CD204 and M2 macrophage activation

Idiopathic pulmonary fibrosis is characterized by abundant collagen production and accumulation of alternatively activated macrophages (M2) in the lower respiratory tract. Mechanisms as to how alveolar macrophages are activated by collagen breakdown products are unknown. Alveolar macrophages were obtained by bronchoalveolar lavage from 30 patients with idiopathic pulmonary fibrosis (IPF) and 37 healthy donors (HD). Alveolar macrophages were cultured in the presence of collagen type I, III, IV and V monomers w/wo a neutralizing antibody against scavenger receptor I class A (CD204). Culture supernatants were assayed for the M2 markers CCL18, CCL2, and interleukin-1 receptor antagonist (IL-1ra) by ELISA. Furthermore, expression of phospho-Akt was measured using ELISA and expression of CD204 by RT-PCR and flow cytometry. Stimulation with collagen type I and III monomers significantly up-regulated CCL18, IL-1ra production of alveolar macrophages. Furthermore, expression of CCL2 and CD204 were up-regulated by collagen type I exposure. In addition, collagen type I stimulation increased pospho-Akt expression. Collagen type I effects were abrogated by neutralizing antiCD204 and a non-selective Phosphatidylinositide 3-kinase inhibitor (LY294002). Spontaneous CD204 expression of alveolar macrophages was significantly increased in patients with IPF. In conclusion, our findings demonstrate that monomeric collagen type I via CD204 induces phospho-Akt expression shifting alveolar macrophages to the profibrotic M2 type. Innate immune responses induced by collagen monomers might perpetuate pulmonary fibrosis.

Which form of collagen is suitable for nerve cell culture?

In this study, we investigated the effects of hydrolyzed and non-hydrolyzed collagen and two-dimensional and three-dimensional collagen matrices on cell survival, attachment and neurite outgrowth of primary cultured nerve cells using 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) colorimetric assay and inverted microscopy. Hydrolyzed collagen facilitated nerve cell survival and neurite outgrowth, but it had no obvious influences on cell attachment. In contrast, non-hydrolyzed two-dimensional collagen matrix had no obvious effects on neurite outgrowth. These findings suggest that hydrolyzed collagen is an ideal nerve cell culture media.

Role of macrophage scavenger receptors in atherosclerosis

Accumulating evidence indicates that atherosclerosis is a chronic inflammatory disease. The key innate immune cells that are involved in the pathogenesis of atherosclerosis are circulating monocytes and plaque macrophages. Complex interplay between immune and metabolic processes results in pathological activity of these cells. The best understood pathological process mediated by macrophages is their inability to process modified lipoproteins properly resulting in the formation of foamy cells, which are a dangerous component of atherosclerotic plaques. Key molecules involved in the recognition and processing of modified lipoproteins are scavenger receptors (SR). This is a large family of surface expressed structurally heterogeneous receptors with a broad spectrum of endogenous and exogenous ligands. The common functional feature of SR is internalisation of extracellular components and targeting them for lysosomal degradation. However, these relatively simple functions can have complex consequences, since they are linked to diverse specific signalling pathways and to other membrane transport pathways. Moreover, scavenger receptors can co-operate with other types of receptors increasing the variability of the macrophage response to multiple extracellular ligands. At least some SRs respond to modified lipoproteins by amplification of inflammation and accumulation of macrophages in the plaque, while some SRs may support tolerogenic reactions. Outcome of different SR activities will be the decision of monocytes and macrophage to guard homeostatic balance, support atherosclerosis progression and plaque instability by inflammatory reactions, or support rapid fibrotic processes in the plaque that stabilise it. Despite the accumulating knowledge about the molecular mechanisms of scavenger receptor action, their role in the progression of atherosclerosis remains controversial. The activities of scavenger receptors that can contribute to each of these processes are a subject of current review.

Embryology and anatomy of the vesicoureteric junction with special reference to the etiology of vesicoureteral reflux

Concerning the ureterovesical junction - the region most important for the anti-reflux mechanism - there is still a lot of misunderstanding and misinterpretation with regard to normal fetal development. Data are scarce on possible causes of primary vesicoureteral reflux and on involved mechanisms of the so-called maturation process of refluxing ureteral endings. The ratio of the intravesical ureteral length to the ureteral diameter is obviously lower than assumed so far, as clearly revealed by some studies. Therefore it can be doubted that the length and course of the intravesical ureter is of sole importance in the prevention of reflux. Additionally refluxing intravesical ureteral endings present with dysplasia, atrophy, and architectural derangement of smooth muscle fibers. Besides, a pathologically increased matrix remodeling combined with deprivation of the intramural nerve supply has been confirmed. Consequently, symmetrical narrowing of the very distal ureteral smooth muscle coat creating the active valve mechanism to defend reflux is not achievable. It is apparent that primary congenital vesicoureteral reflux seems to be the result of an abnormality within the ureterovesical junction with an insufficient muscular wrap. Nature is believed to establish much more sophisticated mechanisms than the so-called passive anti-reflux mechanism. Remodeling processes within the ureterovesical junction of refluxing ureteral endings support that maturation itself is nothing else than wound or defect healing and not a restitution of a morphological normal ureterovesical junction. Lacking the nerve supply a restoration of any muscular structure can not be achieved.

In vitro response of monocyte-derived macrophages to a decellularized pericardial biomaterial

Decellularized tissue-derived heart valves are an example of biomaterials derived from natural scaffolds. These types of implants are increasing in popularity although their in vivo performance is still only poorly understood and has, at times, been catastrophic. It is apparent that better understanding is required before these biomaterials can be used safely. In this study, the human monocyte-derived macrophage (MDM) response to decellularized bovine pericardium (DBP) was used as a model to predict the biological performance of these materials on implantation. Human monocytes differentiated on tissue culture polystyrene (TCPS) for 14 days were trypsinized and reseeded onto DBP, TCPS, and polydimethylsiloxane (PDMS) for 48 h. The MDMs on DBP contained less intracellular and extracellular esterase activity compared with MDMs on TCPS and PDMS, as well as less acid phosphatase activity than on TCPS. As well, morphologically, MDMs on DBP were less spread, less multinucleated and did not display many lamellipodia. Taken together, these data represent the first evidence of the MDM response to intact, native extracellular matrix, demonstrating that these cells reacted with an altered, possibly reduced foreign body response on this natural scaffold compared with the two control surfaces. This in vitro MDM cell model may provide a novel method for predicting and elucidating the biological performance of tissue-derived biomaterials, thereby directing a more rational design of biomaterials for tissue regeneration purposes.

Macrophage scavenger receptor A mediates adhesion to apolipoproteins A-I and E

Macrophage scavenger receptor A (SR-A) is a multifunctional, multiligand pattern recognition receptor with roles in innate immunity, apoptotic cell clearance, and age-related degenerative pathologies, such as atherosclerosis and Alzheimer's disease. Known endogenous SR-A ligands are polyanionic and include modified lipoproteins, advanced glycation end products, and extracellular matrix proteins. No native plasma ligands have been identified, but it is known that SR-A recognition of unidentified serum components mediates integrin-independent macrophage adhesion, which may drive chronic local inflammation. In this study, we used a high-throughput fractionation and screening method to identify novel endogenous SR-A ligands that may mediate macrophage adhesion. SR-A was found to recognize the exchangeable apolipoproteins A-I and E (apo A-I and apo E, respectively) in both lipid-free and lipid-associated form, suggesting the shared amphipathic alpha-helix as a potential recognition motif. Adhesion of RAW 264.7 macrophages to surfaces coated with apo A-I and apo E4 proved to be integrin-independent and could be blocked by anti-SR-A antibodies. The presence of apo A-I and apo E in pathological deposits, such as atherosclerotic lesions and neurotoxic Alzheimer's plaques, suggests a possible contribution of SR-A-dependent adhesion of macrophages to an inflammatory microenvironment.

Regulation of class A scavenger receptor-mediated cell adhesion and surface localization by PI3K: identification of a regulatory cytoplasmic motif

The importance of cytoplasmic motifs in differentially regulating SR-A function was demonstrated by deleting the first 49 cytoplasmic aa (SR-A(Delta1-49)), which abolished SR-A-mediated ligand internalization without reducing cell adhesion. To identify additional cytoplasmic motifs within the first 49 aa that regulate SR-A function, the acidic residues in a conserved motif (EDAD) were changed to their amide derivatives (SR-A(QNAN)). The function and regulation of SR-A(QNAN) were compared with that of SR-A(Delta1-49) and SR-A in transfected HEK-293 cells. Blocking PI3K activation inhibited SR-A, but not SR-A(Delta1-49)- or SR-A(QNAN)-mediated cell adhesion. Although deleting (SR-A(Delta1-49)) or mutating (SR-A(QNAN)) the EDAD motif abolished the PI3K sensitivity of SR-A-mediated cell adhesion, these mutations did not affect ligand internalization or PI3K activation during cell adhesion. To define the mechanism by which PI3K regulates SR-A-mediated cell adhesion, the cellular localization of wild-type and mutant SR-A was examined. PI3K inhibition reduced surface localization of SR-A but not of SR-A(Delta1-49) or SR-A(QNAN). The regulation of SR-A surface localization by PI3K was confirmed in peritoneal macrophages, which endogenously express SR-A. Together, these results suggest a pathway in which SR-A binding to an immobilized ligand activates PI3K to recruit more receptor to the plasma membrane and enhances cell adhesion.

Punta Toro virus (Bunyaviridae, Phlebovirus) infection in mice: strain differences in pathogenesis and host interferon response

The Adames strain of Punta Toro virus (PTV-A, Bunyaviridae, Phlebovirus) causes an acute lethal disease in hamsters and mice. The Balliet strain of the virus (PTV-B) is generally considered to be avirulent. The difference in hamster susceptibility is likely due to the ability of PTV-A to suppress interferon (IFN)-beta similarly to that described for Rift Valley fever virus. Here we investigated strain differences in PTV pathogenesis and the IFN response in mice. Although PTV-B infection in mice did not induce systemic IFN-beta release, primary macrophages produced dramatically higher levels when exposed to the virus in culture. The importance of IFN in resistance to PTV infection was borne out in studies employing STAT-1 knock-out mice. Also, a number of genes specific to IFN response pathways were upregulated in PTV-B-infected macrophages. Our findings provide new insights into the type I IFN response during PTV infection in the mouse model of phleboviral disease.

Conserved domains of the class A scavenger receptors: evolution and function

The class A scavenger receptors are phagocytic pattern recognition receptors that are well represented in vertebrate genomes. The high level of conservation among vertebrates implies that this is an evolutionarily conserved family of receptors and indicates the presence of a common ancestral gene. The identity of this ancestral gene is not clear, as it appears that many of the domains of the scavenger receptors (e.g. collagenous, scavenger receptor cysteine rich) originated early in evolutionary history and are found in many combinations, often in genes of unknown function. These early receptors may function in cell-cell recognition, aggregation, or lipid recognition, and their involvement in pattern recognition, phagocytosis, and homeostasis may have been adaptations of such conserved patterns. Herein, we reclassify the class A scavenger receptors based on recent discoveries of new members of this family, describe the evolution of the various domains of the class A scavenger receptors, and discuss the appearance and function of these domains through evolutionary history.

Collagens in the progression and complications of atherosclerosis

Collagens constitute a major portion of the extracellular matrix in the atherosclerotic plaque, where they contribute to the strength and integrity of the fibrous cap, and also modulate cellular responses via specific receptors and signaling pathways. This review focuses on the diverse roles that collagens play in atherosclerosis; regulating the infiltration and differentiation of smooth muscle cells and macrophages; controlling matrix remodeling through feedback signaling to proteinases; and influencing the development of atherosclerotic complications such as plaque rupture, aneurysm formation and calcification. Expanding our understanding of the pathways involved in cell-matrix interactions will provide new therapeutic targets and strategies for the diagnosis and treatment of atherosclerosis.

Class A scavenger receptor-mediated macrophage adhesion requires coupling of calcium-independent phospholipase A(2) and 12/15-lipoxygenase to Rac and Cdc42 activation

Class A scavenger receptors (SR-A) participate in multiple macrophage functions including adhesion to modified extracellular matrix proteins present in various inflammatory disorders such as atherosclerosis and diabetes. By mediating macrophage adhesion to modified proteins and increasing macrophage retention, SR-A may contribute to the inflammatory process. Eicosanoids produced after phospholipase A(2) (PLA(2))-catalyzed release of arachidonic acid (AA) are important regulators of macrophage function and inflammatory responses. The potential roles of AA release and metabolism in SR-A-mediated macrophage adhesion were determined using macrophages adherent to modified protein. SR-A-dependent macrophage adhesion was abolished by selectively inhibiting calcium-independent PLA(2) (iPLA(2)) activity and absent in macrophages isolated from iPLA(2) beta(-/-) mice. Our results further demonstrate that 12/15-lipoxygenase (12/15-LOX)-derived, but not cyclooxygenase- or cytochrome P450-dependent epoxygenase-derived AA metabolites, are specifically required for SR-A-dependent adhesion. Because of their role in regulating actin polymerization and cell adhesion, Rac and Cdc42 activation were also examined and shown to be increased via an iPLA(2)- and LOX-dependent pathway. Together, our results identify a novel role for iPLA(2)-catalyzed AA release and its metabolism by 12/15-LOX in coupling SR-A-mediated macrophage adhesion to Rac and Cdc42 activation.

A new class of bioactive and biodegradable soybean-based bone fillers

The reconstruction of large bone defects in periodontal, maxillofacial, and orthopedic surgery relies on the implantation of biomaterials able to support the growth of new tissue. None of the materials currently available is able to combine all the properties required, which are (i) easy handling, (ii) biodegradation, (iii) low immunogenicity, and more importantly, (iv) induction of tissue regeneration. A new class of biodegradable biomaterials has been obtained by simple thermosetting of defatted soybean curd. The final material can be processed into films, porous scaffolds, and granules for different surgical needs. When incubated in physiological solutions the material shows water uptake of 80%, elongation at break of 0.9 mm/mm, and 25% (w/w) degradation in 7 days. Soybean-based biomaterial granules are shown to reduce the activity of the monocytes/macrophages and of the osteoclasts and to induce osteoblast differentiation in vitro, thus demonstrating a bone regeneration potential suitable for many clinical applications.

Scavenger Receptors SR-AI/II and MARCO limit pulmonary dendritic cell migration and allergic airway inflammation

The class A scavenger receptors (SR-A) MARCO and SR-AI/II are expressed on lung macrophages (MPhis) and dendritic cells (DCs) and function in innate defenses against inhaled pathogens and particles. Increased expression of SR-As in the lungs of mice in an OVA-asthma model suggested an additional role in modulating responses to an inhaled allergen. After OVA sensitization and aerosol challenge, SR-AI/II and MARCO-deficient mice exhibited greater eosinophilic airway inflammation and airway hyperresponsiveness compared with wild-type mice. A role for simple SR-A-mediated Ag clearance ("scavenging") by lung MPhis was excluded by the observation of a comparable uptake of fluorescent OVA by wild-type and SR-A-deficient lung MPhis and DCs. In contrast, airway instillation of fluorescent Ag revealed a significantly higher traffic of labeled DCs to thoracic lymph nodes in SR-A-deficient mice than in controls. The increased migration of SR-A-deficient DCs was accompanied by the enhanced proliferation in thoracic lymph nodes of adoptively transferred OVA-specific T cells after airway OVA challenge. The data identify a novel role for SR-As expressed on lung DCs in the down-regulation of specific immune responses to aeroallergens by the reduction of DC migration from the site of Ag uptake to the draining lymph nodes.

Integrin α2β1 Is Required for Regulation of Murine Wound Angiogenesis but Is Dispensable for Reepithelialization

The alpha2beta1 integrin functions as the major receptor for collagen type I on a large number of different cell types, including keratinocytes, fibroblasts, endothelial cells, and a variety of inflammatory cells. Recently, we demonstrated that adhesion of keratinocytes to collagen critically depends on alpha2beta1, whereas fibroblasts can partly compensate for loss of alpha2beta1 in simple adhesion to collagen. However, in three-dimensional collagen matrices, alpha2beta1-null fibroblasts are hampered in generating mechanical forces. These data suggested a pivotal role for alpha2beta1 during wound healing in vivo. Unexpectedly, reepithelialization of excisional wounds of alpha2beta1-null mice was not impaired, indicating that keratinocytes do not require adhesion to or migration on collagen for wound closure. Whereas wound contraction and myofibroblast differentiation were similar, wound tensile strain was reduced in alpha2beta1-null mice, suggesting subtle changes in organization of the extracellular matrix. In addition, we observed reduced influx of mast cells into the granulation tissue, whereas infiltration of other inflammatory cells was not impaired. Interestingly, ablation of alpha2beta1 resulted in strong enhancement of neovascularization of granulation tissue and sponge implants. Both ultrastructurally and functionally, these new blood vessels appeared intact. In conclusion, our data show unique and overlapping functions of alpha2beta1 integrin during murine cutaneous wound healing.

Class A scavenger receptor-mediated cell adhesion requires the sequential activation of Lyn and PI3-kinase

Class A scavenger receptors (SR-A) participate in multiple macrophage functions including macrophage adhesion to modified proteins. SR-A-mediated adhesion may therefore contribute to chronic inflammation by promoting macrophage accumulation at sites of protein modification. The mechanisms that couple SR-A binding to modified proteins with increased cell adhesion have not been defined. In this study, SR-A expressing HEK cells and SR-A+/+ or SR-A-/- macrophages were used to delineate the signaling pathways required for SR-A-mediated adhesion to modified protein. Inhibiting G(i/o) activation, which decreases initial SR-A-mediated cell attachment, did not prevent the subsequent spreading of attached cells. In contrast, inhibition of Src kinases or PI3-kinase abolished SR-A-dependent cell spreading without affecting SR-A-mediated cell attachment. Consistent with these results, the Src kinase Lyn and PI3-kinase were sequentially activated during SR-A-mediated cell spreading. Furthermore, activation of both Lyn and PI3-kinase was required for enhancing paxillin phosphorylation. Activation of a Src kinase-PI3-kinase-Akt pathway was also observed in cells expressing a truncated SR-A protein that does not internalize indicating that SR-A-mediated activation of intracellular signaling cascades following adhesion to MDA-BSA is independent of receptor internalization. Thus SR-A binding to modified protein activates signaling cascades that have distinct roles in regulating initial cell attachment and subsequent cell spreading.

Influence of collagen denaturation on the nanoscale organization of adsorbed layers

Adsorption (at 37 degrees C) of type I collagen, in native and heat-denatured (30 min at 40 and 90 degrees C) forms, on polystyrene was studied using quartz crystal microbalance with energy dissipation monitoring (QCM-D), atomic force microscopy (AFM) in tapping mode and X-ray photoelectron spectroscopy (XPS). The significance of the parameters deduced from QCM-D data was examined by comparing different approaches. The adsorbed layer of native collagen has a complex organization consisting of a thin mat of molecules near the surface, in which fibrils develop depending on concentration and time, and of a thicker overlayer containing protruding molecules or bundles which modify noticeably the local viscosity. As a result of drastic denaturation, the ability of collagen to assemble into fibrils in the adsorbed phase is lost and the protrusion of molecules into the aqueous phase is much less pronounced. The adsorbed layer of denatured collagen appears essentially as a monolayer of flattened coils. At low concentration, this is easily displaced upon drying, leading to particular dewetting figures; at high concentration, aggregates add to the first layer. Moderate denaturation leads to an adsorbed phase which shows properties intermediate between those observed with native and extensively denatured collagen, regarding the ability to form fibrillar structures and the adlayer thickness and viscosity.

Uptake of denatured collagen into hepatic stellate cells: evidence for the involvement of urokinase plasminogen activator receptor-associated protein/Endo180

Tissue remodelling is dependent on the integration of signals that control turnover of ECM (extracellular matrix). Breakdown and endocytosis of collagen, a major component of the ECM, is central to this process. Whereas controlled secretion of matrix-degrading enzymes (such as matrix metalloproteinases) has long been known to mediate ECM breakdown, it is becoming clear that uPARAP/Endo180 (where uPARAP stands for urokinase plasminogen activator receptor-associated protein) serves as a receptor that mediates endocytosis of collagen by several types of cells. In the liver, the stellate cells play a major role in turnover of ECM including collagens. These cells synthesize various collagens and also produce matrix metalloproteinases. In the present study, we investigated the capacity of rat hepatic stellate cells to endocytose and degrade 125I-labelled heat-denatured collagen I. It was found that the collagen is efficiently taken up and degraded by these cells. Degradation was inhibited by inhibitors of lysosomal proteases (leupeptin and E-64d) and the vacuolar proton pump (concanamycin A), indicating that it takes place in lysosomes. Furthermore, endocytosed FITC-labelled collagen was shown to reach late endocytic compartments in which it colocalized with LysoTracker (a marker of late endocytic compartments). Competition experiments showed that uPA and unlabelled collagen are capable of inhibiting binding and uptake of [125I]collagen in a dose-dependent manner. Moreover, Western-blot analysis of cell lysate (using a polyclonal rabbit human-Endo180 antiserum) revealed a single band at 180 kDa. In addition, the antiserum was capable of reducing [125I]collagen binding to the cell surface. Finally, using two primers designed from the human uPARAP/Endo180 mRNA sequence, the expression of uPARAP/Endo180 mRNA was detected by reverse transcriptase-PCR. These results together suggest that uPARAP/Endo180 mediates endocytosis of collagen in rat liver stellate cells.

Fetal development of the vesico-ureteric junction, and immunohistochemistry of the ends of refluxing ureters

There is still misunderstanding about the normal fetal development of the vesico-ureteric junction (VUJ), the region that is most important for preventing VUR. There is little information on the causes of primary VUR and on the mechanisms of maturation of refluxing ureteric endings. Some studies show that the ratio of the intravesical ureteric length to diameter is obviously lower than had been assumed. It is doubtful that the length and course of the intravesical ureter is the sole factor in preventing reflux, as previously reported. The intravesical part of refluxing ureters shows dysplasia, atrophy and architectural derangement of smooth muscle fibres. A pathologically increased matrix remodelling combined with deprivation of the intramural nerve supply has been confirmed. Consequently, symmetrical contraction of the distal ureteric smooth muscle coat, creating the active valve mechanism to prevent reflux, is impossible. We reviewed publications using Medline, with the keywords 'human fetal development', 'embryology', 'ureterovesical junction', relevant 'growth data', 'vesico-ureteric reflux', 'children', 'immunohistochemistry', 'extracellular matrix', and 'nerve supply', respectively. Priority was given to articles that correlated specific embryological findings and basic research on possible mechanisms to the genesis and maturation of the VUJ.

Exposure of acidic residues as a danger signal for recognition of fibrinogen and other macromolecules by integrin alphaXbeta2

The structural integrity of tissue proteins is damaged in processes ranging from remodeling of the extracellular matrix to destruction by microbial pathogens. Leukocytes play a prominent role in tissue surveillance and repair. However, it remains enigmatic what features of structurally decayed proteins prompt recognition by leukocyte cell-surface receptors. Here, we report that adhesion of human neutrophil granulocytes to fibrinogen is greatly increased by plasmin digestion in a mode where alphaXbeta2 dominates the integrin-dependent binding. The bacterial protease subtilisin also enhances binding by alphaXbeta2. The alphaX ligand binding domain has an unusually high affinity for carboxyl groups, with KD at approximately 100 microM. Our findings implicate enhanced accessibility of negatively charged residues in structurally decayed proteins as a pattern recognition motif for alphaXbeta2 integrin. Comparisons among integrins show relevance of these findings to the large number of ligands recognized by alphaMbeta2 and alphaXbeta2 but not alphaLbeta2. The observations suggest that the pericellular proteolysis at the leading edge of neutrophils not only facilitates passage through the extracellular matrix but also manufactures binding sites for alphaXbeta2.

Bovine type I collagen inhibits Raw264.7 cell proliferation through phosphoinositide 3-kinase- and mitogen-activated protein kinase-dependent down-regulation of cyclins D1, A and B1

Bovine type I collagen (BIC), which is widely used as a fibrous extracellular matrix component in cell culture models, inhibits the progression of melanoma cell cycle via p27 up-regulation. BIC also induces nitric oxide synthase in macrophages through JunB/AP-1 and NF-kappaB activation. Given the previous observations, this study investigates the effect of BIC on the cell cycle progression and regulatory function of Raw264.7 macrophage cells and the responsible signaling pathways. Cell cycle analysis revealed that BIC completely suppressed proliferation of Raw264.7 cells with inhibition of the percentage of cells in the S phase and the reciprocal decrease in the G0/G1 phase. DNA synthesis was also inhibited by BIC, as evidenced by a decrease in the cellular incorporation of [3H]thymidine. The G1/S arrest induced by BIC was reversed by chemical inhibition of phosphatidylinositol 3-kinase (PI3-kinase) or overexpression of the p85 subunit of PI3-kinase. Either PD98059 or stable transfection with mitogen-activated protein kinase kinase-1 [MKK1(-)] or c-Jun N-terminal kinase 1 [JNK1(-)] also released the cell cycle arrest. Immunoblot analyses revealed that the levels of cyclins D1, A and B1 were partly or completely down-regulated by BIC, but cyclin E, p21 and p27 were minimally changed. Chemical inhibition and dominant negative mutant overexpression experiments revealed that either PI3-kinase inhibition or JNK1(-) transfection prevented the decreases in cyclin D1, A and B1 by BIC, indicating that the PI3-kinase and JNK1 pathways were associated with disruption of the cyclins. The pathway involving MKK1-extracellular signal-regulated kinase-1/2 (ERK1/2) was responsible for the suppression of cyclin A and B1, but not that of cyclin D1. The present study showed that BIC inhibited proliferation of Raw264.7 cells and that the pathways involving PI3-kinase and mitogen-activated protein kinases regulate the cell cycle arrest.

EXTRACELLULAR MATRIX DEGRADATION AND REDUCED NERVE SUPPLY IN REFLUXING URETERAL ENDINGS

PURPOSE

Extracellular matrix (ECM) degrading enzymes and the nerve supply of the ureterovesical junction were investigated using immunohistochemical methods to gain insight into the pattern of refluxing ureteral endings.

MATERIALS AND METHODS

Specimens were obtained from ureterorenal units of 36 children undergoing reflux surgery with a mean age of 62.5 months and 9 age matched controls without reflux. Routine histological paraffin embedded sections were stained for general morphology. Indirect immunohistochemical methods assessing matrix metalloproteinase 1 were used to study the intensity of matrix turnover, and activated macrophage marker CD68 was quantified to describe scavenging of damaged ECM. The intramural neuronal network was explored using nerve specific immunoperoxidase for S-100 protein.

RESULTS

Refluxing ureteral endings demonstrated structural deficiencies of the smooth muscle wrap associated with a 3.8-fold increase of cellular matrix metalloproteinase 1 production and a significant increase of CD68+ macrophages, respectively. The S-100 pattern yielded significant diminution. Lacking B and T lymphocytes in the ECM precluded chronic inflammation.

CONCLUSIONS

Refluxing ureteral endings showed a pathologically increased matrix remodeling combined with deprivation of the intramural nerve supply. Macrophage activation referring to altered morphology was represented by an increased expression of CD68 at the sites of increased ECM turnover.

Development of collagenase-resistant collagen and its interaction with adult human dermal fibroblasts

Collagen is regarded as one of the most useful biomaterials. The excellent biocompatibility and safety due to its biological characteristics, such as biodegradability and weak antigenecity, made collagen the primary source in biomedical application. Collagen has been widely used in the crosslinked form to extend the durability of collagen. The chemical treatment influences the structural integrity of collagen molecule resulting in the loss of triple helical characteristic. The structural characteristic of collagen is importantly related to its biological function for the interaction with cell. In this study, structural stability of collagen was enhanced thought EGCG treatment, resulting in high resistance against degradation by bacterial collagenase and MMP-1, which is confirmed by collagen zymography. The triple helical structure of EGCG-treated collagen could be maintained at 37 degrees C in comparison with collagen, which confirmed by CD spectra analysis, and EGCG-treated collagen showed high free-radical scavenging activity. Also, with fibroblasts culture on EGCG-treated collagen, the structural stability of EGCG-treated collagen provided a favorable support for cell function in cell adhesion and actin filament expression. These observations underscore the need for native, triple helical collagen conformation as a prerequisite for integrin-mediated cell adhesion and functions. According to this experiment, EGCG-treated collagen assumes to provide a practical benefit to resist the degradation by collagenase retaining its structural characteristic, and can be a suitable biomaterial for biomedical application.

Induction of cyclooxygenase-2 by bovine type I collagen in macrophages via C/EBP and CREB activation by multiple cell signaling pathways

Bovine type I collagen (Col-I) is utilized for medical purposes such as cosmetic surgery and wrinkle removal. Cyclooxygenase-2 (COX-2) plays roles in pathophysiological processes including inflammation and tumorigenesis. This study examines the effects of Col-I on the COX-2 expression and the signaling pathways in macrophages. Col-I increased the levels of COX-2 protein and mRNA in serum-stimulated Raw264.7 cells in a time- and concentration-dependent manner. Treatment of cells with Col-I increased CCAAT/enhancer binding protein (C/EBP) DNA binding. Antibody supershift experiments revealed that C/EBP DNA binding activity induced by Col-I depended largely on C/EBPbeta and C/EBPdelta. Immunocytochemistry showed that Col-I induced nuclear translocation of C/EBPbeta and C/EBPdelta, whose activation contributes to COX-2 induction. Overexpression of the dominant-negative mutant form of C/EBP abolished COX-2 induction by Col-I. Col-I also increased cyclic-AMP response element binding protein (CREB) binding to DNA. Inhibition of focal adhesion kinase (FAK) or downstream phosphoinositide 3-kinase and p70S6 kinase by specific chemical inhibitors prevented COX-2 induction by Col-I, and C/EBP and CREB from binding to their consensus DNA oligonucleotides. Experiments using chemical inhibitors or dominant-negative mutant vectors showed that the mitogen-activated protein (MAP) kinase pathways including p38-kinase and extracellular signal-regulated kinase (ERK1/2), but not c-Jun N-terminal kinase (JNK1), simultaneously regulated COX-2 induction by Col-I. This was in agreement with inhibition of Col-I-inducible C/EBP and CREB DNA binding by concomitant treatment with SB203580 and PD98059. These results provide evidence that Col-I induces COX-2 in serum-stimulated macrophages and that the multiple cell signaling pathways involving Src-focal adhesion kinase, phosphoinositide 3-kinase, and MAP kinases regulate COX-2 induction by Col-I via C/EBP and CREB activation.

Cigarette smoke triggers macrophage adhesion and activation: role of lipid peroxidation products and scavenger receptor

Pulmonary emphysema in chronic obstructive pulmonary disease (COPD) is characterized by the destruction of the alveolar walls leading to permanent enlargement of distal respiratory air spaces. A major causal factor is cigarette smoking, which produces conditions of chronic oxidative stress within the lungs. At a cellular level, increased macrophage accumulation and retention within the alveolar interstitial spaces is pivotal to the development of emphysema. To date it has been unclear as to the underlying mechanisms relating chronic oxidative stress to macrophage accumulation and retention. Our study was initiated to ascertain the role of modification of extracellular matrix proteins with cigarette smoke and products of lipid peroxidation on macrophage adhesion and activation. Increased numbers of macrophages were seen adhering to cigarette smoke-modified collagen IV as compared to unmodified collagen, where little or no adherent macrophages were observed. Similar observations were made when collagen was modified with either acrolein or 4-hydroxy-2-nonenal. Adhesion could be blocked with either fucoidan or a monoclonal antibody against the Type A macrophage scavenger receptor. Also, modified collagen triggered both oxidative burst and MCP-1 release in macrophages. These results, therefore, highlight a potential mechanism by which oxidative stress through the production of reactive carbonyls promotes macrophage accumulation, retention, and activation, independently of other proinflammatory stimuli. The implications of this for the development of emphysema in COPD are discussed.

Class A scavenger receptor-mediated adhesion and internalization require distinct cytoplasmic domains

Class A scavenger receptors (SR-A) are transmembrane glycoproteins that mediate both ligand internalization and cell adhesion. Previous studies have identified specific amino acids in the cytoplasmic tail of SR-A that regulate receptor internalization; however, the role of cytoplasmic domains in regulating cell adhesion has not been addressed. To investigate the role of cytoplasmic domains in SR-A-mediated adhesion and to address whether SR-A-mediated adhesion and internalization require distinct cytoplasmic domains, different SR-A constructs were stably expressed in human embryonic kidney (HEK 293) cells. Deleting the entire cytoplasmic tail (SR-A Delta 1-55) greatly reduced receptor protein abundance. Retaining the six amino acids proximal to the membrane (SR-A Delta 1-49) restored receptor protein abundance. Although SR-A Delta 1-49 localized to the cell surface, cells expressing this receptor failed to internalize the ligand acetylated low density lipoprotein. Replacing the cytoplasmic tail of SR-A with that of the transferrin receptor (TfR/SR-A) resulted in retention of the chimeric receptor in the endoplasmic reticulum suggesting a specific role for the membrane-proximal amino acids in trafficking SR-A from the endoplasmic reticulum to the Golgi. Like SR-A expressing cells, cells expressing SR-A Delta 1-49 displayed increased spreading and adhesion, demonstrating that the membrane-proximal amino acids were sufficient for SR-A-mediated cell adhesion. Together, our results indicate a critical role for the membrane-proximal amino acids in SR-A trafficking and demonstrate that SR-A-mediated adhesion and internalization require distinct cytoplasmic domains.

Class A scavenger receptors mediate cell adhesion via activation of G(i/o) and formation of focal adhesion complexes

Class A macrophage scavenger receptors (SR-A) are multifunctional receptors with roles in modified lipoprotein uptake, innate immunity, and macrophage adhesion. Our previous studies conducted in mouse peritoneal macrophages demonstrated that pertussis toxin (PTX) mediated inhibition of G(i/o) attenuated SR-A-dependent uptake of modified lipoprotein. The finding that SR-A-mediated lipoprotein internalization was PTX-sensitive led us to hypothesize that SR-A-mediated cell adhesion might be similarly regulated by G(i/o)-dependent signaling pathways. To test this hypothesis, SR-A was expressed in HEK cells under inducible control. Relative to HEK cells that lack SR-A, SR-A expressing cells displayed enhanced adhesion to tissue culture dishes. SR-A-mediated adhesion was significantly reduced following PTX treatment and was insensitive to chelating divalent cations with EDTA. SR-A-expressing cells exhibited a distinct cell morphology characterized by fine filopodia-like projections. Both polymerized actin and vinculin were codistributed with SR-A in the filopodia-like projections indicating the formation of focal adhesion complexes. Overall, our results indicate that the ability of SR-A to enhance cell adhesion involves G(i/o) activation and formation of focal adhesion complexes.

JunB/AP-1 and NF-kappa B-mediated induction of nitric oxide synthase by bovine type I collagen in serum-stimulated murine macrophages

Type I collagen comprises the majority of the total body collagens. In particular, bovine type I collagen is utilized for medical purposes and used widely in a variety of cell culture models as a fibrous component of extracellular matrix. This study was designed to explore the effects of type I collagen on the expression of inducible nitric oxide synthase (iNOS) in serum-stimulated Raw264.7 cells and to study the molecular mechanistic basis. Bovine, but not rat or murine, type I collagen increased NO production in serum-stimulated cells, which resulted from the induction of iNOS, as monitored by Northern and Western blot analyses. Bovine type I collagen in combination with serum activated JunB and JunB/AP-1 transcription complex, as evidenced by supershift and immunodepletion of the retarded AP-1 band with anti-JunB antibody. AP-1 complex was immunodepleted in part by anti-c-Jun or anti-JunD antibody. Extracellular signal-regulated kinase1/2 (ERK1/2), p38 kinase, and c-Jun N-terminal kinase (JNK) were all activated by bovine type I collagen in serum-stimulated cells. PD98059, but not SB203580 or JNK1(-) transfection, inhibited both ERK1/2 phosphorylation and JunB/AP-1 activation. Either PD98059 or MKK1(-) transfection suppressed the iNOS induction. The induction of iNOS accompanied activation of NF-kappa B with degradation of I-kappa B alpha. AP-1 and/or NF-kappa B decoy oligonucleotides and pyrrolidine dithiocarbamate suppressed the iNOS induction, which confirmed involvement of AP-1 and NF-kappa B as transcription factors. These results demonstrated that bovine type I collagen induces iNOS in serum-stimulated murine macrophages through JunB/AP-1 and NF-kappa B activation and that activation of ERK1/2 plays an essential role in JunB/AP-1 activation.

Lectin-like oxidized low density lipoprotein receptor-1 (LOX-1) supports cell adhesion to fibronectin

Lectin-like oxidized lipoprotein receptor-1 (LOX-1) is a specific receptor for atherogenic oxidized low density lipoprotein (OxLDL) which belongs to the scavenger receptor family. In the present report, we show that LOX-1 can also support cell adhesion to fibronectin (FN) in a divalent cation-independent fashion. CHO-K1 cells stably expressing bovine LOX-1 (BLOX-1-CHO), but not untransfected CHO-K1 cells, can adhere to FN-coated plates, but not to collagen-coated plates, in the presence of EDTA. BLOX-1-CHO adhesion to FN-coated plates can also be suppressed by scavenger receptor ligands, such as OxLDL, polyinosinic acid (poly I), and dextran sulfate, but not by native LDL, acetylated LDL, polycytidylic acid (poly C), or chondroitin sulfate. Cultured bovine aortic endothelial cells can similarly adhere to FN-coated plates, which was inhibited by OxLDL, poly I, and dextran sulfate in the presence of EDTA. LOX-1 may play an important role in cell adhesion to FN in an integrin-independent manner.